Analysis of Cracking Causes of Some Stainless Steel Bolt in a Nuclear Power Plant

Some stainless steel bolt cracked in a nuclear power plant. The microstructure, fracture morphology and dislocation structure of the cracked bolt were observed by optical microscopy, scanning electron microscopy and transmission electron microscopy. And the reasons for cracking of the bolt were analyzed. The results show that the fracture surface displayed obvious characteristics of fatigue striation, and the space between the fatigue striations was quite small. In the microstructure near the fracture, the dislocation density was high, and lots of persistent slip bands (PSBs) were formed; while in the structure far away from the fracture, the dislocation density was low, and there were no PSBs formed. Considering service conditions of the cracked bolt, it could be concluded that high-cycle fatigue fracture was the main failure reason of the bolt.