A neural network interatomic potential (NNIP) has been developed for the ternary system of \(\alpha \) -iron, carbon, and hydrogen to clarify the degradation behavior of Fe-C steels in hydrogen-rich environments. The NNIP was trained on an extensive reference database generated from spin-polarized density functional theory (DFT) calculations. It demonstrates remarkable performance in various scenarios relevant to Fe and Fe-C systems under hydrogen, including the diffusion kinetics of H and C in Fe and their thermodynamic interactions with iron vacancies, grain boundaries, screw dislocations, cementite, and cementite–ferrite interfaces. Using this NNIP, we conducted large-scale (one-million-atom) molecular dynamics (MD) simulations of uniaxial tensile tests on C-containing \(\alpha \) -Fe both with and without H, showing that hydrogen enhances defect accumulation during plastic deformation, which may eventually lead to material failure.
