WO2024203359A1

WO2024203359A1 - Method for producing refractory for gas-blowing nozzle, refractory for gas-blowing nozzle, and gas-blowing nozzle

Info

Publication number: WO2024203359A1
Application number: PCT/JP2024/009888
Authority: WO
Inventors: 聖司細原; 善幸中村; 敦久飯田; 宏樹吉岡
Original assignee: Ｊｆｅスチール株式会社; 品川リフラクトリーズ株式会社
Priority date: 2023-03-27
Filing date: 2024-03-13
Publication date: 2024-10-03

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

Manufacturing method of refractory for gas blowing nozzle, refractory for gas blowing nozzle, and gas blowing nozzle

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

In converters or electric furnaces, a so-called 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 in order to improve refining efficiency and alloy yield. Examples of bottom blowing methods include the following (1) to (3). Method (1) is a double-tube method in which oxygen for decarburization is blown from the inner tube, and a hydrocarbon gas (such as propane) for cooling the molten steel contact area is blown from the outer tube. Method (2) is a method (slit method) in which slit-shaped openings are made in the gap between the metal tube 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 tubes are embedded in carbon-containing bricks, and an inert gas is supplied to the metal tubes from the bottom of the bricks through a gas introduction tube and a gas reservoir, and the inert gas is blown from the metal tubes.

In methods (1) and (2), the tuyere bricks are manufactured in advance by standard methods. After that, the installation section of the metal pipe that forms the double pipe or slit is processed. Alternatively, it is common to divide it into two or four parts to create a space to install the metal pipe, and during construction, the metal pipe for blowing gas is set in place beforehand, and the tuyere bricks are installed around it.

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 said that this MHP can control a gas flow rate 1 to 20 times (0.01 to 0.20 Nm ³ /min). For this reason, the MHP is easier to adopt than the double tube method or the 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, unlike double-tube or slit-type nozzles, the following method is used for their manufacture.

In other words, raw materials, which are made by adding a carbon source such as scaly graphite, pitch, metal species, and binders such as phenolic resin to aggregates such as magnesia raw materials, are kneaded using a kneading means such as a high-speed mixer with high dispersion performance. A kneaded material that will form a carbon-containing refractory material in which metal tubes are embedded is obtained. The metal tubes are then laid on top of this kneaded material to embed them in a layered configuration, and molded at a specified pressure using a press. After that, a method of performing a specified drying (the metal tubes are then welded to a member for gas storage), or a method of previously welding the metal tubes to a member for gas storage, filling the kneaded material around it, and molding at a specified pressure using a press. Then, a MHP is manufactured by a method such as performing a specified drying.

Because bottom blowing nozzles are subject to greater damage (wear and tear) than refractory materials such as furnace walls and are an important component that determines the furnace lifespan, various proposals have been made to prevent damage to them, 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 the pre-dissolution and wear from the joints. However, damage to the MHP also occurs in the part where the metal capillaries are embedded. Therefore, this technology is not a very effective measure.
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 a stainless steel metal tube by thermal spraying in order to suppress carburization of the metal tube embedded in a carbon-containing refractory such as mag-carbon. However, in refining furnaces that are used for long periods such as converters (for example, those used for periods of two to six months), the oxide layer is not thick enough, and the carburization suppression effect is small.

Patent Document 4 also proposes disposing a refractory sintered body between the metal tube and the carbon-containing refractory material in order to suppress carburization of the metal tube. This technology is effective in suppressing carburization. However, in a nozzle in which many metal tubes are embedded, it is difficult to dispose a refractory sintered body because the intervals between the metal tubes are narrow, making it difficult to put into practical use.

Japanese Patent Application Publication No. 59-31810 Japanese Unexamined Patent Publication No. 63-24008 JP 2000-212634 A JP 2003-231912 A 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 refractory, various studies have been conducted on the refractory material or structure to improve durability, but the current situation is that sufficient improvements have not been achieved.

The object of the present invention is therefore to solve the problems of the prior art as described above. The object of the present invention is to provide a method for manufacturing 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, and which can improve the durability of the gas injection nozzle.

The cause of damage to MHPs used in converters or electric furnaces has been thought to be mainly wear and tear caused by the molten steel flow near the nozzle working surface, because gas is blown in forcefully from the metal tube. The countermeasures in Patent Document 2 are based on this idea. There is also a view that the damage becomes greater when the metal tube is worn out first due to carburization, and methods such as those in Patent Document 3 and Patent Document 4 have been used to prevent carburization of the metal tube. On the other hand, there was a view that the refractory material is cooled during blowing because inert gas is blown in forcefully, and spalling damage occurs due to the temperature difference between blowing and non-blowing. Furthermore, there was a view that the strength of carbon-containing refractories is lowest at around 600°C, so cracks develop in the working surface at that part, causing damage. As such, there have been various ideas, and no conclusion has been reached. As a result, sufficient measures have not been taken, and the current situation is that satisfactory durability is not necessarily achieved as described above.

In order to find the true cause of the 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 500-600°C had occurred inside the refractory at a depth of about 10-20 mm from the working surface, and furthermore, a crack parallel to the working surface was confirmed in this area. As a result of repeated detailed investigations of the working surface area of this used MHP, it was concluded that the damage to the MHP was mainly due to thermal shock caused by the sudden temperature gradient occurring near the working surface, rather than damage due to melting or wear.

Up until now, the idea behind thermal shock resistance has been to prevent cracks from occurring in the carbon-containing refractory itself, which is the base material of the nozzle, and improvements have been made to reduce the elastic modulus, thermal expansion, and strength of the material. However, under conditions such as those described above where sudden temperature changes occur in a very narrow range of the operating surface, it is difficult to stop the occurrence of cracks. Therefore, the inventors have been investigating methods to improve the situation by making it 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 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 the refractory due to thermal stress, and a crack is generated by this energy, the greater the fracture energy, the more difficult it is for the crack to propagate.

So far, 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 that it reduces the packing properties of carbon-containing refractories, and therefore this method has not been put to practical use at present.

Conventionally, a technique of non-oxidizing firing and impregnating an organic substance into a refractory for lining a furnace is known for the purpose of improving the corrosion resistance or heat spalling resistance of the refractory. For example, in Patent Document 5, a mag-carbon brick to which metal Al powder has been added 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. In Patent Document 6, a mag-carbon brick to which 0.5 to 10% by weight of calcined anthracite is added is fired in a reducing atmosphere at 600 to 1500°C, improving slag erosion resistance and heat spalling resistance by reducing the elastic modulus. In Patent Document 6, the elastic modulus after reduction firing at 1400°C is evaluated as an index of spalling resistance, and it is important that the elastic modulus is 1.2×10 ⁴ MPa or less. Furthermore, it is explained that tar may be impregnated after reduction firing, and that this impregnation serves to seal pores, increase strength, and improve slaking resistance, but no examples are given.

As described above, the conventional technique of non-oxidizing firing of a refractory and impregnating it with an organic substance was aimed at improving the corrosion resistance or heat spalling resistance of the refractory for lining a furnace. 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 impregnation with an organic substance) is effective in improving the fracture energy.
Here, the reason why the fracture energy of a carbon-containing refractory increases by non-oxidative firing and impregnating it with an organic substance is not entirely clear, but it is thought to be as follows.

Carbon-containing refractories (bricks) are generally manufactured using phenolic resins and other binders. Phenol resins are pyrolyzed at high temperatures, leaving some carbon behind, which functions as a binder for carbon-containing refractories. However, the degree of bonding is large. Also, when cracks occur, they easily expand, so the fracture energy is not very large. In contrast, when organic matter is impregnated after non-oxidizing firing, the organic matter diffuses and penetrates evenly into the interior of the refractory, and the organic matter penetrates into the matrix part of the refractory or between the layers of scaly graphite. These organic matter decomposes when heated when the nozzle is used, and carbon bonds are formed. As a result, loose bonds are formed between the carbon material, such as scaly graphite, and the refractory aggregate, and the degree of bonding increases. As a result, even if cracks occur, they are less likely to expand. In addition, because loose bonds are formed, the carbon bonds derived from the organic matter described above are peeled off by moderate stress, and they act as bridges between the brick structure in the same way as when long carbon fibers are added, resulting in an effect of improving pullability, and as a result, increasing fracture energy.

However, as a result of the inventors' investigations, they discovered that the method of Patent Document 7 has limitations in increasing the fracture energy and the associated improvement in durability, and that by carrying out non-oxidizing firing and organic substance impregnation multiple times, the fracture energy increases dramatically.

On the other hand, one of the issues with MHP is the carburization of the metal capillary tubes that occurs when gas is blown from the metal capillary tubes, as shown in Patent Documents 3 and 4. Carburization of the metal capillary tubes occurs when the carbon source contained in the refractory (brick) penetrates into the metal capillary tubes under high temperatures during actual operation, and it is known that this carburization lowers the melting point of the metal capillary tubes and increases the amount of damage to the nozzle. In the present invention, it has been discovered that when manufacturing a refractory for a gas injection nozzle, the fracture energy can be dramatically increased by subjecting a carbon-containing refractory in which a metal capillary tube is embedded to non-oxidizing firing and organic substance impregnation multiple times. However, even in the non-oxidizing firing, depending on the heat treatment conditions, carbon components derived from the carbon-containing refractory penetrate into the metal capillary tubes, causing the melting point of the capillary tubes to be lowered due to carburization. Therefore, the lowering of the melting point of the metal capillary tubes due to carburization is prevented in multiple non-oxidizing firings of a carbon-containing refractory in which a metal capillary tube is embedded. To achieve this, detailed studies were conducted on the non-oxidizing sintering conditions (sintering temperature, sintering time) and the carbon content of the metal tubes after non-oxidizing sintering, and optimal conditions for practical use that can prevent the metal tubes from having a low melting point were found.

As described above, by performing non-oxidizing sintering and organic substance impregnation multiple times on a carbon-containing refractory in which a metal capillary tube for an MHP is embedded, the fracture energy of the refractory surrounding the metal capillary tube can be dramatically improved. This makes it possible to suppress the propagation of cracks that occur near the operating surface of the MHP, and greatly improve the lifespan of the MHP. Furthermore, it was found that it is possible to extend the lifespan of the MHP by optimizing the non-oxidizing sintering conditions and suppressing carburization of the metal capillary tube during the manufacturing process of the MHP.
The present invention has been made based on these findings, and has the following gist.

[1] A method for producing a refractory for a gas-blowing nozzle, comprising embedding one or more metal capillaries for blowing gas into a carbon-containing refractory,
A method for producing a refractory for a gas injection nozzle, comprising the steps of: non-oxidatively 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 the steps multiple times.

[2] A method for producing a refractory material for a gas injection nozzle, comprising the steps of the method for producing the refractory material in the above-mentioned [1], wherein the non-oxidizing firing is performed at a firing temperature of 400 to 1100°C for a firing time of 1 to 20 hours.

[3] A method for producing a refractory material for a gas injection nozzle, comprising the steps of the method for producing the refractory material in the above-mentioned [1], wherein the non-oxidizing firing is performed at a firing temperature of 800 to 1100°C for a firing time of 3 to 20 hours.

[4] A method for producing a refractory material for a gas injection nozzle, comprising the steps of non-oxidizing firing and impregnation with an organic substance, performed two or three times in any one of the methods described above [1] to [3].

[5] A method for manufacturing a refractory for a gas injection nozzle, comprising the steps of: (1) setting the conditions for the non-oxidizing firing such that the total carburization index N during firing in a plurality of non-oxidizing firings is equal to or less than a threshold value, in any one of the manufacturing methods described above in [1] to [4].

[6] A method for producing a refractory for a gas blowing nozzle, 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, in any one of the production methods [1] to [5] above.

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

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

[9] A method for producing a refractory material for a gas injection nozzle, comprising any one of the methods [1] to [7] above, wherein the carbon content of the metal tube after the final non-oxidizing firing is 1.3 mass% or less.

[10] A method for producing a refractory for a gas injection nozzle, in any one of the above methods [1] to [9], characterized in that the organic material 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, comprising a carbon-containing refractory having one or more metal thin tubes for blowing gas embedded therein,
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] The refractory for a gas injection nozzle according to [11] above, characterized in that the porosity of the carbon-containing refractory is 3% or less.

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

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

[15] A gas injection nozzle comprising any one of the refractories for gas injection nozzles described above in [11] to [14].

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

Furthermore, by optimizing the non-oxidizing sintering conditions (sintering temperature, sintering time) and the carbon content of the metal tube after non-oxidizing sintering, 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 in which the metal capillaries are embedded is subjected to non-oxidative firing (non-oxidative firing step), and then the carbon-containing refractory is subjected to an impregnation treatment in which an organic substance having a residual carbon rate of 30 mass% or more is impregnated into the carbon-containing refractory (impregnation treatment step). In other words, the non-oxidative firing and organic substance impregnation are performed multiple times.

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

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 impregnated with an organic substance is a carbon-containing refractory material 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 material in which only a metal capillary is embedded. Alternatively, the object may be a carbon-containing refractory material in which a metal capillary is embedded and in which all or part of a member for a gas reservoir is joined to the metal capillary.

In the present invention, the carbon-containing refractory is subjected to non-oxidative firing and then impregnated with an organic substance. However, impregnation with an organic substance cannot be achieved without non-oxidative firing. Basically, carbon-containing refractories (bricks) are unfired refractories obtained without a firing process, and the porosity of the refractory is very low at only a few percent due to the hardening of the binder. Therefore, it is difficult to impregnate the entire refractory with an organic substance in an unfired product. Therefore, in order to impregnate the organic substance, non-oxidative firing is required in advance. Furthermore, in non-oxidative firing, the entire refractory is heat-treated, so that carbon components derived from the binder, etc., are generated homogeneously as a binding material. Therefore, it is possible to easily impregnate the organic substance while obtaining a homogeneous refractory structure for unfired products, whose refractory structure changes due to heat received during actual operation.

In the present invention, the fracture energy increases dramatically by performing non-oxidizing firing and organic impregnation multiple times, and this is thought to be due to the following reasons. That is, the organic matter impregnated into the carbon-containing refractory during organic impregnation contains a vaporized component (a component that becomes a gas even in the absence of oxygen when the temperature rises, such as alcohol, and dissipates outside the refractory). It also contains a residual carbon component (a component that does not become a gas in the absence of oxygen even when the temperature rises, such as carbon, and remains inside the refractory). Of these, the vaporized component dissipates outside the refractory in the room temperature environment after the refractory is manufactured and in the high temperature environment during actual use, reducing the effect of the organic impregnation. By repeating non-oxidizing firing and organic impregnation multiple times, the following occurs: dissipation of the vaporized component due to non-oxidizing firing → filling of the pores with organic matter due to impregnation → dissipation of the vaporized component due to non-oxidizing firing (the pores are reduced from the previous time due to the residual carbon component) → filling of the pores with organic matter due to impregnation. And the number of pores that remain even when exposed to high temperatures decreases. For example, if an organic material whose volume is halved by non-oxidizing firing is used, after one impregnation, the pore volume will be halved even if the vaporized components dissipate afterwards. After two impregnations, the pore volume will be halved again (one-quarter of the original volume). After three impregnations, the pore volume will be halved again (one-eighth of the original volume). In this way, by performing multiple non-oxidizing firing and organic material impregnations, the pore volume is greatly reduced, and it is believed that the fracture energy will increase dramatically.

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

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, and the impregnation of the organic matter in the impregnation treatment after the non-oxidizing firing may be insufficient, and the fracture energy may not be sufficiently improved. On the other hand, if the firing temperature exceeds 1100°C, the carbon components derived from the carbon-containing refractory may carburize the metal tubes, causing a lower melting point of the metal tubes. In addition, since non-oxidizing firing is performed multiple times in the present invention, if the firing temperature exceeds 1100°C, the embedded metal tubes may melt or become clogged, and the gas-blowing function as a gas-blowing nozzle may be lost.

In addition, to more effectively impregnate organic matter in the impregnation process after non-oxidizing firing, the firing temperature is preferably 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 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 tube may occur, as in the case where the firing temperature exceeds 1100°C, which may result in a lower melting point of the metal tube. From this perspective, a more preferable firing time is 3 to 20 hours.

In particular, in the present invention, since non-oxidizing sintering is performed multiple times, it is preferable to control the total amount of heat treatment for the multiple times. Specifically, it is preferable to set the conditions for non-oxidizing sintering so that the total carburization index N during sintering, shown in the following formula (1), is equal to or less than a threshold value. The conditions for non-oxidizing sintering are explained as including, for example, the number of times sintering is performed, the sintering temperature, and the sintering 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 time of each firing and multiplying the result by ¹⁰⁹ .

In formula (2), D ₀ 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 at firing is an index indicating how much carbon penetrates into the metal tube. The threshold value is a value calculated in advance by repeating tests and is appropriately determined according to the material of the metal tube, and is 118 as an example in this embodiment. 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 at firing when non-oxidizing firing is performed multiple times is 118 or less. If the total carburization index N at firing exceeds the threshold value, the carbon content of the metal tube after non-oxidizing firing exceeds 2.0 mass%, and the durability of the nozzle itself decreases. In addition, since there is no lower limit value for the total carburization index N at firing from the viewpoint of carburization of the metal tube, the lower limit value of the heat treatment amount may be set from other viewpoints such as thermal decomposition of the binder.

In the present invention, the carbon-containing refractory is fired in a non-oxidizing manner in order to prevent the inherent properties of the carbon-containing refractory, such as heat spalling resistance and slag penetration resistance, from being lost. In other words, if the carbon-containing refractory is fired under firing conditions that significantly reduce the amount of carbon contained in the refractory, for example, under conditions of heating at high temperature for a long period of 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 heat spalling resistance and slag penetration resistance, are lost. Therefore, the carbon-containing refractory is fired under non-oxidizing conditions in order to prevent the loss of the above properties.

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 the carbon, such as scaly graphite, contained in the carbon-containing refractory material is not substantially lost. For example, applicable non-oxidizing firing conditions include reducing firing, firing in a reducing atmosphere, firing in a non-oxidizing atmosphere, and short-time firing in an oxidizing atmosphere.

There are no particular limitations on the method for carrying out non-oxidizing firing, and it may be carried out in the usual manner. 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 it. After that, a carbon source such as coke is placed around the carbon-containing refractory, and then a lid is placed on top to block out the outside air, and reduction firing (heat treatment) is carried out at a specified temperature and time.

Furthermore, the firing of carbon-containing refractories can be performed in a reducing atmosphere, in which the firing atmosphere is 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 atmosphere. In the case of reducing atmosphere firing or non-oxidizing atmosphere firing, a sheath or metal container can be omitted.

Furthermore, even if the carbon-containing refractory is fired in an oxidizing atmosphere, it is possible to fire it for a short time, remove the decarburized layer formed on the surface after firing, and use the non-decarburized part inside the refractory. With this method, the surface of the carbon-containing refractory becomes oxidized. However, as the surface oxidizes, this part acts as a protective layer, and the inside of the refractory can be fired under non-oxidizing conditions. Therefore, the inside of the refractory can be considered to have been fired in a substantially non-oxidizing manner. In addition, when firing the carbon-containing refractory, a method of applying an anti-oxidizing glaze to the surface of the carbon-containing refractory in advance 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 is necessary to remove the decarburized layer on the surface.

The carbon content of the metal capillaries (metal capillaries embedded in a 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, and there is a risk that the metal capillaries will melt near the working surface of the nozzle tip, reducing the durability of the nozzle itself. From the above perspective, a more preferable carbon content of the metal capillaries is 1.3% by mass or less.

As a method for making the carbon content of the metal 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 kept low and the non-oxidizing sintering time is not made 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 tube to suppress carburization, but method (i) is particularly effective.

The carbon-containing refractory that has undergone the above non-oxidizing firing process is then subjected to an impregnation process in which an organic substance is impregnated into it.

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

The organic matter to be impregnated includes coal tar pitch (melted by heating), phenolic resin (liquid resin), furan resin (liquid resin), etc., and one or more of these can be used, but among these, coal tar pitch is particularly preferable. This is because coal tar pitch contributes more to improving the breaking energy because the carbon after pyrolysis easily crystallizes. In contrast, phenolic resin carbon after pyrolysis does not easily crystallize, and it tends to become glassy carbon. Therefore, the effect of improving the breaking energy is relatively low compared to coal tar pitch.

There is no particular limitation on the method of impregnating the organic matter. However, it is preferable to impregnate the organic matter under pressure after once reducing the pressure to a vacuum. For example, after reducing the pressure to 100 Torr or less, the pressure is maintained at 5 kgf/ ^cm2 or more for 2 hours or more to impregnate the organic matter. If the vacuum pressure is high, the organic matter may not be homogeneously impregnated into the inside of the refractory when pressurized due to bubbles remaining in the refractory. For this reason, the vacuum pressure when reducing the pressure is preferably 100 Torr or less, more preferably 60 Torr or less. In addition, if the pressure after reducing the pressure is low or the pressure holding time is short, there is a risk that the organic matter 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 . In addition, the pressure holding time is preferably 2 hours or more, more preferably 4 hours or more. By satisfying these impregnation conditions, the organic matter is homogeneously permeated into the carbon-containing refractory, and the effect of improving the fracture energy of the carbon-containing refractory according to the above-mentioned principle is particularly effectively obtained.

As described above, after the carbon-containing refractory is depressurized to a predetermined vacuum pressure, the impregnation process of the organic substance can be performed while maintaining the carbon-containing refractory at a predetermined pressure by using general impregnation process equipment used for impregnating organic substances with slide plates, etc. After impregnation, a drying process at about 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 a certain number of times has been performed, the effect of increasing fracture energy becomes saturated. Therefore, from an economical perspective, it is desirable to perform non-oxidizing firing and organic impregnation two to three times.

The refractory for gas injection nozzle manufactured by the method of the present invention preferably has a fracture energy of 175 J/m2 or ^more for the carbon-containing refractory. If the fracture energy is less than 175 J/ ^m2 , the difference from a conventional one-time impregnated refractory (a refractory obtained by performing non-oxidizing firing and organic impregnation only once) is small. Therefore, the effect of improving the life of the gas injection nozzle is small. In other words, by making the fracture energy of the carbon-containing refractory 175 J/ ^m2 or more, it is possible to effectively suppress the propagation of cracks caused by a steep temperature gradient near the nozzle operating surface, and the life of the gas injection nozzle can be significantly improved.

The fracture energy is measured using a three-point bending test. That is, 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 span of 100 mm. A bending load is applied to the test piece at a rate of 0.1 mm/min to obtain a stress-strain curve, and the fracture energy is obtained from the area 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, then non-oxidatively fired and impregnated with an organic substance as described below, were compared. Sample (i) was a sample that had been subjected to a normal drying treatment. Sample (ii) was a sample that had been further subjected to a non-oxidative firing after drying treatment. Sample (iii) was a sample that had been subjected to a single non-oxidative firing and organic substance impregnation after drying treatment. Sample (iv) was a sample that had been subjected to two non-oxidative firings and organic substance impregnations under the conditions of the present invention after drying treatment. Sample (v) was a sample that had been subjected to three non-oxidative firings and organic substance impregnations under the conditions of the present invention after 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, the fracture energy is effectively increased by performing non-oxidative baking and organic substance impregnation multiple times.

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 was instantly reduced by about 100 mm, and the durability was reduced by about 10%. However, such a phenomenon did not occur in the product of the present invention with a fracture energy of 175 J/ ^m2 .

As mentioned above, one method of increasing the fracture energy of refractories is to add carbon fibers (long carbon fibers). However, although the addition of carbon fibers is effective in increasing fracture energy, the carbon fibers do not blend well with the refractory material, resulting in a porous structure with a very high porosity. As a result, materials with added carbon fibers suffer 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.

In addition, the refractory for gas injection nozzle manufactured by the method of the present invention preferably has a porosity of 3% or less. This porosity is an index of the amount of organic matter impregnated, and a large porosity means a small amount of impregnation, and a small porosity means a large 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 small, the effect of strengthening the refractory structure and improving the toughness is small, and it becomes difficult to ensure a fracture energy of 175 J/m ² or more. 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 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 the metal tubes, and the method of embedding the metal tubes in the carbon-containing refractory.

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

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.

The carbon source is not particularly limited, 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. The amount of carbon source in the carbon-containing refractory is not particularly limited, but generally, about 10 to 25 mass% is appropriate.

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

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

The metal capillary tube is usually a metal tube with an inner diameter of about 1 to 5 mm and a tube thickness of about 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. For example, the material of the metal capillary tube can 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.

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 or more. The number of metal capillaries 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, usually about 60 to 250 metal capillaries are embedded in the carbon-containing refractory. On the other hand, in the case of a nozzle that only flows a small amount of gas, the number of metal capillaries may be one to several. Even in such gas injection nozzles, the tuyere tip cools due to the forceful gas injection, and the extension of cracks due to thermal shock can cause damage, so the present invention can also be applied to such gas injection nozzles.

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 as mentioned above are mixed and kneaded in a mixer. The metal capillaries are laid on top of the kneaded mixture so that the metal capillaries are embedded in a layered configuration, and then the mixture is molded at a specified pressure using a press, and after molding, is dried at an appropriate temperature. The carbon-containing refractory with the metal capillaries embedded in it is then subjected to non-oxidizing firing and organic substance impregnation multiple times according to the method of the present invention, after which a gas reservoir member necessary for the function of the gas injection nozzle is joined (welded) to the metal capillaries to produce the gas injection nozzle product.

In another method, a metal tube is first joined (welded) to the gas reservoir member (top plate), the mixture is filled around it, and then it is molded at a specified pressure using a press, and after molding, it is dried at an appropriate temperature. Then, the carbon-containing refractory material with the metal tube embedded in it is subjected to non-oxidizing firing and organic matter impregnation multiple times according to the method of the present invention to produce a gas injection nozzle product.

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

To mold the kneaded material, a uniaxial molding machine such as a hydraulic press or friction press, or a press commonly used for molding 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 about 5 to 30 hours.

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

The raw materials for the carbon-containing refractory 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 matter to be impregnated into the carbon-containing refractory material. In Tables 1 to 3, the one with a residual carbon ratio of 42% by mass is coal tar pitch. Also, the one with a residual carbon ratio of 15% by mass is phenolic resin. The residual carbon ratio was measured based on the fixed carbon measurement method described in JIS K6910 (phenolic resin test method).

The raw materials of the carbon-containing refractory were mixed in the ratios shown in Tables 1 to 3 and kneaded using an Eirich mixer, and then using a 230 x 200 mm mold, the metal capillaries were embedded in a layered manner while being laid on the kneaded mixture, and then molded using a hydraulic press at a pressure of 2.5 tons/ ^cm2 . The molded refractory was cured and dried in a dryer at 250°C for 10 hours to produce a carbon-containing refractory with embedded metal capillaries.

The carbon-containing refractory produced as described above was non-oxidatively fired in coke breeze according to the conditions shown in Tables 1 to 3, and then impregnated with an organic substance to obtain a refractory for a gas injection nozzle. In the present invention, this non-oxidative firing and impregnation with an organic substance was performed multiple times. In the impregnation with an organic substance, the carbon-containing refractory was held at a specified pressure for 10 hours.

In addition, to measure porosity and fracture energy, a carbon-containing refractory material without embedded metal tubes was prepared using the same materials and methods as above.

In addition, some of the comparative examples were not subjected to non-oxidative firing or organic impregnation, were subjected to only non-oxidative firing without organic impregnation, and 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 the above manner was measured. In addition, 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 was measured according to JIS R2205. The vacuum method was used, and kerosene was used as the soot liquid.

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 test machine used was an Autograph AG-X/R manufactured by Shimadzu Corporation, with a crosshead speed of 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 of the cut surface (25 x 25 mm). It was confirmed that stable fracture had occurred in all cases measured.

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 a quantitative analysis using an analytical instrument. The measurement range was the amount of carbon in a 100 x 100 μm field along the outer circumference of the metal capillaries. 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 _D0 of carbon diffusion in formula (1) and the activation energy Q for carbon diffusion 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 embodiment, 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 this embodiment, the gas constant R in equation (1) is set to 8.314 J/(K·mol).

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

According to Table 3, Comparative Example 1 is a magnesia-carbon brick that is commonly used. Comparative Example 1 has a small fracture energy. Comparative Example 2 is Comparative Example 1 that has been non-oxidatively fired at 1400°C (without impregnation with organic matter). Comparative Example 2 has a small fracture energy. In addition, the total carburization index N during firing exceeds 118, and the carbon content of the metal tube is large at 3.1 mass%. Comparative Example 3 is a case in which the non-oxidative firing temperature is low at 300°C. Comparative Example 3 is a case in which the binder is not sufficiently thermally decomposed by non-oxidative firing, so that impregnation with organic matter cannot be performed, and the fracture energy is small. Comparative Example 4 is a case in which an organic matter with a small residual carbon rate of 15 mass% is used in the impregnation treatment. Comparative Example 4 does not have a satisfactory increase in fracture energy. Comparative Example 5 is a case in which non-oxidative firing and organic matter impregnation are performed only once. Comparative Example 5 has an increase in fracture energy, but it is small compared to the present invention.

Claims

A method for producing a refractory for a gas-blowing nozzle, comprising embedding one or more metal thin tubes for blowing gas into a carbon-containing refractory, the method comprising the steps of:
A method for producing a refractory for a gas injection nozzle, comprising the steps of: non-oxidatively 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 the steps multiple times.
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 any one of claims 1 to 3, characterized in that a series of steps of non-oxidizing firing and impregnation with an organic substance is carried out two or three times.
The method for manufacturing a refractory for a gas injection nozzle according to any one of claims 1 to 4, wherein the conditions of the non-oxidizing firing are set so that the total carburizing index N during firing in multiple non-oxidizing firings is equal to or less than a threshold value.
The method for producing a refractory for a gas blowing nozzle according to any one of claims 1 to 5, 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.
The method for manufacturing a refractory for a gas injection nozzle according to any one of claims 1 to 6, characterized in that the porosity of the carbon-containing refractory constituting the manufactured refractory for a gas injection nozzle is 3% or less.
The method for manufacturing a refractory material for a gas injection nozzle according to any one of claims 1 to 7, 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 any one of claims 1 to 7, characterized in that the carbon content of the metal tube after the final non-oxidizing firing is 1.3 mass% or less.
The method for manufacturing a refractory for a gas injection nozzle according to any one of claims 1 to 9, characterized in that the organic material impregnated into the carbon-containing refractory in the impregnation treatment is one or more selected from coal tar pitch, phenolic resin, and furan resin.
A refractory for a gas injection nozzle, comprising a carbon-containing refractory having one or more metal thin tubes for injecting gas embedded therein,
A refractory for a gas blowing nozzle, characterized in that the fracture energy of the carbon-containing refractory is 175 J/ m2 or more.
The refractory for a gas injection nozzle according to claim 11, characterized in that the porosity of the carbon-containing refractory is 3% or less.
The refractory for a gas injection nozzle according to claim 11 or 12, characterized in that the carbon content of the metal tube is 2.0 mass% or less.
The refractory for a gas injection nozzle according to claim 11 or 12, characterized in that the carbon content of the metal tube is 1.3 mass% or less.
A gas-blowing nozzle comprising the refractory material for a gas-blowing nozzle according to any one of claims 11 to 14.