Inconel 718 – UNS N07718
Precipitation-hardenable nickel-chromium superalloy
Ni-Cr-Fe superalloy hardened by precipitation of γ″ (Ni₃Nb). It reaches a yield strength above 1,000 MPa and keeps its strength up to ~650 °C. The slow precipitation allows welding without strain-age cracking. It is the most used high-strength alloy in aircraft turbines and in wellhead equipment (API Std 6ACRA, which replaced the former 6A718).
Designations and equivalents
| System | Designation |
|---|---|
| UNS | N07718 |
| W.Nr./EN | 2.4668 – NiCr19Fe19Nb5Mo3 |
| DIN | NiCr19NbMo |
| JIS | NCF 718 |
| Trade names | Inconel 718 (Special Metals), Haynes 718, ATI 718, Alloy 718 |
| Others | AMS 5662 / 5663 / 5664 (bar and forging), AMS 5596 (sheet), API 6ACRA |
Standards by product form
| Form | Standard |
|---|---|
| Bar | ASTM B637; AMS 5662 / 5663 |
| Forging | ASTM B637; AMS 5663; API 6ACRA (oil and gas) |
| Plate | ASTM B670; AMS 5596 / 5597 |
| Tube | AMS 5589 / 5590 |
Tolerances and HS codes
- Forged bars (round and square): machining allowance from 2 mm (Ø 6–16 mm) to 24 mm (Ø 400–500 mm) on the diameter. E.g. Ø 100–125 mm finished: +7 mm, tolerance +6 / −0 (length up to 3,500 mm).
- Forged discs: allowance of 4 to 9 mm on the diameter and 3 to 11 mm on the height, plus-only tolerance.
- Cutting and machining: band saw −0 / +5 to +15 mm on length; waterjet +10 % of thickness on the diameter (min. 2 mm); machined parts −0 / +2 to +5 mm on the diameter. See the full tables (INF 002 and INF 003, the same for every alloy).
| Form | NCM (Brazil, 8 digits) | HS (international, 6 digits) | HTS (USA, 10 digits)* | CN (European Union, 8 digits)* |
|---|---|---|---|---|
| Forged bar | 7505.12.10 | 7505.12 | 7505.12.3000 | 7505 12 00 |
| Hot-rolled bar | 7505.12.10 | 7505.12 | 7505.12.3000 | 7505 12 00 |
| Plate (> 10 mm, width ≥ 600 mm) | 7506.20.00 | 7506.20 | 7506.20.3000 | 7506 20 00 |
| Seamless pipe | 7507.12.00 | 7507.12 | 7507.12.0000 | 7507 12 00 |
| Welded pipe | 7507.12.00 | 7507.12 | 7507.12.0000 | 7507 12 00 |
| Flange and fitting | 7507.20.00 | 7507.20 | 7507.20.0000 | 7507 20 00 |
Tariff class: nickel alloy (by chemical composition, under the Chapter 72 Notes and Section XV Note 5).
*: US and EU codes for reference. NCM per current legislation (General Rules of Interpretation, Notes to Chapters 72, 74 and 75 and Section XV Note 5). Confirm the final code with your customs broker according to the item size and finish. HS = first 6 digits of the NCM.
Chemical composition (%)
ASTM B637 / AMS 5662 (UNS N07718)
| Element | Range (%) |
|---|---|
| Ni (+Co) | 50.0 – 55.0 |
| Cr | 17.0 – 21.0 |
| Fe | balance (≈ 18) |
| Nb + Ta | 4.75 – 5.50 |
| Mo | 2.80 – 3.30 |
| Ti | 0.65 – 1.15 |
| Al | 0.20 – 0.80 |
| Co | ≤ 1.00 |
| C | ≤ 0.08 |
| Mn | ≤ 0.35 |
| Si | ≤ 0.35 |
| Cu | ≤ 0.30 |
| B | ≤ 0.006 |
| P / S | ≤ 0.015 / ≤ 0.015 |
Mechanical properties
solution treated + aged (AMS 5663 / ASTM B637)
| Property | Value |
|---|---|
| Yield strength (0.2%) | ≥ 1,034 MPa |
| Tensile strength | ≥ 1,276 MPa |
| Elongation | ≥ 12% |
| Reduction of area | ≥ 15% |
| Hardness | ≥ 331 HB |
| API 6ACRA (oil and gas) | YS 827 – 1,000 MPa; UTS ≥ 1,034 MPa; El. ≥ 20%; RA ≥ 35%; 32 – 40 HRC; Charpy ≥ 47 J at −60 °C |
Typical physical properties
| Property | Value |
|---|---|
| Density | 8.19 g/cm³ |
| Melting range | 1,260 – 1,336 °C |
| Modulus of elasticity | 200 GPa |
| Thermal conductivity (20 °C) | 11.4 W/m·K |
| Thermal expansion (20–100 °C) | 13.0 µm/m·K |
| Electrical resistivity | 125 µΩ·cm |
Heat treatment, welding and machining
| Item | Usual practice |
|---|---|
| Service temperature | From cryogenic (−253 °C) up to ~650 °C with structural strength; above that the γ″ phase coarsens and strength drops. Oxidation acceptable up to ~980 °C. |
| Heat treatment | AMS 5663: solution treat at 940 – 1,010 °C (typically 980 °C) and cool rapidly; age at 720 °C for 8 h, furnace cool at ~55 °C/h to 620 °C and hold until 18 h total, air cooling. API 6ACRA: solution treat at 1,021 – 1,052 °C and age at 774 – 802 °C for 6 – 8 h. |
| Welding | Good weldability for a hardenable alloy (low tendency to strain-age cracking). Consumable AWS A5.14 ERNiFeCr-2. Weld in the solution-treated condition and age afterwards. |
| Machining | Very difficult, especially aged: rough machine in the solution-treated condition; use carbide or ceramic, low speed and a rigid tool. |
Filler metal for welding
The wire composition is usually not identical to the material: each page explains why.
Typical applications
- Discs, shafts and casings of aircraft gas turbines
- Wellhead and completion equipment (API 6A, NACE MR0175)
- Hangers, mandrels and downhole valves
- High-strength fasteners and springs
- Rocket engines and cryogenic components
- Hot-work tooling
Alternatives: Inconel 625 when corrosion and weldability weigh more than strength; 725 in oil and gas with more severe H₂S; Waspaloy or 718Plus above 650 °C; Monel K500 for seawater with lower strength and cost.
Inconel 718: complete guide
What Inconel 718 is
Inconel 718 belongs to the family of nickel alloys, in the group of precipitation-hardenable superalloys. It is not "a special steel alloy": nickel is more than half of the composition and iron, about 18%, is just one of the alloying elements. Strength comes from two precipitates formed during aging, gamma double prime (Ni3Nb), produced by niobium, and gamma prime (Ni3(Al,Ti)); the slow kinetics of the former is what makes 718 the easiest superalloy to weld and fabricate.
Chemical composition
The ASTM B637 limits are: nickel from 50 to 55%, chromium from 17 to 21%, niobium plus tantalum from 4.75 to 5.50%, molybdenum from 2.80 to 3.30%, titanium from 0.65 to 1.15%, aluminum from 0.20 to 0.80%, carbon up to 0.08% and iron as the balance.
Mechanical properties by specification
Solution treated and aged per AMS 5663, the alloy has a minimum yield strength of 1,034 MPa, minimum tensile strength of 1,276 MPa, minimum elongation of 12% and minimum hardness of 331 HBW. In the wellhead equipment version, API 6ACRA, the yield strength is between 827 and 1,000 MPa, the minimum tensile strength is 1,034 MPa, the minimum elongation 20% and the maximum hardness 40 HRC, to meet NACE MR0175.
Corrosion, temperature and applications
718 resists seawater, chlorides, H2S and CO2, organic acids and moderately oxidizing media, similarly to Inconel 625, and keeps its mechanical strength from −253 °C up to about 650 °C. It is used in discs, shafts, casings and fasteners of aircraft and gas turbines, in christmas trees, valves and connectors of oil wells, in high-strength bolts and studs and in cryogenic components. For fasteners up to 700 °C at lower cost, A-286 is the alternative.
Supply forms and Dustre services
Round bars and blocks forged in open die, cut to size on a band saw, with rough or finish machining, solution annealing or annealing in our own furnaces and hardness, tensile and impact testing. All material is supplied with a 3.1 inspection certificate and heat traceability.
Frequently asked questions
What is the chemical composition of Inconel 718?
Per ASTM B637 / AMS 5662 (UNS N07718): Ni (+Co) 50.0 – 55.0; Cr 17.0 – 21.0; Fe balance (≈ 18); Nb + Ta 4.75 – 5.50; Mo 2.80 – 3.30; Ti 0.65 – 1.15.
Which standards cover Inconel 718?
Bar: ASTM B637; AMS 5662 / 5663. Forging: ASTM B637; AMS 5663; API 6ACRA (oil and gas). Plate: ASTM B670; AMS 5596 / 5597. Tube: AMS 5589 / 5590.
Up to what temperature can Inconel 718 be used?
From cryogenic (−253 °C) up to ~650 °C with structural strength; above that the γ″ phase coarsens and strength drops. Oxidation acceptable up to ~980 °C.
Which materials can replace Inconel 718?
Inconel 625 when corrosion and weldability weigh more than strength; 725 in oil and gas with more severe H₂S; Waspaloy or 718Plus above 650 °C; Monel K500 for seawater with lower strength and cost.
