Invar 36: Indispensable for Precision Industrial Applications Thanks to Its Low Thermal Expansion
Invar 36 is a nickel–iron based alloy that stands out for its low thermal expansion, high mechanical strength and machinability. Thanks to these properties it has a wide range of applications in both industrial and scientific fields.
Chemical Composition and Microstructure of Invar 36
Invar 36 is a nickel–iron alloy containing roughly 36% nickel (Ni) with the balance iron (Fe). That specific ratio allows the alloy to reach an abnormally low coefficient of thermal expansion. The chemical composition of the alloy is generally as follows:
- Iron (Fe): 63–64%
- Nickel (Ni): 35–36%
- Carbon (C): ≤0.1%
- Manganese (Mn), Silicon (Si), Sulphur (S): may be present in very low proportions
This composition reduces the linear coefficient of expansion to values as low as 1.2 x 10⁻⁶ /°C, particularly in the 20–100 °C range. Microstructurally, Invar 36 shows a homogeneous and balanced crystal structure, which keeps its thermal expansion behaviour consistent.
Mechanical and Physical Properties of Invar 36
The basic mechanical properties of Invar 36 matter for the durability and machinability of the alloy. Typical properties are as follows:
- Tensile strength: between 450 and 700 MPa, varying with the application and the heat treatment
- Yield strength: between 250 and 450 MPa
- Elongation: around 20%
- Hardness: 150–220 HB (Brinell hardness)
- Density: 8.1 g/cm³
- Electrical resistivity: 0.83 μΩ·m
In addition, the thermal conductivity of Invar 36 is relatively low, and its magnetic properties widen the application fields of the alloy.
Invar 36 Standards and Specifications
Invar 36 is defined by many international standards and specifications. The commonly used standards are:
- AMS 9040: for forged and rolled products
- ASTM A755: general standard for precision alloys
- UNS K93600: Unified Numbering System code
- DIN 1.3912: the equivalent in the German standards
These standards ensure quality control by detailing the chemical composition, mechanical properties and production processes of the material. Commercially, Invar 36 is generally referred to as “FeNi36” or simply “Invar”.
Invar 36 Industrial Applications
Thanks to its low coefficient of expansion and high dimensional stability, Invar 36 is preferred particularly where temperature changes create problems in precision measurement, control and mechanical systems.
- Precision measuring instruments: thermometers, barometers and precision print and pressure sensors benefit from the dimensional stability of Invar 36.
- Aerospace: used in structural components exposed to large temperature differences in aircraft and spacecraft.
- Electronics industry: preferred in the manufacture of semiconductor production equipment and precision circuit elements.
- Optical systems: provides dimensional stability in microscope and telescope frames, optical platforms and other precision optical devices.
- Watchmaking: used in mechanical watches to improve timekeeping accuracy.
- Piping and valve systems: used in systems where expansion caused by temperature changes is critical.
Invar 36 Machinability and Manufacturing Techniques
Despite its high strength, Invar 36 has quite good machinability. It can be shaped with high precision in cutting, milling and turning operations when special cutting tools are used. It is also suitable for welding (TIG, MIG) and brazing methods.
Care must be taken with heat treatments, however, in order to preserve the thermal expansion behaviour. Excessive heat treatment can cause changes in the microstructure, so production processes must be well controlled.
6. Commercial Supply and Purchasing Keywords
Invar 36 is supplied by metal suppliers in bar, plate, strip and tube form.
Advantages
- A very low coefficient of thermal expansion provides dimensional stability in precision applications
- High mechanical strength and durability
- Good machinability and weldability
- Stable performance over a wide temperature range
- Its magnetic properties are an advantage in some special applications
- Widely available in industry and supplied to standards
Disadvantages
- Its temperature capability is more limited than that of cobalt-based alloys
- It is among the higher-cost alloys
- It requires special machining parameters during processing
- Its expansion behaviour can deteriorate at extreme temperatures
- It is not as corrosion resistant as stainless steel
Invar 36 is an indispensable material for precision industrial applications where low thermal expansion is critical. It is used across a wide field, from aerospace to precision measurement systems and from optics to the electronics sector. In purchasing decisions, the material’s conformity with international standards such as AMS and ASTM, its technical data sheets and the reliability of the supplier should all be assessed carefully.
#AMS9040
#ASTMA755
#UNSK93600
#DIN1.3912
| Chemical Composition (INVAR 36, Alloy 36) | | Room Temperature Mechanical Properties | |
|---|---|---|---|
| Grade | Alloy 36 (1.3912, NILO 36) | Properties | Values |
| Ni | 36.0% | Density (Specific Gravity) | 8110 kg/m³ |
| Fe | 64.0% | Melting Point | 1430°C |
| | Yield Strength (20°C) | 240 MPa | |
| | Tensile Strength (20°C) | 490 MPa |
We supply this material
We supply Invar 36 (1.3912 / Alloy 36) — to ASTM F1684, in the size and form required. For stock and pricing:
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