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Studies on decarburization of MgO-c refractories during ladle preheating
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.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
2010 (English)In: Steel GRIP JournalArticle in journal (Other academic) Accepted
Abstract [en]

The effect of ladle pre-heating conditions on the wear of MgO-C refractories at different steel plants has been investigated. The focus has been on refractories used in the slag zone, some including which contain anti-oxidants. This investigation shows that the wear /corrosion of the slagline refractories initiates already at the ladle pre-heating during real industrial conditions. The degree of the decarburization process is dependent both on the refractory composition, time and the pre-heating fuel or environment. For refractories without anti-oxidants, the refractory decarburization is 3.8 times slower when coal gas is used in ladle pre-heating than when a mixture of oil and air is used. Ladle pre-heating of the refractories without anti-oxidants leads to direct wear of the slagline refractories due to total loss of matrix strength, resulting in a sand-like product independent of the pre-heating method. When the refractories containing antioxidants are compared to each other, the decarburization rate was lower when coal gas was used in ladle perheating than when the refractories are pre-heated by electrical means. The cracking tendency of the refractories is enhanced by the increasing size of anti-oxidants. The refractory containing coarser grains of anti-oxidants (<3000 μm) cracked much early than those containing finer grains (<100 μm). For example after 6 weeks in storage, the crack thickness was 1.5 mm for  large-grained refractory whereas 0.3 mm for the fine-grained refractory.

Place, publisher, year, edition, pages
2010.
Keyword [en]
refractories, reduction-oxidation (redox) corrosion, anti-oxidants, pre-heating, decarburization, decarburization rate
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-25116OAI: oai:DiVA.org:kth-25116DiVA: diva2:355879
Note
QC 20101008Available from: 2010-10-08 Created: 2010-10-08 Last updated: 2012-03-20Bibliographically approved
In thesis
1. A study of slag corrosion of oxides and oxide-carbon refractories during steel refining
Open this publication in new window or tab >>A study of slag corrosion of oxides and oxide-carbon refractories during steel refining
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The use of ceramic material as refractories in the manufacturing industry is a common practice worldwide. During usage, for example in the production of steel, these materials do experience severe working conditions including high temperatures, low pressures and corrosive environments. This results in lowered service lives and high consumptions of these materials. This, in turn, affects the productivity of the whole steel plant and thereby the cost. In order to investigate how the service life can be improved, studies have been carried out for refractories used in the inner lining of the steel ladles. More specifically, from the slag zone, where the corrosion is most severe. By combining thermodynamic simulations, plant trails and post-mortem studies of the refractories after service, vital information about the behaviour of the slagline refractories during steel refining and the causes of the accelerated wear in this ladle area has been achieved. The results from these studies show that the wear of the slagline refractories of the ladle is initiated at the preheating station, through reduction-oxidation reactions. The degree of the decarburization process is mostly dependent on the preheating fuel or the environment. For refractories without antioxidants, refractory decarburization is slower when coal gas is used in ladle preheating than when a mixture of oil and air is used. In addition, ladle preheating of the refractories without antioxidants leads to direct wear of the slagline refractories. This is due to the total loss of the matrix strength, which results in a sand-like product. Thermal chemical changes that take place in the slagline refractories are due to the MgO-C reaction as well as the formation of liquid phases from impurity oxides. In addition, the decrease in the system pressure during steel refining makes the MgO-C reaction take place at the steel refining temperatures. This reduces the refractory’s resistance to corrosion. This is a serious problem for both the magnesia-carbon and dolomite-carbon refractories. The studies of the reactions between the slagline refractories and the different slag compositions showed that slags rich in iron oxide lead mostly to the oxidation of carbon/graphite in the carbon-containing refractories. This leads to an increased porosity and wettability and therefore an enhanced penetration of slag into the refractory structure. If the slag contains high contents of alumina and or silica (such as the steel refining slag), reactions between the slag components and the dolomite-carbon refractory are promoted. This leads to the formation of low-temperature melting phases such as calcium-aluminates and silicates. The state of these reaction products during steel refining leads to an accelerated wear of the dolomite-carbon refractory. The main products of the reactions between the magnesia-carbon refractory and the steel refining slag are MgAl2O4 spinels, and calcium-aluminates, and silicates. Due to the good refractory properties of MgAl2O4 spinels, the slag corrosion resistance of the magnesiacarbon refractory is promoted.

Place, publisher, year, edition, pages
Stockholm: US-AB, 2010. x, 50 p.
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-25221 (URN)978-91-7415-743-7 (ISBN)
Presentation
2010-09-13, MAVE konferensrum, KTH, Brinellvägen 23, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20101013Available from: 2010-10-13 Created: 2010-10-13 Last updated: 2010-10-14Bibliographically approved

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