Effect of Electrical Discharge Machining (EDM) on Charpy Test Results from Miniaturized Steel Specimens
Electrical Discharge Machining (EDM) is a manufacturing process whereby a desired shape is obtained through electrical discharges between an electrode and a workpiece, separated by a dielectric fluid. EDM produces a damage layer on the surface of the workpiece, which is harder and more brittle than the base metal, often characterized by microcracks. This type of damage, particularly in the notch region of a mechanical specimen, could adversely affect test results. The objective of the investigation presented in this Internal Report is to assess the possible influence of EDM on miniaturized Charpy test results. We have tests KLST-type Charpy specimens of two reactor pressure vessel (RPV) steels, machined using different combinations of two machining processes (EDM and milling). Comparison of the impact results obtained, combined with additional metallographic observations and microhardness measurements on the recast layers and the base metals, do not indicate a detrimental effect of EDM on the impact toughness of the materials investigated. The maximum thickness of the recast layer is about 16 μm, and the magnitude of the EDM-induced hardening varies between 34 % and 84 %, depending on the carbon content of the steel. No microcracks have been observed.