The HIC susceptibility of steels containing Cr, Ni, and Mo under stress and hydrogen diffusion was been investigated by electrochemical methods. As the content of alloying elements increased, the apparent hydrogen diffusion        coefficient (D) and threshold hydrogen permeation rate (Jth) for hydrogen embrittlement decreased.
Hydrogen content (Co) in the steel in NACE TM-0177 solutions increased due to decreasing D with increased Cr content, although hydrogen permeability (J x L) decreased, and the susceptibility to sulfi de stress cracking (SSC) increased as aresult.

Moreover, Mo exhibited clear effect of decreasing J x L, and consequently
the resistance to SSC improved with increasing Cr content.