Blog 2 — Invar 36 Chemical Composition and Mechanical Properties
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Introduction
Understanding the Invar 36 chemical composition is essential when specifying this low-expansion alloy for precision engineering, dimensional stability and specialised industrial applications. Invar 36 is an iron-nickel alloy containing approximately 36% nickel. It is known for its unusually low thermal expansion over a suitable temperature range.
The material is commonly associated with the designation UNS K93600 and the European material number 1.3912. Buyers and engineers should confirm the exact designation and applicable specification for the product being ordered.
Chemical composition is only one part of material selection. Mechanical properties, heat treatment, product form, operating temperature and fabrication requirements must also be considered. This guide explains the key composition characteristics, mechanical-property considerations and technical checks relevant to Invar 36.
What Is Invar 36 Alloy?
Invar 36 is a nickel-iron alloy developed for applications where dimensional changes caused by temperature variation need to be minimised.
Unlike conventional structural metals selected mainly for strength or corrosion resistance, Invar 36 is often chosen for its low coefficient of thermal expansion. This characteristic can help precision components maintain dimensional stability as temperature changes within the alloy’s suitable operating range.
Common application areas include precision instruments, optical systems, specialised tooling, measuring equipment and certain cryogenic applications. Suitability depends on the actual design, temperature range and mechanical requirements.
Invar 36 Chemical Composition
The chemical composition of Invar 36 helps define its material identity and its characteristic thermal behaviour.
The following table provides a general composition overview, not a substitute for the limits in the applicable product specification or the supplied material test certificate.
| Element | General composition description |
|---|---|
| Nickel (Ni) | Approximately 36% |
| Iron (Fe) | Balance, forming most of the remaining composition |
| Carbon (C) | Controlled residual or specified maximum |
| Manganese (Mn) | Controlled amount, depending on the specification |
| Silicon (Si) | Controlled amount, depending on the specification |
| Other residual elements | Governed by the applicable material specification |
Exact permissible ranges for carbon, manganese, silicon and other elements can vary by specification and product requirements. Always consult the relevant technical datasheet and material certificate before approving material for a critical application.
Why Is Nickel Content Important?
The nickel content is central to Invar 36’s low-expansion behaviour. The iron-nickel alloy composition produces an unusually low coefficient of thermal expansion over a particular temperature range.
However, the material’s thermal behaviour is not determined by nickel content alone. Processing, heat treatment, temperature range and the final material condition can also affect performance.
Why Is Chemical Analysis Important?
Chemical analysis helps confirm whether the supplied material conforms to the specified grade and purchase requirements.
For procurement and quality control, check:
- The stated grade and material designation.
- The applicable specification.
- Reported chemical analysis.
- Heat or lot identification, where applicable.
- Consistency between the certificate and the supplied material.
Do not accept a material solely because its commercial description includes the name “Invar 36.” Verify the documentation required by the purchase order.
Invar 36 Mechanical Properties
The Invar 36 mechanical properties depend on product form, dimensions, material condition, heat treatment and the applicable specification.
For this reason, a single set of tensile strength, yield strength, elongation or hardness values should not be assumed to apply to every Invar 36 round bar, plate or sheet.
The table below explains the principal properties buyers and engineers should review.
| Property | What it means | Why it matters |
|---|---|---|
| Tensile strength | Maximum engineering stress reached during a tensile test | Helps assess material strength under tensile loading |
| Yield strength | Stress associated with the onset of specified permanent deformation | Relevant to components that must resist deformation |
| Elongation | Measure of deformation during a tensile test | Helps evaluate ductility and forming behaviour |
| Hardness | Resistance to local indentation under a defined test | Useful for specified quality checks and processing requirements |
| Elastic modulus | Relationship between stress and elastic strain | Relevant to stiffness calculations and component design |
| Thermal expansion | Change in dimensions with temperature | A key reason Invar 36 is selected for precision applications |
For engineering design, use certified or otherwise authoritative data applicable to the exact product condition and temperature range. Do not use generic internet values as substitutes for the governing specification.
1. Tensile Strength
Tensile strength describes the maximum engineering stress recorded during a tensile test. It is relevant when assessing components subjected to tensile loads.
The required tensile strength should be confirmed from the applicable specification and material condition rather than assumed from the alloy name.
2. Yield Strength
Yield strength indicates the stress associated with the onset of specified permanent deformation. It helps engineers assess whether a component may deform under a planned load.
For precision parts, strength requirements must be evaluated alongside dimensional stability, stiffness, fatigue considerations and the actual service environment.
3. Elongation and Ductility
Elongation is used to evaluate how much a material deforms during a tensile test. Ductility may be important for machining, forming and other fabrication operations.
The required elongation depends on the test method, dimensions, product condition and specification.
4. Hardness
Hardness may be specified for quality control or processing requirements. However, hardness alone does not establish full conformity with the material specification and should not replace required tensile or other tests.
5. Elastic Modulus and Dimensional Stability
Elastic modulus is relevant to stiffness under load. Thermal expansion describes dimensional change as temperature changes.
These are different properties: a material’s low thermal expansion does not mean that it cannot deform under mechanical loading. Both properties should be considered when designing precision components.
Invar 36 Coefficient of Thermal Expansion
The coefficient of thermal expansion describes how much a material expands or contracts when its temperature changes.
Invar 36 is known for a low coefficient of thermal expansion over a defined temperature range. This makes it useful in applications where temperature-driven dimensional changes must be controlled.
The actual coefficient is temperature-dependent. It should be obtained from a suitable technical datasheet or specification that covers the operating range of the component.
Why Does Thermal Expansion Matter?
Even small dimensional changes can be significant in precision equipment. A change in the dimensions of a fixture, measuring component or optical support may affect alignment, calibration or manufacturing tolerances.
Invar 36 can help reduce this source of dimensional change when correctly specified and processed.
However, the material is not completely free from thermal expansion. Engineers should evaluate the full operating temperature range, required tolerances and other sources of dimensional variation.
Factors That Affect Invar 36 Material Properties
Material properties should be evaluated in context rather than treated as fixed values for every supplied product.
Important factors include:
- Product form: Round bar, plate, sheet and other forms may have different requirements.
- Material condition: Processing and heat treatment can affect the resulting properties.
- Operating temperature: Thermal expansion and other characteristics vary with temperature.
- Manufacturing history: Machining, forming and thermal processing may influence dimensional stability.
- Specification requirements: The governing standard determines applicable acceptance criteria.
- Component design: Loads, geometry, constraints and required tolerances influence performance.
For applications requiring exceptionally high dimensional stability, consult a qualified material specialist and use the appropriate processing and stabilisation procedures.
How to Verify Invar 36 Before Purchasing
Before ordering Invar 36 round bar or another product form, confirm the material’s identity and the requirements of the application.
Buyer Verification Checklist
- Confirm the grade name and required designation, such as UNS K93600 where applicable.
- Specify the product form and dimensions.
- Identify the applicable specification and edition.
- State the required material condition.
- Request chemical analysis and relevant mechanical test results where required.
- Confirm traceability and material certificate requirements.
- Review the thermal expansion data relevant to the intended operating range.
- Verify that the proposed material meets the drawing and engineering requirements.
For round bar purchases, also state the required diameter, length, quantity and dimensional tolerances.
Invar 36 Applications and Material Selection
Invar 36 may be selected for precision instruments, optical and laser systems, composite tooling, measuring equipment and certain specialised low-temperature applications.
The selection process should start with the component’s operating requirements. Engineers should consider dimensional stability, mechanical loading, temperature range, fabrication methods, surface finish and environmental exposure.
Where low thermal expansion is a critical design requirement, the specified material condition and processing history may be as important as the alloy designation.
Enquire About Invar 36 with Manan Steel & Metals
Manan Steel & Metals handles industrial metal product enquiries, including enquiries for specialty materials. If your project requires Invar 36 round bar or another product form, provide the exact grade, dimensions, quantity and applicable specification for an availability and requirement review.
To request a quotation, provide:
- Invar 36 product form.
- Required dimensions and quantity.
- Applicable specification and material condition.
- Required material certificate and test documentation.
- Delivery location and expected timeline.
Contact Manan Steel & Metals
- Website: www.manansteel.com
- Email: sales@manansteel.com
- Phone: +91 98198 76962
- Address: Shop No. 2, Hira Building, 97 Khetwadi Main Road (Nanubhai Desai Road), Girgaon, Mumbai – 400004, Maharashtra, India.
Please confirm current availability, product condition, documentation and delivery timelines for the specific order.
Frequently Asked Questions About Invar 36 Properties
What is the chemical composition of Invar 36?
Invar 36 is an iron-nickel alloy containing approximately 36% nickel, with iron forming most of the balance. Exact chemical limits for residual elements must be verified against the applicable specification.
What is the UNS designation for Invar 36?
UNS K93600 is a commonly used designation for Invar 36. Confirm the precise designation and governing specification required for the product.
What are the mechanical properties of Invar 36?
Relevant properties include tensile strength, yield strength, elongation, hardness and elastic modulus. Values depend on product form, condition, heat treatment and specification.
Why does Invar 36 have low thermal expansion?
Its iron-nickel composition produces unusually low thermal expansion over a particular temperature range. The actual behaviour depends on temperature and material condition.
Is Invar 36 suitable for precision engineering?
It can be suitable for applications requiring low thermal expansion and dimensional stability, including selected measuring, optical and tooling components. Suitability must be assessed against the actual operating conditions.
Is Invar 36 stainless steel?
No. Invar 36 is a nickel-iron alloy, not a stainless steel grade.
What documents should I request when purchasing Invar 36?
Depending on the purchase specification, request a material test certificate, chemical analysis, relevant mechanical test results, grade identification and traceability documentation.
Technical References
- Hempel Special Metals — Invar 36 technical information
- Rolled Alloys — Invar 36 technical datasheet
- Manan Steel & Metals — Official website
Use the applicable specification and material documentation for final engineering and purchasing decisions.
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