Abstract: In order to find the failure reason, the chemical composition, microstructure, mechanical properties and fracture morphology of unusual cracking failed 60Si2CrVA steel spring, which was used for 220 kV circuit breaker, were analyzed. The results show that the spring presented a brittle crack characteristic. The cracking reason was that the abnormal high temperature was produced on the surface of supporting ring during the spring grinding process and in the followed water cooling process formed the local quenching martensitic microstructure.