The diffusivity of H in fully annealed specimens was measured, by using an electrochemical permeation method, at temperatures of between 283 and 313K. The temperature and compositional dependences of the diffusion coefficients were explained by using simple trapping models. The strain fields around the substitutional alloying atoms were also studied by monitoring the variation of the lattice constant as a function of alloy content. It was found that the H diffusivity was lowered by alloying (figure 7). This was explained by suggesting that the H interstitial sites around the substitutional atoms acted as trapping sites. The H diffusion behavior was strongly affected by elastic interactions between H and the alloying atoms. The diffusion data for H in pure Fe was described by:

D (m2/s) = 7.39 x 10-8exp[-5.05(kJ/mol)/RT]

These values were hardly affected by the trapping effect of lattice defects and impurity atoms.

Effect of Substitutional Alloying Elements (Al, Si, V, Cr, Mn, Co, Ni, Mo) on Diffusion Coefficient of Hydrogen in α-Iron. H.Hagi: Materials Transactions, 1992, 33[5], 472-9

Table 38

Diffusivity of H in Fe and Steels at 25C