Unveiling the Origin of Work Hardening Behavior in an Ultrafine-Grained Manganese Transformation-Induced Plasticity Stee
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promising strategies to enhance the work hardening rate (H) of ultrafine-grained (UFG) steels, transformation-induced plasticity (TRIP) effect has been subjected of extensive attention owing to the high H arising from the martensite transformation of retained austenite during deformation.[1–3] Massive investigations on the UFG Mn TRIP steels reveal a high dependence of H on the austenite stability.[1,4,5] Factors influencing
XU ZHU and HONGSHAN ZHAO, Ph.D. Candidates, are with the State Key Lab of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, P.R. China. WEI LI, Lecturer, and XUEJUN JIN, Professor, are with the State Key Lab of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, and also with the Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, Shanghai 200240, P.R. China. Contact e-mails: [email protected], [email protected] QIHANG HAN, Research Follow, and LI WANG, Chief Researcher, are with the State Key Laboratory of Development and Application Technology of Automotive Steels (Baosteel), Baosteel Research Institute, Shanghai 201900, P.R. China. HUISHENG JIAO, Application Scientist, is with Tescan China, Shanghai 201102, P.R. China. Manuscript submitted November 29, 2015. Article published online July 8, 2016 4362—VOLUME 47A, SEPTEMBER 2016
the volume fraction and stability of retained austenite, such as its chemical composition, morphology, and grain size, have been particularly highlighted.[1,5–9] Almost all the articles come to the conclusion that the work hardening in UFG Mn TRIP steels originates from the TRIP effect. However, as shown in the inserted map in Figure 1(a), no work hardening was observed in a recently developed UFG Mn TRIP steel although 15.9 pct austenite transformed into martensite.[8] It is reported that the work hardening is absent in UFG (~200 nm) material due to the pronounced dynamic recovery of dislocations,[10] and the high H is related to the dislocation interactions in ferrite in UFG ferrite/martensite dualphase steels.[11] The enhanced H with the prolonged intercritical annealing time is rationally to be ascribed to the change of austenite stability and, then, of the TRIP effect.[8] However, ferrite grain size also increases with the increasing annealing time and, thus, the high H may be associated with the recovered dislocation accumulation in ferrite. Additionally, it is reported in conventional TRIP-assisted multiphase steels that the work hardening rate is related to the generation of supplementary dislocations within ferrite due to the martensitic transformation of retained austenite during deformation.[12] Thus, dislocation accumulation in ferrite and TRIP effect are conceivable for the enhanced H in ultrafine-grained (UFG) Mn TRIP steels. It is generally difficult to separately investigate the role of these two factors on the H, since the stability of austenite and the deformation behavior of ferrite are simultaneously changed by the conve
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