Aug 2 2009
Tungsten Carbide is often referred to as a Hard Metal due to it’s very high hardness in relation to other metals. Typically a Tungsten Carbide Hard Metal can have a hardness value of 1600 HV, whereas mild steel would be in the region of 160 HV a factor of 10 lower.
Although called a hard metal, Tungsten Carbide is actually a composite material with hard particles of Tungsten Carbide embedded in a softer matrix of metallic Cobalt .
What is the Chemical Formula for Tungsten Carbide?
The chemical formula for Tungsten Carbide is WC.
What is the History of Hard Metals or Tungsten Carbide?
Tungsten Carbide was originally developed in Germany in the 1920’s as there was a requirement for die materials that were able to stand up to the high wear encountered in the drawing of tungsten filaments for light bulbs
How is Hard Metal or Tungsten Carbide Made?
Tungsten Carbide Hard Metals are primarily produced using a Powder Metallurgy process, whereby the powdered forms of tungsten carbide and cobalt are mixed using ball mills, a binder material is added to hold the powders together during the next stage of the process which is compaction or pressing.
During the compaction processes, hydraulic presses or isostatic presses are used to compact the powders into a shape which approximates the design of the finished product.
Powder Pressing Video
Die Pressing
Whilst in this condition, the powder compact can be easily machined using conventional metal working tools. This process is often referred to as “Green Machining”. Care has to be taken with the removal of the fine powder particles as they can pose a health hazard so effective extraction methods are required.
Following “Green Machining” the powder compact is then ready to be Sintered. Typically this is done in a vacuum furnace at temperatures between 1300 and 1600°C.
The sintering process causes the tungsten carbide and cobalt matrix to fuse together to produce a dense “Hard Metal”.
After sintering the material is so hard that it can only be machined by diamond grinding, a specialised form of micro machining that is relatively expensive as it is not possible to remove large amounts of materials by this process.
This video from Sandvik Cormat provides a good example of the process mention above as used in the production of Tungsten Carbide cutting tool tips.
Sandvik Coromant - How Coated Cemented Carbide Inserts are made.
Typical Properties of Tungsten Carbide Hard Metals
ISO 513
Class |
Tungsten Carbide
WC %
|
Cobalt
Co %
|
Hardness
HV 30
|
Transverse Rupture Strength
MPa
|
Density
g/cm3
|
Grain Size
µm
|
Description |
| K5 |
93
|
7
|
1850
|
3000
|
14.65
|
0.5
|
Ultra fine grained material with very high hardness and wear resistance |
| K10 |
94
|
6
|
1690
|
2800
|
14.85
|
1.0
|
Fine grain size “workhorse” grade |
| K20 |
92
|
8
|
1710
|
3200
|
14.55
|
0.7
|
Fine grain size good hardness and wear resistance with medium toughness |
This short video illustrates the hardness of Tungsten Carbide by demonstrating what happens when you take a jewellers file to a Gold ring and a Tungsten Carbide ring.
Tungsten Rings Don't Scratch
Applications of Tungsten Carbide and Hard Metals
Tungsten Carbides have a wide range of application in many industry sectors such as metal machining, wear parts for mining and oil industries, metal forming tools, cutting tips for saw blades and have now expanded to include consumer items such as wedding rings and watch cases, plus the ball that is in many ball point pens.
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Figure 1. Tungsten Carbide Wedding Rings
Source: AZoM.com