UNS N07718, Chemistry, Designators, and Bolting Standards
UNS N07718 is the Unified Numbering System designator for the precipitation-hardening nickel-chromium-niobium superalloy commercially branded Inconel 718 by Special Metals and Alloy 718 by other producers. In Europe the equivalent designator is Werkstoff Nr. 2.4668. The same alloy is the subject of ASTM A1014 for bolting components, ASTM B637 for bar and forging stock, SAE AMS 5662 (solution heat treated) and AMS 5663 (solution + precipitation hardened) for aerospace procurement, and ASME PVP Code Case 1993-7 for pressure-vessel service.
UNS N07718 sits in the Unified Numbering System under the "N" prefix for nickel and nickel alloys; ASTM A1014 Table 1 lists it as formerly Grade 718. It is an age-hardenable nickel-chromium alloy that Special Metals lists for use from -423 °F to 1300 °F, in liquid-fueled rocket components, aircraft and land-based gas turbine engine parts, cryogenic tankage, fasteners and instrumentation parts. It strengthens by precipitation of gamma double-prime and gamma prime phases during aging. ASTM A1014 bolting must reach 185 ksi [1275 MPa] minimum tensile strength at room temperature and 145 ksi [1000 MPa] minimum at 1200 °F [650 °C] (Table 2).
| Element | Composition (mass %) |
|---|
| Nickel + Cobalt | 50.0 – 55.0 |
| Chromium | 17.0 – 21.0 |
| Molybdenum | 2.80 – 3.30 |
| Niobium + Tantalum | 4.75 – 5.50 |
| Titanium | 0.65 – 1.15 |
| Aluminum | 0.20 – 0.80 |
| Cobalt, max | 1.0 |
| Carbon, max | 0.08 |
| Iron | Remainder |
Columbium (niobium) plus tantalum, 4.75 to 5.50 %, is the largest aging addition in the Table 1 limits. Special Metals describes the alloy's welding characteristics, especially its resistance to postweld cracking, as outstanding.
| Property | Room Temperature | 1200 °F (650 °C) |
|---|
| Tensile strength, min | 185 ksi (1275 MPa) | 145 ksi (1000 MPa) |
| 0.2% yield strength, min | 150 ksi (1035 MPa) | 125 ksi (860 MPa) |
| Elongation, min | 12 % | 12 % |
| Reduction of area, min | 15 % | 15 % |
| Brinell hardness | 331 – 444 HBW | - |
| Stress rupture (100 ksi) | - | 23 hours minimum |
| Standard | Product Form / Scope |
|---|
| ASTM A1014 / A1014M | Bolting components: bolts, studs, screws (this site) |
| ASTM B637 | Bar, forgings, and forging stock for elevated-temperature service |
| SAE AMS 5662 | Aerospace bar & forging, solution heat treated |
| SAE AMS 5663 | Aerospace bar & forging, solution + age hardened (final bolt condition) |
| SAE AMS 5664 | Aerospace bar & forging, higher-strength solution + age hardened |
| SAE AMS 5596 | Sheet, strip, and plate, solution treated |
| SAE AMS 5597 | Sheet, strip, and plate, age hardened |
| SAE AS 7467 | Aerospace bolts / screws, 185 ksi tensile, stress-rupture rated |
| MS14181 / AS3418 / NAS1351 | Mil-Spec aerospace bolt part numbers in UNS N07718 |
| ASME PVP Code Case 1993-7 | Pressure-vessel code case authorizing UNS N07718 bolting |
For finished bolting in UNS N07718 / Inconel 718, browse the ASME B18 dimensional families covered on this site:
What is UNS N07718?
UNS N07718 is the Unified Numbering System designation of the age-hardenable nickel-chromium alloy sold as Inconel 718 (W.Nr. 2.4668). ASTM A1014 Table 1 limits include nickel plus cobalt 50.0 to 55.0 %, chromium 17.0 to 21.0 %, molybdenum 2.80 to 3.30 % and columbium (niobium) plus tantalum 4.75 to 5.50 %. ASTM A1014 covers it as bolting and ASTM B637 as bars, forgings and forging stock.
Is UNS N07718 the same as Inconel 718?
Yes. UNS N07718 is the generic designation; INCONEL is a Special Metals trade name, and the Special Metals alloy 718 bulletin lists it as UNS N07718 and W.Nr. 2.4668. ASTM A1014 Table 1 calls it UNS N07718 (formerly Grade 718), and A1014 bolting is marked "718".
What standards cover UNS N07718 bolting?
ASTM A1014/A1014M covers UNS N07718 bolting for high temperature service, with ASTM A962/A962M as the common bolting requirements. A1014 references ASTM B637 (bars, forgings and forging stock), ASTM B880 (check analysis), ASME B1.1 (screw threads) and SAE AS 7467 (bolts and screws, 185 ksi, stress rupture rated).
What is the maximum service temperature for UNS N07718?
ASTM A1014 does not state a maximum service temperature; its elevated temperature tensile and stress rupture tests are made at 1200 °F [650 °C]. Special Metals gives the alloy's range of use as -423 °F to 1300 °F.
