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

Possibility of existence of microheterogeneous states in Fe – Mn – C melts was analyzed carried out according to the concepts of chemical thermodynamics. Microheterogeneous state of a chemically inhomogeneous Fe – Mn – C melt was understood as presence of dispersed Fe – C particles in it, which are suspended in Mn – C environment and separated from it by interface. Hypothesis of microheterogeneous state of Fe – Mn – C melts is supported by numerous experimental data on their thermodynamic and physical properties. Identification of anomalies in temperature dependences of physical properties of Fe – Mn – C melts made it possible to determine temperature values above which the melt superheating treatment (MST) leads to destruction of microheterogeneity, i.e., the liquid – liquid structure transition (LLT) in the melt. LLT is understood by authors as a structural transition “microheterogeneous melt – homogeneous solution” and this is expressed in destruction of microheterogeneous state when the melt is heated to a temperature determined for each composition (MST). This paper describes a method for theoretical determination of temperature range where microheterogeneous state of the Fe – Mn – C melt is thermodynamically stable. Thermodynamic stability of dispersed Fe – C particles in the Mn – C medium was estimated according to the equations proposed by Kaptay for a regular solution. It was assumed that interface between the 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. This result of the assessment is consistent with the data on size of the structural units of a viscous flow obtained earlier within framework of the theory of absolute reaction rates.