Which one of the following is the hardest cutting tool material next o...
Hardest Cutting Tool Material after Diamond: Cubic Boron Nitride (CBN)
Cubic Boron Nitride (CBN) is considered the hardest cutting tool material after diamond. It possesses exceptional hardness and thermal stability, making it suitable for various cutting applications. Below are the reasons why CBN is the hardest cutting tool material next only to diamond:
1. Structure and Composition:
- CBN is composed of boron and nitrogen atoms arranged in a crystal lattice structure similar to diamond.
- This crystal structure gives CBN its exceptional hardness and wear resistance.
2. Hardness:
- CBN has a hardness value of approximately 4500 kg/mm², which is just slightly lower than the hardness of diamond (approximately 5000 kg/mm²).
- This high hardness allows CBN to withstand high cutting forces and resist wear even when machining hard materials.
3. Thermal Stability:
- CBN exhibits excellent thermal stability, meaning it can withstand high temperatures during machining without significant loss in hardness or wear resistance.
- This thermal stability allows CBN tools to be used at high cutting speeds and feeds, improving machining efficiency and productivity.
4. Chemical Inertness:
- CBN is chemically inert, meaning it does not readily react with other materials, including metals.
- This inertness prevents the tool material from bonding with the workpiece material during cutting, reducing tool wear and enhancing tool life.
5. Machining Applications:
- CBN is commonly used in machining applications where high hardness and wear resistance are required, especially when cutting hardened steels and superalloys.
- It is often used in the manufacturing of metalworking tools like inserts, grinding wheels, and honing stones.
In conclusion, Cubic Boron Nitride (CBN) is the hardest cutting tool material after diamond due to its exceptional hardness, thermal stability, chemical inertness, and suitability for various machining applications. Its properties make it an ideal choice for cutting hard materials and improving machining efficiency.
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