Improved Mn–segregation bands and its influence on deformation behavior in a severely warm–rolled 10Mn lightweight steel

Abstract

The hot–rolled microstructures of medium Mn lightweight steels led to the formation of Mn–segregation bands due to a relatively high Mn content of 9–12 wt%, ultimately deteriorating their overall mechanical properties. In this study, a multi–pass warm rolling of 95% reduction was proposed to minimize the Mn–segregation bands in the 10 wt% Mn lightweight steel. This was followed by the detailed microstructural examinations and ex–situ tensile testing to evaluate the mechanical behavior response and deformation mechanism operating upon straining. Severe warm rolling accelerated the dynamic ferrite transformation and recrystallization in the Mn–rich austenitic bands, thus improving the microstructural homogeneity. The austenite stability was further improved so as to enable continuous strain hardening by transformation/twinning–induced plasticity (TRIP/TWIP) effects. This, thereby, led to obtain high tensile strength of 985–1201 ± 15 MPa together with large elongation of 34.3–76.0 ± 1.1%. In addition, the strain compatibility between ferrite and austenite also proves to give rise to an alleviation of strain localization at the ferrite/austenite interface, which also postponed the plastic instability and contributed to the large ductility by the coordinated TRIP/TWIP effects.