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

Abstract

In a method for manufacturing a refractory for a gas injection nozzle in which one or more thin metal tubes for gas injection are embedded in a carbon-containing refractory, the following series of steps are performed a plurality of times: a carbon-containing refractory in which thin metal tubes are embedded is subjected to non-oxidative firing; the carbon-containing refractory material is then subjected to an impregnation treatment in which the carbon-containing refractory material is impregnated with an organic material having a carbon residue rate of 30% by mass or more. As a result of this plurality of non-oxidative firing and organic impregnation, the breaking energy of the carbon-containing refractory in which the thin metal tube is embedded is improved, and the propagation of cracks due to a sharp temperature gradient in the vicinity of the nozzle working surface when a gas is blown into the nozzle is suppressed, resulting in a substantial increase in the life of the gas-blown nozzle.

Description

TECHNICAL FIELD

[0001] The present invention aims at improving refining efficiency and alloy yield in a converter or an electric furnace, etc. The present invention relates to a manufacturing method of a gas blowing nozzle refractory for a gas blowing nozzle for blowing a gas into a molten metal from a bottom of a furnace, etc., and is a gas blowing nozzle refractory in which one or more metal pipes for gas blowing are embedded in a carbon-containing refractory. In addition, the present invention also relates to a gas blowing nozzle refractory and a gas blowing nozzle. BACKGROUND

[0002] In a converter or an electric furnace, etc., in order to improve refining efficiency and alloy yield, so-called bottom blowing of stirring gas (usually, nitrogen or Ar or the like non-active gas) or refining gas into a molten metal from a bottom is performed. As a method of this bottom blowing, for example, the following (1) to (3) can be cited. Method (1) is a double pipe method in which oxygen for the purpose of decarburization is blown from an inner pipe and a hydrocarbon gas (propane or the like) for the purpose of cooling a molten steel contact portion is blown from an outer pipe. Method (2) is a method (slit method) in which a slit-shaped opening is provided in a gap between a metal pipe and a brick and a non-active gas is blown from the opening. Method (3) is a method in which a plurality of (several to several hundred) metal pipes are embedded in a carbon-containing brick, a non-active gas is supplied to the metal pipes from a gas introduction pipe and a gas storage chamber via a bottom portion of the brick, and the non-active gas is blown from the metal pipes.

[0003] In methods (1) and (2) among them, a tuyere brick is manufactured in advance by a conventional method. Then, a metal pipe setting portion for forming a double pipe or a slit is processed. Alternatively, a space for setting the metal pipe is usually formed by being divided into two or four sections, and a metal pipe for blowing a gas is installed in advance at the time of construction, and a tuyere brick is built around it.

[0004] On the other hand, a gas blowing tap (nozzle) used in method (3) is called a multiple hole plug (hereinafter referred to as MHP). For example, in Patent Literature 1, the MHP can control a gas flow rate of 1 to 20 times (0.01 to 0.20 Nm 3 / min). Therefore, the MHP is easily adopted in comparison with the double pipe method or the slit method.

[0005] The MHP is a structure in which a plurality of metal pipes connected to a gas storage chamber are embedded in a magnesia-carbon brick or the like carbon-containing refractory. Therefore, its manufacturing is different from that of the nozzle of the double pipe method or the slit method, and the following method is adopted.

[0006] That is, using a high dispersibility high-speed mixer or the like as a kneading means, a raw material to which a carbon source such as flaky graphite, a binder such as pitch, a metallic substance, and a phenol resin is added to an aggregate such as magnesia is kneaded. Further, a kneaded material constituting a carbon-containing refractory in which a metallic fine tube is embedded is obtained. Then, while laying the metallic fine tube, the metallic fine tube is embedded in a layered manner, and then, using a press, molding is performed at a prescribed pressure. Then, a prescribed drying is performed (thereafter, the metallic fine tube is joined to a member for gas storage by welding), or the metallic fine tube is joined to the member for gas storage by welding in advance, and then, after the kneaded material is filled around the same, molding is performed at a prescribed pressure using a press. Then, a prescribed drying is performed, and by such a method or the like, an MHP is manufactured.

[0007] Compared with a refractory of a furnace wall or the like, the damage amount (loss amount) of the bottom blowing nozzle is large, and is an important member that affects the life of the furnace, and therefore, various schemes for suppressing the damage thereof have been conventionally proposed, and for an MHP, for example, the following improvement scheme has been proposed.

[0008] In Patent Document 2, the gas blowing nozzle portion of the MHP is integrated with the surrounding tuyere, and thereby, the advanced melting loss and the abrasion from the joint portion are reduced. However, the damage of the MHP also occurs in a portion in which the metallic fine tube is embedded. Therefore, this technique is not an effective countermeasure.

[0009] Further, as one of the important factors of the damage of the MHP, the low melting point due to carburization of the metallic fine tube embedded in the refractory (advanced damage of the metallic fine tube) can be cited. As a countermeasure thereof, the following scheme has been proposed.

[0010] In Patent Document 3, in order to suppress the carburization of a stainless steel-made metallic fine tube embedded in a carbon-containing refractory such as magnesia carbon, an oxide layer is formed on the surface of the metallic fine tube by thermal spraying. However, in a refining furnace such as a converter that is used for a long period of time (for example, a use period of 2 months to half a year), there is a problem in that the film thickness of the oxide layer is insufficient, and the carburization suppression effect is small.

[0011] Further, in Patent Document 4, in order to suppress the carburization of the metallic fine tube, a scheme in which a refractory sintered body is disposed between the metallic fine tube and the carbon-containing refractory has been proposed. In this technique, the carburization suppression effect can be confirmed. However, in a nozzle in which a plurality of metallic fine tubes are embedded, since the interval of the metallic fine tubes is narrow, it is difficult to dispose the refractory sintered body, and practical use is difficult.

[0012] Prior Art Documents

[0013] Patent Documents

[0014] Patent Document 1: Japanese Patent Application Laid-Open No. 59-31810

[0015] Patent Literature 2: Japanese Patent Application Laid-Open No. 63-24008

[0016] Patent Literature 3: Japanese Patent Application Laid-Open No. 2000-212634

[0017] Patent Literature 4: Japanese Patent Application Laid-Open No. 2003-231912

[0018] Patent Literature 5: Japanese Patent Application Laid-Open No. 58-15072

[0019] Patent Literature 6: Japanese Patent No. 3201678

[0020] Patent Literature 7: Japanese Patent Application Laid-Open No. 2017-144460 SUMMARY

[0021] As described above, in the case of embedding a metal pipe type gas blowing nozzle (MHP or the like) in a carbon-containing refractory, various studies have been made on the refractory material or structure in order to improve the durability, but the current situation is that sufficient improvement effect has not been obtained.

[0022] Therefore, the object of the present application is to solve the problems of the prior art as described above. The object of the present application is to provide a manufacturing method of a gas blowing nozzle refractory in which one or more metal pipes for gas blowing are embedded in a carbon-containing refractory, which is a manufacturing method of a gas blowing nozzle refractory that can improve the durability of the gas blowing nozzle.

[0023] As for the cause of damage to the MHP used in a converter or an electric furnace, it has been considered so far that it is mainly due to the strong blowing of gas from the metal pipe, and the melting loss and the abrasion due to the flow of molten steel near the working surface of the nozzle. The countermeasure of Patent Literature 2 is based on this view. In addition, there is a view that the metal pipe is consumed first due to carburization or the like, and thus the damage becomes large, and therefore, carburization to the metal pipe is prevented by the method of Patent Literature 3 or Patent Literature 4. On the other hand, there is a view that the refractory is cooled by the strong blowing of inactive gas at the time of blowing, and peeling damage occurs due to the temperature difference between the time of blowing and the time of non-blowing. In addition, there is a view that the working surface cracks and is damaged at a portion where the carbon-containing refractory has the lowest strength around 600°C. Thus, although there are various views, no conclusion has been reached. As a result, the current situation is that there is no sufficient countermeasure, and as described above, satisfactory durability has not been obtained.

[0024] Therefore, the present inventors and others have investigated the real cause of MHP damage by recovering used products (MHP) actually used in a furnace and conducting a detailed investigation of the refractory structure in the vicinity of the nozzle working surface. As a result, it was found that a very large temperature change of 500 to 600°C occurs in the refractory at a depth of about 10 to 20 mm from the working surface, and a crack parallel to the working surface can be confirmed at this portion. Based on the results of repeated detailed investigations of the vicinity of the working surface of such actual furnace used products, the following conclusions were reached: the damage pattern of MHP is not damage due to melting or abrasion, but rather damage due to thermal shock caused by the sharp temperature gradient occurring in the vicinity of the working surface.

[0025] As a view on thermal shock resistance up to now, in order to prevent cracks from occurring in the carbon-containing refractory itself as the base material of the nozzle, improvements for achieving low modulus of elasticity, low thermal expansion, and high strength of the material have been conducted. However, under such conditions where a sharp temperature change occurs in a very narrow range of the working surface as described above, it is difficult to prevent the occurrence of cracks themselves. For this reason, the present inventors and others have researched an improvement method in which cracks are difficult to propagate even if cracks occur, and have focused on the fracture energy of the carbon-containing refractory.

[0026] The fracture energy of a refractory is defined as the energy required to form a new surface when a crack propagates to form the surface. A refractory accumulates a certain amount of elastic energy under thermal stress, and a crack occurs due to this energy, so the greater the fracture energy, the more difficult it is for a crack to propagate.

[0027] Up to now, various methods for increasing the fracture energy of a refractory have been researched, and for example, it is known that the fracture energy can be increased by adding carbon long fibers. However, if carbon long fibers are added, there is a disadvantage in that the filling property of the carbon-containing refractory deteriorates, and thus practical use has not been possible to date.

[0028] In the past, a technique of non-oxidative firing and organic impregnation of a refractory has been known, which is mainly aimed at improving the corrosion resistance or thermal spalling resistance of a refractory used for lining a furnace. For example, Patent Document 5 is a technique in which a magnesia carbon brick to which Al powder is added is fired and heated in a non-oxidizing atmosphere at 500 to 1000°C, and then an organic material is impregnated in the pores of the brick at a carbonization yield of 25% or more, thereby achieving an increase in thermal strength and an increase in corrosion resistance. In addition, in Patent Document 6, a magnesia carbon brick to which 0.5 to 10% by weight of precalcined anthracite is added is fired in a reducing atmosphere at 600 to 1500°C, thereby achieving an improvement in slag erosion resistance and an improvement in thermal spalling resistance based on a decrease in modulus of elasticity. In this Patent Document 6, the modulus of elasticity after reduction firing at 1400°C is evaluated as an index of spalling resistance, and it is pointed out that it is important for the modulus of elasticity to be 1.2 x 10 4MPa or less. Although it is further explained that impregnation of tar after reduction firing can be performed to achieve sealing of pores, strength improvement, and improvement of hydration resistance, no examples are described.

[0029] As described above, the conventional technology of performing non-oxidative firing and organic impregnation on a refractory is mainly aimed at improving the corrosion resistance or heat spalling resistance of the refractory used for lining a furnace. In contrast, Patent Document 7 discloses that a method of impregnating a refractory with an organic substance after non-oxidative firing (non-oxidative firing and organic impregnation) is effective for increasing the fracture energy.

[0030] Here, the reason why the fracture energy is increased by performing non-oxidative firing and organic impregnation on a carbon-containing refractory is not clear, but is considered as follows.

[0031] A carbon-containing refractory (brick) is generally manufactured using phenol resin or the like as a binder. Phenol resin is thermally decomposed at high temperatures, and a part thereof forms residual carbon, which functions as a binding material of the carbon-containing refractory. However, the degree of binding is large. In addition, a crack tends to propagate, and thus the fracture energy is not large. In contrast, when an organic substance is impregnated after non-oxidative firing, the organic substance is uniformly diffused and impregnated into the inside of the refractory, and the organic substance enters a matrix portion or interlayer of flaky graphite or the like in the refractory. These organic substances are decomposed by being heated when a nozzle is used, and form carbon bonds. As a result, loose binding is generated between the carbon material such as flaky graphite and the refractory aggregate, and the degree of binding is improved. As a result, even if a crack is generated, it does not easily propagate. Furthermore, since loose binding is generated, the carbon bonds from the organic substance are torn by a moderate stress, and function as a bridge between brick organizations as in the case where carbon long fibers are added, and an effect of improving the pullability, so-called, is obtained, and as a result, the fracture energy is increased.

[0032] However, as a result of the research by the present inventors and the like, it was found that in the method of Patent Document 7, as the fracture energy is increased, there is a limit to the improvement of the durability, and in contrast, by performing non-oxidative firing and organic impregnation a plurality of times, the fracture energy is drastically increased.

[0033] On the other hand, as a problem of MHP, as shown in Patent Documents 3 and 4, there is a phenomenon of carburization to the metal tube when gas is blown from the metal tube. The carburization to the metal tube is known to occur by a carbon source contained in the refractory (brick) to penetrate into the metal tube at a high temperature during actual machine operation, and due to the carburization, the melting point of the metal tube decreases and the nozzle damage amount increases. In the present application, it was found that, in manufacturing the refractory for a gas blowing nozzle, by performing multiple non-oxidative firing and organic matter impregnation on the carbon-containing refractory in which the metal tube is embedded, the fracture energy can be dramatically increased. However, even in this non-oxidative firing, depending on the heat treatment conditions, the carbon component from the carbon-containing refractory can penetrate into the metal tube, and the low melting point of the tube due to carburization can occur. Therefore, in the multiple non-oxidative firing of the carbon-containing refractory in which the metal tube is embedded, the low melting point due to carburization of the metal tube is prevented. Therefore, the non-oxidative firing conditions (firing temperature, firing time), and the carbon content of the metal tube after non-oxidative firing, etc. were studied in detail, and it was found that the optimal conditions for practical use that can suppress the low melting point of the metal tube were discovered.

[0034] As described above, for the carbon-containing refractory in which the metal tube is embedded for MHP, by performing multiple non-oxidative firing and organic matter impregnation, the fracture energy of the refractory formed around the metal tube can be significantly improved. Thereby, the propagation of the cracks generated near the working surface of the MHP can be suppressed, and the life of the MHP can be greatly improved. In addition, it was found that by optimizing the non-oxidative firing conditions, etc., the carburization to the metal tube during the manufacturing process of the MHP is suppressed, and a higher life can be achieved.

[0035] The present application was completed based on such insight, and the gist is as follows.

[0036] [1] A manufacturing method of a refractory for a gas blowing nozzle, characterized by a manufacturing method of a gas blowing nozzle refractory in which one or more metal tubes for gas blowing are embedded in a carbon-containing refractory, wherein a series of processes of performing non-oxidative firing on the carbon-containing refractory in which the metal tube is embedded, and then performing impregnation treatment of impregnating an organic matter having a carbon residue rate of 30 mass% or more in the carbon-containing refractory are performed multiple times.

[0037] [2] The manufacturing method of a refractory for a gas blowing nozzle according to the above [1], characterized in that the non-oxidative firing is performed at a firing temperature of 400 to 1100°C and a firing time of 1 to 20 hours.

[0038] [3] The manufacturing method of a refractory for a gas blowing nozzle according to the above [1], characterized in that the non-oxidative firing is performed at a firing temperature of 800 to 1100°C and a firing time of 3 to 20 hours.

[0039] [4] The method for manufacturing a refractory for a gas injection nozzle according to any one of the above [1] to [3], characterized in that the series of processes of performing non-oxidative firing and impregnation treatment of an organic substance are performed 2 to 3 times.

[0040] [5] The method for manufacturing a refractory for a gas injection nozzle according to any one of the above [1] to [4], characterized in that the conditions of the non-oxidative firing are set in such a way that the total carbon penetration index N at the time of the total firing in the plurality of the above non-oxidative firings is below a threshold value.

[0041] [6] The method for manufacturing a refractory for a gas injection nozzle according to any one of the above [1] to [5], characterized in that the carbon-containing refractory that constitutes the manufactured refractory for a gas injection nozzle has a fracture energy of 175 J / m 2 or more.

[0042] [7] The method for manufacturing a refractory for a gas injection nozzle according to any one of the above [1] to [6], characterized in that the carbon-containing refractory that constitutes the manufactured refractory for a gas injection nozzle has a porosity of 3% or less.

[0043] [8] The method for manufacturing a refractory for a gas injection nozzle according to any one of the above [1] to [7], characterized in that the carbon content of the metal fine tube after the final non-oxidative firing is 2.0 mass% or less.

[0044] [9] The method for manufacturing a refractory for a gas injection nozzle according to any one of the above [1] to [7], characterized in that the carbon content of the metal fine tube after the final non-oxidative firing is 1.3 mass% or less.

[0045]

[10] The method for manufacturing a refractory for a gas injection nozzle according to any one of the above [1] to [9], characterized in that the organic substance that is impregnated in the carbon-containing refractory in the impregnation treatment is one or more selected from the group consisting of coal tar pitch, phenol resin, and furan resin.

[0046]

[11] A refractory for a gas injection nozzle, characterized in that one or more metal fine tubes for gas injection are embedded in a carbon-containing refractory,

[0047] the carbon-containing refractory has a fracture energy of 175 J / m 2 or more.

[0048]

[12] The refractory for a gas injection nozzle according to the above

[11] , characterized in that the carbon-containing refractory has a porosity of 3% or less.

[0049]

[13] The refractory for a gas injection nozzle according to the above

[11] or

[12] , characterized in that the carbon content of the metal fine tube is 2.0 mass% or less.

[0050]

[14] The refractory for a gas injection nozzle according to any one of

[11] to

[12] , characterized in that the carbon content of the metal fine tube is 1.3 mass% or less.

[0051]

[15] A gas injection nozzle characterized by comprising the refractory for a gas injection nozzle according to any one of

[11] to

[14] .

[0052] According to the production method of the present application, a refractory for a gas injection nozzle, in which a carbon-containing refractory having a metal fine tube buried therein has high fracture energy, and the propagation of cracks due to a sharp temperature gradient in the vicinity of the nozzle working surface is suppressed, can be produced. By using the refractory for a gas injection nozzle, the life of the gas injection nozzle can be greatly improved.

[0053] Further, by optimizing the carbon content of the metal fine tube after non-oxidative firing, and the like, by non-oxidative firing conditions (firing temperature, firing time), carburization into the metal fine tube is suppressed, and thus the melting point of the metal fine tube can be prevented from decreasing, and the life of the gas injection nozzle can be further improved. DETAILED DESCRIPTION

[0054] The present application is a production method of a refractory for a gas injection nozzle in which one or more metal fine tubes for gas injection are buried in a carbon-containing refractory. The method is a series of processes in which non-oxidative firing of the carbon-containing refractory having the metal fine tube buried therein is performed (non-oxidative firing process), and then an organic substance having a carbon residue ratio of 30 mass% or more is impregnated in the carbon-containing refractory (impregnation treatment process).

[0055] In the following description, for convenience, a gas injection nozzle in which several tens or more metal fine tubes are buried in a carbon-containing refractory is sometimes referred to as "MHP".

[0056] Note that the material (raw material) and the molding method of the carbon-containing refractory, the material and the number of the metal fine tubes, the method of burying the metal fine tube in the carbon-containing refractory, and the like, used in the production method of the present application will be described in detail later.

[0057] In the present application, the object of the non-oxidative firing and the organic substance impregnation is the carbon-containing refractory having the metal fine tube buried therein. In the case where the gas injection nozzle is of a type having a gas storage chamber, the object can be only the carbon-containing refractory having the metal fine tube buried therein. Alternatively, the carbon-containing refractory can have the metal fine tube buried therein, and all or a part of the member for storing gas can be joined to the metal fine tube.

[0058] In the present application, after non-oxidative firing of the carbon-containing refractory, impregnation treatment of the organic substance is performed, but if non-oxidative firing is not performed, the organic substance cannot be impregnated. Basically, the carbon-containing refractory (brick) is an unfired refractory obtained without a firing process, and as the binder cures, the porosity of the refractory is several percent, which is very low. Therefore, in the state of the unfired product, it is difficult to impregnate the organic substance throughout the refractory. Therefore, in order to impregnate the organic substance, it is necessary to perform non-oxidative firing in advance. Furthermore, at the time of non-oxidative firing, by performing heat treatment on the entire refractory, carbon components from the binder and the like are homogeneously generated as a binding material. Therefore, for the unfired product in which the refractory structure changes due to heating at the time of actual machine operation, both a homogeneous refractory structure and easy impregnation of the organic substance can be obtained.

[0059] In the present application, by performing non-oxidative firing and impregnation of the organic substance a plurality of times, the fracture energy is greatly increased, which is considered to be caused by the following reasons. That is, at the time of impregnation of the organic substance, the organic substance impregnated in the carbon-containing refractory contains a gasification component (a component that becomes a gas and escapes to the outside of the refractory even without oxygen when the temperature rises, such as alcohol) and a residual carbon component (a component that does not become a gas and remains inside the refractory when the temperature rises without oxygen, such as carbon). The gasification component escapes to the outside of the refractory in the normal temperature environment after the manufacture of the refractory and in the high temperature environment at the time of actual machine use, and reduces the effect of impregnation of the organic substance. By repeatedly performing non-oxidative firing and impregnation of the organic substance a plurality of times, the following occurs: escape of the gasification component based on non-oxidative firing → impregnation of the organic substance into the pores based on impregnation → escape of the gasification component based on non-oxidative firing (the pores are reduced from the previous time due to the residual carbon component) → impregnation of the organic substance into the pores based on impregnation. Furthermore, even if exposed to high temperatures, the remaining pores are still reduced. For example, if an organic substance whose volume becomes half due to non-oxidative firing is used, even if the gasification component escapes after 1 time of impregnation, the volume of the pores is still half. In addition, after 2 times of impregnation, the volume of the pores is further halved (one fourth of the original). Furthermore, after 3 times of impregnation, the volume of the pores is further halved (one eighth of the original). Thus, by performing non-oxidative firing and impregnation of the organic substance a plurality of times, the volume of the pores is greatly reduced, and as a result, the fracture energy is greatly increased.

[0060] In addition, if non-oxidative firing and impregnation of the organic substance are performed a plurality of times, since the pores are filled with residual carbon at each time of non-oxidative firing and impregnation of the organic substance, it is also expected to have the effect of improving thermal conductivity, moderating temperature gradients, and reducing thermal shock.

[0061] The firing temperature (heat treatment temperature) during the non-oxidative firing of carbonaceous refractories is preferably 400°C to 1100°C. When the firing temperature is below 400°C, the thermal decomposition of the binder (usually resins such as phenolic resins) does not occur sufficiently, and during the impregnation treatment after non-oxidative firing, the impregnation of organic matter is insufficient, and the fracture energy may not be adequately improved. On the other hand, if the firing temperature exceeds 1100°C, the carburization of the metal capillary by the carbon components from the carbonaceous refractories may lead to a lower melting point of the metal capillary. Furthermore, since multiple non-oxidative firings are performed in this invention, if the firing temperature exceeds 1100°C, the embedded metal capillary may melt or become blocked, and the gas blowing function of the gas blowing nozzle may be lost.

[0062] In addition, in order to more effectively impregnate organic matter in the impregnation treatment after non-oxidative firing, the firing temperature is preferably 800°C or higher.

[0063] The firing time (holding time) for non-oxidative firing is preferably 1 to 20 hours. If the firing time is less than 1 hour, the overall heat treatment of the nozzle may be insufficient. On the other hand, if the firing time exceeds 20 hours, similar to when the firing temperature exceeds 1100°C, carburization into the metal capillary occurs, which may lead to the metal capillary becoming low-melting-point. From this point of view, a more preferred firing time is 3 to 20 hours.

[0064] In particular, in this invention, since multiple non-oxidative firings are performed, it is preferable to control the total amount of heat treatment performed multiple times. Specifically, the conditions for non-oxidative firing are set such that the total carburization index N during firing, as shown in the following formula (1), is below a threshold value. The conditions for non-oxidative firing are described as including, for example, the number of firings, firing temperature, and firing time.

[0065]

[0066] Here, D is the carbon diffusion coefficient, expressed by the following equation (2). It should be noted that the total carburization index N during firing is the carbon diffusion coefficient D integrated over the total firing time of each firing cycle, multiplied by 10. 9 The value obtained.

[0067]

[0068] In equation (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 firing time. The total carburization index N during firing is an indicator of the degree to which carbon penetrates into the metal capillary. The threshold is a value calculated through repeated pre-tests and appropriately determined according to the material of the metal capillary; an example in this embodiment is 118. That is, in this embodiment, it is preferable to set the number of firings, firing temperature, and firing time such that the total carburization index N during firing is 118 or less when multiple non-oxidative firings are performed. If the total carburization index N during firing exceeds the threshold, the carbon content of the metal capillary after non-oxidative firing exceeds 2.0% by mass, and the durability of the nozzle itself decreases. It should be noted that from the viewpoint of carburizing the metal capillary, there is no lower limit value for the total carburization index N during firing; therefore, a lower limit value for the heat treatment amount can be set from other viewpoints such as the thermal decomposition of the binder.

[0069] In this invention, the carbon-containing refractories are fired using a non-oxidizing method to preserve their inherent properties, such as resistance to heat spalling and resistance to slag penetration. Specifically, if firing is performed under conditions that significantly reduce the carbon content of the refractories, such as high-temperature and prolonged heating in an oxidizing atmosphere, the carbon in the refractories will oxidize and disappear. Furthermore, the properties of heat resistance to spalling and resistance to slag penetration will be lost. Therefore, firing is performed under non-oxidizing conditions to prevent the loss of these properties.

[0070] The conditions for non-oxidizing firing are described in terms of the number of firings, firing temperature, and firing time. However, there are no particular restrictions as long as the carbon, such as scaly graphite, contained in the carbon-containing refractory does not substantially disappear. For example, the conditions for non-oxidizing firing can be applied to reduction firing, firing in a reducing atmosphere, firing in a non-oxidizing atmosphere, and short-time firing in an oxidizing atmosphere.

[0071] There are no particular restrictions on the implementation method of non-oxidative firing; it can be carried out according to conventional methods. For example, a sheath made of composite bricks or a metal container is placed on a trolley loaded into the firing furnace, and carbonaceous refractory material (carbonaceous refractory material with embedded metal tubes) for reduction firing is placed inside it. Then, carbon sources such as coke are introduced around the carbonaceous refractory material, and a cover is placed on top to block outside gas, and reduction firing (heat treatment) is carried out at a specified temperature and time.

[0072] Alternatively, the firing of carbonaceous refractories can be carried out in a reducing atmosphere containing a flammable gas such as N2, or in a non-oxidizing atmosphere containing an inactive or non-oxidizing gas such as nitrogen or argon. In the case of firing in a reducing or non-oxidizing atmosphere, a sheath or metal container may not be necessary.

[0073] Further, the carbon-containing refractory can be fired for a short time even if fired in an oxidizing atmosphere, and after firing, the decarburized layer formed on the surface is removed, and the portion of the refractory that has not been decarburized is used. In this method, the surface of the carbon-containing refractory is in an oxidized state. However, with the oxidation of the surface, this portion can function as a protective layer, and the interior of the refractory can be fired under non-oxidizing conditions. Thus, the interior of the refractory can be considered to have been substantially non-oxidatively fired. In addition, the firing of the carbon-containing refractory can also be performed by a method in which an antioxidant glaze or the like is applied to the surface of the carbon-containing refractory in advance.

[0074] However, in the above method, reduction firing, firing in a reducing atmosphere, and firing in a non-oxidizing atmosphere are more preferable. Since the decarburized layer on the surface needs to be removed in firing in an oxidizing atmosphere, this method is not economical.

[0075] The carbon content of the final non-oxidatively fired metal fine tube (metal fine tube embedded in the carbon-containing refractory) is preferably 2.0 mass% or less. If the carbon content of the metal fine tube exceeds 2.0 mass%, the melting point of the metal fine tube decreases, and thus the metal fine tube can melt near the working surface of the tip portion of the nozzle, and the durability of the nozzle itself decreases. In addition, from the above viewpoint, the carbon content of the metal fine tube is more preferably 1.3 mass% or less.

[0076] As a method for making the carbon content of the non-oxidatively fired metal fine tube 2.0 mass% or less (preferably 1.3 mass% or less), for example, (i) reducing the non-oxidative firing temperature and not making the non-oxidative firing time too long can be given. Specifically, the non-oxidative firing temperature is sometimes set to 1000°C or less, and the non-oxidative firing time is set to 20 hours or less. In addition, as another method, for example, (ii) coating a non-permeable coating film on the surface of the metal fine tube to suppress carburization or the like can be given, but method (i) is particularly effective.

[0077] The carbon-containing refractory subjected to the above non-oxidative firing process is subjected to impregnation treatment with an impregnated organic substance.

[0078] In the impregnation treatment of the organic substance, the carbon residue rate of the impregnated organic substance is 30 mass% or more. The carbon residue rate of the organic substance is measured according to the fixed carbon measurement method described in JIS K6910 (Test method for phenol-formaldehyde resin). When the carbon residue rate of the impregnated organic substance is less than 30 mass%, the effect of the refractory structure strengthening by the carbon residue is small, and is not preferable. From this viewpoint, the more preferable carbon residue rate is 35 mass% or more.

[0079] As the organic substance to be impregnated, coal tar pitch (heated and melted product), phenol resin (liquid resin), furan resin (liquid resin), and the like can be given, and one or more of these can be used, but among them, coal tar pitch is particularly preferred. In coal tar pitch, carbon after thermal decomposition is easily crystallized, and thus is more effective in increasing the fracture energy. In contrast, in phenol resin, carbon after thermal decomposition is difficult to crystallize, and easily becomes glassy carbon. Thus, the effect of increasing the fracture energy is lower than that of coal tar pitch.

[0080] The method of impregnating the organic substance is not particularly limited. Among them, it is preferred to first perform vacuum and pressure reduction, 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 under a pressure of 5 kgf / cm 2 for 2 hours or more, and the organic substance is impregnated. If the vacuum pressure is high, the organic substance can not be uniformly impregnated into the interior of the refractory due to air bubbles remaining in the refractory. Thus, the vacuum pressure during pressure reduction is preferably 100 Torr or less, and more preferably 60 Torr or less. In addition, if the pressure after pressure reduction is low or the pressure holding time is short, the organic substance can not be sufficiently impregnated into the refractory. Thus, the pressure after pressure reduction is preferably 5 kgf / cm 2 or more, and more preferably 10 kgf / cm 2 or more. In addition, the pressure holding time is preferably 2 hours or more, and more preferably 4 hours or more. By satisfying these impregnation conditions, the organic substance is uniformly impregnated into the carbon-containing refractory, and according to the principle described above, the effect of increasing the fracture energy of the carbon-containing refractory can be particularly effectively obtained.

[0081] As described above, the apparatus for impregnating the carbon-containing refractory to a prescribed vacuum pressure, and then impregnating the organic substance under a prescribed pressure can use a general impregnation treatment apparatus used when impregnating the organic substance, such as a slide plate. In addition, in order to remove volatile components remaining in the carbon-containing refractory after impregnation, drying treatment at about 200°C can be performed.

[0082] In the present application, by performing multiple non-oxidative firing and organic substance impregnation, the fracture energy is greatly increased. However, if the number of times of implementation reaches a certain degree, the effect of increasing the fracture energy saturates. Thus, in consideration of economy, the number of times of non-oxidative firing and organic substance impregnation is preferably about 2 to 3 times.

[0083] The refractory for gas injection nozzles manufactured by the method of the present application has a fracture energy of the carbon-containing refractory of preferably 175 J / m 2 or more. If the fracture energy is less than 175 J / m 2The difference from the conventional once impregnated refractory (refractory obtained by performing non-oxidative firing and organic matter impregnation only once) is small. Therefore, the life improvement effect of the gas injection nozzle is small. That is, by making the fracture energy of the carbon-containing refractory 175 J / m 2 Thus, the propagation of cracks generated near the working surface of the nozzle due to a sharp temperature gradient can be particularly effectively suppressed, and the life of the gas injection nozzle can be greatly improved.

[0084] The fracture energy is measured using a three-point bending test method. That is, the refractory for the gas injection nozzle is a test piece of 25 x 25 x 140 mm, and a three-point bending test of 100 mm span is performed in a non-active atmosphere at 800°C. Then, a bending load is applied to the test piece at a rate of 0.1 mm / min to obtain a stress-strain curve, and the fracture energy is obtained from the area formed by the stress-strain curve.

[0085] The fracture energy was compared for the carbon-containing refractory of the same material, and the samples (i) to (v) after the following non-oxidative firing and organic matter impregnation were performed after molding. The sample (i) is a sample after the usual drying treatment. The sample (ii) is a sample after further non-oxidative firing after the drying treatment. The sample (iii) is a sample after non-oxidative firing and organic matter impregnation only once after the drying treatment. The sample (iv) is a sample after non-oxidative firing and organic matter impregnation twice under the conditions of the present application after the drying treatment. The sample (v) is a sample after non-oxidative firing and organic matter impregnation three times under the conditions of the present application after the drying treatment. As a result, the fracture energy was 85 J / m 2 for the sample (i), 62 J / m 2 for the sample (ii), 160 J / m 2 for the sample (iii), 187 J / m 2 for the sample (iv), and 193 J / m 2 for the sample (v). Thus, by performing non-oxidative firing and organic matter impregnation multiple times, the fracture energy is effectively increased.

[0086] Here, in the refractory for the gas injection nozzle obtained by the conventional method (fracture energy 160 J / m 2 and below), a crack is generated at a position about 100 mm inside the refractory from the working surface of the nozzle. Also, a phenomenon in which the thickness of the refractory for the gas injection nozzle is instantaneously reduced by about 100 mm occurs, and the durability is reduced by about 10%. However, the present application product having a fracture energy of 175 J / m 2 does not have such a phenomenon.

[0087] It should be noted that as a method for increasing the fracture energy of the refractory, there is a method of adding carbon fibers (carbon long fibers) as described above. However, although the addition of carbon fibers is effective for increasing the fracture energy, it can result in very poor fusion of the carbon fibers with the refractory, a very high porosity, and a porous structure. Therefore, in a material in which carbon fibers are added, the corrosion resistance and the like can be greatly reduced and it is difficult to be practically used. In contrast, the non-oxidative firing and organic matter impregnation can both maintain the density of the refractory structure and increase the fracture energy, and thus are preferable.

[0088] In addition, in the refractory for gas injection nozzles produced by the method of the present application, the porosity of the carbon-containing refractory is preferably 3% or less. This porosity is an index of the amount of organic matter impregnation, and means that if the porosity is large, the amount of impregnation is small, and if the porosity is small, the amount of impregnation is large. If the amount of organic matter impregnation is small and the porosity of the carbon-containing refractory exceeds 3%, the effect of the organic matter impregnation is small, the effect of strengthening the refractory structure and increasing the toughness is small, and it is difficult to ensure a fracture energy of 175 J / m 2 or more. The more preferable porosity of the carbon-containing refractory is 1.5% or less. It should be noted that in order to reduce the porosity of the carbon-containing refractory, it is effective to sufficiently impregnate the organic matter in the carbon-containing refractory.

[0089] Next, the material (raw material) and the molding method of the carbon-containing refractory used in the production method of the present application, the material and the number of the metal fine tubes, the method of embedding the metal fine tubes in the carbon-containing refractory, and the like will be described.

[0090] The raw material of the carbon-containing refractory is generally composed of aggregate, a carbon source, other additive materials, and a binder, and the like.

[0091] As the aggregate, magnesium oxide, aluminum oxide, dolomite, zirconia, chromia, spinel (alumina-magnesia, chromia-magnesia), and the like can be given. Although one or more of these can be used, among these, magnesium oxide is particularly preferable from the viewpoint of corrosion resistance to molten metal and molten slag.

[0092] The carbon source is not particularly limited, and generally used carbon sources such as flaky graphite, earthy graphite, petroleum pitch, carbon black, and the like can be used, and one or more of these can be used. The blending amount of the carbon source in the carbon-containing refractory is not particularly limited, and generally about 10 to 25 mass% is appropriate.

[0093] As the other materials, for example, metallic substances such as metal Al, metal Si, Al-Mg alloy, carbides such as SiC, B4C, and the like can be given, but are not limited to these.

[0094] The binder can also use a phenol resin, liquid pitch, and the like that are generally applicable as binders for shaped refractories.

[0095] The metal tube is generally a metal tube having an inner diameter of about 1 to 5 mm and a tube thickness of about 0.5 to 4 mm. The material of the metal tube is not particularly limited, and a metal material having a melting point of 1300°C or higher is preferably used. For example, the material of the metal tube can include a metal material (metal or alloy) containing one or more of iron, chromium, cobalt, and nickel, and in particular, stainless steel (ferrite system, martensite system, austenite system), ordinary steel, and the like.

[0096] The number of metal tubes embedded in the carbon-containing refractory is not particularly limited. The number of metal tubes is one or more. The number of metal tubes is determined by the inner diameter of the metal tube used and the amount of gas required to be blown. Generally, the MHP for a converter is usually embedded in the carbon-containing refractory with about 60 to 250 metal tubes. On the other hand, in the case of a nozzle that only flows a small amount of gas, the number of metal tubes is one to several. Such a gas blowing nozzle can also be damaged by the expansion of cracks caused by thermal shock due to the strong blowing of gas, and thus the present application can also be applied to such a gas blowing nozzle.

[0097] The method of embedding the metal tube in the carbon-containing refractory is not particularly limited. For example, the raw material of the carbon-containing refractory is mixed and kneaded in a mixer as in the case of the above. The metal tube is embedded in a layered state while being laid on the kneaded material, and then molded using a press at a predetermined pressure, and after molding, drying treatment is performed at an appropriate temperature. Furthermore, with respect to the carbon-containing refractory in which the metal tube is embedded, multiple non-oxidative firing and organic material impregnation are performed according to the method of the present application, and then a member for gas storage required for the function of the gas blowing nozzle is joined (welded) to the metal tube to produce an article of the gas blowing nozzle.

[0098] In addition, as another method, the metal tube is joined (welded) to the member for gas storage (upper plate) in advance, the surrounding is filled with the kneaded material, and then molded using a press at a predetermined pressure, and after molding, drying treatment is performed at an appropriate temperature. Furthermore, with respect to the carbon-containing refractory in which the metal tube is embedded, multiple non-oxidative firing and organic material impregnation are performed according to the method of the present application to produce an article of the gas blowing nozzle.

[0099] The kneading method of the raw material of the carbon-containing refractory is not particularly limited, and a high-speed mixer, a wheel mill mixer (cone mixer), an Eirich mixer, or the like can be used, and a kneading method using a kneading device for a shaped refractory can be used.

[0100] The molding of the kneaded material can use a general press used in the molding of refractories, such as an oil hydraulic press, a friction press, or an isostatic press (CIP).

[0101] Molded carbon-containing refractory materials only need to be dried at a drying temperature of 180℃~350℃ for about 5~30 hours.

[0102] Example

[0103] Tables 1 to 3 show the manufacturing conditions and characteristics of the refractory for gas blowing nozzles manufactured in this embodiment (the present invention example and the comparative example).

[0104] As the raw material for the carbonaceous refractory embedded in the metal tubes, the magnesium oxide raw material used as aggregate is fused magnesium oxide (purity 98.2% by mass), the carbon source is scaly graphite (purity 98.4% by mass, average particle size 0.18 mm), and the binder is phenolic resin with a residual carbon content of 46% by mass.

[0105] As a thin metal tube embedded in carbonaceous refractory, a thin metal tube made of ordinary steel with an outer diameter of 3mm and an inner diameter of 2mm is used.

[0106] Coal tar pitch or phenolic resin can be used as the organic material impregnated with carbonaceous refractory. In Tables 1-3, coal tar pitch has a residual carbon content of 42% by mass. Phenolic resin has a residual carbon content of 15% by mass. The residual carbon content was determined according to the fixed carbon determination method described in JIS K6910 (Test Method for Phenolic Resins).

[0107] The raw materials containing carbonaceous refractory were mixed in the proportions shown in Tables 1 to 3, and then kneaded using an Ellis mixer. Next, using a 230×200mm metal mold, thin metal tubes were laid and layered onto the mixture. Finally, a hydraulic press was used at a speed of 2.5 tons / cm³. 2 The refractory is formed under pressure. The formed refractory is then cured and dried in a dryer at 250°C for 10 hours to produce a carbon-containing refractory with embedded metal tubes.

[0108] The carbonaceous refractories prepared above were subjected to non-oxidative firing in coke dust under the conditions shown in Tables 1 to 3, followed by an organic impregnation treatment to obtain a refractories for gas blowing nozzles. In this invention example, the non-oxidative firing and organic impregnation treatments were performed multiple times. During the organic impregnation treatment, the carbonaceous refractories were held at a specified pressure for 10 hours.

[0109] It should be noted that, for the purpose of determining porosity and fracture energy, carbonaceous refractory without embedded metal tubes is prepared using the same raw materials and methods as described above.

[0110] In addition, some of the comparative examples were those that did not undergo non-oxidative firing and organic impregnation, those that only underwent non-oxidative firing without organic impregnation, and those that only underwent one non-oxidative firing and organic impregnation.

[0111] The carbon content of the metal tube was measured for the refractory obtained above. In addition, the porosity and the fracture energy were measured for the refractory in which the metal tube was not embedded. The results thereof are shown in Tables 1 to 3.

[0112] The porosity of the refractory was measured in accordance with JIS R2205. At this time, the vacuum method was used, and the measuring hole liquid was white kerosene.

[0113] The measurement of the fracture energy of the refractory was performed as follows. The test piece size was 25 x 25 x 140 mm, and a three-point bending test was performed with a 100 mm span. The bending test was performed in a non-reactive atmosphere at 800°C. The test machine was "Autograph AG-X / R" manufactured by Shimadzu Corporation, and the crosshead speed was set to 0.1 mm / min. From the stress-strain curve obtained by the three-point bending test, it was confirmed that a stable crack occurred, and the fracture energy was calculated by dividing the area formed by the stress-strain curve by twice the projected area (25 x 25 mm) of the cut surface. It was confirmed that a stable crack occurred in all measurements.

[0114] The carbon content of the metal tube was measured by grinding the cut surface of the test piece in which the metal tube was embedded after non-oxidative firing, and performing quantitative analysis using an analytical electric heating furnace. The measurement range was in the 100 x 100 μm field of view in the portion along the outer periphery of the metal tube, and the amount of carbon was measured. The analysis device used was "JXA-8230" manufactured by JEOL Ltd.

[0115] Further, the carbonization index n at each time of firing, and the total carbonization index N (n x number of times of firing) at the total number of times of firing at the time of multiple non-oxidative firings were calculated. The results thereof are shown in Tables 1 to 3.

[0116] The calculation of the total carbonization index N at the time of firing was performed under the following conditions. First, the frequency factor D0 of carbon diffusion and the activation energy Q for carbon diffusion in Formula (1) were represented by the following formulae.

[0117] D0 = (4.725 - 5.374 Wc + 1.779 Wc 2 ) x 10 -5

[0118] Q = 154.5 - 21.04 Wc - 3.285 Wc 2

[0119] Here, Wc is the saturation carbon concentration, and in the present embodiment, Wc = 2.14%. Wc is also referred to as the carbon solid solution limit. The portion exceeding the carbon solid solution limit precipitates cementite. When Wc = 2.14%, D0 = 1.37E-05 (m 2 / s), and Q = 94.43041 (kJ / mol).

[0120] In addition, in the present embodiment, the gas constant R in formula (1) = 8.314 J / (K-mol).

[0121] According to Tables 1 to 2, the inventive examples are all low in porosity and also high in fracture energy. In particular, inventive examples 1 to 5, 7 to 11, and 13 to 16 are all 118 or less in the total carbonation index N at firing, and the carbon content of the metal fine tube after non-oxidative firing is 2.0 mass% or less.

[0122] According to Table 3, Comparative Example 1 is a magnesium oxide-carbon brick that is commonly used. The fracture energy of Comparative Example 1 is small. Comparative Example 2 is obtained by subjecting Comparative Example 1 to non-oxidative firing at 1400°C (without organic impregnation treatment). The fracture energy of Comparative Example 2 is small. In addition, the total carbonation index N at firing exceeds 118, and the carbon content of the metal fine tube is large, at 3.1 mass%. In Comparative Example 3, the non-oxidative firing temperature is less than 300°C. In Comparative Example 3, the thermal decomposition of the binder due to non-oxidative firing does not sufficiently occur, and thus the organic substance cannot be impregnated, and the fracture energy is small. In Comparative Example 4, 15 mass% of an organic substance having a small carbon residue rate is used in the impregnation treatment. The increase in the fracture energy of Comparative Example 4 does not reach a satisfactory level. In Comparative Example 5, only one non-oxidative firing-organic impregnation is performed. In Comparative Example 5, although an increase in the fracture energy is found, it is less than that of the inventive examples.

[0123]

[0124] [Table 2]

[0125]

[0126] [Table 3]

[0127]

Claims

1. A method for manufacturing a refractory for a gas blowing nozzle, characterized in that: A method for manufacturing a refractory for a gas blowing nozzle, wherein one or more thin metal tubes for gas blowing are embedded in a carbonaceous refractory, wherein... The process involves a series of steps, including: non-oxidative firing of carbonaceous refractory with embedded metal tubes, followed by impregnation treatment in which organic matter with a residual carbon content of 30% by mass or more is impregnated into the carbonaceous refractory.

2. The method for manufacturing refractory for gas blowing nozzles according to claim 1, characterized in that, Non-oxidative firing is carried out at a firing temperature of 400–1100℃ and a firing time of 1–20 hours.

3. The method for manufacturing refractory for gas blowing nozzles according to claim 1, characterized in that, Non-oxidative firing is carried out at a firing temperature of 800–1100℃ and a firing time of 3–20 hours.

4. The method for manufacturing a refractory for a gas blowing nozzle according to any one of claims 1 to 3, characterized in that, The series of processes involving non-oxidative firing and impregnation of organic matter will be carried out 2 to 3 times.

5. The method for manufacturing a refractory for a gas blowing nozzle according to any one of claims 1 to 4, characterized in that, The conditions for non-oxidative firing are set such that the total carburization index N during the combined firing of multiple non-oxidative firings is below a threshold.

6. A method for manufacturing a refractory for a gas blowing nozzle according to any one of claims 1 to 5, characterized in that, The fracture energy of the carbonaceous refractory constituting the gas blowing nozzle is 175 J / m. 2 above.

7. The method for manufacturing a refractory for a gas blowing nozzle according to any one of claims 1 to 6, characterized in that, The porosity of the carbonaceous refractory constituting the gas-blowing nozzle is less than 3%.

8. A method for manufacturing a refractory for a gas blowing nozzle according to any one of claims 1 to 7, characterized in that, The carbon content of the final non-oxidative sintered metal capillary is less than 2.0% by mass.

9. A method for manufacturing a refractory for a gas blowing nozzle according to any one of claims 1 to 7, characterized in that, The carbon content of the final non-oxidative sintered metal capillary is less than 1.3% by mass.

10. A method for manufacturing a refractory for a gas blowing nozzle according to any one of claims 1 to 9, characterized in that, In the impregnation treatment, the organic material impregnated in the carbonaceous refractory is selected from one or more of coal tar pitch, phenolic resin, and furan resin.

11. A refractory for a gas blowing nozzle, characterized in that, One or more thin metal tubes for gas blowing are embedded in the carbonaceous refractory. The fracture energy of carbon-containing refractory is 175 J / m. 2 above.

12. The refractory for a gas blowing nozzle according to claim 11, characterized in that, The porosity of carbon-containing refractory is less than 3%.

13. The refractory for a gas blowing nozzle according to claim 11 or 12, characterized in that, The carbon content of the metal capillary is less than 2.0% by mass.

14. The refractory for a gas blowing nozzle according to claim 11 or 12, characterized in that, The carbon content of the metal capillary is less than 1.3% by mass.

15. A gas blowing nozzle, characterized in that, A refractory for a gas blowing nozzle comprising any one of claims 11 to 14.

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