Reasons Analysis on Fracture of Valve Bolts

Fracture of 304 stainless steel valve bolts occurred during the service process, and means such as macro examination, chemical compositions analysis, hardness test, fracture analysis, energy spectrum analysis, metallographic examination and intergranular corrosion test were used to analyse the fracture property and reasons of the bolts. The results show that the fracture of the bolts was intergranular stress corrosion fracture under the coactions of sulfur and chloride corrosive medium, working stress and residual stress. The chemical compositions of the bolts were unqualified with the carbon content being higher than the standard value and chromium content being lower than the standard value resulted in grain boundary poor chromium, which increased the sensitivity of the bolts to stress corrosion fracture.