Modelling and experimental study of the bainitic transformation, residual stresses and deformations in the quenching process of middle alloyed steel parts

Abstract
Big efforts have been made these last twenty years in order to model the behaviour of steel parts in heat treatment processes [1]. Models for microstructural evolutions during continuous cooling, coupled with thermomechanical calculations do exist, but complete experimental validations of these models are still necessary. Here, we mainly present a complete experimental validation procedure from the scale of small homogeneous specimen to the scale of massive pieces with thermal gradients. Comparisons between experimental and calculated results (transformation kinetics and thermomechanical behaviour) are presented first. Then, massive cylinders quenched in air, cold oil and cold water are considered and numerical simulation results in terms of microstructure distributions, residual stresses and deformation are compared to experimental ones. The whole study concerns more specifically the bainitic transformation of a middle alloyed steel and it is shown that the effect of internal stresses on the transformation kinetics is a first order parameter in order to predict correctly microstructural gradients developed in a quenched part.