Abstract: A certain car experienced transmission system failure while driving on extremely poor and bumpy roads.Upon inspection, it was found that the universal joint bearing sleeve had fractured. To investigate the cause of sleeve fracture failure, the fracture morphology, microstructure, chemical composition, vickers hardness, etc. were tested.The results show that poor carburizing and quenching processes are the main reasons for the fracture of universal joint bearing sleeve. The surface structure of the sleeve is composed of coarse needle martensite and a large amount of retained austenite, with visible microcracks between martensite in some areas. There is widmannstatten structure in the center. The above structures result in poor impact toughness of the sleeve, making it unable to withstand harsh road conditions and leading to brittle fracture.