The effect of the microstructure upon steady-state permeation was studied at 15 to 80C, and a H-pressure of 1bar, by using electrochemical methods. In annealed pure Fe, the permeation was described by the expression:

P (mol/cm s bar½) = 2.57 x 10-7 exp[-34.32(kJ/mol)/RT]

The permeability was not greatly affected by impurities, oxide inclusions, or high densities of lattice defects. Varying the steel microstructure from pearlitic, via martensitic, to bainitic decreased the permeability by a factor of between 4 and 8. The presence of carbide precipitates in the tempered martensite did not change the permeation coefficient. Cold-rolling to 15% deformation had no effect upon the steady-state permeation. Cold-rolling to greater than 40% deformation significantly decreased the permeation. There were no changes in the temperature dependence.

E.Riecke: Werkstoffe und Korrosion, 1981, 32[2], 66-72