Cause of Fracture on 45 Steel Drive Shaft

A 45 steel drive motor shaft fractured in the early stage in use. The causes of fracture on shaft were analyzed by means of macro and micro analysis, chemical composition analysis, hardness test and metallographic examination.The results show that the fracture property of the drive shaft is rotational bending fatigue fracture, and the fatigue source is located at the root of shaft shoulder. The main reason was that the stress concentration caused by the small radius of root rounding and the fatigue strength was low due to unqualified quenching and tempering treatment, which led to the early fatigue fracture of drive shaft under alternating load finally.