Laser-shock processing effects on surface microstructure and mechanical properties of low carbon steel

The effects of laser-shock processing (LSP) on the microstructure, microhardness, and residual stress of low carbon steel were studied. Laser-shock processing was performed using a Nd:glass phosphate laser with≈600 ps pulse width and up to 120 J pulse energy at power densities above 1012 W cm−2. The effects of shot peening were also studied for comparison. Laser-shock induced plastic deformation caused the surface to be recessed by≈1.5 μm and resulted in extensive formation of dislocations. Surface hardness increased by up to 80% after the LSP. The microstructure and mechanical properties were altered up to≈100 μm in depth. The LSP strengthening effect on low carbon steel was attributed to the presence of a high dislocation density. Shot peening resulted in a relatively higher compressive residual stress throughout the specimen than did LSP.