Constitutive modeling for flow stress of 55SiMnMo bainite steel at hot working conditions

• The flow behavior of 55SiMnMo steel was obtained by isothermal hot compression.
• The influence of dynamic softening mechanism on flow stress was analyzed.
• Flow stress was formulated by considering work-hardening and dynamic recovery.
• Propose a new model of flow stress after the peak based on the dislocation theory.

The hot deformation behavior of 55SiMnMo bainite steel was studied through isothermal hot compression tests conducted using a Gleeble 3500 at 950–1100 °C, with strain rates of 0.01 s−1 to 10 s−1. A constitutive equation was established using the experimental results to describe the stress–strain relationship based on the dislocation density variation, considering the influence of the dynamic softening mechanism. When dynamic recovery is the only softening mechanism, a constitutive equation for flow stress was obtained from the variation of the dislocation density during hot deformation based on work hardening and dynamic recovery. When dynamic recrystallization occurs, the relationship between the dislocation density and the volume fraction of dynamic recrystallization was used to predict the flow stress after the peak. The reliability of the model was verified through a comparison between the predicted flow stress curves from the model and the experimental data.