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Iron
carbide is an interstitial compound of iron and carbon with the composition
Fe- 6.68 wt % Carbon. It is a brittle ceramic material and is produced
in carbon steels or cast irons during pseudo-equilibrium cooling from above
the eutectoid temperature (723 C). The equilibrium phase in the iron-carbon
binary system is graphite, but normal metallurgical conditions favor the
formation of iron carbide, which is metastable to conversion to graphite
at elevated temperatures.
The
photograph shows an etched sample of white cast iron (x 100). The material
is hyper eutectoid and the room temperature microstructure shown has regions
of primary cementite (white) and pearlite (aFe
+ Fe3C)
crystallites (gray). The cementite is a hard brittle material and the cast-iron
tends to fail by transgranular brittle fracture. The metal has a low shock
resistance but good wear properties and high acoustic damping. |
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