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Sample records for 316ln austenitic stainless

  1. Damage structure of austenitic stainless steel 316LN irradiated at low temperature in HFIR

    Hashimoto, N.; Robertson, J.P.; Grossbeck, M.L.; Rowcliffe, A.F. [Oak Ridge National Lab., TN (United States); Wakai, E. [Japan Atomic Energy Research Inst. (Japan)

    1998-03-01

    TEM disk specimens of austenitic stainless steel 316LN irradiated to damage levels of about 3 dpa at irradiation temperatures of either about 90 C or 250 C have been investigated by using transmission electron microscopy. The irradiation at 90 C and 250 C induced a dislocation loop density of 3.5 {times} 10{sup 22} m{sup {minus}3} and 6.5 {times} 10{sup 22} m{sup {minus}3}, a black dot density of 2.2 {times} 10{sup 23} m{sup {minus}3} and 1.6 {times} 10{sup 23} m{sup {minus}3}, respectively, in the steels, and a high density (<1 {times} 10{sup 22} m{sup {minus}3}) of precipitates in matrix. Cavities could be observed in the specimens after the irradiation. It is suggested that the dislocation loops, the black dots, and the precipitates cause irradiation hardening, an increase in the yield strength and a decrease in the uniform elongation, in the 316LN steel irradiated at low temperature.

  2. Carburization behavior of AISI 316LN austenitic stainless steel - Experimental studies and modeling

    AISI type 316LN austenitic stainless steel was exposed to flowing sodium at 798 K for 16,000 h in the bi-metallic (BIM) sodium loop. A modified surface layer of 10 μm width having a ferrite structure was detected from X-ray diffraction and electron micro probe based analysis. Beneath the modified surface layer a carburized zone of 60 μm width was identified which was found to consist of M23C6 carbides. A mathematical model based on finite difference technique was developed to predict the carburization profiles in sodium exposed austenitic stainless steel. In the computation, effect of only chromium on carbon diffusion was considered. Amount of carbon remaining in solution was determined from the solubility parameter. The predicted profile showed a reasonably good match with the experimental profile. Calculations were extended to simulate the thickness of the carburized layer after exposure to sodium for a period of 40 years. Attempt was also made to predict the carburization profiles based on equilibrium calculations using Dictra and Thermocalc which contain both thermodynamic and kinetic databases for the system under consideration.

  3. Carburization behavior of AISI 316LN austenitic stainless steel - Experimental studies and modeling

    Sudha, C.; Sivai Bharasi, N.; Anand, R.; Shaikh, H.; Dayal, R. K.; Vijayalakshmi, M.

    2010-07-01

    AISI type 316LN austenitic stainless steel was exposed to flowing sodium at 798 K for 16,000 h in the bi-metallic (BIM) sodium loop. A modified surface layer of 10 μm width having a ferrite structure was detected from X-ray diffraction and electron micro probe based analysis. Beneath the modified surface layer a carburized zone of 60 μm width was identified which was found to consist of M 23C 6 carbides. A mathematical model based on finite difference technique was developed to predict the carburization profiles in sodium exposed austenitic stainless steel. In the computation, effect of only chromium on carbon diffusion was considered. Amount of carbon remaining in solution was determined from the solubility parameter. The predicted profile showed a reasonably good match with the experimental profile. Calculations were extended to simulate the thickness of the carburized layer after exposure to sodium for a period of 40 years. Attempt was also made to predict the carburization profiles based on equilibrium calculations using Dictra and Thermocalc which contain both thermodynamic and kinetic databases for the system under consideration.

  4. Carburization behavior of AISI 316LN austenitic stainless steel - Experimental studies and modeling

    Sudha, C. [Physical Metallurgy Division, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, Tamilnadu (India); Sivai Bharasi, N. [Corrosion Science and Technology Division, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, Tamilnadu (India); Anand, R. [Physical Metallurgy Division, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, Tamilnadu (India); Shaikh, H., E-mail: hasan@igcar.gov.i [Corrosion Science and Technology Division, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, Tamilnadu (India); Dayal, R.K. [Corrosion Science and Technology Division, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, Tamilnadu (India); Vijayalakshmi, M. [Physical Metallurgy Division, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, Tamilnadu (India)

    2010-07-31

    AISI type 316LN austenitic stainless steel was exposed to flowing sodium at 798 K for 16,000 h in the bi-metallic (BIM) sodium loop. A modified surface layer of 10 {mu}m width having a ferrite structure was detected from X-ray diffraction and electron micro probe based analysis. Beneath the modified surface layer a carburized zone of 60 {mu}m width was identified which was found to consist of M{sub 23}C{sub 6} carbides. A mathematical model based on finite difference technique was developed to predict the carburization profiles in sodium exposed austenitic stainless steel. In the computation, effect of only chromium on carbon diffusion was considered. Amount of carbon remaining in solution was determined from the solubility parameter. The predicted profile showed a reasonably good match with the experimental profile. Calculations were extended to simulate the thickness of the carburized layer after exposure to sodium for a period of 40 years. Attempt was also made to predict the carburization profiles based on equilibrium calculations using Dictra and Thermocalc which contain both thermodynamic and kinetic databases for the system under consideration.

  5. The Mechanical and material properties of 316LN austenitic stainless steel for the fusion application in cryogenic temperatures

    Sas, J.; Weiss, K.-P.; Jung, A.

    2015-12-01

    Due to the constant increase of claims for all materials used in superconducting magnets in "magnetic fusion reactors", the article deals with the possibilities of increasing the mechanical properties of austenitic stainless steel tested at cryogenic conditions that ensure the transport of Helium to magnets. The aim of the experimental plan was to increase the mechanical properties of the steel grade 316LN tested at 4.2K from the original value Steel A: YS = 1045 MPa, UTS = 1528 MPa, A = 33% to the value of YS = 1204 MPa,UTS = 1642 MPa, A = 34% and Steel B: YS = 1173 MPa, UTS = 1541 MPa, A = 28% to the value of YS = 1351 MPa, UTS = 1645 MPa, A = 17%. The increase in mechanical properties of the steel grade under examination has been made by means of heat processing in the conditions of annealing: Th1 = 625 ° C / th1 = 696 h. The mechanical properties of steel were evaluated using static tension tests at 4,2 K. The samples were placed in a cryostat filled with liquid helium. Except for the mechanical properties, there were also evaluated structural changes depending on the conditions of heat processing by light optical microscopy and EBSD (Electron Backscatter Diffraction). The increase of steel properties used in low temperatures was achieved by heat processing.

  6. Effect of oxidation behavior on the corrosion fatigue crack initiation and propagation of 316LN austenitic stainless steel in high temperature water

    The effect of oxidation behavior on the corrosion fatigue crack initiation and propagation of 316LN austenitic stainless steel (SS) in 320 °C water and air environments was investigated by corrosion fatigue cracking test system, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and nanoindentation. The experimental results indicated that the cracks were found to be initiated at first 20% of fatigue life of the specimens tested in 320 °C water, while only a few cracks were found until fracture when tested in 320 °C air. The crack propagation rates of the specimens tested in 320 °C water were obviously faster than those tested in 320 °C air especially at lower strain amplitude of ±0.5%. This can be attributed to the oxidation behavior of the 316LN SS specimens tested in 320 °C water was more serious than those tested in 320 °C air. The compositions were more complex of the oxide films formed in 320 °C water than those tested in 320 °C air, which lead to crack initiation easier in the former. Moreover, the 320 °C water made the mechanical properties of the oxide films worse, resulting in a faster fatigue crack propagation rate at crack tip

  7. Effect of oxidation behavior on the corrosion fatigue crack initiation and propagation of 316LN austenitic stainless steel in high temperature water

    Wu, H.C. [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Yang, B., E-mail: byang@ustb.edu.cn [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Collaborative Innovation Center of Universal Iron & Steel Technology, Beijing 100083 (China); Wang, S.L.; Zhang, M.X. [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China)

    2015-05-01

    The effect of oxidation behavior on the corrosion fatigue crack initiation and propagation of 316LN austenitic stainless steel (SS) in 320 °C water and air environments was investigated by corrosion fatigue cracking test system, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and nanoindentation. The experimental results indicated that the cracks were found to be initiated at first 20% of fatigue life of the specimens tested in 320 °C water, while only a few cracks were found until fracture when tested in 320 °C air. The crack propagation rates of the specimens tested in 320 °C water were obviously faster than those tested in 320 °C air especially at lower strain amplitude of ±0.5%. This can be attributed to the oxidation behavior of the 316LN SS specimens tested in 320 °C water was more serious than those tested in 320 °C air. The compositions were more complex of the oxide films formed in 320 °C water than those tested in 320 °C air, which lead to crack initiation easier in the former. Moreover, the 320 °C water made the mechanical properties of the oxide films worse, resulting in a faster fatigue crack propagation rate at crack tip.

  8. Dynamic Recrystallization and Hot Workability of 316LN Stainless Steel

    Chaoyang Sun

    2016-07-01

    Full Text Available To identify the optimal deformation parameters for 316LN austenitic stainless steel, it is necessary to study the macroscopic deformation and the microstructural evolution behavior simultaneously in order to ascertain the relationship between the two. Isothermal uniaxial compression tests of 316LN were conducted over the temperature range of 950–1150 °C and for the strain rate range of 0.001–10 s−1 using a Gleeble-1500 thermal-mechanical simulator. The microstructural evolution during deformation processes was investigated by studying the constitutive law and dynamic recrystallization behaviors. Dynamic recrystallization volume fraction was introduced to reveal the power dissipation during the microstructural evolution. Processing maps were developed based on the effects of various temperatures, strain rates, and strains, which suggests that power dissipation efficiency increases gradually with increasing temperature and decreasing stain rate. Optimum regimes for the hot deformation of 316LN stainless steel were revealed on conventional hot processing maps and verified effectively through the examination of the microstructure. In addition, the regimes for defects of the product were also interpreted on the conventional hot processing maps. The developed power dissipation efficiency maps allow optimized processing routes to be selected, thus enabling industry producers to effectively control forming variables to enhance practical production process efficiency.

  9. Understanding and modelling of the aniso-thermal cyclic mechanical behaviour of the AISI 316LN austenitic stainless steel

    The main subject of this report consists in proposing a mechanical model of the viscoplastic behaviour of an austenitic stainless steel under isothermal and aniso-thermal low cycle fatigue loadings at high temperatures (550-900 K). In this domain, numerous phenomena linked to dynamic strain ageing (DSA) and to dipolar dislocation structure formation may appear. Isothermal and aniso-thermal low cycle fatigue tension-compression tests were performed in order to verify some aspects about the effect of temperature on the mechanical behaviour. The study of the hysteresis loops and the observation of dislocation structures carried on transmission electron microscopy establish two different DSA mechanisms during isothermal tests. The effect of temperature history is shown for for particular temperature sequences. It is demonstrated that the stress amplitude increase when the sample is submitted to cycles at 'high temperature' is linked to the second mechanism of DSA. It comes from the increase of short range interaction between dislocations (chromium segregation), but it is also the consequence of the lack of dipolar structure annihilation at low temperature. From the experimental analysis of DSA mechanisms and dipolar restoration, a macroscopic aniso-thermal model is developed using physical internal variables (densities of dislocations). The equations of a polycrystalline model are rewritten with the aim of getting a simple multi-scale approach which can be used on finite elements analysis software. Between 550 and 873 K, the simulation results are in good accordance with the macroscopic and microscopic observations of low cycle fatigue, relaxation, and 2D-ratchetting tests. (author)

  10. TRIBOLOGICAL BEHAVIORS OF PLASMA NITRIDED AISI 316 LN TYPE STAINLESS STEEL IN AIR AND HIGH VACUUM ATMOSPHERE AT ROOM TEMPERATURE

    A.DEVARAJU

    2010-09-01

    Full Text Available In this work, tribological behaviors of the plasma nitrided AISI 316 LN type austenitic stainless steel specimens (both pins and rings have been analyzed. The experiments have been conducted in high vacuum and in air atmosphere using Vacuum based high temperature Pin-on-disc tribometer. The tribological parameters such as friction coefficient and wear resistance have been analyzed by Origin graphs. The wear mechanisms involved have been identified by recording surface morphology on the wear track and pin surface through scanning electron microscope (SEM and Optical profilometer. The self mating of AISI 316 LN type stainless steel (316LN exhibits strong adhesion between the contact surfaces and severe surface damage both in air and in vacuum atmosphere. But, the self mating of Plasma Nitrided 316LN (CrN/CrN reveals mild wear till the CrN coating peeled off from the pin surface. It has also been proved that Plasma Nitrided (CrN layer on 316 LN ring was wear resistant layer when it issliding against the untreated 316 LN pin in air and high vacuum atmosphere.

  11. Nitrogen segregation and blister formation of 316LN austenitic steels during electron beam welding

    Full text of publication follows: High nitrogen austenitic stainless steel (316LN) has been selected as the structure material in shield blanket and the gravity support system in ITER due to its excellent erosion/corrosion resistance, high strength and toughness. However, most of nitrogen in this steel exists in the form of solid solution. The nitrogen can segregate from the matrix material and form small blisters or defects in the welding area, resulting in mechanical property reduction, which should be considered in the design and manufacture processing. In this study, we have investigated the blister and defect formation processing during electron beam welding. Focused electron beam with 100-150 kV high voltage, 300-500 mA beam current has been applied to weld the 316LN austenitic stainless steel components under vacuum condition. The blister formation in the welding area has been observed by both SEM and TEM directly, and was further confirmed by the micro-area composition analysis. The size and density distribution of blisters and defects with the welding depth, the vacuum condition and electron beam parameters has been investigated. At the same time, the tensile strength of the welded components was examined and compared with that of the matrix material. In this report, the mechanism of nitrogen blisters formation and its effects on the mechanical property of the welding components has also been discussed. (authors)

  12. Helium and hydrogen induced hardening in 316LN stainless steel

    Hunn, J. D.; Lee, E. H.; Byun, T. S.; Mansur, L. K.

    2000-12-01

    In certain radiation environments, such as the spallation neutron source (SNS) presently in design and construction, the high transmutation production rate for helium and hydrogen, concomitant with displacement damage, may affect the mechanical properties of structural materials. To better understand this effect, we have studied type 316LN stainless steel specimens implanted with medium energy Fe-, He-, and H-ions, alone and in combination. In this report, we present nanoindentation measurements of the incremental increase in hardness caused by 360 keV He-ions implanted at 200°C to concentrations from 2 to 200 000 appm. The He-induced hardening was found to saturate at twice the level measured for Fe-induced displacement damage alone. The additional hardening at high helium concentrations was associated with the presence of helium filled cavities (bubbles), observed by transmission electron microscopy (TEM). We also found that co-injection of helium and hydrogen resulted in more hardening than was observed for He-implantation alone.

  13. Helium and hydrogen induced hardening in 316LN stainless steel

    In certain radiation environments, such as the spallation neutron source (SNS) presently in design and construction, the high transmutation production rate for helium and hydrogen, concomitant with displacement damage, may affect the mechanical properties of structural materials. To better understand this effect, we have studied type 316LN stainless steel specimens implanted with medium energy Fe-, He-, and H-ions, alone and in combination. In this report, we present nanoindentation measurements of the incremental increase in hardness caused by 360 keV He-ions implanted at 200 deg. C to concentrations from 2 to 200,000 appm. The He-induced hardening was found to saturate at twice the level measured for Fe-induced displacement damage alone. The additional hardening at high helium concentrations was associated with the presence of helium filled cavities (bubbles), observed by transmission electron microscopy (TEM). We also found that co-injection of helium and hydrogen resulted in more hardening than was observed for He-implantation alone

  14. Generation of Constant Life Diagram under Elevated Temperature Ratcheting of 316LN Stainless Steel

    Sarkar, Aritra; Nagesha, A.; Sandhya, R.; Mathew, M. D.

    2016-04-01

    Combined influence of mean stress and stress amplitude on the cyclic life under elevated temperature (823-923 K) ratcheting of 316LN austenitic stainless steel is discussed. Constant life Haigh diagrams have been generated, using different combinations of stress amplitude and mean stress. In the plastic domain, the allowable stress was found to increase or decrease with mean stress depending on the temperature and combination of mean stress - stress amplitude employed. Strong influence of dynamic strain aging (DSA) was found at 823 K which affected the mode of deformation of the material in comparison with 923 K. Failure mode expressed through a fracture mechanism map was found to change from fatigue to necking depending on the test temperature as well as combinations of mean stress and stress amplitude. Occurrence of DSA at 823 K proved to be beneficial by way of extending the safe zone of operation to higher R-ratios in comparison with 923 K.

  15. Numerical approach of cyclic behaviour of 316LN stainless steel based on a polycrystal modelling including strain gradients

    A non-local polycrystal approach, taking into account strain gradients, is proposed to simulate the 316LN stainless steel fatigue life curve in the hardening stage. Material parameters identification is performed on tensile curves corresponding to several 316LN polycrystals presenting different grain sizes. Applied to an actual 3D aggregate of 316LN stainless steel of 1200 grains, this model leads to an accurate prediction of cyclic curves. Geometrical Necessary Dislocation densities related to the computed strain gradient are added to the micro-plasticity laws. Compared to standard models, this model predicts a decrease of the local stresses as well as a grain size effect. (authors)

  16. A study on low magnetic permeability gas tungsten arc weldment of AISI 316LN stainless steel for application in electron accelerator

    Highlights: • AISI 316LN is a suitable material for vacuum chamber of Injector Microtron. • Formed component need not be annealed to obtain low magnetic permeability. • GTAW with high Mn filler produced a crack-free non-magnetic weld. • The weld exhibited acceptable mechanical properties. • Results are also important for future indigenous accelerators. - Abstract: Low magnetic permeability is an important criterion in selection of the material of construction of beam pipes and vacuum chambers of electron accelerators for safeguarding against distortion of the magnetic field. In the modified design of new 20 MeV/30 mA Injector Microtron for the existing synchrotron radiation sources Indus-1 and Indus-2, AISI 316 LN stainless steel has been identified as the material of construction of its vacuum chamber. Welding of AISI 316LN stainless steel with conventional filler alloys like ER316L and ER317L of AWS A5.9 produces duplex weld metal with 3–8% ferro-magnetic delta ferrite to avoid solidification cracking. The results of the study has demonstrated that GTAW of AISI 316LN SS with high Mn adaptation of W 18 16 5 N L filler produced a crack free non-magnetic weld with acceptable mechanical properties. Moreover, AISI 316LN stainless steel is not required to be solution annealed after the final forming operation for obtaining a low magnetic permeability, thereby avoiding solution annealing of large vacuum chamber in vacuum/controlled atmosphere furnace and associated problems of distortion. Besides Injector Microtron, the study also provides useful input for design of future indigenous accelerators with vacuum chambers of austenitic stainless steel

  17. Evaluation of Cavitation-Erosion Resistance of 316LN Stainless Steel in Mercury Containing Metallic Solutes

    Pawel, Steven J [ORNL; Mansur, Louis K [ORNL

    2006-08-01

    Room temperature cavitation tests of vacuum annealed type 316LN stainless steel were performed in pure Hg and in Hg with various amounts of metallic solute to evaluate potential mitigation of erosion/wastage. Tests were performed using an ultrasonic vibratory horn with specimens attached at the tip. All of the solutes examined, which included 5 wt% In, 10 wt% In, 4.4 wt% Cd, 2 wt% Ga, and a mixture that included 1 wt% each of Pb, Sn, and Zn, were found to increase cavitation-erosion as measured by increased weight loss and/or surface profile development compared to exposures for the same conditions in pure Hg. Qualitatively, each solute appeared to increase the post-test wetting tenacity of the Hg solutions and render the Hg mixture susceptible to manipulation of droplet shape.

  18. Influence of Heat Treatment on Mercury Cavitation Resistance of Surface Hardened 316LN Stainless Steel

    Pawel, Steven J [ORNL; Hsu, Julia [Massachusetts Institute of Technology (MIT)

    2010-11-01

    The cavitation-erosion resistance of carburized 316LN stainless steel was significantly degraded but not destroyed by heat treatment in the temperature range 500-800 C. The heat treatments caused rejection of some carbon from the carburized layer into an amorphous film that formed on each specimen surface. Further, the heat treatments encouraged carbide precipitation and reduced hardness within the carburized layer, but the overall change did not reduce surface hardness fully to the level of untreated material. Heat treatments as short as 10 min at 650 C substantially reduced cavitation-erosion resistance in mercury, while heat treatments at 500 and 800 C were found to be somewhat less detrimental. Overall, the results suggest that modest thermal excursions perhaps the result of a weld made at some distance to the carburized material or a brief stress relief treatment will not render the hardened layer completely ineffective but should be avoided to the greatest extent possible.

  19. Fatigue properties of type 316LN stainless steel in air and mercury

    An extensive fatigue testing program on 316LN stainless steel was recently carried out to support the design of the mercury target container for the spallation neutron source (SNS) that is currently under construction at the Oak Ridge National Laboratory in the United States. The major objective was to determine the effects of mercury on fatigue behavior. The S-N fatigue behavior of 316LN stainless steel is characterized by a family of bilinear fatigue curves which are dependent on frequency, environment, mean stress and cold work. Generally, fatigue life increases with decreasing stress and levels off in the high cycle region to an endurance limit below which the material will not fail. For fully reversed loading as well as tensile mean stress loading conditions mercury had no effect on endurance limit. However, at higher stresses a synergistic relationship between mercury and cyclic loading frequency was observed at low frequencies. As expected, fatigue life decreased with decreasing frequency, but the response was more pronounced in mercury compared with air. As a result of liquid metal embrittlement (LME), fracture surfaces of specimens tested in mercury showed widespread brittle intergranular cracking as opposed to typical transgranular cracking for specimens tested in air. For fully reversed loading (zero mean stress) the effect of mercury disappeared as frequency increased to 10 Hz. For mean stress conditions with R-ratios of 0.1 and 0.3, LME was still evident at 10 Hz, but at 700 Hz the effect of mercury had disappeared (R 0.1). Further, for higher R-ratios (0.5 and 0.75) fatigue curves for 10 Hz showed no environmental effect. Finally, cold working (20%) increased tensile strength and hardness, and improved fatigue resistance. Fatigue behavior at 10 and 700 Hz was similar and no environmental effect was observed

  20. Study of magnetism in Ni-Cr hardface alloy deposit on 316LN stainless steel using magnetic force microscopy

    Kishore, G. V. K.; Kumar, Anish; Chakraborty, Gopa; Albert, S. K.; Rao, B. Purna Chandra; Bhaduri, A. K.; Jayakumar, T.

    2015-07-01

    Nickel base Ni-Cr alloy variants are extensively used for hardfacing of austenitic stainless steel components in sodium cooled fast reactors (SFRs) to avoid self-welding and galling. Considerable difference in the compositions and melting points of the substrate and the Ni-Cr alloy results in significant dilution of the hardface deposit from the substrate. Even though, both the deposit and the substrate are non-magnetic, the diluted region exhibits ferromagnetic behavior. The present paper reports a systematic study carried out on the variations in microstructures and magnetic behavior of American Welding Society (AWS) Ni Cr-C deposited layers on 316 LN austenitic stainless steels, using atomic force microscopy (AFM) and magnetic force microscopy (MFM). The phase variations of the oscillations of a Co-Cr alloy coated magnetic field sensitive cantilever is used to quantitatively study the magnetic strength of the evolved microstructure in the diluted region as a function of the distance from the deposit/substrate interface, with the spatial resolution of about 100 nm. The acquired AFM/MFM images and the magnetic property profiles have been correlated with the variations in the chemical compositions in the diluted layers obtained by the energy dispersive spectroscopy (EDS). The study indicates that both the volume fraction of the ferromagnetic phase and its ferromagnetic strength decrease with increasing distance from the deposit/substrate interface. A distinct difference is observed in the ferromagnetic strength in the first few layers and the ferromagnetism is observed only near to the precipitates in the fifth layer. The study provides a better insight of the evolution of ferromagnetism in the diluted layers of Ni-Cr alloy deposits on stainless steel.

  1. Thick-section weldments in 21-6-9 and 316LN stainless steel for fusion energy applications

    The Burning Plasma Experiment (BPX), formerly known as the Compact Ignition Tokomak, will be a major advance in the design of a fusion reactor. The successful construction of fusion reactors will require extensive welding of thick-section stainless steel plates. Severe service conditions will be experienced by the structure. Operating temperatures will range from room temperature (300 K) to liquid nitrogen temperature (77 K), and perhaps even lower. The structure will be highly stressed, and subject to sudden impact loads if plasma disruptions occur. This demands a combination of high strength and high toughness from the weldments. Significant portions of the welding will be done in the field, so preweld and postweld heat treatments will be difficult. The thick sections to be welded will require a high deposition rate process, and will result in significant residual stresses in the materials. Inspection of these thick sections in complex geometries will be very difficult. All of these constraints make it essential that the welding procedures and alloys be well understood, and the mechanical properties of the welds and their heat-affected zones must be adequately characterized. The candidate alloy for structural applications in the BPX such as the magnet cases was initially selected as 21-6-9 austenitic stainless steel, and later changed to 316LN stainless steel. This study examined several possible filler materials for thick-section (25 to 50 mm) weldments in these two materials. The tensile and Charpy V-notch properties were measured at room temperature and 77 K. The fracture toughness was measured for promising materials

  2. Study of magnetism in Ni–Cr hardface alloy deposit on 316LN stainless steel using magnetic force microscopy

    Nickel base Ni–Cr alloy variants are extensively used for hardfacing of austenitic stainless steel components in sodium cooled fast reactors (SFRs) to avoid self-welding and galling. Considerable difference in the compositions and melting points of the substrate and the Ni–Cr alloy results in significant dilution of the hardface deposit from the substrate. Even though, both the deposit and the substrate are non-magnetic, the diluted region exhibits ferromagnetic behavior. The present paper reports a systematic study carried out on the variations in microstructures and magnetic behavior of American Welding Society (AWS) Ni Cr–C deposited layers on 316 LN austenitic stainless steels, using atomic force microscopy (AFM) and magnetic force microscopy (MFM). The phase variations of the oscillations of a Co–Cr alloy coated magnetic field sensitive cantilever is used to quantitatively study the magnetic strength of the evolved microstructure in the diluted region as a function of the distance from the deposit/substrate interface, with the spatial resolution of about 100 nm. The acquired AFM/MFM images and the magnetic property profiles have been correlated with the variations in the chemical compositions in the diluted layers obtained by the energy dispersive spectroscopy (EDS). The study indicates that both the volume fraction of the ferromagnetic phase and its ferromagnetic strength decrease with increasing distance from the deposit/substrate interface. A distinct difference is observed in the ferromagnetic strength in the first few layers and the ferromagnetism is observed only near to the precipitates in the fifth layer. The study provides a better insight of the evolution of ferromagnetism in the diluted layers of Ni–Cr alloy deposits on stainless steel. - Highlights: • Study of evolution of ferromagnetism in Comonoy-6 deposit on austenitic steel. • Magnetic force microscopy (MFM) exhibited ferromagnetic matrix in first two layers. • The maximum MFM

  3. Thick-section weldments in 21-6-9 and 316LN stainless steel for fusion energy applications

    The mechanical properties of several weldments in 21-6-9 and 316LN stainless steel metals have been measured at 77 K and room temperature. Filler metals for the 211-6-9 included Nitronic 35W and 40W, 21-6-9, Inconel 82, 182, 625, and 625 PLUS. For the 316LN base metal, 316L, 316L-T3, 316L-4K-O, and Inconel 82 filler metals were used. At room temperature all of the filler metals had yield strengths that exceeded those of the base metals. At 77K only the Nitronics and the 21-6-9 filler metals exceeded those of the base metals, and the Inconel filler metals were significantly weaker. The impact properties of the weld metals were very good at room temperature, with the exception of Inconel 625. At 77 K the impact toughness was greatly reduced for all of the filler metals, with the dramatic exception of Inconel 82. The 316L-4K-O filler metal showed higher impact energies than the other ferrite-containing filler metals, although the levels were still much lower than for the Inconel filler metals. The Inconel 82 filler had excellent fracture toughness at both temperatures

  4. Effect of flowing sodium on corrosion and tensile properties of AISI type 316LN stainless steel at 823 K

    AISI type 316LN stainless steel was exposed to flowing sodium in mass transfer loop (MTL) at 823 K for 16 000 h and then examined for changes in the tensile properties due to the mass transfer and corrosion effects. Comparisons in microstructural and mechanical properties were made between annealed, thermally aged and sodium exposed materials. Microstructural examination of thermally aged and sodium exposed materials revealed precipitation of carbides at the grain boundaries. The sodium exposed samples contained a degraded layer at the surface up to a depth of around 10 μm and a surface carburized layer of about 30 μm. There was about 15% increase in yield strength and a decrease of about 20% in ductility for the sodium exposed material vis-a-vis thermally aged material and this was attributed to carburization effects and microstructural changes

  5. Assessment of Cavitation-Erosion Resistance of 316LN Stainless Steel Following a Nitro-Carburizing Surface Treatment

    Pawel, Steven J [ORNL

    2009-11-01

    A nitro-carburizing surface treatment known domestically as the Melonite process was applied to type 316LN stainless steel test pieces and exposed to sonication conditions in mercury using a vibratory horn technique. Cavitation-erosion damage was evaluated for extended exposures and compared to other surface treatments on the same substrate alloy. The results indicate that the Melonite process substantially retards weight loss and crater development for extended periods, but gradually is eroded/destroyed leading to exposure of the substrate and cavitation-erosion behavior similar to untreated specimens. Compared with other surface treatments, cavitation-erosion results indicate that specimens treated with Melonite perform similarly to specimens treated with a simple nitriding process. Neither the simple nitriding nor the Melonite treatment is quite as effective as a previously evaluated low temperature carburizing treatment, the latter being about a factor of three better than Melonite in terms of weight loss during sonication in mercury.

  6. Non local approach in crystalline plasticity: study of mechanical behaviour of AISI 316LN stainless steel during low cycle fatigue

    If fatigue crack initiation is currently quite well understood for pure single crystals, its comprehension and prediction in cases of polycrystal alloys such as AISI 316LN stainless steel remain complicated. Experimentally our study focuses on the characterisation of the mechanical behaviour and on the study at different scales of the phenomenon leading to low cycle fatigue crack initiation in 316LN stainless steel. For straining amplitudes of?e/2 = 0,3 and 0,5%, the cyclic softening observed during testing has been related to the organisation of dislocations in band structures. These bands, formed due to the activation of slip systems having the greatest Schmid's factor, carry the most part of the deformation. Their emergence at free surfaces leads to the formation of intrusions and extrusions which help cracks initiate and spread. Numerically we worked on the mesoscopic scale, proposing a new model of crystalline plasticity. This model integrates geometrically necessary dislocations (GND) directly computed from the lattice curvature. Implemented in the finite element code AbaqusTM and Cast3mTM, it is based on single crystal finite deformations laws proposed by Peirce et al. (1983) and Teodosiu et al. (1993). Extended for polycrystals by Hoc (2001) and Erieau (2003), it has been improved by the introduction of GND (Acharya and Bassani, 2000). The simulations performed on different types of aggregates (2D/3D) have shown that taking GND into account enables:- the prediction of the grain size effect on a macroscopic and on a local scale,- a finer computation of local stress field.The influence of the elasticity and interaction matrices on the values and the evolution of the isotropic and kinematic mean stresses has been shown. The importance of boundary conditions on computed mechanical fields could also be pointed out. (author)

  7. Detection of crevice corrosion in AISI type 316LN stainless steel in presence of pseudomonas bacteria using electrochemical noise technique

    Gram-negative pseudomonas sp. was used as the test organism for the biofilm formation and growth on 316 LN stainless and electrochemical noise (EN) monitoring studies, since this genus has been identified as the major biofilm former on stainless steels. EN studies were conducted for 21 days on the galvanically coupled specimens exposed to the dilute nutrient culture with pseudomonas sp. The visual records of the current potential EN, analysis of statistical and power spectral density (PSD) parameters of current and potential along with shot-noise parameters showed increase in the localized corrosion during initial 2-11 days exposure; thereafter the specimens showed passive behaviour. Raman spectra taken inside the pit for the specimen exposed for 21 days showed the peak corresponding to Cr3+ ions signifying repassivation process. Similarly, Raman spectra on the surface outside the pits on the specimens exposed for 7, 10 and 15 days showed steady growth of the peak corresponding to Cr3+ ions. This implied steady enrichment of Cr on the surface of the specimen which accounted for the gradual passivation with increased exposure time. (author)

  8. Nitrogen segregation and blister formation of 316LN austenitic steel during electron beam welding tests for ITER gravity supports

    316LN has been widely applied in the design of ITER components, such as shield blanket and gravity supports, due to its excellent corrosion resistance and high strength. The behavior of nitrogen in this steel during welding is important for the mechanical properties of the components. In this study, a focused 150 kv high voltage electron beam with 300 mA beam current has been used to weld 316LN steel under vacuum condition. The microstructure and composition of the welding area were observed and analyzed. The influence of welding on the shock resistance and tensile strength at both room temperature and low temperature were examined. It was found that the mechanical properties are strongly related to the defects formed in the welding process.

  9. Corrosion Behavior of 316LN and 316 Stainless Steels During Long-term Exposure to Aerated 0.5 M NaCl Using Electrochemical Noise Technique

    Pujar, M. G.; Parvathavarthini, N.; Jena, Sidhartha S.; Tata, B. V. R.; Dayal, R. K.; Khatak, H. S.

    2008-12-01

    In the present work 316LN as well as 316 stainless steel (SS) coupons each of dimensions (0.025 × 0.018 × 0.006 m3) in well-polished condition were used as two nominal electrodes which were immersed in the aerated solution of 0.5 M NaCl. Correlated current and potential electrochemical noise (EN) signals were collected at 1 Hz sampling frequency for 1 h daily over a period of 30 days. The detrended EN data were used to calculate the noise resistance ( R N) as well as the spectral noise resistance at zero frequency ( R {SN/o}) values and other statistical parameters. To study the nature of pits and distribution of their diameters as well as depths, extensive observations of the pitted and the blank specimens were carried out using Confocal Laser Scanning Microscopy (CLSM). The current and the potential records of the two alloys showed distinct differences in their corrosion behavior. It was observed that within less than 4 h of immersion, 316SS showed signals indicative of unstable pitting and onset of stable pitting was noticed after 48 h of exposure. However, until about 24 h, 316LN showed just the random signals and unstable pitting was observed after 28 h. The signals clearly indicated continuous growth of the stable pits in 316SS as against the repassivation of the unstable pits in 316LN after 7 days exposure. It was observed that R N values showed a continuous decrease in the case of 316SS, but were quite stable in the case of 316LN over the exposure period. Concurrent to these observations it was observed that 316SS specimen was extensively pitted. The frequency distributions of pit diameters as well pit depths were observed to be highest at 10-20 μm and 5-10 μm, respectively. However, pits with as large as 70-80 μm diameter and as deep as 20-25 μm too were observed. No pits were observed in case of 316LN even after 30 days of exposure, an observation that corroborates well with the stable R N values. Thus, in the present investigation, the long

  10. Study on the weld characteristics of 316LN by magnetization measurement

    Full text of publication follows: For the structural material of superconductor magnet system in fusion reactors, austenitic stainless steel is extensively used due to its high mechanical strength at low temperature. 316LN, one of the austenitic steels, is considered to be used for ITER TF magnet structure and TF conductor conduit material. Although the crystal structure of 316LN is FCC at ambient temperature, it tends to undergo a structural transformation into BCC metal during cooling from higher temperature above 900 deg. C. Because BCC metals show brittle behaviour at low temperature due to the ductile-to-brittle transition, the welding technique of 316LN steel to prevent the BCC metal formation and the relevant characterization of the welded joint are required. In this work, we studied the characteristics of 316LN welded joints produced by different welding conditions. Since the ferritic or martensitic phase that could be formed in welding has higher magnetic susceptibility, quantitative comparison on the formation of secondary phases can be made by magnetization measurement. We present our results of magnetization measurement of 316LN welded joints in the temperature range from 300 K down to 4 K and in magnetic field up to 1 T. The effect of using high Mn-content welding wire on the weld property is discussed based on the result. (authors)

  11. ITERTF导体铠甲316LN不锈钢管的力学性能%Mechanical Properties of 316LN Stainless Steel Tube for ITER TF Jacket

    金环; 武玉; 刘华军; 韩奇阳

    2012-01-01

    Based on the ITER TF 316LN austenitic stainless steel tubes, the influence of welding, 8% cold working and 200 h aging at 650℃ on the 316LN austenitic stainless steel tubes were investigated. The test samples were sampled from the base metal, the welded tube and the welded tube with the treatment of cold working and aging. Their tensile and impact properties were tested at room temperature and 4.2 K, and the tensile and impact fracture surfaces were observed by scanning electron microscopy morphology (SEM). The results show that the elongation and impact toughness decrease in turn of the base metal, the welded joint and the welded joint with the treatment of cold working and aging, the yield strength of the welded joint after deformation and aging treatment are higher than the welded joint without any treatment and the base metal about 50--60 MPa. The base metal's elongation after failure at 4.2 K decreases to 44% from 48% at room temperature, on the contrary, the elongation after failure of the welded joint and the welded joint with the treatment of cold working and aging increase to 41% and 38% from 37% and 23%, respectively. Three kinds of test samples' strength are all high at 4.2K, and the ultimate tensile strength and 0.2% off-set yield strength are two to three times higher than at room temperature.%以ITERTF316LN奥氏体不锈钢无缝管为研究对象,研究了焊接、8%冷变形和650℃、200h的老化处理对316LN不锈钢管性能的影响。分别取母材、焊接接头、经过冷变形和老化处理的焊接接头进行了室温和液氦温度4.2K下的拉伸和冲击性能的研究,并利用扫描电镜对拉伸和冲击断口的微观形貌进行了观察。结果表明,母材、焊接接头和经过冷变形和老化处理的焊接接头在4.2K的断后伸长率和冲击韧性依次降低,经过冷变形和老化处理的焊接接头相比母材和未经过任何处理的焊接接头的抗拉强

  12. Creep Deformation and Rupture Behavior of Single- and Dual-Pass 316LN Stainless-Steel-Activated TIG Weld Joints

    Vijayanand, V. D.; Vasudevan, M.; Ganesan, V.; Parameswaran, P.; Laha, K.; Bhaduri, A. K.

    2016-06-01

    Creep deformation and rupture behavior of single-pass and dual-pass 316LN stainless steel (SS) weld joints fabricated by an autogenous activated tungsten inert gas welding process have been assessed by performing metallography, hardness, and conventional and impression creep tests. The fusion zone of the single-pass joint consisted of columnar zones adjacent to base metals with a central equiaxed zone, which have been modified extensively by the thermal cycle of the second pass in the dual-pass joint. The equiaxed zone in the single-pass joint, as well as in the second pass of the dual-pass joint, displayed the lowest hardness in the joints. In the dual-pass joint, the equiaxed zone of the first pass had hardness comparable to the columnar zone. The hardness variations in the joints influenced the creep deformation. The equiaxed and columnar zone in the first pass of the dual-pass joint was more creep resistant than that of the second pass. Both joints possessed lower creep rupture life than the base metal. However, the creep rupture life of the dual-pass joint was about twofolds more than that of the single-pass joint. Creep failure in the single-pass joint occurred in the central equiaxed fusion zone, whereas creep cavitation that originated in the second pass was blocked at the weld pass interface. The additional interface and strength variation between two passes in the dual-pass joint provides more restraint to creep deformation and crack propagation in the fusion zone, resulting in an increase in the creep rupture life of the dual-pass joint over the single-pass joint. Furthermore, the differences in content, morphology, and distribution of delta ferrite in the fusion zone of the joints favors more creep cavitation resistance in the dual-pass joint over the single-pass joint with the enhancement of creep rupture life.

  13. Creep Deformation and Rupture Behavior of Single- and Dual-Pass 316LN Stainless-Steel-Activated TIG Weld Joints

    Vijayanand, V. D.; Vasudevan, M.; Ganesan, V.; Parameswaran, P.; Laha, K.; Bhaduri, A. K.

    2016-03-01

    Creep deformation and rupture behavior of single-pass and dual-pass 316LN stainless steel (SS) weld joints fabricated by an autogenous activated tungsten inert gas welding process have been assessed by performing metallography, hardness, and conventional and impression creep tests. The fusion zone of the single-pass joint consisted of columnar zones adjacent to base metals with a central equiaxed zone, which have been modified extensively by the thermal cycle of the second pass in the dual-pass joint. The equiaxed zone in the single-pass joint, as well as in the second pass of the dual-pass joint, displayed the lowest hardness in the joints. In the dual-pass joint, the equiaxed zone of the first pass had hardness comparable to the columnar zone. The hardness variations in the joints influenced the creep deformation. The equiaxed and columnar zone in the first pass of the dual-pass joint was more creep resistant than that of the second pass. Both joints possessed lower creep rupture life than the base metal. However, the creep rupture life of the dual-pass joint was about twofolds more than that of the single-pass joint. Creep failure in the single-pass joint occurred in the central equiaxed fusion zone, whereas creep cavitation that originated in the second pass was blocked at the weld pass interface. The additional interface and strength variation between two passes in the dual-pass joint provides more restraint to creep deformation and crack propagation in the fusion zone, resulting in an increase in the creep rupture life of the dual-pass joint over the single-pass joint. Furthermore, the differences in content, morphology, and distribution of delta ferrite in the fusion zone of the joints favors more creep cavitation resistance in the dual-pass joint over the single-pass joint with the enhancement of creep rupture life.

  14. The effects of dissolved hydrogen contents on the low cycle fatigue behaviors of a 316LN stainless steel in simulated PWR conditions

    The effects of dissolved hydrogen on the low cycle fatigue behaviors of a 316LN stainless steel in pressurized water reactor environments were investigated. Round bar-type specimens were tested at 310°C in a deoxygenated water, and simulated pressurized water reactor water chemistry with normal and high dissolved hydrogen contents. The test results showed that the fatigue life of 316LN stainless steel was slightly improved with increasing DH level, showing larger increase at large strain amplitude. However, the fatigue surface and crack morphology showed no significant differences due to different hydrogen contents. To understand the role of dissolved hydrogen during low cycle fatigue tests, hydrogen contents of tested bulk specimen and near the crack tip was measured, but the results showed no significant differences. It is thought that bulk dissolved hydrogen level have little effect on hydrogen absorption into stainless steel due to barrier role of oxide film. To clearly understand the effect of dissolved hydrogen on low cycle fatigue behaviors of structural materials in nuclear power plant, additional analysis about oxide film and hydrogen distribution near main crack tip should be performed. (author)

  15. Study of Magnetism in Colmonoy-6 (AWS NiCr-C) Deposit on 316LN Stainless Steel

    Chakraborty, Gopa, E-mail: gopa_mjs@igcar.gov.in [Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamilnadu (India); Ramasubbu, V., E-mail: vrsubbu@igcar.gov.in [Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamilnadu (India); Albert, S.K., E-mail: shaju@igcar.gov.in [Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamilnadu (India); Bhaduri, A.K., E-mail: bhaduri@igcar.gov.in [Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamilnadu (India); Murugesan, S., E-mail: smurug@igcar.gov.in [Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamilnadu (India); Raj, Baldev, E-mail: dir@igcar.gov.in [Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamilnadu (India)

    2010-06-15

    Considerable difference in melting points between the austenitic stainless steel (SS) substrate and Ni-base Colmonoy (AWS NiCr) hardfacing alloys results in significant dilution of the hardface deposit from the substrate. In the present study, it is found that the dilution also affects the magnetic property of the deposit. Although both austenitic SS and the undiluted Ni-base hardfacing alloy deposit are non-magnetic, the deposit diluted by austenitic SS becomes magnetic. Magnetism at different dilution levels of the deposit is measured using Magnegage and Feritscope, and the results correlated with the dilution of the deposit that is estimated from its Fe and Ni contents using SEM-EDS analysis. A good correlation between dilution and magnetic property could be obtained. As dilution also affects the hardness of the deposit, it was also possible to correlate the magnetic property of the deposit with its hardness. These findings have potential application in using magnetic measurement as a non-destructive method for estimating the hardness and/or dilution of the deposit on actual components not amenable for in-situ hardness measurements. The possible origin of magnetism in the deposit layers has been examined. The small variations in the lattice parameters of the deposit with dilution (composition) could be well correlated with variation in magnetic property.

  16. Study of Magnetism in Colmonoy-6 (AWS NiCr-C) Deposit on 316LN Stainless Steel

    Considerable difference in melting points between the austenitic stainless steel (SS) substrate and Ni-base Colmonoy (AWS NiCr) hardfacing alloys results in significant dilution of the hardface deposit from the substrate. In the present study, it is found that the dilution also affects the magnetic property of the deposit. Although both austenitic SS and the undiluted Ni-base hardfacing alloy deposit are non-magnetic, the deposit diluted by austenitic SS becomes magnetic. Magnetism at different dilution levels of the deposit is measured using Magnegage and Feritscope, and the results correlated with the dilution of the deposit that is estimated from its Fe and Ni contents using SEM-EDS analysis. A good correlation between dilution and magnetic property could be obtained. As dilution also affects the hardness of the deposit, it was also possible to correlate the magnetic property of the deposit with its hardness. These findings have potential application in using magnetic measurement as a non-destructive method for estimating the hardness and/or dilution of the deposit on actual components not amenable for in-situ hardness measurements. The possible origin of magnetism in the deposit layers has been examined. The small variations in the lattice parameters of the deposit with dilution (composition) could be well correlated with variation in magnetic property.

  17. Effects of environment and frequency on the fatigue behavior of the spallation neutron source (SNS) target container material - 316 LN stainless steel

    Tian, Hongbo

    As the candidate target container material of the new Spallation Neutron Source (SNS) being designed and constructed at the Oak Ridge National Laboratory (ORNL), Type 316 low-carbon nitrogen-added (LN) stainless steel (SS) will operate in an aggressive environment, subjected to intense fluxes of high-energy protons and neutrons while exposed to liquid mercury. The current project is oriented toward materials studies regarding the effects of test environment and frequency on the fatigue behavior of 316 LN SS. In order to study the structural applications of this material and improve the fundamental understanding of the fatigue damage mechanisms, fatigue tests were performed in air and mercury environments at various frequencies and R ratios (R = sigma min/sigmamax, sigmamin and sigmamax are the applied minimum and maximum stresses, respectively). Fatigue data were developed for the structural design and engineering applications of this material. Specifically, high-cycle fatigue tests, fatigue crack-propagation tests, and ultrahigh cycle fatigue tests up to 10 9 cycles were conducted in air and mercury with test frequencies from 10 Hz to 700 Hz. Microstructure characterizations were performed using optical microscopy (OM), scanning-electron microscopy (SEM), and transmission-electron microscopy (TEM). It was found that mercury doesn't seem to have a large impact on the crack-initiation behavior of 316 LN SS. However, the crack-propagation mechanisms in air and mercury are different in some test conditions. Transgranular cracks seem to be the main mechanism in air, and intergranular in mercury. A significant specimen self-heating effect was found during high-cycle faituge. Theoretical calculation was performed to predict temperature responses of the material subjected to cyclic deformation. The predicted cyclic temperature evolution seems to be in good agreement with the experimental results.

  18. Triple ion-beam studies of radiation damage effects in a 316LN austenitic alloy for a high power spallation neutron source

    Lee, E.H.; Rao, G.R.; Hunn, J.D.; Rice, P.M.; Lewis, M.B.; Cook, S.W.; Farrell, K.; Mansur, L.K.

    1997-09-01

    Austenitic 316LN alloy was ion-irradiated using the unique Triple Ion Beam Facility (TIF) at ORNL to investigate radiation damage effects relevant to spallation neutron sources. The TIF was used to simulate significant features of GeV proton irradiation effects in spallation neutron source target materials by producing displacement damage while simultaneously injecting helium and hydrogen at appropriately high gas/dpa ratios. Irradiations were carried out at 80, 200, and 350 C using 3.5 MeV Fe{sup ++}, 360 keV He{sup +}, and 180 keV H{sup +} to accumulate 50 dpa by Fe, 10,000 appm of He, and 50,000 appm of H. Irradiations were also carried out at 200 C in single and dual ion beam modes. The specific ion energies were chosen to maximize the damage and the gas accumulation at a depth of {approximately} 1 {micro}m. Variations in microstructure and hardness of irradiated specimens were studied using transmission electron microscopy (TEM) and a nanoindentation technique, respectively. TEM investigation yielded varying damage defect microstructures, comprising black dots, faulted and unfaulted loops, and a high number density of fine bubbles (typically less than 1 nm in diameter). With increasing temperature, faulted loops had a tendency to unfault, and bubble microstructure changed from a bimodal size distribution to a unimodal distribution. Triple ion irradiations at the three temperatures resulted in similar increases in hardness of approximately a factor of two. Individually, Fe and He ions resulted in a similar magnitude of hardness increase, whereas H ions showed only a very small effect. The present study has yielded microstructural information relevant to spallation neutron source conditions and indicates that the most important concern may be radiation induced hardening and associated ductility loss.

  19. Triple Ion-Beam Studies of Radiation Damage Effects in a 316LN Austenitic Alloy for a High Power Spallation Neutron Source

    Lee, EH

    2001-08-01

    Austenitic 316LN alloy was ion-irradiated using the unique Triple Ion Beam Facility (TIF) at ORNL to investigate radiation damage effects relevant to spallation neutron sources. The TIF was used to simulate significant features of GeV proton irradiation effects in spallation neutron source target materials by producing displacement damage while simultaneously injecting helium and hydrogen at appropriately high gas/dpa ratios. Irradiations were carried out at 80, 200, and 350 C using 3.5 MeV Fe{sup 2}, 360 keV He{sup +}, and 180 keV H{sup +} to accumulate 50 dpa by Fe, 10,000 appm of He, and 50,000 appm of H. Irradiations were also carried out at 200 C in single and dual ion beam modes. The specific ion energies were chosen to maximize the damage and the gas accumulation at a depth of {approx} 1 {micro}m. Variations in microstructure and hardness of irradiated specimens were studied using transmission electron microscopy (TEM) and a nanoindentation technique, respectively. TEM investigation yielded varying damage defect microstructures, comprising black dots, faulted and unfaulted loops, and a high number density of fine bubbles (typically less than 1 nm in diameter). With increasing temperature, faulted loops had a tendency to unfault, and bubble microstructure changed from a bimodal size distribution to a unimodal distribution. Triple ion irradiations at the three temperatures resulted in similar increases in hardness of approximately a factor of two. Individually, Fe and He ions resulted in a similar magnitude of hardness increase, whereas H ions showed only a very small effect. The present study has yielded microstructural information relevant to spallation neutron source conditions and indicates that the most important concern may be radiation induced hardening and associated ductility loss.

  20. Triple Ion-Beam Studies of Radiation Damage Effects in a 316LN Austenitic Alloy for a High Power Spallation Neutron Source

    Austenitic 316LN alloy was ion-irradiated using the unique Triple Ion Beam Facility (TIF) at ORNL to investigate radiation damage effects relevant to spallation neutron sources. The TIF was used to simulate significant features of GeV proton irradiation effects in spallation neutron source target materials by producing displacement damage while simultaneously injecting helium and hydrogen at appropriately high gas/dpa ratios. Irradiations were carried out at 80, 200, and 350 C using 3.5 MeV Fe2, 360 keV He+, and 180 keV H+ to accumulate 50 dpa by Fe, 10,000 appm of He, and 50,000 appm of H. Irradiations were also carried out at 200 C in single and dual ion beam modes. The specific ion energies were chosen to maximize the damage and the gas accumulation at a depth of ∼ 1 microm. Variations in microstructure and hardness of irradiated specimens were studied using transmission electron microscopy (TEM) and a nanoindentation technique, respectively. TEM investigation yielded varying damage defect microstructures, comprising black dots, faulted and unfaulted loops, and a high number density of fine bubbles (typically less than 1 nm in diameter). With increasing temperature, faulted loops had a tendency to unfault, and bubble microstructure changed from a bimodal size distribution to a unimodal distribution. Triple ion irradiations at the three temperatures resulted in similar increases in hardness of approximately a factor of two. Individually, Fe and He ions resulted in a similar magnitude of hardness increase, whereas H ions showed only a very small effect. The present study has yielded microstructural information relevant to spallation neutron source conditions and indicates that the most important concern may be radiation induced hardening and associated ductility loss

  1. Triple ion-beam studies of radiation damage effects in a 316LN austenitic alloy for a high power spallation neutron source

    Austenitic 316LN alloy was ion-irradiated using the unique Triple Ion Beam Facility (TIF) at ORNL to investigate radiation damage effects relevant to spallation neutron sources. The TIF was used to simulate significant features of GeV proton irradiation effects in spallation neutron source target materials by producing displacement damage while simultaneously injecting helium and hydrogen at appropriately high gas/dpa ratios. Irradiations were carried out at 80, 200, and 350 C using 3.5 MeV Fe++, 360 keV He+, and 180 keV H+ to accumulate 50 dpa by Fe, 10,000 appm of He, and 50,000 appm of H. Irradiations were also carried out at 200 C in single and dual ion beam modes. The specific ion energies were chosen to maximize the damage and the gas accumulation at a depth of ∼ 1 microm. Variations in microstructure and hardness of irradiated specimens were studied using transmission electron microscopy (TEM) and a nanoindentation technique, respectively. TEM investigation yielded varying damage defect microstructures, comprising black dots, faulted and unfaulted loops, and a high number density of fine bubbles (typically less than 1 nm in diameter). With increasing temperature, faulted loops had a tendency to unfault, and bubble microstructure changed from a bimodal size distribution to a unimodal distribution. Triple ion irradiations at the three temperatures resulted in similar increases in hardness of approximately a factor of two. Individually, Fe and He ions resulted in a similar magnitude of hardness increase, whereas H ions showed only a very small effect. The present study has yielded microstructural information relevant to spallation neutron source conditions and indicates that the most important concern may be radiation induced hardening and associated ductility loss

  2. Effect of nitrogen alloying on the semiconducting properties of passive films and metastable pitting susceptibility of 316L and 316LN stainless steels

    The beneficial effect of nitrogen alloying on the corrosion resistance of stainless steels has been attributed to the increase of the local pH within the active sites and the enhanced repassivation of the metastable pits. In order to better understand the effect of nitrogen alloying, in situ capacitance measurements and potentiostatic polarization were conducted for 316L and 316LN stainless steels with different nitrogen contents in deaerated 0.1 M Na2SO4 and 0.1 M NaCl aqueous solutions. The Mott-Schottky plots obtained from the in situ capacitance measurements offered information on the donor concentration and the thickness of the space charge region within the passive film. The metastable pitting susceptibility was investigated by performing potentiostatic polarization tests. The results showed that nitrogen alloying decreased the donor densities and the number of metastable pits, while the absorption of chloride ions on the passive film had the opposite effect. Auger electron spectroscopy (AES) analysis demonstrated that nitrogen alloying enriched the chromium within the passive film. The relationship between the semiconducting properties of the passive film and the metastable pitting susceptibility was elucidated.

  3. The study on the factors affecting the high temperature continuous low-cycle fatigue life of the welded 316LN stainless steel by GTAW

    The influence of weld defect on the continuous low cycle fatigue property for type 316LN stainless steel base metal and weldment was investigated with a strain rate of 4x10-3/sec in air atmosphere. Low cycle fatigue test were conducted at temperature of 823K and 873K. Total strain amplitude was controlled to be 0.4-0.6%. The 308L stainless steel was used as the welding rod. The welding was done by the GTAW process with the welding direction perpendicular to the rolling direction of the base metal. The microstructures of the base metal and weldment are γ phase γ/δ duplex-ferrite, respectively. The fatigue lives of the base metal had twice higher than those of weldment having no visible defect. From the tensile result, the uniform elongation of the base metal had twice higher than that of the weldment. For the base metal and HAZ, the fatigue lives at the same condition were reliable. But some results of the fatigue lives in the weldment had the lowest fatigue life at the same condition. From the observation of the fracture surface after fatigue tests, there were porosities and welding defects. For weldments having the many porosities and welding defects, the fatigue lives decreased 50% and 60-70%, respectively. From the observation of the microstructure near the internal crack, the internal weld defects was existed at the interface among the dendrites grown along the different direction

  4. Effect of Multipass TIG and Activated TIG Welding Process on the Thermo-Mechanical Behavior of 316LN Stainless Steel Weld Joints

    Ganesh, K. C.; Balasubramanian, K. R.; Vasudevan, M.; Vasantharaja, P.; Chandrasekhar, N.

    2016-04-01

    The primary objective of this work was to develop a finite element model to predict the thermo-mechanical behavior of an activated tungsten inert gas (ATIG)-welded joint. The ATIG-welded joint was fabricated using 10 mm thickness of 316LN stainless steel plates in a single pass. To distinguish the merits of ATIG welding process, it was compared with manual multipass tungsten inert gas (MPTIG)-welded joint. The ATIG-welded joint was fabricated with square butt edge configuration using an activating flux developed in-house. The MPTIG-welded joint was fabricated in thirteen passes with V-groove edge configuration. The finite element model was developed to predict the transient temperature, residual stress, and distortion of the welded joints. Also, microhardness, impact toughness, tensile strength, ferrite measurement, and microstructure were characterized. Since most of the recent publications of ATIG-welded joint was focused on the molten weld pool dynamics, this research work gives an insight on the thermo-mechanical behavior of ATIG-welded joint over MPTIG-welded joint.

  5. Effects of mercury on fatigue behavior of Type 316 LN stainless steel: application in the spallation neutron source

    Tian, H.; Liaw, P. K.; Strizak, J. P.; Mansur, L. K.

    2003-05-01

    The high-cycle fatigue behavior of Type 316 stainless steel (SS), the prime candidate target-container material for the spallation neutron source (SNS), was investigated in air and mercury at frequencies of 0.2 and 10 Hz with a R ratio of -1, and at 10 and 700 Hz with a R ratio of 0.1. Here R equals the ratio of the applied minimum to maximum loads during fatigue experiments. A decrease in the fatigue life in mercury was observed, relative to that in air, at 0.2 Hz. Correspondingly, intergranular fracture was found on the fracture surfaces of specimens tested in mercury at 0.2 Hz, which is a typical fracture mode caused by liquid metal embrittlement (LME). Heating by mechanical working was observed during fatigue tests at 10 Hz and a R of -1, and at 700 Hz and a R of 0.1, which resulted in great increases in specimen temperatures and shorter fatigue lives for large stress amplitudes (⩾210 MPa), relative to those in mercury. However, in the fatigue tests at 10 and 700 Hz, the fatigue lives in air with cooling and those in mercury seemed to be comparable, indicating little influence of the mercury. Thus, both specimen self-heating and LME need to be considered in understanding fatigue behavior of Type 316 SS in air and mercury.

  6. The Investigation on Welding Processes for SUS316LN Tubes Used in Superconducting Magnetic System of EAST

    Wu Jiefeng; Chen Siyue; Weng Peide; Gao Daming

    2005-01-01

    The force flow cooled superconducting cable-in-conduit conductor (CICC) is used in both of EAST toroidal field (TF) and poloidal field (PF) coils. The conductor consists of multi-stage NbTi superconducting cable and 1.5 mm thick square jacket. The cable is pulled through in a thin wall circular jacket and then compacted to square cross-section conductor. The jacket material is SUS316LN austenitic stainless steel seamless tubes (about 10 m each), which is assembled by butt-welding up to 600 m. The results of the welding procedure investigation and quality assurance procedures carrying out are described in this paper.

  7. The Investigation on Welding Processes for SUS316LN Tubes Used in Superconducting Magnetic System of EAST

    Wu, Jiefeng; Chen, Siyue; Weng, Peide; Gao, Daming

    2005-08-01

    The force flow cooled superconducting cable-in-conduit conductor (CICC) is used in both of EAST toroidal field (TF) and poloidal field (PF) coils. The conductor consists of multi-stage NbTi superconducting cable and 1.5 mm thick square jacket. The cable is pulled through in a thin wall circular jacket and then compacted to square cross-section conductor. The jacket material is SUS316LN austenitic stainless steel seamless tubes (about 10 m each), which is assembled by butt-welding up to 600 m. The results of the welding procedure investigation and quality assurance procedures carrying out are described in this paper.

  8. A powder metallurgy austenitic stainless steel for application at very low temperatures

    Sgobba, Stefano; Liimatainen, J; Kumpula, M

    2000-01-01

    The Large Hadron Collider to be built at CERN will require 1232 superconducting dipole magnets operating at 1.9 K. By virtue of their mechanical properties, weldability and improved austenite stability, nitrogen enriched austenitic stainless steels have been chosen as the material for several of the structural components of these magnets. Powder Metallurgy (PM) could represent an attractive production technique for components of complex shape for which dimension tolerances, dimensional stability, weldability are key issues during fabrication, and mechanical properties, ductility and leak tightness have to be guaranteed during operation. PM Hot Isostatic Pressed test plates and prototype components of 316LN-type grade have been produced by Santasalo Powdermet Oy. They have been fully characterized and mechanically tested down to 4.2 K at CERN. The fine grained structure, the absence of residual stresses, the full isotropy of mechanical properties associated to the low level of Prior Particle Boundaries oxides ...

  9. An experience with in-service fabrication and inspection of austenitic stainless steel piping in high temperature sodium system

    Highlights: • Procedure for changing 304L SS pipe to 316L SS in sodium loop has been established. • Hot leg made of 304L SS was isolated from existing cold leg made of 316LN SS. • Innovative welding was used in joining the new 316L SS pipe with existing 316LN SS. • The old components of 304L SS piping have been integrated with the new piping. - Abstract: A creep testing facility along with dynamic sodium loop was installed at Indira Gandhi Centre for Atomic Research, Kalpakkam, India to assess the creep behavior of fast reactor structural materials in flowing sodium. Type 304L austenitic stainless steel was used in the low cross section piping of hot-leg whereas 316LN austenitic stainless steel in the high cross section cold-leg of the sodium loop. The intended service life of the sodium loop was 10 years. The loop has performed successfully in the stipulated time period. To enhance its life time, it has been decided to replace the 304L piping with 316L piping in the hot-leg. There were more than 300 welding joints involved in the integration of cold-leg with the new 316L hot-leg. Continuous argon gas flow was maintained in the loop during welding to avoid contamination of sodium residue with air. Several innovative welding procedures have been adopted for joining the new hot-leg with the existing cold-leg in the presence of sodium residue adopting TIG welding technique. The joints were inspected for 100% X-ray radiography and qualified by performing tensile tests. The components used in the discarded hot-leg were retrieved, cleaned and integrated in the renovated loop. A method of cleaning component of sodium residue has been established. This paper highlights the in-service fabrication and inspection of the renovation

  10. Cryogenic fracture behavior of 316LN in magnetic fields up to 14.6 T

    Chan, J.W.; Chu, D.; Tseng, C.; Morris, J.W. Jr. [Lawrence Berkeley Lab., CA (United States)]|[California Univ., Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering

    1993-07-01

    Some of the proposed magnet case alloys for the International Thermonuclear Experimental Reactor (ITER) are metastable austenitic stainless steels. The case will be subjected to high loads and can be as much as 100 mm thick. Case assembly will probably require thick section welding with its attendant chemical inhomogeneity. Even alloys that are thermally stable with respect to martensitic transformation can, under these conditions of high stresses, cryogenic temperature, and high magnetic fields, undergo transformation. Previous work at 8 T has shown a measurable magnetic field effect on the 4.2K tensile and fracture toughness properties of AISI300 series metastable austenitic stainless steels. Thus, it is important to understand how these alloys will behave under conditions of high magnetic fields and cryogenic temperature, particularly at the higher magnetic fields that will be used in ITER. 4.2K data for 316LN indicates that the change in fracture toughness is not monotonic. It initially decreases and then later increases with applied field.

  11. Implications of radiation-induced reductions in ductility to the design of austenitic stainless steel structures

    In the dose and temperature range anticipated for ITER, austenitic stainless steels exhibit significant hardening with a concomitant loss in work hardening and uniform elongation. However, significant post-necking ductility may still be retained. When uniform elongation (eu) is well defined in terms of a plastic instability criterion, eu is found to sustain reasonably high values out to about 7 dpa in the temperature range 250-350 C, beyond which it decreases to about 0.3% for 316LN. This loss of ductility has significant implications to fracture toughness and the onset of new failure modes associated with hear instability. However, the retention of a significant reduction in area at failure following irradiation indicates a less severe degradation of low-cycle fatigue life in agreement with a limited amount of data obtained to date. Suggestions are made for incorporating these results into design criteria and future testing programs

  12. Effects of low temperature neutron irradiation on deformation behavior of austenitic stainless steels

    Pawel, J.E.; Rowcliffe, A.F.; Alexander, D.J.; Grossbeck, M.L. [Oak Ridge National Laboratory, TN (United States); Shiba, K.

    1996-04-01

    An austenitic stainless steel, designated 316LN-IG, has been chosen for the first wall/shield (FW/S) structure for the International Thermonuclear Experimental Reactor (ITER). The proposed operational temperature range for the structure (100 to 250{degree}C) is below the temperature regimes for void swelling (400-600{degree}C) and for helium embrittlement (500-700{degree}C). However, the proposed neutron dose is such that large changes in yield strength, deformation mode, and strain hardening capacity could be encountered which could significantly affect fracture properties. Definition of the irradiation regimes in which this phenomenon occurs is essential to the establishment of design rules to protect against various modes of failure.

  13. Effects of Thermocapillary Forces during Welding of 316L-Type Wrought, Cast and Powder Metallurgy Austenitic Stainless Steels

    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...

  14. Thermal fatigue cracking of austenitic stainless steels

    This report deals with the thermal fatigue cracking of austenitic stainless steels as AISI 316 LN and 304 L. Such damage has been clearly observed for some components used in Fast Breeder reactors (FBR) and Pressure Water Reactor (PWR). In order to investigate thermal fatigue, quasi-structural specimen have been used. In this frame, facilities enforcing temperature variations similar to those found under the operation conditions have been progressively developed. As for components, loading results from impeded dilatation. In the SPLASH facility, the purpose was to establish accurate crack initiation conditions in order to check the relevance of the usual component design methodology. The tested specimen is continuously heated by the passage of an electrical DC current, and submitted to cyclic thermal down shock (up to 1000 deg C/s) by means of periodical spraying of water on two opposite specimen faces. The number of cycles to crack initiation Ni is deduced from periodic examinations of the quenched surfaces, by means of optical microscopy. It is considered that initiation occurs when at least one 50μm to 150□m long crack is observed. Additional SPLASH tests were performed for N >> Ni, with a view to investigate the evolution of a surface multiple cracking network with the number of cycles N. The CYTHIA test was mainly developed for the purpose of assessing crack growth dynamics of one isolated crack in thermal fatigue conditions. Specimens consist of thick walled tubes with a 1 mm circular groove is spark-machined at the specimen centre. During the test, the external wall of the tube is periodically heated by using a HF induction coil (1 MHz), while its internal wall is permanently cooled by flowing water. Total crack growth is derived from post-mortem examinations, whereby the thermal fatigue final rupture surface is oxidized at the end of the test. The specimen is broken afterwards under mechanical fatigue at room temperature. All the tests confirm that usual

  15. Post irradiation fatigue tests of type 316 LN stainless steel. Final report for the ITER Task T511, Subtask 1. European Technology Programme Task GB5-T217

    The main objective of this Subtask was to estimate the corrosion fatigue behaviour of 316L Stainless Steel (SS) and SS/SS joints, and to check among others the influence of irradiation. Joints were produced by solid Hot Isostatic Pressure (HIP) and powder HIP. Conventional material was used for comparison. The specimens were supplied by EFDA and were irradiated to 4 dpa in Dimitrovgrad (Russia). All specimens were tested at 150 deg C in hydrogenated high purity water. Testing was performed with a stepwise decrease in ΔK keeping Kmax constant. The crack growth rates of irradiated as well as unirradiated specimens tested earlier are of the same magnitude, around 2x10-5 mm/cycle at ΔK= 18 MPa√m. Thus, irradiation does not seem to enhance the fatigue crack growth rate, at least not up to irradiation levels of 4 dpa. But it is worth noting that the exponents in the da/dN versus ΔK equation, also known as Paris' law, seems to fall within two areas, either around 3.5 or just below 2. Both Powder HIPed and Solid HIPed specimens are found in both groups. The reason for this is not evident. The fracture surfaces of the specimens show typical fatigue appearance

  16. High Mn austenitic stainless steel

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

    2010-07-13

    An austenitic stainless steel alloy includes, in weight percent: >4 to 15 Mn; 8 to 15 Ni; 14 to 16 Cr; 2.4 to 3 Al; 0.4 to 1 total of at least one of Nb and Ta; 0.05 to 0.2 C; 0.01 to 0.02 B; no more than 0.3 of combined Ti+V; up to 3 Mo; up to 3 Co; up to 1W; up to 3 Cu; up to 1 Si; 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, and wherein the alloy forms an external continuous scale including alumina, nanometer scale sized particles distributed throughout the microstructure, the particles including at least one of NbC and TaC, and a stable essentially single phase FCC austenitic matrix microstructure that is essentially delta-ferrite-free and essentially BCC-phase-free.

  17. Several aspects of the temperature history in relation to the cyclic behaviour of an austenitic stainless steel

    A consistent mechanical and transmission electron microscopy (TEM) database is proposed to discuss the consequences of dynamic strain ageing (DSA) on the temperature history memory effect observed under the cyclic loading of a 316LN austenitic stainless steel. Two DSA mechanisms have been identified in relation with two temperature regimes: the first of which may be related to the Suzuki effect (in the low temperature regime) and the second is linked to solute segregation at dislocation node (in the high temperature regime). The temperature history memory effect is a function of the temperature range and can be explained in terms of chromium segregation and the potentiality to obtain 'stability' in dipolar dislocation structures. Both aspects are discussed based on the measurement of internal stress changes. (authors)

  18. Effect of Specimen Diameter on Tensile Properties of Austenitic Stainless Steels in Liquid Hydrogen and Gaseous Helium at 20K

    Fujii, H.; Ohmiya, S.; Shibata, K.; Ogata, T.

    2006-03-01

    Tensile tests using round bar type specimens of 3, 5 and 7 mm in diameter were conducted at 20K in liquid hydrogen and also in gaseous helium at the same temperature for three major austenitic stainless steels, JIS SUS304L, 316L and 316LN, extensively used for cryogenic applications including liquid hydrogen transportation and storage vessels. Stress-strain curves were considerably different between circumstances and also specimen diameter, resulting in differences of strength and ductility. In liquid hydrogen, serrated deformation appeared after considerable work hardening and more active in specimens with larger diameter. Meanwhile serrated deformation was observed from the early stage of plastic deformation in gaseous helium at 20 K and serration was more frequent in specimens with smaller diameter. The serrated deformation behaviors were numerically simulated for 304L steel with taking thermal properties such as thermal conductivity, specific heat, heat transfer from specimens to cryogenic media into account, and some agreement with the experiments was obtained.

  19. Experiences with procurement of 316LN steel and machining of components for PFBR subassemblies

    The manufacture of PFBR core subassemblies requires the bulk procurement of 316LN stainless steel as almost all the subassembly components except the wrapper and the clad tubes are made of this material. The material specification of SS 316LN specified for PFBR core subassemblies is quite stringent than that of AISI/ASTM standard specifications for 316LN as the chemical composition range for different elements are narrowed down to very small margins with addition of ranges for a few extra elements like Niobium, Titanium, Copper, Cobalt and Boron. Also additional requirements of high temperature yield strength, inclusion content, ferrite content, grain size are specified which are difficult to be met. Eddy Current Testing and Ultrasonic Testing methods with tight specifications are recommended as quality checks. Both overseas and indigenous sources for manufacture and supply of the material were developed for the first time. To meet the immediate requirement overseas sources were identified, however, for long term continuous future requirement indigenous sources also were developed. Machining of PFBR subassembly components having intricate profile with high degree of dimensional and geometrical tolerances requirement from SS 316LN also posed several challenges like continuous chip formation because o flow sulfur content. Coated Carbide tool inserts were used to overcome the problem. Higher strength of the material necessitated reduction in the feed rate of machining which made the process slow. The above problems contributed heavily towards the higher cost of material as well as machining. All the problems incurred in the first time procurement and machining of SS 316LN material were successfully overcome and the PFBR core subassemblies are being supplied to BHAVINI. (author)

  20. Laser etching of austenitic stainless steels for micro-structural evaluation

    Baghra, Chetan; Kumar, Aniruddha; Sathe, D. B.; Bhatt, R. B.; Behere, P. G.; Afzal, Mohd

    2015-06-01

    Etching is a key step in metallography to reveal microstructure of polished specimen under an optical microscope. A conventional technique for producing micro-structural contrast is chemical etching. As an alternate, laser etching is investigated since it does not involve use of corrosive reagents and it can be carried out without any physical contact with sample. Laser induced etching technique will be beneficial especially in nuclear industry where materials, being radioactive in nature, are handled inside a glove box. In this paper, experimental results of pulsed Nd-YAG laser based etching of few austenitic stainless steels such as SS 304, SS 316 LN and SS alloy D9 which are chosen as structural material for fabrication of various components of upcoming Prototype Fast Breeder Reactor (PFBR) at Kalpakkam India were reported. Laser etching was done by irradiating samples using nanosecond pulsed Nd-YAG laser beam which was transported into glass paneled glove box using optics. Experiments were carried out to understand effect of laser beam parameters such as wavelength, fluence, pulse repetition rate and number of exposures required for etching of austenitic stainless steel samples. Laser etching of PFBR fuel tube and plug welded joint was also carried to evaluate base metal grain size, depth of fusion at welded joint and heat affected zone in the base metal. Experimental results demonstrated that pulsed Nd-YAG laser etching is a fast and effortless technique which can be effectively employed for non-contact remote etching of austenitic stainless steels for micro-structural evaluation.

  1. Recycle of radiologically contaminated austenitic stainless steels

    The United States Department of Energy owns large quantities of radiologically contaminated austenitic stainless steel which could by recycled for reuse if appropriate release standards were in place. Unfortunately, current policy places the formulation of a release standard for USA industry years, if not decades, away. The Westinghouse Savannah River Company, Idaho National Engineering Laboratory and various university and industrial partners are participating in initiative to recycle previously contaminated austenitic stainless steels into containers for the storage and disposal of radioactive wastes. This paper describes laboratory scale experiments which demonstrated the decontamination and remelt of stainless steel which had been contaminated with radionuclides

  2. The Laser Welding with Hot Wire of 316LN Thick Plate Applied on ITER Correction Coil Case

    Fang, Chao; Wu, Weiyue; Wei, Jing; Zhang, Shuquan; Li, Hongwei; Dolgetta, N; Libeyre, P; Cormany, C; Sgobba, S

    2014-01-01

    ITER correction coil (CC) cases have characteristics of small cross section, large dimensions, and complex structure. The cases are made of heavy thick (20 mm), high strength and high toughness austenitic stainless steel 316LN. The multi-pass laser welding with hot wire technology is used for the case closure welding, due to its low heat input and deformation. In order to evaluate the reliability of this welding technology, 20 mm welding samples with the same groove structure and welding depth as the cases were welded. High purity argon was used as the shielding gas to prevent oxidation because of the narrowness and depth of the weld. In this paper investigation of, microstructure characteristics and mechanical properties of welded joints using optimized welding parameters are presented. The results show that the base metal, fusion metal, and heat affected zone (HAZ) are all have fully austenitic microstructure, and that the grain size of fusion metal was finer than that of the base metal. The welding resulte...

  3. Cast alumina forming austenitic stainless steels

    Muralidharan, Govindarajan; Yamamoto, Yukinori; Brady, Michael P

    2013-04-30

    An austenitic stainless steel alloy consisting essentially of, in terms of weight percent ranges 0.15-0.5C; 8-37Ni; 10-25Cr; 2.5-5Al; greater than 0.6, up to 2.5 total of at least one element selected from the group consisting of Nb and Ta; up to 3Mo; up to 3Co; up to 1W; up to 3Cu; up to 15Mn; up to 2Si; up to 0.15B; up to 0.05P; up to 1 total of at least one element selected from the group consisting of Y, La, Ce, Hf, and Zr; alumina, and a stable essentially single phase FCC austenitic matrix microstructure, the austenitic matrix being essentially delta-ferrite free and essentially BCC-phase-free. A method of making austenitic stainless steel alloys is also disclosed.

  4. Explosive Surface Hardening of Austenitic Stainless Steel

    Kovacs-Coskun, T.

    2016-04-01

    In this study, the effects of explosion hardening on the microstructure and the hardness of austenitic stainless steel have been studied. The optimum explosion hardening technology of austenitic stainless steel was researched. In case of the explosive hardening used new idea mean indirect hardening setup. Austenitic stainless steels have high plasticity and can be easily cold formed. However, during cold processing the hardening phenomena always occurs. Upon the explosion impact, the deformation mechanism indicates a plastic deformation and this deformation induces a phase transformation (martensite). The explosion hardening enhances the mechanical properties of the material, includes the wear resistance and hardness. In case of indirect hardening as function of the setup parameters specifically the flayer plate position the hardening increased differently. It was find a relationship between the explosion hardening setup and the hardening level.

  5. Tritium in austenitic stainless steel vessels

    Austenitic stainless steels are normally recommended for components of hydrogen-handling equipment in applications where high in-service reliability is required. The literature leading to this recommendation is reviewed, and it is shown that AISI Type 316L stainless is particularly suitable for use in tritium-handling and storage systems. When made of this steel, the storage vessels will be extremely resistant to any degradation from tritium in both routine and accident conditions. (author)

  6. Ball Indentation Studies on the Effect of Nitrogen on the Tensile Properties of 316LN SS

    Mathew, M. D.; Ganesh Kumar, J.; Ganesan, V.; Laha, K.

    2015-12-01

    Type 316L(N) stainless steel (SS) containing 0.02-0.03 wt% carbon and 0.06-0.08 wt% nitrogen is used as the major structural material for the components of fast reactors. Research is underway to improve the high-temperature mechanical properties of 316LN SS by increasing the nitrogen content in the steel above the level of 0.08 wt%. In this investigation, ball indentation (BI) technique was used to evaluate the effect of nitrogen content on the tensile properties of 316LN SS. BI tests were conducted on four different heats of 316LN SS containing 0.07, 0.11, 0.14 and 0.22 wt% nitrogen in the temperature range 300-923 K. The tensile properties such as yield strength and ultimate tensile strength increased with increase in nitrogen content at all the investigated temperatures. These results were consistent with the corresponding uniaxial tensile test results. These studies showed that BI technique can be used to optimize the chemical composition during alloy development by evaluating tensile properties with minimum volume of material.

  7. Austenitic stainless steels for cryogenic service

    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.

  8. Corrosion of plasma nitrided austenitic stainless steels

    The corrosion behaviour of plasma nitrided austenitic stainless steel grades AISI 304, 316 and 321 was studied at various temperatures. Certain plasma nitriding cycles included a post-oxidation treatment. The corrosion rates were measured using linear polarisation technique. Results showed that corrosion rate increased with the plasma nitriding temperature. Minimum deterioration occurred at 653K. (author). 2 tabs., 4 figs., 10 refs

  9. Austenitic stainless steels for cryogenic service

    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

  10. Expanded austenite in nitrided layers deposited on austenitic and super austenitic stainless steel grades

    In this work nitrided layers deposited on austenitic and super austenitic stainless steels were analyzed through optical microscopy and X-rays diffraction analysis (XRD). It was observed that the formation of N supersaturated phase, called expanded austenite, has promoted significant increment of hardness (> 1000HV). XRD results have indicated the anomalous displacement of the diffracted peaks, in comparison with the normal austenite. This behavior, combined with peaks broadening, it was analyzed in different nitriding temperatures which results showed good agreement with the literature. (author)

  11. Embrittlement of austenitic stainless steel welds

    To prevent hot-cracking, austenitic stainless steel welds generally contain a small percent of delta ferrite. Although ferrite has been found to effectively prevent hot-cracking, it can lead to embrittlement of welds when exposed to elevated temperatures. The aging behavior of type-308 stainless steel weld has been examined over a range of temperatures 475--850 C for times up to 10,000 hrs. Upon aging, and depending on the temperature range, the unstable ferrite may undergo a variety of solid state transformations. These phase changes creep-rupture and Charpy impact properties

  12. Pitting corrosion resistant austenite stainless steel

    van Rooyen, D.; Bandy, R.

    A pitting corrosion resistant austenite stainless steel comprises 17 to 28 wt. % chromium, 15 to 26 wt. % nickel, 5 to 8 wt. % molybdenum, and 0.3 to 0.5 wt. % nitrogen, the balance being iron, unavoidable impurities, minor additions made in the normal course of melting and casting alloys of this type, and may optionally include up to 10 wt. % of manganese, up to 5 wt. % of silicon, and up to 0.08 wt. % of carbon.

  13. Ultrasonic testing of austenitic stainless steel welds

    Ultrasonic testing of austenitic stainless steel welds has been considered difficult because of the high noise level and remarkable attenuation of ultrasonic waves. To improve flaw detectability in this kind of steel, various inspection techniques have been studied. A series of tests indicated: (1) The longitudinal angle beam transducers newly developed during this study can detect 4.8 mm dia. side drilled holes in dissimilar metal welds (refraction angle: 550 from SUS side, 450 from CS side) and in cast stainless steel welds (refraction angle: 450, inspection frequency: 1 MHz). (2) Cracks more than 5% t in depth in the heat affected zones of fine-grain stainless steel pipe welds can be detected by the 450 shear wave angle beam method (inspection frequency: 2 MHz). (3) The pattern recognition method using frequency analysis technology was presumed useful for discriminating crack signals from spurious echoes. (author)

  14. Electron beam welding of austenitic stainless steel

    Austenitic stainless steel is used for liquid metal-cooled fast breeder reactors with operating temperature of about 550 deg C, because its elevated temperature properties are excellent and the results of use are abundant. The welded joints in LMFBRs require high degree of safety, and the application of electron beam welding is studied to make welding joints of high quality. When the inelastic deformation in a certain limit is allowed as prescribed in the ASME Code, Case 1592, the elevated temperature properties of the welded joints of structures are particularly important. The materials tested were 10 mm thick plates of SUS 304, SUS 316 and SUS 321 steels, and 150 kV - 40 mA electron beam welder was employed. The method of welding was one side, one pass Uranami welding, and first, the appropriate welding conditions were decided. Elevated temperature tensile test was carried out on the parent materials and welded joints by electron beam welding and coated arc welding. Creep rupture test and elevated temperature fatigue test were also carried out. In EB-welded austenitic stainless steel, delta ferrite is scattered finely in austenite, and its quantity is very small and less than 1.5%. The tensile strength and 0.2% proof stress of EB-welded joints are almost same as those of parent materials. The creep rupture and fatigue properties of the joints are also close to those of parent materials. (Kako, I.)

  15. Compatibility between Be12Ti and SS316LN

    Beryllides have good properties and are one of the candidate materials for the neutron multiplier of the DEMO reactor in which good performance is required at 600-800 deg. C. Therefore, a good compatibility with structural materials is expected for the beryllides. In this study, a compatibility test between Be12Ti and SS316LN was carried out as first step to evaluate the compatibility between beryllides and structural materials. The thickness of the reaction layer between Be12Ti and SS316LN at 800 deg. C after 1000 h was approximately 30 μm, whereas that of beryllium metal was 300 μm. At 600 deg. C after 1000 h, the thickness of the reaction layers as to Be12Ti and Be was less than 10 and 100 μm, respectively. The compatibility between Be12Ti and SS316LN was evaluated and Be12Ti was perfectly better than that between beryllium metal and SS316LN at high temperature (600-800 deg. C). The advantage of beryllides as a neutron multiplier in the Demo reactor was proved

  16. Austenitic stainless steels with cryogenic resistance

    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

  17. Ion-nitriding of austenitic stainless steels

    Although ion-nitriding is an extensively industrialized process enabling steel surfaces to be hardened by nitrogen diffusion, with a resulting increase in wear, seizure and fatigue resistance, its direct application to stainless steels, while enhancing their mechanical properties, also causes a marked degradation in their oxidation resistance. However, by adaption of the nitriding process, it is possible to maintain the improved wear resistant properties while retaining the oxidation resistance of the stainless steel. The controlled diffusion permits the growth of a nitrogen supersaturated austenite layer on parts made of stainless steel (AISI 304L and 316L) without chromium nitride precipitation. The diffusion layer remains stable during post heat treatments up to 650 F for 5,000 hrs and maintains a hardness of 900 HV. A very low and stable friction coefficient is achieved which provides good wear resistance against stainless steels under diverse conditions. Electrochemical and chemical tests in various media confirm the preservation of the stainless steel characteristics. An example of the application of this process is the treatment of Reactor Control Rod Cluster Assemblies (RCCAs) for Pressurized Water Nuclear Reactors

  18. Flow lines and microscopic elemental inhomogeneities in austenitic stainless steels

    Mosley, Jr, W C

    1982-01-01

    Flow lines in mechanically formed austenitic stainless steels are known to influence fracture behavior. Enhancement of flow lines by chemical etching is evidence of elemental inhomogeneity. This paper presents the results of electron microprobe analyses to determine the nature of flow lines in three austenitic stainless steels: 21Cr-6Ni-9Mn, 304L, and 19Ni-18Cr.

  19. Nickel-free austenitic stainless steels for medical applications

    Ke Yang and Yibin Ren

    2010-01-01

    The adverse effects of nickel ions being released into the human body have prompted the development of high-nitrogen nickel-free 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 in medical stainless steels, the advantages of nitrogen in stainless steels, and emphatically, the development of high-nitrogen nickel-free stainl...

  20. Nickel-free austenitic stainless steels for medical applications

    Ke Yang and Yibin Ren

    2010-01-01

    Full Text Available The adverse effects of nickel ions being released into the human body have prompted the development of high-nitrogen nickel-free 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 in medical stainless steels, the advantages of nitrogen in stainless steels, and emphatically, the development of high-nitrogen nickel-free stainless steels for medical applications. By combining the benefits of stable austenitic structure, high strength and good plasticity, better corrosion and wear resistances, and superior biocompatibility compared to the currently used 316L stainless steel, the newly developed high-nitrogen nickel-free stainless steel is a reliable substitute for the conventional medical stainless steels.

  1. Several aspects of the temperature history in relation to the cyclic behaviour of an austenitic stainless steel

    Gentet, D., E-mail: david.gentet@cea.fr [CEA, DEN, DER/SESI/LE2S, Cadarache, F-13108 Saint Paul-lez-Durance (France); Feaugas, X. [LEMMA, Universite de la Rochelle, Avenue Michel Crepeau, 17 042 La Rochelle Cedex 01 (France); Risbet, M. [Laboratoire Roberval, Universite de Technologie de Compiegne, BP 20529, 60 205 Compiegne (France); Lejeail, Y. [CEA, DEN, DER/SESI/LE2S, Cadarache, F-13108 Saint Paul-lez-Durance (France); Pilvin, P. [LIMATB, Universite de Bretagne-Sud, 56 321 Lorient Cedex (France)

    2011-09-25

    Highlights: {center_dot} Dynamic strain ageing consequences on the temperature history memorization effect. {center_dot} Temperature is mainly focused at a temperature range equal to 293-923 K. {center_dot} Two peaks are observed on the curve describing saturation stress amplitude. {center_dot} Cyclic behaviour is a function of the temperature range explored. {center_dot} Cyclic temperature history is mainly associated with chromium segregation. - Abstract: A consistent mechanical and transmission electron microscopy (TEM) database is proposed to discuss the consequences of dynamic strain ageing (DSA) on the temperature history memory effect observed under the cyclic loading of a 316LN austenitic stainless steel. Two DSA mechanisms have been identified in relation with two temperature regimes: the first of which may be related to the Suzuki effect (in the low temperature regime) and the second is linked to solute segregation at dislocation node (in the high temperature regime). The temperature history memory effect is a function of the temperature range and can be explained in terms of chromium segregation and the potentiality to obtain 'stability' in dipolar dislocation structures. Both aspects are discussed based on the measurement of internal stress changes.

  2. Several aspects of the temperature history in relation to the cyclic behaviour of an austenitic stainless steel

    Highlights: · Dynamic strain ageing consequences on the temperature history memorization effect. · Temperature is mainly focused at a temperature range equal to 293-923 K. · Two peaks are observed on the curve describing saturation stress amplitude. · Cyclic behaviour is a function of the temperature range explored. · Cyclic temperature history is mainly associated with chromium segregation. - Abstract: A consistent mechanical and transmission electron microscopy (TEM) database is proposed to discuss the consequences of dynamic strain ageing (DSA) on the temperature history memory effect observed under the cyclic loading of a 316LN austenitic stainless steel. Two DSA mechanisms have been identified in relation with two temperature regimes: the first of which may be related to the Suzuki effect (in the low temperature regime) and the second is linked to solute segregation at dislocation node (in the high temperature regime). The temperature history memory effect is a function of the temperature range and can be explained in terms of chromium segregation and the potentiality to obtain 'stability' in dipolar dislocation structures. Both aspects are discussed based on the measurement of internal stress changes.

  3. Heat sink welding of austenitic stainless steel pipes to control distortion and residual stress

    Kumar, H.; Albert, S.K.; Bhaduri, A.K. [Materials Technology Div., Indira Gandhi Centre for Atomic Research, Kalpakkam (India)

    2007-07-01

    Construction of India's Prototype Fast Breeder Reactor (PFBR) involves extensive welding of austenitic stainless steels pipes of different dimensions. Due to high thermal expansion coefficient and poor thermal conductivity of this class of steels, welding can result in significant distortion of these pipes. Attempts to arrest this distortion can lead to high levels of residual stresses in the welded parts. Heat sink welding is one of the techniques often employed to minimize distortion and residual stress in austenitic stainless steel pipe welding. This technique has also been employed to repair welding of the piping of the Boiling Water Reactors (BWRs) subjected to radiation induced intergranular stress corrosion cracking (IGSCC). In the present study, a comparison of the distortion in two pipe welds, one made with heat sink welding and another a normal welds. Pipes of dimensions 350{phi} x 250(L) x 8(t) mm was fabricated from 316LN plates of dimensions 1100 x 250 x 8 mm by bending and long seam (L-seam) welding by SMAW process. Two fit ups with a root gap of 2 mm, land height of 1mm and a groove angle of 70 were prepared using these pipes for circumferential seam (C-seam) welding. Dimensions at predetermined points in the fit up were made before and after welding to check the variation in radius, circumference and and ovality of the pipes. Root pass for both the pipe fit up were carried out using conventional GTAW process with 1.6 mm AWS ER 16-8-2 as consumables. Welding of one of the pipe fit ups were completed using conventions GTAW process while the other was completed using heat sink welding. For second and subsequent layers of welding using this process, water was sprayed at the root side of the joint while welding was in progress. Flow rate of the water was {proportional_to}6 1/minute. Welding parameters employed were same as those used for the other pipe weld. Results of the dimensional measurements showed that there is no circumferential shrinkage in

  4. Friction Stir Welding of austenitic stainless steels

    C. Meran

    2010-11-01

    Full Text Available Purpose: Friction Stir Welding (FSW was applied austenitic stainless steels that is difficult to weld using FSW technique. Proper weld can be obtained by using appropriate welding parameter. In this paper, the effect of different tool rotational speeds, traverse speeds, compressive tool forces, and tool angles was investigated.Design/methodology/approach: The dimension of 3 mm x 75 mm x 150 mm two stainless steel plates were used and butt welded by FSW method using 7.5 kW vertical head milling machine. All welded test specimens were prepared perpendicular to the weld line in order to determine the mechanical properties and tested with 12 MPa/sec stress rate under stress control using a servo-hydraulic Instron 8801. Microstructure of the welding zone and macrograph of the heat affected zone was investigated by SEM.Findings: The average grain size in the SZ was between 3 and 7 μm, which is smaller than that in the BM. The average grain size in the HAZ was about 20 μm, which is half of that in the BM.Fine-grained microstructures are present the welded area. The dark bands observed in the weld zone were also detected the microstructure of the transition zone. Dark and narrow bands do not consist of pores or cavities. It was determined that these bands do not process an ultra fine-grained microstructure. They are Cr2O3 oxide layers which over the surface of stainless steels may have been ruptured during friction stir welding and may form bands inside the welding bead due to stirring.Research limitations/implications: The proper cooling system helps to prevent the stirrer tool from the deformation.Practical implications: The strength of the welded zone of AISI 304 stainless steel can be easily found by implementing welding design parameters and high quality joints can be obtained.Originality/value: This study was performed in the frame of the TUBITAK project no 106M504, „Friction Stir Weldability of Stainless Steels and Investigation of the

  5. He blisters on welded austenitic stainless steel

    Surface blisters of single-crystal and polycrystalline metals induced by He-ion irradiation have been investigated by many researchers and several blister-formation mechanisms have been proposed. But there is no report on what blister densities and blister sizes are to be expected on a welded 316 austenitic stainless steel in use as a fusion reactor material. An experiment was carried out, and details are given. The exfoliation of blisters was almost not observed until the total dose of 2 x 1022 ions m-2 was reached. A figure shows the blister densities for every increment in blister diameter of 0.5 μm on the base and weld metals. A second figure shows the corresponding blister densities on the base and weld metals annealed at 653 K for 4.5 ksec after He-ion irradiation. The total blister densities of the base metals decrease to 4.3 to 5.5 x 1010 blisters m-2 and the average blister sizes increase to 2.8 to 3.2 μm. This phenomenon indicates that the implanted He ions diffuse in the weld and base metals. The blister sizes on the weld metals are smaller than those on the base metals and the densities on the weld metals are greater than those on the base metals. (author)

  6. 76 FR 43981 - Circular Welded Austenitic Stainless Pressure Pipe From the People's Republic of China: Final...

    2011-07-22

    ... International Trade Administration Circular Welded Austenitic Stainless Pressure Pipe From the People's Republic... antidumping duty order on circular welded austenitic stainless pressure pipe from the People's Republic of..., 2010. \\1\\ See Circular Welded Austenitic Stainless Pressure Pipe From the People's Republic of...

  7. Failure of austenitic stainless steel tubes during steam generator operation

    M. Głowacka; J. Łabanowski; S. Topolska

    2012-01-01

    Purpose: of this study is to analyze the causes of premature failure of steam generator coil made of austenitic stainless steel. Special attention is paid to corrosion damage processes within the welded joints.Design/methodology/approach: Examinations were conducted several segments of the coil made of seamless cold-formed pipes Ø 23x2.3 mm, of austenitic stainless steel grade X6CrNiTi18-10 according to EN 10088-1:2007. The working time of the device was 6 months. The reason for the withdrawa...

  8. Thermal fatigue of austenitic and duplex stainless steels

    Virkkunen, Iikka

    2001-01-01

    Thermal fatigue behavior of AISI 304L, AISI 316, AISI 321, and AISI 347 austenitic stainless steels as well as 3RE60 and ACX-100 duplex stainless steels was studied. Test samples were subjected to cyclic thermal transients in the temperature range 20 - 600°C. The resulting thermal strains were analyzed with measurements and numerical calculations. The evolution of thermal fatigue damage was monitored with periodic residual stress measurements and replica-assisted microscopy. The elastic strai...

  9. Welding technology trend of austenitic stainless steels for cryogenic services

    At present, the large use of stainless steel in cryogenic field is the storage and transport system for liquefied gas represented by LNG and the nuclear fusion reactors utilizing superconductivity. Most of the stainless steel used for the LNG system is austenitic stainless steel SUS 304. The main use of stainless steel for fusion reactors is the support structures for superconductive magnets, and the thick plates over 150 mm are used. In the experiment, SUS 304L and 316L were used, but the development of a new high strength stainless steel is actively advanced. The target specification of the cryogenic structural material for the fusion experimental reactor (FER) was proposed in 1982. The proof stress is not lower than 1200 MPa, and the fracture toughness value is not lower than 200 MPa √m at 4 K. Six kinds of nitrogen-strengthened austenitic stainless steels and high manganese austenitic steels are developed. As the problems of the welded parts, the toughness and strength at extremely low temperature, the susceptibility to high temperature cracking, the material quality design of the welded metals and so on are examined. The welding methods are GTAW and GMAW. (K.I.)

  10. Nanostructured nickel-free austenitic stainless steel/hydroxyapatite composites.

    Tulinski, Maciej; Jurczyk, Mieczyslaw

    2012-11-01

    In this work Ni-free austenitic stainless steels with nanostructure and their nanocomposites with hydroxyapatite are presented and characterized by means of X-ray diffraction and optical profiling. The samples were synthesized by mechanical alloying, heat treatment and nitriding of elemental microcrystalline powders with addition of hydroxyapatite (HA). In our work we wanted to introduce into stainless steel hydroxyapatite ceramics that have been intensively studied for bone repair and replacement applications. Such applications were chosen because of their high biocompatibility and ability to bond to bone. Since nickel-free austenitic stainless steels seem to have better mechanical properties, corrosion resistance and biocompatibility compared to 316L stainless steels, it is possible that composite made of this steel and HA could improve properties, as well. Mechanical alloying and nitriding are very effective technologies to improve the corrosion resistance of stainless steel. Similar process in case of nanocomposites of stainless steel with hydroxyapatite helps achieve even better mechanical properties and corrosion resistance. Hence nanocrystalline nickel-free stainless steels and nickel-free stainless steel/hydroxyapatite nanocomposites could be promising bionanomaterials for use as a hard tissue replacement implants, e.g., orthopedic implants. In such application, the surface roughness and more specifically the surface topography influences the proliferation of cells (e.g., osteoblasts). PMID:23421285

  11. Austenitic stainless steel patterning by plasma assisted diffusion treatments

    The new concept of surface texturing or surface patterning on austenitic stainless steel by plasma assisted diffusion treatment is presented in this paper. It allows the creation of uniform micro or nano relief with regularly shaped asperities or depressions. Plasma assisted diffusion treatments are based on the diffusion of nitrogen and/or carbon in a metallic material at moderate to elevated temperatures. Below 420 deg. C, a plasma assisted nitriding treatment of austenitic stainless steel produces a phase usually called expanded austenite. Expanded austenite is a metastable nitrogen supersaturated solid solution with a disordered fcc structure and a distorted lattice. The nitrided layer with the expanded austenite is highly enriched in nitrogen (from 10 to 35 at%) and submitted to high compressive residual stresses. From mechanical consideration, it is shown that the only possible deformation occurs in the direction perpendicular to the surface. Such an expansion of the layer from the initial surface of the substrate to the gas phase is used here for surface patterning of stainless steel parts. The surface patterning is performed by using masks (TEM grid) and multi-dipolar plasmas.

  12. Nitrogen bearing austenitic stainless steels for surgical implants

    Tschiptschin, A.P.; Aidar, C.H.; Alonso-Falleiros, N. [Sao Paulo Univ. (Brazil). Escola Politecnica; Neto, F.B. [Instituto de Pesquisas Tecnologicas, Sao Paulo (Brazil)

    1999-07-01

    Nitrogen addition promotes substantial improvements on general and localized corrosion performance of stainless steels. In recent times high nitrogen (up to 0.6 wt%) and Mn bearing super austenitic stainless steel has been studied for medical applications due to its low Ni content, the so called body friendly alloys. 18%Cr, 0.4%N and 15%Mn stainless steels were cast either from electrolytic or commercial master alloys in induction furnace, forged, solubilized at 1423K for 3 hours and water quenched. Delta ferrite and carbide precipitate free structures were observed. (orig.)

  13. Tritium in austenitic stainless steel vessels

    The vessel used for the long-term storage of tritium (titanium tritide) will be of welded 316L stainless steel construction. The 316L stainless is chosen partially because of its excellent resistance, in the wrought condition, to any degradation of mechanical properties from contact with hydrogen isotopes. The work reported here was undertaken to check that the welds in the vessel would have a satisfactory response to the hydrogen isotopes. A satisfactory response has been demonstrated, leading to a general conclusion that the titanium tritide/316L stainless steel vessel combination provides an extremely reliable storage facility for the tritium

  14. Ferrite stability in duplex austenitic stainless steel welds

    The presence of ferrite in austenitic stainless steel welds is known to be beneficial in avoiding hot cracking problems. In particular, the primary delta ferrite mode of solidification is important. For alloy compositions in which primary ferrite forms, it has been shown that up to approximately 40% ferrite may exist in the as-solidified structures. With further cooling, the ferrite becomes unstable, transforming to austenite. However, under typical welding conditions, the cooling rate is sufficiently high to suppress the complete transformation of ferrite and some residual ferrite is retained. For example, for Type 308 austenitic stainless steel filler metal, gas-tungsten arc welds contain 6 to 10% ferrite, although under equilibrium conditions at elevated temperatures, this same alloy can be homogenized into a fully austenitic structure. Thus, it is clear the retained ferrite in such duplex structure welds is unstable and transforms during elevated temperature applications. The stability of ferrite was investigated by measuring its composition after several different thermal treatments. The composition was measured by means of analytical electron microscopy of thinned foils, and only the major constituents, iron, chromium, and nickel, were analyzed. The composition of ferrite was measured as a function of aging time and temperature. It was found that, during aging, the ferrite composition changes and approaches a metastable equilibrium limit before eventually transforming to sigma phase or austenite. This limiting composition was determined as a function of temperature

  15. The influence of fabricating conditions and stability of austenite on forming behaviour of austenitic stainless steels

    The object of the investigation is the effect of various conditions of cold rolling austenitic stainless steels on the mechanical and technological properties and on the behaviour during forming with requirements in stretching and deep drawing. Fabricating 3 coils of various stability of austenite the degree of cold forming between the annealing processes is varied by cold rolling from the thickness of hot rolled coil to final thickness without or with one or two intermediate annealings. The most important results for cold forming sheets are: most favourable stretch forming behaviour is gained with instable austenitic steels, becomes better with increasing sheet thickness most favourable deep drawing behaviour is gained with highest degrees of cold rolling before final annealing, is undependent from the stability of austenite. Favourable is cold rolling to the highest degree before intermediate annealing, whilst the deformation before final annealing is of greater importance. According to the results conditions can be given for cold rolling to get best forming behaviour. (orig.)

  16. Oxidation resistant high creep strength austenitic stainless steel

    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.

  17. Influence of Martensite Fraction on the Stabilization of Austenite in Austenitic-Martensitic Stainless Steels

    Huang, Qiuliang; De Cooman, Bruno C.; Biermann, Horst; Mola, Javad

    2016-05-01

    The influence of martensite fraction ( f α') on the stabilization of austenite was studied by quench interruption below M s temperature of an Fe-13Cr-0.31C (mass pct) stainless steel. The interval between the quench interruption temperature and the secondary martensite start temperature, denoted as θ, was used to quantify the extent of austenite stabilization. In experiments with and without a reheating step subsequent to quench interruption, the variation of θ with f α' showed a transition after transformation of almost half of the austenite. This trend was observed regardless of the solution annealing temperature which influenced the martensite start temperature. The transition in θ was ascribed to a change in the type of martensite nucleation sites from austenite grain and twin boundaries at low f α' to the faults near austenite-martensite (A-M) boundaries at high f α'. At low temperatures, the local carbon enrichment of such boundaries was responsible for the enhanced stabilization at high f α'. At high temperatures, relevant to the quenching and partitioning processing, on the other hand, the pronounced stabilization at high f α' was attributed to the uniform partitioning of the carbon stored at A-M boundaries into the austenite. Reduction in the fault density of austenite served as an auxiliary stabilization mechanism at high temperatures.

  18. Solidification cracking in austenitic stainless steel welds

    V Shankar; T P S Gill; S L Mannan; S Sundaresan

    2003-06-01

    Solidification cracking is a significant problem during the welding of austenitic stainless steels, particularly in fully austenitic and stabilized compositions. Hot cracking in stainless steel welds is caused by low-melting eutectics containing impurities such as S, P and alloy elements such as Ti, Nb. The WRC-92 diagram can be used as a general guide to maintain a desirable solidification mode during welding. Nitrogen has complex effects on weld-metal microstructure and cracking. In stabilized stainless steels, Ti and Nb react with S, N and C to form low-melting eutectics. Nitrogen picked up during welding significantly enhances cracking, which is reduced by minimizing the ratio of Ti or Nb to that of C and N present. The metallurgical propensity to solidification cracking is determined by elemental segregation, which manifests itself as a brittleness temperature range or BTR, that can be determined using the varestraint test. Total crack length (TCL), used extensively in hot cracking assessment, exhibits greater variability due to extraneous factors as compared to BTR. In austenitic stainless steels, segregation plays an overwhelming role in determining cracking susceptibility.

  19. Precipitation effects in austenitic stainless weld metals

    Creep-rupture specimen of similar welded joints of X6CrNi 18 11 (1.4948/AISI 304) and X6CrNiMo 17 13 (1.4919/AISI 316) show only low elongation after longtime testing. The reason for this loss of ductility was found by metallographic investigations. The weld metal of five joints had ferrite contents from 3 to 7.5%, due to a primary ferritic solidification. During creep testing in the temperature range from 500 to 800deg C carbide precipitation takes place at the austenite-ferrite grain boundaries, because delta ferrite is not in a state of equilibrium at these temperatures. After carbon has been used up, the remaining delta ferrite changes into sigma phase, if its alloying element content is high enough. In the upper temperature range, coagulation of sigma phase is dominating. At these large particles grain boundary migration is hindered. During the grain boundary sliding sigma phase particles break and initiate creep cracks. In fully austenintic weld metal sigma precipitation starts at austenite - austenite grain boundaries. During creep testing, void formation starts at sigma particles. Growing of voids leads to grain separations. (orig.)

  20. Austenite Formation from Martensite in a 13Cr6Ni2Mo Supermartensitic Stainless Steel

    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 stage

  1. Microstructural characterisation of carbon implanted austenitic stainless steel

    Low carbon (316L) austenitic stainless steel has been implanted with carbon ions with a fluence of 5 x 1017 C ions/cm2 using an ion energy of 75 keV. The effect of carbon ion implantation on the microstructure of the austenitic steel has been examined in cross-section using transmission electron microscopy (TEM) both before and after implantation, and the implantation data correlated with a computer based simulation, TRIM (Transport and Range of Ions in Matter). It has been found that the high-fluence carbon ion implantation modified the microstructure of the steel, as demonstrated by the presence of two amorphous layers separated by a layer of expanded austenite

  2. Microstructural characterisation of carbon implanted austenitic stainless steel

    Murphy, M.E. [Scientific Affairs Research Group, Stryker Orthopaedics, Raheen Business Park, Limerick (Ireland)]. E-mail: matthew.murphy@stryker.com; Insley, G.M. [Scientific Affairs Research Group, Stryker Orthopaedics, Raheen Business Park, Limerick (Ireland); Laugier, M.T. [Department of Physics, University of Limerick, Limerick (Ireland); Newcomb, S.B. [Sonsam Ltd., Glebe Laboratories, Newport, Tipperary (Ireland)

    2005-06-01

    Low carbon (316L) austenitic stainless steel has been implanted with carbon ions with a fluence of 5 x 10{sup 17} C ions/cm{sup 2} using an ion energy of 75 keV. The effect of carbon ion implantation on the microstructure of the austenitic steel has been examined in cross-section using transmission electron microscopy (TEM) both before and after implantation, and the implantation data correlated with a computer based simulation, TRIM (Transport and Range of Ions in Matter). It has been found that the high-fluence carbon ion implantation modified the microstructure of the steel, as demonstrated by the presence of two amorphous layers separated by a layer of expanded austenite.

  3. Failure of austenitic stainless steel tubes during steam generator operation

    M. Głowacka

    2012-12-01

    Full Text Available Purpose: of this study is to analyze the causes of premature failure of steam generator coil made of austenitic stainless steel. Special attention is paid to corrosion damage processes within the welded joints.Design/methodology/approach: Examinations were conducted several segments of the coil made of seamless cold-formed pipes Ø 23x2.3 mm, of austenitic stainless steel grade X6CrNiTi18-10 according to EN 10088-1:2007. The working time of the device was 6 months. The reason for the withdrawal of the generator from the operation was leaks in the coil tube caused by corrosion damage. The metallographic investigations were performed with the use of light microscope and scanning electron microscope equipped with the EDX analysis attachment.Findings: Examinations of coil tubes indicated severe corrosion damages as pitting corrosion, stress corrosion cracking, and intergranular corrosion within base material and welded joints. Causes of corrosion was defined as wrong choice of austenitic steel grade, improper welding technology, lack of quality control of water supply and lack of surface treatment of stainless steel pipes.Research limitations/implications: It was not known the quality of water supply of steam generator and this was the reason for some problems in the identification of corrosion processes.Practical implications: Based on the obtained research results and literature studies some recommendations were formulated in order to avoid failures in the application of austenitic steels in the steam generators. These recommendations relate to the selection of materials, processing technology and working environment.Originality/value: Article clearly shows that attempts to increase the life time of evaporator tubes and steam coils by replacing non-alloy or low alloy structural steel by austenitic steel, without regard to restrictions on its use, in practice often fail.

  4. Fatigue behavior of welded austenitic stainless steel in different environments

    D. S. Yawas; S.Y. Aku; S.O. Aluko

    2014-01-01

    The fatigue behavior of welded austenitic stainless steel in 0.5 M hydrochloric acid and wet steam corrosive media has been investigated. The immersion time in the corrosive media was 30 days to simulate the effect on stainless steel structures/equipment in offshore and food processing applications and thereafter annealing heat treatment was carried out on the samples. The findings from the fatigue tests show that seawater specimens have a lower fatigue stress of 0.5 × 10−5 N/mm2 for the heat...

  5. Manifestations of DSA in austenitic stainless steels and inconel alloys

    The aim of the investigation was to examine and compare different types of DSA (Dynamic Strain Aging) manifestations in AISI 316 austenitic stainless steel (SS) and Inconel 600 and Inconel 690 alloys by means of slow strain rate tensile testing, mechanical loss spectrometry (internal friction) and transmission electron microscopy (TEM). Another aim was to determine differences in the resulting dislocation structures and internal friction response of materials showing and not showing DSA behaviour

  6. Creep embrittlement of austenitic stainless steels with titanium addition

    Some cold-worked austenitic stainless steels of the 316 type with titanium addition exhibit a low creep ductility and a notch sensitivity in the temperature range of 5500C to 7500C and for times to rupture from 10 to 10000 hours. It has been shown that this embrittlement increases highly with cold-work percentage, with solution annealing temperature, and depends on chemical composition because these factors can modify the difference of hardness between grains and grain boundaries

  7. Study of irradiation damage structures in austenitic stainless steels

    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.

  8. Corrosion Behavior of Austenitic and Duplex Stainless Steels in Lithium Bromide

    Ayo Samuel AFOLABI; Alaneme, K.K.; Samson Oluwaseyi BADA

    2009-01-01

    The corrosion behavior of austenitic and duplex stainless steels in various concentrations of lithium, bromide solution was investigated by using the conventional weight loss measurement method. The results obtained show that corrosion of these steels occurred due to the aggressive bromide ion in the medium. Duplex stainless steel shows a greater resistance to corrosion than austenitic stainless steel in the medium. This was attributed to equal volume proportion of ferrite and austenite in th...

  9. Amorphous stainless steel coatings prepared by reactive magnetron-sputtering from austenitic stainless steel targets

    Cusenza, Salvatore; Schaaf, Peter

    2009-01-01

    Stainless steel films were reactively magnetron sputtered in argon/methane gas flow onto oxidized silicon wafers using austenitic stainless-steel targets. The deposited films of about 200 nm thickness were characterized by conversion electron Mössbauer spectroscopy, magnetooptical Kerr-effect, X-ray diffraction, scanning electron microscopy, Rutherford backscattering spectrometry, atomic force microscopy, corrosion resistance tests, and Raman spectroscopy. These complementary methods were us...

  10. Fatigue behavior of welded austenitic stainless steel in different environments

    D.S. Yawas

    2014-01-01

    Full Text Available The fatigue behavior of welded austenitic stainless steel in 0.5 M hydrochloric acid and wet steam corrosive media has been investigated. The immersion time in the corrosive media was 30 days to simulate the effect on stainless steel structures/equipment in offshore and food processing applications and thereafter annealing heat treatment was carried out on the samples. The findings from the fatigue tests show that seawater specimens have a lower fatigue stress of 0.5 × 10−5 N/mm2 for the heat treated sample and 0.1 × 10−5 N/mm2 for the unheat-treated sample compared to the corresponding hydrochloric acid and steam samples. The post-welding heat treatment was found to increase the mechanical properties of the austenitic stainless steel especially tensile strength but it reduces the transformation and thermal stresses of the samples. These findings were further corroborated by the microstructural examination of the stainless steel specimen.

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

    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

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

    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

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

    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.

  14. Determination of delta ferrite volumetric fraction in austenitic stainless steel

    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)

  15. Corrosion resistance of kolsterised austenitic 304 stainless steel

    Abudaia, F. B., E-mail: fabudaia@yahoo.com; Khalil, E. O., E-mail: ekhalil9@yahoo.com; Esehiri, A. F., E-mail: Hope-eseheri@hotmail.co.uk; Daw, K. E., E-mail: Khawladaw@yahoo.com [University of Tripoli Department of Materials and Metallurgical Eng, Tripoli-Libya P.O.Box13589 (Libya)

    2015-03-30

    Austenitic stainless suffers from low wear resistance in applications where rubbing against other surfaces is encountered. This drawback can be overcome by surface treatment such as coating by hard materials. Other treatments such as carburization at relatively low temperature become applicable recently to improve hardness and wear resistance. Carburization heat treatment would only be justified if the corrosion resistance is unaffected. In this work samples of 304 stainless steels treated by colossal supersaturation case carburizing (known as Kolsterising) carried out by Bodycote Company was examined for pitting corrosion resistance at room temperature and at 50 °C. Comparison with results obtained for untreated samples in similar testing conditions show that there is no deterioration in the pitting resistance due to the Kolsterising heat treatment. X ray diffraction patterns obtained for Kolsterising sample showed that peaks correspond to the austenite phase has shifted to lower 2θ values compared with those of the untreated sample. The shift is an indication for expansion of austenite unit cells caused by saturation with diffusing carbon atoms. The XRD of Kolsterising samples also revealed additional peaks appeared in the patterns due to formation of carbides in the kolsterised layer. Examination of these additional peaks showed that these peaks are attributed to a type of carbide known as Hagg carbide Fe{sub 2}C{sub 5}. The absence of carbides that contain chromium means that no Cr depletion occurred in the layer and the corrosion properties are maintained. Surface hardness measurements showed large increase after Kolsterising heat treatment.

  16. Thermal fatigue cracking of austenitic stainless steels; Fissuration en fatigue thermique des aciers inoxydables austenitiques

    Fissolo, A

    2001-07-01

    This report deals with the thermal fatigue cracking of austenitic stainless steels as AISI 316 LN and 304 L. Such damage has been clearly observed for some components used in Fast Breeder reactors (FBR) and Pressure Water Reactor (PWR). In order to investigate thermal fatigue, quasi-structural specimen have been used. In this frame, facilities enforcing temperature variations similar to those found under the operation conditions have been progressively developed. As for components, loading results from impeded dilatation. In the SPLASH facility, the purpose was to establish accurate crack initiation conditions in order to check the relevance of the usual component design methodology. The tested specimen is continuously heated by the passage of an electrical DC current, and submitted to cyclic thermal down shock (up to 1000 deg C/s) by means of periodical spraying of water on two opposite specimen faces. The number of cycles to crack initiation N{sub i} is deduced from periodic examinations of the quenched surfaces, by means of optical microscopy. It is considered that initiation occurs when at least one 50{mu}m to 150{open_square}m long crack is observed. Additional SPLASH tests were performed for N >> N{sub i}, with a view to investigate the evolution of a surface multiple cracking network with the number of cycles N. The CYTHIA test was mainly developed for the purpose of assessing crack growth dynamics of one isolated crack in thermal fatigue conditions. Specimens consist of thick walled tubes with a 1 mm circular groove is spark-machined at the specimen centre. During the test, the external wall of the tube is periodically heated by using a HF induction coil (1 MHz), while its internal wall is permanently cooled by flowing water. Total crack growth is derived from post-mortem examinations, whereby the thermal fatigue final rupture surface is oxidized at the end of the test. The specimen is broken afterwards under mechanical fatigue at room temperature. All the

  17. Effect of shot peening on metastable austenitic stainless steels

    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.

  18. Effect of shot peening on metastable austenitic stainless steels

    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

  19. Defect microstructures and deformation mechanisms in irradiated austenitic stainless steels

    Microstructural evolution and deformation behavior of austenitic stainless steels are evaluated for neutron, heavy-ion and proton irradiated materials. Radiation hardening in austenitic stainless steels is shown to result from the evolution of small interstitial dislocation loops during light-water-reactor (LWR) irradiation. Available data on stainless steels irradiated under LWR conditions have been analyzed and microstructural characteristics assessed for the critical fluence range (0.5 too 10 dpa) where irradiation-assisted stress corrosion cracking susceptibility is observed. Heavy-ion and proton irradiations are used to produce similar defect microstructures enabling the investigation of hardening and deformation mechanisms. Scanning electron, atomic force and transmission electron microscopies are employed to examine tensile test strain rate and temperature effects on deformation characteristics. Dislocation loop microstructures are found to promote inhomogeneous planar deformation within the matrix and regularly spaced steps at the surface during plastic deformation. Twinning is the dominant deformation mechanism at rapid strain rates and at low temperatures, while dislocation channeling is favored at slower strain rates and at higher temperatures. Both mechanisms produce highly localized deformation and large surface slip steps. Channeling, in particular, is capable of creating extensive dislocation pileups and high stresses at internal grain boundaries which may promote intergranular cracking

  20. A review of hot cracking in austenitic stainless steel weldments

    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

  1. Fatigue crack growth of a metastable austenitic stainless steel

    Martelo, D.F.; Mateo García, Antonio Manuel; Chapetti, M.D.

    2015-01-01

    The fatigue crack growth behavior of an austenitic metastable stainless steel AISI 301LN in the Paris region is investigated in this work. The fatigue crack growth rate curves are evaluated in terms of different parameters such as the range of stress intensity factor Delta K, the effective stress intensity factor Delta K-eff, and the two driving force parameter proposed by Kujawski K*.; The finite element method is used to calculate the stress intensity factor of the specimens used in this in...

  2. On the Development of the Brass-Type Texture in Austenitic Stainless Steel

    Singh, C. D.

    1993-01-01

    It has been clarified and demonstrated that the conclusions drawn by Singh, Ramaswamy and Suryanarayana (1992) in an investigation of development of rolling textures in an austenitic stainless steel are correct. The observations and reinterpretations drawn by Leffers (1993) are without any proper scientific basis and do not hold good at least in austenitic stainless steel.

  3. 75 FR 70908 - Circular Welded Austenitic Stainless Pressure Pipe From the People's Republic of China: Extension...

    2010-11-19

    ... International Trade Administration Circular Welded Austenitic Stainless Pressure Pipe From the People's Republic... of the antidumping duty order on circular welded austenitic stainless pressure pipe from the People's... for Revocation in Part, 75 FR 22107 (April 27, 2010). The period of review (``POR'') is September...

  4. Precipitation and cavity formation in austenitic stainless steels during irradiation

    Microstructural evolution in austenitic stainless steels subjected to displacement damage at high temperature is strongly influenced by the interactions 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 cavitry. Data are presented which support these ideas. It is shown that during nickel ion irradiation of a titanium-modified stainless steel at 6750C the rate of injection of helium has a strong effect on the total swelling and also on the nature and distribution of precipitate phases

  5. Hydrogen embrittlement of SUS 316 austenitic stainless steel weldments

    In order to understand the degrading behavior of hydrogen embrittlement of SUS 316 austenitic stainless steel weldment, base metal and welded joints which were welded with EBW and SMAW and heat-treated at 650 0C - 24 hr for carbide and 850 0C - 6 hr for Sigma-phase precipitation after welding were evaluated in tensile test at room temperature with and without hydrogen charging in the autoclave at 450 0C - 220 atm - 48 hr treatment. As a result the drastic degrading to 40 % in reduction in area of the welded joint was observed when hydrogen of 41 ppm was contained in the welded joint of SUS 316 stainless steel. (author)

  6. Ion beam nitriding of single and polycrystalline austenitic stainless steel

    Polycrystalline and single crystalline [orientations (001) and (011)] AISI 316L austenitic stainless steel was implanted at 400 deg. C with 1.2 keV nitrogen ions using a high current density of 0.5 mA cm-2. The nitrogen distribution profiles were determined using nuclear reaction analysis (NRA). The structure of nitrided polycrystalline stainless steel samples was analyzed using glancing incidence and symmetric x-ray diffraction (XRD) while the structure of the nitrided single crystalline stainless steel samples was analyzed using x-ray diffraction mapping of the reciprocal space. For identical treatment conditions, it is observed that the nitrogen penetration depth is larger for the polycrystalline samples than for the single crystalline ones. The nitrogen penetration depth depends on the orientation, the being more preferential for nitrogen diffusion than . In both type of samples, XRD analysis shows the presence of the phase usually called 'expanded' austenite or γN phase. The lattice expansion depends on the crystallographic plane family, the (001) planes showing an anomalously large expansion. The reciprocal lattice maps of the nitrided single crystalline stainless steel demonstrate that during nitriding lattice rotation takes place simultaneously with lattice expansion. The analysis of the results based on the presence of stacking faults, residual compressive stress induced by the lattice expansion, and nitrogen concentration gradient indicates that the average lattice parameter increases with the nitrided layer depth. A possible explanation of the anomalous expansion of the (001) planes is presented, which is based on the combination of faster nitriding rate in the (001) oriented grains and the role of stacking faults and compressive stress

  7. Austenite Formation from Martensite in a 13Cr6Ni2Mo Supermartensitic Stainless Steel

    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 stages. This is probably due to inhomogeneous distribution of the austenite-stabilizing elements Ni and Mn, resulting from their slow diffusion from martensite into austenite and carbide and nitride dis...

  8. Expanded austenite in nitrided layers deposited on austenitic and super austenitic stainless steel grades; Analise da austenita expandida em camadas nitretadas em acos inoxidaveis austeniticos e superaustenitico

    Casteletti, L.C.; Fernandes, F.A.P.; Heck, S.C. [Universidade de Sao Paulo (EESC/USP), Sao Carlos, SP (Brazil). Escola de Engenharia. Dept. de Engenharia de Materais, Aeronautica e Automobilistica; Oliveira, A.M. [Instituto de Educacao, Ciencia e Tecnologia do Maranhao (IFMA), Sao Luis, MA (Brazil); Gallego, J., E-mail: gallego@dem.feis.unesp.b [UNESP, Ilha Solteira, SP (Brazil). Dept. Engenharia Mecanica

    2010-07-01

    In this work nitrided layers deposited on austenitic and super austenitic stainless steels were analyzed through optical microscopy and X-rays diffraction analysis (XRD). It was observed that the formation of N supersaturated phase, called expanded austenite, has promoted significant increment of hardness (> 1000HV). XRD results have indicated the anomalous displacement of the diffracted peaks, in comparison with the normal austenite. This behavior, combined with peaks broadening, it was analyzed in different nitriding temperatures which results showed good agreement with the literature. (author)

  9. Mechanical Properties of Austenitic Stainless Steel Made by Additive Manufacturing.

    Luecke, William E; Slotwinski, John A

    2014-01-01

    Using uniaxial tensile and hardness testing, we evaluated the variability and anisotropy of the mechanical properties of an austenitic stainless steel, UNS S17400, manufactured by an additive process, selective laser melting. Like wrought materials, the mechanical properties depend on the orientation introduced by the processing. The recommended stress-relief heat treatment increases the tensile strength, reduces the yield strength, and decreases the extent of the discontinuous yielding. The mechanical properties, assessed by hardness, are very uniform across the build plate, but the stress-relief heat treatment introduced a small non-uniformity that had no correlation to position on the build plate. Analysis of the mechanical property behavior resulted in four conclusions. (1) The within-build and build-to-build tensile properties of the UNS S17400 stainless steel are less repeatable than mature engineering structural alloys, but similar to other structural alloys made by additive manufacturing. (2) The anisotropy of the mechanical properties of the UNS S17400 material of this study is larger than that of mature structural alloys, but is similar to other structural alloys made by additive manufacturing. (3) The tensile mechanical properties of the UNS S17400 material fabricated by selective laser melting are very different from those of wrought, heat-treated 17-4PH stainless steel. (4) The large discontinuous yielding strain in all tests resulted from the formation and propagation of Lüders bands. PMID:26601037

  10. Thermal deformation behavior and microstructure of nuclear austenitic stainless steel

    2009-01-01

    Gleeble-1500D thermal simulation tester was employed in the hot-compression investigation of as-cast nuclear 304 austenitic stainless steel under conditions: deformation temperature 950―1200℃; deformations 30% and 50%; deformation rates 0.01 and 0.1 s?1. The results show that the flow stress decreases with temperature rise under the same strain rate and deformation, that the flow stress increases with deformation under the same temperature and strain rate, and that the flow stress increases with strain rate under the same temperature condition, i.e., work hardening becomes distinct. Materials exhibit better strength-toughness when the strain rate is 0.01 s-1, the deformation is 50%, and the temperature is 1050℃.

  11. Low temperature sensitization of austenitic stainless steel weldments

    The effect of long heat treatments on the structure and degree of sensitization of the HAZ in an austenitic stainless steel weld joint were studied. In the literature review sensitization as a phenomenon and the various metallurgical factors that affect sensitization are presented. Sensitization that occurs at temperatures well below the normal sensitization range, the so called low temperature sensitization (LTS), is described and the various variables affecting the susceptibility to LTS are considered. Transmission electron microscopy revealed that M23C6 carbides precipitate on rain boundaries in the HAZ. After welding the carbides are small and the degree of sensitization is low, but aging at temperatures below the precipitation range caused the growth of previously nucleated carbides. At the same time the degree of sensitization increased considerably. The degree of sensitization was evaluated with various intergranular corrosion tests. The electrochemical EPR-test proved to be suitable for measuring small changes in the degree of sensitization. (author)

  12. Lattice dynamics of high-pressure hydrogenated austenitic stainless steels

    Hoelzel, M [Darmstadt University of Technology, Institute for Materials Science, Petersenstrasse 23, 64287 Darmstadt (Germany); Rajevac, V [Darmstadt University of Technology, Institute for Materials Science, Petersenstrasse 23, 64287 Darmstadt (Germany); Danilkin, S A [Bragg Institute, ANSTO, New Illawarra Road, Lucas Heights, NSW 2234PMB 1, Menai (Australia); Udovic, T J [National Institute of Standards and Technology, NIST Center for Neutron Research, 100 Bureau Drive, MS 8562, Gaithersburg, MD 20899-8562 (United States); Wipf, H [Darmstadt University of Technology, Institute for Solid State Physics, Hochschulstrasse 6, 64289 Darmstadt (Germany); Fuess, H [Darmstadt University of Technology, Institute for Materials Science, Petersenstrasse 23, 64287 Darmstadt (Germany)

    2005-06-15

    The vibrational spectra of hydrogenated austenitic stainless steels AISI 304 (Fe/Cr18/Ni10) and AISI 310 (Fe/Cr25/Ni20) were investigated by inelastic neutron scattering. Based on the results of previous neutron diffraction studies, the data have been analysed by model calculations. The peaks corresponding to the optical modes show a significant broadening because of the variation of vibrational energies from one hydrogen site to another in the alloys. At high hydrogen contents (hydrogen-to-metal atomic ratios H/Me {approx}1) the peak profile is dominated by hydrogen-hydrogen interactions. Correspondingly, the optical peaks show a splitting into longitudinal and transverse modes for H/Me {approx}1. A continuous lowering of the vibrational energies with increasing hydrogen content was observed for both steels, reflecting a weakening of the hydrogen-metal interactions with increasing hydrogen-metal atomic distance.

  13. Lattice dynamics of high-pressure hydrogenated austenitic stainless steels

    The vibrational spectra of hydrogenated austenitic stainless steels AISI 304 (Fe/Cr18/Ni10) and AISI 310 (Fe/Cr25/Ni20) were investigated by inelastic neutron scattering. Based on the results of previous neutron diffraction studies, the data have been analysed by model calculations. The peaks corresponding to the optical modes show a significant broadening because of the variation of vibrational energies from one hydrogen site to another in the alloys. At high hydrogen contents (hydrogen-to-metal atomic ratios H/Me ∼1) the peak profile is dominated by hydrogen-hydrogen interactions. Correspondingly, the optical peaks show a splitting into longitudinal and transverse modes for H/Me ∼1. A continuous lowering of the vibrational energies with increasing hydrogen content was observed for both steels, reflecting a weakening of the hydrogen-metal interactions with increasing hydrogen-metal atomic distance

  14. Interaction of deuterium with SS316 austenitic stainless steel

    Accumulation and desorption of deuterium implanted in SS316 austenitic stainless steel to concentrations ∼1 at.%, the influence of helium and radiation-induced defects on the process of mass transfer of deuterium and the mechanical properties of steel at different levels of damage were studied. The samples were irradiated with 15 keV/D, 30 keV/He and 1.4 MeV/Ar ions. For modeling of the defect structure formed in the materials of nuclear power plants, the irradiation with high-energy argon ions was performed. Studies were carried out by means of ion implantation, nuclear reactions D(3He,p)4He with analyzing beam of 3He (E = 0.3...1.4 MeV), thermal desorption spectroscopy, transmission electron microscopy and nanoindentation. It was found that the retention of deuterium in steel is increased significantly in the presence of radiation damage created by helium and argon pre-implantation

  15. Thermal stability of ultrafine-grained austenitic stainless steels

    Ultrafine-grained 316 and 304 austenitic stainless steel samples have been produced by high pressure torsion. Their microstructure, after deformation and annealing at a temperature in the 350-900 deg. C range, has been characterized using several techniques (transmission electron microscopy, X-ray diffraction, Moessbauer spectroscopy). The average grain size in the ultrafine-grained 316 is about 40 nm while it is larger in the ultrafine-grained 304 due to a smaller deformation. Results show the formation of α'-martensite during deformation in both steels while ε-martensite is formed only in the 304 steel. Annealing at 350 deg. C induces the decrease of α'-martensite content in the 316 steel. The trend is different in the 304 steel, in which the α'-martensite content increases. Recrystallization of grains is observed from 700 deg. C. Moessbauer spectroscopy shows a reduction of the level of solute atoms in α'-martensite during annealing.

  16. Small punch creep test in a 316 austenitic stainless steel

    Saucedo-Munoz, M. L.; Komazaki, S. I.; Hashida, T.; Lopez-Hirata, V. M.

    2015-03-30

    The small punch creep test was applied to evaluate the creep behavior of a 316 type austenitic stainless steel at temperatures of 650, 675 and 700 degree centigrade. The small punch test was carried out using a creep tester with a specimen size of 10x10x0.3 mm at 650, 675 and 700 degree centigrade using loads from 199 to 512 N. The small punch creep curves show the three stages found in the creep curves of the conventional uniaxial test. The conventional creep relationships which involve parameters such as creep rate, stress, time to rupture and temperature were followed with the corresponding parameters of small punch creep test and they permitted to explain the creep behavior in this steel. The mechanism and activation energy of the deformation process were the grain boundary sliding and diffusion, respectively, during creep which caused the intergranular fracture in the tested specimens. (Author)

  17. Formability analysis of austenitic stainless steel-304 under warm conditions

    Lade, Jayahari; Singh, Swadesh Kumar; Banoth, Balu Naik; Gupta, Amit Kumar

    2013-12-01

    A warm deep drawing process of austenitic stainless steel-304 (ASS-304) of circular blanks with coupled ther mal analysis is studied in this article. 65 mm blanks were deep drawn at different temperatures and thickness distribution is experimentally measured after cutting the drawn component into two halves. The process is simulated using explicit fin ite element code LS-DYNA. A Barlat 3 parameter model is used in the simulation, as the material is anisotropic up to 30 0°C. Material properties for the simulation are determined at different temperatures using a 5 T UTM coupled with a furn ace. In this analysis constant punch speed and variable blank holder force (BHF) is applied to draw cups without wrinkle.

  18. Small punch creep test in a 316 austenitic stainless steel

    The small punch creep test was applied to evaluate the creep behavior of a 316 type austenitic stainless steel at temperatures of 650, 675 and 700 degree centigrade. The small punch test was carried out using a creep tester with a specimen size of 10x10x0.3 mm at 650, 675 and 700 degree centigrade using loads from 199 to 512 N. The small punch creep curves show the three stages found in the creep curves of the conventional uniaxial test. The conventional creep relationships which involve parameters such as creep rate, stress, time to rupture and temperature were followed with the corresponding parameters of small punch creep test and they permitted to explain the creep behavior in this steel. The mechanism and activation energy of the deformation process were the grain boundary sliding and diffusion, respectively, during creep which caused the intergranular fracture in the tested specimens. (Author)

  19. Residual stresses of water-jet peened austenitic stainless steel

    The specimen material was austenitic stainless steel, SUS316L. The residual stress was induced by water-jet peening. The residual stress was measured using the 311 diffraction with conventional X-rays. The measured residual stress showed the equi-biaxial stress state. To investigate thermal stability of the residual stress, the specimen was aged thermally at 773K in air to 1000h. The residual stress kept the equi-biaxial stress state against the thermal aging. Lattice plane dependency of the residual stress induced by water-jet peening was evaluated using hard synchrotron X-rays. The residual stress measured by the soft lattice plane showed the equi-biaxial stress state, but the residual stress measured by the hard lattice plane did not. In addition, the distributions of the residual stress in the depth direction were measured using a strain scanning method with hard synchrotron X-rays and neutrons. (author)

  20. Mechanized welding of austenitic precision stainless steel tubes

    Austenitic stainless steel tubes of material no. 1,4541 and 1,4550 are used for the tube systems to transport active and inactive gases in reactor experiments. A fully mechanical method was developed for the joining of these tubes by welding which makes use of an electrode holder with surrounding W electrode. This method, whose application is described here, enables the joining of the tubes in all welding positions. A pulsating direct current is used as welding current. Breaking tests on the welded samples gave values corresponding to the strength of the materials mentioned. The welded seams are subjected to the helium leak test and to the X-ray test. (GSCH/LH)

  1. Corrosion of an austenite and ferrite stainless steel weld

    BRANIMIR N. GRGUR

    2011-07-01

    Full Text Available Dissimilar metal connections are prone to frequent failures. These failures are attributed to the difference in the mechanical properties across the weld, the coefficients of thermal expansion of the two types of steels and the resulting creep at the interface. For the weld analyzed in this research, it was shown that corrosion measurements can be used for a proper evaluation of the quality of weld material and for the prediction of whether or not the material, after the applied welding process, can be in service without failures. It was found that the corrosion of the weld analyzed in this research resulted from the simultaneous activity of different types of corrosion. In this study, electrochemical techniques including polarization and metallographic analysis were used to analyze the corrosion of a weld material of ferrite and austenitic stainless steels. Based on surface, chemical and electrochemical analyses, it was concluded that corrosion occurrence was the result of the simultaneous activity of contact corrosion (ferrite and austenitic material conjuction, stress corrosion (originating from deformed ferrite structure and inter-granular corrosion (due to chromium carbide precipitation. The value of corrosion potential of –0.53 V shows that this weld, after the thermal treatment, is not able to repassivate a protective oxide film.

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

    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 transformation was monitored in situ by magnetometry and data was used to sketch a TTT diagram for transformation. As an alternative treatment, after austenitization the material was immersed in boiling nitrogen and up-quenched to room temperature by immersion in water prior to be subjected to isothermal...

  3. Mechanical Properties of Thermally Aged Austenitic Stainless Steel Welds and Cast Austenitic Stainless Steel

    Conventional test methods for tensile and J-R properties of such weld require large size specimens. Meanwhile, small punch (SP) test has advantages of using small size samples at specific location. In this study, the mechanical property changes caused by the thermal aging were evaluated for the stainless steel welds and CASSs using tensile, J-R, and SP test. Based on the results, correlations were developed to estimate the fracture toughness using the load-displacement curve of SP tests. Finally, the fracture surfaces of compact tension (CT) and SP test specimens are compared and discussed in view of the effect of thermal aging on microstructure. Stainless steel welds of ER316L and ER347 as well as CASS (CF8M) were thermally aged at 400 .deg. C for 5,000 h. So far, tensile properties and fracture toughness of un-aged materials were carried out at room temperature and 320 .deg. C as a reference data. In order to evaluate the effect of thermal aging on mechanical properties, aged specimens are being tested and the changes in these properties will be discussed. In addition, correlations will be developed to estimate the fracture toughness in between J-R curve and SP curve

  4. Hydrogen-related phase transformations in austenitic stainless steels

    Narita, N.; Altstetter, C. J.; Birnbaum, H. K.

    1982-08-01

    The effect of hydrogen and stress (strain) on the stability of the austenite phase in stainless steels was investigated. Hydrogen was introduced by severe cathodic charging and by elevated temperature equilibration with high pressure H2 gas. Using X-ray diffraction and magnetic techniques, the behavior of two “stable” type AISI310 steels and an “unstable” type AISI304 steel was studied during charging and during the outgassing period following charging. Transformation from the fcc γ phase to an expanded fcc phase, γ*, and to the hcp ɛ phase occurred during cathodic charging. Reversion of the γ* and e phases to the original γ structure and formation of the bcc α structure were examined, and the kinetics of these processes was studied. The γ* phase was shown to be ferromagnetic with a subambient Curie temperature. The γ⇆ɛ phase transition was studied after hydrogen charging in high pressure gas, as was the formation of a during outgassing. These results are interpreted as effects of hydrogen and stress (strain) on the stability of the various phases. A proposed psuedo-binary phase diagram for the metal-hydrogen system was proposed to account for the formation of the γ* phase. The relation of these phase changes to hydrogen embrittlement and stress corrosion cracking of stainless steel is discussed.

  5. Effect of Grain Size on Mechanical Properties of Nickel-Free High Nitrogen Austenitic Stainless Steel

    LI Hua-bing; JIANG Zhou-hua; ZHANG Zu-rui; YANG Yan

    2009-01-01

    The fine grained structures of nickel-free high nitrogen austenitic stainless steels had been obtained by means of cold rolling and subsequent annealing.The relationship between microstructure and mechanical properties and gain size of nickel-free high nitrogen austenitic stainless steels was examined.High strength and good ductility of the steel were found.In the grain size range,the Hall-Petch dependency for yield stress,tensile strength,and hardness was valid for grain size ranges for the nickel-free high nitrogen austenitic stainless steel.In the present study,the ductility of cold rolled nickel-free high nitrogen austenitic stainless steel decreased with annealing time when the grain size was refined.The fracture surfaces of the tensile specimens in the grain size range were covered with dimples as usually seen in a ductile fracture mode.

  6. Fabrication of high nitrogen austenitic stainless steels with excellent mechanical and pitting corrosion properties

    Hua-bing Li; Zhou-hua Jiang; Yang Cao; Zu-rui Zhang

    2009-01-01

    18Cr18Mn2Mo0.9N high nitrogen austenitic stainless steel exhibits high strength and good ductility at room temperature. The steel shows typical duc-tile-brittle transition behavior and excellent pitting corrosion resistance properties.

  7. HYDROGEN-ASSISTED FRACTURE IN FORGED TYPE 304L AUSTENITIC STAINLESS STEEL

    Switzner, Nathan; Neidt, Ted; Hollenbeck, John; Knutson, J.; Everhart, Wes; Hanlin, R. [University of Missouri-Kansas City; Bergen, R. [Precision Metal Products; Balch, D. K. [Sandia Natl Laboratory

    2012-09-06

    Austenitic stainless steels generally have good resistance to hydrogen-assisted fracture; however, structural designs for high-pressure gaseous hydrogen are constrained by the low strength of this class of material. Forging is used to increase the low strength of austenitic stainless steels, thus improving the efficiency of structural designs. Hydrogen-assisted racture, however, depends on microstructural details associated with manufacturing. In this study, hydrogen-assisted fracture of forged type 304L austenitic stainless steel is investigated. Microstructural variation in multi-step forged 304L was achieved by forging at different rates and temperatures, and by process annealing. High internal hydrogen content in forged type 304L austenitic stainless steel is achieved by thermal precharging in gaseous hydrogen and results in as much as 50% reduction of tensile ductility.

  8. A study of the microstructural distribution of cathodic hydrogen in austenitic stainless steels by hydrogen microprint

    The cathodic hydrogen distribution in austenitic stainless steel (304L; 316L) microstructure is shwon, at electron microscope scale, using the hydrogen microprint technique. Cathodic hydrogen induced cracking is analysed

  9. Fractographic studies of hydrogen embrittlement of AISI 316L austenitic stainless steel

    This paper concerns a fractographic examination of hydrogen embrittlement of a stable AISI 316L type austenitic stainless steel. The objective is a better understanding of the possible role of hydrogen in stress corrosion cracking processes. (author)

  10. A review on nickel-free nitrogen containing austenitic stainless steels for biomedical applications.

    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. PMID:23910251

  11. The study of high speed fine turning of austenitic stainless steel

    W.S. Lin

    2008-01-01

    Purpose: The purpose of this research paper is focused on the surface roughness variation in high speed fine turning of the austenitic stainless steel.Design/methodology/approach: A series of experimental tests have been done to evaluate the possibility of high speed fine turning of the austenitic stainless steel from the surface roughness variation and machining stability.Findings: It was found that, the smaller the feed rate, the smaller the surface roughness value. But when the feed rate s...

  12. Microstructure and properties of laser surface alloyed PM austenitic stainless steel

    Z. Brytan; M. Bonek; L.A. Dobrzański

    2010-01-01

    Purpose: The purpose of this paper is to analyse the effect of laser surface alloying with chromium on the microstructural changes and properties of vacuum sintered austenitic stainless steel type AISI 316L (EN 1.4404).Design/methodology/approach: Surface modification of AISI 316L sintered austenitic stainless steel was carried out by laser surface alloying with chromium powder using high power diode laser (HPDL). The influence of laser alloying conditions, both laser beam power (between 0.7 ...

  13. Hydrogen Effects on Austenitic Stainless Steels and High-Strength Carbon Steels

    Todoshchenko, Olga

    2015-01-01

    The resistance to hydrogen embrittlement is an important factor in the development of new steel grades for a variety of applications. The thesis describes investigations on hydrogen effects on two classes of steels - austenitic stainless steels and advanced high-strength carbon steels. Hydrogen solubility and diffusion in metastable austenitic stainless steels are studied with thermal desorption spectroscopy (TDS). This method, together with the mathematical modeling of the processes of hy...

  14. Stress corrosion cracking behaviour of gas tungsten arc welded super austenitic stainless steel joints

    M. Vinoth Kumar; Balasubramanian, V.; S. RAJAKUMAR; Shaju K. Albert

    2015-01-01

    Super 304H austenitic stainless steel with 3% of copper posses excellent creep strength and corrosion resistance, which is mainly used in heat exchanger tubing of the boiler. Heat exchangers are used in nuclear power plants and marine vehicles which are intended to operate in chloride rich offshore environment. Chloride stress corrosion cracking is the most likely life limiting failure with austenitic stainless steel tubing. Welding may worsen the stress corrosion cracking susceptibility of t...

  15. Plasma Nitriding of Austenitic Stainless Steel with Severe Surface Deformation Layer

    JI Shi-jun; GAO Yu-zhou; WANG Liang; SUN Jun-cai; HEI Zu-kun

    2004-01-01

    The dc glow discharge plasma nitriding of austenite stainless steel with severe surface deformation layer is used to produce much thicker surface modified layer. This kind of layers has useful properties such as a high surface hardness of about 1500 Hv 0.1 and high resistance to frictional wear. This paper presents the structures and properties of low temperature plasma nitrided austenitic stainless steel with severe surface deformation layer.

  16. Microstructure of 316L austenite stainless steel after charging with deuterium and tritium

    The microstructure of 316L austenite stainless steel after charging with deuterium and tritium for 6 years at room temperature is studied. The results indicate that the morphology of fracture surface after blasting is ductile rupture with dimple, stress produced by blasting of high pressure leads to the martensite transformation. The deuterium and tritium improve the ε martensite transformation of austenite and reduce the fault energy, which reduce the hydrogen-resistant properties of 316L stainless steel

  17. Cyclic behavior of SS 316 LN with respect to thermal ratcheting of main vessel for SFR

    One of the innovative features which are considered for the future Sodium cooled Fast breeder Reactor (SFR) in India is the elimination of main vessel cooling circuit. This would bring out significant economic by saving the cost of entire cooling circuit and also by reducing the main vessel diameter. However, the challenging aspect to be addressed is investigation of thermal ratcheting failure near sodium free level. The sodium free level will vary during the various operating conditions depending up on hot and cold pool temperatures. The thermal fluctuations cause high cycle deformation controlled fatigue damage. These high cycle temperature oscillations cause high cycle deformation controlled fatigue on metal surface. Thermal ratcheting of main vessel enhanced by creep effect which cause radial deformations near the sodium free level during Safety Graded Decay Heat Removal (SGDHR). The strain accumulated due to thermal ratcheting can also cause reduction in buckling strength of main vessel. The accumulated deformations can cause concern for the free movement of in-service inspection equipment. Preliminary assessment indicates that there is a need to develop special SS 316 LN with higher nitrogen content and subsequently to demonstrate that the vessel made of this material can provide a sufficient safety margin against ratcheting. This exercise calls for carrying out many simulated experiments, particularly to predict thermal ratcheting. Some of the recent bi-axial tension-torsion experiments to simulate ratcheting for SS316LN and enhanced nitrogen steel (SS316EN) found that the axial strains predicted by enhanced nitrogen SS316EN steel were much higher than the strains predicted for SS316LN steel for the same set of parameters. Hence it is worthwhile to carryout investigations to predict the cyclic behavior of SS 316LN and enhanced nitrogen steel with respect to thermal ratcheting. Some experiments have been conducted for the SFR scale down model of main vessel

  18. Research on damage evolution and damage model of 316LN steel during forging

    Duan, X.W., E-mail: dxwmike1998@sina.com; Liu, J.S.

    2013-12-20

    The tensile tests and unloading tensile experiments of 316LN steel were conducted. The damage evolution processes were investigated by optical microscope. The fracture was studied using a Scanning Electron Microscope (SEM) and optical microscope, of which, the chemical compositions were analyzed by Energy Dispersive Spectrometer (EDS). The results show that voids nucleate by decohesion of Al{sub 2}O{sub 3} inclusions–matrix interface and mainly along the grain boundary, especially, at triangular grain boundary junctions. The tensile processes were simulated by Deform2D under different deformation conditions. The critical damage values were obtained. The model between the critical damage value, temperature and strain rate was established by regression analysis. A combination of numerical simulation and upsetting experiments was applied for verifying the accuracy and reliability of critical damage value. These damage values can be used to predict the initiation of voids during 316LN steel hot forging. So, they have important instructional effects on designing forging technology of 316LN steel.

  19. Evaluation of stainless steels for their resistance to intergranular corrosion

    Austenitic stainless steels are being considered as structural materials for first wall/blanket systems in the international thermonuclear reactor (ITER). The uniform corrosion of stainless steels in water is well known and is not a critical issue limiting its application for the ITER design. The sensitivity of austenitic steels to intergranular corrosion (IGC) can be estimated rather accurately by means of calculation methods, considering structure and chemical composition of steel. There is a maximum permissible carbon content level, at which sensitization of stainless steel is eliminated: K=Creff-αCeff, where α-thermodynamic coefficient, Creff-effective chromium content (regarding molybdenum influence) and Ceff-effective carbon content (taking into account nickel and stabilizing elements). Corrosion tests for 16Cr11Ni3MoTi, 316L and 316LN steel specimens, irradiated up to 2 x 1022 n/cm2 fluence have proved the effectiveness of this calculation technique for determination of austenitic steels tendency to IGC. This method is directly applicable in austenitic stainless steel production and enables one to exclude complicated experiments on determination of stainless steel susceptibility to IGC. (orig.)

  20. Corrosion Behavior of Austenitic and Duplex Stainless Steels in Lithium Bromide

    Ayo Samuel AFOLABI

    2009-07-01

    Full Text Available The corrosion behavior of austenitic and duplex stainless steels in various concentrations of lithium, bromide solution was investigated by using the conventional weight loss measurement method. The results obtained show that corrosion of these steels occurred due to the aggressive bromide ion in the medium. Duplex stainless steel shows a greater resistance to corrosion than austenitic stainless steel in the medium. This was attributed to equal volume proportion of ferrite and austenite in the structure of duplex stainless steel coupled with higher content of chromium in its composition. Both steels produced electrochemical noise at increased concentrations of lithium bromide due to continuous film breakdown and repair caused by reduction in medium concentration by the alkaline corrosion product while surface passivity observed in duplex stainless steel is attributed to film stability on this steel.

  1. Microstructural evolution in fast-neutron-irradiated austenitic stainless steels

    The present work has focused on the specific problem of fast-neutron-induced radiation damage to austenitic stainless steels. These steels are used as structural materials in current fast fission reactors and are proposed for use in future fusion reactors. Two primary components of the radiation damage are atomic displacements (in units of displacements per atom, or dpa) and the generation of helium by nuclear transmutation reactions. The radiation environment can be characterized by the ratio of helium to displacement production, the so-called He/dpa ratio. Radiation damage is evidenced microscopically by a complex microstructural evolution and macroscopically by density changes and altered mechanical properties. The purpose of this work was to provide additional understanding about mechanisms that determine microstructural evolution in current fast reactor environments and to identify the sensitivity of this evolution to changes in the He/dpa ratio. This latter sensitivity is of interest because the He/dpa ratio in a fusion reactor first wall will be about 30 times that in fast reactor fuel cladding. The approach followed in the present work was to use a combination of theoretical and experimental analysis. The experimental component of the work primarily involved the examination by transmission electron microscopy of specimens of a model austenitic alloy that had been irradiated in the Oak Ridge Research Reactor. A major aspect of the theoretical work was the development of a comprehensive model of microstructural evolution. This included explicit models for the evolution of the major extended defects observed in neutron irradiated steels: cavities, Frank faulted loops and the dislocation network. 340 refs., 95 figs., 18 tabs

  2. Dislocation loop evolution under ion irradiation in austenitic stainless steels

    Etienne, A., E-mail: auriane.etienne@etu.univ-rouen.f [Groupe de Physique des Materiaux, Universite et INSA de Rouen, UMR CNRS 6634, BP 12, 76 801 Saint Etienne du Rouvray Cedex (France); Hernandez-Mayoral, M. [Division of Materials, CIEMAT, Avenida Complutense 22, 28040 Madrid (Spain); Genevois, C.; Radiguet, B.; Pareige, P. [Groupe de Physique des Materiaux, Universite et INSA de Rouen, UMR CNRS 6634, BP 12, 76 801 Saint Etienne du Rouvray Cedex (France)

    2010-05-01

    A solution annealed 304 and a cold worked 316 austenitic stainless steels were irradiated from 0.36 to 5 dpa at 350 deg. C using 160 keV Fe ions. Irradiated microstructures were characterized by transmission electron microscopy (TEM). Observations after irradiation revealed the presence of a high number density of Frank loops. Size and number density of Frank loops have been measured. Results are in good agreement with those observed in the literature and show that ion irradiation is able to simulate dislocation loop microstructure obtained after neutron irradiation. Experimental results and data from literature were compared with predictions from the cluster dynamic model, MFVIC (Mean Field Vacancy and Interstitial Clustering). It is able to reproduce dislocation loop population for neutron irradiation. Effects of dose rate and temperature on the loop number density are simulated by the model. Calculations for ion irradiations show that simulation results are consistent with experimental observations. However, results also show the model limitations due to the lack of accurate parameters.

  3. Dislocation loop evolution under ion irradiation in austenitic stainless steels

    Etienne, A.; Hernández-Mayoral, M.; Genevois, C.; Radiguet, B.; Pareige, P.

    2010-05-01

    A solution annealed 304 and a cold worked 316 austenitic stainless steels were irradiated from 0.36 to 5 dpa at 350 °C using 160 keV Fe ions. Irradiated microstructures were characterized by transmission electron microscopy (TEM). Observations after irradiation revealed the presence of a high number density of Frank loops. Size and number density of Frank loops have been measured. Results are in good agreement with those observed in the literature and show that ion irradiation is able to simulate dislocation loop microstructure obtained after neutron irradiation. Experimental results and data from literature were compared with predictions from the cluster dynamic model, MFVIC (Mean Field Vacancy and Interstitial Clustering). It is able to reproduce dislocation loop population for neutron irradiation. Effects of dose rate and temperature on the loop number density are simulated by the model. Calculations for ion irradiations show that simulation results are consistent with experimental observations. However, results also show the model limitations due to the lack of accurate parameters.

  4. Thermal stability of ultrafine-grained austenitic stainless steels

    Etienne, A.; Radiguet, B.; Genevois, C.; Le Breton, J.-M. [Groupe de Physique des Materiaux, Universite et INSA de Rouen, UMR CNRS 6634, BP 12, 76 801 Saint Etienne du Rouvray Cedex (France); Valiev, R. [Institute of Physics of Advanced Materials, Ufa State Aviation Technical University, 12K. Marx Street, 450000 Ufa (Russian Federation); Pareige, P., E-mail: philippe.pareige@univ-rouen.fr [Groupe de Physique des Materiaux, Universite et INSA de Rouen, UMR CNRS 6634, BP 12, 76 801 Saint Etienne du Rouvray Cedex (France)

    2010-08-20

    Ultrafine-grained 316 and 304 austenitic stainless steel samples have been produced by high pressure torsion. Their microstructure, after deformation and annealing at a temperature in the 350-900 deg. C range, has been characterized using several techniques (transmission electron microscopy, X-ray diffraction, Moessbauer spectroscopy). The average grain size in the ultrafine-grained 316 is about 40 nm while it is larger in the ultrafine-grained 304 due to a smaller deformation. Results show the formation of {alpha}'-martensite during deformation in both steels while {epsilon}-martensite is formed only in the 304 steel. Annealing at 350 deg. C induces the decrease of {alpha}'-martensite content in the 316 steel. The trend is different in the 304 steel, in which the {alpha}'-martensite content increases. Recrystallization of grains is observed from 700 deg. C. Moessbauer spectroscopy shows a reduction of the level of solute atoms in {alpha}'-martensite during annealing.

  5. Stress corrosion cracking of austenitic stainless steel core internal weld

    Microstructural analyses by several advanced metallographic techniques were conducted on austenitic stainless steel mockup and core shroud welds that cracked in boiling water reactors. Contrary to previous beliefs, heat-affected zones of the cracked Type 304L as well as 304 SS core shroud welds and mockup shielded-metal-arc welds were free of grain-boundary carbides, which shows that core shroud failure cannot be explained by classical intergranular stress corrosion cracking. Neither martensite nor delta-ferrite films were present on grain boundaries. However, as a result of exposure to weld fumes, the heat-affected zones of the core shroud welds were significantly contaminated by oxygen and fluorine which migrate to grain boundaries. Significant oxygen contamination seems to promote fluorine contamination and suppress thermal sensitization. Results of slow-strain-rate tensile tests indicate also that fluorine exacerbate the susceptibility of irradiated steels to intergranular stress corrosion cracking. These observations, combined with previous reports on the strong influence of weld flux, indicate that oxygen and fluorine contamination and fluorine-catalyzed stress corrosion play a major role in cracking of core shroud welds

  6. Surface modification of austenitic stainless steel by titanium ion implantation

    The wear properties of AISI 316 austenitic stainless steel implanted with Ti were investigated for ion doses in the range (2.3-5.4)x1016ionscm-2 and average ion energies of 60 and 90keV. The implanted layer was examined by Rutherford backscattering, from which the retained doses were determined, and glow discharge optical emission spectroscopy. Following implantation, the surface microhardness was observed to increase with the greatest change occurring at higher ion energy. Pin-on-disc wear tests and associated friction measurements were also performed under both dry and lubricated conditions using applied loads of 2N and 10N. In the absence of lubrication, breakthrough of the implanted layer occurred after a short sliding time; only for a dose of 5.1x1016ionscm-2 implanted at an average energy of 90keV was the onset of breakthrough appreciably delayed. In contrast, the results of tests with lubrication showed a more gradual variation, with the extent of wear decreasing with implant dose at both 2N and 10N loads. Finally, the influence of Ti implantation on possible wear mechanisms is discussed in the light of information provided by several surface characterization techniques. ((orig.))

  7. Antibacterial and corrosive properties of copper implanted austenitic stainless steel

    Juan Xiong; Bo-fan Xu; Hong-wei Ni

    2009-01-01

    Copper ions were implanted into austenitic stainless steel (SS) by metal vapor vacuum arc with a energy of 100 keV and an ions dose range of (0.5-8.0)x 1017 cm-2. The Cu-implanted SS was annealed in an Ar atmosphere furnace. Glancing X-ray diffraction (GXRD), transmission electron microscopy (TEM) and Auger electron spectroscopy (AES) were used to reveal the phase com-positions, microstructures, and concentration profiles of copper ions in the implanted layer. The results show that the antibacterialproperty of Cu-implanted SS is attributed to Cu9.9Fe0.1 which precipitated as needles. The depth of copper in Cu-implanted SS with annealing treatment is greater than that in Cu-implanted SS without annealing treatment, which improves the antibacterial property against S. Aureus. The salt wetting-drying combined cyclic test was used to evaluate the corrosion-resistance of antibacterial SS, and the results reveal that the antibacterial SS has a level of corrosion-resistance equivalent to that of un-implanted SS.

  8. Dislocation loop evolution under ion irradiation in austenitic stainless steels

    A solution annealed 304 and a cold worked 316 austenitic stainless steels were irradiated from 0.36 to 5 dpa at 350 deg. C using 160 keV Fe ions. Irradiated microstructures were characterized by transmission electron microscopy (TEM). Observations after irradiation revealed the presence of a high number density of Frank loops. Size and number density of Frank loops have been measured. Results are in good agreement with those observed in the literature and show that ion irradiation is able to simulate dislocation loop microstructure obtained after neutron irradiation. Experimental results and data from literature were compared with predictions from the cluster dynamic model, MFVIC (Mean Field Vacancy and Interstitial Clustering). It is able to reproduce dislocation loop population for neutron irradiation. Effects of dose rate and temperature on the loop number density are simulated by the model. Calculations for ion irradiations show that simulation results are consistent with experimental observations. However, results also show the model limitations due to the lack of accurate parameters.

  9. Austenite Formation from Martensite in a 13Cr6Ni2Mo Supermartensitic Stainless Steel

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

    2016-05-01

    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 stages. This is probably due to inhomogeneous distribution of the austenite-stabilizing elements Ni and Mn, resulting from their slow diffusion from martensite into austenite and carbide and nitride dissolution during the second, higher temperature, stage. A better homogenization of the material causes an increase in the transformation temperatures for the martensite-to-austenite transformation and a lower retained austenite fraction with less variability after tempering. Furthermore, the martensite-to-austenite transformation was found to be incomplete at the target temperature of 1223 K (950 °C), which is influenced by the previous austenitization treatment and the heating rate. The activation energy for martensite-to-austenite transformation was determined by a modified Kissinger equation to be approximately 400 and 500 kJ/mol for the first and the second stages of transformation, respectively. Both values are much higher than the activation energy found during isothermal treatment in a previous study and are believed to be effective activation energies comprising the activation energies of both mechanisms involved, i.e., nucleation and growth.

  10. Overlaying of type 316 austenitic stainless steel with type 430 ferritic stainless steel

    Overlaying of type 316 austenitic stainless steel vessel with type 430 ferritic stainless is proposed for liquid magnesium service. The interface in this type of bimetallic configuration has been shown to be a cause for concern as it contains a hard and brittle martensite micro constituent which becomes susceptible to cracking under certain conditions. This study was carried out to standardize the welding conditions and characterise the interface in order to obtain sound overlay. Some tests were also conducted to simulate the elevated temperature service. The investigation has shown that the interface hardness approaches 400 VPN when no preheating is employed. However, in the preheated samples, appreciable reduction in the peak hardness was observed. This has been attributed to a decrease in the cooling rate of the clad metal with an increase in the preheating temperature which results in softening of the martensite. The minimum recommended preheat is 473 K. The samples exposed to thermal cycle tests to a peak temperature of 1223 K to simulate the service condition did not show any cracking at the interface after 20 cycles of testing. Therefore, this study has demonstrated the stability of the interface between type 316 and 430 stainless steels at the intended temperature of service. (author)

  11. The stainless steel screw as an orthopaedic implant

    Rozman, J. [ITIS d. o. o. Ljubljana, Centre for Implantable Technology and Sensors Lepi pot 11, 1001 Ljubljana (Slovenia); Kmetic, M. [Institute of Materials and Technology Lepi pot 11, University of Ljubljana, 1001 Ljubljana (Slovenia); Bunc, M. [School of Medicine, Institute of Pathophysiology, Zaloska 4, 1001 Ljubljana (Slovenia); Pihlar, B. [Faculty of Chemistry and Chemical Technology, Askerceva 5, 1000 Ljubljana (Slovenia)

    2002-12-01

    The study reported here dealt with the metallographical inspection and analysis of corrosion behavior of screws for mild Slipped Capital Femoral Epiphysis (SCFE), which is a serious orthopedical problem in early adolescence. The screws were fabricated from low carbon, austenitic grade stainless steel type 316L (AISI) with 1600 ppm of nitrogen (316LN2). They were clinically tested in a nearly 25-year-long study where patients in early adolescence were operated with these screws with the fixation in situ. Since the results obtained in all patients were similar, we present the results obtained in screws removed after 3 years of implantation from a 14-year-old boy. Metallographical inspection results reveal that a low content of carbon in the SS 316LN2, and annealing this material at a high temperature ensures the monophasic microstructure of austenitic grains. In the grains twin bands that appeared during mechanical deformation were observed. As the hardness measured at the stalk (262 HV) was lower than that measured at the head of the screw (293 HV) it was concluded that cold mechanical deformation of the head was much more extensive than that of the stalk. Accordingly, corrosion of the head could be more probable than that of the stalk. Corrosion behavior of the screw in simulated physiological media (0.9% NaCl solution), carried out by the electrochemical method, gave an E{sub corr} of -0.124 V (vs. SCE), corrosion current density of 21 nA/cm{sup 2}, and corrosion rate of 0.010 {+-} 0.005 mpy. This low corrosion rate indicates that SS 316LN2 expresses relatively high corrosion resistance in a saline solution. However, potentiodynamic polarization measurements, where the specimen was driven to more than 1.8 V above the E{sub corr.}, showed that in the region between -0.1 and 0.15 V the specimen corroded, while around 0.2 V a small valley appeared where passivation proceeded. The narrow passive region between 0.15 and 0.25 V indicated that chlorides prevented the

  12. Magnetic properties of single crystalline expanded austenite obtained by plasma nitriding of austenitic stainless steel single crystals.

    Menéndez, Enric; Templier, Claude; Garcia-Ramirez, Pablo; Santiso, José; Vantomme, André; Temst, Kristiaan; Nogués, Josep

    2013-10-23

    Ferromagnetic single crystalline [100], [110], and [111]-oriented expanded austenite is obtained by plasma nitriding of paramagnetic 316L austenitic stainless steel single crystals at either 300 or 400 °C. After nitriding at 400 °C, the [100] direction appears to constitute the magnetic easy axis due to the interplay between a large lattice expansion and the expected decomposition of the expanded austenite, which results in Fe- and Ni-enriched areas. However, a complex combination of uniaxial (i.e., twofold) and biaxial (i.e., fourfold) in-plane magnetic anisotropies is encountered. It is suggested that the former is related to residual stress-induced effects while the latter is associated to the in-plane projections of the cubic lattice symmetry. Increasing the processing temperature strengthens the biaxial in-plane anisotropy in detriment of the uniaxial contribution, in agreement with a more homogeneous structure of expanded austenite with lower residual stresses. In contrast to polycrystalline expanded austenite, single crystalline expanded austenite exhibits its magnetic easy axes along basic directions. PMID:24028676

  13. Fracture toughness of austenitic stainless steels after BWR irradiation

    Austenitic stainless steels used for the core internal materials in BWRs are hardened by exposure to fast neutrons, and the fracture toughness is reduced by neutron fluence. It is important for integrity estimation of aged core internals to understand the reduction behavior of fracture toughness by neutron irradiation. In this study, core shroud materials (Type 304 SS) with 38 mm thickness and top guide materials (Type 316 SS) with 9.1 mm thickness, actually used for over twenty years in BWRs, were transported to PIE facility. Neutron fluence of type 304 SS was 1-6*1024 (n/m2, E > 1 MeV) and that of type 316 SS was 3-17*1024 (n/m2, E > 1 MeV). Fracture toughness tests for base metal were performed at 288 C in air using the CT specimen with real thickness of core shroud and top guide to obtain valid fracture toughness. And fracture toughness tests for heat affected zone (HAZ) were conducted using 0.7 TCT by the restriction of weld line direction. JIC and JQ of irradiated type 304 and type 316 base metals decreased with neutron fluence. JIC values of type 304 SS base metal and HAZ were obtained over 140 kJ/m2 at 5*1024 n/m2. JIC values of type 316 SS base metal were obtained over 240 kJ/m2 at 1.7*1025 n/m2. JIC values of type 304 HAZ were similar to those of base metal. JQ values of type 316 SS base metal had a higher value than JIC of type 304 SS base metal at similar neutron fluence. The difference between type 304 SS and type 316 SS is considered to be caused by the orientation effect of microstructure in CT specimen. From the SEM observation of crack surfaces, a linear relationship between JIC and the critical stretched zone width (SZWC) was found to exist in irradiated stainless steel materials. (authors)

  14. Creep behaviour and microstructural evolution in AISI 316LN + Nb steels at 650 deg. C

    Research highlights: → We studied the effect of Nb additions to AISI 316LN steels on creep and microstructure at 650 deg. C. → Nb additions resulted in a reduction of secondary creep rate and shortening of the tertiary stage. → Two nitrogen rich minor phases were present in the niobium-bearing casts: Z-phase and M6X. → The dimensional stability of Z-phase during creep at 650 deg. C was much better than that of M6X. → Nb accelerated σ-phase and η-Laves formation and this surpassed the positive effect of Z-phase. - Abstract: The paper deals with the effect of niobium in the wrought AISI 316LN steels on the long-term creep characteristics at 650 deg. C. Casts B and C contained 0.1 and 0.3 wt.%Nb, respectively. As a reference material the niobium free Cast A was used. Small additions of niobium to the AISI 316LN steel resulted in a significant reduction of the minimum creep rate and shortening of the tertiary creep stage. At time to rupture exceeding 104 h the creep rupture strength of the niobium-bearing Casts B and C was slightly inferior to the Cast A. Two nitrides formed in the Casts B and C: Z-phase and M6X. The minimum creep rate in niobium-bearing casts was favourably affected by precipitation of the Z-phase. The dimensional stability of Z-phase particles was very high, but niobium additions also accelerated the formation and coarsening of η-Laves and σ-phase. Coarse σ-phase particles at grain boundaries contributed significantly to the shortening of the tertiary creep stage.

  15. TEM studies of plasma nitrided austenitic stainless steel.

    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. PMID:20500370

  16. Crack growth in an austenitic stainless steel at high temperature

    This study deals with crack propagation at 650 deg C on an austenitic stainless steel referenced by Z2 CND 17-12 (316L(NN)). It is based on an experimental work concerning two different cracked specimens: CT specimens tested at 650 deg C in fatigue, creep and creep-fatigue with load controlled conditions (27 tests), tube specimens containing an internal circumferential crack tested in four points bending with displacement controlled conditions (10 tests). Using the fracture mechanics tools (K, J and C* parameters), the purpose here is to construct a methodology of calculation in order to predict the evolution of a crack with time for each loading condition using a fracture mechanics global approach. For both specimen types, crack growth is monitored by using a specific potential drop technique. In continuous fatigue, a material Paris law at 650 deg C is used to correlate crack growth rate with the stress intensity factor range corrected with a factor U(R) in order to take into account the effects of crack closure and loading ratio R. In pure creep on CT specimens, crack growth rate is correlated to the evolution of the C* parameter (evaluated experimentally) which can be estimated numerically with FEM calculations and analytically by using a simplified method based on a reference stress approach. A modeling of creep fatigue growth rate is obtained from a simple summation of the fatigue contribution and the creep contribution to the total crack growth. Good results are obtained when C* parameter is evaluated from the simplified expression C*s. Concerning the tube specimens tested in 4 point bending conditions, a simulation based on the actual A 16 French guide procedure proposed at CEA. (authors)

  17. The structure and corrosion behavior of electron beam treated austenitic stainless steels

    The influence of electron beam surface melting of austenitic AISI 304 stainless steel on its microstructure and anodic potentiostatic behavior in 1N sulphuric acid at 25 C has been studied. Delta ferrite formed in the surface melted layer and was found to vary with electron beam current and stainless steel plate thickness. The structure and anodic behavior of AISI 304 specimens conventionally heat treated to provoke ferrite formation were also studied. The length of active region in the anodic potentiostatic curves for both the surface melted and heat treated specimens decreased with increasing ferrite in the austenitic steel. Overall, surface melting using high energy sources has been found to significantly improve the aqueous corrosion resistance of austenitic stainless steel by provoking the formation of duplex microstructures. (author)

  18. Effects of milling process and alloying additions on oxide particle dispersion in austenitic stainless steel

    An oxide dispersion strengthened (ODS) austenitic stainless steel was developed by mechanical alloying (MA) of advanced SUS316 stainless steel. A nano-characterization was performed to understand details of the effect of minor alloying elements in the distribution of dispersoids. It is shown that Y2O3 particles dissolve into the austenitic matrix after the MA for 6 h. Annealing at 1073 K or higher temperatures result in a distribution of fine oxide particles in the recrystallized grains in the ODS austenitic stainless steel. Additions of Hafnium or Zirconium led to the distribution of finer oxide particles than in samples without these elements, resulting in an increase in the hardness of the samples. The most effective concentration of Hf and Zr to increase the hardness was 0.6 and 0.2–0.3 wt%, respectively

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

    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....

  20. Hot ductility of austenitic and duplex stainless steels under hot rolling conditions

    Kömi, J. (Jenni)

    2001-01-01

    Abstract The effects of restoration and certain elements, nitrogen, sulphur, calcium and Misch metal, on the hot ductility of austenitic, high-alloyed austenitic and duplex stainless steels have been investigated by means of hot rolling, hot tensile, hot bending and stress relaxation tests. The results of these different testing methods indicated that hot rolling experiments using stepped specimens is the most effective way to investigate the relationship between the s...

  1. Dependence of nanoindentation hardness with crystallographic orientation of austenite grains in metastable stainless steels

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

    2015-10-01

    The mechanical behaviour of a metastable austenitic stainless steel has been studied by means of nanoindentation of individual grains. Hardness, elastic modulus and estimation of wear resistance were determined as a function of crystallographic orientation. Electron backscattered diffraction, atomic force microscopy and focused ion beam analysis was performed at the residual imprints. Results show that austenitic grains display an anisotropic behaviour as regard as hardness in contrast with the elastic modulus which remained constant and equal to 200 GPa.

  2. Dependence of nanoindentation hardness with crystallographic orientation of austenite grains in metastable stainless steels

    The mechanical behaviour of a metastable austenitic stainless steel has been studied by means of nanoindentation of individual grains. Hardness, elastic modulus and estimation of wear resistance were determined as a function of crystallographic orientation. Electron backscattered diffraction, atomic force microscopy and focused ion beam analysis was performed at the residual imprints. Results show that austenitic grains display an anisotropic behaviour as regard as hardness in contrast with the elastic modulus which remained constant and equal to 200 GPa

  3. X-ray fractography studies on austenitic stainless steels

    Rajanna, K.; Pathiraj, B.; Kolster, B.H.

    1996-01-01

    In this investigation, the fracture surfaces of SS 304 and SS 316 austenitic steels were analysed using the X-ray fractography technique. In both cases, a decrease in the austenite content was observed at the fracture surface as a result of deformation induced martensite, indicating a linear relatio

  4. Key Technique of Austenitic Stainless Steel on-line Solution Treatment

    LI Sheng-li; LI Wei-juan; LIU Shuang; LI Ying; ZHAO Fei

    2004-01-01

    Generally the methods of solution treatment of austenitic stainless steel are bifurcated on-line solution and off-line solution . For a founded enterprise, it is necessary to find out how to get across alterations and search a measure of on -line solution disposal with less investment and higher efficiency. By studying and analysingin laboratory, several key points and the methods settle them are presented, which offers a new route to realize austenitic stainless steel on-line solution. By reducing the cost greatly, it makes the enterprise larger benefits.

  5. Structure Evolution and Solidification Behavior of Austenitic Stainless Steel in Pulsed Magnetic Field

    LI Qiu-shu; LI Hai-bin; ZHAI Qi-jie

    2006-01-01

    To understand the solidification behavior of austenitic stainless steel in pulsed magnetic field, the solidification process is investigated by means of the self-made high voltage pulse power source and the solidification tester. The results show that the solidification structure of austenitic stainless steel can be remarkably refined in pulsed magnetic field, yet the grains become coarse again when the magnetic intensity is exceedingly large, indicating that an optimal intensity range existed for structure refinement. The solidification temperature can be enhanced with an increase in the magnetic intensity. The solidification time is shortened obviously, but the shortening degree is reduced with the increase of the magnetic intensity.

  6. Influence of phase transformation on the hardening of austenitic stainless steels

    The influence of phase transformation on the true stress-true strain curves of austenitic stainless steels was studied. This investigation was carried on one type of AISI 302 steel and one AISI 316 steel. The temperature range varied from -1960C to room temperature. A model for the workhardening of metaestable austenitic stainless steel is proposed. It was concluded that stress induced martensite epsilon may be responsible for the lowering of yield strength as well as the initial plateau on workhardening in these materials. (Author)

  7. The effect of grain size on the mechanical response of a metastable austenitic stainless steel

    Sinclair C.W.

    2013-11-01

    Full Text Available The combination of high environmental resistance and excellent strength, elongation and energy absorption make austenitic stainless steels potentially attractive for transportation applications. In the case of metastable grades that undergo a strain induced martensitic transformation it is possible to significantly change the mechanical properties simply by changing the austenite grain size. Predicting such behaviour using physically based models is, however, extremely challenging. Here, some recent work on the coupling between grain size and mechanical response will be presented for a metastable AISI 301 LN stainless steel. Successes and continuing challenges will be highlighted.

  8. Ferrite and austenite phase identification in duplex stainless steel using SPM techniques

    Guo, L. Q.; Lin, M. C.; Qiao, L. J.; Volinsky, Alex A.

    2013-12-01

    It can be challenging to properly identify the phases in electro-polished duplex stainless steel using optical microscopy or other characterization techniques. This letter describes magnetic force microscopy to properly identify the phases in electropolished duplex stainless steel. The results are also confirmed with the current sensing atomic force and scanning Kelvin probe force microscopy. The difference in topography heights between the ferrite and austenite phases is attributed to the different etching rates during electropolishing, although these phases have different mechanical properties. The current in the austenite is much higher compared with the ferrite, thus current sensing atomic force microscopy can also be used to properly identify the phases.

  9. Measurement techniques of magnetic properties for evaluation of neutron irradiation damage on austenitic stainless steels

    The remote-controlled equipment for measurement of magnetic flux density has been developed in order to evaluate the irradiation damage of austenitic stainless steels. Magnetic flux densities by neutron irradiation in austenitic stainless steels, SUS304 and Fast Breeder Reactor grade type 316 (316FR), have been measured by the equipment. The results show that irradiation damage affected to magnetic flux density, and indicate the measuring method of magnetic flux density using a small magnetizer with a permanent magnet of 2 mm in diameter is less affected by specimen shape. (author)

  10. Crack initiation at high temperature on an austenitic stainless steel

    The study deals with crack initiation at 600 degrees Celsius and 650 degrees Celsius, on an austenitic stainless steel referenced by Z2 CND 17 12. The behaviour laws of the studied plate were update in comparison with existing data. Forty tests were carried out on CT specimens, with continuous fatigue with load or displacement controlled, pure creep, pure relaxation, creep-fatigue and creep-relaxation loadings. The practical initiation definition corresponds to a small crack growth of about the grain size, monitored by electrical potential drop technique. The time necessary for the crack to initiate is predicted with fracture mechanics global and local approaches, with the helps of microstructural observations and finite elements results. An identification of a 'Paris'law' for continuous cyclic loading and of a unique correlation between the initiation time and C*k for creep tests was established. For the local approach, crack initiation by creep can be interpreted as the reaching of a critical damage level, by using a damage incremental rule. For creep-fatigue tests, crack growth rates at initiation are greater than those of Paris'law for continuous fatigue. A calculation of a transition time between elastic-plastic and creep domains shows that crack initiation can be interpreted whether by providing Paris'law with an acceleration term when the dwell period is less than the transition time, or by calculating a creep contribution which relies on C*k parameter when the dwell period and/or the initiation times are greater than the transition time. Creep relaxation tests present crack growth rates at initiation which are less than those for 'equivalent' creep-fatigue tests. These crack growth rates when increasing hold time, but also when temperature decreases. Though, for hold times which are important enough and at lower temperature, there is no effect of the dwell period insofar as crack growth rate is equal to continuous fatigue Paris law predicted ones

  11. Out-of-plane magnetic patterning on austenitic stainless steels using plasma nitriding

    Menéndez, E.; Nogués, Josep

    2010-01-01

    A correlation between the grain orientation and the out-of-plane magnetic properties of nitrogen-enriched polycrystalline austenitic stainless steel surface is performed. Due to the competition between the magnetocrystalline anisotropy, the exchange and dipolar interactions, and the residual stresses induced by nitriding, the resulting effective magnetic easy-axis can lay along unusual directions. It is also demonstrated that, by choosing an appropriate stainless steel texturing, arrays of fe...

  12. Acoustic Emission Technique for Characterizing Deformation and Fatigue Crack Growth in Austenitic Stainless Steels

    Raj, Baldev; Mukhopadhyay, C. K.; Jayakumar, T.

    2003-03-01

    Acoustic emission (AE) during tensile deformation and fatigue crack growth (FCG) of austenitic stainless steels has been studied. In AISI type 316 stainless steel (SS), AE has been used to detect micro plastic yielding occurring during macroscopic plastic deformation. In AISI type 304 SS, relation of AE with stress intensity factor and plastic zone size has been studied. In AISI type 316 SS, fatigue crack growth has been characterised using acoustic emission.

  13. Super austenitic stainless steels - a promising replacement for the currently used type 316L stainless steel as the construction material for flue-gas desulphurization plant

    Rajendran, N.; Rajeswari, S. [University of Madras, Madras (India). Dept. of Analytical Chemistry

    1996-12-15

    Potentiodynamic anodic cyclic polarization experiments on type 316L stainless steel and 6Mo super austenitic stainless steels were carried out in simulated flue-gas desulphurization (FGD) environment in order to assess the localized corrosion resistance. The pitting corrosion resistance was higher in the case of the super austenitic stainless steel containing 6Mo and a higher amount of nitrogen. The accelerated leaching study conducted for the alloys showed that the super austenitic stainless steels have a little tendency for leaching of metal ions such as iron, chromium and nickel at different impressed potentials. This may be due to surface segregation of nitrogen as CrN, which would, in turn, enrich a chromium and molybdenum mixed oxide film and thus impede the release of metal ions. The present study indicates that the 6Mo super austenitics can be adopted as a promising replacement for the currently used type 316L stainless steel as the construction material for FGD plants.

  14. Solidification crack susceptibility in weld metals of fully austenitic stainless steels, (1)

    It has been well known that weld metals of fully austenitic stainless steels exhibit greater susceptibility to hot cracking and austenitic weld metals containing a small amount (in the order of 5%) of delta ferrite are much more resistant during welding. However, it has not been clarified completely why the presence of some delta-ferrite prevents hot cracking in Cr-Ni weld metals. Therefore, the authors have investigated the structural change during solidification from a metallographic standpoint for the both weld metals of fully austenitic stainless steel AISI 310S (25Cr-20Ni; Japanese Industrial Standards: SUS 310S) and austenitic stainless steel AISI 304 (18Cr-8Ni; JIS: SUS 304) containing a small amount of delta-ferrite to which sulphur and phosphorus were added as harmful impurities. Each specimen was rapidly quenched in water during TIG arc bead-on-plate, so that each bead showed the instantaneous structures from solidification front to room temperature along welding direction. Solidification behaviors of the fully austenitic and the duplex microstructures, microsegregation (especially S and P) during solidification and distribution of alloying elements between delta- and γ-phases at high temperature were investigated. (auth.)

  15. Radio-induced brittleness of austenitic stainless steels at high temperatures

    In a first part, the author recalls some metallurgical characteristics and properties of iron (atomic properties, crystalline structure, transformation), of iron carbon systems and steels (ferrite, austenite, cementite, martensite, bainite, phase diagrams of iron chromium alloy and iron nickel alloy), aspects regarding the influence of addition elements in the case of stainless steels (mutual interaction of carbon, chromium and nickel in their iron alloys, indication of the various stainless steels, i.e. martensitic, ferritic, austenitic, austenitic-ferritic, and non ferrous), and presents and discusses various mechanical tests (tensile tests, torsion tests, resilience tests, hardness tests, creep tests). In a second part, he discusses the effects of irradiation on austenitic stainless steels: irradiation and deformation under low temperature, irradiation at intermediate temperature, irradiation at high temperature. The third part addresses mechanisms of intergranular fracture in different temperature ranges (400-600, 700-750, and about 800 C). The author then discusses the effect of Helium on the embrittlement of austenitic steels, and finally evokes the perspective of development of a damage model

  16. Dissimilar Friction Stir Welding Between UNS S31603 Austenitic Stainless Steel and UNS S32750 Superduplex Stainless Steel

    Theodoro, Maria Claudia; Pereira, Victor Ferrinho; Mei, Paulo Roberto; Ramirez, Antonio Jose

    2015-02-01

    In order to verify the viability of dissimilar UNS S31603 austenitic and UNS S32750 superduplex stainless steels joined by friction stir welding, 6-mm-thick plates were welded using a PCBN-WRe tool. The welded joints were performed in position control mode at rotational speeds of 100 to 300 rpm and a feed rate of 100 mm/min. The joints performed with 150 and 200 rpm showed good appearance and no defects. The metallographic analysis of both joints showed no internal defects and that the material flow pattern is visible only in the stirred zone (SZ) of the superduplex steel. On the SZ top, these patterns are made of regions of different phases (ferrite and austenite), and on the bottom and central part of the SZ, these patterns are formed by alternated regions of different grain sizes. The ferrite grains in the superduplex steel are larger than those in the austenitic ones along the SZ and thermo-mechanically affected zone, explained by the difference between austenite and ferrite recrystallization kinetics. The amount of ferrite islands present on the austenitic steel base metal decreased near the SZ interface, caused by the dissolving of the ferrite in austenitic matrix. No other phases were found in both joints. The best weld parameters were found to be 200 rpm rotation speed, 100 mm/min feed rate, and tool position control.

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

    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

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

    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.

  19. Lean-alloyed austenitic stainless steel with high resistance against hydrogen environment embrittlement

    Highlights: · Hydrogen environment embrittlement of austenitic steel. · Novel alloying concept for austenitic stainless steel with improved HEE resistance. · Influence of austenite stability and strain-induced α-martensite on HEE. · Cost efficiency by reduced amounts of nickel and molybdenum. · Influence of silicon on HEE. - Abstract: To address the upcoming austenitic stainless steel market for automotive applications involving hydrogen technology, a novel lean - alloyed material was developed and characterized. It comprises lower contents of nickel and molybdenum compared to existing steels for high - pressure hydrogen uses, for instance 1.4435 (AISI 316L). Alloying with manganese and carbon ensures a sufficient stability of the austenite at 8 wt.% of nickel while silicon is added to improve resistance against embrittlement by dissolved hydrogen. Investigations were performed by tensile testing in air and 400 bar hydrogen at 25 deg. C, respectively. In comparison to a standard 1.4307 (AISI 304L) material, a significant improvement of ductility was found. The materials concept is presented in general and discussed with regard to austenite stability and microstructure.

  20. Progress in EPRI-programs on the inspection of cast austenitic stainless steel

    This document presents the progress in EPRI programs on in-service inspection of Cast austenitic Stainless Steel (CSS). The CSS examination strategy is presented, together with results concerning thermal fatigue cracks and mechanical fatigue cracks. A statistical analysis method is provided, in order to estimate the crack detectability and the false call (a non-crack called crack). (TEC)

  1. Effect of electromagnetic stirring on solidification structure of austenitic stainless steel in horizontal continuous casting

    2007-01-01

    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

  2. Very high cycle regime fatigue of thin walled tubes made from austenitic stainless steel

    Carstensen, J.V.; Mayer, H.; Brøndsted, P.

    2002-01-01

    Fatigue life data of cold worked tubes (diameter 4 mm, wall thicknesses 0.25 and 0.30 mm) of an austenitic stainless steel, AISI 904 L, were measured in the regime ranging from 2 × 105 to 1010 cycles to failure. The influence of the loading frequency was investigated as data were obtained in...

  3. The Formation of Multipoles during the High-Temperature Creep of Austenitic Stainless Steels

    Howell, J.; Nielsson, O.; Horsewell, Andy;

    1981-01-01

    It is shown that multipole dislocation configurations can arise during power-law creep of certain austenitic stainless steels. These multipoles have been analysed in some detail for two particular steels (Alloy 800 and a modified AISI 316L) and it is suggested that they arise either during...

  4. Performance evaluation of vegetable-based oils in drilling austenitic stainless steel

    Belluco, Walter; De Chiffre, Leonardo

    2004-01-01

    The efficiency of six cutting oils was evaluated in drilling AISI 316L austenitic stainless steel using conventional HSS-Co tools by measurements of tool life, tool wear, cutting forces and chip formation. Seven tools were tested with each fluid to catastrophic failure. Cutting forces and chip...

  5. Void Volume Swelling Dependent on Grain Size in Austenitic Stainless Steel

    Singh, Bachu Narain

    1973-01-01

    Describes some of the main findings of a systematic study of the effect of grain size on the void volume swelling. In this study a powder-produced 20 Ni/20 Cr austenitic stainless steel, with 0.02% carbon and without carbide-forming elements was used. Some specimens containing dispersions of...

  6. The efficiency of ion nitriding of austenitic stainless steel 304 using the “active screen”

    Ogórek, M.; Skuza, Z.; T. Frączek

    2015-01-01

    The study examined layers were formed on the outer surface of austenitic stainless steel 304 under glow discharge conditions in the low-temperature and short-term ion nitriding. The outer layers analyzed in the work produced in parallel in the classical process of cathode and a novel method of “active screen”, intensifying the process of nitriding.

  7. The efficiency of ion nitriding of austenitic stainless steel 304 using the “active screen”

    M. Ogórek

    2015-01-01

    Full Text Available The study examined layers were formed on the outer surface of austenitic stainless steel 304 under glow discharge conditions in the low-temperature and short-term ion nitriding. The outer layers analyzed in the work produced in parallel in the classical process of cathode and a novel method of “active screen”, intensifying the process of nitriding.

  8. Welding of super austenitic stainless steels with very high nitrogen contents

    Results of studies performed on the weld of different super austenitic stainless steels show that nitrogen additions as high as 0.5% does not deteriorate the weldability but on the contrary improves the mechanical and corrosion properties of the weld. (A.B.). 5 refs., 5 figs., 6 tabs

  9. The adhesion of hot-filament CVD diamond films on AISI type 316 austenitic stainless steel

    Buijnsters, J.G.; Shankar, P.; Enckevort, W.J.P. van; Schermer, J.J.; Meulen, J.J. ter

    2004-01-01

    Steel ball indentation and scratch adhesion testing of hot filament chemical vapour deposited diamond films onto AISI type 316 austenitic stainless steel substrates using two different interlayer systems, namely chromium nitride and borided steel, have been investigated. In order to compare the adhe

  10. Effect of electromagnetic stirring on solidification structure of austenitic stainless steel in horizontal continuous casting

    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.

  11. Dynamic Recrystallization Behavior of a Fe-Cr-Ni Super-Austenitic Stainless Steel

    A. Hoseini Asli; A. Zarei-Hanzaki

    2009-01-01

    The super-austenitic stainless steels are extensively utilized in the seamless tubes production for oil extraction industries. Due to the importance of thermo-mechanical processing in the production of these tubes, the dynamic recrystallization (DRX) characteristics of a Cr-Ni super austenitic stainless steel (1.4563) were investigated in the present study. This was performed using the hot compression testing method in the temperature range of 950-1150℃ and the strain rate of 10~(-3)-10~(-1)s~(-1). The initiation and evolution of DRX were examined through microstructural analysis. The results indicated that the recrystallized grain formed a necklace type structure at the prior austenite grain boundaries at higher strain rates. In addition, DRX nucleation occurs by bulging and successive strain induced boundary migration (SIBM).

  12. Laser Shock Processing of an Austenitic Stainless Steel and a Nickel-base Superalloy

    Huaming WANG; Xijun SUN; Xiaoxuan LI

    2003-01-01

    An austenitic stainless steel 1Cr18Ni9Ti and a solid solution-strengthened Ni-base superalloy GH30 were shock processed usinga Q-switched pulsed Nd-glass laser. Microstructure, hardness and residual stress of the laser shock processed surface wereinvestigated as functions of laser processing parameters. Results show that high density of dislocations and fine deformationtwins are produced in the laser shock processed surface layers in both the austenitic stainless steel and the nickel-base superalloy.Extensive strain-induced martensite was also observed in the laser shock processed zone of the austenitic steel. The hardnessof the laser shock processed surface was significantly enhanced and compressive stress as high as 400 MPa was produced inthe laser shock processed surface.

  13. Influence of surface texture on the galling characteristics of lean duplex and austenitic stainless steels

    Wadman, Boel; Eriksen, J.; Olsson, M.;

    2010-01-01

    Two simulative test methods were used to study galling in sheet forming of two types of stainless steel sheet: austenitic (EN 1.4301) and lean duplex LDX 2101 (EN 1.4162) in different surface conditions. The pin-on-disc test was used to analyse the galling resistance of different combinations of...... industrial tool used for high volume production of pump components, to compare forming of LDX 2101 and austenitic stainless steel with equal thickness. The forming forces, the geometry and the strains in the sheet material were compared for the same component. It was found that LDX steels can be formed to...... high strain levels in tools normally applied for forming of austenitic steels, but tool adaptations are needed to comply with the higher strength and springback of the material....

  14. Grain refinement of a nickel and manganese free austenitic stainless steel produced by pressurized solution nitriding

    Prolonged exposure at high temperatures during solution nitriding induces grain coarsening which deteriorates the mechanical properties of high nitrogen austenitic stainless steels. In this study, grain refinement of nickel and manganese free Fe–22.75Cr–2.42Mo–1.17N high nitrogen austenitic stainless steel plates was investigated via a two-stage heat treatment procedure. Initially, the coarse-grained austenitic stainless steel samples were subjected to an isothermal heating at 700 °C to be decomposed into the ferrite + Cr2N eutectoid structure and then re-austenitized at 1200 °C followed by water quenching. Microstructure and hardness of samples were characterized using X-ray diffraction, optical and scanning electron microscopy, and micro-hardness testing. The results showed that the as-solution-nitrided steel decomposes non-uniformly to the colonies of ferrite and Cr2N nitrides with strip like morphology after isothermal heat treatment at 700 °C. Additionally, the complete dissolution of the Cr2N precipitates located in the sample edges during re-austenitizing requires longer times than 1 h. In order to avoid this problem an intermediate nitrogen homogenizing heat treatment cycle at 1200 °C for 10 h was applied before grain refinement process. As a result, the initial austenite was uniformly decomposed during the first stage, and a fine grained austenitic structure with average grain size of about 20 μm was successfully obtained by re-austenitizing for 10 min. - Highlights: • Successful grain refinement of Fe–22.75Cr–2.42Mo–1.17N steel by heat treatment • Using the γ → α + Cr2N reaction for grain refinement of a Ni and Mn free HNASS • Obtaining a single phase austenitic structure with average grain size of ∼ 20 μm • Incomplete dissolution of Cr2N during re-austenitizing at 1200 °C for long times • Reducing re-austenitizing time by homogenizing treatment before grain refinement

  15. Grain refinement of a nickel and manganese free austenitic stainless steel produced by pressurized solution nitriding

    Mohammadzadeh, Roghayeh, E-mail: r_mohammadzadeh@sut.ac.ir; Akbari, Alireza, E-mail: akbari@sut.ac.ir

    2014-07-01

    Prolonged exposure at high temperatures during solution nitriding induces grain coarsening which deteriorates the mechanical properties of high nitrogen austenitic stainless steels. In this study, grain refinement of nickel and manganese free Fe–22.75Cr–2.42Mo–1.17N high nitrogen austenitic stainless steel plates was investigated via a two-stage heat treatment procedure. Initially, the coarse-grained austenitic stainless steel samples were subjected to an isothermal heating at 700 °C to be decomposed into the ferrite + Cr{sub 2}N eutectoid structure and then re-austenitized at 1200 °C followed by water quenching. Microstructure and hardness of samples were characterized using X-ray diffraction, optical and scanning electron microscopy, and micro-hardness testing. The results showed that the as-solution-nitrided steel decomposes non-uniformly to the colonies of ferrite and Cr{sub 2}N nitrides with strip like morphology after isothermal heat treatment at 700 °C. Additionally, the complete dissolution of the Cr{sub 2}N precipitates located in the sample edges during re-austenitizing requires longer times than 1 h. In order to avoid this problem an intermediate nitrogen homogenizing heat treatment cycle at 1200 °C for 10 h was applied before grain refinement process. As a result, the initial austenite was uniformly decomposed during the first stage, and a fine grained austenitic structure with average grain size of about 20 μm was successfully obtained by re-austenitizing for 10 min. - Highlights: • Successful grain refinement of Fe–22.75Cr–2.42Mo–1.17N steel by heat treatment • Using the γ → α + Cr{sub 2}N reaction for grain refinement of a Ni and Mn free HNASS • Obtaining a single phase austenitic structure with average grain size of ∼ 20 μm • Incomplete dissolution of Cr{sub 2}N during re-austenitizing at 1200 °C for long times • Reducing re-austenitizing time by homogenizing treatment before grain refinement.

  16. Nanostructured nickel-free austenitic stainless steel composites with different content of hydroxyapatite

    Highlights: ► Ni-free austenitic stainless steel/hydroxyapatite composites were produced. ► Nanocrystalline structure was confirmed by three different techniques. ► Nitriding of the surface slightly increases crystallite size. ► The mean grain size of the obtained materials do not exceed 100 nm. - Abstract: The aim of this work is to show that Ni-free austenitic stainless steels with nanostructure and their nanocomposites with hydroxyapatite can be synthesized by mechanical alloying, heat treatment and nitriding of elemental microcrystalline powders with addition of hydroxyapatite (HA). Hydroxyapatite was introduced into stainless steel because it is intensively studied for bone repair and replacement applications. Nickel-free austenitic stainless steels seem to have better mechanical properties, corrosion resistance and biocompatibility compared to 316L stainless steels. Therefore it's combination with hydroxyapatite that has high biocompatibility and ability to bond to bone could have improved properties, as well. To confirm nanocrystalline structure of obtained material and reveal topographical features of the surface, small-angle X-ray analysis (SAXS) and atomic force microscopy (AFM) were used. Results are consistent and the mean grain size of the obtained materials do not exceed 100 nm.

  17. Magnetic State of Deformed Austenite Before and After Martensite Nucleation in Austenitic Stainless Steels

    GennadiiVSnizhnoi; MariyaSRasshchupkyna’

    2012-01-01

    The effect of the increase in the paramagnetic susceptibility of austenite up to the true value of the deformation-induced martensite transition point es has been experimentally established in steels X6CrNiTil8-10 (correspon& ing to AISI 321 steels). At this point nucleation and accumulation of martensite with the increase in the extent of de- formation but at a constant magnetic state of austenite takes place.

  18. High nitrogen-dosed austenitic-stainless steels and duplex steels

    The austenitic grades represent the most important group in the family of stainless steels. Nitrogen addition to austenitic stainless steels provides much higher yield strength. It was the goal of the present work to develop new high strength austenitic and duplex stainless steels and to investigate the beneficial influence of nitrogen. More than 40 small ingots up to a weight of 1.5 kg were melted in a specially developed high pressure induction furnace. In addition 20 more alloys produced by a pressurized electro slag remelting facility were included in this investigation. The nitrogen content was varied between 0.37 and 1.47 wt.%. New coefficients are proposed for the nickel equivalent in the Schaeffler diagram; these are from 0.12 to 0.24 for manganese and 18 for nitrogen. The increase in yield strength by interstitially dissolved nitrogen is due to solid solution hardening and to increased grain boundary hardening. The addition of 1% nitrogen gives a yield strength of more than 759 MPa. The toughness remains very good. At room temperature nitrogen alloyed Fe-Cr-Mn austenitic steels give the highest product of strength and toughness. Nitrogen containing austenitic stainless steels show a substantial increase in strength at low temperature. From room temperature to 4K the yield strength is more than tripled. Nitrogen alloyed Fe-Cr-Mn austenitic stainless steels exhibit a ductile to brittle transition as the temperature is lowered. This is due to a planar deformation mode which could be caused by low stacking fault energy. Nickel improves the low temperature toughness and also raises the stacking fault energy. In the temperature range from 600 to 900oC, Cr2N precipitate. The minimal time for precipitation is longer by a factor of 10 than in Fe-Cr-Ni grade. Nitrogen decreases the corrosion rate in austenitic and duplex stainless steels. The resistance to pitting corrosion can be described by the equation WL= %Cr + 3.3 %Mo + 30 %N. (author) figs., tabs., refs

  19. Long term corrosion resistance of alumina forming austenitic stainless steels in liquid lead

    Highlights: • Alumina forming austenitic stainless steels (AFA) were exposed to lead at 550 °C. • The influence of Al addition and Ni content was evaluated. • The low Ni (14 wt.%) AFA formed a thin protective Al rich oxide on its surfaces. • 17% ferrite was formed in the 14Ni AFA alloy as a result of the one year exposure. - Abstract: Alumina forming austenitic steels (AFA) and commercial stainless steels have been exposed in liquid lead with 10−7 wt.% oxygen at 550 °C for up to one year. It is known that chromia forming austenitic stainless steels, such as 316L and 15–15 Ti, have difficulties forming protective oxides in liquid lead at temperatures above 500 °C, which is confirmed in this study. By adding Al to austenitic steels, it is in general terms possible to increase the corrosion resistance. However this study shows that the high Ni containing AFA alloys are attacked by the liquid lead, i.e. dissolution attack occurs. By lowering the Ni content in AFA alloys, it is possible to achieve excellent oxidation properties in liquid lead. Following further optimization of the microstructural properties, low Ni AFA alloys may represent a promising future structural steel for lead cooled reactors

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

    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

  1. Role of Austenite in Brittle Fracture of Bond Region of Super Duplex Stainless Steel

    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.

  2. Laser welding of butt joints of austenitic stainless steel AISI 321

    A. Klimpel

    2007-11-01

    Full Text Available Purpose: of this paper: A study of an automated laser autogenous welding process of butt joints of austenitic stainless steel AISI 321 sheets 0.5 [mm] and 1.0 [mm] thick using a high power diode laser HPDL has been carried out.Design/methodology/approach: Influence of basic parameters of laser welding on shape and quality of the butt joints and the range of optimal parameters of welding were determined.Findings: It was showed that there is a wide range of laser autogenous welding parameters which ensures high quality joints of mechanical strength not lower than the strength of the base material (BM. The butt joints of austenitic steel AISI 321 sheets welded by the HPDL diode laser at optimal parameters are very high quality, without any internal imperfections and the structure and grain size of weld metal and HAZ is very small and also the HAZ is very narrow and the fusion zone is very regular.Research limitations/implications: Studies of the weldability of stainless steels indicate that the basic influence on the quality of welded joints and reduction of thermal distortions has the heat input of welding, moreover the highest quality of welded joints of austenitic stainless steel sheets are ensured only by laser welding.Practical implications: The technology of laser welding can be directly applied for welding of butt joints of austenitic steel AISI 321 sheets 0.5 and 1.0 [mm] thick.Originality/value: Application of high power diode laser for welding of austenitic stainless steel AISI 321.

  3. Application Feasibility of PRE 50 grade Super Austenitic Stainless Steel as a Steam Generator Tubing

    Park, Yong Soo [Yonsei University, Seoul (Korea, Republic of); Kim, Young sik [Andong National University, Andong (Korea, Republic of); Kim, Taek Jun; Kim, Sun Tae; Park, Hui Sang [Yonsei University, Seoul (Korea, Republic of)

    1997-07-01

    The aim of this study is to evaluate the properties of the super austenitic stainless steel, SR-50A for application as steam generator tubing material. The microstructure, mechanical properties, corrosion properties, were analyzed and the results were compared between super austenitic stainless steel and Alloy 600 and Alloy 690. Super austenitic stainless steel, SR-50A is superior to Alloy 600, Alloy 690 and Alloy 800 in the mechanical properties(tensile strength, yield strength, and elongation). It was investigated that thermal conductivity of SR-50A was higher than Alloy 600. As a result of thermal treatment on super stainless steel, SR-50A, caustic SCC resistance was increased and its resistance was as much as Alloy 600TT and Alloy 690TT. In this study, optimum thermal treatment condition to improve the caustic corrosion properties was considered as 650 deg C or 550 deg C 15 hours. However, it is necessary to verify the corrosion mechanism and to prove the above results in the various corrosive environments. 27 refs., 6 tabs., 59 figs. (author)

  4. Case histories of microbiologically influenced corrosion of austenitic stainless steel weldments

    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

  5. Study by factorial analysis of the influence of chemical composition on the stress corrosion cracking of austenitic stainless steels

    The stress corrosion cracking of austenitic stainless steels has been treated by factorial correspondence analysis. This statistical method gives a relationship between chemical characteristics and the susceptibility of the steels to the phenomenon

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

    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....

  7. Extended X-Ray Absorption Fine Structure Investigation of Carbon Stabilized Expanded Austenite and Carbides in Stainless Steel AISI 316

    Oddershede, Jette; Christiansen, Thomas; Ståhl, Kenny;

    2011-01-01

    Low temperature carburized AISI 316 stainless steel - carbon expanded austenite - was investigated with EXAFS and synchrotron diffraction together with synthesized carbides of the type M3C2, M7C3 and M23C6. It was found that the chemical environment of carbon expanded austenite is not associated...

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

    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.

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

    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

  10. Effect of cryorolling on the microstructure and tensile properties of bulk nano-austenitic stainless steel

    We report the synthesis of nanostructured austenitic AISI 304L stainless steel (SS) through cryorolling (CR) and reversion annealing in the temperature range of 700–800 °C. Severe CR at sub-zero temperature promotes twinning in γ-austenite, which transform into α'-martensite with lath thickness of 50–100 nm. Whereas, 50–300 nm size γ-grains recrystallize in nano-twinned α' through reversion annealing as confirmed by transmission electron microscopy (TEM) and electron back scattered diffraction (EBSD) imaging. The evolution of highly processable bulk nano-austenitic SS with bimodal grain size distribution on achieving high strength (~1295 MPa), large tensile ductility (~0.47), and true necking strain of 0.59, have been discussed

  11. Review of environmental effects on fatigue crack growth of austenitic stainless steels

    Fatigue and environmentally assisted cracking of piping, pressure vessel cladding, and core components in light water reactors are potential concerns to the nuclear industry and regulatory agencies. The degradation processes include intergranular stress corrosion cracking of austenitic stainless steel (SS) piping in boiling water reactors (BWRs), and propagation of fatigue or stress corrosion cracks (which initiate in sensitized SS cladding) into low-alloy ferritic steels in BWR pressure vessels. Crack growth data for wrought and cast austenitic SSs in simulated BWR water, developed at Argonne National Laboratory under US Nuclear Regulatory Commission sponsorship over the past 10 years, have been compiled into a data base along with similar data obtained from the open literature. The data were analyzed to develop corrosion-fatigue curves for austenitic SSs in aqueous environments corresponding to normal BWR water chemistries, for BWRs that add hydrogen to the feedwater, and for pressurized water reactor primary-system-coolant chemistry

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

    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.

  13. Material for hot rolling of high boron content austenite stainless steel, and hot rolling method

    A hot rolling material made of a high boron content austenite stainless steel of the present invention comprises a slab made of an austenite stainless steel containing from 0.6 to 2.0% by weight of B and a pad-welded metal layer formed on the side surface of the slab. The pad-welded metal layer has δ ferrite amount of from 3 to 12% by volume, B content up to 0.3% by weight, a thickness of 3mm or greater, and is subjected to hot rolling after heated to a temperature of from 1100 to 1200degC. This can prevent occurrence of peripheral cracking and the material can be industrially manufactured stably at a low cost. (T.M.)

  14. Hydrogen Environment Embrittlement on Austenitic Stainless Steels from Room Temperature to Low Temperatures

    Ogata, Toshio

    2015-12-01

    Hydrogen environment embrittlement (HEE) on austenitic stainless steels SUS304, 304L, and 316L in the high pressure hydrogen gas was evaluated from ambient temperature to 20 K using a very simple mechanical properties testing procedure. In the method, the high- pressure hydrogen environment is produced just inside the hole in the specimen and the specimen is cooled in a cooled-alcohol dewar and a cryostat with a GM refrigerator. The effect of HEE was observed in tensile properties, especially at lower temperatures, and fatigue properties at higher stress level but almost no effect around the stress level of yield strength where almost no strain-induced martensite was produced. So, no effect of HEE on austenitic stainless steels unless the amount of the ferrite phase is small.

  15. Prevision of in-service aging of molded austenitic-ferritic stainless steels components

    After having recalled the service conditions of the nuclear PWR boilers, the austenitic-ferritic molded stainless steels and their uses in the primary coolant circuit are described. The main consequences of the thermal aging on the rupture mechanisms and the mechanical properties are recalled too. Then are described the laboratory studies carried out in France and abroad which have allowed the development of an extensive knowledge of the aging reaction kinetics and then of embrittlement anticipation formulae. Measures and sampling carried out on down-rated components or even on in service components are used to verify the quality of the in-service aging anticipation. At last are identified the subjects on which it will be important to advance to improve our knowledge of the behaviour of the austenitic-ferritic stainless steels components. (O.M.)

  16. The Synthesis and Electrochemical Behavior of High-Nitrogen Nickel-Free Austenitic Stainless Steel

    Sun, Shicheng; Wei, Sufeng; Wang, Guoyong; Jiang, Zhonghao; Lian, Jianshe; Ji, Changtao

    2014-11-01

    A new smelting method to synthesize high-nitrogen nickel-free austenitic stainless steel was suggested. The synthesized steel completely consists of austenite and represents more brilliant anti-corrosion ability both in salt solution and sulfuric acid solution. The brilliant anti-corrosion ability is retained even after severe cold-rolling deformation, which ensures its workability in practice. The potentiodynamic polarization curves, electrochemical impedance spectroscopy, and passivating treatment were used to characterize its corrosion properties and uncover its corrosion mechanism in salt solution. X-ray photoelectron spectroscopy was used to clarify the mechanism of passivation. The results demonstrate that the steel has a more uniform and thicker passive film than traditional stainless steel due to the cooperation of nitrogen and chromium.

  17. Wear of plasma nitrided and nitrocarburized AISI 316L austenitic stainless steel

    F.A.P. Fernandes

    2010-06-01

    Full Text Available Purpose: the purpose of the work is to compare the wear resistance, in dry and lubricated conditions, of AISI 316L austenitic stainless steel samples that were plasma nitrided or nitrocarburized at 450°C for 5 and 10 h, respectively.Design/methodology/approach: Hardness and wear resistance of austenitic stainless steel can be increased substantially, without losing corrosion resistance, by plasma nitriding or nitrocarburizing surface treatments. In this work, AISI 316L austenitic stainless steel was plasma nitrided and nitrocarburized at 450°C, for 5 and 10 h respectively.Findings: The obtained layers were characterized by optical microscopy, X-ray diffraction, microhardness and micro-wear tests in dry and lubricated conditions. Optical microscopy and X-ray diffraction analysis demonstrated that the nitrided layer is homogeneous and primarily composed of nitrogen rich expanded austenite with a thickness of about 15 µm. Nitrocarburized samples exhibited an external layer of chromium and iron compounds and a sub-layer of expanded austenite with a total thickness of 45 µm. Microhardness profiles showed that the hardness near to the surface was close to 1100 HV for nitriding and 1300 HV for nitrocarburizing. Plasma nitrided and nitrocarburized layers exhibited substantial wear reduction in dry and lubricated test conditions. The use of a lubricant oil reduces wear by a factor of approximately 200 compared to the dry test results.Research limitations/implications: The plasma nitrided layer yielded the best wear performance in both dry and lubricated conditions.Originality/value: Plasma nitriding resulted in the best wear performance when compared with nitrocarburizing in dry and lubricated sliding which is probably due to reduced layer fragility.

  18. Surface stability and conductivity of a high Cr and Ni austenitic stainless steel plates for PEMFC

    TIAN Rujin; SUN Juncai; WANG Jianli

    2006-01-01

    In order to use stainless steel as bipolar plate for PEMFC, electrochemical behavior of a high Cr and Ni austenitic stainless steel was studied in the solutions containing different concentration of H2SO4 and 2 mg·L-1 F-, and interfacial contact resistance was measured after corrosion tests. The experimental results show that the passive current density lowers with decreasing the concentration of H2SO4. The interfacial contact resistance between carbon paper and passive film formed in the simulated PEMFC environment is higher than the goal of bipolar plate for PEMFC. Surface conductivity should be further reduced by surface modification.

  19. Effect of Electrode Types on the Solidification Cracking Susceptibility of Austenitic Stainless Steel Weld Metal

    J. U. Anaele; O. O. ONYEMAOBI; Nwobodo, C. S.; C. C. Ugwuegbu

    2015-01-01

    The effect of electrode types on the solidification cracking susceptibility of austenitic stainless steel weld metal was studied. Manual metal arc welding method was used to produce the joints with the tungsten inert gas welding serving as the control. Metallographic and chemical analyses of the fusion zones of the joints were conducted. Results indicate that weldments produced from E 308-16 (rutile coated), E 308-16(lime-titania coated) electrodes, and TIG welded joints fall within the range...

  20. Experimental Investigation of Ultrasonic Vibration Assisted Turning of 304 Austenitic Stainless Steel

    Zou, Ping; Xu, Yingshuai; He, Yu; Chen, Mingfang; Wu, Hao

    2015-01-01

    This research study focuses on the experimental analysis of the three-dimensional (3D) surface topography and surface roughness of the workpiece machined with ultrasonic vibration assisted turning (UAT) in comparison to conventional turning (CT). For the challenge that machining difficulties of 304 austenitic stainless steel (ASS 304) and high demands for the machined surface quality and machining precision represent, starting with cutting principle and processing technology, the ultrasonic v...

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

    Chen, Ming; Molin, Sebastian; Zhang, L; Ta, Na; Hendriksen, Peter Vang; Kiebach, Wolff-Ragnar; Y. Du

    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 mo...

  2. Solid solution strengthening effect on creep strength of austenitic stainless steel

    Abouzari, Sara

    2012-01-01

    Sanicro 25 is a newly developed austenitic stainless steel, designed for the next generation of Ultrasupercritical coal-fired boilers in electrical power plants. This material is applicable in reheater and superheater tubes, where the material temperature is up to 700 °C. One of the main strengthening mechanisms in high temperature materials is solid solution strengthening. A combination of this mechanism and precipitation hardening, promotes creep strength of heat resistance materials. The a...

  3. Preparation and characterization of electrolytic alumina deposit on austenitic stainless steel

    El Hajjaji, Souad; El Alaoui, Sidi Mohammed; Simon, Patrice; Guenbour, Abdellah; Ben Bachir, Ali; Puech-Costes, Edith; Maurette, Marie-Thérèse; Aries, Lucien

    2005-01-01

    Conversion coating modified by alumina has been studied as a way for improving the resistance to thermal oxidation of an austenitic stainless steel. Conversion coating, characterized by a particular morphology and strong interfacial adhesion with the substrate, facilitate the electrochemical deposition of ceramic layers and enhance their adhesion to the substrate. The influence of the current density and treatment time on alumina deposit was studied using statistical experimental designs like...

  4. Weld bead center line shift during laser welding of austenitic stainless steels with different sulfur content

    The magnitude of the shift in position of the maximum depth of penetration, the center line shift (CLS), for a laser weld produced between two heats of austenitic stainless steels with large differences in S content was smaller relative to gas tungsten arc (GTA) welds made with both higher and lower heat inputs. The results of this study suggest that both surface tension driven fluid (Marangoni) flow effects and arc shift effects may contribute to the CLS in GTA welding

  5. Multi-response optimization of CO2 laser welding process of austenitic stainless steel

    Benyounis, Khaled; Olabi, Abdul-Ghani; Hashmi, Saleem

    2008-01-01

    Recently, laser welding of austenitic stainless steel has received great attention in industry, due to its wide spread application in petroleum refinement stations, power plant, pharmaceutical industry and households. Therefore, mechanical properties should be controlled to obtain good welded joints. The welding process should be optimized by the proper mathematical models. In this research, the tensile strength and impact strength along with the joint operating cost of laser welded butt join...

  6. Microstructure and properties of laser surface alloyed PM austenitic stainless steel

    Z. Brytan

    2010-05-01

    Full Text Available Purpose: The purpose of this paper is to analyse the effect of laser surface alloying with chromium on the microstructural changes and properties of vacuum sintered austenitic stainless steel type AISI 316L (EN 1.4404.Design/methodology/approach: Surface modification of AISI 316L sintered austenitic stainless steel was carried out by laser surface alloying with chromium powder using high power diode laser (HPDL. The influence of laser alloying conditions, both laser beam power (between 0.7 and 2.0 kW and powder feed rate (1.0-4.5 g/min at constant scanning rate of 0.5m/min on the width of alloyed surface layer, penetration depth, microstructure evaluated by LOM, SEM x-ray analysis, surface roughness and microhardness were presented.Findings: The microstructures of Cr laser alloyed surface consist of different zones, starting from the superficial zone rich in alloying powder particles embedded in the surface; these particles protrude from the surface and thus considerably increase the surface roughness. Next is alloyed zone enriched in alloying element where ferrite and austenite coexists. The following transient zone is located between properly alloyed material and the base metal and can be considered as a very narrow HAZ zone. The optimal microstructure homogeneity of Cr alloyed austenitic stainless steel was obtained for powder feed rate of 2.0 and 4.5 g/min and laser beam power of 1.4 kW and 2 kW.Practical implications: Laser surface alloying can be an efficient method of surface layer modification of sintered stainless steel and by this way the surface chromium enrichment can produce microstructural changes affecting mechanical properties.Originality/value: Application of high power diode laser can guarantee uniform heating of treated surface, thus uniform thermal cycle across treated area and uniform penetration depth of chromium alloyed surface layer.

  7. Wear mechanisms in austenitic stainless steel drilling : A comprehensive wear study

    Dahlström, Alexander

    2015-01-01

    This thesis is meant to serve as part of a competence platform for future product development projects at Sandvik Coromant AB, Solid Round Tools Department, Västberga, Sweden. The project objective is to gain generic knowledge of the wear mechanisms that restrict tool lifetime when drilling austenitic stainless steel. Thus, identifying if the weakest link of the tool is located within the coating, the coating adherence or in the strength of the substrate. A theoretical review of the work-pie...

  8. From micro to nano scales -recent progress in the characterization of nitrided austenitic stainless steels

    Luo, Quanshun; Yang, Shicai

    2015-01-01

    In the frontier of materials science, understanding of materials has been in multiple scales from macro, micro, to atomic levels. This is attributed to the advanced instrumentations such as SEM, TEM, XPS, XRD, as well as several other spectroscopic and metallographic analyses. Fe-Cr-Ni based austenitic stainless steels have a diverse range of modern applications ranging from biomedical prostheses in human bodies, food processing, to chemical engineering and nuclear power generation. The outst...

  9. A new high nitrogen super austenitic stainless steel with improved structure stability and corrosion resistance properties

    A new highly alloyed (Cr, Mo, W, N) super austenitic grade has been developed. This grade offers high mechanical properties combined with excellent corrosion resistance in chloride acid media. This grade is particularly designed for applications in chloride, oxidizing acid media encountered in the chemical, transportation, pollution control, offshore and pulp and paper industries. Mechanical properties, corrosion resistance and weldability of this grade are presented and compared to that of other stainless steels and nickel base alloys

  10. Reducing heat tint effects on the corrosion resistance of austenitic stainless alloys

    Kearns, J.R. (Allegheny Ludlum Corp., Brackenridge, PA (United States)); Moller, G.E. (Allegheny Ludlum Corp., Evergreen, CO (United States))

    1994-05-01

    Arc welding can produce a heat tint on the surface of stainless and nickel-based alloys. In some services, a heat tint can decrease corrosion resistance. The conditions that cause heat tinting are discussed, and laboratory studies on post-weld cleaning procedures for removing this surface oxide scale from a 6% molybdenum super-austenitic alloy (UNS N08367) are reviewed. Cleaning can be done by either mechanical or chemical methods; a combination of both is recommended.

  11. A new high nitrogen super austenitic stainless steel with improved structure stability and corrosion resistance properties

    Gagnepain, J.C.; Charles, J.; Coudreuse, L.; Bonnefois, B. [Creusot-Loire Industrie, Le Creusot (France)

    1996-11-01

    A new highly alloyed (Cr, Mo, W, N) super austenitic grade has been developed. This grade offers high mechanical properties combined with excellent corrosion resistance in chloride acid media. This grade is particularly designed for applications in chloride, oxidizing acid media encountered in the chemical, transportation, pollution control, offshore and pulp and paper industries. Mechanical properties, corrosion resistance and weldability of this grade are presented and compared to that of other stainless steels and nickel base alloys.

  12. Antibacterial Properties of an Austenitic Antibacterial Stainless Steel and Its Security for Human Body

    Ke YANG; Manqi L(U)

    2007-01-01

    An austenitic antibacterial stainless steel is reported in this paper. The very fine and dispersive ε-Cu precipitations in the matrix of the antibacterial steel after the antibacterial treatment endow the steel with antibacterial function. The antibacterial function is strong, long-term and broad-spectrum, and can be maintained even after repeated wear and long time dipping in water. The steel is safe for human body and could be used widely in daily application.

  13. Grain refinement effect on fatigue properties of austenitic stainless steel with deformation induced martensite formation

    Chlupová, Alice; Man, Jiří; Polák, Jaroslav; Škorík, Viktor; Karjalalinen, L.P.

    Ostrava : Tanger, 2014. ISBN 978-80-87294-55-0. [NANOCOM 2014. Internatinal Conference /6./. Brno (CZ), 05.11.2014-07.11.2014] R&D Projects: GA ČR GA13-32665S; GA MŠk(CZ) ED1.1.00/02.0068 Institutional support: RVO:68081723 Keywords : fatigue * 301LN austenitic stainless steel * grain refinement * reversion annealing * phase transformation Subject RIV: JL - Materials Fatigue, Friction Mechanics

  14. Effect of decontamination on oxidation of austenitic stainless steel in reactor conditions

    Austenitic stainless steels were oxidized in static autoclaves in light water reactor conditions. After the autoclave treatments the specimens were decontaminated with the aid of alkaline potassium permanganate (AP) and oxalic and citric acid (CITROX) as well as electrochemically in H3PO4. Alternating oxidation and decontamination tests were performed. An elemental analysis of the surfaces of the specimens was carried out by electron spectroscopy. Changes in structures and thicknesses of the oxide layers were observed. (author)

  15. Effects of a Hydrogen Gas Environment on Fatigue Crack Growth of a Stable Austenitic Stainless Steel

    Kawamoto, Kyohei; Oda, Yasuji; Noguchi, Hiroshi; Higashida, Kenji

    In order to clarify the effects of a hydrogen gas environment on the fatigue crack growth characteristics of stable austenitic stainless steels, bending fatigue tests were carried out in a hydrogen gas, in a nitrogen gas at 1.0 MPa and in air on a SUS316L using the Japanese Industrial Standards (type 316L). Also, in order to discuss the difference in the hydrogen sensitivity between austenitic stainless steels, the fatigue tests were also carried out on a SUS304 using the Japanese Industrial Standards (type 304) metastable austenitic stainless steel as a material for comparison. The main results obtained are as follows. Hydrogen gas accelerates the fatigue crack growth rate of type 316L. The degree of the fatigue crack growth acceleration is low compared to that in type 304. The fracture surfaces of both the materials practically consist of two parts; the faceted area seemed to be brittle and the remaining area occupying a greater part of the fracture surface and seemed to be ductile. The faceted area does not significantly contribute to the fatigue crack growth rate in both austenitic stainless steels. The slip-off mechanism seems to be valid not only in air and in nitrogen, but also in hydrogen. Also, the main cause of the fatigue crack growth acceleration of both materials occurs by variation of the slip behaviour. The difference in the degree of the acceleration, which in type 316L is lower than in type 304, seems to be caused by the difference in the stability of the γ phase.

  16. The Effect of Welding Method on the Electrochemical Behavior of Austenitic Stainless Steel Sheet

    The corrosion of the flexible tube in the automobile exhaust system is caused by the ambient water and chloride ions. Since welding is one of the key processes of the flexible tube manufacturing, it is required to select a proper welding method to prevent the flexible tube corrosion and to increase its lifetime. There are many studies about the efficiency of the welding method, but no systematic study is performed for the effect of welding method on the corrosion property of the austenitic stainless weldment. The aim of the present study is to provide information on the effect of two different welding methods of TIGW (tungsten inert gas welding) and PAW (plasma arc welding) on the corrosion property of austenitic stainless steel weldment. Materials used in this study were two types of the commercial austenitic stainless steel, STS321 and XMI5JI, which were used for flexible tube material for the automotive exhaust system. Microstructure was observed by using optical microscopy (OM) and scanning electron microscopy (SEM). To evaluate the corrosion behavior, potentiodynamic and potentiostatic tests were performed. The chemical state of the passive film was analyzed in terms of XPS depth profile. Metallurgical analysis show that the ferrite content in fusion zone of both STS321 and XMI5JI is higher when welded by PAW than by TIGW. The potentiodynamic and potentiostatic test results show that both STS321 and XMI5JI have higher transpassive potential and lower passive current density when welded by PAW than by TIGW. XPS analysis indicates that the stable Cr2O3 layer at the outermost layer of the passive film is formed when welded by PAW. The result recommends that PAW is more desirable than TIGW to secure corrosion resistance of the flex tube which is usually made of austenitic stainless steel

  17. The effects of fast-neutron irradiation on the mechanical properties of austenitic stainless steel

    The paper reviews the effects of fast-neutron irradiation on the tensile properties of austenitic stainless steels at irradiation temperatures of less than 400 degrees Celcius, using as an example, work carried out at Pelindaba on an AISI 316 type steel produced in South Africa. Damage produced in these steels at higher irradiation temperatures and fluences is also briefly discussed. The paper concludes with a discussion of some methods of overcoming or decreasing the effects of irradiation damage

  18. Development of high strength austenitic stainless steel for conduit of Nb3Al conductor

    Japan Atomic Energy Research Institute (JAERI) started developing new austenitic stainless steel for a conduit (1 - 2 mm) of a Nb3Al conductor in collaboration with Nippon Steel Corporation (NSC). A high strength austenitic stainless steel is required for a conduit of a Nb3Al conductor to make the best use of superconducting properties of a Nb3Al conductor. JAERI and NSC successfully developed the high strength austenitic stainless steel, JN1 (YS ≥ 1,300 MPa, KIc ≥ 200 MPa√m at 4K) for magnet structures having thick section. However, JN1 is not suitable for a conduit material because elongation of JN1 decreases to less than 10 % due to sensitization during reaction heat treatment for Nb3Al. Therefore, modification of JN1 was performed as a first step to develop a new conduit material which withstands Nb3Al reaction heating. Small trial lots heat-treated at 973 - 1173 K for 2 - 200 hours were prepared and evaluated by Charpy impact test and tensile test at 77 K and 4K. A material having yield strength of 1,390 MPa and elongation of 34 % after aging at 973 K x 200 h are developed up to now. This paper describes requirements on the mechanical properties and status of the development work. In addition, empirical equations to predict 4K yield strength, elongation, and Charpy absorbed energy from 77K data are proposed in this paper

  19. Development of a robust modeling tool for radiation-induced segregation in austenitic stainless steels

    Yang, Ying [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Field, Kevin G [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Allen, Todd R. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Busby, Jeremy T [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2015-09-01

    Irradiation-assisted stress corrosion cracking (IASCC) of austenitic stainless steels in Light Water Reactor (LWR) components has been linked to changes in grain boundary composition due to irradiation induced segregation (RIS). This work developed a robust RIS modeling tool to account for thermodynamics and kinetics of the atom and defect transportation under combined thermal and radiation conditions. The diffusion flux equations were based on the Perks model formulated through the linear theory of the thermodynamics of irreversible processes. Both cross and non-cross phenomenological diffusion coefficients in the flux equations were considered and correlated to tracer diffusion coefficients through Manning’s relation. The preferential atomvacancy coupling was described by the mobility model, whereas the preferential atom-interstitial coupling was described by the interstitial binding model. The composition dependence of the thermodynamic factor was modeled using the CALPHAD approach. Detailed analysis on the diffusion fluxes near and at grain boundaries of irradiated austenitic stainless steels suggested the dominant diffusion mechanism for chromium and iron is via vacancy, while that for nickel can swing from the vacancy to the interstitial dominant mechanism. The diffusion flux in the vicinity of a grain boundary was found to be greatly influenced by the composition gradient formed from the transient state, leading to the oscillatory behavior of alloy compositions in this region. This work confirms that both vacancy and interstitial diffusion, and segregation itself, have important roles in determining the microchemistry of Fe, Cr, and Ni at irradiated grain boundaries in austenitic stainless steels.

  20. Microstructure and tensile properties of friction welded SUS 304HCu austenitic stainless steel tubes

    Austenitic stainless steels are used in superheater/reheater tubing for their oxidation resistance and fireside corrosion resistance, in addition to their creep strength. The addition of 3 wt. % Cu to SUS 304HCu austenitic stainless steel to reduce the corrosion, has found to increase the creep performance in temperature range of 650°–750 °C. The addition of Cu to steels can have adverse effects on the mechanical properties of the fusion welded joints. During fusion welding, Cu can form low temperature eutectic phases that preferentially segregate to the grain boundaries and embrittle the alloy. There is a need for a better welding procedure/technique to fabricate this alloy. Friction welding is a solid state welding process which nullifies the adverse effects of low temperature eutectics segregation. Hence, in this investigation an attempt has been made to study the microstructural and tensile properties of the friction welded SUS 304HCu austenitic stainless steel tube joints fabricated using optimized parameters. -- Highlights: • Friction welding of SUS 304HCu tubes is reported. • Microstructures of friction welded SUS 304HCu tubes were reported. • Fracture surface of the tensile samples is characterized using SEM. • XRD analysis of the SUS 304HCu tube is reported

  1. Effect of nitrogen on high temperature mechanical properties of type 316LN SS for fast reactor applications

    Long term creep, low cycle fatigue and creep-fatigue interaction properties as well as compatibility with liquid sodium coolant, govern the choice of materials for out-of-core structural components of sodium cooled fast reactors (SFRs). 316 L(N) SS containing 0.07 Wt.% nitrogen is the current preferred material for all the high temperature structural components of SFRs. For the prototype Fast Breeder Reactor also, which is nearing commissioning at Kalpakkam, 316 LN (SS) has been used for all the major high temperature structural components. It is proposed to design future SFRs for a life of at least 60 years. Therefore materials with higher creep and low cycle fatigue strength are required. Increasing the nitrogen content in 316L(N) SS is one of the approaches being pursued at Indira Gandhi Centre for Atomic Research (IGCAR) to develop a SFR structural material suitable for 60 years design life. Towards this, a strong R and D programme is currently underway at IGCAR. The effect of nitrogen in the range of 0.07 to 0.22 Wt.% on the tensile creep and low cycle fatigue behavior of 316 LN SS has been extensively investigated. Both tensile and creep strength were found to increase with increase in nitrogen content. High temperature low cycle fatigue life was found to peak in 316LN SS containing 0.14 Wt.%. The paper discusses the monotonic and cyclic deformation and fracture mechanisms by which nitrogen improves the creep and low cycle fatigue properties of 316 LN SS. (author)

  2. Mechanical behaviour of an austenitic stainless steel under repeated impacts

    Cyclic indentation tests realised with an energy controlled spherical indenter allow a characterisation of the material behaviour under dynamic solicitations. This solicitation is, for example, able to show erosion and matting phenomenon. This test has been performed on AISI 316 stainless steels samples. Results have shown an increase of the hardness and the depth of the affected area versus the cycles number. With a micrographic optical analysis, we have detected a work hardening effect below the contact area. (authors)

  3. Cytotoxicity study of plasma-sprayed hydroxyapatite coating on high nitrogen austenitic stainless steels.

    Ossa, C P O; Rogero, S O; Tschiptschin, A P

    2006-11-01

    Stainless steel has been frequently used for temporary implants but its use as permanent implants is restricted due to its low pitting corrosion resistance. Nitrogen additions to these steels improve both mechanical properties and corrosion resistance, particularly the pitting and crevice corrosion resistance. Many reports concerning allergic reactions caused by nickel led to the development of nickel free stainless steel; it has excellent mechanical properties and very high corrosion resistance. On the other hand, stainless steels are biologically tolerated and no chemical bonds are formed between the steel and the bone tissue. Hydroxyapatite coatings deposited on stainless steels improve osseointegration, due their capacity to form chemical bonds (bioactive fixation) with the bone tissue. In this work hydroxyapatite coatings were plasma-sprayed on three austenitic stainless steels: ASTM-F138, ASTM-F1586 and the nickel-free Böhler-P558. The coatings were analyzed by SEM and XDR. The cytotoxicity of the coatings/steels was studied using the neutral red uptake method by quantitative evaluation of cell viability. The three uncoated stainless steels and the hydroxyapatite coated Böhler-P558 did not have any toxic effect on the cell culture. The hydroxyapatite coated ASTM-F138 and ASTM-F1586 stainless steels presented cytotoxicity indexes (IC50%) lower than 50% and high nickel contents in the extracts. PMID:17122924

  4. Utilization of Non-Destructive Thermoelectric Power Measurements for Determination of Interstitial Nitrogen Content in Nitrogen-Strengthened Austenitic Stainless Steel Welds

    Through utilization of modern physics concepts, a new non-destructive, portable thermoelectric power device has been designed for the use of rapid material characterization in nitrogen-strengthened austenitic stainless steel weldments. Nitrogen is used as an interstitial strengthener in austenitic stainless steel offering enhancement in mechanical properties and corrosion resistance. A direct correlation exists between the thermoelectric power coefficient as a function of interstitial nitrogen content, revealing microstructural characteristics of the austenitic stainless steel weldment

  5. Effect of martensite to austenite reversion on the formation of nano/submicron grained AISI 301 stainless steel

    The martensite to austenite reversion behavior of 90% cold rolled AISI 301 stainless steel was investigated in order to refine the grain size. Cold rolled specimens were annealed at 600-900 deg. C, and subsequently characterized by scanning electron microscopy, X-ray diffraction, Feritscope, and hardness measurements. The effects of annealing parameters on the formation of fully-austenitic nano/submicron grained structure and the mechanisms involved were studied. It was found that annealing at 800 deg. C for 10 s exhibited the smallest average austenite grain size of 240 ± 60 nm with an almost fully-austenitic structure.

  6. Effect of martensite to austenite reversion on the formation of nano/submicron grained AISI 301 stainless steel

    Karimi, M.; Najafizadeh, A. [Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Kermanpur, A., E-mail: ahmad_k@cc.iut.ac.ir [Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Eskandari, M. [Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of)

    2009-11-15

    The martensite to austenite reversion behavior of 90% cold rolled AISI 301 stainless steel was investigated in order to refine the grain size. Cold rolled specimens were annealed at 600-900 deg. C, and subsequently characterized by scanning electron microscopy, X-ray diffraction, Feritscope, and hardness measurements. The effects of annealing parameters on the formation of fully-austenitic nano/submicron grained structure and the mechanisms involved were studied. It was found that annealing at 800 deg. C for 10 s exhibited the smallest average austenite grain size of 240 {+-} 60 nm with an almost fully-austenitic structure.

  7. Experimental Determination of the Primary Solidification Phase dependency on the solidification velocity for 17 different austenitic stainless steel compositions

    Laursen, Birthe Nørgaard; Olsen, Flemming Ove; Yardy, John;

    1997-01-01

    When studying laser welding of austenitic stainless steel, hot cracking is frequently observed. To prevent hot cracking in laser welded stainless steel it is advantageous to obtain primary solidification of the ferrite phase that subsequently, on cooling, transforms in the solid state to the...

  8. The influence of nitrogen alloying on the pitting and crevice corrosion of austenitic and duplex stainless steels

    The effect of nitrogen alloying on the pitting corrosion resistance of duplex and austenitic stainless steels has been examined. In order to avoid alteration of the phase ratio as a result of nitrogen alloying of the duplex steels, a simultaneous decrease has been made in the nickel content. Austenitic alloys of compositions corresponding to the austenite phase of the duplex steels have been investigated and compared to the behaviour of austenitic steels in which the nitrogen content or the nickel content alone has been varied. Nitrogen has a beneficial effect on pitting and crevice corrosion resistance in all cases but the duplex stainless steel exhibit a lower resistance to pitting and a higher resistance to crevice corrosion than predicted from the austenite nitrogen content. (orig.)

  9. Fatigue crack growth in metastable austenitic stainless steels

    Mei, Z.; Chang, G.; Morris, J.W. Jr.

    1988-06-01

    The research reported here is an investigation of the influence of the mechanically induced martensitic transformation on the fatigue crack growth rate in 304-type steels. The alloys 304L and 304LN were used to test the influence of composition, the testing temperatures 298 K and 77 K were used to study the influence of test temperature, and various load ratios (R) were used to determine the influence of the load ratio. It was found that decreasing the mechanical stability of the austenite by changing composition or lowering temperature decreases the fatigue crack growth rate. The R-ratio effect is more subtle. The fatigue crack growth rate increases with increasing R-ratio, even though this change increases the martensite transformation. Transformation-induced crack closure can explain the results in the threshold regime, but cannot explain the R-ratio effect at higher cyclic stress intensities. 26 refs., 6 figs.

  10. Effect of composition on the electrochemical behavior of austenitic stainless steel in Ringer's solution

    Potentiodynamic cyclic polarization tests on Type 316L stainless steel, a common orthopedic implant alloy, in Ringer's solution show considerable hysteresis and a protection potential more active than the open circuit corrosion potential. This implies that chances of repassivation of actively growing pits in this alloy are limited. Tests in Ringer's solution containing hydrochloric acid show that the open circuit potential of Type 316L steel in this solution may exceed in the noble direction the critical pitting potential in the same solution. This signifies that spontaneous breakdown of passivity may occur in a bulk environment which grossly simulates the electrochemical environment within a crevice. Alloying elements such as Mo, Ni, Cr, all improve the corrosion resistance of Type 316L stainless steel in that the critical pitting potential shifts in the noble direction in the alloys having any of the three alloying elements in a higher proportion than in Type 316L steel. Polarization tests in Ringer's solution on a 20% Cr, 25% Ni, 4.5% Mo, 1.5% Cu austenitic stainless steel, having Mo, Cr, and Ni--all in higher proportions than in Type 316L steel, does not show any critical pitting potential or hysteresis at potentials below that for dissociation of water. However, test in 4% NaCl solution at 60 C, a more aggressive chloride environment than Ringer'ssolution, reveals considerable hysteresis and a very active protection potential, indicating that this behavior is a common feature of austenitic stainless steel in sufficiently aggressive, chloride media

  11. Corrosion Behavior of the Stressed Sensitized Austenitic Stainless Steels of High Nitrogen Content in Seawater

    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.

  12. Dose dependence of the microstructural evolution in neutron-irradiated austenitic stainless steel

    Microstructural data on the evolution of the dislocation loop, cavity, and precipitate populations in neutron-irradiated austenitic stainless steels are reviewed in order to estimate the displacement damage levels needed to achieve the 'steady state' condition. The microstructural data can be conveniently divided into two temperature regimes. In the low temperature regime (below about 200 degrees C) the microstructure of austenitic stainless steel is dominated by 'black spot' defect clusters and faulted interstitial dislocation loops. The dose needed to approach saturation of the loop and defect cluster densities is generally on the order of 1 displacement per atom (dpa) in this regime. In the high temperature regime (∼300 to 700 degrees C), cavities, precipitates, loops and network dislocations are all produced during irradiation; doses in excess of 10 dpa are generally required to approach a 'steady state' microstructural condition. Due to complex interactions between the various microstructural components that form during irradiation, a secondary transient regime is typically observed in commercial stainless steels during irradiation at elevated temperatures. This slowly evolving secondary transient may extend to damage levels in excess of 50 dpa in typical 300-series stainless steels, and to >100 dpa in radiation-resistant developmental steels. The detailed evolution of any given microstructural component in the high-temperature regime is sensitive to slight variations in numerous experimental variables, including heat-to-heat composition changes and neutron spectrum

  13. Comparison of material property specifications of austenitic steels in fast breeder reactor technology

    Austenitic stainless steels are very widely used in components for European Fast Breeder Reactors. The Activity Group Nr.3 ''Materials'', within Working Group ''Codes and Standards'' of the Fast Reactor Co-Ordination Committee of the European Communities, has decided to initiate a study to compare the material property specifications of the austenitic stainless steel used in the European Fast Breeder Technology. Hence, this study would allow one to view rapidly the designation of a particular steel grade in different European countries and to compare given property values for a same grade. There were dissimilarities, differences or voids appear, it could lead to an attempt to complete and/or to uniformize the nationally given values, so that on a practical level interchangeability, availability and use ease design and construction work. A selection of the materials and of their properties has been made by the Working Group. Materials examined are Stainless Steel AISI 304, 304 L, 304 LN, 316, 316 L, 316 LN, 316''Ti stab.'', 316''Nb stab''., 321, 347

  14. Influence of thermal treatment on the caustic SCC of super austenitic stainless steel

    Yoo, Y.R.; Park, Y.B.; Chung, T.J.; Kim, Y.S. [School of Advanced Materials Engineering, Andong National Univ. (Korea); Chang, H.Y. [Korea Power Engineering Co. (Korea); Park, Y.S. [Dept. of Metallurgical Engineering, Yonsei Univ. (Korea)

    2005-07-01

    In general, thermal treatment at 500 C {proportional_to} 900 C ranges depending upon alloy composition of stainless steels can sensitize the steels and promote the intergranular cracking, and their intergranular corrosion resistance is decreased. These behaviors seem to be related to the change of microstructures. So, heat treatment at that temperature range should be avoided in fabrication, especially welding of stainless steels. In this work, it is focused on the effect of thermal treatment on caustic stress corrosion cracking of super austenitic stainless steel - S32050 The low temperature thermal treatment increased greatly the resistance to caustic SCC than those of annealed specimen. This enhancement might be closely related to the reduction of residual stress and slightly large grain, but its resistance was not affected by the anodic polarization behavior. (orig.)

  15. ESD morphology deposition with WZr8 electrode on austenitic stainless steel support

    Perju, M. C.; Ţugui, C. A.; Nejneru, C.; Axinte, M.; Vizureanu, P.

    2016-06-01

    Stainless steels are used to obtain mechanical parts, working in severe conditions with high dynamic loads in wet, chemically active environments. For this reason, these materials have good corrosion resistance in acidic or basic chemical agents. The main drawback is the relatively low wear and resistance to mechanical stress. This paper proposes a remedy by deposition of the hard thin films of tungsten electrode by spark electro-deposition method (ESD). Tungsten is an alfagen element and causes an increase for the mechanical properties at high and low temperatures for the austenitic stainless steels. Tungsten does not alter the corrosion resistance of stainless steels. The morphology for the obtained layers was analyzed using SEM, in 3D images, and profilographs.

  16. Corrosion studies of austenitic and duplex stainless steels in aqueous lithium bromide solution at different temperatures

    The corrosion behavior of three stainless steels EN 14311, EN 14429 (austenitic stainless steels) and EN 14462 (duplex stainless steel) was studied in a commercial LiBr solution (850 g/l LiBr solution containing chromate as inhibitor) at different temperatures (25, 50, 75 and 85 deg C) by electrochemical methods. Open circuit potentials shifted towards more active values as temperature increased, while corrosion potentials presented the opposite tendency. The most resistant alloys to general corrosion were EN 14429 and EN 14462 because they had the lowest corrosion current for all temperatures. In all the cases corrosion current increases with temperature. Pitting corrosion resistance is improved by the EN 14462, which presented the highest pitting potential, and the lowest passivation current for the whole range of temperatures studied. The duplex alloy also presents the worst repassivation behavior (in terms of the narrowest difference between corrosion potential and pitting potential); it does not repassivate from 50 deg C

  17. Tearing resistance of aged cast austenitic stainless steels

    CF8 and CF8M type cast stainless steels containing about 10 to 25 % ferrite are used in the primary piping of light water reactors (PWRs and BWRs). It is now recognized that these materials are embrittled by thermal aging at the operating temperature (between 2900C and 3300C), mainly due to precipitation hardening of the ferrite by α', and other phases. Extensive research programs are under way in several countries to better understand the mechanisms of embrittlement and to determine the mechanical properties of components as a function of aging time and temperature. In earlier studies thermal aging embrittlement was mainly characterized by the evolutions of the tensile and Charpy impact properties. However the evaluation of reactor coolant circuit integrity through mechanical analyses requires the knowledge of fracture toughness properties. The first measurements of the tearing resistance of a CF8M type severely aged material were presented in 1983 by SLAMA, PETREQUIN and MAGER. Other contributions to the knowledge of the fracture toughness of aged materials were published, but were relative to medium or high toughness materials. The objective of this paper is to present the results of tearing resistance measurements made on a large spectrum of severely embrittled materials, which allow to give lower bound properties for aged CF8 and CF8M type cast stainless steels

  18. On the Stress Corrosion Cracking and Hydrogen Embrittlement Behavior of Austenitic Stainless Steels in Boiling Saturated Magnesium Chloride Solutions

    Alyousif, Osama M.; Rokuro Nishimura

    2012-01-01

    The stress corrosion cracking (SCC) and hydrogen embrittlement (HE) behaviors for types 304, 310, and 316 austenitic stainless steels were investigated in boiling saturated magnesium chloride solutions using a constant load method under different conditions including test temperature, applied stress, and sensitization. Both of type 304 and type 316 stainless steels showed quite similar behavior characteristics, whereas type 310 stainless steel showed a different behavior. The time to failure ...

  19. Analysis of elevated temperature cyclic deformation of austenitic stainless steels

    The stress relaxation behavior of 304 and 316 stainless steels during cyclic deformation at 538 and 6500C with various hold times and strain amplitudes has been analyzed in terms of a power-law equation of state which includes internal stress and drag stress as structure variables. At 6500C the internal sress in 304 appears to be zero and microstructural recovery plays an important role in the kinetics of stress relaxation. For deformation at 5380C, the internal stress in 304 is nonzero and microstructural recovery appears minimal. In 316 tested at 6500C the internal stress is zero and again recovery is important. However, the kinetics of recovery differ from those measured in 304. These observations are explained physically in terms of strain and temperature-induced recovery of the structural variables, and provide insights into the procedures for calculating accumulated ''creep'' damage in reactor components

  20. Fatigue crack growth in austenitic stainless steel piping

    The study presented in this paper is being carried out with a view to substantiating the calculations of the fatigue crack growth in pipes made of 316 L stainless steel. The results obtained may be applied to P.W.R. primary piping. It is divided into two parts. First, fatigue tests (cyclic pressure) are carried out under hot and cold conditions with straight pipes machined with notches of various dimensions. The crack propagation and the fatigue crack growth rate are measured here. Second, calculations are made in order to interpret experimental results. From elastic calculations the stress intensity factor is assessed to predict the crack growth rate. The results obtained until now and presented in this paper relate to longitudinal notches

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

    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.

  2. Predicting the toughness of SMA austenitic stainless steel welds at 77 K

    Austenitic stainless steels often provide the best combination of strength and toughness for cryogenic applications: however, the weld toughness is frequently much lower than that of the base metal. This study proposes a more accurate and simpler model for developing improved filler metal compositions. Several previous studies of the weld toughness were analyzed separately and in combination using a stepwise regression method and an expanded variable list. The total data base consisted of chemical composition, ferrite number (FN), and the Charpy V-notch (CVN) toughness at 77 K of 79 austenitic stainless steel welds deposited by the shielded metal arc process. Analysis of the complete data base revealed that the FN calculated from the Schaeffler diagram was the most significant variable for predicting the CVN toughness. The predictive equation produced a better correlation between the measured and predicted values of weld toughness than the previously published predictive equations. The group of 36 fully austenitic welds and the group of 21 type 316 welds in the data base were analyzed by the same procedure. In both cases the ferrite number was found to be the most significant predictor of toughness

  3. Growth of creep life of type-347H austenitic stainless steel by micro-alloying elements

    Research highlights: → B, Ce and N can improve the creep life significantly at high temperature. → The precipitate of B element at the grain boundaries can improve the creep life. → The removing O through Ce provided the steel with longer creep life. → N increased the creep life by stabilizing austenite and solid solution strengthening. - Abstract: The creep life of type-347H austenitic stainless steel modified with B, Ce and N was measured, and microstructures were analyzed by optical microscope, X-ray diffraction, scanning electron microscope and transmission electron microscope equipped with energy dispersive spectroscopy. The results indicate that B, Ce and N can improve the creep life significantly at high temperature. The growth of creep life was mainly due to the precipitate of B in the elemental form at the grain boundaries and the removing O through Ce. N addition made for solid solution strengthening and effectively suppressed the precipitate of δ-ferrite at high temperature. The micro-alloying elements have a beneficial effect on creep life of type-347H austenitic stainless steel at high temperature.

  4. Investigation of shot-peened austenitic stainless steel 304L by means of magnetic Barkhausen noise

    Research highlights: The results and the conclusions drawn in this paper are important for the scientific community and especially for scientist who are looking for method to characterize phase transformations in metallic materials. We show that Barkhausen noise measurements can be successfully used to monitor strain-induced martensite in austenitic stainless steels. - Abstract: Different shot peening conditions were applied to an austenitic stainless steel AISI 304L in order to transform austenite to martensite α' at different depths. Magnetic Barkhausen noise measurements performed on this steel reveal a correlation between the strength of the signal and the depth of the treatment. The combined effect of the volume fraction of martensite and the residual stress in martensite determined using X-ray diffraction analysis were found to be responsible for the evolution of the Barkhausen noise response. Using tensile plastic deformation, the residual stress in martensite was changed, giving rise to a strong increase of the Barkhausen noise activity. This variation was correlated to a modification of the sign and amplitude of the residual stress in the martensite phase. Directional measurements of the Barkhausen noise revealed the anisotropy of the residual stresses induced by the tensile plastic deformation. It is concluded that the Barkhausen noise activity recording could lead to the determination of the residual stresses in martensite induced by shot peening processes.

  5. Investigation of shot-peened austenitic stainless steel 304L by means of magnetic Barkhausen noise

    Kleber, X., E-mail: xavier.kleber@insa-lyon.fr [Universite de Lyon, INSA-Lyon, MATEIS CNRS UMR5510, 7 Avenue Jean Capelle, F-69621 Villeurbanne (France); Barroso, S. Pirfo [Universite de Lyon, INSA-Lyon, MATEIS CNRS UMR5510, 7 Avenue Jean Capelle, F-69621 Villeurbanne (France)

    2010-08-20

    Research highlights: The results and the conclusions drawn in this paper are important for the scientific community and especially for scientist who are looking for method to characterize phase transformations in metallic materials. We show that Barkhausen noise measurements can be successfully used to monitor strain-induced martensite in austenitic stainless steels. - Abstract: Different shot peening conditions were applied to an austenitic stainless steel AISI 304L in order to transform austenite to martensite {alpha}' at different depths. Magnetic Barkhausen noise measurements performed on this steel reveal a correlation between the strength of the signal and the depth of the treatment. The combined effect of the volume fraction of martensite and the residual stress in martensite determined using X-ray diffraction analysis were found to be responsible for the evolution of the Barkhausen noise response. Using tensile plastic deformation, the residual stress in martensite was changed, giving rise to a strong increase of the Barkhausen noise activity. This variation was correlated to a modification of the sign and amplitude of the residual stress in the martensite phase. Directional measurements of the Barkhausen noise revealed the anisotropy of the residual stresses induced by the tensile plastic deformation. It is concluded that the Barkhausen noise activity recording could lead to the determination of the residual stresses in martensite induced by shot peening processes.

  6. Determining Experimental Parameters for Thermal-Mechanical Forming Simulation considering Martensite Formation in Austenitic Stainless Steel

    Schmid, Philipp; Liewald, Mathias

    2011-08-01

    The forming behavior of metastable austenitic stainless steel is mainly dominated by the temperature-dependent TRIP effect (transformation induced plasticity). Of course, the high dependency of material properties on the temperature level during forming means the temperature must be considered during the FE analysis. The strain-induced formation of α'-martensite from austenite can be represented by using finite element programs utilizing suitable models such as the Haensel-model. This paper discusses the determination of parameters for a completely thermal-mechanical forming simulation in LS-DYNA based on the material model of Haensel. The measurement of the martensite evolution in non-isothermal tensile tests was performed with metastable austenitic stainless steel EN 1.4301 at different rolling directions between 0° and 90 °. This allows an estimation of the influence of the rolling direction to the martensite formation. Of specific importance is the accuracy of the martensite content measured by magnetic induction methods (Feritscope). The observation of different factors, such as stress dependence of the magnetisation, blank thickness and numerous calibration curves discloses a substantial important influence on the parameter determination for the material models. The parameters obtained for use of Haensel model and temperature-dependent friction coefficients are used to simulate forming process of a real component and to validate its implementation in the commercial code LS-DYNA.

  7. Microstructure and mechanical properties of annealed SUS 304H austenitic stainless steel with copper

    Research highlights: → SUS 304H austenitic stainless steel containing 3 wt.% Cu was annealed at 700 deg. C for up to 100 h. → Microstructure and mechanical properties of annealed alloys are examined. → Nano-sized Cu-rich precipitation upon annealing. → Strength of the alloy remains invariant with annealing whereas ductility improves. → Fatigue crack growth threshold of 3 wt.% Cu added alloy increases with annealing. - Abstract: An experimental investigation into the effect of Cu on the mechanical properties of 0 and 3 wt.% Cu added SUS 304H austenitic stainless steel upon annealing at 700 deg. C for up to 100 h was conducted. Optical microscopy reveals grain coarsening in both the alloys upon annealing. Observations by transmission electron microscopy revealed the precipitation of nanometer-sized spherical Cu particles distributed within the austenitic grains and the presence of carbides at the dislocations. Both the yield and ultimate tensile strengths of the alloys were found to remain invariant with annealing. Tensile ductility and the threshold stress intensity factor range for fatigue crack growth for 3 wt.% Cu added alloy increase with annealing. These are attributed to the grain coarsening with annealing. In all, the addition of Cu to SUS 304H does not affect the mechanical performance adversely while improving creep resistance.

  8. Study of structural modifications induced by ion implantation in austenitic stainless steel

    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)

  9. Crack growth rates and fracture toughness of irradiated austenitic stainless steels in BWR environments.

    Chopra, O. K.; Shack, W. J.

    2008-01-21

    In light water reactors, austenitic stainless steels (SSs) are used extensively as structural alloys in reactor core internal components because of their high strength, ductility, and fracture toughness. However, exposure to high levels of neutron irradiation for extended periods degrades the fracture properties of these steels by changing the material microstructure (e.g., radiation hardening) and microchemistry (e.g., radiation-induced segregation). Experimental data are presented on the fracture toughness and crack growth rates (CGRs) of wrought and cast austenitic SSs, including weld heat-affected-zone materials, that were irradiated to fluence levels as high as {approx} 2x 10{sup 21} n/cm{sup 2} (E > 1 MeV) ({approx} 3 dpa) in a light water reactor at 288-300 C. The results are compared with the data available in the literature. The effects of material composition, irradiation dose, and water chemistry on CGRs under cyclic and stress corrosion cracking conditions were determined. A superposition model was used to represent the cyclic CGRs of austenitic SSs. The effects of neutron irradiation on the fracture toughness of these steels, as well as the effects of material and irradiation conditions and test temperature, have been evaluated. A fracture toughness trend curve that bounds the existing data has been defined. The synergistic effects of thermal and radiation embrittlement of cast austenitic SS internal components have also been evaluated.

  10. Effect of heavy ion irradiation on microstructural evolution in CF8 cast austenitic stainless steel

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

    2016-04-01

    The microstructural evolution in ferrite and austenitic in cast austenitic stainless steel (CASS) CF8, as received or thermally aged at 400 °C for 10,000 h, was followed under TEM with in situ irradiation of 1 MeV Kr ions at 300 and 350 °C to a fluence of 1.9 × 1015 ions/cm2 (∼3 dpa) at the IVEM-Tandem Facility. For the unaged CF8, the irradiation-induced dislocation loops appeared at a much lower dose in the austenite than in the ferrite. At the end dose, the austenite formed a well-developed dislocation network microstructure, while the ferrite exhibited an extended dislocation structure as line segments. Compared to the unaged CF8, the aged specimen appeared to have lower rate of damage accumulation. The rate of microstructural evolution under irradiation in the ferrite was significantly lower in the aged specimen than in the unaged. This difference is attributed to the different initial microstructures in the unaged and aged specimens, which implies that thermal aging and irradiation are not independent but interconnected damage processes.

  11. Modelling grain-scattered ultrasound in austenitic stainless-steel welds: A hybrid model

    Nowers, O.; Duxbury, D. J. [NDE Research, Support and Development, Rolls-Royce Marine, Derby, PO BOX 2000, DE21 7XX (United Kingdom); Velichko, A.; Drinkwater, B. W. [Department of Mechanical Engineering, University Walk, University of Bristol, Bristol BS8 1TR (United Kingdom)

    2015-03-31

    The ultrasonic inspection of austenitic stainless steel welds can be challenging due to their coarse grain structure, charaterised by preferentially oriented, elongated grains. The anisotropy of the weld is manifested as both a ‘steering’ of the beam and the back-scatter of energy due to the macroscopic granular structure of the weld. However, the influence of weld properties, such as mean grain size and orientation distribution, on the magnitude of scattered ultrasound is not well understood. A hybrid model has been developed to allow the study of grain-scatter effects in austenitic welds. An efficient 2D Finite Element (FE) method is used to calculate the complete scattering response from a single elliptical austenitic grain of arbitrary length and width as a function of the specific inspection frequency. A grain allocation model of the weld is presented to approximate the characteristic structures observed in austenitic welds and the complete scattering behaviour of each grain calculated. This model is incorporated into a semi-analytical framework for a single-element inspection of a typical weld in immersion. Experimental validation evidence is demonstrated indicating excellent qualitative agreement of SNR as a function of frequency and a minimum SNR difference of 2 dB at a centre frequency of 2.25 MHz. Additionally, an example Monte-Carlo study is presented detailing the variation of SNR as a function of the anisotropy distribution of the weld, and the application of confidence analysis to inform inspection development.

  12. Hydrogen embrittlement of super austenitic stainless steel welded joints; Fragilizacao por hidrogenio em juntas soldadas de acos inoxidaveis superausteniticos

    Paredes, Ramon S. Cortes [Parana Univ., Curitiba, PR (Brazil). Centro Politecnico. Inst. de Tecnologia para o Desenvolvimento (LACTEC); Berthier, Thiana; Kuromoto, Neide K. [Parana Univ., Curitiba, PR (Brazil). Lab. de Materiais e Tratamento de Superficies. Lab. de Nanopropriedades Mecanicas

    2004-09-15

    The austenitic stainless steel embrittlement is usually present on sulphurous medium due to the hydrogen presence, resulting on cracks and corrosion on acid medium. Several researches carried out on the behaviour of hydrogenated stainless steel structures, had shown that the hydrogen induces superficial phase transformation during hydrogenation period and cracks formation after this period. These are due to the permeation of the hydrogen into the material, which is apprehended on preferential site, resulting on high pressure zones of molecular hydrogen. These zones may lead the crack formation, compromising the mechanical properties. There are few results on austenitic and super austenitic stainless steel, considering the transformations induced on welded unions. This work evaluates the cracks nucleation on welded unions of super austenitic stainless steel AISI 904L exposed to hydrogen rich environments and its relation to the reduction of material ductility. The samples were welded by the Mig/Mag process, followed by hydrogenation which were cathodic on sulfuric acid solution at room temperature. The results showed that the tested super austenitic stainless steel has a significant amount of cracks and no phase transformation has occurred after hydronization. (author)

  13. Influence of localized deformation on A-286 austenitic stainless steel stress corrosion cracking in PWR primary water

    Irradiation-assisted stress corrosion cracking (IASCC) of austenitic stainless steels is known to be a critical issue for structural components of nuclear reactor cores. The deformation of irradiated austenitic stainless steels is extremely heterogeneous and localized in deformation bands that may play a significant role in IASCC. In this study, an original approach is proposed to determine the influence of localized deformation on austenitic stainless steels SCC in simulated PWR primary water. The approach consists in (i) performing low cycle fatigue tests on austenitic stainless steel A-286 strengthened by γ' precipitates Ni3(Ti,Al) in order to shear and dissolve the precipitates in intense slip bands, leading to a localization of the deformation within and in (ii) assessing the influence of these γ'-free localized deformation bands on A-286 SCC by means of comparative CERT tests performed on specimens with similar yield strength, containing or not γ'-free localized deformation bands. Results show that strain localization significantly promotes A-286 SCC in simulated PWR primary water at 320 and 360 C. Moreover, A-286 is a precipitation-hardening austenitic stainless steel used for applications in light water reactors. The second objective of this work is to gain insights into the influence of heat treatment and metallurgical structure on A-286 SCC susceptibility in PWR primary water. The results obtained demonstrate a strong correlation between yield strength and SCC susceptibility of A-286 in PWR primary water at 320 and 360 C. (author)

  14. Self-healing of creep cavities formed in austenitic stainless steel

    In austenitic stainless steels creep cavities nucleate at grain boundaries by long time use at high temperatures. These creep cavities grow along grain boundaries, form grain boundary cracks by linking up each other, and cause premature and low ductility fracture. Therefore long time creep rupture life and ductilities chiefly depend upon the behavior of nucleation and growth of creep cavities. If the growth of creep cavities could be suppressed, creep rupture life and ductilities should be improved remarkably. The present work is intended to propose a self-healing process for the cavitation by utilization of thin filmy precipitation at creep cavity surface and improve the creep rupture properties by the self-healing process. In ordinary austenitic stainless steels, sulfur is contained as impurity and segregates to creep cavity surface because of its high surface activity. It is thought that a stable compound can precipitate at creep cavity surface if the sulfur is completely removed. Therefore in order to remove sulfur completely and precipitate a stable compound at creep cavity surface, a modified 304 stainless steel added with cerium, titanium, boron and nitrogen was laboratory-melted. The modified steel showed high rupture strength and high rupture ductilities, and it was confirmed that boron nitride precipitates at creep cavity surface in the steel. It was thought that the boron nitride at creep cavity surface suppresses the creep cavity growth and improves creep rupture properties by the self-healing effect on creep cavities. (author)

  15. Development of nickel-free austenitic stainless steels for ambient and cryogenic applications

    Haddick, G.T.; Thompson, L.D.; Parker, E.R.; Zackay, V.F.

    1978-02-01

    A series of alloys have been developed as possible replacements for some austenitic stainless steels. These alloys utilized a Mn substitution for Ni and a reduced Cr concentration from the 18% ordinarily found in the AISI 300 series stainless steels to a concentration of 13%. The base system studied was an alloy containing Fe-16%Mn-13%Cr while other elements added included small additions of N, Si and Mo. A range of microstructures was produced from the alloying additions. The base composition had a triplex (fcc, hcp, bcc) structure while the most highly modified compositions were fully austenitic. Mechanical testing included tensile testing and Charpy V-notch testing conducted at various temperatures between -196/sup 0/C to 23/sup 0/C. Excellent combinations of strength and ductility were obtained (40--65 ksi yield strength, 100--125 ksi ultimate strength, 45--75% elongation and 60--80% reduction of area) at room temperature. Upper shelf energies in Charpy V-notch testing were as high as 185 ft-lbs with a ductile-brittle transition temperature (DBTT) of -160/sup 0/C. Analysis of fracture surfaces determined that alloys without interstitials had no transition in the mode of failure between room temperature and liquid nitrogen temperature. Results of an ASTM sensitization corrosion test, where the experimental alloys were compared to 347 stainless steel, indicated that the alloys were not susceptible to intergranular attack.

  16. Stress corrosion cracking behaviour of gas tungsten arc welded super austenitic stainless steel joints

    M. Vinoth Kumar

    2015-09-01

    Full Text Available Super 304H austenitic stainless steel with 3% of copper posses excellent creep strength and corrosion resistance, which is mainly used in heat exchanger tubing of the boiler. Heat exchangers are used in nuclear power plants and marine vehicles which are intended to operate in chloride rich offshore environment. Chloride stress corrosion cracking is the most likely life limiting failure with austenitic stainless steel tubing. Welding may worsen the stress corrosion cracking susceptibility of the material. Stress corrosion cracking susceptibility of Super 304H parent metal and gas tungsten arc (GTA welded joints were studied by constant load tests in 45% boiling MgCl2 solution. Stress corrosion cracking resistance of Super 304H stainless steel was deteriorated by GTA welding due to the formation of susceptible microstructure in the HAZ of the weld joint and the residual stresses. The mechanism of cracking was found to be anodic path cracking, with transgranular nature of crack propagation. Linear relationships were derived to predict the time to failure by extrapolating the rate of steady state elongation.

  17. Residual and trace element effects on the high-temperature creep strength of austenitic stainless steels

    The heat-to-heat variation in the creep strength and ductility of austenitic stainless steels was reviewed from the viewpoint of residual and trace element effects. Based on data reported in the literature the creep strength of unstabilized alloys such as types 304 and 316 stainless steel increased with residual element and trace element content. Niobium appeared to be the most potent strengthener. There was no direct evidence that trace elements such as sulfur and phosphorus had a deleterious effect on either strength and ductility. It was assumed that the creep strength and ductility of the unstabilized grades of austenitic stainless steels are controlled by the precipitate characteristics. It follows from this that thermomechanical treatment or residual element additions that affect the precipitate characteristics influence subsequent time dependent mechanical properties. This view is consistant with most of the information in the literature. It was concluded that more systematic studies of trace and residual element effects would be beneficial to the improvement of steels. Incorporated into the studies should be quantitative characterization of evolving precipitate morphology and composition as they are in fluenced by residual elements. This information should be incorporated into modeling studies of nonequilibrium segregation. Ultimately, optimum elevated-temperature strength could be developed based on a materials science approach

  18. Repair welding of cracked steam turbine blades using austenitic and martensitic stainless-steel consumables

    The procedure for repair welding of cracked steam turbine blades made of martensitic stainless steels has been developed using the gas tungsten arc welding process. Weld repair procedures were developed using both ER 316L austenitic and ER 410 martensitic stainless-steel filler wire. The overall development of the repair welding procedure included selection of welding consumables (for austenitic filler metal), optimisation of post-weld heat treatment parameters, selection of suitable method for local pre-heating and post-weld heat treatment (PWHT) of the blades, determination of mechanical properties of weldments in as-welded and PWHT conditions, and microsturctural examination. After various trials using different procedures, the procedure of local PWHT (and preheating when using martensitic stainless-steel filler wire) using electrical resistance heating on the top surface of the weldment and monitoring the temperature by placing a thermocouple at the bottom of the weld was found to give the most satisfactory results. These procedures have been developed and/or applied for repair welding of cracked blades in steam turbines

  19. Repair welding of cracked steam turbine blades using austenitic and martensitic stainless-steel consumables

    Bhaduri, A.K. E-mail: bhaduri@igcar.ernet.in; Gill, T.P.S.; Albert, S.K.; Shanmugam, K.; Iyer, D.R

    2001-06-01

    The procedure for repair welding of cracked steam turbine blades made of martensitic stainless steels has been developed using the gas tungsten arc welding process. Weld repair procedures were developed using both ER 316L austenitic and ER 410 martensitic stainless-steel filler wire. The overall development of the repair welding procedure included selection of welding consumables (for austenitic filler metal), optimisation of post-weld heat treatment parameters, selection of suitable method for local pre-heating and post-weld heat treatment (PWHT) of the blades, determination of mechanical properties of weldments in as-welded and PWHT conditions, and microsturctural examination. After various trials using different procedures, the procedure of local PWHT (and preheating when using martensitic stainless-steel filler wire) using electrical resistance heating on the top surface of the weldment and monitoring the temperature by placing a thermocouple at the bottom of the weld was found to give the most satisfactory results. These procedures have been developed and/or applied for repair welding of cracked blades in steam turbines.

  20. HEALING OF HYDROGEN ATTACK CRACK IN AUSTENITE STAINLESS STEEL UNDER HEAT TREATMENT

    X.G. Li; C.F. Dong; H. Chen

    2002-01-01

    The specimens of 304 austenite stainless steel with the hydrogen attack bubbles orcracks were heat treated at 600℃ for 6h. The SEM and TEM observations on thespecimens before and after the heat treatment showed that the bubbles or cracks could behealed completely by heat treatment. The healing of hydrogen attack bubbles or cracksis closely related to heat diffusion of Fe and C atoms in austenite. The driving forceof crack healing results fram the plastic deforming energy Es induced by the growthof hydrogen attack bubbles or cracks. The critical condition of healing of bubbles orcracks is Es ≥ 2γ/r (where γγ is the surface tension, r is the radius of bubbles or halflength of crack). During healing of the hydrogen attack bubbles or cracks, the recovery,polygonization and recrystallization of the sub-grain also occured.

  1. Hydrogen embrittlement of martensitic and austenitic stainless steels for fusion applications

    In this study the Disk Pressure Method was employed to investigate the mechanical behaviour of several stainless steels with potential application in fusion reactors. Tests were carried out on as-received material and on specimens charged with different hydrogen concentrations. The DPT tests were performed at hydrogen concentrations ranging from 1 to 15 wt ppm for martensitic materials and at a maximum concentration of 30 wt ppm for austenitic steel. The mechanical properties of martensitic steels were greatly affected by the presence of hydrogen only above well defined concentrations. The critical concentration values measured are reported and discussed in terms of hydrogen diffusion and trapping, as well as microstructural parameters such as prior austenitic grain size. No significant mechanical effects were found in the case of 316L at the hydrogen concentrations indicated. (orig.)

  2. Thermal property characterization of a titanium modified austenitic stainless steel (alloy D9)

    Banerjee, Aritra [Physical Metallurgy Section, Materials Characterisation Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102 (India); Raju, S. [Physical Metallurgy Section, Materials Characterisation Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102 (India)]. E-mail: sraju@igcar.ernet.in; Divakar, R. [Physical Metallurgy Section, Materials Characterisation Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102 (India); Mohandas, E. [Physical Metallurgy Section, Materials Characterisation Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102 (India); Panneerselvam, G. [Fuel Chemistry Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102 (India); Antony, M.P. [Fuel Chemistry Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102 (India)

    2005-12-01

    The temperature dependence of lattice parameter and enthalpy increment of alloy D9, a titanium modified nuclear grade austenitic stainless steel were studied using high temperature X-ray diffraction and inverse drop calorimetry techniques, respectively. A smooth variation of the lattice parameter of the austenite with temperature was found. The instantaneous and mean linear thermal expansion coefficients at 1350 K were estimated to be 2.12 x 10{sup -5} K{sup -1} and 1.72 x 10{sup -5} K{sup -1}, respectively. The measured enthalpy data were made use of in estimating heat capacity, entropy and Gibbs energy values. The estimated isobaric heat capacity C {sub p} at 298 K was found to be 406 J kg{sup -1} K{sup -1}. An integrated theoretical analysis of the thermal expansion and enthalpy data was performed to obtain approximate values of bulk modulus as a function of temperature.

  3. Mechanism of fatigue crack initiation in austenitic stainless steels in light water reactor environments

    This paper examines the mechanism of fatigue crack initiation in austenitic stainless steels (SSs) in light water reactor (LWR) coolant environments. The effects of key material and loading variables on the fatigue lives of wrought and cast austenitic SSs in air and LWR environments have been evaluated. The influence of reactor coolant environments on the formation and growth of fatigue cracks in polished smooth SS specimens is discussed. The results indicate that the fatigue lives of these steels are decreased primarily by the effects of the environment on the growth of cracks <200 μm and, to a lesser extent, on enhanced growth rates of longer cracks. The fracture morphology in the specimens has been characterized. Exploratory fatigue tests were conducted to study the effects of surface micropits or minor differences in the surface oxide on fatigue crack initiation. (author)

  4. Stress and Composition of Carbon Stabilized Expanded Austenite on Stainless Steel

    Christiansen, Thomas; Somers, Marcel A. J.

    2009-01-01

    Low-temperature gaseous carburizing of stainless steel is associated with a colossal supersaturation of the fcc lattice with carbon, without the development of carbides. This article addresses the simultaneous determination of stress and composition profiles in layers of carbon xpanded austenite...... obtained by low-temperature gaseous carburizing of AISI 316. X-ray diffraction was applied for the determination of lattice spacing depth profiles by destructive depth profiling and reconstruction of the original lattice spacing profiles from the measured, diffracted intensity weighted, values. The...... compressive stress depth distributions correlate with the depth distribution of the strain-free lattice parameter, the latter being a measure for the depth distribution of carbon in expanded austenite. Elastically accommodated compressive stress values as high as -2.7 GPa were obtained, which exceeds the...

  5. Embrittlement and strain hardining of the hydrogenated AISI 304 austenitic stainless steel

    The influence of hydrogen the mechanical properties of type AISI 304 austenitic stainless steel was analysed. Hydrogenation was performed cathodically, at room temperature, in a 1N H2SO4 solution. The variables controlled for analysis were current density and time. Uniaxial tensile tests were conducted with constant nominal strain rate. Fracture morphology was analysed by scanning electron microscopy and the kinetics of strain hardening by applying Ludwick's equation to the resulting stress-strain curves. It was verified that hydrogen embrittles markedly, the austenitic AISI 304 steel, leading to a significant loss of ductility and modifying the fracture made, from essentially ductile to a transgrannular fragile fracture, containing small regions of intergranular fracture. With increasing amounts of hydrogen there was also a decrease in the maximum uniform stress, the strength coefficient, the strain hardening exponent and in the range the deformation stages II and III extended. (Author)

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

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

    2016-01-01

    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 accompan......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. 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...

  7. Effects of Strain Rate and Plastic Work on Martensitic Transformation Kinetics of Austenitic Stainless Steel 304

    Fang PENG; Xiang-huai DONG; Kai LIU; Huan-yang XIE

    2015-01-01

    The martensitic transformation behavior and mechanical properties of austenitic stainless steel 304 were studied by both experiments and numerical simulation. Room temperature tensile tests were carried out at various strain rates to investigate the effect on volume fraction of martensite, temperature increase and flow stress. The results show that with increasing strain rate, the local temperature increases, which suppresses the transformation of martensite. To take into account the dependence on strain level, strain rate sensitivity and thermal effects, a kinetic model of martensitic transformation was proposed and constitutive modeling on stress-strain response was conducted. The validity of the proposed model has been proved by comparisons between simulation results and experimental ones.

  8. Basic creep models for 25Cr20NiNbN austenitic stainless steels

    Sandström, Rolf; Farooq, Muhammad; Zurek, Joanna

    2013-01-01

    Basic models for solid solution and precipitation hardening during creep are presented for the austenitic stainless steels 25Cr20NiNbN (TP310HNbN, HR3C, DMV310N). The solid solution hardening is a result of the formation of Cottrell clouds of solutes around the dislocations. In addition to slowing down the creep, the solutes increase the activation energy for creep. The increase in activation energy corresponds to the maximum binding energy between the solutes and the dislocations. The format...

  9. Caustic stress corrosion cracking of austenitic stainless steels with thermal treatment(TT)

    This paper dealt with the effects of TT(Thermal Treatment) and nitrogen content on caustic stress corrosion cracking of austenitic stainless steels. Nitrogen content and grain size had affected on the caustic SCC resistance. Increasing nitrogen content, SCC resistance was increased due to the enhanced repassivation rate, but at high nitrogen content, the resistance was decreased because of the dual effects between mechanical and repassivation behavior. Regardless of nitrogen content, TT improved the caustic SCC resistance and this behavior was reviewed on the points of residual stress, grain size, and dislocation array

  10. Laser welding of butt joints of austenitic stainless steel AISI 321

    A. Klimpel; A. Lisiecki

    2007-01-01

    Purpose: of this paper: A study of an automated laser autogenous welding process of butt joints of austenitic stainless steel AISI 321 sheets 0.5 [mm] and 1.0 [mm] thick using a high power diode laser HPDL has been carried out.Design/methodology/approach: Influence of basic parameters of laser welding on shape and quality of the butt joints and the range of optimal parameters of welding were determined.Findings: It was showed that there is a wide range of laser autogenous welding parameters w...

  11. HYDROGEN ABSORPTION INDUCED SLOW CRACK GROWTH IN AUSTENITIC STAINLESS STEELS FOR PETROCHEMICAL PRESSURE VESSEL INDUSTRIES

    Ronnie Higuchi Rusli

    2010-01-01

    Type 304L and 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 neces...

  12. Reverse-Martensitic Hardening of Austenitic Stainless Steel upon Up-quenching

    Sato, Kiminori; Guo, Defeng; Li, Xiaohong; Zhang, Xiangyi

    2016-08-01

    Reverse-martensitic transformation utilizing up-quenching was demonstrated for austenitic stainless steel. Up-quenching was done following the stress-induced phase modification to martensite and then enrichment of the body-centered-cubic ferrite. Transmission-electron-microscopy observation and Vickers hardness test revealed that the reverse-martensitic transformation yields quench hardening owing to an introduction of highly-concentrated dislocation. It is furthermore found that Cr precipitation on grain boundaries caused by isothermal aging is largely suppressed in the present approach.

  13. Mechanical properties of austenitic stainless steel single crystals: Influence of nitrogen and hydrogen content

    Sucre, Y.R.; Iost, A.; Vogt, J.B.; Najjar, D.; Chumlyakov, Y.I.

    2000-01-01

    The effect of cathodically charged hydrogen in austenitic stainless steels with or without nitrogen addition was studied by microhardness experiments carried out on single crystals. With the authors experimental conditions, it can be demonstrated that hydrogen penetration depth is near 25 {micro}m and induced a higher apparent hardness. In fact, the hardness improvement is mainly a consequence of the residual stresses induced by hydrogen diffusion. By studying the variation of hardness with the reciprocal length of the indentation print obtained with load varying between 0.5 and 200 N, it was observed that the slope (VHN vs 1/d) only depends on the aging time.

  14. Effects of helium and hydrogen on radiation-induced microstructural changes in austenitic stainless steel

    Jin, Hyung-Ha, E-mail: hhajin2@kaeri.re.kr; Ko, Eunsol; Lim, Sangyeop; Kwon, Junhyun

    2015-09-15

    Microstructural changes in austenitic stainless steel by helium, hydrogen, and iron ion irradiation were investigated with transmission electron microscopy. Typical radiation-induced changes, such as the formation of Frank loops in the matrix and radiation-induced segregation (RIS) or depletion at grain boundaries, were observed after ion irradiation. The helium ion irradiation led to the formation of cavities both at grain boundaries and in the matrix, as well as the development of smaller Frank loops. The hydrogen ion irradiation generated stronger RIS behavior at the grain boundaries compared to irradiation with helium and iron ions. The effects of helium and hydrogen on radiation-induced microstructural changes were discussed.

  15. THEORETICAL STUDY ON THE INCOHERENT TWIN BOUNDARIES IN AUSTENITIC STAINLESS STEEL

    Mori, M; Masuda-Jindo, K.; K.Tanaka; Ishida, I

    1990-01-01

    The structure of incoherent Σ=3 (112) twin boundaries in the austenitic stainless steel is investigated using the tight-binding recursion method and the model fcc iron crystal. To estimate the change in the total energy due to the atomic displacements, 15 pairs of recursion coefficients (an, bn ; n⩽15) are calculated for the atomic clusters containing 2100 atoms : The short-range repulsive energy contribution is also taken into account using the Born-Mayer potential. It is found that the sign...

  16. The evolution of cluster of grains with Σ3n relationship in austenitic stainless steel

    The evolution of cluster of grains with Σ3n relationship (Σ3n CG) in austenitic stainless steel was investigated by in situ microstructural observations using electron backscatter diffraction (EBSD). The results showed that, after cold rolling with thickness reduction of 6%, Σ3n CG developed from several existing grains during annealing at 1173 K. As annealing proceeded, Σ3n CG was growing larger with the so-called strain induced boundary migration (SIBM), and in the meantime, the connectivity of random high angle grain boundaries (HABs) network was interrupted by low Σ-coincidence site lattice boundaries (ΣCSLBs) effectively.

  17. Microscopic investigation of pitting corrosion in plasma nitrided austenitic stainless steel

    UNS 31603 austenitic stainless steel was nitrided using different techniques, and pitting corrosion resistance was analysed in a chloride solution. All nitriding techniques, LEII, PI. and convectional DC nitriding produced a nitrided layer called S phase which is corrosion resistant. Pits morphology and layer structure was investigated using optical and electronic microscopy, SEM-FIB, EDS, and a 3D reconstruction of a pit was assessed using FIB tomography. It was concluded that pits are initiated in MnS inclusions and a channel was generated passing through the nitrided layer, connecting the steel with the electrolyte. Base alloy dissolution was observed beneath the nitrided layer.

  18. Pitting corrosion in austenitic stainless steel water tanks of hotel trains

    The water storage tanks of hotel trains suffered pitting corrosion. To identify the cause, the tanks were subjected to a detailed metallographic study and the chemical composition of the austenitic stainless steels used in their construction was determined. Both the tank water and the corrosion products were further examined by physicochemical and microbiological testing. Corrosion was shown to be related to an incompatibility between the chloride content of the water and the base and filler metals of the tanks. These findings formed the basis of recommendations aimed at the prevention and control of corrosion in such tanks. (Author) 18 refs.

  19. Influence on corrosion resistance of superficial strain hardening of parts made of austenitic stainless steels

    Reactivity of strain hardened stainless steel 18-10 and 18-10 Mo in oxidizing media is very different at the surface and in the metal core. Surface corrosion or protection is very sensitive to superficial strain hardening resulting of mechanical treatments. Three physical phenomena are directly strain hardening dependent and have important consequences on corrosion resistance: 1) increase of diffusion rate of the different alloy elements, especially chromium; 2) residual superficial strain influence on stress corrosion and 3) structural transformation of metastable austenite

  20. Electrochemical Mechanisms for Radiation Corrosion Processes of 316 Austenitic Stainless Steel in Chloride Environment

    The effects of gamma radiation (Ce137, 1.5x105 rad/hr) on the electrochemical mechanisms of 316 austenitic stainless steel in 1.5M NaCl solution (pH: 2) at 25 .deg. C have been investigated. When gamma irradiation is initiated, corrosion potential shifts in the positive direction are observed for 316 SS. These potential shifts are associated with the irradiation-induced production of hydrogen peroxide. The electrochemical mechanisms involved in the corrosion potential shifts, as well as the subsequent effect on pitting resistance, are considered

  1. Evaluation of thermal embrittlement susceptibility in cast austenitic stainless steel using artificial neural network

    Cast austenitic stainless steel is used for several components, such as primary coolant piping, elbow, pump casing and valve bodies in light water reactors. These components are subject to thermal aging at the reactor operating temperature. Thermal aging results in spinodal decomposition of the delta-ferrite leading to increased strength and decreased toughness. This study shows that ferrite content can be predicted by use of the artificial neural network. The neural network has trained learning data of chemical components and ferrite contents using backpropagation learning process. The predicted results of the ferrite content using trained neural network are in good agreement with experimental ones

  2. Effects of helium and hydrogen on radiation-induced microstructural changes in austenitic stainless steel

    Microstructural changes in austenitic stainless steel by helium, hydrogen, and iron ion irradiation were investigated with transmission electron microscopy. Typical radiation-induced changes, such as the formation of Frank loops in the matrix and radiation-induced segregation (RIS) or depletion at grain boundaries, were observed after ion irradiation. The helium ion irradiation led to the formation of cavities both at grain boundaries and in the matrix, as well as the development of smaller Frank loops. The hydrogen ion irradiation generated stronger RIS behavior at the grain boundaries compared to irradiation with helium and iron ions. The effects of helium and hydrogen on radiation-induced microstructural changes were discussed

  3. Effects of alloy and solution chemistry on the fracture of passive films on austenitic stainless steel

    The Taguchi analysis method was used to simultaneously study the effects of alloy chemistry, pH, and halide ion concentrations on the fracture of electrochemically grown passive films using a nanoindentation technique. Three austenitic stainless steels, 304L, 316L, and 904L were potentiostatically polarized in hydrochloric acid solutions. The fracture load was dominated primarily by alloy chemistry. Passive films mechanically weaken as the atomic iron concentration increases in the film. Prolonged anodic ageing time increases the fracture load of passive films

  4. Effects of alloy and solution chemistry on the fracture of passive films on austenitic stainless steel

    Alamr, A. [School of Mechanical and Materials Engineering, Washington State University, P.O. Box 642920, Pullman, WA 99164-2920 (United States)]. E-mail: alamrz@wsu.edu; Bahr, D.F. [School of Mechanical and Materials Engineering, Washington State University, P.O. Box 642920, Pullman, WA 99164-2920 (United States)]. E-mail: bahr@mail.wsu.edu; Jacroux, Michael [Department of Statistics, Washington State University, Pullman, WA 99164-3144 (United States) ]. E-mail: jacroux@wsu.edu

    2006-04-15

    The Taguchi analysis method was used to simultaneously study the effects of alloy chemistry, pH, and halide ion concentrations on the fracture of electrochemically grown passive films using a nanoindentation technique. Three austenitic stainless steels, 304L, 316L, and 904L were potentiostatically polarized in hydrochloric acid solutions. The fracture load was dominated primarily by alloy chemistry. Passive films mechanically weaken as the atomic iron concentration increases in the film. Prolonged anodic ageing time increases the fracture load of passive films.

  5. Behaviour in aqueous H2S of austenitic stainless steels AISI 316L and AISI 304

    Embrittlement by hydrogen in aqueous H2S medium of austenitic stainless steels was studied. Embrittlement in the hyper-quenched and sensitized state was characterized by slow traction tests. The susceptibility to hydrogen increases with the decrease of the charging speed and the increase of the sensitization time. The value of the piling defect energy, the presence of martensite ε and the transportation of hydrogen through dislocations seem to be very determining parameters for embrittlement by hydrogen in H2S medium. (authors). 19 refs., 9 figs., 2 tabs

  6. Potential high fluence response of pressure vessel internals constructed from austenitic stainless steels

    Many of the in-core components in pressurized water reactors are constructed of austenitic stainless steels. The potential behavior of these components can be predicted using data on similar steels irradiated at much higher displacement rates in liquid-metal reactors or water-cooled mixed-spectrum reactors. Consideration of the differences between the pressurized water environment and that of the other reactors leads to the conclusion that significant amounts of void swelling, irradiation creep, and embrittlement will occur in some components, and that the level of damage per atomic displacement may be larger that the level of damage per atomic displacement may be larger in the pressurized water environment

  7. Joining silicon carbide to austenitic stainless steel through diffusion welding; Stellingen behorende bij het proefschrift

    Krugers, Jan-Paul

    1993-01-19

    In this thesis, the results are presented of a study dealing with joining silicon carbide to austenitic stainless steel AIS316 by means of diffusion welding. Welding experiments were carried out without and with the use of a metallic intermediate, like copper, nickel and copper-nickel alloys at various conditions of process temperature, process time, mechanical pressure and interlayer thickness. Most experiments were carried out in high vacuum. For reasons of comparison, however, some experiments were also carried out in a gas shielded environment of 95 vol.% Ar and 5 vol.% H2.

  8. Effect of oxygen in sodium upon radionuclide release from austenitic stainless steel

    This paper deals with the effect of oxygen in sodium upon radionuclide release from austenitic stainless steel. The work described herein was conducted in Source Term Control Loop (STCL-1) with a specimen temperature of 604C, a loop minimum temperature of 427C, sodium velocity at the specimens of 6.7 to 7.6m/s. Weight losses of Fe, Cr, Mn and Ni from the steel specimen were analysed. Release data for 54Mn and 60Co are calculated. Future work is briefly described

  9. Metallographic screening of grain boundary engineered type 304 austenitic stainless steel

    An electrochemical etching method for the identification of grain boundary engineered type 304 austenitic stainless steel microstructures is described. The method can be applied for rapid microstructure screening to complement electron backscatter diffraction analysis. A threshold parameter to identify grain boundary engineered microstructure is proposed, and the application of metallographic etching for characterising the degree of grain boundary engineering discussed. - Highlights: • As-received (annealed) and grain boundary engineered microstructures were compared. • Electro-chemical polarisation in nitric acid solutions was carried out. • A metallographic screening method has been developed. • The screening method complements EBSD analysis for microstructure identification

  10. Depth distribution analysis of Martensitic transformations in Xe implanted austenitic stainless steel

    Johnson, E.; Gerritsen, E.; Chechenin, N.G.;

    1989-01-01

    implanted Xe as calculated by the TRIM computer simulation code. Simulations using the MARLOWE code indicate that the thickness of the transformed layer coincides with the range of the small fraction of ions channeled under random implantation conditions. Using cross sectional TEM on the Xe implanted...... 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...

  11. Martensitic transformation in an intergranular corrosion area of austenitic stainless steel during thermal cycling

    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

  12. Role of alloyed molybdenum in austenitic stainless steels in the inhibition of pitting in neutral halide solutions

    Sugimoto, K.; Sawada, Y.

    1976-09-01

    In the passive region of austenitic stainless steels alloyed with Mo, the formation of MoO/sub 4//sup 2 -/ ions can be expected in neutral halide solutions by the transpassive dissolution of Mo. It has been shown that MoO/sub 4//sup 2 -/ ions added to neutral NaCl solutions act as an effective inhibitor against pitting of austenitic stainless steels with and without Mo. The interaction between alloyed Mo in the steels and added MoO/sub 4//sup 2 -/ ions in the solutions is appreciable. It is likely that the inhibition of pit growth by the adsorption of MoO/sub 4//sup 2 -/ ions which are thought to result from the dissolution of the steels at the initial stage of pitting leads to increased pitting resistance of austenitic stainless steels containing Mo.

  13. Development of neural network models for the prediction of solidification mode, weld bead geometry and sensitisation in austenitic stainless steels

    Quantitative models describing the effect of weld composition on the solidification mode, ferrite content and process parameters on the weld bead geometry are necessary in order to design composition of the welding consumable to ensure primary ferritic solidification mode, proper ferrite content and to ensure right choice of process parameters to achieve good bead geometry. A quantitative model on sensitisation behaviour of austenitic stainless steels is also necessary to optimise the composition of the austenitic stainless steel and to limit the strain on the material in order to enhance the resistance to sensitisation. The present paper discuss the development of quantitative models using artificial neural networks to correlate weld metal composition with solidification mode, process parameter with weld bead geometry and time for sensitisation with composition, strain in the material before welding and the temperature of exposure in austenitic stainless steels. (author)

  14. Effect of Free Surface on the Stability of Individual Retained Austenite Grains in a Duplex Stainless Steel

    He, B. B.; Huang, M. X.; Ngan, A. H. W.; van der Zwaag, S.

    2014-10-01

    The present work explored the effect of free surface on the stability of individual austenite grains in a duplex stainless steel. It was found that martensitic transformation took place automatically in the retained austenite grain when a free surface was introduced. This is due to the fact that the martensite nucleation energy barrier can be lowered to a thermally surmountable value as the strain energy induced by martensitic transformation is largely lowered when the matrix constraints were removed.

  15. Welding hot cracking in an austenitic stainless steel

    The occurrence of hot cracking is linked to several conditions, in particular, the composition of the material and the local strains due to clambering. The aim of this study is to better analyse the implied mechanisms and to lead to a local thermomechanical criterion for hot cracking. The example studied is an AISI 321-type stainless steel (X10CrNiTi18-12) strongly prone to cracking. Two weldability tests are studied: - the first one consists in carrying out a fusion line by the TIG process on a thin sheet. In the case of the defect occurrence, the crack is longitudinal and follows the back of the molten bath. The influence of the operating conditions welding (speed, welding heat input, width test sample) is studied. - the second one is the Varestraint test. It is widely used to evaluate the sensitivity of a material to hot cracking. It consists in loading the material by bending during a fusion line by the TIG process and in characterising the defects quantity (length, number). Various thermal and mechanical instrumentation methods were used. The possibilities of a local instrumentation instrumentation being limited because of the melting, the experimental results were complemented by a numerical modelling whose aim is to simulate the thermomechanical evolution of the loading thanks to the finite element analysis code ABAQUS. First, the heat input for thermal simulation is set by the use of an inverse method in order to optimise the energy deposit mode during welding in the calculation. Then, the mechanical simulation needs the input of a constitutive law that fits the mechanical behaviour over a wide temperature range from ambient to melting temperature. Thus, a mechanical characterization is performed by selecting strain values and strain rates representative of what the material undergoes during the tests. The results come from tensile and compressive tests and allow to settle an elasto-visco-plastic constitutive law over temperatures up to liquidus. Once

  16. Influence of Silicon on Swelling and Microstructure in Russian Austenitic Stainless Steels Irradiated to High Neutron Doses

    Porollo, S.I.; Shulepin, S.V.; Konobeev, Y.V.; Garner, F. [Pacific Northwest National Laboratory, P.o. Box 999, Richland WA, AK 99352 (United States)

    2007-07-01

    Full text of publication follows: For some applications in fusion devices austenitic stainless steels are still considered to be candidates for use as structural components, but high neutron exposures must be endured by the steels. Operational experience of fast reactors in Western Europe, USA and Japan provides evidence of the possible use of austenitic steels up to {approx} 150 dpa. Studies aimed at improvement of existing Russian austenitic steels are being carried out in Russia. For improvement of irradiation resistance of Russian steels it is necessary to understand the basic mechanisms responsible for deterioration of steel properties. This understanding can be achieved by continuing detailed investigations of the microstructure of cladding steels after irradiation to high doses. By investigating the evolution of radiation-induced microstructure in neutron irradiated steels of different chemical composition one can study the effect of chemical variations on steel properties. Silicon is one of the most important chemical elements that strongly influence the behavior of austenitic steel properties under irradiation. In this paper results are presented of investigations of the effect of silicon additions on void swelling and microstructure of base austenitic stainless steel EI-847 (0.06C-16Cr-15Ni- 3Mo-Nb) irradiated as fuel pin cladding of both regular and experimental assemblies in the BOR-60, BN-350 and BN-600 fast reactors to neutron doses up to 49 dpa. The possible mechanisms of silicon's effect on void swelling in austenitic stainless steels are presented and analyzed. (authors)

  17. Structure and composition of phases occurring in austenitic stainless steels in thermal and irradiation environments

    Lee, E.H.; Maziasz, P.J.; Rowcliffe, A.F.

    1980-01-01

    Transmission electron diffraction techniques coupled with quantitative x-ray energy dispersive spectroscopy have been used to characterize the phases which develop in austenitic stainless steels during exposure to thermal and to irradiation environments. In AISI 316 and Ti-modified stainless steels some thirteen phases have been identified and characterized in terms of their crystal structure and chemical composition. Irradiation does not produce any completely new phases. However, as a result of radiation-induced segregation principally of Ni and Si, and of enhanced diffusion rates, several major changes in phase relationships occur during irradiation. Firstly, phases characteristic of remote regions of the phase diagram appear unexpectedly and dissolve during postirradiation annealing (radiation-induced phases). Secondly, some phases develop with their compositions significantly altered by the incorporation of Ni or Si (radiation-modified phases).

  18. Research of estimation method of thermal aging embrittlement on cast austenitic stainless steel

    Thermal aging embrittlement of cast austenitic stainless steel components from the decommissioned Advanced Thermal prototype Reactor (ATR) Fugen power station has been characterized. Cast stainless steel materials were obtained from recirculation pump casing. The actual time at temperature for the materials was 138,000 h at 275°C. The Fugen serviced material show modest decrease in Charpy-impact properties and a small increase in micro-Vickers hardness in ferrite phase because of thermal aging at relatively low service temperatures. The fracture toughness prediction method (H3T model) predicts slightly lower values for Charpy-impact energy obtained from the Fugen material. The results from microstructural analysis suggest that the prediction method have the potential to provide higher accuracy by considering activation energy for embrittlement at low service temperatures. (author)

  19. Evaluation of the corrosion resistance of plasma nitrided austenitic stainless steel

    Mareci, Daniel; Bolat, Georgiana [Technical Univ. Iasi (Romania). Faculty of Chemical Engineering and Environmental Protection; Strugaru, Sorin Iacob; Munteanu, Corneliu [Technical Univ. Iasi (Romania). Faculty of Mechanical Engineering; Souto, Ricardo M. [Univ. of La Laguna, Tenerife (Spain). Dept. of Chemistry

    2015-03-15

    Plasma nitriding at 500 C for 14 h was applied to austenitic 304 stainless steel for surface hardening. The effect of surface treatment on the corrosion resistance of the material was investigated in naturally-aerated 0.5 M NaCl solution for 30 days using linear potentiodynamic polarization and electrochemical impedance spectroscopy methods. Both as-cast and plasma nitrided stainless steel samples underwent spontaneous passivation, though the nitrided sample exhibited more positive zero current potential, higher breakdown potential, and lower anodic current densities than the as-cast material. Impedance spectra were interpreted in terms of a duplex passive film, corrosion resistance mainly arising from a thin inner compact layer, whereas the outer layer was more porous and less sealing. Capacitive behaviour and high corrosion resistance were observed in the low and medium frequency ranges for the nitrided samples.

  20. Stress corrosion cracking susceptibility of various austenitic stainless steel pipe welds in high temperature oxygenated water

    Stress corrosion cracking (SCC) susceptibility of various austenitic stainless steel pipe welds has been studied by means of constant load tensile tests and pipe tests in 2880C water containing 26 ppm dissolved oxygen. The results obtained are summarized as follows: (1) SCC susceptibility of SUS 304 pipe welds is comparatively low under the condition of as-welded. It becomes, however, high remarkably by grinder operation and/or low temperature sensitization heat treatment. The distribution of time of failure on SUS 304 pipe welds can be expressed as a log-normal or Weibull distribution. (2) SUS 304L, 304NG, 316NG, and 347 stainless steel pipe welds have a good SCC resistance and sensitization resistance. Furthermore, the life estimation on alternate pipe welds was conducted statistically. (author)

  1. Evaluation of the corrosion resistance of plasma nitrided austenitic stainless steel

    Plasma nitriding at 500 C for 14 h was applied to austenitic 304 stainless steel for surface hardening. The effect of surface treatment on the corrosion resistance of the material was investigated in naturally-aerated 0.5 M NaCl solution for 30 days using linear potentiodynamic polarization and electrochemical impedance spectroscopy methods. Both as-cast and plasma nitrided stainless steel samples underwent spontaneous passivation, though the nitrided sample exhibited more positive zero current potential, higher breakdown potential, and lower anodic current densities than the as-cast material. Impedance spectra were interpreted in terms of a duplex passive film, corrosion resistance mainly arising from a thin inner compact layer, whereas the outer layer was more porous and less sealing. Capacitive behaviour and high corrosion resistance were observed in the low and medium frequency ranges for the nitrided samples.

  2. Suggested solutions to improve the surface hardness of austenitic stainless steels without loosing their corrosion resistance

    Ionic nitridation is a process which is already used industrially. Indeed, by nitrogen diffusion, it is possible to harden the surfaces and then to improve the wear, seizure, and fatigue resistances. Nevertheless, the direct application to stainless steels induces a strong degradation of their un-oxidizable character. But this process can be optimized in order to maintain a good oxidation resistance. One way consists to work with a nitrogen plasma or with a carbon plasma. The materials properties obtained with a nitrogen plasma are discussed. Example of control elements of a PWR type reactor are given. This process is then compared with those whose plasma is a carbon plasma. According to the studied process, it is possible to increase the wear resistance of the austenitic stainless steel by a factor of 60 to 700 while entirely conserving the corrosion resistance of the untreated steel. (O.M.)

  3. Stress corrosion cracking of Ti- and Nb-stabilized austenitic stainless steels in 288 C water

    Intergranular stress corrosion cracking of stabilized austenitic stainless steels in 288 C water has been studied experimentally. Fracture mechanics crack growth rates were obtained with double cantilever beam specimens. Three Ti-stabilized and two Nb-stabilized stainless steels all exhibited intergranular stress corrosion cracking in simulated, faulted BWR water. The crack growth rates were similar to those of 316 NG, i.e. about one nun per year at stress intensities beyond 20 MPa√m. Extreme sensitization and coarse grains result in crack growth rates up to one hundred times faster. It is shown that weld sensitization in a very narrow zone (several hundred micrometers from the fusion line) can cause chromium carbide precipitation and corresponding chromium depletion and corresponding susceptibility to stress corrosion cracking in BWR water

  4. Hydrogen solubility and diffusion in austenitic stainless steels studied with thermal desorption spectroscopy

    Yagodzinskyy, Y.; Todoshchenko, O.; Papula, S.; Haenninen, H. [Laboratory of Engineering Materials, School of Science and Technology, Aalto University, Espoo (Finland)

    2011-01-15

    Hydrogen solubility and diffusion in austenitic stainless steels, namely AISI 310, AISI 301LN and AISI 201, are studied with thermal desorption spectroscopy (TDS) after electrochemical potentiostatic hydrogen pre-charging. Temperature dependencies of hydrogen desorption for all studied steels manifest a complex main peak caused by hydrogen releasing from the steel lattice by diffusion. Depending on the steel and heating rate the peak is situated from 350 to 500 K and its shape reflects a specific of hydrogen diffusion in stainless steels, which are multicomponent alloys. Analysis of the TDS curves is based on the hydrogen diffusion model taking into account trapping of hydrogen atoms in the energetically deep interstitial positions in the steel crystal lattice. Diffusion coefficient of hydrogen and its total content after the same charging procedure are obtained from the TDS curves and compared for the studied steels. (Copyright copyright 2011 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

  5. Stochastic aspects of evolution of creep damage in austenitic stainless steel

    A stochastic model for the creep damage evolution and associated scatter in austenitic stainless steel has been developed in terms of a discontinuous Markov process. The magnitude of damage has been described in the form of a probability distribution function whose evolution in time characterizes the nondeterministic nature of the damage accumulation process. The long-term creep behavior on samples obtained from different locations of a thick walled SS304 LN steel pipe are studied under an identical stress and temperature condition so as to observe the scatter in creep deformation and failure data. Also the occurrences of damage and its accumulation due to creep deformation were evaluated through microstructural assessment using light optical microscope and scanning electron microscope. The validity of the model has been established by repeat data of SS304 LN steel and 316 stainless steel .

  6. Effect on spot welding variables on nugget size and bond strength of 304 austenitic stainless steel

    Resistance spot welding (RSW) has revolutionized mechanical assembly in the automotive industry since its introduction in the early 1970s. Currently, one mechanical assembly in five is welded using spot welding technology, with welding of stainless steel sheet becoming increasingly common. Consequently, this research paper examines the spot welding of 2 mm thick 304 austenitic stainless steel sheet. The size of a spot weld nugget is primarily determined by the welding parameters: welding current, welding time, electrode force and electrode tip diameter However, other factors such as electrode deformation, corrosion, dissimilar materials and material properties also affect the nugget size and shape. This paper analyzes only the effects of current, weld time and force variations with unchanged electrode tip diameter. A pneumatically driven 75kVA spot welder was used to accomplish the welding process and the welded samples were subjected to tensile, hardness and metallurgical testing to characterize the size and shape of the weld nugget and the bond strength.

  7. Creep and LCF Behaviors of Newly Developed Advanced Heat Resistant Austenitic Stainless Steel for A-USC

    Chai, Guocai; Boström, Magnus; Olaison, Magnus; Forsberg, Urban

    2013-01-01

    Austenitic stainless steel grade UNS S31035 (Sandvik Sanicro® 25) has been developed for use in super-heaters and reheaters in the next generation of A-USC power plants. This new grade shows very good resistances to steam oxidation and hot corrosion, and higher creep rupture strength than other austenitic stainless steels available today. This makes it an interesting alternative for super-heaters and reheaters in future high-efficient coal fired boilers. This paper will mainly focus on the st...

  8. Experimental Analysis of Residual Stresses in Samples of Austenitic Stainless Steel Welded on Martensitic Stainless Steel Used for Kaplan Blades Repairs

    Vasile Cojocaru; Viorel Constantin Campian; Calin-Octavian Miclosina

    2011-01-01

    Residual stresses occur in materials as a result of mechanical processes: welding, machining, grinding etc. If residual stresses reach high values they can accelerate the occurrence of cracks and erosion of material. An experimental research was made in order to study the occurrence of residual stresses in the repaired areas of hydraulic turbine components damaged by cavitation erosion. An austenitic stainless steel was welded in various layer thicknesses on a martensitic stainless steel base...

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

    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.

  10. Enhancement of mechanical properties of a TRIP-aided austenitic stainless steel by controlled reversion annealing

    Hamada, A.S., E-mail: atef.hamada@suezuniv.edu.eg [Centre for Advanced Steels Research, Box 4200, University of Oulu, 90014 Oulu (Finland); Metallurgical and Materials Engineering Department, Faculty of Petroleum & Mining Engineering, Suez University, Box 43721, Suez (Egypt); Kisko, A.P. [Centre for Advanced Steels Research, Box 4200, University of Oulu, 90014 Oulu (Finland); Sahu, P. [Department of Physics, Jadavpur University, Kolkata 700032 (India); Karjalainen, L.P. [Centre for Advanced Steels Research, Box 4200, University of Oulu, 90014 Oulu (Finland)

    2015-03-25

    Controlled martensitic reversion annealing was applied to a heavily cold-worked metastable austenitic low-Ni Cr–Mn austenitic stainless steel (Type 201) to obtain different ultrafine austenite grain sizes to enhance the mechanical properties, which were then compared with the conventional coarse-grained steel. Characterization of the deformed and reversion annealed microstructures was performed by electron back scattered diffraction (EBSD), X-ray diffraction (XRD) and light and transmission electron microscopy (TEM). The steel with a reverted grain size ~1.5 μm due to annealing at 800 °C for 10 s showed significant improvements in the mechanical properties with yield stress ~800 MPa and tensile strength ~1100 MPa, while the corresponding properties of its coarse grained counterpart were ~450 MPa and ~900 MPa, respectively. However, the fracture elongation of the reversion annealed steel was ~50% as compared to ~70% in the coarse grained steel. A further advantage is that the anisotropy of mechanical properties present in work-hardened steels also disappears during reversion annealing.

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

    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.

  12. A Hybrid Low Temperature Surface Alloying Process for Austenitic Stainless Steels

    Y. Sun

    2004-01-01

    This paper describes a novel, hybrid process developed to engineer the surfaces of austenitic stainless steels at temperatures below 450℃ for the improvement in wear and corrosion resistance. The process is carried out in the plasma of a glow discharge containing both nitrogen and carbon reactive species, and facilitates the incorporation of both nitrogen and carbon into the austenite surface to form a dual-layer structure comprising a nitrogen-rich layer on top of a carbon-rich layer.Both layers can be precipitation-free at sufficiently low processing temperatures, and contain nitrogen and carbon respectively in supersaturated fcc austenite solid solutions. The resultant hybrid structure offers several advantages over the conventional low temperature nitriding and the newly developed carburizing processes in terms of mechanical and chemical properties, including higher surface hardness, a hardness gradient from the surface towards the layer-core interface, uniform layer thickness, and much enhanced corrosion resistance. This paper discusses the main features of this hybrid process and the various structural and properties characteristics of the resultant engineered surfaces.

  13. Enhancement of mechanical properties of a TRIP-aided austenitic stainless steel by controlled reversion annealing

    Controlled martensitic reversion annealing was applied to a heavily cold-worked metastable austenitic low-Ni Cr–Mn austenitic stainless steel (Type 201) to obtain different ultrafine austenite grain sizes to enhance the mechanical properties, which were then compared with the conventional coarse-grained steel. Characterization of the deformed and reversion annealed microstructures was performed by electron back scattered diffraction (EBSD), X-ray diffraction (XRD) and light and transmission electron microscopy (TEM). The steel with a reverted grain size ~1.5 μm due to annealing at 800 °C for 10 s showed significant improvements in the mechanical properties with yield stress ~800 MPa and tensile strength ~1100 MPa, while the corresponding properties of its coarse grained counterpart were ~450 MPa and ~900 MPa, respectively. However, the fracture elongation of the reversion annealed steel was ~50% as compared to ~70% in the coarse grained steel. A further advantage is that the anisotropy of mechanical properties present in work-hardened steels also disappears during reversion annealing

  14. The microstructural, mechanical, and fracture properties of austenitic stainless steel alloyed with gallium

    Kolman, D. G.; Bingert, J. F.; Field, R. D.

    2004-11-01

    The mechanical and fracture properties of austenitic stainless steels (SSs) alloyed with gallium require assessment in order to determine the likelihood of premature storage-container failure following Ga uptake. AISI 304 L SS was cast with 1, 3, 6, 9, and 12 wt pct Ga. Increased Ga concentration promoted duplex microstructure formation with the ferritic phase having a nearly identical composition to the austenitic phase. Room-temperature tests indicated that small additions of Ga (less than 3 wt pct) were beneficial to the mechanical behavior of 304 L SS but that 12 wt pct Ga resulted in a 95 pct loss in ductility. Small additions of Ga are beneficial to the cracking resistance of stainless steel. Elastic-plastic fracture mechanics analysis indicated that 3 wt pct Ga alloys showed the greatest resistance to crack initiation and propagation as measured by fatigue crack growth rate, fracture toughness, and tearing modulus. The 12 wt pct Ga alloys were least resistant to crack initiation and propagation and these alloys primarily failed by transgranular cleavage. It is hypothesized that Ga metal embrittlement is partially responsible for increased embrittlement.

  15. Mechanism and estimation of fatigue crack initiation in austenitic stainless steels in LWR environments.

    Chopra, O. K.; Energy Technology

    2002-08-01

    The ASME Boiler and Pressure Vessel Code provides rules for the construction of nuclear power plant components. Figures I-9.1 through I-9.6 of Appendix I to Section III of the Code specify fatigue design curves for structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. Existing fatigue strain-vs.-life ({var_epsilon}-N) data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. This report provides an overview of fatigue crack initiation in austenitic stainless steels in LWR coolant environments. The existing fatigue {var_epsilon}-N data have been evaluated to establish the effects of key material, loading, and environmental parameters (such as steel type, strain range, strain rate, temperature, dissolved-oxygen level in water, and flow rate) on the fatigue lives of these steels. Statistical models are presented for estimating the fatigue {var_epsilon}-N curves for austenitic stainless steels as a function of the material, loading, and environmental parameters. Two methods for incorporating environmental effects into the ASME Code fatigue evaluations are presented. The influence of reactor environments on the mechanism of fatigue crack initiation in these steels is also discussed.

  16. Cutting Properties of Austenitic Stainless Steel by Using Laser Cutting Process without Assist Gas

    Hitoshi Ozaki

    2012-01-01

    Full Text Available Recently, laser cutting is used in many industries. Generally, in laser cutting of metallic materials, suitable assist gas and its nozzle are needed to remove the molten metal. However, because of the gas nozzle should be set closer to the surface of a workpiece, existence of the nozzle seems to prevent laser cutting from being used flexible. Therefore, the new cutting process, Assist Gas Free laser cutting or AGF laser cutting, has been developed. In this process, the pressure at the bottom side of a workpiece is reduced by a vacuum pump, and the molten metal can be removed by the air flow caused by the pressure difference between both sides of the specimen. In this study, cutting properties of austenitic stainless steel by using AGF laser cutting with 2 kW CO2 laser were investigated. Laser power and cutting speed were varied in order to study the effect of these parameters on cutting properties. As a result, austenitic stainless steel could be cut with dross-free by AGF laser cutting. When laser power was 2.0 kW, cutting speed could be increased up to 100 mm/s, and kerf width at specimen surface was 0.28 mm.

  17. Formability and fracture studies of austenitic stainless steel 316 at different temperatures

    Syed Mujahed Hussaini

    2014-07-01

    Full Text Available Deep drawing is one of the most important sheet metal forming processes in automotive, aerospace and nuclear industries. In this process, the sheet metal blank is formed into a cup shape by an application of punch into the die. The present work is aimed at studying the formability and the nature of fracture for one of the important materials in industrial applications, austenitic stainless steel 316 at different temperatures. Circular blanks were deep drawn at room temperature, 150 and 300 °C using a 20 Ton hydraulic press coupled with a furnace and found that formability of the austenitic stainless steel 316 increased as the temperature was increased. This material underwent dynamic strain aging between 350 and 550 °C. Fractured surface of the broken tensile test specimen at different regions were studied and analyzed using scanning electron microscope. It was observed that the nature of the fracture was brittle in dynamic strain aging region.

  18. Corrosion properties of S-phase layers formed on medical grade austenitic stainless steel.

    Buhagiar, Joseph; Dong, Hanshan

    2012-02-01

    The corrosion properties of S-phase surface layers formed in AISI 316LVM (ASTM F138) and High-N (ASTM F1586) medical grade austenitic stainless steels by plasma surface alloying with nitrogen (at 430°C), carbon (at 500°C) and both carbon and nitrogen (at 430°C) has been investigated. The corrosion behaviour of the S-phase layers in Ringer's solutions was evaluated using potentiodynamic and immersion corrosion tests. The corrosion damage was evaluated using microscopy, hardness testing, inductive coupled plasma mass spectroscopy and X-ray diffraction. The experimental results have demonstrated that low-temperature nitriding, carburising and carbonitriding can improve the localised corrosion resistance of both industrial and medical grade austenitic stainless steels as long as the threshold sensitisation temperature is not reached. Carburising at 500°C has proved to be the best hardening treatment with the least effect on the corrosion resistance of the parent alloy. PMID:22160745

  19. The Effect of Hydrogen on Plasma Nitriding of Austenitic Stainless Steel: Kinetic Modeling

    Moskalioviene, Teresa; Galdikas, Arvaidas

    2015-12-01

    The kinetic model of adsorption and stress-induced diffusion of nitrogen in austenitic stainless steels taking place during plasma nitriding using various mixtures of nitrogen and hydrogen is proposed. On the basis of proposed model, a numerical study has been undertaken to analyze and describe the effect of hydrogen on plasma nitriding of austenitic stainless steel. It was shown that the addition of hydrogen with concentrations in the range ~(30 to 40) pct enhances nitrogen penetration into steel. This is due to two factors: (1) reduction of the surface oxide due to chemical etching of the oxygen by hydrogen and (2) increase of NH radicals which are converted to active nitrogen atoms on the steel surface, i.e., the amount of adsorbed and diffused nitrogen increases. As a result, the thicker nitrogen-containing layer is observed. Moreover, results of numerical prediction show that an excessive amount of hydrogen (more than ~70 pct) in the gas mixture retards the nitriding process in comparison with nitriding in pure nitrogen plasma.

  20. Test and research on stress corrosion crack of austenitic stainless steel in ocean environment

    The applicability of stress corrosion test performance on wedge opened self-loaded samples to study stress corrosion property of austenitic stainless steels in ocean environment including Cl-. The studied materials were 0Cr18Ni10Ti(321) austenitic stainless steel, using NaCl solution with concentration of 3.5%, 15% and 26.5% to simulate ocean and condensable ocean situation. The average stress corrosion crack propagating rate existed in 3.34 X 10-9 mm/s∼1.31 X 10-8 mm/s and incubation time were 792∼1752 h or even more when stress intensity factor K1 in scope of 35 MPa √m∼60 MPa √m. Stress corrosion crack propagating rate was immune to differing concentration of NaCl, crack incubation got shorter along with stress intensity factor K1 was higher. That was showed prefabricated fatigue crack area, stress corrosion crack propagation area and toughness fracture area connected with each other on fracture surface. (authors)

  1. Analysis of tensile deformation and failure in austenitic stainless steels: Part II - Irradiation dose dependence

    Kim, Jin Weon; Byun, Thak Sang

    2010-01-01

    Irradiation effects on the stable and unstable deformation and fracture behavior of austenitic stainless steels (SSs) have been studied in detail based on the equivalent true stress versus true strain curves. An iterative finite element simulation technique was used to obtain the equivalent true stress-true strain data from experimental tensile curves. The simulation result showed that the austenitic stainless steels retained high strain hardening rate during unstable deformation even after significant irradiation. The strain hardening rate was independent of irradiation dose up to the initiation of a localized necking. Similarly, the equivalent fracture stress was nearly independent of dose before the damage (embrittlement) mechanism changed. The fracture strain and tensile fracture energy decreased with dose mostly in the low dose range SS were less sensitive to irradiation than those for 316 SS, although their uniform tensile properties showed almost the same dose dependencies. It was confirmed that the dose dependence of tensile fracture properties evaluated by the linear approximation model for nominal stress was accurate enough for practical use without elaborate calculations.

  2. High corrosion resistance of austenitic stainless steel alloyed with nitrogen in an acid solution

    Metikos-Hukovic, M., E-mail: mmetik@fkit.h [Department of Electrochemistry, Faculty of Chemical Engineering and Technology, University of Zagreb, Savska 16, P.O. Box 177, 100000 Zagreb (Croatia); Babic, R. [Department of Electrochemistry, Faculty of Chemical Engineering and Technology, University of Zagreb, Savska 16, P.O. Box 177, 100000 Zagreb (Croatia); Grubac, Z. [Department of General and Inorganic Chemistry, Faculty of Chemistry and Technology, University of Split, 21000 Split (Croatia); Petrovic, Z. [Department of Electrochemistry, Faculty of Chemical Engineering and Technology, University of Zagreb, Savska 16, P.O. Box 177, 100000 Zagreb (Croatia); Lajci, N. [Faculty of Mine and Metallurgy, University of Prishtina, 10000 Prishtina, Kosovo (Country Unknown)

    2011-06-15

    Highlights: {yields} ASS alloyed with nitrogen treated at 1150 {sup o}C exhibits microstructure homogeneity. {yields} Passivation peak of ASS corresponds to oxidation of metal and absorbed hydrogen. {yields} Transfer phenomena and conductivity depend on the film formation potential. {yields} Electronic structure of the passive film and its corrosion resistance correlate well. {yields} Passive film on ASS with nitrogen is low disordered and high corrosion resistant. - Abstract: Passivity of austenitic stainless steel containing nitrogen (ASS N25) was investigated in comparison with AISI 316L in deareated acid solution, pH 0.4. A peculiar nature of the passivation peak in a potentiodynamic curve and the kinetic parameters of formation and growth of the oxide film have been discussed. The electronic-semiconducting properties of the passive films have been correlated with their corrosion resistance. Alloying austenitic stainless steel with nitrogen increases its microstructure homogeneity and decreases the concentration of charge carriers, which beneficially affects the protecting and electronic properties of the passive oxide film.

  3. High corrosion resistance of austenitic stainless steel alloyed with nitrogen in an acid solution

    Highlights: → ASS alloyed with nitrogen treated at 1150 oC exhibits microstructure homogeneity. → Passivation peak of ASS corresponds to oxidation of metal and absorbed hydrogen. → Transfer phenomena and conductivity depend on the film formation potential. → Electronic structure of the passive film and its corrosion resistance correlate well. → Passive film on ASS with nitrogen is low disordered and high corrosion resistant. - Abstract: Passivity of austenitic stainless steel containing nitrogen (ASS N25) was investigated in comparison with AISI 316L in deareated acid solution, pH 0.4. A peculiar nature of the passivation peak in a potentiodynamic curve and the kinetic parameters of formation and growth of the oxide film have been discussed. The electronic-semiconducting properties of the passive films have been correlated with their corrosion resistance. Alloying austenitic stainless steel with nitrogen increases its microstructure homogeneity and decreases the concentration of charge carriers, which beneficially affects the protecting and electronic properties of the passive oxide film.

  4. Survey report on unmanned site welding of austenitic stainless steel pipe and its ultrasonic examination

    In the field welding of austenitic stainless steel pipings and its non-destructive test in complicated and narrow places, reliable welding method and non-destructive testing method are required, and also, it is desirable to mechanize them (unmanned operation). In this study, the present state of the automatic welding of austenitic stainless steel pipings and ultrasonic flaw detection was investigated through the literatures in Japan and foreign countries. As the result, it was clarified that energetic research has been made recently to mechanize the welding, and though many points are left for future research and development, it is promising. In the ultrasonic flaw detection, many technical problems concerning the detectability of flaws remain at present, but is is expected to become feasible by future systematic research and development. The design of weld joints, the welding method and the remote automatic control of welding operation must be appropriate for guaranteeing the quality of welding, and these points were surveyed. The problems in the ultrasonic flaw detection are the attenuation of ultrasonic waves, the conditions of probes, the mode of wave motion and frequency, and the welding suitable to the ultrasonic flaw detection. (Kako, I.)

  5. Mitigating the Risk of Stress Corrosion of Austenitic Stainless Steels in Advanced Gas Cooled Reactor Boilers

    Advanced Gas-Cooled Reactors (AGRs) operated in the UK by EDF Energy have once-through boilers, which deliver superheated steam at high temperature (∼500 deg. C) and pressure (∼150 bar) to the HP turbine. The boilers have either a serpentine or helical geometry for the tubing of the main heat transfer sections of the boiler and each individual tube is fabricated from mild steel, 9%Cr1%Mo and Type 316 austenitic stainless steel tubing. Type 316 austenitic stainless steel is used for the secondary (final) superheater and steam tailpipe sections of the boiler, which, during normal operation, should operate under dry, superheated steam conditions. This is achieved by maintaining a specified margin of superheat at the upper transition joint (UTJ) between the 9%Cr1%Mo primary superheater and the Type 316 secondary superheater sections of the boiler. Operating in this mode should eliminate the possibility of stress corrosion cracking of the Type 316 tube material on-load. In recent years, however, AGRs have suffered a variety of operational problems with their boilers that have made it difficult to maintain the specified superheat margin at the UTJ. In the case of helical boilers, the combined effects of carbon deposition on the gas side and oxide deposition on the waterside of the tubing have resulted in an increasing number of austenitic tubes operating with less than the specified superheat margin at the UTJ and hence the possibility of wetting the austenitic section of the boiler. Some units with serpentine boilers have suffered creep-fatigue damage of the high temperature sections of the boiler, which currently necessitates capping the steam outlet temperature to prevent further damage. The reduction in steam outlet temperature has meant that there is an increased risk of operation with less than the specified superheat margin at the UTJ and hence stress corrosion cracking of the austenitic sections of the boiler. In order to establish the risk of stress

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

    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.

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

    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

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

    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

  9. Nanoscopic strength analysis of work-hardened low carbon austenitic stainless steel, 316SS

    Stress corrosion cracking (SCC) occurs in shrouds and piping of low carbon austenitic stainless steels at nuclear power plants. A work-hardened layer, where the transgranular SCC initiates, is considered to be one of the probable cause for this occurrence. In order to clarify the microstructural characteristics of work-hardened layer at the surface of shrouds or piping, the strengthen analysis of low carbon austenitic stainless steel, 316SS, rolled at the reduction in area, RA, of 10, 20, 30, 40 and 50% at room temperature were conducted on a nanoscopic scale, using an ultra-microhardness tester, TEM and SEM. TEM and SEM observation showed that the microstructural parameters are the dislocation cell size, dcel, coarse slip spacing, lcsl, and austenitic grain size, dγ. Referring 10dcel and 10lcsl, Vickers hardness, HV, corresponding to macro strength was expressed as Hυ=Hυ*bas + Hυ*sol + Hυ*dis + Hυ*cel + Hυ*csl. Hυ*bas (=100) is the base hardness, Hυ*sol is the solid solution strengthening hardness, Hυ*dis is the dislocation strengthening hardness in the dislocation cell, and Hυ*cel and Hυ*csl are the fine grain strengthening hardness due to the dislocation cell and coarse slip. Hυ*sol was about 50, independently of RA. Hυ*dis was zero at RA 30%. Hυ*cel and Hυ*csl increased with increasing in RA and were kept constant at about 50 and 120 at RA=20 and 30%, respectively. It was suggested from these results that all dislocations introduced by rolling might be dissipated for the creation of dislocation cells and coarse slips at RA 30%. (author)

  10. Nanoscopic strength analysis of work-hardened L-grade austenitic stainless steel, 316(NG)

    Stress corrosion cracking (SCC) occurs in shrouds and piping of L-grade austenitic stainless steels at nuclear power plants. A work-hardened layer, where the transgranular SCC initiates, is considered to be one of the probable cause for this occurrence. In order to clarify the microstructural characteristics of work-hardened layer at the surface of shrouds or piping, the strengthen analysis of L-grade austenitic stainless steel, 316(NG), rolled at the reduction in area, RA, of 10, 20, 30, 40 and 50% at room temperature were conducted on a nanoscopic scale, using an ultra-microhardness tester, TEM and SEM. TEM and SEM observation showed that the microstructural parameters are the dislocation cell size, dcel, coarse slip spacing, lcsl, and austenitic grain size, dγ. Referring 10dcel and 10lcsl, Vickers hardness, Hυ, corresponding to macro strength was expressed as Hυ = Hυ*bas + Hυ*sol + Hυ*dis + Hυ*cel + Hυ*csl. Hυ*bas(=100) is the base hardness, Hυ*sol is the solid solution strengthening hardness, Hυ*dis is the dislocation strengthening hardness in the dislocation cell, and Hυ*cel and Hυ*csl are the fine grain strengthening hardness due to the dislocation cell and coarse slip. Hυ*sol was about 50, independently of RA. Hυ*dis was zero at RA30%. Hυ*cel and Hυ*csl increased with increasing in RA and were kept constant at about 50 and 120 at RA=20 and 30%, respectively. It was suggested from these results that all dislocations introduced by rolling might be dissipated for the creation of dislocation cells and coarse slips at RA30%. (author)

  11. Notch tensile measurements and fracture toughness correlations for austenitic stainless steels

    Thirty-two alloys were included in a study of conventional notch tensile testing as a method of fracture toughness characterization for austenitic stainless steels at liquid helium temperature, 4 K. For the same austenitic stainless steels, tensile and J-integral fracture toughness (K/sub Ic/(J)) measurements have also been conducted. For these materials the notch tensile strength (sigma/sub NTS) generally increases with yield strength (sigma/sub y/), and the contains/sub NTS//sigma/sub y/ ratios are typically much greater than 1.0. Correlations between sigma/sub NTS/, K/sub Ic/(J), and sigma/sub y/ were assessed. The best data fit was found between the ratio, sigma/NTS/K/sub Ic/(J), and the toughness, K/sub Ic/(J). Unfortunately, from this relation there is not uniqueness of K/sub Ic/ from sigma/sub NTS/. Therefore at this time it is not considered practical to obtain estimates of K/sub Ic/ from notch tensile tests for austenitic steels at 4 K. However, one may compare the J-integral fracture toughness and cylindrical bar notch tensile measurements. There are three regions: (1) linear elastic (sigma/sub NTS/ increases as K/sub Ic/(J) increases); (2) elastic-plastic (sigma/sub NTS/ is essentially independent of K/sub Ic/(J); (3) plastic (sigma/sub NTS/ decreases as K/sub Ic/(J) increases. The elastic-plastic (transition) region is associated with a plastic zone that extends completely through the notched cross-sectional area

  12. Thick-section Laser and Hybrid Welding of Austenitic Stainless Steels

    Kujanpää, Veli

    Austenitic stainless steels are generally known to have very good laser weldability, when ordinary grades of sheets are concerned. But it is not necessarily the case, if special grades of fully austenitic structures with e.g. high molybdenum, or thick-section are used. It is also known that hot cracking susceptibility is strictly controlled by composition and welding parameters. If solidification is primary ferritic, hot cracking resistance is dramatically increased. It is also well known that laser welding needs a careful control of weld edge preparation and air gap between the edges. The dependence on edge quality can be decreased by using filler metal, either cold wire, hot wire or hybrid laser-arc welding. An additional role is high molybdenum contents where micro segregation can cause low local contents in weld which can decrease the corrosion properties, if filler metal is not used. Another feature in laser welding is its incomplete mixing, especially in thick section applications. It causes inhomogeneity, which can make uneven microstructure, as well as uneven mechanical and corrosion properties In this presentation the features of laser welding of thick section austenitic stainless steels are highlighted. Thick section (up to 60 mm) can be made by multi-pass laser or laser hybrid welding. In addition to using filler metal, it requires careful joint figure planning, laser head planning, weld parameter planning, weld filler metal selection, non-destructive and destructive testing and metallography to guarantee high-quality welds in practice. In addition some tests with micro segregation is presented. Also some examples of incomplete mixing is presented.

  13. Automatic orbital TIG-welding of small bore austenitic stainless steel tubes for nuclear fuel reprocessing plant

    Traditionally, manual welding techniques have been employed for shop and site fabrication of small bore austenitic stainless steel tubes in the nuclear fuel reprocessing plant of British Nuclear Fuels Limited (BNFL). This Paper describes an evaluation programme carried out to develop welding procedures for both 18Cr-13Ni-1Nb and 18Cr-10Ni low carbon stainless steel small bore tubing, the type of equipment used, and the modifications required for application to shop and site environments. (author)

  14. Corrosion of silicon-containing austenitic stainless steels under trans-passive conditions

    This research thesis addresses austenitic stainless steels which are used in installations for the chemical treatment of nuclear fuels, and are there in contact with nitric acid solutions the oxidising character of which generally promotes metal passivity. However, if this nitric environment becomes too oxidising, these steels may face severe corrosion problems. More particularly, this thesis addresses the study of intergranular corrosion, and aims at analysing various aspects of the corrosion of these austenitic stainless steels in trans-passive conditions. The author aims at determining and distinguishing the contributions due to silicon and those related to the presence of other impurities and addition elements by comparing the behaviours of industrial grade steels and high purity alloys in rigorously controlled electrochemical conditions. Another objective is to study the influence of the intergranular structure on silicon segregation by means of an attack technique in trans-passive conditions. After a report of a bibliographical study on the addressed topics and a presentation of the studied materials and implemented experimental techniques, the author reports the study of steel behaviour with respect to generalised dissolution in trans-passive conditions, as well in the nitric environment as in a sulphuric acid solution at imposed potential. Localised intragranular corrosion phenomena are discussed. A trans-passive intragranular corrosion model is proposed, and its possibilities in the analysis of intergranular segregation analysis are discussed. Experimental results of trans-passive intergranular corrosion of stainless steels are presented and interpreted by using the McLean segregation model. The influence of steel composition and of experimental conditions is discussed, as well as the role of grain boundary structure in the corrosion process

  15. Investigations on the Corrosion Behaviour and Structural Characteristics of Low Temperature Nitrided and Carburised Austenitic Stainless Steel

    D. M(u)nter; H.-J. Spies; H. Biermann; Chr. Eckstein

    2004-01-01

    The wear resistance of austenitic stainless steels can be improved by thermo-chemical surface treatment with nitrogen and carbon. However, it is possible that the corrosion resistance will be impaired by the precipitation of chromiumnitrid or -carbide. The present contribution deals with investigations of the corrosion behaviour and structural characteristics of a low temperature nitrided and carburised austenitic stainless steel.The material investigated was AISI 316L (X2CrNiMo17-12-2) austenitic stainless steel. A commercial plasma-nitriding unit (pulsed dc) was used for the nitriding and carburising process. Additional samples were treated by the gasoxinitriding process for a comparison between plasma- and gasoxinitriding. The nitrided and carburised layer of austenltic stainless steel consists of the nitrogen or carbon S-phase (expanded austenite), respectively. X-ray diffraction investigations show the typical shift of the peaks to lower angles, indicating expansion of the fcc lattice. Also the X-ray diffraction technique was employed to study the residual stresses in the nitrogen and carbon S-phase. The corrosion behaviour of surface engineered samples was investigated with electrochemical methods. Anodic potentiodynamic polarisation curves were recorded for testing the resistance against general corrosion (in H2SO4) and pitting corrosion (in NaCl).

  16. Effect of Grain Size on Void Formation during High-Energy Electron Irradiation of Austenitic Stainless Steel

    Singh, Bachu Narain

    1974-01-01

    Thin foils of an ‘ experimental ’ austenitic stainless steel, with and without dispersions of aluminium oxide particles, are irradiated with 1 MeV electrons in a High Voltage Electron Microscope at 600°C. Evidence of grain size dependent void nucleation, void concentration, and void volume swelling...

  17. Calculation of microsegregation and amount of retained δ-ferrite in Fe-Cr-Ni austenitic stainless steel

    In equilibrium, 304 stainless steel has only γ-austenite phase below about 1170 .deg. C and solutes are uniformly distributed in γ-austenite. Due to incomplete solid-state diffusion, it has retained δ-ferrite as well as γ-austenite and the solute distribution becomes inhomogeneous in each phase. To further understand the solidification behavior of 304 stainless steel, the variation of δ-ferrite amount with temperature and the solute concentration in each phase across the phase boundary are calculated in this study. The calculated solute contents at the interface are in good agreement with experimental data available. It is shown that the equilibrium calculation using 304 steel composition itself produces better results than using equivalent composition. The calculated amounts of retained δ-ferrite using 304 equivalent composition are somewhat higher than experimentally observed values. Much better agreement between calculation results and experimental data is expected if more reliable experimental data can be obtained

  18. Prediction of Irradiation Damage by Artificial Neural Network for Austenitic Stainless Steels

    The internal structures of pressurized water reactors (PWR) located close to the reactor core are used to support the fuel assemblies, to maintain the alignment between assemblies and the control bars and to canalize the primary water. In general these internal structures consist of baffle plates in solution annealed (SA) 304 stainless steel and baffle bolts in cold worked (CW) 316 stainless steel. These components undergo a large neutron flux at temperatures between 280 and 380 .deg. C. Well-controlled irradiation-assisted stress corrosion cracking (IASCC) data from properly irradiated, and properly characterized, materials are sorely lacking due to the experimental difficulties and financial limitations related to working with highly activated materials. In this work, we tried to apply the artificial neural network (ANN) approach, predicted the susceptibility to an IASCC for an austenitic stainless steel SA 304 and CW 316. G.S. Was and J.-P. Massoud experimental data are used. Because there is fewer experimental data, we need to prediction for radiation damage under the internal structure of PWR. Besides, we compared experimental data with prediction data by the artificial neural network

  19. Pre-immersion effect on IASCC susceptibility in austenitic stainless steel

    Irradiation assisted stress corrosion cracking (IASCC) is now recognized as one of the major engineering concerns for extending the operating life of light water reactors (LWRs). IASCC appears in the form of intergranular stress corrosion cracking (IGSCC) and the threshold fluence level has been reported to be about 5 x 10 24n/m2 (E>1MeV) in austenitic stainless steels such as types 304 and 316 SSs. In order to investigate the effect of oxide film on the initiation of irradiation assisted stress corrosion (IASCC), UCL (uniaxial constant load) tests of highly irradiated type 304 stainless steel (neutron fluence: 1.4 x 1026n/m2, E > 1MeV) with oxide film by pre-immersion were conducted in high temperature oxygenated pure water. IASCC susceptibilities were not observed even over the IASCC threshold stress level at 463--523 MPa during 2,000 hour tests. Analysis of TTF (times to failure) results in polished specimen of highly irradiated steels also supported the idea that the surface oxide film on irradiated specimens would affect the IASCC initiation mechanism, but not for IGSCC in unirradiated sensitized stainless steel. The mechanism of IASCC behavior was discussed from the viewpoint of the relationship between chromium depletion at a grain boundary and the surface oxide film

  20. Microstructural characterization of dissimilar welds between Incoloy 800H and 321 Austenitic Stainless Steel

    In this work, the microstructural character of dissimilar welds between Incoloy 800H and 321 Stainless Steel has been discussed. The microscopic examination of the base metals, fusion zones and interfaces was characterized using an optical microscope and scanning electron microscopy. The results revealed precipitates of Ti (C, N) in the austenitic matrix along the grain boundaries of the base metals. Migration of grain boundaries in the Inconel 82 weld metal was very extensive when compared to Inconel 617 weldment. Epitaxial growth was observed in the 617 weldment which increases the strength and ductility of the weld metal. Unmixed zone near the fusion line between 321 Stainless Steel and Inconel 82 weld metal was identified. From the results, it has been concluded that Inconel 617 filler metal is a preferable choice for the joint between Incoloy 800H and 321 Stainless Steel. - Highlights: • Failure mechanisms produced by dissimilar welding of Incoloy 800H to AISI 321SS • Influence of filler wire on microstructure properties • Contemplative comparisons of metallurgical aspects of these weldments • Microstructure and chemical studies including metallography, SEM–EDS • EDS-line scan study at interface

  1. Prediction of microsegregation and pitting corrosion resistance of austenitic stainless steel welds by modelling

    Vilpas, M. [VTT Manufacturing Technology, Espoo (Finland). Materials and Structural Integrity

    1999-07-01

    The present study focuses on the ability of several computer models to accurately predict the solidification, microsegregation and pitting corrosion resistance of austenitic stainless steel weld metals. Emphasis was given to modelling the effect of welding speed on solute redistribution and ultimately to the prediction of weld pitting corrosion resistance. Calculations were experimentally verified by applying autogenous GTA- and laser processes over the welding speed range of 0.1 to 5 m/min for several austenitic stainless steel grades. Analytical and computer aided models were applied and linked together for modelling the solidification behaviour of welds. The combined use of macroscopic and microscopic modelling is a unique feature of this work. This procedure made it possible to demonstrate the effect of weld pool shape and the resulting solidification parameters on microsegregation and pitting corrosion resistance. Microscopic models were also used separately to study the role of welding speed and solidification mode in the development of microsegregation and pitting corrosion resistance. These investigations demonstrate that the macroscopic model can be implemented to predict solidification parameters that agree well with experimentally measured values. The linked macro-micro modelling was also able to accurately predict segregation profiles and CPT-temperatures obtained from experiments. The macro-micro simulations clearly showed the major roles of weld composition and welding speed in determining segregation and pitting corrosion resistance while the effect of weld shape variations remained negligible. The microscopic dendrite tip and interdendritic models were applied to welds with good agreement with measured segregation profiles. Simulations predicted that weld inhomogeneity can be substantially decreased with increasing welding speed resulting in a corresponding improvement in the weld pitting corrosion resistance. In the case of primary austenitic

  2. Effect of cold work and type of load in the SCC behaviour of austenitic stainless steels in PWR conditions

    Austenitic stainless steels are susceptible to SCC in high temperature water, even in reducing environment such as the PWR primary water. Both laboratory results and field evidences confirm that stainless steels are susceptible to SCC when these materials are in a cold work condition. CGR experiments have been performed in order to assess the factors influencing SCC propagation in stainless steels. Compact tension specimens were fabricated of 316 L, 304 L and 347 SS to evaluate the influence of degree of cold work and its way of application, water chemistry, temperature and loading conditions. (authors)

  3. Stress corrosion cracking of austenitic stainless steel in glycerol solution and chloride solution at elevated temperature

    Stress Corrosion Cracking (SCC) is an environmentally assisted failure caused by exposure to a corrodant while under a sustained tensile stress. SCC is most often rapid, unpredictable and catastrophic. Failure can occur in as little as a few hours or take years to happen. Most alloys are susceptible to SCC in one or more environments requiring careful consideration of alloy type in component design. In aqueous chloride environments austenitic stainless steels and many nickel based alloys are known to perform poorly. One of products Oleo chemical is glycerol solution. Glycerol solution contains chloride with concentration 50 ppm - 150 ppm. Austenitic stainless steel is usually used in distillation construction tank and pipe line of glycerol. Material AISI 304 will be failure in this glycerol solution with this concentration in 5 years. In production process, concentration of chloride in glycerol becomes more than 150 ppm at temperature 150 degree Celsius. The reason is that the experiment I conducted in high chloride with concentration such as 6000 ppm, 9000 ppm, and 12000 ppm. The stress corrosion cracking of the austenitic stainless steels of types AISI 304, 316 and 316L in glycerol solution at elevated temperature 150 degree Celsius is investigated as a function variation of chloride concentration, namely 50, 6000, 9000 and 12000 ppm using a constant load method with two kinds of initial tensile stress as 50 % and 70 % yield strength. The experiment uses a spring loaded fixture type and is based on ASTM G49 for experiment method, and E292 for geometry of specimen. Pitting corrosion occurs on the surface specimen until the stress level reaches the ultimate strength. Pitting corrosion attack and depletion occur on the surface as initiation of SCC failure as the stress reaches the ultimate strength. Failure has occurred in catastrophic brittle fracture type of transgranular. AISI 304 was more susceptible for all conditions. In chloride solution with concentration of

  4. Verification of cutting zone machinability during drilling of austenitic stainless steels

    Jurko, Jozef

    2008-11-01

    Automated production of, in the sense of, machine production has characteristic features: a reduction of production costs, stimulation of the development of cutting tools, and changes in the construction of machine tools, all of which work against the creation of optimal technological methods, which thrusts the technological process of cutting into a more important position. These trends confirm that the cutting process remains one of the basic manufacturing technologies. A condition of the economic usage of modern, automated programmed drilling machines is the optimal course of the cutting process, i.e. the use of optimal work conditions. A summary of optimal work conditions requires knowledge of the laws of cutting theory and knowledge of the practical conditions of their application. This article presents the results of experiments that concerned the verification of machinability of work pieces of difference types of X12CrNi 18 8 austenitic stainless steel. Steel X12CrNi 18 8 is the chief representative of the austenitic stainless steels, and this steel falls into the category of materials that are difficult to machine. The rapid development of industry is marked by the development and application of new materials with characteristics that broaden their applicable uses. Precise and reliable information on the machinability of a material before it enters the machining process is a necessity, and hypotheses must be tested through verification of actual methods. This article presents conclusions of machinability tests on austenitic stainless steels and describes appropriate parameters for the cutting zone during the process of drilling with the goal of proposing recommendations for this steels, and to integrate current knowledge in this field with drilling and praxis. This article concerns itself with the evaluation of selected domains of machinability in compliance with EN ISO standards. The experiments were performed in laboratory conditions and verified in real

  5. Characterization and understanding of ion irradiation effect on the microstructure of austenitic stainless steels

    Austenitic stainless steels are widely used in nuclear industry for internal structures. These structures are located close to the fuel assemblies, inside the pressure vessel. The exposure of these elements to high irradiation doses (the accumulated dose, after 40 years of operation, can reach 80 dpa), at temperature close to 350 C, modifies the macroscopic behavior of the steel: hardening, swelling, creep and corrosion are observed. Moreover, in-service inspections of some of the reactor internal structures have revealed the cracking of some baffle bolts. This cracking has been attributed to Irradiation Assisted Stress Corrosion Cracking (IASCC). In order to understand this complex phenomenon, a first step is to identify the microstructural changes occurring during irradiation, and to understand the mechanisms at the origin of this evolution. In this framework, a large part of the European project 'PERFORM 60' is dedicated to the study of the irradiation damage in austenitic stainless steels. The objective of this PhD work is to bring comprehensive data on the irradiation effects on microstructure. To reach this goal, two model alloys (FeNiCr and FeNiCrSi) and an industrial austenitic stainless steel (316 steel) are studied using Atom Probe Tomography (APT), Transmission Electron Microscope (TEM) and Positron Annihilation Spectroscopy (PAS). They are irradiated by Ni ions in CSNSM (Orsay) at two temperatures (200 and 450 C) and three doses (0.5, 1 and 5 dpa). TEM observations have shown the appearance of dislocation loops, cavities and staking fault tetrahedra. The dislocation loops in 316 steel were preferentially situated in the vicinity of dislocations, while they were randomly distributed in the FeNiCr alloy. APT study has shown the redistribution of Ni and Si under irradiation in FeNiCrSi model alloy and 316 steel, leading to the appearance of (a) Cottrell clouds along dislocation lines, dislocation loops and other non-identified crystalline defects and (b

  6. Development of nitride-layer of AISI 304 austenitic stainless steel during high-temperature ammonia gas-nitriding

    Ammonia-gas nitriding of AISI 304 austenitic stainless steel was studied at temperatures higher than 800 deg. C using SEM and X-ray diffraction. The result showed that S-phase, an expanded austenite, was formed even at such high temperatures due to a high nitriding potential of ammonia gas. The equilibrium phase, CrN was formed through a decomposition of S-layer in two different modes; the one was through continuous precipitation of particles at the surface-side of S-layer due to a higher nitriding potential; the other through a discontinuous(-like) precipitation at the austenite interface-side, producing a fine lamellar structure of austenite and CrN. The γ-phase in the surface-side resulting from the precipitation of CrN particles subsequently transformed into Fe4N because of a fast enrichment of N atoms and a limited mobility of Cr atoms at the surface-side. A coarse lamellar structure made of austenite and Cr2N was developed in front of fine lamellae composed of austenite and CrN by the decomposition of supersaturated austenite through a discontinuous precipitation via grain boundary movement.

  7. XPS spectroscopic and electrochemical study of passivation and localized corrosion of austenitic stainless steels treated by ionic implantation of molybdenum

    As molybdenum is known to have a beneficial impact on corrosion resistance of austenitic stainless steels, this research thesis aims at characterizing and explaining the role of molybdenum in this corrosion resistance in the case of Fe-19 Cr-10 Ni steels implanted with molybdenum. After having presented the main notions, the author presents the sample preparation and both electrochemical techniques which have been used: conventional and ring-disk techniques. The author presents the XPS (X-ray photoelectron spectroscopy) technique and additional techniques (Rutherford backscattering spectrometry or RBS, electronic microscopy), and reports and discusses the XPS-based quantitative analysis. Calibration issues and characterization of the implanted material are discussed, and an experimental protocol is proposed. The author also discusses the passivation of molybdenum-implanted stainless steels, the influence of the implanted molybdenum on localized corrosion of austenitic stainless steels

  8. Elastic and plastic strains and the stress corrosion cracking of austenitic stainless steels. Final report

    The influence of elastic (stress) and plastic (cold work) strains on the stress corrosion cracking of a transformable austenitic stainless steel was studied in several aqueous chloride environments. Initial polarization behavior was active for all deformation conditions as well as for the annealed state. Visual observation, potential-time, and current-time curves indicated the development of a pseudo-passive (flawed) film leading to localized corrosion, occluded cells and SCC. SCC did not initiate during active corrosion regardless of the state of strain unless severe low temperature deformation produced a high percentage of martensite. Both elastic and plastic deformation increased the sensitivity to SCC when examined on the basis of percent yield strength. The corrosion potential, the critical cracking potential, and the potential at which the current changes from anodic to cathodic were essentially unaffected by deformation. It is apparent that the basic electrochemical parameters are independent of the bulk properties of the alloy and totally controlled by surface phenomena

  9. Investigation of Residual Stress Distributions of Induction Heating Bended Austenitic Stainless Steel (316 Series) Piping

    The induction heating bending process, which has been recently applied to nuclear piping, can generate residual stresses due to thermomechanical mechanism during the process. This residual stress is one of the crack driving forces that have important effects on crack initiation and propagation. However, previous studies have focused only on geometric shape variations such as the change in thickness and ovality. Moreover, very few studies are available on the effects of process variables on residual stresses. This study investigated the effects of process variables on the residual stress distributions of induction heating bended austenitic stainless steel (316 series) piping using parametric finite element analysis. The results indicated that the heat generation rate and feed velocity have significant effects on the residual stresses whereas the moment and bending angle have insignificant effects

  10. Evaluation of welding residual stresses in austenitic stainless steel using diffraction spot trace method

    A diffraction spot trace method (DSTM) was developed to measure internal stresses of materials with coarse grains. The DSTM was applied to light metals, such as aluminum alloy and magnesium alloy. In this study, validity of the DSTM was examined using high energy synchrotron X-rays of 70 keV. The specimen was a welded plate of austenitic stainless steel (SUS316L). The thickness of the specimen was 9 mm. The improved rotating slit-system was used, and PILATUS was used as an area detector. It was difficult to detect the high energy X-rays due to the reduction of counting efficiency of the PILATUS. However, the residual stress map of the welding specimen was obtained spending long exposure time. The residual stresses of the welding specimen were simulated by a finite element method (FEM). The outline of the residual stress measured by the DSTM coincided with that by the FEM. (author)

  11. Surface Modification by Nitrogen Plasma Immersion Ion Implantation on Austenitic AISI 304 Stainless Steel

    Miguel CASTRO-COLIN; William DURRER; Jorge ALPEZ; Enrique RAMIREZ-HOMS

    2016-01-01

    Surfaces of AISI 304 austenitic stainless steel plates nitrided by plasma immersion ion implantation (PIII) technology were studied by means of Auger electron spectroscopy (AES)and X-ray photoelectron spectroscopy (XPS)to determine the effect of the nitriding process on the surface and subjacent layers.Elemental compositions obtained by AES and XPS at varying depths indicate that the saturation of N is relatively constant as a function of depth,indicating the reliability of PIII technology for subsurface saturation.It is concluded that the concentrations of both Cr and O increase with depth,the subjacent oxide is driven by the Ar+ sputtering process used to access the lower layers,and then N is bound to Cr.

  12. Evaluation of welding residual stresses in austenitic stainless steel using diffraction spot trace method

    A diffraction spot trace method (DSTM) was developed to measure internal stresses of materials with coarse grains. The DSTM was applied to light metals, such as aluminum alloy and magnesium alloy. In this study, validity of the DSTM was examined using high energy synchrotron X-rays of 70 keV. The specimen was a welded plate of austenitic stainless steel (SUS316L). The thickness of the specimen was 9 mm. The improved rotating slit-system was used, and PILATUS was used as an area detector. It was difficult to detect the high energy X-rays due to the reduction of counting efficiency of the PILATUS. However, the residual stress map of the welding specimen was obtained by long exposure time. The residual stresses of the welding specimen were simulated by a finite element method (FEM). The outline of the residual stress measured by the DSTM coincided with that by the FEM. (author)

  13. Correlation between locally deformed structure and oxide film properties in austenitic stainless steel irradiated with neutrons

    Chimi, Yasuhiro; Kitsunai, Yuji; Kasahara, Shigeki; Chatani, Kazuhiro; Koshiishi, Masato; Nishiyama, Yutaka

    2016-07-01

    To elucidate the mechanism of irradiation-assisted stress corrosion cracking (IASCC) in high-temperature water for neutron-irradiated austenitic stainless steels (SSs), the locally deformed structures, the oxide films formed on the deformed areas, and their correlation were investigated. Tensile specimens made of irradiated 316L SSs were strained 0.1%-2% at room temperature or at 563 K, and the surface structures and crystal misorientation among grains were evaluated. The strained specimens were immersed in high-temperature water, and the microstructures of the oxide films on the locally deformed areas were observed. The appearance of visible step structures on the specimens' surface depended on the neutron dose and the applied strain. The surface oxides were observed to be prone to increase in thickness around grain boundaries (GBs) with increasing neutron dose and increasing local strain at the GBs. No penetrative oxidation was observed along GBs or along surface steps.

  14. Cyclic deformation behavior of a 316L austenitic stainless steel processed by high pressure torsion

    The influence of severe plastic deformation (SPD) on the fatigue behavior of a modified 316L austenitic stainless steel is investigated. Different ultrafine-grained and nanocrystalline microstructures are obtained by changing the processing parameters and applying a post heat treatment procedure. Samples are fatigued using both, load and strain controlled experiments. High pressure torsion processing makes it possible to reach a saturation microstructure, which is cyclically stable up to a stress level three times higher than the stress level of the coarse-grained structure. Fracture surface investigations and surface damage clearly show that the failure behavior of the SPD states under cyclic loading is different to their coarse-grained counterparts. For these microstructures, localized deformation in shear bands seems to play a major role for crack initiation and propagation. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  15. Relative merits of duplex and austenitic stainless steels for applications in the oil and gas industry

    Johansson, Elisabeth; Wegrelius, Lena; Pettersson, Rachel [Outokumpu Stainless AB, Avesta (Sweden)

    2012-07-01

    The broad range of available stainless steel grades means that these materials can fulfil a wide variety of requirements within the oil and gas industry. The duplex grades have the advantage of higher strength than standard austenitic grades, while the superaustenitic grades provide a cost-effective alternative to nickel-base alloys in a number of cases. The paper presents the results of various types of laboratory testing to rank the grades in terms of resistance to pitting, crevice corrosion and stress corrosion cracking. Results from field testing in actual or simulated service conditions are discussed and a number of application examples, including process piping flexible, heat exchangers and topside equipment are presented. (author)

  16. Electron irradiation induced solute segregation near grain boundaries in austenitic stainless steel

    Radiation-induced solute segregation near internal defect sinks such as high angle grain boundaries was investigated, through the interaction between point defects and solute atom in austenitic stainless steel and its model alloys. Electron irradiation was performed in a high voltage electron microscope (H V E M) at a dose rate of about 2 multiple 10-3 d p a.S-1 at a temperature range of 350-600 degree C. Solute concentration profile near grain boundaries was measured by E D X in S T E M mode. Strong enrichment and depletion of solutes were observed on grain boundaries during irradiation and segregation rate went through a maximum at 450 degree C. These facts indicate that grain boundaries act as preferential sinks for radiation-induced point defects

  17. Report on Japanese performance demonstration examinations for depth sizing of SCC in austenitic stainless steel pipes

    The PD Center of Central Research Institute of Electric Power Industry (CRIEPI) commenced Performance Demonstration examinations for flaw depth sizing of austenitic stainless steel pipes in March 2006. As of January 2013, 37 examination sessions have been completed and 44 candidates have passed the examination. The total number of tests administered including re-tests and re-certification was 89. It was noted that depth sizing using a phased array plus the manual UT technique was the procedure most used by successful PD applicants. A major reason for failure is 'the overestimation caused by the lack of skill in distinguishing the base metal-to-weld metal interface echo and the SCC tip echo'. Moreover, the possibility of psychological bias is also incontrovertible because candidates are under pressure not to make a -4.4 mm critical mistake. (author)

  18. Influence of localized plasticity on oxidation behaviour of austenitic stainless steels under primary water reactor

    Cissé, Sarata [CEA Saclay, DEN/DANS/DMN/SEMI, 91191 Gif-sur-Yvette Cedex (France); Laffont, Lydia, E-mail: lydia.laffont@ensiacet.fr [Institut CARNOT, CIRIMAT-ENSIACET, 4 allée Emile Monso, 31030 Toulouse Cedex 4 (France); Lafont, Marie-Christine [Institut CARNOT, CIRIMAT-ENSIACET, 4 allée Emile Monso, 31030 Toulouse Cedex 4 (France); Tanguy, Benoit [CEA Saclay, DEN/DANS/DMN/SEMI, 91191 Gif-sur-Yvette Cedex (France); Andrieu, Eric [Institut CARNOT, CIRIMAT-ENSIACET, 4 allée Emile Monso, 31030 Toulouse Cedex 4 (France)

    2013-02-15

    The sensitivity of precipitation-strengthened A286 austenitic stainless steel to stress corrosion cracking was studied by means of slow-strain-rate tests. First, alloy cold working by low cycle fatigue (LCF) was investigated. Fatigue tests under plastic strain control were performed at different strain levels (Δε{sub p}/2 = 0.2%, 0.5%, 0.8% and 2%) to establish correlations between stress softening and the deformation microstructure resulting from the LCF tests. Deformed microstructures were identified through TEM investigations. The interaction between oxidation and localized deformation bands was also studied and it resulted that localized deformation bands are not preferential oxide growth channels. The pre-cycling of the alloy did not modify its oxidation behaviour. However, intergranular oxidation in the subsurface under the oxide layer formed after exposure to PWR primary water was shown.

  19. Behavior of super-austenitic stainless steels in chlorinated brackish seawater

    Ives, M.B. [McMaster Univ., Hamilton, Ontario (Canada)

    1994-12-31

    A series of highly-alloyed austenitic stainless steels has been exposed in a model heat exchanger cooled with water from a brackish inlet in southeast Florida. The behavior of the alloys has been found to depend significantly on the formation of adherent surface deposits. These deposits may occur under certain conditions when natural seawater is used, but the use of chlorination has been found invariably to produce significant deposits, beneath which even the more highly alloyed tubing suffered considerable localized corrosion. It is suggested from noise analysis of the electrochemical potential of individual electrically isolated tubes that the noise analysis might be appropriate as an on-line corrosion monitoring technique for complete heat exchangers, as an alternative to the use of independent monitoring probes.

  20. Experimental and field achievements in the ultrasonic examination of austenitic stainless steel

    In spite of the many disturbances caused in the propagation of acoustic waves by the metallurgical structure of austenitic stainless steel, ultrasonic examination can provide in many cases key information in the process of assessing the structural integrity of industrial installations made from such materials. Indeed the steel structure variability makes every cases peculiar, with the consequence that the achievement of a dedicated feasibility study will often enhance drastically the examination performance. Such an exploratory exercise imposes to use a careful methodology regarding transducer and pulser selection, data analysis, performance evaluation, procedure qualification and field implementation. Through various examples from the nuclear industry field, the paper illustrates that kind of approach, as well as the extent to which it has been made possible to optimize the actual inspection capability and reliability. (author)

  1. Banded structure and its distribution in friction stir processing of 316L austenitic stainless steel

    Highlights: ► Friction stir processing (FSP) as a repair method. ► Sigma phase formed in the FSP zone. ► Low heat input contributes to restrain sigma phase precipitation. - Abstract: Banded structures, which vary with welding parameters, were observed in friction stir processing of 316L austenite stainless steel. Sigma phase precipitation was detected in banded structures by transmission electron microscopy. The amount of banded structure had direct ratio relations with heat input. The higher the heat input, the larger the area of banded structures. This is attributable to slower cooling rate at high heat input, which results in longer exposure to the temperature range for precipitation. The formation of sigma phase produced Cr depletion, which resulted in largely degraded corrosion resistance. The present study suggests that low heat input (i.e. low rotation speeds, low working loads and high welding speed) contributes to restrain sigma phase precipitation.

  2. AE monitoring of chloride stress corrosion cracking of austenitic stainless steel

    We analyzed the fracture dynamics of chloride-SCC of austenitic stainless steel AISI304 by AE source simulation method. Using the varied mechanical and thermal loading systems in 35-38 mass % MgCl2 solution at 95 to 98degC, we produced transgranular (TG) and intergranular (IG) type SCC. We monitored no AE from the transgranular (TG) type-SCC even by using an AE monitoring system with 80dB amplification, but did monitor a large amount of AEs by using 40dB amplification system, from intergranular (IG) type SCC. Source dynamics estimated by unique waveform simulation of Lamb So-packet revealed grain-size fractures with fast source rise time of 0.17 to 1.05 μs. Though the mechanism of SCC is not well-understood, it is confirmed that IG-SCC does emit AEs. (author)

  3. AE monitoring of chloride stress corrosion cracking of austenitic stainless steel

    Fujimoto, Shinya; Takemoto, Mikio [Aoyama Gakuin Univ., Faculty of Science and Engineering, Tokyo (Japan); Ono, Kanji [UCLA, Dept. of Materials Science and Engineering, Los Angeles, CA (United States)

    2000-07-01

    We analyzed the fracture dynamics of chloride-SCC of austenitic stainless steel AISI304 by AE source simulation method. Using the varied mechanical and thermal loading systems in 35-38 mass % MgCl{sub 2} solution at 95 to 98degC, we produced transgranular (TG) and intergranular (IG) type SCC. We monitored no AE from the transgranular (TG) type-SCC even by using an AE monitoring system with 80dB amplification, but did monitor a large amount of AEs by using 40dB amplification system, from intergranular (IG) type SCC. Source dynamics estimated by unique waveform simulation of Lamb So-packet revealed grain-size fractures with fast source rise time of 0.17 to 1.05 {mu}s. Though the mechanism of SCC is not well-understood, it is confirmed that IG-SCC does emit AEs. (author)

  4. Influence of localized plasticity on oxidation behaviour of austenitic stainless steels under primary water reactor

    The sensitivity of precipitation-strengthened A286 austenitic stainless steel to stress corrosion cracking was studied by means of slow-strain-rate tests. First, alloy cold working by low cycle fatigue (LCF) was investigated. Fatigue tests under plastic strain control were performed at different strain levels (Δεp/2 = 0.2%, 0.5%, 0.8% and 2%) to establish correlations between stress softening and the deformation microstructure resulting from the LCF tests. Deformed microstructures were identified through TEM investigations. The interaction between oxidation and localized deformation bands was also studied and it resulted that localized deformation bands are not preferential oxide growth channels. The pre-cycling of the alloy did not modify its oxidation behaviour. However, intergranular oxidation in the subsurface under the oxide layer formed after exposure to PWR primary water was shown

  5. Study of austenitic stainless steel creep between 5500C and 6500C

    This work is a contribution to identification and analysis of microscopic mechanisms of creep damages in austenitic stainless steels used for steam generators of fast neutron reactors. Statistical analysis of slip at the grain boundaries and tests on polycrystalline of alloy 800 grade II indicate the role of structural parameters: matrix reinforcement and boundary slip. Microstructure analysis shows the deformation mechanisms and the differences between steel 316 and alloy 800. In situ tests on bicrystalline samples of steel ZCN17/13 show the event chronology. Characteristic data on damaging at the nanometer scale (cavity size, crack dimensions) are determined. From these results a beginning of simulation is attempted for the two types of damage. 67 refs

  6. Study of ultrasound waves attenuation: application to the nondestructive control of austenitic stainless steel welds

    Ultrasonic propagation simulation in anisotropic and heterogeneous media is essential for nondestructive testing by ultrasounds of multipass austenitic stainless steel welds that are specific of piping in nuclear power stations. Scattering at grain boundaries leads to a strong attenuation as a function of grain orientation. Attenuation measurement is complex. The implemented technique allows taking into account the physical reality of the beams and the material anisotropy. Ultrasonic propagation through the samples is modeled with transmission coefficients calculated with any incidence on a triclinic material. This method results in an increase of the attenuation versus grain orientation. For the first time, measured attenuation coefficients are integrated into a simulation code that validated them by comparison with experience. (author)

  7. Role of heat tint on pitting corrosion of 304 austenitic stainless steel in chloride environment

    The effect of simulated heat tint produced by air oxidation at a wide range of temperatures 200, 400, 600, 800 and 1050 deg. C on pitting potential of 304 austenitic stainless steel was studied in environment of different chloride concentration. It was found that the heat tint effect depends on the heating temperature. The most effective heat tint was that produced at the high temperature up to 1050 deg. C and hence less pitting potential and low corrosion resistance. In order to improve the surface pitting corrosion resistance, acid pickling of hydrochloric acid was applied at different time and temperatures of 15 and 60 min, room temperature and 60 deg. C, respectively. Improvement in pitting potential was achieved as the pickling time and temperature increase. This is can be attributed to the removal of depleted chromium oxide film produced during the heat tint. (authors)

  8. Development of corrosion-resistant improved Al-doped austenitic stainless steel

    Kondo, Keietsu; Miwa, Yukio; Okubo, Nariaki; Kaji, Yoshiyuki; Tsukada, Takashi

    2011-10-01

    Aluminum-doped type 316L SS (316L/Al) has been developed for the purpose of suppressing the degradation of corrosion resistance induced by irradiation in austenitic stainless steels (SSs). The electrochemical corrosion properties of this material were estimated after Ni-ion irradiation at a temperature range from 330 °C to 550 °C. When irradiated at 550 °C up to 12 dpa, 316L/Al showed high corrosion resistance in the vicinity of grain boundaries (GBs) and in grains, while severe GB etching and local corrosion in grains were observed in irradiated 316L and 316 SS. It is supposed that aluminum enrichment was enhanced by high-temperature irradiation at GBs and in grains, to compensate for lost corrosion resistance induced by chromium depletion.

  9. TEM, XRD and nanoindentation characterization of Xenon ion irradiation damage in austenitic stainless steels

    Huang, H. F.; Li, J. J.; Li, D. H.; Liu, R. D.; Lei, G. H.; Huang, Q.; Yan, L.

    2014-11-01

    Cross-sectional and bulk specimens of a 20% cold-worked 316 austenitic stainless steel (CW 316 SS) has been characterized by TEM, XRD and nanoindentation to determine the microstructural evolution and mechanical property changes of 316 SS after irradiation with 7 MeV Xe26+ ions. TEM results reveal the presence of dislocation loops with a number density of approximately 3 × 1022 m-3 and sizes between 3 to 10 nm due to the collapse of vacancy rich cores inside displacement cascades. Peak broadening observed in XRD diffraction patters reveal systematic changes to lattice parameters due to irradiation. The calculated indentation values in irradiated 316 SS were found to be much higher in comparison to the unirradiated specimen, indicating the dose dependent effect of irradiation on hardness. The relationship between irradiation induced microstructural evolution and the changes to the mechanical properties of CW 316 SS are discussed in the context of fluence and irradiation temperature.

  10. A study on corrosion behavior of austenitic stainless steel in liquid metals at high temperature

    The purpose of this study is to investigate the interaction between austenitic stainless steel, AISI 316L, and gallium liquid metal at a high temperature, for the potential application to advanced fast reactor coolants. Test specimens of AISI 316L were exposed to static gallium at 500 °C for up to 700 h in two different cover-gas conditions, including air and vacuum. Similar experimental tests were conducted in gallium alloy liquid metal environments, including Ga–14Sn–6Zn and Ga–8Sn–6Zn, in order to study the effect of addition of alloying elements. The results have shown that the weight change and metal loss of specimens were generally reduced in Ga–14Sn–6Zn and Ga–8Sn–6Zn compared to those in pure gallium at a high temperature.

  11. Influence of the austenitic stainless steel microstructure on the void swelling under ion irradiation

    Rouxel Baptiste

    2016-01-01

    Full Text Available To understand the role of different metallurgical parameters on the void formation mechanisms, various austenitic stainless steels were elaborated and irradiated with heavy ions. Two alloys, in several metallurgical conditions (15Cr/15Ni–Ti and 15Cr/25Ni–Ti, were irradiated in the JANNUS-Saclay facility at 600 °C with 2 MeV Fe2+ ions up to 150 dpa. Resulting microstructures were observed by Transmission Electron Microscopy (TEM. Different effects on void swelling are highlighted. Only the pre-aged samples, which were consequently solute and especially titanium depleted, show cavities. The nickel-enriched matrix shows more voids with a smaller size. Finally, the presence of nano-precipitates combined with a dense dislocation network decreases strongly the number of cavities.

  12. Abnormal image appearing in radiographic film of continuously cast austenite stainless steel

    Investigation of abnormal image appearance in radiographic films and the analysis of its cause have been performed with test pieces of coarse grain sizes cut from a continuously cast billet of austenitic stainless steel. The image is a long, narrow and stripped pattern in horizontally cut test piece and squamouse pattern in vertically cut test pieces, although the pattern of the macrostructure were identical. It has been experimentally verified that this abnormal image is caused mainly by X-ray diffraction which occurs when X-ray penetrates the solidified structure in the test piece and is not due to any segregation of chemical compositions; and further that the precipitated Δ-ferrite is the factor that affects the contrast of the abnormal image. (author)

  13. Numeric ultrasonic image processing method: application to non-destructive testing of stainless austenitic steel welds

    A bibliographic research on the means used to improve the ultrasonic inspection of heterogeneous materials such as stainless austenitic steel welds has shown, taking into account the first analysis, a signal assembly in the form of an image (space, time) which carries an original solution to fault detection in highly noisy environments. A numeric grey-level ultrasonic image processing detection method is proposed based on the research of a certain determinism, in the way which the ultrasonic image evolves in space and time in the presence of a defect: the first criterion studies the horizontal stability of the gradients in the image and the second takes into account the time-transient nature of the defect echo. A very important rise in the signal-to-noise ratio obtained in welding inspections evidencing defects (real and artificial) is shown with the help of a computerized ultrasonic image processing/management system, developed for this application

  14. Microstructure and Nanoindentation Characterization of Low Temperature Hybrid Treated layer on Austenitic Stainless Steel

    Triwiyanto, Askar; Hussain, Patthi; Che Ismail, Mokhtar

    2013-06-01

    In this work, the hybrid treated layer on austenitic AISI 316L stainless steels were characterized to investigate the improvement on its surface properties. Characterization of this resulting layer was performed by FESEM (Field Emission Scanning Electron Microscope), USPM (Universal Scanning Probe Microscope) and nanoindentation. By using these methods, changes in the mechanical properties due to the diffusion of carbon and nitrogen at low temperature treatments have been traced. This hybrid treated sample has confirmed a considerable increase in hardness and a small rise in the elastic modulus compared to the untreated sample. It is found that all treated samples have enhance E/H ratio which exhibited the decreasing tendency to plastic deformation and reduced the mismatch of properties, while keeping deformation within the elastic range.

  15. Evaluation of material property of austenitic stainless steel using nano-indentation

    In order to evaluate some material properties of very small area on small specimens which are sampled from components in service and to predict macroscopic material properties from the data of the small specimens, nano-indentation is considered to be quite effective. However, there are few reports formularize the dependence of load on hardness values evaluated from the results of indentation tests with loads from 10 mg to 100 g. In this study, systematic tests of indentation were conducted to specimens of austenitic stainless steel SUS304 using a Berkovich indenter and a Vickers indenter with loads varying from 10 mg to 100 g. From these results numerical formulae which relate the calculated hardness values to the loads were made. In addition, the relation between Vickers hardness and nano-indentation hardness was obtained. As a result, it became possible to predict Vickers hardness from nano-indentation with loads as low as about 100 mg. (author)

  16. Microstructure and Nanoindentation Characterization of Low Temperature Hybrid Treated layer on Austenitic Stainless Steel

    In this work, the hybrid treated layer on austenitic AISI 316L stainless steels were characterized to investigate the improvement on its surface properties. Characterization of this resulting layer was performed by FESEM (Field Emission Scanning Electron Microscope), USPM (Universal Scanning Probe Microscope) and nanoindentation. By using these methods, changes in the mechanical properties due to the diffusion of carbon and nitrogen at low temperature treatments have been traced. This hybrid treated sample has confirmed a considerable increase in hardness and a small rise in the elastic modulus compared to the untreated sample. It is found that all treated samples have enhance E/H ratio which exhibited the decreasing tendency to plastic deformation and reduced the mismatch of properties, while keeping deformation within the elastic range.

  17. TEM, XRD and nanoindentation characterization of Xenon ion irradiation damage in austenitic stainless steels

    Cross-sectional and bulk specimens of a 20% cold-worked 316 austenitic stainless steel (CW 316 SS) has been characterized by TEM, XRD and nanoindentation to determine the microstructural evolution and mechanical property changes of 316 SS after irradiation with 7 MeV Xe26+ ions. TEM results reveal the presence of dislocation loops with a number density of approximately 3 × 1022 m−3 and sizes between 3 to 10 nm due to the collapse of vacancy rich cores inside displacement cascades. Peak broadening observed in XRD diffraction patters reveal systematic changes to lattice parameters due to irradiation. The calculated indentation values in irradiated 316 SS were found to be much higher in comparison to the unirradiated specimen, indicating the dose dependent effect of irradiation on hardness. The relationship between irradiation induced microstructural evolution and the changes to the mechanical properties of CW 316 SS are discussed in the context of fluence and irradiation temperature

  18. Crack growth of intergranular stress corrosion cracks in austenitic stainless steel pipes of boiling water reactors

    Intergranular stress corrosion cracking (IGSCC) of boiling water reactor (BWR) piping is considered from the crack growth rate point of view. Crack growth rate of sensitized austenitic stainless steel welds is dependent on the degree of sensitization of the material and the severity of the environment as well as the stress state. In evaluation of actual crack growth rate there are three major sources of uncertainty: knowledge of actual crack size and shape, actual stress distribution in he area of the crack and the degree of sensitization. In the report the crack growth calculations used in the USA and in Sweden are presented. Finally, the crack growth rate predictions based on mechanistic modelling of IGSCC and some needs of further research in Finland are considered

  19. Numerical simulation and experimental investigation of laser dissimilar welding of carbon steel and austenitic stainless steel

    Nekouie Esfahani, M. R.; Coupland, J.; Marimuthu, S.

    2015-07-01

    This study reports an experimental and numerical investigation on controlling the microstructure and brittle phase formation during laser dissimilar welding of carbon steel to austenitic stainless steel. The significance of alloying composition and cooling rate were experimentally investigated. The investigation revealed that above a certain specific point energy the material within the melt pool is well mixed and the laser beam position can be used to control the mechanical properties of the joint. The heat-affected zone within the high-carbon steel has significantly higher hardness than the weld area, which severely undermines the weld quality. A sequentially coupled thermo-metallurgical model was developed to investigate various heat-treatment methodology and subsequently control the microstructure of the HAZ. Strategies to control the composition leading to dramatic changes in hardness, microstructure and service performance of the dissimilar laser welded fusion zone are discussed.

  20. Evaluation of residual stress distribution in austenitic stainless steel pipe butt-welded joint

    This paper reports measured and estimated results of residual stress distributions of butt-welded austenitic stainless steel pipe in order to improve estimation accuracy of welding residual stress. Neutron diffraction and strain gauge method were employed for the measurement of the welding residual stress and its detailed distributions on inner and outer surface of the pipe as well as the distributions within the pipe wall were obtained. Finite element method was employed for the estimation. Transient and residual stresses in 3D butt-welded joint model were computed by employing Iterative Substructure Method and also commercial FEM code ABAQUS for a reference. The measured and estimated distributions presented typical characteristic of straight butt-welded pipe which had decreasing trend along the axial direction and bending type distributions through wall of the pipe. Both results were compared and the accuracy of measurement and estimation was discussed. (author)

  1. Welding of tube-to-tube joints between martensitic and austenitic stainless steels for reactor applications

    Studies of the welding of tube-to-tube joints between dissimilar steels are described. The material combination was martensitic F6NM (0Cr13Ni4Mo) and austenitic AISI 347 stainless steels. Such joints are important parts in the primary circuit of a pressurized water reactor. A welding procedure was developed based on a series of weldability tests. The joints were subjected to various mechanical property tests including tensile test, bending test and impact test at various temperatures. A prototype product was made and subjected to pressure testing. Results of various tests indicated that the quality of the tube-to-tube joints is satisfactory for meeting all the design requirements. The joints can be used in the primary circuit of a pressurized water reactor. (author)

  2. The Effect of Calcium Treatment on Pitting Corrosion of Type 316L Austenitic Stainless steel

    Pitting in chloride containing aqueous solution occurs mainly on manganese sulphide. Adding a slight amount of Ca as an alloying element prevents the MnS formation, since Ca is a stronger sulphide former than Mn. In this work, calcium treated Type 316L austenitic stainless steels have been investigated electrochemically to evaluate the effect of modified inclusions on pitting corrosion. Staircase polarization measurements were performed in 3.5% NaCl solution, where the occurrence of pits in materials caused current spikes. During staircase polarization test, steels with calcium treatment show low and discontinuous current spikes while those without calcium treatment show high and continuous current spikes. The results show that calcium treatment in Ca/S ratio of 1 ∼ 2 leads to an increase in the pitting potential of several hundred mV. A relationship between the calcium treatment and pit initiation sites was described

  3. Microstructural observations of HFIR-irratiated austenitic stainless steels including welds from JP9-16

    Sawai, T.; Shiba, K.; Hishinuma, A.

    1996-04-01

    Austenitic stainless steels, including specimens taken from various electron beam (EB) welds, have been irradiated in HFIR Phase II capsules, JP9-16. Fifteen specimens irradiated at 300, 400, and 500{degrees}C up to 17 dpa are so far examined by a transmission electron microscope (TEM). In 300{degrees}C irradiation, cavities were smaller than 2nm and different specimens showed little difference in cavity microstructure. At 400{degrees}C, cavity size was larger, but still very small (<8 nm). At 500{degrees}C, cavity size reached 30 nm in weld metal specimens of JPCA, while cold worked JPCA contained a small (<5 nm) cavities. Inhomogeneous microstructural evolution was clearly observed in weld-metal specimens irradiated at 500{degrees}C.

  4. The PISC parametric study on the effect of the texture of cast austenitic stainless steel

    Within the framework of Action 4 (Austenitic Steel Testing) of PISC III, a parametric study was carried out on a set of centrifugally cast stainless steel samples, representative of the main coolant piping of pressurized water nuclear reactors. The samples are obtained from different manufacturers, and feature various grain textures and dimensions. Artificial and realistic flaws were used to assess the detection and sizing capability of ultrasonic examination techniques. The paper analyzes the data as a function of the metal structure and of the main parameter of the testing techniques, which include TRL contact probes and immersion focusing transducers. Guidelines are deduced as to the selection of inspection techniques, in relation with the metallurgical texture of each specimen. In addition, the influence of the presence of a weld across the wavepath is evaluated, as well as the similarity between the responses obtained from crack-like machined reflectors and mechanical fatigue cracks

  5. Initiation of stress corrosion cracking in pre-stained austenitic stainless steels exposed to primary water

    Austenitic stainless steels are widely used in primary circuits of Pressurized Water Reactors (PWR) plants. However, a limited number of cases of Intergranular Stress Corrosion Cracking (IGSCC) has been detected in cold-worked (CW) areas of non-sensitized austenitic stainless steel components in French PWRs. A previous program launched in the early 2000's identified the required conditions for SCC of cold-worked stainless steels. It was found that a high strain hardening coupled with a cyclic loading favoured SCC. The present study aims at better understanding the role of pre-straining on crack initiation and at developing an engineering model for IGSCC initiation of 304L and 316L stainless steels in primary water. Such model will be based on SCC initiation tests on notched (not pre-cracked) specimens under 'trapezoidal' cyclic loading. The effects of pre-straining (tensile versus cold rolling), cold-work level and strain path on the SCC mechanisms are investigated. Experimental results demonstrate the dominating effect of strain path on SCC susceptibility for all pre-straining levels. Initiation can be understood as crack density and crack depth. A global criterion has been proposed to integrate both aspects of initiation. Maps of SCC initiation susceptibility have been proposed. A critical crack depth between 10 and 20 μm has been demonstrated to define transition between slow propagation and fast propagation for rolled materials. For tensile pre-straining, the critical crack depth is in the range 20 - 50 μm. Experimental evidences support the notion of a KISCC threshold, whose value depends on materials, pre-straining ant load applied. The initiation time has been found to depend on the applied loading as a function of (σmaxmax/YV)11,5. The effect of both strain path and surface hardening is indirectly taken into account via the yield stress. In this study, material differences rely on strain path effect on mechanical properties. As a result, a stress high

  6. Irradiation-Assisted Stress Corrosion Cracking of Austenitic Stainless Steels in BWR Environments

    The internal components of light water reactors are exposed to high-energy neutron irradiation and high-temperature reactor coolant. The exposure to neutron irradiation increases the susceptibility of austenitic stainless steels (SSs) to stress corrosion cracking (SCC) because of the elevated corrosion potential of the reactor coolant and the introduction of new embrittlement mechanisms through radiation damage. Various nonsensitized SSs and nickel alloys have been found to be prone to intergranular cracking after extended neutron exposure. Such cracks have been seen in a number of internal components in boiling water reactors (BWRs). The elevated susceptibility to SCC in irradiated materials, commonly referred to as irradiation-assisted stress corrosion cracking (IASCC), is a complex phenomenon that involves simultaneous actions of irradiation, stress, and corrosion. In recent years, as nuclear power plants have aged and irradiation dose increased, IASCC has become an increasingly important issue. Post-irradiation crack growth rate and fracture toughness tests have been performed to provide data and technical support for the NRC to address various issues related to aging degradation of reactor-core internal structures and components. This report summarizes the results of the last group of tests on compact tension specimens from the Halden-II irradiation. The IASCC susceptibility of austenitic SSs and heat-affected-zone (HAZ) materials sectioned from submerged arc and shielded metal arc welds was evaluated by conducting crack growth rate and fracture toughness tests in a simulated BWR environment. The fracture and cracking behavior of HAZ materials, thermally sensitized SSs and grain-boundary engineered SSs was investigated at several doses (3 dpa). These latest results were combined with previous results from Halden-I and II irradiations to analyze the effects of neutron dose, water chemistry, alloy compositions, and welding and processing conditions on IASCC. The

  7. Irradiation-Assisted Stress Corrosion Cracking of Austenitic Stainless Steels in BWR Environments

    Chen, Y. [Argonne National Lab. (ANL), Argonne, IL (United States); Chopra, O. K. [Argonne National Lab. (ANL), Argonne, IL (United States); Gruber, Eugene E. [Argonne National Lab. (ANL), Argonne, IL (United States); Shack, William J. [Argonne National Lab. (ANL), Argonne, IL (United States)

    2010-06-01

    The internal components of light water reactors are exposed to high-energy neutron irradiation and high-temperature reactor coolant. The exposure to neutron irradiation increases the susceptibility of austenitic stainless steels (SSs) to stress corrosion cracking (SCC) because of the elevated corrosion potential of the reactor coolant and the introduction of new embrittlement mechanisms through radiation damage. Various nonsensitized SSs and nickel alloys have been found to be prone to intergranular cracking after extended neutron exposure. Such cracks have been seen in a number of internal components in boiling water reactors (BWRs). The elevated susceptibility to SCC in irradiated materials, commonly referred to as irradiation-assisted stress corrosion cracking (IASCC), is a complex phenomenon that involves simultaneous actions of irradiation, stress, and corrosion. In recent years, as nuclear power plants have aged and irradiation dose increased, IASCC has become an increasingly important issue. Post-irradiation crack growth rate and fracture toughness tests have been performed to provide data and technical support for the NRC to address various issues related to aging degradation of reactor-core internal structures and components. This report summarizes the results of the last group of tests on compact tension specimens from the Halden-II irradiation. The IASCC susceptibility of austenitic SSs and heat-affected-zone (HAZ) materials sectioned from submerged arc and shielded metal arc welds was evaluated by conducting crack growth rate and fracture toughness tests in a simulated BWR environment. The fracture and cracking behavior of HAZ materials, thermally sensitized SSs and grain-boundary engineered SSs was investigated at several doses (≤3 dpa). These latest results were combined with previous results from Halden-I and II irradiations to analyze the effects of neutron dose, water chemistry, alloy compositions, and welding and processing conditions on IASCC

  8. Low temperature thermal aging of austenitic stainless steel welds: Kinetics and effects on mechanical properties

    Highlights: ► Embrittlement of 304L and 316L welds after aging up to 20,000 h. ► Spinodal decomposition and G-phase precipitation in ferrite at 400 °C. Only spinodal decomposition at 335 and 365 °C. ► Charpy impact, microhardness and tensile tests for evaluation of aging embrittlement and its kinetics determined. - Abstract: Austenitic stainless steel welds in components used in light water reactors are susceptible to thermal aging embrittlement at reactor operating temperature of around 300 °C after a long service life. In this study, low temperature aging embrittlement of types 304L and 316L stainless steel welds with 10% ferrite was investigated on the basis of changes in mechanical properties and microstructure after aging up to 20,000 h at 335, 365 and 400 °C. Spinodal decomposition and G-phase precipitation in the ferrite was observed after aging which lead to embrittlement in the material. In contrast to the small effect on tensile properties, the impact toughness was significantly degraded after aging. Charpy impact test of the aged samples showed decrease in upper-shelf and lower-shelf energy and increase in ductile brittle transition temperature. Large increase in the microhardness of ferrite phase was observed with no change in austenite hardness. The embrittlement in 316L weld was higher compared to 304L weld for similar aging condition. The kinetics of aging embrittlement was established based on Arrhenius relationship. A constant activation energy was determined for 304L weld in the temperature range 335–400 °C, however, 316L weld showed different activation energy values in each temperature range.

  9. Low temperature thermal aging of austenitic stainless steel welds: Kinetics and effects on mechanical properties

    Chandra, K., E-mail: kchandra@barc.gov.in [Materials Science Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Kain, Vivekanand [Materials Science Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Bhutani, Vikas [Punjab Engineering College, Chandigarh 160 012 (India); Raja, V.S. [Indian Institute of Technology, Mumbai 400 076 (India); Tewari, R.; Dey, G.K. [Materials Science Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Chakravartty, J.K. [Mechanical Metallurgy Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India)

    2012-02-01

    Highlights: Black-Right-Pointing-Pointer Embrittlement of 304L and 316L welds after aging up to 20,000 h. Black-Right-Pointing-Pointer Spinodal decomposition and G-phase precipitation in ferrite at 400 Degree-Sign C. Only spinodal decomposition at 335 and 365 Degree-Sign C. Black-Right-Pointing-Pointer Charpy impact, microhardness and tensile tests for evaluation of aging embrittlement and its kinetics determined. - Abstract: Austenitic stainless steel welds in components used in light water reactors are susceptible to thermal aging embrittlement at reactor operating temperature of around 300 Degree-Sign C after a long service life. In this study, low temperature aging embrittlement of types 304L and 316L stainless steel welds with 10% ferrite was investigated on the basis of changes in mechanical properties and microstructure after aging up to 20,000 h at 335, 365 and 400 Degree-Sign C. Spinodal decomposition and G-phase precipitation in the ferrite was observed after aging which lead to embrittlement in the material. In contrast to the small effect on tensile properties, the impact toughness was significantly degraded after aging. Charpy impact test of the aged samples showed decrease in upper-shelf and lower-shelf energy and increase in ductile brittle transition temperature. Large increase in the microhardness of ferrite phase was observed with no change in austenite hardness. The embrittlement in 316L weld was higher compared to 304L weld for similar aging condition. The kinetics of aging embrittlement was established based on Arrhenius relationship. A constant activation energy was determined for 304L weld in the temperature range 335-400 Degree-Sign C, however, 316L weld showed different activation energy values in each temperature range.

  10. Ultrasonic inspectability of austenitic stainless steel and dissimilar metal weld joints

    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.)

  11. Three dimensional observations and modelling of intergranular stress corrosion cracking in austenitic stainless steel

    Stress corrosion cracking is a life-limiting factor in many components of nuclear power plant in which failure of structural components presents a substantial hazard to both safety and economic performance. Uncertainties in the kinetics of short crack behaviour can have a strong influence on lifetime prediction, and arise due both to the complexity of the underlying mechanisms and to the difficulties of making experimental observations. This paper reports on an on-going research programme into the dynamics and morphology of intergranular stress corrosion cracking in austenitic stainless steels in simulated light water environments, which makes use of recent advances in high resolution X-ray microtomography. In particular in situ, three dimensional X-ray tomographic images of intergranular stress corrosion crack nucleation and growth in sensitised austenitic stainless steel provide evidence for the development of crack bridging ligaments, caused by the resistance of non-sensitised special grain boundaries. In parallel a simple grain bridging model, introduced to quantify the effect of crack bridging on crack development, has been assessed for thermo-mechanically processed microstructures via statically loaded room temperature simulant solution tests and as well as high temperature/pressure autoclave studies. Thermo-mechanical treatments have been used to modify the grain size, grain boundary character and triple junction distributions, with a consequent effect on crack behaviour. Preliminary three-dimensional finite element models of intergranular crack propagation have been developed, with the aim of investigating the development of crack bridging and its effects on crack propagation and crack coalescence

  12. Fatigue crack growth threshold of austenitic stainless steels in simulated PWR primary water

    Many studies have revealed that fatigue crack growth (FCG) rate of austenitic stainless steels is accelerated in light water reactor environment compared to that in air at room temperature. Major driving factors in the acceleration of FCG rate are stress ratio, temperature and stress rise time. Based on this knowledge, FCG curves have been developed considering these factors as parameters. However, there are few data of FCG threshold ΔKth in light water reactor environment. Hence it is necessary to clarify FCG rate under near-threshold condition for more accurate evaluation of fatigue crack growth behavior under cyclic stress with relatively low ΔK. In the present study, therefore, ΔKth was determined for austenitic stainless steels in simulated PWR primary water, and FCG behavior under near-threshold condition was revealed by collecting fatigue crack propagation data. The results are summarized as follows: No propagation of fatigue crack was found in high temperature water, and there was a definite ΔKth. Average ΔKeff,th was 4.3 MPa·m0.5 at 325degC, 3.3 MPa·m0.5 at 100degC, and there was no considerable reduction compared to currently known ΔKeff,th in air. Thus, it was revealed tha ambient conditions had minimal effect, on ΔKeff,th, ΔKth increases with increasing temperature and decreasing frequency. As a result of fracture surface observation, oxide-induced-crack-closure was considered to be a cause of the dependency described above. In addition, it was suggested that changes in material properties also had influence on ΔKth, since ΔKeff,th itself increased at elevated temperature. (author)

  13. Energy absorption behaviour of austenitic and duplex stainless steels in a crash box geometry

    Ratte, E.; Bleck, W. [Dept. of Ferrous Metallurgy, RWTH Aachen Univ., Aachen (Germany); Leonhardt, S. [Honda R und D Europe (Deutschland), Offenbach/ Main (Germany); Franzen, M.; Urban, P. [Inst. fuer Kraftfahrwesen, RWTH Aachen Univ., Aachen (Germany)

    2006-09-15

    The improvement of the passive safety plays an important role in the development of new steels for automotive parts. At the same time aspects of weight reduction as well as the industrial feasibility have to be considered. Powered by these objectives, the development and application of new steel concepts for various purposes is promoted. For the present investigation especially weight reduction combined with an improvement of the passive safety are emphasised. As example one representative part of the body structure, the crash box, is considered. At the moment different steel grades (dual phase-, TRIP-and HSLA-steels) as well as fibre reinforced materials are applied. New materials for this special purpose have to exhibit outstanding formability, a high capacity to absorb energy during a possible crash and should be cost effective compared to already existing material concepts. During this project different grades of austenitic stainless steels with varying stability were compared to duplex stainless steels and a TRIP grade with regard to their possible application as crash-box material. The austenitic grades show excellent gradual formability according to their strength level. All of them exhibit an extraordinary strain hardening behaviour. The duplex grades show a lower formability but on a much higher yield level. Besides the determination of classical material data such as uni- and multi-axial flow curves, dynamic tensile tests and forming tests for the determination of forming limit curves were performed. The material data were used in the simulation of a drop tower test which is commonly used to evaluate the performance of different materials in car components. The results were then evaluated with regard to the absorbed energy, the folding behaviour and the resulting forces. (orig.)

  14. Hydrogen-Assisted Crack Propagation in Austenitic Stainless Steel Fusion Welds

    Somerday, B. P.; Dadfarnia, M.; Balch, D. K.; Nibur, K. A.; Cadden, C. H.; Sofronis, P.

    2009-10-01

    The objective of this study was to characterize hydrogen-assisted crack propagation in gas-tungsten arc (GTA) welds of the nitrogen-strengthened, austenitic stainless steel 21Cr-6Ni-9Mn (21-6-9), using fracture mechanics methods. The fracture initiation toughness and crack growth resistance curves were measured using fracture mechanics specimens that were thermally precharged with 230 wppm (1.3 at. pct) hydrogen. The fracture initiation toughness and slope of the crack growth resistance curve for the hydrogen-precharged weld were reduced by as much as 60 and 90 pct, respectively, relative to the noncharged weld. A physical model for hydrogen-assisted crack propagation in the welds was formulated from microscopy evidence and finite-element modeling. Hydrogen-assisted crack propagation proceeded by a sequence of microcrack formation at the weld ferrite, intense shear deformation in the ligaments separating microcracks, and then fracture of the ligaments. One salient role of hydrogen in the crack propagation process was promoting microcrack formation at austenite/ferrite interfaces and within the ferrite. In addition, hydrogen may have facilitated intense shear deformation in the ligaments separating microcracks. The intense shear deformation could be related to the development of a nonuniform distribution of hydrogen trapped at dislocations between microcracks, which in turn created a gradient in the local flow stress.

  15. Effect of thermal cycles on heavily cold deformed AISI 304L austenitic stainless steel

    The solution treated commercial grade AISI 304L austenitic stainless steel plate was heavily cold rolled to 90% of thickness reduction. Cold rolled specimens were annealed at various temperatures by thermal cycles and isothermal annealing. Strain-induced phase transformations and microstructure studies were carried out both in the cold rolled and annealed conditions. The X-ray diffraction and magnetic measurements were used for phase transformation studies. The transmission electron microscope characterisation revealed that the cyclic thermal process resulted in ultrafine grain austenite formation whereas, the isothermal annealing developed coarser grain size microstructure. The different microstructural evolutions by the above two processes largely influenced the development of the recrystallisation texture. The thermal cycling produced a distinct γ-fibre texture while the isothermal annealing resulted in a cube texture component along with the γ-fibre. The γ-fibre texture evolution was attributed to the over critical subgrains or nuclei and {1 0 0} cube texture to the coarser grains of micrometer size.

  16. Solidification and solid-state transformations of high energy density austenitic stainless steel welds

    Much work has been undertaken in studying the solidification and solid-state transformations of austenitic stainless steel welds. Considerable confusion existed as to both the solidification mechanics and solid-state transformations which lead to a wide range of ferrite morphologies. It has been found that both the primary phase of solidification and the ferrite morphologies are controlled primarily by the Cr/Ni ratio. The application of analytical electron microscopy was very beneficial in leading to a clearer understanding of the microstructural evolution of the rather complex weld structures. In the investigations, the authors are studying the solidification behavior and solid-state transformations of high energy density welds (electron beam and laser) and comparing these to GTA welds. Fe-Ni-CR ternary alloys covering a range of Cr/Ni ratios typical of those of the AISI 300 series alloys are being investigated. Extensive analysis including electron microprobe, TEM, and STEM (scanning transmission electron microscopy) analytical microscopy were used to characterize GTA welds which solidified both as primary ferrite and primary austenite and exhibited, when welded, a wide range in ferrite morphologies. Solidification modeling of microsegregation of the welds was also conducted. The model incorporates three dimensional finite difference analysis, solute partitioning between the liquid and solid, and solid-state diffusion in the three components system. The results of the modeling were extremely valuable in leading to an understanding of the effect of solidification microsegregation on both the measured microsegregation and solid-state transformations

  17. Effect of prior cold work on creep properties of a titanium modified austenitic stainless steel

    Prior cold worked (PCW) titanium-modified 14Cr–15Ni austenitic stainless steel (SS) is used as a core-structural material in fast breeder reactor because of its superior creep strength and resistance to void swelling. In this study, the influence of PCW in the range of 16–24% on creep properties of IFAC-1 SS, a titanium modified 14Cr–15Ni austenitic SS, at 923 K and 973 K has been investigated. It was found that PCW has no appreciable effect on the creep deformation rate of the steel at both the test temperatures; creep rupture life increased with PCW at 923 K and remained rather unaffected at 973 K. The dislocation structure along with precipitation in the PCW steel was found to change appreciably depending on creep testing conditions. A well-defined dislocation substructure was observed on creep testing at 923 K; a well-annealed microstructure with evidences of recrystallization was observed on creep testing at 973 K

  18. Application of strain scanning method to stress measurement of austenitic stainless steel

    A strain scanning method was applied to the stress measurement of austenitic stainless steel (SUS304L). The sizes of its gauge volume were a width of 2 mm and a height of 0.2 mm, and the grain size of the specimen was 37 micrometers. Enough accuracy of the measured stress was not obtained due to the coarse grain of the specimen. To improve the coarse grain problem, three methods of oscillation were examined such as in-plane rotation, out-of-plane tilt and translation. The translation method can increase the number of the grains by changing the amplitude. For the translation method, the accurate measurement is possible if it is 10000 numbers or more of grains. However, the numbers of the grains by the other oscillations were not enough. For the translation method, a strict parallel between the specimen surface and the translation plane was necessary. It succeeded in adjusting the strict parallel. The residual stress distribution of the shot-peened austenitic steel was measured by our method. (author)

  19. Deformation localization and dislocation channel dynamics in neutron-irradiated austenitic stainless steels

    Gussev, Maxim N.; Field, Kevin G.; Busby, Jeremy T.

    2015-05-01

    The dynamics of deformation localization and dislocation channel formation were investigated in situ in a neutron-irradiated AISI 304 austenitic stainless steel and a model 304-based austenitic alloy by combining several analytical techniques including optic microscopy and laser confocal microscopy, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy (TEM). Channel formation was observed at ∼70% of the polycrystalline yield stress of the irradiated materials (σ0.2). It was shown that triple junction points do not always serve as a source of dislocation channels; at stress levels below the σ0.2, channels often formed near the middle of the grain boundary. For a single grain, the role of elastic stiffness value (Young's modulus) in channel formation was analyzed; it was shown that in the irradiated 304 steels the initial channels appeared in "soft" grains with a high Schmid factor located near "stiff" grains with high elastic stiffness. The spatial organization of channels in a single grain was analyzed; it was shown that secondary channels operating in the same slip plane as primary channels often appeared at the middle or at one-third of the way between primary channels. The twinning nature of dislocation channels was analyzed for grains of different orientation using TEM. In the AISI 304 steel, channels in grains oriented close to ||TA (tensile axis) and ||TA were twin free and grain with ||TA and grains oriented close to a Schmid factor maximum contained deformation twins.

  20. Ultrasonic flaw detection of austenitic stainless steel longitudinally welded pipe and tubing

    Recently there has been the trend that the welded austenitic stainless steel pipe and tubing are used in the nuclear industry in place of the seamless pipe and tubing. For most of the nuclear components, the pipe and tubing must be examined with ultrasonic method by the demands of ASME SA-655. But the ultrasonic flaw detection of the austenitic welds is generally difficult because of scattering and deflection of the acoustic beam due to the coarse grained and elastically anisotropic preferred oriented structure of dendrite. For the thinner welds of pipe and tubing, the attenuation and deflection of the beam do not make the serious problems, however, the deterioration of the signal-to-noise ratio by the coherent structural noise from the welds may still disturb the flaw detection. The longitudinal wave can be employed to suppress the structural noise. This depends upon its longer wave length. In the automatic examination of the pipe and tubing, however, the customary shear wave angle beam technique must be applied to use the skipped beam

  1. Effects of Nitrogen Concentration on Microstructure and Antibac-terial Property of Copper-Bearing Austenite Stainless Steels

    Zhixia ZHANG; Laizhu JIANG; Gang LIN; Zhou XU

    2008-01-01

    Austenite antibacterial stainless steels have been found to have wide applications in hospitals and food indus-tries. In recent years epsilon copper precipitation in antibacterial stainless steels has obtained much research interest due to its antibacterial action. The objective of this study was to determine the effects of nitro-gen concentration on the precipitation of epsilon copper and antibacterial property. Two kinds of austenite antibacterial stainless steels containing copper and different nitrogen concentration (0.02 and 0.08 wt pct, re-spectively) were prepared and the microstructures were characterized by a combination of electron microscopy and thermodynamic analysis. A mathematical expression was deduced to predict the effect of nitrogen con-centration on the activity coefficient of copper, In(fCu/focu)=0.53524+4.11xN-0.48x2N. Higher nitrogen was found to increase the free energy difference of copper concentration distribution between precipitation phase and austenite matrix, stimulate the aggregation of copper atoms from austenite, increase the precipitation amount and consequently enhance the antibacterial property of steel.

  2. High temperature oxidation behavior of austenitic stainless steel AISI 304 in steam of nanofluids contain nanoparticle ZrO2

    The objective of this study is to evaluate high temperature oxidation behavior of austenitic stainless steel SS 304 in steam of nanofluids contain nanoparticle ZrO2. The oxidation was performed at high temperatures ranging from 600 to 800°C. The oxidation time was 60 minutes. After oxidation the surface of the samples was analyzed by different methods including, optical microscope, scanning electron microscope (SEM) and X-ray diffraction (XRD). X-ray diffraction examination show that the oxide scale formed during oxidation of stainless steel AISI 304 alloys is dominated by iron oxide, Fe2O3. Minor element such as Cr2O3 is also appeared in the diffraction pattern. Characterization by optical microscope showed that cross section microstructure of stainless steel changed after oxidized with the oxide scale on the surface stainless steels. SEM and x-ray diffraction examination show that the oxide of ZrO2 appeared on the surface of stainless steel. Kinetic rate of oxidation of austenite stainless steel AISI 304 showed that increasing oxidation temperature and time will increase oxidation rate

  3. Correlation between the Cyclic Stress Behavior and Microstructure in 316LN based on the Analysis of Hysteresis Loops

    CHANG Bo; ZHANG Zheng

    2014-01-01

    Total strain controlled cyclic test was performed on 316LN under uniaxial loadings. Through the partitioning of hysteresis loops, the evolution of two components of cyclic flow stress, the internal and effective stresses, was reported. The former one determines the cyclic stress response. Based on the transmission electron microscopic (TEM) observation on specimens loaded with scheduled cycles, it is found that planar dislocation structures prevail during the entire cyclic process at low strain amplitude, while a remarkable dislocation rearrangement from planar structures to heterogeneous spatial distributions is companied by a cyclic softening behavior at high strain amplitude. The competition between the evolution of the intergranular and the intragranular components of the internal stress caused by the transition of slip mode induces the cyclic hardening and softening at high strain levels. The intergranular internal stress represents the most part of the internal stress at low strain level.

  4. Orientation dependence of nitrogen supersaturation in austenitic stainless steel during low-temperature gas-phase nitriding

    A hardened surface layer was produced on 316L austenitic stainless steel via low-temperature gas-phase nitriding. The effects of nitriding temperature, nitrogen activity and processing time were systematically studied. Concentration–depth profiling by Auger electron spectroscopy revealed very high levels (up to 25 at.%) of interstitial nitrogen in solid solution. This causes a lattice parameter expansion of up to 10% at the alloy surface. X-ray diffractometry revealed that the expansion – and thus the level of nitrogen supersaturation – strongly depends on the crystallographic orientation. We attribute this effect to the elastic anisotropy of austenite, exacerbated by a nitrogen-induced paramagnetic-to-ferromagnetic transition

  5. Investigations on structure–property relationships of activated flux TIG weldments of super-duplex/austenitic stainless steels

    Devendranath Ramkumar, K., E-mail: ramdevendranath@gmail.com; Bajpai, Ankur; Raghuvanshi, Shubham; Singh, Anshuman; Chandrasekhar, Aditya; Arivarasu, M.; Arivazhagan, N.

    2015-06-25

    This research work articulated the effect of SiO{sub 2} flux assisted tungsten inert gas (TIG) welding on the microstructure and mechanical properties of marine grade stainless steel weldments, such as super-duplex stainless steel (UNS S32750) and austenitic stainless steel (AISI 316L). The studies showed that the use of flux decreased the heat input required to obtain complete penetration. Microstructure studies revealed the presence of ferrite at the heat affected zone of AISI 316L and the fusion zone which obviated the hot cracking tendency. Tensile studies corroborated that the joint strength was sufficiently greater than that of the parent metals. Impact toughness slightly impoverished owing to the presence of large platelets of Widmanstätten austenite in the fusion zone. The study also explored the structure–property relationships of the flux assisted weldments using the combined techniques of optical and scanning electron microscopy analysis. Owing to the better metallurgical and mechanical properties, this study recommends the use of SiO{sub 2} flux for joining the dissimilar metals involving austenitic and super-duplex stainless steels.

  6. Investigations on structure–property relationships of activated flux TIG weldments of super-duplex/austenitic stainless steels

    This research work articulated the effect of SiO2 flux assisted tungsten inert gas (TIG) welding on the microstructure and mechanical properties of marine grade stainless steel weldments, such as super-duplex stainless steel (UNS S32750) and austenitic stainless steel (AISI 316L). The studies showed that the use of flux decreased the heat input required to obtain complete penetration. Microstructure studies revealed the presence of ferrite at the heat affected zone of AISI 316L and the fusion zone which obviated the hot cracking tendency. Tensile studies corroborated that the joint strength was sufficiently greater than that of the parent metals. Impact toughness slightly impoverished owing to the presence of large platelets of Widmanstätten austenite in the fusion zone. The study also explored the structure–property relationships of the flux assisted weldments using the combined techniques of optical and scanning electron microscopy analysis. Owing to the better metallurgical and mechanical properties, this study recommends the use of SiO2 flux for joining the dissimilar metals involving austenitic and super-duplex stainless steels

  7. Study of austenitic stainless steels behaviour under creep and fatigue crack growth modes at 5500C

    The behaviour of three austenitic stainless steels used for fast reactor vessels is examined under creep and fatigue crack growth modes. The behaviour of this type of material (ductile characteristic) can be described essentially by a power law (primary creep). No unique correlation can be established between creep crack growth rate and the usual load geometry parameters. An unique correlation exists between the creep crack growth initiation time and a global load geometry parameter C*exp. Time versus C* diagrams were established from the C* calculations with the semi-analytical simulations of load-point displacements, and then used for life prediction purposes in engineering applications. Under fatigue loading, the influence of experimental parameters such as frequency and R ratio has been studied as well as the effects of age hardening and cold work. The latter increases the material resistance to crack growth. A reduction in frequency and an increase in the R ratio result in increasing crack growth rate. The rupture modes of specimens were determined through metallographical examinations. The rupture was intergranular in creep tests, whilst in fatigue tests it was mixed at low Δ K values, becoming intergranular at low frequencies or transgranular at moderate frequencies. Only M23C6 carbides were found in these steels when tested at 5500C. The M23C6 precipitation was found to be accelerated by loading. It is necessay to know the microstructural evolution in order to understand the macroscopic stainless steel behaviour

  8. Electronic structures and nitride formation on ion-implanted AISI 304L austenitic stainless steel

    Chang, G.S.; Son, J.H.; Kim, S.H.; Chae, K.H.; Whang, C.N. (Yonsei Univ., Seoul (Korea, Republic of). Dept. of Physics); Menthe, E.; Rie, K.-T.; Lee, Y.P.

    1999-02-01

    A N[sub 2][sup +] implantation technique was employed to improve the surface hardness of stainless steel, and the electronic structures and nitride formation of the ion-implanted layer were investigated and compared with those produced using other techniques, including plasma nitriding. AISI 304L austenite stainless steel was irradiated by 80 keV N[sub 2][sup +] with a dosage ranging from 1.0 x 10[sup 16] to 1.0 x 10[sup 18] ions cm[sup -2] at room temperature. The formation of various nitrides was confirmed by X-ray diffraction. The quantitative hardness of the samples was measured by using a Knoop microhardness tester. X-ray photoelectron spectroscopy was also carried out to elucidate the chemical states and electronic structures of the ion-implanted layers. The measurements were repeated after post-annealing at 400 C for 1 h in a high vacuum. Changes in phase, chemical state and electronic structures were observed according to the ion dose and heat treatment. (orig.) 12 refs.

  9. Evaluation of neutron irradiation effect on SCC crack growth behaviour for austenitic stainless steels

    Austenitic stainless steels are widely used as structural components in reactor pressure vessel internals because of their high strength, ductility, and fracture toughness. However, exposure to neutron irradiation results in changes in microstructure, mechanical properties and microchemistry of the steels. Irradiation assisted stress corrosion cracking (IASCC) caused by the effect of neutron irradiation during long term plant operation in high temperature water environments is considered to take the form of intergranular stress corrosion cracking (IGSCC) and the critical fluence level has been reported to be about 5x1024n/m2 (E>1MeV) in Type 304 stainless steel in BWR environment. JNES had been conducting IASCC project during the JFY (2000) - JFY (2008) period, and prepared an engineering database on IASCC. However, the data of Crack Growth Rate (CGR) below the critical fluence level are not sufficient. So, this project was initiated to obtain the CGR data below the critical fluence level. Test specimens have been irradiated in the Halden reactor, operating by the OECD Halden Reactor Project, and the post irradiation examination (PIE) will be conducted from JFY (2011) to JFY (2013), finally the modified IASCC guide will be prepared in JFY (2013). (author)

  10. INVESTIGATING SPOT WELD GROWTH ON 304 AUSTENITIC STAINLESS STEEL (2 mm SHEETS

    NACHIMANI CHARDE

    2013-02-01

    Full Text Available Resistance spot welding (RSW has revolutionized automotive industries since early 1970s for its mechanical assemblies. To date one mechanical assembly out five is welded using spot welding technology in various industries and stainless steel became very popular among common materials. As such this research paper analyses the spot weld growth on 304 austenitic stainless steels with 2mm sample sheets. The growth of a spot weld is primarily determined by its parameters such as current, weld time, electrode tip and force. However other factors such as electrode deformations, corrosions, dissimilar materials and material properties are also affect the weld growth. This paper is intended to analyze only the effects of nuggets growth due to the current and weld time increment with constant force and unchanged electrode tips. A JPC 75kVA spot welder was used to accomplish it and the welded samples were undergone tensile test, hardness test and metallurgical test to characterize the formation of weld nuggets.

  11. Laser beam welding of high-nitrogen-containing austenitic stainless steel

    Iamboliev, T.; Zumbilev, A. (Technical Univ. of Plovidiv (Bulgaria)); Christov, S.; Kalev, L. (Bulgarian Academy of Science, Sofia (Bulgaria)); Ianev, V. (Optical Technology Inst., Plovdiv (Bulgaria)); Stang, R.G. (Univ. of Washington, Seattle, WA (United States). Dept. of Materials Science and Engineering)

    1999-07-01

    A continuous wave CO[sub 2] laser was used to weld 2- and 6-mm-high nitrogen-containing stainless steel plates with a composition of 18% Cr-0.6% N-12% Mn. A study of the weld properties revealed that defect-free welds were produced. The N content in the porosity-free welds was in the range of 70--78% of the N content in the base metal using Ar shielding and 77--88% when N was used as a shielding gas. The microstructure of the weld metal was fully austenitic. The yield strength joint efficiency was 83--87% and ductility was in the range of 88--92% compared to the base metal values. It is proposed that the degradation of the mechanical properties is due to the decrease in N in the weld metal. The intergranular corrosion resistance was studied after sensitization and immersion in boiling sulfuric acid and lactic acid. The corrosion resistance of the welds, for the alloy studied, was almost equal to that for a conventional stainless alloy 18% Cr-10% Ni-0.6% Ti in the as-welded condition. After sensitizing, the corrosion resistance was reduced.

  12. Effect of triple ion beam irradiation on mechanical properties of high chromium austenitic stainless steel

    A high-chromium austenitic stainless steel has been developed for an advanced fuel cladding tube considering waterside corrosion and irradiation embrittlement. The candidate material was irradiated in triple ion (Ni, He, H) beam modes at 573 K up to 50 dpa to simulate irradiation damage by neutron and transmutation product. The change in hardness of the very shallow surface layer of the irradiated specimen was estimated from the slope of load/depth-depth curve which is in direct proportion to the apparent hardness of the specimen. Besides, the Swift's power low constitutive equation (σ=A(ε0 + ε)n, A: strength coefficient, ε0: equivalent strain by cold rolling, n: strain hardening exponent) of the damaged parts was derived from the indentation test combined with an inverse analysis using a finite element method (FEM). For comparison, Type304 stainless steel was investigated as well. Though both Type304SS and candidate material were also hardened by ion irradiation, the increase in apparent hardness of the candidate material was smaller than that of Type304SS. The yield stress and uniform elongation were estimated from the calculated constitutive equation by FEM inverse analysis. The irradiation hardening of the candidate material by irradiation can be expected to be lower than that of Type304SS. (author)

  13. Structure and composition of phases occurring in austenitic stainless steels in thermal and irradiation environments

    Transmission electron diffraction techniques coupled with quantitative x-ray energy dispersive spectroscopy have been used to characterize the phases which develop in austenitic stainless steels during exposure to thermal and to irradiation environments. In AISI 316 and Ti-modified stainless steels some thirteen phases have been identified and characterized in terms of their crystal structure and chemical composition. Irradiation does not produce any completely new phases. However, as a result of radiation-induced segregation principally of Ni and Si, and of enhanced diffusion rates, several major changes in phase relationships occur during irradiation. Firstly, phases characteristic of remote regions of the phase diagram appear unexpectedly and dissolve during postirradiation annealing (radiation-induced phases). Secondly, some phases develop with their compositions significantly altered by the incorporation of Ni or Si (radiation-modified phases). In addition, several phases devear preheating unit anium southward as well as to deeper dened al half-lives with experimental ones, over a range of 24 orders of magnitude was obtained. This is a strong argument that the alpha decay could be considered a fission process with very high mass asymmetry and charge density asymmetry

  14. An auger spectroscopy investigation of the surfaces of austenitic stainless steels

    Full text.Various studies have been shown that during annealing of stainless steels, various impurities and alloying elements segregate to the surface of the material, leading to a considerable effect on the properties. The object of this work is to study the segregation of elements such as chromium, phosphorous, sulphur and nitrogen to the surface of an austenitic stainless steel made by UGINE (France) and BCR (Algeria). The investigation is carried out by in-situ annealing inside the ultra-vacuum chamber of an Auger electron spectrometer (AES). The specimens are initially homogenised by an anneal at 1050 celsius degree inside evacuated silica capsules. They are then introduced inside the vacuum chamber of the AES where they are first of all activated, at room temperature, by ionic bombardment and then heat treated at various temperatures ranging from 600 celsius degree to 900 celsius degree. the results are obtained in the form of AES spectra recorded in the differential mode. It is found that the surface of the material undergoes alterations, some of which are temporary and others durable. These alterations are : co-segregation of nitrogen and chromium, segregation of sulphur and competition between nitrogen and sulphur and between phosphorous and sulphur. The driving force of segregation is in the following order : S>P>N

  15. An evaluation of creep rupture strength of advanced austenitic stainless steel (PNC1520)

    Advanced austenitic stainless steel (15Cr-20Ni-2.5Mo-0.25Ti-0.1Nb: PNC1520 ) was developed to improve swelling resistance and the high temperature creep rupture strength far beyond the modified 316 stainless steel (PNC316) . Material strength standards and physical properties of PNC1520 was established in 1992 . In this study, design creep rupture strength and creep rupture strength coefficient were evaluated using the revised in-reactor creep rupture data . Following results were obtained. (1) The correlation of design creep rupture strength of PNC1520 was made by means of evaluating all data of PNC1520 and PNC316 . (2) The correlation of in-reactor creep rupture strength of PNC1520 was made. Following correlation was proposed to evaluate the in-reactor creep rupture strength, in stead of previous method which used creep rupture strength coefficient. SR*=Min (SR, SR*Na, SR*irr.) where, SR*: In-reactor Creep Rupture Strength (MPa), SR: Design Creep Rupture Strength (MPa), SR*Na: Creep Rupture Strength in Sodium(MPa), SR*irr.: Creep Rupture Strength under Irradiation(MPa). (author)

  16. Effect of Colouring Process on Pitting Susceptibility of Austenitic Stainless Steel

    S.S.Mahmoud; M.M.Ahmed

    2008-01-01

    Colouring of the austenitic stainless steel alloy (20.45% Cr, 8.57% Ni) was carried out in NaNO3-KNO3 eutectic melt without and with additions of Na2O2, NaCl and their mixtures at different temperatures ranging from 400-600℃, under open-circuit and galvanostatic anodic polarization conditions. The produced colours greatly depend on the thickness of oxide films, which in turn depends on the composition of the molten bath and its temperature. The more attractive, bright, adherent and uniform coloured oxide films can be obtained at 400, 450 and 500℃ in molten nitrate bath containing NaCl and Na2O2 mixtures. The pitting corrosion susceptibility of the coloured oxide films was tested in FeCl3 and NaCl as corrosive media. The obtained results indicate that the pitting corrosion susceptibility of the coloured oxide films greatly depends on the previous operating conditions of the colouring process of the stainless steel specimens such as the composition of molten bath, temperature and technique of colouring process.

  17. The Effect of Constant and Pulsed Current Gas Tungsten Arc Welding on Joint Properties of 2205 Duplex Stainless Steel to 316L Austenitic Stainless Steel

    Neissi, R.; Shamanian, M.; Hajihashemi, M.

    2016-05-01

    In this study, dissimilar 316L austenitic stainless steel/2205 duplex stainless steel (DSS) joints were fabricated by constant and pulsed current gas tungsten arc welding process using ER2209 DSS as a filler metal. Microstructures and joint properties were characterized using optical and electron scanning microscopy, tensile, Charpy V-notch impact and micro-hardness tests, and cyclic polarization measurements. Microstructural observations confirmed the presence of chromium nitride and delta ferrite in the heat-affected zone of DSS and 316L, respectively. In addition, there was some deviation in the austenite/ferrite ratio of the surface welding pass in comparison to the root welding pass. Besides having lower pitting potential, welded joints produced by constant current gas tungsten arc welding process, consisted of some brittle sigma phase precipitates, which resulted in some impact energy reduction. The tensile tests showed high tensile strength for the weld joints in which all the specimens were broken in 316L base metal.

  18. The Effect of Constant and Pulsed Current Gas Tungsten Arc Welding on Joint Properties of 2205 Duplex Stainless Steel to 316L Austenitic Stainless Steel

    Neissi, R.; Shamanian, M.; Hajihashemi, M.

    2016-04-01

    In this study, dissimilar 316L austenitic stainless steel/2205 duplex stainless steel (DSS) joints were fabricated by constant and pulsed current gas tungsten arc welding process using ER2209 DSS as a filler metal. Microstructures and joint properties were characterized using optical and electron scanning microscopy, tensile, Charpy V-notch impact and micro-hardness tests, and cyclic polarization measurements. Microstructural observations confirmed the presence of chromium nitride and delta ferrite in the heat-affected zone of DSS and 316L, respectively. In addition, there was some deviation in the austenite/ferrite ratio of the surface welding pass in comparison to the root welding pass. Besides having lower pitting potential, welded joints produced by constant current gas tungsten arc welding process, consisted of some brittle sigma phase precipitates, which resulted in some impact energy reduction. The tensile tests showed high tensile strength for the weld joints in which all the specimens were broken in 316L base metal.

  19. Electron work functions of ferrite and austenite phases in a duplex stainless steel and their adhesive forces with AFM silicon probe

    Guo, Liqiu; Hua, Guomin; Yang, Binjie; Lu, Hao; Qiao, Lijie; Yan, Xianguo; Li, Dongyang

    2016-02-01

    Local electron work function, adhesive force, modulus and deformation of ferrite and austenite phases in a duplex stainless steel were analyzed by scanning force microscopy. It is demonstrated that the austenite has a higher electron work function than the ferrite, corresponding to higher modulus, smaller deformation and larger adhesive force. Relevant first-principles calculations were conducted to elucidate the mechanism behind. It is demonstrated that the difference in the properties between austenite and ferrite is intrinsically related to their electron work functions.

  20. Cyclic plasticity of an austenitic-ferritic stainless steel under biaxial non proportional loading

    Austenitic-ferritic stainless steels are supplied since about 30 years only, so they are yet not well-known. Their behaviour in cyclic plasticity was studied under uniaxial loading but not under multiaxial loading, whereas only a thorough knowledge of the phenomena influencing the mechanical behaviour of a material enables to simulate and predict accurately its behaviour in a structure. This work aims to study and model the behaviour of a duplex stainless steel under cyclic biaxial loading. A three step method was adopted. A set of tension-torsion tests on tubular specimen was first defined. We studied the equivalence between loading directions, and then the influence of loading path and loading history on the stress response of the material. Results showed that duplex stainless steel shows an extra-hardening under non proportional loading and that its behaviour depends on previous loading. Then, in order to analyse the results obtained during this first experimental stage, the yield surface was measured at different times during cyclic loading of the same kind. A very small plastic strain offset (2*10-5) was used in order not to disturb the yield surface measured. The alteration of isotropic and kinematic hardening variables were deduced from these measures. Finally, three phenomenological constitutive laws were identified with the experimental set. We focused our interest on the simulation of stabilized stress levels and on the simulation of the cyclic hardening/softening behaviour. The comparison between experimental and numerical results enabled the testing of the relevance of these models. (authors)

  1. Characterization of oxide layers grown on D9 austenitic stainless steel in lead bismuth eutectic

    Lead bismuth eutectic (LBE) is a possible coolant for fast reactors and targets in spallation neutron sources. Its low melting point, high evaporation point, good thermal conductivity, low reactivity, and good neutron yield make it a safe and high performance coolant in radiation environments. The disadvantage is that it is a corrosive medium for most steels and container materials. This study was performed to evaluate the corrosion behavior of the austenitic stainless steel D9 in oxygen controlled LBE. In order to predict the corrosion behavior of steel in this environment detailed analyses have to be performed on the oxide layers formed on these materials and various other relevant materials upon exposure to LBE. In this study the corrosion/oxidation of D9 stainless steel in LBE was investigated in great detail. The oxide layers formed were characterized using atomic force microscopy, magnetic force microscopy, nanoindentation, and scanning electron microscopy with wavelength-dispersive spectroscopy (WDS) to understand the corrosion and oxidation mechanisms of D9 stainless steel in contact with the LBE. What was previously believed to be a simple double oxide layer was identified here to consist of at least 4 different oxide layers. It was found that the inner most oxide layer takes over the grain structure of what used to be the bulk steel material while the outer oxide layer consists of freshly grown oxides with a columnar structure. These results lead to a descriptive model of how these oxide layers grow on this steel under the harsh environments encountered in these applications

  2. Characterization of oxide layers grown on D9 austenitic stainless steel in lead bismuth eutectic

    Hosemann, P. [CD Laboratory of Localized Corrosion, Montanuniversitaet Leoben, Franz-Josef Strasse 18, 8700 Leoben (Austria); Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87544 (United States)], E-mail: peterh@lanl.gov; Hawley, M. [Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87544 (United States); Koury, D. [University of Nevada, 4505 S. Maryland Parkway, Las Vegas, NV 89154 (United States); Swadener, J.G. [Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87544 (United States); Welch, J.; Johnson, A.L. [University of Nevada, 4505 S. Maryland Parkway, Las Vegas, NV 89154 (United States); Mori, G. [CD Laboratory of Localized Corrosion, Montanuniversitaet Leoben, Franz-Josef Strasse 18, 8700 Leoben (Austria); Li, N. [Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87544 (United States)

    2008-04-30

    Lead bismuth eutectic (LBE) is a possible coolant for fast reactors and targets in spallation neutron sources. Its low melting point, high evaporation point, good thermal conductivity, low reactivity, and good neutron yield make it a safe and high performance coolant in radiation environments. The disadvantage is that it is a corrosive medium for most steels and container materials. This study was performed to evaluate the corrosion behavior of the austenitic stainless steel D9 in oxygen controlled LBE. In order to predict the corrosion behavior of steel in this environment detailed analyses have to be performed on the oxide layers formed on these materials and various other relevant materials upon exposure to LBE. In this study the corrosion/oxidation of D9 stainless steel in LBE was investigated in great detail. The oxide layers formed were characterized using atomic force microscopy, magnetic force microscopy, nanoindentation, and scanning electron microscopy with wavelength-dispersive spectroscopy (WDS) to understand the corrosion and oxidation mechanisms of D9 stainless steel in contact with the LBE. What was previously believed to be a simple double oxide layer was identified here to consist of at least 4 different oxide layers. It was found that the inner most oxide layer takes over the grain structure of what used to be the bulk steel material while the outer oxide layer consists of freshly grown oxides with a columnar structure. These results lead to a descriptive model of how these oxide layers grow on this steel under the harsh environments encountered in these applications.

  3. Characterization of oxide layers grown on D9 austenitic stainless steel in lead bismuth eutectic

    Hosemann, P.; Hawley, M.; Koury, D.; Swadener, J. G.; Welch, J.; Johnson, A. L.; Mori, G.; Li, N.

    2008-04-01

    Lead bismuth eutectic (LBE) is a possible coolant for fast reactors and targets in spallation neutron sources. Its low melting point, high evaporation point, good thermal conductivity, low reactivity, and good neutron yield make it a safe and high performance coolant in radiation environments. The disadvantage is that it is a corrosive medium for most steels and container materials. This study was performed to evaluate the corrosion behavior of the austenitic stainless steel D9 in oxygen controlled LBE. In order to predict the corrosion behavior of steel in this environment detailed analyses have to be performed on the oxide layers formed on these materials and various other relevant materials upon exposure to LBE. In this study the corrosion/oxidation of D9 stainless steel in LBE was investigated in great detail. The oxide layers formed were characterized using atomic force microscopy, magnetic force microscopy, nanoindentation, and scanning electron microscopy with wavelength-dispersive spectroscopy (WDS) to understand the corrosion and oxidation mechanisms of D9 stainless steel in contact with the LBE. What was previously believed to be a simple double oxide layer was identified here to consist of at least 4 different oxide layers. It was found that the inner most oxide layer takes over the grain structure of what used to be the bulk steel material while the outer oxide layer consists of freshly grown oxides with a columnar structure. These results lead to a descriptive model of how these oxide layers grow on this steel under the harsh environments encountered in these applications.

  4. Investigation of the Effects of Solution Temperature on the Corrosion Behavior of Austenitic Low-Nickel Stainless Steels in Citric Acid using Impedance and Polarization Measurements

    Mulimbayan Francis M.; Mena Manolo G.

    2015-01-01

    Stainless steels may be classified according to alloy microstructure – ferritic, austenitic, martensitic, duplex, and precipitation hardening grades. Among these, austenitic grade has the largest contribution to market due to the alloy’s numerous industrial and domestic applications. In this study, the corrosion behavior of low-Nickel stainless steel in citric acid was investigated using potentiodynamic polarization techniques and Electrochemical Impedance Spectroscopy (EIS). The corrosion cu...

  5. Features of phase composition of stainless austenitic steels and possibility of selection tubes of these steels in accordance with their steel grades by means of eddy current method

    Studies on mechanical, magnetic and electric characteristics of some types of chromium-nickel and chromium-nickel-molybdenum austenitic steels used for manufacturing hot-rolled tubes are carried out. A possibility of nondestructive control of stainless austenitic steel by grades is disclosed. A mock-up of an eddy device with a superposed transformer for measurements on samples of tubes is described

  6. Effect of heat treatment on an AISI 304 austenitic stainless steel evaluated by the ultrasonic attenuation coefficient

    The properties of metals can be substantially changed by various methods, one of them is using heat treatment processes. Moreover, ultrasonic testing is the most preferred and effective, nondestructive testing technique for characterization of mechanical material properties. Austenitic stainless steel AISI 304 serves in many applications due to high strength and corrosion resistance. In certain applications, it is important to evaluate the mechanical properties of AISI 304 stainless steel. In this study, the ultrasonic method (attenuation measurement technique) is used to evaluate the hardness of AISI 304 stainless steel samples which were heat treated at different levels. Due to the heat treatment process, each sample has its specific microstructure and hardness which attenuate ultrasonic waves appropriately. The ultrasonic and hardness test show that it is possible to evaluate the hardness of AISI 304 stainless steel by ultrasonic attenuation coefficient. In addition, the relationship between ultrasonic attenuation coefficients and time of heat treatment is investigated.

  7. Effect of heat treatment on an AISI 304 austenitic stainless steel evaluated by the ultrasonic attenuation coefficient

    Moghanizadeh, Abbas; Farzi, Abolfazl [Islamic Azad Univ., Esfarayen (Iran, Islamic Republic of). Dept. of Civil Engineering

    2016-07-01

    The properties of metals can be substantially changed by various methods, one of them is using heat treatment processes. Moreover, ultrasonic testing is the most preferred and effective, nondestructive testing technique for characterization of mechanical material properties. Austenitic stainless steel AISI 304 serves in many applications due to high strength and corrosion resistance. In certain applications, it is important to evaluate the mechanical properties of AISI 304 stainless steel. In this study, the ultrasonic method (attenuation measurement technique) is used to evaluate the hardness of AISI 304 stainless steel samples which were heat treated at different levels. Due to the heat treatment process, each sample has its specific microstructure and hardness which attenuate ultrasonic waves appropriately. The ultrasonic and hardness test show that it is possible to evaluate the hardness of AISI 304 stainless steel by ultrasonic attenuation coefficient. In addition, the relationship between ultrasonic attenuation coefficients and time of heat treatment is investigated.

  8. Microstructural Evolutions During Annealing of Plastically Deformed AISI 304 Austenitic Stainless Steel: Martensite Reversion, Grain Refinement, Recrystallization, and Grain Growth

    Naghizadeh, Meysam; Mirzadeh, Hamed

    2016-08-01

    Microstructural evolutions during annealing of a plastically deformed AISI 304 stainless steel were investigated. Three distinct stages were identified for the reversion of strain-induced martensite to austenite, which were followed by the recrystallization of the retained austenite phase and overall grain growth. It was shown that the primary recrystallization of the retained austenite postpones the formation of an equiaxed microstructure, which coincides with the coarsening of the very fine reversed grains. The latter can effectively impair the usefulness of this thermomechanical treatment for grain refinement at both high and low annealing temperatures. The final grain growth stage, however, was found to be significant at high annealing temperatures, which makes it difficult to control the reversion annealing process for enhancement of mechanical properties. Conclusively, this work unravels the important microstructural evolution stages during reversion annealing and can shed light on the requirements and limitations of this efficient grain refining approach.

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

    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.)

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

    Vilpas, M. [VTT Manuf. Technol. (Finland); Haenninen, H. [Helsinki Univ. of Technol., Espoo (Finland). Lab. of Eng. Mater.

    1999-07-01

    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.)

  11. Microstructural Evolutions During Annealing of Plastically Deformed AISI 304 Austenitic Stainless Steel: Martensite Reversion, Grain Refinement, Recrystallization, and Grain Growth

    Naghizadeh, Meysam; Mirzadeh, Hamed

    2016-06-01

    Microstructural evolutions during annealing of a plastically deformed AISI 304 stainless steel were investigated. Three distinct stages were identified for the reversion of strain-induced martensite to austenite, which were followed by the recrystallization of the retained austenite phase and overall grain growth. It was shown that the primary recrystallization of the retained austenite postpones the formation of an equiaxed microstructure, which coincides with the coarsening of the very fine reversed grains. The latter can effectively impair the usefulness of this thermomechanical treatment for grain refinement at both high and low annealing temperatures. The final grain growth stage, however, was found to be significant at high annealing temperatures, which makes it difficult to control the reversion annealing process for enhancement of mechanical properties. Conclusively, this work unravels the important microstructural evolution stages during reversion annealing and can shed light on the requirements and limitations of this efficient grain refining approach.

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

    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

  13. A proposal to alloy design for low activation high manganese austenitic stainless steel - role of carbon and nitrogen

    The role of carbon and nitrogen in high Mn-Cr-Fe base alloy has been investigated in order to propose a favorable starting composition for a low activation austenitic stainless steel. The base composition of Fe-12% Cr-15% Mn was selected by the results of our previous study, because of prevention of δ ferrite formation and retardation of σ phase. The combined addition of carbon and nitrogen is very beneficial in making a stable γ phase, preventing σ phase formation and increasing high-temperature strength at around 875 K. Cold work of 20% is also very useful in increasing creep rupture strength because of finely dispersed precipitation of carbide during creep. From the consideration of these results, an alloy system of Fe-12% Cr-15% Mn-0.2% C-0.2% N has been designed as one of the preferable primary low activation austenitic stainless steel. (orig.)

  14. Benefic effects of high nitrogen contents on properties of super austenitic stainless steels for very severe corrosive applications

    New highly allowed austenitic stainless steels (PREN included in the 40/60 range) have been investigated. The effects of allowing elements on mechanical properties, structure stability and corrosion resistance have been defined. As a result, we determine the best equilibria for structure stability and corrosion resistance: the tungsten additions are particularly interesting, since this element, as molybdenum, increases the localised corrosion resistance but presents a lower segregation rate than molybdenum (what is very important for manufacturing heavy plates or bars). This study made us optimize the chemical analysis of a new high nitrogen, high strength, super austenitic stainless steel (URANUS B 66), the properties of which will be described in this paper. (authors). 5 refs., 11 figs., 4 tabs

  15. Narrow gap TIG and electron beam weld inspection in austenitic stainless steel using pulse echo, TOFD and phased array ultrasonics

    'Full-text:' Narrow gap Tungsten Inert Gas (TIG) and Electron Beam (EB) welding techniques are being considered for the splice joint welds on the austenitic stainless steel Vacuum Vessel in the next generation of experimental Fusion Power stations under the ITER programme. Under the programme there is a requirement to develop automated ultrasonic NDT techniques to inspect material up to 60 mm thick in both weld types. These narrow welds are difficult to inspect because of the steep fusion faces made more difficult in this project by the beam scattering effects of austenitic stainless steel welds and the very limited access from only one side of the vessel. The paper details the development of the combined Pulse Echo, TOFD and Phased Array techniques on behalf of ITER. The authors describe the philosophy behind the inspections, results and possible transfer of the technology to other sectors of industry. (author)

  16. Precipitation Study in a High Temperature Austenitic Stainless Steel using Low Voltage Energy Dispersive X-ray Spectroscopy

    Gharehbaghi, Ali

    2012-01-01

    Precipitation of second phase particles is a key factor dominating the mechanical properties of high temperature alloys. In order to control and optimize the precipitation effect it is of great importance to study the role of alloying elements in the formation and stability of precipitates. As a favored family of corrosion and creep resistant austenitic stainless steels the 20Cr-25Ni alloy was modified by addition of copper, molybdenum, nitrogen, niobium and vanadium. A set of alloys with sim...

  17. OPTIMIZATION OF SURFACE ROUGHNESS AND TOOL FLANK WEAR IN TURNING OF AISI 304 AUSTENITIC STAINLESS STEEL WITH CVD COATED TOOL

    M. Kaladhar; K. Venkata Subbaiah; CH. SRINIVASA RAO

    2013-01-01

    AISI 304 austenitic stainless steel is a popularly used grade in the various fields of manufacturing because of its high ductility, high durability and excellent corrosion resistance. High work hardening, low heat conductivity and high built up edge (BUE) formation made this as difficult-to- machine material. Poor surface quality and rapid tool wear are the common problems encountered while machining it. In the present work, an attempt has been made to explore the influence of machining para...

  18. The effect of surface mechanical attrition treatment on low temperature plasma nitriding of an austenitic stainless steel

    Chemkhi, Mahdi; Retraint, Delphine; Roos, Arjen; Garnier, Claude; Waltz, Laurent; Demangel, Clémence; Proust, Gwénaëlle

    2013-01-01

    The combined effect of superficial nanocrystallisation by SMAT (Surface Mechanical Attrition Treatment) followed by plasma nitriding on the mechanical properties of a medical grade austenitic stainless steel was studied. SMAT conditions were optimised to enhance nitrogen diffusion. Experimental observations (energy dispersive X-ray spectroscopy profiles, cross-sectional optical micrographs, phase analysis by X-ray diffraction and micro-hardness profiles) show that polishing away a very thin l...

  19. Heat transfer during Nd: Yag pulsed laser welding and its effect on solidification structure of austenitic stainless steels

    This paper reports theoretical and experimental investigations carried out to determine the effect of process parameters on weld metal microstructures of austenitic stainless steels during pulsed laser welding. Laser welds made on four austenitic stainless steels at different power levels and scanning speeds were considered. A transient heat transfer model that takes into account fluid flow in the weld pool was employed to simulate thermal cycles and cooling rates experienced by the material under various welding conditions. The weld metal thermal cycles and cooling rates are related to features of the solidification structure. For the conditions investigated, the observed fusion zone structure ranged from duplex austenite (γ) + ferrite (δ) to fully austenitic or fully ferritic. Unlike welding with a continuous wave laser, pulsed laser welding results in thermal cycling from multiple melting and solidification cycles in the fusion zone, causing significant post-solidification solid-state transformation to occur. There was microstructural evidence of significant recrystallization in the fusion zone structure that can be explained on the basis of the thermal cycles. The present investigation demonstrates the potential of the computational model to provide detailed information regarding the heat transfer conditions experienced during welding

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

    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

  1. Effect of Nitrogen Shielding Gas on Laser Weldability of Austenitic Stainless Steel

    Katayama, Seiji; Yoshida, Daisuke; Matsunawa, Akira

    YAG and CO2 laser weldability of Type 304 steel in nitrogen (N2) shielding gas was evaluated by investigating melting characteristics, porosity formation tendency, N content, microstructural characteristics and cracking sensitivity. Melting characteristics of weld beads produced below 4 kW were not so much different between YAG and CO2 laser. Porosity was remarkably reduced in any welds produced with nitrogen gas in comparison with normal welds made with Ar or He gas. This was attributed to the decrease in N content in a keyhole due to the reaction with evaporated Cr vapor as well as the absorption in the keyhole molten surface. The N contents absorbed in Type 304 weld fusion zones were larger under any welding conditions with CO2 laser than with YAG laser. On the other hand, in the case of several CO2 laser weld metals, solidification cracks occurred along the grain boundaries of a fully austenitic phase. Primary solidification of delta-ferrite phase normally took place in Type 304 weld metals, but a primary austenite phase was formed owing to the N enrichment, and micro-segregation of P and S increased along the grain boundaries. Consequently, cracking was induced by enhancement of cracking sensitivity due to a wider BTR. It was concluded that a great effect of nitrogen on the weldability of stainless steel was noted more remarkably in CO2 laser weld fusion zones than in YAG laser ones. It must be attributed to the N plasma formation leading to higher temperatures and consequent generation of more active N during CO2 laser welding.

  2. Deformation localization and dislocation channel dynamics in neutron-irradiated austenitic stainless steels

    Gussev, Maxim N., E-mail: gussevmn@ornl.gov; Field, Kevin G.; Busby, Jeremy T.

    2015-05-15

    The dynamics of deformation localization and dislocation channel formation were investigated in situ in a neutron-irradiated AISI 304 austenitic stainless steel and a model 304-based austenitic alloy by combining several analytical techniques including optic microscopy and laser confocal microscopy, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy (TEM). Channel formation was observed at ∼70% of the polycrystalline yield stress of the irradiated materials (σ{sub 0.2}). It was shown that triple junction points do not always serve as a source of dislocation channels; at stress levels below the σ{sub 0.2}, channels often formed near the middle of the grain boundary. For a single grain, the role of elastic stiffness value (Young’s modulus) in channel formation was analyzed; it was shown that in the irradiated 304 steels the initial channels appeared in “soft” grains with a high Schmid factor located near “stiff” grains with high elastic stiffness. The spatial organization of channels in a single grain was analyzed; it was shown that secondary channels operating in the same slip plane as primary channels often appeared at the middle or at one-third of the way between primary channels. The twinning nature of dislocation channels was analyzed for grains of different orientation using TEM. In the AISI 304 steel, channels in grains oriented close to 〈0 0 1〉||TA (tensile axis) and 〈1 0 1〉||TA were twin free and grain with 〈1 1 1〉||TA and grains oriented close to a Schmid factor maximum contained deformation twins.

  3. Deformation localization and dislocation channel dynamics in neutron-irradiated austenitic stainless steels

    The dynamics of deformation localization and dislocation channel formation were investigated in situ in a neutron-irradiated AISI 304 austenitic stainless steel and a model 304-based austenitic alloy by combining several analytical techniques including optic microscopy and laser confocal microscopy, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy (TEM). Channel formation was observed at ∼70% of the polycrystalline yield stress of the irradiated materials (σ0.2). It was shown that triple junction points do not always serve as a source of dislocation channels; at stress levels below the σ0.2, channels often formed near the middle of the grain boundary. For a single grain, the role of elastic stiffness value (Young’s modulus) in channel formation was analyzed; it was shown that in the irradiated 304 steels the initial channels appeared in “soft” grains with a high Schmid factor located near “stiff” grains with high elastic stiffness. The spatial organization of channels in a single grain was analyzed; it was shown that secondary channels operating in the same slip plane as primary channels often appeared at the middle or at one-third of the way between primary channels. The twinning nature of dislocation channels was analyzed for grains of different orientation using TEM. In the AISI 304 steel, channels in grains oriented close to 〈0 0 1〉||TA (tensile axis) and 〈1 0 1〉||TA were twin free and grain with 〈1 1 1〉||TA and grains oriented close to a Schmid factor maximum contained deformation twins

  4. Micro-mechanical investigation for effects of helium on grain boundary fracture of austenitic stainless steel

    Highlights: • We investigate effects of helium on grain boundary fracture of stainless steel. • We conduct micro-tensile tests on helium ion-implanted type 316 stainless steel. • Brittle fracture occur on grain boundaries on which small bubbles formed densely. • Formation of bubbles both on grain boundary and in matrix promotes brittle fracture. • Grain boundary segregated helium atoms may have a role in grain boundary fracture. - Abstract: Effects of helium (He) on grain boundary (GB) fracture of austenitic stainless steel were investigated by micro-tensile tests. Micro-bicrystal tensile specimens were fabricated for non-coincidence site lattice boundaries of He ion-irradiated 316 stainless steel by focused ion beam (FIB) micro-processing. Micro-tensile tests were conducted in a vacuum at room temperature in the FIB system. Specimens containing more than 2 at.% He fractured at GBs. The criteria for brittle fracture occurrence on GBs were: (1) He concentrations higher than 2 at.%; (2) formation of He bubbles on the GBs with less than a 5 nm spacing; and (3) matrix hardening to more than 4.6 GPa (nano-indentation hardness). The fracture stress of GB brittle fracture was lower for a specimen with higher He concentration while the size and areal density of the GB He bubbles were the same. The specimens that contained 10 at.% He and had been annealed at 923 K after irradiation fractured at the GB nominally in a brittle manner; however the inter-bubble matrix at the GB experienced ductile fracture. The annealing caused He bubbles to grow but decreased the areal density so that the spacing of the GB He bubbles widened and the hardness decreased, therefore the fracture mode changed from brittle to ductile. The findings revealed that He promotes GB fracture by weakening the GB strength and hardening the matrix due to the formation of He bubbles both on GBs and in the matrix. In addition, the findings suggested that GB segregated He atoms may have a role in GB

  5. Corrosion behavior of cold-worked austenitic stainless steels in liquid lead–bismuth eutectic

    Kurata, Yuji, E-mail: kurata.yuji@jaea.go.jp

    2014-05-01

    Highlights: • Austenitic stainless steels cold-worked up to 50% were exposed to lead–bismuth. • Lead–bismuth with the low oxygen concentration caused deep ferritization at 550 °C. • Ferritization also occurred at 550 °C during 3000 h under the high oxygen condition. • Cold working accelerated ferritization and Pb–Bi penetration without a protective film. • Attention should be also focused on the cold-working effect on corrosion behavior. - Abstract: The effect of cold working on the corrosion behavior of austenitic stainless steels in liquid lead–bismuth eutectic (LBE) was studied to develop accelerator-driven systems for the transmutation of long-lived radioactive wastes and lead–bismuth cooled fast reactors. Corrosion tests on solution-treated, 20% cold-worked and 50% cold-worked 316SS and JPCA (15Cr–15Ni–Ti) were conducted in oxygen-controlled LBE. Slight ferritization caused by Ni dissolution and Pb–Bi penetration were observed for all specimens in the corrosion test conducted at 500 °C for 1000 h in liquid LBE with an intermediate oxygen concentration (1.4 × 10{sup −7} wt.%). In the corrosion test performed at 550 °C for 1000 h in liquid LBE with a low oxygen concentration (4.2 × 10{sup −9} wt.%), the depth of the ferritization of 316SS and JPCA increased with the extent of cold working. Only oxidation was observed in the corrosion test that was performed at 550 °C for 1000 h in liquid LBE with a high oxygen concentration (approximately 10{sup −5} wt.%). Cold working accelerated the formation of the double layer oxide and increased the thickness of the oxide layer slightly. In contrast, the ferritization accompanied by Pb–Bi penetration was widely observed with oxidation for all specimens corrosion tested at 550 °C for 3000 h under the high-oxygen condition. Cold working increased the depth of the ferritization of 316SS and JPCA. It is considered that cold working accelerated the ferritization and Pb–Bi penetration

  6. An investigation on microstructure and mechanical propertiesof a Nb-microalloyed nano/ultrafine grained 201 austenitic stainless steel

    The present study was aimed to investigate the mechanical properties of a nano/ultrafine grained Nb-containing 201 austenitic stainless steel. For this purpose, 90% cold rolled sheets with fully martensitic microstructure were isothermally annealed at 900 °C for different times of 1 to 1800 s, leading to the reversion of strain- induced α′-martensite to austenite and significant grain refinement. Ferritescopy, X-ray diffractometery and optical/electron microscopy techniques along with hardness measurements and tensile tests were used to study the evolution in microstructure and mechanical properties in the course of annealing. It was found that heavy cold-rolling promoted formation of Nb-rich carbonitrides which effectively retarded the growth of fine reverted austenite grains. The obtained results showed that the complete transformation of martensite to austenite took about 60 s with the corresponding austenite grain size of about 90 nm. This sample had an ultrahigh yield strength of 1170 MPa, which was almost four times higher than that of the raw material and outstanding elongation of 37%. Further, the true stress–strain curves of the reversion annealed samples revealed two distinct uniform elongation stages (stage I and stage II), whereas, the onset of stage II was concurrent with pronounced strain hardening. This was related to the sharp increase in the formation of α′-martensite upon tensile straining

  7. Investigation on the Behavior of Austenite and Ferrite Phases at Stagnation Region in the Turning of Duplex Stainless Steel Alloys

    Nomani, J.; Pramanik, A.; Hilditch, T.; Littlefair, G.

    2016-06-01

    This paper investigates the deformation mechanisms and plastic behavior of austenite and ferrite phases in duplex stainless steel alloys 2205 and 2507 under chip formation from a machine turning operation. SEM images and EBSD phase mapping of frozen chip root samples detected a build-up of ferrite bands in the stagnation region, and between 65 and 85 pct, more ferrite was identified in the stagnation region compared to austenite. SEM images detected micro-cracks developing in the ferrite phase, indicating ferritic build-up in the stagnation region as a potential triggering mechanism to the formation of built-up edge, as transgranular micro-cracks found in the stagnation region are similar to micro-cracks initiating built-up edge formation. Higher plasticity of austenite due to softening under high strain is seen responsible for the ferrite build-up. Flow lines indicate that austenite is plastically deforming at a greater rate into the chip, while ferrite shows to partition most of the strain during deformation. The loss of annealing twins and activation of multiple slip planes triggered at high strain may explain the highly plastic behavior shown by austenite.

  8. Investigation on the Behavior of Austenite and Ferrite Phases at Stagnation Region in the Turning of Duplex Stainless Steel Alloys

    Nomani, J.; Pramanik, A.; Hilditch, T.; Littlefair, G.

    2016-04-01

    This paper investigates the deformation mechanisms and plastic behavior of austenite and ferrite phases in duplex stainless steel alloys 2205 and 2507 under chip formation from a machine turning operation. SEM images and EBSD phase mapping of frozen chip root samples detected a build-up of ferrite bands in the stagnation region, and between 65 and 85 pct, more ferrite was identified in the stagnation region compared to austenite. SEM images detected micro-cracks developing in the ferrite phase, indicating ferritic build-up in the stagnation region as a potential triggering mechanism to the formation of built-up edge, as transgranular micro-cracks found in the stagnation region are similar to micro-cracks initiating built-up edge formation. Higher plasticity of austenite due to softening under high strain is seen responsible for the ferrite build-up. Flow lines indicate that austenite is plastically deforming at a greater rate into the chip, while ferrite shows to partition most of the strain during deformation. The loss of annealing twins and activation of multiple slip planes triggered at high strain may explain the highly plastic behavior shown by austenite.

  9. Parameters influencing the transgranular stress corrosion cracking behaviour of austenitic stainless steels in systems conveying reactor coolant

    During replacement of an auxiliary system in the German PWR KKS (NPP Stade) a damage was detected in a valve housing and in the connected piping both made from stabilised austenitic stainless steel. During operation stagnant conditions are present in this area. Based on the failure analysis chloride induced stress corrosion cracking (SCC) was found as the dominating root cause. In the open literature many cases of corrosion observed in the water/steam interface in valve components as well as in adjacent portions of auxiliary circuits made of un-stabilized stainless steels are mentioned. A common feature of the reported cases is that transgranular cracking was found. Extensive laboratory investigations revealed that non-stabilised austenitic stainless steels are also sensitive to transgranular cracking in boric acid solutions particularly in concentrated solutions. Often these solutions are contaminated with chlorides and/or oxygen is present. Taking into account the literature data the question could arise whether the above mentioned cracking may be also caused by boric acid attack. Thus, for stabilised stainless steels laboratory exposure tests at 80 C in saturated aerated boric acid solution and at 300 C in (at 100 C) saturated, oxygen free boric acid solution have been performed. Double-U-bend specimens and wedge loaded 1T-CT specimens made of Ti- and Nb-stabilised austenitic stainless steels were used. The results revealed no evidence of crack initiation and crack growth. Based on the laboratory results and the literature data an attempt is undertaken to separate parameters influencing chloride induced SCC from the effect of boric acid. (authors)

  10. Formation of Inclusions in Ti-Stabilized 17Cr Austenitic Stainless Steel

    Yin, Xue; Sun, Yanhui; Yang, Yindong; Bai, Xuefeng; Barati, Mansoor; Mclean, Alex

    2016-04-01

    The behavior and formation mechanisms of inclusions in Ti-stabilized, 17Cr Austenitic Stainless Steel produced by the ingot casting route were investigated through systematic sampling of liquid steel and rolled products. Analysis methods included total oxygen and nitrogen contents, optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results indicate that the composition of inclusions was strongly dependent on the types of added alloying agents. During the AOD refining process, after the addition of ferrosilicon alloy and electrolytic manganese, followed by aluminum, the composition of inclusions changed from manganese silicate-rich inclusions to alumina-rich inclusions. After tapping and titanium wire feeding, pure TiN particles and complex inclusions with Al2O3-MgO-TiO x cores containing TiN were found to be the dominant inclusions when [pct Ti] was 0.307 mass pct in the molten steel. These findings were confirmed by thermodynamic calculations which indicated that there was a driving force for TiN inclusions to be formed in the liquid phase due to the high contents of [Ti] and [N] in the molten steel. From the start of casting through to the rolled bar, there was no further change in the composition of inclusions compared to the titanium addition stage. Stringer-shaped TiN inclusions were observed in the rolled bar. These inclusions were elongated along the rolling direction with lengths varying from 17 to 84 µm and could have a detrimental impact on the corrosion resistance as well as the mechanical properties of the stainless steel products.

  11. Study of stress relief cracking in titanium stabilized austenitic stainless steel

    The heat affected zone (HAZ) of titanium stabilised austenitic stainless steel welds (AISI 321) may exhibit a serious form of intercrystalline cracking during service at high temperature. This type of cracking, called 'stress relief cracking', is known to be due to work hardening but also to ageing: a fine and abundant intragranular Ti(C,N) precipitation appears near the fusion line and modifies the mechanical behaviour of the HAZ. This study aims to better know the accused mechanism and to succeed in estimating the risk of such cracking in welded junctions of 321 stainless steel. To analyse this embrittlement mechanism, and to assess the lifetime of real components, different HAZ are simulated by heat treatments applied to the base material which is submitted to various cold rolling and ageing conditions in order to reproduce the HAZ microstructure. Then, we study the effects of work hardening and ageing on the titanium carbide precipitation, on the mechanical (tensile and creep) behaviour of the resulting material and on its stress relief cracking sensitivity. It is shown that work hardening is the main parameter of the mechanism and that ageing do not favour crack initiation although it leads to titanium carbide precipitation. The role of this precipitation is also discussed. Moreover, a creep damage model is identified by a local approach to fracture. Materials sensitive to stress relief cracking are selected. Then, creep tests are carried out on notched bars in order to quantify the intergranular damage of these different materials; afterwards, these measurements are combined with calculated mechanical fields. Finally, it is shown that the model gives good results to assess crack initiation for a compact tension (CT) specimen during relaxation tests, as well as for a notched tubular specimen tested at 600 deg. C under a steady torque. (author)

  12. Thermal fatigue of austenitic stainless steel: influence of surface conditions through a multi-scale approach

    Some cases of cracking of 304L austenitic stainless steel components due to thermal fatigue were encountered in particular on the Residual Heat Removal Circuits (RHR) of the Pressurized Water Reactor (PWR). EDF has initiated a R and D program to understand assess the risks of damage on nuclear plant mixing zones. The INTHERPOL test developed at EDF is designed in order to perform pure thermal fatigue test on tubular specimen under mono-frequency thermal load. These tests are carried out under various loadings, surface finish qualities and welding in order to give an account of these parameters on crack initiation. The main topic of this study is the research of a fatigue criterion using a micro:macro modelling approach. The first part of work deals with material characterization (stainless steel 304L) emphasising the specificities of the surface roughness link with a strong hardening gradient. The first results of the characterization on the surface show a strong work-hardening gradient on a 250 microns layer. This gradient does not evolved after thermal cycling. Micro hardness measurements and TEM observations were intensively used to characterize this gradient. The second part is the macroscopic modelling of INTHERPOL tests in order to determine the components of the stress and strain tensors due to thermal cycling. The third part of work is thus to evaluate the effect of surface roughness and hardening gradient using a calculation on a finer scale. This simulation is based on the variation of dislocation density. A goal for the future is the determination of the fatigue criterion mainly based on polycrystalline modelling. Stocked energy or critical plane being available that allows making a sound choice for the criteria. (author)

  13. Study of crack initiation in low-cycle fatigue of an austenitic stainless steel

    The material studied is an austenitic stainless steel, that is widely used in nuclear equipment for its very high corrosion resistance combined to good mechanical properties. Although crack initiation is proved to play an important role in fatigue, its mechanisms have not been fully understood. Some crack initiation criteria based on physical mechanisms of plastic deformation have been defined. However, these criteria are not easy to use and valid, as they need local variables at the grain scale. The present study aims at establishing a crack initiation criterion in low-cycle fatigue, which should be usable under variable amplitude loading conditions. Tension-compression fatigue tests were first carried out to characterize the mechanical behavior of the stainless steel AISI 316L. The mechanical behavior was simulated using a self-consistent model using a crystalline plastic law based on dislocation densities. The evolution of surface damage was observed during a fatigue test using an in situ optical microscopic device. Cracks were analyzed after 2000 cycles and their crystallographic characteristics calculated. As surface grains exhibit larger strain because they are less constraint by neighbor grains, a specific numerical frame is necessary to determine stress state in surface grains. A localization law specific to surface grains under cyclic loading was identified from finite element simulations. The proposed form needs an intergranular accommodation variable, on the pattern of the localization law of Cailletaud-Pilvin. Stress-strain state in surface grains was simulated. Potential indicators for crack initiation were then compared on a same experimental data base. Indicators based on the equivalent plastic strain were found to be suitable indicators of fatigue damage. (author)

  14. Investigation into the high temperature oxidation of Cu-bearing austenitic stainless steel using simultaneous electron backscatter diffraction-energy dispersive spectroscopy analysis

    Highlights: •EBSD–EDS simultaneous analysis was introduced for the complex oxide scale analysis. •High temperature oxidation of Cu-bearing austenitic stainless steel was investigated. •Multi-layered external and internal oxide scales were developed at 700 °C. •Copper addition induced spinel structured oxide solid solution at the oxide surface. -- Abstract: The oxide scales of high-alloyed steel are composed of complex phases that are difficult to differentiate with conventional analysis techniques. Here, we used simultaneous electron backscatter diffraction (EBSD) and energy dispersive X-ray spectroscopy (EDS) to analyze the complex oxide layers formed on a Cu-bearing austenitic stainless steel. Multi-layered structures of external hematite, external magnetite, internal chromite, internal chromium oxide, and austenite matrix were clearly identified using the simultaneous EBSD–EDS analysis technique. The addition of Cu into the austenitic stainless steel induced spinel structured oxide formation at the top surface of the external oxide

  15. Cracking behavior of thermally aged and irradiated CF-8 cast austenitic stainless steel

    Chen, Y.; Alexandreanu, B.; Chen, W.-Y.; Natesan, K.; Li, Z.; Yang, Y.; Rao, A. S.

    2015-11-01

    To assess the combined effect of thermal aging and neutron irradiation on the cracking behavior of CF-8 cast austenitic stainless steel, crack growth rate (CGR) and fracture toughness J-R curve tests were carried out on compact-tension specimens in high-purity water with low dissolved oxygen. Both unaged and thermally aged specimens were irradiated at ∼320 °C to 0.08 dpa. Thermal aging at 400 °C for 10,000 h apparently had no effect on the corrosion fatigue and stress corrosion cracking behavior in the test environment. The cracking susceptibility of CF-8 was not elevated significantly by neutron irradiation at 0.08 dpa. Transgranular cleavage-like cracking was the main fracture mode during the CGR tests, and a brittle morphology of delta ferrite was often seen on the fracture surfaces at the end of CGR tests. The fracture toughness J-R curve tests showed that both thermal aging and neutron irradiation can induce significant embrittlement. The loss of fracture toughness due to neutron irradiation was more pronounced in the unaged than aged specimens. After neutron irradiation, the fracture toughness values of the unaged and aged specimens were reduced to a similar level. G-phase precipitates were observed in the aged and irradiated specimens with or without prior aging. The similar microstructural changes resulting from thermal aging and irradiation suggest a common microstructural mechanism of inducing embrittlement in CF-8.

  16. Influence of delta ferrite content and welding variables on notch toughness of austenitic stainless steel weldments

    Two series of austenitic stainless steel weld deposits are evaluated to explore the separate contributions of delta ferrite content and welding variables to apparent notch toughness. Charpy-V and Dynamic Tear test determinations are used for weld deposit comparisons. The investigation represents the first part of a two part study of variable weld notch toughness in preirradiation and postirradiation conditions for the temperature range 750F (240C) to 11000F (5930C). Weld Series 1, represented by four 21/2-in. thick AISI Type 308 weld deposits (shielded metal arc) exhibited delta ferrite contents ranging from ferrite number 5.2 to 19.0. Variations in delta ferrite content within this range did not appear to be a major factor in observed toughness trends. Weld Series 2, formed of six 1-in. thick AISI Type 316 weld deposits (submerged arc), indicated that welding parameters and minor differences in flux lot formulations can contribute to variable notch toughness. Initial radiation tests demonstrate that a fluence of 8 to 9 x 1019 n/cm2 greater than 0.1 MeV at 500 to 5500F (260 to 2880C) can produce large reductions in Charpy-V notch ductility for Types 308 and 316 weld deposits

  17. Coarsening of TiC in austenitic stainless steel - experiments and simulations in comparison

    One way to increase the creep properties and corrosion resistance of austenitic stainless steels is to alloy with titanium, which forms small particles of TiC. When the steels are used at high temperature these particles undergo coarsening and the creep-resistance decreases. There exist two size distributions of TiC, one with sparsely distributed particles of micrometer size and a secondary one of densely distributed particles with sizes of a tenth of a micrometer. The sizes of the secondary TiC have been determined by transmission electron microscopy on samples of an ASTM 316Ti steel that have been heat-treated at 900 C for different times up to 6600 h. The measurements were compared with coarsening simulations with the DICTRA software, which takes into account the multicomponent effects on thermodynamics and diffusion. A good agreement between experiments and calculations is achieved if the interfacial energy, the only adjustable parameter in the simulations, is assumed to be round 0.2 J m-2. (orig.)

  18. Modeling of cavity swelling-induced embrittlement in irradiated austenitic stainless steels

    During long-time neutron irradiation occurred in Pressurized Water Reactors (PWRs), significant changes of the mechanical behavior of materials used in reactor core internals (made of 300 series austenitic stainless steels) are observed, including irradiation induced hardening and softening, loss of ductility and toughness. So far, much effect has been made to identify radiation effects on material microstructure evolution (dislocations, Frank loops, cavities, segregation, etc.). The irradiation-induced cavity swelling, considered as a potential factor limiting the reactor lifetime, could change the mechanical properties of materials (plasticity, toughness, etc.), even lead to a structure distortion because of the dimensional modifications between different components. The principal aim of the present PhD work is to study qualitatively the influence of cavity swelling on the mechanical behaviors of irradiated materials. A micromechanical constitutive model based on dislocation and irradiation defect (Frank loops) density evolution has been developed and implemented into ZeBuLoN and Cast3M finite element codes to adapt the large deformation framework. 3D FE analysis is performed to compute the mechanical properties of a polycrystalline aggregate. Furthermore, homogenization technique is applied to develop a Gurson-type model. Unit cell simulations are used to study the mechanical behavior of porous single crystals, by accounting for various effects of stress triaxiality, of void volume fraction and of crystallographic orientation, in order to study void effect on the irradiated material plasticity and roughness at polycrystalline scale. (author)

  19. Stress corrosion cracking susceptibility of austenitic stainless steels in supercritical water conditions

    Within the 6th Framework Program HPLWR-2 project (High Performance Light Water Reactor - Phase 2), stress corrosion cracking (SCC) susceptibilities of selected austenitic stainless steels, 316L and 316NG, were studied in supercritical water (SCW) with the aim to identify and describe the specific failure mechanisms prevailing during slow strain-rate tensile (SSRT) tests in ultra-pure demineralised SCW water solution. The SSRT tests were performed using a step-motor controlled loading device in an autoclave at 350 deg. C, 500 deg. C and 550 deg. C. Besides water temperature, the pressure, the oxygen content and the strain rate (resp. crosshead speed) were varied in the series of tests. The specimens SSRT tested to failure were subjected to fractographic analysis, in order to characterise the failure mechanisms. The fractography confirmed that failure was due to a combination of transgranular SCC and transgranular ductile fracture. The share of SCC and ductile fracture in the failure process of individual specimens was affected by the parameters of the SSRT tests, so that the environmental influence on SCC susceptibility could be assessed, in particular, the SCC sensitising effects of increasing oxygen content, decreasing strain rate and increasing test temperature. (author)

  20. Effect of grain size in compression deformation on the microstructural evolution of an austenitic stainless steel

    Rehrl, Christian, E-mail: christian.rehrl@oeaw.ac.at [Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Jahnstr. 12, 8700 Leoben (Austria); Kleber, Siegfried [Boehler Edelstahl GmbH, Kapfenberg, Mariazeller Str. 25, 8605 Kapfenberg (Austria); Renk, Oliver; Pippan, Reinhard [Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Jahnstr. 12, 8700 Leoben (Austria)

    2012-04-01

    Highlights: Black-Right-Pointing-Pointer Increasing the starting grain size retards the dynamic recrystallization process. Black-Right-Pointing-Pointer Forming compatibility is achieved by grain fragmentation in coarser structures. Black-Right-Pointing-Pointer The stored GND density increases for smaller starting grain sizes. Black-Right-Pointing-Pointer Nucleation process of new grains is driven by the stored deformation energy. Black-Right-Pointing-Pointer Cast structured state promotes dynamic recovery as softening mechanism. - Abstract: The influence of initial grain size on the dynamic recrystallization behavior has been investigated in a commercial austenitic stainless steel. Compression tests were performed at constant temperatures of 810, 980 and 1150 Degree-Sign C at an average strain rate {epsilon}{sup .} of 0.01 s{sup -1} and 0.1 s{sup -1}. In order to capture the microstructural evolution after the deformation the electron back scatter diffraction technique (EBSD) was used. The results show that nucleation of new grains is strongly grain size dependent. Increasing the grain size of the material reduces the stored energy measured in terms of kernel average misorientation, well known as driving force for dynamic recrystallization. This leads to the problem of grain refinement in coarse structured materials. Applying large plastic strains or using static recrystallization in a double hit forming process seems promising for an efficient refinement strategy.