Fracture Analysis of High-strength Stainless Steel Bolt in Tropical Reef Environment of Low Latitude

Delayed fracture occurred to a high-strength stainless steel 05Cr17Ni4Cu4Nb bolt after short-term service in the reef atmosphere environment of low latitude. The fracture mechanism of the bolt was investigated by chemical composition testing, microstructure examination, mechanical properties and hardness testing, and fracture morphology. The results show that the microstructure of the bolt is normal, and its chemical composition, mechanical properties and hardness meet the standard requirements. The fracture morphology shows the typical stress corrosion fracture characteristics of dendritic crack and intergranular fracture. Combined with the assembly structure, force and service environment, the environmental brittleness mechanism of the bolt can be determined as stress corrosion cracking. This type of bolts has never fractured due to delayed cracking after long service in Hainan, and other coastal marine environments in tropical, subtropical and temperate regions of China, which indicates that the stress corrosion cracking (SCC) of the 05Cr17Ni4Cu4Nb bolt in the assembly structure was promoted by the reef atmosphere environment of low latitude, with frequently alternating dry and wet, as well as high salt spray, temperature and humidity.