Investigation of Hydrogen Transport Related Fracture in Stainless Steels

Abstract

Stress-assisted hydrogen diffusion analysis was performed on arc-shaped tension specimen (C-specimen) fabricated from Type 21-6-9 stainless steel. Two-dimensional finite element method was applied for the determination of elastic-plastic crack front stress fields, which was later coupled with hydrogen diffusion analyses. The extension of Fick's rule was used as the governing equation for the diffusion analysis. The distributions of hydrogen concentration were compared under various Internal Hydrogen Embrittlement (IHE) and Hydrogen Environment Embrittlement (HEE) conditions. Without any external hydrogen pressure in IHE conditions, the increment of hydrogen concentration driven by the gradient of hydrostatic stress was offset by the out-gasing driven by gradient of hydrogen concentration at the crack front region. As the hydrogen pressure increases, the hydrogen concentration at the crack front region becomes dominant and show peak value around the crack tip. Compared with the results of IHE cases, the hydrogen concentrations in HEE conditions could reach the level of steady state in a relatively short time which is attributed to the high solubility and diffusivity of the material at high temperature.