Abstract

Hydrogen embrittlement (HE) significantly impacts high-strength steels by reducing ductility and promoting brittleness. Research has shifted towards multifaceted approaches, with molecular dynamics (MD) simulations at the atomic scale being crucial. In this research, MD was employed using two interatomic potentials to investigate the role of hydrogen in Fe-C systems. The atomic models maintained a consistent carbon concentration while varying concentrations of hydrogen and progressed from single-crystalline through bicrystalline to polycrystalline models, increasing complexity and incorporating grain boundaries (GBs). Results showed a general decline in mechanical properties of the Fe-C system with increasing hydrogen content, with the failure outcome being influenced by simulation boundary conditions such as fully-periodic compared to shrink-wrapped in the pulling direction. The impact of hydrogen varied by crystal direction, highlighting anisotropy. Hydrogen significantly increased local vacancy and void formation, leading to earlier fracture initiation, and strongly suggesting the hydrogen-enhanced strain-induced vacancies (HESIV) mechanism among those commonly proposed for HE. Although evidence for the hydrogen-enhanced decohesion (HEDE) mechanism was limited, a potential synergistic effect with HESIV was suggested. The influence of hydrogen on dislocation density varied, and phase transformations (BCC to FCC/HCP) were frequent, driven by stress, crystal orientation, and potential type. Despite limitations, MD provides key insights into HE, underscoring the need to integrate simulation results with experimental data for a comprehensive understanding.