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A Study of Different Methods for Inclusion Characterization towards On-line use during Steelmaking
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The interest of gaining on-line information related to non-metallic inclusions during the steelmaking process has recently increased due to the development as well as the promising results of the Pulse Distribution Analysis with Optical Emission Spectroscopy method (PDA/OES). Even though, the time from sampling to presented results on inclusions is only about 5-10 minutes, the method has also shown limitations with respect to the determination of some inclusion characteristics.

Therefore, a first step was to perform a study on other methods such as the cross-section method (CS) on a polished sample surface, the cross-section after etching method (CSE), the bromine-methanol extraction method (BME), and the electrolytic extraction method (EE). This study focused on the evaluation of these methods with respect to the time consumption for preparation and analysis of a sample, the analyzed volume and the determination of inclusion and cluster characteristics such as size, number, particle size distribution (PSD) and composition. The CS and CSE methods were found to be suitable in the determination of the largest cluster in a sample which can be recommended in order to select proper extraction parameters for further studies. The BME method was considered to be fast with the possibility of analyzing a large volume. However, the used solution is chemically stronger compared to electrolytic extraction solutions, which can affect the results. In most aspects, the EE method was found to be the most stable, reliable and accurate method with some limitations regarding the time aspect.

Based on this conclusion, the EE method was selected for a comparative study with the PDA/OES method. Reliably detected size ranges by using the PDA/OES method were defined for two low-alloyed steel grades. These are 2.0-5.7 μm and 1.4-5.7 μm for steel samples taken before and after a Ca-addition during the secondary steelmaking, respectively. Moreover, agreements between the EE and PDA/OES methods were observed in the average size and number of detected inclusions when only inclusions with the size > 2 μm were considered. Also, a theoretical minimum size and a maximum number ofinclusions present in the steel sample, which can be detected by using the PDA/OES method, were estimated.

The work continued by successfully applying the EE method to study correlations between inclusions observed in the liquid steel samples and in a clogged nozzle (clogging material). It was found that the average sizes of spherical and non-spherical inclusions observed in the steel corresponded well with those observed in the clogging material. However, there were some differences in the frequencies of these inclusions. This was explained by a possible transformation of the present inclusions due to a reoxidation and a reaction with the nozzle refractory of the steel melt. The results of this study may contribute in the selection of proper process parameters or inclusion characteristics for future studies on the improvement and application of on-line methods.

Finally, suggestions on how to present and interpret data obtained by the PDA/OES method during production of stainless steels were given in the present thesis. More specifically, the possibilities of defining operating windows with respect to inclusion composition and the use of a B-factor for Al (the total content of Al in inclusions detected by using the PDA/OES method) during the secondary steelmaking were discussed. In addition, a correlation study between B-factors for Al and numbers of inclusions (dV > 4 μm) obtained by using the PDA/OES method on process samples, and corresponding slivers indices from plate products was performed. The results showed a moderate correlation between these parameters as well as an increase of the slivers index with increased values of the chosen PDA/OES data. This indicates that it could be possible to predict when there is an increased risk of having slivers on the final rolled product at an early stage of the steelmaking process.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , xii, 62 p.
Keyword [en]
on-line method, PDA/OES, electrolytic extraction, inclusions, clusters, nozzle clogging, secondary steelmaking
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-167799ISBN: 978-91-7595-592-6 (print)OAI: oai:DiVA.org:kth-167799DiVA: diva2:813449
Public defence
2015-06-08, Sal B2, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150525

Available from: 2015-05-25 Created: 2015-05-22 Last updated: 2015-05-25Bibliographically approved
List of papers
1. Application of Different Extraction Methods for Investigation of Nonmetallic Inclusions and Clusters in Steels and Alloys
Open this publication in new window or tab >>Application of Different Extraction Methods for Investigation of Nonmetallic Inclusions and Clusters in Steels and Alloys
2014 (English)In: Advances in Materials Science and Engineering, ISSN 1687-8434, E-ISSN 1687-8442, Vol. 2014, 210486- p.Article in journal (Refereed) Published
Abstract [en]

The characterization of nonmetallic inclusions is of importance for the production of clean steel in order to improve the mechanical properties. In this respect, a three-dimensional (3D) investigation is considered to be useful for an accurate evaluation of size, number, morphology of inclusions, and elementary distribution in each inclusion particle. In this study, the application of various extraction methods (chemical extraction/etching by acid or halogen-alcohol solutions, electrolysis, sputtering with glow discharge, and so on) for 3D estimation of nonmetallic Al2O3 inclusions and clusters in high-alloyed steels was examined and discussed using an Fe-10 mass% Ni alloy and an 18/8 stainless steel deoxidized with Al. Advantages and limitations of different extraction methods for 3D investigations of inclusions and clusters were discussed in comparison to conventional two-dimensional (2D) observations on a polished cross section of metal samples.

National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-141967 (URN)10.1155/2014/210486 (DOI)000330568800001 ()2-s2.0-84893194638 (Scopus ID)
Funder
VINNOVA
Note

QC 20140227

Available from: 2014-02-27 Created: 2014-02-27 Last updated: 2017-12-05Bibliographically approved
2. Evaluation of Inclusion Characteristics in Low-Alloyed Steels by Mainly Using the PDA/OES Method
Open this publication in new window or tab >>Evaluation of Inclusion Characteristics in Low-Alloyed Steels by Mainly Using the PDA/OES Method
2015 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 55, no 10, 2173-2181 p.Article in journal (Refereed) Published
Abstract [en]

The characteristics of non-metallic inclusions (such as number, size and volume fraction) in liquid steel samples taken during ladle treatment and casting of industrial heats of two low-alloyed Ca-treated steel grades were evaluated by using the Pulse Distribution Analysis with Optical Emission Spectroscopy (PDA/OES) method. These results were compared to data obtained by Scanning Electron Microscope observations of inclusions after electrolytic extraction from steel samples (the EE method). It was found that the PDA/OES method can be used for a relative estimation of the homogeneity of the distribution of non-metallic inclusions in steel samples. Bottom and middle parts of the steel samples showed more homogeneous results with respect to the characteristics of the investigated Al2O3, CaO-Al2O3 and CaO-Al2O3-CaS inclusions. The numbers of inclusions in the size ranges 2.0-5.7 mu m and 1.4-5.7 mu m in samples taken before and after a Ca addition, respectively, showed a relatively good agreement between both methods. Furthermore, the calculated volume fractions for inclusions in the size range 2-13 mu m obtained by the PDA/OES method agreed satisfactorily well with those obtained from the EE method. Finally, the minimum sizes of inclusions in steel samples, which can reliably be detected by the PDA/OES method, were estimated for steels with different concentrations of Al in steel and Al2O3 in inclusions.

Place, publisher, year, edition, pages
IRON STEEL INST JAPAN KEIDANREN KAIKAN, 2015
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-167987 (URN)10.2355/isijinternational.ISIJINT-2015-172 (DOI)000363914400017 ()2-s2.0-8498349425 (Scopus ID)
Note

Updated from manuscript to article.

QC 20151202

Available from: 2015-05-25 Created: 2015-05-25 Last updated: 2017-12-04Bibliographically approved
3. A Study of Cluster Characteristics in Liquid Stainless Steel and in a Clogged Nozzle
Open this publication in new window or tab >>A Study of Cluster Characteristics in Liquid Stainless Steel and in a Clogged Nozzle
2015 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 86, no 11, 1271-1278 p.Article in journal (Refereed) Published
Abstract [en]

Clusters of Al2O3 inclusions in a liquid stainless steel (18/8) and in a clogged ZrO2 nozzle after casting were studied during a pilot plant trial. Samples were taken from the melt at different holding times after an addition of 0.1 mass% Al. The characteristics (composition, size, number, and morphology) of clusters and clustered inclusions in the steel samples and in the clogged nozzle were investigated after electrolytic extraction and etching by using SEM. It was found that the Al2O3 inclusions in the clusters are transformed from a spherical into irregular and regular (with sharp edges) shape during the holding time. Most of the inclusions in the clusters (>80%) after a 6 min holding time are regular inclusions, which have sharp edges and flat faces. The size of the inclusions in clusters in the melt increased on average from 1.0 μm at a 1 min to 5.2 μm at a 12 min holding time. While the sizes of different types of inclusions in the clogged nozzle correspond to those present in the liquid steel at respective time, the frequency of spherical inclusions in the clogged nozzle is about 2–4 times larger (particularly near the nozzle wall) compared to that in the melt. Growth and transformation of Al2O3 clusters in the liquid steel at different holding times after an addition of Al and during casting were considered based on the obtained results.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2015
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-167986 (URN)10.1002/srin.201400316 (DOI)000363679600006 ()2-s2.0-84945451269 (Scopus ID)
Funder
VINNOVA
Note

QC 20151120

Available from: 2015-05-25 Created: 2015-05-25 Last updated: 2017-12-04Bibliographically approved
4. Application of the PDA/OES method during Production of Duplex Stainless Steel
Open this publication in new window or tab >>Application of the PDA/OES method during Production of Duplex Stainless Steel
(English)Manuscript (preprint) (Other academic)
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-167988 (URN)
Note

QS 2015

Available from: 2015-05-25 Created: 2015-05-25 Last updated: 2015-05-25Bibliographically approved

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