Effect of surface nanocrystallization produced by laser shock processing on the corrosion fatigue behavior of 300M steel

The effect of surface nanocrystallization produced by laser shock processing (LSP) on the corrosion fatigue behavior of 300M steel was systematically investigated. The surface integrity, microstructure evolution and residual stresses before and after corrosion fatigue were characterized. The results showed that afte LSP the surface grain size of 300M steel was sufficiently refined down to nanoscale after LSP, and a large residual compressive stress formed. Under the same loading stress level, the corrosion fatigue life of LSP-treated 300M steel was improved significantly. This improvement increased with increase of LSP pulse energy. After corrosion fatigue, the surface grain of LSP-treated 300M steel remained at the nanoscale, showing a good stability. The dislocation density and the number of deformation twins in the subsurface layer became higher with increase of LSP pulse energy to accommodate deformation. Surface residual compressive stress induced by LSP has a relaxation during corrosion fatigue, depending on the laser pulse energy and fatigue loading force.