MODELLING THERMOMECHANICAL PROCESSING OF AUSTENITE

摘要

This work is divided in two parts. First, a mathematical modelling of the austenite transformation during deformation operations at high temperature is presented. The model introduced by Estrin, Mecking and Bergstrom is employed in predicting the dynamic recovery step while the additional softening by dynamic recrystallization is modelled according to the Laasraoui and Jonas approach. Second, a prediction of the volume fraction of martensite, bainite and ferrite-pearlite formed during cooling is also presented. Most existing models can only be applied under conventional heat treatments. They cannot be used in welding or other hot working operations, where the austenite grain size is out of equilibrium conditions. The model here presented, which is a modification of the Ion, Easterling and Ashby model, is found to depend on the chemical composition and on the initial austenitic grain size. Finally, a practical coupling of the latter models is presented. For this purpose, a Finite Element Analysis of a hot forging operation is performed under different working conditions (temperature, strain rate, initial grain size) and different cooling conditions.