Electro discharge machining (EDM) causes a white layer at the surface of a workpiece. The research work, described in this paper, aims to acquire a profound knowledge of this layer. The influence of workpiece material, electrode material and type of dielectric on the composition and the metallographic phases of the white layer is discussed.
The measurements yield that the use of an oil dielectric increases the carbon content in the white layer. A water dielectric on the other hand, causes a decarbonisation. The carbon in the white layer machined in an oil dielectric appears as iron carbides (Fe3C) in columnar, dendritic structures. This is a result of the very rapid re-solidification of the molten material. In between the carbide dendrites, rest austenite and also some ferrite can be found.