During recent years, in parallel with major technological changes that have transformed the productivity of the steel industry, there have been increasing demands for improved steel quality. These demands are being met by advances in our knowledge of the chemical, physical, and thermal interactions between steel, gas, slag, and refractory phases which take place within individual reactors as well as during transfer between reactor and the next. The traditional concepts of slag capacities and basicity ratios are used in order to characterize slag behavior as well as the relatively new concept of optical basicity. Examples are presented of how optical basicity can be used to optimize the design of slags so that they will possess properties that are most appropriate for different operating conditions such as desulfurization and/or hydrogen control. Transfer operations must be precisely controlled in order to preserve steel quality; otherwise, quality achieved within one reactor can be lost during transfer to the next. In addition to the generation and preservation of steel quality during processing, novel sensor technologies are finding increasing application for the monitoring and evaluation of metallurgical operations so that the occurrence of any detrimental variations due to perturbations or imperfections within the processing system can be detected and corrected at an early stage.

Permanent magnet stirring (PMS) featuring low power dissipation and high-intensity magnetic field was investigated as a means of decreasing internal solidification defects. In this study, the magnetic Taylor number (Ta) was used to quantify the melt flow. Initial research of PMS involved a laboratory study of the solidification of Sn-20 wt-% Pb alloy. An industrial plant trial with continuously cast tire cord steel confirmed that PMS, in accord with the laboratory findings, produced an improvement in central cavities in the cast product. Moreover, it was established that PMS is an alternative method for reducing carbon macrosegregation in tire cord steel billets with different section sizes. It was also found that PMS (Ta = 8.97 x 10(7)) was more effective for improving central carbon macrosegregation of tire cord steel than electromagnetic stirring (Ta =6.33 x 10(7)) due to the larger Ta related to the driven-flow intensity of the residual melt.

The formation and characteristics of non-metallic inclusions in 316L stainless steel produced by the AOD (argon oxygen decarburization)-ladle furnace-continuous casting process were investigated. The morphology and composition of inclusions changed significantly during the refining and casting processes. After de-oxidation with Si/Mn additions, spherical complex inclusions mainly consisting of calcium silicates were observed. The contents of MgO and Al2O3 in these inclusions continuously increased as the steel moved from the AOD through ladle processing to the tundish. As the temperature decreased from the tundish through to solidification, harmful crystals of MgO/Al2O3 spinel were precipitated within the steel melt as well as within the calcium silicate matrix of existing inclusions. The results obtained from thermodynamic calculations carried out using FactSage (TM) commercial software agreed well with the information derived from evaluation of the industrial samples enabling recommendations to be made for the avoidance of detrimental spinel inclusions.

The melting behaviour of mould powder during continuous casting is an important consideration with respect to caster performance, production rate and steel quality. Two important factors, powder composition and carbon addition, are critical to control the properties and melting behaviour of the mould flux. In this study, the effect of different carbonaceous materials on the melting characteristics of mould powders was evaluated. Correlations were established between the structural factors and chemical reactivity of carbon and melting behaviour of mould flux. In addition, two examples are given of the effect of flux composition on casting performance for specific steels. A flux with reasonable basicity and additives was designed for the casting of heat-resistant steel (Incoloy 800) to reduce surface cracks. Another flux was designed for the casting of non-magnetic steel containing high aluminium by partially replacing SiO2 with Al2O3 to limit aluminium oxidation by SiO2.

Using an electromagnetic levitation technique, the kinetics of decarburisation of Fe-Cr-C alloy droplets by oxygen-argon gas mixtures containing up to 10 vol.-% oxygen was investigated at 1873 K. The observed decarburisation rates were less than predicted using conventional formulation of governing mass transport numbers. It is hypothesised that the effects of thermal diffusion caused by the steep temperature gradient (similar to 1550 degrees) between the incoming gas stream and the surface of the droplet, is responsible for the difference observed between the well established mass transfer model and the experimental data for decarburisation kinetics. This finding has important implications with respect to the application of appropriate mass/heat transport equations when using commercial software to model pyro-metallurgical processes, such as stainless steel refining, where large temperature gradients are an inherent component of the system.

In the petroleum industry catalysts are often used to accelerate the reaction rate and remove the hazardous sulphur and arsenic from crude oil. A large quantity of spent catalyst material is generated every year and this represents a relatively cheap source of nickel supply. In order to use this nickel for the production of stainless steel or nickel alloys, the phosphorus, sulphur and arsenic in the material must be removed. The aim of this project is to remove these impurities from the nickel-based alloy produced from recovery of spent catalyst without incurring a significant loss of other valuable elements. Slag refining of nickel alloy was carried out in a 10 kw induction furnace. The effects of an oxidizing slag, a weak reducing slag and a strong reducing slag were examined. It was found that a strong reducing slag containing 70wt% CaC2 and 30wt% CaF2 was most suitable for the simultaneous removal of phosphorus, sulphur and arsenic without incurring a significant loss of valuable metal elements. With this slag, more than 70wt% sulphur, 67wt% arsenic, and about 30wt% phosphorus were removed.

A considerable amount of waste slag from the pyrite roasting process is produced every year. Recovery of iron from the waste slag is of great interest for maximum use of mineral resource, reduction of environment impact and improvement of economical benefits to the related companies. The objectives of the present work are focused on: compare various options for recovery of iron from the waste slag and select the most advantageous option for industrial trial which is roasting of the waste slag under reducing condition followed by magnetic separation; investigate the optimum conditions for maximum recovery of iron from the waste slag. The experimental results show that under the treatment condition in this work about 70% of the iron was recovered from the waste slag, where the iron content in the concentrate is 57%. After the further treatment with chlorinated segregation-magnetic separation, the iron content in the recovered slag can reach 83%. After the treatment, sulphur content in the concentrate was reduced significantly and gangue materials, such as SiO2, Al2O3 and TiO2, were reduced effectively. This paper is mainly focused on the results of reduction roasting-magnetic separation.

A. Abbasalizadeh, L. Muhmood, A. Danaei, Y.D. Yang, M. Barati, A. McLean and S. Seetharaman Department of Materials Science and Engineering, KTH; Royal Institute of Technology, Brinellvägen 23, SE-114 28 Stockholm, Sweden CSIRO, Melbourne, Australia Department of Mechanical and Industrial Engineering, Ryerson University, Toronto, Ontario, Canada Department of Materials Science and Engineering, University of Toronto, Toronto, Ontario, Canada _______________________________________________________________________________________ Abstract: Reactions at interfaces such as inclusion separation and refractory attack are extremely important for steel refining. These phenomena involve study of interfacial tensions and contact angles at the heterogeneous interface. In the present work, the contact angle between molten iron and alumina substrate and the surface tension of iron alloys containing different amounts of sulfur and carbon were determined experimentally using the Sessile Drop Technique. A CCD video-camera was utilized to image the melt profile. The contact angle and surface tension were calculated from computer generated solutions of the Young-Laplace equation. In the present study, contact angles and surface tensions of molten iron alloys with different sulfur contents in the range of 0.0092-0.651 wt% and also iron-0.035 wt% sulfur containing 0.5-4.0 wt% carbon were measured at 1873K in an argon-5% hydrogen gas atmosphere. The addition of sulfur to liquid iron caused a decrease in both the contact angle between liquid iron and alumina substrate and the surface tension of molten iron. On the other hand, addition of carbon to liquid iron at constant sulfur content caused an increase in the contact angle between molten iron and alumina substrate and also the surface tension of iron-carbonsulfur alloys. Considering the data for iron alloys with 0.035% sulfur and various carbon contents, it was concluded that carbon decreases the surface tension of the liquid iron by increasing the activity of sulphur in the bulk, however carbon itself increases the surface tension of molten iron and the over-all effect is that the surface tension increases with carbon content.

The melting behaviour of mould powder during continuous casting is an important consideration with respect to caster performance, production rate and steel quality In this experimental study the effect of different carbonaceous materials on the melting characteristics of mould powders was evaluated. Using X-ray diffraction, different types of carbon were quantitatively characterized in terms of their internal structure and reactivity experiments were conducted to investigate potential relationships between the structural morphology of carbons and their reactivity High temperature microscopy and drip test experiments were then used to investigate the melting behaviour of mould powders containing different carbonaceous materials. From the results obtained, correlations were established between the structural factors, chemical reactivity and melting behaviour.

Melting behaviour is a critical index in the selection of mold powders for the optimization of continuous casting. At the present time it is accepted that for a given mineralogical composition of mold powder, the carbon type, amount and particle size primarily determine the melting behaviour. However, there is no evidence in the literature that any attention has been given to the investigation of the relative amounts of amorphous and crystalline structures present in the carbonaceous materials together with their combustion reactivity and the correlation of these parameters with melting behaviour. To investigate these aspects, a novel approach has been employed that involves quantitative X-ray diffraction analysis (QXRDA), high-resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FESEM), evaluation of combustion reactivity using a fixed bed reactor, and determination of combustion temperature of carbon using a multiphase gas analyzer, the melting behaviour of mold powder using pan box tests and high temperature cell microscopy. The research has been directed towards evaluation of the chemical structure and surface characteristics of different carbonaceous materials. The relationship between these parameters and the combustion reactivity of the different materials was then determined and this information subsequently correlated with the melting behaviour of different mold powders.

In this paper, the fundamental aspects of oxide melts pertaining to the removal of impurities from hot metal and liquid steel are discussed with particular emphasis on the concepts of slag basicity and slag capacity. The capacities of various species in molten slags are evaluated using the traditional method of empirical ratios to describe slag basicity as well as the relatively new concept of optical basicity. Examples are provided to illustrate how these concepts can be used to control the behaviour of alkalies in the blast furnace as well as phosphorus, sulphur, water vapour and nitrogen during steelmaking. It is shown that optical basicity avoids the confusion that can arise from the use of empirical basicity ratios, particularly with regard to the effect of magnesia, and in addition, facilitates the design-of slags with appropriate characteristics and properties for the treatment of hot metal and liquid steel.

In this paper, the thermodynamic aspects of alkali behavior in the blast furnace operation are considered with particular emphasis on alkali control through the modification and optimization of slag chemistry. Three factors that affect alkali dissolution in slags are reviewed: temperature, magnesia content and slag basicity. Two concepts, the basicity ratio and optical basicity, are used to characterize slag performance, and the results obtained by these two methods are compared. Potassium oxide capacity of blast furnace slag was calculated using data from published papers and a linear relationship established with optical basicity. From correlations of alkali and sulfide capacities with optical basicity, a new relationship is proposed by means of which it is possible to design blast furnace slags that will possess a high alkali capacity and a reasonable desulfurization ability.

The phosphate capacity of CaO-CaCl2-CaF2 slags with X-CaO = 0.2 and X-CaCl2 + X-CaF2 = 0.8 was measured in the temperature range of 1175 degrees C to 1350 degrees C. The activity coefficient of PO2.5 was calculated using phosphorus distribution data. The sulphide capacity was calculated from a correlation between phosphate and sulphide capacities.It was observed that the phosphate capacity increased with increasing CaF2 mole fraction and decreasing temperature. At 1200 degrees C the log gamma(PO.25), decreased from -9.7 in a CaO-CaCl2 binary slag to about -10.4 in a CaO-CaCl2-CaF2 ternary slag. The effect of temperature on log gamma(PO2.5) was observed to be smaller than the experimental error. A linear relationship between phosphate and sulphide capacities and optical basicity was observed at different temperatures. (C) 1998 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.

Experiments were carried out at 1175–1350°C to study the phosphate capacity of CaO‐CaCl2 slags and the sulphide capacity was calculated according to the correlation between the two capacities. At 1200°C the logarithm of the phosphate capacity increased from 24.5 to 26.5 with increasing CaO mole fraction from 0 to 0.22 in the slags and it decreased with increasing temperature. Sulphide capacity increased both with increasing CaO mole fraction and temperature.A good linear correlation was found between slag carbonate capacity and phosphate capacity as well as sulphide capacity. Optical basicity was used to evaluate the property of the CaO‐CaCl2 slag in the present study. The value of optical basicity of CaCl2 is established as 0.63. The correlations of optical basicity with above mentioned three capacities were found to be linear.