Abstract：The crankshaft of one mining vehicle suddenly broke at the 7th and 8th cranks after service for 1 269 h. To investigate the cause of the failure, it was found that the 7th crank was the first fracture through the macroscopic analysis of fracture surface, and there were casting defects such as holes at the intersection of the 7th crank and the 4th connecting rod fillet. Then, the surface morphology, microstructure, and material composition of hole defects were analyzed by scanning electron microscopy, optical microscopy, and energy dispersive spectroscopy. Finally, it was confirmed that the hole defect was an invasive air hole. The invasive air hole destroyed the fatigue strength of the crankshaft. As the mining vehicle worked at full load, the stress exceeded the fatigue limit of the defect location, which promoted the rapid formation and propagation of fatigue cracks, leading to the rapid fracture of the 7th crankshaft. After the fatigue fracture of the 7th crank, the crankshaft continued to rotate due to inertia, resulting in an instantaneous overload of the 8th crank, which in turn led to the instantaneous failure and fracture of the 8th crank. In response to the reasons for the formation of defects, some improvement measures were proposed for the content and moisture content of gas generating substances in molding sand and core sand, the depth of gas holes, and furnace material management, in order to improve the quality of castings.
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