Enhanced Strength and Ductility of 2.4 GPa Hot‐Stamped Steel with an Extremely Thin Oxide Layer

Abstract

The novel 47Mn3CrNbV hot‐stamped steel shows high hardenability and low critical‐cooling rate about 0.5 °C s−1 due to its high carbon and high chromium. Compared to the traditional 22MnB5 hot‐stamped steel, it shows an excellent strength and ductility, and the thickness of the oxide layer is thinner than that of the traditional steel during the hot‐stamping process. By adopting austenization at 930 °C for 15 min, the obtained cold‐rolled hot‐stamped steel with 47Mn3CrNbV shows its best comprehensive mechanical properties that the yield strength is 1207 MPa, the ultimate tensile strength (UTS) is 2436 MPa, and the total elongation (TE) is 7%. The UTS of studied steel is guaranteed by the martensite and high dislocation density (5.1 × 1015 m−2). The low‐angle grain boundaries, the coincidence site lattice grain boundaries with lath martensite and M7C3 precipitates promote the TE of the tested steel. In addition, the cold‐rolled sheet with an extremely thin oxidization layer (4.9 μm) is obtained by hot‐stamping at 900 °C for 5 min. The oxidation layer is significantly reduced because the high content of Cr content, resulting in the increase of antioxidant properties within the studied steel.