Effect of Oblique LSP on the Wear Resistance of Plasma-Nitrided H13 Tool Steel

H13 tool steel is widely used in precision injection molds; however, severe wear in confined regions, such as ejector pin holes, limits its service life, while conventional strengthening techniques remain difficult to apply in these areas. In this study, a combined plasma nitriding and oblique laser shock peening (OLSP) treatment was proposed, and the effects of laser incidence angle on microstructure, mechanical properties, and wear behavior were systematically investigated through electron backscatter diffraction (EBSD), X-ray diffraction (XRD) residual stress analysis, and ball-on-disk (BOD) wear tests. The results demonstrate that OLSP promotes grain refinement, dislocation accumulation, and the introduction of high-magnitude compressive residual stress. The NLSP1 sample exhibited the optimum strengthening effect, with a maximum compressive residual stress of −1033 MPa. It also achieved the lowest wear depth, wear volume, and specific wear rate, with a specific wear rate of 1.64 × 10−6 mm3/(N·m), representing a 54.3% reduction compared with the untreated sample. The enhanced wear resistance was attributed to the synergistic effects of hardness improvement, microstructural refinement, and compressive residual stress. These findings demonstrate that optimizing the laser incidence angle can improve strengthening efficiency and provide an effective strategy for surface modification of critical regions in complex molds.