Computer simulation of carbonitride precipitation during deformation in Nb-Ti microalloyed steels

A thermo/kinetics computer model has been developed to predict the precipitation behavior of complex precipitates in Nb-Ti bearing steels under hot deformation condition. The equilibrium concentration of substitutional elements in austenite and the driving force for precipitation are calculated by the thermodynamic model. The time dependence of volume fraction and mean radius of precipitates is predicted by the kinetics model on the basis of classical nucleation and growth theory. In the kinetics model, the effect of hot deformation on precipitation is taken into account in terms of increase in nucleation sites and the enhanced diffusivity of substitutional solutes along dislocation, the decrease of solute concentration in austenite, and the driving force for precipitation are determined by a mean field approximation method. More importantly, the present model treats nucleation and growth as a concomitant process by using the finite differential method, which is different from the traditional one that treats nucleation and growth as a sequential stage. The model has been further validated by the experimental data in the literature.