ISO P — Steel · P20
P20 — Alloy steel (heat treated)
Hardness range: 200–300 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 — P20
- ISO designation
- P20 (ISO P — Steels)
- Material
- Alloy steel (heat treated)
- Hardness
- 200–300 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 42CrMo4 / 4140 (heat-treated) — starting point
- ISO application class
- P (steel). Match the insert's ISO class, not the brand name. Sandvik, Kennametal, Iscar, Walter, Seco and Mitsubishi each publish a P-class grade — pick by ISO class, then confirm the exact grade for your condition.
- Grade & coating
- CVD-coated carbide for crater resistance. Heat-treated alloy steels like 42CrMo4 / 4140 (≈ 28–34 HRC) reward a hard CVD top layer: roughing around P25–P35, finishing around P10–P20.
- Geometry
- Negative geometry is fine and economical for roughing steel; switch to positive for finishing, thin walls and low-rigidity setups. A honed or chamfered edge adds security in interrupted cuts.
- Starting parameters (carbide)
- Carbide Vc ≈ 150–250 m/min, fn ≈ 0.10–0.40 mm/rev; lower the band as hardness climbs. Typical starting band — confirm in the advisor or on a sample part.
Selection table: heat-treated alloy steel (42CrMo4 / 4140)
| Operation | Geometry | ISO class | Coating family | Coolant | First check |
|---|---|---|---|---|---|
| Roughing | Negative geometry, economical for roughing | P25–P35 | CVD-coated carbide with a hard top layer for crater resistance | Check coolant delivery | Crater wear on the rake face: ease Vc |
| Finishing | Positive geometry for finishing | P10–P20 | CVD-coated carbide | Check coolant delivery | Plastic deformation: edge too hot, drop Vc and feed |
| Interrupted cut | Honed or chamfered edge for security | P25–P35 | CVD-coated carbide | Check coolant delivery | Edge security in interruptions; lower the band as hardness climbs |
| Low rigidity / thin wall | Positive geometry for thin walls and low-rigidity setups | P10–P20 | CVD-coated carbide | Check coolant delivery | Built-up edge at low speed: raise Vc |
42CrMo4 / 4140 (heat-treated): what goes wrong, and what to check first
- Crater wear on the rake face
- Heat at higher speeds wears a crater behind the edge. Use a CVD grade, ease Vc, and check coolant delivery. See the tool-wear guide.
- Plastic deformation (edge rounds or depresses)
- The edge is too hot for the grade — too much Vc or feed. Drop Vc and feed, or move to a harder, more deformation-resistant grade.
- Flank wear
- Normal abrasion that sets tool life. Balance Vc and pick a harder grade for longer runs.
- Built-up edge at low speed
- Raise Vc into the band, use a sharper edge, and add coolant.
Reference data
Frequently asked questions
What insert grade should I use for 42CrMo4 / 4140 heat-treated?
Use a CVD-coated carbide in the ISO P class, around P15–P25, with a hard top layer for crater resistance. Match the ISO P class across brands rather than the brand name and confirm the exact grade in the advisor.
What cutting speed for heat-treated alloy steel with carbide?
Roughly Vc 150–250 m/min and fn 0.10–0.40 mm/rev, lowering the band as hardness rises. Treat this as a starting band and confirm on a sample part.
My edge is rounding or depressing on hardened steel — why?
That is plastic deformation: the edge is running too hot for the grade. Reduce cutting speed and feed, or move to a harder, more deformation-resistant grade.
Negative or positive insert for turning 42CrMo4?
Negative geometry is fine and more economical for roughing steel; switch to a positive geometry for finishing, thin walls, or low-rigidity setups.
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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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