Kinetics of Silicothermic Reduction of Manganese Oxide for Advanced High-Strength Steel Production

The kinetics of silicothermic reduction of manganese oxide from MnO–SiO₂–CaO–Al₂O₃ slags reacting with Fe-Si droplets were studied in the temperature range of 1823 K to 1923 K (1550 °C to 1650 °C). The effects of initial droplet mass, initial droplet silicon content, and initial slag manganese oxide content were studied. Data obtained for 15 pct silicon showed agreement with control by mass transport of MnO in the slag with a mass transfer coefficient (k _s) of 4.0 × 10^?5 m/s at 1873 K (1600 °C). However, when this rate-determining step was tested at different initial silicon contents, the agreement was lost, suggesting mixed control between silicon transport in the metal and manganese oxide transport in the slag. Increasing the temperature resulted in a decrease in the rate of reaction because of an increase in the favorability of SiO as a product. Significant gas generation was found during all experiments, as a result of silicon monoxide production. The ratio of silicon monoxide to silica formation was increased by factors favoring silicon transport over that of manganese, further supporting the conclusion that the reaction is under mixed control by transports of both silicon and manganese oxide.     

Mass Transfer of Nickel-Base Alloy Covered Electrode During Shielded Metal Arc Welding

The mass transfer in shielded metal arc welding of a group of nickel-base alloy covered electrodes according to AWS specification A5.11-A5.11M was investigated by directly measuring their deposited metal compositions. The results indicate that the chromium mass-transfer coefficient is in the range of 86 to 94 pct, iron in the range of 82 to 89 pct, manganese in the range of 60 to 73 pct, niobium in the range of 44 to 56 pct, and silicon in the range of 41 to 47 pct. The metal mass-transfer coefficient from the core wire is markedly higher than that from the coating. The basicity of slag, the metal contents in the flux coating, and the welding current together affect the mass transfer. As the basicity of slag increases, the mass-transfer coefficients of Mn, Fe, and Cr slightly increase, but those of Nb and Si decrease significantly. As the niobium and manganese contents increase in the coating, their mass-transfer coefficients also increase. However, iron is different. The content of iron in the coating in the range of 8 to 20 wt pct results in the optimal effective mass transfer. The lower, or higher, iron content leads to lower mass-transfer coefficient. As the welding current increases, the mass-transfer coefficients of niobium and manganese decrease, but chromium and silicon increase. Iron has the lowest mass-transfer coefficient when welded under the operating current of 100 A.     

Effects of transition metals on the kinetics of slag-refractory reactions

The dissolution kinetics of dense alumina discs in calcium aluminosilicate based melts was determined with a rotating disc technique at 1560 °C to 1590 °C, under a controlled atmosphere of Ar-CO-CO₂. The effects of rotation speed and the concentration of iron and manganese oxides on the dissolution rate of alumina into slags were measured by monitoring the concentration of species in the slag. Analysis of the results obtained indicated that at low concentrations of these transition metal oxides in 53 pct CaO-5 pct MgO-12 pct SiO₂-30 pct Al₂O₃ slags, the dissolution rate is most likely controlled by mass transfer in the slag phase. The rate data obtained also showed that the addition of iron oxide or manganese oxide results in considerable increase in the mass transfer by increasing the apparent diffusivities of species in the slag. Comparison of these results with published data on the diffusivities of species in similar slags are made and practical implications of the findings are briefly discussed.     

The effect of alumina in slag on manganese and silicon distributions in silicomanganese smelting

The distribution ratios of manganese and silicon between silicomanganese alloy and slag, in equilibrium with carbon, were investigated at 1500 °C. The alumina content of the slag was varied from about 9 to 32 pct. Both distribution ratios decreased as A1₂O₃ increased to about 20 pct and, thereafter, remained constant. The value of the “apparent equilibrium constant” displayed a maximum at about 24 pct A1₂O₃, mainly because of the variation in the values of the activity coefficients of SiO₂ and MnO. It was concluded that the slag and silicomanganese alloy in a submerged arc furnace are at, or at least close to, equilibrium.     

Thermodynamic Modeling of Metal Desulfurization with Boron-Containing Slags of the CaO–SiO<Subscript>2</Subscript>–MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript> System

In thermodynamic modeling of the desulfurization of steel by CaO–SiO₂–MgO–Al₂O₃–B₂O₃ slag on the basis of HSC 6.12 Chemistry software (Outokumpu), the influence of the temperature (1500–1700°C), the slag basicity (2–5), and the B₂O₃ content (1–4%)1 on the desulfurization is analyzed. It is found that the sulfur content is reduced with increase in the temperature from 1500 to 1700°C, within the given range of slag basicity. At 1600°C, the sulfur content in the metal is 0.0052% for slag of basicity 2; at 1650°C, by contrast, its content is 0.0048%. Increase in slag basicity from 2 to 5 improves the desulfurization, which increases from 80.7 to 98.7% at 1600°C. If the B₂O₃ content in the slag rises, desulfurization is impaired. At 1600°C, the sulfur content in the metal may be reduced to 0.0052 and 0.0098% when using slag of basicity 2 with 1 and 4% B₂O₃, respectively; in the same conditions but with slag of basicity 5, the corresponding values are 0.00036 and 0.00088%, respectively. Note that desulfurization is better for slag without B₂O₃. According to thermodynamic modeling, metal with 0.0039 and 0.00019% S is obtained at 1600°C when using slag of basicity 2 and 5, respectively, that contains no B₂O₃. The results obtained by thermodynamic modeling for the desulfurization of metal by CaO–SiO₂–MgO–Al₂O₃–B₂O₃ slag of basicity 2–5 in the range 1500–1700°C are consistent with experimental data and may be used in improving the desulfurization of steel by slag that contains boron.     

The settling of metallic lead from lead blast furnace slag

As a consequence of inadequate working methods, excessive losses of lead can occur in the slags of lead blast furnaces. The settling of metallic lead from a slag containing 20.5 pct SiO₂, 33.4 pct FeO, 16.8 pct CaO, 12.4 pct ZnO, 0.9 pct S, and 6.1 pct Pb has been studied as a function of the temperature (1200 to 1300 °C), composition (addition of CaO, ZnO, and Fe), and time (up to 2 hours). Under these conditions sufficient, although not total, sedimentation of the metal retained is achieved. The best conditions were obtained at 1260 °C with no modification to the composition of the slag. The settled lead was visible macroscopically in a section of the lower part of the melts.     

使用菱镁石调整渣型和使用铝渣型冶炼锰硅合金生产的探讨(Ⅱ)

论述了使用菱镁石调整渣型生产锰硅合金的特点。采用钙镁渣型,炉渣中MgO含量控制在16%～18%,CaO含量控制在12%～14%;采用镁渣型,炉渣中MgO含量控制在18%～21%。增加渣中MgO含量可提高元素的还原效率,提高炉温,降低炉渣黏度,而相对于钙渣型,可提高硅的利用率,减少焦炭和硅石用量,同时降低渣中跑锰;使用铝渣型(与钙渣型和镁渣型相比)会有更高的炉温,硅的利用率和元素回收率增加,若原料搭配合理,使用铝渣型生产锰硅合金可不另配入硅石。通过比较得出:配入菱镁石调整渣型冶炼锰硅合金是完全可行的。     

A Study of Some Elemental Distributions Between Slag and Hot Metal During Tapping of the Blast Furnace

This paper investigates the distribution of elements between slag and hot metal from a blast furnace through calculation of distribution coefficients from actual production data. First, samples of slag and hot metal tapped from a commercial blast furnace were taken continually at 10‐minute intervals for a production period of 68 hours. Distribution coefficients of manganese, silicon, sulphur and vanadium were then calculated from the results of the sample analyses. A major conclusion drawn from examination of the results was that the behaviour of the studied elements was as could be expected when approaching the equilibrium reactions from thermodynamic theory. The distributions of the elements in the slag‐metal system showed clear tendencies which did not appear to be influenced by the operational conditions of the furnace. For example, for manganese, vanadium and sulphur, it was found that a higher basicity led to a decreased distribution coefficient L_Mn and L_V, but an increased L_S, which is according to theory. Another observed relationship was that slag basicity increased with an increased carbon content in the hot metal, which indicated that SiO₂ was reduced to [Si] when the oxygen potential decreased. Furthermore, it was found that sulphur and silica behaviour likened that of acidic slag components, while the manganese oxide and vanadium oxide behaviour was similar to that of basic slag components.     

Kinetics of oxidation of carbon in liquid iron-carbon-silicon-manganese-sulfur alloys by carbon dioxide in nitrogen

The oxidation of carbon with the simultaneous oxidation of silicon, manganese, and iron of liquid alloys by carbon dioxide in nitrogen and the absorption of oxygen by the alloys from the gas were studied using 1-g liquid iron droplets levitated in a stream of the gas at 1575 °C to 1715 °C. Oxidation of carbon was favored over oxidation of silicon and manganese when cast iron (3.35 pct C, 2.0 pct Si, 0.36 pct Mn, and 0.05 pct S) reacted with CO₂/N₂ gas at 1635 °C. An increase in the flow rate of CO₂/N₂ gas increased the decarburization rate of cast iron. The rate of carbon oxidation by this gas mixture was found to be independent of temperature and alloying element concentrations (in the range of silicon = 0 to 2.0 pct manganese = 0 to 0.36 pct and sulfur = 0 to 0.5 pct) within the temperature range of the present study. Based on the results of a kinetic analysis, diffusion of CO₂ in the boundary layer of the gas phase was found to be the rate-limiting step for the reactions during the earlier period of the reaction when the contents of carbon, silicon, and manganese are higher. However, the limiting step changed to diffusion of the elements in the metal phase during the middle period of the reaction and then to the diffusion of CO in the gas phase during the later period of the reaction when the content of the elements in the metal were relatively low. For the simultaneous oxidation reactions of several elements in the metal, however, the diffusion of CO₂ in the gas phase is the primary limiting step of the reaction rate for the oxidation of carbon during the later period of reaction. Formerly Visiting Assistant Research Scientist, Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109     

Kinetics of mass transfer of manganese and silicon between liquid iron and slags

The kinetics of mass transfer of Mn and Si between liquid iron and slags were investigated in laboratory experiments at 1600°C in MgO crucibles with 1500 g iron and 250 g slag. Three different slags consisting of CaO-MgO-MnO-SiO₂, MgO-MnO-SiO₂ and MgO-MnO-Al₂O₃-SiO₂ were used. The concentration-vs.-time curves, experimentally measured under defined flow conditions generated by gas stirring, were evaluated by application of a multi-component transport model in order to obtain the mass transfer coefficients. The numerical values of the thus determined measured mass transfer coefficients were compared with values calculated by a theory of mass transfer at liquid-liquid interfaces. The measured and theoretical values were in good agreement with each other in the case of reduction of MnO from the slag by Si in the metal, provided that the measurements had been carried out below a critical stirring intensity, above which metal droplets were emulsified in the slag. Experiments, where sulphur was dissolved in the metal melt and where the sulphur contents were systematically varied, showed no changes of the mass transfer coefficient in comparison to sulphur-free melts. The experimental mass transfer coefficients for the reduction of silica from the slag by manganese in the metal were smaller than those calculated by the mentioned mass transfer theory. This could be explained by inhibition of surface renewal under the influence of solid reaction products precipitated at the interface.     

使用菱镁石调整渣型和使用铝渣型冶炼锰硅合金生产的探讨(Ⅰ)

论述了使用菱镁石调整渣型生产锰硅合金的特点。采用钙镁渣型,炉渣中MgO含量控制在16%～18%,CaO含量控制在12%～14%;采用镁渣型,炉渣中MgO含量控制在18%～21%。增加渣中MgO含量可提高元素的还原效率,提高炉温,降低炉渣黏度,而相对于钙渣型,可提高硅的利用率,减少焦炭和硅石用量,同时降低渣中跑锰;使用铝渣型(与钙渣型和镁渣型相比)会有更高的炉温,硅的利用率和元素回收率增加,若原料搭配合理,使用铝渣型生产锰硅合金可不另配入硅石。通过比较得出:配入菱镁石调整渣型冶炼锰硅合金是完全可行的。     

Thermodynamics of iron-manganese aluminate spinel inclusions in steel

The effect of manganese on the residual oxygen concentrations of liquid iron in equilibrium with alumina saturated iron-manganese aluminate spinel solid solutions was investigated at temperatures of 1550, 1600, and 1650°C. The relationship between the equilibrium concentrations of manganese and oxygen in iron melts containing up to 6 wt pct manganese has been established. The compositions of the spinel deoxidation products, (Fe _x Mn _j-x ) O · Al₂O₃, which were formed during equilibration with the iron melts were determined with electron microprobe and neutron activation analysis. From these results, new thermodynamic data pertaining to galaxite formation reactions have been derived and their implications with respect to the deoxidation of aluminum semikilled, silicon free, steels have been discussed.     

Thermodynamic Simulation of the Influence of the Temperature and the Basicity of a Boron-Containing Slag on Steel Desulfurization

The results of thermodynamic simulation of the desulfurization of a medium-carbon steel by slags of the CaO–SiO₂–MgO–Al₂O₃–B₂O₃ system are presented. The HSC Chemistry 6.12 software package is used for the simulation. The thermodynamic simulation is performed for 20 various chemical compositions of slags with various B₂O₃ contents (1–4%)¹ and basicities ((CaO)/(SiO₂) = 2–5). The computations are performed using the Equilibrium Compositions module in the temperature range from 1500 to 1700°C with an increment of 50°C at a gas phase pressure of 0.1 MPa. The main results of the calculations are presented as the dependences of the change in the sulfur content in steel [S] on the temperature, the content of B₂O₃, and the slag basicity. An increase in the temperature of metal desulfurization from 1500 to 1700°C exerts a favorable effect on the sulfur content for the studied range of slag basicities. In particular, the sulfur content in steel decreases from 0.012 to 0.009% when steel is processed with the slag having 3% B₂O₃ and a basicity (CaO)/(SiO₂) = 2. A positive effect of an increase in the slag basicity from 2 to 5 on metal desulfurization is observed: the degree of desulfurization increases from 61.1 to 97.2% at 1600°C and 3% B₂O₃ content in the slag. As the B₂O₃ content in a slag increases from 1 to 4%, its refining properties decrease significantly in the range of basicity not higher than 2. In the range of high slag basicities (3–4), the negative effect of acidic oxide B₂O₃ on the refining properties of the slag decreases, providing low sulfur contents (which do not exceed [S] = 0.003–0.004% at 4% B₂O₃). At a slag basicity of 5, the sulfur content in steel decreases to 0.001%, all other things being equal. The simulation results can be used for the calculation of steel desulfurization processed by slags containing B₂O₃.     

Chemical equilibria between silicon and slag melts

The equilibria between silicon and slags of the systems CaO-SiO₂, Na₂O-SiO₂, and CaO-SiO₂-Y with Y being A1₂O₃, MgO, TiO_x, B₂O₃, and Na₂O have been investigated in silica crucibles. The calcium content under silica-saturated CaO-SiO₂ slag is 262 parts per million (ppm) at 1500 °C. The aluminum and magnesium contents increase with increasing alumina or magnesium oxide contents, respectively, reaching about 1800 ppm Al at silica/mullite or about 390 ppm Mg at silica/protoenstatite saturation. Boron has a distribution ratio [B]/(B₂O₃) of 0.18. The sodium content under silica-saturated Na₂O-SiO₂ slag is 25 ppm at 1500 °C. In contrast, the titanium content of the silicon, if Y is TiO_x, and (Ti) is in the percent range, is highand varies with the titanium content of the slag according to [wt Pct Ti] = 2.7 √(wt pctTi). In other experiments, it is shown that metallurgical grade (MG) silicon can be purified from aluminum, magnesium, and calcium by treatment with suitable silicate slags.     

Dissolution Mechanism of Indium in CaO-Al2O3-SiO2 Slag at Low Silica Region

The solubility of indium was measured in the low-silica region (<20?mass pct SiO₂) of the CaO-Al₂O₃-SiO₂ system by a thermochemical equilibration technique. The dissolution mechanism of indium into the CaO-Al₂O₃-SiO₂ slag at 1773?K (1500?°C) under a reducing atmosphere was elucidated. The indium solubility increases in the calcium silicate-based flux and decreases in the calcium aluminate-based flux with increasing oxygen partial pressure. Also, the solubility was found to decrease initially with increasing slag basicity until the basicity reached a critical level after which the solubility increases. This behavior is believed to indicate that the indium dissolution mechanism changes according to the basicity of the slag.     

Effect of BaO,Basicity and Temperature on Manganese Distribution between Slag and Hot Metal in Blast Furnace

Daily average data obtained on the 1033 m³ blast furnace No.3 of the Egyptian Iron and Steel Company (EISCO) were used to investigate the effects of BaO, basicity and temperature on the activity coefficient and activity of MnO in the slag as well as on the manganate capacity and manganese distribution between slag and metal. The activity coefficient was estimated by using the regular ionic solution model. Both activity coefficient and activity increase with increasing basicity and BaO content of the slag. The activity, manganate capacity and manganese distribution ratio are largely dependent on temperature and change only slightly with the basicity. The relative partial molar enthalpy of solution of MnO in the slag is 107 kJ/mol. The relationship between activity and concentration of MnO in the slag is linear over the whole ranges of temperature (1400 to 1450°C) and basicity, (CaO/SiO₂ = 0.61‐0.95). The concentration dependence of manganese activity in hot metal is also linear and the activity coefficient of Mn in hot metal is 0.51. The distribution ratios calculated by using the concept of manganate capacity were correlated with the relevant values obtained from the slag and metal analyses. The calculated partition ratios are in agreement with the observed values. In all cases, empirical equations have been derived.     

Influence of chemical compositions of slag and graphite on the phenomena occurring in the graphite/slag interfacial region

Silica reduction reactions taking place in the slag/carbon interfacial region were investigated for synthetic/natural graphite in the temperature range 1500 °C to 1700 °C. Two silica-rich blast furnace slags, with low levels of iron oxide, were used in this study. Silica concentration in these slags, labeled as 1 and 2, was 30.80 pct and 36.80 pct with a respective basicity of 1.67 and 1.22. Reaction rate investigations were supplemented with wettability measurements on these systems with an aim to probe a possible interdependence between wetting characteristics and reaction rates of silica reduction. Wettability and slag/carbon reactions were studied in a horizontal tube resistance furnace in argon atmosphere, using the sessile drop approach. While the contact angles were measured by recording live images of the assembly with a charge-coupled device camera, the volumes of CO and CO₂ evolved were obtained from an analysis of off-gases with the help of a mass spectrometer. Reaction rates for silica reduction showed a wide variation for different systems. Synthetic graphite showed nonwetting behavior with both slags. Natural graphite, however, showed dynamic wetting with slag 2, resulting in low contact angles. This is attributed to the difference in the deposition of Si-based reaction products in the interfacial region, which in turn influences wettability. Temperature had a significant effect on both the wettability and silica reduction rate of the graphite/slag system. Activation energies for silica reduction in slags 1 and 2 with natural graphite were estimated to be 253 and 241 kJ/mol, respectively. Chemical composition of carbonaceous materials and slags were found to play a very important role in dictating overall reaction rates and wetting characteristics.     

Parameters affecting manganese oxidation in top blown basic oxygen converter

The data obtained from 84 heats carried out in a 90-t top blown basic oxygen converter were used to study the effects of slag composition and temperature on the activity coefficient and activity of manganous oxide in the slag as well as on the manganate capacity and the manganese distribution between slag and metal. In addition, the dependence of manganese activity in the metal on the concentration of maganese and temperature was also investigated. The present study carried out in wide ranges of temperature, 1350–1690°C, and slag basicity expressed as (CaO)/(SiO₂), 1.4–10.6, clarifies the dependence of MnO activity coefficient mainly on temperature. The activity coefficient of MnO increases by decreasing the temperature. On the other hand, activity of MnO increases by increasing MnO concentration and temperature. Both activity coefficient and activity of MnO in the slag slightly increase by increasing the slag basicity. At constant temperature, the activity of Mn in the molten metal varies linearly with Mn concentration and tends also to increase with increasing temperature at constant Mn concentration. The increase in manganese activity by increasing Mn concentration is much steeper at high temperatures. The manganate capacity as well as manganese distribution ratio decrease with increasing temperature at constant basicity and tend also to slightly decrease with increasing slag basicity at constant temperature. Equations describing the parameters affecting activity coefficient and activity of manganous oxide in the slag, manganese activity in the metal, manganate capacity and manganese distribution ratio have been derived.     

Thermodynamics of MnO, FeO, and phosphorus in steelmaking slags with high MnO contents

The thermodynamics of managanese oxide and iron oxide and the phosphate capacity of CaO-SiO₂-MnO-Fe _t O-P₂O₅-MgO_sat slags with high MnO contents relevant to the smelting of MnO ores in steelmaking were investigated. Previous data were limited to about 5 pct MnO, whereas in this study MnO contents up to 25 pct were studied. The activity of MnO showed positive deviation from ideal behavior and increased with basicity, while that of Fe _t O decreased with basicity. This is reflected in that the manganese distribution ratio at a given Fe _t O content decreases with basicity and high Mn in the metal is favored by high basicity. CaF₂ additions up to 4 pct did not affect the activities of MnO and Fe _t O. The activity coefficient of P₂O₅ decreases and the phosphate capacity increases with basicity. There was not adverse effect of high MnO contents on the dephosphorizing abilities of the slags.     

Sulfide capacity of CaO-CaF2-SiO2 slags

The sulfide capacityC _S ^2- = (pct S^2-) · (P _{O 2}/P _{S 2})^1/2) of CaO-CaF₂-SiO₂ slags saturated with CaO, 3CaO · SiO₂ or 2CaOSiO₂ was determined at 1200 °C, 1250 °C, 1300 °C, and 1350 °C by equilibrating molten slag, molten silver, and CO-CO₂ gas mixtures. Higher sulfide capacities were obtained for CaO-saturated slags. A drastic decrease was observed in those values when the ratio pct CaO/pct SiO₂ is less than 2. The sulfur partition between carbon-saturated iron melts and presently investigated slags was calculated by using the sulfide capacities obtained and the activity coefficient of sulfur in carbon-saturated iron, which was also experimentally determined. For slags saturated with CaO, partitions of sulfur as high as 10,000 were obtained at 1300 °C and 1350 °C. Correlations between the sulfide capacity and other basicity indexes such as carbonate capacity and theoretical optical basicity were also discussed. Formerly with the Department of Metallurgy, The University of Tokyo.