Effect of hydrogen on plasma post-oxidation of ferrous alloys

The effect of hydrogen on plasma post-oxidation following plasma nitriding of a ferrous alloy was investigated. The increase in the hydrogen concentration in the plasma progressively reduces the hematite/magnetite concentration ratio in the outermost oxide layer down to zero at 25% H2 concentration. Atomic hydrogen originating from scission of hydrogen molecules in the plasma leads to reduction of Fe(III) in hematite into Fe(II) in magnetite by controlling the gas mixture reduction potential.