Dislocation Transport of Hydrogen in Steel

It has been proposed that the transport of hydrogen by dislocations is an important factor in the embrittlement of alloys. For example, it has been shown that plastic deformation increases the absorption of hydrogen from the environment due to the motion of dislocations during plastic deformation.1 In addition, there are experiments which show increased solubility and decreased diffusivity of hydrogen for samples that have been cold worked prior to permeation experiments.2,3 These results indicate that there is an interaction between hydrogen and dislocations and therefore should be considered when evaluating the mechanism of hydrogen embrittlement. Considerable controversy has arisen with respect to the exact role which dislocation transport plays in the embrittlement process. Some workers have suggested that the dislocations transport hydrogen to fracture initiation sites such as inclusions, microvoids or grain boundaries where eventually sufficient pressures develop to promote embrittlement.4 Others have proposed that transport is a necessary but not sufficient condition for embrittlement in which kinetic factors limit the hydrogen supersaturation and pressures at discontinuities.5