Modelling discontinuous dynamic recrystallization using a quantitative multi-order-parameter phase-field method

A multi-order-parameter phase-field model was built by coupling a phase-field model with a physically-based statistical nucleation model to predict the microstructure evolution and flow stress responses of discontinuous dynamic recrystallization in 304L stainless steel. Individual growth kinetics simulations of recrystallized nucleus showed that the critical nuclei size was determined by balance between the local stored energy difference and grain boundary energy. This was different from the widely-used semi-analytical Roberts-Alhblom model of nucleation criterion and showed good agreement with Bailey-Hirsch model. The migration rate of the recrystallization interface did not follow the monotone change but strongly depended on the deformation conditions. The overall simulations of dynamic recrystallization agreed well with experimental observation. The characteristic features such as effect of deformation conditions on the peak stress, critical strains and grain size were quantitatively captured by the model. The sensitivity of grain boundary mobility to both temperature and strain rate was found from simulation. If the initial grain size decreased to a critically small value, the enhanced work hardening effect due to grain refinement maybe results in the dramatic increase of nucleation density, and hence finer steady-state grain size. The transition from single peak flow behaviors to multiple peak implies the change of dominating recrystallization behavior from nucleation to interface migration.