Characterization of the martensite phase formed during hydrogen ion irradiation in austenitic stainless steel

Science.gov (United States)

Jin, Hyung-Ha; Lim, Sangyeob; Kwon, Junhyun

2017-10-01

Microstructural changes in austenitic stainless steel caused by hydrogen ion irradiation were investigated using transmission electron microscopy (TEM). It has been confirmed that the irradiation induced the formation of martensite along the grain boundary; the martensite phase exhibited a crystal orientation relationship with the adjacent austenite phase. The results of this study also indicate that the concentration of Cr in the martensite phase is lower compared to that in the austenite matrix. The TEM results showed the development of asymmetric radiation-induced segregation (RIS) near the grain boundary, which leads to local changes in the chemical composition such as reduction of Cr near the grain boundary. The asymmetric RIS serves as a prerequisite for the formation of the martensite under hydrogen irradiation.

On the cryogenic magnetic transition and martensitic transformation of the austenite phase of 7MoPLUS duplex stainless steel

Energy Technology Data Exchange (ETDEWEB)

Lo, K.H., E-mail: KHLO@umac.m [Department of Electromechanical Engineering, University of Macau, Macau (China); Department of Physics and Materials Science, City University of Hong Kong (Hong Kong); Lai, J.K.L. [Department of Physics and Materials Science, City University of Hong Kong (Hong Kong)

2010-08-15

The magnetic behaviour and martensitic transformation at cryogenic temperatures (down to 4 K) of the austenite phase of the duplex stainless steel (DSS), 7MoPLUS, were studied. As regards the prediction of Neel temperature, the empirical expressions for austenitic stainless steels are not applicable to the austenite phase of 7MoPLUS, although the composition of the austenite phase falls within the composition ranges within which the expressions were developed. Regarding the prediction of martensitic point Ms, the applicability of 'old' and recently developed expressions has been examined. The recently developed expressions, which take into account more alloying elements and their interactions, are not suitable for the austenite phase of 7MoPLUS. But for the 'old', simpler expressions, they seem to be valid in the sense that they all predict high stability of the austenite phase. Results obtained from 7MoPLUS were qualitatively the same as those obtained from another DSS, designated as 2205. Reasons for the applicability and inapplicability of these empirical expressions are suggested.

Ultrahigh strength martensite–austenite dual-phase steels with ultrafine structure: The response to indentation experiments

International Nuclear Information System (INIS)

Misra, R.D.K.; Venkatsurya, P.; Wu, K.M.; Karjalainen, L.P.

2013-01-01

In medium to high carbon steels, characterized by martensite–austenite microstructure processed by quenching and partitioning process, martensite potentially provides high strength, while austenite provides work hardening [Fu, Wu, and Misra, DOI: 10.1179/1743284712/068]. Given the significant interest in these steels in the steel community, the paper reports for the first time the nanoscale deformation experiments and accompanying microstructural evolution to obtain micromechanical insights into the deformation behavior of ultrahigh strength-high ductility dual-phase steels with significant retained austenite fraction of ∼0.35. During deformation experiments with nanoindenter, dislocations were distributed on several slip systems, whereas strain-induced twinned martensite and twinning were the deformation mechanisms in carbon-enriched and thermally stabilized retained austenite. Furthermore, ultrafine dual-phase steels exhibited high strain rate sensitivity.

Ultrahigh strength martensite-austenite dual-phase steels with ultrafine structure: The response to indentation experiments

Energy Technology Data Exchange (ETDEWEB)

Misra, R.D.K., E-mail: dmisra@louisiana.edu [Laboratory for Excellence in Advanced Steel Research, Center for Structural and Functional Materials, University of Louisiana at Lafayette, P.O. Box 44130, Lafayette, LA 70504 (United States); Venkatsurya, P. [Laboratory for Excellence in Advanced Steel Research, Center for Structural and Functional Materials, University of Louisiana at Lafayette, P.O. Box 44130, Lafayette, LA 70504 (United States); Wu, K.M. [International Research Institute for Steel Technolgy, Wuhan University of Science and Technology, Wuhan 430081 (China); Karjalainen, L.P. [Centre for Advanced Steels Research, University of Oulu, P.O. Box 4200, 90014 Oulu (Finland)

2013-01-10

In medium to high carbon steels, characterized by martensite-austenite microstructure processed by quenching and partitioning process, martensite potentially provides high strength, while austenite provides work hardening [Fu, Wu, and Misra, DOI: 10.1179/1743284712/068]. Given the significant interest in these steels in the steel community, the paper reports for the first time the nanoscale deformation experiments and accompanying microstructural evolution to obtain micromechanical insights into the deformation behavior of ultrahigh strength-high ductility dual-phase steels with significant retained austenite fraction of {approx}0.35. During deformation experiments with nanoindenter, dislocations were distributed on several slip systems, whereas strain-induced twinned martensite and twinning were the deformation mechanisms in carbon-enriched and thermally stabilized retained austenite. Furthermore, ultrafine dual-phase steels exhibited high strain rate sensitivity.

Phase transformation of the L1{sub 2} phase to kappa-carbide after spinodal decomposition and ordering in an Fe–C–Mn–Al austenitic steel

Energy Technology Data Exchange (ETDEWEB)

Cheng, Wei-Chun, E-mail: weicheng@mail.ntust.edu.tw [Department of Mechanical Engineering, National Taiwan University of Science and Technology, 43 Keelung Road, Section 4, Taipei 106, Taiwan (China); Cheng, Chih-Yao; Hsu, Chia-Wei [Department of Mechanical Engineering, National Taiwan University of Science and Technology, 43 Keelung Road, Section 4, Taipei 106, Taiwan (China); Laughlin, David E. [Department of Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA (United States)

2015-08-26

Fe–C–Mn–Al steels have the potential to substitute for commercial Ni–Cr stainless steels. For the development of Fe–C–Mn–Al stainless steels, phase transformations play an important role. Our methods of studying the phase transformations of the steel include heating, cooling, and/or annealing. The results of our study show that spinodal decomposition, an atomic ordering reaction and the transformation of the L1{sub 2} phase to kappa-carbide occur in the Fe–C–Mn–Al steel. After cooling, the austenite decomposes by the spinodal mechanism into solute-lean and solute-rich austenite phases. The solute-rich austenite phase also transforms into the L1{sub 2} phase via the ordering reaction upon cooling to lower temperatures. After quenching and prolonged annealing, the L1{sub 2} phase grows in the austenite and finally transforms into kappa-carbide. This L1{sub 2} phase to kappa-carbide transformation has not been observed previously.

Precipitation of Second Phases in High-Interstitial-Alloyed Austenitic Steel

Science.gov (United States)

Lee, Tae-Ho; Ha, Heon-Young; Kim, Sung-Joon

2011-12-01

The precipitation reaction of an austenitic stainless steel containing N + C was investigated using transmission electron microscopy. The main precipitate formed during isothermal aging at 1123 K (850 °C) was M23C6 carbide, and its morphology gradually changed in a sequence of intergranular (along grain boundary) → cellular (or discontinuous) → intragranular (within grain interior) form with aging time. Irrespective of different morphologies, the M23C6 was consistently related to austenite matrix in accordance with the cube-on-cube orientation relationship. Based on the analysis of electron diffraction, two variants of intragranular M23C6 were identified, and they were related to each other by twin relation. Prolonged aging produced other types of precipitates—the rod-shaped Cr2N and the coarse irregular intermetallic sigma phase. The similarities and differences in precipitation behavior between N only and N + C alloyed austenitic stainless steels are briefly discussed.

Phase Transformation of Metastable Austenite in Steel during Nano indentation

International Nuclear Information System (INIS)

Ahn, Taehong; Lee, Sung Bo; Han, Heung Nam; Park, Kyungtae

2013-01-01

These can produce geometrical softening accompanied by a sudden displacement excursion during load-controlled nanoindentation, which referred to in the literature as a pop-in. In this study, phase transformation of metastable austenite to stress-induced ε martensite which causes pop-ins during nanoindentation of steel will be reported and discussed. This study investigated the relationship between pop-in behavior of austenite in the early stage of nanoindentation and formation of ε martensite based on microstructural analyses. The load-displacement curve obtained from nanoindentation revealed stepwise pop-ins in the early stage of plastic deformation. From analyses of high resolution TEM images, a cluster of banded structure under the indent turned out a juxtaposition of (111) planes of γ austenite and (0001) planes of ε martensite. The calculation of displacement along indentation axis for (111) slip system by formation of ε martensite showed that geometrical softening can also occur by ε martensite formation when considering that the stress-induced ε martensite transformation is the predominant deformation mode in the early stage of plastic deformation and its monopartial nature as well. These microstructural investigations strongly suggest that the pop-in behavior in the early stage of plastic deformation of austenite is closely related to the formation of ε martensite

Phase Transformation of Metastable Austenite in Steel during Nano indentation

Energy Technology Data Exchange (ETDEWEB)

Ahn, Taehong [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Lee, Sung Bo; Han, Heung Nam [Seoul National Univ., Seoul (Korea, Republic of); Park, Kyungtae [Hanbat National Univ., Daejeon (Korea, Republic of)

2013-05-15

These can produce geometrical softening accompanied by a sudden displacement excursion during load-controlled nanoindentation, which referred to in the literature as a pop-in. In this study, phase transformation of metastable austenite to stress-induced ε martensite which causes pop-ins during nanoindentation of steel will be reported and discussed. This study investigated the relationship between pop-in behavior of austenite in the early stage of nanoindentation and formation of ε martensite based on microstructural analyses. The load-displacement curve obtained from nanoindentation revealed stepwise pop-ins in the early stage of plastic deformation. From analyses of high resolution TEM images, a cluster of banded structure under the indent turned out a juxtaposition of (111) planes of γ austenite and (0001) planes of ε martensite. The calculation of displacement along indentation axis for (111) slip system by formation of ε martensite showed that geometrical softening can also occur by ε martensite formation when considering that the stress-induced ε martensite transformation is the predominant deformation mode in the early stage of plastic deformation and its monopartial nature as well. These microstructural investigations strongly suggest that the pop-in behavior in the early stage of plastic deformation of austenite is closely related to the formation of ε martensite.

Determination of local carbon content in austenite during intercritical annealing of dual phase steels by PEELS analysis

International Nuclear Information System (INIS)

Garcia-Junceda, A.; Caballero, F.G.; Capdevila, C.; Garcia de Andres, C.

2007-01-01

Parallel electron energy loss spectroscopy has allowed to analyse and quantify local variations in the carbon concentration of austenite islands transformed during the intercritical annealing treatment of commercial dual-phase steels. These changes in the carbon content of different austenite regions are responsible for the different volume fractions of tempered martensite, martensite and retained austenite obtained after intercritical annealing and overaging treatment. This technique reveals how carbon distribution in austenite evolves as the transformation process advances

Phase transformation system of austenitic stainless steels obtained by permanent compressive strain

Energy Technology Data Exchange (ETDEWEB)

Okayasu, Mitsuhiro, E-mail: mitsuhiro.okayasu@utoronto.ca; Tomida, Sai

2017-01-27

In order to understand more completely the formation of strain-induced martensite, phase structures were investigated both before and after plastic deformation, using austenitic stainless steels of various chemical compositions (carbon C=0.007–0.04 mass% and molybdenum Mo=0–2.10 mass%) and varying pre-strain levels (0–30%). Although the stainless steels consisted mainly of γ austenite, two martensite structures were generated following plastic deformation, comprising ε and α′ martensite. The martensitic structures were obtained in the twin deformation and slip bands. The severity of martensite formation (ε and α′) increased with increasing C content. It was found that α′ martensite was formed mainly in austenitic stainless steel lacking Mo, whereas a high Mo content led to a strong ε martensite structure, i.e. a weak α′ martensite. The formation of α′ martensite occurred from γ austenite via ε martensite, and was related to the slip deformation. Molybdenum in austenitic stainless steel had high slip resistance (or weak stress-induced martensite transformation), because of the stacking fault energy of the stainless steel affecting the austenite stability. This resulted in the creation of weak α′ martensite. Models of the martensitic transformations γ (fcc)→ε (hcp)→α′ (bcc) were proposed on both the microscopic and nanoscopic scales. The α′ martensite content of austenitic stainless steel led to high tensile strength; conversely, ε martensite had a weak effect on the mechanical strength. The influence of martensitic formation on the mechanical properties was evaluated quantitatively by statistical analysis.

Z phase stability in AISI 316LN + Nb austenitic steels during creep at 650 C

Energy Technology Data Exchange (ETDEWEB)

Vodarek, Vlastimil [Technical Univ. Ostrava (Czech Republic)

2010-07-01

The creep resistance of austenitic CrNi(Mo) steels strongly depends on microstructural stability during creep exposure. Nitrogen additions to CrNi(Mo) austenitic steels can significantly improve the creep strength. One of the most successful methods of improving the long-term creep resistance of austenitic steels is based on increasing the extent of precipitation strengthening during creep exposure. The role of precipitates in the achievements of good creep properties has been extensively studied for a long time. Although many minor phases are now well documented there are still contractions and missing thermodynamic data about some minor phases. This contribution deals with results of microstructural studies on the minor phase evolution in wrought AISI 316LN niobium stabilised steels during long-term creep exposure at 650 C. Microstructural investigations were carried out on specimens taken from both heads and gauge lengths of ruptured test-pieces by means of optical metallography, transmission and scanning electron microscopy. The attention has been paid to evaluation of thermodynamic and dimensional stability of Z phase and other nitrogen bearing minor phases. Only two nitrogen-bearing minor phases formed in the casts investigated: Z phase and M{sub 6}X. The dimensional stability of Z phase particles was very high. (orig.)

Determination of Stress Profiles in Expanded Austenite by Combining Successive Layer Removal and GI-XRD

DEFF Research Database (Denmark)

Fernandes, Frederico Augusto Pires; Christiansen, Thomas Lundin; Somers, Marcel A. J.

2014-01-01

The present work deals with the evaluation of the residual-stress profile in expanded-austenite by successive removal steps using GI-XRD. Preliminary results indicate stresses of several GPa's from 111 and 200 diffraction lines. These stresses appear largest for the 200 reflection. The strain......-free lattice parameter decayed smoothly with depth, while for the compressive stress a maximum value is observed at some depth below the surface. Additionally a good agreement was found between the nitrogen profile determined with GDOES analysis and the strain-free lattice parameter from XRD....

The kinetics of phase transformations of undercooled austenite of the Mn-Ni iron based model alloy

OpenAIRE

E. Rożniata; R. Dziurka; J. Pacyna

2011-01-01

Purpose: Present work corresponds to the research on the kinetics of phase transformations of undercooled austenite of Mn-Ni iron based model alloy. The kinetics of phase transformations of undercooled austenite of investigated alloy was presented on CCT diagram (continuous cooling transformation). Also the methodology of a dilatometric samples preparation and the method of the critical points determination were described.Design/methodology/approach: The austenitising temperature was defined ...

G-phase precipitation in austenitic stainless steel deformed by high pressure torsion

International Nuclear Information System (INIS)

Shuro, I.; Kuo, H.H.; Sasaki, T.; Hono, K.; Todaka, Y.; Umemoto, M.

2012-01-01

Highlights: ► Using TEM and APT analyses, G-phase precipitation was observed in HPTed SUS304 with no trace of spinodal decomposition. ► G-phase precipitation occurred much shorter time than previous studies probably due to the elimination of prior SD and enhanced diffusion by severe plastic deformation. ► G-phase composition is a function of aging time. ► Tensile tests showed that in SUS304 embrittlement occurs solely due to G-phase precipitation. - Abstract: G phase an intermetallic silicide has been observed in martensite of precipitation hardened stainless steels and in the ferrite of dual (austenite and ferrite) phase stainless steels. In both cases, before G-phase precipitates, the matrix composition changes due to spinodal decomposition and solute partitioning between ferrite and austenite. Thus in the present study, single bcc phase and high Ni content stainless steel, was selected to study G-phase precipitation expecting elimination of the interference from spinodal decomposition and solute partitioning. Fe–18Cr–8Ni (SUS304) austenitic stainless steel samples were deformed at room temperature by high pressure torsion to obtain 100% volume fraction of deformation induced martensite (α′). HPT deformation was chosen due to its ability to induce high strength by grain refinement and also attain 100% α′ at room temperature. After annealing at 400 °C for 500 h, G-phase precipitation was observed in the fully martensitic matrix without spinodal decomposition. Crystallographic analysis of annealed samples using high resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy (EDS) detected a Mn–Ni–Si rich G-phase with fcc crystal structure with lattice parameter of 1.16 nm. The value of lattice parameter corresponds well with previously reported values. Chemical analysis by atom probe tomography (APT) showed G-phase of composition Mn 21 Ni 50 Si 24 Fe 4 Cr. Tensile tests showed that G-phase precipitation leads to

G-phase precipitation in austenitic stainless steel deformed by high pressure torsion

Energy Technology Data Exchange (ETDEWEB)

Shuro, I., E-mail: innoshuro@martens.me.tut.ac.jp [Functional Materials Engineering, Toyohashi University of Technology, 1-1, Toyohashi, Aichi 441-8580 (Japan); Kuo, H.H. [Functional Materials Engineering, Toyohashi University of Technology, 1-1, Toyohashi, Aichi 441-8580 (Japan); Sasaki, T.; Hono, K. [National Institute for Materials Sciences, Sengen 1-2-1, Tsukuba 305-0047 (Japan); Todaka, Y.; Umemoto, M. [Functional Materials Engineering, Toyohashi University of Technology, 1-1, Toyohashi, Aichi 441-8580 (Japan)

2012-08-30

Highlights: Black-Right-Pointing-Pointer Using TEM and APT analyses, G-phase precipitation was observed in HPTed SUS304 with no trace of spinodal decomposition. Black-Right-Pointing-Pointer G-phase precipitation occurred much shorter time than previous studies probably due to the elimination of prior SD and enhanced diffusion by severe plastic deformation. Black-Right-Pointing-Pointer G-phase composition is a function of aging time. Black-Right-Pointing-Pointer Tensile tests showed that in SUS304 embrittlement occurs solely due to G-phase precipitation. - Abstract: G phase an intermetallic silicide has been observed in martensite of precipitation hardened stainless steels and in the ferrite of dual (austenite and ferrite) phase stainless steels. In both cases, before G-phase precipitates, the matrix composition changes due to spinodal decomposition and solute partitioning between ferrite and austenite. Thus in the present study, single bcc phase and high Ni content stainless steel, was selected to study G-phase precipitation expecting elimination of the interference from spinodal decomposition and solute partitioning. Fe-18Cr-8Ni (SUS304) austenitic stainless steel samples were deformed at room temperature by high pressure torsion to obtain 100% volume fraction of deformation induced martensite ({alpha} Prime ). HPT deformation was chosen due to its ability to induce high strength by grain refinement and also attain 100% {alpha} Prime at room temperature. After annealing at 400 Degree-Sign C for 500 h, G-phase precipitation was observed in the fully martensitic matrix without spinodal decomposition. Crystallographic analysis of annealed samples using high resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy (EDS) detected a Mn-Ni-Si rich G-phase with fcc crystal structure with lattice parameter of 1.16 nm. The value of lattice parameter corresponds well with previously reported values. Chemical analysis by atom probe tomography

Characterization of phase properties and deformation in ferritic-austenitic duplex stainless steels by nanoindentation and finite element method

International Nuclear Information System (INIS)

Schwarm, Samuel C.; Mburu, Sarah; Ankem, Sreeramamurthy

2016-01-01

The phase properties and deformation behavior of the δ–ferrite and γ–austenite phases of CF–3 and CF–8 cast duplex stainless steels were characterized by nanoindentation and microstructure-based finite element method (FEM) models. We evaluated the elastic modulus of each phase and the results indicate that the mean elastic modulus of the δ–ferrite phase is greater than that of the γ–austenite phase, and the mean nanoindentation hardness values of each phase are approximately the same. Furthermore, the elastic FEM model results illustrate that greater von Mises stresses are located within the δ–ferrite phase, while greater von Mises strains are located in the γ–austenite phase in response to elastic deformation. The elastic moduli calculated by FEM agree closely with those measured by tensile testing. Finally, the plastically deformed specimens exhibit an increase in misorientation, deformed grains, and subgrain structure formation as measured by electron backscatter diffraction (EBSD).

Stability of retained austenite in multi-phase microstructure during austempering and its effect on the ductility of a low carbon steel

Energy Technology Data Exchange (ETDEWEB)

Xie, Z.J.; Ren, Y.Q.; Zhou, W.H. [School of Materials Science and Engineering, University of Science and Technology, Beijing (China); Yang, J.R. [Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan (China); Shang, C.J., E-mail: cjshang@ustb.edu.cn [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, Institute for Material Research and Innovation, University of Louisiana at Lafayette, P.O. Box 44130, Lafayette, LA 70503 (United States)

2014-05-01

The contribution of multi-phase microstructure and retained austenite on mechanical properties of austempered and intercritical annealed Fe–0.23C–1.8Mn–1.35Si (wt%) steel was studied. The multi-phase microstructure comprised of intercritical ferrite (IF), bainite/martensite, and retained austenite. During austempering, the retained austenite was stabilized, which was studied using a combination of experimental (XRD, TEM) and thermodynamic analysis. The termination of bainitic transformation combined with carbon rejection into residual austenite during the second step austempering treatment is believed to be the underlying basis for stabilization of retained austenite. This led to significant increase in uniform and total elongation (25% and 36%, respectively) and the product of tensile strength and % elongation was 33 GPa%. The work hardening behavior of retained austenite exhibited a three-stage process such that necking was delayed. The increased work hardening rate is attributed to the multi-phase microstructure and TRIP effect.

Phase transformation by fatigue in austenitic stainless steel

International Nuclear Information System (INIS)

Jo, Y.S.; Kwun, S.I.

1988-01-01

The effect of strain induced martensite on the fatigue behavior of AISI 304 austenitic stainless steel was investigated. During low cycle fatigue, the austenitic stainless steel showed a continuous cyclic hardening until fracture. The extent of cyclic hardening increased with decreasing austenite stability. The austenite stability was controlled by different aging time and temperature, which resulted in different carbide morphologies. The fatigue crack propagation rate near ΔK th varied also with the austenite stability inside the plastic zone at the crack up. Especially, the near-threshold fatigue crack propagation rate of the grain boundary carbide precipitated condition was the lowest. This was considered to be due to the roughness induced closure caused by intergranular facet. A new model for the intergranular facet formation and the fatigue crack propagation of grain boundary carbide precipitated condition was proposed. (Author)

Phase Transformations of an Fe-0.85 C-17.9 Mn-7.1 Al Austenitic Steel After Quenching and Annealing

Science.gov (United States)

Cheng, Wei-Chun

2014-09-01

Low-density Mn-Al steels could potentially be substitutes for commercial Ni-Cr stainless steels. However, the development of the Mn-Al stainless steels requires knowledge of the phase transformations that occur during the steel making processes. Phase transformations of an Fe-0.85 C-17.9 Mn-7.1 Al (wt.%) austenitic steel, which include spinodal decomposition, precipitation transformations, and cellular transformations, have been studied after quenching and annealing. The results show that spinodal decomposition occurs prior to the precipitation transformation in the steel after quenching and annealing at temperatures below 1023 K and that coherent fine particles of L12-type carbide precipitate homogeneously in the austenite. The cellular transformation occurs during the transformation of high-temperature austenite into lamellae of austenite, ferrite, and kappa carbide at temperatures below 1048 K. During annealing at temperatures below 923 K, the austenite decomposes into lamellar austenite, ferrite, κ-carbide, and M23C6 carbide grains for another cellular transformation. Last, when annealing at temperatures below 873 K, lamellae of ferrite and κ-carbide appear in the austenite.

Diffusion of nitrogen in austenitic phase: Application to nitriding of stainless steels

Directory of Open Access Journals (Sweden)

Torchane Lazhar

2014-04-01

Full Text Available The nitriding treatment of the martensitic stainless steels aims to harden and to introduce compressive stresses on the surface of steel. Hardening is resulting of the martensitic transformation of the austenitic matrix enriched into nitrogen during cooling and of the germination and the nitride growth. In order to preserve the stainless character of the nitrided layer, it is imperative to control precipitation within the zone affected by the treatment. Our task consists in showing that is possible to control the composition of the gas atmosphere containing ammonia and argon and to carry out on the surface of nitrided samples at 1050°C two types of configuration of layers : a single phase layer made up by martensite enriched in nitrogen α’N and or a two phase layer made up by austenite γN and martensite α’N enriched in nitrogen.

On the S-phase formation and the balanced plasma nitriding of austenitic-ferritic super duplex stainless steel

Science.gov (United States)

de Oliveira, Willian R.; Kurelo, Bruna C. E. S.; Ditzel, Dair G.; Serbena, Francisco C.; Foerster, Carlos E.; de Souza, Gelson B.

2018-03-01

The different physical responses of austenite (γ) and ferrite (α) iron structures upon nitriding result in technical challenges to the uniform modification of α-γ materials, as the super duplex stainless steel (SDSS). The effects of voltage (7-10 kV), frequency and pulse width on the nitrogen plasma immersion ion implantation of SDSS (α ∼ 56%, γ ∼ 44%) were investigated, correlated with structural, morphological and mechanical analyses. By controlling the treatment power, temperatures ranged from 292 °C to 401 °C. Despite the overall increase in hardness for any of the employed parameters (from ∼6 GPa to ∼15 GPa), the structure of individual grains was strikingly dissimilar at the same temperatures, depending on the energetic conditions of implantation. Modified-α grains containing iron nitrides (ε-Fe2-3N, γ‧ -Fe4N) presented intense brittleness, whereas the expanded phase γN (S-phase) laid principally in modified-γ grains, exhibiting ductile-like deformation features and thicker layers. The γN was the dominant phase in both α-γ grains at ∼401 °C, providing them with balanced structure and mechanical behavior. These phenomena corroborate with γN as mediator of the process, through a mechanism involving the nitrogen-promoted ferrite to austenite conversion and nitrides dissolution at high temperatures. An approximately linear correlation of the γN content with respect to the ion energy per pulse was demonstrated, which properly embodies limiting effects to the treatment. This can be a parameter for the α-γ steel surface modification, consisting in a better adjustment to obtain more precise control along with temperature.

The Investigation on Strain Strengthening Induced Martensitic Phase Transformation of Austenitic Stainless Steel: A Fundamental Research for the Quality Evaluation of Strain Strengthened Pressure Vessel

Science.gov (United States)

Li, Bo; Cai Ren, Fa; Tang, Xiao Ying

2018-03-01

The manufacture of pressure vessels with austenitic stainless steel strain strengthening technology has become an important technical means for the light weight of cryogenic pressure vessels. In the process of increasing the strength of austenitic stainless steel, strain can induce the martensitic phase transformation in austenite phase. There is a quantitative relationship between the transformation quantity of martensitic phase and the basic mechanical properties. Then, the martensitic phase variables can be obtained by means of detection, and the mechanical properties and safety performance are evaluated and calculated. Based on this, the quantitative relationship between strain hardening and deformation induced martensite phase content is studied in this paper, and the mechanism of deformation induced martensitic transformation of austenitic stainless steel is detailed.

Applying Ultrasonic Phased Array Technology to Examine Austenitic Coarse-Grained Structures for Light Water Reactor Piping

International Nuclear Information System (INIS)

Anderson, Michael T.; Cumblidge, Stephen E.; Doctor, Steven R.

2003-01-01

Pacific Northwest Laboratory is evaluating the capabilities and limitations of phased array (PA) technology to detect service-type flaws in coarse-grained austenitic piping structures. The work is being sponsored by the U.S. Nuclear Regulatory Commission, Office of Research. This paper presents initial work involving the use of PA technology to determine the effectiveness of detecting and accurately characterizing flaws on the far-side of austenitic piping welds

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.

The kinetics of phase transformations of undercooled austenite of the 38MnCrNi6-4-4 hypoeutectoid steel

OpenAIRE

R. Dąbrowski; R. Dziurka; E. Rożniata

2012-01-01

Purpose: Present work corresponds to the research on the kinetic of phase transformation of undercooled austenite of 38MnCrNi6-4-4 hypoeutctoid steel. The kinetic of phase transformation of under cooled austenite of investigated alloy was presented on CCT diagram (continuous cooling transformation). Also the methodology of a dilatometric samples preparation and the method of the critical points determination were described.Design/methodology/approach: The austenitising temperature was defined...

Strain hardening of cold-rolled lean-alloyed metastable ferritic-austenitic stainless steels

Energy Technology Data Exchange (ETDEWEB)

Papula, Suvi [Aalto University School of Engineering, Department of Mechanical Engineering, P.O. Box 14200, FI-00076 Aalto (Finland); Anttila, Severi [Centre for Advanced Steels Research, University of Oulu, P.O. Box 4200, 90014 Oulu (Finland); Talonen, Juho [Outokumpu Oyj, P.O. Box 245, FI-00181 Helsinki (Finland); Sarikka, Teemu; Virkkunen, Iikka; Hänninen, Hannu [Aalto University School of Engineering, Department of Mechanical Engineering, P.O. Box 14200, FI-00076 Aalto (Finland)

2016-11-20

Mechanical properties and strain hardening of two pilot-scale lean-alloyed ferritic-austenitic stainless steels having metastable austenite phase, present at 0.50 and 0.30 volume fractions, have been studied by means of tensile testing and nanoindentation. These ferritic-austenitic stainless steels have high strain-hardening capacity, due to the metastable austenite phase, which leads to an improved uniform elongation and higher tensile strength in comparison with most commercial lean duplex stainless steels. According to the results, even as low as 0.30 volume fraction of austenite seems efficient for achieving nearly 40% elongation. The austenite phase is initially the harder phase, and exhibits more strain hardening than the ferrite phase. The rate of strain hardening and the evolution of the martensite phase were found to depend on the loading direction: both are higher when strained in the rolling direction as compared to the transverse direction. Based on the mechanical testing, characterization of the microstructure by optical/electron microscopy, magnetic balance measurements and EBSD texture analysis, this anisotropy in mechanical properties of the cold-rolled metastable ferritic-austenitic stainless steels can be explained by the elongated dual-phase microstructure, fiber reinforcement effect of the harder austenite phase and the presence and interplay of rolling textures in the two phases.

Transformation in austenitic stainless steel sheet under different loading directions

NARCIS (Netherlands)

van den Boogaard, Antonius H.; Krauer, J.; Hora, P.

2011-01-01

The stress-strain relation for austenitic stainless steels is based on 2 main contributions: work hardening and a phase transformation from austenite to martensite. The transformation is highly temperature dependent. In most models for phase transformation from austenite to martensite, the stress

Transformation in Austenitic Stainless Steel Sheet under Different Loading Directions

NARCIS (Netherlands)

van den Boogaard, Antonius H.; Krauer, J.; Hora, P.

2011-01-01

The stress-strain relation for austenitic stainless steels is based on 2 main contributions: work hardening and a phase transformation from austenite to martensite. The transformation is highly temperature dependent. In most models for phase transformation from austenite to martensite, the stress

Impact Strength of Austenitic and Ferritic-Austenitic Cr-Ni Stainless Cast Steel in -40 and +20°C Temperature

Directory of Open Access Journals (Sweden)

Kalandyk B.

2014-10-01

Full Text Available Studies described in this paper relate to common grades of cast corrosion resistant Cr-Ni steel with different matrix. The test materials were subjected to heat treatment, which consisted in the solution annealing at 1060°C followed by cooling in water. The conducted investigations, besides the microstructural characteristics of selected cast steel grades, included the evaluation of hardness, toughness (at a temperature of -40 and +20oC and type of fracture obtained after breaking the specimens on a Charpy impact testing machine. Based on the results of the measured volume fraction of ferrite, it has been found that the content of this phase in cast austenitic steel is 1.9%, while in the two-phase ferritic-austenitic grades it ranges from 50 to 58%. It has been demonstrated that within the scope of conducted studies, the cast steel of an austenitic structure is characterised by higher impact strength than the two-phase ferritic-austenitic (F-A grade. The changing appearance of the fractures of the specimens reflected the impact strength values obtained in the tested materials. Fractures of the cast austenitic Cr-Ni steel obtained in these studies were of a ductile character, while fractures of the cast ferritic-austenitic grade were mostly of a mixed character with the predominance of brittle phase and well visible cleavage planes.

Effect of martensitic phase transformation on the behavior of 304 austenitic stainless steel under tension

Energy Technology Data Exchange (ETDEWEB)

Wang, H., E-mail: wanghm@lanl.gov [Materials Science and Technology, Los Alamos National Laboratory, Los Alamos, NM (United States); Jeong, Y. [Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD (United States); Clausen, B.; Liu, Y.; McCabe, R.J. [Materials Science and Technology, Los Alamos National Laboratory, Los Alamos, NM (United States); Barlat, F. [Graduate Institute of Ferrous Technology, POSTECH (Korea, Republic of); Tomé, C.N. [Materials Science and Technology, Los Alamos National Laboratory, Los Alamos, NM (United States)

2016-01-01

The present work integrates in-situ neutron diffraction, electron backscatter diffraction and crystal plasticity modeling to investigate the effect of martensitic phase transformation on the behavior of 304 stainless steel under uniaxial tension. The macroscopic stress strain response, evolution of the martensitic phase fraction, texture evolution of each individual phase, and internal elastic strains were measured at room temperature and at 75 °C. Because no martensitic transformation was observed at 75 °C, the experimental results at 75 °C were used as a reference to quantify the effect of formed martensitic phase on the behavior of 304 stainless steel at room temperature. A crystallographic phase transformation model was implemented into an elastic–viscoplastic self-consistent framework. The phase transformation model captured the macroscopic stress strain response, plus the texture and volume fraction evolution of austenite and martensite. The model also predicts the internal elastic strain evolution with loading in the austenite, but not in the martensite. The results of this work highlight the mechanisms that control phase transformation and the sensitivity of modeling results to them, and point out to critical elements that still need to be incorporated into crystallographic phase transformation models to accurately describe the internal strain evolution during phase transformation.

On the determination of stress profiles in expanded austenite by grazing incidence X-ray diffraction and successive layer removal

DEFF Research Database (Denmark)

Fernandes, Frederico Augusto Pires; Christiansen, Thomas L.; Winther, Grethe

2015-01-01

Surface layers of expanded austenite resulting from nitriding typically exhibit large gradients in residual stress and composition. Evaluation of residual-stress profiles is explored by means of grazing incidence X-ray diffraction (GI-XRD), probing shallow depths, combined with successive layer...... removal. Several factors complicating the stress determination are analysed and discussed: (1) ghost stresses arising from a small variation in the shallow information depths probed with GI-XRD, (2) selection of the grain interaction model used to calculate the X-ray elastic constants for conversion...

Martensite shear phase reversion-induced nanograined/ultrafine-grained Fe-16Cr-10Ni alloy: The effect of interstitial alloying elements and degree of austenite stability on phase reversion

Energy Technology Data Exchange (ETDEWEB)

Misra, R.D.K., E-mail: dmisra@louisiana.edu [Center for Structural and Functional Materials, University of Louisiana at Lafayette, Madison Hall Room 217, P.O. Box 44130, Lafayette, LA 70504-1430 (United States); Zhang, Z.; Venkatasurya, P.K.C. [Center for Structural and Functional Materials, University of Louisiana at Lafayette, Madison Hall Room 217, P.O. Box 44130, Lafayette, LA 70504-1430 (United States); Somani, M.C.; Karjalainen, L.P. [Department of Mechanical Engineering, University of Oulu, P.O. Box 4200, Oulu 90014 (Finland)

2010-11-15

Research highlights: {yields} Development of a novel process involving phase-reversion annealing process. {yields} Austensite stability strongly influences development of nanograined structure. {yields} Interstitial elements influence microstructural evolution during annealing. - Abstract: We describe here an electron microscopy study of microstructural evolution associated with martensitic shear phase reversion-induced nanograined/ultrafine-grained (NG/UFG) structure in an experimental Fe-16Cr-10Ni alloy with very low interstitial content. The primary objective is to understand and obtain fundamental insights on the influence of degree of austenite stability (Fe-16Cr-10Ni, 301LN, and 301 have different austenite stability index) and interstitial elements (carbon and nitrogen) in terms of phase reversion process, microstructural evolution during reversion annealing, and temperature-time annealing sequence. A relative comparison of Fe-16Cr-10Ni alloy with 301LN and 301 austenitic stainless steels indicated that phase reversion in Fe-16Cr-10Ni occurred by shear mechanism, which is similar to that observed for 301, but is different from the diffusional mechanism in 301LN steel. While the phase reversion in the experimental Fe-16Cr-10Ni alloy and 301 austenitic stainless steel occurred by shear mechanism, there were fundamental differences between these two alloys. The reversed strain-free austenite grains in Fe-16Cr-10Ni alloy were characterized by nearly same crystallographic orientation, where as in 301 steel there was evidence of break-up of martensite laths during reversion annealing resulting in several regions of misoriented austenite grains in 301 steel. Furthermore, a higher phase reversion annealing temperature range (800-900 deg. C) was required to obtain a fully NG/UFG structure of grain size 200-600 nm. The difference in the phase reversion and the temperature-time sequence in the three stages is explained in terms of Gibbs free energy change that

Stainless austenitic steels strengthened due to reversible phase transformations and by ageing

International Nuclear Information System (INIS)

Sagaradze, V.V.; Kositsyna, I.I.; Ozhiganov, A.V.

1981-01-01

The effect of the reversible phase transformations, consisting in the conduction of the direct and reverse martensite transformations and aging, during which the intermetallide γ'-phase of the composition Ni 3 Ti is formed, on the streng-thening of alloys in the Fe-Cr-Ni-Ti system is considered. Stainless austenitic steels Kh12N12T3 and Kh12N14T3, which acquire high mechanical properties: σsub(0.2)=685-785 MPa, σsub(B)=1275 MPa, delta >= 20%, as a result of reversible phase transformations and aging, are suggested. After the reversible phase transformations and ageing the steels possess a high resistance to γ-α-transformation during cold treatment [ru

Effect of the low temperature ion nitriding on the wear and corrosion resistance of 316L austenitic stainless steel biomaterials

International Nuclear Information System (INIS)

Sudjatmoko; Bambang Siswanto; Wirjoadi; Lely Susita RM

2012-01-01

In the present study has been completed done the ion nitriding process and characterization of the 316L SS samples. The ion nitriding process has been conducted on the samples for nitriding temperature variation of 350, 400, 450, 500, and 550 °C, the optimum nitrogen gas pressure of 1.8 mbar and optimum nitriding time of 3 hours. The micro-structure, elemental composition and the phase structure of the nitride layer formed on the surface of samples were observed using the techniques of SEM-EDAX and XRD, respectively. It is known that a thin layer of iron nitrides has been formed on the surface of the samples. Iron nitride layer has a phase structure including ε-Fe_2_-_3N, γ'-Fe_4N, CrN, Cr_2N and expanded austenite γN. The characterization results of the wear resistance of the 316L SS samples showed an increasing of about 2.6 times the wear resistance of standard samples after nitriding temperature of 350 °C. From the corrosion test by using the Hanks solution was obtained 29.87 mpy corrosion rate or the increasing of corrosion resistance of about 137%. Thus it can be seen that by using ion nitriding technique the iron nitride layer has been formed on the surface of the 316L SS samples, and they have an excellent properties of wear resistance and corrosion resistance, which were caused especially due to the formation of an expanded austenite γN. Properties of the high hardness and has the good corrosion resistance, especially due to the formation of iron nitride and expanded austenite phases γN at low temperature nitriding process. (author)

Constitutive modeling of metastable austenitic stainless steel (CD-rom)

NARCIS (Netherlands)

Perdahcioglu, Emin Semih; Geijselaers, Hubertus J.M.; Huetink, Han; Boisse, P.

2008-01-01

A stress-update algorithm is developed for austenitic metastable steels which undergo phase evolution during deformation. The material initially comprises only the soft and ductile austenite phase which due to the phenomenon of mechanically induced martensitic transformation, transforms completely

In situ TEM study of G-phase precipitates under heavy ion irradiation in CF8 cast austenitic stainless steel

Science.gov (United States)

Chen, Wei-Ying; Li, Meimei; Zhang, Xuan; Kirk, Marquis A.; Baldo, Peter M.; Lian, Tiangan

2015-09-01

Thermally-aged cast austenitic stainless steels (CASS) CF8 was irradiated with 1 MeV Kr ions at 300, 350 and 400 °C to 1.88 × 1019 ions/m2 (∼3 dpa) at the IVEM-Tandem Facility at the Argonne National Laboratory. Before irradiation, the distribution of G-phase precipitates in the ferrite showed spatial variations, and both their size and density were affected by the ferrite-austenite phase boundary and presence of M23C6 carbides. Under 300 °C irradiation, in situ TEM observation showed G-phase precipitates were relatively unchanged in the vicinity of the phase boundary M23C6 carbides, while the density of G-phase precipitates increased with increasing dose within the ferrite matrix. Coarsening of G-phase precipitates was observed in the vicinity of phase boundary M23C6 carbides at 350 °C and 400 °C.

In-situ characterization of transformation plasticity during an isothermal austenite-to-bainite phase transformation

International Nuclear Information System (INIS)

Holzweissig, M.J.; Canadinc, D.; Maier, H.J.

2012-01-01

This paper elucidates the stress-induced variant selection process during the isothermal austenite-to-bainite phase transformation in a tool steel. Specifically, a thorough set of experiments combining electron backscatter diffraction and in-situ digital image correlation (DIC) was carried out to establish the role of superimposed stress level on the evolution of transformation plasticity (TP) strains. The important finding is that TP increases concomitant with the superimposed stress level, and strain localization accompanies phase transformation at all stress levels considered. Furthermore, TP strain distribution within the whole material becomes more homogeneous with increasing stress, such that fewer bainitic variants are selected to grow under higher stresses, yielding a more homogeneous strain distribution. In particular, the bainitic variants oriented along [101] and [201] directions are favored to grow parallel to the loading axis and are associated with large TP strains. Overall, this very first in-situ DIC investigation of the austenite-to-bainite phase transformation in steels evidences the clear relationship between the superimposed stress level, variant selection, and evolution of TP strains. - Highlights: ► Local variations of strain were observed by DIC throughout the phase transformation. ► The study clearly established the role of the stress-induced variant selection. ► Variant selection is a key parameter that governs distortion.

Reverted austenite in PH 13-8 Mo maraging steels

International Nuclear Information System (INIS)

Schnitzer, Ronald; Radis, Rene; Noehrer, Matthias; Schober, Michael; Hochfellner, Rainer; Zinner, Silvia; Povoden-Karadeniz, E.; Kozeschnik, Ernst; Leitner, Harald

2010-01-01

The mechanical properties of maraging steels are strongly influenced by the presence of reverted austenite. In this study, the morphology and chemical composition of reverted austenite in a corrosion resistant maraging steel was characterized using transmission electron microscopy (TEM) and atom probe tomography (APT). Two types of austenite, i.e. granular and elongated, are present after aging at 575 o C, whereby the content of the latter increases during aging. The investigations revealed that the austenite phase is enriched in Ni, which prevents the transformation to martensite during cooling. Inside and next to the austenitc areas, Mo and Cr-rich carbides, which form during the aging treatment, were found. Various aging treatments were performed to obtain the activation energy for the formation of reverted austenite. Additionally, the experimental data are compared with thermodynamic and kinetic simulations. Based on these results and the chemical composition changes of the phases, a model for the formation of reverted austenite is presented. It is concluded that precipitation of B2-ordered NiAl and formation of reverted austenite take place simultaneously during aging and that dissolution of precipitates is not essential for the initial formation of reverted austenite.

On the determination of stress profiles in expanded austenite by grazing incidence X-ray diffraction and successive layer removal

International Nuclear Information System (INIS)

Fernandes, Frederico A.P.; Christiansen, Thomas L.; Winther, Grethe; Somers, Marcel A.J.

2015-01-01

Surface layers of expanded austenite resulting from nitriding typically exhibit large gradients in residual stress and composition. Evaluation of residual-stress profiles is explored by means of grazing incidence X-ray diffraction (GI-XRD), probing shallow depths, combined with successive layer removal. Several factors complicating the stress determination are analysed and discussed: (1) ghost stresses arising from a small variation in the shallow information depths probed with GI-XRD, (2) selection of the grain interaction model used to calculate the X-ray elastic constants for conversion of lattice strains into residual stress and (3) the composition dependence of these elastic constants

In situ TEM study of G-phase precipitates under heavy ion irradiation in CF8 cast austenitic stainless steel

Energy Technology Data Exchange (ETDEWEB)

Chen, Wei-Ying [Argonne National Laboratory, Argonne, IL 60439 (United States); University of Illinois at Urbana-Champaign, Urbana, IL 61801 (United States); Li, Meimei; Zhang, Xuan; Kirk, Marquis A.; Baldo, Peter M. [Argonne National Laboratory, Argonne, IL 60439 (United States); Lian, Tiangan [Electric Power Research Institute, Palo Alto, CA 94304 (United States)

2015-09-15

Thermally-aged cast austenitic stainless steels (CASS) CF8 was irradiated with 1 MeV Kr ions at 300, 350 and 400 °C to 1.88 × 10{sup 19} ions/m{sup 2} (∼3 dpa) at the IVEM-Tandem Facility at the Argonne National Laboratory. Before irradiation, the distribution of G-phase precipitates in the ferrite showed spatial variations, and both their size and density were affected by the ferrite–austenite phase boundary and presence of M{sub 23}C{sub 6} carbides. Under 300 °C irradiation, in situ TEM observation showed G-phase precipitates were relatively unchanged in the vicinity of the phase boundary M{sub 23}C{sub 6} carbides, while the density of G-phase precipitates increased with increasing dose within the ferrite matrix. Coarsening of G-phase precipitates was observed in the vicinity of phase boundary M{sub 23}C{sub 6} carbides at 350 °C and 400 °C.

In-situ characterization of transformation plasticity during an isothermal austenite-to-bainite phase transformation

Energy Technology Data Exchange (ETDEWEB)

Holzweissig, M.J., E-mail: martinh@mail.upb.de [University of Paderborn, Lehrstuhl fuer Werkstoffkunde (Materials Science), 33095 Paderborn (Germany); Canadinc, D., E-mail: dcanadinc@ku.edu.tr [Koc University, Advanced Materials Group, Department of Mechanical Engineering, 34450 Istanbul (Turkey); Maier, H.J., E-mail: hmaier@mail.upb.de [University of Paderborn, Lehrstuhl fuer Werkstoffkunde (Materials Science), 33095 Paderborn (Germany)

2012-03-15

This paper elucidates the stress-induced variant selection process during the isothermal austenite-to-bainite phase transformation in a tool steel. Specifically, a thorough set of experiments combining electron backscatter diffraction and in-situ digital image correlation (DIC) was carried out to establish the role of superimposed stress level on the evolution of transformation plasticity (TP) strains. The important finding is that TP increases concomitant with the superimposed stress level, and strain localization accompanies phase transformation at all stress levels considered. Furthermore, TP strain distribution within the whole material becomes more homogeneous with increasing stress, such that fewer bainitic variants are selected to grow under higher stresses, yielding a more homogeneous strain distribution. In particular, the bainitic variants oriented along [101] and [201] directions are favored to grow parallel to the loading axis and are associated with large TP strains. Overall, this very first in-situ DIC investigation of the austenite-to-bainite phase transformation in steels evidences the clear relationship between the superimposed stress level, variant selection, and evolution of TP strains. - Highlights: Black-Right-Pointing-Pointer Local variations of strain were observed by DIC throughout the phase transformation. Black-Right-Pointing-Pointer The study clearly established the role of the stress-induced variant selection. Black-Right-Pointing-Pointer Variant selection is a key parameter that governs distortion.

In situ x-ray diffraction investigations during low energy ion nitriding of austenitic stainless steel grade 1.4571

International Nuclear Information System (INIS)

Manova, D; Mändl, S; Gerlach, J W; Hirsch, D; Neumann, H; Rauschenbach, B

2014-01-01

Insertion of nitrogen into austenitic stainless steel leads to anomalously fast nitrogen diffusion and the formation of an expanded face-centred cubic phase which is known to contain a large amount of mechanical stress. In situ x-ray diffraction (XRD) measurements during low energy nitrogen ion implantation into steel 316Ti at 300–550 °C allow a direct view into diffusion and phase formation. While the layer growth is directly observable from the decreasing substrate reflection intensity, the time evolution of the intensities for the expanded phase reflection is much more complex: several mechanisms including at least formation and annealing of defects, twinning, reduction of the crystal symmetry, or grain rotation may be active inside the expanded phase, besides the thermally activated decay of the metastable expanded phase. This locally varying coherence length or scattering intensity from the expanded phase is furthermore a function of temperature and time, additionally complicating the deconvolution of XRD spectra for stress and concentration gradients. As no concise modelling of this coherence length is possible at present, a simple qualitative model assuming a dependence of the scattering intensity on the depth, influence by stress and plastic flow during the nitriding process is proposed for understanding the underlying processes. (paper)

The effect of manganese on the kinetics of phase transformations of austenite in structural steels

International Nuclear Information System (INIS)

Pacyna, J.; Jedrzejewska-Strach, A.

1995-01-01

The aim of this work was to examine the effect of Mn on the kinetics of phase transformations of supercooled austenite. It was executed the 4 CCT diagrams for alloys of a variable Mn content. The obtained results indicate that with the increase of Mn concentrations in austenite in the range 0.73-2.94% the times to the beginning of its transformation are lengthened and the temperatures of these transformations into ferrite and the bainitic transformations are lengthened slightly whole only the time to the beginning of a pearlitic transformation is lengthened more strongly. In the range of 2.0-2.94% Mn the times to the beginnings of all transformations grow very strongly. (author)

Modeling precipitation thermodynamics and kinetics in type 316 austenitic stainless steels with varying composition as an initial step toward predicting phase stability during irradiation

Energy Technology Data Exchange (ETDEWEB)

Shim, Jae-Hyeok, E-mail: jhshim@kist.re.kr [Department of Nuclear Engineering, University of Tennessee, Knoxville, TN 37996 (United States); High Temperature Energy Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Povoden-Karadeniz, Erwin [Christian Doppler Laboratory for Early Stages of Precipitation, Vienna University of Technology, A-1040 Vienna (Austria); Kozeschnik, Ernst [Institute of Materials Science and Technology, Vienna University of Technology, A-1040 Vienna (Austria); Wirth, Brian D. [Department of Nuclear Engineering, University of Tennessee, Knoxville, TN 37996 (United States)

2015-07-15

Highlights: • We model the precipitation kinetics in irradiated 316 austenitic stainless steels. • Radiation-induced phases are predicted to form at over 10 dpa segregation conditions. • The Si content is the most critical for the formation of radiation-induced phases. - Abstract: The long-term evolution of precipitates in type 316 austenitic stainless steels at 400 °C has been simulated using a numerical model based on classical nucleation theory and the thermodynamic extremum principle. Particular attention has been paid to the precipitation of radiation-induced phases such as γ′ and G phases. In addition to the original compositions, the compositions for radiation-induced segregation at a dose level of 5, 10 or 20 dpa have been used in the simulation. In a 316 austenitic stainless steel, γ′ appears as the main precipitate with a small amount of G phase forming at 10 and 20 dpa. On the other hand, G phase becomes relatively dominant over γ′ at the same dose levels in a Ti-stabilized 316 austenitic stainless steel, which tends to suppress the formation of γ′. Among the segregated alloying elements, the concentration of Si seems to be the most critical for the formation of radiation-induced phases. An increase in dislocation density as well as increased diffusivity of Mn and Si significantly enhances the precipitation kinetics of the radiation-induced phases within this model.

Structure and phase composition of titanium nitride coating on austenitic steel

International Nuclear Information System (INIS)

Dubovitskaya, N.V.; Kolenchenko, L.D.; Larikov, L.N.

1989-01-01

Structure and phase composition of titanium nitride coating deposited on 08Kh18N10T steel substrate using ''Bulat'' device are studied. Use of complex investigation methods permitted despite small coating thickness (1μm) to aquire information on hardness, porosity, to study phase composition in all coating thickness. The surface layer (∼0.1 μm) consists of ε-Ti 2 N, TiN 0.6 , TiC 0.35 , that is formed with carbon participation from oil vacuum. In more deeper layers beside ε-Ti 2 N TiC 0.14 N 0.77 is present. Effect of carbon diffusion from substrate to forming coating is stated. Gradient of element concentrations in the substrate-coating interface causes recrystallization of austenite

Alumina-Forming Austenitic Stainless Steels Strengthened by Laves Phase and MC Carbide Precipitates

Science.gov (United States)

Yamamoto, Y.; Brady, M. P.; Lu, Z. P.; Liu, C. T.; Takeyama, M.; Maziasz, P. J.; Pint, B. A.

2007-11-01

Creep strengthening of Al-modified austenitic stainless steels by MC carbides or Fe2Nb Laves phase was explored. Fe-20Cr-15Ni-(0-8)Al and Fe-15Cr-20Ni-5Al base alloys (at. pct) with small additions of Nb, Mo, W, Ti, V, C, and B were cast, thermally-processed, and aged. On exposure from 650 °C to 800 °C in air and in air with 10 pct water vapor, the alloys exhibited continuous protective Al2O3 scale formation at an Al level of only 5 at. pct (2.4 wt pct). Matrices of the Fe-20Cr-15Ni-5Al base alloys consisted of γ (fcc) + α (bcc) dual phase due to the strong α-Fe stabilizing effect of the Al addition and exhibited poor creep resistance. However, adjustment of composition to the Fe-15Cr-20Ni-5Al base resulted in alloys that were single-phase γ-Fe and still capable of alumina scale formation. Alloys that relied solely on Fe2Nb Laves phase precipitates for strengthening exhibited relatively low creep resistance, while alloys that also contained MC carbide precipitates exhibited creep resistance comparable to that of commercially available heat-resistant austenitic stainless steels. Phase equilibria studies indicated that NbC precipitates in combination with Fe2Nb were of limited benefit to creep resistance due to the solution limit of NbC within the γ-Fe matrix of the alloys studied. However, when combined with other MC-type strengtheners, such as V4C3 or TiC, higher levels of creep resistance were obtained.

Modelling the evolution of composition-and stress-depth profiles in austenitic stainless steels during low-temperature nitriding

DEFF Research Database (Denmark)

Jespersen, Freja Nygaard; Hattel, Jesper Henri; Somers, Marcel A. J.

2016-01-01

. In the present paper solid mechanics was combined with thermodynamics and diffusion kinetics to simulate the evolution of composition-depth and stress-depth profiles resulting from nitriding. The model takes into account a composition-dependent diffusion coefficient of nitrogen in expanded austenite, short range......Nitriding of stainless steel causes a surface zone of expanded austenite, which improves the wear resistance of the stainless steel while preserving the stainless behaviour. During nitriding huge residual stresses are introduced in the treated zone, arising from the volume expansion...... that accompanies the dissolution of high nitrogen contents in expanded austenite. An intriguing phenomenon during low-temperature nitriding is that the residual stresses evoked by dissolution of nitrogen in the solid state, affect the thermodynamics and the diffusion kinetics of nitrogen dissolution...

Transformation of austenite to duplex austenite-ferrite assembly in annealed stainless steel 316L consolidated by laser melting

Energy Technology Data Exchange (ETDEWEB)

Saeidi, K.; Gao, X. [Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm (Sweden); Lofaj, F. [Institute of Materials Research of the Slovak Academy of Sciences, Watsonova 47, Košice (Slovakia); Faculty of Materials Science and Technology in Trnava, Slovak University of Technology in Bratislava, 916 24 Trnava (Slovakia); Kvetková, L. [Institute of Materials Research of the Slovak Academy of Sciences, Watsonova 47, Košice (Slovakia); Shen, Z.J. [Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm (Sweden)

2015-06-05

Highlights: • Mechanical properties, phase and microstructure stability of laser melted steel was studied. • Duplex austenite-ferrite assembly with improved mechanical properties was formed. • Dissolution of Mo in the steel matrix resulted in ferrite stabilization and stress relief. • Enhanced mechanical properties were achieved compared to conventionally casted and annealed steel. - Abstract: Laser melting (LM), with a focused Nd:YAG laser beam, was used to form solid bodies from 316L austenite stainless steel powder and the laser melted samples were heat treated at various temperatures. The phase changes in heat treated samples were characterized using X-ray diffraction (XRD). Samples heat treated at 800 °C and 900 °C remained single austenite while in samples heat treated at 1100 °C and 1400 °C a dual austenite-ferrite phase assembly was formed. The ferrite formation was further verified by electron back scattering diffraction (EBSD) and selective area diffraction (SAD). Microstructural changes were studied by scanning and transmission electron microscopy (SEM, TEM). In samples heat treated up to 900 °C, coalescence of the cellular-sub grains was noticed, whereas in sample heat treated at and above 1100 °C the formation of ferrite phase was observed. The correlation between the microstructure/phase assembly and the measured strength/microhardness were investigated, which indicated that the tensile strength of the laser melted material was significantly higher than that of the conventional 316L steel even after heat treatment whereas caution has to be taken when laser melted material will be exposed to an application temperature above 900 °C.

Inspection of austenitic welds with ultrasonic phased array technology

Energy Technology Data Exchange (ETDEWEB)

Garcia, A.; Fernandez, F. [Tecnatom (Spain); Dutruc, R.; Ferriere, R. [Metalscan (France)

2011-07-01

This series of slides presents the use of ultrasonic phased array technology in the inspection of austenitic welds. The inspection from outside surface (the inspection is performed in contact using wedges to couple the probe to the outer surface of the component) shows that longitudinal wave is the most adequate for perpendicular scans and transversal ultrasonic wave is the most adequate for parallel scans. Detection and length sizing are performed optimally in perpendicular scans. The inspection from inside surface shows: -) Good results in the detection of defects (Sizing has met the requirements imposed by the Authority of the Russian Federation); -) The new design of the mechanical equipment and of the numerous ultrasonic beams refracted by the array probes has increased the volume inspected. The design of the mechanical equipment has also allowed new areas to be inspected (example a piping weld that was not accessible from the outer surface; -) The ultrasonic procedure and Inspection System developed have been validated by the Authority of the Russian Federation. Phase array technique supplies solutions to solve accessibility concerns and improve the ultrasonic inspections of nuclear components

Probing the electronic structure of Ni–Mn–In–Si based Heusler alloys thin films using magneto-optical spectra in martensitic and austenitic phases

Energy Technology Data Exchange (ETDEWEB)

Novikov, A. [Department of Physics, Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Sokolov, A., E-mail: asokol@unlserve.unl.edu [Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, NE 68588 (United States); Gan’shina, E.A. [Department of Physics, Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Quetz, Abdiel; Dubenko, I.S. [Department of Physics, Southern Illinois University, Carbondale, IL 62901 (United States); Stadler, S. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); Ali, N. [Department of Physics, Southern Illinois University, Carbondale, IL 62901 (United States); Titov, I.S.; Rodionov, I.D. [Department of Physics, Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Lähderanta, E. [Lappeenranta University of Technology, 53851 (Finland); Zhukov, A. [Dpto. de Física de Materiales, Fac. Químicas, UPV/EHU, 20018 San Sebastian (Spain); IKERBASQUE, Basque Foundation for Science, 48011 Bilbao (Spain); Granovsky, A.B. [Department of Physics, Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Sabirianov, R. [Department of Physics, University of Nebraska at Omaha, Omaha, NE 68182 (United States)

2017-06-15

Highlights: • Magneto-optical properties of NiMnIn thin films with a magnetostructural transition. • Comparative analysis of magnetic properties in martensitic and austenite phases. • DFT calculations of the MO Kerr effect and site-resolved DOS agree with experiment. • The electronic structure does not change significantly with Martensitic transition. - Abstract: Thin films of Ni{sub 52}Mn{sub 35−x}In{sub 11+x}Si{sub 2} were fabricated by magnetron sputtering on MgO (0 0 1) single crystal substrates. Magnetization as function of temperature for Ni{sub 52}Mn{sub 35}In{sub 11}Si{sub 2} exhibits features consistent with a magnetostructural transition (MST) from an austenitic phase to a martensitic phase, similar to the bulk material. We observed that the martensitic transformation is externally sensitive to small changes in chemical composition and stoichiometry. It has been found that thin films of Ni{sub 52}Mn{sub 34−x}In{sub 11+x}Si{sub 2} with x = 0 and 1 undergo a temperature-induced MST or remain in a stable austenitic phase, respectively. Comparison of magneto-optical transverse Kerr effect spectra obtained at 0.5–4.0 eV in the 35–300 K temperature interval reveal insignificant differences between the martensitic and austenite phases. We found that the field and temperature dependencies of the transverse Kerr effect are quite different from the magnetization behavior, which is attributed to magnetic inhomogeneity across the films. To elucidate the effects of magnetostructural phase transitions on the electronic properties, we performed density functional calculations of the magneto-optical Kerr effect.

Austenite reversion in low-carbon martensitic stainless steels – a CALPHAD-assisted review

DEFF Research Database (Denmark)

Niessen, Frank

2018-01-01

Low-carbon martensitic stainless steels with 11.5–16 wt-% Cr and martensite upon inter-critical annealing. The review treats...... the mechanisms governing the formation and stabilisation of reverted austenite and is assisted by the computation of phase equilibria. Literature data on Cr and Ni concentrations of the reverted austenite/martensite dual-phase microstructure are assessed with respect to predicted concentrations. Reasonable...... agreement was found for concentrations in martensite. Systematic excess of Cr in austenite of approx. 2 wt-% relative to calculations was suspected to originate from the growth of M23C6 with a coherent interface to austenite. Within large scatter, measured values of Ni in austenite were on average 2 wt...

Effect of laser welding parameters on the austenite and martensite phase fractions of NiTi

Energy Technology Data Exchange (ETDEWEB)

Oliveira, J.P., E-mail: jp.oliveira@campus.fct.unl.pt [CENIMAT/i3N, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa (Portugal); Braz Fernandes, F.M. [CENIMAT/i3N, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa (Portugal); Miranda, R.M. [UNIDEMI, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa (Portugal); Schell, N. [Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Max-Planck-Str. 1, D-21502 Geesthacht (Germany); Ocaña, J.L. [Centro Láser UPM, Universidad Politécnica de Madrid, Edificio “La Arboleda”, Ctra. Valencia, km 7,300, Campus Sur UPM, 28031 Madrid (Spain)

2016-09-15

Although laser welding is probably the most used joining technique for NiTi shape memory alloys there is still a lack of understanding about the effects of laser welding parameters on the microstructural induced changes: in both the heat affected and fusion zones martensite may be present, while the base material is fully austenitic. Synchrotron X-ray diffraction was used for fine probing laser welded NiTi joints. Through Rietveld refinement the martensite and austenite phase fractions were determined and it was observed that the martensite content increases towards the weld centreline. This is related to a change of the local transformation temperatures on these regions, which occurs due to compositional variation in those regions. The martensite phase fraction in the thermally affected regions may have significant implications on functional properties on these joints. - Highlights: •Synchrotron X-ray diffraction was used for fine probing of the microstructure in laser welded NiTi joints. •Rietveld refinement allowed to determine the content of martensite along the heat affected and fusion zones. •The martensite content increases from the base material towards the weld centreline.

STRUCTURAL STABILITY OF HIGH NITROGEN AUSTENITIC STAINLESS STEELS

Directory of Open Access Journals (Sweden)

Jana Bakajová

2011-05-01

Full Text Available This paper deals with the structural stability of an austenitic stainless steel with high nitrogen content. The investigated steel was heat treated at 800°C using different annealing times. Investigation was carried out using light microscopy, transmission electron microscopy and thermodynamic calculations. Three phases were identified by electron diffraction: Cr2N, sigma – phase and M23C6. The thermodynamic prediction is in good agreement with the experimental result. The only is the M23C6 carbide phase which is not thermodynamically predicted. Cr2N is the majority secondary phase and occurs in the form of discrete particles or cells (lamellas of Cr2N and austenite.

Retained Austenite in SAE 52100 Steel Post Magnetic Processing and Heat Treatment

Energy Technology Data Exchange (ETDEWEB)

Pappas, Nathaniel R [ORNL; Watkins, Thomas R [ORNL; Cavin, Odis Burl [ORNL; Jaramillo, Roger A [ORNL; Ludtka, Gerard Michael [ORNL

2007-01-01

Steel is an iron-carbon alloy that contains up to 2% carbon by weight. Understanding which phases of iron and carbon form as a function of temperature and percent carbon is important in order to process/manufacture steel with desired properties. Austenite is the face center cubic (fcc) phase of iron that exists between 912 and 1394 C. When hot steel is rapidly quenched in a medium (typically oil or water), austenite transforms into martensite. The goal of the study is to determine the effect of applying a magnetic field on the amount of retained austenite present at room temperature after quenching. Samples of SAE 52100 steel were heat treated then subjected to a magnetic field of varying strength and time, while samples of SAE 1045 steel were heat treated then subjected to a magnetic field of varying strength for a fixed time while being tempered. X-ray diffraction was used to collect quantitative data corresponding to the amount of each phase present post processing. The percentage of retained austenite was then calculated using the American Society of Testing and Materials standard for determining the amount of retained austenite for randomly oriented samples and was plotted as a function of magnetic field intensity, magnetic field apply time, and magnetic field wait time after quenching to determine what relationships exist with the amount of retained austenite present. In the SAE 52100 steel samples, stronger field strengths resulted in lower percentages of retained austenite for fixed apply times. The results were inconclusive when applying a fixed magnetic field strength for varying amounts of time. When applying a magnetic field after waiting a specific amount of time after quenching, the analyses indicate that shorter wait times result in less retained austenite. The SAE 1045 results were inconclusive. The samples showed no retained austenite regardless of magnetic field strength, indicating that tempering removed the retained austenite. It is apparent

Free-piston reciprocating cryogenic expander utilizing phase controller

Science.gov (United States)

Cha, Jeongmin; Park, Jiho; Kim, Kyungjoong; Jeong, Sangkwon

2017-02-01

In a free-piston expander which eliminates mechanical linkages, a prescribed behaviour of the free-piston movement is the key to an expander performance. In this paper, we have proposed an idea of reducing complexity of the free-piston expander. It is to replace both multiple solenoid valves and reservoirs that are indispensable in a previous machine with a combination of a single orifice-reservoir assembly. It functions as a phase controller like that of a pulse tube refrigerator so that it generates time-delay of pressure variation between the warm-end and the reservoir resulting in the intended expansion of the cold-end volume down to the pre-set reservoir pressure. The modeling of this unique free-piston reciprocating expander utilizing phase controller is developed to understand and predict the performance of the new-type expander. Additionally, the operating parameters are analysed at the specified conditions to enable one to develop a more efficient free-piston type cryogenic expander.

Neutron depolarisation study of the austenite grain size in TRIP steels

International Nuclear Information System (INIS)

Dijk, N.H. van; Zhao, L.; Rekveldt, M.Th.; Fredrikze, H.; Tegus, O.; Brueck, E.; Sietsma, J.; Zwaag, S. van der

2004-01-01

We have performed combined neutron depolarisation and magnetisation measurements in order to obtain an in situ determination of the average grain size and volume fraction of the retained austenite phase in TRIP steels. The average grain size of the retained austenite was found to decrease for an increase in austenite volume fraction at two different annealing temperatures

The mechanical stability of retained austenite in low-alloyed TRIP steel under shear loading

Energy Technology Data Exchange (ETDEWEB)

Blondé, R., E-mail: r.j.p.blonde@tudelft.nl [Fundamental Aspects of Materials and Energy, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands); Materials Innovation Institute, Mekelweg 2, 2628 CD Delft (Netherlands); Jimenez-Melero, E., E-mail: enrique.jimenez-melero@manchester.ac.uk [Dalton Cumbrian Facility, The University of Manchester, Westlakes Science and Technology Park, Moor Row, Cumbria CA24 3HA (United Kingdom); Zhao, L., E-mail: lie.zhao@tudelft.nl [Materials Innovation Institute, Mekelweg 2, 2628 CD Delft (Netherlands); Department of Materials Science and Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft (Netherlands); Schell, N., E-mail: norbert.schell@hzg.de [Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Max Planck Strasse 1, 21502 Geesthacht (Germany); Brück, E., E-mail: e.h.bruck@tudelft.nl [Fundamental Aspects of Materials and Energy, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands); Zwaag, S. van der, E-mail: s.vanderzwaag@tudelft.nl [Novel Aerospace Materials Group, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft (Netherlands); Dijk, N.H. van, E-mail: n.h.vandijk@tudelft.nl [Fundamental Aspects of Materials and Energy, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands)

2014-01-31

The microstructure evolution during shear loading of a low-alloyed TRIP steel with different amounts of the metastable austenite phase and its equivalent DP grade has been studied by in-situ high-energy X-ray diffraction. A detailed powder diffraction analysis has been performed to probe the austenite-to-martensite transformation by characterizing simultaneously the evolution of the austenite phase fraction and its carbon concentration, the load partitioning between the austenite and the ferritic matrix and the texture evolution of the constituent phases. Our results show that for shear deformation the TRIP effect extends over a significantly wider deformation range than for simple uniaxial loading. A clear increase in average carbon content during the mechanically-induced transformation indicates that austenite grains with a low carbon concentration are least stable during shear loading. The observed texture evolution indicates that under shear loading the orientation dependence of the austenite stability is relatively weak, while it has previously been found that under tensile load the {110}〈001〉 component transforms preferentially. The mechanical stability of retained austenite in TRIP steel is found to be a complex interplay between the interstitial carbon concentration in the austenite, the grain orientation and the load partitioning.

Spinodal decomposition of austenite in long-term-aged duplex stainless steel

International Nuclear Information System (INIS)

Chung, H.M.

1989-02-01

Spinodal decomposition of austenite phase in the cast duplex stainless steels CF-8 and -8M grades has been observed after long- term thermal aging at 400 and 350/degree/C for 30,000 h (3.4 yr). At 320/degree/C, the reaction was observed only at the limited region near the austenite grain boundaries. Ni segregation and ''worm-holes'' corresponding to the spatial microchemical fluctuations have been confirmed. The decomposition was observed only for heats containing relatively high overall Ni content (9.6--12.0 wt %) but not in low-Ni (8.0--9.4 wt %) heats. In some specimens showing a relatively advanced stage of decomposition, localized regions of austenite with a Vickers hardness of 340--430 were observed. However, the effect of austenite decomposition on the overall material toughness appears secondary for aging up to 3--5 yr in comparison with the effect of the faster spinodal decomposition in ferrite phase. The observation of the thermally driven spinodal decomposition of the austenite phase in cast duplex stainless steels validates the proposition that a miscibility gap occurs in Fe-Ni and ancillary systems. 16 refs., 7 figs., 1 tab

Diffraction study of the retained austenite content in TRIP steels

Energy Technology Data Exchange (ETDEWEB)

Gnaeupel-Herold, T., E-mail: tg-h@nist.gov [NIST Center for Neuron Research, 100 Bureau Dr., Gaithersburg MD 20899-6102 (United States); University of Maryland, Department of Material Science and Engineering., College Park MD 20742-2142 (United States); Creuziger, A., E-mail: adam.creuziger@nist.gov [NIST Metallurgy Division, 100 Bureau Dr., Gaithersburg MD 20899-8553 (United States); Kent State University, Kent, OH 44242 (United States)

2011-04-25

Research highlights: {yields} Novel orientation averaging scheme for retained austenite content measurement. {yields} assumption of random grain orientation generally not justified. {yields} Averaging scheme allows to disregard texture. {yields} unlike Rietveld method, averaging method does not orientation density function. {yields} Two independent (hkl) are necessary for retained austenite content. - Abstract: The results of a study of using neutron diffraction for determining the retained austenite content of TRIP steels are presented. The study covers a wide area of materials, deformation modes (uniaxial, biaxial and plane strain), strains, and the retained austenite content as a result of these variables. It was determined using basic principles of statistics that a minimum of two reflections (hkl) for each phase is necessary to calculate a phase mass fraction and the associated standard deviation. Texture from processing the steel is the largest source of uncertainty. Through the method of complete orientation averaging described in this paper, the texture effect and with it the standard deviation of the austenite mass fraction can be substantially reduced, regardless of the type or severity of the texture.

Kinetics of phase transformations of undercooled austenite in 18CrNiMo7-6 steel applied for toothed wheels

Directory of Open Access Journals (Sweden)

J. Krawczyk

2010-07-01

Full Text Available Toothed wheels constitute essential part of the steel structural elements market. The most often hypereutectoid structural steels forcarburizing are used for toothed wheels. The final producers of toothed wheels are not demanding regarding a microstructure, providedthat the determined requirements will be fulfilled (e.g. metallurgical purity determined by ultrasounds. Therefore delivered forgings can be in an annealed or quenched state. This results from the situation that the final heat treatment or heat-chemical one is being done at one of the last stages of the toothed wheel production. An essential factor allowing to develop the proper heat treatment is the knowledge of the kinetics of phase transformations of undercooled austenite and its relating to technological conditions, being at the producer disposal, as well as to forging dimensions. Such investigations should be carried out on real melts used for forgings for toothed wheels production together with an analysis of microstructure changes on the forging cross-section. They should be based on calculation methods determining the distribution of cooling rates on its cross-section in dependence of an applied cooling medium.The mentioned above problems in relation to 18CrNiMo7-6 steel - are elucidated in this paper. The aim of the investigations wasthe description of the kinetics of phase transformations of undercooled austenite in this steel. The CCT diagram was constructed for the austenitizing temperature determined on the basis of phase transformations temperatures (the so-called critical points.

Self-stabilization of untransformed austenite by hydrostatic pressure via martensitic transformation

International Nuclear Information System (INIS)

Nakada, Nobuo; Ishibashi, Yuji; Tsuchiyama, Toshihiro; Takaki, Setsuo

2016-01-01

For improving the understanding of austenite stability in steel, hydrostatic pressure in untransformed austenite that is generated via martensitic transformation was evaluated from macro- and micro-viewpoints, and its effect on austenite stability was investigated in a Fe-27%Ni austenitic alloy. X-ray diffractometry revealed that the lattice parameter of untransformed austenite is continuously decreased via martensitic transformation only when martensite becomes the dominant phase in the microstructure. This suggests that the untransformed austenite is isotropically compressed by the surrounding martensite grains, i.e., hydrostatic pressure is generated in untransformed austenite dynamically at a later stage of martensitic transformation. On the other hand, microscopic strain mapping using the electron backscatter diffraction technique indicated that a finer untransformed austenite grain has a higher hydrostatic pressure, while a high density of dislocations is also introduced in untransformed austenite near the austenite/martensite interface because of lattice-invariant shear characterized by non-thermoelastic martensitic transformation. Furthermore, it was experimentally demonstrated that the hydrostatic pressure stabilizes the untransformed austenite; however, the austenite stabilization effect alone is not large enough to fully explain a large gap between martensite start and finish temperatures in steel.

Theoretical and experimental study of carburisation and decarburisation of a meta-stable austenitic steel

Directory of Open Access Journals (Sweden)

Charles West

2005-12-01

Full Text Available Metastable austenitic stainless steels are known to undergo a partial transformation of austenite to martensite as a consequence of plastic deformation. In the case of cyclic loading, a certain level of plastic strain must be exceeded, and phase formation takes place after an incubation period, during which the necessary amount of plastic deformation is accumulated. The susceptibility of the austenitic phase to deformation-induced martensite formation is strongly affected by the temperature of loading and the stability of austenite, which itself depends on the chemical composition. A key element in this regard is carbon which stabilizes the austenitic phase. It is shown in this study that the carbon concentration can be analysed systematically and reproducible by means of annealing treatments, if the parameters of these treatments are carefully defined on the basis of advanced theoretical thermodynamic and kinetic considerations. First results on the effect of carbon concentration and temperature of fatigue testing on the austenite/martensite transformation are presented, in order to illustrate the significance of these parameters on the martensite formation rate.

Kinetics analysis of two-stage austenitization in supermartensitic stainless steel

DEFF Research Database (Denmark)

Nießen, Frank; Villa, Matteo; Hald, John

2017-01-01

The martensite-to-austenite transformation in X4CrNiMo16-5-1 supermartensitic stainless steel was followed in-situ during isochronal heating at 2, 6 and 18 K min−1 applying energy-dispersive synchrotron X-ray diffraction at the BESSY II facility. Austenitization occurred in two stages, separated...... that the austenitization kinetics is governed by Ni-diffusion and that slow transformation kinetics separating the two stages is caused by soft impingement in the martensite phase. Increasing the lath width in the kinetics model had a similar effect on the austenitization kinetics as increasing the heating-rate....

Effect of cold working on nitriding process of AISI 304 and 316 austenitic stainless steel

International Nuclear Information System (INIS)

Pereira, Silvio Andre de Lima

2012-01-01

The nitriding behavior of AISI 304 and 316 austenitic stainless steel was studied by different cold work degree before nitriding processes. The microstructure, thickness, microhardness and chemical micro-composition were evaluated through optical microscopy, microhardness, scanner electronic microscopy and x ray diffraction techniques. Through them, it was observed that previous plastic deformations do not have influence on layer thickness. However, a nitrided layer thicker can be noticed in the AISI 304 steel. In addition, two different layers can be identified as resulted of the nitriding, composed for austenitic matrix expanded by nitrogen atoms and another thinner immediately below expanded by Carbon atoms. (author)

Effects of cooling rate, austenitizing temperature and austenite deformation on the transformation behavior of high-strength boron steel

International Nuclear Information System (INIS)

Mun, Dong Jun; Shin, Eun Joo; Choi, Young Won; Lee, Jae Sang; Koo, Yang Mo

2012-01-01

Highlights: ► Non-equilibrium segregation of B in steel depends strongly on the cooling rate. ► A higher austenitization temperature reduced the B hardenability effect. ► An increase in B concentration at γ grain boundaries accelerates the B precipitation. ► The loss of B hardenability effect is due to intragranular borocarbide precipitation. ► The controlled cooling after hot deformation increased the B hardenability effect. - Abstract: The phase transformation behavior of high-strength boron steel was studied considering the segregation and precipitation behavior of boron (B). The effects of cooling rate, austenitizing temperature and austenite deformation on the transformation behavior of B-bearing steel as compared with B-free steel were investigated by using dilatometry, microstructural observations and analysis of B distribution. The effects of these variables on hardenability were discussed in terms of non-equilibrium segregation mechanism and precipitation behavior of B. The retardation of austenite-to-ferrite transformation by B addition depends strongly on cooling rate (CR); this is mainly due to the phenomenon of non-equilibrium grain boundary segregation of B. The hardenability effect of B-bearing steel decreased at higher austenitizing temperature due to the precipitation of borocarbide along austenite grain boundaries. Analysis of B distribution by second ion mass spectroscopy confirmed that the grain boundary segregation of B occurred at low austenitizing temperature of 900 °C, whereas B precipitates were observed along austenite grain boundaries at high austenitizing temperature of 1200 °C. The significant increase in B concentration at austenite grain boundaries due to grain coarsening and a non-equilibrium segregation mechanism may lead to the B precipitation. In contrast, solute B segregated to austenite grain boundaries during cooling after heavy deformation became more stable because the increase in boundary area by grain

Five-parameter crystallographic characteristics of the interfaces formed during ferrite to austenite transformation in a duplex stainless steel

Science.gov (United States)

Haghdadi, N.; Cizek, P.; Hodgson, P. D.; Tari, V.; Rohrer, G. S.; Beladi, H.

2018-05-01

The crystallography of interfaces in a duplex stainless steel having an equiaxed microstructure produced through the ferrite to austenite diffusive phase transformation has been studied. The five-parameter interface character distribution revealed a high anisotropy in habit planes for the austenite-ferrite and austenite-austenite interfaces for different lattice misorientations. The austenite and ferrite habit planes largely terminated on (1 1 1) and (1 1 0) planes, respectively, for the austenite-ferrite interfaces associated with Kurdjumov-Sachs (K-S) and Nishiyama-Wasserman (N-W) orientation relationships. This was mostly attributed to the crystallographic preference associated with the phase transformation. For the austenite-ferrite interfaces with orientation relationships which are neither K-S nor N-W, both austenite and ferrite habit planes had (1 1 1) orientations. Σ3 twin boundaries comprised the majority of austenite-austenite interfaces, mostly showing a pure twist character and terminating on (1 1 1) planes due to the minimum energy configuration. The second highest populated austenite-austenite boundary was Σ9, which tended to have grain boundary planes in the tilt zone due to the geometrical constraints. Furthermore, the intervariant crystallographic plane distribution associated with the K-S orientation relationship displayed a general tendency for the austenite habit planes to terminate with the (1 1 1) orientation, mainly due to the crystallographic preference associated with the phase transformation.

Low temperature plasma carburizing of AISI 316L austenitic stainless steel and AISI F51 duplex stainless steel

OpenAIRE

Pinedo,Carlos Eduardo; Tschiptschin,André Paulo

2013-01-01

In this work an austenitic AISI 316L and a duplex AISI F51 (EN 1.4462) stainless steel were DC-Plasma carburized at 480ºC, using CH4 as carbon carrier gas. For the austenitic AISI 316L stainless steel, low temperature plasma carburizing induced a strong carbon supersaturation in the austenitic lattice and the formation of carbon expanded austenite (γC) without any precipitation of carbides. The hardness of the carburized AISI 316L steel reached a maximum of 1000 HV due to ∼13 at% c...

Low temperature plasma carburizing of AISI 316L austenitic stainless steel and AISI F51 duplex stainless steel

OpenAIRE

Pinedo, Carlos Eduardo; Tschiptschin, André Paulo

2013-01-01

In this work an austenitic AISI 316L and a duplex AISI F51 (EN 1.4462) stainless steel were DC-Plasma carburized at 480ºC, using CH4 as carbon carrier gas. For the austenitic AISI 316L stainless steel, low temperature plasma carburizing induced a strong carbon supersaturation in the austenitic lattice and the formation of carbon expanded austenite (γC) without any precipitation of carbides. The hardness of the carburized AISI 316L steel reached a maximum of 1000 HV due to ∼13 at% carbon super...

Phase stability of high manganese austenitic steels for cryogenic applications

CERN Document Server

Couturier, K

2000-01-01

The aim of this work is to study the austenitic stability against a' martensitic transformation of three non-magnetic austenitic steels : a new stainless steel X2CrMnNiMoN 19-12-11-1 grade, a traditional X8CrMnNiN 19-11-6 grade and a high manganese X8MnCrNi 28-7-1 grade. Measurements of relative magnetic susceptibility at room temperature are performed on strained tensile specimens at 4.2 K. A special extensometer for high precision strain measurements at low temperature has been developed at CERN to test specimens up to various levels of plastic strain. Moreover, the high precision strain recording of the extensometer enables a detailed study of the serrated yield phenomena associated with 4.2 K tensile testing and their influence on the evolution of magnetic susceptibility. The results show that high Mn contents increase the stability of the austenitic structure against a' martensitic transformation, while keeping high strength at cryogenic temperature. Moreover, proper elaboration through primary and possi...

Development of cryogenic free-piston reciprocating expander utilizing phase controller

Energy Technology Data Exchange (ETDEWEB)

Cha, Jeong Min; Park, Ji Ho; Kim, Kyung Joong; Jeong, Sang Kwon [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of)

2016-06-15

A free-piston reciprocating expander is a device which operates without any mechanical linkage to a stationary part. Since the motion of the floating piston is only controlled by the pressure difference at two ends of the piston, this kind of expander may indispensably require a sophisticated active control system equipped with multiple valves and reservoirs. In this paper, we have suggested a novel design that can further reduce complexity of the previously developed cryogenic free-piston expander configuration. It is a simple replacement of both multiple valves and reservoirs by a combination of an orifice valve and a reservoir. The functional characteristic of the integrated orifice-reservoir configuration is similar to that of a phase controller applied in a pulse tube refrigerator so that we designate the one as a phase controller. Depending on the orifice valve size in the phase controller, the different PV work which affects the expander performance is generated. The numerical model of this unique free-piston reciprocating expander utilizing a phase controller is established to understand and analyze quantitatively the performance variation of the expander under different valve timing and orifice valve size. The room temperature experiments are carried out to examine the performance of this newly developed cryogenic expander.

Development of cryogenic free-piston reciprocating expander utilizing phase controller

International Nuclear Information System (INIS)

Cha, Jeong Min; Park, Ji Ho; Kim, Kyung Joong; Jeong, Sang Kwon

2016-01-01

A free-piston reciprocating expander is a device which operates without any mechanical linkage to a stationary part. Since the motion of the floating piston is only controlled by the pressure difference at two ends of the piston, this kind of expander may indispensably require a sophisticated active control system equipped with multiple valves and reservoirs. In this paper, we have suggested a novel design that can further reduce complexity of the previously developed cryogenic free-piston expander configuration. It is a simple replacement of both multiple valves and reservoirs by a combination of an orifice valve and a reservoir. The functional characteristic of the integrated orifice-reservoir configuration is similar to that of a phase controller applied in a pulse tube refrigerator so that we designate the one as a phase controller. Depending on the orifice valve size in the phase controller, the different PV work which affects the expander performance is generated. The numerical model of this unique free-piston reciprocating expander utilizing a phase controller is established to understand and analyze quantitatively the performance variation of the expander under different valve timing and orifice valve size. The room temperature experiments are carried out to examine the performance of this newly developed cryogenic expander

Effect of shot peening on metastable austenitic stainless steels

Energy Technology Data Exchange (ETDEWEB)

Fargas, G., E-mail: gemma.fargas@upc.edu [CIEFMA - Departament de Ciència dels Materials i Enginyeria Metallúrgica, Universitat Politècnica de Catalunya, 08028 Barcelona (Spain); CRnE, Centre de Recerca en Nanoenginyeria, Universitat Politècnica de Catalunya, 08028 Barcelona (Spain); Roa, J.J.; Mateo, A. [CIEFMA - Departament de Ciència dels Materials i Enginyeria Metallúrgica, Universitat Politècnica de Catalunya, 08028 Barcelona (Spain); CRnE, Centre de Recerca en Nanoenginyeria, Universitat Politècnica de Catalunya, 08028 Barcelona (Spain)

2015-08-12

In this work, shot peening was performed in a metastable austenitic stainless steel EN 1.4318 (AISI 301LN) in order to evaluate its effect on austenite to martensite phase transformation and also the influence on the fatigue limit. Two different steel conditions were considered: annealed, i.e., with a fully austenitic microstructure, and cold rolled, consisting of a mixture of austenite and martensite. X-ray diffraction, electron back-scattered diffraction and focus ion beam, as well as nanoindentation techniques, were used to elucidate deformation mechanisms activated during shot peening and correlate with fatigue response. Results pointed out that extensive plastic deformation and phase transformation developed in annealed specimens as a consequence of shot peening. However, the increase of roughness and the generation of microcracks led to a limited fatigue limit improvement. In contrast, shot peened cold rolled specimens exhibited enhanced fatigue limit. In the latter case, the main factor that determined the influence on the fatigue response was the distance from the injector, followed successively by the exit speed of the shots and the coverage factor.

Characterization of microstructure and texture across dissimilar super duplex/austenitic stainless steel weldment joint by austenitic filler metal

International Nuclear Information System (INIS)

Eghlimi, Abbas; Shamanian, Morteza; Eskandarian, Masoomeh; Zabolian, Azam; Szpunar, Jerzy A.

2015-01-01

The evolution of microstructure and texture across an as-welded dissimilar UNS S32750 super duplex/UNS S30403 austenitic stainless steel joint welded by UNS S30986 (AWS A5.9 ER309LMo) austenitic stainless steel filler metal using gas tungsten arc welding process was evaluated by optical micrography and EBSD techniques. Due to their fabrication through rolling process, both parent metals had texture components resulted from deformation and recrystallization. The weld metal showed the highest amount of residual strain and had large austenite grain colonies of similar orientations with little amounts of skeletal ferrite, both oriented preferentially in the < 001 > direction with cub-on-cube orientation relationship. While the super duplex stainless steel's heat affected zone contained higher ferrite than its parent metal, an excessive grain growth was observed at the austenitic stainless steel's counterpart. At both heat affected zones, austenite underwent some recrystallization and formed twin boundaries which led to an increase in the fraction of high angle boundaries as compared with the respective base metals. These regions showed the least amount of residual strain and highest amount of recrystallized austenite grains. Due to the static recrystallization, the fraction of low degree of fit (Σ) coincident site lattice boundaries, especially Σ3 boundaries, was increased in the austenitic stainless steel heat affected zone, while the formation of subgrains in the ferrite phase increased the content of < 5° low angle boundaries at that of the super duplex stainless steel. - Graphical abstract: Display Omitted - Highlights: • Extensive grain growth in the HAZ of austenitic stainless steel was observed. • Intensification of < 100 > orientated grains was observed adjacent to both fusion lines. • Annealing twins with Σ3 CSL boundaries were formed in the austenite of both HAZ. • Cub-on-cube OR was observed between austenite and ferrite in the weld

Characterization of microstructure and texture across dissimilar super duplex/austenitic stainless steel weldment joint by austenitic filler metal

Energy Technology Data Exchange (ETDEWEB)

Eghlimi, Abbas, E-mail: a.eghlimi@ma.iut.ac.ir [Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Shamanian, Morteza [Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Eskandarian, Masoomeh [Department of Materials Engineering, Shiraz University, Shiraz 71348-51154 (Iran, Islamic Republic of); Zabolian, Azam [Department of Natural Resources, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Szpunar, Jerzy A. [Department of Mechanical Engineering, University of Saskatchewan, Saskatoon, SK S7N 5A9 (Canada)

2015-08-15

The evolution of microstructure and texture across an as-welded dissimilar UNS S32750 super duplex/UNS S30403 austenitic stainless steel joint welded by UNS S30986 (AWS A5.9 ER309LMo) austenitic stainless steel filler metal using gas tungsten arc welding process was evaluated by optical micrography and EBSD techniques. Due to their fabrication through rolling process, both parent metals had texture components resulted from deformation and recrystallization. The weld metal showed the highest amount of residual strain and had large austenite grain colonies of similar orientations with little amounts of skeletal ferrite, both oriented preferentially in the < 001 > direction with cub-on-cube orientation relationship. While the super duplex stainless steel's heat affected zone contained higher ferrite than its parent metal, an excessive grain growth was observed at the austenitic stainless steel's counterpart. At both heat affected zones, austenite underwent some recrystallization and formed twin boundaries which led to an increase in the fraction of high angle boundaries as compared with the respective base metals. These regions showed the least amount of residual strain and highest amount of recrystallized austenite grains. Due to the static recrystallization, the fraction of low degree of fit (Σ) coincident site lattice boundaries, especially Σ3 boundaries, was increased in the austenitic stainless steel heat affected zone, while the formation of subgrains in the ferrite phase increased the content of < 5° low angle boundaries at that of the super duplex stainless steel. - Graphical abstract: Display Omitted - Highlights: • Extensive grain growth in the HAZ of austenitic stainless steel was observed. • Intensification of < 100 > orientated grains was observed adjacent to both fusion lines. • Annealing twins with Σ3 CSL boundaries were formed in the austenite of both HAZ. • Cub-on-cube OR was observed between austenite and ferrite in the weld

Study of Ferrite During Refinement of Prior Austenite Grains in Microalloyed Steel Continuous Casting

Science.gov (United States)

Liu, Jiang; Wen, Guanghua; Tang, Ping

2017-12-01

The formation of coarse prior austenite grain is a key factor to promote transverse crack, and the susceptibility to the transverse crack can be reduced by refining the austenite grain size. In the present study, the high-temperature confocal laser scanning microscope (CLSM) was used to simulate two types of double phase-transformation technologies. The distribution and morphology of ferrites under different cooling conditions were analyzed, and the effects of ferrite distribution and morphology on the double phase-transformation technologies were explored to obtain the suitable double phase-change technology for the continuous casting process. The results indicate that, under the thermal cycle TH0 [the specimens were cooled down to 913 K (640 °C) at a cooling rate of 5.0 K/s (5.0 °C/s)], the width of prior austenite grain boundaries was thick, and the dislocation density at grain boundaries was high. It had strong inhibition effect on crack propagation; under the thermal cycle TH1 [the specimens were cooled down to 1073 K (800 °C) at a cooling rate of 5.0 K/s (5.0 °C/s) and then to 913 K (640 °C) at a cooling rate of 1.0 K/s (1.0 °C/s)], the width of prior austenite grain boundary was thin, and the dislocation density at grain boundaries was low. It was beneficial to crack propagation. After the first phase change, the developed film-like ferrite along the austenite grain boundaries improved the nucleation conditions of new austenitic grains and removed the inhibition effect of the prior austenite grain boundaries on the austenite grain size.

Study of retained austenite and nano-scale precipitation and their effects on properties of a low alloyed multi-phase steel by the two-step intercritical treatment

Energy Technology Data Exchange (ETDEWEB)

Xie, Z.J.; Han, G., E-mail: hangang@mater.ustb.edu.cn; Zhou, W.H.; Zeng, C.Y.; Shang, C.J., E-mail: cjshang@ustb.edu.cn

2016-03-15

Microstructure evolution and properties were studied in a low carbon low alloyed hot-rolled bainitic steel by annealing and annealing plus tempering. Microstructure of the hot-rolled steel consists of lath bainite and martensite. By annealing at 720 °C for 30 min and water quenching, multi-phase microstructure consisting of intercritical ferrite, tempered bainite/martensite, retained austenite and fresh martensite was obtained. With increasing annealing temperature to 760 °C, microstructure of the steel consisted of intercritical ferrite, fresh martensite without retained austenite. After the second step of tempering at 680 °C for samples annealed both at 720 °C and 760 °C, ~ 8–9% volume fraction of retained austenite was obtained in the multi-phase microstructure. Moreover, fine precipitates of VC with size smaller than 10 nm and copper precipitates with size of ~ 10–50 nm were obtained after tempering. Results from scanning transmission electron microscopy (STEM) give evidence to support that the partitioning of Mn, Ni and Cu is of significance for retained austenite stabilization. Due to the combined contribution of multiphase microstructure, the transformation-induced-plasticity effect of retained austenite and strengthening effect of nanometer-sized precipitates, yield strength greater than 800 MPa, yield to tensile ratio of 0.9, uniform elongation of ~ 9% and good low temperature impact toughness of 147 J at − 40 °C were achieved. - Highlights: • Stable retained austenite was produced in a low alloyed steel. • Partition of Mn, Ni and Cu was confirmed by STEM for austenite stabilization. • Nano-sized VC and Cu precipitates were achieved by second tempering. • High strength–high toughness with low Y/T ratio was obtained.

Modelling study on the three-dimensional neutron depolarisation response of the evolving ferrite particle size distribution during the austenite-ferrite phase transformation in steels

Science.gov (United States)

Fang, H.; van der Zwaag, S.; van Dijk, N. H.

2018-07-01

The magnetic configuration of a ferromagnetic system with mono-disperse and poly-disperse distribution of magnetic particles with inter-particle interactions has been computed. The analysis is general in nature and applies to all systems containing magnetically interacting particles in a non-magnetic matrix, but has been applied to steel microstructures, consisting of a paramagnetic austenite phase and a ferromagnetic ferrite phase, as formed during the austenite-to-ferrite phase transformation in low-alloyed steels. The characteristics of the computational microstructures are linked to the correlation function and determinant of depolarisation matrix, which can be experimentally obtained in three-dimensional neutron depolarisation (3DND). By tuning the parameters in the model used to generate the microstructure, we studied the effect of the (magnetic) particle size distribution on the 3DND parameters. It is found that the magnetic particle size derived from 3DND data matches the microstructural grain size over a wide range of volume fractions and grain size distributions. A relationship between the correlation function and the relative width of the particle size distribution was proposed to accurately account for the width of the size distribution. This evaluation shows that 3DND experiments can provide unique in situ information on the austenite-to-ferrite phase transformation in steels.

Welding metallurgy of austenitic stainless steels

International Nuclear Information System (INIS)

Ibrahim, A.N.

1983-01-01

Austenitic stainless steels welds are commonly found in nuclear reactor systems. The macrostructure and the transformation of delta -phase into γ - phase which occur during rapid solidification of such welds are discussed. Finally, several types of defects which are derived from the welding operation, particularly defects of crack type, are also discussed in brief. (author)

On the role of interlath retained austenite in the deformation of lath martensite

International Nuclear Information System (INIS)

Maresca, F; Kouznetsova, V G; Geers, M G D

2014-01-01

Literature presents extensive experimental evidence of large deformation and ductile fracture behaviour of lath martensite in martensitic and multi-phase high strength steels under quasi-static, uniaxial loading conditions. The physical origin of this apparent ductile behaviour of martensite is not clear, since martensite generally provides a high material strength. The presence of thin films of interlath retained austenite may trigger the observed apparent martensite ductility. The present contribution investigates the role played by interlath retained austenite on the mechanics of lath martensite by means of crystal plasticity simulations. It is shown that independently from the interlath retained austenite volume fraction and the exact lath morphology, localized shearing along the lath habit plane occurs as long as there are enough carriers for plasticity. The austenite film acts like a ‘greasy’ plane on which the stiffer laths can slide. The shearing mechanism is not a mere consequence of the lower flow stress in the austenitic phase, but it is largely due to the orientation relationship between the retained austenite face centred cubic lattice and the body centred cubic lath crystals. (paper)

Role of Austenitization and Pre-Deformation on the Kinetics of the Isothermal Bainitic Transformation

Science.gov (United States)

Lambers, H.-G.; Tschumak, S.; Maier, H. J.; Canadinc, D.

2009-06-01

The role of time-temperature path on the isothermal austenite-to-bainite phase transformation of low alloy 51 CrV 4 steel was investigated and the corresponding microstructures were analyzed. The important finding is that an incomplete initial austenitization treatment leaves undissolved carbides in the matrix, such that lower carbon and chromium content in the matrix result, eventually accelerating the phase transformation. Furthermore, the residual carbides constitute additional nucleation sites for the bainite plates, speeding up the process even further. Also, both plastic pre-deformation of the supercooled austenite and application of external elastic stresses during the phase transformation lead to transformation plasticity by enhancing the stress fields, providing a driving force for the growth of bainite plates along a preferred orientation. Overall, the current results constitute the first step toward establishing a database for constructing a realistic microstructure-based model for simulating metal forming operations involving austenite-to-bainite phase transformation.

Solidification behavior of austenitic stainless steel filler metals

International Nuclear Information System (INIS)

David, S.A.; Goodwin, G.M.; Braski, D.N.

1980-02-01

Thermal analysis and interrupted solidification experiments on selected austenitic stainless steel filler metals provided an understanding of the solidification behavior of austenitic stainless steel welds. The sequences of phase separations found were for type 308 stainless steel filler metal, L + L + delta + L + delta + γ → γ + delta, and for type 310 stainless steel filler metal, L → L + γ → γ. In type 308 stainless steel filler metal, ferrite at room temperature was identified as either the untransformed primary delta-ferrite formed during the initial stages of solidification or the residual ferrite after Widmanstaetten austenite precipitation. Microprobe and scanning transmission electron microscope microanalyses revealed that solute extensively redistributes during the transformation of primary delta-ferrite to austenite, leading to enrichment and stabilization of ferrite by chromium. The type 310 stainless steel filler metal investigated solidifies by the primary crystallization of austenite, with the transformation going to completion at the solidus temperature. In our samples residual ferrite resulting from solute segregation was absent at the intercellular or interdendritic regions

Study of irradiation damage structures in austenitic stainless steels

Energy Technology Data Exchange (ETDEWEB)

Hamada, Shozo [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

1997-08-01

The irradiation damage microstructures in austenitic stainless steels, which have been proposed to be a candidate of structural materials of a fusion reactor, under ions and neutrons irradiation have been studied. In ion irradiation experiments, cross-sectional observation of the depth distribution of damage formed due to ion irradiation became available. Comparison and discussion between experimental results with TEM and the calculated ones in the depth profiles of irradiation damage microstructures. Further, dual-phase stainless steels, consisted of ferritic/austenitic phases, showed irradiation-induced/enhanced precipitation during ion irradiation. High Flux Isotope Reactor with high neutron fluxes was employed in neutron-irradiation experiments. Swelling of 316 steel showed irradiation temperature dependence and this had strong correlation with phase instability under heavy damage level. Swelling resistance of Ti-modified austenitic stainless steel, which has good swelling resistance, decreased during high damage level. This might be caused by the instability of Ti-carbide particles. The preparation method to reduce higher radioactivity of neutron-irradiated TEM specimen was developed. (author). 176 refs.

Study of irradiation damage structures in austenitic stainless steels

International Nuclear Information System (INIS)

Hamada, Shozo

1997-08-01

The irradiation damage microstructures in austenitic stainless steels, which have been proposed to be a candidate of structural materials of a fusion reactor, under ions and neutrons irradiation have been studied. In ion irradiation experiments, cross-sectional observation of the depth distribution of damage formed due to ion irradiation became available. Comparison and discussion between experimental results with TEM and the calculated ones in the depth profiles of irradiation damage microstructures. Further, dual-phase stainless steels, consisted of ferritic/austenitic phases, showed irradiation-induced/enhanced precipitation during ion irradiation. High Flux Isotope Reactor with high neutron fluxes was employed in neutron-irradiation experiments. Swelling of 316 steel showed irradiation temperature dependence and this had strong correlation with phase instability under heavy damage level. Swelling resistance of Ti-modified austenitic stainless steel, which has good swelling resistance, decreased during high damage level. This might be caused by the instability of Ti-carbide particles. The preparation method to reduce higher radioactivity of neutron-irradiated TEM specimen was developed. (author). 176 refs

Materials model for describing the austenite-martensite phase transformation considering transformation-induced plasticity; Ein Materialmodell zur Beschreibung der Austenit-Martensit Phasentransformation unter Beruecksichtigung der transformationsinduzierten Plastizitaet

Energy Technology Data Exchange (ETDEWEB)

Oberste-Brandenburg, C.

1999-06-01

In this thesis, a model to describe the austenite martensite transformation was developed. The transformation induced plasticity (TRIP) was taken into consideration. The model can be used to design complex structures. A local examination of the energy and entropy balance at the phase boundary serves as the starting point for the identification of the thermodynamical driving force and the thermodynamic flow. For both, a tensorial description is necessary for a general nonhydrostatically stressed solid. In the second part, a material law for the description of TRIP-Steels was developed based on the values derived in the first part. The different mechanical behavior of the phases, especially the differing yield stresses, was taken into account. The model developed was implemented into the finite element program MARC. Simulations of the material and the structural behavior were performed. The experimentally observed strong dependence of the transformation kinetics on the yield stress of the austenite and the dependence of the orientation of the martensite inclusion on the stress state could be verified. (orig.) [German] Im Rahmen dieser Arbeit wurde ein Materialmodell zur Beschreibung der Austenit-Martensit Phasenumwandlung unter Beruecksichtigung der transformationsinduzierten Plastizitaet (TRIP) entwickelt. Das Modell ist zur Berechnung ausgedehnter Strukturen einsetzbar. Eine lokale Betrachtung der Energie- und Entropiebilanz an der Phasengrenze bildet den Ausgangspunkt zur Identifikation der thermodynamischen Kraft und des thermodynamischen Flusses bei Beschreibung der Transformationskinetik. Fuer beide Groessen muss fuer den allgemein nichthydrostatischen Spannungszustand eine tensorielle Beschreibung verwendet werden. Im zweiten Teil der Arbeit bilden diese Groessen die Basis zur Entwicklung eines Stoffgesetzes zur Beschreibung des TRIP-Phaenomens. Es wird das unterschiedliche mechanische Verhalten der Phasen, insbesondere die stark unterschiedlichen

Strain direction dependency of martensitic transformation in austenitic stainless steels: The effect of gamma-texture

NARCIS (Netherlands)

Hilkhuijsen, P.; Geijselaers, Hubertus J.M.; Bor, Teunis Cornelis; Perdahcioglu, Emin Semih; van den Boogaard, Antonius H.; Akkerman, Remko

2013-01-01

Uniaxial tensile tests on both a non-textured and a highly textured, fully austenitic stainless steel were performed in both the rolling and the transverse directions. Both materials show mechanically induced phase transformation from the austenitic FCC to the martensitic BCC phase. Differences in

Interaction of stress and phase transformations during thermochemical surface engineering

DEFF Research Database (Denmark)

Jespersen, Freja Nygaard

and diffusion kinetics to simulate the evolution of composition-depth and stress-depth profiles resulting from nitriding of austenitic stainless steel. The model takes into account a composition-dependent diffusion coefficient of nitrogen in expanded austenite, short range ordering (trapping) of nitrogen atoms......Low temperature nitriding of austenitic stainless steel causes a surface zone of expanded austenite, which improves the wear resistance of the stainless steel while preserving the stainless behavior. During nitriding huge residual stresses are introduced in the treated zone, arising from the volume...... expansion that accompanies the dissolution of high nitrogen contents in expanded austenite. An intriguing phenomenon during low-temperature nitriding, is that the residual stresses evoked by dissolution of nitrogen in the solid state, affect the thermodynamics and the diffusion kinetics of nitrogen...

Influence of Plastic Deformation on Low Temperature Surface Hardening of Austenitic and Precipitation Hardening Stainless Steels by Gaseous Nitriding

DEFF Research Database (Denmark)

Bottoli, Federico; Winther, Grethe; Christiansen, Thomas Lundin

2015-01-01

This article addresses an investigation of the influence of plastic deformation on low temperature surface hardening by gaseous nitriding of three commercial austenitic stainless steels: AISI 304, EN 1.4369 and Sandvik Nanoflex® with various degrees of austenite stability. The materials were...... case included X-ray diffraction analysis, reflected light microscopy and microhardness. The results demonstrate that a case of expanded austenite develops and that, in particular, strain-induced martensite has a large influence on the nitrided zone....

Influence of Plastic Deformation on Low Temperature Surface Hardening of Austenitic Stainless Steel by Gaseous Nitriding

DEFF Research Database (Denmark)

Bottoli, Federico; Winther, Grethe; Christiansen, Thomas Lundin

2015-01-01

This article addresses an investigation of the influence of plastic deformation on low temperature surface hardening by gaseous nitriding of two commercial austenitic stainless steels: AISI 304 and EN 1.4369. The materials were plastically deformed to different equivalent strains by uniaxial...... demonstrate that a case of expanded austenite develops and that, in particular, strain-induced martensite has a large influence on the nitrided zone....

Standard practice for X-Ray determination of retained austenite in steel with near random crystallographic orientation

CERN Document Server

American Society for Testing and Materials. Philadelphia

2003-01-01

1.1 This practice covers the determination of retained austenite phase in steel using integrated intensities (area under peak above background) of X-ray diffraction peaks using chromium Kα or molybdenum Kα X-radiation. 1.2 The method applies to carbon and alloy steels with near random crystallographic orientations of both ferrite and austenite phases. 1.3 This practice is valid for retained austenite contents from 1 % by volume and above. 1.4 If possible, X-ray diffraction peak interference from other crystalline phases such as carbides should be eliminated from the ferrite and austenite peak intensities. 1.5 Substantial alloy contents in steel cause some change in peak intensities which have not been considered in this method. Application of this method to steels with total alloy contents exceeding 15 weight % should be done with care. If necessary, the users can calculate the theoretical correction factors to account for changes in volume of the unit cells for austenite and ferrite resulting from vari...

Study on paraffin/expanded graphite composite phase change thermal energy storage material

International Nuclear Information System (INIS)

Zhang Zhengguo; Fang Xiaoming

2006-01-01

A paraffin/expanded graphite composite phase change thermal energy storage material was prepared by absorbing the paraffin into an expanded graphite that has an excellent absorbability. In such a composite, the paraffin serves as a latent heat storage material and the expanded graphite acts as the supporting material, which prevents leakage of the melted paraffin from its porous structure due to the capillary and surface tension forces. The inherent structure of the expanded graphite did not change in the composite material. The solid-liquid phase change temperature of the composite PCM was the same as that of the paraffin, and the latent heat of the paraffin/expanded graphite composite material was equivalent to the calculated value based on the mass ratio of the paraffin in the composite. The heat transfer rate of the paraffin/expanded graphite composite was obviously higher than that of the paraffin due to the combination with the expanded graphite that had a high thermal conductivity. The prepared paraffin/expanded graphite composite phase change material had a large thermal storage capacity and improved thermal conductivity and did not experience liquid leakage during its solid-liquid phase change

Deformation behavior of austenitic stainless steel at deep cryogenic temperatures

Science.gov (United States)

Han, Wentuo; Liu, Yuchen; Wan, Farong; Liu, Pingping; Yi, Xiaoou; Zhan, Qian; Morrall, Daniel; Ohnuki, Somei

2018-06-01

The nonmagnetic austenite steels are the jacket materials for low-temperature superconductors of fusion reactors. The present work provides evidences that austenites transform to magnetic martensite when deformation with a high-strain is imposed at 77 K and 4.2 K. The 4.2 K test is characterized by serrated yielding that is related to the specific motion of dislocations and phase transformations. The in-situ transmission electron microscope (TEM) observations in nanoscale reveal that austenites achieve deformation by twinning under low-strain conditions at deep cryogenic temperatures. The generations of twins, martensitic transformations, and serrated yielding are in order of increasing difficulty.

Magnetic properties near the ferromagnetic-paramagnetic transformation in the austenite phase of Ni43Mn44X2Sn11 (X = Fe and Co) Heusler alloys

Science.gov (United States)

Nan, W. Z.; Thanh, T. D.; You, T. S.; Piao, H. G.; Yu, S. C.

2018-03-01

In this work, we present a detail study on the magnetic properties in the austenitic phase (A phase) Ni43Mn44X2Sn11 alloy with X = Fe and Co, which were prepared by an arc-melting method in an argon atmosphere. The M(T) curves of two samples exhibits a single magnetic phase transition at the Curie temperature of the ferromagnetic (FM) austenitic phase with TCA = 298 K and 334k for (X = Fe and Co) respectively. Based on the Landau theory and M(H) data measured at different temperatures, we found that the FM-PM phase transitions around TCA in both samples were the second-order phase transition. Under an applied field change of 30 kOe, around TCA , the magnetic entropy changes were found to be 0.66 J Kg-1 K-1 and 1.62 J Kg-1 K-1 for (X = Fe and Co) respectively.

Microstructure and local texture evolution by plasma nitriding in a 316L austenitic stainless steel and consequences on its fatigue durability

International Nuclear Information System (INIS)

Stinville, Jean-Charles

2010-01-01

The present study concerns the surface and mechanical properties induced by specific low temperature (∼400 C) plasma nitriding of an AISI 316L austenitic stainless steel largely used for structural component in nuclear and chemical industries. It focuses especially on its influence on the fatigue durability. The great advantages of this plasma nitriding process are to produce thick nitrided layers with a high concentration of nitrogen atoms in solid solution into the material and to preserve the stainless character of the substrate. As a consequence a new phase named expanded austenite or γ N phase is formed and the lattice expansion associated with the high supersaturation of interstitial nitrogen atoms results in residual compressive stresses at the surface that exceed 2 GPa. The surface is then strongly modified as a result of complex effects including some crystallographic plane rotation, plasticity and damage in some grains depending on their orientation. The considerable increase of hardness and wear resistance produced by plasma nitriding of austenitic stainless steels is now well documented but there are practically no data on the influence on fatigue properties. Series of fatigue tests in air at room temperature carried out in the low cycle fatigue range show a significant improvement of the fatigue life. The results are discussed especially taking into account the compressive residual stresses induced by the nitrided layer. (authors)

Microstructural evolution of a 2.25Cr - 1 Mo steel during austenitization and temper: austenite grain growth, carbide precipitation sequence and effects on mechanical properties

International Nuclear Information System (INIS)

Depinoy, Sylvain

2015-01-01

This work aims at optimizing tensile and toughness properties of a 2.25Cr - 1Mo steel by controlling its microstructure through heat treatments. To this aim, phase transformations during austenitization, quenching and tempering have to be understood. Quantitative microstructural analyses were performed by means of SEM, TEM and XRD to characterize and model metallurgical evolution of the steel at each step of the heat treatment. The evolution of austenite during the austenitization stage, and its influence on the resulting as-quenched microstructure were thoroughly investigated. Austenite grain growth was modelled in order to understand its mechanisms, including the limited growth phenomenon observed at lower temperatures. The effect of austenitization conditions on further decomposition of austenite and on mechanical properties after quenching + tempering was experimentally determined. An optimal austenitization condition was selected and applied to study the tempering stage. Carbide precipitation was studied for various tempering temperatures and amounts of time. M3C carbides precipitate first, followed by M2C and M7C3; M23C6 are the equilibrium carbides. The influence of carbide precipitation on mechanical properties was studied. Tensile properties are closely linked to the tempering conditions in the range investigated, while impact toughness remains stable. (author) [fr

Precipitation of ferromagnetic phase induced by defect energies during creep deformation in Type 304 austenitic steel

Energy Technology Data Exchange (ETDEWEB)

Tsukada, Yuhki, E-mail: tsukada@silky.numse.nagoya-u.ac.j [Department of Materials, Physics and Energy Engineering, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Shiraki, Atsuhiro; Murata, Yoshinori [Department of Materials, Physics and Energy Engineering, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Takaya, Shigeru [Japan Atomic Energy Agency, 4002 Narita-cho, O-arai-machi, Higashi-ibaraki-gun, Ibaraki 311-1393 (Japan); Koyama, Toshiyuki [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Morinaga, Masahiko [Department of Materials, Physics and Energy Engineering, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan)

2010-06-15

The correlation of defect energies with precipitation of the ferromagnetic phase near M{sub 23}C{sub 6} carbide during creep tests at high temperature in Type 304 austenitic steel was examined by estimating the defect energies near the carbide, based on micromechanics. As one of the defect energies, the precipitation energy was calculated by assuming M{sub 23}C{sub 6} carbide to be a spherical inclusion. The other defect energy, creep dislocation energy, was calculated based on dislocation density data obtained from transmission electron microscopy observations of the creep samples. The dislocation energy density was much higher than the precipitation energy density in the initial stage of the creep process, when the ferromagnetic phase started to increase. Creep dislocation energy could be the main driving force for precipitation of the ferromagnetic phase.

Precipitation of ferromagnetic phase induced by defect energies during creep deformation in Type 304 austenitic steel

International Nuclear Information System (INIS)

Tsukada, Yuhki; Shiraki, Atsuhiro; Murata, Yoshinori; Takaya, Shigeru; Koyama, Toshiyuki; Morinaga, Masahiko

2010-01-01

The correlation of defect energies with precipitation of the ferromagnetic phase near M 23 C 6 carbide during creep tests at high temperature in Type 304 austenitic steel was examined by estimating the defect energies near the carbide, based on micromechanics. As one of the defect energies, the precipitation energy was calculated by assuming M 23 C 6 carbide to be a spherical inclusion. The other defect energy, creep dislocation energy, was calculated based on dislocation density data obtained from transmission electron microscopy observations of the creep samples. The dislocation energy density was much higher than the precipitation energy density in the initial stage of the creep process, when the ferromagnetic phase started to increase. Creep dislocation energy could be the main driving force for precipitation of the ferromagnetic phase.

Sandblasting induced stress release and enhanced adhesion strength of diamond films deposited on austenite stainless steel

Science.gov (United States)

Li, Xiao; Ye, Jiansong; Zhang, Hangcheng; Feng, Tao; Chen, Jianqing; Hu, Xiaojun

2017-08-01

We firstly used sandblasting to treat austenite stainless steel and then deposited a Cr/CrN interlayer by close field unbalanced magnetron sputtering on it. After that, diamond films were prepared on the interlayer. It is found that the sandblasting process induces phase transition from austenite to martensite in the surface region of the stainless steel, which decreases thermal stress in diamond films due to lower thermal expansion coefficient of martensite phase compared with that of austenite phase. The sandblasting also makes stainless steel's surface rough and the Cr/CrN interlayer film inherits the rough surface. This decreases the carburization extent of the interlayer, increases nucleation density and modifies the stress distribution. Due to lower residual stress and small extent of the interlayer's carburization, the diamond film on sandblast treated austenite stainless steel shows enhanced adhesion strength.

Consitutive modeling of metastable austenitic stainless steel

NARCIS (Netherlands)

Perdahcioglu, Emin Semih; Perdahcioglu, Emin Semih

2008-01-01

Metastable austenitic stainless steels combine high formability and high strength, which are generally opposing properties in materials. This property is a consequence of the martensitic phase transformation that takes place during deformation. This transformation is purely mechanically induced

Formation and stabilization of reversed austenite in supermartensitic stainless steel

DEFF Research Database (Denmark)

Nießen, Frank; Grumsen, Flemming Bjerg; Hald, John

2017-01-01

of the reversed austenite phase fraction. Annealing at higher temperatures led to a gradual increase in hardness which was caused by formation of fresh martensite from reversed austenite. It was demonstrated that stabilization of reversed austenite is primarily based on chemical stabilization by partitioning......The formation and stabilization of reversed austenite upon inter-critical annealing was investigated in a X4CrNiMo16-5-1 (EN 1.4418) supermartensitic stainless steel by means of scanning electron microscopy, electron backscatter-diffraction, transmission electron microscopy, energy-dispersive X......-ray spectroscopy and dilatometry. The results were supported by thermodynamics and kinetics models, and hardness measurements. Isothermal annealing for 2 h in the temperature range of 475 to 650 °C led to gradual softening of the material which was related to tempering of martensite and the steady increase...

The Formation of Martensitic Austenite During Nitridation of Martensitic and Duplex Stainless Steels

Science.gov (United States)

Zangiabadi, Amirali; Dalton, John C.; Wang, Danqi; Ernst, Frank; Heuer, Arthur H.

2017-01-01

Isothermal martensite/ferrite-to-austenite phase transformations have been observed after low-temperature nitridation in the martensite and δ-ferrite phases in 15-5 PH (precipitation hardening), 17-7 PH, and 2205 (duplex) stainless steels. These transformations, in the region with nitrogen concentrations of 8 to 16 at. pct, are consistent with the notion that nitrogen is a strong austenite stabilizer and substitutional diffusion is effectively frozen at the paraequilibrium temperatures of our experiments. Our microstructural and diffraction analyses provide conclusive evidence for the martensitic nature of these phase transformations.

Phase-field modelling and synchrotron validation of phase transformations in martensitic dual-phase steel

International Nuclear Information System (INIS)

Thiessen, R.G.; Sietsma, J.; Palmer, T.A.; Elmer, J.W.; Richardson, I.M.

2007-01-01

A thermodynamically based method to describe the phase transformations during heating and cooling of martensitic dual-phase steel has been developed, and in situ synchrotron measurements of phase transformations have been undertaken to support the model experimentally. Nucleation routines are governed by a novel implementation of the classical nucleation theory in a general phase-field code. Physically-based expressions for the temperature-dependent interface mobility and the driving forces for transformation have also been constructed. Modelling of martensite was accomplished by assuming a carbon supersaturation of the body-centred-cubic ferrite lattice. The simulations predict kinetic aspects of the austenite formation during heating and ferrite formation upon cooling. Simulations of partial austenitising thermal cycles predicted peak and retained austenite percentages of 38.2% and 6.7%, respectively, while measurements yielded peak and retained austenite percentages of 31.0% and 7.2% (±1%). Simulations of a complete austenitisation thermal cycle predicted the measured complete austenitisation and, upon cooling, a retained austenite percentage of 10.3% while 9.8% (±1%) retained austenite was measured

Effect of small addition of Cr on stability of retained austenite in high carbon steel

Energy Technology Data Exchange (ETDEWEB)

Hossain, Rumana; Pahlevani, Farshid, E-mail: f.pahlevani@unsw.edu.au; Sahajwalla, Veena

2017-03-15

High carbon steels with dual phase structures of martensite and austenite have considerable potential for industrial application in high abrasion environments due to their hardness, strength and relatively low cost. To design cost effective high carbon steels with superior properties, it is crucial to identify the effect of Chromium (Cr) on the stability of retained austenite (RA) and to fully understand its effect on solid-state phase transition. This study addresses this important knowledge gap. Using standard compression tests on bulk material, quantitative X-ray diffraction analysis, nano-indentation on individual austenitic grains, transmission electron microscopy and electron backscatter diffraction–based orientation microscopy techniques, the authors investigated the effect of Cr on the microstructure, transformation behaviour and mechanical stability of retained austenite in high carbon steel, with varying Cr contents. The results revealed that increasing the Cr %, altered the morphology of the RA and increased its stability, consequently, increasing the critical pressure for martensitic transformation. This study has critically addressed the elastoplastic behaviour of retained austenite – and provides a deep understanding of the effect of small additions of Cr on the metastable austenite of high carbon steel from the macro- to nano-level. Consequently, it paves the way for new applications for high carbon low alloy steels. - Highlights: • Effect of small addition of Cr on metastable austenite of high carbon steel from the macro- to nano-level • A multi-scale study of elastoplastic behaviour of retained austenite in high carbon steel • The mechanical stability of retained austenite during plastic deformation increased with increasing Cr content • Effect of grain boundary misorientation angle on hardness of individual retained austenite grains in high carbon steel.

First order phase transition of expanding matter and its fragmentation

International Nuclear Information System (INIS)

Chikazumi, Shinpei; Iwamoto, Akira

2002-01-01

Using an expanding matter model with a Lennard-Jones potential, the instability of the expanding system is investigated. The pressure, the temperature, and the density fluctuations are calculated as functions of density during the time evolution of the expanding matter, which are compared to the coexistence curve calculated by the Gibbs ensemble. The expanding matter undergoes the first order phase transition in the limit of the quasistatic expansion. The resultant fragment mass distributions are also investigated. (author)

Simulation of the Growth of Austenite from As-Quenched Martensite in Medium Mn Steels

Science.gov (United States)

Huyan, Fei; Yan, Jia-Yi; Höglund, Lars; Ågren, John; Borgenstam, Annika

2018-04-01

As part of an ongoing development of third-generation advanced high-strength steels with acceptable cost, austenite reversion treatment of medium Mn steels becomes attractive because it can give rise to a microstructure of fine mixture of ferrite and austenite, leading to both high strength and large elongation. The growth of austenite during intercritical annealing is crucial for the final properties, primarily because it determines the fraction, composition, and phase stability of austenite. In the present work, the growth of austenite from as-quenched lath martensite in medium Mn steels has been simulated using the DICTRA software package. Cementite is added into the simulations based on experimental observations. Two types of systems (cells) are used, representing, respectively, (1) austenite and cementite forming apart from each other, and (2) austenite forming on the cementite/martensite interface. An interfacial dissipation energy has also been added to take into account a finite interface mobility. The simulations using the first type of setup with an addition of interfacial dissipation energy are able to reproduce the observed austenite growth in medium Mn steels reasonably well.

Low temperature thermal ageing embrittlement of austenitic stainless steel welds and its electrochemical assessment

International Nuclear Information System (INIS)

Chandra, K.; Kain, Vivekanand; Raja, V.S.; Tewari, R.; Dey, G.K.

2012-01-01

Highlights: ► Embrittlement study of austenitic stainless steel welds after ageing up to 20,000 h. ► Spinodal decomposition and G-phase precipitation in ferrite at 400 °C. ► Spinodal decomposition of ferrite at 335 and 365 °C. ► Large decrease in corrosion resistance due to G-phase precipitation. ► Good correlation between electrochemical properties and the degree of embrittlement. - Abstract: The low temperature thermal ageing embrittlement of austenitic stainless steel welds is investigated after ageing up to 20,000 h at 335, 365 and 400 °C. Spinodal decomposition and G-phase precipitation after thermal ageing were identified by transmission electron microscopy. Ageing led to increase in hardness of the ferrite phase while there was no change in the hardness of austenite. The degree of embrittlement was evaluated by non-destructive methods, e.g., double-loop and single-loop electrochemical potentiokinetic reactivation tests. A good correlation was obtained between the electrochemical properties and hardening of the ferrite phase of the aged materials.

Effect of sigma phase in the repassivation potential of austenitic-ferritic stainless steel SEW 410 Nr. 14517; Efeito da fase sigma no potencial de repassivacao do aco inoxidavel austeno-ferritico SEW 410 Nr. 14517

Energy Technology Data Exchange (ETDEWEB)

Itman Filho, A.; Pimenta, C.C.; Santos, C.M.L. [Instituto Federal do Espirito Santo, Vitoria (Brazil)], e-mail: andrei@ifes.edu.br; Casteletti, L.C. [Escola de Engenharia de Sao Carlos - EESC/USP, SP (Brazil)

2010-07-01

The austenitic-ferritic stainless steels, due to the optimum compromise between mechanical properties and corrosion resistance, are being used in many applications, as chemical and oil industries. In the oil exploitation, the effect of erosion-corrosion in acid environment is responsible for the increment in the equipment maintenance costs. Regarding the interest in researches of deep water oil exploitation, the proposal of this study was to evaluate the effect of the heat treatment at 850 degree C of the austenitic-ferritic stainless steel SEW 410 Nr.14517. Microstructural characterizations, microhardness measurements of the phases and corrosion tests were accomplished to evaluate the samples. The pitting potential values were obtained by galvanostatic tests in H{sub 2}SO{sub 4} acid solution. The results showed that the volumetric percentages of sigma phase increased while the ferritic phase percentages decreased, when the heat treatment time increased. The sigma phase promoted hardness increase with little corrosion resistance decrease in the austenitic-ferritic stainless steel, too. (author)

Effect of hydrogen on the microstructure, mechanical properties and phase transformations in austenitic steels

International Nuclear Information System (INIS)

Li, Y.Y.; Xing, Z.S.

1989-01-01

Effect of high-pressure hydrogen charging on the microstructure, mechanical properties and phase transformations in austenitic steels has been investigated and discussed. The results show that the strength and impact toughness of the steels increase slightly and that the ductility decreases after hydrogen charging. The existence of δ-ferrite deteriorates the resistance to hydrogen embrittlement (HE) of the steels. The occurrence of carbide in the steel resulted from aging reduces the ductility of the steel and makes the steel sensitive to HE. The existence of sufficient hydrogen promotes the ε-martensitic transformation and suppresses the α'-martensitic transformation. The permeabilities and diffusivities of hydrogen in the steels have also been determined. (orig.)

Effect of Austenitic and Austeno-Ferritic Electrodes on 2205 Duplex and 316L Austenitic Stainless Steel Dissimilar Welds

Science.gov (United States)

Verma, Jagesvar; Taiwade, Ravindra V.

2016-11-01

This study addresses the effect of different types of austenitic and austeno-ferritic electrodes (E309L, E309LMo and E2209) on the relationship between weldability, microstructure, mechanical properties and corrosion resistance of shielded metal arc welded duplex/austenitic (2205/316L) stainless steel dissimilar joints using the combined techniques of optical, scanning electron microscope, energy-dispersive spectrometer and electrochemical. The results indicated that the change in electrode composition led to microstructural variations in the welds with the development of different complex phases such as vermicular ferrite, lathy ferrite, widmanstatten and intragranular austenite. Mechanical properties of welded joints were diverged based on compositions and solidification modes; it was observed that ferritic mode solidified weld dominated property wise. However, the pitting corrosion resistance of all welds showed different behavior in chloride solution; moreover, weld with E2209 was superior, whereas E309L exhibited lower resistance. Higher degree of sensitization was observed in E2209 weld, while lesser in E309L weld. Optimum ferrite content was achieved in all welds.

Evaluation of the low corrosion resistant phase formed during the sigma phase precipitation in duplex stainless steels

Directory of Open Access Journals (Sweden)

Darlene Yuko Kobayashi

1999-10-01

Full Text Available The duplex stainless steels, having a volumetric fraction of 50% ferrite and 50% austenite, conciliate high corrosion resistance with good mechanical properties. But, in many circumstances different phase transformations may occur, such as that responsible for sigma phase precipitation, which make the steel susceptible to localized corrosion. During the sigma phase precipitation a new austenitic phase is formed with a very low corrosion resistance. In the present research the composition of this new austenitic phase was evaluated in four duplex stainless steels, with different Mo, N and Cu contents. After the solution anneal at 1050 °C, samples of these steels were aged at 850 °C during 1 h and 5 h for sigma phase precipitation. Using the ferritoscope and an image analyzer it was possible to determine the volumetric fractions of ferrite and sigma phase, respectively, while those of austenite and the new austenitic phase were determined by difference to 100% volume. Finally, by using mass balance it was possible to determine theoretically the composition of the new austenitic phase. This phase is poor in Cr and Mo free, which explains its poor corrosion resistance.

Model for the interaction between interface migration and carbon diffusion during annealing of martensite-austenite microstructures in steels

International Nuclear Information System (INIS)

Santofimia, M.J.; Zhao, L.; Sietsma, J.

2008-01-01

The interaction between carbon partitioning from martensite to austenite and interface migration during annealing of martensite-austenite microstructures is modeled, assuming the same chemical potential of carbon in martensite and austenite at the interface and allowing the motion of the phase interface when a free-energy difference occurs. The simulations show that the motion of the martensite-austenite interface can be significant and can takes place in either direction

Parametrical limits of SCC-susceptibility of austenitic and austenitic-ferritic Cr-Ni steels

International Nuclear Information System (INIS)

Starosvetskij, D.I.; Baru, R.L.; Bondarenko, A.I.; Bogoyavlenskij, V.L.; Timonin, V.A.

1990-01-01

Comparative investigations into corrosion cracking (CC) of austenitic (12Kh18N10T) and austenitic-ferritic (08Kh22N6T) chromium-nickel steels are performed for various chloride media in a wide range of chloride concentrations and temperatures. It is shown that the ratio between steels in terms of their CC-susceptibility is not definite and can undergo a reversal depending on parameters of medium, level and conditions of loading. Differences in mechanisms of corrosion cracking of austenitic and austenitic-ferritic steels are established

A discrete dislocation–transformation model for austenitic single crystals

International Nuclear Information System (INIS)

Shi, J; Turteltaub, S; Remmers, J J C; Van der Giessen, E

2008-01-01

A discrete model for analyzing the interaction between plastic flow and martensitic phase transformations is developed. The model is intended for simulating the microstructure evolution in a single crystal of austenite that transforms non-homogeneously into martensite. The plastic flow in the untransformed austenite is simulated using a plane-strain discrete dislocation model. The phase transformation is modeled via the nucleation and growth of discrete martensitic regions embedded in the austenitic single crystal. At each instant during loading, the coupled elasto-plasto-transformation problem is solved using the superposition of analytical solutions for the discrete dislocations and discrete transformation regions embedded in an infinite homogeneous medium and the numerical solution of a complementary problem used to enforce the actual boundary conditions and the heterogeneities in the medium. In order to describe the nucleation and growth of martensitic regions, a nucleation criterion and a kinetic law suitable for discrete regions are specified. The constitutive rules used in discrete dislocation simulations are supplemented with additional evolution rules to account for the phase transformation. To illustrate the basic features of the model, simulations of specimens under plane-strain uniaxial extension and contraction are analyzed. The simulations indicate that plastic flow reduces the average stress at which transformation begins, but it also reduces the transformation rate when compared with benchmark simulations without plasticity. Furthermore, due to local stress fluctuations caused by dislocations, martensitic systems can be activated even though transformation would not appear to be favorable based on the average stress. Conversely, the simulations indicate that the plastic hardening behavior is influenced by the reduction in the effective austenitic grain size due to the evolution of transformation. During cyclic simulations, the coupled plasticity

Numerical simulation of hydrogen-assisted crack initiation in austenitic-ferritic duplex steels

International Nuclear Information System (INIS)

Mente, Tobias

2015-01-01

Duplex stainless steels have been used for a long time in the offshore industry, since they have higher strength than conventional austenitic stainless steels and they exhibit a better ductility as well as an improved corrosion resistance in harsh environments compared to ferritic stainless steels. However, despite these good properties the literature shows some failure cases of duplex stainless steels in which hydrogen plays a crucial role for the cause of the damage. Numerical simulations can give a significant contribution in clarifying the damage mechanisms. Because they help to interpret experimental results as well as help to transfer results from laboratory tests to component tests and vice versa. So far, most numerical simulations of hydrogen-assisted material damage in duplex stainless steels were performed at the macroscopic scale. However, duplex stainless steels consist of approximately equal portions of austenite and δ-ferrite. Both phases have different mechanical properties as well as hydrogen transport properties. Thus, the sensitivity for hydrogen-assisted damage is different in both phases, too. Therefore, the objective of this research was to develop a numerical model of a duplex stainless steel microstructure enabling simulation of hydrogen transport, mechanical stresses and strains as well as crack initiation and propagation in both phases. Additionally, modern X-ray diffraction experiments were used in order to evaluate the influence of hydrogen on the phase specific mechanical properties. For the numerical simulation of the hydrogen transport it was shown, that hydrogen diffusion strongly depends on the alignment of austenite and δ-ferrite in the duplex stainless steel microstructure. Also, it was proven that the hydrogen transport is mainly realized by the ferritic phase and hydrogen is trapped in the austenitic phase. The numerical analysis of phase specific mechanical stresses and strains revealed that if the duplex stainless steel is

Influence of low-temperature nitriding on the strain-induced martensite and laser-quenched austenite in a magnetic encoder made from 304L stainless steel

Science.gov (United States)

Leskovšek, Vojteh; Godec, Matjaž; Kogej, Peter

2016-01-01

We have investigated the possibility of producing a magnetic encoder by an innovative process. Instead of turning grooves in the encoder bar for precise positioning, we incorporated the information in 304L stainless steel by transforming the austenite to martensite after bar extrusion in liquid nitrogen and marking it with a laser, which caused a local transformation of martensite back into austenite. 304L has an excellent corrosion resistance, but a low hardness and poor wear resistance, which limits its range of applications. However, nitriding is a very promising way to enhance the mechanical and magnetic properties. After low-temperature nitriding at 400 °C it is clear that both ε- and α′-martensite are present in the deformed microstructure, indicating the simultaneous stress-induced and strain-induced transformations of the austenite. The effects of a laser surface treatment and the consequent appearance of a non-magnetic phase due to the α′ → γ transformation were investigated. The EDS maps show a high concentration of nitrogen in the alternating hard surface layers of γN and α′N (expanded austenite and martensite), but no significantly higher concentration of chromium or iron was detected. The high surface hardness of this nitride layer will lead to steels and encoders with better wear and corrosion resistance. PMID:27492862

Effect of Si and Mn additions on ferrite and austenite phase fractions in 25Cr-7Ni-1.5Mo-3W base super duplex stainless steels

International Nuclear Information System (INIS)

Jeong, S.W.; Lee, Z.-H.; Lee, H.M.

2000-01-01

The effect of heat treatment and Si and Mn additions on the ferrite and austenite phase fractions of the super duplex stainless steel (SDSS), Fe-25Cr-7Ni-1.5Mo-3W-Si-Mn-0.25N (numbers are all in wt.% unless specified otherwise), was investigated. The thermodynamic calculations of phase equilibria and phase fractions were performed using the Thermo-Calc program. Based on the calculated results, specific compositions of Si and Mn were selected and alloys with these compositions were analysed by Feritscope, X-ray diffractometry and scanning electron microscopy. The calculated phase fractions and experimentally analysed ones were compared and there was a good agreement between calculations and measurements. The optimum heat treatment condition for Fe-25Cr-7Ni-1.5Mo-3W-0.5Si-0.5Mn-0.25N is to hold at 1050 to 1100 C for 2 h in considering the ferrite to austenite ratio of 50:50 and to avoid second phase precipitation such as the σ phase. It was suggested that an excessive addition of more than 0.8Si and 1.0Mn may induce the σ phase precipitation. (orig.)

Oxidation resistant high creep strength austenitic stainless steel

Science.gov (United States)

Brady, Michael P.; Pint, Bruce A.; Liu, Chain-Tsuan; Maziasz, Philip J.; Yamamoto, Yukinori; Lu, Zhao P.

2010-06-29

An austenitic stainless steel displaying high temperature oxidation and creep resistance has a composition that includes in weight percent 15 to 21 Ni, 10 to 15 Cr, 2 to 3.5 Al, 0.1 to 1 Nb, and 0.05 to 0.15 C, and that is free of or has very low levels of N, Ti and V. The alloy forms an external continuous alumina protective scale to provide a high oxidation resistance at temperatures of 700 to 800.degree. C. and forms NbC nanocarbides and a stable essentially single phase fcc austenitic matrix microstructure to give high strength and high creep resistance at these temperatures.

Thermal stability of retained austenite in TRIP steels studied by synchrotron X-ray diffraction during cooling

International Nuclear Information System (INIS)

Dijk, N.H. van; Butt, A.M.; Zhao, L.; Sietsma, J.; Offerman, S.E.; Wright, J.P.; Zwaag, S. van der

2005-01-01

We have performed in situ X-ray diffraction measurements at a synchrotron source in order to study the thermal stability of the retained austenite phase in transformation induced plasticity steels during cooling from room temperature to 100 K. A powder analysis of the diffraction data reveals a martensitic transformation of part of the retained austenite during cooling. The fraction of austenite that transforms during cooling is found to depend strongly on the bainitic holding time and the composition of the steel. It is shown that that austenite grains with a lower average carbon concentration have a lower stability during cooling

Hydrogen-Induced Delayed Cracking in TRIP-Aided Lean-Alloyed Ferritic-Austenitic Stainless Steels

Directory of Open Access Journals (Sweden)

Suvi Papula

2017-06-01

Full Text Available Susceptibility of three lean-alloyed ferritic-austenitic stainless steels to hydrogen-induced delayed cracking was examined, concentrating on internal hydrogen contained in the materials after production operations. The aim was to study the role of strain-induced austenite to martensite transformation in the delayed cracking susceptibility. According to the conducted deep drawing tests and constant load tensile testing, the studied materials seem not to be particularly susceptible to delayed cracking. Delayed cracks were only occasionally initiated in two of the materials at high local stress levels. However, if a delayed crack initiated in a highly stressed location, strain-induced martensite transformation decreased the crack arrest tendency of the austenite phase in a duplex microstructure. According to electron microscopy examination and electron backscattering diffraction analysis, the fracture mode was predominantly cleavage, and cracks propagated along the body-centered cubic (BCC phases ferrite and α’-martensite. The BCC crystal structure enables fast diffusion of hydrogen to the crack tip area. No delayed cracking was observed in the stainless steel that had high austenite stability. Thus, it can be concluded that the presence of α’-martensite increases the hydrogen-induced cracking susceptibility.

Production and several properties of single crystal austenitic stainless steels

International Nuclear Information System (INIS)

Okamoto, Kazutaka; Yoshinari, Akira; Kaneda, Junya; Aono, Yasuhisa; Kato, Takahiko

1998-01-01

The single crystal austenitic stainless steels Type 316L and 304L were grown in order to improve the resistance to stress corrosion cracking (SCC) using a unidirectional solidification method which can provide the large size single crystals. The mechanical properties and the chemical properties were examined. The orientation and temperature dependence of tensile properties of the single crystals were measured. The yield stress of the single crystal steels are lower than those of the conventional polycrystal steels because of the grain boundary strength cannot be expected in the single crystal steels. The tensile properties of the single crystal austenitic stainless steel Type 316L depend strongly on the orientation. The tensile strength in orientation are about 200 MPa higher than those in the and orientations. The microstructure of the single crystal consists of a mixture of the continuous γ-austenitic single crystal matrix and the δ-ferrite phase so that the effects of the γ/δ boundaries on the chemical properties were studied. The effects of the δ-ferrite phases and the γ/δ boundaries on the resistance to SCC were examined by the creviced bent beam test (CBB test). No crack is observed in all the CBB test specimens of the single crystals, even at the γ/δ boundaries. The behavior of the radiation induced segregation (RIS) at the γ/δ boundaries in the single crystal austenitic stainless steel Type 316L was evaluated by the electron irradiation test in the high voltage electron microscope (HVEM). The depletion of oversized solute chromium at the γ/δ boundary in the single crystal austenitic stainless steel Type 316L is remarkably lower than that at the grain boundary in the polycrystalline-type 316L. (author)

In Situ Investigation of the Evolution of Lattice Strain and Stresses in Austenite and Martensite During Quenching and Tempering of Steel

Science.gov (United States)

Villa, M.; Niessen, F.; Somers, M. A. J.

2018-01-01

Energy dispersive synchrotron X-ray diffraction was applied to investigate in situ the evolution of lattice strains and stresses in austenite and martensite during quenching and tempering of a soft martensitic stainless steel. In one experiment, lattice strains in austenite and martensite were measured in situ in the direction perpendicular to the sample surface during an austenitization, quenching, and tempering cycle. In a second experiment, the sin2 ψ method was applied in situ during the austenite-to-martensite transformation to distinguish between macro- and phase-specific micro-stresses and to follow the evolution of these stresses during transformation. Martensite formation evokes compressive stress in austenite that is balanced by tensile stress in martensite. Tempering to 748 K (475 °C) leads to partial relaxation of these stresses. Additionally, data reveal that (elastic) lattice strain in austenite is not hydrostatic but hkl dependent, which is ascribed to plastic deformation of this phase during martensite formation and is considered responsible for anomalous behavior of the 200 γ reflection.

Evolution of secondary phases in 0.17C-16Cr-11Mn-0.43N austenitic stainless steel at 800 and 850°C: Thermodynamic modeling of phase equilibria and experimental kinetic studies

Directory of Open Access Journals (Sweden)

Čička R.

2012-01-01

Full Text Available The precipitation of secondary phases was investigated in the 0.17C-16Cr-11Mn-0.43N austenitic stainless steel during annealing at 800 and 850°C for times between 5 min and 100 h. Light microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy, and differential thermal analysis were used in experiments. Thermodynamic calculations were done by the ThermoCalc database software package. Cr2N and M23C6 were considered to be stable phases at the annealing temperatures. Cells consisting of alternating Cr2N and austenite lamellae were observed in the steel microstructure after sufficiently long annealing. The metastable chi phase was also found in all the annealed samples. After 100 h of annealing the equilibrium sigma started to precipitate. The thermodynamically predicted M6C was not confirmed experimentally in any of the annealed samples. DTA analysis showed the initial precipitation stage was followed by the phase dissolution. For the investigated steel the computational thermodynamics can be used only for qualitative interpretation of the experimental results as the measured endothermal peaks were found to be shifted of about 50 ÷ 70°C related to the computed results.

Diffusive Phenomena and the Austenite/Martensite Relative Stability in Cu-Based Shape-Memory Alloys

Science.gov (United States)

Pelegrina, J. L.; Yawny, A.; Sade, M.

2018-02-01

The main characteristic of martensitic phase transitions is the coordinate movement of the atoms which takes place athermally, without the contribution of diffusion during its occurrence. However, the impacts of diffusive phenomena on the relative stability between the phases involved and, consequently, on the associated transformation temperatures and functional properties can be significant. This is particularly evident in the case of Cu-based shape-memory alloys where atomic diffusion in both austenite and martensite metastable phases might occur even at room-temperature levels, giving rise to a variety of intensively studied phenomena. In the present study, the progresses made in the understanding of three selected diffusion-related effects of importance in Cu-Zn-Al and Cu-Al-Be alloys are reviewed. They are the after-quench retained disorder in the austenitic structure and its subsequent reordering, the stabilization of the martensite, and the effect of applied stress on the austenitic order. It is shown how the experimental results obtained from tests performed on single crystal material can be rationalized under the shed of a model developed to evaluate the variation of the relative stability between the phases in terms of atom pairs interchanges.

Formation of austenite in high Cr ferritic/martensitic steels by high fluence neutron irradiation

Science.gov (United States)

Lu, Z.; Faulkner, R. G.; Morgan, T. S.

2008-12-01

High Cr ferritic/martensitic steels are leading candidates for structural components of future fusion reactors and new generation fission reactors due to their excellent swelling resistance and thermal properties. A commercial grade 12%CrMoVNb ferritic/martensitic stainless steel in the form of parent plate and off-normal weld materials was fast neutron irradiated up to 33 dpa (1.1 × 10 -6 dpa/s) at 400 °C and 28 dpa (1.7 × 10 -6 dpa/s) at 465 °C, respectively. TEM investigation shows that the fully martensitic weld metal transformed to a duplex austenite/ferrite structure due to high fluence neutron irradiation, the austenite was heavily voided (˜15 vol.%) and the ferrite was relatively void-free; whilst no austenite phases were detected in plate steel. Thermodynamic and phase equilibria software MTDATA has been employed for the first time to investigate neutron irradiation-induced phase transformations. The neutron irradiation effect is introduced by adding additional Gibbs free energy into the system. This additional energy is produced by high energy neutron irradiation and can be estimated from the increased dislocation loop density caused by irradiation. Modelling results show that neutron irradiation reduces the ferrite/austenite transformation temperature, especially for high Ni weld metal. The calculated results exhibit good agreement with experimental observation.

Investigation of strain-induced martensitic transformation in metastable austenite using nanoindentation

International Nuclear Information System (INIS)

Ahn, T.-H.; Oh, C.-S.; Kim, D.H.; Oh, K.H.; Bei, H.; George, E.P.; Han, H.N.

2010-01-01

Strain-induced martensitic transformation of metastable austenite was investigated by nanoindentation of individual austenite grains in multi-phase steel. A cross-section prepared through one of these indented regions using focused ion beam milling was examined by transmission electron microscopy. The presence of martensite underneath the indent indicates that the pop-ins observed on the load-displacement curve during nanoindentation correspond to the onset of strain-induced martensitic transformation. The pop-ins can be understood as resulting from the selection of a favorable martensite variant during nanoindentation.

Investigation of Strain-Induced Martensitic Transformation in Metastable Austenite using Nanoindentation

Energy Technology Data Exchange (ETDEWEB)

Ahn, T.-H. [Seoul National University; Oh, C.-S. [Korean Institute of Materials Science; Kim, D. H. [Seoul National University; Oh, K. H. [Seoul National University; Bei, Hongbin [ORNL; George, Easo P [ORNL; Han, H. N. [Seoul National University

2010-01-01

Strain-induced martensitic transformation of metastable austenite was investigated by nanoindentation of individual austenite grains in multi-phase steel. A cross-section prepared through one of these indented regions using focused ion beam milling was examined by transmission electron microscopy. The presence of martensite underneath the indent indicates that the pop-ins observed on the load-displacement curve during nanoindentation correspond to the onset of strain-induced martensitic transformation. The pop-ins can be understood as resulting from the selection of a favorable martensite variant during nanoindentation.

Evaluation of welds on a ferritic-austenitic stainless steel

International Nuclear Information System (INIS)

Pleva, J.; Johansson, B.

1984-01-01

Five different welding methods for the ferritic-austenitic steel 22Cr6Ni3MoN have been evaluated on mill welded heavy wall pipes. The corrosion resistance of the weld joints has been tested both in standard tests and in special environments, related to certain oil and gas wells. The tests were conclusive in that a welding procedure with the addition of sufficient amounts of filler metal should be employed. TIG welds without or with marginal filler addition showed poor resistance to pitting, and to boiling nitric acid. Contents of main alloying elements in ferrite and austenite phases have been measured and causes of corrosion attack in welds are discussed

Discontinuous precipitation in a nickel-free high nitrogen austenitic stainless steel on solution nitriding

Science.gov (United States)

Mohammadzadeh, Roghayeh; Akbari, Alireza; Grumsen, Flemming B.; Somers, Marcel A. J.

2017-10-01

Chromium-rich nitride precipitates in production of nickel-free austenitic stainless steel plates via pressurised solution nitriding of Fe-22.7Cr-2.4Mo ferritic stainless steel at 1473 K (1200 °C) under a nitrogen gas atmosphere was investigated. The microstructure, chemical and phase composition, morphology and crystallographic orientation between the resulted austenite and precipitates were investigated using optical microscopy, X-ray Diffraction (XRD), Scanning and Transmission Electron Microscopy (TEM) and Electron Back Scatter Diffraction (EBSD). On prolonged nitriding, Chromium-rich nitride precipitates were formed firstly close to the surface and later throughout the sample with austenitic structure. Chromium-rich nitride precipitates with a rod or strip-like morphology was developed by a discontinuous cellular precipitation mechanism. STEM-EDS analysis demonstrated partitioning of metallic elements between austenite and nitrides, with chromium contents of about 80 wt.% in the precipitates. XRD analysis indicated that the Chromium-rich nitride precipitates are hexagonal (Cr, Mo)2N. Based on the TEM studies, (Cr, Mo)2N precipitates presented a (1 1 1)γ//(0 0 2)(Cr, Mo)2N, ?γ//?(Cr, Mo)2N orientation relationship with respect to the austenite matrix. EBSD studies revealed that the austenite in the regions that have transformed into austenite and (Cr, Mo)2N have no orientation relation to the untransformed austenite.

Cast heat-resistant austenitic steel with improved temperature creep properties and balanced alloying element additions and methodology for development of the same

Science.gov (United States)

Pankiw, Roman I; Muralidharan, Govindrarajan; Sikka, Vinod Kumar; Maziasz, Philip J

2012-11-27

The present invention addresses the need for new austenitic steel compositions with higher creep strength and higher upper temperatures. The new austenitic steel compositions retain desirable phases, such as austenite, M.sub.23C.sub.6, and MC in its microstructure to higher temperatures. The present invention also discloses a methodology for the development of new austenitic steel compositions with higher creep strength and higher upper temperatures.

High Nb, Ta, and Al creep- and oxidation-resistant austenitic stainless steel

Science.gov (United States)

Brady, Michael P [Oak Ridge, TN; Santella, Michael L [Knoxville, TN; Yamamoto, Yukinori [Oak Ridge, TN; Liu, Chain-tsuan [Oak Ridge, TN

2010-07-13

An austenitic stainless steel HTUPS alloy includes, in weight percent: 15 to 30 Ni; 10 to 15 Cr; 2 to 5 Al; 0.6 to 5 total of at least one of Nb and Ta; no more than 0.3 of combined Ti+V; up to 3 Mo; up to 3 Co; up to 1 W; up to 0.5 Cu; up to 4 Mn; up to 1 Si; 0.05 to 0.15 C; up to 0.15 B; up to 0.05 P; up to 1 total of at least one of Y, La, Ce, Hf, and Zr; less than 0.05 N; and base Fe, wherein the weight percent Fe is greater than the weight percent Ni wherein said alloy forms an external continuous scale comprising alumina, nanometer scale sized particles distributed throughout the microstructure, said particles comprising at least one composition selected from the group consisting of NbC and TaC, and a stable essentially single phase fcc austenitic matrix microstructure, said austenitic matrix being essentially delta-ferrite-free and essentially BCC-phase-free.

Martensitic transformation of austenitic stainless steel orthodontic wires during intraoral exposure.

Science.gov (United States)

Izquierdo, Paula P; de Biasi, Ronaldo S; Elias, Carlos N; Nojima, Lincoln I

2010-12-01

Our purpose was to study the mechanical properties and phase transformations of orthodontic wires submitted to in-vivo exposure in the mouth for different periods of time. Stainless steel wires were tied to fixed orthodontic appliances of 30 patients from the orthodontics clinic of Universidade Federal do Rio de Janeiro School of Dentistry in Brazil. According to the duration of the clinical treatment, the patients were divided into 3 groups. After in-vivo exposure, the samples were studied by mechanical testing (torsion) and ferromagnetic resonance. Statistical analyses were carried out to evaluate the correlation between time of exposure, mechanical properties, and austenite-to-martensite transformation among the groups. The results were compared with as-received control samples. The torque values increased as time in the mouth increased. The increase in torque resistance showed high correlations with time of exposure (P = 0.005) and austenite-martensite phase transformation. The resistance of stainless steel orthodontic wires increases as the time in the mouth increases; this effect is attributed to the austenite-to-martensite transformation. Copyright © 2010 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.

Magnetic properties of cyclically deformed austenite

Energy Technology Data Exchange (ETDEWEB)

Das, Arpan, E-mail: dasarpan1@yahoo.co.in

2014-06-01

In meta-stable austenitic stainless steels, low cycle fatigue deformation is accompanied by a partial stress/strain-induced solid state phase transformation of paramagnetic γ(fcc) austenite phase to ferromagnetic α{sup /}(bcc) martensite. The measured characteristic of magnetic properties, which are the saturation magnetization, susceptibility, coercivity, retentivity, and the area under the magnetic hysteresis loop are sensitive to the total strain amplitude imposed and the corresponding material behaviour. The morphologies and nucleation characteristics of deformation induced martensites (i.e., ϵ(hcp), α{sup /}(bcc)) have been investigated through analytical transmission electron microscope. It has been observed that deformation induced martensites can nucleate at a number of sites (i.e., shear band intersections, isolated shear bands, shear band–grain boundary intersection, grain boundary triple points, etc.) through multiple transformation sequences: γ(fcc)→ϵ(hcp), γ(fcc)→ϵ(hcp)→α{sup /}(bcc), γ(fcc)→ deformation twin →α{sup /}(bcc) and γ(fcc)→α{sup /}(bcc). - Highlights: • LCF tests were done at various strain amplitudes of 304LNSS. • Quantification of martensite was done through ferritecope. • Magnetic properties were characterised through VSM. • Correlation of magnetic properties with the cyclic plastic response was done. • TEM was done to investigate the transformation micro-mechanisms.

A preliminary study of thermo-mechanical stability of carbon S-phase formed in austenitic stainless steel

Energy Technology Data Exchange (ETDEWEB)

Li, Wei; Chiu, Yu Long; Dong, Hanshan, E-mail: wsgddf@hotmail.com [School of Metallurgy and Materials, College of Physical and Engineering Sciences, The University of Birmingham, Birmingham (United Kingdom)

2010-07-01

Carbon S-phase was generated in the surface of AISI316 austenitic stainless steel by plasma carburising at 500°C for 10h in a gas mixture of 1.5%CH4 and 98.5%H{sub 2}. The thermo-mechanical stability of the carbon S-phase was studied by stressing the 'dog-bone' tensile specimens in the range of 0-200MPa at temperatures ranging from 400 to 500°C for 100-150h. Post-test characterisation was conducted using XRD, SEM, TEM and micro-indentation. The experimental results demonstrate that when tested at a fix temperature the thickness of the carbon S-phase layer increased with the stress applied to the tensile specimens during the thermo-mechanical stability tests. This indicates that tensile stress promotes the diffusion of carbon in the carbon-S-phase. When stressed at 400°C the microstructure of the carbon S-phase was not affected by the stress level; however, when stressed at 450 and 500°C for 100MPa or above, the corrosion resistance of the carbon S-phase slightly deteriorated. The application of a tensile stress during annealing of S-phase layer can retard the deduction of its hardness. This is believed to be related to the early stage precipitation of carbides in the S-phase, which could be facilitated by the applied tensile stress during thermal annealing. (author)

Modelling the interaction between plasticity and the austenite-martensite transformation

NARCIS (Netherlands)

Kouznetsova, V.G.; Geers, M.G.D.

2007-01-01

Many advanced steels, such as high strength steels and TRIP steels, owe their excellent combination of strength and ductility to the complex microstructural behaviour involving the austenite to martensite phase transformation. In this paper a physically-based model for martensitic transformation

Concurrent microstructural evolution of ferrite and austenite in a duplex stainless steel processed by high-pressure torsion

International Nuclear Information System (INIS)

Cao, Y.; Wang, Y.B.; An, X.H.; Liao, X.Z.; Kawasaki, M.; Ringer, S.P.; Langdon, T.G.; Zhu, Y.T.

2014-01-01

A duplex stainless steel with approximately equal volume fractions of ferrite and austenite was processed by high-pressure torsion. Nano-indentation, electron backscatter diffraction and transmission electron microscopy were used to investigate the hardness and microstructure evolutions of the steel. Despite the different strain-hardening rates of individual ferrite and austenite, the microstructures of the two phases evolved concurrently in such a way that the neighbouring two phases always maintained similar hardness. While the plastic deformation and grain refinement of ferrite occurred mainly via dislocation activities, the plastic deformation and grain refinement process of austenite were more complicated and included deformation twinning and de-twinning in coarse grains, grain refinement by twinning and dislocation–twin interactions, de-twinning in ultrafine grains and twin boundary subdivision

Site-specific atomic-scale characterisation of retained austenite in a strip cast TRIP steel

International Nuclear Information System (INIS)

Xiong, Z.P.; Saleh, A.A.; Marceau, R.K.W.; Taylor, A.S.; Stanford, N.E.; Kostryzhev, A.G.; Pereloma, E.V.

2017-01-01

Knowledge of carbon content in retained austenite (RA) with different neighbouring phases is essential to understand the chemical stability of RA, which is useful for microstructure tuning of transformation-induced plasticity (TRIP) steels. The present study investigates different morphologies and chemical compositions of RA by correlating electron backscattering diffraction, transmission electron microscopy and atom probe tomography. The effect of neighbouring phases, such as polygonal ferrite, bainitic ferrite lath, ferrite in granular bainite and carbides, on the carbon content in the RA is investigated. The results reveal that the film RA morphology does not always have a higher carbon content than the blocky RA; as coarse RA sometimes displays a higher carbon content than the fine RA films or islands depending on the neighbouring phases. The diffusion of carbon and manganese between austenite and ferrite in bainitic ferrite/granular bainite has been explained according to either diffusionless and/or diffusional mechanism of bainitic ferrite formation followed by tempering. -- Highlights: •The effect of neighbouring phases on retained austenite (RA) features was investigated. •A lower carbon content in fine/film RA compared to coarse/blocky RA was experimentally demonstrated. •At least locally controlled diffusion of substitutional solutes across the RA/bainitic ferrite lath interface was suggested.

Comprehensive Deformation Analysis of a Newly Designed Ni-Free Duplex Stainless Steel with Enhanced Plasticity by Optimizing Austenite Stability

DEFF Research Database (Denmark)

Moallemi, Mohammad; Zarei-Hanzaki, Abbas; Eskandari, Mostafa

2017-01-01

A new metastable Ni-free duplex stainless steel has been designed with superior plasticity by optimizing austenite stability using thermodynamic calculations of stacking fault energy and with reference to literature findings. Several characterization methods comprising optical microscopy, magnetic......, including an ultimate tensile strength of ~900 MPa and elongation to fracture of ~94 pct due to the synergistic effects of transformation-induced plasticity and twinning-induced plasticity. The deformation mechanism of austenite is complex and includes deformation banding, strain-induced martensite...... formation, and deformation-induced twinning, while the ferrite phase mainly deforms by dislocation slip. Texture analysis indicates that the Copper and Rotated Brass textures in austenite (FCC phase) and {001}〈110〉 texture in ferrite and martensite (BCC phases) are the main active components during...

In-situ investigation of strain-induced martensitic transformation kinetics in an austenitic stainless steel by inductive measurements

NARCIS (Netherlands)

Alonso de Celada Casero, C.; Kooiker, Harm; Groen, Manso; Post, J; San Martin, D

2017-01-01

An inductive sensor developed by Philips ATC has been used to study in-situ the austenite (γ) to martensite (α′) phase transformation kinetics during tensile testing in an AISI 301 austenitic stainless steel. A correlation between the sensor output signal and the volume fraction of α′-martensite

Microstructure of super-austenitic steels after long-term annealing

Czech Academy of Sciences Publication Activity Database

Kraus, M.; Kroupa, Aleš; Miodownik, P.; Svoboda, Milan; Vřešťál, J.

2010-01-01

Roč. 101, č. 6 (2010), s. 729-735 ISSN 1862-5282 R&D Projects: GA ČR(CZ) GA106/07/1078 Institutional research plan: CEZ:AV0Z20410507 Keywords : phase equilibria * microstructure * super-austenitic steel Subject RIV: BJ - Thermodynamics Impact factor: 0.860, year: 2010

Phase-preserving beam expander for biomedical X-ray imaging

International Nuclear Information System (INIS)

Martinson, Mercedes; Samadi, Nazanin; Bassey, Bassey; Gomez, Ariel; Chapman, Dean

2015-01-01

Building on previous work, a phase-preserving bent Laue beam-expanding monochromator was developed with the capability of performing live animal phase contrast dynamic imaging at the Biomedical Imaging and Therapy beamline at the Canadian Light Source. The BioMedical Imaging and Therapy beamlines at the Canadian Light Source are used by many researchers to capture phase-based imaging data. These experiments have so far been limited by the small vertical beam size, requiring vertical scanning of biological samples in order to image their full vertical extent. Previous work has been carried out to develop a bent Laue beam-expanding monochromator for use at these beamlines. However, the first attempts exhibited significant distortion in the diffraction plane, increasing the beam divergence and eliminating the usefulness of the monochromator for phase-related imaging techniques. Recent work has been carried out to more carefully match the polychromatic and geometric focal lengths in a so-called ‘magic condition’ that preserves the divergence of the beam and enables full-field phase-based imaging techniques. The new experimental parameters, namely asymmetry and Bragg angles, were evaluated by analysing knife-edge and in-line phase images to determine the effect on beam divergence in both vertical and horizontal directions, using the flat Bragg double-crystal monochromator at the beamline as a baseline. The results show that by using the magic condition, the difference between the two monochromator types is less than 10% in the diffraction plane. Phase fringes visible in test images of a biological sample demonstrate that this difference is small enough to enable in-line phase imaging, despite operating at a sub-optimal energy for the wafer and asymmetry angle that was used

A macroscopic model to simulate the mechanically induced martensitic transformation in metastable austenitic stainless steels

International Nuclear Information System (INIS)

Perdahcıoğlu, E.S.; Geijselaers, H.J.M.

2012-01-01

Mechanically induced martensitic transformation and the associated transformation plasticity phenomena in austenitic stainless steels are studied. The mechanisms responsible for the transformation are investigated and put into perspective based on experimental evidence. The stress and strain partitioning into the austenite and martensite phases are formulated using a mean-field homogenization approach. At this intermediate length-scale the average stress in the austenite phase is computed and utilized to compute the mechanical driving force resolved in the material. The amount of transformation and the transformation plasticity is derived as a function of the driving force. The mechanical response of the material is obtained by combining the homogenization and the transformation models. The model is verified by mechanical tests under biaxial loading conditions during which different transformation rates are observed. As a final verification of the model, a bending test is used which manifests the stress-state dependency of the transformation.

Influence of Ti on the Hot Ductility of High-manganese Austenitic Steels

Science.gov (United States)

Liu, Hongbo; Liu, Jianhua; Wu, Bowei; Su, Xiaofeng; Li, Shiqi; Ding, Hao

2017-07-01

The influence of Ti addition ( 0.10 wt%) on hot ductility of as-cast high-manganese austenitic steels has been examined over the temperature range 650-1,250 °C under a constant strain rate of 10-3 s-1 using Gleeble3500 thermal simulation testing machine. The fracture surfaces and particles precipitated at different tensile temperatures were characterized by means of scanning electron microscope and X-ray energy dispersive spectrometry (SEM-EDS). Hot ductility as a function of reduction curves shows that adding 0.10 wt% Ti made the ductility worse in the almost entire range of testing temperatures. The phases' equilibrium diagrams of precipitates in Ti-bearing high-Mn austenitic steel were calculated by the Thermo-Calc software. The calculation result shows that 0.1 wt% Ti addition would cause Ti(C,N) precipitated at 1,499 °C, which is higher than the liquidus temperature of high-Mn austenitic steel. It indicated that Ti(C,N) particles start forming in the liquid high-Mn austenitic steel. The SEM-EDS results show that Ti(C,N) and TiC particles could be found along the austenite grain boundaries or at triple junction, and they would accelerate the extension of the cracks along the grain boundaries.

Improved ductility of a transformation-induced-plasticity steel by nanoscale austenite lamellae

Energy Technology Data Exchange (ETDEWEB)

Shen, Y.F., E-mail: shenyf@smm.neu.edu.cn [Key Laboratory for Anisotropy and Texture of Materials (MOE), School of Materials and Metallurgy, Northeastern University, Shenyang 110004 (China); Liu, Y.D. [Key Laboratory for Anisotropy and Texture of Materials (MOE), School of Materials and Metallurgy, Northeastern University, Shenyang 110004 (China); Sun, X. [Pacific Northwest National Laboratory, PO Box 999, Richland, WA 99352 (United States); Wang, Y.D.; Zuo, L. [Key Laboratory for Anisotropy and Texture of Materials (MOE), School of Materials and Metallurgy, Northeastern University, Shenyang 110004 (China); Misra, R.D.K. [Laboratory for Excellence in Advanced Steel Research, Center for Structural and Functional Materials, Institute for Materials Research and Innovation, University of Louisiana at Lafayette, P.O. Box 44130, Lafayette, LA 70504 (United States)

2013-10-20

TRIP (transformation-induced-plasticity) steel with a chemical composition of 0.19C–0.30Si–1.76Mn–1.52Al (weight percentage, wt%) have been treated by intercritical annealing and austempering process. The microstructures of the obtained samples consist of the ferrite, the bainite and the retained austenite phase. The volume fractions of the bainite and the retained austenite gradually increase with increasing the temperature of the intercritical annealing. Consequently, significantly different mechanical properties have been observed. The sample annealed at 820 °C (for 120 s) and partitioned at 400 °C (for 300 s) has the best combination of ultimate tensile strength (UTS, ∼682 MPa) and elongation to failure (∼70%) with about 26% of bainitic ferrite plates and 17% retained austenite in its microstructure. The retained austenite has a lamella morphology with 100‒300 nm in thickness and 2‒5 µm in length. On the contrary, the sample annealed at the same temperature without the partitioning process yields much lower UTS and elongation to failure.

An application of the eddy-current method for inspections of austenitic cladding

International Nuclear Information System (INIS)

Kubis, S.; Herka, M.; Krajcovic, R.

1999-01-01

The application of the eddy-current method for inspections of austenitic cladding by means of pancake probes. Phase and amplitude characteristics of artificial defects and anticipated interference signals. Optimization of inspection parameters

Effect of nitrogen and boron on weldability of austenitic stainless steels

International Nuclear Information System (INIS)

Bhaduri, A.K.; Albert, S.K.; Srinivasan, G.; Divya, M.; Das, C.R.

2012-01-01

Hot cracking is a major problem in the welding of austenitic stainless steels, particularly the fully austenitic grades. A group of alloys of enhanced-nitrogen 316LN austenitic stainless steel is being developed for structural components of the Indian Fast Reactor programme. Studying the hot cracking behaviour of this nitrogen-enhanced austenitic stainless steel is an important consideration during welding, as this material solidifies without any residual delta ferrite in the primary austenitic mode. Nitrogen has potent effects on the solidification microstructure, and hence has a strong influence on the hot cracking behaviour. Different heats of this material were investigated, which included fully austenitic stainless steels containing 0.070.22 wt% nitrogen. Also, borated austenitic stainless steels, such as type 304B4, have been widely used in the nuclear applications primarily due to its higher neutron absorption efficiency. Weldability is a major concern for this alloy due to the formation of low melting eutectic phase that is enriched with iron, chromium, molybdenum and boron. Fully austenitic stainless steels are prone to hot cracking during welding in the absence of a small amount of delta ferrite, especially for compositions rich in elements like boron that increases the tendency to form low melting eutectics. Detailed weldability investigations were carried out on a grade 304B4 stainless steel containing 1.3 wt% boron. Among the many approaches that have been used to determine the hot cracking susceptibility of different alloys, Variable-Restraint (Varestraint) weld test and Hot Ductility (Gleeble) tests are commonly used to evaluate the weldability of austenitic alloys. Hence, investigations on these materials consisted of detailed metallurgical characterization and weldability studies that included studying both the fusion zone and liquation cracking susceptibility, using Varestraint tests at 0.254.0%, strain levels and Gleeble (thermo

Heat treatment giving a stable high temperature micro-structure in cast austenitic stainless steel

Science.gov (United States)

Anton, Donald L.; Lemkey, Franklin D.

1988-01-01

A novel micro-structure developed in a cast austenitic stainless steel alloy and a heat treatment thereof are disclosed. The alloy is based on a multicomponent Fe-Cr-Mn-Mo-Si-Nb-C system consisting of an austenitic iron solid solution (.gamma.) matrix reinforced by finely dispersed carbide phases and a heat treatment to produce the micro-structure. The heat treatment includes a prebraze heat treatment followed by a three stage braze cycle heat treatment.

A review of compatibility of IFR fuel and austenitic stainless steel

International Nuclear Information System (INIS)

Keiser, D.D. Jr.

1996-01-01

Interdiffusion experiments have been conducted to investigate the compatibility of various austenitic stainless steels with U-Pu-Zr alloys, which are alloys to be employed as fuel for the Integral Fast Reactor being developed by Argonne National Laboratory. These tests have also studied the compatibility of austenitic stainless steels with fission products, like the minor actinides (Np and Am) and lanthanides (Ce and Nd), that are generated during the fission process in an IFR. This paper compares the results of these investigations in the context of fuel-cladding compatibility in IFR fuel elements, specifically focusing on the relative Interdiffusion behavior of the components and the types of phases that develop based on binary phase diagrams. Results of Interdiffusion tests are assessed in the light of observations derived from post-test examinations of actual irradiated fuel elements

Development of high nickel austenitic steels for the application to fast reactor cores, (I). Alloy design with the aid of the d-electrons concept

International Nuclear Information System (INIS)

Murata, Yoshinori; Morinaga, Masahiko; Yukawa, Natsuo; Ukai, Shigeharu; Nomura, Shigeo; Okuda, Takanari; Harada, Makoto

1999-01-01

The design of high nickel austenitic steels for the core materials of the fast reactors was performed following the d-electrons concept devised on the basis of molecular orbital calculations of transition-metal based alloys. In this design two calculated parameters are mainly utilized. The one is the d-orbital energy level (Md) of alloying transition elements, and the other is the bond order (Bo) that is a measure of the covalent bond strength between atoms. Using the Md-bar - Bo-bar phase stability diagram accurate prediction become possible for the phase stability of the austenite phase and 5% swelling at 140 dpa for nickel ions. Here, Md-bar and Bo-bar are the compositional average of Md and Bo parameters, respectively. On the basis of the phase stability diagram and preliminary experiments, guidelines for the alloy design of carbo-nitrides precipitated high nickel austenitic steels were constructed. Following the guidelines several new austenitic steels were designed for the fast reactors core material. (author)

In situ synchrotron X-ray diffraction studies of the effect of microstructure on tensile behavior and retained austenite stability of thermo-mechanically processed transformation induced plasticity steel

Energy Technology Data Exchange (ETDEWEB)

Yan, Kun [School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, NSW 2522 (Australia); Liss, Klaus-Dieter [School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, NSW 2522 (Australia); Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234 (Australia); Timokhina, Ilana B. [Institute for Frontier Materials, Deakin University, Geelong, VIC 3217 (Australia); Pereloma, Elena V., E-mail: elenap@uow.edu.au [School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, NSW 2522 (Australia)

2016-04-26

Transmission electron microscopy and in situ synchrotron high-energy X-ray diffraction were used to investigate the martensitic transformation and lattice strains under uniaxial tensile loading of Fe-Mn-Si-C-Nb-Mo-Al Transformation Induced Plasticity (TRIP) steel subjected to different thermo-mechanical processing schedules. In contrast with most of the diffraction analysis of TRIP steels reported previously, the diffraction peaks from the martensite phase were separated from the peaks of the ferrite-bainite α-matrix. The volume fraction of retained γ-austenite, as well as the lattice strain, were determined from the diffraction patterns recorded during tensile deformation. Although significant austenite to martensite transformation starts around the macroscopic yield stress, some austenite grains had already experienced martensitic transformation. Hooke’s Law was used to calculate the phase stress of each phase from their lattice strain. The ferrite-bainite α-matrix was observed to yield earlier than austenite and martensite. The discrepancy between integrated phase stresses and experimental macroscopic stress is about 300 MPa. A small increase in carbon concentration in retained austenite at the early stage of deformation was detected, but with further straining a continuous slight decrease in carbon content occurred, indicating that mechanical stability factors, such as grain size, morphology and orientation of the retained austenite, played an important role during the retained austenite to martensite transformation.

Overview of Strategies for High-Temperature Creep and Oxidation Resistance of Alumina-Forming Austenitic Stainless Steels

Science.gov (United States)

Yamamoto, Y.; Brady, M. P.; Santella, M. L.; Bei, H.; Maziasz, P. J.; Pint, B. A.

2011-04-01

A family of creep-resistant, alumina-forming austenitic (AFA) stainless steel alloys is under development for structural use in fossil energy conversion and combustion system applications. The AFA alloys developed to date exhibit comparable creep-rupture lives to state-of-the-art advanced austenitic alloys, and superior oxidation resistance in the ~923 K to 1173 K (650 °C to 900 °C) temperature range due to the formation of a protective Al2O3 scale rather than the Cr2O3 scales that form on conventional stainless steel alloys. This article overviews the alloy design approaches used to obtain high-temperature creep strength in AFA alloys via considerations of phase equilibrium from thermodynamic calculations as well as microstructure characterization. Strengthening precipitates under evaluation include MC-type carbides or intermetallic phases such as NiAl-B2, Fe2(Mo,Nb)-Laves, Ni3Al-L12, etc. in the austenitic single-phase matrix. Creep, tensile, and oxidation properties of the AFA alloys are discussed relative to compositional and microstructural factors.

Microstructure Evolution and Mechanical Behavior of a CMnSiAl TRIP Steel Subjected to Partial Austenitization Along with Quenching and Partitioning Treatment

Science.gov (United States)

Kong, H.; Chao, Q.; Cai, M. H.; Pavlina, E. J.; Rolfe, B.; Hodgson, P. D.; Beladi, H.

2018-02-01

The present study investigated the microstructure evolution and mechanical behavior in a low carbon CMnSiAl transformation-induced plasticity (TRIP) steel, which was subjected to a partial austenitization at 1183 K (910 °C) followed by one-step quenching and partitioning (Q&P) treatment at different isothermal holding temperatures of [533 K to 593 K (260 °C to 320 °C)]. This thermal treatment led to the formation of a multi-phase microstructure consisting of ferrite, tempered martensite, bainitic ferrite, fresh martensite, and retained austenite, offering a superior work-hardening behavior compared with the dual-phase microstructure (i.e., ferrite and martensite) formed after partial austenitization followed by water quenching. The carbon enrichment in retained austenite was related to not only the carbon partitioning during the isothermal holding process, but also the carbon enrichment during the partial austenitization and rapid cooling processes, which has broadened our knowledge of carbon partitioning mechanism in conventional Q&P process.

Electron microscopy and plastic deformation of industrial austenitic stainless steels

International Nuclear Information System (INIS)

Thomas, Barry

1976-01-01

The different mechanisms of plastic deformation observed in austenitic stainless steels are described and the role of transmission electron microscopy in the elucidation of the mechanisms is presented. At temperatures below 0,5Tm, different variants of dislocation glide are competitive: slip of perfect and partial dislocations, mechanical twinning and strain-induced phase transformations. The predominance of one or other of these mechanisms can be rationalized in terms of the temperature and composition dependence of the stacking fault energy and the thermodynamic stability of the austenite. At temperatures above 0,5Tm dislocation climb and diffusion of point defects become increasingly important and at these temperatures recovery, recrystallization and precipitation can also occur during deformation [fr

Deformation mechanisms induced under high cycle fatigue tests in a metastable austenitic stainless steel

Energy Technology Data Exchange (ETDEWEB)

Roa, J.J., E-mail: joan.josep.roa@upc.edu [CIEFMA-Departament de Ciència dels Materials i Enginyeria Metallúrgica, ETSEIB, Universitat Politècnica de Catalunya, Avda. Diagonal 647, 08028 Barcelona (Spain); CRnE, Campus Diagonal Sud, Edificio C’, Universitat Politècnica de Catalunya, C/ Pascual i Vila 15, 08028 Barcelona (Spain); Fargas, G. [CIEFMA-Departament de Ciència dels Materials i Enginyeria Metallúrgica, ETSEIB, Universitat Politècnica de Catalunya, Avda. Diagonal 647, 08028 Barcelona (Spain); Jiménez-Piqué, E. [CIEFMA-Departament de Ciència dels Materials i Enginyeria Metallúrgica, ETSEIB, Universitat Politècnica de Catalunya, Avda. Diagonal 647, 08028 Barcelona (Spain); CRnE, Campus Diagonal Sud, Edificio C’, Universitat Politècnica de Catalunya, C/ Pascual i Vila 15, 08028 Barcelona (Spain); Mateo, A. [CIEFMA-Departament de Ciència dels Materials i Enginyeria Metallúrgica, ETSEIB, Universitat Politècnica de Catalunya, Avda. Diagonal 647, 08028 Barcelona (Spain)

2014-03-01

Advanced techniques were used to study the deformation mechanisms induced by fatigue tests in a metastable austenitic stainless steel AISI 301LN. Observations by Atomic Force Microscopy were carried out to study the evolution of a pre-existing martensite platelet at increasing number of cycles. The sub-superficial deformation mechanisms of the austenitic grains were studied considering the cross-section microstructure obtained by Focused Ion Beam and analysed by Scanning Electron Microscopy and Transmission Electron Microscopy. The results revealed no deformation surrounding the pre-existing martensitic platelet during fatigue tests, only the growth on height was observed. Martensite formation was associated with shear bands on austenite, mainly in the {111} plane, and with the activation of the other intersecting austenite {111}〈110〉 slip system. Furthermore, transmission electron microscopy results showed that the nucleation of ε-martensite follows a two stages phase transformation (γ{sub fcc}→ε{sub hcp}→α'{sub bcc})

Grain boundary precipitation in an austenitic stainless steel

International Nuclear Information System (INIS)

Jones, A.R.; Howell, P.R.; Ralph, B.

The precipitation of second phase particles of niobium carbide in an austenitic stainless steel is shown to be considerably influenced by the degree of deformation introduced prior to the ageing treatment. Sites for the nucleation of second phase particles are identified and the importance of one type of nucleation site, extrinsic dislocations, to the evolution of the final boundary precipitate distributions is emphasized. Further, it is shown that the presence of a grain boundary can effect precipitation processes for some considerable distance into the matrix on either side of the boundary. (author)

Case histories of microbiologically influenced corrosion of austenitic stainless steel weldments

International Nuclear Information System (INIS)

Borenstein, S.W.; Buchanan, R.A.; Dowling, N.J.E.

1990-01-01

Microbiologically influenced corrosion (MIC) is initiated or accelerated by microorganisms and is currently recognized as a serious problem affecting the construction and operation of many industrial facilities, including nuclear power plants. The purpose of this paper is to review how biofouling and MIC can occur and discuss current mechanistic theories. A case history of MIC attack in power plants is examined with emphasis on the role of welding and heat treatment variables using laboratory electrochemical analyses. Although MIC can occur on a variety of alloys, pitting corrosion failures of austenitic stainless steels are often associated with weldments. MIC occurs as the result of a consortium of microorganisms colonizing on the metal surface and their variety (fungi, bacteria, algae, mold, and slimes) enables them to form support systems for cross feeding to enhance survival. The metabolic processes influence corrosion behaviour of materials by destroying protective coatings, producing a localized acid environment, creating corrosive deposits, or altering anodic and cathodic reactions. On stainless steels, biofilms destroy the passive oxide film on the surface of the steels and subject them to localized forms of corrosion. Many of the MIC failures in industry result in pitting to austenitic stainless steel weldments. Pitting primarily occurs in the weld metal, heat affected zones, and adjacent to the weld in the base metal. Depending on the conditions of the concentration cell created by the biofilm, either phase of the two-phase duplex stainless steel, austenite or delta ferrite, may be selectively attacked. Theories have been proposed about the mechanism of MIC on austenitic stainless steel and and a general understanding is that some function associated with the biofilm formation directly affects the electrochemical process

Nature of gallium focused ion beam induced phase transformation in 316L austenitic stainless steel

International Nuclear Information System (INIS)

Babu, R. Prasath; Irukuvarghula, S.; Harte, A.; Preuss, M.

2016-01-01

The microstructural evolution and chemistry of the ferrite phase (α), which transforms from the parent austenite phase (γ) of 316L stainless steel during gallium (Ga) ion beam implantation in Focused Ion Beam (FIB) instrument was systematically studied as a function of Ga"+ ion dose and γ grain orientations. The propensity for initiation of γ → α phase transformation was observed to be strongly dependent on the orientation of the γ grain with respect to the ion beam direction and correlates well with the ion channelling differences in the γ orientations studied. Several α variants formed within a single γ orientation and the sputtering rate of the material, after the γ → α transformation, is governed by the orientation of α variants. With increased ion dose, there is an evolution of orientation of the α variants towards a variant of higher Ga"+ channelling. Unique topographical features were observed within each specific γ orientation that can be attributed to the orientation of defects formed during the ion implantation. In most cases, γ and α were related by either Kurdjumov-Sachs (KS) or Nishiyama-Wassermann (NW) orientation relationship (OR) while in few, no known OR's were identified. While our results are consistent with gallium enrichment being the cause for the γ → α phase transformation, some observations also suggest that the strain associated with the presence of gallium atoms in the lattice has a far field stress effect that promotes the phase transformation ahead of gallium penetration.

Image based EFIT simulation for nondestructive ultrasonic testing of austenitic steel

International Nuclear Information System (INIS)

Nakahata, Kazuyuki; Hirose, Sohichi; Schubert, Frank; Koehler, Bernd

2009-01-01

The ultrasonic testing (UT) of an austenitic steel with welds is difficult due to the acoustic anisotropy and local heterogeneity. The ultrasonic wave in the austenitic steel is skewed along crystallographic directions and scattered by weld boundaries. For reliable UT, a straightforward simulation tool to predict the wave propagation is desired. Here a combined method of elastodynamic finite integration technique (EFIT) and digital image processing is developed as a wave simulation tool for UT. The EFIT is a grid-based explicit numerical method and easily treats different boundary conditions which are essential to model wave propagation in heterogeneous materials. In this study, the EFIT formulation in anisotropic and heterogeneous materials is briefly described and an example of a two dimensional simulation of a phased array UT in an austenitic steel bar is demonstrated. In our simulation, a picture of the surface of the steel bar with a V-groove weld is scanned and fed into the image based EFIT modeling. (author)

Austenitic Reversion of Cryo-rolled Ti-Stabilized Austenitic Stainless Steel: High-Resolution EBSD Investigation

Science.gov (United States)

Tiamiyu, A. A.; Odeshi, A. G.; Szpunar, J. A.

2018-02-01

In this study, AISI 321 austenitic stainless steel (ASS) was cryo-rolled and subsequently annealed at 650 and 800 °C to reverse BCC α'-martensite to FCC γ-austenite. The texture evolution associated with the reversion at the selected temperatures was investigated using high-resolution EBSD. After the reversion, TiC precipitates were observed to be more stable in 650 °C-annealed specimens than those reversed at 800 °C. {110} texture was mainly developed in specimens subjected to both annealing temperatures. However, specimens reversed at 650 °C have stronger texture than those annealed at 800 °C, even at the higher annealing time. The strong intensity of {110} texture component is attributed to the ability of AISI 321 ASS to memorize the crystallographic orientation of the deformed austenite, a phenomenon termed texture memory. The development of weaker texture in 800 °C-annealed specimens is attributed to the residual strain relief in grains, dissolution of grain boundary precipitates, and an increase in atomic migration along the grain boundaries. Based on the observed features of the reversed austenite grains and estimation from an existing model, it is suspected that the austenite reversion at 650 and 800 °C undergone diffusional and martensitic shear reversion, respectively.

High temperature strength and aging behavior of 12%Cr-15%Mn austenitic steels

International Nuclear Information System (INIS)

Miyahara, Kazuya; Bae, Dong-Su; Sakai, Hidenori; Hosoi, Yuzo

1993-01-01

High Mn-Cr austenitic steels are still considered to be an important high temperature structural material from the point of view of reduced radio-activation. The objective of the present study is to make a fundamental research of mechanical properties and microstructure of 12%Cr-15%Mn austenitic steels. Especially the effects of alloying elements of V and Ti on the mechanical properties and microstructure evolution of high Mn-Cr steels were studied. Precipitation behaviors of carbides, nitrides and σ phase are investigated and their remarkable effects on the high temperature strength are found. The addition of V was very effective for strengthening the materials with the precipitation of fine VN. Ti was also found to be beneficial for the improvement of high temperature strength properties. The results of high temperature strengths of the 12Cr-15Mn austenitic steels were compared with those of the other candidate and/or reference materials, for example, JFMS (modified 9Cr-2Mo ferritic stainless steel) and JPCAs (modified 316 austenitic stainless steels). (author)

The stability of retained austenite at different locations during straining of I&Q&P steel

Energy Technology Data Exchange (ETDEWEB)

Song, Chenghao [School of Materials Science and Engineering, University of Science & Technology Beijing, 30 Xueyuan Road, Haidian District, Beijing 100083 (China); Yu, Hao, E-mail: yuhao@ustb.edu.cn [School of Materials Science and Engineering, University of Science & Technology Beijing, 30 Xueyuan Road, Haidian District, Beijing 100083 (China); Li, Lili; Zhou, Tao; Lu, Jun [School of Materials Science and Engineering, University of Science & Technology Beijing, 30 Xueyuan Road, Haidian District, Beijing 100083 (China); Liu, Xihui [Qingzhou Construction Quality and Safety Supervision Station, Shandong 262500 (China)

2016-07-18

This paper presents a detailed investigation of the transformation behavior of retained austenite at different locations of intercritical heating, quenching and partitioning (I&Q&P) steel. The consumption of retained austenite at different strains is investigated by X-ray diffraction (XRD). Results indicate that retained austenite can transform into martensite progressively during the whole deformation process, which is in favor of a good combination of strength and ductility, contributing to a high product of strength and elongation (PSE) of 31.9 GPa%. The transformation characteristics of retained austenite at different locations after different strains are characterized by electron back scattered diffraction (EBSD) and transmission electron microscopy (TEM). Results show that the transformation preferentially occurs in the retained austenite at ferrite grain boundaries, subsequently the one within ferrite grains (at 10% strain) and eventually the one between martensite laths (at 15% strain). In FCC phase, the average local misorientations are 0.547° and 0.674° at 5% and 10% strain, respectively; however, the values are not more than 0.7° at 15% and 20% strain due to the TRIP effect. For the retained austenite within ferrite grains, the interior part preferentially transforms into twin martensite, while the interface still remains due to alloying elements segregation.

Localized corrosion and stress corrosion cracking behavior of austenitic stainless steel weldments containing retained ferrite. Annual progress report, June 1, 1978--March 31, 1979

International Nuclear Information System (INIS)

Savage, W.F.; Duquette, D.J.

1979-03-01

Localized corrosion and stress corrosion cracking experiments have been performed on single phase 304 stainless steel alloys and autogeneous weldments containing retained delta ferrite as a second phase. The results of the pitting experiments show that the pressure of delta ferrite decreases localized corrosion resistance with pits initiating preferentially at delta ferrite--gamma austenite interphase boundaries. This increased susceptibility is reversible with elevated temperature heat treatments which revert the metastable ferrite phase to the equilibrium austenite phase

Comprehensive Deformation Analysis of a Newly Designed Ni-Free Duplex Stainless Steel with Enhanced Plasticity by Optimizing Austenite Stability

Science.gov (United States)

Moallemi, Mohammad; Zarei-Hanzaki, Abbas; Eskandari, Mostafa; Burrows, Andrew; Alimadadi, Hossein

2017-08-01

A new metastable Ni-free duplex stainless steel has been designed with superior plasticity by optimizing austenite stability using thermodynamic calculations of stacking fault energy and with reference to literature findings. Several characterization methods comprising optical microscopy, magnetic phase measurements, X-ray diffraction (XRD) and electron backscattered diffraction were employed to study the plastic deformation behavior and to identify the operating plasticity mechanisms. The results obtained show that the newly designed duplex alloy exhibits some extraordinary mechanical properties, including an ultimate tensile strength of 900 MPa and elongation to fracture of 94 pct due to the synergistic effects of transformation-induced plasticity and twinning-induced plasticity. The deformation mechanism of austenite is complex and includes deformation banding, strain-induced martensite formation, and deformation-induced twinning, while the ferrite phase mainly deforms by dislocation slip. Texture analysis indicates that the Copper and Rotated Brass textures in austenite (FCC phase) and {001} texture in ferrite and martensite (BCC phases) are the main active components during tensile deformation. The predominance of these components is logically related to the strain-induced martensite and/or twin formation.

Hydrogen embrittlement of austenitic stainless steels revealed by deformation microstructures and strain-induced creation of vacancies

International Nuclear Information System (INIS)

Hatano, M.; Fujinami, M.; Arai, K.; Fujii, H.; Nagumo, M.

2014-01-01

Hydrogen embrittlement of austenitic stainless steels has been examined with respect to deformation microstructures and lattice defects created during plastic deformation. Two types of austenitic stainless steels, SUS 304 and SUS 316L, uniformly hydrogen-precharged to 30 mass ppm in a high-pressure hydrogen environment, are subjected to tensile straining at room temperature. A substantial reduction of tensile ductility appears in hydrogen-charged SUS 304 and the onset of fracture is likely due to plastic instability. Fractographic features show involvement of plasticity throughout the crack path, implying the degradation of the austenitic phase. Electron backscatter diffraction analyses revealed prominent strain localization enhanced by hydrogen in SUS 304. Deformation microstructures of hydrogen-charged SUS 304 were characterized by the formation of high densities of fine stacking faults and ε-martensite, while tangled dislocations prevailed in SUS 316L. Positron lifetime measurements have revealed for the first time hydrogen-enhanced creation of strain-induced vacancies rather than dislocations in the austenitic phase and more clustering of vacancies in SUS 304 than in SUS 316L. Embrittlement and its mechanism are ascribed to the decrease in stacking fault energies resulting in strain localization and hydrogen-enhanced creation of strain-induced vacancies, leading to premature fracture in a similar way to that proposed for ferritic steels

Qualification of phased array ultrasonic examination on T-joint weld of austenitic stainless steel for ITER vacuum vessel

Energy Technology Data Exchange (ETDEWEB)

Kim, G.H. [ITER Korea, National Fusion Research Institute, Daejeon 305-333 (Korea, Republic of); Park, C.K., E-mail: love879@hanmail.net [ITER Korea, National Fusion Research Institute, Daejeon 305-333 (Korea, Republic of); Jin, S.W.; Kim, H.S.; Hong, K.H.; Lee, Y.J.; Ahn, H.J.; Chung, W. [ITER Korea, National Fusion Research Institute, Daejeon 305-333 (Korea, Republic of); Jung, Y.H.; Roh, B.R. [Hyundai Heavy Industries Co. Ltd., Ulsan 682-792 (Korea, Republic of); Sa, J.W.; Choi, C.H. [ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067 St. Paul Lez Durance Cedex (France)

2016-11-01

Highlights: • PAUT techniques has been developed by Hyundai Heavy Industries Co., LTD (HHI) and Korea Domestic Agency (KODA) to verify and settle down instrument calibration, test procedures, image processing, and so on. As the first step of development for PAUT technique, Several dozens of qualification blocks with artificial defects, which are parallel side drilled hole, embedded lack of fusion, embedded repair weld notch, and so on, have been designed and fabricated to simulate all potential defects during welding process. Real UT qualification group-1 for T-joint weld was successfully conducted in front of ANB inspector. • In this paper, remarkable progresses of UT qualification are presented for ITER vacuum vessel. - Abstract: Full penetration welding and 100% volumetric examination are required for all welds of pressure retaining parts of the ITER Vacuum Vessel (VV) according to RCC-MR Code and French Order of Nuclear Pressure Equipment (ESPN). The NDE requirement is one of important technical issues because radiographic examination (RT) is not applicable to many welding joints. Therefore the ultrasonic examination (UT) has been selected as an alternative method. Generally the UT on the austenitic welds is regarded as a great challenge due to the high attenuation and dispersion of the ultrasonic signal. In this paper, Phased array ultrasonic examination (PAUT) has been introduced on double sided T-shape austenitic welds of the ITER VV as a major NDE method as well as RT. Several dozens of qualification blocks with artificial defects, which are parallel side drilled hole, embedded lack of fusion, embedded repair weld notch, embedded parallel vertical notch, and so on, have been designed and fabricated to simulate all potential defects during welding process. PAUT techniques on the thick austenitic welds have been developed taking into account the acceptance criteria. Test procedure including calibration of equipment is derived and qualified through

Precipitation Mechanism of Sigma Phase in Super Duplex Stainless Steels

Science.gov (United States)

Nakade, Katsuyuki; Kuroda, Toshio

The influence of alloying elements on the precipitation behavior of sigma (σ) phase was investigated for conventional SAF2205 and SAF2507 super duplex stainless steel. Time-Temperature-Precipitation (T-T-P) diagram of sigma phase of SAF2507 were shifted toward to shorter times compared to SAF2205. The precipitation of sigma phase was accelerated with increasing Cr and Mo concentration. According to the microstructure observation, the sigma phase began to precipitate at ferrite (α) ⁄ austenite (γ) phase boundaries and grew into ferrite for SAF2507 and SAF2205 steel. In the as-received condition, Cr and Mo concentration in ferrite was clearly higher than that in austenite. Especially, it was found that Mo concentration in ferrite of SAF2507 was higher than that in ferrite of SAF2205. The result of EPMA-measurement showed that sigma phase was mainly Fe-Cr-Mo intermetallic compound and Mo was significantly enriched into sigma phase. The difference of Mo concentration in ferrite significantly affected to the sigma phase precipitation. The secondary austenite formation was also induced by sigma phase precipitation. Cr and Mo were ejected to the remained ferrite ⁄ austenite phase boundaries by secondary austenite formation. Consequently, sigma phase precipitation was more accelerated by the reheating.

Discontinuous precipitation in a nickel-free high nitrogen austenitic stainless steel on solution nitriding

DEFF Research Database (Denmark)

Mohammadzadeh, Roghayeh; Akbari, Alireza; Grumsen, Flemming Bjerg

2017-01-01

Chromium-rich nitride precipitates in production of nickel-free austenitic stainless steel plates via pressurised solution nitriding of Fe–22.7Cr–2.4Mo ferritic stainless steel at 1473 K (1200 °C) under a nitrogen gas atmosphere was investigated. The microstructure, chemical and phase composition......, morphology and crystallographic orientation between the resulted austenite and precipitates were investigated using optical microscopy, X-ray Diffraction (XRD), Scanning and Transmission Electron Microscopy (TEM) and Electron Back Scatter Diffraction (EBSD). On prolonged nitriding, Chromium-rich nitride...... precipitates were formed firstly close to the surface and later throughout the sample with austenitic structure. Chromium-rich nitride precipitates with a rod or strip-like morphology was developed by a discontinuous cellular precipitation mechanism. STEM-EDS analysis demonstrated partitioning of metallic...

Characterization of microstructure and texture across dissimilar super duplex/austenitic stainless steel weldment joint by super duplex filler metal

Energy Technology Data Exchange (ETDEWEB)

Eghlimi, Abbas, E-mail: a.eghlimi@ma.iut.ac.ir [Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Shamanian, Morteza [Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Eskandarian, Masoomeh [Department of Materials Engineering, Shiraz University, Shiraz 71348-51154 (Iran, Islamic Republic of); Zabolian, Azam [Department of Natural Resources, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Szpunar, Jerzy A. [Department of Mechanical Engineering, University of Saskatchewan, Saskatoon SK S7N 5A9 (Canada)

2015-08-15

In the present paper, microstructural changes across an as-welded dissimilar austenitic/duplex stainless steel couple welded by a super duplex stainless steel filler metal using gas tungsten arc welding process is characterized with optical microscopy and electron back-scattered diffraction techniques. Accordingly, variations of microstructure, texture, and grain boundary character distribution of base metals, heat affected zones, and weld metal were investigated. The results showed that the weld metal, which was composed of Widmanstätten austenite side-plates and allotriomorphic grain boundary austenite morphologies, had the weakest texture and was dominated by low angle boundaries. The welding process increased the ferrite content but decreased the texture intensity at the heat affected zone of the super duplex stainless steel base metal. In addition, through partial ferritization, it changed the morphology of elongated grains of the rolled microstructure to twinned partially transformed austenite plateaus scattered between ferrite textured colonies. However, the texture of the austenitic stainless steel heat affected zone was strengthened via encouraging recrystallization and formation of annealing twins. At both interfaces, an increase in the special character coincident site lattice boundaries of the primary phase as well as a strong texture with <100> orientation, mainly of Goss component, was observed. - Graphical abstract: Display Omitted - Highlights: • Weld metal showed local orientation at microscale but random texture at macroscale. • Intensification of <100> orientated grains was observed adjacent to the fusion lines. • The austenite texture was weaker than that of the ferrite in all duplex regions. • Welding caused twinned partially transformed austenites to form at SDSS HAZ. • At both interfaces, the ratio of special CSL boundaries of the primary phase increased.

Study of the Sensitization on the Grain Boundary in Austenitic Stainless Steel Aisi 316

Directory of Open Access Journals (Sweden)

Kocsisová Edina

2014-12-01

Full Text Available Intergranular corrosion (IGC is one of the major problems in austenitic stainless steels. This type of corrosion is caused by precipitation of secondary phases on grain boundaries (GB. Precipitation of the secondary phases can lead to formation of chromium depleted zones in the vicinity of grain boundaries. Mount of the sensitization of material is characterized by the degree of sensitization (DOS. Austenitic stainless steel AISI 316 as experimental material had been chosen. The samples for the study of sensitization were solution annealed on 1100 °C for 60 min followed by water quenching and then sensitization by isothermal annealing on 700 °C and 650 °C with holding time from 15 to 600 min. Transmission electron microscopy (TEM was used for identification of secondary phases. Electron backscattered diffraction (EBSD was applied for characterization of grain boundary structure as one of the factors which influences on DOS.

New kaolinite phases expanded through intercalation with potassium acetate

International Nuclear Information System (INIS)

Frost, R.L.; Kristof, J.; Kloprogge, J.T.

1998-01-01

Full text: Changes in the hydroxyl surfaces of potassium acetate-intercalated kaolinite have been studied over the ambient to predehydroxylation temperature range using a combination of X-ray diffraction and Raman spectroscopy. Upon intercalation, the kaolinite expanded along the c-axis direction to 13.88 Angstroms. Upon heating the intercalation complex over the 50 to 300 deg C range, X-ray diffraction shows the existence of three additional intercalation phases with d-spacings of 9.09, 9.60, and 11.47 Angstroms. The amount of each phase is temperature dependent. These expansions are reversible and upon cooling the intercalation complex returned to its original spacing. The 13.88 Angstroms phase only existed in the presence of water. It is proposed that the expanded kaolinite intercalation phases result from the orientation of the acetate within the intercalation complex. The Raman spectra of the hydroxyl-stretching region (Frost and van der Gaast, 1997) of potassium acetate-intercalated kaolinite has been obtained under an atmosphere of both air and nitrogen using a thermal stage over the 25 to 300 deg C temperature range (Johansson et al., 1998). Raman spectra of the C-C, C=O stretching and O-C-O bending modes show that at least two types of acetate are present in the intercalation complex. These are assigned to two different orientations of the acetate. At 25 deg C, a new band at 3606 cm -1 attributed to the inner surface hydroxyl hydrogen bonded to the acetate ion is observed with a concomitant loss of intensity in the bands attributed to the inner surface hydroxyls (Frost and Kristof, 1997, Frost et al.,1997). Heating the intercalation complex to 50 deg C results in two hydroxyl-stretching frequencies at 3594 and 3604 cm -1 . This change in frequencies is ascribed to phase changes of the potassium acetate-intercalated kaolinite. At 100 deg C, the bands shift to 3600 and 3613 cm -1 . These shifts in frequencies are assigned to new kaolinite expanded phases. At

Environmental Degradation of Dissimilar Austenitic 316L and Duplex 2205 Stainless Steels Welded Joints

Directory of Open Access Journals (Sweden)

Topolska S.

2017-12-01

Full Text Available The paper describes structure and properties of dissimilar stainless steels welded joints between duplex 2205 and austenitic 316L steels. Investigations were focused on environmentally assisted cracking of welded joints. The susceptibility to stress corrosion cracking (SCC and hydrogen embrittlement was determined in slow strain rate tests (SSRT with the strain rate of 2.2 × 10−6 s−1. Chloride-inducted SCC was determined in the 35% boiling water solution of MgCl2 environment at 125°C. Hydrogen assisted SCC tests were performed in synthetic sea water under cathodic polarization condition. It was shown that place of the lowest resistance to chloride stress corrosion cracking is heat affected zone at duplex steel side of dissimilar joins. That phenomenon was connected with undesirable structure of HAZ comprising of large fractions of ferrite grains with acicular austenite phase. Hydrogen assisted SCC tests showed significant reduction in ductility of duplex 2205 steel while austenitic 316L steel remains almost immune to degradation processes. SSR tests of dissimilar welded joints revealed a fracture in the area of austenitic steel.

Mechanisms of ultrafine-grained austenite formation under different isochronal conditions in a cold-rolled metastable stainless steel

Energy Technology Data Exchange (ETDEWEB)

Celada-Casero, C., E-mail: c.celada@cenim.csic.es [MATERALIA group, Dpt. of Physical Metallurgy, Centro Nacional de Investigaciones Metalúrgicas (CENIM-CSIC), Av. Gregorio del Amo 8, 28040 Madrid (Spain); Huang, B.M. [National Taiwan University, Dpt. of Materials Science and Engineering, 1 Roosvelt Road, Section 4, 10617 Taipei, Taiwan, ROC (China); Aranda, M.M. [MATERALIA group, Dpt. of Physical Metallurgy, Centro Nacional de Investigaciones Metalúrgicas (CENIM-CSIC), Av. Gregorio del Amo 8, 28040 Madrid (Spain); Yang, J.-R. [National Taiwan University, Dpt. of Materials Science and Engineering, 1 Roosvelt Road, Section 4, 10617 Taipei, Taiwan, ROC (China); Martin, D. San [MATERALIA group, Dpt. of Physical Metallurgy, Centro Nacional de Investigaciones Metalúrgicas (CENIM-CSIC), Av. Gregorio del Amo 8, 28040 Madrid (Spain)

2016-08-15

The primary objective of this work is to obtain fundamental insights on phase transformations, with focus on the reaustenitization process (α′→γ transformation), of a cold-rolled (CR) semi-austenitic metastable stainless steel upon different isochronal conditions (0.1, 1, 10 and 100 °C/s). For this purpose, an exhaustive microstructural characterization has been performed by using complementary experimental such as scanning and transmission electron microscopy (SEM and TEM), electron backscattered diffraction (EBSD), electron probe microanalysis (EPMA), micro-hardness Vickers and magnetization measurements. It has been detected that all microstructural changes shift to higher temperatures as the heating rate increases. The reaustenitization occurs in two-steps for all heating rates, which is attributed to the chemical banding present in the CR state. The α′→γ transformation is controlled by the migration of substitutional alloying elements across the austenite/martensite (γ/α′) interface, which finally leads to ultrafine-grained reaustenitized microstructures (440–280 nm). The morphology of the martensite phase in the CR state has been found to be the responsible for such a grain refinement, along with the presence of χ-phase and nanometric Ni{sub 3}(Ti,Al) precipitates that pin the austenite grain growth, especially upon slowly heating at 0.1 °C/s. - Highlights: •Ultrafine-grained austenite structures are obtained isochronally at 0.1–100 °C/s •The α′→γ transformation occurs in two steps due to the initial chemical banding •A diffusional mechanism governs the α′→γ transformation for all heating rates •The dislocation-cell-type of martensite promotes a diffusional mechanism •Precipitates located at α′/γ interfaces hinder the austenite growth.

The effect of cooling rate and austenite grain size on the austenite to ferrite transformation temperature and different ferrite morphologies in microalloyed steels

International Nuclear Information System (INIS)

Esmailian, M.

2010-01-01

The effect of different austenite grain size and different cooling rates on the austenite to ferrite transformation temperature and different ferrite morphologies in one Nb-microalloyed high strength low alloy steel has been investigated. Three different austenite grain sizes were selected and cooled at two different cooling rates for obtaining austenite to ferrite transformation temperature. Moreover, samples with specific austenite grain size have been quenched, partially, for investigation on the microstructural evolution. In order to assess the influence of austenite grain size on the ferrite transformation temperature, a temperature differences method is established and found to be a good way for detection of austenite to ferrite, pearlite and sometimes other ferrite morphologies transformation temperatures. The results obtained in this way show that increasing of austenite grain size and cooling rate has a significant influence on decreasing of the ferrite transformation temperature. Micrographs of different ferrite morphologies show that at high temperatures, where diffusion rates are higher, grain boundary ferrite nucleates. As the temperature is lowered and the driving force for ferrite formation increases, intragranular sites inside the austenite grains become operative as nucleation sites and suppress the grain boundary ferrite growth. The results indicate that increasing the austenite grain size increases the rate and volume fraction of intragranular ferrite in two different cooling rates. Moreover, by increasing of cooling rate, the austenite to ferrite transformation temperature decreases and volume fraction of intragranular ferrite increases.

Model Predictive Control of the Exit Part Temperature for an Austenitization Furnace

Directory of Open Access Journals (Sweden)

Hari S. Ganesh

2016-12-01

Full Text Available Quench hardening is the process of strengthening and hardening ferrous metals and alloys by heating the material to a specific temperature to form austenite (austenitization, followed by rapid cooling (quenching in water, brine or oil to introduce a hardened phase called martensite. The material is then often tempered to increase toughness, as it may decrease from the quench hardening process. The austenitization process is highly energy-intensive and many of the industrial austenitization furnaces were built and equipped prior to the advent of advanced control strategies and thus use large, sub-optimal amounts of energy. The model computes the energy usage of the furnace and the part temperature profile as a function of time and position within the furnace under temperature feedback control. In this paper, the aforementioned model is used to simulate the furnace for a batch of forty parts under heuristic temperature set points suggested by the operators of the plant. A model predictive control (MPC system is then developed and deployed to control the the part temperature at the furnace exit thereby preventing the parts from overheating. An energy efficiency gain of 5.3 % was obtained under model predictive control compared to operation under heuristic temperature set points tracked by a regulatory control layer.

In Situ Investigation of the Evolution of Lattice Strain and Stresses in Austenite and Martensite During Quenching and Tempering of Steel

DEFF Research Database (Denmark)

Villa, M.; Niessen, F.; Somers, M. A. J.

2018-01-01

Energy dispersive synchrotron X-ray diffraction was applied to investigate in situ the evolution of lattice strains and stresses in austenite and martensite during quenching and tempering of a soft martensitic stainless steel. In one experiment, lattice strains in austenite and martensite were...... measured in situ in the direction perpendicular to the sample surface during an austenitization, quenching, and tempering cycle. In a second experiment, the sin2ψ method was applied in situ during the austenite-to-martensite transformation to distinguish between macro- and phase-specific micro......-stresses and to follow the evolution of these stresses during transformation. Martensite formation evokes compressive stress in austenite that is balanced by tensile stress in martensite. Tempering to 748 K (475 °C) leads to partial relaxation of these stresses. Additionally, data reveal that (elastic) lattice strain...

Laser borided composite layer produced on austenitic 316L steel

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Mikołajczak Daria

2016-12-01

Full Text Available Abstract Austenitic 316L steel is well-known for its good resistance to corrosion and oxidation. Therefore, this material is often used wherever corrosive media or high temperatures are to be expected. The main drawback of this material is very low hardness and low resistance to mechanical wear. In this study, the laser boriding was used in order to improve the wear behavior of this material. As a consequence, a composite surface layer was produced. The microstructure of laser-borided steel was characterized by only two zones: re-melted zone and base material. In the re-melted zone, a composite microstructure, consisting of hard ceramic phases (borides and a soft austenitic matrix, was observed. A significant increase in hardness and wear resistance of such a layer was obtained.

Design of Wear-Resistant Austenitic Steels for Selective Laser Melting

Science.gov (United States)

Lemke, J. N.; Casati, R.; Lecis, N.; Andrianopoli, C.; Varone, A.; Montanari, R.; Vedani, M.

2018-03-01

Type 316L stainless steel feedstock powder was modified by alloying with powders containing carbide/boride-forming elements to create improved wear-resistant austenitic alloys that can be readily processed by Selective Laser Melting. Fe-based alloys with high C, B, V, and Nb contents were thus produced, resulting in a microstructure that consisted of austenitic grains and a significant amount of hard carbides and borides. Heat treatments were performed to modify the carbide distribution and morphology. Optimal hard-phase spheroidization was achieved by annealing the proposed alloys at 1150 °C for 1 hour followed by water quenching. The total increase in hardness of samples containing 20 pct of C/B-rich alloy powder was of 82.7 pct while the wear resistance could be increased by a factor of 6.

Study of Mechanical Features for Low Cycle Fatigue Samples of Metastable Austenitic Steel AISI 321 by Neutron Stress Analysis under Applied Load

CERN Document Server

Taran, Yu V; Eifler, D; Nebel, Th; Schreiber, J

2002-01-01

The elastoplastic properties of the austenitic matrix and martensitic volume areas induced during cyclic tensile-compressive loading of low carbon metastable austenitic stainless steel were studied in an in situ neutron diffraction stress rig experiment on the ENGIN instrument at the ISIS pulsed neutron facility. Samples prepared from the steel AISI 321 annealed at 1050 ^{\\circ}C and quenched in water were subjected to low-cycle fatigue under total-strain control with an amplitude of 1 % at a frequency of 0.5 Hz. Subsequent applied stress?elastic strain responses of the austenitic and martensitic phases were obtained by Rietveld and Le Bail refinements of the neutron diffraction spectra, and were used to determine the elastic constants of the phases as a function of fatigue level. The results of modified refinements accounting for the elastic anisotropy in polycrystalline materials under load are also presented. The residual strains in the austenitic matrix were determined as a function of fatigue cycling, us...

Nondestructive characterization of austenitic stainless steels

International Nuclear Information System (INIS)

Jayakumar, T.; Kumar, Anish

2010-01-01

The paper presents an overview of the non-destructive methodologies developed at the authors' laboratory for characterization of various microstructural features, residual stresses and corrosion in austenitic stainless steels. Various non-destructive evaluation (NDE) parameters such as ultrasonic velocity, ultrasonic attenuation, spectral analysis of the ultrasonic signals, magnetic hysteresis parameters and eddy current amplitude have been used for characterization of grain size, precipitation behaviour, texture, recrystallization, thermomechanical processing, degree of sensitization, formation of martensite from metastable austenite, assessment of residual stresses, degree of sensitization and propensity for intergranular corrosion in different austenitic steels. (author)

Expanded Operational Temperature Range for Space Rated Li-Ion Batteries, Phase II

Data.gov (United States)

National Aeronautics and Space Administration — Quallion's Phase II proposal calls for expanding the nominal operation range of its space rated lithium ion cells, while maintaining their long life capabilities. To...

Precipitation phases at different processes and heat treat ments as well as their effects on the mechanical properties of super-austenitic stainless steel

Science.gov (United States)

Sun, Hunying; Zhou, Zhangjian; Wang, Man; Li, Shaofu; Zhang, Liwei; Zou, Lei

2013-03-01

A new type lCr30Ni30Mo2TiZr super-austenitic stainless steel has been developed. The microstructures, precipitation phases and mechanical properties of the steel under different deformation processes and heat treatment (solution, stabilized treatment) were investigated using X-ray Diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) as well as mechanical tests. The results indicate that coarse carbides such as Cr-rich M23C6, sigma (σ), and little chi (χ) phases were formed in the steel, and large α' -Cr phases were also detected at three joint grain boundaries, and they were promoted by large strain. The precipitate phases were dissolved or transformed to intermetallic phase even at higher elevated temperature, and influenced the mechanical property obviously. These intermetallic compounds seriously reduced elongation of the rolled steel at room temperature and 700 °C, but increased the forged one at 700 °C. Impact absorbed energies of the stabilized specimens were lower than half of that solution status.

The nucleation of austenite in ferritic ductile cast iron

International Nuclear Information System (INIS)

Chou, J.M.; Hon, M.H.; Lee, J.L.

1992-01-01

Austempered ductile cast iron has recently been receiving increasing attention because of its excellent combination of strength and ductility. Since the austenitization process has a significant influence on the mechanical properties of austempered ductile cast iron, several investigations on the nucleation sites of austenite and diffusion paths of carbon from spheroidal graphite have been reported in ferritic ductile cast iron. However, agreement on this subject has not ben reached. The purpose of this paper is to study the preferential nucleation sites of austenite during austenitization at two austenitizing temperatures in ferritic ductile cast iron. An attempt was made to understand the reasons which give rise to preferential austenite nucleation sites. The carbon diffusion paths from spheroidal graphite were also investigated

CRYSTALLOGRAPHIC RELATIONS OF CEMENTITE–AUSTENITE–FERRITE IN THE DIFFUSIVE DECOMPOSITION OF AUSTENITE

Directory of Open Access Journals (Sweden)

BOLSHAKOV V. I.

2016-05-01

Full Text Available Summary. It was made a search for new and more accurate orientation relations between the crystal lattice in the pearlite and bainite austenite decomposition products. Methods. It were used the methods: transmission electron microscopy, the micro-, mathematical matrix and stereographic analysis. The purpose of the research is with theoretical, numerical and experimental methods to set up to a 0.2 degree angular orientation relations between the lattices of ferrite and cementite in the austenite decomposition products in the temperature range 400 ... 700С. Results. It was established a new, refined value for grids in the diffusion decay of γ → α + (α + θ. Practical significance. It was proposed a new oriented dependence and the corresponding double gnomonic projection with poles to planes α and θ phases, which can be used in patterns of crystallographic lattices relations studies at phase transitions, as well as the subsequent modeling of complex physical processes of structure formation in metals and binary systems.

Evolution behavior of nanohardness after thermal-aging and hydrogen-charging on austenite and strain-induced martensite in pre-strained austenitic stainless steel

Science.gov (United States)

Zheng, Yuanyuan; Zhou, Chengshuang; Hong, Yuanjian; Zheng, Jinyang; Zhang, Lin

2018-05-01

Nanoindentation has been used to study the effects of thermal-aging and hydrogen on the mechanical property of the metastable austenitic stainless steel. Thermal-aging at 473 K decreases the nanohardness of austenite, while it increases the nanohardness of strain-induced ɑ‧ martensite. Hydrogen-charging at 473 K increases the nanohardness of austenite, while it decreases the nanohardness of strain-induced ɑ‧ martensite. The opposite effect on austenite and ɑ‧ martensite is first found in the same pre-strained sample. This abnormal evolution behavior of hardness can be attributed to the interaction between dislocation and solute atoms (carbon and hydrogen). Carbon atoms are difficult to move and redistribute in austenite compared with ɑ‧ martensite. Therefore, the difference in the diffusivity of solute atoms between austenite and ɑ‧ martensite may result in the change of hardness.

Hydrogen Absorption Induced Slow Crack Growth in Austenitic Stainless Steels for Petrochemical Pressure Vessel Industries

Directory of Open Access Journals (Sweden)

Ronnie Rusli

2011-05-01

Full Text Available Type 304Land type 309 austenitic stainless steels were tested either by exposed to gaseous hydrogen or undergoing polarized cathodic charging. Slow crack growth by straining was observed in type 304L, and the formation of α‘ martensite was indicated to be precursor for such cracking. Gross plastic deformation was observed at the tip of the notch, and a single crack grew slowly from this region in a direction approximately perpendicular to the tensile axis. Martensite formation is not a necessary condition for hydrogen embrittlement in the austenitic phase.

Boron content effect on the high-temperature plasticity of corrosion resistant low-carbon austenite type steels

International Nuclear Information System (INIS)

Gol'dshtejn, Ya.E.; Shmatko, M.N.; Chuvatina, S.N.

1976-01-01

With the concept that the state of grain and subgrain boundaries influences the hot plasticity of corrosion resistant steel as a starting point, the study was undertaken of the effect of boron microalloying up on the intergranular strength and of the action boron exerts upon the distribution (redistribution) of other phases present in austenitic 03Kh16N14M3 steels. An electron microscope study of the composition of redundant phases and that of the fine structure of steel have shown the effect of small additions of boron upon the hot plasticity of steel to be linked directly to its influence upon austenite disintegration and the precipitation along the boundaries of crystals of redundant phases in the course of hot plastic deformation. The action of boron upon the process plasticity of steel depends on the temperature and the rate of deformation which govern the kinetics of the precipitation of the redundant phases

Diagnostic experimental results on the hydrogen embrittlement of austenitic steels

Energy Technology Data Exchange (ETDEWEB)

Gavriljuk, V.G.; Shivanyuk, V.N.; Foct, J

2003-03-14

Three main available hypotheses of hydrogen embrittlement are analysed in relation to austenitic steels based on the studies of the hydrogen effect on the interatomic bonds, phase transformations and microplastic behaviour. It is shown that hydrogen increases the concentration of free electrons, i.e. enhances the metallic character of atomic interactions, although such a decrease in the interatomic bonding cannot be a reason for brittleness and rather assists an increased plasticity. The hypothesis of the critical role of the hydrogen-induced {epsilon} martensite was tested in the experiment with the hydrogen-charged Si-containing austenitic steel. Both the fraction of the {epsilon} martensite and resistance to hydrogen embrittlement were increased due to Si alloying, which is at variance with the pseudo-hydride hypothesis. The hydrogen-caused early start of the microplastic deformation and an increased mobility of dislocations, which are usually not observed in the common mechanical tests, are revealed by the measurements of the strain-dependent internal friction, which is consistent with the hypothesis of the hydrogen-enhanced localised plasticity. An influence of alloying elements on the enthalpy E{sub H} of hydrogen migration in austenitic steels is studied using the temperature-dependent internal friction and a correlation is found between the values of E{sub H} and hydrogen-caused decrease in plasticity. A mechanism for the transition from the hydrogen-caused microplasticity to the apparent macrobrittle fracture is proposed based on the similarity of the fracture of hydrogenated austenitic steels to that of high nitrogen steels.

Microstructural and crystallographic characteristics of modulated martensite, non-modulated martensite, and pre-martensitic tweed austenite in Ni-Mn-Ga alloys

International Nuclear Information System (INIS)

Zhou, Le; Schneider, Matthew M.; Giri, Anit; Cho, Kyu; Sohn, Yongho

2017-01-01

A combinatorial approach using diffusion couples and TEM analyses was carried out to investigate the composition-dependent martensitic transformation in NiMnGa alloys. The compositions cover a large portion of the off-stoichiometric Ni 2 MnGa compositions and some Mn-rich compositions. Crystallographic variations of the martensitic phase, including non-modulated (NM) martensite, modulated (5M or 7M) martensite, and austenitic phase were identified in the diffusion couples and investigated with respect to their microstructure and crystallography. The 5M and 7M martensitic structures were only found near the interphase boundary between austenite and martensite, while the NM martensitic structures were found mostly away from the interphase boundary. The tetragonality ratio (c/a) for NM martensite generally increases with e/a ratio, but was also dependent on the composition. The habit plane and martensitic microstructure that consists of twinned variants with differing orientations were documented using electron diffraction. The pre-martensitic state was observed in the austenitic phase that was located near the interphase boundary between austenite and martensite, with distinctive tweed microstructure and a strain field originating from the local lattice distortions. The combinatorial approach proves to be efficient and systematic in studying the composition-dependent martensitic transformation in NiMnGa alloys and can be potentially applied to other shape memory alloys.

Strength of "Light" Ferritic and Austenitic Steels Based on the Fe - Mn - Al - C System

Science.gov (United States)

Kaputkina, L. M.; Svyazhin, A. G.; Smarygina, I. V.; Kindop, V. E.

2017-01-01

The phase composition, the hardness, the mechanical properties at room temperature, and the resistance to hot (950 - 1000°C) and warm (550°C) deformation are studied for cast deformable "light" ferritic and austenitic steels of the Fe - (12 - 25)% Mn - (0 - 15)% Al - (0 - 2)% C system alloyed additionally with about 5% Ni. The high-aluminum high-manganese low-carbon and carbonless ferritic steels at a temperature of about 0.5 T melt have a specific strength close to that of the austenitic steels and may be used as weldable scale-resistant and wear-resistant materials. The high-carbon Fe - (20 - 24)% Mn - (5 - 9)% Al - 5% Ni - 1.5% C austenitic steels may be applied as light high-strength materials operating at cryogenic temperatures after a solution treatment and as scale- and heat-resistant materials in an aged condition.

Impact of phase stability on the corrosion behavior of the austenitic candidate materials for NNWSI [Nevada Nuclear Waste Storage Investigations

International Nuclear Information System (INIS)

Bullen, D.B.; Gdowski, G.E.; McCright, R.D.

1987-10-01

The Nuclear Waste Management Program at Lawrence Livermore National Laboratory is responsible for the development of the waste package design to meet the Nuclear Regulatory Commission licensing requirements for the Nevada Nuclear Waste Storage Investigations (NNWSI) Project. The metallic container component of the waste package is required to assist in providing substantially complete containment of the waste for a period of up to 1000 years. Long term phase stability of the austenitic candidate materials (304L and 316L stainless steels and alloy 825) over this time period at moderate temperatures (100-250 0 C) can impact the mechanical and corrosion behavior of the metal barrier. A review of the technical literature with respect to phase stability of 304L, 316L and 825 is presented. The impact of martensitic transformations, carbide precipitation and intermediate (σ, chi, and eta) phase formation on the mechanical properties and corrosion behavior of these alloys at repository relevant conditions is discussed. The effect of sensitization on intergranular stress corrosion cracking (IGSCC) of each alloy is also addressed. A summary of the impact of phase stability on the degradation of each alloy in the proposed repository environment is included. 32 refs., 6 figs

Elaboration of data and documents intended to complement and expand the German series of nuclear engineering codes. 3. Technical report. Non-destructive testing of austenitic welds and claddings

International Nuclear Information System (INIS)

Waidele, H.

1997-01-01

This 3. technical report presents a literature study on non-destructive testing of austenitic welds and claddings. NDT of claddings was the subject of a previous BMU project report SR 2024, so that this report contains only an update covering the latest developments in this subject area, and NDT of austenitic welds is the major subject of the report in hand. The literature study shows that improvements of ultrasonic test results for austenitic welds are expected to be achieved soon as a result of application of novel testing methods, advanced signal processing algorithms, and reduced anisotropy of austenitic welds due to specific welding techniques. Enhanced information is expected to be achieved from radiography tests through improvements available now, such as digitization of conventional radiographs combined with computer-assisted evaluation methods. As to the inspection of components with wall thickness up to 10 mm, low-frequency methods or eddy current methods will increasingly be applied in future as complementing methods supplying additional information. (orig./CB) [de

Characterization of the austenitic stability of metastable austenitic stainless steel with regard to its formability

Science.gov (United States)

Schneider, Matthias; Liewald, Mathias

2018-05-01

During the last decade, the stainless steel market showed a growing volume of 3-5% p.a.. The austenitic grades are losing market shares to ferritic or 200-series grades due to the high nickel price, but still playing the most important role within the stainless steel market. Austenitic stainless steel is characterized by the strain-induced martensite formation, causing the TRIP-effect (Transformation Induced Plasticity) which is responsible for good formability and high strength. The TRIP-effect itself is highly dependent on the forming temperature, the strain as well as the chemical composition which has a direct influence on the stability of the austenite. Today the austenitic stability is usually characterized by the so called Md30-temperature, which was introduced by Angel and enhanced by several researches, particularly Nohara. It is an empirical formula based on the chemical composition and the grain size of a given material, calculating the temperature which is necessary to gain a 50 % martensite formation after 30 % of elongation in a tensile test. A higher Md30-temperature indicates a lower stability and therefore a higher tendency towards martensite formation. The main disadvantage of Md30 -temperature is the fact that it is not based on forming parameters and only describes a single point instead of the whole forming process. In this paper, an experimental set up for measuring martensite and temperature evolution in a non-isothermal tensile test is presented, which is based on works of Hänsel and Schmid. With this set up, the martensite formation rate for different steels of the steel grade EN 1.4301 and EN 1.4310 is measured. Based on these results a new austenitic stability criterion is defined. This criterion and the determined Md30-temperatures are related to the stretch formability of the materials. The results show that the new IFU criterion is with regard to the formability a much more useful characteristic number for metastable austenitic steels

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%.

Monitoring of Fatigue Degradation in Austenitic Stainless Steels

International Nuclear Information System (INIS)

Kalkhof, D.; Niffenegger, M.; Leber, H.J.

2004-01-01

During cyclic loading of austenitic stainless steel, it was observed that microstructural changes occurred; these affect both the mechanical and physical properties of the material. For certain steels, a strain-induced martensite phase transformation was seen. The investigations showed that, for the given material and loading conditions, the volume fraction of martensite depends on the cycle number, temperature and initial material state. It was also found that the martensite content continuously increased with the cycle number. Therefore, the volume fraction of martensite was used as an indication of fatigue usage. It was noted that the temperature dependence of the martensite formation could be described by a Boltzmann function, and that the martensite content decreased with increasing temperature. Two different heats of the austenitic stainless steel X6CrNiTi18-10 (AISI 321, DIN 1.4541) were investigated. It was found that the martensite formation rate was much higher for the cold-worked than for the solution-annealed material. All applied techniques - neutron diffraction and advanced magnetic methods - were successful in detecting the presence of martensite in the differently fatigued specimens. (author)

Effect of ferrite on the precipitation of σ phase in cast austenitic stainless steel used for primary coolant pipes of nuclear power plants

Energy Technology Data Exchange (ETDEWEB)

Wang, Yongqiang; Li, Na, E-mail: wangyongqiang1124@163.com [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology, Beijing (China)

2017-11-15

The effect of ferrite phase on the precipitation of σ phase in a Z3CN20.09M cast austenitic stainless steel (CASS) used for primary coolant pipes of pressurized water reactor (PWR) nuclear power plants was investigated by using isothermal heat-treatment, optical microscopy (OM), transmission electron microscopy (TEM) and electron probe microanalysis (EPMA) techniques. The influence of different morphologies and volume fractions of ferrite in the σ phase formation mechanism was discussed. The amount of σ phase precipitated in all specimens with different microstructures increased with increasing of aging time, however, the precipitation rate is significant different. The formation of σ phase in specimens with the coarsest ferrite and the dispersively smallest ferrite is slowest. The lowest level Cr content in ferrite and fewest α/γ interfaces in specimen are the main reasons for the slowest σ precipitation due to they are unfavorable for the kinetics and thermodynamics of phase transformation respectively. By contraries, the fastest formation of σ phase takes place in specimens with narrow and long ferrite due to the most α/γ interfaces and higher Cr content in ferrite which are beneficial for preferential nucleation and formation thermodynamics of σ phase. (author)

Mechanical property degradation and microstructural evolution of cast austenitic stainless steels under short-term thermal aging

Science.gov (United States)

Lach, Timothy G.; Byun, Thak Sang; Leonard, Keith J.

2017-12-01

Mechanical testing and microstructural characterization were performed on short-term thermally aged cast austenitic stainless steels (CASS) to understand the severity and mechanisms of thermal-aging degradation experienced during extended operation of light water reactor (LWR) coolant systems. Four CASS materials-CF3, CF3M, CF8, and CF8M-were thermally aged for 1500 h at 290 °C, 330 °C, 360 °C, and 400 °C. All four alloys experienced insignificant change in strength and ductility properties but a significant reduction in absorbed impact energy. The primary microstructural and compositional changes during thermal aging were spinodal decomposition of the δ-ferrite into α/α‧, precipitation of G-phase in the δ-ferrite, segregation of solute to the austenite/ferrite interphase boundary, and growth of M23C6 carbides on the austenite/ferrite interphase boundary. These changes were shown to be highly dependent on chemical composition, particularly the concentration of C and Mo, and aging temperature. The low C, high Mo CF3M alloys experienced the most spinodal decomposition and G-phase precipitation coinciding the largest reduction in impact properties.

Automated flaw detection scheme for cast austenitic stainless steel weld specimens using Hilbert-Huang transform of ultrasonic phased array data

International Nuclear Information System (INIS)

Khan, Tariq; Majumdar, Shantanu; Udpa, Lalita; Ramuhalli, Pradeep; Crawford, Susan; Diaz, Aaron; Anderson, Michael T.

2012-01-01

The objective of this work is to develop processing algorithms to detect and localize flaws using ultrasonic phased-array data. Data was collected on cast austenitic stainless stell (CASS) weld specimens onloan from the U.S. nuclear power industry' Pressurized Walter Reactor Owners Group (PWROG) traveling specimen set. Each specimen consists of a centrifugally cast stainless stell (CCSS) pipe section welded to a statically cst(SCSS) or wrought (WRSS) section. The paper presents a novel automated flaw detection and localization scheme using low frequency ultrasonic phased array inspection singals from the weld and heat affected zone of the based materials. The major steps of the overall scheme are preprocessing and region of interest (ROI) detection followed by the Hilbert-Huang transform (HHT) of A-scans in the detected ROIs. HHT offers time-frequency-energy distribution for each ROI. The Accumulation of energy in a particular frequency band is used as a classification feature for the particular ROI

Fe-15Ni-13Cr austenitic stainless steels for fission and fusion reactor applications. II. Effects of minor elements on precipitate phase stability during thermal aging

International Nuclear Information System (INIS)

Lee, E.H.; Mansur, L.K.

2000-01-01

The precipitate phase stability in Fe-15Ni-13Cr base austenitic alloys was investigated as a function of minor alloying additions after thermally aging at 600 deg. C and 675 deg. C for times ranging from 24 h to one year. Seven major precipitate phases were found in aged specimens, including M 23 C 6 , Laves, Eta (η), TiO, NbC, MC, and M 2 P. The types and amounts of precipitate phases varied with alloying element additions, aging temperature, and aging time. By analyzing the composition of each individual particle, it was possible to determine the essential constituent elements for each phase. From this information, a strategy to promote or suppress certain precipitate phases was developed. Among the seven phases, the most desirable precipitate phases were considered to be MC and M 2 P, because these particles form on a fine scale with a high number density and, therefore, can serve as effective gas atom trap sites under irradiation

Microstructural aspects of crack formation and propagation in the austenitic steel X6CrNiNb18-10 under low cycle fatigue loading

International Nuclear Information System (INIS)

Soppa, E.; Kohler, C.; Roos, E.; Schuler, X.

2012-01-01

The understanding of the crack initiation mechanisms and crack growth in apparently monolithic materials like X6CrNiNb18-10 stainless steel under cyclic loading requires the explicit analysis of the phenomena underlying fatigue on both atomistic and microscopic levels. The permanent delivery of mechanical energy through cyclic loading evokes changes in the microstructure that can lead to a martensitic transformation. The transformation of a metastable cubic face centered austenite and formation of a cubic body centered α'-martensite under cyclic loading at room temperature was found, both, in the experiment and in molecular dynamics simulations. The martensite nucleates prevalently at grain boundaries, triple points and at the specimen free surface and forms small (∝ 1 μm) differently oriented grains, also in the same parent austenitic grain. By a combination of interrupted low cycle fatigue tests (LCF) and electron backscatter diffraction (EBSD) measurements the martensitic transformation and subsequent fatigue crack formation were observed at the same area in the microstructure at different stages of the specimen lifetime. The EBSD measurements showed the following crack initiation scenarios: Cracks started (a) at the phase boundary between austenite and α'-martensite, (b) inside fully martensitic areas in the matrix, (c) at broken or debonded coarse NbCs. It is obvious that formation of a hard α'-martensite in a ductile and soft austenite and forming two-phase material causes a heterogeneous stress and strain distribution on the microscopic level. α'-martensite enhances locally the stress amplitude whereas in a soft austenite the plastic strain amplitude increases. Strain concentration in the austenite along the phase boundary is connected with a stress increase along the interface and can initiate fatigue crack there. Also at the crack tip, a permanent martensitic transformation occurs, so that the growth of the fatigue cracks at room temperature seems

Role of quaternary additions on dislocated martensite, retain austenite and mechanical properties of Fe/Cr/C structural steels

International Nuclear Information System (INIS)

Rao, B.V.N.

1978-02-01

The influence of quaternary alloy additions of Mn and Ni to Fe/Cr/C steels which have been designed to provide superior mechanical properties has been investigated. Transmission electron microscopy and x-ray analysis revealed increasing amounts of retained austenite with Mn up to 2 w/o and with 5 w/o Ni additions after quenching from 1100 0 C. This is accompanied by a corresponding improvement in toughness properties of the quaternary alloys. In addition, the generally attractive combinations of strength and toughness in these quaternary alloys is attributed to the production of dislocated lath martensite from a homogeneous austenite phase free from undissolved alloy carbides. Grain-refining resulted in a further increase in the amount of retained austenite

Deformation mechanisms in austenitic TRIP/TWIP steels at room and elevated temperature investigated by acoustic emission and scanning electron microscopy

Energy Technology Data Exchange (ETDEWEB)

Linderov, M. [Laboratory of Physics of Strength of Materials and Intelligent Diagnostic Systems, Togliatti State University, Togliatti 445667 (Russian Federation); Segel, C.; Weidner, A.; Biermann, H. [Institute of Materials Engineering, Technische Universität Bergakademie Freiberg, 09599 Freiberg (Germany); Vinogradov, A., E-mail: vinogradov@tltsu.ru [Laboratory of Physics of Strength of Materials and Intelligent Diagnostic Systems, Togliatti State University, Togliatti 445667 (Russian Federation)

2014-03-01

The modern austenitic stainless TRIP/TWIP steels have an outstanding combination of strength and ductility, depending on their chemical composition and loading conditions. A critical factor, which strongly affects all deformation-induced processes in metastable austenitic steels, is the temperature. To get a better insight into the effect of temperature on the deformation kinetics and transformation processes in high-alloy CrMnNi TRIP/TWIP steels with different austenite stability due to a varied content of Ni (3, 6 and 9 wt%), an acoustic emission (AE) technique was used during uniaxial tension at two different temperatures – ambient and 373 K. The in-situ AE results were paired with detailed SEM investigations using the electron backscattered diffraction (EBSD) technique to identify the deformation-induced phase transformations and mechnical twinning. The cluster analysis of the AE signals has revealed an excellent correlation of AE features with synergistic complexity of deformation mechanisms involved in various combinations: dislocation glide, stacking faults, martensitic phase transformation and twinning.

Numerical simulation of hydrogen-assisted crack initiation in austenitic-ferritic duplex steels; Numerische Simulation der wasserstoffunterstuetzten Rissbildung in austentisch-ferritischen Duplexstaehlen

Energy Technology Data Exchange (ETDEWEB)

Mente, Tobias

2015-07-01

Duplex stainless steels have been used for a long time in the offshore industry, since they have higher strength than conventional austenitic stainless steels and they exhibit a better ductility as well as an improved corrosion resistance in harsh environments compared to ferritic stainless steels. However, despite these good properties the literature shows some failure cases of duplex stainless steels in which hydrogen plays a crucial role for the cause of the damage. Numerical simulations can give a significant contribution in clarifying the damage mechanisms. Because they help to interpret experimental results as well as help to transfer results from laboratory tests to component tests and vice versa. So far, most numerical simulations of hydrogen-assisted material damage in duplex stainless steels were performed at the macroscopic scale. However, duplex stainless steels consist of approximately equal portions of austenite and δ-ferrite. Both phases have different mechanical properties as well as hydrogen transport properties. Thus, the sensitivity for hydrogen-assisted damage is different in both phases, too. Therefore, the objective of this research was to develop a numerical model of a duplex stainless steel microstructure enabling simulation of hydrogen transport, mechanical stresses and strains as well as crack initiation and propagation in both phases. Additionally, modern X-ray diffraction experiments were used in order to evaluate the influence of hydrogen on the phase specific mechanical properties. For the numerical simulation of the hydrogen transport it was shown, that hydrogen diffusion strongly depends on the alignment of austenite and δ-ferrite in the duplex stainless steel microstructure. Also, it was proven that the hydrogen transport is mainly realized by the ferritic phase and hydrogen is trapped in the austenitic phase. The numerical analysis of phase specific mechanical stresses and strains revealed that if the duplex stainless steel is

Phase transformations in low-carbon manganese steel 6Mn16

Directory of Open Access Journals (Sweden)

J. Lis

2009-01-01

Full Text Available The kinetics of phase transformations of the austenite of 6Mn16 steel during continuous cooling are presented in a CCT diagram. Manganese partitioning between ferrite and austenite during intercritical annealing is enhanced by prior soft annealing. Due to the increased Mn concentration in austenite, the temperatures BS and MS have decreased, as compared to those achieved during cooling from the complete austenite region.

Weldability of newly developed austenitic alloy for cryogenic service

International Nuclear Information System (INIS)

Ogawa, T.; Koseki, T.

1986-01-01

The testing reported in this paper involved typical steels of the new grades such as STEEL-A (0.025C-14Ni-25Cr-0.35N), STEEL-B (0.04C-23Mn-13Cr-0.22N) and STEEL-C (0.20C-25Mn-5Cr), and commercial steels of Type 300 series. Weldments were made mainly using the GTAW, SMAW and SAW processes with experimental and commercial filler metals. Strength and toughness of weldments were examined at 77 K (-321 0 F) and 4 K. The strengthening of material through the addition of nitrogen was far greater in the weld metal that in the base metal at cryogenic temperature. In fact, 0.2% proof stress of weld metals bearging 0.20% to 0.40% nitrogen at 77 K exhibited a higher value by 60 to 150 MPa (8,740 to 21,760 psi) than that of the base metal. Impact absorbed energy of weld metals at 77 K decreased rapidly with nitrogen content, 60-90 J at 0.20%N to 20-50J at 0.35% N. Rather high impact absorbed energy was obtained when the weld metal solidified as primary austenitic phase, resulting in fully austenitic microstructure or austenite-eutectic ferrite mixture at ambient temperature. In addition, oxide inclusions, the number of which strongly depends on welding processes, were detrimental to toughness of weld metals at cryogenic temperature

Microstructural evolution in austenitic heat-resistant cast steel 35Cr25Ni12NNbRE during long-term service

International Nuclear Information System (INIS)

Liu Jiangwen; Jiao Dongling; Luo Chengping

2010-01-01

The microstructural evolution of austenitic heat-resistant cast steel 35Cr25Ni12NNbRE during aging and long-term service was investigated using optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The microstructure of the as cast steel consists of the dendritic austenite, the block-like eutectic carbide M 7 C 3 spreaded among austenitic dendrite, and a small quantity of M 23 C 6 carbide. The microstructure of the steel aged at 600 deg. C consists of eutectic carbide M 23 C 6 transformed from eutectic carbide M 7 C 3 and dendritic austenite in which fine secondary carbide particles M 23 C 6 precipitated. The precipitated carbide M 23 C 6 kept a cubic-cubic orientation relationship (OR) with austenite matrix. There existed a carbide precipitation free zone (PFZ) around the eutectic carbide. For the long-term serviced samples, the secondary carbide precipitated in the austenite strikingly increased and the PFZ disappeared. Part of the M 23 C 6 transformed into M 6 C, which always kept a twin OR, [114] M 6 C //[110] A //[110] M 23 C 6 , with the austenite and the M 23 C 6 secondary carbide. In addition, a small quantity of σ phase FeCr and ε-Cr 2 N were also identified. The effects of alloy composition and service condition on the microstructural evolution of the steel were discussed.

Austenitic stainless steel weld inspection

International Nuclear Information System (INIS)

Mech, S.J.; Emmons, J.S.; Michaels, T.E.

1978-01-01

Analytical techniques applied to ultrasonic waveforms obtained from inspection of austenitic stainless steel welds are described. Experimental results obtained from a variety of geometric and defect reflectors are presented. Specifically, frequency analyses parameters, such as simple moments of the power spectrum, cross-correlation techniques, and adaptive learning network analysis, all represent improvements over conventional time domain analysis of ultrasonic waveforms. Results for each of these methods are presented, and the overall inspection difficulties of austenitic stainless steel welds are discussed

Investigation of phase transformations in ductile cast iron of differential scanning calorimetry

International Nuclear Information System (INIS)

Przeliorz, R; Piatkowski, J

2011-01-01

The effect of heating rate on phase transformations to austenite range in ductile cast iron of the EN-GJS-450-10 grade was investigated. For studies of phase transformations, the technique of differential scanning calorimetry (DSC) was used. Micro structure was examined by optical microscopy. The calorimetric examinations have proved that on heating three transformations occur in this grade of ductile iron, viz. magnetic transformation at the Curie temperature, pearlite→austenite transformation and ferrite→austenite transformation. An increase in the heating rate shifts the pearlite→austenite and ferrite→austenite transformations to higher temperature range. At the heating rate of 5 and 15 deg. C min -1 , local extrema have been observed to occur: for pearlite→austenite transformation at 784 deg. C and 795 deg. C, respectively, and for ferrite+ graphite →austenite transformation at 805 deg. C and 821 deg. C, respectively. The Curie temperature of magnetic transformation was extrapolated to a value of 740 deg. C. Each transformation is related with a specific thermal effect. The highest value of enthalpy is accompanying the ferrite→austenite transformation, the lowest occurs in the case of pearlite→austenite transformation.

Low-temperature creep of austenitic stainless steels

Science.gov (United States)

Reed, R. P.; Walsh, R. P.

2017-09-01

Plastic deformation under constant load (creep) in austenitic stainless steels has been measured at temperatures ranging from 4 K to room temperature. Low-temperature creep data taken from past and unreported austenitic stainless steel studies are analyzed and reviewed. Creep at cryogenic temperatures of common austenitic steels, such as AISI 304, 310 316, and nitrogen-strengthened steels, such as 304HN and 3116LN, are included. Analyses suggests that logarithmic creep (creep strain dependent on the log of test time) best describe austenitic stainless steel behavior in the secondary creep stage and that the slope of creep strain versus log time is dependent on the applied stress/yield strength ratio. The role of cold work, strain-induced martensitic transformations, and stacking fault energy on low-temperature creep behavior is discussed. The engineering significance of creep on cryogenic structures is discussed in terms of the total creep strain under constant load over their operational lifetime at allowable stress levels.

Internal hydrogen-induced subcritical crack growth in austenitic stainless steels

Science.gov (United States)

Huang, J. H.; Altstetter, C. J.

1991-11-01

The effects of small amounts of dissolved hydrogen on crack propagation were determined for two austenitic stainless steel alloys, AISI 301 and 310S. In order to have a uniform distribution of hydrogen in the alloys, they were cathodically charged at high temperature in a molten salt electrolyte. Sustained load tests were performed on fatigue precracked specimens in air at 0 ‡C, 25 ‡C, and 50 ‡C with hydrogen contents up to 41 wt ppm. The electrical potential drop method with optical calibration was used to continuously monitor the crack position. Log crack velocity vs stress intensity curves had definite thresholds for subcritical crack growth (SCG), but stage II was not always clearly delineated. In the unstable austenitic steel, AISI 301, the threshold stress intensity decreased with increasing hydrogen content or increasing temperature, but beyond about 10 wt ppm, it became insensitive to hydrogen concentration. At higher concentrations, stage II became less distinct. In the stable stainless steel, subcritical crack growth was observed only for a specimen containing 41 wt ppm hydrogen. Fractographic features were correlated with stress intensity, hydrogen content, and temperature. The fracture mode changed with temperature and hydrogen content. For unstable austenitic steel, low temperature and high hydrogen content favored intergranular fracture while microvoid coalescence dominated at a low hydrogen content. The interpretation of these phenomena is based on the tendency for stress-induced phase transformation, the different hydrogen diffusivity and solubility in ferrite and austenite, and outgassing from the crack tip. After comparing the embrittlement due to internal hydrogen with that in external hydrogen, it is concluded that the critical hydrogen distribution for the onset of subcritical crack growth is reached at a location that is very near the crack tip.

Detection of secondary phases in duplex stainless steel by magnetic force microscopy and scanning Kelvin probe force microscopy

Energy Technology Data Exchange (ETDEWEB)

Ramírez-Salgado, J. [Instituto Mexicano del Petróleo, Dirección de Investigación y Posgrado, Eje Central Norte Lázaro Cárdenas, No. 152, 07730 D.F., México (Mexico); Domínguez-Aguilar, M.A., E-mail: madoming@imp.mx [Instituto Mexicano del Petróleo, Dirección de Investigación y Posgrado, Eje Central Norte Lázaro Cárdenas, No. 152, 07730 D.F., México (Mexico); Castro-Domínguez, B. [University of Tokyo, Department of Chemical System Engineering, Faculty of Engineering Bldg. 5, 7F 722, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113–8656 (Japan); Hernández-Hernández, P. [Instituto Mexicano del Petróleo, Dirección de Investigación y Posgrado, Eje Central Norte Lázaro Cárdenas, No. 152, 07730 D.F., México (Mexico); Newman, R.C. [University of Toronto, Department of Chemical Engineering and Applied Chemistry, 200 College Street, Toronto M5S 3E5 (Canada)

2013-12-15

The secondary phase transformations in a commercial super duplex stainless steel were investigated by micro-chemical analyses and high resolution scanning probe microscopy. Energy dispersive X-ray and electron probe detected ferrite and austenite as well as secondary phases in unetched aged duplex stainless steel type 25Cr-7Ni-3Mo. Volta potential indicated that nitride and sigma appeared more active than ferrite, while secondary austenite and austenite presented a nobler potential. Reversal order in nobility is thought to be attributable to the potential ranking provided by oxide nature diversity as a result of secondary phase surface compositions on steel. After eutectoid transformation, secondary austenite was detected by electron probe microanalysis, whereas atomic force microscopy distinguished this phase from former austenite by image contrast. Magnetic force microscopy revealed a “ghosted” effect on the latter microstructure probably derived from metal memory reminiscence of mechanical polishing at passivity and long range magnetic forces of ferrite phase. - Highlights: • Nobility detection of secondary phases by SKPFM in DSS particles is not a straightforward procedure. • As Volta potential and contrast are not always consistent SKPFM surface oxides is thought played an important role in detection. • AFM distinguished secondary austenite from former austenite by image contrast though SEM required EPMA.

Effect of nitrogen on the stabilization of austenite in a tungsten-molybdenum high-speed steel

International Nuclear Information System (INIS)

Popandopulo, A.N.; Zhukova, L.T.

1986-01-01

A study was made of the tendency of steels R6M5 and R6Am5 to austenite stabilization after subzero treatment and high-temperature tempering in hot-rolled bars. Data indicate that in steel R6AM5 during quenching there is almost instantaneous austenite stabilization. The data was derived from a study of phase composition (exposure from a microsection in DRON-2.0 equipment in iron K /SUB alpha/ radiation), microstructure, and hardness. The authors conclude that in view of serious difficulties in metallurgical and tool production, steel R6AM5 should be supplied only at the request of the customer

Low-activation Mn-Cr austenitic stainless steel with further reduced content of long-lived radioactive elements

Energy Technology Data Exchange (ETDEWEB)

Onozuka, M.; Saida, T.; Hirai, S. [Mitsubishi Heavy Ind. Ltd., Yokohama (Japan); Kusuhashi, M.; Sato, I.; Hatakeyama, T. [The Japan Steel Works Ltd., Chatsu-machi 4, Muroran 051-8505 (Japan)

1998-06-01

Low-activation austenitic stainless steel based on Mn-Cr non-magnetic steels has been developed. The alloying elements of long-life activation, such as Ni, Mo and Co, were eliminated and substituted with Mn along with an addition of N. A Mn-Cr austenitic stainless steel, 24.5Mn-13.5Cr-0.02C-0.2N, has been developed successfully. Examined material properties, including mechanical, thermal and magnetic properties, as well as weldability and characteristics of corrosion resistance, are presented. It was found that the alloy has excellent material properties virtually equivalent to those of 316SS. In this study, the applicability of the Schaeffler, DeLong and Hull constitution diagrams for the stainless steels with low Ni and high Mn contents was also examined. The boundary conditions distinguishing the single austenite phase from the others have been identified for the Mn-Cr steels. (orig.) 22 refs.

Low-activation Mn Cr austenitic stainless steel with further reduced content of long-lived radioactive elements

Science.gov (United States)

Onozuka, Masanori; Saida, Tomikane; Hirai, Shouzou; Kusuhashi, Mikio; Sato, Ikuo; Hatakeyama, Tsuyoshi

1998-06-01

Low-activation austenitic stainless steel based on Mn-Cr non-magnetic steels has been developed. The alloying elements of long-life activation, such as Ni, Mo and Co, were eliminated and substituted with Mn along with an addition of N. A Mn-Cr austenitic stainless steel, 24.5Mn-13.5Cr-0.02C-0.2N, has been developed successfully. Examined material properties, including mechanical, thermal and magnetic properties, as well as weldability and characteristics of corrosion resistance, are presented. It was found that the alloy has excellent material properties virtually equivalent to those of 316SS. In this study, the applicability of the Schaeffler, DeLong and Hull constitution diagrams for the stainless steels with low Ni and high Mn contents was also examined. The boundary conditions distinguishing the single austenite phase from the others have been identified for the Mn-Cr steels.

The role of nitrogen in improving pitting corrosion resistance of high-alloy austenitic and duplex stainless steel welds

International Nuclear Information System (INIS)

Vilpas, M.; Haenninen, H.

1999-01-01

The effects of nitrogen alloyed shielding gas on weld nitrogen content and pitting corrosion resistance of super austenitic (6%Mo) and super duplex stainless steels have been studied with special emphasis on microsegregation behaviour of Cr, Mo and N. The measurements performed with the 6%Mo steel indicate that all these elements segregate interdendritically in the fully austenitic weld metal. With nitrogen addition to the shielding gas the enrichment of nitrogen to the interdendritic regions is more pronounced than to the dendrite cores due to which the pitting corrosion resistance of the dendrite cores increases only marginally. In the super duplex steel welds nitrogen enriches in austenite increasing its pitting corrosion resistance more effectively. In these welds the pitting corrosion resistance of the ferrite phase remains lower. (orig.)

Crystallography of lath martensite and stabilization of retained austenite

International Nuclear Information System (INIS)

Sarikaya, M.

1982-10-01

TEM was used to study the morphology and crystallography of lath martensite in low and medium carbon steels in the as-quenched and 200 0 C tempered conditions. The steels have microduplex structures of dislocated lath martensite and continuous thin films of retained austenite at the lath interfaces. Stacks of laths form the packets which are derived from different [111] variants of the same austenite grain. The residual parent austenite enables microdiffraction experiments with small electron beam spot sizes for the orientation relationships (OR) between austenite and martensite. All three most commonly observed ORs, namely Kurdjumov-Sachs, Nishiyama-Wassermann, and Greninger-Troiano, operate within the same sample

Crystallography of lath martensite and stabilization of retained austenite

Energy Technology Data Exchange (ETDEWEB)

Sarikaya. M.

1982-10-01

TEM was used to study the morphology and crystallography of lath martensite in low and medium carbon steels in the as-quenched and 200/sup 0/C tempered conditions. The steels have microduplex structures of dislocated lath martensite and continuous thin films of retained austenite at the lath interfaces. Stacks of laths form the packets which are derived from different (111) variants of the same austenite grain. The residual parent austenite enables microdiffraction experiments with small electron beam spot sizes for the orientation relationships (OR) between austenite and martensite. All three most commonly observed ORs, namely Kurdjumov-Sachs, Nishiyama-Wassermann, and Greninger-Troiano, operate within the same sample.

Reversed austenite in 0Cr13Ni4Mo martensitic stainless steels

Energy Technology Data Exchange (ETDEWEB)

Song, Y.Y., E-mail: songyuanyuan@imr.ac.cn [Institute of Metal Research, Chinese Academy of Science, Shenyang 110016 (China); Li, X.Y.; Rong, L.J.; Li, Y.Y. [Institute of Metal Research, Chinese Academy of Science, Shenyang 110016 (China); Nagai, T. [National Institute for Materials Science, Sengen 1-2-1, Tsukuba 305-0047 (Japan)

2014-01-15

The austenite reversion process and the distribution of carbon and other alloying elements during tempering in 0Cr13Ni4Mo martensitic stainless steel have been investigated by in-situ high temperature X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM). The microstructure of the reversed austenite was characterized using transmission electron microscopy (TEM). The results revealed that the amount of the reversed austenite formed at high temperature increased with the holding time. Direct experimental evidence supported carbon partitioning to carbides and Ni to the reversed austenite. The reversed austenite almost always nucleated in contact with lath boundary M{sub 23}C{sub 6} carbides during tempering and the diffusion of Ni promoted its growth. The Ni enrichment and the ultrafine size of the reversed austenite were considered to be the main factors that accounted for the stability of the reversed austenite. - Highlights: • The amount of the reversed austenite formed at high temperature increases with the holding time. • STEM results directly show that carbon is mainly partitioned into the carbides and Ni into the reversed austenite. • The Ni enrichment and the ultrafine size are the main factors leading to the stabilization of the reversed austenite.

Kinetic of martensitic transformations induced by hydrogen in the austenite

International Nuclear Information System (INIS)

Oliveira, Sergio P. de; Saavedra, A.; Miranda, P.E.V. de

1986-01-01

The X-ray diffractometry technique was used, with an automatic data acquisition system to determine the kinetics of hydrogen induced martensitic phase transformations in an AISI 304 austenitic stainless steel type, used in nuclear power plants. Hydrogenation was performed cathodically in a 1N sulfuric acid solution, containing 100 mg/l of arsenic trioxide, at 50 0 C, during 2 hours and with a current density of 200 A/m 2 . It was found that the microstructure of the steel plays a role on the generation of hydrogen induced martensitic phases and surface micro cracks. Both kinetics were slower on a pre-cold rolled steel. (Author) [pt

Microstructure and tribologic behaviour of metastable austenitic FeMn alloys as a function of chromium content; Gefuegeausbildung und Triboverhalten metastabiler austenitischer FeMn-Legierungen in Abhaengigkeit vom Chromgehalt

Energy Technology Data Exchange (ETDEWEB)

Roethig, J. [Magdeburg Univ. (Germany). Inst. fuer Stroemungstechnik und Thermodynamik; Veit, P.; Strassburger, G.; Blaesing, J. [Magdeburg Univ. (Germany). Inst. fuer Experimentelle Physik; Heyse, H. [Magdeburg Univ. (Germany). Inst. fuer Werkstofftechnik und Werkstoffpruefung

1997-12-31

In FeMn20Cr alloys with chromium contents of up to 20%, the solidification process is primarily an eutectic process. The {delta}-ferrite becomes increasingly instable below a temperature of 900 C and gradually disintegrates during slow cooling into austenite and a sigma phase. Tempering of these microstructures at T=450 C (6hours) leads to formation of {epsilon}-martensite in the austenite. Fast quenching starting above 900 C freezes the {delta}-ferrite, so that in the case of chromium contents between 13 and 18%, austenitic-hexagonal-ferritic microstructures form and above 18%, austenitic-ferritic microstructures. Tempering does not remove the {delta}-ferrite, but induces formation of {epsilon}-martensite in the austenite. Trobologic examinations with solutionized and water-quenched alloys showed, as compared to an FeMn20Cr18 alloy, for various types of wear, a very good tribologic performance (except for the alloy FeMn20Cr18 and cavitation). As to abrasion or hot wear, the formation of a sigma-phase or intercalation of metalloid hard phases should be considered. (orig./CB) [Deutsch] FeMn20Cr-Legierungen mit Chromgehalten bis zu 20% erstarren primaer ferritisch. Der {delta}-Ferrit ist unterhalb 900 C nicht mehr stabil und zerfaellt bei langsamer Abkuehlung in Austenit und Sigmaphase. Ein Anlassen dieser Gefuege T=450 C (6 Stunden) fuehrt zur {epsilon}-Martensitbildung im Austenit. Schnelles Abschrecken von oberhalb 900 C friert den {delta}-Ferrit ein, so dass bei Chromgehalten zwischen 13 und 18% austenitisch-hexagonal-ferritische und >18% austenitisch-ferritische Gefuege entstehen. Durch Anlassen kann der {delta}-Ferrit nicht beseitigt werden. Im Austenit kommt es aber zur {epsilon}-Martensitbildung. Tribologische Untersuchungen mit loesungsgegluehten und in Wasser abgeschreckten Legierungen zeigten im Vergleich zu einer FeCrNi-Legierung bei verschiedenen Verschleissarten (mit Ausnahme FeMn20Cr18 bei Kavitation) ein sehr gutes Triboverhalten. Gegenueber Abrasion

Modeling of Ni Diffusion Induced Austenite Formation in Ferritic Stainless Steel Interconnects

DEFF Research Database (Denmark)

Chen, Ming; Alimadadi, Hossein; Molin, Sebastian

2017-01-01

Ferritic stainless steel interconnect plates are widely used in planar solid oxide fuel cell and electrolysis cell stacks. During stack production and operation, nickel from the Ni/yttria stabilized zirconia fuel electrode or from the Ni contact component layer diffuses into the interconnect plate......, causing transformation of the ferritic phase into an austenitic phase in the interface region. This is accompanied with changes in volume, and in mechanical and corrosion properties of the interconnect plates. In this work, kinetic modeling of the inter-diffusion between Ni and FeCr based ferritic...

Influence of steel composition and plastic deformation on the surface properties induced by low temperature thermochemical processing

DEFF Research Database (Denmark)

Bottoli, Federico

to the formation of a supersaturated solid solution known as expanded austenite, or S-Phase. Expanded austenite is characterized by high hardness, up to 1400 Vickers, and high compressive stresses in the surface region, which result in improved wear and fatigue resistance of the components. Along....../nitrocarburizing on the stress distribution. The experimental techniques applied entail X-ray diffraction (XRD), Glow Discharge Optical EmissionSpectroscopy (GD-OES), Scanning electron microscopy (SEM), light optical microscopy (LOM) and hardness measurement....

Phase volume fractions and strain measurements in an ultrafine-grained NiTi shape-memory alloy during tensile loading

International Nuclear Information System (INIS)

Young, M.L.; Wagner, M.F.-X.; Frenzel, J.; Schmahl, W.W.; Eggeler, G.

2010-01-01

An ultrafine-grained pseudoelastic NiTi shape-memory alloy wire with 50.9 at.% Ni was examined using synchrotron X-ray diffraction during in situ uniaxial tensile loading (up to 1 GPa) and unloading. Both macroscopic stress-strain measurements and volume-averaged lattice strains are reported and discussed. The loading behavior is described in terms of elasto-plastic deformation of austenite, emergence of R phase, stress-induced martensitic transformation, and elasto-plastic deformation, grain reorientation and detwinning of martensite. The unloading behavior is described in terms of stress relaxation and reverse plasticity of martensite, reverse transformation of martensite to austenite due to stress relaxation, and stress relaxation of austenite. Microscopically, lattice strains in various crystallographic directions in the austenitic B2, martensitic R, and martensitic B19' phases are examined during loading and unloading. It is shown that the phase transformation occurs in a localized manner along the gage length at the plateau stress. Phase volume fractions and lattice strains in various crystallographic reflections in the austenite and martensite phases are examined over two transition regions between austenite and martensite, which have a width on the order of the wire diameter. Anisotropic effects observed in various crystallographic reflections of the austenitic phase are also discussed. The results contribute to a better understanding of the tensile loading behavior, both macroscopically and microscopically, of NiTi shape-memory alloys.

Probing the Evolution of Retained Austenite in TRIP Steel During Strain-Induced Transformation: A Multitechnique Investigation

Science.gov (United States)

Haidemenopoulos, G. N.; Constantinou, M.; Kamoutsi, H.; Krizan, D.; Bellas, I.; Koutsokeras, L.; Constantinides, G.

2018-06-01

X-ray diffraction analysis, magnetic force microscopy, and the saturation magnetization method have been employed to study the evolution of the percentage and size of retained austenite (RA) particles during strain-induced transformation in a transformation-induced plasticity (TRIP) steel. A low-alloy TRIP-700 steel with nominal composition Fe-0.2C-0.34Si-1.99Mn-1Al (mass%) was subjected to interrupted tensile testing at strain levels of 0-22% and the microstructure subsequently studied. The results of the three experimental techniques were in very good agreement regarding the estimated austenite volume fraction and its evolution with strain. Furthermore, this multitechnique approach revealed that the average particle size of RA reduced as the applied strain was increased, suggesting that larger particles are less stable and more susceptible to strain-induced phase transformation. Such experimentally determined evolution of the austenite size with strain could serve as an input to kinetic models that aim to predict the strain-induced transformation in low-alloy TRIP steels.

Thermodynamic modeling and kinetics simulation of precipitate phases in AISI 316 stainless steels

International Nuclear Information System (INIS)

Yang, Y.; Busby, J.T.

2014-01-01

This work aims at utilizing modern computational microstructural modeling tools to accelerate the understanding of phase stability in austenitic steels under extended thermal aging. Using the CALPHAD approach, a thermodynamic database OCTANT (ORNL Computational Thermodynamics for Applied Nuclear Technology), including elements of Fe, C, Cr, Ni, Mn, Mo, Si, and Ti, has been developed with a focus on reliable thermodynamic modeling of precipitate phases in AISI 316 austenitic stainless steels. The thermodynamic database was validated by comparing the calculated results with experimental data from commercial 316 austenitic steels. The developed computational thermodynamics was then coupled with precipitation kinetics simulation to understand the temporal evolution of precipitates in austenitic steels under long-term thermal aging (up to 600,000 h) at a temperature regime from 300 to 900 °C. This study discusses the effect of dislocation density and difusion coefficients on the precipitation kinetics at low temperatures, which shed a light on investigating the phase stability and transformation in austenitic steels used in light water reactors

First stage of the structural evolution of austenite in Cu-Al-Ni shape memory alloys

International Nuclear Information System (INIS)

Pelosin, V.; Gerland, M.; Riviere, A.

2001-01-01

Two shape memory Cu-Al-Ni alloys, a polycrystal and a single crystal, exhibiting a martensitic transformation close to 130 C (in the as-quenched state) have been studied. Specimens have been quenched after heat treatment at 850 C. The structural evolutions of the high temperature phase (austenite) have been studied for thermal treatments performed below 200 C. Investigations have been carried out using electrical resistivity measurements, TEM (transmission electron microscopy) observations and X-ray diffraction analysis. The main structural modifications are observed in the polycrystalline alloy and concern first, the reordering process of the austenite structure (B2→L2 1 ), and second, the precipitation of the (Cu 9 Al 4 ) γ 2 phase. In the single crystal alloy, the evolutions are very slight and localized on the structural defects. Particular attention is paid to the role of the quenched-in vacancy elimination on the observed mechanisms. In addition, the incidence of the structural evolution on the transformation temperatures is also discussed. (orig.)

Low temperature plasma carburizing of AISI 316L austenitic stainless steel and AISI F51 duplex stainless steel Cementação sob plasma à baixa temperatura do aço inoxidável austenítico AISI 316L e do aço inoxidável duplex AISI F51

OpenAIRE

Carlos Eduardo Pinedo; André Paulo Tschiptschin

2013-01-01

In this work an austenitic AISI 316L and a duplex AISI F51 (EN 1.4462) stainless steel were DC-Plasma carburized at 480ºC, using CH4 as carbon carrier gas. For the austenitic AISI 316L stainless steel, low temperature plasma carburizing induced a strong carbon supersaturation in the austenitic lattice and the formation of carbon expanded austenite (γC) without any precipitation of carbides. The hardness of the carburized AISI 316L steel reached a maximum of 1000 HV due to ∼13 at% c...

Microstructural aspects of crack formation and propagation in the austenitic steel X6CrNiNb18-10 under low cycle fatigue loading

Energy Technology Data Exchange (ETDEWEB)

Soppa, E.; Kohler, C.; Roos, E.; Schuler, X. [Stuttgart Univ. (Germany). MPA

2012-07-01

The understanding of the crack initiation mechanisms and crack growth in apparently monolithic materials like X6CrNiNb18-10 stainless steel under cyclic loading requires the explicit analysis of the phenomena underlying fatigue on both atomistic and microscopic levels. The permanent delivery of mechanical energy through cyclic loading evokes changes in the microstructure that can lead to a martensitic transformation. The transformation of a metastable cubic face centered austenite and formation of a cubic body centered α'-martensite under cyclic loading at room temperature was found, both, in the experiment and in molecular dynamics simulations. The martensite nucleates prevalently at grain boundaries, triple points and at the specimen free surface and forms small (∝ 1 μm) differently oriented grains, also in the same parent austenitic grain. By a combination of interrupted low cycle fatigue tests (LCF) and electron backscatter diffraction (EBSD) measurements the martensitic transformation and subsequent fatigue crack formation were observed at the same area in the microstructure at different stages of the specimen lifetime. The EBSD measurements showed the following crack initiation scenarios: Cracks started (a) at the phase boundary between austenite and α'-martensite, (b) inside fully martensitic areas in the matrix, (c) at broken or debonded coarse NbCs. It is obvious that formation of a hard α'-martensite in a ductile and soft austenite and forming two-phase material causes a heterogeneous stress and strain distribution on the microscopic level. α'-martensite enhances locally the stress amplitude whereas in a soft austenite the plastic strain amplitude increases. Strain concentration in the austenite along the phase boundary is connected with a stress increase along the interface and can initiate fatigue crack there. Also at the crack tip, a permanent martensitic transformation occurs, so that the growth of the fatigue cracks at room

The σ phase formation in annealed UNS S31803 duplex stainless steel: Texture aspects

International Nuclear Information System (INIS)

Souza, C.M.; Abreu, H.F.G.; Tavares, S.S.M.; Rebello, J.M.A.

2008-01-01

The influence of sigma phase precipitation on the texture of austenite in a duplex stainless steel UNS S31803 was investigated. Sigma phase quantification was precisely performed by electron backscattered scanning diffraction (EBSD) for some conditions. It was found that the increase of the sigma phase precipitation enhances the amount of Brass texture in the austenite phase

Application of Differential Scanning Calorimetry (DSC in study of phase transformations in ductile iron

Directory of Open Access Journals (Sweden)

R. Przeliorz

2010-04-01

Full Text Available The effect of heating rate on phase transformations to austenite range in ductile iron of the EN-GJS-450-10 grade was investigated. For studies of phase transformations, the technique of differential scanning calorimetry (DSC was used. Microstructure was examined by optical microscopy. The calorimetric examinations have proved that on heating three transformations occur in this grade of ductile iron, viz. magnetic transformation at the Curie temperature, pearlite→austenite transformation and ferrite→austenite transformation. An increase in the heating rate shifts the pearlite→austenite and ferrite→austenite transformations to higher temperature range. At the heating rate of 5 and 15°C/min, local extrema have been observed to occur: for pearlite→austenite transformation at 784°C and 795°C, respectively, and for ferrite→austenite transformation at 805°C and 821°C, respectively. The Curie temperature of magnetic transformation was extrapolated to a value of 740°C. Each transformation is related with a specific thermal effect. The highest value of enthalpy is accompanying the ferrite→austenite transformation, the lowest occurs in the case of pearlite→austenite transformation.

Overview of microstructural evolution in neutron-irradiated austenitic stainless steels

International Nuclear Information System (INIS)

Maziasz, P.J.

1993-01-01

Austenitic stainless steels are important structural materials common to several different reactor systems, including light water and fast breeder fission, and magnetic fusion reactors (LWR, FBR, and MFR, respectively). The microstructures that develop in 300 series austenitic stainless steels during neutron irradiation at 60-700 C include combinations of dislocation loops and networks, bubbles and voids, and various kinds of precipitate phases (radiation-induced, or -enhanced or -modified thermal phases). Many property changes in these steels during neutron irradiation are directly or indirectly related to radiation-induced microstructural evolution. Even more important is the fact that radiation-resistance of such steels during either FBR or MFR irradiation is directly related to control of the evolving microstructure during such irradiation. The purpose of this paper is to provide an overview of the large and complex body of data accumulated from various fission reactor irradiation experiments conducted over the many years of research on microstructural evolution in this family of steels. The data can be organized into several different temperature regimes which then define the nature of the dominant microstructural components and their sensitivities to irradiation parameters (dose, helium/dpa ratio, dose rate) or metallurgical variables (alloy composition, pretreatment). The emphasis in this paper will be on the underlying mechanisms driving the microstructure to evolve during irradiation or those enabling microstructural stability related to radiation resistance. (orig.)

Ultrasonic inspectability of austenitic stainless steel and dissimilar metal weld joints

Energy Technology Data Exchange (ETDEWEB)

Pudovikov, S.; Bulavinov, A.; Kroening, M. [Fraunhofer-Institut fuer Zerstoerungsfreie Pruefverfahren IZFP, Saarbruecken (Germany)

2008-07-01

Since their invention in 1912, austenitic stainless steel materials are widely used in a variety of industry sectors. In particular, austenitic stainless steel material is qualified to meet the design criteria of high quality, safety related applications, for example, the primary loop of the most of the nuclear power plants in the world, due to high durability and corrosion resistance. Certain operating conditions may cause a range of changes in the integrity of the component, and therefore require nondestructive testing at reasonable intervals. These in-service inspections are often performed using ultrasonic techniques, in particular when cracking is of specific concern. However, the coarse, dendritic grain structure of the weld material, formed during the welding process, is extreme and unpredictably anisotropic. Such structure is no longer direction-independent to the ultrasonic wave propagation; therefore, the ultrasonic beam deflects and redirects and the wave front becomes distorted. Thus, the use of conventional ultrasonic testing techniques using fixed beam angles is very limited and the application of ultrasonic Phased Array techniques becomes desirable. The ''Sampling Phased Array'' technique, invented and developed by Fraunhofer IZFP, allows the acquisition of time signals (A-scans) for each individual transducer element of the array along with image reconstruction techniques using ''SynFoc'' algorithms. The reconstruction considers the sound propagation from each image pixel to the individual sensor element. For anisotropic media, where the sound beam is deflected and the sound path is not known a-priory, we implement a new phase adjustment called ''Reverse Phase Matching'' technique. This algorithm permits the acquisition of phase-corrected A-scans that represent the actual sound propagation in the anisotropic structure; this technique can be utilized for image reconstruction. (orig.)

Effect of plastic deformation on the supercooled austenite transformations of the Cr-Mo steel with Nb, Ti and B microadditions

International Nuclear Information System (INIS)

Adamczyk, J.; Opiela, M.

1998-01-01

Effect of plastic deformation at austenizing temperature was investigated on phase transformations, structure and hardness of the supercooled austenite transformation products of the Cr-Mo constructional steel with Nb, Ti and B microadditions. Basing on the analysis of the phase transformation plots of the supercooled undeformed austenite and of the supercooled and plastically deformed one, it was found out that direct cooling of specimens after completing their plastic deformation in the above mentioned conditions, results in significant acceleration of the α→β, and ferritic and pearlitic transformations, and in the decrease of transformation products hardness. These phenomena are of great importance for working out of the thermo-mechanical treatment of products made from the heat-treated microalloyed steel. (author)

Precipitation kinetics in austenitic 18Cr-30Ni-Nb cast steel

Directory of Open Access Journals (Sweden)

M. Garbiak

2008-08-01

Full Text Available The study presents the results of investigations on the precipitation kinetics in austenitic 18%Cr-30%Ni cast steel stabilised with an addition of 1.84 wt% niobium. Phase analysis of isolates extracted from the alloy subjected to annealing within the temperature range of 600–1000oC during 10–1000 h was made. The phase constitution of the isolates mainly comprised niobium carbides of the NbC type and complex chromium carbides of the Cr23C6 type. In specimens annealed within the temperature range of 700–900oC, a high-silicon G phase was additionally identified. The highest kinetics of the precipitation process was recorded after annealing at the temperatures of 800 and 900oC.

The carbide M7C3 in low-temperature-carburized austenitic stainless steel

International Nuclear Information System (INIS)

Ernst, Frank; Li, Dingqiang; Kahn, Harold; Michal, Gary M.; Heuer, Arthur H.

2011-01-01

Prolonged low-temperature gas-phase carburization of AISI 316L-type austenitic stainless steel can cause intragranular precipitation of the carbide M 7 C 3 (M: randomly dispersed Fe, Cr, Ni). Transmission electron microscopy revealed that the carbide particles have the shape of needles. They grow by a ledge-migration mechanism and in a crystallographic orientation relationship to the austenite matrix that enables highly coherent interphase interfaces. A small solubility limit of Ni in the carbide and restricted Ni diffusivity at the processing temperature leads to Ni pileup around the particles and may explain the extreme aspect ratio of the particle shape. These characteristics closely resemble what has been observed earlier for precipitates of M 5 C 2 under slightly different processing conditions and can be rationalized by considering the particular constraints imposed by carburization at low temperature.

Hydrogen gas embrittlement of stainless steels mainly austenitic steels. Volumes 1 and 2

International Nuclear Information System (INIS)

Azou, P.

1988-01-01

Steel behavior in regard to hydrogen is examined especially austenitic steels. Gamma steels are studied particularly the series 300 with various stabilities and gamma steels with improved elasticity limit for intermetallic phase precipitation and nitrogen additions. A two-phase structure γ + α' is also studied. All the samples are tested for mechanical behavior in gaseous hydrogen. Influence of metallurgical effects and of testing conditions on hydrogen embrittlement are evidenced. Microstructure resulting from mechanical or heat treatments, dislocation motion during plastic deformation and influence of deformation rate are studied in detail [fr

Modeling of Ni Diffusion Induced Austenite Formation in Ferritic Stainless Steel Interconnects

DEFF Research Database (Denmark)

Chen, Ming; Molin, Sebastian; Zhang, L.

2015-01-01

Ferritic stainless steel interconnect plates are widely used in planar solid oxide fuel cell (SOFC) or electrolysis cell (SOEC) stacks. During stack production and operation, nickel from the Ni/YSZ fuel electrode or from the Ni contact component diffuses into the IC plate, causing transformation...... of the ferritic phase into an austenitic phase in the interface region. This is accompanied with changes in volume and in mechanical and corrosion properties of the IC plates. In this work, kinetic modeling of the inter-diffusion between Ni and FeCr based ferritic stainless steel was conducted, using the CALPHAD...

Correlation between microstructure and mechanical properties of stable mixtures formed by austenite and martensite

International Nuclear Information System (INIS)

Eckstein, C.B.

1982-03-01

The influence of martensite in mechanical properties of stable mixtures formed by austenite and martensite was studied by varying the amount of martensite in the mixtures. Microstructural parameters were determined by Optical Quantitative Metallography and used to establish the correlation between the mechanical response of the mixtures in tension and their microstructures. The 'in situ' deformation of each phase in mixtures was determined experimentally in terms of the rule of mixtures. It is shown that the partitioning of the deformation depends on the amount of martensite in the mixture and that it tends to a condition of isostrain at higher martensite volume fractions. Optical observation of fractured specimens showed that the beginning of the fracture process may related to regions of the austenite grain boundaries where they meet martensite plates. (Author) [pt

Real time neutron transmission investigation of the austenite-bainite transformation in grey iron

International Nuclear Information System (INIS)

Meggers, Kay; Priesmeyer, Hans G.; Trela, Walter J.; Bowman, Charles D.; Dahms, Michael

1994-01-01

The first successful application of a new method to investigate phase transformations in real time, like the decomposition of austenite into bainite in grey iron, is described. During the ongoing transformation, transmission spectra of thermal neutrons, which contain Bragg edges corresponding to the crystal structure of the transforming phases, are recorded. By evaluating the height of these Bragg edges, which is a measure of the volume fraction of the phase, at different transformation times, the transformation can be followed in-situ in a time resolved manner. The method is compared to other previously used methods (micrographs, dilatometry, diffraction techniques); also a summary and an outlook are given. ((orig.))

Erosion-corrosion resistance properties of 316L austenitic stainless steels after low-temperature liquid nitriding

Science.gov (United States)

Zhang, Xiangfeng; Wang, Jun; Fan, Hongyuan; Pan, Dong

2018-05-01

The low-temperature liquid nitriding of stainless steels can result in the formation of a surface zone of so-called expanded austenite (S-phase) by the dissolution of large amounts of nitrogen in the solid solution and formation of a precipitate-free layer supersaturated with high hardness. Erosion-corrosion measurements were performed on low-temperature nitrided and non-nitrided 316L stainless steels. The total erosion-corrosion, erosion-only, and corrosion-only wastages were measured directly. As expected, it was shown that low-temperature nitriding dramatically reduces the degree of erosion-corrosion in stainless steels, caused by the impingement of particles in a corrosive medium. The nitrided 316L stainless steels exhibited an improvement of almost 84% in the erosion-corrosion resistance compared to their non-nitrided counterparts. The erosion-only rates and synergistic levels showed a general decline after low-temperature nitriding. Low-temperature liquid nitriding can not only reduce the weight loss due to erosion but also significantly reduce the weight loss rate of interactions, so that the total loss of material decreased evidently. Therefore, 316L stainless steels displayed excellent erosion-corrosion behaviors as a consequence of their highly favorable corrosion resistances and superior wear properties.

Modeling of Non-isothermal Austenite Formation in Spring Steel

Science.gov (United States)

Huang, He; Wang, Baoyu; Tang, Xuefeng; Li, Junling

2017-12-01

The austenitization kinetics description of spring steel 60Si2CrA plays an important role in providing guidelines for industrial production. The dilatometric curves of 60Si2CrA steel were measured using a dilatometer DIL805A at heating rates of 0.3 K to 50 K/s (0.3 °C/s to 50 °C/s). Based on the dilatometric curves, a unified kinetics model using the internal state variable (ISV) method was derived to describe the non-isothermal austenitization kinetics of 60Si2CrA, and the abovementioned model models the incubation and transition periods. The material constants in the model were determined using a genetic algorithm-based optimization technique. Additionally, good agreement between predicted and experimental volume fractions of transformed austenite was obtained, indicating that the model is effective for describing the austenitization kinetics of 60Si2CrA steel. Compared with other modeling methods of austenitization kinetics, this model, which uses the ISV method, has some advantages, such as a simple formula and explicit physics meaning, and can be probably used in engineering practice.

Reversed austenite for enhancing ductility of martensitic stainless steel

Science.gov (United States)

Dieck, S.; Rosemann, P.; Kromm, A.; Halle, T.

2017-03-01

The novel heat treatment concept, “quenching and partitioning” (Q&P) has been developed for high strength steels with enhanced formability. This heat treatment involves quenching of austenite to a temperature between martensite start and finish, to receive a several amount of retained austenite. During the subsequent annealing treatment, the so called partitioning, the retained austenite is stabilized due to carbon diffusion, which results in enhanced formability and strength regarding strain induced austenite to martensite transformation. In this study a Q&P heat treatment was applied to a Fe-0.45C-0.65Mn-0.34Si-13.95Cr stainless martensite. Thereby the initial quench end temperature and the partitioning time were varied to characterize their influence on microstructural evolution. The microstructural changes were analysed by dilatometer measurements, X-ray diffraction and scanning electron microscopy, including electron back-scatter diffraction. Compression testing was made to examine the mechanical behaviour. It was found that an increasing partitioning time up to 30 min leads to an enhanced formability without loss in strength due to a higher amount of stabilized retained and reversed austenite as well as precipitation hardening.

Influence of Plastic Deformation on Low-Temperature Surface Hardening of Austenitic Stainless Steel by Gaseous Nitriding

DEFF Research Database (Denmark)

Bottoli, Federico; Winther, Grethe; Christiansen, Thomas Lundin

2015-01-01

This article addresses an investigation of the influence of plastic deformation on low-temperature surface hardening by gaseous nitriding of two commercial stainless steels: EN 1.4369 and AISI 304. The materials were plastically deformed to several levels of equivalent strain by conventional......, reflected-light microscopy, and microhardness testing. The results demonstrate that a case of expanded austenite develops and that the presence of plastic deformation has a significant influence on the morphology of the nitrided case. The presence of strain-induced martensite favors the formation of Cr...

The characteristics creep fracture of austenitic stainless steels

International Nuclear Information System (INIS)

Monteiro, S.N.; Assis, A.M.C.A.

1977-05-01

The characteristics of fracture on creep of two AISI type 316 austenitic stainless steels tested at constant load from 600 to 800 0 C were studied by scanning electron microscopy. The morphological aspects of the fracture were analysed and correllated to the ductility level attained in creep. A marked change from intergranular to transgranular type of fracture was observed in going from 600 to 800 0 C. At 800 0 C on the other hand, the condition for crack nucleation at sigma phase as well as the special conditions of oxidation, are apparently responsible for that same change with the applied stress. (Author) [pt

New microstructural features occurring during transformation from austenite to ferrite under the kinetic influence of magnetic field in a medium carbon steel

International Nuclear Information System (INIS)

Zhang Yudong; He Changshu; Zhao Xiang; Zuo Liang; Esling, Claude; He, Jicheng

2004-01-01

The effects of magnetic field on nucleation barrier of the phase transformation from austenite to ferrite at different cooling rates in 42CrMo steel have been investigated. The microstructures of ferrite and pearlite aligned along the magnetic field direction (parallel to the hot-rolling direction) are obtained at a cooling rate of 10 deg. C/min, resulting from the kinetic effects of the applied magnetic field during cooling and the microstructural influences of an inhomogeneous deformation occurring during the previous hot rolling. In this case, the formation of ferrite grains at higher temperatures is attributed mainly to the preferential nucleation at austenite boundaries. However, a fairly uniform microstructure of randomly distributed ferrite and pearlite is formed at a high cooling rate of 46 deg. C/min in the magnetic field of 14 T, as a result of both intergranular and intragranular nucleation at relatively low temperatures. Probing into this issue is helpful to gain a better understanding of kinetic influences of magnetic field on the phase transformation from austenite to ferrite

Microstructural evolution in deformed austenitic TWinning Induced Plasticity steels

NARCIS (Netherlands)

Van Tol, R.T.

2014-01-01

This thesis studies the effect of plastic deformation on the stability of the austenitic microstructure against martensitic transformation and diffusional decomposition and its role in the phenomenon of delayed fracture in austenitic manganese (Mn)-based TWinning Induced Plasticity (TWIP) steels.

Effect of Ferrite Morphology on Sensitization of 316L Austenitic Stainless Steels

Energy Technology Data Exchange (ETDEWEB)

Jang, Hun; Lee, Jun Ho; Jang, Changheui [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of)

2013-05-15

The sensitization behaviors of L-grade SSs having predominant austenitic structure with small amount of ferrite have not been well understood. In this regard, the effect of ferrite morphology on sensitization was investigated in this study. The sensitization behaviors of three heats of 316L and 316LN SSs were investigated, Stringer type of ferrite (316L - heat A and B) showed the early sensitization by chromium depletion at ferrite. austenite interface. And, later sensitization is due to GB sensitization. On the other hand, blocky type of ferrite (316L - heat C) showed lower DOS and higher resistance to GB sensitization. It could be due to sufficient supply of chromium from relatively large ferrite phase. As a consequence, the sensitization of 316L SSs could be affected by their ferrite morphology rather than ferrite content. The sensitized region was distinguishable from results of DL-EPR tests. It can be used as an effective method for evaluation of type of sensitization.

Development of Ultra-Fine-Grained Structure in AISI 321 Austenitic Stainless Steel

Science.gov (United States)

Tiamiyu, A. A.; Szpunar, J. A.; Odeshi, A. G.; Oguocha, I.; Eskandari, M.

2017-12-01

Ultra-fine-grained (UFG) structure was developed in AISI 321 austenitic stainless steel (ASS) using cryogenic rolling followed by annealing treatments at 923 K, 973 K, 1023 K, and 1073 K (650 °C, 700 °C, 750 °C, and 800 °C) for different lengths of time. The α'-martensite to γ-austenite reversion behavior and the associated texture development were analyzed in the cryo-rolled specimens after annealing. The activation energy, Q, required for the reversion of α'-martensite to γ-austenite in the steel was estimated to be 80 kJ mol-1. TiC precipitates and unreversed triple junction α'-martensite played major roles in the development of UFG structure through the Zener pinning of grain boundaries. The optimum annealing temperature and time for the development of UFG structure in the cryo-rolled AISI 321 steel are (a) 923 K (650 °C) for approximately 28800 seconds and (b) 1023 K (750 °C) for 600 seconds, with average grain sizes of 0.22 and 0.31 µm, respectively. Annealing at 1023 K (750 °C) is considered a better alternative since the volume fraction of precipitated carbides in specimens annealed at 1023 K (750 °C) are less than those annealed at 923 K (650 °C). More so, the energy consumption during prolonged annealing time to achieve an UFG structure at 923 K (650 °C) is higher due to low phase reversion rate. The hardness of the UFG specimens is 195 pct greater than that of the as-received steel. The higher volume fraction of TiC precipitates in the UFG structure may be an additional source of hardening. Micro and macrotexture analysis indicated {110}〈uvw〉 as the major texture component of the austenite grains in the UFG structure. Its intensity is stronger in the specimen annealed at low temperatures.

Microstructure characterization in domestically-made TP310HNbN austenitic stainless steel after creep test

Science.gov (United States)

Guo, Yan; Lin, Lin; Hou, Shufang; Wang, Bohan

Microstructure characterization of domestically-made TP310HNbN austenitic stainless steel after creep test was investigated by means of transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results revealed that M23C6 carbides precipitated both inside grains and at the grain boundaries and NbCrN particles were located inside grains for creep-rupture samples. It was clear that sigma phase and NbC particles precipitated inside grains for the creep-rupture sample at 670 C. M23C6 carbides with lattice parameter of three times of the austenite matrix grow in a cube to cube orientation relationship with the matrix. The amount of M23C6 carbide particles obviously increased with the testing time prolonged. Deformation hardening induced an enhanced hardness nearby rupture surface for the creep-rupture samples with a short testing time. For the domestically-made TP310HNbN steel, great attention should be paid to the distribution, size and amount of sigma phase and M23C6 during service.

Morphology change of retained austenite during austempering of carbide-free bainitic steel

Energy Technology Data Exchange (ETDEWEB)

Hofer, Christina, E-mail: christina.hofer@unileoben.ac.at [Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, Franz-Josef-Straße 18, 8700 Leoben (Austria); Winkelhofer, Florian [Research and Development - Business Unit Coil, voestalpine Stahl GmbH, voestalpine‐Straße 3, A-4020 Linz (Austria); Clemens, Helmut; Primig, Sophie [Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, Franz-Josef-Straße 18, 8700 Leoben (Austria)

2016-05-10

A change in the mechanical properties of a carbide-free bainitic steel was observed during prolonged holding at austempering temperature after termination of the bainitic transformation. To determine the origin of the property change, the microstructure was investigated by correlative electron microscopy. Although the retained austenite content remains the same during prolonged holding, its morphology changes from thin films separating the individual bainitic sub-units to a more globular structure. Since films of austenite contain a higher C concentration, the blocky austenite becomes gradually enriched in C during this morphology change. The more homogeneous distribution of the C after prolonged austempering leads to higher deformability as a result of a more pronounced TRIP effect. - Highlights: • Higher deformability after prolonged austempering of carbide-free bainite. • Microstructure-property relationship revealed by correlative electron microscopy. • Change in austenite morphology. • Spherodization of film austenite; C enrichment & homogenization of blocky austenite.

Evaluation of Microstructure and Mechanical Properties in Dissimilar Austenitic/Super Duplex Stainless Steel Joint

Science.gov (United States)

Rahmani, Mehdi; Eghlimi, Abbas; Shamanian, Morteza

2014-10-01

To study the effect of chemical composition on microstructural features and mechanical properties of dissimilar joints between super duplex and austenitic stainless steels, welding was attempted by gas tungsten arc welding process with a super duplex (ER2594) and an austenitic (ER309LMo) stainless steel filler metal. While the austenitic weld metal had vermicular delta ferrite within austenitic matrix, super duplex stainless steel was mainly comprised of allotriomorphic grain boundary and Widmanstätten side plate austenite morphologies in the ferrite matrix. Also the heat-affected zone of austenitic base metal comprised of large austenite grains with little amounts of ferrite, whereas a coarse-grained ferritic region was observed in the heat-affected zone of super duplex base metal. Although both welded joints showed acceptable mechanical properties, the hardness and impact strength of the weld metal produced using super duplex filler metal were found to be better than that obtained by austenitic filler metal.

Mechanical and microstructural aspects of severe plastic deformation of austenitic steel

Science.gov (United States)

Rodak, K.; Pawlicki, J.; Tkocz, M.

2012-05-01

The paper presents the effects of severe plastic deformation by multiple compression in the orthogonal directions on the microstructure and the mechanical properties of austenitic steel. Several deformation variants were conducted with different number of passes. FEM simulations were performed in order to evaluate the actual values of the effective strain in the examined, central parts of the compressed samples. The deformed microstructure was investigated by means of the scanning transmission electron microscopy (STEM) and the scanning electron microscopy (SEM) supported by the electron back scattered diffraction (EBSD). X-ray phase analysis was performed to evaluate the martensite volume fraction. The mechanical properties were determined by means of the digital image correlation method and hardness testing. It is shown that the applied forming technique leads to strong grain refinement in the austenitic steel. Moreover, deformation induces the martensitic γ- α' transformation. The microstructural changes cause an improvement in the strength properties. The material exhibits the ultimate tensile strength of 1560 MPa and the yield stress of 1500 MPa after reaching the effective strain of 10.

Mechanical and microstructural aspects of severe plastic deformation of austenitic steel

International Nuclear Information System (INIS)

Rodak, K; Pawlicki, J; Tkocz, M

2012-01-01

The paper presents the effects of severe plastic deformation by multiple compression in the orthogonal directions on the microstructure and the mechanical properties of austenitic steel. Several deformation variants were conducted with different number of passes. FEM simulations were performed in order to evaluate the actual values of the effective strain in the examined, central parts of the compressed samples. The deformed microstructure was investigated by means of the scanning transmission electron microscopy (STEM) and the scanning electron microscopy (SEM) supported by the electron back scattered diffraction (EBSD). X-ray phase analysis was performed to evaluate the martensite volume fraction. The mechanical properties were determined by means of the digital image correlation method and hardness testing. It is shown that the applied forming technique leads to strong grain refinement in the austenitic steel. Moreover, deformation induces the martensitic γ– α' transformation. The microstructural changes cause an improvement in the strength properties. The material exhibits the ultimate tensile strength of 1560 MPa and the yield stress of 1500 MPa after reaching the effective strain of 10.

In-Situ Investigation of Strain-Induced Martensitic Transformation Kinetics in an Austenitic Stainless Steel by Inductive Measurements

Directory of Open Access Journals (Sweden)

Carola Celada-Casero

2017-07-01

Full Text Available An inductive sensor developed by Philips ATC has been used to study in-situ the austenite (γ to martensite (α′ phase transformation kinetics during tensile testing in an AISI 301 austenitic stainless steel. A correlation between the sensor output signal and the volume fraction of α′-martensite has been found by comparing the results to the ex-situ characterization by magnetization measurements, light optical microscopy, and X-ray diffraction. The sensor has allowed for the observation of the stepwise transformation behavior, a not-well-understood phenomena that takes place in large regions of the bulk material and that so far had only been observed by synchrotron X-ray diffraction.

Nearly scale-invariant spectrum of adiabatic fluctuations may be from a very slowly expanding phase of the Universe

International Nuclear Information System (INIS)

Piao Yunsong; Zhou, E.

2003-01-01

In this paper we construct an expanding phase with phantom matter, in which the scale factor expands very slowly but the Hubble parameter increases gradually, and assume that this expanding phase could be matched to our late observational cosmology by the proper mechanism. We obtain the nearly scale-invariant spectrum of adiabatic fluctuations in this scenario; different from the simplest inflation and usual ekpyrotic or cyclic scenario, the tilt of the nearly scale-invariant spectrum in this scenario is blue. Although there exists an uncertainty surrounding the way in which the perturbations propagate through the transition in our scenario, which is dependent on the details of possible 'bounce' physics, compared with inflation and the ekpyrotic or cyclic scenario, our work may provide another feasible cosmological scenario generating the nearly scale-invariant perturbation spectrum

Microstructural features of dissimilar welds between 316LN austenitic stainless steel and alloy 800

International Nuclear Information System (INIS)

Sireesha, M.; Sundaresan, S.

2000-01-01

For joining type 316LN austenitic stainless steel to modified 9Cr-1Mo steel for power plant application, a trimetallic configuration using an insert piece (such as alloy 800) of intermediate thermal coefficient of expansion (CTE) has been sometimes suggested for bridging the wide gap in CTE between the two steels. Two joints are thus involved and this paper is concerned with the weld between 316LN and alloy 800. These welds were produced using three types of filler materials: austenitic stainless steels corresponding to 316,16Cr-8Ni-2Mo, and the nickel-base Inconel 182 1 . The weld fusion zones and the interfaces with the base materials were characterised in detail using light and transmission electron microscopy. The 316 and Inconel 182 weld metals solidified dendritically, while the 16-8-2(16%Cr-8%Ni-2%Mo) weld metal showed a predominantly cellular substructure. The Inconel weld metal contained a large number of inclusions when deposited from flux-coated electrodes, but was relatively inclusion-free under inert gas-shielded welding. Long-term elevated-temperature aging of the weld metals resulted in embrittling sigma phase precipitation in the austenitic stainless steel weld metals, but the nickel-base welds showed no visible precipitation, demonstrating their superior metallurgical stability for high-temperature service. (orig.)

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.

In Situ Local Measurement of Austenite Mechanical Stability and Transformation Behavior in Third-Generation Advanced High-Strength Steels

Science.gov (United States)

Abu-Farha, Fadi; Hu, Xiaohua; Sun, Xin; Ren, Yang; Hector, Louis G.; Thomas, Grant; Brown, Tyson W.

2018-05-01

Austenite mechanical stability, i.e., retained austenite volume fraction (RAVF) variation with strain, and transformation behavior were investigated for two third-generation advanced high-strength steels (3GAHSS) under quasi-static uniaxial tension: a 1200 grade, two-phase medium Mn (10 wt pct) TRIP steel, and a 980 grade, three-phase TRIP steel produced with a quenching and partitioning heat treatment. The medium Mn (10 wt pct) TRIP steel deforms inhomogeneously via propagative instabilities (Lüders and Portevin Le Châtelier-like bands), while the 980 grade TRIP steel deforms homogenously up to necking. The dramatically different deformation behaviors of these steels required the development of a new in situ experimental technique that couples volumetric synchrotron X-ray diffraction measurement of RAVF with surface strain measurement using stereo digital image correlation over the beam impingement area. Measurement results with the new technique are compared to those from a more conventional approach wherein strains are measured over the entire gage region, while RAVF measurement is the same as that in the new technique. A determination is made as to the appropriateness of the different measurement techniques in measuring the transformation behaviors for steels with homogeneous and inhomogeneous deformation behaviors. Extension of the new in situ technique to the measurement of austenite transformation under different deformation modes and to higher strain rates is discussed.

Effect of Prior Austenite Grain Size on the Morphology of Nano-Bainitic Steels

Science.gov (United States)

Singh, Kritika; Kumar, Avanish; Singh, Aparna

2018-04-01

The strength in nanostructured bainitic steels primarily arises from the fine platelets of bainitic ferrite embedded in carbon-enriched austenite. However, the toughness is dictated by the shape and volume fraction of the retained austenite. Therefore, the exact determination of processing-morphology relationships is necessary to design stronger and tougher bainite. In the current study, the morphology of bainitic ferrite in Fe-0.89C-1.59Si-1.65Mn-0.37Mo-1Co-0.56Al-0.19Cr (wt pct) bainitic steel has been investigated as a function of the prior austenite grain size (AGS). Specimens were austenitized at different temperatures ranging from 900 °C to 1150 °C followed by isothermal transformation at 300 °C. Detailed microstructural characterization has been carried out using scanning electron microscopy and X-ray diffraction. The results showed that the bainitic laths transformed in coarse austenite grains are finer resulting in higher hardness, whereas smaller austenite grains lead to the formation of thicker bainitic laths with a large fraction of blocky type retained austenite resulting in lower hardness.

Aspects and mechanisms of austenitic stainless steel corrosion in case of sodium leaks under mineral wool insulation

International Nuclear Information System (INIS)

Bertrand, C.; Ardellier, A.

1996-01-01

Sodium pipe rupture tests representative of Fast Reactors Accidents have been carried out on austenitic stainless steel surfaces. These tests improve our knowledge of small sodium leakage propagation in mineral wool insulation. They explain the new and unexpected aspects of the crevice corrosion phenomenon which has been observed on austenitic stainless steel pipe surfaces. Experimental results show that corrosion is limited to a peripheral annular zone, which extends out in concentric waves. The diameter of this corrosion zone is practically constant. Tests show that sodium does not expand directly on the pipe surface. Sodium sprays through mineral wool insulation, where chemical reaction between silica fibers, occluded oxygen and water vapor occur at the same time. Simultaneously, there is a diffusion phenomenon of liquid Na droplets on the mineral wool fibers. The study allows to prove the electrochemical nature of the corrosion. The excess liquid Na, spraying as droplets induces an anodic dissolution mechanism by differential aeration. This phenomenon explains the random microscopic and macroscopic aspects of material removal. (authors). 1 ref., 16 figs

Reformed austenite transformation during fatigue crack propagation of 13%Cr-4%Ni stainless steel

Energy Technology Data Exchange (ETDEWEB)

Thibault, Denis, E-mail: thibault.denis@ireq.ca [Institut de recherche d' Hydro-Quebec (IREQ), 1800, boul. Lionel-Boulet, Varennes, Quebec, J3X 1S1 (Canada); Bocher, Philippe, E-mail: philippe.bocher@etsmtl.ca [Ecole de technologie superieure, 1100, rue Notre-Dame Ouest, Montreal, Quebec, H3C 1K3 (Canada); Thomas, Marc, E-mail: marc.thomas@etsmtl.ca [Ecole de technologie superieure, 1100, rue Notre-Dame Ouest, Montreal, Quebec, H3C 1K3 (Canada); Lanteigne, Jacques, E-mail: lanteigne.jacques@ireq.ca [Institut de recherche d' Hydro-Quebec (IREQ), 1800, boul. Lionel-Boulet, Varennes, Quebec, J3X 1S1 (Canada); Hovington, Pierre, E-mail: hovington.pierre@ireq.ca [Institut de recherche d' Hydro-Quebec (IREQ), 1800, boul. Lionel-Boulet, Varennes, Quebec, J3X 1S1 (Canada); Robichaud, Patrice, E-mail: patrice.robichaud@riotinto.com [Centre de recherche et de developpement Arvida (CRDA), 1955, boul. Mellon, Jonquiere, Quebec, G7S 4K8 (Canada)

2011-08-15

Highlights: {yields} Reformed austenite in 13%Cr-4%Ni stainless steel transforms during fatigue crack growth. {yields} Low cycle fatigue tests showed that this transformation to martensite is gradual. {yields} XRD spectrums obtained on the fracture surface and have been correlated to LCF results. - Abstract: In the as-quenched state, 13%Cr-4%Ni martensitic stainless steels are essentially 100% martensitic. However, a certain amount of austenite is formed during the tempering of this alloy. This reformed austenite is thermally stable at room temperature but can transform to martensite under stress. This transformation is known to happen during impact testing but it has never been established if it occurs during fatigue crack propagation. This study presents the results of X-ray diffraction measurements of reformed austenite before and after crack growth testing. It has been found that reformed austenite does transform to martensite at the crack tip and that this transformation occurs even at a low stress intensity factor. Low-cycle fatigue tests were conducted to verify austenite transformation under cyclic straining. It was found that reformed austenite transforms only partially during the first strain reversal but that essentially all austenite has disappeared after 100 cycles. The relation between austenite transformation under low-cycle fatigue and its transformation during crack growth is also discussed.

Reformed austenite transformation during fatigue crack propagation of 13%Cr-4%Ni stainless steel

International Nuclear Information System (INIS)

Thibault, Denis; Bocher, Philippe; Thomas, Marc; Lanteigne, Jacques; Hovington, Pierre; Robichaud, Patrice

2011-01-01

Highlights: → Reformed austenite in 13%Cr-4%Ni stainless steel transforms during fatigue crack growth. → Low cycle fatigue tests showed that this transformation to martensite is gradual. → XRD spectrums obtained on the fracture surface and have been correlated to LCF results. - Abstract: In the as-quenched state, 13%Cr-4%Ni martensitic stainless steels are essentially 100% martensitic. However, a certain amount of austenite is formed during the tempering of this alloy. This reformed austenite is thermally stable at room temperature but can transform to martensite under stress. This transformation is known to happen during impact testing but it has never been established if it occurs during fatigue crack propagation. This study presents the results of X-ray diffraction measurements of reformed austenite before and after crack growth testing. It has been found that reformed austenite does transform to martensite at the crack tip and that this transformation occurs even at a low stress intensity factor. Low-cycle fatigue tests were conducted to verify austenite transformation under cyclic straining. It was found that reformed austenite transforms only partially during the first strain reversal but that essentially all austenite has disappeared after 100 cycles. The relation between austenite transformation under low-cycle fatigue and its transformation during crack growth is also discussed.

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

International Nuclear Information System (INIS)

Jiao, Dongling; Luo, Chengping; Liu, Jiangwen; Zhang, Guoqing

2014-01-01

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 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 4 N) packets and (ii) with the ultrafine α-Fe and γ/γ′-Fe 4 N laths interwoven with each other within a single bainitic packet. A cube–cube orientation relationship between the γ (austenite) and γ′-Fe 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 4 N kept a near G-T OR in the grain interior

Investigation of in-plane biaxial low cycle fatigued austenitic stainless steel AISI 321. II. Neutron diffraction stress analysis at the IBR-2 pulsed nuclear reactor

International Nuclear Information System (INIS)

Taran, Yu.V.; Balagurov, A.M.; Sheverev, S.G.; ); Schreiber, J.; Bomas, H.; Korsunsky, A.M.

2007-01-01

The in-plane biaxial low cycle fatigued sample of the cruciform geometry from austenitic stainless steel AISI 321 was investigated on the time-of-flight neutron Fourier stress-diffractometer. The lattice parameters in the austenite matrix and the martensite inclusions created during the fatigue cycling as well as the martensite volume fraction were measured along two mutually perpendicular planar axes of the sample of the cruciform geometry by using the strain neutron scanner. The phase total residual strain components were calculated using the stress equilibrium relations. The separation of the residual stresses into macro- and microstresses was performed using the mixture rule. The measurements of the applied load-phase elastic strain responses were carried out on a uniaxial load machine. The strong difference between the phase elastic moduli was found out

Precipitation and cavity formation in austenitic stainless steels during irradiation

International Nuclear Information System (INIS)

Lee, E.H.; Rowcliffe, A.F.; Mansur, L.K.

1982-01-01

Microstructural evolution in austenitic stainless steels subjected to displacement damage at high temperature is strongly influenced by the interaction between helium atoms and second phase particles. Cavity nucleation occurs by the trapping of helium at partially coherent particle-matrix interfaces. The recent precipitate point defect collector theory describes the more rapid growth of precipitate-attached cavities compared to matrix cavities where the precipitate-matrix interface collects point defects to augment the normal point deflect flux to the cavity. Data are presented which support these ideas. It is shown that during nickel ion irradiation of a titanium-modified stainless steel at 675 0 C the rate of injection of helium has a strong effect on the total swelling and also on the nature and distribution of precipitate phases. (orig.)

Structural transformations in austenitic stainless steel induced by deuterium implantation: irradiation at 100 K.

Science.gov (United States)

Morozov, Oleksandr; Zhurba, Volodymyr; Neklyudov, Ivan; Mats, Oleksandr; Rud, Aleksandr; Chernyak, Nikolay; Progolaieva, Viktoria

2015-01-01

Deuterium thermal desorption spectra were investigated on the samples of austenitic stainless steel 18Cr10NiTi preimplanted at 100 K with deuterium ions in the dose range from 3 × 10(15) to 5 × 10(18) D/cm(2). The kinetics of structural transformation development in the implantation steel layer was traced from deuterium thermodesorption spectra as a function of implanted deuterium concentration. At saturation of austenitic stainless steel 18Cr10NiTi with deuterium by means of ion implantation, structural-phase changes take place, depending on the dose of implanted deuterium. The maximum attainable concentration of deuterium in steel is C = 1 (at.D/at.met. = 1/1). The increase in the implanted dose of deuterium is accompanied by the increase in the retained deuterium content, and as soon as the deuterium concentration attains C ≈ 0.5 the process of shear martensitic structural transformation in steel takes place. It includes the formation of bands, body-centered cubic (bcc) crystal structure, and the ferromagnetic phase. Upon reaching the deuterium concentration C > 0.5, the presence of these molecules causes shear martensitic structural transformations in the steel, which include the formation of characteristic bands, bcc crystal structure, and the ferromagnetic phase. At C ≥ 0.5, two hydride phases are formed in the steel, the decay temperatures of which are 240 and 275 K. The hydride phases are formed in the bcc structure resulting from the martensitic structural transformation in steel.

The sub-zero Celsius treatment of precipitation hardenable semi-austenitic stainless steel

DEFF Research Database (Denmark)

Villa, Matteo; Hansen, Mikkel Fougt; Somers, Marcel A. J.

2015-01-01

A precipitation hardenable semi-austenitic stainless steel AISI 632 grade was austenitized according to industrial specifications and thereafter subjected to isothermal treatment at sub-zero Celsius temperatures. During treatment, austenite transformed to martensite. The isothermal austenite-to-martensite...... treatment. Magnetometry showed that the additional thermal step in boiling nitrogen yields a minor increment of the fraction of martensite, but has a noteworthy accelerating effect on the transformation kinetics, which more pronounced when the isothermal holding is performed at a higher temperature. Data...... is interpreted in terms of instantaneous nucleation of martensite during cooling followed by time dependent growth during isothermal holding....

Comparison of ferritic and austenitic plasma nitriding and nitrocarburizing behavior of AISI 4140 low alloy steel

International Nuclear Information System (INIS)

Fattah, M.; Mahboubi, F.

2010-01-01

This paper compares the ferritic and austenitic plasma nitriding and nitrocarburizing behavior of AISI 4140 low alloy steel carried out to improve the surface corrosion resistance. The gas composition for plasma nitriding was 85% N 2 -15% H 2 and that for plasma nitrocarburizing was 85% N 2 -12% H 2 -3% CO 2 . Both treatments were performed for 5 h, for different process temperatures of 570 and 620 o C for ferritic and austenitic plasma treatment, respectively. Optical microscopy, X-ray diffraction and potentiodynamic polarization technique in 3.5% NaCl solution, were used to study the treated surfaces. The results of X-ray analysis revealed that with increasing the treatment temperature from 570 to 620 o C for both treatments, the amount of ε phase decreased and γ' phase increased. Nitrocarburizing treatment resulted in formation of a more amount of ε phase with respect to nitriding treatment. However, the highest amount of ε phase was observed in the ferritic nitrocarburized sample at 570 o C. The sample nitrided at 620 o C exhibited the thickest layer. The potentiodynamic polarization results revealed that after plasma nitriding and nitrocarburizing at 570 o C, corrosion potential increased with respect to the untreated sample due to the noble nitride and carbonitride phases formed on the surface. After increasing the treatment temperature from 570 to 620 o C, corrosion potential decreased due to the less ε phase development in the compound layer and more porous compound layer formed at 620 o C with respect to the treated samples at 570 o C.

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

International Nuclear Information System (INIS)

You, Yang; Shang, Chengjia; Chen, Liang; Subramanian, Sundaresa

2013-01-01

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

The carbide M{sub 7}C{sub 3} in low-temperature-carburized austenitic stainless steel

Energy Technology Data Exchange (ETDEWEB)

Ernst, Frank, E-mail: frank.ernst@cwru.edu [Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106-7204 (United States); Li, Dingqiang; Kahn, Harold; Michal, Gary M.; Heuer, Arthur H. [Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106-7204 (United States)

2011-04-15

Prolonged low-temperature gas-phase carburization of AISI 316L-type austenitic stainless steel can cause intragranular precipitation of the carbide M{sub 7}C{sub 3} (M: randomly dispersed Fe, Cr, Ni). Transmission electron microscopy revealed that the carbide particles have the shape of needles. They grow by a ledge-migration mechanism and in a crystallographic orientation relationship to the austenite matrix that enables highly coherent interphase interfaces. A small solubility limit of Ni in the carbide and restricted Ni diffusivity at the processing temperature leads to Ni pileup around the particles and may explain the extreme aspect ratio of the particle shape. These characteristics closely resemble what has been observed earlier for precipitates of M{sub 5}C{sub 2} under slightly different processing conditions and can be rationalized by considering the particular constraints imposed by carburization at low temperature.

Change of austenite state before martensite transformation and Msub(el) temperature

International Nuclear Information System (INIS)

Sarrak, V.I.; Suvorova, S.O.

1978-01-01

The N31 alloy austenite behaviour in the premartensite temperature range is investigated. To study the austenite state the method of resistance to microplastic deformation sensitive to the structural state of metals is used. The resistance to microplastic deformation was determined by amplitude dependence of internal friction. The Msub(el) temperature is found at which the change of austenite state is observed due to the appearence of elastic nuclei of martensite below the Msub(el) temperature

Characterization of the dissimilar welding - austenitic stainless steel with filler metal of the nickel alloy

International Nuclear Information System (INIS)

Soares, Bruno Amorim; Schvartzman, Monica Maria de Abreu Mendonca; Campos, Wagner Reis da Costa

2007-01-01

In elevated temperature environments, austenitic stainless steel and nickel alloy has a superior corrosion resistance due to its high Cr content. Consequently, this alloys is widely used in nuclear reactors components and others plants of energy generation that burn fossil fuel or gas, chemical and petrochemical industries. The object of the present work was to research the welding of AISI 304 austenitic stainless steel using the nickel alloy filler metals, Inconel 625. Gas tungsten arc welding, mechanical and metallographic tests, and compositional analysis of the joint were used. A fundamental investigation was undertaken to characterize fusion boundary microstructure and to better understand the nature and character of boundaries that are associated with cracking in dissimilar welds. The results indicate that the microstructure of the fusion zone has a dendritic structure, inclusions, and precipitated phases containing Ti and Nb are present in the inter-dendritic region. In some parts near to the fusion line it can be seen a band in the weld, probably a eutectic phase with lower melting point than the AISI 304, were the cracking may be beginning by stress corrosion. (author)

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.

Recrystallization induced plasticity in austenite and ferrite

International Nuclear Information System (INIS)

Huang Mingxin; Pineau, André; Bouaziz, Olivier; Vu, Trong-Dai

2012-01-01

Highlights: ► Plasticity can be induced by recrystallization in austenite and ferrite. ► Strain rate is proportional to recrystallization kinetics. ► Overall atomic flux selects a preferential direction may be the origin. - Abstract: New experimental evidences are provided to demonstrate that plastic strain can be induced by recrystallization in austenite and ferrite under an applied stress much smaller than their yield stresses. Such Recrystallization Induced Plasticity (RIP) phenomenon occurs because the overall atomic flux during recrystallization follows a preferential direction imposed by the applied stress.

Phase Transformation Behavior of Medium Manganese Steels with 3 Wt Pct Aluminum and 3 Wt Pct Silicon During Intercritical Annealing

Science.gov (United States)

Sun, Binhan; Fazeli, Fateh; Scott, Colin; Yue, Stephen

2016-10-01

Medium manganese steels alloyed with sufficient aluminum and silicon amounts contain high fractions of retained austenite adjustable to various transformation-induced plasticity/twinning-induced plasticity effects, in addition to a reduced density suitable for lightweight vehicle body-in-white assemblies. Two hot rolled medium manganese steels containing 3 wt pct aluminum and 3 wt pct silicon were subjected to different annealing treatments in the present study. The evolution of the microstructure in terms of austenite transformation upon reheating and the subsequent austenite decomposition during quenching was investigated. Manganese content of the steels prevailed the microstructural response. The microstructure of the leaner alloy with 7 wt pct Mn (7Mn) was substantially influenced by the annealing temperature, including the variation of phase constituents, the morphology and composition of intercritical austenite, the Ms temperature and the retained austenite fraction. In contrast, the richer variant 10 wt pct Mn steel (10Mn) exhibited a substantially stable ferrite-austenite duplex phase microstructure containing a fixed amount of retained austenite which was found to be independent of the variations of intercritical annealing temperature. Austenite formation from hot band ferrite-pearlite/bainite mixtures was very rapid during annealing at 1273 K (1000 °C), regardless of Mn contents. Austenite growth was believed to be controlled at early stages by carbon diffusion following pearlite/bainite dissolution. The redistribution of Mn in ferrite and particularly in austenite at later stages was too subtle to result in a measureable change in austenite fraction. Further, the hot band microstructure of both steels contained a large fraction of coarse-grained δ-ferrite, which remained almost unchanged during intercritical annealing. A recently developed thermodynamic database was evaluated using the experimental data. The new database achieved a better agreement

Austenite Formation from Martensite in a 13Cr6Ni2Mo Supermartensitic Stainless Steel

NARCIS (Netherlands)

Bojack, A.; Zhao, L.; Morris, P.F.; Sietsma, J.

2016-01-01

The influence of austenitization treatment of a 13Cr6Ni2Mo supermartensitic stainless steel (X2CrNiMoV13-5-2) on austenite formation during reheating and on the fraction of austenite retained after tempering treatment is measured and analyzed. The results show the formation of austenite in two

Microstructural evolution and mechanical characterization for the A508-3 steel before and after phase transition

Science.gov (United States)

Lu, Chuanyang; He, Yanming; Gao, Zengliang; Yang, Jianguo; Jin, Weiya; Xie, Zhigang

2017-11-01

Nuclear power, as a reliable clean and economical energy source, has gained great attention from all over the world. The A508-3 steel will be introduced as the structural materials for Chinese nuclear reactor pressure vessels (RPVs). This work investigated the temperature-dependence microstructural evolution during high-temperature heat treatments, and built the relationship between the microstructure and mechanical properties for the steel before and after phase transition. The results show that the original steel consists of the bainite, allotriomorphic ferrite, retained austenite and few Mo-rich M2C carbides. The phase-transition temperature of the steel is determined to be 750 °C. The tensile tests performed at 20-1000 °C indicate that both of the yield strength and ultimate tensile strength decrease monotonously with increasing the temperature. Before phase transition, precipitation of cementite from the retained austenite and coarsening of cementite at the austenite-ferrite interphases should be responsible for their sharp decrease. After phase transition, the growth of austenite grain reduces the strength moderately. As for the elongation, however, it increases dramatically when the testing temperature is over 750 °C, due to the dissolution of cementite and formation of austenite. The obtained results will provide some fundamental data to understand and implement the In-Vessel Retention strategy.

Mossbauer and XRD characterization of the phase transformations in a Fe-Mn-Al-C-Mo-Si-Cu as cast alloy during tribology test

Science.gov (United States)

Ramos, J.; Piamba, J. F.; Sánchez, H.; Alcazar, G. A. Pérez

2015-06-01

In present study Fe-29.0Mn-6Al-0.9C-1.8Mo-1.6Si-0.4Cu (%w) alloy was obtained after melted in an induction furnace, and then molded as an ingot. From the as cast ingot it were cut samples for the different characterization measurements. The microstructure of the as-cast sample is of dendritic type and its XRD pattern was refined with the lines of the austenite, with a big volumetric fraction, and the lines of the martensite, with small volumetric fraction. The Mössbauer spectrum of the sample was fitted with a broad singlet which corresponds to disordered austenite. After the tribology test, its XRD pattern was refined with the lines of two austenite phases, one similar to the previous one and other with bigger lattice parameter. The total volumetric fraction of the austenite is smaller than that obtained for sample without wear. It was added the lines of the martensite phase with bigger volumetric fraction than that of the previous sample. The Mössbauer spectrum of the weared sample was fitted with two paramagnetic sites which correspond to the two Fe austenite phases and a hyperfine magnetic field distribution which is associated to the disordered original martensite and the new one which appears in the surface as a consequence of the wear process. These results show that during wear process the original austenite phase is transformed in martensite and in a new austenite phase. The increases of the martensitic phase improves mechanical properties and wear behavior.

Mossbauer and XRD characterization of the phase transformations in a Fe-Mn-Al-C-Mo-Si-Cu as cast alloy during tribology test

Energy Technology Data Exchange (ETDEWEB)

Ramos, J. [Universidad Autónoma de Occidente (Colombia); Piamba, J. F. [Universidad del Valle, Departamento Física (Colombia); Sánchez, H. [Universidad del Valle, Escuela de Materiales (Colombia); Alcazar, G. A. Pérez, E-mail: gpgeperez@gmail.com [Universidad del Valle, Departamento Física (Colombia)

2015-06-15

In present study Fe-29.0Mn-6Al–0.9C-1.8Mo-1.6Si-0.4Cu (%w) alloy was obtained after melted in an induction furnace, and then molded as an ingot. From the as cast ingot it were cut samples for the different characterization measurements. The microstructure of the as-cast sample is of dendritic type and its XRD pattern was refined with the lines of the austenite, with a big volumetric fraction, and the lines of the martensite, with small volumetric fraction. The Mössbauer spectrum of the sample was fitted with a broad singlet which corresponds to disordered austenite. After the tribology test, its XRD pattern was refined with the lines of two austenite phases, one similar to the previous one and other with bigger lattice parameter. The total volumetric fraction of the austenite is smaller than that obtained for sample without wear. It was added the lines of the martensite phase with bigger volumetric fraction than that of the previous sample. The Mössbauer spectrum of the weared sample was fitted with two paramagnetic sites which correspond to the two Fe austenite phases and a hyperfine magnetic field distribution which is associated to the disordered original martensite and the new one which appears in the surface as a consequence of the wear process. These results show that during wear process the original austenite phase is transformed in martensite and in a new austenite phase. The increases of the martensitic phase improves mechanical properties and wear behavior.

Effect of Chemical Composition on Susceptibility to Weld Solidification Cracking in Austenitic Weld Metal

Science.gov (United States)

Kadoi, Kota; Shinozaki, Kenji

2017-12-01

The influence of the chemical composition, especially the niobium content, chromium equivalent Creq, and nickel equivalent Nieq, on the weld solidification cracking susceptibility in the austenite single-phase region in the Schaeffler diagram was investigated. Specimens were fabricated using the hot-wire laser welding process with widely different compositions of Creq, Nieq, and niobium in the region. The distributions of the susceptibility, such as the crack length and brittle temperature range (BTR), in the Schaeffler diagram revealed a region with high susceptibility to solidification cracking. Addition of niobium enhanced the susceptibility and changed the distribution of the susceptibility in the diagram. The BTR distribution was in good agreement with the distribution of the temperature range of solidification (Δ T) calculated by solidification simulation based on Scheil model. Δ T increased with increasing content of alloying elements such as niobium. The distribution of Δ T was dependent on the type of alloying element owing to the change of the partitioning behavior. Thus, the solidification cracking susceptibility in the austenite single-phase region depends on whether the alloy contains elements. The distribution of the susceptibility in the region is controlled by the change in Δ T and the segregation behavior of niobium with the chemical composition.

Manufacture and characterization of austenitic steel welded joints

International Nuclear Information System (INIS)

Simoni, O.; Boerman, D.J.; Krischer, W.

1990-01-01

This paper describes the results of the first phase of the project, i.e. manufacturing and characterization of welded austenitic steel and the test matrix adopted to test the mechanical resistance of the welding. Five different welding methods have been tested and characterized in comparison to the parent material. The reference material was an AISI 316 L type steel close to the French Superphenix composition. The results of the mechanical testing and the relative comparison of the five welding methods are described in separate papers of the same session. As a general conclusion, the vacuum electron-beam welding proved to have better properties than the other weld methods and to attain in most cases the properties of the parent material. (author)

Reduction of residual stresses in internal skin of transient zones of PWR steam generator expanded tubes: tests with a ''rotating brush''

International Nuclear Information System (INIS)

Vidal, P.

1984-04-01

A process aiming at preventing or suppressing cracks under stress corrosion on the primary side in the expanded zones of PWR steam generator tubes has been studied; it consists in hammering the internal skin of tubes in these zones what reduces the level of residual expanding stresses to lower values around 100-150 MPa without modifying the stress level in external skin. Tests in magnesium chloride to estimate the residual stresses of tubes in low carbon stainless austenitic steel 18% Cr-12% Ni with molybdene [fr

What Expands in an Expanding Universe?

Science.gov (United States)

Pacheco, José A De Freitas

2015-01-01

In the present investigation, the possible effects of the expansion of the Universe on systems bonded either by gravitational or electromagnetic forces, are reconsidered. It will be shown that the acceleration (positive or negative) of the expanding background, is the determinant factor affecting planetary orbits and atomic sizes. In the presently accepted cosmology (ΛCDM) all bonded systems are expanding at a decreasing rate that tends to be zero as the universe enters in a de Sitter phase. It is worth mentioning that the estimated expansion rates are rather small and they can be neglected for all practical purposes.

What Expands in an Expanding Universe?

Directory of Open Access Journals (Sweden)

JOSÉ A. DE FREITAS PACHECO

2015-12-01

Full Text Available ABSTRACT In the present investigation, the possible effects of the expansion of the Universe on systems bonded either by gravitational or electromagnetic forces, are reconsidered. It will be shown that the acceleration (positive or negative of the expanding background, is the determinant factor affecting planetary orbits and atomic sizes. In the presently accepted cosmology (ΛCDM all bonded systems are expanding at a decreasing rate that tends to be zero as the universe enters in a de Sitter phase. It is worth mentioning that the estimated expansion rates are rather small and they can be neglected for all practical purposes.

Derivation of tensile flow characteristics for austenitic materials from instrumented indentation technique

International Nuclear Information System (INIS)

Lee, K-W; Kim, K-H; Kim, J-Y; Kwon, D

2008-01-01

In this study, a method for deriving the tensile flow characteristics of austenitic materials from an instrumented indentation technique is presented along with its experimental verification. We proposed a modified algorithm for austenitic materials that takes their hardening behaviour into account. First, the true strain based on sine function instead of tangent function was adapted. It was proved that the sine function shows constant degrees of hardening which is a main characteristic of the hardening of austenitic materials. Second, a simple and linear constitutive equation was newly suggested to optimize indentation flow curves. The modified approach was experimentally verified by comparing tensile properties of five austenitic materials from uniaxial tensile test and instrumented indentation tests

Surface modification of austenitic steel by various glow-discharge nitriding methods

Directory of Open Access Journals (Sweden)

Tomasz Borowski

2015-09-01

Full Text Available Recent years have seen intensive research on modifying glow-discharge nitriding processes. One of the most commonly used glow-discharge methods includes cathodic potential nitriding (conventional method, and active screen plasma nitriding. Each of these methods has a number of advantages. One very important, common feature of these techniques is full control of the microstructure, chemical and phase composition, thickness and the surface topography of the layers formed. Another advantage includes the possibility of nitriding such materials as: austenitic steels or nickel alloys, i.e. metallic materials which do not diffuse nitrogen as effectively as ferritic or martensitic steels. However, these methods have some disadvantages as well. In the case of conventional plasma nitriding, engineers have to deal with the edge effect, which makes it difficult to use this method for complexly shaped components. In turn, in the case of active screen plasma nitriding, the problem disappears. A uniform, smooth layer forms, but is thinner, softer and is not as resistant to friction compared to layers formed using the conventional method. Research is also underway to combine these methods, i.e. use an active screen in conventional plasma nitriding at cathodic potential. However, there is a lack of comprehensive data presenting a comparison between these three nitriding processes and the impact of pulsating current on the formation of the microstructure and functional properties of austenitic steel surfaces. The article presents a characterisation of nitrided layers produced on austenitic X2CrNiMo17-12-2 (AISI 316L stainless steel in the course of glow-discharge nitriding at cathodic potential, at plasma potential and at cathodic potential incorporating an active screen. All processes were carried out at 440 °C under DC glow-discharge conditions and in 100 kHz frequency pulsating current. The layers were examined in terms of their microstructure, phase and

On abnormal decomposition of supercooled austenite in carbon and alloy steels

International Nuclear Information System (INIS)

Parusov, V.V.; Dolzhenkov, I.I.; Podobedov, L.V.; Vakulenko, I.A.

1980-01-01

Residual stresses which appear as a result of thermal cycling in the temperature range of 300-700 deg C are investigated in an austenitic class steel (03Kh18N11) to ground the assumption on the effect of plastic deformation, appearing due to thermal stresses, on the mechanism of supercooled austenite decomposition. The determination of residual stresses is carried out with the help of X-ray diffraction analysis. It is established that the deformation brings about an increase in density of dislocation the interaction of which leads to the formation of a typical austenite substructure which conditions the proceeding of the eutectoid transformation according to an abnormal mechanism. It is noted, that the grain pearlite formation due to plastic and microplastic deformation of supercooled austenite induced by thermal stresses should be taken into account when developing steel heat treatment shedules [ru

Development of microstructure of niobium-microalloyed steels after deformation in two-phase region

International Nuclear Information System (INIS)

Majta, J.; Bator, A.

1999-01-01

The inhomogeneity of microstructure development of hot deformed niobium-microalloyed steels in the austenite and two phase region is effectively described using an integrated computer modeling process. In particular, the effect of varying the finish deformation temperature, strain and strain rate on the inhomogeneity of austenite and ferrite structures are studied. Presented here investigations take into account kinetics of recrystallization, phase transformation, and the resulting mechanical properties. (author)

Use of overlapped reflection for determining the retained austenite by X-ray diffraction

International Nuclear Information System (INIS)

Garin, J.L.; Gonzalez, C.F.

1988-01-01

Retainec austenite in high-carbon steels has been determined by means of new computation techniques applied to the processing of X-ray diffraction data. Instead of using the traditional procedure based on the weak (200) reflections of martensite and austenite, intensity measurements of the overlapped (110) peak of martensite and (111) peak of austenite were performed. The separation of the peaks was based on a Pearson VII function, which is capable of describing all diffraction profiles. The accuracy of integrated intensities was then improved with the beneficial effects of higher precision in the calculation of the amount of retained austenite. (author) [pt

Phase transformations of under-cooled austenite of new bainitic materials for scissors crossovers

Directory of Open Access Journals (Sweden)

J. Pacyna

2008-07-01

Full Text Available The paper contains CCT diagrams presenting a transformation kinetics of under-cooled austenite from two new bainitic cast steels which the scissors crossovers for heavy-duty railway tracks (min. 230kN/axle at the speed up to 200 km/h are made of. The cooling ranges of UIC60 type railway tracks plot on the CCT diagrams indicate that there is a 100% bainitic structure in the scissors crossovers made of these cast steels as well, but mainly it would be a favourable for cracking resistance lower bainite. The achievable hardness of scissors crossovers made of new materials make it possible to use high–temperature tempering resulting in obtaining of good crack resistance. However one should provide a good quality of castings made.

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

Energy Technology Data Exchange (ETDEWEB)

Wang Ying; Zhang Ke; Guo Zhenghong; Chen Nailu [School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Rong Yonghua, E-mail: yhrong@sjtu.edu.cn [School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China)

2012-08-30

Highlights: Black-Right-Pointing-Pointer A new DARA effect in the bainitic steel is proposed. Black-Right-Pointing-Pointer The conditions of DARA effect are proposed. Black-Right-Pointing-Pointer 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.

Relationship between hydrogen-induced phase transformations and pitting nucleation sites in duplex stainless steel

Energy Technology Data Exchange (ETDEWEB)

Guo, Liqiu; Yang, Binjie; Qin, Sixiao [University of Science and Technology Beijing (China). Corrosion and Protection Center

2016-02-15

This paper demonstrates the hydrogen-induced phase transformation and the associated pitting nucleation sites of 2507 duplex stainless steel using scanning Kelvin probe force microscopy and magnetic force microscopy. The low potential sites in Volta potential images, which are considered as the pitting nucleation sites, are strongly dependent on the hydrogen-induced phase transformation. They firstly initiate on the magnetic martensite laths in the austenite phase or at the ferrite/austenite boundaries, and then appear near the needle-shaped microtwins in the ferrite phase, because of the difference in physicochemical properties of hydrogen-induced phase transformation microstructures.

Low ductility creep failure in austenitic weld metals

International Nuclear Information System (INIS)

Thomas, R.G.

Creep tests have been carried out for times of up to approx. 22,000 hrs on three austenitic weld metals of nominal composition 17Cr-8Ni-2Mo, 19Cr-12Ni-3Mo+Nb and 17Cr-10Ni-2Mo. The two former deposits were designed to produce delta-ferrite contents in the range 3-9% while the latter was designed to be fully austenitic. The common feature of all three weld metals was that they all gave very low strains at failure, typically approx. 1%. The microstructures of the failed creep specimens have been studied using optical and electron microscopy and the precipitate structures related to the occurrence of low creep strains. Creep deformation and fracture mechanisms in austenitic materials in general have been reviewed and this has been used as a basis for discussion of the observations of the present work. Finally, some of the factors that can be controlled to improve long-term creep ductility have been appraised

Pulsed magnetic welding application of fast breeder austenitic pins plugging

International Nuclear Information System (INIS)

Gallizzi, H.; Colombe, G.

1986-11-01

For specific nuclear needs, we had to develop pulsed magnetic welding on high resistivity coefficient alloys as austenitic steels. The magnetic force produced by an explosive inductor is transmitted on weld pieces by the use of an aluminium driver. A theoretical work carried out permitted to compare pulsed magnetic welding with explosive welding. With specific recordings, it was possible to study electrical and magnetical behavior during the active welding phase. By means of these informations, we are able to specify and to realize, with the financial help of ANVAR organization, a low impedance high velocity generator permitting to weld with a non destructible inductor. 6 refs [fr

A study of the carbon distribution in retained austenite

International Nuclear Information System (INIS)

Scott, C.P.; Drillet, J.

2007-01-01

Cold-rolled and annealed transformation-induced plasticity (TRIP) steels were overaged to modify the carbon concentrations (C γ ) in retained austenite. Experimental C γ values were directly obtained by electron energy loss spectroscopy and compared with data derived from X-ray diffraction measurements of the austenite lattice parameter (a γ ). In this way, we evaluated the different expressions available in the literature relating C γ to a γ

Simulation of radiation induced segregation and PWSCC susceptibility for austenitic stainless steels

Energy Technology Data Exchange (ETDEWEB)

Fujimoto Koji; Yonezawa, Toshio; Iwamura, Toshihiko [Mitsubishi Heavy Industries Ltd., Takasago, Hyogo (Japan). Takasago R and D Center; Ajiki, Kazuhide [Mitsubishi Heavy Industries Ltd., Kobe (Japan). Kobe Shipyard and Machinery Works; Urata, Sigeru [General Office of Nuclear and Fossil Power Production, Kansai Electric Power Co., Inc., Osaka (Japan)

2000-08-01

Recently, irradiation assisted stress corrosion cracking (IASCC) of austenitic stainless steels for core internal components materials become a subject of discussion in light water reactors (LWRs). IASCC has not been found in Pressurized Water Reactors (PWRs). However, the authors have investigated on the possibility of IASCC of austenitic stainless steels for core internal materials so as to be able to estimate the degradation of PWR plants up to the end of their lifetime. In this study, in order to verify the hypothetical that the IASCC in PWRs shall be caused by the primary water stress corrosion cracking (PWSCC) as a result of radiation induced segregation (RIS) at grain boundaries, the authors simulated RIS at grain boundaries of austenitic stainless steels based on previous study and estimated RIS tendency after long time operation. And the authors melted the test alloys whose bulk compositions simulated the grain boundary compositions of irradiated austenitic stainless steels and made clear chromium-nickel-silicon compositions for PWSCC susceptibility area in austenitic alloys by slow strain rate tensile (SSRT) test. (author)

Simulation of radiation induced segregation and PWSCC susceptibility for austenitic stainless steels

International Nuclear Information System (INIS)

Fujimoto Koji; Yonezawa, Toshio; Iwamura, Toshihiko

2000-01-01

Recently, irradiation assisted stress corrosion cracking (IASCC) of austenitic stainless steels for core internal components materials become a subject of discussion in light water reactors (LWRs). IASCC has not been found in Pressurized Water Reactors (PWRs). However, the authors have investigated on the possibility of IASCC of austenitic stainless steels for core internal materials so as to be able to estimate the degradation of PWR plants up to the end of their lifetime. In this study, in order to verify the hypothetical that the IASCC in PWRs shall be caused by the primary water stress corrosion cracking (PWSCC) as a result of radiation induced segregation (RIS) at grain boundaries, the authors simulated RIS at grain boundaries of austenitic stainless steels based on previous study and estimated RIS tendency after long time operation. And the authors melted the test alloys whose bulk compositions simulated the grain boundary compositions of irradiated austenitic stainless steels and made clear chromium-nickel-silicon compositions for PWSCC susceptibility area in austenitic alloys by slow strain rate tensile (SSRT) test. (author)

On the measurement of austenite in supermartensitic stainless steel by X-ray diffraction

Energy Technology Data Exchange (ETDEWEB)

Tolchard, Julian Richard, E-mail: tolchard@material.ntnu.no [Department of Materials Science and Engineering, Norwegian University of Science and Technology, Trondheim (Norway); Sømme, Astri; Solberg, Jan Ketil [Department of Materials Science and Engineering, Norwegian University of Science and Technology, Trondheim (Norway); Solheim, Karl Gunnar [Statoil, Stavanger (Norway)

2015-01-15

Sections of a 13Cr supermartensitic stainless steel were investigated to determine the optimum sample preparation for measurement of the austenite content by X-ray diffraction. The surface of several samples was mechanically ground or polished using media of grit sizes in the range 1–120 μm. The strained surface layer was afterwards removed stepwise by electropolishing, and the austenite content measured at each step. It was found that any level of mechanical grinding or polishing results in a reduction of the measured austenite fraction relative to the true bulk value, and that coarser grinding media impart greater damage and greater reduction in the measured austenite content. The results thus highlight the importance of the electropolishing step in preparation of such samples, but suggest that the American Society for Testing and Materials standard E975-03 substantially overestimates the amount of material which needs to be removed to recover the true “bulk” content. - Highlights: • Quantitative Rietveld analysis of austenite/martensite ratio in supermartensitic stainless steels • Critical evaluation of sample preparation for residual austenite measurements by X-ray diffraction • Highlighting of the importance of electropolishing as a final preparation step.

Comparison of high temperature steam oxidation behavior of Zircaloy-4 versus austenitic and ferritic steels under light water reactor safety aspects

International Nuclear Information System (INIS)

Leistikow, S.; Schanz, G.; Zurek, Z.

1985-12-01

A comparative study of the oxidation behavior of Zy-4 versus steel No. 1.4914 and steel No. 1.4970 was performed in high temperature steam. Reactor typical tube sections of all three materials were exposed on both sides to superheated steam at temperatures ranging from 600 to 1300 0 C for up to 6 h. The specimens were evaluated by gravimetry, metallography, and other methods. The results are presented in terms of weight gain, corresponding metal (wall) penetration and consumption as function of time and temperature. Concerning the corrosion resistance the ranking position of Zy-4 was between the austenitic and the ferritic steel. Because of the chosen wall dimensions Zy-4 and the austenitic steel behaved similarly in that the faster oxidation of the thicker Zy-4 cladding consumed the total wall thickness in a time equivalent to the slower oxidation of the thinner austenitic steel cladding. The ferritic steel cladding however was faster consumed because of the lower oxidation resistance and the thinner wall thickness compared to the austenitic steel. So besides oxide scale formation, oxygen diffusion into the bulk of the metal forming various oxygen-containing phases were evaluated - also in respect to their influence on mechanical cladding properties and the dimensional changes. (orig./HP) [de

High-Temperature Phase Equilibria of Duplex Stainless Steels Assessed with a Novel In-Situ Neutron Scattering Approach

Science.gov (United States)

Pettersson, Niklas; Wessman, Sten; Hertzman, Staffan; Studer, Andrew

2017-04-01

Duplex stainless steels are designed to solidify with ferrite as the parent phase, with subsequent austenite formation occurring in the solid state, implying that, thermodynamically, a fully ferritic range should exist at high temperatures. However, computational thermodynamic tools appear currently to overestimate the austenite stability of these systems, and contradictory data exist in the literature. In the present work, the high-temperature phase equilibria of four commercial duplex stainless steel grades, denoted 2304, 2101, 2507, and 3207, with varying alloying levels were assessed by measurements of the austenite-to-ferrite transformation at temperatures approaching 1673 K (1400 °C) using a novel in-situ neutron scattering approach. All grades became fully ferritic at some point during progressive heating. Higher austenite dissolution temperatures were measured for the higher alloyed grades, and for 3207, the temperature range for a single-phase ferritic structure approached zero. The influence of temperatures in the region of austenite dissolution was further evaluated by microstructural characterization using electron backscattered diffraction of isothermally heat-treated and quenched samples. The new experimental data are compared to thermodynamic calculations, and the precision of databases is discussed.

Longitudinal wave ultrasonic inspection of austenitic weldments

International Nuclear Information System (INIS)

Gray, B.S.; Hudgell, R.J.; Seed, H.

1980-01-01

Successful volumetric inspection of LMFBR primary circuits, and also much of the secondary circuit, is dependent on the availability of satisfactory examination procedures for austenitic welds. Application of conventional ultrasonic techniques is hampered by the anisotropic, textured structure of the weld metal and this paper describes development work on the use of longitudinal wave techniques. In addition to confirming the dominant effects of the weld structure on ultrasound propagation some results are given of studies utilising deliberately induced defects in Manual Metal Arc Welds in 50 mm plate together with preliminary work on the inspection of narrow austenitic welds fabricated by automatic processes. (author)

Carburizing plasma in a low temperature austenitic stainless steel AISI 304

International Nuclear Information System (INIS)

Mota, W.T.; Ramos, F.D.; Rocha, R.C.; Barcelos, M.V.; Barcelos, M.A.

2014-01-01

The industrial use of thermochemical treatment assisted by the cold plasma has been widely employed in recent years, mainly oriented to the excellent results obtained in the surface modification of engineering materials, when compared to more traditional methods. In this work, we studied the plasma carburizing low temperature steel AISI 304 mechanical parts used in construction. The thermochemical treatment was performed at a fixed gas atmosphere 7% CH 4 (g) and 93 % H 2 (g), 350 ° C and times of 1, 3 and 5 hours. Samples being tested for Vickers hardness, abrasive microwear, microstructure evaluation by optical microscopy and SEM and X-ray diffraction. The results show significant improvement in surface hardness, wear resistance and good formation of expanded austenite layer and no identifiers peaks of carbides. The results achieved are due to diffusion/adsorption of carbon present in the gaseous atmosphere to the evaluated samples. (author)

Effect of multiple austenitizing treatments on HT-9 steels

International Nuclear Information System (INIS)

Emigh, R.A.

1985-12-01

The effect of multiple austenitizing treatments on the toughness of an Fe-12Cr-1.0Mo-0.5W-0.3V (HT-9) steel was studied. The resulting microstructures were characterized by their mechanical properties, precipitated carbide distribution, and fracture surface appearance. It was proposed that multiple transformations would refine the martensite structure and improve toughness. Optical and scanning electron microscopic observations revealed that the martensite packet structure was somewhat refined by a second austenite transformation. Transmission electron microscopy studies of carbon extraction replicas showed that this multiple step treatment had eliminated grain boundary carbide films seen in single treated specimens on prior austenite grain boundaries. The 0.2% yield strength, tensile strength, and elongation were relatively unchanged, but the toughness measured by fatigue pre-cracked Charpy impact tests increased for the multiple step specimens

Thermal conductivity of an organic phase change material/expanded graphite composite across the phase change temperature range and a novel thermal conductivity model

International Nuclear Information System (INIS)

Ling, Ziye; Chen, Jiajie; Xu, Tao; Fang, Xiaoming; Gao, Xuenong; Zhang, Zhengguo

2015-01-01

Highlights: • Expanded graphite can improve thermal conductivity of RT44HC by 20–60 times. • Thermal conductivity of PCM/EG composites keeps constant before/after melting. • Thermal conductivity of PCMs nearly doubled during phase changing. • Thermal conductivity of composite PCM increases with density and percentage of EG. • The simple model predicts thermal conductivity of EG-based composites accurately. - Abstract: This work studies factors that affect the thermal conductivity of an organic phase change material (PCM), RT44HC/expanded graphite (EG) composite, which include: EG mass fraction, composite PCM density and temperature. The increase of EG mass fraction and bulk density will both enhance thermal conductivity of composite PCMs, by up to 60 times. Thermal conductivity of RT44HC/EG composites remains independent on temperature outside the phase change range (40–45 °C), but nearly doubles during the phase change. The narrow temperature change during the phase change allows the maximum heat flux or minimum temperature for heat source if attaching PCMs to a first (constant temperature) or second (constant heat flux) thermal boundary. At last, a simple thermal conductivity model for EG-based composites is put forward, based on only two parameters: mass fraction of EG and bulk density of the composite. This model is validated with experiment data presented in this paper and in literature, showing this model has general applicability to any composite of EG and poor thermal conductive materials

TEM studies of plasma nitrided austenitic stainless steel.

Science.gov (United States)

Stróz, D; Psoda, M

2010-03-01

Cross-sectional transmission electron microscopy and X-ray phase analysis were used to study the structure of a layer formed during nitriding the AISI 316L stainless steel at temperature 440 degrees C. It was found that the applied treatment led to the formation of 6-microm-thick layer of the S-phase. There is no evidence of CrN precipitation. The X-ray diffraction experiments proved that the occurred austenite lattice expansion - due to nitrogen atoms - depended on the crystallographic direction. The cross-sectional transmission electron microscopy studies showed that the layer consisted of a single cubic phase that contained a lot of defects such as dislocations, stacking faults, slip bands and twins. The high-resolution electron microscopy observations were applied to study the defect formation due to the nitriding process. It was shown that the presence of great number of stacking faults leads to formation of nanotwins. Weak, forbidden {100} reflections were still another characteristic feature of the S-phase. These were not detected in the X-ray spectra of the phase. Basing on the high-resolution electron microscopy studies it can be suggested that the short-range ordering of the nitrogen atoms in the octahedral sites inside the f.c.c. matrix lattice takes place and gives rise to appearance of these spots. It is suggested that the cubic lattice undergoes not only expansion but also slight rombohedral distortion that explains differences in the lattice expansion for different crystallographic directions.

Precipitation sensitivity to alloy composition in Fe-Cr-Mn austenitic steels developed for reduced activation for fusion application

International Nuclear Information System (INIS)

Maziasz, P.J.; Klueh, R.L.

1988-01-01

Special austenitic steels are being designed in which alloying elements like Mo, Nb, and Ni are replaced with Mn, W, V, Ti, and/or Ta to reduce the long-term radioactivity induced by fusion reactor irradiation. However, the new steels still need to have properties otherwise similar to commercial steels like type 316. Precipitation strongly affects strength and radiation-resistance in austenitic steels during irradiation at 400--600/degree/C, and precipitation is also usually quite sensitive to alloy composition. The initial stage of development was to define a base Fe-Cr-Mn-C composition that formed stable austenite after annealing and cold-working, and resisted recovery or excessive formation of coarse carbide and intermetallic phases during elevated temperature annealing. These studies produced a Fe-12Cr-20Mn-0.25C base alloy. The next stage was to add the minor alloying elements W, Ti, V, P, and B for more strength and radiation-resistance. One of the goals was to produce fine MC precipitation behavior similar to the Ti-modified Fe-Cr-Ni prime candidate alloy (PCA). Additions of Ti+V+P+B produced fine MC precipitation along network dislocations and recovery/recrystallization resistance in 20% cold worked material aged at 800/degree/C for 166h, whereas W, Ti, W+Ti, or Ti+P+B additions did not. Addition of W+Ti+V+P+B also produced fine MC, but caused some σ phase formation and more recrystallization as well. 29 refs., 14 figs., 9 tabs

Influence of grain structure on the deformation mechanism in martensitic shear reversion-induced Fe-16Cr-10Ni model austenitic alloy with low interstitial content: Coarse-grained versus nano-grained/ultrafine-grained structure

Energy Technology Data Exchange (ETDEWEB)

Challa, V.S.A. [Laboratory for Excellence in Advanced Steel Research, Department of Metallurgical, Materials Engineering, and Biomedical Engineering, University of Texas at El Paso, El Paso, TX 79968 (United States); Misra, R.D.K., E-mail: dmisra2@utep.edu [Laboratory for Excellence in Advanced Steel Research, Department of Metallurgical, Materials Engineering, and Biomedical Engineering, University of Texas at El Paso, El Paso, TX 79968 (United States); Somani, M.C. [Center for Advanced Steels Research, The University of Oulu, P.O. Box 4200, 90014 Oulu (Finland); Wang, Z.D. [State Key Laboratory for Rolling and Automation, Northeastern University, 3-11 Wenhua Road, Shenyang 110819 (China)

2016-04-20

Nanograined/ultrafine-grained (NG/UFG) materials characterized by high strength-high ductility combination are excellent vehicles to obtain an unambiguous understanding of deformation mechanisms vis-à-vis their coarse-grained counterparts. In this context, the innovative concept of phase reversion-induced NG/UFG structure enabled achieving high strength besides comparable ductility, for instance, in metastable austenitic stainless steels. In the phase reversion process, severe deformation of austenite at room temperature (typically ~60–80%) transforms face-centered cubic austenite (γ) to body centered cubic martensite (α′). Upon annealing, martensite reverts to austenite leading to extensive grain refinement. The objective of the present study to fundamentally understand the deformation mechanisms in NG/UFG structure in relation to that of the coarse-grained (CG) structure was accomplished by combining depth-sensing nanoscale experiments on an Fe-16Cr-10Ni model austenitic alloy conducted at different strain rates, followed by the study of structural evolution in the deformed zone using transmission electron microscopy (TEM). In the high strength NG/UFG steel (YS~585 MPa), stacking faults and nanotwins contributed to the enhanced ductility (El~35%), while in the case of low strength (YS~260 MPa) coarse-grained (CG) counterpart, ductility was also high (El~40%), but chiefly due to strain-induced martensite, which points to a clear case of grain size effect (and the corresponding level of strength). The distinct change in the deformation mechanism from stacking faults and twinning-induced plasticity (TWIP) in the NG structure to transformation-induced plasticity (TRIP) in the CG structure is elucidated in terms of austenite stability-strain energy relationship. The insights on the relationship between grain structure (and strength) and deformation mechanisms are envisaged to be important in providing a new direction for the futuristic design of high strength

Ultrasonic inspection of austenitic welds

Energy Technology Data Exchange (ETDEWEB)

Tomlinson, J R; Wagg, A R; Whittle, M J [N.D.T. Applications Centre, CEGB, Manchester (United Kingdom)

1980-11-01

The metallurgical structure of austenitic welds is described and contrasted with that found in ferritic welds. It is shown that this structure imparts a marked elastic anisotropy in the ultrasonic propagation parameters. Measurements of variations in the apparent attenuation of sound and deviations in the beam direction are described. The measurements are interpreted in terms of the measured velocity anisotropy. Two applications of the fundamental work are described. In the first it is shown how, by using short pulse compression wave probes, and with major modification of the welding procedure, a stainless steel fillet weld in an AGR boiler can be inspected. In the second application, alternative designs of a transition butt weld have been compared for ease of ultrasonic inspection. The effects of two different welding processes on such an inspection are described. Finally, the paper examines the prospects for future development of inspection and defect-sizing techniques for austenitic welds. (author)

Quantitative evaluation of ultrasonic wave propagation in inhomogeneous anisotropic austenitic welds using 3D ray tracing method. Numerical and experimental validation

International Nuclear Information System (INIS)

Kolkoori, Sanjeevareddy

2014-01-01

Austenitic welds and dissimilar welds are extensively used in primary circuit pipes and pressure vessels in nuclear power plants, chemical industries and fossil fuelled power plants because of their high fracture toughness, resistance to corrosion and creep at elevated temperatures. However, cracks may initiate in these weld materials during fabrication process or stress operations in service. Thus, it is very important to evaluate the structural integrity of these materials using highly reliable non-destructive testing (NDT) methods. Ultrasonic non-destructive inspection of austenitic welds and dissimilar weld components is complicated because of anisotropic columnar grain structure leading to beam splitting and beam deflection. Simulation tools play an important role in developing advanced reliable ultrasonic testing (UT) techniques and optimizing experimental parameters for inspection of austenitic welds and dissimilar weld components. The main aim of the thesis is to develop a 3D ray tracing model for quantitative evaluation of ultrasonic wave propagation in an inhomogeneous anisotropic austenitic weld material. Inhomogenity in the anisotropic weld material is represented by discretizing into several homogeneous layers. According to ray tracing model, ultrasonic ray paths are traced during its energy propagation through various discretized layers of the material and at each interface the problem of reflection and transmission is solved. The influence of anisotropy on ultrasonic reflection and transmission behaviour in an anisotropic austenitic weld material are quantitatively analyzed in three dimensions. The ultrasonic beam directivity in columnar grained austenitic steel material is determined three dimensionally using Lamb's reciprocity theorem. The developed ray tracing model evaluates the transducer excited ultrasonic fields accurately by taking into account the directivity of the transducer, divergence of the ray bundle, density of rays and phase

Quantitative evaluation of ultrasonic wave propagation in inhomogeneous anisotropic austenitic welds using 3D ray tracing method. Numerical and experimental validation

Energy Technology Data Exchange (ETDEWEB)

Kolkoori, Sanjeevareddy

2014-07-01

Austenitic welds and dissimilar welds are extensively used in primary circuit pipes and pressure vessels in nuclear power plants, chemical industries and fossil fuelled power plants because of their high fracture toughness, resistance to corrosion and creep at elevated temperatures. However, cracks may initiate in these weld materials during fabrication process or stress operations in service. Thus, it is very important to evaluate the structural integrity of these materials using highly reliable non-destructive testing (NDT) methods. Ultrasonic non-destructive inspection of austenitic welds and dissimilar weld components is complicated because of anisotropic columnar grain structure leading to beam splitting and beam deflection. Simulation tools play an important role in developing advanced reliable ultrasonic testing (UT) techniques and optimizing experimental parameters for inspection of austenitic welds and dissimilar weld components. The main aim of the thesis is to develop a 3D ray tracing model for quantitative evaluation of ultrasonic wave propagation in an inhomogeneous anisotropic austenitic weld material. Inhomogenity in the anisotropic weld material is represented by discretizing into several homogeneous layers. According to ray tracing model, ultrasonic ray paths are traced during its energy propagation through various discretized layers of the material and at each interface the problem of reflection and transmission is solved. The influence of anisotropy on ultrasonic reflection and transmission behaviour in an anisotropic austenitic weld material are quantitatively analyzed in three dimensions. The ultrasonic beam directivity in columnar grained austenitic steel material is determined three dimensionally using Lamb's reciprocity theorem. The developed ray tracing model evaluates the transducer excited ultrasonic fields accurately by taking into account the directivity of the transducer, divergence of the ray bundle, density of rays and phase

Thermal Effects That Arise upon Different Heat Treatments in Austenitic Steels Alloyed with Titanium and Phosphorus

Science.gov (United States)

Arbuzov, V. L.; Berger, I. F.; Bobrovskii, V. I.; Voronin, V. I.; Danilov, S. E.; Kazantsev, V. A.; Kataev, N. V.; Sagaradze, V. V.

2018-04-01

Structural and microstructural changes that arise in the course of the heat treatment of Cr-Ni-Mo austenitic stainless steels with different concentrations of titanium and phosphorus have been studied. It has been found that the alloying with phosphorus decreases the lattice parameter of these steels. The phosphorus contribution to this effect is 0.015 ± 0.002 Å/at %. Aging at a temperature of 670 K for about 20 h leads to the precipitation of dispersed needle-like particles, which are most likely to be iron phosphides. In the temperature range of 700-800 K, in austenitic steels, the atomic separation of the solid solution occurs, the intensity of which decreases upon alloying with titanium or phosphorus at concentrations of 1.0 and 0.1 wt %, respectively. At higher temperatures (about 950 K), the formed precipitates of the Ni3Ti (γ') phase increase in size to 7-10 nm.

Three-dimensional modeling for deformation of austenitic NiTi shape memory alloys under high strain rate

Science.gov (United States)

Yu, Hao; Young, Marcus L.

2018-01-01

A three-dimensional model for phase transformation of shape memory alloys (SMAs) during high strain rate deformation is developed and is then calibrated based on experimental results from an austenitic NiTi SMA. Stress, strain, and martensitic volume fraction distribution during high strain rate deformation are simulated using finite element analysis software ABAQUS/standard. For the first time, this paper presents a theoretical study of the microscopic band structure during high strain rate compressive deformation. The microscopic transformation band is generated by the phase front and leads to minor fluctuations in sample deformation. The strain rate effect on phase transformation is studied using the model. Both the starting stress for transformation and the slope of the stress-strain curve during phase transformation increase with increasing strain rate.

The effects of retained austenite on dry sliding wear behavior of carburized steels

Energy Technology Data Exchange (ETDEWEB)

Kim, Hyung-Jun [Research Inst. of Industrial Science and Technology, Steel Products Dept., Pohang (Korea, Republic of); Kweon, Young-Gak [Research Inst. of Industrial Science and Technology, Steel Products Dept., Pohang (Korea, Republic of)

1996-04-01

Ring-on-square tests on two kinds of low-alloy carburized steel which were AISI 8620 and 4140 were carried out to study the dry sliding wear behavior. The influence of different retained austenite level of 6% to 40% was evaluated while trying to eliminate other factors. Test results show that the effects of grain size and carburized steel species are negligible in dry sliding wear behavior. While the influence of retained austenite is negligible at 20 kg load condition, wear resistance is decreased at 40 kg load condition as the retained austenite level is increased from 6% to 30%. However, wear resistance is again increased above about 30% of retained austenite level at 40 kg load condition. (orig.)

Intermetallic Strengthened Alumina-Forming Austenitic Steels for Energy Applications

Energy Technology Data Exchange (ETDEWEB)

Hu, Bin [Dartmouth College, Hanover, NH (United States); Baker, Ian [Dartmouth College, Hanover, NH (United States)

2016-03-31

In order to achieve energy conversion efficiencies of >50 % for steam turbines/boilers in power generation systems, the materials required must be strong, corrosion-resistant at high temperatures (>700°C), and economically viable. Austenitic steels strengthened with Laves phase and L1₂ precipitates, and alloyed with aluminum to improve oxidation resistance, are potential candidate materials for these applications. The creep resistance of these alloys is significantly improved through intermetallic strengthening (Laves-Fe₂Nb + L1₂-Ni₃Al precipitates) without harmful effects on oxidation resistance. Microstructural and microchemical analyses of the recently developed alumina-forming austenitic (AFA) steels (Fe-14Cr-32Ni-3Nb-3Al-2Ti-based) indicated they are strengthened by Ni₃Al(Ti) L1₂, NiAl B₂, Fe₂Nb Laves phase and MC carbide precipitates. Different thermomechanical treatments (TMTs) were performed on these stainless steels in an attempt to further improve their mechanical properties. The thermo-mechanical processing produced nanocrystalline grains in AFA alloys and dramatically increased their yield strength at room temperature. Unfortunately, the TMTs didn’t increase the yield strengths of AFA alloys at ≥700ºC. At these temperatures, dislocation climb is the dominant mechanism for deformation of TMT alloys according to strain rate jump tests. After the characterization of aged AFA alloys, we found that the largest strengthening effect from L1₂ precipitates can be obtained by aging for less than 24 h. The coarsening behavior of the L1₂ precipitates was not influenced by carbon and boron additions. Failure analysis and post-mortem TEM analysis were performed to study the creep failure mechanisms of these AFA steels after creep tests. Though the Laves and B2-NiAl phase precipitated along the boundaries can improve the creep properties, cracks were

Tailoring plasticity of austenitic stainless steels for nuclear applications: Review of mechanisms controlling plasticity of austenitic steels below 400 °C

Energy Technology Data Exchange (ETDEWEB)

Meric de Bellefon, G., E-mail: mericdebelle@wisc.edu [University of Wisconsin-Madison (United States); Duysen, J.C. van [EDF R& D (France); University of Tennessee-Knoxville (United States); Unité Matériaux et Transformation (UMET) CNRS, Université de Lille (France)

2016-07-15

AISI 304 and 316 austenitic stainless steels were invented in the early 1900s and are still trusted by materials and mechanical engineers in numerous sectors because of their good combination of strength, ductility, and corrosion resistance, and thanks to decades of experience and data. This article is part of an effort focusing on tailoring the plasticity of both types of steels to nuclear applications. It provides a synthetic and comprehensive review of the plasticity mechanisms in austenitic steels during tensile tests below 400 °C. In particular, formation of twins, extended stacking faults, and martensite, as well as irradiation effects and grain rotation are discussed in details. - Highlights: • This article is part of an effort to tailor the plasticity of 304L and 316L steels for nuclear applications. • It reviews mechanisms controlling plasticity of austenitic steels during tensile tests. • Formation of twins, extended stacking faults, and martensite, grain rotation, and irradiation effects are discussed.

Microstructural Variations Across a Dissimilar 316L Austenitic: 9Cr Reduced Activation Ferritic Martensitic Steel Weld Joint

Science.gov (United States)

Thomas Paul, V.; Karthikeyan, T.; Dasgupta, Arup; Sudha, C.; Hajra, R. N.; Albert, S. K.; Saroja, S.; Jayakumar, T.

2016-03-01

This paper discuss the microstructural variations across a dissimilar weld joint between SS316 and 9Cr-RAFM steel and its modifications on post weld heat treatments (PWHT). Detailed characterization showed a mixed microstructure of austenite and martensite in the weld which is in agreement with the phases predicted using Schaeffler diagram based on composition measurements. The presence of very low volume fraction of δ-ferrite in SS316L has been identified employing state of the art electron back-scattered diffraction technique. PWHT of the ferritic steel did not reduce the hardness in the weld metal. Thermal exposure at 973 K (700 °C) showed a progressive reduction in hardness of weld joint with duration of treatment except in austenitic base metal. However, diffusion annealing at 1073 K (800 °C) for 100 hours resulted in an unexpected increase in hardness of weld metal, which is a manifestation of the dilution effects and enrichment of Ni on the transformation characteristics of the weld zone. Migration of carbon from ferritic steel aided the precipitation of fine carbides in the austenitic base metal on annealing at 973 K (700 °C); but enhanced diffusion at 1073 K (880 °C) resulted in coarsening of carbides and thereby reduction of hardness.

Electron backscatter and X-ray diffraction studies on the deformation and annealing textures of austenitic stainless steel 310S

Energy Technology Data Exchange (ETDEWEB)

Nezakat, Majid, E-mail: majid.nezakat@usask.ca [Canadian Light Source Inc., 44 Innovation Boulevard, Saskatoon, SK, S7N 2V3 (Canada); Akhiani, Hamed [Westpower Equipment Ltd., 4451 54 Avenue South East, Calgary, AB T2C 2A2 (Canada); Sabet, Seyed Morteza [Department of Ocean and Mechanical Engineering, Florida Atlantic University, Boca Raton, FL 33431 (United States); Szpunar, Jerzy [Department of Mechanical Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, SK, S7N 5A9 (Canada)

2017-01-15

We studied the texture evolution of thermo-mechanically processed austenitic stainless steel 310S. This alloy was cold rolled up to 90% reduction in thickness and subsequently annealed at 1050 °C. At the early stages of deformation, strain-induced martensite was formed from deformed austenite. By increasing the deformation level, slip mechanism was found to be insufficient to accommodate higher deformation strains. Our results demonstrated that twinning is the dominant deformation mechanism at higher deformation levels. Results also showed that cold rolling in unidirectional and cross rolling modes results in Goss/Brass and Brass dominant textures in deformed samples, respectively. Similar texture components are observed after annealing. Thus, the annealing texture was greatly affected by texture of the deformed parent phase and martensite did not contribute as it showed an athermal reversion during annealing. Results also showed that when the fraction of martensite exceeds a critical point, its grain boundaries impeded the movement of austenite grain boundaries during annealing. As a result, recrystallization incubation time would increase. This caused an incomplete recrystallization of highly deformed samples, which led to a rational drop in the intensity of the texture components. - Highlights: •Thermo-mechanical processing through different cold rolling modes can induce different textures. •Martensite reversion is athermal during annealing. •Higher fraction of deformation-induced martensite can increase the annealing time required for complete recrystallization. •Annealing texture is mainly influenced by the deformation texture of austenite.

The effect of cold work, heat treatment, and composition on the austenite to R-phase transformation temperature of Ni-Ti shape memory alloys

International Nuclear Information System (INIS)

Thoma, P.E.; Angst, D.R.; Schachner, K.D.

1995-01-01

The influence of cold work (CW) and heat treatment (HT) on the austenite to R-Phase (A→R) transformation temperature (TT) of a near equiatomic and three other Ti rich NiTi SMA is examined. For the SMA having a near equiatomic composition, the A→R TT increases with increasing CW at low HT temperatures. For the SMA having the maximum possible Ti content, the A→R TT decreases with increasing CW at low HT temperatures. For all compositions, the A→R TT is not sensitive to CW at high HT temperatures. At a Ti content slightly below the maximum possible, the A→R TT is relatively insensitive to CW and HT temperature. For all of the SMA investigated, the A→R TT increases with increasing Ti content for a specific CW and HT temperature, and this effect is greatest at low CW and at high HT temperatures. (orig.)

Crystallography of sigma phase precipitation in superaustenitic Fe-22Cr-21Ni-6Mo-0.3N stainless steels

International Nuclear Information System (INIS)

Lee, Tae Ho; Jung, Yun Chul; Kim, Sung Joon

1999-01-01

The crystallographic features of sigma phase precipitation in super austenitic Fe-22Cr-21Ni-6Mo-(0.3N) stainless steels during isothermal aging were investigated utilizing transmission electron microscopy. The sigma phase precipitated along the austenite grain boundaries even after solution treatment due to higher Mo contents and remained stable throughout aging at 900 .deg. C up to 168 hours. The sigma phase observed in this study was found to be ternary Fe-Cr-Mo sigma phase and had tetragonal structure with lattice parameters of a=9.17A and c=4.74A. The orientation relationships between the sigma phase and austenite were determined from the analyses of selected area diffraction patterns taken by various zone axes and stereo graphic analyses. The orientation relationships between sigma and austenite phases obtained in this study were as follows; 1) (110) γ ll (110) σ , [111] γ ll [001] σ and (112) γ ll (110) σ , [111] γ ll [001] σ and 2) (110) γ ll (110) σ , [112] γ ll [113] σ and (111) γ ll (332) σ , [112] γ ll [113] σ . However, the former orientation relationship was predominant throughout aging and the latter orientation relationship was scarcely observed in very limited aging condition

Preparation, characterization and thermal properties of binary nitrate salts/expanded graphite as composite phase change material

Energy Technology Data Exchange (ETDEWEB)

Xiao, Junbing [School of Materials and Energy, Guangdong University of Technology, 510006 Guangzhou (China); Huang, Jin, E-mail: huangjiner@126.com [School of Materials and Energy, Guangdong University of Technology, 510006 Guangzhou (China); Zhu, Panpan; Wang, Changhong [School of Materials and Energy, Guangdong University of Technology, 510006 Guangzhou (China); Li, Xinxi [School of Materials and Energy, Guangdong University of Technology, 510006 Guangzhou (China); Center for Nanochemistry, Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University, Beijing (China)

2014-07-01

Highlights: • The expanded graphite enhanced thermal conductivity coefficient greatly. • The aqueous solution method adopting ultrasonic was utilized to disperse EG. • The combination of composite was physical without chemical reaction. • The reduction on total latent heat was slight after the adding EG. - Abstract: The binary nitrate salts/expanded graphite (EG) composite phase change material (PCM) were prepared via adding different mass rate of EG to binary nitrate salts consisting of NaNO{sub 3} and KNO{sub 3} (6:4) by aqueous solution method adopting ultrasonic. The morphology and chemical composition of EG and the composite PCM were characterized and investigated by X-ray diffraction (XRD), scan electron microscope (SEM), energy dispersive spectrometer (EDS), transmission electron microscope (TEM), respectively. Laser thermal conductivity instrument and differential scanning calorimeter (DSC) were employed to measure thermo physical properties. Drawing the conclusion from investigation, that EG had enhanced thermal conductivity coefficient which largely increased to 4.884 W/(m K) and reduced total latent heat by mostly 11.0%. The morphology and phase structure results indicated that EG were well dispersed into and physically combined with molten salts. In general, the prepared composite PCM could be a suitable phase change material for thermal energy storage.

Preparation, characterization and thermal properties of binary nitrate salts/expanded graphite as composite phase change material

International Nuclear Information System (INIS)

Xiao, Junbing; Huang, Jin; Zhu, Panpan; Wang, Changhong; Li, Xinxi

2014-01-01

Highlights: • The expanded graphite enhanced thermal conductivity coefficient greatly. • The aqueous solution method adopting ultrasonic was utilized to disperse EG. • The combination of composite was physical without chemical reaction. • The reduction on total latent heat was slight after the adding EG. - Abstract: The binary nitrate salts/expanded graphite (EG) composite phase change material (PCM) were prepared via adding different mass rate of EG to binary nitrate salts consisting of NaNO 3 and KNO 3 (6:4) by aqueous solution method adopting ultrasonic. The morphology and chemical composition of EG and the composite PCM were characterized and investigated by X-ray diffraction (XRD), scan electron microscope (SEM), energy dispersive spectrometer (EDS), transmission electron microscope (TEM), respectively. Laser thermal conductivity instrument and differential scanning calorimeter (DSC) were employed to measure thermo physical properties. Drawing the conclusion from investigation, that EG had enhanced thermal conductivity coefficient which largely increased to 4.884 W/(m K) and reduced total latent heat by mostly 11.0%. The morphology and phase structure results indicated that EG were well dispersed into and physically combined with molten salts. In general, the prepared composite PCM could be a suitable phase change material for thermal energy storage

Retained austenite thermal stability in a nanostructured bainitic steel

International Nuclear Information System (INIS)

Avishan, Behzad; Garcia-Mateo, Carlos; Yazdani, Sasan; Caballero, Francisca G.

2013-01-01

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 T 0 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

Retained austenite thermal stability in a nanostructured bainitic steel

Energy Technology Data Exchange (ETDEWEB)

Avishan, Behzad, E-mail: b_avishan@sut.ac.ir [Faculty of Materials Engineering, Sahand University of Technology, Tabriz (Iran, Islamic Republic of); Garcia-Mateo, Carlos, E-mail: cgm@cenim.csic.es [Department of Physical Metallurgy, National Centre for Metallurgical Research (CENIM-CSIC), MATERALIA Research Group, Avda. Gregorio del Amo, 8, 28040, Madrid (Spain); Yazdani, Sasan, E-mail: yazdani@sut.ac.ir [Faculty of Materials Engineering, Sahand University of Technology, Tabriz (Iran, Islamic Republic of); Caballero, Francisca G., E-mail: fgc@cenim.csic.es [Department of Physical Metallurgy, National Centre for Metallurgical Research (CENIM-CSIC), MATERALIA Research Group, Avda. Gregorio del Amo, 8, 28040, Madrid (Spain)

2013-07-15

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 T{sub 0} 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.

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.

Simulation Kinetics of Austenitic Phase Transformation in Ti+Nb Stabilized IF and Microalloyed Steels

Science.gov (United States)

Ghosh, Sumit; Dasharath, S. M.; Mula, Suhrit

2018-05-01

In the present study, the influence of cooling rates (low to ultrafast) on diffusion controlled and displacive transformation of Ti-Nb IF and microalloyed steels has been thoroughly investigated. Mechanisms of nucleation and formation of non-equiaxed ferrite morphologies (i.e., acicular ferrite and bainitic ferrite) have been analyzed in details. The continuous cooling transformation behavior has been studied in a thermomechanical simulator (Gleeble 3800) using the cooling rates of 1-150 °C/s. On the basis of the dilatometric analysis of each cooling rate, continuous cooling transformation (CCT) diagrams have been constructed for both the steels to correlate the microstructural features at each cooling rate in different critical zones. In the case of the IF steel, massive ferrite grains along with granular bainite structures have been developed at cooling rates > 120 °C/s. On the other hand, a mixture of lath bainitic and lath martensite structures has been formed at a cooling rate of 80 °C/s in the microalloyed steel. A strong dependence of the cooling rates and C content on the microstructures and mechanical properties has been established. The steel samples that were fast cooled to a mixture of bainite ferrite and martensite showed a significant improvement of impact toughness and hardness (157 J, for IF steel and 174 J for microalloyed steel) as compared to that of the as-received specimens (133 J for IF steel and 116 J for microalloyed steel). Thus, it can be concluded that the hardness and impact toughness properties are correlated well with the microstructural constituents as indicated by the CCT diagram. Transformation mechanisms and kinetics of austenitic transformation to different phase morphologies at various cooling rates have been discussed in details to correlate microstructural evolution and mechanical properties.

Elaboration of austenitic stainless steel samples with bimodal grain size distributions and investigation of their mechanical behavior

Science.gov (United States)

Flipon, B.; de la Cruz, L. Garcia; Hug, E.; Keller, C.; Barbe, F.

2017-10-01

Samples of 316L austenitic stainless steel with bimodal grain size distributions are elaborated using two distinct routes. The first one is based on powder metallurgy using spark plasma sintering of two powders with different particle sizes. The second route applies the reverse-annealing method: it consists in inducing martensitic phase transformation by plastic strain and further annealing in order to obtain two austenitic grain populations with different sizes. Microstructural analy ses reveal that both methods are suitable to generate significative grain size contrast and to control this contrast according to the elaboration conditions. Mechanical properties under tension are then characterized for different grain size distributions. Crystal plasticity finite element modelling is further applied in a configuration of bimodal distribution to analyse the role played by coarse grains within a matrix of fine grains, considering not only their volume fraction but also their spatial arrangement.

A Short review on wrought austenitic stainless steels at high temperatures: processing, microstructure, properties and performance

Directory of Open Access Journals (Sweden)

Ronald Lesley Plaut

2007-12-01

Full Text Available Wrought austenitic stainless steels are widely used in high temperature applications. This short review discusses initially the processing of this class of steels, with emphasis on solidification and hot working behavior. Following, a brief summary is made on the precipitation behavior and the numerous phases that may appear in their microstructures. Creep and oxidation resistance are, then, briefly discussed, and finalizing their performance is compared with other high temperature metallic materials.

Corrosion of austenitic stainless steel

Energy Technology Data Exchange (ETDEWEB)

Silva, M C.M. [Instituto Nacional de Tecnologia, Rio de Janeiro (Brazil)

1977-01-01

Types of corrosion observed in a heat exchanger pipe and on a support of still of molasses fermented wort, both in austenitic stainless steel, are focused. Not only are the causes which might have had any kind of influence on them examined, but also the measures adopted in order to avoid and lessen its occurence.

Rapid nickel diffusion in cold-worked type 316 austenitic steel at 360-500 C

Energy Technology Data Exchange (ETDEWEB)

Arioka, Koji [Institute of Nuclear Safety Systems, Inc., Mihama (Japan); Iijima, Yoshiaki [Tohoku Univ., Sendai (Japan). Dept. of Materials Science; Miyamoto, Tomoki [Kobe Material Testing Laboratory Co. Ltd., Harima (Japan)

2017-10-15

The diffusion coefficient of nickel in cold-worked Type 316 austenitic steel was determined by the diffusion couple method in the temperature range between 360 and 500 C. A diffusion couple was prepared by electroless nickel plating on the surface of a 20 % cold-worked Type 316 austenitic steel specimen. The growth in width of the interdiffusion zone was proportional to the square root of diffusion time until 14 055 h. The diffusion coefficient of nickel (D{sub Ni}) in cold-worked Type 316 austenitic steel was determined by extrapolating the concentration-dependent interdiffusion coefficient to 11 at.% of nickel. The value of D{sub Ni} at 360 C was about 5 000 times higher than the lattice diffusion coefficient of nickel in Type 316 austenitic steel. The determined activation energy 117 kJ mol{sup -1} was 46.6 % of the activation energy 251 kJ mol{sup -1} for the lattice diffusion of nickel in Type 316 austenitic steel.

Interactions between the phase stress and the grain-orientation-dependent stress in duplex stainless steel during deformation

International Nuclear Information System (INIS)

Jia, N.; Peng, R. Lin; Wang, Y.D.; Chai, G.C.; Johansson, S.; Wang, G.; Liaw, P.K.

2006-01-01

The development of phase stress and grain-orientation-dependent stress under uniaxial compression was investigated in a duplex stainless steel consisting of austenite and ferrite. Using in situ neutron diffraction measurements, the strain response of several h k l planes to the applied compressive stress was mapped as a function of applied stress and sample direction. Analysis based on the experimental results and elastoplastic self-consistent simulations shows that phase stresses of thermal origin further increase during elastic loading but decrease with increased plastic deformation. Grain-orientation-dependent stresses become significant in both austenite and ferrite after loading into the plastic region. After unloading from the plastic regime, a considerable intergranular stress remains in the austenitic phase and dominates over the phase stress. This study provides fundamental experimental inputs for future micromechanical modeling aiming at the evaluation and prediction of the mechanical performance of multiphase materials

Modification of the Strength Anisotropy in an Austenitic ODS Steel

International Nuclear Information System (INIS)

Kim, T. K.; Jang, J.; Kim, S. H.; Lee, C. B.; Bae, C. S.; Kim, D. H.

2007-01-01

Among many candidate alloys for Gen IV reactors, the oxide dispersion strengthened (ODS) alloy is widely considered as a good candidate material for the in-reactor component, like cladding tube. The ODS alloy is well known due to its good high temperature strength, and excellent irradiation resistance. For the previous two decades in the nuclear community, the ODS alloy developments have been mostly focused on the ferritic martensitic (F-M) steel-based ones. On the other hand, the austenitic stainless steels (e.g. 316L or 316LN) have been used as a structural material due to its good high temperature strength and a good compatibility with a media. However, the austenitic stainless steel showed unfavorable characteristics in the dimensional stability under neutron irradiation and cracking behavior with the media. It is thus expected that the austenitic ODS steels restrain the dimension stability under neutron irradiation. However, the ODS alloys usually reveal the anisotropic characteristic in mechanical strength in the hoop and longitudinal directions, which is attributed to the grain morphology strongly developed parallel to the rolling direction with a high aspect ratio. This study focuses on a modification of the strength anisotropy of an austenitic ODS alloy by a recrystallization heat treatment

Quantification by image analysis of grain size of the high temperature phase (austenite) of martensitic steels 9Cr-1Mo

International Nuclear Information System (INIS)

Barcelo, F.; Brachet, J.C.

1993-01-01

In martensitic steels, the austenitic grain size before transformation may influence mechanical properties. 9Cr-1Mo steel (EM10) is used in hexagonal pipes fabrication in fast neutrons reactors. Image analysis allows to quantify the older grain size in function of the austenization heat treatment conditions. (A.B.). 2 figs

Application of Moessbauer effect in the study of austenite retained in low carbon steel

International Nuclear Information System (INIS)

Azevedo, A.L.T. de; Silva, E.G. da

1979-01-01

Moessbauer effect measurements of two samples of low carbon alloy having micro-structure of granular bainite type and martensite type have been done. The concentration of the retained austenite in both samples was determined by Moessbauer effect and x-rays there, being agreement for the higher austenite content sample. Concentration of carbon in the MA (Martensite - Austenite) constituents of bainite is also ditermined, the results being in agreement with metallographic considerations. Carbon enrichments are shown as responsible by the stabilization of the austenite in the granular bainite. Spectra of both samples present three magnetic configurations for α-iron with medium magnetic fields iqual to 335, 307 and 280 KOe. (A.R.H.) [pt

Austenitic stainless steels with cryogenic resistance

International Nuclear Information System (INIS)

Tarata, Daniela Florentina

1999-01-01

The most used austenitic stainless steels are alloyed with chromium and nickel and have a reduced carbon content, usually lower than 0.1 % what ensures corresponding properties for processing by plastic deformation at welding, corrosion resistance in aggressive environment and toughness at low temperatures. Steels of this kind alloyed with manganese are also used to reduce the nickel content. By alloying with manganese which is a gammageneous element one ensures the stability of austenites. Being cheaper these steels may be used extensively for components and equipment used in cryogenics field. The best results were obtained with steels of second group, AMnNi, in which the designed chemical composition was achieved, i.e. the partial replacement of nickel by manganese ensured the toughness at cryogenic temperatures. If these steels are supplementary alloyed, their strength properties may increase to the detriment of plasticity and toughness, although the cryogenic character is preserved

Synergistic Computational and Microstructural Design of Next- Generation High-Temperature Austenitic Stainless Steels

Energy Technology Data Exchange (ETDEWEB)

Karaman, Ibrahim [Texas A& M Engineering Experiment Station, College Station, TX (United States); Arroyave, Raymundo [Texas A& M Engineering Experiment Station, College Station, TX (United States)

2015-07-31

The purpose of this project was to: 1) study deformation twinning, its evolution, thermal stability, and the contribution on mechanical response of the new advanced stainless steels, especially at elevated temperatures; 2) study alumina-scale formation on the surface, as an alternative for conventional chromium oxide, that shows better oxidation resistance, through alloy design; and 3) design new generation of high temperature stainless steels that form alumina scale and have thermally stable nano-twins. The work involved few baseline alloys for investigating the twin formation under tensile loading, thermal stability of these twins, and the role of deformation twins on the mechanical response of the alloys. These baseline alloys included Hadfield Steel (Fe-13Mn-1C), 316, 316L and 316N stainless steels. Another baseline alloy was studied for alumina-scale formation investigations. Hadfield steel showed twinning but undesired second phases formed at higher temperatures. 316N stainless steel did not show signs of deformation twinning. Conventional 316 stainless steel demonstrated extensive deformation twinning at room temperature. Investigations on this alloy, both in single crystalline and polycrystalline forms, showed that deformation twins evolve in a hierarchical manner, consisting of micron–sized bundles of nano-twins. The width of nano-twins stays almost constant as the extent of strain increases, but the width and number of the bundles increase with increasing strain. A systematic thermomechanical cycling study showed that the twins were stable at temperatures as high as 900°C, after the dislocations are annealed out. Using such cycles, volume fraction of the thermally stable deformation twins were increased up to 40% in 316 stainless steel. Using computational thermodynamics and kinetics calculations, we designed two generations of advanced austenitic stainless steels. In the first generation, Alloy 1, which had been proposed as an alumina

The high temperature oxidation behaviour of austenitic stainless steels

International Nuclear Information System (INIS)

Hales, R.

1977-04-01

High temperature annealing in a dynamic vacuum has been utilised to induce the growth of duplex oxide over the whole surface of stainless steel specimens. It is found that duplex oxide grows at a rate which does not obey a simple power law. The oxidation kinetics and oxide morphology have also been studied for a series of ternary austenitic alloys which cover a range of composition between 5 and 20% chromium. A model has been developed to describe the formation of duplex oxide and the subsequent formation of a 'healing layer' which virtually causes the oxidation process to stop. This phase tends to form at grain boundaries and a relationship has been derived for the reaction kinetics which relates the reaction rate with grain size of the substrate. (author)

Phase transformation of 316L stainless steel from wire to fiber

International Nuclear Information System (INIS)

Shyr, Tien-Wei; Shie, Jing-Wen; Huang, Shih-Ju; Yang, Shun-Tung; Hwang, Weng-Sing

2010-01-01

In this work, quantitative crystalline phase analysis of 316L stainless steel from wire to fiber using a multi-pass cold drawing process was studied using the Rietveld whole XRD profile fitting technique. The different diameters of the fibers: 179, 112, 75, 50, 34, 20, and 8 μm, were produced from an as-received wire with a diameter of 190 μm. The crystalline phases were identified using MDI Jade 5.0 software. The volume fractions of crystalline phases were estimated using a Materials Analysis Using Diffraction software. XRD analysis revealed that the crystal structure of as-received wire is essentially a γ-austenite crystalline phase. The phase transformation occurred during the 316L stainless steel from wire to fiber. Three crystalline phases such as γ-austenite, α'-martensite, and sigma phase of the fine fiber were observed. A cold drawing accelerates the sigma phase precipitates, particularly during the heat treatment of the fiber.

Low-temperature gaseous surface hardening of stainless steel: the current status

DEFF Research Database (Denmark)

Christiansen, Thomas; Somers, Marcel A. J.

2009-01-01

a hardened case at the surface, while maintaining the superior corrosion performance. This can be achieved by dissolving colossal amounts of nitrogen and/or carbon without forming nitrides and/or carbides, thus developing so-called expanded austenite. The present work gives an overview over results obtained...... on homogeneous expanded austenite and covers the crystallography for nitrogen- and carbon-stabilised expanded austenite, the solubility for nitrogen and carbon, the diffusion of these interstitials as well as the stability of expanded austenite with respect to nitride and carbide formation. Subsequently...

Mechanical Behaviour of 304 Austenitic Stainless Steel Processed by Room Temperature Rolling

Science.gov (United States)

Singh, Rahul; Goel, Sunkulp; Verma, Raviraj; Jayaganthan, R.; Kumar, Abhishek

2018-03-01

To study the effect of room temperature rolling on mechanical properties of 304 Austenitic Stainless Steel, the as received 304 ASS was rolled at room temperature for different percentage of plastic deformation (i.e. 30, 50, 70 and 90 %). Microstructural study, tensile and hardness tests were performed in accordance with ASTM standards to study the effect of rolling. The ultimate tensile strength (UTS) and hardness of a rolled specimen have enhanced with rolling. The UTS has increased from 693 MPa (as received) to 1700 MPa (after 90% deformation). The improvement in UTS of processed samples is due to combined effect of grain refinement and stress induced martensitic phase transformation. The hardness values also increases from 206 VHN (as received) to 499 VHN (after 90% deformation). Magnetic measurements were also conducted to confirm the formation of martensitic phase.

Structure and tensile properties of ferro-martensitic alloys hardened by chi phase precipitation

International Nuclear Information System (INIS)

Alamo, A.; Aubert, H.; Laniesse, J.; Lelong, C.; Pigoury, M.; Foucher, C.

1985-08-01

Transformation of ferrite into austenite and of austenite into martensite, precipitation of intermetallic phases and tensile properties of the steel Cr13-Mo1.5 are studied in function of Ti additions (from 0 to 3%) and Ni additions (from 2 to 8%) for its mechanical resistance at 400-650 0 C. 12 references are given [fr

Tailoring plasticity of austenitic stainless steels for nuclear applications: Review of mechanisms controlling plasticity of austenitic steels below 400 °C

Science.gov (United States)

Meric de Bellefon, G.; van Duysen, J. C.

2016-07-01

AISI 304 and 316 austenitic stainless steels were invented in the early 1900s and are still trusted by materials and mechanical engineers in numerous sectors because of their good combination of strength, ductility, and corrosion resistance, and thanks to decades of experience and data. This article is part of an effort focusing on tailoring the plasticity of both types of steels to nuclear applications. It provides a synthetic and comprehensive review of the plasticity mechanisms in austenitic steels during tensile tests below 400 °C. In particular, formation of twins, extended stacking faults, and martensite, as well as irradiation effects and grain rotation are discussed in details.

Attenuation capability of low activation-modified high manganese austenitic stainless steel for fusion reactor system

Energy Technology Data Exchange (ETDEWEB)

Eissa, M.M. [Steel Technology Department, Central Metallurgical Research and Development Institute (CMRDI), Helwan (Egypt); El-kameesy, S.U.; El-Fiki, S.A. [Physics Department, Faculty of Science, Ain Shams University, Cairo (Egypt); Ghali, S.N. [Steel Technology Department, Central Metallurgical Research and Development Institute (CMRDI), Helwan (Egypt); El Shazly, R.M. [Physics Department, Faculty of Science, Al-Azhar University, Cairo (Egypt); Saeed, Aly, E-mail: aly_8h@yahoo.com [Nuclear Power station Department, Faculty of Engineering, Egyptian-Russian University, Cairo (Egypt)

2016-11-15

Highlights: • Improvement stainless steel alloys to be used in fusion reactors. • Structural, mechanical, attenuation properties of investigated alloys were studied. • Good agreement between experimental and calculated results has been achieved. • The developed alloys could be considered as candidate materials for fusion reactors. - Abstract: Low nickel-high manganese austenitic stainless steel alloys, SSMn9Ni and SSMn10Ni, were developed to use as a shielding material in fusion reactor system. A standard austenitic stainless steel SS316L was prepared and studied as a reference sample. The microstructure properties of the present stainless steel alloys were investigated using Schaeffler diagram, optical microscopy, and X-ray diffraction pattern. Mainly, an austenite phase was observed for the prepared stainless steel alloys. Additionally, a small ferrite phase was observed in SS316L and SSMn10Ni samples. The mechanical properties of the prepared alloys were studied using Vickers hardness and tensile tests at room temperature. The studied manganese stainless steel alloys showed higher hardness, yield strength, and ultimate tensile strength than SS316L. On the other hand, the manganese stainless steel elongation had relatively lower values than the standard SS316L. The removal cross section for both slow and total slow (primary and those slowed down in sample) neutrons were carried out using {sup 241}Am-Be neutron source. Gamma ray attenuation parameters were carried out for different gamma ray energy lines which emitted from {sup 60}Co and {sup 232}Th radioactive sources. The developed manganese stainless steel alloys had a higher total slow removal cross section than SS316L. While the slow neutron and gamma rays were nearly the same for all studied stainless steel alloys. From the obtained results, the developed manganese stainless steel alloys could be considered as candidate materials for fusion reactor system with low activation based on the short life

Interface segregation behavior in thermal aged austenitic precipitation strengthened stainless steel

Energy Technology Data Exchange (ETDEWEB)

Li, Hui [Key Laboratory for Microstructures, Shanghai University, Shanghai 200444 (China); Technical Department, Jiuli Hi-Tech Metals Co., Ltd., Huzhou 313008 (China); Song, Hui [Key Laboratory for Microstructures, Shanghai University, Shanghai 200444 (China); Liu, Wenqing, E-mail: wqliu@staff.shu.edu.cn [Key Laboratory for Microstructures, Shanghai University, Shanghai 200444 (China); Institute of Materials, Shanghai University, Shanghai 200072 (China); Xia, Shuang; Zhou, Bangxin [Institute of Materials, Shanghai University, Shanghai 200072 (China); Su, Cheng; Ding, Wenyan [Technical Department, Jiuli Hi-Tech Metals Co., Ltd., Huzhou 313008 (China)

2015-12-15

The segregation of various elements at grain boundaries, precipitate/matrix interfaces were analyzed using atom probe tomography in an austenitic precipitation strengthened stainless steel aged at 750 °C for different time. Segregation of P, B and C at all types of interfaces in all the specimens were observed. However, Si segregated at all types of interfaces only in the specimen aged for 16 h. Enrichment of Ti at grain boundaries was evident in the specimen aged for 16 h, while Ti did not segregate at other interfaces. Mo varied considerably among interface types, e.g. from segregated at grain boundaries in the specimens after all the aging time to never segregate at γ′/γ phase interfaces. Cr co-segregated with C at grain boundaries, although carbides still did not nucleate at grain boundaries yet. Despite segregation tendency variations in different interface types, the segregation tendency evolution variation of different elements depending aging time were analyzed among all types of interfaces. Based on the experimental results, the enrichment factors, Gibbs interface excess and segregation free energies of segregated elements were calculated and discussed. - Highlights: • Solute atoms segregated at interfaces were analyzed in an austenitic stainless steel. • The comparison of segregation in different interfaces was studied by APT. • The evolution of interface segregation during aging treatment was discussed.

Assessment of Retained Austenite in AISI D2 Tool Steel Using Magnetic Hysteresis and Barkhausen Noise Parameters

Science.gov (United States)

Kahrobaee, Saeed; Kashefi, Mehrdad

2015-03-01

Inaccurate heat treatment process could result in excessive amount of retained austenite, which degrades the mechanical properties, like strength, wear resistance, and hardness of cold work tool steel parts. Thus, to control the mechanical properties, quantitative measurement of the retained austenite is a critical step in optimizing the heat-treating parameters. X-ray diffraction method is the most frequently used technique for this purpose. This technique is, however, destructive and time consuming. Furthermore, it is not applicable to 100% quality inspection of industrial parts. In the present paper, the influence of austenitizing temperature on the retained austenite content and hardness of AISI D2 tool steel has been studied. Additionally, nondestructive magnetic hysteresis parameters of the samples including coercivity, magnetic saturation, and maximum differential permeability as well as their magnetic Barkhausen noise features (RMS peak voltage and peak position) have been investigated. The results revealed direct relations between magnetic saturation, differential permeability, and MBN peak amplitude with increasing austenitizing temperature due to the retained austenite formation. Besides, both parameters of coercivity and peak position had an inverse correlation with the retained austenite fraction.

Reduced-activation austenitic stainless steels: The Fe--Mn--Cr--C system

International Nuclear Information System (INIS)

Klueh, R.L.; Maziasz, P.J.

1988-01-01

Nickel-free manganese-stabilized steels are being developed for fusion-reactor applications. As the first part of this effort, the austenite-stable region in the Fe--Mn--Cr--C system was determined. Results indicated that the Schaeffler diagram developed for Fe--Ni--Cr--C alloys cannot be used to predict the constituents expected for high-manganese steels. This is true because manganese is not as strong an austenite stabilizer relative to δ-ferrite formation as predicted by the diagram, but it is a stronger austenite stabilizer relative to martensite than predicted. Therefore, the austenite-stable region for Ne--Mn--Cr--C alloys occurs at lower chromium and hugher combinations of manganese and carbon than predicted by the Schaeffler diagram. Development of a manganese-stabilized stainless steel should be possible in the composition range of 20 to 25% Mn, 10 to 15% Cr, and 0.01 to 0.25%C. Tensile behavior of an Fe--20%Mn--12%Cr--0.25%C alloy was determined. The strength and ductility of this possible base composition was comparable to type 316 stainless steel in both the solution-annealed and cold-worked condition

Temperature dependent measurement of internal damping of austenitic stainless steels

Directory of Open Access Journals (Sweden)

Oravcová Monika

2018-01-01

Full Text Available This article is aimed on the analysis of the internal damping changes of austenitic stainless steels AISI 304, AISI 316L and AISI 316Ti depending from temperature. In experimental measurements only resonance method was used which is based on continuous excitation of oscillations of the specimens and the whole apparatus vibrates at the frequency near to the resonance. Microplastic processes and dissipation of energy within the metals are evaluated and investigated by internal damping measurements. Damping capacity of materials is closely tied to the presence of defects including second phase particles and voids. By measuring the energy dissipation in the material, we can determine the elastic characteristics, Youngs modulus, the level of stress relaxation and many other.

Influence of titanium on the tempering structure of austenitic steels

International Nuclear Information System (INIS)

Ghuezaiel, M.J.

1985-10-01

The microstructure of titanium-stabilized and initially deformed (approximately 20%) austenitic stainless steels used in structures of fast neutrons reactors has been studied after one hour duration annealings (500 0 C) by X-ray diffraction, optical microscopy, microhardness and transmission electron microscopy. The studied alloys were either of industrial type CND 17-13 (0.23 to 0.45 wt% Ti) or pure steels (18% Cr, 14% Ni, 0 or 0.3 wt% Ti). During tempering, the pure steels presented some restauration before recristallization. In the industrial steels, only recristallization occurred, and this only in the most deformed steel. Precipitation does not occur in the titanium-free pure steel. In industrial steels, many intermetallic phases are formed when recristallization starts [fr

Anelastic mechanical loss spectrometry of hydrogen in austenitic stainless steels

International Nuclear Information System (INIS)

Yagodzinskyy, Y.; Andronova, E.; Ivanchenko, M.; Haenninen, H.

2009-01-01

Atomic distribution of hydrogen, its elemental diffusion jumps and its interaction with dislocations in a number of austenitic stainless steels are studied with anelastic mechanical loss (AML) spectrometry in combination with the hydrogen thermal desorption method. Austenitic stainless steels of different chemical composition, namely, AISI 310, AISI 201, and AISI 301LN, as well as LDX 2101 duplex stainless steel are studied to clarify the role of different alloying elements on the hydrogen behavior. Activation analyses of the hydrogen Snoek-like peaks are performed with their decomposition to sets of Gaussian components. Fine structure of the composite hydrogen peaks is analyzed under the assumption that each component corresponds to diffusion transfer of hydrogen between octahedral positions with certain atomic compositions of the nearest neighbouring lattice sites. An additional component originating from hydrogen-dislocation interaction is considered. Binding energies for hydrogen-dislocation interaction are also estimated for the studied austenitic stainless steels.

Martensitic transformation in an intergranular corrosion area of austenitic stainless steel during thermal cycling

International Nuclear Information System (INIS)

La Fontaine, Alexandre; Yen, Hung-Wei; Trimby, Patrick; Moody, Steven; Miller, Sarah; Chensee, Martin; Ringer, Simon; Cairney, Julie

2014-01-01

An oxidation-assisted martensitic phase transformation was observed in an austenitic stainless steel after thermal cycling up to 970 °C in air in a solar thermal steam reformer. The intergranular corrosion areas were investigated by electron backscatter diffraction (EBSD), transmission Kikuchi diffraction (TKD) and transmission electron microscopy (TEM). The structural-and-chemical maps revealed that within intergranular corrosion areas this martensitic transformation primarily occurs in oxidation-induced chromium-depleted zones, rather than due to only sensitization. This displacive transformation may also play a significant role in the rate at which intergranular corrosion takes place

Study on the crystallographic orientation relationship and formation mechanism of reversed austenite in economical Cr12 super martensitic stainless steel

International Nuclear Information System (INIS)

Ye, Dong; Li, Shaohong; Li, Jun; Jiang, Wen; Su, Jie; Zhao, Kunyu

2015-01-01

Effect of carbides and crystallographic orientation relationship on the formation mechanism of reversed austenite of economical Cr12 super martensitic stainless steel (SMSS) has been investigated mainly by transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The results indicate that the M_2_3C_6 precipitation and the formation of the reversed austenite have the interaction effect during tempering process in SMSS. The reversed austenite forms intensively at the sub-block boundary and the lath boundary within a misorientation range of 0–60°. M_2_3C_6 has the same crystallographic orientation relationship with reversed austenite. There are two different kinds of formation modes for reversed austenite. One is a nondiffusional shear reversion; the other is a diffusion transformation. Both are strictly limited by crystallographic orientation relationship. The austenite variants are limited to two kinds within one packet and five kinds within one prior austenite grain. - Highlights: • Reversed austenite forms at martensite boundaries with misorientation of 0–60° • M_2_3C_6 precipitation and reversed austenite formation have the interaction effect. • Two austenite variants with different orientations can be formed inside a packet. • Two reversed austenite formation modes: shear reversion; diffusion transformation

Study on the crystallographic orientation relationship and formation mechanism of reversed austenite in economical Cr12 super martensitic stainless steel

Energy Technology Data Exchange (ETDEWEB)

Ye, Dong; Li, Shaohong; Li, Jun; Jiang, Wen [Faculty of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093 (China); Su, Jie [Institute for Structural Materials, Central Iron and Steel Research Institute, Beijing 100081 (China); Zhao, Kunyu, E-mail: kyzhaoy@sina.com [Faculty of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093 (China)

2015-11-15

Effect of carbides and crystallographic orientation relationship on the formation mechanism of reversed austenite of economical Cr12 super martensitic stainless steel (SMSS) has been investigated mainly by transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The results indicate that the M{sub 23}C{sub 6} precipitation and the formation of the reversed austenite have the interaction effect during tempering process in SMSS. The reversed austenite forms intensively at the sub-block boundary and the lath boundary within a misorientation range of 0–60°. M{sub 23}C{sub 6} has the same crystallographic orientation relationship with reversed austenite. There are two different kinds of formation modes for reversed austenite. One is a nondiffusional shear reversion; the other is a diffusion transformation. Both are strictly limited by crystallographic orientation relationship. The austenite variants are limited to two kinds within one packet and five kinds within one prior austenite grain. - Highlights: • Reversed austenite forms at martensite boundaries with misorientation of 0–60° • M{sub 23}C{sub 6} precipitation and reversed austenite formation have the interaction effect. • Two austenite variants with different orientations can be formed inside a packet. • Two reversed austenite formation modes: shear reversion; diffusion transformation.

Effect of alloying elements on solidification of primary austenite in Ni-Mn-Cu cast iron

Directory of Open Access Journals (Sweden)

A. Janus

2011-04-01

Full Text Available Within the research, determined were direction and intensity of alloying elements influence on solidification way (directional orvolumetric of primary austenite dendrites in hypoeutectic austenitic cast iron Ni-Mn-Cu. 50 cast shafts dia. 20 mm were analysed.Chemical composition of the alloy was as follows: 1.7 to 3.3 % C, 1.4 to 3.1 % Si, 2.8 to 9.9 % Ni, 0.4 to 7.7 % Mn, 0 to 4.6 % Cu, 0.14 to0.16 % P and 0.03 to 0.04 % S. The discriminant analysis revealed that carbon influences solidification of primary austenite dendrites most intensively. It clearly increases the tendency to volumetric solidification. Influence of the other elements is much weaker. This means that the solidification way of primary austenite dendrites in hypoeutectic austenitic cast iron Ni-Mn-Cu does not differ from that in an unalloyed cast iron.

Behaviour and damage of aged austenitic-ferritic steels: a micro-mechanical approach

International Nuclear Information System (INIS)

Bugat, St.

2000-12-01

The austenitic-ferritic steels are used in the PWR primary cooling system. At the running temperature (320 C), they are submitted to a slow aging, which leads to the embrittlement of the ferritic phase. This embrittlement leads to a decrease of the mechanical properties, in particular of the crack resistance of the austenitic-ferritic steels. The damage and rupture of the austenitic-ferritic steels have been approached at the ENSMP by the works of P. Joly (1992) and of L. Devilliers-Guerville (1998). These works have allowed to reveal a damage heterogeneity which induces a strong dispersion on the ductilities and the toughnesses as well as on the scale effects. Modeling including the damage growth kinetics measured experimentally, have allowed to verify these effects. Nevertheless, they do not consider the two-phase character of the material and do not include a physical model of the cleavage cracks growth which appear in the embrittled ferrite. In this study, is proposed a description of the material allowing to treat these aspects while authorizing the structure calculation. In a first part, the material is studied. The use of the ESBD allows to specify the complex morphology of these steels and crystal orientation relations between the two phases. Moreover, it is shown that the two phases keep the same crystal orientation in the zones, called bicrystals, whose size varies between 500 μm and 1 mm. The study of the sliding lines, coupled to the ESBD, allows to specify too the deformation modes of the two phases. At last, tensile and tensile-compression tests at various deformation range are carried out to characterize the macroscopic mechanical behaviour of these materials. Then, a micro-mechanical modeling of the material behaviour is proposed. This one takes into account the three scales identified at the preceding chapter. The first scale, corresponding to the laths is described as a monocrystal whose behaviour includes both an isotropic and a kinematic strain

Modeling of austenite to ferrite transformation

Indian Academy of Sciences (India)

395–398. c Indian Academy of Sciences. Modeling of austenite to ferrite transformation. MOHSEN KAZEMINEZHAD. ∗. Department of Materials Science and Engineering, Sharif University of Technology, Azadi Avenue, Tehran, Iran. MS received 17 January 2011; revised 9 July 2011. Abstract. In this research, an algorithm ...

Cryogenic properties of austenitic stainless steels for superconducting magnet

International Nuclear Information System (INIS)

Nohara, K.; Kato, T.; Ono, Y.; Sasaki, T.; Suzuki, S.

1983-01-01

The present study examines the magnetic and mechanical properties of a variety of austenitic stainless steels and high maganese steel which are candidate materials for the superconducting magnet attached to high energy particle accelerators. The effect of a specified heat treatment for the precipitation of intermetallic compound Nb3Sn to be used as superconductor on ductility and toughness are especially examined. It is found that nitrogen-strengthened austenitic stainless steels have high strength and good ductility and toughness, but that these are destroyed by precipitation treatment. The poor ductility and toughness after precipitation are caused by a weakening of the grain boundaries due to the agglomerated chromium carbide percipitates. The addition of vanadium suppresses this effect by refining the grain. Austenitic steels are found to have low magnetic permeabilities and Neel temperatures, and show serrated flow in traction test due to strained martensitic transformation. High manganese steel has extremely low permeability, a Neel temperature about room temperature, and has a serrated flow in traction test due to adiabatic deformation at liquid helium temperature

Site preference and phase stability of Ti doping Ni–Mn–Ga shape memory alloys from first-principles calculations

International Nuclear Information System (INIS)

Gao, Zhiyong; Chen, Baishu; Meng, Xianglong; Cai, Wei

2013-01-01

Highlights: •Site preference and phase stability of NiMnGaTi are studied by first-principles. •The Ti atoms prefer to occupy the Ga sites in the Ni 2 MnGa austenitic phase. •The phase stability becomes worse when Ga is replaced by Ti. •The phase stability is discussed based on the densities of states. -- Abstract: The effects of Ti content on martensitic transformation and phase stability of Ni 50 Mn 25 Ga 25−x Ti x shape memory alloys were investigated from first-principles calculations based on density functional theory. The formation energy results indicate that the added Ti preferentially occupies the Ga sites in Ni 2 MnGa alloy due to the lowest formation energy. The total energy difference between austenite and martensite increases with Ti alloying, being relevant to the experimentally reported changes in martensitic transformation temperature. The phase stability of Ni 50 Mn 25 Ga 25−x Ti x austenite decreases with increasing Ti content, which results from the reduced Ni 3d–Mn 3d hybridization when Ga is replaced by Ti

Effect of phosphorus on the swelling and precipitation behavior of austenitic stainless steels during irradiation

International Nuclear Information System (INIS)

Lee, E.H.; Mansur, L.K.; Rowcliffe, A.F.

1983-01-01

It has been observed that increasing the volume fraction of the needle-shaped iron phosphide phase in austenitic stainless steels tends to inhibit void swelling during neutron irradiation. An earlier analysis showed that this effect could not be accounted for in terms of enhanced point defect recombination at particle-matrix interfaces. The behavior of the iron phosphide phase has been further examined using dual ion beam irradiations. It was found that the particle-matrix interface serves as a site for the nucleation of a very fine dispersion of helium bubbles. It is thought that since a high number density of cavities lowers the number of helium atoms per cavity, the irradiation time for the cavities to accumulate the critical number of gas atoms for bias-driven growth is correspondingly increased. Although the phosphide phase nucleates rapidly, it eventually undergoes dissolution if either the G or Laves phase develops with increasing dose

Microstructural Characterization of Low Temperature Gas Nitrided Martensitic Stainless Steel

DEFF Research Database (Denmark)

Fernandes, Frederico Augusto Pires; Christiansen, Thomas Lundin; Somers, Marcel A. J.

2015-01-01

The present work presents microstructural investigations of the surface zone of low temperature gas nitrided precipitation hardening martensitic stainless steel AISI 630. Grazing incidence X-ray diffraction was applied to investigate the present phases after successive removal of very thin sections...... of the sample surface. The development of epsilon nitride, expanded austenite and expanded martensite resulted from the low temperature nitriding treatments. The microstructural features, hardness and phase composition are discussed with emphasis on the influence of nitriding duration and nitriding potential....

Some data of second sequence non standard austenitic ingot, A2

International Nuclear Information System (INIS)

Nurdin Effendi; Aziz K Jahja; Bandriana; Wisnu Ari Adi

2012-01-01

Synthesis of second sequence austenite stainless steel named A2 using extracted minerals from Indonesian mines has been carried out. The starting materials for austenite alloy consist of granular ferro scrap, nickel, ferro-chrome, ferro-manganese, and ferro-silicon. The second sequence composition differs from the former first sequence. This A2 sequence contained more nickel, meanwhile titanium element had not been added explicitly to it, and just been found from raw materials contents or impurities, as well as carbon content in the alloy. However before the actual alloying work started, the first important step was to carry out the determination of the fractional amount of each starting material necessary to form an austenite stainless steel alloy as specified. Once the component fraction of each base alloy-element was determined, the raw materials are weighed on the mini-balance. After the fractional quantities of each constituent have been computed, an appropriate amount of these base materials are weighed separately on the micro scale. The raw materials were then placed in the induction foundry furnace, which was operated by an electromagnetic inductive-thermal system. The foundry furnace system performs the stirring of the molten materials automatically. The homogenized molten metals were poured down into sand casting prepared in advance. Some of the austenite stainless steel were normalized at 600°C for 6 hours. The average density is 7.8 g cm -1 and the average hardness value of 'normalized' austenite stainless-steels is in the range of 460 on the Vickers scale. The microstructure observation concludes that an extensive portion of the sample's structure is dendritic and the surface turns out to be homogenous. X-ray diffraction analysis shows that the material belongs to the fcc crystallographic system, which fits in with the austenite class of the alloy. The experimental fractional elemental composition data acquired by OES method turn out to

Residual stress studies of austenitic and ferritic steels

International Nuclear Information System (INIS)

Chrenko, R.M.

1978-01-01

Residual studies have been made on austenitic and ferritic steels of the types used as structural materials. The residual stress results presented here will include residual stress measurements in the heat-affected zone on butt welded Type 304 stainless steel pipes, and the stresses induced in Type 304 austenitic stainless steel and Type A508 ferritic steel by several surface preparations. Such surface preparation procedures as machining and grinding can induce large directionality effects in the residual stresses determined by X-ray techniques and some typical data will be presented. A brief description is given of the mobile X-ray residual stress apparatus used to obtain most of the data in these studies. (author)

The Effect of Ultrafast Heating on Cold-Rolled Low Carbon Steel: Formation and Decomposition of Austenite

Directory of Open Access Journals (Sweden)

Felipe Manuel Castro Cerda

2016-12-01

Full Text Available The effect of heating rate on the formation and decomposition of austenite was investigated on cold-rolled low carbon steel. Experiments were performed at two heating rates, 150 °C/s and 1500 °C/s, respectively. The microstructures were characterized by means of scanning electron microscopy (SEM and electron backscattered diffraction (EBSD. Experimental evidence of nucleation of austenite in α/θ, as well as in α/α boundaries is analyzed from the thermodynamic point of view. The increase in the heating rates from 150 °C/s to 1500 °C/s has an impact on the morphology of austenite in the intercritical range. The effect of heating rate on the austenite formation mechanism is analyzed combining thermodynamic calculations and experimental data. The results provide indirect evidence of a transition in the mechanism of austenite formation, from carbon diffusion control to interface control mode. The resulting microstructure after the application of ultrafast heating rates is complex and consists of a mixture of ferrite with different morphologies, undissolved cementite, martensite, and retained austenite.

A Review on the Potential Use of Austenitic Stainless Steels in Nuclear Fusion Reactors

Science.gov (United States)

Şahin, Sümer; Übeyli, Mustafa

2008-12-01

Various engineering materials; austenitic stainless steels, ferritic/martensitic steels, vanadium alloys, refractory metals and composites have been suggested as candidate structural materials for nuclear fusion reactors. Among these structural materials, austenitic steels have an advantage of extensive technological database and lower cost compared to other non-ferrous candidates. Furthermore, they have also advantages of very good mechanical properties and fission operation experience. Moreover, modified austenitic stainless (Ni and Mo free) have relatively low residual radioactivity. Nevertheless, they can't withstand high neutron wall load which is required to get high power density in fusion reactors. On the other hand, a protective flowing liquid wall between plasma and solid first wall in these reactors can eliminate this restriction. This study presents an overview of austenitic stainless steels considered to be used in fusion reactors.

Effect of Cr Contents and Heat Treating on Reverted Austenite in Maraging Steel Weldments

Science.gov (United States)

Kim, S. W.; Lee, H. W.

2018-05-01

By conducting flux cored arc welding (FCAW) on maraging steels with Cr contents of 1.4 and 5.2 wt%, this study observed the effects of Cr content and heat treating on reverted austenite formation in welded maraging steel. Aging treatment was carried out at the temperatures of 450, 480 and 530 °C for 3 h in each condition. As the aging temperature increased, reverted austenite was formed along the interdendritic and intercellular grain boundaries, and the proportion of reverted austenite increased with increasing Cr addition. The aging process led to the segregation of Ti and Mo along the interdendritic and intercellular grain boundaries. Some of the welded specimens were subjected to solution heat treatment at 820 and 1250 °C for 1 h after welding, resulting in a decrease in reverted austenite fraction.

Application of Ab Initio Electronic Structure Calculations in Construction of Phase Diagrams of Metallic Systems with Complex Phases

Czech Academy of Sciences Publication Activity Database

Šob, Mojmír; Kroupa, Aleš; Pavlů, Jana; Vřešťál, Jan

2009-01-01

Roč. 150, č. 1 (2009), s. 1-28 ISSN 1012-0394 R&D Projects: GA MŠk OC 147; GA ČR GA106/07/1078 Institutional research plan: CEZ:AV0Z20410507 Keywords : Ab initio calculations * CALPHAD method * Laves phases * sigma phase * ternary systems * super-austenitic steels Subject RIV: BM - Solid Matter Physics ; Magnetism

Influence of Short Austenitization Treatments on the Mechanical Properties of Low-Alloy Steels for Hot Forming Applications

Science.gov (United States)

Holzweissig, Martin Joachim; Lackmann, Jan; Konrad, Stefan; Schaper, Mirko; Niendorf, Thomas

2015-07-01

The current work elucidates an improvement of the mechanical properties of tool-quenched low-alloy steel by employing extremely short austenitization durations utilizing a press heating arrangement. Specifically, the influence of different austenitization treatments—involving austenitization durations ranging from three to 15 seconds—on the mechanical properties of low-alloy steel in comparison to an industrial standard furnace process was examined. A thorough set of experiments was conducted to investigate the role of different austenitization durations and temperatures on the resulting mechanical properties such as hardness, bending angle, tensile strength, and strain at fracture. The most important finding is that the hardness, the bending angle as well as the tensile strength increase with shortened austenitization durations. Furthermore, the ductility of the steels exhibits almost no difference following the short austenitization durations and the standard furnace process. The enhancement of the mechanical properties imposed by the short heat treatments investigated, is related to a refinement of microstructural features as compared to the standard furnace process.

Changes in austenitic steel surface induced by thermal and implantation treatments studied by Mössbauer spectroscopy

Czech Academy of Sciences Publication Activity Database

Jirásková, Yvonna; Schneeweiss, Oldřich; Blawert, C.

2006-01-01

Roč. 38, č. 4 (2006), s. 348-351 ISSN 0142-2421. [ECASIA´05. European Conference on Applications of Surface and Interface Analysis /11./. Vienna, 25.09.2005-30.09.2005] R&D Projects: GA MŠk ME 645; GA AV ČR IBS2041105 Institutional research plan: CEZ:AV0Z20410507 Keywords : Mössbauer spectroscopy ion implantation * diffusion and migration ion implantation, * austenitic steel surface phase composition Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.427, year: 2006

Depth distribution analysis of Martensitic transformations in Xe implanted austenitic stainless steel

DEFF Research Database (Denmark)

Johnson, E.; Gerritsen, E.; Chechenin, N.G.

1989-01-01

In recent years the implantation of noble gases in metals has been found to induce some exciting phenomena such as formation of inclusions containing solid gas at extremely high pressures. In stainless steels these inclusions are the origin of a stress-induced martensitic fcc → bcc phase...... transformation in the implanted layer. In this work we present results from a depth distribution analysis of the martensitic phase change occurring in Xe implanted single crystals of austenitic stainless steel. Analysis was done by in situ RBS/channeling analysis, X-ray diffraction and cross-section transmission...... electron microscopy (XTEM) of the implanted surface. It is found that the martensitic transformation of the surface layer occurs for fluences above 1 × 1020 m−2. The thickness of the transformed layer increases with fluence to ≈ 150 nm at 1 × 10 21 m−2, which far exceeds the range plus straggling...

Constitutive modeling of metastable austenitic stainless steel

NARCIS (Netherlands)

Perdahcioglu, Emin Semih; Geijselaers, Hubertus J.M.; Huetink, Han; Khan, A.

2010-01-01

A physically based, macroscale constitutive model has been developed that can describe the complex mechanical behavior of metastable austenitic stainless steels. In the developed model a generalized model for the mechanically induced martensitic transformation is introduced. Mechanical tests have

Ferrite channel effect on ductility and strain hardenability of ultra high strength dual phase steel

Energy Technology Data Exchange (ETDEWEB)

Ravi, Kumar B., E-mail: ravik@nmlindia.org [CSIR-National Metallurgical Laboratory, Jamshedpur 831007 (India); Patel, Nand Kumar [O.P Jindal University, Raigarh 496001 (India); Mukherjee, Krishnendu; Walunj, Mahesh; Mandal, Gopi Kishor [CSIR-National Metallurgical Laboratory, Jamshedpur 831007 (India); Venugopalan, T. [Tata Steel Limited, Jamshedpur 831001 (India)

2017-02-08

This study describes an effect of controlled austenite decomposition on microstructure evolution in dual phase steel. Steel sheets austenitized at various annealing temperatures were rapidly cooled to the inter-critical annealing temperature of 800 °C for the isothermal decomposition of austenite and then ultra fast cooled to room temperature. The scanning electron microscope analysis of evolving microstructure revealed ferrite nucleation and growth along prior austenite grain boundaries leading to ferrite network/channel formation around martensite. The extent of ferrite channel formation showed a strong dependence on the degree of undercooling in the inter-critical annealing temperature regime. Uniaxial tensile deformation of processed steel sheets showed extensive local inter-lath martensite damage activity. Extension/propagation of these local micro cracks to neighboring martensite grains was found to be arrested by ferrite channels. This assisted in delaying the onset of global damage which could lead to necking and fracture. The results demonstrated an alternate possible way of inducing ductility and strain hardenability in ultra high strength dual phase steels.

Analysis of recrystallization behavior of hot-deformed austenite reconstructed from electron backscattering diffraction orientation maps of lath martensite

International Nuclear Information System (INIS)

Kubota, Manabu; Ushioda, Kohsaku; Miyamoto, Goro; Furuhara, Tadashi

2016-01-01

The recrystallization behavior of hot-deformed austenite of a 0.55% C steel at 800 °C was investigated by a method of reconstructing the parent austenite orientation map from an electron backscattering diffraction orientation map of lath martensite. Recrystallized austenite grains were clearly distinguished from un-recrystallized austenite grains. Very good correlation was confirmed between the static recrystallization behavior investigated mechanically by double-hit compression tests and the change in austenite microstructure evaluated by the reconstruction method. The recrystallization behavior of hot-deformed 0.55% C steel at 800 °C is directly revealed and it was observed that by addition of 0.1% V the recrystallization was significantly retarded.

Phase Transformation Study in Nb-Mo Microalloyed Steels Using Dilatometry and EBSD Quantification

Science.gov (United States)

Isasti, Nerea; Jorge-Badiola, Denis; Taheri, Mitra L.; Uranga, Pello

2013-08-01

A complete microstructural characterization and phase transformation analysis has been performed for several Nb and Nb-Mo microalloyed low-carbon steels using electron backscattered diffraction (EBSD) and dilatometry tests. Compression thermomechanical schedules were designed resulting in the undeformed and deformed austenite structures before final transformation. The effects of microalloying additions and accumulated deformation were analyzed after CCT diagram development and microstructural quantification. The resulting microstructures ranged from polygonal ferrite and pearlite at slow cooling ranges, to a combination of quasipolygonal ferrite and granular ferrite for intermediate cooling rates, and finally, to bainitic ferrite with martensite for fast cooling rates. The addition of Mo promotes a shift in the CCT diagrams to lower transformation start temperatures. When the amount of Nb is increased, CCT diagrams show little variations for transformations from the undeformed austenite and higher initial transformation temperatures in the transformations from the deformed austenite. This different behavior is due to the effect of niobium on strain accumulation in austenite and its subsequent acceleration of transformation kinetics. This article shows the complex interactions between chemical composition, deformation, and the phases formed, as well as their effect on microstructural unit sizes and homogeneity.

Proceedings of the specialists' meeting on reliability of the ultrasonic inspection of austenitic materials

Energy Technology Data Exchange (ETDEWEB)

NONE

1980-07-01

The contributions of this meeting addressed several topics: the fundamentals of ultrasonic examination of austenitic materials (effect of anisotropy on propagation, improvement of ultrasonic testing to thick bimetallic welds, aspects of the ultrasonic testing of austenitic steel structures, utilization of a Fisher linear discriminant function in intergranular stress corrosion cracking or IGSCC detection, case of coarse grain austenitic welds, efforts of the Argonne National Laboratory), instruments and methods (longitudinal wave ultrasonic inspection, Grass echo suppression technique during the ultrasonic inspection of fuel cladding tubes, inspections of fillet and butt welds, improvement by signal averaging techniques, multiple bearing angle crack detector for cladded pipes examinations, flow-to-grain echo enhancement by split-spectrum processing, ultrasonic imaging techniques, ultrasonic inspection of pipe weldments for IGSCC), industrial practice (ultrasonic testing techniques for fabrication and in-service inspection, experiences in ultrasonic examination of austenitic steel components, experience and practice on nuclear piping in Spain, detection of underclad defects, sizing of cracks perpendicular to stainless overlay), and reliability (survey of ultrasonic testing in austenitic weld material, examination of electron beam welds, factors affecting the reliability of ultrasonic examination, detectability of IGSCC, ultrasonic inspection reliability for primary piping systems)

Proceedings of the specialists' meeting on reliability of the ultrasonic inspection of austenitic materials

International Nuclear Information System (INIS)

1980-01-01

The contributions of this meeting addressed several topics: the fundamentals of ultrasonic examination of austenitic materials (effect of anisotropy on propagation, improvement of ultrasonic testing to thick bimetallic welds, aspects of the ultrasonic testing of austenitic steel structures, utilization of a Fisher linear discriminant function in intergranular stress corrosion cracking or IGSCC detection, case of coarse grain austenitic welds, efforts of the Argonne National Laboratory), instruments and methods (longitudinal wave ultrasonic inspection, Grass echo suppression technique during the ultrasonic inspection of fuel cladding tubes, inspections of fillet and butt welds, improvement by signal averaging techniques, multiple bearing angle crack detector for cladded pipes examinations, flow-to-grain echo enhancement by split-spectrum processing, ultrasonic imaging techniques, ultrasonic inspection of pipe weldments for IGSCC), industrial practice (ultrasonic testing techniques for fabrication and in-service inspection, experiences in ultrasonic examination of austenitic steel components, experience and practice on nuclear piping in Spain, detection of underclad defects, sizing of cracks perpendicular to stainless overlay), and reliability (survey of ultrasonic testing in austenitic weld material, examination of electron beam welds, factors affecting the reliability of ultrasonic examination, detectability of IGSCC, ultrasonic inspection reliability for primary piping systems)

Creep and precipitation behaviors of AL6XN austenitic steel at elevated temperatures

Science.gov (United States)

Meng, L. J.; Sun, J.; Xing, H.

2012-08-01

Creep behaviors of the solution-treated AL6XN austenitic stainless steel have been investigated at 873-1023 K and 120-260 MPa. The results showed that the creep stress exponent and activation energy of the AL6XN steel are 5 and 395.4 kJ/mol, respectively in the power-law breakdown regime. TEM observations revealed that dislocations distributed homogenously in grains. The creep deformation mechanism is mainly attributed to viscous dislocation glide. Precipitates in the steel after creep deformation were additionally analyzed by TEM, and the results showed that there are four different types of precipitates, such as M23C6, M6C, σ phase and Laves phase. The M23C6 carbides were observed at grain boundaries in the steel after creep at 873 K. The M6C, σ phase and Laves phase precipitates were found when the creep temperature increases to 923-1023 K. Although the AL6XN steel exhibited low steady state creep rates, a high volume fraction of brittle precipitates of σ and Laves phases reduced the creep lifetime of the steel at elevated temperatures.

Creep and precipitation behaviors of AL6XN austenitic steel at elevated temperatures

Energy Technology Data Exchange (ETDEWEB)

Meng, L.J. [School of Materials Science and Engineering, Shanghai Jiaotong University, Dongchuan Road 800, Shanghai 200240 (China); Sun, J., E-mail: jsun@sjtu.edu.cn [School of Materials Science and Engineering, Shanghai Jiaotong University, Dongchuan Road 800, Shanghai 200240 (China); Xing, H. [School of Materials Science and Engineering, Shanghai Jiaotong University, Dongchuan Road 800, Shanghai 200240 (China)

2012-08-15

Creep behaviors of the solution-treated AL6XN austenitic stainless steel have been investigated at 873-1023 K and 120-260 MPa. The results showed that the creep stress exponent and activation energy of the AL6XN steel are 5 and 395.4 kJ/mol, respectively in the power-law breakdown regime. TEM observations revealed that dislocations distributed homogenously in grains. The creep deformation mechanism is mainly attributed to viscous dislocation glide. Precipitates in the steel after creep deformation were additionally analyzed by TEM, and the results showed that there are four different types of precipitates, such as M{sub 23}C{sub 6}, M{sub 6}C, {sigma} phase and Laves phase. The M{sub 23}C{sub 6} carbides were observed at grain boundaries in the steel after creep at 873 K. The M{sub 6}C, {sigma} phase and Laves phase precipitates were found when the creep temperature increases to 923-1023 K. Although the AL6XN steel exhibited low steady state creep rates, a high volume fraction of brittle precipitates of {sigma} and Laves phases reduced the creep lifetime of the steel at elevated temperatures.

Microstructure and mechanical properties of resistance upset butt welded 304 austenitic stainless steel joints

International Nuclear Information System (INIS)

Sharifitabar, M.; Halvaee, A.; Khorshahian, S.

2011-01-01

Graphical abstract: Three different microstructural zones formed at different distances from the joint interface in resistance upset butt welding of 304 austenitic stainless steel. Highlights: → Evaluation of microstructure in resistance upset welding of 304 stainless steel. → Evaluation of welding parameters effects on mechanical properties of the joint. → Introducing the optimum welding condition for joining stainless steel bars. -- Abstract: Resistance upset welding (UW) is a widely used process for joining metal parts. In this process, current, time and upset pressure are three parameters that affect the quality of welded products. In the present research, resistance upset butt welding of 304 austenitic stainless steel and effect of welding power and upset pressure on microstructure, tensile strength and fatigue life of the joint were investigated. Microstructure of welds were studied using scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis was used to distinguish the phase(s) that formed at the joint interface and in heat affected zone (HAZ). Energy dispersive spectroscopy (EDS) linked to the SEM was used to determine chemical composition of phases formed at the joint interface. Fatigue tests were performed using a pull-push fatigue test machine and the fatigue properties were analyzed drawing stress-number of cycles to failure (S-N) curves. Also tensile strength tests were performed. Finally tensile and fatigue fracture surfaces were studied by SEM. Results showed that there were three different microstructural zones at different distances from the joint interface and delta ferrite phase has formed in these regions. There was no precipitation of chromium carbide at the joint interface and in the HAZ. Tensile and fatigue strengths of the joint decreased with welding power. Increasing of upset pressure has also considerable influence on tensile strength of the joint. Fractography of fractured samples showed that formation of hot spots at

Influence of austenite grain size on recrystallisation-precipitation interaction in a V-microalloyed steel

International Nuclear Information System (INIS)

Quispe, A.; Medina, S.F.; Gomez, M.; Chaves, J.I.

2007-01-01

By means of torsion tests using small specimens, the influence of austenite grain size on strain induced precipitation kinetics has been determined in a vanadium microalloyed steel. Determination of recrystallisation-precipitation-time-temperature (RPTT) diagrams for two austenite grain sizes allows values of the aforementioned magnitudes to be determined. An ample discussion is made of the quantitative influence found and its relation with nucleation and growth mechanisms of precipitates. The results are compared with the quantitative influence exerted by the other variables, reaching the conclusion that the austenite grain size has a notable influence on strain induced precipitation kinetics which should not be underestimated. Finally, the influence of austenite grain size is included in a strain induced precipitation model constructed by the authors of this work and which also takes into account the other aforementioned variables

The Influence of Austenite Grain Size on the Mechanical Properties of Low-Alloy Steel with Boron

Directory of Open Access Journals (Sweden)

Beata Białobrzeska

2017-01-01

Full Text Available This study forms part of the current research on modern steel groups with higher resistance to abrasive wear. In order to reduce the intensity of wear processes, and also to minimize their impact, the immediate priority seems to be a search for a correlation between the chemical composition and structure of these materials and their properties. In this paper, the correlation between prior austenite grain size, martensite packets and the mechanical properties were researched. The growth of austenite grains is an important factor in the analysis of the microstructure, as the grain size has an effect on the kinetics of phase transformation. The microstructure, however, is closely related to the mechanical properties of the material such as yield strength, tensile strength, elongation and impact strength, as well as morphology of occurred fracture. During the study, the mechanical properties were tested and a tendency to brittle fracture was analysed. The studies show big differences of the analysed parameters depending on the applied heat treatment, which should provide guidance to users to specific applications of this type of steel.

On the evaluation of temperature dependence of elastic constants of martensitic phases in shape memory alloys from resonant ultrasound spectroscopy studies

International Nuclear Information System (INIS)

Landa, Michal; Sedlak, Petr; Sittner, Petr; Seiner, Hanus; Heller, Ludek

2008-01-01

Elastic constants of austenite and martensite phases in shape memory alloys reflect fundamental thermodynamic properties of these materials-i.e. important physical information can be deduced not just from the values of the constants but, mainly from their temperature and stress dependencies. As regards to the parent austenite phase, such information is available in the literature for most of the known shape memory alloys. For the martensitic phases, however, only few reliable experimental data exist, due to the experimental difficulties with the preparation of martensite single crystals as well as due to the difficulties with the ultrasonic measurement of elastic properties of strongly anisotropic media with low symmetry. In this work, the temperature dependence of all elastic constants of cubic austenite and orthorhombic 2H martensite phases in Cu-Al-Ni alloy determined by resonance ultrasound spectroscopy (RUS) is reported. Experimental and theoretical improvements of the RUS method which had to be made to perform the successful measurements on strongly anisotropic and martensitic phases are discussed

Niobium effects on the austenitic grain growth and hardenability of steels for mechanical construction

International Nuclear Information System (INIS)

Vieira, R.R.; Arruda Camargo, L.M. de; Oliveira Junior, G.G. de; Dias Filho, A.G.C.

1983-01-01

The austenitic grain growth and hardenability of SAE 86XX and 5120 steels modified with 0,001 to 0,20 per-cent niobium content were studied when submitted to case hardening and quenching heat treatments. The results show that niobium controlS the austenite grain size better than molybdenum up to 950 0 C austenitization temperature. The hardenability, evaluated by the Jominy test which the modified SAE 8640 steels, is more strongly inflencied by the grain refining resulting from niobium addition than by any other supposed effect. (Author) [pt

Effects of Thermocapillary Forces during Welding of 316L-Type Wrought, Cast and Powder Metallurgy Austenitic Stainless Steels

CERN Document Server

Sgobba, Stefano

2003-01-01

The Large Hadron Collider (LHC) is now under construction at the European Organization for Nuclear Research (CERN). This 27 km long accelerator requires 1248 superconducting dipole magnets operating at 1.9 K. The cold mass of the dipole magnets is closed by a shrinking cylinder with two longitudinal welds and two end covers at both extremities of the cylinder. The end covers, for which fabrication by welding, casting or Powder Metallurgy (PM) was considered, are dished-heads equipped with a number of protruding nozzles for the passage of the different cryogenic lines. Structural materials and welds must retain high strength and toughness at cryogenic temperature. AISI 316L-type austenitic stainless steel grades have been selected because of their mechanical properties, ductility, weldability and stability of the austenitic phase against low-temperature spontaneous martensitic transformation. 316LN is chosen for the fabrication of the end covers, while the interconnection components to be welded on the protrud...

Austenite Grain Growth Behavior of AISI 4140 Alloy Steel

Directory of Open Access Journals (Sweden)

Lin Wang

2013-01-01

Full Text Available AISI 4140 alloy steel is widely applied in the manufacture of various parts such as gears, rams, and spindles due to its good performance of strength, toughness, and wear resistance. The former researches most focused on its deformation and recrystallization behaviors under high temperature. However, the evolution laws of austenite grain growth were rarely studied. This behavior also plays an important role in the mechanical properties of parts made of this steel. In this study, samples are heated to a certain temperature of 1073 K, 1173 K, 1273 K, and 1373 K at a heating rate of 5 K per second and hold for different times of 0 s, 120 s, 240 s, 360 s, and 480 s before being quenched with water. The experimental results suggest that the austenite grains enlarge with increasing temperature and holding time. A mathematical model and an application developed in Matlab environment are established on the basis of previous works and experimental results to predict austenite grains size in hot deformation processes. The predicted results are in good agreement with experimental results which indicates that the model and the application are reliable.

Precipitation sequences in austenitic Fe-22Cr-21Ni-6Mo-(N) stainless steels

International Nuclear Information System (INIS)

Kim, S.-J.; Lee, T.-H.

1999-01-01

Precipitation sequence of nitrogen containing Fe-22Cr-21Ni-6Mo-N austenitic stainless steel has been investigated after aging at high temperatures, and compared with nitrogen free steel. The σ phases and M 23 C 6 carbides were observed along the grain boundaries as well as in the matrix in both of the solution treated specimens. The M 6 C carbides and chi phase appeared successively in between 3 hours and 24 hours depending on the nitrogen content. Main difference in aging behavior was the precipitation of fine nitrides. Aging for 24 hours and 168 hours of nitrogen containing steel resulted in the formation of fine Cr 2 N and faceted AlN nitrides. The crystallography, structure and morphology were analyzed with analytical electron microscopy. (orig.)

The Cracking Mechanism of Ferritic-Austenitic Cast Steel

Directory of Open Access Journals (Sweden)

Stradomski G.

2016-12-01

Full Text Available In the high-alloy, ferritic - austenitic (duplex stainless steels high tendency to cracking, mainly hot-is induced by micro segregation processes and change of crystallization mechanism in its final stage. The article is a continuation of the problems presented in earlier papers [1 - 4]. In the range of high temperature cracking appear one mechanism a decohesion - intergranular however, depending on the chemical composition of the steel, various structural factors decide of the occurrence of hot cracking. The low-carbon and low-alloy cast steel casting hot cracking cause are type II sulphide, in high carbon tool cast steel secondary cementite mesh and / or ledeburite segregated at the grain solidified grains boundaries, in the case of Hadfield steel phosphorus - carbide eutectic, which carrier is iron-manganese and low solubility of phosphorus in high manganese matrix. In duplex cast steel the additional factor increasing the risk of cracking it is very “rich” chemical composition and related with it processes of precipitation of many secondary phases.

Analysis of the non-isothermal austenite-martensite transformation in 13% Cr-type martensitic stainless steels

International Nuclear Information System (INIS)

Garcia-De-Andris, C.; Alvarez, L.F.

1996-01-01

In martensitic stainless steels, as in other alloyed containing carbide-forming elements, the carbide dissolution and precipitation processes that take place during heat treatment can cause modifications to the chemical composition of the austenite phase of these steels. The chemical composition of this phase is a fundamental factor for the evolution of the martensitic transformation. As a result of their influence on the dissolution and precipitation processes, the parameters of the quenching heat treatment exert a strong influence on the behavior of the martensitic transformation in these steels. In the present study, the effect of the heating temperature and the cooling rate on the martensitic transformation in two 13% Cr-type martensitic stainless steels with different carbon contents were properly evaluated. (author)

Thermodynamic stability of austenitic Ni-Mn-Cu cast iron

Directory of Open Access Journals (Sweden)

A. Janus

2014-07-01

Full Text Available The performed research was aimed at determining thermodynamic stability of structures of Ni-Mn-Cu cast iron castings. Examined were 35 alloys. The castings were tempered at 900 °C for 2 hours. Two cooling speeds were used: furnace-cooling and water-cooling. In the alloys with the nickel equivalent value less than 20,0 %, partial transition of austenite to martensite took place. The austenite decomposition ratio and the related growth of hardness was higher for smaller nickel equivalent value and was clearly larger in annealed castings than in hardened ones. Obtaining thermodynamically stable structure of castings requires larger than 20,0 % value of the nickel equivalent.

A review on nickel-free nitrogen containing austenitic stainless steels for biomedical applications.

Science.gov (United States)

Talha, Mohd; Behera, C K; Sinha, O P

2013-10-01

The field of biomaterials has become a vital area, as these materials can enhance the quality and longevity of human life. Metallic materials are often used as biomaterials to replace structural components of the human body. Stainless steels, cobalt-chromium alloys, commercially pure titanium and its alloys are typical metallic biomaterials that are being used for implant devices. Stainless steels have been widely used as biomaterials because of their very low cost as compared to other metallic materials, good mechanical and corrosion resistant properties and adequate biocompatibility. However, the adverse effects of nickel ions being released into the human body have promoted the development of "nickel-free nitrogen containing austenitic stainless steels" for medical applications. Nitrogen not only replaces nickel for austenitic structure stability but also much improves steel properties. Here we review the harmful effects associated with nickel and emphatically the advantages of nitrogen in stainless steel, as well as the development of nickel-free nitrogen containing stainless steels for medical applications. By combining the benefits of stable austenitic structure, high strength, better corrosion and wear resistance and superior biocompatibility in comparison to the currently used austenitic stainless steel (e.g. 316L), the newly developed nickel-free high nitrogen austenitic stainless steel is a reliable substitute for the conventionally used medical stainless steels. Copyright © 2013 Elsevier B.V. All rights reserved.

Study of structural modifications induced by ion implantation in austenitic stainless steel; Etude des modifications structurales induites par implantation ionique dans les aciers austenitiques

Energy Technology Data Exchange (ETDEWEB)

Dudognon, J

2006-12-15

Ion implantation in steels, although largely used to improve the properties of use, involves structural modifications of the surface layer, which remain still prone to controversies. Within this context, various elements (N, Ar, Cr, Mo, Ag, Xe and Pb) were implanted (with energies varying from 28 to 280 keV) in a 316LVM austenitic stainless steel. The implanted layer has a thickness limited to 80 nm and a maximum implanted element concentration lower than 10 % at. The analysis of the implanted layer by grazing incidence X ray diffraction highlights deformations of austenite lines, appearance of ferrite and amorphization of the layer. Ferritic phase which appears at the grain boundaries, whatever the implanted element, is formed above a given 'threshold' of energy (produced of fluency by the energy of an ion). The formation of ferrite as well as the amorphization of the implanted layer depends only on energy. In order to understand the deformations of austenite diffraction lines, a simulation model of these lines was elaborated. The model correctly describes the observed deformations (broadening, shift, splitting) with the assumption that the expansion of the austenitic lattice is due to the presence of implanted element and is proportional to the element concentration through a coefficient k'. This coefficient only depends on the element and varies linearly with its radius. (author)

Plasticity induced by phase transformation in steel: experiment vs modeling

International Nuclear Information System (INIS)

Tahimi, Abdeladhim

2011-01-01

The objectives of this work are: (i) understand the mechanisms and phenomena involved in the plasticity of steels in the presence of a diffusive or martensitic phase transformation. (ii) develop tools for predicting TRIP, which are able to correctly reproduce the macroscopic deformation for cases of complex loading and could also provide information about local elasto-visco-plastic interactions between product and parent phases. To this purpose, new experimental tests are conducted on 35NCD16 steel for austenite to martensite transformation and on 100C6 steel for austenite to pearlite transformation. The elasto viscoplastic properties of austenite and pearlite of the 100C6 steel are characterized through tension compression and relaxation tests. The parameters of macro-homogeneous and crystal-based constitutive laws could then be identified such as to analyse different models with respect to the experimental TRIP: the analytical models of Leblond (1989) and Taleb and Sidoroff (2003) but also, above all, different numerical models which can be distinguished by the prevailing assumptions concerning the local kinetics and the constitutive laws. An extension of the single-grain model dedicated to martensitic transformations developed during the thesis of S. Meftah (2007) is proposed. It consists in introducing the polycrystalline character of the austenite through a process of homogenization based on a self-consistent scheme by calculating the properties of an Equivalent Homogeneous Medium environment (EHM). (author)

The effect of prior tempering on cryogenic treatment to reduce retained austenite

International Nuclear Information System (INIS)

Stratton, Paul

2010-01-01

The consensus view is that a high carbon case gives gears the best overall properties provided that there is no carbide network and that the retained austenite has been reduced below 20% by cryogenic treatment. This view is effectively enshrined in the SAE AMS 2759/7 standard. The cryogenic treatment usually takes place immediately after the quench to avoid austenite stabilisation. However, for some parts with complex geometries that might crack during the treatment, a short low temperature temper is carried out first. Little is known on how this temper affects the subsequent cryogenic treatment. Three carburizing steels used extensively in the aerospace industry were carburized to produce high retained austenite levels in the case using two different, but typical carburizing cycles. The retained austenite was determined by XRD before and after cryogenic treatment carried out in accordance with the standard and compared with that obtained when an intermediate temper was used. This study shows that for three typical carburizing steels, carburized using typical cycles, the efficacy of the cryogenic treatment is reduced only slightly after the temper, and not enough to be industrially significant. (author)

A review of hot cracking in austenitic stainless steel weldments

International Nuclear Information System (INIS)

Shankar, V.; Gill, T.P.S.; Mannan, S.L.; Rodriguez, P.

1991-01-01

The occurrence of hot cracking in austenitic stainless steel weldments is discussed with respect to its origin and metallurgical contributory factors. Of the three types of hot cracking, namely solidification cracking, liquation and ductility dip cracking, solidification cracking occurs in the interdendritic regions in weld metal while liquation and ductility dip cracking occur intergranularly in the heat-affected zone (HAZ). Segregation of impurity and minor elements such as sulphur, phosphorous, silicon, niobium, boron etc to form low melting eutectic phases has been found to be the major cause of hot cracking. Control of HAZ cracking requires minimisation of impurity elements in the base metal. In stabilized stainless steels containing niobium, higher amounts of delta-ferrite have been found necessary to prevent cracking than in unstabilized compositions. Titanium compounds have been found to cause liquation cracking in maraging steels and titanium containing stainless steels and superalloys. In nitrogen added stainless steels, cracking resistance decreases when the solidification mode changes to primary austenitic due to nitrogen addition. A review of the test methods to evaluate hot cracking behaviour showed that several external restraint and semi-self-restraint tests are available. The finger Test, WRC Fissure Bend Test, the PVR test and the Varestraint Test are described along with typical test results. Hot ductility testing to reveal HAZ cracking tendency during welding is described, which is of particular importance to stabilized stainless steels. Based on the literature, recommendations are made for welding stabilized and nitrogen added steels, indicating areas of further work. (author). 81 refs., 30 figs., 1 tab

Resistance to pitting corrosion in ferritic and austenitic/ferritic steels

International Nuclear Information System (INIS)

De Bouvier, O.

1995-01-01

Stainless steel tubes carrying raw water are potentially vulnerable to pitting corrosion. With a view to minimizing the corrosion risk in the river-water-cooled condensers at PWR power plant, a study was conducted to determine initiation conditions and incubation durations for pitting corrosion in stagnant water. As a result, condenser tubes in Z2 CI 18 (439) or Z2 CT 18-10 (304L) steels were phased out in favour of Z2 CND 16-32 (316L) stainless steel. The same question can be yield for other applications and especially for all types of exchangers for use in electrical applications. This study sought to assess alternative methods for estimating pitting corrosion, and to check the results of these methods against the actual behaviour of studied steels. The study covered ferritic steels (439, 444, 290Mo), austenitic steel (316L) and austenitic/ferritic steels (Uranus 35N, 45N, 47N, 52N). Two approaches were adopted: laboratory tests to compare pitting corrosion risks on different materials, and tests for characterizing the behaviour of steels exposed to river water. The study begins with a laboratory tests that yield an arbitrary parameter for quantifying pitting corrosion resistance. One method involves measuring the pitting temperature in an aggressive ferric chloride solution. Other methods measure the pitting potential, either statistically (Multipit method) or deterministically (polarization curve). We then go on to discuss tests under simulated life-like conditions, involving repeated immersions in water from the Seine. (author). 9 refs., 13 figs, 9 tabs

Electron backscatter diffraction study of deformation and recrystallization textures of individual phases in a cross-rolled duplex steel

Energy Technology Data Exchange (ETDEWEB)

Zaid, Md; Bhattacharjee, P.P., E-mail: pinakib@iith.ac.in

2014-10-15

The evolution of microstructure and texture during cross-rolling and annealing was investigated by electron backscatter diffraction in a ferritic–austenitic duplex stainless steel. For this purpose an alloy with nearly equal volume fraction of the two phases was deformed by multi-pass cross-rolling process up to 90% reduction in thickness. The rolling and transverse directions were mutually interchanged in each pass by rotating the sample by 90° around the normal direction. In order to avoid deformation induced phase transformation and dynamic strain aging, the rolling was carried out at an optimized temperature of 898 K (625 °C) at the warm-deformation range. The microstructure after cross warm-rolling revealed a lamellar structure with alternate arrangement of the bands of two phases. Strong brass and rotated brass components were observed in austenite in the steel after processing by cross warm-rolling. The ferrite in the cross warm-rolling processed steel showed remarkably strong RD-fiber (RD//< 011 >) component (001)< 011 >. The development of texture in the two phases after processing by cross warm-rolling could be explained by the stability of the texture components. During isothermal annealing of the 90% cross warm-rolling processed material the lamellar morphology was retained before collapse of the lamellar structure to the mutual interpenetration of the phase bands. Ferrite showed recovery resulting in annealing texture similar to the deformation texture. In contrast, the austenite showed primary recrystallization without preferential orientation selection leading to the retention of deformation texture. The evolution of deformation and annealing texture in the two phases of the steel was independent of one another. - Highlights: • Effect of cross warm-rolling on texture formation is studied in duplex steel. • Brass texture in austenite and (001)<110 > in ferrite are developed. • Ferrite shows recovery during annealing retaining the (001

Development of a high temperature austenitic stainless steel for Stirling engine components

International Nuclear Information System (INIS)

Anton, D.L.; Lemkey, F.D.

1986-01-01

An alloy, designed NASAUT 4G-A1, was developed which exhibited an excellent balance of oxidation resistance and high temperature strength while maintaining an austenitic matrix necessary for hydrogen compatibility. This alloy, having the composition 15Cr-15Mn-2Mo-1Nb-1Si-1.5C-bal. Fe in wt%, was microstructurally characterized and shown to contain a fine M/sub 23/C/sub 6/ precipitated phase. Subsequent heat treatments were shown to substantially modify this microstructure resulting in improved mechanical properties. Yield, creep and low cycle fatigue strengths were found to be superior to the best iron base alloy thus far identified as a potential heater head candidate material, XF-818

The Kinetics of Phase Transformations During Tempering in Laser Melted High Chromium Cast Steel

Science.gov (United States)

Li, M. Y.; Wang, Y.; Han, B.

2012-06-01

The precipitation of secondary carbides in the laser melted high chromium cast steels during tempering at 300-650 °C for 2 h in air furnace was characterized and the present phases was identified, by using transmission electron microscopy. Laser melted high chromium cast steel consists of austenitic dendrites and interdendritic M23C6 carbides. The austenite has such a strong tempering stability that it remains unchanged at temperature below 400 °C and the secondary hardening phenomenon starts from 450 °C to the maximum value of 672 HV at 560 °C. After tempering at 450 °C fine M23C6 carbides precipitate from the supersaturated austenite preferentially. In addition, the dislocation lines and slip bands still exist inside the austenite. While tempering at temperature below 560 °C, the secondary hardening simultaneously results from the martensite phase transformation and the precipitation of carbides as well as dislocation strengthening within a refined microstructure. Moreover, the formation of the ferrite matrix and large quality of coarse lamellar M3C carbides when the samples were tempered at 650 °C contributes to the decrease of hardness.

Low-temperature nitriding of austenitic steel in a vibrofluidized bed

Science.gov (United States)

Baraz, V. R.; Grachev, S. V.

1999-11-01

The prospects for use of a vibrofluidized bed (VFB) for low-temperature nitrogen saturation of high-strength austenitic steel based on Cr-Ni-Mn (12Kh17N8G2S2MF) are considered. The positive effect of preliminary plastic deformation on the intensity of nitriding is described. The temperature and time parameters of nitriding in a VFB for strain-aging austenitic steel 12Kh17N8G2S2MF are shown to be adequate for the regimes of the final heat-treatment operation of aging. This creates the possibility of combining the operations of surface alloying and strain aging into a single cycle. This combined treatment increases substantially the resistance of the steel to cyclic loads while preserving the strength parameters. It is shown that the presented method of low-temperature nitriding in a VFB is expedient for improving the service characteristics of austenitic steel 12Kh17N8G2S2MF used for production of force springs of automobile brake systems.

Determination of delta ferrite volumetric fraction in austenitic stainless steel

International Nuclear Information System (INIS)

Almeida Macedo, W.A. de.

1983-01-01

Measurements of delta ferrite volumetric fraction in AISI 304 austenitic stainless steels were done by X-ray diffraction, quantitative metallography (point count) and by means of one specific commercial apparatus whose operational principle is magnetic-inductive: The Ferrite Content Meter 1053 / Institut Dr. Foerster. The results obtained were comparated with point count, the reference method. It was also investigated in these measurements the influence of the martensite induced by mechanical deformation. Determinations by X-ray diffraction, by the ratio between integrated intensities of the ferrite (211) and austenite (311) lines, are in excelent agreement with those taken by point count. One correction curve for the lectures of the commercial equipment in focus was obtained, for the range between zero and 20% of delta ferrite in 18/8 stainless steels. It is demonstrated that, depending on the employed measurement method and surface finishing of the material to be analysed, the presence of martensite produced by mechanical deformation of the austenitic matrix is one problem to be considered. (Author) [pt

Determination of delta ferrite volumetric fraction in austenitic stainless steels

International Nuclear Information System (INIS)

Almeida Macedo, W.A. de.

1983-01-01

Measurements of delta ferrite volumetric fraction in AISI 304 austenitic stainless steels were done by X-ray difraction, quantitative metallography (point count) and by means of one specific commercial apparatus whose operational principle is magnetic-inductive: The Ferrite Content Meter 1053 / Institut Dr. Forster. The results obtained were comparated with point count, the reference method. It was also investigated in these measurements the influence of the martensite induced by mechanical deformation. Determinations by X-ray diffraction, by the ratio between integrated intensities of the ferrite (211) and austenite (311) lines, are in excelent agreement with those taken by point count. One correction curve for the lectures of the commercial equipment in focus was obtained, for the range between zero and 20% of delta ferrite in 18/8 stainless steels. It is demonstrated that, depending on the employed measurement method and surface finishing of the material to be analysed, the presence of martensite produced by mechanical deformation of the austenitic matrix is one problem to be considered. (Author) [pt

Corrosion Behavior of the Stressed Sensitized Austenitic Stainless Steels of High Nitrogen Content in Seawater

Directory of Open Access Journals (Sweden)

A. Almubarak

2013-01-01

Full Text Available The purpose of this paper is to study the effect of high nitrogen content on corrosion behavior of austenitic stainless steels in seawater under severe conditions such as tensile stresses and existence of sensitization in the structure. A constant tensile stress has been applied to sensitized specimens types 304, 316L, 304LN, 304NH, and 316NH stainless steels. Microstructure investigation revealed various degrees of stress corrosion cracking. SCC was severe in type 304, moderate in types 316L and 304LN, and very slight in types 304NH and 316NH. The electrochemical polarization curves showed an obvious second current peak for the sensitized alloys which indicated the existence of second phase in the structure and the presence of intergranular stress corrosion cracking. EPR test provided a rapid and efficient nondestructive testing method for showing passivity, degree of sensitization and determining IGSCC for stainless steels in seawater. A significant conclusion was obtained that austenitic stainless steels of high nitrogen content corrode at a much slower rate increase pitting resistance and offer an excellent resistance to stress corrosion cracking in seawater.

Austenitic stainless steels for cryogenic service

International Nuclear Information System (INIS)

Dalder, E.N.C.; Juhas, M.C.

1985-01-01

Presently available information on austenitic Fe-Cr-Ni stainless steel plate, welds, and castings for service below 77 K are reviewed with the intent (1) of developing systematic relationships between mechanical properties, composition, microstructure, and processing, and (2) of assessing the adequacy of these data bases in the design, fabrication, and operation of engineering systems at 4 K

Austenitic stainless steels for cryogenic service

Energy Technology Data Exchange (ETDEWEB)

Dalder, E.N.C.; Juhas, M.C.

1985-09-19

Presently available information on austenitic Fe-Cr-Ni stainless steel plate, welds, and castings for service below 77 K are reviewed with the intent (1) of developing systematic relationships between mechanical properties, composition, microstructure, and processing, and (2) of assessing the adequacy of these data bases in the design, fabrication, and operation of engineering systems at 4 K.

Microstructural Evolutions During Reversion Annealing of Cold-Rolled AISI 316 Austenitic Stainless Steel

Science.gov (United States)

Naghizadeh, Meysam; Mirzadeh, Hamed

2018-06-01

Microstructural evolutions during reversion annealing of a plastically deformed AISI 316 stainless steel were investigated and three distinct stages were identified: the reversion of strain-induced martensite to austenite, the primary recrystallization of the retained austenite, and the grain growth process. It was found that the slow kinetics of recrystallization at lower annealing temperatures inhibit the formation of an equiaxed microstructure and might effectively impair the usefulness of this thermomechanical treatment for the objective of grain refinement. By comparing the behavior of AISI 316 and 304 alloys, it was found that the mentioned slow kinetics is related to the retardation effect of solute Mo in the former alloy. At high reversion annealing temperature, however, an equiaxed austenitic microstructure was achieved quickly in AISI 316 stainless steel due to the temperature dependency of retardation effect of molybdenum, which allowed the process of recrystallization to happen easily. Conclusively, this work can shed some light on the issues of this efficient grain refining approach for microstructural control of austenitic stainless steels.

Effect of deformation temperature on niobium clustering, precipitation and austenite recrystallisation in a Nb–Ti microalloyed steel

International Nuclear Information System (INIS)

Kostryzhev, Andrii G.; Al Shahrani, Abdullah; Zhu, Chen; Ringer, Simon P.; Pereloma, Elena V.

2013-01-01

The effect of deformation temperature on Nb solute clustering, precipitation and the kinetics of austenite recrystallisation were studied in a steel containing 0.081C–0.021Ti–0.064 Nb (wt%). Thermo-mechanical processing was carried out using a Gleeble 3500 simulator. The austenite microstructure was studied using a combination of optical microscopy, transmission electron microscopy, and atom probe microscopy, enabling a careful characterisation of grain size, as well as Nb-rich clustering and precipitation processes. A correlation between the austenite recrystallisation kinetics and the chemistry, size and number density of Nb-rich solute atom clusters, and NbTi(C,N) precipitates was established via the austenite deformation temperature. Specifically, we have determined thresholds for the onset of recrystallisation: for deformation levels above 75% and temperatures above 825 °C, Nb atom clusters <8 nm effectively suppressed austenite recrystallisation

Thermodynamic and kinetic characteristics of the austenite-to-ferrite transformation under high magnetic field in medium carbon steel

International Nuclear Information System (INIS)

Zhang Yudong; He Changshu; Zhao Xiang; Zuo Liang; Esling, Claude

2005-01-01

The thermodynamic and kinetic characteristics of austenite-to-ferrite phase transformation in medium carbon steel in the high magnetic fields were investigated. Results showed that the magnetic field could obviously change the γ/α+γ phase equilibrium-by increasing the amount of ferrite obtained during cooling-and greatly accelerate the transformation. Thus the microstructure obtained under fast cooling with high magnetic field was still ferritic and pearlitic, while that obtained without the magnetic field under the same cooling conditions was bainitic. Exploration in this area contributes both to enriching the new theory on electromagnetic processing of materials (EPM) and in establishing new techniques for materials processing

Effect of austenitization conditions on kinetics of isothermal transformation of austenite of structural steels

International Nuclear Information System (INIS)

Konopleva, E.V.; Bayazitov, V.M.; Abramov, O.V.; Kozlova, A.G.

1987-01-01

Effect of austenization of kinetics of pearlite and bainite transformations for steels with different carbon content differing by alloying character and degree has been investigated. Austenization temperature increase is shown to leads to retardation of ferrite-pearlite transformation in low- and medium-carbon alloyed steels. Step-like holding in the region of austenite stable state (850, 950 deg) after high-temperature heating (1100 deg C) increases the rate of transformation partially recovering its kinetics and decomposition velocity after low-temperature heating in steels alloyed advantageously with carbide-forming elements (08Kh2G2F, 30Kh3) and does not affect kinetics in the 35Kh, 30KhGSN2A, 45N5 steels. Increase of heating temperature and growth of an austenite grain cause considerable acceleration of bainite transformation, increase of the temperaure of bainite transformation beginning and increase of the transformation amplitude in the 08Kh2G2F, 30Kh3 steels and affect weakly kinetics in steels with mixed alloying (30KhGSN2A) or low-alloy one (35Kh). The bainite transformation rate in the 45N5 steelite does not depend on austenization. The effect of additional acceleration of bainite transformation as a result holding after high-temperature heating in those steels, where activation of transformation occurs with increase of heating temperature

Effect of nitrogen ion dose on the corrosion resistance, the microstructure and the phase structure of the biomaterials austenitic stainless steel 316L

International Nuclear Information System (INIS)

Lely Susita RM; Bambang Siswanto; Ihwanul Aziz; Anjar Anggraini H

2016-01-01

The succeed of the use of biomaterials for orthopedic implant device is determined by its mechanical properties, chemical stability and biocompatibility in tissues and body fluids. The corrosion resistance is one of the main property of biomaterials to determine for successful orthopedic implant in body tissues. Surface modification is carried out to improve biomaterial surface properties of austenitic stainless steel 316L with nitrogen ion implantation technique and ion nitriding. Nitrogen ion implantation performed on 60 keV ion energy and ion dose variations 2 x 10"1"6 ions/cm"2- 2 x 10"1"7 ions/cm"2. The corrosion resistance of austenitic stainless steel 316L in Hanks solution is measured by using a potentiostat, and corrosion resistance optimum of a sample is obtained at an ion dose of 5 x 10"1"6 ions/cm"2 and increase by a factor of 2.1 if compared to the sample without the nitrogen ion implantation. Further the sample of austenitic stainless steel 316L with the optimum corrosion resistance is processed by ion nitriding technique at a nitriding temperature of 350 °C and nitriding time of 4 hours. Based on corrosion test of the sample produced by ion nitriding is obtained an increasing the corrosion resistance by a factor of 2.96 when compared to the sample before nitrogen ion implantation. The improvement of corrosion resistance of the sample is caused by the formation of iron nitride ξ-Fe2N and γ- Fe4N which has excellent corrosion resistance properties. (author)

Phase identification and internal stress analysis of steamside oxides on superheater tubes by means of X-ray diffraction

DEFF Research Database (Denmark)

Pantleon, Karen; Montgomery, Melanie

Steamside oxides formed on plant exposed superheated tubes were investigated using X-ray diffraction. Phase identification and stress analysis revealed that on ferritic X20CrMoV12-1 pure Hematite and pure Magnetite formed and both phases are under tensile stress. IN contrast, on austenitic TP347H...... Mn-, Cr- and/or Ni-containing oxides are observed, instead of pure Magnetite, underneath a pure Hematite surface layer. Oxides on the austenitic steel are under compressive stress or even stress-free....

Effect of Ti additions on the swelling of electron irradiated austenitic steels and Ni alloys

International Nuclear Information System (INIS)

Gilbon, D.; Didout, G.; Le Naour, L.; Levy, V.

1979-01-01

It has been shown that titanium is a beneficial additive for the swelling of austenitic steels. The amplitude of the effects observed depends much on the nature and concentration of the other additives in the austenitic matrix [fr

Computer simulations of austenite decomposition of microalloyed 700 MPa steel during cooling

Science.gov (United States)

Pohjonen, Aarne; Paananen, Joni; Mourujärvi, Juho; Manninen, Timo; Larkiola, Jari; Porter, David

2018-05-01

We present computer simulations of austenite decomposition to ferrite and bainite during cooling. The phase transformation model is based on Johnson-Mehl-Avrami-Kolmogorov type equations. The model is parameterized by numerical fitting to continuous cooling data obtained with Gleeble thermo-mechanical simulator and it can be used for calculation of the transformation behavior occurring during cooling along any cooling path. The phase transformation model has been coupled with heat conduction simulations. The model includes separate parameters to account for the incubation stage and for the kinetics after the transformation has started. The incubation time is calculated with inversion of the CCT transformation start time. For heat conduction simulations we employed our own parallelized 2-dimensional finite difference code. In addition, the transformation model was also implemented as a subroutine in commercial finite-element software Abaqus which allows for the use of the model in various engineering applications.

Effect of austenite deformation temperature on Nb clustering and precipitation in microalloyed steel

International Nuclear Information System (INIS)

Pereloma, E.V.; Kostryzhev, A.G.; AlShahrani, A.; Zhu, C.; Cairney, J.M.; Killmore, C.R.; Ringer, S.P.

2014-01-01

The effect of thermomechanical processing conditions on Nb clustering and precipitation in both austenite and ferrite in a Nb–Ti microalloyed steel was studied using electron microscopy and atom probe tomography. A decrease in the deformation temperature increased the Nb-rich precipitation in austenite and decreased the extent of precipitation in ferrite. Microstructural mechanisms that explain this variation are discussed

Prediction of long-term precipitate evolution in austenitic heat-resistant steels

Energy Technology Data Exchange (ETDEWEB)

Shim, Jae-Hyeok; Jung, Woo-Sang; Cho, Young Whan [Korea Institute of Science and Technology, Seoul (Korea, Republic of). Materials/Devices Div.; Kozeschnik, Ernst [Vienna Univ. of Technology (Austria). Inst. of Materials Science and Technology

2010-07-01

Numerical prediction of the long-term precipitate evolution in five different austenitic heat-resistant stainless steels, NF709, Super304H, Sanicro25, CF8C-PLUS and HTUPS has been carried out. MX and M{sub 23}C{sub 6} are predicted to remain as major precipitates during long-term aging in these steels. The addition of 3 wt% Cu produces very fine Cu-rich precipitates during aging in Super304H and Sanicro25. It is found that the amount of Z phase start to increase remarkably between 1,000 and 10,000 hours of aging at the expense of MX precipitates in the steels containing a high nitrogen content. However, the growth rate of Z phase is relatively slow and its average size reaches at most a few tens of nanometers after 100,000 hours of aging at 700 C, compared with 9-12% Cr ferritic/martensitic heat-resistant steels. The predicted precipitation sequence and precipitate size during aging are in general agreement with experimental observations. (orig.)

Thermally Stable Ni-rich Austenite Formed Utilizing Multistep Intercritical Heat Treatment in a Low-Carbon 10 Wt Pct Ni Martensitic Steel

Science.gov (United States)

Jain, Divya; Isheim, Dieter; Zhang, Xian J.; Ghosh, Gautam; Seidman, David N.

2017-08-01

Austenite reversion and its thermal stability attained during the transformation is key to enhanced toughness and blast resistance in transformation-induced-plasticity martensitic steels. We demonstrate that the thermal stability of Ni-stabilized austenite and kinetics of the transformation can be controlled by forming Ni-rich regions in proximity of pre-existing (retained) austenite. Atom probe tomography (APT) in conjunction with thermodynamic and kinetic modeling elucidates the role of Ni-rich regions in enhancing growth kinetics of thermally stable austenite, formed utilizing a multistep intercritical ( Quench- Lamellarization- Tempering (QLT)-type) heat treatment for a low-carbon 10 wt pct Ni steel. Direct evidence of austenite formation is provided by dilatometry, and the volume fraction is quantified by synchrotron X-ray diffraction. The results indicate the growth of nm-thick austenite layers during the second intercritical tempering treatment (T-step) at 863 K (590 °C), with austenite retained from first intercritical treatment (L-step) at 923 K (650 °C) acting as a nucleation template. For the first time, the thermal stability of austenite is quantified with respect to its compositional evolution during the multistep intercritical treatment of these steels. Austenite compositions measured by APT are used in combination with the thermodynamic and kinetic approach formulated by Ghosh and Olson to assess thermal stability and predict the martensite-start temperature. This approach is particularly useful as empirical relations cannot be extrapolated for the highly Ni-enriched austenite investigated in the present study.

Laser cladding crack repair of austenitic stainless steel

CSIR Research Space (South Africa)

Van Rooyen, C

2009-06-01

Full Text Available Laser cladding crack repair of austenitic stainless steel vessels subjected to internal water pressure was evaluated. The purpose of this investigation was to develop process parameters for in-situ repair of through-wall cracks in components...

In-situ observation of weld joint of austenitic stainless steel due to helium irradiation

International Nuclear Information System (INIS)

Hamada, S.; Hojou, K.; Hishinuma, A.

1992-01-01

Microstructural evolution during helium ions irradiation in a weld metal containing 10% delta-ferrite of a weld joint of Ti-modified austenitic stainless steel were in-situ observed through a transmission electron microcopy. Very fine helium bubbles were observed in high number density in both a delta ferrite phase and a matrix to a dose of 3 x 10 19 ions·m -2 . Entirely different behavior appeared in both phases with increasing dose. Bubbles in a delta-ferrite phase were readily converted into voids during slight increment of dose, and these rapidly grew with additional increasing of dose. On the other hand, finer bubbles in a matrix were very stable during irradiation and did not grow any more up to 2 x 10 20 ions·m -2 . Swelling became much larger in a delta-ferrite phase than in a fcc matrix phase, resultantly ; This means an inverse phenomenon for conventional results that swelling is smaller in a ferrite phase than in a fcc phase. Sigma phase radiation-enhanced precipitated at the grain boundary between a delta-ferrite phase and a matrix at a dose 9 x 10 19 ions·m -2 . This phase grew in two dimensions with increasing dose. The chemical composition of the sigma phase observed during irradiation showed Cr and Mo enrichment, and Fe and Ni depletion compared with those of a sigma phase thermally produced. (author)

Solution and precipitation of excess phases and nitrogen partition between solid solution and nitrides in corrosion-resistant steel

International Nuclear Information System (INIS)

Kaputkina, L.M.; Svyazhin, A.G.; Prokoshkina, V.G.

2006-01-01

Experimental study results on dissolution and precipitation of nitrides during crystallization and heat treatment of high nitrogen austenitic steels are presented. It is established that even on rapid crystallization most of nitrogen is in nitrides, and for their dissolution high temperatures and long-term holding at heat are needed. A nitrogen content in the steel should be optimized according to the structure required (austenite or austenite + excess phases). It is noted that a high nitrogen concentration in the steel is not necessarily efficient to attain a high strength [ru

The stress rupture properties of austenitic steel weld metals

International Nuclear Information System (INIS)

Wood, D.S.

Elevated temperature stress rupture data on Mo containing and Mo free austenitic weld metals have been collected from French, Dutch, German and UK sources and the results analysed. The stress rupture strength of Mo containing weld metal is significantly higher than that of Mo free weld metal. At 10,000h the rupture strength of Mo containing weld metal is higher than that of Type 316 steel whereas the Mo free weld metal is about 20% lower than that of Type 304 steel. Austenitic weld metal can give low stress rupture ductility values. It is concluded that there are insufficient data to permit reliable extrapolations to long times and it is recommended that long term tests are performed to overcome this situation

Effects of austenitizing temperature in quenched niobium steels

International Nuclear Information System (INIS)

Mello, F.B.C. de; Assuncao, F.C.R.

1980-01-01

Three steel compositions with varying Nb content were austenitized at different temperatures and quenched in cold water. Metallographic examination and hardness measurements provided a basis for explaining the hardening mechanism and the role of Nb on the process. (Author) [pt

Role of Austenite in Brittle Fracture of Bond Region of Super Duplex Stainless Steel

Science.gov (United States)

Kitagawa, Yoshihiko; Ikeuchi, Kenji; Kuroda, Toshio

Weld simulation of heat-affected zone (HAZ) was performed to investigate the mechanism by which austenite affects the toughness of super duplex stainless steel. Thermal cycles of various peak temperatures in the range from 1373 K to 1673 K corresponding to the HAZ were applied to SAF2507 super duplex stainless steel specimens. Charpy impact test was carried out using the specimens after the weld simulation, and the fracture surfaces were observed by SEM using three-dimensionally reconstruction technique. Austenite content decreased with increasing the peak temperature when the peak temperature exceeded 1473 K and the impact value decreased with increasing the peak temperature and decreasing the austenite content. The thermal cycle of the peak temperature of 1673 K corresponding to weld bond region caused decreasing of austenite content which was 22% lower than that of the base metal. The ductile-brittle transition temperature was measured. As a result the temperature increased rapidly in the weld bond region, the peak temperature of which exceeded 1623 K by the grain growth of ferrite matrix occurring subsequently to the completely dissolution of austenite. The morphology of the fracture surfaces after impact testing at 77 K showed cleavage fracture of ferrite. The {100} orientations of cleavage fracture facets were measured using three-dimensional images of the fracture surfaces and the results were visualized as the orientation color maps. The results showed that there were cleavage fractures consisting of a few facets parallel to each other. It was considered that a few facets existed in one ferrite grain. It was concluded that Widmanstätten austenite divided the large fracture into smaller cleavage facets in a ferrite grain and then suppressed the degradation of bond toughness of duplex stainless steel.

Manufacture and characterization of austenitic steel welded joints. Joint final report - Vol. 1

International Nuclear Information System (INIS)

Simoni, O.; Boerman, D.J.; Krischer, W.

1990-07-01

This report describes the results of the first phase of the project, i.e. manufacturing and characterization of welded austenitic steel and the test matrix adopted to test the mechanical resistance of the weldings. Five different welding methods have been produced and characterized in comparison to the parent material. The reference material was an AISI 316L type steel close to the French Superphenix composition. The results of the mechanical testing and the relative comparison of the five welding methods are described in a second volume. As a general conclusion, the vacuum electron-beam welding proved to have better properties than the other weld methods and to attain in most cases the properties of the parent material

Prediction of microsegregation and pitting corrosion resistance of austenitic stainless steel welds by modelling

Energy Technology Data Exchange (ETDEWEB)

Vilpas, M. [VTT Manufacturing Technology, Espoo (Finland). Materials and Structural Integrity

1999-07-01

solidification, the dendrite cores were predicted to be the weakest link with respect to weld pitting corrosion resistance. In primary ferritic solidification, the second phase austenite in the vicinity of d/g interfaces was predicted to show lowest pitting corrosion resistance. Solidification parameters used in the modelling were verified by cooling rate and dendrite arm spacing measurements as well as by analytical calculations. Experimental investigations using electron probe microanalyses (EPMA, CMA), electron microscopy (SEM, FEG-STEM), microstructural investigations and pitting corrosion tests were used in assessing the calculated microsegregation and CPT-temperatures and showed a reasonably good compatibility with the results of modelling. (orig.)

Application of Moessbauer effect to the study of austenite retained in low carbon steels

International Nuclear Information System (INIS)

Azevedo, A.L.T. de; Silva, E.G. da

1979-01-01

Moessbauer effect measurements were performed in two samples of low carbon, low alloy steels, one with a bainite granular microstructure and the other a martensitic one. The concentration of the retained austenite was determined in both samples by Moessbauer spectrometry and X radiation, a very good agreement for the sample with a greater austenite content having been observed. From the assumption that the carbon atoms in the f.c.c. matrix repel one another due to Coulomb interactions, giving origin to quadrupolar interactions, it was possible to determine carbon concentration in the MA (Martensite Austenite) components of bainite, the results being in good agreement with the one obtained from metallographic considerations. (I.C.R.) [pt

Occurence and prediction of sigma phase in fuel cladding alloys for breeder reactors

International Nuclear Information System (INIS)

Anantatmula, R.P.

1982-01-01

In sodium-cooled fast reactor systems, fuel cladding materials will be exposed for several thousand hours to liquid sodium. Satisfactory performance of the materials depends in part on the sodium compatibility and phase stability of the materials. This paper mainly deals with the phase stability aspect, with particular emphasis on sigma phase formation of the cladding materials upon extended exposures to liquid sodium. A new method of predicting sigma phase formation is proposed for austenitic stainless steels and predictions are compared with the experimental results on fuel cladding materials. Excellent agreement is obtained between theory and experiment. The new method is different from the empirical methods suggested for superalloys and does not suffer from the same drawbacks. The present method uses the Fe-Cr-Ni ternary phase diagram for predicting the sigma-forming tendencies and exhibits a wide range of applicability to austenitic stainless steels and heat-resistant Fe-Cr-Ni alloys

The interfacial orientation relationship of oxide nanoparticles in a hafnium-containing oxide dispersion-strengthened austenitic stainless steel

Energy Technology Data Exchange (ETDEWEB)

Miao, Yinbin, E-mail: miao2@illinois.edu [Department of Nuclear, Plasma and Radiological Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801 (United States); Mo, Kun [Nuclear Engineering Division, Argonne National Laboratory, Lemont, IL 60493 (United States); Cui, Bai [Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588 (United States); Department of Material Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801 (United States); Chen, Wei-Ying [Department of Nuclear, Plasma and Radiological Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801 (United States); Miller, Michael K.; Powers, Kathy A. [Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37830 (United States); McCreary, Virginia; Gross, David [Department of Material Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801 (United States); Almer, Jonathan [X-ray Science Division, Argonne National Laboratory, Lemont, IL 60493 (United States); Robertson, Ian M. [Department of Material Science and Engineering, University of Wisconsin-Madison, Madison, WA 53706 (United States); Department of Material Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801 (United States); Stubbins, James F. [Department of Nuclear, Plasma and Radiological Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801 (United States)

2015-03-15

This work reports comprehensive investigations on the orientation relationship of the oxide nanoparticles in a hafnium-containing austenitic oxide dispersion-strengthened 316 stainless steel. The phases of the oxide nanoparticles were determined by a combination of scanning transmission electron microscopy–electron dispersive X-ray spectroscopy, atom probe tomography and synchrotron X-ray diffraction to be complex Y–Ti–Hf–O compounds with similar crystal structures, including bixbyite Y{sub 2}O{sub 3}, fluorite Y{sub 2}O{sub 3}–HfO{sub 2} solid solution and pyrochlore (or fluorite) Y{sub 2}(Ti,Hf){sub 2−x}O{sub 7−x}. High resolution transmission electron microscopy was used to characterize the particle–matrix interfaces. Two different coherency relationships along with one axis-parallel relation between the oxide nanoparticles and the steel matrix were found. The size of the nanoparticles significantly influences the orientation relationship. The results provide insight into the relationship of these nanoparticles with the matrix, which has implications for interpreting material properties as well as responses to radiation. - Highlights: • The oxide nanoparticles in a hafnium-containing austenitic ODS were characterized. • The nanoparticles are Y–Hf–Ti–O enriched phases according to APT and STEM–EDS. • Two coherency and an axis-parallel orientation relationships were found by HR-TEM. • Particle size has a prominent effect on the orientation relationship (OR). • Formation mechanism of the oxide nanoparticles was discussed based on the ORs.

Effect of Plastic Pre-straining on Residual Stress and Composition Profiles in Low-Temperature Surface-Hardened Austenitic Stainless Steel

DEFF Research Database (Denmark)

Bottoli, Federico; Christiansen, Thomas Lundin; Winther, Grethe

2016-01-01

The present work deals with the evaluation of the residual stress profiles in expanded austenite by applying grazing incidence X-ray diffraction (GI-XRD) combined with successive sublayer removal. Annealed and deformed (εeq=0.5) samples of stable stainless steel EN 1.4369 were nitrided...... or nitrocarburized. The residual stress profiles resulting from the thermochemical low-temperature surface treatment were measured. The results indicate high-residual compressive stresses of several GPa’s in the nitrided region, while lower-compressive stresses are produced in the carburized case. Plastic...... deformation in the steel prior to thermochemical treatment has a hardly measurable influence on the nitrogen-rich zone, while it has a measurable effect on the stresses and depth of the carbon-rich zone....

Mechanical stability of individual austenite grains in TRIP steel studied by synchrotron X-ray diffraction during tensile loading

Energy Technology Data Exchange (ETDEWEB)

Blondé, R. [Fundamental Aspects of Materials and Energy, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands); Materials Innovation Institute, Mekelweg 2, 2628 CD Delft (Netherlands); Jimenez-Melero, E. [Dalton Cumbrian Facility, The University of Manchester, Westlakes Science and Technology Park, Moor Row, Cumbria, CA24 3HA (United Kingdom); Zhao, L. [Materials Innovation Institute, Mekelweg 2, 2628 CD Delft (Netherlands); Department of Materials Science and Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft (Netherlands); Wright, J.P. [European Synchrotron Radiation Facility, 6 Rue Jules Horowitz, BP 220, 38043 Grenoble Cedex (France); Brück, E. [Fundamental Aspects of Materials and Energy, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands); Zwaag, S. van der [Novel Aerospace Materials Group, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS, Delft (Netherlands); Dijk, N.H. van, E-mail: N.H.vanDijk@tudelft.nl [Fundamental Aspects of Materials and Energy, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands)

2014-11-17

The stability of individual metastable austenite grains in low-alloyed TRIP steels has been studied during tensile loading using high-energy X-ray diffraction. The carbon concentration, grain volume and grain orientation with respect to the loading direction was monitored for a large number of individual grains in the bulk microstructure. Most austenite grains transform into martensite in a single transformation step once a critical load is reached. The orientation-dependent stability of austenite grains was found to depend on their Schmid factor with respect to the loading direction. Under the applied tensile stress the average Schmid factor decreased from an initial value of 0.44 to 0.41 at 243 MPa. The present study reveals the complex interplay of microstructural parameters on the mechanical stability of individual austenite grains, where the largest grains with the lowest carbon content tend to transform first. Under the applied tensile stress the average carbon concentration of the austenite grains increased from an initial value of 0.90 to 1.00 wt% C at 243 MPa, while the average grain volume of the austenite grains decreased from an initial value of 19 to 15 µm{sup 3} at 243 MPa.

Austenite stability in reversion-treated structures of a 301LN steel under tensile loading

Czech Academy of Sciences Publication Activity Database

Järvenpää, A.; Jaskari, M.; Man, Jiří; Karjalainen, L. P.

2017-01-01

Roč. 127, MAY (2017), s. 12-26 ISSN 1044-5803 R&D Projects: GA ČR GA13-32665S Institutional support: RVO:68081723 Keywords : austenitic stainless steel * austenite stability * grain size * reversion annealing * tensile straining * deformation induced martensite Subject RIV: JL - Materials Fatigue, Friction Mechanics OBOR OECD: Audio engineering, reliability analysis Impact factor: 2.714, year: 2016

Dissolution mechanism of austenitic stainless steels in lead-bismuth eutectic at 500 deg. C

International Nuclear Information System (INIS)

Roy, M.

2012-01-01

In the framework of the future nuclear power plants studies, lead-bismuth eutectic (LBE) is foreseen as a coolant in the primary or the secondary circuit in three nuclear systems. The use of this liquid alloy induces corrosion issues for structural steels. In liquid lead alloys, steels can undergo two corrosion phenomena: dissolution or oxidation depending on the temperature and the dissolved oxygen content in LBE. The goal of this study is to identify the dissolution mechanisms of austenitic steels in LBE at 500 deg. C. Four Fe-Cr-Ni model austenitic steels, the 316L steel and five other industrial steels were corroded in LBE up to, respectively, 3000, 6000 and 200 h. The dissolution mechanism is identical for all steels: it starts by a preferential dissolution of chromium and nickel. This dissolution leads to the formation of a ferritic corrosion layer penetrated by LBE and containing between 5 and 10 at% of chromium and almost no nickel. This study demonstrates that dissolutions of nickel and chromium are linked. Otherwise, the corrosion kinetics is linear whatever the tested austenitic steel. The controlling steps of the austenitic steels' corrosion rates have been identified. Natural convection in the LBE bath leads to the formation of a diffusion boundary layer at the steel surface. Chromium diffusion in this diffusion boundary layer seems to control the corrosion rates of the model and industrial austenitic steels except the 316L steel. Indeed, the corrosion rate of the 316L steel is controlled by an interfacial reaction which is either the simultaneous dissolution of nickel and chromium in Ni, Cr compounds or the nickel and chromium dissolution catalyzed by the dissolved oxygen in LBE. This study has permitted to highlight the major role of chromium on the corrosion mechanisms and the corrosion rates of austenitic steels: the corrosion rate increases when chromium activity increases. Finally, the impact of the dissolved oxygen and the minor alloying

Effect of electromagnetic stirring on solidification structure of austenitic stainless steel in horizontal continuous casting

Directory of Open Access Journals (Sweden)

ZHOU Shu-cai

2007-08-01

Full Text Available An investigation on the influence of low frequency rotary electromagnetic stirring on solidification structure of austenitic stainless steel in horizontal continuous casting was experimentally conducted and carried out on an industrial trial basis. The results show that application of appropriate electromagnetic stirring parameters can obviously improve the macrostructure of austenitic stainless steel, in which both columnar and equiaxed grains can be greatly refined and shrinkage porosity or cavity zone along centerline can be remarkably decreased due to eliminating intracrystalline and enlarging equiaxed grains zone. The industrial trials verify that the electromagnetic stirring intensity of austenitic stainless steel should be higher than that of plain carbon steel. Electromagnetic stirring has somewhat affected the macrostructure of austenitic stainless steel even if the magnetic flux density of the electromagnetic stirring reaches 90 mT (amplitude reaches 141 mT in average at frequency f=3-4Hz, which provides a reference for the optimization of design and process parameters when applying the rotary electromagnetic stirrer.

Fatigue behavior of austenitic steels. Subproject. Mechanism oriented investigation of the fatigue behavior of austenitic steel X6CrNiNb1810 in the HCF and VHCF regime. Final report; Ermuedungsverhalten Austenit. Teilprojekt. Mechanismenorientierte Untersuchung des Ermuedungsverhaltens des austenitischen Stahles X6CrNiNb1810 im HCF- und VHCF-Bereich. Abschlussbericht

Energy Technology Data Exchange (ETDEWEB)

Sorich, A.; Smaga, M.; Eifler, D.

2015-01-23

In addition to load cycles in the Low Cycle Fatigue (LCF)-regime due to start up and shut down procedures of power plants, in some components additional high-frequency loadings in the High Cycle Fatigue (HCF)- and Very High Cycle Fatigue (VHCF)-regime occur. These loadings are induced e.g. by stresses due to thermal cyclic fluctuations and fluid dynamic processes. Therefore it is necessary to characterize experimentally the cyclic deformation behavior of metastable austenitic steels at operating temperature particularly in the HCF- and VHCF-regime and to develop a nondestructive method to detect fatigue processes. This joint research project was conducted in cooperation between the Institute of Materials Science and Engineering (WKK) of the University of Kaiserslautern and the Fraunhofer-Institute for Non-Destructive Testing (IZFP) in Saarbruecken. WKK was focused on experimental investigations to characterize the cyclic deformation behavior of the metastable austenitic steel in the HCF- and VHCF-range, taking into account cyclic hardening and softening processes and in particular to consider fatigue-induced changes in microstructure. The IZFP has focused on the development and application of a testing concept based on electromagnetic ultrasonic measurements. The isothermal cyclic deformation behavior of the metastable austenitic steel X6CrNiNb1810 (1.4550, AISI 347) at 300 C in the HCF-range is characterized by cyclic softening until specimen failure. At strain amplitudes of 0.10 % ≤ ε{sub a,t} ≤ 0.15 % and the stress amplitude σ{sub a} = 160 MPa cyclic softening is followed by cyclic hardening, which results in a significant increase in life time, up to the limiting number of cycles, which was defined at N{sub I} = 10{sup 7} in HCF-regime. The cyclic hardening is determined by a transformation induced phase formation from face-centered cubic (fcc) austenite to body-centered cubic (bcc) α{sup '}-martensite and/or in hexagonal (hcp) ε-martensite. In

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...... 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...

Oxidization and stress corrosion cracking initiation of austenitic alloys in supercritical water

International Nuclear Information System (INIS)

Behnamian, Y.; Li, M.; Luo, J.L.; Chen, W.X.; Zheng, W.; Guzonas, D.A.

2012-01-01

This study determined the stress corrosion cracking behaviour of austenitic alloys in pure supercritical water. Austenitic stainless steels 310S, 316L, and Inconel 625 were tested as static capsule samples at 500 o C for up to 5000 h. After that period, crack initiations were readily observed in all samples, signifying susceptibility to stress corrosion cracking. The microcracks in 316L stainless steel and Inconel 625 were almost intergranular, whereas transgranular microcrack initiation was observed in 310S stainless steel. (author)

Oxidization and stress corrosion cracking initiation of austenitic alloys in supercritical water

Energy Technology Data Exchange (ETDEWEB)

Behnamian, Y.; Li, M.; Luo, J.L.; Chen, W.X. [Univ. of Alberta, Dept. of Chemical and Materials Engineering, Edmonton, Alberta (Canada); Zheng, W. [Materials Technology Laboratory, NRCan, Ottawa, Ontario (Canada); Guzonas, D.A. [Atomic Energy of Canada Limited, Chalk River, Ontario (Canada)

2012-07-01

This study determined the stress corrosion cracking behaviour of austenitic alloys in pure supercritical water. Austenitic stainless steels 310S, 316L, and Inconel 625 were tested as static capsule samples at 500{sup o}C for up to 5000 h. After that period, crack initiations were readily observed in all samples, signifying susceptibility to stress corrosion cracking. The microcracks in 316L stainless steel and Inconel 625 were almost intergranular, whereas transgranular microcrack initiation was observed in 310S stainless steel. (author)

Hot working effect on austenite transformations in structural steel in continuous cooling

International Nuclear Information System (INIS)

Zajmovskij, V.A.; Kisteh, N.V.; Samedov, O.V.

1979-01-01

Austenite transformations in 40, 40Kh, 40KhN and 40KhNMA steels under hot working at 900 deg C with 20% reduction degree and continuous cooling with 1,7-16 0 /s are investigated. Changing of cooling rate in various ways affects the temperature range of austenite transformation in pearlite and bainite regions. Regulating the cooling rate after hot working one can essentially change the impact strength and steel ductility as a result of high temperature thermomechanical treatment effect

Image security based on iterative random phase encoding in expanded fractional Fourier transform domains

Science.gov (United States)

Liu, Zhengjun; Chen, Hang; Blondel, Walter; Shen, Zhenmin; Liu, Shutian

2018-06-01

A novel image encryption method is proposed by using the expanded fractional Fourier transform, which is implemented with a pair of lenses. Here the centers of two lenses are separated at the cross section of axis in optical system. The encryption system is addressed with Fresnel diffraction and phase modulation for the calculation of information transmission. The iterative process with the transform unit is utilized for hiding secret image. The structure parameters of a battery of lenses can be used for additional keys. The performance of encryption method is analyzed theoretically and digitally. The results show that the security of this algorithm is enhanced markedly by the added keys.

Low temperature surface hardening of stainless steel; the role of plastic deformation

DEFF Research Database (Denmark)

Bottoli, Federico; Jespersen, Freja Nygaard; Hattel, Jesper Henri

2016-01-01

: - plastic deformation of metastable austenitic stainless steels leads to the development of strain-induced martensite, which compromises the uniformity and the homogeneity of the expanded austenite zone. - during low temperature surface engineering composition and stress profiles develop. On numerical......Thermochemical surface engineering by nitriding of austenitic stainless steel transforms the surface zone into expanded austenite, which improves the wear resistance of the stainless steel while preserving the stainless behavior. As a consequence of the thermochemical surface engineering, huge...