ISO S — Superalloys & Titanium · S20
S20 — Nickel superalloys (Inconel 718)
Hardness range: 280–380 HB. Part of the ISO S — Superalloys & Titanium group. Superalloys and titanium are the most challenging ISO group: low thermal conductivity concentrates heat at the cutting edge, and high strength persists at elevated temperatures. High-pressure coolant (70–100 bar) is mandatory. Low Vc, consistent DOC, and sharp geometry are non-negotiable. Tool life is short — plan changeovers.
Material profile — S20
- ISO designation
- S20 (ISO S — Superalloys & Titanium)
- Material
- Nickel superalloys (Inconel 718)
- Hardness
- 280–380 HB
- ISO group colour
- Superalloys & Titanium
Tooling guidance — S-group
- Group summary
- Most difficult ISO group. High-pressure coolant mandatory. Low Vc, consistent DOC, sharp positive geometry.
Insert selection for Inconel 718 — starting point
- ISO application class
- S (superalloys). Match the insert's ISO class, not the brand name. Sandvik, Kennametal, Iscar, Walter, Seco and Mitsubishi each publish S-class carbide and ceramic grades for nickel alloys — pick by ISO class, then confirm the exact grade for your condition.
- Grade & coating
- Tough fine-grain PVD carbide for general work; whisker-reinforced or SiAlON ceramic for high-speed roughing of aged 718, which runs in a separate, much higher speed regime.
- Geometry
- Positive but strong, honed edge. A round or large-nose insert spreads heat and resists depth-of-cut notching; avoid fragile sharp corners.
- Starting parameters (carbide)
- Carbide Vc ≈ 20–45 m/min, fn ≈ 0.10–0.25 mm/rev, high-pressure coolant essential. Ceramic runs far higher in its own regime. Typical starting band — confirm in the advisor or on a sample part.
Selection table: Inconel 718
| Operation | Geometry | ISO class | Coating family | Coolant | First check |
|---|---|---|---|---|---|
| Roughing | Positive but strong, honed edge; round or large-nose insert spreads heat | S (S-class grade) | Tough fine-grain PVD carbide; whisker-reinforced or SiAlON ceramic for high-speed roughing of aged 718 | High-pressure coolant essential | Depth-of-cut notch wear: vary DOC between passes |
| Finishing | Positive, honed edge; avoid fragile sharp corners | S (S-class grade) | Tough fine-grain PVD carbide | High-pressure coolant essential | Rapid cratering and heat: coolant to the edge, hold Vc in band |
| Interrupted cut | Strong honed edge, round insert where possible | S (S-class grade) | Tough fine-grain PVD carbide | High-pressure coolant essential | Edge chipping or built-up edge: sharp honed positive edge |
| Low rigidity / thin wall | Positive but strong edge; keep the tool moving | S (S-class grade) | Tough fine-grain PVD carbide | High-pressure coolant essential | Work-hardened skin: keep DOC above the hardened layer |
Inconel 718: what goes wrong, and what to check first
- Depth-of-cut notch wear
- The classic 718 killer: abrasion and oxidation concentrate at the DOC line. Vary the depth of cut between passes, use a larger lead angle or a round insert to spread the load, and ease Vc. See the tool-wear guide.
- Rapid cratering and heat
- Low thermal conductivity dumps heat into the edge. Get high-pressure coolant to the edge, hold Vc in the carbide band, and never let the tool dwell.
- Work-hardened skin
- An inconsistent DOC or a dwelling tool leaves a hardened layer the next pass re-cuts. Keep DOC above the hardened layer and keep the tool moving.
- Edge chipping / built-up edge
- Too-low speed or welded material. Use a sharp honed positive edge, adequate Vc, and coolant at the edge.
Reference data
Frequently asked questions
What insert should I use for Inconel 718?
Use an ISO S-class tough fine-grain PVD carbide for general work, or whisker-reinforced / SiAlON ceramic for high-speed roughing of aged 718. Match the ISO S class across brands rather than the brand name, and confirm the exact grade in the advisor.
Why does Inconel 718 notch at the depth-of-cut line?
Abrasion and oxidation concentrate at the depth-of-cut line on nickel alloys. Vary the depth of cut between passes, use a larger lead angle or a round insert to spread the load, and ease the cutting speed.
What is a typical carbide cutting speed for Inconel 718?
Roughly Vc 20–45 m/min and fn 0.10–0.25 mm/rev with high-pressure coolant for carbide; ceramic runs far higher in a different regime. Treat this as a starting band and confirm on a sample part.
Why does my tool burn up so fast in 718?
Inconel 718's low thermal conductivity concentrates heat at the edge. Get high-pressure coolant to the edge, keep the speed in the carbide band, use a honed positive edge, and do not let the tool dwell.
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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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