ISO P — Steel · P50
P50 — High-strength steel
Hardness range: 280–350 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 — P50
- ISO designation
- P50 (ISO P — Steels)
- Material
- High-strength steel
- Hardness
- 280–350 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 high-strength steel — starting point
- ISO application class
- P (steel), high-strength. Higher strength means higher cutting forces and heat, so run a tougher grade and a lower speed, with a rigid setup. 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
- Tough CVD-coated carbide, P25–P35, with a secure edge.
- Geometry
- Negative geometry with a honed edge for roughing security; rigid clamping and short overhang.
- Starting parameters
- Vc ≈ 120–220 m/min (lower than mild steel), fn ≈ 0.10–0.35 mm/rev. Confirm in the advisor or on a sample part.
Selection table: high-strength steel
| Operation | Geometry | ISO class | Coating family | Coolant | First check |
|---|---|---|---|---|---|
| Roughing | Negative geometry with a honed edge; rigid clamping, short overhang | P25–P35 | Tough CVD-coated carbide | Per process | Cutting forces and deflection: shorten overhang |
| Finishing | Negative with honed edge, secure edge | P25–P35 | Tough CVD-coated carbide | Per process | Plastic deformation: drop Vc and feed or use a harder grade |
| Interrupted cut | Negative with a honed edge for security | P25–P35 | Tough CVD-coated carbide | Per process | Crater and flank wear from heat: ease the speed |
| Low rigidity / thin wall | Short overhang, rigid clamping, robust edge | P25–P35 | Tough CVD-coated carbide | Per process | Chatter: rigidity first, then a robust edge |
high-strength steel: what goes wrong, and what to check first
- High cutting forces and deflection
- High-strength steel pushes back; shorten overhang, clamp rigidly, use a robust edge.
- Crater and flank wear from heat
- Use a CVD grade and ease the speed.
- Plastic deformation
- If the edge rounds or depresses it is too hot; drop Vc and feed or use a harder, more deformation-resistant grade.
- Chatter
- Rigidity first; then a robust edge.
Reference data
Frequently asked questions
What insert for high-strength steel?
A tough CVD-coated carbide, P25–P35, with a secure edge. Match the ISO P class across brands and confirm in the advisor.
Why a lower cutting speed than mild steel?
Higher strength generates more force and heat, so the speed must come down to control wear and deformation.
What cutting speed for high-strength steel?
Roughly Vc 120–220 m/min, fn 0.10–0.35 mm/rev. Confirm on a sample part.
My edge is rounding on high-strength steel — why?
Plastic deformation from heat; reduce speed and feed, or move to a harder, more deformation-resistant grade.
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