Inconel 718 (UNS N07718 / W.Nr. 2.4668) is a nickel-chromium alloy containing niobium (Nb), molybdenum (Mo), and iron (Fe). It belongs to the precipitation-hardened superalloy family, offering exceptional high-temperature strength, corrosion resistance, and excellent weldability.
History of Inconel 718
To address the issues of stress corrosion cracking and insufficient strength in traditional Inconel alloys (such as Inconel 600 and 625) under high-temperature and high-pressure conditions—particularly in applications like aircraft engines and gas turbines—the International Nickel Company (INCO) (now part of Special Metals Corporation) developed Inconel 718 in 1959.
Starting in the 1960s, Inconel 718 was widely adopted in the aerospace industry, including components for NASA’s space program engines. It became a key material for commercial and military jet engine turbine disks, casings, fasteners, springs, and seals. Due to its exceptional corrosion resistance and high strength, it was also used in nuclear power and deep-sea drilling equipment. The development of Inconel 718 marked a significant breakthrough in high-temperature alloys for the aerospace and energy sectors.
Common Trade Names
- Inconel® 718 (Special Metals)
- Alloy 718
- Haynes® 718
- ATI 718 (Allegheny Technologies)
- Udimet® 718
Inconel 718 Equivalent Grades
| Standard | Equivalent Grade | Notes |
| UNS | N07718 | Unified Numbering System designation |
| Werkstoff Nr. | 2.4668 | German standard designation |
| ASTM | ASTM B637 (bar), B670 (plate), B670M | Standard for various forms |
| AMS | AMS 5662 / AMS 5663 / AMS 5596 / AMS 5664 | Aerospace Material Specs (bar, plate, sheet, forgings) |
| ISO | ISO 15156-3 (NACE MR0175 compliance) | Applicable in sour gas environments |
| AFNOR | NC19FeNb | French designation |
| BS | NA 51 | British Standard |
| JIS | NCF 718 | Japanese Industrial Standard |
| GE / Boeing / Rolls-Royce | Various internal codes | Used in aerospace OEM specifications |
Key Advantages of Inconel 718
| Advantage | Description |
| 🔩 Excellent High-Temperature Strength | Maintains outstanding tensile, creep, and fatigue strength at temperatures up to 650°C. |
| 🔧 Superior Weldability | Unlike many high-strength nickel alloys, Inconel 718 can be welded without cracking and generally does not require post-weld heat treatment. |
| ⛓ Exceptional Corrosion Resistance | Exhibits strong resistance to oxidation, pitting, crevice corrosion, and aggressive chemical environments. |
| 🧪 Good Machinability | Offers favorable formability and machinability in the solution-annealed condition, suitable for turning, milling, etc. |
| 🌀 Excellent Precipitation Hardening | Strengthened by γ″ and γ′ phases; allows precise control of mechanical properties through heat treatment. |
| 🛠 High Structural Stability | Provides dimensional stability, resistance to deformation, and stress relaxation under prolonged high-temperature service. |
| 🛰 Ideal for Harsh Environments | Designed for aerospace engines, nuclear reactors, deep-sea drilling, and other extreme applications. |
Applications of Inconel 718
✈️ Aerospace: Gas turbine engine components, turbine blades, combustion chambers, fasteners, landing gear parts, nozzles, and thermal shielding structures.
⚙️ Energy & Power Generation: Nuclear reactor components, steam generator tube sheets, high-pressure bolts, and hot-section parts of gas turbines.
🛢 Oil & Gas: Downhole tools, wellhead equipment, BOP parts, valves, and components exposed to sour gas (H₂S) environments.
🧪 Chemical Processing: Reactors, heat exchangers, pump housings, and internal parts of pressure vessels in corrosive and high-temperature conditions.
🚢 Marine & Offshore: Submersible pump shafts, propeller systems, corrosion-resistant fasteners, and subsea connectors—especially in chloride-rich seawater.
🏥 Medical Devices: Surgical tools, high-strength implants, and corrosion-resistant components (after appropriate processing).
🚀 Defense & Space: Rocket nozzles, solid-propellant motor cases, missile components, and aerospace structural supports.
Typical Chemical Composition of Inconel 718
| Element | Content (%) | Function |
| Ni (Nickel) | 50.0–55.0 | Base element; provides high-temperature strength and corrosion resistance. |
| Cr (Chromium) | 17.0–21.0 | Offers oxidation resistance and forms a protective oxide film. |
| Fe (Iron) | Balance (approx. 17%) | Balances the alloy composition and improves machinability. |
| Nb + Ta (Niobium + Tantalum) | 4.75–5.50 | Forms the γ″ (Ni₃Nb) strengthening phase; main hardening elements. |
| Mo (Molybdenum) | 2.80–3.30 | Enhances strength and pitting corrosion resistance. |
| Ti (Titanium) | 0.65–1.15 | Works with aluminum to form γ′ (Ni₃(Al,Ti)) phase; improves thermal strength. |
| Al (Aluminum) | 0.20–0.80 | Contributes to γ′ precipitation strengthening and oxidation resistance. |
| Co (Cobalt) | ≤ 1.0 | Enhances hot strength; usually a residual element. |
| C (Carbon) | ≤ 0.08 | Increases strength; excessive amounts may cause carbide precipitation. |
| Mn (Manganese) | ≤ 0.35 | Improves hot workability and acts as a deoxidizer. |
| Si (Silicon) | ≤ 0.35 | Aids in deoxidation; improves metallurgical processing. |
| S (Sulfur) | ≤ 0.015 | Harmful impurity; should be minimized to enhance toughness and ductility. |
| Cu (Copper) | ≤ 0.30 | Usually a residual element with limited influence. |
Main Strengthening Mechanisms
Inconel 718 achieves its high strength primarily through precipitation hardening, involving:
- γ″ phase (Ni₃Nb): Main strengthening phase, providing excellent creep and tensile strength at elevated temperatures.
- γ′ phase (Ni₃(Al,Ti)): Secondary strengthening phase, contributing to heat resistance and structural stability.
Physical Properties of Inconel 718
| Property | Value | Unit |
| Density | 8.19 | g/cm³ |
| Melting Range | 1260 – 1336 | °C |
| Specific Heat Capacity | 0.435 | J/g·°C |
| Thermal Conductivity | 11.4 (at 100°C) | W/m·K |
| Coefficient of Thermal Expansion | 13.0 (20–100°C) | µm/m·°C |
| Electrical Resistivity | 1.2 | μΩ·m |
| Magnetic Properties | Non-magnetic (at room temperature) | — |
Mechanical Properties (at room temperature, heat-treated)
| Property | Typical Value |
| Tensile Strength (Rm) | ≥ 1240 MPa |
| Yield Strength (Rp0.2%) | ≥ 1035 MPa |
| Elongation (A5) | ≥ 12% |
| Hardness (Rockwell C) | 36 – 44 HRC |
| Impact Toughness (notched) | High |
Heat treatment: Solution annealed + aged (precipitation hardening)
Inconel 718 Available Forms
- Pipes & Tubes (Seamless & Welded)
- Forged Flanges
- Fittings (Elbow, Tee, Reducer, Cap)
- Plates & Sheets
- Rods, Bars, and Fasteners
Standards & Specifications
- ASTM B637, AMS 5662 / 5663
- UNS N07718, DIN 2.4668
- ISO 15156 / NACE MR0175
- ASME Boiler & Pressure Vessel Code approved
Machinability of Inconel 718
Inconel 718 is a high-strength nickel-based alloy with excellent corrosion resistance and high-temperature strength. However, due to its strengthening mechanism (precipitation hardening), high toughness, and strong work-hardening tendency, it is classified as a difficult-to-machine material.
Inconel® 718 is a high-strength nickel-based alloy known for its excellent corrosion resistance and high-temperature performance, but it is also classified as a difficult-to-machine material due to its work-hardening tendency and toughness. During machining, the alloy tends to harden rapidly, generates significant heat at the cutting edge, and causes rapid tool wear. To achieve optimal results, it is recommended to use coated carbide, ceramic, or CBN tools, and to apply high-pressure, high-flow coolant to manage heat. Cutting speeds should be kept low, with steady feed rates and minimal tool engagement to avoid built-up edges and surface hardening. Machining is more effective in the annealed condition, and rigid machine setups are essential to withstand the high cutting forces. Despite its challenges, proper tool selection, optimized cutting parameters, and thermal management can significantly improve machining efficiency and surface quality when working with Inconel 718.
Inconel 718 in 3D Printing and Its Applications
Inconel 718’s compatibility with 3D printing allows engineers to harness its high-performance properties in intricate geometries—making it a top choice for mission-critical, high-temperature, and corrosion-resistant applications in extreme environments.
Inconel 718 enables the creation of complex, lightweight geometries such as lattice structures that are difficult or impossible to machine conventionally. It also reduces material waste and lead time while supporting rapid prototyping and customization of high-performance parts.
Key Application Areas:
Inconel 718 3D printed components are widely used in aerospace (turbine blades, nozzles, combustor parts), automotive motorsport (turbo housings, heat shields), medical (custom implants, surgical tools), oil & gas (downhole tools, corrosion-resistant valves), power generation (turbomachinery components), and space & defense (rocket parts, satellite brackets).
FAQ
It performs reliably in temperatures ranging from -253°C to 700°C, and can withstand even higher temperatures for short durations, making it ideal for extreme environments.
Yes, it has good weldability, particularly suitable for TIG and electron beam welding. Post-weld heat treatment is usually not required to maintain performance.
Inconel 718 is precipitation-hardened for higher strength, ideal for load-bearing applications. Inconel 625 relies on solid solution strengthening and offers better corrosion resistance, suitable for marine and chemical environments.
Yes, it exhibits excellent resistance to high-temperature oxidation, stress corrosion, and seawater environments.
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