Fractographic study of fatigue cracks in a steel car wheel

• Fatigue failure mechanism of a fractured steel wheel is revealed.
• The failure locations are mainly around the cooling hole and the bolt hole.
• Multiple crack origins are detected on the surface of the disc.
• These failures mechanism are modes of fretting fatigue damage and consequence of stress concentration.

The aim of this study is to reveal the fatigue failure mechanism of the fractured steel wheel after the cornering fatigue test. High power scanning electron microscopy is performed to analyse the fractured surfaces of the wheel and to examine the fatigue cracks in greater detail. The results show that the failure locations are mainly around the cooling hole and the bolt hole of the disc. The fatigue cracks are distributed along the circumference of the disc, and their lengths are approximately equal to each other. Further fractographic analysis reveals that multiple crack origins are detected on the surface of the disc, at the same time the fatigue crack features are very obvious. In addition, transgranular cleavage, ductile fatigue striations and brittle striations are also found. These failures are modes of fretting fatigue damage and consequence of stress concentration, which are attributed to the surface quality, the thickness variation and the corner radius of the disc.