NI · superalloy
Nickel Superalloy Inconel 718 (UNS N07718)
The bottom of our scale and the reason the scale exists. Published index around 12% against B1112 = 100%. It keeps its strength at the cutting temperature, so the chip is abrasive and the edge has no relief.
Quoting this material
- Typical lead time
- 20–35 working days
- Condition
- Solution treated and aged, or annealed for machining where the part allows
- Achievable finish
- Ra 1.6 µm typical · Ra 0.4 µm best
Machined in-house to your drawing: see the precision CNC machining service and the machine and inspection capability it runs on.
Machinability
Our own 1–10 shop ranking, not a published index: 10 is free-cutting brass C360, 1 is Inconel 718. It ranks how a material behaves on the floor - cycle time, chip control and tool life together. Where a published index exists it is quoted in the note.
The bottom of our scale and the reason the scale exists. Published index around 12% against B1112 = 100%. It keeps its strength at the cutting temperature, so the chip is abrasive and the edge has no relief.
Properties as supplied
| Parameter | Value | Unit |
|---|---|---|
| Tensile strength (aged) | 1,240–1,300 | MPa |
| Yield strength (aged) | 1,035 | MPa |
| Elongation (aged) | 12 | % |
| Hardness (aged) | ~36 | HRC |
| Service temperature | To 700 | °C |
| Thermal conductivity | 11.4 | W/m·K |
Hardness, tensile and thermal figures are typical published values for the condition stated. Actual mill certificates govern; send the specification with the drawing and we confirm against the certificate before the material is cut.
Condition
Solution treated and aged, or annealed for machining where the part allows
Heat treatment
Solution treat around 980–1,020 °C, then age in two steps at roughly 720 °C and 620 °C. The aged condition is what gives it 1,300 MPa and strength retention to 700 °C - and it is also what makes the finishing passes a slow, expensive operation.
Achievable surface finish
Ra 1.6 µm
Ra 0.4 µm
Surface integrity is critical: a machining-induced white layer or a torn surface is a fatigue initiator in turbine hardware.
Tooling and cutting parameters
Cutting speed
- 20–40 m/min (carbide) · 150–250 m/min with ceramic for roughing
Feed
- 0.05–0.15 mm/rev turning · 0.04–0.10 mm/tooth milling
Tooling
- Fine-grain carbide with a tough substrate at low speeds; whisker-reinforced ceramic for roughing; no uncoated general-purpose grades
Coolant
- High-pressure through-tool, and generous. Heat at the edge is the whole problem
Starting points for carbide on a rigid setup, not a guarantee. The right numbers depend on the machine, the toolholder and the fixturing - ask and we will say what we would actually run.
Typical applications
- Turbine discs and engine components
- Rocket and launch vehicle hardware
- High-temperature fasteners
- Nuclear reactor components
- Oil and gas downhole tooling
DFM notes for this grade
- Never let the tool dwell or rub: Inconel 718 work-hardens in a single revolution, and the hardened layer is harder than the tool that has to cut under it
- Rigidity is a requirement, not a preference - a flexible setup produces chatter, a hardened surface and a scrapped part in that order
- Plan the heat treatment into the sequence: most 718 parts are roughed in the annealed or solution-treated state and finished after ageing, which is why the machining allowance matters
Questions buyers ask
- Why is Inconel 718 so much more expensive to machine than titanium?
- Heat and strength together. Titanium is difficult because it does not conduct heat away; 718 is difficult because it is still strong at the temperature the cutting edge reaches, and it work-hardens instantly. Both mean slow speeds and short tool life, but 718 combines them with an abrasive carbide structure.
- Should the part be machined annealed or aged?
- Rough annealed, finish aged - the same logic as any precipitation-hardening alloy, and here the difference is large. Most of the metal removal happens while the material is relatively soft, then the age brings the strength and the finishing passes are kept minimal.
Grades we would quote instead
Waspaloy
1/10A precipitation-hardened nickel alloy for turbine discs: harder than 718 at temperature and comparable to machine, which is to say slowly and with planned tool consumption.
Inconel 625
2/10Harder to machine than the 600-series grades and easier than 718.
Nimonic 80A
1/10A precipitation-hardened nickel-chromium alloy for exhaust valves and high-temperature springs.