Quantitative Studies of Machining-Induced Microstructure Alteration and Plastic Deformation in AISI 316 Stainless Steel Using EBSD

Surface machining can result in a heavily plastic deformed layer in the subsurface. The microstructure alterations and the extent of plastic deformation of a milled 316 austenitic stainless steel were investigated using electron backscatter diffraction (EBSD) technique in this study. The microstructure alteration of the deformed layer was characterized by the generation of grain and subgrain boundaries. The plastic deformation was evaluated by kernel average misorientation (KAM) and grain average misorientation (GAM). The local deformation within grains was assessed by the misorientation from adjacent point (MFAP). The EBSD results indicated gradients of microstructure and plastic deformation along the depth direction. High-angle grain boundaries were generated within the depth of 40 mu m, and subgrain boundaries were produced up to the depth of 150 mu m. Estimated by KAM and GAM, the plastic strain was about 0.7 at the depth of 25 mu m and decreased to 0.1 at the depth of 115 mu m The MFAP analysis revealed that the local deformation varied within individual grains. Additionally, the change of micro-hardness along the depth direction showed a strong correlation with KAM and GAM values.