The electrical discharge machining process is an effective way to machine hard alloys. A homogenized dual phase Fe-24.0% Mn-8.3% Al-5.0% Cr-0.38% Si-0.34% Mo-0.45% C (wt%) alloy casting piece was employed to study the phase transformation and microstructure phenomena of recast layers by means of electrical discharge machining. The wave-like recast layers appear with micro cracks. The thickness of the recast layer increases with pulse duration. When the pulse duration ranges from 200 to 300 mus, the discharge current has no influence on the thickness of the recast layer. The copper concentration is high in the recast layer caused by the melting of the copper electrode. The copper contents of the recast layer increase with the pulse duration and the discharge current. The novel solidification microstructures of the recast layer can be classified as ( 1) a dense and fine dendritic outermost sublayer, (2) a coarse dendritic intermediate sublayer and ( 3) an innermost. recast zone. The average chemical composition of the recast sublayers is Fe-19.007% Mn-8.377% Al-2.981% C-4.505% Cr-0.627% Cu-0.377% Mo-0.376% Si ( wt%). The novel structure of the recast sublayer is identified as (Fe, Mn)(3)AlCx, which was formed due to the re-melting of the matrix and the carburization of the cracked dielectric fluid. The precise lattice parameter, a(o), of the (Fe, Mn)(3)AlCx phase measured by extrapolation against cos(2)theta/sintheta is 0.3801 nm. The microhardness of the recast layers is as high as Hmv574 due to the existence of (Fe, Mn)(3)AlCx carbide. (C) 2003 Kluwer Academic Publishers.