Fracture reason of 40CrMoA steel shaft of cement separator

The 40CrMoA steel shaft of a cement separator fractured after 10 days of service. The fracture causes were analyzed by means of macroscopic observation, chemical composition analysis, mechanical property test and metallographic examination. The results show that the microstructure of the steel shaft was tempered sorbite＋strip or block ferrite. There were non－metallic inclusions such as sulfide and banded structure in the microstructure, which was easy to produce stress concentration at the inclusions and banded structure. The crack initiated and propagated at the defect, eventually leading to the fracture of the steel shaft.