JPH0587465B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a refractory composition disposed at the boundary between different types of refractory material layers in refractories such as submerged nozzles, long nozzles, long stoppers, etc. [Prior Art] As the continuous casting method becomes more widely used, there is a growing demand for improving the durability of refractory equipment or appliances used therein, such as immersion nozzles, long nozzles, and long stops. Summer. Conventionally adopted methods to improve durability include arranging zirconia graphite refractories with high corrosion resistance in the parts that come into contact with the mold powder for immersion nozzles, and placing zirconia graphite refractories that have high corrosion resistance in the parts that come into contact with the slag for long nozzles. Examples include placing graphite refractories. Further, the long stopper is required to have a function of controlling the flow rate of molten steel due to its use. Therefore, in order to suppress the erosion of the tip as much as possible, a zirconia graphite refractory is sometimes used for the tip. As described above, conventionally, zirconia graphite refractories have been used in areas where corrosion resistance is required. However, this zirconia graphite refractory has a large coefficient of thermal expansion and is expensive. Therefore, it is common practice to combine zirconia graphite refractories with alumina graphite refractories, which have a lower coefficient of thermal expansion and are cheaper than zirconia graphite refractories, to improve spalling resistance and prevent cost increases. It is adopted by However, the coefficient of thermal expansion of zirconia graphite refractories varies depending on the zirconia content, but at 1000℃,
It is 0.4-0.7%. On the other hand, that of alumina graphite refractories is usually in the range of 0.2 to 0.5% at 1000°C. When materials with different expansion coefficients are combined in this way, the thermal stress generated during use increases at their boundaries, creating a new problem of cracking due to spalling. In order to reduce the thermal stress generated at this boundary, the following methods have been proposed so far. (1) To reduce the difference in thermal expansion coefficient between alumina graphite refractories and zirconia graphite refractories,
How to adjust the composition of both materials. (2) Materials with compositions intermediate between both materials, e.g.
A method of placing ZrO ₂ -A ₂ O ₃ -SiO ₂ -C ceramics at the boundary. (3) To make the boundary between both materials non-linear,
A method for forming alumina graphite refractories and zirconia graphite refractories. [Problems to be Solved by the Invention] All of the above methods are considered to be effective in reducing thermal stress at the boundary where materials change discontinuously. However, method (1) imposes restrictions on the composition of the refractory material used. In particular, since the zirconia content in zirconia graphite refractories is limited, products with excellent corrosion resistance cannot be obtained. Furthermore, when using methods (2) and (3), ZrO ₂ −A ₂ O ₃ is present at the boundary where the material changes discontinuously.
A _-SiO2 -C type composition is present.
However, this type of composition accelerates the deterioration of corrosion resistance due to the lower melting point of SiO ₂ . In view of these problems in the prior art, the present invention aims to reduce the occurrence of melting loss and thermal stress at the boundary where materials change discontinuously, and to prevent cracks due to spalling at the boundary. , was developed. [Means for Solving the Problems] In order to achieve the object, the refractory composition of the present invention is a composite refractory consisting of an alumina graphite refractory and a zirconia graphite refractory. In between, fused silica 0-5% by weight, zirconia 0-10% by weight, alumina 50-80% by weight, graphite 10-10% by weight.
It is characterized by having a fire-resistant composition composed of 40% by weight and the balance being other fire-resistant materials. [Operation] An investigation of a used submerged nozzle in which local erosion occurred at the boundary between alumina graphite refractory and zirconia graphite refractory revealed that the alumina graphite refractory was in contact with the zirconia graphite refractory. It was found that the disappearance of fused silica in the refractory was remarkable, and the degree of disappearance became more severe as it approached the zirconia-graphite refractories. Then, due to the disappearance of this fused silica, cavities were created in the alumina graphite, and the structure of the alumina graphite refractory was weakened. That is,
Erosion loss at the boundary where the material changes discontinuously occurs due to SiO ₂ in the ZrO ₂ -A ₂ O ₃ -SiO ₂ -C system in the refractory.
We have identified a phenomenon that occurs due to wear and tear. Therefore, the present invention reduces the content of zirconia and fused silica in the composition of the refractory used at the boundary, thereby reducing ZrO ₂ −A ₂ O ₃ −
This reduces the erosion loss at the boundary caused by SiO ₂ -C-based reaction products. In addition, by adjusting the composition of the refractory placed at the boundary to have an expansion coefficient intermediate between alumina graphite refractory and zirconia graphite refractory, the thermal stress generated at the boundary can be reduced. Prevent spalling. In the refractory composition of the present invention used for the interface, the amount of fused silica powder contained in the refractory mixed powder must be within the range of 0 to 5% by weight. When the fused silica powder exceeds 5% by weight, ZrO ₂ -A forms at the boundary with the zirconia graphite refractory.
A decrease in corrosion resistance is observed due to the formation of ₂ O ₃ --SiO ₂ --C-based reactants. By the way, the alumina-graphite refractory used for the main body contains 5 to 30% by weight of fused silica in most cases to reduce its coefficient of thermal expansion and impart spalling resistance. In this connection, the content of ZrO ₂ powder should be in the range from 0 to 10% by weight. That is, when the content of _ZrO2 powder exceeds 10% by weight,
At the boundary with the alumina graphite refractory used as the main body, a decrease in corrosion resistance is observed due to the formation of ZrO ₂ -A ₂ O ₃ -SiO ₂ -C-based reactants. Further, the graphite content needs to be within the range of 10 to 40% by weight. If the graphite content is less than 10% by weight, sufficient spalling resistance cannot be obtained, and if it exceeds 40% by weight, corrosion resistance and abrasion resistance will decrease. Further, the alumina content needs to be within the range of 50 to 80% by weight. If the alumina content is less than 50% by weight, the expansion rate will be low, and if it exceeds 80% by weight, the expansion rate will be high.
In either case, the effect of reducing thermal stress at the boundary between the zirconia graphite refractory and the alumina graphite refractory used for the main body cannot be obtained. As the other refractories constituting the remainder, refractory substances that are normally added to refractories are appropriately selected and used. Carbides such as SiC and B ₄ C, and metals such as Si, A, and Fe-Si can also be added to the refractory composition of the present invention for the purpose of imparting oxidation resistance and sinterability. The fireproof composition of the present invention is kneaded using an organic binder such as a phenolic resin or an epoxy resin, and then molded into a required shape. Here, in relation to the alumina graphite refractory and the zirconia graphite refractory, the zirconia content and the fused silica content in the composition of the refractory composition of the present invention play an important role in preventing erosion at the boundary. Explain specifically what is happening. The alumina-graphite refractories used for the main body include 5 to 30% by weight of fused silica, 30 to 70% by weight of alumina, and 30 to 70% by weight of alumina in order to obtain sufficient spalling resistance.
A material consisting of 10-40% by weight of graphite and the balance other refractory materials is used. If the content of fused silica is less than 10% by weight, the spalling resistance will be poor, and if it exceeds 30% by weight, the corrosion resistance will be reduced. In addition, if the graphite content is less than 10% by weight, the spalling resistance will decrease,
If it exceeds 40% by weight, corrosion resistance will decrease. The table shows the influence of the zirconia content in the refractory composition on the erosion loss that occurs at the interface with the alumina-graphite refractory. In the table, the erosion test was conducted by immersing a 20 x 20 x 150 mm test piece in electrolytic iron at 1600°C melted in a high frequency furnace for 80 minutes, and measuring the amount of erosion. In addition, the test piece was made by molding and firing the alumina graphite refractory in the upper part and the refractory composition with different fused silica contents in the lower part, and cutting it into the size of 20 x 20 x 150 mm. Created.

[Table] As is clear from this table, when the content of zirconia powder exceeds 10% by weight, at the boundary with the alumina graphite refractory used as the main body,
A decrease in corrosion resistance is observed due to the generation of ZrO ₂ -A ₂ O ₃ -SiO ₂ -C-based reaction products. In addition, the zirconia-graphite refractories used in the mold powder and slag parts, which are exposed to harsh atmospheres, have a composition range of 60 to 90% by weight of zirconia, 5 to 30% by weight of graphite, and the balance other refractory materials. A material with excellent corrosion resistance is used. In the zirconia graphite refractory, if the zirconia content is less than 60%, corrosion resistance is insufficient, and if it exceeds 90%, spalling resistance is reduced. In addition, if the graphite content is less than 5% by weight, the spalling resistance will decrease, and if it exceeds 30% by weight, the corrosion resistance will decrease. The table shows the influence of the content of fused silica in the refractory composition on the erosion loss that occurs at the interface with the zirconia graphite refractory. In the table, the erosion test was conducted under the same conditions as in the table. In addition, the test piece was made by molding and firing a zirconia graphite refractory in the upper part and a refractory composition with different fused silica contents in the lower part, and cutting it into the size of 20 x 20 x 150 mm. Created.

〔Example〕

The details of the present invention will be explained below using comparative examples and examples shown in the table. Comparative Examples 1 and 2 are ordinary alumina graphite refractories, which are materials used for the bodies of immersion nozzles and long nozzles. Comparative Example 3 is a low-silica alumina graphite refractory mainly used for the long stopper body. Comparative Example 4 is a zirconia graphite refractory combined with alumina graphite of the main body. Comparative Examples 5 to 8 and Examples 1 and 2 are materials that exhibit an intermediate coefficient of thermal expansion between the alumina graphite refractories (Comparative Examples 1 to 3) and the zirconia graphite refractories (Comparative Example 4). , is appropriately selected depending on the combination of alumina graphite refractory and zirconia graphite refractory, and is applied to the boundary between the two materials. The corrosion index in the table is 1600℃ in a high frequency furnace.
The refractory was immersed in the molten steel held in the molten steel for 80 minutes, and the reduction rate of the refractory in the molten steel immersed portion was measured and expressed as an index with Comparative Example 1 set as 100. As is clear from the table, Comparative Examples 1 to 3 and Example 1,
It can be seen that in the alumina graphite refractory of No. 2, the amount of melting loss decreases as the amount of fused silica decreases (the amount of alumina increases). Furthermore, the zirconia graphite refractory (Comparative Example 4) exhibits the best corrosion resistance.
On the other hand, in Comparative Examples 5 to 8 in which A ₂ O ₃ , SiO ₂ , ZrO ₂ , and C were mixed, the higher the content of fused silica and zirconia, the greater the erosion loss, especially in the comparative examples outside the scope of the present invention. When the number is 5 to 8, the corrosion resistance is poor and the erosion index exceeds 100.

【table】

[Table] The refractories listed in this table are actually combined to create long nozzles, immersed nozzles, long stoppers, etc., and how each part of them was eroded is described. - The main body part 1, slug part 2a, and boundary part 3 of the long nozzle shown in FIG. 1 were constructed from the materials shown in the table, and the melting loss of each part is also shown in the table. In addition, the table listed below ~
The degree of erosion is expressed as an index, with the degree of erosion of the alumina graphite refractory of the main body being 100.

[Table] - The main body part 1, mold powder part 2b, and boundary part 3 of the immersion nozzle shown in FIG. 2 are made of the materials shown in the table, and the melting loss of each part is also shown in the table.

[Table] - Main body part 1 of the long stopper shown in Figure 3,
The tip portion 2c and the boundary portion 3 are each made of the materials shown in the table, and the melting loss of each portion is also shown in the table. Note that the tendency of melting loss shown in this example is not limited to the long stopper, but is the same at other locations that come into contact with molten steel.

〔Effect of the invention〕

As explained above, the fireproof composition of the present invention is
Since the zirconia content is suppressed, ZrO ₂ −A ₂ O ₃ −SiO ₂ − is added to the boundary with the alumina graphite refractory.
There is no decrease in corrosion resistance due to the generation of C-based reaction products. Furthermore, since the fused silica content is suppressed, reaction products that cause embrittlement are not generated at the interface with the zirconia graphite refractory. Moreover, since the coefficient of thermal expansion of the refractory composition is an intermediate value between alumina graphite refractories and zirconia graphite refractories, thermal stress generated at the boundary can be reduced. Therefore, long nozzles, immersion nozzles,
It has become possible to significantly extend the life of refractories used in continuous casting equipment such as long stops.

[Brief explanation of the drawing]

Fig. 1 shows an example in which the refractory composition of the present invention is applied to a long nozzle, which is a type of refractory for continuous casting, Fig. 2 shows an example in which the same is applied to an immersion nozzle, and Fig. 3 shows an example in which the refractory composition of the present invention is applied to a long nozzle, which is a type of refractory for continuous casting. Here is an example applied to par.

Claims (1)

[Claims] 1 In a composite refractory consisting of an alumina graphite refractory and a zirconia graphite refractory, 0 to 5% by weight of fused silica, 0 to 10% by weight of zirconia, and 50 to 80% by weight of alumina are present between the two types of refractories. , graphite 10~
1. A refractory composition for continuous casting, comprising a refractory composition comprising 40% by weight and the balance consisting of other refractory materials.