The hardest cutting tool material next to diamond is Cubic Boron Nitride (CBN) . CBN is renowned for its exceptional hardness and thermal stability, which make it highly suitable for a variety of cutting applications. Here are some key reasons why CBN is considered the hardest cutting tool material after diamond:
Structure and Composition: CBN is composed of boron and nitrogen atoms arranged in a crystal lattice structure similar to that of diamond, which gives it its remarkable hardness and wear resistance .
Hardness: With a hardness value of approximately 4500 kg/mm², CBN is only slightly less hard than diamond, which has a hardness of about 5000 kg/mm² . This high hardness allows CBN to resist wear even when cutting the hardest of materials.
Thermal Stability: CBN exhibits excellent thermal stability, meaning it can endure high temperatures during machining without a significant loss in hardness or wear resistance. This allows CBN tools to be used at high cutting speeds and feeds, enhancing machining efficiency and productivity .
Chemical Inertness: CBN is chemically inert, which means it does not readily react with other materials, including metals. This property prevents the tool material from bonding with the workpiece material during cutting, reducing tool wear and extending tool life .
Machining Applications: CBN is commonly used in machining applications where high hardness and wear resistance are required, particularly when cutting hardened steels and superalloys. It is often used in the manufacturing of metalworking tools such as inserts, grinding wheels, and honing stones.
