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Cementite (or iron carbide) is a compound of iron and carbon, more precisely an intermediate transition metal carbide with the formula Fe 3 C. By weight, it is 6.67% carbon and 93.3% iron. It has an orthorhombic crystal structure. [4]
iron: ferrite, ferritic steel; iron: austenite, austenitic steel; iron carbide: cementite, Fe3C. It shows a eutectic and a eutectoid; these phases crystallise as a stacking of fine strips of pure phases (iron and cementite) in case of the eutectoid, or a pure iron containing small balls of cementite for the eutectic.
Low-pressure phase diagram of pure iron. BCC is body centered cubic and FCC is face-centered cubic. Iron-carbon eutectic phase diagram, showing various forms of Fe x C y substances. Iron allotropes, showing the differences in structure. The alpha iron (α-Fe) is a body-centered cubic (BCC) and the gamma iron (γ-Fe) is a face-centered cubic (FCC).
English: Iron-carbon binary phase diagram: metastable (cementite) in plain line; stable (graphite) in dashed line. Caption: Fe 3 C: cementite (iron carbide); L: liquid; α: ferrite (alpha iron), body-centered cubic; δ: delta-iron, body-centered cubic; γ: austenite (gamma iron), face-centered cubic; solvus A 1: lower limit of existence of ...
Boron carbide, B 4 C, on the other hand, has an unusual structure which includes icosahedral boron units linked by carbon atoms. In this respect boron carbide is similar to the boron rich borides. Both silicon carbide (also known as carborundum) and boron carbide are very hard materials and refractory. Both materials are important industrially.
Martensite is formed in carbon steels by the rapid cooling of the austenite form of iron at such a high rate that carbon atoms do not have time to diffuse out of the crystal structure in large enough quantities to form cementite (Fe 3 C). Austenite is gamma-phase iron (γ-Fe), a solid solution of iron and alloying elements.
Pearlite occurs at the eutectoid of the iron-carbon phase diagram (near the lower left). Pearlite is a two-phased , lamellar (or layered) structure composed of alternating layers of ferrite (87.5 wt%) and cementite (12.5 wt%) that occurs in some steels and cast irons .
Iron-carbon phase diagram, showing the iron-carbon phase diagram (near the lower left).. In iron and steel metallurgy, ledeburite is a mixture of 4.3% carbon in iron and is a eutectic mixture of austenite and cementite.