The thermal stability and the structural evolution of graphene grown on Fe(110) has been studied upon annealing in ultra-high vacuum conditions (UHV, P ≤ 10⁻⁹ mbar) and in the presence of gaseous ethylene at a pressure of ∼10⁻⁶ mbar by grazing incidence X-ray diffraction. It was observed that upon annealing at temperatures below 630 °C, graphene on Fe is thermally stable. Exposure to ethylene at these temperatures promotes the formation of graphene while inhibiting its deterioration. Annealing graphene/Fe(110) at temperatures above 630 °C results in a fast degradation of graphene followed by carburization of the sample, that is the irreversible formation of various iron carbides, with the most common phases being Fe₃C (cementite) and Fe₇C₃ (Eckström-Adcock carbide). Annealing of the carburized sample does not result in the formation of a detectable graphitic structure.