Effect of Shot Peening on Friction and Wear Behaviors of Cr-Ni-Mo High Strength Steel

With the increase of the demand for power density of high speed and heavy duty vehicles, fatigue failure caused by insufficient strength of vehicle transmission system severely limited the carrying capacity and acceleration performance. In order to solve the fatigue problem of the mechanical transmission system of high-speed and heavy-duty vehicles, a novel Cr-Ni-Mo high-strength steel was developed by the Central Iron and Steel Research Institute. And the Cr-Ni-Mo high-strength steel was strengthening treated by shot peening treatment with different shot peening jet pressure and shot peening coverage parameters. Also, the friction and wear behavior of the Cr-Ni-Mo steel samples with and without shot peening were investigated by using a pin-on-disk tester at room temperature under lubricating conditions. The effects of different shot peening treatment parameters on the surface morphology, microstructure, microhardness, residual compressive stress and tribological behavior were comprehensive studied. Moreover, the strengthening mechanisms of shot peening treatment in the process of pin-disk contact friction was further revealed. The results showed that the plastic deformation layer and microscopic dislocations region were generated at the surface material after shot peening treatment, and with the increased of shot peening jet pressure from 0.2 MPa to 0.6 MPa, the microhardness of material surface layer and top surface residual compressive stress were significantly improved after shot peening strengthening treatment. And the increased of shot peening coverage from 100% to 300% also had significant effect. It also should be noted that the shot peening craters formed on the top surface increased the oil storage and improved the interfacial lubrication effect during the pin-on-disk tribological tests. The friction coefficient and wear rate of the Cr-Ni-Mo steel samples after shot peening strengthening treatment were lower than the samples without shot peening treatment. Compared with the untreated sample, the friction coefficient of the samples after shot peening treatment was reduced from 0.073 to 0.023, which reduced by 68.49%, and the wear rate of the shot peening treated samples were reduced from 1.25×10⁻⁵ mm³/(N·m) to 0.81×10⁻⁵ mm³/(N·m), which was 35.20% lower than the wear rate of the untreated sample. And the processing traces produced in the samples preparation were basically covered after shot peening treatment, the surface roughness value were increased. In addition, from the analysis of wear morphology characteristics by the SEM and EDS, the wear mechanisms of the samples with and without the shot peening treatment could be determined. The wear mechanisms of the samples without shot peening treatment were mainly the surface materials peeling caused by ploughing wear, and the wear mechanisms of the shot peening treated samples were mainly ploughing, oxidative wear and adhesive wear. The strengthening mechanisms were attributed to the inhibition of cracks initiation and propagation by plastic deformation and residual compressive stress induced by shot peening.