Effect of distribution status of the spot matrix on tensile behavior for 42CrMoV when conducting discrete laser surface strengthening: Based on experiment and simulation

High strength and high toughness are important indicators of material load-bearing capacity and reliability. The challenge remains on how to improve the material strength while maintaining its toughness during conventional surface treatments, such as overall hardening. This paper proposed a multi-pass discrete laser spot hardening (DLSH) process based on time-domain energy modulation. The characteristics of 42CrMoV alloy steel treated with multi-pass DLSH process, compared with conventional DLSH process, were investigated in terms of surface quality, microstructure evolution, and tensile properties. The results demonstrated that the surface quality of the hardened point lattice using multi-pass processing was significantly improved, and the microstructure was refined after multiple rapid austenitization cycles. Additionally, different “soft-hard” distribution states were formed on the sample surface. The ultimate tensile strength of the samples treated with conventional DLSH and multi-pass DLSH processes was increased by 9.5% and 5.2% respectively. However, the latter exhibited significantly higher elongation at fracture and showed a ductile fracture, while the former displayed brittle fracture. The multi-pass DLSH process maintained the original material toughness while enhancing its strength. Therefore, the multi-pass DLSH process holds significant importance in improving surface quality and material toughness in laser hardening applications.