JP2014148430A - Refractory, manufacturing method of refractory, and immersion nozzle for continuous molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refractory for an aeration of an immersion nozzle inhibiting changes of aeration property with molding time passage, stabilizing aeration property during molding and capable of preventing damage accidents during molding around a powder part.SOLUTION: There is provided a refractory containing a secondary particles having length of over 0.05 mm and 2 mm or less formed by aggregating a primary particles which are flat shape alumina particles having an aspect ratio of 5 to 50, and containing 55 mass% to 90 mass% of the secondary particles after a heating treatment in a non-oxidation atmosphere at 1500°C for 3 hours, AlOof 98 mass% or more as a component excluding carbon in the secondary particles, and as chemical components, free carbon of 3 mass% to 45 mass%, SiC of 1 mass% to 10 mass%, and having the total content of single compounds SiO, an alkali metal oxide, an alkaline earth metal oxide, TiOand other inevitable components from a production view point of 2 mass% or less.

Description

  The present invention relates to a refractory material that can be used for ventilation, for preventing the attachment or blockage of inclusions in the bore of an immersion nozzle in continuous casting of steel, particularly in continuous casting of steel containing aluminum. The present invention relates to a manufacturing method of a product, and a continuous casting immersion nozzle using the refractory material for ventilation.

A continuous casting immersion nozzle that injects molten steel from the tundish into the mold is used to prevent the molten steel from being oxidized by contact with air during injection and to prevent the molten steel from scattering. In addition, the continuous casting immersion nozzle prevents entanglement of non-metallic inclusions and mold floats into the slab by rectifying the pouring.
The continuous casting immersion nozzle is mainly composed of graphite (about 20% by mass) and aluminum oxide (50 to 70% by mass), and further composed of a material containing silicon oxide (10 to 25% by mass) and a small amount of silicon carbide. Has been. (Hereafter, also referred to as “silica-containing alumina graphite”.)
However, when casting aluminum killed steel or the like, aluminum in the steel is oxidized, and alumina (Al ₂ O ₃ ) generated thereby adheres to the inner wall of the immersion nozzle, and the immersion nozzle is likely to be blocked.
Casting of multiple castings is being promoted from the standpoint of productivity improvement, but if the immersion nozzle is clogged due to adhesion of alumina, the flow control of the molten steel becomes impossible and it becomes difficult to continue the multiple casting.
In addition, obstructions may peel off due to the flow of molten steel during casting. One of the factors that cause defects in the slab is that the peeled blockage is mixed into the molten steel in the mold and taken into the slab.

As disclosed in Patent Document 1, the following contents are known for the clogging mechanism of the silica-containing alumina graphite nozzle.
Silica in the material of the silica-containing alumina graphite nozzle is added in an amount of 10 to 30% as amorphous fused silica (SiO ₂ ), which is a low thermal expansion aggregate, in order to ensure thermal shock resistance.
However, silica easily wets the molten steel and forms a low melting point compound between the steel components such as FeO and MnO, combined with the loss of carbon into the molten steel, causing the elution of the aggregate part and causing damage. Is significantly encouraged.
In addition, SiO (g) volatilizes and disappears due to the reaction shown in the following formulas 1 to 3 in the refractory during casting (hot), creating voids on the surface of the immersion nozzle and weakening the structure. , Surface roughness is promoted, surface smoothness is lost, and deposits physically accumulate.

2C (S) + O ₂ (g) → 2CO (g) ……… Formula 1
SiC (S) + 2CO (g) → SiO ₂ (S) + 3C ( ₂ )
SiO ₂ (S) + C (S) → SiO (g) + CO (g) ……… Formula 3
Further, the products SiO (g) and CO (g) cause precipitation and generation of alumina by the reaction of the following formulas 4 to 5 in the steel, and the alumina adheres to the surface of the immersion nozzle.
3SiO (g) + 2Al → Al ₂ O ₃ (S) + 3Si (4)
3CO (g) + 2Al → Al ₂ O ₃ (S) + 3C

On the other hand, in continuous casting, there is a method in which an inert gas is continuously supplied from the inner wall of the immersion nozzle to prevent adhesion of inclusions such as alumina to the inner hole wall.
In this gas blowing method, due to the disappearance of silica due to the mechanism described above, the voids in the refractory increase and the amount increases, the gas passage resistance decreases, and the gas pressure (back pressure) decreases. It will be discharged into the molten steel as a large bubble from a small part of the refractory material for ventilation.
When the ventilation characteristics are deteriorated as described above, the effect of preventing the adhesion to the inner hole wall is also reduced.
The equipment related to gas supply and management in this gas blowing method monitors the pressure of the gas blown into the submerged nozzle. When the pressure falls below a certain level, the slab quality deteriorates. To maintain the slab quality, Casting (operation) will be stopped.
In this way, the silica component also has an undesirable function in the casting of high-grade clean steel from the viewpoint of gas aeration characteristics and the resulting deterioration in the quality of the slab. Many attempts have been made to reduce the amount or to prevent the silica from being contained.

For example, in Patent Document 2, Ar gas is blown from the stagnation part of the molten steel corresponding to the position of 10 to 80 mm above the discharge hole at the lower end of the inner hole body ventilation portion with the SiO ₂ content of the inner hole body being 5% or less, A method for preventing nozzle blockage is disclosed.
Patent Document 3 discloses a composition of a gas refractory for gas blowing for a continuous casting nozzle that does not contain silica, utilizing the properties of mesophase carbon such as viscoelasticity, crack growth prevention effect, and oxidation resistance. Has been.
When these amorphous silica contents are reduced or amorphous silica is not contained, the ventilation refractory itself is generally highly expanded as compared with a system containing silica. The stress relaxation ability of the material itself may be reduced, and the inner hole body itself or the immersion nozzle itself may be destroyed during casting, or an accident such as a hole in the ventilation material may be caused due to a decrease in molten steel wear resistance. .
Furthermore, cracks and breakage are likely to occur in the ZrO ₂ -graphitic refractory (hereinafter also referred to as “ZG”) portion in the vicinity of the powder line, where the melt thickness has progressed due to long-time casting and the remaining thickness has decreased. It is also known to have the problem of becoming. (For example, Non-Patent Document 1).
The damage accident near the powder line is mainly caused by the fact that stress is continuously generated in the refractory for ventilation and the refractory of the submerged nozzle body over a long period of time, and its relaxation ability is not sufficient.
Since accidents during casting operations as described above cause significant damage to the slab production plan to productivity and slab quality, priority is given to preventing these accidents first. However, a method for preventing accidents without containing amorphous silica has not been proposed.
For this reason, it is unavoidable to take measures such as containing a certain amount of amorphous silica for the purpose of lowering the expansion, and further containing a large amount of carbon components such as graphite that may adversely affect the steel. However, there is no satisfactory method for productivity and prevention of deterioration of slab quality in a refractory system for gas ventilation that does not contain silica.

JP 2000-42696 A JP 05-285613 A JP 05-097506 A

Iron and steel, vol. 81 (1995), P-535

  The problem to be solved by the present invention is to stabilize the air permeability during casting by suppressing the change in air permeability (lowering of back pressure) with the lapse of casting time, and to submerge the powder near the powder. An object of the present invention is to provide a refractory material that can be used for ventilation, which can prevent a damage accident during casting of the nozzle, a method for manufacturing the refractory material, and an immersion nozzle provided with the refractory material.

The refractory of the present invention relates to a refractory for ventilation, and is based on the fact that it does not contain amorphous silica particles in order to suppress or prevent the deterioration of the ventilation characteristics.
Furthermore, the refractory material for ventilation of the present invention is provided with the refractory material in order to prevent the resistance to the damage accident of the submerged nozzle body including the ZG portion from being lowered due to the absence of amorphous silica particles. The basic principle is to relieve the stress generated inside.

The fluctuation of back pressure under the condition of constant gas flow rate during casting disappears due to the reduction reaction (gasification) by the silica particles in the refractory for ventilation through which the gas passes. It is generated by increasing the passage route of the gas in the refractory by hollowing out the portion where the silica particles have disappeared.
In order to suppress or prevent the deterioration of the ventilation characteristics due to such a mechanism, there is a method in which the content of silica particles in the refractory for ventilation is reduced or not contained. However, the silica particles in the refractory for ventilation exist as amorphous silica particles for the purpose of low expansion. Such a refractory material for ventilation that does not contain low-expansion silica has a problem that the inner hole body itself or the immersion nozzle body made of the refractory material for ventilation is cracked.
As a solution to this problem other than containing amorphous silica particles, there is a method of solving the problem by adding a large amount of graphite particles. However, if a large amount of graphite particles is added, the refractory material for ventilation itself has problems such as a decrease in ventilation characteristics, wear resistance, corrosion resistance, and oxidation resistance, and a large amount of carbon elution into molten steel. The problem also arises.

  The refractory of the present invention is an alumina-graphite-based ventilation refractory that does not contain silica particles and does not contain a large amount of graphite. This solves the problems of the splitting of the submerged nozzle body and back pressure fluctuation caused by the difference in thermal expansion between the body and the submerged nozzle body. That is, it is possible to reduce the stress generated in the inner hole body and to suppress the back pressure fluctuation under a constant gas flow rate during operation.

  The present invention is the refractory described in 1 to 2 below and the immersion nozzle for continuous casting described in 3 to 4.

Flat particles having an aspect ratio of 5 or more and 50 or less are used as primary particles, and secondary particles having a length of more than 0.05 mm and 2 mm or less are formed by assembling a plurality of the primary particles with an inorganic binder. Refractory,
After the refractory was heat treated in a non-oxidizing atmosphere at 1500 ° C. for 3 hours,
The secondary particles are contained in an amount of 55% by weight to 90% by weight,
The component excluding carbon in the secondary particles is 98% by mass or more of Al ₂ O ₃ ,
As chemical components, free carbon is contained in an amount of 3% by mass to 45% by mass, SiC is contained in an amount of 1% by mass to 10% by mass, and a single compound SiO ₂ , alkali metal oxide, alkaline earth metal oxide, TiO ₂ and a total content of other components inevitable in production is 2% by mass or less.

(1)
Flat particles having an aspect ratio of 5 or more and 50 or less are used as primary particles, and secondary particles having a length of more than 0.05 mm and 2 mm or less are formed by assembling a plurality of the primary particles with an inorganic binder. Refractory,
After the refractory was heat treated in a non-oxidizing atmosphere at 1500 ° C. for 3 hours,
The secondary particles are contained in an amount of 55% by weight to 90% by weight,
The component excluding carbon in the secondary particles is 98% by mass or more of Al ₂ O ₃ ,
As chemical components, free carbon is contained in an amount of 3% by mass to 45% by mass, SiC is contained in an amount of 1% by mass to 10% by mass, and a single compound SiO ₂ , alkali metal oxide, alkaline earth metal oxide, TiO ₂ and a total content of other components inevitable in production is 2% by mass or less.

(2)
The apparent porosity after heat-treating refractory for 3 hours in non-oxidizing atmosphere at 1500 ° C. Maximum stress generated during heating of refractory from room temperature to 1500 ° C under restraint conditions in non-oxidizing atmosphere The refractory according to (1) above, wherein the value is 18 MPa or less.

(3)
As chemical components after heat treatment in a non-oxidizing atmosphere at 1500 ° C. for 3 hours, Al ₂ O ₃ is 54 mass% to 90 mass%, free carbon is 3 mass% to 45 mass%, and SiC is 1 mass% or more. Refractory containing 10% by mass or less and having a total content of SiO ₂ , alkali metal oxides, alkaline earth metal oxides, TiO ₂ , and other components inevitable in production, of 2% by mass or less. A mixing step in which an inorganic binder is added to a powder of primary particles of flat alumina and kneaded, and the resulting mixture is kneaded to form secondary particles that are aggregates of primary particles. A granulating step for forming a granulated product, a classification step for classifying the obtained granulated product into a plurality of secondary particles having a length of more than 0.05 mm and not more than 2 mm, and a plurality of obtained secondary The particles are used as a raw material for Al ₂ O ₃ component, A compounding raw material for forming SiC, and a compounding raw material for forming free carbon, together with a binder, kneading to obtain a forming soil for forming, and CIP forming the above-mentioned soil. A CIP molding step and a firing step of firing the resulting molded product, and in the mixing step, the components excluding carbon of the secondary particles produced in the granulation step are 98 mass% or more of Al ₂ O ₃ The inorganic binder is added so that the plurality of secondary particles are present in a proportion of 55% by mass or more and 90% by mass or less in the molding soil in the forming earth forming step. A method for producing a refractory, characterized by being formulated as follows.

  (4) An immersion nozzle for continuous casting in which the refractory according to (1) or (2) is disposed as at least a part of a surface in contact with molten steel, the refractory layer and a backside thereof A space through which gas can pass is arranged between the continuous casting immersion nozzle body and the refractory, and the space is a gas introduction hole for communicating with a gas supply facility outside the continuous casting immersion nozzle. An immersion nozzle for continuous casting, characterized by communicating with

  (5) The region where the refractory according to (1) or (2) above is disposed is a part or all of the wall surface of the straight barrel portion on the inner hole side of the continuous casting immersion nozzle, or the inner wall surface of the discharge hole. The immersion nozzle for continuous casting according to the above (4), which is a region including one or more of some or all of them.

  In the present invention, “free carbon” refers to carbon other than compounds, and specifically, graphite, carbon black, carbon having a binding function (for example, carbon remaining from resin, pitch, etc.) and the like. .

By applying the refractory, the refractory manufacturing method, and the immersion nozzle of the present invention, it is possible to stabilize the ventilation characteristics during casting by suppressing changes in the ventilation characteristics (reduction of back pressure) with the lapse of casting time. it can. In addition, it is possible to prevent damage accidents during casting of the immersion nozzle, such as breakage near the powder part.
As a result, the casting time intended for the continuous casting operation is not hindered, that is, it is possible to suppress the decrease in productivity and the deterioration of the quality of the slab.

Image of flat (plate) alumina SEM photo of flat (plate) alumina Particle size distribution of flat (plate-like) alumina used in Examples (Nippon Light Metal Co., Ltd., “A21” example) SEM photograph of secondary particles SEM photograph of secondary particles (enlarged about 5 times that of Fig. 4) EPMA photo illustrating the refractory structure of the present invention Image of the generated stress measurement device Example of immersion nozzle provided with the refractory of the present invention An example of an immersion nozzle in which the refractory material of the present invention is also disposed in the column next to the discharge hole Example of immersion nozzle in which the refractory of the present invention is also provided around the discharge hole

  Hereinafter, embodiments of the refractory according to the present invention will be described in detail including actions and the like.

The refractory of the present invention contains Al ₂ O ₃ component, C component, SiC component, does not contain SiO ₂ as a component that volatilizes or disappears (except for inevitable impurities mixed in the manufacturing process), and is continuously cast. The first feature is that the main structure is a structure having a space for allowing a sufficient amount of gas to pass through the nozzle.
It does not contain SiO ₂ as a component that volatilizes or disappears, for example, in a reducing atmosphere and at a high temperature, such as an immersion nozzle used for continuous casting operations, other than in the form of a compound with other components such as Al ₂ O _3. It means that it contains almost no particles composed of SiO ₂ components, such as amorphous silica (fused silica particles, etc.), which is reduced and volatilized in the region. When SiO ₂ is in the form of a compound with Al ₂ O ₃ , for example, when it is contained as mullite mineral particles, this SiO ₂ component will not volatilize or disappear.
Such a tissue structure itself also has a certain stress relaxation function due to a large amount of space. However, in the case where such a structure exists integrally or continuously in the entire refractory material, it may not contain low-expansion fused silica that is generally included for the purpose of lowering the thermal expansion, so that the refractory There is a high possibility that the crack resistance of the product will be reduced.
Therefore, the present invention provides a graphite or carbon bond in which the structure is formed as a single structure having a length of more than 0.05 mm and not more than 2 mm, that is, secondary particles are formed and stress relaxation is provided between the secondary particles. The presence of a structure, etc. ensures crack resistance as a refractory and also ensures corrosion resistance and infiltration resistance against molten steel or slag components derived from molten steel. Furthermore, the structure of the tissue having many spaces, that is, the primary particles are flat (substantially synonymous with plate shape).
The structure formed by the aggregation of a plurality of primary particles, which are flat single particles like this, is a structure that is irregularly oriented in many directions without being oriented in a certain direction, and complicatedly entangled with each other. It is preferable for increasing the stress dispersion effect and obtaining uniformity and stability of mechanical properties.
Even within the secondary particles of the present invention, the aggregate of primary particles has the above-mentioned structure, and the primary particles have a complex structure including a plurality of irregularly joined or overlapping layers. Many spaces are also formed between the primary particles (FIGS. 4 and 5). This complex structure including many spaces also plays a role in relieving the stress generated in the secondary particles.

A single particle that is a general alumina aggregate, in other words, regardless of whether the outer surface is a polygon or a shape that is close to a curved surface to a sphere, when expressed in terms of an aspect ratio, it is a monolithic alumina particle of around 1 In the case of, the inside of this single particle is dense and has almost no deformability or stress relaxation ability.
Compared to this, the secondary particles of the present invention are capable of flexibly deforming or moving between primary particles with respect to external force, and thereby have a high ability to relieve stress generated in the secondary particles.
The secondary particles are preferably more than 0.05 mm and 2 mm or less, and are as close to spherical as possible from the viewpoints of stress relaxation ability, filling properties, tissue uniformity, and the like.
The reason why the size of the secondary particles is more than 0.05 mm and 2 mm or less is to obtain a uniform refractory structure with few defects. The structural structure of the secondary particles has a great influence on the stress relaxation characteristics and ventilation characteristics of the refractory according to the present invention. Therefore, it is important to disperse these secondary particles with increasing uniformity throughout the refractory. If the size of the secondary particles is larger than 2 mm, this uniformity is reduced and local damage to the refractory tends to occur. When the size of the secondary particles is 0.05 mm or less, it is difficult to obtain a secondary particle structure ideally having a composite structure including a layered structure in which a plurality of primary particles are joined at irregular points or overlapped. As a result, secondary particles with a small void ratio and poor air permeability of a dense structure are likely to be formed.

  Another reason is to obtain a uniform refractory structure by preventing segregation and the like when filling the mold when CIP (Cold Isostatic Press) molding is performed as a layer on the inner hole side of the immersion nozzle. But there is. If the size of the secondary particles is less than 0.05 mm, it becomes a non-uniform structure as described above, so that the molded body is liable to crack, and if it exceeds 2 mm, segregation increases and the structure is non-uniform. It tends to occur and may cause destruction of the layer itself.

The shape of the flat single particle, which is the primary particle relative to the secondary particle, preferably has a maximum length of about ½ or less of the size of the secondary particle, more preferably about ¼ or less. preferable. The reason for this is that in order to obtain an ideal structure in which the primary particles are entangled randomly in multiple directions in the secondary particles and have a large number of bonding points, It is necessary to make the maximum length small so as not to divide the interior space of the next particle greatly. For this purpose, when the secondary particle is regarded as a sphere, the maximum length of the primary particle needs to be geometrically about ½ or less of the diameter of the sphere. Even when the diameter is about ½ or less of the diameter of the sphere, depending on the position within the sphere, the internal space is likely to be largely divided, so it is more preferably about ¼ or less. If it is about 1/4 or less, the probability of dividing the internal space significantly decreases.
Considering such geometric factors, the size of the primary particles of the refractory according to the present invention, that is, the maximum length is preferably 1 mm or less, and more preferably 0.5 mm or less.
The minimum length need not be a specific value. However, as the size of the flat particles becomes smaller, the action due to the flat shape decreases and the behavior becomes almost spherical, so the porosity of the secondary particles set according to the use conditions etc. In order to adjust the pore diameter, strength, etc. to an arbitrary range, the minimum size and content may be appropriately adjusted.
The film thickness around the primary particles formed by the inorganic binder that binds the primary particles in the secondary particles varies depending on the properties of the inorganic binder, the manufacturing method of the secondary particles, etc. In order to increase the aspect ratio of the primary particles including the coating to 5 or more, the minimum length of the primary particles needs to be 10 times or more the coating thickness of the inorganic binder.
In the present invention, when the minimum size is up to about 1 μm, it has been confirmed that the effect of the present invention can be obtained while maintaining the aspect ratio of the primary particles including the inorganic binder coating film at 5 or more.

Here, the maximum lengths of the primary particles and the secondary particles are based on a method based on JIS Z 8815 “General Rules for Screening Test Methods” and JIS Z 8801-1 “Sieving for Testing—Part 1: Metal Mesh Screen”.
For example, when the primary particle exceeds 1 μm and is 1 mm or less, it does not pass through a 1 μm opening (such as a sieve; a wet classification method can also be used), and passes through a 1 mm opening (such as a sieve). The size corresponding to the size. Also, for example, when the secondary particle is larger than 0.05 mm and not larger than 2 mm, the opening does not pass through a 0.05 mm mesh (such as a sieve) and the opening passes through a 2 mm mesh (such as a sieve). , Meaning.

  The flatness of the primary particles needs to be a plate shape having an aspect ratio of 5 to 50.

Here, the aspect ratio of 5 to 50 means that the maximum length of each single particle (a in FIG. 1) and the plate-like plane are substantially perpendicular to each other (hereinafter referred to as “thickness”). The ratio of the minimum portion to the minimum portion (b in FIG. 1).
In other words, the shape of a flat particle is composed of these three elements, where the planar part is “length” × “width” and the length in the direction substantially perpendicular to the planar part is “thickness”. The aspect ratio is the ratio of length / thickness.
In the production of the refractory according to the present invention, the maximum length and aspect ratio may be obtained by using raw materials that have been manufactured and sized in advance so that the maximum length is 1 mm or less and the aspect ratio is 5 or more and 50 or less.

The basic feature of the present invention is that flat alumina having this feature is used as primary particles.
Moreover, this primary particles and aggregates consisting of the inorganic binder, Al ₂ O ₃ consists of more than 98 wt% as chemical components.

In the above-mentioned secondary particles in the refractory of the present invention, the component excluding carbon in the secondary particles, that is, the total component of the primary particles and the inorganic binder (except for carbon) for making them an aggregate is 1500. By maintaining 98% by mass or more as Al ₂ O ₃ in the refractory after heat treatment in a non-oxidizing atmosphere at 3 ° C., while maintaining the original shape of the primary particles without causing excessive softening or melting, It becomes possible to maintain the stress relaxation ability and gas passage ability inside the secondary particles. When Al ₂ O ₃ is 98% by mass or more, reaction with inclusions in the molten steel is unlikely to occur, so that melting or wear due to such reaction is unlikely to occur.

The reason for this is that alumina having a purity of 98% by mass or more, that is, corundum (α-Al ₂ O ₃ ) is used as the primary particles, and the hardness and strength of the corundum itself is extremely large, and the components derived from the molten steel are This is because the main component is alumina, so there is little possibility of a reaction that causes softening or melting. Depending on the types of components other than Al ₂ O ₃ , there is a risk of causing or increasing melting damage due to reaction with inclusions and deposits derived from molten steel. For example, primary particles and inorganic binders may contain Al ₂ O _{When a} large amount of SiO ₂ component that is not a compound with No. 3 is included, mineral changes such as mullite formation occur during use (hot), and the primary particles or secondary particles themselves expand greatly, reducing the stress relaxation function. Or destroy the refractory itself.
The purity of Al ₂ O ₃ composed of corundum as the primary particle and inorganic binder component is 98% by mass or more to prevent disappearance in a reducing atmosphere or deterioration of the refractory structure observed in the silica component. It also leads to things.
In addition, although it is flat, low alumina purity, for example, so-called clay minerals such as β-Al ₂ O ₃ , mica, etc., softening or melting occurs hot, and corrosion resistance, wear resistance, etc. are extremely low. Therefore, it cannot be adopted as a refractory component for a continuous casting nozzle.

  The flat alumina single particles as the primary particles can be produced by, for example, the Bayer method.

In addition, the flat alumina single particles, which are the primary particles, may be commercially available products. For example, trade names “A11” and “A21” manufactured by Nippon Light Metal Co., Ltd., manufactured by Kinsei Matech Corporation. The product name “Seraph” can be used. The former product is a corundum material (α-Al ₂ O ₃ ) having a length of about 1 μm to 300 μm or less, an aspect ratio of 5 to 50 and a chemical composition of Al ₂ O _{3 of} 98% by mass or more. Satisfy the requirements for flat alumina primary particles.

As an inorganic binder that binds primary particles, shape retention ability should be provided after heat treatment at about 1000 ° C or higher, and it should be strong enough to withstand the stress and external force during use as an immersion nozzle. It is possible to use various inorganic solutions, emulsions, suspensions, etc., such as alumina sol. Among these, alumina sol is preferable because it has high strength development ability, high dispersibility, and does not generate a low-melting material with primary particles.
In addition, for example, SiO ₂ inorganic binders such as silica sol and silicate can be used. In these cases, Al ₂ O ₃ is used as a component of the total amount of primary particles and inorganic binder. It is necessary to adjust the amount of use so that it may become 98 mass% or more.

  The secondary particles of the present invention do not actively contain a carbon component. When forming the refractory of the present invention by covering the secondary particles with an organic binder, the organic binder, fine carbon particles, etc. may permeate or adhere into the secondary particles. The carbon component present is derived from such carbon. Such a carbon amount and existence form in the secondary particles do not affect the effect of the present invention. Therefore, the secondary particles of the present invention specify components other than carbon.

The refractory material of the present invention is affected by the stress generated by the flow and discharge of gas accompanying ventilation, and mechanical external force such as impact of molten steel flow when it is installed in the immersion nozzle bore. Also affected by. Further, the refractory of the present invention may be exposed to an environment in which melting damage or the like is likely to occur due to reaction with molten steel or inclusions derived from molten steel.
Therefore, in order to obtain a refractory having necessary and sufficient durability even under such conditions, the secondary particles are contained in the refractory by 55 to 90% by mass. When the amount is less than 55% by mass, the properties of the matrix structure other than the secondary particles are dominant with respect to the properties of the entire refractory, and the stress relaxation ability and air permeability characteristics of the secondary particles are reduced. When it exceeds 90% by mass, the matrix structure other than the secondary particles becomes relatively small, the bonding function between the secondary particles in the matrix structure is lowered, the strength as a refractory is insufficient, or the wear resistance is lowered. There is a risk of coming.

In order to make the content of secondary particles within the scope of the present invention, when producing the refractory of the present invention, the refractory component after heat-treating the previously produced secondary particles in a non-oxidizing atmosphere at about 1500 ° C. Among them, the secondary particles may be blended so that the mass ratio of the secondary particles is 55% by mass or more and 90% by mass or less with respect to other components.
The content of secondary particles is such that the refractory is heated at 600 ° C. in an oxidizing atmosphere and decarburized (the carbon material and the carbon derived from the binder are removed so that the bonds are lost and the particles return to the state of particles. ), Separating the alumina secondary particles and silicon carbide with a color sorter, measuring the weight of the secondary particles, and subtracting the weight of the lost carbon and silicon carbide from the initial sample weight. You can also.

In addition, the content of Al ₂ O ₃ in the components excluding carbon in the secondary particles is determined by using JIS R2216 “Refractory Products It can be measured according to the “X-ray fluorescence analysis method”.

  The chemical composition of the refractory according to the present invention is a value measured by a method in accordance with JIS R2216 “Fluorescence X-ray analysis method for refractory products” of the sample after reducing and firing the refractory at 1500 ° C. for 3 hours. . This is because the refractory of the present invention used for casting molten steel at about 1500 ° C. needs to be evaluated based on the state during the casting. The continuous casting immersion nozzle or the like provided with the refractory according to the present invention undergoes a heat treatment at about 1100 ° C. or less when it is put into operation as a product. This heat treatment temperature is different from the chemical component in the state of being subjected to the heat treatment at about 1500 ° C., which is in the casting state, because the change of the component contained in the refractory is not completed.

The Al ₂ O ₃ content in the refractory according to the present invention is substantially determined by the content ratio of secondary particles. That is, this corresponds to the necessary amount of the secondary particles described above, and almost coincides with the value converted into the Al ₂ O ₃ content of the secondary particles.
In addition, 54% by mass of Al ₂ O ₃ in the whole refractory (rounded to the value obtained by multiplying the lower limit of 98% by mass of the Al ₂ O ₃ component amount of the secondary particles by the lower limit of 55% by mass of the secondary particle content. If the value is less than the above value), the carbon substrate material is increased instead of Al ₂ O ₃ , but in that case, there is a problem that wear resistance, corrosion resistance, etc. are likely to be lowered.
In such a case, Al ₂ O ₃ as corundum is included outside the secondary particles, that is, in the matrix structure of the refractory, for the purpose of meeting the operating conditions or the required properties such as corrosion resistance and wear resistance. Also good. In other words, the amount of the Al ₂ O ₃ component in the refractory according to the present invention can be the balance with respect to the total value of SiC, free carbon, and components that are unavoidable in production.

The refractory contains 1 mass% or more and 10 mass% or less of SiC. SiC is mainly
1. Prevents oxidation of carbon substrate material as free carbon (hereinafter simply referred to as “antioxidation function”).
2. To improve the wear resistance of the refractory against the molten steel flow (hereinafter simply referred to as “wear resistance improving function”),
To play a role.
When SiC is less than 1% by mass, the carbon matrix material has insufficient anti-oxidation function and wear resistance improving function, ie, partial oxidation of the carbon matrix material in the refractory and partial wear of the refractory structure. This may cause collapse of the refractory layer of the present invention.
SiC is distributed in the bonded carbon in the refractory structure or in contact with the carbon matrix material so as to reinforce the bonding function and the carbon matrix material itself. When SiC is less than 1% by mass, the non-uniformity of the distribution state increases, and there is a possibility that a site where SiC does not exist is generated with respect to the carbon substrate material.
Oxidation of refractories is mainly caused by high-temperature air (oxygen gas) during preheating and oxidizing inclusions such as FeO derived from molten steel during casting. Precedes. Then, tissue collapse occurs from the weakened part of the bond function.
Moreover, when SiC exceeds 10 mass%, SiC itself will oxidize to become SiO and SiO ₂ , and the SiO ₂ reacts with Al ₂ O _{3 and the} like in the refractory to produce new minerals to form the refractory. There is a risk of expansion and destruction, and there is a risk of causing Al ₂ O ₃ and molten steel-derived oxides and low melts in the refractory to cause softening of the refractory layer, deterioration of corrosion resistance, destruction, etc. There is. Furthermore, especially when there is a relatively large amount of secondary SiC (which does not exist as a raw material and refers to SiC formed during heat treatment), the number of hard (high elastic modulus) bonded portions increases, resulting in improved thermal shock resistance and resistance. There is a possibility that the splitting property is lowered.

Free carbon is contained in an amount of 3% by mass to 45% by mass, which is the amount of necessary components such as Al ₂ O ₃ and SiC, and the content of the inevitable components (described later) as the balance. In the present invention, the carbon matrix material is a bond carbon mainly responsible for bonding between secondary particles, and is present in a state where it is mixed with bond carbon mainly between secondary particles and has a maximum particle size of about 500 μm or less having stress relaxation ability. Graphite, amorphous fine particles (maximum particle size of about 0.5 μm or less), so-called carbon black, and the like. Here, the carbon having a binding function needs to contain 3% by mass or more in order to form or maintain a refractory structure. When free carbon exceeds 45 mass%, there exists a possibility that abrasion resistance and corrosion resistance may fall. The cause of this is thought to be the disappearance of chemical reaction due to mechanical wear and wear due to the low hardness of the carbon component, oxidation, and elution into the molten steel.
Free carbon is measured by a method based on JIS R2011 “Method for chemical analysis of refractories containing carbonized and silicon carbide”.

In addition to the above, the refractory of the present invention may contain a single compound of SiO ₂ , alkali metal oxide, alkaline earth metal oxide, TiO ₂ , and other components inevitable in production. The total content of these inevitable components must be 2% by mass or less. If it exceeds 2% by mass, particularly in the region where the carbon substrate material is near the lower limit, the bond strength of the refractory is lowered, or a reaction occurs between Al ₂ O ₃ in the secondary particles, that is, the primary particles. , There is a risk of causing sintering of primary particles, formation of a low-melting material, or partial collapse of the secondary particle structure.
Here, the SiO ₂ of a single compound in the present invention is a SiO ₂ containing only Si as metal elements such as amorphous silica, SiO ₂ compound containing a metal element other than Si, such as mullite (complex It is distinguished from the compound SiO ₂ ).
Further, SiO ₂ content of a single compound in the component except for the carbon in the secondary particles may be evaluated by the following methods.
First, as described in the method for calculating the content of secondary particles described above, the refractory is heated at 600 ° C. in an oxidizing atmosphere to decarburize it, and then the secondary particles of alumina are processed by a color sorter. And silicon carbide. Thereafter, in the secondary particles after the separation, the total amount of SiO ₂ is measured according to JIS R2216 “Fluorescence X-ray analysis method for refractory products” using a standard sample of the refractory technical association. Next, the amount of mullite is quantified by powder X-ray diffraction by the Rietveld method, and the amount of SiO _{2 in} mullite is measured from the stoichiometric ratio based on the numerical value. Finally, a numerical value obtained by subtracting the amount of SiO _{2 in} mullite calculated from powder X-ray diffraction from the total amount of SiO ₂ determined by fluorescent X-rays is identified as the amount of SiO ₂ of a single compound. If it contains SiO ₂ in other complex compounds other than mullite measures the amount of SiO ₂ in these complex compounds, likewise, is identified from the total amount of SiO ₂ is also pulled the SiO ₂ amount.

The refractory material of the present invention includes a single compound SiO ₂ , that is, SiO that volatilizes in a reducing atmosphere and in a high temperature range other than a form as a compound with other components such as amorphous silica. _Since almost no _two components are contained, there is almost no variation in the air permeability characteristics with the lapse of casting time. In addition, since SiO ₂ in the composite compound such as mullite is bonded to other components, even if it is contained in a small amount, it is difficult to volatilize and hardly changes the air permeability.

However, even in such a system, if the apparent porosity, that is, the value corresponding to the volume ratio of open pores is extremely low or extremely high, the ventilation characteristics set according to the individual operating conditions. It may be difficult to obtain. The ventilation characteristics are determined by many factors such as individual operating conditions, that is, the size of the equipment, the casting speed, the amount and speed of gas to be introduced, the pressure of the gas, the area of the portion to be vented of the immersion nozzle, and the like. Thus, it should be changed according to individual conditions, and the porosity of the refractory is an element that can be changed according to these conditions.
For this reason, the problem cannot be solved unless the porosity of the refractory is in a specific range, and it is reasonable to show a preferable range in consideration of general operating conditions.
The refractory according to the present invention preferably has an apparent porosity of 30% or more and 50% or less according to the method of JIS R2205 after heat treatment in a non-oxidizing atmosphere at 1500 ° C. for 3 hours.
If the apparent porosity is less than 30%, the back pressure tends to increase and the ventilation rate tends to decrease. If the apparent porosity exceeds 50%, the back pressure decreases greatly and the ventilation rate is too high. In addition, the discharge gas in the molten steel tends to be non-uniform because the size of the discharged gas becomes large.

The refractory according to the present invention may further be characterized by being able to suppress the generated stress during the heat.
Specifically, the maximum generated stress value during heating of the refractory from room temperature to 1500 ° C. under a restraint condition in a non-oxidizing atmosphere is 18 MPa or less.
The method for measuring the generated stress is as follows.
The refractory is formed or cut into a cylindrical shape having a diameter of 30 mm and a height of 30 mm to obtain a measurement sample. A carbon plate is placed on the upper and lower surfaces of the sample, and a carbon rod connected to a stress measuring device is placed on the carbon plate with a thickness of 0. A load of 2 MPa is applied. In this state, the maximum stress value generated when the temperature is raised from room temperature to 1500 ° C. at a rate of temperature rise of 5 ° C./min in an N 2 gas atmosphere is measured.
The refractory of the present invention has a maximum generated stress value of 18 MPa or less by this measuring method. The present inventors have found that destruction of the refractory does not occur when the maximum generated stress value is 18 MPa or less (see Example A below).

Next, a method for producing the refractory according to the present invention and a method for producing an immersion nozzle provided with the refractory according to the present invention will be described.
The refractory of the present invention can be obtained according to a general method for manufacturing an immersion nozzle including the following steps.
1. Mixing step: For example, primary particles of flat alumina having a purity of 98% by mass or more are mixed with an appropriate amount of an inorganic binder, and uniformly mixed using a mixing apparatus that applies as little shearing force as possible.
In this mixing, it is preferable that an inorganic binder is gradually added to the weighed primary particle powder to uniformly disperse the inorganic binder around the primary particles without segregation.
As the inorganic binder, an alumina sol or the like that remains with Al ₂ O ₃ as a main component after heating at about 1000 ° C. or higher is preferable.
Also, in this step, the type and amount of the inorganic binder are adjusted so that the components excluding carbon in the secondary particles produced in the following granulation step are 98% by mass or more of Al ₂ O _3. Add.
2. Granulation step: The mixture obtained in the blending step is kneaded with a kneading apparatus having a granulation function such as rotating and flowing, and the mixture is granulated into particles, that is, an aggregate of primary particles. Some secondary particles are formed.
In this granulation step, it is preferable to adjust the secondary porosity so that the apparent porosity according to the method of JIS R2205 is 40% or more and 80% or less. This is because the above-mentioned structure inside the secondary particles can be maintained without collapsing even after a pressure treatment such as CIP molding. The range of the apparent porosity of the secondary particles can be appropriately adjusted according to the pressure during CIP molding, the arrangement structure of the refractory of the present invention in the nozzle, and the like.
The apparent porosity of the secondary particles can be adjusted by adding the ratio of the primary particles to the inorganic binder or adding a solvent that dissolves the inorganic binder by heat treatment such as water, and the flow velocity in the mixing device and kneading device. Or by changing / adjusting the flow form (stirring method).
3. Classification step: The granulated product obtained in the granulation step is classified into a plurality of secondary particles (secondary particle group) having a length of more than 0.05 mm and 2 mm or less. As a specific means, for example, sieving may be performed, and the granulated product is sieved with a 2 mm sieve, and the bottom of the sieve is collected, and the collected material is sieved with a 0.05 mm sieve. By collecting the top, secondary particles having a size of more than 0.05 mm and 2 mm or less can be obtained.
4). Forming step for forming earth: The secondary particle group obtained in the classification step is used as a raw material of Al ₂ O ₃ component, and further, a raw material of SiC component, a raw material of free carbon (particulate carbon Mix with substrate material, eg graphite. Moreover, you may add the other raw material which does not inhibit the effect of the subject solution of this invention as needed.
Part or all of SiC is converted into the mass when SiO ₂ having a maximum particle size of about 10 μm or less, or metal Si or the like is converted into SiC, and 1 in the refractory after reduction firing at 1500 ° C. for 3 hours. You may add so that it may become content of 10 mass% or less of the mass%.
SiO ₂ with a maximum particle size of 10 μm or less is reduced by carbon materials such as graphite or carbon derived from binders in the refractory, and the reaction of SiO ₂ + 3C = SiC + 2CO proceeds to produce secondary SiC that is a stable condensed phase. Therefore, there is no problem because SiO ₂ having a small particle diameter is blended with the raw material in this way because almost no single compound SiO ₂ remains in the refractory after reduction firing at 1500 ° C. for 3 hours. Similarly, metal Si reacts with carbon derived from a carbon raw material such as graphite or carbon derived from a binder in a refractory material to generate secondary SiC which is a stable condensed phase.
Then, an organic binder such as phenol resin or pitch, which can form a carbon bond after heat treatment, is added to these blends and kneaded to obtain a molding clay.
Further, in this step, the secondary particles are present in the molding soil in a proportion of 55% by mass or more and 90% by mass or less in the refractory after heat treatment in a non-oxidizing atmosphere at 1500 ° C. for 3 hours. Formulate as follows.
5. CIP molding process: Fills the space in the mold for CIP molding with the organic partition plate used as the gas passage path and the soil to be the main body from the soil obtained by the molding soil generation process. And press-mold.
The conditions such as the molding pressure can be optimally set according to the individual conditions in order to obtain the shape and structure of the immersion nozzle, the physical properties required of the set refractory layer or molded body, and the like.
6). Firing step: The molded body obtained by the CIP molding step is subjected to a predetermined heat treatment (firing treatment) at a temperature of 800 ° C. to 1200 ° C., for example, and then the gas introduction hole and its joining structure are installed, and surface grinding is performed.・ Processing such as application of antioxidants.

The case where the refractory according to the present invention is disposed in the inner hole of the immersion nozzle as a refractory layer for ventilation will be described below with reference to FIGS.
A gas introduction hole 16 for communicating with a gas supply facility (not shown) communicates between the 13 layers of the refractory material for ventilation which is the refractory material of the present invention and the refractory material of the immersion nozzle body behind the refractory material. A space (gas passage 14) through which gas can pass is disposed. The gas is supplied from this space to the refractory 13 layer of the present invention, passes through this layer, and is discharged from the inner hole surface of the immersion nozzle into the molten steel. Further, a zirconia-graphite refractory 15 is disposed at a site in contact with the powder outside the gas passage 14.
One of the factors to be considered in determining the arrangement area as this layer is prevention of inclusions such as alumina derived from molten steel on the surface of the immersion nozzle in contact with the molten steel.
Since the state and degree of such inclusions attached depend on the specifications of the individual operating equipment, the type of molten steel to be cast, the operating method, etc., the region where the ventilated refractory 13 of the present invention is disposed in the immersion nozzle. The methods and methods need to be optimized according to the conditions and circumstances of each operation.

The refractory 13 of the present invention is disposed as a layer on at least a part of the surface of the continuous casting immersion nozzle that contacts the molten steel. Further, the region to be disposed is a region including one or more of the wall surface of the straight barrel part on the inner hole side of the immersion nozzle for continuous casting, or part or all of the inner wall surface of the discharge hole 23. Can do.
That is, when it is necessary to dispose the ventilation refractory 13 of the present invention in an area where inclusions are likely to adhere, the refractory 13 of the present invention is set to an optimum area according to the individual adhesion situation. Can do.
In addition to the above-described regions, they may be disposed at the bottom (the discharge hole periphery 22, etc.). In this case, the column part 21 beside the discharge hole may be provided.

Since the vertical length of the portion to be arranged in the region below the submerged nozzle from the general meniscus is about 100 mm or more, the vertical fire length of the present invention is not necessary for this vertical length. Considering the strength of the object, in such a case, if the thickness of the layer is less than 5 mm, the layer itself tends to crack or peel off.
On the other hand, as the gas passage from the gas introduction hole becomes longer, the amount of gas flowing out from that position tends to decrease gradually. In particular, when the length of a general immersion nozzle inner hole straight body portion is about 400 mm or more, this tendency becomes remarkable when the thickness of the refractory layer for ventilation exceeds 15 mm.
Therefore, it is preferable to arrange the ventilation refractory according to the present invention as a layer having a thickness of 5 mm or more and 15 mm or less (see FIGS. 8 to 10).

  Next, the refractory and continuous casting nozzle of the present invention will be described with reference to examples.

[Example A]
Example A is an example in which the influence of the primary particles and the chemical components of the inorganic binder on the refractory of the present invention was investigated.
As the flat (plate-like) primary particles, “A21” manufactured by Nippon Light Metal Co., Ltd. was used. The primary particles are made of corundum having an Al ₂ O ₃ purity of 98% by mass or more, and the particle size is measured by a laser diffraction method in the range of about 1 μm to 262 μm, and the average value is about 80 μm (the particle size shown in FIG. 3). The aspect ratio is 5 or more and 50 or less.
Since it is difficult to adjust the Al ₂ O ₃ purity itself of flat alumina particles, wherein the By combining the β-Al ₂ O ₃ in the flat alumina particles of the present invention, Al ₂ O as a refractory ₃ content was adjusted. The flat alumina particles were subjected to a test with a relatively high purity (99% by mass) product and a normal product (98% by mass) by sorting.
The primary particles were produced according to the above production method using alumina sol as an inorganic binder. This was dried at 110 ° C. to remove moisture, and then classified with a predetermined sieve according to each of the following examples to obtain secondary particles. The above-mentioned secondary particles are mixed with raw material particles such as silica powder and metal silicon powder according to each of the following examples, and carbonaceous raw materials such as scaly graphite and carbon black, and carbon bonds are bonded to the mixture after heat treatment. While adding the phenol resin to be formed, kneading was performed to obtain a molding earth.
This soil is formed into a cylindrical shape with an outer diameter of 150 mm, an inner diameter of 50 mm, and a height of 300 mm by CIP generally used for forming a casting nozzle, and is subjected to drying treatment and heat treatment in a nitrogen atmosphere having a maximum temperature of about 1000 ° C. A sample was obtained by performing a baking treatment.

The effects of the present invention for each example were evaluated relative to the typical refractories according to the prior art with respect to the rate of change in ventilation characteristics, the generated stress, the wear resistance, and the corrosion resistance.
Specifically, the rate of change in ventilation characteristics is an item relating to the main problem of the present invention, and indicates the degree of the back pressure reduction phenomenon. The refractory according to the present invention is required to have a remarkably superior ventilation characteristic change rate as compared with the refractory according to the prior art.
Even if good results are obtained regarding the rate of change in ventilation characteristics, the conditions that can be used for operation are resistance to destruction, wear, and erosion. Based on the relative or better than the refractory by. With respect to these evaluations, an example in which characteristics comparable to those of the prior art were recognized was used as a refractory (accepted example) that recognized the effect of the present invention.
The comparative examples used as criteria for judging the effects were all selected from refractories according to the prior art that are regularly operated. With respect to the rate of change in air permeability and resistance to breakage and abrasion, Comparative Example 1 shown in Table 1 containing 10% by mass of amorphous silica (fused silica) was used. Regarding resistance to erosion, Comparative Example 2 shown in Table 1 containing 19% by mass of amorphous silica (fused silica) was used.

These evaluation methods and criteria are as follows.
The rate of change in aeration characteristics is a test method disclosed in Japanese Patent Application Laid-Open No. 2010-112945 for measuring a change in gas back pressure between refractories during heat. In summary, the following steps 1 to 4 are included. Is the method. 1. 1. Place the refractory of the example or comparative example on a part of the tube wall of the tubular sample body whose upper and lower ends are closed and have a hollow portion inside; 2. immerse this refractory in a molten metal bath; 3. Gas is introduced into the hollow part of the sample body while controlling the temperature (1500 ° C) of the molten metal bath by high frequency heating. Gas is blown into the molten metal bath from the outer peripheral surface of the refractory disposed on the tube wall of the sample body.
The rate of change in ventilation characteristics is the value of the rate of change of back pressure per unit time obtained by dividing the value obtained by subtracting the minimum back pressure from the maximum back pressure with the gas flow rate constant, by the gas flow (test) time (3 hours). And The smaller the rate of change, the less the back pressure is reduced during casting and the better the airflow stability. This rate of change in ventilation characteristics was evaluated by an index where the rate of change in ventilation characteristics of Comparative Example 1 was set to 100, and an example in which the effect of the present invention was observed was an example in which the rate of change was significantly lower than this.
Regarding resistance to fracture, relative values of the generated stress, specifically, the maximum generated stress value during the temperature rise of the refractory from room temperature to 1500 ° C under the restraint condition of non-oxidizing atmosphere, are relatively evaluated. did.
The method for measuring the maximum generated stress value is as follows.
The refractory is formed or cut into a cylindrical shape having a diameter of 30 mm and a height of 30 mm to obtain a measurement sample. A carbon plate is placed on the upper and lower surfaces of the sample, and a carbon rod connected to a stress measuring device is placed on the carbon plate with a thickness of 0. A load of 2 MPa is applied. In this state, the maximum stress value generated when the temperature is raised from room temperature to 1500 ° C. at a rate of temperature rise of 5 ° C./min in an N 2 gas atmosphere is measured.
An example in which the maximum generated stress value of Comparative Example 1 by this measuring method is 18 MPa and the maximum generated stress value is 18 MPa or less was set as the acceptable range of the refractory of the present invention.
Wear resistance, which is the resistance to abrasion, is determined by immersing a 50 x 80 x 25 mm sample in pig iron (1500 ° C) melted in a high-frequency induction furnace and applying a thermal load, and then performing a wear test by the BS method. The measured value of the amount of wear was relatively evaluated.
The amount of wear in Comparative Example 1 is taken as an index of 100, <98 (98 is an index of Comparative Example 2): ◎ (with improvement effect), 98 to 100: ◯ (equivalent to conventional technology),> 100: × (conventional technology) It was evaluated as inferior).
Corrosion resistance, which is resistance to erosion, is the addition of FeO slag as an erosion material in a high-frequency induction furnace (2% with respect to molten steel) and molten steel at 1550 ° C. The maximum erosion dimension after immersion was measured. The maximum erosion dimension of Comparative Example 2 is set to 100, <86 (86 is an index of Comparative Example 1): ◎ (there is an improvement effect), 86 to 100: ○ (equivalent to the prior art),> 100: × (conventional Inferior to technology).
As a comprehensive evaluation, the refractory that recognizes the effect of the present invention is an example in which the improvement effect of the rate of change in ventilation characteristics is remarkable and the maximum generated stress value, wear resistance, and corrosion resistance all exhibit the same or better characteristics than the above standards. (Passed example).
The flat (plate-like) primary particles and other raw materials, the method for preparing the sample, the evaluation method, and the like are the same in the following Examples B to H.

Details of Example A are shown in Table 1.

In addition, the notation of “Al ₂ O ₃ (mass%)” in “secondary particles” in Table 1 indicates the proportion of Al ₂ O ₃ in the components excluding carbon of the secondary particles. Hereinafter, the same applies to Tables 2-8.

From this result, the total Al ₂ O ₃ purity of primary particles which are flat particles and the inorganic binder thereof is 98% by mass or more, and in both Examples 1 and 2 which do not contain fused silica, the air permeability characteristics The rate of change is significantly lower than that of the comparative examples 1 and 2 of the prior art including fused silica, and the maximum stress value, wear resistance, and corrosion resistance are all improved with respect to the above standards. I understand. In Comparative Example 4 where the total Al ₂ O ₃ purity of the primary particles and the inorganic binder is 96% by mass, the rate of change in air permeability characteristics is significantly lower than that in Comparative Example 1, but from Examples 1 and 2. It can be seen that the corrosion resistance is lower than that of the comparative example. Therefore, the total Al ₂ O ₃ purity of the primary particles which are flat particles and the inorganic binder thereof needs to be 98% by mass or more.
On the other hand, Comparative Example 3 using dense non-flat single particles resulted in inferior wear resistance to Comparative Example 1 and Comparative Example 2 even though the Al ₂ O ₃ purity was 98% by mass, Furthermore, the generated stress increased. It should be noted that the rate of change in ventilation characteristics of Comparative Example 3 was not measured.

[Example B]
Example B is an example in which the effect of the aspect ratio of flat alumina particles was investigated.

Details are shown in Table 2.

From these results, in Examples 3 to 6 in which the aspect ratio is 5 or more and 50 or less, the change rate of the airflow characteristics is remarkably reduced to 19 to 35 with respect to Comparative Example 1, and the generated stress. It can be seen that the value is smaller than that of Comparative Example 1 and all other evaluation items are “◎” or “又 は”.
On the other hand, in Comparative Example 5 in which the aspect ratio is less than 5 (≦ 4), the generated stress is larger than that in Comparative Example 1, and it can be seen that the stress relaxation ability is not sufficient. Moreover, in the case of the comparative example 6 with an aspect ratio exceeding 50, it turns out that abrasion resistance and corrosion resistance fall. This is thought to be due to the rough structure. Moreover, when the aspect ratio exceeds 50, there is a possibility that it is difficult to obtain the uniformity of secondary particles. It should be noted that the rate of change in airflow characteristics of Comparative Examples 5 and 6 was not measured.

[Example C]
Example C is an example in which the effect of the secondary particle content was investigated.

Table 3 shows details.

From this result, in Example 7 to Example 11 in which the content of secondary particles is 55% by mass or more and 90% by mass or less, the rate of change in air permeability is significantly reduced to 21 to 40 compared to Comparative Example 1. In addition, it can be seen that the generated stress value is also smaller than that of Comparative Example 1, and all the other evaluation items are “」 ”or“ ○ ”. On the other hand, in the case of Comparative Example 7 in which the content of secondary particles is 50% by mass, it is understood that the ability to relax the generated stress is not sufficient, and the wear resistance and corrosion resistance are further reduced. This is thought to be due to chemical wear and loss due to the low hardness of the carbon component, chemical reaction disappearance due to oxidation, elution into the molten steel, and the like.
In the case of Comparative Example 8 in which the content of secondary particles is 94% by mass, it is understood that although the ability to relax the generated stress is sufficient, the wear resistance and corrosion resistance are reduced. This is thought to be due to the rough structure.
Note that the rate of change in air permeability characteristics of Comparative Example 7 was not measured.
Along with the optimal content of the secondary particles being 55% by mass or more and 90% by mass or less, the content of the chemical component Al ₂ O _{3 in} the refractory is 54% by mass (55% by mass of the secondary particles A value obtained by multiplying the content ratio of Al ₂ O ₃ (98% of the lower limit) rounded off the decimal point) to 90% by mass (90% by mass of the Al ₂ O ₃ content of the secondary particles (upper limit of 100 %) Is rounded off to the nearest decimal point). In addition, when the content of secondary particles is small, carbon substrate materials, especially particulate carbon such as graphite other than bonded carbon, are used for the purpose of improving corrosion resistance and wear resistance according to the requirements of individual operating conditions. Thus, non-flat alumina particles may be included in the matrix portion of the refractory. Example 12 is this example, and in the case where the content ratio of the secondary particles is 55% by mass or more, an example is obtained in which 5% by mass of non-flat alumina particles are contained in the matrix portion of the refractory instead of graphite. It is. It can be seen that in Example 12, the rate of change in air permeability characteristics was significantly reduced to 27 compared to Comparative Example 1, and all other evaluation items were “◎”.

[Example D]
Example D is an example in which the effect of secondary particle size was investigated.

Table 4 shows details.

From these results, in Examples 13 to 15 in which the size of the secondary particles is more than 0.05 mm and not more than 2.0 mm, the change rate of the aeration characteristic is remarkably reduced to 21 to 44 compared to Comparative Example 1. , And the generated stress value is smaller than that of Comparative Example 1, and all other evaluation items are “項目”.
On the other hand, in the case of Comparative Example 9 where the size of the secondary particles is 0.05 mm or less and Comparative Example 10 exceeding 2.0 mm, it can be seen that the ability to relax the generated stress is not sufficient. Further, in the case of Comparative Example 10 in which the size of the secondary particles exceeds 2.0, the air flow rate R indicating the degree of variation in the air flow rate with Example 14 being 100 (subtract the minimum value from the maximum value of the air flow rate). It is considered that the uniformity of the refractory structure was lowered due to segregation of secondary particles in the soil during molding.
It should be noted that the rate of change in airflow characteristics of Comparative Example 9 and Comparative Example 10 was not measured.

The following [Example E] to [Example G] are examples in which the effects of chemical components as refractories are investigated.
These components are measured values for the sample after heat treatment of the refractory at 1500 ° C. in a nitrogen gas atmosphere.

[Example E]
Example E is an example of investigating the effect of carbon among chemical components.

Table 5 shows the details.

From these results, in Examples 16 to 18 in which the carbon content is 3% by mass or more and 45% by mass or less, the change rate of the aeration characteristic is significantly reduced to 19 to 40 with respect to Comparative Example 1, and other evaluation items Are all “わ か る” or “○”.
It can be seen that in Comparative Example 11 in which carbon is less than 3% by mass (= 2% by mass), the generated stress is high. This is thought to be due to the fact that the alumina ratio is relatively high, the thermal expansion coefficient and the elastic modulus are high, and the stress relaxation ability is not sufficient due to the lack of graphite and the like that bear the stress relaxation ability.
Further, in Comparative Example 12 in which the carbon content exceeds 45 mass% (= 47 mass%), the rate of change in air permeability characteristics is significantly reduced to 47 as compared with Comparative Example 1, but the wear resistance and corrosion resistance are reduced. I understand. This is considered to be due to chemical wear and loss due to the low hardness of the carbon component, chemical reaction disappearance due to oxidation and elution into the molten steel.
It should be noted that the rate of change in ventilation characteristics of Comparative Example 11 was not measured.

[Example F]
Example F is an example in which the effect of SiC among the chemical components was investigated.

Table 6 shows details.

From these results, in Examples 19 to 21 where SiC is 1.0% by mass or more and 10.0% by mass or less, the rate of change in air permeability characteristics is significantly reduced to 19 to 29 compared to Comparative Example 1. In addition, it can be seen that the generated stress value is smaller than that of Comparative Example 1 and all other evaluation items are “◎” or “「 ”.
On the other hand, it can be seen that Comparative Example 13 with SiC of 0.5 mass% is inferior in wear resistance, although the rate of change in the air permeability characteristics is remarkably reduced to 18 with respect to Comparative Example 1. Moreover, it turns out that the comparative example 14 whose SiC is 11.0 mass% is inferior in corrosion resistance. This is because when SiC is less than 1.0% by mass, it is impossible to obtain a dispersion state in the matrix sufficient to obtain an effect of improving wear resistance, and when it exceeds 10.0% by mass, its oxidation, molten steel, etc. This is considered to be due to the progress of reaction melting loss due to the inclusion of non-metallic inclusions.

[Example G]
Example G is a total content of other chemical components other than those described above, that is, alkali metal oxides, alkaline earth metal oxides, SiO ₂ excluding fused silica, TiO ₂ and other components inevitable in production. It is the example which investigated the effect of.

Table 7 shows the details.

From these results, in Examples 22 to 25 in which the total content of other components is 0.5% by mass or more and 2.0% by mass or less, the change rate of air permeability characteristics is remarkably reduced to 23 to 40 compared to Comparative Example 1. In addition, it can be seen that the generated stress value is smaller than that of Comparative Example 1, and all other evaluation items are “◎”.
However, Comparative Example 15 in which the total content of other components exceeds 2.0% by mass (= 2.5% by mass) is improved with respect to Comparative Example 2 in terms of the change rate of air permeability characteristics, the generated stress, and the wear resistance. Although it shows the same effect, it can be seen that the corrosion resistance is greatly inferior. This is because, when the total content of other components exceeds 2.0% by mass, these components react with other components in the refractory structure to form a low melt and soften the refractory structure and wear. This is thought to be due to facilitating, oxidizing carbon (particularly bonded carbon) to weaken the refractory structure, and promoting reaction erosion with molten steel (including non-metallic inclusions derived from molten steel).

[Example H]
Example H is an example in which the effect of the porosity of the refractory was investigated. This porosity is a measured value of the apparent porosity according to the method of JIS R2205 for a sample after heat-treating the refractory at 1500 ° C. in a nitrogen gas atmosphere.
Note that the ventilation rate when an air pressure of 0.1 MPa was applied to the internal space of a sample having an inner diameter of φ80 mm and a ventilation area of 500 cm ² was measured and the apparent porosity was 40%. Expressed as an index with the amount as 100.

Table 8 shows details.

From this result, it can be seen that when the porosity is less than 30%, the air flow rate (index) tends to decrease slightly, and when the porosity exceeds 50%, the air flow rate (index) increases significantly.
Since all of Examples 26 to 30 do not contain silica as particles, the index of the change rate of air permeability characteristics is as good as 18 to 45. Further, the generated stress value is smaller than that of Comparative Example 1 in any of the porosity of these examples, and it can be seen that the wear resistance and the corrosion resistance are all “◎” or “○”.
However, in the case of the present example, it is recognized that the air flow rate tends to decrease as the porosity decreases. In addition, the generated stress tends to increase with decreasing porosity, and the wear resistance and corrosion resistance tend to decrease with increasing porosity. The air flow rate, generated stress value, wear resistance, and corrosion resistance can be controlled by means other than the porosity, so the porosity is not an absolute requirement, but it may be 30% or more and less than 50%. .

a Length a 'Width b Thickness 1 Primary particle (flat alumina)
2 Secondary particle 3 Space in secondary particle 4 Matrix part of refractory consisting of carbonaceous, SiC, and other components outside secondary particle, 5 SiC
6 Specimen 7 Carbon Spacer 8 Carbon Block 9 Pressure Rod 10 Heating Element 11 Protective Wall 12 Crosshead 13 Refractory of the Present Invention (Breathable Refractory)
14 Gas passage (isobaric zone)
15 Zirconia-graphite refractory (refractory for powder part)
16 Gas introduction hole 21 Column next to discharge hole 22 Around discharge hole 23 Discharge hole

Claims (5)

Flat particles having an aspect ratio of 5 or more and 50 or less are used as primary particles, and secondary particles having a length of more than 0.05 mm and 2 mm or less are formed by assembling a plurality of the primary particles with an inorganic binder. Refractory,
After the refractory was heat treated in a non-oxidizing atmosphere at 1500 ° C. for 3 hours,
The secondary particles are contained in an amount of 55% by weight to 90% by weight,
The component excluding carbon in the secondary particles is 98% by mass or more of Al ₂ O ₃ ,
As chemical components, free carbon is contained in an amount of 3% by mass to 45% by mass, SiC is contained in an amount of 1% by mass to 10% by mass, and a single compound SiO ₂ , alkali metal oxide, alkaline earth metal oxide, TiO ₂ and a total content of other components inevitable in production is 2% by mass or less.   The apparent porosity after heat-treating the refractory in a non-oxidizing atmosphere at 1500 ° C. for 3 hours is 30% or more and 50% or less, and the refractory is heated from room temperature to 1500 ° C. at 5 ° C./min. The refractory according to claim 1, wherein the maximum generated stress value is 18 MPa or less. As chemical components after heat treatment in a non-oxidizing atmosphere at 1500 ° C. for 3 hours, Al ₂ O ₃ is 54 mass% to 90 mass%, free carbon is 3 mass% to 45 mass%, and SiC is 1 mass% or more. Refractory containing 10% by mass or less and having a total content of SiO ₂ , alkali metal oxides, alkaline earth metal oxides, TiO ₂ , and other components inevitable in production, of 2% by mass or less. A manufacturing method of
A mixing step of adding an inorganic binder to the powder of primary particles of flat alumina and mixing;
A granulation step of kneading the obtained admixture to form a granulated product of secondary particles that is an aggregate of primary particles;
Classifying the obtained granulated product into a plurality of secondary particles having a length of more than 0.05 mm and 2 mm or less;
The obtained secondary particles are used as a raw material to be Al ₂ O ₃ component, and a raw material to be SiC component and a raw material to be free carbon are added and kneaded to form a binder. Yes, the production process of forming soil for obtaining soil,
A CIP molding step of CIP molding the soil;
Having a firing step of firing the resulting molded product,
In the mixing step, the inorganic binder is added so that the component excluding carbon of the secondary particles generated in the granulation step is 98% by mass or more of Al ₂ O ₃ ,
In the step of producing the molding earth, the plurality of secondary particles are blended in the molding earth so as to be present in a proportion of 55% by mass or more and 90% by mass or less. Production method.   A continuous casting immersion nozzle in which the refractory according to claim 1 or 2 is disposed as at least a part of a layer in contact with molten steel, the refractory layer and a continuous casting immersion nozzle behind the refractory layer. A space through which gas can pass is arranged between the main body refractories, and the space communicates with a gas introduction hole for communicating with a gas supply facility outside the immersion nozzle for continuous casting. An immersion nozzle for continuous casting.   The region where the refractory according to claim 1 or 2 is disposed is a part or all of the wall surface of the straight barrel portion on the inner hole side of the immersion nozzle for continuous casting, or a part or all of the inner wall surface of the discharge hole. The continuous casting immersion nozzle according to claim 4, which is a region including any one or more.