The effect of thermal annealing upon shot-peened type-304 stainless steel was examined using electron back-scattering diffraction and X-ray diffraction. The objective was to evaluate the potential for surface property control by grain boundary engineering. The near surface microstructure of shot-peened material showed a gradual change of the grain boundary character distribution with depth. Twin (Σ3) and higher-order twin grain boundaries (Σ9, Σ27) identified closer to the shot-peened surface had significant deviations from their optimum misorientation. The changes of the near surface microstructure, with variations in grain size, low Σ coincident site lattice grain boundary populations and their deviation from optimum misorientation. Microstructure developments were dependent upon the applied heat treatment, with the near surface microstructures showing similarities to microstructures obtained through bulk thermo-mechanical processing. Shot peening, followed by annealing, could therefore be used to control the near-surface microstructure of components.

Surface Grain Boundary Engineering of Shot-Peened Type 304 Stainless Steel. O.M.Alyousif, D.L.Engelberg, T.J.Marrow: Journal of Materials Science, 2008, 43[4], 1270-7

subsequent application of annealing treatments caused depth-dependent