Wagner Viana Bielefeldt

Evaluation of Secondary Steelmaking Slags and Their Relation with Steel Cleanliness

Based on data provided from an industrial plant and FactSage commercial software use, a study of secondary refining slags and inclusion cleanliness was performed. Six heats of two slag series, namely, A and B, with average chemical composition (wt pct) of 43.00CaO-25.90SiO2-12.96Al2O3-18.13MgO for series A and 49.98CaO-23.88SiO2-10.11Al2O3-11.99MgO-4.03CaF2 for series B, were used for the study. Both series used DIN 38MnS6 modified steel. The effective viscosity, solid fraction, composition of the liquid fraction, and slag saturation degree in MgO (calculated through thermodynamic software) were related to the experimental results obtained for the inclusion cleanliness. The B slags showed lower effective viscosity than the A slags, due to their high liquid fraction. Regarding the capacity of slags in the inclusion removal, slag B5 resulted in the lowest inclusion density and was considered as the best choice among the slags studied. The inclusion species formed using B slags are constituted especially of CaO-Al2O3-SiO2 and MgO-Al2O3 and are Al2O3 rich. The presence of sulfide-type inclusions (AlMnS and CaS) were more pronounced among A slags.

Assessment of viscosity calculation for calcium-silicate based slags using computational thermodynamics

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.

Free opening performance of steel ladle as a function of filler sand properties

The secondary steel refining process uses filler sand as a thermal insulating barrier that separates the liquid metal from direct contact with slide-gate system of the steel ladle. The effective use of this practice must provide a high free opening rate, impacting on increased productivity and quality of steel, reducing the number of stops, thermal loss and even the steel re-oxidation. Both operational parameters and material properties have influence on the free opening rate. In the present work, two chromite-silica sands were analyzed, and some composition changes were proposed. The properties of these materials and the relevant process parameters were evaluated according to the free opening rate under normal operational conditions. The increases in carbon content and in particle size were considered the main factors relating to the filler sand. The percentage of free opening is also strongly influenced by time and temperature of the steel contact.

Slag Evaluation to Reduce Energy Consumption and EAF Electrical Instability

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.

INFLUÊNCIA DA PROPORÇÃO ENTRE AS VAZÕES DE OXIGÊNIO E GÁS NATURAL DO SISTEMA DE INJEÇÃO DE UM FORNO ELÉTRICO A ARCO NO CONSUMO DE ENERGIA TOTAL

In electric steelmaking, consumption of inputs plays an important role on the final billet cost, with particular emphasis to the energy consumption in the electric arc furnace, which can represent up to 30% of the operational cost in a melt shop. To quantify the contribution of different types of energy in EAF, it is used the performance indicator of total energy consumption, which associates equivalency factors for each type of energy, so that their measurement unit can be transformed to the base unit kWh/t. In this work, a test was conducted on a design of experiments format, varying the flow of natural gas and/or oxygen in a burner mode and in three lance modes, in order to modify their O2/GN ratio and evaluate the impact in total energy consumption.

ESTUDO DA PARTIÇÃO DO FÓSFORO DE ESCÓRIAS DE UM FORNO ELÉTRICO A ARCO ATRAVÉS DA TERMODINÂMICA COMPUTACIONAL

Resumo O fósforo é um elemento crítico para a qualidade dos aços, tornando a redução dos teores desse elemento uma exigência para a indústria siderúrgica. Uma forma de se medir a eficiência da desfosforação é através do coeficiente de partição do fósforo (Lp=%P(escória)/%P(aço)). O objetivo principal deste trabalho é avaliar escórias de um forno elétrico a arco através da comparação entre o Lp real com o Lp calculado por simulação termodinâmica, avaliando, também, o comportamento da partição de fósforo com relação à composição química. A partir de dados de composição química de amostras de escória e aço de uma usina siderúrgica, foram feitas simulações termodinâmicas utilizando o software FactSage. Com base nesses resultados, concluiu-se que o cálculo computacional através do software descreve bem o comportamento termodinâmico, mas tende a superestimar o Lp, provavelmente por questões cinéticas e/ou de transferência de massa e calor. Palavras-chave: Desfosforação; Partição de fósforo; Forno elétrico a arco; Termodinâmica computacional.

ANÁLISE DA SATURAÇÃO DE MgO PARA ESCÓRIAS DO SISTEMA CaO-SiO2-FeO-MgO-Al2O3

Electric arc furnaces (EAF) slags have multiple functions, one of them is the improvement of energy efficiency through the “slag foaming” phenomenon. It is the reason that slag studies are important to EAF’s improvements. One of the main factors that determine the foamy quality and its efficiency is the presence of solid particles, so the MgO saturation is extremely important. Not only to guarantee the presence of solid particles, but also the chemistry compatibility, avoiding the refractory consumption. The present work aims to study the MgO saturation in the CaO-SiO2-FeO-MgO-Al2O3 slag system, evaluating the influence which binary basicity, FeO and Al2O3 content have in the MgO saturation levels. It was carried out ternary diagrams, to see the influence that Al2O3 have in the liquid field and other present phases. Isothermal saturation diagrams (ISD’s) were used to find the same points dual saturations that were found in the ternary diagram. To validate the ISD’s some heats were plotted and them a comparison was made. The heats that were close to the MgO saturation line had a better energy consumption.

Thermodynamic study of non-metallic inclusion formation in SAE 1141 steel

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.

Caracterização e estudo termodinâmico de inclusões do aço SAE 8620 produzido via Aciaria Elétrica

The concept of quality is strongly linked to the steel micro-inclusionary cleanness. The aims of the correct refining practices are: 1) to adequate the non-metallic inclusions amount to acceptable values; and 2) to guarantee that the remaining inclusions will not be detrimental to the mechanical properties of steels. To reach such aims, the present work will evaluate the non-metallic inclusions analysis during steel making via EAF process. The characterization of inclusions consisted in the sampling of steel during the SAE 8620 refining. This steel is used in the production of automotive components industry. The characterization of steel inclusions consisted in analyzing 1) area occupied by inclusions and their size and; 2) chemical composition. The results were analyzed via ternary and pseudo-ternary phase diagrams. Some correlations between inclusion composition and steel making process were also done. The inclusions appear mainly as Si/Mn oxides in the beginning of the ladle furnace processing, and as Ca-Al oxides in the beginning of the continuous casting. The inclusions medium size was determined in the range of 4 to 10Pm. It was also observed a gradual decreasing of the occupied area by inclusions during the process, which is an important aim of the refining practices. A thermodynamic study was carried out were the results of inclusion analysis was compared with FactSage simulations and the results are compatible. The results of this work shown that the application of different techniques becomes possible the study and development of high quality steels. Key words: SAE 8620 steel, characterization, inclusions, FactSage.