| 1. |
- Zhang, Zhi, 1982-
(författare)
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A study of flow fields during filling of a sampler
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- More and more attention has been paid to decreasing the number and size of non-metallic inclusions existing in the final products recently in steel industries. Therefore, more efforts have been made to monitor the inclusions' size distributions during the metallurgy process, especially at the secondary steelmaking period. A liquid sampling procedure is one of the commonly applied methods that monitoring the inclusion size distribution in ladles, for example, during the secondary steelmaking. Here, a crucial point is that the steel sampler should be filled and solidified without changing the inclusion characteristics that exist at steel making temperatures. In order to preserve the original size and distributions in the extracted samples, it is important to avoid their collisions and coagulations inside samplers during filling. Therefore, one of the first steps to investigate is the flow pattern inside samplers during filling in order to obtain a more in-depth knowledge of the sampling process to make sure that the influence is minimized. The main objective of this work is to fundamentally study the above mentioned sampler filling process. A production sampler employed in the industries has been scaled-up according to the similarity of Froude Number in the experimental study. A Particle Image Velocimetry (PIV) was used to capture the flow field and calculate the velocity vectors during the entire experiment. Also, a mathematical model has been developed to have an in-depth investigate of the flow pattern in side the sampler during its filling. Two different turbulence models were applied in the numerical study, the realizable k-ε model and Wilcox k-ω model. The predictions were compared to experimental results obtained by the PIV measurements. Furthermore, it was illustrated that there is a fairly good agreement between the measurements obtained by PIV and calculations predicted by the Wilcox k-ω model. Thus, it is concluded that the Wilcox k-ω model can be used in the future to predict the filling of steel samplers.
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| 2. |
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| 3. |
- Strandh, Jenny
(författare)
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A study of solid and liquid inclusion separation at the steel-slag interface
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis work aimed to provide a better knowledge of inclusion behavior at the steel-slag interface. All results are based on mathematical modeling of liquid and solid inclusion separation to the slag. The model descriptions of the inclusion transfer are based on the equation of motion at the system. It is assumed that the inclusion transfer is governed by four forces acting on the inclusion as it has reached the steel-slag interface. These are the buoyancy force, the added mass force, the drag force and the rebound force. The models assume two cases of inclusion separation depending on the inclusion Reynolds number. In the case where Reynolds number is larger or equal to unity, Re≥1, a steel film is formed between the inclusion and the slag. This steel film must first be drained before the inclusion can separate to the slag. If Reynolds number, Re<1, then no steel film is formed and the inclusion will be in direct contact with the slag. The mathematical models also propose three types of inclusion behavior as the inclusion crosses the steel-slag interface. The inclusion can either, pass and separate to the slag, oscillate at the interface with the possibility of reentering the steel bath with the steel flow or it can remain at the interface not completely separated to the slag. A parameter study for 20 μm inclusions showed that the most important parameters controlling the inclusion behavior at the steel-slag interface are the slag viscosity and the interfacial tensions between the phases. For 100μm inclusions also the inclusion density affects the inclusion behavior. The models were applied to ladle and tundish conditions. Since the slags in the chosen industrial conditions have not been studied experimentally before, estimations of the important physical property parameters were made. Future measurements will therefore be needed in order to make predictions of inclusion transfer behavior at the steel-slag interface which are more relevant for the industry. The main conclusion is that useful plots can be made in order to illustrate the tendency for the inclusion transfer and how to manipulate the physical property parameters in order to increase the inclusion separation in ladles and tundishes.
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| 4. |
- Björklund, Johan, 1979-
(författare)
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A study of slag-steel-inclusion interaction during Ladle treatment
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis is based on two supplements with two major objectives. In the first supplement equilibrium top slag-steel bulk and inclusions-steel bulk were investigated by comparison between calculated and measured oxygen activity values. This was done by applying different oxide activity models for slags combined with thermodynamic calculations. In the second supplement the inclusion composition is studied during the ladle refining process. The inclusion composition is related to top slag composition and other parameters during ladle treatment. The work was carried out by collecting data during well controlled sampling procedures at two different steel plants. Extensive inclusion analyses in Scanning Electron Microscope, SEM, were done. The data was used together with thermodynamics for a description of the interaction between slag-steel-inclusion interaction during ladle treatment. Evaluation of inclusion composition during the ladle refining have revealed that the majority of the inclusions belonged to the system Al2O3-CaO-MgO-SiO2 and 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 composition after vacuum treatment was found to be close to the top slag composition. Small process parameter changes and practical variations during ladle refining were proven to give large differences of the inclusion composition. Finally, it was concluded that equilibrium does not exist between top slag and steel bulk, with respect to oxygen, for the studied conditions. However, the equilibrium does exist between the steel bulk and inclusion.
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| 5. |
- Björklund, Johan, 1979-
(författare)
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Thermodynamic Aspects on Inclusion Composition and Oxygen Activity during Ladle Treatment
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 6. |
- Doostmohammadi, Hamid, 1980-
(författare)
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A Study of Slag/Metal Equilibrium and Inclusion Characteristics during Ladle Treatment and after Ingot Casting
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 7. |
- Ericsson, Ola, 1984-
(författare)
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An Experimental Study of Liquid Steel Sampling
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sampling of liquid steel to control the steel making process is very important in the steel industry. However, there are numerous types of disposable samplers and no united standard for sampling. The goal in this study is to investigate the effect of slag protection type and sample geometry on sampling parameters and sample homogeneity. Three sample geometries were selected: i) Björneborg ii) Lollipop with a 6 mm thickness and iii) Lollipop with a 12 mm thickness. These sample geometries have been tested with two types of slag protection: metal-cap-protection and argon-protection. The filling velocity and solidification rate of steel samples have been experimentally measured during plant trials. The sample homogeneity with respect to total oxygen content and inclusion size distribution has been determined in different parts of the samples. The study shows that argon-protected samplers have lower, more even, filling velocities (0.19±0.09 m/s) compared to metal-cap-protected samplers (1.28±2.23 m/s). The solidification rate measurements of the different samplers show that the 6 mm thick Lollipop has the highest solidification rate (99~105 °C/s). Measurements of total oxygen content in argon-protected samples showed little variation between different zones of the samples. However, metal-cap-protected samples contained much higher total oxygen contents. Light optical microscope studies showed that the increase in total oxygen content was probably caused by entrapment of top slag during sampling. Furthermore, it was found that the contamination of top slag in the metal samples increased with a decreased sample weight. Determination of inclusion size distribution in argon-protected Lollipop samples showed that a larger number of primary inclusions are found in the top part compared to the middle and the bottom part of the samples.
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| 8. |
- Ersson, Mikael, 1977-
(författare)
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Fundamental Experimental and Numerical Investigation Focusing on the Initial Stage of a Top-Blown Converter Process
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis work is to increase the knowledge of phenomena taking place during the initial stage in a top blown converter. The work has been done in a few steps resulting in four different supplements. Water model experiments have been carried out using particle image velocimetry (PIV) technology. The system investigated was a fundamental top blown converter where an air jet was set to impinge on a water surface. The flow field of the combined blown case, where an air jet was introduced through a bottom nozzle, was also captured by the PIV. The work clearly showed that the flow field caused by an impinging top blown jet alone could not match that of the bottom blown case. The main re-circulation loop (or vortex) was investigated with respect to position and it was found that an increased flow rate pushes the center of the re-circulation loop downwards into the bath. However, for the top-blown case there is a point when the flow rate is too large to cause a distinguishable re-circulation loop since the jet becomes more plunging (i.e. penetrates deep into the bath) than impinging, with large surface agitation and splashing as a result.A numerical model with the same dimensions as the experimental system was then created. Three different turbulence models from the same family were tested: standard-, realizable- and a modified-(slight modification of one of the coefficients in order to produce less spreading of the air jet) k-ε turbulence model. It could be shown that for the family of k-ε turbulence models the difference in penetration depth was small and that the values corresponded well to literature data. However, when it comes to the position of the re-circulation loop it was shown that the realizable k-ε model produced better results when comparing the results to the experimental data produced from the PIV measurements, mentioned earlier.It was then shown how the computational fluid dynamics (CFD) model could be coupled to thermodynamics databases in order to solve for both reactions and transport in the system. Instead of an air-water system, a gas-steel-slag system was created using the knowledge obtained in the previous simulation step described above. Reactions between gas-steel, gas-slag, steel-slag and gas-steel-slag were considered. Extrapolation of data from a few seconds of simulation was used for comparison to experimental data from the literature and showed reasonable agreement. The overall conclusion was that it is possible to make a coupling of the Thermo-Calc databases and a CFD software to make dynamic simulations of metallurgical processes such as a top-blown converter.A parametric study was then undertaken where two different steel grades were tested; one with high initial carbon content (3.85 mass-%) and one with lower carbon content (0.5 mass-%). The initial silicon content was held constant at 0.84 mass-%. Different initial temperatures were tested and also some variation in initial dissolved oxygen content was tried. It was found that the rate of decarburization/desiliconization was influenced by the temperature and carbon concentration in the melt, where a high temperature as well as a high carbon concentration favors decarburization over desiliconization. It was also seen that the region affected by a lower concentration of alloys (or impurities) was quite small close to the axis where the impinging jet hits the bath. Add the oscillating nature of the cavity and it was realized that sampling from this region during an experiment might be quite difficult.
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| 9. |
- Hallgren, Line
(författare)
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Effect of swirling blade on flow pattern in nozzle for up-hill teeming
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The fluid flow in the mold during up-hill teeming is of great importance for the quality of the cast ingot and therefore the quality of the final steel products. At the early stage of the filling of an up-hill teeming mold, liquid steel enters, with high velocity, from the runner into the mold and the turbulence on the meniscus could lead to entrainment of mold flux. The entrained mold flux might subsequently end up as defects in the final product. It is therefore very important to get a mild and stable inlet flow in the entrance region of the mold. It has been acknowledged recently that swirling motion induced using a helix shaped swirl blade, in the submerged entry nozzle is remarkably effective to control the fluid flow pattern in both the slab and billet type continuous casting molds. This result in increased productivity and quality of the produced steel. Due to the result with continuous casting there is reason to investigate the swirling effect for up-hill teeming, a casting method with similar problem with turbulence. With this thesis we will study the effect of swirling flow generated through a swirl blade inserted into the entry nozzle, as a new method of reducing the deformation of the rising surface and the unevenness of the flow during filling of the up-hill teeming mold. The swirling blade has two features: (1) to generate a swirling flow in the entrance nozzle and (2) to suppress the uneven flow, generated/developed after flowing through the elbow. The effect of the use of a helix shaped swirl blade was studied using both numerical calculations and physical modelling. Water modelling was used to assert the effect of the swirling blade on rectifying of tangential and axial velocities in the filling tube for the up-hill teeming and also to verify the results from the numerical calculations. The effect of swirl in combination with diverged nozzle was also investigated in a similar way, i. e. with water model trials and numerical calculations.
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| 10. |
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