Residual stress evolution and relaxation in carbon S phase layers on AISI 316 austenitic stainless steel

Abstract

X-ray diffraction has been employed to study the residual stresses and lattice strains in the carbon S phase layers produced in AISI 316 stainless steel by low temperature plasma carburising. The results show that the carbon S phase layers are under a compressively stressed condition, to a level between 1.5 and 3.5 GPa. Analysis of the evolution of stresses revealed that, among various contributing factors including composition profile, lattice misfit and thermal effects, the build up of a carbon composition profile in the layer is mainly responsible for the development of a compressive residual stress during the carburising process. A simple model has been developed to predict the residual stress in the S phase layer. The model predicted that the compressive stress developed during carburising should be much higher than the values measured by XRD. This discovery suggests that stress relaxation has occurred during the carburising process. Further analysis revealed that the strain induced in the S phase by carbon supersaturation is mainly accommodated by plastic deformation, which leads to stress relaxation.