Du Y. Development and research of technology for the production of refined manganese alloys in a converter with bottom purge

The dissertation on competition of a scientific degree of the candidate of technical sciences on a specialty 05.16.02 - Metallurgy of ferrous and nonferrous metals and special alloys. National Metallurgical Academy of Ukraine, Specialized Academic Council D.08.084.03. Dnipro, 2020. The dissertation is devoted to the solution of the actual problem in the field of theory and technology of refining of high - carbon ferromanganese for receiving medi-um - carbon ferromanganese in converters with bottom blast. An assessment of the current state and problems of obtaining low-carbon manganese ferroalloys. Based on the analysis of physicochemical features of the known methods and mechanism of dephosphorization of manganese alloys and conditions for achieving the required de-grees of conversion of phosphorus into the slag phase, the expediency of the process of dephosphorization of the alloy in one stage using a mixture comprising iron oxide is substantiated. sodium orthosilicate, which increased the throughput of manganese from the raw material. Exclusion from the composition of materials for dephospho-rization of fluorine compounds has increased the environmental friendliness of the re-fining process. Thermodynamic analysis of phase equilibrium in the metal-slag-gas system with respect to the complex heterogeneous system Mn-Si-Fe-Ca-P-C-O is performed and the influence of parameters on the equilibrium distribution of elements between phases in the interaction of manganese charge with carbon and silicon is established. The presence of silicon in the melt and its high affinity for oxygen leads to the predominant oxidation of silicon and blocking the oxidation of manganese. The degree of reduction of manganese depends on the content of the reducing agent - silicon in the alloy. Decreased manganese reduction was observed at a silicon content of more than 50%, which may be due to an increase in the viscosity of the formed acid slag, which reduces the rate of mass transfer processes at the slag-metal interface. The optimal content of silicon in the alloy for the reduction of manganese is 20-22.5%, which corresponds to commercial silicomanganese. Developed ideas about the laws of mass transfer and thermal processes in the silicothermal reduction of manganese oxides from slag melt in a converter with a bottom blast. For a balanced heat treatment mode, ensuring the stability of the converter lining and intensification of mass transfer between slag and metal, the frequency of oxygen and argon supply is used, which provides an increase in the useful extraction of manganese. An innovative technology for obtaining medium-carbon ferromanganese by the duplex process "arc electric furnace - gas-oxygen converter with bottom energy supply" has been developed, which provides an increase in the useful extraction of manganese from raw materials from 83% to 86%. In the conditions of the plant of the company "Shanxi Yida Special Steel Group Co.Ltd" in Taiyunan, China on industrial melting in a 15t converter with purge of oxygen and argon in refining manganese alloys to obtain a given chemical composition of medium carbon ferromanganese and metallic manganese obtained refined manganese alloys, the compositions of which correspond to standard values. The manganese content in the experimental alloy is 85… 86%, which corresponds to the manganese content in medium carbon ferromanganese and reaches up to 95% in metallic manganese without deterioration of metallurgical properties; the total use of manganese in the converter redistribution increased and the losses of manganese with slag decreased; high productivity of the converter equipment at technological simplicity of realization of the developed technology is reached. Key words: high-carbon alloy, refining, carbon, phosphorus, converter, bottom purge, oxygen, argon.