Production of low-sulfur steel with limited hydrogen content

Abstract

Requirements on steel quality are constantly rising. The content of sulfur and hydrogen is a particular con cern. In current practice, desulfurization occurs in several stages. Ladle desulfurization of hot metal is not generally used at Russian metallurgical enterprises. Some portion of the sulfur must be removed in the converter or the electrofurnace, although its absolute content will increase. The addition of solid slag form ing mixture consisting of lime and fluorspar to the ladle has a pronounced effect during discharge of the metal. As a rule, most of the sulfur is removed in the ladle-furnace unit, where additional limestone pieces are added to the slag formed at discharge from the steel smelter, so as to obtain high basicity. In the production of superlow sulfur steel (0.003-0.005% S), fluidized lime is introduced in an inert gas flux in the latest ladle-furnace units.In the production of low sulfur alloy steel, the metal is considerably saturated with hydrogen as a result of the increased addition of lime and ferroalloy pieces and especially treatment with fluidized lime. That calls for vacuum treatment of the steel in the ladle, with corre sponding increase in the treatment time.To assess the possibility of producing steel with a low sulfur content and standardized hydrogen con tent, we analyze the smelting and ladle treatment of steel in the oxygen converter shop at OAO MMK. In Fig. 1, we show the variation in mean sulfur content in the metal during the production cycle, including desulfurization of the hot metal, converter smelting of the steel, its treatment in the ladle-furnace unit, vac uum treatment, and continuous casting.To determine the effectiveness of desulfurization by solid slag forming mixture, we consider 92 melts in 2013 without treatment by fluidized lime. In Fig. 2a, we show the dependence of the degree of desulfurization D s , %, of the steel (the difference between the sulfur content in the discharge sample and in the final melt) on the total consumption of solid slag forming mixture at discharge from converter and in the ladle-furnace unit. As we see from the approximating straight line, the degree of des ulfurization is proportional to the consumption of solid slag forming mixture.A very effective method of reducing the sulfur con tent in the steel is the addition of fluidized lime. To assess the effectiveness of such desulfurization, we analyze 120 melts from 2013, with fluidized lime con sumption of 200-1200 kg, and estimate the desulfur ization from the ladle-furnace unit to the final steel. The results are shown in Fig. 2b. The determination coefficient is relatively low (R 2 = 0.1389), because we have ignored the influence of the solid slag forming mixture on the desulfurization. As we see, fluidized lime effectively removes sulfur from the steel.Abstract-The converter production of steel with low sulfur content is analyzed. Existing desulfurization methods greatly increase the hydrogen content in the steel. Options for reducing the hydrogen content asso ciated with the solid ...

Sulphur removal in ironmaking and oxygen steelmaking

“…When no lime is used to prevent this, the sulphur concentration of the HM will increase significantly before converter charging. Resulphurisation can sometimes undo the desulphurisation process almost completely 20,36 .…”

Prospects for the Use of Hollow Electrodes for Deep Desulfurization of Steel in the Ladle-Furnace Unit

“…Basically, this process is determined by the properties of the induced slag. When developing the technology for the oxygen-converter shop of PJSC «Magnitogorsk Iron and Steel Works», it was found that for slag guidance it is necessary to consume at least 10 kg/t of lump calx, 1,5 kg/t of fluorspar, aluminum, and if necessary, fluidized calx [4,5]. Under these conditions, the ladle forms a slag of the required chemical composition and liquid mobility, providing the sulfur content in the finished steel is not more than 0,005 %, and in some cases not more than 0,0015 % with the degree of desulfurization of the metal not less than 75-90 % (rel.).…”

Physical and chemical characteristics of high-magnesian siderites

“…Проведенные исследования позволили пред-ложить сидеритовую руду в качестве комплексно-го магнезиального флюса-охладителя для стале-плавильного производства [14][15][16][17]. В условиях ОАО «Челябинский металлургический комбинат» было испытано около 900 т этого материала в ки-слородно-конвертерном и электросталеплавиль-ном цехе № 2.…”