Hydrogen induced cracking tests of high strength steels and nickel-iron base alloys using the bolt-laded specimen

摘要

Hydrogen induced cracking tests were conducted on thih strength steels and nckel-iron base alloys using the constant displacement bolt-loaded compact specimen. The blot-loaded specimen was subjected to both acid and elecrochemical cell environments in order to produce hydrogen. The materials tested were A723, Maraging 2000, PH 13-8 Mo, Alloy 718, Alloy 706, and A286, and ranged in yield sltrength from 760-1400 MPa. The effects of chemical composition, refinement, heat treatment, and strength on hydrogen induced crack growth rates and thresholds were expamined. In general, all high strength steels tested exhibited similar crack growth rates and threshold levels. In comparision, the nickel-iron based alloys tested exhibvited up to three orders of magnitude lower crack grwoth rates than the high strength steels tested. It is widely known that high strength steels and nickel base alloys exhibit different crack growth rates, in part, because of their different crystall cell structure. In the high strength steels tested, refinement and heat treatment had some effect on hydrogen induced cracking, though strength was the predominant factor influencing susceptibility to cracking. When the yield strength of one of the high strength steels tested was increased moderately, from 1130 MPa to 1275 MPa, the incubation times decreased by over two orders of magnitude, the crack growth rates increased byan order of magnitude, and the threshold stress intensity was slightly lower.