- Practice · 3+3 marks
Cutting tool materials and carbon steels
List the properties required of a cutting tool material. Compare high speed steel, cemented carbide and ceramic tools, and state the carbon content and uses of low, medium and high carbon steels.
Required properties of a cutting tool material
- Hot hardness: retain hardness at the high temperature generated at the tool tip.
- High wear resistance and hardness (much harder than the work).
- Toughness to withstand shock and interrupted cuts.
- Low coefficient of friction with the chip and good thermal conductivity.
- Reasonable cost and ease of grinding.
Comparison
| Property | High speed steel | Cemented carbide | Ceramic (Al2O3) |
|---|---|---|---|
| Composition | 18% W, 4% Cr, 1% V (18-4-1), or Mo type | Tungsten carbide grains with cobalt binder | Aluminium oxide, sintered |
| Hot hardness limit | About 600 °C | About 900 °C | Over 1200 °C |
| Cutting speed | 20 to 40 m/min | 100 to 200 m/min | 300 to 600 m/min |
| Toughness | High | Medium | Low (brittle) |
| Form | Solid tools, ground | Brazed tips or inserts | Inserts |
| Uses | Drills, taps, form tools, milling cutters | Turning steel, cast iron, mass production | High speed finishing of cast iron and hard steel |
Carbon steels
| Type | Carbon % | Properties and uses |
|---|---|---|
| Low (mild) | 0.05 to 0.25 | Soft, ductile, weldable; sheets, wires, nails, bolts, structural sections |
| Medium | 0.25 to 0.60 | Strong, can be heat treated; shafts, axles, gears, connecting rods |
| High | 0.60 to 1.5 | Hard, wear resistant, less ductile; files, chisels, springs, hand tools, dies |
Hot rolled steel is rolled above recrystallisation temperature (scaly surface, loose tolerance); cold rolled steel is finished at room temperature (smooth, accurate, stronger).
✓ Answer checked by Claude Opus 5.5 (high effort)
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