Constitutive Model and Micro Hardening and Softening Mechanism for Nonoriented Electrical Steel

Because of the occurrence at a high temperature of the phase transformations, hot finishing rolling of the non-oriented electrical steel inevitably takes place in its multiphase condition. Because of the difference in lattice structure between ferrite and austenite, the constitutive model and softening mechanism should consider the phase differences. The combined effect of work hardening and dynamic softening is related not only to temperature, but also to the phase structure. In the present study, steady stress is determined to approximately represent the average deformation resistance referring to the characteristics of stress–strain curves and practice-connected rolling requirements. The constitutive models of the ferrite and austenite regions are established correspondingly by the Arrhenius equation. Metallographic observations revealed that the dominant softening mechanism in the austenite region is dynamic recrystallization and that in the ferrite region is dynamic recovery, which contributes to the elimination of some discrepancies over this issue. Furthermore, according to the relationship between steady stress and dislocation multiplication and annihilation from the dislocation model, an indicator called the hardening–softening ratio is proposed, which is proportional to the square of steady stress. It can be used to link up the macro steady stress and micro dislocation evolution and to quantify the combined effect of work hardening and dynamic softening in different phase regions.