Influences of hot stamping parameters on mechanical properties and microstructure of 30MnB5 and 22MnB5 quenched in flat die

The influences of hot stamping parameters such as heating temperature, soaking time, deformation temperature and cooling medium on the phase transformation, microstructure and mechanical properties of 30MnB5 and 22MnB5 are investigated and analyzed in this work. The quenching experiment, tensile testing, hardness measurement and microstructure observation were conducted to obtain the mechanical and microstructural data. The results indicate that 30MnB5 possesses a higher tensile strength but a lower elongation than 22MnB5, if hot stamped at the same process parameter. The tensile strength and hardness of the hot stamped specimens decrease under inappropriate heating conditions for two reasons, insufficient austenitization or coarse austenite grains. The austenitic forming rate of 30MnB5 is higher than that of 22MnB5, because more cementite leads to higher nucleation rate and diffusion coefficient of carbon atom. More amount of fine martensite forms under the higher deformation temperature or the quicker cooling rate.