A novel approach for modeling the flow stress curves of austenite under transient deformation conditions

A novel differential form of the integrated constitutive description earlier advanced by Jonas et al., for modeling the flow stress of austenite, is developed. The temperature and strain rate dependencies are introduced in the formalism through the temperature-dependent shear modulus of the material, the yield, saturation and steady-state stresses, as well as the time to achieve 50% dynamic recrystallization. The correlation between each of the above stresses and the Zener-Hollomon parameter is carried out by means of the Sellars-Tegart-Garofalo model employing the activation energy for the self-diffusion of Fe in austenite (Q=284 kJ mol−1). The proposed formalism involves the determination of the flow stress of the material by means of the numerical integration of three differential equations. In this way, it is possible to compute the flow stress both during the work-hardening and dynamic recovery stage, as well as from the onset of dynamic recrystallization up to the work softening transient and final achievement of the steady-state stress. Therefore, it is possible to predict the flow stress curves of austenite under both sharp and ramped transient loading conditions leading to the occurrence of dynamic recrystallization, a novel feature that cannot be accomplished by means of the early advanced model.