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Effect of Slag Protection System and Sample Geometry on Homogeneity of Total Oxygen Content in Samples from Liquid Steel
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.
2011 (English)In: Steel Research International, ISSN 1611-3683, Vol. 82, no 3, 222-229 p.Article in journal (Refereed) Published
Abstract [en]

Many kinds of disposable samplers are available for sampling of liquid steel during steelmaking. Depending on slag protection, they can be divided into two main groups: metal-cap-protected and argon-protected samplers. For high quality steels, a correct determination of inclusion characteristics in metal samples is important for an improved process control. This paper seeks to investigate the effect of slag protection system, and sample geometry, on deviation and total content of oxygen within samples from the ladle treatment of liquid duplex stainless steel. The homogeneity with respect to total oxygen content was determined for different zones in the body, pin and inlet part of Bjorneborg and Lollipop (6 and 12mm thickness) samples. The results showed low, and stable, contents of oxygen in the argon-protected samples. However, the total oxygen content, and deviation of oxygen, in metal-cap-protected samples was much higher, especially in the body part of the samples. Finally, it was found that the oxygen content heterogeneity in the metal-cap-protected samples increased with a decreased sample weight. Based on the obtained results, the 6mm thick Lollipop sample with argon-protection is recommended for determination of total oxygen content and oxide inclusion characteristics.

Place, publisher, year, edition, pages
2011. Vol. 82, no 3, 222-229 p.
Keyword [en]
sampling, steel, reoxidation, homogeneity, slag protection, oxygen content
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-26095DOI: 10.1002/srin.201000136ISI: 000289061100009Scopus ID: 2-s2.0-79952219898OAI: oai:DiVA.org:kth-26095DiVA: diva2:369918
Note
QC 20101112 Uppdaterad från accepted till published (20110420).Available from: 2010-11-12 Created: 2010-11-12 Last updated: 2011-04-20Bibliographically approved
In thesis
1. An Experimental Study of a Liquid Steel Sampling Process
Open this publication in new window or tab >>An Experimental Study of a Liquid Steel Sampling Process
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

During the steelmaking process samples are taken from the liquid steel, mainly to assess the chemical composition of the steel. Recently, methods for rapid determination of inclusion characteristics (size and composition) have progressed to the level where they can be implemented in process control. Inclusions in steel can have either good or detrimental effects depending on their characteristics (size, number, composition and morphology). Thereby, by determination of the inclusion characteristics during the steelmaking process it is possible to steer the inclusion characteristics in order to increase the quality of the steel. However, in order to successfully implement these methods it is critical that the samples taken from the liquid steel represent the inclusion characteristics in the liquid steel at the sampling moment.

 

The purpose of this study is to investigate the changes in inclusion characteristics during the liquid steel sampling process. Experimental studies were carried out at steel plants to measure filling velocity and solidification rate in real industrial samples. The sampling conditions for three sample geometries and two slag protection types were determined. Furthermore, the dispersion of the total oxygen content in the samples was evaluated as a function of sample geometry and type of slag protection. In addition, the effects of cooling rate as well as oxygen and sulfur content on the inclusion characteristics were investigated in laboratory and industrial samples. Possibilities to separate primary (existing in the liquid steel at sampling moment) and secondary (formed during cooling and solidification) inclusions depending on size and composition were investigated. Finally, in order to evaluate the homogeneity and representative of the industrial samples the dispersion of inclusion characteristics in different zones and layers of the samples were investigated.

 

It was concluded that the type of slag protection has a significant effect on the filling velocity and the sampling repeatability. Furthermore, that the thickness of the samples is the main controlling factor for the solidification rate. It was shown that top slag can contaminate the samples. Therefore, the choice of slag protection type is critical to obtain representative samples. It was shown that the cooling rate has a significant effect on the number of secondary precipitated inclusions. However, the number of primary inclusions was almost constant and independent on the cooling rate. In most cases it is possible to roughly separate the secondary and primary oxide inclusions based on the particle size distributions. However, in high-sulfur steels a significant amount of sulfides precipitate heterogeneously during cooling and solidification. This makes separation of secondary and primary inclusions very difficult. Moreover, the secondary sulfides which precipitate heterogeneously significantly change the characteristics (size, composition and morphology) of primary inclusions. The study revealed that both secondary and primary inclusions are heterogeneously dispersed in the industrial samples. In general, the middle zone of the surface layer is recommended for investigation of primary inclusions.

 

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. xiii, 52 p.
Keyword
liquid steel sampling, inclusion characteristics, sampling conditions, sample homogeneity.
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-26048 (URN)978-91-7415-792-5 (ISBN)
Public defence
2010-11-26, E3, Lindstedsvägen 3, KTH, Stockholm, 09:00 (English)
Opponent
Supervisors
Note
QC 20101112Available from: 2010-11-12 Created: 2010-11-10 Last updated: 2011-04-20Bibliographically approved

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