Cementite

Encyclopedia : C : CE : CEM : Cementite

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Iron alloy phases
Austenite (γ-iron; hard) Bainite Martensite Cementite (iron carbide; Fe3C) Ferrite (α-iron; soft) Pearlite (88% ferrite, 12% cementite)
Types of Steel
Plain-carbon steel (up to 2.1% carbon) Stainless steel (alloy with chromium) HSLA steel (high strength low alloy) Tool steel (very hard; heat-treated)
Other Iron-based materials
Cast iron (>2.1% carbon) Wrought iron (almost no carbon) Ductile iron

Cementite or iron carbide is a chemical compound with the formula Fe₃C, and an orthorhombic crystal structure. It is a hard, brittle material, normally classified as a ceramic in its pure form, though it is more important in metallurgy.

It forms directly from the melt in the case of white cast iron. In carbon steel, it either forms from austenite during cooling or from martensite during tempering. It mixes with ferrite, the other product of austenite, to form lamellar structures called pearlite and bainite. Much larger lamellae, visible to the naked eye, make up the structure of Damascus steel, though the process has been lost to history (see article for information on attempted reconstruction of the process).

Fe₃C is also known as cohenite, particularly when found mixed with nickel and cobalt carbides in meteorites. This form, a hard, shiny silver mineral, was first described by E. Weinschenk in 1889.

External links

• [Crystal Structure of Cementite, Cambridge University]

• For a full list of external links to MSDSs, spectroscopic data, commercial chemicals suppliers etc. for this compound, see [Chemical sources].

 

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