St. Petersburg State Mining University (St. Petersburg, Russia):

Shakhnazarov K. Yu., Cand. Eng., Ass. Prof., the Chair of Material Science and Technology of Art Objects, e-mail: karen812@yandex.ru
Pryakhin E. I., Dr. Eng., Prof., Head of the Chair of Material Science and Technology of Art Objects, e-mail: mthi@spmi.ru

Many literary sources includes state diagrams of binary alloys with smooth lines of phase transformations, differing from the experimental data. At the same time, the true trajectory of these lines, which determines in particular the actual interval of solidification, plays an important role in the analysis of influence of the features of the crystallization interval on the performance parameters of the alloys. The lines of the state diagram of alloys are considered as concentration dependences of the extent in relation to the temperature of crystallization and recrystallization intervals. Qualitative variation of these intervals is a fundamental feature of congruent and incongruent melting phases, as well as compounds such as σ-phase, that are ordered in the solid state compounds (Kurnakov point), and which are interesting not with their structure, but with their special properties. Qualitative variation of crystallization (recrystallization) intervals and anomalies of properties are the fundamental features of these compounds. The term «Qualitative variation of crystallization interval» (QVCI) is explained on the example of Fe – C diagram. QVCI occurs in the point E (~ 2% C) due to solidus line bending and in the point B (~ 0,5% C) due to liquidus line bending. Thus, any non-monotonicity in liquidus (or solidus) with a monotonic course of the solidus (or liquidus) generates QVCI. Qualitative variation of recrystallization interval takes place in the point S (~ 0,85% C), where three lines (GOS, ES and PSK) cross. About century ago, the name «gardenit» and Fe₂₄C formula (Arnold’s subcarbide) has been given to austenite eutectoid composition. An attempt to link the anomalies of steel properties with ~ 0.5–0.85 and ~ 2% C with intermediate phases of Fe₄₂C, Fe₂₄C and Fe₁₀C composition and to build the respective vertical lines across these phases in the Fe – C diagram, has been made in this paper.

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