Hydrogen-Assisted Subcritical Crack Growth Rate in Cr-Mo Steels

Hydrogen substantially reduces fracture properties such as threshold stress intensity factor K_IH and tearing resistance dJ/da in conventional Cr-Mo steels. In order to enable the life assessment of a reactor with a hydrogen-induced crack using a failure assessment diagram (FAD), an experimental database of hydrogen-assisted subcritical crack growth rates da/dt is requisite. However, there are very few studies concerning the effects of hydrogen- and temper-embrittlement on da/dt at ambient temperatures in 2.25Cr-1Mo steels with high and low impurity levels. In this paper, vacuum melted lab heats of 2.25Cr-1Mo steel were supplied with compositional controls. Some specimens were embrittled by step cooling heat treatment (SCHT). Subcritical crack growth rate at a constant load was obtained by means of the potential drop method for 2.25Cr-1Mo steel with initial internal hydrogen (3.2 mass ppm).