PREDICTION OF THERMODYNAMIC PROPERTIES OF MELTS OF MgO—Al2O3—SiO 2—CaF 2 SYSTEM

The calculation procedure is proposed for prediction of thermodynamic properties of simple slag melts, allowing for liquidus coordinates of constitutional diagrams. Excess integral functions calculated for more complex systems are given. The possibility of controlling the thermodynamic activity of SiO2 in slag and, hence, silicon reduction process is shown. Step-by-step implementation of new high-strength steels has been taking place in the recent years. High requirements are made to toughness and strength of welded joints manufactured from these steels. For their fulfillment it is necessary to have a possibility for control of a content of oxygen and sulfur in weld metal, processes of microalloying, formation of non- metallic inclusions and structure in a process of so- lidification and cooling of a weld. Silicon oxide are to be included in a flux for pro- viding the necessary welding-technological properties (for pipes, for example, defect-free formation of the welds in multiarc welding with speed higher than 100 m/h are to be provided). However, presence of the latter in the flux during welding of modern steels results in silicon reduction in the weld metal and for- mation of non-metallic silicate inclusions, which is the reason of deterioration of mechanical properties of the weld metal. A slag system and flux composition, providing combination of optimum technological and metallurgical indices, are, in particular, the aim of our investigations. Thermodynamic properties of welding consu- mables are to be known for prediction of metallurgical and technological characteristics. The experimental investigations of oxide melts are complex due to their aggressive behavior and refractoriness. Therefore, the calculation methods for prediction of thermodynamic properties of such melts are widely used in the recent years using similar data for solid compounds and phase equilibriums (1—3). Present paper proposes a proce- dure for prediction of thermodynamic properties of melts by liquidus coordinates of constitutional dia- grams in area of solid component—solution equilibri- ums which being described by the following equations: