Cracking Failure Analysis of 40Cr Drive Shaft

The longitudinal and transverse cracks were discovered at the center position of the 40Cr drive shaft quenched and tempered during machining in an enterprise. The cracking causes of the drive shaft were analyzed through chemical composition analysis, macroscopic and microscopic morphology observation of fracture surfaces, energy dispersive X-ray spectroscopy analysis, analysis of non-metallic inclusions, and microstructure analysis. The results indicate that the cracking reason of the shaft is caused by the combined action of the increased quenching stress caused by the banded structure and the presence of sulfide inclusions. The existence of banded structures leads to a significant increase in stress during quenching, causing cracks to form at sulfide inclusions, which then propagate into internal cracks distributed longitudinally. The fracture mechanism is brittle fracture.