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

Abstract

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. © 2022 National University of Science and Technology MISIS. All rights reserved.