Characterisation of the effects of grinding on residual stresses

The surface mechanical treatments induce plastic deformations in the material. This deformation, more or less intense and deep, superficially modifies the microstructure of the material and therefore its mechanical characteristics [1]. It toughens the work hardened material and change the roughness of the part (improvement or degradation). But the essential effect is the creation of residual stresses. These residual stresses are now considered as a characteristic that must be taken into account just as the chemical composition or the mechanical characteristics of the materials. In the nuclear industry, during the assembling of a number of parts, grinding operations are generally used to prepare surfaces or improve surface state before or after welding. We have focussed on the influence of grinding on the residual stresses on several metallic materials and an experimental study has been carried out on two materials, a low carbon welding steel (A42) and an austenitic stainless steel (316L). A test rig using a portable machine of the type of building materials disk grinders enabling to control necessary parameters and to reproduce grinding operations was perfected. The hardness and the roughness have been measured and the method of X-ray diffraction that allows to make surface measurements was chosen to determine residual stresses. The results obtained on the first batteries of grinding show a structural modification and the presence of significant tension residual stresses.