The effect of cold work on H permeation in samples which contained 30 or 110ppm of C was studied, at temperatures of between 273 and 333K, by using an electrochemical permeation method. It was found that H diffusivity in the fully annealed material was independent of the C content, and could be described by:

D (m2/s) = 7.69 x 10-8 exp[-5.80(kJ/mol)/RT]

The decrease in H diffusivity due to cold-work was much larger in specimens with a higher C content. The trap density, which was estimated from permeation data, was linearly dependent upon the inverse square of the average cell-size. This indicated that the reduction in the H diffusivity of cold-worked specimens depended upon the dislocation density, and that differences in C content affected the diffusivity indirectly via dislocation multiplication. The binding energy of the traps was deduced to be between 23 and 27kJ/mol. These values were of the same order as that of the elastic field of a dislocation.

S.Hinotani, Y.Ohmori: Transactions of the Japan Institute of Metals, 1985, 26[9], 622-9

Table 18

Diffusivity of H in Fe at 25C