JPH0352423B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to refractories used for members of continuous casting equipment, such as nozzles such as long nozzles and immersion nozzles, and stoppers such as long stoppers and stopper heads. [Technical background] Typical nozzles for continuous casting of molten steel include long nozzles and immersion nozzles that connect the ladle, tundish, and mold. used. When these continuous casting nozzles are in use, they are rapidly heated by the molten steel flow from inside the nozzle, so a large temperature difference occurs between the inner wall and the outer periphery, and the inside of the material is subjected to large thermal stress due to the difference in expansion. Therefore, the refractories constituting these continuous casting nozzles are required to have particularly excellent thermal shock resistance. Furthermore, since the nozzle inner hole is exposed to severe wear due to the flow of molten steel, which is sometimes accompanied by air entrainment due to seal leakage, it is also necessary to have excellent wear resistance and oxidation resistance. Furthermore, in normal continuous casting methods, the lower end of the nozzle is used while immersed in molten steel and is attacked by molten slag with various compositions on the upper surface of the molten steel, so it is also necessary to have excellent slag erosion resistance. It is said that [Prior art] Fused silica, alumina-graphite, etc. have traditionally been used as materials for such continuous casting nozzles, but recently, due to the trend toward multiple continuous casting, materials with relatively excellent corrosion resistance have been used. The latter, alumina-graphite, is becoming mainstream. This alumina-graphite material, which is a combination of only graphite and alumina, has excellent chemical corrosion resistance due to slag, but has the disadvantage that it is extremely weak against wear caused by molten steel flow that involves air etc. ,for example,
There was a problem in that parts of the inner hole that were not immersed in molten steel sometimes suffered abnormally large amounts of wear. As a method that improves the drawbacks of such alumina-graphite refractory materials, there is a fused raw material (ZRM) consisting of zirconia, mullite, and glass parts, and by using this as an aggregate, it is possible to eliminate abnormal internal hole erosion. We have succeeded in creating a highly durable nozzle. It is also known that by using 15 to 30% by weight of silica glass, the material has low expansion properties and the spalling resistance of the alumina-graphite refractory material is improved. As described above, aggregates containing silica exhibit many excellent aspects when used in appropriate amounts in alumina-graphite materials. For this reason, the current alumina
In most cases, graphite contains aggregates containing silica.
It is used by adding 50% by weight. However, on the other hand, when this silica component is placed under a high temperature of 1500℃ or higher in a reducing atmosphere such as in a section immersed in molten steel, it undergoes the reaction shown in the following equation.
Disappears as SiO and Si vapor. SiO ₂ +2C→Si+2CO↑ SiO ₂ +Si→2SiO↑ Therefore, when used for a long time, the aggregate portion containing this silica component becomes hollow and the structure becomes weak. In continuous casting, such a weakened structure is easily washed away due to the rapid movement of the molten steel flow, shortening the life of the refractory member. [Object of the Invention] An object of the present invention is to improve the durability of refractories for parts of continuous casting equipment, such as nozzles and stoppers, which are made by adding silica to such conventional graphite-alumina materials. [Structure of the invention] The above purpose is basically to obtain two out of alumina powders.
This is achieved by using an easily sinterable ultrafine alumina raw material in which ~10% by weight has an average particle diameter of 1 μm or less and a specific surface area of 3.0 m ² /g or more when measured by the BET method. . The BET method is a method in which nitrogen gas is adsorbed onto the surface of fine powder, the amount of nitrogen gas required for this is measured, and the specific surface area of the powder is determined based on the BET adsorption isotherm. The BET specific surface area in the present invention is
Micromeritics Instrument Corporation
The results measured using Model 220C are shown. In the present invention, the graphite contained in the refractory mixed powder must be in the range of 10 to 40% by weight, but this means that if the graphite is less than 10% by weight, sufficient spalling resistance will be imparted. Moreover, if the content exceeds 40% by weight, the refractory will melt into the molten steel, resulting in poor corrosion resistance. Furthermore, if the alumina powder, including ultrafine powder, is less than 30% by weight, the corrosion resistance will be poor, and if it is more than 70% by weight, spalling will occur easily, so a range of 30 to 70% by weight is appropriate. Alumina raw materials can be broadly divided into fused alumina, calcined alumina, etc., and the crystal phase is generally corundum α phase, but anhydrous alumina also has ρ, χ, η, γ, δ, θ, κ. It is known that intermediate aluminas such as Any of these ultrafine powders may be used as the alumina ultrafine powder used in the present invention, but it is preferable to use one with a purity of 95% or higher. The average particle size is 1 μm or less, and the specific surface area value by BET method is 3.0 m ² /
g or more, and if any of these conditions are lacking, the sufficient effect on sintering described above cannot be obtained. Calcined alumina is the most economical raw material for ultrafine powder, and it is preferable to use it, but as long as predetermined conditions such as particle size are met, pulverized products such as electrofused products will not lose their effectiveness. Table 1 shows the sintering test results for various alumina raw materials. In the table, A and B are ultrafine alumina powders used in the present invention, which exhibit sufficient sintering properties near the temperature of molten steel in continuous casting, and C, D, and E meet the above conditions. The degree of sintering is also insufficient. If the amount of ultrafine powder alumina such as A and B is less than 2% by weight, the alumina as a whole will not be sintered sufficiently and will not be effective, and if it exceeds 10% by weight, sintering will proceed too much and the elastic modulus will be high. It is difficult to use because it becomes vulnerable to thermal spalling. Furthermore, aggregates containing silica have a low silica content.
If it is less than 10% by weight, the effect of the silica component described above cannot be exhibited. Further, if the amount of aggregate containing silica is less than 5% by weight, there is no effect, and if it exceeds 50% by weight, corrosion resistance will decrease even if aggregate with a low silica content is used. As the other refractory materials constituting the remainder, refractory materials commonly used in the refractory industry are appropriately selected and used. This also includes metals such as Al and Si that are added for the purpose of preventing oxidation and imparting strength under hot conditions. Since an organic binder is usually used in the preparation of the refractory molding compound of the present invention, it has relatively high air permeability after molding and heating. Therefore, in the early stage of pouring molten steel, gases such as Si, CO, and SiO, which are the products shown in the chemical reaction formula described above, quickly leave the system, and the reduction of silica proceeds quickly, and the silica containing these gases quickly leaves the system. The aggregate becomes hollow. However, by having an appropriate amount of the above ultrafine alumina powder, the heating during nozzle use promotes sintering of the entire alumina particles, causing the entire substrate to shrink and at the same time significantly reducing the air permeability of the nozzle. . Therefore, when sintering of alumina particles begins, Si, CO, and SiO generated according to the above formula become difficult to escape from the system, and the partial pressure of these gas components increases, preventing the reaction from proceeding any further. As a method of crushing the pores of such a refractory substrate, for example, a trace amount of a low-melting point component is added to a carbon-containing material, and the low-melting point component, which is melted by heating, closes the pores and makes the refractory substrate oxidation-resistant. However, if this method is applied to alumina-graphite, this melt will have a negative effect on corrosion resistance and will gradually be eroded away from the surface in contact with molten steel. However, since the refractory material of the present invention does not contain a low melting point component, a nozzle manufactured using the refractory material has sufficient corrosion resistance even on the surface that comes in contact with molten steel. The refractory material of the present invention is prepared by sufficiently mixing the respective constituent materials using a V-type mixer, a W-cone type mixer, etc., and then adding an organic binder and kneading to obtain a compound for molding. As the organic binder, phenol resin, tarpitz, etc. can be used, but phenol resin is preferably used because of its excellent moldability. For molding, it is preferable to use a hydrostatic press in order to increase the uniformity of the material, but extrusion molding, a uniaxial pressure type press, etc. can of course be used. Further, in order to prevent explosion due to volatile components, the volatile components are removed by firing in a non-oxidizing atmosphere as necessary, but in other cases, it is not necessary to particularly perform heat treatment. [Example] Next, Examples of the present invention are shown in Table 2 together with Comparative Examples. At the blending ratio in the same table, ultrafine alumina A,
B, C, D, and E (*1) shown in Table 1 were used. ZRM-A and ZRM-B (*2) are raw materials made by electromelting and pulverizing the compositions shown in Table 3.
Mineralogically, it consists of monoclinic zirconia, mullite, and glass. (ZRM-B includes corundum.) The same electrofused silica/zirconia (*3)
It is obtained by electrically melting SiO ₂ /ZrO ₂ in a weight ratio of 8/2, and mineral-wise it consists of monoclinic zirconia and glass. Corrosion resistance evaluation (*4) of molded products and quality after heating is performed by using each test material as the lining of a high-frequency furnace, melting SS41 steel at 1600℃, holding it for 60 minutes, and measuring the melting loss by the reduction rate. The results of evaluating corrosion resistance are shown below. In addition, the spalling resistance evaluation (*5) was conducted for 1 minute and 30 minutes when pig iron was heated at 1600℃ in a high frequency furnace.
After being immersed for 20 seconds, the sample was cooled in water for 20 seconds, and the elastic modulus before and after this is shown by the ratio R=E1/E0 of elastic modulus E0 and E1. Among the evaluation items, S is R≧0.95, A is 0.95>R≧0.90,
B indicates the case where 0.90>R≧0.80, and C indicates the case where R<0.8.
In this evaluation item, it is desirable to achieve a rating of A or higher for practical use, but depending on the usage conditions, it is possible to use the product up to a rating of B. In addition, the quality after heating shown in the lower column of the same table (*6)
The sample was immersed in molten steel in a high frequency furnace at 1600°C for 3 hours and then allowed to cool. Examples 1 to 2 and Comparative Examples 1 to 3 show examples of using ultrafine alumina A. When the blending amount is less than 2% by weight (Comparative Examples 1 and 2), corrosion resistance decreases due to compositional deterioration after heating, and when it exceeds 10% by weight (Comparative Example 3), the spalling resistance is poor. On the other hand, it can be seen that each example is particularly excellent in corrosion resistance and spalling resistance. Examples 3 to 4 and Comparative Examples 4 to 6 show the influence of the average particle diameter and specific surface area of the ultrafine alumina powder used on the product, and show the effects of A, B, C, and
This is a comparison of D and E. Only A and B, which fall within the limited range of the present invention, have good corrosion resistance after heating. In addition, ultrafine powder alumina A shown in the formulation example of Example 3
When a γ-alumina raw material, which is an intermediate alumina, was used instead, a product with excellent corrosion resistance and spalling resistance was obtained both after molding treatment and after heating. It was confirmed through microscopic observation that all the particle sizes of this γ-alumina were less than 1μm, and
The non-surface area determined by the BET method was as large as 70 m ² /g. Furthermore, in order to conduct a similar confirmation test on ρ-alumina, which is an intermediate alumina, the average particle size was 10 μm,
When a ρ-alumina raw material with a BET non-surface area of 180 m ² /g was pulverized to a particle size of 1 μm or less, and 8% by weight was used in place of the ultrafine alumina A in Example 3, it also showed corrosion resistance and scratch resistance. Both polling properties were excellent. Examples 5 to 7 and Comparative Example 7 show the effects of various silica-containing aggregates when using ultrafine alumina that falls within the scope of the present invention.
In Comparative Example 7, which used raw material ZRM-B with a silica content of 6% by weight, there was no deterioration of the structure after heating, but
Both corrosion resistance and spalling resistance showed poor results. Examples 8 to 10 and Comparative Examples 8 to 9 show the influence of the amount of silica-containing aggregate used. It can be seen that in Examples 8 to 10, in which the amount of silica-containing aggregate used was within the range of 5% to 50% by weight, both corrosion resistance and spalling resistance were superior to those outside the range.

【table】

【table】

【table】

【table】

[Overall effect]

As shown in the above examples, the refractory material according to the present invention can fully exhibit the effect of adding silica to alumina-graphite, and the durability of the nozzle obtained from it is superior to that of conventional ones. It is possible to exhibit the effect that the durability can be more than three times that of the conventional one.

Claims (1)

[Claims] 1 Graphite 10-40%, alumina powder 30-70% by weight
%, and 5 to 50% refractory aggregate powder containing 10% or more of SiO ₂ as a component, and the balance consisting of other refractory substances, wherein the alumina powder has an average particle size of 1 μm or less and has a BET ratio. A refractory material for continuous casting equipment parts, characterized by containing 2 to 10% by weight of an easily sinterable ultrafine alumina raw material having a surface area of 3.0 m ² /g or more.