O objetivo deste trabalho consiste no desenvolvimento e aplicação de um software de simulação para o processo de lingotamento contínuo que seja capaz de simular com precisão e confiabilidade a solidificação de tarugos de aço, possibilitando a otimização do processo de fabricação dos produtos siderúrgicos. Para a validação do software, utilizou-se de resultados obtidos experimentalmente de medições de temperaturas em planta e de amostras de aços lingotados. As medidas de temperatura foram realizadas com a inserção de termopares ao longo da parede de moldes e com uso de pirômetro óptico posicionado em diferentes regiões da máquina de LC. O modelo desenvolvido mostrou-se bastante coerente e preciso quando seus resultados foram comparados com os dados experimentais do processo. Foram analisados lingotes de seção quadrada de 240 mm, 180 mm e 150 mm. Com a simulação de uma seqüência de corridas monitoradas foi possível obter resultados para ajuste de parâmetros térmicos como os coeficientes de transferência de calor nas interfaces metal/molde e metal/ambiente. Posteriormente, aferições foram realizadas com dados reais de processo e com outros programas numéricos da literatura aplicados ao processo de LC. Com o programa de simulação devidamente aferido, correlações numéricas e experimentais foram realizadas para verificar a influência de parâmetros térmicos (ρ, c, k, TL, TS), parâmetros de processo (TV, VL, CQ) e parâmetros estruturais (λ1, λ2, TCE) na evolução da casca solidificada e perfil térmico dos tarugos. Dessa forma, equações empíricas que correlacionam esses parâmetros foram analisadas e posteriormente adotadas no programa numérico. / The development and application of simulation software for the continuous casting process is proposed in this work. The heat transfer and solidification models were validated with experimental results of temperature measurements in an industrial plant as well as with steel billets samples. Thermocouples embedded in the mold walls were used to measure temperatures along the mold length and non-contact pyrometers positioned at different locations along the machine were used to monitored the strand surface temperatures. The model seemed to predict quite accurately the continuous casting simulation when calculated results were compared with experimental measurements. In this study, steel billet with square section of 240 mm, 180 mm and 150 mm were analyzed. Some of the monitored heats were used to adjust thermal parameters as the heat transfer coefficients. After, the model results were compared with results from a heat transfer model of literature. With the simulation software properly calibrated, numerical and experimental correlations were performed to analyze the influence of thermal parameters (ρ, c, k, TL, TS), process parameters (TV, VL, CQ) and structural parameters (λ1, λ2, TCE) in the evolution of solidified shell and thermal profile of the billets. Therefore, empirical equations that correlate these parameters were analyzed and subsequently adopted in the numerical model.

A aplicação de modelos matemáticos baseados em técnicas numéricas aumentou com o avanço da informática através da criação de microprocessadores mais velozes e periféricos de armazenamento de dados com grande capacidade. Buscando uma maior produtividade e a melhoria da qualidade final do produto solidificado, propõe-se neste trabalho, desenvolver um modelo computacional de origem físico para o crescimento de grão no Lingotamento Contínuo. O modelo é simulado utilizando o Método de Monte Carlo juntamente com o Método das Diferenças Finitas, com o objetivo de obter e caracterizar a transição colunar-equiaxial através desse método. As simulações foram realizadas utilizando a programação Fortran 90/95 no ambiente Linux através do software Developer Studio e aplicados nos aços SAE 1015 e 1020. A seguir, foram realizadas comparações entre as macroestruturas simuladas e as macroestruturas das amostras dos aços obtidas pelo Laboratório de Fundição (LAFUN) da UFRGS. Destas simulações observou-se que o modelo oferece a possibilidade da simulação de diferentes condições operacionais para prever a evolução macroestrutural de lingotes. / The application of mathematical models based on numerical techniques increased with the advancement of information technology by creating faster microprocessors and peripherals with high data storage capacity. Seeking for a major productivity and the improvement of the final quality of the solidified product. In this assignment, the development of a computational model with a physical origen for the growth of the continuous casting, is proposed. The model is simulated by using the Monte Carlo Method with the Finite Differences Method, the goal is to obtain and characterize the columnar-equiaxed transition through this method. The simulations were performed using the Fortran 90/95 programming in Linux environment using the Developer Studio software and applied to the steel SAE 1015 and 1020. Following it, comparisons were made between the macro and simulated macrostructures of the samples obtained by the Laboratory of Steel Casting - Laboratório de Fundição (LAFUN) at UFRGS. From these simulations, it was observed that the modified model offers the possibility of simulating different operating conditions to predict the evolution of macrostructural ingots.

O presente estudo teve como objetivo a obtenção de equações empíricas permitindo a correlação da morfologia estrutural de aços com os parâmetros de solidificação: variação dos espaçamentos dendríticos secundários com a posição (l2xP) e variação dos espaçamentos dendríticos secundários com as taxas de resfriamento (l2x •T), como também o desenvolvimento de uma metodologia para determinação do início de transição colunarequiaxial e sua relação com a seção e composição química do aço. Para isso foram utilizadas técnicas de metalografia e um sistema de aquisição de imagens para a análise de macro e microestrutura (transição colunar-equiaxial, espaçamentos dendríticos secundários), de aços especiais obtidos por lingotamento contínuo. Foram selecionadas amostras retiradas de lingotes com três diferentes seções: 150x150mm, 180x180mm e 240x240 mm, englobando aços com diferentes valores de carbono equivalente, totalizando nove qualidades analisadas. Simulações foram geradas empregando um software do lingotamento contínuo (InALC), obtendo-se resultados das condições de solidificação em relação a taxas de resfriamento ( •T), para os parâmetros operacionais (composição química, velocidades e temperaturas de lingotamento). As equações dos parâmetros microestruturais obtidas experimentalmente foram implementadas no software InALC+, permitindo simulações também com previsão estrutural para os aços analisados. Pode-se concluir que o aumento da seção proporcionou maiores zonas colunares, independente da composição química dos aços, e que para um teor de carbono equivalente de 0,11%Ceq observou-se uma relação direta e linear entre os valores de início de TCE, tamanho da seção e taxa de resfriamento. As equações para EDS em função da distância para aços com valores de Ceq iguais apresentaram maiores valores na seção de 240 mm e 180 mm, seguidos pela seção de 150 mm. Nas equações de EDS em função da taxa de resfriamento simulada para aços com valores de Ceq iguais a 0,11%Ceq, os maiores valores de EDS ocorrem na seção 150mm, seguido pela seção 240mm e 180mm. Na comparação dos aços com valores de carbono equivalente em torno de 0,40%Ceq, o valor de EDS apresentou um aumento em função do aumento das seções. Em comparação a aços de mesma seção, as equações apresentaram um aumento do valor de EDS em função do aumento do Ceq. / The objective of this study was to obtain empirical equations permitting the relationships between as-cast structural morphology and solidification conditions: variation of the secondary dendrite arm spacings with positions (l2xP), variation of the secondary dendrite arm spacings with cooling rates (l2x • T ), as well as to develop a methodology to determine the start of the colunar-equiaxed transition and its correlation with mold section and chemical composition of the steel. Metallographic techniques and image acquisition system were used to analyze both macrostructures and microstructures (colunar-equiaxed transition and secondary dendrite arm spacings) of special steels produced by continuous casting. Transversal specimens were cut from the solidified ingots with different sections: 150x150mm, 180x180mm e 240x240mm, and with different equivalent carbon, totalizing nine steel types. Based on a heat transfer and solidification mathematical model of the continuous casting process (InALC+), results have been developed correlating the cooling rates as a function of operational parameters (chemical composition, casting speed and casting temperature). The correlation of these expressions with experimental equations relating dendrite spacings and colunar-equiaxed transition were implemented into the InALC+ software, providing an insight into the preview of structural characteristics for special steels. It can be concluded that the increasing of the section lead to bigger columnar zones, independent of the chemical compositions of the steels, and for 0.11%Ceq it was observed a direct and linear relation between the initial of the columnar-equiaxed transition, strand section and cooling rate. The expressions for SDAS in function of the distance for steels with equals Ceq presented bigger values for 240 and 180 mm, followed by 150 mm. In the expressions for SDAS in function of the simulated cooling rate for steels with 0.11%Ceq the bigger values were observed to 150 mm followed by 240 and 180 mm. In the comparison between the steels with 0.40% Ceq the SDAS values presented an increase in function of the increase of the section. For the same section the expression presented an increase in the SDAS value in function of the increase of the Ceq.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-09-27T11:59:15Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) DISSERT_Francisco_Diego_Araruna_da_Silva.pdf: 17898343 bytes, checksum: abfd80794cd6d40a804ad123aa5fb4e4 (MD5) / Made available in DSpace on 2016-09-27T11:59:15Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) DISSERT_Francisco_Diego_Araruna_da_Silva.pdf: 17898343 bytes, checksum: abfd80794cd6d40a804ad123aa5fb4e4 (MD5) Previous issue date: 2016-05-24 / O processo de lingotamento contínuo tem sido empregado em larga escala na indústria do aço no mundo inteiro. A necessidade de elevados patamares de competitividade na indústria do aço tem levado à utilização cada vez mais frequente, por parte daqueles que utilizam lingotamento contínuo, de ferramentas de modelagem matemática da solidificação. A literatura possui diversas referências acerca da construção de modelos matemáticos da transferência de calor no lingotamento contínuo. Entretanto, ainda existem poucos trabalhos mostrando a utilização desses modelos na resolução de problemas metalúrgicos reais, como os de qualidade e estabilidade do processo. Dessa forma, o presente trabalho tem como objetivo empregar um modelo matemático de transferência de calor para propor melhorias em uma máquina de lingotamento contínuo utilizada na fabricação de tarugos de aço. Para a validação do modelo, foi realizado um comparativo de simulações com seis diferentes equações do coeficiente de transferência de calor (hg) disponíveis na literatura – três para o molde e três para a zona de sprays – com os dados reais da máquina. Foi desenvolvida ainda uma ferramenta de otimização da refrigeração secundária (com base no método de Nelder-Mead) que minimiza uma função custo integral construída especificamente para o processo de lingotamento contínuo. Os resultados das simulações com as nove combinações de equações de coeficientes de transferência de calor foram comparadas com dados reais de processo. Esse comparativo contemplou dados de pirometria na saída do molde, zona de sprays e zona de radiação livre, bem como avaliações com base em quatro critérios metalúrgicos de qualidade e processo, no qual foram utilizadas também macrografias de amostras de tarugos. A ferramenta de otimização se mostrou bastante eficiente na definição de parâmetros ótimos da refrigeração secundária, resultando em perfis de temperatura da superfície com baixos níveis de reaquecimento. As análises realizadas com o modelo de transferência de calor mostraram que a inclusão de mais uma zona de sprays (usando vazões por zona definidas pela ferramenta de otimização) e o incremento da seção quadrada para 130x130mm, reduzem a probabilidade de ocorrer trincas por reaquecimento e aumenta a probabilidade da formação uma estrutura equiaxial no centro do tarugo, respectivamente. / The process of continuous casting has been employed on a large scale in the steel industry worldwide. The need for high levels of competitiveness in the steel industry has led to an increasingly use of modeling tools, including those of the continuous casting solidification process. The literature has many references about the construction of mathematical models of heat transfer in continuous casting. However, there are still few studies showing the use of these models to solve real metallurgical problems such as the product quality and process stability ones. The aim of the present work is to employ a heat transfer mathematical model to propose improvements in a continuous casting machine used in the production of steel billets. To validate the model, it was performed a comparative study of between simulations using six different equations for the heat transfer coefficient (hg) available in the literature - three for the mold and three for spray cooling - and the actual data from the machine. It was also developed an optimization tool for the secondary cooling zone (based on the Nelder-Mead method) which minimizes an integral cost function constructed specifically for the continuous casting process. Simulation results using all heat transfer equations combination were compared to real process data. This comparison included temperature data at all three zones (mold exit, spray cooling and radiation), as well as evaluations based on four metallurgical quality and process criteria, using billet macrographs. The optimization tool was very efficient in determining optimum parameters of secondary cooling, resulting in surface temperature profiles with low reheating levels. The analysis performed using the heat transfer model shown that the addition of one more sprays zone (using water flows by zone defined by the optimization tool) and the increase of square section to 130x130mm, reduce the likelihood of reheating midway cracks occurrence and increases the likelihood of forming an equiaxial structure at the center of the billet, respectively.

O fluxante é uma escória sintética que influencia na qualidade superficial do aço e na estabilidade do processo de lingotamento contínuo. Este produto é aplicado diretamente sobre o aço líquido na região do molde de cobre refrigerado a água e atua diretamente no resfriamento primário do aço. O fluxante tem as propriedades físico-químicas adaptadas para cada tipo de aço e também para as condições de lingotamento. Na superfície do aço líquido, o fluxante funde e forma uma poça líquida, atuando como isolante térmico, protegendo o aço da reoxidação e absorvendo inclusões principalmente de Al2O3. A poça líquida escoa, lubrificando e controlando a transferência de calor na interface entre o molde e a pele de aço em solidificação. O problema de qualidade superficial do aço, quando relacionado ao fluxante, se resume a alarmes de colamento, trincas de quina, marcas de oscilação profundas e trincas longitudinais, sendo este último um problema particular do aço médio carbono. Neste trabalho, foram analisados diferentes fluxantes baseados inicialmente no fluxante comercial aplicado no lingotamento contínuo de placas de aço médio carbono. Todos os fluxantes foram desenvolvidos com composições químicas similares. O objetivo foi avaliar o impacto da substituição de fontes de matérias-primas em diferentes composições de modo a avaliar as propriedades físico-químicas com base no fluxante comercial de referência. Como resultado, de todas as propriedades físico-químicas, foi a temperatura de cristalização que sofreu a alteração mais significativa. / The mould flux is a synthetic slag which influences the quality of steel surface and also the stability of the continuous casting process. This product is applied in direct contact with the surface of liquid steel in the region of the water cooled cupper mold and acts directly on the primary cooling of steel. The mould flux has the physical and chemical properties adapted for each type of steel as weel as casting conditions. On the surface of liquid steel, the mould flux melts and forms the liquid pool, working as an insulator, protecting the steel against reoxidation and also absorbing mainly Al2O3 inclusions. The liquid pool flows, lubricating and controlling the heat transfer in the interface between the mold and the steel shell during solidification. The surface quality issues when related with mould flux can cause alarms of breakout, corner cracks, deep oscillation marks, longitudinal cracks that is a particular problem in medium carbon steel grade. In this study, different mould fluxes were investigated and compared to a commercial mould flux applied to the continuous casting of slabs in the medium carbon steel grade. All mould fluxes were developed with a similar chemical composition. The main goal was to evaluate the impact of changing raw material sources on the physicochemical properties of the different mould fluxes and the results was compared with a commercial standard mould flux. As result, variations in the crystallization temperatures were observed more than others properties analyzed.

In this thesis an equation of heat conduction including phase and structural changes is derived, involving various boundary conditions. It seems to be the most suitable to calculate the equation by enthalpy method. In this equation not only enthalpy occurs, but also the temperature, and in consequence the relationship between these variables is quite complicated. In this paper I use the values measured or calculated using solidifcation models. The calculation is implemented in Matlab Simulink, which is a very popular blocks scheme in common practice of regulation. The calculation is based on steady state set up with help of experts and as a result, the program could be put into practice. The program calculates the intensity of cooling according to the initial casting speed, casting inlet temperature and the desired temperature curves. The rate of inuence of cooling can be changed according to the given criteria. The thesis compares the surface temperatures and cooling in the case of a predictive controller is or is not applied in the program.

Due to the high efficiency and productivity of continuous casting process, this method has been the most employed process to produce steel in past decades. The need to improve and optimize the finished product made it essential to gain more knowledge about the process, types of defects that may occur and the reasons for them. Moreover, the solutions for reducing the shortcomings in continuous casting process have been an intriguing subject to study. Many attempts have been done in order to reach this goal. Understanding, determining and optimizing the mould flux slag properties is especially important, since it plays an important and significant role in this process. For this, it is of outmost importance to acquire more knowledge about different properties of mould flux powders. Hence, there has been a world wide effort to measure and model the properties of mould flux properties, such as liquidus and solidus temperatures, heat capacity, enthalpy, thermal expansion, density, viscosity, electrical conductivity, surface tension and thermal conductivity. This thesis presents a brief review on continuous casting process, mould flux powder and its properties and characteristics. Furthermore, it focuses on the thermo-physical properties of mould fluxes. In present work, different industrial mould flux powders have been analyzed to measure their viscosity, break temperature, physical properties such as density, flowablity of powder, slag structure and chemical composition. The experimental data have been compared to some of the most commonly used models such as Riboud model, Urbain model, Iida model and KTH model.

Mould powders are synthetic slags that contain mixtures of silica (SiO2), lime (CaO), sodium oxide (Na2O), fluorspar (CaF2), and carbon (C). When heated to elevated temperatures these powders liquefy and float on the liquid steel in the mould. Mould oscillation helps the liquid flux to penetrate the tiny gap between the mould and the newly formed solid steel shell. In this position the liquid flux partially solidifies against the water cooled mould, while a small portion of the flux remains liquid next to the steel shell to provide lubrication between the moving parts. Effective horizontal heat transfer in the mould is critical for solidifying the liquid steel inthe mould. This process is largely influenced by the thickness and the nature of the flux layer that infiltrates the mould/shell gap. When casting titanium stabilised stainless steels the alloying element reacts with the molten flux, ultimately changing the behaviour of the flux. During the casting process, titanium from the liquid steel reacts with the molten flux producing solids at high temperatures known as perovskite (CaTiO3). Research has shown that perovskite reduces the lubrication capabilities of casting fluxes leading to detrimental effects on product quality while posing a serious threat of machine damage (breakout). The focus of this study is to investigate the effect of titanium pickup on the solidification nature of mould flux and the consequences on horizontal heat transfer. To achieve this, an experimental setup was constructed to simulate the behaviour of mould flux during continuous casting. Analyses of the test flux indicated that the liquid flux closest to the cold side (mould) instantly froze to produce a glassy solid structure. Closer to the hot side (steel shell), solid particles such as perovskite, cuspidine (Ca4Si2O7F2), olivine (Ca,Mg,Mn)2SiO4 and nepheline (Na2O.Al2O3.(SiO2)2) could be identified. Similar solid particles were also found in a slag rim sample taken during the industrial casting of 321- titanium stabilised stainless steel using SPH-KA1 mould powder. Further investigations of the crystalline flux layers showed the entrapment of many tiny gas bubbles during solidification. This porous structure acted as a thermal heat barrier limiting horizontal heat transfer. Experimental testing on 3.0 and 6.0mm flux thickness revealed that the overall thermal conductivity of mould flux decreased as the flux porosity increased. Larger amounts of gas entrapment (in the solid flux structure) resulted in higher thermal resistances which ultimately reduced the heat transfer capabilities of the flux. A second heat barrier, which has a far more dominating effect on the overall heat transfer, is created on mould surface during flux solidification. This thermal contact resistance is also found to be the result of entrapped gas bubbles. Experimental results concluded that the effect of titanium pickup on heat transfer is primarily overshadowed by the larger effect of the thermal contact resistance that is formed during mould flux solidification. The contact resistance in combination with gas entrapment in the solid crystalline structure is considered to be the key factors preventing horizontal heat transfer during continuous casting. / Dissertation (MEng (Metallurgical Engineering))--University of Pretoria, 2006. / Materials Science and Metallurgical Engineering / MEng / unrestricted

Scania has experienced difficulties with large variations of the slope of the back plane after press quenching of case hardened crown wheels of especially type R780 Steg supplied from ingot cast material. This leads to that a large number of crown wheels has to be remeasured and sorted according to back slope which is time consuming for operators. Also, after sorting of the crown wheels, hard machining has to be adjusted according to the different slopes of the back plane of the crown wheels. In some cases, it also leads to scrapping of the crown wheels.This master’s thesis was divided in two parts. The aim of the first part was to confirm that the crown wheel type and casting technique that exhibits the largest variations in slope of the back plane is the R780 Steg originating from ingot cast material. The crown wheel types that were compared were the R780 Steg, R780 Slät and R885 Slät. Crown wheels manufactured from ingot cast material and from continuous cast material were compared. Hence, 6 combinations were examined. The slope of the back plane was measured with the measuring probe FARO after press quenching. The slope of the crown wheels was found to depend on both casting technique and the geometry of the crown wheel. The results confirmed that the crown wheel type and supplier combination that by far yields the largest variations in slope of the back plane is the R780 Steg supplied by Steel Plant A who uses the ingot casting technique. For this combination the variation exceeds 0,1 mm. All other combinations of crown wheels and suppliers yield acceptable variations.The second part of this master’s thesis was composed of determining if segregations in the cast ingot are the cause of the variations in slope of the back plane of the crown wheel type R780 Steg. This was done by measuring if there is a correlation between the slope of the back plane of the crown wheel after press quenching, the chemical composition and the original position of the crown wheel in the ingot. As in the first part of the study, the distortion was measured by the measuring probe FARO. The samples were sent to Degerfors Laboratorium for chemical analysis. Analyses of C, S and N were made by using combustion analyses. For As, P, B and Al optic spectrometry (spark) was used. All other elements were analysed by x-ray fluorescence. Segregations were found to be present and in combination with the geometry of R780 Steg to be the cause of the large variations in slope of the crown wheels.The results of this thesis show that, for the crown wheel type R780 Steg, Scania should not use suppliers that employ the ingot casting technique. Instead, only suppliers using the continuous casting technique should be used. However, for the other crown wheel types ingot or continuously cast material can be used.

<p>Continuous casting is a vital process in the production of semi-finished steel, converting molten metal into solid form. Primary cooling, a critical stage of this process, uses water to cool the solidifying shell as it descends through the mold. The quality of the final cast product is significantly influenced by the fluid flow characteristics during this phase. Given the inherent complexities and costs associated with experimental studies in this area, numerical modeling has emerged as a crucial tool for understanding, predicting, and optimizing fluid flow dynamics within the mold. This research focuses on the implications of argon injection within the mold during the primary cooling stage of the continuous casting process.</p><p>In this thesis, a comprehensive computational investigation of the transportation, entrapment, and fluid dynamic effects of argon injection is presented. Through an exploration of bubble sizes, SEN submergence depths, and slide gate openings, the study reveals how these parameters can significantly influence the casting process.</p><p>The research finds that argon bubble size plays a critical role in determining bubble trajectories and residence times, with smaller bubbles showing a longer residence time and increased boundary interaction due to the dominance of drag forces. The submergence depth of the submerged entry nozzle (SEN) also influences these factors, with deeper submergence resulting in longer bubble trajectories and greater residence times. The study highlights how bubble diameter impacts their entrapment probability, with bubbles ranging from 0.3mm to 0.6mm being most prone to entrapment.</p><p>The effects of argon injection on fluid flow within the SEN demonstrate an enhancement of turbulence, thus promoting a uniform outflow. However, excessively high argon flow rates risk a critical reduction in meniscus velocity, which could lead to overcooling. The research further elucidates the influence of argon on X-velocity near the mold's narrow faces, indicating a potential method for controlling dendritic growth and enhancing the final product quality.</p><p>This work underlines the complex and multifaceted impacts of argon injection on the continuous casting process. It suggests that through careful manipulation of argon bubble size, SEN submergence depth, and slide gate opening, it is possible to optimize the transportation and entrapment of argon bubbles, manage fluid flow dynamics, and ultimately, improve the quality of the cast product.</p>