ISO K — Cast Iron · K40
K40 — Compacted graphite iron
Hardness range: 160–250 HB. Part of the ISO K — Cast Iron group. Cast iron is abrasive and brittle — short chips, no built-up-edge. CVD alumina (Al₂O₃) coatings resist the high-temperature abrasion. Dry machining is acceptable for grey iron; coolant helps with nodular grades. Main failure mode: flank wear. High-speed machining is effective.
Material profile — K40
- ISO designation
- K40 (ISO K — Cast Iron)
- Material
- Compacted graphite iron
- Hardness
- 160–250 HB
- ISO group colour
- Cast Iron
Tooling guidance — K-group
- Group summary
- CVD alumina coatings excel. Dry machining acceptable for grey CI. Abrasive wear is the main failure mode.
Insert selection for compacted graphite iron (CGI) — starting point
- ISO application class
- K (cast iron). CGI is far harder on tools than grey iron: it lacks the protective film grey iron forms, so tool life drops sharply and speeds must come down. Match the ISO K class across brands rather than the brand name (Sandvik, Kennametal, Iscar, Walter, Seco and Mitsubishi each publish one), then confirm the exact grade for your condition.
- Grade & coating
- Wear-resistant CVD alumina-coated carbide; CBN or ceramic for high-volume finishing (for example engine blocks). Expect shorter life than grey iron.
- Geometry
- Negative geometry, honed edge, rigid setup.
- Starting parameters
- Vc much lower than grey iron, ≈ 80–200 m/min, fn ≈ 0.10–0.30 mm/rev. Confirm in the advisor or on a sample part.
Selection table: compacted graphite iron (CGI)
| Operation | Geometry | ISO class | Coating family | Coolant | First check |
|---|---|---|---|---|---|
| Roughing | Negative geometry, honed edge, rigid setup | K10–K20 | Wear-resistant CVD alumina-coated carbide | Per process; speed far lower than grey iron | Do not carry grey-iron speeds over to CGI |
| Finishing | Negative geometry, honed edge | K10–K20 | CBN or ceramic for high-volume finishing; otherwise CVD alumina carbide | Per process | Rapid wear: no protective film as on grey iron |
| Interrupted cut | Honed edge, robust grade, rigid setup | K10–K20 (tougher end) | Robust CVD alumina carbide | Per process | Edge chipping: honed edge, rigid setup |
| Low rigidity / thin wall | Negative geometry; rigid setup | K10–K20 | CVD alumina carbide | Per process | Heat at the edge: keep the speed down |
compacted graphite iron (CGI): what goes wrong, and what to check first
- Rapid wear (the defining problem)
- CGI does not form the protective sulfide film grey iron does, so abrasive and adhesive wear accelerate. Drop the speed and use a wear-resistant grade.
- Edge chipping
- Use a honed edge, a robust grade, and a rigid setup.
- Heat at the edge
- Higher strength than grey iron loads the edge; keep the speed down.
- Inconsistent life vs grey iron
- Do not carry grey-iron speeds over to CGI; they will halve tool life.
Reference data
Frequently asked questions
What insert for compacted graphite iron (CGI)?
A wear-resistant CVD alumina-coated carbide, with CBN or ceramic for high-volume finishing. Match the ISO K class across brands and confirm in the advisor.
Why is CGI so much harder on tools than grey iron?
CGI does not form the protective manganese-sulfide film that grey iron does, and it is stronger, so tool wear accelerates and speeds must drop.
What cutting speed for CGI?
Much lower than grey iron, roughly Vc 80–200 m/min, fn 0.10–0.30 mm/rev. Confirm on a sample part.
Can I use grey-iron tooling speeds on CGI?
No; grey-iron speeds will sharply shorten tool life on CGI. Use a wear-resistant grade at a lower speed.
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