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Slag/Metal Metallurgy in Iron and Steel Melts
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.ORCID iD: 0000-0002-9872-3738
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this work, the metal and slag phase mixing in three steps of a ladle refining operation of steel melts and for an oxygen balance during cooling of cast iron melts have been studied at two Swedish steel plants and at two Swedish cast iron foundries, respectively. In order to predict the oxygen activity in the steel bulk in equilibrium with the top slag as well as in metal droplets in the top slag in equilibrium with the top slag, three slag models were used. In addition, the assumptions of a sulphur-oxygen equilibrium between steel and slag and the dilute solution model for the liquid steel phase were utilized in the calculations. Measured oxygen activities in steel bulk, which varied between 3.5-6 ppm, were compared to predicted oxygen activities. The differences between the predicted and measured oxygen activities were found to be significant (0-500%) and the reasons for the differences are discussed in the thesis. Slag samples have been evaluated to determine the distribution of the metal droplets. The results show that the relatively largest numbers of metal droplets are present in the slag samples taken before vacuum degassing. Also, the projected interfacial area between steel bulk and top slag has been compared to the interfacial area between the metal droplets and slag.

The results show that the droplet-slag interfacial area is 3 to 14 times larger than the flat projected interfacial area between the steel and top slag. Furthermore, the effect of the reactions between top slag and steel and the slag viscosity on the metal droplet formation is discussed. The results show significant differences between the steel bulk and steel droplet compositions and the reasons for the differences are discussed in the thesis. The oxygen activity in different cast irons was studied. Plant trials were performed at three occasions for lamellar, compacted and nodular iron melts. The results show that at temperatures close to the liquidus temperature the oxygen activities were 0.03-0.1 ppm for LGI, around 0.02 ppm for CGI, and 0.001ppm for SGI. In addition, it was found that as the oxygen activities increased with time after an Mg treatment, the ability to form a compact graphite or a nodular graphite in Mg-treated iron melts was decreased. Also, extrapolated oxygen activity differences up to 0.07 ppm were found for different hypoeutectic iron compositions for lamellar graphite iron at the liquidus temperature. Overall, the observed differences in the dissolved oxygen levels were believed to influence how graphite particles are incorporated into the austenite matrix and how the graphite morphology will be in the cast product.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. , 36 p.
Keyword [sv]
austenit, syreaktivitet, slagg, fördelning, primär dendrit, metalldroppar, lamellär grafit, svavel, kompaktgrafit, skänk, nodulär grafit, raffinering
National Category
Metallurgy and Metallic Materials
Research subject
Metallurgical process science
Identifiers
URN: urn:nbn:se:kth:diva-187228ISBN: 978-91-7595-940-5 (print)OAI: oai:DiVA.org:kth-187228DiVA: diva2:929355
Public defence
2016-06-07, B2, Brinellvägen 23, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20160518

Available from: 2016-05-18 Created: 2016-05-18 Last updated: 2016-05-20Bibliographically approved
List of papers
1. Slag-metal equilibrium calculations for estimation of oxygen activity in molten steel during ladle treatment
Open this publication in new window or tab >>Slag-metal equilibrium calculations for estimation of oxygen activity in molten steel during ladle treatment
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In the present paper three different methods to calculate the equilibrium oxygen activity have been compared with measured oxygen activities and oxygen activities based on sulphur equilibrium between slag and steel during ladle treatment at Scana Björneborg.

Three slag models were used to estimate the oxide component activities of Al2O3 and SiO2 in the top slag and in the equilibrium calculations the dilute solution model for the liquid steel phase was used. The results show significant discrepancies between the calculated and measured oxygen activities and the reasons for the differences are discussed.

Keyword
oxygen activity, slag model, sampling, plant trial
National Category
Metallurgy and Metallic Materials
Research subject
Production Engineering
Identifiers
urn:nbn:se:kth:diva-187307 (URN)
Note

QC 20160519

Available from: 2016-05-19 Created: 2016-05-19 Last updated: 2016-05-19Bibliographically approved
2. Distribution of metal droplets in top slags during ladle treatment
Open this publication in new window or tab >>Distribution of metal droplets in top slags during ladle treatment
2008 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 35, no 8, 575-588 p.Article in journal (Refereed) Published
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.

Keyword
Metal droplets, Slag, Ladle, Refining, Distribution
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-33169 (URN)10.1179/174328108X318914 (DOI)000261735800003 ()2-s2.0-55849142233 (Scopus ID)
Note
QC 20110502Available from: 2011-05-02 Created: 2011-04-29 Last updated: 2017-12-11Bibliographically approved
3. Theoretical study of equilibrium reactions between metal droplets and slag
Open this publication in new window or tab >>Theoretical study of equilibrium reactions between metal droplets and slag
2007 (English)In: Steel Research International, ISSN 1611-3683, Vol. 78, no 2, 109-116 p.Article in journal (Refereed) Published
Abstract [en]

The dispersion of metal droplets in slag was investigated through analysis of slag samples taken during ladle refining at Scana Steel in Bjorneborg, Sweden. The chemical composition of steel droplets found in the ladle slag was determined for five industrial-scale heats. Possible reactions occurring between the steel droplets and slag were identified, as were differences in steel-droplet and steel-bulk composition. Three different slag models were used to calculate the activities of oxide components (Al2O3 and SiO2) in the slag. These results were then used in the dilute-solution model, whereby oxygen activities in the steel droplets were calculated and compared with measured oxygen activities in the steel bulk. Significant differences were found in the comparison of both the calculated and measured oxygen activities and the steel bulk and droplet compositions.

Keyword
metal droplets, slag, ladle, composition, oxygen activity, liquid liquid interfaces, bubbles, iron, entrainment
Identifiers
urn:nbn:se:kth:diva-16487 (URN)000245189300004 ()2-s2.0-33847769048 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2016-05-18Bibliographically approved
4. A STUDY OF OXYGEN ACTIVITIES BEFORE THE START OF SOLIDIFICATION OF CAST IRONS
Open this publication in new window or tab >>A STUDY OF OXYGEN ACTIVITIES BEFORE THE START OF SOLIDIFICATION OF CAST IRONS
2016 (English)In: International Journal of metalcasting, ISSN 1939-5981, E-ISSN 2163-3193, Vol. 10, no 4Article in journal (Refereed) Published
Abstract [en]

Focus in this work was to study dissolved oxygen content and oxygen activities in different cast irons. Plant trials were performed at three occasions for lamellar, compacted and nodular iron melts. The results show that at temperatures close to the liquidus temperature the oxygen activities ranged from 0.03-0.1 ppm for LGI, around 0.02 ppm for CGI and 0.001ppm for SGI. In addition, it was found that as oxygen activities increase with time after an Mg treatment, the ability to form compacted graphite or nodular graphite in Mg-treated iron melts was lowered. Also, oxygen activity differences up to 0.07 ppm were found for different hypoeutectic iron compositions for lamellar graphite iron at the liquidus temperature. Overall, the observed differences in the dissolved oxygen levels are believed to influence how graphite particles are incorporated into the austenite matrix and how the graphite morphology will be in the cast product.

Keyword
austenite, primary dendrite, lamellar graphite, compacted graphite, nodular graphite, oxygen
National Category
Metallurgy and Metallic Materials
Research subject
Production Engineering
Identifiers
urn:nbn:se:kth:diva-187309 (URN)10.1007/s40962-016-0067-x (DOI)000384434100013 ()2-s2.0-84992650094 (Scopus ID)
Note

QC 20160520. Endast accepted vid disputation. Publicerad Oct. 2016.

Available from: 2016-05-19 Created: 2016-05-19 Last updated: 2017-11-30Bibliographically approved

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