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Martensite is formed in carbon steels by the rapid cooling (quenching) 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 (Fe3C). Austenite is Î³-Fe, (gamma-phase iron), a solid solution of iron and alloying elements. As a result of the quenching, the face-centered cubic austenite transforms to a highly strained body-centered tetragonal form called martensite that is supersaturated with carbon.
taconite-a variety of chert containing magnetite and hematite; mined as a low-grade iron ore. haematite, hematite-the principal form of iron ore; consists of ferric oxide in crystalline form; occurs in a red earthy form. lepidocrocite-a red to reddish brown mineral consisting of iron oxide hydroxide; often found in iron ores together with goethite.