The Tensile Ductility of a High-Strength Steel in an Atmosphere of Hydrogen

Comparison of the tensile ductility of a hot-work die steel when tested in a gaseous hydrogen environment (at pressures up to 1 atm) with that obtained under vacuum, or in air, reveals a dependence upon hydrogen pressure, strain rate, and temperature. The increasing embrittlement at higher hydrogen pressures, slower strain rates and decreasing temperature (down to −70°C), as well as a dependence on the amount of metal surface exposed to hydrogen, is shown to be consistent with a proposed model where the dissociated hydrogen adsorbed on the metal surface may migrate to a slowly propagating crack and sustain low-strain propagation. Embrittlement becomes less at temperatures below −70°C because of the restricted migration of the adsorbed hydrogen. In the material concerned,the presence of hydrogen results in the early attainment of a critical crack size for catastrophic propagation, because of the inherent notch sensitivity.