Inconel 718 Chemical Composition, Mechanical Properties and Heat Treatment
Inconel 718 Chemical Composition Inconel 718 is a precipitation-hardenable nickel-based superalloy widely used in demanding engineering applications where high strength, oxidation resistance and reliable performance at elevated temperatures are important. Also known as Alloy 718, UNS N07718 and W.Nr. 2.4668, this material is used in aerospace components, gas turbines, oil and gas equipment, and specialised industrial machinery.
Understanding the chemical composition, mechanical properties and heat treatment of Inconel 718 is essential when selecting the correct material for a specific application.
What Is Inconel 718?
Inconel 718 is a nickel-chromium alloy strengthened through precipitation hardening. Its combination of nickel, chromium, niobium, molybdenum and other alloying elements gives it a useful balance of strength, corrosion resistance and high-temperature performance.
Unlike conventional stainless steels, Inconel 718 is specifically engineered for applications requiring high mechanical strength under demanding operating conditions.
Common material designations include:
- Inconel 718
- Alloy 718
- UNS N07718
- W.Nr. 2.4668
The applicable specification and material condition should always be confirmed against the purchase requirement and material test certificate.
Inconel 718 Chemical Composition
The chemical composition of Inconel 718 is carefully controlled to achieve its characteristic mechanical and metallurgical properties.
The following table gives commonly referenced composition limits. Actual acceptance requirements must be checked against the applicable material specification and product form.
| Element | Typical specification range or limit |
|---|---|
| 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) | 1.0% maximum |
| Carbon (C) | 0.08% maximum |
| Manganese (Mn) | 0.35% maximum |
| Silicon (Si) | 0.35% maximum |
| Phosphorus (P) | 0.015% maximum |
| Sulphur (S) | 0.015% maximum |
Role of Important Alloying Elements
Nickel: Forms the principal matrix of the alloy and contributes to its high-temperature strength and corrosion resistance.
Chromium: Helps provide resistance to oxidation and corrosion in demanding environments.
Niobium: Plays a major role in precipitation strengthening and the development of high mechanical strength.
Molybdenum: Contributes to solid-solution strengthening and improves the alloy’s overall performance.
Titanium and Aluminium: Participate in precipitation strengthening and help develop the required mechanical properties after heat treatment.
Iron: Forms the balance of the alloy and contributes to its overall metallurgical structure.
Inconel 718 Mechanical Properties
The mechanical properties of Inconel 718 depend on the product form, heat-treatment condition, manufacturing route, dimensions and applicable specification.
Its most important characteristics include:
- High tensile strength after suitable precipitation-hardening treatment
- High yield strength in specified aged conditions
- Good fatigue resistance in appropriately manufactured components
- Useful creep resistance at elevated temperatures
- Good resistance to oxidation in demanding service environments
- Retention of useful mechanical properties across a broad temperature range
Tensile Strength and Yield Strength
Inconel 718 is valued for its high tensile and yield strength, particularly after the prescribed solution treatment and ageing process.
However, mechanical-property values should not be treated as universal figures. Requirements for round bars, forgings, plates and other product forms may differ.
For procurement, always confirm:
- Minimum tensile strength
- Minimum yield strength
- Elongation requirements
- Hardness range
- Test temperature, where applicable
- Material condition and heat-treatment details
The material test certificate should be checked against the exact specification and ordered condition.
Hardness and Fatigue Performance
Inconel 718 can achieve high hardness through precipitation hardening. Its fatigue performance also makes it useful in components exposed to repeated loading and demanding operating conditions.
Actual performance depends on heat treatment, surface finish, component geometry, manufacturing quality and service conditions.
Inconel 718 Heat Treatment Process
Heat treatment is one of the most important factors influencing the mechanical properties of Inconel 718.
The alloy is commonly supplied in conditions involving solution treatment followed by precipitation ageing. The exact procedure depends on the governing specification and required application.
1. Solution Treatment
Solution treatment is used to establish a suitable metallurgical condition before ageing. The temperature, holding time and cooling method must follow the applicable material specification or approved heat-treatment procedure.
2. Precipitation Ageing
After solution treatment, controlled ageing develops strengthening precipitates within the alloy’s microstructure.
The principal strengthening phases include:
- Gamma double-prime (γ″): A major strengthening phase in Inconel 718.
- Gamma-prime (γ′): Also contributes to precipitation strengthening.
The formation and distribution of these phases help produce the high strength associated with properly heat-treated Inconel 718.
3. Verification After Heat Treatment
Following heat treatment, the material should be evaluated against the applicable acceptance requirements. Depending on the order, this may include hardness testing, tensile testing and review of the material test certificate.
Do not assume that every Inconel 718 product has identical properties simply because it carries the same alloy designation.
Why Heat Treatment Matters for Industrial Applications
Selecting the correct heat-treatment condition is important because it affects the performance of the finished component.
For example:
- Aerospace components may require tightly controlled mechanical properties.
- Gas turbine parts need suitable strength and performance at elevated temperatures.
- Oil and gas equipment may require specific strength and environmental-resistance requirements.
- Precision-engineered components need material condition and dimensional requirements to be considered together.
The correct selection should be based on the component design, operating environment and governing specification.
Standards and Specifications for Inconel 718
Inconel 718 is covered by different material standards depending on the product form and application.
Commonly referenced specifications include:
- ASTM B637: Specification covering precipitation-hardening nickel alloy bars, forgings and forging stock, including applicable grades and conditions.
- AMS 5662: Aerospace material specification for Inconel 718 in specified bar, forging and ring forms and conditions.
- AMS 5663: Aerospace material specification covering specified solution-treated and precipitation-hardened forms and conditions.
These standards are not interchangeable in every purchasing situation. Confirm the exact specification, revision, product form, dimensions and heat-treatment condition before placing an order.
For standards information, refer to ASTM International and the relevant aerospace material specifications.
You can also refer to Special Metals for manufacturer technical information on Alloy 718.
Inconel 718 Material Selection and Procurement Checklist
Before purchasing Inconel 718, buyers and engineering teams should confirm the following:
- Grade: Confirm Inconel 718 / Alloy 718 / UNS N07718.
- Product form: Specify round bar, forging, plate or another required form.
- Dimensions: Clearly mention diameter, thickness, length and tolerances.
- Specification: State the required ASTM or AMS standard.
- Condition: Confirm solution-treated, aged or other specified material condition.
- Testing: Specify the required mechanical tests and inspection documents.
- Documentation: Request the applicable material test certificate.
- Application: Confirm suitability for the intended operating temperature, loading and environment.
A clearly defined purchase specification helps reduce material-selection errors and procurement delays.
Inconel 718 Round Bar Supplier in India
Manan Steel & Metals supplies specialty metals and alloy materials for industrial and engineering requirements. Buyers looking for Inconel 718 should share their required grade, product form, dimensions, specification and material condition so that the enquiry can be evaluated accurately.
For related material requirements, explore our round bar product range and round bar weight chart.
For enquiries about Inconel 718 and other specialty alloys, contact Manan Steel & Metals through our contact page.
Frequently Asked Questions About Inconel 718
1. What is the chemical composition of Inconel 718?
Inconel 718 primarily contains nickel, chromium, iron, niobium, molybdenum, titanium and aluminium. Nickel generally falls within 50–55%, while chromium is commonly specified within 17–21%, subject to the applicable specification.
2. What gives Inconel 718 its high strength?
Its high strength is mainly achieved through precipitation hardening. Gamma double-prime and gamma-prime precipitates strengthen the alloy after suitable heat treatment.
3. Is Inconel 718 heat treatable?
Yes. Inconel 718 is a precipitation-hardenable alloy. Its mechanical properties are developed through controlled solution treatment and ageing procedures.
4. What is the difference between Inconel 718 and Alloy 718?
Inconel 718 and Alloy 718 are commonly used names for the same nickel-based superalloy, generally identified by UNS N07718.
5. Which standards are used for Inconel 718 round bars?
ASTM B637 and relevant aerospace material specifications such as AMS 5662 and AMS 5663 may apply, depending on the product form, condition and purchasing requirement.
6. Does every Inconel 718 round bar have the same mechanical properties?
No. Properties depend on dimensions, manufacturing route, heat-treatment condition and the governing specification. Buyers should verify the material test certificate.
Conclusion
Inconel 718 is an important nickel-based superalloy for engineering applications that require high strength, controlled heat-treatment response and reliable performance under demanding conditions. Its chemical composition and precipitation-hardening mechanism make it suitable for specialised aerospace, energy and industrial applications.
For successful procurement, buyers should verify the exact grade, product form, applicable specification, heat-treatment condition and mechanical test requirements before ordering.
Enquire with Manan Steel & Metals for your Inconel 718 material requirements.
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