Fracture Reason Analysis on Coil Spring Used in Train

Means of optical emission spectrometer,optical microscope,scanning electronic microscope were used to analyze the fracture reason of spring which broke after 4 years service. Study results indicated that the fracture was corrosion fatigue. Spaces existed in the organic coating of spring’s surface,so the external water vapor and corrosive ions could penetrate the organic coating,insult in corrosion to the base metal and produce corrosive pits which became stress concentration points. The fracture source formed at the coactions of cyclic loading and corrosive ambient and led to the final corrosion fatigue fracture.