Sulphide Capacities of CaO‐SiO2‐Al2O3‐MgO Slags

In Japanese steelworks, hot metal is now being produced by a scrap melting process. With this process, removals of sulphur is very much handicapped because of very high sulphur levels (0.04‐ to 0.09‐ pct by weight) and relatively low tapping temperatures (1623 to 1723 K). In order to overcome such handicaps, the authors explored on the respective phase diagrams. These explorations revealed that {CaO‐SiO₂‐Al₂O₃‐MgO} slags with Al₂O₃ contents of 30‐ to 35‐pct by weight would be good candidates as reagents for sulphur removal from high sulphur hot metal at relatively low temperatures. For better understanding of the thermodynamic properties of the candidate slags, in this study, sulphide capacities were determined through gas/slag equilibrium technique. The experimental results suggest that there would be, at least, a “window” to remove sulphur from high sulphur hot metal as relatively low temperatures.     

Water Capacity Model of Al2O3‐CaO‐MgO‐SiO2 Quaternary Slag System

The focus of the present work was to develop a water capacity model for the quaternary slag system Al₂O₃‐CaO‐MgO‐SiO₂. In the model, a silicate melt was considered to consist of two ion groupings, viz. cation grouping and oxygen ion. The water capacity of a melt is supposed to depend on the interactions between the cations in the presence of oxygen ions. These interactions were determined on the basis of the experimentally measured water solubility data. Only binary interactions were employed in the model. For the system CaO‐SiO₂, disagreement in the literature data was found. Since the interaction between Ca²⁺ and Si⁴⁺ would play an important role, experiments were carried out to determine the water capacities of some CaO‐SiO₂ slags. For this purpose a thermogravimetric method was employed. Iso‐lines of water capacities at constant MgO contents were predicted by the model and compared with the experimental data from literature. The model calculations agreed well with the experimental results.     

The Effect of MgO on the Viscosity of the CaO‐SiO2‐20 wt%Al2O3‐MgO Slag System

The viscosities of CaO‐SiO₂‐20 wt%Al₂O₃‐MgO slags (CaO/SiO₂ = 1.0–1.2, wt%MgO = 5–13) were measured to estimate the effect of MgO on the viscous behaviour at elevated temperatures. The slag viscosity at 1773 K decreased with increasing MgO contents, which was typical of a basic oxide component at relatively low basicity (CaO/SiO₂) of 1.0. The FT‐IR spectroscopic analysis of the slag structure seems to verify this behaviour. However, an unexpected contradiction with the temperature dependence was observed above 10 wt%MgO and above CaO/SiO₂ of 1.2. Although the apparent activation energy was expected to decrease with additions of the basic oxide component MgO, the apparent activation energy increased. This unexpected behaviour seems to be related to the change in the primary phase field correlating to the phase diagram corresponding to the slag composition. Therefore, in order to understand the viscosity at both high Al₂O₃ and MgO, not only should the typical depolymerization of the slag structure with high MgO content be considered but also the primary phases of which the molten slag originates.     

Viscosities of the Quaternary Al2O3‐CaO‐MgO‐SiO2 Slags

Viscosities of some quaternary slags in the Al₂O₃‐CaO‐MgO‐SiO₂ system were measured using the rotating cylinder method. Eight different slag compositions were selected. These slag compositions ranging in the high basicity region were directly related to the secondary steel making operations. The measurements were carried out in the temperature range of 1720 to 1910 K. Viscosities in this system and its sub‐systems were expressed as a function of temperature and composition based on the viscosity model developed earlier at KTH. The iso‐viscosity contours in the Al₂O₃‐CaO‐MgO‐SiO₂ system relevant to ladle slags were calculated at 1823 K and 1873 K for 5 mass% MgO and 10 mass% MgO sections. The predicted results showed good agreement with experimental values and the literature data.     

Composition Control of CaO‐MgO‐Al2O3‐SiO2 Inclusions in Tire Cord Steel ‐ a Thermodynamic Analysis

The effect of oxide component content on the low melting point zone (LMP) in the CaO‐MgO‐Al₂O₃‐SiO₂ system has been analysed using FactSage software. The contents of dissolved elements [Si], [Mg], [O] and [Al] in liquid steel in equilibrium with the LMP inclusions in the CaO‐MgO‐Al₂O₃‐SiO₂ system have been calculated. The results show that the CaO‐MgO‐Al₂O₃‐SiO₂ system has the largest LMP zone (below 1400°C) when the Al₂O₃ content is 20% or the MgO content is 10%. The LMP zone becomes wide with the increase in CaO content (within the range of 0~30 mass%) and the decrease in SiO₂ (from 25 to 5 mass%). To obtain the LMP (below 1400°C) inclusions, the [Mg], [Al] and [O] contents must be controlled within the range of 0.2~2 ppm, 1.0~2.0 ppm and 60~100 ppm, respectively.     

高铝渣对济钢3200m~3高炉冶炼的影响

针对高铝渣特有的黏度高、流动性差、脱硫能力差的特点,济钢3200 m3高炉通过调整热制度和布料制度,在烧结时提高MgO含量,控制渣中镁铝比0.6,使渣中MgO含量在8%~11%,高炉的整体操作炉型适应了高铝渣的冶炼要求。在渣铁比升高43 kg/t的条件下,高炉生铁含硅降低,炉渣脱硫能力增强,基本杜绝了三类铁。     

Influence of SiO2 Addition on the Properties of Al2O3‐CaO‐CaF2 Slag

The Al₂O₃‐CaO‐CaF₂ slag system is used in making special quality steels by the electro‐slag re‐melting process (ESR). The purpose of our investigation was to analyse ESR slag that contained SiO₂. The slag samples with different SiO₂ fractions (0 ‐ 20 mass %) were examined by chemical analysis, differential thermal analysis, simultaneous thermal analysis, X‐ray diffraction, electron microscopy and wetting angle measurement. With addition of SiO₂ the polymerization of slags was increased due to the formation of new silicate complex compounds that influenced their melting points and wetting angles.     

Thermodynamics of Composition Control of CaO‐MnO‐Al2O3‐SiO2 Inclusions in Tire Cord Steel

The effect of oxide component content on the low melting point zone (simplified as LMP) in the CaO‐MnO‐Al₂O₃‐SiO₂ system has been analysed by FactSage. The contents of [Si], [Mn], [O] and [Al] in liquid steel which are in equilibrium with the LMP inclusions in the CaO‐MnO‐Al₂O₃‐SiO₂ system have been calculated. The results show that the CaO‐MnO‐Al₂O₃‐SiO₂ system has the largest LMP zone (below 1400°C) when the Al₂O₃ content is 20% or the CaO content is 15%, and that the LMP zone becomes wider with increase in SiO₂ and MnO contents (within the range of 0~25%). To obtain LMP inclusions (below 1400°C), [Si] and [Mn] can be controlled within a wide range, but [Al] and [O] must be controlled within the range of 0.5~5 ppm and 50~120 ppm, respectively.