A novel Cu-Ni added medium Mn steel: Precipitation of Cu-rich particles and austenite reversed transformation occurring simultaneously during ART annealing

Two elements, Cu and Ni, were deliberately added into a typical medium Mn steel during smelting for further improving mechanical properties through the precipitation of Cu particles simultaneously with austenite reversed transformation (ART). The characteristics of microstructure and mechanical properties due to the addition of Cu and Ni was investigated. From the results, the feasibility that Cu-rich particles precipitate within recrystallized ferritic grains or tempered martensitic laths during ART annealing is proved, and the size of Cu-rich particles are nano-scaled, of which the diameter is less than 20 nm. The addition of Cu and Ni in medium Mn steel not only benefits the increase of reversed austenite fraction, but also the formation of a considerable amount of annealing twins during ART annealing, which contributes to split and further refine the austenite grains. Additionally, the addition of Cu and Ni enables a significant increase of tensile strength, about 90-150 MPa while do not improve the yield strength, and moreover results in the deterioration of tensile ductility. Yet even so, the optimal product of tensile strength and total elongation (PSE) is above 42 GPa%. Furthermore, it is confirmed that at high stain rates medium Mn steels still have an outstanding comprehensive properties.