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Study of Non-metallic Inclusion in Alloy 825
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

It is well known that inclusions affect the properties of steels and alloys. Therefore, it is important to understand what type of inclusions that exist and how they behave and especially with a focus on large size inclusions. Thus, the large size non-metallic inclusions in ferroalloy FeTi70R were investigated in two dimensions (2D) by using scanning electron microscopy (SEM) in combination with an energy dispersive technique (EDS). It was found that the FeTi70R ferroalloy contain complex oxide inclusions consisting mostly of CaO, SiO2 and TiOx. Furthermore, experimental trials were performed to investigate how these inclusions behaved when entering a melt. More specifically, a comparison between pure Fe and an Alloy 825 grade were made. These results determined the parameters effect on the transformation of the inclusions in the melt.

The large size non-metallic inclusions in Alloy 825 during the ladle treatment were investigated during industrial trials by using both two dimensional (2D) and three dimensional (3D) microscopic investigations. The results showed that inclusions consisted of spherical oxides and clusters made up of oxides and nitrides. Further investigations found that the spherical inclusions were transformed from existing NMI in the FeTi70R ferroalloy and slag particles. As for the clusters, they originate from deoxidation products. Furthermore, small inclusions precipitated in the local zones around the added FeTi70R ferroalloy and titanium nitrides. Investigations also found that only Al2O3-MgO and TiN clusters exist after casting.

Industrial trials were performed during the last period of the ladle treatment and using a combined electromagnetic (EMS) and gas (GS) stirring. The purpose to investigate the effect of different EMS directions on the agglomeration and on the removal of Al2O3-MgO and TiN clusters. The investigations were then performed in 3D after an electrolytic extraction of the metal samples. The results show that electromagnetic stirring in the upwards direction is best for the agglomeration of the Al2O3-MgO and TiN clusters. However, electromagnetic stirring in the downwards direction is more effective to remove clusters from the melt. This is in agreement with the theoretical predictions based on Stokes’, Brownian and Turbulent collisions. Also, the calculations showed that for Al2O3-MgO clusters with sizes <20 μm the Turbulent collision is the defining factor for agglomeration. However, both Stokes’ and Turbulent collisions are dominant for larger inclusions. For the TiN clusters, turbulent collisions is the dominant factor.

Further investigations with more heats and stirring modes were done by using 2D microscopic investigations. More specifically, the number, size, composition and morphology of different inclusions were determined by using SEM in combination with EDS and Inca Feature analyses. The results show that the EMS in downwards direction with a 0.04 m3 min-1 gas flow rate promotes a general removal of Al2O3-MgO and TiN inclusions. Furthermore, that the upwards EMS direction promotes a drastically increase of inclusions having an equivalent size smaller than 11.2 μm. Moreover, the stirring with a 0.02 m3 min-1 gas flow rate has a better removal rate for both downwards and upwards stirring directions compared to the stirring with a 0.04 m3 min-1 gas flow rate. However, no influence on the inclusion composition and morphology could be seen from the different stirring modes.

Abstract [sv]

Det är välkänt att inneslutningar påverkar egenskaperna i stål och legeringar. Därför är det viktigt att förstå vilken sorts inneslutningar som existerar samt hur de beter sig, särskilt stora inneslutningar. Således undersöktes de stora icke-metalliska inneslutningarna i ferrolegeringen FeTi70R i två dimensioner (2D) genom att använda svepelektronmikroskopi (SEM) i kombination med energidispersionsteknik (EDS). Det visade sig att ferrolegeringen FeTi70R innehåller komplexa oxidinneslutningar bestående huvudsakligen av CaO, Si02 och TiOx. Vidare utfördes laborativa försök för att undersöka hur dessa inneslutningar uppträder när de kommer ner i det smälta stålet. Mer specifikt så gjordes en jämförelse mellan rent Fe och Alloy 825 legeringen. Dessa resultat fastställde hur olika parametrar påverkade inneslutningarnas omvandling i smältan.

De stora icke-metalliska inneslutningarna i Alloy 825 legeringen under skänkugnsbehandlingen undersöktes vid industriella försök med hjälp av både tvådimensionella (2D) och tredimensionella (3D) mikroskopiska undersökningar. Resultaten visade att inneslutningarna bestod av sfäriska oxider och kluster uppbyggda av oxider och nitrider. Ytterligare undersökningar visade att de sfäriska inneslutningarna omvandlades från befintliga icke-metalliska inneslutningar i ferrolegeringen FeTi70R och slaggpartiklar. När det gäller kluster härrör de från desoxidationsprodukter. Vidare så bildades små inneslutningar i de lokala zonerna kring den tillsatta FeTi70R legeringen och kring titanitriderna. Undersökningarna fann också att endast Al2O3-MgO och TiN-kluster existerar efter gjutning.

De industriella försöken utfördes under den sista perioden av skänkugnsbehandlingen och med en kombinerad elektromagnetisk (EMS) och gas (GS) omröring. Syftet med detta var att undersöka effekten av olika riktningar på EMS omrörningen på agglomerationen och avskiljningen av Al2O3-MgO- och TiN klustren. Undersökningarna utfördes sedan i 3D efter en elektrolytisk extraktion av metallproverna. Resultaten visar att en uppåtriktad elektromagnetisk omröring är bäst för agglomereringen av Al2O3-MgO inneslutningar och TiN kluster. Emellertid så är en nedåtriktad elektromagnetisk omröring effektivare för att avlägsna kluster från smältan. Dessa resultat överensstämmer med de teoretiska förutsägelserna baserade på Stokes, Brownian och Turbulent kollisionsvolymer. Dessutom visade beräkningarna att för Al2O3-MgO kluster med storlekar <20 μm är det turbulenta kollisioner som är den avgörande faktorn för agglomerering. Dock är det både Stokes och de Turbulenta kollisionerna som dominerar för större inneslutningar. För TiN klustren är det de turbulenta kollisionerna som är den dominerande faktorn.

Ytterligare undersökningar med fler charger av Alloy 825 och olika omrörningsmetoder gjordes baserade på 2D mikroskopiska undersökningar. Mer specifikt så bestämdes antalet, storleken, sammansättningen och morfologin för olika inneslutningar med användning av SEM i kombination med EDS och Inca Feature analyser. Resultaten visar att en nedåtriktad EMS i kombination med ett gasflöde på 0,04 m3 min-1 främjar ett generellt avlägsnande av Al2O3-MgO och TiN inneslutningar. Vidare främjar den uppåtriktade EMS omrörningen en drastisk ökning av inneslutningar med en ekvivalent storlek av 11,2 μm eller mindre. Vidare har omröringen med ett gasflöde på 0,02 m3 min-1 en bättre avskiljningshastighet för inneslutningar i både nedåt och uppåtgående omrörningsriktningar jämfört med omrörningen med ett gasflöde på 0,04 m3 min-1. Emellertid kunde inget inflytande på sammansättningen och morfologin ses från de olika omrörningssätten.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. , p. 61
Keywords [en]
Alloy 825, FeTi70R alloy, non-metallic inclusions, inclusion distribution, clusters, electromagnetic and gas stirring, ladle treatment, electrolytic extraction, stirring directions
Keywords [sv]
Alloy 825, FeTi70R legering, icke-metalliska inneslutningar, inneslutnings fördelning, kluster, elektromagnetisk och gas omrörning, skänkugnsbehandling, elektrolytisk extraktion, omrörningshåll
National Category
Metallurgy and Metallic Materials
Research subject
Metallurgical process science
Identifiers
URN: urn:nbn:se:kth:diva-218036ISBN: 978-91-7729-582-2 (print)OAI: oai:DiVA.org:kth-218036DiVA, id: diva2:1159208
Public defence
2017-12-12, B1, Brinellvägen 23, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20171122

Available from: 2017-11-22 Created: 2017-11-22 Last updated: 2017-11-22Bibliographically approved
List of papers
1. Evolution of Non-Metallic Inclusions from FeTi70R Alloys during Alloying of Fe-40Ni-20Cr Steels
Open this publication in new window or tab >>Evolution of Non-Metallic Inclusions from FeTi70R Alloys during Alloying of Fe-40Ni-20Cr Steels
2016 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344XArticle in journal (Refereed) Published
Abstract [en]

In this study, the composition, size, and number of large non-metallic inclusions (&gt;20μm) are investigated in a commercial refined FeTi70R alloy, which is used for deoxidation and alloying of different industrial high-quality steels. It is found that this ferroalloy contains different complex oxide inclusions, which sizes vary from 20 to 260μm. These different complex inclusions contain mostly CaO, SiO2, and TiOx. When adding FeTi70R alloy in the steel during the final stage of ladle treatment, these large size inclusions can significantly decrease the cleanliness and mechanical properties of steel. Therefore, the evolution and behavior of these inclusions after addition of this ferroalloy into the liquid iron or Fe-40Ni-20Cr steel are investigated in laboratory experiments. In addition, the results from the laboratory scale experiments are compared to results obtained from industrial heats using Alloy 825. A consideration of the evolution mechanism of large inclusions after an addition of a FeTi70R alloy helps to understand their behavior in the melt. It also helps to estimate their possible harmful effects on the quality of this steel grade during commercial production.

Place, publisher, year, edition, pages
John Wiley & Sons, 2016
Keywords
Alloy 825, FeTi70R alloy, Non-metallic inclusions, Alloying, Iron compounds, Nickel, Commercial productions, Evolution mechanism, Harmful effects, High quality steels, In-laboratory experiments, Ladle treatment, Large inclusions, Alloy steel
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-186770 (URN)10.1002/srin.201500428 (DOI)000387018800009 ()2-s2.0-84963815499 (Scopus ID)
Note

QC 20160527

Available from: 2016-05-27 Created: 2016-05-13 Last updated: 2017-11-30Bibliographically approved
2. Estimation of Non-Metallic Inclusions in Industrial Ni Based Alloys 825
Open this publication in new window or tab >>Estimation of Non-Metallic Inclusions in Industrial Ni Based Alloys 825
Show others...
2017 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 88, no 4, article id UNSP 1600024Article in journal (Refereed) Published
Abstract [en]

It is well known that inclusions affect the properties of the steel and other alloys. The importance of understanding the behavior of the inclusions during production can never be overstated. This study has examined the main types of big size (> 10 mu m) inclusions that exist in Ni-based Alloy at the end of ladle treatment and after casting during industrial production of Ni based Alloys 825. Sources, mechanisms of formation and behavior of different type large size inclusions in Alloy 825 are discussed based on 2 and 3D investigations of inclusion characteristics (such as, morphology, composition, size, and number) and thermodynamic considerations. The large size inclusions found can be divided in spherical (Type I and II) inclusions and in clusters (Type III-V). Type I-A inclusions (Al2O3-CaO-MgO) originate from the slag. Type I-B inclusions and Type II inclusions consist of CaO-Al2O3-MgO and Al2O3-TiO2-CaO, respectively. Both types originate from the FeTi70R alloy. Type III clusters (Al2O3-MgO-CaO) are formed during an Al deoxidation of the Ni-based alloy. Type IV clusters (Al2O3-TiO2-CaO) formed from small inclusions, which are precipitated in local zones which contain high Ti and Al levels. These clusters are transformed to Type III clusters over time in the ladle. Finally, Type V clusters are typical TiN clusters.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2017
Keywords
Alloy 825, inclusion distribution, non-metallic inclusions
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-206287 (URN)10.1002/srin.201600024 (DOI)000398639200012 ()2-s2.0-85014553773 (Scopus ID)
Note

QC 20170509

Available from: 2017-05-09 Created: 2017-05-09 Last updated: 2017-11-22Bibliographically approved
3. Effect of the Stirring Mode on the Behavior of Al2O3–MgO Particles and Clusters during Ladle Treatment of Ni-based Alloy 825
Open this publication in new window or tab >>Effect of the Stirring Mode on the Behavior of Al2O3–MgO Particles and Clusters during Ladle Treatment of Ni-based Alloy 825
2017 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 87, article id 1700165Article in journal (Refereed) Published
Abstract [en]

It is well known that inclusions affect the properties of alloys. Therefore, the importance of understanding what inclusions exist and how they behave cannot be overstated. This study has examined the behavior of Al2O3–MgO particles and clusters in the melt during the ladle treatment of Alloy 825, who is a Ni-based Alloy. The effect of different stirring directions of electromagnetic stirring in combination with gas stirring is discussed based on three-dimensional investigations of the clustered particles. More specifically, the composition, size, and number of particles and clusters are determined after electrolytic extraction of metal samples by using SEM in combination with EDS. The results show that the agglomeration of Al2O3–MgO particles in the melt is faster for an upward induction stirring combined with a gas stirring in comparison to a downward stirring combined with a gas stirring. However, the total removal of clusters from the melt is more effective when using a downward induction stirring compared to when using an upward induction stirring, especially for large size clusters (>11.2 mm). The effect of the different stirring modes on the behavior of the Al2O3–MgO particles and clusters in the melt for the ladle treatment experiments agree with the theoretical predictions based on Stokes’, Brownian, and Turbulent collisions.

Place, publisher, year, edition, pages
Weinheim: Wiley-VCH Verlagsgesellschaft, 2017
Keywords
Alloy 825;Clusters; Electrolytic Extraction; Electromagnetic and gas stirring;Ladle treatment; Stirring directions
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-215871 (URN)10.1002/srin.201700165 (DOI)000417137300011 ()2-s2.0-85037524685 (Scopus ID)
Note

QC 20171122

Available from: 2017-11-21 Created: 2017-11-21 Last updated: 2017-12-29Bibliographically approved
4. Investigations of TiN Particles and Clusters during Ladle Treatments of Ni-based Alloy 825 using Different Stirring Modes
Open this publication in new window or tab >>Investigations of TiN Particles and Clusters during Ladle Treatments of Ni-based Alloy 825 using Different Stirring Modes
2017 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 58, no 2Article in journal (Refereed) Accepted
Abstract [en]

Today, Titanium is often used in steelmaking not only for deoxidation but also for micro-alloying and alloying for a wide range of steel grades. Therefore, many studies are focused on investigations on the formation and behavior of Ti-containing non-metallic inclusions (such as oxides, nitrides and carbides) during production of different Ti-containing steels and their effect on final steel properties. This study has examined the behavior of TiN clusters and particles in the melt during the ladle treatment of Alloy 825 containing up to 1.2wt% of Ti. The industrial trials were performed at the end of the ladle treatment by using argon gas in combination with electromagnetic stirring using an upwards or a downwards stirring direction. Metal samples were taken before and after ladle treatment to enable three-dimensional investigations of non-metallic inclusions and clusters. The composition, size and number of particles and clusters were determined after electrolytic extraction of the metal samples by using SEM in combination with EDS. It was found that agglomerations of TiN clusters and particles in the melt are faster during an upwards stirring in comparison to a downwards stirring. However, the removal of clusters from the melt is more effective when using a downwards stirring direction compared to when using an upwards stirring in dombination with gas stirring. It was also found that the Turbulent collision is the dominant factor for the agglomeration of TiN particles in the melt.

Keywords
Ni-base Alloy 825, ladle treatment, electromagnetic and gas stirring, electrolytic extraction, TiN inclusions and clusters
National Category
Metallurgy and Metallic Materials
Research subject
Metallurgical process science
Identifiers
urn:nbn:se:kth:diva-218034 (URN)
Note

QCR 20171122

Available from: 2017-11-21 Created: 2017-11-21 Last updated: 2017-11-22Bibliographically approved
5. Effect of Stirring Mode on Non-Metallic Inclusions in Alloy 825 during Ladle Treatment
Open this publication in new window or tab >>Effect of Stirring Mode on Non-Metallic Inclusions in Alloy 825 during Ladle Treatment
(English)Manuscript (preprint) (Other academic)
Abstract [en]

It is well known thatinclusions affect the properties of steels and alloys. Therefore, it is essentialto understand what types of inclusions that exist and how they behave duringthe production. This study has examined the behavior of Al2O3-MgOand TiN inclusions in the melt during the ladle treatment of Ni-based Alloy825. The effects of different directions of electromagnetic stirring (EMS) incombination with different gas flows were investigated based on two dimensionaldeterminations of the inclusion characteristics on a polished surface of themetal samples by using Inca Feature analysis. More specifically, the number,size, composition and morphology of different inclusions were determined byusing SEM in combination with EDS. The results show that the use of EMS in thedownwards direction in combination with a 0.04 m3 min-1gas flow rate promotes a significant removal of Al2O3-MgO and TiN inclusions. Furthermore, the use of an upwards EMSstirring direction promotes a drastical increase of the amount of inclusionshaving an equivalent size smaller than 11.2 µm. Also, the use of both stirringdirections in combination with a 0.02 m3 min-1 gasflow rate promote a ~20% to ~60% removal of Al2O3-MgO and TiN inclusions for most heats. No influence on the composition andmorphology could be seen from the different stirring modes.

Keywords
Ni-based Alloy 825, ladle treatment, stirring conditions, non-metallic inclusions
National Category
Metallurgy and Metallic Materials
Research subject
Metallurgical process science
Identifiers
urn:nbn:se:kth:diva-218058 (URN)
Note

QC 20171122

Available from: 2017-11-22 Created: 2017-11-22 Last updated: 2017-11-22Bibliographically approved

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