Failure of Wheels Due to Improper Manufacturing Process

摘要

Premature cracking of wheels was observed in the prime movers used for logistic services. The fractures were located between the stud-holes and between stud-holes and hand-holes. A detailed study was carried out to investigate root cause(s) of these failures. Although chemical composition and mechanical properties of bulk material were the same, there was a difference in microstructure and hardness at the edges of stud-holes. In addition, metallography revealed the presence of burr at the circumference of the stud-holes. A number of hairline cracks and a severely distorted structure were also observed at this location. Fractography, using an SEM, confirmed the presence of sharp cracks at the root of the burr. The hardness at the edge was also higher than the bulk material. The problem was found to be due to the manufacturing process which may be inducing more work hardening and deformation than permissible at regions near the holes edges. This deformation and hardening created a material condition that led to fine cracks in this region. The resulting fine cracks grew during service under fatigue and caused premature failure of the wheels.