The electrochemical permeation technique was used to investigate the effect of microstructure, H activity, and stationary dislocations generated by tensile straining on the permeation and degassing of H. A conventional 2.25Cr-1Mo steel and a 3Cr-1Mo-V steel were selected. The effective diffusion coefficient of H derived from permeation and degassing transients showed a slower diffusivity in the V-containing steel at room temperature, regardless of the H activity. A large plastic deformation obtained by tensile straining in the homogeneous deformation domain only led to a moderate decrease in the H diffusivity in both steels. The results were compared with the literature data on H permeation in Fe and ferritic steels. On the other hand, the H content was measured with the melt extraction method after cathodic charging and subsequent aging at room temperature for different times to determine the diffusible (lattice + reversibly trapped) H concentration. It was shown that the latter was larger in 3Cr-1Mo-V steel, which contained, in addition, a large fraction of "strong reversible" traps. A good concordance was found between the diffusible H concentration values computed from steady-state permeation measurements and from graphical integration of decay transients.

Quantification of Hydrogen Diffusion and Trapping in 2.25Cr-1Mo and 3Cr-1Mo-V Steels with the Electrochemical Permeation Technique and Melt Extractions. A.M.Brass, F.Guillon, S.Vivet: Metallurgical and Materials Transactions A, 2004, 35[5], 1449-67