Fracture analysis of large helical compression spring under pressure test

The causes of fracture of large helical compression spring in pressure test were analyzed by means of macroscopic examination，fracture micro morphology analysis，chemical composition analysis，metallographic analysis and hardness test. The result showed because of the limit of the hardenability of the spring material，the spring was not fully quenched during quenching. At this time，the residual stress belonging to thermal stress was larger，which caused the circular transverse crack inside. During the subsequent spring pressure test，the surface of the spring steel was not enough to bear the test stress，the transverse fracture of the spring occurred.