Cementite

Cementite is iron carbide, Fe₃C, a hard, brittle phase in steels and cast irons. Its distribution with softer phases strongly influences the properties of ferrous alloys.

Iron–carbon phase diagram: A map of the stable phases in iron–carbon alloys as temperature and composition change. It locates cementite and shows the transformations that create or consume it.
Eutectoid reaction: A solid-state reaction in which one solid phase transforms into two different solid phases at a specific composition and temperature. It produces ferrite and cementite together from austenite.
Hardness: A material’s resistance to localized plastic deformation, often measured by indentation or scratching. Cementite’s high hardness raises the hardness of carbide-containing structures.
René-Antoine Ferchault de Réaumur: An eighteenth-century French scientist who studied metals and developed methods for making malleable cast iron. His cast-iron experiments helped establish early understanding of iron’s carbon-bearing constituents.
Ferrite: A soft, relatively low-carbon phase of iron with a body-centered cubic crystal structure. Ferrite commonly forms the softer partner in microstructures containing cementite.
Eutectic reaction: A reaction in which one liquid phase solidifies into two solid phases at a specific composition and temperature. In the iron–carbon system, it forms austenite and cementite together.
Abrasive wear: Material loss caused when hard particles or surface asperities cut or scratch a contacting surface. Cementite can resist abrasion, though brittle particles may fracture or detach.
Henry Clifton Sorby: An English geologist and microscopist who pioneered the use of microscopy to study the structure of metals. His metallographic methods made steel’s microscopic constituents, including cementite, observable.
Austenite: A face-centered cubic phase of iron that can dissolve substantially more carbon than ferrite. Austenite transforms into cementite-bearing structures during cooling.
Spheroidizing: A heat treatment that turns carbide networks or plates into rounded particles within a softer matrix. It changes cementite’s shape to improve machinability and ductility.

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