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.

It is well known that REMs are strong oxide and sulphide formers that can easily form large clusters which have harmful effect on the casting process as well as the quality of the final steel product. By adding these elements right before casting, the number of narrow transfer parts are eliminated (compared to if added in ladle) Also, the REM inclusions has less time to sinter together to form large clusters, preventing clogging. The general idea behind this alloying method in the continuous casting machine is to feed a wire of FeSiRE powder blend, coated with a metal strip, into the melt in the chilled Cu mold (CC mold) Adding REMs to the steel, in particular Ce, can increase the resistance to oxidation at high temperatures by improving the properties of the chromia layer. This is of big interest for SANDVIK as it can improve their corrosion resistant grades and may also, in the future, enable alloying in with other volatile elements such as Zr. This master thesis has the objective to find out the dissolution time of the wire, coated with three different metal strips; Steel, Cu and Al. The experiments were performed with steel grade 316L, provided by SMT, in a 2kg melt in a lab scaled induction furnace at 1500oC, 1510oC and 1530oC. The operations were performed both with and without FeSiRE powder inside. The results obtained with powder inside at 1500oC showed that the Al wire experienced the shortest dissolution time ( 0,5 to 1s) followed by Cu (≤10s) and Steel (18 to 20s). In addition to this, sampling procedures was implemented ( 1, 1, 3, 5 10 and 29mins after wire addition) in a depth of 40mm for each wire. Here, the yield of Ce 1 minute after wire addition was highest for the Steel wire (41.9%) followed by Cu wire (25%) and Al wire (<14.8%). From samples taken 1 and 5mins after wire addition in the Al wire experiment, inclusions were extracted and collected on a film filter after electrolytic extraction and filtration. The film filter was observed in SEM. The morphology and compositions were analysed and compared. It was found that Ce and La was present as Ce La oxy sulfides both individually and on Al Mg O clusters.

Surface defects in steel slabs during continuous casting pose significant challengesfor quality control and product integrity in the steel industry. Predicting and classifyingthese defects accurately is crucial for ensuring product quality and minimizing productionlosses. This thesis investigates the effectiveness of machine learning models in predictingsurface defects of varying severity levels (ordinal classes) during the primary coolingstage of continuous casting. The study evaluates four machine learning algorithms,namely, XGBoost (main and baseline models), Decision Tree, and One-vs.-Rest SupportVector Machine (O-SVM), all trained with imbalanced defect class data. Model evaluationis conducted using a set of performance metrics, including precision, recall, F1-score,accuracy, macro-averaged Mean Absolute Error (MAE), Receiver Operating Characteristic(ROC) curves, Weighted Kappa and Ordinal Classification Index (OCI). Results indicatethat the XGBoost main model demonstrates robust performance across most evaluationmetrics, with high accuracy, precision, recall, and F1-score. Furthermore, incorporatingtemperature data from the primary cooling process inside the mold significantly enhancesthe predictive capabilities of machine learning models for defect prediction in continuouscasting. Key process parameters associated with defect formation, such as tundish temperature,casting speed, stopper rod argon pressure, and submerged entry nozzle (SEN) argonflow, are identified as significant contributors to defect severity. Feature importance andSHAP (SHapley Additive exPlanations) analysis reveal insights into the relationship betweenprocess variables and defect formation. Challenges and trade-offs, including modelcomplexity, interpretability, and computational efficiency, are discussed. Future researchdirections include further optimization and refinement of machine learning models andcollaboration with industry stakeholders to develop tailored solutions for defect predictionand quality control in continuous casting processes.

The thesis deals with optimization of the continuous slab casting process. The thesis summarizes the basic analytical and empirical findings concerning to the solidification process, the numerical modeling and the selected optimization techniques. Physical conditions and factors that affect the quality of steel including their relationships are also described. The basis of the solution strategy is the original numerical model of the temperature field in its off-line version. The numerical model was verified by the real historical data. The optimization part is based on the fuzzy logic implemented above the numerical model. The optimization algorithm is used for the optimal control of the casting process. The universal usage of the optimization model is demonstrated on several cases, e.g. the finding of optimal casting parameters that ensure the high quality of products, the optimal reactions on breakdown situations, the determination of an optimal relationship between casting parameters, etc. Based on optimization results, the suitable caster modification to increase the surface temperature at the unbending point was proposed. The whole concept of the numerical and optimization model is general and it can be applied to arbitrary slab or billet continuous casting.

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.

Un système est souvent caractérisé par plusieurs modes de fonctionnement, chacun pouvant alors être décrit par un modèle qui lui est propre. Dans le cas où la commutation entre les modes de fonctionnement résulte d'un processus inconnu (un défaut, un changement de condition,...), il est difficile de manipuler ces systèmes et d'appliquer les commandes appropriées. Cette thèse traite du problème de la détection du changement de mode d'un système. A partir d'un système partiellement supervisé (connaissance du nombre de mode de fonctionnement du système ainsi que de la structure du modèle représentant chaque mode), une méthode est développée pour détecter le mode de fonctionnement actif du système à chaque instant. Pour cela, l'analyse du gradient des résidus obtenu par la multiplication des modèles locaux entre-eux, permet de caractériser le mode de fonctionnement. Une application de cette méthode est réalisée sur des données simulées et réelles de coulée continue de l'acier, afin de détecter un phénomène particulier : le collage. Finalement, une méthode par rejet de mode est mise en place sur des données réelles thermiques dans le même but (la détection des collages en lingotière de coulée continue) / Most of time a system is characterized by few operating modes, each of them could be describe by a model. In the case of the commutation between each operating mode is due to unknown process (fault, changing in condition,) it could be difficult to operate with this system and used the appropriate commands. With a partially supervised system (knowing of number of operating mode and model structure that represent each mode), a method is developed to detect the active operating mode at each time. Indeed, the analyses of the residual gradient, that obtain by product each local model together, permit to characterize the operating mode. Application of this method is presented with simulated data and industrial data of continuous casting to detect a particular phenomenon: the sticker. Finally, a rejection mode method is used on industrial thermal data in the same aim (detection of stickers in continuous casting)

<p>The present dissertation describes part of the efforts directed towards the development of computational tools to support process modeling. This work is also a further development of the Thermoslag software developed in the Division of Materials Process Science, KTH.</p><p>The essential parts of the thesis are</p><p>a) development of a semi-empirical model for the estimation of the molar volumes/densities of multicomponent slags with a view to incorporate the same in the model for viscosities and</p><p>b) further development of the viscosity model for application towards fluorid- containing slags, as for example, mould flux slags.</p><p>The model for the estimation of molar volume is based on a correlation between the relative integral molar volume of a slag system and the relative integral molar enthalpies of mixing of the same system. The integral molar enthalpies of the relevant systems could be evaluated from the Gibbs energy data available in the Thermoslag software. The binary parameters were evaluated from experimental measurements of the molar volumes. Satisfactory correlations were obtained in the case of the binary silicate and aluminate systems. The model was extended to ternary and multi component systems by computing the molar volumes using the binary parameters. The model predictions showed agreements with the molar volume data available in literature. The model was used to estimate the molar volumes of industrial slags as well as to trace the trends in molar volume due to compositional variations. The advantage of the present approach is that it would enable prediction of molar volumes of slags that are compatible with the thermodynamic data available.</p><p>With a view to extend the existing model for viscosities to F--containing slags, the viscosities of mould flux slags for continues casting in steel production have been investigated in the present work. The measurements were carried out utilizing the rotating cylinder method. Seven mould fluxes used in the Swedish steel industry and the impact of Al₂O₃pick up by mould flux slags on viscosities were included in the study. The results showed that even relatively small additions of Al₂O₃ are related with a significant increase in viscosity</p>

Submitted by Ronildo Prado (ronisp@ufscar.br) on 2017-08-23T14:10:16Z No. of bitstreams: 1 DissPICC.pdf: 9243099 bytes, checksum: d5c4984be722eda91236fbec51d566f6 (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-08-23T14:10:24Z (GMT) No. of bitstreams: 1 DissPICC.pdf: 9243099 bytes, checksum: d5c4984be722eda91236fbec51d566f6 (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-08-23T14:10:29Z (GMT) No. of bitstreams: 1 DissPICC.pdf: 9243099 bytes, checksum: d5c4984be722eda91236fbec51d566f6 (MD5) / Made available in DSpace on 2017-08-23T14:10:35Z (GMT). No. of bitstreams: 1 DissPICC.pdf: 9243099 bytes, checksum: d5c4984be722eda91236fbec51d566f6 (MD5) Previous issue date: 2017-02-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / New materials from cellulose have been developed, such as cellulose nanocrystals (CNC) and cellulose nanofibrils (CNF). Different morphologies of the cellulose can lead to the formation of films with different thermal, mechanical and optical properties in relation to conventional cellulose films. The objective of this work was to evaluate the effect of different dimensional scales of cellulose, micro and nanometric, on the production of cellulose films from two vegetable species and their thermal, mechanical, morphological and optical properties. Eucalyptus fibers and pineapple leave fiber (curauá) (PALF) were used as cellulosic fibers for this study. The films of eucalyptus and pineapple cellulosic fibers were prepared by filtration and casting, and the CNC and CNF films were obtained by continuous casting. The CNC and CNF films showed mechanical tensile strength in the order of 9 to 35 MPa higher than the films of cellulose fibers, regardless of the origin of the fiber. The continuous casting process produced CNC and CNF films that presented different mechanical resistance in the longitudinal direction of the process with respect to the transverse direction. This behavior may be related to how hydrogen bonds and mechanical anchorages occur between nanofibers. The thermal stability of the nanocellulose films was lower in the order of 20 to 150 ºC than in the films of fibers due to the routes of obtaining the CNC and CNF. Nanofiber films presented lower opacity in the order of 3 to 60% lower than the films of fibers due to the diameter of the nanocelluloses. Curauá fibers had the highest crystallinity index (Ic) reaching 87%. It is concluded that the properties studied were influenced by the type of nanocellulose (CNC or CNF), the origin of the cellulose (eucalyptus or pineapple), and the micro and nanometric scale of the fibers. / Novos materiais a partir da celulose tem sido obtidos, como os nanocristais de celulose (CNC) e as nanofibrilas de celulose (CNF). Diferentes morfologias da celulose podem levar a formação de filmes com propriedades térmicas, mecânicas e ópticas diferentes de filmes de celulose convencional. O objetivo deste trabalho foi avaliar o efeito de diferentes morfologias de fibras de celulose, micro e nanométricas, na obtenção de filmes - provenientes de duas espécies vegetais – e em suas propriedades térmicas, mecânicas, ópticas e morfológicas. Utilizou-se como fibras celulósicas para este estudo as fibras de eucalipto e fibras de folhas de abacaxi (curauá) (PALF). Os filmes de fibras celulósicas de eucalipto e de abacaxi foram confeccionados por filtragem e casting, e os filmes de CNC e CNF foram obtidos por continuous casting. Os filmes de CNC e CNF apresentaram resistência mecânica à tração, na ordem de 9 a 35 MPa superior aos filmes de fibras de celulose, independente da origem da fibra. O processamento por continuous casting produziu filmes de CNC e CNF que apresentaram resistência mecânica diferente no sentido longitudinal ao processo com relação ao sentido transversal. Este comportamento pode estar relacionado de que forma ocorrem às ligações de hidrogênio e os emaranhamentos mecânicos entre as nanofibras. A estabilidade térmica dos filmes de nanofibra foi menor na ordem de 20 a 150 ºC do que aos filmes de fibras devido às rotas de obtenção das CNC e CNF. Os filmes de nanofibra apresentaram menor opacidade, na ordem de 3 a 60% inferior, que os filmes de fibras devido ao diâmetro das nanofibras. As fibras de curauá apresentaram o maior índice cristalinidade (Ic) chegando a 87%. Conclui-se que a propriedades estudadas foram influenciadas pelo tipo de nanofibra (CNC ou CNF), pela origem da celulose (eucalipto ou abacaxi), e pela escala micro e nanométrica das fibras.

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.

The demand for higher quality steel and higher production rates in the production of steel slabs is ever increasing. These slabs are produced using a continuous casting process. The molten steel flow patterns inside the components of the caster play an important role in the quality of these products. A simple yet effective design method that yields optimum designs is required to design the systems influencing the flow patterns in the caster. The tundish is one of these systems. Traditionally, experimental methods were used in the design of these tundishes, making use of plant trials or water modelling. These methods are both costly and time consuming. More recently, Computational Fluid Dynamics (CFD) has established itself as a viable alternative to reduce the number of experimentation required, resulting in a reduction in the time scales and cost of the design process. Furthermore, CFD provides more insight into the flow process that is not available through experimentation only. The CFD process is usually based on a trial-and-error basis and relies heavily on the insight and experience of the designer to improve designs. Even an experienced designer will only be able to improve the design and does not necessarily guarantee optimum results. In this thesis, a more efficient design methodology is proposed. This methodology involves the combination of a mathematical optimiser with CFD to automate the design process. The methodology is tested on a four different industrial test cases. The first case involves the optimisation of a simple dam-weir configuration of a single strand caster. The position of the dam and weir relative to inlet region is optimised to reduce the dead volume and increase the inclusion removal. The second case involves the optimisation of a pouring box and baffle of a two-strand caster. In this case, the pouring box and baffle geometry is optimised to maximise the minimum residence time at operating level and a typical transition level. The third case deals with the geometry optimisation of an impact pad to reduce the surface turbulence that should result in a reduction in the particle entrainment from the slag layer. The last case continues from the third case where a dam position and height is optimised in conjunction with the optimised impact pad to maximise the inclusion removal on the slag layer. The cases studies show that a mathematical optimiser combined with CFD is a superior alternative compared to traditional design methods, in that it yields optimum designs for a tundish in a continuous casting system. / Thesis (PhD (Mechanical Engineering))--University of Pretoria, 2006. / Mechanical and Aeronautical Engineering / unrestricted