Tool Material Hardness Sequence Explained

Understanding the hardness of different tool materials is crucial for selecting the right cutting tool for specific machining operations. Hardness refers to a material's resistance to scratching or indentation, which directly impacts its ability to cut harder materials and its wear resistance.

Comparing Tool Material Hardness

The hardness of common tool materials varies significantly. Generally, materials increase in hardness as you move from traditional steels to advanced engineered materials. Let's look at the materials mentioned in the options:

• High-Speed Steel (HSS): This is a type of tool steel known for its high hardness, red hardness, and wear resistance. It's a common material for drills, taps, and milling cutters.
• Tungsten Carbide: This is a composite material made of tungsten and carbon atoms. It is significantly harder and more brittle than HSS, offering better performance at higher cutting speeds.
• Cubic Boron Nitride (CBN): This is a synthetic material, second only to diamond in hardness. It exhibits excellent hot hardness and wear resistance, making it suitable for machining hardened steels and cast irons.
• Diamond: This is the hardest naturally occurring substance and the hardest material known. It is used for machining very hard and abrasive materials, especially non-ferrous metals and non-metallic composites.

Sequence of Increasing Hardness

Based on their properties, the sequence of these tool materials in increasing order of hardness is as follows:

Importance in Machining

Selecting a tool material with appropriate hardness ensures:

• Effective Material Removal: Harder tools can cut harder workpiece materials.
• Tool Life: Increased hardness generally leads to better wear resistance and longer tool life.
• Surface Finish: Appropriate tool selection contributes to a better surface finish on the machined part.

Therefore, the correct sequence representing increasing hardness is High-Speed Steel (HSS), followed by Tungsten Carbide, then Cubic Boron Nitride (CBN), and finally Diamond.