Failure analysis of fatigue fracture for 60Si2Mn steel fastening clip in the track of high-speed railway

Abstract

A 60Si2Mn steel fastening clip in the track of high-speed railway fractured abnormally during service, and its service life was 8 years. The microstructure and the fracture morphology of the fractured fastening clip were analyzed. In addition, the Finite element model was built to simulate and analyze the stress of the fastening clip in the service process. The results showed that the microstructure of the failed clip was normal, which was uniformly distributed tempered troostite and residual ferrite. The depth of decarburization layer and hardness of fractured clip were 115 μm and 44.7 HRC, respectively, which satisfied the standard requirements. The inclusions were also not found at the crack initiation on the fracture. However, significant rusting occurred at the fracture source and the anticorrosive coating was damaged in this position, which led to the initiation of fatigue cracks. The finite element simulation results of the stress showed that the stress on the fracture position was smaller as 600 MPa under the service condition. The maximum stress position of clip was 1459 MPa in another position, but the cracks was not formed in the position with the highest stress. Therefore, it was proved that the crack was caused by corrosion. The analysis of the normally fractured fastening clip in service showed that the position of fatigue fracture was consistent with the results of the finite element simulation. It was suggested to optimum and strictly control the process of spraying anticorrosive coating thus to obtain a uniform anticorrosive coating on the surface.