Hydrogen-Induced Crack Propagation in a QT-Steel Weldment

A hydrogen-induced fracture process in the HAZ of a QT-steel weldment is studied numerically. Two-dimensional models are used to estimate the transient distributions of stress and hydrogen during the cooling and during the subsequent crack propagation. The distributions of hydrogen in front of a blunted crack are studied for different void volumes in the fracture zone corresponding to brittle and ductile fracture mechanisms. It is tentatively concluded that the incubation time at slow crack growth is not controlled by the hydrostatic stress. A ductile fracture mechanism leading to a relative void volume of 0.02-0.05 in the fracture zone is found to imply long incubation times resulting in a low average crack propagation speed.