JP7793783B2 - Method for manufacturing refractory for gas-blowing nozzle, refractory for gas-blowing nozzle, and gas-blowing nozzle - Google Patents

Description

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

In converters or electric furnaces, bottom blowing is used to inject a stirring gas (usually an inert gas such as nitrogen or Ar) or a refining gas into the molten metal from the bottom of the furnace to improve refining efficiency and alloy yield. Examples of bottom blowing methods include (1) to (3) below. 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 area in contact with the molten steel. Method (2) is a slit method in which slit-shaped openings are created in the gap between the metal pipe and the brick, and inert gas is blown through these openings. Method (3) is a method in which multiple (several to several hundred) metal capillaries are embedded in carbon-containing bricks, and inert gas is supplied to the metal capillaries from the bottom of the bricks via a gas inlet pipe and gas reservoir, and the inert gas is blown through these metal capillaries.

In methods (1) and (2), the tuyere bricks are manufactured in advance using standard methods. The area where the metal pipe that will form the double pipe or slit will be installed is then processed. Alternatively, the space for installing the metal pipe is generally created by dividing the pipe into two or four parts. During construction, the metal pipe through which the gas will be blown is set in place beforehand, and the tuyere bricks are installed around it.

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

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, their manufacture differs from that of double-tube or slit-type nozzles and involves the following method:

That is, raw materials consisting of aggregate such as magnesia raw material, a carbon source such as scaly graphite, pitch, metal species, and a binder such as phenolic resin are mixed using a mixing device with high dispersion performance, such as a high-speed mixer. A kneaded mixture is then obtained that will form the carbon-containing refractory material in which the metal capillaries will be embedded. The metal capillaries are then laid on top of this kneaded mixture, forming them into a layered structure, and then molding them at a predetermined pressure using a press. This is then followed by a predetermined drying method (the metal capillaries are then welded to a gas reservoir component), or by welding the metal capillaries to a gas reservoir component in advance, filling the surrounding area with the kneaded mixture, and then molding at a predetermined pressure using a press. An MHP is then manufactured by this method, followed by a predetermined drying method, or the like.

Bottom blowing nozzles are subject to greater damage (wear and tear) than refractory materials such as furnace walls, and are important components that determine the furnace's lifespan. Therefore, various proposals have been made to reduce damage, and for MHPs, the following improvements have been proposed:

In Patent Document 2, the gas injection nozzle of the MHP is integrated with the surrounding tuyere to reduce premature erosion and wear from the joints. However, damage to the MHP also occurs in the parts where the metal capillaries are embedded. Therefore, this technology is not a very effective solution.
One of the causes of damage to MHPs is the lowering of the melting point of the metal tubes embedded in the refractory due to carburization (pre-damage to the metal tubes). The following countermeasures have been proposed:

Patent Document 3 proposes forming an oxide layer on the surface of stainless steel metal tubes embedded in a carbon-containing refractory material such as mag-carbon by thermal spraying in order to suppress carburization of the metal tubes. However, in refining furnaces used for long periods of time (for example, two to six months), such as converters, the oxide layer is not thick enough, resulting in a small carburization suppression effect.

Patent Document 4 also proposes placing a refractory sintered body between the metal capillary tubes and the carbon-containing refractory material to suppress carburization of the metal capillary tubes. This technology is effective in suppressing carburization. However, in nozzles with many embedded metal capillaries, the narrow spacing between the metal capillaries makes it difficult to place a refractory sintered body, making it difficult to put into practical use.

Japanese Patent Application Publication No. 59-31810 Japanese Unexamined Patent Publication No. 63-24008 Japanese Patent Application Laid-Open No. 2000-212634 Japanese Patent Application Laid-Open No. 2003-231912 Japanese Unexamined Patent Publication No. 58-15072 Patent No. 3201678 JP 2017-144460 A

As described above, in gas blowing nozzles (such as MHPs) that have metal tubes embedded in carbon-containing refractories, various studies have been conducted on the refractory materials and structures to improve durability, but the current situation is that sufficient improvements have not been achieved.

Therefore, an object of the present invention is to solve the problems of the prior art described above. An object of the present invention is to provide a method for manufacturing a refractory for a gas-blowing nozzle, in which one or more thin metal tubes for gas injection are embedded in a carbon-containing refractory, which can improve the durability of the gas-blowing nozzle.

The cause of damage to MHPs used in converters or electric furnaces has traditionally been thought to be primarily due to melting and abrasion caused by the flow of molten steel near the nozzle working surface, due to the forceful gas injection from the metal tubes. The countermeasures in Patent Document 2 are based on this concept. Another theory is that the metal tubes are worn out first by carburization, leading to greater damage, and methods such as those in Patent Documents 3 and 4 have been used to prevent carburization of the metal tubes. On the other hand, another theory is that the refractory material 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, it is thought that the strength of carbon-containing refractories is lowest around 600°C, causing cracks and damage to the working surface at that temperature. As such, various theories exist, and no conclusion has been reached. As a result, sufficient countermeasures have not been implemented, and as described above, satisfactory durability is not necessarily achieved.

To investigate 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. The results revealed that a very large temperature change of 500-600°C had occurred within the refractory approximately 10-20 mm deep from the working surface, and furthermore, cracks parallel to the working surface were confirmed in this area. Based on the results of this detailed investigation of the working surface and its vicinity in the used MHP, it was concluded that the damage to the MHP was primarily due to thermal shock caused by the sudden temperature gradient occurring near the working surface, rather than damage due to melting or wear.

Until now, the approach to thermal shock resistance has been to prevent cracks from occurring in the carbon-containing refractory that forms the base material of the nozzle, and improvements have been made to reduce the material's elastic modulus, thermal expansion, and strength. However, under conditions such as those described above, where sudden temperature changes occur over a very narrow range of the operating surface, it is difficult to prevent cracks from occurring. Therefore, the inventors have been investigating methods to improve this by making it more difficult for cracks to propagate even if they do occur, and have focused on the fracture energy of carbon-containing refractories.

The fracture energy of refractory is defined as the energy required to form a new surface when a crack propagates. If a refractory is subjected to thermal stress and a certain amount of elastic energy is stored, and a crack is generated by this energy, the greater the fracture energy, the more difficult it is for the crack to propagate.

Various methods have been investigated to improve the fracture energy of refractories. For example, it is known that adding long carbon fibers can improve fracture energy. However, adding long carbon fibers has the disadvantage of worsening the packing properties of carbon-containing refractories, and therefore this method is not currently in practical use.

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 furnace lining refractories. For example, Patent Document 5 discloses that magma-carbon bricks containing added metal Al powder are 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 magma-carbon bricks containing added 0.5 to 10 wt% calcined anthracite are fired in a reducing atmosphere at 600 to 1500°C, improving slag erosion resistance and heat spalling resistance by reducing the elastic modulus. Patent Document 6 evaluates the elastic modulus after reduction firing at 1400°C as an indicator of spalling resistance, and states that it is important that the elastic modulus be 1.2 × 10 ⁴ MPa or less. Furthermore, it is explained that tar may be impregnated after reduction firing, and that this impregnation seals the pores, increases strength, and improves slaking resistance, but no examples are given.

As described above, the conventional technique of non-oxidizing firing of a refractory material and impregnating it with an organic substance has been aimed at improving the corrosion resistance or heat spalling resistance of the refractory material for use in furnace linings. In contrast, Patent Document 7 discloses that a method of firing a refractory material 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 of a carbon-containing refractory increases when it is fired non-oxidatively and impregnated with an organic substance is not entirely clear, but is thought to be as follows.

Carbon-containing refractories (bricks) are generally manufactured using binders such as phenolic resin. Phenolic resins undergo thermal decomposition at high temperatures, leaving some carbon residue, which functions as a binder for carbon-containing refractories. However, the degree of bonding is strong. Furthermore, cracks that occur easily 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 refractory, penetrating into the matrix or between the layers of flake graphite. These organic matter decomposes when heated during nozzle use, forming carbon bonds. This results in loose bonds between carbon materials such as flake graphite and the refractory aggregate, enhancing the degree of bonding. As a result, cracks are less likely to propagate evenly. 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. This improves pullability and ultimately increases fracture energy.

However, after further investigations, the inventors discovered that the method described in Patent Document 7 has limitations in increasing fracture energy and the associated improvement in durability, and that performing non-oxidizing firing and organic impregnation multiple times dramatically increases fracture energy.

On the other hand, one issue with MHP is the carburization of metal capillaries that occurs when gas is blown through them, as described in Patent Documents 3 and 4. Carburization of metal capillaries occurs when carbon sources contained in refractories (bricks) penetrate into the metal capillaries at high temperatures during actual operation. This carburization is known to lower the melting point of the metal capillaries and increase the amount of nozzle damage. In this invention, we have discovered that when manufacturing refractories for gas injection nozzles, the fracture energy can be dramatically increased by subjecting carbon-containing refractories with embedded metal capillaries to multiple non-oxidizing firings and organic impregnation. However, even during non-oxidizing firing, depending on the heat treatment conditions, carbon components derived from the carbon-containing refractory penetrate into the metal capillaries, causing the melting point of the capillaries to decrease due to carburization. Therefore, we aim to prevent the melting point of the metal capillaries from decreasing due to carburization during multiple non-oxidizing firings of carbon-containing refractories with embedded metal capillaries. 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.

As described above, by repeatedly performing non-oxidizing firing and organic impregnation on carbon-containing refractories in which metal tubes for MHPs are embedded, the fracture energy of the refractory surrounding the metal tubes can be dramatically improved. This can suppress the propagation of cracks that occur near the working surface of the MHP, significantly improving the lifespan of the MHP. Furthermore, it was discovered that optimizing the non-oxidizing firing conditions and suppressing carburization of the metal tubes during the MHP manufacturing process can further extend the lifespan of the MHP.
The present invention was made based on these findings and has the following gist.

[1] A method for manufacturing a refractory for a gas-blowing nozzle, in which one or more metal thin tubes for gas blowing are embedded in a carbon-containing refractory,
A method for producing a refractory for a gas-blowing nozzle, comprising the steps of: non-oxidizing firing a carbon-containing refractory having a metal capillary embedded therein; and then impregnating the carbon-containing refractory with an organic substance having a residual carbon rate of 30 mass% or more; and repeating this series of steps multiple times.

[2] A method for producing a refractory material for a gas injection nozzle, 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 in the manufacturing method of [1] above.

[3] A method for producing a refractory material for a gas injection nozzle, 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 in the manufacturing method of [1] above.

[4] A method for manufacturing a refractory material for a gas injection nozzle, characterized in that, in any of the manufacturing methods described above in [1] to [3], a series of steps of non-oxidizing firing and organic substance impregnation treatment are carried out two to three times.

[5] A method for manufacturing a refractory material for a gas injection nozzle, in any of the manufacturing methods [1] to [4] above, characterized in that the conditions for the non-oxidizing firing are set so that the total carburization index N during firing over multiple non-oxidizing firings is below a threshold value.

[6] A method for producing a refractory for a gas blowing nozzle according to any one of the above [1] to [5], wherein the fracture energy of the carbon-containing refractory constituting the produced refractory for a gas blowing nozzle is 175 J/ ^m2 or more.

[7] A method for manufacturing a refractory for a gas-blowing nozzle, in any of the manufacturing methods [1] to [6] above, characterized in that the porosity of the carbon-containing refractory constituting the manufactured refractory for a gas-blowing nozzle is 3% or less.

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

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

[10] A method for producing a refractory for a gas-blowing nozzle, in any of the manufacturing methods [1] to [9] above, characterized in that 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.

[11] A refractory for a gas-blowing nozzle, in which one or more metal thin tubes for gas blowing are embedded in a carbon-containing refractory,
A refractory for a gas-blowing nozzle, characterized in that the fracture energy of the carbon-containing refractory is 175 J/ ^m2 or more.

[12] A refractory for a gas-blowing nozzle according to [11] above, characterized in that the porosity of the carbon-containing refractory is 3% or less.

[13] A refractory material for a gas injection nozzle according to [11] or [12] above, characterized in that the carbon content of the metal capillary is 2.0 mass% or less.

[14] A refractory material for a gas injection nozzle according to [11] or [12] above, characterized in that the carbon content of the metal capillary is 1.3 mass% or less.

[15] A gas injection nozzle characterized by comprising a refractory material for a gas injection nozzle according to any one of [11] to [14] above.

The manufacturing method of the present invention makes it possible to produce a refractory material for gas injection nozzles, in which the fracture energy of the carbon-containing refractory material with embedded metal capillaries is high and the propagation of cracks caused by a sudden temperature gradient near the nozzle operating surface is suppressed. Use of this refractory material for gas injection nozzles can significantly extend the life of the gas injection nozzle.

Furthermore, by optimizing the non-oxidizing firing conditions (firing temperature, firing time) and the carbon content of the metal tube after non-oxidizing firing, 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 lifespan of the gas injection nozzle.

The present invention is a method for manufacturing a refractory for a gas injection nozzle, in which one or more metal capillaries for gas injection are embedded in a carbon-containing refractory. The carbon-containing refractory with the embedded metal capillaries is subjected to non-oxidative firing (non-oxidative firing step), and then the carbon-containing refractory is impregnated with an organic substance having a residual carbon content of 30% by mass or more (impregnation step). In other words, the non-oxidative firing and organic substance impregnation process is repeated multiple times.

In the following explanation, a gas injection nozzle with dozens or more metal tubes embedded in a carbon-containing refractory material may be referred to as an "MHP" for convenience of explanation.

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.

In the present invention, the object to be non-oxidatively fired and organically impregnated is a carbon-containing refractory material in which a metal capillary tube is embedded. If the gas injection nozzle is of a type that has a gas reservoir, the object may be a carbon-containing refractory material in which only a metal capillary tube is embedded. Alternatively, the object may be a carbon-containing refractory material in which a metal capillary tube is embedded and to which all or part of a gas reservoir member is joined.

In this invention, the carbon-containing refractory is impregnated with an organic substance after non-oxidizing firing. 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 just 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 beforehand to impregnate the organic substance. Furthermore, non-oxidizing firing involves heat-treating the entire refractory, which allows carbon components derived from the binder and other materials to be homogeneously formed as a binding agent. Therefore, it is possible to easily impregnate an unfired refractory, whose structure changes due to heat exposure during actual operation, while still maintaining a homogeneous refractory structure.

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: The organic matter impregnated into the carbon-containing refractory during organic impregnation contains vaporizable components (components that, like alcohol, become gaseous even in the absence of oxygen when the temperature rises and dissipate outside the refractory). It also contains residual carbon components (components that, like carbon, do not become gaseous even in the absence of oxygen when the temperature rises 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 vaporized components due to non-oxidizing firing → filling of pores with organic matter due to impregnation → dissipation of vaporized 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 matter due to impregnation. As a result, the pores remaining even when exposed to high temperatures are reduced. 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.

In addition, if non-oxidizing firing and organic impregnation are performed multiple times, the pores will be filled with residual carbon each time, which is expected to improve thermal conductivity, alleviate temperature gradients, and reduce thermal shock.

The firing temperature (heat treatment temperature) for non-oxidizing firing of carbon-containing refractories is preferably 400°C or higher and 1100°C or lower. At firing temperatures below 400°C, the thermal decomposition of the binder (usually a resin such as phenolic resin) may not occur sufficiently, resulting in insufficient impregnation of the organic material during the impregnation treatment after non-oxidizing firing, and thus insufficient improvement in fracture energy. On the other hand, firing temperatures above 1100°C may result in the carburization of the metal capillaries by carbon components derived from the carbon-containing refractory, lowering the melting point of the metal capillaries. Furthermore, since non-oxidizing firing is performed multiple times in the present invention, firing temperatures above 1100°C may cause the embedded metal capillaries to melt or become clogged, resulting in the loss of their gas-blowing function as gas-blowing nozzles.

In addition, to more effectively impregnate organic substances in the impregnation process after non-oxidizing firing, it is preferable that the firing temperature be 800°C or higher.

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 entire nozzle is likely to be insufficiently heat-treated. On the other hand, if the firing time exceeds 20 hours, carburization of the metal capillary may occur, as occurs when 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.

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

Here, D is the carbon diffusion coefficient, and is expressed by the following formula (2): The total carburization index N during firing is the value obtained by integrating the carbon diffusion coefficient D over the total firing time of each firing and multiplying the result by ¹⁰ .

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 index indicating how much carbon penetrates into the metal capillary. The threshold value is 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 based on other perspectives, such as the thermal decomposition of the binder.

In the present invention, the carbon-containing refractory is fired under non-oxidizing conditions to prevent the loss of its inherent properties, such as heat spalling resistance and slag penetration resistance. Specifically, if the carbon-containing refractory is fired under firing conditions that significantly reduce the carbon content, such as heating at high temperatures for a long period of time in an oxidizing atmosphere, the carbon in the carbon-containing refractory will be oxidized and lost. As a result, the carbon-containing refractory's properties, such as heat spalling resistance and slag penetration resistance, will be lost. Therefore, the carbon-containing refractory is fired under non-oxidizing conditions to prevent the loss of these properties.

The non-oxidizing firing conditions have been described as including the number of firings, firing temperature, and firing time, but there are no particular limitations as long as the conditions do not substantially eliminate the carbon, such as flaky graphite, contained in the carbon-containing refractory. For example, applicable non-oxidizing firing conditions include reducing firing, firing in a reducing atmosphere, firing in a non-oxidizing atmosphere, and short-term firing in an oxidizing atmosphere.

There are no particular restrictions on the method for carrying out non-oxidizing firing, and it can be carried out using conventional methods. For example, a sheath made of assembled bricks or a metal container is placed on a cart that is loaded into the firing furnace, and the carbon-containing refractory to be subjected to reduction firing (carbon-containing refractory with embedded metal tubes) is placed inside. A carbon source such as coke is then placed around the carbon-containing refractory, and a lid is placed on top, and reduction firing (heat treatment) is carried out at a specified temperature and for a specified time while blocking out outside air.

Furthermore, the firing of carbon-containing refractories can be performed in a reducing atmosphere containing a flammable gas such as NX gas, or in a non-oxidizing atmosphere in which the firing atmosphere is an inert gas such as nitrogen or argon, or a non-oxidizing gas. In the case of reducing or non-oxidizing atmosphere firing, a sheath or metal container may not be necessary.

Furthermore, when firing carbon-containing refractories, even if firing is performed in an oxidizing atmosphere, it is possible to fire for a short period of time, remove the decarburized layer formed on the surface after firing, and use the undecarburized portion of the interior of the refractory. In this method, the surface of the carbon-containing refractory becomes oxidized. However, as the surface oxidizes, this 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 essentially under non-oxidizing conditions. Furthermore, when firing carbon-containing refractories, methods such as applying an anti-oxidation glaze to the surface of the carbon-containing refractory beforehand can also be used.

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.

The carbon content of the metal capillaries (metal capillaries 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 capillaries exceeds 2.0% by mass, the melting point of the metal capillaries will decrease, which may cause the metal capillaries to melt near the working surface of the nozzle tip, reducing the durability of the nozzle itself. From the above perspectives, a more preferable carbon content of the metal capillaries is 1.3% by mass or less.

One method for keeping the carbon content of the metal tubes after non-oxidizing sintering to 2.0% by mass or less (preferably 1.3% by mass or less) is to (i) lower the non-oxidizing sintering temperature and not extend the non-oxidizing sintering time excessively. Specifically, the non-oxidizing sintering temperature can be set to 1000°C or less and the non-oxidizing sintering time to 20 hours or less. Another method is to (ii) apply a gas-impermeable coating film to the surface of the metal tubes to suppress carburization, but method (i) is particularly effective.

After undergoing the above-mentioned non-oxidizing firing process, the carbon-containing refractory material is subjected to an impregnation process in which it is impregnated with an organic substance.

During the organic impregnation process, the residual carbon content of the organic material to be impregnated must be 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 undesirable. From this perspective, a residual carbon content of 35% by mass or more is more preferable.

Organic materials for impregnation 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 its carbon after pyrolysis, contributing to greater improvement in fracture energy. In contrast, phenolic resin does not easily crystallize its carbon after pyrolysis, and tends to become glassy carbon. As a result, its effect in improving fracture energy is relatively lower than that of coal tar pitch.

There are no particular limitations 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, the organic material is impregnated by applying a pressure of 5 kgf/cm2 ^or more for two hours or more. If the vacuum pressure is too high, bubbles remaining in the refractory may prevent the organic material 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 pressure after reducing the pressure is low or the pressure holding time is short, the organic material may not be sufficiently impregnated into the refractory. For this reason, the pressure after reducing the pressure is preferably 5 kgf/ ^cm2 or more, more preferably 10 kgf/ ^cm2 or more. Furthermore, the pressure holding time is preferably two hours or more, more preferably four hours or more. By satisfying these impregnation conditions, the organic material is uniformly impregnated into the carbon-containing refractory, and the effect of improving the fracture energy of the carbon-containing refractory based on the above-mentioned principle is particularly effectively achieved.

As described above, after the carbon-containing refractory has been depressurized to a predetermined vacuum pressure, it can be impregnated with an organic substance while maintaining the pressure at a predetermined level. This can be achieved using general impregnation equipment used for impregnating organic substances with slide plates, etc. After impregnation, a drying process at approximately 200°C can be performed to remove any volatile matter remaining in the carbon-containing refractory.

In the present invention, the fracture energy increases dramatically by performing non-oxidizing firing and organic impregnation multiple times. However, once the process has been performed a certain number of times, the effect of increasing fracture energy saturates. Therefore, from an economical standpoint, it is desirable to perform non-oxidizing firing and organic impregnation two to three times.

In the refractory for a gas blowing nozzle produced by the method of the present invention, the fracture energy of the carbon-containing refractory is preferably 175 J/ ^m2 or more. If the fracture energy is less than 175 J/ ^m2 , the difference from conventional single-impregnation refractories (refractories obtained by non-oxidizing firing and organic impregnation only once) is small. Therefore, the effect of improving the life of the gas blowing nozzle is small. In other words, if the fracture energy of the carbon-containing refractory is 175 J/ ^m2 or more, it becomes possible to particularly effectively suppress the propagation of cracks caused by a sudden temperature gradient near the nozzle operating surface, and the life of the gas blowing nozzle can be significantly improved.

Fracture energy is measured using a three-point bending test. Specifically, for refractory materials for gas injection nozzles, a three-point bending test is performed on a 25 x 25 x 140 mm test piece in an inert atmosphere at 800°C over a 100 mm span. 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 this stress-strain curve.

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

Here, in the refractory for gas injection nozzles obtained by the conventional method (fracture energy of 160 J/ ^m2 or less), cracks occurred at a location about 100 mm into the interior of the refractory from the nozzle operating surface. The thickness of the refractory for gas injection nozzles instantly decreased by about 100 mm, resulting in a decrease in durability of about 10%. However, this phenomenon did not occur in the product of the present invention, which has a fracture energy of 175 J/ ^m2 .

As mentioned above, one method of increasing the fracture energy of refractories is to add carbon fiber (long carbon fiber). However, while adding carbon fiber is effective in increasing fracture energy, the carbon fiber and refractory material do not mix well, resulting in a highly porous structure with a very high porosity. As a result, materials containing added carbon fiber 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, as they can increase fracture energy while maintaining the density of the refractory structure.

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 indicator of the amount of organic matter impregnated, where a larger porosity indicates a smaller amount of impregnation, and a smaller porosity indicates 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 it becomes difficult to ensure a fracture energy of 175 J/ ^m2 or more. A more preferable porosity of the carbon-containing refractory is 1.5% or less. Note that, in order to reduce the porosity of the carbon-containing refractory, it is effective to sufficiently impregnate the carbon-containing refractory with an organic matter.

Next, we will explain 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 metal capillaries, and the method of embedding the metal capillaries in the carbon-containing refractory.

The raw materials for carbon-containing refractories generally consist of aggregate, a carbon source, other additives, and a binder.

Examples of aggregates include magnesia, alumina, dolomite, zirconia, chromia, and spinel (alumina-magnesia, chromia-magnesia). One or more of these can be used, but magnesia is particularly preferred from the standpoint of corrosion resistance to molten metal and molten slag.

There are no particular restrictions on the carbon source, and commonly used carbon sources such as flake graphite, soil graphite, petroleum pitch, and carbon black can be used, and one or more of these can be used. There are no particular restrictions on the amount of carbon source added to the carbon-containing refractory, but a range of approximately 10 to 25% by mass is generally appropriate.

Examples of other materials include, but are not limited to, metal species such as metallic Al, metallic Si, and Al-Mg alloys, and carbides such as SiC and B ₄ C.

Binders that can be used include phenolic resins, liquid pitch, and other materials that are generally applicable as binders for shaped refractories.

Metal capillaries are typically metal tubes with an inner diameter of approximately 1 to 5 mm and a wall thickness of approximately 0.5 to 4 mm. There are no particular restrictions on the material of the metal capillary tube, but it is preferable to use a metal material with a melting point of 1300°C or higher. Examples of materials for metal capillary tubes include metal materials (metals or alloys) containing one or more of iron, chromium, cobalt, and nickel, with stainless steel (ferritic, martensitic, or austenitic) or ordinary steel being particularly common.

There is no particular limit to the number of metal capillaries embedded in the carbon-containing refractory. The number of metal capillaries can be one to several. The number is determined by the inner diameter of the metal capillaries used and the required amount of gas injection. In a typical MHP for a converter, approximately 60 to 250 metal capillaries are typically embedded in the carbon-containing refractory. On the other hand, nozzles that only flow small amounts of gas can have one to several metal capillaries. Even in such gas injection nozzles, the tuyere tip cools 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.

There are no particular limitations on the method for embedding metal capillaries in a carbon-containing refractory. 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 at a specified pressure using a press. After molding, the carbon-containing refractory with the embedded metal capillaries is subjected to multiple non-oxidizing firing and organic substance impregnation processes in accordance with the method of the present invention. After that, a gas reservoir component, necessary for the function of the gas injection nozzle, is joined (welded) to the metal capillary tube to produce a gas injection nozzle product.

Another method involves joining (welding) a metal tube to a gas reservoir component (top plate) in advance, filling the area around it with the kneaded material, and then molding it at a specified pressure using a press. After molding, the material is dried at an appropriate temperature. The carbon-containing refractory material with the embedded metal tube is then 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.

There are no particular restrictions on the method for mixing the raw materials for carbon-containing refractories, and mixing means used as mixing equipment for shaped refractories, such as a high-speed mixer, tire mixer (Conner mixer), or Eirich mixer, can be used.

To form the kneaded material, a uniaxial molding machine such as a hydraulic press or friction press, or a common press used for forming refractories, such as a cold isostatic press (CIP), can be used.

The molded carbon-containing refractory can be dried at a temperature of 180°C to 350°C for a drying time of approximately 5 to 30 hours.

Tables 1 to 3 show the manufacturing conditions and characteristics of the refractories for gas injection nozzles manufactured in this example (invention example, comparative example).

The raw materials for the carbon-containing refractory material in which the metal tubes are embedded were electrofused magnesia (purity 98.2% by mass) as the magnesia raw material 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.

The metal tubes 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.

Coal tar pitch or phenolic resin was used as the organic material impregnated into the carbon-containing refractory. In Tables 1 to 3, coal tar pitch is used for the material with a residual carbon ratio of 42% by mass. Phenolic resin is used for the material with a residual carbon ratio of 15% by mass. The residual carbon ratio was measured based on the fixed carbon measurement method described in JIS K6910 (Testing Method for Phenolic Resins).

The raw materials for the carbon-containing refractories were blended in the proportions shown in Tables 1 to 3, kneaded using an Eirich mixer, and 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, followed by molding using a hydraulic press at a pressure of 2.5 tons/ ^cm2 . The molded refractories were cured and dried in a dryer at 250°C for 10 hours to produce carbon-containing refractories with embedded metal capillaries.

The carbon-containing refractory prepared as described above was subjected to non-oxidative firing in a coke breeze under the conditions shown in Tables 1 to 3, followed by an organic impregnation treatment to obtain a refractory for a gas injection nozzle. In the present invention, this non-oxidative firing and organic impregnation treatment was performed multiple times. During the organic impregnation treatment, the carbon-containing refractory was held at a specified pressure for 10 hours.

In addition, for measuring porosity and fracture energy, carbon-containing refractories without embedded metal tubes were prepared using the same materials and methods as above.

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

The carbon content of the metal tubes in the refractories for gas injection nozzles obtained in this manner was measured. Furthermore, the porosity and fracture energy of the refractories without embedded metal tubes were measured. The results are shown in Tables 1 to 3.

The porosity of the refractory material was measured in accordance with JIS R2205. The vacuum method was used, and white kerosene was used as the soot liquid.

The fracture energy of refractories was measured as follows. Test specimens measured 25 x 25 x 140 mm, and a three-point bending test was performed with a span of 100 mm. 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, with a crosshead speed of 0.1 mm/min. Stable fracture was confirmed to have occurred 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 of the cut surface (25 x 25 mm). Stable fracture was confirmed to have occurred in all measurements.

The carbon content of the metal capillaries was measured by polishing the cut surface of the test piece after non-oxidizing firing with the metal capillaries embedded, and performing quantitative analysis using an analytical instrument. The measurement range was a 100 x 100 μm field of view along the outer circumference of the metal capillaries, measuring the amount of carbon. The analytical device used was the JXA-8230 manufactured by JEOL Ltd.

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

The total carburization index N during firing was calculated under the following conditions: First, the frequency factor D ₀ of carbon diffusion and the activation energy Q for carbon diffusion in formula (1) are expressed by the following formula.

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

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

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

According to Tables 1 and 2, all of the invention examples have 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 tubes after non-oxidizing firing was 2.0 mass% or less.

According to Table 3, Comparative Example 1 is 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 tubes is high at 3.1% by mass. Comparative Example 3 is fired at a low non-oxidative firing temperature of 300°C. Comparative Example 3 does not achieve organic impregnation due to insufficient thermal decomposition of the binder caused by non-oxidative firing, resulting in a low fracture energy. Comparative Example 4 uses an organic material with a low residual carbon ratio of 15% by mass during the impregnation process. Comparative Example 4 does not achieve a satisfactory increase in fracture energy. Comparative Example 5 is fired non-oxidatively and impregnated with organic matter only once. Comparative Example 5 exhibits an increase in fracture energy, but it is smaller than the present invention examples.

Claims (9)

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, includes non-oxidizing firing the carbon-containing refractory in which the metal capillaries are embedded, and then carrying out a series of steps multiple times to impregnate the carbon-containing refractory with an organic substance having a residual carbon rate of 30 mass% or more,
The conditions of the non-oxidizing firing are set so that the total carburization index N during firing calculated based on the conditions of a plurality of times of the non-oxidizing firing is equal to or less than a threshold value.
1. A method for producing a refractory material for a gas-blowing nozzle, comprising: The method for manufacturing a refractory material for a gas injection nozzle according to claim 1, 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. The method for manufacturing a refractory material for a gas injection nozzle according to claim 1, 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. The method for manufacturing a refractory material for a gas injection nozzle according to claim 1, characterized in that the series of steps of non-oxidizing firing and organic substance impregnation treatment is carried out two to three times. The method for manufacturing a refractory for a gas-blowing nozzle according to claim 1, characterized in that the fracture energy of the carbon-containing refractory constituting the manufactured refractory for a gas-blowing nozzle is 175 J/m2 or more. The method for manufacturing a refractory for a gas-blowing nozzle according to claim 1, characterized in that the porosity of the carbon-containing refractory constituting the manufactured refractory for a gas-blowing nozzle is 3% or less. The method for manufacturing a refractory material for a gas injection nozzle according to claim 1, characterized in that the carbon content of the metal tube after the final non-oxidizing firing is 2.0 mass% or less. The method for manufacturing a refractory material for a gas injection nozzle according to claim 1, characterized in that the carbon content of the metal capillary after the final non-oxidizing firing is 1.3 mass% or less. 9. The method for producing a refractory for a gas blowing nozzle according to claim 1, wherein the organic substance 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.