The surface characteristics of P/M high-speed steel (ASP 23) multi-cut with wire electrical discharge machine (WEDM)

High-speed steel (ASP 23), which was made by powder-metallurgy (P/M) process and widely used as the material for IC-packaging mold was subjected to multi-cutting with wire electrical discharge machine (WEDM) by using a brass wire electrode. Before WEDM, the steel was quenched at 1180degreesC and then three-times tempered at 560degreesC to acquire suitable mechanical properties. The cut surface was examined with scanning electron microscope (SEM) and analyzed with anodic polarization measurement in 1 M CH3COOH. The results show that surface alloying between the steel and wire electrode materials was observed in the recast layer; meanwhile, martensitic transformation can be found. Surface alloying and phase transformation of the cut surface can be characterized with their anodic polarization curves measured in 1 M CH3COOH. An obvious passive current can be detected in the martensitic structure by anodic polarization curve in higher overpotential, while such passive current did not occur in the tempered structure. A wide potential range corresponding to the potential range of passive current and higher breakdown potential of the anodic polarization curve was found on the cut surface after WEDM. This effect was caused by surface alloying in the recast layer and martensitic transformation in the workpiece adjacent to the cut surface. (C) 2003 Elsevier B.V. All rights reserved.