Abstract: A small number of fracture accidents occurred in the turning process of 40Cr steel hub bolts produced by a factory. The fracture causes of the hub bolts were analyzed by means of fracture analysis, chemical composition analysis, metallographic examination and hardness test. The results show that the hub bolts were burned locally in the heating furnace, which reduced the intergranular adhesion of this part, and caused brittle fracture of the bolts in the turning process.