Effects of mechanical and chemical heterogeneity on the strength-ductility synergy of a heterostructured medium Mn steel

A medium Mn steel with both mechanical and chemical heterogeneities is designed in this study, demonstrating an excellent combination of high strength and ductility. Compared to the conventional cold-rolled medium Mn steel, the heterostructured steel showed a significant increase in ultimate tensile strength from 988 MPa to 1289 MPa without a decrease in total elongation, achieving a superior product of strength and elongation exceeding 60 GPa·%. The microstructural evolution of the heterogeneous medium Mn steel during deformation was analyzed to investigate how variations in microstructure affect its mechanical properties. The martensitic transformation and strain partitioning behaviors reveal that the brilliant work-hardening capability and mechanical properties of the heterostructured experimental steel result from the synergy between the pronounced transformation induced plasticity (TRIP) effect and significant hetero-deformation induced (HDI) strengthening. • The designed steel features a heterogeneous microstructure combining both mechanical and chemical heterogeneities. • The heterostructured sample exhibited ultra-high ultimate strength of 1289 MPa, and the PSE could reach 60.22 GPa·%. • The austenite in the heterostructured steel exhibited inhomogeneous austenite stabilities, enabling a more significant TRIP effect over a wide strain range, thereby enhancing the strain hardening ability. • The excellent mechanical properties of the heterostructed sample also rely on the more pronounced HDI strengthening.