JPH0130784B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a sliding nozzle plate (hereinafter referred to as SN plate) which is a refractory member of a sliding nozzle device such as a ladle or a tundish.
The present invention relates to a manufacturing method. The SN plate consists of multiple plates with outflow holes, and controls the flow rate of molten steel by opening and closing the outflow holes by sliding. For this reason, it is significantly different from other refractories, and has strict characteristics such as good smoothness of the sliding surface, little damage due to expansion of outflow holes, and no cracks in the sliding surface due to thermal shock. required. Traditionally, the material for SN plates is based on alumina raw materials with the addition of high alumina raw materials, such as mullite raw materials and sillimanite raw materials, and then kneaded, formed, and
The fired product is impregnated with pitch or tar, and the volatile heat of pitch or tar alleviates the thermal shock during rapid heating, suppressing the occurrence of cracks on the sliding surface. Carbon, metallic silicon, metallic aluminum, etc. are added, and after kneading and molding with pitch, phenolic resin, etc., it is fired in a non-oxidizing atmosphere to impart thermal shock resistance and erosion resistance by forming a carbon bond or metal carbide bond. Therefore, materials such as alumina-carbon materials with improved durability are used. However, the former creates a poor working environment due to smoke emitted from tar and pitch during use, and after the tar and pitch volatilize, its thermal shock resistance deteriorates extremely and cannot withstand long-term use. When heated above ℃, the carbon bond and metal carbide bond are oxidized, causing structural deterioration, and it is difficult to maintain sliding surface accuracy for a long period of time. Each bond has its advantages and disadvantages. As a result of research to solve the drawbacks of the above-mentioned conventional materials, the inventors of the present invention have developed a fused alumina material with a chemical composition of 35 to 90% by weight of Al ₂ O ₃ , 10 to 50% by weight of ZrO ₂ , and 25% by weight of SiO ₂ . After kneading, molding, and firing 5 to 50% by weight of zirconia raw material and the remainder of alumina raw material and/or high alumina raw material, impregnation with one or more selected from pitch, tar, phenol resin, and furan resin. By further heat-treating, there is no fuming during use due to pitch, tar, etc., and there is no structural deterioration due to oxidation.
Furthermore, an SN plate with excellent thermal shock resistance and erosion resistance has been obtained. The present invention will be explained in detail as follows. The fused alumina-zirconia raw material (hereinafter simply referred to as alumina-zirconia raw material) used in the present invention imparts thermal shock resistance to the SN plate. The mechanism is that ZrO ₂ present in the structure of the alumina-zirconia raw material undergoes a volume change due to transformation to monoclinic ←→tetragonal crystal at around 1000°C (as shown in Figure 1), and coexisting Al ₂ O ₃ Due to the balance between thermal expansion and contraction of _SiO2 , etc., the coefficient of thermal expansion appears to be very small at temperatures above 1000°C. By adding this raw material, the SN plate becomes a low-expansion material. alumina·
The amount of _ZrO2 in the zirconia raw material is 10-50% by weight
Must. If it is less than 10% by weight, the volume change due to ZrO ₂ transformation is too small and coexist.
Thermal expansion and contraction of Al ₂ O ₃ and SiO ₂ become dominant, and when the concentration exceeds 50% by weight, the transformation volume change of ZrO ₂ becomes dominant. This is because the apparent coefficient of thermal expansion of Considering the balance of expansion and contraction, both Al ₂ O ₃ and SiO ₂ in the alumina-zirconia raw material should be 35 to 90% by weight of Al ₂ O ₃ and 25% by weight of SiO ₂ or less. Note that as the SiO ₂ component increases, the coefficient of thermal expansion decreases and the thermal shock resistance further improves, but if it is too large, the erosion resistance against molten steel slag decreases. The alumina-zirconia raw material uses alumina and zircon, or alumina and zirconia as main raw materials, and is produced by electrofusion. Table 1 shows electrofused alumina-zirconia raw materials with different chemical components of Al ₂ O ₃ , ZrO ₂ , and SiO ₂ . Among these, symbols D to H have chemical compositions within the scope of the present invention.

[Table] Figure 2 shows the thermal expansion curves of each alumina-zirconia raw material shown in Table 1 above.
For this measurement, 1 alumina-zirconia raw material was used.
Grind into pieces less than mm and add methylcellose and water.
A test piece was used that was pressure-molded at 1000 Kg/cm ² , dried, and then fired at 1500°C for 5 hours. The amount of alumina/zirconia raw materials added is 5 to 50
Weight%. If it is less than 5% by weight, the effect of improving thermal shock resistance will not appear, and if it exceeds 50% by weight, the relative amount of alumina raw material and/or high alumina raw material, which is effective in improving erosion resistance, will decrease, and it will not be sufficient as an SN plate. This is because corrosion resistance cannot be obtained. Alumina raw materials are electrically fused products containing 90% by weight or more of Al ₂ O ₃ components. The high alumina raw material is a raw material containing 50% by weight or more of Al ₂ O ₃ component and 10% by weight or more of SiO ₂ component, and generally refers to a material consisting of minerals such as mullite, sillimanite, and andalusite. These raw materials are necessary to impart corrosion resistance to the SN plate, and the higher the Al ₂ O ₃ content, the greater the effect, so alumina raw materials are mainly used, and the high alumina raw materials are 20% by weight of the entire composition. % or less. Furthermore, when chromium oxide is added to the above formulation in an amount of 10% by weight or less, preferably 1 to 8% by weight, Cr ₂ O ₃
During firing, the component forms a solid solution with the Al ₂ O ₃ component, which works to suppress the penetration of iron oxides from molten steel slag into the SN plate structure, further improving corrosion resistance. The purity of chromium oxide is preferably 90% by weight or more and the particle size is preferably 10μ or less. If the proportion exceeds 10% by weight, thermal shock resistance will deteriorate. In the present invention, the above-mentioned raw materials are blended in a predetermined amount, and then a binder commonly used for molding refractories such as clay, water, resin, and wax is added using a conventional method, and the mixture is kneaded using a Flett-Eyrich mixer or the like, followed by an oil press. ,
Form into an SN plate shape using a forming machine such as a friction press. After the obtained base material is sufficiently dried, it is fired at a temperature at which an oxide-ceramic bond is formed. Generally, the temperature is 1300°C or higher, preferably 1400°C to 1700°C. The fired body thus obtained is impregnated with one or more selected from pitch, tar, phenolic resin, and furan resin, and then heat-treated in a non-oxidizing atmosphere at, for example, 350°C or higher, preferably 400 to 1100°C. . This heat treatment leaves carbonized carbon such as pitch, tar, phenolic resin, and furan resin in the SN plate structure. Carbon has the property of not being easily wetted by molten steel and slag.
It suppresses the intrusion of molten steel and slag into the structure of the SN plate, significantly reduces base metal adhesion and slag adhesion to the sliding surface of the SN plate, and at the same time improves the erosion resistance of the sliding surface and nozzle hole. If heat treatment is performed in a non-oxidizing atmosphere above 350℃, pitch, tar,
Volatile smoke components in phenolic resins and furan resins are completely volatilized, leaving only residual carbon.
As a result, the SN plate does not emit smoke during use, improving the working environment. As described above, the SN plate obtained by the method of the present invention maintains stable thermal shock resistance from beginning to end due to the alumina-zirconia raw materials, has the effect of suppressing the penetration of carbon into molten steel and slag at the initial stage of use, and also has the effect of suppressing the penetration of carbon into molten steel and slag. Even if carbon is lost by oxidation, it has high corrosion resistance due to the effects of alumina and high alumina raw materials, and there is no structural deterioration due to carbon loss, and sliding surface precision can be maintained for a long time. It is the material. Examples of the present invention and comparative examples thereof are shown in Table 2. The alumina-zirconia raw material in each example is
Those shown in the table were used. The alumina raw material is sintered alumina with 98% by weight of Al ₂ O ₃ , and the high alumina raw material is 70% by weight of Al ₂ O ₃ .
Synthetic mullite with 28% by weight of SiO ₂ was used in each case. The Comparative Example and Example formulations were all kneaded in a fret, formed into a predetermined SN plate shape by a friction press, dried at 80 to 150°C for 48 hours, and then fired in a tunnel kiln at 1600°C for 5 hours. The test method is shown below. (Table 2)

【table】

[Table] Thermal shock resistance: The outflow hole of the SN plate was heated with a propane gas burner, and the time until cracks appeared around the outflow hole was measured. The larger the number, the greater the thermal shock resistance. Erosion resistance: 1650℃ x 3hr using a rotating drum type erosion tester
The erosion dimensions were measured by heating with a propane gas burner using a 100% iron corrosive agent under the following conditions. Among the respective erosion dimensions, the erosion dimension of Example No. 1 was set as 100, and the erosion dimensions of the other examples were expressed as relative values. The smaller the number, the better the erosion resistance. Smoke generation due to burner heating; When measuring thermal shock resistance due to burner heating,
It was visually observed whether smoke was generated. From the table, it can be seen that the materials of the examples of the present invention have excellent thermal shock resistance and erosion resistance. Furthermore, in order to confirm the effects of the present invention, the oxidation resistance, thermal shock resistance, and erosion resistance are compared with conventionally frequently used materials such as high alumina and alumina-carbon materials, and the results are shown in Table 3. Conventional Examples 1 and 2 were made in exactly the same manner as in the Example, and Conventional Examples 3 and 4 were made in the same manner as in the Example up to molding, except that they were reduced and fired in a coke breeze at 1400° C. for 6 hours.

[Table] Thermal shock resistance A, melting resistance, and smoke generation by burner heating were conducted in the same manner as described above. Strength after carbon oxidation A test piece of 20 x 20 x 120 mm was cut out from the SN plate shape and oxidized at 800°C for 5 hours in an electric furnace atmosphere, and then the bending strength of the piece was measured. Thermal shock resistance B SN plate was heated at 800℃ in an electric furnace atmosphere.
After 5H oxidation, thermal shock resistance was tested in the same manner as in A. As can be seen from Table 3, Examples Nos. 3 and 7 have higher thermal shock resistance after oxidation than Conventional Examples Nos. 1 and 2, and have higher thermal shock resistance than Conventional Examples Nos. 3 and 4 after oxidation. It can be seen that the bending strength is large. In addition, when the present invention examples No. 3 and No. 7 were installed and tested on a ladle sliding device by Company A with 250 tons, it was found that the high alumina SN plate used conventionally,
For alumina/carbon SN plates, ladle 3~
It was durable for about 5 charges, but the example of the present invention
No. 3 and No. 7 had dramatically improved durability with 5 to 8 charges. When we observed conventional plates after use, we found that the ones made of high alumina had many cracks around the outflow holes, and the ones made of alumina carbon had deteriorated microstructure due to oxidation on the sliding surface of the SN plate, resulting in poor surface accuracy. I couldn't maintain it. Inventive product No. 3 seemed to have a lifespan of 8 charges at its limit, but the sliding surface of No. 7, which had chromium oxide added, was hardly rough and surface accuracy was maintained, and the product had a lifespan of about 2 charges. was possible.

[Brief explanation of drawings]

FIG. 1 is a thermal expansion/contraction curve diagram of ZrO ₂ , and FIG. 2 is a thermal expansion/contraction curve diagram of an alumina-zirconia raw material.

Claims (1)

[Claims] 1 Al ₂ O ₃ 35-90% by weight, ZrO ₂ 10-50% by weight,
After kneading, molding, and firing 5 to 50% by weight of the fused alumina/zirconia raw material with a chemical composition of 25% by weight or less of SiO ₂ and the remainder of the alumina raw material and/or high alumina raw material, pitch, tar, phenolic resin, A method for producing a sliding nozzle plate, comprising impregnating it with one or more selected from furan-based resins and further heat-treating it. 2 _Al2O3 35-90% by weight _{, ZrO2} 10-50% by weight,
After kneading, molding, and firing 5 to 50% by weight of fused alumina/zirconia raw material having a chemical composition of 25% by weight or less of SiO ₂ , 10% by weight or less of chromium oxide, and the balance of alumina raw material and/or high alumina raw material, pitch is prepared.
A method for manufacturing a sliding nozzle plate, comprising impregnating it with one or more selected from tar, phenolic resin, and furan resin, and further heat-treating.