Behavior of oxygen in the ladle treatment of 08X18H10T high-alloy steel

The actual activity of oxygen in liquid metal is determined by means of sensors during the ladle treatment of 08X18H10T high-alloy steel. The activity of the components of the metallic and oxide solutions is calculated by means of models of a pseudosubregular solution for the liquid metal and a pseudoregular solution for the oxide slag. The corresponding energy parameters were determined in previous research. A formula is derived for the activity of oxygen in equilibrium with the components of Fe-Cr-Ni-Mn-Si-C-Al-Ti liquid steel, eight-component FeO-MnO-CaO-MgO-SiO₂-CrO_1.5-AlO_1.5-TiO₂ slag, and the gas phase. It is found that the metal-slag-gas system at the end of reduction is considerably closer to equilibrium than at the end of oxidation. The development of the reduction process is studied in terms of the difference in chemical potentials of the actual and equilibrium oxygen.     

Some metallurgical aspects of steelmaking with sponge iron in electric arc furnaces

Test charges containing sponge iron proportions varying from 38.7–95.4 wt% of the metallic input were melted in a UHP electric arc furnace with a design capacity of 70 tons per heat. After melting started, samples of molten metal and the corresponding slag were taken simultaneously at different time intervals and analysed. The time dependence of the chemical composition of the metal and slag as well as the variation of the temperature of the melt with time are given. Thermodynamic calculations using different methods for finding the activity of ferrous oxide show that there is a linear relationship between a_(FeO) and the total ferrous oxide content in the slag. It is also found that the total ferrous oxide content in the slag and the oxygen concentration in the metal vary linearly with the iron proportion from sponge iron in the metallic input. The activity of ferrous oxide decreases with increasing slag basicity due to the formation of calcium ferrites. The relationship between the oxygen concentration and the reciprocal of the carbon content in liquid steel is almost linear. A formula showing the influence of some important factors on the oxygen content in molten steel is given. The effect of sponge iron on the sulphur concentration in the steel is also investigated. The present results indicate that the sulphur content in the steel can be reduced from 0.02 to 0.004 wt% by increasing the iron proportion from sponge iron in the metallic input from 35 to 95 wt %. Using the boundary layer diffusion model, it is found that the rate of decarburization of a steel bath is enhanced by increasing the sponge iron proportion in the metallic input. The activation energy of the decarburization reaction is found to be 56.9 kJ/mol and the mass transfer coefficient of carbon has a value of 0.0161 cm/s at 1 600°C. In a way similar to that used for decarburization, it is also found that the rate of oxidation of manganese dissolved in the bath is enhanced by increasing the sponge iron proportion in the metallic input.     

Selective oxidation of copper from liquid copper-silver alloys

In this work, the oxygen refining of liquid copper-silver alloys with a borosilicate slag was studied. First, a comprehensive thermodynamic analysis was performed using the data available in the literature. The results indicate that since silver oxide is relatively unstable in silicate-based slags, then it should be thermodynamically feasible to oxidize copper from copper-silver alloys with a very low silver loss to the silicate slag. In actual practice, although relatively low copper levels can be achieved in the metal phase, the silver losses to the slag are excessive. Therefore, in the present work, both kinetic and equilibrium experiments were performed on a molten copper-silver alloy containing 12.68 mass pct silver in order to elucidate the mechanism of silver loss to the slag. The kinetic experimental results indicated that copper levels of less than 2 mass pct could be achieved with silver recoveries of about 95 pct after relatively short refining times of 15 minutes. In the equilibrium experiments, the copper contents of the metal were less than 1 mass pct, and these values were in good agreement with those which were calculated from the data of previous researchers. In order to explain the relatively high silver losses to the slag, a model was developed which is based on the transport of silver from the metal phase to the slag phase both in metallic form and as silver oxide in the copper oxide oxidation product. The copper and silver oxides and the metallic copper-silver alloy are all transported into the slag by the oxidizing gas bubbles. It is proposed that once in the slag, the silver oxide is unstable and decomposes into metallic silver which is not easily recovered in the metal phase. Also, the transfer of the copper-silver alloy into the slag, by the gas bubbles, promotes the slag-metal exchange reaction, which again results in the generation of silver particles in the slag.     

A model of post-combustion in iron-bath reactors,part 4: results for post-combustion with preheated air

This paper describes calculated results of post-combustion with pre-heated air, heat transfer from gas to the melt via a mixture of metal and slag droplets, reoxidation at the metal droplets, CO evolution rate from the melt, production rate of the reactor, and carbon consumption of various process modes of a 15-t reactor with or without oxygen blowing through the vessel bottom. Using pre-heated air, the achievable post-combustion degree is higher than using pure oxygen. Nevertheless, slag droplets as heat carrier are necessary. With 50 % slag droplets the real post-combustion degree can be higher than 45 %. With 90 % slag droplets it can be even higher than 80 %. The operating point of the reactor is discussed.     

Activity of Ferric Oxide in Steelmaking Slag

Refining reactions in steelmaking primarily involve oxidation of impurity element(s). The oxidation potential of the slag and the activity of oxygen in the metal (h_O) are the major factors controlling these chemical reactions. In turn, the oxidation potential of the slag is influenced strongly by the equilibrium distribution of oxygen between ferrous and ferric oxides. We recently investigated the activity coefficient of FeO in steelmaking slag and the effect of chemical composition thereon. This work is focused on estimation of the activity coefficient of Fe₂O₃.     

Preliminary Investigation of Mathematical Modeling of Stainless Steelmaking in an AOD Converter: Mathematical Model of the Process

Mathematical modeling of stainless steelmaking in an AOD (argon‐oxygen decarburisation) converter with side and top combined blowing has been preliminarily investigated. The actual situations of the side and top combined blowing AOD process were analysed. A mathematical model for the whole refining process of stainless steel has been proposed and developed. The model is based on the assumption that one part of the oxygen blown through a top lance reacts with CO escaping from the bath, another part of the oxygen oxidizes the elements in the molten steel droplets splashed by the oxygen jet, and the remaining oxygen penetrates and dissolves into the molten steel through the pit stroked by the jet. All the oxygen entering into the bath oxidizes C, Cr, Si, and Mn dissolved in the steel and also the Fe of the steel melt, but the FeO generated is also an oxidant of C, Cr, Si, and Mn in the steel. During the process, all possible oxidation‐reduction reactions occur simultaneously and reach their equilibria, respectively their combined equilibrium, in competition at the liquid/bubble and liquid/slag interfaces. In the simple side blowing after the top blowing operation is finished, the possible reactions take place simultaneously and reach a combined equilibrium in competition at the liquid/bubble interfaces. The overall decarburization rate in the refining process is the sum of the contributions of both the top and side blowing processes. It is also assumed that at high carbon concentrations, the oxidation rates of elements are mainly dependent upon the supplied oxygen rate, and at low carbon contents, the rate of decarburisation is primarily related to the mass transfer of carbon from the molten steel bulk to the interface. It is further assumed that the non‐reacting oxygen blown into the bath does not accumulate in the steel and will escape from the bath and react with CO in the atmosphere above the bath. The study presents calculations of the refining rate and the mass and heat balances of the system for the whole process. Additionally, the influences of the operating factors, including addition of slag materials, scrap, and alloy agents, the non‐isothermal conditions, the changes in the amounts of metal and slag during the whole refining process, and others have all been considered.     

钛微合金钢炉外精炼相平衡研究与热力学分析

摘要：为了解钛微合金钢炉外精炼过程中Ti元素在渣 钢间的平衡分配行为及走向,应用分子相互作用体积模型（MIVM）,通过规范子二元系活度标准态和优化模型参数,建立了CaO-Al2O3-FeO-TiO2熔渣活度计算模型,并预测渣中各组元活度;在含钛钢炉外精炼条件下,应用MIVM和Wagner公式研究了Ti在精炼渣CaO-Al2O3-FeO-TiO2与含钛钢液Fe-Al-Ti O间的平衡分配及影响因素。研究结果显示：渣中FeO的活度预测值与实验值符合较好,平均相对误差为9%;Ti在渣-钢两相间平衡分配比的计算值与工业数据符合较好;分配比随钢液中Al含量的降低、温度的升高和渣中CaO与Al2O3质量比的增加而增大,该规律与实际生产相一致。因此MIVM对多元含钛熔渣体系组元活度具有较好的预测效果,所设计的相平衡研究方法合理可行。本研究可为含钛合金钢化学冶金的基础理论研究提供一定的参考。     

Theoretical Study of Equilibrium Reactions between Metal Droplets and Slag

The dispersion of metal droplets in slag was investigated through analysis of slag samples taken during ladle refining at Scana Steel in Björneborg, Sweden. The chemical composition of steel droplets found in the ladle slag was determined for five industrial‐scale heats. Possible reactions occurring between the steel droplets and slag were identified, as were differences in steel‐droplet and steel‐bulk composition. Three different slag models were used to calculate the activities of oxide components (Al₂O₃ and SiO₂) in the slag. These results were then used in the dilute‐solution model, whereby oxygen activities in the steel droplets were calculated and compared with measured oxygen activities in the steel bulk. Significant differences were found in the comparison of both the calculated and measured oxygen activities and the steel bulk and droplet compositions.     

Metal loss and charge heating in the melt in an electric arc furnace

The heat exchange between a metallic melt and a slag with a charge is simulated with allowance for possible formation of a skull on the charge surface. It is shown that the charge melting rate in the melt is determined by the coefficient of heat transfer between the metal and the charge and the ratio of the mass of a charge fragment to its surface area interacting with the melt. A skull is found to form on the charge surface at a low coefficient of heat transfer between the metal and the charge. The main heat parameters, the control of which by an automatic control system ensures an increase in the charge melting rate in the melt and a decrease in the metal loss, are formulated.     

Thermodynamics of copper matte converting: Part I. Fundamentals of the noranda process

This paper presents a computer-oriented thermodynamic method to analyze copper matte smelting and converting, the system of which was ideally defined as consisting of five major components: Cu, Fe, S, O and SiO2. As an example of its application, the method was demonstrated in establishing a steady-state model for the Noranda Process producing either metallic copper or high grade matte. Process variables such as temperature, oxygen enrichment, charge (or concentrate) composition, matte grade and magnetite content of slag are integrated into one computer model. The model gives the chemical composition of metallic copper, matte and slag phases for any specified condition. Mathematical formulae accounting for physical entrainment in the melts are also presented to correlate the computed melt composition with that observed. The computer model can provide predictions as to the effects of operating and chemical parameters and can contribute to improved metallurgical control.     

Thermodynamics of copper matte converting: Part I. Fundamentals of the noranda process

This paper presents a computer-oriented thermodynamic method to analyze copper matte smelting and converting, the system of which was ideally defined as consisting of five major components: Cu, Fe, S, O and SiO2. As an example of its application, the method was demonstrated in establishing a steady-state model for the Noranda Process producing either metallic copper or high grade matte. Process variables such as temperature, oxygen enrichment, charge (or concentrate) composition, matte grade and magnetite content of slag are integrated into one computer model. The model gives the chemical composition of metallic copper, matte and slag phases for any specified condition. Mathematical formulae accounting for physical entrainment in the melts are also presented to correlate the computed melt composition with that observed. The computer model can provide predictions as to the effects of operating and chemical parameters and can contribute to improved metallurgical control.     

Thermodynamic analysis of the reduction of pipe steel

In thermodynamic calculations, the activity of oxygen in equilibrium with Al, Mn, and Ce is determined for four melts of pipe steel. Pure gaseous oxygen under pressure is adopted as the standard state of oxygen dissolved in liquid metal. The actual (above-equilibrium) activity of oxygen is calculated on the basis of electrochemical measurements in liquid steel by oxygen sensors. For the melts, the difference between the actual and equilibrium chemical potentials, which may be regarded as the factor that drives reduction, is 14–20 kJ/mol. The conditions for microalloying of the melt with cerium are assessed.     

Mathematical modeling of the argon-oxygen decarburization refining process of stainless steel: Part I. Mathematical model of the process

Some available mathematical models for the argon-oxygen decarburization (AOD) stainless steelmaking process have been reviewed. The actual situations of the AOD process, including the competitive oxidation of the elements dissolved in the molten steel and the changes in the bath composition, as well as the nonisothermal nature of the process, have been analyzed. A new mathematical model for the AOD refining process of stainless steel has been proposed and developed. The model is based on the assumption that the blown oxygen oxidizes C, Cr, Si, and Mn in the steel and Fe as a matrix, but the FeO formed is also an oxidant of C, Cr, Si, and Mn in the steel. All the possible oxidation-reduction reactions take place simultaneously and reach a combined equilibrium in competition at the liquid/bubble interfaces. It is also assumed that at high carbon levels, the oxidation rates of elements are primarily related to the supplied oxygen rate, and at low carbon levels, the rate of decarburization is mainly determined by the mass transfer of carbon from the molten steel bulk to the reaction interfaces. It is further assumed that the nonreacting oxygen blown into the bath does not accumulate in the liquid steel and will escape from the bath into the exhaust gas. The model performs the rate calculations of the refining process and the mass and heat balances of the system. Also, the effects of the operating factors, including adding the slag materials, crop ends, and scrap, and alloy agents; the nonisothermal conditions; the changes in the amounts of metal and slag during the refining; and other factors have all been taken into account. []—metal phase; ()—slag phase; {}—gaseous phase; and 〈〉—solid phase     

The solubility of nickel and cobalt in iron silicate slags

The solubility of nickel and cobalt in silica saturated iron silicate slags in equilibrium with nickel-gold and cobalt-gold alloys has been investigated under controlled oxygen pressures in the temperature range of 1250 to 1350°C. It was found that the metal solubility increased with 1) decreasing temperature, 2) increasing oxygen pressure, and 3) increasing metal content of the alloy. The solubility of cobalt in the slag was found to be much higher than that of nickel. The solubility of the metal in the slag from its alloy can be explained by a simple oxidation process.     

Manganese Distribution between FeO‐MnO‐SiO2–CaO–MgO‐Al2O3 Slags and Molten Iron

Pretreatment of high manganese hot metal is suggested to produce hot metal suitable for further processing to steel in conventional LD converter and rich manganese slags satisfy the requirements for the production of silicomanganese alloys. Manganese distribution between slag and iron represents the efficiency of manganese oxidation from hot metal. The present study has been done to investigate the effect of temperature, slag basicity and composition of oxidizer mixture on the distribution coefficient of manganese between slag and iron. Ferrous oxide activity was determined in molten synthetic slag mixtures of FeO‐MnO‐SiO₂–CaO–MgO‐Al₂O₃. The investigated slags had chemical compositions similar to either oxidizer mixture or slags expected to result from the treatment of high manganese hot metal. The technique used to measure the ferrous oxide activity in the investigated slag systems was the well established one of gas‐slag‐metal equilibration in which molten slags contained in armco iron crucibles are exposed to a flowing gas mixture with a known oxygen potential until equilibrium has been attained. After equilibration, the final chemical analysis of the slags gave compositions having a particular ferrous oxide activity corresponding to the oxygen potential of the gas mixture. The determined values of ferrous oxide activity were used to calculate the equilibrium distribution of manganese between slag and iron. Higher manganese distribution between slag and iron was found to be obtained by using oxidizer containing high active iron oxide under acidic slag and relatively low temperature of about 1350°C.     

HIsmelt熔融还原主反应器能质流转模型构建与验证

 HIsmelt熔融还原炼铁工艺以铁矿粉和煤粉作为原料,流程中不需要烧结、球团和焦化,与高炉炼铁流程相比具有降碳减排等优势。明晰能质流转过程对HIsmelt熔融还原炼铁实际生产具有指导意义。基于物料平衡、热平衡方程,对输入和输出HIsmelt主反应器物质和能量进行平衡计算,建立能质流转模型,并结合FactSage中Equilib模块计算的各元素在渣铁两相间的质量分配比及实际生产数据对其进行修正。该模型可以计算原料和燃料成分、矿煤质量比、二次燃烧率、热风氧含量等参数对铁水温度、炉渣成分、热风量、煤气量等主要冶炼指标的影响。其次依据该模型,进行了物料平衡、热平衡计算,依据实际生产数据对模型计算结果进行了验证,结果表明该模型与实际生产数据契合度较高。探究了矿煤质量比对冶炼的影响,矿煤质量比为1.39～1.45时,矿煤质量比降低0.1,会使二次燃烧率降低0.23%,进而造成煤气化学能的利用率降低,同时需要更多的热风使煤粉燃烧,热风量和煤气产生量增加,可以通过适当提高热风氧含量以提高二次燃烧率并使煤气量降低来改善;矿煤质量比降低0.001,会使铁水温度升高3.76 ℃,有利于铁水后续的加工处理,但铁水温度升高使铁元素在铁液与渣中的比值降低,使炉渣FeO质量分数升高0.026%,增加铁损,可通过降低富氧热风喷吹量来降低铁的氧化量,从而降低铁损。     

Kinetics of simultaneous reactions between liquid iron-carbon alloys and slags containing MnO

The oxidation rates of carbon, phosphorus, and silicon; the desulfurization rate of liquid iron; and the simultaneous reduction rate of MnO from slag were examined at 1450 °C to 1550 °C by using high carbon iron alloys and CaO-SiO₂-CaF₂ slags containing MnO and FeO. The reaction rates were well reproduced by a kinetic model describing the reaction between the slag and multicomponent iron alloys. The controlling steps applied for the reactions considered in the present kinetic simulation were as follows. The rate of decarburization is controlled by the chemical reaction at the slag-metal interface, and those of the other reactions are controlled by the transport in slag and metal phases. Both observation and simulation results showed that MnO was not a strong oxidizer compared with FeO in the slag, but was an effective component for desulfurization. The simulation results also showed that the interfacial oxygen activity using MnO-based slag was much lower than that using FeO-based slag. The apparent equilibrium constants of phosphorus and sulfur, which were obtained by the kinetic modeling of experimental results, were found to increase with increasing the (MnO + CaO)/SiO₂ ratio of the slag. The controlling step(s) of each element transport across the slag-metal interface was discussed with the aid of the kinetic model.     

A model of post-combustion in iron-bath reactors,part 2: results for combustion with oxygen

The paper describes calculated results of post-combustion of CO, of heat transfer and of reoxidation for the conditions of a 170-t bottom-blown oxygen converter obtained on the basis of a model published in a previous paper. Calculations were carried out for heat transfer from gas to melt alternately via slag and via metal droplets suspended in the gas phase and acting as the transfer medium. In the case of slag droplets, heat transfer efficiencies of 80% are attainable. In the case of metal droplets, reoxidation limits the heat transfer efficiencies below 50%. The real degrees of post-combustion remain below 20%. Radiative heat transfer amounts to about 20% of total heat transfer.     

Mass Exchange at the Metal‐Mould Flux Interface

Mass exchange between liquid steel and the mould flux leads to the oxidation of some elements in the steel and the reduction of slag components. In the continuous casting process, where metal initially solidifies at the metal‐slag interface, reaction products generated there can be cached by the growing solidification front. The disruptions of the interface promote the entrapment of flux particles additionally. They can cause surface defects with quality damages of the cast products as a consequence. These investigations are focused on the contact area between liquid mould flux and metal. The samples were taken from the mould during the continuous casting process. The results show that layers up to approximately 300 nm from the slag/metal interface represent a specific reaction space. The transport of oxygen near the interface and the charge transfer is explained on the basis of the ionic character of the slag. Sodium in this layer on the slag side plays a special role in the oxygen transport besides of the iron ions. The mass transfer rate of oxygen crossing the interface is calculated from measured data and conclusions concerning the stability of the interfacial tension are made.