Diffusion and trapping mechanisms were studied in order to improve Hydrogen embrittlement (HE) resistance of high yield strength steels. Investigations were carried on Fe–C–Mo model steel with a quenched and tempered martensitic microstructure. Hydrogen diffusion was studied by using the electrochemical permeation technique. The influence of the charging current densities in 1 M H2SO4 at ambient temperature shows a relation between the apparent diffusion coefficient Dapp and the apparent subsurface concentration of hydrogen C0app. Two domains could be separated and were mainly associated with a competition between two distinct processes: hydrogen trapping and hydrogen diffusion. These results were correlated to the quantities of reversible and irreversible traps into the membrane. Moreover, the experimental results revealed that the apparent diffusion coefficient increases and the total amount of trapped hydrogen decreases with temperature. The activation energy of the diffusion process (0.26eV) and the trapping process (0.58eV) were supposed to be, respectively, affiliated with lattice diffusion and with trapping on incidental dislocations and/or on martensitic lath interfaces due to misorientations (geometric necessary dislocations).

Study of the Hydrogen Diffusion and Segregation into Fe–C–Mo Martensitic HSLA Steel using Electrochemical Permeation Test. S.Frappart, X.Feaugas, J.Creus, F.Thebault, L.Delattre, H.Marchebois: Journal of Physics and Chemistry of Solids, 2010, 71[10], 1467-79