X-ray diffraction study of distribution of macroscopic residual stresses in surface layers of bearing steel after grinding

The focus of this contribution is analysis of the state of residual stress in surface layers of ground bearing steel of grade DIN 17210-86 (ĆSN 14 220). The influence of various coolants on macroscopic residual stress was investigated. Three forms of cooling were applied: dry grinding, liquid coolant and flow of cold air from a Ranque- Hilsch vortex tube. The surfaces of the samples were analysed by X- ray diffraction technique in six azimuths in order to acquire complete strain tensors. Since -vs.-sin y/ dependances in grinding direction are non-linear and exhibit psi splitting, the method proposed by Dólle and Hauk [1] was used to evaluate tensors of anisotropic trialxial state of residual stress. The effective penetration depth of CrKa X-ray radiation into ferrous materials for sin2 y/= 0,4 is approximately 4 um and therefore removal of surface layers is a necessity in order to pinpoint the distribution of residual stresses beneath the surface. The impact of material removal should cause minimal or neglecting mechanical and thermal distortions to the investigated state of stress. Electro-chemical polishing, which was used, is acknowledged as the most appropriate tool [2].