Tungsten carbide – what actually is it?

More than just a material.

Tungsten carbide belongs to the composite materials. In fact, it consists of alloys made of metallic hard materials – the so-called carbides – and a binding metal. 

It typically features a very high hardness and an exceptionally high wear resistance. 

 

Tungsten carbide – what’s inside?

Tungsten carbide is usually made of a combination of  tungsten carbide and cobalt (WC+Co). In addition to tungsten (WC), titanium (TiC), tantalum (TaC), chromium (CrC) or other carbides are used as hard materials as well. Cobalt (Co), nickel (Ni), iron (FE), and nickel-chromium (NiCr) are the most frequently used binding agents. 

 

Tungsten carbide – who invented it?

In 1914, Lohman and Voigtlaender patented their cast tungsten carbide, but at first, they failed to establish it on the market due to its brittleness. It was only accomplished with the development of sintered tungsten carbide by Karl Schroeter and Heinrich Baumhauer nine years later. Their patent was taken over by Osram in 1923. The beginning of the industrial use in 1926 got things moving. Krupp Hartmetall successfully launched this material named Widia for diamond. From 1929, this tungsten carbide has been developed as Pobedit by the company of the same name in the USSR. 

 

Tungsten carbide – tungsten what?

Due to its extraordinary hardness, tungsten carbide is often compared to diamond. It is made of the most important tungsten ores wolframite and scheelite. These are mainly quarried in China, Russia, Canada, Austria, and Portugal. Tungsten carbide is produced by adding carbon and tungsten powder. This process is called carbuzation. It describes a metal treatment process that adds carbon to the metal surface, which features low carbon content – and which finally increases the hardness of the metal.

 

It’s a matter of binding? True!

The main binder is usually cobalt, because it has a positive impact on the sintering process. If increased corrosion resistance is required, a nickel-binder is the right choice. Taken as a whole, the most common binding agents in today’s tungsten carbide production are cobalt (Co), nickel (Ni), iron (Fe), and nickel-chromium (NiCr).

 

One material, many advantages – this is what tungsten carbide offers!

Tungsten carbide is highly versatile and provides numerous advantages. For most DURIT customers, the following three features are the most important ones.

Wear resistance

In numerous industrial processes, there are abrasive effects between different materials, which results in early wear of one of the two materials. Tungsten carbide offers – due to its versatility – ideal possibilities for reducing wear.

Hardness

The degree of hardness is determined by the Vickers method. The force of a weight of 30 kg or 294 Newton, respectively is used for inducing a measurable surface indentation by reference to a defined diamond. The degree of hardness of the tungsten carbide component increases while the binder content and the grain size decreases.

Pressure resistance

Compared to other materials, tungsten carbide is characterized by an enormously high pressure resistance. It increases while the binder content and the grain size decreases. Those tungsten carbide grades with a low carbide grain size and a low binder content attain a pressure resistance of approximately 7,000 N/mm2.

 

Tungsten carbide production in brief: This is how it’s done!

The powder, consisting of tungsten carbide and the chosen binder, is mixed and pulverized in the desired composition. Subsequently, it is  dried. The resulting granules are then  pressed into shape. For this process, different methods of direct and indirect shaping are available. The pellet or the so-called green compact is then ready for the  mechanical processing. Following this, the sintering is effected at about 1,300 to 1,500 °C. 

 

Powder, pellet, green compact - what exactly does that mean?

The chalk-like powder pellet is technically called green compact. During the sintering process, porosity and volume are considerably reduced.

 

Sintering – a pretty hot process.

Sintering is a method for producing or modifying materials – a thermal process under anaerobic conditions. Sintering processes are of great importance in ceramic production and metallurgy. In tungsten carbide production, the carbides are thus firmly embedded into a binding matrix. For this purpose, the binder in the green compact is heated and liquefied.  It is then filling the interstitial spaces and surrounding the carbides. An HIP sintering process includes an injection of argon after the liquefying process. The tungsten carbide gets thus even more densified and gains a homogeneous, non-porous structure.

 

The blank – destined for further processing.

The blank represents a workpiece that has to pass further processing steps. In tungsten carbide production, the blank is the product resulting from the sintering process. Good to know:  Blanks by DURIT feature a low grinding excess – perfectly prepared for further processing.

 

How long does the finished tungsten carbide component take?

Tungsten carbides are not created equal. The particular production time depends on the component size, the desired geometries, and the required quality. So there is no general reference regarding the production time – it is individually determined for  every single component.

 

Which grade of tungsten carbide for which application?

Depending on composition and microstructure, tungsten carbide features many different properties. Basically, there are  three types.

» GD

Tungsten carbide for forming technology, wear and corrosion protection.

» BD

Tungsten carbide for forming and mining technologies

» KD

Tungsten carbide for metal cutting technology

 

Binder, binder content, grain size – it makes the difference!

Tungsten carbides feature many different INDIVIDUAL properties since they have to accomplish diverse purposes. They basically differ in their binders, binder contents and grain sizes.

 

 

 

From nano-fine grain to extra coarse grain – grain sizes.

The balance of hardness and wear resistance as well as toughness makes tungsten carbide that special. The exact features are determined by the composition. One decisive factor is the choice of the used grain sizes. That means: The finer the grain, the higher its hardness and its wear resistance. The coarser the grain, the higher its toughness.

The grain sizes are classified as follows:


The finer the alloy, the higher its hardness and its wear resistance.

» nano-fine grain < 0.2 µm

» ultra-fine grain 0.2 – 0.5 µm

» micro grain 0.5 – 0.8 µm

» fine grain 0.8 – 1.3 µm

» medium grain 1.3 – 2.5 µm

» coarse grain 2.5 – 6.0 µm

» extra coarse grain > 6.0 µm

 

What makes a good match? Which materials can be combined with tungsten carbide?

Tungsten carbide can be processed  in many different ways. This material can be brazed, shrink-fitted, glued, screwed, clamped or pressed. Accordingly, tungsten carbide can be combined with many other materials: In addition to suitable plastics, all metallic materials may be applied. 

 

What are the fastening possibilities?

The choice of the most useful fastening system is essentially dependent on the field of application of the respective workpiece. Tungsten carbide ultimately offers  numerous options: including brazing, gluing, shrink-fitting, casting or mechanical fastening.

 

Brazing tungsten carbide

Tungsten carbide can be brazed to suitable steel components. An adequate structure for brazing the tungsten carbide components has to be considered. It is also necessary to bear in mind that the  thermal expansion of tungsten carbide is about half as high compared to engineering steel.

 

Gluing tungsten carbide

Before gluing tungsten carbide, the adhesive surface must be treated and mechanically roughened. The glues that we use feature a HIGH THERMAL STABILITY AT UP TO 200°C. This material can be easily glued. Nevertheless, the adhesive surface has to be mechanically pre-treated and roughened, respectively. In many cases, gluing is a good alternative to brazing. The used glues still feature a GOOD THERMAL STABILITY AT UP TO 200°C. At higher temperatures, brazing is the only alternative.

 

Shrink-fitting tungsten carbide

Thermal shrink-fitting is the  perfect fastening method for braced rounded tools in the forming technology. The steel holder is heated to 450°C and subsequently, the tungsten carbide core is inserted.

 

Casting tungsten carbide

Cast steel components can be directly linked to cobalt-containing tungsten carbide components by a specific casting method. In this process, a mixed section of tungsten carbide and cast steel is generated – with excellent adhesion.

 

Mechanically fastening tungsten carbide

Tungsten carbide components can be  easily screwed. The thread in the carrier material should be included in the construction process. It is important to consider that the integration of threads into solid tungsten carbide is usually very complex.

 

How precisely can tungsten carbide be processed?

The precision degree of the processing of tungsten carbide is dependent on the geometry of the workpiece. In some cases, contoured components can only be cost-efficiently processed as a green compact. Due to the shrinkage of the green compact, accuracy to a tenth can be realized in the sintering process. Rounded or regular geometrical solids can be processed considerably more precise: precision up to 3 µm.

 

Hard, harder, tungsten carbide – this is how hard it can be!

The hardness of tungsten carbide is recorded in Vickers throughout Europe.  In the US, the Rockwell test (HRA) is preferred. Tungsten carbide actually offers  a broad range of available grades of hardness. It ranges from “soft” grades with a hardness of 770HV30 to highly wear-resistant grades with a hardness of up to 2,000HV30.

 

Tungsten carbide corrodes - but only on the surface.

Tungsten carbide is basically unsusceptible to corrosion. Indeed, it starts to corrode after a while, but only on the surface. For instance, the cobalt content of cobalt-bound tungsten carbide could be exposed to surface oxidation. But this does not destroy the basic structure as is the case with steel.

 

IS TUNGSTEN CARBIDE ELECTRICALLY CONDUCTIVE?

Tungsten carbide definitely conducts electricity. Due to its tungsten carbide content, it is in fact  a very good conductor. The average resistance is 20 µΩ/cm.

 

Is tungsten carbide magnetic?

The magnetic properties  of tungsten carbide are contingent upon the binding materials cobalt and nickel. A specific sintering method could  strongly reduce the magnetizability of nickel-bound tungsten carbide.

 

Can tungsten carbide be coated?

Tungsten carbide can be coated by means of PVD or CVD processes. The PVD method with low coating temperatures of around 450°C is preferable to the CVD method with coating temperatures of 900-1,100°C. Tungsten carbide is frequently used as a basis for coatings since it features a high pressure resistance and it thus prevents an egg shell effect when using coated components.