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A Study of Cluster Characteristics in Liquid Stainless Steel and in a Clogged Nozzle
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
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.
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. Vol. 86, no 11, 1271-1278 p.
National Category
Materials Engineering
URN: urn:nbn:se:kth:diva-167986DOI: 10.1002/srin.201400316ISI: 000363679600006ScopusID: 2-s2.0-84945451269OAI: diva2:813683

QC 20151120

Available from: 2015-05-25 Created: 2015-05-25 Last updated: 2015-11-20Bibliographically approved
In thesis
1. A Study of Different Methods for Inclusion Characterization towards On-line use during Steelmaking
Open this publication in new window or tab >>A Study of Different Methods for Inclusion Characterization towards On-line use during Steelmaking
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.
on-line method, PDA/OES, electrolytic extraction, inclusions, clusters, nozzle clogging, secondary steelmaking
National Category
Metallurgy and Metallic Materials
urn:nbn:se:kth:diva-167799 (URN)978-91-7595-592-6 (ISBN)
Public defence
2015-06-08, Sal B2, Brinellvägen 23, KTH, Stockholm, 10:00 (English)

QC 20150525

Available from: 2015-05-25 Created: 2015-05-22 Last updated: 2015-05-25Bibliographically approved

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Janis, DianaKarasev, AndreyJönsson, Pär G.
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