Failure Analysis on Fracture of 9Cr18MoV Steel Screw Trunnion

By means of fracture macro and micro analysis, metallographic examination, chemical compositions analysis and hardness testing, the early fracture failure reasons of 9Cr18MoV steel screw trunnion during combined testing were analyzed. The results show that the screw trunnion fracture was mainly because that the carbon content of raw material was beyond standard requirement, which made the microstructure have a large number of network eutectic carbide and greatly reduced the strength and plastic of the steel. At the same time, the transition arc radius of the screw trunnion was less than technical requirement of the design drawings, which resulted in stress concentration. So, under the action of biaxiality bending stress during the test, the screw trunnion fractured early.