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  • 1.
    Svensson, Jennie
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH, Tillämpad processmetallurgi.
    An Experimental Study to Improve the Casting Performance of Steel Grades Sensitive for Clogging2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this study, the goal is to optimize the process and to reduce the clogging tendency during the continuous casting process. The focus is on clogging when the refractory base material (RBM) in the SEN is in contact with the liquid steel. It is difficult or impossible to avoid non-metallic inclusions in the liquid steel, but by a selection of a good RBM in the SEN clogging can be reduced.

     

    Different process steps were evaluated during the casting process in order to reduce the clogging tendency. First, the preheating of the SEN was studied. The results showed that the SEN can be decarburized during the preheating process. In addition, decarburization of SEN causes a larger risk for clogging. Two types of plasma coatings were implemented to protect the RBM, to prevent reactions with the RBM, and to reduce the clogging tendency. Calcium titanate (CaTiO3) mixed with yttria stabilized zirconia (YSZ) plasma coatings were tested in laboratory and pilot plant trials, for casting of aluminium-killed low-carbon steels. For casting of cerium alloyed stainless steels, YSZ plasma coatings were tested in laboratory, pilot plant and industrial trials. The results showed that the clogging tendency was reduced when implementing both coating materials.

     

    It is also of importance to produce clean steel in order to reduce clogging. Therefore, the steel cleanliness in the tundish was studied experimentally. The result showed that inclusions originated from the slag, deoxidation products and tundish refractory and that they were present in the tundish as well as in the final steel product.

  • 2.
    Svensson, Jennie
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH, Tillämpad processmetallurgi.
    The submerged entry nozzle: a study of how to reduce decarburization and clogging2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    During continuous casting the submerged entry nozzle (SEN) is one of the critical points. This since sequence casting is favourable, clogging of the SEN results in fever sequences or aborted castings. In this study the preheating of SEN has been evaluated at different steel plants. This since it earlier  has been found, preheating resulted in decarburisation of  the refractory base material (RBM)  which in turn resulted in clogging of the SEN. During the industrial preheating trials it was found that decarburisation of  the SEN is possible.The decarburisation results in a higher oxygen potential near the SEN wall. This in turn makes it possible for aluminum in the molten steel to form alumina particles. For low carbon aluminum killed steel grades, accretion of alumina clusters on the SEN internal wall result in clogging which hinder or reduces the steel flow through the SEN. For this reason, laboratory trials were performed to establish the formation of a liquid phase. Thus simulating the formation of liquid inclusions when alumina clusters attaches to the SEN wall, and which can be washed away by the steel flow. Formation of a liquid phase was indicated at the temperatures 1550-1600°C, and plasma coated nozzles were tried in pilot plant trials. The coating contained of 5-9 pct, 99.9 pct pure, calcium titanate (CaTiO3) mixed with yttria stabilized zirconia (YSZ).

  • 3.
    Svensson, Jennie
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Larsson, F.
    Memarpour, A.
    Ekerot, S.
    Brabie, Voicu
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Jönsson, P.G.
    Implementation of an YSZ coating material to prevent clogging of the submerged entry nozzle (SEN) during continuous casting of Ce-treated steels2018In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 45, no 2, p. 105-113Article in journal (Other academic)
    Abstract [en]

    The possibility to reduce clogging in the submerged entry nozzle (SEN) during continuous casting of Ce alloyed stainless steels has been studied. This was done by implementing a new plasma coating material, consisting of yttria stabilized zirconia (YSZ). The coating was first tested in pilot-plant trials; where the amount of steel teemed through the plasma coated nozzles was monitored. Thereafter, samples of the coatings from the nozzles were studied using a FEG-SEM equipped with EDS. In addition, the coating material was tested in industrial trials where the performance was judged with respect to the clogging tendency detected as the movement of the stopper rod. The results from both the pilot-plant trials and industrial trials showed that the use of an YSZ coating led to a decreased clogging tendency during the casting in comparison to when using an uncoated SEN. Specifically, the pilot-plant trials showed that the clogging factor was lowered when implementing the YSZ coatings. Furthermore, the industrial trials showed that the clogging tendency, measured by the stopper rod movements, were lower when implementing the YSZ coating.

  • 4.
    Svensson, Jennie
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Larsson, Fredrik
    Outokumpu, Avesta SE-774 22, Sweden.
    Memarpour, Arashk
    Dalarna University, School of Technology and Business Studies, Materials Technology. Sandvik Materials Technology, Sandviken SE-811 81, Sweden.
    Brabie, Voicu
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Jönsson, Pär
    Royal Institute of Technology, Brinellvägen 23, Stockholm SE-100 44, Sweden.
    Post-mortem Studies of Submerged Entry Nozzles (SEN) Coated with Yttria Stabilized Zirconia (YSZ)2015In: The 6th International Congress on the Science and Technology of Steelmaking (ICS2015), China, May 12-14, 2015 in Beijing / [ed] Organized by The Chinese Society for Metals (CSM), 2015Conference paper (Refereed)
    Abstract [en]

    During continuous casting of Ce-treated stainless steel grades an accumulation of inclusions at the submerged entry nozzle’s (SEN) internal wall can cause disturbances or even prevent the molten steel flow. Plasma sprayed yttria stabilized zirconia (YSZ) coating of the SEN’s inlet and stopper rod have been implemented in order to decrease the clogging effect. The coating thickness was 210 µm and the plant trials were conducted during continuous casting of slabs. The clogging tendency was measured by the stopper rod position during the casting process. The results of the measured positions were then compared to experimentally determined information from samples cut out from the SEN’s inlet after casting. Specifically, the samples were analysed using a field emission gun scanning electron microscope (FEG-SEM) equipped with an energy dispersive X-ray spectrometry (EDS). Sample with the dimensions of ̴15x10x5 mm were electrolytic extracted before analysis. The chemical composition at the interface between the solidified steel and refractory base materials were analysed, and traces of the YSZ coating were determined.

    The movement of the stopper position indicated that the clogging tendency was reduced for the coated SEN. However, the FEG-SEM analyses showed that clogging of the SEN had occurred during the casting.

  • 5.
    Svensson, Jennie
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH.
    Memarpour, Arashk
    Brabie, Voicu
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH.
    Jönsson, Pär
    KTH.
    Studies of the decarburisation phenomena during preheating of submerged entry nozzles (SEN) in continuous casting processes2017In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 44, no 2, p. 108-116Article in journal (Refereed)
    Abstract [en]

    Decarburisation of the submerged entry nozzles (SEN) during the preheating process wasinvestigated based on plant trials and thermodynamic modelling at three different steel plants.During the trials the preheating processes were mapped, the temperature profiles wereregistered and post-mortem studies of the SENs with scanning electron microscopy wereperformed. Typically, the glass/silicon powder will form a dense and protective layer inside theSEN when heated over 1100°C. However, this study found that the temperature distributioninside the SEN did not always reach this critical temperature. Thus, decarburisation of the SENwas found at all steel plants. The overall results illustrate that the control of the preheatingprocess needs to be improved at all steel plants. It is suggested that future research should befocused on the development of new coating materials to prevent decarburisation of therefractory base material, which would decrease the chances of clogging during casting.

  • 6.
    Svensson, Jennie
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH, Tillämpad processmetallurgi.
    Memarpour, Arashk
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Brabie, Voicu
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Jönsson, Pär
    KTH, Tillämpad processmetallurgi.
    Studies of the decarburization phenomena during heating of submerged entry nozzles (SEN) in continuous casting processesManuscript (preprint) (Other academic)
  • 7.
    Svensson, Jennie
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Memarpour, Arashk
    Ekerot, Sven
    Brabie, Voicu
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Jönsson, Pär
    Tillämpad processmetallurgi, KTH.
    Studies of new coating materials to prevent clogging of the submerged entry nozzle (SEN) during continuous casting of Al killed low carbon steels2017In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 44, no 2, p. 117-127Article in journal (Refereed)
    Abstract [en]

    The possibility to reduce clogging in the submerged entry nozzle (SEN) when casting Al killed low carbon steel has been evaluated. The coating materials have been tested in laboratory trials and pilot plant trials. Totally, 2 mixes of the coating material has been tested; containing 4.8 and 9.1 % CaTiO3 mixed with yttria stabilised zirconia (YSZ) powder. The chemical composition was analysed by using an FEG-SEM equipped with EDS.The major result showed that alumina reacted with CaTiO3 in the temperature interval from 1550-1600°C. In addition, the clogging ratio showed a decreased clogging tendency for coated nozzles compared to standard nozzles. Also, the results showed that an approximately three times higher steel mass could be teemed through the coated nozzles before clogging occurred compared to trials with uncoated standard nozzles. Overall, it is concluded that plasma sprayed CaTiO3 coatings can reduce the clogging tendency during the continuous casting process.

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