Abstract The continuous casting tundish is the last metallurgical reactor where molten metal flows before solidifying in the continuous casting mold. A tundish covering powder can be used for improving steel cleanliness; in this case it is named ‘active tundish slag’. The objective of this work is to evaluate, in laboratory, the effect of three kinds of tundish covering powders on cleanliness for a SAE 1055 modified steel - a Ca-aluminate, a Ca-Mg-aluminate, and an Al-silicate powder, analysing their interaction with rice hull ash. The forementioned materials were molten on liquid steel, representing different kinds of tundish covering powders which are used in the steel industry: a Ca-Mg-aluminate, an Al-silicate, and a Ca-aluminate. Experiments were performed with and without a top layer of rice hull ash, simulating industrial conditions. Distribution, density, and mean diameter of inclusions were measured through automated inclusion analyses. Through computational thermodynamics it was possible to evaluate deviation from saturation (considering Al2O3 and MgO from refractory) and slag viscosity. It can be stated that the Ca-aluminate tundish covering powder gives better results regarding cleanliness for the SAE 1055 modified steel under laboratory conditions.

Abstract Al2O3 (alumina) and MgO·Al2O3 (spinel) inclusions cause valve obstruction (clogging) in continuous casting and can deteriorate the quality of the final product. In this context, industrial heats of the bearing steel SAE 52100 was examined. Samples were collected in the final steps of the steelmaking process, both after vacuum treatment and during continuous casting. A scanning electron microscope (SEM) equipped with a energy-dispersive spectrometer (EDS) and automated particle characterization analysis was used to characterize the inclusions present in the steel samples. Thermodynamic calculations were performed with the commercial software FactSageTM 7.2. Based on thermodynamic predictions, parameters such as solid fraction, liquid fraction, MgO saturation point of the slags, content of dissolved elements in steel (Al, Mg, Ca,...) and the construction of a phase stability diagram were determined. The results in this study showed a tendency for increase in MgO content in the inclusions with the decrease of %FeO and SiO2 contents in the slag, an increase of binary basicity (%CaO/%SiO2). It is verified that the MgO contents in the slag were close to the saturation, increasing the probability for the formation of inclusions rich in MgO and/or spinel. On the other hand, stability diagrams confirm the formation of spinel inclusions for each of the heats analyzed. During the final step of the steelmaking process, there is a tendency for re-oxidation, which is verified by an increase in the density of inclusions (or total oxygen TO values).

Abstract The amount of Electric Arc Furnace Dust (EAFD) is continuously increasing in mini-mill steel plants. This dust is considered a hazardous waste because of the presence of elements like lead, cadmium and chromium. Among many different treatment processes for this issue, there is the possibility of returning the EAFD back to the Electric Arc Furnace. This article presents a study of the compressive strength of self-reducing cold bonded pellets as well as their zinc removal, in an agglomerate containing EAFD, petroleum coke (PET) and Portland cement. The effects of the reductant and binder employed were discussed. Moreover, an apparatus was built to prevent zinc gas reoxidation inside an electric vertical laboratory furnace. Thus, the fraction of weight loss complemented the result of a previous study indicating the optimal content of PET source usage between 10 to 15%, in mass. Zinc removal and additional X Ray Diffraction outcomes are shown and discussed, concluding that 80% of zinc removal for this system could indicate the possibility of the EAFD reuse.

Abstract Electric Arc Furnace Dust (EAFD) is a solid waste originated from electric steelmaking furnaces. Currently, according to some authors, there is an estimated generation of 15 to 25 kg of dust per ton of steel produced. The formation of the dust is related to the following steps of the process: furnace charge, metal volatilization, iron vaporization under the arc, drag of solid particles and, mainly by the collapse of CO bubbles from metallic bath decarburation. The dust has metals that are harmful to the environment. Otherwise, it is mostly composed of the elements iron, zinc and oxygen. Due to increasing costs for disposal and because it is considered a hazardous waste, industry is looking at the possibility of returning the dust to the steelmaking process. One of the alternatives is by reintroducing the waste in an electric melting shop using self-reducing agglomerates as part of the furnace burden. In this study, self-reducing mixtures are prepared with EAFD and petroleum coke (PET), presenting chemical and physical characterizations. An evaluation about the behavior of the mixtures is carried out in thermobalance, regarding the possibility of use in measuring accurate PET content in self-reducing pellets. As results it could be stated that the elements of economic interest, Zn and Fe, represent, respectively, 34.23 and 22.80%, in weight. These elements are present in chemical species frankilinite, zincite and magnetite and the reducible oxygen was estimated as 17.90%. Also, it was concluded the optimal content of petroleum coke in the mixtures varies from 10 to 15%, in weight. Therefore, the utilization potential of the thermogravimetric technique in the industrial field for adjustment of carbon content in batches of self-reducing pellets is satisfactory.

Abstract This study focuses on the viscosity calculation of molten slags using computational thermodynamics. Different slag systems and their measured viscosities from different references were used and compared with those obtained through FactSage software. To calculate the viscosity of each slag the Viscosity module available in FactSage 6.4 was used. In order to perform the evaluation of computational thermodynamics in viscosity calculation, six different slag systems were presented, all of which were formed of calcium-silicate melts. In total, 162 slags, in temperatures ranges from 1423 K (1150 ºC) to 2089 K (1816 °C) were presented for all slag systems. The software showed a tendency to produce viscosity values lower than those found in the literature measured by an experimental method. The relative deviation between the measured and calculated viscosity values is in the range of 13.31 to 37.53% for evaluated systems. Considering all references and systems, the average deviation between measured and calculated viscosities is 23.61%, which, according to literature, is an acceptable value. The CaO-SiO2-Al2O3 and CaO-SiO2-FeO systems showed the best agreement between the experimental method and the method calculated through FactSage 6.4 with a very good fitting between viscosity values.

Electric arc furnace (EAF) slag has a range of functions, including improving energy efficiency through the "slag foaming" phenomenon. As such, the study of slag is important in EAFs. One of the factors that determine foaming quality and efficiency is the presence of solid particles. MgO saturation is highly significant since, in addition to ensuring the presence of solid particles, it also ensures chemical compatibility to minimize refractory consumption. The present study aims to examine MgO saturation, using the software FactSage v.6.4 for all calculations, in the CaO-SiO2-FeO-MgO-Al2O3 slag system and the influence of binary basicity, FeO and Al2O3 content on this system. Ternary diagrams revealed the influence of Al2O3 content on the liquid field and other phases present. Isothermal saturation diagrams (ISDs) were constructed, showing the same dual saturation points found in the ternary diagrams. The ISDs were validated by comparing the results of different heats in terms of the electrical energy consumption. The closer the heat is to the MgO saturation line, the less energy is consumed.

Secondary refining slag samples with different chemical compositions (45-54 % CaO, 7-13 % Al2O3, 20-29 % SiO2, 9-16 % MgO, 0-5 % CaF2) were investigated to verify the influence of their effective viscosity on inclusion cleanliness of DIN 38MnS6 in a steelmaking plant. The steel samples were collected during the production process for analysis of inclusions. Using the commercial software FactSage 6.4, thermodynamic calculations were performed to determine the effective viscosity, solid fraction, liquid fraction and MgO saturation point of these slags at 1560ºC. The results showed that all the slags were saturated in MgO, revealing a better protection of the ladle refractory. The addition of 2 to 5 % of CaF2 reduced the effective viscosity values for the analyzed slags from 0.45 Pa∙s to 0.10 Pa∙s , in comparison to the slags without the addition of CaF2, with an effective viscosity of 0.40 Pa∙s, 0.27 Pa∙s and 0.22 Pa∙s, decreasing the level of non-metallic inclusions for some of the analysed heats. However, it was detected during the manufacturing process that high slag fluidity and re-oxidation events continue to be a challenge associated with reducing the level of non-metallic inclusions.

The process of vacuum degassing occurs during the secondary refining of special steels. Its main function is to remove undesirable gases. However, during this process, flotation phenomenon and inclusions absorption are reported. The aim of the present work was to study the slag viscosity and vacuum degassing (tank type) capacity in steel cleanliness from an industry perspective. To achieve this objective, slag and steel samples were taken before and after the vacuum stage. The results in steel cleanliness were related to a kinetic stirring parameter (βs) of the vacuum station and to the effect of slag viscosity. The removal of inclusions during the vacuum stage reached 64, 75 and 78% in the diameter ranges of 2.5-5, 5-15 and ≥ 15 µm, respectively. After the degassing process, the composition of non-metallic inclusions seemed to approach the slags' chemical compositions. The stirring process in the vacuum degassing station promotes a significant decrease in the inclusion densities for the 2.5-15 µm diameter range and also in the sulfur content in liquid steel. Regarding the effective viscosities of slags, it was concluded that lower values (0.20 Pa.s) increased slag capacity in inclusion removal, whereas higher values (> 0.40 Pa.s) were detrimental to steel cleanliness.

Slag foaming is part of steelmaking process and could bring several benefits: it helps to save energy, improves productivity, enhances the refractory service life, decreases noise pollution and protects the bath from nitrogen incorporation. Unfortunately, slag foaming is a highly dynamic process that is difficult to control. There are factors that limit the quality of the foam generated on the slag, such as: basicity, FeO content, surface tension, viscosity, carbon and oxygen injection. This paper aims to discuss the main factor that induces foaming, mathematical models proposed by different authors and the use of isothermal solubility diagram (ISD) to predict the foam quality.

In steel mills that operate with electric arc furnaces (EAF), it is interesting to ensure greater stability to the electric arc to aim at less distortion in the electrical system, with consequent reduction in electric power consumption. The slag foaming increases electric arc stability by reducing the total harmonic distortion (THD) between EAF phases. In this study, information about the chemical composition of the slag and electrical parameters of an EAF were collected. With the composition data, it was possible to determine the FeO and MgO content and basicity of the foamy slag which caused a reduction in THD and in electric power consumption. The effective viscosity of foaming slag was calculated and an increase in the effective viscosity provided a decrease in THD. A reduction of THD showed a decrease in the consumption of electric power in the EAF refining stage.

Charcoal is a very important reducing agent in Brazil, the world’s largest steel industry based on charcoal blast furnace. Charcoal generates large amounts of charcoal fines during its production and processing. A good alternative for harnessing this fuel is the injection into coke-based blast furnaces via PCI process (Pulverized Coal Injection), a key technology for reducing use of coke in ironmaking. This study aimed to evaluate the combustibility and reactivity to CO2 of binary blends of charcoal fines and coals with purpose to PCI. Moreover, it was also attempted to identify the reasons for the different behavior of coals. The work was carried out by thermogravimetric analysis (TGA). The proportions of charcoal used were 10, 20 and 50% in mass. Charcoal showed the highest combustibility and reactivity among tested fuels and the blends formulated had higher combustibility and reactivity than single coals.

For about 10 years the steel industry in Brazil has used pulverized coal injection (PCI) technology in the blast furnaces based on imported coals. In order to decrease the dependence on imported coals, Brazilian coal, which has limited use due to high ash content, was suggested to be mixed with imported coal and charcoal. The aim was to examine the reactivity of the samples. The charcoal use in the steel industry contributes to the CO2 emission reduction, since it represents a renewable source of energy. The reactivity of the coals, charcoal and mixtures was evaluated through simultaneous thermal analyses. Results of this study are presented and discussed.

The main purpose of this paper is the thermodynamic study of non-metallic inclusion formation in the CC tundish for SAE 1141 steel. The specific purposes are: 1) obtaining inclusions as function of steel composition and casting temperature. 2) establishing steel chemical composition to form less harmful inclusions to the SAE 1141 steel castability. Simulations using the commercial software FactSage and databases were carried out. Results showed both different solid oxides and liquid phase formation in inclusions by varying calcium content in the steel. Thus, it was possible: 1) to determine both the inclusion composition as a function of aluminum and calcium content of SAE 1141 steel. 2) to establish a range of calcium content in which inclusions are formed predominantly by liquid phase. 3) to calculate percentage of liquid and solid phases in inclusions, and oxides composition as well.

A fabricação primária de alumínio dá-se em fornos onde banho e metal líquidos são movimentados a partir de Forças de Lorentz. Esse artigo apresenta a validação experimental em cubas reais de uma metodologia 3-D de análise eletromagnética de cubas eletrolíticas anteriormente desenvolvida com o pacote comercial de Elementos Finitos ANSYS 9.0. Os resultados numéricos representam, adequadamente, a forma das componentes mais importantes de para a tecnologia ensaiada (B X e B Z), observando-se a incerteza de medição e. A maior diferença observada entre resultados numéricos e experimentais para a componente longitudinal B X, é de 33% e, para a componente vertical B Z, é de 60%. Foram observadas correlações entre dados medidos e calculados de 98,8% para B X e 93,5% para B Z.

Primary aluminum is produced in electrolytic cells where bath and metal flow due to Lorentz Forces. This work presents the experimental validation in real pots of a previously introduced 3-D magnetic field analysis methodology develop with the commercial Finite Element package ANSYS 9.0. Numerical results represent fairly the most important components for the simulated technology (B X and B Y), considering the measurement error e. Maximum differences observed between experimental and numerical results are 33% for B X and 60% for B Z. Correlation between measured and calculated values are up to 98,8% for B X and 93,5% for B Z.

Esse trabalho, realizado com a aplicação da termodinâmica computacional, trata dos fundamentos da produção de aços inoxidáveis na aciaria. A compreensão dos equilíbrios termodinâmicos, que se estabelecem durante o processo, contribui para a melhoria do controle operacional e do rendimento do Cr, um insumo comparativamente caro. A metodologia consistiu em utilizar os bancos de dados e a rotina de minimização da Energia de Gibbs do software FactSage, para calcular os equilíbrios envolvendo os sistemas Fe-Cr-O e Fe-Cr-O-C-Ni. Os valores calculados para o teor de O em equilíbrio com o Cr são próximos aos resultados obtidos com base em equações e dados da literatura. Em relação ao teor de Cr limite, no qual o óxido sólido em equilíbrio muda de FeO·Cr2O3 para Cr2O3, os resultados desse trabalho aproximam-se dos valores estabelecidos na literatura, mas mostram discrepância em relação a trabalhos recentes. Ressaltam-se, além disso, alguns aspectos sobre os quais se embasa a tecnologia - o efeito do vácuo e da temperatura, durante a operação de refino.

This work, done with the application of computational thermodynamics, deals with the fundamental aspects of the stainless steel production in the steelmaking. The understanding of the thermodynamics equilibria that occur during the process contribute for the improvement of operating controls and the yield of chromium - a comparatively expensive material. The methodology consisted to use the databases and the Gibbs Energy minimization routine of the FactSage software to calculate equilibria involving the systems Fe-Cr-O and Fe-Cr-O-C-Ni. The calculated values for the O content in equilibrium with Cr are in good accord with the obtained results using equations and data from literature. About the critical Cr concentration, at which the equilibrium oxide changes from FeO·Cr2O3 to Cr2O3, the results from this work are in good agreement with that values well known from literature, but show discrepancy when compared with recent works. Moreover, some aspects over which the technology is based are highlighted - the vacuum and temperature effects during refining process.