Diamond is aabrasive known , there are actually two kinds : 1.SDC - (SYNTHETIC DIAMOND COATING), the market said diamond or Double Disc Grinding    , can grind tungsten steel ( carbide ) , ceramics, magnets , glass, precious stones , stone and all other non- carbon Fund is a mechanical material . 2. CBN - (CUBIC BROZON NITRID) hardness only to diamond , cubic boron nitride that is , the appearance of the diamond almost, not a professional who can not distinguish from the appearance of so many people also put CBN also called diamond . CBN grinding all carbon fund is only as tool steel (SKD-11), high-speed steel (HSS SKH9 , etc. ) , all kinds of high-carbon steel . alloy steel hardened metal material for at least 55HRC Why such as those classified ? because SDC is carbon-based , metal material is carbon-based , both cutting grinding heat generated will have a " carbonation " , metal materials would be thereby metallurgical damage , SDC will reduce the abrasive grinding wheel hardness lose cutting forces. conclusions: 1. diamond the CBN can be processed metals , SDC most not . 2. SDC diamond metal materials can be processed but limited to grinding energy is less than 200 degrees Celsius below, or finely ground 400 # to fine grinding does not generate excessive heat