TWI899907B - Method for manufacturing refractory for gas injection nozzle, refractory for gas injection nozzle, and gas injection nozzle - Google Patents

Abstract

The present invention discloses a method for manufacturing a refractory for a gas injection nozzle, wherein one or more metal tubes for gas injection are embedded in a carbon-containing refractory. The method comprises a series of steps, including non-oxidizing calcination of the carbon-containing refractory with the embedded metal tubes, followed by multiple impregnation treatments with an organic material having a residual carbon content of 30% by mass or greater. These multiple non-oxidizing calcinations and organic material impregnations enhance the destructive properties of the carbon-containing refractory with the embedded metal tubes, thereby suppressing the propagation of cracks caused by the rapid temperature gradient near the nozzle operating surface during use of the gas injection nozzle. Consequently, the life of the gas injection nozzle can be significantly extended.

Description

Method for manufacturing refractory for gas injection nozzle, refractory for gas injection nozzle, and gas injection nozzle

The present invention aims to improve refining efficiency and alloy yield in rotary furnaces or electric furnaces. It relates to a refractory for a gas injection nozzle, which injects gas into the melt from the furnace bottom or other locations. The invention also relates to a method for manufacturing a refractory for a gas injection nozzle, wherein one or more gas injection metal tubes are embedded in a carbon-containing refractory. Furthermore, the invention relates to a refractory for the gas injection nozzle and the gas injection nozzle.

In order to improve the refining efficiency and alloy yield in rotary furnaces or electric furnaces, a so-called "bottom blowing" method is adopted in which a stirring gas (usually an inert gas such as nitrogen or Ar) or a refining gas is blown into the melt from the bottom of the furnace. Examples of such bottom blowing methods include the following (1) to (3). Method (1) is a double-tube method in which oxygen for decarburization is blown from the inner tube, and hydrocarbon gas (propane, etc.) for cooling the contact parts of the molten steel is blown from the outer tube. Method (2) is a method in which a slit-shaped opening is provided in the gap between the metal tube and the brick, and an inert gas is blown from the opening (slit method). Method (3) is to bury a plurality of (several to hundreds of) metal tubes in the carbon-containing bricks, and then supply inert gas to the metal tubes from the bottom of the bricks through the gas inlet pipe and the gas storage tank, and then blow the inert gas from the metal tubes.

In the above methods (1) and (2), the bricks for the tuyere are pre-made by conventional methods. Then, they are processed to form a double-layer tube or a narrow metal pipe installation portion. Alternatively, the space for installing the metal pipe is usually formed by dividing the bricks into two or four parts. During construction, the metal pipe for blowing gas is pre-installed, and the bricks for the tuyere are then constructed around it.

On the other hand, the gas injection plug (nozzle) used in method (3) is commonly known as a "multiple hole plug" (hereinafter referred to as "MHP"). For example, in Patent Document 1, this MHP can control the gas flow rate by 1 to 20 times (0.01 to 0.20 Nm ³ /min). Therefore, compared with the double-tube method or the slit method, the MHP is easier to use.

The MHP is a structure consisting of multiple thin metal tubes connected to a gas storage tank, embedded in a carbon-containing refractory material such as magnesium oxide-carbon bricks. Therefore, its manufacturing method differs from double-tube or slit nozzles, and instead adopts the following method.

Specifically, raw materials such as magnesium oxide, to which a carbon source such as scaly graphite, asphalt, metal species, and a binder such as a phenolic resin are added, are kneaded using a high-dispersion high-speed mixer or other mixing method. This produces a kneaded material that will form a carbon-containing refractory material in which the metal tubes are embedded. The metal tubes are then layered onto this kneaded material, and then formed using a press at a predetermined pressure. Then, a predetermined drying method is applied (the metal capillary is subsequently welded to the gas storage tank member), or the metal capillary is welded to the gas storage tank member in advance, the kneaded material is filled around it, and then formed using a press at a predetermined pressure. MHP is then manufactured using a predetermined drying method.

Compared to refractory materials such as the furnace wall, bottom-blowing nozzles are subject to greater damage (loss) and are a critical component that affects the life of the furnace. Therefore, various proposals have been made to reduce this damage, including the following improvement proposals for MHP.

Patent Document 2 integrates the MHP gas injection nozzle with the surrounding tuyere, aiming to reduce premature damage and wear at the joint. However, MHP damage also occurs in areas where metal tubes are embedded, making this technology unlikely to be an effective countermeasure. Furthermore, one of the main causes of MHP damage is carburization of the metal tubes embedded in the refractory, which lowers their melting point (precursor damage to the metal tubes). The following countermeasures have been proposed.

Patent Document 3 proposes forming an oxide layer on the surface of stainless steel tubes embedded in carbon-containing refractory materials such as magnesium oxide carbon by spraying. However, in refining furnaces used for extended periods (e.g., two to six months), such as converters, the oxide layer thickness is insufficient, resulting in a limited effect on carburization suppression.

Furthermore, Patent Document 4 proposes placing a refractory sintered body between the metal tube and a carbon-containing refractory material to suppress carburization. This technology has been shown to suppress carburization. However, in nozzles with multiple buried metal tubes, the narrow spacing between the tubes makes it difficult to place the refractory sintered body, hindering practical application. [Prior Art Document] [Patent Document]

Patent Document 1: Japanese Patent Application Publication No. 59-31810 Patent Document 2: Japanese Patent Application Publication No. 63-24008 Patent Document 3: Japanese Patent Application Publication No. 2000-212634 Patent Document 4: Japanese Patent Application Publication No. 2003-231912 Patent Document 5: Japanese Patent Application Publication No. 58-15072 Patent Document 6: Japanese Patent Application No. 3201678 Patent Document 7: Japanese Patent Application Publication No. 2017-144460

(Invent the problem you want to solve)

As mentioned above, in order to improve the durability of metal capillary type gas nozzles (MHP, etc.) embedded in carbon-containing refractory materials, various studies have been conducted on the refractory materials and structures, but sufficient improvement effects have not yet been achieved.

Therefore, the present invention aims to solve the aforementioned problems in the prior art. It aims to provide a method for manufacturing a refractory for a gas injection nozzle in which one or more metal tubes for gas injection are embedded in a carbon-containing refractory, thereby improving the durability of the gas injection nozzle. (Technical Means for Solving the Problem)

The main cause of damage to MHP used in converters and electric furnaces has been believed to be the strong injection of gas from the metal capillary, which causes molten steel flow near the nozzle operating surface, leading to damage and wear. The countermeasures in Patent Document 2 are based on this concept. It is also believed that carburization, etc., causes the metal capillary to be consumed first, causing greater damage. Using the methods of Patent Documents 3 and 4 can prevent carburization of the metal capillary. On the other hand, it is believed that the strong injection of inert gas during blowing cools the refractory, causing peeling damage due to the temperature difference between blowing and non-blowing periods. Furthermore, since carbon-containing refractories reach their lowest strength around 600°C, cracking can occur on the working surface in this area, causing damage. While various proposals have been made, no definitive solution has been found. Consequently, there are currently no adequate countermeasures, and as mentioned above, satisfactory durability may not be achieved.

To investigate the true cause of MHP damage, the inventors recovered spent material (MHP) from actual blast furnaces and conducted a detailed investigation of the refractory structure near the nozzle operating surface. They discovered that within the refractory, approximately 10 to 20 mm from the operating surface, a significant temperature fluctuation of 500 to 600°C occurred, and cracks parallel to the operating surface were observed in this area. Based on repeated investigations of spent material near the operating surface of actual blast furnaces, they concluded that the damage to MHP was not due to melting or wear, but rather to thermal shock caused by the rapid temperature gradient near the operating surface.

Until now, improvements to thermal shock resistance have been aimed at preventing gouging cracks in the carbon-containing refractory material that forms the nozzle base material. These improvements have been made to achieve lower elastic modulus, lower thermal expansion, and higher strength. However, as mentioned above, under conditions of rapid temperature fluctuations within a very narrow operating range, preventing gouging cracks is difficult. Therefore, the inventors examined methods to improve the properties of gouging cracks, even if they do occur, and focused on the destructive energy of carbon-containing refractory materials.

The destructive energy of a refractory is defined as the energy required to form a new surface when a tortoise crack extends. When thermal stress is applied to a refractory, a certain amount of elasticity is stored. If this energy causes a tortoise crack to form, the greater the destructive energy, the less likely the tortoise crack will extend.

Various methods have been studied to improve the destructive energy of refractory materials. One method, for example, is to add carbon long fibers. However, this method has not yet been put into practical use because it reduces the packing capacity of carbon-containing refractory materials.

It is known that technologies for non-oxidizing calcination and organic impregnation of refractory materials are primarily used to improve the corrosion resistance and thermal spalling resistance of furnace-bonded refractories. For example, Patent Document 5 describes calcining magnesium oxide carbon bricks to which metallic aluminum powder has been added in a non-oxidizing environment at 500-1000°C. The bricks are then impregnated with an organic material with a carbonization yield of 25% or more to improve thermal strength and corrosion resistance. Furthermore, Patent Document 6 attempts to improve thermal spalling resistance, which is caused by reduced slag erosion resistance and elastic modulus, by calcining magnesium oxide carbon bricks to which 0.5-10% by weight of precalcined smokeless carbon has been added in a reducing environment at 600-1500°C. In Patent Document 6, spalling resistance is evaluated based on the elastic modulus after reduction calcination at 1400°C, with an elastic modulus below 1.2× ^10⁴ MPa being crucial. Furthermore, while it is stated that tar can be impregnated after reduction calcination to achieve pore sealing, increased strength, and improved digestion resistance, this is not mentioned in the examples.

As mentioned above, the known technique of non-oxidizing calcination/organic impregnation of refractory materials is primarily intended to improve the corrosion resistance or thermal spalling resistance of furnace-bonded refractory materials. In contrast, Patent Document 7 discloses a method of calcining refractory materials under non-oxidizing conditions and then impregnating them with an organic material (non-oxidizing calcination/organic impregnation), which is effective in improving destructive energy. While the reasons for increasing destructive energy through non-oxidizing calcination/organic impregnation of carbon-containing refractory materials are not entirely clear, the following are presumed reasons.

Carbon-containing refractories (bricks) are generally manufactured using phenolic resins and other binders. Phenolic resins undergo thermal decomposition at high temperatures, leaving a portion of residual carbon that functions as a binder for carbon-containing refractories. However, the degree of this bonding is relatively high. Also, since turtle cracks tend to extend when they occur, the destructive energy is not very high. In contrast, when organic matter is impregnated after non-oxidizing calcination, the organic matter will diffuse and penetrate evenly into the interior of the refractory, penetrating into the matrix or between scaly graphite layers within the refractory. These organic matter will be heated and decomposed when using the nozzle, forming carbon bonds. As a result, a loose bond is created between the carbon material, such as scaly graphite, and the refractory aggregate, enhancing the bond. Consequently, even if a crack does occur, it is less likely to extend. Furthermore, due to the loose bond, moderate stress pulls apart the carbon bonds originating from the organic materials. This, similar to the case of adding carbon fibers, acts as a crosslink between the brick structures, resulting in an increase in the so-called pull-apart properties, ultimately increasing the destructive energy.

However, the inventors of the present invention have found that the method of Patent Document 7 has a limit to the improvement in durability associated with an increase in destructive energy. In contrast, the destructive energy can be significantly increased by performing non-oxidative calcination/organic impregnation multiple times.

Meanwhile, the subject of MHP is the phenomenon of carburization into the metal tubes when gas is blown from them, as shown in Patent Documents 3 and 4. Carburization into the metal tubes occurs when carbon sources contained in the refractory (bricks) penetrate into the metal tubes at the high temperatures of actual machine operation. This carburization lowers the melting point of the metal tubes, which can increase nozzle damage. The present invention discovered that by manufacturing the refractory for gas injection nozzles, the carbon-containing refractory in which the metal tubes are embedded can significantly increase its destructive energy by performing multiple non-oxidizing calcinations and organic impregnations on the refractory during production. However, even during this non-oxidizing calcination, depending on the heat treatment conditions, carbon components from the carbon-containing refractory can still penetrate into the metal tubes, causing the tubes to lower their melting point due to carburization. Therefore, performing multiple non-oxidizing calcinations on the carbon-containing refractory in which the metal tubes are embedded can prevent the lowering of the metal tubes' melting point due to carburization. Therefore, a detailed examination of the non-oxidizing calcination conditions (calcination temperature, calcination time), as well as the carbon content of the metal tubes after non-oxidizing calcination, has led to the discovery of practically optimal conditions that suppress the lowering of the metal tubes' melting point.

As described above, by subjecting a carbon-containing refractory material containing embedded metal tubes for MHP to multiple cycles of non-oxidizing calcination and organic impregnation, the destructive energy of the refractory surrounding the metal tubes can be significantly enhanced. This suppresses the propagation of cracks near the working surface of the MHP, significantly increasing the lifespan of the MHP. Furthermore, the authors discovered that by optimizing the non-oxidizing calcination conditions, carburization into the metal tubes during the MHP manufacturing process can be suppressed, further extending the lifespan. The present invention was developed based on this discovery, and its main principles are as follows.

[1] A method for manufacturing a refractory for a gas injection nozzle, wherein one or more metal tubes for gas injection are embedded in a carbon-containing refractory; the method is characterized in that: after the carbon-containing refractory in which the metal tubes are embedded is subjected to non-oxidizing calcination, the carbon-containing refractory is subjected to a series of impregnation treatments in which the carbon-containing refractory is impregnated with an organic material having a residual carbon content of 30% by mass or more a plurality of times.

[2] A method for manufacturing a refractory for a gas injection nozzle as described in [1] above, wherein the non-oxidizing calcination is carried out at a calcination temperature of 400-1100°C and a calcination time of 1-20 hours.

[3] A method for manufacturing a refractory for a gas injection nozzle as described in [1] above, wherein the non-oxidizing calcination is carried out at a calcination temperature of 800-1100°C and a calcination time of 3-20 hours.

[4] A method for manufacturing a refractory for a gas injection nozzle as described in any one of [1] to [3] above, wherein a series of steps of non-oxidizing calcination and organic matter impregnation treatment are carried out 2 to 3 times.

[5] A method for manufacturing a refractory for a gas injection nozzle as described in any one of [1] to [4] above, wherein the conditions for the non-oxidizing calcination are set in such a way that the total carburizing index N of the plurality of non-oxidizing calcinations is below a critical value.

[6] A method for manufacturing a refractory for a gas injection nozzle as described in any one of [1] to [5] above, wherein the carbon-containing refractory constituting the manufactured refractory for a gas injection nozzle has a destructive energy of 175 J/ ^m2 or more.

[7] A method for manufacturing a refractory for a gas injection nozzle as described in any one of [1] to [6] above, wherein the porosity of the carbon-containing refractory constituting the manufactured refractory for a gas injection nozzle is less than 3%.

[8] A method for manufacturing a refractory for a gas injection nozzle as described in any one of [1] to [7] above, wherein the carbon content of the metal tube after the final non-oxidizing calcination is set to less than 2.0 mass%.

[9] A method for manufacturing a refractory for a gas injection nozzle as described in any one of [1] to [7] above, wherein the carbon content of the metal tube after the final non-oxidizing calcination is set to be less than 1.3 mass%.

[10] A method for manufacturing a refractory for a gas injection nozzle as described in any one of [1] to [9] above, wherein the organic substance impregnated into the carbon-containing refractory during the impregnation treatment is one or more selected from coal tar asphalt, phenol resin, and furan resin.

[11] A refractory for a gas injection nozzle, wherein one or more metal tubes for gas injection are embedded in a carbon-containing refractory; the refractory is characterized in that: the destructive energy of the carbon-containing refractory is 175 J/ ^m2 or more.

[12] The refractory for the gas injection nozzle as described in [11] above, wherein the porosity of the carbon-containing refractory is less than 3%.

[13] A refractory material for a gas injection nozzle as described in [11] or [12] above, wherein the carbon content of the metal tube is less than 2.0 mass%.

[14] The refractory material for the gas injection nozzle of [11] or [12] above, wherein the carbon content of the metal tube is less than 1.3 mass%.

[15] A gas injection nozzle having a refractory material for a gas injection nozzle according to any one of the above-mentioned [11] to [14]. (Compared with the effects of the prior art)

The manufacturing method of the present invention enables the production of a refractory for gas injection nozzles that has a high destructive energy and a carbon-containing refractory embedded with a metal capillary. This refractory can suppress the growth of tortoise cracks caused by the rapid temperature gradient near the nozzle operating surface. The use of this refractory for gas injection nozzles can significantly extend the life of the gas injection nozzles.

Furthermore, by optimizing the non-oxidizing calcination conditions (calcination temperature, calcination time) and the carbon content of the metal tube after non-oxidizing calcination, carburization into the metal tube is suppressed, which can prevent the melting point of the metal tube from decreasing and further increase the life of the gas injection nozzle.

This invention relates to a method for manufacturing a refractory for a gas injection nozzle, in which one or more metal tubes for gas injection are embedded within a carbon-containing refractory. The method involves performing a series of non-oxidizing calcination/organic impregnation steps, namely, non-oxidizing calcination of the carbon-containing refractory with the embedded metal tubes (non-oxidizing calcination step), followed by impregnation of the carbon-containing refractory with an organic material having a residual carbon content of 30% by mass or greater (impregnation step).

In the following description, for the sake of convenience, the gas injection nozzle with dozens or more metal tubes embedded in carbon-containing refractory is sometimes referred to as "MHP".

The material (raw material) and forming method of the carbon-containing refractory used in the manufacturing method of the present invention, the material and number of the metal tubes, and the method of embedding the metal tubes in the carbon-containing refractory will be described in detail later.

In the present invention, the object of non-oxidizing calcination/organic impregnation is a carbon-containing refractory material in which a metal capillary is embedded. If the gas injection nozzle is a type equipped with a gas storage tank, the object may be a carbon-containing refractory material simply in which the metal capillary is embedded. Alternatively, the carbon-containing refractory material may have a metal capillary embedded therein and the metal capillary bonded to all or part of a gas storage tank member.

The present invention involves subjecting carbon-containing refractory materials to non-oxidizing calcination and then subjecting them to an impregnation treatment with an organic substance. However, if non-oxidizing calcination is not performed, organic impregnation is impossible. Basically, carbon-containing refractory materials (bricks) are uncalcined refractory materials obtained without a calcination step. As the binder hardens, the porosity of the refractory material becomes very low, at a few percent. Therefore, it is difficult to impregnate the entire refractory material with an organic substance in the uncalcined state. Therefore, in order to impregnate the organic substance, non-oxidizing calcination must be performed in advance. In addition, during non-oxidizing calcination, the entire refractory material is heat-treated, and carbon components derived from the binder, etc., are uniformly generated as a binder. Therefore, for uncalcined products whose refractory structure changes due to heating during actual machine operation, a homogeneous refractory structure can be obtained, making it easier to impregnate organic matter.

The present invention significantly increases destructive energy by performing multiple cycles of non-oxidizing calcination/organic impregnation. This phenomenon is believed to be caused by the following reasons. Specifically, the organic matter impregnated into the carbon-containing refractory during organic impregnation contains vaporized components (such as alcohols, which, even in the absence of oxygen, become vaporized when the temperature rises and dissipate outside the refractory). Furthermore, it also contains residual carbon components (such as carbon, which, even in the absence of oxygen, does not become vaporized even at elevated temperatures and remains within the refractory). These vaporized components dissipate outside the refractory at room temperature after refractory manufacture and at the high temperatures encountered during actual use, reducing the effectiveness of the organic impregnation. By repeating multiple cycles of non-oxidizing calcination and organic impregnation, the following occurs: the vaporized components caused by non-oxidizing calcination escape → the organic components are filled into the pores by impregnation → the vaporized components caused by non-oxidizing calcination escape (the pores are reduced compared to the previous cycle due to the residual carbon content) → the organic components are filled into the pores by impregnation. Furthermore, even after exposure to high temperatures, the remaining pores will continue to decrease. For example, if an organic material whose volume is halved by non-oxidizing calcination is used, after one impregnation, even if the vaporized components escape, the pore volume will still be halved. Furthermore, after a second impregnation, the pore volume will be further halved (1/4 of the initial volume). Furthermore, after a third impregnation, the pore volume will be further halved (1/8 of the initial volume). Thus, by performing multiple cycles of non-oxidative calcination/organic impregnation, the volume of pores can be significantly reduced, resulting in a significant increase in destructive energy.

Furthermore, if multiple non-oxidizing calcination/organic impregnation cycles are performed, the pores will be filled with residual carbon each time the non-oxidizing calcination/organic impregnation cycles are performed, thereby also being expected to improve thermal conductivity, moderate temperature gradients, and reduce thermal shock.

The calcination temperature (heat treatment temperature) of carbon-containing refractory during non-oxidizing calcination is preferably 400°C or higher and 1100°C or lower. If the calcination temperature is lower than 400°C, the thermal decomposition of the binder (usually a resin such as phenolic resin) will not occur sufficiently, resulting in insufficient impregnation of organic matter during the impregnation treatment after non-oxidizing calcination, and the destructive energy may not be fully improved. On the other hand, if the calcination temperature exceeds 1100°C, there is a risk that the melting point of the metal tube will be lowered due to carburization of carbon components from the carbon-containing refractory into the metal tube. Furthermore, since the present invention performs multiple non-oxidizing calcinations, if the calcination temperature exceeds 1100°C, the embedded metal capillary may melt or become clogged, and there is a risk that the gas injection nozzle will lose its gas ejection function.

Furthermore, in the impregnation treatment after non-oxidative calcination, in order to allow the organic matter to be impregnated more effectively, the calcination temperature is preferably above 800°C.

The optimal calcination time (holding time) for non-oxidizing calcination is 1-20 hours. If the calcination time is less than 1 hour, the overall nozzle may not be adequately heat treated. On the other hand, if the calcination time exceeds 20 hours, carburization into the metal tube may occur, similar to calcination temperatures exceeding 1100°C, potentially lowering the melting point of the metal tube. From this perspective, the more optimal calcination time is 3-20 hours.

In particular, since the present invention performs multiple non-oxidizing calcinations, it is preferable to control the total amount of heat treatment during these multiple calcinations. Specifically, it is preferable to set the non-oxidizing calcination conditions so that the total carburization index N during calcination falls below a critical value as shown in the following formula (1). The non-oxidizing calcination conditions are described in terms of, for example, the number of calcinations, calcination temperature, and calcination time.

[Number 1]

Here, D is the carbon diffusion coefficient, which is expressed by the following formula (2). In addition, the total carburization index N during calcination is the value obtained by integrating the carbon diffusion coefficient D with the total calcination time and multiplying it by 10 ⁹ .

[Number 2]

In formula (2), _D0 is the frequency factor of carbon diffusion, Q is the activation energy for carbon diffusion, R is the gas constant, and T is the calcination time. The total carburization index N during calcination is an indicator of the extent to which carbon has penetrated into the metal tube. The critical value is a value calculated by repeated experiments in advance and is appropriately determined according to the material of the metal tube. In one example of this embodiment, it is 118. That is, in this embodiment, it is preferable to set the number of calcination times, calcination temperature, and calcination time so that the total carburization index N during calcination is 118 or less when multiple non-oxidizing calcinations are performed. If the total carburization index (N) during calcination exceeds the critical value, the carbon content of the metal tube after non-oxidative calcination will exceed 2.0% by mass, reducing the durability of the nozzle itself. Furthermore, from the perspective of carburization of the metal tube, the total carburization index (N) during calcination is not a lower limit. Therefore, the lower limit of the heat treatment amount can be set based on other considerations such as binder thermal decomposition.

The reason for calcining carbon-containing refractory materials in the present invention using a non-oxidizing calcination method is to avoid compromising the inherent properties of carbon-containing refractory materials, such as thermal spalling resistance and slag permeability resistance. Specifically, if the carbon content of carbon-containing refractory materials is significantly reduced under calcination conditions, such as calcination under high-temperature and long-term heating conditions in an oxidizing environment, the carbon in the materials will oxidize and disappear. This, in turn, will result in the loss of the inherent properties of carbon-containing refractory materials, such as thermal spalling resistance and slag permeability resistance. Therefore, calcination is performed under non-oxidizing conditions to prevent the loss of these properties.

While the conditions for non-oxidizing calcination are described in terms of the number of calcinations, calcination temperature, and calcination time, there are no particular limitations as long as the carbon, such as scaly graphite, contained in the carbon-containing refractory material is not substantially eliminated. For example, non-oxidizing calcination conditions may include reduction calcination, calcination in a reducing environment, calcination in a non-oxidizing environment, and short-term calcination in an oxidizing environment.

There are no particular restrictions on the method for implementing non-oxidative calcination; conventional methods can be used. For example, a sheath or metal container containing assembled bricks is placed on a trolley placed in a calciner, and a carbon-containing refractory (a carbon-containing refractory with embedded metal capillaries) for reduction calcination is installed inside. A carbon source such as coke is then introduced around the carbon-containing refractory, and a lid is placed on top. While shielding the refractory from the outside air, reduction calcination (heat treatment) is carried out at a predetermined temperature and for a predetermined time.

Furthermore, carbon-containing refractory materials can be calcined in a reducing atmosphere containing a combustible gas such as NX gas, or in a non-oxidizing atmosphere using an inert gas such as nitrogen or argon, or a non-oxidizing gas. In both cases, a sheath or metal container is not required.

Furthermore, even when calcining carbon-containing refractory materials in an oxidizing environment, calcination can still be performed for a short time, and after calcination, the decarburized layer formed on the surface is removed, and the undecarburized portion of the refractory interior is reused. In this method, the surface of the carbon-containing refractory is in an oxidized state. However, as the surface oxidizes, this portion can function as a protective layer, and the interior of the refractory can be calcined under non-oxidizing conditions. Therefore, the interior of the refractory can be considered to be calcined in a substantially non-oxidizing manner. In addition, calcining carbon-containing refractory materials can also be performed by applying a glaze to the surface of the carbon-containing refractory material to prevent oxidation.

However, among the above methods, reduction calcination, calcination in a reducing environment, and calcination in a non-oxidizing environment are more preferred. Calcination in an oxidizing environment requires removal of the decarburized layer on the surface, which is not economical.

The carbon content of the final non-oxidatively calcined metal thin tube (the metal thin tube has been embedded in the carbon-containing refractory) is preferably 2.0 mass% or less. If the carbon content of the metal thin tube exceeds 2.0% by mass, the melting point of the metal thin tube will be lowered, so there is a possibility that the metal thin tube will melt near the operating surface of the nozzle front end, and the durability of the nozzle itself will be reduced. Furthermore, from the above viewpoint, the carbon content of the metal thin tube is more preferably 1.3% by mass or less.

Methods for reducing the carbon content of the metal tube after non-oxidizing calcination to 2.0 mass% or less (preferably 1.3 mass% or less) include, for example: (i) lowering the non-oxidizing calcination temperature to a short non-oxidizing calcination time. Specifically, the non-oxidizing calcination temperature is set to 1000°C or less, and the non-oxidizing calcination time is set to 20 hours or less. Another method, such as (ii), is to apply a non-gas-permeable coating to the surface of the metal tube to inhibit carburization, but method (i) is particularly effective.

The carbon-containing refractory material having undergone the non-oxidative calcination step as described above is subjected to an impregnation treatment in which an organic substance is impregnated.

During the organic material impregnation treatment, the residual carbon content of the impregnated organic material is set to 30% by mass or greater. This residual carbon content is measured using the fixed carbon determination method described in JIS K6910 (Testing methods for phenolic resins). A residual carbon content of less than 30% by mass is considered insufficient because the residual carbon does not strengthen the refractory structure. Therefore, a more optimal residual carbon content is 35% by mass or greater.

Examples of the impregnated organic material include coal tar pitch (heat-melted product), phenolic resin (liquid resin), and furan resin (liquid resin). One or more of these can be used, with coal tar pitch being particularly preferred. Coal tar pitch, as it is the carbon produced by thermal decomposition, readily crystallizes, thus contributing to a higher destructive energy. In contrast, the carbon produced by thermal decomposition of phenolic resins is less likely to crystallize and tends to form glassy carbon. Consequently, the destructive energy improvement effect is relatively lower than that of coal tar pitch.

There are no particular restrictions on the method of impregnating the organic substance. However, it is preferable to temporarily reduce the pressure to a vacuum and then impregnate the organic substance under pressure. For example, after reducing the pressure to a vacuum pressure of 100 Torr or less, the organic substance is impregnated at a pressure of 5 kgf/cm2 or more for more than ² hours. If the vacuum pressure is too high, the organic substance may not be uniformly impregnated into the refractory during pressurization due to bubbles remaining in the refractory. Therefore, the vacuum pressure during decompression is preferably 100 Torr or less, and more preferably 60 Torr or less. In addition, if the pressure after decompression is too low or the pressurization time is too short, the organic substance may not be fully impregnated into the refractory. Therefore, the pressure after decompression is preferably 5 kgf/cm² or ^greater , more preferably 10 kgf/cm² or ^greater . Furthermore, the pressurization duration is preferably 2 hours or greater, more preferably 4 hours or greater. By meeting these impregnation conditions, the organic matter uniformly permeates the carbon-containing refractory. Based on the principle described above, this can effectively enhance the destructive energy of the carbon-containing refractory.

As described above, after reducing the pressure of the carbon-containing refractory to a predetermined vacuum pressure, the equipment for impregnating the carbon-containing refractory with the organic substance while maintaining the predetermined pressure can be used. Conventional impregnation equipment used for organic substance impregnation using slides, etc., can also be used. Furthermore, to remove volatile components remaining in the carbon-containing refractory after impregnation, a drying treatment at approximately 200°C may be performed.

This invention significantly increases destructive energy by performing multiple cycles of non-oxidative calcination/organic impregnation. However, the destructive energy increase effect saturates after a certain number of cycles. Therefore, considering economic efficiency, the ideal number of cycles of non-oxidative calcination/organic impregnation is approximately two to three.

The refractory for the gas injection nozzle produced by the method of the present invention preferably has a destructive energy of 175 J/ ^m² or greater for carbon-containing refractory. If the destructive energy is less than 175 J/ ^m² , the difference between the destructive energy and the conventional single-impregnation refractory (a refractory obtained by only performing a single non-oxidizing calcination/organic impregnation) is small. Therefore, the effect of improving the life of the gas injection nozzle is small. In other words, by having a destructive energy of 175 J/ ^m² or greater for carbon-containing refractory, the extension of turtle cracks caused by the rapid temperature gradient near the nozzle operating surface can be particularly effectively suppressed, thereby significantly improving the life of the gas injection nozzle.

The fracture energy is measured using a three-point bending test. Specifically, a 25×25×140mm specimen is subjected to a three-point bending test with a span of 100mm in an inert atmosphere at 800°C. A bending load is applied to the specimen at a rate of 0.1mm/min to obtain a stress/strain curve. The fracture energy is then calculated from the area formed by this stress/strain curve.

For carbon-containing refractory materials of the same material, samples (i) to (v) were subjected to the following non-oxidizing calcination/organic impregnation treatments after forming, and their destructive energy was compared. Sample (i) was subjected to the usual drying treatment. Sample (ii) was subjected to non-oxidizing calcination after drying. Sample (iii) was subjected to only one non-oxidizing calcination/organic impregnation treatment after drying. Sample (iv) was subjected to two non-oxidizing calcinations/organic impregnation treatments according to the conditions of the present invention after drying. Sample (v) was subjected to three non-oxidizing calcinations/organic impregnation treatments according to the conditions of the present invention after drying. The results showed that the destructive energy was 85 J/m ² for sample (i), 62 J/m ² for sample (ii), 160 J/m ² for sample (iii), 187 J/m ² for sample (iv), and 193 J/m ² for sample (v). Repeated non-oxidizing calcination/organic impregnation can effectively increase the destructive energy.

Among them, a gas injection nozzle refractory obtained using conventional methods (with a destructive energy of less than 160 J/ ^m² ) exhibited cracking approximately 100 mm from the nozzle operating surface into the refractory. Furthermore, the thickness of the gas injection nozzle refractory instantly decreased by approximately 100 mm, resulting in a decrease in durability by approximately 10%. However, the present invention's product, with a destructive energy of 175 J/ ^m² , did not exhibit this phenomenon.

Another method for increasing the destructive energy of refractory materials is to add carbon fibers (carbon long fibers), as mentioned above. However, while adding carbon fibers is effective in increasing the destructive energy, it results in very poor fusion between the carbon fibers and the refractory, and a very high porosity, resulting in a porous structure. Therefore, the corrosion resistance of the material with the addition of carbon fibers is greatly reduced, making it difficult to put into practical use. In contrast, non-oxidizing calcination/organic impregnation is more preferable because it can increase the destructive energy while maintaining the density of the refractory structure.

Furthermore, the refractory for the gas blowing nozzle manufactured according to the method of the present invention preferably has a porosity of 3% or less for the carbon-containing refractory. The porosity is an indicator of the amount of organic matter impregnation, which means that if the porosity is large, the impregnation amount is small, and if the porosity is small, the impregnation amount is large. If the organic matter impregnation amount is small and the porosity of the carbon-containing refractory exceeds 3%, the effect caused by the organic matter impregnation becomes smaller, and the effect of strengthening the refractory structure and improving the toughness becomes smaller, and it is more difficult to ensure that the destructive energy is above 175J/ ^m2 . The more preferable porosity of the carbon-containing refractory is 1.5% or less. In addition, in order to reduce the porosity of the carbon-containing refractory, it is effective to fully impregnate the organic matter into the carbon-containing refractory.

Next, the material (raw material) and forming method of the carbon-containing refractory used in the manufacturing method of the present invention, the material and number of the metal tubes, and the method of embedding the metal tubes in the carbon-containing refractory are explained.

The raw materials of carbon-containing refractory generally include aggregate, carbon source, other additives and binders.

Aggregates include magnesium oxide, aluminum oxide, dolomite, zirconium dioxide, chromium oxide, spinel (aluminum oxide-magnesium oxide, chromium oxide-magnesium oxide), etc. One or more of these can be used, but magnesium oxide is particularly preferred from the perspective of corrosion resistance to molten metal and molten slag.

The carbon source is not particularly limited; commonly used materials include scaly graphite, soil graphite, petroleum-based asphalt, and carbon black, and one or more of these materials may be used. The amount of carbon source incorporated into the carbon-containing refractory is not particularly limited; however, a range of 10-25% by mass is generally appropriate.

Other materials include, but are not limited to, metals such as Al, Si, and Al-Mg alloys; and carbides such as SiC and B ₄ C.

The binders that can be used are: phenolic resin, liquid asphalt, etc., which are generally used as binders for shaped refractories.

Metal tubes typically have an inner diameter of approximately 1-5 mm and a thickness of approximately 0.5-4 mm. While the material of these tubes is not particularly limited, metals with a melting point of 1300°C or higher are preferred. Examples of metal tube materials include metals (metals or alloys) containing at least one of iron, chromium, cobalt, and nickel. Stainless steel (ferrous, ferrous, or austenitic) or standard steel are particularly common.

There is no particular restriction on the number of metal tubes embedded in carbon-containing refractory. The number of metal tubes is set to one or more. The number of metal tubes is determined by the inner diameter of the metal tubes used and the required gas injection volume. The MHP used in a general converter usually has about 60 to 250 metal tubes embedded in the carbon-containing refractory. On the other hand, in the case of a nozzle that only circulates a small amount of gas, the number of metal tubes is one to several. This type of gas injection nozzle will still cause the front end of the tuyere to cool due to the violent injection of gas, and the thermal shock will cause turtle cracks to extend and become the cause of damage. Therefore, the present invention is also applicable to this type of gas injection nozzle.

There is no particular limitation on the method of embedding the metal tubes into the carbon-containing refractory. For example, the carbon-containing refractory raw materials listed above can be mixed and kneaded using a mixer. The metal tubes are laid on the mixture while being buried in layers, and then formed using a press at a predetermined pressure. After forming, the mixture is dried at an appropriate temperature. Furthermore, the carbon-containing refractory in which the metal tubes are buried is subjected to a plurality of non-oxidizing calcinations/organic impregnations according to the method of the present invention, and then the gas storage tank required for the function of the gas blowing nozzle is joined (welded) to the metal tubes using a component to produce a gas blowing nozzle product.

Another method involves pre-welding (welding) the metal tubes to the gas storage tank member (top plate), filling the surrounding area with the kneaded material, and then forming the mixture using a press at a predetermined pressure. After forming, the mixture is dried at an appropriate temperature. Furthermore, the carbon-containing refractory material with the embedded metal tubes undergoes multiple cycles of non-oxidative calcination and organic impregnation according to the present invention to create a gas injection nozzle.

The mixing method of the carbon-containing refractory raw material is not particularly limited, and a high-speed mixer, a tire mixer (cone mixer), an Eirich mixer, etc., which can be used as a mixing means for shaped refractory mixing equipment, can be used.

The mixture can be formed using a single-axis forming machine such as a hydraulic press or a friction screw press, or a common press used for forming refractory materials, such as cold isostatic pressing (CIP).

The formed carbon-containing refractory material can be dried at a temperature of 180°C to 350°C for 5 to 30 hours. [Example]

Tables 1 to 3 show the manufacturing conditions and properties of the refractories for gas injection nozzles produced in the present embodiments (inventive examples and comparative examples).

The raw materials for the carbon-containing refractory material used to embed the metal tubes include fused magnesium oxide (98.2% purity by mass) as the aggregate, scaly graphite (98.4% purity by mass, average particle size 0.18mm) as the carbon source, and a phenolic resin with a residual carbon content of 46% by mass as the binder.

The metal tubes embedded in the carbon-containing refractory are made of ordinary steel with an outer diameter of 3mm and an inner diameter of 2mm.

The organic material impregnated into the carbon-containing refractory is either coal tar pitch or phenolic resin. In Tables 1-3, the one with a residual carbon percentage of 42% by mass represents coal tar pitch. Furthermore, the one with a residual carbon percentage of 15% by mass represents phenolic resin. The residual carbon percentage was measured according to the fixed carbon determination method described in JIS K6910 (Testing Methods for Phenolic Resins).

The raw materials for the carbon-containing refractory were blended in the proportions shown in Tables 1 to 3 and kneaded using an Ehrlich mixer. A 230×200mm mold was then used to lay metal tubes on the kneaded mixture while embedding them in a layered pattern. The molded refractory was then formed using a hydraulic press at a pressure of 2.5 tons/ ^cm² . The formed refractory was then hardened and dried in a dryer at 250°C for 10 hours to produce a carbon-containing refractory embedded with metal tubes.

The carbon-containing refractory produced in the above manner was subjected to non-oxidizing calcination in coke breeze according to the conditions shown in Tables 1 to 3, followed by an organic impregnation treatment to obtain a refractory for gas injection nozzles. In this embodiment, these non-oxidizing calcination and organic impregnation treatments were performed multiple times. During the organic impregnation treatment, the carbon-containing refractory was maintained at a predetermined pressure for 10 hours.

In addition, for the purpose of measuring porosity and destructive energy, a carbon-containing refractory without embedded metal tubes was produced using the same raw materials and method as above.

In addition, some comparative examples were prepared in which no non-oxidizing calcination/organic impregnation was performed, only non-oxidizing calcination was performed without organic impregnation, and only one non-oxidizing calcination/organic impregnation was performed.

The carbon content of the metal tubes in the gas injection nozzle refractory obtained in the above manner was measured. Furthermore, the porosity and destructive energy of the refractory without embedded metal tubes were measured. These results are shown in Tables 1 to 3.

The porosity of refractory materials is measured according to JIS R2205. The vacuum method is used, and white kerosene is used.

The fracture energy of refractory materials was determined in the following manner. The specimen size was set to 25×25×140 mm, and a three-point bending test with a span of 100 mm was performed. The bending test was performed in an inert environment at 800°C. The testing machine used was the "autograph AG-X/R" manufactured by Shimadzu Corporation, and the chuck speed was set to 0.1 mm/min. From the stress/strain curve obtained from the three-point bending test, it was confirmed that stable fracture occurred. The fracture energy was calculated by dividing the area formed by the stress/strain curve by twice the projected area of the cross section (25×25 mm). Stable fracture was confirmed in all the measurement cases.

The carbon content of the metal capillary was determined by grinding a cross-section of a specimen obtained after non-oxidizing calcination and embedding the capillary. The carbon content was measured within a 100 × 100 μm field of view along the periphery of the capillary. The analyzer used was a JXA-8230 manufactured by JEOL Ltd.

Furthermore, the carburization index n for each calcination during non-oxidizing calcination and the total carburization index N (n × number of calcinations) for multiple calcinations during non-oxidizing calcination were calculated. These results are shown in Tables 1 to 3.

The calculation of the total carburization index N during calcination is carried out under the following conditions. First, the frequency factor D ₀ of carbon diffusion in formula (1) and the activation energy Q for carbon diffusion are shown below.

D ₀ =(4.725-5.374Wc+1.779Wc ² )×10 ^-5 Q=154.5-21.04Wc-3.285Wc ²

Wc represents the saturated carbon concentration, set at 2.14% in this example. Wc is also known as the "carbon solubility limit." Above this limit, ferrocarbon precipitates. At 2.14%, D ₀ = 1.37E-05 (m ² /s) and Q = 94.43041 (kJ/mol) are obtained.

Furthermore, in this embodiment, the gas constant R in formula (1) is 8.314 J/ (K·mol).

According to Tables 1 and 2, all of the examples of this invention exhibit low porosity and high destructive energy. In particular, the total carburization index (N) of Examples 1-5, 7-11, and 13-16 during calcination was below 118, and the carbon content of the metal tubes after non-oxidizing calcination was below 2.0 mass%.

According to Table 3, Comparative Example 1 is a commonly used magnesium oxide/carbon brick. The destructive energy of Comparative Example 1 is a smaller value. Comparative Example 2 is obtained by subjecting Comparative Example 1 to non-oxidizing calcination at 1400°C (without impregnation with organic matter). The destructive energy of Comparative Example 2 is a smaller value. In addition, the total carburization index N during calcination exceeds 118, and the carbon content of the metal tube is a large value of 3.1 mass%. Comparative Example 3 is obtained by setting the non-oxidizing calcination temperature to a lower temperature of 300°C. In Comparative Example 3, since the thermal decomposition of the binder caused by non-oxidizing calcination does not fully occur, the organic matter cannot be impregnated, and the destructive energy is a smaller value. Comparative Example 4 used an organic material with a residual carbon content of less than 15% by mass during the impregnation treatment. However, this did not achieve a satisfactory increase in destructive energy. Comparative Example 5 performed only a single non-oxidizing calcination/organic material impregnation cycle. While an increase in destructive energy was observed in Comparative Example 5, it was less than that observed in the present invention.

[Table 1] Table 1 This invention example No. 1 2 3 4 5 6 7 8 9 10 11 12 Refractory raw materials Magnesium oxide (mass %) 85 85 85 85 85 85 85 85 85 85 85 85 Scaly graphite (mass %) 15 15 15 15 15 15 15 15 15 15 15 15 Phenolic resin (added mass%) 3 3 3 3 3 3 3 3 3 3 3 3 Number of metal tubes 90 90 90 90 90 90 90 90 90 90 90 90 Non-oxidizing calcination conditions Calcination temperature (℃) 1000 400 800 1100 1200 1400 1000 1000 1000 1000 1000 1000 Calcination time (h) 5 5 5 5 5 5 0.5 1 3 15 20 30 Carburization index n(-) during calcination 16.01 0.00 2.87 31.54 56.87 151.11 7.77 8.69 12.35 34.33 43.49 61.81 Organic matter impregnation conditions Types of organic matter Coal tar asphalt Coal tar asphalt Coal tar asphalt Coal tar asphalt Coal tar asphalt Coal tar asphalt Coal tar asphalt Coal tar asphalt Coal tar asphalt Coal tar asphalt Coal tar asphalt Coal tar asphalt Organic carbon residue rate (mass %) 42 42 42 42 42 42 42 42 42 42 42 42 Including impregnation pressure reduction (torr) 10 10 10 10 10 10 10 10 10 10 10 10 Impregnation pressure (kgf/cm ² ) 15 15 15 15 15 15 15 15 15 15 15 15 Number of non-oxidative calcination/organic impregnation (times) 2 2 2 2 2 2 2 2 2 2 2 2 Total carburization index N(-) during calcination 32.03 0.01 5.75 63.08 113.74 302.22 15.54 17.37 24.70 68.66 86.98 123.61 Characteristics of the refractory for gas injection Porosity (%) 0.6 0.7 0.6 0.6 0.6 0.7 0.6 0.6 0.7 0.6 0.6 0.7 Destructive energy (J/m ² ) 187 136 176 188 180 179 125 135 178 185 178 179 Carbon content of non-oxidizing calcined metal tubes (mass %) 0.5 0.2 0.3 0.9 1.9 3.1 0.2 0.3 0.4 0.9 1.3 2.1

[Table 2] Table 2 This invention example No. 13 14 15 16 Refractory raw materials Magnesium oxide (mass %) 85 85 85 85 Scaly graphite (mass %) 15 15 15 15 Phenolic resin (added mass%) 3 3 3 3 Number of metal tubes 90 90 90 90 Non-oxidizing calcination conditions Calcination temperature (℃) 1000 1000 1000 1000 Calcination time (h) 5 5 5 5 Carburization index n(-) during calcination 16.01 16.01 16.01 16.01 Organic matter impregnation conditions Types of organic matter Coal tar asphalt Coal tar asphalt Coal tar asphalt Coal tar asphalt Organic carbon residue rate (mass %) 42 42 42 42 Including impregnation pressure reduction (torr) 100 60 10 10 Impregnation pressure (kgf/cm ² ) 15 15 5 10 Number of non-oxidative calcination/organic impregnation (times) 3 4 5 6 Total carburization index N(-) during calcination 48.04 64.05 80.07 96.08 Characteristics of the refractory for gas injection Porosity (%) 0.6 0.5 0.5 0.5 Destructive energy (J/m ² ) 193 193 193 194 Carbon content of non-oxidizing calcined metal tubes (mass %) 0.5 0.5 0.5 0.5

[Table 3] Table 3 Comparative example No. 1 2 3 4 5 Refractory raw materials Magnesium oxide (mass %) 85 85 85 85 85 Scaly graphite (mass %) 15 15 15 15 15 Phenolic resin (added mass%) 3 3 3 3 3 Number of metal tubes 90 90 90 90 90 Non-oxidizing calcination conditions Calcination temperature (℃) - 1400 300 1000 1000 Calcination time (h) - 5 5 5 5 Carburization index n(-) during calcination 0 151.11 0.00 16.01 16.01 Organic matter impregnation conditions Types of organic matter - - Coal tar asphalt Phenolic resin Coal tar asphalt Organic carbon residue rate (mass %) - - 42 15 35 Including impregnation pressure reduction (torr) - - 10 10 10 Impregnation pressure (kgf/cm ² ) - - 15 15 15 Number of non-oxidative calcination/organic impregnation (times) 0 0 0 0 1 Total carburization index N(-) during calcination 0 151.11 0.00 16.01 16.01 Characteristics of the refractory for gas injection Porosity (%) 3.2 10.3 0.8 0.8 0.9 Destructive energy (J/m ² ) 85 62 92 109 160 Carbon content of non-oxidizing calcined metal tubes (mass %) 0.2 3.1 0.2 0.5 0.5

Claims (15)

A method for manufacturing a refractory for a gas injection nozzle comprises embedding one or more metal capillaries for gas injection in a carbon-containing refractory. The method comprises: After non-oxidizing calcining the carbon-containing refractory with the embedded metal capillaries, the carbon-containing refractory is subjected to a series of impregnation treatments, wherein the carbon-containing refractory is impregnated multiple times with an organic material having a residual carbon content of 30% by mass or greater. In the method for manufacturing a refractory for a gas injection nozzle according to claim 1, the non-oxidizing calcination is carried out at a calcination temperature of 400-1100°C and a calcination time of 1-20 hours. In the method for manufacturing a refractory for a gas injection nozzle according to claim 1, the non-oxidizing calcination is carried out at a calcination temperature of 800-1100°C and a calcination time of 3-20 hours. A method for manufacturing a refractory for a gas injection nozzle according to any one of claims 1 to 3, wherein the series of steps of performing non-oxidizing calcination and impregnation with an organic substance is performed 2 to 3 times. The method for manufacturing a refractory for a gas injection nozzle according to any one of claims 1 to 3, wherein the conditions for the non-oxidizing calcination are set so that the total carburization index N of the plurality of non-oxidizing calcinations is below a critical value. The method for manufacturing a refractory for a gas injection nozzle according to any one of claims 1 to 3, wherein the carbon-containing refractory constituting the manufactured refractory for a gas injection nozzle has a destructive energy of 175 J/ ^m2 or more. The method for manufacturing a refractory for a gas injection nozzle according to any one of claims 1 to 3, wherein the porosity of the carbon-containing refractory constituting the manufactured refractory for a gas injection nozzle is 3% or less. In the method for manufacturing a refractory for a gas injection nozzle according to any one of claims 1 to 3, the carbon content of the metal tube after the final non-oxidizing calcination is set to 2.0 mass% or less. In the method for manufacturing a refractory for a gas injection nozzle according to any one of claims 1 to 3, the carbon content of the metal tube after the final non-oxidizing calcination is set to be less than 1.3% by mass. In the method for producing a refractory for a gas injection nozzle according to any one of claims 1 to 3, the organic substance impregnated into the carbon-containing refractory during the impregnation treatment is at least one selected from coal tar asphalt, phenol resin, and furan resin. A refractory for a gas injection nozzle is a refractory having one or more gas injection metal tubes embedded in a carbon-containing refractory. The refractory is characterized in that: the destructive energy of the carbon-containing refractory is greater than 175 J/ ^m2 . In the refractory for the gas injection nozzle of claim 11, the porosity of the carbon-containing refractory is less than 3%. In the refractory material for the gas injection nozzle of claim 11 or 12, the carbon content of the metal tube is 2.0 mass% or less. In the refractory material for the gas injection nozzle of claim 11 or 12, the carbon content of the metal tube is 1.3% by mass or less. A gas injection nozzle comprises the refractory material for a gas injection nozzle according to any one of claims 11 to 14.