Abstract: Thermal simulation compression test of SCM435 steel was carried out under the deformation temperature of 750-1100 ℃ and the strain rate of 0.1-20 s^-1 by Gleeble-3500 thermal simulation testing machine. Based on the stress-strain curves of the steel, the influence of deformation temperature and deformation rate on the flow stress was analyzed. The constitutive equation of SCM435 steel with strain of 0.6 was established, and the microstructure evolution and deformation mechanism were discussed. The results show that the flow stress decreases with the increase of deformation temperature and increases with the increase of strain rate. By constructing the strain-compensated Arrhenius constitutive model, the hot deformation activation energy (Q) of the SCM435 steel is about 344.564 kJ/mol, the linear correlation coefficient (R) and the average relative error (AARE) of the established constitutive model are about 0.9921 and 4.39%, respectively. With the increase of deformation temperature, the deformation mechanism of the SCM435 steel changes from dynamic recovery (DRV) to dynamic recrystallization (DRX), and with the increase of strain rate, DRX grains gradually refine, indicating that increasing deformation temperature and increasing strain rate can promote the occurrence of DRX behavior and inhibit grain growth. The average misorientation angle of the SCM435 steel under high temperature and low strain rate (1100 ℃, 0.1 s^-1) is the smallest, which is 1.27°, indicating that the dislocation density is the lowest.

Key words: SCM435 cold heading steel, thermal compression deformation, constitutive equation, microstructure evolution