TUNGSTEN CARBIDE

With optimum grade selection, sub micron grain size tungsten carbide can be sharpened to a razor edge without the inherent brittleness frequently associated with conventional carbide. Although not as shock-resistant as steel, carbide is extremely wear-resistant, with hardness equivalent to Rc 75-80. Blade life of at least 50X conventional blade steels can be expected if chipping and breakage is avoided.

Just as in the case of steel selection, choosing the optimum grade of tungsten carbide (WC) is a complex process involving compromised choices between wear-resistance and toughness/shock resistance. Cemented tungsten carbide is made by sintering (at high temperature) a combination of tungsten carbide powder with powdered cobalt (Co), a ductile metal that serves as a "binder" for the extremely hard tungsten carbide particles. The heat of the sintering process does not involve a reaction of the 2 constituents, but rather causes the cobalt to reach a near-liquid state and become like an encapsulating glue matrix for the WC particles (which are unaffected by the heat). Two parameters, namely the ratio of Cobalt to WC and the WC particle size, significantly control the bulk material properties of the resulting "cemented tungsten carbide" piece.

Specifying a large WC particle size and a high percentage of Cobalt will yield a highly shock resistant (and high impact strength) part. The finer the WC grain size (and therefore the more WC surface area that has to be coated with Cobalt) and the less Cobalt used, the harder and more wear-resistant the resulting part will become. To get the best performance from carbide as a blade material, it is important to avoid premature edge failures caused by chipping or breakage, while simultaneously assuring optimum wear resistance.

As a practical matter, the production of extremely sharp, acutely angled cutting edges dictates that a fine grained carbide be used in blade applications (in order to prevent large nicks and rough edges). Given the use of carbide which has an average grain size of 1 micron or less, carbide blade performance therefore becomes largely influenced by the % of Cobalt and the edge geometry specified. Cutting applications that involve moderate to high shock loads are best dealt with by specifying 12-15 percent Cobalt and edge geometry having an included edge angle of about 40º. Applications that involve lighter loads and place a premium on long blade life are good candidates for carbide that contains 6-9 percent cobalt and has an included edge angle in the range of 30-35º.

Specialty Blades stands ready to assist you in achieving the optimum balance of properties that will allow you to get maximum performance from your carbide blades.

Need more information? call 1-800-252-3371
Please Note: This data is provided at no charge for the intended purpose of providing material application options to potential blade users. It is offered subject to the usual disclaimer that we have used sources and estimates believed to be reliable in the development of this information, but do not guarantee its accuracy in specific applications. Please note that the chemical elements noted by % are believed to be the major elements affecting performance. Other trace levels of elements may be found depending on supplier and heat number. This data should not be relied on in lieu of application-specific testing. Further, if you see data in these charts that you do not believe is accurate, we would appreciate your calling us with that information at 800-252-3371.