
Malleable iron is cast as White iron, the structure being a metastable carbide in a pearlitic matrix. Through an annealing heat treatment, the brittle structure as first cast, is transformed into the malleable form. Carbon agglomerates into small roughly spherical aggregates of graphite leaving a matrix of ferrite or pearlite according to the exac...
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http://en.wikipedia.org/wiki/Malleable_iron

Iron castings which have been made less brittle by heat treatment. There are two types, known as blackheart and whiteheart. See also SG iron.
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http://www.metalbulletin.com/Glossary.html

A cast iron made by prolonged annealing of white iron in which decarburization,graphitization or both take place to eliminate some or all of the cementite. The graphite is in the form of temper carbon. If decarburization is the predominant reaction, the product will exhibit a light fracture surface; hence whiteheart malleable. Otherwise, the fractu...
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https://steelforge.com/literature/steelog-the-5000-word-metals-glossary/

A mixture of iron and carbon, including smaller amounts of silicon, manganese, phosphorus, and sulfur, which after being cast
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https://www.metaltek.com/resources/glossary/
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