The so-called diffusible H in steels was observed by using autoradiography techniques. Specimens which contained diffusible H were prepared by means of electrochemical cathodic charging, while those without diffusible H were prepared by annealing (373K) after H-charging. Transmission electron microscopic autoradiographs suggested, on the basis of the Ag grains which developed, that the H-trapping sites were grain boundaries and internal interfaces of ferrite-cementite and ferrite-lath structures. The Ag grains disappeared upon keeping the samples at 373K. Most of the H-trapping sites released almost all of the H at 373K. It was concluded that these sites, in high-strength steels, supplied the so-called diffusible H. The H absorption characteristics of quench-hardened and tempered steels were evaluated by using thermal desorption spectrometry. The results of T electron microscopic autoradiography, and thermal desorption spectrometric analysis of 360 to 370K peaks, revealed the diffusing H which was released over a few days. The diffusible H from trapping sites such as the internal interfaces of ferrite-cementite or ferrite-lath structures was distinguished from diffusing H.

Observation of Hydrogen Distribution in High-Strength Steel. G.Katano, K.Ueyama, M.Mori: Journal of Materials Science, 2001, 36[9], 2277-86