Effects of laser pulse energy on surface microstructure and mechanical properties of high carbon steel

Abstract

Surface microstructure and mechanical properties of pearlitic Fe–0.8%C (mass fraction) steel after laser shock processing (LSP) with different laser pulse energies were investigated by scanning electron microscopy(SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD) and microhardness measurements. After LSP, the cementite lamellae were bent, kinked and broken into particles. Fragmentation and dissolution of the cementite lamellae were enhanced by increasing the laser pulse energy. Due to the dissolution of carbon atoms in the ferritic matrix, the lattice parameter of α-Fe increased. The grain size of the surface ferrite was refined, and the microstructure changed from lamellae to ultrafine micro-duplex structure (ferrite (α)+cementite (θ)) with higher laser pulse energy, accompanied by the residual stress and microhardness increase.