Analysis on Fracture Reasons of the Axis Pin of Operation Mechanism for the 550 kV Breaker

The 30CrNi3 alloy steel nitride axis pin fractured during mechanical operational testing of the breaker for 1 000-2 000 times. The fracture reasons of the axis pin were analyzed by chemical composition analysis, fracture analysis, macro examination, metallographic examination and mechanical property testing. The results show that:the fracture property of the axis pin was the biaxial bending fatigue fracture; veined nitrides existed in the nitride layer of the axis pin material, and interior defects such as porosity, large-scale inclusions and bubbles also existed, which reduced the mechanical property of the material; under the action of periodic rotating bending force, cracks appeared on the position of surface defects and constantly extended, and finally resulted in the fatigue fracture of the axis pin.