JPH0530546B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a breathable refractory having excellent corrosion resistance and thermal shock resistance, which is mainly used for stoppers, nozzles, immersion nozzles, etc. of tundishes for continuous casting of steel. [Prior Art] In continuous casting of steel containing aluminum, stoppers and tundish nozzles that limit the flow rate of molten steel, as well as immersion nozzles that serve as flow paths, are made of alumina (e.g., JP-A No. 54-126631). Publications), alumina-carbon materials (e.g., JP-A-1988-
167715, Japanese Patent Application Laid-open No. 61-95756), but when casting aluminum-containing steel, aluminum oxide precipitates from the molten steel and adheres to the walls of the channel. As a result, the amount of deposits gradually increases, making it impossible to obtain a proper flow of molten steel. As a countermeasure to this, a breathable refractory is used on the wall of the flow channel, and an inert gas such as argon gas is blown into the breathable refractory and discharged into the flow channel.
A method is being used to prevent aluminum oxide from adhering to the wall surface of the flow path. As is well known, carbon-containing refractories such as alumina-carbon materials have excellent corrosion resistance and thermal shock resistance against steel, so they are suitable as refractories for continuous casting of steel. It is used. [Problems to be Solved] Conventional carbon-containing refractories such as alumina-carbon materials have the drawback that the carbon is easily oxidized during use, and as a result, the above-mentioned corrosion resistance, thermal shock resistance, etc. are reduced. This tendency is particularly remarkable for refractories that are porous and have a large surface area, such as breathable refractories. Although oxidation is somewhat prevented when an inert gas is blown into the breathable refractory, oxidation still progresses to a considerable extent, and as the oxidation progresses, the melting loss progresses. As the casting time elapses, a problem arises in that the gas flow rate increases.
An increase in the gas flow rate affects the movement of the molten steel in the mold, and there is a risk of serious problems such as molten steel scattering or breaking the solidified layer. requires monitoring of work and flow rate adjustment using gas pressure. In addition, steel types that do not require inert gas injection, or steel types that only require a small amount of inert gas injection, have the disadvantage that the oxidation loss of the air-permeable refractory becomes even greater. The use of steel is also limited by the type of steel. The reason why conventional carbon-containing refractories are damaged in this way is that their corrosion resistance and oxidation resistance decrease due to oxidation of carbon. In order to prevent oxidation of carbon-containing refractories, a method of adding a low-melting substance such as glass to the refractory, melting it at the temperature during use, and coating it with carbon is considered. There are problems in that it is difficult to prevent oxidation, such as its use being restricted because it impairs the air permeability of refractories. Table 1 compares the corrosion resistance of dense refractories and breathable refractories of alumina-carbon refractories having the same composition. As is clear from this comparison, since air-permeable refractories are porous, the oxidation loss of carbon is more significant than that of dense refractories, which means that their corrosion resistance against molten steel and slag is reduced. There is.

【table】

[Means and actions for solving problems]

One applicant of the present application previously developed a nozzle for connected casting containing aluminum oxynitride in order to prevent oxidation of carbon at high temperatures and impart fire resistance to carbon-containing refractories that have excellent corrosion resistance and thermal shock resistance. was developed and filed (see Japanese Unexamined Patent Publication No. 1983-7671). In the present invention, this is applied to a breathable refractory for gas injection, and by containing aluminum oxynitride, it prevents carbon oxidation and improves fire resistance, and also has excellent corrosion resistance and thermal shock resistance due to the carbon content. Furthermore, by mixing and kneading a predetermined amount of small-diameter, highly rigid polyester hard resin fibers as a pore-forming material, a large number of pores are uniformly distributed throughout the refractory. In addition to providing uniform air permeability throughout the entire refractory, the aluminum oxynitride improves fire resistance and corrosion resistance, allowing for stable use without changing the amount of gas blown during use. A refractory is obtained, and the above object of the present invention is achieved. Aluminum oxynitride is a refractory material that has heat resistance of over 2000℃, a coefficient of thermal expansion that is approximately 10% smaller than that of aluminum oxide, and a property that does not easily react with molten metal.Aluminum oxynitride When heated in an oxidizing atmosphere, it generates nitrogen gas and becomes aluminum oxide. When carbon-containing breathable refractories contain aluminum oxynitride, oxidation can be prevented to a large extent when sufficient inert gas is blown into the material, but if the amount of blown inert gas is reduced or Even if an oxidizing atmosphere occurs, such as in the case of steel types that do not require blowing, nitrogen gas is generated as described above depending on the degree of oxidation, preventing carbon oxidation loss and maintaining good corrosion resistance and thermal shock resistance. can do. Note that aluminum oxynitride itself also has better corrosion resistance and thermal shock resistance than aluminum oxide. The amount of aluminum oxynitride used depends on the carbon content. In areas where carbon usage is low, about half of the amount of carbon is sufficient, but in areas where carbon usage is high, the amount of aluminum oxynitride used depends on the carbon content. Also increase the amount. The amount used is approximately 10 to 40% by weight based on the total amount of the refractory material. If it is less than 10% by weight, the antioxidant effect of carbon will be insufficient, and if it is more than 40% by weight, other necessary components will be insufficient, and the corrosion resistance and thermal shock resistance of the refractory will be insufficient. The appropriate carbon content is usually about 20 to 35% by weight. The refractories used in continuous steel casting are heated to about 1000 ml before use, in order to alleviate the thermal shock caused by molten steel.
Preheat to ~1300℃, but if the carbon content is less than 20%, the thermal conductivity will decrease and the coefficient of thermal expansion will increase.
It has the disadvantage that it lacks thermal shock resistance and breaks down in a short period of time. Further, if the content exceeds 35% by weight, it becomes difficult to prevent decarburization by molten steel, and the refractory material becomes noticeably eroded. As the carbon, amorphous carbon, artificial graphite, natural graphite, etc. can be used. Natural graphite is particularly suitable from the viewpoint of improved thermal shock resistance, oxidation resistance, etc. A suitable proportion of alumina is 15 to 70% by weight.
Alumina has high corrosion resistance against molten metal. Silicon carbide can improve the corrosion resistance and thermal shock resistance of refractories, and can also improve the oxidation resistance of carbon, so it is added in an amount of approximately 15% or less as necessary. To obtain air permeability, organic fibers that disappear or carbonize during the firing process are mixed into the refractory mixture, and the air permeability obtained is approximately 30 to 250 ^c.c.cm/cm2 .
min (Kg/cm ² ) is optimal. Organic fibers with a diameter of 30 to 100 μm and a length of 3 to 15 mm are added to the fire-resistant raw material mixture.
0.5-2% by weight is mixed, shaped and fired in a non-oxidizing atmosphere. If the diameter is less than 30 μm, the mixing will be uneven and stable air permeability will not be obtained, and if the diameter is more than 100 μm, the molten steel will disappear after firing and enter the formed pores, resulting in poor air permeability. In addition, if the length is less than 3 mm, communication between pores is poor and ventilation is insufficient.
If it exceeds mm, the mixing will be non-uniform. Suitable fibers are hard ones, for example those with high rigidity such as polyester resin fibers. If the fibers are soft, fiber beads will form during mixing, resulting in poor dispersion. ventilation rate
If it is less than 30c.c.cm/cm ² -min (Kg/cm ² ), the ventilation will be insufficient and the amount of gas blown will be insufficient. Also
At 250c.c.cm/cm ²・min (Kg/cm ² ) or more, the refractory structure becomes brittle and corrosion resistance is significantly reduced. Compressive strength of at least 270Kg/ ^cm2 is required, so the amount of organic fiber mixed is between 0.5 and 270Kg/cm2.
It is desirable to limit it to %. By using this organic fiber, as mentioned above, fine pores of appropriate length are dispersed in random directions and communicated with each other in the refractory, so that the conventional scattered air bubbles contact each other and communicate with each other. Compared to other materials, the pores have better contact with each other and provide stable ventilation. Desirably, an organic binder such as a novolak type phenolic resin or a resol type phenolic resin is mixed into these mixtures, followed by molding and baking. [Example] Next, an example of the present invention will be described. Table 2 compares the corrosion resistance of a conventional alumina-carbon air-permeable refractory and the air-permeable refractory of the present invention, which has the same amount of carbon. The product of the present invention exhibits significantly less erosion in the slag and molten steel parts than conventional products. The breathable refractory of the present invention was mixed with 0.8% by weight of polyester resin fibers having a diameter of 50 μm and a length of 5 mm, and 20.5% by weight of aluminum oxynitride, which corresponds to about 80% of the amount of carbon, was used.

〔Effect of the invention〕

As described above, the present invention contains an appropriate amount of aluminum oxynitride in a carbon-containing breathable refractory material corresponding to the amount of carbon, thereby preventing oxidation loss of carbon by nitrogen gas generated in an oxidizing atmosphere and making it fireproof. It has the advantage of maintaining excellent corrosion resistance and thermal shock resistance due to its carbon content.
In addition, in the present invention, in order to obtain air permeability as described above, highly rigid polyester hard resin fibers with a diameter of approximately 30 to 100 μm and a length of 3 to 15 mm are used as a pore forming material in a proportion of 100% by weight of the fire-resistant raw material. Since it contains 0.5 to 2% by weight of the refractory, fine pores of appropriate length are uniformly distributed in random directions and intertwined.
Because they communicate with each other, uniform air permeability can be obtained throughout the refractory, and as shown in Table 2, the aluminum oxynitride improves corrosion resistance.It also improves fire resistance, and as shown in Fig. It has the advantage that the pore diameter does not change, the amount of gas blown hardly changes, and it can be used in a more stable state than conventional ones. In addition, the following good results were obtained in actual work. (1) When the product of the present invention is used as a refractory for the channel of continuous casting of aluminum-containing steel and gas is blown into the channel, there is no accumulation of aluminum oxide in the channel, and a proper flow of molten steel is obtained. It became like that. (2) Since changes in the flow rate during gas injection due to oxidation and erosion of the refractory no longer occur, the flow of molten steel is stabilized, and the burden of monitoring the gas flow rate during casting is reduced. (3) It has become possible to apply a wide range of steel types without being limited by cast steel types. Since the product of the present invention is a breathable refractory with excellent corrosion resistance as described above, it can be used for stoppers, tundish nozzles, immersion nozzles, and porous plugs for refining ladles.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view showing examples of stopper, tundish nozzle, and immersion nozzle using the product of the present invention, and Fig. 2 is a diagram comparing the conventional product and the product of the present invention with respect to changes in gas injection amount. , 3rd
The figure is a chart showing the relationship between the carbon content of steel and the corrosion loss rate of the inner holes of the molten steel flow path. In Figure 1, 1...stopper, 2...tandish nozzle, 3...immersion nozzle, 4...iron shell,
5... Lining refractory brick.

Claims (1)

[Claims] 1 By weight: 10-40% aluminum oxynitride, 20-35% carbon, 15-75% alumina, 15% silicon carbide
A highly rigid polyester-based hard resin fiber with a diameter of approximately 30 to 100 μm and a length of 3 to 15 mm is added to a fire-resistant raw material containing the following, along with a binder.
A breathable refractory made by blending 0.5 to 2% by weight of 100% by weight, kneading, molding and firing.