LAUSR

To optimize the toughness and hardness of laser surface‐hardened high‐carbon–chromium (52100) steel, the effect of preheating on microstructure evolution and impact property is studied, and the impact fracture mechanism is analyzed. The results indicate that preheating deepens the hardened depth, facilitating grain coarsening and cementite dissolution near the surface. Regardless of preheating, the size distribution of cementite follows a typical lognormal distribution. Laser surface hardening leads to a decrease in impact absorbed energy. Preheating at 160 °C increases the impact absorbed energy by ≈25%, at which point the maximum hardness is still as high as 860 HV0.3. The impact absorbed energy of spheroidized microstructure tends to be larger before laser hardening and reduces after laser hardening. The impact toughness is the combined result of the brittleness of the hardened layer, residual stress, and substrate microstructure. Under the impact load, microcracks nucleate near the surface of the hardened layer and propagate in the form of intergranular fracture and then propagate in the form of transgranular fracture toward the inside of the hardening layer and substrate. Herein, a novelty research work on optimizing the impact properties during laser hardening through preheating and adjusting initial microstructure is provided.