EFFECTS OF SURFACE TREATMENTS ON MICROSTRUCTURE, HARDNESS AND RESIDUAL STRESS IN TYPE 316L STAINLESS STEEL

摘要

Recent studies on SCC under simulated BWR environment revealed that SCC occurred on the cold worked surface of L-grade stainless steels. It is generally considered that microstructure, hardness and residual stress are some factors for SCC initiation. In this study, microstructure, hardness and residual stress in the surface layer, on which several surface treatments were applied, were investigated in Type 316L stainless steel. Flapper Wheel (FW) polishing, Clean N Strip (CNS) polishing and Water Jet Peening (WJP) did not form the heavily deformed cold worked layers but Shot Peening (SP) formed it. While fine grain and slip band layers were observed in the surface layer treated by FW polishing, CNS polishing and SP, only dislocation networks were observed in the surface layer treated by WJP. Meanwhile, each surface treatment was effective in improving the surface residual stresses, and WJP and SP could improve the residual stress deeper than the other surface treatments.