钨颗粒复合喷丸对55CrSi弹簧钢表面完整性及疲劳性能的影响OA

Fine particle shot peening is an advanced surface strengthening technique in which fine shots with particle sizes ranging from 20 to 200 μm are accelerated by high-pressure air to impact the workpiece surface at high velocity.This process introduces a stable compressive residual stress layer in the near-surface region while effectively suppressing excessive surface damage,thereby ensuring good surface integrity.Owing to its high strength,excellent elastic recovery and superior fatigue resistance,55CrSi spring steel is widely used in critical load-bearing components such as automotive suspension springs.To further enhance the fatigue performance of spring steel through the synergistic optimization of surface integrity and subsurface strengthening,55CrSi spring steel is selected as the research material.The samples are first treated by conventional shot peening(SP)using cut steel wire shots with a diameter of 0.8 mm and a hardness of 670 HV at an Almen intensity of 0.645 mmA.Subsequently,a multi-pass tungsten particle shot peening(TPSP)process is applied on the basis of SP.Ultrafine tungsten particles with diameters of 50-150 μm and a high density of 19.0 g/cm3 are employed as the peening media,with the peening pressure maintained at 0.6 MPa.The effects of different shot peening processes on surface integrity,microstructural evolution,mechanical properties,and fatigue behaviors are systematically investigated by surface morphology characterization,electron backscatter diffraction(EBSD),residual stress measurements,microhardness testing,and three-point bending fatigue experiments.The results indicate that,compared with conventional shot peening,two-pass TPSP treatment leads to a pronounced improvement in surface integrity.The surface profile height variation is effectively reduced,with the peak-to-valley height difference along the x-direction decreasing to 22.18 μm.Meanwhile,the surface roughness is markedly reduced and stabilized at approximately 2.25 μm,demonstrating effective suppression of surface damage.With increasing TPSP passes,the thickness of the plastically deformed surface layer gradually increases,reaching approximately 30 μm.EBSD analysis reveals the formation of a strong 〈001〉preferred crystallographic orientation along the normal direction(ND).In addition,the kernel average misorientation(KAM)in the near-surface region increases notably,and the fraction of low-angle grain boundaries rises to 37.9%,indicating enhanced dislocation accumulation and intensified plastic deformation.After two-pass TPSP treatment,the compressive residual stress layer is significantly deepened,with the maximum compressive residual stress reaching approximately-963.7 MPa at a depth of about 70 μm below the surface.At a depth of approximately 10 μm,the microhardness is increased to 725HV,representing an improvement of 39%compared with the SP-treated sample.A continuous hardened layer with a thickness of approximately 80 μm is formed.Meanwhile,the surface grains are refined to 0.49 μm,and a pronounced fine-grained layer is obtained.Benefiting from the combined effects of improved surface integrity and enhanced subsurface strengthening,the fatigue life increases to 5.44×104 cycles,corresponding to an 82%improvement over that of conventionally shot-peened samples.Fractographic analysis further indicates that,after TPSP treatment,the fatigue crack initiation behavior changes from multiple crack origins to a single dominant crack origin.This transition suggests that the improved surface integrity and reduced stress concentration effectively suppress the formation of premature microcracks at the surface,thereby delaying crack initiation under cyclic loading.In addition,the presence of a deep and stable compressive residual stress field,together with the enhanced subsurface hardness,contributes to the retardation of crack propagation during the early stages of fatigue damage.Overall,the two-pass tungsten particle composite shot peening process effectively improves surface quality while achieving deep-layer strengthening,and its multiscale synergistic strengthening mechanism plays a critical role in enhancing the fatigue performance of 55CrSi spring steel.