Fatigue properties and fatigue strength evaluation of railway axle steel: Effect of micro-shot peening and artificial defect

Abstract In this study, the effects of micro-shot peening and artificial defect on the fatigue properties of EA4T railway axle steel were evaluated. Un-peened (UP) and micro-shot peened (MSP) EA4T axle steel specimens were drilled to introduce artificial defects on the surface. Then the fatigue tests were conducted on a rotary bending fatigue machine (R = −1). The test results showed that the fatigue limit of the UP specimens was improved by 25% after MSP; when the equivalent defect sizes were less than 60 and 70 μm respectively, they had no negative effect on the fatigue strength of the UP and MSP drilled specimens, otherwise the fatigue strength of both specimens decreased with the increase of the defect size. The fracture surfaces were analyzed by scanning electron microscopy (SEM) observations, which indicated that crack initiation sites for the as-prepared UP and MSP specimens were on the surface, while for the drilled specimens, they were on the vicinity of hole defects. The effect of artificial defect size on the fatigue strength of the UP and MSP specimens and the critical defect size were analyzed with fracture mechanics approach, the results of which showed that the relationship between defect size and fatigue strength of the UP and MSP specimens can be well evaluated by the modified Haddad model, and the critical defect size of the UP specimens was 65 μm while that of the MSP specimens was increased to 76 μm due to the introduction of compressive residual stress.