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Invar 36 Round Bar
Alloy 36
UNS K93603
Invar 36 1.3912
Invar 36 Material
Invar 36 Low Expansion Alloy
Nickel Iron Alloy
Invar 36 Supplier India
ASTM F1684

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Table of Contents

What Is Invar 36?
Why Is Invar 36 Different?
Invar 36 International Designations
Invar 36 Chemical Composition
How Invar 36 Controls Thermal Expansion
Key Properties of Invar 36
Invar 36 Round Bar
Invar 36 Applications
ASTM F1684 and Invar 36
Why Industries Choose Invar 36
What to Check Before Buying Invar 36
Why Source Invar 36 from Manan Steel & Metals?
Frequently Asked Questions
Conclusion

What Is Invar 36?

Invar 36 is a nickel-iron alloy containing approximately 36% nickel and is specifically known for its very low thermal expansion.

Unlike conventional engineering metals, which can undergo noticeable dimensional changes when temperature changes, Invar 36 is designed for applications where maintaining dimensional stability is important.

The alloy is commonly identified as:

Invar 36
Alloy 36
36% Nickel-Iron Alloy
UNS K93603
1.3912
Ni36

Voestalpine identifies Alloy 36 as 1.3912 / Invar 36, with UNS designations in the K93600–K93603 family depending on the specific material form and variant. ASTM F1684 is listed for bar products.

The defining characteristic of Invar 36 is its low coefficient of thermal expansion, making it useful when temperature-related dimensional changes must be minimized.

Why Is Invar 36 Different?

Imagine a precision component manufactured to a very tight dimension.

If that component expands or contracts significantly when its temperature changes, its dimensional accuracy can be affected.

This becomes particularly important in:

Precision instruments
Optical systems
Aerospace tooling
Composite manufacturing
Electronic equipment
Cryogenic systems
Dimensional reference components

Invar 36 addresses this challenge through its controlled nickel-iron composition.

Carpenter Technology describes Invar 36 as a 36% nickel-iron alloy whose thermal expansion rate is approximately one-tenth that of carbon steel at temperatures up to 400°F (204°C).

That makes Invar 36 fundamentally different from ordinary structural metals where thermal expansion may be a more significant design consideration.

Invar 36 International Designations

When purchasing specialty materials internationally, the same material may appear under different names.

Designation	Meaning
Invar 36	Common commercial name
Alloy 36	Alloy designation
36% Ni-Fe	Composition-based description
UNS K93603	UNS designation used for a standard Invar 36 material
1.3912	Material number
Ni36	EN designation
ASTM F1684	Important specification for Invar material

Voestalpine identifies 1.3912, Ni36 and ASTM F1684 for Alloy 36, while Hempel identifies Invar 36 / 1.3912 with UNS K93603.

When requesting a quotation, providing both the commercial name and technical designation helps reduce ambiguity.

Invar 36 Chemical Composition

The primary characteristic of Invar 36 comes from its nickel-iron chemistry.

A representative composition for Invar 36 includes approximately:

Element	Typical / Specification Value
Nickel (Ni)	Approximately 36%
Iron (Fe)	Balance
Carbon (C)	Controlled low level
Silicon (Si)	Controlled
Manganese (Mn)	Controlled
Chromium (Cr)	Controlled low level
Cobalt (Co)	Controlled

For example, Hempel lists nickel at 35.5–36.5% with iron as the balance and controlled limits for other elements for its Invar 36 material.

Carpenter Technology gives a nominal composition of approximately 36% nickel, 0.20% silicon, 0.35% manganese and balance iron for its Invar 36 alloy.

The exact chemistry requirement should always be checked against the applicable material specification and the MTC supplied with the material.

How Invar 36 Controls Thermal Expansion

The most important reason industries use Invar 36 is its unusually low thermal expansion.

Every material changes dimensions to some degree when its temperature changes.

For precision engineering, even a small dimensional change can matter.

Invar 36 has a microstructure and composition that produce exceptionally low thermal expansion around normal operating temperatures.

A technical data sheet from Aperam identifies Invar as an iron-nickel alloy with very low thermal expansion over a broad temperature range and reports a typical coefficient of linear thermal expansion of ≤1.5 × 10⁻⁶/°C between 20°C and 100°C for its referenced material.

This characteristic is commonly referred to as the Invar effect.

Why Does This Matter?

Low thermal expansion can help engineers maintain dimensional stability in components exposed to temperature changes.

This is especially valuable where precision is more important than simply achieving high structural strength.

Key Properties of Invar 36

Invar 36 is primarily selected for its dimensional stability.

Important characteristics include:

Very Low Thermal Expansion

The alloy experiences relatively small dimensional changes with temperature compared with many conventional metals.

Dimensional Stability

This makes it useful for precision components and tooling.

Good Low-Temperature Performance

Technical data from Hempel notes that Invar 36 retains good strength at cryogenic temperatures.

Nickel-Iron Composition

Its approximately 36% nickel content and iron balance are central to its controlled-expansion behaviour.

Machinability

Invar 36 can be machined, although machining procedures should be selected according to the exact material condition and component requirements.

Weldability

The alloy can be fabricated using appropriate procedures, with process controls depending on the application and specification.

Invar 36 Round Bar

Invar 36 Round Bar is a solid cylindrical form of the alloy used as starting material for machined and engineered components.

Round bar can be supplied for applications involving:

Precision shafts
Pins
Bushings
Instrument components
Mechanical components
Optical equipment
Tooling
Fixtures
Precision-machined parts

The required diameter, length, tolerance and condition should be specified when purchasing the material.

Voestalpine lists bar among the forms covered for Alloy 36 and identifies ASTM F1684 as the applicable ASTM standard for bar.

Invar 36 Applications

The low thermal expansion of Invar 36 makes it useful in industries where dimensional accuracy is important.

Aerospace

Invar 36 can be used for aerospace-related tooling and components where dimensional stability during temperature changes is important.

Applications include composite manufacturing tooling and selected aircraft-related components.

Optical and Laser Systems

Optical equipment often requires accurate positioning and stable dimensions.

Carpenter Technology identifies Invar 36 for precision optical and laser measuring structures.

Composite Manufacturing

Invar 36 is widely associated with tooling and dies used to manufacture composite components.

The low expansion helps tooling maintain dimensional accuracy when subjected to temperature changes during manufacturing processes.

Electronics

Invar alloys can be used in selected electronic and radio-related components where controlled thermal expansion is valuable.

Cryogenic Equipment

Invar 36 retains useful mechanical properties at low temperatures and is used for selected cryogenic components.

Precision Instruments

Measurement equipment and dimensional-reference components can benefit from a material whose dimensions remain relatively stable with temperature.

ASTM F1684 and Invar 36

ASTM F1684 is an important specification associated with Invar-type controlled-expansion alloys.

Voestalpine identifies ASTM F1684 for Alloy 36 bar, while Hempel also lists ASTM F1684 for Invar 36.

When purchasing Invar 36 Round Bar, buyers should confirm:

Applicable ASTM specification
UNS designation
Chemical composition
Product form
Dimensions
Material condition
Mechanical requirements
Inspection requirements
Certification requirements

Do not assume that every product sold under the name “Invar 36” automatically has identical specifications.

Technical Reference

ASTM International provides the official standards platform for material specifications and testing standards.

Why Industries Choose Invar 36

The decision to use Invar 36 is generally driven by a specific engineering requirement: controlling dimensional change caused by temperature.

It can be useful when an application requires:

Stable dimensions
Low thermal expansion
Precision manufacturing
Temperature-sensitive tooling
Accurate optical alignment
Controlled movement
Cryogenic dimensional stability

Carpenter Technology identifies aerospace, consumer, defense, industrial and medical applications for Invar 36.

The material is therefore not simply chosen because it is a nickel alloy. Its main value comes from its controlled-expansion behaviour.

What to Check Before Buying Invar 36

Before ordering Invar 36 Round Bar, buyers should provide complete technical information.

Material

Invar 36 / Alloy 36

UNS

Specify the required UNS designation according to the applicable specification.

Standard

For bar requirements, confirm whether ASTM F1684 applies.

Dimensions

Mention:

Diameter
Length
Tolerance

Quantity

State the required number of pieces or approximate weight.

Condition

Mention the required metallurgical condition.

Finish

Specify whether the requirement is for a particular surface finish.

Documentation

Mention whether an MTC or inspection certificate is required.

Application

If the component is for aerospace tooling, optical equipment, cryogenic equipment or another precision application, include this information in the enquiry.

Why Source Invar 36 from Manan Steel & Metals?

Manan Steel & Metals lists Invar 36 Round Bars among its specialty round-bar products.

For industrial requirements, buyers can provide the complete material specification along with:

Required diameter
Length
Quantity
Applicable standard
Condition
Finish
Testing requirements
Certificate requirements
Delivery location

This allows the requirement to be reviewed before quotation.

Manan Steel & Metals

Shop No. 2, Hira Building
97 Khetwadi Main Road (Nanubhai Desai Road)
Girgaon, Mumbai – 400004
Maharashtra, India

Phone: 7977369869
Email: manansteel@gmail.com
Website: https://www.manansteel.com/

Related Resources

Manan Steel & Metals – Round Bar Products

Manan Steel & Metals – Invar 36 Round Bar

For independent technical information, see Carpenter Technology – Invar 36 and voestalpine Specialty Metals – Alloy 36.

Frequently Asked Questions

What is Invar 36?

Invar 36 is a nickel-iron alloy containing approximately 36% nickel and known for its very low coefficient of thermal expansion.

What is the UNS number of Invar 36?

UNS designations can vary by specific Invar material variant. UNS K93603 is associated with standard Invar 36 material covered by ASTM F1684.

What is the Werkstoff number of Invar 36?

The commonly associated material number is 1.3912.

What is Invar 36 used for?

Invar 36 is used for applications requiring low thermal expansion and dimensional stability, including aerospace tooling, optical systems, electronics, precision instruments and cryogenic components.

Why is Invar 36 called a low-expansion alloy?

Its approximately 36% nickel-iron composition produces unusually low thermal expansion over important operating temperature ranges.

Is Invar 36 a stainless steel?

No. Invar 36 is a nickel-iron alloy, not a conventional stainless-steel grade.

Is Invar 36 available as round bar?

Yes. Alloy 36 is available in bar and round forms, with ASTM F1684 identified for bar applications.

What is ASTM F1684?

ASTM F1684 is a specification associated with controlled-expansion iron-nickel alloys such as Invar 36.

Is Invar 36 suitable for cryogenic applications?

Invar 36 is used for selected cryogenic components and retains useful strength at low temperatures. The actual suitability should be verified against the specific service conditions and engineering specification.

What information should I provide when buying Invar 36 Round Bar?

Provide the material designation, UNS designation, applicable standard, diameter, length, quantity, condition, finish, testing requirements, certification requirements and delivery location.

Conclusion

Invar 36 is a specialized nickel-iron alloy whose main advantage is its very low thermal expansion and resulting dimensional stability.

Known internationally as Alloy 36, 1.3912, Ni36 and, for relevant material specifications, UNS K93603, it is used in applications where temperature-related dimensional changes need to be minimized.

Its applications include:

Aerospace tooling
Composite forming tools
Optical systems
Laser equipment
Precision instruments
Electronics
Cryogenic components
Specialized industrial equipment

For Invar 36 Round Bar, the material designation, applicable specification, dimensions, condition and documentation should be clearly stated before ordering.

If you are sourcing Invar 36 Round Bar in India, send your required diameter, length, quantity, specification and delivery location to Manan Steel & Metals.

Request an Invar 36 Quotation

Manan Steel & Metals
Shop No. 2, Hira Building,
97 Khetwadi Main Road (Nanubhai Desai Road),
Girgaon, Mumbai – 400004, Maharashtra, India