Enhancing the Mechanical Properties of Al‐Containing Medium Mn Steel Through Warm Rolling and Intercritical Annealing

Abstract

This investigation attempts to further enhance the mechanical properties of an Al‐containing medium Mn steel, Fe‐0.25C‐8.5Mn‐0.5Si‐2.5Al (wt%), through warm rolling (WR) and subsequent intercritical annealing (IA) treatments. Two schedules of WR processes were applied with a total thickness reduction of ≈60%. The results show that an ultrafine‐grained (UFG) lamellar structure was well developed after WR, while subsequent IA led to a coarsening of the microstructure as well as the formation of bimodal‐morphological ferrite and retained austenite (RA) grains, i.e., lamellar and equiaxed. Compared with warm rolled samples with clear discontinuous yielding and large yield point elongation, the IA treatment after WR could eliminate this phenomenon mainly due to microstructure coarsening. A significantly enhanced combination of strength and ductility (the product of the ultimate tensile strength and total elongation) as high as ≈75 GPa% was obtained for the WR + IA sample. This enhancement is notably superior to that of previously investigated medium Mn steels with similar Mn contents and is similar or even better than that of twinning‐induced plasticity (TWIP) steels with high‐Mn content. It is thus suggested that WR plus subsequent IA is a promising and feasible approach to further enhance the mechanical properties of medium Mn steel.