Measurements of H evolution rates were used to study the lattice, and overall, diffusion rates. Classical reaction kinetics were used to describe the movement of H in ferritic steels at 100 to 350C. The processes of H lattice diffusion and H release from traps in the metal were treated as being consecutive reactions, with the former being the rate-controlling one at high temperatures and the latter controlling at low temperatures. In the intermediate region, where neither process was predominant, there was a gradual transition from one mode of reaction to another. The true lattice and overall diffusivity coefficients were calculated in the intermediate-temperature region (table 49).

F.R.Coe, J.Moreton: Metal Science Journal, 1969, 3, 209-15

Table 49

Diffusivity of H in Fe-0.73%C