Experimental investigation of boron steel at hot stamping conditions

The effect of deformation temperature and strain rate on the fracture and strain hardening of boron steel was investigated through the analysis of large amount of experimental data tested using a Gleeble (3800) materials simulator. These features were further modelled by using a set of unified viscoplastic damage constitutive equations. To study the deformation behavior, isothermal uniaxial tension tests of 1500 MPa boron steel at different strain rates of 0.01-5.0 s^-1 and different deformation temperatures of 550-850 °C were performed on a Gleeble 3800 materials simulator. Considering the difference between the deformation of the necking cross section and the centre measuring cross section of specimen at necking stage, a correction method of measuring strain at the necking cross section was developed. In addition, by taking temperature rise during deformation into account, a correction method of measuring stress was proposed. The true stress-strain curves were obtained based on the two corrections methods. The influence of deformation temperature and strain rate on the fracture and hardening was analyzed. A set of unified constitutive equations was adopted and determined from experimental data. The correlation between the numerical-computed and experimental true stress-strain data is presented. The average relative error is within the range of allowable experimental conditions and the predicted and experimental values can almost be consistent.