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Inconel 718 is a precipitation-hardenable nickel-based superalloy known for its high strength, good weldability, fatigue resistance, and balanced performance across a broad range of engineering applications. Identified by UNS N07718 and commonly associated with the Chinese grade GH4169, Inconel 718 is widely used in aerospace engines, gas turbines, high-strength fasteners, cryogenic structures, oil and gas equipment, and selected nuclear applications.
Unlike alloys designed primarily for the highest possible service temperatures, Inconel 718 combines mechanical strength with good fabrication characteristics and a well-established precipitation-hardening process. Its strength is derived mainly from γ″ and γ′ precipitates formed during heat treatment.
This guide explains Inconel 718 chemical composition, physical and mechanical properties, strengthening mechanisms, heat treatment, service-temperature considerations, alloy comparisons, and typical industrial applications.
Property | Description |
Alloy name | Inconel 718 |
UNS designation | N07718 |
Common Chinese counterpart | GH4169; confirm equivalence against the applicable specification |
European material number | 2.4668 |
Alloy classification | Wrought nickel-based, precipitation-hardenable superalloy |
Principal strengthening phases | γ″ and γ′ |
Density | Approximately 8.19 g/cm³ |
Melting range | Approximately 1260–1336°C (2300–2437°F) |
Temperature capability | Depends on stress, exposure duration, environment, product form, and design requirements |
Common product forms | Plate, sheet, strip, bar, billet, wire, tube, and forgings, subject to applicable specifications |
Typical industries | Aerospace, gas turbines, cryogenic engineering, oil and gas, and selected nuclear applications |
Note: These are general reference values. The applicable material specification, product form, heat-treatment condition, certified test results, and engineering design criteria take precedence.
Inconel 718 was developed to meet the demanding requirements of aircraft engines and gas turbines, where components must combine high mechanical strength with fatigue resistance, fabrication capability, and reliable performance after appropriate heat treatment.
The alloy is one of the most widely used wrought nickel-based superalloys. Its popularity reflects not one isolated property, but a useful balance of strength, weldability, forging capability, and industrial processability.
Inconel 718 is commonly associated with the Chinese grade GH4169. However, the two designations should not be treated as automatically interchangeable for every application. Equivalence must be established by comparing the governing standards, chemistry limits, product form, heat treatment, mechanical-property requirements, testing, and traceability documentation.
Key characteristics include:
● High tensile and yield strength after appropriate precipitation heat treatment
● Good fatigue performance in properly manufactured and qualified components
● Useful creep and stress-rupture properties within the applicable design range
● Good resistance to oxidation and corrosion in many engineering environments
● Good weldability relative to many precipitation-hardenable nickel-based superalloys
● Suitability for a broad range of wrought product forms and complex forgings
● Useful mechanical performance at cryogenic temperatures
These properties make Inconel 718 a common candidate for engine disks, turbine rings, shafts, casings, fasteners, structural components, and selected low-temperature equipment.
The alloy is not the strongest material in every category, nor is it the best option for every corrosive environment. Its principal advantage is the combination of mechanical performance, manufacturability, and established industrial use.
Inconel 718 is commonly used in applications involving temperatures up to approximately 650–704°C (1200–1300°F), depending on the component, stress level, required life, environment, and applicable design criteria.
At elevated temperatures, the γ″ strengthening precipitates can coarsen, and changes in the niobium-rich phases can reduce strengthening effectiveness. For long-duration service, creep, stress rupture, oxidation, microstructural stability, and the required design life must all be evaluated.
A nominal temperature figure should not be interpreted as a universal allowable operating temperature. For critical applications, consult the applicable design code, material specification, and qualified engineering data.
Inconel 718 is a nickel-chromium-iron alloy strengthened primarily by niobium-bearing precipitates. The table below summarizes commonly published composition limits. Exact limits and reporting conventions must be verified against the specification governing the purchased product.
Element | Commonly Published Composition Limit (wt.%) | Function |
Nickel (Ni) | 50.00–55.00, subject to the applicable reporting convention | Provides the principal matrix and contributes to strength, toughness, and corrosion resistance |
Chromium (Cr) | 17.00–21.00 | Supports oxidation resistance and corrosion resistance in many environments |
Niobium + Tantalum (Nb + Ta) | 4.75–5.50 | Provides the principal contribution to γ″ precipitation strengthening |
Molybdenum (Mo) | 2.80–3.30 | Contributes to solid-solution strengthening |
Titanium (Ti) | 0.65–1.15 | Participates in γ′ precipitation strengthening |
Aluminum (Al) | 0.20–0.80 | Participates in γ′ precipitation strengthening |
Cobalt (Co) | 1.00 max. | Controlled alloying constituent |
Carbon (C) | 0.08 max. | Influences carbide formation and grain-boundary behavior |
Manganese (Mn) | 0.35 max. | Controlled minor constituent |
Silicon (Si) | 0.35 max. | Controlled minor constituent |
Copper (Cu) | 0.30 max. | Controlled minor constituent |
Phosphorus (P) | 0.015 max. | Controlled impurity |
Sulfur (S) | 0.015 max. | Controlled impurity |
Boron (B) | 0.006 max. | Controlled minor element |
Iron (Fe) | Balance | Major matrix constituent |
Important: Some standards and technical publications use specific conventions for nickel and cobalt reporting. The governing specification and material test certificate must be used for acceptance.
Niobium is central to the precipitation-hardening response of Inconel 718. During suitable heat treatment, it contributes to the formation of the γ″ phase, which provides much of the alloy's high yield strength.
However, the final performance of Inconel 718 depends on more than bulk chemistry. Segregation during solidification, forging practice, grain structure, solution treatment, aging conditions, and the distribution of precipitates all influence the resulting properties.
For demanding applications, procurement and quality assurance should therefore verify chemical composition alongside manufacturing controls, heat-treatment condition, inspection requirements, and mechanical-test results.
Inconel 718 achieves its characteristic strength through precipitation hardening, supported by solid-solution strengthening and microstructural control. The γ″ and γ′ phases are the principal strengthening precipitates, while the δ phase requires careful control during processing.
The γ″ phase is a niobium-rich, metastable Ni₃Nb precipitate with a body-centered tetragonal structure. It is the principal strengthening phase in conventionally heat-treated Inconel 718.
Fine γ″ precipitates impede dislocation motion and contribute significantly to yield strength. Their size, distribution, and stability depend on alloy chemistry, processing history, and heat treatment.
During prolonged exposure to elevated temperatures, γ″ precipitates can coarsen and lose effectiveness. The associated evolution of niobium-rich phases is an important consideration when evaluating the alloy for long-term high-temperature service.
The γ′ phase, commonly described as Ni₃(Al,Ti), has a face-centered cubic structure and provides additional precipitation strengthening.
Although γ′ is generally less dominant than γ″ in conventional Inconel 718, the two phases work together to produce the alloy's useful balance of strength and toughness.
The δ phase is an equilibrium Ni₃Nb phase. Its amount, morphology, and distribution are important considerations during processing and heat treatment.
Controlled δ-phase precipitation can help regulate grain growth during certain processing operations. Excessive or unfavorably distributed δ phase may consume niobium that would otherwise contribute to γ″ strengthening and can adversely affect mechanical performance.
The objective is not necessarily to eliminate δ phase completely, but to control its formation and distribution to achieve the required grain structure and properties.
Heat treatment plays a critical role in determining Inconel 718's final mechanical properties. Solution treatment establishes an appropriate microstructural condition, while subsequent precipitation aging develops the strengthening phases.
Special Metals describes more than one solution-treatment and aging route for Inconel 718. The appropriate route depends on the intended application and required property balance.
One commonly published route uses:
1. Solution annealing: Approximately 927–1010°C (1700–1850°F), followed by rapid cooling.
2. First aging stage: Approximately 718°C (1325°F) for 8 hours.
3. Controlled furnace cooling: Approximately 11°C/hour (20°F/hour) to 621°C (1150°F).
4. Second aging stage: Hold at approximately 621°C (1150°F) to complete the specified aging duration, followed by air cooling.
Another published route uses a higher solution-annealing temperature, approximately 1038–1066°C (1900–1950°F), followed by aging at approximately 760°C (1400°F) and a subsequent lower-temperature hold.
These schedules are examples of documented processing routes, not interchangeable universal instructions. The exact temperature, holding time, cooling rate, and total aging duration must be taken from the applicable specification or approved manufacturing procedure.
The mechanical properties of Inconel 718 depend strongly on the final heat-treatment condition. Solution-treated material generally does not have the same strength as material that has undergone the specified precipitation-aging process.
For purchasing, manufacturing, and incoming inspection, confirm:
● Required heat-treatment condition
● Governing product specification
● Tensile strength and yield strength requirements
● Elongation and hardness requirements, where applicable
● Test methods and acceptance criteria
● Material certificate and heat or lot traceability
Inconel 718 has good weldability for a precipitation-hardenable nickel-based superalloy. Appropriate welding procedures and compatible filler metals can be used for many applications.
ERNiFeCr-2 is one filler-metal designation associated with welding Inconel 718, but filler selection must be confirmed against the base material, joint design, required properties, and applicable welding procedure.
Post-weld heat treatment should not be assumed to be unnecessary. The need for solution treatment, aging, or other thermal processing depends on the component requirements, base-metal condition, welding process, applicable construction code, and qualified welding procedure. Preheating and interpass requirements must also be established for the specific procedure.
Physical and mechanical properties vary with product form, heat treatment, section size, test temperature, and the applicable material specification. The following values are intended for preliminary reference rather than universal acceptance criteria.
Property | Reference Value | Notes |
Density | Approximately 8.19 g/cm³ | Commonly published reference value |
Melting range | Approximately 1260–1336°C (2300–2437°F) | Reference range; confirm the source used for engineering calculations |
Magnetic behavior | Depends on condition and measurement requirements | Do not assume the alloy is universally non-magnetic |
Thermal expansion | Temperature-dependent | Use a verified data table for the required temperature interval |
Low-temperature capability | Used in selected applications down to approximately −253°C (−423°F) | Verify the required mechanical properties and system compatibility |
The values in a design calculation should be appropriate to the actual material condition and operating temperature. Thermal expansion data should always identify the temperature interval and whether the value is a mean or instantaneous coefficient.
Inconel 718 mechanical properties depend on the product form, processing route, heat treatment, dimensions, and governing specification.
Material Condition | General Property Trend | What Must Be Verified |
Solution-treated / solution-annealed | Typically lower strength and higher ductility than the precipitation-aged condition | Applicable minimum tensile and yield strength, elongation, and hardness requirements |
Precipitation-aged | Higher strength due to γ″/γ′ precipitation | Aging condition, tensile strength, yield strength, elongation, and any hardness limits |
Application-specific condition | May require dedicated processing and qualification | Industry specification, inspection scope, testing, and traceability |
A single set of tensile and yield strength values should not be applied to all Inconel 718 product forms. Plate, sheet, bar, billet, wire, and forgings may be governed by different specifications and acceptance requirements.
Where specific minimum properties are required, identify the applicable standard and heat-treatment condition in the purchase order rather than relying on generic handbook values.
Inconel 718 is used in selected cryogenic applications because it can retain useful mechanical properties at very low temperatures. Potential applications include cryogenic structural components, fasteners, and selected equipment operating at temperatures approaching −253°C.
Low-temperature mechanical performance does not automatically establish compatibility with every cryogenic fluid. Liquid oxygen systems, for example, require separate assessment of material compatibility, cleanliness, ignition risks, and system-level safety requirements.
Alloy selection should consider operating temperature, applied stress, design life, corrosion environment, fabrication method, product form, qualification requirements, and total cost. A nominal service-temperature figure alone is not sufficient for material selection.
Alloy | Principal Strengthening Approach | Main Selection Consideration | Typical Applications |
Inconel 718 | γ″/γ′ precipitation strengthening | High strength, fatigue performance, weldability, and broad manufacturing capability | Engine disks, rings, shafts, fasteners, structural components |
A-286 / GH2132 | Fe-Ni-Cr precipitation strengthening | Alternative when its specification and performance satisfy design requirements | Selected fasteners, turbine components, structural hardware |
Inconel X-750 | γ′ precipitation strengthening | Springs and fasteners requiring suitable strength and temperature performance | Springs, bolts, elastic components |
Inconel 625 | Solid-solution strengthening, including Mo and Nb | Corrosion resistance in many aggressive environments | Chemical processing, marine equipment, corrosion-resistant components |
Inconel 617 | Solid-solution strengthening, including Co and Mo | Candidate for selected higher-temperature applications | Industrial high-temperature systems and energy equipment |
● High-strength forged components: Inconel 718 is often a strong candidate when the operating temperature and design requirements align with its properties.
● Corrosion-focused applications: Inconel 625 may be worth evaluating, depending on the medium, temperature, stress, and exposure conditions.
● Selected higher-temperature applications: Inconel 617 may be appropriate when supported by the relevant design data and qualification requirements.
● Springs and selected fasteners: Inconel X-750 may be considered when its specific heat-treated condition meets the design requirements.
● Cost-sensitive designs: A-286/GH2132 may be evaluated if its mechanical properties, environmental performance, and qualification requirements are adequate.
These are preliminary selection guidelines, not automatic substitution rules. Verify the design conditions and applicable standards before changing alloy grades.
Inconel 718 is widely used in aerospace and gas-turbine components requiring high strength, fatigue performance, and reliable manufacturing quality.
Typical applications include:
● Engine disks and rings
● Rotating shafts
● Casings and structural components
● High-strength fasteners
● Selected formed components
● Welded assemblies and engineered hardware
Critical rotating components require careful control of forging quality, grain structure, heat treatment, defect acceptance, fatigue performance, and material traceability.
Selected nuclear applications use Inconel 718 for structural and mechanical components, subject to the applicable design and material qualification requirements.
Nuclear applications may require additional controls over chemistry, impurities, manufacturing processes, inspection, documentation, and traceability. Suitability must be established against the relevant nuclear code and component specification rather than inferred from the alloy name alone.
Inconel 718 is used in selected oilfield components, including downhole tools, valves, connectors, and other high-strength hardware.
For hydrogen-sulfide-containing environments, suitability depends on material condition, hardness, manufacturing route, environmental parameters, and applicable requirements such as ISO 15156/NACE MR0175 or relevant oilfield specifications.
General-purpose Inconel 718 should not automatically be assumed suitable for sour service. Verify the material qualification and hardness requirements for the intended operating conditions.
Inconel 718's useful low-temperature mechanical performance makes it a candidate for selected cryogenic structural components, fasteners, and equipment.
The material must still be assessed against the relevant design requirements. Compatibility with the intended fluid, particularly liquid oxygen, requires a separate engineering and safety evaluation.
Inconel 718 and GH4169 are commonly treated as corresponding nickel-based superalloy grades. However, their specifications, permitted composition ranges, product forms, processing controls, and mechanical-property requirements may differ.
Before substitution, compare the applicable standards, heat-treatment condition, required properties, testing, and certification. Do not assume that every batch of one grade is automatically interchangeable with every batch of the other.
Price differences may reflect:
● Product form and dimensions
● Material origin and manufacturing route
● Governing specification and revision
● Heat-treatment condition
● Mechanical-property requirements and testing
● Inspection, traceability, and certification requirements
● Order quantity, processing, cutting, and delivery requirements
Price alone does not establish that a product is aerospace-grade or nuclear-grade. Buyers should compare the actual specification, certificates, test results, and traceability requirements.
Inconel 718 is commonly selected for applications up to approximately 650–704°C, depending on the design conditions. Suitability near or above this range requires careful evaluation of exposure duration, stress, creep and stress-rupture behavior, oxidation, and microstructural stability.
For sustained higher-temperature service, Inconel 617 may warrant evaluation. Inconel 625 may be considered where corrosion resistance is a primary requirement, but it should not be treated as a direct substitute for a high-strength component without engineering review.
Yes. Inconel 718 has good weldability for a precipitation-hardenable nickel-based superalloy and can be welded using suitable procedures and compatible filler metals.
ERNiFeCr-2 is one possible filler-metal designation for compatible applications. Filler selection, preheating, interpass control, and post-weld heat treatment must follow the qualified welding procedure and applicable code.
Potential causes include:
● Incorrect heat-treatment condition
● A mismatch between product form and the specified requirements
● Nonconforming material or processing
● Incomplete or incorrect certification
● Inadequate incoming inspection
Solution-treated material should not be assumed to meet the same strength requirements as appropriately precipitation-aged material. Incoming inspection should verify material identity, traceability, chemistry, heat-treatment condition, and the required mechanical-test results.
A clear purchase specification should identify:
● Grade and governing standard
● Product form and dimensions
● Required heat-treatment condition
● Minimum mechanical properties and any hardness limits
● Testing and inspection requirements
● Material test certificate and traceability requirements
● Surface condition, dimensional tolerances, cutting, and packaging requirements
For aerospace, nuclear, sour-service, or other critical applications, specify any additional qualification and documentation requirements at the inquiry stage.
Bozhong Alloy supplies Inconel 718 in a range of product forms, subject to current availability and the applicable specifications.
Available product forms may include:
● Plates and sheets
● Bars and billets
● Tubes
● Strips
● Wires
● Forgings
Depending on stock availability and order requirements, Bozhong Alloy can support:
● Domestic mill supply and imported material sourcing
● Warehouse coordination in Shanghai and Wuxi
● Dispatch of standard sizes, subject to stock confirmation
● Material certificates and batch traceability documentation
● Spectrochemical verification, where arranged
● Precision cutting and small-batch orders
To confirm material suitability and obtain an accurate quotation, please specify the grade, product form, dimensions, quantity, applicable standard, heat-treatment condition, mechanical-property requirements, and delivery destination.
For aerospace, nuclear, sour-service, or other critical applications, please identify any additional qualification, inspection, certification, or traceability requirements at the inquiry stage.
Contact Bozhong Alloy to discuss Inconel 718 plates, bars, tubes, strips, wires, and forgings for your project.
Technical disclaimer: This guide is intended for general reference and preliminary material selection. It does not replace the applicable material specification, certified test results, engineering design data, or application-specific qualification. Verify critical requirements against the current governing standard and the actual material certificate before purchase or use.
