Surface morphology evolution and tribological behavior in nanosecond pulsed laser polishing of S136 mold steel

Laser polishing (LP) is anticipated to become a new generation of surface polishing technology for the industrial field due to its high efficiency, reliability, and environmental friendliness, while few studies have reported the effect of LP on tribological behavior. Herein, the surface morphology, surface roughness, phase composition, surface hardness, and tribological behavior of S136 mold steel after nanosecond pulsed LP were investigated. The results of the orthogonal experiment suggested that the effect on surface roughness was in the following order: laser fluence > scanning speed > overlap factor along Y direction. A smooth and defect-free surface with a surface roughness Sa of 80 nm and a surface roughness reduction rate of 55.8% was achieved using the optimal LP parameters, and the LP mechanism was identified as the shallow surface melting. The wear tests indicated that LP weakened the wear resistance of S136 mold steel, which was attributed to the appearance of the γ-Fe phase on polished surface resulting in an 8% decrease in surface hardness, but this phenomenon is tolerable and controllable. Moreover, a combined action of abrasive wear and adhesive wear was confirmed on the LP specimens, whereas the abrasive wear was determined on the original specimen