If you need a superalloy that delivers unmatched strength, creep resistance, and high-temperature stability for the most demanding applications—UNS N07718 (Inconel 718) is the industry standard. Used in aerospace jet engines, gas turbines, and nuclear reactors, this alloy solves the critical problem of material failure under extreme heat and pressure. This guide covers its properties, applications, and manufacturing methods.
What are the key properties of UNS N07718?
UNS N07718’s superalloy status comes from its unique composition: niobium-titanium-aluminum precipitates for strength, chromium for corrosion resistance, and nickel for a tough, heat-resistant base.
Chemical composition
Every element is engineered to work in harmony—maximizing strength at high temperatures without sacrificing corrosion resistance.
| Element | Content Range (%) | Key Role |
|---|---|---|
| Nickel (Ni) | 50.0 – 55.0 | Base element, provides high-temperature stability |
| Chromium (Cr) | 17.0 – 21.0 | Forms protective oxide layer, resists oxidation |
| Iron (Fe) | 17.0 – 21.0 | Enhances workability, balances cost |
| Molybdenum (Mo) | 2.80 – 3.30 | Boosts creep resistance and high-temperature strength |
| Niobium (Nb) + Tantalum | 4.75 – 5.50 | Forms γ” precipitates for ultra-high tensile strength |
| Titanium (Ti) | 0.65 – 1.15 | Enhances high-temperature strength and creep resistance |
| Aluminum (Al) | 0.20 – 0.80 | Aids precipitate formation, improves oxidation resistance |
| Carbon (C) | ≤ 0.08 | Kept low to avoid brittleness |
Physical properties
These properties reflect UNS N07718’s ability to withstand extreme heat and pressure.
- Density: 8.19 g/cm³ – higher than steel due to nickel and molybdenum
- Melting point: 1,260–1,320°C – resists softening in gas turbines
- Thermal conductivity: 11.4 W/(m·K) at 100°C; 19.0 W/(m·K) at 600°C – low heat transfer retains structural integrity
- Thermal expansion: 12.6 × 10⁻⁶/°C (20–100°C); 16.8 × 10⁻⁶/°C (20–600°C) – stable expansion for precision parts
- Specific heat capacity: 435 J/(kg·K) at 25°C – absorbs heat without rapid temperature changes
Mechanical properties
UNS N07718’s mechanical properties are unmatched for high-stress, high-temperature applications. Its strength actually increases with heat up to 650°C due to precipitate formation.
| Property | Typical Value (Age-Hardened) |
|---|---|
| Hardness (HRC) | 40 – 45 |
| Tensile strength | ≥ 1,240 MPa |
| Yield strength (0.2% offset) | ≥ 1,030 MPa |
| Elongation | ≥ 15% |
| Impact toughness | ≥ 50 J at 20°C |
| Creep resistance | 207 MPa at 650°C (10⁵ hours) |
| Fatigue strength | ~550 MPa (10⁷ cycles) |
A U.S. power generation company faced creep deformation in Inconel 625 gas turbine rotors after 12 years at 1,050°C. Switching to UNS N07718 extended rotor life to 20 years—a 67% improvement. Power output increased by 5% due to higher operating temperatures. Maintenance costs fell by $800,000 per year.
Other key properties
- Corrosion resistance: Very good. Resists oxidation up to 870°C, seawater corrosion and pitting, and mild acids and alkalis.
- Oxidation resistance: Excellent. Forms a dense oxide layer preventing further oxidation at 800–870°C.
- Weldability: Good with care. Requires preheating to 200–300°C and post-weld heat treatment. Use ERNiFeCr-2 filler metal.
- Machinability: Fair. Work hardens rapidly. Use sharp carbide tools, slow cutting speeds of 5–10 m/min for turning, and high-pressure cutting fluids.
- Formability: Moderate. Hot forming at 980–1,150°C. Cold forming requires intermediate annealing.
Where is UNS N07718 used?
UNS N07718 is used in applications where failure is catastrophic—industries where component strength and reliability directly impact safety and efficiency.
Aerospace and jet engines
Used for turbine blades, combustion chambers, afterburner components, and aircraft structural parts. A U.S. aerospace manufacturer used UNS N07718 for turbine blades—blade life increased by 500% compared to Inconel 625.
Gas turbines (energy industry)
Used for turbine rotors, stator vanes, and combustion liners in power generation. A German energy firm used UNS N07718 for turbine rotors—rotor life extended to 20 years versus 12 years for other superalloys.
Oil and gas industry
Used for downhole tools in high-temperature, high-pressure reservoirs, subsea wellheads, and pipeline components for sour gas. A Saudi Arabian oil company used UNS N07718 downhole tools—tools operated for 10 years without failure versus 3 years for stainless steel.
Nuclear reactors
Used for reactor pressure vessel components, control rod housings, and fuel handling systems. A French nuclear operator used UNS N07718 for control rod housings—no maintenance issues in 18 years.
Automotive (high-performance)
Used for turbocharger rotors and exhaust components in high-performance cars. A Japanese automaker used UNS N07718 for turbo rotors—turbo life doubled compared to stainless steel rotors.
How is UNS N07718 manufactured?
UNS N07718’s manufacturing is complex. Its precipitate strengthening requires precise heat treatment, and its work-hardening nature demands careful machining.
Melting and forming
- Melting: Raw materials melt in a vacuum induction furnace followed by vacuum arc remelting or electroslag remelting. Dual melting ensures ultra-low impurities and uniform composition.
- Casting and forging: Molten alloy casts into ingots up to 5 tons or investment-cast into near-net-shape components like turbine blades. Ingots are hot-forged at 980–1,150°C to align grain structure.
- Rolling: Hot rolling at 950–1,100°C produces plates, bars, or tubes. Cold rolling is limited to thin sheets and requires intermediate annealing.
Heat treatment (critical for strength)
Heat treatment unlocks UNS N07718’s full strength through precipitate formation.
| Process | Temperature | Result |
|---|---|---|
| Solution annealing | 950–1,050°C, water quench | Dissolves excess carbides, prepares for aging |
| Intermediate aging | 700–760°C, hold 2–4 hours | Forms small γ’ precipitates |
| Final aging | 620–650°C, hold 8–12 hours | Forms large γ” precipitates for ultra-high strength |
Machining and welding
- Machining: Use carbide tools with negative rake angles. Cutting speeds of 5–8 m/min for turning, 3–5 m/min for milling. Use high-pressure cutting fluids at 100–150 bar.
- Welding: Preheat to 200–300°C. Use TIG welding with ERNiFeCr-2 filler metal. Post-weld heat treatment with solution annealing and full age hardening restores strength.
How does UNS N07718 compare to other superalloys?
Understanding how UNS N07718 stacks up helps with material selection for high-stress, high-temperature applications.
| Material | Tensile Strength (MPa) | Creep Resistance (650°C, 10⁵h) | High-Temp Stability (°C) | Cost vs. UNS N07718 | Best For |
|---|---|---|---|---|---|
| UNS N07718 | ≥ 1,240 | 207 | 700 | 100% | High-stress, high-heat (aerospace, turbines) |
| Inconel 625 | ≥ 827 | 138 | 650 | 80% | Severe corrosion, less stress |
| Hastelloy C276 | ≥ 690 | 90 | 650 | 180% | Extreme corrosion, no high stress |
| Titanium Grade 5 | ≥ 860 | 40 | 400 | 150% | Lightweight aerospace, low heat |
| 316 stainless | ≥ 515 | 10 | 870 | 20% | Mild stress and heat |
Key takeaways:
- UNS N07718 is the strongest superalloy for high-stress, high-temperature applications
- It outperforms Inconel 625 in strength and creep resistance
- It’s more cost-effective than Hastelloy C276 for most aerospace and energy applications
Conclusion
UNS N07718 superalloy delivers exceptional strength, creep resistance, and high-temperature stability for the most demanding applications. Its niobium-aluminum-titanium precipitates provide tensile strength above 1,240 MPa and creep resistance at 650°C that outperforms most alternatives. For aerospace jet engines, gas turbines, oil and gas downhole tools, and nuclear reactors where failure isn’t an option, it offers proven reliability and long service life.
FAQ
What’s the maximum operating temperature for UNS N07718?
For long-term service, it operates reliably up to 650°C. For short-term exposure, it can handle temperatures up to 700°C. Above this, creep deformation accelerates and the γ” precipitates begin to coarsen, reducing strength.
How does UNS N07718 compare to Inconel 625?
UNS N07718 has significantly higher tensile strength at 1,240 MPa vs. 827 MPa and better creep resistance at 207 MPa vs. 138 MPa at 650°C. Inconel 625 offers better corrosion resistance in severe chemical environments. Choose N07718 for high-stress, high-temperature applications; choose 625 for extreme corrosion with moderate stress.
Does UNS N07718 require special welding procedures?
Yes. Preheat to 200–300°C to reduce thermal stress. Use TIG welding with ERNiFeCr-2 filler metal. Post-weld heat treatment with solution annealing at 980°C followed by full age hardening is critical to restore strength in the heat-affected zone.
What machining speeds work best for UNS N07718?
Use carbide tools with cutting speeds of 5–8 m/min for turning and 3–5 m/min for milling. Feed rates of 0.05–0.10 mm/rev. High-pressure cutting fluids at 100–150 bar are essential to prevent work hardening and tool wear.
What heat treatment is required to achieve maximum strength?
Solution anneal at 950–1,050°C followed by water quenching. Then age harden with a two-step process: 700–760°C for 2–4 hours, then 620–650°C for 8–12 hours. This forms the γ” precipitates that give UNS N07718 its ultra-high strength.
Discuss Your Projects with Yigu Rapid Prototyping
At Yigu Rapid Prototyping, we supply UNS N07718 (Inconel 718) superalloy for aerospace, energy, and oil and gas applications. Our material meets ASTM B637 standards, and we offer custom forging, heat treatment, and machining services. Contact us to discuss your next high-temperature, high-stress project.