Abstract: The reasons for fracture failure of car hub bearing flange in finishing process were analyzed by observation of macroscopic and microscopic fracture morphology, microstructure and detection of chemical composition. The results show that the car hub bearing flange broke as brittle fracture mode. The main reasons of car hub bearing flange fracture were overheating and overburning in large R corner in middle frequency induction heating processes. Cracks initiated from the surface of the large R corner, and expanded rapidly until fracture under the action of external force in machining.