Morphology of spark-affected surface layers produced on pure iron and steels by electro-discharge machining

Abstract

Structural changes occurring in pure iron and certain low-carbon steels machined by the electro-discharge technique have been investigated. The determination of the quantity of carbon diffused into the white layer by using the electron probe microanalyser has enabled the authors to reveal the structure of the spark-affected zone through the technique ofmetallographic etching. The diffusion of carbon, mainly due to the release of pyrolysis products following dielectric cracking, increases the carbon content in the white layer up to a maximum of 3.40%. Optical, electron, and scanning electron microscopical examinations have shown that the white layer consists of carbides, in acicular or globular form, diffused in an austenite matrix by an amount independent of the composition of the electrode or workpiece materials.