Analysis on fatigue property of microshot peened railway axle steel

▶ The alloy railway axle steel has fatigue limit in very high cycle regime. ▶ The railway axle steel cannot fracture from internal defect after the treatment. ▶ The fatigue strength is improved after microshot peening treatment. ▶ The improvement of fatigue strength is related to the relaxation of residual stress. In this paper alloy railway axle steel and medium carbon railway axle steel were shot peened by steel balls with a diameter of 100μm and the 109 cycles fatigue tests with the specimens unpeened and peened were carried out. The fatigue property and mechanism of surface compress residual stress relaxation were investigated. The results of fracture surface observation show that all the cracks initiate from the surface and the specimens both peened and unpeened have the conventional fatigue limit in the very high cycle fatigue regime. The fatigue limits of peened alloy steel and medium carbon steel increase by 10% and 35%, respectively. The improvement of fatigue limit is related to the residual stress relaxation while the degree of residual stress relaxation depends on the yield strength of surface hardening layer, the yield strength of original material and the applied stress amplitude. For the alloy steel which has the high yield-tensile ratio it relaxes quickly at the first cycles and then remains stable, while for the medium carbon steel which has the low yield-tensile ratio the residual stress relaxes quickly at the initial cycles and relaxes slowly afterwards.