ISO P — Steel · P40
P40 — Free-cutting steel
Hardness range: 160–230 HB. Part of the ISO P — Steels group. Steel is the most widely machined material. Carbon and alloy steels are the target material for the majority of turning and milling operations. Hardness ranges from ~125 HB (low-carbon) to 350 HB (high-strength structural). CVD-coated carbide (TiCN/Al₂O₃ multilayer) dominates. Positive geometry for finishing, negative for heavy roughing.
Material profile — P40
- ISO designation
- P40 (ISO P — Steels)
- Material
- Free-cutting steel
- Hardness
- 160–230 HB
- ISO group colour
- Steel
Tooling guidance — P-group
- Group summary
- CVD-coated carbide at Vc 200–400 m/min. Positive geometry for finishing, negative for roughing.
Insert selection for free-cutting steel (12L14, 1215) — starting point
- ISO application class
- P (steel). Free-cutting steels (resulfurized or leaded) contain inclusions that break chips and lubricate the edge, so they run fast and clean. Match the ISO P 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
- Coated carbide, P10–P25. Chip control is easy thanks to the manganese-sulfide inclusions.
- Geometry
- Positive sharp edge; chip control is rarely a problem on free-cutting grades.
- Starting parameters
- High speeds, Vc ≈ 200–350 m/min, fn ≈ 0.10–0.40 mm/rev. Confirm in the advisor or on a sample part.
Selection table: free-cutting steel (12L14, 1215)
| Operation | Geometry | ISO class | Coating family | Coolant | First check |
|---|---|---|---|---|---|
| Roughing | Positive sharp edge; chip control is rarely a problem | P10–P25 | Coated carbide | Per process | Speed in band: built-up edge is the one common issue |
| Finishing | Positive sharp edge | P10–P25 | Coated carbide | Per process | Finish drop with a dull edge: replace a worn edge |
| Interrupted cut | Positive edge with a light hone | P10–P25 (tougher end) | Coated carbide | Per process | Lead-free substitutes machine differently: re-tune speeds |
| Low rigidity / thin wall | Positive sharp edge | P10–P25 | Coated carbide | Per process | Mostly low speed or a dull edge |
free-cutting steel (12L14, 1215): what goes wrong, and what to check first
- Built-up edge at low speed
- The one common issue; raise the speed into the band.
- Finish drop with a dull edge
- Free-cutting steel finishes easily; replace a worn edge to keep it.
- Lead-free substitutes machine differently
- Bismuth or high-sulfur replacements for leaded steel behave a little differently; re-tune speeds.
- Otherwise minimal
- These grades are designed to machine; most problems are low speed or a dull edge.
Reference data
Frequently asked questions
What insert for free-cutting steel like 12L14?
A coated carbide, P10–P25; chip control is easy. Match the ISO P class across brands and confirm in the advisor.
Why is free-cutting steel so easy to machine?
Manganese-sulfide (and sometimes lead or bismuth) inclusions break chips and lubricate the edge, allowing high speeds and clean finishes.
What cutting speed for free-cutting steel?
High, roughly Vc 200–350 m/min, fn 0.10–0.40 mm/rev. Confirm on a sample part.
Do lead-free free-cutting steels machine the same?
Close, but bismuth or high-sulfur substitutes behave a little differently; re-tune speeds and watch chip formation.
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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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