Characterizations of the microstructure and chemical composition of oxide films formed on 316NG stainless steel following exposure experiments in high temperature water with various dissolved hydrogen(DH)concentrations were conducted.The results showed that the oxide film formed at different DH concentrations had a double-layer structure.The outer layer consisted of Fe-rich spinel oxide and small hematite particles,while the inner layer was Cr-rich spinel oxide.Increasing DH concentrations resulted in decrease of Cr-but increase of Fe-concentrations in the inner layer of the oxide film.Further,along the thickness direction,a continuous decrease of Cr-and increase of Fe-concentrations was observed from the outer to the inner layer.The DH effect was attributed to the enhanced oxidative dissolution of Fe as well as the accelerated diffusion of Fe from the substrate to the oxide film by hydrogen.