Cemented carbide blank suitable for electric discharge machining and cemented carbide body made by electric discharge machining

Abstract

A cemented carbide blank suitable for fabrication by electric discharge machining that includes a carbide phase that includes tungsten carbide (and optionally vanadium carbide) present in an amount equal to between about 77.7 weight percent and about 93.6 weight percent of the cemented carbide blank. The cemented carbide blank further includes chromium present in an amount equal to between about 0.3 weight percent and about 1.5 weight percent of the cemented carbide blank, cobalt present in an amount equal to between about 8 weight percent and about 17 weight percent of the cemented carbide blank, nickel optionally present in an amount equal to 0 weight percent up to about 5 weight percent of the cemented carbide blank, and molybdenum present in an amount equal to between about 0.1 weight percent and about 1.0 weight percent of the cemented carbide blank. The cemented carbide blank having a magnetic saturation as measured according to ASTM B886-03 ranging between about 151×10−6 T m3 / kilogram cobalt and about 182×10−6 T m3 / kilogram cobalt.

Description

BACKGROUND OF THE INVENTION [0001] The present invention pertains to a cemented carbide blank that is suitable for electric discharge machining (EDM), as well as a cemented carbide body made by an EDM process from the cemented carbide blank. More specifically, the present invention pertains to a cemented tungsten carbide blank, as well as a cemented tungsten carbide body made by an EDM process from the cemented tungsten carbide blank, that has a cobalt-based binder wherein the cemented carbide blank contains additives of chromium and molybdenum, and in some cases nickel. The cemented tungsten carbide blank is suitable for EDM, and especially prolonged EDM in excess of 30 hours and even in excess of 100 hours and even still in excess of 500 hours, wherein the exposed surface is essentially free of defects caused by electrolytic corrosion or the EDM process. [0002] Very basically, electric discharge machining (EDM) is a process for making a body that typically has a complex shape. An ...

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Problems solved by technology

The EDM finished cemented carbide body can also experience pitting or corrosion of material underneath (and near to) the surface.

The EDM finished cemented carbide body may also experience cracking caused by the EDM process.

The EDM finished cemented carbide body may also suffer a decrease in the strength of the material.

It appears that there is an electrochemical corrosion phenomena that takes place so as to remove by corrosion the binder material (e.g., cobalt in the case of a cobalt cemented tungsten carbide body) from the body so as to create these surface pits or the sub-surface pitting as well as result in the cracking.

The presence of the pitting and cracking has also resulted in a decrease in the strength of the body.

While the Lackner et al. patent and the L{haeck over (a)}mmle et al. article each says that it discloses an alloy that has resistance to “pitting” as a result of EDM, because “pitting” is an undesirable result, it still remains as a goal to provide a cemented carbide (e.g., tungsten carbide-based material that contains cobalt) that is suitable for EDM without suffering “pitting” or any significant “pitting” as a result of the EDM process.

The use of these exotic elements as additives in cemented carbides, such as, for example, cobalt cemented tungsten carbide, makes the material more expensive.

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