Impinging oxygen jets are widely used in steelmaking industries. The momentum transfer from the gas to liquid and resulting instability affect the overall productivity and operational stability. The purpose of this research is to understand the surface deformation, its stability and momentum transfer from the gas to the liquid. Video imaging and Particle Image Velocimetry were used along with water modelling techniques. Surface deformations mainly followed the dimensionless relationship of previous researchers. The surface instability was interpreted with Blowing number and Kelvin-Helmholtz instability. Spatial and time oscillation behaviour were analyzed with Power Spectral Density analysis. A new mathematical model with the full stress boundary condition at the surface was developed. The technique combines the Cartesian Cut Cell and Volume of Fluid method and the surface boundary was modelled a a pressure boundary. The numerical code was tested with the Broken Dam and wave instability problems. Both showed good agreement with the reported physical phenomena. Numerical tests of impinging jets showed similar surface depression depth with the water model experiments. The model was compared with other models. The liquid momentum level was higher as the gas fiowrate increased and the effects of physical property changes on surface instability and momentum transfer efficiency were investigated with the mathematical model. With observations from the numerical test, momentum transfer mechanisms were proposed. Simulations of momentum transfer at industrial flow rates were also carried out. / Thesis / Doctor of Philosophy (PhD)

The cleanliness of steel impacts the success of steel production and the physical and chemical properties of the final product. Improving the cleanliness of steel, therefore, becomes a necessity in the present time, with an ever-increasing demand for high-quality steel products. The cleanliness can be improved by removing the harmful inclusions through flotation or by modifying their composition and morphology to less detrimental forms. The present study focuses on better understanding the second approach, a specific modification method commonly known as the calcium (Ca) treatment in advanced high strength steel (AHSS) production. The chemical and morphological evolutions of Al2O3 inclusions under experimental and industrial conditions, as well as the formation of CaS and MnS inclusions, were studied in this work. Six laboratory experiments with different combinations of calcium and sulfur contents of liquid steel were conducted. Samples were taken at different time durations after calcium addition. The inclusions on the sample cross-sections were analyzed using an automated SEM-EDS system to obtain their chemical, size distribution, population, and morphological information. Similar steps were taken in the analysis of industrial samples. The findings obtained based on the automated SEM-EDS analyses were further supported and validated against other analysis results such as manual SEM analysis, thermodynamics, and kinetics calculations. The modification mechanism for Al2O3 inclusions was established in the first part of the study. After adding 10 ppm, 20 ppm, and 35 ppm Ca, small-sized calcium aluminates CAx (C and A denote CaO and Al2O3, respectively) inclusions become the primary oxygen bearer instead of Al2O3 inclusions. The modification extent of the CAx inclusions depends on the Ca content. CaS inclusions also form at the early stage of calcium treatment. In the later stage, CaS inclusions act as the Ca source to modify the remaining Al2O3 inclusions to CAx inclusions and simultaneously modify the existing CAx inclusions until equilibrium is reached. CaO inclusions only form in steel containing 20 ppm S and 35 ppm Ca; the primary oxygen bearer will change from Al2O3 to CaO, followed by a transformation from CaO to CaS. In other S and Ca contents, CaO inclusions do not form. This finding clarified that modification of Al2O3 inclusions is mainly driven by dissolved Ca and CaS inclusions, with CaO showing a minor direct impact. Moreover, the experimental studies showed that total area fractions of liquid and semi-liquid inclusions, which are inclusions that are partially liquid and partially solid, are correlated with the thermodynamic stability of CaS inclusions. The fraction of liquid inclusions decreases after the area fraction of CaS inclusions drastically increases when steel chemistries allow stable CaS inclusions to precipitate. The correlation between the steel chemistries and inclusions was improved by iv incorporating more data from industrial heats. Three modification indexes were proposed to estimate the control of CAx, CaS, and MnS inclusions. The fraction of CAx inclusions with more than 50 pct liquid, and the area fraction of CaS and MnS inclusions in tundish samples were correlated with the Ca, Al, Mn, and S contents of liquid steel. Later, these modification indexes were incorporated to evaluate the effectiveness of calcium treatment quantitatively. This makes the present study the first to discuss the correlations between Ca, Al, Mn, and S contents and the number of inclusions in the open literature. The correlations were validated against industrial data, they may be used in industry to determine the optimum Ca content for inclusion control and modification. Based on the experimental and industrial data, the coarsening of CaS inclusions was initially governed by mass transport, then shifted to collision-related mechanisms. When agitation is absent, Brownian motion shows the most significant impact on the growth of CaS inclusions, while turbulent flow is the critical cause of collision and coagulation when the melt is stirred, such as in industrial conditions. It has been found that CAx inclusion growth mainly occurs in the early stage after Ca addition. The potential reason is that the lack of attraction prevents coagulation after CAx inclusions are modified to liquid and semi-liquid. / Thesis / Doctor of Philosophy (PhD)

<p><strong> </strong></p> <p><strong> </strong></p> <p>Considerable attention has been paid to the reaction between molten iron oxide containing slag and iron droplets or solid carbon due to the critical roles it plays in various metallurgical processes. However, during the last two decades, most of the studies have been carried out on iron droplets, for which the size remains constant. Another important phenomenon, that the droplet will swell has not been paid the same attention. Knowledge of the extent of droplet swelling is essential in predicting residence times in BOF steelmaking. The objective of this study is to develop the understanding for droplet swelling and produce a predictive model that predicts droplet swelling over the range of oxygen steelmaking conditions.</p> <p>Several workers have observed swelling of high carbon droplets when exposed to oxidizing slags. In the present work, the measurements on swelling rates were made using X-ray fluoroscopy. Comparing the swelling rate with the total volume of gas evolved during the reaction, it is shown that only a small percentage of the gas generated is retained in the droplet to contribute to swelling. The gas generation rate is shown to be controlled by the rate of nucleation of CO bubbles inside the droplet. The critical supersaturation pressure for nucleation is found to be two orders of magnitude less than predicted from theory, which is in keeping with many other studies on nucleation of gases in liquids. However, the effect of surface tension, temperature and saturation pressure shows quantitative agreement with theory.</p> <p>In order to predict the droplet swelling rate, CO bubble escape rate has to be known. In this research, the escape mechanism has been proposed; it is the film rupture around the iron droplet surface. The rupture rate is mainly influenced by viscosity, surface tension and bubble size. For a given experimental condition, the calculated film thickness is 1.5 μm at the maximum drop diameter, assuming the bubble radius is 0.3 mm. The CO escape rate is 2.51 cm³/s, it agrees well with 1 to 12 cm³/s when gas escapes from steelmaking slags considering the differences of surface tensions and viscosities between metal and slag.</p> / Doctor of Philosophy (PhD)

京都大学 / 新制・課程博士 / 博士(エネルギー科学) / 甲第25403号 / エネ博第482号 / 京都大学大学院エネルギー科学研究科エネルギー応用科学専攻 / (主査)准教授 長谷川 将克, 教授 土井 俊哉, 教授 藤本 仁 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: In modern steelmaking a tundish serves as an important metallurgical reactor to remove inclusions and maintain thermal and chemical homogeneity in the product. In this study the flow behaviour in a four strand tundish was investigated by means of a 1/2 scale water model, based on Froude number similarity, as well as by using numerical modelling. Both the numerical study and physical model were used to characterise residence time distribution (RTD) in the vessel and to calculate properties pertaining to the tundish flow regime. The three different tundish configurations investigated in this study are: a bare tundish with no flow control devices, a tundish with a turbulence inhibitor and a tundish using a turbulence inhibitor with holes in combination with dams. Preliminary investigations focussed on the framework for obtaining an accurate numerical solution within reasonable computational times. The effect of assuming symmetry and dynamically steady flow in the numerical model was shown to be small relative to the effect of grid size and justifiable by the savings in computational time. The grid independence study indicated the importance of using a finer mesh in areas of high velocity gradients to obtain realistic results and also to limit the number of computational cells. A procedure using gradient adaptation was used to refine the mesh automatically in the required regions for different tundish geometries. Results also showed that the inlet boundary of the numerical model should be selected at the ladle outlet, since assuming a flat velocity profile at the nozzle port resulted in significant changes in the RTD response. Comparison of the results obtained using the numerical model with those from physical experiments yielded an average error of less than 10%. This was assumed to be a good prediction, considering the assumptions employed in the numerical model. Both the physical and numerical models showed that a tundish without flow control devices was prone to significant short circuiting. The addition of a turbulence inhibitor was shown to be successful in preventing short circuiting and provided surface directed flow, which is thought to aid inclusion removal in the slag. Additionally, the minimum, peak and mean residence times and plug flow volume fraction were increased significantly, while the dead volume fraction decreased. However, using a turbulence inhibitor with holes in combination with dams showed that this configuration may cause increased refractory wear together with increased risk of slag entrainment due to flow patterns with increased surface turbulence. It also showed that the short-circuiting might not be eliminated completely. This indicates that certain design changes to tundish flow control systems can introduce problems that outweigh the benefits of the altered flow patterns. Furthermore, the numerical method, which was based on the water model, was modified to simulate the high temperature steel process. A very good match was obtained between the results using the two different numerical models. This serves as additional evidence that tundish water modelling based on Froude number similarity provides a good representation of the actual industrial process. Using the numerical model based on the high temperature steel process the effect of turbulence inhibitor shape was studied for four different turbulence inhibitor designs. Results showed the best performance, based on flow characteristic properties and surface turbulence values, was achieved for the design using a rectangular box-like shape with flanges at the top. However, the comparison emphasized the effect of the turbulence inhibitor shape on the flow behaviour, as each design yielded completely different flow patterns. It was also observed that a good turbulence inhibitor provided an optimum amount of turbulent suppression. Insufficient suppression would cause fast flows, which will result in insufficient residence time for inclusion flotation and high surface turbulence values, which may cause slag entrainment. On the other hand, too much suppression may increase the variation between strands. / AFRIKAANSE OPSOMMING: Die verdeeltrog speel ‘n belangrike rol in die moderne staalvervaardigingsproses deur inklusies te verwyder en termiese en chemiese homogeniteit in die produk te verseker. In hierdie studie is die vloeigedrag in ‘n verdeeltrog met vier uitlate bestudeer deur middel van ‘n 1:2-skaal watermodel, gebaseer op Froude-getal gelykheid, sowel as deur numeriese modellering. Beide die numeriese en watermodel is gebruik om die verblyftyd-distribusie in die trog te karakteriseer en om waardes te bereken wat die vloeigedrag in die verdeeltrog beskryf. Drie verskillende verdeeltrog-opstellings is in hierdie studie bestudeer, naamlik: ‘n leë verdeeltrog met geen vloeibeheertoestelle nie, ‘n verdeeltrog met ‘n turbulensie- inhibeerder en ‘n verdeeltrog wat gebruik maak van ‘n turbulensie-inhibeerder met gate, gekombineer met lae damwalle. Vroeë ondersoeke het gefokus op ‘n metode om akkurate numeriese resultate binne aanvaarbare tye te verkry. Die invloed van die aannames van simmetrie en dinamiese gestadigde vloei op die resultate is bepaal om klein te wees teenoor dié van die roostergrootte. Die gebruik van die aannames is dus geregverdig deur die afname in berekeningstyd wat dit meebring. Die roosteronafhanklikheidstudie het getoon dat dit belangrik is om die vloeivergelykings oor klein volume-eenhede op te los in areas van hoë snelheidsgradiënte, beide om realistiese resultate te verseker en om die aantal volume-eenhede te beperk. ‘n Prosedure wat gebruik maak van gradiëntaanpassing is gebruik om die roostergrootte outomaties te verklein in die areas met hoë snelheidsgradiënte vir verskillende verdeeltrog-opstellings. Resultate het ook getoon dat dit belangrik is om die inlaatgrens van die numeriese model by die smeltpot se uitlaat te kies, aangesien noemenswaardige verskille in die verblyftyd-distribusie waargeneem is wanneer ‘n uniforme snelheidsprofiel aanvaar is waar die metaal die verdeeltrog binnegaan. Daar is gevind dat die resultate by die numeriese en watermodelle verskil met ‘n gemiddelde fout van ongeveer 10%. Dit word beskou as ‘n goeie ooreenstemming, as die aannames wat in die numeriese model gebruik word in ag geneem word. Beide die numeriese en watermodelle het getoon dat die metaalvloei in die leë verdeeltrog geneig is om die kortste roete na die uitlate te kies. Deur van ‘n turbulensie inhibeerder gebruik te maak word hierdie probleem opgelos deur die metaalvloei opwaarts te forseer. In die proses neem die minimum-, piek- en gemiddelde verblyftye, sowel as die propvloei volumefraksie, toe, terwyl die dooievloei fraksie afneem. Die turbulensie inhibeerder met die gate en die lae damwalle is egter meer geneig tot erosie van die vuurvaste materiaal en kan ook vloeipatrone veroorsaak wat metaalskuimdruppels in die metaal kan opneem. Verder volg ‘n klein fraksie van die vloei steeds ‘n kortpad na die uitlaat. Hierdie resultate toon dat sekere veranderings aan verdeeltrog vloeibeerheerstelsels nadelige gevolge kan hê wat enige positiewe gevolge uitkanselleer. Verder is die numeriese metode wat tot dusver op die watersisteem gebaseer is, aangepas om die vloei in die hoëtemperatuur staalproses te simuleer. ‘n Baie goeie vergelyking is verkry tussen die resultate wat die twee numeriese modelle voorspel. Hierdie dien as ‘n verdere bewys dat ‘n watermodel, wat op Froude-getal gelykheid gebaseer is, die industriële proses akkuraat kan simuleer. Deur gebruik te maak van die numeriese model van die hoë temperatuur staalproses, is die effek van die turbulensie-inhibeerder se vorm vir vier verskillende ontwerpe bestudeer. Die studie het getoon dat die beste resultate vir vloeikarakteriserende eienskappe en oppervlak- turbulensie verkry is met ‘n reghoekige ontwerp. Die resultate beklemtoon egter die belangrikheid van die invloed van die turbulensie-inhibeerder se vorm op die vloeigedrag in die verdeeltrog, aangesien elke vorm noemenswaardige verskillende vloeipatrone opgelewer het. Daar is opgemerk dat ‘n goeie turbulensie-inhibeerder ‘n optimale hoeveelheid turbulensie onderdrukking veroorsaak. In die geval van te min onderdrukking is die verblyftye te kort en die oppervlak turbulensie te hoog. Te veel onderdrukking kan egter lei tot groot variasie in die eienskappe van die metaal by die verskillende uitlate.

The interest of gaining on-line information related to non-metallic inclusions during the steelmaking process has recently increased due to the development as well as the promising results of the Pulse Distribution Analysis with Optical Emission Spectroscopy method (PDA/OES). Even though, the time from sampling to presented results on inclusions is only about 5-10 minutes, the method has also shown limitations with respect to the determination of some inclusion characteristics. Therefore, a first step was to perform a study on other methods such as the cross-section method (CS) on a polished sample surface, the cross-section after etching method (CSE), the bromine-methanol extraction method (BME), and the electrolytic extraction method (EE). This study focused on the evaluation of these methods with respect to the time consumption for preparation and analysis of a sample, the analyzed volume and the determination of inclusion and cluster characteristics such as size, number, particle size distribution (PSD) and composition. The CS and CSE methods were found to be suitable in the determination of the largest cluster in a sample which can be recommended in order to select proper extraction parameters for further studies. The BME method was considered to be fast with the possibility of analyzing a large volume. However, the used solution is chemically stronger compared to electrolytic extraction solutions, which can affect the results. In most aspects, the EE method was found to be the most stable, reliable and accurate method with some limitations regarding the time aspect. Based on this conclusion, the EE method was selected for a comparative study with the PDA/OES method. Reliably detected size ranges by using the PDA/OES method were defined for two low-alloyed steel grades. These are 2.0-5.7 μm and 1.4-5.7 μm for steel samples taken before and after a Ca-addition during the secondary steelmaking, respectively. Moreover, agreements between the EE and PDA/OES methods were observed in the average size and number of detected inclusions when only inclusions with the size &gt; 2 μm were considered. Also, a theoretical minimum size and a maximum number ofinclusions present in the steel sample, which can be detected by using the PDA/OES method, were estimated. The work continued by successfully applying the EE method to study correlations between inclusions observed in the liquid steel samples and in a clogged nozzle (clogging material). It was found that the average sizes of spherical and non-spherical inclusions observed in the steel corresponded well with those observed in the clogging material. However, there were some differences in the frequencies of these inclusions. This was explained by a possible transformation of the present inclusions due to a reoxidation and a reaction with the nozzle refractory of the steel melt. The results of this study may contribute in the selection of proper process parameters or inclusion characteristics for future studies on the improvement and application of on-line methods. Finally, suggestions on how to present and interpret data obtained by the PDA/OES method during production of stainless steels were given in the present thesis. More specifically, the possibilities of defining operating windows with respect to inclusion composition and the use of a B-factor for Al (the total content of Al in inclusions detected by using the PDA/OES method) during the secondary steelmaking were discussed. In addition, a correlation study between B-factors for Al and numbers of inclusions (dV &gt; 4 μm) obtained by using the PDA/OES method on process samples, and corresponding slivers indices from plate products was performed. The results showed a moderate correlation between these parameters as well as an increase of the slivers index with increased values of the chosen PDA/OES data. This indicates that it could be possible to predict when there is an increased risk of having slivers on the final rolled product at an early stage of the steelmaking process. / <p>QC 20150525</p>

The thesis starts by giving a motivation to materials modeling as a way to increase profitability but also a possibility decrease the environmental impact. Fundamental concepts of relevance for this work are introduced, this include the materials genome, ICME and of course the CALPHAD method. As a demonstration promising results obtained by an ICME approach using genetic algorithms and CALPHAD on the vacuum degassing process are presented. In order to make good predictive calculations and process models it is important to have good thermodynamic descriptions. Thus most part of the work has concerned the thermodynamic assessments of systems of importance for steelmaking, corrosion and similar processes. The main focus has been the assessment of sulfur-containing systems and thermodynamic descriptions of the Fe-Mn-Ca-Mg-S, Fe-Ca-O-S, Fe-Mg-O and Mg-Mn-O systems are presented. In addition, heat capacity measurements of relevance for the Mg-Mn-O system have been performed. To summarize the efforts some application examples concerning thermodynamic calculations related to steelmaking and inclusion formation are shown. / <p>QC 20160829</p> / COMPASS

[pt] O presente estudo foca o comportamento da redução da ferrita de zinco produzida em laboratório e a contida nos pós de aciaria elétrica (PAE) pelo CO puro e misturas COCO2, esta última tomada como exemplo de um caso real. Este trabalho se iniciou com a caracterização dos principais compostos presentes no PAE (óxido de ferro (III), óxido de zinco e ferrita de zinco) usando técnicas, metodologias e equipamentos para caracterizações térmica (ATD-ATG), estrutural (DRX), microscópica (MEV-MET analise de EDS), física (porosidade do briquete, massa especifica, tamanho médio e área superficial específica das partículas) e química. Constatou-se que as partículas dos materiais estudados são predominantemente de geometria esférica e, em particular o estudo via MET da ferrita de zinco, revelou aglomerados micrométricos e homogêneos tipo clusters, formados por partículas arredondadas e constituídas por alguns monocristais com tamanhos da ordem de 100 nm. Com a finalidade de estudar a cinética de redução da ferrita de zinco, foram realizados ensaios de redução por CO puro e misturas gasosas formadas por: 75 por cento CO-25 por cento CO2 e 50 por cento CO-50 por cento CO2 nas temperaturas de 1073, 1173, 1223, 1273 e 1373K. O tempo máximo de redução foi de 105 min. Os resultados obtidos permitiram propor uma sequência cinética de redução, ao longo da qual os principais produtos de redução da ferrita de zinco foram caracterizados via MEV, visando estabelecer a fenomenologia/morfologia da redução. Conclui-se que a fenomenologia morfológica e cinética da redução da ferrita de zinco, embora complexa, é similar a da redução dos óxidos de ferro, dependendo das composições gasosas, temperatura e tempo de reação. O estudo morfológico permitiu constatar que a redução da ferrita de zinco evidencia sua decomposição nos óxidos constituintes (ZnO e Fe2O3), na faixa de 1073 a 1273K e a redução sequencial do óxido de zinco e dos óxidos de ferro. Os típicos produtos sólidos da redução são: óxido de zinco (ZnO), wüstita (FeO), óxidos mistos do tipo (Zn, Fe)O e ferro metálico. O estudo cinético estabeleceu ainda que ocorre uma rápida redução do óxido de zinco, liberando zinco gasoso, evidenciando a seguinte sequência de redução: primeiramente, o óxido de zinco se reduz, seguido dos óxidos de ferro. Isto ocorre significativamente nas temperaturas entre 1223 e 1373K. Estabeleceu-se um modelo geral de redução da ferrita de zinco usando a metodologia de superfície resposta (RSM), que envolveu o planejamento estatístico fatorial 3(4) para avaliar a influência dos fatores preestabelecidos sobre a (porcentagem) Redução (temperatura e tempo de reação, composição gasosa, e massa da amostra). Os modelos cinéticos que melhor ajustaram os mecanismos de redução foram: o modelo de reação química de interface-simetria esférica, seguido pelo modelo exponencial de reação contínua, representados por: [1 - raiz cúbica de (1 -alfa)] = kt e −ln(1 -alfa) igual a kt , respectivamente. O modelo de reação química de interface - simetria esférica, representado por: [1 - raiz cúbica de (1 - alfa)] = kt foi o que melhor adequou-se à redução da ferrita de zinco sintética. Os parâmetros cinéticos obtidos foram: (a) 100 por cento CO: Ea de 55,60 kJ/mol e A igual a 8,833 mHz; (b) 75 por cento CO-25 por cento CO2: Ea igual a 88,21 kJ/mol e A igual a 127,74 mHz; (c) 50 por cento CO-50 por cento CO2: Ea igual a 95,21 kJ/mol e A igual a 193,37 mHz; De maneira similar, no caso da redução da ferrita de zinco presente no PAE, o modelo que melhor representou o processo, também foi o modelo de reação química de interface - simetria esférica, representado por: [1 - raiz cúbica de (1 - alfa)] igual a kt , sendo, Ea (energia de ativação aparente) e A (constante pré-exponencial de Arrhenius), os parâmetros cinéticos obtidos: (d) 100 por cento CO: Ea igual a 52,34 kJ/mol, e A igual a 4,98 mHz; (b) 75 por cento CO-25 por cento CO2: Ea igual a 66,70 kJ/mol e A igual a 76,06 mHz; (c) 50 por cento CO-50 por cento CO2: Ea igual a 86,28 kJ/mol e A igual a 289,59 mHz. A comparação entre as energias de ativação aparente, permitiu concluir que tanto a redução da ferrita de zinco sintética como a redução dos Pós de Aciaria Elétrica-PAE, tiveram como etapa controladora da reação global a redução dos óxidos de ferro, particularmente para a redução com 100 por cento CO. No caso da redução com misturas COCO2, isto não foi observado para a ferrita de zinco sintética, embora possa ser válida para os Pós de Aciaria Elétrica-PAE, considerando seu baixo teor de zinco. Assim, para o caso da redução da ferrita de zinco por misturas CO-CO2, propõe-se como etapa controladora a redução simultânea do óxido de zinco e dos óxidos de ferro. / [en] This work deals with the behavior of the synthetic zinc ferrite reduction as well as a case study for the same process using electric arc furnace dusts (EAFD). These processes were conducted under pure CO atmosphere and CO-CO2 gas mixtures. The research here reported onsets with the characterization of the compounds present in EAFD - Iron (III) oxide, zinc oxide and zinc ferrite - using techniques, methodologies and equipments for thermal characterization (DTA-TGA), structural (XRD), microscopic (SEM-TEM coupled to EDS), physical (briquette porosity, specific gravity, average size and particle specific surface) and chemical analysis. It was found that the studied materials particles showed predominantly spherical geometry and in particular, the TEM scans in the zinc ferrite, reveled cluster type micrometric and homogeneous agglomerates formed from single crystal round particles having the size of circa 100 nm. Aiming at the study of the kinetics of the zinc ferrite reduction experiments were conducted using synthetic and EAFD materials submitted to pure CO gas and mixtures of it with CO2 in the following proportions: 75 per cent CO-25 per cent CO2 e 50 per cent CO-50 per cent CO2. The runs were conducted at the temperatures 1073, 1173, 1223, 1273 e 1373K and the maximum reaction time was 105 min. The obtained results permitted the proposal of a kinetic reduction reaction chain. In the course of the study, also, the main zinc ferrite reduction products were characterized by the SEM analysis. This analysis also permitted the observation of phenomenological and morphological correlations during the process. It was concluded that the morphological and kinetic zinc ferrite reduction, in spite being a complex process, it is similar to iron oxides reduction, meaning, dependent on the gaseous compositions, temperature and reaction times. The morphological prism permitted to propose that the zinc ferrite reduction denounces its instantaneous decomposition in their constituent oxides (ZnO and Fe2O3) when submitted to temperatures in the range of 1073 to 1273K and also the sequential reduction of zinc and iron oxides. The typical reduction products were zinc oxide (ZnO), wüstite (FeO) and mix oxides type (Zn, Fe) O and metallic iron. Again, the kinetic study established that a rapid reduction of the zinc oxide occurs, as compared to the other present oxides, through the sequence: firstly the zinc oxide reduction takes place, and this is followed by the iron oxides reduction. The last processes occur significantly for temperatures in the range of circa 1223 to 1373K. A general model of the zinc ferrite reduction by the gaseous mixture of CO-CO2 was proposed using the response surface methodology (RSM) for the factorial analysis 3(4). This was done evaluating the effect of the following variables: temperature, reducing atmosphere composition, specimen mass and reaction time over the (percentage)Reduction. The kinetic models that presented the better adjustment for the reduction were the boundary chemical reaction model for spherical symmetry (BCRM ss) with the equation [1 - cubic root (1 - alfa)] equal kt and the model of simple exponential continuous reaction obeying the relation: − ln(1 - alfa) equal kt . The kinetic parameters obtained (Ea, apparent activation energy, and A, Arrhenius preexponential frequency fator) were for the first model, that is synthetic zinc ferrite: (a) 100 per cent CO gas: Ea equal 55,60 kJ/mol & A equal 8,83 mHz; (b) 75 per cent CO-25 per cent CO2: Ea equal 88,21 kJ/mol and Aequal 127,74 mHz; (c) 50 per cent CO-50 per cent CO2: Ea equal 95,21 kJ/mol and A equal 193,37 mHz. And for the second material, zinc ferrite contained in the EAF dusts: (a) 100 per cent CO gas: Ea equal 52,34 kJ/mol and A equal 4,98 mHz; (b) 75 per cent CO-25 per cent CO2: Ea equal 66,70 kJ/mol and A equal 76,06 mHz; (c) 50 per cent CO-50 per cent CO2: Ea equal 86,28 kJ/mol and A equal 289,59 mHz. The comparison between the apparent activation energy obtained from the best fitting kinetic models permitted to conclude that the zinc ferrite reduction as well as the electric arc furnace dusts reduction global reactions rates are controlled by iron oxides reduction, this in particular for the case of the reduction with 100 per cent CO. As for the reduction with the CO-CO2 gas mixtures, this was not observed for the synthetic zinc ferrite, although, for the reduction of the electric arc furnace dust, this could be the case due to their low zinc content. Considering these facts and the experimental results of this work, it is suggested that the zinc ferrite reduction by CO-CO2 gas mixtures has the global reaction rate controlled simultaneously by the reduction of both zinc and iron oxides.

O uso de escoria de aciaria, principal subproduto das industrias siderúrgicas do processo de conversão do ferro gusa em aço, como matéria-prima na produção de cimento Portland a partir de substituições de parte da escoria de alto forno, apresenta benefícios econômicos e ecológicos, visto que um resíduo industrial tornar-se-á matéria-prima na fabricação do cimento, reduzindo custo de energia, material e depósitos para estocagem de resíduos. Para tal estudo, a escória de aciaria foi submetida a refusão e a diferentes taxas resfriamento, com o objetivo de formar escorias com diferentes graus de cristalinidade. Após resfriamento foram conformados corpos de prova com adição ao cimento Portland de 0; 1,8; 3,6 e 5,4% em peso de escoria de aciaria. Foram determinados tempo de início e final pega, resistência a compressão após 3, 7, 28 e 91 dias da conformação dos corpos de prova, expansibilidade a quente e a frio. Os resultados confirmam que a escória de aciaria apresenta potencial para ser utilizada na indústria cimenteira. A verificação da influência da adição das escorias dará suporte para a Companhia Siderúrgica Nacional (CSN) decidir quanto a viabilidade da mudança do processo atual de resfriamento e quanto a destinação do resíduo. / The use of steel slag, the main byproduct of the steel industries of the process of converting pig iron into steel as raw material for the production of Portland cement by replacing part of blast furnace slag, offering economic and ecological benefits, as that an industrial - waste becomes the raw material in cement production, reducing energy costs, equipment and tanks for storage of waste. For this study, steel slag was subjected to remelting and cooled at different rates, with the goal of forming slag with different degrees of crystallinity. After cooling, specimens with addition to Portland cement of 0, 1,8; 3,6 and 5,4% steel slag were conformed. Were determined the start time and end handle, compressive strength after 3, 7, 28 and 91 days of conformation, hot and cold expandability. The results confirm that the steel slag has the potential to be used in the cement industry. The verification of the influence of the addition of slag will support the National Steel Company (CSN) on the feasibility of changing the current cooling process and the allocation of the new waste.

O aumento da demanda por aços cada vez mais exigentes, em termos de composição química e limpidez interna, faz com que as condições de refino nas aciarias sejam cada vez mais severas. Ao mesmo tempo, o aumento dos tempos de tratamento do aço, aliado às outras variáveis operacionais como quantidades e tipos de adições químicas, etc. fazem com que haja um aumento no tempo de contato entre o revestimento refratário das panelas de transporte de aço e escórias com conseqüente redução do desempenho (vida) de tais revestimentos refratários. Apesar dos esforços no intuito de redução de custos com redução de consumos de refratários, é cada vez maior a pressão sobre os custos de produção e de segurança operacional. Neste sentido, a construção de modelos de previsão de vida em função de tais variáveis é de extrema importância para a gestão de processos e contratos, estabilidade operacional e segurança. Além disso, os estudos de post-mortem podem contribuir no sentido de compreensão física e química de tais fenômenos e mecanismos de desgaste, contribuindo assim para a validação de tais modelos determinísticos. Neste estudo, buscou-se verificar quais variáveis operacionais influem no desempenho (vida) das panelas através de correlações estatísticas. O modelamento levou em consideração os dados de 6 meses de operação da aciaria de uma usina integrada com capacidade de 4,5 Mt/ano. O estudo post-mortem realizado em uma das panelas, após o final de sua campanha, mostrou-se eficiente na validação de tais correlações e no entendimento físico e químico dos possíveis fenômenos e mecanismos de desgaste. As análises mostraram que as variáveis que impactam a vida das panelas de aço são a temperatura de vazamento do aço, temperatura do aço na panela pós vazamento, quantidade de aço chapas grossas (CG) produzido, rota de tratamento dessulfurado, tempo de panela cheia, participação do forno panela no refino secundário, condições da panela, carga de aço na panela, adições de nefelina, escória sintética, fios de cálcio silício (CaSi) e ferro alumínio cálcio (FeAlCa), ligas de manganês e tempos de tratamento no refino secundário. O estudo de post-mortem de amostras de refratário da linha de escória extraída de uma das panelas revelou que o principal mecanismo de desgaste desta região é a corrosão química pela escória que é facilitada pelas adições de nefelina. / The increased demand for increasingly demanding steels, in terms of chemical composition and internal sanity, makes the conditions of refining in steelmaking plants are increasingly stringent and select. At the same time, increasing metallurgical treatment times, combined with the various other operating variables such as the quantities and types of chemical additions, etc. makes that there is an increase in contact time between the refractory coating of steel transport ladles and slag with a consequent reduction in performance (life) of such refractory linings. Despite efforts in order to reduce costs with a reduction of refractory consumption, it is increasing the pressure on the costs of production and operational safety. In this sense, the construction of life prediction models according to such variables is extremely important for cost reduction, process management and procurement, operational stability and safety. Moreover, post-mortem studies can contribute towards chemical and physical understanding of such phenomena and wear mechanisms, thus contributing to the validation of such deterministic models. In this study, we sought to determine which operating variables really influence the performance (life) of the ladles through statistics correlations. The modeling took into account data from 6 months of operation of an integrated steelmaking plant with capacity of 4.5 Mt / year. The study post-mortem conducted on some ladles, after the end of their campaigns, was effective in the validation of such correlations and in the physical and chemical understanding of possible phenomena and wear mechanisms. The analysis showed that the variables that impact in the life of steel\'s ladles are the steel taping temperature, the steel taping temperature in the ladle after taping, amount of produced plate mill (CG) steel, desulfurized treatment route, ladle full time, participation of the ladle furnace in the secondary refining, ladle conditions, steel load in the ladle, nepheline additions, synthetic slag, calcium silicon (CaSi) and iron aluminium calcium (FeAlCa) wires, manganese alloys and treatment times in the secondary refining. The post-mortem study of slagline\'s refractory samples extracted from ladles in operation revealed that the main wear mechanism in this region is the chemical corrosion by slag and is facilitated by additions of nepheline.