Mathematical Modeling Study on Combined Side and Top Blowing AOD Refining Process of Stainless Steel

Abstract

Mathematical modeling of the combined side and top blowing AOD refining process of stainless steel has further been studied. A new model proposed is generally based on the analysis and assumptions made for the process in our previous investigation. Particularly, the heat transfer characteristics of the vessel are analyzed in terms of the two-dimensional transient heat-conduction problems of composite walls. The heat and mass balances of the system are more comprehensively and precisely performed. The model has been applied to 28 heats of 304-grade austenitic stainless steel refining in a 120 t AOD converter. The results present that the changes in the composition and temperature of the liquid steel with the time during the whole process can be accurately predicted using the model. The competitive oxidation among the elements in the steel during the oxidative refining with the relevant oxygen distribution ratios, and the competitive reduction of the oxides in the slag during the Ar agitating and reductive refining with the appropriate oxygen supply ratios can be well characterized and reasonably determined using the Gibbs free energies of the reactions. The critical carbon concentrations (after which the decarburization alters to be limited by the mass transfer of carbon in liquid steel) for the top, side and combined blowing of 304-grade steel in this work are in the ranges of 0.895 to 0.942, 0.078 to 0.224, 0.144 to 0.255 mass%, respectively. The effects of some factors on the refining result and the optimization of blowing technology have been considered from the model predictions. The model can provide a reliable basis and useful information for determining and optimizing the technology of this AOD process of stainless steel, and controlling the process in real time and on-line.