The surface integrity of ultra-fine grain steel, Electrical discharge machined using Iso-pulse and resistance–capacitance-type generator

Abstract

Ultra-fine grained materials with high strength and low weight are eventually considered to be used in industries. To produce ultra-fine grained materials, equal channel angular pressing is a functional method, imposing severe plastic deformation on the workpiece. Electrical discharge machining is an indispensable process in manufacturing industrial parts with high accuracy and precision. However, electrical discharge machining has thermo-physical consequences, damaging the surface layers of the workpiece. On the other hand, the ultra-fine grained materials are thermodynamically unstable and tend to microstructural evolution. Thus, electrical discharge machining process affects the ultra-fine grained materials more than coarse grain materials. In this study, the effects of electrical discharge machining on the ultra-fine grained steel were investigated and the undesirable influences of the electrical discharge machining were diminished by adjusting the electrical discharge machining parameters. The ultra-fine grained steel samples were electrical discharge machined in two methods including Iso-pulse (roughing mode and finishing mode) and with resistance–capacitance-type generator. The surface integrity parameters, including thickness and microstructure of the recast layer and heat-affected zone, the cracks density and hardness, which for all three types of samples, were investigated by scanning electron microscopy, optical microscopy, X-ray diffraction technique, and micro-hardness tester. The results show that electrical discharge machining with resistance–capacitance-type generator has the minimum effects on the surface integrity of the ultra-fine grained samples because of the different material removal mechanism of resistance–capacitance-type electrical discharge machining.