Modeling of High-Temperature Flow Stress of VN and Nb-Ti Microalloyed Steels during Hot Compressive Deformation

A simple mathematical model has been developed which describes the flow curve behavior up to the peak true stress or a true strain of 0.6 in unstable austenite. The hot working behavior was analyzed by compression tests over a temperature range of 750–1000 °C and at strain rates of 0.1–50 s−1. The constitutive behavior focused on the interaction between work hardening and dynamic softening attributed to recovery, recrystallization and dynamic austenite to ferrite transformation. This model extends the application of the well-established Estrin and Mecking (EM) work-hardening model in the unstable austenite region. The work hardening is countered by softening kinetics, represented in this model by JMAK-type expressions for both dynamic transformation and recrystallization. The predicted results correlate well with experimental results in VN and Nb-Ti microalloyed steels.