It was pointed out that previous data on the diffusivity of H through this body-centered cubic material had been inconsistent. A statistical analysis of the data indicated that only those results which had been obtained by using electrochemical and H-gas equilibration methods involving ultra-high vacuum and Pd-coated membranes were reliable. It was concluded that, at temperatures between -40 and 80C, the most trustworthy expression for D was:

D (m2/s) = 7.23 x 10-8 exp[-5.69(kJ/mol)/RT]

At temperatures of between and 50 and 550C, the best expression was suggested to be based upon a pre-exponential factor of between 10-7 and 2.52 x 10-7m2/s and an activation energy of between 6.70 and 7.12kJ/mol. It was proposed that the differing diffusivities were the result of an increase, with increasing temperature, of the fraction of H atoms which hopped from octahedral, rather than from tetrahedral, sites. The diffusion of H in deformed Fe was analyzed by using a semi-quantitative model in which it was assumed that the retarding effect of trapping sites upon diffusion was partially compensated by pipe diffusion along dislocations.

The Solubility and Diffusivity of Hydrogen in Well-Annealed and Deformed Iron. K.Kiuchi, R.B.McLellan: Acta Metallurgica, 1983, 31[7], 961-84

Table 35

Rate of H Transport by Dislocations in Fe at a Strain Rate of 10-5/s

Table 36

Trapping Energies for H in Fe Alloys

a: first-order interaction coefficient, b: trap energy