Characteristics of the rough-cut surface of quenched and tempered martensitic stainless steel using wire electrical discharge machining

Abstract

This article studies the surface characteristics of quench-and temper-treated AISI 440A martensitic stainless steels, which were rough cut using wire electrical discharge machining (WEDM). The microstructure of the recast layer on the cut surface was investigated using scanning and transmission electron microscopes, and the phase compositions were analyzed with an energy-dispersive X-ray (EDX) spectrometer. Experimental results showed that the thickness of the recast layer varied with the heat-treatment condition of the workpiece, the largest thickness was obtained with a quenched specimen, and the thickness decreased with increasing tempering temperature. Intergranular surface cracks were observed only from the as-quenched specimen, whereas surface cracks were not found in the rough-cut specimens after tempering above 200°C. It is reckoned that reliefing of the thermal residual stress in the quenched workpiece induced the surface intergranular cracks. Microstructures of the recast layer on the rough-cut surfaces of the 600°C tempered specimen were examined using cross-sectional transmission electron microscopy (TEM) specimens. An amorphous layer exists at some parts of the outermost cut surface. A high density of wire electrode droplets of spherical shape, approximately 10 to 60 nm in size, was found throughout the porous recast layer. Besides, many highchromium containing sigma spheres with sizes of approximately 120 to 200 nm were precipitated at the bottom part of the recast layer, and its formation mechanism was proposed. Adjacent to the recast layer was a heat-affected zone (HAZ) with a thickness of about 4 m, in which temper-induced carbides were fully dissolved. The HAZ comprised basically two distinct regions: the first region adjacent to the recast layer was composed of a lath martensite structure, while the other region was an annealed ferrite structure.

Microstructure Analysis and Material Transformation of Pure Titanium and Tool Wear Surface After Wire Electric Discharge Machining Process

“…These features of deposit can represented as "Bull eye." Moreover, these deposits were consistently covered with oxide layer showed the same effect in WEDM of finish cut for martensitic steel (Huang et al, 2004).…”

“…The microstructure analysis of the fine surface martensitic steel by WEDM was performed using EDX, SEM and TEM (Huang et al, 2004). The effects such as dimensional error, surface roughness and MRR were studied for WEDM of hot die steel.…”

White Layer Composition, Heat Treatment, and Crack Formation in Electric Discharge Machining Process

“…They have showed dense crack networks within the white layer with possibly some penetrating cracks between when machining was performed in a hydrocarbon-based dielectric liquid, especially at high pulse-on duration and low discharge current. [14,16] In contrast, researchers [9,16] using a non-carbon-based dielectric liquid during EDM presented some examples of penetrating cracks to the base material. However, none of them gave sufficient explanations about crack formation.…”

“…This layer is composed of several microscopic metallurgical layers, and its composition is dependent on the machining conditions. [7][8][9][10] The melted material contracts more than the unaffected parent part during the cooling process, and when the stress in the surface exceeds the material's ultimate tensile strength, cracks are formed. [2,7,11] Results from previous studies [7,8,[11][12][13] have indicated that cracking increases as the pulse energy increases.…”

A progress review in wire electrical discharge machining process

“…The EDX profile of the cut specimen revealed that as the number of passes increased, the rate of deposition of wire electrode material onto the machined surface increased. The SEM and TEM images revealed the formation of fine spherical nodules with multi passes due to reduced surface energy during solidification [50,51]. The thickness of the recast layer (RCLT) formation, Heat Affected Zone (HAZ), and inter-granular cracking on quenched and tempered AISI 440A was also analysed by using SEM and TEM micrographs.…”