Modelling of NbC precipitation kinetics in hot deformed austenite on Nb bearing low carbon steels

In order to pedict microstructure and mechanical properties in hot rolled HSLA steels, a precipitation model of NbC in austenite was developed. The effects of Nb content, prior austenite grain size and condition of deformation on the precipitation kinetics were quantitatively determined by extraction replica. The modelling was basically constructed with the classical nucleation and growth theory, and the precipitation fraction was estimated from the supersaturation of Nb in solution. As effects of deformation on precipitation, a strain energy term was added to the driving force of nucleation. The increase in nucleation sites and the enhancement of diffusibity of Nb were expressed as functions of the dislocation density. The experimental results concerning the acceleration of precipitation due to strain and the interaction between recrystallization and precipitation were quantitatively explained by the present model.