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 [(NH 2 ) 2 CO] 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, heataffected 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 Fe 11 N found in the samples.

Sub-Microstructure of Surface and Subsurface Layers after Electrical Discharge Machining Structural Materials in Water

“…A similar character is seen in Figure 11 for 2024 (D16) duralumin. The studies [2,11,[15][16][17]19,[46][47][48] show that penetration (adsorption in the recast layer) of the tool electrode material components can reach a depth of 10 µm (from 2.55 up to 50 µm depending on used materials of electrodes, dielectric medium, and experiment factors). At the same time, this uneven distribution of the workpiece and wire elements can be explained by sublimation phenomena of the recast layers (similar to laser ablation during heating with the concentrated energy flows such as laser, plasma, electric discharges, fast energy neutral atoms [49][50][51][52]), when components of workpiece material sublimate primarily [53,54].…”

“…The surface layer of tool AISI H13 steel (SKD-61, X40CrMoV5-1) after die-sinking electrical discharge machining with a copper tool electrode was improved (microhardness) by adding nitrogen-containing components into a deionized water medium [15]. The formed nitrides and recast layers were detected at the minimum depth of 31.0 ± 4.6 µm with pulse time on and off equal to 100 µs, correspondingly.…”

“…Figure15. Submicrostructure and mechanism of material removal mechanism for electrical discharge machining of metals: (a) micro-chipping and burn marks on the surface of the sample at the end of the operation, where (1) is plastic deformation zone formed in the last microseconds of the operation under the weight of the workpiece, (2) is short circuit zone formed because of clamping the tool electrode between the workpiece and the detachable part (sample), (3) is regular machined surface, (4) is erosion wells after short-circuiting, (5) is regular erosion wells; (b) submicrostructure.…”

Effects of Sodium Octaborate on AISI 4140 Steel Machined by Die-sinking EDM

“…Regarding surface treatments, several researchers have studied surface modification through die-sinking electrical discharge machining (EDM), with significant improvements reported [28][29][30] . For instance 29 , reported that the layer produced on the component surface machined by EDM was enriched with carbon from the hydrocarbon-based dielectric fluid due to the decomposition reaction.…”

Influence of Process Parameters on the Microstructural Characteristics and Mechanical Properties of Recast Layer Thickness Coating on Die Steel Machined Surface after Electrical Discharge Machining

“…Electrical discharge machining (EDM) is widely used to shape the surface of moulds and tools. In this method, the material of the workpiece with any mechanical properties can be processed by the electrode with much lower mechanical properties [1]. This will facilitate overcoming difficulties with the mechanical requirements of tools in traditional machining.…”