Inconel 718 (UNS N07718)
The premier high-strength nickel superalloy — 185 ksi tensile and 150 ksi yield from cryogenic temperatures to 1200 °F, with corrosion and sour-gas resistance to match.
What Inconel 718 is.
Inconel 718 is a nickel-chromium alloy strengthened by niobium, with molybdenum, titanium and aluminum additions. A solution treatment followed by a two-step age precipitates gamma-double-prime particles that give it 185 ksi tensile and 150 ksi yield, and because the age is sluggish the alloy can be welded and machined before hardening. It holds its strength to 1200 °F and its toughness to −423 °F.
ASTM B637 governs 718 bar and forgings, with a stress-rupture requirement at 1200 °F. We machine 718 studs, bolts, nuts and components from certified B637 or AMS bar and have them aged to the specification, with the cycle on the certificate.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Nickel | Ni | 50.0 | 55.0 |
| Chromium | Cr | 17.0 | 21.0 |
| Niobium + tantalum | Nb+Ta | 4.75 | 5.50 |
| Molybdenum | Mo | 2.80 | 3.30 |
| Titanium | Ti | 0.65 | 1.15 |
| Aluminum | Al | 0.20 | 0.80 |
| Cobalt | Co | — | 1.0 |
| Carbon | C | — | 0.08 |
| Manganese | Mn | — | 0.35 |
| Silicon | Si | — | 0.35 |
| Phosphorus | P | — | 0.015 |
| Sulfur | S | — | 0.015 |
| Boron | B | — | 0.006 |
| Copper | Cu | — | 0.30 |
| Iron | Fe | balance | — |
Values per ASTM B637-16 Table 1 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Mechanical properties.
| Condition | Tensile strength, min (ksi) | Yield strength 0.2%, min (ksi) | Elongation, min (%) | Reduction of area, min (%) | Hardness, min |
|---|---|---|---|---|---|
| Solution + precipitation hardened | 185 | 150 | 12 | 15 | 331 HBW |
Values per ASTM B637-16 Table 3 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team. The reduced 6 % elongation and 8 % reduction of area apply only to specimens taken tangentially near the centre of disk forgings over 50 in.² in section, or radially from rings 3 in. or more thick (Table 3 footnote E).
| Test temperature | Stress (ksi) | Time to rupture, min (h) | Elongation, min (%) |
|---|---|---|---|
| 1200 °F (649 °C) | 100 | 23 | 5 |
Values per ASTM B637-16 Table 4 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
| Step | Cycle |
|---|---|
| Solution treatment | 1700–1850 °F (924–1010 °C), hold ½ h minimum, cool at a rate equivalent to air cool or faster |
| Precipitation hardening | 1325 ± 25 °F (718 °C), hold 8 h, furnace cool to 1150 ± 25 °F (621 °C), hold until total time reaches 18 h, air cool |
Values per ASTM B637-16 Table 2 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Specifications that apply.
How Inconel 718 ships from Houston.
- Studs, hex and 12-point bolts, cap screws
- Hex and heavy hex nuts in the same alloy
- Wellhead, tree and subsea components machined to print
- Turbine and exhaust hardware
- Certified B637 / AMS bar, solution treated or aged
Inconel 718 fasteners we make.
Every item is manufactured to your drawing or standard in Inconel 718, imperial or metric, with an EN 10204 3.1 certificate.
What is Inconel 718?
Alloy 718 is a nickel-base superalloy in which niobium, rather than the aluminum and titanium of most superalloys, forms the main strengthening precipitate. That makes its response to ageing slow and controllable, so components can be welded and machined in the soft solution-treated state and then hardened without cracking. The finished material has 185 ksi tensile and 150 ksi yield, retains most of that to 1200 °F, resists oxidation, chlorides and hydrogen sulfide, and stays tough and non-magnetic at cryogenic temperatures.
718 in oil and gas
API 6A and NACE MR0175 recognise 718 for wellhead and downhole components in sour, high-pressure service, usually with a hardness cap of 40 HRC and the two-step age shown above. It is the material of choice for tree and manifold bolting where duplex is not strong enough or the temperature is too high, and for hanger and packer parts exposed to wet hydrogen sulfide.
Fastener manufacture
We rough machine and thread 718 in the solution-treated condition, then age harden, then finish inspect. Threads are rolled before or after ageing as the order requires; rolling after ageing keeps the compressive stress at the thread root. Anti-seize or silver-plated nuts are recommended because 718 galls readily.
Testing, certification and marking
- Tensile and hardness tested per lot on the finished product
- Grade or alloy marking 718 with heat number and manufacturer's identification on every piece
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
- Stress-rupture and hardness tested per heat-treat lot to B637
- API 6A and NACE compliance statements on request
Recent Inconel 718 jobs.
ASTM A453 Grade 660 (A-286)
A-286 bolting for the hottest joints — 130 ksi at room temperature and rated by stress-rupture at 1200 °F, for gas and steam turbines, exhaust and high-temperature process equipment.
ASTM F468 / F467 fasteners · ASTM B865 barMonel K-500 (UNS N05500)
Monel 400 corrosion resistance with more than twice the strength — 130 ksi tensile, 90 ksi yield and 24 to 37 HRC — for pump shafts, subsea fasteners and oil-tool components.
ASTM A1082 bolting · ASTM A276 / A479 bar · ASTM A182 F53Super Duplex 2507 Stainless (UNS S32750)
25 Cr super duplex with a PREN above 40 — 116 ksi tensile and 80 ksi yield for the most aggressive seawater, sour and chloride bolting.