Abstract: A physicometallurgical model of flow stress, recovery, recrystallization and precipitation was developed to simultaneous-ly calculate the change in dislocation density, the nucleation and growth of recrystallized grains and the carbonitride precipitation of steel during hot rolling. The agreement of the laboratory simulation results by this model with experimental data indicates that the volume fraction of recrystallization and the grain size of niobium-containing micro-alloyed steel can be predicted with the model in different hot rolling processes. The model contains essential description of the observed metallurgical phenomena, and can be in principle adapted to different kinds of alloyed steels by changing some basic constants of materials.