CBN wheels are used to grind tool steels and Stellite type materials with hardness above 42 Rc. Cubic Boron Nitride is far superior to synthetic or natural diamond for grinding Ferrous materials. They have proven time and time again to be a cost effective replacement for conventional abrasives. CBN wheels should ideally be used with grinding coolants to maximize wheel life and generally should be used at increased surface feet speeds compared to diamond wheels.