Hydrogen-induced delayed fracture behaviour of V+Nb-microalloyed high-strength bolt steel with internal and environmental hydrogen

Hydrogen-induced delayed fracture (HIDF) behaviour of a V+Nb microalloyed 1300-GPa-grade high-strength bolt steel was explored by slow strain rate tensile (SSRT) tests under pre-hydrogen-charging (internal hydrogen) and dynamic hydrogen-charging (environmental hydrogen) conditions. The tested steel exhibited much lower HIDF resistance in the condition of environmental hydrogen than that of internal hydrogen, which is primarily due to the difference in hydrogen diffusion and accumulation characteristics and the hydrogen trapping effect of MC carbides. Therefore, for applications of high-strength bolt steels based primarily on the designing strategy of hydrogen trapping, it is extremely important to prevent environmental hydrogen entry in service.