ABNT 4140 steel mechanical properties after nitriding by EDM process

摘要

Electrical Discharge Machining process (EDM) is a non-conventional cutting method applicable for the machining of electrically conductible or semi-conductible, with no contact between the tool and the work piece which consists in an electrode and a work piece both submerged in a dielectric fluid and connected into a direct current source. Initially, the fluid behaves in an insulating way so that there is no electric current until a minimum gap between the electrode and the work piece is reached. Once this gap is reached, the dielectric fluid starts behaving in a conductive way creating a plasma channel due to the electric arc generated. Ion are emitted between the anode and the cathode thus colliding with the dielectric fluid molecules obtaining enough energy to fuse/vaporize and consequently removing material from the work piece/electrode. The main objective of this study was to adapt the conventional EDM machine, so that it could allow performing the NDE (Nitriding by Electrical Discharge) while the test sample rotates. Therefore, it became possible to evaluate the results of the NDE process on test samples submitted on the traction resistance test. In order to evaluate the gain in surface hardness and the substract hardness after NDE, it was necessary to elaborate a triparted proof body, allowing the removal of proof body central part for a subsequent microhardness evaluation. In this way, it became possible to preserve the machined surface and consequently better results during the microhardness evaluation. As a dielectric fluid utilized on the test was a deionized water with urea concentration varying among 0g/l, 20g/l, 40g/l, 60g/l and 80g/l, the purpose of the urea variation was evaluate the influence of urea concentration on the surface hardness and nitrided layer depth.