An electrochemical permeation technique was applied to mild steel and medium-C steel. It was found that mild steel exhibited a higher H permeation rate and diffusivity than those of medium-C steel. The highest permeability and diffusivity in heat-treated medium-C steel was found for the spherodized condition. The lowest permeability and diffusivity were found for the martensitic condition. Annealed and normalized structures exhibited an intermediate permeation and diffusion behavior. The results of contact chemical printing techniques confirmed that the main diffusion path was via lattice and carbide/ferrite interfaces in pearlitic and spherodized samples, and via lath interfaces in martensitic samples.

W.C.Luu, J.K.Wu: Corrosion Science, 1996, 38[2], 239-45