Tungsten carbide cemented

The cermet class of materials contains a large number of compositions (57). Most cermets are carbide-based, eg, WC and titanium carbide [12070-08-5] TiC. Cemented tungsten carbides are widely used for cutting tools and car parts. 

Fig. 9. Representative micrographs of (a) single (TiC) and (b) double (TiN and TiC) coatings on cemented tungsten carbide (9).

Cemented tungsten carbides also find use as a support for polycrystalline diamond (PCD) cutting tips, or as a matrix alloy with cobalt, nickel, copper, and iron, ia which diamond particles are embedded. These tools are employed ia a variety of iadustries including mineral exploration and development oil and gas exploration and production and concrete, asphalt, and dimension stone cutting. 

CEMENTED TUNGSTEN CARBIDES by Go pal S. Upadhyaya CERAMIC CUTTING TOOLS edited by E. Dow Whitney... 

Occupational Exposure to Tungsten and Cemented Tungsten Carbide. Department of Health, Education, and Welfare, Pub No. 77-227, NTIS Pub. No. PB-275-594. Springfield, VA, National Technical Information Service (NIOSH), 1977... 

Tungsten is recovered mostly from mineral scheebte and wolframite. The recovery process depends on the mineral, the cost, and the end use i.e., the commercial products to be made. Typical industrial processes have been developed to convert tungsten ores to tungsten metal and alloy products, tungsten steel, non-ferrous alloys, cast and cemented tungsten carbides, and tungsten compounds. A few processes are mentioned briefly below. 

Natural single-crystal diamond and carbonado can now be replaced in many industrial uses by sintered diamond tool blanks. Such tool blanks are available in disks and cores. The disks, or sectors of disks, consist of a thin (0.5—1.5 mm) layer of sintered diamond up to about 50 mm diameter on a cemented tungsten carbide-base block about 3—6 mm thick. Using diamond abrasive, such blanks can be formed into cutting tools of various shapes. Typical tool blanks are shown in Figure 9. The wire dies have diamond cores up to 10 mm in diameter and 10 mm in length, which are encased in a cemented tungsten carbide sleeve up to 25 mm in diameter. 

Special carbide tools also will often contain various percentages of titanium, tantalum, niobium icolumbium). and hafnium carbides, along witii die tungsten carbide. Chromium and vanadium carbides are also added to produce special, fine-grain-size grades of cemented tungsten carbide-cobalt materials. See Fig. 1. 

Fig. 1. Cemented tungsten carbide compacts and mud nozzles for oil well drilling. (Fansteel)...

Figure 2.4 Representative microstructures of steel-cutting grades of cemented tungsten carbide (a) 94%WC-6%Co alloy, submicron grain size, (b) 94%WC-6%Co alloy, medium grain size, (c) 86%WC-8% (Ti, Ta, Nb)C-6%Co alloy, medium grain size. The gray angular particles are WC, and the dark gray, rounded particles are solid-solution carbides. The white areas are cobalt binder. (Ref. 14).

A second technique involves heating the cemented tungsten carbide to the solidus—liquidus temperature region of the binder phase in a decarburizing atmosphere, such as C02 gas (93). Decarburization occurs at the surface whereby the carbon concentration at the surface is reduced to reach the solidus line of the binder phase, and the liquid phase solidifies. As a result, the liquid phase is supplied to the inner portion, and this also reaches near the surface where it is decarburized to reach the solidus line and this again solidifies. This procedure is repeated until Co is enriched in the zone near the rake face. 

Tungsten is a very hard metal which has enormous resistance to heat and is therefore useful for many different industrial purposes. The majority of tungsten is made into cemented tungsten carbide. Only small amounts are present in food and water, and little is known about the toxicity of different forms of tungsten. Tungsten and its compounds are not, however, considered an important health hazard. 

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