Strontium effect on the nature of phase equilibria in liquid metal containing calcium and aluminum

The use of complex strontium-containing alloys with alkaline-earth metals for steel out-of-furnace treatment makes it possible to increase the efficiency of the refining process and steel modifying. In this work based on the binary phase diagrams of SrO – CaO, SrO – Al2O3 , Al2O3 – CaO binary systems and data on possibility of the solid solution formation, the phase diagram of the SrO – Al2O3 – CaO system is modeled in the temperature range 1600 – 2600 °С. When constructing liquidus lines, the theories of perfect solutions (for solid solutions of strontium and calcium aluminates), regular solutions (for solid solutions of oxides) and irregular ionic solutions (for oxide melt) were used to calculate the activity of components. Thermodynamic analysis of the Fe – Sr – Ca – Al – O system was carried out as applied to the refining steel processes with alloys containing calcium and strontium at a temperature of 1600 °C. The simulation results showed that in in the process of refining the aluminium-deoxidized steel, a complex mechanism of interaction of active elements with oxygen will be realized. The interaction of calcium and strontium with oxygen occurs both for elements dissolved in iron and along the boundary of the gas phase containing calcium and strontium with the liquid iron melt. As a result of the interaction of calcium and strontium with oxygen in the presence of aluminium (0.05 %), the probability of formation of liquid oxide melts SrO – Al2O3 – CaO is high, which greatly facilitates the removal of reaction products from the melt. The resulting non-metallic inclusions are most likely to be complex calcium and strontium aluminates, which, due to the presence of strontium, are easily assimilated by slag. The formation of undesirable corundum inclusions during metal processing with complex alloys containing strontium and calcium is unlikely.