JPH11246265A - High corrosion resistant fused silica-containing refractory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the corrosion resistance without lowering spalling resistance of alumia-silica-graphite base refractory suitable for a continuous cast nozzle structural material. SOLUTION: This alumia-silica-graphite base refractory forms a covered layer consisting of a high corrosion resistant refractory raw material such as zirconia, magnesia, alumina, zircon, spinel, zirconia-mullite and alumnia- zirconia and carbon on the surface of fused silica. By making the thickness of the covered layer on the fused silica into >=0.02 mm-<=0.2 mm, the adverse effect to other physical properties is made minimum and the corrosion resistance is further improved by the covered layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a long nozzle used for pouring molten metal from a ladle into a tundish in continuous casting of metal such as steel, and a dipping used for pouring molten metal from a tundish to a mold. The present invention relates to a high corrosion resistant fused silica-containing refractory suitably used for a refractory for continuous casting such as a nozzle and a long stopper for controlling a flow rate of molten steel.

[0002]

2. Description of the Related Art Nozzles, such as long nozzles and immersion nozzles, play an important role, such as rectifying molten steel, preventing oxidation due to contact with the atmosphere, and preventing scattering of molten steel for safe casting. .

[0003] In this nozzle, molten steel is injected without receiving sufficient preheating, so that the inner hole side is rapidly heated and thermal stress is generated, which often causes cracks in the nozzle, leading to steel leakage and large operation. May be problematic.

Japanese Patent Publication No. 47-49409 discloses a refractory having improved spall resistance by adding fused silica having a small thermal expansion to an alumina-graphite refractory. -Silica-graphite refractories are widely applied to immersion nozzle bodies, long nozzles, long stoppers and the like. In addition, when applying it, a large amount of silica is added to the unimmersed part where the preheating temperature tends to be low, and the amount of silica added is reduced to the immersed part where preheating is relatively good and corrosion resistance is important. They are used properly.

Fused silica has a particularly small thermal expansion among various refractory raw materials. Therefore, as the added amount increases, the thermal expansion of the refractory decreases and the spall resistance improves. However, fused silica has a higher erosion rate for slag and molten steel than high-corrosion-resistant refractory raw materials such as zirconia and magnesia, so increasing the amount of addition improves spall resistance but decreases corrosion resistance. There is a problem of doing.

On the other hand, in order to improve the corrosion resistance of silica, coating silica with alumina is disclosed in Japanese Unexamined Patent Publication No.
No. 127944.

[0007] In the silica coated with alumina, slag and mold powder are apt to infiltrate into the coating layer only by coating with alumina, and therefore, the protective effect of fused silica by the coating layer of alumina is not exerted. Although it is effective for the main body and immersion part of the immersion nozzle which is hardly available, it is effective for the immersion part of the long nozzle that is in contact with the slag, the slag line of the long stopper and the immersion nozzle that may come in contact with the mold powder. There is a problem that a sufficient effect is not exhibited.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to improve the corrosion resistance in a well-balanced manner without lowering the spall resistance of an alumina-silica-graphite refractory.

[0009]

SUMMARY OF THE INVENTION The present invention provides a high-corrosion-resistant refractory material such as zirconia, magnesia, and alumina on the surface of a fused silica and carbon to maintain the low thermal expansion characteristic of the fused silica. It is completed by the knowledge that corrosion resistance can be improved, and in an alumina-silica-graphite refractory containing fused silica, fused silica having a particle diameter of 0.1 mm or more is coated with a coating layer made of a high corrosion-resistant refractory raw material and carbon. It is characterized by having.

Alumina-silica containing fused silica
The erosion of graphite-based refractories proceeds mainly when the fused silica selectively erodes into the slag. Therefore, if a coating layer having excellent corrosion resistance is provided on the surface of the fused silica, when the molten silica comes into contact with the slag on the operating surface, the slag first reacts with the coating layer having excellent corrosion resistance, so that the erosion rate is reduced. Further, if the thickness of the coating layer is small, the influence on the thermal expansion of the fused silica is small, and the low thermal expansion property is maintained.

The high-corrosion-resistant refractory raw material used in the present invention means a raw material which is more excellent in corrosion resistance to molten steel slag than fused silica and does not decrease in corrosion resistance even when reacted with fused silica. In particular, alumina, zirconia, magnesia , Zircon, spinel, zirconia-mullite, alumina-zirconia, and mullite are preferred in terms of corrosion resistance and economy.

Further, in the present invention, in order to improve the corrosion resistance of the coating layer, it is necessary to use carbon together with a high corrosion resistant refractory raw material. Since carbon has poor wettability to slag, infiltration of slag can be prevented.
Although various types of carbon can be used as the carbon, graphite is most preferable in consideration of oxidation resistance and reactivity with molten steel. Various graphites such as natural scaly graphite and artificial graphite can be used as the graphite. The combined use of graphite also has the effect of lowering the modulus of elasticity of the coating layer, and is therefore effective in improving spall resistance.

The particle size of the fused silica to be coated is 0.1 mm
The above is preferred. This is because even if fused silica having a particle size of 0.1 mm or less is added to the alumina-graphite refractory, the effect of improving the spall resistance is very small, so that it is not necessary to add fused silica.

The thickness of the high corrosion-resistant refractory raw material to be coated is particularly preferably from 0.02 mm to 0.2 mm.
If the thickness is less than 0.02 mm, the coating layer is rapidly melted and the effect of improving corrosion resistance is reduced. Conversely, if the thickness exceeds 0.2 mm, the thermal expansion of the coated fused silica increases due to the effect of the coating layer having a large thermal expansion, and the effect of improving the spall resistance decreases.

The present invention can exert its effect according to the application ratio even if it is applied only to a part of the fused silica having a particle size of 0.1 mm or more. The effect is particularly remarkable when at least 60% by weight of the coating is coated with a high corrosion-resistant refractory raw material and carbon.

Although there is no particular problem even if a part of the coating thickness is out of the range of the present invention, 60% by weight or more of the coated fused silica is in the range of 0.02 mm to 0.2 mm. It is preferably coated with.

The present invention is also directed to a coating layer in contact with fused silica, that is, a first coating layer. Depending on the kneading step of the powder raw material, two or more coating layers may be formed, but the effect of the present invention is remarkably exhibited by the first coating layer.

The particle size of the high corrosion resistant refractory raw material to be coated is 20
The thickness is preferably not more than 20 μm, and if it exceeds 20 μm, the adhesion to the fused silica is deteriorated and the intended coating layer cannot be obtained.

The particle size of the carbon to be coated is preferably 50 μm or less, and if it exceeds 50 μm, the adhesion to the fused silica is deteriorated and the desired coating layer cannot be obtained. The fused silica coated with the high corrosion resistant refractory raw material and carbon can be used in an alumina-silica-graphite-based composition in an amount of 2 to 40% by weight, preferably 5 to 30% by weight. If it is less than 2% by weight, the effect of improving the spalling resistance is not sufficiently exhibited, and if it exceeds 40% by weight, the alumina in the matrix portion is relatively reduced, so that the corrosion resistance is lowered.

The ratio of the high corrosion-resistant refractory raw material to carbon in the coating layer is preferably 5 to 50% by weight of carbon on the basis of 100% by weight of the high corrosion-resistant raw material. If the amount of carbon is less than 5% by weight, the effect of suppressing the infiltration of slag becomes insufficient.

The alumina-silica-graphite compound of the present invention is used for long nozzles, immersion nozzles or long stoppers, etc., and generally contains 40 to 80% by weight of alumina and 2 to 40% by weight of silica. % By weight, 12 to 40% by weight of graphite.

Further, in the high corrosion resistant fused silica-containing refractory of the present invention, zirconia, magnesia, mullite,
One or more of refractory raw materials such as zirconia mullite, alumina zirconia, and silicon carbide may be added and blended. Further, pitch, B ₄ C, various metals, and the like can be added as long as the effects of the present invention are not impaired.

In order to obtain a composition in which only a surface of fused silica is coated with a coating layer comprising a predetermined high corrosion-resistant refractory raw material and carbon, first, fused silica as a pre-kneading raw material, a high corrosion-resistant refractory raw material and carbon Then, an appropriate amount of a binder is added and kneaded to obtain a kneaded material having a coating layer formed on the surface of the fused silica, and the remaining compounding materials for subsequent kneading are added and kneaded again.

[0024]

Embodiments of the present invention will be described below with reference to embodiments.

Embodiment 1

[Table 1] Table 1 shows, as examples of the present invention, the mixing ratio of the raw material for pre-kneading and the raw material for post-kneading, the thickness of the obtained coating layer, and the characteristics of the refractory obtained by using this as a raw material for mixing, along with comparative examples.

In the table, No. 1 to No. No. 3 shows a comparative example. 4-No. 8 shows an embodiment of the present invention. As a conventional example, no. No. 1 is a general alumina-silica-graphite material; No. 2 is No. No. 1 was mixed with ultra-fine alumina uniformly. 3 shows an example in which fused silica was coated with alumina. No. 1 and No. As for No. 2, the whole amount of the compounding ratio shown in Table 1 was mixed from the beginning, and an appropriate amount of phenol resin was added and kneaded to obtain a compound.

No. of Comparative Example No. 3 and Example No. 3 of the present invention. 4-No. In the case of No. 8, in order to coat a predetermined high corrosion-resistant refractory raw material on the fused silica, first, an appropriate amount of phenol resin is added as a binder to the raw material for pre-kneading and kneaded in advance to produce granulated particles. Thereafter, the raw materials for kneading were added and further kneaded to obtain a blend.
The obtained composition was CIP-molded into a nozzle shape at a pressure of 1000 kg / cm ² , embedded in coke, and reduced and fired at a maximum temperature of 1000 ° C.

When the cross section of the fired sample was observed with a microscope, one or two coating layers could be confirmed around the fused silica, and the coating thickness of the first layer almost coincided with the calculated value in Table 1. Was to do.

From the fired nozzle, the bending strength, elastic modulus,
The coefficient of thermal expansion and corrosion resistance were investigated. The measurement results and the results of the thermal shock resistance coefficient representing the spall resistance are shown in the same table. The bending strength was measured by a three-point bending method, the elastic modulus was measured by an ultrasonic method, and the thermal expansion coefficient was measured by a commercially available thermal dilatometer, and showed an average linear expansion coefficient up to 1500 ° C. The thermal shock resistance coefficient was calculated by the following equation since the Poisson's ratio was almost constant. The larger the number, the better the spall resistance.

(Bending strength) / [(Elastic modulus) × (Coefficient of thermal expansion)] The corrosion resistance is as follows: steel having a carbon content of 0.01% by weight is 1600.
° C, 40% CaO and 30% SiO ₂ on the surface
%, Al ₂ O ₃ 10%, magnesia 10%, slag containing manganese dioxide 7%, and 20 m on each side
m was immersed for 30 minutes, and the amount of erosion at the maximum erosion portion was measured. The numbers shown in Table 1 are No. The erosion rate of 1 is indexed as 100, and the smaller the number, the better the corrosion resistance.

As is clear from the results of the quality measurement, the comparative example No. 1 was a comparative example. No. 1 to No. No. 3, which is an embodiment of the present invention, as compared with No. 3. 4 to No. 4. No. 8 shows that the corrosion resistance is greatly improved although the thermal shock resistance is maintained due to the coating effect of the high corrosion resistant refractory raw material and carbon on the fused silica. In particular, no. 3 and No. Comparing No. 4, both the thermal shock resistance and the corrosion resistance are improved by the inclusion of carbon in the coating layer on the fused silica, and the effect of the present invention is remarkably exhibited.

Embodiment 2

[Table 2] In order to investigate the effect of the thickness of the coating layer, No. 2 in Table 2 was used. 9 to No. 9 Fifteen kinds of seven kinds of compounds were kneaded. N of Comparative Example
o. 9 is Comparative Example No. 9 shown in Table 1. Kneaded uniformly as in Example 1. No. 10 to No. No. 15 is No. 3
From No. Kneading was performed in the same manner as in Example 8 to increase the coating thickness of the ultrafine powder alumina and graphite on the fused silica. The molding, firing, quality evaluation, and the like after the preparation of the blend were performed in exactly the same manner as in Example 1. As a result of the quality evaluation, the embodiment of the present invention, N
o. 10 to No. No. 15 of Comparative Example No. 9 has better corrosion resistance. However, the coating thickness is 0.02m
m. No. 10 has a relatively small corrosion resistance improving effect. In addition, No. No. 15 is No. 14
Although the corrosion resistance is superior to that of the above, the spall resistance is remarkably reduced particularly with an increase in the coefficient of thermal expansion, which is not preferable. For this reason, the more preferable thickness of the coating layer is 0.1.
It turns out that it is 0.2 mm from 0.2 mm. Example 3 In this example, an alumina-silica-graphite refractory containing fused silica coated with a coating layer of ultrafine alumina and graphite obtained according to the present invention was applied to a long nozzle and subjected to a real furnace test. Here is an example. No. shown in Table 1. 1 and No.
The material No. 4 was applied to a slag line to produce a long nozzle, which was subjected to an actual furnace test using a continuous slab casting machine. Ladle capacity is 3
The casting time per charge of 00 tons is about 40 minutes. The number of the test pieces was 5, each of which was used for about 12 charges on average. As a result of collecting the used nozzle and investigating the erosion rate of the slag line, the nozzle No. 4
Is No. It was found that the erosion rate was reduced by about 20% as compared with No. 1. Thus, it can be seen that the durability of the nozzle is improved by applying the product of the present invention to the slag line portion of the long nozzle.

[0033]

(1) By applying the refractory of the present invention to a long nozzle, a dipping nozzle or the like, the durability is remarkably improved.

(2) Zirconia, magnesia, alumina, zircon, and high-corrosion-resistant refractory raw materials constituting the coating layer
By using spinel, zirconia / mullite, alumina / zirconia, or the like, a coating layer having high corrosion resistance can be formed economically.

(3) By using graphite as the carbon constituting the coating layer, a refractory having an effect of preventing slag infiltration and having excellent corrosion resistance can be obtained.

(4) The thickness of the fused silica coating layer is 0.0
By specifying the thickness to be 2 mm or more and 0.2 mm or less, it is possible to minimize the adverse effect on other physical properties and maximize the effect of improving the corrosion resistance by the coating layer.

(5) Out of the fused silica in the refractory having a coating layer of 60% by weight or more, the corrosion resistance can be further improved and the durability can be improved.

(6) By specifying the particle size of the highly corrosion-resistant raw material and carbon constituting the coating layer to 20 μm or less and 50 μm or less, respectively, a strong and dense coating layer on the fused silica surface is formed. Peeling of the layer can be prevented, and moreover, corrosion resistance is improved when a refractory is used.

(7) By setting the weight ratio of the highly corrosion-resistant raw material to carbon constituting the coating layer to 100: 5 to 50, the corrosion resistance of the coating layer structure can be improved and the durability of the refractory is improved. I do.

Claims (7)

[Claims] 1. An alumina-silica-graphite refractory containing fused silica, characterized in that fused silica having a particle diameter of 0.1 mm or more is coated with a coating layer made of a highly corrosion-resistant refractory raw material and carbon. High corrosion resistance fused silica containing refractory. 2. The high corrosion resistant fused silica-containing refractory according to claim 1, wherein at least 60% by weight of the fused silica in the refractory is covered by a coating layer comprising a high corrosion resistant refractory raw material and carbon. Stuff. 3. The high-corrosion-resistant refractory raw material forming the coating layer is one or more of zirconia, magnesia, alumina, zircon, spinel, zirconia-mullite, alumina-zirconia, and mullite. The high corrosion resistant fused silica-containing refractory according to claim 1 or 2. 4. The high corrosion resistant fused silica-containing refractory according to claim 1, wherein the carbon forming the coating layer is made of graphite. 5. The high corrosion-resistant melt according to claim 1, wherein the particle size of the high corrosion-resistant raw material forming the coating layer is 20 μm or less, and the particle size of the carbon is 50 μm or less. Silica containing refractories. 6. The method according to claim 1, wherein the ratio of the high corrosion-resistant raw material to carbon to be coated is 5 to 50% by weight of carbon on the basis of 100% by weight of the high corrosion-resistant raw material. High corrosion resistance fused silica containing refractory. 7. The coating layer has a thickness of 0.02 mm or more and 0.2 or more.
7 mm or less.
The high corrosion resistant fused silica-containing refractory according to any one of the above.