Inconel 718 (UNS N07718, also branded Alloy 718) is a precipitation-hardening nickel-chromium-niobium superalloy; ASTM A1014 bolting has a minimum tensile strength of 185 ksi [1275 MPa] at room temperature and 145 ksi [1000 MPa] at 1200 °F [650 °C]. For bolting components, the controlling specification is ASTM A1014 / A1014M; aerospace bar stock procurement is governed by SAE AMS 5662 (solution-treated) and AMS 5663 (precipitation-hardened). This page consolidates the chemistry, mechanical, and physical properties of Inconel 718 as a single engineering reference for procurement, design, and quality teams.
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The chemistry of UNS N07718 is closely controlled to enable the precipitation of γ″ (gamma double-prime, Ni₃Nb) and γ′ (gamma prime, Ni₃(Al,Ti)) strengthening phases during age hardening. Niobium content is the discriminating element vs Inconel 625 and other nickel superalloys.
| Element | Composition (mass %) | Role |
|---|
| Nickel (Ni) | 50.0 – 55.0 | Austenite stabilizer, matrix |
| Chromium (Cr) | 17.0 – 21.0 | Corrosion + oxidation resistance |
| Molybdenum (Mo) | 2.80 – 3.30 | Solid-solution strengthening |
| Niobium plus Tantalum (Nb+Ta) | 4.75 – 5.50 | γ″ (Ni₃Nb) precipitation |
| Titanium (Ti) | 0.65 – 1.15 | γ′ precipitation |
| Aluminum (Al) | 0.20 – 0.80 | γ′ precipitation |
| Cobalt (Co), max | 1.0 | Solid-solution element |
| Carbon (C), max | 0.08 | Carbide control |
| Manganese (Mn), max | 0.35 | - |
| Silicon (Si), max | 0.35 | - |
| Phosphorus (P), max | 0.015 | - |
| Sulfur (S), max | 0.015 | - |
| Boron (B), max | 0.006 | Grain-boundary control |
| Copper (Cu), max | 0.30 | - |
| Iron (Fe) | Remainder | Cost-effective bulk |
Source: ASTM A1014 / A1014M-16ε1 Table 1. Iron is determined arithmetically by difference. If a product (check) analysis is performed, conformance is to ASTM B880 limits.
The minimums below are ASTM A1014 Table 2 values for Inconel 718 bolting; all tests are made after aging (7.1).
| Property | Minimum |
|---|
| Tensile strength | 185 ksi (1275 MPa) |
| 0.2% offset yield strength | 150 ksi (1035 MPa) |
| Elongation in 2 in. or 50 mm (or 4D) | 12 % |
| Reduction of area | 15 % |
| Brinell hardness | 331 – 444 HBW (≈ 36 – 47 HRC) |
| Property | Minimum |
|---|
| Temperature | 1200 °F (650 °C) |
| Stress | 100 ksi (690 MPa) |
| Time to rupture | 23 hours |
| Elongation at rupture | 5 % |
| Property | Minimum |
|---|
| Tensile strength | 145 ksi (1000 MPa) |
| 0.2% offset yield strength | 125 ksi (860 MPa) |
| Elongation | 12 % |
| Reduction of area | 15 % |
The physical properties below are not specified by ASTM A1014. Values are drawn from the Special Metals INCONEL alloy 718 technical bulletin and Inco Alloys Engineering Properties (commonly cited in the engineering literature).
| Property | Value |
|---|
| Density at room temperature | 8.19 g/cm³ (0.296 lb/in³) |
| Melting range | 1260 – 1336 °C (2300 – 2437 °F) |
| Coefficient of thermal expansion (20-100 °C) | 13.0 × 10⁻⁶ /°C (7.2 × 10⁻⁶ /°F) |
| Coefficient of thermal expansion (20-650 °C) | 14.4 × 10⁻⁶ /°C (8.0 × 10⁻⁶ /°F) |
| Thermal conductivity at 25 °C | 11.4 W/m·K |
| Specific heat at 25 °C | 435 J/kg·K |
| Modulus of elasticity at 25 °C | 200 GPa (29 × 10⁶ psi) |
| Electrical resistivity at 25 °C | 1.25 μΩ·m |
| Curie temperature | Below -112 °C (-170 °F), non-magnetic at all service temps |
ASTM A1014 5.2 fixes the cycle below; temperatures and cooling rates are controlled within the tolerances shown (5.2.1.1, 5.2.2.1).
- Temperature: 1725 – 1850 °F (940 – 1010 °C), ± 25 °F (± 14 °C)
- Hold time: commensurate with cross-sectional thickness
- Cooling rate: air cool or faster
- First age: heat to 1325 °F (720 °C), hold 8 hours minimum, ± 15 °F (± 8 °C)
- Furnace cool: to 1150 °F (620 °C) at 100 °F (55 °C) per hour
- Second age: hold at 1150 °F for 8 hours
- Final cool: to room temperature. Alternatively, furnace cool to 1150 °F at any rate, with the time at 1150 °F adjusted so the total precipitation treatment is 18 hours minimum (5.2.2)
Straightening of bolting components is permitted only AFTER solution treatment and BEFORE aging. Straightening after aging is prohibited (5.3).
Why engineers specify Inconel 718 for high temperature bolting:
- Strength + temperature: ASTM A1014 Table 2 minimum tensile strength is 185 ksi [1275 MPa] at room temperature and 145 ksi [1000 MPa] at 1200 °F [650 °C], with a 23 hour minimum stress rupture life at 1200 °F and 100 ksi [690 MPa].
- Corrosion + oxidation: 17.0 to 21.0 % chromium (Table 1); Special Metals describes the alloy as a high-strength, corrosion-resistant nickel chromium material.
- Weldability: Special Metals describes its welding characteristics, especially its resistance to postweld cracking, as outstanding.
- Cryogenic to high temperature: Special Metals lists a range of use of -423 °F to 1300 °F, with applications in liquid-fueled rockets, aircraft and land-based gas turbine engines, cryogenic tankage, fasteners and instrumentation parts.
| Standard | Scope |
|---|
| ASTM A1014 / A1014M | Precipitation-hardening bolting in UNS N07718 (this site's master spec) |
| ASTM B637 | Bar / forging stock for UNS N07718 (raw material for A1014 bolts) |
| SAE AMS 5662 | Aerospace UNS N07718 bar / forging, solution heat treated |
| SAE AMS 5663 | Aerospace UNS N07718 bar / forging, solution + precipitation hardened (final bolt heat-treat condition) |
| SAE AMS 5664 | Aerospace UNS N07718 bar / forging, solution + precipitation hardened, higher strength |
| SAE AS 7467 | Aerospace procurement spec for UNS N07718 bolts / screws, 185 ksi tensile, stress-rupture rated |
| ASME PVP Code Case 1993-7 | ASME pressure-vessel code case authorizing UNS N07718 bolting |
| MIL-DTL / NAS / MS specs | MS14181, AS3418, NAS1351 family, proprietary aerospace Inconel 718 bolt part numbers |
ASTM A1014 sets the material, heat treatment and tests; thread stress areas follow ASME B1.1 (7.3). TorqBolt makes Inconel 718 bolting to the dimensional standards below:
- Imperial hex: Hex Bolts (B18.2.1), Heavy Hex Bolts, Hex Cap Screws, Heavy Hex Cap Screws, Heavy Hex Screws, Hex Lag Screws / Lag Bolts
- Imperial socket: Socket Head Cap Screws (B18.3), Shoulder Bolts, Countersunk Cap Screws, Spline Socket Cap Screws
- Metric: Metric Hex Cap Screws (B18.2.3.1M), Metric Heavy Hex Screws, Metric Hex Bolts, Metric Socket Head Cap Screws (B18.3.1M), Metric Machine Screws
- Studs + Nuts: B16.5 Flange Studs, Double-End Studs, Metric Clamping Studs, Metric Hex Nuts, Metric Heavy Hex Nuts
What are the chemical composition limits of Inconel 718 (UNS N07718)?
ASTM A1014 Table 1: nickel plus cobalt 50.0 to 55.0 %, chromium 17.0 to 21.0 %, molybdenum 2.80 to 3.30 %, columbium (niobium) plus tantalum 4.75 to 5.50 %, titanium 0.65 to 1.15 %, aluminum 0.20 to 0.80 %, boron 0.006 % max, carbon 0.08 % max, manganese 0.35 % max, silicon 0.35 % max, phosphorus 0.015 % max, sulfur 0.015 % max, cobalt 1.0 % max, copper 0.30 % max, iron remainder.
What is the density and melting range of Inconel 718?
Typical values from the Special Metals INCONEL alloy 718 bulletin (not specification limits): density 0.296 lb/in³ (8.19 g/cm³) annealed, melting range 2300 to 2437 °F (1260 to 1336 °C), specific heat 0.104 Btu/lb·°F (435 J/kg·°C). ASTM A1014 does not specify physical properties.
What is the hardness of Inconel 718 bolting per ASTM A1014?
331 to 444 HBW after aging (Table 2). The other room temperature minimums are tensile strength 185 ksi [1275 MPa], 0.2 % offset yield strength 150 ksi [1035 MPa], elongation 12 % and reduction of area 15 %.
What is the maximum service temperature for Inconel 718 bolting?
ASTM A1014 sets no maximum service temperature. It tests at 1200 °F [650 °C]: minimum tensile 145 ksi [1000 MPa], yield 125 ksi [860 MPa], and a stress rupture life of 23 hours minimum at 100 ksi [690 MPa]. Special Metals gives the alloy's range of use as -423 °F to 1300 °F.
