Hydrogen trapping ability of steels with different microstructures

The effects of microstructure on the hydrogen trapping ability and effective diffusivity in steels with different carbon content have been studied. The sites for trapping hydrogen in pure iron, ferrite/pearlite steel, and the martensitic structure etc. have been identified. The hydrogen pick-up was generally increased with the amount of grain boundary area in the steel. The hydrogen content of a steel after hydrogen charging increases and its hydrogen apparent diffusivity decreases, with a lowering of the transformation temperature. Thus a fully martensitic structure occludes the largest amount of hydrogen and possesses the lowest hydrogen apparent diffusivity. This microstructure retains a large portion of hydrogen even after high temperature outgassing. However, the hydrogen content reduces when the martensitic structure is tempered before charging. The effect of carbon content of the steel on the hydrogen occlusivity will also be discussed.