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Diffusion and trapping mechanisms are 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 1M H 2 SO 4 at ambient temperature shows a relation between the apparent diffusion coefficient D app and the apparent subsurface concentration of hydrogen C 0app . Two domains can be separated and are mainly associated with a competition between two distinct processes: hydrogen trapping and hydrogen diffusion. These results are 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 diffusion processes (0.26eV) and trapping processes (0.58eV) are 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).

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