Abstract
The paper introduces the results of the experiments on synthetic slag desulphurization and deoxidizing using slag belonging to the ternary system CaO-Al2O3-TiO2. The experiments have been done in a 10 kg induction furnace. In order to obtain the reducing slag we used a mixture of lime, alumina and titanium oxide, representing 2 % of the charge weight. The experiments were done on mechanical mixtures produced according to various recipes; for each experiment, the slag was sampled in order to determine its chemical composition and the steel was also sampled, in order to determine its contents in sulphur and oxygen. The resulting data have been processed in EXCEL, which gave the correlation equations between the desulphurization and deoxidizing output and the chemical composition of the synthetic slag, respectively the ratio and sum of the oxides.
Highlights
Steel refining with liquid slag or with various powdery mixtures of synthetic slag is based on the boosting of the passage of unwanted impurities from the molten steel into the slag, mainly by diffusion, or partially by draining some suspensions alongside with the synthetic slag particles which are decanted in the steel bath under treatment
Synthetic slag deoxidizing uses slag belonging to the following binary systems: CaO-Al O ; CaO-TiO and CaO-CaF
According to reference literature data, the best results were obtained with synthetic slag belonging to the binary system CaO-Al O, with a 50-52 % content of CaO and 38-42 % Al O [1]
Summary
Steel refining with liquid slag or with various powdery mixtures of synthetic slag is based on the boosting of the passage of unwanted impurities (sulphur, nonmetallic suspensions, oxygen) from the molten steel into the slag, mainly by diffusion, or partially by draining some suspensions alongside with the synthetic slag particles which are decanted in the steel bath under treatment. An increase of slag viscosity from 0.15 to 0.45 Ns/m2 (1.5 to 4.5 Poise) leads to a 30 % reduction of the steel-slag interaction surface. It is of utmost importance to grant, during steel processing with synthetic slag, an optimal temperature regime, specific to each type of slag in use, in order to obtain an appropriate fluidity (viscosity). For the synthetic slag steel processing temperatures, the minimum viscosity is that of the slag containing 56 % CaO; but, considering the industrial conditions, it is likely to have frequent deviations from this optimal composition (by 1-2 %). As the rate of diffusion into the slag increases with temperature T and with the reduction of viscosity h, it results that synthetic slag viscosity, respectively its fluidity f = 1/h is important in the process of steel treatment with synthetic slag. The larger the contact surface between the synthetic slag and the metal bath, the faster the passage into the slag of the elements under consideration, this aspect being, alongside with viscosity, fundamental in steel treatment with synthetic slag[5]
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