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  • 1.
    Ahmed, Hesham M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    El-Geassy, Abdel-Hady A.
    Viswanathan, Nurni Neelakantan
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Kinetics and Mathematical Modeling of Hydrogen Reduction of NiO-WO(3) Precursors in Fluidized Bed Reactor2011In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 51, no 9, p. 1383-1391Article in journal (Refereed)
    Abstract [en]

    In the present work, Fluidized bed reduction of NiO-WO(3) precursors was investigated isothermally at temperatures 973-1 273 K. The reaction progress was monitored by analysis of H(2)O evolved during the reaction process using a gas chromatograph instrument. A theoretical model based on intrinsic chemical reaction rate constants and thermodynamic equilibria was developed to estimate the apparent reaction rate constant for the reduction reaction. In developing the model, the particles are considered to be in a completely mixed condition and gas flow is described as plug flow. The proposed model is also suitable for scale-up calculations. The interfacial chemical reaction model was found to fit the experimental results. The apparent activation energy values of the reduction process at different stages were calculated accordingly. The present investigation proved that the fluidized bed technique can be successfully utilized in bulk production of intermetallics containing W and a transition metal (or a composite material) wherein the process conditions would have a strong impact on the particle size of the end product.

  • 2.
    Ahmed, Hesham M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Viswanathan, N. N.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    On The Kinetics of Hydrogen Reduction of NiO-WO3 Precursors in Fluidized Bed- A Modeling Approach2011In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 51, no 9, p. 1383-1391Article in journal (Refereed)
    Abstract [en]

    In the present work, Fluidized bed reduction of NiO-WO3 precursors was investigated isothermally at temperatures 973-1 273 K. The reaction progress was monitored by analysis of H2O evolved during the reaction process using a gas chromatograph instrument. A theoretical model based on intrinsic chemical reaction rate constants and thermodynamic equilibria was developed to estimate the apparent reaction rate constant for the reduction reaction. In developing the model, the particles are considered to be in a completely mixed condition and gas flow is described as plug flow. The proposed model is also suitable for scale-up calculations. The interfacial chemical reaction model was found to fit the experimental results. The apparent activation energy values of the reduction process at different stages were calculated accordingly. The present investigation proved that the fluidized bed technique can be successfully utilized in bulk production of intermetallics containing W and a transition metal (or a composite material) wherein the process conditions would have a strong impact on the particle size of the end product.

  • 3. Alexis, J.
    et al.
    Ramirez, M.
    Trapaga, G.
    Jönsson, Pär
    KTH, Superseded Departments, Materials Science and Engineering.
    Modeling of a DC electric arc furnace - Heat transfer from the arc2000In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 40, no 11, p. 1089-1097Article in journal (Refereed)
    Abstract [en]

    A mathematical model describing heat and fluid flow in an electric are has been developed and used to predict heat transfer from the are to the steel bath in a DC Electric Are Furnace. The are model takes he separate contributions to the heat transfer from each involved mechanism into account, i.e. radiation, convection, condensation and energy transported by electrons. The model predicts heat transfer for different currents and are lengths. Model predictions show that are efficiency is higher for lower power input. The model also predicts shear stresses and current density distribution at the steel surface. This information can be used as boundary condition input to simulate the effect of heating with electrodes in a DC EAF on the heat and fluid flow in the steel bath.

  • 4.
    Alexis, Jonas
    et al.
    Swerea-Mefos.
    Jönsson, Pär
    KTH, Superseded Departments, Applied Process Metallurgy.
    Jonsson, Lage
    KTH, Superseded Departments, Applied Process Metallurgy.
    A model of an induction-stirred ladle accounting for slag and surface deformation1999In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 39, no 8, p. 772-778Article in journal (Refereed)
  • 5.
    Alexis, Jonas
    et al.
    Swerea-Mefos.
    Jönsson, Pär
    KTH, Superseded Departments, Metallurgy.
    Jonsson, Lage
    Heating and electromagnetic stirring in a ladle furnace – a simulationmodel2000In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 40, no 11, p. 1098-1104Article in journal (Refereed)
    Abstract [en]

    A three-dimensional simulation model coupling heating and induction stirring in an ASEA-SKF ladle furnace was developed. Data of the heat transfer from the area to the steel bath were predicted in a separate model and included as boundary conditions in a ladle model. The are model considers the contributions of heat transferred by of each of the following mechanisms: radiation, convection, condensation and energy transported by electrons. Predictions were made to simulate the change of temperature distribution in the ladle during simultaneous heating with electrodes and stirring by induction. A first attempt was made to compare the predictions with measured temperatures from a 100 t ASEA-SKF ladle. The agreement was found to be fairly good when heat-flux data for a 25 cm are length were used as input to the ladle model. This indicates that the model can be used for more in-depth studies of the effects of heating for ladles that are inductively stirred.

  • 6.
    Andersson, Margareta A. T.
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Jonsson, Lage T. I.
    KTH, Superseded Departments, Materials Science and Engineering.
    Jonsson, P. G.
    A thermodynamic and kinetic model of reoxidation and desulphurisation in the ladle furnace2000In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 40, no 11, p. 1080-1088Article in journal (Refereed)
    Abstract [en]

    A thermodynamic and kinetic model of reoxidation and desulphurisation in the ladle furnace has been developed by using a two-dimensional fluid-flow model combined with equations expressing the thermodynamics of reoxidation and desulphurisation. More specifically ladle vacuum treatment of a gas-stirred ladle has been simulated. In order to describe the activities of the oxide components of the slag, expressions by Ohta and Suito(1)) were adopted. The thermodynamic model describes the slag/metal equilibria between Al, Si, O, Mn and S in the molten steel and Al2O3, SiO2, FeO, MnO and S in the slag. A fluid dynamic model that considers the slag, steel and argon phases derives the kinetics. Results from an isothermal calculation have been heuristically compared with industrial plant data and they show good agreement. The model results have also revealed that the reduction of silica plays a part in aluminium loss during ladle treatment.

  • 7.
    Andersson, Margareta
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Appelberg, Jesper
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Tilliander, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Nakajima, Keiji
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Shibata, Hiroyuki
    Tohoku University, Institute of Multidisciplinary Research for Advanced Materials.
    Kitamura, Shinya
    Tohoku University, Institute of Multidisciplinary Research for Advanced Materials.
    Jonsson, Lage
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Some Aspects on Grain Refining Additions with Focus on Clogging during Casting2006In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 46, no 6, p. 814-823Article in journal (Refereed)
    Abstract [en]

    Some ideas of how to study optimum conditions for implementation of grain refining in liquid steel processing with focus on how to avoid clogging are discussed. It is assumed that the inclusions most beneficial for grain refining are known from studies by physical metallurgists. The challenge for a process metallurgist is how to provide a homogeneous distribution of grain refiners at the onset of solidification. Four different ways of providing information to succeed with this are discussed. Thermodynamic modeling can be used to predict what additions to make to create potential grain refiners, if relevant thermodynamic data is available. Mathematical fluid-flow modeling can be used to study where to add potential grain refiners. It is discussed that the tundish is the most appropriate reactor to add grain refiners, since enough time is given to a complete mixing of the grain refiner into the steel before the steel enters the mold. By using the scanning laser microscopy technique it is possible to study which potential grain refiners has the lowest attraction forces between each other. This is important in order to minimise growth of inclusions when they collide during transport in the tundish, which can lead to the formation of larger inclusions that do not serve as useful grain refiners. Finally, it is suggested that laboratory experiments are carried out in order to study the tendency for nozzle clogging, before the use of grain refiners is tested in industrial scale.

  • 8.
    Arzpeyma, Niloofar
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Widlund, Ola
    Ersson, Mikael
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Mathematical Modeling of Scrap Melting in an EAF Using Electromagnetic Stirring2013In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 53, no 1, p. 48-55Article in journal (Refereed)
    Abstract [en]

    Numerical modeling has been used to investigate the influence of electromagnetic stirring on melting of a single piece of scrap in an eccentric bottom tapping (EBT) electric arc furnace (EAF). The heat transfer and fluid flow in the melt for both conditions with and without electromagnetic stirring were studied. The buoyancy and electromagnetic forces were considered as the source terms for momentum transfer in the studied conditions. The enthalpy-porosity technique was applied to track the phase change of a scrap piece defined in the EBT region of the furnace. Different scrap sizes, preheating temperatures, stirring directions and force magnitudes were considered, and the heat transfer coefficient was estimated from the heat transfer rate at the melt-scrap interface. The results showed that electromagnetic stirring led to a reduced melting time and an increased heat transfer coefficient by a factor of four. The results for Nusselt number versus Grashof number for natural convection and Reynolds number for electromagnetic stirring were compared with those obtained through correlations from previous studies.

  • 9.
    Bai, Haitong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Ersson, Mikael
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär G.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    An Experimental and Numerical Study of Swirling Flow Generated by TurboSwirl in an Uphill Teeming Ingot Casting Process2016In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 56, no 8, p. 1404-1412Article in journal (Refereed)
    Abstract [en]

    A swirling flow has been demonstrated to be beneficial for making the flow pattern even and to reduce turbulence during filling in ingot casting. A new swirling flow generation device, TurboSwirl, was applied to improve the flow pattern of the liquid steel as it flows into the mold so that a more stable flow could be obtained. A water model was built including the TurboSwirl with different flaring angles of the divergent nozzle, according to a former numerical study indicating that a much more beneficial flow pattern could be obtained by reducing the flaring angle. To validate the mathematical model, the air-core vortex formed in the water model experiment was used, and the length of the vortex was measured and compared to the numerical predictions. Different turbulence models including the standard k-epsilon, realizable k-epsilon and Reynolds stress model were tested. It was found that only the Reynolds stress model could most accurately simulate the high swirling flow including a vortex. In addition, the radial velocity of the water around the vortex was measured by an ultrasonic velocity profiler (UVP). The experimental results revealed a high turbulence of the swirling flow and strong fluctuations of the vortex. The radial velocity of the water around the upper part of the vortex could be predicted well compared to the experimental results by the UVP measurements.

  • 10. Ban-Ya, S.
    et al.
    Hino, M.
    Hayashi, M.
    Sano, N.
    Fredriksson, Patrik
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Comments on "Evaluation of thermodynamic activity of metallic oxide in a ternary slag from the sulphide capacity of the slag"2005In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 45, no 11, p. 1754-1757Article in journal (Refereed)
  • 11.
    Basu, Somnath
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Lahiri, Ashok Kumar
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    A model for activity coefficient of P2O5 in BOF slag and phosphorus distribution between liquid steel and slag2007In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 47, no 8, p. 1236-1238Article in journal (Refereed)
  • 12.
    Basu, Somnath
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Lahiri, Ashok Kumar
    KTH.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Halder, Jayanta
    Change in phosphorus partition during blowing in a commercial BOF2007In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 47, no 5, p. 766-768Article in journal (Refereed)
  • 13.
    Bi, Yanyan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Karasev, Andrey
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär G.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Three Dimensional Evaluations of REM Clusters in Stainless Steel2014In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 54, no 6, p. 1266-1273Article in journal (Refereed)
    Abstract [en]

    It is known that clusters in liquid steel have a harmful effect on the casting process and the quality of the final steel product. In this study, clusters. of rare earth metals (REM) were investigated in steel samples of a S30185 stainless steel grade from a pilot trial (PT, 250 kg) and from an industrial heat (IH, 100 t). Samples were taken from the liquid steel at different holding times after the addition of mischmetal. Thereafter, REM clusters collected on film filters after electrolytic extraction and filtration were investigated in three dimensions (3D) by SEM in combination with EDS. The morphology, composition, number and size of clusters in PT and IH steel samples were analyzed and compared as a function of holding time. It was found that typical clusters with regular and irregular inclusions were the main type of clusters (69%-98%) in all PT and IH steel samples. The composition of inclusions in clusters corresponded mostly to REM-oxides. The size of clusters that were observed in different samples varied mainly from 2 to 23 mu m. In addition, the size and number of most clusters in PT are larger than those in IH samples. Furthermore, the formation mechanisms and evolution of different type of REM clusters were discussed in both PT and IH heats.

  • 14.
    Bi, Yanyan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Karasev, Andrey Vladimirovich
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär G.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Evolution of Different Inclusions during Ladle Treatment and Continuous Casting of Stainless Steel2013In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 53, no 12, p. 2099-2109Article in journal (Refereed)
    Abstract [en]

    The inclusions and clusters in steel samples of two similar steel grades of high-silicon non-calcium treated (HSiNC) stainless steels were investigated and compared during ladle treatment and continuous casting. Samples of liquid steel and slag were taken at different stages of the ladle treatment and casting during two plant trials: Low Al steel (LAI) and High Al steel (HAI). After electrolytic extraction of the steel samples, characteristics of inclusions and clusters (such as morphology, composition, size and number) were investigated in three dimensions (3D) by SEM in combination with EDS. Moreover, the composition of typical inclusions and clusters was analyzed on a polished cross section of steel samples. Spherical (SP), irregular and regular (IR) inclusions and clusters (CL) were observed in the samples from both heats. It was found that the morphology and composition of inclusions and clusters in both heats were significantly changed during the ladle treatment and casting. Most of inclusions (44-98%) in a Low Al steel are MgO-CaO-SiO2-Al2O3 spherical inclusions. The compositions of IR inclusions and clusters in steel samples of a High Al steel were mostly MgO center dot Al2O3 spinet, but also the complex SP inclusions containing Al2O3-MgO-CaO-SiO2. In addition, phase stability diagram based on Darken's quadratic formalism and Redlich-Kister type polynomial was estimated for both heats at a non-infinite solution.

  • 15. Bjurstrom, M.
    et al.
    Tilliander, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Iguchi, M.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Physical-modeling study of fluid flow and gas penetration in a side-blown AOD converter2006In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 46, no 4, p. 523-529Article in journal (Refereed)
    Abstract [en]

    The main fluid-flow pattern that results in a converter with side gas injection was studied using physical modeling. Having roughly the same viscosity as liquid steel, water was used in the experiments. The velocity of the water was determined for different positions in the vessel symmetry plane by laser Doppler velocimetry. Experiments were performed using combinations of three different bath heights and four different gas-flow rates. The results showed penetration of the gas plume into the steel bath both at the tuyere and bath level to increase with an increased gas-flow rate. Also, the penetration depth of the gas both at the tuyere and bath surface level were more affected by an increased gas-flow rate than an increased bath height. Finally, the overall fluid-flow pattern in the system was found to change both with an increased bath height and an increased gas-flow rate.

  • 16.
    Björklund, Johan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Miki, Takahiro
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Andersson, Margareta
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Effect of Temperature on Oxygen Activity during Ladle Treatment2008In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 48, no 4, p. 438-445Article in journal (Refereed)
    Abstract [en]

    The effect of temperature on oxygen activity in steel was studied in plant trials where temperature and oxygen activity were measured at two depths and at the same time during different parts of ladle refining. The results show that large temperature gradients exist towards the surface of the steel melt for the sampling occasion when no slag is present on the steel surface, as can be expected. It was also observed that the oxygen activity is higher in the lower measurement position than in the upper during the majority of the ladle refining. This is explained by the oxygen activity's temperature dependence. By using the data from this study and previously reported plant trials it was shown that Si-SiO2 or Al-Al2O3 equilibrium controls the oxygen activity.

  • 17.
    Bäcke, Linda
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Modeling the Effect of Solute Drag on Recovery and Recrystallization during Hot Deformation of Nb Microalloyed Steels2010In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 50, no 2, p. 239-247Article in journal (Refereed)
    Abstract [en]

    The effect of solute drag on recovery and recrystallization during hot deformation of Nb microalloyed steels has been modeled using a newly developed microstructure model. The model is based on dislocation theory and the calculated dislocation density determines the driving force for recrystallization. Subgrains act as nuclei for recrystallization and have to reach a critical size and configuration in order for recrystallization to start. In the model, the solute drag effect of Nb in solution is described. Nb retards both dislocation and grain boundary movement giving retardation in both recovery and recrystallization. Calculations were compared to experimental results from axisymmetric compression tests combined with stress relaxation. In order to model the effect of solute drag, the experiments were carried out at temperatures where precipitation of Nb(C, N) should not occur. The calculated flow stresses for the compression tests show good fit with experimental data. Also, the calculated results of the relaxation tests show good agreement with experimental data.

  • 18.
    Bölke, Kristofer
    et al.
    KTH.
    Ersson, Mikael
    KTH.
    Imris, Matej
    ScanArc Plasma Technol AB, SE-81321 Hofors, Sweden..
    Jönsson, Pär Göran
    KTH.
    Importance of the Penetration Depth and Mixing in the IRONARC Process2018In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 58, no 7, p. 1210-1217Article in journal (Refereed)
    Abstract [en]

    One of the most important parameters for gas injection into liquid baths is the penetration depth of the gas into the bath. This is due to that it strongly influences the flow structure and hence the stirring and plume behavior in metallurgical processes. The IRONARC process is a new energy efficient process for reduction of iron oxide to produce pig iron. The future goal is to continuously scale up the process to an industrial scale from the current pilot scale. In this process, gas is injected horizontally through a submerged nozzle into a slag bath. Hence, the penetration depth is of great importance since it greatly affect several parameters in this process. Moreover, this information is essential when scaling up the reactor from a pilot scale to an industrial scale. In this work, the penetration depth of gas injection into water in a small scale side blown converter was studied numerically. Two different approaches with different multiphase models were tested, namely the Volume of Fluid (VOF) model and Eulerian multiphase model (EE). The penetration depth could be accurately determined for both numerical models, with a small expected deviation of 13.9% from the physical experiment results. Also, the simulation time was shorter for the Eulerian multiphase model. The penetration depth was then determined for the IRONARC pilot plant process. The results show that the plume is detached from the nozzle wall, which in turn results in a better energy usage of the gas along with a small refractory wear.

  • 19.
    Dahl, Fredrik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Brandberg, Jenny
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Characterization of melting of some slags in the Al2O3-CaO-MgO-SiO2 quaternary system2006In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 46, no 4, p. 614-616Article in journal (Refereed)
    Abstract [en]

    A number of slag compositions in the Al2O 3-CaO-MgO-SiO2 quaternary system was investigated. The Al2O3, CaO, and SiO2 oxide powders were calcinated at 1073 K for 24 hours before being mixed in an agate mortar. The oxide mixtures were further pressed into small pellets and sealed in a glass bottle. A horizontal platinum furnace and platinum crucibles were used and each slag composition was investigated four times to confirm the reproductibility of the process. Efforts were made to carry out the experiments with identical quenching speed. The slags were quenched from 1793 K to examine the liquidity of the slag samples at lower temperatures. It was revealed that the quenched samples were multi-phase mixtures instead of melting at the experimental temperature under the influence of the phase diagrams.

  • 20.
    Deng, Zhiyin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Northeastern University, China.
    Zhu, Miaoyong
    Zhong, Baojun
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Attachment of Liquid Calcium Aluminate Inclusions on Inner Wall of Submerged Entry Nozzle during Continuous Casting of Calcium-Treated Steel2014In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 54, no 12, p. 2813-2820Article in journal (Refereed)
    Abstract [en]

    In the present study, inclusions in calcium-treated steel after RH treatment, in the tundish and in bloom were studied. Only two types of inclusions were detected in all steel samples, namely liquid calcium aluminate inclusions and inclusions of two phases with spinel in the center surrounded by the liquid calcium aluminate. The attachment of the inclusions on the inner surface of SEN was investigated for two types of refractory materials. The results indicated that liquid calcium aluminate inclusions could attach on the wall of SEN, when the refractory had big grain size and big cavities on the surface. On the other hand, tiny grain size and smooth surface of the SEN showed no attachment of the inclusions. The different behaviors of the two types of SEN were well explained using the results of flow calculation in the nozzle. The mechanism of the attachment was also discussed based on the experimental results and the CFD calculation. The tiny nodules formed on the surface of the inner nozzle due to inclusion attachment could be a source of macro inclusions.

  • 21.
    Elfsberg, Jessica
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Matsushita, Taishi
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Experimental study of interfacial phenomena between commercial steel and mould flux slag: influence of oxide additions to the mould fluxIn: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460Article in journal (Other academic)
  • 22.
    Eriksson, Robert
    et al.
    KTH, Superseded Departments, Metallurgy.
    Jonsson, Lage
    KTH, Superseded Departments, Metallurgy.
    Jönsson, Pär G.
    KTH, Superseded Departments, Metallurgy.
    Effect of entrance nozzle design on the fluid flow in an ingot mold during filling2004In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 44, no 8, p. 1358-1365Article in journal (Refereed)
    Abstract [en]

    Earlier studies have shown that the mold powder reacts with Steel during filling of the mold during ingot casting of ball-bearing and tool steels, which results in formation of inclusions. Since all inclusions are bad for the material properties for these grades, this is a phenomenon that needs to be avoided. In this study, fundamental mathematical modeling of the filling of an ingot has been used to predict the fluid flow characteristics. A special effort has been made to model the effect of a modified inlet allowing for a larger volume flow. Predictions made by the presently used numerical model, indicates that a successive increase in the opening angle of the inlet nozzle leads to a gradual decrease in the disturbance of the free surface, during mold filling. Furthermore, the horizontal velocities are lower, which results in lower values of the Weber number which is an indication of less chances for mold powder entrapment into steel. It is concluded that both these improvements leads to decreased possibilities for the creation of inclusions in the steel due to interaction with the mold powder.

  • 23.
    Ersson, Mikael
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Tilliander, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jonsson, Lage
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Dynamic Coupling of Computational Fluid Dynamics and Thermodynamics Software: Applied on a Top Blown Converter2008In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 48, no 2, p. 147-153Article in journal (Refereed)
    Abstract [en]

    A novel modeling approach is presented where a computational fluid dynamics software is coupled to thermodynamic databases to obtain dynamic simulations of metallurgical process phenomena. The modeling approach has been used on a fundamental model of a top-blown converter. Reactions between gas-steel, gas-slag, steel-slag and gas-steel-slag have been considered. The results show that the mass transport in the surface area is totally controlled by convection. Also, that a large amount of CO produced during the decarburization might slow down the rate of decarburization in droplets ejected from the bath. For the present simulation conditions reflecting laboratory experiments, it was also seen that the amount of slag (FeO and/or SiO2) created is close to zero, i.e. only gas (CO+CO2) is created as the oxygen jet hits the steel bath. It was also illustrated how an extrapolation of the decarburization rate, sampled from a few seconds of simulation, could be done to get a rough estimate of the carbon content at a later stage in the process as long as the carbon content is relatively high. The overall conclusion is that it is possible to make a dynamic coupling of the Thermo-Calc databases and a CFD software to make dynamic simulations of metallurgical processes such as a top-blown converter.

  • 24.
    Ersson, Mikael
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Tilliander, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jonsson, Lage
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Dynamic Modeling of Steel, Slag and Gas Reactions during Initial Blowing in a Top-Blown Converter2008In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460Article in journal (Other academic)
    Abstract [en]

    A dynamic modeling approach is presented where a computational fluid dynamics software is coupled to a thermodynamics software to obtain simulations of reactions between steel, slag and gas in a top-blown converter. For each simulation the transport of momentum, energy and mass of species as well as the thermodynamic equilibrium in each cell containing at least two phases was treated. The overall conclusion is that the present calculation procedure is successful for dynamic simulations of interaction between an oxygen gas jet with a melt and a slag. The predicted rate of decarburization was found to agree well with experimental data from laboratory trials. In addition, four cases where simulated for which the temperature, the dissolved carbon content and the dissolved oxygen content were varied. The most important findings from these comparisons were that: i) a higher initial oxygen concentration in the melt yields a larger decarburization rate, ii) carbon content also plays a big role for the desiliconization where a low carbon content is required for desiliconization to take place, iii) decarburization and desiliconization is largely influenced by the temperature at which reactions take place, where low temperature favors desiliconization and iv) the region affected by a lower carbon/silicon concentration (hot-spot region) directly below the jet was approximately 10 mm for the current setup.

  • 25.
    Ersson, Mikael
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Tilliander, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Iguchi, Manabu
    Hokkaido Univ, Grad Sch Engn, Div Mat Sci & Engn.
    Jonsson, Lage
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Fluid Flow in a Combined Top and Bottom Blown Reactor2006In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 46, no 8, p. 1137-1142Article in journal (Refereed)
    Abstract [en]

    Physical modeling was done to study the flow field in a cylindrical bath agitated by bottom purging, top lance blowing and a combination of both injection types. A particle image velocimetry (PIV) system has been used to capture the velocity field of all three cases mentioned above. Special attention was paid to the recirculation loop. Top blowing creates a re-circulation loop in a relatively small volume close to the surface, compared to bottom- and combined-blowing. Increasing bottom flow rate moves the center of the re-circulation loop downwards into the liquid. When top blowing is combined with bottom blowing the center of the re-circulation loop is moved downwards into the liquid with increasing top lance flow rate.

  • 26.
    Ersson, Mikael
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Tilliander, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jonsson, Lage
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    A Mathematical Model of an Impinging Air Jet on a Water Surface2008In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 48, no 4, p. 377-384Article in journal (Refereed)
    Abstract [en]

    A fundamental mathematical model of the flow field and surface deformation caused by an impinging jet in a top blown reactor has been developed. The results have been validated against water model experiments. More specifically, the predicted penetration depth has been found to agree well with surface deformation measurements and predictions using analytical equations. Furthermore, the predictions of the location of a vortex have been found to agree fairly well with PIV measurements. Calculations were also done to compare the widely used standard k-ε model against the realizable extension of the standard k-ε model to calculate the turbulent conditions of the flow. It was found that the penetration depth caused by the impinging jet on the liquid surface is relatively unaffected by the choice of turbulence model employed. However, when the main re-circulation loop in the bath was investigated there was a clear distinction in the flow fields produced when the two different turbulence models were used.

  • 27.
    Grip, Carl-Erik
    et al.
    Luleå Tekniska Universitet.
    Jonsson, Lage
    KTH, Superseded Departments, Applied Process Metallurgy.
    Jönsson, Pär
    KTH, Superseded Departments, Applied Process Metallurgy.
    Prediction of emptying flows in ladles and verification with data fromtrace element plant trials1997In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 37, no 11, p. 1081-1090Article in journal (Refereed)
  • 28.
    Grip, Carl-Erik
    et al.
    Luleå Tekniska Universitet.
    Jonsson, Lage
    KTH, Superseded Departments, Applied Process Metallurgy.
    Jönsson, Pär
    KTH, Superseded Departments, Applied Process Metallurgy.
    Jonsson, Kjell Olov
    Numerical predication and experimental verification of thermalstratification in pilot plant and production ladles1999In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 39, no 7, p. 715-721Article in journal (Refereed)
  • 29. Gustafson, A.
    et al.
    Ågren, John
    KTH, Superseded Departments, Metallurgy.
    Possible effect of Co on coarsening of M23C6 carbide and Orowan stress in a 9% Cr steel2001In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 41, no 4, p. 356-360Article in journal (Refereed)
    Abstract [en]

    it has long been known that a cobalt addition increases the resistance to tempering in steels. This may be due to the fact that Co raises the Curie-temperature which retards diffusion. In the present work the effect of Co on coarsening of M23C6 in the 9% Cr steel P92 is studied by computer simulations. The results show that a final average radius of the carbides after 30 000 h at 600 degreesC decreases with 30 % with a Co addition of 10 mass %. This raises the Orowan stress with 30 %. Moreover, ii is assumed that slower particle coarsening also leads to a retarded coarsening of the martensite lath structure.

  • 30.
    Gustavsson, Joel
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Andersson, Margareta A.T.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    A thermodynamic study of silicon containing gas around a blast furnace raceway2005In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 45, no 5, p. 662-668Article in journal (Refereed)
    Abstract [en]

    The equilibrium conditions for silicon transfer from ash to the liquid metal phase via SiO gas have been discussed by several authors. However, no published calculations have been found using the most modern thermodynamic models available. Since there are major differences in the results of calculations using different thermodynamic models and the models are continuously being improved, new equilibrium calculations on SiO and SiS gas formation have been performed using the recently developed models. Different ingoing compositions of coke ash, coal powder ash and blast air were used in the calculations. The compositions chosen represent blast furnace no. 3 at SSAB in Lulea, Sweden. Temperature was found to be the major factor influencing the equilibrium silicon level in the gas phase. At low temperatures (below 1 600 degrees C the total gas pressure was also seen to influence the silicon content in the gas phase. The main reason for this is that below 1 600 degrees C, the amount of liquid slag at equilibrium increases with the total gas pressure. Liquid slag contains large amounts of silica that then can not be found in the gas phase. Higher carbon activity is usually expected to result in higher SiO gas levels in the blast furnace. The equilibrium calculations show that increased carbon activity increases the amount of silicon in the gas phase at temperatures up to about 1 600 degrees C, but that at higher temperatures SiC is formed that decreases the equilibrium silicon level in the gas phase.

  • 31.
    Hallberg, Malin
    et al.
    KTH, Superseded Departments, Metallurgy.
    Jonsson, Lage T. I.
    KTH, Superseded Departments, Metallurgy.
    Jönsson, Pär G.
    KTH, Superseded Departments, Metallurgy.
    A new approach to using modelling for on-line prediction of sulphur and hydrogen removal duving ladle refining2004In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 44, no 8, p. 1318-1327Article in journal (Refereed)
    Abstract [en]

    A simplified model has been developed for on-line determination of sulphur and hydrogen contents in the steel during vacuum degassing in an ASEA-SKF ladle furnace at Ovako Steel in Hofors, Sweden. The simplified model was developed based on results from fundamental mathematical model simulations of hydrogen and sulphur refining for a number of cases representing normal production situations. More specifically, mass-transfer coefficients were determined from the simulations and thereafter used to develop separate simplified models for sulphur and hydrogen refining. Predictions from using the simplified process models agreed well with sulphur and hydrogen data from full-scale plant trials. It was therefore concluded that the main purpose of the study, namely to achieve a less time-consuming model suitable for production applications, was fulfilled. The final part of the paper presents how the simplified models can provide engineers or operators with off-line or on-line guidelines on performing the vacuum degassing operation such that quality requirements regarding sulphur and hydrogen contents in the steel product are met.

  • 32.
    Hallgren, Line
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Takagi, Shigeo
    Eriksson, Robert
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Yokoya, Shinichiro
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jonsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Effect of nozzle swirl blade on flow pattern in runner during uphill teeming2006In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 46, no 11, p. 1645-1651Article in journal (Refereed)
    Abstract [en]

    Recent research has found a swirling flow induced by a twist-tape swirl blade inserted in the submerged entry nozzle of both slab and billet continuous casting molds to be remarkably effective for controlling the fluid-flow pattern in mold filling. The objective of the work reported on in this paper was to investigate usage of the swirl blade in the filling of molds in uphill teeming. Both mathematical and physical modeling were employed. Resulting velocity predictions and measurements corresponding to different positions in the water model were compared. Specific focus was on manipulation of the flow pattern by the swirl blade and its affect on flow unevenness, i.e. tangential and axial velocities. Good agreement was observed between the calculated and experimental results. The study's findings strongly suggest that equipping the entry nozzle of the uphill-teeming mold with a swirl blade would be a highly effective means of reducing flow unevenness during filling.

  • 33.
    Hallgren, Line
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Tilliander, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Yokoya, Shinichiro
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär G.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Hagman, Solve
    A First Attempt to Implement a Swirl Blade in Production of Ingots2010In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 50, no 12, p. 1763-1769Article in journal (Refereed)
    Abstract [en]

    Plant trials were carried out to test if it would be possible to place a ceramic swirl blade in the runner channel during filling of ingots The initial experiments showed that no production disturbances were found More specifically no problems with unusual refractory wear or cracks in the refractory were found Thus it was concluded that the use of swirl blade has a potential in the future to be used to influence the initial filling conditions Also mathematical modeling was done in order to illustrate how it was possible to improve the layout of the runner system in order to increase the potential for use of swirl for the current plant conditions The results showed that the meniscus was not dampened as much when the swirl blade is positioned in a horizontal direction in the runner channel compared to the results of a previous physical modeling study where the swirl blade was placed in a vertical direction just before the steel entered the mold However if a horizontally positioned swirl blade is used in combination with an inlet with an angle of 15 degrees the hump height at the initial filling stage can be lowered from 100 to 58 mm compared to a case without a swirl blade This illustrates the potential to apply mold powder closer to the bottom without risking reoxidation due to reactions with steel and mold powder

  • 34. Hara, Kyosuke
    et al.
    Matsushita, Taishi
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Nagata, Kazuhiro
    In-situ X-ray Transmission Observation of Carbothermic Reduction of Magnetite Powder and Macroscopic Agglomeration of Reduced Iron2013In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 53, no 6, p. 1010-1019Article in journal (Refereed)
    Abstract [en]

    The agglomeration behaviour of reduced iron, made from magnetite powder by carbothermic reduction, was observed by using the in-situ X-ray transmission observation technique. The iron particles, above 1 mm, were clearly observed as black points. Further, the reduction speed was examined by using the thermogravimetric analysis. The bulk density of the packed powder layer and the grain size distribution of magnetite powder and carbon black powder were changed and the effects of them on the reduction speed and the agglomeration degree were examined. The agglomeration degree was evaluated with diameter of iron particles on the X-ray photographs, taken during heating, and the weight of collected iron particles after the observation experiments. Neither the bulk density of powder layer nor the grain size distribution of powder mixture affected to the reduction speed. The agglomeration degree decreased when the bulk density of the powder layer was increased by compacting. On the other hand, the agglomeration degree was increased when the grain size distribution of powder mixture was widened. Further, the height change of powder layer was also measured on the X-ray photographs and compared with the iron particles appearing behaviour to estimate the microscopic agglomeration behaviour. The mechanisms that grain size distribution affected the agglomeration degree were discussed.

  • 35.
    Hayashi, Miyuki
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Abdul Abas, Raid
    KTH, Superseded Departments, Materials Science and Engineering.
    Seetharaman, Seshadri
    KTH, Superseded Departments, Materials Science and Engineering.
    Effect of crystallinity on thermal diffusivities of mould fluxes for the continuous casting of steels2004In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 44, no 4, p. 691-697Article in journal (Refereed)
    Abstract [en]

    The thermal diffusivities of mould flux having the glassy and crystalline states were measured as a function of temperature by the laser flash method to obtain the relationship between the thermal diffusivity and the degree of crystallization. The thermal diffusivities of the liquid mould flux were also measured to compare the data with those of the solid samples. The thermal diffusivity increases roughly linearly with an increase in the degree of crystallization. The thermal diffusivities of glassy and liquid samples having the ratios of NBO/T 1.48, 1.65 and 2.11 exhibit roughly the same values of 4.6 x 10(-7) m(2)s(-1) and 4.0 x 10(-7) m(2)s(-1), respectively. It is considered that because the silicate network is largely broken down, there is not a significant change of the structure for these samples.

  • 36.
    Hayashi, Miyuki
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Abdul Abas, Riad
    KTH, Superseded Departments, Materials Science and Engineering.
    Seetharaman, Seshadri
    KTH, Superseded Departments, Materials Science and Engineering.
    Effect of Crystallinity on the Thermal Diffusivity of Mould Fluxes for the Continuous Casting of Steels2004In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 44, no 4, p. 691-697Article in journal (Refereed)
    Abstract [en]

    The thermal diffusivities of mould flux having the glassy and crystalline states were measured as a function of temperature by the laser flash method to obtain the relationship between the thermal diffusivity and the degree of crystallization. The thermal diffusivities of the liquid mould flux were also measured to compare the data with those of the solid samples. The thermal diffusivity increases roughly linearly with an increase in the degree of crystallization. The thermal diffusivities of glassy and liquid samples having the ratios of NBO/T=1.48, 1.65 and 2.11 exhibit roughly the same values of 4.6*10-7 m2 s-1 and 4.0*10-7 m2 s-1, respectively. It is considered that because the silicate network is largely broken down, there is not a significant change of the structure for these samples.

  • 37.
    Hayashi, Miyuki
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Sano, Nobuo
    Fredriksson, Patrik
    KTH, Superseded Departments, Materials Science and Engineering.
    Evaluation of thermodynamic activity of a metallic oxide in a ternary slag from the sulphide capacity of the slag2004In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 44, no 11, p. 1783-1786Article in journal (Refereed)
    Abstract [en]

    The correlation between the activity of a metallic oxide in a ternary slag system and the sulphide capacity of the slag was investigated. The solubility of sulphur in the binary systems CaO-SiO2 and Al2O3-CaO along with its sulphide capacity of the Al2O3-CaO-SiO2 system respectively have been used to estimate the activities of CaO at the compositions of some Al2O3-CaO-SiO2 intermediate compounds. Estimation has been carried out assuming that the Gibbs free energy of fusion for the ternary composition is additive of those for pure substances. The estimated values of the activities are in good agreement with the measured values. This correlation is not only used to evaluate the activity but also, by comparing the estimated activities with the measured ones, it is possible to elucidate the applicability of Henry's law to the activity of a metallic sulphide and to determine the order in the affinity of a cation to sulphur between two metallic oxides in a slag.

  • 38. Hertzman, Staffan N.
    The influence of nitrogen on microstructure and properties of highly alloyed stainless steel welds2001In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 41, no 6, p. 580-589Article in journal (Refereed)
    Abstract [en]

    The influence of nitrogen on the microstructure and properties of austenitic and duplex stainless steel welds is reviewed. Three aspects are covered: intermetallic phase formation, nucleation and growth of austenite in ferrite and nitrogen balance in TIG welding. The effect of nitrogen on the precipitation of deleterious intermetallic phases is analysed for duplex and austenitic steels by thermodynamic means and the differences in response of nitrogen alloying illuminated, Also the replacement of molybdenum by tungsten is discussed. Nitrogen alloying made the duplex grades weldable. The duplex steels, designed to comprise approximately equal amounts of ferrite and austenite, solidify in a ferritic mode and a rapid transformation of ferrite to austenite is a prerequisite. Nitrogen has a beneficial effect on the austenite reformation in the HAZ (Heat Affected Zones) on cooling. This has been confirmed by both experiments and calculations. Attempts have been made to improve the nucleation of austenite and thus to increase the possibilities for welding by more demanding techniques which involve rapid cooling through the critical temperature range 1350 degreesC to 1000 degreesC. Nitrogen is added to many of the modem stainless steels because of its favourable effects on both strength and corrosion resistance. This implies that the welding procedure must consider the risk of nitrogen escape from the weld pool. Avoiding nitrogen losses may be accomplished by applying e.g. nitrogen-containing shielding gas. Applying balanced shielding gases is generally successful but on occasion reproducibility problems may arise. Correcting measures require insights in the process and the mechanisms controlling the nitrogen fluxes in TIG welding. These can be illuminated using a simple process model that accounts for alloy composition, shielding gas nitrogen content, weld pool shape and size. It is suggested that the main reasons for lack of reproducibility may be found in the batch to batch variation in surfactant content that controls the weld pool shape via the Marangoni effect and surface mass transfer reactions.

  • 39.
    Hou, Ziyong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy. Northeastern University, China .
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Xu, Yunbo
    Di, Wu
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy. AB Sandvik Materials Technology, RandD Centre, Sweden .
    Microstructure of Martensite in Fe-C-Cr and its Implications for Modelling of Carbide Precipitation during Tempering2014In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 54, no 11, p. 2649-2656Article in journal (Refereed)
    Abstract [en]

    The microstructure of as-quenched martensite in four Fe-C-Cr alloys (0.15C-1Cr, 0.15C-4Cr, 1C-1Cr, 1C-4Cr, mass%) has been investigated. Moreover, the microstructures served as input for setting up modeling of carbide precipitation during tempering of martensite. The modelling was conducted using the Langer-Schwartz approach and the software TC-PRISMA, which retrieves thermodynamic data from the Thermo-Calc databank. It was found that the martensite in the low carbon steels is predominantly lath martensite with units arranged parallel to each other. On the other hand, the plate martensite dominates the microstructure in the high carbon steels. The ratio of high-angle to low-angle grain boundaries was found to increase with increasing Cr in the low carbon steels, which indicates that Cr has a similar effect as C on the lath martensite microstructure, however, the micro-hardness remained unaffected by the addition of Cr. Finally, the precipitation modeling clearly demonstrates the importance of proper definition of the initial microstructure for predictive modelling. Parameters such as dislocation density and frequency of high-angle grain boundaries have a drastic effect on e.g. the mean size of carbides.

  • 40. Hu, X.
    et al.
    Teng, Lidong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Wang, H.
    Sundqvist Ökvist, L.
    Yang, Q.
    Björkman, B.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Carbothermic reduction of synthetic chromite with/without the addition of iron powder2016In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 56, no 12, p. 2147-2155Article in journal (Refereed)
    Abstract [en]

    Carbothermic reduction of chromite is an important industrial process for extracting chromium from the chromite. To have a better understanding of the effect of iron on the carbothermic reduction of chromite, the reduction of synthetic chromite (FeCr2O4) by graphite with/without the addition of iron powder was investigated in this paper by Thermogravimetric Analysis (TGA) in argon atmosphere. The fractional reduced samples were examined by SEM/EDS and XRD analysis, and the reduction process was thermodynamically and kinetically evaluated. The experimental results show that the iron powder addition enhances the reduction of FeCr2O4 and this effect increases when increased amounts of iron powder are added. This phenomenon is attributed to the in situ dissolution of chromium into the iron and mixed carbide (Cr,Fe)7C3, which can decrease the activity of the nascent chromium formed by the reduction of the FeCr2O4. The experimental results indicate that the reduction of FeCr2O4 with up to 80 wt.% iron powder addition is likely to be a single-step process and the kinetic analysis suggests that the reduction reaction is likely to be either (a) chemical reaction at the surface of FeCr2O4 or (b) diffusional dissolution of the product (FeCr2) into the iron/alloy particles or the mixed control of (a) and (b).

  • 41.
    Huyan, Fei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Larker, Richard
    Rubin, Per
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Effect of Solute Silicon on the Lattice Parameter of Ferrite in Ductile Irons2014In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 54, no 1, p. 248-250Article in journal (Refereed)
    Abstract [en]

    The effect of solute silicon on the ferrite lattice parameter has been investigated using X-ray diffraction in cast ductile irons (DI) with nominal Si contents between 2.50 and 4.56 wt%. It was found that silicon changes the ferrite lattice parameter by –0.00185 Å per wt% Si. This contraction coefficient is three times larger than the most commonly used Si coefficient in the literature. Since substitutional solution by silicon contracts the ferrite lattice while the interstitial solution by carbon expands the lattice, the Si contraction coefficient found will have a significant effect on subsequent evaluation of the carbon content in austempered Si-alloyed ductile irons and steels.

  • 42.
    Janis, Diana
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Karasev, Andrey
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär G.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Evaluation of Inclusion Characteristics in Low-Alloyed Steels by Mainly Using the PDA/OES Method2015In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 55, no 10, p. 2173-2181Article in journal (Refereed)
    Abstract [en]

    The characteristics of non-metallic inclusions (such as number, size and volume fraction) in liquid steel samples taken during ladle treatment and casting of industrial heats of two low-alloyed Ca-treated steel grades were evaluated by using the Pulse Distribution Analysis with Optical Emission Spectroscopy (PDA/OES) method. These results were compared to data obtained by Scanning Electron Microscope observations of inclusions after electrolytic extraction from steel samples (the EE method). It was found that the PDA/OES method can be used for a relative estimation of the homogeneity of the distribution of non-metallic inclusions in steel samples. Bottom and middle parts of the steel samples showed more homogeneous results with respect to the characteristics of the investigated Al2O3, CaO-Al2O3 and CaO-Al2O3-CaS inclusions. The numbers of inclusions in the size ranges 2.0-5.7 mu m and 1.4-5.7 mu m in samples taken before and after a Ca addition, respectively, showed a relatively good agreement between both methods. Furthermore, the calculated volume fractions for inclusions in the size range 2-13 mu m obtained by the PDA/OES method agreed satisfactorily well with those obtained from the EE method. Finally, the minimum sizes of inclusions in steel samples, which can reliably be detected by the PDA/OES method, were estimated for steels with different concentrations of Al in steel and Al2O3 in inclusions.

  • 43.
    Janis, Jesper
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Karasev, Andrey
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Nakajima, Keiji
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jönsson, Pär Göran
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Effect of Secondary Nitride Particles on Grain Growth in a Fe-20 mass% Cr Alloy Deoxidised with Ti and Zr2013In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 53, no 3, p. 476-483Article in journal (Refereed)
    Abstract [en]

    The pinning effects of different particles on grain growth were investigated in Fe-20 mass% Cr alloys deoxidised with Ti and Zr. More specifically, in-situ observations of the specimen surface were made during heat treatment at 1 200 and 1 400 degrees C in a High Temperature - Confocal Scanning Laser Microscope (HT-CSLM). Initially, primary and secondary particles were investigated using thermodynamic equilibrium calculations and the SEM/EDX observations. Thereafter, the pinning effect of secondary nitride particles on grain boundary migration and the kinetics of the grain growth process were investigated. It was found that secondary nitride particles generally have a considerable effect on the pinning of grain boundary migration during heating treatment. This is especially true for heat treatment at 1 400 degrees C. Despite that the pinning effect of TIN particles decreases due to dissolution of these particles, the implicit pinning effects of ZrO2, ZrO2-ZrN and ZrO2-ZrN-TiN particles appear. Thus, despite that TIN individually is ineffective in causing grain-boundary pinning at high-temperature, TiN is effective as a compound with ZrO2 and ZrN in pinning grain-boundaries at high temperatures. The changing of the uniformity of grain size distributions during grain growth at different N contents and temperatures was discussed based on the consideration of the geometric standard deviation of the grain size distribution (sigma(g)).

  • 44.
    Janis, Jesper
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Nakajima, Keiji
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Karasev, Andrey
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Inoue, Ryo
    Jönsson, Pär Göran
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Effects of Primary Oxide and Oxide-Nitride Particles on the Solidification Structure in a Fe-20 mass%Cr Alloy Deoxidised with Ti and M (M = Zr or Ce)2013In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 53, no 2, p. 221-229Article in journal (Refereed)
    Abstract [en]

    The ratio of equiaxed grains on a cross section and the size of equiaxed grains in a Fe-20 mass% Cr alloy deoxidised with Ti/M (M = Zr or Ce) were studied as function of nitrogen content and particle characteristics such as size distribution, morphology and composition. Fe-20 mass% Cr alloys were melted at 1 600 degrees C, deoxidised, and cooled to 1 400 degrees C followed by water quenching. Thereafter, the particles were separated from the matrix using electrolytic extraction using a 10%AA electrolyte and collected on a film-filter surface. The inclusion characteristics were determined using SEM. It was found that the number of particles increases with an increased N content. Furthermore, that the solidification structure was clearly affected by the number of primary oxide and oxide-nitride particles in the Ti/Zr deoxidation experiments. However, a similar effect could not be detected in the Ti/Ce deoxidation experiments.

  • 45.
    Jansson, Sune
    et al.
    Arvika Gjuteri AB.
    Brabie, Voicu
    Dalarna University.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Corrosion mechanism of commercial MgO-C refractories in contact with different gas atmospheres2008In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 48, no 6, p. 760-767Article in journal (Refereed)
    Abstract [en]

    Corrosion of MgO-C refractories in different gas atmospheres consisting of air, Ar, CO or Ar/CO was studied in laboratory experiments. In total, 103 experiments were carried out in the temperature range 1 173 to 1 773 K and for holding times between 2 to 120 min. The reaction rate of the MgO-C material was determined from measurements of the weight loss of the samples. The results showed that the refractory weight loss increased with an increased temperature or an increased holding time. The thermodynamic conditions and the experimental results showed that magnesium gas and carbon monoxide gas should form during ladle refining of steel when the refractory material consists of MgO-C. It was suggested that the reaction rate is directly dependent on the oxygen potential in the ambient atmosphere.

  • 46.
    Jonsson, Lage
    et al.
    KTH, Superseded Departments, Metallurgy.
    Jönsson, Pär
    Modeling of the fluid flow conditions around the slag/metal interface in a gas-stirred ladle1996In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 36, no 9, p. 1127-1134Article in journal (Refereed)
    Abstract [en]

    A three-phase model of a gas-stirred steel bath covered with a slag layer has been developed. Predicted steel surface velocities have been shown to be in at least five times greater agreement with experimental data compared to predicted velocities from a model which excludes the effect of a slag phase. It has also been shown that it is possible to predict the amount of slag dispersed into the steel.

  • 47.
    Jonsson, Lage
    et al.
    KTH, Superseded Departments, Metallurgy.
    Jönsson, Pär
    Sichen, Du
    Prediction and experimental verification of hydrogen refining parameters during vacuum degrassing in a  ladle furnace: Part 1 - theoretical model1998In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460Article in journal (Other academic)
  • 48.
    Jonsson, Lage
    et al.
    KTH, Superseded Departments, Metallurgy.
    Jönsson, Pär
    Sichen, Du
    Prediction and experimental verification of hydrogen refining parameters during vacuum degrassing in a  ladle furnace: Part 2 - Plant trials and verifications1998In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460Article in journal (Other academic)
  • 49.
    Jonsson, Lage
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    A new approach to model sulphur refining in a gas-stirred ladle: A couple CFD and thermodynamic model of sulphur refiningin a gas-stirred ladle1998In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 38, no 3, p. 260-267Article in journal (Refereed)
  • 50.
    Jönsson, Pär
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jonsson, Lage
    KTH, Superseded Departments, Metallurgy.
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Viscosities of ld slags and their impact on ladle refining1997In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 37, no 5, p. 484-491Article in journal (Other academic)
1234 1 - 50 of 156
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