Fracture Analysis of 40Cr Steel Oil Pump Shaft

The fracture of an engine oil pump shaft was investigated by means of chemical compositions analysis, macro-fracture analysis, hardness test and microstructure examination. The results show that the fracture of the pump shaft was early fatigue fracture. The main cause for the fatigue fracture resulted from no quenching and tempering treatment, which led the mechanical property of the material could not meet with the design requirement and fatigue strength of the pump shaft decreased.