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