Cracking causes of a certain type of motor shaft

A certain type of motor vibrated abnormally during use, and during shutdown inspection, cracks were found on the surface of the motor shaft. The reasons for the cracking of the motor shaft were studied using methods such as macroscopic observation, chemical composition analysis, metallographic examination, mechanical performance testing and scanning electron microscopy analysis. The results show that the fracture surface of the motor shaft exhibited a characteristic morphology of rapid propagation of multi source fatigue. Improper welding process resulted in lower hardness of the welding layer and the formation of brittle self tempered martensite. During operation, the motor shaft mainly bore torsional load, and the surface of the shaft was subjected to the maximum stress. Therefore, microcracks were preferentially formed on the surface of the shaft by welding. During the propagation process, cracks converged to form multiple fatigue sources, and under the action of torque, the crack propagated in an eight－shaped shape, ultimately led to the occurrence of cracking in the motor shaft.