On the hot working of FeSi ferritic steels

The high temperature deformation behavior of FeSi electrical steels (ferritic at the testing temperature) was studied under hot compression conditions. The flow curves of these steels exhibit a conventional dynamic recovery behavior. The analysis of the hot working data was carried out by applying the classical hyperbolic-sine equation to derive the peak stress in the flow curve by determining the apparent stress exponent, n, and the activation energy, Q. A modified hyperbolic-sine equation showed a better correlation with experimental data. The modified equation assumes that the rate controlling mechanism is the glide and climb of dislocations. Consequently, Q can be taken equal to the iron self-diffusion in ferrite (Q=239 kJ/mol) and the creep exponent can be set equal to 5. The whole flow curves were also characterized by the one variable approach which in turn requires deriving characteristic dynamic recovery and work hardening terms at any processing conditions. A direct relationship between the hardening and softening terms and the Si content of the steels was obtained. Finally all the flow curves were discussed and modeled as a function of the processing parameters and chemical composition. Finally, a universal constitutive equation to describe the high temperature deformation of these steels taking account of the chemical composition is proposed.