Method for producing refractory for gas-blowing nozzle, refractory for gas-blowing nozzle, and gas-blowing nozzle

Abstract

In this method for producing a refractory for a gas blowing nozzle, the refractory comprising a carbon-containing refractory having one or more gas-blowing fine metal pipes embedded therein, a series of steps for subjecting a carbon-containing refractory having fine metal pipes embedded therein to non-oxidative firing, and then performing an impregnation treatment in which the carbon-containing refractory is impregnated with an organic substance having a percentage residual carbon of 30 mass% or higher is performed multiple times. The non-oxidative firing and the organic-substance impregnation performed multiple times enhance the fracture energy of the carbon-containing refractory having fine metal pipes embedded therein, and extension of cracks caused by a steep temperature gradient around the working surface of the nozzle is inhibited when the gas-blowing nozzle is used. As a result, the life of the gas-blowing nozzle is greatly increased.

Description

Method for manufacturing refractory for gas-blowing nozzle, refractory for gas-blowing nozzle, and gas-blowing nozzle

[0001] The present invention aims to improve refining efficiency and alloy yield in converters, electric furnaces, etc. The present invention relates to a refractory for a gas-blowing nozzle for injecting gas into molten metal from the bottom of the furnace, the refractory comprising one or more metal capillaries for gas injection embedded in a carbon-containing refractory, and a method for manufacturing the refractory. The present invention also relates to a refractory for a gas-blowing nozzle and a gas-blowing nozzle.

[0002] In converters, electric furnaces, and the like, bottom blowing is performed, in which a stirring gas (usually an inert gas such as nitrogen or Ar) or a refining gas is blown into the molten metal from the bottom of the furnace, with the aim of improving refining efficiency and alloy yield. Examples of bottom blowing methods include the following (1) to (3). Method (1) is a double-pipe method in which oxygen is blown into the inner pipe for decarburization, and a hydrocarbon gas (such as propane) is blown into the outer pipe for cooling the contact area with the molten steel. Method (2) is a method (slit method) in which slit-shaped openings are provided in the gap between the metal pipe and the brick, and an inert gas is blown through the openings. Method (3) is a method in which multiple (several to several hundred) metal capillaries are embedded in carbon-containing bricks, and an inert gas is supplied to the metal capillaries from the bottom of the bricks via a gas inlet pipe and a gas reservoir, and the inert gas is blown through the metal capillaries.

[0003] In methods (1) and (2), tuyere bricks are manufactured in advance by a standard method. Then, the installation area for the metal pipe that forms the double pipe or slit is processed. Alternatively, the space for installing the metal pipe is formed by dividing the pipe into two or four parts. During construction, the metal pipe for blowing gas is set in advance, and tuyere bricks are installed around it.

[0004] On the other hand, the gas injection plug (nozzle) used in the method (3) is called a multiple hole plug (hereinafter referred to as MHP). For example, in Patent Document 1, it is stated that in this MHP, the gas flow rate is 1 to 20 times (0.01 to 0.20 Nm ３ / min) can be controlled. Therefore, MHP is easier to adopt than the double pipe method or slit method.

[0005] MHPs have a structure in which multiple metal tubes connected to a gas reservoir are embedded in a carbon-containing refractory material such as magnesia-carbon bricks. Therefore, unlike double-tube or slit-type nozzles, their manufacturing method is as follows:

[0006] That is, raw materials, which are obtained by adding a carbon source such as scaly graphite, pitch, metal species, and a binder such as phenolic resin to an aggregate such as a magnesia raw material, are kneaded using a kneading means such as a high-speed mixer with high dispersion performance. A kneaded mixture that will constitute the carbon-containing refractory in which the metal capillaries are embedded is then obtained. The metal capillaries are then laid on top of this kneaded mixture to form a laminated structure, and the resulting mixture is molded at a predetermined pressure using a press. This is followed by a method in which a predetermined drying is performed (the metal capillaries are then welded to a gas reservoir member), or by previously welding the metal capillaries to a gas reservoir member, filling the surrounding area with the kneaded mixture, and molding at a predetermined pressure using a press. An MHP is then manufactured by a method such as a method in which a predetermined drying is performed.

[0007] The bottom blowing nozzle is subject to greater damage (wear) than refractory materials such as furnace walls, and is an important component that determines the furnace life. Therefore, various proposals have been made to suppress damage to the bottom blowing nozzle. For example, the following improvements have been proposed for MHPs:

[0008] In Patent Document 2, the gas injection nozzle portion of the MHP and the surrounding tuyere are integrated to reduce pre-existing erosion and wear from the joints. However, damage to the MHP also occurs in the portion where the metal capillaries are embedded. Therefore, this technology is not a very effective countermeasure. Furthermore, one of the causes of damage to the MHP is the lowering of the melting point due to carburization of the metal capillaries embedded in the refractory (pre-existing damage to the metal capillaries). The following countermeasures have been proposed:

[0009] Patent Document 3 proposes forming an oxide layer on the surface of a stainless steel metal tube embedded in a carbon-containing refractory such as mag-carbon by thermal spraying in order to suppress carburization of the metal tube. However, in a refining furnace such as a converter that is used for a long period of time (for example, for a period of use of two to six months), the oxide layer is not thick enough, resulting in a small carburization suppression effect.

[0010] Furthermore, Patent Document 4 proposes disposing a refractory sintered body between a metal capillary tube and a carbon-containing refractory in order to suppress carburization of the metal capillary tube. This technique is effective in suppressing carburization. However, in a nozzle in which many metal capillary tubes are embedded, the narrow spacing between the metal capillary tubes makes it difficult to dispose a refractory sintered body, making it difficult to put into practical use.

[0011] Japanese Patent Application Laid-Open No. 59-31810 Japanese Patent Application Laid-Open No. 63-24008 Japanese Patent Application Laid-Open No. 2000-212634 Japanese Patent Application Laid-Open No. 2003-231912 Japanese Patent Application Laid-Open No. 58-15072 Japanese Patent No. 3201678 Japanese Patent Application Laid-Open No. 2017-144460

[0012] As described above, in the case of gas-blowing nozzles (such as MHPs) in which a metal capillary tube is embedded in a carbon-containing refractory, various studies have been conducted on the refractory material or structure in order to improve durability, but at present, sufficient improvement effects have not been obtained.

[0013] Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a method for manufacturing a refractory for a gas-blowing nozzle, which comprises a carbon-containing refractory having one or more metal capillaries for gas injection embedded therein, and which can improve the durability of the gas-blowing nozzle.

[0014] Regarding the cause of damage to MHPs used in converters or electric furnaces, it has been thought that the main cause is melting and abrasion caused by the flow of molten steel near the nozzle working surface, due to the forceful gas injection from the metal capillary tube. The countermeasures in Patent Document 2 are based on this concept. Another theory is that the metal capillary tube is worn out first by carburization, causing greater damage, and methods such as those in Patent Documents 3 and 4 have been used to prevent carburization of the metal capillary tube. On the other hand, another theory is that the refractory is cooled during blowing due to the forceful injection of inert gas, and the temperature difference between blowing and non-blowing causes spalling damage. Furthermore, another theory is that the strength of carbon-containing refractories is lowest at around 600°C, causing cracks and damage to the working surface at that temperature. As such, various theories have existed, and no conclusion has been reached. As a result, sufficient countermeasures have not been taken, and as described above, satisfactory durability is not necessarily achieved.

[0015] Therefore, in order to identify the true cause of damage to the MHP, the inventors recovered a used MHP from an actual furnace and conducted a detailed investigation of the refractory structure near the nozzle working surface. As a result, it was discovered that a very large temperature change of 500 to 600°C had occurred inside the refractory at a depth of approximately 10 to 20 mm from the working surface, and furthermore, cracks parallel to the working surface were confirmed in this location. From the results of this detailed investigation of the working surface and its vicinity of the used MHP, it was concluded that the damage to the MHP was mainly due to thermal shock caused by a sudden temperature gradient occurring near the working surface, rather than damage due to melting or wear.

[0016] To date, the concept of thermal shock resistance has been to prevent cracks from occurring in the carbon-containing refractory itself, which is the base material of the nozzle. Improvements have been made to reduce the elastic modulus, thermal expansion, and strength of the material. However, under conditions such as the above where abrupt temperature changes occur in a very narrow range of the operating surface, it is difficult to prevent cracks from occurring. Therefore, the present inventors have been studying methods to improve the resistance by making it difficult for cracks to propagate even if they occur, and have focused on the fracture energy of carbon-containing refractories.

[0017] The fracture energy of a refractory is defined as the energy required to form a new surface when a crack propagates. If a certain amount of elastic energy is stored in a refractory when thermal stress is applied, and this energy is used to generate a crack, the greater the fracture energy, the more difficult it is for the crack to propagate.

[0018] Various methods for improving the fracture energy of refractories have been investigated, and it is known that the fracture energy can be improved by adding long carbon fibers, but the addition of long carbon fibers has the drawback of worsening the packing property of the carbon-containing refractory, and therefore this method has not been put to practical use at present.

[0019] Conventionally, techniques for non-oxidizing firing and impregnating refractories with organic substances have been known, primarily for the purpose of improving the corrosion resistance or heat spalling resistance of refractories used in furnace linings. For example, Patent Document 5 discloses that a magma-carbon brick containing added metal Al powder is fired and heated in a non-oxidizing atmosphere at 500 to 1000°C, and then an organic substance with a carbonization yield of 25% or more is impregnated into the brick pores, thereby improving hot strength and corrosion resistance. Patent Document 6 also discloses that a magma-carbon brick containing added 0.5 to 10 wt% calcined anthracite is fired in a reducing atmosphere at 600 to 1500°C, thereby improving slag erosion resistance and heat spalling resistance by reducing the elastic modulus. Patent Document 6 reports that spalling resistance is evaluated based on the elastic modulus after reduction firing at 1400°C, with an elastic modulus of 1.2 × 10 ４ Furthermore, it is explained that the material may be impregnated with tar after reduction firing, and that this impregnation seals the pores, increases strength, and improves slaking resistance, but no examples are given.

[0020] As described above, the conventional technique of non-oxidizing firing of a refractory and impregnating it with an organic substance has been aimed mainly at improving the corrosion resistance or heat spalling resistance of refractories for furnace linings. In contrast, Patent Document 7 discloses that a method of firing a refractory under non-oxidizing conditions and then impregnating it with an organic substance (non-oxidizing firing and organic substance impregnation) is effective in improving fracture energy. Here, the reason why the fracture energy increases when a carbon-containing refractory is fired under non-oxidizing conditions and impregnated with an organic substance is not necessarily clear, but it is thought to be as follows.

[0021] Carbon-containing refractories (bricks) are generally manufactured using a binder such as phenolic resin. Phenolic resins undergo thermal decomposition at high temperatures, leaving a portion of the phenolic resin as a carbonaceous binder, which functions as a binder for carbon-containing refractories. However, the degree of bonding is high. Furthermore, cracks readily propagate, resulting in low fracture energy. In contrast, when organic matter is impregnated into the refractory after non-oxidizing firing, the organic matter diffuses and penetrates evenly into the interior of the refractory, penetrating into the matrix or between the layers of flake graphite. These organic matter decomposes upon heating during nozzle use, forming carbon bonds. This results in loose bonds between the carbon material, such as flake graphite, and the refractory aggregate, enhancing the degree of bonding. As a result, cracks are less likely to propagate even when they do occur. Furthermore, the loose bonds allow the aforementioned organic carbon bonds to peel off under moderate stress, acting as bridges between the brick structure, similar to the addition of long carbon fibers, resulting in improved pullability and increased fracture energy.

[0022] However, as a result of investigations by the present inventors, it was found that the method of Patent Document 7 has limitations in increasing fracture energy and the accompanying improvement in durability, and that by performing non-oxidizing firing and organic substance impregnation multiple times, fracture energy increases dramatically.

[0023] On the other hand, one of the issues with MHP is the carburization of the metal capillary tubes that occurs when gas is blown through them, as described in Patent Documents 3 and 4. Carburization of the metal capillary tubes occurs when a carbon source contained in the refractory (brick) penetrates into the metal capillary tubes at high temperatures during actual operation. It is known that this carburization lowers the melting point of the metal capillary tubes and increases the amount of nozzle damage. In the present invention, we have discovered that, when manufacturing a refractory for a gas injection nozzle, the fracture energy can be dramatically increased by subjecting a carbon-containing refractory with embedded metal capillary tubes to multiple non-oxidizing firings and organic substance impregnation. However, even during this non-oxidizing firing, depending on the heat treatment conditions, carbon components derived from the carbon-containing refractory penetrate into the metal capillary tubes, causing a lower melting point of the capillary tubes due to carburization. Therefore, we aim to prevent the lower melting point of the metal capillary tubes due to carburization during multiple non-oxidizing firings of a carbon-containing refractory with embedded metal capillary tubes. To this end, detailed studies were conducted on the non-oxidizing firing conditions (firing temperature, firing time), as well as the carbon content of the metal tubes after non-oxidizing firing, and optimal conditions for practical use that can prevent the melting point of the metal tubes from decreasing were found.

[0024] As described above, by repeatedly performing non-oxidizing firing and organic impregnation on a carbon-containing refractory in which metal capillaries for an MHP are embedded, the fracture energy of the refractory surrounding the metal capillaries can be dramatically improved. This makes it possible to suppress the propagation of cracks that occur near the working surface of the MHP, thereby significantly improving the life of the MHP. Furthermore, it has been found that optimizing the non-oxidizing firing conditions and suppressing carburization of the metal capillaries during the MHP manufacturing process can extend the life of the MHP. The present invention was made based on these findings and is summarized as follows.

[0025] [1] A method for producing a refractory for a gas-blowing nozzle, in which one or more thin metal tubes for gas blowing are embedded in a carbon-containing refractory, the method comprising: non-oxidizing firing the carbon-containing refractory in which the thin metal tubes are embedded; and then performing an impregnation treatment on the carbon-containing refractory multiple times, the impregnation treatment being to impregnate the carbon-containing refractory with an organic substance having a residual carbon rate of 30 mass% or more.

[0026] [2] A method for producing a refractory for a gas-blowing nozzle according to the method of [1] above, characterized in that the non-oxidizing firing is carried out at a firing temperature of 400 to 1100°C for a firing time of 1 to 20 hours.

[0027] [3] A method for producing a refractory for a gas-blowing nozzle according to the method of [1] above, characterized in that the non-oxidizing firing is carried out at a firing temperature of 800 to 1100°C for a firing time of 3 to 20 hours.

[0028] [4] A method for producing a refractory for a gas-blowing nozzle according to any one of the above [1] to [3], characterized in that a series of steps of non-oxidizing firing and impregnation treatment with an organic substance is carried out two or three times.

[0029] [5] A method for producing a refractory for a gas-blowing nozzle according to any one of the above [1] to [4], characterized in that the conditions for the non-oxidizing firing are set so that the total carburization index N during firing in a plurality of non-oxidizing firings is equal to or less than a threshold value.

[0030] [6] In the manufacturing method according to any one of the above [1] to [5], the fracture energy of the carbon-containing refractory constituting the manufactured refractory for a gas blowing nozzle is 175 J / m ２ The method for producing a refractory material for a gas-blowing nozzle, characterized by the above.

[0031] [7] A method for producing a refractory for a gas-blowing nozzle according to any one of the above [1] to [6], wherein the porosity of the carbon-containing refractory constituting the produced refractory for a gas-blowing nozzle is 3% or less.

[0032] [8] A method for producing a refractory for a gas-blowing nozzle according to any one of the above [1] to [7], characterized in that the carbon content of the metal capillary after the final non-oxidizing firing is 2.0 mass% or less.

[0033] [9] A method for producing a refractory for a gas-blowing nozzle according to any one of the above [1] to [7], characterized in that the carbon content of the metal capillary after the final non-oxidizing firing is 1.3 mass% or less.

[0034]

[10] The method for producing a refractory for a gas-blowing nozzle according to any one of the above [1] to [9], wherein the organic substance impregnated into the carbon-containing refractory in the impregnation treatment is one or more selected from coal tar pitch, phenolic resin, and furan resin.

[0035]

[11] A refractory for a gas injection nozzle, in which one or more metal thin tubes for gas injection are embedded in a carbon-containing refractory, wherein the fracture energy of the carbon-containing refractory is 175 J / m ２ A refractory for a gas-blowing nozzle characterized by the above.

[0036]

[12] The refractory for a gas-blowing nozzle according to

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

[0037]

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

[11] or

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

[0038]

[14] The refractory for a gas-blowing nozzle according to the above

[11] or

[12] , wherein the carbon content of the metal capillary is 1.3 mass % or less.

[0039]

[15] A gas-blowing nozzle comprising the refractory for a gas-blowing nozzle according to any one of

[11] to

[14] above.

[0040] According to the manufacturing method of the present invention, it is possible to manufacture a refractory for a gas-blowing nozzle, in which the fracture energy of the carbon-containing refractory material having the metal capillaries embedded therein is high and the propagation of cracks caused by a steep temperature gradient near the nozzle working surface is suppressed. By using this refractory for a gas-blowing nozzle, the life of the gas-blowing nozzle can be significantly improved.

[0041] Furthermore, by optimizing the non-oxidizing firing conditions (firing temperature, firing time), the carbon content of the metal tube after non-oxidizing firing, etc., it is possible to suppress carburization of the metal tube, thereby preventing a decrease in the melting point of the metal tube and further improving the life of the gas injection nozzle.

[0042] The present invention relates to a method for producing a refractory for a gas-injection nozzle, which comprises a carbon-containing refractory having one or more metal capillaries for gas injection embedded therein. The method comprises a series of steps, namely, non-oxidizing firing of the carbon-containing refractory having the embedded metal capillaries (non-oxidizing firing step), and then impregnating the carbon-containing refractory with an organic substance having a residual carbon rate of 30 mass% or more (impregnation treatment step), in which the non-oxidizing firing and organic substance impregnation are repeated multiple times.

[0043] In the following description, a gas injection nozzle having several tens of metal thin tubes embedded in a carbon-containing refractory material may be referred to as an "MHP" for convenience of explanation.

[0044] The material (raw material) and molding method of the carbon-containing refractory used in the manufacturing method of the present invention, the material and number of the metal capillaries, and the method of embedding the metal capillaries in the carbon-containing refractory will be described in detail later.

[0045] In the present invention, the object to be non-oxidatively fired and organically impregnated is a carbon-containing refractory in which a metal capillary is embedded. In the case where the gas injection nozzle is of a type having a gas reservoir, the object may be a carbon-containing refractory in which only a metal capillary is embedded. Alternatively, the object may be a carbon-containing refractory in which a metal capillary is embedded and to which all or part of a member for a gas reservoir is joined.

[0046] In the present invention, the carbon-containing refractory is subjected to non-oxidizing firing and then impregnated with an organic substance. However, impregnation with an organic substance is not possible without non-oxidizing firing. Carbon-containing refractories (bricks) are essentially unfired refractories obtained without a firing process, and the porosity of the refractory is extremely low, at only a few percent, due to the hardening of the binder. Therefore, it is difficult to impregnate the entire unfired refractory with an organic substance. Therefore, non-oxidizing firing is required in advance to impregnate the organic substance. Furthermore, non-oxidizing firing involves heat-treating the entire refractory, thereby homogeneously generating carbon components derived from the binder and the like as a binding material. Therefore, it is possible to easily impregnate an unfired refractory, whose structure changes due to heat exposure during actual operation, while still obtaining a homogeneous refractory structure.

[0047] In the present invention, the fracture energy increases dramatically when non-oxidizing firing and organic impregnation are performed multiple times. This is believed to be due to the following reasons. Specifically, the organic material impregnated into the carbon-containing refractory during organic impregnation contains vaporizable components (components that, like alcohol, become gaseous at elevated temperatures even in the absence of oxygen and dissipate outside the refractory). It also contains residual carbon components (components that, like carbon, do not become gaseous at elevated temperatures in the absence of oxygen and remain inside the refractory). These vaporizable components dissipate outside the refractory in the room-temperature environment after refractory manufacture and in the high-temperature environment during actual use, reducing the effectiveness of the organic impregnation. Repeating non-oxidizing firing and organic impregnation multiple times leads to the following sequence: dissipation of vaporizable components due to non-oxidizing firing → filling of pores with organic material due to impregnation → dissipation of vaporizable components due to non-oxidizing firing (the pores are reduced compared to the previous firing due to the residual carbon components) → filling of pores with organic material due to impregnation. Consequently, the number of pores remaining even when exposed to high temperatures decreases. For example, if an organic substance whose volume is halved by non-oxidizing calcination is used, the pore volume will be halved after one impregnation, even if the vaporized components subsequently dissipate. Furthermore, after two impregnations, the pore volume will be halved again (to one-quarter of the original volume). Furthermore, after three impregnations, the pore volume will be halved again (to one-eighth of the original volume). Thus, by performing non-oxidizing calcination and organic substance impregnation multiple times, the pore volume is significantly reduced, and it is thought that the fracture energy will increase dramatically.

[0048] Furthermore, if non-oxidizing firing and organic impregnation are performed multiple times, the pores are filled with residual carbon with each non-oxidizing firing and organic impregnation, which is expected to improve thermal conductivity, alleviate temperature gradients, and reduce thermal shock.

[0049] The firing temperature (heat treatment temperature) in the non-oxidizing firing of the carbon-containing refractory is preferably 400°C or higher and 1100°C or lower. If the firing temperature is lower than 400°C, the thermal decomposition of the binder (usually a resin such as a phenolic resin) does not occur sufficiently, which may result in insufficient impregnation of the organic substance in the impregnation treatment after the non-oxidizing firing, and insufficient improvement in the fracture energy. On the other hand, if the firing temperature exceeds 1100°C, the carbon components derived from the carbon-containing refractory may carburize the metal capillaries, resulting in a lower melting point of the metal capillaries. Furthermore, since the non-oxidizing firing is performed multiple times in the present invention, if the firing temperature exceeds 1100°C, the embedded metal capillaries may melt or become clogged, resulting in a loss of the gas-blowing function as a gas-blowing nozzle.

[0050] In order to more effectively impregnate the organic substance in the impregnation treatment after non-oxidizing firing, the firing temperature is preferably 800° C. or higher.

[0051] The firing time (holding time) for non-oxidizing firing is preferably 1 to 20 hours. If the firing time is less than 1 hour, the heat treatment of the entire nozzle is likely to be insufficient. On the other hand, if the firing time exceeds 20 hours, carburization of the metal capillary occurs, as in the case where the firing temperature exceeds 1100°C, which may result in a lower melting point of the metal capillary. From this perspective, a more preferable firing time is 3 to 20 hours.

[0052] In particular, in the present invention, since non-oxidizing firing is performed multiple times, it is preferable to control the total amount of heat treatment performed multiple times. Specifically, it is preferable to set the conditions for non-oxidizing firing so that the total carburization index N during firing, expressed by the following formula (1), is equal to or less than a threshold value. The conditions for non-oxidizing firing will be explained as including, for example, the number of firings performed, the firing temperature, and the firing time.

[0053]

[0054] Here, D is the carbon diffusion coefficient, and is expressed by the following formula (2): The total carburization index N during firing is calculated by integrating the carbon diffusion coefficient D over the total firing time of each firing. ９ is the value multiplied by

[0055]

[0056] In formula (2), D０ where Q 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 index indicating how much carbon penetrates into the metal capillary. The threshold value is a value calculated in advance by repeated testing and is appropriately determined depending on the material of the metal capillary. In this embodiment, the threshold value is 118, for example. That is, in this embodiment, it is preferable to set the number of firings, the firing temperature, and the firing time so that the total carburization index N during firing after multiple non-oxidizing firings is 118 or less. If the total carburization index N during firing exceeds the threshold value, the carbon content of the metal capillary after non-oxidizing firing will exceed 2.0 mass%, thereby reducing the durability of the nozzle itself. Note that there is no lower limit for the total carburization index N during firing from the perspective of carburization of the metal capillary. Therefore, the lower limit of the heat treatment amount can be set from other perspectives, such as the thermal decomposition of the binder.

[0057] In the present invention, the carbon-containing refractory is fired under non-oxidizing conditions in order to prevent the inherent properties of the carbon-containing refractory, such as thermal spalling resistance and slag penetration resistance, from being impaired. That is, if the carbon-containing refractory is fired under firing conditions that significantly reduce the carbon contained in the carbon-containing refractory, for example, under conditions of heating at a high temperature for a long time in an oxidizing atmosphere, the carbon in the carbon-containing refractory is oxidized and lost. As a result, the properties of the carbon-containing refractory, such as thermal spalling resistance and slag penetration resistance, are lost. Therefore, the carbon-containing refractory is fired under non-oxidizing conditions in order to prevent the above-mentioned properties from being lost.

[0058] Although the non-oxidizing firing conditions have been described as including the number of firings, the firing temperature, and the firing time, there are no particular limitations as long as the conditions are such that carbon such as flaky graphite contained in the carbon-containing refractory is not substantially lost. For example, the non-oxidizing firing conditions that can be applied include reducing firing, firing in a reducing atmosphere, firing in a non-oxidizing atmosphere, and short-time firing in an oxidizing atmosphere.

[0059] The method for performing non-oxidizing firing is not particularly limited, and may be performed by a conventional method. For example, a sheath made of bricks or a metal container is placed on a cart to be loaded into a firing furnace, and a carbon-containing refractory to be subjected to reduction firing (a carbon-containing refractory with metal capillaries embedded therein) is placed inside. Thereafter, a carbon source such as coke is placed around the carbon-containing refractory, and a lid is placed on top, and reduction firing (heat treatment) is performed at a predetermined temperature and for a predetermined time while blocking the outside air.

[0060] The firing of the carbon-containing refractory may be performed in a reducing atmosphere containing a combustible gas such as NX gas, or in a non-oxidizing atmosphere such as nitrogen or argon, or in an inert gas atmosphere such as a non-oxidizing gas. In the case of the reducing atmosphere firing or non-oxidizing atmosphere firing, the sheath or metal container may be unnecessary.

[0061] Furthermore, when firing a carbon-containing refractory, even if firing is performed in an oxidizing atmosphere, it is possible to perform firing for a short time, remove the decarburized layer formed on the surface after firing, and use the undecarburized portion inside the refractory. In this method, the surface of the carbon-containing refractory becomes oxidized. However, as the surface oxidizes, this portion acts as a protective layer, allowing the interior of the refractory to be fired under non-oxidizing conditions. Therefore, the interior of the refractory can be considered to have been fired substantially under non-oxidizing conditions. In addition, when firing a carbon-containing refractory, a method of applying an anti-oxidation glaze to the surface of the carbon-containing refractory in advance can also be used.

[0062] However, among the above methods, reducing firing, firing in a reducing atmosphere, and firing in a non-oxidizing atmosphere are more preferable. Firing in an oxidizing atmosphere is not economical because it requires removing the decarburized layer on the surface.

[0063] The carbon content of the metal capillary tubes (metal capillary tubes embedded in the carbon-containing refractory) after the final non-oxidizing firing is preferably 2.0% by mass or less. If the carbon content of the metal capillary tubes exceeds 2.0% by mass, the melting point of the metal capillary tubes decreases, which may cause the metal capillary tubes to melt near the working surface of the nozzle tip, thereby reducing the durability of the nozzle itself. From the above viewpoints, the carbon content of the metal capillary tubes is more preferably 1.3% by mass or less.

[0064] As a method for making the carbon content of the metal capillary tube after non-oxidizing sintering 2.0 mass % or less (preferably 1.3 mass % or less), for example, (i) the non-oxidizing sintering temperature is set low and the non-oxidizing sintering time is not excessively long. Specifically, the non-oxidizing sintering temperature is set to 1000°C or less and the non-oxidizing sintering time is set to 20 hours or less. Another method is, for example, (ii) applying a gas-impermeable coating film to the surface of the metal capillary tube to suppress carburization, but method (i) is particularly effective.

[0065] The carbon-containing refractory material that has undergone the non-oxidizing firing process described above is then subjected to an impregnation treatment in which an organic substance is impregnated therein.

[0066] In the impregnation treatment of the organic material, the residual carbon content of the organic material to be impregnated is set to 30% by mass or more. The residual carbon content of this material is measured based on the fixed carbon measurement method described in JIS K6910 (phenolic resin test method). If the residual carbon content of the organic material to be impregnated is less than 30% by mass, the effect of the residual carbon on strengthening the refractory structure is small, which is not preferable. From this viewpoint, a more preferable residual carbon content is 35% by mass or more.

[0067] Examples of organic materials to be impregnated include coal tar pitch (heat-dissolved material), phenolic resin (liquid resin), and furan resin (liquid resin). One or more of these can be used, but coal tar pitch is particularly preferred. This is because coal tar pitch easily crystallizes carbon after pyrolysis, contributing to greater improvement in fracture energy. In contrast, phenolic resin does not easily crystallize carbon after pyrolysis, and tends to become glassy carbon. Therefore, its effect in improving fracture energy is relatively lower than that of coal tar pitch.

[0068] There is no particular limitation on the method for impregnating the organic material. However, it is preferable to first reduce the pressure to a vacuum and then impregnate the organic material under pressure. For example, after reducing the pressure to 100 Torr or less, a pressure of 5 kgf / cm is applied. ２The refractory is impregnated with the organic substance by holding the refractory at this pressure for 2 hours or more. If the vacuum pressure is too high, bubbles remaining in the refractory may prevent the organic substance from being uniformly impregnated into the interior of the refractory when pressurized. For this reason, the vacuum pressure when reducing the pressure is preferably 100 Torr or less, more preferably 60 Torr or less. Furthermore, if the applied pressure after reducing the pressure is low or the applied pressure holding time is short, the organic substance may not be sufficiently impregnated into the refractory. For this reason, the applied pressure after reducing the pressure is 5 kgf / cm ２ More preferably, 10 kgf / cm ２ It is preferable that the pressure holding time is 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 the effect of improving the fracture energy of the carbon-containing refractory due to the above-mentioned principle can be particularly effectively obtained.

[0069] As described above, as equipment for carrying out the impregnation treatment with an organic substance while maintaining the carbon-containing refractory at a predetermined pressure after decompressing the carbon-containing refractory to a predetermined vacuum pressure, a general impregnation treatment equipment used for impregnating an organic substance with a slide plate, etc. After the impregnation, a drying treatment at about 200°C may be carried out to remove volatile matter remaining in the carbon-containing refractory.

[0070] In the present invention, the fracture energy increases dramatically by performing the non-oxidizing calcination and organic impregnation multiple times. However, the effect of increasing fracture energy saturates after a certain number of times. Therefore, from an economical standpoint, it is desirable to perform the non-oxidizing calcination and organic impregnation two to three times.

[0071] The refractory for gas injection nozzles manufactured by the method of the present invention has a fracture energy of 175 J / m ２ It is preferable that the fracture energy is 175 J / m or more. ２ If the fracture energy of the carbon-containing refractory is less than 175 J / m, the difference from the conventional single-impregnation refractory (a refractory obtained by non-oxidizing firing and organic impregnation only once) is small. Therefore, the effect of improving the life of the gas injection nozzle is small. ２As a result, it is possible to effectively suppress the propagation of cracks that occur due to a steep temperature gradient near the nozzle operating surface, and the life of the gas injection nozzle can be significantly improved.

[0072] The fracture energy is measured by a three-point bending test. Specifically, a 25×25×140 mm test piece of the refractory for a gas injection nozzle is subjected to a three-point bending test with a span of 100 mm in an inert atmosphere at 800° C. 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 calculated from the area of ​​the stress-strain curve.

[0073] The fracture energies of samples (i) to (v) were compared for carbon-containing refractories made of the same material, which were molded and then subjected to the following non-oxidizing firing and organic substance impregnation. Sample (i) was a sample that had been subjected to a normal drying treatment. Sample (ii) was a sample that had been subjected to a non-oxidizing firing and organic substance impregnation only once after the drying treatment. Sample (iv) was a sample that had been subjected to non-oxidizing firing and organic substance impregnation twice under the conditions of the present invention after the drying treatment. Sample (v) was a sample that had been subjected to non-oxidizing firing and organic substance impregnation three times under the conditions of the present invention after the drying treatment. As a result, the fracture energies of sample (i) were 85 J / m ２ , 62 J / m for sample (ii) ２ , 160 J / m for sample (iii) ２ , 187 J / m for sample (iv) ２ , 193 J / m for sample (v) ２ By repeatedly performing non-oxidizing baking and organic impregnation in this way, the fracture energy is effectively increased.

[0074] Here, the refractory material for gas injection nozzles obtained by the conventional method (fracture energy 160 J / m ２ In the case of the test piece (see below), cracks occurred at a location about 100 mm inside the refractory from the nozzle operating surface. The thickness of the refractory for the gas injection nozzle was instantly reduced by about 100 mm, resulting in a decrease in durability by about 10%. However, the fracture energy was 175 J / m ２ Such a phenomenon did not occur in the product of the present invention.

[0075] As mentioned above, one method for increasing the fracture energy of refractories is to add carbon fibers (long carbon fibers). However, although adding carbon fibers is effective in increasing the fracture energy, the carbon fibers do not blend well with the refractory, resulting in a highly porous structure with a very high porosity. As a result, materials containing carbon fibers suffer from a significant decrease in corrosion resistance, making them difficult to put into practical use. In contrast, non-oxidizing firing and organic impregnation are preferable because they can increase the fracture energy while maintaining the denseness of the refractory structure.

[0076] Furthermore, in the refractory for a gas-blowing nozzle manufactured by the method of the present invention, the porosity of the carbon-containing refractory is preferably 3% or less. This porosity is an index of the amount of organic matter impregnated, and a larger porosity means a smaller amount of impregnation, and a smaller porosity means a larger amount of impregnation. If the amount of organic matter impregnated is small and the porosity of the carbon-containing refractory exceeds 3%, the effect of the organic matter impregnation is reduced, the effect of strengthening the refractory structure and improving toughness is reduced, and the fracture energy is also reduced to 175 J / m ２ It becomes difficult to ensure the above. A more preferable porosity of the carbon-containing refractory is 1.5% or less. In order to reduce the porosity of the carbon-containing refractory, it is effective to thoroughly impregnate the carbon-containing refractory with an organic substance.

[0077] Next, the material (raw material) and molding method of the carbon-containing refractory used in the manufacturing method of the present invention, the material and number of the metal capillaries, and the method of embedding the metal capillaries in the carbon-containing refractory will be described.

[0078] The raw materials for carbon-containing refractories generally consist of aggregate, a carbon source, other additive materials, a binder, and the like.

[0079] Examples of aggregates include magnesia, alumina, dolomite, zirconia, chromia, spinel (alumina-magnesia, chromia-magnesia), etc. One or more of these can be used, but among these, magnesia is particularly preferred from the viewpoint of corrosion resistance against molten metal and molten slag.

[0080] The carbon source is not particularly limited, and commonly used carbon sources such as flaky graphite, soil graphite, petroleum pitch, carbon black, etc. can be used, and one or more of these can be used. The amount of the carbon source to be blended in the carbon-containing refractory is not particularly limited, but is generally appropriate to be about 10 to 25 mass %.

[0081] Other materials include metals such as metal Al, metal Si, and Al-Mg alloys, SiC, B ４ Examples of suitable materials include, but are not limited to, carbides such as C.

[0082] As the binder, phenol resin, liquid pitch, or the like, which can be generally used as a binder for shaped refractories, can be used.

[0083] The metal capillary tube is typically a metal tube having an inner diameter of about 1 to 5 mm and a tube wall thickness of about 0.5 to 4 mm. The material of the metal capillary tube is not particularly limited, but it is preferable to use a metal material having a melting point of 1300°C or higher. For example, the material of the metal capillary tube may be a metal material (metal or alloy) containing one or more of iron, chromium, cobalt, and nickel, and among these, stainless steel (ferritic, martensitic, austenitic) or ordinary steel is particularly common.

[0084] There is no particular limit to the number of metal capillaries embedded in the carbon-containing refractory. The number of metal capillaries may be one to more than one. The number of metal capillaries is determined by the inner diameter of the metal capillaries used and the required gas injection amount. In a typical MHP for a converter, approximately 60 to 250 metal capillaries are usually embedded in the carbon-containing refractory. On the other hand, nozzles that only allow a small amount of gas to flow may have one to several metal capillaries. Even in such gas injection nozzles, tuyere tip cooling occurs due to the forceful gas injection, and crack propagation due to thermal shock can cause damage, so the present invention can also be applied to such gas injection nozzles.

[0085] The method for embedding the metal capillaries in the carbon-containing refractory is not particularly limited. For example, the raw materials for the carbon-containing refractory, such as those listed above, are mixed and kneaded in a mixer. The metal capillaries are laid on top of the kneaded mixture, embedding the metal capillaries in a layered configuration, and then molding is performed using a press at a predetermined pressure. After molding, the carbon-containing refractory with the embedded metal capillaries is subjected to non-oxidizing firing and organic substance impregnation multiple times according to the method of the present invention. After that, a gas reservoir member necessary for the function of the gas injection nozzle is joined (welded) to the metal capillaries to produce a gas injection nozzle product.

[0086] In another method, a metal capillary tube is previously joined (welded) to a member (top plate) for a gas reservoir, and the kneaded material is filled around it, followed by molding at a predetermined pressure using a press, and after molding, drying at an appropriate temperature. Then, this carbon-containing refractory material with the metal capillary tube embedded therein is subjected to non-oxidizing firing and organic substance impregnation multiple times according to the method of the present invention to produce a gas injection nozzle product.

[0087] There are no particular limitations on the method for kneading the raw materials for the carbon-containing refractory, and kneading means used as kneading equipment for shaped refractories, such as a high-speed mixer, a tire mixer (Conner mixer), or an Eirich mixer, may be used.

[0088] For molding the kneaded product, a uniaxial molding machine such as a hydraulic press or a friction press, or a general press used for molding refractories, such as a cold isostatic press (CIP), can be used.

[0089] The formed carbon-containing refractory may be dried at a temperature of 180° C. to 350° C. for a drying time of about 5 to 30 hours.

[0090] Tables 1 to 3 show the manufacturing conditions and properties of the refractories for gas injection nozzles manufactured in the present examples (inventive examples and comparative examples).

[0091] The raw materials for the carbon-containing refractory in which the metal tubes were embedded were electrofused magnesia (purity 98.2% by mass) as the magnesia raw material serving as the aggregate, flake graphite (purity 98.4% by mass, average particle size 0.18 mm) as the carbon source, and phenolic resin with a residual carbon content of 46% by mass as the binder.

[0092] The metal capillaries embedded in the carbon-containing refractory were made of ordinary steel and had an outer diameter of 3 mm and an inner diameter of 2 mm.

[0093] Coal tar pitch or phenol resin was used as the organic material impregnated into the carbon-containing refractory. In Tables 1 to 3, the material with a residual carbon rate of 42 mass% was coal tar pitch. The material with a residual carbon rate of 15 mass% was phenol resin. The residual carbon rate was measured based on the fixed carbon measurement method described in JIS K6910 (Test method for phenolic resins).

[0094] The raw materials for the carbon-containing refractories were blended in the proportions shown in Tables 1 to 3, and the blend was kneaded using an Eirich mixer. Then, using a 230 x 200 mm mold, metal capillaries were laid on the kneaded mixture while embedding the metal capillaries in a layered configuration. Then, the mixture was pressurized with a hydraulic press at 2.5 ton / cm. ２ The formed refractory was hardened and dried at 250° C. for 10 hours using a dryer to prepare a carbon-containing refractory having a metal capillary embedded therein.

[0095] The carbon-containing refractories prepared as described above were subjected to non-oxidative firing in a coke breeze under the conditions shown in Tables 1 to 3, and then to an organic substance impregnation treatment to obtain refractories for gas injection nozzles. In the present invention, the non-oxidative firing and organic substance impregnation treatment were performed multiple times. In the organic substance impregnation treatment, the carbon-containing refractories were held at a predetermined pressure for 10 hours.

[0096] For the purpose of measuring the porosity and fracture energy, a carbon-containing refractory without embedded metal tubes was prepared using the same raw materials and method as above.

[0097] In addition, some of the comparative examples were those that were not subjected to non-oxidative firing or organic substance impregnation, those that were subjected to non-oxidative firing only but not organic substance impregnation, and those that were subjected to non-oxidative firing and organic substance impregnation only once.

[0098] The carbon content of the metal capillary tubes in the refractories for gas-blowing nozzles obtained as described above was measured. Furthermore, the porosity and fracture energy of the refractories without the metal capillary tubes embedded therein were measured. The results are shown in Tables 1 to 3.

[0099] The porosity of the refractory was measured in accordance with JIS R2205, using a vacuum method and white kerosene as the soot liquid.

[0100] The fracture energy of the refractory was measured as follows. The test piece size was 25 x 25 x 140 mm, and a three-point bending test with a span of 100 mm was performed. The bending test was performed in an inert atmosphere at 800°C. The testing machine used was an "Autograph AG-X / R" manufactured by Shimadzu Corporation, and the crosshead speed was 0.1 mm / min. The occurrence of stable fracture was confirmed from the stress-strain curve obtained from the three-point bending test, and the fracture energy was calculated by dividing the area of ​​the stress-strain curve by twice the projected area (25 x 25 mm) of the cut surface. It was confirmed that stable fracture occurred in all measurement cases.

[0101] The carbon content of the metal capillaries was measured by polishing the cut surface of the test piece after non-oxidizing firing in which the metal capillaries were embedded, and performing quantitative analysis using an analytical denshi. The measurement range was the amount of carbon in a 100 x 100 μm field of view along the outer periphery of the metal capillaries. The analyzer used was the "JXA-8230" manufactured by JEOL Ltd.

[0102] Furthermore, the carburization index n per non-oxidizing firing and the total carburization index N (n × number of firings) for multiple non-oxidizing firings were calculated. The results are shown in Tables 1 to 3.

[0103] The total carburization index N during firing was calculated under the following conditions: First, the carbon diffusion frequency factor D in Equation (1) ０ and the activation energy Q for carbon diffusion is given by the following formula:

[0104] D ０ =(4.725-5.374Wc+1.779Wc ２ ) x 10 ―５ Q=154.5-21.04Wc-3.285Wc ２

[0105] Here, Wc is the saturated carbon concentration, and in this example, Wc=2.14%. Wc is also called the carbon solubility limit. When Wc exceeds the carbon solubility limit, cementite precipitates. When Wc=2.14%, D ０=1.37E-05(m ２ / s), Q = 94.43041 (kJ / mol).

[0106] In this example, the gas constant R in equation (1) was set to 8.314 J / (K·mol).

[0107] According to Tables 1 and 2, all of the invention examples had low porosity and high fracture energy. In particular, invention examples 1 to 5, 7 to 11, and 13 to 16 all had a total carburization index N during firing of 118 or less, and the carbon content of the metal capillaries after non-oxidizing firing was 2.0 mass% or less.

[0108] According to Table 3, Comparative Example 1 uses a commonly used magnesia-carbon brick. The fracture energy of Comparative Example 1 is low. Comparative Example 2 is Comparative Example 1, which was non-oxidatively fired at 1,400°C (without organic impregnation). The fracture energy of Comparative Example 2 is also low. Furthermore, the total carburization index N during firing exceeds 118, and the carbon content of the metal tube is high at 3.1 mass%. Comparative Example 3 uses a low non-oxidative firing temperature of 300°C. Comparative Example 3 does not undergo sufficient thermal decomposition of the binder due to non-oxidative firing, preventing impregnation with organic matter, resulting in a low fracture energy. Comparative Example 4 uses an organic material with a low residual carbon rate of 15 mass% during impregnation. Comparative Example 4 does not achieve a satisfactory increase in fracture energy. Comparative Example 5 is a brick that underwent non-oxidative firing and organic impregnation only once. Comparative Example 5 exhibits an increase in fracture energy, but it is smaller than that of the present invention examples.

[0109]

[0110]

[0111]

Claims

1. A method for producing a refractory for a gas-blowing nozzle, in which one or more metal capillaries for gas blowing are embedded in a carbon-containing refractory, comprising carrying out a series of steps multiple times, the steps including non-oxidative firing of the carbon-containing refractory in which the metal capillaries are embedded, and then impregnating the carbon-containing refractory with an organic substance having a residual carbon rate of 30 mass% or more.

2. 2. The method for producing a refractory material for a gas-blowing nozzle according to claim 1, wherein the non-oxidizing firing is carried out at a firing temperature of 400 to 1100° C. for a firing time of 1 to 20 hours.

3. 2. The method for producing a refractory material for a gas-blowing nozzle according to claim 1, wherein the non-oxidizing firing is carried out at a firing temperature of 800 to 1100° C. for a firing time of 3 to 20 hours.

4. 2. The method for producing a refractory material for a gas injection nozzle according to claim 1, wherein a series of steps of non-oxidizing firing and impregnation with an organic substance is carried out two or three times.

5. 2. The method for producing a refractory for a gas injection nozzle according to claim 1, wherein the conditions of said non-oxidizing firing are set so that a total carburization index N during firing in a plurality of said non-oxidizing firings is equal to or less than a threshold value.

6. 2. The method for producing a refractory for a gas blowing nozzle according to claim 1, characterized in that the fracture energy of the carbon-containing refractory constituting the produced refractory for a gas blowing nozzle is 175 J / m2 or more.

7. 2. The method for producing a refractory for a gas-blowing nozzle according to claim 1, wherein the porosity of the carbon-containing refractory constituting the produced refractory for a gas-blowing nozzle is 3% or less.

8. 2. The method for producing a refractory for a gas-blowing nozzle according to claim 1, wherein the carbon content of the metal tube after the final non-oxidizing firing is set to 2.0 mass % or less.

9. 2. The method for producing a refractory for a gas-blowing nozzle according to claim 1, wherein the carbon content of the metal tube after the final non-oxidizing firing is 1.3 mass % or less.

10. 10. The method for producing a refractory for a gas blowing nozzle according to claim 1, wherein the organic material with which the carbon-containing refractory is impregnated in the impregnation treatment is one or more selected from the group consisting of coal tar pitch, phenolic resin, and furan resin.

11. A refractory for a gas-blowing nozzle, comprising a carbon-containing refractory having one or more metal thin tubes for blowing gas embedded therein, the refractory having a fracture energy of 175 J / m2 or more.

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

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

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

15. A gas-blowing nozzle comprising the refractory material for a gas-blowing nozzle according to any one of claims 11 to 14.