ISO K — Cast Iron · K20
K20 — Nodular / ductile iron
Hardness range: 170–260 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 — K20
- ISO designation
- K20 (ISO K — Cast Iron)
- Material
- Nodular / ductile iron
- Hardness
- 170–260 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 ductile / nodular iron — starting point
- ISO application class
- K (cast iron). Match the insert's ISO class, not the brand name. Sandvik, Kennametal, Iscar, Walter, Seco and Mitsubishi each publish a K-class grade — pick by ISO class, then confirm the exact grade for your condition.
- Grade & coating
- CVD alumina (Al₂O₃)-coated carbide, K10–K20, to resist high-temperature abrasion. Ductile iron is tougher than grey iron, so a slightly tougher edge than a grey-iron grade helps.
- Geometry
- Negative geometry is fine. Use a honed edge for cast skin, scale and interrupted cuts.
- Starting parameters (carbide)
- Carbide Vc ≈ 150–300 m/min, fn ≈ 0.10–0.40 mm/rev, dry or with coolant. Typical starting band — confirm in the advisor or on a sample part.
Selection table: ductile / nodular iron
| Operation | Geometry | ISO class | Coating family | Coolant | First check |
|---|---|---|---|---|---|
| Roughing | Negative geometry, honed edge for skin and scale | K10–K20 | CVD alumina (Al₂O₃)-coated carbide | Dry or with coolant | Abrasive flank wear: keep the speed sensible |
| Finishing | Negative geometry, clean sharp-honed edge | K10–K20 | CVD alumina carbide | Dry or with coolant | Built-up edge at low speed: raise Vc into the band |
| Interrupted cut | Honed edge for skin, scale and interruptions | K10–K20 (tougher end) | Slightly tougher CVD alumina carbide than for grey iron | Dry or with coolant | Edge chipping: tougher grade, ease into the cut |
| Low rigidity / thin wall | Negative geometry; shorten overhang and support the part | K10–K20 | CVD alumina carbide | Dry or with coolant | Chatter is rigidity, not the grade |
ductile / nodular iron: what goes wrong, and what to check first
- Abrasive flank wear
- Free graphite and the matrix abrade the edge. Use a CVD-alumina K-grade and keep the speed sensible. See the tool-wear guide.
- Edge chipping on cast skin / interrupted cuts
- The abrasive skin and any interruptions chip a fragile edge. Use a tougher K-grade with a honed edge and ease into the first cut.
- Built-up edge at low speed
- Unlike grey iron, ductile iron is ductile enough to build up at low speed. Raise Vc into the band and keep a clean edge.
- Chatter on thin sections
- This is rigidity, not the grade. Shorten overhang and support the part.
Reference data
Frequently asked questions
What insert grade should I use for ductile / nodular iron?
Use a CVD alumina-coated carbide in the ISO K class, around K10–K20. Ductile iron is tougher than grey iron, so a slightly tougher edge helps. Match the ISO K class across brands rather than the brand name and confirm the exact grade in the advisor.
What cutting speed for ductile iron with carbide?
Roughly Vc 150–300 m/min and fn 0.10–0.40 mm/rev, dry or with coolant. Treat this as a starting band and confirm on a sample part.
Why do I get built-up edge on ductile iron?
Unlike grey iron, ductile (nodular) iron is ductile enough to build up at low speed. Raise the cutting speed into the working band and keep a clean edge.
How do I stop edge chipping on cast-iron skin?
The abrasive cast skin and any interruptions chip a fragile edge. Use a tougher K-grade with a honed edge and ease into the first cut.
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Grade designations in this group
Each page cross-references the EN, Werkstoffnummer, AISI/UNS and JIS designations for one material, with the ISO machining group it falls in.
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