Empress Catherine II Saint Petersburg Mining University, St. Petersburg, Russia

K. Yu. Shakhnazarov, Dr. Eng., Prof., Dept. of Materials Science and Technology of Art Products, e-mail: karen812@yandex.ru
S. A. Vologzhanina, Dr. Eng., Prof., Dept. of Materials Science and Technology of Art Products, e-mail: vologzhanina_sa@pers.spmi.ru
R. M. Khuznakhmetov, Postgraduate Student, Dept. of Materials Science and Technology of Art Products

It is difficult to overestimate the significance of the Fe–C phase diagram, the construction of which was initiated by D. K. Chernov, which allowed to open new boundaries in understanding the properties of iron-based alloys. At the same time, anomalies in properties and the lack of connection between them and the structure of alloy mixtures and the phase diagram have been known for about a century, but have not been explained. A. A. Bochvar, studying the properties of alloy mixtures consisting of obviously pure components, concluded: “As it turned out, there is no unambiguous relationship between composition and properties at all.” I. I. Kornilov came to the same conclusion: “But it is difficult to establish any strict connection between hardness and the phase diagram.” N. I. Belyaev and N. T. Gudtsov noted much more sharply: “The apparent elastic limit has no connection with the structure of steel.” E. Gudremon, hiding an obvious anomaly (the maximum yield strength), drew a curve past the experimental point at ~0.5 % C. The maximum yield strength of annealed steels at ~0.5 % C was shown by P. Obergoffer in 1915, but left without comment. The analysis of the Fe – C phase diagram is performed taking into account three verticals plotted by D. K. Chernov in 1916, which were not taken into account in subsequent editions of the diagram. N.S. Kurnakov’s rule connects changes in the properties of alloys with the type of phase diagram, but does not explain numerous anomalies in the physical and mechanical properties of alloys. In this regard, a new approach to the analysis of the phase diagram is proposed, taking into account the three verticals of D.K. Chernov and the lines of the phase diagram taking into account concentration dependencies and qualitative intervals of crystallization (recrystallization). Based on the established numerous anomalies in the physical and mechanical properties of melts, austenite, martensite and ferrite-cementite mixture, intermediate phases (~Fe₄₂C, ~Fe₂₄C, ~Fe₁₀C) are declared, allowing a new look at the diagram discovered more than 100 years ago. The intermediate phases declared in the article can be used to explain the anomalies of the physical and mechanical properties of industrially used steels

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