MODELING THE MICROSTRUCTURE EVOLUTION DURING HOT DEFORMATION OF MICROALLOYED STEELS

Abstract

A physically based model has been developed to describe static recrystallization and grain coarsening of recrystallized grains during hot rolling of Nb microalloyed austenite. Key feature of recrystallization model is detailed description of the nucleation process; the model predicts recrystallization incubation time as well as time evolution of recrystallization nucleation rate along with recrystallized grain size. In addition to this, effect of static recovery, solute drag of Nb and precipitation of Nb(C,N) are captured in both recrystallization nucleation and growth models. Once recrystallization is complete, fine recrystallized austenite grains tend to coarsen driven by its surface energy, which is captured in a physically based model. The present grain coarsening model takes into consideration effect of solute drag of Nb using Cahn’s model and precipitates using Zener drag. The model predictions are validated using the available experimental database in literature. The model is applied to analyze quantitatively grain coarsening problem encountered between the end of roughing and the start of finish rolling under industrial processing conditions. The model enabled quantitative analysis of the effect of cooling rate on key metallurgical parameters, which determine the coarsening kinetics. Based on these results, an engineering solution