What is Tungsten Carbide?

What is Tungsten Carbide?

What is Tungsten Carbide?

Solid Tungsten Carbide & Tungsten Carbide tipped tools are in daily use throughout the world today, from industrial plants to individuals on building sites.

First & foremost its meaning is derived from the Swedish words tung sten, which mean “heavy stone.”

In German, it’s referred to as Hard Metal (Hart Metall or HM) & for good reason because of it’s very heavy density ( roughly twice) compared to ordinary steel.

Cemented carbide is a hard material used extensively in industrial cutting tools for machining, as well as other applications. It consists of fine particles of carbide cemented by mixing with a binder metal such as: Cobalt, Titanium, Tantalum & other elements to confer specific properties. Cemented carbides commonly use tungsten carbide (WC), titanium carbide (TiC), or tantalum carbide (TaC) as the aggregate. Mentions of “carbide” or “tungsten carbide” in industrial contexts usually refer to these cemented composites.

Carbide cutters will leave a superior surface finish on the part, and allows faster machining than high-speed steel or other tool steels. Carbide tools can withstand much higher temperatures at the cutter-workpiece interface than standard high-speed steel tools (which is a principal reason for the faster machining). Carbide is usually superior for the cutting of tough materials such as carbon steel or stainless steel, cast iron, Titanium alloys as well as in situations where other cutting tools would wear away faster, such as high-quantity production runs.To give you an idea of it’s properties; we’ll compare it against the most well known metals as follows:

Density of metals.

Tungsten: 15.6 tons per cubic metre

Steel: 7.1 tons per cubic metre

Titanium: 4.5 tons per cubic metre

Aluminium: 2.7 tons per cubic metre

Magnesium: 1.7 tons per cubic metre

Melting points of metal :

Tungsten: 2870 degrees Centigrade

Steel: 1370/1500 degrees Centigrade

Titanium: 1668 degrees Centigrade

Aluminium: 660 degrees Centigrade

Magnesium: 650 degrees Centigrade

Grain size has also a bearing on it’s qualities; generally a fine grain will offer a better wear resistance characteristic whilst a coarse grain will yield a better impact resistance ( such as hammer drill bits for example). An extra fine grain will yield an even greater hardness whilst a much coarser grain will yield a more extreme impact resistance. The mixing of different elements is a bit of a black art & always is a delicate compromise between wear & impact resistance. If one adds more Cobalt to large grains then one gets even more toughness. However there is a limit to how tough one can make carbide or want to make carbide. If one gets it too “tough” then it is too soft. The term ‘tough’ here is the opposite of hard.

If one adds too much Cobalt to coarser grains for example, the carbide will move and deform under pressure. Finer grain carbide offers more surface area that has to be coated with Cobalt &/ other binder) and the less Cobalt used, the harder and more wear-resistant the resulting part will become.

Trying to achieve the best performance from carbide as a blade material, it is imperative to avoid premature edge failures caused by chipping or breakage, while simultaneously assuring optimum wear resistance.

One of the major strengths of carbide is its ability to handle pressure or compressive force but not tensile. If it is too soft it loses that ability. Here again the varying mixed elements used as binders result in different qualities to the carbide.

It’s also so hard to finish it off for sharpening &/ polishing, one needs to use abrasives that are much harder such as Cubic boron nitride &/ industrial diamond.

As you can see it’s weight makes it quite dense compared to steel & requires a very high temperature to melt which is one of it’s major attributes for speeding up machining processes by operating under more extremes feeding rates (up to constant 500° Celsius without deformation) as well as giving an extended service life time.

Just as with alloyed steels, Carbides are offered with different “recipes” so as create a specific quality for a given application.There are literally thousands of combinations &/ grades.

Sintering is the process of compacting and forming a solid mass of material by heat and pressure without melting it to the point of liquefaction.

Micro grains

Micro grain and nano grain tungsten carbides are at one end of the scale. Tighter grains can improve wear and a tougher tungsten carbide & thus give a longer service life. Typically they wear longer, retain a better edge longer and polish better.

Our blades are manufactured with H10 grade carbide which is a sub micron grade thus offering the best wear characteristic for an extended lifespan & excellent cut quality. When we introduce metal cutting blades, the grade will in all likelihood change as the carbide will have to resist impact without damage so as give the best possible compromise between service life & cut quality.

Some of the Properties of Tungsten Carbide

1)Extremely high compressive strength but poor in tensile forces just like concrete 
2) Rigidity: approximately 2.5 times that of steel and 5 times of cast iron and brass 
3) High Heat Properties Retention
4) Impact Resistant about equal to hard tool steels
5) Oxidation resistance: approximately 538° Celsius in oxygen and 816° Celsius in vacuum or protective atmospheres.
6) Cryogenic toughness and strength to approximately 232° Celsius
7) Twice as Thermally Conductive as steel.
8) Electrical Conductivity about that of steel.
9) Hot Hardness: hardness retention up to 704° Celsius
10) Lubricity: tungsten carbide can be polished to a relatively low friction surface
11) Wear Resistance about 100 times that of steel 
12) Dimensional Stability: Tungsten carbide itself has a very low coefficient of thermal expansion, and have values approximately half that of steel. Can withstand continuous exposure to temperatures up to 500° Celsius without significant deterioration in properties.

Brazing is one of the cheapest, most reliable, and efficient ways of making a joint. In the early years of Tungsten tipped production, virtually all carbide cutting tools were fabricated by the brazing of carbide tips onto steel. Brazing is mostly suitable for the fabrication of small area, short-length joints, sometimes can be applied satisfactorily to larger joints following certain design principles. The process takes advantage of the ability of certain molten filler metals to penetrate small gaps between metal surfaces by capillary action. Under suitable conditions the brazing alloy wets and bonds by surface diffusion alloying to form a strong joint. Welding or bronze welding differs significantly from a joint for brazing. 
Brazing metals range from silver solders of low melting point to pure copper, giving brazing temperatures from around 600 0 C to over 10500 C. The most common method nowadays is silver solder used for the brazing of Tungsten consists of 48% silver, 18 per cent cadmium, 16 per cent zinc, 15 per cent copper, and 3 per cent nickel. These proportions may differ somewhat according to design specifications. Although tungsten carbide is readily wetted by all brazing alloys, alternative surface treatments have been exploited over the years to enhance the mutual “wettability”. 
Examples of successful surface treatments prior to brazing are grit blasting, surface grinding, ultrasonic cleaning, copper coating. Another important factor is the choice of suitable flux as a brazing aid, and over the years special products have been developed to overcome the problems associated with poor “wettability”.