We have performed in situ X-ray diffraction measurements under high pressure and high temperature to study hydrogen solubility in Fe3C carbide. Hydrogen solubility can be estimated from a volume expansion associated with hydrogen incorporation into metal. The lattice volumes and phase relations of Fe3C-H system and Fe3C were measured up to 14 GPa and 1973 K. The lattice volumes of Fe3C measured in this study are well fitted using the 3rd order Birch-Murnaghan equation of state with the reported elastic parameters of Fe3C. Obtained lattice volumes of Fe3C-H are quite consistent with those of Fe3C. No difference between the melting temperatures of Fe3C-H and Fe3C was observed. These results demonstrate that hydrogen incorporation into Fe3C does not occur and hydrogen is unlikely to coexist with carbon in iron-alloy up to 14 GPa.
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