Researches concerning influence of magnesium, aluminum and titanium lime on steel desulfurization

Abstract

Abstract. The paper presents the results of laboratory experiments on steel desulphurisation with slag from the system MgO-Al 2 O 3 -TiO 2 . To determine the influence, on the desulphurisation process, of the titanium oxide added in calcium aluminate slag, we experimented, in the laboratory phase, the steel treatment with a mechanical mixture consisting of lime, aluminous slag and slag obtained from the titanium making process through the aluminothermic technology. The steel melting was carried out in an induction furnace of 10 kg capacity, existent in the Metallic Melts laboratory of the Engineering Faculty of Hunedoara. During the research, we aimed to establish correlation equations between the sulphur distribution coefficient and the slag components (MgO, Al 2 O 3 , TiO 2 ). The data obtained in the experiments were processed in MATLAB programs, resulting multiple correlation equations, which allowed the elucidation of some physical-chemical phenomena specific to the desulphurisation processes. General considerationsThe steel refining with liquid slag or various powder mixtures of synthetic slag is based on the intensification of the unwanted impurities (sulphur, non-metallic suspensions & oxygen) passage from the liquid steel in the slag, mainly by diffusion, or partly through the entrainment of some suspensions by settling the synthetic slag particles found in the treated steel bath. The synthetic slag can be also obtained by adding mechanical mixture directly in the casting ladle; in this case, for compensating the cooling of the steel in the casting ladle due to the addition of materials (melting and superheating), the steel temperature should be at least 20-40 o C higher than the normal one [1]. In the practice of deoxidation with synthetic slag, we usually use slag that correspond to the binary systems CaO-Al 2 O 3 , CaO-TiO 2 and CaO-CaF 2 , or to the ternary systems CaO-SiO 2 -Al 2 O 3 , CaO-CaF 2 -Al 2 O 3 and MgOAl 2 O 3 -TiO 2 , [2].The viscosity of the synthetic slag has significant influence on the development of physical and chemical processes during the treatment of the liquid steel, interfering with significant weight on the emulsifying capacity of slag. The increase of the slag viscosity from 0,15 to 0,45 Ns/m 2 (from 1,5 to 4,5 Poise) determines the decrease with approx. 30% of the steel-slag interaction surface. Such increasing of the calcium aluminate slag viscosity can be seen when its temperature is decreasing (for example, from 1600 o C to 1470 o C). Therefore, it is very important to ensure, during processing the steel with liquid slag, the optimum thermal regime specific to the chosen slag type and to realize its convenient fluidity (viscosity).