METALLURGICAL TECHNOLOGIES
Analysis of the existing trends in development of technologies for production of welding and surfacing fluxes showed that one of the actively developing areas is the production of fluxes using man-made waste (including metallurgical one) as components of the initial charge. This is due to the fact that the slag waste of metallurgical production contains a large amount of manganese and silicon, which in turn are the basis in welding fluxes. Within the framework of this direction development, the article describes principal possibility and efficiency of using materials based on ladle electric steelmaking slag from JSC “EVRAZ United West Siberian Metallurgical Combine” and slag produced by silicomanganese from LLC “West Siberian Electrometallurgical Plant” in the charge for production of fluxes used in the surfacing of rolling rolls. All the laboratory tests were made using the equipment of the scientific and production center “Welding Processes and Technologies”. For surfacing steel samples, the authors used a flux additive obtained by mixing ladle electric steelmaking slag of a fraction less than 0.2 mm with liquid sodium glass in a ratio of 62 and 38 %. The resulting flux additive was mixed with slag from the production of silicomanganese of a fraction of 0.45 - 2.50 mm in various ratios. Studies of the chemical composition (by the spectral method) and metallographic studies of the deposited layer revealed a tendency to an increase in sulfur content and in contamination with non-metallic inclusions in it with an increase in content of the flux additive in the charge of more than 20 %. According to the results of visual quality control of the deposited layer macrostructure, the absence of defects was established with a flux additive content of up to 30 %.
Experimental studies carried out in the conditions of a laboratory rolling mill have determined the regularities of the processes of metal flow and roll-out defects of billets during deformation in roughing stands of a universal rail and structural mill. In relation to the box size and gauges types "lying trapeze" and "trapeze", we have determined a significant irregularity of drawing coefficients of the surface layers by roll length and width, as well as the irregularity of drawing in the cross-section of the roll during rolling. It is shown that during deformation the surface zones adjacent to the ends of the roll are subjected to the greatest drawing, and dependence of irregularity of the drawing coefficients over the cross-section of the roll on the shape of the deformation zone has a distinct power-law character. We have established a significant effect of the drawing coefficient, as well as the location and spatial orientation of the billet defects, while the geometric dimensions of the defects don't have such influence on their roll-out coefficients. According to the obtained data, the defects located on the rolling edges are rolled out most intensively both in depth and width, and the transverse defects are rolled out the least intensively. At the same time, the rollability of any defects increases with the growth of drawing coefficient. It is determined that near the side edges of the roll there is an increase in the width (disclosure) of transverse and inclined defects relative to the rolling axis, as well as the disclosure of defects occurs at the end sections of the roll in relation to longitudinal defects. For internal defects, it was found that, similar to surface defects, an increase in the drawing coefficient during rolling contributes to an increase in their roll-out, while the rollout coefficient of internal defects in absolute value is significantly lower than this indicator for surface defects. It was determined that the minimum roll-out coefficient of internal defects occurs when they are located in the core of the sample, while the roll-out coefficient of such defects increases linearly when moving towards the roll surface. The influence of the location, spatial orientation, and drawing coefficient on the rollability of surface and internal defects is generalized in the form of regression equations. It makes it possible to use them in practice to predict the quality of finished rolled metal when changing rolling modes.
The article presents results of the study of possibilities of selective laser melting (SLM), or so-called additive technologies, for production of permanent magnets. This process makes it possible to produce not only product models and prototypes, but also finished functional products using layer-by-layer addition of material and binding of particles and layers to each other. An alloy based on Fe - Cr - Co system has been chosen as the material for evaluation of the compared technologies for permanent magnets production. The application fields of selective laser melting (SLM/SLP) were considered. The powders obtained by different methods are taken for the research. Classical technology of magnetic alloy casting also was analyzed. The studies of magnetic materials and comparisons of the properties of powder magnets with standard data were carried out. On the basis of 25Kh15KA alloy powder sprayed by gas atomization, permanent magnets with a material density of 7.59 - 7.55 g/cm3 can be manufactured at the SLP plant. They meet the requirements recommended by the state standard GOST 24897 - 81, and achieve characteristics of magnets made by classical metallurgical technologies. To study the magnetic and physical properties, four samples were produced with the same geometry in the shape of a cube. During production of each of the test samples, different operating modes of the plant were selected. Samples were made on the basis of the “Kurchatov Institute” NRS enterprise (the “Prometheus” Central Research Institute of Construction Materials) as part of the NIO-35 technological complex. It was established that characteristics of the powders obtained by gas atomization qualitatively exceed characteristics of the powders obtained by other methods, and the produced magnets meet all the requirements for magnets.
RESOURCE SAVING IN FERROUS METALLURGY
The article presents results of theoretical and experimental studies of the processes of iron solid-phase reduction from an iron-containing concentrate obtained as a result of hydrometallurgical dressing of ferromanganese and polymetallic manganese-containing ores with coals of grades D (long-flame) and 2B (brown). The method of thermodynamic modeling using TERRA software complex was used to study the reducing properties of hydrocarbons by calculating equilibrium compositions in the temperature range of 373 - 1873 K. The authors obtained the dependences of compositions and volume of the gas phase formed as a result of the release of volatile components during heating on the temperature for the coals of the grades under consideration. As a result of thermodynamic modeling, the optimal temperatures and consumption are determined, which ensure the complete iron reduction from an iron-containing concentrate. The results of experimental studies were obtained by modern research methods using laboratory and analytical equipment, as well as methods of statistical processing. Results of the coals analysis carried out using the Setaram LabSys Evo thermal analyzer showed that the process of thermal decomposition of coals of the studied grades proceeds according to general laws. The process of thermal decomposition of long-flame coal proceeds less intensively than of brown coal. The results of an experimental study of the processes of thermal decomposition of reducing agents have shown that volumes of the gas phases, formed when coals are heated to a temperature of 1173 K in an argon atmosphere, practically coincide with the calculated values. As a result of thermodynamic modeling and experimental study, the optimal consumption of D and 2B grades of coal is determined at a temperature of 1473 K. The best reducing agent with a minimum specific consumption is long-flame coal of D grade. When determining the optimal amount of reducing agent in charge mixtures during the study of metallization processes, it was found that with an excess of reducing agent, it is possible to achieve almost complete extraction (98 - 99 %) of iron from the concentrate.
MATERIAL SCIENCE
In this study, we discuss the structure and properties of high-entropy AlCoCrFeNi alloy after casting, cold deformation, and heat treatment. Ingots of the investigated alloys were obtained by arc melting method in argon atmosphere. In order to ensure a homogeneous chemical composition, ingots were remelted several times. Cylindrical samples of 5 mm in diameter and 8 mm in height were cut from ingots by electrospark method for mechanical tests. Subsequently, samples were subjected to uniaxial compression by 5, 11, and 23 %. During the tests, compression curves were recorded, and limit of proportionality of the analyzed alloys was calculated. High-temperature annealing and thermal studies were performed using thermogravimetric analyzer. Thermal studies were carried out in a cyclic mode (3 cycles, including heating up to 1200 °C at a rate of 20 °C/min and cooling at a rate of 20 °C/min). High-temperature annealing was carried out at a temperature of 1200 °C for 5 hours. Such annealing of cast alloys promotes material homogenization and eliminates dendritic structure. The alloy presents limited plasticity. Grain boundaries are effective barriers preventing crack propagation. The studies indicate that plastic deformation has a significant effect on development of relaxation processes during subsequent heat treatment. An increase in strain during the compression leads to a higher rate of healing processes of defects in crystal structure.
From accumulated information on structure, properties, stability, and methods of manufacturing the high-entropy alloys (HEA) created early in the 21 century it follows that they possess a whole complex of useful properties that suggests their perspective application in different branches of industry. The authors have made a short review of scientific articles on analysis of possibilities of HEA application in specific science-consuming branches of the last 5 years. In biomedicine the protective coatings made of (TiZrNbHfTa)N and (TiZrNbHfTa)O HEAs possess biocompatibility, high level of mechanical properties, high wear- and corrosion resistance in physiological media, and excellent adhesion. Products made of (MoTa)χNbTiZr passed clinical tests successfully when being implanted to living muscular tissue. The developed HEAs based on rare-earth elements and metals of Fe group such as YbTbDyAlMe (Me = Fe, Co, Ni) possess magnetocaloric effect, have Curie temperature close to room one and may be used in modern refrigerator mechanisms. Changing in stoichiometric composition of CoCrFeNiTi HEAs, alloying them and performing thermal treatment, the researchers succeed in obtaining soft magnetic materials. Fields of HEA application are presented as following: catalysts of ammonia oxidation - (PtPdRhRuCe), ammonia decomposition - (RuRhCoNiIr), oxidation of aromatic alcohols - (Co0,2Ni0,2Cu0,2Mg0,2Zn0,2 ), electric catalysts of hydrogen extraction - (Ni20Fe20Mo10Cr15Co35 ), redox reactions (AlCuNiPtMn and AlNiCuPtPdAu), and oxidation of methanol/ethanol. HEAs can be used as electrodes - anodes and cathodes for Li-ion and Na-ion accumulators. Synthesized nanoporous HEA AlCoCrFeNi has high bulk density up to 700 F/cm3 and cyclic stability (>3000 cycles) and is used in supercapacitors. High-entropy oxides such as (MgNiCoCuZn)0.95Li0.05O with high dielectric properties in a wide frequency range may be used in electronic converters. Examples of HEA application are given: as coatings of ship parts being operated in sea water, various welded joints, parts of nuclear reactors. Perspectives of widening the fields of HEA application are indicated.
INNOVATIONS IN METALLURGICAL INDUSTRIAL AND LABORATORY EQUIPMENT, TECHNOLOGIES AND MATERIALS
Today there is an urgency of creating high-performance continuous processes for the production of bimetals. The article describes the main tasks of improving the quality of the materials under consideration. Two stages of the technology for producing steel three-layer bimetallic strips on the unit of a combined continuous casting and deformation process are considered. The authors give recommendations on the conduct of the technological process in order to obtain high-quality bimetallic strips on such unit. The problem statement is presented. The material considers initial data for determining the temperature of the steel base strip and the stress-strain state of the metals of the cladding layers and the strip in deformation center of a three-layer bimetallic ingot. A model for calculating and a method for solving problems of thermal conductivity and elastoplasticity are shown. Regularities of the temperature change of the main steel strip are given during its passage through the molten metal of the cladding layer. Stress-strain state of the metals of the main strip and cladding layers in the deformation center was determined when three-layer bimetallic steel strips were obtained on the unit of combined continuous casting and deformation process. The authors describe the values of compression of the main steel strip and mutual displacement of the layers during compression of the bimetallic ingot by the strikers. Regularities of the distribution of axial and tangential stresses are shown along the contact line of the cladding layer with the striker. The evaluation of the process of obtaining bimetal steel 09G2S - steel 13KhFA - steel 09G2S was made on a pilot unit for continuous casting and deformation. Microstructure of the main strip and cladding layers of a three-layer bimetallic steel strip is shown when a combined continuous casting and deformation process is obtained in one unit.
PHYSICO-CHEMICAL BASICS OF METALLURGICAL PROCESSES
The possibility of joint selective solid-phase reduction of iron and phosphorus in ferromanganese ore has been experimentally confirmed. The experiments were carried out in a Tamman laboratory furnace at a temperature of 1000 °C and holding for two and five hours. The article presents results of the study of phase composition and phases' quantitative ratio of the reduction products, as well as chemical composition of the phases. It was established that reduction roasting in CO atmosphere provides a transition from oxide phase to metal phase only of iron and phosphorus. At the same time, the concentration of manganese oxide MnO increases in the ore oxide phase. The use of solid carbon as a reducing agent under the same conditions leads to transition to the metallic phase together with iron and phosphorus of a part of manganese. Based on the obtained data, it is proposed to selectively reduce iron and phosphorus at a temperature of 1000 °C with a reducing gas. Gas reduction will make it possible to use existing gas furnaces, in particular, multi-pod furnaces, for metallization of iron and phosphorus in ferromanganese ore, and natural gas, including hydrogen -enriched gas, and even pure hydrogen, as a reducing agent and energy carrier. Due to this, at the stage of ore metallization in production of manganese alloys, greenhouse gas CO2 emissions can be reduced. The results of the work can be used in the development of theoretical and technological bases for processing ferromanganese ores with a high content of phosphorus, which are not processed by existing technologies.
Phase diagram of the ternary oxide system FeO - SrO -Al2O3 was constructed for the first time. In this system, the following compounds can be formed: hercynite FeAl2O4 and five strontium aluminates - Sr4Al2O7 , Sr3Al2O6 , SrAl2O4 , SrAl4O7 , SrAl12O19 . According to the calculations performed, solid solutions of oxides are not formed in the system, as it is confirmed by the literature data. In the course of modeling, the optimal energy parameters of the theory of subregular ionic solutions were selected for the components of the oxide melt (FeO, SrO, Al2O3 ). Thermodynamic analysis of strontium deoxidizing ability in liquid iron at presence of aluminum was carried out using the technique for constructing the surface of solubility of strontium and aluminum in metal for steelmaking temperatures (1550 and 1600 °C) and carbon concentrations of 0.1 and 0.4 %. The equilibrium constants of the reactions of formation of strontium aluminates Sr3Al2O6 and SrAl2O4 from the components of the metal melt were calculated for the temperature range of 1550 - 1650 °C. It was found that the rest of strontium aluminates can be formed in liquid metal only at temperatures above 1750 °C. The base of thermodynamic data for the studied systems is given: temperature dependences of equilibrium constants for reactions occurring between components; values of interaction parameters of the first order (according to Wagner) for elements in liquid iron; values of energy parameters of the theory of subregular ionic solutions (for oxide melt). It follows from the calculations that the formation of strontium monoaluminate SrAl2O4 and corundum Al2O3 is most probable as the interaction products in Fe -Al - Sr - O and Fe -Al - Sr - C - O systems.
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