The hydrogen embrittlement (HE) susceptibility of precipitation age hardened stainless steels (17-4 PH, PH 15-5, PH 13-8 Mo, and others) is well established in the literature. Susceptibility is a strong function of strength and hence lower aging temperatures produce alloys which are more prone to HE. Recently it was shown that uniformly distributed PdAl precipitates improve the HE resistance of a palladium (Pd) modified version of PH 13-8 Mo stainless steel at a yield strength of 1,250 MPa. Intergranular cracking on prior austenite grain boundaries is minimized and transgranular cracking is observed. Trapping analysis of hydrogen permeation data supports the notion that PdAl particles act as beneficial trap sites. However, the effect of PdAl on the HE resistance of higher strength tempers has not been established. Secondly, the influence of dual phase microstructures typical of cast or as-welded PH 13-8 Mo on the PdAl effect has not been investigated. In the present study, the authors examine the influence of Pd on the HE susceptibility of PH 13-8 Mo stainless steel (SS) over a range of strengths levels and also for a dual phase as-welded microstructure. Specifically, the authors compare the HE behavior of conventional wrought PH 13-8 Mo SS tomore » wrought PH 13-8 SS alloyed with 0.4, 0.75 and 1.0 wt. % palladium and similarly alloyed, autogenous electron beam welded PH 13-8 Mo SS. Wrought alloys were examined after aging to yield strengths of nominally 1000, 1140, and 1440 MPa in accordance with the H1100, H1050 and H925 tempers, respectively. The as-welded material was similar in hardness to the wrought H1100 condition.« less