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Effect of Stirring Practice on Sulphur and Nitrogen Refining as well as Inclusion Removal in Ladle Treatment
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.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.ORCID iD: 0000-0002-3548-8638
2015 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 86, no 12, 1498-1507 p.Article in journal (Refereed) Published
Abstract [en]

The effect of different stirring conditions during ladle treatment on the steel cleanliness was studied in the steel plant of SSAB Special Steels in Oxelosund, Sweden. The cleanliness was examined with regards to the contents of sulfur, nitrogen, and large inclusion (>10 mu m). The results showed that vacuum degassing increased the amount of inclusions larger than 10 mu m and that subsequent induction stirring suggested a possible positive effect on the inclusion removal. A shortening of the vacuum degassing time from 24 to 15 min did not affect the nitrogen or sulphur refining. Overall, all heats reached the desired composition and cleanliness levels regardless of the treatment time.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2015. Vol. 86, no 12, 1498-1507 p.
Keyword [en]
vacuum degassing, induction stirring, inclusions, sulphur, nitrogen
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-167360DOI: 10.1002/srin.201400501ISI: 000368435400009Scopus ID: 2-s2.0-84923238160OAI: oai:DiVA.org:kth-167360DiVA: diva2:813243
Note

QC 20160216

Available from: 2015-05-22 Created: 2015-05-22 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Influence of Stirring on the Inclusion Characteristics during Vacuum Degassing in a Ladle
Open this publication in new window or tab >>Influence of Stirring on the Inclusion Characteristics during Vacuum Degassing in a Ladle
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Steel cleanliness as a function of stirring practice during vacuum degassing treatment have been investigated in industrial studies at the steel plants of SSAB Special Steels in Oxelösund and Uddeholm AB in Hagfors. The cleanliness was examined with regards to the contents of sulphur, nitrogen and large inclusions (>10µm).

The stirring practice during the vacuum degassing treatment has been studied with respect to time, namely by shortening the vacuum degassing treatment time from 24 to 15 minutes. Furthermore, the effect of the stirring intensity was studied by measuring the open eye zone using camera recordings. The focus has been to study the effect of a shortened vacuum degassing time as well as a controlled stirring intensity on the steel cleanliness. Moreover, study the effect of subsequent induction stirring, after vacuum degassing, on the amount of inclusions. By taking steel and slag samples taken before and after the vacuum degassing treatment, the different stirring practices could be investigated. It should be noted that all heats reached the desired composition regardless of the treatment time and stirring practice.

The results from the trials at SSAB Special Steels showed that the stirring practice during vacuum degassing have an effect on the total number of inclusions. The strong argon stirring during vacuum degassing with visible open eyes resulted in an average increase of 400% of the total amount of inclusions >10µm. However, no difference between a vacuum degassing time of 24 or 15 minutes was seen with respect to the increased amount of inclusions, denitrogenization or desulphurization. During the subsequent induction stirring, which was softer with no open eyes, the effect of the stirring practice was unclear due to overlapping confidence intervals. An average decrease of 65% of the total amount of inclusions >10 µm was seen for the heats  with non-overlapping confidence intervals. Based on these results it can be suggested that the use of a soft induction stirring after the vacuum degassing treatment as a possible process change to reach lower amounts of large inclusions.

The stirring intensity during the vacuum degassing treatment was measured as the average ladle eye size during the trials at Uddeholm AB. This, due to that stronger stirring results in larger ladle eye zone. The results show that the amount of smaller inclusions (<11.2 μm) decrease by up to 90% compared to the original amount, regardless of the stirring intensity. A stronger stirring showed tendency to increase the amount of large inclusion (>22.4 μm). Moreover, the denitrogenization and desulphurization was not affected by the changed stirring intensity during vacuum degassing. It was also found that the average ladle eye size did not correlate to the logged average argon flow. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xi, 38 p.
Keyword
Vacuum degassing treatment, inclusions, ladle eye, stirring intensity, denitrogenization, desulphurization.
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-167110 (URN)978-91-7595-605-3 (ISBN)
Presentation
2015-06-05, Sal Sefström, M131, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150522

Available from: 2015-05-22 Created: 2015-05-21 Last updated: 2015-05-22Bibliographically approved

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