Influence of Ni Addition on the Microstructure and Mechanical Properties of 3.5Mn Medium-Mn Steel

The influence of Ni addition on the microstructure evolution and mechanical properties of Fe–0.2C–3.5Mn medium Mn steel after intercritical annealing (IA) is investigated in this study. It is found that the Ni addition refines the grains and increases the retained austenite (RA) volume fraction significantly. Moreover, due to the partitioning behavior of Ni between ferrite and austenite during IA, the mechanical stability of RA is greatly improved, which effectively enhances the combination of tensile strength and elongation of 3.5Mn steel. The product of the ultimate tensile strength and total elongation (UTS × TE) of 3.5Mn–1Ni steel can reach 42.5 GPa pct after IA at 660 °C for 6 hours, which is better than the UTS × TE values of steels containing 3.5–7 wt. pct Mn. The nanoindentation analysis further confirms the highly favorable effect of Ni addition on austenite stability and its mechanical responses, which is helpful for the improvement in both the strength and plasticity of the steel.