Abstract: Constitutive relationship of boron steel at high temperature is one of the most necessary mathematical models in the numerical simulation of hot stamping. It describes the relationship of the flow stress with strain, strain rate and temperature. In order to build the constitutive equations of boron steel B1500HS, some isothermal uniaxial tensile tests are performed at 600～900 ℃ with strain rate 0.01 s–1, 0.1 s–1, 1.0 s–1 and 10 s–1 by Gleeble 1500D thermo-mechanical simulator, and the true stress-strain curves at the relative conditions are gained. The modified Arrhenius model, which is a hyperbolic sine function including the deformation activation energy and deformation temperature, is used to describe the hot deformation activation character of austenite microstructure of boron steel. The material parameters depending on the strain, and the constitutive equations depending on the strain rate and deformation temperature, are attained by the regression analysis of experimental data. The experimental results show that, the flow stress rises with the decrease of the deformation temperature and the flow stress rises with the increase of the strain rate. The results show that the computational data using the constitutive relationships are consistent with the experimental data.

Key words: Boron steel, Constitutive equations, Hot forming, Tensile testing