XRD and EBSD studies of severe shot peening induced martensite transformation and grain refinements in austenitic stainless steel

Effects of severe shot peening (SSP) on the phase transformation and grain refinements of stainless steel 304 have been studied, driven by potential performance improvements via grain refinements in advanced surface enhancements, by employing X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). XRD measurements reveal a monotonic increase in martensite transformations (MT) when the shot peening coverage (SPC) is increased from 100% to 1500% and the increase exhibits a strong correlation with that of the compressive residual stress (CRS). They also reveal that the maximum MT locates under the processed surface and shifts deeper into the material when the SPC is increased. This variation trend, except for the different locations in depth, is similar to that of the maximum CRS. The depth-dependence of MT measured by XRD is consistent with that measured by EBSD at a scanning step of 0.3 μm; however, discrepancies are observed when either increasing or decreasing the scanning step by about one order of magnitude. The discrepancies are attributable to the SSP-induced grain refinements, which exhibit a monotonic decrease as a function of the depth under the peened surface, while the severely refined grains are most dominated by martensite. [Display omitted] •High-intensity shot peening have been done on SS304 with coverages up to 1500%•Plastic deformation, phase-transformation, and residual stress were measured by XRD•Their depth-profiles along with grain refinements were studied by XRD and EBSD•Consistencies and discrepancies between the XRD and EBSD measurements are observed•They have been discussed and attributed to the depth-dependent grain refinements