Chromium nitride coatings were formed on the surface of a grade of martensitic steel by pack nitriding process with an aim to increase acid corrosion resistance of such steel grade so as to enable it to be used as a material for bipolar plates in proton exchange membrane fuel cells. The effects of processing conditions on phase and layer structures of the coatings were investigated to identify favourable conditions for forming a coating structure consisting of an outer chromium nitride layer and a Cr enriched alloy surface layer underneath so that corrosion resistance of such coated steel can be maximised. The corrosion resistance of the coated steel was confirmed by gravimetric test in which the specimen was immersed in a H₂SO₄ solution and then weighed at regular intervals by taking it out of the solution.

chromium nitride coating,martensitic stainless steel,corrosion resistance