JPH1157957A - Sliding nozzle plate and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the thermal-shock resistance and corrsion resistance even when a sliding nozzle for controlling flow-rate of molten metal is repeatedly subjected to severe thermal shock between high temp. heating and cooling. SOLUTION: This is in alumina-carbon sliding nozzle plate for controlling the flow rate of the molten metal and in the alumina-carbon the main mineral phase of which is corundum and monoclinic system zirconia, electromelted alumina-zirconia material consisting of coarse particle, medium particle and fine particle having a chemical composition of 75-80 wt.% alumina and 20-25 wt.% zirconia is contained by 5-50 wt.%. The thermal shock resistance and corrosion resistance are improved by containing the fine powder of particle size of 200-10 μm by 5-20 wt.% in the electromelted alumina-zirconia material having the particle size of 4 mm-10 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sliding nozzle plate mounted on the bottom of a molten steel container such as a ladle or a tundish used in the field of iron making for controlling the flow rate of molten steel, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Since a sliding nozzle plate is used under severe temperature conditions, it is required to have not only excellent corrosion resistance but also excellent thermal shock resistance. Therefore, several inventions characterized by blending a refractory aggregate composed of alumina and zirconia have been disclosed.

[0003] For example, in Japanese Patent Publication No. 61-2620, a refractory aggregate containing 80 to 98% by weight of alumina and 2 to 20% by weight of zirconia as the main mineral phase is composed of corundum and monoclinic zirconia. Alumina used
A carbonaceous sliding nozzle plate is disclosed.

In Japanese Patent Publication No. 64-11589, alumina is 58 to 78% by weight and zirconia is 2% by weight.
An alumina-carbonaceous sliding nozzle plate using 2 to 50% by weight of coarse and / or medium-sized fused alumina / zirconia raw materials containing 0 to 40% by weight is disclosed.

Further, Japanese Patent No. 2,509,093 discloses a fired sliding nozzle plate using an electrofused raw material containing no mullite and containing 30 to 75% by weight of alumina and 25 to 70% by weight of zirconia.

[0006]

Recently, in each steelworks, the number of use of the sliding nozzle has been increased for the purpose of reducing the cost of refractories, and after use, the nozzle has been cooled to room temperature.
Intermittent use such as re-use has become common.

Therefore, when a fused alumina-zirconia raw material having a high zirconia content as described in Japanese Patent No. 2509093 is used, the thermal expansion coefficient when intermittently used as described above is higher than that of alumina. The problem of large surface roughness is caused by tissue separation due to spalling based on relatively large zirconia.

Further, the effect of adding the zirconia-containing refractory aggregate is such that the effect of preventing crack elongation accompanying the phase transition of zirconia distributed in the aggregate acts to alleviate the thermal shock. It was found that when the amount was large, the generation was large, and on the contrary, the sliding nozzle was weakened due to repeated thermal changes.

On the other hand, as disclosed in JP-B-61-2620, when the content of zirconia in the molten alumina-zirconia raw material is too small, the zirconia originally considered to have better corrosion resistance to molten steel than alumina. Is less effective in improving the corrosion resistance of the plate itself,
There is a problem that high durability cannot be expected so much.

Furthermore, since the thermal expansion coefficient of a fused alumina / zirconia raw material having a low zirconia content is close to that of alumina, when blended in a sliding nozzle plate, the difference in the thermal expansion between the two materials causes an increase in the brick structure within the brick structure. There is a problem that the generation of microcracks is small, the heat resistance of the plate is insufficient, the resistance to a rapid thermal change is reduced, and cracks due to thermal spalling are likely to occur.

Further, the zirconia content of 20 to 40% by weight contained in the fused alumina-zirconia disclosed in Japanese Patent Publication No. 11589/1989 is generally in the direction of solving the above-mentioned problem. Particle size is coarse or /
Fine grains are not to be blended because the strength of the matrix part of the plate structure is increased, crack generation is promoted, and the propagation path becomes linear, and the structure is easily peeled. I have.

As described above, it is apparent that the molten alumina-zirconia raw material is originally superior in corrosion resistance to molten steel as compared with alumina due to the inclusion of zirconia, and that the sliding nozzle plate is damaged. The morphology is often damaged by premature erosion from the matrix portion of the tissue.

Therefore, in order to achieve high durability by improving the corrosion resistance, it is important to strengthen the matrix portion, that is, to preferentially mix a high corrosion-resistant material into the matrix portion. Even if effective, there is a problem that improvement in corrosion resistance cannot be expected so much.

[0014]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above points, and in order to solve the above problems, an alumina-carbon sliding nozzle plate for controlling the flow rate of molten metal is provided. Wherein the main mineral phases are corundum and monoclinic zirconia, and alumina 75 to 80
It is an object of the present invention to provide a sliding nozzle plate containing 5 to 50% by weight of a coarse, medium or fine fused alumina / zirconia material having a chemical composition of 20 to 25% by weight of zirconia, and a method for producing the same.

[0015]

DETAILED DESCRIPTION OF THE INVENTION A sliding nozzle plate and a method of manufacturing the same according to the present invention are alumina-carbon sliding nozzle plates for controlling the flow rate of molten metal, wherein the main mineral phase is corundum and monoclinic zirconia. Characterized in that it contains 5 to 50% by weight of coarse, medium and fine fused alumina / zirconia raw materials having a chemical composition of 75 to 80% by weight of alumina and 20 to 25% by weight of zirconia. In addition, the distribution amount of alumina and zirconia is well balanced, and coarse, medium, and fine particles of the fused alumina / zirconia raw material are blended.

The electrofused alumina-zirconia aggregate is obtained by electrofusing and cooling alumina and zirconia, and has monoclinic zirconia precipitated at corundum grain boundaries. This monoclinic zirconia is known to contract due to a crystal transition at about 1000 ° C., and thereby imparts thermal shock resistance by reducing the expansion coefficient and generating microcracks.

The aggregate has a well-balanced mixing ratio of zirconia of 20 to 25% by weight with respect to 75 to 80% by weight of alumina to improve thermal shock resistance and corrosion resistance.

When the zirconia content is less than 20% by weight,
The effect of the above transition is slight, and no effect is observed in improving the thermal shock resistance. Further, the zirconia content in the aggregate is too small, and the effect of improving corrosion resistance is poor.

On the other hand, if it exceeds 25% by weight, relatively large cracks are formed, which leads to a decrease in the strength of the sliding nozzle plate.

Further, since the content of zirconia is large, the coefficient of thermal expansion of the aggregate is large, and the content of the fused alumina-zirconia aggregate is 5 to 50% by weight, and 5% by weight or less. In this case, the effect of the transition does not appear, and no effect is observed in improving the thermal shock resistance. On the other hand, when the content exceeds 50% by weight, the generated microcracks become excessive, and the strength of the sliding nozzle plate is lowered, which is not preferable. The rest is compounded with alumina and carbon,
Si necessary, Al, a metal of B ₄ C, etc. 1-3 wt%
It can also be added.

When the particle size of the fused alumina-zirconia aggregate is 10 μm or less, the zirconia is released without being fixed in the alumina, the sinterability is poor, and the strength of the sliding nozzle plate is reduced. On the other hand, if the particle size exceeds 4 mm, the generated cracks become large,
This results in a decrease in strength after thermal shock.

From these facts, it is necessary that the particle size of the fused alumina-zirconia aggregate is smaller than 4 mm and larger than 10 μm, and desirably, the fine particles having a particle size of 200 μm or less are 5 to 5 μm.
Most preferably, it contains 20% by weight. This is because from detailed experimental results, particles of 200 μm to 4 mm contribute to thermal shock resistance, and particles of 200 μm to 10 μm exist in the matrix, which contributes to improvement of the corrosion resistance of the matrix.

In the use of the fused alumina-zirconia aggregate in the sliding nozzle plate, as described above, it is important to select the amount of zirconia contained in the aggregate and the particle size of the aggregate. This is important as a means for maximizing the performance of the sliding nozzle, taking into account the balance between heat resistance and corrosion resistance, which is considered to be the most important characteristic of the sliding nozzle.

The composition whose particle size has been adjusted according to the above composition is kneaded at room temperature or under heating using a phenol resin or the like as a binder. Then, the obtained mixture is formed into a sliding nozzle plate shape by a friction press, an oil press, or the like, and then fired in a reducing atmosphere at 900 to 1500 ° C. After firing, the sliding nozzle plate is impregnated with tar pitch or the like for the purpose of densifying the structure, imparting slidability, and improving corrosion resistance.

[0025]

EXAMPLES The chemical composition of fused alumina-zirconia aggregates is shown as A, B, and C in Table 1, and the above-described fused alumina-zirconia aggregates are used for ladle sliding nozzle plates based on alumina-carbon. Table 2 for 3 types
Were examined with the composition shown in FIG.

Table 1 Chemical composition of aggregate

[Table 1]

After adjusting the prescribed composition, 4% of a phenol resin was added and molded into an actual shape by a friction press. Then, firing was performed in a reducing atmosphere to obtain a fired body. Physical properties and bending strength of these were measured as shown in Table 2,
Further, a thermal spalling test and a corrosion resistance test were performed to evaluate. As a result, it was confirmed that the formulations of the examples of the present invention were improved in both the heat-resistant spall resistance and the corrosion resistance as compared with the conventional example of the comparative example.

Table 2 Composition and properties

[Table 2]

In particular, Example 3 and Comparative Example 8 were used on ordinary steel with a heat size of 250 t / ch, 60 minutes / ch on an actual machine.

As a result, after the completion of 5 ch in Comparative Example 8, the surface roughness was large and the service life was reached.
Even after the use of the channel, the surface roughness was slight. Thus, the product of the present invention has improved the life of the sliding nozzle plate.

[0031]

As described above, according to the present invention, even if the molten metal is heated to a high temperature through circulation and then cooled to room temperature intermittently and repeatedly used at a high temperature, the alumina can be used even if intermittently used. Since zirconia is used in an appropriate amount, the balance between heat spalling and corrosion resistance is maintained.
Thermal shock resistance and corrosion resistance can be improved.

Further, by blending coarse particles, medium particles and fine particles as the fused alumina-zirconia aggregate,
The thermal shock resistance is improved, and particularly the corrosion resistance of the matrix is improved by containing fine particles.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Seijiro Tanaka 2 Kawasaki Reactor Co., Ltd.

Claims (3)

[Claims] An alumina-carbon sliding nozzle plate for controlling the flow rate of molten metal, wherein the main mineral phases are corundum and monoclinic zirconia,
A sliding nozzle plate comprising 5 to 50% by weight of a coarse, medium or fine electrofused alumina / zirconia material having a chemical composition of 75 to 80% by weight of alumina and 20 to 25% by weight of zirconia. 2. An electro-fused alumina-zirconia raw material having a thickness of 4 mm
The particle size of the fine powder is 200 to 10 μm.
2. The sliding nozzle plate according to claim 1, wherein the sliding nozzle plate contains 5 to 20% by weight. 3. A method for producing an alumina-carbon sliding nozzle plate for controlling the flow rate of molten metal, wherein the main mineral phases are corundum and monoclinic zirconia, 75 to 80% by weight of alumina and 20% by weight of zirconia.
It is characterized in that coarse, medium, and fine electrofused alumina and zirconia raw materials having a chemical composition of about 25% by weight are blended in an amount of 5 to 50% by weight, and the refractory is kneaded, molded and fired. Manufacturing method of sliding nozzle plate.