Abstract: The invention relates to an improved composite used as a bipolar separator plate in fuel cells. The composite of the invention comprises a steel substrate having a carbon coating thereon, the carbon coating comprises a carbon layer derived by pyrolysis of an acetylenic polymer having a content of carbon of at least 90%, the carbon layer protects the substrate against corrosion and improves long term contact resistivity, the polymer is soluble at a temperature below 110° C. in an organic solvent, and the carbon layer contacts said steel substrate. A process for preparing the composite according to the invention is also disclosed.