hard metal

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Carbide thread milling cutter

Hard metals are metal matrix composite materials in which hard materials , which are present as small particles, are held together by a matrix made of metal .

As a result, hard metals are a little less hard than pure hard materials, but are much tougher . On the other hand, they are harder than pure metals, alloys and hardened steel , but more susceptible to breakage .

Carbides are mainly used as cutting material for tools (such as lathes , drills and milling tools ) and as wear-resistant matrices e.g. B. used in forming or punching tools . Due to the temperature resistance of hard metals, which reaches up to around 900 ° C, cutting speeds are three times as high as with high-speed steel (HSS). Some cutting materials such as cutting ceramics , boron nitride and diamond are even harder than hard metals.


The history of hard metal begins at the beginning of the twentieth century with the use of tungsten wires in electric light bulbs. After William David Coolidge produced the first tungsten wires in 1907/8, the advantages of using them as filaments quickly became apparent. Compared to the carbon filaments used up until then, the tungsten wires were significantly lighter with lower power consumption. To produce the wires were drawing dies from diamonds used and there have been numerous attempts to replace the diamonds with cheaper materials. Initially there were attempts by Karl Schröter , among others , who worked in the research department of Deutsche Gasglühlicht AG (DGA) from 1908, to replace diamond drawing dies with ones made of molten tungsten carbide. The powdered and pressed tungsten carbide was melted in a vacuum arc furnace and then rapidly cooled. The products produced in this way had a high degree of hardness, but were unsuitable due to the high internal mechanical stresses. In 1914 Hugo Lohmann and Otto Voigtländer patented a process for the production of workpieces from tungsten carbide, which were produced by sintering just below the melting point, but were also too brittle for use as drawing dies.

In 1918, Deutsche Gasglühlicht AG spun off its lamp activities and founded Osram Werke GmbH , which was later converted into a limited partnership (KG). In 1920 the two other large German light bulb manufacturers, Allgemeine Elektrizitäts Gesellschaft (AEG) and Siemens and Halske , joined the KG and brought in their light bulb factories and holdings, and the largest European light bulb manufacturer was created. The research was continued in the Osram Study Society , which was founded in 1916 from the research departments of the three companies under Franz Skaupy of the DGA. Due to the sharp rise in prices for industrial diamonds, Osram resumed research into replacement products. In the former Siemens factory in Berlin Charlottenburg, sintered porous tungsten carbide molded bodies were infiltrated with liquid iron , which significantly improved the quality of the drawing dies, and the process was registered for patent in 1922 with Heinrich Baumhauer as the inventor. Karl Schröter further improved the process by first carburizing the finest tungsten powder and then mixing, pressing and sintering the resulting tungsten carbide powder with iron, cobalt or nickel powder . In the tests with drawing dies produced in this way, the cobalt-based hard metal shows by far the best results. As early as March 1923, the Patent Treuhand-Gesellschaft für electrical light bulbs mbH registered several patents with Karl Schröter as the inventor for the process and the workpieces manufactured with it.

In December 1925, Friedrich Krupp AG took over the patents from the Patent Treuhand-Gesellschaft for electrical light bulbs mbH and registered Widia ( Wi e Dia mant) as a trade name for metal carbides and their alloys and tools on December 25, 1925 . Carbide production began in 1926 under strict secrecy in the premises of the Krupp Widia Research Institute in sintering furnaces specially manufactured by Krupp. The first product Widia-N (WC-6Co) , which does not differ significantly in its composition from today's hard metals, was presented at the Leipzig spring fair in 1927. The production volume of Krupp Widia rose from one ton in 1927 to 60 tons in 1938 to around 500 tons in 1944. After negotiations with Krupp, General Electric received the license rights for the entire US market at the end of the 1920s; However, Krupp retained the rights to continue exporting Widia carbide to the USA. General Electric produced hard metals in the newly founded company Carboloy for this purpose and sold them under the same trade name. In addition, General Electric granted sub-licenses to Firth-Sterling and Ludlum Steel (now Allegheny Technologies ). Their trade names were Dimondite and Strass Metal . In the early days, carbide was extremely expensive, at the beginning of the 1930s it cost US dollars per gram and was therefore more expensive than gold .

Pobedit , consisting of about 90% tungsten carbide, 10% cobalt and small additions of carbon, was developed in 1929 in the USSR by the company of the same name.


Due to their composition, hard metals can be divided into three groups:

Tungsten Carbide Cobalt Hard Metals (WC-Co)

Tungsten carbide-cobalt hard metals represent the standard grades that are of the greatest importance in terms of quantity. In addition to WC, they contain no or only small amounts (<0.8%) of other carbides such as vanadium carbide (VC), chromium carbide (Cr 2 C 3 ) and tantalum-niobium carbide (Ta, Nb) C. The WC grain size can be varied in a wide range from less than one to approx. 20  μm and the cobalt content between three and 30%, which means that they can be well adapted for almost all applications. Due to the diffusion of iron at elevated temperatures, they are not very suitable for machining soft steel.

Carbide grades for steel processing (WC- (Ti, Ta, Nb) C-Co)

Compared to the WC-Co types, carbide grades for steel processing contain even larger amounts of other carbides / mixed carbides (MC), such as titanium carbide, tantalum-niobium carbide and zirconium carbide (ZrC). They are characterized by improved hot hardness / high temperature strength and oxidation resistance. Due to their better diffusion resistance compared to ferrous materials, they are particularly suitable for machining steel materials, where temperatures of around 1000 ° C can occur at the cutting edge. They are divided into two groups according to their composition: Group A> 10% mixed carbides and Group B <10% mixed carbides.


These hard metals contain little or no tungsten carbide, but rather other hard materials, in particular titanium carbide and titanium nitride . The binding phase consists of nickel , cobalt and molybdenum . These hard metals, known as cermets ( ceramic + metal ), are characterized by a further increased heat resistance and hardness and by a very low diffusion and adhesion tendency . This enables even higher cutting speeds for finishing metal. For this reason, the cermet cutting materials are mainly used for high speed cutting (HSC) processes.


Tungsten carbide  (WC) is mostly used as the hard material, but it can also be titanium carbide  (TiC), titanium nitride  (TiN), niobium carbide , tantalum carbide or vanadium carbide . Cobalt is used as the binding metal for the matrix in WC types , otherwise mainly nickel or mixtures of both.

Most WC-Co cemented carbides are composed of 73–97% tungsten carbide and 3–27% cobalt . However, there are also special types in which nickel is used as a binder . As a result, the hard metal has a particularly high corrosion resistance and is generally not magnetizable . There is also the option of using particularly tough binders made from an iron-nickel-cobalt mixture. The tungsten carbide grains average about 0.2-6 micrometers in size. A rough classification of the different grain sizes is made in the following table.

Grain size WC [µm] Description in German Name in English
<0.2 Nano Nano
0.2-0.5 Ultra fine Ultra-fine
0.5-0.8 Finest Submicron
0.8-1.3 Fine Fine
1.3-2.5 medium medium
2.5-6.0 Rough Coarse
> 6.0 Extra coarse Extracoarse

Stellites (hard alloys) are also used to process fresh wood . The advantage of Stellite in a wood saw application is that it is comparatively easy to solder onto the saw body. It can then be ground to the desired geometry using inexpensive grinding wheels. Stellite saws can be sharpened more often than carbide saws . With thin wood saws, it is problematic to attach the hard metal cutting edge firmly to the saw body. Even when manufacturing with plasma welding devices, tooth loss occurs again and again while the saw is in use. Another disadvantage is that hard metal saws have to be sharpened with an expensive diamond grinding wheel, while the base body should be sharpened with a stone wheel, since the carbon of the diamond has a high affinity for steel and the diamond grains wear out.


Hard metals differ from steels in particular with regard to the following properties:

Many hard metals have a modulus of elasticity between 400 and 650 GPa. Steels here are between 180 and 240 GPa. For Co-bonded hard metals, it can be assumed that the modulus of elasticity increases approximately linearly with decreasing cobalt content. This is due to the increasing influence of the hard material layer in the form of tungsten carbide. Due to the higher modulus of elasticity compared to steel, hard metals can be used to achieve a much more rigid structure with the same moment of inertia . The density of hard metals is usually between 12.75 and 15.20 g / cm 3 . In comparison, most steels are around 7.85 g / cm 3 . The hardness of hard metals can reach up to 2200  HV30 . Here, too, it can be seen that the hardness increases as the cobalt content decreases. The compressive strength of hard metals can reach values ​​of over 8000 MPa and also increases with decreasing cobalt content. The flexural strength can typically be expected to be between about 2000 and 4000 MPa.

In general, it can be assumed that a reduction in the grain size has a positive effect on the bending strength, hardness and compressive strength of the hard metals. However, it should be noted at this point that this significantly increases the cost of manufacturing the hard metals. Not only do finer powders have to be made available as the starting material, but special process management is also required when sintering the hard metals.


The production of hard metal takes place in a multi-stage process. The following steps in hard metal production can be roughly distinguished:

  • Mixing / grinding / granulate production
  • Shaping
  • Sintering

Then follow, depending on the application and workpiece:

  • Finishing
  • Coating

Grinding and mixing

As part of this process, the desired ingredients of the hard metal are ground to a very fine powder with grain sizes down to 0.2 µm and mixed at the same time. This process often takes place in ball mills or an attritor . These mills have to be operated with various safety devices, including an extraction system, because cobalt is harmful to humans and the very fine dust that is produced could possibly be respirable. As a rule, organic solvents are used as grinding liquid, but in the recent past water has been used more and more. By adding an organic binder, for example paraffin , towards the end of the grinding process, a malleable mass is obtained after drying, which can be pressed into a green compact in the next step. Drying is carried out by evaporating the grinding liquid or spray drying .


The powder prepared and dried in the previous step is pressed into a so-called green compact in this step. This green compact already has all the geometric properties of the desired finished component, but shrinkage must still be taken into account here, since there is a change in volume during sintering. Common processes for the production of green compacts are divided into direct and indirect methods:

  • Direct methods such as die pressing, injection molding, and extrusion
  • Indirect methods such as cold isostatic pressing and processing of green parts


Then, depending on the manufacturing process, the green compact is sintered at temperatures of up to 1600 ° C in a vacuum or in a protective atmosphere and pressures of up to 5000 bar. When sintering , so-called hot isostatic pressing (HIP) is used in a sintering furnace in most cases . This makes use of the fact that the hard material phase (α-phase) and the binder phase (β-phase) have different melting points. As a rule, the α-phase has a significantly higher melting point than the β-phase. Different, usually active gases that support the sintering process are used. During sintering, the temperature is set in the process so that the organic binders are first removed in the first step (pre-sintering). The temperature is then increased in a vacuum so that it is above the melting point of the binder phase but below the melting point of the hard material phase. The external pressure then applied during the HIP compresses the mixture of α and β phases and, ideally, produces a material free of defects . After the binder phase has cooled and solidified, the hard metal that has now formed can be used again. Alternatively, the powder granulate can be packed in a die or in welded steel sheets and heated and compressed under vacuum.

In order to achieve special properties of the hard metals, there are also three-phase hard metals which have an additional γ phase in addition to an α and β phase. Classic representatives for this include titanium carbide (TiC) and tantalum carbide (TaC) . These additives usually improve the oxidation resistance and thermal stability and inhibit grain growth during the HIP process.


Because of their high hardness, cemented carbides are usually machined using spark erosion processes, for example spark erosion , or machining processes with a geometrically undefined cutting edge , including grinding .

In metal forming technology , grinding is almost always followed by polishing . As a result, on the one hand, residual compressive stresses can be introduced into the surface and, on the other hand, the roughness is minimized, which has a positive effect on the notch effect of the surface. These two mechanisms cause a significant increase in the tool life.

However, there are hard metals, especially in the field of metal forming, which can also be machined by cutting processes using geometrically defined cutting edges, for example turning and milling. As a result, significant cost savings can be achieved compared to eroding or grinding. These special hard metals have a high cobalt content of over 20%.


For the most common application, carbide indexable inserts, the following operations are often grinding (bottom, possibly top, edges, radii), coating ( CVD process, PVD process, vacuum electrode deposition, etc.), labeling and packaging.


According to ISO 513, hard metals are divided into different groups. The groups shown in the table below are common.

ISO class Material to be processed Example of material
P Unalloyed steel / cast steel S235JR, S355JR
Low-alloy steel / cast steel C45, 16MnCr5
High-alloy steel / cast steel X153CrMoV12, X210Cr12
M. Stainless steel / cast stainless steel G45CrNiMo4-2, G-X6CrNiMo 18-10
K Cast iron with spheroidal graphite (GGG) EN-GJS-400-18, EN-GJS-900-2
Gray cast iron (GG) EN-GJL-150, EN-GJL-350
Malleable cast iron EN-GJMW-350-4, EN-GJMW-550-4
N Wrought aluminum alloy AlMg3, AlMgSi1
Quenched and tempered cast aluminum G-AlMg3, G-AlCu4TiMg
Copper alloys CuZn28, CuZn38Pb0.5
General non-metallic materials Plastic , wood
S. High temperature alloys / superalloys Hastelloy , Inconel
Titanium alloy Ti99.8, TiAl6Zr5
H Hardened steel X153CrMoV12, X210Cr12
Chilled cast iron GX165CrMoV12
cast iron EN-GJL-150, EN-GJL-350

The grade identification is followed by an index that describes the wear behavior and toughness. The smaller the number, the greater the wear resistance, but the lower the toughness. Typical key figures are: 01, 10, 20, 30, 40, 50 (e.g. P 01, M 30, K 05). Endings F and UF mean fine or ultrafine (e.g. K40UF)

application areas

Use as cutting material

Main article: Cutting material

In contrast to conventional cutting materials, for example high-speed steels , hard metals have a low fracture toughness and thermal shock resistance. In contrast, however, there are significant advantages such as greater hardness and temperature resistance. The high hardness in particular leads to a high level of abrasive wear resistance . This alone enables higher cutting speeds. These can also be achieved because hard metals have a temperature resistance of up to 1100 ° C. As a result, they have long been used as a cutting material for machining, as cutting speeds of more than 350 m / min can be achieved. In comparison, HSS achieve values ​​of approx. 75 m / min. A classic application of carbide tools is the machining of metals by turning, milling and drilling. There are also a number of other use cases; For example, the knives of cigarette paper cutters are made of hard metal. The use of tools in rock mills and mines is also a domain of hard metals: drilling rocks, opening tunnels with the help of cutting machines , shearer loaders , roadheading machines or shield tunneling machines are all predestined for the use of hard metal-tipped drilling and cutting tools. Another application is the cutting of hardwoods from the tropics with hard metal saws. It is often not possible to cut such pieces of wood with conventional stellite saws .

Use in forming

Hard metals are used in a large number of forming processes for the production of active elements, for example dies and punches. This is mainly due to the fact that they have a significantly higher wear resistance compared to tool steels. Active elements made of hard metal are often used in the following forming processes:

In addition to applications in forming technology, hard metals are also used in the textile industry. For example, nozzles are made from hard metal when spinning textiles .


During the manufacture and processing of hard metals and the processing of hard metal tools, employees can be exposed to hazardous substances . As part of the risk assessment , the hazardous substances occurring at the workplace must be determined and suitable protective measures must be defined. The information on hard metal workplaces can be used in the risk assessment for activities with hard metals. It defines criteria for compliance with the state of the art and provides assistance for the effectiveness check according to TRGS 402.


In German-speaking countries, the manufacturers of hard metal, as well as the suppliers of metal powders and systems technology, have joined forces in the Association of Powder Metallurgy (FPM) . Internationally active carbide manufacturers include:

Individual evidence

  1. ^ A b Wolf-Dieter Schubert , Erik Lassner : Tungsten . International Tungsten Industry Association, 2013, ISBN   0-95300086-2-2  ( defective ) , OCLC 939075516 , p. 42-44 .
  2. a b c d Hans Kolaska : Powder metallurgy of hard metals . Powder Metallurgy Association , December 1992, p. 1 / 1–1 / 14 .
  3. Patent DE000000289066A : Process for the production of pieces of any size from tungsten and molybdenum carbide or from a mixture of these carbides for tools and utensils of all kinds. Registered on January 3, 1914 , published on December 2, 1915 , applicant: METALL-FABRIKATIONS-GES . mbH, inventor: Voigtländer & Lohmann.
  4. a b 100 years of OSRAM (company publication 2006, pdf 4.66 MB)
  5. Patent DE000000443911A : Process for the production of shaped pieces and tools, in particular drawing dies. Registered on March 19, 1922 , published on May 27, 1927 , applicant: Patent Treuhand-Gesellschaft for electrical light bulbs mbH, inventor: Heinrich Baumhauer.
  6. Patent US00000152191A : HARD TOOL AND IMPLEMENT AND IN PROCESS OF MAKING. Registered December 27, 1922 , published October 21, 1924 , Applicant: General Electric Company, Inventor: Heinrich Baumhauer.
  7. Patent DE000000420689A : Sintered hard metal alloy and process for their production. Registered on March 30, 1923 , published on October 30, 1925 , applicant: Patent Treuhand-Gesellschaft for electrical light bulbs mbH, inventor: Karl Schröter.
  8. Patent DE000000498349A : Process for the production of a hard fused alloy for work tools, in particular drawing dies. Registered on March 22nd, 1923 , published on May 22nd, 1930 , applicant: Patent Treuhand-Gesellschaft for electrical light bulbs mbH, inventor: Karl Schröter.
  9. Patent DE000000434527A : Sintered hard metal alloy for work equipment and tools. Registered on March 30, 1923 , published on May 8, 1925 , Applicant: Patent Treuhand-Gesellschaft for electrical light bulbs mbH, Inventor: Karl Schröter.
  10. Widia registered trademark at the German Patent and Trademark Office
  11. Werner Degner, Hans Lutz, Erhard Smejkal: Spanende Formung. Carl Hanser Verlag, 2002, ISBN 3-446-22138-7 , p. 67.
  12. Wolfgang Filì: The creative times are only just beginning.  ( Page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. In: Industrieanzeiger.de@1@ 2Template: Toter Link / www.industrieanzeiger.de  
  13. ^ A b Hans Kolaska: Carbide - yesterday, today and tomorrow . In: METALL - specialist magazine for metallurgy . tape 61 , no. 12 . GDMB , 2007, p. 825-832 .
  14. General Carbide: The designer's guide to tungsten carbide (pdf)
  15. a b c Wirtschaftsvereinigung Stahl , Merkblatt 137 Zerspanen von Stahl , 2008, Section 2.3, pages 11-13 ( pdf )
  16. Overview of cemented carbide binders ( Memento of the original dated November 23, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.hartmetall-estech.ch
  17. Werner Schatt, Klaus-Peter Wieters, Bernd Kieback: Powder Metallurgy . Technologies and materials. In: VDI book . Springer-Verlag, Berlin, Heidelberg, New York 2007, ISBN 978-3-540-23652-8 , pp. 517 ( limited preview in Google Book search).
  18. ^ KJ Brookes: World Directory and Handbook of Hardmetals and Hard Materials. 5th edition. International Carbide Data, United Kingdom 1992, ISBN 0-9508995-2-6 .
  19. Kolja Andreas: Influence of surface properties on tool usage behavior during cold extrusion. In: Manufacturing Technology Erlangen. No. 275, Meisenbach, Bamberg, 2015, ISBN 978-3-87525-398-6 .
  20. zps-fn.de ( Memento of the original from November 23, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / www.zps-fn.de
  21. German statutory accident insurance e. V. (DGUV): DGUV Information 213-724 - Recommendations for hazard identification by the accident insurance institutions (EGU) according to the Hazardous Substances Ordinance - hard metal workplaces. Retrieved October 15, 2019 .
  22. ^ IMC Companies. In: imc-companies.com. Retrieved December 21, 2016 .
  23. Sandvik company Presentation 2015/2016 ( Memento of the original from December 22, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF file). @1@ 2Template: Webachiv / IABot / www.home.sandvik


  • Wolfgang Schedler: Carbide for the practitioner: structure, manufacture, properties and industrial application of a modern group of materials . 1st edition. VDI-Verlag, 1998, ISBN 3-540-62119-9 .
  • HE Exner: Physical and chemical nature of cemented carbides . In: International Metals Reviews . tape 24 , 1979, pp. 149–173 , doi : 10.1179 / imtr . 1979.24.1.149 .

Web links

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