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an iron carbide, Fe3C; a phase and structural component of iron-carbon alloys (seeIRON-CARBON ALLOYS). Cementite has an orthorhombic crystal lattice. It is very hard and brittle and is slightly magnetic at temperatures up to 210°C. It is a metastable phase; the formation of the stable phase—graphite—is in many cases difficult. Cementite is precipitated from a melt consisting of austenite and ferrite. Depending on the crystallization conditions and subsequent treatment, it can have various forms, such as equiaxial grains, lattices along grain boundaries, and plates; it can also exhibit a Widmannstatten structure. Cementite is a constituent of the structural components of steel and cast iron—ledeburite, pearlite, bainite, and tempered sorbite.