Invar 36 Alloy: Properties, Specifications and Industrial Buying Guide
Invar 36 Alloy Invar 36 is a specialised nickel-iron alloy recognised for its exceptionally low coefficient of thermal expansion. Unlike conventional engineering metals, which expand and contract noticeably with temperature changes, Invar 36 maintains relatively stable dimensions across a useful temperature range.
This characteristic makes Invar 36 alloy an important material for precision engineering, aerospace tooling, optical equipment, measuring instruments and selected cryogenic applications.
Also known as Alloy 36, FeNi36 and 1.3912, Invar 36 typically contains approximately 36% nickel, with iron forming the balance. Its dimensional stability makes it valuable in applications where even small changes in component dimensions can affect performance.
This guide covers Invar 36 properties, composition, applications, product forms, material identification and important procurement considerations for industrial buyers.
What Is Invar 36 Alloy?
Invar 36 is a nickel-iron alloy developed for applications requiring very low thermal expansion.
Its most important characteristic is its ability to minimise dimensional changes when temperatures vary. This property is particularly useful in precision components, where dimensional accuracy must be maintained under changing environmental conditions.
Common material designations include:
- Invar 36
- Alloy 36
- FeNi36
- UNS K93600
- UNS K93603
- Werkstoff Number 1.3912
Different designations and specifications may apply to particular product forms or material conditions. Buyers should verify the exact designation against the purchase specification and material certificate.
Key Properties of Invar 36
Invar 36 is selected primarily for its dimensional stability rather than simply for conventional strength or corrosion resistance.
1. Low Coefficient of Thermal Expansion
The defining property of Invar 36 is its low thermal expansion.
It expands and contracts considerably less than ordinary carbon steel over certain temperature ranges. This helps precision components maintain their dimensions when exposed to temperature variation.
2. Dimensional Stability
Dimensional stability is essential in equipment where small changes in size can affect accuracy or alignment.
Invar 36 is therefore considered for measuring instruments, precision tooling, optical assemblies and other specialised components.
3. Cryogenic Performance
Invar 36 retains useful strength and toughness at cryogenic temperatures. This makes it relevant to selected low-temperature engineering applications.
4. Machinability
Invar 36 can be machined using suitable conventional metalworking processes. Tool selection, cutting conditions and material condition should be considered to achieve the required dimensional accuracy and surface finish.
5. Fabrication and Welding
The alloy can be formed and welded using appropriate procedures and compatible filler materials. Fabrication practices should be selected according to the component design and service requirements.
Invar 36 Chemical Composition
The chemical composition of Invar 36 is responsible for its distinctive low-expansion behaviour.
The alloy typically contains approximately 36% nickel, with iron forming the balance. Other elements are controlled within limits specified by the applicable material specification or manufacturer.
| Element | Typical composition information |
|---|---|
| Nickel (Ni) | Approximately 35–37% in commonly referenced specifications |
| Iron (Fe) | Balance |
| Manganese (Mn) | Controlled residual/alloying addition |
| Silicon (Si) | Controlled limit |
| Carbon (C) | Controlled limit |
| Chromium (Cr) | Controlled limit |
| Cobalt (Co) | Controlled limit |
| Phosphorus (P) | Controlled limit |
| Sulphur (S) | Controlled limit |
Exact limits can vary with the governing specification, producer and product form. The applicable material standard and heat-specific Material Test Certificate should be used for acceptance.
Invar 36 Thermal Expansion Characteristics
Thermal expansion describes how much a material changes in size when its temperature changes.
For many ordinary metals, temperature increases cause noticeable expansion. Invar 36 is different because its nickel-iron composition produces an unusually low coefficient of thermal expansion over a specific temperature range.
This characteristic is important in:
- Precision measuring equipment
- Optical and laser assemblies
- Aerospace composite tooling
- Dimensional reference components
- Cryogenic equipment
- Temperature-sensitive instruments
The coefficient of thermal expansion is not a single universal value across all temperatures. It varies with temperature, material condition and processing history.
For critical engineering calculations, use the manufacturer’s technical data for the actual material condition and operating temperature.
Invar 36 Mechanical and Physical Characteristics
Invar 36 provides a useful combination of mechanical characteristics and low thermal expansion.
Typical published data for annealed material can include tensile strength around 490 MPa, yield strength around 240–260 MPa and elongation above 30%. These are indicative values from particular supplier data and are not universal acceptance limits.
| Characteristic | General information |
|---|---|
| Material family | Nickel-iron alloy |
| Nickel content | Approximately 36% |
| Density | Approximately 8.0–8.1 g/cm³ |
| Thermal expansion | Very low over a specific temperature range |
| Structure | Austenitic nickel-iron alloy |
| Machining | Possible with suitable tooling and conditions |
| Welding | Possible using suitable procedures and filler |
| Cryogenic behaviour | Retains useful strength and toughness |
Actual mechanical properties depend on the material condition, dimensions, manufacturing route and governing specification.
Industrial Applications of Invar 36
Invar 36 is used in specialised applications where dimensional stability is more important than selecting a conventional general-purpose metal.
1. Aerospace Composite Tooling
Composite manufacturing often requires tooling that maintains dimensional accuracy during temperature changes in the production process.
Invar 36 is used in selected moulds, tools and dies for aerospace composite structures.
2. Precision Measuring Instruments
Measuring systems and dimensional reference equipment can be sensitive to thermal expansion.
Invar 36 helps minimise dimensional changes in components used for precision measurement.
3. Optical and Laser Equipment
Optical assemblies may require stable positioning and alignment. Invar 36 can be considered for selected structural and support components where thermal dimensional stability is important.
4. Cryogenic Equipment
The alloy’s low thermal expansion and useful low-temperature mechanical characteristics make it relevant to selected cryogenic components and equipment.
5. Instrumentation and Electronics
Specialised instruments and electronic assemblies may use Invar 36 where dimensional stability helps maintain component alignment or measurement accuracy.
Invar 36 Available Product Forms
Invar 36 is used in different semi-finished product forms depending on the intended component and manufacturing process.
| Product form | Typical industrial requirements |
|---|---|
| Invar 36 Round Bars | Precision machining and engineering components |
| Invar 36 Rods | Turned parts and specialised components |
| Invar 36 Sheets | Formed components and precision assemblies |
| Invar 36 Plates | Tooling, dies and fabricated structures |
| Invar 36 Flats | Specialised fabrication and machining |
| Invar 36 Strips | Precision components and formed parts |
| Invar 36 Tubes | Selected specialised engineering applications |
Product availability, dimensions, tolerances and supply condition should be confirmed for each requirement.
Invar 36 Standards and Material Identification
Invar 36 may be identified using different material designations depending on the applicable specification and product form.
Common references include:
- UNS K93600 and related Invar 36 designations: Used for material identification in technical and procurement documentation.
- Werkstoff Number 1.3912: A commonly used European material designation.
- FeNi36: A general nickel-iron alloy designation.
- ASTM F1684: A historical specification reference associated with iron-nickel and iron-nickel-cobalt controlled-expansion alloys.
Do not assume that an older specification reference automatically represents a current purchasing requirement. Confirm the latest applicable standard status, product form and revision with the buyer’s engineering team and supplier before placing an order.
For technical verification, consult ASTM International and the relevant manufacturer’s material data sheet.
Important Factors Before Purchasing Invar 36
Invar 36 is a specialised material, so buyers should provide clear technical information before requesting a quotation.
1. Confirm the Exact Grade
Specify Invar 36, Alloy 36 or FeNi36 as applicable. Confirm the required UNS or other designation against the drawing or purchase specification.
2. Specify the Product Form
Mention whether the requirement is for round bars, rods, sheets, plates, flats or another product form.
3. Provide Exact Dimensions
Include diameter, thickness, width and length, together with any required dimensional tolerances.
4. Confirm Material Condition
Material condition and manufacturing history can influence dimensional stability and mechanical properties. Specify the required condition where the application demands it.
5. Check Thermal Requirements
Provide the intended operating temperature range and dimensional stability requirements. This is particularly important for precision and cryogenic applications.
6. Request Material Documentation
Ask for the relevant Material Test Certificate and check grade identification, heat number and reported chemical composition.
7. Verify Application Suitability
Invar 36 is not a general replacement for stainless steel or nickel-based corrosion-resistant alloys. Its selection should be based on thermal expansion requirements, mechanical performance and the service environment.
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 material specification.
Our team can assist with understanding the material requirement and quotation process.
Explore Manan Steel & Metals or contact our team through the contact page for Invar 36 product enquiries.
Frequently Asked Questions About Invar 36
1. What is Invar 36 alloy used for?
Invar 36 is used in aerospace composite tooling, precision measuring instruments, optical systems, laser components, instrumentation and selected cryogenic applications.
2. What is the composition of Invar 36?
Invar 36 is a nickel-iron alloy containing approximately 36% nickel, with iron forming the balance. Other elements are controlled according to the applicable material specification.
3. Why does Invar 36 have low thermal expansion?
Its particular nickel-iron composition produces an unusually low coefficient of thermal expansion over a specific temperature range, helping components maintain dimensional stability.
4. Is Invar 36 stainless steel?
No. Invar 36 is a nickel-iron controlled-expansion alloy, not a chromium-based stainless steel grade. Its primary purpose is low thermal expansion rather than general corrosion resistance.
5. Can Invar 36 be machined?
Yes. It can be machined using suitable tooling and metal-cutting processes. Cutting conditions and material condition should be considered to achieve the required accuracy.
6. Can Invar 36 be welded?
Yes. Invar 36 can be welded using suitable procedures and compatible filler materials. Welding requirements should be confirmed for the particular joint and application.
7. What are the common designations for Invar 36?
Commonly encountered designations include Alloy 36, FeNi36, UNS K93600, related UNS designations and Werkstoff Number 1.3912. The correct designation should be verified against the applicable specification.
Conclusion
Invar 36 is a specialised nickel-iron alloy designed for applications requiring exceptionally low thermal expansion and dimensional stability. Its use in precision tooling, aerospace composite manufacturing, optical equipment, instrumentation and cryogenic engineering makes it an important material for specialised industrial requirements.
Before purchasing, confirm the grade designation, product form, dimensions, material condition and applicable specification. For Invar 36 enquiries, contact Manan Steel & Metals with your technical and dimensional requirements.