JP6974115B2 - Refractory for gas blowing nozzle - Google Patents

Description

The present invention is a refractory for a gas blowing nozzle for blowing gas into a molten metal from a furnace bottom or the like for the purpose of improving refractory efficiency and alloy yield in a converter or an electric furnace, and is a carbon-containing refractory. The present invention relates to a refractory material for a gas blowing nozzle in which one or more metal thin tubes for gas blowing are embedded.

In converters and electric furnaces, so-called bottom blowing is used in which agitated gas (usually an inert gas such as nitrogen or Ar) or refining gas is blown into the molten metal from the bottom of the furnace for the purpose of improving refining efficiency and alloy yield. Will be done. As this bottom blowing method, (1) a double pipe method in which oxygen for the purpose of decarburization is blown from the inner pipe and hydrocarbon gas (propane, etc.) for the purpose of cooling the molten steel contact part is blown from the outer pipe. , (2) A slit-shaped opening is provided in the gap between the metal pipe and the brick, and an inert gas is blown through the opening (slit method). There is a method of burying the metal thin tube of the book), supplying the inert gas from the bottom of the brick to the metal thin tube through the gas introduction pipe and the gas reservoir, and blowing the inert gas from the metal thin tube.

Of these, in the methods (1) and (2), bricks for tuyere are manufactured in advance by a conventional method, and the installation part of the double pipe or the metal pipe forming the slit is processed or divided into two or four. By doing so, it is common to form a space for installing the metal pipe, set the metal pipe to which gas is blown in advance at the time of construction, and construct the tuyere brick around it.
On the other hand, the gas blowing plug (nozzle) used in the method (3) is called a multiple hole plug (hereinafter referred to as MHP). For example, in Patent Document 1 (Japanese Unexamined Patent Publication No. 59-31810), it is defined that the gas flow rate (0.01 to 0.20 Nm ³ / min) can be controlled 1 to 20 times with this MHP. Therefore, MHP is easier to adopt than the double pipe method or the slit method.

MHP has a structure in which multiple metal thin tubes connected to a gas reservoir are embedded in a carbon-containing refractory such as magnesia-carbon brick, so its manufacture is different from double tube type and slit type nozzles. , The following methods are adopted.
That is, a raw material obtained by adding a carbon source such as scaly graphite, a binder such as pitch, a metal species, and a phenol resin to an aggregate such as a magnesia raw material is kneaded using a kneading means such as a high-speed mixer having high dispersion performance to obtain a metal. Obtain a kneaded material that should constitute a carbon-containing refractory material in which a thin tube is embedded. Then, a method in which the metal thin tubes are embedded in a laminated manner while laying the metal thin tubes on the kneaded product, the metal thin tubes are formed at a predetermined pressure by a press machine, and then heat treatment such as predetermined drying and firing is performed. (The metal thin tube is then joined to the gas reservoir member by welding), or the metal thin tube is joined to the gas reservoir member by welding in advance, filled with the kneaded material around it, and then pressed. MHP is manufactured by a method of molding at a predetermined pressure by a machine and then performing a predetermined drying.

Since the bottom blowing nozzle has a larger amount of damage (amount of wear) than a refractory material such as a furnace wall and is an important member that affects the life of the furnace, various proposals for suppressing damage have been made in the past, and MHP. For example, the following improvements have been proposed.
In Patent Document 2 (Japanese Unexamined Patent Publication No. 63-24008), the gas blowing nozzle portion of the MHP and the peripheral tuyere are integrated to reduce pre-melting damage and wear from the joint portion. However, this technology has little effect and cannot be an effective countermeasure.

In addition, the following proposals have been made as measures to lower the melting point (preceding damage of the metal capillaries) by carburizing the metal capillaries embedded in the refractory.
In Patent Document 3 (Japanese Unexamined Patent Publication No. 2000-212634), an oxide layer is formed on the surface of a metal capillary tube by thermal spraying in order to suppress carburizing of a stainless steel capillary tube embedded in a carbon-containing refractory such as magcarbon. It has been proposed to form. However, in a smelting furnace that is used for a long period of time such as a converter (for example, a usage period of 2 months to 6 months), there is a problem that the thickness of the oxide layer is not sufficient and the effect of suppressing carburization is small.

Further, Patent Document 4 (Japanese Unexamined Patent Publication No. 2003-231912) proposes to dispose a fire-resistant sintered body between the metal thin tube and the carbon-containing refractory in order to suppress carburizing of the metal thin tube. ing. However, although this technology has the effect of suppressing carburizing, it is difficult to dispose a refractory sintered body in a nozzle in which a large number of metal capillaries are embedded because the intervals between the metal capillaries are narrow, and this technology is put into practical use. Is difficult.

On the other hand, the following proposals have been made as adopting a method of impregnating a carbon-containing refractory with an organic substance after reducing and firing it once.
In Patent Document 5 (Japanese Unexamined Patent Publication No. 58-015072), a magcarbon brick to which a metal Al powder is added is fired and heated at 500 to 1000 ° C., and then an organic substance having a carbonization yield of 25% or more is impregnated into the brick pores. The heat strength is improved and the corrosion resistance is improved. Further, in Patent Document 6 (Japanese Patent No. 3201678), a heat-resistant spall by reducing the elastic modulus by reducing and firing a magcarbon brick to which 0.5 to 10% by weight of calcined anthracite is added at 600 to 1500 ° C. It is said that sexuality will be improved. Further, tar may be impregnated after firing, and it is said that this impregnation can seal pores, increase strength, and improve digestibility. However, these technologies have little effect and cannot be effective countermeasures.

Japanese Unexamined Patent Publication No. 59-31810 Japanese Unexamined Patent Publication No. 63-24008 Japanese Unexamined Patent Publication No. 2000-21624 Japanese Unexamined Patent Publication No. 2003-231912 Japanese Unexamined Patent Publication No. 58-15072 Japanese Patent No. 3201678

As described above, various studies have been conducted on the refractory material and structure of the type of gas blowing nozzle (MHP, etc.) in which a metal thin tube is embedded in a carbon-containing refractory in order to improve its durability. Is not obtained at present.
Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and to have high durability in a refractory material for a gas blowing nozzle in which one or more metal thin tubes for gas blowing are embedded in a carbon-containing refractory material. It is an object of the present invention to provide a refractory material for a gas blowing nozzle having the above.

As for the cause of damage to MHP used in converters and electric furnaces, it has been considered that the main cause of damage is melting and wear due to the molten steel flow near the nozzle operating surface because gas is blown vigorously from the metal capillaries. rice field. The measures in Patent Document 2 are based on this idea. Further, there is also an idea that the metal thin tube is consumed first due to carburizing or the like, and the damage is increased. Therefore, carburizing of the metal thin tube has been prevented by a method as in Patent Document 3 and Patent Document 4. On the other hand, during blowing, the refractory is cooled in order to blow the inert gas vigorously, and the temperature difference between the blowing and non-blowing may cause spalling damage, and further, carbon-containing refractory. Since the strength of the object becomes the lowest at around 600 ° C, there are various ways of thinking that the working surface may be cracked and damaged at that part, and no conclusion has been reached. As a result, sufficient measures have not been taken, and the current situation is that satisfactory durability has not always been obtained as described above.

Therefore, in order to find out the true cause of damage to the MHP, the present inventors recovered the after-use product (MHP) used in the actual furnace and investigated the refractory structure near the nozzle operating surface in detail. As a result, it was found that a very large temperature change of 500 to 600 ° C. occurred inside the refractory with a depth of about 10 to 20 mm from the working surface, and a crack parallel to the working surface was confirmed in this part. I was able to. From the results of repeated detailed investigations in the vicinity of the operating surface of the product after using the actual furnace, the damage form of the MHP is not due to damage due to melting or wear, but due to the rapid temperature gradient occurring near the operating surface. It was concluded that the damage caused by the thermal shock was the main cause.

Therefore, as a result of diligent studies on material improvement to reduce the thermal stress generated in the refractory for tuyere, the present inventors have high thermal conductivity with a high C content (the temperature gradient becomes smaller due to the high thermal conductivity). ), It was found that a refractory with a low coefficient of thermal expansion is effective. However, when the C content is increased, the wear resistance and the melt resistance are significantly lowered, and the life is significantly shortened due to the wear and the melt damage caused by the molten metal. Therefore, as a result of further studies, a high C content MgO-C material was placed around the most cooled metal capillary tube (center of a predetermined range), and the periphery (outer circumference) contained normal C. It was found that the problem can be solved by adopting a structure in which the amount of MgO-C material is used. That is, by using a refractory material (MgO-C material) having a normal C content for the outer peripheral portion, deterioration of wear resistance and erosion resistance can be suppressed, while the peripheral portion of the metal capillary tube contains C. By using a refractory material (MgO-C material) with a high amount of high thermal conductivity and low thermal expansion rate, it is possible to suppress the occurrence of cracks due to thermal shock, and because of the high thermal conductivity, it is cooled by the gas flowing through the metal slag tube. By doing so, a solidified film of slag or metal (so-called mushroom) is formed on the working surface side, and this solidified film blocks (protects) the refractory surface from the molten steel, and has the effect of suppressing wear due to wear and melting. I found that I could get it.

The present invention has been made based on such findings, and has the following gist.
[1] In a refractory for gas blowing nozzles in which one or more metal thin tubes for gas blowing are embedded in a carbon-containing refractory.
It is composed of a central refractory (a) in which a metal thin tube is embedded and an outer peripheral refractory (b) surrounding the outer periphery of the central refractory (a).
In the plane of the refractory for the gas blowing nozzle, when the radius of the virtual circle (x) with the minimum radius including all the embedded metal capillaries is R (mm), the outer shape of the central refractory (a) is , A circle concentric with the virtual circle (x) and having a radius of R + 10 mm to R + 150 mm.
The central refractory (a) is composed of MgO-C quality brick having a carbon content of 30 to 80% by mass, and the outer peripheral refractory (b) has an MgO-C having a carbon content of 10 to 25% by mass. A refractory material for gas blowing nozzles, which is characterized by being composed of quality bricks.

[2] In the above-mentioned [1] refractory for gas blowing nozzle, the outer shape of the central refractory (a) is concentric with the virtual circle (x) and has a radius in the plane of the refractory for gas blowing nozzle. A refractory material for a gas blowing nozzle, characterized in that is a circle of R + 40 mm to R + 70 mm.
[3] In the refractory material for the gas injection nozzle according to the above [1] or [2], the central refractory material (a) is composed of MgO-C material brick having a carbon content of 50 to 70% by mass, and has an outer periphery. The refractory part (b) is a refractory material for a gas blowing nozzle, which is composed of MgO-C material brick having a carbon content of 15 to 25% by mass.
[4] A gas blowing nozzle comprising a refractory material for the gas blowing nozzle according to any one of the above [1] to [3].

The refractory material for a gas blowing nozzle of the present invention has high durability because the generation of cracks due to thermal shock is suppressed. Therefore, by using this refractory material for the gas blowing nozzle, it is possible to obtain a gas blowing nozzle having a low damage rate and a long life.

A plan view showing an embodiment of the refractory material for a gas blowing nozzle of the present invention.

The present invention is 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 central refractory a in which the metal thin tubes are embedded, and a central refractory thereof. It is composed of an outer peripheral refractory b that surrounds the outer periphery of the object a.
As mentioned above, the main cause of wear of the MHP tuyere is thermal shock. In particular, since the peripheral portion of the metal capillary of the MHP tuyere is cooled by the gas flowing through the metal capillary, the thermal stress also increases. In order to suppress thermal shock and thermal stress, it is effective to increase the C content of MgO-C brick, but on the other hand, if the C content is increased, it becomes easier to melt in molten steel and it is resistant. It is known that wear resistance and erosion resistance are reduced. In this regard, the present inventors have found that the peripheral portion of the metal capillary tube having a high C content is cooled by the gas flowing through the metal capillary tube due to its high thermal conductivity, and as a result, slag and metal solidify on the working surface side. It has been found that a film (mushroom) is formed, and this solidified film protects the surface of the refractory from molten steel and has the effect of suppressing wear due to wear and melting. Therefore, in the present invention, the refractory material for the gas blowing nozzle is composed of a central refractory material a in which a metal thin tube is embedded and an outer peripheral refractory material b surrounding the outer periphery of the central refractory material a, and the central refractory material b. The object a is composed of MgO-C refractory brick with a high C content.

Here, the central refractory a made of MgO-C brick having a high C content needs to have a predetermined size (outer shape) as shown below in order to obtain the above-mentioned effects. .. As shown in FIG. 1, in the plane (operating surface) of the refractory refractory for the gas blowing nozzle (that is, when viewed as a plane), the radius of the minimum radius virtual circle x including all the embedded metal tubules is defined as the radius. When R (mm), the outer shape of the central refractory a is concentric with the virtual circle x and has a radius of R + 10 mm to R + 150 mm. That is, in FIG. 1, the circle forming the outer shape of the central refractory a has a radius of R + r and r = 10 to 150 mm. If the radius of the circle forming the outer shape of the central refractory a is less than R + 10 mm, the metal thin tube is too close to the boundary with the outer peripheral refractory b, so that the metal thin tube may be deformed during molding of the refractory. If the radius of the circle forming the outer shape of the central refractory a exceeds R + 150 mm, a portion not covered by the so-called mushroom is formed on the moving surface of the central refractory a, and damage is caused by contact with the molten steel.
From the above viewpoint, a more preferable condition is that the outer shape of the central refractory a is concentric with the virtual circle x and has a radius of R + 40 mm to R + 70 mm, that is, in FIG. 1, the central refractory a It is preferable that the radius of the circle forming the outer shape is R + r and r = 40 to 70 mm.

The central refractory a is composed of MgO-C brick having a carbon content of 30 to 80% by mass, preferably 50 to 70% by mass. If the carbon content of this MgO-C brick is less than 30% by mass, the thermal impact resistance is not sufficient, while if it exceeds 80% by mass, the corrosion resistance to molten steel is inferior and the reliability is poor.
On the other hand, the outer peripheral refractory b is composed of MgO-C brick having a carbon content of 10 to 25% by mass, preferably 15 to 25% by mass. If the carbon content of this MgO-C brick is less than 10% by mass, the damage due to thermal shock becomes large, while if it exceeds 25% by mass, the wear resistance and erosion resistance are inferior, so that satisfactory durability is obtained. I can't.

The material of the metal capillary is not particularly limited, but it is preferable to use a metal material having a melting point of 1300 ° C. or higher. Examples thereof include metal materials (metals or alloys) containing one or more of iron, chromium, cobalt and nickel, and in particular, stainless steel (ferrite-based, martensitic-based, austenitic-based), ordinary steel, heat-resistant steel and the like. Is common. The metal thin tube usually has an inner diameter of about 1 to 4 mm and a tube thickness of about 1 to 2 mm. If the inner diameter of the metal tube is less than 1 mm, it may be difficult to supply sufficient gas for stirring the molten metal in the furnace, and if it exceeds 4 mm, the molten metal may flow into the metal capillary and block it.
The number of metal capillaries embedded in the carbon-containing refractory is not particularly limited, and is appropriately selected depending on the required gas blowing flow rate and the area of the moving part. In a converter or the like that requires a high flow rate, about 60 to 250 metal thin tubes are generally embedded. Further, when the gas blowing flow rate is small as in an electric furnace or a ladle, generally one to several tens of metal thin tubes are embedded.

Next, a method for manufacturing a refractory for a gas blowing nozzle of the present invention will be described.
The main raw materials of the carbon-containing refractory (central refractory a, outer peripheral refractory b) are aggregate and carbon source, but may include other additive materials and binders.
Magnesia, alumina, dolomite, zirconia, chromia, spinel (alumina-magnesia, chromia-magnesia) and the like can be applied to the aggregate of the carbon-containing refractory, but in the present invention, from the viewpoint of corrosion resistance to molten metal and molten slag. Magnesia is used as the main aggregate.

The carbon source of the carbon-containing refractory is not particularly limited, and commonly used substances such as scaly graphite, expanded graphite, soil graphite, calcined anthracite, petroleum-based pitch, and carbon black can be applied. The amount of the carbon source added is determined according to the carbon content of the central refractory a and the outer peripheral refractory b described above.
The additive material other than the aggregate and a carbon source as described above include, for example, metal Al, metal Si, metal species such as Al-Mg alloy, SiC, B 4 _C include carbides such, these one or more In some cases. The blending amount of these additive materials is usually 3.0% by mass or less.
The raw material for the carbon-containing refractory generally contains a binder. As the binder, a binder such as a phenol resin or a liquid pitch that can be generally applied as a binder for a standard refractory can be used. The blending amount of the binder is usually about 1 to 5% by mass (external mass%).

A known manufacturing method can be applied to the manufacture of the refractory material for a gas blowing nozzle of the present invention, and an example thereof is given below, but the present invention is not limited thereto.
First, each refractory raw material for the central refractory a and the outer peripheral refractory b is mixed and kneaded with a mixer to obtain a kneaded product. After arranging the metal thin tube at a predetermined position in the kneaded material for the central refractory a, the metal thin tube is molded by a uniaxial press to manufacture the central refractory a in which the metal thin tube is embedded. Further, after filling the periphery of the central refractory a with a kneaded material for the outer peripheral refractory b, the base material is integrated by isotropic static pressure molding (CIP molding) to become a refractory for the gas blowing nozzle. To mold. After that, the base material is subjected to a predetermined heat treatment such as drying by a conventional method. Further, if necessary, processing for adjusting the outer shape may be performed as appropriate.

As a pressure molding method for the central fireproof material a, a small amount of kneaded material is first filled in the molding frame, pressure is applied, a metal capillary tube is placed at a predetermined position, and then a predetermined amount of kneaded material is filled. A multi-stage pressure molding method that repeatedly pressurizes and pressurizes, and while holding both ends of the metal thin tube so that the metal thin tube moves with the movement of the kneaded material during pressurization, with one pressurization together with the total amount of kneaded material. It can be performed by a single pressure molding method or the like.
Further, the joining between the metal thin tube and the gas reservoir is a method of welding the two at any stage after the molding of the refractory material a in the center, the molding of the base metal, or the heat treatment of the base metal, and the fire resistance in the center. At the time of molding the object a, a method of arranging a metal thin tube to which the upper surface plate of the gas reservoir is welded in advance in the kneaded material for the central refractory a can be appropriately selected.

The method of kneading the raw material of the carbon-containing refractory is not particularly limited, and a kneading means used as a kneading facility for a standard refractory such as a high-speed mixer, a tire mixer (Connor mixer), and an Erich mixer may be used.
For forming the kneaded product, a uniaxial forming machine such as a hydraulic press or a friction press, or a general pressing machine used for forming a refractory material such as isotropic static pressure forming (CIP) can be used.
The molded carbon-containing refractory may be dried at a drying temperature of 180 ° C. to 350 ° C. and a drying time of about 5 to 30 hours.

As shown in FIG. 1, a refractory material for a gas blowing nozzle in which 81 metal thin tubes were arranged concentrically was manufactured under the conditions shown in Tables 1 to 4.
In the plane of the refractory for the gas blowing nozzle, the radius R of the virtual circle x with the minimum radius including all the embedded metal capillaries is 50 mm, and the radius of the central refractory a in the range of r = 8 to 200 mm. R + r was changed.
As the metal thin tube to be embedded in the carbon-containing refractory, a tube made of ordinary steel or stainless steel (SUS304) having an outer diameter of 3.5 mm and an inner diameter of 2.0 mm was used.
Each refractory material was mixed at the ratios shown in Tables 1 to 4, and kneaded with a mixer. The metal thin tube was placed in the kneaded material for the central refractory a, and the central refractory a was formed by a uniaxial press. Further, a kneaded material for the outer peripheral refractory b was filled around the central refractory a, and then the base metal was formed by CIP molding. Then, the base material was dried by a conventional method to obtain a product.

The manufactured refractories for gas blowing nozzles of the invention example and the comparative example were used for the bottom brick around the bottom blowing tuyere of the 250-ton converter. After using 2500 to 2800 channels respectively, the wear rate (mm / ch) was obtained from the residual thickness of the brick, and the wear rate ratio (index) with the wear rate of Comparative Example 1 as “1” was obtained. The results are shown in Tables 1 to 4.
As shown in Tables 1 to 4, it can be seen that the refractory material for the gas blowing nozzle of the present invention has a low wear rate and excellent durability. Further, among the examples of the present invention, the carbon content of the MgO-C material brick in the central refractory a is 50 to 70% by mass, and the carbon content of the MgO-C material brick in the outer peripheral refractory b is 15 to. Those with 25% by mass have particularly excellent durability. Further, among the examples of the present invention, those having a radius of the central refractory a of R + 40 mm to R + 70 mm have particularly excellent durability.

a Central refractory b Outer perimeter refractory x virtual circle

Claims (4)

In a fireproof material for gas blowing nozzles in which one or more metal thin tubes for gas blowing are embedded in a carbon-containing fireproof material.
It is composed of a central refractory (a) in which a metal thin tube is embedded and an outer peripheral refractory (b) surrounding the outer periphery of the central refractory (a).
When the radius of the virtual circle (x) with the minimum radius including all the embedded metal capillaries is R (mm) on the plane of the refractory for the gas blowing nozzle, the outer shape of the central refractory (a) is , A circle that is concentric with the virtual circle (x) and has a radius of R + 10 mm to R + 150 mm.
The central refractory (a) is composed of MgO-C quality brick having a carbon content of 30 to 80% by mass, and the outer peripheral refractory (b) has an MgO-C having a carbon content of 10 to 25% by mass. A refractory material for gas blowing nozzles, which is characterized by being composed of quality bricks. According to claim 1, the outer shape of the central refractory (a) is concentric with the virtual circle (x) and has a radius of R + 40 mm to R + 70 mm in the plane of the refractory for the gas blowing nozzle. The described refractory for gas blowing nozzles. The central refractory (a) is composed of MgO-C quality brick having a carbon content of 50 to 70% by mass, and the outer peripheral refractory (b) is composed of MgO-C having a carbon content of 15 to 25% by mass. The refractory material for a gas blowing nozzle according to claim 1 or 2, wherein the refractory is composed of peptic bricks. A gas blowing nozzle comprising the refractory material for the gas blowing nozzle according to any one of claims 1 to 3.

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