The gear shaft of condenser condensate pump fractured during operation,the gear shaft is made of 42CrMo material.The cause of broken shaft was analyzed by using methods of fracture analysis,mechanical performance testing,metallographic structure analysis,scanning electron microscopy observation and energy spectrum analysis.The findings revealed that Cl-in the medium induces pitting on the surface of gear shaft,cracks originate from pitting pits.The pitting pits become fatigue source due to stress concentration.When the condensate pump operates at high speed,the pump shaft bears a large alternating load.Due to low strength of the material,the pump shaft is peculiarly prone to fatigue fracture.The microcracks generated at the fatigue source gradually expand under alternating loads,continuously reducing the effective bearing area of the pump shaft.The pump shaft fractures when its area reaches the critical value of shaft remaining bearing area.
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