Abstract
Despite the great technological importance of hydrogen embrittlement in many metals and alloys, and the many investigations thereby motivated, no firm consensus exists on the mechanism in any one case. This review concentrates on the degradation of ferrous alloys by hydrogen, discussing the often conflicting results of experiments on the effects of hydrogen on the plastic properties of iron and steels. The decohesion model and the localized slip model, both depending on the electronic disturbance at the adjoining metal atoms caused by hydrogen, and the experiments supporting one or the other point of view, are critically discussed. The versatility of hydrogen, which is capable of producing diverse effects, challenges the experimentalist to elucidate which characteristic of hydrogen predominates in a given set of circumstances.
