A
The change occurs in the distribution of carbon in iron-carbon solid solution present: get different proportions of austenite, pearlite and martensite, iron may also change its crystalline form: alpha-iron and gamma-iron from memory.
The alloys change, not the chemistry. Unless heat the steel to a temperature that it instantaneously combusts with oxygen.
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B.Tech (mfg & mech), MIIE, gradTIEAust
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Adelaide