ISO M — Stainless Steel · M20
M20 — Ferritic stainless
Hardness range: 160–220 HB. Part of the ISO M — Stainless Steel group. Stainless steel presents work-hardening as the main challenge. Austenitic grades (304, 316L) built-up-edge and notch-wear rapidly. Positive, sharp geometry with high-pressure coolant at 15–20 bar is standard. Consistent depth of cut prevents re-cutting the hardened chip ramp.
Material profile — M20
- ISO designation
- M20 (ISO M — Stainless Steel)
- Material
- Ferritic stainless
- Hardness
- 160–220 HB
- ISO group colour
- Stainless Steel
Tooling guidance — M-group
- Group summary
- Work hardening is the main challenge. Sharp positive geometry, high-pressure coolant 15–20 bar, consistent DOC.
Insert selection for ferritic stainless (430, 409) — starting point
- ISO application class
- M (stainless). Ferritic stainless work-hardens less than austenitic 304/316 but is still gummy, so a keen edge matters more than extreme toughness. Match the ISO M 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
- PVD-coated M-class carbide with a sharp positive edge.
- Geometry
- Positive, sharp, honed edge; polished chipbreaker; coolant.
- Starting parameters
- Vc ≈ 120–200 m/min (higher than austenitic — less work-hardening), fn ≈ 0.10–0.30 mm/rev. Confirm in the advisor or on a sample part.
Selection table: ferritic stainless (430, 409)
| Operation | Geometry | ISO class | Coating family | Coolant | First check |
|---|---|---|---|---|---|
| Roughing | Positive, sharp, honed edge; polished chipbreaker | M (M-class grade) | PVD-coated M-class carbide | Coolant on the edge | Consistent depth of cut; do not dwell |
| Finishing | Keen positive edge that shears instead of rubbing | M (M-class grade) | PVD-coated M-class carbide, sharp edge | Coolant on the edge | Built-up edge or smeared finish: raise Vc, sharper edge |
| Interrupted cut | Positive honed edge, tougher edge | M (tougher M-class grade) | PVD-coated M-class carbide | Coolant on the edge | Notch wear at the DOC line: vary the depth of cut |
| Low rigidity / thin wall | Sharp positive edge; polished chipbreaker | M (M-class grade) | PVD-coated M-class carbide | Coolant on the edge | Poor finish from rubbing: keep the edge sharp |
ferritic stainless (430, 409): what goes wrong, and what to check first
- Built-up edge / smeared finish
- Speed too low or a dull edge. Raise Vc, use a sharp positive polished edge, and aim coolant at the edge.
- Work-hardening (milder than austenitic)
- Keep a consistent depth of cut and do not dwell.
- Notch wear at the DOC line
- Vary the depth of cut and use a tougher edge.
- Poor finish from rubbing
- A keen positive edge shears instead of rubbing; keep the edge sharp.
Reference data
Frequently asked questions
What insert for ferritic stainless like 430?
A PVD-coated M-class carbide with a sharp positive edge. Match the ISO M class across brands and confirm in the advisor.
Is ferritic stainless easier to machine than 316?
Yes, it work-hardens less than austenitic 304/316, so it tolerates a higher speed; it is still gummy, so keep a keen edge.
What cutting speed for ferritic stainless?
Roughly Vc 120–200 m/min, fn 0.10–0.30 mm/rev. Confirm on a sample part.
Why do I get built-up edge on ferritic stainless?
Cutting too slow or with a dull edge. Raise the speed, use a sharp positive polished edge, and aim coolant at the edge.
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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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