Bryansk State Technical University (Bryansk, Russia):

S. V. Davydov, Dr. Eng., Prof., Dept. of Tribotechnical Materials Science and Materials Technology, e-mail: fulleren_grafen@mail.ru

At present, in addition to cement θ-Fe3C, only three types of carbides are objectively identified in the iron-carbon system: ε-Fe2C carbide, Hegga carbide χ-Fe₅C₂ and Extreme-Adcoccus carbide æ-Fe₇C₃, which are chemically located to the right of the cement line and are not shown in the status diagram. To clarify the phase composition in the “cemented” area of the diagram, it is necessary, firstly, to complete physical and chemical identification of carbides, and secondly, to obtain and examine alloys with carbon content from 6.0 % to 10.0 %. On the basis of extensive analysis of available scientific and experimental data, it is shown that iron compounds with carbon, currently defined as iron carbides, are not such, because their “physical” behavior in the alloys contradicts the properties of the classical chemical compound. Carbides have been found to be non-stoichiometric compounds, i.e. phases of variable composition, containing stoichiometric composition or solid solutions of the second kind based on colourfastonides and bertollides. It is shown that the whole set of structural organization of phases (alloys) on the “iron-carbon” diagram from 6.67 % C (cement θ-Fe₃C) to 9.7 % C (carbide ε-Fe₂C) can be characterized as a single isomorphic quasicarbide solid solution, which includes the introduction phases of the stoichiometric compositions of θ-Fe₃C cement, Hegg carbide χ-Fe₅C₂, Extreme-Adcoccus carbide æ-Fe₇C₃ and ε-Carbide Fe₂C. Since the solid cement slurry cannot be a component of the alloy state diagram, the component of the diagram is a chemical compound of bertolide ε-Fe₂C and the “iron-cement” diagram can be renamed to the “ironcarbide ε-Fe₂C” alloy state diagram in the concentration region from 0 % C to 9.7 % C with good reason.

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