Is Invar 36 Magnetic

Invar 36, also known as UNS K93600 or FeNi36, is a well-known iron-nickel alloy famous for its uniquely low coefficient of thermal expansion. This property makes it ideal for applications requiring dimensional stability under temperature changes, such as precision instruments, aerospace components, and electronic devices. But one common question often arises:

Is Invar 36 magnetic?

The answer is yes — but with some nuances.

1. Basic Magnetic Properties of Invar 36
Invar 36 is ferromagnetic at room temperature, meaning it can be magnetized and attracted to a magnet. This is because its main component is iron (Fe), which is inherently ferromagnetic. The 36% nickel content modifies some of its magnetic characteristics but does not eliminate its magnetic behavior.

Curie Temperature: Invar 36 has a relatively low Curie temperature, around 230°C (446°F).

Below the Curie temperature: The alloy remains magnetic.

Above the Curie temperature: It becomes paramagnetic, meaning it loses permanent magnetization but still responds weakly to external magnetic fields.

2. Comparison with Other Alloys
Alloy Magnetic? Notes
Invar 36 Yes (ferromagnetic) Magnetic below Curie temperature
304 Stainless Steel No (generally) Austenitic and non-magnetic
430 Stainless Steel Yes Ferritic and magnetic
Permalloy (Ni80Fe20) Strongly magnetic High permeability, used in transformers

Invar 36’s magnetic strength is moderate, less than that of pure iron or high-permeability alloys like Permalloy, but stronger than many stainless steels.

3. Magnetic Behavior in Real-World Applications
Understanding its magnetic behavior is important for specific use cases:

Electronics & Sensors: Magnetic properties may interfere with magnetic sensors or inductive devices. Engineers must consider this during material selection.

Cryogenic Applications: Invar 36 is used at cryogenic temperatures where it remains ferromagnetic and retains dimensional stability.

Shielding: Invar 36 is not suitable for magnetic shielding, as it does not have high magnetic permeability.

4. Effect of Heat Treatment and Cold Working
The magnetic properties of Invar 36 can be slightly altered by heat treatment and mechanical deformation:

Annealing: Can reduce internal stress and stabilize magnetic domains.

Cold working: Can increase coercivity (resistance to demagnetization) but may introduce residual magnetism.