Effect of transformation plasticity on residual stress fields in laser surface hardening treatment

Abstract

In the laser surface hardening process, the thermal stress is induced by the temperature gradient and the martensitic phase transformation. The martensitic phase transformation is a dominant factor in formation of the residual stress. For the accurate prediction of internal stresses during laser surface hardening treatment, therefore, a particular effort is needed to model the progress in the martensitic phase transformation. In this study, the effect of the transformation plasticity was considered by using an additional strain in the numerical analysis of laser surface hardening treatments. The simulation results showed that the deviation between the residual stresses when considering the transformation plasticity and when not considering it on the hardened surface is large, so that it cannot be considered a negligible factor. In the nonhardened region, however, the shapes of the isostress lines were very similar to each other. Experimental results obtained by irradiating the test specimen with a 2.4 kW CW-CO2 laser showed a better agreement with the residual stress predicted by considering the transformation plasticity than by neglecting it. © 1991 Springer-Verlag New York Inc.