Steel (0.16 to 0.99%C) specimens were saturated with H by means of cathodic charging in aqueous solutions, and the H diffusion coefficients were deduced from measured H evolution rates during subsequent annealing. The diffusion coefficients were found to vary with the steel structure, and to be at a minimum when the H solubility was at a maximum. The diffusivity decreased with increasing C content. This behavior was consistent with the theory that interfaces between ferrite and carbide acted as traps for diffusing H.

J.F.Newman, L.L.Shreir: Journal of the Iron and Steel Institute, 1969, 207[10], 1369-72