Invar (Alloy 36), Alloy 42, & Super Invar
Low expansion alloys are iron-nickel alloys with face-centered cubic crystal structure. These alloys have very low coefficients of thermal expansion over certain temperature ranges, which are related to ferromagnetism. Each low expansion alloy’s Curie temperature, the temperature below which it is ferromagnetic, results in a low thermal expansivity anomaly, often referred to as the “Invar Effect.”
Thanks to a very high magnetic permeability, low expansion alloys are useful in transformers, cores, and laminations for efficient motors, relays and solenoids. They are used extensively where changes in mechanical properties with temperature could be a problem.
Invar: Also called Alloy 36 or Invar 36, Invar is a low expansion alloy whose name is derived from “invariable” because it won’t react to thermal expansion. Invar is used predominantly in precision instruments like stencils, fine line etching and laser cutting, as well as scientific instruments, physics laboratory devices, motor valves and solar panel manufacturing tools.
42 Alloy: Very similar to Invar, 42 Alloy has a slightly different coefficient of thermal expansion. 42 Alloy is well-suited for the lid, lead frames, stencil/etching and aircraft industries. Easily machined and formed hot or cold, 42 Alloy is also used extensively in the medical, electronics and automotive industries.
Super Invar Alloy: Super Invar is made up of 31% Nickel & 5% Carbon balance. This alloy has a coefficient of thermal expansion that is close to zero over a restricted temperature range. Super Invar’s useful temperature range is between negative 32 degrees Celsius to 275 degrees Celsius. As the alloy reaches negative 32 degrees, it begins to transform from Austenite to Martinsite.