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Slag-metal equilibrium calculations for estimation of oxygen activity in molten steel during ladle treatment
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.ORCID iD: 0000-0002-9872-3738
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
(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 [en]
oxygen activity, slag model, sampling, plant trial
National Category
Metallurgy and Metallic Materials
Research subject
Production Engineering
Identifiers
URN: urn:nbn:se:kth:diva-187307OAI: oai:DiVA.org:kth-187307DiVA: diva2:929554
Note

QC 20160519

Available from: 2016-05-19 Created: 2016-05-19 Last updated: 2016-05-19Bibliographically approved
In thesis
1. Slag/Metal Metallurgy in Iron and Steel Melts
Open this publication in new window or tab >>Slag/Metal Metallurgy in Iron and Steel Melts
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
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:nbn:se:kth:diva-187228 (URN)978-91-7595-940-5 (ISBN)
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

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