Modelling of phase transformation kinetics in steels and coupling with heat treatment residual stress predictions

Abstract
One keypoint for the prediction of heat treatment residual stresses is the modelling of phase transformation kinetics and of their consequences on the thermomechanical behaviour of the material. In that paper, we focus on recent extensions of our model for calculating phase transformation kinetics in steels mainly for taking into account the chemical composition variation of the steel and the tempering/selftempering kinetics. This model is coupled to the calculation of temperature, stress and strain evolutions in a massive specimen submitted to chemical composition gradients (here carbon gradients). The consequences of the stress-phase transformation interactions on the microstructure and stress evolutions during cooling are analysed in the specific case of gaz quenching of a case hardened specimen. It is shown that the internal stresses can have a large effect on the bainitic transformation kinetics and on the stress evolutions during cooling but the effect on the residual stress state remains relatively small.