Magnesium aluminate spinel inclusions are a concern in the steelmaking industry since these particles affect the processing and the properties of steel. During the refining of low carbon aluminum killed steel in the ladle furnace; the initial alumina inclusions shift their composition towards higher contents of MgO and eventually they become magnesium aluminate spinel inclusions. This research developed a kinetic model for the transformation of alumina inclusions to spinel in liquid steel. The aspects of simultaneous deoxidation and of solid state cation counterdiffusion were addressed in the model. Coupling the model for spinel inclusions to a kinetic model for the slag-steel reactions in the ladle furnace allowed verifying the modeled concentrations in the inclusions with the plant data measurements of ArcelorMittal Dofasco operations. Good agreement between the experimental and calculated Mg contents in the inclusions was obtained for most of the industrial heats analyzed. Finally, a sensitivity analysis of the coupled kinetic model was performed to compare the effect of the different processing conditions and mass transfer rates on the amount of Mg and spinel in the inclusions. Several results from this work indicate that the rate limiting step on the formation of magnesium aluminate spinel inclusions is the supply rate of dissolved [Mg] from the slag-steel reaction; the supply of [Mg] is in turn controlled by the changes at the slag-steel interface. / Thesis / Master of Applied Science (MASc)

<p>The present work was to study the role of ladle glaze as apotential supplier of inclusions to the steel melt during theladle refining process. In this study, the total number ofinclusions at the beginning and at the end of the ladletreatment process was found to be increasing with ladle age,which is the number of heats, the ladle being used. Asubstantial increase in inclusion population was noticed aftera certain ladle age.</p><p>Totally four types of inclusions named as; type-1 (MgO),type-2 (spinel), type-3 (an oxide solution) and type-4 (spinelin the center surrounded by the oxide solution of type-3) wereobserved in the beginning of the ladle refining process.Thermodynamic calculation revealed that the type-3 and type-4inclusions were generated by the reactions between EAF slag andladle glaze. Even a part of inclusions of type-2 (spinel phase)could be formed by these reactions. Three types of inclusionswere found before casting, viz. type-5 (oxide solution with lowcontents of MgO and SiO2), type-6 (small MgO islands embeddedin an oxide solution) and type-7 (spinel in the centersurrounded by the oxide solution of type-5). Inclusions of bothtype-5 and type-7 were the products of the reaction betweeninclusions of type-2 and the liquid metal. On the other hand,the occurrence of pieces of MgO having sharp edges in the oxidesolution suggested that the type-6 inclusions were generated bythe ladle glaze.</p><p>A preliminary examination on the possibility of inclusionseparation by bubble floatation, experiments using cold modelswere also carried out. De-ionised water and silicon oil wereused as the bulk phase. Charcoal particles of different sizeranges were employed as the dispersed phase. The examination ofcharcoal-water-gas system indicated that the positivefloatation coefficient is not a sufficient condition for theinclusion separation. The experimental results were found to bein contradiction with the prediction of a typical model thatconsiders interfacial energies. The omitting of the drag forcewas believed to be the reason causing the failure of the modelprediction in the charcoal-water-gas system. The failure of themodel prediction suggested a need of a new model taking intoaccount interfacial energies, drag force, buoyancy force andgravity force.</p><p><b>Key words:</b>oxide inclusions, ladle metallurgy, ladleglaze, inclusion population, ladle age, interfacial tension,inclusion separation</p>

&Ccedil / EMTAS Steel Plant produces alloy steels used principally by the automotive industry. Demands of customers for cleaner steel with &ldquo / fewer, smaller and homogenously distributed inclusions&rdquo / are getting tighter with time. The tight demands of the customers are checked by ultrasonic testing and faulty regions are cut off and scrapped which results in production losses in steel plants. Decreasing production losses due to scrapping by producing cleaner steels is therefore a major concern. The objective of this study is to investigate factors affecting the cleanliness of the steels produced by &Ccedil / EMTAS. With this objective, the steelmaking practice used was thoroughly investigated and the possible origins of inclusions in the final product was tried to be found. Based on the findings, process parameters like temperature, time, quantities of additives to steel, intensity of stirring etc. were varied with the objective of determining the optimum production practice.

The present work was to study the role of ladle glaze as apotential supplier of inclusions to the steel melt during theladle refining process. In this study, the total number ofinclusions at the beginning and at the end of the ladletreatment process was found to be increasing with ladle age,which is the number of heats, the ladle being used. Asubstantial increase in inclusion population was noticed aftera certain ladle age. Totally four types of inclusions named as; type-1 (MgO),type-2 (spinel), type-3 (an oxide solution) and type-4 (spinelin the center surrounded by the oxide solution of type-3) wereobserved in the beginning of the ladle refining process.Thermodynamic calculation revealed that the type-3 and type-4inclusions were generated by the reactions between EAF slag andladle glaze. Even a part of inclusions of type-2 (spinel phase)could be formed by these reactions. Three types of inclusionswere found before casting, viz. type-5 (oxide solution with lowcontents of MgO and SiO2), type-6 (small MgO islands embeddedin an oxide solution) and type-7 (spinel in the centersurrounded by the oxide solution of type-5). Inclusions of bothtype-5 and type-7 were the products of the reaction betweeninclusions of type-2 and the liquid metal. On the other hand,the occurrence of pieces of MgO having sharp edges in the oxidesolution suggested that the type-6 inclusions were generated bythe ladle glaze. A preliminary examination on the possibility of inclusionseparation by bubble floatation, experiments using cold modelswere also carried out. De-ionised water and silicon oil wereused as the bulk phase. Charcoal particles of different sizeranges were employed as the dispersed phase. The examination ofcharcoal-water-gas system indicated that the positivefloatation coefficient is not a sufficient condition for theinclusion separation. The experimental results were found to bein contradiction with the prediction of a typical model thatconsiders interfacial energies. The omitting of the drag forcewas believed to be the reason causing the failure of the modelprediction in the charcoal-water-gas system. The failure of themodel prediction suggested a need of a new model taking intoaccount interfacial energies, drag force, buoyancy force andgravity force. <b>Key words:</b>oxide inclusions, ladle metallurgy, ladleglaze, inclusion population, ladle age, interfacial tension,inclusion separation / NR 20140805

Presence of inclusions in high manganese steel are a major concern in the steel making industry, since these particles affect the processing and properties of the steel. During the refining of high manganese steel in the ladle furnace, the types of inclusions present and their growth in the liquid steel, or during solidification of the steel, caused by the addition of manganese and other alloying elements are to be examined. This research developed a kinetic model for the presence and growth of inclusions in the liquid high manganese steel for the ladle metallurgy process. The diffusion of dissolved elements, and the seed of inclusions for the growth and consumption of inclusions, were both addressed in the model. The present model for inclusions was coupled to the updated kinetic model for slag-steel reactions in the ladle furnace for high manganese steel. The coupled model allows for verifying the process analysis plant data for the highest manganese concentration presently available in the steel industry. Finally, an analysis of the coupled kinetic model was performed to compare the effect of the different processing conditions, and the presence and growth of inclusions in the high manganese steel from the ladle metallurgy process. / Thesis / Master of Applied Science (MASc)

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>The inclusions are harmful to the steel cleanliness; process parameters such as stirring and steel and slag oxidation must be controlled to obtain a final number of inclusions in the steel whose size is smaller than the critical size for each steel product.</p> <p>A simple mathematical model was developed to analyze the impact of bubbling, slag and initial oxidation level on inclusion distribution control (quantity and size of them) during the process in a Ladle Metallurgy Furnace (LMF).</p> <p>The initial inclusion size distribution is calculated and adjusted with the samples analyzed by SEM-EDAX, this initial distribution decreases by removal mechanisms such as bubbling and slag and they can increases by reoxidation.</p> <p>The model allows predicting the inclusion removal by bubbling mechanism as a function of gas flow rate and inclusion size and it proves which a softer stirring is better for removal inclusion than stronger one. An interesting point analyzed is the effect of stirring level on small and large inclusions.</p> <p>According to the inclusion number removal by slag, it is possible to appreciate like larger inclusions are removed easier than smaller ones. This mechanism is the most important to remove inclusions calculated by this model.</p> / Master of Science (MSc)

<p dir="ltr">The global steel industry, serving as a fundamental cornerstone of modern civilization and essential to infrastructure, manufacturing, and technological advancements, continually strives to meet the increasing demand for high-quality steel. Achieving this goal necessitates ongoing innovations in the realm of secondary steelmaking processes, which have become indispensable for refining steel properties after the primary production phase. Ladle metallurgy provides a means to actively control the steel’s composition and properties. However, the intricacies of molten steel flow within a ladle have been challenging to decipher under the extreme conditions it presents. Gas stirring is an essential component of this procedure, where inert gas is introduced into molten metal to ensure consistent mixing, thereby homogenizing the chemical composition and eliminating inclusions. This method improves the quality and mechanical properties of steel while reducing defects in the final product. The turbulence created by gas injection enhances the interaction between molten steel and slag, particularly through the formation of the slag eye, facilitating chemical reactions and impurity removal. To deepen our comprehension of these complex processes, extensive research employing dynamically scaled water models has been undertaken to comprehensively grasp the underlying mechanisms in ladle metallurgy.</p><p dir="ltr">In this thesis, we have developed dynamically scaled water ladle models, to replicate the stirred flow field and address the intricate issue of controlling micro-inclusions. In the first experiment, an advanced Particle-Tracking-Velocimetry system of the Shake-the-Box was implemented on a cylindrical water ladle model, to resolve the three-dimensional flow field inside a 6 × 6 × 2 cm domain. In total, eight conditions of compress air injections were investigated. Then, a two-dimensional water ladle model tank was scaled to focus on flow-induced slag entrainment at the water-oil (steel-slag) interface. Our endeavor is dedicated to improving the quality and consistency of steel, thereby making a significant contribution to the steel industry’s relentless pursuit of excellence.</p>