Diagram of the phase composition of the Fe - Si - Al system and its isothermal sections

Abstract

The diagram of the phase composition of the Fe – Si – Al system and its isothermal sections within the temperature range of 300-3000 K are plotted. Thermodynamic data of Fe 3 Si, Fe 2 Si, Fe 5 Si 3 , FeSi, FeSi 2 silicides, FeAl, FeAl 2 , FeAl 3 , Fe 2 Al 5 aluminides and Al 2 Fe 2 Si, Al 3 FeSi, Al 2 FeSi, Al 11 Fe 3 Si 6 , Al 14 Fe 3 Si 3 ternary compounds are used. The diagram consists of 20 elementary triangles of coexisting phases, the number of which decreases to 6 at the temperature 1900 K and more. At the temperatures above 2900 K, the equilibrium of the condensed phases is disturbed due to the transition of such metal components of the low-melting aluminum corner of the diagram as Al, Al 2 , Fe, Si and Si 2 , leading to losses of valuable elements, to the gas phase. Crystallization fields are assessed by calculating the squares of elementary triangles, as well as the prevalence of each compound in the phase space by taking into account its participation in the construction of adjacent triangles. Using our own method, the mathematical model of the diagram was created in the form of equations for dependence of the amount of the formed phase on the chemical composition of examined metal. The computer program was developed based on the established equations. The examples of calculation of the phase composition of two grades of ferrosilicon FeSi65 and FeSi75, which are the most common in metallurgy, as well as two grades of ferrosilicoaluminum FeSi45Al15 and FeSi55Al20 are presented. Correspondence of the calculated and instrumentally found phase composition of the industrial metal has been revealed. Presence of mathematical models makes it possible to accelerate selection of the metal with the required composition and from the set of planned for smelting.