Theory for hydrogen desorption in ferritic steel

After a concise review of the analytical models available for the interpretation of thermal desorption rates for hydrogen effusion from steel, a numerical method that incorporates the essence of local equilibrium and detrapping kinetics has been implemented to account for the real complexity of practical experiments. For example, the model permits the treatment of multiple kinds of traps, uses very few fitting parameters, and has been tested against new experimental data and to assess the influence of a variety of variables such as trap density, on the nature of the desorption process. There remain, however, significant discrepancies when attempts are made to rationalise diverse observations reported in the literature. In particular, comparisons made between the trapping of hydrogen in pure iron and interstitial-free steel indicate a much stronger binding energy for hydrogen in the former case.