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Three-dimensional investigations of inclusions in ferroalloys
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.
2014 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 85, no 4, 659-669 p.Article in journal (Refereed) Published
Abstract [en]

As the requirements on material properties increase, there has been a demand on an additional knowledge on the effect of impurities in the ferroalloys on the properties. Thus, the number, morphology, size, and composition of inclusions in four different ferroalloys (FeTi, FeNb, FeSi, and SiMn) were investigated. This was done in three dimensions (3D) by using scanning electron microscopy in combination with energy dispersive spectroscopy after electrolytic extraction of the ferroalloy samples. The non-metallic and metallic inclusions were successfully analyzed on the surface of film filter. Thereafter, the particle size distribution was plotted for most of the non-metallic inclusions. The non-metallic inclusions were found to be REM oxides in FeTi, FeSi, and SiMn, Al2O3, Ti-Nb-S-O oxides in FeNb and silicon oxides in SiMn. Moreover, the intermetallic inclusions were found to be a Ti-Fe phase in FeTi, Ca-Si, and Fe-Si-Ti phases in FeSi and a Mn-Si phase in SiMn. In addition, the almost pure single metallic phases were found to be Ti in FeTi, Nb in FeNb, and Si in FeSi. As the requirements on material properties increase, the effect of impurities in ferroalloys on the steelmaking process is increasingly becoming more important. The characteristic of inclusions (morphology, number, size, and composition) in ferroalloys investigated in three-dimensional after electrolytic extraction is a good method for studying the evolution of inclusions during steelmaking.

Place, publisher, year, edition, pages
2014. Vol. 85, no 4, 659-669 p.
Keyword [en]
electrolytic extraction, ferroalloy, non-metallic and metallic inclusions, three-dimensional investigations
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-145665DOI: 10.1002/srin.201300157ISI: 000333909700018Scopus ID: 2-s2.0-84898068584OAI: oai:DiVA.org:kth-145665DiVA: diva2:719501
Note

QC 20140526

Available from: 2014-05-26 Created: 2014-05-26 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Three Dimensional Determinations of Inclusions in Ferroalloys and Steel Samples
Open this publication in new window or tab >>Three Dimensional Determinations of Inclusions in Ferroalloys and Steel Samples
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

As the requirements on material properties increase, there has been a demand on an additional knowledge on the effect of impurities in the ferroalloyson the steel cleanness. Thus, the number, morphology, size and composition of inclusions in sixdifferent ferroalloys (FeTi, FeNb, FeSi,SiMn, LC and HC FeCr) were investigatedin this study. This was done in three dimensions (3D) by using a SEM in combination with EDS after electrolytic extraction of the ferroalloy samples. Theresults show that thenon-metallic and metallic inclusions can besuccessfully analyzed on the surface of a film filterafter a separation of the inclusions from the matrix. Overall, the inclusions canbe divided into two categories depending on the melting point. Furthermore, the possible transformation of different kinds of inclusions after their addition to the liquid steel canalso be determined.

The inclusions and clusters in steel samples of two similar steel grades of high-silicon non-calcium treated (HSiNC) stainless steels were also investigated and compared during ladle treatment and continuous casting. Samples of liquid steel and slag were taken at different stages of the ladle treatment and casting during two plant trials: a low Al steel (LAl) and a high Al steel (HAl). Spherical (SP), irregular and regular (IR) inclusions and clusters (CL) were observed in the samples from both heats. It wasfound that the morphology and composition of inclusions and clusters in both heats were significantly changed during the ladle treatment and casting. Most of inclusions (44-98%) in a low Al steel are MgO-CaO-SiO2-Al2O3spherical inclusions. The compositions of irregular and regularinclusions and clusters in steel samples of a high Al steel were mostly MgO·Al2O3spinel, but also complex sphericalinclusions containing Al2O3-MgO-CaO-SiO2. In addition, the phase stabilitydiagram based on Darken’s quadratic formalism and Redlich-Kister type polynomial was estimated for both heats at a non-infinite solution.

It is known that clusters in liquid steel have a harmful effect on the casting process and the quality of the final steel product. Therefore, clusters of rare earth metals (REM) were investigated in steel samples of a S30185 stainless steel grade from a pilot trial (PT, 250 kg) and from an industrial heat (IH, 100 t). Samples were taken from the liquid steel at differentholding times after the addition of a mischmetal. The morphology, composition, number and size of clusters in PT and IH steel samples were analyzed and compared as a function of the holding time. It was found that typical clusters with regular and irregular inclusions were the main type of clusters (69%-98%) in all PT and IH steel samples. The composition of inclusions in clusters corresponded mostly to REM-oxides. The size of clusters that were observed in different samples varied mainly from 2 to 23 μm. In addition, the size and number of most clusters in PT are larger than those in IH samples.

Largesize inclusions are recognized to be crucially harmful for the mechanical properties of steel products. Therefore, predictionsof the maximum size of Al2O3-CaO spherical inclusions in an Fe-10 mass% Ni alloy have been examined based on two dimensional (2D) and three dimensional (3D) investigations. The effects of the number of measurements and unit volume on the estimated 3D results were also investigated.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. vii, 67 p.
Keyword
Three dimensional, Ferroalloy, Inclusion, Spinel inclusion, T hermodynamic calculation, REM clusters, Formation mechanism, Statistical analysis, Maximum size
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-145225 (URN)978-91-7595-156-0 (ISBN)
Public defence
2014-06-11, Sal B1, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
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Note

QC 20140526

Available from: 2014-05-26 Created: 2014-05-14 Last updated: 2014-05-26Bibliographically approved

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