Simulation numérique par éléments finis en 3D du comportement thermomécanique au cours du traitement thermique d'aciers : application à la trempe de pièces forgées ou coulées

摘要

This work presents a general solution for the 3D heat treatment of steels. The cooling or quenching of steel workpieces involves thermal microstructural and mechanical phenomena. In order to predict residual stresses and to limit distorsions, it is necessary to take into account strong coupling of the three phenomena. This dissertation describes a coupled finite element formulation for computing stress, Strain and temperature fields as well as microstructure evolutions during cooling.This work presents a general solution for the 3D heat treatment of steels. The cooling or quenching of steel workpieces involves thermal microstructural and mechanical phenomena. In order to predict residual stresses and to limit distorsions, it is necessary to take into account strong coupling of the three phenomena. This dissertation describes a coupled finite element formulation for computing stress, strain and temperature fields as well as microstructure evolutions during cooling.We first present the thermo-mechanical resolution. The thermal elastic visco-plastic THEVP constitutive equation is chosen to cover a large domain of deformation, from purely viscoplatic at high temperature to elastic-platic at the end of the heat treatment process, with non linear kinematic/isotropic hardening laws. A 3D mixed finite element (velocity/pressure) is used with the same interpolation for mechanical and thermal discretisation. This formulation is based on an original treatment of the P1+P1 finite element formulation for linear and non linear cases, in order to satisfy compatibility conditions.We introduce a modelling scheme for transformation kinetics. A metallurgical model is set up in order to determine phase volume fractions during cooling. The model includes temperature rate, the stress state and the carbon heterogeneity as variables.