Thermodynamic stability of microheterogenous states in Fe – Mn – C melts

The probability of the existence of microheterogeneous states in Fe – Mn – C melts has been analyzed in accordance with the concepts of chemical thermodynamics. The microheterogeneous state of a chemically heterogeneous Fe – Mn – C melt was understood as the presence of dispersed Fe – C particles in it. These are suspended in the Mn – C medium and separated from it by an interface. The microheterogeneous state in Fe – Mn – C melts is destroyed as a result of heating to a temperature specific for each composition. The hypothesis of the microheterogeneous state of Fe – Mn – C melts is supported by a wide range of numerous experimental data on their thermodynamic and physical properties. The identification of anomalies in temperature dependences of physical properties of Fe – Mn – C melts has allowed for temperature values above which the melt superheating treatment (MST) causes destruction of microheterogeneity to be determined, i.e., liquid – liquid structure transition (LLT) in the melt. LLT is understood by the authors as a structural transition “microheterogeneous melt – homogeneous solution”. This is expressed as the destruction of the microheterogeneous state when the Fe – Mn – C melt is heated to a temperature specific for each composition (MST). The authors have previously analyzed the effect of LLT in Fe – Mn – C melts on the microstructure, crystal structure and mechanical properties of solid metal in submicrovolumes. This paper describes a method of theoretical determination of the temperature range where the microheterogeneous state of the Fe – Mn – C melt is thermodynamically stable. The thermodynamic stability of dispersed Fe – C particles in the Mn – C medium has been estimated according to the equations proposed by G. Kaptay for a regular solution. It was assumed that the interface between the dispersed particle (Fe – C) and the dispersion medium (Mn – C) is enriched with carbon. The paper demonstrates the possibility of existence in the Fe – Mn – C melt of dispersed Fe – C particles with sizes from 2 to 34 nm, distributed in the Mn – C dispersion medium and separated from it by an interface with increased carbon content. The estimated result is consistent with the data on the size of structural units of a viscous flow, obtained earlier within the framework of the theory of absolute reaction rates.

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