Simulation of Residual Stresses after Straightening of Induction Hardened Components

Abstract

Abstract Straightening is a manufacturing process where a component is bent, and plastically deformed, in order to reach a desired straightness. It is an unwanted but in many cases necessary process. For instance heat treatment operations such as carburizing and induction hardening may give distortions of magnitude that a straightening operation is required. The main disadvantage with straightening, apart from the extra processing step, is that it alters the residual stresses which decrease the fatigue strength of the component. In this paper, the straightening of a surface hardened shaft is simulated by FEM. The paper brings new insight into the complexity in the changes in residual stress that deviates far from the simplified views presented in literature. It will be shown that there are fundamental differences between a through hardened shaft and a surface hardened one as well as between shafts with shallow and deep surface hardening depths. The material studied is 42CrMo4 induction hardened by single shot. It is shown that the change in residual stresses is rather complex with decreased compressive residual stresses in a number of locations around the circumference while other locations have increased stresses. The amount of change in the residual stresses are largely governed by the required bending but by doing the straightening operation in an optimal way the negative effect can be reduced.