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  • 1. Andersson, Annika J.
    et al.
    Andersson, Margareta A. T.
    KTH, Superseded Departments, Materials Science and Engineering.
    Jönsson, Pär G.
    KTH, Superseded Departments, Materials Science and Engineering.
    Variation in hot metal and stag composition during tapping of blast furnace2004In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 31, no 3, p. 216-226Article in journal (Refereed)
    Abstract [en]

    To determine the quality of the hot metal and the thermal conditions inside the blast furnace, the composition of the hot metal and slag must be known. Obtaining representative metal and slag samples during tapping is thus highly important to blast furnace operation. The study covered in the present report focused on hot metal and slag composition variation during tapping from a commercial blast furnace. From the results, optimal sampling time points for obtaining elemental concentrations that can be taken as representative for the whole tapping sequence were identified. It was furthermore concluded, that the reliability of hot metal composition data is significantly improved by averaging elemental concentrations determined from two samples, each taken at a particular time point. One sampling, however, was found to be adequate for slag. Results from the study also showed a fairly strong correlation between amounts of silicon and carbon, sulphur and carbon, and silicon and sulphur in the hot metal, while a weaker correlation between hot metal temperature and each of these elements was observed.

  • 2.
    Andersson, Margareta A. T.
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Jonsson, P. G.
    Hallberg, M.
    Optimisation of ladle slag composition by application of sulphide capacity model2000In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 27, no 4, p. 286-293Article in journal (Refereed)
    Abstract [en]

    The sulphur distribution ratio for ladle slags at Ovako Steel AB has been determined by calculating the sulphide capacity using the Royal Institute of Technology (KTH) model and the alumina activity via an empirical expression suggested by Ohta and Suite, and by using the well established theories for sulphur refining. A parameter study was carried out based on plant data from a previous study on desulphurisation, The effect of carbon and aluminium in the steel, the temperature of the steel, and alumina and lime in the slag on the sulphur distribution ratio was investigated, it was shown that the Al2O3/CaO ratio had the largest influence on the conditions studied, and that when it increased the sulphur distribution ratio decreased. Based on these results, new plant trials were carried out, in which the alumina content in the slag was changed. The calculated sulphur distribution ratios for these trials were found to be in good agreement with experimentally determined sulphur distribution ratios. It is concluded that the present approach can be used to optimise multicomponent ladle slags with respect to sulphur refining. I&S/1493.

  • 3.
    Andersson, Margareta A.T.
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Hallberg, Malin
    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.
    Slag-metal reactions during ladle treatment with focus on desulphurisation2002In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 29, no 3, p. 224-232Article in journal (Refereed)
    Abstract [en]

    Within several cooperative projects, KTH (Royal Institute of Technology), Ovako Steel AB, and MEFOS have investigated the desulphurisation of bearing steel during vacuum degassing. The work includes thermodynamic calculations of the slag-metal equilibrium, CFD modelling of slag-metal reactions, and plant trials. Results from the various studies are presented and discussed in this paper. Models for predicting slag properties (sulphide capacity, viscosity, and oxide activities) in liquid slags as functions of slag composition and temperature have been used for the calculation of data which have been employed in static and dynamic modelling of sulphur refining. The results from static modelling show that the method allows fast and easy evaluation of the theoretical desulphurisation conditions during degassing at Ovako Steel AB, as well as theoretical determination of the parameters that have the greatest influence on the equilibrium sulphur distribution. The conclusion from dynamic modelling is that the vacuum degassing operation can be described dynamically with the present knowledge of sulphide capacity, sulphur distribution, viscosity, and oxide activities of ladle slags if this knowledge is combined with fluid flow modelling to derive the overall kinetics. The presented model approaches have been found useful in understanding the sulphur refining process at Ovako Steel AB. The dynamic modelling concept is also believed to have potential for dynamic descriptions of other slag-metal reactions in steelmaking.

  • 4.
    Andersson, Nils
    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.
    Fundamental decarburisation model of AOD process2013In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 40, no 5, p. 390-397Article in journal (Refereed)
    Abstract [en]

    A mathematical fluid flow model of gas injection in an argon–oxygen decarburisation (AOD) converter process has been coupled with a high temperature thermodynamic model. The current model is a further enhancement of an earlier developed three-dimensional, three-phase model, to also include some thermodynamics of the process. The model is based on fundamental transport equations and includes separate solutions for the steel, slag and the gas phases and their coupling by friction. The AOD model has been used to predict the first injection stage of decarburisation in an AOD converter. The predictions have been found to agree well with the corresponding results from an industrial process control model. One of the important observations from the simulations was that large concentration gradients of carbon exist in the AOD at an early stage and as the first injection step approaching its end the carbon gradients diminish. Also, the results show, in accordance with theory, that the local decarburisation rate is decreased at elevated pressures.

  • 5.
    Andersson, Nils
    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.
    Preliminary investigation of influence of temperature on decarburisation using fundamental AOD model2013In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 40, no 7, p. 551-558Article in journal (Refereed)
    Abstract [en]

    A high temperature thermodynamics model was earlier coupled with a fundamental mathematical model describing the fluid flow in an argon–oxygen decarburisation (AOD) converter and was initially validated for an idealised temperature description. More specifically, a linear average temperature relation was used such that the temperature would be isolated from other effects such as reactions and mixing. Thereafter, the effect of the starting temperature on the decarburisation was studied. The purpose is to provide some initial knowledge about how temperature affects the decarburisation in an AOD converter. The results suggest that the thermodynamic limit for carbon concentration after reaching the carbon removal efficiency (CRE) maxima is vertically translated downwards at higher temperatures. Furthermore, when plotting the mass ratio between CO and CO2, there is an indication of a point that may relate to a CRE maximum.

  • 6.
    Andersson, Nils Å. I.
    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 T. I.
    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.
    A fundamental decarburization model of the AOD processIn: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812Article in journal (Other academic)
  • 7.
    Andersson, Nils Å. I.
    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 T. I.
    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.
    Preliminary investigation of temperatur dependencies on decarburization in a fundamental AOD modelIn: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812Article in journal (Other academic)
  • 8.
    Aune, Ragnhild E.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Hayashi, M.
    Sridhar, S.
    Thermodynamic approach to physical properties of silicate melts2005In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 32, no 2, p. 141-150Article in journal (Refereed)
    Abstract [en]

    The thermophysical properties of silicate melts are strongly structure dependent. It is well known that the viscosity of slags increases with increasing degree of polymerisation of the silicate anion. Even the thermodynamic properties of slags are dependent on the species type and population in the melt. Thus, a link between the thermophysical and thermochemical properties of silicate melts is logically expected. The present paper elucidates the salient features of Darken's excess stability approach to the Gibbs energy of solution as applied to the viscosities of silicate melts. It is demonstrated that the second derivatives of the viscosities of binary silicate melts with respect to composition indicate maxima corresponding to the existence of stable compounds in these systems. The concept has been successfully applied to the following systems: Al2O3-SiO2, CaO-SiO2, FeO-SiO2, MgO-SiO2 and MnO-SiO2. In all cases, the second derivative plots of viscosities with respect to composition show peaks corresponding to the metasilicates. The second derivatives of the activation energies of viscous flow with respect to temperature have earlier been shown to reflect the formation of associates/embryos in homogeneous silicate melts, indicating the readiness of the melt to separate a solid phase. Thermodynamic coupling of thermal diffusivities in the case of the CaO-Al2O3-SiO2 system from laser flash measurements of these slags, as a function of temperature, has been examined as part of the present study. Densities have been estimated from integral molar enthalpies in the case of silicate systems, and the results are presented.

  • 9.
    Beheshti, Reza
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Nothern Research Institute Narvik, Norway.
    Moosberg-Bustnes, J.
    Kennedy, M. W.
    Aune, R. E.
    Reduction of commercial hematite pellet in isothermal fixed bed-experiments and numerical modelling2016In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 43, no 1, p. 31-38Article in journal (Refereed)
    Abstract [en]

    In the present work, fixed bed reduction experiments were conducted at 1173 K over a range of H-2/CO ratios from 0.8 to 2.0 and subsequently modelled numerically (R). The model consists of two one-dimensional, isothermal and time dependent models. The gas-solid reactions were kinetically modelled using a modified shrinking core approach, and the equations were solved using the commercial software COMSOL Multiphysics H. The simulation results agree with thermal gravity experimental data with an average difference of 2.5%. A sensitivity analysis was conducted using the numerical model to establish the optimum operational conditions. The effects of the reducing gas ratio and flow rate, pellet radius and porosity, and the total bed height on the overall degree of reduction were also investigated.

  • 10.
    Beheshti, Reza
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Northern Research Institute Narvik, Norway.
    Moosberg-Bustnes, John
    Kennedy, Mark W.
    Aune, Ragnhild E.
    Reduction kinetics of commercial haematite pellet in a fixed bed at 1123-1273 K2016In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 43, no 5, p. 394-402Article in journal (Refereed)
    Abstract [en]

    In the present study a model for future use in the modelling of moving bed direct reduction reactors has been developed. The model of a fixed bed reactor for the production of sponge iron from haematite incorporates both heat-and mass-transfer, as well as the chemical reduction rate. The model results were compared to the experimental data obtained from a lab scale reactor in the temperature range 1123-1273 K, as well as to the output from a simple model assuming isothermal conditions. The H-2/CO ratio (beta) of the reducing gas was in all cases varied from 0.8 to 2.0. Overall the non-isothermal model developed permits a more accurate representation of the experimental data than the isothermal estimates, with a typical discrepancy of only 1.3%.

  • 11. Beskow, Kristina
    et al.
    Dayal, Pranesh
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Björkvall, Johan
    Nzotta, Mselly
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    A new approach for the study of slag-metal interface in steelmaking2006In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 33, no 1, p. 74-80Article in journal (Refereed)
    Abstract [en]

    The main focus of the present work was to develop a sampler to obtain the physical description of the slag-metal interface in the presence of bulk flow. Industrial trial experiments were carried out in the ladles at Uddeholm Tooling, Hagfors, Sweden using the designed sampler. Samples of the slag-metal interface were successfully taken in both gas stirring and induction stirring modes. The similarities of the appearance as well as the micrographs of the samples suggested that the slag-metal interfaces in the two stirring modes were very similar except in the open eye area. In the case of both stirring modes, metal droplets were found in the slag bulk. On the other hand, no appreciable amount of slag was detected in the metal bulk. Further systematic investigation using a large number of samples is required to obtain a quantitative description of the interface.

  • 12.
    Beskow, Kristina
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Sichen, Du
    KTH, Superseded Departments, Materials Science and Engineering.
    Ladle glaze: major source of oxide inclusions during ladle treatment of steel2004In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 31, no 5, p. 393-400Article in journal (Refereed)
    Abstract [en]

    Samples of ladle lining covered by glaze were taken from industrial ladles of different ages at Uddeholm Tooling AB, Hagfors, Sweden. It was found in the samples taken at and below the slag line that a slag infiltrated layer was covered by an outer layer containing many MgO 'islands' of various sizes. The microstructure of the infiltrating slag was the same as the matrix of the outer layer. The slag was found to decompose into the compound 3CaO. Al2O3 and a liquid phase during the cooling process. The former phase along with tiny MgO particles from the ladle glaze was found to be one of the major sources of inclusions during the degassing and flotation periods of ladle treatment. Thermodynamic analysis indicated that the reaction between the ladle glaze and the slag from the electric arc furnace resulted in the formation of MgO-Al2O3 spinel and an oxide solution, which were also the main inclusions found at the initial stages of ladle treatment. Evidence of this reaction was found in the lining samples taken above the slag line.

  • 13.
    Beskow, Kristina
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Tripathi, Nagendra N.
    KTH, Superseded Departments, Materials Science and Engineering.
    Nzotta, M.
    Sandberg, A.
    Sichen, Du
    KTH, Superseded Departments, Materials Science and Engineering.
    Impact of slag-refractory lining reactions on the formation of inclusions in steel2004In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 31, no 6, p. 514-518Article in journal (Refereed)
    Abstract [en]

    The present study was carried out to investigate the impact of slag-refractory lining reactions on the formation of inclusions during ladle treatment of steel. The experiments were conducted on an industrial scale in the ladle at Uddeholm Tooling AB in Hagfors, Sweden. The inclusion chemistry and population during ladle treatment were studied along with the composition of the ladle glaze, taken from the ladle lining. The inclusions in the steel were classified into four groups according to the Swedish standard SS 111116. SEM/EDS analyses were carried out to identify the phases present in both the inclusions and the ladle glaze. The number of inclusions in the steel before deoxidation was found to increase with the ladle age, i.e. the number of times the ladle had been in use. A similar increase was also found after vacuum degassing and before casting. A great portion of inclusions before casting was found to be supplied by ladle glaze. This observation was further confirmed and explained by thermodynamic analysis. The present results show that ladle glaze is a major source of inclusions in the ladle at Uddeholm Tooling.

  • 14.
    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.
    Investigations of inclusions in ferrochromium alloys2014In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 41, no 10, p. 756-762Article in journal (Refereed)
    Abstract [en]

    Ferrochromium alloys are commonly added during different stages of steelmaking processes according to the specific steel grade being produced. Depending upon the ferrochromium quality, the addition can also lead to a supply of deleterious inclusions to the liquid steel. Therefore, the number, size, morphology and composition of inclusions in LCFeCr and HCFeCr alloys were investigated. The alloy samples were first treated with electrolytic extraction, followed by filtration to gather the inclusions on a film filter. Thereafter, the characteristics of the inclusions and clusters were investigated in three dimensions by SEM in combination with energy dispersive spectroscopy. The results show that the main inclusion types found in LCFeCr alloys are different to those found in HCFeCr alloys. More specifically, the inclusions in LCFeCr alloys were found to consist of Si-Cr-O and Cr-O oxides as well as intermetallic Cr-Fe inclusions. Moreover, the inclusions in HCFeCr alloys were found to consist of Cr-Mn-S, Cr-C-N, Si-Al-Ca-Mg-O and Ca-O-P inclusions. Overall, the inclusions can be divided into two categories depending on the melting point. Furthermore, the possible transformation of different inclusions after their addition to the liquid steel is discussed.

  • 15. Bjorkvall, J.
    et al.
    Du, S. C.
    Seetharaman, Seshadri
    KTH, Superseded Departments, Materials Science and Engineering.
    Thermodynamic model calculations in multicomponent liquid silicate systems2001In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 28, no 3, p. 250-257Article in journal (Refereed)
    Abstract [en]

    A thermodynamic model developed earlier in the present laboratory for oxidic melts was applied to some multicomponent systems, namely CaO-FeO-MgO-SiO2, Al2O3-CaO-MgO-SiO2, Al2O3-FeO-MnO-SiO2, and Al2O3-CaO-FeO-MgO-MnO-SiO2. Model calculations were carried out using only the parameters corresponding to the binary systems, which, in turn, were based on the available thermodynamic information for these systems. The predicted thermodynamic activities of the component oxides in higher order systems were compared with the experimental data published in the literature. In general, the agreement between the model predictions and the experimental values was found to be satisfactory within the limits of experimental uncertainties and limitations of the model calculations. Examples of model predictions for some typical slag compositions, relevant to the Swedish steel industry and used in the blast furnace, electric arc furnace, and ladle furnace are also presented.

  • 16.
    Björklund, Johan
    et al.
    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.
    Equilibrium between slag, steel and inclusions during ladle treatment: comparison with production data2007In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 34, no 4, p. 312-324Article in journal (Refereed)
    Abstract [en]

    The primary purpose of the investigation was to determine whether equilibrium conditions exist between slag and steel and inclusions and steel after silicon deoxidation and aluminium deoxidation. In doing so, the performance of three different models for predicting oxide component activities was also evaluated. The results from the oxide activity models were used to calculate oxygen activities in the steel melt. Industrial data such as steel, slag and inclusion component concentrations, as well as temperature, were used as input to the calculations. One general conclusion drawn was that although the results from the different models showed similar trends, the models did not predict the same actual values for specific calculations. Predicted theoretical equilibrium oxygen activity values were compared with plant measurements of oxygen activity. Here, it was found that the oxygen activity values pertaining to the equilibrium between steel and inclusions were higher than corresponding measured values. The calculations for the equilibrium between the top slag and steel melt, however, resulted in theoretical oxygen activity values considerably lower than corresponding measurements. It was thus concluded that equilibrium conditions did not exist between the top slag and the steel bulk with respect to oxygen. Overall, the models proved useful in predicting oxide activities, but the lack of equilibrium between top slag and molten steel made the calculation of oxygen activity difficult.

  • 17.
    Brandberg Hurtig, Jenny
    et al.
    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.
    Hydrogen pick-up after vacuum degassing2015In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 42, no 1, p. 49-54Article in journal (Refereed)
    Abstract [en]

    The present work aimed at determining the major source for hydrogen pick-up of the steel after vacuum degassing but before casting. Samples of slag and metal were taken at different stages during ladle treatment at SSAB. Hydrogen increase after vacuum treatment was observed. Moisture contents of the industrial slags were analysed and their water capacities were calculated. It could be seen that the hydrogen increase was correlated to the amount of moisture in the slag and the water capacity. The study showed that the slag containing most water was also the heat having the largest hydrogen increase. The slag with most water had the highest water capacity. It could be concluded that the major source for hydrogen increase after degassing was due to the slag-metal reaction.

  • 18. Cheng, J.
    et al.
    Eriksson, R.
    Jönsson, Pär
    KTH, Superseded Departments, Materials Science and Engineering.
    Determination of macroinclusions during clean steel production2003In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 30, no 1, p. 66-72Article in journal (Refereed)
    Abstract [en]

    There are very few macroinclusions in clean steel, but the few that exist are very harmful for material properties of the final steel product. To date, very little information on large, so called macroinclusions in clean steel production has been presented. Therefore, the present study has focused on providing information on these inclusions during different stages of the steelmaking process, based on plant trials carried out at Uddeholm Tooling, Hagfors, Sweden. Macroinclusion size distributions have been determined using optical microscopy and classified according to a modified version of the Swedish standard SS 111116, as well as using immersed ultrasonic scanning. For the sake of completeness, the size distribution of microinclusions has also been determined using optical microscopy. Inclusion compositions were determined using a scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS). Two types of liquid steel sampler were used in the investigation: a rapid solidifying (RS) sampler and the LSHR (liquid sampling hot rolling) sampler, suitable for immersed ultrasonic scanning. The results are critically discussed with respect to process conditions, such as alloy additions that took place during the plant trials.

  • 19.
    Dahlin, Anders
    et al.
    LKAB, Malmberget, Sweden.
    Eriksson, Johan
    Swerea MEFOS AB, Process Metallurgy Department, Luleå, Sweden.
    Tilliander, Anders
    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.
    Influence of ladle slag additions on BOF process under production conditions2012In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 39, no 5, p. 318-326Article in journal (Refereed)
    Abstract [en]

    The influence of recycled ladle slag on the basic oxygen furnace (BOF) process under production conditions was investigated in plant trials. More specifically, 25 heats with ladle slag additions and 23 heats without ladle slag additions were studied. Both steel and slag samples were collected, from which the chemical compositions were determined. In addition, several process parameters were monitored. Overall, it was found that recirculation of ladle slag during normal production conditions works fine. On the positive side, it was seen that the steel quality concerning the phosphorus and sulphur contents of liquid steel has, in accordance with previous studies, not been affected by the ladle slag additions. Furthermore, no major differences in the slag composition occur when the recycling of ladle slag to BOF is performed. Finally, in comparison to previous studies, the increased tendency for slopping when adding ladle slag could be eliminated with a change in the lance schedule. However, on the negative side, it was seen that the addition of ladle slag leads to an increased blowing time due to lower iron ore additions. Moreover, the slag weight at tapping increased due to an increased weight of added slag formers.

  • 20.
    Dahlin, Anders
    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.
    Eriksson, Johan
    Swerea MEFOS AB, Process Metallurgy Department, Luleå, Sweden.
    Jönsson, Pär G.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Influence of ladle slag additions on BOF process performance2012In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 39, no 5, p. 378-385Article in journal (Refereed)
    Abstract [en]

    A plant trial has been performed, with recycling of ladle slag to the LD converter at SSAB EMEA, Lulea, Sweden. The effect of ladle slag addition on the slag and steel composition, together with the slag weight, was investigated with sampling both during the blow and at blow end. The addition of ladle slag resulted in an increase in slag weight between 1 and 2 t throughout the blow and an increase of 3 wt-% in the slag Al2O3 content. This indicated that the ladle slag melted during the initial stages of the blow and enhanced the early slag formation. Lime additions were reduced with 3.5 kg t(-1) liquid steel without drawbacks on the phosphorus or sulphur refining. Heats with added ladle slag had an increase in blowing time with similar to 4% and an increased tendency for slopping. However, this can be handled by different lance and addition programmes.

  • 21. Dayal, P.
    et al.
    Beskow, K.
    Bjorkvall, J.
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Study of stag/metal interface in ladle treatment2006In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 33, no 6, p. 454-464Article in journal (Refereed)
    Abstract [en]

    In order to gain an insight into the mixing behaviour of slag and metal under different stirring conditions, samples of slag/metal interface were collected from an industrial 65 ton ladle furnace using a new sampling technique. Different stirring conditions and sampling positions in the ladle were chosen. Complementary cold model experiments were also performed. The experimental results strongly suggested that the shear force between the two liquids played an important role in slag-metal mixing. Evidence for the existence of slag droplets each surrounded by a very thin metal film was found in the samples taken under both gas stirred and induction stirred conditions. This observation strongly suggested that slag-metal system behaved similarly as oil-water system, wherein, the shear force owing to the bulk flow led to a packed 'sphere bed' of oil droplets each coated by a thin water film above the water bath. On the basis of the experimental results, preliminary mathematical models were developed to describe the rate of mass exchange at the slag/metal interface.

  • 22.
    Deng, Tengfei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Dissolution mechanism of dolomite in converter slag at 1873K2014In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 41, no 1, p. 75-80Article in journal (Refereed)
    Abstract [en]

    The mechanism of dolomite dissolution in converter slag was studied and found to proceed by two steps: decomposition of dolomite into CaO and MgO and dissolution of the product into the slag. The first step was found to be controlled by heat transfer, which was confirmed by theoretical calculation. The decomposed dolomite had many pores, which allowed easy slag penetration. A discontinuous 2CaO.SiO2 layer along with MgO.Fe2O3 particles was found on the surface of the samples. Some 2CaO.SiO2 islands were found in the vicinity of the samples in the slag, revealing that the dissolution was dominated by peeling-off of the layer of 2CaO.SiO2- MgO.Fe2O3 mixture. 2CaO.SiO2, (Mg, Fe)Oss along with super cooled liquid phases were found inside dolomite samples close to the surface. 2CaO.SiO2 phase was replaced gradually by 3CaO.SiO2 towards the centre of the decomposed sample. While addition of small amounts of dolomite directly into the slag could be considered in steelmaking converter, too much would result in slow dissolution and waste of the raw materials.

  • 23.
    Ek, Mattias
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Huber, Jean-Christophe
    Brosse, Guillaume
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Capacities of some CaO-SiO2-FeO-MnO-MgO slags and slag-solid mixtures in capturing phosphorous2013In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 40, no 4, p. 305-311Article in journal (Refereed)
    Abstract [en]

    Slag is of great importance for dephosphorisation in converter steelmaking. In the present study, slag samples were equilibrated with copper at 1923 K to study their capacities in capturing phosphorous. The phosphate capacities of the slags were calculated. Some of the samples were liquid-solid mixtures. The solid phases in these samples were identified by SEM analysis, and the identified phases were found to agree well with Thermocalc calculations. On the other hand, the fractions of the solid phase did not agree with the Thermocalc calculation. Phosphorous distributions in the different phases were examined, and the phosphate capacities of the samples were evaluated. The MgO content did not show any appreciable impact on the phosphate capacity. The activities of FeO in the pure liquid slag samples were calculated and found to deviate positively from ideality.

  • 24.
    Ek, Mattias
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Shu, Q. F.
    van Boggelen, J.
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    A new approach towards dynamic modelling of dephosphorisation in converter process2012In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 39, p. 77-84Article in journal (Refereed)
    Abstract [en]

    A new approach was made to model the dephosphorisation process in a 300 tons basic oxygen furnace converter with three argon gas inlets. The main feature of the new approach was to utilise the velocity vectors obtained by computational fluid dynamics (CFD) simulation in a standalone model. The CFD simulation was carried out using commercial software COMSOL Multiphysics. In the standalone model, the steel melt domain was sliced into 1000 cells. The calculated velocity vector in each cell was assumed constant. Based on the imported velocity vectors from the CFD calculation, the mass transfer of carbon and phosphorus was calculated by taking into account the slag-metal reactions. The mass exchange between slag and metal was considered to be dominated by the metal droplet formation due to the oxygen jet. The convergence of the model calculation and the promising comparison between the model prediction and the industrial data strongly suggested that the proposed approach would be a powerful tool in dynamic process control. As a preliminary step, the model only simulated the process after the formation of slag-metal-gas emulsion. Note that the present work is intended to establish a structure of the model. More precise descriptions of other process aspects need to be included before the model can be practically employed in a dynamic controlling system.

  • 25. Ekengard, J.
    et al.
    Andersson, Margareta A.T.
    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.
    Distribution of metal droplets in top slags during ladle treatment2008In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 35, no 8, p. 575-588Article in journal (Refereed)
    Abstract [en]

    The investigation focused on the mixing of the metal and slag phases during ladle refining from the point of tapping the EAF to casting. Steel droplet distributions were determined for slag samples taken at different stages in the ladle refining process at two different steel plants in Sweden. The droplet distributions were determined using light optical microscopy and classification according to the standard SS111116. Sample analysis results showed the slag samples taken before vacuum degassing to contain the greatest concentration of steel droplets. The total interfacial area between the steel droplets and slag was determined to be 3-14 times larger than the projected flat interfacial area between the steel and slag. The effects of slag viscosity and reactions between steel and slag on metal droplet formation in slag were also considered.

  • 26.
    El-Bealy, Mostafa Omar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Spray cooling pattern and microthermomechanical rigidity criterion for improving inner quality in continuously cast steel slabs2013In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 40, no 3, p. 167-188Article in journal (Refereed)
    Abstract [en]

    A new concept has been developed to assess, and a new technique developed to improve, the microthermomechanical rigidity of the solidifying shell in the secondary cooling zones during continuous casting of steel. This is to maximise the coherent solid shell resistance 'I-c' against thermometallurgical and mechanical stresses at different levels from meniscus. The idea behind this concept is to optimise the degree of homogeneity of the cooling pattern between a pair of rolls. The effect of the degree of homogeneity of the cooling pattern between a pair of rolls 'HDCP', in different spray cooling zones on the different types of centreline segregates has been investigated. A number of plant trials with two different water cooling patterns between a pair of rolls have been performed. The metallographic investigation contains examinations and measurements of the level of centreline segregates of collected samples. A one dimensional (1D) transient finite difference mathematical model of thermal, solidification, solid shell resistance and cooling conditions has been developed to test the different effects of spray patterns on the microthermomechanical rigidity concept and therefore on the mechanism of centreline macrosegregation level. The results indicate that the increase in the degree of homogeneity of the cooling conditions is proportional to the increase in slab internal microquality. The results show that the degree of homogeneity of the cooling pattern affects centreline macrosegregation significantly. This depends significantly on the degree of homogeneity of cooling pattern between a pair of rolls, its location from the meniscus and, generally, on the increase microthermomechanical rigidity concept.

  • 27.
    Eriksson, Conny
    et al.
    KTH, Superseded Departments, Production Engineering.
    Lundberg, S.-E.
    Working range of roll pass sequences in wire rod rolling with interstand tensions2004In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 31, no 1, p. 81-92Article in journal (Refereed)
    Abstract [en]

    In the high speed rolling of wire rod in blocks, interstand tensions are utilised in order to keep the process stable. However, interstand tensions influence the rolling process, and especially the spread and forward slip, which are dependent of tensions between the stands. By the influence on spread, the tolerances of the rolled product depend on the tensions and usually the interstand tensions are kept as low as possible in order to obtain required tolerances. A narrow spread technology is used to utilise interstand tensions in order to increase the working range of a pass sequence and move the product range towards smaller sizes. By adapting a certain amount of interstand tensions, smaller sizes can be rolled by a given roll pass schedule. A practical problem in this method is the fixed gearings in the common blocks, which require a certain and given level of interstand tensions and corresponding reductions. In the latest generation of blocks, where the stands are arranged in units, two by two, with each unit driven by a dedicated electrical motor, it is possible to introduce 'inter unit' tensions, and by this method extend the working range of the pass sequence. A special computer program for analysis of interstand tensions has been developed by combining a program TENSION, developed at the Royal Institute of Technology in Stockholm, dealing with the basic principles of rolling with interstand tensions, with the recently published program WORKRAN, which analyses the working range of any roll pass sequence built up by common two-symmetrical grooves. From the analysis and experimental data it is shown that interstand tensions at the level of 10% of the yield stress of the material increase the working range in a six stand block by 2% and reduce the lower limit of the exit section area by about 15%. Higher tension levels have a larger effect both on the extension of the working range and on the reduction of the minimum exit area but it becomes more difficult to control the tolerances at higher tension levels. The influence of interstand tensions on the reduction and on the working range of the pass sequence is mainly obtained by the influence on the round passes, while the oval passes have a counteracting effect on the influence of interstand tensions.

  • 28.
    Fredriksson, Patrik
    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.
    Thermodynamic studies of stags containing FeO and their impact on ladle refining process2005In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 32, no 1, p. 47-53Article in journal (Refereed)
    Abstract [en]

    In the ladle refining process, the FeO content of the ladle slag is of great importance in the chemistry as well as the energetics of the process. Optimisation of the process requires an accurate knowledge of the thermodynamic activities of FeO in the ladle slags. Due to the discrepancies in existing data, renewed attempts are being made at the Royal Institute of Technology to generate reliable data for binary, ternary and multicomponent slags containing FeO at steelmaking temperatures. In order to measure the activities of FeO in the slags, a gas equilibration technique was employed in the present work. The slags, kept in Pt crucibles were equilibrated with a CO-CO2-Ar gas mixture and quenched after equilibration. The chemical composition of the slag was analysed. From knowledge of the thermodynamics of the Fe-Pt system, the 'FeO' activities in the slag were evaluated. The results of the present studies, together with other literature values, were optimised in the slag software THERMOSLAG developed at the Royal Institute of Technology, Sweden. The results of the optimisation are presented. Model calculations were performed with the KTH slag software THERMOSLAG using plant data from Ovako Steel, Hofors, Sweden. It was found that oxygen estimations in the metal from the FeO analyses of slags, obtained by a conventional sampling and analysis method were less reliable. Estimation of the oxygen levels utilising the sulphur partition between the slag and the metal were carried out using the THERMOSLAG software. Reasonable estimations of the oxygen content in the metal confirmed that this could be a very useful tool for the plant operator.

  • 29.
    Gauffin, Alicia
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Andersson, N. A. I.
    Storm, P.
    Tilliander, Anders
    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.
    Use of volume correlation model to calculate lifetime of end-of-life steel2015In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 42, no 2, p. 88-96Article in journal (Refereed)
    Abstract [en]

    A new mathematical model for calculating the lifetime of steel on an annual basis, called the volume correlation model is presented. The model compares the quantities of scrap collection with the steel consumption as well as evaluates the time difference between the two data sets. The lifetime of steel was calculated for the collected end-of-life steel amounts. The calculations were performed by assuming a full recovery of the steel consumption or a non-re-circulated accumulated steel stock in society denoted the full and true lifetime of steel. Based on the volume correlation model, the lifetime of steel was calculated for the total steel, low alloyed and special steel, and stainless steel in Sweden between 1898 and 2010. Previous studies on the lifetime of steel are based on experimental measurements and numerical calculations. The full lifetime of the total amount of steel from previous studies is 31 and 35 years for the years 2000 and 2006 respectively. Based on the volume correlation model the lifetime for the total steel amount, when assuming a full recovery of the material, was calculated as 34 and 37 years for these two years. This indicates that the lifetime of steel from the volume correlation model is in a similar range, but slightly higher, compared to previously reported data. The present results show that the model could be an alternative method to calculate the lifetime of steel and other recyclable materials on an annual basis. Results show that the lifetime of the total steel amount has continuously increased between 1975 and 2010. This indicates that the accumulated steel stock in society is still large enough to withstand the high collection rate of steel scrap. Furthermore, that there are as yet no lack of untapped resource of end-of-life steel scrap assets in Swedish society.

  • 30.
    Gran, Jimmy
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Thunman, Mikael
    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.
    Effects of slag composition and cooling rate on formation of glaze on MgO refractory2010In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 37, no 1, p. 27-34Article in journal (Refereed)
    Abstract [en]

    The formation of a slag glaze layer on dense and porous MgO rods was studied by dipping MgO rods into liquid slag at 1873 K and thereafter cooling the rods at a predetermined cooling rate. Three different slag compositions and three different cooling rates were employed. It was found that the phases formed upon cooling were mostly dependent on slag composition and to a minor extent on the cooling rate. The initially liquid slag was transformed into crystalline phases for all the samples except the ones terminated at 1573 K and one of the samples with high cooling rate. In addition, the three slags were equilibrated at 1773, 1673 and 1573 K in order to get an understanding of the equilibrium phases and their relationship during cooling. On the basis of the experimental results, the mechanism regarding entrainment of exogenous inclusions from the refractory lining was also discussed.

  • 31.
    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.
    Comparison of calculated equilibrium and operation data for blast furnace with focus on silicon2009In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 36, no 5, p. 341-353Article in journal (Refereed)
    Abstract [en]

    An investigation of reactions involving blast furnace hot metal, slag and gas at equilibrium was carried out. Performed calculations were based on estimated total gas pressures, measured temperatures and hot metal and slag compositions. Calculated element contents of liquid phases were found to be very similar to their corresponding values determined through measurement when formation of the gas phase was suppressed. This resulted in higher equilibrium CO partial pressures compared to the measured total gas pressure in the bustle ring. When only equilibrium conditions were considered, the predicted amount of silicon was much higher than the measured. A comparison of activity coefficients of elements in the hot metal using different calculation models was also carried out. Two different models based on dilute solutions were compared with the TCFe3 database developed for the software Thermo-Calc, which can handle higher alloying concentrations. Considerably different calculation results were found among the different models studied.

  • 32.
    Ipek, Nulifer
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Faxén Laboratory. KTH, School of Engineering Sciences (SCI), Mechanics.
    Lior, Noam
    University of Pennsylvania, Dept. Mech. Eng. and Appl. Mechanics.
    Eklund, A.
    AvestaPolarit AB.
    Improvement of the electrolytic metal pickling process by inter-electrode insulation2005In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 32, no 1, p. 87-96Article in journal (Refereed)
    Abstract [en]

    The existing industrial electrolytic steel pickling process is only 30% current efficient. Use of approximate modelling of the process and solution of the model predicts that inter-electrode insulation improves the current and energy efficiency, and this paper describes the experimental work that has validated this prediction. Some of the main results are: (a) the current efficiency varied from 20% without insulation to 100% with complete insulation, (b) the use of just partial insulations yielded a significant improvement in the process efficiency and at the same time maintained good electrolyte mixing and homogeneity which can not be attained with complete insulation. The theoretical foundations of this method and its various consequences are discussed. The method is relatively easy to apply to existing industrial electrolytic pickling tanks, and also provides system control flexibility for optimal pickling of different steel grades. The method's application cost is relatively low and saves investment in new equipment if a retrofit of an existing system is desired.

  • 33.
    Janis, Diana
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär Göran
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Appell, A.
    Janis, J.
    Application of pulse distribution analysis with optical emission spectroscopy (PDA/OES) method during production of duplex stainless steel2016In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 43, no 2, p. 121-129Article in journal (Refereed)
    Abstract [en]

    Liquid steel samples were taken during ladle treatment and continuous casting of 37 heats of two duplex stainless steel grades. These samples were used to study inclusion characteristics and potential process control using the pulse distribution analysis with optical emission spectroscopy method (PDA/OES). In addition, a few samples were chosen for a scanning electron microscope examination. A simplified approach of presenting the inclusion composition in ternary diagrams using the PDA/OES method is discussed. More specifically, by defining an operating window, potential deviations can be identified early in the steelmaking process. The variation of the B factor for A(l) (B-Al) with process time was presented showing similar tendencies for several heats. For that reason, the B factor is considered to be a reliable parameter to study any process changes with respect to inclusion characteristics. Parameters such as B-Al and the number of inclusions per unit volume larger than 4 mu m obtained using the PDA/OES method showed a moderate correlation with a slivers index. Statistically, more data have to be collected for further studies. Nevertheless, the PDA/OES method is judged to be a promising tool to determine a slivers risk factor at an early stage of the process.

  • 34.
    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 doloma refractories in contact with CaO-Al2O3-SiO2-MgO slag2008In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 35, no 2, p. 99-107Article in journal (Refereed)
    Abstract [en]

    The dissolution of three doloma based refractories in liquid CaO-Al2O3-SiO2-MgO slag was studied. Cylindrical refractory specimens of doloma, carbon bonded doloma, and magnesia doloma were rotated in a stationary crucible of molten slag under forced convection conditions. Slag composition, temperature, rod rotation speed and rod immersion time were varied. The refractory dissolution rate was determined from the change in diameter of the cylindrical specimens. The corrosion rate was found to increase with temperature and rod rotation speed and decrease when the slag was nearly saturated with MgO. The findings of the study substantiate the assumption that the diffusion of magnesium oxide through the slag boundary layer controls the corrosion process. The results indicated the overall corrosion process to be the dissolution of refractory material into the slag, followed by slag penetration of the pores and grain boundaries and finally, dispersion of the grains into the slag.

  • 35.
    Jansson, Sune
    et al.
    Arvika Gjuteri AB.
    Brabie, Voicu
    Dalarna University, Campus Borlänge.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Magnesia-carbon refractory dissolution in Al killed low carbon steel2006In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 33, no 5, p. 389-397Article in journal (Refereed)
    Abstract [en]

    The effects of rotation speed, steel temperature and steel composition on the rate of dissolution of MgO-C refractory into Al deoxidised molten steel were investigated using the rotating cylinder method. Cylinders or rods of MgO-C refractory material were immersed in an Al deoxidised molten steel. Experiments were performed for steel temperatures between 1873 and 1973 K and rotation speeds between 100 and 800 rev min(-1) as well as for different immersion times. For each case, the dissolution rate of MgO-C material was determined from measurement of the decrease in the rod radius. The experimental results showed that the dissolution rate of the MgO-C refractory material increased with an increase in steel temperature and rotation speed. The findings strongly suggest the diffusion of magnesium through the slag layer formed around the refractory rods to be a rate determining step. This thin oxide layer at the steel/refractory interface was found to be owing to reaction between magnesium vapour and CO generated by the reaction between MgO and C in the refractory. Oxide inclusions were also found in the steel melt and they were shown to mainly consist of MgO and Al2O3 or a mixture of the two.

  • 36.
    Kang, Young Jo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Yu, Liang
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Mechanism Study of inclusion removal around open-eye in ladle treatment2007In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 34, no 3, p. 253-261Article in journal (Refereed)
    Abstract [en]

    In the present study, the inclusion removal mechanism by rising bubbles around the open eye in a gas stirred ladle was investigated using a cold model. Water and silicone oils were employed to simulate liquid metal and slag respectively, Both fine silicone oil droplets and charcoal particles were used to simulate inclusions. Around the open eye, the oil layer exhibited a sphere bed structure when a critical gas flowrate was reached. The sphere bed was composed of many oil droplets, each of which was coated with a thin water film. The injected inclusions mostly followed the stream of water flow and were brought up to the open eye by the gas-water plume. A fraction of the inclusions were captured by the sphere bed when passing through the openings between the oil droplets, while the rest of the inclusions came back to the water bath and joined the stream of the flow again. The sphere bed was found to function as a filter to the tiny particles or oil droplets. On the basis of this mechanism, a preliminary comparison of the contribution of inclusion removal by metal-gas plume in the open eye region with the contribution of buoyancy was made.

  • 37.
    Kapilashrami, Era
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Sahajwalla, V.
    Seetharaman, Seshadri
    KTH, Superseded Departments, Materials Science and Engineering.
    Slag formation during high temperature interactions between refractories containing SiO2 and iron melts with oxygen2004In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 31, no 6, p. 509-513Article in journal (Refereed)
    Abstract [en]

    Refractory-metal interactions and associated reactions are important during casting as they can lead to the formation of inclusions. High temperature interactions between aluminosilicate refractories and molten steel were studied in the present investigation using the sessile drop method. Changes in the contact angles between molten iron with well defined oxygen levels and substrates of silica, mullite (3Al(2)O(3).2SiO(2)) as well as commercial refractories, were measured in the dynamic mode. In all cases, the reaction led to slag formation. The experiments were performed under isothermal conditions at 1823 and 1873 K. A known and constant oxygen partial pressure was imposed above the iron drop, through appropriate CO-CO2-Ar mixtures. For all substrates, the contact angles started decreasing due to lowering of the surface tension of iron, as oxygen was imposed onto the system. When a critical level of oxygen was reached, slag started forming at the drop/substrate interface and at this stage, the contact angle dropped suddenly. Subsequent behaviour of silica and mullite was observed to be different, with SiO2 showing a non-wetting behaviour. In the case of SiO2 substrate, there were also deep erosions along the periphery of the drops and there was slag accumulation at the sides of the metal drop, probably due to Marangoni flow and/or SiO(g) formation. SEM and EDS analysis of the substrates revealed that the formed slag was fayalite. The thermodynamic criteria for slag formation and possible mechanisms of the reaction are discussed in the light of the experiments.

  • 38. Kasimagwa, I.
    et al.
    Brabie, V.
    Jönsson, Pär G.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Slag corrosion of MgO-C refractories during secondary steel refining2014In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 41, no 2, p. 121-131Article in journal (Refereed)
    Abstract [en]

    Studies of the reactions between the MgO-C refractory and a CaO-Al2O3-SiO2-MgO slag system have been carried out through thermodynamic simulations, laboratory experiments and microscopy studies of the microstructure of the refractory samples after the experimental procedures. Corrosion experiments were conducted using the rotating immersion method of the MgO-C refractory rods in a liquid slag: in the temperature range of 1773-1923 K, revolution speed of 200 rev min(-1), with varying slag compositions and times ( 2700-8100 s). Laboratory experiments have shown that the time during which the ladle lining is exposed to a liquid slag with high stirring and slag composition are two important parameters which have large effect on the kinetics of the refractory wear. The rate constants calculated in the present work are in the range of 4 x 10(-7) to 1 x 10(-6) ms(-1). The estimated activation energy from the experimental results is 26 kJ mol(-1)

  • 39.
    Kojola, Niklas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Ekerot, Stefan
    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.
    Pilot plant study of clogging rates in low carbon and stainless steel grades2011In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 38, no 2, p. 81-89Article in journal (Refereed)
    Abstract [en]

    In the present paper, the clogging tendency of aluminium or silicon killed low carbon and stainless steel grades has been investigated using pilot scale equipment. Steel was melted and deoxidised in a 600 Hz induction furnace, then teemed through a temperature controlled nozzle into a mould situated on a scale measuring the teemed mass. The steel and nozzle temperatures could be adjusted within +/- 1 degrees C. It was found that the clogging rate, when teeming through a hot nozzle, increased with an increasing amount of alumina phase present in the steel melt. This, in combination with composition analysis and a detailed crystallographic investigation using electron backscatter diffraction, suggested that the clogging was created by deoxidation products from the steel melt. Furthermore, it was found that the freezing effect onto the nozzle wall when teeming non-clogging steel through a cold nozzle was of the same order of magnitude as the clogging rate of the aluminium killed steels teemed through a hot nozzle. Successful trials were also performed where the nozzle accretion during teeming was eliminated by the addition of negative oxygen interacting elements such as aluminium or silicon to the melt. A theoretical assessment based on a mass balance and thermodynamic equilibrium predicted that the removal efficiency increased with a decreased total oxygen content of the steel melt.

  • 40.
    Kojola, Niklas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Ekerot, Sven
    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.
    Pilot plant study of nozzle clogging mechanisms during casting of REM treated stainless steels2011In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 38, no 1, p. 1-11Article in journal (Refereed)
    Abstract [en]

    A pilot scale bottom teemed high frequency furnace with a nominal capacity of 600 kg and an adjustable nozzle temperature was used to study clogging of rare earth metal (REM) treated stainless steels. The influence of the following variables on the clogging was studied: amount of REM, fraction of oxide clusters, total oxygen content in the steel, reoxidation, aluminium additions before REM additions and silicon additions during casting. Overall, the results show that, during the present experimental conditions, mainly two typical clogging rates could be identified, fast and slow clogging. Two main differences could be detected between the fast and slow clogging rates. Steel containing mainly small single inclusions clogged faster than steel containing mainly large inclusion clusters. The reason was believed to be that the small inclusions could stick to the nozzle wall at narrow passages where the steel flow velocity was high while the larger ones could not. The source of the small inclusions was believed to be reoxidation. It was also found that the main part of the nozzle accretion was caused by agglomeration of inclusions and inclusion clusters, while only a thin oxide film along the nozzle wall was caused by oxide precipitation at the nozzle wall.

  • 41.
    Korojy, Bahman
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Nassar, Hani
    Fredriksson, H
    Hot crack formation during peritectic reaction in steels2010In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 37, no 1, p. 63-72Article in journal (Refereed)
    Abstract [en]

    Hot crack formation during solidification was investigated during the peritectic reaction in steels. A series of in situ solidification experiments was performed using a MTS tensile testing machine combined with a mirror furnace. Sample temperature and force change were measured during the solidification process. The force measurements showed a sudden drop during the solidification of samples, which occurred around the peritectic temperature of the alloy, were accompanied by cracks or refilled cracks in the microstructure. Furthermore, the peritectic reaction types were studied theoretically and experimentally to understand their effects on the force change during solidification. The theoretical analyses showed that the volume change due to the peritectic transformation is one of the reasons for crack formation. In addition, when the peritectic reaction occurs in a diffusionless (partition less) manner in an alloy with sufficiently high primary precipitation, crack formation is more probable.

  • 42. Lee, J.
    et al.
    Shin, M.
    Park, J. H.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Studies of wetting characteristics of liquid Fe-Cr alloys on oxide substrates by sessile drop technique2010In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 37, no 7, p. 512-515Article in journal (Refereed)
    Abstract [en]

    The purpose of this study was to investigate the wetting characteristics of three different oxide substrates (alumina, magnesia and dolomite) in order to examine the work of adhesion of Fe-Cr alloys on these substrates. The contact angle of a liquid drop (Fe-Cr alloy) on the oxide substrates was investigated at 1823 K under a H-2 atmosphere by the sessile drop technique. The contact angle slightly decreased on the alumina and dolomite substrates with increasing chromium concentration, but did not change as much on the magnesia substrate. Among the tested substrates, alumina exhibited the highest contact angle and dolomite exhibited the lowest one. Accordingly, dolomite had the strongest work of adhesion, which was in agreement with the observations in the practical process.

  • 43.
    Malmberg, Kristofer J.
    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.
    Nzotta, Mselly
    Uddeholm AB, Hagfors, Sweden.
    Alexis, Jonas
    SWEREA-MEFOS, Luleå, Sweden.
    Jönsson, Pär G.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Influence of the final stirring treatment on the inclusion numer in tool steel2012In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812Article in journal (Other academic)
  • 44.
    Malmberg, Kristofer
    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.
    Nzotta, M.
    Alexis, J.
    Jönsson, Pär G.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Influence of final stirring treatment on inclusion number in tool steel2013In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 40, no 6, p. 407-412Article in journal (Refereed)
    Abstract [en]

    The focus was to study the elimination of non-metallic inclusions during the final part of the ladle refining of tool steel (AISI H13). More specifically, the final stirring treatment in a ladle before casting was modified to study how the number of inclusions could be decreased. The following three stirring treatments were tested: a conventional induction stirring with a 650 A current for 20 min, a short induction stirring with a 650 A current during 10 min, and a combined gas and induction stirring during 20 min (no open eye and a 600 A current). Steel samples were collected from the ladle before and after the final stirring period of the ladle treatment. Thereafter, the numbers of inclusions in steel samples were determined using a light optical microscope based on a classification according to the Swedish standard SS111116 (JK Scale II). Overall, the results showed that a combined gas and induction stirrings was the most efficient way of decreasing the number of DM, DH and DP inclusions. The decrease in the inclusion number in four heats was the following for the different size classes for a combined stirring procedure: 15-40% for DM type inclusions, 30-61% for DH type inclusions and 50-100% for DP inclusions. In addition, it should be mentioned that a stirring practice with induction stirring during 10 min resulted in a 67-100% decrease in the DH type inclusions. However, the results for a combined stirring case for DH type inclusions were more stable than those for a shorter induction stirring time.

  • 45.
    Malmberg, Kristofer
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Nzotta, M.
    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.
    Optimisation of stirring conditions during vacuum degassing in order to lower inclusion content in tool steel2013In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 40, no 3, p. 231-237Article in journal (Refereed)
    Abstract [en]

    In the production of tool steel, the control of secondary metallurgy plays an important role to meet the rapidly increasing demands for clean steel, as impurities and non-metallic inclusions can reduce its mechanical properties. This study focuses on the influence of stirring rate during the vacuum degassing of liquid steel on the inclusion characteristics. During this treatment, both gas and induction stirring are used; thus, fluid flow simulations were made for the vacuum treatment of melts at high (900 A + 100 L min(-1) Ar) and low (700 A + 10 L min(-1) Ar) stirring rates. By decreasing the Weber number to a value smaller than the critical value (We(crit)=12.3) at a lower stirring rate, the probability for dispersion and entrapping of slag inclusions into the liquid steel significantly decreases. Five plant heats were carried out with different rates of induction stirring and argon flow in the ladle during vacuum treatment. The results gained by light optical microscopy investigation show that the total amount of large size single inclusions (>11.3 mm) in steel samples after vacuum treatment and in the final product decreases considerably with a lowered stirring rate. Thus, the experimental results support the theoretical results based on the Weber number.

  • 46. Memarpour, Arashk
    et al.
    Brabie, Voicu
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Studies of effect of glass/silicon powder coatings on clogging behaviour of submerged entry nozzles when using REM alloyed stainless steels2011In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 38, no 3, p. 229-239Article in journal (Refereed)
    Abstract [en]

    The internal surfaces of modern submerged entry nozzles (SENs) were coated with a glass/silicon powder layer to prevent SEN graphite oxidation during preheating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied. The results indicated that penetration of the formed alkaline rich glaze into the alumina/graphite base refractory occurs during preheating. More specifically, the glaze reacts with graphite to form carbon monoxide gas. Thereafter, dissociation of CO at the SEN/molten metal interface takes place. This leads to reoxidation of dissolved rare earth metals, which form 'in situ' rare earth metal oxides at the interface between the SEN and the molten steel. In addition, the interaction of the penetrated glaze with alumina in the SEN base refractory materials leads to the formation of a high viscous alumina rich glaze during the SEN preheating process. This, in turn, creates a very uneven surface at the SEN internal surface. The 'in situ' formation of the rare earth metal oxides together with the uneven internal surface of the SEN may facilitate the accumulation of the primary inclusions on the refractory walls.

  • 47.
    Mostafaee, Saman
    et al.
    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.
    Petrographic and thermodynamic study of slags in EAF stainless steelmaking2010In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 37, no 6, p. 425-436Article in journal (Refereed)
    Abstract [en]

    A study of the typical characteristics of electrical arc furnace (EAF) slags in the production of the stainless steel (AISI 304L) was carried out. Twenty-eight slag samples were taken from 14 heats. Simultaneously with each slag sampling, the temperature of the steel was measured, and one steel sample was taken. The selected slag samples were studied both using SEM-EDS and light optical microscopy. Computational thermodynamics was used as a tool to predict the equilibrium phases in the top slag as well as the amount of these phases at the process temperatures. It was observed that, at process temperature, the stainless EAF slag generally consists of liquid oxides, spinel particles and metallic droplets. Under normal operation, the amount of spinel particles is 26 wt-%. In addition, the influence of the slag temperature, basicity, MgO content and Cr2O3 content on the amount of spinel precipitates and thereby on the foaming index of the top slag is also illustrated and discussed. More specifically, it was found that, within the compositional range of the slag samples, the critical parameter affecting the amount of solid spinel particles in the slag is the chromium oxide content.

  • 48.
    Mostafaee, Saman
    et al.
    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.
    Petrographical study of microstructural evolution of EAF duplex stainless steelmaking slags2011In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 38, no 2, p. 90-100Article in journal (Refereed)
    Abstract [en]

    A novel study to characterise electric arc furnace (EAF) slags in the production of duplex stainless steel at the process temperatures was performed. The investigation is focused on determining the microstructural evolution of the EAF slag during and at the end of the refining period. In this regard, slag sampling was done at three stages from seven EAF duplex stainless steel heats (21.5-22.5 wt-%Cr, 1.6-5.7 wt-%Ni and 0.3-3.2 wt-%Mo). More specifically, the samples were collected before FeSi addition, after FeSi injection and just before tapping. Collected samples were analysed by light optical microscopy and SEM energy dispersive X-ray spectroscopy to characterise the high temperature microstructure of the slag phases. In addition, X-ray diffraction analysis was used to verify the petrographical results. It was observed that at all process stages, the duplex steel slag contains molten oxides, magnesiochromite spinels and metallic droplets. However, before the FeSi addition, the slag also contains calcium chromite crystals. In this stage, the slag has a high viscosity, which drops to lower level after FeSi injection. Furthermore, depending on the basicity, the slag may contain other solid phases such as perovskite and calcium silicate.

  • 49.
    Mostafaee, Saman
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Selleby, Malin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    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.
    Computational thermodynamics as a tool to study the microstructural evolution of EAF duplex stainless steelmaking slags2012In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 39, no 1, p. 51-58Article in journal (Refereed)
    Abstract [en]

    Computational thermodynamics was used as a tool to study and determine the microstructural evolution of the electrical arc furnace (EAF) slag during and at the end of the refining period in the production of duplex stainless steel. At all the process stages, the slag contains magnesiochromite spinels. Before FeSi addition to the furnace, the slag can also contain calcium chromite crystals. After FeSi addition, the amount of magnesiochromite spinels decreases considerably from similar to 15 to similar to 6 wt-%. In addition, dependent on the basicity and the temperature, the slag may contain solid dicalcium silicate. More specifically, during the refining stage of the EAF duplex steelmaking process, a slag basicity of > 1.55 leads to the precipitation of the dicalcium silicate phase. It has been shown that computational thermodynamics can be used as a powerful and relative reliable tool to study the slag (or slag/steel) equilibriums for different stainless steelmaking processes.

  • 50.
    Nassar, Hani
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Korojy, Bahman
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    A study of shell growth irregularities in continuously cast 310S stainless steel2009In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 36, no 7, p. 521-528Article in journal (Refereed)
    Abstract [en]

    Growth irregularities in continuous casting are believed to be associated with crack formation and breakouts. Differential thermal analysis on 310S stainless steel samples indicated primary precipitations of both austenite and ferrite during solidification. In tensile tests on solidifying samples, abrupt shrinkages in volume were detected in the peritectic range of temperatures. Micrographic and microsegregation analysis on samples extracted from a breakout shell revealed high ratios of primary-precipitated austenite in the thick sections of the shell, and high ratios of primary-precipitated ferrite in the thin sections. Alternating precipitations of austenite and ferrite are proposed to occur during solidification. Regions of the shell with high ratios of primary austenite remain in contact with the mould and exhibit high growth rates, whereas regions with high ratios of primary ferrite shrink in volume due to the ferrite to austenite transformation, which results in the formation of air gaps between the shell and the mould and reductions in growth rate.

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