Invar 36 Chemical Composition, Mechanical Properties and Thermal Expansion
Invar 36 Chemical Composition & Mechanical Properties
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Image caption: Invar 36 nickel-iron alloy with low thermal expansion for precision engineering applications.
Invar 36 is a specialised nickel-iron alloy known for its exceptionally low coefficient of thermal expansion over a specific temperature range. This characteristic makes it valuable in precision engineering, aerospace tooling, optical equipment, instrumentation and selected cryogenic applications.
Understanding the Invar 36 chemical composition and mechanical properties is essential when selecting this alloy for components that require dimensional stability, predictable performance and accurate material identification.
Also known as Alloy 36 and FeNi36, Invar 36 typically contains approximately 36% nickel, with iron forming the balance. Its performance depends on its composition, heat treatment, manufacturing history and operating temperature.
This technical guide explains its composition, mechanical characteristics, thermal expansion behaviour and important material verification requirements.
What Is the Chemical Composition of Invar 36?
Invar 36 is primarily a nickel-iron controlled-expansion alloy. Its low thermal expansion behaviour is associated with the specific balance of nickel and iron.
The following table gives an indicative composition range commonly associated with Invar 36. Exact limits must be confirmed against the applicable product specification and manufacturer’s certificate.
| Element | Typical composition information |
|---|---|
| Nickel (Ni) | Approximately 35–37% |
| Iron (Fe) | Balance |
| Carbon (C) | Controlled, low limit |
| Manganese (Mn) | Controlled addition |
| Silicon (Si) | Controlled limit |
| Chromium (Cr) | Controlled limit |
| Cobalt (Co) | Controlled limit |
| Phosphorus (P) | Controlled limit |
| Sulphur (S) | Controlled limit |
The exact permitted values for minor elements vary according to the governing specification and product form. Buyers should not use indicative values as a substitute for the material standard or heat-specific Material Test Certificate.
Why Does Nickel Content Matter in Invar 36?
Nickel is the key alloying element responsible for the distinctive thermal expansion behaviour of Invar 36.
At approximately 36% nickel, the nickel-iron alloy exhibits unusually low thermal expansion over a particular temperature range.
This makes the material useful in applications where temperature-related dimensional changes must be minimised.
Role of Iron in Invar 36
Iron forms the balance of the alloy and contributes to its overall metallurgical structure and mechanical characteristics.
The nickel-iron balance is important because changes in composition can influence thermal expansion behaviour and other material properties.
Invar 36 Mechanical Properties
Mechanical properties describe how a material behaves when subjected to forces, deformation and loading.
For Invar 36, these properties can vary depending on:
- Annealed or cold-worked condition
- Product form and dimensions
- Manufacturing route
- Heat treatment
- Testing method
- Applicable material specification
Indicative published data for annealed material may include the following values. These should be treated as reference figures rather than guaranteed acceptance requirements.
| Mechanical property | Indicative information |
|---|---|
| Tensile strength | Around 490 MPa |
| Yield strength | Around 240–260 MPa |
| Elongation | Often above 30% |
| Hardness | Depends on material condition |
| Density | Approximately 8.0–8.1 g/cm³ |
Always obtain the mechanical test results for the actual supplied product and condition before using the material in a critical engineering design.
1. Tensile Strength
Tensile strength measures the maximum stress a material can withstand during a tensile test before failure.
Invar 36 offers useful tensile properties for precision components and specialised fabricated assemblies. The actual value depends on the material condition and product form.
2. Yield Strength
Yield strength indicates the stress at which permanent deformation begins under a specified test method.
Engineers should use the certified value for the actual material condition when calculating component loads and design margins.
3. Elongation
Elongation measures how much a material stretches before fracture.
It provides an indication of ductility and is relevant when evaluating forming, bending and fabrication requirements.
4. Hardness
Hardness varies according to annealing, cold working and other processing conditions. It should be verified using the required test method rather than assumed from the alloy designation alone.
Invar 36 Thermal Expansion Characteristics
The most important feature of Invar 36 is its low coefficient of thermal expansion.
The coefficient of thermal expansion measures the change in a material’s dimensions as its temperature changes.
Many metals expand noticeably when heated. Invar 36 exhibits significantly lower expansion over a specific temperature range, which makes it suitable for applications where dimensional accuracy is critical.
Why Is Low Thermal Expansion Important?
In precision engineering, even a small dimensional change can affect the alignment, accuracy or performance of a component.
For example:
- Measuring instruments require dimensional stability for accurate readings.
- Optical equipment requires stable component positioning.
- Aerospace composite tooling needs dimensional consistency during controlled manufacturing cycles.
- Precision fixtures may need to maintain alignment across temperature changes.
Invar 36 helps address these requirements by minimising thermal dimensional changes within its useful temperature range.
Does Invar 36 Have the Same Thermal Expansion at Every Temperature?
No. Its coefficient of thermal expansion varies with temperature and material condition.
The alloy’s low-expansion behaviour is most useful within a particular temperature range. It should not be assumed to maintain the same coefficient across all operating temperatures.
For precision calculations, engineers should obtain temperature-dependent expansion data from the material producer for the exact grade and condition.
Invar 36 Physical Properties
The following table summarises general physical characteristics of Invar 36.
| Physical characteristic | General information |
|---|---|
| Material family | Nickel-iron alloy |
| Nickel content | Approximately 36% |
| Density | Approximately 8.0–8.1 g/cm³ |
| Thermal expansion | Exceptionally low over a specific temperature range |
| Magnetic behaviour | Generally ferromagnetic |
| Electrical resistivity | Depends on temperature and material condition |
| Thermal conductivity | Depends on temperature and material condition |
These are general material characteristics, not substitutes for certified technical data.
Factors That Influence Invar 36 Properties
The performance of Invar 36 is not determined by chemical composition alone.
Several manufacturing and operating factors can influence its behaviour.
1. Heat Treatment
Heat treatment can influence residual stress, dimensional stability and mechanical properties.
For precision components, the selected heat-treatment procedure should be compatible with the intended dimensional tolerances and service conditions.
2. Cold Working
Cold working can change hardness, strength and dimensional behaviour.
The material condition should therefore be specified when the application requires consistent performance.
3. Machining
Machining can introduce residual stresses or local heating. These factors may affect dimensional accuracy in precision components.
Suitable cutting conditions, machining sequence and stress-relief practices should be considered where required.
4. Operating Temperature
The alloy’s thermal expansion characteristics vary with temperature. Engineers should evaluate the full operating range rather than relying on one reference value.
Invar 36 Standards and Material Identification
Invar 36 may be identified by several designations depending on the applicable material specification.
Common designations include:
- Invar 36
- Alloy 36
- FeNi36
- UNS K93600 and related grade designations
- Werkstoff Number 1.3912
A commonly referenced specification is ASTM F1684, covering iron-nickel and iron-nickel-cobalt controlled-expansion alloys. Its current status, applicable grade and product requirements should be confirmed before specifying it in a purchase order.
For technical and standards verification, consult ASTM International, Special Metals and Goodfellow.
How to Verify Invar 36 Chemical Composition and Properties Before Buying
Industrial buyers should verify the supplied material against the actual project specification.
Important checks include:
- Grade identification: Confirm Invar 36 or the specified equivalent designation.
- Chemical composition: Check the reported nickel, iron and minor-element values.
- Mechanical test results: Review tensile strength, yield strength and elongation where specified.
- Thermal expansion data: Request suitable technical data for applications requiring dimensional stability.
- Product form: Confirm whether the requirement is for round bars, sheets, plates, flats or another form.
- Material condition: Specify annealed, cold-worked or other required conditions where relevant.
- Traceability: Verify the heat number and corresponding Material Test Certificate.
For precision engineering, the thermal expansion data and material condition may be just as important as the chemical composition.
Invar 36 Material Enquiries at Manan Steel & Metals
Manan Steel & Metals, Mumbai, deals in specialty metals and engineering materials for industrial requirements.
For Invar 36 enquiries, buyers can share their required product form, dimensions, quantity and technical specification.
When requesting a quotation, mention whether the application requires specific thermal expansion characteristics, mechanical test results or material documentation.
Visit Manan Steel & Metals or contact our team through the contact page for product enquiries.
Frequently Asked Questions About Invar 36 Properties
1. What is the chemical composition of Invar 36?
Invar 36 is a nickel-iron alloy containing approximately 36% nickel, with iron forming the balance. Minor elements are controlled according to the applicable material specification.
2. What is the tensile strength of Invar 36?
Published values for annealed material can be around 490 MPa, but the actual tensile strength depends on the product form, material condition and governing specification.
3. What makes Invar 36 have low thermal expansion?
Its specific nickel-iron composition produces an unusual metallurgical effect that results in very low thermal expansion over a particular temperature range.
4. What is the density of Invar 36?
Its density is approximately 8.0–8.1 g/cm³, although the value used for engineering calculations should be confirmed against the producer’s technical data.
5. Is Invar 36 magnetic?
Yes. Invar 36 is generally ferromagnetic because of its iron-rich nickel-iron composition.
6. Does Invar 36 retain its low expansion at every temperature?
No. Its thermal expansion coefficient changes with temperature. Engineers should use temperature-dependent technical data for the intended operating range.
7. What documents should be requested when purchasing Invar 36?
Buyers should request a relevant Material Test Certificate containing grade identification, heat number and chemical composition. Mechanical test results and thermal expansion data should also be requested when required by the application.
Conclusion
Invar 36 is a specialised nickel-iron alloy valued for its exceptionally low thermal expansion and dimensional stability. Its chemical composition, mechanical characteristics and temperature-dependent behaviour make it useful for precision engineering, aerospace tooling, instrumentation and selected cryogenic applications.
Before selecting or purchasing the alloy, verify its composition, material condition, mechanical properties and thermal expansion data against the actual application requirements.
For Invar 36 material enquiries, contact Manan Steel & Metals with your required product form, dimensions and technical specifications.