Reason Analysis on Cracking of a 45 Steel Flange after Quenching and Tempering Treatment

A 45 steel flange cracked on the edge of the inner hole after quenching and tempering treatment. The cracking reasons of the 45 steel flange were analyzed by macroscopic examination, hardness testing, chemical composition analysis and metallographic examination. The results show that:the main reason for the cracking of the flange was that the hole edge of the flange wasn't chamfered, which produced large tensile stress on the surface during quenching process and caused the tensile stress cracking; in addition, dendrite structure existed in the matrix and reduced the strength and toughness of the material; in the process of heat treatment, the severe decarburization layer appeared on the surface of the flange, which further reduced the surface strength of the material, and eventually led to the cracking on the edge of the inner hole.