Microstructural Evolution and Hardness Gradient in Transition Zones Between Laser Cladding and Laser Quenching on H13 Curved Die Steel

Complex hot-stamping dies are prone to concentrated wear in protruding die-surface regions, such as rounded corners, under high loads during service, whereas friction between the sheet and adjacent die surfaces mainly occurs before die closure. Consequently, different die-surface regions require different strengthening methods, with a gradual transition in mechanical properties between adjacent strengthened regions. In this study, a zoned strengthening method combining Fe901 laser cladding and laser quenching was proposed for H13 die steel. A Fe901 cladding layer was deposited in the high-wear rounded-corner region, laser quenching was applied to the adjacent region, and a transition zone between the cladding and quenching regions was constructed. Based on cladding microstructural strengthening, beveled geometric transition, and quenching microstructural strengthening, relationships among microstructure, elemental distribution, and cross-sectional hardness in the transition zone were analyzed. The microstructural continuity, hardness transition behavior, and geometric continuity of the transition zone were evaluated through a comparison of SEM/EDS characterization, cross-sectional microhardness testing, and curved-specimen zoned-strengthening experiments. Adjacent laser quenching refined columnar crystals in the top region and disrupted cellular crystals in the bottom region, accompanied by C and Cr enrichment, attenuated B segregation, and localized elemental redistribution. The curved transition zone between the Fe901 cladding layer and the adjacent laser-quenched region mitigated abrupt hardness changes and enabled a continuous hardness gradient.