Inclusion size evaluation and fatigue strength analysis of 35CrMo alloy railway axle steel

摘要

The axial loading fatigue tests of 35CrMo alloy railway axle steel were carried out with the untreated specimens and those treated by nitrocarburization. It is found that the untreated 35CrMo steel specimens fracture from surface, while those of the treated specimens fracture from internal inclusions. In order to investigate the inclusion size in the material, the ultrasonic fatigue tests were conducted for the 35CrMo steel by applying large risk volume specimens with straight section after nitrocarburization. The results show that the cracks of all the specimens initiate from the internal inclusion. The statistics of extreme values (SEV) method was applied to evaluate the maximum inclusion size in the large volume material and the full-scale axle. Based on the evaluated maximum inclusion sizes and the fracture mechanics, different fracture behaviors of axial loading specimens and full-scale axle as well as the effect of inclusion size on fatigue strength of full-scale axles were analyzed based on the fracture mechanics.