The effect of dislocation arrangements, upon H permeation in spheroidized low-alloy steel (0.89C, 2.06Mn, 0.32wt%Cr), were studied by using electrochemical methods. Specimens were cyclically deformed in H or ultra-high vacuum so as to produce dislocation structures which exhibited various degrees of cell formation. In the case of undeformed material, the density and mean binding energy of the H traps were determined by using trapping theory. The permeability of this material was described by:

P (mol/cm-bar½s) = 1.2 x 10-7 exp[-33.2(kJ/mol)/RT]

The dislocation cell structure which formed during fatigue reduced the apparent diffusion coefficient as the trap density was increased. The steady-state H permeation flux increased because the dislocation cores acted as short-circuit diffusion paths.

H.J.Maier, A.Schettler, H.Kaesche: Werkstoffe und Korrosion, 1991, 42[5], 212-8

Table 72

Parameters for H Diffusion in Fe-Ni at 600 to 800C