JP2008151425A - Repair method of magnesia carbon brick - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a repair method improving adhesive property of low carbon type magnesia carbon brick and a thermally sprayed body. <P>SOLUTION: Thermal spraying is performed to magnesia carbon brick with 13 mass% or less (without including 0) of fixed carbon content. Magnesia carbon brick to be thermally sprayed is preferably obtained by adding an organic binder in a fireproof raw material mixture of 10-50 mass% of magnesia clinker with a grain size of 1-5 mm, 10-70 mass% of magnesia clinker with a grain size of 75-1,000 μm, 10 mass% or less (including 0) of magnesia clinker with a grain size of 75 μm or less, 3 mass% or less (including 0) of flaky graphite with a grain size less than 45 μm and 3 mass% or less of Al or an Al alloy as Al content, and kneading, molding and then applying heat treatment. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a magnesia carbon brick repair method used as a refractory for lining a molten metal container such as a converter, electric furnace, ladle, degassing furnace, or melting furnace.

  Magnesia carbon brick is a refractory brick composed mainly of magnesia and graphite and bonded by carbon bond, usually containing 20-30% by mass of graphite, mainly melting in converters, electric furnaces, ladles, etc. Used as a lining brick for metal containers.

  In recent years, higher quality of steel products and stricter composition control have been demanded in the steelmaking process. Therefore, the problem of contamination of the molten steel due to the phenomenon that the carbon contained in the magnesia carbon brick dissolves into the molten steel (hereinafter referred to as “carbon pickup”) has become apparent. Furthermore, since carbon has a high thermal conductivity, magnesia carbon bricks have recently been used due to various problems such as heat loss such as a drop in molten steel temperature, iron core deformation of the converter, and CO gas emission accompanying carbon combustion. Low carbon is desired.

  In recent years, therefore, various attempts have been made to reduce the carbon content of magnesia carbon bricks. For example, Patent Document 1 discloses that in a raw material blend including a refractory raw material and a carbonaceous raw material containing carbon, the fixed carbon content of the carbonaceous raw material is 100% by weight of the hot residue of the raw material blend. A pitch of 0.2 to 5% by weight, wherein at least a part of the carbonaceous raw material has an organic binder having a fixed carbon content of 25% by weight or more and a viscosity of 200 poise or less and a β-resin content of 10% by mass or less. A low carbonaceous carbon-containing refractory using and is disclosed.

  Patent Document 2 discloses a magnesia carbon brick containing mesophase-containing pitch powder. In this magnesia carbon brick, since the liquid crystalline mesophase is rich in viscosity and forms a strong carbon bond, thermal stress is applied. In order to relax and improve thermal shock resistance, durability is said to be improved. As an example, a low carbon magnesia carbon brick having a graphite amount of 10% by mass or less is disclosed.

  By the way, magnesia carbon bricks lined in converters are significantly worn due to carbon oxidation or erosion by slag. Further, the degree of wear varies depending on the portion of the converter, and in order to extend the life of the converter, it is necessary to repair the previously worn portion at an early stage. For this reason, in general, repairs are repeatedly used with an irregular refractory material, etc., which makes it durable for thousands of uses. Repair methods include dry spraying, baking, slag coating, or thermal spraying.

  Among these repair methods, thermal spraying is a method in which a part of the refractory material is melted and sprayed with a flame, and it does not contain evaporation components such as water and solvents like dry spraying and baking, and compared with slag coating. And since the melting point of a construction body is high, the construction body excellent in durability is obtained. However, in practice, some steelworks are expensive because the thermal spraying equipment is expensive, the thermal spraying work is complicated and labor-intensive, and it is difficult to obtain the durability of the construction body to meet these thermal spraying costs. It is currently used only in Japan.

  On the other hand, a technique for improving the durability of the thermal spray material has been studied. For example, Patent Document 3 discloses that in a magnesia-based thermal spray material, sintered calcia-magnesia clinker is 5 to 40 wt%, sintered magnesia clinker and / or electrofused magnesia is 30 to 70 wt%, and slag is 10 to 50 wt%. A blended thermal spray material is disclosed. As a result, it is said that a thermal spray material having superior adhesion and corrosion resistance compared to conventional materials can be obtained.

Further, at the time of thermal spraying, the surface of the magnesia carbon brick is covered with slag, which is considered to reduce the adhesiveness of the thermal spray material. This improvement is disclosed in Patent Document 4. That is, a flame spraying method is disclosed in which the temperature of a refractory surface to be sprayed is raised to 1000 ° C. or higher, and the refractory fine powder is sprayed toward the refractory surface in a state where the temperature of the refractory surface is 1000 ° C. or higher. Has been. This method gradually cools the molten or semi-molten refractory fine powder that has come in, increases the contact area between the sprayed material and the adhered slag, and increases the adhesion between the sprayed layer and the lining refractory. It is said that sex will increase. In addition, it does not damage the lining refractories, and even if the lining refractory is a graphite-containing refractory, it does not oxidize the graphite in the refractory, firmly bonds the sprayed layer and the lining refractory, and has high durability It is said that a sprayed layer can be obtained.
Japanese Patent Laid-Open No. 11-322405 Japanese Patent Laid-Open No. 5-4861 JP-A-11-71183 JP 2002-107065 A

  When the low carbon type magnesia carbon bricks of Patent Document 1 and Patent Document 2 are actually used in a converter, there are many conventional graphites (20 to 30% by mass) depending on the use environment such as slag composition during steelmaking. Contained) There are cases where sufficient durability cannot be obtained compared to magnesia carbon brick.

  The durability of magnesia carbon bricks used in converters is affected by the amount of (FeO) in steelmaking slag. In other words, for the temporary and local increase in slag (FeO) due to the reduction of the blown carbon level in the steelmaking process or the increase in the amount of oxygen during blowing, the liquid of carbon in the refractory by (FeO) Phase oxidation dominates wear and reducing the graphite content is effective in improving durability. However, because the amount of (FeO) in the slag or the basicity of the magnesia in the brick greatly affects the wear, it is difficult to expect an improvement effect in reducing the graphite content of the brick. Sites appear and can still be a bottleneck in converter life. In addition, reducing the graphite content reduces spalling resistance, and as a result, low carbon type magnesia carbon bricks do not provide sufficient durability, and in particular, converters have not yet reached a full-scale practical stage. .

  On the other hand, it is conceivable to improve the durability by improving the repair method of the low carbon type magnesia carbon brick. However, in the improvement of the thermal spray material as in Patent Document 3, a material superior in adhesion and corrosion resistance can be obtained as compared with the conventional material, but the durability of the thermal spray construction body corresponding to the aforementioned thermal spraying construction cost is pointed out. That is not enough.

  In general, the durability of the thermal sprayed body is greatly influenced by the adhesiveness with the surface to be repaired, so how to bond and firmly bond this adhesive interface is an important factor. In other words, if the thermal sprayed construction body itself does not have high adhesiveness no matter how much the durability is improved, the thermal sprayed construction body will be peeled off and the durability will be insufficient.

  Therefore, in the method of Patent Document 4 described above, the adhesion between the thermal spray powder and the slag is improved, but according to this method, the adhesion interface is most heated by the spraying rather than the heating before thermal spraying. This is due to heat storage after the powder adheres, and as a result, the adhesion interface will be exposed to a high temperature of 2000 ° C. or higher for a long time, so that the adhesive strength of the thermal sprayed construction body decreases due to gas generation as described below. Sufficient durability cannot be obtained.

In particular, the surface of magnesia carbon brick among the refractories to be constructed is exposed to oxygen gas by the flame of thermal spraying and becomes high temperature due to adhesion of the thermal spray material close to 2000 ° C. As a result, gas is generated from the vicinity of the brick surface, and this gas stays in the interface between the brick and the sprayed body during spraying or in the slag interposed between the brick and the sprayed body. It is presumed that the thermal sprayed body peels off. As a result, thermal spraying on magnesia carbon bricks is considered not to have the expected high durability even though the construction body itself is superior in durability compared to other repaired construction bodies. . The gas generated from the brick includes CO and CO ₂ resulting from oxidation of the carbon component in the brick, and further, Mg generated by reduction of the magnesia clinker by the carbon component in the brick or Al added as an antioxidant. Gas or CO can be considered.

  The problem to be solved by the present invention is to improve the adhesion between the low carbon type magnesia carbon brick and the thermal sprayed construction body in order to improve the life of the molten metal container lined with the low carbon type magnesia carbon brick. The purpose is to provide a repair method.

  The present inventor considered that the adhesive strength between the magnesia carbon brick and the thermal sprayed construction body is strongly related to the amount of carbon component in the brick. Therefore, various experiments were conducted on the relationship between the amount of carbon components in the brick (fixed carbon amount) and the adhesive strength between the thermal sprayed construction bodies. As a result, it has been found that the smaller the amount of fixed carbon, the higher the adhesive strength, and that the adhesive strength is remarkably increased when the amount of fixed carbon is 13% by mass or less. And by making this amount of fixed carbon 13 mass% or less, the adhesive strength is more than twice as compared with the case of 20 mass% fixed carbon, and by repairing by thermal spraying, the life of the molten metal container is greatly increased. It was found that it could be stretched.

  That is, the present invention is a method for repairing a magnesia carbon brick lined on a molten metal container, wherein the magnesia carbon brick having a fixed carbon content of 13% by mass or less (excluding 0) is sprayed. It is what. Here, the amount of fixed carbon is measured according to JIS-M8812.

  The smaller the amount of fixed carbon in the magnesia carbon brick, the higher the adhesion strength with the thermal sprayed construction body, and the effect of thermal spraying becomes a practical level by setting it to 13% by mass or less. The content is preferably 10% by mass, and more preferably 1 to 7% by mass.

  When the amount of fixed carbon exceeds 13% by mass, the total area of the magnesia clinker in contact with the thermal spray material decreases, the adhesion is insufficient due to gas retention at the adhesion interface due to the increase in the amount of gas generated, and further spraying due to the gas retention. It is considered that the adhesive force is greatly reduced due to the fact that the temperature of the sprayed material is instantaneously reduced and the particles in a semi-molten state do not adhere and rebound.

  In the present invention, thermal spray repair is performed in a molten metal container lined with magnesia carbon having a fixed carbon content of 13 mass% or less. A known apparatus and a known material can be used for the thermal spraying. Thermal spraying is preferably performed at least once while the molten metal container is used 15 times. If it exceeds 15 times, damage to the refractory increases, and even if it is sprayed, it is difficult to obtain a life extension effect. More preferably, the molten metal container is sprayed 1-3 times while being used 15 times. Here, the term “use once” refers to the period from when the molten metal is received until the molten metal is discharged and then the molten metal is received.

  Thermal spraying is effective when applied to a brick lined to a site where the effect of other repair materials is small or to which other repair materials cannot be applied. Except for these parts, dry spraying or baking repair can be mainly used, and the cost is lower than when only spraying repair is performed. Specifically, with respect to the frequency of use of thermal spraying and other repair methods, the ratio of sprayed material: dry spraying material and baking repair material can be 1: 3 to 1:10, depending on the amount ratio of consumed materials. As a result, a long service life can be achieved with low-cost repair.

  As the thermal spray material, a thermal spray material mainly composed of MgO and CaO can be used. More specifically, by using a thermal spray material in which the total amount of MgO and CaO is 70% by mass or more, a construction body having high adhesive strength can be obtained.

  The magnesia carbon brick used in the present invention has a fixed carbon content of 13% by mass or less. Specifically, an appropriate amount of an organic binder is added and kneaded to a refractory raw material composition containing 60 to 99% by mass of magnesia clinker, 1 to 10% by mass of scaly graphite and, if necessary, an antioxidant such as metal. It is obtained by heat treatment after molding. However, the carbon-containing raw material to be used is blended so that the total amount of fixed carbon in each carbon-containing raw material is 13% by mass or less in the manufactured brick. In addition, an appropriate amount of a general refractory raw material used in known magnesia carbon bricks such as dolomite, spinel, carbon black, and / or coke can be used for the refractory raw material composition.

In addition, magnesia carbon bricks are made of Al, Mg, Ca, Si, alloys combining them, carbides such as SiC, B ₄ C, and metal borides in order to prevent oxidation of carbonaceous materials such as graphite. Applicable. Among these, for Al or Al alloy, if the total content of Al is 3% by mass or less (including 0) as a proportion of the refractory raw material composition, an effect of suppressing gas generation during thermal spraying can be obtained. . Accordingly, the content of Al or Al alloy in the refractory raw material composition is preferably 3% by mass or less (including 0) as the Al content. If it exceeds 3% by mass, the magnesia clinker is reduced by Al near the surface of the brick during spraying, and gas tends to be generated. In addition, it is considered that the Al powder that is too much near the surface of the brick causes an oxidation reaction earlier than the reduction reaction of magnesia.

  The magnesia clinker in the refractory raw material composition should be reduced in the content of fine powder in order to suppress the reduction reaction by carbon or metal Al, and the particle size of 75 μm or less accounts for 10% by mass or less in the refractory raw material composition. (Including 0) is preferable. When the particle size of 75 μm or less exceeds 10% by mass, gas tends to be generated during thermal spraying, so that the adhesive force with the thermal sprayed construction body tends to decrease.

  Further, the magnesia clinker having a particle size of more than 75 μm to 1000 μm is preferably contained in an amount of 10 to 70% by mass, more preferably 20 to 60% by mass in terms of the refractory raw material composition, from the viewpoint of the adhesive strength with the thermal sprayed body. % Content. If it is less than 10% by mass, the brick structure becomes rough and the strength is insufficient, so that the adhesion of the thermal sprayed construction body is lowered. When it exceeds 70% by mass, sintering between magnesia in the bricks or the thermal sprayed body becomes excessive, so that the structural difference from the original brick part becomes large, and cracks occur at the boundary part in the process of temperature cycle, Thermal sprayed body is stable and difficult to bond.

  Furthermore, it is preferable to use 10 to 50% by mass of magnesia clinker having a particle size of more than 1 mm to 5 mm in the ratio to the refractory raw material composition. If it is less than 10% by mass, cracks are likely to occur in the brick due to thermal shock during thermal spraying, and if it exceeds 50% by mass, the porosity becomes high and the carbon component is oxidized during the thermal spraying, and gas is easily generated.

  On the other hand, as the scaly graphite used in the magnesia carbon brick, it is preferable to use 1 to 10% by mass of a particle having a particle size in the range of 45 to 1000 μm for the purpose of reducing the gas generated during spraying. Further, if the particle size is less than 45 μm, gas is likely to be generated, but if it is 3% by mass or less (including 0) in the refractory raw material composition, the effect of reducing gas generation can be obtained.

  From the above, the magnesia carbon brick to be sprayed by the repair method of the present invention is 10 to 50% by mass of magnesia clinker having a particle size of more than 1 mm to 5 mm, and 10 to 70 magnesia clinker having a particle size of more than 75 μm to 1000 μm. 10% by mass (including 0) of magnesia clinker having a particle size of 75 μm or less, 1 to 10% by mass of scaly graphite having a particle size of 45 to 1000 μm, and 3% by mass or less of scaly graphite having a particle size of less than 45 μm (0 Most preferably obtained by adding an organic binder to a refractory raw material composition having an Al or Al alloy content of 3 mass% or less, kneading, and heat-treating after molding.

  In addition, about the organic binder used at the time of manufacture of a magnesia carbon brick, if it is normally used as an organic binder of a carbon containing refractory material, it can be used without being specifically limited. Specifically, it is at least one selected from the group consisting of phenol resins, furan resins, pitches, phenols, furfuryl alcohols, furfuryl aldehydes, tars and the like.

  According to the present invention, the lifetime of the low-carbon type magnesia carbon brick can be significantly improved by thermal spraying, so that it is possible to improve the durability of the molten metal container that is sufficiently commensurate with the cost increase due to thermal spraying. As a result, molten metal containers using low carbon type magnesia carbon bricks can be used with a stable life span, so by expanding the number of molten metal containers to be applied, the characteristics of the carbon pickup It is possible to obtain the effects of energy saving and the like by improving the quality of steel by the reduction or by reducing the thermal conductivity.

  Hereinafter, embodiments of the present invention will be described by way of examples.

  Tables 1 to 3 show the composition of the refractory raw material composition and the test results of the refractory obtained from the refractory raw material composition. A phenol resin was added as an organic binder to the refractory raw material formulations shown in Tables 1 to 3 and kneaded. After pressure-molding in parallel using a friction press, the mixture was heated at 250 ° C. for 24 hours. The phenol resin used was diluted with a solvent containing ethylene glycol as a main component and adjusted in viscosity. The refractory raw material formulations in Tables 1 to 3 had a maximum particle size of 5 mm. The obtained test refractories were measured for corrosion resistance and adhesive strength. Corrosion resistance was measured by the rotary erosion method after erosion at 1700 ° C. for 5 hours using a converter slag, and the erosion dimension was measured. The refractory of Example 3 had a bulk specific gravity of 3.2, an apparent porosity of 3%, and a hot bending strength at 1400 ° C. of 15 MPa. The amount of fixed carbon was measured according to JIS-M8812.

FIG. 1 is a schematic view showing a method for measuring the adhesive strength between a thermal sprayed construction body and a test refractory material to be constructed. A carbonaceous plate 1 provided with a uniform notch 1a is set so as to be in close contact with a test refractory (magnesia carbon brick) 2 in which slag is melted and adhered to a thickness of 10 mm, and then a notched portion 1a is formed by a thermal spray burner 3. The sprayed body 4 was sprayed until the thickness reached 50 mm. And after standing to cool until the surface temperature of the thermal spraying construction body 4 reaches 1100 ° C., the jack 5 pushes the thermal spraying construction body 4 together with the carbonaceous plate 1 vertically upward, and the value obtained by dividing the numerical value when sheared by the adhesion area Was defined as adhesive strength. As the thermal spray material, a material containing 20% by mass of sintered calcia-magnesia clinker, 60% by mass of magnesia clinker (MgO purity 97% by mass) and 20% by mass of slag was used. The sintered calcia-magnesia clinker was 41% by mass of MgO and 58% by mass of CaO. As the slag, a converter slag containing 44% by mass of CaO, 27% by mass of FeO, 13% by mass of SiO ₂ and 5% by mass of MgO was used.

  Table 1 shows the results of investigating the influence of the amount of fixed carbon in magnesia carbon brick on the adhesive strength with the thermal sprayed construction body by changing the amount of scale graphite added. In Examples 1 to 5, the amount of fixed carbon is 13% by mass or less, and the adhesive strength is 3 Mpa or more. Especially Example 3 and Example 4 are excellent in the balance of corrosion resistance and adhesive strength, and are a very good level as comprehensive evaluation. Since Example 1 and Example 2 have less scaly graphite, the corrosion resistance is slightly inferior to that of Example 3 and Example 4. On the other hand, in Comparative Examples 1 to 3, the amount of fixed carbon is outside the range of the present invention, and the adhesive strength is significantly lower than that in Example 5.

  The adhesive strengths of Examples 1 to 5 are significantly improved by a factor of 2 or more compared to the adhesive strength of Comparative Example 3 in which the conventional fixed carbon amount is 20 mass% and 1.7 MPa. Further, in the adhesion test, in Examples 1 to 5, the brick was broken from the inside, but in Comparative Examples 1 to 3, it was broken from the adhesion interface or the vicinity of the interface in the thermal sprayed construction body. That is, in Examples 1 to 5, it is considered that the interfacial adhesive force and the thermal sprayed body strength were clearly higher than the brick strength. Moreover, the fracture surface of Examples 1-5 is in the state which has few pores by gas in the thermal spraying construction body itself, and is holding the sound layer, and conversely, the adhesion interface of Comparative Examples 1-3 and the thermal spraying construction body fracture surface. In this case, cracks propagated because many pores were connected or the pores were close to each other. From these test results, it can be said that magnesia carbon bricks having a fixed carbon content of 13 mass% or less are remarkably improved in durability in an actual furnace by repairing by thermal spraying.

  In Table 2, Examples 6-10 investigate the influence which the ratio for which the scale-like graphite with a particle size of less than 45 micrometers in a refractory raw material composition has on adhesiveness with a thermal spraying construction body. The smaller the proportion of scaly graphite having a particle size of less than 45 μm, the higher the adhesive strength with the thermal sprayed construction, and Examples 6 to 8 are superior to Examples 9 and 10 in both adhesive strength and corrosion resistance. It has become.

  Examples 11-14 investigate the influence which the ratio for which the magnesia clinker with a particle size of 75 micrometers or less in a refractory raw material composition has affects the adhesiveness with a thermal spraying construction body. The smaller the proportion of the magnesia clinker having a particle size of 75 μm or less, the higher the adhesive strength with the thermal sprayed construction body. In Example 11 and Example 12, both adhesive strength and corrosion resistance are higher than those in Example 13 and Example 14. Excellent results.

  Examples 15-18 investigate the influence which the ratio for which the magnesia clinker with a particle size of more than 75 micrometers-1000 micrometers in the refractory raw material composition has on adhesiveness with a thermal spraying construction body. Example 15 in which the proportion of magnesia clinker having a particle size of more than 75 μm to 1000 μm occupies as small as 5% by mass and Example 18 as large as 75% by mass has a slightly low adhesive strength with the thermal sprayed body.

Table 3 shows the effect of the addition ratio of Al or Al alloy powder on the adhesion with the thermal sprayed body. It can be seen that the smaller the amount of Al or Al alloy powder added, the higher the adhesive strength.

It is the schematic which shows the measuring method of the adhesive strength of the thermal spray construction body and the test refractory which is a to-be-constructed body.

Explanation of symbols

1 Carbonaceous plate 1a Notch 2 Refractory specimen (magnesia carbon brick)
3 Thermal spray burner 4 Thermal spray body 5 Jack

Claims (3)

  A method for repairing a magnesia carbon brick lined in a molten metal container, wherein the magnesia carbon brick is sprayed on a magnesia carbon brick having a fixed carbon content of 13 mass% or less (excluding 0).   The magnesia carbon brick uses a refractory raw material composition in which Al or Al alloy has an Al content of 3% by mass or less (including 0), and magnesia clinker having a particle size of 75 μm or less is 10% by mass or less (including 0). 2. The magnesia carbon brick repair method according to claim 1, wherein the magnesia carbon brick is repaired.   The magnesia carbon brick is 10 to 50% by mass of magnesia clinker having a particle size of 1 to 5 mm, 10 to 70% by mass of magnesia clinker having a particle size of 75 to 1000 μm, and 10% by mass or less of magnesia clinker having a particle size of 75 μm or less ( 1 to 10% by weight of scaly graphite having a particle size of 45 to 1000 μm, 3% by weight or less of scaly graphite having a particle size of less than 45 μm (including 0), and 3% by weight of Al or Al alloy as the Al content. 2. The magnesia carbon brick repair method according to claim 1, wherein the magnesia carbon brick repair method is obtained by adding an organic binder to a refractory raw material composition having a content of 1% or less, kneading, and heat-treating after molding.

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