Diamond and cubic boron nitride (CBN) are considered to be the hardest known grinding materials and are therefore often referred to as „super-abrasives". For this reason they are suitable for machining materials which are difficult or even impossible to grind with conventional abrasives such as silicon carbide or corundum.
Diamond and CBN have the same crystal structure, with diamond consisting of pure carbon, whilst CBN is made up of the elements boron and nitrogen.
Comparison of hardness of different materials
Due to its extreme hardness, Diamond is particularly suitable for machining the following materials:
- All carbide metal grades
- Oxide and non-oxide ceramics
- PCD / PCB
- Hard facing alloys
- Sapphire, glass
- Fiber reinforced synthetics
- Precious and semi-precious stones
Steel has a high affinity to carbon. Since Diamond consists of pure carbon, it is not suitable for machining steel. The high temperatures produced in the grinding process cause the steel to extract carbon atoms from the Diamond, eroding the Diamond grinding grit.
CBN (cubic boron nitride)
CBN consists of the elements boron and nitrogen. In contrast to Diamond, CBN has no carbon atoms, making it suitable for machining steel. CBN is better suited for machining the following materials:
- Hardened steel over approx. 54 HRc hardness
- High-speed steel (HSS)
- Nickel-based special alloys
As the following graph shows, another significant advantage of CBN over Diamond is its thermal stability. Whereas Diamond suffers a massive loss of hardness at about 700 °C, the hardness of CBN remains virtually unchanged at over 1000 °C.
Thermal performance of Diamond an CBN