Cutting tool materials

The conventional uncoated hardmetals comprise a variety of mature grades. Their applications mainly include operations involving light cuts requiring sharp cutting edges and operations demanding very high toughness. Uncoated hardmetal grades are also used on non-ferrous metals and non-metallic materials.

In most steel and cast iron applications, coated hardmetals are preferred because they offer much longer life and/or higher cutting speeds and thus permit more cost-effective production.

Coated hardmetals (ISO group HC)

Highest wear resistance and good toughness can be combined by appropriate coating techniques. The preferred process is chemical vapour deposition. In the CVD process extremely hard, thin layers of coating material (e.g TiC, TiN, Al₂O₃ ) are deposited on tougher hardmetal substrates at tempratures of around 1000⁰ C. Multi-layer coatings reach thickness of up to 15µm.

A more recently developed coating technique is the advanced plasma- CVD process, by which hardmetals can be coated at much lower temperatures of around 500⁰ C.

The much longer life and higher cutting speeds attainable through coating, boost cost- efficiency and productivity. Inventory  requirements are also reduced. Thanks to the wider range of application of coated grades.

Cermets ( ISO group HT )

Cermets are hardmetals based on Titanium carbonitride (TiC, TiN) with a Cobalt/Nickel binder. They display high strength at elevated temperatures and great resistance to oxidation. They offer outstanding cutting edge strength and are particularly suitable for finishing operations at high cutting speeds, producing excellent surface finishes.

Ceramic cutting materials ( ISO group C )

Ceramic cutting materials display good hot hardness and high compressive strength at elevated temperatures, permitting very high cutting speeds. Their main application is the turning of grey  cast iron, in which the tougher nitride ceramics have generally found greater acceptance than the more wear-resistant oxide or dispersion ceramics (based on AL₂0₃)

Ceramics are suitable for cutting steel only under favourable conditions. Because of the lack of suitable chip control geometries chip breakage problems can occur.

Polycrystalline cutting materials

These include polycrystalline  cubic boron nitride (CBN) and polycystralline diamond (PCD).Both materials are produced by high temperature/high pressure synthesis. Their applications are limited and they are mainly seen as complementing hardmetals in specialized applications.

Cubic boron nitride ( ISO group BN )

Cubic boron nitride (CBN), the hardest cutting material after diamond, possesses great wear resistance, even at cutting edge temperatures over 1000⁰ C. Used on hardened materials, chilled cast iron and high temperature Ni/Co alloys.

In contrast to monocrystalline diamond , polycrysatline diamond is completely isotropic and thus less susceptible to breakage. Its fine grain structure makes it possible to produce very sharp, burr-free cutting edges.

Used on all non-ferrous metals,particularly cast aluminium
alloys, at very high cutting speeds. Excellent surface finishes. Further apllications include fibre reinforced plastics.

Cutting material chart

As well as hard materials the extended standard DIN ISO 513 also includes ceramic cutting materials, the superhard polycrysatlline materials, boron nitride and diamond, specifying additional identification symbols for these cutting material groups.