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Cutting tool materials and their properties

Short answer

Desirable properties: hot hardness, toughness, wear resistance, chemical stability. HSS (Fe alloy) works up to 600°C, carbide (WC-Co) to 900°C, ceramics (Al2O3) above 1200°C, CBN for hardened steel, diamond for nonferrous. Coated carbide inserts combine a tough substrate with a hard, wear-resistant TiC/TiN/Al2O3 layer for higher speeds and longer life.

List the desirable properties of a cutting tool material. Compare high speed steel, cemented carbide, ceramics, cubic boron nitride and diamond with respect to composition, properties and applications. Why are coated carbide inserts used?

Desirable properties

  1. Hot hardness - hardness retained at cutting temperature (up to 1000 degree C).
  2. Toughness - resists shocks and interrupted cuts without chipping.
  3. Wear resistance - long life against abrasion, adhesion and diffusion.
  4. Chemical stability - does not react with the work material.
  5. Low coefficient of friction and good thermal conductivity; and reasonable cost.

No material has all properties at once: hardness and toughness are in conflict.

Comparison

MaterialCompositionHot hardness limitUse
HSSFe with W, Mo, Cr, V (18-4-1)about 600 degree CDrills, taps, milling cutters, complex tools, low speeds
Cemented carbideWC grains bonded with Co (6-12 %)about 900 degree CMost turning and milling of steel, cast iron
CeramicsAl2_2O3_3 (with TiC or ZrO2_2), Si3_3N4_4above 1200 degree CHigh speed finishing of cast iron and steel; brittle
CBNCubic boron nitrideabout 1300 degree CHardened steel (above 50 HRC), superalloys
DiamondSynthetic polycrystalline diamondabout 700 degree C in airNon-ferrous metals, composites, plastics; reacts with iron

Cutting speeds rise in about the same order, from 20-60 m/min for HSS to more than 500 m/min for ceramics on cast iron.

Coated carbide

A thin layer (3-10 micrometre) of TiC, TiN, Al2_2O3_3 or a multilayer is deposited by CVD or PVD. The substrate provides toughness while the coating gives wear resistance, a thermal barrier and lower friction. Coated inserts allow 2-3 times the speed of uncoated ones, and give longer tool life.

Economics

Tool cost per piece depends on the tool price, number of regrinds or edges of an insert, and tool life. Disposable indexable inserts remove regrinding cost and give consistent size. A costly tool is justified when it reduces the cost per piece through higher speed, as in CNC and automatic production.

✓ Answer checked by Claude Opus 5.5 (high effort)

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