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<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>

<p>The growth and removal of inclusions in stirred ladles hasbeen studied. First, the importance of different growthmechanisms suggested in the literature were studied. Simulationresults from a fundamental model of an induction-stirred ladlehave been used as input in the calculations. Based on thegrowth calculations it was concluded that four of the growthmechanisms need not to be considered since they contribute solittle: i) diffusion of oxygen and aluminum to the inclusionsurface, ii) diffusion coalescence, iii) Brown motioncollision, and iv) laminar shear collision. The majorcontributor to inclusion growth is turbulent collision. Growthdue to Stoke's collisions is also somewhat important if largedifferences among inclusion sizes exist.</p><p>Growth of inclusions in gas stirred ladles was studied usinga similar approach as the one for induction stirred ladles, butwith use of simulation results from a fundamental mathematicalmodel of a gas-stirred ladle. Similarly to what was found inthe case of induction stirring, it was found that turbulentcollisions and Stokes collisions appeared to be the majormechanisms for inclusion growth. The contribution of laminarshear collisions to growth was deemed negligible compared tothat of turbulent collisions.</p><p>For the gas stirred ladle different removal mechanisms werealso studied, based on input data from a mathematical model ofa gas-stirred ladle. It was found that different modelssuggested to predict the inclusion removal due to bubbleflotation gave very different results. Also, all models assumeda spherical shape of the gas bubbles, which was found to beless realistic. Therefore, a new model for inclusion removal byspherical cap bubble flotation was developed. In the newcalculations, the most important mechanisms of inclusionremoval were found to be removal to the top slag and removal bybubble flotation, assuming spherical-cap bubbles and planecontact. When the bubbles were assumed to be spherical,resulting removal rates were lower than when they were assumedto be spherical caps. Based on these results it is concludedthat more research is needed to obtain a better understandingof the importance of bubble flotation on inclusion removal.Experiments are clearly needed to determine which modelconcepts produce predictions in best agreement withcorresponding data from actual steelmaking processes.</p>

<p>Steel refining via ladle treatment is critical to final product quality in the steel manufacturing process. The process of ladle refining serves to assist in the removal of non-metallic inclusions, which can impact steel product fatigue strength, impact toughness, and corrosion resistance. While the steelmaking industry has in place best practices for the process, it remains costly to performing trial and error testing on the ladle. In addition, an understanding of the flow phenomena within the ladle during operation can provide industry with key knowledge necessary to improve the efficiency and throughput of the process.</p> <p> </p> <p>The method by which this research aims to address this is through the development of a comprehensive computational fluid dynamics (CFD) model of the steelmaking ladle. Such a model, capable of predicting the inclusion removal process and flow patterns within the ladle, would serve to provide the necessary information to advance steelmaking efficiency and improve product quality. A full scale unsteady state three dimensional CFD model has been developed to predict removal of inclusion during gas-stirring in a ladle. The Eulerian-Eulerian model was used to simulate the multiphase flow, the Population Balanced Model (PBM) has been used to describe the inclusion distribution. The phenomena of bottom-blow argon bubble coalescence and breakup were considered. </p> <p> </p> <p>Additionally, a model has been developed to predict inclusion removal during operation. For the inclusion removal model, the CFD-PBM coupled method has been proposed to investigate the inclusion behavior. This includes representing phenomena such as inclusion-bubble collision, inclusion removal by attachment to the ladle refractory, and inclusion capture by slag floating on the surface of the melt. The unified computational model for simulation of fluid flow and inclusion removal was validated against industry measurements provided by Nucor Steel. </p> <p> </p> <p>Using this CFD model and a ladle geometry and set of baseline conditions provided by Nucor Steel, studies were carried out to examine flow development, gas bubble distribution, and inclusion removal. Examining the impacts of inclusion size on removal rate indicated that larger inclusions are removed faster. This agreed with both industry expectations and data found in published literature. In addition, the model predicts that bubble-inclusion collision are primarily responsible for 99% inclusion removal in a gas-stirred ladle.</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.

<p>The overall purpose of this thesis work has been to further our understanding of the growth and removal of inclusions in gas- and induction-stirred ladles. The primary focus has been on alumina inclusions. </p><p>Growth mechanisms were studied using data from fundamental mathematical models of gas- and induction-stirred ladles. The results showed the turbulence mechanism to be the most dominant in alumina inclusion growth. The dynamic growth and removal of inclusions in a gas-stirred ladle was studied using mathematical modelling. The model results showed concentration gradients of inclusions. The effect was most obvious in the steel flow past the removal sites: top slag, ladle refractory, and gas plume (bubble flotation). A new removal model was developed for large spherical caps bubbles. </p><p>In order to verify the predicted concentration gradients for the size population of inclusions, three experiments were carried out in production. The sampling equipment enabled sampling at five different positions and different locations at the same time. The results showed that concentration gradients of inclusions do exist both in induction-stirred and gas-stirred ladles. A theoretical analysis showed that the drag force on the inclusions to be the dominating force and that therefore inclusions follow the fluid flow. </p><p>The cluster behaviour of alumina inclusions were examined on steel samples taken in an industrial-scale deoxidation experiment in a ladle. The samples were examined by microscope and the results used to study cluster growth. It was found that there was rapid cluster growth due to collision during stirring and that at the end of the deoxidation experiment a majority of the small inclusions were bound in clusters. The cluster growth data determined using the microscopic results were compared with predicted cluster-growth data. A method was developed for converting the experimental data observed per unit area into data given per unit volume and vice versa. An expression for the collision diameter of the cluster was also developed. The results showed that the predicted cluster growth agreed well with the microscopic observations for the assumptions made in the growth model.</p>

The overall purpose of this thesis work has been to further our understanding of the growth and removal of inclusions in gas- and induction-stirred ladles. The primary focus has been on alumina inclusions. Growth mechanisms were studied using data from fundamental mathematical models of gas- and induction-stirred ladles. The results showed the turbulence mechanism to be the most dominant in alumina inclusion growth. The dynamic growth and removal of inclusions in a gas-stirred ladle was studied using mathematical modelling. The model results showed concentration gradients of inclusions. The effect was most obvious in the steel flow past the removal sites: top slag, ladle refractory, and gas plume (bubble flotation). A new removal model was developed for large spherical caps bubbles. In order to verify the predicted concentration gradients for the size population of inclusions, three experiments were carried out in production. The sampling equipment enabled sampling at five different positions and different locations at the same time. The results showed that concentration gradients of inclusions do exist both in induction-stirred and gas-stirred ladles. A theoretical analysis showed that the drag force on the inclusions to be the dominating force and that therefore inclusions follow the fluid flow. The cluster behaviour of alumina inclusions were examined on steel samples taken in an industrial-scale deoxidation experiment in a ladle. The samples were examined by microscope and the results used to study cluster growth. It was found that there was rapid cluster growth due to collision during stirring and that at the end of the deoxidation experiment a majority of the small inclusions were bound in clusters. The cluster growth data determined using the microscopic results were compared with predicted cluster-growth data. A method was developed for converting the experimental data observed per unit area into data given per unit volume and vice versa. An expression for the collision diameter of the cluster was also developed. The results showed that the predicted cluster growth agreed well with the microscopic observations for the assumptions made in the growth model.

<p>A comprehensive study of inclusion aggregation and removal in different bottom gas-stirred ladles has been conducted. The unsteady, three dimensional, isothermal, multiphase computational fluid dynamics (CFD) model was developed. A ladle with two bottom plugs was used in the study. Effects of plug separation angles (180° and 90°) and argon flow rate combinations (5/5 SCFM, 5/20 SCFM and 20/20 SCFM) were investigated. The whole study can be divided into two parts: first, the flow field, slag eye size and wall shear stress have been studied; second, inclusion aggregation and removal in different ladles have been investigated. In the first part, argon bubble breakup and coalescence has been considered. The slag eye size was validated with plant measurement. When the flow rate increases, the size of slag eye will increase while the wall shear stress increases as well. In the second part, a parametric study of ladle design and argon flow rate on inclusion aggregation and removal has been conducted. Turbulence shear collision shows the most dominant effect on inclusion aggregation. The argon flow rate is positively related to inclusion aggregation and removal. When the argon flow rate is fixed, a larger plug separation angle shows higher inclusion aggregation and removal efficiency. </p><br>

The growth and removal of inclusions in stirred ladles hasbeen studied. First, the importance of different growthmechanisms suggested in the literature were studied. Simulationresults from a fundamental model of an induction-stirred ladlehave been used as input in the calculations. Based on thegrowth calculations it was concluded that four of the growthmechanisms need not to be considered since they contribute solittle: i) diffusion of oxygen and aluminum to the inclusionsurface, ii) diffusion coalescence, iii) Brown motioncollision, and iv) laminar shear collision. The majorcontributor to inclusion growth is turbulent collision. Growthdue to Stoke's collisions is also somewhat important if largedifferences among inclusion sizes exist. Growth of inclusions in gas stirred ladles was studied usinga similar approach as the one for induction stirred ladles, butwith use of simulation results from a fundamental mathematicalmodel of a gas-stirred ladle. Similarly to what was found inthe case of induction stirring, it was found that turbulentcollisions and Stokes collisions appeared to be the majormechanisms for inclusion growth. The contribution of laminarshear collisions to growth was deemed negligible compared tothat of turbulent collisions. For the gas stirred ladle different removal mechanisms werealso studied, based on input data from a mathematical model ofa gas-stirred ladle. It was found that different modelssuggested to predict the inclusion removal due to bubbleflotation gave very different results. Also, all models assumeda spherical shape of the gas bubbles, which was found to beless realistic. Therefore, a new model for inclusion removal byspherical cap bubble flotation was developed. In the newcalculations, the most important mechanisms of inclusionremoval were found to be removal to the top slag and removal bybubble flotation, assuming spherical-cap bubbles and planecontact. When the bubbles were assumed to be spherical,resulting removal rates were lower than when they were assumedto be spherical caps. Based on these results it is concludedthat more research is needed to obtain a better understandingof the importance of bubble flotation on inclusion removal.Experiments are clearly needed to determine which modelconcepts produce predictions in best agreement withcorresponding data from actual steelmaking processes. / NR 20140805