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Some Fundamental Aspects Concerning Secondary Steelmaking
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present thesis deals with some aspects concerning secondary metallurgy of steel where there is little or very inconsistent information in the literature. More specifically, it is devoted to the studies on high temperature phase equilibria in the Al2O3-CaO-MgO-SiO2 system, the formation of ladle glaze and the thermodynamics of magnesium in liquid iron.

First, the solidification of different slags on MgO based refractories was studied in order to reveal the mechanism behind the formation of “ladle glaze”. The formation of the slag glaze layer was studied by dipping MgO rods, dense or porous, into liquid slags at 1873 K. The rods were thereafter cooled at a predetermined rate. From a later SEM-EDS microscopy, it was found that the initial slag composition had the most profound effect on the phases found in the solidified slag layer. It was found that the type of MgO rod used and cooling speed had a minor impact on the morphology on the solidified samples. In addition, the slags used in the study were equilibrated at 1773 K, 1673 K 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.

Secondly, phase diagram studies in the high basicity region of the Al2O3-CaO-MgO-SiO2 system were performed using the quench technique followed by EPMA analysis. The main focus in the study was to find the liquidus surfaces for MgO and CaO saturation at 1773 and 1873 K. Based on the experimental data, phase diagrams for the 25, 30 and 35 mass percent alumina sections were constructed for silica contents generally less than 20 mass percent.. The results generally agreed very well with previous, well established phase diagrams. In addition, the activities of MgO, CaO and Al2O3 were estimated using the phase diagram information.

At last, the thermodynamics of magnesium in liquid iron at 1823 K were studied. In a pre-study, the thermodynamics of Ag-Mg solutions were studied, necessary for the Fe-Mg system. For the Ag-Mg system, two different experimental techniques were used; the vapor pressure method and the gas equilibration technique. The temperature range of the Ag-Mg study was 1573 to 1823 K. It was found that the excess Gibbs energy of this system can be described quite well with a sub-regular solution model. In the Fe-Mg study, the partition of Mg between liquid iron and liquid silver were studied at 1823 K. Using the results from the pre-study, the activity coefficient of Mg in liquid iron and the self-interaction parameter were determined at 1823 K.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , 44 p.
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-31131ISBN: 978-91-7415-901-1OAI: oai:DiVA.org:kth-31131DiVA: diva2:402811
Public defence
2011-04-01, Sal D2, Lindstedtsvägen 5, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20110314Available from: 2011-03-14 Created: 2011-03-09 Last updated: 2011-03-23Bibliographically approved
List of papers
1. Effects of slag composition and cooling rate on formation of glaze on MgO refractory
Open this publication in new window or tab >>Effects of slag composition and cooling rate on formation of glaze on MgO refractory
2010 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, Vol. 37, no 1, 27-34 p.Article in journal (Refereed) Published
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.

Keyword
Ladle glaze, Slag-refractory reaction, Inclusions, ferritic stainless-steel, ladle treatment, inclusions, aluminum
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-19141 (URN)10.1179/174328109x463039 (DOI)000273918200005 ()2-s2.0-77949456990 (ScopusID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-03-14Bibliographically approved
2. Experimental determination of the liquidus in the high basicity region in the Al2O3(30 mass%)-CaO-MgO-SiO2 system
Open this publication in new window or tab >>Experimental determination of the liquidus in the high basicity region in the Al2O3(30 mass%)-CaO-MgO-SiO2 system
2011 (English)In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 35, no 2, 249-254 p.Article in journal (Refereed) Published
Abstract [en]

The liquidus in the high basicity region in the Al2O3(30 mass%)-CaO-MgO-SiO2 system were determined experimentally at 1773 and 1873 K using the quench technique followed by EPMA analysis. Based on the experimental data, a phase diagram of the Al2O3(30 mass%)-CaO-MgO-SiO2(< 20 mass%) section was constructed for 1773 and 1873 K. The solubilities of 2CaO center dot SiO2 and 3CaO center dot SiO2 at 1773 K were found to be considerably higher in comparison with the existing phase diagram. Even the solubility of MgO at 1873 K was found to be somewhat higher. In addition, the activities of MgO, CaO and Al2O3 at 1773 K were estimated using the phase diagram information.

Keyword
Al2O3-CaO-MgO-SiO2, Phase diagram, Solubility, EPMA
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-31123 (URN)10.1016/j.calphad.2010.11.004 (DOI)000292238000013 ()2-s2.0-79957983501 (ScopusID)
Note
QC 20110314Available from: 2011-03-09 Created: 2011-03-09 Last updated: 2012-08-22Bibliographically approved
3. Experimental determination of the liquidus in the high basicity region in the Al2O3(25 mass%)-CaO-MgO-SiO2 and Al2O3(35 mass%)-CaO-MgO-SiO2 systems
Open this publication in new window or tab >>Experimental determination of the liquidus in the high basicity region in the Al2O3(25 mass%)-CaO-MgO-SiO2 and Al2O3(35 mass%)-CaO-MgO-SiO2 systems
2011 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 42, no 5, 1008-1016 p.Article in journal (Refereed) Published
Abstract [en]

Liquidus in the Al(2)O(3)(25 mass pct)-CaO-MgO-SiO(2)(<20 mass pct) and Al2O3(35 mass pct)-CaO-MgO-SiO(2)(<20 mass pct) systems were determined experimentally in the high-CaO-containing region at 1873 K (1600 degrees C). For the Al(2)O(3)(35 mass pct)-CaO-MgO-SiO(2)(<20 mass pct) system, liquidus data were also determined for 1773 K (1500 degrees C). The equilibrating and quenching technique with subsequent electron probe microanalyzer (EPMA) microanalysis were employed. Based on the data, liquidus lines were constructed for the 25 and 35 mass pct alumina planes at silica contents generally below 20 mass pct. The current results showed a slightly lower solubility of CaO and a higher solubility of MgO at 1873 K (1600 degrees C) for the 25 mass pct Al(2)O(3) section compared with the existing phase diagram. At 1773 K (1500 degrees C), the result showed a slightly lower solubility of both CaO and MgO in the 35 mass pct Al(2)O(3) section compared with the existing phase diagram. In addition, the activities of MgO, CaO, and Al(2)O(3) were estimated at 1773 K and 1873 K (1500 degrees C and 1600 degrees C) using the phase diagram information.

Keyword
Electron probe micro analyzer, Experimental determination, Liquidus, Liquidus lines, Silica content, Phase behavior, Phase diagrams, Silica, Silicon compounds, Solubility
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-31125 (URN)10.1007/s11663-011-9530-5 (DOI)000297251300009 ()2-s2.0-80054926265 (ScopusID)
Note
QC 20110314. Updated from submitted to published.Available from: 2011-03-09 Created: 2011-03-09 Last updated: 2011-12-19Bibliographically approved
4. Activity of magnesium in liquid Ag-Mg alloys
Open this publication in new window or tab >>Activity of magnesium in liquid Ag-Mg alloys
2012 (English)In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 36, 89-93 p.Article in journal (Refereed) Published
Abstract [en]

Activity measurements of magnesium in liquid Ag-Mg solutions were carried out at 1573, 1673. 1773 and 1823 K using two different techniques. While most measurements were carried out using the vapor pressure method at 1573 and 1673 K, a number of measurements were made at 1773 and 1873 K using the gas equilibration technique. The latter method was used mostly for obtaining Ag-Mg solution at very low Mg contents. It was found that magnesium had a negative deviation from ideality in Ag-Mg solutions. The excess Gibbs energy of Ag-Mg solutions seemed to have a quite weak temperature dependency in the temperature region studied. The excess Gibbs energy of Ag-Mg solution can be described as;

National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-31128 (URN)10.1016/j.calphad.2011.12.001 (DOI)000300863000013 ()2-s2.0-84855519175 (ScopusID)
Note
QC 20110314. Updated from submitted to published 20120326Available from: 2011-03-09 Created: 2011-03-09 Last updated: 2012-03-26Bibliographically approved
5. Experimental determination of Mg activities in Fe-Mg solutions
Open this publication in new window or tab >>Experimental determination of Mg activities in Fe-Mg solutions
2011 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 42, no 5, 921-924 p.Article in journal (Refereed) Published
Abstract [en]

The thermodynamics of magnesium in liquid iron was determined at 1823 K (1550 degrees C). For this purpose, liquid iron was equilibrated with Ag-Mg alloys in a semienclosed molybdenum vessel. From the partition of magnesium between iron and silver, the activity coefficient of Mg and the self-interaction parameter e(Mg)(Mg) were determined.

Keyword
DISSOLUTION EQUILIBRIUM, MOLTEN IRON, LIQUID-IRON, MAGNESIUM, STEEL, VAPOR, SOLUBILITY, CALCIUM, SULFUR
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-31129 (URN)10.1007/s11663-011-9557-7 (DOI)000297251300001 ()2-s2.0-80054931056 (ScopusID)
Note
QC 20110314. Updated from submitted to published.Available from: 2011-03-09 Created: 2011-03-09 Last updated: 2011-12-19Bibliographically approved

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