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Metal science and Metallography
ArticleName Phase equilibriums in the carbide area of the «iron-carbon» diagram. Part 1. Physico-chemical identification of carbide phases
DOI 10.17580/chm.2021.09.09
ArticleAuthor S. V. Davydov
ArticleAuthorData

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

Abstract

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.

keywords Cementite θ-Fe3C, ε-Carbide Fe2C, Hegga carbide χ-Fe5C2, Extreme-Adcocca carbide æ-Fe7C3, bertollide, daltonide, isomorphic quasicarbide solid solution
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