invar tube is a nickel-iron alloy that is noted for its uniquely low coefficient of thermal expansion. It contains 36% nickel and has a rate of thermal expansion approximately one-tenth that of carbon steel at temperatures up to 400degF (204degC).
Invar is used in applications requiring high dimensional stability for large, complex shapes, such as valves in engines, large aerostructure molds, or high temperature parts. Invar also resists changes in dimensional stability due to oxidation, heat, and environmental stress.
Several Invar grades are available. The best known is Invar 36.
It is a low-temperature alloy with a controlled coefficient of thermal expansion, and it has excellent magnetic properties at lower than its Curie point. It is a very good choice for reducing the effects of cryogenic shrinkage on components or moulds made from stainless steel, allowing them to be more cost-effective and maintain a higher level of quality and consistency.
Welding: Invar 36 can be welded using conventional methods, but care must be taken to avoid molten metal spatter or indentations in the weld area. A low carbon content is preferred, as it minimizes the risk of thermal expansion resulting in stick-to-paste.
Machinability: It is a bit harder to machine than steel, and it requires careful attention to machining parameters. It can be difficult to pierce, and it requires slow cutting speeds and large tooling.
Corrosion Resistance: Invar is not highly corrosion resistant in water, but it does hold up well to a wide range of conditions. It is a good choice for components that require a high degree of corrosion resistance, such as glass sealing.