CBN is the second hardest known material after diamond. Tools made of CBN wear much more slowly than other cutting materials when used appropriately. On the one hand, this makes it possible to achieve higher form and dimensional accuracy, and on the other hand, hard materials (steel up to 70HRC) can be machined reliably. There are no different grades of CBN. Differentiation is based on the CBN volume fraction, the fillers, the grain size and the ceramic/metallic binder phase (cobalt/nickel). This results in different CBN substrates. Hard machining with CBN cutting materials is mostly done dry. This is possible because the cutting material has a high high-temperature strength and the high temperature within the chip formation zone has a positive effect. Insufficient supply of the cooling lubricant or interruptions in cutting lead to high, thermally induced stresses in the microstructure of the insert. This can lead to cracks in the microstructure and thus destroy the insert under certain circumstances. In hard machining, most of the heat generated in the shear zone is dissipated via the chip. While carbide already suffers a massive loss of hardness at around 800˚ C, the hardness of CBN still remains almost unchanged at up to 1,200˚ C. Another important advantage is the chemical resistance, especially at the prevailing temperatures.