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Three Dimensional Determinations of Inclusions in Ferroalloys and Steel Samples
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
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 [en]
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: urn:nbn:se:kth:diva-145225ISBN: 978-91-7595-156-0 (print)OAI: oai:DiVA.org:kth-145225DiVA: diva2:717295
Public defence
2014-06-11, Sal B1, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20140526

Available from: 2014-05-26 Created: 2014-05-14 Last updated: 2014-05-26Bibliographically approved
List of papers
1. Three-dimensional investigations of inclusions in ferroalloys
Open this publication in new window or tab >>Three-dimensional investigations of inclusions in ferroalloys
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.

Keyword
electrolytic extraction, ferroalloy, non-metallic and metallic inclusions, three-dimensional investigations
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-145665 (URN)10.1002/srin.201300157 (DOI)000333909700018 ()2-s2.0-84898068584 (Scopus ID)
Note

QC 20140526

Available from: 2014-05-26 Created: 2014-05-26 Last updated: 2017-12-05Bibliographically approved
2. Investigations of inclusions in ferrochromium alloys
Open this publication in new window or tab >>Investigations of inclusions in ferrochromium alloys
2014 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 41, no 10, 756-762 p.Article in journal (Refereed) Published
Abstract [en]

Ferrochromium alloys are commonly added during different stages of steelmaking processes according to the specific steel grade being produced. Depending upon the ferrochromium quality, the addition can also lead to a supply of deleterious inclusions to the liquid steel. Therefore, the number, size, morphology and composition of inclusions in LCFeCr and HCFeCr alloys were investigated. The alloy samples were first treated with electrolytic extraction, followed by filtration to gather the inclusions on a film filter. Thereafter, the characteristics of the inclusions and clusters were investigated in three dimensions by SEM in combination with energy dispersive spectroscopy. The results show that the main inclusion types found in LCFeCr alloys are different to those found in HCFeCr alloys. More specifically, the inclusions in LCFeCr alloys were found to consist of Si-Cr-O and Cr-O oxides as well as intermetallic Cr-Fe inclusions. Moreover, the inclusions in HCFeCr alloys were found to consist of Cr-Mn-S, Cr-C-N, Si-Al-Ca-Mg-O and Ca-O-P inclusions. Overall, the inclusions can be divided into two categories depending on the melting point. Furthermore, the possible transformation of different inclusions after their addition to the liquid steel is discussed.

Keyword
LCFeCr, HCFeCr, Inclusions, Electrolytic extraction, Three-dimensional investigations
National Category
Materials Engineering Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-145666 (URN)10.1179/1743281214Y.0000000192 (DOI)000346147000005 ()2-s2.0-84907965895 (Scopus ID)
Note

QC 20150108. Updated from manuscript to article in journal.

Available from: 2014-05-26 Created: 2014-05-26 Last updated: 2017-12-05Bibliographically approved
3. Evolution of Different Inclusions during Ladle Treatment and Continuous Casting of Stainless Steel
Open this publication in new window or tab >>Evolution of Different Inclusions during Ladle Treatment and Continuous Casting of Stainless Steel
2013 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 53, no 12, 2099-2109 p.Article in journal (Refereed) Published
Abstract [en]

The inclusions and clusters in steel samples of two similar steel grades of high-silicon non-calcium treated (HSiNC) stainless steels were 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: Low Al steel (LAI) and High Al steel (HAI). After electrolytic extraction of the steel samples, characteristics of inclusions and clusters (such as morphology, composition, size and number) were investigated in three dimensions (3D) by SEM in combination with EDS. Moreover, the composition of typical inclusions and clusters was analyzed on a polished cross section of steel samples. Spherical (SP), irregular and regular (IR) inclusions and clusters (CL) were observed in the samples from both heats. It was found 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-Al2O3 spherical inclusions. The compositions of IR inclusions and clusters in steel samples of a High Al steel were mostly MgO center dot Al2O3 spinet, but also the complex SP inclusions containing Al2O3-MgO-CaO-SiO2. In addition, phase stability diagram based on Darken's quadratic formalism and Redlich-Kister type polynomial was estimated for both heats at a non-infinite solution.

Keyword
stainless steel, clogging, electrolytic extraction, inclusion, spinel, cluster, non-infinite solution
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-140394 (URN)10.2355/isijinternational.53.2099 (DOI)000328928000011 ()2-s2.0-84893291343 (Scopus ID)
Funder
Vinnova
Note

QC 20140123

Available from: 2014-01-23 Created: 2014-01-23 Last updated: 2017-12-06Bibliographically approved
4. Three Dimensional Evaluations of REM Clusters in Stainless Steel
Open this publication in new window or tab >>Three Dimensional Evaluations of REM Clusters in Stainless Steel
2014 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 54, no 6, 1266-1273 p.Article in journal (Refereed) Published
Abstract [en]

It is known that clusters in liquid steel have a harmful effect on the casting process and the quality of the final steel product. In this study, 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 different holding times after the addition of mischmetal. Thereafter, REM clusters collected on film filters after electrolytic extraction and filtration were investigated in three dimensions (3D) by SEM in combination with EDS. The morphology, composition, number and size of clusters in PT and IH steel samples were analyzed and compared as a function of 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 mu m. In addition, the size and number of most clusters in PT are larger than those in IH samples. Furthermore, the formation mechanisms and evolution of different type of REM clusters were discussed in both PT and IH heats.

Keyword
stainless steel, REM clusters, electrolytic extraction, cluster size distribution
National Category
Materials Engineering Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-145670 (URN)10.2355/isijinternational.54.1266 (DOI)000337984000013 ()2-s2.0-84904977580 (Scopus ID)
Funder
Vinnova
Note

QC 20140808. Updated from manuscript to article in journal.

Available from: 2014-05-26 Created: 2014-05-26 Last updated: 2017-12-05Bibliographically approved
5. Statistical Analysis of the Maximum size of Inclusions in Metal Samples
Open this publication in new window or tab >>Statistical Analysis of the Maximum size of Inclusions in Metal Samples
(English)Manuscript (preprint) (Other academic)
Keyword
Clusters, Electrolytic extraction, Non-metallic inclusions, Steel
National Category
Materials Engineering Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-145671 (URN)
Note

QS 2014

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

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