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[en] DECARBURIZATION AND SLAG FORMATION MODEL FOR THE ELECTRIC ARC FURNACE / [pt] MODELO DE DESCARBURAÇÃO E FORMAÇÃO DE ESCÓRIAS NA PRODUÇÃO DE AÇO EM ACIARIA ELÉTRICARAIMUNDO AUGUSTO FERRO DE OLIVEIRA FORTES 23 May 2019 (has links)
[pt] Um modelo de descarburação e formação de escórias foi
desenvolvido e aplicado ao processo de fabricação de aço em forno
elétrico a arco de 120 ton de capacidade, com carga de ferro gusa e de
sucata ferrosa. O carregamento de carbono foi significativamente variado
para testar a consistência do modelo, considerando a cinética de
oxidação do carbono, oxidação do fósforo e de redução do óxido de ferro.
Gusa e coque foram empregados como fontes mais relevantes de
carbono, resultando na entrada de 15 a 35 kg carbono/ton. As taxas de
fusão do gusa e da sucata governam a disponibilidade dos elementos
mais relevantes tais como carbono, fósforo e silício em solução, portanto,
afetam as taxas de descarburação e de formação de escórias. A principal
fonte de fósforo na carga ferrosa é o gusa. Desta forma, a evolução do
teor de fósforo na fase metal mostrou-se importante para as estimativas
das taxas de fusão do gusa, uma vez que o fósforo pode ser empregado
como traçador adicional ao carbono. Modelos cinéticos envolvendo as
reações do fósforo e silício operam simultaneamente com os modelos
cinéticos referentes às reações do carbono e do ferro.
Integrações numéricas associadas a um algoritmo de gradientes
reduzidos generalizado foi empregado para o sistema não linear com
restrições, de forma a determinar a maioria dos parâmetros cinéticos do
modelo. A taxa de fusão global da carga de sucata foi maior do que a taxa
de fusão aparente do gusa. Supõe-se que, o gusa apesar de ter relações
geométricas desfavoráveis à transferência de calor em relação à sucata,
poderia fundir mais rapidamente influenciado pelo seu baixo ponto de
fusão. Entretanto, devido à formação de camada solidificada a partir da
massa líquida na qual é imerso, é provável que mesmo fundido
posteriormente, ocorra um processo de encapsulamento temporário,
conferindo-lhe uma taxa aparente de fusão mais baixa. A constante
cinética da reação de descarburação quando o teor de carbono é inferior
ao carbono crítico de 0.19 por cento em massa e pelo menos 60 por cento da carga
ferrosa estão fundidas, foi estimada em 0.74 min-1, taxas comparáveis às
obtidas em aciaria a oxigênio.
A principal fonte de oxigênio para oxidação do ferro é
disponibilizada por lanças supersônicas. Estima-se que 20 por cento do oxigênio
injetado via lanças sejam consumidos para a formação de óxido de ferro.
Entretanto, cerca de 31 por cento e 26 por cento do oxigênio oriundo de injetores de póscombustão
podem contribuir na formação de óxido de ferro ou são
captados pelo sistema de exaustão de gases, respectivamente. Os
resultados indicam que em torno de 15-30 por cento do carbono injetado podem
não reagir no forno, sendo removidos com a escória. Adicionalmente ao
estado de não-equilíbrio no sistema Fe-C-O observado, a dispersão nas
estimativas de carbono solúvel na fase metal também pode ter sido
influenciada pela intensidade de penetração da injeção de coque.
O algoritmo proposto se constitui num promissor simulador de
práticas que visam otimizar o rendimento metálico do ferro, a partir da
dependência da cinética de redução do óxido de ferro com sua atividade
química na escória. / [en] A decarburization and slag formation model was developed and
applied to a steelmaking process based on scrap and pig iron mixes
melted in a conventional AC electric arc furnace (EAF) with 120 ton
capacity. The amount of carbon input was varied significantly in order to
evaluate the model consistency regarding mainly the kinetics of carbon
oxidation, phosphorus oxidation and iron oxide formation and reduction.
Pig iron and coke were used as sources of carbon, resulting in variation of
total carbon input in the range of 15 to 35 kg carbon/ton. The pig iron and
scrap melting rates determine the availability of the most relevant
elements such as carbon, phosphorus and silicon in solution in Fe-C
melts, and therefore, affecting the decarburization as well the slag
formation rates. The pig iron is the main source of phosphorus in the
ferrous charge. Hence, the evolution of the phosphorus content in the
metal phase is important to predict the pig iron melting rate, since
phosphorus can be used as a tracer element in addition to carbon. Kinetic
models regarding phosphorus and silicon were applied simultaneously to
kinetic models of carbon and iron reactions.
A numerical integration method supported a generalized reduced
gradient algorithm for non-linear and constrained system (GRG) was
applied to determine most of the kinetic model parameters. The scrap
melting rates were found to be higher than pig iron apparent melting rates.
This is expected that, even though the heat transfer issues related to
significant differences in the area to volume ratio compared to scrap, pig
iron may melt faster influenced by its low melting point. However, a
solidified shell maybe created from the hot heel where pig iron is
immersed, even when further melting occur, Fe-rich carbon melts could be
encapsulated temporarily and present lower apparent melting rate. The
decarburization rate parameter, when at least 60 percent of the charge is
melted, was estimated as 0.74 min-1, when carbon content is lower than
the critical carbon 0.19 percent wt, which is similar to the rate range observed in
oxygen steelmaking facilities. Around 31 percent and 26 percent of the oxygen input
through post combustion injectors were addressed to iron oxidation and to
the off-gas system, respectively.
The main source of oxygen taking part of iron oxidation is available
from supersonic lances. Approximately 20 percent of the oxygen input through
lancing are consumed to form iron oxide. The results also indicate about
15-30 percent of the injected carbon may not react and leave EAF during slagoff.
In addition to the observed non-equilibrium state in Fe-C-O system,
the dispersive behavior of the prediction of soluble carbon content in the
metal phase could also be influenced by the intensity of penetration coke.
The model framework is a promising tool to work preliminarily in
what-if process scenario builder as a static model for iron yield
optimization, regarding the kinetics of iron oxide reduction reaction and the
proposed dependence on its chemical activity in the slag phase.
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An Experimental Study of Submerged Entry Nozzles (SEN) Focusing on Decarburization and CloggingMemarpour, Arashk January 2011 (has links)
The submerged entry nozzle (SEN) is used to transport the molten steel from a tundish to a mould. The main purpose of its usage is to prevent oxygen and nitrogen pick-up by molten steel from the gas. Furthermore, to achieve the desired flow conditions in the mould. Therefore, the SEN can be considered as a vital factor for a stable casting process and the steel quality. In addition, the steelmaking processes occur at high temperatures around 1873 K, so the interaction between the refractory materials of the SEN and molten steel is unavoidable. Therefore, the knowledge of the SEN behaviors during preheating and casting processes is necessary for the design of the steelmaking processes The internal surfaces of modern SENs are coated with a glass/silicon powder layer to prevent the SEN graphite oxidation during preheating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied. A large number of accretion samples formed inside alumina-graphite clogged SENs were examined using FEG-SEM-EDS and Feature analysis. The internal coated SENs were used for continuous casting of stainless steel grades alloyed with Rare Earth Metals (REM). The post-mortem study results clearly revealed the formation of a multi-layer accretion. A harmful effect of the SENs decarburization on the accretion thickness was also indicated. In addition, the results indicated a penetration of the formed alkaline-rich glaze into the alumina-graphite base refractory. More specifically, the alkaline-rich glaze reacts with graphite to form a carbon monoxide gas. Thereafter, dissociation of CO at the interface between SEN and molten metal takes place. This leads to reoxidation of dissolved alloying elements such as REM (Rare Earth Metal). This reoxidation forms the “In Situ” REM oxides at the interface between the SEN and the REM alloyed molten steel. Also, the interaction of the penetrated glaze with alumina in the SEN base refractory materials leads to the formation of a high-viscous alumina-rich glaze during the SEN preheating process. This, in turn, creates a very uneven surface at the SEN internal surface. Furthermore, these uneven areas react with dissolved REM in molten steel to form REM aluminates, REM silicates and REM alumina-silicates. The formation of the large “in-situ” REM oxides and the reaction of the REM alloying elements with the previously mentioned SEN´s uneven areas may provide a large REM-rich surface in contact with the primary inclusions in molten steel. This may facilitate the attraction and agglomeration of the primary REM oxide inclusions on the SEN internal surface and thereafter the clogging. The study revealed the disadvantages of the glass/silicon powder coating applications and the SEN decarburization. The decarburization behaviors of Al2O3-C, ZrO2-C and MgO-C refractory materials from a commercial Submerged Entry Nozzle (SEN), were also investigated for different gas atmospheres consisting of CO2, O2 and Ar. The gas ratio values were kept the same as it is in a propane combustion flue gas at different Air-Fuel-Ratio (AFR) values for both Air-Fuel and Oxygen-Fuel combustion systems. Laboratory experiments were carried out under nonisothermal conditions followed by isothermal heating. The decarburization ratio (α) values of all three refractory types were determined by measuring the real time weight losses of the samples. The results showed the higher decarburization ratio (α) values increasing for MgO-C refractory when changing the Air-Fuel combustion to Oxygen-Fuel combustion at the same AFR value. It substantiates the SEN preheating advantage at higher temperatures for shorter holding times compared to heating at lower temperatures during longer holding times for Al2O3-C samples. Diffusion models were proposed for estimation of the decarburization rate of an Al2O3-C refractory in the SEN. Two different methods were studied to prevent the SEN decarburization during preheating: The effect of an ZrSi2 antioxidant and the coexistence of an antioxidant additive and a (4B2O3 ·BaO) glass powder on carbon oxidation for non-isothermal and isothermal heating conditions in a controlled atmosphere. The coexistence of 8 wt% ZrSi2 and 15 wt% (4B2O3 ·BaO) glass powder of the total alumina-graphite refractory base materials, presented the most effective resistance to carbon oxidation. The 121% volume expansion due to the Zircon formation during heating and filling up the open pores by a (4B2O3 ·BaO) glaze during the green body sintering led to an excellent carbon oxidation resistance. The effects of the plasma spray-PVD coating of the Yttria Stabilized Zirconia (YSZ) powder on the carbon oxidation of the Al2O3-C coated samples were investigated. Trials were performed at non-isothermal heating conditions in a controlled atmosphere. Also, the applied temperature profile for the laboratory trials were defined based on the industrial preheating trials. The controlled atmospheres consisted of CO2, O2 and Ar. The thicknesses of the decarburized layers were measured and examined using light optic microscopy, FEG-SEM and EDS. A 250-290 μm YSZ coating is suggested to be an appropriate coating, as it provides both an even surface as well as prevention of the decarburization even during heating in air. In addition, the interactions between the YSZ coated alumina-graphite refractory base materials in contact with a cerium alloyed molten stainless steel were surveyed. The YSZ coating provided a total prevention of the alumina reduction by cerium. Therefore, the prevention of the first clogging product formed on the surface of the SEN refractory base materials. Therefore, the YSZ plasma-PVD coating can be recommended for coating of the hot surface of the commercial SENs. / <p>QC 20111014</p>
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An Experimental Study of Submerged Entry Nozzles (SEN) Focusing on Decarburization and CloggingMemarpour, Arashk January 2011 (has links)
The submerged entry nozzle (SEN) is used to transport the molten steel from a tundish to a mould. The main purpose of its usage is to prevent oxygen and nitrogen pick-up by molten steel from the gas. Furthermore, to achieve the desired flow conditions in the mould. Therefore, the SEN can be considered as a vital factor for a stable casting process and the steel quality. In addition, the steelmaking processes occur at high temperatures around 1873 K, so the interaction between the refractory materials of the SEN and molten steel is unavoidable. Therefore, the knowledge of the SEN behaviors during preheating and casting processes is necessary for the design of the steelmaking processes The internal surfaces of modern SENs are coated with a glass/silicon powder layer to prevent the SEN graphite oxidation during preheating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied. A large number of accretion samples formed inside alumina-graphite clogged SENs were examined using FEG-SEM-EDS and Feature analysis. The internal coated SENs were used for continuous casting of stainless steel grades alloyed with Rare Earth Metals (REM). The post-mortem study results clearly revealed the formation of a multi-layer accretion. A harmful effect of the SENs decarburization on the accretion thickness was also indicated. In addition, the results indicated a penetration of the formed alkaline-rich glaze into the alumina-graphite base refractory. More specifically, the alkaline-rich glaze reacts with graphite to form a carbon monoxide gas. Thereafter, dissociation of CO at the interface between SEN and molten metal takes place. This leads to reoxidation of dissolved alloying elements such as REM (Rare Earth Metal). This reoxidation forms the “In Situ” REM oxides at the interface between the SEN and the REM alloyed molten steel. Also, the interaction of the penetrated glaze with alumina in the SEN base refractory materials leads to the formation of a high-viscous alumina-rich glaze during the SEN preheating process. This, in turn, creates a very uneven surface at the SEN internal surface. Furthermore, these uneven areas react with dissolved REM in molten steel to form REM aluminates, REM silicates and REM alumina-silicates. The formation of the large “in-situ” REM oxides and the reaction of the REM alloying elements with the previously mentioned SEN´s uneven areas may provide a large REM-rich surface in contact with the primary inclusions in molten steel. This may facilitate the attraction and agglomeration of the primary REM oxide inclusions on the SEN internal surface and thereafter the clogging. The study revealed the disadvantages of the glass/silicon powder coating applications and the SEN decarburization. The decarburization behaviors of Al2O3-C, ZrO2-C and MgO-C refractory materials from a commercial Submerged Entry Nozzle (SEN), were also investigated for different gas atmospheres consisting of CO2, O2 and Ar. The gas ratio values were kept the same as it is in a propane combustion flue gas at different Air-Fuel-Ratio (AFR) values for both Air-Fuel and Oxygen-Fuel combustion systems. Laboratory experiments were carried out under nonisothermal conditions followed by isothermal heating. The decarburization ratio (α) values of all three refractory types were determined by measuring the real time weight losses of the samples. The results showed the higher decarburization ratio (α) values increasing for MgO-C refractory when changing the Air-Fuel combustion to Oxygen-Fuel combustion at the same AFR value. It substantiates the SEN preheating advantage at higher temperatures for shorter holding times compared to heating at lower temperatures during longer holding times for Al2O3-C samples. Diffusion models were proposed for estimation of the decarburization rate of an Al2O3-C refractory in the SEN. Two different methods were studied to prevent the SEN decarburization during preheating: The effect of an ZrSi2 antioxidant and the coexistence of an antioxidant additive and a (4B2O3 ·BaO) glass powder on carbon oxidation for non-isothermal and isothermal heating conditions in a controlled atmosphere. The coexistence of 8 wt% ZrSi2 and 15 wt% (4B2O3 ·BaO) glass powder of the total alumina-graphite refractory base materials, presented the most effective resistance to carbon oxidation. The 121% volume expansion due to the Zircon formation during heating and filling up the open pores by a (4B2O3 ·BaO) glaze during the green body sintering led to an excellent carbon oxidation resistance. The effects of the plasma spray-PVD coating of the Yttria Stabilized Zirconia (YSZ) powder on the carbon oxidation of the Al2O3-C coated samples were investigated. Trials were performed at non-isothermal heating conditions in a controlled atmosphere. Also, the applied temperature profile for the laboratory trials were defined based on the industrial preheating trials. The controlled atmospheres consisted of CO2, O2 and Ar. The thicknesses of the decarburized layers were measured and examined using light optic microscopy, FEG-SEM and EDS. A 250-290 μm YSZ coating is suggested to be an appropriate coating, as it provides both an even surface as well as prevention of the decarburization even during heating in air. In addition, the interactions between the YSZ coated alumina-graphite refractory base materials in contact with a cerium alloyed molten stainless steel were surveyed. The YSZ coating provided a total prevention of the alumina reduction by cerium. Therefore, the prevention of the first clogging product formed on the surface of the SEN refractory base materials. Therefore, the YSZ plasma-PVD coating can be recommended for coating of the hot surface of the commercial SENs.
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An Experimental Study to Improve the Casting Performance of Steel Grades Sensitive for CloggingSvensson, Jennie January 2017 (has links)
In this study, the goal is to optimize the process and to reduce the clogging tendency during the continuous casting process. The focus is on clogging when the refractory base material (RBM) in the SEN is in contact with the liquid steel. It is difficult or impossible to avoid non-metallic inclusions in the liquid steel, but by a selection of a good RBM in the SEN clogging can be reduced. Different process steps were evaluated during the casting process in order to reduce the clogging tendency. First, the preheating of the SEN was studied. The results showed that the SEN can be decarburized during the preheating process. In addition, decarburization of SEN causes a larger risk for clogging. Two types of plasma coatings were implemented to protect the RBM, to prevent reactions with the RBM, and to reduce the clogging tendency. Calcium titanate (CaTiO3) mixed with yttria stabilized zirconia (YSZ) plasma coatings were tested in laboratory and pilot plant trials, for casting of aluminium-killed low-carbon steels. For casting of cerium alloyed stainless steels, YSZ plasma coatings were tested in laboratory, pilot plant and industrial trials. The results showed that the clogging tendency was reduced when implementing both coating materials. It is also of importance to produce clean steel in order to reduce clogging. Therefore, the steel cleanliness in the tundish was studied experimentally. The result showed that inclusions originated from the slag, deoxidation products and tundish refractory and that they were present in the tundish as well as in the final steel product. / VINNOVA
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Výroba dvoufázových austeniticko-feritických korozivzdorných ocelí s využitím vakuové metalurgie / Manufacture of two-phase austenitic-ferritic stainless steels with the use of vacuum metallurgyTučková, Eva January 2018 (has links)
stainless steel, duplex steel, vakuum metallurgy, decarburization
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