JP3312373B2 - Long nozzle for continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a long nozzle for continuous casting which has excellent wear resistance to molten steel, and also has excellent spalling resistance and corrosion resistance.

[0002]

2. Description of the Related Art Conventionally, in continuous casting of steel, a nozzle for transferring molten steel from a ladle to a tundish or from a tundish to a mold has a role of preventing oxidation and turbulence of the molten steel and adjusting the amount of molten steel discharged. Since the quality of the material greatly affects the quality of the steel product, it is an especially important part in the continuous casting equipment.

[0003] The characteristics required of such a continuous casting nozzle are that the inner hole of the nozzle is exposed to severe wear at a high temperature due to the flow of molten steel, so that the nozzle has excellent wear resistance against molten steel and has a high resistance to the inner surface of the nozzle in the early stage of casting. Rapid heating results in a large temperature gradient between the inner surface and the outer periphery of the nozzle, which means that the nozzle has spalling resistance.

As a material satisfying these characteristics, Al ₂ O
Refractories ₃ -SiO ₂ -C system is frequently used. Refractory material, by combining a graphite having a _Al2 O ₃ aggregates with excellent thermal conductivity of high fire resistance, is obtained by excellent properties melting loss resistance and spalling resistance. In order to cope with even more severe thermal shock, 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 the mixture, form, and then perform reduction firing.

Al which is frequently used as a nozzle for continuous casting
Various improvements have been proposed for the ₂ O ₃ -SiO ₂ -C nozzle in order to improve the required properties such as corrosion resistance and spalling resistance. For example, in the invention described in Japanese Patent Publication No. 63-48823, in an Al ₂ O ₃ —SiO ₂ —C nozzle to which 0.05 to ₂ wt% of boron carbide is added, a part of carbon has an average particle diameter of 5 μm or less. By adjusting the particle size of carbon by blending a car pump rack, the spalling resistance and the decrease in hot strength due to the addition of boron carbide are prevented, and the antioxidant action of boron carbide is effectively exhibited. .

According to the invention described in Japanese Patent Application Laid _- Open No. 1-212274, alumina as a component of the nozzle has a particle diameter of 45 μm.
The following fine alumina powder has a particle size distribution occupying 30 to 60% by weight of the total amount of alumina and gives alumina a tendency to coarsen, thereby greatly improving spalling resistance and erosion resistance. In the invention described in Japanese Patent Application Laid-Open No. H4-100664, the alumina constituting the nozzle is 0.05 mm or less, _{40 to} 75 wt%, the particle size of alumina is refined to improve the abrasion resistance of molten steel, and a special pitch is used. By doing so, deterioration of spalling resistance is prevented.

In the invention described in JP-A-5-339046,
Al ₂ O ₃ , SiO ₂ , ZrO ₂ , MgO, C
The aO oxide refractories use a self-curing special polymer phenolic resin to improve corrosion resistance and mechanical strength. In the invention described in JP-A-5-228591,
Alumina 40 ~ 70wt%, silica 0 ~ 20wt%, carbon 15 ~ 30wt
%, The particle size of carbon is 300μ
m or less is set to 50 wt% or less of the carbon addition amount to prevent a decrease in spalling resistance. In the invention described in Japanese Patent Application Laid _- Open No. Hei 6-23501, spalling resistance is improved by substituting a part of fused quartz with cristobalite in an Al ₂ O ₃ —SiO ₂ —C nozzle.

[0008]

The Al ₂ O ₃ -SiO ₂ -C nozzle having various improvements as described above often causes problems in practical use. In particular, in a long nozzle located between a ladle and a tangish dish, depending on how the sliding nozzle installed on the ladle is throttled, severe drift occurs in the molten steel, and the molten steel collides violently with the upper portion of the nozzle. The wear caused by the flow of the molten steel often causes local erosion, which often causes a problem that the durability is greatly impaired.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a long nozzle for continuous casting which has excellent wear resistance and spalling resistance and erosion resistance of molten steel. Hereinafter, it may be simply referred to as “long nozzle”)
Is provided.

[0010]

As described above, when a long nozzle that locally melts due to abrasion due to molten steel flow is closely observed, the working surface side is often decarburized and an embrittlement layer is often formed. In addition, they have noticed that molten steel is often solidified and fixed directly in contact with such an embrittled layer.

Further, the present inventors have proposed that “refractory” 49 (1)
1) In (1997), regarding the reactivity of alumina-fused quartz-graphitic materials with slag, we found that reducing the amount of graphite and increasing the amount of fused quartz facilitated the formation of a reaction layer on the surface of the refractory. Reveals.

The present inventors have found that, in a long nozzle, an Al ₂ O ₃ —SiO ₂ —C—MgO-based system reacts with the molten steel and slag on the inner hole working surface in contact with the molten steel during use. Al ₂ O ₃ -SiO ₂ -CaO or Al ₂ O ₃ -SiO ₂ -Mg composed of at least three components
The inventors have found that a reaction layer of O, Al ₂ O ₃ —SiO ₂ —MgO system is formed, and that this reaction layer controls erosion such as abrasion and decarburization caused by molten steel flow, and the present invention has been completed.

According to the present invention, a wear layer against the flow of molten steel is increased by forming a reaction layer on the working surface side of an inner hole portion which is in contact with the molten steel during use, and the spoiling resistance and the erosion resistance are improved. An object of the present invention is to provide an excellent continuous casting long nozzle.

That is, the long nozzle for continuous casting according to the present invention is composed of 35 to 64% by weight of alumina and 1 to 10% by weight of calcined alumina.
%, Fused quartz 20 to 40 wt%, carbon 15 to 30 wt%, and at least a part of the inner hole is made of a refractory material having a fused quartz / carbon weight ratio of 0.5 to 3. Long nozzle for continuous casting. (Claim 1) as the gist (items specifying the invention).

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is directed to a long nozzle for continuous casting, characterized in that a reaction layer is formed on the working surface side of a nozzle inner hole portion which is in contact with molten steel during use.
That is, the long nozzle of the present invention, at the time of use, on the working surface side of the nozzle inner hole portion that is in contact with the molten steel, the nozzle reacts with the molten steel and slag, at least the Al ₂ O ₃ -SiO ₂ -C-MgO system
Al ₂ O ₃ -SiO ₂ -CaO system composed of three components, Al ₂ O ₃ -SiO ₂ -MgO system,
An Al ₂ O ₃ —SiO ₂ —MgO-based reaction layer is formed, and this reaction layer controls erosion such as wear and decarburization caused by the molten steel flow.

Hereinafter, the long nozzle of the present invention will be described in detail. Usually, a slag exists above the molten steel in the ladle to which the long nozzle is connected. The composition of this slag is not constant and varies depending on the type of lining refractory, spraying material, and type of molten steel, but it is mainly composed of CaO-MgO-SiO ₂ system. These slags float on the molten steel, but at the end of casting, the molten steel surface is lowered, so that the slag is discharged through the long nozzle. In particular, since the molten steel is discharged while forming a vortex at the end of casting, the slag is also drawn into the vortex and discharged.

The discharged slag reacts with the long nozzle refractory when passing through the long nozzle. At this time, the long nozzle of the present invention forms a reaction layer on the surface by reaction with slag. This reaction layer is considered to serve as a coating layer for protecting the long nozzle from molten steel in the subsequent casting. Usually, since the long nozzle is used many times, if such a protective layer is formed after the first use, the amount of damage in subsequent use is reduced, and the durability is further improved.

The portion of the long nozzle operating surface that is in contact with the molten steel is presumed to have almost reached the molten steel temperature. However, since the portion is cooled from outside the long nozzle, the temperature inside the operating surface is considerably higher than the molten steel temperature. It is settled as falling. Therefore, it has been determined that the temperature of the reaction layer formed by reacting with the slag is lower than the original melting point, and it is considered that the long nozzle surface is protected by the reaction layer even during casting. Therefore, it is determined that such a reaction layer functions as a protective layer.

The reaction layer formed on the surface of the long nozzle inner hole is generally composed of a CaO-Al ₂ O ₃ -SiO ₂ -MgO quaternary system. These reaction layers have a higher viscosity and a higher melting point as the C / S is larger. Depending on the location, there may be four components, three components, and sometimes two components. However, basically, four components of CaO-Al ₂ O ₃ -SiO ₂ -MgO or
CaO-Al ₂ O ₃ -SiO ₂ , Al ₂ O ₃ -SiO ₂ -MgO, CaO-Al ₂ O ₃ -MgO
Often consists of components.

The composition of these reaction layers is, of course, affected by the composition of the refractory. When the composition of the refractory of the long nozzle is within a certain composition range, a reaction layer between the slag and the refractory of the long nozzle is easily generated, and a coating layer is formed. It does not mean that the composition of the long nozzle refractory may be anything. When the composition is within a certain range, such slag coating property becomes good.

That is, the composition of the refractory is 35 to 64 wt% of alumina.
%, Calcined alumina 1 to 10 wt%, fused quartz 20 to 40 wt%, carbon 15 to 30 wt%, and good slag coating properties when the fused quartz / carbon weight ratio is 0.5 to 3 It becomes.

"Alumina" is "alumina other than calcined alumina", and may be either fused alumina or sintered alumina, and its ratio is 35 to 64 wt%. More preferably
40 to 55 wt%. If the amount of alumina is less than 35% by weight, corrosion resistance cannot be obtained, and if it exceeds 64% by weight, a reaction layer is hardly formed, which is inappropriate.

The calcined alumina has an Al ₂ O ₃ content of 99.0 wt%.
The above is desirable, and the particle diameter is desirably 0.03 mm or less. The particle size is more preferably mainly 0.004 mm or less, from the viewpoint of enhancing the moldability of the nozzle and the composition of the matrix portion. The amount of calcined alumina is 1-1.
0 wt%. More preferably, it is 2 to 7% by weight. 1 wt
%, Moldability and a dense structure cannot be obtained. If it exceeds 10% by weight, oversintering tends to proceed at the time of casting, and the heat-resistant sboring property deteriorates, which is inappropriate.

The proportion of the fused quartz is 20 to 40% by weight. 20
If the content is less than wt%, a reaction layer is hardly formed, and wear and loss due to molten steel increases. On the other hand, if the content exceeds 40 wt%, the effect of increasing the porosity due to the decomposition of the fused quartz increases, the structure of the working surface deteriorates, and the corrosion resistance decreases. It is preferable that the particle size of the fused quartz to be added is 0.1 mm or more, and the particle size is 50 wt% or more in the whole amount of the fused quartz to be added. This is 0.1
This is because if there is a large amount of fused quartz with a particle size of less than mm, the reactivity with slag decreases.

The carbon of the present invention can be used regardless of whether it is crystalline or non-crystalline, and scaly graphite, earthy graphite, coke, carbon black and the like can be used, but it is preferable to use mainly scaly graphite. The proportion is 15 to 30% by weight. Carbon content
If it exceeds 30 wt%, the wettability of refractories and slag will deteriorate,
It is not preferable because the reaction between the slag and the refractory hardly occurs. Generally, it is common sense that refractory materials have good corrosion resistance so that they are hardly wet with slag, but they have found that a smaller carbon content is better in suppressing damage to the long nozzle inner hole. On the other hand, the lower limit of carbon content is 15wt%
It is. The wettability with slag is better as less carbon is,
If the amount is too small, the heat-resistant boring performance of the refractory decreases, and there is a risk that the refractory cracks due to thermal shock when passing through molten steel. Therefore, the lower limit of carbon is 15% by weight. There is no particular limitation on the size of carbon.

The ratio of fused quartz to carbon is from 2: 1 by weight.
The ratio of 3: 1 is preferable. When the weight ratio of the fused quartz is less than 2, the formation of the reaction layer becomes thin. On the other hand, when the weight ratio of the fused quartz exceeds 3, the reaction layer is easily melted.

Further, other components such as mullite, zirconia, electrofused zirconia armlite, alumina-zirconia and the like can also be contained as long as the effects of the present invention are not impaired. Preferably, the amount is less than 20% of the refractory.

In the present invention, Si, SiC, B ₄ C, Si ₃ N ₄
And other components can be added. Usually, these additives are added as an antioxidant or a trace component for exhibiting strength. In the present invention, however, these additives can be added in a refractory in an enclosure of 5 wt% or less. . 5wt%
Above is inappropriate because the formation of the reaction layer is suppressed.

Although the method for producing the long nozzle of the present invention is not particularly limited, it can be produced, for example, by the following method. A phenol resin, tar pitch, or the like can be used as the binder. In forming, the mixture is kneaded at room temperature or under heat, kneaded under pressure as necessary, formed by an isostatic press, and then fired in a reducing or low oxygen partial pressure atmosphere at 900 ° C. or higher.

The refractory constituting the long nozzle 1 of the present invention is used not only for the entire long nozzle, but also as shown in FIG.
Or the material of the inner hole of the specific refractory part 1A above the immersion part 2.

[0031]

EXAMPLES Next, the present invention will be described in detail with reference to Examples of the present invention and Comparative Examples. Examples 1 to 11 and Comparative Examples 1 to 3 The respective raw materials shown in Table 1 were blended, kneaded, and press-molded.
The resultant was baked at 1600 ° C. for 3 hours in an argon atmosphere.

[0032]

[Table 1]

The following tests were performed on the samples obtained in Examples 1 to 11 and Comparative Examples 1 to 3, and the results are shown in Table 1. The bending strength was 25 × 25 from the sample shown in Table 1.
A test piece of × 120 mm was cut out, and was cut according to JIS R2213.
Measured over a span of mm. As for the elastic modulus, the dynamic elastic modulus of the test piece having the bending strength was measured by the impact method.

In the slag reaction test, a test piece having an outer diameter of 50 mm ¢, an inner diameter of 30 mm ¢ and a depth of 30 mm was cut out from the sample shown in Table 1 to prepare a crucible, and a synthetic slag (a ladle slag) was assumed in the crucible. C / S = 3.4) and heated in an Ar atmosphere at 1600 ° C. for 3 hours, and the presence or absence of slag permeation into the brick was confirmed from the cut surface, microscopic observation, and EPMA observation. (As shown in Table 1, in Examples 1 to 11, bricks and slag formed a reaction layer, but in Comparative Example 1, there was no fused silica, no reaction layer was formed, and in Comparative Example 2, the reaction layer was not formed. (There was no calcined alumina, no reaction layer was formed, and in Comparative Example 3, a large amount of graphite was added, making it difficult to wet with slag, and no reaction layer was formed.)

The samples obtained in Examples 3, 4, and 8 of the present invention were applied to an actual furnace. Comparative Example 2 was used for comparison. The residual thickness after use was measured for each of the specific refractory portions 1A of the long nozzle shown in FIG. 1, and the erosion amount per unit time was compared by dividing by the casting time. Table 2 shows the results.

[0036]

[Table 2]

From the above test results, it is clear that the long nozzle of the present invention is more effective against the inner tube portion erosion than the comparative long nozzle. Further, as a result of observation of the structure after use, a reaction layer due to reaction with slag was observed in the inner hole of the long nozzle of the present invention, but no reaction layer was observed in the long nozzle for comparison. .

[0038]

According to the present invention, as described in detail above, 35 to 64% by weight of alumina, 1 to 10% by weight of calcined alumina, 20 to
Due to the fact that at least a part of the inner hole is made of a refractory material containing 40 wt% and 15 to 30 wt% carbon and having a weight ratio of fused quartz / carbon of 0.5 to 3, wear resistance to molten steel is particularly high. It has an excellent effect of being able to provide a continuous casting nozzle that is excellent in spattering properties and also excellent in spalling resistance and corrosion resistance.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a long nozzle for continuous casting of the present invention.

[Description of Signs] 1 Long nozzle 1A Specific refractory part 2 Immersion part

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-31346 (JP, A) JP-A-56-14061 (JP, A) JP-A-56-41871 (JP, A) JP-A-61-346 83673 (JP, A) JP-A-54-38233 (JP, A) JP-A-1-212274 (JP, A) JP-A-4-100664 (JP, A) JP-A-5-339046 (JP, A) JP-A-5-228591 (JP, A) JP-A-6-23501 (JP, A) JP-B-63-48823 (JP, B2) JP-A-9-503445 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B22D 11/10 330 B22D 11/10 320 B22D 41/54 C04B 35/103

Claims (1)

(57) [Claims] 1. Alumina 35-64 wt%, calcined alumina 1-
At least a part of the inner hole is made of a refractory material containing 10wt%, fused quartz 20-40wt%, carbon 15-30wt%, and the fused quartz / carbon weight ratio is 0.5-3. Long nozzle for continuous casting.