JP2764342B2 - Manufacturing method of nozzle for continuous casting - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a continuous casting nozzle having excellent wear resistance and spalling resistance to molten steel.

(Conventional technology) In continuous casting of steel, a nozzle that transfers molten steel from a ladle to a tundish or from a tundish to a mold has a role to prevent oxidation and turbulence of molten steel and to adjust molten steel pouring amount. Since the quality of the material greatly affects the quality of a steel product, it is a particularly important member in continuous casting equipment. The characteristics required of such a nozzle for continuous casting are that the inner hole of the nozzle is exposed to severe wear at high temperatures due to the molten steel flow, so it has excellent wear resistance against molten steel and rapidly heats from the inner surface of the nozzle at the beginning of casting. As a result, a large temperature gradient is generated between the inner surface and the outer periphery of the nozzle, so that the nozzle has spalling resistance. Al ₂ O is a material satisfying these characteristics.
₃ material of -SiO ₂ -C system is frequently used. This is a combination of high refractory Al ₂ O ₃ aggregate and graphite with excellent thermal conductivity, which demonstrates excellent characteristics of erosion resistance and spalling resistance, and further severe thermal shock In order to cope with this problem, it is common to mix fused silica having low thermal expansion, add an organic substance such as tar pitch or resin as a binder, knead, mold, and then perform reduction firing.

Al ₂ O ₃ -SiO ₂ frequently used as a nozzle for continuous casting
Various improvements have been proposed for the -C nozzles in order to improve the required corrosion resistance and spalling resistance. For example, Japanese Patent Publication No. 63-48828 discloses an Al ₂ O ₃ —SiO ₂ containing 0.05 to ₂ wt% of boron carbide.
A carbon black having an average particle size of 5 μm or less is blended with a part of carbon in a C-type nozzle to adjust the particle size of carbon to prevent the spalling resistance and hot strength from being reduced by the addition of boron carbide, and to prevent carbonization. It is said that the antioxidant effect of boron is effectively exhibited. In Japanese Patent Application Laid-Open No. 1-212274, regarding alumina as a component of the nozzle, fine powder having a particle size of 45 μm or less is 30 to 60 wt% of the alumina amount.
By giving alumina a tendency to coarsen as a particle size distribution occupying the same, spalling resistance and erosion resistance are greatly improved. Furthermore, in Japanese Patent Publication No. 64-11588, A
It is stated that in carbon-oxide refractories such as l ₂ O ₃ —SiO ₂ —C, the strength is improved by using a specific type of pitch and a phenol formaldehyde resin together as a binder.

(Problems to be Solved by the Invention) Even in the Al ₂ O ₃ —SiO ₂ —C nozzle having various improvements as described above, problems often occur in practical use. In particular, in the long nozzle located between the ladle and the tundish, a sharp drift is generated in the molten steel due to a narrowing method of the sliding nozzle installed above and an increase in the injection temperature, and the nozzle collides violently with the upper portion of the nozzle. The wear caused by the molten steel flow often causes local erosion and greatly impairs the durability. Therefore, the present invention provides a method for manufacturing an excellent continuous casting nozzle in which the particle size composition of alumina is refined to greatly improve the abrasion resistance of molten steel and the spalling resistance is prevented from deteriorating by using a special pitch. Things.

(Means for Solving the Problems) In order to achieve the object, a method for producing a nozzle for continuous casting of Al ₂ O ₃ —SiO ₂ —C according to the present invention uses 40 to 75 wt% of alumina having a particle size of 0.05 mm or less. %, Fused silica 10 with particle size 0.5mm or less
Phenol resin is added as a binder to 3 to 10% by weight of pitch of 0.05mm or less heat-treated at 400 ° C or more to total of 100% to 30% by weight, phosphorous graphite 15 to 30% by weight, and alumina, fused silica and phosphorous graphite. It is characterized by performing reduction firing after kneading and molding.

(Operation) The present inventors have conducted various studies in order to eliminate the decrease in durability due to the erosion caused by the wear caused by the molten steel. As a result, it was found that the wear resistance of molten steel was improved by reducing the particle size of alumina in the aggregate. That is, it was found that setting the particle size of alumina to be incorporated in the product of the present invention to 0.05 mm (50 μm) or less was very effective. In the conventional Al ₂ O ₃ -SiO ₂ -C electrolyte nozzle the maximum particle size of the alumina and silica that of about 0.5~0.3mm is used has been customary. By refining this particle size, the matrix portion (the portion excluding aggregates such as graphite and fused silica) in the brick structure is composed of a uniform structure of fine alumina particles and carbon bonds (generated by pitch and resin),
In addition, it has been found that even when the alumina content is the same, the matrix becomes more alumina-rich even when the amount of alumina is the same, which is advantageous for the abrasion of the molten steel flow.
The alumina used here can be either an electrofused product or a sintered clinker. The purity of alumina is not limited, but a high-purity product is preferred from the viewpoint of corrosion resistance. FIG. 1 shows the relationship between the amount of fine particles of 0.05 mm or less in the alumina aggregate and the wear of molten steel. The evaluation method was as follows: A sample immersed in molten steel melted in a high frequency furnace at 1550 ° C for 1 hour was subjected to a vibration of 3.5 mm amplitude at 1500 rpm.
It was carried out by a vibration erosion method that gives molten steel wear by adding cycles.

The phosphorous graphite which is a constituent material of the product of the present invention is not particularly limited, but from the viewpoint of corrosion resistance, high purity is desirable and the fixed carbon amount is preferably about 93% or more. 15 to 30
The reason for setting the wt% is that when the content is 15 wt% or less, the spalling resistance is poor, and when the content is 30 wt% or more, the erosion increases. Fused silica is added to suppress the thermal expansion of this refractory. However, if it is less than 10 wt%, the low expansion property of silica is not sufficiently exhibited, so that the spalling resistance is inferior. In a large amount to reduce the corrosion resistance. Although the particle size of this silica is 0.5 mm or less, it is better to be fine from the viewpoint of the particle size composition and packing properties of the entire refractory, but if it is too fine, it will react with the fine alumina to reduce the mullite of low melt by heating during use. Easier to generate. Therefore, the particle size of the silica is 0.5 mm or less, preferably 0.3 to 0.
1mm is appropriate.

Although the resistance to molten steel wear is improved by making the alumina particle size as fine as 0.05 mm or less as described above, on the other hand, spalling resistance is reduced by making the particle size finer. FIG. 2 shows the relationship between the amount of Al ₂ O ₃ —SiO ₂ —C in the alumina of 0.05 mm or less and the spalling resistance. As described above, when the amount of fine powder in alumina is increased, the spalling resistance decreases. The spalling resistance was evaluated by uniformly heating a hollow cylindrical sample with an outer diameter of 200 mm (prepared by cutting a nozzle) at a predetermined temperature, and then rapidly cooling the outer peripheral surface with water cooling to form an inner hole surface and an outer peripheral surface. The temperature gradient was generated on the surface, and the occurrence of cracks due to the thermal shock was observed by the ΔT spall method.

As a result of various studies, the present inventors have found that after adding pitch heat-treated at 400 ° C. or higher, phenolic resin is added, kneaded and formed, and reduced and fired to prevent deterioration of spalling resistance. FIG. 3 and FIG. 4 show the relationship between the amount of the high softening point pitch, the hot bending strength and the elastic modulus. The increase in the amount of the high softening point pitch increases the strength and decreases the elastic modulus. I understand. That is, since the strength / elasticity ratio can be regarded as a parameter of the fracture resistance coefficient, it has been found that the addition of the high softening point pitch is effective for improving the spalling resistance. (FIG. 5) In the above-mentioned Japanese Patent Publication No. 64-11588, a combination use of pitch and phenolic resin is described, and the effect is to improve the breaking strength. The pitch in this case is BS
It is a so-called hard pitch having a component of 45 wt% or more and a QI component of 20 wt% or less, and has a softening point of 150 ° C. or less. The pitch used in the present invention has been subjected to a heat treatment at 400 ° C. or higher, and as a result, the softening point is a high temperature of 300 ° C. or higher, and the volatile content is 1
It has the characteristic that it is as low as 0 to 15 wt% and the fixed carbon amount is as high as about 85 wt%. At the same time, since the liquid crystal (mesophase) is contained in the composition in the process of heat treatment, coalescence between the liquid crystals proceeds during firing, and a strong carbon bond is obtained. The carbon bond formed in this way has a carbonized structure showing a flow structure and a structure with high flexibility, and forms a soft bond advantageous to spalling resistance. On the other hand, it is considered that a carbonized structure starting from phenolic resin has a high strength, but has a hard and brittle property and forms a hard bond.

As described above, by reducing the alumina particle diameter to 0.05 mm or less to improve the wear resistance of molten steel and adding pitch heat-treated at 400 ° C. or more, a decrease in spalling resistance was prevented. The reason why the addition amount of the high softening point pitch is 3 to 10% by weight based on the total of 100 of alumina, fused silica and phosphorous graphite is that if it is less than 3% by weight, the effect on spalling resistance is small, and if it exceeds 10% by weight, it is filled. This is not preferred because the properties deteriorate and the strength decreases. The grain size of the high softening point pitch is 0.05 mm or less in order to uniformly disperse and form a strong carbon bond.

The phenolic resin is added to the material thus selected and kneaded. The amount of addition is suitably about 2 to 10% by weight in view of the filling property of the clay and the strength of the product. The molding is usually performed by an isostatic press and reduced and fired at about 1000 ° C. to obtain the product of the present invention.

In the present invention, boron carbide (B ₄ C) or silicon carbide (SiC) can be added to prevent oxidation.

(Example) An example of the present invention will be described. The compositions shown in Table 1 were kneaded, rubber-molded under a pressure of 1000 kg / cm ² , and reduced and fired at 1000 ° C. to obtain the same physical properties as shown in Table 1. No.−
Nos. 1-4 are products of the present invention, and Nos. -5-8 are comparative products.

The material No. 5 in Table 1 was conventionally used as a long nozzle capable of obtaining extremely high spalling resistance under intermittent use conditions. However, local erosion often occurred at the upper part of the nozzle. The average service life was 1 when using No. 1 of the product of the present invention.
The improvement was remarkably improved to 0.3 times and the spalling resistance was maintained.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the amount of fine particles of 0.05 mm or less in alumina aggregate and the wear of molten steel, and FIG. 2 is the relationship between the amount of 0.05 mm or less in alumina and the spalling resistance in Al ₂ O ₃ —SiO ₂ —C. FIG. 3 is a diagram showing the relationship between the added amount of the high softening point pitch and the hot bending strength, FIG. 4 is a diagram showing the relationship between the added amount of the high softening point pitch and the elastic modulus, FIG. FIG. 3 is a relationship diagram showing the amount of high softening point pitch added and the ratio of hot bending strength / elastic modulus.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoichi Yokoyama 1-3-1 Shinhama, Araimachi, Takasago City, Hyogo Prefecture Inside Rima Ceramics Co., Ltd. (72) Inventor Masami Nishikawa 1-3-1 Shinama, Araimachi, Takasago City, Hyogo Prefecture C (56) References JP-A-61-178465 (JP, A) JP-A-2-268953 (JP, A) JP-A-51-63809 (JP, A) (58) Fields investigated ( Int.Cl. ⁶ , DB name) B22D 11/10 330 B22D 11/54 C04B 35/00-35/22

Claims (1)

(57) [Claims] An alumina having a particle size of 0.05 mm or less is 40 to 75 wt%.
10-30 wt% of fused silica with a particle size of 0.5 mm or less, phosphorous graphite 15
Phenol resin is added as a binder to a pitch of 3 to 10 wt% with a particle size of 0.05 mm or less, which is heat-treated at a temperature of 400 ° C. or more with respect to a total of 100 wt% of alumina, fused silica and phosphorous graphite. A method for producing a continuous casting nozzle.