Fracture Analysis of Coupling Bolt of Pump Spindle for Water Circulating Pump

The fracture reason of a coupling bolt of pump spindle for water circulating pump with material of 35CrMo steel was analyzed by means of chemical compositions analysis, mechanical properties testing at room temperature and metallographic examination. The results show that the wrong specification of heat treatment after the hot forming process which caused the hardness and strength of the bolt reduced, irregular shape of the bolt head and the stress concentration because of no transition at the joints of the bolt head and screw arbor coacted and resulted in the fatigue fracture of the bolt under the periodic vibration of the shaft in the course of pump operation.