Invar 36 Chemical Composition, Thermal Expansion & Mechanical Properties
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Invar 36 thermal expansion, Invar 36 properties, Invar 36 mechanical properties, Invar 36 chemical composition, Alloy 36 composition, UNS K93603, UNS K93601, 1.3912 Invar, Ni36 alloy, ASTM F1684, ASTM B753, Invar 36 round bar
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Table of Contents
- What Is Invar 36?
- Invar 36 Chemical Composition
- Why Nickel Content Matters in Invar 36
- Invar 36 Thermal Expansion
- Physical Properties of Invar 36
- Invar 36 Mechanical Properties
- Invar 36 International Designations and Standards
- Why Thermal Stability Matters in Engineering
- Buying Invar 36: What Specifications Should You Check?
- Why Source Invar 36 from Manan Steel & Metals?
- Frequently Asked Questions
- Conclusion
What Is Invar 36?
Invar 36 is a nickel-iron alloy developed for applications where dimensional stability is important when temperature changes.
It is commonly known as Alloy 36, Ni36, and 1.3912 Invar. Depending on the product form, grade and applicable specification, UNS designations such as K93600, K93601 and K93603 may appear in technical documentation.
The defining characteristic of Invar 36 is its exceptionally low thermal expansion compared with conventional engineering metals. Carpenter Technology describes Invar 36 as a 36% nickel-iron alloy whose thermal expansion is approximately one-tenth that of carbon steel up to about 204°C (400°F).
This makes the alloy useful when a component must maintain close dimensional tolerances despite temperature fluctuations.
Invar 36 Chemical Composition
The chemical composition of Invar 36 is primarily based on nickel and iron, with controlled quantities of carbon, manganese and silicon.
A published material specification from Hempel Special Metals gives the following composition for Invar 36 under ASTM F1684:
| Element | Typical / Maximum Content |
|---|---|
| Nickel (Ni) | 35.5–36.5% |
| Carbon (C) | 0.01% max |
| Silicon (Si) | 0.20% max |
| Manganese (Mn) | 0.20–0.40% |
| Sulfur (S) | 0.002% max |
| Phosphorus (P) | 0.07% max |
| Chromium (Cr) | 0.15% max |
| Cobalt (Co) | 0.50% max |
| Iron (Fe) | Balance |
Other producers and specifications may publish somewhat different chemistry limits. For example, Carpenter Technology lists nominal values of approximately 36% nickel, 0.35% manganese, 0.20% silicon and 0.02% carbon, with iron as the balance.
Important: When purchasing Invar 36, the chemical composition should always be checked against the exact material specification and supplied Mill Test Certificate (MTC) rather than relying only on a generic online composition table.
Why Nickel Content Matters in Invar 36
The approximately 36% nickel content is central to the low-expansion behavior of Invar 36.
The alloy’s unusual dimensional stability results from the interaction between its magnetic and lattice characteristics. This phenomenon is commonly associated with the Invar effect.
Rather than simply being a high-strength alloy, Invar 36 is engineered for a special physical property: controlled and very low thermal expansion.
That distinction is important when selecting materials for precision applications.
Invar 36 Thermal Expansion
Thermal expansion describes how much a material changes dimension when its temperature changes.
For ordinary metals, heating normally causes measurable expansion. In precision equipment, even a small dimensional change can affect alignment, calibration, positioning or component fit.
Invar 36 is different.
Its thermal expansion is very low over an important temperature range. Carpenter Technology states that its expansion is approximately one-tenth that of carbon steel up to around 204°C.
Published data from voestalpine shows that the coefficient of expansion increases progressively with temperature:
| Temperature | Published Expansion Coefficient* |
|---|---|
| 50°C | 0.8 × 10⁻⁶ m/m·K |
| 100°C | 1.2 × 10⁻⁶ m/m·K |
| 150°C | 1.6 × 10⁻⁶ m/m·K |
| 200°C | 2.2 × 10⁻⁶ m/m·K |
| 300°C | 4.5 × 10⁻⁶ m/m·K |
| 400°C | 7.5 × 10⁻⁶ m/m·K |
| 500°C | 9.2 × 10⁻⁶ m/m·K |
| 600°C | 10.7 × 10⁻⁶ m/m·K |
*Published values are product/data-source specific and should be checked against the applicable material certificate and specification.
This is why Invar 36 should not simply be described as a material that “does not expand.” It does expand, but its expansion is unusually low within its useful temperature range.
Physical Properties of Invar 36
Physical properties can vary slightly according to product form, processing route and test condition.
Published data for Ni36 / 1.3912 includes:
| Property | Typical Published Value |
|---|---|
| Density | Approximately 8.2 g/cm³ |
| Thermal Conductivity at 20°C | Approximately 13 W/m·K |
| Electrical Resistivity | Approximately 0.76 Ω·mm²/m |
| Material Type | Nickel-Iron Low-Expansion Alloy |
| Nickel Content | Approximately 36% |
These properties help explain why Invar 36 is used in applications requiring both mechanical integrity and dimensional control.
Invar 36 Mechanical Properties
Although thermal expansion is the main reason engineers select Invar 36, mechanical properties are also important during machining, fabrication and service.
Published room-temperature values for annealed Invar 36 include:
| Mechanical Property | Typical Published Value |
|---|---|
| Yield Strength | Approximately 270 MPa |
| Tensile Strength | Approximately 440–640 MPa |
| Elongation | ≥30% depending on specification |
| Brinell Hardness | Approximately 130–170 HB |
Another published Invar 36 data source gives annealed/descaled material with a tensile strength of approximately 430 MPa and elongation above 30%, demonstrating why values should always be connected to the relevant specification and material condition.
Why Material Condition Matters
Annealed, cold-worked, machined and otherwise processed material may not have identical mechanical properties.
Therefore, a procurement specification should identify:
- Material grade
- Applicable standard
- Product form
- Size
- Heat treatment or condition
- Chemical composition
- Mechanical requirements
- Inspection requirements
- MTC requirements
Invar 36 International Designations and Standards
International buyers may use different terminology when searching for the same family of material.
| Designation | Reference |
|---|---|
| Invar 36 | Common commercial name |
| Alloy 36 | Common alloy designation |
| Ni36 | European designation |
| 1.3912 | Werkstoff number |
| UNS K93600 | Listed for Ni36 / Alloy 36 by some suppliers |
| UNS K93601 / K93603 | Associated with Invar 36 by Carpenter Technology |
| ASTM F1684 | Common specification associated with Invar materials |
| ASTM B753 | Also associated with certain Invar 36 products/forms |
A Note About UNS Numbers
Buyers should be careful when searching only by UNS number.
Different published sources associate different UNS numbers with Invar 36 depending on product type, variant and specification. For example, Carpenter lists K93601/K93603, while voestalpine lists K93600 for Ni36 / 1.3912.
Therefore, the safest procurement practice is to specify the material name + applicable standard + product form + required certification, rather than relying on a single designation alone.
Why Thermal Stability Matters in Engineering
Temperature-related dimensional movement can become a major engineering issue when components require precise positioning.
Invar 36 can therefore be considered for applications such as:
- Precision measuring equipment
- Optical and laser systems
- Electronic components
- Aerospace tooling
- Aircraft control components
- Temperature-sensitive assemblies
- Cryogenic equipment
- Composite forming tools
- Precision mechanical components
Carpenter Technology and Hempel Special Metals both identify aerospace, optical, electronic and industrial applications for Invar 36.
The material is particularly relevant where dimensional stability is more important than simply maximizing strength.
Buying Invar 36: What Specifications Should You Check?
When purchasing Invar 36 round bars or other forms, do not evaluate the material only by its name.
A professional purchase specification should include:
1. Material Designation
Clearly state:
Invar 36 / Alloy 36 / Ni36 / 1.3912
and identify the applicable UNS or specification where required.
2. Product Form
Specify whether you require:
- Round bar
- Flat bar
- Square bar
- Sheet
- Plate
- Wire
- Billet
- Machined component
3. Applicable Standard
Confirm the required ASTM, EN or other applicable standard before placing the order.
For example, published industry data associates ASTM F1684 with Invar materials, while ASTM B753 is also listed for certain Alloy 36 products.
4. Size and Quantity
Always provide the required:
- Diameter or dimensions
- Length
- Quantity
- Cut length requirements
- Tolerance
5. Material Test Certificate
For industrial procurement, request an MTC showing relevant chemical and mechanical test results against the agreed specification.
6. Surface and Delivery Requirements
Depending on the application, buyers may also need to specify:
- Surface condition
- Straightness
- Machining allowance
- Packing
- Inspection requirements
- Certification requirements
Why Source Invar 36 from Manan Steel & Metals?
Manan Steel & Metals supplies special and industrial metal products for customers requiring specific material grades and dimensions.
Our product range includes Invar 36 Round Bars, making the material available for industrial procurement and engineering requirements.
You can explore our round bar product range here:
Manan Steel & Metals Round Bars:
https://manansteel.com/round-bar-manufacturer-supplier/
For company information and other industrial metal products:
Manan Steel & Metals:
https://www.manansteel.com/
When sending an enquiry, provide the material name, size, quantity, required standard and certification requirements. This helps us understand your requirement and respond with the appropriate commercial details.
Frequently Asked Questions
What is the chemical composition of Invar 36?
Invar 36 is primarily an iron-nickel alloy containing approximately 36% nickel, with controlled quantities of carbon, silicon, manganese and other elements depending on the applicable specification.
Why does Invar 36 have low thermal expansion?
Its low thermal expansion is associated with the special physical behavior of its nickel-iron composition and the Invar effect, making it suitable for applications where temperature-related dimensional movement needs to be minimized.
What is the thermal expansion of Invar 36?
Invar 36 has a very low coefficient of thermal expansion over its useful low-expansion temperature range. Published values vary with temperature, product and specification, so the applicable technical data should be checked for the exact material being purchased.
Is Invar 36 the same as 1.3912?
1.3912 is a Werkstoff designation associated with Ni36 / Alloy 36 / Invar materials. The exact specification should still be confirmed on the purchase order and MTC.
What is the UNS number for Invar 36?
Published sources associate Invar 36 with several UNS designations depending on product and specification, including K93600, K93601 and K93603.
Which ASTM standards are associated with Invar 36?
ASTM F1684 and ASTM B753 are both associated with Invar/Alloy 36 materials in published industry references. The correct standard depends on the specific product and specification.
Is Invar 36 suitable for precision engineering?
Yes. Its low thermal expansion and dimensional stability make it useful in precision measuring equipment, optical systems, electronics, aerospace tooling and other applications where temperature-related dimensional changes need to be controlled.
Conclusion
Invar 36 chemical composition and thermal expansion characteristics are the key reasons this nickel-iron alloy is selected for precision applications.
Its approximately 36% nickel content, low coefficient of thermal expansion and useful mechanical properties make Invar 36 / Alloy 36 / Ni36 / 1.3912 an important material for applications where dimensional stability matters.
However, published chemical and mechanical values can vary according to specification, product form and material condition. For industrial procurement, the correct approach is to confirm the required standard, dimensions, condition and certification before ordering.
If you are looking for Invar 36 Round Bar for an industrial or engineering requirement, contact Manan Steel & Metals with your required size and quantity.
Manan Steel & Metals
Shop No. 2, Hira Building, 97 Khetwadi Main Road,
Girgaon, Mumbai – 400004, Maharashtra, India
Phone: 7977369869
Email: manansteel@gmail.com
Website: https://www.manansteel.com/
Technical References
- Carpenter Technology – Invar 36: https://www.carpentertechnology.com/alloy-finder/invar-36
- Hempel Special Metals – Invar 36: https://www.hempel-metals.com/en/material/exotic-metals/invar-36
- voestalpine Specialty Metals – Ni36 / 1.3912 / Alloy 36: https://www.voestalpine.com/specialtymetals/eu/en/ni-36-1.3912/