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Abstract

Hydrogen impurities in steels can lead to a degradation of the mechanical properties of the materials. Due to the complexity of this problem, the fundamental mechanisms of this hydrogen-embrittlement in steel industries has not been fully understood. One possible cause is that H impurities may weaken the bonding of Fe atoms near the grain boundaries, leading to an embrittlement of the bulk material. In this work, we study the interactions of H interstitials with Σ3 and Σ5 grain boundary (GB) in bcc Fe, and investigate the migration processes of H within the GB, using density functional theory. We show that the interface of a Σ3 and a Σ5 GB can provide an energy trap of up to 0.3 eV and 0.6 eV for interstitial H, respectively. The energy landscape of a H interstitial within a Σ5 GB, including the energetics of various stable sites and transition barriers between these sites, is carefully studied. Based on energetic information, we setup a lattice kinetic Monte Carlo model to study the dynamics of H diffusion in the vicinity of the GB.