Cubic Boron Nitride (CBN)

Cubic Boron Nitride (CBN) is next in hardness only to diamond (Knoop hardness ~ 4700 kg/mm2). Not a natural material, it is produced in the laboratory using a high temperature/high pressure process similar to the making of artificial diamond.

CBN is less reactive with materials like hardened steels, hard chill cast iron, and nickel base and cobalt based super alloys and hence it is extensively used for machining these alloys. They are more expensive than cemented carbides but have higher accuracy which makes productivity possible for difficult to-machine materials.