A Hot‐Stamped Medium‐Mn Steel with Superior Strength–Ductility–Bendability Combination and Thin Oxidation Layer

Abstract

A hot‐stamped medium‐Mn steel containing 3.84 wt% Mn is designed for the manufacture of hot‐stamped automotive components. The effects of intercritical temperatures employed for hot forming on the microstructure, tensile properties, and three‐point bending behaviors are investigated. The result shows that the microstructure can be controlled by intercritical temperatures, leading to different phase fractions of martensite, retained austenite, and ferrite in the steels. Besides, the tensile strength increases with increasing intercritical temperature, while both the total elongation and the bending angle show reverse change trend, which are related to the various phase fractions and the different transformation‐induced plasticity effects during deformation. Importantly, the medium‐Mn steel subjected to heat treatment at 800 °C possesses tensile strength of 1535 MPa, total elongation of 13.8%, and bending angle of ≈56°. Therefore, its total elongation is significantly higher than hot‐stamped 22MnB5 steel under the same tensile strength grade, and the bending angle of the former is close to the latter. Moreover, the thickness of oxidation layer on the medium‐Mn steel is only ≈3.5 μm after heat treatment at 800 °C, much thinner than the ≈57 μm‐thick oxidation layer on the 22MnB5 steel after austenitizing at 930 °C.