Influence of the electrode material on the nitriding of medium carbon steel using sink electrical discharge machining

Among the various processes that produce enrichment on metal surfaces, there are those that use nitriding through electrical discharge machining (EDM). In this process, the nitrogen source is an aqueous solution of water and urea. The objective of this study is to show the influence exerted by the electrode material in EDM through the nitriding process of AISI 4140 steel. The authors performed tests through use of a sink EDM machine. The dielectric fluid used in the experiments was deionized water solution containing 10 g/l of commercially available urea. The electrodes were made up of copper and graphite. The samples characterization analysis was performed through x-ray diffraction (XRD), optical microscopy, and microhardness. This procedure demonstrated, in both electrodes, the formation of a hardened layer with a thickness around 20 μm. There was no difference in the hardness of the samples when using different electrodes. The constituting materials of the electrodes act in the process where copper and carbon are transferred onto the surface of the steel. When using the copper electrode, one observes the formation of nitrides. In addition, with the graphite electrode, one observes the formation of iron carbide and nitride γ′. These differences were attributed to changes in the thermodynamic process.