UNS N07718 is a precipitation-hardenable nickel-chromium alloy containing significant amounts of iron, niobium, and molybdenum, along with minor additions of aluminum and titanium. Developed specifically for high-temperature and high-stress applications, this superalloy has become the standard material across aerospace, energy, and oil & gas industries.
The alloy combines excellent corrosion resistance with exceptional mechanical strength and outstanding weldability, including resistance to post-weld cracking — a unique property among precipitation-hardened alloys. UNS N07718 maintains its mechanical properties from cryogenic temperatures (-250°C) up to 700°C (1290°F), making it the preferred choice for demanding applications where both heat and stress are factors.
| Parameter | Details |
|---|---|
| Standard | ASTM B670 (Plate/Sheet/Strip), ASTM B637 (Bar/Forging), ASTM B983 (Tube), ASME SB670 |
| Grade / UNS | UNS N07718 |
| Product Forms | Tube / Pipe / Bar / Rod / Wire / Plate / Sheet / Strip / Forgings |
| Outer Diameter (Tube/Pipe) | 6.0 mm – 610 mm (1/8″ – 24″) |
| Wall Thickness (Tube/Pipe) | 0.5 mm – 50 mm (SCH 5S – XXS) |
| Bar Diameter | 3.0 mm – 300 mm (1/8″ – 12″) |
| Length | 3 m – 12 m, or random lengths |
| Process | Cold drawn / Cold rolled / Hot rolled / Forged |
| Finish | Annealed / Solution treated & aged / Turned / Ground / Polished |
| Packaging | Hexagonal bundles + plastic end caps + seaworthy wooden crates or spools |
The unique age-hardenable characteristics come from a precise balance of niobium (columbium), titanium, and aluminum, which form strengthening precipitates (gamma double-prime and gamma prime) during heat treatment.
| Element | Content (%) | Role |
|---|---|---|
| Nickel (Ni) | 50.0 – 55.0 | Base element – provides corrosion resistance & austenitic stability |
| Chromium (Cr) | 17.0 – 21.0 | Oxidation resistance & protection against sulfur compounds |
| Iron (Fe) | Balance (Rem) | Provides cost-effective stability & structural integrity |
| Niobium + Tantalum (Nb+Ta) | 4.75 – 5.50 | Primary strengthening element (gamma double-prime precipitate) |
| Molybdenum (Mo) | 2.80 – 3.30 | Pitting resistance & solid-solution strengthening |
| Titanium (Ti) | 0.65 – 1.15 | Secondary strengthener (gamma prime precipitate) |
| Aluminum (Al) | 0.20 – 0.80 | Secondary strengthener (gamma prime precipitate) |
| Cobalt (Co) | 1.00 max | Limited for nuclear compatibility |
| Carbon (C) | 0.08 max | Controlled for carbide stability |
| Manganese (Mn) | 0.35 max | Trace element |
| Silicon (Si) | 0.35 max | Trace element |
| Phosphorus (P) | 0.015 max | Controlled for ductility |
| Sulfur (S) | 0.015 max | Controlled for hot workability |
| Boron (B) | 0.006 max | Grain boundary strengthener |
| Copper (Cu) | 0.30 max | Trace element |
Niobium is also referred to as Columbium (Cb) in older specifications. The combined Nb+Ta content is critical for precipitation hardening.
Inconel 718 is supplied in two main conditions: Solution Annealed (for fabrication) and Aged (precipitation-hardened for maximum strength). The aged condition delivers the alloy's signature high-temperature performance.
| Product Form | Condition | Tensile Strength (KSI / MPa) | Yield Strength 0.2% Offset (KSI / MPa) | Elongation (%) | Hardness |
|---|---|---|---|---|---|
| Sheet (AMS 5596) | Solution Annealed | 140 KSI (965 MPa) | 80 KSI (552 MPa) | 30 | 102 HRB max |
| Sheet (AMS 5596) | Aged | 180 KSI (1241 MPa) | 150 KSI (1034 MPa) | 12 | ≥36 HRC |
| Sheet (AMS 5597) | Solution Annealed | 140 KSI (965 MPa) | 75 KSI (517 MPa) | 30 | ≤25 HRC |
| Sheet (AMS 5597) | Aged | 180 KSI (1241 MPa) | 150 KSI (1034 MPa) | 15 | ≥38 HRC |
| Bar / Rod (ASTM B637) | Solution Annealed + Aged | 185 KSI min (1276 MPa) | 150 KSI min (1034 MPa) | 12 min | 36 HRC min |
At 1200°F (649°C): Retains approximately 70% of room temperature yield strength.
Creep Rupture: Excellent resistance to creep deformation up to 1300°F (700°C).
Fatigue Strength: Superior to most other superalloys in the high-cycle fatigue regime.
Cryogenic Performance: Elongation can exceed 20% at -320°F (-196°C) with no ductile-to-brittle transition.
We supply Inconel 718 in all standard mill forms, cut to size, with full traceability to AMS, ASTM, and ASME standards. Custom dimensions and special heat treatments are available upon request.
| Product Form | Size Range | Key Specifications |
|---|---|---|
| Round Bar / Rod | Dia: 6mm – 300mm (0.25" – 12") | ASTM B637, ASME SB637, AMS 5662, AMS 5663, AMS 5664, ISO 9723, DIN 17752 |
| Wire | Dia: 0.1mm – 12mm | AMS 5832, ISO 9724, DIN 17753 |
| Plate / Sheet / Strip | Thk: 0.5mm – 100mm | ASTM B670, ASTM B906, AMS 5596, AMS 5597, AMS 5598, AMS 5862, ISO 6208, DIN 17750 |
| Seamless Pipe / Tube | OD: 6mm – 219mm | SAE AMS 5589, SAE AMS 5590, ASTM B983 |
| Welded Pipe / Tube | OD: up to 914mm | SAE AMS 5590 (welded annealed), ASTM B983 |
| Fittings (Flanges, Elbows, Tees) | All schedules | ASTM B366, ASME SB366 |
| Forgings (Rings, Discs, Blocks) | Custom sizes | ASTM B637, ASME SB637, AMS 5663, ISO 9725, DIN 17754 |
| Fastener Stock | Custom | ASTM B637 (Condition A or Aged), AMS 5662 |
| Feature | Benefit |
|---|---|
| Precipitation-hardenable | Achieves high strength through heat treatment |
| Excellent creep-rupture strength | Maintains performance up to 700°C (1290°F) |
| Outstanding weldability | Resists post-weld cracking — unique for precipitation-hardened alloys |
| Good corrosion resistance | Performs well in aggressive environments |
| Wide temperature range | From cryogenic (-250°C) to elevated temperatures |
| Good fatigue resistance | Suitable for cyclic loading applications |
UNS N07718 requires specific heat treatment to achieve its precipitation-hardened properties:
| Treatment | Temperature | Duration | Purpose |
|---|---|---|---|
| Solution Treatment | 954 – 1066°C (1750 – 1950°F) | 1 hour + air cool | Dissolves strengthening phases |
| Aging (Precipitation Hardening) | 718°C (1325°F) | 8 hours + furnace cool to 621°C | Precipitates γ" and γ' phases for high strength |
| Second Aging | 621°C (1150°F) | 8 hours + air cool | Completes the precipitation process |
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