--- title: "Cutting tool materials and their properties" subject: "Manufacturing and Production Processes" chapter: 7 key: "semester_4/manufacturing_and_production_processes:cutting-tool-materials-characteristics-economics" source: https://www.bctengineer.com/q/semester_4/manufacturing_and_production_processes/cutting-tool-materials-characteristics-economics site: BCT Engineering --- # Cutting tool materials and their properties Manufacturing and Production Processes · Chapter 7: Material Removal Processes: “ Chip-forming” - Asked in: year not given, 5 marks - Video: [cutting tool materials | cutting tool materials and their properties | Selection of cutting Tool](https://www.youtube.com/watch?v=lphJHxaWC-g) — Modi Mechanical Engineering Tutorials - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_4/manufacturing_and_production_processes/cutting-tool-materials-characteristics-economics - Whole chapter: https://www.bctengineer.com/md/semester_4/manufacturing_and_production_processes/chapter-7 ## Question 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? ## 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. ## Answer #### 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 | Material | Composition | Hot hardness limit | Use | |---|---|---|---| | HSS | Fe with W, Mo, Cr, V (18-4-1) | about 600 degree C | Drills, taps, milling cutters, complex tools, low speeds | | Cemented carbide | WC grains bonded with Co (6-12 %) | about 900 degree C | Most turning and milling of steel, cast iron | | Ceramics | Al$_2$O$_3$ (with TiC or ZrO$_2$), Si$_3$N$_4$ | above 1200 degree C | High speed finishing of cast iron and steel; brittle | | CBN | Cubic boron nitride | about 1300 degree C | Hardened steel (above 50 HRC), superalloys | | Diamond | Synthetic polycrystalline diamond | about 700 degree C in air | Non-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, Al$_2$O$_3$ 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. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why is hot hardness the first required property of a cutting tool? A. Tools are only used when hot B. It makes the tool tougher at room temperature C. The tool must retain hardness at cutting temperature, which can reach about 1000 deg C D. It lowers the friction coefficient Answer: C. Cutting temperatures are high, so a tool that softens wears fast. (Key point: Hot hardness) 2. What is the trade-off among tool properties? A. Hard tools are always tough B. Toughness increases with hot hardness C. Cost falls as hardness rises D. Hardness and toughness conflict; no material has all properties at once Answer: D. Hard materials such as ceramics are brittle, while tough HSS is softer. (Key point: Hardness vs toughness) 3. Which tool material suits hardened steel above 50 HRC and superalloys? A. Cubic boron nitride B. High speed steel C. Polycrystalline diamond D. Uncoated carbide Answer: A. CBN keeps hardness to about 1300 deg C and does not react with iron; diamond reacts with iron. (Key point: Tool material use) 4. Why are coated carbide inserts used? A. The coating makes the substrate softer and tougher B. The substrate gives toughness while the thin coating gives wear resistance, thermal barrier and lower friction C. The coating replaces the need for cutting speed limits D. The coating makes the insert reground more often Answer: B. Coated inserts allow 2-3 times the speed of uncoated ones with longer life. 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