First-principle study of hydrogen solubility in bcc iron

To design safe steel hydrogen gas pipelines, it is necessary to understand hydrogen solubility in iron in order to reduce the risk of hydrogen embrittlement. Here, density functional theory (DFT) and quasi-harmonic approximation (QHA) are used to compute the solution energy, and thus predict the lattice solubility of hydrogen in bcc iron in equilibrium with hydrogen gas for temperature up to 1000 K and pressure up to 1 GPa. Our results reveal that the solubility increases with temperature and pressure, and the well-known Sieverts’ law is obeyed within a wide range of conditions except at near 0 K, where a partial volume term dominates. Furthermore, the underlying driving force for this dependence comes from the gas component of the solution energy.