Fracture cause analysis of inclined shaft skip pull rod

The inclined shaft skip pull rod of the raw coal lifting device for coal mines was made of 45 steel. After 35 d of use, a pull rod fracture accident occurred. The fracture morphology, chemical composition, hardness, impact properties, tensile properties and microstructure of the skip pull rod were analyzed by electron probe, direct reading spectrometer, hardness tester, impact testing machine, tensile testing machine and metallographic microscope, respectively, and the failure cause was discussed. The results showed that the failure mode of skip pull rod was brittle cleavage fracture. The main reason was that the metallographic microstructure of pull rod consisted of reticular ferrite, pearlite and widmanstatten structure with some local coarse grains, which led to a significant reduction in the impact resistance of skip pull rod. At R-angle of pull rod, there was a clear cutting tool mark processing defect, which intensified the stress concentration, and the skip pull rod undergoed an early cleavage fracture due to the impact force.