Steel Micro-alloying with Boron: A Perspective Direction to Reduce the Consumption of Manganese Ferroalloys

Manganese ferroalloys occupy a strategically important place in the total production of ferroalloys, since no steel grade can be made without the manganese addition. Today, the metallurgical complex of Russia is fully dependent on imports of manganese products (raw ore and ferroalloys), so special attention should be paid to the issues of more rational use of manganese. In particular, one should more widely use the methods of direct micro-alloying of steel with manganese in steel-smelting units and ladle-furnaces unit (LFU) and expand the range of high-strength steel with reduced manganese content, micro-alloyed with high-performance elements. Among the micro-alloying elements, a special place is occupied by boron. Its introduction into the metal in the amount of 0.001–0.005% makes it possible to save expensive and scarce alloying elements, in particular manganese, and to provide an increase in the strength of steel without reducing ductility. The results of the studies of the physicochemical properties of slags of the system CaO–SiO2–B2O3–Al2O3–MgO had formed the basis for the technology development for the formation of basic boron-containing slags, that implementation at the LFU in the converter shop of JSC “ArcelorMittal Temirtau” provided the smelting of boron-containing steel economically doped with manganese with low-content of sulfur and high strength and plastic properties. The developed technology provided, depending on the steel grade, a boron content of 0.001–0.008% by weight, low concentration of sulfur in the metal, not more than 0.004–0.014% by weight, and reducing the manganese ferroalloys consumption from 0.5 to 1.4 kg/ton of steel. Keywords: pipe steel, manganese, sulfur, boron, mechanical properties, structur

Study of possibility of cerium reduction from slags of CaO-SiO2-Ce2O3-15%Al2O3-8%MgO system

By means of theoretical and experimental studies it is shown that it is possible to reduction cerium from the slags of the CaO-SiO2-Ce2O3 system containing 15%Al2O3 and 8 % MgO, by aluminum dissolved in metal, at temperatures of 1550 and 1650 C. The results of mathematical modeling are presented graphically as 'composition - equilibrium content of cerium in metal' diagrams. It is found that depending on temperature of metal, basicity of slag and the content of cerium oxide, from 0.055 to 16 ppm cerium passes into metal containing 0.06 % of carbon, 0.25 % of silicon and 0.055 % of aluminium. Positive influence of the temperature factor, basicity of slags and the content of cerium oxide in a studied range of chemical composition on process of cerium reduction is explained from the perspective of phase structure of formed slags and thermodynamics of reactions of cerium reduction. The possibility of reduction of cerium from slags of CaO-SiO2-Ce2O3 system, containing 15 % Al2O3 and 8 % MgO, has been experimentally confirmed. It has been shown that at basicity of 5 and 4 % of Ce2O3 in slag up to 16 ppm cerium passes into metal during 10 minutes exposure. © Published under licence by IOP Publishing Ltd.The work was supported by RFBR grant 19-08-00825

РАВНОВЕСНОЕ РАСПРЕДЕЛЕНИЕ БОРА МЕЖДУ МЕТАЛЛОМ СИСТЕМЫ FE - C - SI - AL И БОРСОДЕРЖАЩИМ ШЛАКОМ

Using the HSC 6.1 Chemistry software package (Outokumpu) and simplex-lattice planning, the thermodynamic modeling of the boron equilibrium distribution between iron containing 0.2 % of C, 0.35 % of Si, 0.028 % of Al (in the terms and hereinafter indicated mass. %) and slag of the system СаО – SiO2 – Аl2O3 – 8 % МgO – 4 % В2O3 was carried out in a wide range of chemical composition and at temperatures of 1550 °С and 1600 °С. Adequate mathematical models in the form of III degree polynomial obtained for each temperature, describes the equilibrium distribution of boron between slag and metal depending on the slag composition. Mathematical modeling results are presented graphically in the form of diagrams of composition – boron equilibrium distribution. It is shown that slag basicity affects on the boron distribution coefficient. Thus, increasing the slag basicity from 5 to 8 at temperature of 1550 °С reduces the boron distribution coefficient from 160 to 120 and, as a consequence, increase the boron content in the metal from 0.021 % at LB = 159 to 0.026 % at LB = 121, that is, growth slag basicity is beneficial to the development of boron recovery process. The positive effect of the slag basicity on boron recovery process in the researched range of the chemical composition can be explained according to the slag phase composition and thermodynamics of boron reduction reactions. The temperature growth of the metal negatively affects the boron recovery. Equilibrium boron distribution coefficient increases by an average of 10 units with an increase in temperature to 1600 °C. The diagrams contain marked field of slag chemical composition with 53 – 58 % of CaO, 8.5 – 10.5 % of SiO2 and 20 – 27 % of Al2O3, providing boron distribution coefficients at level of 140 – 170 at temperature range of 1550 – 1600 °C and allowing to expect boron concentration in the metal at the level of 0.020 % at LB = 168 % and 0.023 % at LB = 139 at the 4 % of B2O3 in the slag initial. © 2017 National University of Science and Technology MISIS. All rights reserved

Effect of basicity and chromium oxide on the viscosity of boron-containing slags

The main diluent for chromium-containing slags is CaF2. However, fluorspar disadvantages make it necessary to search for a replacement. As a substitute, boron oxide allows to improve slag physical properties and environmental situation. The paper presents the experimental study results of the chemical composition and temperature influence on viscosity of slags of CaO-SiO2-Cr2O3 system containing 8% MgO, 3% Al2O3 and 6% B2O3. It was found that a slag free of chromium oxide with basicity of 1.0 has a sufficiently high fluidity of 0.2-0.6 Pa•s in a wide temperature range of 1200-1350 C, due to high concentration of low-melting phases, reaching 22%, and only 11 % high-melting. A slag with 18% Cr2O3 and the same basicity retains a low viscosity of 0.1-1.0 Pa•s but at higher temperature of 1450-1570 C due to increase in high-melting compound content to 27%. The viscosity of a slag with basicity of 2.5 without chromium oxide is 0.07-1.0 Pa•s in a narrow temperature range of 1650-1700 C and 0.14-1.0 Pa•s for a 'shorter' slag with 18% Cr2O3 and same basicity in even narrower range of 1650-1670 C. These slags have the highest high-melting phase content of about 50%. © Published under licence by IOP Publishing Ltd

Effect of Basicity on the Physical Properties of the СaО-SiO2- Cr2O3-B2O3-Аl2O3-МgO Slag System with a High Content of Chromium Oxide

In the work, viscosity, beginning of crystallization temperature, phase composition, and structure of the CaO–SiO2–Cr2O3–B2O3–Al2O3–MgO slag system were studied in the basicity range from 1.0 to 2.5 using vibrational viscometry, phase composition thermodynamic modeling, and Raman spectroscopy.Работа выполнена в рамках исполнения государственного задания ИМЕТ УрО РАН с использованием оборудования ЦКП "Состав вещества" ИВТЭ УрО РАН

Study of the viscosity of slags of ??? - SiO2 - ?2?3 - 25 % Al2O3 - 8 % MgO System

The effect of the B2O3 content and the slag basicity on the viscosity of the CaO–SiO2–B2O3 system containing 25 % Al2O3 and 8 % MgO2 was studied using a simplex-lattice method of experiment planning that allows obtaining mathematical models describing the dependence of the property on the composition as a continuous function. Synthetic slags, corresponding to the composition of simplex under study, were smelted in graphite crucibles from pre-calcined oxides. The composition of slags, corresponding to the remaining points of the local simplex plan, was obtained by counter-packing the slags of simplexes. The viscosity of the slag was measured in molybdenum crucibles by means of an electrovib-rational viscometer in an argon flow with continuous cooling of the melt from a homogeneous-liquid to a solid state. Mathematical models were constructed that describe the relationship between the temperature of a given viscosity and the composition of the oxide system using experimental data. Then, a set of viscosity isolines was obtained by combining the obtained composition-temperature diagrams of the given viscosity with the isothermal section of the composition-viscosity diagram. The generalization of mathematical modeling results and graphical imaging on the isothermal profile of the composition-viscosity diagram made it possible to obtain new data on the viscosity of the CaO–SiO2–B2O3 oxide system containing 25 % Al2O3 and 8 % MgO in the basic 2–5 range and 1–10 % B2O3 content. The slags of the oxide system under study in the temperature range of 1400–1500 °C are characterized by low viscosity. At a temperature of 1400 °C, the viscosity of slag with basicity 2.0–2.5, containing 7–10 % B2O3 does not exceed 3–4 Ps. The displacement of the slag into the basicity of 3–5 is accompanied by a decrease in B2O3 content to 2–6 % by increasing the slag viscosity to 12 Ps. An increase in temperature to 1450 °C leads to a significant decrease in the viscosity of slags with basicity of 2–3, even for slag with B2O3 content of 4 %, it does not exceed 4 Ps and increases to 6 Ps in the basicity of 3–5 and B2O3 content of 1–3 %. The slag viscosity in the basicity of 3–5 at B2O3 content of 1–4 % does not exceed 4 Ps at a temperature of 1500 °C. © 2017, National University of Science and Technology MISIS. All rights reserved