<p> </p><p>In order to optimise the ladle treatment mass transfer modelling of aluminium addition and homogenisation time was carried out. It was stressed that incorporating slag-metal reactions into the mass transfer modelling strongly would enhance the reliability and amount of information to be analyzed from the CFD calculations.</p><p> </p><p>In the present work, a thermodynamic model taking all the involved slag metal reactions into consideration was incorporated into a 2-D fluid flow model of an argon stirred ladle. Both thermodynamic constraints and mass balance were considered. The activities of the oxide components in the slag phase were described using the thermodynamic model by Björkvall and the liquid metal using the dilute solution model. Desulphurization was simulated using the sulphide capacity model developed by KTH group. A 2-D fluid flow model considering the slag, steel and argon phases was adopted.</p><p> </p><p>The model predictions were compared with industrial data and the agreement was found quite satisfactory. The promising model calculation would encourage new CFD simulation of 3-D along this direction.</p><p> </p>

The present study was carried out to investigate theformation and chemical development of non-metallic inclusionsduring ladle treatment of steel. To begin with, an investigation of the deoxidation processand the impact of aluminium addition was carried out. For thispurpose, a new experimental setup was constructed. The setupallowed the examination of the deoxidation process as afunction of time by using a quenching technique. Preliminaryexperiments showed that homogeneous nucleation of alumina tookplace in the areas supersaturated with aluminium. Theseexperiments also showed that agglomeration of alumina particleswas a very rapid process, even when the convection in the meltwas negligible. In order to examine whether aluminium supersaturation occursduring industrial practice, the deoxidation of liquid steelwith aluminium wire injection in a gas-stirred ladle wassimulated by mathematical modeling using a Computational FluidDynamics (CFD) approach. The results showed that theconcentration of aluminium in the vicinity of the aluminiumwire injection was high enough to generate homogeneousnucleation of alumina. Aiming at an understanding of the inclusion chemistry duringthe ladle process, an industrial study was performed atUddeholm Tooling AB. The impact of slag-lining reactions andladle glaze as a source of inclusions in the melt was alsostudied. The experimental results were analysed from athermodynamic viewpoint to gain an insight into the origins ofthe inclusions and their changes along the process of the ladletreatment. Six types of inclusions were found in the steel. Thetypes of inclusions present varied along the history of theladle treatment. Three types of inclusions were found in theliquid steel before deoxidation, namely type A (a liquidinclusion with high SiO2 concentration), type B (spinel) andtype C (a combination of type A and type B). Thermodynamicanalysis indicated that these types of inclusions could begenerated by the reaction between the Electric Arc Furnace(EAF) slag and the ladle glaze, during the filling of theladle. The addition of aluminium resulted in the formation ofalumina inclusions (type E), which agglomerated and separatedfrom the steel very fast. The spinel inclusions of type B werefound to be unstable at low oxygen potentials. The inclusionsof this type would react with the liquid metal forming theinclusions of type F (spinel in the centre surrounded by anoxide solution containing Al2O3, CaO and MgO). Further,reaction between the liquid metal and inclusions of type Fwould result in the inclusions of type G, an oxide solutionmostly consisting of Al2O3 and CaO with small amounts of MgOand SiO2. The inclusions of type G were the only inclusionsfound in the steel before casting.

<p>The present study was carried out to investigate theformation and chemical development of non-metallic inclusionsduring ladle treatment of steel.</p><p>To begin with, an investigation of the deoxidation processand the impact of aluminium addition was carried out. For thispurpose, a new experimental setup was constructed. The setupallowed the examination of the deoxidation process as afunction of time by using a quenching technique. Preliminaryexperiments showed that homogeneous nucleation of alumina tookplace in the areas supersaturated with aluminium. Theseexperiments also showed that agglomeration of alumina particleswas a very rapid process, even when the convection in the meltwas negligible.</p><p>In order to examine whether aluminium supersaturation occursduring industrial practice, the deoxidation of liquid steelwith aluminium wire injection in a gas-stirred ladle wassimulated by mathematical modeling using a Computational FluidDynamics (CFD) approach. The results showed that theconcentration of aluminium in the vicinity of the aluminiumwire injection was high enough to generate homogeneousnucleation of alumina.</p><p>Aiming at an understanding of the inclusion chemistry duringthe ladle process, an industrial study was performed atUddeholm Tooling AB. The impact of slag-lining reactions andladle glaze as a source of inclusions in the melt was alsostudied. The experimental results were analysed from athermodynamic viewpoint to gain an insight into the origins ofthe inclusions and their changes along the process of the ladletreatment. Six types of inclusions were found in the steel. Thetypes of inclusions present varied along the history of theladle treatment. Three types of inclusions were found in theliquid steel before deoxidation, namely type A (a liquidinclusion with high SiO2 concentration), type B (spinel) andtype C (a combination of type A and type B). Thermodynamicanalysis indicated that these types of inclusions could begenerated by the reaction between the Electric Arc Furnace(EAF) slag and the ladle glaze, during the filling of theladle. The addition of aluminium resulted in the formation ofalumina inclusions (type E), which agglomerated and separatedfrom the steel very fast. The spinel inclusions of type B werefound to be unstable at low oxygen potentials. The inclusionsof this type would react with the liquid metal forming theinclusions of type F (spinel in the centre surrounded by anoxide solution containing Al2O3, CaO and MgO). Further,reaction between the liquid metal and inclusions of type Fwould result in the inclusions of type G, an oxide solutionmostly consisting of Al2O3 and CaO with small amounts of MgOand SiO2. The inclusions of type G were the only inclusionsfound in the steel before casting.</p>

Two industrial studies and one set of lab scale trials have been done. In addition, a theoretical study has been done. The main focus has been on non metallic inclusion composition during the ladle refining operation in industrial steel production. Sampling has been done together with careful inclusion determination. The inclusion composition is related to different variables. In the industrial trials samples have been taken at different steps during the ladle refining period. Steel and slag composition as well as temperature and oxygen activity have been determined. The thesis is based on five supplements with different major objectives, all related to the inclusion composition. The equilibrium top slag-steel bulk and inclusions-steel bulk were investigated by comparison between calculated and measured oxygen activity values. The oxygen activity and relation to temperature has also been discussed as well as oxygen activity and temperature gradients. The effect of vacuum pressure on inclusion composition has been evaluated in a theoretical study as well as lab scale trials. The inclusion composition has been studied during the industrial ladle treatment process. The inclusion composition was related to top slag composition and other parameters during ladle treatment. The major findings in the thesis are the lack of equilibrium conditions with respect to top-slag and steel bulk before vacuum treatment. The inclusions have been found to be closer to equilibrium with the steel bulk. Al/Al2O3 equilibrium has been found to control the oxygen activity after Al-deoxidation. Evaluation of inclusion composition during the ladle refining has revealed that the majority of the inclusions showed a continuous composition change throughout the ladle refining process, from high Al2O3, via MgO-spinel to finally complex types rich in CaO and Al2O3. The final inclusion composition after vacuum treatment was found to be close to the top slag composition. Vacuum pressure has been found to have a theoretical effect on inclusion composition at very low pressures. / QC 20100712

No description available.

No description available.

Nous étudions par simulation numérique le transport et le dépôt turbulent d’inclusions d’oxydes métalliques (de l’ordre de 10 µm de diamètre) en suspension dans l’acier liquide. Deux surfaces de dépôt sont envisagées : l’interface acier liquide/paroi solide et l’interface métal liquide/laitier. Dans les deux cas, nous nous focalisons sur la couche limite adjacente à l’interface. Le comportement des inclusions en suspension est examiné à l’aide d’un suivi lagrangien où le poids, la poussée d’Archimède, la force d’accélération en volume, la force de masse ajoutée et la force de traînée sont prises en compte dans l’équation de la dynamique. Dans le cas de la paroi solide, nous nous appuyons sur une représentation schématique de l’écoulement du métal liquide dans la sous-couche visqueuse et dans la zone tampon, où les structures turbulentes qui apportent le liquide à la paroi (sweeps) ou l’éjectent (bursts) sont décrites analytiquement (modèle d’Ahmadi). Les simulations numériques montrent que les mécanismes principaux de dépôt des inclusions sont la sédimentation et dans une moindre mesure l’interception directe. Notons cependant que la contribution de l’interception directe croît avec l’intensité turbulente de l’écoulement et peut devenir prépondérante pour les vitesses de frottement les plus élevées (au-delà de 0,1 m.s-1). Les effets inertiels ont, quant à eux, une contribution négligeable sur le dépôt des inclusions (contrairement au cas des aérosols). Enfin, la prise en compte des interactions hydrodynamiques entre les inclusions et la paroi solide conduit à une diminution significative de la vitesse de dépôt des inclusions. Dans le cas de l’interface acier liquide/laitier, l’écoulement du métal liquide est calculé par simulation numérique directe (DNS) à l’échelle de la couche de surface. La turbulence, générée à distance de l’interface par un forçage aléatoire, diffuse vers l’interface métal liquide/laitier modélisée comme une surface libre indéformable. L’évolution des inclusions en suspension est obtenue par un suivi lagrangien à l’aide d’un couplage one-way. Le nombre de Reynolds de surface des simulations varie de 68 à 235. Le diamètre des inclusions varie de 10-5m à 5.10-5m et le rapport entre la densité des inclusions et la densité du métal varie de 0,5 (inclusions d’alumine) à 1 (inclusions fictives). Il apparaît que le dépôt des inclusions d’alumine est contrôlé par la sédimentation. En l’absence d’effet gravitaire, le dépôt d’inclusions est contrôlé par l’interception directe et dépend fortement du nombre de Reynolds de surface. Dans ce dernier cas, nous montrons que la vitesse de dépôt adimensionnée par la vitesse de Kolmogorov de surface est proportionnelle au diamètre des inclusions adimensionné par la longueur de Kolmogorov de surface. La prise en compte des interactions hydrodynamiques entre les inclusions et la surface libre conduit à une diminution de moitié de la contribution de l’interception directe mais affecte peu la contribution gravitationnelle. En outre, en l’absence d’effet gravitaire, la linéarité entre la vitesse de dépôt adimensionnée et le diamètre des inclusions adimensionné est conservée. / The deposition of metallic oxide inclusions (of about 10 µm in diameter) suspended in liquid steel is studied by numerical simulation. Two types of deposition surface are investigated, i.e., the liquid steel/solid wall interface and the liquid steel/liquid slag interface. In both cases, we focus on the boundary layer adjacent to the interface. The inclusion behavior is examined thanks to Lagrangian particle tracking: Newton’s second law governing inclusion motion includes the buoyancy force, the pressure gradient force, the added mass force and the steady drag force.For the liquid steel/solid wall interface, the inclusion behavior is analyzed in the buffer layer and in the viscous layer. These layers are described according to Ahmadi’s model, which provides a kinematic representation of the turbulent structures responsible for deposition, i.e., the sweeps and the bursts of liquid. The numerical simulations show that the deposition is mainly controlled by sedimentation. However, since the direct interception contribution increases with the turbulence intensity, direct interception becomes dominant for the highest values of the friction velocity (greater than 0.1 m.s-1). When the hydrodynamic interactions between the inclusions and the solid surface are taken into account, the deposition velocity is significantly reduced. Finally, it should be noted that the inertial forces have a negligible effect on the inclusion deposition velocity. For the liquid steel/liquid slag interface, the inclusion turbulent deposition is investigated using direct numerical simulation of the liquid flow combined with Lagrangian particle tracking under conditions of one-way coupling. The interface is modeled as a non-deformable free-slip surface. Unsheared turbulence is generated by random forcing in a finite-height region parallel to the free-slip surface. In between, the turbulence diffuses toward the free surface. The Reynolds number at the interface varies from 68 to 235. The inclusion diameter varies from 10-5m to 5.10-5m and the particle to liquid density ratio from 0.5 (alumina inclusions) to 1 (fictitious inclusions). It appears that the deposition of alumina inclusions is controlled by sedimentation whereas direct interception is the only deposition mechanism for non-buoyant inclusions. In the latter case, the deposition velocity strongly depends on the surface Reynolds number. It is shown that the deposition velocity made dimensionless by the free surface characteristic velocity scales as the inclusion diameter made dimensionless by the Kolmogorov length scale calculated at the free surface. When the hydrodynamic interactions between the inclusions and the free surface are taken into account, the direct interception contribution of the deposition velocity is significantly reduced (about half of the value without hydrodynamic retardation) but the scaling law is conserved.

QC 20101126

In order to optimise the ladle treatment mass transfer modelling of aluminium addition and homogenisation time was carried out. It was stressed that incorporating slag-metal reactions into the mass transfer modelling strongly would enhance the reliability and amount of information to be analyzed from the CFD calculations.   In the present work, a thermodynamic model taking all the involved slag metal reactions into consideration was incorporated into a 2-D fluid flow model of an argon stirred ladle. Both thermodynamic constraints and mass balance were considered. The activities of the oxide components in the slag phase were described using the thermodynamic model by Björkvall and the liquid metal using the dilute solution model. Desulphurization was simulated using the sulphide capacity model developed by KTH group. A 2-D fluid flow model considering the slag, steel and argon phases was adopted.   The model predictions were compared with industrial data and the agreement was found quite satisfactory. The promising model calculation would encourage new CFD simulation of 3-D along this direction. / QC 20110414

Today, there is a high demand on clean steel for high performance materialproperties. Thus, steel producers try to deliver a steel product with the highestquality and cleanliness to the market. The number of parameters that affect thesteel cleanliness may vary depending on the required material properties of thefinal product. However, the non-metallic inclusion characteristics represent one ofthe most important parameters. More specifically, the composition, size, numberand morphology affect steel cleanliness. In this work, selected parameters affectingthe inclusion characteristics were studied using the following methods: i)thermodynamic calculations (including computational thermodynamiccalculations), ii) inclusion determinations using a cross sectional (CS) method (2Dinvestigations) and iii) inclusion determinations using an electrolytic extraction(EE) method (3D investigations). The computational thermodynamic calculations of the slag-steel and inclusion-steelequilibriums were carried out using the Thermo-Calc software. With the help ofthese calculations, the influence of the slag carryover on the top slag, aluminumcontent in steel and sulfur distribution ratio as well as predictions of stable phasesof inclusions were studied. In addition, inclusion determinations of tool steel gradesamples collected during various stages of the ladle treatment in a scrap-based steelplant were carried out using both 2D and 3D methods. Furthermore, inclusiondeterminations of bearing steel grade samples from a runner system after ingotcasting were performed using a 2D metallographic method (CS-method). Also, theINCAFeature software was used, when using cross sectional method, in order tocollect more statistics of the inclusion characteristics. It was found that slag carryover has a large influence on the composition of theactual top slag as well as the aluminum content in the steel as well as the sulfurdistribution ratio. In addition, steel and slag were found to be in “near”-equilibriumconditions, after the completion of the vacuum degassing operation. Furthermore,the composition of small-size inclusions in samples taken from tool steel was foundto be very scattered. Moreover, the composition of the large-size inclusions wasfound to be less scattered. Furthermore, closer to the top slag composition insamples collected after vacuum degassing. Finally, the accuracy of the inclusioncomposition determinations of tool steel samples using the electrolytic extractionmethod was found to be better than for the cross sectional method. The worseaccuracy of the CS-method is due to a considerable effect of matrix elements oninclusion composition. / QC 20100709