Materials Science Forum Vol. 946

Abstract: In this paper the analysis of the processes for spontaneous decay of slags from the production of refined ferroalloy grades is performed. It is shown that the main reason for the decay is the formation of a dicalcium silicate in highly basic melts with CaO / SiO₂ ratio of 1.5-3.1. Based on the performed studies, three main promising directions for the stabilization of slags of ferroalloy production have been formed. First direction is the replacement of the calcium cation (or transformation) in a dicalcium silicate, for example, with the magnesium cation or the production of non-decaying compounds of the gehlenite type (2CaO·Al₂O₃·SiO₂), mainly due to the application of phase composition peculiarities of the waste rock for ferroalloy raw materials. Second direction is the reduction of the dicalcium silicate content with a decrease in the ratio of CaO / SiO₂ in the slag less than 1.4, due to the separation of the silicothermic reduction process into two stages, obtaining in the first stage a low-basic (CaO / SiO₂ = 1.3-1.4) non-decaying tailing slag, and on the second one - highly basic return slag (1.8-1.9), which is used in the first stage of this technological chain. The third direction is the replacement of the SiO anion of dicalcium silicate with other anions, for example, ВО by means of small additions of calcium borate, colemanite, etc. A possibility for stabilization of ferroalloy production slags with obtaining of construction crushed stone corresponding to the requirements of TU 0798-69-00186499-2014 "Crushed stone and sand from ferroalloy slags. Technical conditions», is shown experimentally.

Abstract: In this article the time and heat dependence of the nitrogen distribution upon steel alloying of 04Cr20Ni6Mn11Mo2NVNb steel grade by the nitrided manganese of Mn85N10 grade at the holding in the air atmosphere from 2 to 30 minutes in the temperature range 1450-1550 °С was experimentally determined. It was determined that the highest degree of nitrogen transition into steel is 99% and is observed with a short holding time of 2 min (after the introduction of nitrided manganese into the steel melt) in the low-temperature region ~ 1450 °С. Further holding and / or temperature growth results in the release of nitrogen in the gaseous form, due to the thermal dissociation of the nitrogen-containing compounds contained in the melt and removal of nitrogen from the melt into the gas phase, which leads to a decrease in the degree of nitrogen transition to the steel. The key possibility for obtaining a steel of the indicated grades group with a nitrogen content of 0.45-0.6% is shown when alloying in an air atmosphere in a low-temperature region (1450-1500°C), while optimizing the holding time.

Abstract: A mathematical model of the overall material and thermal balance of the ferromanganese smelting in blast furnaces of JSC "Satka Iron Smelting Works" is presented. Completeness of chemical reactions was taken into account in calculations based on thermodynamic analysis and technological data. Data on the thermochemical properties of substances; on the thermal effects of chemical reactions; on the degree of carbon graphitization in coke; on the heats of formation of metallic and slag solutions; on the thermochemical characteristics of ferromanganese, slag and gas phase were systematized and corrected. Heat losses for a particular type of blast furnaces are taken into account. The mathematical model is implemented in the computer program environment Lazarus. Test calculations of material and heat balances of ferromanganese blast furnace smelting were carried out. The calculation results correspond to the technological data. The developed software allows you to manage quickly the production process, to predict the optimal composition of charge materials for obtaining a product of a specific composition without experimental smelting. The software is used in the "consultant" mode at the JSC "Satka Iron Smelting Works".

Abstract: The process of a eutectic alloy crystallization is considered when the eutectic alloy is instantly cooled from the liquid state to below the eutectic transformation temperature. The features of such crystallization are considered. The mathematical model of the process is constructed that takes into account the nucleation of new phases particles, their growth and the associated change the concentrations of the melt components. The nuclei of new phases are supposed be spherical. As they grow, they come into contact and become lamellar. The developed approach was applied to the amorphization process of the eutectic alloys. An amorphous state has been reached if the clusters of solid phases can’t grow above nanosize. The model allows researching the necessary amorphization conditions.

Abstract: The results of thermodynamic modeling of the effect of aluminum (0.005–0.1%), contained in the metal at constant silicon concentrations (0.2%) and carbon (0.1%) on the boron reduction process from the slag of the system CaO-SiO₂-MgO-Al₂O₃-B₂O₃ basicity (CaO)/(SiO₂) equal to 5 in the temperature range 1400–1700 °C, in steps of 50 °C are presented. For modeling, the software complex HSC Chemistry 6.12 developed by Outokumpu Research Oy (Finland) was used. The calculations using the Equilibrium Compositions module at a gas-phase pressure of 1 atm, containing 2.24 m³ of N₂ (gas) as a neutral additive were performed. The obtained simulation results indicate the thermodynamic possibility of boron reduction from the slag of the CaO-SiO₂-MgO-Al₂O₃-B₂O₃ system by silicon and aluminum, whose concentration in the metal is insignificant – 0.2 and 0.005–0.1%, respectively. It was found that an increase in the initial aluminum content in the steel promotes an increase in the concentration of reduced boron in the metal with a content of 4% B₂O₃ and a given temperature. Thus, at a process temperature of 1650 °C, an increase in the initial aluminum content from 0.005 to 0.1% made it possible to increase the boron concentration in the metal by 28.5%. The results of thermodynamic modeling characterizing the effect of temperature on the degree of boron reduction at different aluminum contents are presented. Experiments on the inter-phase distribution of boron between the slag of the CaO-SiO₂-MgO-Al₂O₃-B₂O₃ system and the metal were carried out in a high-temperature Tamman resistance furnace. Low-carbon steel containing 0.005% Al was used. It was shown that aging of the metal under the slag containing 4.3% of B₂O₃ is accompanied by reduction of boron, the amount of which in the finished steel is 0.0089%. The coefficient of boron assimilation (K_B) is 5.8%, which is in principle correlated with the results of thermodynamic modeling. The obtained results of thermodynamic modeling and experimental data showed that it is possible in principle to directly microlite boron steel by reducing it with aluminum and silicon contained in the metal.

Abstract: Electro-slag re-melting (ESR) is a process that combines all important elements of steel melting conversion. JSC “RPA “CNIITMASH” continuously developed ways to use ESR to manufacture critically important parts for power engineering, including nuclear power engineering, heavy-duty machine engineering and other machine building industries. Enhanced performance of product is an important competitive advantage that ESR provides in comparison to other metallurgical processes. Present report reflects results of the latest research work aimed at resolving issues related to control and management of refining and crystallization processes, cost reduction for ESR products. Practical relevance of developed approach to control of ESR metal quality is revealed by data of achieved parameters which characterize properties of pipes and pipeline elements in energy and nuclear power industries which rely on ESR ingots as work-piece blanks.

Abstract: It is shown that the value of the equilibrium oxygen partial pressure, Po₂ as a value available for measurements is possible to be taken as a measure of slag redox potential of, taking into account its electronic system performance. Application of the electromotive force method (EMF) allowed establishing the character of a change in the average oxidation state of iron ν_Fe depending on Po₂, the temperature and slag composition. The study of Mössbauer absorption spectra of quenched slag samples confirmed the possibility of simultaneous presence of iron in the flux in oxidation states from 0 to +3.

Abstract: A significant part of the cost of released products in the smelting of steel is the cost of graphite electrodes, so reducing their specific consumption is an urgent task. The aim of the work is to study on a computer model and analyze the efficiency of using evaporative cooling to reduce the consumption of graphite electrodes in electric arc furnaces of three-phase alternating and direct current of small capacity. A computer simulation of the thermal state and fame of graphite electrodes for arc furnaces of three-phase and direct current with the capacity of 12 tons was performed. The efficiency of using evaporative cooling of graphite electrodes was revealed. It is established that for arc furnaces operating on direct and three-phase alternating current, the use of electrodes water cooling allows to reduce the consumption of graphite by about one and a half times. It is established that the water supply to the evaporative cooling system is the most rational during 1–2 minutes after the current is turned on. The use of evaporative cooling of graphite electrodes in arc furnaces can be recommended to reduce their consumption on operating and designed small capacity alternating and direct current arc furnaces.

Abstract: We have studied the influence of oxidation-reduction reactions on the structure and strength behavior of the Kachkanar fluxed pellets both in their initial condition and during reduction. It has been discovered that at heating rates and temperatures found in industrial units the roasted pellets that are not oxidized to a full extent and are characterized by zonal structure do not meet the requirements imposed for the blast-furnace smelting raw materials. To develop a process that would ensure high metallurgical properties, we have analyzed the hematite dissociation reaction. It was found that the temperature and the content of slag-forming oxides influence this reaction. A sinter pot was used to carry out the research and determine metallurgical properties of partially dissociated pellets. The obtained results helped to develop a process to dissociate hematite at lower temperatures with calcium ferrosilicate melt. Such pellets are reduced at the temperatures of over 700^оС, which prevents their destruction in blast furnaces.

Abstract: Kinetics of the siderite ore roasting in the air, helium and hydrogen flows has been studied in a gasometrical unit with continuous mass variation logging. We have derived the expression for determination of an apparent degree of calcination and identified its dependence on the size of the prill, the heat treatment duration, and gas-phase composition. Using a generalized chemical kinetics equation, we have obtained a formula for calculation of the decomposition period for siderite ore samples. It has been found that calcination rate increases with the temperature rise, irrespective of the sample size and atmospheric composition. Calcination process has been studied at low temperatures. We have demonstrated that it is feasible to describe the process of siderite ore thermal dissociation by a first-order kinetics equation. We have obtained the expression to calculate the duration of this process depending on different parameters. Using a generalized chemical kinetics equation, we have obtained a formula for checking the expressions that describe the experimental data. We have studied kinetics of the reduction of roasted ore samples at various temperatures using different sizes of the samples. The obtained results have been applied for optimization of the design values and operating conditions of the siderite ore roasting in shaft furnaces. These will also be used for designing a shaft furnace consisting of a calcination zone, reduction zone (metallization zone) and metallized product cooling zone, which will increase iron content in the end-product to 65-70%.