For the efficient turning of high hardened steel, Mitsubishi Materials has an extensive range of coated CBN insert grades, the BC8100 series. Four grades make up the complete range: BC8105 for the highest speeds and fine surface finishing. This grade can provide long tool life and fine surface finishes of Ra 0.6?m or better due to the improved lubricity of the CrAlN and TiAlN layered coating. BC8110 is the first choice for continuous high speed and light interrupted machining up to 310 m/min cutting speeds. BC8120 for general applications delivers a substantially better wear resistance and cutting edge toughness through use of a substrate with a new micro-particle binder that prevents crack development. This micro particle binder is also adopted across the whole 8100 series. BC8130 is for the toughest workpieces and for heavily interrupted cutting. Peeling of the coating, usually caused by the impact of interrupted machining, is prevented by the adoption of a high CBN content substrate and a customised ceramic coating.