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UNS NUMBER
N07718
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ALLOY FAMILY
Ni-Cr-Fe-Nb-Mo
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HARDENING
Precipitation
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UTS (AGED)
≥1240 MPa
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MAX TEMP
~650°C
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DENSITY
8.19 g/cm³
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Inconel 718 (UNS N07718) is a precipitation-hardenable nickel-chromium alloy with significant additions of iron, niobium (columbium), and molybdenum. The alloy's outstanding strength from cryogenic temperatures up to 650°C (1200°F) comes from the precipitation of γ″ (gamma double prime, Ni₃Nb) and γ′ (gamma prime) phases during heat treatment. Inconel 718 is the most widely used nickel superalloy for aerospace applications — turbine discs, compressor blades, and engine mounts — and is also used in oil & gas downhole tools where high strength at moderate temperatures is required.
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Ni
50-55%
Base element
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Cr
17-21%
Oxidation resistance
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★ Nb+Ta
5.0-5.5%
Forms γ″ (age hardening)
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Fe
16-20%
Balance element
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UTS (AGED)
≥1240 MPa
Age-hardened condition
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YS (0.2% AGED)
≥1030 MPa
Yield strength
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ELONGATION
≥12%
Aged condition, min
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SERVICE TEMP
-253 to 650°C
Cryogenic to high temp
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What is Inconel 718?
Inconel 718 is the most widely used precipitation-hardenable nickel superalloy. Its unique combination of high strength (UTS ≥1240 MPa), good ductility, and excellent weldability — even in the age-hardened condition — has made it the standard material for aerospace gas turbine and turbofan engines. The alloy achieves its strength through the precipitation of γ″ (Ni₃Nb, body-centered tetragonal) and γ′ (Ni₃(Al,Ti), face-centered cubic) phases during heat treatment at 718°C.
Beyond aerospace, Inconel 718 is also used in oil & gas downhole tools, fasteners for high-temperature service, and cryogenic applications (down to -253°C / 20K) where its toughness remains excellent. The alloy is covered by numerous aerospace material specifications (AMS 5662, AMS 5663, AMS 5664) and ASTM standards (B637 for bar/forging, B670 for plate).
Chemical Composition (Weight %)
| Element |
Min (%) |
Max (%) |
Role in Alloy |
| Nickel (Ni) |
50.0 |
55.0 |
Base element; high-temp strength |
| Chromium (Cr) |
17.0 |
21.0 |
Oxidation & corrosion resistance |
| Iron (Fe) |
16.0 |
20.0 |
Balance; cost reduction |
| Niobium + Tantalum (Nb+Ta) |
5.00 |
5.50 |
Forms γ″ precipitate (age hardening) |
| ★ Niobium (Nb) |
5.00 |
5.50 |
Key hardening element (γ″) |
| Molybdenum (Mo) |
2.80 |
3.30 |
Solid-solution strengthening |
| Titanium (Ti) |
0.65 |
1.15 |
Forms γ′ precipitate (co-precipitant) |
| Aluminum (Al) |
0.20 |
0.80 |
Forms γ′ precipitate |
| Carbon (C) |
— |
0.08 |
Kept low to avoid carbide precipitation |
| Manganese (Mn) |
— |
0.35 |
Impurity control |
| Silicon (Si) |
— |
0.35 |
Impurity control |
| Sulfur (S) |
— |
0.015 |
Kept very low for hot workability |
| Phosphorus (P) |
— |
0.015 |
Impurity; keep low |
| Cobalt (Co) |
— |
1.00 |
Optional; limited in some specs |
| Boron (B) |
— |
0.006 |
Grain boundary strengthener (some specs) |
★ Niobium (columbium) is the defining age-hardening element in Inconel 718, forming the γ″ (Ni₃Nb) precipitate that provides the alloy's exceptional strength. The Nb content is tightly controlled at 5.00-5.50%.
Mechanical Properties
Inconel 718 is typically supplied in the solution-annealed condition (AMS 5662) or the solution-annealed plus aged condition (AMS 5663/5664). The aging response is sensitive to the aging temperature and time.
| Condition |
UTS (MPa) |
YS 0.2% (MPa) |
Elong. (%) |
Reduction of Area (%) |
| Solution Annealed |
965-1100 |
517-690 |
≥30 |
≥40 |
| Aged (AMS 5663) |
≥1240 |
≥1030 |
≥12 |
≥15 |
| Aged (High-Strength) |
≥1310 |
≥1105 |
≥10 |
≥12 |
| Property |
Value |
| Young's Modulus (E, 21°C) |
200 GPa |
| Shear Modulus (G) |
77 GPa |
| Poisson's Ratio (ν) |
0.30 |
Physical Properties
| Property |
Value |
Note |
| Density |
8.19 g/cm³ |
Room temperature |
| Melting Range |
1260-1336°C |
Solidus-liquidus |
| Thermal Cond. (21°C) |
11.2 W/m·K |
Similar to Incoloy 925 |
| Elec. Resistivity (21°C) |
1.22 μΩ·m |
— |
| Specific Heat (21°C) |
435 J/kg·K |
— |
| Curie Temperature |
-193°C (80K) |
Ferromagnetic transition |
| Magnetic Permeability |
≤1.01 (annealed) |
Non-magnetic at room temperature |
Heat Treatment & Processing
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① Solution Anneal
Heat to 927-1041°C (typically 954°C), hold 1 hour per 25mm, water quench or air cool. This dissolves the γ″ and γ′ precipitates and establishes the soft condition for machining or forming.
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② Intermediate Anneal (Optional)
For heavy sections or complex shapes, a second solution anneal at 954°C may be performed after rough machining to relieve residual stresses before final aging. This prevents distortion during aging.
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③ Age Hardening
Age at 718°C (1325°F) for 8 hours, furnace cool at 56°C/h to 621°C (1150°F), hold at 621°C for total aging time of 18 hours (including the 718°C hold), then air cool. This is the standard AMS 5663/5664 cycle.
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Important — Aging Cycle Sensitivity: Inconel 718's strength is highly sensitive to the aging cycle. The standard "718°C → furnace cool to 621°C → air cool" cycle must be Strictly control. Over-aging (too long at temperature) coarsens the γ″ precipitates and reduces strength. Under-aging leaves the alloy too soft. Always follow the applicable AMS or ASTM specification for the exact cycle.
Corrosion Resistance
General Corrosion
Inconel 718 has good resistance to oxidation and general corrosion in air up to about 650°C (1200°F). Its chromium content (17-21%) provides a protective Cr₂O₃ scale. However, it is not as corrosion-resistant as Inconel 625 in aggressive chloride or acid environments — Inconel 718 is primarily a high-strength alloy, not a corrosion-resistant alloy.
Stress-Corrosion Cracking (SCC)
Inconel 718 has good resistance to chloride-induced stress-corrosion cracking at temperatures up to about 260°C (500°F). Above this temperature, SCC susceptibility increases. For sour-gas (H₂S) service, Inconel 718 is not typically specified — Incoloy 925 or Inconel 625 are preferred for NACE applications.
Post-Fabrication Heat Treatment
After welding, Inconel 718 should be solution-annealed and re-aged to restore the full strength in the heat-affected zone (HAZ). Welding in the aged condition without post-weld heat treatment leaves the HAZ in an over-aged, softer condition. Stress-relief without full solution anneal is not recommended for structural applications.
Inconel 718 vs. Similar Alloys
| Alloy |
UTS (MPa) |
Service Temp |
Corrosion Resist. |
When to Choose |
| Inconel 718 (this page) |
≥1240 (aged) |
to 650°C |
Good |
Aerospace, high strength to 650°C |
| Inconel 625 |
827-1030 (ann.) |
to 980°C |
Excellent |
Higher temp or corrosion is primary need |
| Incoloy 925 |
≥965 (aged) |
to 650°C |
Good (NACE) |
Sour service, oil & gas (lower cost) |
| Inconel X-750 |
≥1170 (aged) |
to 704°C |
Good |
Lower cost than 718, lower strength |
Industry Applications
| Industry |
Typical Applications |
| Aerospace (Gas Turbine) |
Turbine discs, compressor blades, turbine shafts, engine mounts, casings |
| Aerospace (Airframe) |
Landing gear components, fasteners, hydraulic tubing |
| Oil & Gas |
Downhole tools, instrumentation housings, high-strength fasteners |
| Cryogenic |
Liquid hydrogen & liquid nitrogen storage, rocket components (tough to -253°C) |
| Fasteners |
High-temperature bolts, studs, and nuts for turbine and reactor applications |
Applicable Standards
| Standard |
Product Form |
| AMS 5662 |
Bars, forgings, rings (solution annealed only) |
| AMS 5663 |
Bars, forgings, rings (solution annealed + aged) |
| AMS 5664 |
Bars, forgings (higher strength variant) |
| ASTM B637 |
Bar, forging stock, and forgings |
| ASTM B670 |
Plate, sheet, and strip |
HT PIPE Supply — Inconel 718 Products
| Product Form |
Dimensions |
Note |
| Seamless Pipe & Tube |
1/2" - 6" (OD) |
Solution annealed, AMS 5662 available |
| Butt-Welding Fittings |
1/2" - 6" (SCH 80/160/XXS) |
Elbows, tees, reducers, seamless construction |
| Forged Fittings & Flanges |
1/2" - 4" (3000 / 6000 LB) |
Couplings, unions, WNRF flanges |
| Bar & Forging Stock |
20-300mm (diameter) |
AMS 5662/5663 certification available |
HT PIPE Project Experience
HT PIPE has supplied Inconel 718 seamless pipes and forged fittings to aerospace and high-temperature industrial projects. Our supply includes material with AMS 5662 (solution annealed) and AMS 5663 (solution annealed + aged) certifications. All material is supplied with full MTR (Material Test Report) and third-party inspection (TPI) by SGS, BV, or DNV upon request.
Related project reference: Aerospace Gas Turbine Component Supply (2024) — Inconel 718 3" SCH 160 seamless pipe and forged fittings for high-temperature turbine auxiliary piping.
Frequently Asked Questions
Q1: What is the difference between Inconel 718 and Inconel 625?
Inconel 625 is a solid-solution strengthened alloy with excellent corrosion resistance (PREN ~48) and good strength (UTS ~827-1030 MPa in annealed condition). Inconel 718 is precipitation-hardenable, achieving much higher strength (UTS ≥1240 MPa) but with slightly lower corrosion resistance. Choose Inconel 625 for corrosive environments (seawater, acids) and Inconel 718 when high strength at elevated temperatures is the primary requirement.
Q2: Can Inconel 718 be welded?
Yes — Inconel 718 has excellent weldability, one of the reasons it is so widely used. It can be welded in the solution-annealed condition using GTAW (TIG), SMAW (stick), and GMAW (MIG) with ERNiFeCr-2 filler metal (AMS 5832). After welding, the component should be solution-annealed and re-aged to restore full strength in the HAZ. Welding in the fully aged condition without post-weld heat treatment leaves the HAZ over-aged and softer.
Q3: What is the standard heat treatment for Inconel 718?
The standard aging cycle (AMS 5663/5664) is: solution anneal at 954°C (1750°F), water quench, then age at 718°C (1325°F) for 8 hours, furnace cool at 56°C/h (100°F/h) to 621°C (1150°F), hold at 621°C for a total aging time of 18 hours (including the 718°C hold), then air cool. This "dual-stage" aging cycle optimizes the γ″ and γ′ precipitation for maximum strength.
Q4: Is Inconel 718 suitable for cryogenic service?
Yes — Inconel 718 maintains excellent toughness at cryogenic temperatures down to -253°C (20K, liquid hydrogen temperature). It has no ductile-to-brittle transition. This makes it suitable for cryogenic storage, rocket components, and LNG applications. The alloy is actually stronger at cryogenic temperatures than at room temperature (UTS increases to ~1450 MPa at -196°C).
Q5: Why does Inconel 718 have a specific aging temperature of 718°C?
The aging temperature of 718°C (1325°F) is specifically chosen to optimize the precipitation of the γ″ (Ni₃Nb) phase, which is the primary strengthening precipitate in Inconel 718. At 718°C, the γ″ precipitates form with the optimal size and distribution. Lower temperatures (e.g., 650°C) can also be used but require much longer times. The number "718" in the alloy name is coincidentally the same as the optimal aging temperature in °C — though some sources say the name comes from the original alloy development number, not the aging temperature.
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Need Inconel 718 Pipes or Fittings?
HT PIPE supplies Inconel 718 in all product forms, with AMS 5662/5663 certification and full MTR.
Request a Quote → |
Related Resources
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