Depth-profiling of residual stress and microstructure for austenitic stainless steel surface treated by cavitation, shot and laser peening

Abstract

While the general characteristics of various peening techniques have been established, there have been few comparative studies. Here we compare the variation of the residual stresses and microstructural characteristics with depth for 316L austenitic stainless steel treated by cavitation peening (CP), shot peening (SP) and laser peening (LP) all peened to similar intensity levels. While the plastically affected depths were similar in all cases (~400 μm), the SP specimen showed the most extensive near surface plastic deformation, deformation twinning, dislocation density and compressive residual stress. To counterbalance this, the compressive residual stresses extended deeper for the LP and CP. Across the three treatments, a similar dependency was found between diffraction peak broadening and hardness. The dislocation density at the surface determined by the diffraction line profile analysis (LPA) for the SP specimen (4.9 × 10 15 m −2 ) was approximately 2.5 times that for the CP and LP specimens (2.0 × 10 15 and 2.1 × 10 15 m −2 ). Electron backscatter diffraction (EBSD) shows that the extensive work introduced by the SP had generated planar defects near to the surface. The increase in yield stress estimated from the hardness corresponded with the increase in dislocation density obtained by the LPA. • Shot peening (SP) introduces larger near-surface stresses while cavitation peening and laser peening penetrate deeper. • SP gives the highest nearsurface hardness of the three treatments. • SP also introduces a larger number of dislocations and planar defects than the others. • The hardness at a given FWHM is broadly the same regardless of the kind of the peening treatment. • The increase in yield stress estimated from the hardness correlates with the increase in dislocation density.