On effects of composition and single and double annealing of medium-manganese steels for hot press forming: a review

Abstract Recent breakthroughs in medium-manganese steels have redefined paradigms for metastable austenite engineering in advanced high-strength steels. The present contribution elucidates the thermodynamic and kinetic principles governing microstructure evolution during intercritical annealing and subsequent hot/warm forming. Particular attention is given to steel processing, highlighting how double annealing and hot/warm stamping can tailor mechanical properties (e.g., achieving 1000 MPa of tensile strength with 35% total elongation) through controlled austenite retention. Emerging evidence suggests that strain-induced martensite transformation kinetics during stamping are critically dependent on prior austenite grain morphology—a relationship requiring further atomistic investigation. The discussion analyses different roadmaps for implementing medium-Mn steels for various components in the automotive body-in-white, requiring different properties. It also identifies unresolved questions regarding how the chemistry of the steel, in addition to the processing parameters, influences the retained austenite fraction and its impact on the tensile properties.