Martensite Reversion Duality Behavior in a Cold-Rolled High Mn Transformation-Induced Plasticity Steel
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INTRODUCTION
THE practice of strain-induced martensite reversion treatment (SIMRT) has been recognized as a promising scheme to extremely refine the austenite grain size in some austenitic stainless steels.[1–3] Using the concept of P. DASTUR, A. ZAREI-HANZAKI, and M. MOALLEMI are with the The Complex Laboratory of Hot Deformation & ThermoMechanical Processing of High Performance Engineering Materials, School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran. Contact e-mail: [email protected] R. RAHIMI is with the Institute of Iron and Steel Technology, Technische Universita¨t Bergakademie Freiberg, Germany. V. KLEMM is with the Institute of Materials Science, Technische Universita¨t Bergakademie Freiberg, 09599 Freiberg, Germany. B.C. DE COOMAN is with the Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Pohang, Gyeongbuk, 790-784 South Korea. J. MOLA is with the Institute of Iron and Steel Technology, Technische Universita¨t Bergakademie Freiberg and also with the Materials Design and Structural Integrity Laboratory, Faculty of Engineering and Computer Sciences, Osnabru¨ck University of Applied Sciences, 49076 Osnabru¨ck, Germany. Manuscript submitted December 2, 2018. B.C. De Cooman: Deceased August 29, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
reverse transformation in the pre-existing SIM microstructure to increase the efficiency of the grain refinement during cold roll-annealing processes is considered as the main idea behind the SIMRT practice. In terms of influencing parameters, the potential of the existing martensite (forming through SIM processing) to properly respond to the reverse transformation (known as martensite stability) phenomena should be considered as the underlining factor in controlling the reversion temperature range and the involved mechanisms. Tomimura et al.[4] proposed a model based on the Gibbs free energy change during the reverse transformation to correlate the stability of martensite to steel chemical composition. In this model, the initial volume fraction of the compromising chemical elements was merely used as the variable function of the reverse driving force. In addition, Tomimura et al.[4] also assigned a critical value (500 J/mol) on the obtained reverse driving force as a means to determine the reversion mechanism. However, using the chemical Gibbs energy was recognized as being useful just as a starting point. Kapoor et al.[5] studied the martensite reverse transformation (MRT) in an 18 wt pct Ni maraging steel. They reported a change in the reversion
temperature range through continuous annealing; this was attributed to the precipitation of Ni-rich particles at intermediate heating temperatures. This variation could also be explained in terms of chemical instability of martensite during annealing. Takaki et al.[6] examined that the reversion temperature range was highly interdependent with the cold rolling reduction in an austenitic stainless steel; this was related to a change in t
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