ironnickel

Iron-nickel, or ironnickel, refers to iron-nickel alloys in which nickel is the principal alloying element. Nickel contents are widely variable, from a few percent in meteoritic kamacite to about half the alloy in taenite; industrial alloys typically fall in between. In meteorites, kamacite contains roughly 5–7% Ni, while taenite ranges from about 20–50% Ni. These phases can produce distinctive Widmanstätten patterns when the material cools slowly.

Properties of iron-nickel alloys depend on composition. Nickel generally increases ductility and corrosion resistance and can stabilize the austenitic phase. Some compositions, notably invar with around 36% nickel, have a very low coefficient of thermal expansion, making them useful for precision instruments. Nickel-rich variants can also exhibit high strength and good toughness at cryogenic temperatures.

Occurrence and production: Natural iron-nickel alloys occur in iron meteorites and are thought to be major constituents of some planetary cores. Industrial production is achieved by smelting iron with nickel-containing ore or metal, followed by alloying and refining to achieve the desired composition and microstructure. Impurities such as sulfur, phosphorus, and carbon are controlled to tailor properties.

Uses: Iron-nickel alloys are employed in precision instruments, cryogenic components, magnetic shielding, and certain low-expansion or corrosion-resistant steels. Some specialized compositions find use in aerospace and electronics.

Related topics include kamacite, taenite, meteorites, and nickel-iron alloys.