Reason Analysis on Delay Brittle Fracture of 30MnSi Steel Bars for Pipe Piles

To solve the delay brittle fracture problem of 30MnSi steel bars for pipe piles (PC steel bars), the fracture reasons were analyzed from mechanical properties, chemical compositions, microstructure, surface quality, fracture morphology and follow-up heat treatment processing technology and other aspects. The results show that the delay brittle fracture of the PC steel bars was mainly due to the unstable tempering temperature during the final heat treatment process which results in the formation of local abnormal martensite structure. Because of the existence of internal stress from the martensite structure and inside hydrogen, when receiving external force, fracture source would gradually form at the abnormal martensite zone over a period of time, and resulted in the sudden brittle fracture of the PC steel bars after being placed for a few days.