JP2007076980A - Magnesia carbon brick - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnesia carbon brick having excellent thermal shock resistance and corrosion resistance by uniformly impregnating with tar or pitch even to the center part and the detailed part in the low carbon type magnesia carbon brick treated at a low temperature and impregnated with the tar or the pitch. <P>SOLUTION: A refractory raw material composition comprises 90-99 mass% magnesia-based raw material and 0.1-10 mass% metal powder where in the magnesia-based raw material, the particles having >10-500 μm particle diameter occupies 20-50 mass% and the particles having ≤10 μm particle diameter occupies 0 to 5 mass%. The magnesia carbon brick is obtained by adding an organic binder to the refractory raw material composition, kneading and forming the resultant mixture and after heating the formed product at 300-1,000°C, impregnating it with the tar or pitch. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnesia carbon brick applied to a molten metal container or the like.

  Conventionally, magnesia carbon bricks are mainly used for molten metal containers such as converters, electric furnaces, ladles, vacuum degassing furnaces and the like. Usually, this magnesia carbon brick is manufactured by adding an organic binder such as a phenol resin to a refractory raw material composition mainly composed of magnesia and scaly graphite and heat-treating at 200 to 300 ° C. This magnesia carbon brick has excellent corrosion resistance by containing magnesia as a main component, and excellent thermal shock resistance and slag resistance can be obtained by containing scaly graphite. As a binder, an organic binder such as a phenol resin that is excellent in wettability with respect to scaly graphite and has a high carbonization yield is generally used.

In addition, metals such as Al, Mg, Ca, and Si, or alloys thereof, alloys such as SiC and B ₄ C, and metal boride compounds are generally added to the refractory raw material composition. These are added to prevent the oxidation of carbon in the refractory during use, and to maintain the denseness of the brick by forming a ceramic bond in the brick.

  However, magnesia carbon bricks are applied in refining vessels such as converters and RH, for example, but erosion of bricks due to slag is one of the bottlenecks for extending the service life. This is because the graphite in the magnesia carbon brick is oxidized by the iron oxide in the slag. Further, this graphite has a drawback in that it has a high thermal conductivity, which causes heat loss due to a decrease in the temperature of the molten metal, and also causes a so-called carbon pickup that dissolves in the molten steel and lowers the quality of the steel product.

  In this sense, it is desirable to reduce the carbon content in the carbon-containing brick, particularly the graphite content, as much as possible within a range that does not reduce the thermal shock resistance.

  In magnesia carbon brick, scaly graphite and phenol resin are mainly used as a carbon raw material, and pitch, carbon black, coke, or the like is used supplementarily. Recently, as a means for further reducing the carbon content of the magnesia carbon brick, the use of specific carbon raw materials such as mesophase pitch, expanded graphite, graphitized carbon black and the like has been frequently reported. All of these are used for the purpose of compensating for the decrease in thermal shock resistance caused by reducing the graphite as the carbon raw material.

  For example, in Patent Document 1, it is said that thermal expansion / contraction of magnesia and the like can be improved by using expanded graphite, and thermal shock resistance can be improved. In the examples, magnesia carbon brick using 5% by mass of expanded graphite is used. Is described. The use of expanded graphite can surely improve the thermal shock resistance, but it is difficult to apply as a use for a general converter furnace wall because it lacks the denseness after receiving heat and has a problem in corrosion resistance.

  Further, many methods utilizing pitch have been studied. For example, Patent Document 2 discloses that a specific organic binder and β-resin are used in combination with a pitch of 10% by mass or more. In the process of heating the refractory, this pitch melts and softens the pitch dispersed in the tissue and expands into the surrounding tissue, penetrates into fine voids, diffuses between the aggregate particle surface and the aggregate particles, It penetrates to form a pitch film. As a result, thermal shock resistance is improved by suppressing oversintering of aggregate particles at high temperatures.

  Patent Document 3 discloses a magnesia carbon brick containing no scaly graphite using mesophase pitch. It is described that when a mesophase pitch is used, the thermal shock resistance is improved because carbon fibers are produced.

  However, although these low carbon type magnesia carbon bricks have been used in actual furnaces, they are still inferior in thermal shock resistance compared to the conventional magnesia carbon bricks that use a large amount of graphite. Further improvement is required to expand the system.

  In Patent Document 2 or Patent Document 3, a powder pitch is used. When these powder pitches are heated, they liquefy and penetrate into the refractory structure, but the pitch cannot be completely dispersed in the structure as a liquid, and the pitches are discontinuous. When the pitch is used as a powder, after the pitch is liquefied by heating, a portion where the pitch was present remains as a void. Since this void is several tens of microns, the corrosion resistance is reduced. Therefore, when the powder pitch is used, the pitch cannot be uniformly dispersed to the details of the brick structure, so that the function is not sufficiently exhibited.

  On the other hand, a method for impregnating pitch-treated refractories with heat treatment is also generally known. For example, in a sliding nozzle plate, pitch impregnation is generally performed to improve oxidation resistance and wear resistance. However, in magnesia carbon bricks, pitch impregnation methods have been tried in the past, but only some magnesia carbon bricks fired at high temperatures have been put to practical use.

  As an example, Patent Document 4 describes a method in which a magnesia carbon brick molded body is heat treated at 1200 ° C., and then the operation of impregnating the pitch and firing is repeated twice or more. And it is described that creep deformation can be prevented because the binder (organic binder) is carbonized by firing. Further, it is described that the refractory structure can be densified to improve the corrosion resistance. Moreover, it is supposed that corrosion resistance will improve by making 5-15 mass% of refractory raw material particles of 10 μm or less in the refractory aggregate. For this reason, it is said that it is suitable for the use condition which receives remarkable molten steel stirring and a thermal stress especially around a tuyere.

  However, in lining bricks, which are the majority of uses of magnesia carbon bricks, the present situation is that magnesia carbon bricks impregnated with pitch are not put into practical use because there is not much difference in durability compared with bricks without impregnation. The reason for this is that when metal powder is added as an antioxidant to suppress the oxidation of magnesia carbon brick carbon, the metal powder is changed to carbide or oxide by the above heat treatment, and the expected antioxidant One reason is that the function does not work effectively.

  Therefore, a method of impregnating tar and pitch after heat treatment in a temperature region in which the metal does not change has been proposed for a long time. For example, in Patent Document 5, after heat treatment of magnesia carbon brick at 500 to 1000 ° C., Impregnation with tar pitch is described. And by this method, it is possible to suppress joint opening due to expansion and contraction during use, prevent intrusion and internal cracking of molten steel and slag, and also prevent increase in porosity due to decomposition of the binder (organic binder). Are listed. Furthermore, it is described that it can be used in combination with a castable containing water to increase digestion resistance and hot strength.

However, the magnesia carbon brick obtained by this method can surely obtain the above-mentioned merits, but particularly when it is applied to a low carbon region where graphite is 15% by mass or less, the thermal shock resistance is poor and the effects of tar and pitch are not good. There was a problem that could not be obtained sufficiently. Therefore, the present inventor heat treated magnesia carbon brick for converter by this method, impregnated with pitch, cut out the test piece and confirmed the physical properties, the center of the brick is insufficiently impregnated with pitch, The physical properties were not much different from the unimpregnated brick.
Japanese Patent Laid-Open No. 5-301772 Japanese Patent Laid-Open No. 11-322405 JP 2005-139062 A Japanese Patent Laid-Open No. 9-328378 JP-A-58-15072

  The problem to be solved by the present invention is that a low carbon type magnesia carbon brick impregnated with tar or pitch by heat treatment at a low temperature is uniformly impregnated with tar or pitch to the center and details, The object is to provide a magnesia carbon brick having excellent corrosion resistance.

  Usually, in order to increase the impregnation amount of tar or pitch in magnesia carbon brick, it is conceivable to increase the porosity. In order to increase the porosity, it is conceivable to lower the molding pressure to lower the filling property, or to make a particle size constitution with a low filling property, but there is a problem that the corrosion resistance is lowered simply by increasing the porosity. Therefore, the present inventor does not contain or limit the ultrafine powder having a specific particle size or less in the magnesia-based raw material in order to uniformly impregnate the tar or pitch more uniformly into the center portion and details while suppressing the deterioration of the corrosion resistance. Focusing on the fact, we examined the effect of the ultrafine powder on the physical properties of the particle size and the amount used. As a result, it was found that if ultrafine powder of 10 μm or less is not used or if it is used at 5% by mass or less, tar or pitch penetrates to the center and there is almost no decrease in corrosion resistance. Furthermore, we have newly discovered that the effect of improving the spalling resistance is extremely high.

  That is, according to one aspect of the magnesia carbon brick of the present invention, the refractory raw material composition is composed of 90 to 99% by mass of magnesia-based material and 0.1 to 10% by mass of metal powder, and the particle size in this magnesia-based material is 10 μm. Ultra-500 μm particles are 20-50% by mass of the refractory raw material formulation, and particles having a particle size of 10 μm or less are 0-5% by mass or less of the refractory raw material formulation. It is characterized by being kneaded and molded by adding a binder, heat-treated at 300 to 1000 ° C., and then impregnated with tar or pitch.

  In another aspect of the magnesia carbon brick of the present invention, the refractory raw material composition is composed of 83 to 98 mass% of magnesia-based material, 0.1 to 10 mass% of metal powder, and 1 to 15 mass% of scaly graphite. In the magnesia-based raw material, particles having a particle size of more than 10 μm to 500 μm are 20 to 50% by mass of the refractory raw material composition, and particles having a particle size of 10 μm or less are 0 to 5% by mass or less of the refractory raw material composition. Then, an organic binder is added to the refractory raw material composition, kneaded and molded, heat-treated at 300 to 1000 ° C., and then impregnated with tar or pitch.

  The upper limit of the particle size of the ultrafine powder to be restricted in the magnesia-based raw material is 10 μm from the viewpoint of durability. When the particle size is larger than 10 μm, the impregnation amount of tar or pitch increases, but the matrix portion becomes rough, and the corrosion resistance deteriorates rapidly. On the other hand, since the ultrafine powder of 10 μm or less has an effect of improving the corrosion resistance, it can be used as long as it is 5% by mass or less in the ratio to the refractory raw material composition. When it exceeds 5% by mass, tar or pitch is hardly penetrated to the center and details.

  Further, the magnesia carbon brick of the present invention has a very small decrease in spalling resistance even if the amount of scaly graphite is reduced. For example, when compared with conventional magnesia carbon bricks using scaly graphite in excess of 15% by mass and those having about 10% by mass of the scaly graphite of the present invention, the spalling resistance is comparable. This is because tar or pitch penetrates uniformly and continuously into the fine gaps in the matrix portion by restricting the use of ultrafine powder of 10 μm or less in the present invention. For this reason, since the sintering of the magnesia grains due to heat reception is suppressed to the details and evenly in the entire structure, it is considered that the spalling resistance is drastically improved.

  Furthermore, the refractory raw material having a particle size of more than 10 μm to 500 μm in the magnesia-based raw material needs to be contained in an amount of 20 to 50% by mass in the proportion of the refractory raw material mixture from the viewpoint of corrosion resistance and spalling resistance. If it is less than 20% by mass, the corrosion resistance is lowered, and if it exceeds 50% by mass, impregnation with tar or pitch becomes insufficient, so that the spalling resistance is lowered.

  The heat treatment temperature of the brick before impregnating the tar or pitch is set to 300 to 1000 ° C. from the viewpoint of forming a bond having a large impregnation amount of tar or pitch and excellent in spalling resistance. If it is less than 300 ° C., the organic binder is not sufficiently decomposed and the closed pores remain in the brick, and the open pores are not sufficiently formed, so that tar or pitch is hardly impregnated to the center. If the temperature exceeds 1000 ° C, the metal powder changes to carbides or oxides. For example, in the case of metal aluminum powder, the amount of aluminum carbide or alumina produced increases, and is not suitable because it is not sufficient as a means for preventing the oxidation of carbon in bricks. It is.

  Further, the heat treatment temperature of the brick before impregnation is more preferably 450 to 800 ° C. from the viewpoint of generating a composite carbon bond derived from tar or pitch and an organic binder. When the organic binder in the brick is heated, the solvent evaporates at a low temperature, the polymer resin is more actively decomposed from around 500 ° C., and is carbonized at around 1200 ° C. When the heat treatment temperature is in the range of 450 to 800 ° C., the organic binder is still porous and the connective structure is insufficient. By impregnating tar or pitch in this porous state, tar or pitch penetrates into the organic binder, and then heated to generate a composite carbon bond in which the tar or pitch and the organic binder are physically entangled. be able to. This composite carbon bond has high flexibility with respect to a glassy carbon bond, and can be a brick having high strength and low elasticity, that is, excellent spalling resistance.

  In the present invention, since tar and pitch penetrate into the gaps between fine refractory raw materials, it seems that the point is that this composite carbon bond can be obtained even in a microscopic structure. In other words, the above-mentioned oxide raw material is prevented from oversintering and the formation of this composite bond is made even to a microscopic structure, so the effect is obtained synergistically, and magnesia carbon brick with extremely high spalling resistance is obtained. Estimated.

  Even if the magnesia carbon brick of the present invention does not contain any scaly graphite, the impregnated tar or pitch penetrates every corner of the matrix structure and spreads three-dimensionally. Greatly superior to magnesia carbon bricks that do not contain graphite. When no scaly graphite is contained, magnesia carbon bricks having low thermal conductivity, almost no carbon pickup, and excellent oxidation resistance are obtained. Therefore, it is more suitable for vacuum degassing such as RH or refractory such as VOD.

  On the other hand, for applications in which the spalling resistance is more important, scaly graphite can be appropriately added at 15% by mass or less, more preferably less than 10% by mass. If it exceeds 15% by mass, tar or pitch will not be impregnated to the details of the brick matrix due to the influence of the scaly graphite orientation during molding. Thus, since it contains more scaly graphite, it is more excellent in thermal shock resistance, so it can be used in place of a conventionally used magnesia carbon brick with a large amount of graphite in a converter, electric furnace, RH, or the like.

  The magnesia carbon brick of the present invention described above does not contain scaly graphite or is contained at 15% by mass or less, and is therefore characterized by a low carbon content. For this reason, it can be used in place of conventional magnesia carbon bricks as magnesia carbon bricks having excellent oxidation resistance, low thermal conductivity and few carbon pickup problems. Furthermore, by suppressing the carbon content in the magnesia carbon brick to 10% by mass or less, more preferably less than 5% by mass, even if it is a secondary refining brick such as RH, there is less carbon pickup and resistance to spalling. Excellent bricks.

  The magnesia carbon brick of the present invention preferably has an apparent porosity of 10% or less after impregnation into tar or pitch and after reduction firing at 1400 ° C. That is, in a magnesia carbon brick that has a dense structure as a refractory and is impregnated with tar or pitch up to the center, the corrosion resistance is very excellent when the apparent porosity is 10% or less. In the present invention, tar and pitch uniformly penetrate to the center and details of the structure, and this tar and pitch are carbonized by heating, but at the same time, partly decomposes. Need to identify organizational status. Therefore, it was decided to specify after reducing firing at 1400 ° C.

  Although the magnesia carbon brick of the present invention is a low carbon type, it is dense, excellent in corrosion resistance, and excellent in spalling resistance, so that it has excellent durability. Therefore, for example, when it is used as a lining brick of a molten metal container, its durability is improved. In addition, since it contains no graphite or is low in content, it has low thermal conductivity and has an energy saving effect, and since there are few carbon pickups, the quality of steel is improved.

  The magnesia-based raw material of the present invention is a mixture of refractory raw materials containing 90% by mass or more of magnesia raw materials alone or magnesia raw materials (magnesia content). The magnesia raw material can be used without any problem as long as it is a magnesia clinker usually used in magnesia carbon bricks. When the magnesia-based raw material is a mixture, the remainder other than the magnesia raw material is powder pitch, coke, carbon black, mesophase carbon, artificial graphite, alumina, silica, zirconia, zircon, calcium oxide, silicon carbide, silicon nitride, boride Alternatively, one or more of frit and the like can be used at 10% by mass or less.

Further, as the magnesia-based material, a mixture of 60 to 95% by mass of magnesia material and 4 to 30% by mass of spinel (MgO.Al ₂ O ₃ ), dolomite, or magnesia chrome is used. Further, one or more of powder pitch, coke, carbon black, mesophase carbon, artificial graphite, alumina, silica, zirconia, zircon, calcium oxide, silicon carbide, silicon nitride, boride, frit, etc. May be a mixture used at 10% by mass or less as required.

  The magnesia-based raw material is used in an amount of 90 to 99% by mass so as to provide sufficient corrosion resistance as magnesia carbon brick when no scaly graphite is used. Moreover, when using scaly graphite at 15 mass% or less, 83-98 mass% of magnesia type raw materials are used.

  Scaly graphite is used for imparting spalling resistance, and can be used without any problem as long as it is generally marketed for refractories. It is also possible to use expansive graphite as scaly graphite.

  Expansive graphite is a kind of scaly graphite, but it is a raw material obtained by subjecting scaly graphite to chemical treatment to expand, and there are several types such as thin graphite or thin graphite, all of which are used in the present invention. Is possible.

  The metal powder can be used without any problem as long as it is usually used in magnesia carbon bricks. For example, one or more metals of Al, Mg, Ca, Si, and B, and one or more of their alloys can be used. The metal powder is used in an amount of 0.1 to 10% by mass, more preferably 1 to 5% by mass in order to impart oxidation resistance during use. When it exceeds 10 mass%, the corrosion resistance at the time of use will fall.

  The organic binder is used for developing sufficient strength for handling by pressure molding and heat treatment and for generating a carbon bond by heating. As the organic binder, a thermosetting organic resin is more preferable. For example, one or more of a phenol resin and a furan resin can be used in a liquid state, and various modified phenol resins can also be applied. Further, tar, pitch and the like can be included in the organic binder.

  And an organic binder is added and kneaded to a refractory raw material compound, and it heat-processes after shaping | molding. The heat treatment is performed at 300 to 1000 ° C. in an atmosphere with little oxygen or a non-oxidizing atmosphere from the viewpoint of suppressing oxidation of carbon in the brick as much as possible.

  After heat treatment, tar or pitch is impregnated by a general method. In the impregnation method, brick is immersed and held in heated tar or pitch. It is also effective to dip the tar or pitch to be impregnated into the tar or pitch under high pressure in order to infiltrate the brick interior or the details of the matrix.

  In order to make the apparent porosity after impregnation into tar or pitch after reduction and firing at 1400 ° C. to 10% or less, under the above conditions, for example, by appropriately forming the particle size composition of the refractory raw material composition and molding at high pressure Appropriate production conditions are selected in a known method such as production of a dense molded body or impregnation under high pressure after heat treatment to adjust the temperature and viscosity of tar and pitch during the impregnation operation.

Tables 1 to 4 show examples and comparative examples.

  The blends in each table were kneaded, and bricks having a length of 150 mm, a width of 150 mm, and a length of 810 mm were formed by a vacuum friction press, and heat-treated at the temperatures shown in each table. The heat treatment was performed in a non-oxidizing atmosphere. After the heat treatment, the brick was impregnated by holding at 15 atm × 6 h in tar heated to 200 ° C. After the impregnation, each test piece was cut out from the center of the brick and used for the test. The magnesia-based raw material used (magnesia clinker) was 98.5% pure electrofused magnesia, and the carbon raw material used was 98% pure natural scale-like graphite or expansive graphite obtained by volume expansion of this by chemical treatment. . As the phenol resin as the organic binder, those generally marketed for refractories are used, but the viscosity is adjusted with a solvent mainly composed of ethylene glycol and phenol.

  The apparent porosity of the produced brick was measured according to JIS-R2205. Whether the impregnated tar penetrated into the interior was judged by whether or not the apparent porosity difference between the surface portion and the interior of the brick after impregnation was within 0.3%. That is, when the apparent porosity difference was within 0.3%, it was judged that the tar had penetrated into the interior, and when it exceeded 0.3%, it was judged that the brick had not sufficiently penetrated into the interior.

  The hot bending strength was measured according to the measurement method of JIS-R2656. In addition, the corrosion resistance was evaluated based on the erosion dimension by the rotary erosion method. As the erodible material, C / S = 3, T.I. Using converter slag of Fe = 20% by mass, erosion was performed at 1700 ° C. for 4 hours. And it represented with the index | exponent which makes the amount of erosion of the comparative example 7 which is non-fired which added 9 mass% of scaly graphite and 3 mass% of Al powder | flour 100 as 100.

  The spalling resistance was comparatively evaluated by repeating the operation of immersing the cut brick sample in hot metal at 1650 ° C. five times, and by the degree of cracks generated on the cut surface after the test. Furthermore, as a comprehensive evaluation, a comparative example 7 was set to 3, and a five-level evaluation was performed with an evaluation of 5 being excellent in the comprehensive evaluation.

  The carbon content was measured according to JIS-R2011 after impregnation with tar.

  About Example 1, Example 2, Example 5, and Comparative Examples 2-4, the influence of the ratio of the particle size of 10 micrometers or less in a magnesia-type raw material is compared and investigated. In Tables 1 and 2, it can be seen that the apparent porosity after reduction firing at 1400 ° C. increases and the spalling resistance tends to decrease as the amount of particles having a particle size of 10 μm or less increases. When the ratio of the particle size of 10 μm or less is 7% by mass or more, the degree of internal impregnation of brick suddenly deteriorates. That is, it can be seen that Comparative Examples 2 to 4 do not sufficiently penetrate the details of the structure of the tar brick. For this reason, the amount of particles having a particle size of 10 μm or less is preferably 5% by mass or less.

  Example 3 is an example in which no graphite is used, but has almost the same performance as Example 4 using 3% by mass of scaly graphite. Further, these two examples have almost the same spalling resistance as compared with Comparative Example 8 which is a type using 15% by mass of scaly graphite without impregnation with conventional tar or pitch. . Further, Examples 1, 2, and 5 have a scaled graphite content of 6% by mass, but have almost the same spalling resistance as Comparative Example 5 in which the amount of scaled graphite added is 17% by mass. . As these experimental results show, in the present invention, the spalling resistance is remarkably improved by impregnating with tar or pitch. From these results, tar or pitch penetrates uniformly and continuously into very fine gaps in the refractory structure, thereby forming a connective structure in which the organic binder and tar or pitch are combined in a microscopic area, and flexible. The synergistic effect of preventing the oversintering of the oxide particles at the same time as forming the connective structure is presumed to be a structure with excellent spalling resistance even if the graphite is greatly reduced.

  The example shown in Table 3 is a case in which a raw material other than electrofused magnesia is used in combination as a magnesia-based raw material and a case where the ratio of the particle size of 10 μm to 500 μm in the magnesia-based raw material is different. The brick has good internal impregnation and good physical properties.

  In Table 4, the influence of the maximum particle size of the ultrafine powder cut in the magnesia-based raw material is comparatively investigated. It can be seen that when the size of the maximum particle size to be cut is 15 μm or more, the degree of internal impregnation of the brick is good, but the corrosion resistance deteriorates rapidly. From this, it can be said that the maximum particle size to be cut is preferably 10 μm or less.

  The magnesia carbon brick of the present invention is applicable to molten metal containers such as converters, electric furnaces, ladles, and vacuum degassing furnaces.

Claims (3)

  The refractory raw material composition is composed of 90 to 99% by mass of magnesia-based raw material and 0.1 to 10% by mass of metal powder, and particles having a particle size of more than 10 μm to 500 μm in the magnesia-based raw material are 20 to 50% by mass and particles having a particle size of 10 μm or less are 0 to 5% by mass or less of the refractory raw material composition, and an organic binder is added to the refractory raw material composition and kneaded and molded at 300 to 1000 ° C. A magnesia carbon brick which is impregnated with tar or pitch after heat treatment.   The refractory raw material composition is composed of 83 to 98% by mass of magnesia-based material, 0.1 to 10% by mass of metal powder and 1 to 15% by mass of scaly graphite, and particles having a particle size of more than 10 μm to 500 μm in the magnesia-based material Is 20 to 50% by mass of the refractory raw material composition, and particles having a particle size of 10 μm or less are 0 to 5% by mass or less of the refractory raw material composition, and an organic binder is added to the refractory raw material composition and kneaded. A magnesia carbon brick, which is molded and heat-treated at 300 to 1000 ° C. and then impregnated with tar or pitch.   The magnesia carbon brick according to claim 1 or 2, wherein the apparent porosity after impregnation into tar or pitch and reduction firing at 1400 ° C is 10% or less.