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A study on the Submerged Entry Nozzels (SEN) respecting clogging and decarburization
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The submerged entry nozzle (SEN) has been used to transport the molten steel from tundish to the mould. The main purpose of the SEN usage is both to prevent oxygen and nitrogen pick-up by molten steel and to achieve the desired flow condition in the mould. Therefore, the SEN can be considered as a vital factor for a stable casting process and the steel quality. Furthermore, the steelmaking processes occur at high temperatures around 1873 K so the interaction between the refractory materials of the SEN and molten steel is unavoidable. Therefore, the knowledge of the SEN behaviors during pre-heating and casting is necessary for the design of the steelmaking processes. The internal surfaces of modern SENs are coated with a glass/silicon powder layer to prevent the SEN graphite oxidation during pre-heating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied in supplement 1. The results of the study indicated the penetration of the formed alkaline-rich glaze into the Alumina/graphite base refractory during pre-heating. More specifically, the alkaline-rich glaze reacts with graphite to form carbon monoxide gas. Thereafter, dissociation of CO at the SEN/molten metal interface takes place. This leads to reoxidation of dissolved REM (Rare Earth Metal), which form the “In Situ” REM oxides at the interface between the SEN and the REM alloyed molten steel. Also, the interaction of the penetrated glaze with alumina in the SEN base refractory materials leads to a formation of a high-viscous alumina-rich glaze during the SEN pre-heating process. This in turn, creates a very uneven surface at the SEN internal surface. The “In Situ” formation of the REM oxides together with the uneven internal surface of the SEN may facilitate the accumulation of the primary inclusions. Supplement 1 revealed the disadvantages of the glass/silicon powder layer. On the other hand the carbon oxidation is a main industrial problem for un-coated Alumina/Graphite Submerged Entry Nozzles (SEN) during pre-heating. This led to the proposal of a new refractory material for the SEN. In supplement 2, the effect of ZrSi2 antioxidant and the coexistence of antioxidant additive and (4B2O3 ·BaO) glass powder on carbon oxidation were investigated at simulated non-isothermal heating conditions in a  controlled atmosphere. Also, the effect of ZrSi2 antioxidant on carbon oxidation was investigated at isothermal temperatures at 1473 K and 1773 K. The specimens’ weight losses and temperatures were plotted versus time and compared to each others. The thickness of the oxide areas were measured and also examined using XRD, FEG-SEM and EDS. The coexistence of 8 wt% ZrSi2 and 15 wt% (4B2O3 ·BaO) glass powder of the total alumina/Graphite base refractory materials, presented the most effective resistance to carbon oxidation. The 121% volume expansion due to the Zircon formation during heating and filling up the open pores by (4B2O3 ·BaO) glaze during green body sintering led to an excellent carbon oxidation resistance. In supplement 3, decarburization behaviors of Al2O3-C, ZrO2-C and MgO-C refractory materials constituting a commercial Submerged Entry Nozzle (SEN), have been investigated in different gas atmosphere consisting of CO2, O2 and Ar. The (CO2/O2) ratio values were kept the same as it is in propane combustion flue gas at Air Fuel Ratio (AFR) values equal to 1.5 and 1 for both Air-fuel and Oxygen-fuel combustions. Laboratory experiments were carried out non-isothermally in the temperature range 873 K to 1473 K at 15 K/min followed by isothermal heating at 1473 K for 60 min. The decarburization ratio (α) values of the three refractory types were determined by measuring the weight losses of the samples. The results showed that the decarburization ratio (α) values of the MgO-C refractory became 3.1 times higher for oxygen-fuel combustion compared to air-fuel combustion both at AFR equal to 1.5 in the temperature range 873 K to 1473 K. The decarburization ratio (α) values for Al2O3-C samples were the same as for the isothermal heating at 1473 K and non-isothermal heating in the temperature range 473  to 1773 K with a 15 K/min heating rate. It substantiates the SEN preheating advantage at higher temperatures for shorter holding times instead of heating at lower temperatures for longer holding times. Jander’s diffusion model was proposed for estimating the decarburization rate of Al2O3-C refractory in the SEN. The activation energy for Al2O3-C samples heated at AFR equal to 1.5, for air-fuel and oxygen-fuel combustions were found to be 84.5 KJ/mol and 95.5 KJ/mol respectively during non-isothermal heating in the temperature range 873 K to 1473 K.

 

Place, publisher, year, edition, pages
Stockholm: US-AB , 2010. , ix, 35 p.
Keyword [en]
Refractory, SEN, Clogging, REM, Coating, glaze, alkaline, Refractory, ZrSi2, Graphite, Alumina, Oxidation, Al2O3-C, ZrO2-C, MgO-C, decarburization, reaction mechanism
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-25110ISBN: 978-91-7415-664-5 (print)OAI: oai:DiVA.org:kth-25110DiVA: diva2:355830
Presentation
2010-06-10, MAVE konferensrum, KTH, Brinellvägen 23, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20101008Available from: 2010-10-08 Created: 2010-10-08 Last updated: 2010-10-08Bibliographically approved
List of papers
1. Studies of the glass/silicon powder coating of the commercial submerged entry nozzles respecting clogging of a rare earth metals (REM) alloyed stainless steel
Open this publication in new window or tab >>Studies of the glass/silicon powder coating of the commercial submerged entry nozzles respecting clogging of a rare earth metals (REM) alloyed stainless steel
(English)Manuscript (preprint) (Other academic)
Abstract [en]

 

The internal surfaces of modern SENs are coated with a glass/silicon powder layer to prevent the SEN graphite oxidation during pre-heating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied. The results of the study indicated the penetration of the formed alkaline-rich glaze into the Alumina/graphite base refractory during pre-heating. More specifically, the alkaline-rich glaze reacts with graphite to form carbon monoxide gas. Thereafter, dissociation of CO at the SEN/molten metal interface takes place. This leads to reoxidation of dissolved REM, which form the “In Situ” REM oxides at the interface between the SEN and the molten steel. Also, the interaction of the penetrated glaze with alumina in the SEN base refractory materials leads to a formation of a high-viscous alumina-rich glaze during the SEN pre-heating process. This in turn, creates a very uneven surface at the SEN internal surface. The “In Situ” formation of the REM oxides together with the uneven internal surface of the SEN may facilitate the accumulation of the primary inclusions.

Keyword
Refractory, SEN, Clogging, REM, Coating, glaze, alkaline
Identifiers
urn:nbn:se:kth:diva-25073 (URN)
Note
QC 20101007Available from: 2010-10-07 Created: 2010-10-07 Last updated: 2010-10-08Bibliographically approved
2. Studies on the decarburization of the commercial Submerged Entry Nozzles
Open this publication in new window or tab >>Studies on the decarburization of the commercial Submerged Entry Nozzles
2011 (English)In: Steel Grips - Journal of Steel and Related Materials, ISSN 1611-4442, Vol. 9Article in journal (Refereed) Published
Abstract [en]

Decarburization behaviors of Al2O3-C, ZrO2-C and MgO-C refractory materials constituting a commercial Submerged Entry Nozzle (SEN), have been investigated in different gas atmosphere consisting of CO2, O2 and Ar. The (CO2/O2) ratio values were kept the same as it is in propane combustion flue gas at Air Fuel Ratio (AFR) values equal to 1.5 and 1 for both Air-fuel and Oxygen-fuel combustions. Laboratory experiments were carried out nonisothermally in the temperature range 873 K to 1473 K at 15 K/min followed by isothermal heating at 1473 K for 60 min. The decarburization ratio (α) values of the three refractory types were determined by measuring the weight losses of the samples. The results showed that the decarburization ratio (α) values of the MgO-C refractory became 3.1 times higher for oxygen-fuel combustion compared to air-fuel combustion both at AFR equal to 1.5 in the temperature range 873 K to 1473 K. The decarburization ratio (α) values for Al2O3-C samples were the same as for the isothermal heating at 1473 K and non-isothermal heating in the temperature range 1473 K to 1773 K with a 15 K/min heating rate. It substantiates the SEN pre-heating advantage at higher temperatures for shorter holding times instead of heating at lower temperatures for longer holding times. Jander’s diffusion model was proposed for estimating the decarburization rate of Al2O3-C refractory in the SEN. The activation energy for Al2O3-C samples heated at AFR equal to 1.5, for air-fuel and oxygen-fuel combustions were found to be 84.5 KJ/mol and 95.5 KJ/mol respectively during non-isothermal heating in the temperature range 873 K to 1473 K.

Keyword
Al2O3-C, ZrO2-C; MgO-C, decarburization, reaction mechanism.
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-25100 (URN)10.5161/steel/2011/g02349 (DOI)
Note
QC 20101008 Uppdaterad från Manuskript till ArtikelAvailable from: 2010-10-08 Created: 2010-10-08 Last updated: 2011-10-14Bibliographically approved
3. The effect of Zirconium Disilicide (ZrSi2) additions on the carbon oxidation behavior of alumina/Graphite refractory materials
Open this publication in new window or tab >>The effect of Zirconium Disilicide (ZrSi2) additions on the carbon oxidation behavior of alumina/Graphite refractory materials
2010 (English)In: ISIJ International, ISSN 0915-1559, Vol. 50, no 11, 1612-1621 p.Article in journal (Refereed) Published
Abstract [en]

Carbon oxidation is a main industrial problem for Alumina/Graphite Submerged Entry Nozzles (SEN) during pre-heating. Thus, the effect of ZrSi2 antioxidants and the coexistence of antioxidant additive and (4B2O3 ·BaO) glass powder on carbon oxidation were investigated at simulated non-isothermal heating conditions in a controlled atmosphere. Also, the effect of ZrSi2 antioxidants on carbon oxidation was investigated at isothermal temperatures at 1473 K and 1773 K. The specimens’ weight loss and temperature were plotted versus time and compared to each others. The thickness of the oxide areas were measured and examined using XRD, FEG-SEM and EDS. The coexistence of 8 wt% ZrSi2 and 15 wt% (4B2O3 ·BaO) glass powder of the total alumina/Graphite base refractory materials, presented the most effective resistance to carbon oxidation. The 121% volume expansion due to the Zircon formation during heating and filling up the open pores by (4B2O3 ·BaO) glaze during green body sintering led to an excellent carbon oxidation resistance.

Keyword
refractory, ZrSi2, graphite, alumina, oxidation
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-25097 (URN)000284967700013 ()2-s2.0-79551609986 (Scopus ID)
Note
QC 20101008 Uppdaterad från manuskript till artikel(20110104).Available from: 2010-10-08 Created: 2010-10-08 Last updated: 2011-10-14Bibliographically approved

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