Hydrogen generation during repassivation on ultra-high-strength steel

Hydrogen embrittlement in ultra-high-strength steel (UHSS) poses a critical risk of catastrophic failure, yet the mechanisms of hydrogen permeation remain insufficiently understood. In this work, hydrogen permeation was measured in a Devanathan-Stachurski cell using Pd-coated UHSS samples of the type DP1000, where the Pd deposition protocol was optimized to improve surface quality and interface integrity, and thereby sensitivity of the approach. Incorporating a dedicated reduction step before Pd metallization improved both Pd surface quality and the UHSS-Pd interface via removal of residual interfacial oxides, as confirmed by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The optimization of the Pd coating enables stable and highly reproducible detection of substantially lower hydrogen permeation currents. Cathodic permeation tests confirmed that the optimized protocol enables detection of lower permeation currents, while estimated diffusion coefficients remain unchanged. Further, measurements on the anodic side of the OCP revealed measurable hydrogen permeation during self-repassivation, detectable due to the optimized protocol. These results demonstrate that hydrogen generation and permeation can be effectively captured under slow and self-passivating corrosion conditions, highlighting the relevance of the method for assessing the impact of hydrogen-assisted damage in actual service environments.