On the role of austenite stability in yielding behavior of a medium Mn steel with a duplex austenite-martensite microstructure

Low yield strength and the presence of Lüders bands constitute principal impediments to the extensive applications of conventional medium Mn steels with a duplex microstructure of ferrite and austenite. Flash heating and the concept of chemical heterogeneity have been combined to engineer a duplex austenite-martensite microstructure in medium Mn steels, which has proven effective in augmenting the yield strength and mitigating the occurrence of Lüders bands. However, the underlying mechanisms remain ambiguous. In the present work, the effect of austenite stability on yielding behavior was systematically investigated in an austenite-martensite duplex medium Mn steel with a chemical composition of Fe–0.18C–4.95Mn–0.4Si (wt.%). Austenite stability was identified as the critical factor governing yield strength, where reduced stability promotes early-stage deformation-induced martensite transformation, thereby decreasing yield strength. Diminished austenite stability may as well induce enhanced work hardening, thereby result in the inclination and eventual elimination of yield plateau, concomitant with the disappearance of Lüders bands. These observations expand our current understanding of the yielding behavior in medium Mn steels and offer insights for the design of other advanced high strength steels.