[Tool material] Cubic boron nitride (CBN) [Properties] 
Stable. Expensive. Being the second hardest substance known, it is also the second most fragile. It offers extremely high resistance to abrasion at the expense of much toughness. It is generally used in a machining process called "hard machining", which involves running the tool or the part fast enough to melt it before it touches the edge, softening it considerably. Used almost exclusively on turning tool bits. Hardness higher than HRC95. Sharp edges generally not recommended.