Effects of laser shock processing on surface microstructure and mechanical properties of ultrafine-grained high carbon steel

Ultrafine micro-duplex structure (ferrite (α)+cementite (θ)) formed in a pearlitic Fe–0.8C steel after four passes of equal channel angular pressing (ECAP) at 923 K via route Bc. Subsequently the surface of the ultra-micro-duplex structure was treated by multiple laser shock processing (LSP) impacts with different laser pulse energies. The microstructure was obviously refined due to the ultra-high plastic strain induced by LSP. The lattice parameter of α-Fe increased with the laser pulse energy, indicating that the cementite dissolution was enhanced. In addition, residual stress and microhardness increased with the LSP pulse energy.