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Sample records for bainite

  1. Very Strong Bainite

    OpenAIRE

    García Caballero, Francisca

    2004-01-01

    Steel with an ultimate tensile strength of 2500 MPa, a hardness at 600-670 HV and toughness in excess of 30-40 MPa m1/2 is the result of exciting new developments with bainite. The simple process route involved avoids rapid cooling so that residual stresses can in principle be avoided even in large pieces. The microstructure is generated at temperatures which are so low that the diffusion of iron is inconceivable during the course of the transformation to bainite. As a result, slender plates ...

  2. Influence of bainite morphology on impact toughness of continuously cooled cementite free bainitic steels

    OpenAIRE

    García Caballero, Francisca; Roelofs, H; Hasler, St; Capdevila, Carlos; Chao, Jesús; Cornide, Juan

    2012-01-01

    The influence of bainite morphology on the impact toughness behaviour of continuously cooled cementite-free low carbon bainitic steels has been examined. In these steels, bainitic microstructures formed mainly by lath-like upper bainite, consisting of thin and long parallel ferrite laths, were shown to exhibit higher impact toughness values than those with a granular bainite, consisting of equiaxed ferrite structure and discrete island of marteniste/austenite (M/A) constituent....

  3. Dual phase bainitic linepipe steels

    Energy Technology Data Exchange (ETDEWEB)

    Boyd, D.; Yakubtsov, I.; Zhang, R. [Queen' s Univ., Kingston, ON (Canada). Dept. of Mechanical and Materials Engineering; Poruks, P. [Atomic Energy of Canada Ltd., Chalk River, ON (Canada); Turi, T. [Stelco Lake Erie, Nanticoke, ON (Canada); Emadi, D.; Essadiqi, E. [Natural Resources Canada, Ottawa, ON (Canada). CANMET Materials Technology Lab

    2005-07-01

    Over the past 50 years, the strength of commercial linepipe steel has increased at a steady rate of about 70 MPa per decade due to advances in steelmaking, plate processing and microstructural design. API X100 grade steel, which has a yield strength of 690 MPa, is currently available, and X120 steels are under development. The microstructure of linepipe steels has evolved from predominantly polygonal ferrite to fine bainite. For the X120 steels, lower bainite-, tempered lath martensite- and dual phase microstructures are being examined. This study obtained the microstructures of ultrafine bainite with dispersed particles of the carbon-rich martensite-austenite (M-A) phase. The objective was to obtain a matrix of mostly intragranularly-nucleated bainitic ferrite containing a high volume fraction of dispersed M-A particles. The mechanical properties of bainitic linepipe steels were also examined. Basic studies of phase transformations and mechanical properties in these steels established significant relationships between processing schedule and the evolution of microstructure, and between final microstructure and mechanical properties. The optimal combination of strength and toughness properties was obtained with a microstructure consisting of a matrix of intragranularly-nucleated bainite and small dispersed particles of martensite. This microstructure was described as being a dual phase acicular ferrite (AF) with M-A. The window of steel composition and processing parameters which give the dual phase AF-M-A microstructure was determined in an experimental study on 15 mm thick plate. The minimum strength and toughness properties for Grade 621 (X90) linepipe steel can be achieved by either a lean steel composition with extreme processing parameters, or by a higher alloy composition with a more industrially realistic processing schedule. This study also proposed how this approach can be extended to obtain high strength linepipe grades. 15 refs., 9 tabs., 10 figs.

  4. Bimodal Size-distribution of Bainite Plates

    OpenAIRE

    Hase, K.; García Mateo, Carlos; Bhadeshia, H. K. D. H.

    2006-01-01

    There are two well-known phenomena associated with the bainite reaction, which have been exploited in the present work to enhance the mechanical behaviour of steel. Firstly, the bainite plate size decreases as the transformation temperature is reduced. Secondly, it is bad to have large regions of untransformed austenite in the microstructure; this is because they can transform, under the influence of external stress, into corresponding large regions of untempered, brittle martensite. By ad...

  5. Ultra-high–strength Bainitic Steels

    OpenAIRE

    García Mateo, Carlos; García Caballero, Francisca

    2005-01-01

    Novel bainitic microstructures, consisting of slender ferrite plates (tens of nm) in a matrix of retained austenite, have reported maximum yield strength of 1.4 GPa, ultimate tensile strength of 2.2 GPa, 30% ductility and respectable levels of fracture toughness (∼51 MPa m0.5). The unusual combination of properties is attributed to the fine bainitic plates and the presence of retained austenite in the microstructure.

  6. Advanced Ultra high Strength Bainitic Steels

    OpenAIRE

    García Caballero, Francisca; García Mateo, Carlos; Capdevila, Carlos; García de Andrés, Carlos

    2007-01-01

    The addition of about 2 wt.% of silicon to steel enables the production of a distinctive microstructure consisting of a mixture of bainitic ferrite, carbon-enriched retained austenite, and some martensite. With careful design, impressive combinations of strength and toughness have been reported for high-silicon bainitic steels. More recently, it has been demonstrated experimentally that models based on phase transformation theory can be applied successfully to the design of carbide-free baini...

  7. Crystallography of carbide-free bainite in a hard bainitic steel

    International Nuclear Information System (INIS)

    The convergent beam Kikuchi line diffraction technique has been used to accurately determine the orientation relationships between bainitic ferrite and retained austenite in a hard bainitic steel. A reproducible orientation relationship has been uniquely observed for both the upper and lower bainite. It is(111)A0.70±0.45ofrom(101)B,[1-bar 01]A2.5+/-1.5ofrom[1-bar 11]B However, the habit plane of upper bainite is different from that of lower bainite. The former has habit plane that is either within 5 deg. of (221)A or of (259)A. The latter only corresponds with a habit plane that is within 5 deg. of (259)A. The determined orientation relationship is completely consistent with reported results determined using the same technique with an accuracy of +/-0.5 deg. in lath martensite in an Fe-20wt.% Ni-6wt.% Mn alloy and in a low carbon low alloy steel. It also agrees well with the orientation relationship between granular bainite and austenite in an Fe-19wt.% Ni-3.5wt.% Mn-0.15wt.% C steel. Hence it is believed that, at least from a crystallographic point view, the bainite transformation has the characteristics of martensitic transformation

  8. XRD and TEM study of bainitic ferrite plate thickness in nanostructured, carbide free bainitic steels

    International Nuclear Information System (INIS)

    It is well documented that much of the strength and hardness of nanostructured, carbide free bainitic steels come from the very small thickness of bainitic ferrite plates. In the current work, the Williamson–Hall method has been used to determine the bainitic ferrite plate thickness. The fitting of X-ray peaks to various functions showed good coefficient of determination values for Gaussian function compared to the Cauchy and Pseudo-Voigt functions. The thickness of bainitic ferrite plates was measured by distinguishing the contribution of very small plates on peak broadening from the lattice microstrain and instrumental effects. The results showed that by decreasing the transformation temperature the bainitic ferrite plate thickness decreases. The determined thicknesses were compared with that of measured from transmission electron microscope micrographs. There is a good qualitative and quantitative agreement between the thicknesses measured using both methods. - Highlights: • A Williamson–Hall technique is proposed for bainitic ferrite thickness measurement. • The technique relies on full width at half maximum of XRD peaks. • The measured sizes were compared with that of determined from TEM micrographs. • There is a good qualitative and quantitative agreement between both methods. • Austenite strength and nucleation driving force lead to microstructural refinement

  9. XRD and TEM study of bainitic ferrite plate thickness in nanostructured, carbide free bainitic steels

    Energy Technology Data Exchange (ETDEWEB)

    Yoozbashi, M.N., E-mail: n_yoozbashi@sut.ac.ir [University of Applied Science and Technology, Tabriz (Iran, Islamic Republic of); Yazdani, S., E-mail: yazdani@sut.ac.ir [Faculty of Materials Engineering, Sahand University of Technology, Tabriz (Iran, Islamic Republic of)

    2015-06-15

    It is well documented that much of the strength and hardness of nanostructured, carbide free bainitic steels come from the very small thickness of bainitic ferrite plates. In the current work, the Williamson–Hall method has been used to determine the bainitic ferrite plate thickness. The fitting of X-ray peaks to various functions showed good coefficient of determination values for Gaussian function compared to the Cauchy and Pseudo-Voigt functions. The thickness of bainitic ferrite plates was measured by distinguishing the contribution of very small plates on peak broadening from the lattice microstrain and instrumental effects. The results showed that by decreasing the transformation temperature the bainitic ferrite plate thickness decreases. The determined thicknesses were compared with that of measured from transmission electron microscope micrographs. There is a good qualitative and quantitative agreement between the thicknesses measured using both methods. - Highlights: • A Williamson–Hall technique is proposed for bainitic ferrite thickness measurement. • The technique relies on full width at half maximum of XRD peaks. • The measured sizes were compared with that of determined from TEM micrographs. • There is a good qualitative and quantitative agreement between both methods. • Austenite strength and nucleation driving force lead to microstructural refinement.

  10. Acceleration of Low-temperature Bainite

    OpenAIRE

    García Mateo, Carlos; García Caballero, Francisca; Bhadeshia, H. K. D. H.

    2003-01-01

    Recent work has shown that bainitic ferrite plates produced by transformation at low temperatures can be as thin as 20 nm with a hardness in excess of 650 HV. However, it may take several days in order to achieve the required degree of transformation at low temperatures. In this work we report methods for accelerating the rate of reaction without compromising strength.

  11. Characterization of Bainitic Microstrucutres in Low Carbon Hsla Steels

    Science.gov (United States)

    Kang, Ju Seok; Park, Chan Gyung

    The austenite phase of low carbon steels can be transformed to various bainitic microstructures such as granular bainite, acicular ferrite and bainitic ferrite during continuous cooling process. In the present study site-specific transmission electron microscope (TEM) specimens were prepared by using focused ion beam (FIB) to identify the bainitic microstructure in low carbon high strength low alloy (HSLA) steels clearly. Granular bainite was composed of fine subgrains and 2nd phase constituents like M/A or pearlite located at grain and/or subgrain boundaries. Acicular ferrite was identified as an aggregate of randomly orientated needle-shaped grains. The high angle relations among acicular ferrite grains were thought to be caused by intra-granular nucleation, which could be occur under the high cooling rate condition. Bainitic ferrite revealed uniform and parallel lath structure within the packet. In some case, however, the parallel lathes showed high angle relations due to packet overlapping during grow of bainitic ferrite, resulting in high toughness properties in bainitic ferrite based steels.

  12. Enhanced thermal stability in nanostructured bainitic steel

    International Nuclear Information System (INIS)

    We report an attempt at increasing the thermal stability of nanocrystalline bainite to tempering heat treatments by enhancing the silicon concentration of the alloy. Validation experiments have been conducted using synchrotron X-irradiation during tempering heat treatment. It is found that the change in alloying successfully stabilizes the austenite at elevated temperatures by retarding cementite formation to temperatures as high as 500 °C. Other changes reflected in the lattice parameters of the major phases have revealed further information about the mechanisms involved

  13. THE BAINITIC STEELS FOR RAILS APPLICATIONS

    Directory of Open Access Journals (Sweden)

    Ivo Hlavatý

    2009-10-01

    Full Text Available Actual trends of worldwide railway transport development are characterized by increasing speed and growth of railway’s axels load. Increasing load together with transverse, longitudinal wheel displacement and braking on the rails results into heavy surface tension. One of many applications for bainitic steel is in railway transport for highly strength and wear resistant rails. Rail steel must be designed to be able to resist plastic deformation, wear, rolling contact fatigue, bending stress and thermal stress during rail welding process and rails resurfacing.

  14. Retained austenite thermal stability in a nanostructured bainitic steel

    International Nuclear Information System (INIS)

    The unique microstructure of nanostructured bainite consists of very slender bainitic ferrite plates and high carbon retained austenite films. As a consequence, the reported properties are opening a wide range of different commercial uses. However, bainitic transformation follows the T0 criteria, i.e. the incomplete reaction phenomena, which means that the microstructure is not thermodynamically stable because the bainitic transformation stops well before austenite reaches an equilibrium carbon level. This article aims to study the different microstructural changes taking place when nanostructured bainite is destabilized by austempering for times well in excess of that strictly necessary to end the transformation. Results indicate that while bainitic ferrite seems unaware of the extended heat treatment, retained austenite exhibits a more receptive behavior to it. - Highlights: • Nanostructured bainitic steel is not thermodynamically stable. • Extensive austempering in these microstructures has not been reported before. • Precipitation of cementite particles is unavoidable at longer austempering times. • TEM, FEG-SEM and XRD analysis were used for microstructural characterization

  15. Nanostructured Bainite-Austenite Steel for Armours Construction

    Directory of Open Access Journals (Sweden)

    Burian W.

    2014-10-01

    Full Text Available Nanostructured bainite-austenite steels are applied in the armours construction due to their excellent combination of strength and ductility which enables to lower the armour weight and to improve the protection efficiency. Mechanical properties of the bainite-austenite steels can be controlled in the wide range by chemical composition and heat treatment. In the paper the results of investigation comprising measuring of quasi - static mechanical properties, dynamic yield stress and firing tests of bainite-austenite steel NANOS-BA® are presented. Reported results show that the investigated bainite-austenite steel can be used for constructing add-on armour and that the armour fulfils requirements of protection level 2 of STANAG 4569. Obtained reduction in weight of the tested NANOS-BA® plates in comparison with the present solutions is about 30%.

  16. The microstructure of continuously cooled tough bainitic steel

    OpenAIRE

    García Caballero, Francisca; Capdevila, Carlos; Chao, Jesús; Cornide, J.; García Mateo, Carlos; Roelofs, H; Hasler, St; Mastrogiacomo, G.

    2010-01-01

    The influence of bainite morphology on the impact toughness behaviour of a continuously cooled cementite free low carbon C-Mn-B type of steel has been examined. Different bainite morphologies were obtained by cooling from the austenite regime to ambient temperature with different cooling rates. The resulting microstructures have been quantitatively analysed using light optical microscopy (LOM), scanning electron microscopy (SEM) and electron back scatter diffraction (EBSD) techniques. The rel...

  17. Creation of Air-Cooled Mn Series Bainitic Steels

    Institute of Scientific and Technical Information of China (English)

    FANG Hong-sheng; FENG Chun; ZHENG Yan-kang; YANG Zhi-gang; BAI Bing-zhe

    2008-01-01

    The development and mechanical performances of new type air-cooled Mn series bainitie steels including granular bainitie steels,FGBA/BG duplex steels,CFB/M duplex steels,medium carbon bainite/martensite steels,cast hainitic steels invented by the authors are summarized.The novel series of bainitie steels are alloyed with Mn,and several series bainitic duplex microstructures can be easily obtained under the condition of air cooling through unique composition design.The invented idea,the principle of alloying design,the strengthening mechanism,and the evolution of the microstructure of new type air-cooled Mn series bainitic steels are presented.Furthermore,the applications in different fields of these Mn series air-cooled bainitic steels with different strength level are also introdueed.It is suggested that the significance of the development of the air-cooled Mn series bainitic steel can be summarized as follows:reducing costs of both raw materials and production;good combination of strength and toughness;self-hardening with high bainitic hardenability by air cooling from hot working without additional quenching-tempering treatment or quenching procedure;large savings in energy resources;and reduced environmental pollution.

  18. Microstructural characterization of Charpy-impact-tested nanostructured bainite

    Energy Technology Data Exchange (ETDEWEB)

    Tsai, Y.T.; Chang, H.T.; Huang, B.M. [Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan, ROC (China); Huang, C.Y. [Iron and Steel R& D Department, China Steel Corporation, Kaohsiung, Taiwan, ROC (China); Yang, J.R., E-mail: jryang@ntu.edu.tw [Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan, ROC (China)

    2015-09-15

    In this work, a possible cause of the extraordinary low impact toughness of nanostructured bainite has been investigated. The microstructure of nanostructured bainite consisted chiefly of carbide-free bainitic ferrite with retained austenite films. X-ray diffractometry (XRD) measurement indicated that no retained austenite existed in the fractured surface of the Charpy-impact-tested specimens. Fractographs showed that cracks propagated mainly along bainitic ferrite platelet boundaries. The change in microstructure after impact loading was verified by transmission electron microscopy (TEM) observations, confirming that retained austenite was completely transformed to strain-induced martensite during the Charpy impact test. However, the zone affected by strained-induced martensite was found to be extremely shallow, only to a depth of several micrometers from the fracture surface. It is appropriately concluded that upon impact, as the crack forms and propagates, strain-induced martensitic transformation immediately occurs ahead of the advancing crack tip. The successive martensitic transformation profoundly facilitates the crack propagation, resulting in the extremely low impact toughness of nanostructured bainite. Retained austenite, in contrast to its well-known beneficial role, has a deteriorating effect on toughness during the course of Charpy impact. - Highlights: • The microstructure of nanostructured bainite consisted of nano-sized bainitic ferrite subunits with retained austenite films. • Special sample preparations for SEM, XRD and TEM were made, and the strain-affected structures have been explored. • Retained austenite films were found to transform into martensite after impact loading, as evidenced by XRD and TEM results. • The zone of strain-induced martensite was found to extend to only several micrometers from the fracture surface. • The poor Charpy impact toughness is associated with the fracture of martensite at a high strain rate during

  19. Microstructural characterization of Charpy-impact-tested nanostructured bainite

    International Nuclear Information System (INIS)

    In this work, a possible cause of the extraordinary low impact toughness of nanostructured bainite has been investigated. The microstructure of nanostructured bainite consisted chiefly of carbide-free bainitic ferrite with retained austenite films. X-ray diffractometry (XRD) measurement indicated that no retained austenite existed in the fractured surface of the Charpy-impact-tested specimens. Fractographs showed that cracks propagated mainly along bainitic ferrite platelet boundaries. The change in microstructure after impact loading was verified by transmission electron microscopy (TEM) observations, confirming that retained austenite was completely transformed to strain-induced martensite during the Charpy impact test. However, the zone affected by strained-induced martensite was found to be extremely shallow, only to a depth of several micrometers from the fracture surface. It is appropriately concluded that upon impact, as the crack forms and propagates, strain-induced martensitic transformation immediately occurs ahead of the advancing crack tip. The successive martensitic transformation profoundly facilitates the crack propagation, resulting in the extremely low impact toughness of nanostructured bainite. Retained austenite, in contrast to its well-known beneficial role, has a deteriorating effect on toughness during the course of Charpy impact. - Highlights: • The microstructure of nanostructured bainite consisted of nano-sized bainitic ferrite subunits with retained austenite films. • Special sample preparations for SEM, XRD and TEM were made, and the strain-affected structures have been explored. • Retained austenite films were found to transform into martensite after impact loading, as evidenced by XRD and TEM results. • The zone of strain-induced martensite was found to extend to only several micrometers from the fracture surface. • The poor Charpy impact toughness is associated with the fracture of martensite at a high strain rate during

  20. Bainitic chromium-tungsten steels with 3 pct chromium

    International Nuclear Information System (INIS)

    Previous work on 3Cr-1.5MoV (nominally Fe-3Cr-2.5Mo-0.25V-0.1C), 2.25Cr-2W (Fe-2.25Cr-2W-0.1C), and 2.25Cr-2WV (Fe-2.25Cr-2W-0.25V-0.1C) steels indicated that the impact toughness of these steels depended on the microstructure of the bainite formed during continuous cooling from the austenization temperature. Microstructures formed during continuous cooling can differ from classical upper and lower bainite formed during isothermal transformation. Two types of nonclassical microstructures were observed depending on the cooling rate: carbide-free acicular bainite at rapid cooling rates and granular bainite at slower cooling rates. The Charpy impact toughness of the acicular ferrite was considerably better than for the granular bainite. It was postulated that alloying to improve the hardenability of the steel would promote the formation of acicular bainite, just as increasing the cooling rate does. To test this, chromium and tungsten were added to the 2.25Cr-2W and 2.25Cr-2WV steel compositions to increase their hardenability. Charpy testing indicated that the new 3Cr-W and 3Cr-WV steels had improved impact toughness, as demonstrated by lower ductile-brittle transition temperatures and higher upper-shelf energies. This improvement occurred with less tempering than was necessary to achieve similar toughness for the 2.25Cr steels and for high-chromium (9 to 12 pct Cr) Cr-W and Cr-Mo steels

  1. New experimental evidence of the diffusionless transformation nature of bainite

    Energy Technology Data Exchange (ETDEWEB)

    Caballero, F.G., E-mail: fgc@cenim.csic.es [Centro Nacional de Investigaciones Metalúrgicas (CENIM-CSIC), Avda Gregorio del Amo, 8, Madrid, E-28040 (Spain); Miller, M.K. [Oak Ridge National Laboratory (ORNL), Materials Science and Technology Division, Oak Ridge, TN 37831-6136 (United States); Garcia-Mateo, C.; Cornide, J. [Centro Nacional de Investigaciones Metalúrgicas (CENIM-CSIC), Avda Gregorio del Amo, 8, Madrid, E-28040 (Spain)

    2013-11-15

    Highlights: ► A new generation of steels has been designed, which on transformation at low temperature (200–350 °C), lead to a nano-scale microstructure, known as NanoBain. The microstructure consists of slender crystals of ferrite, whose controlling scale compares well with that of carbon nanotubes (20–40 nm). ► NanoBain present the highest strength/toughness combinations ever recorded in bainitic steels (∼2.5 GPa/40 MPa m{sup 1/2}). This structure can be produced without any severe heat treatment, without deformation, simply by phase changes occurring slowly at low temperatures. ► The characterization of NanoBain at the atomic scale has led to revealed extremely important detail on the atomic mechanisms of phase transformations which have been controversial for the last seventy years. ► The results reported in this work have proven beyond doubt that the bainite phase change is essentially displacive in nature. -- Abstract: Since the discovery of bainite, research over many decades has revealed a substantial amount of information about the mechanism of the bainite transformation in steels. Elements of the theory are now routinely being used in many parts of the world in the design of novel alloys and in the interpretation of a variety of experimental data. However, current experimental and theoretical understanding is limiting technological progress. The purpose of this atom probe tomography study was to track atom distributions during the bainite reaction in a nanocrystalline steel. The results are providing new experimental evidence on subjects critically relevant to the understanding of the atomic mechanisms controlling bainitic ferrite formation, such as the incomplete transformation phenomenon, the carbon supersaturation of ferrite, and the plastic accommodation of the surrounding austenite.

  2. Bainite Morphology in Two Experimental Mo-Cr and Mo-Cr-V-Ti Steels

    Directory of Open Access Journals (Sweden)

    Ławrynowicz Z.

    2014-10-01

    Full Text Available The paper presents an investigation of the bainite morphology in two experimental Mo-Cr and Mo-Cr-V-Ti steels using TEM, high speed dilatometry backed by thermodynamic analysis. The microstructure was investigated using metallography and TEM method. After austenitisation at 1200oC followed by bainitic reaction in upper and lower temperatures of isothetmal transformation the bainite was in the form of classical sheaves. The amont, distribution and morphology of retained austenite and bainitic ferrite depend on prior austenitisation and isothermal transformation temperatures within the bainitic range.

  3. Influence of Holding Time After Deformation on Bainite Transformation in Niobium Microalloyed Steel

    Institute of Scientific and Technical Information of China (English)

    YI Hai-long; DU Lin-xiu; WANG Guo-dong; LIU Xiang-hua

    2007-01-01

    Using Gleeble-1500 system, the influence of holding time on bainite transformation in deformed niobium microalloyed steel during continuous cooling was analyzed, and the carbides in upper bainite were also systematically researched. The results show that the occurrence of the static recrystallization decreases the amount of bainite with an increase in the holding time and the emergence of retained austenite (RA) with the longer holding time. Two types of carbides were observed in upper bainite with regard to their precipitation sites. They either existed between the bainite ferrite laths or co-existed with RA. The formation mechanism of two kinds of carbides was analyzed by combining TEM micrographs with the model.

  4. Crystallographic similarity between the lath martensite and lower bainite in medium-carbon alloy steels

    Institute of Scientific and Technical Information of China (English)

    LIU Jiangwen; LUO Chengping; WU Dongxiao

    2005-01-01

    Progress in the crystallography of lath martensitic and lower bainitic transformations is briefly reviewed, followed by a presentation of the experimentally measured crystallographic characteristics of both lath martensite and lower bainite formed in mediumcarbon steels containing Si, Mn and Mo. It is found that the bainite plates relate to each other by a relative rotation of 54.7°or 60°about the normal to their common close-packed planes {110} b, which ensures a pseudo- {112}b twin relationship between two adjacent plates,and that all bainite variants formed in a single packet keep a unique G-T orientation relationship with the austenite matrix. These two types of OR of lower bainite are similar to that of the lath martensite, respectively. Furthermore, the measured habit planes of both the lower bainite and lath martensite are all {335} f type, which can verify the crystallographic similarity between the lath martensite and lower bainite.

  5. Carbon distribution in bainitic steel subjected to deformation

    Energy Technology Data Exchange (ETDEWEB)

    Ivanov, Yu. F., E-mail: yufi55@mail.ru [Institute of High Current Electronics SB RAS, Tomsk, 634055 (Russian Federation); National Research Tomsk State University, Tomsk, 634050 (Russian Federation); Nikitina, E. N., E-mail: Nikitina-EN@mail.ru; Gromov, V. E., E-mail: gromov@physics.sibsiu.ru [Siberian State Industrial University, Novokuznetsk, 654007 (Russian Federation)

    2015-10-27

    Analysis of the formation and evolution of carbide phase in medium carbon steel with a bainitic structure during compressive deformation was performed by means of transmission electron diffraction microscopy. Qualitative transformations in carbide phase medium size particles, their density and volume concentration depended on the degree of deformation.

  6. Carbon distribution in bainitic steel subjected to deformation

    International Nuclear Information System (INIS)

    Analysis of the formation and evolution of carbide phase in medium carbon steel with a bainitic structure during compressive deformation was performed by means of transmission electron diffraction microscopy. Qualitative transformations in carbide phase medium size particles, their density and volume concentration depended on the degree of deformation

  7. Formation of bainite in ferrous and nonferrous alloys through sympathetic nucleation and ledgewise growth mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Fang, H.S.; Wang, J.J.; Yang, Z.G.; Li, C.M.; Zheng, Y.K.; Li, C.X. [Tsinghua Univ., Beijing (China). Dept. of Materials Science and Engineering

    1996-06-01

    The subunits constituting a bainitic sheaf in an Fe-C-Cr-Si alloy were discovered by scanning tunneling microscopy (STM) to consist of sub-subunits, and sub-subunits were also composed of sub-sub-subunits. Detailed investigation shows that a bainitic relief is composed of many smaller reliefs, which correspond to a different structure of bainite, i.e., subunits, sub-subunits, and sub-sub-subunits. It is determined by STM that the surface relief arising from the formation of bainite in an Fe-C-Cr alloy is tent shaped rather than an invariant plane strain (IPS) types of surface relief. Careful observation shows that the relief obtained from a sub-sub-subunit is also tent shaped. It is discovered by STM that an {alpha}{sub 1} plate, i.e., bainite formed in Cu-Zn-Al alloys, is composed of subunits. This is also demonstrated by transmission electron microscopy (TEM). The preceding results indicate that bainitic plates in Cu-Zn-Al alloys and bainitic subunits in steels are not the smallest structural units. Based on the preceding results on the ultrafine structure and the nature of surface relief accompanying bainite, it is proposed that the bainitic structure forms through a sympathetic nucleation and ledgewise growth (SNLG) mechanism. This article shows that the SNLG mechanism can be successfully applied to interpret the complicated structure of bainite.

  8. Microstructure evolution of Fe-based nanostructured bainite coating by laser cladding

    International Nuclear Information System (INIS)

    Highlights: • The laser cladding and isothermal holding are used to fabricate nanobainite coating. • Fine prior austenite is obtained to accelerate the bainite transformation. • Low transformation temperature results in fine bainite ferrite and film austenite. • Retained austenite volume fraction in bainite coating is determined by XRD. • Evolution of carbon content in austenite and ferrite is analyzed. - Abstract: A Fe-based coating with nano-scale bainitic microstructure was fabricated using laser cladding and subsequent isothermal heat treatment. The microstructure of the coating was observed and analyzed using optical microscope (OM), field-emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). The results showed that nanostructured bainitic ferrite and carbon-enriched retained austenite distributed uniformly in the coating. Blocky retained austenite was confined to the prior austenite grain boundaries resulting from the elements segregation. The bainitic microstructure obtained at 250 °C had a finer scale compared with that obtained at 300 °C. The volume fraction of austenite increased with increasing transformation temperature for the fully transformed bainitic coating. The bainitic transformation was accelerated as a result of the fine prior austenite generated during the laser cladding. The evolution of the carbon contents in bainitic ferrite and retained austenite revealed the diffusionless mechanism of the bainitic transformation

  9. Correlative microscopy of a carbide-free bainitic steel.

    Science.gov (United States)

    Hofer, Christina; Bliznuk, Vitaliy; Verdiere, An; Petrov, Roumen; Winkelhofer, Florian; Clemens, Helmut; Primig, Sophie

    2016-02-01

    In this work a carbide-free bainitic steel was examined by a novel correlative microscopy approach using transmission Kikuchi diffraction (TKD) and transmission electron microscopy (TEM). The individual microstructural constituents could be identified by TKD based on their different crystal structure for bainitic ferrite and retained austenite and by image quality for the martensite-austenite (M-A) constituent. Subsequently, the same area was investigated in the TEM and a good match of these two techniques regarding the identification of the area position and crystal orientation could be proven. Additionally, the M-A constituent was examined in the TEM for the first time after preceded unambiguous identification using a correlative microscopy approach. The selected area diffraction pattern showed satellites around the main reflexes which might indicate a structural modulation.

  10. Microstructure Characterisation of Bainitic HSLA Steel for Pressure Vessels

    OpenAIRE

    Lopez, Vanessa Valle

    2014-01-01

    The microstructure and mechanical properties in the midsection of a high thickness HSLA bainitic steel, was investigated in this master thesis. A homogeneous microstructure and good mechanical properties can be difficult to achieve in high thickness steels, due to slow cooling rates in the midsection. The different cooling rates at the surface and in the midsection of the steel can cause a difference in microstructure and mechanical properties through the thicknes...

  11. QUALITY CONTROL ON THE AUSTENITIC-BAINITIC DUCTILE IRON GEAR

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    By reasonable casting, spheroidizing , inoculating and heat treating processes to control cupola metallurgy and the lipuid iron chemical compositions, a new kind of austenitic-bainitic ductile iron which can substitute for 20CrMnTi carburizing steel is studied. The gears made by the cast iron are high in quality,low in weight and the production cost is greatly reduced. The mechanical properties of the gear, including wear resistance, fatigue resistance, durability and others, can be greatly improved.

  12. Development and processing of low carbon bainitic steels

    OpenAIRE

    Suikkanen, P. (Pasi)

    2009-01-01

    Abstract The aim of this work was to study systematically the effects of composition and processing on austenite grain growth and static recrystallization (SRX) kinetics, austenite decomposition under controlled cooling as well as microstructures, mechanical properties and weldability of hot rolled low carbon bainitic (LCB) steels. The results showed that the coarsening of austenite grain structure is influenced by the chemical composition. Steels with Nb-Ti alloying exhibited fine and uni...

  13. Design of novel bainitic steels | Diseno de nuevos aceros bainiticos

    OpenAIRE

    García Caballero, Francisca; Bhadeshia, H. K. D. H.; Mawella, K.J.A; Jones, D G; P Brown

    2002-01-01

    Mixed microstructures consisting of fine plates of upper bainitic ferrite separated by thin films of stable retained austenite have seen many applications in recent years because of their impressive combination of strength and toughness. There may also be some martensite present in the microstructure, but its formation can be controlled increasing the stability of the retained austenite. On the other hand, carbides are avoided by the judicious use of silicon as an alloying element. The aim of...

  14. Mechanism of Bainite Nucleation in Steel, Iron and Copper Alloys

    Institute of Scientific and Technical Information of China (English)

    Mokuang KANG; Ming ZHU; Mingxing ZHANG

    2005-01-01

    During the incubation period of isothermal treatment(or aging) within the bainitic transformation temperature range in a salt bath (or quenching in water) immediately after solution treatment, not only are the defects formed at high temperatures maintained, but new defects can also be generated in alloys, iron alloys and steels. Due to the segregation of the solute atoms near defects through diffusion, this leads to non-uniform distributions of solute atoms in the parent phase with distinct regions of both solute enrichment and solute depletion. It is proposed that when the Ms temperature at the solute depleted regions is equal to or higher than the isothermal (or aged) temperature,nucleation of bainite occurs within these solute depleted regions in the manner of martensitic shear. Therefore it is considered that, at least in steel, iron and copper alloy systems, bainite is formed through a shear mechanism within solute depleted regions, which is controlled and formed by the solute atoms diffusion in the parent phase.

  15. TEM Study of the Orientation Relationship Between Cementite and Ferrite in a Bainitic Low Carbon High Strength Low Alloy Steel

    OpenAIRE

    Illescas Fernandez, Silvia; Brown, A P; He, K.; Fernández, Javier; Guilemany Casadamon, Josep Maria

    2005-01-01

    Two different bainitic structures are observed in a steel depending on the sample heat treatment. The different types of bainitic structures exhibit different orientation relationships between cementite and the ferrite matrix. Upper bainite presents a Pitsch orientation relationship and lower bainite presents a Bagaryatski orientation relationship. Different heat treatments of low carbon HSLA steel samples have been studied using TEM in order to find the orientation relationshi...

  16. Effect of Rare Earth Elements on Isothermal Transformation Kinetics in Si-Mn-Mo Bainite Steels

    Science.gov (United States)

    Liang, Yilong; Yi, Yanliang; Long, Shaolei; Tan, Qibing

    2014-12-01

    Isothermal heat treatments to Si-Mn-Mo steel specimens were performed, and time-temperature-transformation curves (C-curves) were plotted by DIL805A/D differential dilatometer. The effect of rare earth (RE) elements on bainite transformation kinetics was systematically studied by adopting the empirical electron theory of solids and molecules, Johnson-Mehl-Avrami equation calculation, dilatometry, and metallography. Experimental results show that the addition of RE in Si-Mn-Mo bainite steels leads to the C-curves moving to bottom right and prolongs incubation period of bainite transformation. Moreover, RE addition increases the values of phase structure factors ( n A, F {C/D}) and activation energy of bainite transformation, inhibits the formation of granular bainite, and refines microstructures of bainitic ferrite and substructures. During the bainite transformation process, bainite transformation is delayed due to the drag effect, which is induced by the segregation of RE at the ferrite interphase and the retardation of Fe-C-RE (segregation units) on carbon diffusion.

  17. Bainite Formation in Medium-Carbon Low-Silicon Spring Steels Accounting for Chemical Segregation

    Science.gov (United States)

    Goulas, C.; Mecozzi, M. G.; Sietsma, J.

    2016-06-01

    In this paper, the effect of chemical inhomogeneity on the isothermal bainite formation is investigated in medium-carbon low-silicon spring steel by dilatometry and microscopy. The analysis of the microstructure at different times during transformation shows that chemical segregation of substitutional alloying elements resulting from casting strongly affects the bainite formation by retarding the transformation kinetics and limiting the maximum achievable bainite fraction. During holding at temperatures close to and above the martensite start temperature, a homogeneous lower bainitic microstructure can be eventually obtained, whereas at higher temperatures, incomplete bainitic reaction is evident. It was also found that at the early stages of the transformation, differences in the bainite formation kinetics, due to local inhomogeneities in Cr and Mn concentration, result in retardation of the growth of bainite in the high Mn and Cr concentration regions. The calculated difference in driving force for nucleation between the enriched and the depleted areas is not by itself sufficient to explain the microstructures obtained and thus significant influence of growth on bainite formation is observed. Particularly, it was calculated and experimentally observed that Cr partitions in the carbides in the high Mn, Cr regions during the isothermal treatment, limiting the transformation kinetics.

  18. In situ measured growth rates of bainite plates in an Fe-C-Mn-Si superbainitic steel

    Institute of Scientific and Technical Information of China (English)

    Zhang-wei Hu; Guang Xu; Hai-jiang Hu; Li Wang; Zheng-liang Xue

    2014-01-01

    The growth rates of bainite plates in an Fe-C-Mn-Si superbainitic steel were investigated by in situ observation. The lengthening rates of ferrite bainite during both cooling and isothermal holding processes were observed and the growth rates of bainite plates nucleating at grain boundaries, within grains and on preformed bainite were measured. It is indicated that the lengthening rates of bainite plates during the cooling and isothermal processes were different, and that the growth rates of bainite plates nucleating at different types of sites also demon-strated diversity. The bainite plates initiating at grain boundaries during cooling grew the fastest, while the plates nucleating on preformed bainite did the slowest. However, the growth rate of the bainite plates nucleating at grain boundaries during isothermal transformation de-creased the most, whereas the bainite plates initiating within grains grew the fastest. In addition, the growth rate of ferrite bainite in the study supported the diffusion transformation mechanism of bainite from the viewpoint of growth rate.

  19. Effect of B and B + Nb on the bainitic transformation in low carbon steels

    Energy Technology Data Exchange (ETDEWEB)

    Zhu Kangying, E-mail: kangying.zhu@arcelormittal.com [ArcelorMittal Maizieres, Research and Development, BP 30320, 57283 Maizieres-les-Metz Cedex (France); Oberbillig, Carla, E-mail: carla.oberbillig@arcelormittal.com [ArcelorMittal Maizieres, Research and Development, BP 30320, 57283 Maizieres-les-Metz Cedex (France); Musik, Celine, E-mail: celine.musik@arcelormittal.com [ArcelorMittal Maizieres, Research and Development, BP 30320, 57283 Maizieres-les-Metz Cedex (France); Loison, Didier, E-mail: didier.loison@arcelormittal.com [ArcelorMittal Maizieres, Research and Development, BP 30320, 57283 Maizieres-les-Metz Cedex (France); Iung, Thierry, E-mail: thierry.iung@arcelormittal.com [ArcelorMittal Maizieres, Research and Development, BP 30320, 57283 Maizieres-les-Metz Cedex (France)

    2011-05-15

    Research highlights: {yields} B retards slightly the bainite transformation kinetics. {yields} Combined addition of B + Nb delayed dramatically bainite transformation kinetics. {yields} B refines the microstructure and promotes lath morphology of bainite. {yields} Larger packets of laths and longer laths are observed in the B + Nb steel. {yields} More free boron/finer borocarbide precipitates on {gamma} grain boundaries in B + Nb steel. - Abstract: Development of new, advanced high and ultra-high strength bainitic steels requires the selection of the optimum balance of bainite promoting elements allowing the production of the desired bainitic microstructure over a wide range of cooling rates. The addition of boron or a combined addition of boron and niobium is well known to retard strongly the polygonal ferrite formation but very little knowledge has been acquired on the bainitic transformation. Therefore, the purpose of this study is to investigate the influence of boron and boron plus niobium on the bainite transformation kinetics, microstructural evolution and mechanical properties in a low carbon steel (Fe-0.05C-1.49Mn-0.30Si). Isothermal and continuous cooling transformation diagrams were determined and followed by a detailed quantitative characterisation of the bainite microstructure and morphology using complementary advanced metallographic techniques (FEG-SEM-EBSD, SIMS and TEM). The relationship between microstructure and hardness has been evaluated. Finally, results of SIMS and TEM analyses coupled with microstructural investigations enable to propose a mechanism to explain the effect of the synergy between boron and niobium on the bainitic transformation and the resultant microstructure.

  20. An assessment of the contributing factors to the nanoscale structural refinement of advanced bainitic steels

    Energy Technology Data Exchange (ETDEWEB)

    Cornide, J., E-mail: jca@cenim.csic.es [Centro Nacional de Investigaciones Metalúrgicas (CENIM-CSIC), Avda Gregorio del Amo 8, Madrid E-28040 (Spain); Garcia-Mateo, C., E-mail: cgm@cenim.csic.es [Centro Nacional de Investigaciones Metalúrgicas (CENIM-CSIC), Avda Gregorio del Amo 8, Madrid E-28040 (Spain); Capdevila, C., E-mail: ccm@cenim.csic.es [Centro Nacional de Investigaciones Metalúrgicas (CENIM-CSIC), Avda Gregorio del Amo 8, Madrid E-28040 (Spain); Caballero, F.G., E-mail: fgc@cenim.csic.es [Centro Nacional de Investigaciones Metalúrgicas (CENIM-CSIC), Avda Gregorio del Amo 8, Madrid E-28040 (Spain)

    2013-11-15

    A new generation of steels has been designed, which on transformation at low temperature (200–350 °C), leads to a nano-scale microstructure, known as NANOBAIN. The microstructure consists of slender crystals of ferrite, whose controlling scale compares well with that of carbon nanotubes (20–40 nm). These advanced steels present the highest strength/toughness combinations ever recorded in bainitic steels. Their properties are mainly a consequence of the formation of nanoscale bainitic ferrite plates at very low temperatures. Transmission electron microscopy observations have shown that plastic relaxation in the austenite adjacent to the bainite plates may control the final size of the bainitic ferrite plates. The dislocation debris generated in this process resists the advance of the bainitic ferrite–austenite interface, the resistance being greatest for strong austenite. The yield strength of the austenite must then feature in any assessment of plate size. In this scenario, the plates are expected to become thicker at high temperatures because the yield strength of the austenite will then be lower. The goal of this study is to evaluate the influence of yield strength of austenite to the nanoscale structural refinement of advanced bainitic steels. In this sense, in situ measurements of austenite strength before bainite formation using a deformation dilatometer Bähr 805D have been performed in a medium carbon high silicon steel transforming at intermediate temperatures (325–400 °C) to a submicron structure of bainite and in a high carbon high silicon steel transforming at low temperatures (200–350 °C) to nanostructured bainite. The role of the transformation driving force on the bainite plate thickness will be also discussed.

  1. Numerical generation and study of synthetic bainitic microstructures

    Energy Technology Data Exchange (ETDEWEB)

    Osipov, N.; Gourgues-Lorenzon, A.F.; Cailletaud, G. [Centre des Materiaux Mines Paris, Paristech CNRS UMR 7633, 91 - Evry (France); Diard, O. [Electricite de France, Div. R and D, Centre des Renardieres, 77 - Moret sur Loing (France); Marini, B. [CEA Saclay (SRMA), 91 - Gif-sur-Yvette (France)

    2006-07-01

    Models classically used to describe the probability of brittle fracture in nuclear power plants are written on the macroscopic scale. Its is not easy to surely capture the physical phenomena in such a type of approach, so that the application of the models far from their identification domain (temperature history, loading path) may become questionable. To improve the quality of the prediction of resistance and life time, microstructural information, describing the heterogeneous character of the material and its deformation mechanisms has to be taken into consideration. This paper is devoted to 16MND5 bainitic steel. Bainitic packets grow in former austenitic grains, and are not randomly oriented. Knowing the macroscopic stress is thus not sufficient to describe the stress-strain state in ferrite. An accurate model must take into account the actual microstructure, in order to provide realistic local stress and strain fields, to be used as inputs of a new class of cleavage models based on the local behavior. The paper shows the approach used to generate a synthetic microstructure and demonstrates that the resulting morphologies present a quantitative agreement with the experimental images. (authors)

  2. A new effect of retained austenite on ductility enhancement in high strength bainitic steel

    International Nuclear Information System (INIS)

    Highlights: ► A new DARA effect in the bainitic steel is proposed. ► The conditions of DARA effect are proposed. ► The mechanism of retained austenite on ductility enhancement is clarified. - Abstract: A designed high strength bainitic steel with considerable amount of retained austenite is presented in order to study the effect of retained austenite on the ductility enhancement in bainitic steels. Transformation induced plasticity (TRIP) effect is verified by both X-ray diffraction (XRD) measurement of retained austenite fraction in various deformation stages and transmission electron microscopy observation of the deformed twin-type martensite. Results from XRD line profile analysis reveal that the average dislocation density in bainite during the deformation is lower than that before deformation, and such a phenomenon can be explained by a new effect, dislocations absorption by retained austenite (DARA) effect, based on our previous investigation of martensitic steels. DARA effect availably enhances the compatibility of deformation ability of bainite with retained austenite. In view of microstructure similarity of bainitic steels with martensitic steels, the conditions of DARA effect are proposed. The effects of retained austenite on the ductility enhancement in bainitic steels are clarified.

  3. Low temperature bainitic ferrite: Evidence of carbon super-saturation and tetragonality

    International Nuclear Information System (INIS)

    Experimental evidence indicates that bainitic ferrite formed by transformation at low temperatures (200–350 °C) contains quantities of carbon in solid solution far beyond those expected from para-equilibrium. A change in the conventional symmetry of the bainitic ferrite lattice from cubic to tetragonal explains the abnormal solid solubility detected. This carbon supersaturation was measured by atom probe tomography, and the tetragonality of the bainitic ferrite, was characterized by means of X-ray diffraction analysis and high resolution transmission electron microscopy

  4. Modeling the austenite decomposition into ferrite and bainite

    Science.gov (United States)

    Fazeli, Fateh

    2005-12-01

    Novel advanced high-strength steels such as dual-phase (DP) and transformation induced plasticity (TRIP) steels, are considered as promising materials for new generation of lightweight vehicles. The superior mechanical properties of these steels, compared to classical high strength steels, are associated with their complex microstructures. The desired phase configuration and morphology can only be achieved through well-controlled processing paths with rather tight processing windows. To implement such challenging processing stages into the current industrial facilities a significant amount of development efforts, in terms of mill trials, have to be performed. Alternatively, process models as predictive tools can be employed to aid the process development' and also to design new steel grades. Knowledge-based process models are developed by virtue of the underlying physical phenomena occurring during the industrial processing and are validated with experimental data. The goal of the present work is to develop an integrated microstructure model to adequately describe the kinetics of austenite decomposition into polygonal ferrite and bainite, such that for complex thermal paths simulating those of industrial practice, the final microstructure in advanced high strength steels can reasonably be predicted. This is in particular relevant to hot-rolled DP and TRIP steels, where the intercritical ferrite evolution due to its crucial influence on the onset and kinetics of the subsequent bainite formation, has to be quantified precisely. The calculated fraction, size and spatial carbon distribution of the intercritical austenite are employed as input to characterize adequately the kinetic of the bainite reaction. Pertinent to ferrite formation, a phenomenological, physically-based model was developed on the ground of the mixed-mode approach. The model deals with the growth stage since nucleation site saturation at prior austenite grain boundaries is likely to be attained

  5. The crystallography of carbide-free bainites in thermo-mechanically processed low Si transformation-induced plasticity steels

    Energy Technology Data Exchange (ETDEWEB)

    Pereloma, Elena V. [School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, New South Wales 2522 (Australia); Electron Microscopy Centre, University of Wollongong, New South Wales 2500 (Australia); Al-Harbi, Fayez [School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, New South Wales 2522 (Australia); Gazder, Azdiar A., E-mail: azdiar@uow.edu.au [Electron Microscopy Centre, University of Wollongong, New South Wales 2500 (Australia)

    2014-12-05

    Highlights: • First EBSD study comparing ferrite in granular bainite and bainitic laths in two TRIP steels. • Both TRIP steels (base and with Nb–Ti additions) subjected to the same TMP schedule. • Crystallography of the ferrite in the 2 bainites studied using the K–S orientation relationship. • Variants in GB associated with self-accommodation. • BF variant selection linked to RA plastic accommodation and limited volume. - Abstract: Carbide-free bainites are important microstructural constituents in bainitic, nanobainitic and transformation-induced plasticity (TRIP) steels. A comparison of the crystallography of ferrite in granular bainite and bainitic ferrite lath morphologies, both of which were simultaneously present in a base and a Nb–Ti containing TRIP steel, has been carried out using electron back-scattering diffraction. Ferrite in granular bainite was characterised by the realisation of nearly all 24 variants of the Kurdjumov–Sachs orientation relationship; which in turn was associated with the self-accommodation of the transformation strain. On the other hand, bainitic ferrite comprised a mostly parallel lath structure between thick interlayers of retained austenite and exhibited variant selection such that one or more crystallographic packets are not realised and sometimes only 1–2 variants formed in a crystallographic packet. The variant selection in bainitic ferrite laths was associated with: (i) the plastic accommodation of transformation strain by retained austenite and, (ii) the limited available volume for its formation.

  6. The crystallography of carbide-free bainites in thermo-mechanically processed low Si transformation-induced plasticity steels

    International Nuclear Information System (INIS)

    Highlights: • First EBSD study comparing ferrite in granular bainite and bainitic laths in two TRIP steels. • Both TRIP steels (base and with Nb–Ti additions) subjected to the same TMP schedule. • Crystallography of the ferrite in the 2 bainites studied using the K–S orientation relationship. • Variants in GB associated with self-accommodation. • BF variant selection linked to RA plastic accommodation and limited volume. - Abstract: Carbide-free bainites are important microstructural constituents in bainitic, nanobainitic and transformation-induced plasticity (TRIP) steels. A comparison of the crystallography of ferrite in granular bainite and bainitic ferrite lath morphologies, both of which were simultaneously present in a base and a Nb–Ti containing TRIP steel, has been carried out using electron back-scattering diffraction. Ferrite in granular bainite was characterised by the realisation of nearly all 24 variants of the Kurdjumov–Sachs orientation relationship; which in turn was associated with the self-accommodation of the transformation strain. On the other hand, bainitic ferrite comprised a mostly parallel lath structure between thick interlayers of retained austenite and exhibited variant selection such that one or more crystallographic packets are not realised and sometimes only 1–2 variants formed in a crystallographic packet. The variant selection in bainitic ferrite laths was associated with: (i) the plastic accommodation of transformation strain by retained austenite and, (ii) the limited available volume for its formation

  7. Subgrains and boron distribution of low carbon bainitic steels

    Institute of Scientific and Technical Information of China (English)

    Xuemin Wang; Bing Cao; Chengjia Shang; Xueyi Liu; Xinlai He

    2005-01-01

    The structure variation of deformed austenite during the relaxation stage after deformation at various temperatures in an Nb-B ultra low carbon bainitic steel and Fe-Ni alloy was studied by the thermo-simulation. Optical microscope and TEM were applied to analyze the microstructure after RPC (Relaxation-precipitation-controlling phase transformation technique) and the evolution of dislocation configuration. The particle tracking autoradiography (PTA) technique, revealing the distribution of boron, was employed to show the change of boron segregation after different relaxation times. The results indicate that during the relaxation stage the recovery occurs in the deformed austenite, the dislocations rearrange and subgrains form. During the subsequent cooling the boron will segregate at the boundaries of subgrains.

  8. Charpy notch toughness and hardness of reheated martensite and lower bainite

    Directory of Open Access Journals (Sweden)

    F. Vodopivec

    2010-07-01

    Full Text Available A high strength low alloyed (HSLA V-Nb steel was heat treated to martensite and lower bainite with different grain size, reheated for 3 seconds at 750 °C and air cooled. Charpy notch tests were performed from -100 °C to 60 °C and the hardness assessed at room temperature. For as delivered steel and lower bainite, the upper shelf toughness was above 200 J and the transition temperature low, while, for martensite the upper shelf toughness threshold was aproximateky at 0 °C. After reheating, notch toughness was decreased moderatly for martensite and strongly for lower bainite. Independently on grain size, lower bainite was more propensive than martensite to embritlement after short reheating in the (α + β range. For martensite, the change of notch toughness was not related to change of hardness, as by lower hardness lower, also toughness was lower.

  9. Nanomechanical characterization of nanostructured bainitic steel: Peak Force Microscopy and Nanoindentation with AFM.

    Science.gov (United States)

    Morales-Rivas, Lucia; González-Orive, Alejandro; Garcia-Mateo, Carlos; Hernández-Creus, Alberto; Caballero, Francisca G; Vázquez, Luis

    2015-01-01

    The full understanding of the deformation mechanisms in nanostructured bainite requires the local characterization of its mechanical properties, which are expected to change from one phase, bainitic ferrite, to another, austenite. This study becomes a challenging process due to the bainitic nanostructured nature and high Young's modulus. In this work, we have carried out such study by means of the combination of AFM-based techniques, such as nanoindentation and Peak Force Quantitative Nanomechanical Mapping (PF-QNM) measurements. We have addressed critically the limits and advantages of these techniques and been able to measure some elastoplastic parameters of both phases. Specifically, we have analyzed by PF-QNM two nanostructured bainitic steels, with a finer and a coarser structure, and found that both phases have a similar Young's modulus. PMID:26602631

  10. Carbide-Free Bainitic Weld Metal: A New Concept in Welding of Armor Steels

    Science.gov (United States)

    Krishna Murthy, N.; Janaki Ram, G. D.; Murty, B. S.; Reddy, G. M.; Rao, T. J. P.

    2014-12-01

    Carbide-free bainite, a fine mixture of bainitic ferrite and austenite, is a relatively recent development in steel microstructures. Apart from being very strong and tough, the microstructure is hydrogen-tolerant. These characteristics make it well-suited for weld metals. In the current work, an armor-grade quenched and tempered steel was welded such that the fusion zone developed a carbide-free bainitic microstructure. These welds showed very high joint efficiency and ballistic performance compared to those produced, as per the current industrial practice, using austenitic stainless steel fillers. Importantly, these welds showed no vulnerability to cold cracking, as verified using oblique Y-groove tests. The concept of carbide-free bainitic weld metal thus promises many useful new developments in welding of high-strength steels.

  11. Atomic scale observations of bainite transformation in a high carbon high silicon steel

    OpenAIRE

    García Caballero, Francisca; Miller, M. K.; Babu, S. S.; García Mateo, Carlos

    2007-01-01

    A fine-scale bainitic microstructure with high strength and high toughness has been achieved by transforming austenite at 200 ºC. X-ray diffraction analysis showed the carbon concentration of these bainitic ferrite plates to be higher than expected from paraequilibrium. Atom probe tomography revealed that a substantial quantity of carbon was trapped at dislocations in the vicinity of the ferrite/austenite interface. These results suggest that the carbon trapping at dislocations...

  12. On the role of microstructure in governing the fatigue behaviour of nanostructured bainitic steels

    OpenAIRE

    Rementeria, R.; Morales-Rivas, L.; Kuntz, M.; García Mateo, Carlos; Kerscher, E.; Sourmail, T.; García Caballero, Francisca

    2015-01-01

    © 2015 Elsevier B.V. Nanostructured bainite is not a novel laboratory-scale steel anymore and the interest on the commercial production of these microstructures by steelmakers and end-users is now conceivable. These microstructures are achieved through the isothermal transformation of high-carbon high-silicon steels at low temperature, leading to nanoscale plates of ferrite with thickness of 20-40nm and retained austenite. Nanostructured bainitic steels present the highest strength/toughness ...

  13. Mechanical properties of low-alloy-steels with bainitic microstructures and varying carbon content

    Science.gov (United States)

    Weber, A.; Klarner, J.; Vogl, T.; Schöngrundner, R.; Sam, G.; Buchmayr, B.

    2016-03-01

    Materials used in the oilfield industry are subjected to special conditions. These requirements for seamless steel tubes are between the priorities of strength, toughness and sour gas resistance. Steels with bainitic microstructure provide a great opportunity for those harsh environmental conditions. With different morphologies of bainite, like carbide free, upper or lower bainite, the interaction of high tensile strength and elongation is assumed to be better than with tempered martensite. To form carbide free bainite two ways of processing are proposed, isothermal holding with accurate time control or controlled continuous cooling. Both require knowledge of time-temperature transformation behaviour, which can be reached through a detailed alloying concept, focused on the influence of silicon to supress the carbide nucleation and chromium to stabilize the austenite fraction. The present work is based on three alloys with varying silicon and chromium contents. The carbide free microstructure is obtained by a continuous cooling path. Additionally different heat treatments were done to compare the inherent performance of the bainitic morphologies. The bainitic structures were characterized metallographically for their microstructure and the primary phase by means of transmission electron microscopy. The mechanical properties of carbide-free structures were analysed with quasi-static tensile tests and Charpy impact tests. Moreover, investigations about hydrogen embrittlement were done with focus on the effect of retained austenite. The results were ranked and compared qualitatively.

  14. Effect of Mo Content on Microstructure and Property of Low-Carbon Bainitic Steels

    Directory of Open Access Journals (Sweden)

    Haijiang Hu

    2016-07-01

    Full Text Available In this work, three low-carbon bainitic steels, with different Mo contents, were designed to investigate the effects of Mo addition on microstructure and mechanical properties. Two-step cooling, i.e., initial accelerated cooling and subsequent slow cooling, was used to obtain the desired bainite microstructure. The results show that the product of strength and elongation first increases and then shows no significant change with increasing Mo. Compared with Mo-free steel, bainite in the Mo-containing steel tends to have a lath-like morphology due to a decrease in the bainitic transformation temperature. More martensite transformation occurs with the increasing Mo, resulting in greater hardness of the steel. Both the strength and elongation of the steel can be enhanced by Mo addition; however, the elongation may decrease with a further increase in Mo. From a practical viewpoint, the content of Mo could be ~0.14 wt. % for the composition design of low-carbon bainitic steels in the present work. To be noted, an optimal scheme may need to consider other situations such as the role of sheet thickness, toughness behavior and so on, which could require changes in the chemistry. Nevertheless, these results provide a reference for the composition design and processing method of low-carbon bainitic steels.

  15. Rationalisation of Austenite Transformation to Upper or Lower Bainite in Steels

    Directory of Open Access Journals (Sweden)

    Ławrynowicz Z.

    2014-06-01

    Full Text Available The paper presents an analytical evaluation of transition temperature from upper to lower bainite in Fe-C-Cr steel. The calculations was based on the model constructed by Matas and Hehemann which involves a comparison between the times needed to precipitate cementite within the bainitic ferrite plates (tθ, with the time required to decarburise supersaturated ferrite plates (td. The transition between upper and lower bainite is found to occur over a narrow range of temperatures (350-410°C and depends on the thickness of bainitic ferrite laths and the volume fraction of precipitated cementite. On comparing the td and tθ times it was found that the transition temperature from upper to lower bainite reaction (LS of about 350oC could be predicted if the thickness of bainitic ferrite laths is set as wo = 0.1 μm and volume fraction of cementite is set as ξ = 0.01

  16. Effect of microstructure on the fracture toughness of ferrite-martensite-bainite steels

    International Nuclear Information System (INIS)

    The effect of microstructure on the fracture toughness of ferrite-martensite -bainite steels was investigated with Fe-0.11C-1.64Mn-0.78Si composition. One inch compact tension specimens (1T-CTSs) were machined from hot rolled plates. The microstructure of ferrite-martensite-bainite was introduced to the specimens by the heat treatment of intercritical annealing at 800deg C and isothermal holding at 350deg C. Holding at 350deg C increased volume fraction of bainite, while decreased that of martensite, and refined martensite particles. Single specimen unloading compliance method was used in fracture test to obtain J-resistance (J-R) curve and to determine the fracture toughness(JIC). Introduction of bainite to the ferrite-martensite steel improved the fracture toughness due to the deformation of bainite which relaxed the stress concentration on the interface of ferrite and martensite. Observation of fracto-graphs through the scanning electron microscope(SEM) identified the fracture mechanism of ferrite-martensite-bainite steels as dimple nucleation and crack growth by decohesion of ferrite matrix and second phase particles and by microvoid coales cence. (Author)

  17. TEM study of bainitic low-carbon HSLA steel: the orientation relationships of cementite; TEM-Untersuchung eines kohlenstoffarmen bainitischen HSLA-Stahls: die Orientierungsbeziehungen von Zementit

    Energy Technology Data Exchange (ETDEWEB)

    Illescas, S.; Fernandez, J.; Guilemany, J.M. [Barcelona Univ. (Spain). Dept. de Ciencia dels Materials i Enginyeria Metallurgica; Asensio, J. [Oviedo Univ. (Spain). Dept. de Ciencia de los Materiales e Ingenieria Metalurgica

    2007-07-15

    Two different bainitic structures can be present in steel depending on the heat treatment to which the samples are subjected. The two different types of bainitic structures exhibit a different orientation relationship between the cementite and the ferrite matrix. The Pitsch orientation relationship is observed in upper bainite while the Bagaryatski orientation relationship is observed in lower bainite. Different heat treatment samples of low-carbon high strength low alloy (HSLA) steel were studied using TEM observations in order to ascertain the orientation relationship between ferrite and carbide in the different bainitic structures and to determine whether this relationship may indicate the type of bainitic structure. (orig.)

  18. Microscopic deformation and strain hardening analysis of ferrite–bainite dual-phase steels using micro-grid method

    International Nuclear Information System (INIS)

    The local strain measurement method using nanometer-scaled micro grids printed on the surface of a specimen by an electron lithography technique (the micro-grid method) has been established. Microscopic deformation behavior of the ferrite–bainite steels with different bainite volume fraction, 16% and 40% of bainite, was evaluated. Strain localization in the ferrite phase adjacent to the ferrite/bainite boundary was clearly observed and visualized. Highly strained regions expanded toward the inner region of the ferrite phase and connected each other with an increase of macroscopic strain. The existence of hard bainite phase plays an important role for inducing strain localization in the ferrite phase by plastic constraint in the boundary parallel to the tensile direction. In order to obtain further understanding of microscopic deformation behavior, finite element analysis using the representative volume element, which is expressed by the axisymmetric unit cell containing a hard phase surrounded by a soft phase matrix, was conducted. It was found that the macroscopic stress–strain behavior of ferrite–bainite steels was well simulated by the unit cell models. Strain concentration in the ferrite phase was highly enhanced for the ferrite-40% bainite steel, and this imposed higher internal stress in the bainite phase, resulting in higher strain hardening rate in the early stage of the deformation. However, smaller ferrite volume fraction of ferrite-40% bainite steel induced bainite plastic deformation in order to fulfill the macroscopic strain of the steel. Accordingly, strain hardening capacity of the ferrite-40% bainite steel was reduced to a significant degree, resulting in a smaller uniform elongation than the ferrite-16% bainite steel

  19. Mechanical properties of steels with a microstructure of bainite/martensite and austenite islands

    Science.gov (United States)

    Syammach, Sami M.

    Advanced high strength steels (AHSS) are continually being developed in order to reduce weight and improve safety for automotive applications. There is need for economic steels with improved strength and ductility combinations. These demands have led to research and development of third generation AHSS. Third generation AHSS include steel grades with a bainitic and tempered martensitic matrix with retained austenite islands. These steels may provide improved mechanical properties compared to first generation AHSS and should be more economical than second generation AHSS. There is a need to investigate these newer types of steels to determine their strength and formability properties. Understanding these bainitic and tempered martensitic steels is important because they likely can be produced using currently available production systems. If viable, these steels could be a positive step in the evolution of AHSS. The present work investigates the effect of the microstructure on the mechanical properties of steels with a microstructure of bainite, martensite, and retained austenite, so called TRIP aided bainitic ferrite (TBF) steels. The first step in this project was creating the desired microstructure. To create a microstructure of bainite, martensite, and austenite an interrupted austempering heat treatment was used. Varying the heat treatment times and temperatures produced microstructures of varying amounts of bainite, martensite, and austenite. Mechanical properties such as strength, ductility, strain hardening, and hole-expansion ratios were then evaluated for each heat treatment. Correlations between mechanical properties and microstructure were then evaluated. It was found that samples after each of the heat treatments exhibited strengths between 1050 MPa and 1350 MPa with total elongations varying from 8 pct to 16 pct. By increasing the bainite and austenite volume fraction the strength of the steel was found to decrease, but the ductility increased. Larger

  20. Refinement of packet size in low carbon bainitic steel by special thermo-mechanical control process

    Institute of Scientific and Technical Information of China (English)

    Chengjia Shang; Xuemin Wang; Shanwu Yang; Xinlai He

    2004-01-01

    The packet size of bainitic steel can be refined by a special relaxation-precipitation-control phase transformation (RPC)technology. When processed by RPC process, the low carbon bainitic steel composes of two kinds of main intermediate transformation phases. One is ultra-fine lath-like bainitic ferrite and the lath is less than 1 μm in width and about 6 μm in length; the alignment of laths forms a refined packet, and the size of packets is about 5-7 μm in length and about 3-4 μm in width. The other is acicular structure. The morphology and distribution of these acicular structures are influenced by relaxation process, the thin and short acicular structures cut the prior austenite grain and refine the bainitic packet size. For the optimum relaxation time, the packet size can be refined to the finest. The mechanical properties are influenced by relaxation time and the 800 Mpa grade low carbon bainitic steel with excellent toughness can be obtained by RPC process.

  1. Nano-sized precipitation and properties of a low carbon niobium micro-alloyed bainitic steel

    International Nuclear Information System (INIS)

    The present work focuses on microstructure evolution and precipitation strengthening during tempering at region of 550–680 °C to elucidate the structure–property relationship in the steel. The effect of tempering on the development of a 700 MPa grade high strength hot rolled cost-effective bainitic steel was studied for infrastructure applications. Granular bainite with dispersed martenisit–austenite (M–A) constituents in the bainitic ferrite matrix was obtained after hot rolling and air cooling to room temperature. The decomposition of M–A constituents to cementite carbides and the precipitation of nano-sized NbC carbides in bainitic matrix on tempering were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Nano-sized precipitates of NbC precipitated during tempering were in average diameter of ~4.1–6.1 nm. There were ~86–173 MPa increases in yield strength after tempering at region of 550–680 °C. It is noticeable that those nano-sized NbC precipitates provide an effective way to significantly increase the strength of the low carbon bainitic steel. High yield strength of 716 MPa with high ductility (uniform elongation of 9.3% and total elongation of 22.4%), low yield to tensile ratio of 0.9 and good low temperature toughness of 47 J (half thickness) at –40 °C was obtained after tempering at 680 °C for 30 min

  2. Nano-sized precipitation and properties of a low carbon niobium micro-alloyed bainitic steel

    Energy Technology Data Exchange (ETDEWEB)

    Xie, Z.J. [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Department of Materials Science and Engineering, McMaster University, Hamilton L8S 4L8 (Canada); Ma, X.P. [Department of Materials Science and Engineering, McMaster University, Hamilton L8S 4L8 (Canada); Shang, C.J., E-mail: cjshang@ustb.edu.cn [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Wang, X.M. [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Subramanian, S.V. [Department of Materials Science and Engineering, McMaster University, Hamilton L8S 4L8 (Canada)

    2015-08-12

    The present work focuses on microstructure evolution and precipitation strengthening during tempering at region of 550–680 °C to elucidate the structure–property relationship in the steel. The effect of tempering on the development of a 700 MPa grade high strength hot rolled cost-effective bainitic steel was studied for infrastructure applications. Granular bainite with dispersed martenisit–austenite (M–A) constituents in the bainitic ferrite matrix was obtained after hot rolling and air cooling to room temperature. The decomposition of M–A constituents to cementite carbides and the precipitation of nano-sized NbC carbides in bainitic matrix on tempering were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Nano-sized precipitates of NbC precipitated during tempering were in average diameter of ~4.1–6.1 nm. There were ~86–173 MPa increases in yield strength after tempering at region of 550–680 °C. It is noticeable that those nano-sized NbC precipitates provide an effective way to significantly increase the strength of the low carbon bainitic steel. High yield strength of 716 MPa with high ductility (uniform elongation of 9.3% and total elongation of 22.4%), low yield to tensile ratio of 0.9 and good low temperature toughness of 47 J (half thickness) at –40 °C was obtained after tempering at 680 °C for 30 min.

  3. On the role of microstructure in governing the fatigue behaviour of nanostructured bainitic steels

    Energy Technology Data Exchange (ETDEWEB)

    Rementeria, Rosalia, E-mail: rosalia.rementeria@cenim.csic.es [Department of Physical Metallurgy, Spanish National Center for Metallurgical Research (CENIM-CSIC), Avda. Gregorio del Amo 8, E-28040 Madrid (Spain); Morales-Rivas, Lucia, E-mail: lucia.morales@cenim.csic.es [Department of Physical Metallurgy, Spanish National Center for Metallurgical Research (CENIM-CSIC), Avda. Gregorio del Amo 8, E-28040 Madrid (Spain); Kuntz, Matthias, E-mail: matthias.kuntz2@de.bosch.com [Robert Bosch GmbH, Materials and Processing Department, Renningen, 70465 Stuttgart (Germany); Garcia-Mateo, Carlos, E-mail: cgm@cenim.csic.es [Department of Physical Metallurgy, Spanish National Center for Metallurgical Research (CENIM-CSIC), Avda. Gregorio del Amo 8, E-28040 Madrid (Spain); Kerscher, Eberhard, E-mail: kerscher@mv.uni-kl.de [University of Kaiserslautern, Materials Testing, Gottlieb-Damiler-Straße, 67663 Kaiserslautern (Germany); Sourmail, Thomas, E-mail: thomas.sourmail@ascometal.com [Ascometal-CREAS (Research Centre) Metallurgy, BP 70045, Hagondange Cedex 57301 (France); Caballero, Francisca G., E-mail: fgc@cenim.csic.es [Department of Physical Metallurgy, Spanish National Center for Metallurgical Research (CENIM-CSIC), Avda. Gregorio del Amo 8, E-28040 Madrid (Spain)

    2015-04-10

    Nanostructured bainite is not a novel laboratory-scale steel anymore and the interest on the commercial production of these microstructures by steelmakers and end-users is now conceivable. These microstructures are achieved through the isothermal transformation of high-carbon high-silicon steels at low temperature, leading to nanoscale plates of ferrite with thickness of 20–40 nm and retained austenite. Nanostructured bainitic steels present the highest strength/toughness combinations ever recorded in bainitic steels (2.2 GPa/40 MPa m{sup 1/2}) and the potential for engineering components is alluring. However, fatigue properties, responsible of the durability of a component, remain to be examined. In order to understand the role of the microstructure during the fatigue crack propagation, the crack path in three nanoscale bainitic structures has been analysed on the basis of the relationships between grain misorientations and grain boundaries by Electron Backscatter Diffraction. Active slip systems in bainitic ferrite and crack deflection at grain boundaries have been identified, while retained austenite is cast doubt on its role.

  4. In situ heating SEM observation of the bainitic transformation process in Cu-17Al-11Mn (at.%) alloys.

    Science.gov (United States)

    Motomura, Shunichi; Soejima, Yohei; Miyoshi, Takayuki; Hara, Toru; Omori, Toshihiro; Kainuma, Ryosuke; Nishida, Minoru

    2016-04-01

    To understand the bainitic transformation behavior in Cu-17Al-11Mn (at.%) alloys, dynamicin situobservation during heating was carried out in a scanning electron microscope (SEM). In this study, after optimizing the sample preparation method and observation conditions, we successfully observed the transformation process with sufficient resolution and contrast. From the observation results, bainite is first formed preferentially at the grain boundaries of the parent phase. Bainite is also formed inside the grains to relax the elastic strain generated by the initial bainite. Regarding the growth mode, in the early stage of the transformation, bainite grows along the longitudinal direction, and in the late stage, it grows along the lateral direction. The growth rate of the bainite was also evaluated by continuous observation of the same plate. Dynamicin situobservation of a martensitic transformation in the same alloy was also performed to compare the growth mode with that of bainite, and it was found that the behavior is considerably different between bainitic and the martensitic transformations.

  5. Weldability of 1 000 MPa Grade Ultra-low Carbon Bainitic Steel

    Institute of Scientific and Technical Information of China (English)

    Qing-mei JIANG; Xiao-qiang ZHANG; Li-qing CHEN

    2016-01-01

    Maximum hardness test in weld heat-affected zone (HAZ),oblique Y-groove cracking test and mechanical property test of welding joint of 1 000 MPa grade ultra-low carbon bainitic steel were carried out,so as to research the weldability of the steel.The results show that the steel has lower cold cracking sensitivity,and preheating tem-perature of 100 ℃ can help completely eliminate cold cracks,generating good process weldability.The increase of preheating temperature can reduce the hardening degree of heat-affected zone.The strength of welding joint decreases and hardness reduces when heat inputs increase,and excellent mechanical properties can be obtained when low weld-ing heat inputs are used.Fine lath bainites of different orientations combined with a few granular bainites that effec-tively split the original coarse austenite grains are the foundation of good properties.

  6. The Varying Effects of Uniaxial Compressive Stress on the Bainitic Transformation under Different Austenitization Temperatures

    Directory of Open Access Journals (Sweden)

    Mingxing Zhou

    2016-05-01

    Full Text Available In this study, thermal simulation experiments under different austenitization temperatures and different stress states were conducted. High-temperature laser scanning confocal microscopy (LSCM, thermal dilatometry, and scanning electron microscope (SEM were used to quantitatively investigate the effects of the uniaxial compressive stress on bainitic transformation at 330 °C following different austenitization temperatures. The transformation plasticity was also analyzed. It was found that the promotion degree of stress on bainitic transformation increases with the austenitization temperature due to larger prior austenite grain size as well as stronger promoting effect of mechanical driving force on selected variant growth at higher austenitization temperatures. The grain size and the yield strength of prior austenite are other important factors which influence the promotion degree of stress on bainitic transformation, besides the mechanical driving force provided by the stress. Moreover, the transformation plasticity increases with the austenitization temperature.

  7. In situ observations of austenite grain growth in Fe-C-Mn-Si super bainitic steel

    Institute of Scientific and Technical Information of China (English)

    Feng Liu; Guang Xu; Yu-long Zhang; Hai-jiang Hu; Lin-xin Zhou; Zheng-liang Xue

    2013-01-01

    In situ observations of austenite grain growth in Fe-C-Mn-Si super bainitic steel were conducted on a high-temperature laser scanning confocal microscope during continuous heating and subsequent isothermal holding at 850, 1000, and 1100◦C for 30 min. A grain growth model was proposed based on experimental results. It is indicated that the austenite grain size increases with austenitizing temperature and holding time. When the austenitizing temperature is above 1100◦C, the austenite grains grow rapidly, and abnormal austenite grains occur. In addition, the eff ect of heating rate on austenite grain growth was investigated, and the relation between austenite grains and bainite morphology after bainitic transformations was also discussed.

  8. Modeling of mechanical behaviour of HSLA low carbon bainitic steel thermomechanically processed

    Science.gov (United States)

    Santos, D. B.; Rodrigues, P. C. M.; Cota, A. B.

    2003-10-01

    A comparative study of the microstructure characterization and mechanical properties was done in a HSLA low carbon (0.08%) bainitic steel containing boron, developed by industry as a bainitic steel grade APIX80. The steel was submitted to two different thermomechanical processes. In the first one, controlled rolling followed by accelerated cooling was applied in laboratory mill. In the second processing, specimens of the same steel were submitted to hot torsion testing. The influence of cooling conditions like start cooling temperature, cooling rates and finish cooling temperature on the microstructure and mechanical properties were investigated. The final microstructure obtained was a complex mixture of polygonal ferrite, perlite, bainite and martensite/retained austenite constituent. The use of multiple regression analysis allowed the establishment of quantitative relationships between the accelerated cooling variables and mechanical properties of the steel available from Vickers microhardness and tensile tests.

  9. Investigation on tempering of granular bainite in an offshore platform steel

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Yanlei; Jia, Tao; Zhang, Xiangjun [The State Key Laboratory of Rolling and Automation, Northeastern University, P.O. Box 105, No. 11, Lane 3, Wenhua Road, HePing District, Shenyang 110819 (China); Liu, Zhenyu, E-mail: zyliu@mail.neu.edu.cn [The State Key Laboratory of Rolling and Automation, Northeastern University, P.O. Box 105, No. 11, Lane 3, Wenhua Road, HePing District, Shenyang 110819 (China); Misra, R.D.K. [Department of Metallurgical and Materials Engineering, University of Texas at El Paso, 500 W. University Avenue, El Paso, TX 79968-0521 (United States)

    2015-02-25

    Granular bainite, where M-A constituents dispersed in bainitic ferrite matrix usually presents at the half thickness region in thermo-mechanically processed heavy gauge offshore platform steel. In the present work, the decomposition of M-A constituents during tempering at 600 °C was firstly revealed by transmission electron microscopy (TEM) analysis, which primarily involves the precipitation of cementite, recovery and recrystallization of highly dislocated ferrite matrix. Then, the effect of tempering on mechanical properties was investigated by tempering at different temperature for 60 min. Results indicated that, at tempering temperature of 500–600 °C, large quantity of micro-alloying carbides precipitated and partially compensated the loss of strength mainly due to the decomposition of M-A constituents. Compared with the as-rolled state, the decomposition of M-A constituents and softening of bainitic ferrite matrix after tempering have resulted in higher density of microvoids and substantial plastic deformation before impact failure.

  10. A FIM-atom probe investigation of the bainite transformation in CrMo steel

    International Nuclear Information System (INIS)

    To obtain a better understanding of the role played by Cr and Mo in the bainite transformation a Field-Ion Microscope - Atom Probe was constructed in order to study the distribution of the alloying elements near various types of boundaries on atomic scale. The distribution of alloying elements measured with this instrument is not so smooth on atomic scale as suggested by microprobe analysis. In a coherent twin boundary, formed during the bainite transformation, a depletion of the substitutionals Cr and Mo and an enhancement of the C content is observed, which is in accordance with the atomic model of a B.C.C. twin. In the twin plane the interstitial sites are even larger than the F.C.C. octahedral sites and this plane can act as an effective sink for the carbon atoms from bainitic ferrite. The depletion of Cr and Mo from the twin plane is due to interface coherency. (Auth.)

  11. Effect of zirconium addition on the austenite grain coarsening behavior and mechanical properties of 900 Mpa low carbon bainite steel

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The ultra-free bainitic microstructure of a 900 MPa low carbon bainitic Cu-Ni-Mo-B steel was obtained by a newly developed relaxation precipitation control (RPC) phase transformation processing.In a pan-cake like prior-anstenite grain,the microstructure consisted of lath bainite,a little of abnormal granular bainite,and acicular ferrite.The effect of zirconium carbonitrides on the austenite grain coarsening behavior was studied by transmission electron microscopy (TEM).The results show that,the lath is narrower with increasing cooling rate.The ratio of all kinds of bainitic microstructure is proper with the intermediate cooling rate;and Zr-containing precipitates distribute uniformly,which restrains austenite grain growing in heat-affected welding zone.

  12. Continuous Cooling Bainite Transformation Characteristics of a Low Carbon Microalloyed Steel under the Simulated Welding Thermal Cycle Process

    Institute of Scientific and Technical Information of China (English)

    Xiangwei Kong; Chunlin Qiu

    2013-01-01

    Continuous cooling transformation of a low carbon microalloyed steel was investigated after it was subjected to the simulation welding thermal cycle process and the interrupted cooling test.Microstructure observation was performed by optical microscopy and transmission electron microscopy.On the basis of the dilatometric data and microstructure observation,the continuous cooling transformation (CCT) diagram was determined,which showed that the main microstructure changes from a mixture of lath martensite and bainitic ferrite to full granular bainite with the increase in the cooling time t8/5 from 10 to 600 s,accompanied with a decrease in the microhardness.The interrupted cooling test confirmed that the bainitic ferrite can form attached to grain boundaries at the beginning of transformation even if the final microstructure contains a mixture of granular bainite and bainitic ferrite.

  13. Improved toughness in a bainitic 38MnV7 steel

    OpenAIRE

    Rancel, Lucía; Hernández, Ana; Gómez, Manuel; Calvo, Jessica; Medina, Sebastián F.; Cabrera, José M.

    2013-01-01

    High toughness can be obtained in médium carbón microalloyed bainitic stee (38MnV7) after a careful control of the chemistry and heat treatment. A specific chemical composition of 38MnV7 steel has been developed , providing impact energies after Charpy-V tests at room temperatura as high as 40J (the steel in bainitic state). Present work is oriented to an optimization of the above chemical composition by control of the Transformation Time Temperature (TTT) curves as well as the Precipitation ...

  14. Design of Novel Bainitic Steels: Moving from UltraFine to Nanoscale Structures

    Science.gov (United States)

    Caballero, F. G.; Garcia-Mateo, C.; Miller, M. K.

    2014-05-01

    The concepts of phase transformation theory can be exploited to design nanostructured steels that transform to bainite at temperatures as low as 150°C. The microstructure obtained is so refined that it is possible to achieve strength in excess of 2.5 GPa in a material that has considerable toughness (40 MPam1/2). Such a combination of properties has never been achieved before with bainite. A description of the characteristics and significance of this remarkable microstructure in the context of the mechanism of transformation is provided.

  15. A study on controlled cooling process for making bainitic ductile iron

    Institute of Scientific and Technical Information of China (English)

    2004-01-01

    In the present research, TTT curve of bainitic ductile iron under the condition of controlled cooling was generated. The cooling rate of grinding ball and its temperature distribution were also measured at the same time. It can be concluded that the bainitic zone of TTT curve is separated from the pearlitic zone. As compared to the water-quenching condition, more even cooling rate and temperature distribution can be achieved in the controlled cooling process. The controlled cooling can keep away from pearlitic zone in the high temperature cooling stage and produce similar results to the process of traditional isothermal cooling with a low cooling rate in the low temperature cooling stage.

  16. Mechanical properties and hot-rolled microstructures of a low carbon bainitic steel with Cu-P alloying

    International Nuclear Information System (INIS)

    Highlights: → Mechanical properties and microstructures of low carbon bainite steel are examined. → Cu-P alloying promotes strengthening and uniform plastic deformation. → Cu-P alloying delays recovery process during rolling interval. → Lowering rolling temperature is favorable to increasing toughness. - Abstract: A low carbon bainitic steel with Cu-P alloying was developed. The new steel aims to meet the demand of high strength, high toughness and resistance to chloride ion corrosion for the components used in the environment of sea water and oceanic atmosphere. Mechanical properties of the steel were tested and strengthening and toughening mechanisms were analyzed by comparing hot-rolled microstructures of the low carbon bainitic steels with and without Cu-P alloying. The results show that Cu-P alloying provided strong solution strengthening with weak effect on ductility. The toughness loss caused by Cu-P alloying could be balanced by increasing the amount of martensite/remained austenite (M/A island) at lower finishing temperature. The static recovery process during rolling interval was delayed by the interaction of phosphorous, copper atoms with dislocations, which was favorable to the formation of bainitic plates. Super-fine Nb(C, N) particles precipitated on dislocations had coherency with bainite ferrite at 830 deg. C finishing temperature. Raising finishing temperature to 880 deg. C, Nb(C, N) particles were prone to coarsening and losing coherency. It was also found that no accurate lattice match relationship among retained austenite, martensite and bainite in granular bainitic microstructure.

  17. Mechanical properties and hot-rolled microstructures of a low carbon bainitic steel with Cu-P alloying

    Energy Technology Data Exchange (ETDEWEB)

    Cui, W.F., E-mail: wenfangcui@yahoo.com.cn [Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Shenyang 110004 (China); Zhang, S.X. [Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Shenyang 110004 (China); Technology Center of Laiwu Iron and Steel (Group) Co. Ltd., Laiwu 271104 (China); Jiang, Y. [School of Chemical Engineering, University of Queensland, Brisbane 4072 (Australia); Dong, J. [Technology Center of Laiwu Iron and Steel (Group) Co. Ltd., Laiwu 271104 (China); Liu, C.M. [Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Shenyang 110004 (China)

    2011-08-15

    Highlights: {yields} Mechanical properties and microstructures of low carbon bainite steel are examined. {yields} Cu-P alloying promotes strengthening and uniform plastic deformation. {yields} Cu-P alloying delays recovery process during rolling interval. {yields} Lowering rolling temperature is favorable to increasing toughness. - Abstract: A low carbon bainitic steel with Cu-P alloying was developed. The new steel aims to meet the demand of high strength, high toughness and resistance to chloride ion corrosion for the components used in the environment of sea water and oceanic atmosphere. Mechanical properties of the steel were tested and strengthening and toughening mechanisms were analyzed by comparing hot-rolled microstructures of the low carbon bainitic steels with and without Cu-P alloying. The results show that Cu-P alloying provided strong solution strengthening with weak effect on ductility. The toughness loss caused by Cu-P alloying could be balanced by increasing the amount of martensite/remained austenite (M/A island) at lower finishing temperature. The static recovery process during rolling interval was delayed by the interaction of phosphorous, copper atoms with dislocations, which was favorable to the formation of bainitic plates. Super-fine Nb(C, N) particles precipitated on dislocations had coherency with bainite ferrite at 830 deg. C finishing temperature. Raising finishing temperature to 880 deg. C, Nb(C, N) particles were prone to coarsening and losing coherency. It was also found that no accurate lattice match relationship among retained austenite, martensite and bainite in granular bainitic microstructure.

  18. The Effect of Interfacial Element Partitioning on Ferrite and Bainite Formation

    Science.gov (United States)

    Chen, Hao; van der Zwaag, Sybrand

    2016-05-01

    The formation of bainitic ferrite and that of grain boundary ferrite in low alloy steels have been two of the most important and interesting research topics in the field of solid state ferrous phase transformation for several decades, and various aspects of these two transformations have been discussed extensively in the literature. Recently, a so-called Gibbs energy balance (GEB) model was proposed by the authors to evaluate alloying element effects on the growth of bainitic ferrite and grain boundary ferrite. The model predicts a growth mode transition from paraequilibrium, negligible partitioning to partitioning during the isothermal formation of bainitic ferrite and grain boundary ferrite. Transformation stasis and bay phenomenon are well explained by the GEB model and both of them are found to be due to alloying element diffusion at the interface. This overview gives a summary of the authors' recent progress in the understanding of the growth of bainitic ferrite and grain boundary ferrite, with particular focus on the growth mode transition, the transformation stasis phenomenon and the bay phenomenon.

  19. Atomic configuration in bainite of a Cu45Zn40Au15 alloy examined by ALCHEMI

    International Nuclear Information System (INIS)

    The atomic configuration in the bainite of a Cu45Zn40Au15 alloy with a L21 type ordered structure in parent phase has been studied by means of ALCHEMI. Thin bainite plates which are supposed to be at early stages of formation possess the 18R type structure like the martensite of the same alloy system formed at subzero temperature. As far as electron diffraction is concerned, it appears that they inherit the ordered configuration of atoms in the parent phase completely. However, when closely examined by ALCHEMI, the atomic configuration is found to differ slightly from that in the parent phase. A part of Cu and Zn atoms in the bainite interchange their sites with each other, which are in the first nearest neighbor relation in the parent phase. This type of disordering is different from that recently observed in the martensite formed at subzero temperature and subsequently aged sufficiently at room temperature. These facts suggest that the bainite is not the martensite subjected to aging at temperature after its formation. (orig.)

  20. A Novel kind of Air Cooling Bainite Nitriding Steel and Plasma Nitriding Test

    Institute of Scientific and Technical Information of China (English)

    LI Xin-sheng; LIANG Shu-rong

    2004-01-01

    In order to avoid serious distortion and cracking that may occur with nitrided parts while quenching and tempering, a novel kind of air cooling bainite nitriding steel consisting of Ct, Mo, Mn and Si was developed. After normalized and high temperature tempered, the tested steel has satisfactory strength, toughness and microstructure as well as good nitriding properties.

  1. Characterization of coarse bainite transformation in low carbon steel during simulated welding thermal cycles

    Energy Technology Data Exchange (ETDEWEB)

    Lan, Liangyun, E-mail: lanly@me.neu.edu.cn [School of Mechanical Engineering and Automation, Northeastern University, Shenyang 110819 (China); State Key Laboratory of Rolling Technology and Automation, Northeastern University, Shenyang 110819 (China); Kong, Xiangwei [School of Mechanical Engineering and Automation, Northeastern University, Shenyang 110819 (China); Qiu, Chunlin [State Key Laboratory of Rolling Technology and Automation, Northeastern University, Shenyang 110819 (China)

    2015-07-15

    Coarse austenite to bainite transformation in low carbon steel under simulated welding thermal cycles was morphologically and crystallographically characterized by means of optical microscope, transmission electron microscope and electron backscattered diffraction technology. The results showed that the main microstructure changes from a mixture of lath martensite and bainitic ferrite to granular bainite with the increase in cooling time. The width of bainitic laths also increases gradually with the cooling time. For a welding thermal cycle with relatively short cooling time (e.g. t{sub 8/5} is 30 s), the main mode of variant grouping at the scale of individual prior austenite grains changes from Bain grouping to close-packed plane grouping with the progress of phase transformation, which results in inhomogeneous distribution of high angle boundaries. As the cooling time is increased, the Bain grouping of variants becomes predominant mode, which enlarges the effective grain size of product phase. - Highlights: • Main microstructure changes and the width of lath structure increases with cooling time. • Variant grouping changes from Bain zone to close-packed plane grouping with the transformation. • The change of variant grouping results in uneven distribution of high angle grain boundary. • Bain grouping is main mode for large heat input, which lowers the density of high angle boundary.

  2. Stress–strain behavior of ferrite and bainite with nano-precipitation in low carbon steels

    International Nuclear Information System (INIS)

    We systematically investigate stress–strain behavior of ferrite and bainite with nano-sized vanadium carbides in low carbon steels; the ferrite samples were obtained through austenite/ferrite transformation accompanied with interphase precipitation and the bainite samples were via austenite/bainite transformation with subsequent aging. The stress–strain curves of both samples share several common features, i.e. high yield stress, relatively low work hardening and sufficient tensile elongation. Strengthening contributions from solute atoms, grain boundaries, dislocations and precipitates are calculated based on the structural parameters, and the calculation result is compared with the experimentally-obtained yield stress. The contributions from solute atoms and grain boundaries are simply additive, whereas those from dislocations and precipitates should be treated by taking the square root of the sum of the squares of two values. Nano-sized carbides may act as sites for dislocation multiplication in the early stage of deformation, while they may enhance dislocation annihilation in the later stage of deformation. Such enhanced dynamic recovery might be the reason for a relatively large elongation in both ferrite and bainite samples

  3. Investigation of deformation and microstructure of bainite in Cu-9.97%Al-4.62%mn alloy

    Directory of Open Access Journals (Sweden)

    Aldirmaz E.

    2014-01-01

    Full Text Available In this study, some physical and mechanical properties in Cu-9.97%Al-4.62%Mn (wt% alloy were investigated by X-ray diffraction (XRD, Scanning Electron Microscopy (SEM and compression deformation test. Bainite phase were obtained in the samples according to SEM and XRD analyses. Compression stress was applied on the alloy in order to investigate the deformation effect on the bainite phase transformation. On the surface of the Cu-9.97%Al-4.62%Mn alloy after the deformation, both bainite and martensite variants formed.

  4. A Rationalization of Sympathetic Nucleation-Ledgewise Growth Theory of Bainite Transformation in Fe-C Alloys

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Based on the classic diffusion controlled nucleation and growth theory, the sympathetic nucleationledgewise growth mechanism of bainite was studied theoretically for Iow carbon Fe-C alloys. The rationality of the occurrence of sympathetic nucleation on the terraces of ledges competing with lateral ledge growth and other sites nucleation was demonstrated by the present work quantitatively. The calculations indicated that Iow reaction temperatures and high carbon concentrations may favor the sympathetic nucleation, thus accounting for the formation of multilayer structures of bainite.

  5. Variant selection during the γ-to-αb phase transformation in hot-rolled bainitic TRIP-aided steels

    International Nuclear Information System (INIS)

    The variant selection phenomenon during the austenite to bainite phase transformation in hot-rolled TRIP-aided steels was quantitatively characterized at the level of individual austenite grains. The reconstruction of the electron backscatter diffraction maps provided evidence that bainite grows by packets of laths sharing a common {1 1 1}γ plane in the austenite. The affect of hot deformation is to reduce the number of packets that form. It is suggested that slip activity is important in understanding this effect.

  6. A Study of the Influence of Thermomechanical Controlled Processing on the Microstructure of Bainite in High Strength Plate Steel

    Science.gov (United States)

    Liang, Xiaojun; DeArdo, Anthony J.

    2014-10-01

    Steels with compositions that are hot rolled and cooled to exhibit high strength and good toughness often require a bainitic microstructure. This is especially true for plate steels for linepipe applications where strengths in excess of 690 MPa (100 ksi) are needed in thicknesses between approximately 6 and 30 mm. To ensure adequate strength and toughness, the steels should have adequate hardenability (C. E. >0.50 and Pcm >0.20), and are thermomechanically controlled processed, i.e., controlled rolled, followed by interrupted direct quenching to below the Bs temperature of the pancaked austenite. Bainite formed in this way can be defined as a polyphase mixture comprised a matrix phase of bainitic ferrite plus a higher carbon second phase or micro-constituent which can be martensite, retained austenite, or cementite, depending on circumstances. This second feature is predominately martensite in IDQ steels. Unlike pearlite, where the ferrite and cementite form cooperatively at the same moving interface, the bainitic ferrite and MA form in sequence with falling temperature below the Bs temperature or with increasing isothermal holding time. Several studies have found that the mechanical properties may vary strongly for different types of bainite, i.e., different forms of bainitic ferrite and/or MA. Thermomechanical controlled processing (TMCP) has been shown to be an important way to control the microstructure and mechanical properties in low carbon, high strength steel. This is especially true in the case of bainite formation, where the complexity of the austenite-bainite transformation makes its control through disciplined processing especially important. In this study, a low carbon, high manganese steel containing niobium was investigated to better understand the effects of austenite conditioning and cooling rates on the bainitic phase transformation, i.e., the formation of bainitic ferrite plus MA. Specimens were compared after transformation from recrystallized

  7. Direct measurement of carbon enrichment in the incomplete bainite transformation in Mo added low carbon steels

    International Nuclear Information System (INIS)

    The overall kinetics and carbon enrichment in austenite during the incomplete isothermal bainite transformation in Fe–0.1C–1.5Mn–(0, 0.03, 0.3, 0.5, 1)Mo (mass%) alloys were investigated with quantitative metallography and Electron Probe Microanalysis in the transformation temperature range of 773–873 K. The incomplete transformation appears at 823–873 K when Mo addition exceeds 0.3 mass%; at 773 K substantial carbide precipitation accompanies bainite transformation and no transformation stasis is observed. Transformed fractions in the stasis stage are hardly affected by prior austenite grain size. Carbon concentrations in austenite in the stasis stage are lower than T0 line and decrease with the increase of Mo addition and temperature. T0′ limit, solute drag and WBs limit theories are used to examine the experimentally measured carbon concentration limits in austenite, and their respective flaws are pointed out

  8. Effect of microstructure on the impact toughness of a bainitic steel bloom for large plastic molds

    Science.gov (United States)

    Zhang, Zheng; Wu, Xiao-chun; Zhou, Quan; Duan, Li-li

    2015-08-01

    The correlation between the impact toughness and microstructural characteristics of a large bainitic steel bloom has been investigated. The study focuses on microcrack nucleation and propagation in the basic cleavage plane. To analyze the phase transformation during the wind-cooling process, the temperature field of the bloom was acquired by computer simulation, and a continuous cooling transformation experiment was conducted. The results show that compared with the surface of the bloom, the toughness of the bloom's core is decreased by the increase in proeutectoid ferrite and the coarsening of tempered martensite-austenite constituents. The proeutectoid ferrite decreases the toughness via its effects on carbide precipitation, the formation of martensite-austenite constituents, and the bainite transformation. The relatively large tempered martensite-austenite constituents are conducive to microcrack nucleation and propagation.

  9. Effects of LCF Loadings on the HCF Life of Notched Specimens in Ferritic-Bainitic Steel

    OpenAIRE

    Bidouard, Hadrien; PALIN-LUC, Thierry; Saintier, Nicolas; Dumas, Christian; EL DSOKI, Chalid; KAUFMANN, Heinz; SONSINO, Cetin Morris

    2009-01-01

    Fatigue tests were performed on ferritic bainitic steel notched specimens (Kt = 2.5) under load controlled constant amplitude loading. These tests show that under constant amplitude tension compression loading, periodical overloads application have a detrimental effect on the fatigue crack initiation strength for fully reversed load ratio (R σ = — 1), while they have no influence under pulsating loading (R σ = 0). A finite element analysis shows that in the fully reversed tension (R σ = — ...

  10. MECHANICAL PROPERTIES IN AN INTERCRITICALLY HEAT-TREATED BAINITE-TRANSFORMED 2%Si STEEL

    Institute of Scientific and Technical Information of China (English)

    Z.Li; D.Wu

    2004-01-01

    A significant amount of austenite can be retained by rapid cooling following intercritical annealing and holding at the bainite transformation range in steel with comparatively low carbon and silicon contents. Retained austenite is blocky and very fine and moderately stabilized due to C enrichment. The elongation and the strength-ductility balance of the steel can be enhanced considerably due to strain-induced martensite transformation and transformation-induced plasticity (TRIP) of retained austenite.

  11. Design of carbide-free low-temperature ultra high strength bainitic steels

    OpenAIRE

    García Mateo, Carlos; García Caballero, Francisca

    2007-01-01

    There are severe limitations to attaining submicrostructured steels by means of continuous cooling, the achievement of fine grain sizes is limited by the need to dissipate enthalpy during rapid transformation, so that the actual grain size obtained is more than an order of magnitude greater than can be obtained theoretically. Bainitic microstructures obtained by isothermal heat treatment at low temperatures, can overcome the recalescence limitations and at the same time provide a very fine mi...

  12. Powder metallurgical nanostructured medium carbon bainitic steel: Kinetics, structure, and in situ thermal stability studies

    Energy Technology Data Exchange (ETDEWEB)

    Lonardelli, I., E-mail: il244@cam.ac.uk [University of Cambridge, Materials Science and Metallurgy, Pembroke Street, Cambridge CB2 3QZ (United Kingdom); University of Trento, Materials Engineering and Industrial Technologies, via Mesiano 77, 38123 Trento (Italy); Bortolotti, M. [Fondazione Bruno Kessler, via Sommarive 18, 38123 Trento (Italy); Beek, W. van [Swiss-Norwegian Beamlines, ESRF, BP 220, 38043 Grenoble Cedex (France); Girardini, L.; Zadra, M. [K4-Sint, via Dante 300, 38057 Pergine Valsugana (Italy); Bhadeshia, H.K.D.H. [University of Cambridge, Materials Science and Metallurgy, Pembroke Street, Cambridge CB2 3QZ (United Kingdom)

    2012-10-15

    It has been possible to produce incredibly fine plates of bainitic ferrite separated by a percolating network of retained austenite in a medium carbon steel produced by mechanical alloying followed by spark plasma sintering and isothermal heat treatment. This is because the sintering process limits the growth of the austenite grains to such an extent that the martensite-start temperature is suppressed in spite of the medium carbon concentration. Furthermore, the fine austenite grain size accelerates the bainite transformation, which can therefore be suppressed to low temperatures to obtain a nanostructure. Microscopy and in situ synchrotron X-ray diffraction were used to investigate the morphology and the thermal stability of the retained austenite during continuous heating. These latter experiments revealed a gradient of carbon concentration in the retained austenite and a reduced thermal stability in high carbon film-austenite. It was also possible to correlate the evolution of defect density and carbon depletion in both retained austenite and bainitic ferrite during tempering.

  13. Powder metallurgical nanostructured medium carbon bainitic steel: Kinetics, structure, and in situ thermal stability studies

    International Nuclear Information System (INIS)

    It has been possible to produce incredibly fine plates of bainitic ferrite separated by a percolating network of retained austenite in a medium carbon steel produced by mechanical alloying followed by spark plasma sintering and isothermal heat treatment. This is because the sintering process limits the growth of the austenite grains to such an extent that the martensite-start temperature is suppressed in spite of the medium carbon concentration. Furthermore, the fine austenite grain size accelerates the bainite transformation, which can therefore be suppressed to low temperatures to obtain a nanostructure. Microscopy and in situ synchrotron X-ray diffraction were used to investigate the morphology and the thermal stability of the retained austenite during continuous heating. These latter experiments revealed a gradient of carbon concentration in the retained austenite and a reduced thermal stability in high carbon film-austenite. It was also possible to correlate the evolution of defect density and carbon depletion in both retained austenite and bainitic ferrite during tempering.

  14. A multiscale perspective on the kinetics of solid state transformations with application to bainite formation

    Directory of Open Access Journals (Sweden)

    Claas Hüter

    2015-09-01

    Full Text Available We give an excerpt of recent developments in the experimentally benchmarked modeling of bainite formation in the press hardening process. As the press hardening process poses a heavily multi-parameter dependent modeling challenge, we focus on three main branches which complement each other. We emphasise the combination of basic sharp interface and phase field models with pragmatically adapted multi phase field models and experimentally parametrized implementations of the Johnson-Mehl-Avrami model. In the basic thermodynamic modeling part, we review fundamental aspects of displacive and diffusional-displacive transformations to predict dominant transformation morphologies. These results provide a link to multi-phase-field implementations which allow to simulate isothermal bainitic transformations, supported by available material data from thermodynamic databases. Excellent agreement with experiments, e.g. scanning electron microscopy for the transformed bainite in the high-carbon steel 100Cr6 shows the value of these model implementations. The further connection to Johnson-Mehl-Avrami models offers to extend the understanding to transformation plasticity for the press hardening steel 22MnB5.

  15. Study on laser welded heat-affected zone in new ultralow carbon bainitic steel

    Institute of Scientific and Technical Information of China (English)

    Lin Zhao; Wuzhu Chen; Xudong Zhang; Jiguo Shan

    2007-01-01

    800 MPa grade ultralow carbon bainitic (NULCB) steel is the recently developed new generation steel, which was produced by thermo mechanical controlled processing & relaxation-precipitation controlling transformation (TMCP&RPC) technique. The microstructure and the mechanical properties of the heat-affected zone (HAZ) in NULCB steel under laser welding conditions were investigated by using a Gleeble-1500 thermal simulator. The experimental results indicate that the simplex microstructure in the HAZ is granular bainite that consists of bainite-ferrite (BF) lath and M-A constituent when the cooling time from 800 to 500°C (t8/5) is 0.3-30 s, and the M-A constituent consists of twinned martensite and residual austenite. As t8/5 increases, the hardness and tensile strength of HAZ decreases, but they are higher than that of the base metal, indicating the absence of softened zone after laser welding. The impact toughness of HAZ increases at first and then decreases when tw increases. The impact energy of HAZ is much higher than that of the base metal when t8/5 is between 3 and 15 s. It indicates that excellent low temperature toughness can be obtained under appropriate laser welding conditions.

  16. Microstructural evolution of bainitic steel severely deformed by equal channel angular pressing.

    Science.gov (United States)

    Nili-Ahmadabadi, M; Haji Akbari, F; Rad, F; Karimi, Z; Iranpour, M; Poorganji, B; Furuhara, T

    2010-09-01

    High Si bainitic steel has been received much of interest because of combined ultra high strength, good ductility along with high wear resistance. In this study a high Si bainitic steel (Fe-0.22C-2.0Si-3.0Mn) was used with a proper microstructure which could endure severe plastic deformation. In order to study the effect of severe plastic deformation on the microstructure and properties of bainitic steel, Equal Channel Angular Pressing was performed in two passes at room temperature. Optical, SEM and TEM microscopies were used to examine the microstructure of specimens before and after Equal Channel Angular Pressing processing. X-ray diffraction was used to measure retained austenite after austempering and Equal Channel Angular Pressing processing. It can be seen that retained austenite picks had removed after Equal Channel Angular Pressing which could attributed to the transformation of austenite to martensite during severe plastic deformation. Enhancement of hardness values by number of Equal Channel Angular Pressing confirms this idea. PMID:21133137

  17. Effects of Cooling Conditions on Microstructure, Tensile Properties, and Charpy Impact Toughness of Low-Carbon High-Strength Bainitic Steels

    Science.gov (United States)

    Sung, Hyo Kyung; Shin, Sang Yong; Hwang, Byoungchul; Lee, Chang Gil; Lee, Sunghak

    2013-01-01

    In this study, four low-carbon high-strength bainitic steel specimens were fabricated by varying finish cooling temperatures and cooling rates, and their tensile and Charpy impact properties were investigated. All the bainitic steel specimens consisted of acicular ferrite, granular bainite, bainitic ferrite, and martensite-austenite constituents. The specimens fabricated with higher finish cooling temperature had a lower volume fraction of martensite-austenite constituent than the specimens fabricated with lower finish cooling temperature. The fast-cooled specimens had twice the volume fraction of bainitic ferrite and consequently higher yield and tensile strengths than the slow-cooled specimens. The energy transition temperature tended to increase with increasing effective grain size or with increasing volume fraction of granular bainite. The fast-cooled specimen fabricated with high finish cooling temperature and fast cooling rate showed the lowest energy transition temperature among the four specimens because of the lowest content of coarse granular bainite. These findings indicated that Charpy impact properties as well as strength could be improved by suppressing the formation of granular bainite, despite the presence of some hard microstructural constituents such as bainitic ferrite and martensite-austenite.

  18. EBSD as a tool to identify and quantify bainite and ferrite in low-alloyed Al-TRIP steels.

    Science.gov (United States)

    Zaefferer, S; Romano, P; Friedel, F

    2008-06-01

    Bainite is thought to play an important role for the chemical and mechanical stabilization of metastable austenite in low-alloyed TRIP steels. Therefore, in order to understand and improve the material properties, it is important to locate and quantify the bainitic phase. To this aim, electron backscatter diffraction-based orientation microscopy has been employed. The main difficulty herewith is to distinguish bainitic ferrite from ferrite because both have bcc crystal structure. The most important difference between them is the occurrence of transformation induced geometrically necessary dislocations in the bainitic phase. To determine the areas with larger geometrically necessary dislocation density, the following orientation microscopy maps were explored: pattern quality maps, grain reference orientation deviation maps and kernel average misorientation maps. We show that only the latter allow a reliable separation of the bainitic and ferritic phase. The kernel average misorientation threshold value that separates both constituents is determined by an algorithm that searches for the smoothness of the boundaries between them. PMID:18503676

  19. Continuous Cooling Transformation Behavior and Kinetic Models of Transformations for an Ultra-Low Carbon Bainitic Steel

    Institute of Scientific and Technical Information of China (English)

    ZHANG Zhi-min; CAI Qing-wu; YU Wei; LIXiao-lin; WANG Li-dong

    2012-01-01

    The aim was to investigate transformation behavior and transformation kinetics of an ultra-low carbon bai- nitic steel during continuous cooling. Continuous cooling transformation (CCT) curves of tested steel were measured by thermal dilatometer and metallographic structures at room temperature were observed by optical microscope. Then transformation kinetic equation of austenite to ferrite as well as austenite to bainite was established by analyzing the relationship of lnln]-l/(1--f)] and lnt in the kinetic equation on the basis of processed experimental data. Finally, the measured and calculated kinetic behaviors of the steel during continuous cooling were compared and growth pat- terns of transformed ferrite and bainite were analyzed. Results showed that calculated result was in reasonable agree- ment with the experimental data. It could be concluded that the growth modes of transformed ferrite and bainite were mainly one dimension as the Avrami exponents were between 1 and 2.

  20. Effect of Tempering Temperature on the Microstructure and Hardness of a Super-bainitic Steel Containing Co and Al

    OpenAIRE

    Hu, Feng; Wu, Kaiming; Hou, Tingping; Shirzadi, Amir Abbas

    2014-01-01

    The effect of tempering temperature, within the range of 400 to 700°C, on the microstructure and hardness of two super-bainitic steels, one as the control parent sample and the other with added Co & Al was investigated. Post-tempering examinations of the super-bainitic samples showed that low temperature tempering cycles (400–500°C) resulted in carbides formation, and some increases in the hardness possibly due to precipitation strengthening in the Co & Al contained steel. Once the tempering ...

  1. In-situ tensile test of high strength nanocrystalline bainitic steel

    Energy Technology Data Exchange (ETDEWEB)

    Haddad, Mike, E-mail: mike.haddad@uni-ulm.de [Institute of Micro and Nanomaterials, University of Ulm, Ulm (Germany); Ivanisenko, Yulia; Courtois-Manara, Eglantine [Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe (Germany); Fecht, Hans-Jörg [Institute of Micro and Nanomaterials, University of Ulm, Ulm (Germany)

    2015-01-03

    Because of its great importance in modern engineering and technology applications, steel continues to be highly relevant in the modern research field of nanocrystalline materials. Innovative processing methods and procedures are required for the production of such materials, which possess superior properties compared to their conventional counter parts. In this research, the original microstructure of a commercial C45 steel (Fe, 0.42–0.5 wt% C, 0.5–0.8 wt% Mn) was modified from ferritic–pearlitic to bainitic. Warm high pressure torsion for 5 rotations at 6 GPa and 350 °C was used to process the bainitic sample leading to an ultrafine/nano-scale grain size. A unique nano-crystalline microstructure consisting of equiaxed and elongated ferrite grains with a mean size smaller than 150 nm appeared in images taken by Transmission Electron Microscopy. Results of in-situ tensile testing in a scanning electron microscope showed very high tensile strength, on the order of 2100 MPa with a total elongation of 4.5% in comparison with 800 MPa and around 16% in the original state. Fracture occurred abruptly, without any sign of necking, and was typically caused by the stress concentration at a surface flaw. Also, stress concentrations near all surface defects were observed on the sample, visualized by the formation of shear bands. The fracture surface was covered with dimples, indicating ductile fracture. These properties are fully comparable with high strength, high alloyed steels.

  2. Effect of tempering upon the tensile properties of a nanostructured bainitic steel

    Energy Technology Data Exchange (ETDEWEB)

    Hasan, H.S. [University of Technology, Baghdad (Iraq); Peet, M.J., E-mail: mjp54@cam.ac.uk [Department of Materials Science and Metallurgy, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom); Avettand-Fènoël, M-N. [Unité Matériaux Et Transformations (UMET) UMR CNRS 8207, Université, Lille 1, 59655 Villeneuve D' ASCQ (France); Bhadeshia, H.K.D.H. [Department of Materials Science and Metallurgy, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom)

    2014-10-06

    The tensile properties of a nanostructured carbide-free bainitic steel formed at 200–250 °C are compared against those after tempering sufficiently to remove the retained austenite. Although significant ductility is observed following tempering, a comparison of tempered and untempered samples shows that it is in fact reduced when a comparison is made at identical strength. The shape of the stress–strain curves shows clear evidence that the capacity for work hardening is reduced with the loss of austenite. The nanostructure of the steel transformed at 250 °C is examined by transmission electron microscopy, to compare the as-transformed to the tempered structure. In this case after tempering at 500 °C the energy absorbed during the tensile test is lower, due to the lower strength. Reduction of strength is caused by the slight coarsening of the bainite plates, and lower dislocation density after tempering. Considering the formation of carbide particles in high strength steel, impressive ductility is exhibited even in the tempered condition.

  3. Phase Equilibrium and Austenite Decomposition in Advanced High-Strength Medium-Mn Bainitic Steels

    Directory of Open Access Journals (Sweden)

    Adam Grajcar

    2016-10-01

    Full Text Available The work addresses the phase equilibrium analysis and austenite decomposition of two Nb-microalloyed medium-Mn steels containing 3% and 5% Mn. The pseudobinary Fe-C diagrams of the steels were calculated using Thermo-Calc. Thermodynamic calculations of the volume fraction evolution of microstructural constituents vs. temperature were carried out. The study comprised the determination of the time-temperature-transformation (TTT diagrams and continuous cooling transformation (CCT diagrams of the investigated steels. The diagrams were used to determine continuous and isothermal cooling paths suitable for production of bainite-based steels. It was found that the various Mn content strongly influences the hardenability of the steels and hence the austenite decomposition during cooling. The knowledge of CCT diagrams and the analysis of experimental dilatometric curves enabled to produce bainite-austenite mixtures in the thermomechanical simulator. Light microscopy (LM, scanning electron microscopy (SEM, and transmission electron microscopy (TEM were used to assess the effect of heat treatment on morphological details of produced multiphase microstructures.

  4. Structural characterization of “carbide-free” bainite in a Fe–0.2C–1.5Si–2.5Mn steel

    Energy Technology Data Exchange (ETDEWEB)

    Hofer, Christina, E-mail: christina.hofer@unileoben.ac.at [Department of Physical Metallurgy and Materials Testing, Montanuniversitaet Leoben, Franz-Josef-Straße 18, 8700 Leoben (Austria); Leitner, Harald [Böhler Edelstahl GmbH & Co KG, Mariazeller Straße 25, 8605 Kapfenberg (Austria); Winkelhofer, Florian [voestalpine Stahl Linz GmbH, voestalpine-Straße 3, 4020 Linz (Austria); Clemens, Helmut; Primig, Sophie [Department of Physical Metallurgy and Materials Testing, Montanuniversitaet Leoben, Franz-Josef-Straße 18, 8700 Leoben (Austria)

    2015-04-15

    Low-alloyed, low C containing carbide-free bainitic steels are attractive candidates for applications in the automotive industry due to their well-balanced combination of high strength and ductility achieved in an economic way. In this work, their complex microstructure consisting of a mixture of bainitic ferrite, austenite with different morphologies and stabilities, martensite, M/A constituent and a few carbides has been investigated with metallographic and high-resolution techniques. After specific isothermal heat treatments in a dilatometer, a combination of LePera and Nital etching was applied to distinguish between bainite and martensite. Site-specific atom probe tips were prepared by means of scanning electron microscopy, electron backscatter diffraction and focused ion beam, revealing that “carbide-free” bainite consists of C depleted bainitic ferrite, C enriched retained austenite and occasional ε-carbides. Furthermore, it was found that the M/A constituent is highly dislocated and mainly martensitic. Its C content is increased compared to the nominal composition, but below the values obtained for retained austenite, explaining the lower transformation resistance. - Highlights: • Detailed top-down characterization of low C “carbide-free” bainitic steel • APT of all constituents in “carbide-free” bainite • Identification of ε-carbide based on its C content determined by APT • M/A constituent is mainly martensitic with austenitic areas at the boundaries • Lower C content of M/A constituent explains its lower stability.

  5. Effects of B and Cu Addition and Cooling Rate on Microstructure and Mechanical Properties in Low-Carbon, High-Strength Bainitic Steels

    Science.gov (United States)

    Sung, Hyo Kyung; Shin, Sang Yong; Hwang, Byoungchul; Lee, Chang Gil; Lee, Sunghak

    2012-10-01

    The effects of B and Cu addition and cooling rate on microstructure and mechanical properties of low-carbon, high-strength bainitic steels were investigated in this study. The steel specimens were composed mostly of bainitic ferrite, together with small amounts of acicular ferrite, granular bainite, and martensite. The yield and tensile strengths of all the specimens were higher than 1000 MPa and 1150 MPa, respectively, whereas the upper shelf energy was higher than 160 J and energy transition temperature was lower than 208 K (-65 °C) in most specimens. The slow-cooled specimens tended to have the lower strengths, higher elongation, and lower energy transition temperature than the fast-cooled specimens. The Charpy notch toughness was improved with increasing volume fraction of acicular ferrite because acicular ferrites favorably worked for Charpy notch toughness even when other low-toughness microstructures such as bainitic ferrite and martensite were mixed together. To develop high-strength bainitic steels with an excellent combination of strength and toughness, the formation of bainitic microstructures mixed with acicular ferrite was needed, and the formation of granular bainite was prevented.

  6. Effect of La2O3 on granular bainite microstructure and wear resistance of hardfacing layer metal

    Institute of Scientific and Technical Information of China (English)

    王亚军; 陈继刚; 杨健; 郝飞飞; 淡婷; 杨育林; 杨庆祥

    2014-01-01

    The purpose of this work was to investigate the effect of La2O3 on the granular bainite microstructure and wear resistance of hardfacing layer metal. The hardfacing layer metals with different contents of La2O3 were prepared. The microstructures of the hardfacing layer metals were observed by field emission scanning electron microscopy (FESEM) and transmission electron micros-copy (TEM). The hardness and wear resistance of the hardfacing layer metals were measured respectively. The results indicated that with the increasing content of La2O3, the amount of granular bainite increased, while that of martensite decreased and that of retained austenite did not change obviously. When the content of La2O3 was 2.55 wt.%, the volume fraction of the granular bainite in the hardfacing layer metal was 73.2%. Meanwhile, the wear resistance of the hardfacing layer metal was the largest, which was 12100 min/g. The mismatch between the face (100) of LaAlO3 and the face (100) ofδ-Fe was 7.1%. Therefore, LaAlO3 could act as moder-ate effective heterogeneous nuclei ofδ-Fe and the granular bainite could be refined.

  7. Microstructure and mechanical properties of a low carbon carbide-free bainitic steel co-alloyed with Al and Si

    International Nuclear Information System (INIS)

    Highlight: ► A low carbon carbide-free bainitic steel was produced. ► Co-alloying with Al and Si suppresses the precipitation of cementite. ► Fine carbide-free bainite laths and thin film-like retained austenite obtained. ► Excellent combination of strength, ductility and toughness enabled. -- Abstract: A low carbon, low alloy steel has been investigated for producing low carbon carbide-free bainitic microstructure by co-addition of alloying elements of aluminum and silicon. The influence of heat treatment process on microstructure, impact toughness as well as tensile properties was investigated by light optical microscopy, transmission electron microscopy, X-ray diffraction and mechanical property tests. The results demonstrate that the co-addition of aluminum and silicon in the investigated steel plays an effective role in suppressing the precipitation of cementite. A desired microstructure consisting of mainly fine-scale carbide-free bainitic ferrite and thin film-like retained austenite located between the ferrite laths was obtained and accordingly an excellent combination of toughness, ductility and strength was achieved by optimized heat treatments, i.e. by isothermal treatment at 320 °C for ∼84 min or more. The microstructure-mechanical property relationships are discussed.

  8. Interaction of Hydrogen and Retained Austenite in Bainite/Martensite Dual-Phase High Strength Steel

    Institute of Scientific and Technical Information of China (English)

    GU Jia-lin; CHANG Kai-di; FANG Hong-sheng; YANG Zhi-gang; BAI Bing-zhe

    2004-01-01

    The hydrogen trapping phenomena in two bainite/martensite dual-phase high strength steels (U20Si and U20DSi) were investigated by electrochemical permeation technique. The hydrogen diffusivity was calculated from data of permeation delay time, and the diffusion coefficient in U20Si is far less than that in U20DSi. Moreover, the hydrogen diffusivity decreases as the volume percent of retained austenite increases. The experiment results show that there are different hydrogen trappings and different volume percents of retained austenite in U20Si and U20DSi. The retained austenite is precipitated as films. The trap binding energy for the retained austenite and hydrogen is calculated to be 40.4 kJ·mol-1.

  9. Research on microstructural evolution and dynamic recrystallization behavior of JB800 bainitic steel by FEM

    Institute of Scientific and Technical Information of China (English)

    Qingjun Chen; Yonglin Kang; Hao Yu; Chunmei Wang; Chengxiang Li

    2008-01-01

    Single pass compression tests were conducted on Gleeble1500 thermal simulator. The effect of different deformation parameters on the grain size of dynamically recrystallized austenite was analyzed. A mathematical model of dynamic recrystallization and a material database of JB800 steel, whose tensile strength is above 800 Mpa, were set up. A subprogram was compiled using Fortran language and called by Marc finite element software. A thermal coupled elastoplastic finite element model was established to simulate the compression process. The grain size of recrystallized austenite obtained by different recrystailization models was simulated. The results show that the optimized dynamic recrystallization model of JBS00 bainitic steel has a higher precision and yields good agreement with metallographic observations.

  10. Development of a heat treatment method to form a duplex microstructure of lower bainite and martensite in AISI 4140 stee

    OpenAIRE

    Claesson, Erik

    2014-01-01

    Research on bainite and martensite structures has indicated that lower bainite needles have a refining effect on the lath martensitic structure. Lower bainte needles partitions prior austenite grains and will consequently have a refining effect on the subsequent formed lath martensite. Smaller austenite grains will result in smaller lath martensitic packets and blocks and will result in enhanced mechanical properties.   In order to create a variation of lower bainte structure in a matrix of m...

  11. Morphological and chemical analysis of bainite in Cu-17Al-11Mn (at.%) alloys by using orthogonal FIB-SEM and double-EDS STEM.

    Science.gov (United States)

    Motomura, Shunichi; Hara, Toru; Omori, Toshihiro; Kainuma, Ryosuke; Nishida, Minoru

    2016-06-01

    In this study, new microscopy techniques were developed for understanding the mechanism for the bainitic transformation in a Cu-17Al-11Mn (at%) alloy. An orthogonally arranged focused ion beam and a scanning electron microscope were employed to observe three-dimensional (3D) morphology of the bainite phase, in addition to compositional analysis by using a scanning transmission electron microscope equipped with a double-detector energy-dispersive X-ray spectrometer system. The 3D morphology of these samples was observed at different aging times and aging temperatures; the results obtained indicated that with increasing aging time and/or aging temperature, the bainite phase at the initial stage of formation exhibits a plate-like shape, which changes to a lenticular form. A habit plane was uniquely determined as ∼{9 3 2} by the combination of 3D image reconstruction and an electron back-scattered diffraction technique. The compositional analysis revealed the spatial distribution of the compositional variation between the bainite and matrix phases in the initial stages of the transformation. In the bainite phase, the Cu concentration was higher, while the concentrations of Al and Mn were lower than those in the surrounding matrix, indicative of the diffusion of the constituent elements with the growth of the bainite phase. PMID:26884617

  12. Preperation of carbide-free bainitic steels for EBSD investigations; Praeparation von karbidfreien bainitischen Staehlen fuer EBSD-Untersuchungen

    Energy Technology Data Exchange (ETDEWEB)

    Hofer, Christina; Clemens, Helmut; Primig, Sophie [Montanuniv. Leoben (Austria). Dept. Metallkunde und Werkstoffpruefung

    2015-10-01

    Carbide-free bainitic steels are composed of bainitic ferrite laths, which are separated by films and larger islands of austenite, which is stabilized by carbon enrichment. Due to their multi-phase microstructure, the preparation of such steels for a characterization by means of electron backscatter diffraction (EBSD) represents a challenge. Attention must particularly be paid to prevent the transformation of the retained austenite to martensite during the preparation. This study compares the sample preparation by vibratory polishing using different suspensions to the electrolytic preparation. During vibratory polishing, it must be ensured that very little force is applied in order to prevent the metastable austenite from transforming. No influence of the different suspensions could be found. Electropolishing with a voltage of 40 V for 10 s at 23 C is well suited for microstructural investigations. However, the surface relief is too pronounced for EBSD analyses. OP-U polishing for 15 min subsequent to electropolishing accomplishes the best results.

  13. Structure-Property-Fracture Mechanism Correlation in Heat-Affected Zone of X100 Ferrite-Bainite Pipeline Steel

    Science.gov (United States)

    Li, Xueda; Ma, Xiaoping; Subramanian, S. V.; Misra, R. D. K.; Shang, Chengjia

    2015-03-01

    Structural performance of a weld joint primarily depends on the microstructural characteristics of heat-affected zone (HAZ). In this regard, the HAZ in X100 ferrite-bainite pipeline steel was studied by separating the HAZ into intercritically reheated coarse-grained (ICCG) HAZ containing and non-containing regions. These two regions were individually evaluated for Charpy impact toughness and characterized by electron back-scattered diffraction (EBSD). Low toughness of ~50 J was obtained when the notch of impact specimen encountered ICCGHAZ and high toughness of ~180 J when the notch did not contain ICCGHAZ. Fracture surface was ~60 pct brittle in the absence of ICCGHAZ, and 95 pct brittle (excluding shear lip) in the presence of ICCGHAZ in the impact tested samples. The underlying reason is the microstructure of ICCGHAZ consisted of granular bainite and upper bainite with necklace-type martensite-austenite (M-A) constituent along grain boundaries. The presence of necklace-type M-A constituent notably increases the susceptibility of cleavage microcrack nucleation. ICCGHAZ was found to be both the initiation site of the whole fracture and cleavage facet initiation site during brittle fracture propagation stage. Furthermore, the study of secondary microcracks beneath CGHAZ and ICCGHAZ through EBSD suggested that the fracture mechanism changes from nucleation-controlled in CGHAZ to propagation-controlled in ICCGHAZ because of the presence of necklace-type M-A constituent in ICCGHAZ. Both fracture mechanisms contribute to the poor toughness of the sample contained ICCGHAZ.

  14. A Unified Constitutive Equation of a Bainite Steel During Hot Deformation

    Science.gov (United States)

    Li, Lixin; Ye, Ben; Liu, Sheng; Hu, Shengde; Liao, Hanqing

    2016-10-01

    A constitutive model has been established based on dislocation theory, work hardening and dynamic recovery theory, and softening mechanisms of dynamic recrystallization. The stress-strain curves of a bainite steel have been measured with hot compression experiments at temperatures of 1173, 1273, 1373 and 1473 K with strain rates of 0.01, 0.1, 1 and 10 s-1 on a thermo-mechanical simulator (Gleeble-1500). The material constants involved in the constitutive model have been optimized by an inverse analysis of the stress-strain curves using the method of coordinate rotation, determining the strain-stress relationship or the constitutive equation, the kinetic models of dynamic recovery and dynamic recrystallization, and a few material constants of the investigated steel. Comparison of the calculated flow stress with the experimental data suggests that the relationship between the flow stress and the strain rate, temperature, strain of the steel during hot deformation can be described by the constitutive model, and that the underlying materials science can be captured from the material constants determined by the stress-strain curves.

  15. Ratcheting led surface failure of medium carbon bainitic steel under mild operation conditions

    Institute of Scientific and Technical Information of China (English)

    Peng Dou; Youguo Li; Kaiming Liang; Bingzhe Bai

    2005-01-01

    The behavior of rolling contact fatigue (RCF) of medium carbon bainitic back-up roll steel was investigated under its actual work conditions. A kind of asperity-scale surface originated cracks, which is lying parallel or at an acute angle to the surfaces, initiated after unidirectional plastic flow of the material in thin surface layer had occurred. Theoretical analysis indicates that they nucleate due to plastic ratcheting induced by asperity contact stresses, and consequently are named as ratcheting cracks. After nucleating and initially propagating, they arrest at some depth and resume propagating till about 70%-80% of the RCF failure life by initially turning parallel to contact surfaces. Their behavior of initiation and propagation is confined to a thin layer prior to the formation of surface distress. According to the critical principle of the preventive grinding strategy, removing the asperity influenced surface layer at about 70%-80% of the RCF failure life can effectively prevent the ratcheting cracks from developing into surface distress, which can lead to the formation of macro-RCF failure soon.

  16. Creep-rupture behavior of 3Cr-3W-V bainitic steels

    Energy Technology Data Exchange (ETDEWEB)

    Klueh, R.L. [Oak Ridge National Laboratory, TN 37831-6138 (United States)]. E-mail: kluehrl@ornl.gov; Evans, N.D. [Oak Ridge National Laboratory, TN 37831-6138 (United States); Maziasz, P.J. [Oak Ridge National Laboratory, TN 37831-6138 (United States); Sikka, V.K. [Oak Ridge National Laboratory, TN 37831-6138 (United States)

    2007-01-15

    A nominally Fe-3.0Cr-3.0W-0.25 V (3Cr-3WV) steel and this composition with 0.07% Ta (3Cr-3WVTa) were developed for elevated-temperature service in the power-generation and petrochemical industries. Creep-rupture strengths of the new steels to 600 deg. C exceeded those of the two advanced commercial 2.25Cr steels T23 (Fe-2.25Cr-1.6W-0.25V-0.05Nb-0.07C) and T24 (Fe-2.25Cr-1.0Mo-0.25V-0.07Ti-0.005B-0.07C). Moreover, the strength of 3Cr-3WVTa approached that of modified 9Cr-1Mo (T91) at 650 deg. C. Elevated-temperature strength in the new steels is obtained from a bainitic microstructure with a high number density of fine needle-like MX precipitates in the matrix. The presence of tantalum promotes a finer MX precipitate in the 3Cr-3WVTa than in the 3Cr-3WV, and it suppresses the coarsening of these fine precipitates during creep.

  17. Mechanical properties of nanostructured, low temperature bainitic steel designed using a thermodynamic model

    International Nuclear Information System (INIS)

    Nanostructured, low temperature bainitic steels with remarkable combination of ultimate tensile strength of about 2.5 GPa and high uniform elongation have been developed in the recent decade. To reduce the production cost of these steels, two chemical compositions were designed by using a thermodynamic model which was developed in Cambridge University by Bhadeshia. To attain optimum mechanical properties, the designed steels were transformed isothermally at the temperature range of 200-300 deg. C for different times. The optimum times for each temperature were estimated by evaluation of hardness and XRD results. The measurements of tensile properties and the fracture surface examination by scanning electron microscopy indicated that by modification of chemical composition the cost production of steel not only reduces, but also the mechanical properties particularly total elongation enhances slightly. The results of this study suggest that by using a thermodynamic model and without try and error it is possible to design a new steel with remarkable combination of mechanical properties.

  18. A Unified Constitutive Equation of a Bainite Steel During Hot Deformation

    Science.gov (United States)

    Li, Lixin; Ye, Ben; Liu, Sheng; Hu, Shengde; Liao, Hanqing

    2016-08-01

    A constitutive model has been established based on dislocation theory, work hardening and dynamic recovery theory, and softening mechanisms of dynamic recrystallization. The stress-strain curves of a bainite steel have been measured with hot compression experiments at temperatures of 1173, 1273, 1373 and 1473 K with strain rates of 0.01, 0.1, 1 and 10 s-1 on a thermo-mechanical simulator (Gleeble-1500). The material constants involved in the constitutive model have been optimized by an inverse analysis of the stress-strain curves using the method of coordinate rotation, determining the strain-stress relationship or the constitutive equation, the kinetic models of dynamic recovery and dynamic recrystallization, and a few material constants of the investigated steel. Comparison of the calculated flow stress with the experimental data suggests that the relationship between the flow stress and the strain rate, temperature, strain of the steel during hot deformation can be described by the constitutive model, and that the underlying materials science can be captured from the material constants determined by the stress-strain curves.

  19. Fatigue crack growth behaviors in hot-rolled low carbon steels: A comparison between ferrite–pearlite and ferrite–bainite microstructures

    International Nuclear Information System (INIS)

    The roles of microstructure types in fatigue crack growth behaviors in ferrite–pearlite steel and ferrite–bainite steel were investigated. The ferrite–bainite dual-phase microstructure was obtained by intermediate heat treatment, conducted on ferrite–pearlite hot-rolled low carbon steel. This paper presents the results from investigation using constant stress-controlled fatigue tests with in-situ scanning electron microscopy (SEM), fatigue crack growth (FCG) rate tests, and fatigue fractography analysis. Microscopy images arrested by in-situ SEM showed that the fatigue crack propagation in F–P steel could become unstable more ealier compared with that in F–B steel. The fatigue cracks in ferrite–pearlite were more tortuous and could propagate more freely than that in ferrite–bainite microstructures. However, frequent crack branching were observed in ferrite–bainite steel and it indicated that the second hard bainite phase effectively retarded the crack propagation. The variation of FCG rate (da/dN) with stress intensity factor range (ΔK) for F–P and F–B steels was discussed within the Paris region. It was shown that FCG rate of F–P steel was higher than that of F–B steel. Moreover, the fatigue fracture surface analysis proved that grain boundaries could also play a role in the resistance of crack propagation.

  20. CORROSION RESISTANCE OF PEARLITIC AND BAINITIC CAST IRON IN A SYNTHETIC SOLUTION OF CONDENSED GAS FROM COMBUSTION

    Directory of Open Access Journals (Sweden)

    Sandra Matos Cordeiro Costa

    2015-03-01

    Full Text Available The corrosion of engine components of the combustion chamber is usually related to the formation of acids such as sulfuric and nitric. These acids are generated by the condensation of combustion gases that usually occur in vehicle exhaust systems. However, with the development of new technologies to reduce emissions, condensation is also being promoted in vehicle combustion chambers. This fact is associated with high exhaust gas recirculation rates, known as EGR (English term for Exhaust Gas Recirculation. Consequently, corrosion problems in the engine components are increasing, especially in cylinder liners alloy manufactured using cast iron. In this study, the corrosion resistance of two cast iron alloys, one with a pearlitic microstructure and the other with a bainite microstructure in a solution simulating the composition of the condensate obtained from the combustion gases. It was found that the microstructure of the cast iron is an important factor affecting the corrosion behavior. The results showed that none of the two materials investigated is resistant to corrosion in the test medium, and the small difference observed between the behavior of the two cast iron was related to its microstructure, which are dependent on their chemical compositions. The cast iron with a pearlitic microstructure showed less formation of corrosion products than the bainitic cast iron. This result is related to the presence of steadite phase, highly stable and resistant to corrosion in pearlitic microstructure. This phase (steadite anchors the corrosion products formed on the surface and act as a partial barrier slowing the progress of the corrosion process, that was more pronounced in the bainitic cast iron.

  1. Properties and application of new bainitic and martensitic creep resistance steels

    International Nuclear Information System (INIS)

    Supercritical operating parameters of lower emission power units, require novel creep resisting steels to be applied for boiler and pipe systems. Among them are T23 bainitic steels for water walls of boiler combustion chamber and martensitic VM12 steels for superheater coils were tested. RAFAKO S.A. has been co-operating with the Silesian Technical University in Katowice, the Institute of Welding and the Institute for Ferrous Metallurgy in Gliwice for several years now, initiating research and development programmes, implementing the new creep-resistant steels and actively participating in European programmes COST522 and COST536. This paper contains selected information and test results before implementation of the new creep-resistant steels, including: evaluation of working parameters, temperature conditions of main boiler components, which influence reliability and safety, selection of steels for furnace chamber components (approx. 2.5 % Cr) and steam superheater components (9-12 % Cr) destination, evaluation of the requested level of welded joints technological and strength properties, measurements and non-destructive examinations, evaluation of welded joints and HAZ structure by means of LM, TEM and SEM methods in the welding technology implementation process, evaluation of corrosion mechanisms and creep-resistance results - loss of service life - for selected evaporator and steam superheater components, as crucial elements in evaluation of reliability and safety of boiler equipment. Such an examination program includes assessment of steel structure stability during operation period in actual operational conditions. It was clearly shown that operation period have little impact on changes occurring in microstructure and other properties of examined steel grades. (author)

  2. Evolution of microstructure in 100Cr6 steel after cooling from a thixoforming temperature to bainitic transformation ranges

    Energy Technology Data Exchange (ETDEWEB)

    Rogal, Łukasz, E-mail: l.rogal@imim.pl [Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 Reymonta Street, 30-059 Krakow (Poland); Korpala, Grzegorz [Institut für Metallformung, TU Bergakademie Freiberg, 4 Bernhard-von-Cotta-Straße, 09596 Freiberg (Germany); Dutkiewicz, Jan [Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 Reymonta Street, 30-059 Krakow (Poland)

    2015-01-29

    A new concept for the isothermal heat treatment of thixo-elements, consisting of controlled cooling from a semi-solid metal processing (SSM) range, was proposed. 100Cr6 steel (0.97% C, 1.4% Cr, 0.4% Si, 0.4% Mn bal. Fe) after forging was used as the starting material. The DSC analysis was used to determine the liquid phase fraction vs temperature in the solidus–liquidus range. The temperatures and kinetics of bainite transformation after cooling the steel in the semi-solid state were calculated based on the Chester and Bhadeshia models. The steel was heated up to 1425 °C in order to obtain about 25% of the liquid fraction. Then it was cooled in oil at three different temperatures: 135 °C, 235 °C and 335 °C, at which the samples were held for 5 h. The microstructure of the samples annealed at 135 °C consisted of globular grains (the average size of 323 µm), where coarse needles of martensite were observed. They were surrounded by an eutectic mixture of chemical composition different from that of the globular grains. The electron diffraction pattern (SAEDP) showed reflections from α′-Fe and from Fe{sub 3}C carbides. The X-ray diffraction confirmed the presence of martensite, austenite and carbides to the amount of 74.5%, 22% and 3.5% respectively. The average hardness of samples was 735HV{sub 10}, while the compression strength attained 3810 MPa at the plastic strain of 8.6%. The samples cooled down to 235 °C also showed globular grains surrounded by the eutectic mixture. The TEM studies allowed researchers to identify lower bainite with a plate thickness of about 500 nm (SAEDP from that area showed reflections from α-Fe and Fe{sub 3}C carbides). X-ray diffraction confirmed the presence of 90% ferrite, 6% austenite and 4% carbide. The average hardness of samples annealed at 235 °C decreased to 627HV{sub 10}, while the compression strength decreased to 3100 MPa. The plastic strain increased to 32%. The microstructure of the samples after cooling and

  3. Evolution of microstructure in 100Cr6 steel after cooling from a thixoforming temperature to bainitic transformation ranges

    International Nuclear Information System (INIS)

    A new concept for the isothermal heat treatment of thixo-elements, consisting of controlled cooling from a semi-solid metal processing (SSM) range, was proposed. 100Cr6 steel (0.97% C, 1.4% Cr, 0.4% Si, 0.4% Mn bal. Fe) after forging was used as the starting material. The DSC analysis was used to determine the liquid phase fraction vs temperature in the solidus–liquidus range. The temperatures and kinetics of bainite transformation after cooling the steel in the semi-solid state were calculated based on the Chester and Bhadeshia models. The steel was heated up to 1425 °C in order to obtain about 25% of the liquid fraction. Then it was cooled in oil at three different temperatures: 135 °C, 235 °C and 335 °C, at which the samples were held for 5 h. The microstructure of the samples annealed at 135 °C consisted of globular grains (the average size of 323 µm), where coarse needles of martensite were observed. They were surrounded by an eutectic mixture of chemical composition different from that of the globular grains. The electron diffraction pattern (SAEDP) showed reflections from α′-Fe and from Fe3C carbides. The X-ray diffraction confirmed the presence of martensite, austenite and carbides to the amount of 74.5%, 22% and 3.5% respectively. The average hardness of samples was 735HV10, while the compression strength attained 3810 MPa at the plastic strain of 8.6%. The samples cooled down to 235 °C also showed globular grains surrounded by the eutectic mixture. The TEM studies allowed researchers to identify lower bainite with a plate thickness of about 500 nm (SAEDP from that area showed reflections from α-Fe and Fe3C carbides). X-ray diffraction confirmed the presence of 90% ferrite, 6% austenite and 4% carbide. The average hardness of samples annealed at 235 °C decreased to 627HV10, while the compression strength decreased to 3100 MPa. The plastic strain increased to 32%. The microstructure of the samples after cooling and treatment at 335

  4. Effect of isothermal bainitic transformation temperature on retained austenite fraction in C-Mn-Si-Al-Nb-Ti TRIP-type steel

    OpenAIRE

    A. Grajcar; H. Krztoń

    2009-01-01

    Purpose: The aim of the paper is to determine the influence of isothermal bainitic transformation temperature on a fraction of retained austenite for a new-developed C-Mn-Si-Al-Nb-Ti TRIP-type steel.Design/methodology/approach: The thermo-mechanical processing was realized in a multi-stage compression test by the use of the Gleeble 3800 thermomechanical simulator. The steel was subjected to six variants of processing with an isothermal bainitic transformation temperature in a range from 250 t...

  5. Ultrahigh strength and low yield ratio of niobium-microalloyed 900 MPa pipeline steel with nano/ultrafine bainitic lath

    International Nuclear Information System (INIS)

    An ultra-low carbon niobium-microalloyed steel with yield strength of ∼900 MPa has been processed on a pilot-plant scale. The microstructure of the steel is primarily characterized by lower bainite and acicular ferrite, with small fraction of lath-martensite and martensite-austenite (MA) constituents. Bainite is present as fine domains. A combination of niobium and titanium precipitates was observed at the grain boundaries and in the interior of the grains and includes irregular (∼40-150 nm of (Nb, Ti)(C, N)) and fine cuboidal/spherical particles of NbC (∼30-50 nm). It was observed that accelerated cooling inhibited the precipitation of Nb and Ti carbides. The Charpy impact toughness at -20 deg. C was 200 J and tensile elongation was 15% with the yield ratio of less than 0.84. The good matching of high strength and low yield ratio was realized by two-stage thermo-mechanical rolling combined with fast cooling.

  6. Analysis of microstructural variation and mechanical behaviors in submerged arc welded joint of high strength low carbon bainitic steel

    International Nuclear Information System (INIS)

    Microstructural variation in high strength low carbon bainitic steel weldment was investigated in detail by means of optical microscope, transmission electron microscope and scanning electron microscope equipped with electron backscattered diffraction. The results showed that the welded joint has various microstructures such as acicular ferrite, coarse granular ferrite and fine polygonal ferrite. The martensite–austenite (MA) constituent has a variable structure in each sub-zone, which includes fully martensite and fully retained austenite. Meanwhile, the fine grained heat affected zone has higher content of retained austenite than the welded metal (WM) and coarse grained heat affected zone (CGHAZ). The orientation relationship between retained austenite and product phases in the WM and CGHAZ is close to Kurdjumov–Sachs relationship. However, the polygonal ferrite in the fine grained HAZ has no specific orientation relationship with the neighboring retained austenite. The toughness of the coarse grained region is much lower than that of the WM because the coarse bainite contains many large MA constituents to assist the nucleation of microcracks and coarse cleavage facet lowers the ability to inhibit the crack propagation.

  7. Analysis of microstructural variation and mechanical behaviors in submerged arc welded joint of high strength low carbon bainitic steel

    Energy Technology Data Exchange (ETDEWEB)

    Lan, Liangyun, E-mail: lly.liangyun@gmail.com [State Key Laboratory of Rolling Technology and Automation, Northeastern University, Shenyang 110819 (China); Qiu, Chunlin; Zhao, Dewen; Gao, Xiuhua; Du, Linxiu [State Key Laboratory of Rolling Technology and Automation, Northeastern University, Shenyang 110819 (China)

    2012-12-15

    Microstructural variation in high strength low carbon bainitic steel weldment was investigated in detail by means of optical microscope, transmission electron microscope and scanning electron microscope equipped with electron backscattered diffraction. The results showed that the welded joint has various microstructures such as acicular ferrite, coarse granular ferrite and fine polygonal ferrite. The martensite-austenite (MA) constituent has a variable structure in each sub-zone, which includes fully martensite and fully retained austenite. Meanwhile, the fine grained heat affected zone has higher content of retained austenite than the welded metal (WM) and coarse grained heat affected zone (CGHAZ). The orientation relationship between retained austenite and product phases in the WM and CGHAZ is close to Kurdjumov-Sachs relationship. However, the polygonal ferrite in the fine grained HAZ has no specific orientation relationship with the neighboring retained austenite. The toughness of the coarse grained region is much lower than that of the WM because the coarse bainite contains many large MA constituents to assist the nucleation of microcracks and coarse cleavage facet lowers the ability to inhibit the crack propagation.

  8. Room Temperature Microstructure and Property Evaluation of a Heat Treated Fully Bainitic 20CrMoVTiB410 Steel

    Science.gov (United States)

    Srivatsa, Kulkarni; Srinivas, Perla; Balachandran, G.; Balasubramanian, V.

    2016-08-01

    The room temperature mechanical behavior of the fully bainitic steel grade 20CrMoVTiB410 was studied in the as-quenched and tempered conditions. The hardenability response of the steel during heat treatment was assessed. In the as-quenched condition itself, the steel exhibited a good combination of strength, ductility and toughness. Tempering the quenched steel till to 550°C, showed uniform mechanical properties. Tempering at 650°C showed secondary hardening behaviour, where the highest strength and least impact toughness was observed. Tempering at 700°C showed a sharp decrease in strength but with significant enhancement of toughness. The properties obtained were correlated with the microstructure and phase analysis was established using optical, scanning electron microscope, transmission electron microscope and x-ray diffraction techniques.

  9. Effect of Morphology for Novel Bainite/Martensite Dual-Phase High Strength Steel on Its Hydrogen Embrittlement Susceptibility

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The susceptibility to hydrogen embrittlement ofbainite/martensite dual-phase high strength steel with different morphologies obtained by the conventional and thermo-mechanical heat treatments has been investigated by means of electrolytic hydrogen charging. The results showed that the finer the microstructure, the lower the sensitivity of steel to hydrogen embrittlement. The fractographic analysis suggested that the fracture mode of the hydrogen-charged specimens is of a mixture of quasicleavage and dimple for both treating processes. The quasicleavage facet of the thermomechanical treated specimen is smaller than that of the conventional heated one, which is probably the reason for reducing the susceptibility to hydrogen embrittlement. Fracture metallographic observations showed that the crack propagates preferentially along bainite/martensite laths boundary, and suggested that the fracture mode is of predominantly lath boundary separation.

  10. Room Temperature Microstructure and Property Evaluation of a Heat Treated Fully Bainitic 20CrMoVTiB410 Steel

    Science.gov (United States)

    Srivatsa, Kulkarni; Srinivas, Perla; Balachandran, G.; Balasubramanian, V.

    2016-10-01

    The room temperature mechanical behavior of the fully bainitic steel grade 20CrMoVTiB410 was studied in the as-quenched and tempered conditions. The hardenability response of the steel during heat treatment was assessed. In the as-quenched condition itself, the steel exhibited a good combination of strength, ductility and toughness. Tempering the quenched steel till to 550°C, showed uniform mechanical properties. Tempering at 650°C showed secondary hardening behaviour, where the highest strength and least impact toughness was observed. Tempering at 700°C showed a sharp decrease in strength but with significant enhancement of toughness. The properties obtained were correlated with the microstructure and phase analysis was established using optical, scanning electron microscope, transmission electron microscope and x-ray diffraction techniques.

  11. Temperature dependant polycrystal model application to bainitic steel behavior under tri-axial loading in the ductile-brittle transition

    International Nuclear Information System (INIS)

    A polycrystal finite element (FE) model describing the temperature evolution of low carbon steel is proposed in order to forecast the local mechanical fields as a function of temperature, for bainitic microstructure submitted to tri-axial loading. The model is designed for finite strains, large lattice rotations and temperatures ranging into the brittle-ductile transition domain. The dislocation densities are the internal variables. At low temperature in Body Centred Cubic (BCC) materials, plasticity is governed by double kink nucleation of screw dislocations, whereas at high temperature, plasticity depends on interactions between mobile dislocations and the forest dislocations. In this paper, the constitutive law and the evolution of the dislocation densities are written as a function of temperature and describe low and high temperature mechanisms. The studied aggregates are built from Electron Back Scattering Diffraction (EBSD) images of real bainitic steel. The aggregate is submitted to a tri-axial loading in order to describe the material at a crack tip. Mechanical parameters are deduced from mechanical tests. The local strain and stress fields, computed for different applied loadings, present local variations which depend on temperature and on tri-axial ratio. The distribution curves of the maximal principal stresses show that heterogeneities respectively increase with temperature and decrease with tri-axial ratio. A direct application of this model provides the evaluation of the rupture probability within the aggregate, which is treated as the elementary volume in the weak link theory. A comparison with the Beremin criterion calibrated on experimental data, shows that the computed fracture probability dispersion induced by the stress heterogeneities is of the same order than the measured dispersion. Temperature and stress tri-axiality ratio effects are also investigated. It is shown that these two parameters have a strong effect on fracture owing to their

  12. The influence of martensite, bainite and ferrite on the as-quenched constitutive response of simultaneously quenched and deformed boron steel – Experiments and model

    International Nuclear Information System (INIS)

    Highlights: • Gleeble tests were conducted to quench and simultaneously deform boron steel. • Different as-quenched vol. fractions of martensite, bainite and ferrite were observed. • Low to int. strain rate tensile tests were conducted on the as-quenched materials. • The presence of ferrite improved the uniform elongation, hardening rate and toughness. • A rate sensitive const. model was developed for varying vol fract. mart/bain/ferrite. - Abstract: This paper examines the relationship between as-formed microstructure and mechanical properties of a hot stamped boron steel used in automotive structural applications. Boron steel sheet metal blanks were austenized and quenched at cooling rates of 30 °C/s, 15 °C/s and 10 °C/s within a Gleeble thermal–mechanical simulator. For each cooling rate condition, the blanks were simultaneously deformed at temperatures of 600 °C and 800 °C. A strain of approximately 0.20 was imposed in the middle of the blanks, from which miniature tensile specimens were extracted. Depending on the cooling rate and deformation temperature imposed on the specimens, some of the as-quenched microstructures consisted of predominantly martensite and bainite, while others consisted of martensite, bainite and ferrite. Optical and SEM metallographraphic techniques were used to quantify the area fractions of the phases present and quasi-static (0.003 s−1) uniaxial tests were conducted on the miniature tensile specimens. The results revealed that an area fraction of ferrite greater than 6% led to an increased uniform elongation and an increase in n-value without affecting the strength of the material for equivalent hardness levels. This finding resulted in improved energy absorption due to the presence of ferrite and showed that a material with a predominantly bainitic microstructure containing 16% ferrite (with 257 HV) resulted in a 28% increase in energy absorption when compared to a material condition that was fully bainitic with a

  13. Effect of deep cryogenic treatment and tempering on microstructure and mechanical behaviors of a wear-resistant austempered alloyed bainitic ductile iron

    OpenAIRE

    Chen Liqing; Cui Junjun; Tong Weiping

    2015-01-01

    In this paper, the effect of deep cryogenic treatment in combination with conven- tional heat treatment process was investigated on microstructure and mechanical behaviors of alloyed bainitic ductile iron. Three processing schedules were employed to treat this alloyed ductile iron including direct tempering treatment, tempering.+deep cryogenic treatment and deep cryogenic treatment.+tempering treatments. The microstructure and mechanical behavior, especially the wear resistance, have been eva...

  14. Development of Fine-Grained, Low-Carbon Bainitic Steels with High Strength and Toughness Produced Through the Conventional Hot-Rolling and Air-Cooling

    Science.gov (United States)

    Dhua, Sanjay Kumar; Sarkar, Partha Pratim; Saxena, Atul; Jha, Bimal Kumar

    2016-09-01

    Low-carbon bainitic steels have created enormous interest among scientists across the world in the past few decades because of their high strength, toughness, and weldability replacing the conventional quenched and tempered medium-carbon steels. Three experimental steels with varying alloy additions were made in a 100-kg laboratory induction furnace and cast into 100-mm-diameter cylindrical ingots. These ingots were hot-rolled and air-cooled to 6-mm plates in an experimental rolling mill with selected thermomechanical parameters. Steels processed through this process provided an ultrafine low-carbon bainitic microstructure with maximum yield strength (YS) and ultimate tensile strength (UTS) 575 and 705 MPa, respectively. The Charpy impact toughness of the experimental steels was excellent, and at 253 K (-20 °C), it varied from 114 to 170 Joules. Cu-B-added steel was found to give an optimum combination of strength, YS-575 MPa, and toughness, 114 J at 253 K (-20 °C). Thus, fine-grained, low-carbon bainitic steels could be developed with a proper combination of alloying elements and thermomechanical parameters even by air-cooling.

  15. Effect of bainitic transformation temperature on the mechanical behavior of cold-rolled TRIP steels studied with in-situ high-energy X-ray diffraction

    International Nuclear Information System (INIS)

    The effect of bainitic transformation temperature (400 and 450 °C) after intercritical annealing on the mechanical behavior of a low alloyed C–Mn–Al–Si cold-rolled TRIP steel was investigated using the in-situ high-energy X-ray diffraction technique. It was found that the mechanical behaviors of TRIP steels were dominated by the micromechanical behaviors of constituent phases, such as yield strength of each phase and stress partitioning among different phases, as well as the transformation kinetics of retained austenite during plastic deformation. The microstructures obtained at different bainitic transformation temperatures were similar, but exhibited obviously different mechanical behaviors. The retained austenite in the sample treated at 450 °C with lower carbon content and yield strength was less stable and transformed into martensite at a relatively faster speed during deformation leading to a higher ultimate tensile strength but a smaller uniform elongation. In addition, stress partitioning among constituent phases was also obtained for the investigated steels in such a way that the ferrite matrix undertook smaller stresses and the bainitic ferrite, martensite and retained austenite bore larger ones during plastic deformation. The retained austenite in the sample treated at 400 °C with higher carbon content displayed significantly higher strength and relatively stronger work-hardening capabilities during deformation in comparison to those of the sample treated at 450 °C

  16. Structure Character of M-A Constituent in CGHAZ of New Ultra-Low Carbon Bainitic Steel under Laser Welding Conditions

    Institute of Scientific and Technical Information of China (English)

    Lin ZHAO; Wuzhu CHEN; Xudong ZHANG; Jiguo SHAN

    2006-01-01

    800 MPa grade new ultra-low carbon bainitic (NULCB) steel is the recently developed new generation steel.The microstructure in the coarse-grained heat-affected zone (CGHAZ) of NULCB steel under laser welding conditions was investigated by thermal simulation. The influence of the cooling time from 800℃ to 500℃,t8/5 (0.3~30 s), on the microstructure of the CGHAZ was discussed. The experimental results indicate that the microstructure of the CGHAZ is only the granular bainite which consists of bainitic ferrite (BF) lath and M-A constituent while t8/5 is 0.3~30 s. The M-A constituent consists of twinned martensite and residual austenite, and the change of the volume fraction of the residual austenite in the M-A constituent is very small when t8/5 is between 0.3 and 30 s. The morphology of the M-A constituent obviously changes with the variation of t8/5. As t8/5 increases, the average width, gross and shape parameter of the M-A constituent increase, while the line density of the M-A constituent decreases.

  17. Ultra-high cycle fatigue behavior of high strength steel with carbide-free bainite/martensite complex microstructure

    Institute of Scientific and Technical Information of China (English)

    Xue-xia Xu; Yang Yu; Wen-long Cui; Bing-zhe Bai; Jia-lin Gu

    2009-01-01

    The ultra-high cycle fatigue behavior of a novel high strength steel with carbide-free bainite/martensite (CFB/M) complex microstructure was studied. The ultra-high cycle fatigue properties were measured by ultrasonic fatigue testing equipment at a fre-quency of 20 kHz. It is found that there is no horizontal part in the S-N curve and fatigue fracture occurs when the life of specimens exceeds 107 cycles. In addition, the origination of fatigue cracks tends to transfer from the surface to interior of specimens as the fa-tigue cycle exceeds 107 , and the fatigue crack originations of many specimens are not induced by inclusions, but by some kind of "soft structure". It is shown that the studied high strength steel performs good ultra-high cycle fatigue properties. The ultra-high fa-tigue mechanism was discussed and it is suggested that specific CFB/M complex microstrueture of the studied steel contributes to itssuperior properties.

  18. Effect of boron addition on the microstructures and mechanical properties of thermomechanically processed and tempered low carbon bainitic steels

    Institute of Scientific and Technical Information of China (English)

    Liangyun LAN; Chunlin QIU; Ping ZHOU; Dewen ZHAO; Canming LI; Xiuhua GAO; Linxiu DU

    2011-01-01

    Thermomechanical process and tempering heat treatment were employed to produce the experimental steel plates.The effect of boron addition on the microstructure and mechanical properties of low carbon bainitic steels was studied in this paper.Microstructure observation and crystallographic features were conducted by using optical microscopy,SEM,TEM and electron back scattering diffraction (EBSD) analysis.The results showed that under the same rolling processes and heat treatment conditions,a substantial increase in strength is obtained by addition of boron into steel,but accompanied by an obvious drop in toughness.New martensite phase forms along the grain boundaries on tempering at 650 ℃ mainly due to boron segregation,which can further deteriorate impact toughness of the boron bearing steel.The EBSD analysis showed that high angle grain boundary,is not responsible for the deteriorated toughness of the boron bearing steel because it has relatively higher percentage of high angle grain boundary than the boron free steel.The low toughness of the boron bearing steel is mainly attributed to the coarse boride precipitated particles according to the results of fractograph observation.

  19. Effects of Cu and B addition on microstructure and mechanical properties of high-strength bainitic steels

    International Nuclear Information System (INIS)

    Effects of Cu and B addition on microstructure and mechanical properties of high-strength bainitic steels were investigated in this study. Six kinds of steels were fabricated by controlling the amount of Cu and B addition, and their microstructures and tensile and Charpy impact properties were investigated. Their effective grain sizes were also characterized by the electron back-scatter diffraction analysis. The tensile test results indicated that the B- or Cu-containing steels had the higher yield and tensile strengths than the B- or Cu-free steels because their volume fractions of acicular ferrite and martensite were quite high. The B- or Cu-free steels had the higher upper shelf energy than the B- or Cu-containing steels because of their lower volume fraction of martensite. In the steel containing 10 ppm B without Cu, the best combination of high strengths, high upper shelf energy, and low energy transition temperature could be obtained by the decrease in effective grain size due to the presence of acicular ferrite having fine effective grain size.

  20. Effect of heat treatment and cleanness of ultra low carbon bainitic (ULCB) steel on its impact toughness

    International Nuclear Information System (INIS)

    The small variations in sulphur and carbon concentrations can have a major influence on the impact transition temperature (ITT) of ultra low carbon HSLA-100 steel which has been quenched in water and tempered (WQ and T). Since the average carbon concentration is very low thus sensitivity of ITT to heat treatment parameters depends also on the yield strength increase due to precipitation effect of εCu phase. The regression analysis has been used to establish equations taking into account those parameters. The properties of a mixed microstructure formed from partially austenitic regions have been also considered. The fine austenitic grains transform into more desirable fine bainitic ferrite phases with lower hardness values and higher toughness. On the other hand, if cooling rate is sufficiently large, then the carbon enriched austenite transforms partially into hard martensite and some of remaining untransformed austenite being retained to ambient temperature. Because hard martensite islands are located in much softer surroundings consisting of tempered ferrite, they do not cause a general reduction in impact toughness tests. Due to further grain refinement of microstructure the measured toughness on Charpy V specimens can be very high at low temperatures. The very detrimental effect of sulphur in ULCB steel has been confirmed by presented results. (author)

  1. Study on High Strength Low Alloy Bainitic Steel Rails%低合金高强度贝氏体钢轨的试验研究

    Institute of Scientific and Technical Information of China (English)

    陈朝阳; 周清跃; 张银花; 刘丰收; 陈昕

    2013-01-01

    根据我国铁路技术装备发展的需要,开展低合金高强度贝氏体钢轨的实验室研究及工业性试制、显微组织及性能试验研究、焊接性能及铺设使用研究.结果表明:贝氏体钢轨具有优良的强韧性配合,室温抗拉强度达到1 240 MPa,断后伸长率15.3%,平均冲击功达到142 J,-20℃断裂韧性KIC为48 MPa.m1/2;钢轨全断面显微组织为无碳化物贝氏体;焊接性能研究结果表明:贝氏体钢轨具有良好的焊接性,其接触焊、气压焊和铝热焊接头的各项性能均达到我国铁路钢轨的铺设使用要求.试铺结果表明:贝氏体钢轨的耐磨性能与高强度热处理钢轨相当,抗接触疲劳伤损性能突出,综合使用性能优于珠光体型热处理钢轨及热轧钢轨.%To meet the dramatic growth needs of China railways,the systematic research work of bainitic steel rails was conducted,including laboratory study,trial production,microstruture and properties study and welding performance,laying & operation study.The results show as follows:At room temperature,the average tensile strength,tensile elongation and CUN impact toughness of rail cross section reach respectively 1240 MPa,15.3% and 142 J;the fracture toughness (KIC) at-20 ℃ was up to 48 MPa · m1/2 ; the microstructure of the whole rail section is carbon-free bainite;the bainitic rails possess good weldability,their performance with flash butt welding,gas pressure welding and thermit welding all satisfy requirements of laying and operation of rails of China railways;the bainitic rails have better spalling resistance and wear resistance than rolled and heat hardened pearlitic rails so that they provide better comprehensive operating characteristics.

  2. Effect of deep cryogenic treatment and tempering on microstructure and mechanical behaviors of a wear-resistant austempered alloyed bainitic ductile iron

    Directory of Open Access Journals (Sweden)

    Chen Liqing

    2015-01-01

    Full Text Available In this paper, the effect of deep cryogenic treatment in combination with conven- tional heat treatment process was investigated on microstructure and mechanical behaviors of alloyed bainitic ductile iron. Three processing schedules were employed to treat this alloyed ductile iron including direct tempering treatment, tempering.+deep cryogenic treatment and deep cryogenic treatment.+tempering treatments. The microstructure and mechanical behavior, especially the wear resistance, have been evaluated after treated by these three schedules. The results show that martensite microstructure can be obviously refined and the precipitation of dispersed carbides is promoted by deep cryogenic treatment at .−196 ∘C for 3 h after tempered at 450 ∘C for 2 h. In this case, the alloyed bainitic ductile iron possesses rather high hardness and wear-resistance than those processed by other two schedules. The main wear mechanism of the austempered alloyed ductile iron with deep cryogenic treatment and tempering is micro-cutting wear in association with plastic deformation wear.

  3. Direct Observations of Austenite, Bainite and Martensite Formation During Arc Welding of 1045 Steel using Time Resolved X-Ray Diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Elmer, J; Palmer, T; Babu, S; Zhang, W; DebRoy, T

    2004-02-17

    In-situ Time Resolved X-Ray Diffraction (TRXRD) experiments were performed during stationary gas tungsten arc (GTA) welding of AISI 1045 C-Mn steel. These synchrotron-based experiments tracked, in real time, phase transformations in the heat-affected zone of the weld under rapid heating and cooling conditions. The diffraction patterns were recorded at 100 ms intervals, and were later analyzed using diffraction peak profile analysis to determine the relative fraction of ferrite ({alpha}) and austenite ({gamma}) phases in each diffraction pattern. Lattice parameters and diffraction peak widths were also measured throughout the heating and cooling cycle of the weld, providing additional information about the phases that were formed. The experimental results were coupled with a thermofluid weld model to calculate the weld temperatures, allowing time-temperature transformation kinetics of the {alpha} {yields} {gamma} phase transformation to be evaluated. During heating, complete austenitization was observed in the heat affected zone of the weld and the kinetics of the {alpha} {yields} {gamma} phase transformation were modeled using a Johnson-Mehl-Avrami (JMA) approach. The results from the 1045 steel weld were compared to those of a 1005 low carbon steel from a previous study. Differences in austenitization rates of the two steels were attributed to differences in the base metal microstructures, particularly the relative amounts of pearlite and the extent of the allotriomorphic ferrite phase. During weld cooling, the austenite transformed to a mixture of bainite and martensite. In situ diffraction was able to distinguish between these two non-equilibrium phases based on differences in their lattice parameters and their transformation rates, resulting in the first real time x-ray diffraction observations of bainite and martensite formation made during welding.

  4. 评刘宗昌等关于贝氏体铁素体形核的工作%Comment on Works Concerning the Nucleation of Bainitic Ferrite Authored by LIU Zongchang et al

    Institute of Scientific and Technical Information of China (English)

    徐祖耀

    2013-01-01

    评述了刘宗昌等关于贝氏体铁素体形核的工作,包括:(1)过少有关贝氏体铁素体形核机制文献综述;(2)实验工作远不够形核所要求的精确;(3)母相(奥氏体)中的成分和结构等起伏(涨落)不能成为贝氏体铁素体形核的基础;(4)提出的所谓“贝氏体形成属非切变非扩散机制”未得到先进相变理论和精细实验的支持。%Comment on works concerning the nucleation of bainitic ferrite , authored by Liu Zongchang et al , containing :(1) few literature concerning nucleation mechanism of bainitic ferrite was cited;(2) the experiments were far away from the required precision; ( 3 ) the composition and structural fluctuations in parent phase (austenite) can not effectively act as the nucleation of bainitic ferrite and (4)the suggested mechanism so called as“non-shear-diffusionless” has not been supported by advanced theory of phase transformation or precise experimental result .

  5. 回火对Si-Mn-Mo系贝氏体钢组织性能的影响%Influence of Tempering on Microstructure and Mechanical Property of Si-Mn-Mo Bainite Steel

    Institute of Scientific and Technical Information of China (English)

    杨玉; 陈昕; 杜振民; 金纪勇

    2011-01-01

    The influence of tempering at different temperature on microstructure and mechanical property of Si-Mn-Mo bainitic steel after quenching is studied in laboratory. It is found that strength and plasticity of this steel can be significantly improved through tempering after quenching. Mechanical properties of the bainitic steels tempered at 300 °C or 350 °C after quenching are similar while the strength and hardness is reduced and toughness and plasticity is slightly improved after tempering at 450 °C. The microstructure of the bainitic steel is composed of bainitic ferrite and residual austenite(flaky and blocky M-A island). Tempering properly after quenching can accelerate the decomposition of the M-A island, so percentage composition of the bainitic ferrite lath is increased and the stability of residual austenite can be improved. Thus, the stability of microstructure and mechanical property of this steel is improved.%研究了淬火后不同温度回火对Si-Mn-Mo系贝氏体钢显微组织与力学性能的影响.结果表明,采用淬火后回火的工艺可以显著提高Si-Mn-Mo系贝氏体钢的强度和塑性.淬火后300℃回火与350℃回火,该钢的力学性能相差不大,而450℃回火后强度、硬度相对较低,韧塑性略有提高.组织观察表明,该钢为贝氏体铁素体和残余奥氏体(片状和块状M-A岛)的复合组织,适当温度回火可以促进块状M-A岛分解,增加板条铁素体含量,提高残余奥氏体的机械稳定性,进而稳定其组织性能..

  6. Crystallographic Reconstruction Study of the Effects of Finish Rolling Temperature on the Variant Selection During Bainite Transformation in C-Mn High-Strength Steels

    Science.gov (United States)

    Bernier, Nicolas; Bracke, Lieven; Malet, Loïc; Godet, Stéphane

    2014-12-01

    The effect of finish rolling temperature on the austenite-( γ) to-bainite ( α) phase transformation is quantitatively investigated in high-strength C-Mn steels using an alternative crystallographic γ reconstruction procedure, which can be directly applied to experimental electron backscatter diffraction mappings. In particular, the current study aims to clarify the respective contributions of the γ conditioning during the hot rolling and the variant selection during the phase transformation to the inherited texture. The results confirm that the sample finish rolled at the lowest temperature [1102 K (829 °C)] exhibits the sharpest transformation texture. It is shown that this sharp texture is exclusively due to a strong variant selection from parent brass {110}, S {213} and Goss {110} grains, whereas the variant selection from the copper {112} grains is insensitive to the finish rolling temperature. In addition, a statistical variant selection analysis proves that the habit planes of the selected variants do not systematically correspond to the predicted active γ slip planes using the Taylor model. In contrast, a correlation between the Bain group to which the selected variants belong and the finish rolling temperature is clearly revealed, regardless of the parent orientation. These results are discussed in terms of polygranular accommodation mechanisms, especially in view of the observed development in the hot-rolled samples of high-angle grain boundaries with misorientation axes between γ and γ.

  7. 贝氏体耐候钢模拟工业大气腐蚀交流阻抗谱分析*%Bainite Weathering Steel Industrial Atmospheric Corrosion Simulation of AC Impedance Spectroscopy Analysis

    Institute of Scientific and Technical Information of China (English)

    邵长静

    2015-01-01

    主要阐述了实验目的、实验方法和实验结果等具体内容,提出了提高贝氏体耐候钢耐蚀性作用的方法和具体实验判定过程。%This paper mainly described the experiment purpose, experiment method and experiment results of the specific content, put forward methods to improve bainite weathering steel corrosion resistance effect and the specific experimental process of judgment.

  8. Effect of Si on Wear Resistance of Bainitic Cast Steel under High Stress Impact%硅对贝氏体铸钢高应力冲击磨损性能的影响

    Institute of Scientific and Technical Information of China (English)

    黄进峰; 方鸿生; 徐平光; 郑燕康

    2001-01-01

    The high stress-wear resistance and mechanism for bainitic cast steels with different Si content (0.7 %~2.4 %) have been studied systematically.The experiments have shown that the wear loss of high Si bainitic cast steels is only about 1/2 times as that of low Si baini tic cast steels, showing better wear resistance of the former under high stress impact.The reason is that the impact wear mechanism is different for low and hi gh Si bainitic cast steels.Low Si bainitic cast steel has poor wear resistance under high stress impact because of its low toughness, coarse dendrite and micro -segregation, etc.So the damage cracks are easily formed in the wear surface b efore formation of white layer, and propagate inside the deformation zone and ma trix, exhibiting mechanism of deformation zone and matrix delamination.The imp act toughness of high Si bainitic cast steels are improved apparently for the re ason that the brittle cementite is replaced by ductile retained austentite film, resulting in the brittle delamination of white layer.%研究了不同硅含量(0.7 %~2.4 %,质量分数,下 同)贝氏体铸钢的抗高应力磨损性能和失效机制。结果表明:高硅贝氏体铸钢的耐磨性能较 低硅钢显著提高,其磨损失重约是低硅贝氏体铸钢的1/2。这是因为硅使贝氏体铸钢在高应 力冲击磨损下表现出不同的失效机制。低硅(0.7 %)贝氏体铸钢由于韧性低、组织结构粗大 及树枝晶的微区成分偏析,故材料抵抗冲击的能力很低,常在表面还未形成强烈变形层(白 层)甚至变形层时,就在变形层和材料基体内产生裂纹并扩展,故低硅贝氏体铸钢的失效方 式为变形层和基体剥落机制。而硅含量为1.6 %~2.4 %的高硅贝氏体铸钢,因脆性的渗碳体 被韧性的残余奥氏体所代替,钢的韧性显著提高,失效方式表现为白层的剥落机制。

  9. Aspectos cinéticos e microestruturais da transformação bainítica incompleta em ferros nodulares austemperados Kinetic and microstructural aspects of incomplete bainite transformation in austempered ductile irons

    Directory of Open Access Journals (Sweden)

    Marcio Ferreira Hupalo

    2012-06-01

    Full Text Available Nesse trabalho, foram estudados aspectos cinéticos da transformação bainítica incompleta em ligas de ferro nodular, contendo 2,36 e 2,68% Si. As amostras foram austenitizadas a 900°C, durante 90 minutos, e austemperadas a 320 e 370ºC, em tempos entre 1,5 e 60 minutos. A caracterização microestrutural foi realizada pelas técnicas de microscopia óptica (MO, microscopia eletrônica de varredura (MEV, difração de Raios X (DRX e microdureza Vickers. Foi desenvolvido um método de quantificação das frações transformadas por microscopia óptica. Devido ao elevado teor de silício, as ligas apresentaram o fenômeno de estase da transformação bainítica. As amostras tratadas a 320°C apresentaram microestrutura mais refinada e maiores frações transformadas para o início da estase da reação. As frações transformadas obtidas por DRX foram menores que as encontradas por MO. Esse fenômeno foi mais intenso para a menor temperatura de austêmpera. Curvas de transformação isotérmica foram obtidas para todas as condições estudadas. A cinética de transformação bainítica incompleta foi analisada segundo o modelo de Johnson-Mehl-Avrami-Kolmogorov (JMAK. Os valores do expoente n da equação JMAK variaram entre 0,15 e 0,67.This work aimed at studying the kinetic aspects of the incomplete bainite transformation of ductile cast iron containing 2.36 and 2.68% silicon (in wt %. Samples were initially austenitized at 900°C during 90 minutes and then austempered at 320 and 370°C in times ranging from 1.5 to 60 minutes. Microstructural characterization was performed by light optical microscopy (LOM, scanning electron microscopy (SEM, X-ray diffraction (XRD and Vickers microhardness tests. A LOM-based method for transformed fractions quantification has been developed. Due to its high silicon content, both alloys presented the bainite transformation stasis phenomenon. Samples austempered at 320°C displayed more refined microstructures

  10. 回火工艺对低碳贝氏体高强钢组织与性能的影响%Effect of tempering process on microstructure and properties of a low carbon bainitic steel

    Institute of Scientific and Technical Information of China (English)

    张楠; 董现春; 章军

    2013-01-01

    采用两阶段控轧控冷工艺轧制低碳贝氏体高强钢,在不同温度下进行一定时间的回火处理,检测回火处理前后钢板的力学性能,并对比分析了显微组织.结果表明,析出强化在回火处理前后起主导作用;随着回火温度的提高,组织从粒状贝氏体向准多边形铁素体过渡;在600 ~750℃进行回火处理,试验钢中的析出相粒子均匀弥散析出,屈服强度上升了90~135 MPa,抗拉强度上升了15 ~ 55 MPa;准多边形铁素体组织在-20℃的冲击功不低于30 J.%A low carbon bainitic (LCB) steel was tempered at different temperatures after controlled rolling and controlled cooling.The mechanical properties of the LCB steel before and after tempering treatment were tested and its microstructure was also examined.The results show that the precipitation strengthening plays a key role in the rolled steel both before and after tempering.The microstructure of the rolled steel changes from granular bainite to quasi-polygonal ferrite gradually with increasing tempering temperature.The uniformly distributed precipitates are observed in the tested steel tempered at 600-750 ℃.The yield strength and tensile strength of the steel tempered at 600-750 ℃ increases by 90-135 MPa and 15-55 MPa,respectively,compared with that of the as-rolled steel while the impact energy at-20 ℃ of the tested steel with quasi-polygonal ferrite is not lower than 30 J.

  11. Effect of Aging Temperature on the Mechanical Properties of Cold Hardening Microalloyed Bainitic Steel%时效温度对贝氏体型冷作强化非调质钢力学性能的影响

    Institute of Scientific and Technical Information of China (English)

    杨金峰; 惠卫军; 于同仁; 孙维; 龙晋明

    2011-01-01

    研究了时效温度对一种低碳Mn-B-Ti系贝氏体型冷作强化非调质钢力学性能的影响。结果表明:试验料的强度随时效温度的升高先是增加,并在250℃时存在一个峰值,随后强度又随时效温度的升高而降低,当温度升高到400℃以上时强度明显降低;试验料的塑性和屈强比则随时效温度的升高逐渐增加,其中后者增加的幅度更显著。与未充氢试样相比,试验料拉拔并充氢后的延迟断裂性能显著降低。随着时效温度的升高,充氢试样中的氢含量降低,缺口抗拉强度RBN和延迟断裂强度比R缓慢增加,当时效温度大于200℃时,RBN和R则明显增加。因此,在满足保载永久伸长变形量及强度和塑性要求的前提下,应选择合适的时效温度,以保证材料的延迟断裂性能。%The effect of aging temperature on the mechanical properties of low carbon Mn-B-Ti type cold hardening mieroalloyed bainitic steel was investigated. Experimental results show that strength increases at first and reaches a peak at about 250 ℃, and then decreases with the increase of aging temperature. The decrease of strength is more significant when aging temperature is higher than 400℃. Both ductility and strength ratio increase with increasing aging temperature, while the latter is more significant. The charging of hydrogen significantly impairs the delayed fracture property of the steel subject to 30% cold drawing. Hydrogen content decreases with increasing aging tern perature and thus both notch tensile strength and delayed fracture strength ratio increase. The increase of notch ten- sile strength and delayed fracture strength ratio is more noticeable when aging temperature is higher than 200℃. Therefore, with the precondition of required low permanent deformation, strength and ductility, aging temperature should be chosen carefully to maintain a relatively high application property of delayed fracture resistance.

  12. Effect of deformation on mechanical properties of cold hardening microalloyed bainitic steel%变形量对贝氏体型冷作强化非调质钢力学性能的影响

    Institute of Scientific and Technical Information of China (English)

    杨金峰; 惠卫军; 龙晋明; 于同仁; 孙维

    2011-01-01

    研究了变形量对一种低碳Mn-B-Ti系贝氏体型冷作强化非调质钢力学性能的影响。结果表明,随着变形量的增加,实验材料的强度逐渐增加而塑性逐渐降低,其中屈服强度较抗拉强度增加的幅度大。应变硬化指数n随γ增大为先增加后降低,即约在γ=30%时,n出现一峰值。冷拔变形后1/3冷镦变形时的压缩应力随γ增加基本不变,临界压缩变形量则随γ增大而不断降低。随着γ的增加,实验钢未充氢样的慢拉伸缺口抗拉强度逐渐增加,而充氢后试样的缺口抗拉强度σBN和延迟断裂强度比R则显著降低。实验钢拉拔后再经400℃时效处理能够使其延迟断裂%Effect of deformation on mechanical properties of a low carbon Mn-B-Ti cold hardening microalloyed bainitic steel was studied.Experimental results show that with the increase of cold drawing reduction γ,strength increases and ductility decreases,and the increase of yield strength is more significant than that of tensile strength.The work hardening exponent n increases with increasing γ to the maximum value at γ=30% and then decreases.The compression stress of 1/3 cold heading after cold drawing keeps almost constant with the increase of γ,while the critical compression ratio after cold-drawing decreases with the increase of γ.The notch tensile strength increases with the increase of γ for the specimen without hydrogen charging,while both notch tensile strength and delayed fracture strength ratio significantly decrease with the increase of γ after hydrogen charging.It is found that the delayed fracture resistance could be significantly improved after annealing at 400 ℃.Therefore,with the precondition of required strength,γ should be chosen carefully to maintain a relatively high performance such as cold heading capability and delayed fracture resistance.

  13. EFFECT OF BAINITIC TRANSFORMATION TEMPERATURE ON THE MICROSTRUCTURES AND MECHANICAL PROPERTIES OF THE HOT ROLLED TRIP STEEL CONTAINING Ti AND Mo AND ITS PRECIPITATION CHARACTERISTICS%贝氏体相变温度对含Ti和Mo低碳热轧TRIP钢的组织与力学性能影响及析出相的微观结构表征

    Institute of Scientific and Technical Information of China (English)

    王长军; 孙新军; 雍岐龙; 李昭东; 张熹; 江陆

    2013-01-01

    With the increasing consciousness for reducing fuel consumption and improving automobiles safety, the automotive industry is urgent to develop a new-type of steel with high strength and excellent formability. Among many high strength steels, the transformation induced plasticity (TRIP) steel may be a good candidate for automotive applications, as it drastically improves the balance between strength and ductility compared to precipitation hardened and solution hardened steels. While the tensile strength of conventional hot rolled TRIP steels are usually between 500 and 600 MPa, the TRIP steel with higher tensile strength, especially in excess of 750 MPa, is becoming increasingly important for the automotive industry. Thus, many strengthening mechanisms, such as precipitation strengthening, solution strengthening, refinement strengthening and dislocation strengthening, have been employed to improve the strength of the TRIP steel. Among them, microalloying with Nb, V and Ti, may provide effective means for further strengthening via grain refinement and precipitation strengthening. So far, many researches about the Ti-microalloyed high strength low alloy (HSLA) steel have been reported. However, the influences of alloying elements Ti and Mo on the hot rolled TRIP steel, especially the precipitation characteristics and their effects on mechanical properties, were rarely reported. Therefore, in this work the microstructure, retained austenite contents, mechanical properties and precipitation characteristics of the hot rolled TRIP steel containing Ti and Mo after bainitic transformation at different temperatures, were studied by using SEM, XRD and HRTEM. The results show that the bainitic transformation temperature has a significant effect on organizational morphology, retained austenite contents and mechanical properties of the TRIP steel. The optimal bainitic transformation temperature is 400 ℃, in which the retained austenite content and the balance of strength and

  14. MICROSTRUCTURAL CHARACTERS AND TOUGHNESS OF DIFFERENT SUB-REGIONS IN THE WELDING HEAT AFFECTED ZONE OF LOW CARBON BAINITIC STEEL%低碳贝氏体钢焊接热影响区中不同亚区的组织特征与韧性

    Institute of Scientific and Technical Information of China (English)

    兰亮云; 邱春林; 赵德文; 李灿明; 高秀华; 杜林秀

    2011-01-01

    根据焊接热影响区中不同亚区的热循环特征对低碳贝氏体钢进行了焊接热模拟实验.采用示波器载荷冲击试验机检测焊接热模拟试样的冲击韧性,结合OM,SEM,TEM以及EBSD技术对模拟显微组织的观察,分析了不同亚区的显微组织特征与冲击韧性之间的关系.结果表明,当冷却时间ts/5=30 s时,各亚区的裂纹形核功相差并不太大,其值在40-70 J之间.细晶区(FGHAZ)具有良好的止裂能力,裂纹扩展功高达122 J;而部分相变区(ICHAZ)和粗晶区(CGHAZ)的裂纹扩展功较小,分别为51.8和17 J.随t8/5的延长,各亚区的裂纹形核功和扩展功均下降,其中CGHAZ的裂纹形核功和FGHAZ的裂纹扩展功的下降最为显著.不同冷却速率下,M-A组元尺寸和形态的变化是影响裂纹形核功的重要因素.对于裂纹扩展功来说,高冷却速率下,具有高密度大角晶界的FGHAZ具有良好的抗裂纹迅速扩展的能力,但当冷却速率降低,由于原始奥氏体晶粒长大而使裂纹扩展功下降.ICHAZ有效晶粒尺寸不均匀,并随冷却速率的降低,晶粒尺寸明显增大,裂纹扩展功下降.而在CGHAZ中原始奥氏体晶粒显著粗化,大角晶界密度的下降导致裂纹扩展功降低;随冷却速率的降低,原始奥氏体晶粒内的取向变得更为单一,裂纹扩展功进一步降低.%It is generally recognized that welding heat affected zone (WHAZ) is the poorest toughness region in the welded joint of low carbon bainitic steels. The thermomechanical simulator was employed to simulate the welding thermal cycle processes of different sub-regions in WHAZ of low carbon bainitic steel in this work. The toughness of simulated specimens were tested on the instrumented drop weight impact tester with oscilloscope, and miscrostructure features were observed by means of OM, SEM, TEM and EBSD. The results showed that when cooling time (t8/5) was 30 s, the crack initiation energy of various sub-regions was

  15. Wrought Cr--W--V bainitic/ferritic steel compositions

    Energy Technology Data Exchange (ETDEWEB)

    Klueh, Ronald L.; Maziasz, Philip J.; Sikka, Vinod Kumar; Santella, Michael L.; Babu, Sudarsanam Suresh; Jawad, Maan H.

    2006-07-11

    A high-strength, high-toughness steel alloy includes, generally, about 2.5% to about 4% chromium, about 1.5% to about 3.5% tungsten, about 0.1% to about 0.5% vanadium, and about 0.05% to 0.25% carbon with the balance iron, wherein the percentages are by total weight of the composition, wherein the alloy is heated to an austenitizing temperature and then cooled to produce an austenite transformation product.

  16. Properties of bainitic T/P24 steel welded joints

    International Nuclear Information System (INIS)

    Examination results of T/P24 steel tube and pipe welded joints are presented, which find their application in conventional power installations for water-walls, headers and superheater tubes. Welded test joints without post-weld heat treatment (PWHT) and after stress relieving have been subjected to examinations and tests. The examination results proof, that PWHT is not necessary for thin-walled tubes made of T24 steel. In the case of thick elements, as the tested P24 steel pipes (φ 406 x 32 mm), PWHT is mandatory, but their application not always ensures the required impact strength 41 J. The decisive influence on the impact strength of welded joints, made in P24 steel pipes, has the bead deposition technique. (author)

  17. Experimental study and local approach of cleavage crack arrest in a bainitic steel

    International Nuclear Information System (INIS)

    EDF wants to complete the assessment of reactor pressure vessels, usually based on crack initiation concept, by crack arrest concept. The work aims at improving the knowledge of cleavage crack arrest in a reactor pressure vessel steel. For that purpose, isothermal crack arrest experiments were performed for temperatures ranging from - 150 C up to - 50 C on compact tensile specimens and on pre-cracked rings submitted to compressive loading. Fractographic observations revealed that the whole crack propagation and arrest occurs by cleavage even if ductile tearing occurs before initiation of the unstable crack propagation. A local cleavage crack arrest criterion is applied in finite element computations carried out in elasto-visco-plasticity and in full dynamics: the crack propagates since the largest principal stress reaches a critical stress. The application of this criterion on the experiments leads to a good prediction of the crack speed and of the crack length and shows that the critical stress increases with the temperature in relation with dissipation features observed on the fracture surfaces. Dependence to the geometry is observed; it can be due to the assumption used for the 2D computations. The study of the structural dynamic shows that the crack arrest phenomenon is very linked to the global dynamics of the structure: crack arrest and crack closure occur approximately at the same time. (author)

  18. Vertical Short Crack Initiation in Medium Carbon Bainitic Steel Under Mild Tractive Rolling Contact

    Institute of Scientific and Technical Information of China (English)

    DOU Peng; SUO Shuang-fu; BAI Bing-zhe; YANG Zhi-gang; LI You-guo

    2008-01-01

    To improve the current grinding procedure of the back-up roll of CVC hot rolling mills so that the back-up roll service life can be extended, the crack initiation and propagation behavior of medium carbon bainitie back-up roll steel was investigated, a kind of asperity-scale, surface originated vertical short cracks occurred at 5 × 102 -1 × 104 cycles. Theoretical analysis indicated that the maximum tensile stress occurring at the back edge of the contact of as-perities keeps at above 1 347. 97 MPa, and ratcheting and cyclic plastic deformation take place at such sites within 1 × 104 cycles. The early initiation of the vertical short cracks is caused by the asperity contact. According to the crack initi-ation mechanism, short crack behavior and preventive grinding strategy, steel consumption can be reduced considera-bly by decreasing the surface roughness and removing the asperity influenced surface thin layer at about 70%-80% of the surface distress life.

  19. Behavior of precipitation in bainitic steel during relaxation processing of RPC technique

    Institute of Scientific and Technical Information of China (English)

    Shanwu Yang; Shaoqiang Yuan; Xuemin Wang; Huibin Wu; Xinlai He

    2004-01-01

    Thermal simulation test, TEM (Transmission Electron Microscope) and nanobeam EDS (Energy Dispersed x-ray Spectrum) techniques were used to investigate the precipitation behavior of Nb, Ti, Mo etc. In HSLA (High Strength Low Alloy) steel.The strain induced precipitation occurred during the isothermal relaxation stage after deformed in the non-recrystallization temperature region. After 30% predeformation at 850 and 900℃, there are two kinds of particles, (Ti,Nb)(C,N) and a few Nb(C,N), to precipitate during holding. The content of Nb in particles rises with the relaxation time increasing. During the final holding stage, some Nb and Ti atoms in the lattice sites of the precipitates would be replaced by Mo atoms, and the Mo content in the precipitates increases with the relaxation time. The results were compared with the refinement effect of microstructures caused by relaxationprecipitation controlling transformation (RPC) processing.

  20. INFLUENCE OF BAINITE STRUCTURE ON MECHANICAL CHARACTERISTICS OF HIGH-CARBON WIRE

    Directory of Open Access Journals (Sweden)

    A. Ju. Borisenko

    2009-01-01

    Full Text Available Influence of structure of beynit is explored on mechanical properties after thermal treatment of wire from the steel 80. The structural state of beynit, providing the high complex of mechanical properties of high-carbon wire, is definite.

  1. Fracture Toughness and Strength in a New Class of Bainitic Chromium-Tungsten Steels

    Energy Technology Data Exchange (ETDEWEB)

    Mao, S. X.; Sikka, V. K.

    2006-06-01

    This project dealt with developing an understanding of the toughening and stengthening mechanisms for a new class of Fe-3Cr-W(V) steels developed at Oak Ridge National Laboratory (ORNL) in collaboration with Nooter Corporation and other industrial partners. The new steele had 50% higher tensile strength up to 650 degrees Celsius than currently used steels and the potential for not requiring any postweld heat treatment (PWHT) and for reducing equipment weight by 25%. This project was closely related to the Nooter project described in the report Development of a New Class of Fe-3Cr-W(V) Ferritic steels for Industrial Process Applications (ORNL/TM-2005/82). The project was carried out jointly by the University of Pittsburgh and ORNL. The University of Pittsburgh carried out fracture toughness measurements and microstructural analysis on base metal and welded plates prepared at ORNL. The project focused on three areas. The first dealt with detailed microstructural analysis of base compositions of 3Cr-3WV and 3Cr-3WBV(Ta) in both normalized (N) and normalized and tempered (NT) conditions. The second aspect of the prject dealt with determining tensile properties and fracture toughness values of K{subIC} at room temperature for both 3Cr-3Wv and 3Cr-3WV(Ta) compositions. The third focus of the project was to measure the fracture toughness values of the base metal and the heat-affectged zone (HAZ) of a plate of Fe-3Cr-W(Mo)V steel plate welded by the gas tungsten are (GTA) process. The HAZ toughness was measured in both the as-welded and the PWHT condition.

  2. Strong tough low-carbon bainite structural steels exposed to heat treatment and mechanical working

    International Nuclear Information System (INIS)

    A review of results of studying the mechanical properties and structure of extremely strong construction low-pearlite and pearlite-free steels subjected to thermomechanical processing (TMP) is presented. The development of TMP of low-pearlite and pearlite-free steels has led to creation of steel of the following composition: 0.06% of C; 1.8% of Mn; 0.3% of Mo; 0.05-0.09% of Nb. Depending on the kind of TMP the most important parameters of which are the temperature of the termination of rolling and the total deformation below 900 deg C, transformation in these steels occurs partially or completely in the intermediate domain. The increased density of dislocations of beinite structure affects substantially the increase in the yield limit. High degrees of squeezing at temperatures below 870 deg C promote formation of ferrite nuclei. The laboratory rolling demonstrates that by selecting the conditions of TMP one can control the mechanical properties of a steel. The sheets of 13 mm thick allow to obtain the guaranteed values of the yield limit of 70 kgf/mm2 the transition temperature T50 = -25 deg C, whereas after rolling under different conditions the low-temperature limit of cold shortness is - 125 deg C, and the yield limit - 45 kgf/mm2. As followed from the estimate of numerous industrial experiments, with sheets 20 mm thick in hot-rolled state one can obtain the yield limit no less than 50 kgf/mm2. On rolling mills that make possible to produce large deformation at low temperature these values can be increased. For instance, with sheets 30 mm thick one can obtain the yield limit of 56 kgf/mm2 and the transition temperature of - 60 deg C. The dependence of the yield limit on the holding time in steel tempering is given. The steel possesses a considerable reserve of the increase of strength due to dispersion hardening, which after tempering at 600-625 deg C constitutes 8-12 kgf/mm2. Because of low carbon content, this steel is characterized by good weldability

  3. CORROSION RESISTANCE OF PEARLITIC AND BAINITIC CAST IRON IN A SYNTHETIC SOLUTION OF CONDENSED GAS FROM COMBUSTION

    OpenAIRE

    Sandra Matos Cordeiro Costa; Emerson Igor Reginaldo; Isolda Costa

    2015-01-01

    The corrosion of engine components of the combustion chamber is usually related to the formation of acids such as sulfuric and nitric. These acids are generated by the condensation of combustion gases that usually occur in vehicle exhaust systems. However, with the development of new technologies to reduce emissions, condensation is also being promoted in vehicle combustion chambers. This fact is associated with high exhaust gas recirculation rates, known as EGR (English term for ...

  4. On the relations between cyclic contraction ratio flowstress and deformation mechanisms in bainitic CrMoV steels

    International Nuclear Information System (INIS)

    The cyclic diametral strain and stress response of macroscopically untextured (nominally isotropic) bainitc Cr-Mo-V steels has been studied. The total axial strain amplitudes were controlled and chosen so that a range of ratios of plastic and elastic elongations were used extending from 0.04 to 5. The trend of the cyclic diametral strain was sometimes found to drastically deviate from the commonly used Poisson's ratio when the ratio of plastic and elastic elongation was around 3 for the uncycled material. The unusual initial increase in cyclic contraction ratio for these conditions was attributed to strain concentration and the decrease to strain decentration. A condition for these unpredictable macroscopic effects seems to be that the effective strengthening structure should be sufficiently unstable during the cyclic strain applied. At room temperature fatigue slip bands of high local density and number are created in these conditions. At elevated temperature applied strains larger than ∼ 0.3% give rise to an increasing mechanically activated dynamic recovery which operates despite a dense carbide dispersion. The amount of recovery and simultaneous dislocation annihilation increase and act to lower the flow strength with rising strain. Their extent depend on the strain rate. An apparent maximum in dynamic recovery was observed as a minimum in cyclic yield strength at the same strain for which the pronounced unpredictable diametral strain was observed. Similar diametral strain effects in monotonic tension tests on different materials reported in the published literature indicate that the effects are most probably related to the particular dominant mode of slip at strain levels for which the ratio of plastic and elastic strain (ep/eE) is around three. Slip is then dominantly planar. Careful shape control of the specimen gauge section is necessary for reproducible diametral strain because of the unstable nature of the material in the actual conditions of the cyclic straining which produce the unexpected behaviour

  5. The quantitative microstructural characterization of multipass TIG ultra low carbon bainitic steel weldments and correlation with mechanical properties

    OpenAIRE

    Butler, Daniel E.

    1993-01-01

    Approved for public release; distribution is unlimited. The U.S. Navy has maintained a continuous research, development and certification program in ULCB steels as a possible replacement for the HY and HSLA steels currently being used in ship construction. The overall aim of this program is to develop a high strength steel with improved weldability. Improved weldability could eliminate the requirement of preheating, (a necessary and costly step required to prevent weld metal cracking in HY...

  6. Influence of Thermomechanical Control Process on the Evolution of Austenite Grain Size in a Low-Carbon Nb-Ti-Bearing Bainitic Steel

    Science.gov (United States)

    Chen, Jun; Lv, Meng-yang; Tang, Shuai; Liu, Zhen-yu; Wang, Guo-dong

    2015-10-01

    On the basis of hot rolling practice, the effects of thermomechanical control process parameters on the evolution of austenite grain size before the deformation at non-recrystallization zone were investigated in detail. The inflections in the strain hardening rate versus true stress curves show that the dynamic recrystallization (DRX) has initiated for different deformation conditions studied in the present work. But the volume fractions of the equiaxed grains in the specimens which were immediately water quenched to room temperature after deformation are different from each other. Moreover, the main refinement mechanisms for different deformation conditions have been differentiated. It is interesting to note that the austenite grain size can be refined significantly with increasing the strain from 0.0 to 0.5 for different deformation temperatures. However, when the strain increases to 0.8, the austenite grain size cannot be further refined for the higher deformation temperature range, while the austenite grain size can be further refined for the lower deformation temperature range. In addition, the effect of strain rate on the austenite grain refinement is vigorous for the higher deformation temperatures. Moreover, the empirical equation to estimate the austenite grain size for different deformation parameters was established.

  7. EFFECTS OF TEST TEMPERATURE AND STRAIN RATE ON THE MECHANICAL PROPERTIES IN AN INTERCRITICALLY HEAT-TREATED BAINITE-TRANSFORMED STEEL

    Institute of Scientific and Technical Information of China (English)

    Z. Li; D. Wu

    2004-01-01

    Larger amount of austenite could be retained in an intercritically heat-treated bainitetransformed steel. The elongation and the strength-ductility balance of the steel could be enhanced considerably due to strain-induced martensite transformation and transformationinduced plasticity (TRIP) of retained austenite. The effects of test temperature and strain rate on the mechanical properties and strain induced transformation behavior of retained austenite in the steel were investigated. Total elongation and strength-ductility balance of the specimen reached maximum when it strained at a strain rate of 2.8×10-4s-1 and at 350℃. The relation between test temperature and tensile properties showed the same tendency at three kinds of strain rates. Flow stress increased considerably with decreasing the strain rate.

  8. STRUCTURE AND CHARACTERISTICS OF PATENTED HIGH-CARBON WIRE

    Directory of Open Access Journals (Sweden)

    A. Ju. Borisenko

    2011-01-01

    Full Text Available The influence of bainite structure on mechanical characteristics of wire of steel 80 after patenting is studied. The quantity and structure state of bainite, providing high complex of mechanical characteristics of high-carbon wire, is determined.

  9. Low-chromium reduced-activation chromium-tungsten steels

    Energy Technology Data Exchange (ETDEWEB)

    Klueh, R.L.; Alexander, D.J.; Maziasz, P.J. [Oak Ridge National Lab., TN (United States)

    1996-10-01

    Bainitic microstructures formed during continuous cooling can differ from classical upper and lower bainite formed during isothermal transformation. Two types of non-classical bainite were observed depending on the cooling rate: carbide-free acicular bainite at rapid cooling rates and granular bainite at slower cooling rates. The Charpy impact toughness of the acicular ferrite was found to be considerably better than for the granular bainite. It was postulated that alloying to improve the hardenability of the steel would promote the formation of acicular bainite, just as increasing the cooling rate does. To test this, chromium and tungsten were added to the 2 1/4Cr-2W and 2 1/4Cr-2WV steel compositions to increase their hardenability, and the microstructures and mechanical properties were examined.

  10. Aspectos cinéticos e microestruturais da transformação bainítica incompleta em ferros nodulares austemperados Kinetic and microstructural aspects of incomplete bainite transformation in austempered ductile irons

    OpenAIRE

    Marcio Ferreira Hupalo; Daniele da Silva Ramos; Alexsandro Rabelo; Nelson Batista de Lima

    2012-01-01

    Nesse trabalho, foram estudados aspectos cinéticos da transformação bainítica incompleta em ligas de ferro nodular, contendo 2,36 e 2,68% Si. As amostras foram austenitizadas a 900°C, durante 90 minutos, e austemperadas a 320 e 370ºC, em tempos entre 1,5 e 60 minutos. A caracterização microestrutural foi realizada pelas técnicas de microscopia óptica (MO), microscopia eletrônica de varredura (MEV), difração de Raios X (DRX) e microdureza Vickers. Foi desenvolvido um método de quantificação da...

  11. STUDY ON JOINT STRUCTURE AND PROPERTIES OF FLASH BUTT WELDING TO META-BAINITE STEEL%准贝氏体钢闪光对焊的组织及性能

    Institute of Scientific and Technical Information of China (English)

    程巨强; 康沫狂

    2001-01-01

    研究了新型准贝氏体钢制造的矿用圆环链闪光对焊焊缝的组织与性能.结果表明,闪光对焊后中频感应淬火、回火热处理后,准贝氏体钢焊缝组织为低碳马氏体和准贝氏体组织,焊缝强度损失小、韧性高,准贝氏体钢具有良好的闪光焊接性能.

  12. A correlative approach to segmenting phases and ferrite morphologies in transformation-induced plasticity steel using electron back-scattering diffraction and energy dispersive X-ray spectroscopy.

    Science.gov (United States)

    Gazder, Azdiar A; Al-Harbi, Fayez; Spanke, Hendrik Th; Mitchell, David R G; Pereloma, Elena V

    2014-12-01

    Using a combination of electron back-scattering diffraction and energy dispersive X-ray spectroscopy data, a segmentation procedure was developed to comprehensively distinguish austenite, martensite, polygonal ferrite, ferrite in granular bainite and bainitic ferrite laths in a thermo-mechanically processed low-Si, high-Al transformation-induced plasticity steel. The efficacy of the ferrite morphologies segmentation procedure was verified by transmission electron microscopy. The variation in carbon content between the ferrite in granular bainite and bainitic ferrite laths was explained on the basis of carbon partitioning during their growth.

  13. A correlative approach to segmenting phases and ferrite morphologies in transformation-induced plasticity steel using electron back-scattering diffraction and energy dispersive X-ray spectroscopy.

    Science.gov (United States)

    Gazder, Azdiar A; Al-Harbi, Fayez; Spanke, Hendrik Th; Mitchell, David R G; Pereloma, Elena V

    2014-12-01

    Using a combination of electron back-scattering diffraction and energy dispersive X-ray spectroscopy data, a segmentation procedure was developed to comprehensively distinguish austenite, martensite, polygonal ferrite, ferrite in granular bainite and bainitic ferrite laths in a thermo-mechanically processed low-Si, high-Al transformation-induced plasticity steel. The efficacy of the ferrite morphologies segmentation procedure was verified by transmission electron microscopy. The variation in carbon content between the ferrite in granular bainite and bainitic ferrite laths was explained on the basis of carbon partitioning during their growth. PMID:25126753

  14. A correlative approach to segmenting phases and ferrite morphologies in transformation-induced plasticity steel using electron back-scattering diffraction and energy dispersive X-ray spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Gazder, Azdiar A., E-mail: azdiar@uow.edu.au [Electron Microscopy Centre, University of Wollongong, New South Wales 2500 (Australia); Al-Harbi, Fayez; Spanke, Hendrik Th. [School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, New South Wales 2522 (Australia); Mitchell, David R.G. [Electron Microscopy Centre, University of Wollongong, New South Wales 2500 (Australia); Pereloma, Elena V. [Electron Microscopy Centre, University of Wollongong, New South Wales 2500 (Australia); School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, New South Wales 2522 (Australia)

    2014-12-15

    Using a combination of electron back-scattering diffraction and energy dispersive X-ray spectroscopy data, a segmentation procedure was developed to comprehensively distinguish austenite, martensite, polygonal ferrite, ferrite in granular bainite and bainitic ferrite laths in a thermo-mechanically processed low-Si, high-Al transformation-induced plasticity steel. The efficacy of the ferrite morphologies segmentation procedure was verified by transmission electron microscopy. The variation in carbon content between the ferrite in granular bainite and bainitic ferrite laths was explained on the basis of carbon partitioning during their growth. - Highlights: • Multi-condition segmentation of austenite, martensite, polygonal ferrite and ferrite in bainite. • Ferrites in granular bainite and bainitic ferrite segmented by variation in relative carbon counts. • Carbon partitioning during growth explains variation in carbon content of ferrites in bainites. • Developed EBSD image processing tools can be applied to the microstructures of a variety of alloys. • EBSD-based segmentation procedure verified by correlative TEM results.

  15. Vanadium Effect on a Medium Carbon Forging Steel

    Directory of Open Access Journals (Sweden)

    Carlos Garcia-Mateo

    2016-05-01

    Full Text Available In the present work the influence of vanadium on the hardenability and the bainitic transformation of a medium carbon steel is analyzed. While V in solid solution enhances the former, it hardly affects bainitic transformation. The results also reveal an unexpected result, an increase of the prior austenite grain size as the V content increases.

  16. A correlative approach to segmenting phases and ferrite morphologies in transformation-induced plasticity steel using electron back-scattering diffraction and energy dispersive X-ray spectroscopy

    International Nuclear Information System (INIS)

    Using a combination of electron back-scattering diffraction and energy dispersive X-ray spectroscopy data, a segmentation procedure was developed to comprehensively distinguish austenite, martensite, polygonal ferrite, ferrite in granular bainite and bainitic ferrite laths in a thermo-mechanically processed low-Si, high-Al transformation-induced plasticity steel. The efficacy of the ferrite morphologies segmentation procedure was verified by transmission electron microscopy. The variation in carbon content between the ferrite in granular bainite and bainitic ferrite laths was explained on the basis of carbon partitioning during their growth. - Highlights: • Multi-condition segmentation of austenite, martensite, polygonal ferrite and ferrite in bainite. • Ferrites in granular bainite and bainitic ferrite segmented by variation in relative carbon counts. • Carbon partitioning during growth explains variation in carbon content of ferrites in bainites. • Developed EBSD image processing tools can be applied to the microstructures of a variety of alloys. • EBSD-based segmentation procedure verified by correlative TEM results

  17. Influence of two different heat treatment procedures on mechanical and fracture properties of 65 Si 7 steel

    International Nuclear Information System (INIS)

    This paper deals with the results of investigations of two different heat treatment procedures and their influence on some mechanical properties as well as on the magnitude of some fracture mechanics parameters for a particular type of steel. The experimental investigations were performed on the specimens made of 65Si7 steel. The processes occurring by tempering of two different microstructures of the steel, i. e. martensite and lower bainite were investigated. An advantage of austempering over hardening and tempering is in obtaining the bainite microstructure. Steel of bainite microstructure has a greater toughness, ductility, contraction, fatigue strength and a better fracture toughness than a tempered martensite of the same type of steel. A bainite microstructure also gives a better resistance to thermal fatigue in comparison with martensite microstructure. The above mentioned improved values of mechanical properties refer to the untempered state of bainite. (author)

  18. Microstructure and mechanical properties of railway wheels manufactured with low-medium carbon Si-Mn-Mo-V steel

    Institute of Scientific and Technical Information of China (English)

    Mingru Zhang; Haicheng Gu

    2008-01-01

    The suitability of carbide-free bainite steel as railway wheel materials was investigated. The low-medium carbon Si-Mn-Mo-V steel was designed to make railway wheels by forging and rolling. The slack quenching with water was conducted on the tread of rim section by programmed control to simulate isothermal heat treatment after being austenitized. Microstructures and mechanical properties have been studied. The results indicate that the microstructure of the rim is mainly carbide-free bainite, and the mixed mi- crostructure of bainitic ferrite and granular bainite is observed in web and hub. The mechanical properties are superior to both the standard requirements and the commercial production, such as CL60 plain carbon. The Charpy impact energy is relatively high at room and/or subzero temperatures. The force-displacement curves and fractographies reveal the excellent ability of resistance to crack initiation and propagation.

  19. Effects of deformation and boron on microstructure and continuous cooling transformation in low carbon HSLA steels

    Energy Technology Data Exchange (ETDEWEB)

    Jun, H.J. [Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of); Kang, J.S. [Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of); Seo, D.H. [Technical Research Laboratories, POSCO, Pohang 545-090 (Korea, Republic of); Kang, K.B. [Technical Research Laboratories, POSCO, Pohang 545-090 (Korea, Republic of); Park, C.G. [Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of)]. E-mail: cgpark@postech.ac.kr

    2006-04-25

    The continuous-cooling-transformation (CCT) diagram and continuous cooled microstructure were investigated for low carbon (0.05 wt.% C) high strength low alloy steels with/without boron. Microstructures observed in continuous cooled specimens were composed of pearlite, quasi-polygonal ferrite, granular bainite, acicular ferrite, bainitic ferrite, lower bainite, and martensite depending on cooling rate and transformation temperature. A rapid cooling rate depressed the formation of pearlite and quasi-polygonal ferrite, which resulted in higher hardness. However, hot deformation slightly increased transformation start temperature, and promoted the formation of pearlite and quasi-polygonal ferrite. Hot deformation also strongly promoted the acicular ferrite formation which did not form under non-deformation conditions. Small boron addition effectively reduced the formation of pearlite and quasi-polygonal ferrite and broadened the cooling rate region for bainitic ferrite and martensite.

  20. Thermal Stability of Nanocrystalline Structure In X37CrMoV5-l Steel

    OpenAIRE

    Skołek E.; Marciniak S.; Świątnicki W.A.

    2015-01-01

    The aim of the study was to investigate the thermal stability of the nanostructure produced in X37CrMoV5-1 tool steel by austempering heat treatment consisted of austenitization and isothermal quenching at the range of the bainitic transformation. The nanostructure was composed of bainitic ferrite plates of nanometric thickness separated by thin layers of retained austenite. It was revealed, that the annealing at the temperature higher than temperature of austempering led to formation of ceme...

  1. Microstructure-Fracture Behavior Relationships of Slot-Welded Rail Steels

    Science.gov (United States)

    Allie, Aldinton; Aglan, Heshmat; Fateh, Mahmood

    2011-09-01

    Microstructural analyses of the parent pearlitic and bainitic rail steels were performed, and the results were compared with the microstructure of the welded pearlitic and bainitic steels. An increase in the ASTM grain size number of the heat-affected zone (HAZ) for both pearlitic and bainitic slot welds was observed. The microstructural features that were identified in the weldment of both slot-welded steels were very similar. This was expected since the same welding wire was used to weld both rail steels. The weld consisted of mainly ferrite and had similar grain size. The fusion zones of the welded pearlitic and bainitic rail steels were examined after flexural tests to determine if there were any cracks present due to improper or weak fusion. Examination of the entire fusion zone under high optical magnification revealed no cracks, indicating that a perfect fusion was achieved. The three-point flexural behavior of the parent pearlitic and bainitic steels was evaluated and compared with that of the slot-welded steels. It was found that that the welded pearlitic steel has superior fracture resistance properties when compared to the parent pearlitic steel. The average fracture resistance of the parent pearlitic steel was 79 MPa√m compared to 119 MPa√m for the welded pearlitic steel. The slot-welded bainitic steel, however, showed similar fracture resistance properties to the parent bainitic steel with average values of 121 and 128 MPa√m, respectively. The failure mechanism of the welded and parent pearlitic and bainitic steels was also identified. Microvoid coalescence was observed in both welded rail steel samples. This was manifested by dimpled features, which are associated with ductile failure.

  2. Structure and Properties of Thermomechanically-processedHSLA Steels for Naval Applications

    OpenAIRE

    Ghosh, A; Kundu, S.; Chatterjee, S

    2007-01-01

    Four high-strength low-alloy (HSLA) steels with varying chemical compositions were forgedin two different temperature ranges followed by cooling in various media. Microstructures andmechanical properties of the steels were evaluated. The microstructures obtained in water–quenchedlow-carbon HSLA steels were lath martensite packet within the pancaked grains. On air or sandcooling predominantly bainitic ferrite or granular bainite structure forms. The strength propertiesof these steels decreased...

  3. Study of the mechanical properties of low carbon content HSLA steels

    OpenAIRE

    Illescas, S.; Fernández, J.; Asensio, J.; Sánchez-Soto, M.; Guilemany, J. M.

    2009-01-01

    Two high strength low alloy steels (HSLA) with the same bulk composition and slight microalloying content differences were studied. The main purpose of the study was to determine the effect of different heat treatments and the influence of vanadium (V) on the microstructure and mechanical properties of the bainite present in each steel. For that purpose, standard tests were conducted to determine the hardness, toughness, tensile and yield stress of the different bainite-acicular ferrite struc...

  4. Microstructure and mechanical properties of HSLA-100 steel

    OpenAIRE

    Mattes, Victor R.

    1990-01-01

    Approved for public release; distribution is unlimited. Light microscopy, scanning electron microscopy, and transmission electron microscopy were employed to examine the microstructural basis for the mechanical properties of as-quenched and tempered HSLA-100 steel. Examination of the alloy revealed granular bainite with martensite and retained austenite in the as-quenched state which upon aging at temperatures below the lower transformation temperature, 677 C, formed tempered bainite with ...

  5. Obtención y caracterización mecánica de un acero bainítico aleado con boro (10 y 20 ppm)

    OpenAIRE

    M. A. Sierra; Olaya, J.J.; R. Rodríguez-Baracaldo

    2012-01-01

    Bainitic steels have become one of the metals most widely investigated in the last decade, due to the exceptional combination of mechanical properties. The advantage of such materials is to obtain free carbide structures that combine good mechanical strength with excellent toughness. In this work were established and properly controlled conditions to cast a bainitic steel with 10 and 20 ppm of boron, and subsequently thermomechanical treatment of rolling process between 1000 °C and 1200 °C. T...

  6. Effect of isothermal holding temperature on retained austenite fraction in medium- carbon Nb/Ti-microalloyed TRIP steel

    OpenAIRE

    H. Krztoń; A. Grajcar

    2011-01-01

    Purpose: The aim of the paper is to determine the effect of the isothermal holding temperature in a bainitic transformation range on a fraction of retained austenite for a new-developed medium-carbon TRIP steel containing Nb and Ti microadditions. Design/methodology/approach: The thermo-mechanical processing was carried out by a multi-stage compression test using the Gleeble thermomechanical simulator. The steel was subjected to 5 variants of processing with an isothermal bainitic transformat...

  7. Morphological features of retained austenite in thermo-mechanically processed C-Mn-Si-Al-Nb-Ti multiphase steel

    OpenAIRE

    A. Grajcar

    2010-01-01

    Purpose: The aim of the paper is to determine the influence of isothermal bainitic transformation temperature on morphological features and a fraction of retained austenite in a new-developed thermo-mechanically processed C-Mn-Si-Al-Nb-Ti multiphase steel.Design/methodology/approach: The thermo-mechanical processing was realized in a multi-stage compression test by the use of the Gleeble thermomechanical simulator. The steel was isothermally held for 600 s in a bainitic transformation tempera...

  8. Effects of aging treatment on the microstructure and superelasticity of columnar-grained Cu71Al18Mn11 shape memory alloy

    Science.gov (United States)

    Liu, Ji-li; Huang, Hai-you; Xie, Jian-xin

    2016-10-01

    The effect of aging treatment on the superelasticity and martensitic transformation critical stress in columnar-grained Cu71Al18Mn11 shape memory alloy (SMA) at the temperature ranging from 250°C to 400°C was investigated. The microstructure evolution during the aging treatment was characterized by optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results show that the plate-like bainite precipitates distribute homogeneously within austenitic grains and at grain boundaries. The volume fraction of bainite increases with the increase in aging temperature and aging time, which substantially improves the martensitic transformation critical stress of the alloy, whereas the bainite only slightly affects the superelasticity. This behavior is attributed to a coherent relationship between the bainite and the austenite, as well as to the bainite and the martensite exhibiting the same crystal structure. The variations of the martensitic transformation critical stress and the superelasticity of columnar-grained Cu71Al18Mn11 SMA with aging temperature and aging time are described by the Austin-Rickett equation, where the activation energy of bainite precipitation is 77.2 kJ·mol-1. Finally, a columnar-grained Cu71Al18Mn11 SMA with both excellent superelasticity (5%-9%) and high martensitic transformation critical stress (443-677 MPa) is obtained through the application of the appropriate aging treatments.

  9. Effect of Initial Microstructure on Impact Toughness of 1200 MPa-Class High Strength Steel with Ultrafine Elongated Grain Structure

    Science.gov (United States)

    Jafari, Meysam; Garrison, Warren M.; Tsuzaki, Kaneaki

    2014-02-01

    A medium-carbon low-alloy steel was prepared with initial structures of either martensite or bainite. For both initial structures, warm caliber-rolling was conducted at 773 K (500 °C) to obtain ultrafine elongated grain (UFEG) structures with strong //rolling direction (RD) fiber deformation textures. The UFEG structures consisted of spheroidal cementite particles distributed uniformly in a ferrite matrix of a transverse grain size of about 331 and 311 nm in samples with initial martensite and bainite structures, respectively. For both initial structures, the UFEG materials had similar tensile properties, upper shelf energy (145 J), and ductile-to-brittle transition temperatures 98 K (500 °C). Obtaining the martensitic structure requires more rapid cooling than is needed to obtain the bainitic structure and this more rapid cooling promote cracking. As the UFEG structures obtained from initial martensitic and bainitic structures have almost identical properties, but obtaining the bainitic structure does not require a rapid cooling which promotes cracking suggests the use of a bainitic structure in obtaining UFEG structures should be examined further.

  10. Microstructure-properties correlation in fiber laser welding of dual-phase and HSLA steels

    International Nuclear Information System (INIS)

    Similar and dissimilar welds of dual-phase (DP) and high strength low alloy (HSLA) steels were made by fiber laser welding (FLW). The welds were characterized with respect to microstructure, micro- and nano-hardness, and tensile properties. The fusion zone (FZ) in the DP welds consisted of fully martensitic structure; whereas HSLA and dissimilar weld FZ microstructure were mixture of martensite and bainite. Analytical transmission electron microscopy (TEM) confirmed bainite structures containing bainitic ferrite laths with intralath and interlath cementite. Precipitation of single variant carbides inside the bainitic ferrite laths were confirmed by measuring the interplanar spacing. The cooling rate in the FZ, estimated using Rosenthal equation, and continuous-cooling-transformation diagrams corroborated the microstructure formed. Nanoindentation was used to verify the hardness of these individual microconstituents, since a much lower nano-hardness for bainite (4.11 GPa) was observed compared to martensite (6.57 GPa) phase. Tensile failure occurred in the tempered area of the heat affected zone (HAZ) in the DP steel welded, which was confirmed by typical cup-like dimple fracture; likewise failure in the HSLA base metal, which occurred in dissimilar and HSLA welds, indicated distinctive dimple and shear dimple ductile morphology

  11. Microstructure-properties correlation in fiber laser welding of dual-phase and HSLA steels

    Energy Technology Data Exchange (ETDEWEB)

    Saha, D.C., E-mail: dcsaha@uwaterloo.ca [Department of Mechanical and Mechatronics Engineering, University of Waterloo, 200 University Avenue West, Waterloo, ON, Canada N2L 3G1 (Canada); Westerbaan, D.; Nayak, S.S. [Department of Mechanical and Mechatronics Engineering, University of Waterloo, 200 University Avenue West, Waterloo, ON, Canada N2L 3G1 (Canada); Biro, E. [ArcelorMittal Global Research, 1390 Burlington Street East, Hamilton, ON, Canada L8N 3J5 (Canada); Gerlich, A.P.; Zhou, Y. [Department of Mechanical and Mechatronics Engineering, University of Waterloo, 200 University Avenue West, Waterloo, ON, Canada N2L 3G1 (Canada)

    2014-06-01

    Similar and dissimilar welds of dual-phase (DP) and high strength low alloy (HSLA) steels were made by fiber laser welding (FLW). The welds were characterized with respect to microstructure, micro- and nano-hardness, and tensile properties. The fusion zone (FZ) in the DP welds consisted of fully martensitic structure; whereas HSLA and dissimilar weld FZ microstructure were mixture of martensite and bainite. Analytical transmission electron microscopy (TEM) confirmed bainite structures containing bainitic ferrite laths with intralath and interlath cementite. Precipitation of single variant carbides inside the bainitic ferrite laths were confirmed by measuring the interplanar spacing. The cooling rate in the FZ, estimated using Rosenthal equation, and continuous-cooling-transformation diagrams corroborated the microstructure formed. Nanoindentation was used to verify the hardness of these individual microconstituents, since a much lower nano-hardness for bainite (4.11 GPa) was observed compared to martensite (6.57 GPa) phase. Tensile failure occurred in the tempered area of the heat affected zone (HAZ) in the DP steel welded, which was confirmed by typical cup-like dimple fracture; likewise failure in the HSLA base metal, which occurred in dissimilar and HSLA welds, indicated distinctive dimple and shear dimple ductile morphology.

  12. Characterization of dual-phase steel microstructure by combined submicrometer EBSD and EPMA carbon measurements.

    Science.gov (United States)

    Pinard, Philippe T; Schwedt, Alexander; Ramazani, Ali; Prahl, Ulrich; Richter, Silvia

    2013-08-01

    Electron backscatter diffraction (EBSD) and electron probe microanalysis (EPMA) measurements are combined to characterize an industrial produced dual-phase steel containing some bainite fraction. High-resolution carbon mappings acquired on a field emission electron microprobe are utilized to validate and improve the identification of the constituents (ferrite, martensite, and bainite) performed by EBSD using the image quality and kernel average misorientation. The combination eliminates the ambiguity between the identification of bainite and transformation-induced dislocation zones, encountered if only the kernel average misorientation is considered. The detection of carbon in high misorientation regions confirms the presence of bainite. These results are corroborated by secondary electron images after nital etching. Limitations of this combined method due to differences between the spatial resolution of EBSD and EPMA are assessed. Moreover, a quantification procedure adapted to carbon analysis is presented and used to measure the carbon concentration in martensite and bainite on a submicrometer scale. From measurements on reference materials, this method gives an accuracy of 0.02 wt% C and a precision better than 0.05 wt% C despite unavoidable effects of hydrocarbon contamination.

  13. Effect of microstructure on the stability of retained austenite in transformation-induced-plasticity steels

    Science.gov (United States)

    Timokhina, I. B.; Hodgson, P. D.; Pereloma, E. V.

    2004-08-01

    Two Fe-0.2C-1.55Mn-1.5Si (in wt pct) steels, with and without the addition of 0.039Nb (in wt pct), were studied using laboratory rolling-mill simulations of controlled thermomechanical processing. The microstructures of all samples were characterized by optical metallography, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The microstructural behavior of phases under applied strain was studied using a heat-tinting technique. Despite the similarity in the microstructures of the two steels (equal amounts of polygonal ferrite, carbide-free bainite, and retained austenite), the mechanical properties were different. The mechanical properties of these transformation-induced-plasticity (TRIP) steels depended not only on the individual behavior of all these phases, but also on the interaction between the phases during deformation. The polygonal ferrite and bainite of the C-Mn-Si steel contributed to the elongation more than these phases in the C-Mn-Si-Nb-steel. The stability of retained austenite depends on its location within the microstructure, the morphology of the bainite, and its interaction with other phases during straining. Granular bainite was the bainite morphology that provided the optimum stability of the retained austenite.

  14. Analytical Investigation of Prior Austenite Grain Size Dependence of Low Temperature Toughness in Steel Weld Metal

    Institute of Scientific and Technical Information of China (English)

    X.F. Zhang; P. Hall; H. Terasak; M. Sato; Y. Komizo

    2012-01-01

    Prior austenite grain size dependence of the low temperature impact toughness has been addressed in the bainitic weld metals by in situ observations.Usually,decreasing the grain size is the only approach by which both the strength and the toughness of a steel are increased.However,low carbon bainitic steel with small grain size shows a weakening of the low temperature impact toughness in this study.By direct tracking of the morphological evolution during phase transformation,it is found that large austenite grain size dominates the nucleation of intragranular acicular ferrite,whereas small austenite grain size leads to grain boundary nucleation of bainite.This kinetics information will contribute to meet the increasing low temperature toughness requirement of weld metals for the storage tanks and offshore structures.

  15. A study on welded joint toughness of X-60 steel

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Charpy impact test and COD test were performed on the specimens subjected to simulated welded thermal cycle and the specimens taken from welded joint. The optical microscope, TEM, SEM, EDAX and XRD analysis have been used to investigate the behaviors of second phase particles and the effects of microstructure on toughness separately. The results are as follows. The dispersed second phase particles can effectively retard the growth of austenite grain in the coarse-grained HAZ (CGHAZ), and improve the toughness. When t8/5 is different, the behaviors of the particles are also different in dissolving, coarsening and re-precipitating. The ability of retarding the growth of austenite grain will be affected. When t8/5 increases from 10 s to 70 s, the microstructure of CGHAZ will transform from upper bainite and granular bainite to granular bainite, and the size of austenite grain will grow a little, thus the toughness of the materials decreases slightly.

  16. Thermo-stability of ultra-fine non-equilibrium microstructures

    Institute of Scientific and Technical Information of China (English)

    Huibin Wu; Shanwu Yang; Aimin Guo; Shaoqiang Yuan; Chengjia Shang; Xinlai He

    2004-01-01

    The evolution of the microstructures and hardness of a bainitic plate steel during tempering at 650℃ has been investigated.The steel was manufactured by RPC (relaxation-precipitation controlling phase transformation) technique. A part of the plate was reheated to 930℃ and held for 1 h before quenched into water (RQ). No obvious change was detected by means of optical microscopy in the RPC steel tempering for 0.5 h, while dislocation cells were formed inside the bainite laths, accompanied by an obvious drop of hardness. The bainite laths started to coalesce in some regions, but the sample hardness kept nearly constant during tempering from 1 to 7 h. With further tempering, polygonal ferrite was formed in local regions while the hardness decreased dramatically. The RQ samples softened faster during tempering and finally transformed into the polygonal ferrite completely. These results indicate that the thermo-stability of fine non-equilibrium microstructures is tightly related to their history.

  17. Development of banded microstructure in 34CrNiMo6 steel

    Directory of Open Access Journals (Sweden)

    A. Nagode

    2016-07-01

    Full Text Available In this paper the development of a banded microstructure in hot-rolled 34CrNiMo6 steel which consisted of bainitic and martensitic bands is explained. The chemical compositions of the bands were measured with energy dispersive x-ray spectroscopy (EDS, which showed that the martensitic bands contained more alloying elements (Mn, Cr, Mo, Si than bainitic bands. By using Oberhoffer reagent, the segregations of phosphorus were also revealed. These phosphorus segregations coincided with the positive segregations of the alloying elements. The continuous cooling transformation (CCT diagrams of steel were calculated. They confirmed the formation of martensite in positive segregations and the formation of bainite in negative segregations.

  18. Obtención y caracterización mecánica de un acero bainítico aleado con boro (10 y 20 ppm

    Directory of Open Access Journals (Sweden)

    M. A. Sierra

    2012-01-01

    Full Text Available Bainitic steels have become one of the metals most widely investigated in the last decade, due to the exceptional combination of mechanical properties. The advantage of such materials is to obtain free carbide structures that combine good mechanical strength with excellent toughness. In this work were established and properly controlled conditions to cast a bainitic steel with 10 and 20 ppm of boron, and subsequently thermomechanical treatment of rolling process between 1000 °C and 1200 °C. The microstructure characterization was carried out by optical microscopy and scanning electron microscopy, and mechanical characterization by hardness, strength-strain and toughness test at room temperature. The results show an ultimate strength of 1800 MPa and elongations of 16%. Also, it is noticeable increase in mechanical properties with increasing boron content in the steels. Probably boron acts as grain refiner and decrease the nucleation of the ferrite grain on austenite boundaries, improving the formation of Bainite.

  19. Phase transformation theory: A powerful tool for the design of advanced steels

    Science.gov (United States)

    Caballero, F. G.; Miller, M. K.; Garcia-Mateo, C.; Capdevila, C.; Garcia de Andrés, C.

    2008-12-01

    An innovative design procedure based on phase transformation theory alone has been successfully applied to design steels with a microstructure consisting of a mixture of bainitic ferrite, retained austenite, and some martensite. An increase in the amount of bainitic ferrite is needed in order to avoid the presence of large regions of untransformed austenite, which under stress decompose to brittle martensite. The design procedure addresses this diffi culty by adjusting the T'o curve to greater carbon concentrations with the use of substitutional solutes such as manganese and chromium. The concepts of bainite transformation theory can be exploited even further to design steels with strength in excess of 2.5 GPa and considerable toughness.

  20. In-situ SEM observation on fracture behavior of austempered silicon alloyed steel

    Institute of Scientific and Technical Information of China (English)

    Chen Xiang; Vuorinen Esa; Grahn Jonny

    2009-01-01

    Crack initiation,propagation and microfracture processes of austempered high silicon cast steel have been investigated by using an in-situ tensile stage installed inside a scanning electron microscope chamber. It is revealed that micro cracks always nucleate at the yielding near imperfections and the boundary of matrix-inclusions due to the stress concentration. There are four types of crack propagations in the matrix:crack propagates along the boundary of two clusters of bainitic ferrite;crack propagates along the boundary of ferrite-austenite in bainitic ferrite laths;crack propagates into bainitic ferrite laths;crack nucleates and propagates in the high carbon brittle plate shape martensite which is transformed from some blocky retained austenite due to plastic deformation.Based on the observation and analysis of microfracture processes,a schematic diagram of the crack nucleation and propagation process of high silicon cast steel is proposed.

  1. The effect of coiling temperature on the microstructure and mechanical properties of a niobium–titanium microalloyed steel processed via thin slab casting

    Energy Technology Data Exchange (ETDEWEB)

    Challa, V.S.A.; Zhou, W.H. [Laboratory for Excellence in Advanced Steel Research, Center for Structural and Functional Materials, Institute for Material Research and Innovation, University of Louisiana at Lafayette, P.O. Box 44130, Lafayette, LA 70503 (United States); Misra, R.D.K., E-mail: dmisra@louisiana.edu [Laboratory for Excellence in Advanced Steel Research, Center for Structural and Functional Materials, Institute for Material Research and Innovation, University of Louisiana at Lafayette, P.O. Box 44130, Lafayette, LA 70503 (United States); O' Malley, R. [Nucor Decatur Sheet Mill, 4301 Iverson Blvd., Trinity, AL 35673 (United States); Jansto, S.G. [CBMM North America, 1000 Old Pond Road, Bridgeville, PA 15017 (United States)

    2014-02-10

    We describe here the influence of coiling temperature on the microstructure and mechanical properties, especially toughness, in a low carbon niobium microalloyed steel processed via thin slab casting. The objective is to elucidate the impact of coiling temperature on the nature and distribution of microstructural constituents (including different phases, precipitates, and dislocations) that contribute to variation in the strength–toughness relationship of these steels. In general, the microstructure primarily consisted of fine lath-type bainite and polygonal ferrite, and NbC, TiC and (Nb, Ti)C precipitates of size ∼2–10 nm in the matrix and at dislocations. However, the dominance of bainite and distribution of precipitates was a function of coiling temperature. The lower coiling temperature provided superior strength–toughness combination and is attributed to predominantly bainitic microstructure and uniform precipitation of NbC, TiC, and (Nb, Ti)C during the coiling process, consistent with continuous cooling transformation diagrams.

  2. Microstructural study on retained austenite in advanced highstrength multiphase 3Mn-1.5Al and 5Mn-1.5Al steels

    Directory of Open Access Journals (Sweden)

    A. Grajcar

    2012-10-01

    Full Text Available Purpose: The aim of the paper is to describe crystallographic and morphological features of retained austenite in thermomechanically processed bainite-martensite multiphase steels containing 3 and 5% Mn.Design/methodology/approach: Two groups of steels were designed and investigated: 3Mn-1.5Al and 5Mn-1.5Al were reference steels, whereas next two steels were microalloyed with niobium. The steels were thermomechanically processed using the Gleeble simulator. The isothermal holding temperature to enrich austenite in carbon was between 350 and 450°C. Metallographic investigations were carried out using light (LM and scanning electron microscopy (SEM. The retained austenite amount and its carbon concentration was evaluated by X-ray analysis.Findings: Manganese addition results in the high hardenability of steels leading to bainitic-martensitic microstructures. A high-Al concept and isothermal holding of steel in a bainitic transformation range allow to obtain a high fraction of retained austenite as a result of an incomplete bainitic transformation phenomenon. New complex bainitic morphologies like degenerate upper and lower bainite were identified using SEM. The microstructure and retained austenite characteristics were correlated with the carbon content in γ phase.Research limitations/implications: Further investigations (TEM, EBSD to describe in detail the identified structural constituents and the effect of Nb microalloying on microstructure and mechanical properties are needed.Practical implications: The knowledge of the influence of the isothermal holding temperature on the microstructure and hardness of thermomechanically processed steels are of primary importance for hot rolling of these multiphase high-strength steels.Originality/value: A problem of the stabilization of retained austenite in advanced high-strength multiphase Nb-free and Nb-microalloyed steels with increased Mn content is discussed.

  3. Phase transformation and mechanical behavior of thermomechanically controlled processed high strength ordnance steel

    International Nuclear Information System (INIS)

    A new low carbon titanium and niobium microalloyed steel has been thermomechanically processed in a pilot plant unit. Phase transformation phenomenon of the above steel during continuous cooling has been assessed. Evolution of microstructure and mechanical properties has also been studied at different finish rolling temperatures. A mixture of intragranular ferrite with granular bainite and bainitic ferrite along with inter-lath and intra-lath precipitation of (Ti, Nb)CN particles are the characteristic microstructural feature of air cooled steel. However, mixture of lower bainite and lath martensitic structure along with similar type (Ti, Nb)CN precipitate is observed in water quenched steel. High yield strength (896–948 MPa) with high tensile strength (974–1013 MPa) has been achieved with moderate ductility (16–17%) for the selected range of finish rolling temperature for air cooled steel. However, the water quenched steel yields higher yield strength (1240–1260 MPa) as well as higher tensile strength (1270–1285 MPa) but with lower ductility (13–14%) for the selected range of finish rolling temperature. Fairly good impact toughness values in the range of 50–89 J are obtained for the air cooled steel which are marginally higher than those of water quenched steel (42–81 J). - Highlights: ► New high strength steel has been processed in a pilot plant scale. ► Primarily granular bainite and bainitic ferrite are obtained in air cooled steel. ► Mixture of lower bainite and lath martensite is obtained in water quenched steel. ► (Ti, Nb)CN precipitate is obtained for both air cooled and water quenched steels. ► Highest strength with reasonable ductility has been achieved after water quenching

  4. Phase transformation and mechanical behavior of thermomechanically controlled processed high strength ordnance steel

    Energy Technology Data Exchange (ETDEWEB)

    Bandyopadhyay, P.S. [Ordnance Development Centre, Metal and Steel Factory, Ishapore 743 144 (India); Ghosh, S.K., E-mail: skghosh@metal.becs.ac.in [Department of Metallurgy and Materials Engineering, Bengal Engineering and Science University, Shibpur, Howrah 711 103 (India); Kundu, S.; Chatterjee, S. [Department of Metallurgy and Materials Engineering, Bengal Engineering and Science University, Shibpur, Howrah 711 103 (India)

    2013-02-15

    A new low carbon titanium and niobium microalloyed steel has been thermomechanically processed in a pilot plant unit. Phase transformation phenomenon of the above steel during continuous cooling has been assessed. Evolution of microstructure and mechanical properties has also been studied at different finish rolling temperatures. A mixture of intragranular ferrite with granular bainite and bainitic ferrite along with inter-lath and intra-lath precipitation of (Ti, Nb)CN particles are the characteristic microstructural feature of air cooled steel. However, mixture of lower bainite and lath martensitic structure along with similar type (Ti, Nb)CN precipitate is observed in water quenched steel. High yield strength (896–948 MPa) with high tensile strength (974–1013 MPa) has been achieved with moderate ductility (16–17%) for the selected range of finish rolling temperature for air cooled steel. However, the water quenched steel yields higher yield strength (1240–1260 MPa) as well as higher tensile strength (1270–1285 MPa) but with lower ductility (13–14%) for the selected range of finish rolling temperature. Fairly good impact toughness values in the range of 50–89 J are obtained for the air cooled steel which are marginally higher than those of water quenched steel (42–81 J). - Highlights: ► New high strength steel has been processed in a pilot plant scale. ► Primarily granular bainite and bainitic ferrite are obtained in air cooled steel. ► Mixture of lower bainite and lath martensite is obtained in water quenched steel. ► (Ti, Nb)CN precipitate is obtained for both air cooled and water quenched steels. ► Highest strength with reasonable ductility has been achieved after water quenching.

  5. Mechanical Properties and Retained Austenite Transformation Mechanism of TRIP-Aided Polygonal Ferrite Matrix Seamless Steel Tube

    Institute of Scientific and Technical Information of China (English)

    ZHANG Ming-ya; ZHU Fu-xian; ZHENG Dong-sheng

    2011-01-01

    Through the comparison of microstructure for polygonal ferrite (PF) matrix transformation induced plasticity (TRIP) seamless steel tube at different positions before and after tensile rupture, the transformation behavior of retained austenite (RA) was studied. The results showed that there were no yield points in tensile process and the splendid elongation and tensile strength were contributed by the uniform ferrite/bainite grains and the transformation of RA. The stability of RA was to some extent in inverse proportion with the ability of transformation induced plas ticity. The coarse retained austenite located in ferrite and ferrite/bainite laths were all transformed into martensite during the tensile process.

  6. Local texture of microstructural inhomogeneities in rolled microalloyed steel

    Science.gov (United States)

    Zolotorevsky, N.; Panpurin, S.; Kazakov, A.; Pakhomova, O.; Petrov, S.

    2015-04-01

    Specific inhomogeneities consisting of coarse-grained bainite are observed in the microstructure of low carbon microalloyed steels after hot rolling. Earlier a special etching method has been developed allowing to reveal that these inhomogeneities markedly affect a fracture toughness of steels. In the present work their crystal geometry was studied using EBSD technique, and orientations of former austenite grains were reconstructed. The austenite, from which the coarse-grained bainite regions have been produced, is shown to have orientations concentrated predominantly within the brass component of austenite rolling texture. The inhomogeneities of steel microstructure are promoted by orientation dependency of the deformation substructure of heavily deformed austenite grains.

  7. Study of the mechanical properties of low carbon content HSLA steels

    Energy Technology Data Exchange (ETDEWEB)

    Illescas, S.; Fernandez, J.; Asensio, J.; Sanchez-Soto, M.; Guilemany, J. M.

    2009-07-01

    Two high strength low alloys steels (HSLA) with the same bulk composition and slight microalloying content differences were studied. The main purpose of the study was to determine the effect of different heat treatments an the influence of vanadium (V) on the microstructure and mechanical properties of the bainite present in each steel. For that purpose, standard tests were conducted to determine the hardness, toughness, tensile and yield stress of the different bainite-acicular ferrite structures found in both steels. The results show how the V content promoted the formation of acicular ferrite, resulting in a decrease in hardness and tensile strength while improving toughness. (Author) 30 refs.

  8. Effect of Thermomechanical Processing on Microstructures of TRIP Steel

    Institute of Scientific and Technical Information of China (English)

    TANG Zheng-you; DING Hua; DU Lin-xiu; DING Hao; ZHANG Xin

    2007-01-01

    In order to control retained austenite, the effect of hot deformation in the intercritical region on the microstructure of hot-rolled transformation-induced plasticity (TRIP) steel was studied on a Gleeble 1500 hot simulator. Compressive strains varying in amounts from 0 to 60% were imposed in the intercritical region, and effects on the formation of polygonal ferrite, carbide-free bainite and retained austenite were determined. With increasing the hot deformation amount and the ferrite content and decreasing the carbide-free bainite content, the volume fraction of retained austenite decreases. Increased dislocation density, grain refinement of ferrite and carbon enrichment are the main factors which control retained austenite stability.

  9. Significance of the state of segregation of the carbide phase on the toughness properties of 20 MnMoNi 5 5 forgings

    International Nuclear Information System (INIS)

    When measured in the heat treated wall thickness of heavy forgings, 20 Mn Mo Ni 5 5 steel is so low in allow that it is unavoidable that large parts of higher bainite will occur in the structure of the pieces. In order to obtain the best possible notch impact strength values, tempering is of particular importance. It must be done so that there is the least possible segregation of molybdenum carbide Mo2C in the bainite ferrite. This requires the use of not too high tempering temperatures together with an upper limit of tempering time. Similar considerations apply for stress relieving treatment. (orig.)

  10. Microstructure and crack resistance of low carbon Cr-Ni and Cr-Ni-W steel after austempering

    Science.gov (United States)

    Avdjieva, Tatyana; Tsutsumanova, Gichka; Russev, Stoyan; Staevski, Konstantin

    2013-09-01

    The microstructure of the low carbon Cr-Ni steel after slow cooling from austenization temperature represents a mix of granulated bainite with islands from carbon-rich martensite and carbon-poor austenite. After quick cooling throwing in salt bath from austenization temperature the microstructure is lath bainite. However, in the same treatment conditions, the microstructure of the low carbon Cr-Ni-W steel is different — clusters consist from lath ferrite and retained austenite, disposed in the frame of parent's austenite grains. The cooling velocity has no effect upon the structure making. The impact toughness of the steel with tungsten content is bigger than the steel without tungsten.

  11. Plasticity and fracture modeling of quench-hardenable boron steel with tailored properties

    NARCIS (Netherlands)

    Eller, T.K.; Greve, L.; Andres, M.T.; Medricky, M.; Hatscher, A.; Meinders, V.T.; Boogaard, van den A.H.

    2014-01-01

    In this article, a constitutive model for quench-hardenable boron steel is presented. Three sets of boron steel blanks are heat treated such that their as-treated microstructures are close to fully martensitic, bainitic and ferritic/pearlitic, respectively. Hardness measurements show that the result

  12. Influence of Composition and Hot Rolling on the Subsurface Microstructure and Bendability of Ultrahigh-Strength Strip

    Science.gov (United States)

    Kaijalainen, Antti Juhani; Liimatainen, Mia; Kesti, Vili; Heikkala, Jouko; Liimatainen, Tommi; Porter, David A.

    2016-08-01

    The effect of subsurface microstructure on the bendability of three 8-mm-thick low-alloyed hot-rolled and direct-quenched ultrahigh-strength strip steels with yield strengths in the range 800 to 1100 MPa has been investigated. Rolling to lower finish rolling temperatures increased austenite pancaking, leading to the formation of ferritic/granular bainitic subsurface microstructures that are softer than the upper bainitic microstructures found with higher finish rolling temperature. In addition, increased austenite pancaking was found to increase the intensities of {112}α and {110}α to {110}α texture components in the surface layers, especially in upper bainitic microstructures. It is shown that the bendability of ultrahigh-strength steels is governed by subsurface hardness and crystallographic texture. Bendability was found to be related to mean microhardness 0.1 to 0.4 mm below the surface, such that excellent bendability was achieved with a relatively soft subsurface layer down to a depth of 0.4 mm, i.e., 5 pct of the sheet thickness. Intense {112}α texture combined with upper bainite containing MA islands in the subsurface region is shown to be detrimental to bendability when the bend axis is perpendicular to the rolling direction probably as a result of geometrical softening combined with high hardness.

  13. Ageing phenomena in ULCB-NiCu steels

    International Nuclear Information System (INIS)

    Effect od ageing time and temperature on microstructure development, precipitation of εCu, advancement of recrystallization process and their influence on yield strength and fracture toughness properties KIC as well as high Charpy V impact energy CVN = 84 J at 120oC of ultra low carbon bainitic copper bearing steels have ben discussed. (author)

  14. Low-Temperature Toughening Mechanism in Thermomechanically Processed High-Strength Low-Alloy Steels

    Science.gov (United States)

    Hwang, Byoungchul; Lee, Chang Gil; Kim, Sung-Joon

    2011-03-01

    High-strength low-alloy (HSLA) steels were fabricated by varying thermomechanical processing conditions such as rolling and cooling conditions in the intercritical region, and the low-temperature toughening mechanism was investigated in terms of microstructure and the associated grain boundary characteristics. The steels acceleratedly cooled to relatively higher temperature had lower tensile strength than those acceleratedly cooled to room temperature due to the increased volume fraction of granular bainite or polygonal ferrite (PF) irrespective of rolling in the intercritical region, while the yield strength was dependent on intercritical rolling, and start and finish cooling temperatures, which affected the formation of PF and low-temperature transformation phases. The steel rolled in the intercritical region and cooled to 673 K (400 °C) provided the best combination of high yield strength and excellent low-temperature toughness because of the presence of fine PF and appropriate mixture of various low-temperature transformation phases such as granular bainite, degenerate upper bainite (DUB), lower bainite (LB), and lath martensite (LM). Despite the high yield strength, the improvement of low-temperature toughness could be explained by the reduction of overall effective grain size based on the electron backscattered diffraction (EBSD) analysis data, leading to the decrease in ductile-to-brittle transition temperature (DBTT).

  15. Influence of Composition and Hot Rolling on the Subsurface Microstructure and Bendability of Ultrahigh-Strength Strip

    Science.gov (United States)

    Kaijalainen, Antti Juhani; Liimatainen, Mia; Kesti, Vili; Heikkala, Jouko; Liimatainen, Tommi; Porter, David A.

    2016-06-01

    The effect of subsurface microstructure on the bendability of three 8-mm-thick low-alloyed hot-rolled and direct-quenched ultrahigh-strength strip steels with yield strengths in the range 800 to 1100 MPa has been investigated. Rolling to lower finish rolling temperatures increased austenite pancaking, leading to the formation of ferritic/granular bainitic subsurface microstructures that are softer than the upper bainitic microstructures found with higher finish rolling temperature. In addition, increased austenite pancaking was found to increase the intensities of {112}α and {110}α to {110}α texture components in the surface layers, especially in upper bainitic microstructures. It is shown that the bendability of ultrahigh-strength steels is governed by subsurface hardness and crystallographic texture. Bendability was found to be related to mean microhardness 0.1 to 0.4 mm below the surface, such that excellent bendability was achieved with a relatively soft subsurface layer down to a depth of 0.4 mm, i.e., 5 pct of the sheet thickness. Intense {112}α texture combined with upper bainite containing MA islands in the subsurface region is shown to be detrimental to bendability when the bend axis is perpendicular to the rolling direction probably as a result of geometrical softening combined with high hardness.

  16. Austenite grain growth and microstructure control in simulated heat affected zones of microalloyed HSLA steel

    International Nuclear Information System (INIS)

    The roles of microalloying niobium, titanium and vanadium for controlling austenite grain growth, microstructure evolution and hardness were investigated at different simulated heat affected zones (HAZ) for high strength low alloy (HSLA) S690QL steel. High resolution FEG-SEM has been used to characterize fine bainitic ferrite, martensite and nanosized second phases at simulated coarse and fine grain HAZs. It was found that for Ti bearing steel (Ti/N ratio is 2) austenite grain had the slowest growth rate due to the presence of most stable TiN. The fine cuboidal particles promoted intragranular acicular ferrite (IGF) formation. Nb bearing steel exhibited relatively weaker grain growth retardation compared with titanium bearing steels and a mixed microstructure of bainite and martensite was present for all simulated HAZs. IGF existed at coarse grain HAZ of Ti+V bearing steel but it was totally replaced by bainite at fine grain HAZs. Hardness result was closely related to the morphology of bainitic ferrite, intragranular ferrite and second phases within ferrite. The microstructure and hardness results of different simulated HAZs were in good agreement with welded experimental results

  17. Microstructures and Mechanical Properties of Si-Al-Mn TRIP Steel with Niobium

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Microstructure consisting of ferrite, bainite and retained austenite can be obtained through intercritical annealing and isothermal treatment in bainite transformation region for low silicon TRIP (transformation induced plasticity) steel containing niobium. Effects of strain rate, Nb content and soaking temperature in bainite region on microstructure and mechanical properties of test steels were investigated. It is shown that as strain rate ranges from 10-2 to 10-4 s-1, the volume fraction of transformed martensite from retained austenite,as well as tensile strength, elongation rate and strength-ductility product, increases. When Nb is added, the volume fraction of retained austenite decreases, but tensile strength and yield strength increase. While Nb content reaches 0.014%, the steel exhibits high elongation and combination of strength and ductility. Higher retained austenite volume fraction and good mechanical properties are obtained in the test steels when the soaking temperature in bainite region is 400℃. The maximum values of tensile strength, total elongation rate and strength-ductility product can reach 739 MPa, 38% and 28082 MPa%, respectively.

  18. The forty years of vermicular graphite cast iron development in China (Part Ⅲ)

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    @@ 5 Heat treatment of VGCI Research work has shown that the microstructure of VGCI can be modified by heat treatment to give improved properties;martensitic, bainitic, sorbitic and pearlitic structures can be produced by quenching, quenching plus tempering,austempering and normalisation respectively.

  19. Thermal Stability of Nanocrystalline Structure In X37CrMoV5-l Steel

    Directory of Open Access Journals (Sweden)

    Skołek E.

    2015-04-01

    Full Text Available The aim of the study was to investigate the thermal stability of the nanostructure produced in X37CrMoV5-1 tool steel by austempering heat treatment consisted of austenitization and isothermal quenching at the range of the bainitic transformation. The nanostructure was composed of bainitic ferrite plates of nanometric thickness separated by thin layers of retained austenite. It was revealed, that the annealing at the temperature higher than temperature of austempering led to formation of cementite precipitations. At the initial stage of annealing cementite precipitations occurred in the interfaces between ferritic bainite and austenite. With increasing temperature of annealing, the volume fraction and size of cementite precipitations also increased. Simultaneously fine spherical Fe7C3 carbides appeared. At the highest annealing temperature the large, spherical Fe7C3 carbides as well as cementite precipitates inside the ferrite grains were observed. Moreover the volume fraction of bainitic ferrite and of freshly formed martensite increased in steel as a result of retained austenite transformation during cooling down to room temperature.

  20. Size Effects in Residual Stress Formation during Quenching of Cylinders Made of Hot-Work Tool Steel

    Directory of Open Access Journals (Sweden)

    Manuel Schemmel

    2015-01-01

    Full Text Available The present work investigates the residual stress formation and the evolution of phase fractions during the quenching process of cylindrical specimens of different sizes. The cylinders are made of hot-work tool steel grade X36CrMoV5-1. A phase transformation kinetic model in combination with a thermomechanical model is used to describe the quenching process. Two phase transformations are considered for developing a modelling scheme: the austenite-to-martensite transformation and the austenite-to-bainite transformation. The focus lies on the complex austenite-to-bainite transformation which can be observed at low cooling rates. For an appropriate description of the phase transformation behaviour nucleation and growth of bainite are taken into account. The thermomechanical model contains thermophysical data and flow curves for each phase. Transformation induced plasticity (TRIP is modelled by considering phase dependent Greenwood-Johnson parameters for martensite and bainite, respectively. The influence of component size on residual stress formation is investigated by the finite element package Abaqus. Finally, for one cylinder size the simulation results are validated by X-ray stress measurements.

  1. Austenite grain growth and microstructure control in simulated heat affected zones of microalloyed HSLA steel

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Lei [Department of Machine Tools and Factory Management, Technical University of Berlin, Pascalstraße 8 – 9, 10587, Berlin (Germany); Federal Institute for Materials Research and Testing, Unter den Eichen 87, 12205, Berlin (Germany); Kannengiesser, Thomas [Federal Institute for Materials Research and Testing, Unter den Eichen 87, 12205, Berlin (Germany); Institute of Materials and Joining Technology, Otto von Guericke University Magdeburg, Universitetsplatz 2, 39106, Magdeburg (Germany)

    2014-09-08

    The roles of microalloying niobium, titanium and vanadium for controlling austenite grain growth, microstructure evolution and hardness were investigated at different simulated heat affected zones (HAZ) for high strength low alloy (HSLA) S690QL steel. High resolution FEG-SEM has been used to characterize fine bainitic ferrite, martensite and nanosized second phases at simulated coarse and fine grain HAZs. It was found that for Ti bearing steel (Ti/N ratio is 2) austenite grain had the slowest growth rate due to the presence of most stable TiN. The fine cuboidal particles promoted intragranular acicular ferrite (IGF) formation. Nb bearing steel exhibited relatively weaker grain growth retardation compared with titanium bearing steels and a mixed microstructure of bainite and martensite was present for all simulated HAZs. IGF existed at coarse grain HAZ of Ti+V bearing steel but it was totally replaced by bainite at fine grain HAZs. Hardness result was closely related to the morphology of bainitic ferrite, intragranular ferrite and second phases within ferrite. The microstructure and hardness results of different simulated HAZs were in good agreement with welded experimental results.

  2. 球轴承

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    Ball bearing components of 100Cr6 (AISI52109), choice of bainitic transformation or martensitic hardening processes?;Bearings for extreme special environment (5) -linear motion bearings and unit products;Chemical mechanical polishing process for silicon nitride ball;Condition monitoring methods for vane axial fans……

  3. Nanoprecipitation in bearing steels

    Energy Technology Data Exchange (ETDEWEB)

    Barrow, A.T.W. [SKF University Technology Centre, Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ (United Kingdom); Rivera-Diaz-del-Castillo, P.E.J., E-mail: pejr2@cam.ac.uk [SKF University Technology Centre, Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ (United Kingdom)

    2011-11-15

    {theta}-phase is the main hardening species in bearing steels and appears in both martensitically and bainitically hardened microstructures. This work presents a survey of the microstrucural features accompanying nanoprecipitation in bearing steels. Nanoprecipitate structures formed in 1C-1.5Cr wt.% with additions of Cr, Mn, Mo, Si and Ni are studied. The work is combined with thermodynamic calculations and neural networks to predict the expected matrix composition, and whether this will transform martensitically or bainitically. Martensite tetragonality, composition and the amount of retained austenite are related to hardness and the type of nanoprecipitate structures in martensitic grades. The {theta}-phase volume fraction, the duration of the bainite to austenite transformation and the amount of retained austenite are related to hardness and a detailed quantitative description of the precipitate nanostructures. Such description includes compositional studies using energy-dispersive spectroscopy, which shows that nanoprecipitate formation takes place under paraequilibrium. Special attention is devoted to a novel two-step bainite tempering process which shows maximum hardness; we prove that this is the most effective process for incorporating solute into the precipitates, which are finer than those resulting from one-step banitic transformation processes.

  4. A Novel Ni-Containing Powder Metallurgy Steel with Ultrahigh Impact, Fatigue, and Tensile Properties

    Science.gov (United States)

    Wu, Ming-Wei; Shu, Guo-Jiun; Chang, Shih-Ying; Lin, Bing-Hao

    2014-08-01

    The impact toughness of powder metallurgy (PM) steel is typically inferior, and it is further impaired when the microstructure is strengthened. To formulate a versatile PM steel with superior impact, fatigue, and tensile properties, the influences of various microstructures, including ferrite, pearlite, bainite, and Ni-rich areas, were identified. The correlations between impact toughness with other mechanical properties were also studied. The results demonstrated that ferrite provides more resistance to impact loading than Ni-rich martensite, followed by bainite and pearlite. However, Ni-rich martensite presents the highest transverse rupture strength (TRS), fatigue strength, tensile strength, and hardness, followed by bainite, pearlite, and ferrite. With 74 pct Ni-rich martensite and 14 pct bainite, Fe-3Cr-0.5Mo-4Ni-0.5C steel achieves the optimal combination of impact energy (39 J), TRS (2170 MPa), bending fatigue strength at 2 × 106 cycles (770 MPa), tensile strength (1323 MPa), and apparent hardness (38 HRC). The impact energy of Fe-3Cr-0.5Mo-4Ni-0.5C steel is twice as high as those of the ordinary high-strength PM steels. These findings demonstrate that a high-strength PM steel with high-toughness can be produced by optimized alloy design and microstructure.

  5. Intergranular brittle fracture of a low alloy steel induced by grain boundary segregation of impurities: influence of the microstructure

    International Nuclear Information System (INIS)

    The study contributes to improve the comprehension of intergranular embrittlement induced by the phosphorus segregation along prior austenitic grain boundaries of low alloy steels used in pressurized power reactor vessel. A part of this study was performed using a A533 steel which contains chemical fluctuations (ghost lines) with two intensities. Axi-symmetrically notched specimens were tested and intergranular brittle de-cohesions were observed in the ghost lines. The fracture initiation sites observed on fracture surfaces were identified as MnS inclusions. A bimodal statistic obtained in a probabilistic model of the fracture is explained by the double population of ghost lines' intensities. A metallurgical study was performed on the same class of steel by studying the influence of the microstructure on the susceptibility to temper embrittlement. Brittle fracture properties of such microstructures obtained by dilatometric experiments were tested on sub-sized specimens to measure the V-notched fracture toughness. Fraction areas of brittle fracture modes were determined on surface fractures. A transition of the fracture mode with the microstructure is observed. It is shown that tempered microstructures of martensite and lower bainite are more susceptible to intergranular embrittlement than tempered upper bainitic microstructure. The intergranular fracture is the most brittle mode. The analysis of crystalline mis-orientations shows a grain boundary structure appreciably more coherent for tempered microstructures of martensite and lower bainite. The higher density of random grain boundaries is susceptible to drag the phosphorus in the upper bainitic matrix and to make the quantity of free phosphorus decreasing. Microstructure observations show a difference in the size and the spatial distribution of carbides, essentially cementite, between tempered martensite and upper bainite. It can explain the bigger susceptibility of this last microstructure to cleavage mode

  6. Intergranular brittle fracture of a low alloy steel induced by grain boundary segregation of impurities: influence of the microstructure; Rupture intergranulaire fragile d'un acier faiblement allie induite par la segregation d'impuretes aux joints de grains: influence de la microstructure

    Energy Technology Data Exchange (ETDEWEB)

    Raoul, St

    1999-07-01

    The study contributes to improve the comprehension of intergranular embrittlement induced by the phosphorus segregation along prior austenitic grain boundaries of low alloy steels used in pressurized power reactor vessel. A part of this study was performed using a A533 steel which contains chemical fluctuations (ghost lines) with two intensities. Axi-symmetrically notched specimens were tested and intergranular brittle de-cohesions were observed in the ghost lines. The fracture initiation sites observed on fracture surfaces were identified as MnS inclusions. A bimodal statistic obtained in a probabilistic model of the fracture is explained by the double population of ghost lines' intensities. A metallurgical study was performed on the same class of steel by studying the influence of the microstructure on the susceptibility to temper embrittlement. Brittle fracture properties of such microstructures obtained by dilatometric experiments were tested on sub-sized specimens to measure the V-notched fracture toughness. Fraction areas of brittle fracture modes were determined on surface fractures. A transition of the fracture mode with the microstructure is observed. It is shown that tempered microstructures of martensite and lower bainite are more susceptible to intergranular embrittlement than tempered upper bainitic microstructure. The intergranular fracture is the most brittle mode. The analysis of crystalline mis-orientations shows a grain boundary structure appreciably more coherent for tempered microstructures of martensite and lower bainite. The higher density of randomgrain boundaries is susceptible to drag the phosphorus in the upper bainitic matrix and to make the quantity of free phosphorus decreasing. Microstructure observations show a difference in the size and the spatial distribution of carbides, essentially cementite, between tempered martensite and upper bainite. It can explain the bigger susceptibility of this last microstructure to cleavage mode

  7. Influence of hot and warm deformation on austenite decomposition

    Directory of Open Access Journals (Sweden)

    D. Jandová

    2006-08-01

    Full Text Available Purpose: The substructure of austenite influences phase transformations during the austenite decomposition andconsequently the final properties of the steel.Design/methodology/approach: Steel 0.5C-1Cr-0.8Mn-0.3Si was processed using the thermo-mechanicalcycling simulator. Different methods of the thermo-mechanical processing were applied including austenitizationat 950°C, compression deformation at 950°C or 650°C and isothermal dwell at temperatures in the range(350°C÷450°C. Microstructure was investigated using light and transmission electron microscopy.Findings: It was demonstrated that straining in austenitic region accelerated the ferrite and pearlite transformations.Bainite reaction depended on the temperature of austenite deformation, the strain level and the temperature ofisothermal dwell. Hot deformation slightly accelerated the transformation to upper bainite and retarded thetransformation to lower bainite. Warm deformation resulted in mixture structures containing pearlite, ferrite andbainite; bainitic reactions were accelerated. Fine ferritic grains, pearlitic nodules and clusters of individual ferrite/carbide units enclosed with martensitic matrix were observed in heavy strained parts of specimens.Practical implications: Different morphologies of ferritic structures which can occur in the wrought steel canresult in deterioration of mechanical properties. This fact has to be taken into account in numerical simulationsof thermo-mechanical processing of low alloy steels.Originality/value: Of this paper consists in elucidation of the processes taking place in heavy strained austeniticstructure during its isothermal decomposition at temperatures in bainitic region.

  8. Theory and Modeling of Phase Transformations under Stress in Steel

    Institute of Scientific and Technical Information of China (English)

    T.Y. Hsu (XU Zu-yao)

    2004-01-01

    Thermodynamic prediction of the increment of the formation temperature of proeutectoid ferrite by applied stress is nearly consistent with the experimental data. Kinetics models for ferrite, pearlite and bainite transformations can be shown as modified Johnson-Mehl-Avrami equation in which parameter b(σ) varies with the level of applied stress.The effects of tensile and compressive stresses on enhancement of the ferrite/pearlite and bainite transformations are discussed. The necessity and approach of modification of additivity hypothesis are introduced and the results from modified equation in which some parameters are obtained by regression of two experimental results or taken from TTT and CCT diagrams of a certain steel are superior than that from Scheil's equation. Thermodynamic calculation of Ms and nucleation kinetics equations of martensitic transformation under stress are suggested. Modeling of phase transformations under stress in ferrous alloys is briefly described.

  9. Computation of parent austenite grain orientation from product grain orientations upon displacive phase transformations

    International Nuclear Information System (INIS)

    A reverse computation procedure is proposed for calculating parent austenite orientations, which are experimentally challenging to obtain, based on the final texture after austenite-to-bainite and austenite-to-martensite phase transformations. Specifically, post-transformation electron backscatter diffraction scans of bainite and martensite were carried out in order to identify the product crystal orientations within a single former austenite grain. Subsequently, the Kurdjumov–Sachs relationship was utilized to compute the parent austenite crystal orientation based on these data. The proposed method provided a unique solution for the initial austenite grain orientation in most of the cases. Overall, the proposed computational procedure constitutes a means of understanding the factors influencing microstructural evolution in displacive phase transformations. (paper)

  10. Effect of welding parameters on the mechanical properties of GMA-welded HY-80 steels

    International Nuclear Information System (INIS)

    In this publication, investigations of HY-80 steels joined by gas metal arc welding by using different welding parameters are described. Different samples obtained from the welded joints were subjected to mechanical testing by means of tensile, hardness and impact toughness tests. The tensile test results showed that the strength of weld metal and heat affected zone were higher than of base metal. Similar Charpy impact toughness test results were obtained for weld metal and heat affected zone. Weld metal hardness was almost similar to the base metal hardness, nevertheless, the heat affected zone indicated higher values. The base metal has ferritic-perlitic structure with fine grains. Martensite needles and bainite are seen in the heat affected zone. Weld metal has martensite needles, partial bainite and residual austenite.

  11. Ag-rich precipitates formation in the Cu–11%Al–10%Mn–3%Ag alloy

    Energy Technology Data Exchange (ETDEWEB)

    Silva, R.A.G., E-mail: galdino.ricardo@gmail.com [Departamento de Ciências Exatas e da Terra, UNIFESP, 09972-270 Diadema, SP (Brazil); Paganotti, A.; Jabase, L. [Departamento de Ciências Exatas e da Terra, UNIFESP, 09972-270 Diadema, SP (Brazil); Adorno, A.T.; Carvalho, T.M.; Santos, C.M.A. [Departamento de Físico-Química, Instituto de Química, UNESP, 14801-970 Araraquara, SP (Brazil)

    2014-12-05

    Highlights: • Cu-rich nanoprecipitates are formed in the presence of Ag. • Bainite precipitation is shifted to higher temperatures in the Cu–11%Al–10%Mn–3%Ag alloy. • The eutectoid α phase and bainite α{sub 1} phase compete by the Cu atoms during precipitation process. - Abstract: The formation of Ag-rich precipitates in the Cu–11%Al–10%Mn–3%Ag alloy initially quenched from 1123 K was analyzed. The results showed that nanoprecipitates of a Cu-rich phase are produced at about 523 K. In higher temperatures these nanoparticles grow and the relative fraction of Ag dissolved in it is increased, thus forming the Ag-rich phase.

  12. Influence of Subsurface Structure on the Linear Reciprocating Sliding Wear Behavior of Steels with Different Microstructures

    Science.gov (United States)

    Sharma, S.; Sangal, S.; Mondal, K.

    2014-12-01

    The present work investigates the influence of subsurface microstructure on the linear reciprocating sliding wear behavior of a number of steels with ferrite-pearlitic, pearlitic, bainitic, and martensitic microstructures under dry unlubricated condition. The change in the underlying microstructure with depth from worn-out surface of steel sample intimately relates to the associated hardness variation and wear volume. The present paper is not about comparison of wear resistance of steels with different structures; rather it is on mutual influence of wear and substructure for individual microstructure. Inherent toughness of the matrix and ability of microstructural components to get deformed under the reciprocating action of the ball decide the wear resistance of the steels. Bainite has good amount of stability to plastic deformation. Ferrite shows severe banding due to wear action. Work hardening renders pearlite to be wear resistant. Temperature rise and associated tempering of martensite are observed during wear.

  13. Ag-rich precipitates formation in the Cu–11%Al–10%Mn–3%Ag alloy

    International Nuclear Information System (INIS)

    Highlights: • Cu-rich nanoprecipitates are formed in the presence of Ag. • Bainite precipitation is shifted to higher temperatures in the Cu–11%Al–10%Mn–3%Ag alloy. • The eutectoid α phase and bainite α1 phase compete by the Cu atoms during precipitation process. - Abstract: The formation of Ag-rich precipitates in the Cu–11%Al–10%Mn–3%Ag alloy initially quenched from 1123 K was analyzed. The results showed that nanoprecipitates of a Cu-rich phase are produced at about 523 K. In higher temperatures these nanoparticles grow and the relative fraction of Ag dissolved in it is increased, thus forming the Ag-rich phase

  14. Effect of silicon and prior deformation of austenite on isothermal transformation in low carbon steels

    Institute of Scientific and Technical Information of China (English)

    Minghui CAI; Hun DING; Jiansu ZHANG; Long LI

    2009-01-01

    Isothermal transformation (TTT) behavior of the low carbon steels with two Si con-tents (0.50 wt pct and 1.35 wt pct) was investigated with and without the prior deformation. The results show that Si and the prior deformation of the austenite have significant effects on the transformation of the ferrite and bainite. The addition of Si refines the ferrite grains, accelerates the polygonal ferrite transformation and the formation of M/A constituents, leading to the improvement of the strength. The ferrite grains formed under the prior deformation of the austenite become more ho-mogeneous and refined. However, the influence of deformation on the tensile strength of both steels is dependent on the isothermal temperatures. Thermodynamic calcu-lation indicates that Si and prior deformation reduce the incubation time of both ferrite and bainite transformation, but the effect is weakened by the decrease of the isothermal temperatures.

  15. The Influence of Heat Treatment on the Microstructure and Machinability of a Prehardened Mold Steel

    Science.gov (United States)

    Hoseiny, Hamed; Caballero, Francisca G.; M'Saoubi, Rachid; Högman, Berne; Weidow, Jonathan; Andrén, Hans-Olof

    2015-05-01

    The machinability performance of a modified AISI P20 steel, heat treated to have the same hardness but three different microstructures, lower bainite, tempered martensite, and primary spheroidized carbides in a tempered martensite matrix, was studied. The microstructures were characterized using light optical and scanning electron microscopy and X-ray diffraction, and mechanical properties were compared by means of tensile and Charpy V-notch impact tests. The influence of microstructure and the resultant mechanical properties on machinability was studied in the context of single tooth end milling operation. The results showed that the material containing primary spheroidized carbides exhibited a superior machinability at the expense of a marginal loss of tensile strength and impact toughness, with comparable yield strength to that of the material containing tempered martensite. By contrast, the material with bainitic microstructure showed the lowest yield strength and the poorest machinability performance while having the highest uniform elongation.

  16. Steel Microstructure Effect on Mechanical Properties and Corrosion Behavior of High Strength Low Carbon Steel

    Science.gov (United States)

    Barraza-Fierro, Jesus Israel; Campillo-Illanes, Bernardo; Li, Ximing; Castaneda, Homero

    2014-08-01

    Different thermomechanical treatments were applied to a high strength low carbon steel with a novel chemical composition. As a result, three different microstructures were produced with dissimilar mechanical and corrosion properties. Subsequently, a tempering heat treatment was applied to redistribute the phases in the steel. Microstructure A with 56 pct martensite and 32 pct bainite presented high strength but medium ductility; microstructure C with 95 pct ferrite and 3 pct martensite/austenite resulted in low strength and high ductility, and finally microstructure B with 98 pct bainite and 2 pct martensite/austenite resulted in high strength and ductility. Alternatively the corrosion behavior obtained by polarization curves was characterized in 0.1 M H2SO4, 3 M H2SO4, 3.5 wt pct NaCl, and NS4 solutions resulting in similar magnitudes, while the corrosion behavior acquired by electrochemical impedance spectroscopy had slightly differences in 3 M H2SO4.

  17. Nanocrystalline Steels’ Resistance to Hydrogen Embrittlement

    Directory of Open Access Journals (Sweden)

    Skołek E.

    2015-04-01

    Full Text Available The aim of this study is to determine the susceptibility to hydrogen embrittlement in X37CrMoV5-1 steel with two different microstructures: a nanocrystalline carbide-free bainite and tempered martensite. The nanobainitic structure was obtained by austempering at the bainitic transformation zone. It was found, that after hydrogen charging, both kinds of microstructure exhibit increased yield strength and strong decrease in ductility. It has been however shown that the resistance to hydrogen embrittlement of X37CrMoV5-1 steel with nanobainitic structure is higher as compared to the tempered martensite. After hydrogen charging the ductility of austempered steel is slightly higher than in case of quenched and tempered (Q&T steel. This effect was interpreted as a result of phase composition formed after different heat treatments.

  18. TDA method application to austenite transformation in nodular cast iron with carbides assessment

    Directory of Open Access Journals (Sweden)

    G. Gumienny

    2011-07-01

    Full Text Available In this paper the possibility of TDA method using to austenite transformation in nodular cast iron with carbides assessment is presented. Studies were conducted on cast iron with about 2% molybdenum and 0,70% to 4,50% nickel. On diagrams, where TDA curves are pre- sented, on time axis a logarithmic scale was applied. It has not been used up to now. It was found, that during cooling and crystallization of cast iron in TDA probe, on the derivative curve there is a slight thermal effect from austenite to upper bainite or martensite transformation. Depending on nickel concentration austeniteupper bainite transformation start temperature changed (Bus, while MS temperature was independent of it. An influence of nickel on eutectic transformation temperature in nodular cast iron with carbides was determined too.

  19. Chromium and copper influence on the nodular cast iron with carbides microstructure

    Directory of Open Access Journals (Sweden)

    G. Gumienny

    2010-10-01

    Full Text Available In this paper chromium to 1,00% and copper to 1,50% influence at constant molybdenum content of about 1,50% on the nodular cast ironwith carbides microstructure has been presented. It was found, that as a result of synergic addition of above-mentioned elements there isthe possibility obtaining an ausferrite in nodular cast iron with carbides castings. Conditions have been given, when in nodular cast iron with carbides at cooling at first in the form, then air-cooling austenite transformation to upper bainite, its mixture with lower bainite, martensite or ausferrite takes place. Transformations proceed during cooling and the crystallization of cast iron have been determined and the casting hardness has been presented.

  20. Stability of Ultra-fine Microstructures during Tempering

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The stability of ultra-fine microstructure during tempering at 650℃ was investigated on a Nb-containing steel. The steel had undergone 5 passes controlled rolling, then was relaxed (air cooled) to 730℃ and cooled in water. The evolution of microstructure was that, in early stage of tempering, no obvious change was detected by means of optical microscopy while dislocation cells were formed inside bainitic laths. With further tempering, bainitic laths started to coalesce in some regions. Finally, polygonal ferrite was formed while hardness decreased dramatically.Some samples taken from the same primary plate were reheated at 930℃ for 0.5h followed by quenching into water before tempering. Despite their lower original hardness, the reheated samples softened faster during tempering. Ferrite was quickly formed in the reheated samples. These results indicate that the evolution of microstructures towards equilibrium during tempering of the steel is mainly determined by whether dislocations are pinned rather than the dislocation density.

  1. Effects of Carbon on the CG HAZ Toughness and Transformation of X80 Pipeline Steel

    Institute of Scientific and Technical Information of China (English)

    Xiaohuai XUE; Luhai WU; Bainian QIAN; Jingli LI; Songnian LOU

    2003-01-01

    X80 pipeline steel produced by TMCP has high strength and high toughness with ultrafine grain microstructure. The microstructure coarsens and the toughness worsens at the coarse grained (CG) HAZ apparently after weld simulation. The experimental results indicated that the bainitic ferrite and the second phases formed at cooling are differently as the variation of carbon in base metal. In low carbon steels, the bainitic ferrite laths are long and narrow, the second phases are complex including residual austenite, martensite, the M-A constituent and the Fe3C carbide. The formation of Fe3C carbide is the main reason of the poor toughness in CG HAZ. The ultralow carbon in base metal, however, can improve the CG HAZ toughness through restraining the formation of carbides, decreasing the M-A constituent, increasing the residual austenite content, which are beneficial to the CG HAZ toughness.

  2. The Effect of Stepped Austempering on Phase Composition and Mechanical Properties of Nanostructured X37CrMoV5-1 Steel

    Directory of Open Access Journals (Sweden)

    Marciniak S.

    2015-04-01

    Full Text Available This paper presents the results of studies of X37CrMoV5-1 steel subjected to quenching processes with a one-step and a two-step isothermal annealing. The TEM observation revealed that steel after one-step treatment led is composed of carbide-free bainite with nanometric thickness of ferrite plates and of high volume fraction of retained austenite in form of thin layers or large blocks. In order to improve the strength parameters an attempt was made to reduce the austenite content by use of quenching with the two-step isothermal annealing. The temperature and time of each step were designed on the basis of dilatometric measurements. It was shown, that the two-step heat treatment led to increase of the bainitic ferrite content and resulted in improvement of steel's strength with no loss of steel ductility.

  3. Nanostructured/ultrafine multiphase steel with enhanced ductility obtained by mechanical alloying and spark plasma sintering of powders

    International Nuclear Information System (INIS)

    A nanostructured/ultrafine steel with a complex microstructure comprising bainitic ferrite, austenite and martensite was obtained by mechanical alloying and spark plasma sintering of powders. Transmission electron microscopy and X-ray diffraction analysis were employed to investigate the microstructural morphologies and the nature of bainitic ferrite and retained austenite formed during sintering process. The presence of a complex microstructure with elongated ferritic lamellae separated by thin layers of retained austenite was revealed. Some ferritic equiaxed grains are also present. The steel displays a large uniform plastic deformation, thanks to its work hardenability provided by the microstructural characteristics: the bimodal distribution of ferrite, the multiphase microstructure and the TRIP phenomenon provided by austenite.

  4. Moessbauer study of the annealing effect on low-alloyed steels

    International Nuclear Information System (INIS)

    Structural analyses of Fe-Cr and Fe-Cr-Ni low-alloyed steels before and after annealing at 600 deg. C using Moessbauer spectrometry, X-ray diffraction and scanning electron microscopy are reported. At the received state, the two steels present a fine bainitic microstructure with equal hardness. From Moessbauer analysis, two iron sites are identified as substitutional by Cr, Mo, Ni atoms and as insertional by carbon in bainitic ferrite. Both sites are locally deformed by residual stresses. The presence of small quantities of retained austenite and ε carbide has been observed. Annealing for one hour at 600 deg. C causes a decrease in hardness for both steels with a decrease of retained austenite. After longer time of annealing, precipitation of (Fe,Ni)23C6 occurs in the Fe-Cr-Ni steel and increases hardness

  5. Study on microstructure and hardness uniformity of non-quenched prehardened steel for large section plastic mould

    International Nuclear Information System (INIS)

    Microstructures throughout a 460 mm x 800 mm cross-section of non-quenched prehardened (NQP) steel for plastic mould were characterized by optical microscopy, scanning electronic microscopy and transmission electronic microscopy. Strength and hardness of the NQP steel block was also tested. It is found that mechanical properties at core are close to that at surface and hardness distributes between 37 and 40 HRC through the whole section. Grains at core are coarser and deformation bands are observed at surface, while microstructures both at core and at surface are composed of bainitic ferrite laths with high dislocation density and interlath cementite and/or residual austensite. Considering continuous cooling transformation of the NQP steel, the small variation in hardness throughout the section is caused by the main microstructure bainite which possesses high hardenability. Moreover, the differences of the lath widths and dislocation density in baintic ferrite lath make hardness at surface a little higher than that at core

  6. Continuous Cooling Transformations in Nuclear Pressure Vessel Steels

    Science.gov (United States)

    Pous-Romero, Hector; Bhadeshia, Harry K. D. H.

    2014-10-01

    A class of low-alloy steels often referred to as SA508 represent key materials for the manufacture of nuclear reactor pressure vessels. The alloys have good properties, but the scatter in properties is of prime interest in safe design. Such scatter can arise from microstructural variations but most studies conclude that large components made from such steels are, following heat treatment, fully bainitic. In the present work, we demonstrate with the help of a variety of experimental techniques that the microstructures of three SA508 Gr.3 alloys are far from homogeneous when considered in the context of the cooling rates encountered in practice. In particular, allotriomorphic ferrite that is expected to lead to a deterioration in toughness, is found in the microstructure for realistic combinations of austenite grain size and the cooling rate combination. Parameters are established to identify the domains in which SA508 Gr.3 steels transform only into the fine bainitic microstructures.

  7. Fracture toughness prediction of steel type 10MnNi2Mo

    International Nuclear Information System (INIS)

    A model is presented of the prediction of fracture toughness of the 10MnNi2Mo steel used for pressure components of the primary circuit of nuclear power plants with a mixed bainitic-ferritic structure. Next to the initiation of fission microcracks in carbides the initiation was also considered of microcracks in the ferrite using the Cottrel model of dislocation coalescence. The model led to very good agreement between predicted and experimental values of the stress intensity factor for the values of the parameter of shape of the plastic zone near the face of the crack and the parameter of the participation of carbide particles excluded in the bainite, and the participation of ferrite grains. (author)

  8. Controlled Rolling and Controlled Cooling Technology of Ultra-High Strength Steel with 700 Mpa Grade

    Institute of Scientific and Technical Information of China (English)

    QI Shi-ze; ZHANG Pi-jun; DU Lin-xiu; LIU Xiang-hua; WANG Guo-dong

    2004-01-01

    With Gleeble-1500 system, the influences of rolling temperature, finishing temperature and cooling rate on the mechanical properties of two ultra-high strength steels were analyzed. The microstructure of the hot rolled specimens was observed by optical microscope, TEM and SEM. The TRIP of HSLA steels was studied. The results show that the yield stress of 700 Mpa can be reached for two steels. The controlled rolling and controlled cooling technology has different effects on two steels, but it is rational to adopt finishing temperature 800 ℃ for both of them. The microstructure of the steels is mainly bainite, and the influence factors of mechanical properties are the size of bainite, and the size, distribution, composition and morphology of secondary phases. The deformation of high molybdenum steels at a high temperature with a high cooling rate would promote TRIP.

  9. The properties and microstructure of padding welds built up on the surface of forging dies

    Directory of Open Access Journals (Sweden)

    S. Pytel

    2010-07-01

    Full Text Available The study presents selected results of the examinations of the properties and microstructure of weld overlays built up with the UTOP38,F-812 and F-818 welding wires on a substrate of the 42CrMo4 structural steel. Among others, the following investigations were carriedout: bend tests, hardness measurements and determination of ferrite content in a bainitic-martensitic microstructure of UTOP38 and F-812layers.

  10. Microstructure Evolution during Friction Stir Spot Welding of TRIP steel

    OpenAIRE

    Lomholt, Trine Colding; Somers, Marcel A. J.; da Silva Fanta, Alice Bastos; Pantleon, Karen

    2013-01-01

    TRansformation Induced Plasticity (TRIP) stål er udviklet til anvendelse i bilindustrien på grund af den fremragende kombination af høj styrke og formbarhed. Mikrostrukturen af TRIP stål er en kompleks blanding af mange mikrostruktur-dele: ferrit, bainit, martensit og austenit. TRIP effekten er aktiveret under indflydelse af ekstern mekanisk belastning, der fører til en martensitisk transformation af austenit. Martensit-dannelsen under deformation bidrager til de fremragende mekaniske egenska...

  11. Effect of microstructures on magnetic Barkhausen noise level in the weld HAZ of an RPV steel

    Science.gov (United States)

    Kim, Joo-Hag; Park, Duck-Gun; Ok, Chi-Il; Yoon, Eui-Pak; Hong, Jun-Hwa

    1999-05-01

    Microstructural state and magnetic Barkhausen noise (BN) level have been correlated in the weld heat-affected zone (HAZ) of a pressure vessel steel. The BN level increased with increasing size of carbide, and the tempered bainite structure showed higher BN signal than the tempered martensite. The results indicated that heat-treated materials may result in microstructurally different domain wall pinning obstacles at different thermal cycles.

  12. Hydrogen-Induced Cold Cracking in High-Frequency Induction Welded Steel Tubes

    Science.gov (United States)

    Banerjee, Kumkum

    2016-04-01

    Detailed investigation was carried out on 0.4C steel tubes used for the telescopic front fork of two-wheelers to establish the root cause for the occurrence of transverse cracks at the weld heat-affected zone of the tubes. Fractographic and microstructural observations provide evidences of delayed hydrogen-induced cracking. The beneficial microstructure for avoiding the transverse cracks was found to be the bainitic-martensitic, while martensitic structure was noted to be deleterious.

  13. Super High Strength Steel for automotive applications

    OpenAIRE

    CONFENTE, Mario; SCHNEIDER, Emmanuel; BOMONT, Olivier; LESCALIER, Christophe; BOMONT-ARZUR, Anne

    2008-01-01

    Intensive weight savings and out-sizing programs are developed in automotive industry and lead to increase the mechanical properties of the material of the automotive parts. ArcelorMittal has developed specific steel grades known as Super High Strength Steels which are designed for both high ductility and toughness and fatigue resistance. This paper investigates machinability for a drilling operation using an experimental methodology. One of the materials is a new low bainitic steel grade. Ex...

  14. 车床

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    Correcting distortion caused in a book on page turning machine, Cutting speed influence of surface integrity of hard turned bainite steel,Dental amalgam - the effect of the technology of alloy powder preparation on the corrosion behavior and the release of mercury,DEPTH PROFILING OF MACHINED SURFACES USING CROSS CORRELATION OF BARKHAUSEN NOISE BUTTERFLY CURVES,Determination and evaluation of machine tool dynamic characteristics obtained during stable cutting process.

  15. Wearing Quality of Austenitic, Duplex Cast Steel, Gray and Spheroidal Graphite Iron

    Directory of Open Access Journals (Sweden)

    S. Pietrowski

    2012-04-01

    Full Text Available The current work presents the research results of abrasion wear and adhesive wear at rubbing and liquid friction of new austenitic, austenitic-ferritic (“duplex” cast steel and gray cast iron EN-GJL-250, spheroidal graphite iron EN-GJS-600-3, pearlitic with ledeburitic carbides and spheroidal graphite iron with ledeburitic carbides with a microstructure of the metal matrix: pearlitic, upper bainite, mixture of upper and lower bainite, martensitic with austenite, pearlitic-martensitic-bainitic-ausferritic obtained in the raw state. The wearing quality test was carried out on a specially designed and made bench. Resistance to abrasion wear was tested using sand paper P40. Resistance to adhesive wear was tested in interaction with steel C55 normalized, hardened and sulfonitrided. The liquid friction was obtained using CASTROL oil. It was stated that austenitic cast steel and “duplex” are characterized by a similar value of abrasion wear and adhesive wear at rubbing friction. The smallest decrease in mass was shown by the cast steel in interaction with the sulfonitrided steel C55. Austenitic cast steel and “duplex��� in different combinations of friction pairs have a higher wear quality than gray cast iron EN-GJL- 250 and spheroidal graphite iron EN-GJS-600-3. Austenitic cast steel and “duplex” are characterized by a lower wearing quality than the spheroidal graphite iron with bainitic-martensitic microstructure. In the adhesive wear test using CASTROL oil the tested cast steels and cast irons showed a small mass decrease within the range of 1÷2 mg.

  16. Microstructural characterization and formation mechanism of abnormal segregation band of hot rolled ferrite/pearlite steel

    International Nuclear Information System (INIS)

    In order to further reveal the microstructural characterization and formation mechanism of abnormal segregation band of hot rolled ferrite/pearlite steel, the microstructure of this type steel was intensively studied with Scanning Auger Microprobe (SAM), etc. The results show that severe C–Mn segregation exists in the abnormal segregation band region at the center of hot rolled ferrite/pearlite steel, which results from the Mn segregation during solidification process of the continuous casting slab. The C–Mn segregation causes relative displacement of pearlite transformation curve and bainite transformation curve of C curve in the corresponding region, leading to bay-like shaped C curve. The bay-like shaped C curve creates conditions for the transformation from supercooling austenite to bainite at relatively lower cooling rate in this region. The Fe–Mn–C Atomic Segregation Zone (FASZ) caused by C–Mn segregation can powerfully retard the atomic motion, and increase the lattice reconstruction resistance of austenite transformation. These two factors provide thermodynamic and kinetic conditions for the bainite transformation, and result in the emergence of granular bainitic abnormal segregation band at the center of steel plate, which leads to lower plasticity and toughness of this region, and induces the layered fracture. - Highlights: • Scanning Auger Microprobe (SAM) is applied in the fracture analysis. • The abnormal segregation band region appears obvious C–Mn segregation. • The C–Mn segregation leads to bay-like shaped C curve. • The C–Mn segregation leads to Fe–Mn–C Atomic Segregation Zone

  17. Hot-working in the γ+α region of TRIP-aided microalloyed steel

    Directory of Open Access Journals (Sweden)

    A. Grajcar

    2007-12-01

    Full Text Available Purpose: The aim of the paper is to investigate the influence of hot-working in the γ+α range and isothermal holding temperature in a bainitic range on a stability of retained austenite in a TRIP-aided microalloyed steel.Design/methodology/approach: The thermomechanical processing in the γ+α range to obtain multiphase structures with the retained austenite in a microalloyed steel was realized. It consisted of plastic deformation of specimens at 750°C or 780°C, oil cooling and isothermal holding in a bainitic region. Degree of deformation was 28 or 50%. To reveal the multiphase structure optical and transmission electron microscopy were used. X-ray diffraction method was employed to determine a volume fraction of retained austenite.Findings: It was found that hot-working in the two-phase region influences essentially a multiphase structure of investigated steel. The ferrite fraction is comparable for heat-treated and thermo-mechanically processed specimens but the ferrite grain size is twice smaller in a case of plastically-deformed specimens. The optimum isothermal holding temperature in a bainitic range is 300°C, independent on austenitizing temperature. The specimens forged in the γ+α range and isothermally held at this temperature made it possible to obtain about 10% of retained austenite.Research limitations/implications: Investigations concerning the influence of isothermal holding time in a bainitic range on the stability of retained austenite should be carried out.Practical implications: The established conditions of the thermomechanical processing can be useful in a development of the hot-rolling technology for TRIP-aided microalloyed steels.Originality/value: The realized thermomechanical processing enabled to obtain about 10% fraction of retained austenite in a steel containing 0.5% Si.

  18. 12MnNiVR钢的连续冷却转变行为及相变动力学%Continuous cooling transformation behavior and transformation kinetics of 12MnNiVR steel

    Institute of Scientific and Technical Information of China (English)

    张志敏; 蔡庆伍; 余伟

    2013-01-01

    用热膨胀仪测定了12MnNiVR钢的连续冷却转变曲线,并结合显微组织观察和硬度测定,研究了低冷速下奥氏体向铁素体转变及向贝氏体转变的动力学,分析了铁素体转变及贝氏体转变的生长方式.实验钢在连续冷却过程中的计算相变动力学结果与实测相变数据吻合很好.研究结果表明实验钢在低冷速下冷却时奥氏体向铁素体转变,形核位置主要在晶棱处,生长方式主要为二维长大,奥氏体向贝氏体转变,形核位置主要在界面处,生长方式主要为一维长大.%Continuous cooling transformation curves of 12MnNiVR steel were measured by a thermal dilatometer, and then transformation kinetics of austenite to ferrite at low cooling rate as well as austenite to bainite was studied and growth modes of transformed ferrite and bainite were analyzed on the basis of measured CCT curves, and observation of microstructure and hardness measurement. The calculated result of transformation kinetics for the tested steel during continuous cooling is in reasonable agreement with experimental data. Results show that nucleation sites of ferrite transformed from austenite at low cooling rate are mainly at crystal edges and ferrite grains grow mainly following two-dimensional mode whereas nucleation sites of transformed bainite are mainly at austenite grain boundaries and bainite grains grow mainly following one-dimensional mode.

  19. Effect of Silicon Content on Thermodynamics of Austenite Decomposition in C-Si-Mn TRIP Steels

    Institute of Scientific and Technical Information of China (English)

    ZHU Li-juan; WU Di; ZHAO Xian-ming

    2006-01-01

    Some numerical models such as central atoms model (CAM) and superelement model were used to simulate the thermodynamics of austenite decomposition in the Fe-C-Mn-Si TRIP (transformation induced plasticity) steels. Thermodynamic calculations were carried out under a para-equilibrium (PE) condition. The results show that certain silicon content can accelerate the polygonal ferritic transformation and increase the volume fraction and stability of retained austenite by retarding the precipitation of carbides during the bainitic transformation.

  20. Microstructure and Mechanical Properties of 50SiMnNiNb Steel by a Novel Quenching-Partitioning-Austempering Heat Treatment

    Institute of Scientific and Technical Information of China (English)

    LI Hongyan; JIN Xuejun

    2009-01-01

    For the purpose of reducing weight of steel parts, save raw materials and keep or even improve safety standards, the development of advanced high strength steels is increasingly demanded in the automotive industry and engineering applications. We have proposed a novel heat treatment (quenching-partitioning-austempering treatment, Q-P-A) to obtain steel parts with high strength and good ductility. The Q-P-A process is intended to produce microstructure consisted of carbon-depleted martensite, carbon-enriched retained austenite and nanostructured bainite. Quenching(Q) treatment fabricates mixed microstructure of carbon-supersaturated martensite and certain amounts of untransformed austenite. Partitioning(P) thermal treatment accomplishes fully diffusing of carbon from the supersaturated martensite phase to the untransformed austenite phase and enriching the amount of carbon in untransformed austenite. Further low-temperature austempering(A) process induces incredible thin bainite from the carbon-enriched untransformed austenite. A study of the microstructure and mechanical properties of 50SiMnNiNb steel subjected to the novel Q-P-A treatment is presented. Microstructure is assessed by optical microscope(OM), field emission scanning electron microscope(FESEM) and transmission electron microscope(TEM), and the corresponding mechanical properties are measured. The experimental results indicate that attractive mechanical properties of steels during the Q-P-A process are attributed to the complex multi-phase structure. Slender plates of bainite with 20-40 nm thick are generated in the medium carbon steel. Meanwhile, with increasing of the volume fraction of nanostructured bainite, yield strength of steel parts is increased with little degradation of ultimate tensile strength. In this paper, a novel quenching-partitioning-austempering heat treatment is proposed, and the attractive mechanical properties of steels are obtained during the Q-P-A process.

  1. Influence of nonmartensitic transformation products on mechanical properties of tempered martensite

    Science.gov (United States)

    Hodge, J M; Lankford, W T

    1952-01-01

    The influence of nonmartensitic transformations products on the mechanical properties of tempered martensite is presented for samples of a SAE 4340 steel, partially isothermally transformed to specific high-temperature transformation products and quenched and tempered to hardness values of from 25 to 40 Rockwell c. The effects of upper bainite in amounts of 1,5, 10, 20 and 50 percent, of 5 percent ferrite, and of 5 percent pearlite on the tensile, impact, and fatigue properties are evaluated. (author)

  2. Improvement of weld HAZ toughness at low heat input by controlling the distribution of M-A constituents

    OpenAIRE

    Laitinen, R

    2006-01-01

    Abstract This research work focuses on how to improve the toughness of heat affected zones (HAZs) of low heat input welds in the case of high strength thermomechanically processed (TMCP) and recrystallization controlled rolled and accelerated cooled (RCR) plates with yield strengths of 355–500 MPa. Experimental work was aimed at the investigation of the intragranular nucleation of acicular ferrite or bainite in hot-rolled plates and the evaluation of the Charpy V and CTOD toughness of ...

  3. The properties and microstructure of padding welds built up on the surface of forging dies

    OpenAIRE

    Pytel, S.; Turek, J; S. Okoński; K. Zarębski

    2010-01-01

    The study presents selected results of the examinations of the properties and microstructure of weld overlays built up with the UTOP38,F-812 and F-818 welding wires on a substrate of the 42CrMo4 structural steel. Among others, the following investigations were carriedout: bend tests, hardness measurements and determination of ferrite content in a bainitic-martensitic microstructure of UTOP38 and F-812layers.

  4. Prediction of the mechanical behaviour of TRIP steel

    OpenAIRE

    Perdahcioglu, E.S.; Geijselaers, H.J.M.; Tekkaya, A. E.; Hirt, G.

    2011-01-01

    TRIP steel typically contains four different phases, ferrite, bainite, austenite and martensite. During deformation the metastable retained austenite tends to transform to stable martensite. The accompanying transformation strain has a beneficial effect on the ductility of the steel during forming. By changing the alloy composition, the rolling procedure and the thermal processing of the steel, a wide range of different morphologies and microstructures can be obtained. Interesting parameters ...

  5. Improving the fracture toughness of dualphase austempered ductile iron

    OpenAIRE

    Hidalgo García, Javier

    2009-01-01

    Dual Phase Austempered Ductile Irons, DPADI alloys have a microstructure with a combination of ausferrite and pro-eutectoid ferrite along with graphite and residual/retained austenite. To reach this particular microstructure ductile iron is austenized in the austenitepro- eutectoid ferrite region before being carried though an isothermal heat treatment somewhere between the bainite-start and martensite-start temperature. The special austenization procedure makes DPADI prime candidates for app...

  6. Microstructural characterization and formation mechanism of abnormal segregation band of hot rolled ferrite/pearlite steel

    Energy Technology Data Exchange (ETDEWEB)

    Feng, Rui [School of Materials Science and Engineering, Shandong University, Jinan 250061 (China); Engineering Research Center of Large Size Alloy Structural Steel Bars of Shandong Province, Jinan 250061 (China); School of Materials Science and Engineering, Shandong University of Technology, Zibo 255049 (China); Li, Shengli, E-mail: lishengli@sdu.edu.cn [School of Materials Science and Engineering, Shandong University, Jinan 250061 (China); Engineering Research Center of Large Size Alloy Structural Steel Bars of Shandong Province, Jinan 250061 (China); Zhu, Xinde [School of Materials Science and Engineering, Shandong University, Jinan 250061 (China); Ao, Qing [School of Materials Science and Engineering, Shandong University, Jinan 250061 (China); Engineering Research Center of Large Size Alloy Structural Steel Bars of Shandong Province, Jinan 250061 (China)

    2015-10-15

    In order to further reveal the microstructural characterization and formation mechanism of abnormal segregation band of hot rolled ferrite/pearlite steel, the microstructure of this type steel was intensively studied with Scanning Auger Microprobe (SAM), etc. The results show that severe C–Mn segregation exists in the abnormal segregation band region at the center of hot rolled ferrite/pearlite steel, which results from the Mn segregation during solidification process of the continuous casting slab. The C–Mn segregation causes relative displacement of pearlite transformation curve and bainite transformation curve of C curve in the corresponding region, leading to bay-like shaped C curve. The bay-like shaped C curve creates conditions for the transformation from supercooling austenite to bainite at relatively lower cooling rate in this region. The Fe–Mn–C Atomic Segregation Zone (FASZ) caused by C–Mn segregation can powerfully retard the atomic motion, and increase the lattice reconstruction resistance of austenite transformation. These two factors provide thermodynamic and kinetic conditions for the bainite transformation, and result in the emergence of granular bainitic abnormal segregation band at the center of steel plate, which leads to lower plasticity and toughness of this region, and induces the layered fracture. - Highlights: • Scanning Auger Microprobe (SAM) is applied in the fracture analysis. • The abnormal segregation band region appears obvious C–Mn segregation. • The C–Mn segregation leads to bay-like shaped C curve. • The C–Mn segregation leads to Fe–Mn–C Atomic Segregation Zone.

  7. Mixed structures in continuously cooled low-carbon automotive steels

    OpenAIRE

    Khalid, F.; Edmonds, D.

    1993-01-01

    Mixed microstructures have been studied in low- carbon microalloyed steels suitable for automotive applications, after continuous cooling from the hot-rolled condition. Microstructural features such as polygonal ferrite, bainitic and acicular ferrite and microphase constituent are identified using transmission electron microscopy. The influence of these mixed structures on the tensile strength, impact toughness and fracture behaviour is examined. It is found that improvements in impact toughn...

  8. ATOM PROBE MICROANALYSIS OF WELD METAL IN A SUBMERGED ARC WELDED CHROMIUM-MOLYBDENUM STEEL

    OpenAIRE

    Josefsson, B.; Kvist, A.; Andrén, H.

    1987-01-01

    A submerged arc welded 2.25Cr - 1Mo steel has been investigated using electron microscopy and atom probe field ion microscopy. The bainitic microstructure of the as-welded steel consisted of ferrite and martensite. During heat treatment at 690°C the martensite transformed to ferrite and cementite and needle-shaped (Cr,Mo)2C carbides precipitated. Together with a substantial decrease in dislocation density, this resulted in an improvement of the toughness.

  9. Mechanical properties of a pipe workpiece at the stages of JCOE pipe forming

    Science.gov (United States)

    Shabalov, I. P.; Solov'ev, D. M.; Filippov, G. A.; Livanova, O. V.

    2015-04-01

    The mechanical properties (strength, plasticity, strain aging sensitivity, impact toughness, resistance to crack nucleation and propagation) of a ferritic-bainitic steel of strength class K60 are studied at the stages of JCOE pipe forming (sheet, pipe workpiece, finished pipe) and after artificial aging. The dependence of the change of the mechanical properties of the pipe workpiece along the perimeter on the degree of deformation action of a working tool in pipe forming is found.

  10. Diseño de nuevos aceros bainíticos.

    OpenAIRE

    Caballero, F. G.; Bhadeshia, H. K. D. H.; Mawella, K.J.A; Jones, D G; P Brown

    2002-01-01

    Mixed microstructures consisting of fine plates of upper bainitic ferrite separated by thin films of stable retained austenite have seen many applications in recent years because of their impressive combination of strength and toughness. There may also be some martensite present in the microstructure, but its formation can be controlled increasing the stability of the retained austenite. On the other hand, carbides are avoided by the judicious use of silicon as an alloying element. The aim of...

  11. The electronic microscope analysis used to study the martensite morphology in high strength low alloy steels

    OpenAIRE

    Isac, M.

    1993-01-01

    The class of HSLA steels have a great development due to the spread of quenched and tempered steels. The present paper has in view the research by means of electronic microscope analysis of structural characteristics of a HSLA steel after quenching and tempering. The martensite-bainite structure is investigated by means of secondary electrons images, transmitted electrons images or by diffraction of electrons on selected areas. Martensite has an aspect in slats, it is made up of packets with ...

  12. Understanding toughness and ductility in novel steels with mixed microstructures

    OpenAIRE

    Fielding, Lucy Chandra Devi

    2014-01-01

    The purpose of the work presented in this thesis was to explore and understand the mechanisms governing toughness, ductility and ballistic performance in a class of nanostructured carbide-free bainite-austenite steels, sometimes known as ?superbainite?. The mechanical properties of these alloys have been extensively reported, but their interpretation is not clear. The thesis begins with an introduction to both the relevant nanostructures and some of the difficulties involved in explaining obs...

  13. The Effect of Nb on the Continuous Cooling Transformation Curves of Ultra-Thin Strip CASTRIP© Steels

    Directory of Open Access Journals (Sweden)

    Kristin R. Carpenter

    2015-10-01

    Full Text Available The effect of Nb on the hardenability of ultra-thin cast strip (UCS steels produced via the unique regime of rapid solidification, large austenite grain size, and inclusion engineering of the CASTRIP© process was investigated. Continuous cooling transformation (CCT diagrams were constructed for 0, 0.014, 0.024, 0.04, 0.06 and 0.08 wt% Nb containing UCS steels. Phase nomenclature for the identification of lower transformation product in low carbon steels was reviewed. Even a small addition of 0.014 wt% Nb showed a potent effect on hardenability, shifting the ferrite C-curve to the right and expanding the bainitic ferrite and acicular ferrite phase fields. Higher Nb additions increased hardenability further, suppressed the formation of ferrite to even lower cooling rates, progressively lowered the transformation start and finish temperatures and promoted the transformation of bainite instead of acicular ferrite. The latter was due to Nb suppressing the formation of allotriomorphic ferrite and allowing bainite to nucleate at prior austenite grain boundaries, a lower energy site than that for the intragranular nucleation of acicular ferrite at inclusions. Strength and hardness increased with increasing Nb additions, largely due to microstructural strengthening and solid solution hardening, but not from precipitation hardening.

  14. HEAT TREATING OF SINTERED Fe—1.5Mo—0.7C STEELS AND THEIR SLIDING WEAR BEHAVIOR

    Institute of Scientific and Technical Information of China (English)

    J.A.Wang; Y.He; 等

    2003-01-01

    The influence of heat treating on mechanical properties as well as on the sliding wear gehavior of sintered Fe-1.5Mo-0.7C steels was experimentally studied.The microstruc-tures of sintered steels change from upper bainite to martensite,tempered martensite,pearlite and lower bainite depending on the heat treating conditions.Heat treating increases the hardness of sintered steels but high tempering temperature,i.e.700℃,causes the hardness to be even lower than that of the as-sintered ones.The impact energy of sintered steels increases with increasing tempering temperature and arrives the highest at 700℃,while the steels tempered at 200℃ have the highest transverse rupture strength.Austempering results in fair good overall properties,such as hard-ness,impact energy,and transverse rupture strenght.When the sintered steels were austempered,oil-quenched or tempered belw 400℃ after quenched,the wear coef-ficient becomes considerably lower.Fair high hardness,such as HV30>380,and structures of martensite,tempered martensite or lower bainite are beneficial to low-ering the wear coefficient.Under the wear test conditions given,delanination and oxidational wear are the main wear regimes for sintered Fe-1.5Mo-0.7C steels.Fe3O4 in the wear debris is beneficial to lowering wear coefficient.

  15. HEAT TREATING OF SINTERED Fe-1.5Mo-0.7C STEELS AND THEIR SLIDING WEAR BEHAVIOR

    Institute of Scientific and Technical Information of China (English)

    J.A. Wang; Y. He; H. Danninger

    2003-01-01

    The influence of heat treating on mechanical properties as well as on the sliding wearbehavior of sintered Fe-1.SMo-0.7C steels was experimentally studied. The microstruc-tures of sintered steels change from upper bainite to martensite, tempered martensite,pearlite and lower bainite depending on the heat treating conditions. Heat treatingincreases the hardness of sintered steels but high tempering temperature, i.e. 700℃,causes the hardness to be even lower than that of the as-sintered ones. The impactenergy of sintered steels increases with increasing tempering temperature and arrivesthe highest at 700℃, while the steels tempered at 200℃ have the highest transverserupture strength. Austempering results in fair good overall properties, such as hard-ness, impact energy, and transverse rupture strength. When the sintered steels wereaustempered, oil-quenched or tempered below 400℃ after quenched, the wear coef-ficient becomes considerably lower. Fair high hardness, such as HV30 > 380, andstructures of martensite, tempered martensite or lower bainite are beneficial to low-ering the wear coefficient. Under the wear test conditions given, delamination andoxidational wear are the main wear regimes for sintered Fe-1.5Mo-0.7C steels. Fe3O4in the wear debris is beneficial to lowering wear coefficient.

  16. Weldability of 780 MPa Super-High Strength Heavy-Duty Truck Crossbeam Steel

    Institute of Scientific and Technical Information of China (English)

    WANG Xiao-nan; DI Hong-shuang; ZHANG Chit; DU Lin-xiu; DONG Xue-xir

    2012-01-01

    CO2-shielded welding experiments of newly developed, 780 MPa super-high strength heavy-duty truck crossbeam steel were conducted, and the microstructure, microhardness, mechanical properties, and impact tough- hess of the welded joint were studied. The evolution of the microstructure of the welded joint occurred as follows.. welding seam (acicular ferrite+proeutectoid ferrite)→fusion zone (granular bainite-long strip M/A island)→coarse grain zone (granular bainite-long strip or short bar M/A island)→fine grain zone (ferrite+ pearlite+ blocky M/A is- land)→mixed grained zone (ferrite+granular bainite+blocky M/A island)→base metal (proeutectoid ferrite+gran- ular bainite-hlocky or granular M/A island). Increasing the density of the grain boundaries can effectively improve the impact toughness, and the blocky M/A island hindered crack propagation more effectively than the long strip M/A island. The new hot-rolled 780 MPa super-high strength steel had excellent weldability. The welding technology was applied under the following conditions: welding voltage was 20 to 21 V, welding current was 200 to 210 A, and the gas flow rate was 25 L/rain.

  17. Evolution of weld metal microstructure in shielded metal arc welding of X70 HSLA steel with cellulosic electrodes: A case study

    International Nuclear Information System (INIS)

    The microstructure of weld joint in X70 line pipe steel resulted from shielded metal arc welding with E6010 cellulosic electrodes is characterized using optical and electron microscopy. A range of ferritic morphologies have been identified ranging from polygonal inter- and intra-prior austenite grains allotriomorphic, idiomorphic ferrites to Widmanstätten, acicular and bainitic ferrites. Electron Backscatter Diffraction (EBSD) analysis using Image Quality (IQ) and Inverse Pole Figure (IPF) maps through superimposition of IQ and IPF maps and measurement of percentages of high and low angle grain boundaries was identified to assist in differentiation of acicular ferrite from Widmanstätten and bainitic ferrite morphologies. In addition two types of pearlitic structures were identified. There was no martensite detected in this weld structure. The morphology, size and chemistry of non-metallic inclusions are also discussed briefly. - Highlights: • Application of EBSD reveals orientation relationships in a range of phases for shielded metal arc welding of HSLA steel. • Nucleation sites of various ferrite morphologies identified • Formation of upper and lower bainite and their morphologies

  18. Effects of Nb on microstructure and continuous cooling transformation of coarse grain heat-affected zone in 610 MPa class high-strength low-alloy structural steels

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Y.Q. [Department of Materials Science and Engineering, Shanghai Jiaotong University, Shanghai 200030 (China)], E-mail: yingqiaozhang@yahoo.com.cn; Zhang, H.Q. [Department of Materials Science and Engineering, Shanghai Jiaotong University, Shanghai 200030 (China); Research Institute for Advanced Structural Steel, R and D Center, Baoshan Iron and Steel Limited Company, Shanghai 201900 (China); Liu, W.M. [Department of Materials Science and Engineering, Shanghai Jiaotong University, Shanghai 200030 (China); Hou, H. [Research Institute for Advanced Structural Steel, R and D Center, Baoshan Iron and Steel Limited Company, Shanghai 201900 (China)

    2009-01-15

    Continuous cooling transformation diagrams of the coarse grain heat-affected zone and microstructure after continuous cooling were investigated for 610 MPa class high-strength low-alloy (HSLA) structural steels with and without niobium. For the steel without Nb, grain boundary ferrite, degenerate pearlite and acicular ferrite are produced at slower cooling rates. Bainite phase is formed at faster cooling rates. However, for the steel with Nb, granular bainite is dominant at a large range of cooling rates. At cooling rates <32 K/s, transformation start temperature is decreased by 20 K approximately in the steel with Nb compared with that without Nb. Ferrite nucleation at prior austenite grain boundaries is suppressed and the cooling rate region for granular bainite transformation is broadened. At cooling rates >32 K/s, Nb addition has no obvious influence on transformation start temperature, but it influences microstructure transformation significantly. Martensite is observed in steel with Nb at faster cooling rates, but not produced in steel without Nb.

  19. The Determining Role of Finish Cooling Temperature on the Microstructural Evolution and Precipitation Behavior in an Nb-V-Ti Microalloyed Steel in the Context of Newly Developed Ultrafast Cooling

    Science.gov (United States)

    Li, Xiaolin; Wang, Zhaodong; Deng, Xiangtao; Wang, Guodong; Misra, R. D. K.

    2016-05-01

    We have studied here the impact of finish cooling temperature on the microstructural evolution and precipitation behavior in Nb-V-Ti microalloyed steel through thermo-mechanical simulation in the context of newly developed ultrafast cooling system. The microstructural evolution was studied in terms of morphology and crystallography of precipitates using high-resolution transmission electron microscopy. At finish cooling temperature of 933 K and 893 K (660 °C and 620 °C), the microstructure primarily consisted of polygonal ferrite, together with a small amount of wedge-shaped acicular ferrite and lamellar pearlite, while, at 853 K and 813 K (580 °C and 540 °C), the microstructure consisted of lath bainite with fine interlath cementite and granular bainite with martensite/austenite (M/A) constituent. In all the finish cooling temperatures studied, the near-spherical precipitates of size range ~2 to 15 nm were randomly dispersed in ferrite and bainite matrix. The carbide precipitates were identified as (Nb,V)C with NaCl-type crystal structure. With a decrease in the finish cooling temperature, the size of the precipitates was decreased, while the number density first increased with a peak at 893 K (620 °C) and then decreased. Using Ashby-Orowan model, the contribution of the precipitation strengthening to yield strength was ~149 MPa at the finish cooling temperature of 893 K (620 °C).

  20. Microstructures and Toughness of Weld Metal of Ultrafine Grained Ferritic Steel by Laser Welding

    Institute of Scientific and Technical Information of China (English)

    Xudong ZHANG; Wuzhu CHEN; Cheng WANG; Lin ZHAO; Yun PENG; Zhiling TIAN

    2004-01-01

    3 mm thick 400 MPa grade ultrafine grained ferritic steel plates were bead-on-plate welded by CO2 laser with heat input of 120~480 J/mm. The microstructures of the weld metal mainly consist of bainite, which form is lower bainite plates or polygonal ferrite containing quantities of dispersed cementite particles, mixed with a few of low carbon martensite laths or ferrite, depending on the heat input. The hardness and the tensile strength of the weld metal are higher than those of the base metal, and monotonously increase as the heat input decreases. No softened zone exists inheat affected zone (HAZ). Compared with the base metal, although the grains of laser weld are much larger, the toughness of the weld metal is higher within a large range of heat input. Furthermore, as the heat input increases, the toughness of the weld metal rises to a maximum value, at which point the percentage of lower bainite is the highest, and then drops.

  1. Mechanism of Secondary Hardening in Rapid Tempering of Dual-Phase Steel

    Science.gov (United States)

    Saha, Dulal Chandra; Nayak, Sashank S.; Biro, Elliot; Gerlich, Adrian P.; Zhou, Y.

    2014-12-01

    Dual-phase steel with ferrite-martensite-bainite microstructure exhibited secondary hardening in the subcritical heat affected zone during fiber laser welding. Rapid isothermal tempering conducted in a Gleeble simulator also indicated occurrence of secondary hardening at 773 K (500 °C), as confirmed by plotting the tempered hardness against the Holloman-Jaffe parameter. Isothermally tempered specimens were characterized by analytic transmission electron microscopy and high-angle annular dark-field imaging. The cementite (Fe3C) and TiC located in the bainite phase of DP steel decomposed upon rapid tempering to form needle-shaped Mo2C (aspect ratio ranging from 10 to 25) and plate-shaped M4C3 carbides giving rise to secondary hardening. Precipitation of these thermodynamically stable and coherent carbides promoted the hardening phenomenon. However, complex carbides were only seen in the tempered bainite and were not detected in the tempered martensite. The martensite phase decomposed into ferrite and spherical Fe3C, and interlath-retained austenite decomposed into ferrite and elongated carbide.

  2. Evolution of weld metal microstructure in shielded metal arc welding of X70 HSLA steel with cellulosic electrodes: A case study

    Energy Technology Data Exchange (ETDEWEB)

    Ghomashchi, Reza, E-mail: reza.ghomashchi@adelaide.edu.au; Costin, Walter; Kurji, Rahim

    2015-09-15

    The microstructure of weld joint in X70 line pipe steel resulted from shielded metal arc welding with E6010 cellulosic electrodes is characterized using optical and electron microscopy. A range of ferritic morphologies have been identified ranging from polygonal inter- and intra-prior austenite grains allotriomorphic, idiomorphic ferrites to Widmanstätten, acicular and bainitic ferrites. Electron Backscatter Diffraction (EBSD) analysis using Image Quality (IQ) and Inverse Pole Figure (IPF) maps through superimposition of IQ and IPF maps and measurement of percentages of high and low angle grain boundaries was identified to assist in differentiation of acicular ferrite from Widmanstätten and bainitic ferrite morphologies. In addition two types of pearlitic structures were identified. There was no martensite detected in this weld structure. The morphology, size and chemistry of non-metallic inclusions are also discussed briefly. - Highlights: • Application of EBSD reveals orientation relationships in a range of phases for shielded metal arc welding of HSLA steel. • Nucleation sites of various ferrite morphologies identified • Formation of upper and lower bainite and their morphologies.

  3. Effect of Post-weld Heat Treatment on Microstructure and Fracture Toughness of 30CrMnSiNi2A Steel Welded Joints

    Institute of Scientific and Technical Information of China (English)

    Lixing HUO; Furong CHEN; Yufeng ZHANG; Li ZHANG; Fangjun LIU; Gang CHEN

    2003-01-01

    The electron beam local post-weld heat treatment (EBLPWHT) is a rather new method that provides the advantages ofhigh precision, flexibility and efficiency, energy saving and higher productivity. This paper studies the effect of two post-weldheat treatment processes on the microstructure, mechanical properties and fracture toughness of an electron beam weldedjoints in 30CrMnSiNi2A steel. EBLPWHT, in a vacuum chamber, immediately after welding and a traditional furnace wholepost-weld heat treatment (FWPWHT) were compared. The experimental results show that, after EBLPWHT treatment, themain microstructure of weld was changed from coarse acicular martensite into lath martensite, HAZ was changed from lathmartensite, bainite into lower bainite, and base metal was changed from ferrite and pearlite into upper bainite and residualaustenite. The microstructures of different zones of joints in FWPWHT condition were tempered sorbite. The properties ofwelded joints can be improved by the EBLPWHT in some extent, and especially largely for the fracture toughness of weldedjoints. However the value of fracture toughness of base metal is comparatively low, so appropriate heat treatment parametersshould be explored in the future.

  4. Process Integrated Heat Treatment of a Microalloyed Medium Carbon Steel: Microstructure and Mechanical Properties

    Science.gov (United States)

    Herbst, Sebastian; Schledorn, Mareike; Maier, Hans Jürgen; Milenin, Andrij; Nürnberger, Florian

    2016-04-01

    Air-water spray cooling was employed during a heat treatment to enhance the mechanical properties of microalloyed medium carbon steel test cylinders (38MnVS6, 88 mm diameter). Using appropriate cooling times and intensities, the test cylinders' surfaces could be quenched and subsequently self-tempered by the residual heat of the core. Simultaneously, it was possible to keep the core regions of the cylinders in the bainitic regime and carry out a quasi-isothermal holding. The resulting microstructures consisted of tempered martensite (near-surface) and bainite with pearlite and ferrite (core). Compared to the standard heat treatment (controlled air cooling), the tensile properties (proof stress and ultimate tensile strength) could be improved for both near-surface and core regions with the adapted spray cooling. A hardness profile with 450 HV10 surface hardness and a hardening depth of more than 11 mm could be realized. In addition, an increase of the impact toughness for the core was achieved, resulting in approximately 25 J charpy impact energy. This is a substantial improvement compared to standard heat treatment procedure and values reported in the literature and can be attributed to the reduced pearlite volume fraction and the increased amount of fine bainite.

  5. Development of third generation advanced high strength steels

    Science.gov (United States)

    McGrath, Meghan Colleen

    Lightweight duplex steels with combinations of either bainite, acicular ferrite, and austenite or martensite and austenite were investigated as third generation advanced high strength steels targeted for automotive applications. Large additions of manganese (> 13 wt%) and carbon (Strength and ductility were increased while density was decreased with aluminum additions between 2.4 and 5.5 wt% to the steel. This research addressed the dependence of alloying on microstructures and mechanical behavior for high manganese and aluminum duplex steels that were cast and subsequently hot rolled. Duplex steels with different volume fractions of primary delta-ferrite were used to study the crystallography of austenite fanned during the peritectic reaction. Solute profiles across the peritectic interface showed aluminum segregated near the interface which promoted bainitic ferrite formation. Thermal treatments were used to manipulate the concentration and type of oxides and the ferrite plate density was found to correlate with inclusions of low misfit in steels with austenite grain size of 16.5 microm. A steel with bainite and acicular ferrite produced an ultimate tensile strength of 970 MPa and elongation of 40%. The mechanical prope1iies depended on the strengths and size of the microstructural constituents. Work hardening behavior was examined in a steel exhibiting multiple martensitic transformation induced plasticity (gamma-austenite→epsilon-smartensite→alpha-martensite). A strain hardening exponent as high as 1.4 was observed with ultimate tensile strength and elongation as high as 1,165 MPa and 34%.

  6. Atomic scale effects of alloying, partitioning, solute drag and austempering on the mechanical properties of high-carbon bainitic–austenitic TRIP steels

    International Nuclear Information System (INIS)

    Understanding alloying and thermal processing at an atomic scale is essential for the optimal design of high-carbon (0.71 wt.%) bainitic–austenitic transformation-induced plasticity (TRIP) steels. We investigate the influence of the austempering temperature, chemical composition (especially the Si:Al ratio) and partitioning on the nanostructure and mechanical behavior of these steels by atom probe tomography. The effects of the austempering temperature and of Si and Al on the compositional gradients across the phase boundaries between retained austenite and bainitic ferrite are studied. We observe that controlling these parameters (i.e. Si, Al content and austempering temperature) can be used to tune the stability of the retained austenite and hence the mechanical behavior of these steels. We also study the atomic scale redistribution of Mn and Si at the bainitic ferrite/austenite interface. The observations suggest that either para-equilibrium or local equilibrium-negligible partitioning conditions prevail depending on the Si:Al ratio during bainite transformation.

  7. Characterization of microstructural morphology of austempered ductile iron by electron microscopy.

    Science.gov (United States)

    Guo, X L; Su, H Q; Wu, B Y; Liu, Z G

    1998-02-15

    Mechanical properties of austempered ductile iron (ADI) are mainly controlled by its unique microstructure. The objectives of this paper are to characterize the microstructural morphology and the phase distribution of ADI using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and to determine the mechanism of strengthening and toughening of ADI. The experimental results show that, in the microstructure of ADI composing of upper bainite, retained austenite, graphitic nodule, and a small amount of martensite, the upper bainite is composed of sub-units of ferrite in the shape of "wheat ears" on which the "wheat grains" grow at an angle of about 60 degrees to the long axis of the "wheat ears." The retained austenite is connected with each other in the shape of a continuous net. The wheat-ear like bainite with a homogeneous distribution in the continuous austenite net plays an important role to the strengthening and toughening of ADI. The metastable austenite appears in the shape of a large plate in which the martensite is preferentially formed. The appearance of martensite can be suppressed at the time when retained austenite remains stable, which is of benefit to the continuity and homogeneity of austenite net. PMID:9523764

  8. Effects of Retained Austenite Volume Fraction, Morphology, and Carbon Content on Strength and Ductility of Nanostructured TRIP-assisted Steels

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Yongfeng; Qiu, LN; Sun, Xin; Zuo, Liang; Liaw, Peter K.; Raabe, Dierk

    2015-06-01

    With a suite of multi-modal and multi-scale characterization techniques, the present study unambiguously proves that a substantially-improved combination of ultrahigh strength and good ductility can be achieved by tailoring the volume fraction, morphology, and carbon content of the retained austenite (RA) in a transformation-induced-plasticity (TRIP) steel with the nominal chemical composition of 0.19C-0.30Si-1.76Mn-1.52Al (weight percent, wt.%). After intercritical annealing and bainitic holding, a combination ultimate tensile strength (UTS) of 1,100 MPa and true strain of 50% has been obtained, as a result of the ultrafine RA lamellae, which are alternately arranged in the bainitic ferrite around junction regions of ferrite grains. For reference, specimens with a blocky RA, prepared without the bainitic holding, yield a low ductility (35%) and a low UTS (800 MPa). The volume fraction, morphology, and carbon content of RA have been characterized using various techniques, including magnetic probing, scanning electron microscopy (SEM), electron-backscatter-diffraction (EBSD), and transmission electron microscopy (TEM). Interrupted tensile tests, mapped using EBSD in conjunction with the kernel average misorientation (KAM) analysis, reveal that the lamellar RA is the governingmicrostructure component responsible for the higher mechanical stability, compared to the blocky one. By coupling these various techniques, we quantitatively demonstrate that in addition to the RA volume fraction, its morphology and carbon content are equally important in optimizing the strength and ductility of TRIP-assisted steels.

  9. Effects of retained austenite volume fraction, morphology, and carbon content on strength and ductility of nanostructured TRIP-assisted steels

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Y.F., E-mail: shenyf@smm.neu.edu.cn [Key Laboratory for Anisotropy and Texture of Materials (MOE), Northeastern University, 3 Wenhua Road, Shenyang 110004 (China); Qiu, L.N. [Key Laboratory for Anisotropy and Texture of Materials (MOE), Northeastern University, 3 Wenhua Road, Shenyang 110004 (China); Sun, X. [Pacific Northwest National Laboratory, PO Box 999, Richland, WA 99352 (United States); Zuo, L. [Key Laboratory for Anisotropy and Texture of Materials (MOE), Northeastern University, 3 Wenhua Road, Shenyang 110004 (China); Liaw, P.K. [Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996 (United States); Raabe, D. [Max-Planck-Institut fuer Eisenforschung, Max-Planck-Str. 1, 8, 40237 Düsseldorf (Germany)

    2015-06-11

    With a suite of multi-modal and multi-scale characterization techniques, the present study unambiguously proves that a substantially-improved combination of ultrahigh strength and good ductility can be achieved by tailoring the volume fraction, morphology, and carbon content of the retained austenite (RA) in a transformation-induced-plasticity (TRIP) steel with the nominal chemical composition of 0.19C–0.30Si–1.76Mn–1.52Al (weight percent, wt%). After intercritical annealing and bainitic holding, a combination of ultimate tensile strength (UTS) of 1100 MPa and true strain of 50% has been obtained, as a result of the ultrafine RA lamellae, which are alternately arranged in the bainitic ferrite around junction regions of ferrite grains. For reference, specimens with a blocky RA, prepared without the bainitic holding, yield a low ductility (35%) and a low UTS (800 MPa). The volume fraction, morphology, and carbon content of RA have been characterized using various techniques, including the magnetic probing, scanning electron microscopy (SEM), electron-backscatter-diffraction (EBSD), and transmission electron microscopy (TEM). Interrupted tensile tests, mapped using EBSD in conjunction with the kernel average misorientation (KAM) analysis, reveal that the lamellar RA is the governing microstructure component responsible for the higher mechanical stability, compared to the blocky one. By coupling these various techniques, we quantitatively demonstrate that in addition to the RA volume fraction, its morphology and carbon content are equally important in optimizing the strength and ductility of TRIP-assisted steels.

  10. Morphology and crystallographic orientation relationship in isothermally transformed Fe–N austenite

    International Nuclear Information System (INIS)

    The 225 °C isothermal transformation of a high-nitrogen austenite with Fe–2.71 wt.% N was investigated by means of electron microscopy. It was found that the transformation products were composed of ultrafine α-Fe and γ′-Fe4N plus retained austenite γ, which were in two types of morphologies, namely, (i) with the retained austenite patches dispersed among the (α-Fe + γ′-Fe4N) packets and (ii) with the ultrafine α-Fe and γ/γ′-Fe4N laths interwoven with each other within a single bainitic packet. A cube–cube orientation relationship between the γ (austenite) and γ′-Fe4N, and a near Greninger–Troiano (G–T) one between the γ (austenite) and the bainitic α-ferrite were detected. The morphology, orientation relationship and high hardness (> 1000 HV) of the transformation products indicated that the isothermal transformation of the high nitrogen austenite was analogous to a bainitic one. - Highlights: • Isothermal transformation products consisted of nano-sized α-Fe + γ′ + γ (retained). • The hardness of transformation product exceeded 1000 HV. • The α-Fe and γ/γ′-Fe4N kept a near G-T OR in the grain interior

  11. Morphology and crystallographic orientation relationship in isothermally transformed Fe–N austenite

    Energy Technology Data Exchange (ETDEWEB)

    Jiao, Dongling, E-mail: dljiao@scut.edu.cn [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Luo, Chengping; Liu, Jiangwen [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Zhang, Guoqing [Science and Technology on Advanced High Temperature Structural Materials Laboratory, Beijing Institute of Aeronautical Materials, Beijing 100095 (China)

    2014-02-15

    The 225 °C isothermal transformation of a high-nitrogen austenite with Fe–2.71 wt.% N was investigated by means of electron microscopy. It was found that the transformation products were composed of ultrafine α-Fe and γ′-Fe{sub 4}N plus retained austenite γ, which were in two types of morphologies, namely, (i) with the retained austenite patches dispersed among the (α-Fe + γ′-Fe{sub 4}N) packets and (ii) with the ultrafine α-Fe and γ/γ′-Fe{sub 4}N laths interwoven with each other within a single bainitic packet. A cube–cube orientation relationship between the γ (austenite) and γ′-Fe{sub 4}N, and a near Greninger–Troiano (G–T) one between the γ (austenite) and the bainitic α-ferrite were detected. The morphology, orientation relationship and high hardness (> 1000 HV) of the transformation products indicated that the isothermal transformation of the high nitrogen austenite was analogous to a bainitic one. - Highlights: • Isothermal transformation products consisted of nano-sized α-Fe + γ′ + γ (retained). • The hardness of transformation product exceeded 1000 HV. • The α-Fe and γ/γ′-Fe{sub 4}N kept a near G-T OR in the grain interior.

  12. Thermal distortion analysis method for TMCP steel structures using shell element

    Science.gov (United States)

    Ha, Yunsok; Rajesh, S. R.

    2009-12-01

    As ships become larger, thicker and higher tensile steel plate are used in shipyard. Though special chemical compositions are required for high-tensile steels, recently they are made by the TMCP (Thermo-Mechanical control process) methodology. The increased Yield / Tensile strength ofTMCP steels compared to the normalized steel of same composition are- induced by suppressing the formation of Ferrite and Pearlite in favor of strong and tough Bainite -while being transformed from Austenite. But this Bainite phase could be vanished by another additional thermal cycle like welding and heating. As thermal deformations are deeply related by yield stress of material, the study for prediction of plate deformation by heating should reflect the principle of TMCP steels. The present study is related to the development of an algorithm which could calculate inherent strain. In this algorithm, not only the mechanical principles of thermal deformations, but also the initial portion of Bainite is considered when calculating inherent strain. Distortion analysis results by these values showed good agreements with experimental results for normalized steels and TMCP steels during welding and heating. This algorithm has also been used to create an inherent strain database of steels in Class rule.

  13. Effect of microalloying elements and hot deformation on microstructure of direct-quenched steel plates

    International Nuclear Information System (INIS)

    The effects of microalloys (Nb, V, Ti and Nb-Ti) and hot deformation on microstructure were investigated in direct-quenched HSLA steels. Nb and Ti were shown to improve both strength and toughness of the steels, while V showed little effectiveness in improving the strength of the steels. Quantitative analysis showed that dissolved NB and Ti in austenite increased the hardenability of austenite, so that they refined the ferrite grain size and increased the fraction of bainite in the steels. On the other hand, dissolved V was much less effective in increasing;the hardenability of austenite. It was found that an addition of 0.03%Nb decreases the strength of Ti bearing steels reheated to a low temperature. Combined additions of microalloying elements decreases the solubility of carbonitrides and reduces the amount of dissolved microalloying elements in austenite during reheating through the formation of complex precipitates. Controlled rolling below 950 C had a considerable effect on improving the toughness of Nb bearing direct-quenched steels. Deformation of more than 50% in the un-recrystallized austenite region significantly refined the bainite microstructure, while deformation of less than 30% was less effective. It was shown that the increase in toughness due to the heavy deformation of un-recrystallized austenite resulted from the decrease in the length of lathlike ferrite and the decrease in the packet size of bainite

  14. Effect of Cooling Rate and Deformation on Microstructures and Critical Phase-Transformation Temperature of Boron-Nickel Added HSLA H-Beams

    Institute of Scientific and Technical Information of China (English)

    WANG Xiao; WANG Zuo-cheng; WANG Xie-bin; WANG Yi-ran; GAO Jun-qing; ZHAO Xiu-ling

    2012-01-01

    Microstructures and critical phase-transformation temperature of boron-nickel added Nb-treated high strength low alloy (HSLA) H-beams cooled at different cooling rate, with different deformation were investigated. Continuous cooling transformation (CCT) diagram of this new type of steel was obtained by using Gleeble 1500 ther- momechanical simulator. Microstructures and hardness, especially micro-hardness of the experimental steel were in- vestigated by optical microscopy (OM), scanning electron microscope (SEM), Rockwell and Vickers hardness tests. Phase analysis was also studied by X~ray diffraction (XRD). The results indicated that with increase of cooling rate, microstructures of continuous cooled specimens gradually transformed from polygonal ferrite and pearlite, grain boundary ferrite and bainite, bainite and martensite to single martensite. The CCT diagram revealed that slow cool- ing was needed to avoid austenite-bainite transformation to ensure toughness of this steel. By plastic deformation of 40%, austenite-ferrite transformation temperature increased by 46℃, due to deformation induced ferrite transfor- mation during continuous cooling, but Rockwell hardness has little change.

  15. Friction Stir Welding of Steel: Heat Input, Microstructure, and Mechanical Property Co-relation

    Science.gov (United States)

    Husain, Md. M.; Sarkar, R.; Pal, T. K.; Prabhu, N.; Ghosh, M.

    2015-09-01

    Friction stir welding was performed to join carbon steel plates at tool rotational rate of 800-1400 rpm. Microstructure and microhardness of welded specimens were evaluated across weld centerline. Torque base index, peak temperature, cooling rate, strain, strain rate, volumetric material flow rate, and width of extruded zone at weld nugget were calculated. Peak temperature at weld nugget was ~1300-1360 K. At this temperature, ferrite transformed to austenite during welding. Austenite was decomposed in to ferrite and bainite at cooling rate of ~4-7.5 K/s. The presence of bainite was endorsed by increment in microhardness with respect to base material. Ferrite grain size at weld nugget was finer in comparison to as-received alloy. With the increment in tool rotational rate strain, strain rate, total heat input, and peak temperature at weld nugget were increased. High temperature at weld nugget promoted increment in ferrite grain size and reduction in area fraction of bainite. Heat-affected zone also experienced phase transformation and exhibited enhancement in ferrite grain size in comparison to base alloy at all welding parameters with marginal drop in microhardness. Maximum joint strength was obtained at the tool rotational rate of 1000 rpm. Increment in tool rational rate reduced the joint efficiency owing to increment in ferrite grain size and reduction in pearlite area fraction at heat-affected zone.

  16. Segregation of alloying elements in thermomechanically rolled medium-Mn multiphase steels

    Directory of Open Access Journals (Sweden)

    A. Grajcar

    2012-12-01

    Full Text Available Purpose: The aim of the paper is to assess the tendency of alloying elements to macro- and microsegregation during hot-forging and successive thermomechanical rolling of medium-Mn Al-bearing steel sheets.Design/methodology/approach: The macro- and microsegregation of alloying elements was assessed by EDS and WDS measurements across the thickness of the roughly-forged flats and thermomechanically processed 3.3 mm sheets. The microstructure was revealed using combined methods of optical microscopy (OM and scanning electron microscopy (SEM. Morphological features of microstructural constituents were discussed with focusing on retained austenite. Findings: It was found that the final multiphase microstructure is mainly dependent on the Mn content and the effect of Nb microaddition is relatively low. The 3Mn steels possess very fine bainite-based microstructures whereas the steels containing 5% Mn are characterized by lath bainitic-martensitic microstructures. All the steels contain retained austenite as fine granules or layers located between bainitic ferrite laths. Some fraction of martensite-austenite (M-A islands was also identified. The tendency of Mn and Al to macrosegregation was found after the initial hot-forging. It disappears after successive rough and thermomechanical rolling whereas thin martensite and martensite-austenite microbands as a result of Mn microsegregation locally occur.Research limitations/implications: Further investigations are required to quantify the local changes of chemical composition especially in formed microbands and X-ray quantitative phase analysis should be applied to assess a fraction of retained austenite.Practical implications: The knowledge of the macro- and microsegregation of alloying elements in advanced medium-Mn steels containing retained austenite can be useful in designing the thermomechanical rolling procedures of multiphase steel sheets.Originality/value: A problem of macro- and microsegregation of

  17. Deformation and fracture of low alloy steels at high temperature

    Energy Technology Data Exchange (ETDEWEB)

    Marriott, D.L.; Stubbins, J.F.; Leckie, F.A.; Muddle, B.

    1988-12-01

    This project formed part of the initiative in the AR TD program to characterize high temperature, time-dependent damage processes in low alloy steels, for use in the construction of coal-gasification plant. This project was broadly aimed at adding to the knowledge base for this bainitic form of 2.25Cr 1Mo steel, as it related to time-dependent performance at elevated temperature. Its original intention was to obtain information in specific grades of 2.25Cr 1Mo steel, in particular those containing reduced residual elements and microalloyed modifications, which were being considered as candidate materials at the time. This objective was subsequently modified, in the course of the contract period, to a more generic study of bainitic steel, using the 2.25Cr 1Mo material as a representative of the class. The main thrust of the project was directed initially at the detrimental effect of cyclic loading on creep resistance and manifesting itself in an apparently severe creep-fatigue interaction. Three subtasks were eventually identified. These are: a study of the evolution of microstructural changes in bainitic materials during steady load creep and under constant amplitude cyclic deformation, investigation of the effect of cyclic softening on the fatigue and creep strength of complex geometries, focusing on circumferentially notched bars, and investigation of the influence of environment as a possible cause of observed fatigue/elevated temperature interaction through its effects on crack initiation and propagation, using EDM notched specimens tested in air and vacuum. Results are discussed. 24 refs., 40 figs., 5 tabs.

  18. Continuous Cooling Phase Transformation of ERW-N80-1 Steel for Oil Casting%石油套管用钢ERW-N80-1的连续冷却相变

    Institute of Scientific and Technical Information of China (English)

    黄明浩; 黄国建; 张英慧; 李桂艳

    2011-01-01

    采用Gleebl-3800热摸拟试验机,测定了石油套管用钢ERW-N80-1的动态CCT曲线,并通过光学显微镜和电子显微镜对连续冷却后的组织和第二相析出物进行了观察和分析。结果表明:随着冷却速度的提高,在连续冷却转变组织中依次出现多边形铁素体、粒状贝氏体、板条状贝氏体、针状贝氏体、板条状马氏体和针状马氏体,M/A组织的形貌依次为细长形、三角形、方形或圆形,高硬度相逐渐增多,试样的宏观硬度逐渐增加;同时,第二相粒子的尺寸趋于均匀,并逐渐细化。%The CCT carve of ERW-N80-1 steel was determined with Gleeble-3800 thermal simulation testing machine.Microstructures and secondary phase after different cooling rates were characterized by optical microscope and electronic microscope(SEM and TEM).The results show that along with increase of cooling speed the microstructures are changed in turn from polygonal ferrite,granular bainite,lath bainite,needle-like bainite,lath martensite and needle-type martensite,slender form,triangle,quadratic form or circle for M/A microstructures.With increase in high hardness phase,sample′s macrohardness is high.At the same time,the size of the secondary phase is homogeneous and fine gradually.

  19. Relationship between crystallographic structure of the Ti2O3/MnS complex inclusion and microstructure in the heat-affected zone (HAZ) in steel processed by oxide metallurgy route and impact toughness

    International Nuclear Information System (INIS)

    A new method based on electron back scattered diffraction (EBSD) is proposed to determine the structure of titanium oxide/MnS complex inclusion which induced the formation of intragranular acicular ferrite (IAF) in heat-affected zone (HAZ) in steel processed by oxide metallurgy route. It was found that the complex inclusion was Ti2O3/MnS, the orientation relationship between Ti2O3 and MnS was also examined, and the crystallographic orientation relationship among IAF, Ti2O3/MnS complex inclusion, austenite, bainite formed at lower temperature is researched systematically. It was observed that MnS precipitated on Ti2O3 at specific habit plane and direction and MnS had a specific orientation relationship ((0001) Ti2O3//(111) MnS), <10–10> Ti2O3//<110> MnS) with respect to Ti2O3. Intragranular acicular ferrite (IAF) nucleated on MnS part of the Ti2O3/MnS complex inclusion had no specific orientation relationship with MnS. IAF and the surrounding bainite had different Bain groups, so that there was an increase in high angle boundaries, which was beneficial for the toughness of HAZ. - Highlights: • The inclusion of TiOx/MnS that induced IAF formation is identified to be Ti2O3/MnS. • The inclusion is identified based on electron back scattered diffraction (EBSD). • MnS and Ti2O3 had specific orientation relationship of Ti2O3/MnS complex inclusion. • The IAFs formed on the same inclusion tend to be in one Bain group. • IAF and the surrounding bainite tend to be in different Bain groups

  20. Ferrite morphology and residual phases in continuously cooled low carbon steels

    International Nuclear Information System (INIS)

    Although much research has been conducted on the isothermal transformation products of medium to high carbon hardenable steels, relatively little has been reported for transformation of low carbon structural steels under continuous cooling conditions. The trend towards reduced carbon levels (less than about 0.1 wt% C) has been driven by demands for formability and weldability, challenging steel designers to maintain strength by microalloying and/or thermomechanical controlled processing. Although control of the ferritic products formed in low carbon steels after hot rolling, normalising and welding is essential in order to ensure adequate strength and toughness, understanding of the microstructures formed on continuous cooling is still limited. In addition, transformation mechanisms remain controversial because of polarisation of researchers into groups championing diffusional and displacive theories for the transformation of austenite over a wide range of cooling rates. The present review compares and draws together the main ferrite classification schemes, and discusses some critical issues on kinetics and mechanisms, in an attempt to rationalise the effects of cooling rate, prior austenite structure and composition on the resulting ferrite structure and its mechanical properties. It is concluded that with increasing cooling rate the ferritic product becomes finer, more plate-like, more dislocated, more carbon supersaturated, more likely to be formed by a displacive mechanism, harder and stronger. Other conclusions are that: (i) 'bainitic ferrite', which is a pervasive form of ferrite in continuously cooled low carbon steels, is different from the conventional upper and lower bainites observed in higher carbon steels, insofar as the co-product 'phase' is typically martensite-austenite islands rather than cementite; and (ii) low carbon bainite rather than martensite is the dominant product at typical fast cooling rates (<500K/s) associated with commercial

  1. Investigation on the crystallography of the transformation products of reverted austenite in intercritically reheated coarse grained heat affected zone

    International Nuclear Information System (INIS)

    Highlights: ► Area of reverted austenite is traced out by crystallographic information. ► Bainite and martensite regions were confirmed within it. ► The martensite region is considered as the blocky MA particles. ► Martensite region has high deformation to initiate fracture. ► More uniform transformation of the reverted austenite is good for toughness. -- Abstract: In present study the intercritically reheated coarse grained heat affected zone (ICCGHAZ) showing the worst impact toughness in the heat affected zone of multi-pass welding was simulated by Gleeble-1500, and its microstructure was investigated in detail by means of scanning electron microscope (SEM) and electron backscattering diffraction (EBSD). With the crystallographic information from EBSD scanning the area of a single reverted austenite grain which formed during the thermal cycles of second pass simulation was traced out. Within it two regions with different characteristic both in morphology and crystallography were found out, showing an un-uniform transformation of the reverted austenite. The region I is a bainitic region containing larger bainitic ferrite grains, while the region II is made up of several clusters containing tiny grains. Based on the crystallographic information each cluster was determined as martensite island thereby should be considered as blocky Martensite/Austenite constituent (M/A), which is hard phase and harmful for toughness. Analysis on the level of deformation shows that the region II is much higher deformed than the region I, indicating there is high stress concentration within the region II. The possible influence of the region I and the region II on fracture is discussed under the early proposed M/A’s fracture-initiating mechanisms. It suggests that the main cause of the toughness reduction is the un-uniform transformation of the reverted austenite, and the toughness performance of the ICCGHAZ could be improved if the transformation of the reverted

  2. Effect of Aluminum and Silicon on Transformation Induced Plasticity of the TRIP Steel

    Institute of Scientific and Technical Information of China (English)

    Lin LI; B.C. De Cooman; P. Wollants; Yanlin HE; Xiaodong ZHOU

    2004-01-01

    With the sublattice model, equilibrium compositions of ferrite (α) and austenite (γ) phases, as well as the volume percent of austenite (γ) at 780℃ in different TRIP steels were calculated. Concentration profiles of carbon, Mn, Al and Si in the steels were also estimated under the lattice fixed frame of reference so as to understand the complex mechanical behavior of TRIP steels after different isothermal bainitic transformation treatments. The effect of Si and Mn on transformation induced plasticity (TRIP) was discussed according to thermodynamic and kinetic analyses. It is recognized that Al also induces phase transformation in the steels but its TRIP effect is not as strong as that of Si.

  3. Friction stir processing on high carbon steel U12

    Energy Technology Data Exchange (ETDEWEB)

    Tarasov, S. Yu., E-mail: tsy@ispms.ru; Rubtsov, V. E., E-mail: rvy@ispms.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); National Research Tomsk Polytechnic University, Tomsk, 634050 (Russian Federation); Melnikov, A. G., E-mail: melnikov-ag@tpu.ru [National Research Tomsk Polytechnic University, Tomsk, 634050 (Russian Federation)

    2015-10-27

    Friction stir processing (FSP) of high carbon steel (U12) samples has been carried out using a milling machine and tools made of cemented tungsten carbide. The FSP tool has been made in the shape of 5×5×1.5 mm. The microstructural characterization of obtained stir zone and heat affected zone has been carried out. Microhardness at the level of 700 MPa has been obtained in the stir zone with microstructure consisting of large grains and cementitte network. This high-level of microhardness is explained by bainitic reaction developing from decarburization of austenitic grains during cementite network formation.

  4. Mechanical properties and microstructure of TRIP steels produced using TSCR process

    Institute of Scientific and Technical Information of China (English)

    Yinghui Zhang; Yanli Ma; Yonglin Kang; Hao Yu

    2006-01-01

    C-Si-Mn TRIP steels were produced using the thin slab casting and rolling (TSCR) process under simulation in laboratory. The results of tensile tests show that the yield strength, tensile strength, and the total elongation of the experimental TRIP steels are 430 MPa, 610 MPa, and 28.4%, respectively. Optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed to identify the microstructures of the TRIP steels. The final microstructures consist of ferrite, bainite, and retained austenite. The results of quantitative color metallography show that the fraction of the retained austenite is about 5.8%.

  5. Development of an optimized methodology for tensile testing of carbon steels in hydrogen environment

    OpenAIRE

    Cuadros Fernández, Pau; Baró, M.D.

    2009-01-01

    The study was performed at OCAS, the Steel Research Centre of ArcelorMittal for the Industry market. The major aim of this research was to obtain an optimized tensile testing methodology with in-situ H-charging to reveal the hydrogen embrittlement in various high strength steels. The second aim of this study has been the mechanical characterization of the hydrogen effect on hight strength carbon steels with varying microstructure, i.e. ferrite-martensite and ferrite-bainite grades. The optima...

  6. TRIP型ベイニティックフェライト鋼板の伸びフランジ性に及ぼすYAGレーザ切断パルスエネルギーの影響

    OpenAIRE

    長坂, 明彦; 窪田, 優一; 川尻, 將洋; 三尾, 敦; 北條, 智彦; 槙井, 浩一; NAGASAKA, Akihiko; Kubota, Yuichi; KAWAZIRI, Hiromasa; MIO, Atsushi; HOJO, Tomohiko; MAKII, Koichi

    2007-01-01

    In the present work, effect of YAG laser cutting pulse energy on stretch-flangeability in 0.2C-1.5Si-1.5Mn ultra high-strength TRIP-aided sheet steel with bainitic ferrite matrix (TBF steel) which were austempered at 375 or 450℃ was investigated for automotive applications. The tensile strength (TS) of TBF steel austempered at 375℃ was higher than that of TBF steel austempered at 450℃. The press formability of laser cut surface layer was investigated by hole-expanding test. On the other hand,...

  7. EXPERIMENTAL STUDY ON MACRO AND MICRO-STRUCTURE OF METALLIC PARTS BUILT BY LOW-POWER LASER CLADDING

    Institute of Scientific and Technical Information of China (English)

    Liu Jichang; Li Lijun

    2005-01-01

    A low-power CO2 laser is used to deposit Fe powder and mixture of Fe and carbon powder on substrates respectively, and the macro and micro-structure of the formed samples are investigated.It is demonstrated that most grains of these samples are equi-axed. This is derived from the high nucleation velocity in the shallow melt pool besides rapid solidification of the liquid-state alloy or metal. Bainitic structure,combination of pearlite and ferrite structure and ferrite structure are seen respectively in the samples involving various amounts of carbon owing to no martensitic transformation in these small samples.

  8. Factors Influencing the Wear Behavior of Sintered Steels%影响烧结钢磨损行为的因素

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A review was made on the research progress of wear behavior of sintered steels in recent years. Wear is not an intrinsic property of sintered steels, which is strongly influenced by the wear test conditions. However, many other factors that determine the mechanical properties of sintered steels also affect the wear behavior. Porosity has different effects on the wear of sintered steels depending on the application conditions. Under dry sliding condition, higher porosity results in lower wear resistance. The influence of microstructures on wear resistance is in the order: carbide, martensite, bainite and lamellar pearlite. The wear resistance increases with hardness, but this relationship changes with the porosity and microstructures of sintered steels.

  9. Structural investigations of local non-homogeneities in thermally treated nitrided layers in carbon steels

    International Nuclear Information System (INIS)

    In order to improve steel performance in some applications the nitrided layers in steel may be subjected to additional heat treatment. One of the forms of such treatment is the incorporate quench hardening from the diphase α-γ area on the Fe-C diagram. This treatment results in secondary diffusion of nitrogen into the base metal, decompose of the surface nitride layer and an increase in the thickness of the hardened layer. An incomplete α-γ transition creates zones of varied bainite-martensite structures with varying nitrogen concentration and hardness. (author)

  10. Method for the calculation of volumetric fraction of retained austenite through the software for analysis of digital images; Metodo para o calculo da fracao volumetrica de austenita retida atraves do software de analise digital de imagens

    Energy Technology Data Exchange (ETDEWEB)

    Lombardo, S.; Costa, F.H.; Hashimoto, T.M.; Pereira, M.S., E-mail: sandro_Lombardo@hotmail.co [UNESP, Guaratingueta, SP (Brazil). Fac. de Engenharia; Abdalla, A.J. [Centro Tecnico Aeroespacial (CTA-IEAv), Sao Jose dos Campos, SP (Brazil). Inst. de Estudos Avancados

    2010-07-01

    In order to calculate the volume fraction of the retained austenite in aeronautic multiphase steels, it was used a digital analysis software for image processing. The materials studied were steels AISI 43XX with carbon content between 30, 40 and 50%, heat treated by conventional quenching and isothermal cooling in bainitic and intercritical region, characterized by optical microscopy, etching by reagent Sodium Metabisulfite (10%) for 30 seconds, with forced drying. The results were compared with the methods of X-Ray Diffraction and Magnetic Saturation through photomicrographs, showing that with this technic it is possible to quantify the percentage of retained austenite in the martensitic matrix, in the different types of steels. (author)

  11. Multi scale study of the plasticity at low temperature in α-iron: application for the cleavage

    International Nuclear Information System (INIS)

    An accident inside a nuclear power plant may lead to the cleavage of the nuclear vessel made of bainitic steel. In order to understand the origin of this fracture, we studied BCC-iron plasticity at low temperature using numerical simulations at different scales. Molecular Dynamics simulations show the high dependency of screw dislocation motion with temperature and stress. Results from these simulations were added to experiment data to develop a new Dislocation Dynamics code dedicated to BCC iron at low temperature. The code was used to model plasticity into a ferritic lath for various temperatures. This work confirms that cleavage is favoured by low temperatures. (author)

  12. Mössbauer studies on an AISI 1137 type steel

    Indian Academy of Sciences (India)

    E Güler; H Akta

    2006-06-01

    An AISI 1137 type medium carbon steel was studied by means of scanning electron microscopy and Mössbauer spectroscopy. This steel in as received state at room temperature was ferritic. Different heat treatments on related steel exhibited different microstructures such as pearlite and bainite. Also magnetism of these product phases was determined as 32.7 T and 32.6 T relatively where ferromagnetism of ferritic phase in as received state was 33.05 T. Mössbauer parameters such as isomer shifts and % volumes were also determined before and after transformations.

  13. FACTORS INFLUENCING THE WEAR BEHAVIOR OF PM STEELS

    Institute of Scientific and Technical Information of China (English)

    J.A. Wang; H. Danninger

    2001-01-01

    A review was made on the research progress of wear behavior of PM steels in recentyears. Wear is not an intrinsic property of PM steels, which is strongly influencedby the wear test conditions. However, many other factors that determine the me-chanical properties of PM steels also affect the wear behavior. Porosity has differenteffects on the wear of PM steels depending on the application conditions. Under drysliding condition, higher porosity results in lower wear resistance. The influence ofmicrostructures on wear resistance was in the order: carbide, martensite, bainite andlamellar pearlite. The wear resistance increases with hardness, but this relationshipchanges with the porosity and microstructures of PM steels.``

  14. Estimation du risque de rupture fragile de soudures de pipelines en aciers à haut grade : caractérisation et modélisation

    OpenAIRE

    Bilat, Anne-Sophie

    2007-01-01

    As a consequence to reduction of gas transportation costs, pressure inside pipe will tend to increase. To achieve it, ferritic-bainitic steel with high strength, such as X100 (yield strength above 100 ksi, or 690 MPa) were developed. Girth welds of modern line pipe steel X100, issued from a pulsed automatic gas metal arc welding, were tested to check their performance in artic temperature conditions. It is shown that an impact specimen at -20 °C with a notch placed in the middle of the fusion...

  15. Low alloy steel versus ADI – differences and similarities

    Directory of Open Access Journals (Sweden)

    A. Krzyńska

    2009-01-01

    Full Text Available The results of comparison between the microstructure of selected bainitic low alloy steel and austempered ductile iron ADI are presented. The aim of the comparison was to find out differences and similarities existing in these iron carbon commercial alloys. In this paper our own results on ADI structure and literature data were used. It follows from discussion presented here that both microstructure and properties of ADI are very close that which are observed in low alloy carbon steel. Moreover, we suggest that there is no so doubt to treat ADI mechanical properties as steel containing nodular inclusions of graphite.

  16. Prediction of mechanical properties of hot rolled steel by ultrasonic method

    International Nuclear Information System (INIS)

    The ultrasonic attenuation and the velocity in hot rolled steel have been evaluated by ultrasonic contact measurement. The measured attenuation is calibrated by diffraction correction integral suggested by Lommel. The attenuation is also calculated by the model suggested by Mason. The agreement between the experimentally determined attenuation and the calculated one was good. As the results, the mechanical properties of the ferrite plus pearlite steels could be assessed by the ultrasonic attenuation. The mechanical properties of the martensite plus bainite steels could be assessed by the ultrasonic velocity.

  17. Influence of Hot Deformation and Subsequent Austempering on the Mechanical Properties of Hot Rolled Multiphase Steel

    Institute of Scientific and Technical Information of China (English)

    Zhuang LI; Di WU

    2006-01-01

    Influence of hot deformation and subsequent austempering on the mechanical properties of hot rolled multiphase steel was investigated. Thermo-mechanical control processing (TMCP) was conducted by using a laboratory hot rolling mill, where three different kinds of finishing rolling reduction, and austemperings with various isothermal holding duration were applied. The results have shown that a multiphase microstructure consisting of polygonal ferrite, granular bainite and larger amount of stabilized retained austenite can be obtained by controlled rolling processes. Mechanical properties increase with increasing the amount of deformation because of the stabilization of retained austenite. Ultimate tensile strength (σb), total elongation (δ)36% and 28476 MPa%, respectively) at optimal processes.

  18. A Special TMCP Used to Develop a 800MPa Grade HSLA Steel

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The effect of relaxation after finished rolling on structure s and properties of four microalloyed steel with different content of Nb and Ti was investigated. By alloy designing and control rolling+rel axation-precipitation-control phase transformation (RPC) process, a ne w 800MPa grade HSLA plate steel could be obtained, the microstructure is composite ultra-fine lath bainite/martensite. The tempering process and mechanical properties of this kind of HSLA steel were investigate d. The yield strength can achieve 800MPa, and the ductility and impact toughness is satisfied.

  19. Effect of the Carbides and Matrix on the Wear Resistance of Nodular Cast Iron

    Directory of Open Access Journals (Sweden)

    G. Gumienny

    2013-07-01

    Full Text Available This paper presents the results of the abrasive wear resistance of selected types of nodular cast iron, including ADI, cooperating with quartz sand and 100 grit abrasive paper. It has been shown that carbides in nodular cast iron cause an increase in wear resistance of 6 to 12% depending on the surface fraction of the carbides and type of the matrix. For the same unit pressure the mass loss of the cast iron cooperating with quartz sand is many times larger than the cast iron cooperating with abrasive paper. For both abrasives the highest wear resistance showed nodular cast iron with upper and lower bainite and carbides.

  20. Modeling of Austenite Decomposition in Low Si-Mn TRIP Steel During Cooling

    Institute of Scientific and Technical Information of China (English)

    ZHU Li-juan; WU Di; ZHAO Xian-ming

    2008-01-01

    Transformation behavior in low carbon Si-Mn TRIP steel was investigated by means of microstructural observation and computer modelling. A transformation model in which transformation is controlled by carbon diffusion was suggested,which well described the volume fractional change of ferrite,pearlite,and bainite during continuous cooling.The influence of Si content and austenite grain size was thoroughly investigated.The calculated results indicated that Si retards pearlite transformation,accelerates polygonal ferrite transformation,refines the austenite grain,and increases the ferrite transformation rate.

  1. Effect of Austenite Deformation on Continuous Cooling Transformation Microstructures for 22CrSH Gear Steel

    Institute of Scientific and Technical Information of China (English)

    WANG Bing-xin; JIANG Ying-tian; XU Xu-dong; LIU Xiang-hua; WANG Guo-dong

    2007-01-01

    The effect of compressive deformation of austenite on continuous cooling transformation microstructures for 22CrSH gear steel has been investigated using a Gleeble 1500 thermal simulator. The experimental results show that the deformation of austenite promotes the formation of proeutectoid ferrite and pearlite, and leads to the increase of critical cooling rate of proeutectoid ferrite plus pearlite microstructure. The grain boundary allotriomorphic ferrite occupies the austenite grain surfaces when the prior deformation takes place or the cooling rate is decreased, which causes a transition from bainite to acicular ferrite. The deformation enhances the stability of transformation from austenite to acicular ferrite, which results in an increase of M/A constituent.

  2. EFFECT OF AUSTEMPERING ON TRANSFORMATION INDUCED PLASTICITY OF HOT ROLLED MULTIPHASE STEELS

    Institute of Scientific and Technical Information of China (English)

    Z.Li; D. Wu

    2007-01-01

    Effect of austempering on the transformation induced plasticity (TRIP) of hot rolled multiphase steel was investigated. Polygonal ferrite, granular bainite, and a large amount of stabilized retained austenite could be obtained in the hot rolled multiphase steel. Strain induced martensite transformation (SIMT) of retained austenite and TRIP effectively occur under straining owing to austempering after hot rolling, and mechanical properties of the present steel remain at a relatively high constant value for austempering at 400℃. The mechanical properties of the steel exhibited a good combination of tensile strength (791MPa) and total elongation (36%) because the stability of retained austenite is optimal when the steel is held for 20min.

  3. Application of neural networks to forecasting the CCT curves

    International Nuclear Information System (INIS)

    The paper presents methodology of modeling using neural networks of the relationship between the chemical composition and austenitising temperature, and the supercooled austenite transformation kinetics during the continuous cooling. The model worked out makes it possible to calculate a complete CCT diagram for the steel with a known chemical composition and analysis of the influence of particular elements on the characteristic points and transformation curves of supercooled austenite, and also the hardness resulting from cooling. It makes also possible forecasting of the structure developed in the steel as a result of cooling at a particular rate, by the quantitative description of the percentages of ferrite, pearlite, bainite and martensite with retained austenite. (author)

  4. Abnormal relationship between rust particles size and rust layer compactness of weathering steels

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    In order to reveal evolution of the rust layer during atmospheric corrosion,commercial weathering steel(WS) 09CuPCrNi and a recently developed bainite WS were subjected to a salt fog test.The protection and compactness of the rust layer were evaluated by electrochemical analysis,absorption-desorption test,etc.The experimental results indicate that more compact rust layer could be derived from the rust particles with larger size.The well-established notion that the rust particle growth can induce the decreme...

  5. Experimental Study of Microstructure Evolution during Tempering of Quenched Steel and Its Application

    Institute of Scientific and Technical Information of China (English)

    SHIWei; YAOKe-fu; CHENNan; WANGHong-peng

    2004-01-01

    Microstructure evolution during tempering of quenched steel was studied via dilatometric experiments.Temperature ranges of transformation were determined by a relative dilation curve. The thermal expansion coefficient of quenched steel was defined as a function of temperature. The transformation expansion is determined by subtracting thermal expansion from a measured diameter dilation curve. A kinetic equation based on tempering parameter was proposed to predict the microstructure evolution fraction of martensite and bainite of Ni3.SCrMoV and C45 steel. The kinetic equation was used in an in-house FEM code. The internal stress evolution of a quenched generator rotor was investigated.

  6. Experimental Study of Microstructure Evolution during Tempering of Quenched Steel and Its Application

    Institute of Scientific and Technical Information of China (English)

    SHI Wei; YAO Ke-fu; CHEN Nan; WANG Hong-peng

    2004-01-01

    Microstructure evolution during tempering of quenched steel was studied via dilatometric experiments.Temperature ranges of transformation were determined by a relative dilation curve. The thermal expansion coefficient of quenched steel was defined as a function of temperature. The transformation expansion is determined by subtracting thermal expansion from a measured diameter dilation curve. A kinetic equation based on tempering parameter was proposed to predict the microstructure evolution fraction of martensite and bainite of Ni3.5CrMoV and C45 steel. The kinetic equation was used in an in-house FEM code. The internal stress evolution of a quenched generator rotor was investigated.

  7. Transformation Behavior and Microstructure in a 40Cr2Ni2MoV Cast Steel

    Institute of Scientific and Technical Information of China (English)

    Cheng Liu; Zhenbo Zhao; Sanjiwan. D. Bhole1; Derek O. Northwood

    2004-01-01

    The transformation behavior of a 40Cr2Ni2MoV cast steel manufactured by electroslag remelting (ESR) has been investigated. Compared to a forged steel, the incubation periods for both the pearlite and bainite transformations are shorter, but the transformation times are longer. The austenite is easier to transform into martensite. Optical microscopy and TEM indicated that there were variations in microstructure during the super-cooled austenite transformation. This is attributed to an inhomogeneous austenite, resulting from the segregation of elements during the ESR solidification.

  8. Investigation on the Strengthening and Toughening Mechanism of 500 MPa V-Nb Microalloyed Anti-Seismic Rebars

    OpenAIRE

    Chen, Wei; Cao, Jianchun; Yang, Yinhui; Shi, Zhe; Zhang, Weiqiang; Huang, Min

    2015-01-01

    Two types of 500 MPa anti-seismic rebars were produced by V-Nb microalloyed combined with controlled rolling and cooling technology, the strengthening and toughening mechanism of which were investigated. The complex phase microstructures of specimens consist of ferrite, pearlite and bainite (6 – 10 %). Furthermore, a large number of V(C,N) and Nb(C,N) precipitates with size of 5 – 30 nm formed in the ferrite matrix, grain boundaries and on dislocation lines, promoting the precipitation streng...

  9. As-rolled multi-phase microalloyed steel bars with improved properties: Valjane večfazne mikrolegirane jeklene palice z izboljšanimi lastnostmi:

    OpenAIRE

    Drobnjak, Djordje; Koprivica, A.

    1997-01-01

    A series of experimental steels, based on a 0.3 C, 1.5 Mn, 0.1 V composition, with and without 0.01% Ti addition, was made by laboratory and full scale casting, and fabricated into 22 mmdia bars by full-scale hot-rolling. Multi phase Polygonal Ferrite-Pearlite-Non Polygonal Ferrite (PF-P-NPF) structures with varying amount of NPF are obtained in as-rolled bars. Acicular Ferrite (AF) and classical Bainite Sheaves (BS) are found to be dominant NPF morphologies in steels with a low (40%) fractio...

  10. Luders bands in RPV Steel

    OpenAIRE

    Johnson, D H

    2013-01-01

    The R6 procedure is used for the prevention and prediction of crack behaviour and other defects in the reactor pressure vessel(RPV). The RPV material is an upper-bainitic, low alloy steel structure, which deforms inhomogeneously when yielding. The current codes that are used to design and calculate the fracture, within an RPV, assume that the material yields continuously as the size of the L¨uders strain is less than 2%. However, the work of Wenman et al[1] has shown that the inclusion of a L...

  11. Friction stir processing on high carbon steel U12

    International Nuclear Information System (INIS)

    Friction stir processing (FSP) of high carbon steel (U12) samples has been carried out using a milling machine and tools made of cemented tungsten carbide. The FSP tool has been made in the shape of 5×5×1.5 mm. The microstructural characterization of obtained stir zone and heat affected zone has been carried out. Microhardness at the level of 700 MPa has been obtained in the stir zone with microstructure consisting of large grains and cementitte network. This high-level of microhardness is explained by bainitic reaction developing from decarburization of austenitic grains during cementite network formation

  12. Micro Structural Comparison of Friction Stir Weldment and Shielded Metal Arc Welding in API-X65 Pipe Line

    Directory of Open Access Journals (Sweden)

    Amin Shahinfar

    2015-04-01

    Full Text Available The study was conducted to investigate the microstructure and microhardness properties of the friction stir welded zones and shielded metal arc welded. Microstructural analysis of the weld was carried out using optical microscopy. Under FSW process base metal microstructure fully changed. Different heat inputs were obtained using a fix travel (welding speed in combination with several spindle speeds. Heat input during welding process had a significant influence on the microstructure and mechanical proprieties in the various weld regions.it can be concluded that with decrease in heat input the bainitic structure in the hard zone becomes finer and so hard zone hardness increase.

  13. Multi scale study of the plasticity at low temperature in {alpha}-iron: application for the cleavage; Etude multiechelle de la plasticite du fer-{alpha} a basse temperature application au clivage

    Energy Technology Data Exchange (ETDEWEB)

    Chaussidon, J

    2007-10-15

    An accident inside a nuclear power plant may lead to the cleavage of the nuclear vessel made of bainitic steel. In order to understand the origin of this fracture, we studied BCC-iron plasticity at low temperature using numerical simulations at different scales. Molecular Dynamics simulations show the high dependency of screw dislocation motion with temperature and stress. Results from these simulations were added to experiment data to develop a new Dislocation Dynamics code dedicated to BCC iron at low temperature. The code was used to model plasticity into a ferritic lath for various temperatures. This work confirms that cleavage is favoured by low temperatures. (author)

  14. Usage of abrasion-resistant materials in agriculture

    Directory of Open Access Journals (Sweden)

    J Votava

    2014-06-01

    Full Text Available Agricultural soil-processing machines are subject to an extensive abrasive wear. This paper analyses technical materials and their fitness to exchangeable parts of plough bottoms, such as edge-tools and whole plough cutting edges. There were tested abrasion-resistant steels with different microstructures: austenite, martensite-bainite, and carbide. Steel with the pearlite-ferrite structure was used as an etalon. Abrasion resistance tests were processed in compliance with the norm CSN 01 5084, which is a test of abrasion wear on abrasive cloth.

  15. Superbainita. Una nueva microestructura bainítica de alta resistencia Superbainite

    Directory of Open Access Journals (Sweden)

    García-Mateo, C.

    2005-06-01

    Full Text Available In this work very recent results are shown that reveals the possibility of obtaining bainite by isothermal transformation at very low temperatures, of about 150°C, in high carbon high silicon steels. The microstructure thus obtained is a mixture of fine plates of bainitic ferrite (20-40 nm thickness and thin films of carbon enriched austenite. These microstructures are very hard (600 HV and strong (2.5 GPa.

    En este trabajo se muestran los resultados de investigaciones muy recientes que revelan la posibilidad de obtener bainita por transformación isotérmica a temperaturas muy bajas, del orden de 150 °C, en aceros de alto carbono y silicio. La microestructura así obtenida no tiene cementita y está formada por placas de ferrita bainítica extremadamente finas (20-40 nm de espesor y láminas delgadas de austenita enriquecida en carbono. Estas microestructuras son extraordinariamente duras (600 HV y resistentes (2,5 GPa

  16. Effect of welding conditions on transformation and properties of heat-affected zones in LWR (light-water reactor) vessel steels

    Energy Technology Data Exchange (ETDEWEB)

    Lundin, C.D.; Mohammed, S. (Tennessee Univ., Knoxville, TN (USA). Welding Research and Engineering)

    1990-11-01

    The continuous cooling transformation behavior (CCT) and isothermal transformation (IT) behavior were determined for SA-508 and SA-533 materials for conditions pertaining to standard heat treatment and for the coarse-grained region of the heat-affected zone (HAZ). The resulting diagrams help to select welding conditions that produce the most favorable microconstituent for the development of optimum postweld heat treatment (PWHT) toughness levels. In the case of SA-508 and SA-533, martensite responds more favorably to PWHT than does bainite. Bainite is to be avoided for the optimum toughness characteristics of the HAZ. The reheat cracking tendency for both steels was evaluated by metallographic studies of simulated HAZ structures subjected to PWHT cycles and simultaneous restraint. Both SA-533, Grade B, Class 1, and SA-508, Class 2, cracked intergranularly. The stress rupture parameter (the product of the stress for a rupture life of 10 min and the corresponding reduction of area) calculated for both steels showed that SA-508, Class 2, was more susceptible to reheat cracking than SA-533, Grade B, Class 1. Cold cracking tests (Battelle Test and University of Tennessee modified hydrogen susceptibility test) indicated that a higher preheat temperature is required for SA-508, Class 2, to avoid cracking than is required for SA-533, Grade B, Class 1. Further, the Hydrogen Susceptibility Test showed that SA-508, Class 2, is more susceptible to hydrogen embrittlement than is SA-533, Grade B, Class 1.

  17. High performance low cost steels with ultrafine grained and multi-phased microstructure

    Institute of Scientific and Technical Information of China (English)

    LIU XiangHua; LAN HuiFang; DU LinXiu; LIU WeiJie

    2009-01-01

    I;trafome gltrafine grained ferrite was obtained through tempering cold rolled martensite with an average grain size of 200--400 nm in a low carbon and a microalloyed steel.Thermal and mechanical stability of the two steels was studied.Due to the pinning effect of microalloyed precipitates on the movement of dislocations and grain boundaries,the recrystallization and grain growth rate were retarded,and the thermal stability of ultrafine grained microstructure was improved.The ultrafine grained ferritic steel was strengthened,but its strain hardening rate was reduced.It seems that the tiny carbide precipitates have no significant effect on work hardening rate.The ultrafine grained ferrite+martensite dual phase microstructure was obtained in the microalloyed steel through intercritically annealing cold rolled martensite.The resulting multiphase microstructure has a tensile strength higher than 1.0 GPa with a yield ratio lower than 0.7.Another type of multiphase microstructure with nanoscaled lath bainite+ retained austenite was obtained through an isothermal heat treatment in low temperature bainite transformation region in high carbon steel.The tensile strength was as high as 1.64 GPa with a yield ratio of 0.84.

  18. Thin slab processing of acicular ferrite steels with high toughness

    Energy Technology Data Exchange (ETDEWEB)

    Reip, Carl-Peter; Hennig, Wolfgang; Hagmann, Rolf [SMS Demag Aktiengesellschaft, Duesseldorf (Germany); Sabrudin, Bin Mohamad Suren; Susanta, Ghosh; Weng Lan Lee [Megasteel Sdn Bhd, Banting (Malaysia)

    2005-07-01

    Near-net-shape casting processes today represent an important option in steelmaking. High productivity and low production cost as well as the variety of steel grades that can be produced plus an excellent product quality are key factors for the acceptance of such processes in markets all over the world. Today's research focuses on the production of pipe steel with special requirements in terms of toughness at low temperatures. The subject article describes the production of hot strip made from acicular ferritic / bainitic steel grades using the CSP thin-slab technology. In addition, the resulting strength and toughness levels as a function of the alloying concepts are discussed. Optimal control of the CSP process allows the production of higher-strength hot-rolled steel grades with a fine-grain acicular-ferritic/bainitic microstructure. Hot strip produced in this way is characterized by a high toughness at low temperatures. In a drop weight tear test, transition temperatures of up to -50 deg C can be achieved with a shear-fracture share of 85%. (author)

  19. Weld metal microstructures of hardfacing deposits produced by self-shielded flux-cored arc welding

    International Nuclear Information System (INIS)

    The molten pool weld produced during self-shielded flux-cored arc welding (SSFCAW) is protected from gas porosity arising from oxygen and nitrogen by reaction ('killing') of these gases by aluminium. However, residual Al can result in mixed micro-structures of δ-ferrite, martensite and bainite in hardfacing weld metals produced by SSFCAW and therefore, microstructural control can be an issue for hardfacing weld repair. The effect of the residual Al content on weld metal micro-structure has been examined using thermodynamic modeling and dilatometric analysis. It is concluded that the typical Al content of about 1 wt% promotes δ-ferrite formation at the expense of austenite and its martensitic/bainitic product phase(s), thereby compromising the wear resistance of the hardfacing deposit. This paper also demonstrates how the development of a Schaeffler-type diagram for predicting the weld metal micro-structure can provide guidance on weld filler metal design to produce the optimum microstructure for industrial hardfacing applications.

  20. Corrosion fatigue studies on A533-B, C-Mn and Ducol W30 pressure vessel steels at ambient temperature and pressure in aqueous environments

    International Nuclear Information System (INIS)

    Corrosion fatigue crack growth tests have been performed on three pressure vessel steels, A533-B, Ducol W30 and a C-Mn steel, in simulated water reactor environments at ambient temperature and pressure. A533-B and Ducol W30 had a bainitic, and the C-Mn a ferritic-pearlitic, microstructure- above a cyclic stress intensity level of 25 MN.msup(3/2), crack growth rates are in general greater for the ferritic-pearlitic material. Tests have covered a range of stress ratios and frequencies, there being a strong effect of frequency on growth rates, but a small effect of stress ratio. Examination of several specimen orientations has shown there to be no significant effect of growth rates. Mechanisms of corrosion fatigue have been discussed in the light of features observed on specimen fracture surfaces. The ferritic-pearlitic steel has shown a transition in fracture mode from transgranular quasi-cleavage to intergranular cracking on lowering the cyclic stress intensity, the transition occurring when the plastic zone size at the crack tip became less than four times the grain size. The cleavage mode indicates that this material is susceptible to hydrogen embrittlement in these aqueous environments at ambient temperature. The bainitic steels have not in general shown these fracture modes and appear less susceptible to hydrogen embrittlement. The enhancement of growth rates, above those obtained in air, is controlled by a dissolution mechanism. (author)

  1. Improvement in the production of cylinder shirt of inner diesel combustion engines; Mejoras en la construccion de camisas de cilindro de motores de combustion interna ciclo diesel

    Energy Technology Data Exchange (ETDEWEB)

    Martinez-Perez, F.; Barroso-Moreno, A.

    2013-06-01

    This study deals with the different types of wear as well as other parameters present in the tribological system piston segment- cylinder in a combustion engine. By means of engineering methods were defined the wear rates in the three components of the system. The biggest wear in the analysis resulted in the cylinder shirt. Specialized methods applied were used to analyze the prevailing metallographic characteristics in its original construction, obtaining a gray melted iron with perlitic matrix. A new material with bainitic matrix has been proposed for increasing wear resistance. To demonstrate the efficiency of this new product, the experimental techniques carried out, were based on a dynamometric testing in a internal combustion engine diesel cycle Scania of 150 kW. It was exposed to a full charge during 500 h with 30 % of potency rising. Compared with the perlitic one, it has been proved that the bainitic matrix allows a better result. Besides, a superior dimensional stability was obtained. The piston segments had a similar wear rate in both materials in reference to the original tribological pair of the project. (Author)

  2. Evaluation of 2 1/4 Cr-1 Mo steel for liquid lithium containment. II. Effects of post-weld heat treatment and niobium content. Annual report, 1979

    International Nuclear Information System (INIS)

    The lithium corrosion resistance of the regular grade of 2 1/4 Cr-1 Mo steel can be vastly improved with a proper postweld heat treatment, but even greater improvements are needed. Results indicate that if weldments were tempered sufficiently long at 760C to remove all Mo2C from the microstructure, even greater resistance to attack by low nitrogen lithium could be achieved. Corrosion tests should eventually be performed on regular grade 2 1/4 Cr-1 Mo steel weldments which have been given a long-term (> 25 h) post-weld temper at 760C. Lithium corrosion resistance of regular grade 2 1/4 Cr-1 Mo steel may also be improved by employing a quench and temper heat treatment. Quenched microstructures have more homogenous distribution of carbides than isothermally annealed microstructures, and if properly tempered, should provide excellent lithium corrosion resistance. Furthermore, the toughness of such a lower bainite microstructure should be better than that of the ferrite-bainitic microstructure created by an isothermal anneal. Numerous parameters, all potentially deleterious to the lithium corrosion resistance of 2 1/4 Cr-1 Mo steel, remain to be investigated; two such variables are velocity effects and lead content in the lithium

  3. Study of the mechanical properties of low carbon content HSLA steels

    Directory of Open Access Journals (Sweden)

    Illescas, S.

    2009-12-01

    Full Text Available Two high strength low alloy steels (HSLA with the same bulk composition and slight microalloying content differences were studied. The main purpose of the study was to determine the effect of different heat treatments and the influence of vanadium (V on the microstructure and mechanical properties of the bainite present in each steel. For that purpose, standard tests were conducted to determine the hardness, toughness, tensile and yield stress of the different bainite-acicular ferrite structures found in both steels. The results show how the V content promoted the formation of acicular ferrite, resulting in a decrease in hardness and tensile strength while improving toughness.

    Se han estudiado dos aceros HSLA (high strength low alloy que presentan composiciones similares, a excepción del contenido en elementos microaleantes. El propósito del estudio es determinar el efecto del tratamiento térmico y la influencia del contenido en vanadio (V sobre la microestructura y las propiedades mecánicas de la bainita en cada uno de los aceros. Para ello, se han realizado ensayos de dureza, de impacto y de tracción para cada una de las estructuras bainíticas-ferrita acicular obtenidas por medio de los diferentes tratamientos térmicos realizados. Los resultados muestran como el contenido en V promueve la formación de ferrita acicular, presentando valores bajos de dureza y resistencia mecánica pero mejorando la tenacidad.

  4. Structure and Properties of Thermomechanically-processedHSLA Steels for Naval Applications

    Directory of Open Access Journals (Sweden)

    A. Ghosh

    2007-07-01

    Full Text Available Four high-strength low-alloy (HSLA steels with varying chemical compositions were forgedin two different temperature ranges followed by cooling in various media. Microstructures andmechanical properties of the steels were evaluated. The microstructures obtained in water–quenchedlow-carbon HSLA steels were lath martensite packet within the pancaked grains. On air or sandcooling predominantly bainitic ferrite or granular bainite structure forms. The strength propertiesof these steels decreased with decrease in cooling rate and is accompanied by an increase inelongation and impact toughness values. The ductile-to-brittle transition temperature of HSLA-100grade steel was found to be – 40 oC. The impact fracture surface of air cooled HSLA-100 steel showedductile failure with formation of dimples at 20 oC and at – 20 oC. The fracture mode changed to brittlefailure with formation of cleavage and river pattern at – 40 oC and at – 60 oC. The microstructuresof the ultra-low carbon HSLA steel show lath ferrite or granular ferrite in water-quenched condition.With slower cooling rate, the volume fraction of lath ferrite decreased with an increase in formationof polygonal ferrite. The maximum strength value obtained in air-cooled condition is achieved dueto precipitation of fine microalloying carbides and carbonitrides. Slower cooling rate increases thevolume fraction of polygonal ferrite which increases the toughness value.

  5. Effects of Alloy Element and Microstructure on Corrosion Resistant Property of Deposited Metals of Weathering Steel

    Institute of Scientific and Technical Information of China (English)

    Xiao-ming XIAO; Yun PENG; Cheng-yong MA; Zhi-ling TIAN

    2016-01-01

    Alloy element and microstructure are key factors that dominate mechanical and corrosion resistant properties of weathering steel.The effect of Mo on microstructure,mechanical properties and corrosion resistant property of depos-ited metal was investigated.Experimental results show that with the increase of Mo content in deposited metals,the phase transformation temperature decreases,and the ferrite zone in CCT diagram moves rightward,resulting in en-larged bainite zone and reduced ferrite and pearlite zone.The addition of 0�24 mass% Mo in deposited metal results in the increase of tensile strength,more M-A constituent and less high angle grain which reduce the low temperature toughness.It is found that Mo can raise the weathering resistance of deposited metal in industrial atmosphere.Analy-sis indicates that Mo may enrich in the inner rust layer,produce MoO3 ,enhance the formation of compact rust film and impede the anode dissolution reaction.Granular bainite in deposited metals displays better corrosion resistance than acicular ferrite during the initial corrosion stage,but its long-term influence on the corrosion resistance is limited.

  6. The significance of ultrafine film-like retained austenite in governing very high cycle fatigue behavior in an ultrahigh-strength MN–SI–Cr–C steel

    International Nuclear Information System (INIS)

    We elucidate here the very high cycle fatigue (VHCF) behavior of an ultrahigh-strength medium carbon Mn–Si–Cr–C steel processed using the approach of bainite-based quenching and partitioning (BQ&P). The microstructure of BQ&P process comprised of bainite, carbon-depleted martensite, retained austenite (RA) and small amount of martensite/austenite island (M/A). The tensile strength (Rm) and fatigue limit strength after 109 cycles (σw9) and in the non-failed condition were 1688 MPa and 875 MPa, respectively such that σw9/Rm exceeded conventional steels and was 0.52. Two types of failure modes were observed depending on the surface and microstructure, notably surface-induced failure and non-inclusion-induced failure, where the non-inclusion-induced failure was influenced by the microstructure. Inclusion-induced failure was absent. The study underscores that film-like retained austenite was the underlying reason for superior fatigue properties, hitherto not previously obtained

  7. Network structure and its effects on the strength of Fe-C-Si-Mn alloy castings

    Institute of Scientific and Technical Information of China (English)

    ZHANG Ding-fei; PENG Jian; XU Xing-zhi

    2004-01-01

    Fe-C-Si-Mn alloy castings used as blades in hydroelectric generators are studied and found to contain network structures after some heat treatments. Castings after annealing and normalizing were analyzed by microscope and transmission electron microscopy (TEM). The network formed during annealing was proved by TEM to be pearlite with very fine slices, while that formed during normalizing was proved by TEM and micro-hardness to be martensite or bainite. A theoretical analysis together with experimental studies has proved that the pearlite network is caused by carbon content increase in the interdendritic regions to which carbon atoms transfered from dendritic arms due to lower manganese content there during annealing, while the martensite or bainite network results from the higher hardenability of interdendritic regions where manganese content is higher.Experiments reveal that higher heating temperature or longer heating time enlarges the network size due to manganese homogenization. The network structure has a strengthening function like reinforcing rib, and the smaller the network size, the greater its strengthening capability.

  8. Effect of cooling rate on the microstructure and mechanical properties of Nb-microalloyed steels

    International Nuclear Information System (INIS)

    We describe here the effect of cooling rate on the microstructure and mechanical properties of Nb-microalloyed steels that were processed as structural beams at three different cooling rates. Nb-microalloyed steels exhibited increase in yield strength with increase in cooling rate during processing. However, the increase in the yield strength was not accompanied by loss in toughness. The microstructure at conventional cooling rate, primarily consisted of polygonal ferrite-pearlite microconstituents, while at intermediate cooling rate besides polygonal ferrite and pearlite contained significant fraction of degenerated pearlite and lath-type ferrite. At higher cooling rate, predominantly, lath-type (acicular) or bainitic ferrite was obtained. The precipitation characteristics were similar at the three cooling rates investigated with precipitation occurring at grain boundaries, on dislocations, and in the ferrite matrix. The fine scale (∼8-12 nm) precipitates in the ferrite matrix were MC type of niobium carbides. The microstructural studies suggest that the increase in toughness of Nb-microalloyed steels with increase in cooling rate is related to the change in the microstructure from predominantly ferrite-pearlite to predominantly bainitic ferrite

  9. Effect of cooling rate on the microstructure and mechanical properties of Nb-microalloyed steels

    Energy Technology Data Exchange (ETDEWEB)

    Shanmugam, S. [Center for Structural and Functional Materials, University of Louisiana at Lafayette, Lafayette, LA 70504-4130 (United States); Ramisetti, N.K. [Department of Chemical Engineering, University of Louisiana at Lafayette, Lafayette, LA 70504-4130 (United States); Misra, R.D.K. [Center for Structural and Functional Materials, University of Louisiana at Lafayette, Lafayette, LA 70504-4130 (United States); Department of Chemical Engineering, University of Louisiana at Lafayette, Lafayette, LA 70504-4130 (United States)], E-mail: dmisra@louisiana.edu; Mannering, T. [Nucor-Yamato Steel, P.O. Box 1228, 5929 East State Highway 18, Blytheville, AR 72316 (United States); Panda, D. [Nucor-Yamato Steel, P.O. Box 1228, 5929 East State Highway 18, Blytheville, AR 72316 (United States); Jansto, S. [Reference Metals, 1000 Old Pond Road, Bridgeville, PA 15017 (United States)

    2007-07-15

    We describe here the effect of cooling rate on the microstructure and mechanical properties of Nb-microalloyed steels that were processed as structural beams at three different cooling rates. Nb-microalloyed steels exhibited increase in yield strength with increase in cooling rate during processing. However, the increase in the yield strength was not accompanied by loss in toughness. The microstructure at conventional cooling rate, primarily consisted of polygonal ferrite-pearlite microconstituents, while at intermediate cooling rate besides polygonal ferrite and pearlite contained significant fraction of degenerated pearlite and lath-type ferrite. At higher cooling rate, predominantly, lath-type (acicular) or bainitic ferrite was obtained. The precipitation characteristics were similar at the three cooling rates investigated with precipitation occurring at grain boundaries, on dislocations, and in the ferrite matrix. The fine scale ({approx}8-12 nm) precipitates in the ferrite matrix were MC type of niobium carbides. The microstructural studies suggest that the increase in toughness of Nb-microalloyed steels with increase in cooling rate is related to the change in the microstructure from predominantly ferrite-pearlite to predominantly bainitic ferrite.

  10. Wear Behavior of Austempered Ductile Iron with Nanosized Additives

    Directory of Open Access Journals (Sweden)

    J. Kaleicheva

    2014-03-01

    Full Text Available The microstructure and properties of austempered ductile iron (ADI strengthened with nanosized addtives of titanium nitride + titanium carbonitride (TiN + TiCN, titanium nitride TiN and cubic boron nitride cBN are investigated. The TiN, TiCN and cBN, nanosized particles are coated by electroless nickel coating EFTTOM-NICKEL prior to the edition to the melt. The spheroidal graphite iron samples are undergoing an austempering, including heating at 900 оС for an hour, after that isothermal retention at 280 оС, 2 h and 380 оС, 2h. The metallographic analysis by optical metallographic microscope GX41 OLIMPUS and hardness measurements by Vickers Method are performed. The structure of the austempered ductile iron consists of lower bainite and upper bainite.Experimental investigation of the wear by fixed abrasive are also carried out. The influence of the nanosized additives on the microstructure, mechanical and tribological properties of the austempered ductile irons (ADI is studied.

  11. Generalization of the existing relations between microstructure and yield stress from ferrite-pearlite to high strength steels

    Energy Technology Data Exchange (ETDEWEB)

    Iza-Mendia, A., E-mail: aiza@ceit.es [CEIT and Tecnun (University of Navarra), Manuel de Lardizabal 15, 20018 Donostia-San Sebastian, Basque Country (Spain); Gutierrez, I. [CEIT and Tecnun (University of Navarra), Manuel de Lardizabal 15, 20018 Donostia-San Sebastian, Basque Country (Spain)

    2013-01-20

    A series of available equations allows the yield and the tensile strength of low carbon ferrite-pearlite microstructures to be expressed as a function of the optical grain size, steel composition and interstitials in solution. Over the years, as the complexity of steel microstructures has increased, some additional terms have been added to account for precipitation and forest dislocation contributions. In theory, this opens the door for an extension of these equations to bainitic microstructures. Nevertheless, there is a series of difficulties that needs to be overcome in order to improve prediction accuracy. In the present work, different microstructures (ferrite-pearlite, bainite, quenched, and quenched and tempered) were produced and tension tested in a C-Mn-Nb steel. Optical microscopy and EBSD (Electron Back Scattered Diffraction) were applied and the results were compared as a function of the tolerance angle. Based on this work, an adaptation to Pickering's equation is proposed, including its extension to other microstructures rather than ferrite-pearlite.

  12. The mathematical modeling of phase transformation of steel during quenching

    Energy Technology Data Exchange (ETDEWEB)

    Jahanian, S. [Temple Univ., Philadelphia, PA (United States). Dept. of Mechanical Engineering; Mosleh, M. [Howard Univ., Washington, D.C. (United States). Dept. of Mechanical Engineering

    1999-02-01

    In the heat treatment of steel, uneven cooling invariably introduces residual stresses in the workpiece. These residual stresses can combine with the thermomechanical stresses encountered in operation to cause premature fatigue failure of the material. A prediction of the residual and thermoelastoplastic stresses developed during heat treatment would be beneficial for component design. In this article a numerical model is developed to predict the thermoelastoplastic and residual stresses during rapid cooling of a long solid cylinder. The total strains developed during cooling of the cylinder comprise elastic, thermal, and plastic strains and strains due to phase transformation. For plastic deformation an extension of Jiang`s constitutive equations developed by Jahanian is adopted. The properties of the material are assumed to be temperature dependent and characterized by nonlinear strain hardening. For phase transformation two parts are considered: nucleation according to Scheil`s method and phase growth according to Johnson and Mehl`s law. For martensitic transformation, a law established by Koisteinin and Marburger is used. Non-additivity of pearlitic and bainitic nucleation suggested by Manning and Lorig is taken into account by means of a correction factor to Scheil`s summation of the transition from pearlitic to bainitic. The effect of phase transformation and temperature dependence of material properties is investigated. It is shown that by neglecting the temperature dependency and phase transformation in numerical calculations, the results are underestimated. The numerical results are compared with the available experimental data in the literature, and good agreement is observed.

  13. On-line spheroidization process of medium-carbon low-alloyed cold heading steel

    Institute of Scientific and Technical Information of China (English)

    Yu Fu; Hao Yu; Pan Tao

    2014-01-01

    Conventionally manufactured 35CrMo cold heading steel must undergo spheroidization annealing before the cold heading process. In this paper, different types of deformation processes with various controlled cooling periods were operated to achieve on-line spheroidal cementite using the Gleeble-3500 simulation technique. According to the measured dynamic ferrite transformation temperature (Ad3), the deformation could be divided into two types:low temperature deformation at 810 and 780°C;“deformation-induced ferrite transformation”(DIFT) deformation at 750 and 720°C. Compared with the low temperature deformation, the DIFT deformation followed by accelerated cooling to 680°C is beneficial for the formation of spheroidal cementite. Samples subjected to both the low-temperature deformation and DIFT deformation can obtain granular bainite by accelerated cooling to 640°C;the latter may contribute to the formation of a fine dispersion of secondary constituents. Granular bainite can transform into globular pearlite rapidly during subcritical annealing, and the more the dis-perse phase, the more homogeneously distributed globular cementite can be obtained.

  14. Master curve characterization of the fracture toughness behavior in SA508 Gr.4N low alloy steels

    Science.gov (United States)

    Lee, Ki-Hyoung; Kim, Min-Chul; Lee, Bong-Sang; Wee, Dang-Moon

    2010-08-01

    The fracture toughness properties of the tempered martensitic SA508 Gr.4N Ni-Mo-Cr low alloy steel for reactor pressure vessels were investigated by using the master curve concept. These results were compared to those of the bainitic SA508 Gr.3 Mn-Mo-Ni low alloy steel, which is a commercial RPV material. The fracture toughness tests were conducted by 3-point bending with pre-cracked charpy (PCVN) specimens according to the ASTM E1921-09c standard method. The temperature dependency of the fracture toughness was steeper than those predicted by the standard master curve, while the bainitic SA508 Gr.3 steel fitted well with the standard prediction. In order to properly evaluate the fracture toughness of the Gr.4N steels, the exponential coefficient of the master curve equation was changed and the modified curve was applied to the fracture toughness test results of model alloys that have various chemical compositions. It was found that the modified curve provided a better description for the overall fracture toughness behavior and adequate T0 determination for the tempered martensitic SA508 Gr.4N steels.

  15. The Effect of the Initial Microstructure on Recrystallization and Austenite Formation in a DP600 Steel

    Science.gov (United States)

    Kulakov, M.; Poole, W. J.; Militzer, M.

    2013-08-01

    The effects of initial microstructure and thermal cycle on recrystallization, austenite formation, and their interaction were studied for intercritical annealing of a low-carbon steel that is suitable for industrial production of DP600 grade. The initial microstructures included 50 pct cold-rolled ferrite-pearlite, ferrite-bainite-pearlite and martensite. The latter two materials recrystallized at similar rates, while slower recrystallization was observed for ferrite-pearlite. If heating to an intercritical temperature was sufficiently slow, then recrystallization was completed before austenite formation, otherwise austenite formed in a partially recrystallized microstructure. The same trends as for recrystallization were found for the effect of initial microstructure on kinetics of austenite formation. The recrystallization-austenite formation interaction accelerated austenization in all the three starting microstructures by providing additional nucleation sites and enhancing growth rates, and drastically altered morphology and distribution of austenite. In particular, for ferrite-bainite-pearlite and martensite, the recrystallization-austenite formation interaction resulted in substantial microstructural refinement. Recrystallization and austenite formation from a fully recrystallized state were successfully modeled using the Johnson-Mehl-Avrami-Kolmogorov approach.

  16. Effect of Mn on hardenability of 25CrMo axle steel by an improved end-quench test

    Directory of Open Access Journals (Sweden)

    Zhang Yutuo

    2012-11-01

    Full Text Available With the sixth large-scale railway speed-up, the quality of the axles is essential to the safety of the locomotive. According to the high-speed axle technical standard for the control of alloy elements in axle steel, optimization experiments of 25CrMo steel composition were performed by vacuum inductive melting. In order to study the hardenability of high-speed rail axles, an improved end-quench test was put forward. The advantage is that it enables the heat to transfer along the axial direction, thus avoiding edge effects. The hardenability of 25CrMo axle steels with Mn content of 0.60wt.% and 0.80wt.% was investigated mainly by means of optical microscopy and hardness tests. The experimental results indicate that the Mn has a pronounced effect on the hardenability of the steel. With an increase in Mn content from 0.60wt.% and 0.80wt.%, the hardenability of 25CrMo axle steel increases and the hard microstructure is maintained at an increasing distance from the quenched end. From the surface of the water quenched end to the center of the sample, the microstructure is martensite, martensite with bainite, and bainite.

  17. Microstructures and Mechanical Properties of Austempering SUS440 Steel Thin Plates

    Directory of Open Access Journals (Sweden)

    Cheng-Yi Chen

    2016-02-01

    Full Text Available SUS440 is a high-carbon stainless steel, and its martensite matrix has high heat resistance, high corrosion resistance, and high pressure resistance. It has been widely used in mechanical parts and critical materials. However, the SUS440 martempered matrix has reliability problems in thin plate applications and thus research uses different austempering heat treatments (tempering temperature: 200 °C–400 °C to obtain a matrix containing bainite, retained austenite, martensite, and the M7C3 phase to investigate the relationships between the resulting microstructure and tensile mechanical properties. Experimental data showed that the austempering conditions of the specimen affected the volume fraction of phases and distribution of carbides. After austenitizing heat treatment (1080 °C for 30 min, the austempering of the SUS440 thin plates was carried out at a salt-bath temperature 300 °C for 120 min and water quenching was then used to obtain the bainite matrix with fine carbides, with the resulting material having a higher tensile fracture strength and average hardness (HRA 76 makes it suitable for use as a high-strength thin plate for industrial applications.

  18. Microstructure and mechanical properties of CuNiMo austempered ductile iron

    Directory of Open Access Journals (Sweden)

    Erić Olivera

    2004-01-01

    Full Text Available Microstructure and mechanical properties of Cu, Ni and Mo alloyed cast ductile iron have been investigated after austempering. Samples were austenitised at 860oC for 1h and then austempered at 320oC and 400oC in the interval from 0,5 to 5h. The X-ray diffraction technique and the light microscopy were utilized to investigate the bainitic transformation, while tensile and impact tests were performed for characterization of mechanical properties. By austempering at 320oC in the range between 2 and 5h, a microstructure typical for austempered ductile iron was produced, i.e. a mixture of free bainitic ferrite and highly carbon enriched retained austenite. The characteristic of the whole range of austempering at 400oC is the appearance of martensitic structure. The maximum impact energy (133 J coincides with the maximum value of volume fraction of retained austenite that was obtained after 2,5h of austempering at 320oC. The appearance of martensite during austempering at 400oC is the main cause for much lower tensile properties than at 320oC.

  19. Determination of bearing steel heat treatment with the use of the acoustic emission method

    Directory of Open Access Journals (Sweden)

    T.Z. Woźniak

    2010-07-01

    Full Text Available A study on the control of an extremely important stage of the martensitic-bainitic austempering and obtaining the M-B structure in the 100CrMnSi6-4 steel with the use of the acoustic emission (AE has been undertaken. In order to enrich retained austenite with carbon,steels are austempered at appropriately low temperatures. A martensitic transformation, resulting from diffusionless and displacive transformation is associated with significant AE signs. The strain energy produced during growth due to the shape change is reduced by plastic deformation. Predominant source of (AE is the movement of dislocations in order to relieve internal stresses.The heat treatment was performed in a modern, purpose-constructed device which simultaneously records acoustic emission effects. The signals were recorded with the use of an AE analyzer 20–800 kHz, and they were received by means of a broadband piezoelectric transducer with the use of a specialist card with a sampling frequency of 1200 kHz. The results regarding a correlation of austempering temperature and the maximum number of AE events and dilatometric results have been presented. This parameter can be used for precise Ms temperatureestimation. Basing on microstructural investigations, it has been found that previously formed martensite with midrib morphology alsoaccelerates the bainitic transformation.

  20. Determination of bearing steel heat treatment with the use of the acoustic emission method

    Directory of Open Access Journals (Sweden)

    T. Z. Wozniak

    2010-10-01

    Full Text Available A study on the control of an extremely important stage of the martensitic-bainitic austempering and obtaining the M-B structure in the 100CrMnSi6-4 steel with the use of the acoustic emission (AE has been undertaken. In order to enrich retained austenite with carbon, steels are austempered at appropriately low temperatures. A martensitic transformation, resulting from diffusionless and displacive transformation is associated with significant AE signs. The strain energy produced during growth due to the shape change is reduced by plastic deformation. Predominant source of (AE is the movement of dislocations in order to relieve internal stresses.The heat treatment was performed in a modern, purpose-constructed device which simultaneously records acoustic emission effects. The signals were recorded with the use of an AE analyzer 20–800 kHz, and they were received by means of a broadband piezoelectric transducer with the use of a specialist card with a sampling frequency of 1200 kHz. The results regarding a correlation of austempering temperature and the maximum number of AE events and dilatometric results have been presented. This parameter can be used for precise Ms temperature estimation. Basing on microstructural investigations, it has been found that previously formed martensite with midrib morphology also accelerates the bainitic transformation.

  1. Effect of Cooling Method on Microstructure and Mechanical Properties of Hot-Rolled C-Si-Mn TRIP Steel%Effect of Cooling Method on Microstructure and Mechanical Properties of Hot-Rolled C-Si-Mn TRIP Steel

    Institute of Scientific and Technical Information of China (English)

    LIU Ji-yuan; ZHANG Zi-cheng; ZHU Fu-xian; LI Yan-mei; Manabe Ken-ichi

    2012-01-01

    The controlled cooling technology following hot rolling process is a vital factor that affects the final micro- structure and mechanical properties of the hot-rolled transformation induced plasticity (TRIP) steels. In the present study, low alloy C-Si-Mn TRIP steel was successfully fabricated by hot rolling process with a 4450 hot roiling mill. To maximize the volume fraction and stability of retained austenite of the steel, two different cooling methods (aircooling and ultra-fast cooling "AC-UFC" and ultrmfast cooling, air cooling and ultra-fast cooling "UFC-AC-UFC") were conducted. The effects of the cooling method on the microstructure of hot-rolled TRIP steel were investigated via optical microscope, transmission electron microscope and conversion electron Mossbauer spectroscope. The mechanical properties of the steel were also evaluated by conventional tensile test. The results indicated that ferrite and bainite in the microstructure were refined with the cooling method of UFC-AC-UFC. The morphology of retained austenite was also changed from small islands distributing in bainite district (obtained with AC-UFC) to granular shape locating at the triple junction of the ferrite grain boundaries (obtained with UFC-AC-UFC). As a result, the TRIP steel with a content of retained austenite of 11. 52%, total elongation of 32% and product of tensile strength and total elongation of 27 552 MPa·% was obtained.

  2. Constitutive relationships of hot stamping boron steel B1500HS based on the modified Arrhenius and Johnson–Cook model

    International Nuclear Information System (INIS)

    Constitutive relationship of boron steel is one of the most necessary mathematical models in the numerical simulation of hot stamping; it describes the relationship of the flow stress with strain, strain rate and temperature. In order to attain the constitutive relationship of boron steel B1500HS, four types of samples with microstructure of austenite, ferrite+pearlite, bainite or martensite are prepared by the Gleeble 1500D thermo-mechanical simulator. Isothermal uniaxial tension testings for these specimens are performed at 20–900 °C at the strain rates of 0.01 s–1, 0.1 s–1, 1.0 s–1 and 10 s–1 by Gleeble 1500D, and the true stress–strain curves at the relative conditions are gained. The experimental results show that, the flow stress of samples with relative microstructure rises with the decrease of the deformation temperature, and with the increase of the strain rate. The modified Arrhenius model is used to describe the hot deformation of samples with austenite microstructure, and the modified Johnson–Cook model is used to describe the deformation process of samples with ferrite+pearlite, bainite or martensite microstructure. The constitutive equations depending on the strain, strain rate and temperature are attained by the regression analysis for the experimental data of flow stress, strain, strain rate, temperature, etc. The comparison of the computational data and the experimental results shows that, the computational data using the constitutive relationships are well consistent with the experimental data

  3. Effect of heat treatment and irradiation temperature on impact behavior of irradiated reduced-activation ferritic steels

    Energy Technology Data Exchange (ETDEWEB)

    Klueh, R.L.; Alexander, D.J. [Oak Ridge National Lab., TN (United States)

    1998-03-01

    Charpy tests were conducted on eight normalized-and-tempered reduced-activation ferritic steels irradiated in two different normalized conditions. Irradiation was conducted in the Fast Flux Test Facility at 393 C to {approx}14 dpa on steels with 2.25, 5, 9, and 12% Cr (0.1% C) with varying amounts of W, V, and Ta. The different normalization treatments involved changing the cooling rate after austenitization. The faster cooling rate produced 100% bainite in the 2.25 Cr steels, compared to duplex structures of bainite and polygonal ferrite for the slower cooling rate. For both cooling rates, martensite formed in the 5 and 9% Cr steels, and martensite with {approx}25% {delta}-ferrite formed in the 12% Cr steel. Irradiation caused an increase in the ductile-brittle transition temperature (DBTT) and a decrease in the upper-shelf energy. The difference in microstructure in the low-chromium steels due to the different heat treatments had little effect on properties. For the high-chromium martensitic steels, only the 5 Cr steel was affected by heat treatment. When the results at 393 C were compared with previous results at 365 C, all but a 5 Cr and a 9 Cr steel showed the expected decrease in the shift in DBTT with increasing temperature.

  4. High performance low cost steels with ultrafine grained and multi-phased microstructure

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Ultrafine grained ferrite was obtained through tempering cold rolled martensite with an average grain size of 200―400 nm in a low carbon and a microalloyed steel. Thermal and mechanical stability of the two steels was studied. Due to the pinning effect of microalloyed precipitates on the movement of dislocations and grain boundaries, the recrystallization and grain growth rate were retarded, and the thermal stability of ultrafine grained microstructure was improved. The ultrafine grained ferritic steel was strengthened, but its strain hardening rate was reduced. It seems that the tiny carbide precipitates have no significant effect on work hardening rate. The ultrafine grained ferrite+martensite dual phase microstructure was obtained in the microalloyed steel through intercritically annealing cold rolled martensite. The resulting multiphase microstructure has a tensile strength higher than 1.0 GPa with a yield ratio lower than 0.7. Another type of multiphase microstructure with nanoscaled lath bainite+ retained austenite was obtained through an isothermal heat treatment in low temperature bainite transformation region in high carbon steel. The tensile strength was as high as 1.64 GPa with a yield ratio of 0.84.

  5. Development of ultrafine ferritic sheaves/plates in SAE 52100 steel for enhancement of strength by controlled thermomechanical processing

    Energy Technology Data Exchange (ETDEWEB)

    Chakraborty, J. [Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Kharagpur, W.B. 721 302 (India); Scientific Services and Research and Development, Tata Steel, Jamshedpur 831 001, Jharkhand (India); Manna, I., E-mail: imanna@metal.iitkgp.ernet.in [Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Kharagpur, W.B. 721 302 (India); Central Glass and Ceramic Research Institute (CGCRI), Council of Scientific and Industrial Research (CSIR), 196 Raja S C Mullick Road, Jadavpur, Kolkata 700032 (India)

    2012-06-30

    Highlights: Black-Right-Pointing-Pointer Ultrafine bainite + martensite duplex microstructure developed in SAE 52100 steel. Black-Right-Pointing-Pointer Thermomechanical processing modifies size + morphology of bainitic ferrite. Black-Right-Pointing-Pointer Processing involves hot deformation prior to/during/after austenitizing. Black-Right-Pointing-Pointer Significant improvement in mechanical strength achieved. Black-Right-Pointing-Pointer Similar study on high carbon, low alloy steel not reported in the literature. - Abstract: The present study attempts to tailor the size, morphology and distribution of the ferrite needles/sheaves by thermomechanical processing and develop an ultrafine ferrite + martensite duplex microstructure for enhancement of strength and toughness in SAE 52100 steel. The thermo-mechanical routine included 5% hot deformation before, during or after austenitizing at 950 Degree-Sign C for 15 min followed by austempering at 270 Degree-Sign C for 30 min and subsequent water quenching to room temperature. Optical/electron microscopy along with X-ray diffraction was used to quantitatively monitor the size, morphology and distribution of the phase or phase aggregate. Significant improvement in nanohardness, wear resistance and elastic modulus and was observed in samples subjected to thermomechanical processing, as compared to that following the same austenitizing and austempering routine without hot deformation at any stage. However, improvement in the bulk mechanical property due to the present thermo-mechanical is lower than that obtained in our earlier study comprising cold deformation prior to austenitizing and austempering.

  6. Development of ultrafine ferritic sheaves/plates in SAE 52100 steel for enhancement of strength by controlled thermomechanical processing

    International Nuclear Information System (INIS)

    Highlights: ► Ultrafine bainite + martensite duplex microstructure developed in SAE 52100 steel. ► Thermomechanical processing modifies size + morphology of bainitic ferrite. ► Processing involves hot deformation prior to/during/after austenitizing. ► Significant improvement in mechanical strength achieved. ► Similar study on high carbon, low alloy steel not reported in the literature. - Abstract: The present study attempts to tailor the size, morphology and distribution of the ferrite needles/sheaves by thermomechanical processing and develop an ultrafine ferrite + martensite duplex microstructure for enhancement of strength and toughness in SAE 52100 steel. The thermo-mechanical routine included 5% hot deformation before, during or after austenitizing at 950 °C for 15 min followed by austempering at 270 °C for 30 min and subsequent water quenching to room temperature. Optical/electron microscopy along with X-ray diffraction was used to quantitatively monitor the size, morphology and distribution of the phase or phase aggregate. Significant improvement in nanohardness, wear resistance and elastic modulus and was observed in samples subjected to thermomechanical processing, as compared to that following the same austenitizing and austempering routine without hot deformation at any stage. However, improvement in the bulk mechanical property due to the present thermo-mechanical is lower than that obtained in our earlier study comprising cold deformation prior to austenitizing and austempering.

  7. Study of microstructural evolution, microstructure-mechanical properties correlation and collaborative deformation-transformation behavior of quenching and partitioning (Q and P) steel

    International Nuclear Information System (INIS)

    This paper presents a detailed characterization of the microstructural evolution of quenching and partitioning (Q and P) steel by dilatometer, X-ray diffraction and scanning electron microscopy. Influence of partitioning time on mechanical properties was investigated and the relationship between microstructures and mechanical properties was established. The results indicate that bainite transformation occurs at the preliminary stage of partitioning and the amount is proportional to quenching temperature. Martensite softening, bainite transformation kinetics, amount and stability of retained austenite collaboratively have effects on mechanical properties. The purpose of the EBSD investigation is to study the changes in the microstructure of the Q and P steel during deformation and obtain a better understanding of collaborative deformation-transformation behavior. During deformation, plastic deformation preferentially occurred in the vicinity of ferrite–martensite interfaces and spread to the interior of ferrite grain with strain increasing. Plastic deformation started to occur in martensite after large strain. Furthermore, grain rotation occurred in some austenite grains or divided into subgrains during deformation

  8. Phase quantification in nanobainite via magnetic measurements and X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Solano-Alvarez, W., E-mail: ws298@cam.ac.uk [Department of Materials Science and Metallurgy, University of Cambridge (United Kingdom); Abreu, H.F.G. [Departamento de Engenharia Metalúrgica e de Materiais, Universidade Federal do Ceará, Fortaleza (Brazil); Silva, M.R. da [Instituto de Física e Química, Universidade Federal de Itajubá, Itajubá, Minas Gerais (Brazil); Peet, M.J. [Department of Materials Science and Metallurgy, University of Cambridge (United Kingdom)

    2015-03-15

    Accurate phase quantification of nanostructured bainitic steel is of importance because of the nature of its percolating structure that controls many of its mechanical properties. X-ray diffraction is the technique of choice for such analysis, but magnetic methods can be more rapid and less sensitive to defect structures. In this study, the phase volume fractions measured using both of these techniques for the specific mixtures associated with nanostructured bainite have been compared and contrasted. An expression which relates the volume fraction and the saturation magnetization is obtained and its form is found to be consistent with previous work done on duplex stainless steels and TRIP steels. The fitting constants used in many of such analyses vary significantly so an attempt is made to rationalize the differences by considering the factors that determine the intrinsic saturation magnetization of ferrite. - Author-Highlights: • Magnetic phase quantification of nanobainite is presented for the first time. • Results are compared with x-ray diffraction. • Expression obtained that relates ferrite fraction and saturation magnetization. • Equation derived to calculate intrinsic saturation magnetization of ferrites. • These values agree with experimental data of the literature.

  9. Effect of Al and N on the toughness of heavy section steel plates

    International Nuclear Information System (INIS)

    The effect of Al and N on the notch toughness and tensile strength of heavy section pressure vessel steel plates is investigated. Notch toughness of steel A533B (Mn-Mo-Ni), which has mixed microstructure of ferrite and bainite, is drastically changed by the ratio of sol.N/sol.Al. With metallurgical observations, it is revealed that AlN morphology is influenced by the ratio of sol.N/sol.Al through the level of solute Al(CAl). At the heat treatment of heavy section steel plate, AlN shows OSTWALD ripening and its speed depends upon CAl. When Al is added (Al ≥ 0.010%) in steel and sol.N/sol.Al ≤ 0.5, CAl remains low. This prevents AlN ripening, and brings fine austenite grain size and high toughness. On the other hand, when sol.N/sol.Al Al becomes high and this gives poor toughness through coarse AlN precipitates and coarse austenite grain. Therefore, controll of sol.N/sol.Al over 0.5 is favorable to keep high toughness in A533B steel. In steel A387-22 (Cr-Mo) which has full bainitic microstructure, too fine austenite grain brings about poor hardenability, and polygonal ferrite, which brings about both poor strength and tughness, appears in microstructure. Then sol.N/sol.Al < 0.5 is better to give high hardenability in steel A387-22. (author)

  10. Processing of a new high strength high toughness steel with duplex microstructure (Ferrite + Austenite)

    International Nuclear Information System (INIS)

    Highlights: ► This new steel has exceptional combination of high strength and fracture toughness. ► Austempering treatment resulted in a very fine scale bainitic ferrite microstructure. ► As the austempering temperature increases yield strength and toughness decreases. ► Maximum fracture toughness of 105 MPa √m is obtained after austempering at 371 °C. ► A relationship between fracture toughness and the parameter σy(XγCγ)1/2 was observed. - Abstract: In this investigation a new third generation advanced high strength steel (AHSS) has been developed. This steel was synthesized by austempering of a low carbon and low alloy steel with high silicon content. The influence of austempering temperature on the microstructure and the mechanical properties including the fracture toughness of this steel was also examined. Compact tension and cylindrical tensile specimens were prepared from a low carbon low alloy steel and were initially austenitized at 927 °C for 2 h and then austempered in the temperature range between 371 °C and 399 °C to produce different microstructures. The microstructures were characterized by X-ray diffraction, scanning electron microscopy and optical metallography. Test results show that the austempering heat treatment has resulted in a microstructure consisting of very fine scale bainitic ferrite and austenite. A combination of very high tensile strength of 1388 MPa and fracture toughness of 105 MPa √m was obtained after austempering at 371 °C

  11. Fracture toughness of welded joints of a high strenghth low alloy steel

    International Nuclear Information System (INIS)

    The fracture toughness of welded joints of a high strength low alloy atmospheric corrosion resistant steel was investigated. The welded joints were produced using the manual metal arc welding process and fracture toughness was evaluated by the COD method. An effort was made in order to correlate the microstructure of the different regions of the welded joints and their critical COD values. The results appear to indicate that when the structure of the heat affected zone is formed mainly by bainite and ferritic grains the fracture toughness tends to increase. Also, an increase on the amount of acicular ferrite on the weld metal tends to improve its fracture toughness. The fusion boundary showed a structure formed mainly by bainite and ferrite grains and its fracture toughness was higher than that of the parent metal at room temperature whereas it was lower at 00C. Both at 00C and room temperature the fracture toughness of the weld metal was better than those of the other regions of the welded joints. The correlations between critical values of COD and the microstructures of the different regions of the welded joints were very difficult. (Author)

  12. Effects of complex oxides on HAZ toughness of three API X80 linepipe steels

    International Nuclear Information System (INIS)

    This study is concerned with effects of complex oxides on Charpy impact toughness of Heat Affected Zone (HAZ) of API X80 linepipe steels. Three kinds of steels were fabricated by varying alloying elements such as Ti, Al, and Mg and hot-rolling conditions to form complex oxides, and their microstructures and Charpy impact properties were investigated. The number of complex oxides present in the steel containing excess Ti, Al, and Mg was twice larger than that in the conventional steels, while their size ranged from 1 to 3 μm in the three steels. After the HAZ simulation test, the steel containing a number of oxides contained about 20 vol.% of acicular ferrite in the simulated HAZ, together with bainitic ferrite and martensite, whereas the HAZ microstructure of the conventional steels consisted of bainitic ferrite and martensite with a small amount of acicular ferrite. This formation of acicular ferrite in the oxide-containing steel was associated with the nucleation of acicular ferrite at complex oxides, thereby leading to the great (five times or more) improvement of Charpy impact toughness over the conventional steels

  13. Investigation on the Strengthening and Toughening Mechanism of 500 MPa V-Nb Microalloyed Anti-Seismic Rebars

    Directory of Open Access Journals (Sweden)

    Wei CHEN

    2015-11-01

    Full Text Available Two types of 500 MPa anti-seismic rebars were produced by V-Nb microalloyed combined with controlled rolling and cooling technology, the strengthening and toughening mechanism of which were investigated. The complex phase microstructures of specimens consist of ferrite, pearlite and bainite (6 – 10 %. Furthermore, a large number of V(C,N and Nb(C,N precipitates with size of 5 – 30 nm formed in the ferrite matrix, grain boundaries and on dislocation lines, promoting the precipitation strengthening and inhibiting grain coarsening to controlled cooling microstructure. The mechanical performance of the steels was improved by solution and grain refinement strengthening, precipitation and microstructure strengthening. And the best strengthening effect was obtained by grain refinement, which increased the yield strength more than 35 % strength increment contribution ratio to yield strength. Moreover, about 16.5 % microstructure strengthening increment was obtained due to bainite formation. The plasticity and low-temperature toughness enhancement were mainly attributed to ferrite grain refinement improvement.DOI: http://dx.doi.org/10.5755/j01.ms.21.4.9710

  14. Effects of Dynamic Strain Hardening Exponent on Abnormal Cleavage Fracture Occurring During Drop Weight Tear Test of API X70 and X80 Linepipe Steels

    Science.gov (United States)

    Kang, Minju; Kim, Hyunmin; Lee, Sunghak; Shin, Sang Yong

    2014-02-01

    In this study, drop weight tear tests (DWTT) were conducted on API X70 and X80 linepipe steels fabricated with various compositions and rolling and cooling conditions in order to correlate the strain hardening with the abnormal cleavage fracture occurring in the hammer-impacted area. Area fractions of fracture modes were measured from fractured DWTT specimens, and the measured data were analyzed in relation to microstructures, Charpy impact energy, and strain hardening. All the steels consisted of fine acicular ferrite, together with some bainitic ferrite, granular bainite, and martensite-austenite constituent. As the volume fraction of acicular ferrite increased, the area fraction of DWTT abnormal cleavage fracture decreased because the toughness of acicular ferrite was higher than other microstructures. The area fraction of abnormal cleavage fracture was weakly related with strain hardening exponents obtained from the quasi-static tensile and compressive tests, but showed better correlation with those obtained from the dynamic compressive test. This tendency could be more clearly observed when steels having similar Charpy impact energy levels were grouped. Since the DWTT was performed under a dynamic loading condition, thus, the abnormal cleavage fracture behavior should be related with the strain hardening analyzed under a dynamic loading condition.

  15. Effect of Composition and Deformation on Coarse-Grained Austenite Transformation in Nb-Mo Microalloyed Steels

    Science.gov (United States)

    Isasti, N.; Jorge-Badiola, D.; Taheri, M. L.; López, B.; Uranga, P.

    2011-12-01

    Thermomechanical processing of microalloyed steels containing niobium can be performed to obtain deformed austenite prior to transformation. Accelerated cooling can be employed to refine the final microstructure and, consequently, to improve both strength and toughness. This general rule is fulfilled if the transformation occurs on a quite homogeneous austenite microstructure. Nevertheless, the presence of coarse austenite grains before transformation in different industrial processes is a usual source of concern, and regarding toughness, the coarsest high-angle boundary units would determine its final value. Sets of deformation dilatometry tests were carried out using three 0.06 pct Nb microalloyed steels to evaluate the effect of Mo alloying additions (0, 0.16, and 0.31 pct Mo) on final transformation from both recrystallized and unrecrystallized coarse-grained austenite. Continuous cooling transformation (CCT) diagrams were created, and detailed microstructural characterization was achieved through the use of optical microscopy (OM), field emission gun scanning electron microscopy (FEGSEM), and electron backscattered diffraction (EBSD). The resultant microstructures ranged from polygonal ferrite (PF) and pearlite (P) at slow cooling ranges to bainitic ferrite (BF) accompanied by martensite (M) for fast cooling rates. Plastic deformation of the parent austenite accelerated both ferrite and bainite transformation, moving the CCT curves to higher temperatures and shorter times. However, an increase in the final heterogeneity was observed when BF packets were formed, creating coarse high-angle grain boundary units.

  16. The significance of ultrafine film-like retained austenite in governing very high cycle fatigue behavior in an ultrahigh-strength MN–SI–Cr–C steel

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, P., E-mail: zhaoping12@mails.tsinghua.edu.cn [Key Laboratory of Advanced Materials of Ministry of Education, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Zhang, B.; Cheng, C. [Materials Science and Engineering Research Center, Beijing Jiaotong University, Beijing 100044 (China); Misra, R.D K., E-mail: dmisra2@utep.edu [Laboratory for Excellence in Advanced Steel Research, Department of Metallurgical and Materials Engineering, University of Texas at El Paso, 500 W. University Avenue, El Paso, TX 79968-0520 (United States); Gao, G., E-mail: gaogh@bjtu.edu.cn [Materials Science and Engineering Research Center, Beijing Jiaotong University, Beijing 100044 (China); Bai, B.; Weng, Y. [Key Laboratory of Advanced Materials of Ministry of Education, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Materials Science and Engineering Research Center, Beijing Jiaotong University, Beijing 100044 (China)

    2015-10-01

    We elucidate here the very high cycle fatigue (VHCF) behavior of an ultrahigh-strength medium carbon Mn–Si–Cr–C steel processed using the approach of bainite-based quenching and partitioning (BQ&P). The microstructure of BQ&P process comprised of bainite, carbon-depleted martensite, retained austenite (RA) and small amount of martensite/austenite island (M/A). The tensile strength (R{sub m}) and fatigue limit strength after 10{sup 9} cycles (σ{sub w9}) and in the non-failed condition were 1688 MPa and 875 MPa, respectively such that σ{sub w9}/R{sub m} exceeded conventional steels and was 0.52. Two types of failure modes were observed depending on the surface and microstructure, notably surface-induced failure and non-inclusion-induced failure, where the non-inclusion-induced failure was influenced by the microstructure. Inclusion-induced failure was absent. The study underscores that film-like retained austenite was the underlying reason for superior fatigue properties, hitherto not previously obtained.

  17. 380CL车轮钢闪光对接焊组织与性能%Microstructure and Properties of 380CL Wheel Steel After Electric Flash Butt Welding

    Institute of Scientific and Technical Information of China (English)

    张桂芹; 董建君; 王燕; 赵文成

    2012-01-01

    380CL wheel steel after electric flash butt weld was analyzed by bend property, microstructure and mechanical property. The results show that the microstructure of weld bead obtained by electric flash butt weld is F+W+granular bainitic and the microstructure of HAZ is F+W+lath bainitic. The hardness of the weld bead and HAZ is higher than that of matrix metal. And the tensile and bending property of the welded plate are qualified.%对闪光对接焊后的380CL车轮钢进行了弯曲、金相及力学性能分析.结果表明:380CL车轮钢焊缝处金相组织为铁素体+魏氏组织+粒状贝氏体,热影响区金相组织为铁素体+魏氏组织+条状贝氏体,焊缝及热影响区硬度值均超过母材,焊接钢板拉伸、弯曲性能合格.

  18. Fracture Analysis of Cold Bending 20MnSi Hot Rolling Ribbed Steel Bar%20MnSi热轧带肋钢筋冷弯断裂原因分析

    Institute of Scientific and Technical Information of China (English)

    张朝晖; 杨敏刚

    2013-01-01

    通过化学成分、金相观察、扫描电镜和EDS分析,对某钢公司生产的20MnSi热轧带肋钢筋出现的冷弯断裂现象进行了研究.结果表明:钢材中C、Si、Mn元素含量超标,存在非金属夹杂物、粒状贝氏体和魏氏组织是导致热轧带肋钢筋冷弯断裂的主要原因.结合生产工艺,论述了非金属夹杂物、化学成分、粒状贝氏体和魏氏组织对钢筋冷弯断裂的影响机理.%By the observation and analysis of chemical composition, microstructure, SEM (scanning electron microscope) and EDS (energy dispersive X-ray spectrometry),the cold bending fracture of 20MnSi hot rolling ribbed steel bar was researched. The results show that the key reason for cold bending fracture is due to C, Si, Mn elements of excessive levels of steel, existing non-metallic inclusions, granular bainite and Widmanstatten structure. Combining with production process,the influence mechanism of non-metallic inclusion, chemical composition, granular bainite and Widmanstatten structure on the cold bending fracture of steels was discussed.

  19. 焊接热输入对 Q890钢焊缝金属组织及韧性的影响%Effect of heat input on microstructure and toughness of weld metal for Q890 steel

    Institute of Scientific and Technical Information of China (English)

    崔冰; 彭云; 彭梦都; 宋威; 竺培显

    2016-01-01

    采用熔化极气体保护焊对Q890钢进行不同热输入的对接焊试验。利用金相显微镜、扫描电子显微镜、透射电镜和电子背散射衍射技术研究热输入对焊缝组织及冲击性能的影响。结果表明,3种热输入焊缝金属组织主要由板条马氏体和板条贝氏体及少量的粒状贝氏体和残留奥氏体组成。随着热输入的增加,焊缝组织中板条粗化,而粒状贝氏体逐渐增多,部分板条内析出细小针状碳化物;随着热输入的增加,焊缝分析区域内残留奥氏体量逐渐减少分别为1.2%、0.53%、0.41%。焊缝金属冲击断口形貌从韧脆混合型断裂特征向脆性断裂特征的变化,与焊缝金属冲击吸收能量变化趋势一致。%A series of measurements were carried out by means of optical microscopy , scanning electron microscopy , transmission electron microscopy and electron back-scattered diffraction on specimens of GMAW plates of Q 890 quenched and tempered steel to determine effect of heat input on microstructure and impact toughness of weld metal .The results reveal that microstructure of weld metal mainly consists of lathmartensite/bainite, as well as a small amount of granular bainite and retained austenite for three kinds of heat input .With the increasing of heat input, the lath structure is coarsened , while the number of granular bainite increases , and fine carbides precipitate inside lath ,and the volume fractions of retained austenite decrease in weld metal those are 1.2%, 0.53%and 0.41%,respectively.The fractograph of weld with different heat inputs shows that radiation tendency from ductile /brittle mixed fracture characteristics to brittle fracture one which is consistent with the variation tendency of Charpy impact values of welded metals .

  20. X80管线钢组织和有效晶粒对慢拉伸行为的影响%Effects of microstructure and effective particle size on behavior of slow tension of X80 pipeline steels

    Institute of Scientific and Technical Information of China (English)

    张小立

    2012-01-01

    对系列X80管线钢研究表明,该材料组织特征为含有粒状贝氏体的针状铁素体;粒状贝氏体越细小弥散,其强韧性匹配越好。粒状贝氏体中,M-A岛的作用为阻碍裂纹的扩展;晶粒边界和M-A岛边界易萌生裂纹源。管线钢的有效晶粒决定了材料的塑韧性。具体表现为,当有效晶粒减小时,材料韧脆转变温度降低,断面收缩率提高。随着慢拉伸速率的提高,材料的断裂方式将发生改变。当拉伸速率为0.1 mm/s时,管线钢的延性最佳,而对强度的影响不大。这说明在管线钢富气服役状态下,富气压力有一个最佳值。拉伸速率升高后,断裂逐渐向脆性方式转变。%Study on series X80 pipeline steels shows that microstructure of the steels is characteristic of accicular ferrite containing grannular bainite; the finer size of grannular bainite is, the better the strength and toughness of the steel are. In grannular bainite, the effect of M-A island is to hinder growth of crack,and the grain boundary and island boundary is favourable for formation of crack. Ductility and toughness of pipeline steels depends on the effective grain size. Ductile-brittle transition temperature decreases with decreasing the effective grain size too, but reduction of area increases. With the increase of slow tension rate, the fracture mode is changed. When the tension rate is 0. 1 mm/s, the steels exhibit best tensility and strength of the steels keeps un-changed. Increasing the tension rate, the fracture mode is changed to the brittle.

  1. Microalloyed V-Nb-Ti and V steels Pt. 2 - precipitation behaviour during processing of structural beams

    Energy Technology Data Exchange (ETDEWEB)

    Tanniru, M.; Shanmugam, S.; Misra, R.D.K.; Panda, D.; Jansto, S.

    2005-02-15

    A comparative evaluation of the precipitation behaviour in V-Nb-Ti and V steels using transmission electron microscopy was undertaken to study the effective cumulative role of the microalloying additions. While the mechanical properties were similar, there were significant differences in the precipitation behaviour of the two steels. The microstructure of the V-Nb-Ti and V steels consisted predominantly of polygonal ferrite and fine pearlite; in addition, the former contained a small amount of bainite. The V-Nb-Ti steel exhibited significantly greater precipitation of carbonitrides compared with the V steel. In the V-Nb-Ti steel the carbonitrides precipitated as compounds (triplex and duplex type) of Ti, Nb, and V, while in the V steel they were V(C,N). They were characterised by cuboid (45-70 nm), spherical/irregular (20-45 nm), and fine/needleshaped (10-20 nm) morphology. The carbonitride precipitates grew as multimicroalloying compounds, depending on the processing conditions, as the number of microalloying elements increased. Coarse carbonitrides tended to precipitate preferentially along the grain boundaries, whereas fine carbides were dispersed in the matrix. The stoichiometric ratio of triplex carbonitrides in the V-Nb-Ti steel was Ti{sub 0.55}Nb{sub 0.35}V{sub 0.10}, while those of duplex type were Ti{sub 0.95}V{sub 0.05}, Nb{sub 0.70}V{sub 0.30}, and Ti{sub 0.73}Nb{sub 0.27}. Three microalloying elements (Ti, Nb, V) formed a coherent M{sub 4}C{sub 3} type of carbide in the V-Nb-Ti steel and exhibited short range order with the ferrite matrix, displayed by the diffraction pattern as a 'chemically sensitive' or 'superlattice' reflection. However, Nb formed the finest carbides (< 2 nm) and exhibited a ring form of selected area diffraction pattern. The carbonitrides that precipitated in the ferrite followed Baker-Nutting orientation relationships, and their partitioning was not observed in the pearlite or bainitic ferrite. The bainite

  2. 回火温度对不同冷速淬火 Q690钢组织及力学性能的影响%Effect of tempering temperature on microstructure and mechanical properties of Q690 steel queched under different cooling rates

    Institute of Scientific and Technical Information of China (English)

    王冬雪; 蔡庆伍

    2014-01-01

    Effect of tempering temperature on microstructure and mechanical properties of Q 690 steel under different cooling rates was investigated by using scanning electron microscope (SEM), tensile and impact tests.The results show that the microstructure of quenched specimen is mainly lath bainite ,and after tempering it consists of lath bainite ,granular bainite and polygonal ferrite with different proportion of them for different tempering temperatures .With the increase of the tempering temperature , the yield strength of the Q690 steel stabilizes, tensile strength decreases , elongation increases; when the steel is tempered at 500 ℃, the microstructure and properties are the optimal , Compared with low cooling rate , the strength of Q690 steel is higher, while the elongation and impact absorbed energy are lower when the cooling rate is higher .%利用扫描电镜和拉伸、冲击试验研究了回火温度对不同冷速Q690钢的组织及力学性能的影响。结果表明,试验钢淬火态组织主要为板条贝氏体,经不同温度回火后,组织为板条贝氏体、粒状贝氏体、多边形铁素体的混合组织,不同回火温度下各组织所占比例不同;随着回火温度的升高,Q690钢的屈服强度趋于稳定,抗拉强度呈下降趋势,伸长率总体呈上升趋势;在500℃回火时,组织性能最优。与低冷速相比,高冷速钢强度较高,伸长率及冲击吸收能量较低。

  3. Relationship between crystallographic structure of the Ti{sub 2}O{sub 3}/MnS complex inclusion and microstructure in the heat-affected zone (HAZ) in steel processed by oxide metallurgy route and impact toughness

    Energy Technology Data Exchange (ETDEWEB)

    Xiong, Zhihui; Liu, Shilong [School of Materials Science and Engineering, University of Science and Technology Beijing (China); Wang, Xuemin, E-mail: wxm@mater.ustb.edu.cn [School of Materials Science and Engineering, University of Science and Technology Beijing (China); Shang, Chengjia [School of Materials Science and Engineering, University of Science and Technology Beijing (China); Misra, R.D.K. [Laboratory for Excellence in Advanced Steel Research, Center for Structural and Functional Materials Research and Innovation, Department of Metallurgical and Materials Engineering, University of Texas at El Paso, 500 W. University Avenue, El Paso, TX 79968 (United States)

    2015-08-15

    A new method based on electron back scattered diffraction (EBSD) is proposed to determine the structure of titanium oxide/MnS complex inclusion which induced the formation of intragranular acicular ferrite (IAF) in heat-affected zone (HAZ) in steel processed by oxide metallurgy route. It was found that the complex inclusion was Ti{sub 2}O{sub 3}/MnS, the orientation relationship between Ti{sub 2}O{sub 3} and MnS was also examined, and the crystallographic orientation relationship among IAF, Ti{sub 2}O{sub 3}/MnS complex inclusion, austenite, bainite formed at lower temperature is researched systematically. It was observed that MnS precipitated on Ti{sub 2}O{sub 3} at specific habit plane and direction and MnS had a specific orientation relationship ((0001) Ti{sub 2}O{sub 3}//(111) MnS), <10–10> Ti{sub 2}O{sub 3}//<110> MnS) with respect to Ti{sub 2}O{sub 3}. Intragranular acicular ferrite (IAF) nucleated on MnS part of the Ti{sub 2}O{sub 3}/MnS complex inclusion had no specific orientation relationship with MnS. IAF and the surrounding bainite had different Bain groups, so that there was an increase in high angle boundaries, which was beneficial for the toughness of HAZ. - Highlights: • The inclusion of TiO{sub x}/MnS that induced IAF formation is identified to be Ti{sub 2}O{sub 3}/MnS. • The inclusion is identified based on electron back scattered diffraction (EBSD). • MnS and Ti{sub 2}O{sub 3} had specific orientation relationship of Ti{sub 2}O{sub 3}/MnS complex inclusion. • The IAFs formed on the same inclusion tend to be in one Bain group. • IAF and the surrounding bainite tend to be in different Bain groups.

  4. Effect of annealing temperature on microstructure and mechanical properties of a high Al-low Si TRIP steel

    Directory of Open Access Journals (Sweden)

    Zhao Yang

    2015-01-01

    Full Text Available By using optical microscope (OM, scanning electron microscope (SEM, transmission electron microscope (TEM, X-ray diffraction (XRD, electron back scattered diffraction (EBSD and tensile test, the effect of annealing temperature on microstructure and mechanical properties of a high Al-low Si TRIP steel was investigated. The results show that TRIP effect can be obtained when annealing temperature is above Ac3 due to the existence of δ-ferrite in this high Al-low Si TRIP steel. That is to say, the microstructure consisting of ferrite, bainite and retained austenite can be obtained when annealing temperature is above Ac3. Furthermore, the tensile strength and the product of strength and elongation decrease with increasing annealing temperature when annealing temperature is above Ac3.

  5. Corrosion Mechanism of Corrosion-Resistant Steel Developed for Bottom Plate of Cargo Oil Tanks

    Institute of Scientific and Technical Information of China (English)

    Feilong SUN; Xiaogang LI; Fan ZHANG; Xuequn CHENG; Cheng ZHOU; Nianchun WU; Yuqun YIN

    2013-01-01

    A new type of corrosion-resistant steel consisting of ferrite and bainite phases was developed for cargo oil tanks of crude oil tankers.The corrosion rate of this new steel was 0.22 mm/a,which was equivalent to ca.1/5 of the criterion (≤ 1 mm/a) for corrosion-resistant steels.The composition and element distribution of the corrosion products were investigated by micro-Raman spectrometry and energy dispersive spectrometer.The results demonstrated that the corrosion product was composed of α-FeOOH,Fe3O4 and a continuous Cu enrichment layer.This kind of corrosion product was protective to the steel matrix and accounted for the enhancement of the corrosion resistance of the new developed steel.

  6. Dynamic CCT Diagram of Automobile Beam Steel With High Strength Produced by FTSR Technology

    Institute of Scientific and Technical Information of China (English)

    WANG Xin; KANG Yong-lin; YU Hao; CHEN Li-bin; KONG Qing-fu

    2008-01-01

    The dynamic continuous cooling transformation (CCT) diagram and phase transformation rules of 510 MPa automobile beam steel, which is produced by a continuous casting of thin slab of FTSR technology in Tangshan Iron and Steel Co. Ltd. , are researched by thermal simulation experiment. The mierostructure characteristics of the beam steel under different test conditions are studied by means of optical microscope and scanning electron microscope. The test results show that the critical temperatures of phase transformation Ar3 and Ar1 will all decrease with the increase of the cooling rate. When the cooling rate is lower than 20℃·s-1, the ferrite and pearlite phase transformations are the main parts; when the cooling rate is higher than 20℃· s-1, the bainite phase appears. Moreover, the microstructurea of 510 MPa automobile beam steel produced by FTSR technology are also studied, and the results are basically in accordance with the CCT diagram gained from the test.

  7. Effect of Cooling Rate on Phase Transformations in a High-Strength Low-Alloy Steel Studied from the Liquid Phase

    Science.gov (United States)

    Dorin, Thomas; Stanford, Nicole; Taylor, Adam; Hodgson, Peter

    2015-12-01

    The phase transformation and precipitation in a high-strength low-alloy steel have been studied over a large range of cooling rates, and a continuous cooling transformation (CCT) diagram has been produced. These experiments are unique because the measurements were made from samples cooled directly from the melt, rather than in homogenized and re-heated billets. The purpose of this experimental design was to examine conditions pertinent to direct strip casting. At the highest cooling rates which simulate strip casting, the microstructure was fully bainitic with small regions of pearlite. At lower cooling rates, the fraction of polygonal ferrite increased and the pearlite regions became larger. The CCT diagram and the microstructural analysis showed that the precipitation of NbC is suppressed at high cooling rates, and is likely to be incomplete at intermediate cooling rates.

  8. Reasons Analysis on Laminated Fracture of DH36 Hull Plate During Tensile Test%DH36船板钢拉伸断口分层的原因分析

    Institute of Scientific and Technical Information of China (English)

    张鑫; 郭汉杰; 李宏亮; 吴建中; 刘锦强

    2012-01-01

    The reasons for the laminated fracture tinder tensile test of DH36 hull plate were researched by metallurgical observation and SEM observation. The results show that the main reasons are the aggregation of MnS as well as the martensite and bainite banded structure in the center of plate.%采用金相检验、扫描电镜检验等手段对DH36船板钢拉伸断口分层缺陷进行了分析.结果表明:DH36船板钢拉伸断口分层缺陷主要是由钢板厚度中心条状MnS夹杂和宽大的贝氏体、马氏体带状组织引起的.

  9. Influence of cooling conditions on X70 pipeline steel in-service welding HAZ

    Institute of Scientific and Technical Information of China (English)

    Jin Haicheng; Wang Yong; Han Bin; Chen Yuhua

    2006-01-01

    The chamber device was designed and set up to simulate the in-service welding. The results show: the ts/5, t8/3 and inner wall peak temperature Tp decrease with the cooling rate increases. The welding energy is carried off by flowing medium,the cooling rate increases, and many unbalanced microstructures such as granular bainite, martensite and M-A generate; it worsens the properties of HAZ. Under air-cooling, the cooling rate is slow, the austenite grain grows obviously , the lath ferrite crosses the whole austenite, and it causes the hardness value is also big. The change of HAZ width is not obvious with the increase of cooling rate; and burn-through is not susceptible to the cooling rate. The quench microstructures increase and the hydrogen does not outflow from the HAZ easily when increase the cooling rate, so the susceptibility of hydrogen cracking increases.

  10. Influence of plasma nitro carburization on fatigue properties in a 4340 steel with different microstructure; Infuencia da nitrocarbonetacao a plasma nas propriedades de fadiga de um aco 4340 com diferentes microestruturas

    Energy Technology Data Exchange (ETDEWEB)

    Ranieri, A.; Hashimoto, T.M. [UNESP, Guaratingueta, SP (Brazil). Faculdade de Engenharia (FEG); Baggio-Scheid, V.H.; Abdalla, A.J., E-mail: abdalla@ieav.cta.b [Departamento de Ciencia e Tecnologia Aeroespacial (IEAv/DCTA), Sao Jose dos Campos, SP (Brazil). Inst. de Estudos Avancados

    2010-07-01

    Three different routes of heat treatments were applied in samples of 4340 steel in order to modify the microstructures and mechanical properties. After this initial treatment was applied a plasma nitrocarburizing thermochemical treatment in a part of the samples, forming a layer of nitride (Fe{sub 4}N and Fe{sub 3}N{sub 2}) of about 10{mu}m, with high hardness, in order to improve the surface characteristics. The layer and microstructure were characterized with X-ray analysis, optical microscopy, confocal laser scanning and hardness test by microindentation. Tensile and fatigue tests show the influence of microstructure formed on the mechanical properties, the microstructure predominantly bainitic phase showed a better combination of ductility, toughness and fatigue life. After treatment nitrocarburizing was observed the effect of tempering, with a reduction in hardness of substrate and tensile strength. In steel with martensitic microstructure the fatigue life decreases. (author)

  11. A study on the continuous low cycle fatigue properties of 1%Cr-Mo-V steel and 12%Cr-Mo-V steel used in turbine rotors

    International Nuclear Information System (INIS)

    Continuous low cycle fatigue properties of 1%Cr-Mo-V steel and 12%Cr-Mo-V steel used in turbine rotors were investigated at 298, 773 and 873K in air atmosphere. The microstructure of 1%Cr-Mo-V steel and 12%Cr-Mo-V steel consisted of tempered upper bainite and tempered martensite, respectively. The experimental results show that the effect of the directionality of rotor on the fatigue life was rarely observed. The fatigue life of 1%Cr-Mo-V steel is significantly reduced at high temperature with decreasing plastic strain range, and the reason is considered to be the earlier crack initiation by oxidation damage. However, the effect of temperature on the fatigue life 12%Cr-Mo-V steel is known to be not existing throughout all the plastic strain range. This is suggested to be concerned with the increasing plastic ductility in tensile test with increasing test temperatures. (Author)

  12. A Modified Approach to Modeling of Diffusive Transformation Kinetics from Nonisothermal Data and Experimental Verification

    Science.gov (United States)

    Chen, Xiangjun; Xiao, Namin; Cai, Minghui; Li, Dianzhong; Li, Guangyao; Sun, Guangyong; Rolfe, Bernard F.

    2016-06-01

    An inverse model is proposed to construct the mathematical relationship between continuous cooling transformation (CCT) kinetics with constant rates and the isothermal one. The kinetic parameters in JMAK equations of isothermal kinetics can be deduced from the experimental CCT kinetics. Furthermore, a generalized model with a new additive rule is developed for predicting the kinetics of nucleation and growth during diffusional phase transformation with arbitrary cooling paths based only on CCT curve. A generalized contribution coefficient is introduced into the new additivity rule to describe the influences of current temperature and cooling rate on the incubation time of nuclei. Finally, then the reliability of the proposed model is validated using dilatometry experiments of a microalloy steel with fully bainitic microstructure based on various cooling routes.

  13. Characteristics of Retained Austenite in TRIP Steels with Bainitie Ferrite Matrix

    Institute of Scientific and Technical Information of China (English)

    ZHANG Mingya; ZHU Fuxian; DUAN Zhengtao; MA Shieheng

    2011-01-01

    Heat treatment process for producing cold rolled transformation induced plasticity-aided (TRIP-aided) steels with bainitic ferrite matrix was adopted.Characteristics of retained austenite (RA) in such TRIP steels were investigated.SEM and OM determination results showed that the stable austenite retained at room temperature were mainly located between laths and some of them inside the coarse ferrite.The grains were uniformly distributed in heat treated steel matrix and the regularly dispersed RA represented to be triangular morphology.XRD analysis indicated that RA content in matrix was not less than 10%,and TEM testified that RA inside the matrix were formed at the prior austenite boundaries and represented to be single or twin crystals.The ductile fracture originated from the boundaries of martensite islands from RA and ferrite.The cracks propagated along grain boundaries and some passed through the large ferrite grains and induced transgranular fracture.

  14. Numerical model to predict microstructure of the heat treated of steel elements

    Directory of Open Access Journals (Sweden)

    T. Domański

    2011-04-01

    Full Text Available In work the presented numerical models of tool steel hardening processes take into account thermal phenomena and phase transformations. Numerical algorithm of thermal phenomena was based on the Finite Elements Methods of the heat transfer equations. In the model of phase transformations, in simulations heating process continuous heating (CHT was applied, whereas in cooling process continuous cooling (CCT of the steel at issue. The phase fraction transformed (austenite during heating and fractions during cooling of ferrite, pearlite or bainite are determined by Johnson-Mehl-Avrami formulas. The nescent fraction of martensite is determined by Koistinen and Marburger formula or modified Koistinen and Marburger formula. In the simulations of hardening was subject the fang lathe of cone (axisymmetrical object made of tool steel.

  15. Optimization of RPC technique for refining the intermediate transformation microstructure

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The influence of processing parameters of relaxation-precipitation-controlling phase transformation (RPC) technique, finish rolling temperature, reduction ratio and relaxing time on the microstructurewas studied by thermo-simulation for a low carbon Nb and Ti containing micro-alloyed steel. The microstructure was investigated by optical microscope, transmission electron microscope and electron back scatterdiffraction (EBSD). The statistical results of the packet size were calculated. It shows that, after RPC process, the steel is a composite microstructure of bainite and matensite. The best thermo-simulation process for refinement in this experiment is deformation for 30% at 850℃, and then relaxing at this temperature for 60 s to 200 s. Increasing the reduction ratio from 30% to 60% or decreasing the deformation temperature to 800℃ would cause the best relaxation time to become shorter, increasing the deformation temperature to 900℃ would cause the refinement effect to be weak.

  16. Influence of isothermal quenching of LAMC CrMnSi cast steel on impact toughness

    Institute of Scientific and Technical Information of China (English)

    JIN Bao-shi; HUANG Zhi-qiu; SHEN Da-dong

    2005-01-01

    The influence of isothermal quenching process of low-alloy and medium carbon (LAMC) CrMnSi cast steel on the impact toughness was investigated. The microstructure and mechanical property of LAMC CrMnSi cast steel were analyzed by the laser optical modulator, the scanning electron microscopy, the energy dispersive spectrometer, the hardness and impact tests. The experimental results show that the dual phases of bainite and residual austenite can be obtained by the severity isothermal quenching, the fractographies of specimens change from quasi-cleavage to dimple at 310 ℃ for 60 min, the impact toughness for specimens at the room temperature isothermally achieves 130 J/cm2, meantime and its hardness is more than 45(HRC).

  17. Influence of reheating and cooling conditions on structure and mechanical properties of C-Mn-Si steel

    Directory of Open Access Journals (Sweden)

    T. Kvačkaj

    2008-07-01

    Full Text Available The paper deals with structure and properties development of AHSS (advance high-strength steel and UHSS (ultra high-strength steel steel grades for various groups of automotive parts. C-Mn-Si type steel properties are evaluated based on the results of laboratory controlled rolling and cooling. The important influence on mechanical and plastic properties, amount of residual austenite (RA and final structural type has, except for cooling rate, also starting temperature of intensive cooling (TIC which follows after hot plastic deformations. If TIC is from interval of 620-760°C the final structure predominantly consists of ferrite with RA. Mostly acicular ferrite with RA, as well as bainite with RA was obtained when TIC was kept in the range of 760-850°C.

  18. Change in austenite transformation kinetics under hot rolling action

    International Nuclear Information System (INIS)

    The effect of hot plastic deformation on kinetics of austenite transformation both during continuous cooling and under isothermal conditions, is studied. Experiments are performed using the 40 Kh, 60 KhC2, 40KhNM and 30KhGSN2 steels. It is shown that hot working speeds up isothermal transformation of austenite of low- and medium alloyed steels in pearlite range. In medium-alloyed 30KhGSN2 40KhNM steels hot working does not speed up atherma.l austenite transformation in the pearlite range and somewhat hinders it in the bainite range, due to which hardenability must not reduce at high temperatUre thermomechanical treatment. The difference in the effect of hot working on isothermal and athermal austenite transformations is conditioned by the effect of after-deformation pauses, which are practically inevitable in cases of continuous cooling of products

  19. Further discussion of orientation relationships, surface reliefs and FCC-BCC transformations in steels

    Energy Technology Data Exchange (ETDEWEB)

    Dahmen, U. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials and Molecular Research Division; Univ. of California, Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering

    1981-04-01

    In response to a recent discussion in this journal concerning tent-shaped surface-relief effects and the mechanism of formation of Widmanstätten ferrite and lower bainite, it was shown that Bhadeshia's (1) explanation of surface reliefs is in error. A degeneracy of the fcc → hcp type does not exist for an fcc → bcc transformation. Based on a distinction between the symmetries of the matrix, the transformation product and the strain (5), a general rule was derived for the occurrence of the type of crystallographic degeneracies described by Bhadeshia. The present paper confirmed Aaronson's (4) contention that the transformation is not shear-like (martensitic) in nature but diffusion controlled. Finally, it was argued, however, that the formal treatment of diffusional transformations may involve a shear.

  20. Influence of Hot Rolling Conditions on the Mechanical Properties of Hot Rolled TRIP Steel

    Institute of Scientific and Technical Information of China (English)

    LI Zhuang; WU Di

    2008-01-01

    Influence of hot rolling conditions on the mechanical properties of hot rolled TRIP steel was investigated.Thermomechanical control processing(TMCP)was conducted by using a laboratory hot rolling mill,in which three different kinds of finish rolling temperatures were applied.The results show that polygonal ferrite,granular bainite and larger amount of stabilized retained anstenite can be obtained by controlled rolling processes.The finer ferrite grain size is produced through the deformation induced transformation during deformation rather than after deformation,which affects the mechanical properties of hot rolled TRIP steel.Mechanical properties increase with decreasing finish rolling temperature due to the stabilization of retained austenite.Ultimate tensile strength(UTS),total elongation(TEL)and the product of ultimate tensile strength and total elongation(UTS×TEL)reaches optimal values(791 MPa,36% and 28 476 MPa%,respectively)whenthe specimen was hot rolled for 50% reduction at finish rolling temperature of 700℃.

  1. Effect of Controlled Cooling After Hot Rolling on Mechanical Properties of Hot Rolled TRIP Steel

    Institute of Scientific and Technical Information of China (English)

    WU Di; LI Zhuang; L(U) Hui-sheng

    2008-01-01

    A three-step cooling pattern on the runout table (ROT) was conducted for the hot rolled TRIP steel. Microstructural evolution during thermomechanical controlled processing (TMCP) was investigated. Proeessing condition of controlled cooling on a ROT in the laboratory rolling mill was discussed. The results indicated that the microstructure containing polygonal ferrite, granular bainite and a significant amount of the stable retained austenite can be obtained through three-step cooling on the ROT after hot rolling. TMCP led to ferrite grain refinement. Controlled cooling after hot rolling resulted in the stability of the remaining austenite and a satisfactory TRIP effect. Excellent mechanical properties were obtained through TMCP for the hot rolled TRIP steel.

  2. Effect of Thermomechanical Processing on Mechanical Properties of Hot Rolled Multiphase Steel

    Institute of Scientific and Technical Information of China (English)

    LI Zhuang; WU Di; L(U) Hui-sheng

    2008-01-01

    The effect of thermomechanical processing (TMP) on the mechanical properties of hot rolled multiphase steel was investigated. TMP was conducted using a laboratory hot rolling mill, in which three different kinds of finish rolling deformation degrees and temperatures were applied. The results indicate that polygonal ferrite, granular bainite, and a considerable amount of stabilized retained austenite can be obtained by TMP. The stability of the retained austenite increases with decreasing finish rolling temperature and increasing finish rolling deformation degrees. Ultimate tensile strength (σb), total elongation (δ), and the product of ultimate tensile strength by total elongation (σb·δ) for 50% reduction at finish rolling temperature of 700 ℃ reach maximum values [791 MPa, 36% and 28 476 (MPa·%), respectively].

  3. Austempering of hot rolled transformation-induced plasticity steels

    Institute of Scientific and Technical Information of China (English)

    Zhuang Li; Di Wu

    2008-01-01

    Thermomechanical controlled processing (TMCP) was conducted by using a laboratory hot rolling mill. Austempering inAustempering in the salt bath after hot rolling Was investigated. The effect of isothermal holding time on mechanical properties was studied throughing of the microstructure and mechanical properties of the specimens. The mechanism of transformation-induced plasticity (TRIP) was discussed. The results show that the microstructure of these steels consists of polygonal ferrite, granular bainite, and ad TRIP occur in the hot rolled Si-Mn TRIP steels. Excellent mechanical properties were obtained for various durations at 400℃. Prolonged holdingprecipitation, which destabilized the austenite. The mechanical properties were optimal when the specimen was held for 25 min, and the tensile strength, total elongation, and strength ductility balance reached the maximum values of 776 MPa, 33%,respevtively.

  4. Effects of finishing rolling temperatures and reduction on the mechanical properties of hot rolled multiphase steel

    Institute of Scientific and Technical Information of China (English)

    LI Zhuang; WU Di

    2007-01-01

    Effects of finishing rolling temperatures and reduction on the mechanical properties of hot rolled multiphase steel were investigated. Thermo-mechanical control processing (TMCP) was conducted by using a laboratory hot rolling mill, in which three different kinds of finishing rolling temperatures and reduction and various austempering times were applied. The results showed that polygonal ferrite, granular bainite and larger amount of stabilized retained austenite can be obtained by controlled rolling processes, and that the strain-induced transformation to martensite from the retained austenite can occur gradually when the steel is deformed during tensile test. Mechanical properties increase with decreasing finishing rolling temperature and increasing amount of deformation. The most TRIP (transformation induced plasticity) effect, and ultimate tensile strength (UTS), total elongation (TEL) and the product of ultimate tensile strength and total elongation (UTS× TEL) are obtained at 20 min.

  5. Study on the microstructure and hardness of in-service welded joint of X70 pipeline steel

    Institute of Scientific and Technical Information of China (English)

    Chen Yuhua; Wang Yong; Liu Geping

    2007-01-01

    Hydrogen induced cracking (HIC) is one of the main problems of in-service welding onto active pipeline. Microstructure and hardness of welded joint have a vital effect on hydrogen induced cracking. The microstructure and hardness of welded joint of X70 pipeline steel were studied using simulation in-service welding device. The results show that the main microstructures of in-service welded seam are grain boundary ferrite, intracrystalline acicular ferrite, as well as small amount of widmanstatten structure. The main microstructures of coarse grain heat-affected zone (CGHAZ) are coarse granular bainite, lath ferrite and martensite. Metastable phases such as martensite and lath ferrite are found in CGHAZ because of the too quick cooling velocity and the hardness of the CGHAZ is high.

  6. Mechanisms and modeling of cleavage fracture in simulated heat-affected zone microstructures of a high-strength low alloy steel

    Science.gov (United States)

    Lambert-Perlade, A.; Sturel, T.; Gourgues, A. F.; Besson, J.; Pineau, A.

    2004-03-01

    The effect of the welding cycle on the fracture toughness properties of high-strength low alloy (HSLA) steels is examined by means of thermal simulation of heat-affected zone (HAZ) microstructures. Tensile tests on notched bars and fracture toughness tests at various temperatures are performed together with fracture surface observations and cross-sectional analyses. The influence of martensite-austenite (M-A) constituents and of “crystallographic” bainite packets on cleavage fracture micromechanisms is, thus, evidenced as a function of temperature. Three weakest-link probabilistic models (the “Master-curve” (MC) approach, the Beremin model, and a “double-barrier” (DB) model) are applied to account for the ductile-to-brittle transition (DBT) fracture toughness curve. Some analogy, but also differences, are found between the MC approach and the Beremin model. The DB model, having nonfitted, physically based scatter parameters, is applied to the martensite-containing HAZ microstructures and gives promising results.

  7. Influência da deformação na região de não recristalização da austenita sobre a transformação em resfriamento contínuo em um aço bainítico de baixo carbono

    Directory of Open Access Journals (Sweden)

    André Barros Cota

    2005-06-01

    Full Text Available Estudaram-se os efeitos da deformação na região de não recristalização da austenita e da taxa de resfriamento sobre a temperatura Bi (temperatura de início de transformação bainítica e sobre a microestrutura final, de um aço ARBL bainítico de baixo carbono submetido a resfriamento contínuo, usando ensaios de torção a quente e resfriamento a gás He. As amostras foram submetidas a quatro programas de ensaios de torção, sendo quatro taxas de resfriamento acelerado para cada um. A evolução microestrutural com a taxa de resfriamento foi estudada por microscopia eletrônica de varredura e por medição de dureza Vickers. Os resultados mostram que, para a taxa de resfriamento de 2ºC/s, a microestrutura é constituída de ferrita poligonal e bainita, independente do grau de deformação. Para taxas de resfriamento mais altas, a microestrutura é, predominantemente, bainítica, com uma pequena quantidade de ferrita poligonal fina. Verifica-se que, para um mesmo grau de deformação, uma maior taxa de resfriamento implica uma menor temperatura Bi, sendo esse efeito mais pronunciado para as amostras não deformadas; e que, para uma mesma taxa de resfriamento, uma maior deformação na região de não recristalização resulta em uma maior temperatura Bi.The influence of deformation in the non-recrystallization region of austenite and cooling rates on the bainitic transformation temperature (Bi and final microstructure were studied in HSLA low carbon bainitic steel by means of hot torsion tests and accelerated cooling. The samples were submitted to four programs of torsion tests with four accelerated cooling rates for each one. The microstructure change from the cooling rate was studied by scanning electron microscopy and Vickers hardness. The results show that for a 2ºC/s cooling rate, the microstructure is composed of bainite and polygonal ferrite, independent of the deformation degree. For higher cooling rates, the microstructure is

  8. Fine structure in the inter-critical heat-affected zone of HQ130 super-high strength steel

    Indian Academy of Sciences (India)

    Li Yajiang; Wang Juan; Liu Peng

    2003-02-01

    The microstructure in the inter-critical heat-affected zone (ICHAZ) of HQ130 steel, has been investigated by thermo-simulation test, SEM and TEM. The problem of toughness decrease in the ICHAZ (p = 800°C) as well as the effect of M–A constituent and carbide precipitation on brittleness was analysed. The test results indicated that the microstructure in the ICHAZ of HQ130 steel was mostly a mixture of lath martensite (ML) and granular bainite (Bg) with a fine but nonuniform grain structure. The cause of brittleness in the ICHAZ was related to production of the M–A constituent in the local region and carbide precipitation. By controlling the welding heat input carbide precipitation and the formation of the M–A constituent can be avoided or decreased.

  9. Effect of Mg Content on the Microstructure and Toughness of Heat-Affected Zone of Steel Plate after High Heat Input Welding

    Science.gov (United States)

    Xu, Long-Yun; Yang, Jian; Wang, Rui-Zhi; Wang, Yu-Nan; Wang, Wan-Lin

    2016-07-01

    The effect of Mg content on the microstructure and toughness of the heat-affected zone (HAZ) of steel plates after high heat input welding was investigated by means of welding thermal simulation test and in situ observation through high-temperature laser scanning confocal microscopy. It was found that with the increase of Mg content in the steel, the former austenite grain sizes were greatly decreased and the mainly microstructural constituents in HAZ were changed from the brittle constituents of Widmanstätten ferrite, ferrite side plate and upper bainite to the ductile constituents of intragranular acicular ferrite and polygonal ferrite. The proportion of grain boundary ferrite was decreased greatly with the further addition of Mg from 27 to 99 ppm. As a result, the HAZ toughness after welding with heat input of 400 kJ cm-1 is increased with increasing Mg content in the steel plate.

  10. Mechanical and Microstructural Characterization of an Aluminum Bearing Trip Steel

    Science.gov (United States)

    Monsalve, Alberto; Guzmán, Alexis; De Barbieri, Flavio; Artigas, Alfredo; Carvajal, Linton; Bustos, Oscar; Garza-Montes-de Oca, Nelson F.; Colás, Rafael

    2016-06-01

    The mechanical properties and microstructural characteristics of a steel able to sustain the TRIP-effect were studied. The material was prepared by taking in mind the partial substitution of silicon by aluminum following a processing route that included hot forging, hot and cold rolling, intercritical annealing, and a final bainitic isothermal treatment. The mechanical properties that were obtained resulted to be above those of commercial a 780 TRIP steel. The TRIP phenomenon was confirmed by the change in retained austenite before and after deforming the steel; X-ray diffraction was used to evaluate the volume content of retained austenite. Formability of the steel under study can be rationalized in terms of the texture developed in the material.

  11. Microstructure Evolution during Friction Stir Spot Welding of TRIP steel

    DEFF Research Database (Denmark)

    Lomholt, Trine Colding

    Transformation Induced Plasticity (TRIP) steels have been developed for automotive applications due to the excellent high strength and formability. The microstructure of TRIP steels is a complex mixture of various microstructural constituents; ferrite, bainite, martensite and retained austenite...... deteriorating the uniform elongation. The unique deformation properties can be exploited in automotive applications for crash resistant parts due to the high energy absorption, thus improving passenger safety. Furthermore, the high strength and good formability permits the application of thinner sheet material...... Welding (FSSW) is investigated. The aim of the study is to assess whether high quality welds can be produced and, in particular, to obtain an understanding of the microstructural changes during welding. The microstructure of the welded samples was investigated by means of reflected light microscopy...

  12. Friction stir processing on carbon steel

    Energy Technology Data Exchange (ETDEWEB)

    Tarasov, Sergei Yu., E-mail: tsy@ispms.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055, Russia and National Research Tomsk Polytechnic University, Tomsk, 634050 (Russian Federation); Melnikov, Alexander G., E-mail: melnikov-ag@tpu.ru [National Research Tomsk Polytechnic University, Tomsk, 634050 (Russian Federation); Rubtsov, Valery E., E-mail: rvy@ispms.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation)

    2014-11-14

    Friction stir processing of medium carbon steel samples has been carried out using a milling machine and tools made of cemented tungsten carbide. Samples have been machined from 40 and 40X steels. The tools have been made in the shape of 5×5×1.5 mm and 3×3×1.5 mm tetrahedrons. The microstructure of stirred zone has been obtained using the smaller tool and consists of fine recrystallized 2-3 μm grains, whereas the larger tool has produced the 'onion-like' structures comprising hard quenched 'white' 500-600 MPa layers with 300-350 MPa interlayers of bainite needles. The mean values of wear intensity obtained after measuring the wear scar width were 0.02 mm/m and 0.001 mm/m for non-processed and processed samples, respectively.

  13. Microstructure and Mechanical Properties of Hot Rolled Low Silicon TRIP Steel Containing Phosphorus and Vanadium

    Institute of Scientific and Technical Information of China (English)

    HOU Xiao-ying; XU Yun-bo; ZHAO Yan-feng; WU Di

    2011-01-01

    The microstructure characteristics and mechanical properties of a low-silicon TRIP steel containing phosphorus and vanadium at different finish rolling temperatures were studied by laboratory hot rolling experiments. Dif- ferent ratios of multiphase microstructure (ferrite, granular bainite and retained austenite) are obtained. With a decrease in finish rolling temperature, the volume fractions of ferrite and retained austenite increase. EBSD analysis re veals that most of the ferrite grains are fine, and decreasing of finish rolling temperature leads to an increase in low angle boundaries. Under the joint effects of fine grain strengthening, dislocation strengthening and precipitation strengthening, higher strength is obtained. When the finish rolling temperature is decreased to 800 ℃, the steel has excellent mechanical properties: Rp0.2 =470 MPa; Rm=960 MPa; Rp0. 2/Rm=0. 49; A50 =19.7%; n=0. 25.

  14. Effect of Si, Mn and Al on the Microstructure and Mechanical Properties of ADI Weld Metal

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The effects of Si, Mn and Al on the microstructure and mechanical properties of ADI weld have been studied. The microstructure of ADI weld metal mainly consists of bainitic ferrite and retained austenite. Mechanical properties of ADI weld increase with increasing Si content, but an excess of Si(3.79%) results in decreasing the austemperability owing to decreasing the carbon content of the matrix austenite. Mn increases the retained austenite volume fraction,but the ductility and impact toughness of weld obviously decrease with increasing Mn content because of increased amount of martenite and twin martenite. In the range of 0.13%~0.64%Al, increasing Al content favours improving the mechanical properties of ADI weld. Therefore, it is very important to select suitable Si, Mn and Al contents to improve mechanical properties of ADI weld.

  15. Effect of dislocation configuration on non-equilibrium boron segregation during cooling

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Different densities and configurations of crystal defects were obtained in an austenitic Fe-30%Ni alloy and an ultra low carbon bainitic (ULCB) alloy by undergoing different deformations and annealing treatments at high temperatures. Boron segregation on grain boundaries and subgrain boundaries during air-cooling were revealed by means of the particle tracking autoradiography technique. It is found that non-equilibrium segregation is resisted in deformed grains after recovery and polygonization, boron-depleted zones seem to be quite clear in recrystallized grains than those in deformed original grains during cooling. Subgrain boundaries and polygonized dislocation cells have a significant effect on non-equilibrium boron segregation during the air-cooling. The results implicates that dislocation configuration is a more important factor affecting boron segregation at grain boundaries rather than the density of defects itself in the grain.

  16. The influence of electric ARC activation on the speed of heating and the structure of metal in welds

    Directory of Open Access Journals (Sweden)

    Savytsky Oleksandr M.

    2016-01-01

    Full Text Available This paper presents the results of a research related to the impact of electric arc activation onto drive welding energy and metal weld heating speed. It is confirmed that ATIG and AMIG methods, depending on metal thickness, single pass weldability and chemical composition of activating flux, enable the reduction of welding energy by 2-6 times when compared to conventional welding methods. Additionally, these procedures create conditions to increase metal weld heating speed up to 1,500-5,500°C/s-1. Steel which can be rapidly heated, allows for a hardened structure to form (with carbon content up to 0.4%, together with a released martensitic structure or a mixture of bainitic-martensitic structures. Results of the research of effectiveness of ATIG and AMIG welding showed that increase in the penetration capability of electric arc, which increases welding productivity, is the visible side of ATIG and AMIG welding capabilities.

  17. Study on the microstructure and mechanical properties of medium carbon Cr-Si-Mn-Mo-V steel for cast inserted dies

    Directory of Open Access Journals (Sweden)

    HAO Xiao-yan

    2005-11-01

    Full Text Available The microstructure and mechanical properties of cast inserted dies for automobile covering components were studied. The results show that the as-cast microstructures of cast inserted dies are composed of pearlite, martensite,bainite, and austenite; and that the annealed microstructure is granular pearlite. The mechanical properties of cast inserted dies approach that of forged inserted dies. The tensile strength is 855 MPa, the elongation is 16%, the impact toughness is 177 J/cm2, and the hardness after annealing and quenching are HRC 19 and HRC 60-62. In addition, the cast inserted dies have good hardenability. The depth of the hardening zone and the hardness after flame quenching satisfy the operating requirements. The cast inserted dies could completely replace the forged inserted dies for making the dies of automobile covering components.

  18. Development and formability analysis of TRIP seamless steel tube

    Institute of Scientific and Technical Information of China (English)

    Zhang Zicheng; Zhu Fuxian

    2014-01-01

    In this paper, the production technology of transformation induced plasticity (TRIP) steel was first introduced into the steel tube manufacture field to produce the steel tubes with high strength and plasticity. The TRIP seamless steel tubes with the microstructure of ferrite, bainite, retained austenite and a little martensite were successfully fabricated using a cold-drawn steel tube with two-stage heat treatment technique and continu- ous heat treatment process, respectively. The ring tensile test and cold bend test were carried out to study the formability of the newly developed TRIP seamless steel tube. The results showed that the TRIP seamless steel tubes have a good cold formability, and they are available to be used in the tube hydroforming process. In ad- dition, the equipment of continuous heat treatment developed in the current study can be used to produce TRIP steel tube, and it may serve as an important reference for the industrial production of TRIP steel tube.

  19. Measurement of Dynamic Elastic Constants of RPV Steel Weld due to Localized Microstructural Variation

    Energy Technology Data Exchange (ETDEWEB)

    Cheong, Yong Moo; Kim, Joo Hag; Hong, Jun Hwa; Jung, Hyun Kyu [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2000-10-15

    The dynamic elastic constants of the simulated weld HAZ (heat-affected zone) of SA 508 Class 3 reactor pressure vessel (RPV) steel were investigated by resonant ultrasound spectroscopy (RUS). The resonance frequencies of rectangular parallelepiped samples woe calculated from the initial estimates of elastic stiffness C{sub 11}, C{sub 12} and C{sub 44} with an assumption of isotropic property, dimension and density. Through the comparison of calculated resonant frequencies with the measured resonant frequencies by RUS, very accurate elastic constants of SA 508 Class 3 steel were determined by iteration and convergence processes. Clear differences of Youngs modulus and shear modulus were shown from samples with different thermal cycles and microstructures. Youngs modulus and shear modulus of samples with fine-grained bainite were higher than those with coarse-grained tempered martensite. This tendency was confirmed from other results such as micro-hardness test

  20. Measurement of Dynamic Elastic Constants of RPV Steel Weld due to Localized Microstructural Variation

    International Nuclear Information System (INIS)

    The dynamic elastic constants of the simulated weld HAZ (heat-affected zone) of SA 508 Class 3 reactor pressure vessel (RPV) steel were investigated by resonant ultrasound spectroscopy (RUS). The resonance frequencies of rectangular parallelepiped samples woe calculated from the initial estimates of elastic stiffness C11, C12 and C44 with an assumption of isotropic property, dimension and density. Through the comparison of calculated resonant frequencies with the measured resonant frequencies by RUS, very accurate elastic constants of SA 508 Class 3 steel were determined by iteration and convergence processes. Clear differences of Youngs modulus and shear modulus were shown from samples with different thermal cycles and microstructures. Youngs modulus and shear modulus of samples with fine-grained bainite were higher than those with coarse-grained tempered martensite. This tendency was confirmed from other results such as micro-hardness test

  1. Microstructural parameters and yielding in a quenched and tempered Cr-Mo-V pressure vessel steel

    International Nuclear Information System (INIS)

    In this work the plastic deformation behaviour of a Cr-Mo-V pressure vessel steel is studied at ambient and low temperatures. To produce a wide range of microstructures, different austenitizing, quenching and tempering treatments are performed. The microstructures, including grain and dislocation structures as well as carbides, are evaluated. A qualitative model is proposed for the martensitic and bainitic transformations explaining the morphology and crystallography of the transformation products. Based on microstructural observations of undeformed and deformed materials, as well as the tensile test results, the role of various obstacles to dislocation motion in plastic deformation is evaluated. Finally the strength increment, its temperature dependence and the effect due to combinations of various obstacles are analyzed. The results are intended to serve as basis for further fracture behaviour analyses. (author)

  2. The Numerical Analysis of the Phenomena of Superficial Hardening of the Hot-Work Tool Steel Elements / Analiza Numeryczna Zjawisk Przypowierzchniowego Hartowania Elementów Ze Stali Narzędziowej Do Pracy Na Gorąco

    Directory of Open Access Journals (Sweden)

    Bokota A.

    2015-12-01

    Full Text Available In the paper the complex model of hardening of the hot-work tool steel is presented. Model of estimation of phase fractions and their kinetics is based on the continuous heating diagram (CHT and cooling diagram (CCT. Phase fractions which occur during the continuous heating and cooling (austenite, pearlite or bainite are described by Johnson-Mehl (JM formula. To determine of the formed martensite the modified Koistinen-Marburger (KM equation is used. Model takes into account the thermal, structural, plastic strains and transformation plasticity. To calculate the plastic strains the Huber-Mises plasticity condition with isotopic hardening is used. Whereas to determine transformations induced plasticity the Leblond model is applied. The numerical analysis of phase compositions and residual stresses in the hot-work steel (W360 element is considered.

  3. Partial transformation of austenite in Al-Mn-Si TRIP steel upon tensile straining: an in situ EBSD study

    DEFF Research Database (Denmark)

    Lomholt, Trine Nybo; Adachi, Y.; da Silva Fanta, Alice Bastos;

    2013-01-01

    The transformation of austenite to martensite in an Al–Mn–Si transformation-induced plasticity steel was investigated with in situ electron backscatter diffraction (EBSD) measurements under tensile straining. The visualisation of the microstructure upon straining allows for an investigation...... of the stability of austenite grains against strain-induced transformation, with particular focus on the grain size and the location of the austenite grains. The findings confirm that size and location of austenite grains are significant parameters for their stability. Small austenite grains were observed...... to be more stable than large grains, while austenite grains located beside bainitic ferrite are the most stable. Moreover, it is demonstrated that austenite grains transform gradually...

  4. Microstructural Characterization and Mechanical Properties of Electron Beam Welded Joint of High Strength Steel Grade S690QL

    Directory of Open Access Journals (Sweden)

    Błacha S.

    2016-06-01

    Full Text Available In the paper the results of metallographic examination and mechanical properties of electron beam welded joint of quenched and tempered steel grade S690QL are presented. Metallographic examination revealed that the concentrated electron beam significantly affect the changes of microstructure in the steel. Parent material as a delivered condition (quenched and tempered had a bainitic-martensitic microstructure at hardness about 290 HV0.5. After welding, the microstructure of heat affected zone is composed mainly of martensite (in the vicinity of the fusion line of hardness 420 HV0.5. It should be noted, however, that the microstructure of steel in the heat affected zone varies with the distance from the fusion line. The observed microstructural changes were in accordance with the CCT-S transformation diagram for the examined steel.

  5. Numerical modelling of tools steel hardening. A thermal phenomena and phase transformations

    Directory of Open Access Journals (Sweden)

    T. Domański

    2010-01-01

    Full Text Available This paper the model hardening of tool steel takes into considerations of thermal phenomena and phase transformations in the solid state are presented. In the modelling of thermal phenomena the heat equations transfer has been solved by Finite Elements Method. The graph of continuous heating (CHT and continuous cooling (CCT considered steel are used in the model of phase transformations. Phase altered fractions during the continuous heating austenite and continuous cooling pearlite or bainite are marked in the model by formula Johnson-Mehl and Avrami. For rate of heating >100 K/s the modified equation Koistinen and Marburger is used. Modified equation Koistinen and Marburger identify the forming fraction of martensite.

  6. Metal magnetic memory signals from surface of low-carbon steel and low-carbon alloyed steel

    Institute of Scientific and Technical Information of China (English)

    DONG Li-hong; XU Bin-shi; DONG Shi-yun; YE Ming-hui; CHEN Qun-zhi; WANG Dan; YIN Da-wei

    2007-01-01

    In order to investigate the regularity of metal magnetic signals of ferromagnetic materials under the effect of applied load, the static tensile test of Q235 steel and 18CrNiWA steel plate specimens were conducted and metal magnetic memory signals of specimens were measured during the test process.The influencing factors of metal magnetic memory signals and the relationship between axial appliedload and signals were analyzed. The fracture and microstructure of the specimens were observed.The results show that the magnetic signals corresponding to the measured points change linearly approximately with increasing axial load.The microstructure of Q235 steel is ferrite and perlite, whereas that of l8CrNiWA steel is bainite and low-carbon martensite.The fracture of these two kinds of specimens is ductile rupture;carbon content of specimen materials and dislocation glide give much contribution to the characterisffcs of magnetic curves.

  7. The origin of transformation textures in steel weld metals containing acicular ferrite

    Science.gov (United States)

    Kluken, A. O.; Grong, Ø.; Hjelen, J.

    1991-03-01

    The present investigation is concerned with basic studies of the development of transformation textures in steel weld metals, using the electron backscattering pattern (EBSP) technique. It is shown that the acicular ferrite (AF) plates exhibit an orientation relationship with both the austenite and the prior delta ferrite columnar grains in which they grow. The observed orientation relationship lies within the Bain orientation region and can be described by three texture components, i.e., a component and two complementary components. Each of these texture components is orientated approximately parallel with the original cell/dendrite growth direction. Measurements of the spatial misorientation between neighboring plates confirm that the morphology of AF in low-alloy steel weld metals bears a close resemblance to upper bainite.

  8. As-Cast Acicular Ductile Aluminum Cast Iron

    Institute of Scientific and Technical Information of China (English)

    S M Mostafavi Kashani; S M A Boutorabi

    2009-01-01

    The effects of nickel (2.2%)and molybdenum (0.6%)additions on the kinetics, microstructure, and me-chanical properties of ductile aluminum cast iron were studied under the as-cast and tempered conditions. Test bars machined from cast to size samples were used for mechanical and metallurgical studies. The results showed that adding nickel and molybdenum to the base iron produced an upper bainitic structure, resulting in an increase in strength and hardness. The same trend was shown when the test bars were tempered at 300 ℃ in the range of 300℃ to 400 ℃. The elongation increased with increasing the temperature from 300 ℃ to 400 ℃. The carbon content of the retained austenite also increased with increasing the temperature. The results also showed that the kinetics, mi-crostructure, and mechanical properties of this iron were similar to those of Ni-Mo alloyed silicon ductile iron.

  9. Solid-particle erosion behavior of cast alloys used in the mining industry

    Institute of Scientific and Technical Information of China (English)

    Hakan Atapek; Sinan Fidan

    2015-01-01

    The erosive-wear response of five commercial ferrous-based cast alloys used for crushing was examined in this study. The micro-structures of the alloys were modified to elucidate the effect of microstructural features on wear. Erosion tests were conducted using alumi-num oxide particles (90–125 µm) at 70 m/s and a normal impact angle (90°). The worn surfaces were characterized by scanning electron mi-croscopy and 3D non-contact laser profilometry. It is found that (i) a pearlitic structure exhibiting a greater plastic deformation than both bainitic and martensitic structures shows the greatest resistance to erosive wear at normal impact and (ii) the fracture characteristics of car-bide and graphite particles plays an important role in determining the erosion wear behavior of the cast alloy matrices.

  10. Induction heat treatment of laser welds

    DEFF Research Database (Denmark)

    Bagger, Claus; Olsen, Flemming Ove; Sørensen, Joakim Ilsing

    2003-01-01

    the laser beam as close as possible. After welding, the samples were quality assessed according to ISO 13.919-1 and tested for hardness. The metallurgical phases are analysed and briefly described. A comparison between purely laser welded samples and induction heat-treated laser welded samples is made....... The temperature measurements show that, with the chosen mechanical set-up of laser and induction coil, it is difficult to obtain a quick increase to around 300º C, the temperatures required for efficient heat-treatment with the induction coil alone. Despite this, a reduction in the hardness values of...... both GA260 and CMn were recorded when laser welded samples were induction heat-treated. The reduction was 6 to 8 % for GA260 and 41 to 45 % for CMn, respectively. GA260 displays a ferrite structure in basic and welded form, whereas CMn, with ten times more carbon, shows a ferrite and bainite structure...

  11. Effect of microstructure on the impact toughness of high strength steels

    Energy Technology Data Exchange (ETDEWEB)

    Gutierrez, I.

    2014-07-01

    One of the major challenges in the development of new steel grades is to get increasingly high strength combined with a low ductile brittle transition temperature and a high upper shelf energy. This requires the appropriate microstructural design. Toughness in steels is controlled by different microstructural constituents. Some of them, like inclusions, are intrinsic while others happening at different microstructural scales relate to processing conditions. A series of empirical equations express the transition temperature as a sum of contributions from substitutional solutes, free nitrogen, carbides, pearlite, grain size and eventually precipitation strengthening. Aimed at developing a methodology that could be applied to high strength steels, microstructures with a selected degree of complexity were produced at laboratory in a Nb-microalloyed steel. As a result a model has been developed that consistently predicts the Charpy curves for ferrite-pearlite, bainitic and quenched and tempered microstructures using as input data microstructural parameters. This model becomes a good tool for microstructural design. (Author)

  12. An austempering study of ductile iron alloyed with copper

    Directory of Open Access Journals (Sweden)

    OLIVERA ERIC

    2005-07-01

    Full Text Available Austempered ductile iron (ADI has proved to be an excellent material as it possesses attractive properties: high strength, ductility and toughness are combined with good wear resistance and machinability. These properties can be achieved upon adequate heat treatment which yields the optimum microstructure for a given chemical composition. In this paper the results of an investigation the austempering of ADI alloyed with 0.45 % Cu for a range of times and temperatures are reported. The microstructure and fracture mode developed throughout these treatments have been identified by means of light and scanning electron microscopy and X-ray diffraction analysis. It was shown that the strength, elongation and impact energy strongly depend on the amounts of bainitic ferrite and retained austenite. Based on these results, and optimal processing window was established.

  13. Effect of microstructure on the impact toughness of high strength steels

    International Nuclear Information System (INIS)

    One of the major challenges in the development of new steel grades is to get increasingly high strength combined with a low ductile brittle transition temperature and a high upper shelf energy. This requires the appropriate microstructural design. Toughness in steels is controlled by different microstructural constituents. Some of them, like inclusions, are intrinsic while others happening at different microstructural scales relate to processing conditions. A series of empirical equations express the transition temperature as a sum of contributions from substitutional solutes, free nitrogen, carbides, pearlite, grain size and eventually precipitation strengthening. Aimed at developing a methodology that could be applied to high strength steels, microstructures with a selected degree of complexity were produced at laboratory in a Nb-microalloyed steel. As a result a model has been developed that consistently predicts the Charpy curves for ferrite-pearlite, bainitic and quenched and tempered microstructures using as input data microstructural parameters. This model becomes a good tool for microstructural design. (Author)

  14. Influence of Martensite Volume Fraction on Impact Properties of Triple Phase (TP) Steels

    Science.gov (United States)

    Zare, Ahmad; Ekrami, A.

    2013-03-01

    Ferrite-bainite-martensite triple phase (TP) microstructures with different volume fractions of martensite were obtained by changing heat treatment time during austempering at 300 °C. Room temperature impact properties of TP steels with different martensite volume fractions ( V M) were determined by means of Charpy impact testing. The effects of test temperature on impact properties were also investigated for two selected microstructures containing 0 (the DP steel) and 8.5 vol.% martensite. Test results showed reduction in toughness with increasing V M in TP steels. Fracture toughness values for the DP and TP steels with 8.5 vol.% martensite were obtained from correlation between fracture toughness and the Charpy impact energy. Fractography of Charpy specimens confirmed decrease in TP steels' toughness with increasing V M by considering and comparing radial marks and crack initiation regions at the fracture surfaces of the studied steels.

  15. Toughening mechanisms of a high-strength acicular ferrite steel heavy plate

    Science.gov (United States)

    Cao, Zhi-Qiang; Bao, Yan-Ping; Xia, Zheng-Hai; Luo, Deng; Guo, Ai-Min; Wu, Kai-Ming

    2010-10-01

    An ultra-low carbon acicular ferrite steel heavy plate was obtained with an advanced thermo-mechanical control process-relaxed precipitation controlled transformation (TMCP-RPC) at Xiangtan Steel, Valin Group. The heavy plate has a tensile strength of approximately 600 MPa with a lower yield ratio. The impact toughness of the heavy plate achieves 280 J at -40°C. The fine-grained mixed microstructures of the heavy plate mainly consist of acicular ferrite, granular bainite, and polygonal ferrite. The high strength and excellent toughness of the heavy plate are attributed to the formation of acicular ferrite microstructure. The prevention of blocks of martensite/retained austenite (M/A) and the higher cleanness are also responsible for the superior toughness.

  16. Mechanical And Microstructural Evaluation Of A Wear Resistant Steel; Avaliacao mecanica e microestrutural de um aco resistente ao desgaste

    Energy Technology Data Exchange (ETDEWEB)

    Santos, F.L.F. dos; Vieira, A.G.; Correa, E.C.S.; Pinheiro, I.P., E-mail: falletti@hotmail.co [Centro Federal de Educacao Tecnologica de Minas Gerais (CEFET/MG), Belo Horizonte, MG (Brazil). Dept. de Engenharia de Materiais

    2010-07-01

    In the present work, the analysis of the mechanical properties and the microstructural features of a high strength low alloy steel, containing chromium, molybdenum and boron, subjected to different heat treatments, was conducted. After austenitizing at 910 deg C for 10 minutes, three operations were carried out: oil quenching, oil quenching followed by tempering at 200 deg C for 120 minutes and austempering at 400 deg C for 5 minutes followed by water cooling. The analysis was performed through tensile and hardness tests, optical microscopy and X-ray diffraction. The bainitic structure led to high strength and toughness, both essential mechanical properties for wear resistant steels. The occurrence of allotriomorphic ferrite and retained austenite in the samples also increased the wear resistance. This phenomenon is related to the fact that both structures are able to be deformed and, in the case of the retained austenite, the transformation induced plasticity TRIP effect may take place as the material is used. (author)

  17. Computer Model of Phase Transformation From Hot-Deformed Austenite in Niobium Microalloyed Steels

    Institute of Scientific and Technical Information of China (English)

    XU Yun-bo; YU Yong-mei; LIU Xiang-hua; WANG Guo-dong

    2007-01-01

    Based on thermodynamics and kinetics, a new mathematical model was developed to calculate the CCT diagrams and the transformation kinetics in low carbon niobium steels, in which the effect of deformation on the degree of supercooling was taken into account. The undercooling caused by deformation is the major reason for the increase of the starting transition temperature during continuous cooling. The critical cooling rate of bainite formation is within 2-5 ℃/s for the studied niobium steels and deformation is suitable for the occurrence of pearlite. The ferrite volume fraction increases with the increase of the austenite boundary area, and decreases with the increase of the cooling rate. The calculated CCT diagrams and the volume fraction of each phase are in good agreement with the measurements.

  18. Microstructure Characterization of High-heat-input Welding Joint of HSLA Steel Plate for Oil Storage Construction

    Institute of Scientific and Technical Information of China (English)

    Weihua Sun; Guodong Wang; Jiming Zhang; Dianxiu Xia; Hao Sun

    2009-01-01

    In this paper, microstructure and mechanical properties of welding metals in 610 MPa high strength low alloy (HSLA) were studied after high-heat-input welding. Both the base material and the weld joint proved excellent strength and toughness by vibratory electrogas arc (VEGA) welding under 90 to 100 kJ/cm heat-input. The heat-affected zone (HAZ) was comprised of fine-grain zone (FGZ) and coarse-grain zone (CGZ), which characterizes fine granular structure and lathing-bainite substructure. It has found that large quantity of dispersed TiN and M23C6 precipitates restrain structure growing in HAZ and strengthen the weldment together with dislocations in the welded joint.

  19. Microstructure and mechanical properties of hard zone in friction stir welded X80 pipeline steel relative to different heat input

    Energy Technology Data Exchange (ETDEWEB)

    Aydin, Hakan, E-mail: hakanay@uludag.edu.tr [Engineering and Architecture Faculty, Mechanical Engineering Department, Uludag University, 16059 Gorukle-Bursa (Turkey); Nelson, Tracy W. [Mechanical Engineering Department, Brigham Young University, 435 CTB, Provo, UT 84602 (United States)

    2013-12-01

    The study was conducted to investigate the microstructure and mechanical properties of the hard zone in friction stir welded X80 pipeline steel at different heat inputs. Microstructural analysis of the welds was carried out using optical microscopy, transmission electron microscopy, and microhardness. Heat input during friction stir welding process had a significant influence on the microstructure and mechanical properties in the hard zone along the advancing side of the weld nugget. Based on the results, the linear relationships between heat input and post-weld microstructures and mechanical properties in the hard zone of friction stir welded X80 steels were established. It can be concluded that with decrease in heat input the bainitic structure in the hard zone becomes finer and so hard zone strength increases.

  20. Numerical model of phase transformation of steel C80U during hardening

    Directory of Open Access Journals (Sweden)

    T. Domański

    2007-12-01

    Full Text Available The article concerns numerical modelling of the phase transformations in solid state hardening of tool steel C80U. The transformations were assumed: initial structure – austenite, austenite – perlite, bainite and austenite – martensite. Model for evaluation of fractions of phases and their kinetics based on continuous heating diagram (CHT and continuous cooling diagram (CCT. The dilatometric tests on the simulator of thermal cycles were performed. The results of dilatometric tests were compared with the results of the test numerical simulations. In this way the derived models for evaluating phase content and kinetics of transformations in heating and cooling processes were verified. The results of numerical simulations confirm correctness of the algorithm that were worked out. In the numerical example the simulated estimation of the phase fraction in the hardened axisimmetrical element was performed.

  1. Laser beam welding of new ultra-high strength and supra-ductile steels

    Science.gov (United States)

    Dahmen, Martin

    2015-03-01

    Ultra-high strength and supra-ductile are entering fields of new applications. Those materials are excellent candidates for modern light-weight construction and functional integration. As ultra-high strength steels the stainless martensitic grade 1.4034 and the bainitic steel UNS 53835 are investigated. For the supra-ductile steels stand two high austenitic steels with 18 and 28 % manganese. As there are no processing windows an approach from the metallurgical base on is required. Adjusting the weld microstructure the Q+P and the QT steels require weld heat treatment. The HSD steel is weldable without. Due to their applications the ultra-high strength steels are welded in as-rolled and strengthened condition. Also the reaction of the weld on hot stamping is reflected for the martensitic grades. The supra-ductile steels are welded as solution annealed and work hardened by 50%. The results show the general suitability for laser beam welding.

  2. 亚温调质对F550级船板钢低温韧性的影响%Effect of quenching temperature and tempering on low-temperature toughness of a F550 ship plate steel

    Institute of Scientific and Technical Information of China (English)

    李晓林; 余伟; 朱爱玲; 武会宾; 万德成; 张杰

    2012-01-01

    Microstructure and mechanical properties of F550 ship plate steel after guenching at 820 ℃ ,850 ℃ ,910 ℃ and tempering at 600 ℃ were investigared. The effects of quenching temperature on low temperature toughness of F550 ship plate steel were examined. The morphology, size and distribution of martensite-austenite (M/A) constituents and the volume fraction of M/A islands and polygonal ferritc obtained after different heat treatment processes were observed by optical microscope, scanning electron microscopy (SEM) , transmission electron microscopy (TEM) and quantitative metallographie methods. The results show that after intereritical quenching at 850 ℃ and tempering at 600℃ , the low temperature toughness at -80 ℃ of the steel is the best, which is about 220 J. After complete quenching at 910 0C and tempering at 600 ℃ , the main mierostrueture of the steel is bainite, and the amount of M/A islands with the size above 2 ~m increases and the M/A islands are distributed at grain boundaries or between bainitic ferrite lathes with the form of elongated block and dots, which lead to the decrease of toughness. After sub-critical heat treatment, the microstructure consists of polygonal ferrite (QF) and granular bainite, and polygonal ferrite is fine and distributed uniformly. The amount of M/A islands is smaller compared with that of complete quenching and tempering, and the M/A islands with dot-shape disperse uniformly between bainitic ferrite lathes acting as effective barriers to crack propagation.%研究F550级船板钢在820、850和910℃淬火,600℃回火条件下的热处理工艺对其低温韧性的影响。通过光学显微镜、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等实验方法,分析了组织中多边形铁素体以及M/A岛体积分数、M/A岛的形貌、尺寸及分布情况。结果表明:选择在亚温区850℃淬火后600℃回火试验钢的-80℃低温韧性最佳,达到220J

  3. Constitutive relationships of hot stamping boron steel B1500HS based on the modified Arrhenius and Johnson–Cook model

    Energy Technology Data Exchange (ETDEWEB)

    Li, Huiping; He, Lianfang [School of Materials Science and Engineering, Shandong University of Science and Technology, Qingdao 266590 (China); Zhao, Guoqun, E-mail: zhaogq@sdu.edu.cn [Key Laboratory for Liquid-Solid Structure Evolution and Processing of Materials of Ministry of Education, Shandong University, Jinan 250061 (China); Zhang, Lei [Key Laboratory for Liquid-Solid Structure Evolution and Processing of Materials of Ministry of Education, Shandong University, Jinan 250061 (China)

    2013-09-15

    Constitutive relationship of boron steel is one of the most necessary mathematical models in the numerical simulation of hot stamping; it describes the relationship of the flow stress with strain, strain rate and temperature. In order to attain the constitutive relationship of boron steel B1500HS, four types of samples with microstructure of austenite, ferrite+pearlite, bainite or martensite are prepared by the Gleeble 1500D thermo-mechanical simulator. Isothermal uniaxial tension testings for these specimens are performed at 20–900 °C at the strain rates of 0.01 s{sup –1}, 0.1 s{sup –1}, 1.0 s{sup –1} and 10 s{sup –1} by Gleeble 1500D, and the true stress–strain curves at the relative conditions are gained. The experimental results show that, the flow stress of samples with relative microstructure rises with the decrease of the deformation temperature, and with the increase of the strain rate. The modified Arrhenius model is used to describe the hot deformation of samples with austenite microstructure, and the modified Johnson–Cook model is used to describe the deformation process of samples with ferrite+pearlite, bainite or martensite microstructure. The constitutive equations depending on the strain, strain rate and temperature are attained by the regression analysis for the experimental data of flow stress, strain, strain rate, temperature, etc. The comparison of the computational data and the experimental results shows that, the computational data using the constitutive relationships are well consistent with the experimental data.

  4. Detecting acoustic events during thermal and mechanical loading

    Energy Technology Data Exchange (ETDEWEB)

    Por, Gabor; Bereczki, Peter; Danka, Zsolt; Trampus, Peter [College of Dunaujvaros (Hungary)

    2014-11-01

    We examined Acoustic Emission (AE) events during combined heat and tensile test carried out in different steels (S235JRG2, TRIP and TWIP steels) on Gleeble simulator. The simulator enabled us to control parameters for fast heating and cooling parallel with pressing and tensile the sample until its real break. The aim was to investigate the structural change of the material, phase transformation in the steel at different temperatures, and connect them to signatures measured by acoustic emission sensors. During testing we noticed characteristics of Barkhausen noise. We demonstrate and prove definitely that we were facing Acoustic Barkhausen Noise (ABN) due to AC current used to heating and to maintaining the temperature in the cylindrical ferritic sample. It was observed, that the magnitude of the ABN dropped suddenly to the half when the tensile test started after preheating, and it was growing back when the tensile test went to plastic deformation with elongation of the tested sample. Localization of the ABN sources has been done showing the distribution of the sources along the whole material. ABN sources were observed all along the sample with interesting density growth in the section where the diameter was smaller, thus the tension was higher. Nevertheless, this was not the only observation, since the place of the densest sources was displaced from one position to another position until the break occurred near to the densest place of ANB and AE source. Off-line examination of the structure of material afterward using destructive test proved that we could register those cooling periods, where phase transition took place in the material. Ferrite-bainite and magnetite-bainite transitions were connected to some higher distribution of ANB and AE signals during the test. Rate of hits and sum of hit were connected to material transition during cooling. The first results of AE measurements during tensile test in TWIP materials showed that AE events are connected with

  5. Effects of Mn and Nb on the macro- and microsegregation in high-Mn high-Al content TRIP steels

    Directory of Open Access Journals (Sweden)

    A. Grajcar

    2011-05-01

    Full Text Available Purpose: The aim of the paper is to determine the effects of Mn and Nb on the macro- and microsegregation of new-developed (3-5Mn 1.5Al TRIP steels in the as-cast state and after hot forging.Design/methodology/approach: To assess possible macro- and microsegregation the chemical composition was investigated in the macro scale by OES and by the use of EDS in microregions. To reveal the macrostructure the ingots were etched by Oberhoffer’s reagent. The chemical composition along a diameter of the ingots was tested as well as in different regions of the plastically deformed flats. Metallographic investigations were carried out using optical (OM and scanning electron microscopy (SEM.Findings: The Mn and Nb contents have significant effects on the obtained bainitic-martensitic structures and the morphology of retained austenite. The tendency to macrosegregation of Mn and Al between middle and external parts of the as-cast ingots and hot forged flats was detected. The Nb micoalloying results in the overall refinement of obtained microstructures and reduces the identified segregation of Al and Mn. A little microsegregation of these alloying elements between structural constituents was also detected.Research limitations/implications: Further investigations to describe in detail the identified structural constituents and the tendency of alloying elements to segregation in the thermomechanically rolled sheets are in progress.Practical implications: The knowledge of the macro- and microsegregation of Mn and Al in the TRIP steels with a high fraction of retained austenite is of primary importance for the manufacturing paths of these multiphase structure steels.Originality/value: A problem of segregation of Al and Mn in advanced high strength steels with and without Nb microaddition was described and interesting types of bainitic structures were identified

  6. Microstructure and mechanical properties of 08Ni3DR cryogenic steel after heat treatment%低温用08 Ni3 DR钢热处理后的组织与力学性能

    Institute of Scientific and Technical Information of China (English)

    王彩焕

    2013-01-01

    采用Gleeble 3800热模拟试验机测定了08Ni3DR钢的CCT曲线,观察了不同冷却速度下钢的显微组织,并对其热处理后的组织与性能进行了分析。结果表明,08Ni3DR钢奥氏体化后,冷却速度稍高于8℃/s时,淬火组织中会出现贝氏体;当冷却速度高于15℃/s时,组织逐渐变为马氏体+贝氏体,晶粒均匀细小。08Ni3DR钢加热到850℃,快速水冷到300℃以下,之后进行650℃回火处理后,晶粒细小均匀,组织为回火索氏体,综合力学性能良好。%CCT curves of 08Ni3DR steel were measured by Gleeble 3800 thermal simulation testing machine , and microstructure of the steel was observed under different cooling temperature , and microstructure and mechanical properties of the 08Ni3DR steel after heat treatment was analyzed.The results show that austenitized and cooled with the speed above 8℃/s, bainite appears in the quenched microstructure .When the cooling speed is above 15℃/s, the microstructure is composed of martensite and bainitic , and the crystal line grain is uniform and fine . When 08Ni3DR steel is heated to 850 ℃and then rapidly cooled to 300 ℃, and tempered at 650 ℃, the crystal is uniform and fine , the microstructure is tempered sorbite and the comprehensive mechanical properties is preferable .

  7. 焊后热处理对ASTM 4130钢焊接热影响区组织与性能的影响%Effect of post-weld heat treatment on microstructure and mechanical properties Of HAZ of ASTM 4130 steel

    Institute of Scientific and Technical Information of China (English)

    薄国公; 王勇; 韩涛; 李立英

    2011-01-01

    Effect of post-weld heat treatment (PWHT) on microstructure, hardness,low temperature impact toughness and fracture morphology of heat-affected zone (HAZ) of ASTM 4130 steel was investigated by using optical microscopy (OM), hardness test and scanning electron microscopy (SEM). The results show that hardness levels reduce and toughness levels of coarse-grain HAZ (CGHAZ) and fine-grain HAZ (FGHAZ) improve with prolonging the soaking time. After PWHT,typical microstructure in heat-affected zone (HAZ) is comprised of tempered martensite,ferrite and bainite. Higher hardness and lower impact toughness in CGHAZ is mainly caused by the appearance of bainite and coarse tempered martensite.%通过金相观察、硬度试验和扫描电镜分析,研究了不同焊后热处理保温时间对ASTM 4130钢焊接热影响区显微组织、硬度、低温冲击韧性和断口形貌的影响.结果表明,随焊后热处理保温时间的延长,热影响区硬度降低,粗晶区和细晶区韧性明显改善;经焊后热处理后,热影响区组织主要为回火马氏体、铁素体和贝氏体;造成粗晶区硬度较高、韧性较低的主要原因是该区出现了贝氏体和粗大的回火马氏体.

  8. Characterization by transmission electron microscopy of a JRQ steel subjected to different heat treatments; Caracterizacion por microscopia electronica de transmision de un acero JRQ sometido a diferentes tratamientos termicos

    Energy Technology Data Exchange (ETDEWEB)

    Moreno G, N.

    2014-07-01

    In this work a study was conducted on the steel Astm A-533, Grade B, Class 1 of reference JRQ, for the purpose of carrying out a study by transmission electron microscopy on the size and distribution of precipitates in steel samples JRQ previously subjected to heat treatments. This because the reactor vessels of the nuclear power plant of Laguna Verde, are made of a steel Astm A-533 Grade B, Class 1. It is known that the neutron radiation causes damage primarily embrittlement in materials that are exposed to it. However, observable damage through mechanical tests result from microstructural defects and atomic, induced by the neutron radiation. In previous studies hardening by precipitation of a JRQ steel (provided by the IAEA) was induced by heat treatments, finding that the conditions of heat treatment that reproduce the hardness and stress mechanical properties of a steel Astm A-533, Grade B, Class 1 irradiated for 8 years to a fluence of 3.5 x 10 {sup 17} neutrons/cm{sup 2} and to a temperature of 290 grades C are achieved with annealing treatments at 550 grades C. In the studied samples it was found that the more hardening phase both the heat treatments as the neutron radiation, is the bainite, being the ferrite practically unchanged. Which it gave the tone to believe that the ferrite is the phase that provides at level macro the mechanical properties in stress, since in the irradiated samples such properties remained unchanged with respect to the non-irradiated material, however changes were observed in material ductility, which may be attributable to the change of hardness in the bainite, which opens a possibility for modeling the micromechanical behavior of this material. (Author)

  9. Effect of microstructure on static and dynamic mechanical properties of high strength steels

    Science.gov (United States)

    Qu, Jinbo

    The high speed deformation behavior of a commercially available dual phase (DP) steel was studied by means of split Hopkinson bar apparatus in shear punch (25m/s) and tension (1000s-1) modes with an emphasis on the influence of microstructure. The cold rolled sheet material was subjected to a variety of heat treatment conditions to produce several different microstructures, namely ferrite plus pearlite, ferrite plus bainite and/or acicular ferrite, ferrite plus bainite and martensite, and ferrite plus different fractions of martensite. Static properties (0.01mm/s for shear punch and 0.001s -1 for tension) of all the microstructures were also measured by an MTS hydraulic machine and compared to the dynamic properties. The effects of low temperature tempering and bake hardening were investigated for some ferrite plus martensite microstructures. In addition, two other materials, composition designed as high strength low alloy (HSLA) steel and transformation induced plasticity (TRIP) steel, were heat treated and tested to study the effect of alloy chemistry on the microstructure and property relationship. A strong effect of microstructure on both static and dynamic properties and on the relationship between static and dynamic properties was observed. According to the variation of dynamic factor with static strength, three groups of microstructures with three distinct behaviors were identified, i.e. classic dual phase (ferrite plus less than 50% martensite), martensite-matrix dual phase (ferrite plus more than 50% martensite), and non-dual phase (ferrite plus non-martensite). Under the same static strength level, the dual phase microstructure was found to absorb more dynamic energy than other microstructures. It was also observed that the general dependence of microstructure on static and dynamic property relationship was not strongly influenced by chemical composition, except the ferrite plus martensite microstructures generated by the TRIP chemistry, which exhibited

  10. Strengthening and Toughening of a Heavy Plate Steel for Shipbuilding with Yield Strength of Approximately 690 MPa

    Science.gov (United States)

    Liu, Dongsheng; Cheng, Binggui; Chen, Yuanyuan

    2013-01-01

    HSLA-100 steel with high content of alloying elements (nominally in wt pct, 3.5 Ni, 1.6 Cu, and 0.6Mo) is now used to produce heavy plates for constructing a hull and drilling platform. We proposed here a substantially leaner steel composition (containing 1.7 Ni, 1.1 Cu, and 0.5Mo) to produce a heavy plate to 80 mm thickness with mechanical properties comparable with those of the HSLA-100 grade. A continuous cooling transformation (CCT) diagram of the steel was constructed. Key parameters of thermal treatment and revealing mechanisms of strengthening and toughening were derived based on industrial production trials. The microstructures of the 80-mm-thick plate were lath-like bainite (LB) at near surface of the quarter thickness ( t/4), and granular bainite (GB)+LB at center thickness ( t/2) after solutionizing and water quenching (Q). The effect of tempering (T) on the microstructures and properties of the plate was investigated. Excellent combination of room temperature strength and low-temperature Charpy V-notch (CVN) toughness approximately equivalent to that of the HSLA 100 grade (YS > 690 MPa, CVN energy >100 J even at 193 K [-80 °C]) was achieved in the plate treated by the QT process with tempering temperature of 898 K (625 °C). The combination of strength and toughness at t/4 is superior to that at t/2 of the plate under both as-quenched and QT conditions. This result is attributed to that the fraction of high-angle grain boundaries (HAGBs) at t/4 is higher than that at t/2.

  11. Nanoscale precipitation in hot rolled sheet steel

    Science.gov (United States)

    Sun, Jun

    Some newer hot rolled high strength low alloy (HSLA) steels with a single phase ferrite matrix have obtained substantial strengthening from nanoscale precipitation. These HSLA are reported to have a good combination of strength, ductility and hole-expansion ability. In the current work, Gleeble ® 3500 torsion testing was employed to simulate the hot rolling process with varying run-out table cooling rates and coiling temperatures on five microalloyed steels with additions of Ti, Nb, Mo, Cr and V, to investigate the effects of microalloy additions and processing conditions on microstructures as well as mechanical properties. Subsized tensile specimens obtained from as-twisted torsion samples were used to evaluate mechanical properties. The precipitation states of the five steels with different processing conditions were characterized using extraction replica TEM. Comparison of microstructures and mechanical properties was discussed. Characterization of the microstructure via light optical microscopy showed the matrix microstructure was mainly influenced by coiling temperature, which indicates that the transformation from austenite to ferrite occurred during the coiling period. A higher Ti content was shown to reduce the second constituent fractions. Investigation of carbon extraction replica specimens via TEM revealed the presence of nanoscale precipitation. Extensive nanoscale precipitation was observed in most of the specimens having a polygonal ferrite matrix, while in the granular bainite/ferrite microstructure at lower temperatures, fewer microalloy carbides were present. The specimens with polygonal ferrite had similar or higher yield strength than the specimens with granular bainite microstructure, which suggests the effectiveness of precipitation strengthening from extensive nanoscale precipitates. In the Nb-Mo steel, more significant strengthening due to grain refinement was evident. Yield strength values were less than reported for JFE's "NANOHITEN

  12. Metallurgical products of microalloy constructional steels

    Directory of Open Access Journals (Sweden)

    W. Ozgowicz

    2011-01-01

    Full Text Available Purpose: The aim of the paper is a monographic presentation, based on investigations connected with the elaboration of new kinds of microalloy steels and a technique of heat and thermo-mechanical treatment in the production of a selected group of metallurgical products.Design/methodology/approach: The influence of the chemical composition and metallurgical purity on the homogenisation of austenite was analysed, as well as thermally activated processes and phase transformations in the course of deformation and controlled cooling conditions, concerning micradditives Nb, V, Ti, B and metallurgical products.Findings: The chemical composition of the obtained constructional steels with microadditives was quoted, as well as the technological conditions of forging and rolled products required for industrial purposes.Research limitations/implications: The results of investigations concerning the structure and mechanical properties have been presented, as well as the resistance to fracture, mainly of thick plates and hand-forged and drop-forged products and also elements of sheet structures for the automotive industry, made of AHSS steels.Practical implications: The results of the author’s own investigations concerning microalloy steels indicate the actual possibility of their application in practice in many steelworks, particularly in plants producing semi products and final metallurgical products, among others in hot rolling plants and forging shops, first of all in machine building and automotive industry.Originality/value: The application of modern metallurgical technologies and metalforming has been suggested for selected metallurgical products of microalloy steels of the type HSLA with a ferrite-bainite, bainite or tempered martensite structure and also of HSS steels and UHSS steel with a wide range of mechanical properties and technological formability, which is essential in the case of products of the automotive industry.

  13. Limit of the local approach application of the brittle fracture on hydrogen charged steels

    International Nuclear Information System (INIS)

    The local approach of the brittle fracture by cleavage developed by BEREMIN relies the macroscopic mechanical properties to local criteria. It allows to predict the probability of failure of the structure by performing detailed calculation of the stress and deformation fields in the different element volumes within this structure. It also takes into account the distribution of the defects initiating the fracture in a specific zone. The local approach allows then the determination of a statistical criterion to be applied on cleavage fracture. The cumulative distribution function PR, over a small volume V0 ahead of a crack tip or defect can be expressed as: PR 1 - exp[-σw/σu)m] where σw WEIBULL stress and σu mean cleavage stress defined as the stress / volume leading to PR = 0.63 and m is an empirically determined parameter presenting the degree of scatter in measured strength values. The paper deals with the application of this approach on three steels in absence and in presence of hydrogen: railway steel FM80, with pearlitic structure, 35CD4 steel employed in tool's joints in a tempered martensitic state and a bainitic A508.3 used in nuclear power plants. The goal of this work is to show that in the case hydrogenated steel, the local approach is improved if the defects promoted by high stress triaxiality and local critical hydrogen concentration do not exceed the element volume V0 in which the material is considered to be statistically homogeneous. The results show that in the two first steel the local approach is improved even in presence of hydrogen. In the hydrogenated bainitic steel (A508.3), the application of this method is not possible due to development in the material of fish eyes which the size is very large with respect to V0. (author). 7 refs., 4 figs., 1 tab

  14. Influence of a matrix on properties of mottled cast iron applied for mill rolls

    Directory of Open Access Journals (Sweden)

    J. Krawczyk

    2010-07-01

    Full Text Available Mill rolls are ones of the most expensive tools applied in plastic working processes and have to satisfy several criteria, which allow them to be used. Cast iron mill rolls, due to their fracture toughness and tribological properties, are the most often applied at hot-rolling in the last rolling stands. This results from the smallest dynamic loads of such rolling stands and the decisive influence of the surface quality of these tools on the surface quality of the rolled product. An improper microstructure of rolls can lead to their premature wearing, e.g. broken flanges, pivots twisting off etc. By means of the heat treatment the matrix microstructure and morphology of carbide precipitationscan be modified and this in-turn can influence cast iron properties.Determination of the influence of microstructure changes, caused by the heat treatment, on the properties of EN-GJN-HV300 low-alloycast iron, after its modification and spheroidization – is the aim of the present paper. Those changes are based on the formation pearlitic or bainitic matrices at the similar morphology of graphite and ledeburitic cementite precipitations. The performed investigations should enable designing the heat treatment of cast iron metallurgical rolls in such a way as to obtain the optimal microstructures for functional parameters of these type of tools. The influence of changing the pearlitic matrix into the bainitic one on such properties as: hardness, impact strength, tensile strength, creep limit, bending strength and a stress intensity factor KIc was investigated in this study. Samples for testing, the listed above mechanical properties, were taken from an industrial casting with care to have pieces of very similar crystallization conditions.

  15. Microstructural parameters governing cleavage fracture behaviors in the ductile-brittle transition region in reactor pressure vessel steels

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Won-Jon; Lee, Bong-Sang; Oh, Yong-Jun; Huh, Moo-Young; Hong, Jun-Hwa

    2004-08-15

    The fracture behaviors in the ductile-brittle transition region of reactor pressure vessel (RPV) steels with similar chemical compositions but different manufacturing processes were examined in view of cleavage fracture stress at crack-tip. The steels typically had a variation in grain size and carbide size distribution through the different manufacturing processes. Fracture toughness was evaluated by using a statistical method in accordance to the ASTM standard E1921. From the fractography of the tested specimens, it was found that fracture toughness of the steels increased with increasing distance from the crack-tip to the cleavage initiating location, namely cleavage initiation distance (CID, X{sub f}) and its statistical mean value (K{sub JC(med)}) was proportional to the cleavage fracture stress ({sigma}{sub f}) determined from finite-element (FE) calculation at cleavage initiating location. On the other hand, {sigma}{sub f} could also be calculated by applying the size of microstructural parameters, such as carbide, grain and bainite packet, into the Griffith's theory for brittle fracture. Among the parameters, the {sigma}{sub f} obtained from the mean diameter of the carbides above 1% of the total population was in good agreement with the {sigma}{sub f} value from the FE calculation for the five different steels. The results suggest that the fracture toughness of bainitic RPV steels in the transition region is mostly influenced by only some 1% of total carbides and the critical step for cleavage fracture of the RPV steels should be the propagation of this carbide size crack to the adjacent ferrite matrix.

  16. Selection of Heat Treatment Process and Wear Mechanism of High Wear Resistant Cast Hot-Forging Die Steel

    Institute of Scientific and Technical Information of China (English)

    WEI Min-xian; WANG Shu-qi; WANG Lan; CUI Xiang-hong; CHEN Kang-min

    2012-01-01

    Dry sliding wear tests of a Cr-Mo-V cast hot-forging die steel was carried out within a load range of 50--300 N at 400℃ by a pin-on-disc high temperature wear machine. The effect of heat treatment process on wear resistance was systematically studied in order to select heat treatment processes of the steel with high wear resistance. The morphology, structure and composition were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) ; wear mechanism was also discussed. Tribo-oxide layer was found to form on worn surfaces to reduce wear under low loads, but appear inside the matrix to increase wear under high loads. The tribo-oxides were mainly consisted of Fe3O4 and Fe2O3, FeO only appeared under a high load. Oxidative mild wear, transition of mild-severe wear in oxidative wear and extrusive wear took turns to operate with increasing the load. The wear resistance strongly depended on the selection of heat treatment processes or microstructures. It was found that bainite presented a better wear resistance than martensite plus bainite duplex structure, martensite structure was of the poorest wear resistance. The wear resistance increased with increasing austenizing temperature in the range of 920 to 1 120 ℃, then decreased at up to 1 220 ℃. As for tempering temperature and microstructure, the wear resistance increased in following order: 700℃ (tempered sorbite), 200 ℃ (tempered martensite), 440 to 650 ℃ (tempered troostite). An appropriate combination of hardness, toughness, microstructural thermal stability was re- quired for a good wear resistance in high-temperature wear. The optimized heat treatment process was suggested for the cast hot-forging steel to be austenized at 1020 to 1 120 ℃, quenched in oil, then tempered at 440 to 650℃ for 2 h.

  17. Corrosion Resistance of The Bearing Steel 67SiMnCr6-6-4 with Nanobainitic Structure

    Directory of Open Access Journals (Sweden)

    Skołek E.

    2015-04-01

    Full Text Available The paper describes a comparative study of the corrosion resistance of bearing steel 67SiMnCr6-6-4 after two kinds of nanostructuring treatments and two kinds of conventional quenching and tempering treatments. The nanostructuring treatment consisted of austempering with an isothermal quenching at 240°C and 300°C. The conventional heat treatment consisted on quenching and tempering at 350°C for 1 h and quenching and tempering at 550°C for 1 h. Time and temperature of tempering was chosen so that the hardness of both samples (nanostructured as well as quenched and tempered was similar. The microstructure of steel after each heat treatment was described with the use of transmission electron microscopy (TEM. It was shown, that the austempering conducted at 240°C produced homogenous nanobainitic structure consisting of carbide-free bainite plates with nanometric thickness separated by the layers of retained austenite. The austempering at 300°C produced a sub-micrometric carbide-free bainite with retained austenite in form of layers and small blocks. The conventional heat treatments led to a tempered martensite microstructure. The corrosion resistance study was carried out in Na2SO4 acidic and neutral environment using potentiodynamic and electrochemical impedance spectroscopy (EIS methods. The corrosion resistance of nanostructured steel samples were compared to the steel samples with tempered martensite. The obtained results indicate, that the corrosion resistance of bearing steel with nanobainitic structure is similar to steel with tempered martensite in both acidic and neutral environment. This means that the high density of intercrystalline boundaries in nanobinite does not deteriorate the corrosion properties of the bearing steel.

  18. Development of high strength high toughness third generation advanced high strength steels

    Science.gov (United States)

    Martis, Codrick John

    Third generation advanced high strength steels (AHSS's) are emerging as very important engineering materials for structural applications. These steels have high specific strength and thus will contribute significantly to weight reduction in automotive and other structural component. In this investigation two such low carbon low alloy steels (LCLA) with high silicon content (1.6-2wt %) has been developed. These two steel alloys were subjected to single step and two step austempering in the temperature range of 260-399°C to obtain desired microstructures and mechanical properties. Austempering heat treatment was carried out for 2 hours in a molten salt bath. The microstructures were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and optical metallography. Quantitative analysis was carried out by image analysis technique. The effect of austempering temperature on the mechanical properties of these two alloys was examined. The influence of microstructures on the mechanical properties of alloys was also studied. Austempering heat treatment resulted in fine carbide free bainitic ferrite and high carbon austenite microstructure in the samples austempered above Ms temperature, whereas tempered martensite and austenite microstructure was obtained in samples austempered below Ms temperature. Yield strength, tensile strength and fracture toughness were found to increase as the austempering temperature decreases, whereas ductility increases as the austempering temperature increases. Tensile strength in the range of 1276MPa -1658 MPa and the fracture toughness in the range of 80-141MPa√m were obtained in these two steels. Volume fractions of different phases present and their lath sizes are related to the mechanical properties. Austempered samples consisting of mixed microstructure of bainitic ferrite and tempered martensite phases resulted in the exceptional combination of strength and toughness.

  19. Characterization by transmission electron microscopy of a JRQ steel subjected to different heat treatments

    International Nuclear Information System (INIS)

    In this work a study was conducted on the steel Astm A-533, Grade B, Class 1 of reference JRQ, for the purpose of carrying out a study by transmission electron microscopy on the size and distribution of precipitates in steel samples JRQ previously subjected to heat treatments. This because the reactor vessels of the nuclear power plant of Laguna Verde, are made of a steel Astm A-533 Grade B, Class 1. It is known that the neutron radiation causes damage primarily embrittlement in materials that are exposed to it. However, observable damage through mechanical tests result from microstructural defects and atomic, induced by the neutron radiation. In previous studies hardening by precipitation of a JRQ steel (provided by the IAEA) was induced by heat treatments, finding that the conditions of heat treatment that reproduce the hardness and stress mechanical properties of a steel Astm A-533, Grade B, Class 1 irradiated for 8 years to a fluence of 3.5 x 10 17 neutrons/cm2 and to a temperature of 290 grades C are achieved with annealing treatments at 550 grades C. In the studied samples it was found that the more hardening phase both the heat treatments as the neutron radiation, is the bainite, being the ferrite practically unchanged. Which it gave the tone to believe that the ferrite is the phase that provides at level macro the mechanical properties in stress, since in the irradiated samples such properties remained unchanged with respect to the non-irradiated material, however changes were observed in material ductility, which may be attributable to the change of hardness in the bainite, which opens a possibility for modeling the micromechanical behavior of this material. (Author)

  20. Evaluation of microstructure and mechanical properties of a steam turbine casing after long-term service

    Directory of Open Access Journals (Sweden)

    J. Ćwiek

    2011-11-01

    Full Text Available Purpose: of this paper is to reveal the microstructural changes in Cr-Mo and Cr-Mo-V cast steels steel exposed to long-term service at elevated temperatures. The paper presents results of research and failure analysis undertaken to determine failure causes of a steam turbine casing. After 130,000 hours of service the crack in a outer shell of the turbine casing was found.Design/methodology/approach: Following research were performed in order to determine causes of the casing failure: chemical analysis; microstructure examinations with the use of light microscope, scanning electron microscope (SEM; transmission electron microscopy (TEM; mechanical properties examinations using the Charpy impact test, and Vickers hardness test; fracture mode evaluation with SEM; the energy dispersive X-ray spectrometry (EDS.Findings: The cracking of the outer casing occurred due to various causes. The main cause was stress distribution and stress changes during service of the turbine. The microstructure of ferrite and bainite/perlite is more susceptible to cracking than tempered martensite. Carbides coagulation process occurs at ferrite grain boundaries which increased embrittlement. Big nonmetallic inclusions also contribute to brittleness of material.Research limitations/implications: The whole history of start-ups and shutdowns of the turbine during long term service has not been recorded. There was no possibility to take samples with fracture area. Thus, service conditions of investigated samples and material of cracking area were different.Practical implications: Useability of the method for assessing the current degradation based on analysis of carbides morphology was confirmed for Cr-Mo and Cr-Mo-V cast steels.Originality/value: Microstructure composed of ferrite and perlite/bainite is more liable for degradation processes, during long-term exploitation at elevated temperature, than microstructure of tempered martensite.

  1. Designing of cooling conditions for Si-Al microalloyed TRIP steel on the basis of DCCT diagrams

    Directory of Open Access Journals (Sweden)

    W. Zalecki

    2011-04-01

    Full Text Available Purpose: The aim of the research presented in the paper is to design the cooling routes after plastic deformation ensuring the multiphase structure with a high fraction of retained austenite on the basis of DCCT diagram for a new-developed Si-Al microalloyed TRIP steel.Design/methodology/approach: The CCT and DCCT diagrams were developed. Eight variants of the thermo-mechanical processing were designed on the basis of the DCCT diagram. The thermomechanical processing consisted of a multi-stage compression and various cooling strategies in the γ→α transformation range and isothermal holding temperature at a bainitic transformation region.Findings: The usefulness of DCCT diagram for designing the thermomechanical processing conditions for TRIP steels was demonstrated. The fraction of ferrite and retained austenite are highly dependent on a cooling path applied in the γ→α transformation region and a fraction of retained austenite especially on the isothermal holding temperature. The highest fraction of retained austenite as irregular grains located in a ferritic matrix and fine islands or interlath regions in bainitic regions were obtained at temperature of 400 and 450°C.Research limitations/implications: To determine precisely a fraction of retained austenite, the X-ray investigations has to be applied additionally to the image analysis.Practical implications: The designed cooling conditions are of great importance for the thermomechanical strategy for manufacturing the advanced high strength TRIP steels.Originality/value: The thermomechanical processing was carried out for a new group of TRIP steels with Si partially replaced by Al and containing microadditions of Nb and Ti.

  2. Heat affected zone microstructures and their influence on toughness in two microalloyed HSLA steels

    International Nuclear Information System (INIS)

    Microstructures and Charpy impact properties have been examined in two microalloyed steels following heat treatments to simulate weld heat affected zone (HAZ) structures over a range of heat input conditions, characterised by the cooling time from 800 to 500 °C (Δt8/5). The base materials were low carbon structural steel plates microalloyed with vanadium and nitrogen (V–N) and niobium (Nb), respectively. The toughnesses of the HAZs displayed remarkably different behaviours as shown by their impact transition temperatures. For the V–N steel, the toughness improved with increasingly rapid cooling (low heat input conditions) whereas the Nb steel showed an opposite trend. Some of this behaviour could be explained by the presence of coarse ferrite grains in the slowly cooled V–N steel. However, other conditions where all the structures were bainitic and rather similar in optical micrographs gave widely different toughness values. The recently developed method of five dimensional boundary analysis based on electron backscattering diffraction has been applied to these cases for the first time. This showed that the lath boundaries in the bainite were predominantly on {1 1 0} planes of the ferrite and that the average spacing of these boundaries varied depending on steel composition and cooling rate. Since {1 1 0} is also the slip plane in ferrite, it is considered that close spacing between the lath boundaries inhibits general plasticity at stress concentrations and favours initiation of fracture. The differences between the two steels are believed to be due to their transformation behaviours on cooling where precipitation of vanadium nitride in austenite accelerates ferrite formation and raises the temperature of the phase transformation in V–N steels.

  3. Effect of phosphorous and boron addition on microstructural evolution and Charpy impact properties of high-phosphorous-containing plain carbon steels

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Seokmin [Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of); Shin, Sang Yong [Microstructure Physics and Alloy Design, Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf D-40237 (Germany); Lee, Junghoon [Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of); Lee, Chang-Hoon [Next Generation Products Research Group, Technical Research Laboratories, POSCO, Pohang 790-785 (Korea, Republic of); Lee, Sunghak, E-mail: shlee@postech.ac.kr [Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of)

    2013-03-01

    Four plain carbon steels were fabricated by controlling the addition of P and B, and then isothermal heat-treatments were conducted at 550 °C and 650 °C for 3 h on these steels to make ferrite–pearlite-based or ferrite–bainite-based microstructures, respectively. B was added for controlling the reduction in toughness due to grain boundary segregation of P because B was readily distributed on grain boundaries. In the 550 °C-treated steels, bainite grains were refined by the B addition, whereas the 650 °C-treated steels did not show the grain refinement due to the B addition. According to the critical time analysis for non-equilibrium grain boundary segregation of P and B, the present isothermal treatment time of 3 h was too short for the grain boundary segregation of P, and thus the fracture occurred mostly in a cleavage mode, instead of an intergranular mode. Since this 3 h-treatment time was too long for the grain boundary segregation of B, the grain boundary segregation of B was reduced, and the precipitation of cementites was promoted. In the 550 °C-treated steels, the area fraction of intergranular fracture increased with increasing volume fraction of grain boundary cementites, as they played an important role in initiating the intergranular fracture, although the area fraction of intergranular fracture was lower than 5%. In the 650 °C-treated steels having coarse grains, however, grain boundary cementites did not work for intergranular fracture because the crack readily propagated in a cleavage mode.

  4. Effects of Oxides on Tensile and Charpy Impact Properties and Fracture Toughness in Heat Affected Zones of Oxide-Containing API X80 Linepipe Steels

    Science.gov (United States)

    Sung, Hyo Kyung; Sohn, Seok Su; Shin, Sang Yong; Oh, Kyung Shik; Lee, Sunghak

    2014-06-01

    This study is concerned with effects of complex oxides on acicular ferrite (AF) formation, tensile and Charpy impact properties, and fracture toughness in heat affected zones (HAZs) of oxide-containing API X80 linepipe steels. Three steels were fabricated by adding Mg and O2 to form oxides, and various HAZ microstructures were obtained by conducting HAZ simulation tests under different heat inputs. The no. of oxides increased with increasing amount of Mg and O2, while the volume fraction of AF present in the steel HAZs increased with increasing the no. of oxides. The strengths of the HAZ specimens were generally higher than those of the base metals because of the formation of hard microstructures of bainitic ferrite and granular bainite. When the total Charpy absorbed energy was divided into the fracture initiation and propagation energies, the fracture initiation energy was maintained constant at about 75 J at room temperature, irrespective of volume fraction of AF. The fracture propagation energy rapidly increased from 75 to 150 J and saturated when the volume fraction of AF exceeded 30 pct. At 253 K (-20 °C), the total absorbed energy increased with increasing volume fraction of AF, as the cleavage fracture was changed to the ductile fracture when the volume fraction of AF exceeded 45 pct. Thus, 45 vol pct of AF at least was needed to improve the Charpy impact energy, which could be achieved by forming a no. of oxides. The fracture toughness increased with increasing the no. of oxides because of the increased volume fraction of AF formed around oxides. The fracture toughness did not show a visible correlation with the Charpy absorbed energy at room temperature, because toughness properties obtained from these two toughness testing methods had different significations in view of fracture mechanics.

  5. Effect of rare earths on impact toughness of a low-carbon steel

    International Nuclear Information System (INIS)

    Highlights: → RE as alloying element in steels instead of used to deoxidize and desulfurize. → An appropriate RE content can improve significantly the impact toughness of the low carbon steel. → Excessive RE content induces a volume of martensite precipitates at grain boundaries. → The bainite transformation is benefit from RE additions. → The ferrite reconstructive transformation might be changed by RE enrichment at grain boundaries. -- Abstract: Studies of an industrial low-carbon steel (B450NbRE) suggest that the impact toughness is unexpectedly low under its practical service, probably resulting from the unstable recovery of rare earths (RE) in steelmaking. The purpose of this work is to investigate the effect of RE on the impact toughness in low-carbon steel. The B450NbRE steels with content of 0.0012-0.0180 wt.% RE were produced by vacuum induction furnace. The impact toughness and microstructure were investigated after hot rolled. The Gleeble-1500 thermal simulator was used to validate the effect of RE on the microstructure. The results indicate that the microstructure of hot-rolled steels is characterized by polygonal ferrite, quasi-polygonal ferrite, bainite and pearlite. The impact toughness increases with RE contents reaching the peak with content of 0.0047 wt.% RE, such a change exhibits the same rule as the case of the ferrite amount. However, this improvement in impact toughness is not only due to an increase in ferrite amount, but also the fine grained structure and the cleaner grain boundaries. And content of 0.0180 wt.% RE is excessive. Such an addition of the RE resulted in the martensite precipitates at the grain boundaries, which are extremely detrimental to impact toughness.

  6. Microstructure–hardness relationship in the fusion zone of TRIP steel welds

    International Nuclear Information System (INIS)

    Highlights: ► Fusion zone of TRIP steels in resistance spot welding was analyzed. ► Transmission electron microscopy (TEM) was used for characterizing microstructure. ► Fusion zone microstructure was found to depend on the chemistry. ► Hardness values were in accordance with the microstructural constituents in the fusion zone. - Abstract: Fusion zone of three TRIP steels, categorized as AT: C–Mn–Al, AST: C–Mn–Al–Si and ST: C–Mn–Si, in resistance spot welding was characterized with respect to microstructure, phase analysis, and hardness. The fusion zone microstructure was found to depend on chemistry: (i) AT steel contained ferrite phase surrounded by bainite and martensite regions, (ii) AST steel showed a bainite structures along with martensite laths and interlath retained austenite, whereas (iii) ST steel constituted single phase martensite laths with interlath austenite. X-ray diffraction study indicated that retained austenite fraction in the fusion zone increases with increase in Si content in it. The AST fusion zone hardness lies between those of the AT and ST steels; the ST fusion zone hardness was higher than that of AT steel because of the single phase martensite microstructure. Comparison of fusion zone microstructure and hardness to earlier study on laser welding of the TRIP steels with similar chemistries revealed that higher cooling rate in resistance spot welding led to higher fusion zone hardness compared to laser welding; which was attributed either to decrease in softer ferrite phase (AT steel) in the microstructure or refinement of martensite laths (ST steel).

  7. The influence of aluminum and carbon on the abrasion resistance of high manganese steels

    Science.gov (United States)

    Buckholz, Samuel August

    Abrasive wear testing of lightweight, austenitic Fe-Mn-Al-C cast steel has been performed in accordance with ASTM G65 using a dry sand, rubber wheel, abrasion testing apparatus. Testing was conducted on a series of Fe-30Mn-XAl-YC-1Si-0.5Mo chemistries containing aluminum levels from 2.9 to 9.5 wt.% and carbon levels from 0.9 to 1.83 wt.%. Solution treated materials having an austenitic microstructure produced the highest wear resistance. Wear resistance decreased with higher aluminum, lower carbon, and higher hardness after age hardening. In the solution treated condition the wear rate was a strong function of the aluminum to carbon ratio and the wear rate increased with a parabolic dependence on the Al/C ratio, which ranged from 1.8 to 10.2. Examination of the surface wear scar revealed a mechanism of plowing during abrasion testing and this method of material removal is sensitive to work hardening rate. Work hardening behavior was determined from tensile tests and also decreased with increasing Al/C ratio and after aging hardening. The loss of wear resistance is related to short range ordering of Al and C in the solution treated materials and kappa-carbide precipitation in age hardened materials and both contribute to planar slip and lower work hardening rates. A high carbon tool steel (W1) and a bainitic low alloy steel (SAE 8620) were also tested for comparison. A lightweight steel containing 6.5 wt.% Al and 1.2 wt.% C has wear resistance comparable to within 5% of the bainitic SAE 8620 steel forging currently used for the Bradley Fighting Vehicle track shoe and this cast Fe-Mn-Al-C steel, at equivalent tensile properties, would be 10% lighter.

  8. Mechanical Properties and Microstructural Evolution of Welded Eglin Steel

    Science.gov (United States)

    Leister, Brett M.

    Eglin steel is a new ultra-high strength steel that has been developed at Eglin Air Force Base in the early 2000s. This steel could be subjected to a variety of processing steps during fabrication, each with its own thermal history. This article presents a continuous cooling transformation diagram developed for Eglin steel to be used as a guideline during processing. Dilatometry techniques performed on a Gleeble thermo-mechanical simulator were combined with microhardness results and microstructural characterization to develop the diagram. The results show that four distinct microstructures form within Eglin steel depending on the cooling rate. At cooling rates above about 1 °C/s, a predominately martensitic microstructure is formed with hardness of ˜520 HV. Intermediate cooling rates of 1 °C/s to 0.2 °C/s produce a mixed martensitic/bainitic microstructure with a hardness that ranges from 520 - 420 HV. Slower cooling rates of 0.1 °C/s to 0.03 °C/s lead to the formation of a bainitic microstructure with a hardness of ˜420 HV. The slowest cooling rate of 0.01 °C/s formed a bainitic microstructure with pearlite at the prior austenite grain boundaries. A comprehensive study was performed to correlate the mechanical properties and the microstructural evolution in the heat affected zone of thermally simulated Eglin steel. A Gleeble 3500 thermo-mechanical simulator was used to resistively heat samples of wrought Eglin steel according to calculated thermal cycles with different peak temperatures at a heat input of 1500 J/mm. These samples underwent mechanical testing to determine strength and toughness, in both the `as-simulated' condition and also following post-weld heat treatments. Mechanical testing has shown that the inter-critical heat affected zone (HAZ) has the lowest strength following thermal simulation, and the fine-grain and coarse-grain heat affected zone having an increased strength when compared to the inter-critical HAZ. The toughness of the heat

  9. Hole Expansion Properties of High Strength Automobile Steel Plates with Different Microstructures%汽车用不同显微组织高强钢板的扩孔性能

    Institute of Scientific and Technical Information of China (English)

    吴青松; 祝洪川; 王立新; 刘斌

    2016-01-01

    对热轧铁素体贝氏体双相钢 FB60、铁素体马氏体双相钢 DP600和铁素体珠光体钢SPFH590等三种汽车用高强钢板进行了扩孔试验,利用光学显微镜观察了扩孔裂纹的萌生和扩展,研究了不同钢的扩孔性能及开裂机理。结果表明:FB60钢的扩孔性能最优,DP600钢的最差;SPFH590钢与FB60钢具有相同的屈强比,但其扩孔性能却不及FB60钢的;组织对扩孔性能的影响与扩孔裂纹的萌生和扩展有关,FB60钢的裂纹萌生于铁素体内以及铁素体与贝氏体晶界,绕过贝氏体穿过铁素体扩展;SPFH590钢的裂纹萌生于铁素体与珠光体边界、珠光体内铁素体与渗碳体界面和铁素体内,极易沿铁素体与渗碳体片层扩展;DP600钢的裂纹萌生于铁素体与马氏体晶界,并沿晶界扩展。%Hole expansion tests were conducted for hot-rolled ferrite-bainite dual phase steel FB60,ferrite-martensite dual phase steel DP600 and ferrite-pearlite steel SPFH590.Optical microscope was used to observe formation and propagation of expansion cracks and analyze the hole expansion property and cracking mechanism of the steels.The results show that the FB60 steel exhibits the best hole expansion property,and DP600 steel exhibits the worst hole expansion property.However,the yield ratio of SPFH590 steel was equal to that of FB60 steel,but the hole expansion rate of SPFH590 steel less than that of FB60 steel.The effect of microstructure on hole expansion property was related to the formation and propagation of expansion cracks.The cracks formed not only at ferrite-bainite interfaces but also within ferrite grains in FB60 steel,and propagated along the phase interface between ferrite and bainite and by cutting off ferrite grains.The expansion cracks formed at ferrite-pearlite interfaces,ferrite-cementite interfaces within pearlite and within ferrite grains in SPFH590 steel,and propagated easily along the ferrite-cementite interface.The cracks formed

  10. 冷速及高温回火对低合金高强铸钢组织性能的影响%Effect of cooling rate and high tempering on microstructure and mechanical properties of high-strength low-alloy(HSLA) cast steel

    Institute of Scientific and Technical Information of China (English)

    雷勇; 许晓嫦; 李良; 张奇; 徐浩浩; 赵凤晓

    2014-01-01

    为提高低合金高强铸钢( HSLA)的综合力学性能,满足恶劣环境下的使用要求。采用光学显微镜、扫描电镜、透射电镜、冲击试验机、万能材料试验机研究了3种不同冷速及高温回火对HSLA铸钢组织与力学性能的影响。结果表明:随冷速增加,淬火组织发生由多边形铁素体+针状铁素体+粒状贝氏体→粒状贝氏体+板条贝氏体→准上贝氏体+板条马氏体的演变。冷速为1℃/s的空冷样,具有最高的塑韧性;冷速最大的水冷样,其强度、硬度最高。冷却样经580℃回火,其晶界、板条界均有粒状、短棒状的纳米第二相析出,EDS分析表明,100~200 nm的析出相为合金渗碳体( M3 C),而50 nm以内的析出相为( V,Ti)( C,N)。空冷样回火后有较高强度、最高的塑韧性;油冷、水冷样回火后,Re提高,Rm略有下降,AkU降低与高温回火脆性的发生有关,但-40℃的AkU仍有60、40 J,具有较好的低温冲击韧性。可见,试验HSLA铸钢表现出良好的综合力学性能,能满足在恶劣环境下的使用要求。%To improve comprehensive mechanical properties of high strength low alloy(HSLA) cast steel, and meet application requirements of HSLA cast steel in harsh environments, the mechanical properties and microstructures of HSLA cast steel cooled at three different cooling rates and subsequently tempered at 580℃ were studied by optical microscope, scanning electron microscopy, transmission electron microscopy, impact tester and universal material test. With the cooling rate increasing, the microstructure evolved from ferrite + granular bainite, lath bainite, to lath martensite + quasi upper bainite. Higher plasticity and toughness were obtained at a slower cooling rate of 1℃/s. Water cooled sample had maximum strength and hardness, at the expensive of impact energy slightly. Nano-precipitates of granular, short rod were found along

  11. Evolution of non-uniform grain structure during hot defornnation of a Nb-Ti microalloyed steel

    Directory of Open Access Journals (Sweden)

    Katajarinne, T.

    2004-10-01

    Full Text Available Recrystallisation and the evolution of the abnormally grown austenite grains were investigated for a continuously cast slab of a 0.13 C-1.41 Mn-0.027 Nb-0.012 Ti steel during reheating and after the subsequent deformation. The stability of the recrystallised structure and the uniformity of the final microstructure were also studied. The abnormally grown grains appear in a few minutes at reheating temperatures around 1200 °C. All grains in the bimodal grain structure recrystallised at 1100 °C for strains > 0.2 within about 40 s. The coarse grains are refined, while the fine grains become slightly larger. Some abnormal grain growth can occur again in the recrystallised structure within 10 min. After cooling at 1° C/s the coarse austenite grains transform into large areas of upper bainite, while the finer grains transform to fine ferrite and pearlite. The transformed microstructure in specimens cooled at l°C/s consists of large upper bainitic areas corresponding to the prior coarse austenite grains, surrounded by fine ferrite-pearlite grains.

    Se ha estudiado la recristalización y la evolución del crecimiento anormal de grano, durante el recalentamiento y tras deformaciones sucesivas, en un acero 0,13 C-1,41 Mn-0,027 Nb- 0,012 Ti procedente de colada continua. Se ha estudiado, así mismo, la estabilidad de la estructura recristalizada y la uniformidad de la microestructura final. Para temperaturas de recalentamiento próximas a 1.200 °C, aparece crecimiento anormal de grano en unos pocos minutos. Todos los granos pertenecientes a la estructura bimodal resultante recristalizan durante, aproximadamente, 40 s, a 1.100 °C, para una deformación de 0,2. El tamaño de grano se afina en aquellas regiones con granos más gruesos de partida y crece, ligeramente, en las que tenían un grano m��s fino. En 10 min, se puede desencadenar, de nuevo, un cierto crecimiento anormal de grano en la estructura recristalizada. La microestructura final

  12. Effect of isothermal holding temperature on retained austenite fraction in medium- carbon Nb/Ti-microalloyed TRIP steel

    Directory of Open Access Journals (Sweden)

    H. Krztoń

    2011-12-01

    Full Text Available Purpose: The aim of the paper is to determine the effect of the isothermal holding temperature in a bainitic transformation range on a fraction of retained austenite for a new-developed medium-carbon TRIP steel containing Nb and Ti microadditions. Design/methodology/approach: The thermo-mechanical processing was carried out by a multi-stage compression test using the Gleeble thermomechanical simulator. The steel was subjected to 5 variants of processing with an isothermal bainitic transformation temperature in a range from 250 to 450°C. Identification of structural constituents was done using microscopic observations and X-ray diffraction. To determine the fraction of retained austenite the Rietveld method was applied.Findings: It is possible to obtain a high fraction of retained austenite characterized by the high thermodynamic stability in a C-Mn-Si-Al steel containing 0.43% C. The maximal fraction of austenitic phase equal above 20% was obtained for the wide temperature range of isothermal holding from 350 to 450°C. The maximal carbon content in the retained austenite equal 1.84 wt.% is present for the temperature range from 350 to 400°C. Below 350°C due to relatively low carbon diffusivity and high Msγ temperature, a part of austenite transforms to marteniste. Above 400°C there is still a high fraction of retained austenite but it contains a lower C content.Practical implications: The obtained austenite volume fraction and carbon content in a γ phase determined as a function of isothermal holding temperature can be useful in optimization of thermo-mechanical processing conditions for medium-C TRIP steels.Originality/value: The research was performed on a new-developed medium-carbon Si-Al steel microalloyed with Nb and Ti. There is a lack of data on microstructure and stability of retained austenite in such advanced group of high-strength TRIP steels.

  13. 焊后热处理对ASTM4130钢焊接接头组织与性能的影响%Effect of Post -weld Heat Treatment on Microstructure and Mechanical Properties of Welded Joints of ASTM 4130 Steel

    Institute of Scientific and Technical Information of China (English)

    薄国公; 王勇; 韩涛; 李立英

    2011-01-01

    通过金相观察、硬度和冲击试验,研究了不同保温时间的焊后热处理(PWHT)对ASTM 4130钢焊接接头显微组织、硬度、低温韧性的影响.结果表明,PWHT后,焊缝组织为铁素体、少量珠光体和碳化物,HAZ组织主要为回火索氏体、铁素体和贝氏体;造成熔合线附近硬度较高、韧性较低的原因是组织的粗化和上贝氏体的形成;随PWHT保温时间的延长,接头硬度降低,韧性改善.这主要是由于保温时间延长,使碳化物逐渐析出,其弥散强化效应和回火索氏体中合金元素固溶强化效应降低,同时,碳化物弥散度的降低也使得接头应力集中程度降低.%The effect of post -weld heat treatment (PWHT) on microstructure,hardness,low temperature impact toughness and fracture morphology of welded joints of ASTM 4130 steel was systematically investigated by using optical microscopy, hardness and impact tests. The results show that the microstructures of weld metal are ferrite, a small mount of pearlite and carbide, and typical heat - affected zone ( HAZ) microstructures are comprised of tempered martensite, ferrite and bainite after PWHT. Higher hardness and lower impact toughness in the regions nearby the fusion line is mainly caused by the appearance of coarsen structure and the formation of upper bainite. Hardness levels reduce and toughness levels of welded joints improve with prolonging the soaking time. The main reason may be that the carbide precipitates gradually with prolongation of soaking time, and the effect of dispersion strengthening of carbide and solution strengthening of alloy elements in tempered sorbite is weakening. Meanwhile, the lower dispersity of carbide reduce the stress concentration.

  14. A study of microstructure and phase transformations of CMnAlSi TRIP steel

    Directory of Open Access Journals (Sweden)

    B. Gajda

    2008-12-01

    Full Text Available Purpose: Purpose was to obtain the TRIP-type microstructure in the CMnAlSi steel. Heat treatment consistedof the partial austenitization at 900°C/60s and continuous cooling with rates: 0.5-40°C/s, was examined. Alsothe effect of Al and Si on Ac1 and Ac3 temperatures, and the volume fractions of austenite in CMnSi, CMnAland CMnAlSi steels was investigated.Design/methodology/approach: The effect of alloying elements on Ac1 and Ac3 temperatures was investigatedusing Thermo-calc program. The influence of cooling rates on phase transformations and microstructures ofsamples austenitized at 900°C/60s was examined using dilatometer, light optical microscopy and scanningelectron microscopy. X-ray diffraction technique was used to calculate the amount of retained austenite.Quantitative analyses of phases were done using Image pro Plus 3.0 program. The mechanical properties andVickers hardness (HV10 measurements were also investigated.Findings: The TRIP-aided microstructure consisted of ferrite matrix, bainitic ferrite and metastable retainedaustenite can be obtained for the CMnAlSi steel through intercritical annealing at 900°C/60s and continuouscooling with the rate 20°C/s to the R.T. Isothermal holding at bainitic temperature range (600-400°C duringcooling is not necessary, because of the Al and Si additions to the steel.Practical implications: The CMn steel with addition of 1% Al and Si is well-suited for production of TRIP steelsheets in a large range of temperatures: 800-900°C. The advisable cooling rates are in the range from 10 to 40°C/s.Originality/value: In the TRIP steels the amount of residual austenite in structure at the R.T. strongly dependson the heat treatment parameters such as annealing temperature, cooling rates and amounts of added alloyingelements. It is very important to determine the optimal annealing parameters for each TRIP steel grade to obtainthe steel with the best mechanical properties and microstructure.

  15. The Performance Test and Analysis of the Butt Joint About X90M Steel Plate%X90M钢板对接接头性能测试与分析

    Institute of Scientific and Technical Information of China (English)

    于磊; 李志宏; 莫诚生; 王登树; 檀才保

    2015-01-01

    In this paper, it carried out the mechanical properties test, microstructure observation and SEM scan test for the welded joint of automatic submerged arc welding about X90M pipeline steel plate. The tests showed that the weld microstructure is mainly composed of acicular ferrite and granular bainite,the heat affected zone(HAZ) includes granular bainite and a small amount of blocky ferrite. The hardness test results showed that no obvious softening phenomenon exist in HAZ, the impact absorbed energy of the weld and HAZ are more sensitive to temperature, but the cross distribution of acicular ferrite in the weld and the columnar crystal state leads to the toughness is a bit poor to HAZ. The impact fracture appearance of the base metal and HAZ below 0℃display the dimple shape, and the weld fracture morphology is quasi cleavage feature.%对管线钢用X90M钢板自动埋弧焊对接接头进行了力学性能测试、微观组织观察、 SEM扫描等试验。分析得出焊缝组织主要由针状铁素体和粒状贝氏体组成,热影响区除粒状贝氏体外,还有少量块状铁素体。硬度测试结果表明,热影响区并不存在明显软化现象,焊缝和热影响区的冲击吸收能量均对温度较为敏感,但焊缝中纵横交错分布的针状铁素体和柱状晶状态导致其韧性比热影响区稍差。0℃下的母材和热影响区冲击断口形貌呈韧窝形状,而焊缝断口形貌则为准解理特征。

  16. 复相钢CP800焊缝冷裂纹敏感性研究%COLD CRACKING SUSCEPTIBILITY OF WELDED JOINT OF CP800 STEEL

    Institute of Scientific and Technical Information of China (English)

    韩坤; 李清山; 李健; 孙慧珺; 张梅; 徐云峰

    2012-01-01

    The butt joint, Y shape butt joint, tee joint and control thermal severity (CTS) of the welded joint (lap joint) were studied after the gas shielded arc welding for CP800 steel. The macroscopic morphology, microstructure and properties of different welding points were measured to study the weld ability and cold cracking susceptibility of CP800 steel. The test results showed that the steel was appropriate for various welding forms of automobile parts due to the lower weld cold cracking susceptibility. The microstructure of heat affected zone was granular ferrite, bainite and a small amount of lath bainite, which were well distributed and the fusion was good. The hardness distribution of the four different welding forms was similar and the maximum hardness value was 320 HV, lower than 350 HV. The impact toughness of base metal, heat affected zone and fusion zone of Y shape butt joint was higher than 23 J, and the fracture surface was dimple fracture under the scanning electron microscope.%采用气体保护焊对试验钢CP800分别进行对接、斜Y、T型(角接)、CTS(搭接)焊接,测试分析不同焊接接头形式下的宏观形貌、微观组织和性能的变化,以研究CP800钢的可焊性和冷裂纹敏感性.实验结果表明:试验钢适用于各种焊接形式下的汽车结构件,具有很低的焊缝冷裂纹敏感性.焊接热影响区的组织为粒状铁素体、贝氏体以及少量的板条贝氏体,分布均匀,焊缝熔合良好.4种不同焊接方式下的焊缝硬度分布一致,最高硬度值为320 HV,小于350 HV.斜Y坡口对接接头处的母材、热影响区以及熔合区的冲击性能均大于23 J,其断口形貌均为韧窝形状.

  17. MODIFICATION OF CARBON STEEL BY LASER SURFACE MELTING: PART I: EFFECT OF LASER BEAM TRAVELLING SPEED ON MICROSTRUCTURAL FEATURES AND SURFACE HARDNESS

    Directory of Open Access Journals (Sweden)

    Hashem F. El-Labban

    2013-01-01

    Full Text Available The present study aims to improve the surface hardness of carbon steel by application of laser surface melting of effective conditions. The travelling speed of laser beam during this treatment is one of the important treatment conditions. This study aims to investigate the effect of laser surface melting with different beam speeds on macro and microstructure as well as the hardness distribution through the thickness of carbon steel. To achieve this target, three different travelling speeds (1500, 1000 and 500 mm min-1 at a constant beam power of 800 W were chosen in this study. The resulted laser treated specimens were investigated in macro and microscopically scale using optical and scanning electron microscope. Hardness measurements were also carried out through the thickness of the laser treated specimens. The laser treated areas with all used travelling speeds results in melted and solidified zone on the surface of the steel. In the same time, Plates of acicular martensite structure were observed within the upper part of the melted and solidified zone in almost all experimental conditions, while some bainite structure in ferrite grains are detected in its lower part. By increasing the travelling speed, the depth of the laser treated zone was decreases, while travelling speed has much less significant effect on the laser treated zone width. The size of the formed martensite plates was increased by decreasing the travelling speed from 1500 to 500 mm min-1. On the other hand, the travelling speed has a straight effect on the length of the acicular martensite; as the travelling speed increases, the acicular martensite became longer, while it shows fine acicular martensite at lower travelling speeds. The depth that full martensite structure can be reached is increased by increasing travelling speed. At lower travelling speed (500 mm min-1, large amount of bainite structure is observed at the center of the treated zone up to its lower end. The

  18. Influence of Different Heat Treatment Process on the Microstructure and Properties of 12Cr2Mo1R Steel%热处理工艺对12Cr2Mo1R钢的组织和性能影响

    Institute of Scientific and Technical Information of China (English)

    蒋善玉

    2013-01-01

    The influences of different heat treatment process on the microstructure and properties of 12Cr2Mo1R heat-resistant steel plate were discussed. The results showed that with normalizing temperature rise, the bainite content and the strength rise; after normalizing at 975℃, the microstructure is 100%bainite and (Fe,Cr)3C type cementite;with the increase of tempering temperature and the extension of tempering time, the strength decreases and the nanometer strengthening phase separated in tempering at 600℃grows into a needle, and at the same time, the (Fe,Cr)3C cementite spheroidizes continuously and gradually turns to (Fe,Cr)7C3; the tempering treatment at 650℃after normalizing makes negative creep phenomenon disappearing. In production, 12Cr2Mo1R ought to adopt normalizing+tempering treatment, the normalizing temperature is between 920 and 950℃, the holding time is 1.5-3.0 min/mm, the tempering temperature is 720-750℃and the holding time is 2.0-4.0 min/mm.%探讨了不同热处理工艺对12Cr2Mo1R耐热钢板性能和组织的影响,结果表明:随正火温度的升高贝氏体增加,强度提高,975℃正火后,显微组织为100%贝氏体和(Fe,Cr)3C型渗碳体;随回火温度的提高及回火时间的延长,强度降低,600℃回火时析出的纳米强化相不断长大成针状,同时,(Fe,Cr)3C型渗碳体不断球化,逐渐向(Fe,Cr)7C3型转化;正火处理后再经650℃回火处理,负蠕变现象消失。生产中12Cr2Mo1R钢宜采用正火+回火处理,正火温度920~950℃,保温时间1.5~3.0 min/mm;回火温度720~750℃,保温时间2.0~4.0 min/mm。

  19. MICROALLOYED STEELS FOR THE AUTOMOTIVE INDUSTRY

    Directory of Open Access Journals (Sweden)

    Debanshu Bhattacharya

    2014-12-01

    Full Text Available Two major drivers for the use of newer steels in the automotive industry are fuel efficiency and increased safety performance. Fuel efficiency is mainly a function of weight of steel parts, which in turn, is controlled by gauge and design. Safety is determined by the energy absorbing capacity of the steel used to make the part. All of these factors are incentives for the U.S. automakers to use both Highly Formable and Advanced High Strength Steels (AHSS to replace the conventional steels used to manufacture automotive parts in the past. AHSS is a general term used to describe various families of steels. The most common AHSS is the dual-phase steel that consists of a ferrite-martensite microstructure. These steels are characterized by high strength, good ductility, low tensile to yield strength ratio and high bake hardenability. Another class of AHSS is the complex-phase or multi-phase steel which has a complex microstructure consisting of various phase constituents and a high yield to tensile strength ratio. Transformation Induced Plasticity (TRIP steels is another class of AHSS steels finding interest among the U.S. automakers. These steels consist of a ferrite-bainite microstructure with significant amount of retained austenite phase and show the highest combination of strength and elongation, so far, among the AHSS in use. High level of energy absorbing capacity combined with a sustained level of high n value up to the limit of uniform elongation as well as high bake hardenability make these steels particularly attractive for safety critical parts and parts needing complex forming. A relatively new class of AHSS is the Quenching and Partitioning (Q&P steels. These steels seem to offer higher ductility than the dual-phase steels of similar strengths or similar ductility as the TRIP steels at higher strengths. Finally, martensitic steels with very high strengths are also in use for certain parts. The most recent initiative in the area of AHSS

  20. Diseño de nuevos aceros bainíticos.

    Directory of Open Access Journals (Sweden)

    Caballero, F. G.

    2002-02-01

    Full Text Available Mixed microstructures consisting of fine plates of upper bainitic ferrite separated by thin films of stable retained austenite have seen many applications in recent years because of their impressive combination of strength and toughness. There may also be some martensite present in the microstructure, but its formation can be controlled increasing the stability of the retained austenite. On the other hand, carbides are avoided by the judicious use of silicon as an alloying element. The aim of the present work was to see how far these concepts can be extended in order to achieve the highest ever combination of strength and toughness in bulk-samples subjected to continuous cooling transformation. Three alloys were proposed and manufactured, and the results of metallographic characterisation and mechanical tests have shown that the designed steels have the highest ever combination of strength and toughness for bainitic microstructures, matching even the maraging steels which are at least thirty times more expensive. The experimental results confirm the alloy design procedures.

    En los últimos años se han diseñado aceros con microestmcturas formadas por placas de ferrita bainítica superior y finas regiones de austenita retenida que, por su excelente combinación de propiedades de resistencia y tenacidad, han sido empleados para numerosas aplicaciones. Aunque en estas microestructuras puede haber algo de martensita, su formación puede controlarse aumentando la estabilidad de la austenita retenida. Por otra parte, la presencia de carburos en la bainita, causa de importantes disminuciones de tenacidad en los aceros bainíticos convencionales, se evita gracias al uso del silicio como elemento de aleación. El objetivo de este trabajo es estudiar la posibilidad de optimizar la citada combinación de propiedades, generalmente antagónicas, en muestras masivas para aplicación industrial sujetas a transformaciones por enfriamiento continuo. Para

  1. The effect of long-term service at elevated temperatures on structure and mechanical properties of Cr-Mo-V steel

    Directory of Open Access Journals (Sweden)

    J. Ćwiek

    2011-05-01

    Full Text Available Purpose: of this paper is to reveal the microstructural changes in 13HMF steel exposed to long-term service at elevated temperatures. The degradation of bainite structure was determined and carbides morphology has been examined. The influence of carbides evolution was discussed in dependence of creep rupture strength and mechanical properties of the steel.Design/methodology/approach: Examinations were conducted on 273 mm diameter, 32 mm wall thickness tube made of 13HMF (14MoV6-3 steel. The tube was a segment of stem pipeline used in power plant at 540°C. The service time is 168,000 hours. Microstructure of the material has been examined with the use of light optical microscopy and scanning electron microscopy (SEM. The energy dispersive X-ray spectrometry (EDS analysis was used for phase chemical composition identification. Transmission electron microscopy (TEM of thin foils was used for carbides structure identification. The mechanical properties of the tube material were evaluated in static tensile tests at room temperature, hardness tests and impact Charpy U tests.Findings: Microstructure of 13HMF steel tube shows an advanced level of degradation - coagulation of carbides at ferrite grain boundaries and inside bainitic grains. Precipitates of carbides decorated grain boundaries in chain forms. The presence of M7C3, M23C6, M6C phases were revealed. After extended service M23C6 and M3C carbides were replaced by more stable carbides. This transformation did not occur until the end. This indicates the presence of mainly Mo2C carbide, and only sporadic occurrence of carbide M6C.Practical implications: Useability of the method for assessing the current degradation level and for predicting residual lifetime of creep-resistant tubes based on analysis of carbides morphology was confirmed for Cr-Mo-V steel.Originality/value: Information available in literature does not clearly indicate the influence of microstructure and mechanical properties of Cr

  2. Modified heat treatment for lower temperature improvement of the mechanical properties of two ultrahigh strength low alloy steels

    Science.gov (United States)

    Tomita, Yoshiyuki; Okabayashi, Kunio

    1985-01-01

    In the previous papers, a new heat treatment for improving the lower temperature mechanical propertise of the ultrahigh strength low alloy steels was suggested by the authors which produces a mixed structure of 25 vol pct lower bainite and 75 vol pct martensite through isothermal transformation at 593 K for a short time followed by water quenching (after austenitization at 1133 K). In this paper, two commercial Japanese ultrahigh strength steels, 0.40 pct C-Ni-Cr-Mo (AISI 4340 type) and 0.40 pct C-Cr-Mo (AISI 4140 type), have been studied to determine the effect of the modified heat treatment, coupled above new heat treatment with γ ⇆ α' repctitive heat treatment, on the mechanical properties from ambient temperature (287 K) to 123 K. The results obtained for various test temperatures have been compared with those for the new heat treatment reported previously and the conventional 1133 K direct water quenching treatment. The incorporation of intermediate four cyclic γ ⇆ α' repctitive heat treatment steps (after the initial austenitization at 1133 K and oil quenching) into the new heat treatment reported previously, as compared with the conventional 1133 K direct water quenching treatment, significantly improved 0.2 pct proof stress as well as notch toughness of the 0.40 pct C-Ni-Cr-Mo ultrahigh strength steel at similar fracture ductility levels from 287 to 123 K. Also, this heat treatment, as compared with the conventional 1133 K direct water quenching treatment, significantly improved both 0.2 pct proof stress and notch toughness of the 0.40 pct C-Cr-Mo ultrahigh strength steel with increased fracture ductility at 203 K and above. The microstructure consists of mixed areas of ultrafine grained martensite, within which is the refined blocky, highly dislocated structure, and the second phase lower bainite (about 15 vol pct), which appears in acicular form and partitions prior austenite grains. This newly developed heat treatment makes it possible to modify

  3. 80mm厚高韧性工程机械用Q460级TMCP钢的研制%Development of 80 mm Thick Q460 Grade TMCP Plate with High Toughness for Engineering Machinery

    Institute of Scientific and Technical Information of China (English)

    李德发; 王世森; 邢淑清; 熊涛

    2012-01-01

    Based on low carbon and Cr-Mo with powerful carbide added, the 80mm thick Q460 grade plate for engineering machinery use was successfully trial-produced by TMCP process. Ultrafine grain and precipitated phase and bainite were fully taken advantage of to increase strength. By means of metallo-graphic examination and inspection of mechanical properties, the results showed that the studied steel was composed of uniform ferrite and bainite , and had good mechanical properties including tensile property and low temperature impact toughness; AKV under -60 ℃ was more than 180 J, and the impact fracture exhibited plastic deformation; SEM analysis showed that the area of dimple fracture was about 55% , and small inclusion in dimple was circular oxide. The result of TEM showed that high density dislocation existed in crystalline grain, and a large number of dispersed fine second-phase particles were separated out a-long dislocation line in the steel.%采用低碳Cr-Mo系添加微量强碳化物形成元素的成分设计,通过TMCP工艺控制,获得均匀铁素体/贝氏体组织,充分发挥析出强化、细晶强化和贝氏体组织强化作用,研制80 mm厚高韧性工程机械用Q460钢.试制钢板力学性能均匀,不仅具有良好的拉伸力学性能,且低温冲击韧性优良,-60℃冲击功大于180 J,冲击断口呈明显塑性变形;SEM分析表明,断口微观形貌韧窝特征明显,面积约为55%,韧窝内圆形氧化物夹杂细小;钢板厚度方向铁素体/贝氏体组织均匀,晶粒尺寸约为8~10 μm; TEM分析表明,晶内存在高密度位错,大量细小弥散的第二相粒子沿位错线析出.

  4. Fracture mechanisms in dual phase steels based on the acicular ferrite + martensite/austenite microstructure

    Science.gov (United States)

    Poruks, Peter

    The fracture mechanisms of low carbon microalloyed plate steels based on the acicular ferrite + marten site/austenite microstructure (AF + M/A) are investigated. The final microstructure consists of a dispersed phase of submicron equi-axed martensite particles with a bainitic ferrite matrix. A series of plates with M/A volume fractions of 0.076--0.179 are studied. Brittle fracture is investigated by Instrumented Charpy impact testing of samples at -196°C and subsequent metallography. The M/A particles are identified as the crack nucleation sites and the cleavage fracture stress calculated to be 2400 MPa in a complete AF microstrucuture. This value is significantly larger than in steels that contain significant proportions of conventional bainite. Standard Charpy and Instrumented Charpy impact testing is conducted through a temperature range from -80 to + 22°C to study ductile fracture behaviour. The total absorbed energy is separated into energies of crack nucleation and of crack propagation. It is found that the energy of crack nucleation is weakly dependent on the volume fraction of M/A and completely independent of temperature over the range studied. The crack propagation energy varies significantly with both variables, decreasing with increased volume fraction of M/A and with decreasing temperature. The peak load in the instrumented Charpy data is used to calculate the dynamic fracture toughness, KId, which is found to be 105--120 MPa-m1/2. The void nucleation and void growth stages of ductile fracture are studied by metallographic examination of tensile bars. The sites of void nucleation are identified as inclusions and M/A particles. Voids nucleate at the M/A particles by decohesion of the particle-matrix interface. A constant void nucleation strain of epsilon = 0.90 +/- 0.05 is measured for all of the samples independent of the volume fraction of M/A. A stress-based criterion is used to predict void nucleation and the interface strength is determined to be

  5. Post-machining thermal treatment after surface finishing of hardened steels: Kinetics of XRD line width reduction and improvement in rolling contact lifetime under mixed friction conditions

    Energy Technology Data Exchange (ETDEWEB)

    Gegner, Juergen [SKF GmbH, Department of Material Physics, Ernst-Sachs-Str. 5, D-97424 Schweinfurt (Germany)

    2008-07-01

    Hard surface finishing represents the final manufacturing step for functional areas of machine elements in state-of-the-art production. Raceways of rolling bearing rings are ground and honed to the required low roughness. Plastic deformation is restricted to a narrow edge zone of the hardened steel. Reheating of the machined components below the martensite tempering or bainite transformation temperature results in a marked decrease of the XRD line width on the surface. The investigated samples are made of through-hardened standard bearing steel 100Cr6 (international denotation: SAE 52100). On the basis of a material model that explains the effect as a complex diffusion process of dislocational carbon segregation, i.e. static strain aging, the measured kinetics of the XRD line width reduction is simulated by an Arrhenius-type equation, which describes the rate-controlling reaction step of temper carbide dissolution. The formation of a small white-etching surface layer of around 1 um thickness by post-machining thermal treatment (PMTT) strongly supports this assumption. First rig tests suggest a considerable increase of the lifetime of Hertzian loaded elements that operate under heavy surface loading. PMTT performed in air leads to a beneficial nanoscaled oxide layer.

  6. Comparison on Mechanical Properties of SA508 Gr.3 Cl.1, Cl.2, and Gr.4N Low Alloy Steels for Pressure Vessels

    International Nuclear Information System (INIS)

    In this study, microstructure and mechanical properties of SA508 Gr.3 Cl. 1, Cl.2, and Gr.4N low alloy steels are characterized to compare their properties. To evaluate the fracture toughness in the transition region, the master curve method according to ASTM E1921 was adopted in the cleavage transition region. Tensile tests and Charpy impact tests were also performed to evaluate the mechanical properties, and a microstructural investigation was carried out. The microstructure and mechanical properties of SA508 Gr.3 Cl.1, Cl2 and Gr.4N low alloy steels were characterized.. The predominant microstructure of SA508 Gr.4N model alloy is tempered martensite, while SA508 Gr.3 Cl.1 and Cl.2 steels show a typical tempered upper bainitic structure. SA508 Gr. 4N model alloy shows the best strength and transition behavior among the three SA508 steels. SA508 Gr.3 Cl.2 steel also has quite good strength, but there is a loss of toughness

  7. Effect of Microstructure in TRIP Steel on Its Tensile Behavior at High Strain Rate

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    The relationships between microstructure of 0.195C-1.6Si-1.58Mn TRIP steel and its dynamic mechanical properties at high strain rate were investigated. The effect of microstructures on dynamic properties was discussed and the comparison with its static mechanical properties was also presented. The specimens of TRIP steel via three heat treatment techniques exhibit different morphological structures, responsible for their dynamic mechanical performances. The dynamic tensile testing was performed on self-made pneumatic tensile impact tester. The results showed that the size, volume fraction, morphology and distribution of retained austenite all affect the final mechanical properties at high strain rate. Among them, the second phase (retained austenite+bainite) with net structure severely decreases the elongation of TRIP steel in spite of the fact that it enhances strength because it restrains ferrite deformation. In order to obtain the excellent combination of strength and elongation, rational matching of morphology, size and volume fraction of several phases in TRIP steel can be obtained via proper heat treatment techniques.

  8. A micro-mechanical analysis and an experimental characterisation of the behavior and the damaging processes of a 16MND5 pressure vessel steel at low temperature; Etude micromecanique et caracterisation experimentale du comportement et de l'endommagement de l'acier de cuve 16MND5 a basses temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Pesci, R

    2004-06-15

    As part of an important experimental and numerical research program launched by Electricite De France on the 16MND5 pressure vessel steel, sequenced and in-situ tensile tests are realized at low temperatures [-196 C;-60 C]. They enable to associate the observation of specimens, the complete cartography of which has been made with a scanning electron microscope (damaging processes, initiation and propagation of microcracks), with the stress states determined by X-ray diffraction, in order to establish relevant criteria. All these measurements enable to supply a two-scale polycrystalline modeling of behavior and damage (Mori-Tanaka/self-consistent) which is developed concurrently with the experimental characterization. This model proves to be a very efficient one, since it correctly reproduces the influence of temperature experimentally defined: the stress state in ferrite remains less important than in bainite (the difference never exceeds 150 MPa), whereas it is much higher in cementite. The heterogeneity of strains and stresses for each crystallographic orientation is well rendered; so is cleavage fracture normal to the {l_brace}100{r_brace} planes in ferrite (planes identified by electron back scattered diffraction during an in-situ tensile test at -150 C), which occurs sooner when temperature decreases, for a constant stress of about 700 MPa in this phase. (author)

  9. Microstructure evolution in TRIP-aided seamless steel tube during T-shape hydroforming process

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Jiyuan [State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110004, Liaoning Provence (China); Zhang, Zicheng, E-mail: zhangzicheng2004@126.com [School of Mechanical Engineering and Automation, Northeastern University, Shenyang 110004, Liaoning Provence (China); Manabe, Ken-ichi [Department of Mechanical Engineering, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji-shi, Tokyo 192-0397 (Japan); Li, Yanmei [State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110004, Liaoning Provence (China); Misra, R.D.K. [Center for Structural and Functional Materials, University of Louisiana at Lafayette, 44130 Lafayette, LA 70504-4130 (United States)

    2014-08-15

    Transformation-induced plasticity aided seamless steel tube comprising of ferrite, bainite, and metastable austenite was processed through forging, piercing, cold-drawing, and two-stage heat treatment. T-shape hydroforming is a classic forming method for experimental research and practical production. The current work studied austenite-to-martensite transformation and microcrack initiation and propagation of the tube during T-shape hydroforming using electron backscattering diffraction, scanning electron microscopy, and transmission electron microscopy. The strain distribution in the bcc-phase and fcc-phase was studied by evaluating changes in the average local misorientation. Compared to the compressive stress, metastable austenite with similar strain surrounding or inside the grains transformed easier under tensile loading conditions. The inclusions were responsible for microcrack initiation. The propagation of the cracks is hindered by martensite/austenite constituent due to transformation induced plasticity effect. The volume fraction of untransformed retained austenite decreased with increase in strain implying transformation-induced plasticity effect. - Highlights: • Hydroformed tubes processed via TRIP concept • EBSD provided estimate of micro local strain. • Retained austenite hinders propagation of microcracks.

  10. Twin-wire Submerged Arc Welding Process of a High-strength Low-alloy Steel

    Institute of Scientific and Technical Information of China (English)

    YANG Xiuzhi; XU Qinghua; YIN Niandong; XIAO Xinhua

    2011-01-01

    The measurement of thermal cycle curves of a high-strength low-alloy steel (HSLA)subjected twin-wire submerged arc welding (SAW) was introduced. The thermal simulation test was performed by using the obtained curves. The impact toughness at -50 ℃ temperature of the simulated samples was also tested. OM, SEM and TEM of the heat-affected zone (HAZ) of some simulation specimens were investigated. The results showed that the HSLA endured the twin-wire welding thermal cycle, generally, the low-temperature toughness values of each part of HAZ was lower than that of the parent materials, and the microstructure of coarse-grained zone(CGHAZ) mainly made up of granular bainite is the reason of the toughness serious deterioration. Coarse grain, grain boundary carbide extract and M-A island with large size and irregular polygon, along the grain boundary distribution, are the reasons for the toughness deterioration of CGHAZ. The research also showed that selected parameters of twin-wire SAW can meet the requirements to weld the test steel.

  11. Influences of Mo element on welded microstructure and properties of X80 high Nb pipeline steel%钼对X80高铌管线钢焊接组织与性能的影响

    Institute of Scientific and Technical Information of China (English)

    张婷婷; 卢胜勇; 嵇峰; 葛玉宏; 肖福仁

    2012-01-01

    The influences of welding thermal cycle on the microstructure and properties of two kinds of X80 pipeline steel were investigated by means of welding thermal simulation.The results show that,adding Mo element to the high Nb X80 pipeline steel can suppress formation of the pro-eutectoid ferrite during the welding process,promote transformation of the lower bainite,and as a result of Mo existence,can refine the grain size more effectively,make toughness and microhardness of the steel with Mo element superior to the high Nb pipeline steel.%用热模拟试验机研究了不同线能量的焊接热循环对两种X80高铌管线钢组织和性能的影响。结果表明,在X80高铌管线钢中添加钼元素,可以抑制焊接过程中先共析铁素体的形成,促进下贝氏体转变,钼能够更加有效地细化焊后晶粒尺寸,使得加钼钢获得优于高铌钢的韧性和显微硬度。

  12. Comparative analysis by simulating and testing pole impact for hot stamping front crossbeam of automobile

    Institute of Scientific and Technical Information of China (English)

    Ma Fangwu; Yao Zaiqi; Liu Qiang; Wang Xiaona; Zhao Fuquan; Li Fangfang; Lin Jianping

    2012-01-01

    Hot stamping 22MnB5 steel plate with ultra-high strength has been widely used for body structural members in consideration of automobile safety and lightweight. This paper presents a verification program of simulating and testing pole impact in order to verify if the front crossbeam reinforcement assembly can meet the design requirements, reduce the overall vehicle simulation and test cost and shorten the operation period. In the same condition, the simulation proved conforming to the design requirements; however, the bumper cracked at the impacting point in the course of pole impact test. The analysis of the crack by optical microscope, Vickers and scanning electron microscope indicates that mixture of ferrite, bainite and martensite was produced in the weld heat-affected zone of the 340/590DP tow hook holder and the 22MnB5 front crossbeam; therefore, their hardness and mechanical property were reduced obviously, so that they fractured when impacted. No welding process with continuous weld but spot welding or other bonding method may be employed for the reason that the capacity of the 22MnB5 steel plate in the weld heat-affected zone was reduced obvi- ously.

  13. Enhancement of Heat-Affected Zone Toughness of a Low Carbon Steel by TiN Particle

    Science.gov (United States)

    Zhang, Yu; Li, Xiaobao; Ma, Han

    2016-08-01

    Enhancement of heat-affected zone toughness of a weight percentage of 0.014 pct Ti-bearing low carbon steel by TiN particle was investigated. An increase in nitrogen weight percentage from 0.0031 to 0.0083 pct results in increasing of number density of TiN precipitates from 4 × 103 to 3 × 105/mm2, and reduces prior austenite grain size from 850 to 350 μm with a soaking of 1673 K (1400 °C) for 2000 seconds. Effective refinement of austenite grain prohibits formation of ferrite side plate and/or upper bainite, and densely distributed TiN particles promote intra-granular ferrite formation, which is accompanied by an increase of 40 K to 60 K (40 °C to 60 °C) in austenite decomposition temperature during continuous cooling process. The changes in transformed products improved impact toughness of heat-affected zone efficiently, ex., increase absorbed energy of less than 42 J to more than 320 J with a simulated t 8/5 of 550 seconds.

  14. Development of intercritical heat treatment process for toughness improvement of SA508 Gr.3 reactor pressure vessel steel

    Energy Technology Data Exchange (ETDEWEB)

    Hong, J.H.; Ahn, Y.S.; Byun, T.S.; Kim, H.D.; Lee, B.S. [Korea Atomic Energy Research Institute, Taejon (Korea)

    1998-07-01

    The new heat treatment processes for manufacturing high toughness SA508 Gr.3 steels have been developed by application of intercritical heat treatment (IHT). In the new heat treatment processes, the IHT is added between the quenching and the tempering of the conventional heat treatment process. The application of IHT resulted in the increase of ductility and upper shelf energy and in the decrease of strength and ductile-to-brittle transition temperature (DBTT). The modification of tempering conditions reduced the loss of strength resulting from the IHT. The beneficial effects from the IHT were consistently maintained in spite of the changes of heating and cooling rates. Additionally, the cause of the increase in toughness was investigated in relation to the microstructural change. The IHT produces a composite structure of hard tempered martensite and soft double-tempered bainite. More sub-grain boundaries are contained in the composite structure, and these act as obstacles to cleavage propagation. Furthermore, the coarse and long carbides are much spheroidized and inter-carbide distance becomes longer by IHT. High toughness is measured when the microstructure contains 20 to 60% tempered martensite. It was concluded that the spheroidized carbides with longer inter-particle distance are one of important causes for high toughness. (author). 33 refs., 24 figs., 6 tabs.

  15. Carbon partitioning during quenching and partitioning heat treatment accompanied by carbide precipitation

    International Nuclear Information System (INIS)

    Carbon partitioning from martensite into austenite in the quenching and partitioning (Q&P) process has been suggested to be controlled by the constrained carbon equilibrium (CCE) criterion. It defines an approach for predicting the carbon concentration in austenite under the condition that competing reactions such as carbide formation and bainite transformation are suppressed. Carbide precipitation in martensite is, however, often observed during the partitioning step, even in low-carbon steels as well as in high-carbon steels, even when containing a high amount of Si. Therefore, carbon partitioning from martensite into austenite is studied here, considering carbide precipitation in martensite. Carbon partitioning was investigated by means of a field-emission electron probe micro analysis (FE-EPMA) and atom probe tomography (APT), using 1.07 wt.% and 0.59 wt.% carbon steels with various martensite volume fractions. Carbon partitioning from martensite to austenite was clearly observed in all specimens, even though a considerable amount of carbide precipitated inside the martensite. The austenite carbon concentration after the partitioning step was not influenced by either the martensite volume fraction or the bulk carbon content. A modified model for predicting the austenite carbon concentration after the partitioning step was proposed to explain the experimental results by assuming carbon equilibria between austenite, ferrite and cementite under a constrained condition

  16. Structure–mechanical property relationship in a low carbon Nb–Cu microalloyed steel processed through a three-step heat treatment: The effect of tempering process

    International Nuclear Information System (INIS)

    We describe here the impact of tempering temperature and tempering time on the microstructure and mechanical property in a low carbon Nb–Cu microalloyed steel via a three-step heat treatment. After tempering process, the microstructure primarily comprised of ferrite, retained austenite and tempered bainite/martensite. The ferrite matrix with ultrafine grain size was film-like and enriched with nanometer-sized niobium-containing and copper precipitates. The volume fraction of ferrite increased with the increase in tempering temperature and tempering time. Retained austenite had average grain size less than 1 μm and was enriched with copper precipitates that contributes to enhance the stability of austenite. The retained austenite revealed high thermal stability and remained stable in the range of 20–30% when tempering temperature and time changed. High strength and good ductility were obtained in the tempering temperature range of 450–550 °C, or by prolonging tempering time at 500 °C, where the yield strength was ∼750 MPa and the product of tensile strength and % elongation was ∼32 GPa%, which is attributed to the cooperation of multiphase microstructure, stable retained austenite and nanometer-sized precipitates

  17. The Influence of Post Weld Heat Treatment in Alloy 82/182 Dissimilar Metal Weld between Low Alloy Steel and 316L Stainless Steel

    International Nuclear Information System (INIS)

    Dissimilar metal welds (DMWs) using an Alloy 82/182 are widely used to join low alloy steel components and stainless steel pipes in pressurized water reactors (PWRs). It has been reported that tensile residual stress would be generated within DMWs during the welding processes. It is thought as main reason for primary water stress corrosion cracking (PWSCC) resulting in deterioration of long-term integrity. The application of post weld heat treatment (PWHT) has been considered to reduce the tensile residual stress after welding process. Meanwhile, the PWHT could affect the changes in microstructure, mechanical properties, and corrosion resistance. Therefore, in this study, the effects of PWHT on the microstructure, mechanical properties and corrosion behaviors of base metals of low alloy steel and stainless steel and welding materials of Alloy 82/182 are evaluated. The influence of PWHT in DMW has been investigated. SA 508 and 316L SS exhibited tempered bainite and austenitic grains with a few residual stringer type ferrite. Grain boundary carbides are not precipitated owing to low carbon and insufficient exposure time in 316L SS. The change of mechanicals properties in base metals is not observed. In case of Alloy 182, after PWHT, grain boundaries are covered with film-like continuous Cr-rich carbides

  18. Microstructure and fatigue crack growth behaviour of electron beam welding in 30CrMnSiNi2A steel

    Institute of Scientific and Technical Information of China (English)

    陈芙蓉; 霍立兴; 张玉凤; 张莉; 刘方军; 陈刚

    2003-01-01

    The effects of two post-weld heat treatment processes on the microstructure and fatigue properties of the electron beam welded joints of 30CrMnSiNi2A steel were studied. Electron beam local post-weld heat treatment (EBLPWHT), in a vacuum chamber, immediately after welding and a traditional furnace whole post-weld heat treatment (FWPWHT) were accepted. The experimental results show that, after EBLPWHT, the main microstructure of weld is changed from coarse acicular martensite into lath martensite, and base metal is changed from ferrite and perlite into upper bainite and residual austenite, however the microstructures of different zones of joints in FWPWHT conditions are tempered sorbite. The fatigue crack growth rate da/dN of welds and base metal are not obviously changed among EBLPWHT, FWPWHT test and as-welded (AW) test, as the mechanical properties of materials have a certain but not large effect on the da/dN of welded joints. The resistance to near threshold fatigue crack growth data of welded joints can be largely improved by EBLPWHT and it is related to microstructure and crack closure effect.

  19. Crack initiation and propagation in welded joints of turbine and boiler steels during low cycle fatigue

    International Nuclear Information System (INIS)

    Low cycle fatigue (LCF) tests have been performed at 300 and 565 degrees C on welded joints and on microstructures to be found in or near welded joints in a low alloy ferritic steel 0.5 Cr, 0.5 Mo, 0.25 V. The difference in lifetimes between the 300 degrees C and 565 degrees C tests was small comparing the same microstructures and strain ranges, although the stress amplitude was greater at 300 degrees C. Under constant stress conditions the fatigue life depended on the fatigue life of the parent metal but under constant strain conditions the lifetime was governed by that of the bainitic structures. Strain controlled LCF tests have been performed at 750 degrees C on welded joints in the austenitic steel AISI 316 and on different parent and weld metals used in these joints. In continuously cycled samples all cracks were transgranular and initiated at the surface; hold-time samples displayed internally initiated intergranular cracking in the weld metal. Under constant strain conditions the 316 parent and weld metals exhibited similar lifetimes. When considering a constant stress situation the strength of the microsturctures decreased in the following order: Sanicro weld metal, cold deformed parent metal, undeformed parent metal and weld metal (K.A.E.)

  20. The role of chemical free energy and elastic strain in the nucleation of zirconium hydride

    Energy Technology Data Exchange (ETDEWEB)

    Barrow, A.T.W. [Nuclear Materials Group, Department of Mechanical and Materials Engineering, Queen’s University, Kingston, Ontario K7L 3N6 (Canada); Toffolon-Masclet, C. [CEA-Saclay, Nuclear Materials Department, SRMA/LA2M, F-91191 Gif-Sur-Yvette (France); Almer, J. [Argonne National Laboratory, Argonne, IL 60439 (United States); Daymond, M.R., E-mail: daymond@me.queensu.ca [Nuclear Materials Group, Department of Mechanical and Materials Engineering, Queen’s University, Kingston, Ontario K7L 3N6 (Canada)

    2013-10-15

    In this work a combination of synchrotron X-ray diffraction and thermodynamic modelling has been used to study the dissolution and precipitation of zirconium hydride in α-Zr establishing the role of elastic misfit strain and chemical free energy in the α → α + δ phase transformation. The nucleation of zirconium hydride is dominated by the chemical free energy where the chemical driving force for hydride precipitation is proportional to the terminal-solid solubility for precipitation and can be predicted by a function that is analogous to the universal nucleation parameter for the bainite transformation in ferrous alloys. The terminal-solid solubility for precipitation was found to be kinetically limited ⩾287 °C at a cooling rate of 5 °C min{sup −1} or greater. The terminal solubilities were established using an offset method applied to the lattice strain data where a resolution of ∼10 wppm H can be achieved in the 〈c〉-direction. This is aided by the introduction of intra-granular strains in the 〈c〉-direction during cooling as a result of the thermal expansion anisotropy which increases the anisotropy associated with the misfitting H atoms within the α-Zr lattice.