Technological investigation of binderless nanocrystalline cubic boron nitride (BNNC) as cutting material for groove turning of hardened steels

By using a high-pressure/high-temperature process (HP/HT), it is possible to synthesise new ultra-hard cutting materials called binderless nanocrystalline cubic boron nitride (BNNC). The starting material is a pyrolytically deposited hexagonal boron nitride (pBN), which is converted at temperatures of 1400 °C – 2200 °C and pressures of 10 - 20 GPa in a direct synthesis without any binding material. The average crystallite size of this material is 50 - 100 nm and is thus significantly smaller than conventional polycrystalline cubic boron nitride (PCBN) cutting materials. Compared to conventional PCBN cutting materials, this material has an increased hardness, hot hardness and better temperature resistance. This provides an excellent alternative to extend the process limits for the machining of hardened steels and superalloys. In this conference paper, the first technological results for groove turning in hardened steels with this new promising cutting material will be presented.