Study of the hydrogen diffusion and segregation into Fe–C–Mo martensitic HSLA steel using electrochemical permeation test

Abstract

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).

Reversible hydrogen trapping in a 3.5NiCrMoV medium strength steel

“…Table 3 presents the values of the reversible trap density, N T , evaluated using Eq. (3), using (i) the values of D eff for each transient as listed in Table 3, (ii) D L = 1.29 Â 10 À6 cm 2 s À1 obtained from previous fitting of the two rise transients, see Table 2, (iii) the value of N L = 1.45 Â 10 23 sites cm À3 , obtained for a Fe-0.45 wt% C-1.5 wt% Mo quenched and tempered martensitic steel [28] (this value is not available for the 3.5NiCrMoV steel), and (iv) E b = 29 kJ mol À1 . The value of E b corresponds to a specific type of trap.…”

Effect of structural defects on the hydriding kinetics of nanocrystalline Pd thin films

“…Consequently, part of the hydrogen absorbed by the Pd films should be located in saturable trapping sites, which are readily filled over the whole p H2 -range considered in this study. Hydrogen trapping sites in metals are indeed commonly divided into unsaturable and saturable sites [59,60], part of the latter being irreversible [61,62], i.e. potential wells being too deep to allow hydrogen atoms to escape without external energy.…”

On the Implication of Hydrogen on Inter-granular Fracture

“…The experimental procedure for Electrochemical Permeation (EP) tests is detailed in previous works (Frappart 2010, 2011, 2014. EP involves using two cells separated by a nickel membrane.…”

“…Our experimental procedure consists of two steps: hydrogen charging up to a steady state, followed by a desorption step of hydrogen without any charging conditions. The detail of the method can be checked on specific publications of our group (Frappart et al 2010, 2011,2014. This one allows to determine specially the effective diffusion coefficient associated with diffusive hydrogen D eff , the apparent solubility C H and the amount of deep trap sites N T .…”