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1
Elfsberg, Jessica. "Oscillation Mark Formation in Continuous Casting Processes." Licentiate thesis, KTH, Casting of Metals, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1653.
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Carpenter, Kristin. "The influence of microalloying elements on the hot ductility of thin slab cast steel." Department of Materials Engineering - Faculty of Engineering, 2004. http://ro.uow.edu.au/theses/161.
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Experiments were preformed on a Gleeble 3500 Thermomechanical Simulator to study the hot ductility behaviour of C-Mn-A1 steel and the influence of Nb, Ti and Nb-Ti additions. The simple hot tensile test has been shown to correlate well to the problem of transverse cracking. Therefore, the principle aim of this research is to gain a greater understanding of transverse cracking during the straightening of continuously cast slabs. In particular, attention was paid to thin slab casting conditions. Hot tensile test specimens were either solution treated in melted in-situ (direct cast) and cooled to the deformation temperature. Solution treatment tests simulated conventional casting, where slabs are cooled to room temperature than heated prior to rolling. Direct cast tests simulated hot direct rolling conditions, where slabs are rolled directly after casting without being cooled below the austenite to ferrite transformation. Specimens were cooled to the deformation temperature at two cooling rates, 100K/min and 200K/min. The cooling rate of 100K/min corresponds to the average cooling rate experienced for a conventionally cast slab, 250mm in thickness. The cooling rate of 200K/min corresponds to the average cooling rate for thin-cast slabs, 50mm in thickness. The development of the combination of thin slab casting of hot direct rolling requires hot ductility work to be performed under direct cast conditions and at higher cooling rates. Surface quality is of the utmost importance in thin slab casting so the elimination of transverse cracking is of prime economic importance. There are significant differences between as-cast (direct cast) and reheated (solution treatment) microstructures. In particular, changes in precipitate behaviour, austenite grain size, and the relationship between segregation and the position of austenite gran boundaries was investigated. An attempt has been made to determine what influences these differences in microstructure have on hot ductility. Niobium bearing steels were selected for the reason that there are still problems with Nb steels regarding transverse cracking. Furthermore, there have been contradictory reports on the effects of Ti additions on the transverse cracking behaviour of NB steels. There is evidence from commercial practice that indicates that small additions of Ti improve the transverse cracking susceptibility of Nb steels. However, laboratory results generally show Ti additions have little influence or even a detrimental effect on hot ductility. Disparities in the thermal history simulated in laboratory tests to actual conditions near the surface of a continuously cast slab is the most likely reason for this discrepancy. Therefore, the influence of more closely simulating the thermal history conditions near the surface of a continuously cast slab was evaluated for the Nb-Ti steel. Experimental work involved metallographic and scanning electron microscopy examination of the fracture surface. Transmission electron microscopy was used to determine precipitation characteristics. Tensile tests were conducted to determine mechanical properties, where reduction in area (RA) was used as a measure of ductility. The dendritic structure for direct cast and solution treatment specimens was revealed using a heat treatment procedure (normalising). Particle size was correlated to reduction of area for precipitates in the single-phase austenite temperature region. It was shown that particles below 15nm were detrimental to hot ductility. The relationship between interparticle spacing and reduction of area was also determined. Microalloying additions to C-Mn-A1 steels significantly widen the ductility trough but the depth remains similar. Low ductility was found at higher temperatures in the microalloyed steels due the intergrandular failure as a result of grain boundary sliding in the austenite. Grain boundary sliding was favoured by the slow strain rate and was enhanced by fine microalloyed nitrates and/or carbides. Fine particles can pin austenite grain boundaries, allowing sufficient time for cracks to link together, ultimately causing intergranular fracture. Increasing the cooling rate generally lowered ductility further by promoting finer precipitation. The trough depth is similar in all steels as the formation of thin ferrite films controls ductility at the minimum trough position. The formation of thin films of ferrite allowed strain to concentrate in the softer ferrite phase and intergrandular failure occurred due to microvoid coalescence. Direct cast conditions always led to lower ductility compared to solution treatment conditions. This is explained in terms of differences in the microstructure, namely, grain size, segregation and precipitation. It is recommended that direct cast conditions should be used to determine hot ductility behaviour as it more accurately simulates continuous casting conditions. It was found that simulating the thermal history near the surface of a continuously coast slab, as opposed to cooling directly to the deformation temperature, improved ductility of the Nb-Ti steel. This improvement in ductility was attributed to the thermal history providing favourable conditions for coarsening of NbTi (C,N).
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Ávila, Braz Thaís. "Shrinkage Calculation in the Continuous Casting of Duplex Stainless Steel." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-76516.
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Mimura, Yoshihito. "Sticking-type breakouts during the continuous casting of steel slabs." Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/27941.
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Sticking of the shell in the mold, which often occurs in a high-speed continuous slab casting machine, can be detected with thermocouples in the mold copper plates and prevented from developing into a breakout by reduction of the casting speed. However, a rapid reduction of the casting speed causes some quality problems and a low slab temperature. Thus, sticking-type breakouts remain a concern to the steel industry, and it is still not clear how and why the sticking initiates at the meniscus. The objectives of this study were to identify the causes of sticking at the meniscus, to elucidate the mechanism of sticking and finally to propose methods to reduce the occurrence of sticking.
In order to identify the causes of sticking, it was necessary to examine a sticking-type breakout shell metallurgically, especially the dendrite structure at the shell surface. To link the metallurgical information to the casting conditions, the validity of a correlation in the literature between secondary arm spacing and local cooling rate has been examined. The secondary dendrite arm spacing in the subsurface of a slab has been measured and linked to a local cooling rate calculated from the measured mold heat-flux with this correlation. From this analysis, it was confirmed that Suzuki's correlation between secondary dendrite arm spacing and local cooling rate can be applied for a high cooling rate such as in continuous casting. A sticking-type breakout slab exhibiting five sticking events of 0.08% carbon steel, has been studied and it has been found that small holes exist at the surface in the sticking shells (most likely the site of entrapment, of solid mold flux). The shell which initially sticks exhibits a coarse dendrite structure and, in a longitudinal section, the shape of the initial sticking shell is parabolic. Moreover, with one exception, segregation lines typically 1-3 mm below the surface and almost parallel to the surface have been found in most of the sticking shell. From secondary ion mass spectroscope studies, the solutes concentrating in these segregation lines were determined to be Mn and S.
Apparently, the sticking occurs at the meniscus where heat extraction is greatest and molten mold flux flows between the shell and solid mold flux rim oscillating with the mold. Therefore, to explain these meniscus phenomena, mathematical models of heat transfer at the meniscus and fluid flow in the mold flux channel have been formulated. To analyze the initial sticking event, the meniscus level has been changed in the computer simulations and the following mechanism has been proposed to explain the initiation of a sticking-type breakout. If the meniscus level rises, a deep notch forms in the shell due to the interaction between the mold flux rim and the shell. When a thick mold flux rim moves downward, it contacts the shell above the notch and the shell sticks to the mold flux rim. During the upstroke motion of the mold, tensile forces on the shell cause a rupture at the deep notch which is the hottest and weakest. The predicted solid flux rim profile agrees well with the parabolic shell shape measured in a longitudinal section of the sticking shell.
Since the hot spot is the most likely point to be ruptured, conditions which minimize the hot spot were sought with the models. It was found that most of the conditions required to reduce hot-spot formation are exactly opposite to those required to minimize oscillation mark depth. Notwithstanding this, there are a few techniques to reduce the occurrence of sticking and to improve the surface quality: use a low melting point mold flux and, probably, maintain a deep mold flux pool. An interesting finding with respect to oscillation mark formation is that, if the mold flux rim is thick, the oscillation mark is caused by the interaction of the flux rim with the solidifying shell, while the fluid pressure development in the molten flux film dominates the mark formation in the case of a thin flux rim.
For the analysis of the segregation line, a mass transfer model has been formulated based on a consideration of δ — γ transformation. From this analysis, it was found that the segregation observed in the sticking shell is a band of interdendric segregation enhanced by enlarged primary dendrite arm spacing which, probably, is caused by the appearance of an air gap due to the shell shrinkage.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
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Leckenby, B. M. "Finite element analysis of bulging during the continuous casting of steel slabs and blooms." Thesis, University of Sunderland, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382766.
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Du, Pengfei. "Numerical modeling of porosity and macrosegregation in continuous casting of steel." Diss., University of Iowa, 2013. https://ir.uiowa.edu/etd/2482.
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The continuous casting process is a widely used technique in modern steel plants. However, it is a complicated process that is not well understood. The objective of this research is to model the porosity and macrosegregation due to shrinkage related effects and solid deformation in the continuous casting of steel.
Solid phase movements due to bulging and variable roll gap are modeled with a simple algebraic equation based on assumed slab surface deflection. A simplified single domain fluid flow model is derived to predict the pressure field. When liquid pressure drops to zero, porosity starts to form. The distribution of porosity is calculated using the porosity equation which is based on the mass conservation. A macrosegregation model based on the species conservation is derived. With the relative velocity calculated from the pressure results and the solid velocity, macrosegregation is obtained. Since the solid phase velocity is not zero and mixture density is not assumed to be constant, porosity and macrosegregation due to both solid deformation and shrinkage effects are incorporated.
In order to validate the model, the pressure field of a three-dimensional pure metal solidification system is simulated. The results show the feasibility of the proposed model to predict the fluid flow. The porosity and macrosegregation prediction for different casting conditions are performed. The results confirm the necessity of including solid phase deformation in the prediction of porosity and centerline macrosegregation. The results also reveal the relations between different operating conditions (such as degree of bulging, soft reduction, and casting speed) and the porosity/macrosegregation defects in the final product.
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De, Wet Gideon Jacobus. "CFD modelling and mathematical optimisation of a continuous caster submerge entry nozzle." Pretoria : [s.n.], 2005. http://upetd.up.ac.za/thesis/available/etd-01312006-141026.
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Elahipanah, Zhaleh. "Thermo-Physical Properties of Mould Flux Slags for Continuous Casting of Steel." Thesis, KTH, Materialvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-101270.
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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.
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Yamauchi, Akira. "Heat transfer phenomena and mold flux lubrication in continuous casting of steel /." Stockholm : Tekniska högsk, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3121.
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Hill, N. J. "Visco-plastic and thermal stress analysis in the continuous casting of steel." Thesis, Teesside University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376088.
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Yu, Peter Tong-Kan. "Simulation of transport phenomena during phase change in continuous casting of steel." Thesis, University of Ottawa (Canada), 1985. http://hdl.handle.net/10393/4675.
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Saraswat, Rajil. "Modelling the influence of mould flux on steel shell formation during continuous casting." Thesis, Imperial College London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.434907.
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Damle, Chandrashekharr. "Melt flow, mixing and grade change studies in the continuous casting of steel /." The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487859313344697.
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Sung, Pil Kyung 1961. "Segregation and structure in continuously cast high carbon steel." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277066.
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After hot rolling, the presense of segregation in the center of wire-rod can lead to a nonuniform transformation, resulting in bands of martensite in the microstructure. This is considered to be a defect, called center-martensite, because it can cause cracks and breaks during wire drawing. To identify the mechanism for the formation of center-martensite in wire-rod, the structure, macrosegregation and microsegregation in unworked billets were characterized. Based on measurements of secondary dendrite arm spacings, cooling rates during solidification were estimated. It appears that the macrosegregation of carbon and manganese in the billets manifests itself as the microsegregation in wire-rod, which is an agent in forming the center-martensite. Thus, electromagnetic stirring is proposed as a means to reduce the macrosegregation in the billet and, thereby, reduce the occurrence of center-martensite in wire-rod.
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Siyasiya, Charles Witness. "The transformation behaviour and hot strength of 3CR12 during the continuous casting process." Diss., Pretoria : [s.n.], 2004. http://upetd.up.ac.za/thesis/available/etd-06202005-134528.
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Rocha, José Renê de Sousa. "Modeling and numerical simulation of fluid flow and heat transfer of a steel continuous casting tundish." reponame:Repositório Institucional da UFC, 2017. http://www.repositorio.ufc.br/handle/riufc/24518.
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ROCHA, J. R. S. Modeling and numerical simulation of fluid flow and heat transfer of a steel continuous casting tundish. 2017. 91 f. Dissertação (Mestrado em Ciência de Materiais)-Centro de Tecnologia, Universidade Federal do Ceará, Fortaleza, 2017.Submitted by Hohana Sanders (hohanasanders@hotmail.com) on 2017-07-25T11:20:37Z No. of bitstreams: 1 2017_dis_jrsrocha.pdf: 3666906 bytes, checksum: 42780d960166d0354f84586d96a51b44 (MD5)
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Currently, the continuous casting process is the most used technique to produce steel. Being an inherently component of the caster machine, the tundish has been designed to be not only an intermediate vessel between the ladle and the mold, but also a device to remove inclusions and a metallurgical reactor. Therefore, the tundish has an important role in the continuous casting process. The physical model for heat transfer and fluid flow into the tundish is very complex, thus analytical solutions are not available. Physical studies might present many difficulties for analyzing the process. Hence, Computational Fluid Dynamics (CFD) emerges as an attractive alternative. CFD is based on numerical approaches that are used to solve several classes of engineering problems. The main goal of the present study is to analyze the fluid flow and temperature fields into an actual tundish configuration that is used in continuous casting processes of a local steelmaker company. Based on the performed simulations, some modifications in the geometry of the tundish are proposed in order to improve the steel quality; these modifications make use of weirs and dams. For solving the governing equations arising from the physical model, the Ansys CFX software, which is based on the Element-based Finite-Volume Method (EbFVM) were used. Simulations were performed using water and steel as working fluids for a turbulent flow in a 3D tundish. The results were presented in terms of velocity and temperature fields and Residence Time Distribution (RTD) curves, which evaluated them qualitatively and quantitatively.
O processo de lingotamento contínuo é o processo mais utilizado na produção de aço atualmente. Sendo um importante componente da máquina de lingotamento, o distribuidor tem sido projetado para atuar não apenas como um reservatório entre a panela e o molde, mas também como um dispositivo para remoção de inclusões e servir como um reator metalúrgico. Logo, o distribuidor assume um papel de relevância no processo de lingotamento contínuo. O modelo físico que rege a transferência de calor e escoamento dentro do distribuidor apresenta grande complexidade, tornando a sua solução analítica indisponível. Estudos físicos podem apresentar várias dificuldades para a análise do processo. Portanto, a Dinâmica dos Fluidos Computacional (CFD) surge com uma alternativa viável. CFD é baseada em aproximações numéricas as quais são utilizadas para a solução de várias classes de problemas de engenharia. O principal objetivo do presente trabalho é analisar os campos de escoamento e temperatura no interior de um distribuidor o qual é utilizado nos processos de lingotamento contínuo de uma companhia siderúrgica local. Com base nas simulações realizadas, modificações na geometria do distribuidor são propostas com o intuito de aumentar a qualidade do aço. Essas modificações são feitas através do uso de diques e barragens. Para a solução das equações de conservação originadas do modelo físico, o programa Ansys CFX, o qual utiliza o Método dos Volumes Finitos baseado em Elementos (EbFVM), foi utilizado. As simulações foram feitas utilizando-se aço e água como fluidos de trabalho para um escoamento turbulento em um distribuidor tridimensional. Os resultados foram apresentados em termos de campos de velocidade e temperatura e curvas de Distribuição de Tempo de Residência (RTD) as quais serviram para analisá-los qualitativa e quantitativamente.
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Martins, Marcelo Sampaio [UNESP]. "Fadiga do aço para molas de válvulas SAE 9258 produzido industrialmente por lingotamento convencional e contínuo." Universidade Estadual Paulista (UNESP), 2010. http://hdl.handle.net/11449/94447.
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O presente trabalho tem por objetivo apresentar uma nova proposta de produção do aço para molas de válvulas para motores de combustão interna SAE 9258. Atualmente, este aço é produzido pela rota de lingotamento convencional, e pretende-se adotar o processo de lingotamento contínuo, mantendo-se todas as características mecânicas e metalúrgicas do aço produzido convencionalmente. Cuidados especiais durante o processo de refino secundário (fase líquida) foram levados em consideração para que sejam obtidas inclusões de silicatos deformáveis, essenciais para se conseguir uma vida em fadiga segura para as molas durante a vida útil do motor. Para avaliar essas características do aço foram feitas análises metalográficas da microestrutura em amostras na fase de processamento do aço (fio-máquina) e na fase final do processo (arames), realizados ensaios de tração, ensaios de fadiga axial em corpos-de-prova padronizados (ASTM E 466), ensaios de fadiga por flexão rotativa no arame (Nakamura test), ensaio de fadiga nas molas e análise das superfícies de fratura por fadiga com auxílio de microscopia eletrônica de varredura (MEV), para as duas rotas de produção (lingotamento convencional e contínuo). Os resultados obtidos mostram que não há diferenças com relação a microestrutura, propriedades mecânicas e comportamento em fadiga do aço na fase final de produção (arame) e na forma de produto (molas). Por outro lado, os resultados obtidos para o aço na fase intermediária do processamento (fiomáquina) mostram diferenças com relação à microestrutura, (presença de maior quantidade de carbonetos nas amostras do lingotamento contínuo), e menor redução de área com a consequente redução da resistência à fadiga.
This paper aims to present a new proposal for production of steel for valve springs for internal combustion engines SAE 9258. Currently this steel is produced by ingot casting route, and intended to adopt the continuous casting process, maintaining all the mechanical and metallurgical characteristics of the steel produced conventionally. Special attention during the process of refinement (liquid phase) were taken into account are obtained for silicate inclusions deformable essential to achieving a safe fatigue life for the springs during the life of the engine. To evaluate these features were made of steel metallographic analysis of microstructure in specimens during processing of steel (wire rod) and the final stage (wires) performed tensile tests, axial fatigue tests on specimens standard (ASTM E 466), fatigue tests in rotating bending on the wire (Nakamura test), the fatigue test the springs and examination of the areas of fatigue fracture with the aid of scanning electron microscopy (SEM) for the two production routes (ingot and continuous casting). The results show no differences with respect to microstructure, mechanical properties and fatigue behavior of steel in the final stages of production (wire) and the product form (spring). Moreover, the results obtained for steel in the intermediate stage of processing (wire rod) show differences from the microstructure (the larger amount of carbides in the samples of the continuous casting), lower area reduction with the consequent reduction resistance to fatigue.
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Sakalli, Erhan. "Nozzle Blockage In Continuous Casting Of Al-killed Sae 1006 And Sae 1008 Steel Grades In Iskenderun Iron And Steel Works." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12604856/index.pdf.
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In this work, nozzle clogging in the submerged entry nozzle in continuous casting of Al killed steels has been studied. The study has been based on low silicon Al killed SAE 1006 (1.2006) and SAE 1008 (1.2008) grades. In this study, castabilities of 75 heats for 1.2006 steel grades and 75 heats for 1.2008 steel grades have been investigated. Castabilities of the experimental heats have been found to be affected by Al content in oxide form (Aloxy) and Ca content of the liquid steel. Castabilities have been found to decrease with increase in Aloxy and to increase with increase in Ca content and Ca/Aloxy ratio. Reoxidation has been found not to affect the castability appreciably.
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Björn, Linnéa. "Investigation of Hot Ductility Gradients in Duplex Stainless Steel in the Beginning of the Continuous Casting Proces." Thesis, KTH, Materialvetenskap, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-160892.
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The steel quality is deteriorated at a continuous casting start. Therefore, material from the first cast slab is cut off and re-melted in the melt shop. If too little is discarded, the inferior quality in the retained length can cause defects like edge cracks during subsequent hot rolling. This means that manufacturing resources are wasted on processing inferior material which has to be re-melted anyways at a later stage. On the other hand, if an excessive length of the first slab is re-melted, good material is wasted. In either case, optimizing the length of the start-scrap material is both economically and environmentally beneficial. Edge cracks are more common in the beginning of the first slab, even though a part is cut off. It is likely that the edge cracks arise due to reduced hot ductility in the first cast material. The purpose of this project is to optimize where the cut should be made in order to achieve the best yield. The hot ductility was investigated by performing hot tensile- and bending tests. The hot tensile tests indicate high hot ductility for the investigated specimens. The area reduction, which is correlated to the hot ductility, is above 70 % for all the investigated specimens. When considering the average area reduction while neglecting possible differences between the heats, the specimens from one meter tend to have a lower hot ductility compared to the other specimens. However, the differences are small. No difference can be seen between edge and middle specimens when only looking at the tensile tests. The bending tests did not crack without notches, even though the maximum load and a test temperature of 750 °C was used. That strongly indicates high hot ductility as well. By using notches, the bending tests cracked and it was shown that edge specimens and specimens from one meter cracked the most. No edge cracks were found, after hot rolling, on the first cast slabs from the investigated heats.Vid en stränggjutstart är kvalitén på första slaben sämre. På grund av detta så skärs en bit, av det först gjutna slabet av och smälts om i stålverket. Om för lite material kapas av kan det leda till defekter, såsom kantbrakor, under den efterföljande varmvalsningen. Detta innebär att resurser används i onödan för att tillverka material av otillräcklig kvalitet som sedan ändå måste smältas om i ett senare steg. Skärs istället för mycket material bort så smälts prima material om i onödan. Att optimera startskrotlängden är följaktligen positivt både för miljön och rent ekonomiskt. Under varmvalsningen kan defekten kantbrakor, det vill säga sprickor vid kanterna, uppstå. Trots att en bit av det första gjutna slabet skärs av, så är det första slabet fortfarande mest utsatt för kantbrakor. Detta tros bero på nedsatt varmduktilitet i det första gjutna materialet. Syftet med detta projekt är att optimera längden på startskrotet för att spara så mycket användbart material som möjligt. Varmduktiliteten undersöktes genom drag- och bockprovning. Dragproven indikerar hög varmduktilitet för de undersökta proven. Areakontraktionen, som är ett mått på varmduktiliteten, är över 70 % för alla undersökta prov. Medelareakontraktionen, när man bortser från eventuella skillnader mellan chargerna, visar att prov från en meter generellt har något lägre varmduktilitet än de övriga proven. Det är endast små skillnader som uppfattas. Ingen skillnad kan ses mellan kant- och mittenprov när man enbart tittar på dragprovsresultaten. Bockproven sprack inte trots att maximal last användes och att testtemperaturen var 750 °C. Detta tyder också på hög varmduktilitet. Genom att skapa anvisningar kunde man få bockproven att spricka och det visade sig att kantprov och prov från en meter sprack mest. Inga kantbrakor hade uppstått på de första gjutna slabsen under varmvalsningen av försökschargerna.
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Svensson, Jennie. "An Experimental Study to Improve the Casting Performance of Steel Grades Sensitive for Clogging." Doctoral thesis, KTH, Tillämpad processmetallurgi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-202539.
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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.QC 20170227
VINNOVA
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Grandillo, Angelo M. "A temperature control strategy for Stelco McMaster Works /." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61258.
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In this study, it was shown that improvements in the quality of continuously cast steel billets, similar to those which can be achieved by electromagnetic stirring (EMS) of the liquid pool during solidification, can be obtained if casting superheats can be consistently controlled at low levels. A lack of casting temperature control is not only detrimental to the quality of the cast product, but also to a shop's overall productivity. The important variables for temperature control in the ladle, tundish and mould were quantified and possible methods of controlling these variables were proposed.The thermal state of the ladle lining is one of the major contributors to the variability in casting temperature. It was shown that by reducing energy losses from the refractory ladle lining, by way of incorporating an insulating refractory tile between the ladle shell and the safety lining and by using a ladle lid throughout the cycle of the ladle, temperature losses from the liquid steel can be substantially decreased. (Abstract shortened by UMI.)
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Pinheiro, Carlos A. M. "Mould thermal response, billet surface quality and mould-flux behaviour in the continuous casting of steel billets with powder lubrification." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/nq27226.pdf.
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Bezerra, Maria Carolina Campello. "Avaliação do efeito do carbono em fluxantes para lingotamento contínuo de aços." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-11122006-135151/.
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Para a garantia do bom desempenho dos fluxantes para lingotamento contínuo de aços no molde, a determinação da sua composição química é importante para garantir as propriedades necessárias para o seu perfeito funcionamento. O carbono é adicionado ao fluxante para controlar a velocidade de fusão do fluxante sobre o aço líquido, já que, se adequada, colabora para a disponibilidade de escória líquida suficiente para alimentar o intervalo existente entre a placa de aço em solidificação e o molde, garantindo a perfeita lubrificação. Neste trabalho é demonstrada a influência do efeito de duas fontes de carbono na velocidade de fusão dos fluxantes, através da utilização de uma nova concepção de forno elétrico no qual são colocados dois cadinhos vazados contendo fluxante in natura. Um dos cadinhos é utilizado para avaliação da amostra de referência. O desenvolvimento das reações de fusão do fluxante com o aumento da temperatura resulta em uma escória que, em função de sua fluidez, gera o escorrimento da massa fundida a uma taxa característica, a qual é registrada em um gráfico de massa x temperatura. Desta forma, é demonstrada a eficiência do uso deste equipamento para avaliação da velocidade de fusão, e da influência da fonte e teor de carbono, possibilitando a avaliação de diferentes alternativas de composições. Os ensaios de microscopia com aquecimento e análises térmicas também foram utilizados.In order to assure good performance of mould flux for continuous casting of steel, the chemical composition definition is important to guarantee the properties needs to its perfect behavior in the mould. Carbon is added to the mould flux to control the melting rate, since this property is related to the availability of liquid slag to fill in the gap between the solidified steel and the cupper wall that assure a perfect lubrication. This work presents the influence of two carbon sources evaluated by an apparatus designed for testing the melting rate of mould fluxes. It is an electric resistance furnace in which two perforated at the bottom crucibles contain flux sample in natura. One of the crucibles is used for the reference sample. As the temperature increases and the melting of the flux takes place, liquid slag starts dropping from the crucible, which is attached to a load cell. Weight losses and temperature are simultaneously recorded and a plot of mass (grams) versus temperature (degree Celsius) is produced. The effect of carbon content of the flux mixtures on the melting rate has been investigated. The heating microscope and thermal analysis were also evaluated.
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Martins, Marcelo Sampaio. "Fadiga do aço para molas de válvulas SAE 9258 produzido industrialmente por lingotamento convencional e contínuo /." Guaratinguetá : [s.n.], 2010. http://hdl.handle.net/11449/94447.
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Resumo: O presente trabalho tem por objetivo apresentar uma nova proposta de produção do aço para molas de válvulas para motores de combustão interna SAE 9258. Atualmente, este aço é produzido pela rota de lingotamento convencional, e pretende-se adotar o processo de lingotamento contínuo, mantendo-se todas as características mecânicas e metalúrgicas do aço produzido convencionalmente. Cuidados especiais durante o processo de refino secundário (fase líquida) foram levados em consideração para que sejam obtidas inclusões de silicatos deformáveis, essenciais para se conseguir uma vida em fadiga segura para as molas durante a vida útil do motor. Para avaliar essas características do aço foram feitas análises metalográficas da microestrutura em amostras na fase de processamento do aço (fio-máquina) e na fase final do processo (arames), realizados ensaios de tração, ensaios de fadiga axial em corpos-de-prova padronizados (ASTM E 466), ensaios de fadiga por flexão rotativa no arame (Nakamura test), ensaio de fadiga nas molas e análise das superfícies de fratura por fadiga com auxílio de microscopia eletrônica de varredura (MEV), para as duas rotas de produção (lingotamento convencional e contínuo). Os resultados obtidos mostram que não há diferenças com relação a microestrutura, propriedades mecânicas e comportamento em fadiga do aço na fase final de produção (arame) e na forma de produto (molas). Por outro lado, os resultados obtidos para o aço na fase intermediária do processamento (fiomáquina) mostram diferenças com relação à microestrutura, (presença de maior quantidade de carbonetos nas amostras do lingotamento contínuo), e menor redução de área com a consequente redução da resistência à fadiga.Abstract: This paper aims to present a new proposal for production of steel for valve springs for internal combustion engines SAE 9258. Currently this steel is produced by ingot casting route, and intended to adopt the continuous casting process, maintaining all the mechanical and metallurgical characteristics of the steel produced conventionally. Special attention during the process of refinement (liquid phase) were taken into account are obtained for silicate inclusions deformable essential to achieving a safe fatigue life for the springs during the life of the engine. To evaluate these features were made of steel metallographic analysis of microstructure in specimens during processing of steel (wire rod) and the final stage (wires) performed tensile tests, axial fatigue tests on specimens standard (ASTM E 466), fatigue tests in rotating bending on the wire (Nakamura test), the fatigue test the springs and examination of the areas of fatigue fracture with the aid of scanning electron microscopy (SEM) for the two production routes (ingot and continuous casting). The results show no differences with respect to microstructure, mechanical properties and fatigue behavior of steel in the final stages of production (wire) and the product form (spring). Moreover, the results obtained for steel in the intermediate stage of processing (wire rod) show differences from the microstructure (the larger amount of carbides in the samples of the continuous casting), lower area reduction with the consequent reduction resistance to fatigue.
Orientador: Aelcio Zangrandi
Coorientador: César Alves da Silva Leandro
Banca: Aelcio Zangrandi
Banca: Carlos Kiyan
Banca: Carlos Moura Neto
Mestre
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Ni, Peiyuan. "A Study on Particle Motion and Deposition Rate : Application in Steel Flows." Doctoral thesis, KTH, Tillämpad processmetallurgi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-161915.
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Non-metallic inclusions in molten steel have received worldwide attention due to their serious influence on both the steel product quality and the steel production process. These inclusions may come from the de-oxidation process, the re-oxidation by air and/or slag due to an entrainment during steel transfer, and so on. The presence of some inclusion types can cause a termination of a casting process by clogging a nozzle. Thus, a good knowledge of the inclusion behavior and deposition rate in steel flows is really important to understand phenomena such as nozzle clogging. In this thesis, inclusion behaviors and deposition rates in steel flows were investigated by using mathematical simulations and validation by experiments. A ladle teeming process was simulated and Ce2O3 inclusion behavior during a teeming stage was studied. A Lagrangian method was used to track the inclusions in a steel flow and to compare the behaviors of inclusions of different sizes. In addition, a statistical analysis was conducted by the use of a stochastic turbulence model to investigate the behaviors of different-sized inclusions in different nozzle regions. The results show that inclusions with a diameter smaller than 20 μm were found to have similar trajectories and velocity distributions in the nozzle. The inertia force and buoyancy force were found to play an important role for the behavior of large-size inclusions or clusters. The statistical analysis results indicate that the region close to the connection region of the straight pipe and the expanding part of the nozzle seems to be very sensitive for an inclusion deposition. In order to know the deposition rate of non-metallic inclusions, an improved Eulerian particle deposition model was developed and subsequently used to predict the deposition rate of inclusions. It accounts for the differences in properties between air and liquid metals and considers Brownian and turbulent diffusion, turbophoresis and thermophoresis as transport mechanisms. A CFD model was firstly built up to obtain the friction velocity caused by a fluid flow. Then, the friction velocity was put into the deposition model to calculate the deposition rate. For the case of inclusion/particle deposition in vertical steel flows, effects on the deposition rate of parameters such as steel flow rate, particle diameter, particle density, wall roughness and temperature gradient near a wall were investigated. The results show that the steel flow rate/friction velocity has a very important influence on the rate of the deposition of large particles, for which turbophoresis is the main deposition mechanism. For small particles, both the wall roughness and thermophoresis have a significant influence on the particle deposition rate. The extended Eulerian model was thereafter used to predict the inclusion deposition rate in a submerged entry nozzle (SEN). Deposition rates of different-size inclusions in the SEN were obtained. The result shows that the steel flow is non-uniform in the SEN of the tundish. This leads to an uneven distribution of the inclusion deposition rates at different locations of the inner wall of the SEN. A large deposition rate was found to occur at the regions near the SEN inlet, the SEN bottom and the upper region of two SEN ports. For the case of an inclusion/particle deposition in horizontal straight channel flows, the deposition rates of particles at different locations of a horizontal straight pipe cross- section were found to be different due to the influence of gravity and buoyancy. For small particles with a small particle relaxation time, the gravity separation is important for their deposition behaviors at high and low parts of the horizontal pipe compared to the turbophoresis. For large particles with a large particle relaxation time, turbophoresis is the dominating deposition mechanism.QC 20150326
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Gschwenter, Viviane Lopes da Silva. "Correlação entre parâmetros de solidificação e formação estrutural de aços especiais produzidos pelo processo de lingotamento contínuo." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2009. http://hdl.handle.net/10183/17300.
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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.
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Bothma, Jan Andries. "Heat transfer through mould flux with titanium oxide additions." Diss., Pretoria : [s.n.], 2006. http://upetd.up.ac.za/thesis/available/etd-10182007-161313/.
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Zemanová, Hana. "Prediktivní řízení založené na modelu pro aplikaci plynulého odlévání oceli." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231399.
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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.
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Kholmatov, Shavkat. "On some positive effects of swirling flow for the continuous cast mould billets." Licentiate thesis, Stockholm : Division of Applied Process Metallurgy, School of Industrial Engineering and Management, Royal Institute of Technology, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4453.
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Lu, Yu-Chiao. "Design of Bridgman unidirectional solidification furnace." Thesis, KTH, Materialvetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-261191.
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The thesis work consists of two parts. First, the development of two-dimensional numerical models of a Bridgman unidirectional solidification furnace, and second, the construction work of the furnace at KTH. The aim is to build a Bridgman furnace which is capable of close control over temperature gradient and growth rate such that the solidification structures of a duplex stainless steel (SAF2507) could be replicated at a laboratory scale for different cooling rates.Two numerical models of Bridgman furnace are created using COMSOL Multiphysics. The models are used as predictive tools to simulate the locations of solidification front and the temperature gradients at the solidification fronts, which are parameters difficult to access during experiments. Different hot zone temperatures of the furnace (1500~1550 °C) and different sample pulling rates (0.5~10 mm/s) are studied in simulations. The major finding from modeled results is that the temperature gradient of the sample at the solidification fronts range from 5 ~ 17 K/mm, which are lower than the furnace temperature gradient of ~50 K/mm. The corresponding steady-state cooling rates range between 5 ~ 85 K/s. The next step is to validate the models with experimental temperature profiles of the furnace, and decide whether the furnace design should be modified to achieve the cooling rates of interests.Examensarbetet består av två delar. Först utvecklingen av tvådimensionella numeriska modeller av en Bridgman enkelriktad stelningsugn, och för det andra konstruktionsarbetet för ugnen vid KTH. Syftet är att bygga en Bridgman-ugn som har förmåga att kontrollera temperaturgradienten och tillväxthastigheten så att stelningsstrukturerna i ett duplex-rostfritt stål (SAF2507) skulle kunna replikeras i laboratorieskala för olika kylningshastigheter. Två numeriska modeller av Bridgman-ugnen skapas med COMSOL Multiphysics. Modellerna används som prediktiva verktyg för att simulera placeringen av stelningsfronten och temperaturgradienterna vid stelningsfronterna, vilket är parametrar som är svåra att komma åt under experiment. Olika varmzonstemperaturer i ugnen (1500~1550 °C) och olika provdragningshastigheter (0.5~10 mm/s) studeras i simuleringar. Det viktigaste fyndet från modellerade resultat är att provets temperaturgradient vid stelningsfronterna sträcker sig från 5 ~17 K/mm, vilket är lägre än ugns temperaturgradient på ~ 50 K/mm. Motsvarande stabilitetskylningshastigheter varierar mellan 5 ~ 85 K/s. Nästa steg är att validera modellerna med experimentella temperaturprofiler för ugnen och bestämma om ugnsutformningen ska modifieras för att uppnå intressens kylningshastigheter.
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Faco, Rubens José. "Levantamento das inclusões nos principais grupos de aços produzidos em aciaria do tipo LD." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-14122006-102927/.
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Foram tomadas amostras de aço líquido referentes a três grupos de aço, a saber: (I) aços baixo-carbono (0,02 %C 0,08), acalmados ao alumínio; (II) aços peritéticos (0,09 %C 0,15), acalmados ao alumínio e silício; (III) aços ultrabaixo carbono ( C<35 ppm), acalmados ao alumínio.Os aços foram produzidos em aciaria do tipo LD e foram, a seguir, tratados em equipamentos de refino secundário, adequados a cada um dos casos.As amostras forma colhidas no distribuidor de uma máquina de lingotamento contínuo de placas, segundo critério que minimiza a possibilidade da ocorrência de interferências que pudessem mascarar o resultado do tratamento de refino secundário tais como re-oxidação do aço e coleta simultânea de escória. As amostras foram submetidas à análise de inclusões utilizando-se técnicas de microscopia óptica, microscopia eletrônica e micro-análise. Foi possível caracterizar as inclusões presentes em cada tipo de aço segundo a morfologia, o tamanho, a quantidade e a composição química.Non-metallic inclusions in liquid samples of (I) low-carbon aluminium killed steel (0,02wpct C 0,08wpct), (II) peritetic aluminium and silicon killed steel (0,09wpct C 0,15wpct); (III) extra-low-carbon, aluminium killed steel (C<35 ppm) were taken from the tundish distributor of a continuous casting caster for steel plates according to a procedure that minimizes re-oxidation of steel and/or pick up of liquid slag. The samples were inspected through the following microstructural techniques: optical microscopy, electronic microscopy, and electron microprobe. Were possible to feature present inclusion in each kind of steel according to morphology, size, amout and chemical composition.
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Barcellos, Vinicius Karlinski de. "Desenvolvimento de software de simulação da solidificação de aços no processo de lingotamento contínuo de tarugos." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2011. http://hdl.handle.net/10183/34743.
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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.
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Gomes, Noraldo Hipolito Guimarães. "Estudo comparativo de tubos submersos anti-clogging no processo de lingotamento contínuo." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/97/97134/tde-20082013-162244/.
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O processo de lingotamento contínuo de produtos planos de aço tem sido alvo de incessantes estudos devido a sua importância na produção de bobinas laminadas a partir de placas, para um grupo muito diversificado de clientes, dentre os quais, destacam-se as indústrias automobilística e de eletrodomésticos (\"linha branca\"), que têm se mostrado muito exigentes. No entanto, por tratar-se de aços desoxidados ao alumínio, é comum a ocorrência de formação de um depósito de óxido de alumínio (alumina), no interior do tubo submerso do processo de lingotamento contínuo, o que diminui seu diâmetro interno, levando à restrição de passagem do aço líquido pelo seu interior, provocando a perda de produtividade devido à necessidade de se reduzir a velocidade de lingotamento e até mesmo a contaminação do aço com inclusões de alumina, principalmente naqueles seqüenciais com um elevado tempo de lingotamento, próximo de dez horas. Para tanto, desenvolveu-se um tubo com um material interno anti-clogging que na literatura é chamado de C-less, para minimizar e/ou evitar a deposição de alumina e com uma linha de escória reforçada com uma camada de zircônia (ZrO2) mais espessa e mais nobre, para resistir ao ataque da escória. O objetivo desta dissertação foi comparar tubos de diferentes fornecedores, avaliando as principais variáveis que têm influência direta na sua performance: perfil de aquecimento, taxa de erosão na linha de escória, índice de obstrução e parâmetros físico-químicos através da correlação dos materiais antes e após uso (post-mortem). Os resultados encontrados mostraram uma melhor performance dos tubos do fornecedor \"M\", que apresentaram menores taxas de desgaste e, conseqüentemente, maior potencial de vida (maior tempo de lingotamento) após análise da linha de escória, que pode ser atribuída a uma melhor distribuição dos grãos de zircônia na matriz (maior homogeneidade), além de apresentarem grãos mais finos e desta forma, reduzindo os espaços \"vazios\" na matriz, propícios ao ataque da escória por meio de um desequilíbrio químico entre esta escória líquida e o refratário. Além disto, seu material anti-clogging e projeto de distribuição do mesmo na peça, propiciaram um melhor resultado em relação à obstrução pela deposição de alumina ao longo do corpo do tubo submerso.The continuous casting process of steel plane products has been objective of incessant studies due to its importance in the production of laminated coils starting from slabs, for a very diversified group of customers, among all the automobile industries and of appliances (\"home appliances\"), that have been showing very demanding. However, for being low carbon aluminum killed steels, is common the occurrence of aluminum oxide (alumina) deposit formation, inside of submerged nozzle in continuous casting process, what decreases its internal diameter, taking to the restriction of passage of the liquid steel for its interior, provoking the productivity loss due to the need of being reduced the casting speed and even the contamination of the steel with alumina inclusions, mainly in those sequential with a high casting time, close of ten hours. For so much, a submerged nozzle was developed with a internal anti-clogging material that it is called C-less in the literature, to minimize and/or to avoid the alumina building up and with a slag reinforced line with a zirconium layer (ZrO2) thicker and more noble, slag attack resist to. The dissertation objective was compare submerged nozzles from different suppliers, evaluating the main variables that have direct influence in its performance: heating profile, slag line erosion rate, clogging index and physical-chemical parameters through the materials correlation before and after use (post-mortem). The results showed submerged nozzle\'s better performance from supplier \"M\", that presented smaller waste rates and, consequently, last longer live (larger time of casting) after analysis of the slag line, that can be attributed to a better distribution of the zirconium grains in the head office (larger homogeneity), besides they present finer grains and this way, reducing the empty \" spaces \" in the head office, favorable to slag attack by means of a chemical unbalance between this liquid slag and the refractory. Besides, its anti-clogging material and project distribution in the same piece, they propitiated a better result in relation to the clogging for the alumina building up along the body of the submerged nozzle.
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Spinelli, Jose Eduardo. "Simulação do lingotamento continuo de tiras finas de aços." [s.n.], 2000. http://repositorio.unicamp.br/jspui/handle/REPOSIP/264701.
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Orientador: Amauri GarciaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: Entende-se por modelagem de processo, o desenvolvimento de uma representação quantitativa ou qualitativa dos fenômenos físicos associados ao processo. Neste trabalho são realizadas simulações do processo twin roll de lingotamento contínuo de tiras de aços, utilizando como referência tecnológica o equipamento piloto instalado nas dependências do Instituto de Pesquisas Tecnológicas do Estado de São Paulo. São construídos dois simuladores para o processo: um simulador da solidificação unidirecional, com molde refrigerado de aço e paredes laterais de material refratário, utilizando-se o aço inoxidável 304 como material de simulação; e variando-se as temperaturas de vazamento; e outro simulador a frio, com componentes feitos de acrílico, água como fluido de simulação e permanganato de potássio como corante. Um modelo matemático previamente desenvolvido é utilizado para confrontar perfis térmicos teóricos com perfis experimentais, para a determinação do coeficiente de transferência de calor metal/molde. O levantamento de valores de espaçamento dendrítico secundário é realizado nas amostras, além da observação simultânea das estruturas de solidificação, o que comprovou a eficiência do simulador em caracterizar o processo de solidificação do equipamento piloto. O uso do modelo frio permitiu a caracterização do posicionamento de barreira a 15 cm ou a 20 cm da lateral esquerda do distribuidor como a melhor configuração
Abstract: It can be understood by process modeling the development of a quantitative or qualitative representation of the physical phenomena associated to the process. In this work, simulations concerning the twin roll continuous caster of steels process at IPT (Instituto de Pesquisas Tecnológicas do Estado de São Paulo) are performed. Two simulators were developed: (i) a simulator of unidirectional solidification with cooled steel mold and refractory lateral walls, by using a stainless steel as the reference metal (AISI 304), and varying superheat temperatures; (ii) a physical model, with components made of acrylic, water as the simulation fluid and potassium permanganate as a pigment. A previously developed mathematical model has been used to determine the metal/mold heat transfer coefficient by a method that compares experimenta1ltheoretical temperature curves. Measurement of secondary dendrite arm spacings is performed by microestructural examination of the samples, confirming the simulator efficiency in characterizing the solidification process in the pilot equipment. The use of the physical model has permitted to attain the best configuration for the tundish, by positioning the dam 15 cm or 20 cm from the left side of tundish
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica
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Srba, Jan. "Kombinace numerické matematiky a neuronové sítě pro model predikce průvalu." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-400476.
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This thesis deals with creation of breakout prediction model implemented via artificial neural network in MATLAB, hence it contains theoretical description of artificial neural networks and also presents how the networks were used for the breakout prediction problem. In addition, models of heat conduction through the mold wall were created and used for generating neccesary data for proper training of artificial neural network. The thesis contains proper description of used numerical methods for solving the heat conduction problems. In the thesis are presented partial results and also results of testing created artificial neural network with usage of real data.
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Timmel, Klaus. "Experimentelle Untersuchung zur Strömungsbeeinflussung mittels elektromagnetischer Bremsen beim kontinuierlichen Strangguss von Stahl." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2015. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-165352.
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Beim kontinuierlichen Stranggießen von Stahl werden elektromagnetische Felder zur Strömungsbeeinflussung eingesetzt. In dieser Arbeit wird die Wirkung eines statischen Magnetfeldes auf die Kokillenströmung in einem Modellexperiment untersucht. Das statische Magnetfeld strukturiert die Strömung um, kann lokal die Strömungsgeschwindigkeiten erhöhen und verändert die Ausbildung und Anzahl der für Brammenkokillen typischen großskaligen Wirbel. Es zeigt sich weiterhin, dass die elektrische Leitfähigkeit der Kokillenwände einen entscheidenden Einfluss auf die Wirkung einer elektromagnetischen Bremse hat. Unter isolierenden Wänden werden räumliche Oszillationen des Flüssigmetallstrahles initiiert und es bildet sich zwischen den beiden Kokillenhälften eine asymmetrische Strömung aus. Leitfähige Wände verhindern die Oszillationen und die Kokillenströmung ist symmetrisch. Eine eindeutige bremsende Wirkung der elektromagnetischen Bremse auf den Durchfluss konnte jedoch in beiden Fällen nicht festgestellt werden.
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MILANI, CARLOS AUGUSTO RUPPENTHAL. "IDENTIFICATION AND SOLUTION OF HOT ROLLING CRACKING IN STRUCTURAL STEELS PROCESSED BY CONTINUOUS CASTING." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2016. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=36911@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROO advento e consolidação do processo de lingotamento contínuo, hoje dominante no setor siderúrgico, trouxe à tona os crescentes esforços de investigação e análise dos fenômenos relacionados com o comportamento dos aços a elevadas temperaturas. Diferentemente do lingotamento convencional, o lingotamento contínuo é um processo dinâmico no qual ocorre a oscilação do molde enquanto o veio em solidificação é continuamente extraído ao mesmo tempo que é submetido a um segundo resfriamento dito secundário. No Brasil há um parque industrial de empresas que se dedicam à laminação a quente de semiacabados fornecidos por terceiros como placas de aço, as quais são cortadas a quente sob a forma de tarugos de seção quadrada que são então destinados a laminação. A linha de produção dessas empresas compreende basicamente produtos estruturais tais como barras chatas, barras redondas, barras quadradas, cantoneiras e até perfis especiais destinados à indústria automobilística e de máquinas. Uma série catastrófica de eventos de qualidade relacionados com trincas emergiu da laminação de tarugos de aço SAE 1020 oriundos de placas continuamente lingotadas. Essas trincas, porventura preexistentes ou latentes no interior das placas podem ter sido exacerbadas por efeitos de zonas termicamente afetas durante as operações de corte. A solução proposta para superação dessa contingência foi então a de criação de um aço de substituição com teores inferiores de carbono e maior conteúdo de ligas que preservasse as propriedades mecânicas do material laminado. Teores inferiores de carbono não apenas contribuem para a minimização dos efeitos oriundos das transformações peritéticas como também agem favoravelmente sobre as consequências decorrentes de zonas termicamente afetadas. Essa proposta foi bem sucedida e a composição química desse aço de substituição denominado pseudo-1020 passou a ser desde então padrão de laminação. Amostras do SAE 1020 laminado com ocorrências de trincas e do aço de substituição foram obtidas e transformadas em corpos de prova para a realização de ensaios de tração, dureza e impacto. Essa dissertação objetiva apresentar toda a fenomenologia relacionada com a ocorrência de trincas superfícies e internas em aços continuamente lingotados, em especial os submetidos a transformações peritéticas, e as premissas que fundamentaram a criação do aço de substituição e os resultados auferidos.
The advent and consolidation of the continuous casting process, currently dominant in the Steel Industry, raised the increasing investigation and analyses efforts on the phenomena related to the high-temperature behavior of the steels. Unlike the conventional ingot casting process, the continuous casting is a dynamic process in which occurs the mold oscillation while the strand under solidification is continuously withdrawn and submitted to a secondary cooling operation. In Brazil, it can be found an industrial park of companies dedicated to the hot rolling of semis supplied by third parties as steel slabs, which ones are flame cut in the form of square billets for rolling. The production mix of these companies encompasses structural steels such as flat bars, round bars, angles and even special profiles for the machines and automotive industries. A catastrophic series of quality events related to cracking emerged from the rolling of SAE 1020 billets made from continuously cast slabs. These cracks, perhaps pre-existing or latent in the inner parts of the slabs could be exacerbated by thermal affected zones during the flame-cut operations. The propose solution to overcoming this contingency was the creation of a replacement steel grade with lower carbon content and higher alloy content aiming to preserve the mechanical properties of the as rolled material. Lower carbon contents does not only contributes to the minimization of the effects arising from the peritetic transformations as also act in favor on the consequences coming from thermal affected zones. This proposition was well successful and the chemical composition of this replacement steel called pseudo- 1020 since then became a rolling standard. Samples of the rolled SAE 1020 steel with cracks occurrences and of the replacement steel were taken and transformed in specimens for tensile strengths, hardness and impact tests.This paper aims to present all related phenomena to the occurrence of inner and superficial cracks in continuously cast steels, in special the ones submitted to peritetic transformations, and the premises that support the creation of a replacement steel and the related results.
38
Pustějovský, Michal. "Optimalizace teplotního pole s fázovou přeměnou." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-232173.
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This thesis deals with modelling of continuous casting of steel. This process of steel manufacturing has achieved dominant position not only in the Czech Republic but also worldwide. The solved casted bar cross-section shape is circular, because it is rarely studied in academical works nowadays. First part of thesis focuses on creating numerical model of thermal field, using finite difference method with cylindrical coordinates. This model is then employed in optimization part, which represents control problem of abrupt step change of casting speed. The main goal is to find out, whether the computation of numerical model and optimization both can be parallelized using spatial decomposition. To achieve that, Progressive Hedging Algorithm from the field of stochastic optimization has been used.
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Klimeš, Lubomír. "Optimalizace parametrů sekundárního chlazení plynulého odlévání oceli." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-234206.
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Continuous casting is a dominant production technology of steelmaking which is currently used for more that 95% of the world steel production. Mathematical modelling and optimal control of casting machine are crucial tasks in continuous steel casting which directly influence productivity and quality of produced steel, competitiveness of steelworks, safety of casting machine operation and its impact on the environment. This thesis concerns with the development and implementation of the numerical model of temperature field for continuously cast steel billets and its use for optimal control of the casting machine. The numerical model was developed and implemented in MATLAB. Due to computational demands the model was parallelized by means of the computation on graphics processing units NVIDIA with the computational architecture CUDA. Validation and verification of the model were performed with the use of operational data from Trinecke zelezarny steelworks. The model was then utilized as a part of the developed model-based predictive control system for the optimal control of dynamic situations in the casting machine operation. The behaviour of the developed control system was examined by means of dynamic model situations that have confirmed the ability of the implemented system to optimally control dynamic operations of the continuous casting machine. Both the numerical model of the temperature field and the model-based predictive control system have been implemented so that they can be modified for any casting machine and this allows for their prospective commercial applications.
40
Timmel, Klaus. "Experimentelle Untersuchung zur Strömungsbeeinflussung mittels elektromagnetischer Bremsen beim kontinuierlichen Strangguss von Stahl." Doctoral thesis, Helmholtz-Zentrum Dresden-Rossendorf, 2014. https://tubaf.qucosa.de/id/qucosa%3A22984.
Full textAbstract:
Beim kontinuierlichen Stranggießen von Stahl werden elektromagnetische Felder zur Strömungsbeeinflussung eingesetzt. In dieser Arbeit wird die Wirkung eines statischen Magnetfeldes auf die Kokillenströmung in einem Modellexperiment untersucht. Das statische Magnetfeld strukturiert die Strömung um, kann lokal die Strömungsgeschwindigkeiten erhöhen und verändert die Ausbildung und Anzahl der für Brammenkokillen typischen großskaligen Wirbel. Es zeigt sich weiterhin, dass die elektrische Leitfähigkeit der Kokillenwände einen entscheidenden Einfluss auf die Wirkung einer elektromagnetischen Bremse hat. Unter isolierenden Wänden werden räumliche Oszillationen des Flüssigmetallstrahles initiiert und es bildet sich zwischen den beiden Kokillenhälften eine asymmetrische Strömung aus. Leitfähige Wände verhindern die Oszillationen und die Kokillenströmung ist symmetrisch. Eine eindeutige bremsende Wirkung der elektromagnetischen Bremse auf den Durchfluss konnte jedoch in beiden Fällen nicht festgestellt werden.
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Saleem, Saud. "On the surface quality of continuously cast steels and phosphor bronzes." Doctoral thesis, KTH, Metallernas gjutning, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-187718.
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This thesis work concerns about the importance of the cast surfaces, surface phenomenon such as the formation of the oscillation marks and exudation and related defects including cracks and segregation that happened during the continuous casting. All of the investigated materials were collected during the plant trials while an in-depth analysis on these materials was performed at the laboratory scale with certain explanations supported by the schematic and theoretical models. The work consists on different material classes such as steels and phosphor bronzes with a focus on the surface defects and their improvements. In order to facilitate the theoretical analysis which could be capable of explaining the suggested phenomenon in the thesis, a reduced model is developed which required lesser computational resources with lesser convergence problems.QC 20160527
Oscilation mark formation during continous casting of steel
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Chih-Hao, Chou, and 周志浩. "Optimal nozzle design in continuous steel casting process." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/00459528037713678280.
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碩士國立臺灣大學
化學工程學研究所
87
Abstract A mathematical model was employed to calculate the fluid flow and temperature distribution within the molten steel region of a continuous slab caster. Numerical calculations were based on the real geometry of the slab caster of the China Steel Corporation. Fluid flow and heat transfer phenomena are studied in this research. The FIDAP code was applied to calculate the three-dimension highly turbulent fluid flow and heat transfer using high Renold number K- model and finite element method. This research studied two kinds of submerged entry nozzle (Cases A and B), and investigated the influence of different operating conditions, such as the submerged depth of nozzles and the length of mold wide face, on the fluid flow and heat transfer. The calculated results indicate that :(1)By means of the converging and diverging parts of its SEN pipe , Case B can result in more even steel flow and temperature distribution. The symmetrisity will be increased about 20% and the average temperature difference between the right and left meniscus will be decreased about 1.5℃.(2)If the submerged depth is increased to 160%,the fluctuation level of meniscus will be decreased by 50% and the average temperature of meniscus will be decreased about 3 to 4℃simultaneously .(3) If the length of the mold wide face is increased to 150%, the fluctuation level of meniscus will be increased by 20% and the average temperature of meniscus will also be decreased about 3 to 5℃. The optimal operating condition depends on the product qualities and the purpose of our processing.
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Su, Yu-Guang, and 蘇昱光. "The Study of Continuous Casting for Amorphous Silicon Steel." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/32649051028500342949.
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博士國立臺灣大學
應用力學研究所
104
An amorphous structure improves the physical properties of metal and enhances material performance. Planar flow casting process (PFC) is a rapid solidification method for continuously producing microcrystalline and amorphous ribbons. In the PFC process, molten metal flows through a nozzle onto the chill wheel where the melt is frozen and a continuous ribbon is spun. First, this study reorganizes the related experimental studies and performs the operability diagrams for all kinds of metal ribbons using dimensional analysis. Based on these diagrams, a rapid method that can assist on-site operators to adjust parameters is proposed. The method is able to determine the wheel-nozzle gap, applied pressure difference and wheel speed for the designated the ribbon thickness with a preset nozzle slot breadth. The determined operating variables enable the successful production of continuous ribbon and can serve as a reference for designing and modifying the processes. Then, the puddle development and heat transfer behavior in the PFC process are simulated using the computational fluid dynamics (CFD). A two-dimensional model is developed for the puddle in which the inertial force, viscosity, surface tension, wettability, and heat transfer with phase transformation are incorporated and the volume of fluid (VOF) method is employed to characterize the behaviors of the two-phase flow including the melt and air. The effects of the nozzle shapes and wetting conditions between the puddle/nozzle and puddle/wheel on the puddle shape and ribbon thickness are evaluated and their velocity and temperature fields are examined. The result shows that the nozzle with larger gap in the downstream tends to produce a longer puddle length and a thicker ribbon and it takes more time to reach a steady state for the casting process. In addition, the puddle shape was affected significantly by the wetting condition on the nozzle surface rather than that on the wheel surface. The contact condition between the puddle and nozzle must be non-wetting in order to make the puddle reach a steady state rapidly. However, the wetting contact condition is preferable between the puddle and wheel surface to reduce the amount of air entrainment and the air-pocket frequency on the ribbon surface. At the experimental section, the effects of manufacturing parameters in the PFC process on the ribbon formation and the puddle stability of Fe78B13Si9 alloy are investigated. The ribbon morphology, surface quality, and puddle geometry are examined at different conditions and the transient evolution processes of puddle for molten metal passing through a rectangular nozzle are observed. The successful operability window for the production of Fe78B13Si9 ribbon is established and it is found the scope is different from that of Al-based alloy. The ribbon thickness is found to vary with the applied pressure across the crucible and the wheel speed to the power of 0.45 and , respectively. The formation of small air pockets could be enhanced by increasing the applied pressure difference and wheel speed, or by decreasing the nozzle-wheel gap and the jetting temperature. Next, the influences of surface roughness of chill wheel on ribbon topography and surface quality are examined and the average cooling rate during the PFC process is evaluated. The result reveals that a lower roughness tends to induce the appearance of herringbone pattern on the wheel-side ribbon surface and capture more air at the wheel-melt interface to form larger elongated air pockets on the ribbon surface. On the contrary, less air is trapped at higher roughness and the distribution of air pockets on the ribbon surface is mainly corresponding to the concave spots on the wheel surface. The roughness on the wheel-side ribbon surface increases monotonically with the wheel roughness, while a minimum roughness is observed on the opposite air-side surface exhibiting the smoothest air-side ribbon surface. A higher wheel roughness enhances the thermal contact resistance at the interface between the ribbon and the chill wheel, which reduces the average cooling rate during the casting process and results in the occurrence of crystalline structure in the ribbon formation. Finally, a high-speed imaging system only records the evolution of puddle geometry due to the glare of the melt. The layout for the simulated apparatus of flow field is carried out in order to view the fluid flow in the puddle. According to the experimental data of the PFC process, the required operating variables are calculated, the suitable fluid and seeding particles are selected and the wheel size and the motor specification are designed under the same dimensionless parameters. The whole process is that the silicon oil with seeding particles conveyed by the metering and pressurizing pump is fed through a nozzle onto the rotating wheel and is collected in the recycling tank. The result discovers that a strong clockwise vortex is formed clearly in the upstream region of the puddle. The back views of the puddle are found to vary from convex to waves distinctly with the wheel speed. Simultaneously, the system is predicted the stability by comparing with the theoretical results of the Taylor-Dean flow. The research issues in the future include the puddle stability of the PFC process and the relationship between dynamic contact angles and air pockets. The former is investigated progressively by the results of linear stability analysis for the plate flow and cylinder flow. The latter is studied by the use of the simulated apparatus of flow field and applies the linear stability analysis for the contact line to attain the aim of avoiding the air entrainment.
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Wei, Enfa. "Characterization of mold fluxes for the continuous casting of steel." 2004. http://link.library.utoronto.ca/eir/EIRdetail.cfm?Resources__ID=80991&T=F.
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Lee, Yung-Yu, and 李永裕. "The inclusions morphology and heat behavior in steel in continuous casting." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/60710787384988964612.
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碩士義守大學
材料科學與工程學系碩士班
96
The purpose of this research is to discuss the number and morphology of inclusions with different cooling rates in the continuous casts and their heating behavior after reheating at 1100℃、1250℃ and 1400℃. The experiments in this research showed that the inclusions size is around 5μm and the inclusion number is 162. They are increased to 8μm and 81 more than in the casts after reheating at 1100℃. In contrast, they are decreased to 3μm and 36 less after reheating at 1250℃；the inclusion size and number are furthermore decreased to 300 nm and 73 less in the casts after reheating at 1400℃. From the solidified location point of view the inclusions in the surface of the slab and inclusion number increase from second layer to forth layer by cooling. Meaning of the reheating temperature is: 1100℃ should be lower than the melting temperature of all kind of inclusions, 1250℃ is higher than the melting temperature of manganese sulfide and lower than the other of inclusions; 1400℃ is higher than the melting temperatures of aluminum nitride and manganese sulfide and lower than aluminum oxide and titanium nitride. According to EPMA、SEM-EDS (SEM-linescan and SEM-mapping) analysis the inclusions are complex composed of many kinds of other inclusions like aluminum oxide、titanium nitride、aluminum nitride and manganese sulfide. The sequence of inclusion crystallization and precipitation is aluminum oxide → titanium nitride → aluminum nitride → manganese sulfide.
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Wang, Baofeng. "Mould taper for high speed continuous casting of stainless steel billets." Thesis, 1999. http://hdl.handle.net/2429/9803.
Full textAbstract:
Over the past three decades, continuous casting has emerged as a dominant steel
production technology. Global competition and customer expectations are driving the
mini-mills to improve billet quality and increase productivity through increases in casting
speed. Although high speed casting trials are being carried out at many mini-mills, there is
still a lack of fundamental understanding about the influence of casting speed on mould
heat transfer. At the core of the technology is the water-cooled, oscillating copper mould.
Mould interaction with the billet, both thermal and mechanical, governs billet quality and
productivity. Heat transfer under high speed casting conditions needs to be determined in
order to design the taper of the mould.
The main objectives of this study were: to quantify the thermal-mechanical response
of the mould in the casting of austenitic stainless steel and martensitic stainless steel with
mathematical models; to evaluate the mould-billet interaction using mathematical models;
and to provide practical recommendations for optimum mould taper design in high speed
billet casting. Measurements were conducted on an operating billet casting machine at
Atlas Steel to determine mould-wall temperature profiles for different steel grades,
different casting speeds, mould flux types, oscillation frequency, off-center nozzle
operation. The trial also involved data acquisition on mould displacement, casting speed,
metal level. Samples of the billets cast at the trial were collected and process variables
were recorded. An inverse heat conduction model was utilized to determine mould heat
flux from measured mould wall temperatures and existing mathematical models were
utilized to investigate mould/billet interaction and mould taper using the heat flux as input.
Results from plant measurements, mathematical models and billet sample evaluation were
used to correlate mould thermal response with transverse and longitudinal depressions,
oscillation mark depths for different steel grades.
It was found from this work that mould heat flux is strongly influenced by casting
speed with mould flux lubrication. Increasing casting speed will consistently increase the
heat flux while the shell thickness will be reduced owing to the reduction of the residence
time of the strand in the mould.
This study has also shown the effect of casting conditions such as steel grade,
superheat and casting speed on mould taper requirements. Optimum mould tapers based
on the evaluation of the interaction between the mould and the billets are recommended
for austenitic and martensitic stainless steel billet casting.
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Ho, Yeong-Ho, and 何永和. "Modeling the Influence of Casting Condition on the Cleanliness of Molten Steel in Continuous Casting Mold." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/01422946310090997124.
Full textAbstract:
博士國立成功大學
材料科學(工程)學系
86
Abstract In continuous casting process, there are many factors that could affect the cleanliness of molten steel. One of the important factors is the unsuitable operation. It is necessary to appraise the effect of variable operating conditions for cleanliness of molten steel. In this study, a mathematical model that can calculate the flow pattern in casting mold and the trajectory of inclusions for variable sizes will be developed. The numerical method used in this study is explicit finite difference including full mesh system and partial mesh system. The calculating scheme based on SOLA and SOLA-SURF is developed from Los Alamos Laboratory of USA. And the calculating scheme is expanded to three dimension and it can predict the trajectory of nonmetallic inclusions. For the choice of numerical test, a slab caster with simple geometry is selected to check the mathematical model first. And the submerged nozzle alters the immersed depths and rotated angles. And then the round billet in 160mm diameter including three kinds of submerged nozzles is simulated. The pathlines of nonmetallic inclusions are calculated to estimate the cleanliness of melt. The results are rather satisfied. The geometry contour is more match the real caster in partial mesh system. Finally, to compare between the mathematical mode and water model is used to verify the accuracy.
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Singh, Himanshu. "Mould heat transfer in the high speed continuous casting of steel slabs." Thesis, 1998. http://hdl.handle.net/2429/8265.
Full textAbstract:
This investigation studies mould heat removal in operational slab casters. These include
both the conventional (or thick slab) as well as thin slab (of the CSP type)
casters. Mould wall temperatures and other data measured in-plant were analysed using
mathematical models developed by other researchers, in addition to new models
and commercial finite element software. The primary objective was the calculation of
mould heat fluxes, and how this related to aspects of caster operation and slab surface
quality.
Firstly, the mechanism of heat transfer in slab caster moulds postulated by previous
researchers was validated. Heat fluxes calculated for a billet caster using powder lubrication
showed that reducing cooling water velocities resulted in an increase in heat
transfer. This is due to higher mould hot face temperatures causing the formation of a
smaller slag rim, and a hotter, more fluid liquid flux.
This mechanism of mould heat transfer was used to resolve transverse corner cracking
in a newly commissioned conventional slab caster which had commenced high speed
casting. The problem was traced to inadequate mould lubrication and heat transfer,
caused by inordinately high water velocities. The incidences of cracking fell drastically
after a reduction in cooling water velocities.
Secondly, heat fluxes were calculated for the CSP caster. A big dip in heat fluxes was
seen in the central portion of the fixed broad face. It was postulated that this could
be due to a combination of water flow differential between the two broad faces, and a
squeezing in of the mould pocket bulge in the strand. Additionally, the two broad faces,
as well the narrow faces, were found to have unequal heat extraction rates.
Finally, the effect of the mould hot face temperature on the mould heat transfer was used
to develop a procedure of water velocity variation into the working life of CSP caster
moulds. Models were used to calculate water velocities which maintained a constant
hot face temperature, while the wall thickness reduced. It was found that the current
operational practice grossly over-estimated the water flows required in the latter stages
of the mould life.
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(11173431), Haibo Ma. "ON HEAT TRANSFER MECHANISMS IN SECONDARY COOLING OF CONTINUOUS CASTING OF STEEL SLAB." Thesis, 2021.
Find full textAbstract:
Secondary cooling during continuous casting is a delicate process because the cooling rate of water spray directly affects the slab surface and internal quality. Undercooling may lead to slab surface bulging or even breakout, whereas overcooling can cause deformation and crack of slabs due to excessive thermal residual stresses and strains. Any slab which does not meet the required quality will be downgraded or scrapped and remelted. In order to remain competitive and continuously produce high-quality and high-strength steel at the maximum production rate, the secondary cooling process must be carefully designed and controlled. Efficient and uniform heat removal without deforming or crack the slab is a significant challenge during secondary cooling. In the meantime, the on-site thermal measurement techniques are limited due to the harsh environment. In contrast, experimental measurements are only valid for the tested conditions, and the measurement process is not only labor-intensive, but the result might be inapplicable when changes in the process occur. On the other hand, the high-performance computing (HPC)-powered computational fluid dynamics (CFD) approach has become a powerful tool to gain insights into complex fluid flow and heat transfer problems. Yet, few successful numerical models for heat transfer phenomena during secondary cooling have been reported, primarily due to complex phenomena.
Therefore, the current study has proposed two three-dimensional continuum numerical models and a three-step coupling procedure for the transport of mass, momentum, and energy during the secondary cooling process. The first numerical model features the simulation of water spray impingement heat and mass transfer on the surface of a moving slab considering atomization, droplet dispersion, droplet-air interaction, droplet-droplet interaction, droplet-wall impingement, the effect of vapor film, and droplet boiling. The model has been validated against five benchmark experiments in terms of droplet size prior to impingement, droplet impingement pressure, and heat transfer coefficient (HTC) on the slab surface. The validated model has been applied to a series of numerical simulations to investigate the effects of spray nozzle type, spray flow rate, standoff distance, spray direction, casting speed, nozzle-to-nozzle distance, row-to-row distance, arrangement of nozzles, roll and roll pitch, spray angle, spray water temperature, slab surface temperature, and spray cooling on the narrow face. Furthermore, the simulation results have been used to generate a mathematically simple HTC correlation, expressed as a function of nine essential operating parameters. A graphic user interface (GUI) has been developed to facilitate the application of correlations. The calculated two-dimensional HTC distribution is stored in the universal comma-separated values (csv) format, and it can be directly applied as a boundary condition to on-site off-line/on-line solidification calculation at steel mills. The proposed numerical model and the generic methodology for HTC correlations should benefit the steel industry by expediting the development process of HTC correlations, achieving real-time dynamic spray cooling control, supporting nozzle selection, troubleshooting malfunctioning nozzles, and can further improve the accuracy of the existing casting control systems.
In the second numerical model, the volume-averaged Enthalpy-Porosity method has been extended to include the slurry effect at low solid fractions through a switching function. With the HTC distribution on the slab surface as the thermal boundary condition, the model has been used to investigate the fluid flow, heat transfer, and solidification inside a slab during the secondary cooling process. The model has been validated against the analytical solution for a stationary thin solidifying body and the simulation for a moving thin solidifying body. The effects of secondary dendrite arm spacing, critical solid fraction, crystal constant, switching function constant, cooling rate, rolls, nozzle-to-nozzle distance, and arrangement of nozzles have been evaluated using the validated model. In addition, the solidification model has been coupled with the predictions from the HTC correlations, and the results have demonstrated the availability of the correlations other than on-site continuous casting control. Moreover, the model, along with the three-step coupling procedure, has been applied to simulate the initial solidification process in continuous casting, where a sufficient cooling rate is required to maintain a proper solidification rate. Otherwise, bulging or breakout might occur. The prediction is in good agreement with the measured shell thickness, which was obtained from a breakout incident. With the help of HPC, such comprehensive simulations will continue to serve as a powerful tool for troubleshooting and optimization.
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Mukongo, Tshikele. "Effect of titanium pick-up on mould flux viscosity in continuous casting of titanium-stabilised stainless steel." Diss., 2003. http://hdl.handle.net/2263/28075.
Full textAbstract:
The behaviour of mould fluxes used in continuous casting of two Ti-stabilised stainless steels was investigated in terms of the level of titanium pick-up by the flux and the effect of this absorption of titanium on the viscosity of the fluxes. The two fluxes considered are respectively used for the casting of a ferritic steel (type 409) and an austenitic steel (type 321). Concerning the titanium pick-up (expressed as Ti02), the Ti02 content of the flux stabilised at about 3-4% for the mould flux of the ferritic steel and at about 6% for the mould flux of the austenitic steel after 20 minutes of casting. At the same time due to the reduction of Si02 in the molten flux by TiN and Ti in the steel the basicity of the mould flux of the ferritic steel increased from 0.8 to 0.9 while it increased from 0.95 to 1.2 for the mould flux of the austenitic steel. The SEM/EDS analysis of the sampled flux during casting showed only some spherical metallic droplets in the case of the mould flux of the ferritic steel but for the mould flux of the austenitic steel apart from the metallic droplets, some precipitates rich in Ca, Ti and O were identified in the glassy phases. Rotational viscometry carried out on the two fluxes showed that there is a decrease in the viscosity of the fluxes with the absorption of Ti02, Ti2O3 and Ti3O5 in the range of 2 to 10 wt%, for temperatures from 1400°C to 1200°C. The effect of Ti02 and Ti2O3 has been tested with the mould flux of the austenitic steel at a basicity of 1.2 to match the basicity which arises during casting. For temperatures of 12500C and below, the apparent viscosity of the flux increased markedly with the absorption of 10 % of Ti02 or Ti2O3. In both cases precipitation of perovskite (Ca2 Ti2O6 or Ca2 Ti2O5) was found to be responsible for the increase of the apparent viscosity of the flux of the austenitic steel.Dissertation (M Eng (Metallurgical Engineering))--University of Pretoria, 2006.
Materials Science and Metallurgical Engineering
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