CBN Grinding Wheels
A CBN grinding wheel uses Cubic Boron Nitride, or CBN, as its grinding material. Cubic Boron Nitride is considered a super abrasive. As the name suggests, super abrasives are stronger than normal abrasives like Aluminum Oxide and Silicon Carbide.
CBN is best used to grind hard metals like:
Steels with a hardness rating of at least 45Rc
Cast and wrought irons
It is second in hardness only to diamonds.