Ladle-furnace Unit Research Articles

Production of refining alumina-containing fluxes by sintering from technogenic raw materials

Modern Russian steelmaking plants use predominantly alumina-containing materials for liquefying lime in a ladle-furnace unit, which replaced fluorspar. Alumina-containing materials currently available on the market cannot be used directly in steelmaking without preliminary preparation (refining, heat treatment or briquetting), or are simply unsuitable for ladle processing of steel. This work describes laboratory studies on the production of refining alumina-containing fluxes by sintering in units such as machines for pellets firing or producing agglomerate (in the temperature range of 1200 – 1500 °C) from clean metallurgical waste (fine dust from the production of alumina and burnt lime), meeting the requirements of steelmaking plants by chemical composition and mechanical properties. A comparison was made of sintering technological schemes with the introduction of hydra­ted lime and a mixture of hydrated lime and calcium carbonate in a 1:1 ratio as a source of CaO. We determined that the maximum permissible CaO content in sintered briquettes when using a mixture of hydrated lime and calcium carbonate in the charge, which does not lead to hydration destruction in air, is in the range of 2.3 - 3.6 %, depending on the holding temperature. The maximum permissible content of Al2O3 in sintered briquettes when using hydrated lime in the charge, which does not lead to hydration destruction in air, is in the range of 9.5 – 31.7 %, depending on the holding temperature. In existing fuel units it is possible to obtain fluxes by sintering only when using hydrated lime as a source of CaO, because adding calcium carbonate to the charge (9 – 22 %) requires an increase in holding temperature (above 1500 °C) or holding time (more than 25 min).

Acoustic monitoring of steel production in the ladle-furnace unit

A method of implementing acoustic control of the steel-making process in a ladle-furnace unit using a step-by-step acoustic event recognition model is proposed. The use of the developed model makes it possible to predict metal emissions with an accuracy of 96 %.

Method for Forecasting the Remaining Useful Life of a Furnace Transformer Based on Online Monitoring Data

Implementing the concept of a “smart furnace transformer” should stipulate its information support throughout its life cycle. This requires improving techniques for estimating the transformer’s health and forecasting its remaining useful life (RUL). A brief review of the problem being solved has shown that the known RUL estimation techniques include processing the results of measuring the facility state parameters using various mathematical methods. Data processing techniques (deep learning, SOLA, etc.) are used, but there is no information on their application in online monitoring systems. Herewith, fast (shock) changes in the resource caused by the failures and subsequent recoveries of the facility’s health have not been considered. This reduces the RUL forecasting accuracy for the repairable equipment, including transformers. It is especially relevant to consider the impact of sudden state changes when it comes to furnace transformers due to a cumulative wear effect determined by their frequent connections to the grid (up to 100 times a day). The proposed approach is based on calculating the RUL by analytical dependencies, considering the failures and recoveries of the facility state. For the first time, an engineering RUL forecasting technique has been developed, based on the online diagnostic monitoring data results provided in the form of time series. The equipment’s relative failure tolerance index, calculated with analytical dependencies, has first been used in RUL forecasting. As a generalized indicator, a relative failure tolerance index considering the facility’s state change dynamics has been proposed. The application of the RUL forecasting technique based on the results of dissolved gas analysis of a ladle furnace unit’s transformer is demonstrated. The changes in the transformer state during the operation period from 2014 to 2022 have been studied. The RUL was calculated in the intensive aging interval; the winding dismantling results were demonstrated, which confirmed developing destructive processes in the insulation. The key practical result of the study is reducing accidents and increasing the service life of the arc and ladle furnace transformers. The techno-economic effect aims to ensure process continuity and increase the metallurgical enterprise’s output (we cannot quantify this effect since it depends on the performance of a particular enterprise). It is recommended to use the technique to forecast the RUL of repairable facilities equipped with online monitoring systems.

Методика оцінки фізико-хімічної взаємодії в системі "метал-шлак" як кооперативного іонообмінного процесу під час рафінування сталі

Dephosphorisation and desulphurisation are the most important stages of high-quality steel production, characterized by complex physical and chemical processes of interaction in the metal-slag system. The article is devoted to studying the results and evaluating the efficiency of steel refining processes at different stages of its refinement in modern Ukrainian conditions. The aim of the work is to develop a methodology for assessing the physical and chemical interaction in the metal-slag system during steel refining from the perspective of the concept of a cooperative ion exchange process using the parameters of interatomic interaction in melts. As a result of studying the regularities of sulphur and phosphorus distribution depending on the chemical composition of different steel grades from two plants and their corresponding slags, a methodology has been developed that includes the reasonable use of parameters of interatomic interaction in melts as criteria for assessing the degree of completion of ion exchange processes during steel refining. Along with the use of integral physical and chemical parameters of the chemical and charge state of metal and slag melts (chemical equivalent of metal composition ZY(e) and slag Δe(e), effective charge of element Ze(e)), the paper shows the key role of the influence of the "recharge" parameter of the element ΔZе on the process of interfacial distribution of sulfur and phosphorus. This parameter has also shown its efficiency as a criterion for assessing the deviation of the metal-slag system from equilibrium at different stages of steelmaking and finishing at the ladle furnace unit (LFU). The proposed approach makes it possible to assess the level of completion of steel refining processes in order to develop effective technological solutions. In addition, it lays the foundation for solving specific applied problems at a new level, allowing optimizing existing technologies and developing new methods and reagents for producing steels with reduced sulphur and phosphorus content.

Slag mode regulation in electric arc furnace based on electrical parameters control during melting oxidation period

The results of observation of steelmaking oxidation stage at EAF-135 were analyzed with automated control system of the electrical characteristics. There are three main zones in the furnace working space, which differ by the aggregate state of the materials in them: arc discharge, melt and foamed slag. The distribution data of electric power over the furnace zones is given. There is active powers asymmetry of the arcs under single electrodes affected by asymmetry of the short network. It is shown that the main factors impacting the melt and slag resistances are oxygen blow and electrode movement. The authors studied the influence of magnesia flux feeds on the melt resistance. These feeds correspond to a sharp increase and a subsequent gradual decrease in resistance, and the time for assimilation of additives does not exceed one minute. The average electrical parameters of the working space zones are given for the EAF-135 at single heats. A comparison was made of the nature of change in the arc discharge power and the change in the melt temperature. The profiles match of changes in these characteristics to an increase in the arc power corresponds to increase in the melt temperature. An attempt to correlate FeO content in the slag with the arc power did not give a positive result. However, this methodology should be tested under conditions of steel refining in a ladle-furnace unit. It is noted that the parameter control at changing of the electrical parameters of the arc and slag zones due to the overwhelming influence of intense oxygen blast, melt mixing and electrode displacement does not meet the reliability criterion.

Use of Solid Slag Mixtures in a Ladle Furnace Unit

Use of Solid Slag Mixtures in a Ladle Furnace Unit

Implementation of Steelmaker’s Assistant Software Module in a Ladle-Furnace Unit

Implementation of Steelmaker’s Assistant Software Module in a Ladle-Furnace Unit

Fundamental studies of physicochemical properties of environmentally friendly fluorine-free slags and their use in ladle steel industry

The article describes theoretical and experimental studies of dependence of viscosity, coefficients of sulfur and boron distribution between slag and metal, and wear degree of periclase-carbon refractories on basicity and boron oxide content in slag. It is shown that formed slags have basicity of 2.0 – 5.0 and rather high liquid mobility. These slags are characterized by an equilibrium interfacial distribution coefficient of sulfur increased to 5 – 20, which provides equilibrium sulfur content in the metal reduced to 0.001 – 0.005 %. The results of fundamental studies of the physicochemical properties of refining slags of СаО – SiO2 – В2O3 – Al2O3 – MgO system formed the basis for development of the composition of environmentally friendly fluorine-free ladle slags and technological methods for their formation in ladle-furnace unit. The recommended composition of such slags of low viscosity, which allows deep metal desulfurization, direct steel microalloying with boron and low aggressive effect on periclase-carbon refractories, provides formation of slags with a basicity of 3.0 – 4.0, containing 1 – 4 % B2O3 , 15 % Al2O3 and 8 % MgO. The formation of environmentally friendly ladle slags of the recommended composition was carried out in a ladle-furnace by loading lime, boron-containing material – colemanite (Turkey) containing 39 – 41 % B2O3 , 26 – 28 % CaO, not more than 5 % SiO2 and 3 % MgO, and pyramidal aluminum into the steel-teeming ladle for slag deoxidation and boron recovery. Introduction of the developed technology for the formation of ladle slags of recommended composition ensured the production of economically alloyed low-carbon structural boron-containing steels with a low sulfur content, incl. for large diameter pipes with high strength properties.

Reducing the Cost of Steel Desulfurization during Secondary Refining in a Ladle-Furnace Unit

Reducing the Cost of Steel Desulfurization during Secondary Refining in a Ladle-Furnace Unit

Mathematical modelling of the thermal regime of a ladle- furnace unit considering internal heat sources

We apply mathematical modelling to study heat transfer processes during fire refining of blister copper in a ladle-furnace unit. A ladle-furnace unit was designed to test the refining technology using bottom blowing in a bubble mode by gaseous reducing agents (hydrocarbons) and an oxidiser. Mathematical modelling allows the properties of a real process to be described based on mathematical formalisation of physical laws and regularities. It was proposed to use gaseous reducing agents, rather than expensive residual fuel, as a liquid-reducing agent. The use of gaseous reducing agents in the bottom blowing mode produces higher technical and economic indicators of the process. In addition, some technological operations were transferred directly to the ladle, thereby eliminating the need for re-melting and heating of refined copper. One of the identified problems was the need to maintain the predetermined thermal regime, which provides the very possibility of both performing refining operations and introducing a gaseous reagent (determining the hydro-gas-dynamic parameters) into the melt during bottom blowing. An original method for considering the thermal effects of chemical reactions in mathematical models was presented using an example of exothermic reactions during oxidative refining. The use of two different methods of analysis allowed a comprehensive assessment of the influence of the main exothermic reactions on the thermal regime of the refining process. The presented mathematical models can be used for determining the specific effect of various technological parameters (composition and fuel consumption, temperature and degree of blast enrichment, lining design, etc.) on the dynamics of changes in the temperature field of the melt and the technical and economic parameters of melting as a whole.

Research of the Process of Production of Steel Square Continuous Billets for Rolling Balls of Large Diameter

The paper investigates the technology of production of steel billets continuously cast billets for rolling balls of large diameter. In Kazakhstan, in connection with the development of new copper deposits such as Aktogay and Bozshakol, the need for large diameter steel grinding balls for primary ore processing has increased. The main problem in the operation of large diameter grinding balls is the tendency of the grinding media to break during operation. The authors of the work investigated the process of production of steel billets continuously cast billets with a cross section of 150 × 150 mm for rolling balls of large diameter (d 125 mm) in the PB LLP "KSP Steel", which showed that the breaking of grinding balls is initiated mainly by the presence of internal discontinuities (gas axial looseness) in continuously cast billets. Studies have shown that the technological scheme for the production of grinding balls with a diameter of 125 mm from continuously cast billets with a section of 150 × 150 mm, including steel smelting in an arc furnace with steel finishing on a ladle-furnace unit, deoxidation with aluminum and degassing in a ladle vacuum apparatus, casting steel in a closed jet on a continuous casting and further production of rolled stock on a rough rolling mill ensures the absence of internal discontinuities (gas bubbles, axial looseness) in the workpieces and ensures the production of high quality balls.

Application of ionic theory to calculate sulfide capacity of slags

The article considers the issues of sulfur removal in the ladle-furnace unit. The sulfur distribution coefficient depends on sulfide capacity of the slag, sulfur activity coefficient, oxidizing potential of the medium and equilibrium constant. The sulfide capacity CS of slags is one of the most important characteristics of refining capacity of the slags used in extra-furnace steel processing. One of the factors affecting the sulfide capacity is temperature. The formula was proposed showing the dependence of sulfide capacity on the optical basicity and temperature, in the temperature range of 1650 – 1400 °C and when the optical basicity Λ is not more than 0.75; the error of the presented formula does not exceed 6 %. The formula for calculating the optical basicity is proposed, which takes into account the influence of basic, acidic oxides and amphoteric oxide Al2O3. It is shown that slags, completely consisting of a homogeneous phase, have an increased optical basicity of aluminum oxide. Heterogeneous slags have a reduced optical basicity of Al2O3 in comparison with homogeneous slags. Perhaps, this fact can be explained by the fact that in homogeneous slags there is a deficiency of the basic oxide CaO and in the conditions under consideration Al2O3 compound begins to exhibit more basic properties than acidic ones, thus, in homogeneous slags, the optical basicity of aluminum oxide is increased and approaches optical basicity of CaO oxide. Calculations carried out on the basis of real heats have shown that with an increase in the content of Al2O3 oxide in the slag, its optical basicity decreases. Known value of the optical basicity makes it possible to determine sulfide capacity of the slag, sulfur distribution coefficient between metal and slag, and, accordingly, final sulfur content in the metal. The research results have shown that it is advisable to apply the ionic theory of slags for the sulfide capacity determination.

Efficiency of Using Oxygen and Development of Locally Distributed Methods for Afterburning of Combustible Gases in Electric-Arc Furnace or Ladle Furnace

A review of the literature on the development of electric steelmaking at metallurgical plants indicates the possibility and efficiency of combining arc melting of steel and its extra-furnace treatment by well-known methods. The possibilities of combined steel melting using metallized iron-ore raw materials (MIORM) and scrap metal, followed by extra-furnace treatment of liquid steel with inert gases and continuous casting of steel are analyzed. This study is novel in the use of gas afterburning and distributed feed of MIORM to the bath of an electric ladle furnace unit, partially or not using scrap metal. It is shown that the energy and technology features of the new ladle furnace during arc steel melting combined with extra-furnace treatment are comparable in efficiency and steel quality to those of a typical arc furnace.

Результаты исследования электрических параметров агрегата «печь-ковш» большой мощности и его влияния на питающую сеть

The steel refinement and its chemical composition and temperature finalization processes in a pouring ladle carried out by heating the metal with electric arc have received wide use at modern metallurgical enterprises. The article considers the electrical operating conditions of the ladle furnace unit (LFU) equipped with a 40 MVA electric furnace transformer. It was expected that the LFU load would vary insignificantly, because the electric arc burns between the electrodes and the surface of already molten metal, without the occurrence of short circuits. However, the accomplished studies testify that the LFU load is abruptly variable and nonlinear in nature, and gives rise to significant voltage fluctuations and harmonic distortions in the power supply network. The flicker intensity (severity) factor has been estimated, and the level of current harmonic components generated due to LFU operation has been determined. By using the obtained results, it becomes possible to predict the influence of LFU electric operating conditions on the levels of electric power quality indicators in changing the power supply network parameters, and to adopt circuit engineering solutions for assuring the electric power quality in the plant electric power supply system.

НОВИЙ ПІДХІД ДО ВИРІШЕННЯ ПРОБЛЕМИ СПРЯМОВАНОГО ФОРМУВАННЯ КІНЦЕВИХ РОЗПЛАВІВ ПРИ ДОВЕДЕННІ СТАЛІ НА УСТАНОВЦІ «КІВШ-ПІЧ»

The purpose of the work is to reveal the essence of the proposed new approach to describe the patterns of distribution of elements between the metal and slag phases, the basis for the development of which was the created information and intellectual resources of the knowledge base "Metallurgy" developed in Iron and Steel Institute of Z.I.Nekrasov of the NAS of Ukraine. The information component is a database continuously updated with modern data on the properties of metallurgical melts "Metal", "Slag", "Ferroalloys" and "Metal-Slag-Gas" and containing the results of our own and industrial experimental studies of the properties of metallurgical melts and literary searches (articles, patents, inventions, scientific developments, monographs). As a scientific basis for describing the processes of interactions between phases, the work uses the original concept of directed chemical bonding, as well as the experience accumulated in the department of physicochemical problems of metallurgical processes in creating information and analytical systems for forecasting and controlling the processes of iron and steel smelting. The starting points laid down in the concept of directed chemical bonding are its core and consider melts as chemically unified systems, and simply not mechanical mixtures of components. This approach allows to describe in more detail the physicochemical interactions in a multiphase metallic medium. The main difference between the proposed approach and the existing ones consists in taking into account interatomic bonds in the interaction of metal and slag melts, complex ratios of their physicochemical and thermophysical properties, as well as significant technological parameters during out-of-furnace treatment in a ladle-furnace unit. Adequate mathematical models (R2≥0,9) have been developed, which allow to quantify the efficiency of assimilation and distribution of additives that determine the technological purposefulness of the processing of an intermediate product and determine the selection from these positions of rational compositions of alloying and refining components within the domestic raw material base.

Control of oxide non-metallic inclusions in production of IF steel

Modern trends in the automotive industry are aimed at reducing vehicle weight and increasing its safety. The high ductility of IF-BH steel in combination with increased strength allows the use of thinner rolled products in the car body structure. Achievement of high plastic properties in IF-BH steel is ensured by the low content of nitrogen and carbon (C <40 ppm, N <40 ppm) and controlled carbon content in the solid solution. The majority of sheet surface defects are associated with non-metallic inclusions. The presence of non-metallic inclusions in the finished product violates its homogeneity, deteriorates the surface properties of steel, fatigue strength and plastic characteristics of the metal. As a result of the work performed by the methods of fractional gas and micro-X-ray spectral analysis on a scanning electron microscope, metal samples of three IF-BH steel melts were analyzed, taken along the entire process chain of production. The main types of oxide non-metallic inclusions in the steel were quantitatively determined, as well as the total oxygen and nitrogen content in the metal. It is shown that the main types of oxide non-metallic inclusions in the investigated metal samples are aluminates, silicates and spinel. An increase in nitrogen content in the metal after breakdown of the vacuum on the VD was established, which indicates secondary oxidation of the metal. In metal of the samples in the section between the tundish and the crystallizer, nitrogen content in the metal increases which indicates the secondary metal oxidation. At the same time, the content of inclusions of aluminates in the metal increased and the number of inclusions of aluminum-magnesium spinel decreased. A mathematical model and software have been developed that describe the formation and removal of oxide nonmetallic inclusions. Adequacy of the program was confirmed by good convergence between the calculated and laboratory data on the total content [O] in various types of oxides for the first sample at the ladle-furnace unit and in the slab.

Sulfur partition by process stages of metallurgical production of JSC EVRAZ NTMK

The current level of development of the industry requires the manufacture of steel with high purity in relation to detrimental impurities. Sulfur is one of such impurities that significantly reduces the service properties, the content of which is strictly regulated in the finished product. Deep desulfurization may be achieved through development of cross-cutting technology of metal production as a single process including agglomeration and blast-furnace process and steelmaking. Sulfur partition by metallurgical process stages via conversion from raw materials of the blast-furnace process to steel continuously cast blank is studied in this work. It is shown that removal of sulfur from the half-finished product at the desulfurization plant will not provide the required sulfur content (less than 0.005 %) in the steel ingot. It is determined that the activity plan comprising treatment of the half-finished product at the desulfurization plant, smelting in the converter, treatment of steel at the ladle furnace unit and then in the vacuum vessel is required to obtain the final content of sulfur of less than 0.005%.

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

The article discusses the possibilities of intensifying the process of desulfurization of molten steel in the process of after-furnace treatment of molten steel in the ladle-kiln unit. As one of the techniques, it was proposed to heat the melt with the help of hollow electrodes with argon feed during the operation of the electric arc plant. Comparative thermal balances of the installation in the basic and experimental versions and on the basis of the proposed mathematical model for calculating the mass-average temperature of the melt are given, and graphs of temperature changes during processing are plotted. To assess the efficiency of the desulfurization process, arrays of heats were processed in the basic and experimental mode and original three-parameter graphs were built, allowing to estimate the degree of desulfurization in both modes as a function of processing parameters.

Theoretical Bases and Technology of Steel Exhaustive Metal Desulfurization and Direct Microalloying with Boron Beneath Basic Boron-Containing Slags

Results of theoretical and experimental studies of the physicochemical properties of slags of the CaO–SiO2–B2O3 system containing 15% Al2O3 and 8% MgO lie at the basis for the development of technology for exhaustive desulfurization of metal beneath basic boron-containing slags formed in a steelpouring ladle in a ladle-furnace unit (LFU), and steel direct microalloying with boron. Methods of simplex lattice planning of an experiment, a software complex HSC 6.1 Chemistry (Outokumpu), and the method of electro-vibration viscosimetry are used. Results of thermodynamic modeling of the effect of slag basicity and B2O3 content on sulfur and boron equilibrium distribution coefficient between slag of the oxide system under study and low-carbon metal are presented. The quantitative effect of basicity and B2O3 content on slag viscosity containing 15% Al2O3 and 8% MgO at a temperature of 1600°C and the influence of the slag chemical composition of the oxide system under study on the degree of wear of periclase-carbon refractory material are shown. Results of studying physicochemical properties of slags of the CaO–SiO2–B2O3 system containing 15% Al2O3 and 8% MgO are a basis for developing a ladle slag composition with low viscosity and providing exhaustive metal desulfurization, and direct microalloying of boron steel with low corrosive effect on periclase-carbon refractories. Development of this technology provides, depending on the steel grade, a boron content of 0.001–0.008%, low metal sulfur concentration at 0.004–0.014%, a reduction in manganese ferroalloy consumption from 0.5 kg/ton of steel 08KP to 1.4 kg/ton of steel 09G2S, exclusion of ferroboron and fluorspar additives in the ladle, and achievement of good finished metal product mechanical properties.

Математические модели для исследования теплового состояния тел и управления тепловыми процессами

The purpose of the study is the systematization of problems related to the study of the thermal state of objects and melts in industrial production and ways to solve them. In particular, the problems characteristic for a metallurgical enterprise are: mathematical modeling of electromagnetic fields in systems for induction heating of the hardware industry; development of information support for an energy-saving mode of heating billets before rolling in a continuous-type heating furnace; application of the basis of the classical equations of heat and mass transfer and multivariate analysis to simulate the processes in the ladle furnace unit; development of pseudo-dynamic and quasidynamic models describing the thermal state of an infinitely extended object. All these tasks have a thermal nature and despite the difference in the objects of study, they use mathematical models to study the thermal state of objects and control thermal processes. The implementation of mathematical models is made using modern computer software. All studies were conducted by scientific schools of the Nosov Magnitogorsk State Technical University and were extensively tested and implemented in operating production facilities.