Improvement of the corrosion resistance of a low carbon steel using a two step plasma treatment

The aim of this work was the improvement of the corrosion resistance and mechanical properties of a low alloyed carbon steel using a duplex plasma treatment. The first step of the plasma treatment consisted in a nitriding treatment with a N2/H2 gas mixture. The second step consisted in a carbon treatment using a CH4/H2 gas mixture, the entire treatment occurring in the same inductively coupled plasma reactor without exposition to the atmosphere. Topological and chemical analysis indicated that the superficial layer induced by the plasma treatment was homogeneous, hard, enriched in nitrogen, carbon and oxygen. The surface layers gave good passivation properties to the 30CrMo12 steel. The electrochemical properties of the treated samples were studied by electrochemical impedance spectroscopy and voltammetry in an aerated 0.5 mol/l NaCl solution. For the optimal conditions of treatment, the rate of protection of the duplex steel was more than 99.6% and remained constant for long immersion times.