The middle wire cutting process is a processing method that utilizes the thermal effect of the instantaneous discharge energy to melt and evaporate the workpiece material to meet the dimensional requirements. Since the wire-cut working fluid mostly uses a dielectric liquid, it is accompanied by a certain electrolysis during the processing.
The thermal effect and electrolysis during cutting usually produce a certain thickness of the altered surface on the machined surface. For example, the hardness of the surface layer is reduced and microcracks appear, which causes the mold in the middle wire cutting process to be prone to early wear and directly affect the die blanking gap. The maintenance and the edge of the mold are easily chipped, shortening the service life of the mold.
For carbon steel, the molten layer on the surface of the workpiece (the metamorphic layer consists of the molten solidified layer and the heat-affected layer) appears white on the metallographic photograph and becomes a white layer. It is completely different from the base metal and is a dendritic quenched cast structure. The combination with the inner layer is not very strong. It consists mainly of martensite, a large amount of finely retained austenite and some carbides.