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Heung Nam Han - One of the best experts on this subject based on the ideXlab platform.
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Crystal plasticity finite element modeling of mechanically Induced Martensitic Transformation (MIMT) in metastable austenite
US, 2018Co-Authors: Mg Lee, Sj Kim, Heung Nam HanAbstract:A new crystal plasticity model incorporating the mechanically Induced Martensitic Transformation in metastable austenitic steel has been formulated and implemented into the finite element analysis. The kinetics of martensite Transformation is modeled by taking into consideration of a nucleation-controlled phenomenon, where each potential Martensitic variant based on Kurdjumov-Sachs (KS) relationship has different nucleation probability as a function of the interaction energy between externally applied stress and lattice deformation. Therefore, the transformed volume fractions are determined following selective variants given by the crystallographic orientation of austenitic matrix and applied stress in the frame of the crystal plasticity finite element. The developed finite element program is capable of considering the effect of volume change by the Bain deformation and the lattice-invariant shear during the Martensitic Transformation by effectively modifying the evolution of plastic deformation gradient of the conventional rate-dependent crystal plasticity finite element. The validation of the proposed model has been carried out by comparing with the experimentally measured data under simple loading conditions. Good agreements with the measurements for the stress-strain responses, transformed martenstic volume fractions and the influence of strain rate on the deformation behavior will enable the model to be promising for the future applications to the real forming process of the TRIP aided steel. (C) 2009 Elsevier Ltd. All rights reserved.X1555
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investigation of strain Induced Martensitic Transformation in metastable austenite using nanoindentation
Scripta Materialia, 2010Co-Authors: Taehong Ahn, Donghwan Kim, Hongbin Bei, E P George, Heung Nam HanAbstract:Strain-Induced Martensitic Transformation of metastable austenite was investigated by nanoindentation of individual austenite grains in multi-phase steel. A cross-section prepared through one of these indented regions using focused ion beam milling was examined by transmission electron microscopy. The presence of martensite underneath the indent indicates that the pop-ins observed on the load-displacement curve during nanoindentation correspond to the onset of strain-Induced Martensitic Transformation. The pop-ins can be understood as resulting from the selection of a favorable martensite variant during nanoindentation.
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crystal plasticity finite element modeling of mechanically Induced Martensitic Transformation mimt in metastable austenite
International Journal of Plasticity, 2010Co-Authors: Myounggyu Lee, Sungjoon Kim, Heung Nam HanAbstract:Abstract A new crystal plasticity model incorporating the mechanically Induced Martensitic Transformation in metastable austenitic steel has been formulated and implemented into the finite element analysis. The kinetics of martensite Transformation is modeled by taking into consideration of a nucleation-controlled phenomenon, where each potential Martensitic variant based on Kurdjumov–Sachs (KS) relationship has different nucleation probability as a function of the interaction energy between externally applied stress and lattice deformation. Therefore, the transformed volume fractions are determined following selective variants given by the crystallographic orientation of austenitic matrix and applied stress in the frame of the crystal plasticity finite element. The developed finite element program is capable of considering the effect of volume change by the Bain deformation and the lattice-invariant shear during the Martensitic Transformation by effectively modifying the evolution of plastic deformation gradient of the conventional rate-dependent crystal plasticity finite element. The validation of the proposed model has been carried out by comparing with the experimentally measured data under simple loading conditions. Good agreements with the measurements for the stress–strain responses, transformed Martensitic volume fractions and the influence of strain rate on the deformation behavior will enable the model to be promising for the future applications to the real forming process of the TRIP aided steel.
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design method for trip aided multiphase steel based on a microstructure based modelling for Transformation Induced plasticity and mechanically Induced Martensitic Transformation
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009Co-Authors: Heung Nam Han, Gyosung Kim, Ohjoon KwonAbstract:In recent years, for automotive applications, the need for new advanced high-strength sheet steels (AHSSs) with high ductility has rapidly increased. This is mainly related to the need for more fuel-efficient (and therefore more environmentally friendly) cars, and the increasing consumer demand for safer vehicles. In this research, the Transformation-Induced plasticity (TRIP) that accompanies the mechanically Induced Martensitic Transformation (MIMT) in TRIP-aided multiphase steel was analyzed. The analysis was performed using a computational model that takes the ductile fracture during tensile deformation into account. The TRIP and MIMT phenomena were calculated using the concept of variant selection, which is based on the Kurdjumov–Sachs (K–S) orientation relationship. To consider the localization of the plastic flow in the deforming material, the increase in void nucleation due to the Martensitic Transformation and the void growth based on the yield criterion for porous material were studied. The feasibility of the extra advanced high-strength sheet steel (X-AHSS) was assessed by analyzing the results obtained using various initial volume fractions and various stabilities of the retained austenite in the TRIP-aided multiphase steel. Subsequently, the optimum volume fraction and stability of the retained austenite in the TRIP-aided multiphase steel could be determined.
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a microstructure based analysis for Transformation Induced plasticity and mechanically Induced Martensitic Transformation
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Heung Nam Han, Chang Gil Lee, Dongwoo Suh, Sungjoon KimAbstract:Abstract The Transformation-Induced plasticity (TRIP) accompanying the mechanically Induced Martensitic Transformation (MIMT) in metastable austenitic steel was analyzed with a microstructure-based computational model which takes into account void nucleation and growth. The kinetics of the Martensitic Transformation was modeled using the concept of variant selection, which considers that the probability of nucleation occurring at a given site can be derived for each Martensitic variant as a function of the interaction energy between the externally applied stress state and the lattice deformation based on the Kurdjumov–Sachs (K–S) orientation relationship. To consider the localization of the plastic flow in the deforming material, the increase in void nucleation due to the Martensitic Transformation and the void growth based on the Gurson–Tvergaard yield criterion were adopted. The plastic instability condition was employed to predict the ductility of metastable austenitic steel. The calculated results were compared with the experimental data measured for 301 stainless steel subjected to uniaxial tension. The major cause of the enhancement of the ductility in the TRIP-aided steel was discussed from the viewpoint of the effect of the TRIP strain and the phase-hardening due to the MIMT. In addition, the evolution of the crystallographic texture during deformation and phase Transformation was predicted by using the combination of the proposed model and the crystal plasticity.
Yandong Wang - One of the best experts on this subject based on the ideXlab platform.
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ductile ti rich high entropy alloy controlled by stress Induced Martensitic Transformation and mechanical twinning
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2019Co-Authors: Lu Wang, Yandong Wang, Xidong HuiAbstract:Abstract Body centered cubic type of refractory high-entropy alloys (HEAs) have high strength at room and elevated temperatures, but suffer from the strength-ductility trade-off dilemma, making their application for structural materials severely impeded. In this article, we report a strategy to break this puzzle by introducing successive stress-Induced Martensitic Transformation (SIMT) and mechanical twinning in Ti-rich refractory TiZrHfAlNb HEA via controlling the grain size. The HEA exhibits superior ductility featured by fracture and uniform elongation as high as 40% and 33%, respectively, at ambient temperature. The plasticizing and toughening mechanisms for the HEA with different grain sizes can be described as following: in the HEA with small grains, the SIMT takes place followed by the martensite variants reorientation; in that with coarse grains, mechanical twinning of α″ phase comes up with the preferential orientation relationship of [111]β//[101]α″M//[-10-1]α″T after the SIMT.
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superelastic effect in ti rich high entropy alloys via stress Induced Martensitic Transformation
Scripta Materialia, 2019Co-Authors: Lu Wang, Xidong Hui, Yandong WangAbstract:Abstract This letter reports an outstanding superelastic effect in Ti-rich TiZrHfAlNb high entropy alloys for the first time, which is exhibited by comprehensive combination of the maximum total recovery strain, fully recoverable strain and corresponding tensile strength up to 5.2%, 4.0% and 900 MPa, respectively. It has been confirmed that these alloys are only composed of metastable β and martensite α″ phase, and ω phase is suppressed. The in situ X-ray diffraction experiment reveals that reversible stress-Induced Martensitic Transformation between β ↔ α″ endows the alloys superelasticity, while the plastic deformation and reorientation of martensite inhibit the recovery phase Transformation.
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enhanced work hardening and toughening via contiguous stress Induced Martensitic Transformation and mechanical twinning in ti zr hf nb al high entropy alloys
Social Science Research Network, 2019Co-Authors: Lu Wang, Yandong Wang, Xidong HuiAbstract:Refractory high entropy alloys (HEAs) have been considered as candidate alloys for next-generation high-temperature applications, but encounter the strength-ductility trade-off dilemma. In this article, we proposed a strategy of strengthening and toughening for Ti-rich refractory HEAs by the initiation of Martensitic Transformation and mechanical twinning successively. Three Ti-Zr-Hf-Al-Nb HEAs with the tensile strength and elongation up to 1167 MPa and 34%, respectively, which are superb among most of the reported BCC HEAs, have been successfully prepared. By using the SEM, TEM, HE-XRD and EBSD setups, the as-cast and fully recrystallized microstructures for these HEAs were characterized. And the mechanisms for the Martensitic Transformation and mechanical twinning in these HEAs are deeply explored. It has been clarified that under the as-cast and fully recrystallized state, these HEAs are mainly composed of β phase and a little of α′′ martensite phase. Stress-Induced Martensitic Transformation took place in favor of special variants with the [110]β//LD, which has the maximum Transformation strain of 7.8%. At the later stage, mechanical twinning α′′ phase have formed between the α′′ laths and the β matrix with the preferential orientation relationship of [111]β//[101]α′′M//[-10-1]α′′T.
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reversible deformation Induced Martensitic Transformation in al0 6cocrfeni high entropy alloy investigated by in situ synchrotron based high energy x ray diffraction
Acta Materialia, 2017Co-Authors: Lu Wang, Yandong Wang, Zhihua Nie, Fuchi Wang, Yunfei Xue, Jinlian Zhou, Tangqing Cao, Yang RenAbstract:Abstract The micro-mechanical behavior of Al 0.6 CoCrFeNi high-entropy alloy during tensile deformation was investigated using an in situ synchrotron-based high-energy X-ray diffraction technique. The alloy consisted of face-center-cubic (FCC) and body-center-cubic-based (BCC-based) structure accompanied by a small amount of σ phase. The FCC phase yielded prior to the BCC-based phase during the tensile loading, and the BCC-based phase bore more stress partition during the plastic deformation stage in spite of only ∼23% volume fraction. A reversible deformation-Induced Martensitic Transformation from the BCC-based phase to orthorhombic phase was observed during the plastic deformation stage. The Transformation preferentially occurred in the grains with an orientation of B-[001]//loading direction and B-[110]//transverse direction. The study characterized the micro-mechanical behavior of this alloy, and the reversible Martensitic Transformation is believed to be beneficial to the fracture toughness of such alloys.
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in situ investigation of stress Induced Martensitic Transformation in ti nb binary alloys with low young s modulus
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016Co-Authors: L L Chang, Yandong WangAbstract:Abstract Microstructure evolution, mechanical behaviors of cold rolled Ti–Nb alloys with different Nb contents subjected to different heat treatments were investigated. Optical microstructure and phase compositions of Ti–Nb alloys were characterized using optical microscopy and X-ray diffractometre, while mechanical behaviors of Ti–Nb alloys were examined by using tension tests. Stress-Induced Martensitic Transformation in a Ti–30 at%Nb binary alloy was in-situ explored by synchrotron-based high-energy X-ray diffraction (HE-XRD). The results obtained suggested that mechanical behavior of Ti–Nb alloys, especially Young's modulus was directly dependent on chemical compositions and heat treatment process. According to the results of HE-XRD, α″-V1 martensite generated prior to the formation of α″-V2 during loading and a partial reversible Transformation from α″-V1 to β phase was detected while α″-V2 tranformed to β completely during unloading.
Akinobu Shibata - One of the best experts on this subject based on the ideXlab platform.
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crystallographic orientation dependence of deformation Induced Martensitic Transformation of 1 3 gpa class 0 6 c bainitic steel with retained austenite
Scripta Materialia, 2021Co-Authors: Akinobu Shibata, Kohsaku Ushioda, Yuuji Kimura, Takahito Ohmura, Tadanobu InoueAbstract:Abstract The crystallographic orientation dependence of the stability of retained austenite against deformation-Induced Martensitic Transformation in 0.6 %C alloyed steel was studied. A bainite structure with about 40 % volume fraction of retained austenite was successfully obtained by austempering. Tensile testing at room temperature revealed a high strength of 1.3 GPa with adequate elongation. A change in texture of retained austenite brought about by tensile deformation to several strains was measured. Deformation-Induced Martensitic Transformation occurred preferentially in grains with the tensile axis nearly parallel to fcc. The orientation dependence of the Martensitic Transformation was compatible with that of the {1-11}fcc fcc shear deformation which can be regarded as the first primitive process for the Martensitic Transformation as proposed by Bogers and Burgers. This compatibility is discussed in terms of the elastically normalized Schmid factor for the Transformation dislocation to act for the lattice change.
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crystallographic orientation dependence of deformation Induced Martensitic Transformation of 1 3 gpa class 0 6 c bainitic steel with retained austenite
Social Science Research Network, 2020Co-Authors: Akinobu Shibata, Kohsaku Ushioda, Yuuji Kimura, Takahito Ohmura, Tadanobu InoueAbstract:The crystallographic orientation dependence of the stability of retained austenite against deformation-Induced Martensitic Transformation in 0.6%C alloyed steel was studied. A bainite structure with about 40% volume fraction of retained austenite was successfully obtained by austempering. Tensile testing at room temperature revealed a high strength of 1.3 GPa with adequate elongation. A change in texture of retained austenite brought about by tensile deformation to several strains was measured. Deformation-Induced Martensitic Transformation occurred in grains with the tensile axis nearly parallel to fcc was significantly stabilized. The orientation dependence of the Martensitic Transformation was compatible with that of the {1-11}fcc fcc shear deformation which can be regarded as the first primitive process for the Martensitic Transformation as proposed by Bogers and Burgers. This compatibility is discussed in terms of the elastically normalized Schmid factor for the Transformation dislocation to act for the lattice change.
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relationship between local stress field in austenite and variant selection in deformation Induced Martensitic Transformation in fe 24ni 0 3c alloy
Materials Today: Proceedings, 2015Co-Authors: A Matsumoto, M Chen, Akinobu Shibata, T Miyazawa, M Sato, Nobuhiro TsujiAbstract:Abstract The present study investigated the relationship between local stress fields in austenite grains and variant selections in deformation-Induced Martensitic Transformation in an Fe-24Ni-0.3C (mass %) polycrystalline alloy. The local stress fields in austenite grains were measured by synchrotron radiation X-ray diffraction in SPring-8. We examined the variant selection rule based on the interaction energy between applied stress and shape deformation accompanying Transformation (according to Patel and Cohen model). The results indicated that the formed martensite variants had positive interaction energy calculated using either the local stress field measured or the macroscopic tensile stress as the applied stress. The interaction energy criterion using the measured local stress field could show the better correlation with the observed variant selection in deformation-Induced Martensitic Transformation than that using uniaxial tensile stress, although the variant selection was still not completely explained.
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identical area observations of deformation Induced Martensitic Transformation in sus304 austenitic stainless steel
Materials Transactions, 2013Co-Authors: Meichuan Chen, Akinobu Shibata, Daisuke Terada, Nobuhiro TsujiAbstract:In this study, an identical area of a SUS304 austenitic stainless steel specimen was observed by electron backscattering diffraction measurements at different strains in tensile test at ambient temperature, in order to investigate the details of deformation-Induced Martensitic Transformation. Firstly, a number of thin deformation twins were formed in austenite grains. Most of the martensite crystals were observed either near grain boundary triple junctions or inside the deformation twins. Secondly, it was found that martensite crystals preferentially appeared in the austenite grains whose h001i crystal directions were close to the tensile direction. Furthermore, when austenite grains had several martensite crystals inside, only one or two variants were observed among 24 variants possible under Kurdjumov-Sachs orientation relationship, which indicated the existence of variant selection rules. Patel and Cohen model and BogersBurgers model were examined to understand the variant selection, but both models could not explain the variant selections. The result suggests that complicated stress states govern the deformationInduced Martensitic Transformation in polycrystalline austenite. [doi:10.2320/matertrans.MBW201212]
Lu Wang - One of the best experts on this subject based on the ideXlab platform.
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ductile ti rich high entropy alloy controlled by stress Induced Martensitic Transformation and mechanical twinning
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2019Co-Authors: Lu Wang, Yandong Wang, Xidong HuiAbstract:Abstract Body centered cubic type of refractory high-entropy alloys (HEAs) have high strength at room and elevated temperatures, but suffer from the strength-ductility trade-off dilemma, making their application for structural materials severely impeded. In this article, we report a strategy to break this puzzle by introducing successive stress-Induced Martensitic Transformation (SIMT) and mechanical twinning in Ti-rich refractory TiZrHfAlNb HEA via controlling the grain size. The HEA exhibits superior ductility featured by fracture and uniform elongation as high as 40% and 33%, respectively, at ambient temperature. The plasticizing and toughening mechanisms for the HEA with different grain sizes can be described as following: in the HEA with small grains, the SIMT takes place followed by the martensite variants reorientation; in that with coarse grains, mechanical twinning of α″ phase comes up with the preferential orientation relationship of [111]β//[101]α″M//[-10-1]α″T after the SIMT.
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superelastic effect in ti rich high entropy alloys via stress Induced Martensitic Transformation
Scripta Materialia, 2019Co-Authors: Lu Wang, Xidong Hui, Yandong WangAbstract:Abstract This letter reports an outstanding superelastic effect in Ti-rich TiZrHfAlNb high entropy alloys for the first time, which is exhibited by comprehensive combination of the maximum total recovery strain, fully recoverable strain and corresponding tensile strength up to 5.2%, 4.0% and 900 MPa, respectively. It has been confirmed that these alloys are only composed of metastable β and martensite α″ phase, and ω phase is suppressed. The in situ X-ray diffraction experiment reveals that reversible stress-Induced Martensitic Transformation between β ↔ α″ endows the alloys superelasticity, while the plastic deformation and reorientation of martensite inhibit the recovery phase Transformation.
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enhanced work hardening and toughening via contiguous stress Induced Martensitic Transformation and mechanical twinning in ti zr hf nb al high entropy alloys
Social Science Research Network, 2019Co-Authors: Lu Wang, Yandong Wang, Xidong HuiAbstract:Refractory high entropy alloys (HEAs) have been considered as candidate alloys for next-generation high-temperature applications, but encounter the strength-ductility trade-off dilemma. In this article, we proposed a strategy of strengthening and toughening for Ti-rich refractory HEAs by the initiation of Martensitic Transformation and mechanical twinning successively. Three Ti-Zr-Hf-Al-Nb HEAs with the tensile strength and elongation up to 1167 MPa and 34%, respectively, which are superb among most of the reported BCC HEAs, have been successfully prepared. By using the SEM, TEM, HE-XRD and EBSD setups, the as-cast and fully recrystallized microstructures for these HEAs were characterized. And the mechanisms for the Martensitic Transformation and mechanical twinning in these HEAs are deeply explored. It has been clarified that under the as-cast and fully recrystallized state, these HEAs are mainly composed of β phase and a little of α′′ martensite phase. Stress-Induced Martensitic Transformation took place in favor of special variants with the [110]β//LD, which has the maximum Transformation strain of 7.8%. At the later stage, mechanical twinning α′′ phase have formed between the α′′ laths and the β matrix with the preferential orientation relationship of [111]β//[101]α′′M//[-10-1]α′′T.
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reversible deformation Induced Martensitic Transformation in al0 6cocrfeni high entropy alloy investigated by in situ synchrotron based high energy x ray diffraction
Acta Materialia, 2017Co-Authors: Lu Wang, Yandong Wang, Zhihua Nie, Fuchi Wang, Yunfei Xue, Jinlian Zhou, Tangqing Cao, Yang RenAbstract:Abstract The micro-mechanical behavior of Al 0.6 CoCrFeNi high-entropy alloy during tensile deformation was investigated using an in situ synchrotron-based high-energy X-ray diffraction technique. The alloy consisted of face-center-cubic (FCC) and body-center-cubic-based (BCC-based) structure accompanied by a small amount of σ phase. The FCC phase yielded prior to the BCC-based phase during the tensile loading, and the BCC-based phase bore more stress partition during the plastic deformation stage in spite of only ∼23% volume fraction. A reversible deformation-Induced Martensitic Transformation from the BCC-based phase to orthorhombic phase was observed during the plastic deformation stage. The Transformation preferentially occurred in the grains with an orientation of B-[001]//loading direction and B-[110]//transverse direction. The study characterized the micro-mechanical behavior of this alloy, and the reversible Martensitic Transformation is believed to be beneficial to the fracture toughness of such alloys.
Tadanobu Inoue - One of the best experts on this subject based on the ideXlab platform.
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crystallographic orientation dependence of deformation Induced Martensitic Transformation of 1 3 gpa class 0 6 c bainitic steel with retained austenite
Scripta Materialia, 2021Co-Authors: Akinobu Shibata, Kohsaku Ushioda, Yuuji Kimura, Takahito Ohmura, Tadanobu InoueAbstract:Abstract The crystallographic orientation dependence of the stability of retained austenite against deformation-Induced Martensitic Transformation in 0.6 %C alloyed steel was studied. A bainite structure with about 40 % volume fraction of retained austenite was successfully obtained by austempering. Tensile testing at room temperature revealed a high strength of 1.3 GPa with adequate elongation. A change in texture of retained austenite brought about by tensile deformation to several strains was measured. Deformation-Induced Martensitic Transformation occurred preferentially in grains with the tensile axis nearly parallel to fcc. The orientation dependence of the Martensitic Transformation was compatible with that of the {1-11}fcc fcc shear deformation which can be regarded as the first primitive process for the Martensitic Transformation as proposed by Bogers and Burgers. This compatibility is discussed in terms of the elastically normalized Schmid factor for the Transformation dislocation to act for the lattice change.
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crystallographic orientation dependence of deformation Induced Martensitic Transformation of 1 3 gpa class 0 6 c bainitic steel with retained austenite
Social Science Research Network, 2020Co-Authors: Akinobu Shibata, Kohsaku Ushioda, Yuuji Kimura, Takahito Ohmura, Tadanobu InoueAbstract:The crystallographic orientation dependence of the stability of retained austenite against deformation-Induced Martensitic Transformation in 0.6%C alloyed steel was studied. A bainite structure with about 40% volume fraction of retained austenite was successfully obtained by austempering. Tensile testing at room temperature revealed a high strength of 1.3 GPa with adequate elongation. A change in texture of retained austenite brought about by tensile deformation to several strains was measured. Deformation-Induced Martensitic Transformation occurred in grains with the tensile axis nearly parallel to fcc was significantly stabilized. The orientation dependence of the Martensitic Transformation was compatible with that of the {1-11}fcc fcc shear deformation which can be regarded as the first primitive process for the Martensitic Transformation as proposed by Bogers and Burgers. This compatibility is discussed in terms of the elastically normalized Schmid factor for the Transformation dislocation to act for the lattice change.