The hardest material known to man is cubic nitride boron, or CBN. It is used in various manufacturing processes for its hardness and strength. In fact, it is so hard that it can cut diamonds.

cubic nitride boron was first synthesized as a crystalline compound in 1957 by Robert H. Wentorf at GE. It is a synthetic refractory that is used for grinding and polishing materials. CBN is a very stable material that has high thermal and chemical resistance. It is especially well suited for machining ferrous metals such as iron and its alloys, because it has superior hardness to conventional diamond abrasives. It also has higher thermal stability and is less reactive than diamonds with standard transition metals.

Boron nitride exists in three polymorphic forms: hexagonal boron nitride (h-BN), sphalerite boron nitride (b-BN) and wurtzite boron nitride (g-BN). Hexagonal and sphalerite boron diffraction patterns are similar to graphite and lonsdaleite, respectively. Hexagonal boron nitride and wurtzite boron are very similar to diamond. They have a complex crystal structure and interpenetrating face-centred cubic lattices.

In contrast, b-BN has a simpler tetragonal structure and g-BN is triangular with one atom missing. It is a gray to black solid with a metallic luster. It is very resistant to shock and impact damage, being harder than steel and more resilient than diamond. It has high thermal and chemical stability, making it a popular refractory for crucibles and other furnace parts. It also exhibits good mechanical properties for cutting and grinding applications.