Surface Integrity of a Die Steel after Electrodischarge Machining: 1Structure, Composition, and Hardness

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Abstract
Cylindrical specimens of KEA 145 (AISI type H 13) hot working die steel were electrodischarge machined using roughing and finishing generators to control the discharge. The resulting microstructures were studied by optical and electron microscopy, and microhardness profiles were obtained on transverse sections. Surface roughness and microcrack density were found to increase with increasing pulse energy. Machining using the roughing generator produced rougher surfaces and fewer, but deeper and wider, microcracks than when using the finishing generator. Five distinct microstructural zones were observed: a glassy, featureless surface zone; a fine polygonal ε carbide structure; a fine acicular or martensitic structure; a fine cellular or polygonised structure; and the matrix structure. This variation was found to be associated with a microhardness variation with depth.

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