Understanding the mechanical properties, heat treatment, corrosion resistance, and industrial applications of Inconel 718 alloy in aerospace, energy, oil & gas, and high-temperature environments.
Inconel 718, also known as UNS N07718 or Alloy 718, is one of the most widely used precipitation hardening nickel chromium alloys in modern industry. Developed for demanding high-temperature applications, the alloy combines exceptional strength, excellent corrosion resistance, and outstanding fatigue performance.
Unlike many conventional stainless steels and nickel alloys, Inconel 718 derives its high strength from a precipitation hardening mechanism. Through solution annealing followed by double aging heat treatment, the alloy develops strengthening gamma prime (γ’) and gamma double prime (γ”) phases that significantly increase tensile strength, yield strength, and hardness while maintaining useful ductility.
Today, Inconel 718 is extensively used in aerospace engines, gas turbines, nuclear power systems, oilfield equipment, and other critical applications where materials must withstand both elevated temperatures and aggressive corrosive environments.
For a broader view of the family, our Inconel metal guide explains what Inconel is and how the grades differ.
The popularity of Alloy 718 comes from its unique combination of mechanical strength, corrosion resistance, weldability, and high-temperature stability.
One of the most important characteristics of Inconel 718 is its response to heat treatment. The alloy is specifically designed to achieve superior mechanical properties through precipitation hardening.
The standard process involves:
During aging, strengthening phases precipitate throughout the nickel matrix, dramatically increasing strength and hardness.
After double aging, the alloy may achieve tensile strengths exceeding 1,300 MPa while maintaining reasonable elongation and toughness. The cycle itself is fixed by the governing standard: solution anneal near 940–1010 °C, then age at 718 °C for 8 hours, furnace-cool to 621 °C, hold a further 8 hours, and air cool. The precipitated Ni₃Nb phase — gamma double prime — carries the strength that results.
Because acceptance numbers attach to the aged condition rather than to composition alone, our Inconel metal price analysis separates solution-annealed and aged quotations: the heat-treatment route moves both the price and the lead time.
This is one of the most common questions regarding Alloy 718 manufacturing.
In industrial practice, Alloy 718 round bars are typically supplied in the solution annealed condition. Components are then machined close to their final dimensions before undergoing precipitation hardening heat treatment.
The reason is simple. Solution annealed material has lower hardness and significantly better machinability. Once double aging is completed, strength and hardness increase substantially, resulting in higher cutting forces, faster tool wear, and greater machining costs.
For aerospace components, turbine parts, fasteners, oilfield tools, and other precision parts, manufacturers generally perform most machining operations before final aging treatment and only carry out minor finishing operations afterward.
We supply solution-annealed and aged Inconel 718 products with full MTC (EN 10204 3.1).
The outstanding mechanical properties of Inconel 718 are the primary reason for its widespread use across critical industries. Because the grade is bought in a heat-treated condition, the acceptance figures attach to the ageing state — not to composition alone. The data below is the reference set buyers check before an enquiry, taken from the ASTM form family for UNS N07718.
The limits below apply across the ASTM form family. Niobium plus tantalum is the element pair that drives the gamma-double-prime precipitate, so that window matters more than any other row.
| Element | Content |
|---|---|
| Nickel (Ni) | 50.0–55.0% |
| Chromium (Cr) | 17.0–21.0% |
| Iron (Fe) | Balance |
| Niobium + Tantalum (Nb + Ta) | 4.75–5.50% |
| Molybdenum (Mo) | 2.80–3.30% |
| Titanium (Ti) | 0.65–1.15% |
| Aluminium (Al) | 0.20–0.80% |
| Cobalt (Co) | 1.00% max. |
| Carbon (C) | 0.08% max. |
| Manganese (Mn) | 0.35% max. |
| Silicon (Si) | 0.35% max. |
| Copper (Cu) | 0.30% max. |
| Phosphorus (P) | 0.015% max. |
| Sulfur (S) | 0.015% max. |
| Boron (B) | 0.006% max. |
Minimum values apply to precipitation-hardened product, because ageing develops the full strength of the grade. Condition and thickness bands follow the governing standard, so both belong on the enquiry.
| Product Form | Standard | Condition | Tensile Strength | Yield Strength (0.2%) | Elongation |
|---|---|---|---|---|---|
| Bar and forgings | ASTM B637 | Solution treated + aged | ≥1275 MPa (185 ksi) | ≥1034 MPa (150 ksi) | ≥12% |
| Plate, sheet, strip up to 25.4 mm | ASTM B670 | Solution treated + aged | ≥1241 MPa (180 ksi) | ≥1034 MPa (150 ksi) | ≥12% |
| Plate over 25.4 to 57.2 mm | ASTM B670 | Solution treated + aged | ≥1241 MPa (180 ksi) | ≥1034 MPa (150 ksi) | ≥10% |
| Seamless pipe and tube | ASTM B983 | Solution annealed + precipitation hardened | ≥1034 MPa (150 ksi) | ≥862 MPa (125 ksi) | ≥20% |
Aerospace AMS deliveries carry additional test requirements and condition-specific minimums, so confirm the required condition at enquiry and we quote the matching standard.
| Property | Value |
|---|---|
| Density | Approx. 8.19 g/cm³ |
| Melting range | Approx. 1260–1336 °C |
| Elastic modulus | Approx. 200 GPa |
| Thermal conductivity at 20 °C | Approx. 11.4 W/m·°C |
| Specific heat | Approx. 435 J/kg·°C |
| Expansion coefficient, 20–100 °C | 13.0 µm/m·°C |
| Typical aged hardness | 36–44 HRC |
| Strengthening mechanism | Precipitation (Ni₃Nb) ageing |
The two grades are frequently shortlisted against each other, and they solve different problems. Inconel 625 gains its strength from solid-solution alloying with molybdenum and niobium, so it arrives at full properties without a hardening heat treatment. Alloy 718 gains its strength from precipitation, so the ageing cycle is part of the design.
| Property | Inconel 718 (N07718) | Inconel 625 (N06625) |
|---|---|---|
| Strengthening | Precipitation (Ni₃Nb) ageing | Solid solution (Mo, Nb) |
| Nickel | 50.0–55.0% | Balance (58% min. typical) |
| Chromium | 17.0–21.0% | 20.0–23.0% |
| Molybdenum | 2.80–3.30% | 8.0–10.0% |
| Minimum yield, bar | ≥1034 MPa (150 ksi) aged | ≥414 MPa (60 ksi) Grade 1 |
| Stress-relief anneal after welding | Required for full properties | Not required |
| Typical selection | Strength-led, high-temperature duty | Corrosion-led, weld-fabricated duty |
In practice the choice is straightforward: where the part carries structural load at temperature, Alloy 718 wins on strength per unit weight. Where the part is a weld-fabricated vessel exposed to aggressive chemistry, Alloy 625 wins because it needs no post-weld heat treatment.
This combination of strength and ductility allows engineers to reduce component weight while maintaining safety and reliability.
In addition to its impressive strength, Inconel 718 offers excellent corrosion resistance in many aggressive environments.
Its high nickel and chromium content provides protection against oxidation, while additions of niobium and molybdenum contribute to resistance against localized corrosion.
The alloy performs well in:
These characteristics make Alloy 718 suitable for applications where both mechanical strength and corrosion resistance are essential.
The aerospace industry is the largest consumer of Inconel 718 worldwide.
Typical applications include:
Its exceptional fatigue resistance and high-temperature strength make it ideal for demanding flight environments.
Inconel 718 is widely used in downhole and subsea equipment exposed to high pressure, corrosive fluids, and elevated temperatures.
Power generation facilities use Alloy 718 in gas turbines, steam systems, and high-temperature structural components where long-term reliability is required.
Because of its excellent combination of strength and corrosion resistance, Inconel 718 is frequently used in nuclear reactor systems and associated equipment.
Inconel 718 is available in a wide variety of mill product forms to support different manufacturing requirements.
For pressure systems, heat exchangers, and fluid transportation applications, Inconel 718 pipes and tubing provide an excellent combination of strength, corrosion resistance, and long service life.
For aerospace structures, fabrication projects, and industrial equipment manufacturing, Inconel 718 sheets and plates offer excellent dimensional stability and high-temperature performance.
Among all precipitation hardening nickel-based superalloys, Inconel 718 continues to be one of the most widely specified materials worldwide.
Its popularity comes from a balanced combination of:
Few engineering materials offer such a comprehensive balance of performance across aerospace, energy, oil and gas, marine, and industrial processing sectors.
Inconel 718 is a precipitation hardening nickel chromium alloy that delivers exceptional strength, corrosion resistance, fatigue resistance, and high-temperature performance. Through solution annealing and double aging heat treatment, the alloy develops mechanical properties that significantly exceed those of conventional stainless steels.
Whether used in jet engines, gas turbines, oilfield equipment, nuclear systems, or industrial processing facilities, Alloy 718 remains one of the most trusted engineering materials for applications where durability, reliability, and long-term performance are critical.
We supply ASTM B637 / AMS 5662 Inconel 718 products with strict quality control, full MTC EN10204 3.1/3.2, and global export packaging.
