Investigation of nitride layers deposited on annealed AISI H13 steel by die-sinking electrical discharge machining

Abstract

The performance of electrical discharge machining is dependent mainly on the dielectric fluid and process parameters. Significant attention has been drawn to introducing alternative dielectric fluids in order to achieve superior surface integrity and higher productivity. However, there is a challenge in producing more uniform surface layers in the emerging nitriding process by electrical discharges. Thus, this work studies the relationship between process parameters and the features of the layers produced using surface modification by die-sinking electrical discharge machining employing urea [(NH2)2CO] in deionized water as dielectric fluid. The influence of pulse-on time and pulse-off time on the uniformity and thickness of the recast layer, heat-affected zone, and depth of hardened layer was investigated. The experimental work employed annealed AISI H13 tool steel as base material and electrolytic copper as electrode. In order to characterize the samples and investigate the modifications produced by the process, chemical analysis, optical microscopy, scanning electron microscopy, X-ray diffraction, and microhardness measurements were used. The results indicated an evident influence of the process parameters on uniformity and thickness of the layers. The thickest altered metal zone layer obtained was 53.2 ± 5.5 μm when both pulse-on and -off times of 500 μs were used, while the smallest thickness of 31.0 ± 4.6 μm was obtained for both pulse times of 100 μs. The investigated process increased the surface hardness about three times compared with the non-processed AISI H13 steel. This can be attributed to the iron nitrides such as Fe11N found in the samples.