Formation Mechanisms of Cracks in LZ50 Steel Axles for Railway Vehicles

The longitudinal cracks were often found on the surface of axles for railway vehicles after forging and machining, resulting in axle scrap.The optical microscope, scanning electron microscope, energy dispersive X-ray spectroscopy as well as Vickers hardness tester were employed to investigate the formation mechanism of cracks on the surface of LZ50 steel axle.It was found that the formation mechanism of microcracks on the axle surface could be classed into two types: one was that micro shrinkage porosity in axle billet was not completely healed during forging of flattening;the other was that alumina inclusions in axle billet formed source of crack and resulted in brittle trans-granular fracture of axle microstructure during forging.