The article deals with detailed evaluation of heat affected zone in sub-surface layers of the samples made by technology of wire electrical discharge machining. The samples were produced on EDM-WC machine SP 640-P from two different materials, steel and tungsten carbide. The cutting tool was wire brass electrode of 0.25 mm diameter. The aim of this paper is to determine experimental and with FEA the influence of the heat affected zone and micro-hardness. .