The effect of microstructure and surface condition on hydrogen permeation in AISI 4340 steel

Hydrogen permeation through thin foils of AISI 4340 steel, quenched and tempered with a variety of surface conditions, has been experimentally investigated. As the hardness increased, the permeation rate decreased; while, as the surface finish became rougher, the permeation rate decreased. These results were interpreted in terms of variations in the surface concentration of hydrogen and variations in the apparent diffusion coefficient due to trapping at martensite lath boundaries and martensite/carbide interfaces