The Influence of the Material Heat Treatment and Phase Transformations in Forming Processes

Abstract

The majority of metals undergo thermomechanical treatments at least during some part of their processing history. The aim of these treatments is to achieve material properties that could not be obtained otherwise. However, in heat treatment processes, such as quenching, complex residual stresses fields develop during the cooling process of the material. The influence of heat treatments in the forming process of steels is studied in this work. A thermo-mechanical model that considers generalised multi-phase transformations is applied to predict the material properties and characteristics during the combined heat treatment and plastic deformation, which may or may not occur simultaneously. The plastic transformation of each constituent phase is introduced considering a previous material cooling from austenite at high temperature. The JMAK equation and the Koistinen-Marburger model are used to characterize the non-isothermal transformation kinetics and the diffusionless transformation, respectively. The total strain is the addition of the elastic, plastic and volumetric strain induced from the phase transformation parts. An isotropic yield surface is used for the different phases. Numerical tests were performed to validate the previous models implementation considering continuous cooling. The influence of the heat treatment performed by the cooling conditions is also studied carrying out subsequent forming processes. It is shown that the heat treatment and the resulting material phases have a considerable influence on the forming stage.