A review of available hypotheses for hydrogen embrittlement (HE) in its relation to austenitic steels is presented. It is shown that the hydrogen-enhanced localized plasticity theory adequately describes the features of HE. Nevertheless, being developed within the frame of continuum mechanics, it overestimates the hydrogen-induced shielding of the elastic interaction between dislocations and does not take into account the hydrogen-induced change in the electron structure of austenitic steels. Ab initio calculations and experimental studies of the electron structure show that the hydrogen in austenitic steels increases the concentration of free electrons, nf, and the interpretation of available experimental data shows that when designing steel, alloying the steel with elements that decrease nf improves hydrogen resistance. Experimental tests are carried out, and their results are discussed. Based on the hydrogen-increased concentration of thermodynamic equilibrium vacancies in the interstitial solid solutions, a new model for hydrogen-induced shear localization is proposed.

Hydrogen effects in austenitic steels are studied using the ab initio calculations of the electronic structure, conduction electron spin resonance, internal friction, and mechanical tests. It is shown that the hydrogen-caused elastic shielding of dislocations is not sufficient for interpretation of hydrogen-enhanced localized plasticity (HELP). Similar effects of hydrogen and nitrogen and the opposite effect of carbon on dislocation mobility are demonstrated, which cannot be explained within the framework of continuum mechanics. An interpretation of hydrogen embrittlement in terms of the hydrogen-increased concentration of free (conduction) electrons is proposed. Based on the electronic approach to the HELP phenomenon, practical recommendations for increase in hydrogen resistance of austenitic steels are made and tested.

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