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.
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
Insert grade index
ISO insert-code index
CNMG120408 — general turning
CCMT09T304 — positive finishing
Tool-wear diagnosis
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