Alloying Design and Mechanical Performance Analysis of New Hot-formed Automobile Steel

Aiming at the problem of low strong plastic product caused by insufficient plasticity of traditional 22MnB5 hot stamping steel, the influence of alloying elements such as Mn, Cr, CO and Ni on the critical cooling rate of microstructure of hot-formed steel was simulated and analyzed. Considering the hardenability, alloy cost and the actual production process requirements of hot-formed steel, a new type of automobile hot-formed steel was designed, and the effect of heating temperature on mechanical properties of hot-formed steel was studied. The results show that when the mass fraction of carbon is 0.20%, the mass fraction of manganese is 1.70%-2.00%, and the mass fraction of chromium is 1.50%, the designed steel 20Mn2Cr has excellent hardenability and low cost under the condition of reaching the critical cooling rate required by hot forming. The addition of alloying element Cr can effectively improve the oxidation resistance of hot-formed steel. When simulating hot forming at 890 ℃, 20Mn2Cr steel has excellent mechanical properties with tensile strength of 1 600 MPa, elongation of 12% and strength-ductility product of 19 GPa·%, and its strength-ductility product better than that of 22MnB5 steel.