Increase in Hardness and Corrosion Resistance of a Medium-Carbon Steel Surface Using Cathodic Plasma Electrolytic Nitriding

The structural phase composition and some properties of a modified medium-carbon steel 45 surface after being subjected to cathodic plasma electrolytic nitriding in ammonium chloride and ammonia solution were studied. It was shown that the steel surface cathodic nitriding is accompanied with a high-temperature oxidation along with formation of FeO, Fe2O3, and Fe3O4 oxides, as well as nitrogen diffusion and quenching with formation of FeN, Fe3N, and Fe4N phases, martensite, and residual austenite. A competitive effect was revealed of the surface erosion resulting from the discharges and high-temperature oxidation on the morphology and surface roughness. It was found that the maximum microhardness of the modified layer reaches 1040 HV, and the current density of the nitrided surface corrosion decreases by 1.5–2.4 times.