Advanced High-Strength Medium-Manganese Steels as an Alternative to Conventional Forging Steels: A Review

This review highlights conventional forging steels and advanced medium-Mn steels containing retained austenite (RA), emphasizing their potential for industrial forging applications. Modern steels intended for forgings are required to combine strength, ductility, toughness and fatigue resistance with good hardenability and machinability at minimal cost. Medium-Mn multiphase steels fulfill these requirements by the strain-induced martensitic transformation (SIMT) of fine, lath-type RA, which can create a strength-ductility balance. Ferritic-austenitic steels provide high ductility with moderate strength, martensitic-austenitic steels show very high strength at the expense of ductility, and bainitic-austenitic steels achieve intermediate properties. Impact toughness and fatigue resistance are strongly influenced by the morphology of RA. The lath-type RA enhances energy absorption and delays crack initiation, while blocky RA may promote intergranular fracture. Low carbon (0.2-0.3 wt.%) combined with elevated manganese (3-7 wt.%) contents provides superior hardenability and machinability, enabling cost-effective air-hardening of components with various cross-sections. Advanced medium-Mn steels provide a superior mechanical performance and economically attractive solution for modern forgings, exceeding the limitations of conventional steel grades.