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.
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
Insert grade index
ISO insert-code index
CNMG120408 — general turning
CCMT09T304 — positive finishing
Tool-wear diagnosis
Get cutting parameters for Nodular / ductile iron
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