Formation Mechanism of Irregular Carbides in Raceway ofGCr15 Steel Bearing Inner Ring

The carbide morphology in the GCr15 steel bearing inner ring structure after forging, spheroidizing annealing, and quenching and tempering was observed. Combining with thermal expansion tests and thermodynamic analysis, the dissolution, precipitation and growth behavior of secondary carbides were studied. The forming reasons for large irregular carbides with sharp corners were analyzed. The results show that the secondary carbides precipitated in the alloy element segregation zone of the raceway surface of GCr15 steel bearing inner ring during rolling and forming at a lower temperature were broken, resulting in the appearance of large irregular carbides with sharp corners in the raceway surface structure. During the spheroidizing annealing process, the broken irregular granular carbides on the raceway surface of the bearing inner ring grew up and became round, and these large carbides partially dissolved into the austenite matrix during quenching heating, resulting in the reappearance of edges and corners. The conditions for the appearance of irregular carbides on the raceway surface of bearing inner ring included the presence of a serious alloy element segregation zone on the raceway surface, and the large secondary carbides precipitated from the segregation zone.