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Invar 36 is a specialized nickel-iron alloy known for its uniquely low coefficient of thermal expansion. Composed of approximately 36% nickel and the remainder iron, this material is categorized as a **controlled expansion alloy**. It is widely used in precision engineering applications where dimensional stability under temperature changes is critical. Invar 36 is also referred to by its UNS number K93600 or simply as Alloy 36. It combines good mechanical strength with excellent dimensional control, making it ideal for aerospace, electronics, cryogenics, and tooling applications.
Chemical Composition of Invar 36
Invar 36’s remarkable properties come from its specific ratio of nickel and iron. The composition ensures minimal thermal expansion, especially around room temperature.
| Element | Content (%) |
|---|---|
| Nickel (Ni) | 35.0 – 37.0 |
| Iron (Fe) | Balance |
| Manganese (Mn) | ≤ 0.60 |
| Silicon (Si) | ≤ 0.35 |
| Carbon (C) | ≤ 0.05 |
| Sulfur (S) | ≤ 0.02 |
| Phosphorus (P) | ≤ 0.02 |
Material Classification
Invar 36 belongs to a class of materials called **low expansion alloys**. These alloys are engineered for applications that require minimal dimensional changes with temperature fluctuations. Invar 36 is also classified as a ferromagnetic material at room temperature and is part of the family of **iron-nickel soft magnetic alloys**.
| Classification | Description |
|---|---|
| Alloy Type | Iron-Nickel Alloy |
| Class | Controlled Expansion Alloy |
| Magnetism | Ferromagnetic (at room temperature) |
| Standard Designation | UNS K93600 / ASTM F1684 |
Typical Mechanical Properties
Though not primarily chosen for mechanical strength, Invar 36 offers decent mechanical properties suitable for many engineering uses.
| Property | Typical Value |
|---|---|
| Tensile Strength | 490 MPa (71 ksi) |
| Yield Strength (0.2% offset) | 275 MPa (40 ksi) |
| Elongation | 30% |
| Hardness | ≤ 160 HB |
Common Forms and Uses
Invar 36 is manufactured in various product forms such as round bars, sheets, plates, and wires. It is often used in tools, molds, scientific instruments, and structural components requiring dimensional precision over a wide temperature range.
| Form | Typical Applications |
|---|---|
| Round Bar | Precision tooling, aerospace fixtures |
| Sheet/Plate | LCD shadow masks, cryogenic containers |
| Wire | Thermostatic bimetals, sensors |
Why Choose Invar 36?
Invar 36 is selected for one main reason—its low thermal expansion coefficient (approximately 1.2 x 10⁻⁶ /°C at 20–100°C). This stability ensures components stay dimensionally consistent, especially in temperature-sensitive environments like aerospace structures or cryogenic equipment.
Related Questions
Is Invar 36 a metal or an alloy?
Invar 36 is an alloy made primarily of iron and nickel. It is specifically engineered for low thermal expansion and high dimensional stability.
What is Invar 36 used for?
Invar 36 is used in applications where dimensional stability with temperature changes is critical, such as aerospace molds, cryogenic tanks, and precision instruments.
Is Invar 36 a magnetic material?
Yes, Invar 36 is ferromagnetic at room temperature, meaning it exhibits magnetic properties under normal conditions.