Hot deformation behavior and comparison of different constitutive models of as-cast ER8 steel

To facilitate the numerical simulation of plastic deformation and the determination of thermal deformation process parameters of as-cast ER8 steel, isothermal thermal compression test of ER8 steel was carried out, and the flow stress curves of ER8 steel at high temperature was obtained. The selected deformation temperature was 1173-1523 K and strain rate was 0.001-0.1 s(-1). On this basis, three different constitutive models were established and compared. The results show that the flow stress curves of ER8 steel can be divided into two stages, namely work hardening-dynamic recovery stage and dynamic recrystallization stage. The traditional Fields-Backofen model was modified to predict the flow stress at different deformation temperatures. According to the error analysis, the AARE levels of the modified Fields-Backofen model and the strain-coupled constitutive model are the same, while the AARE of the physically-based constitutive model are smaller. The modified Fields-Backofen model cannot reflect the softening of dynamic recrystallization on the flow stress curves during high temperature deformation, while the strain-coupled constitutive model and the physically-based constitutive model can. In terms of modeling difficulty, the modified Fields-Backofen model is the easiest to model, followed by the strain-coupled constitutive model, while the physically-based constitutive model is relatively complex to model.