Consistency of dynamic recrystallization models from the perspective of physical metallurgy and continuum mechanics

Abstract

Dynamic recrystallization (DRX) is characterized by the nucleation and growth of new grains, which takes place concurrently to plastic deformation. DRX processes are used in industrial hot forming operations to control the microstructure and properties of the workpiece. Various models have been developed that consider the coupled evolution of microstructure and flow stress during hot deformation processes, some from a perspective of physical metallurgy, some from continuum mechanics. It is widely accepted that the onset of DRX is characterized by an inflection point of the strain hardening rate as a function of stress. This criterion was derived by Poliak and Jonas using results from the thermodynamics of irreversible processes. The present paper analyses the conditions that need to be met by DRX models to be consistent with the criterion by Poliak and Jonas. It is shown that for models which use classical Avrami kinetics to describe the evolution of the recrystallized volume fraction, the Avrami exponent should exceed a value of 3 to ensure that the Poliak-Jonas criterion is not violated. Based on this observation, a framework for consistent DRX kinetics is presented and discussed.