JP6254203B2 - Refractory for converter bottom blowing tuyeres - Google Patents

Description

  The present invention relates to a refractory for bottom blowing tuyere, and more particularly to a refractory used for a converter bottom blowing tuyere having excellent thermal shock resistance and repeated heat load characteristics.

  In the steel industry, one of the processes for manufacturing steel products is a process for decarburization treatment. A converter is often used as the reaction vessel used in this step. In recent years, in such converters, various gases are often blown from tuyere provided at the bottom of the furnace in order to obtain excellent metallurgical characteristics with a high stirring force. At present, MgO-C brick is often used as a refractory for such bottom blowing tuyere from the viewpoint of spalling resistance and corrosion resistance.

  However, the refractory disposed around the tuyere at the bottom of the converter, especially around the bottom tuyere, has a faster wear rate than other parts due to the thermal stress generated by cooling with the blown gas. It is a part that determines the refractory life. For this reason, various proposals as described below have been conventionally made as such blast refractories, but they are still insufficient.

  For example, Patent Document 1 discloses an MgO—C brick that uses expanded graphite to relieve thermal stress. However, since this brick becomes worse when the amount of expanded graphite used is increased, when it is added in a large amount, it is necessary to increase the molding pressure, which may limit the product shape.

  Patent Document 2 discloses a magnesia rod-like aggregate having a diameter of 1 mm or more, a length of 5 to 20 mm, a length / diameter ratio of 1.6 to 5 and an average crystal diameter of 60 to 120 μm. MgO—C brick containing 96 mass% or more of MgO is disclosed, but there is a problem that the spalling resistance is insufficient and the effect of reducing the wear rate is small.

Patent Document 3 discloses a technique of inserting a ceramic tube mainly composed of ZrB ₂ between a metal tuyere and a tuyere refractory brick. The tuyere refractory brick cannot be produced by CIP molding, or even if it can be produced, the molding pressure is limited.

  Further, Patent Document 4 discloses a technique capable of preventing breakage and dropping even when a crack occurs in a refractory due to temperature fluctuation by blending a carbon fiber cloth woven in a lattice shape. Yes. However, this technique has a problem that it is not only expensive but also takes time to form a refractory.

Further, Patent Document 5, C amount is 10~25mass%, _Al 2 _{O 3} is 5~20mass%, MgO is refractory 50～80Mass% is disclosed. The material described in this document is superior in spalling resistance compared to the above-mentioned refractories, but when observing the tuyere brick after use, cracks are still seen and wear due to thermal stress is dominant. Therefore, further efforts to improve the spalling resistance have been demanded.

Further, in Patent Document 6, 90 mass% or more of the aggregate excluding carbon is composed of magnesia and an Al ₂ O ₃ .MgO-based spinel, and the sintered or unfired magnesia-spinel having a carbon content of 5 to 25 mass%. A refractory for a DC electric furnace furnace bottom or ladle side wall made of C brick or spinel-magnesia-C brick is disclosed. The refractory described in this document still has many cracks, and wear due to thermal stress is dominant, so that further efforts to improve the spalling resistance have been demanded. In addition, the one disclosed in this document has a decisive problem that the corrosion resistance is inferior.

JP 11-209169 A JP 2003-171171 A JP 07-224311 A JP 58-217473 A JP 2013-100580 A JP 2002-80272 A

  As described above, the refractories for converter bottom blowing tuyeres according to the prior art described in Documents 1 to 6 have an insufficient wear rate reduction effect and inferior spalling resistance. There was a problem of being insufficient.

  Then, the objective of this invention is providing the refractory for converter bottom blowing tuyere with high durability.

Converter bottom-blown tuyere refractories of the present invention is a refractory to be used in the bottom-blown tuyere portion of the _{converter, MgO: 5~60mass%, Al 2} O 3 -MgO spinel: 30~70mass% , C: composed of 10 to 30 mass%, and the Al ₂ O ₃ —MgO spinel has a particle size of 1 mm or more and 10 mm or less in total. It is a thing.

The present invention is also characterized in that the refractory composed of MgO, Al ₂ O ₃ —MgO spinel and C does not contain alumina alone other than alumina forming the spinel.

According to the present invention, a refractory made of magnesia (MgO), spinel (MgO—Al ₂ O ₃ ), and graphite (C) is used as a refractory for a bottom blowing tuyere that blows various gases from the furnace bottom. In this case, since a material not containing alumina (Al ₂ O ₃ ) as a simple substance is used, a highly resistant refractory for a converter bottom blowing tuyere is obtained because of excellent corrosion resistance and thermal shock resistance. be able to.

It is sectional drawing of a bottom blowing tuyere part. It is a graph which shows the relationship between a spinel substitution rate and a thermal expansion coefficient.

  FIG. 1 is a simplified cross-sectional view showing an example of a converter bottom blowing tuyere. 1 is a converter bottom blowing tuyere embedded in a converter bottom brick 5, and 2 is a tuyere brick constituting the outermost part of the bottom blowing tuyere 1. The horizontal cross section is a polygonal, circular or elliptical cylinder. 3 shown in the figure is a pillar-shaped tuyere refractory formed by filling the tuyere brick 2 with an irregular refractory. In the axial direction (up and down direction of the converter) in the tuyere refractory 3, blowout nozzles 4 composed of a large number (about 50 to 100) of metal thin tubes are generally arranged in the radial direction and the circumferential direction. They are buried in a state of being distributed at substantially equal intervals or unequal intervals. In the figure, 6 is a gas supply pipe, 7 is a gas supply header, and 8 is a bottom blowing tuyere holding brick.

  The inventors have intensively studied the wear mechanism of the tuyere refractory 3 in order to suppress the wear of the tuyere refractory 3 in the bottom blowing tuyere 1 of the converter. As a result, it was found that the wear of the tuyere refractory 3 progresses due to the extension of cracks generated during blowing. It has been found that the tuyere refractory 3 is effective to reduce the thermal stress generated inside itself in order to suppress the generation and extension of the cracks.

  By the way, the thermal stress generated in the tuyere refractory 3 is affected by heat input from the furnace bottom brick 5 around the bottom blowing tuyere and heat removal by low temperature gas flowing in the blowing nozzle 4 which is a metal thin tube. It was found to be caused by a temperature gradient caused by. Therefore, various studies were conducted to reduce the thermal stress, and it was found that it is effective to use the following tuyere refractories.

  That is, in order to suppress the thermal stress applied to the tuyere refractory, to suppress the development of cracks, and to reduce the damage rate of the refractory, as described above, the tuyere refractory from the bottom brick. It can be seen that the temperature gradient generated under the influence of heat input to the heat source and heat removal by various gases flowing in the tuyere should be reduced.

Therefore, the inventors made a small sample and tried it, and as a result, the amount of C was 10 to 30 mass%, MgO: 5 to 60 mass%, Al ₂ O ₃ —MgO spinel: 30 to 70 mass%, and Al _2. O ₃ -MgO spinel is refractory having a size (particle size) of 1 mm or more in total, so that the thermal shock resistance is dramatically improved compared to conventional products, and the corrosion resistance is not impaired. I found out.

FIG. 2 shows the relationship between the amount of Al ₂ O ₃ —MgO spinel in the C material and the linear expansion coefficient at 1000 ° C. for a material having a C content of 20 mass%. As shown in this figure, when the amount of spinel in the C material increases, the linear expansion coefficient decreases. In particular, when the amount exceeds 30 mass%, the linear expansion coefficient is 30% or more compared to the case where spinel is not included. It has become smaller. In this respect, if the linear expansion coefficient is small, the strain due to the temperature difference is reduced even in the same temperature distribution, so that the thermal shock resistance can be improved.

From this, it is desirable that the composition of the tuyere refractory has a content of Al ₂ O ₃ —MgO spinel of 30 to 70 mass%. The reason is that if the amount of Al ₂ O ₃ —MgO spinel is less than 30 mass%, the effect of improving thermal shock resistance is reduced, which is not preferable. On the other hand, the amount of Al ₂ O ₃ —MgO spinel is greater than 70 mass%. This is because the case is not preferable because the corrosion resistance to the slag is lowered. A more preferable amount of the Al ₂ O ₃ —MgO spinel amount is 40 to 60 mass%.

In the present invention, the size (particle size) of the Al ₂ O ₃ —MgO spinel is also important. That is, it is desirable that the Al ₂ O ₃ —MgO spinel has a total particle diameter (diameter) of 1 mm or more. The reason for this is that the use of Al ₂ O ₃ —MgO spinel with a fine particle size of less than 1 mm is not preferable because it is inferior in corrosion resistance. On the other hand, when the particle size of the Al ₂ O ₃ —MgO spinel exceeds 10 mm, it is difficult to make the particles themselves uniformly present in the refractory, and systematic segregation occurs, resulting in partial dissolution loss and cracks. This is not preferable because it leads to further promotion. Therefore, the upper limit size of the Al ₂ O ₃ —MgO spinel particles is desirably 10 mm or less, and more desirably 8 mm or less.

As such Al ₂ O ₃ —MgO spinel, there are fused spinel and sintered spinel, but in the present invention, either fused spinel or sintered spinel may be used. However, it is more preferable to use an electrofusion spinel when the electrofusion spinel is used because the corrosion resistance is further improved.

Next, about the amount of C, it is preferable that the amount shall be 10-30 mass%.
The reason is that if the amount of C is less than 10 mass%, the thermal shock resistance is lowered, which is not preferable. On the other hand, if the amount of C is more than 30 mass%, the corrosion resistance against molten steel is lowered, which is not preferable. Therefore, the more preferable amount of C is good to set it as the range of 12-25 mass%.

  In addition, although it does not specifically limit as C source, For example, 1 type, or 2 or more types, such as natural graphite, such as scale graphite and earth-like graphite, artificial graphite, such as expanded graphite, pitch, and carbon black, can be used. . Among these, the use of scaly graphite is more preferable because scaly graphite is excellent in corrosion resistance and thermal shock resistance.

  The refractory for bottom blowing tuyeres according to the present invention contains MgO as the remaining component. The MgO is not particularly limited as long as it is used for general refractories such as electrofused products and sintered products. However, in consideration of corrosion resistance and the like, it is desirable to use high-purity fused magnesia having a purity higher than 98%.

In addition, the refractory for bottom blowing tuyere according to the present invention generally contains carbon such as metals such as Al, Mg, Si, and Ca, or alloys thereof and additives such as B ₄ C, SiC, and CaB _6. Additives included in the refractory can be used.

  As a manufacturing process of the bottom-blown tuyere refractory, a method similar to a manufacturing process of a general carbon-containing refractory can be employed. For example, for kneading, a Conner mixer, a pressurized high speed mixer with a high speed stirring blade, an Eirich mixer, or the like can be used. As for the molding method, a general brick molding press such as a hydraulic press or an isostatic press can be used. Furthermore, in order to make a molded brick, it may be dried by applying a treatment at a drying temperature of 180 ° C. to 350 ° C. and a holding time of about 5 to 30 hours.

The tuyere refractory according to the present invention composed of MgO, Al ₂ O ₃ —MgO spinel and C is characterized in that it contains no alumina component other than alumina forming the spinel. That is, Al ₂ O ₃ which is a component of spinel is not used alone, that is, the Al ₂ O ₃ source and the MgO source are not blended separately. The reason is that when Al ₂ O ₃ is used (mixed) alone, Al ₂ O ₃ and MgO react during use to produce MgAl ₂ O ₄ and cause volume expansion. This is because when this deposition expansion occurs, a large thermal stress is generated inside the refractory, resulting in poor thermal shock resistance. On the other hand, when the Al ₂ O ₃ in the form of spinel is used, rapid thermal expansion during use of the tuyere refractory can be effectively suppressed.

Examples will be described below.
Table 1 shows examples suitable for the present invention, and Table 2 shows comparative examples outside the scope of the present invention. That is, refractory bricks (bottomed tuyere refractories) according to the formulations shown in Tables 1 and 2 were prepared according to a standard method, and the thermal shock resistance, corrosion resistance, and fire resistance in a restrained state of these refractory bricks. Experiments were conducted to evaluate the behavior of bricks.

  The thermal shock resistance was evaluated by immersing the test material in hot metal at 1650 ° C. for 1 minute and using the ratio of elastic modulus before and after immersion (e / e0). It can be said that the closer the ratio (e / e0) is to 1, the less damage is caused by thermal shock.

  For the evaluation of corrosion resistance, the wear rate was measured by measuring the dimensions of a 40 mmφ cylindrical sample before and after being immersed in a slag with a basicity of 2.3 and 1550 ° C. at 1000 rpm for 3 hours. This was calculated and indicated as a melting index. The erosion index at each level was evaluated as an erosion index obtained by indexing the erosion index of Comparative Example 1 in Table 2 as 1. Note that the smaller the erosion index, the better the corrosion resistance.

And about the behavior of the refractory brick in the restrained state, the following simple tests were done. The refractory brick was assembled into a hexagon and held in an Ar atmosphere at 1550 ° C. for 24 hours. This is a simple test to see the behavior of refractory bricks in a restrained state, but only in the horizontal direction. This test simulates the situation of refractories. From the appearance observation after cooling, it was determined that the cracked one was not preferable.
In addition, about a particle size, it is the value screened with the sieve based on JISZ8801-1 "Sieving for a test-1st part: Metal mesh sieve".

  Tables 1 and 2 also show the evaluation results. From these evaluation results, the examples of the present invention obtained excellent results in the evaluation of thermal shock resistance, corrosion resistance, and behavior of refractory bricks in a restrained state.

  On the other hand, Comparative Example 1 is an MgO-C brick (conventional product) that does not contain any spinel, but has poor thermal shock resistance. Comparative Example 2 has a spinel amount of 5 to 1 mm of 20 mass%, but is inferior in thermal shock resistance, and Comparative Example 3 has a spinel amount of 5 to 1 mm of 75 mass%. Although it is inferior in corrosion resistance, the comparative example 4 has a spinel amount of 60 mass% and is in a range suitable for the present invention, but contains 30 mass% of spinel having a particle size of less than 1 mm. Corresponding and inferior in corrosion resistance, Comparative Example 5 is an example in which the amount of carbon is as low as 8 mass% and inferior in thermal shock resistance, and Comparative Example 6 is an example in which the amount of C is as large as 35 mass%. Since the corrosion resistance is inferior, the result is not preferable. Since Comparative Example 7 did not contain any spinel, it was inferior in thermal shock resistance.

From the above test results, the MgO—Al ₂ O ₃ —MgO spinel-C refractory having a configuration suitable for the present invention has no deterioration in corrosion resistance and has excellent thermal shock resistance. It became clear that it was a thing.

  The technology according to the present invention is applied to not only a bottom blow converter, but also applied to refining equipment such as a ladle having various nozzles for injecting various gases into the molten metal from the bottom of the furnace and various refining furnaces. be able to.

1 Bottom blow tuyere 2 Tuyere brick 3 Tuyere refractory 4 Blowout nozzle 5 Furnace bottom brick 6 Gas supply pipe 7 Header 8 Tuyere press brick

Claims (2)

A refractory used in the bottom-blown tuyere portion of the _{converter, MgO: 5~60mass%, Al 2} O 3 -MgO spinel: 30~70mass%, C: consists 10～30Mass% of the component composition, the Al ₂ O ₃ —MgO spinel is a refractory for a converter bottom blowing tuyere characterized by having a total particle size of 1 mm or more and 10 mm or less . Wherein the MgO and Al ₂ O ₃ refractories consisting of -MgO spinel and C, and characterized in that it is free of alumina single than alumina building form the spinel, feather blown converter bottom according to claim 1, wherein Refractory for mouth.

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