Since Fe
3C is an unstable phase, the representation of the Fe-C system as a stable Fe-Fe
3C system, as in the so-called single diagrams, is erroneous. The groundless inclusion of the systems Fe-C and Fe-Fe
3C, which cannot be differentiated experimentally, in the double diagrams is unjustifiable. The proper representation of the system, therefore, would be in the form of a singl diagram of the system iron and graphite.
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