The Physical Chemistry of Steel Deoxidation and Nozzle Clogging in Continuous Casting

Nozzle clogging in continuous casting of steel originates by the adherence of alumina particles and other oxides, precipitated during the liquid steel deoxidation, on the refractory material’s surface. Hence, these particles’ nucleation and growth rates in supersaturated melts are analyzed considering, specifically, the role of the interfacial tensions between alumina, silica, and other oxides and the liquid metal. Weak steel deoxidizers like silicon do not need high supersaturations favoring high nucleation rates, giving particles’ narrow size distributions thanks to fast diffusion and Ostwald-ripening coagulation. Strong deoxidizers, like aluminum, need high supersaturation levels leading to broad size distributions. Besides, the morphology of these particles depends on the nucleation and growth mechanisms. The adhesion forces among the deoxidation particles, forming clusters, depending on the morphology and the oxide’s chemistry. The stability of the nozzle’s clog, adhered to the nozzle’s wall, depends on the interface tensions between the melt and the nozzle’s refractory surface and between the melt and the inclusion. The results obtained here help set up basic recommendations in steel refining and materials specifications of casting nozzles.

On the Application of the FactSage Thermochemical Software and Databases in Materials Science and Pyrometallurgy

The discovery of new metallic materials is of prime importance for the development of new technologies in many fields such as electronics, aerial and ground transportation as well as construction. These materials require metals which are obtained from various pyrometallurgical processes. Moreover, these materials need to be synthesized under extreme conditions of temperature where liquid solutions are produced and need to be contained. The design and optimization of all these pyrometallurgical processes is a key factor in this development. We present several examples in which computational thermochemistry is used to simulate complex pyrometallurgical processes including the Hall–Heroult process (Al production), the PTVI process (Ni production), and the steel deoxidation from an overall mass balance and energy balance perspective. We also show how computational thermochemistry can assist in the material selection in these extreme operation conditions to select refractory materials in contact with metallic melts. The FactSage thermochemical software and its specialized databases are used to perform these simulations which are proven here to match available data found in the literature.

Analysis of the influence of technological parameters of steel smelting in top blowing oxygen converters on metal oxidation

The article considers the influence of technological steelmaking parameters in an oxygen converter on the oxygen content in steel before tapping. Today, CELOX is an effective, but at the same time expensive method for measuring the oxygen content in steel. The information obtained using this device allows you to accurately determine the ferroalloys consumption for deoxidation of steel. Since the oxygen content in steel before production directly affects the ferroalloys and aluminum consumption, necessary for steel deoxidation, the aim of this work was to create a mathematical model that allows determining the oxygen content in steel before tapping, taking into account the controlled melting parameters. The object of the study was a top blowing oxygen converter of 60 t capacity. The following analysis was carried out for 3PS steel grade. To create a mathematical model, the factors that have the greatest influence on the oxygen content in steel before tapping were previously selected by the method of correlation analysis. Such factors included the carbon, manganese, sulfur and phosphorus content in steel before tapping, its temperature and specific consumption of oxygen. Using the method of multiple regression analysis, a mathematical model was determined, which allows determining the oxygen content in steel before tapping at the end of each melt. Comparison of the actual data on the oxygen content in steel before tapping with the results of calculation using the model showed their high convergence, which confirms the adequacy of the obtained model. The application of the developed mathematical model for predicting the oxygen content in steel before tapping in a real metallurgical enterprise will allow reduce consumption of ferroalloys and alumina for deoxidation of crude steel.

Thermodynamic Modeling of the Processes of Interaction of Calcium, Magnesium, Aluminum and Boron with Oxygen in Metallic Melts

A method for calculation of the diagrams of steel deoxidation and modification by calcium, magnesium, aluminum and boron was developed. The coordinates of the liquidus surfaces of the oxide systems B2O3–Al2O3–MgO, B2O3–Al2O3–CaO, B2O3–MgO–CaO were found at 1873 K. The energy parameters were determined for the theory of subregular ionic solutions of the studied oxide systems. The coordinates of the solubility surfaces for the systems Fe–Mg–Al–B–O, Fe–Ca–Al–B–O, Fe–Mg–Ca–Al–B–O were calculated. The effect of the total pressure on solubility of magnesium and calcium in liquid iron was studied. The activity of the components of the metallic melt was calculated using the first-order interaction parameters (Wagner's theory). The activities of the components of solid solutions (oxides and spinels) were equated with their molar fractions. It was shown that during extensive refining of metal from the oxygen, only a small fraction of boron oxidizes and these oxides form fraction of the oxide melts. The major non-metallic oxide inclusions were magnesia spinel, calcium bialuminate and liquid oxide formations. The "free" boron was dissolved in liquid metal in amounts which were in equilibrium with oxide phases.

THERMODYNAMICS OF THE PROCESSES OF INTERACTION OF LIQUID METAL COMPONENTS IN Fe – Mg – Al – La – O SYSTEM

At the present time, rare-earth elements in metallurgy are used in the form of mischmetal – a rare-earth elements natural mixture (with atomic numbers from 57 to 71). It contains about 50 wt. % of cerium. The remaining elements are mainly lanthanum and niobium. The specific composition is determined by the ore deposit. Inconstant composition of the modifier containing rare-earth metals (REM) can significantly reduce its efficiency. Experimentally, for every branded steels composition the ratio of various REMs can’t be selected because of the high costs of obtaining technically pure rare-earth metals. The task of determining the each rare earth element optimum concentrations and complex ligature composition can be solved by thermodynamic modeling. In the framework of thermodynamic modeling, the interaction between magnesium, aluminum and lanthanum with oxygen in liquid iron is presented. And the thermodynamic model of steel deoxidation by these active metals composition is considered. On the basis of available literature data on the phase diagrams of the systems MgO – Al2O3 , MgO – La2O3 and La2O3 – Al2O3 , the coordinates of the invariant equilibria points in the system MgO – La2O3 – Al2O3 were determined. The phase diagram of the system MgO – La2O3 – Al2O3 was constructed. It made possible to establish all phase equilibria realized in the process of deoxidation of steel with magnesium, lanthanum and aluminum and to describe these phase equilibria by chemical reactions equations. The activity of the components in liquid oxide melts was determined using the theory of subregular ionic solutions, which takes into account the dependence of the coordination number of cations on the composition of the oxide melt. The activity of components in metal melts conjugated with oxide systems were determined by Wagner’s theory using the parameters of the first order interaction. Equilibrium constants values for the steel deoxidation reactions are installed indirectly by thermodynamic calculations. On the basis of the obtained data the components solubility surface in the metal melts of Fe – Mg – Al – La – O system was constructed, which allowed to determine the liquid metal composition regions associated with the corresponding oxide phase.