The effects of composite surface modification on the bending fatigue properties of 20CrNiMo steel

Carburizing composite laser shock peening is used for surface layer modification to enhance the service performance of 20CrNiMo steel. The mechanism behind the composite carburization and laser shock peening modification is discussed based on mechanical properties, microstructure analysis, and rotational bending fatigue testing. The results demonstrate significant improvements in surface layer hardness and residual compressive stress, along with significant refinement of surface layer grains. Which increasing laser energy and more impacts during the composite modification, the surface hardness, residual compressive stress, and depth of microstructure refinement in the influencing layer of the specimens increases, before eventually reaching saturation. Following treatment with carburized composite laser shock peening, the surface hardness increased from 375HV0.1 to 958HV0.1, the residual compressive stress on the surface reached -1300 MPa, and the depth of the layer influencing the microstructure refinement reached 29 mu m. The coupling effect of ultra-high hardness, high residual compressive stress, and grain refinement significantly enhanced the fatigue life of the compositemodified samples by approximately 5.25 times compared to the carburized samples. Moreover, following composite surface modification, the cause of fatigue failure mode shifts from discontinuous knife marks to internal inclusions.