Nozzle for continuous casting

Abstract

To provide a technique which can prevent the fusion between a stopper and a continuous casting nozzle even under severe preheating conditions such as a high temperature of 1,300°C or more.SOLUTION: A continuous casting nozzle 1 in Claim 1 which is fitted to a stopper 2 for controlling a flow rate of molten steel in molten steel continuous casting, comprises: a refractory 12 which is arranged at an upper end part including a contact part 11 with the stopper 2; an oxidation prevention agent 14 for covering a surface of the refractory 12; a reaction prevention agent 15 which is arranged so as to include the contact part 11 at a surface side of the oxidation inhibitor 14; and a fusion prevention material 16 which is arranged so as to include the contact part 11 at a surface side of the reaction prevention agent 15. The oxidation prevention agent 14 contains: an SiO2 component of 50 mass% or more and 85 mass% or less; and a B2O3 component of 1 mass% or more and 20 mass% or less, and contents of an Na2O component, a K2O component and a P2O5 are 10 mass% or less (including 0) in total. The reaction prevention agent 15 is carbonaceous. The fusion prevention material 16 is made of at least one kind of alumina fibers and alumina-silica fibers.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a continuous casting nozzle that fits with a stopper for controlling the flow rate of molten steel in continuous casting of molten steel.

Background Art

[0002] In continuous casting of molten steel, molten steel at about 1500 to 1550°C supplied from a ladle into a tundish is poured into a mold through an immersion nozzle (an example of a continuous casting nozzle), and at that time, a stopper may be used to control the flow rate of the molten steel. In this case, the stopper and the immersion nozzle are preheated before use, but during the preheating, the antioxidant coated on the surfaces of the stopper and the immersion nozzle may melt and cause fusion between the stopper and the immersion nozzle, and techniques for preventing the fusion have been studied conventionally.

[0003] For example, Patent Document 1 discloses a technique of attaching a cap made of a ceramic fiber molded body to the tip portion of a stopper that contacts an immersion nozzle. Further, Patent Document 2 discloses a technique of using an antioxidant having a melting point or a freezing point in the range of 700 to 950°C.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of Invention

Problems to be Solved by the Invention

[0005] However, as a result of tests and studies by the present inventors, it has been found that even with these conventional techniques, it is difficult to prevent fusion under severe preheating conditions such as particularly at a high temperature of 1300°C or higher. In other words, even if a ceramic fiber cap is attached to the tip of the stopper, as in the technology described in Patent Document 1, in actual preheating, the tip of the stopper is directly hit by a flame or high-temperature hot air from a burner or the like inserted into the nozzle hole to preheat the continuous casting nozzle, causing the ceramic fiber to melt and resulting in fusion. Furthermore, even if an antioxidant with a melting or solidification point of 700-950°C is used, as in Patent Document 2, fusion will occur at high temperatures of 1300°C or higher.

[0006] Therefore, the problem that the present invention aims to solve is to provide a technology that can prevent fusion between the stopper and the continuous casting nozzle even under harsh preheating conditions such as high temperatures of 1300°C or higher. [Means for solving the problem]

[0007] Based on the actual preheating conditions described above, the inventors of this invention conceived the idea that, in order to prevent fusion between the stopper and the continuous casting nozzle, it is necessary to implement fusion prevention measures on the continuous casting nozzle side. As a result of diligent research into specific means for doing so, they arrived at the present invention.

[0008] In other words, according to one aspect of the present invention, the following continuous casting nozzle is provided. A continuous casting nozzle that fits with a stopper to control the flow rate of molten steel in continuous casting of molten steel, The system comprises a refractory material disposed at the upper end including the contact portion with the stopper, an antioxidant coating the surface of the refractory material, a reaction inhibitor disposed on the surface side of the antioxidant so as to include the contact portion, and a fusion inhibitor disposed on the surface side of the reaction inhibitor so as to include the contact portion. The aforementioned antioxidant contains 50% to 85% by mass of SiO2 component, 1% to 20% by mass of B2O3 component, and the total content of Na2O component, K2O component, and P2O5 component is 10% by mass or less (including 0). The reaction inhibitor is carbonaceous, The aforementioned anti-fusion material comprises at least one of alumina fibers and alumina-silica fibers, in a nozzle for continuous casting. [Effects of the Invention]

[0009] According to the present invention, fusion between the stopper and the continuous casting nozzle can be prevented even under harsh preheating conditions such as high temperatures of 1300°C or higher. [Brief explanation of the drawing]

[0010] [Figure 1] A conceptual cross-sectional view showing the upper end of a continuous casting nozzle, along with the tip of a stopper, which is one embodiment of the present invention. [Modes for carrying out the invention]

[0011] Figure 1 conceptually shows a cross-sectional view of the upper end of a continuous casting nozzle, which is one embodiment of the present invention, together with the tip of the stopper. The continuous casting nozzle 1 shown in the figure is an immersion nozzle, used to pour molten steel from the tundish into the mold during continuous casting of molten steel. A stopper 2 is positioned above the immersion nozzle 1, and the flow rate of molten steel is controlled by raising and lowering this stopper 2 to adjust the degree of engagement with the immersion nozzle 1. Specifically, as shown by the dashed line in the figure, when the stopper 2 is lowered to a position where it is fully engaged with the immersion nozzle 1, the flow rate of molten steel becomes zero, and when the stopper 2 is raised from this position, the flow rate of molten steel changes according to the degree of its rise.

[0012] As described above, the immersion nozzle 1 is fitted with a stopper 2 that controls the flow rate of molten steel in continuous casting of molten steel, and a refractory material 12 for the upper end is placed at the upper end, including the contact portion 11 with the stopper 2. Below the refractory material 12 for the upper end is a refractory material 13 for the main body. The material of the refractory material 12 for the upper end can be, for example, zirconia-graphite, and the material of the refractory material 13 for the main body can be, for example, alumina-graphite. These can be formed integrally by integral molding, or they can be formed by molding them individually and then joining them. The materials of the refractory material 12 for the upper end and the refractory material 13 for the main body can be the same, in which case the entire immersion nozzle 1 can be, for example, made of alumina-graphite.

[0013] The surfaces of the refractory materials constituting the immersion nozzle 1, including the refractory material 12 for the upper end, are coated with an antioxidant 14. A reaction inhibitor 15 is arranged on the surface side of the antioxidant 14, including the contact portion 11 with the stopper 2, and a fusion inhibitor 16 is arranged on the surface side of the reaction inhibitor 15, including the contact portion 11 with the stopper 2.

[0014] Antioxidant 14 is used to prevent deterioration of refractories due to oxidation during preheating. In this invention, it contains 50% to 85% by mass of SiO2 component and 1% to 20% by mass of B2O3 component, while the total content of Na2O component, K2O component, and P2O5 component is 10% by mass or less (including 0). If the SiO2 content in the antioxidant is less than 50% by mass, there is insufficient SiO2 to contribute to oxidation prevention, and therefore it cannot exhibit sufficient antioxidant function. On the other hand, if the SiO2 content exceeds 85% by mass, the melting point (glass transition temperature) of the antioxidant becomes high, preventing glass transition during preheating and thus preventing it from exhibiting sufficient antioxidant function. Furthermore, if the B2O3 content in the antioxidant is less than 1% by mass, there is insufficient B2O3 to contribute to oxidation prevention, and therefore it cannot exhibit sufficient antioxidant function. On the other hand, if the B2O3 content exceeds 20% by mass, the melting point (glass transition temperature) of the antioxidant decreases, leading to excessive melting (vitrification), making it difficult to maintain its function as an antioxidant, and thus preventing it from exhibiting sufficient antioxidant function. Furthermore, if the combined content of Na2O, K2O, and P2O5 components exceeds 10% by mass, the melting point (glass transition temperature) of the antioxidant will similarly decrease, leading to excessive melting (vitrification). Additionally, the reaction with the reaction inhibitor 15 and fusion inhibitor 16 on the surface of the antioxidant 14 will also proceed excessively, preventing it from exhibiting sufficient antioxidant function. Note that the antioxidant 14 may appropriately contain other components such as Al2O3 and ZrO2 in addition to the components mentioned above. The antioxidant 14 can be provided by methods such as immersion (dipping) or coating (brush application), and its thickness can be approximately 0.4 to 0.8 mm. As shown in Figure 1, an antioxidant 21 is also provided at the tip of the stopper 2, but this antioxidant 21 can be the same as the antioxidant 14 described above.

[0015] The reaction inhibitor 15 is used to prevent the reaction between the antioxidant 14 and the anti-fusion material 16, and in this invention, it is carbonaceous. That is, the carbonaceous reaction inhibitor 15 has the property of repelling the molten (vitrified) antioxidant 14, so it can prevent the antioxidant 14 from penetrating the anti-fusion material 16, thereby preventing the antioxidant 14 and the anti-fusion material 16 from reacting and melting the anti-fusion material 16. The reaction inhibitor 15 preferably contains graphite as a carbonaceous refractory material. That is, the inclusion of graphite in the reaction inhibitor 15 makes it easier to arrange in a layer between the antioxidant 14 and the fusion inhibitor 16, thereby improving the reaction prevention function. The reaction inhibitor 15 may contain other carbonaceous refractory materials such as carbon black in place of graphite or together with graphite. However, for the reasons mentioned above, it is preferable that the reaction inhibitor 15 contains graphite as a carbonaceous refractory material, and it is more preferable that it contains only graphite as a carbonaceous refractory material. Thus, the reaction inhibitor 15 containing the carbonaceous refractory material can be provided by applying it to the surface of the antioxidant 14. In this case, a liquid organic binder can be used as the solvent for dispersing the carbonaceous refractory material. Using a liquid organic binder makes the application process easier and allows the reaction inhibitor 15 containing the carbonaceous refractory material to be uniformly provided on the surface of the antioxidant 14. Furthermore, since the liquid organic binder is carbonaceous, it becomes a component of the carbonaceous reaction inhibitor 15 when it dries. Here, it is preferable to use a liquid phenolic resin as the liquid organic binder, because phenolic resin has high heat resistance. The thickness of the reaction inhibitor 15 can be approximately 0.2 to 1.0 mm. This thickness can be controlled by the number of times it is applied.

[0016] The fusion prevention material 16 is intended to prevent fusion between the upper end of the immersion nozzle 1 and the tip of the stopper 2. In this invention, it consists of at least one of alumina fibers and alumina-silica fibers, and is typically made of an alumina fiber sheet formed from alumina fibers or an alumina-silica fiber sheet formed from alumina-silica fibers. Since both alumina fibers and alumina-silica fibers have high melting points, they work in conjunction with the reaction prevention effect of the reaction inhibitor 15 to prevent fusion between the upper end of the immersion nozzle 1 and the tip of the stopper 2. The thickness of the fusion prevention material 16 can be about 1 to 3 mm.

[0017] As described above, the immersion nozzle 1 includes the antioxidant 14 that coats the surface of the refractory 12 for the upper end portion, the reaction inhibitor 15 disposed on the surface side of the antioxidant 14, and the fusion preventive material 16 disposed on the surface side of the reaction inhibitor 15. For the purpose of preventing fusion between the upper end portion of the immersion nozzle 1 and the tip portion of the stopper 2, the reaction inhibitor 15 may be disposed on the surface side of the antioxidant 14 so as to include the contact portion 11 with the stopper 2. That is, the reaction inhibitor 15 does not need to be disposed on the entire surface of the antioxidant 14, and may be disposed, for example, in the range shown in FIG. 1 so as to include at least the contact portion 11 with the stopper 2. Similarly, the fusion preventive material 16 does not need to be disposed on the entire surface of the reaction inhibitor 15, and may be disposed, for example, in the range shown in FIG. 1 so as to include at least the contact portion 11 with the stopper 2. [Examples]

[0018] A plurality of refractory test specimens imitating the refractory 12 for the upper end portion of the immersion nozzle 1 shown in FIG. 1 were prepared, and the surfaces thereof were each provided with a fusion prevention means as shown in Table 1, and the test specimens of each example were subjected to a heating test. In the heating test, the test specimen of each example was placed in a furnace at normal temperature, the inside of the furnace was heated to 1500°C and maintained at the same temperature for 90 minutes, and then the inside of the furnace was returned to normal temperature. After the heating test, the test specimen of each example was taken out from the furnace, and the presence or absence of melting of the fusion prevention means, particularly the fusion preventive material, was investigated. If the fusion preventive material shows "no melting", it means that the fusion preventive material functions effectively, and it is judged that fusion with the stopper can be prevented. In the heating test, the inside of the furnace is heated to 1500°C, which assumes preheating at a high temperature of 1300°C or higher. Further, in the test specimens of each example, the thicknesses of the antioxidant and the fusion preventive material are 0.6 mm and 2 mm respectively, and the thickness of the reaction inhibitor used in examples other than Comparative Example 4 is 0.6 mm. The reaction inhibitor contains graphite, and is specifically formed by dispersing graphite in a liquid phenolic resin and applying the resulting mixture.

[0019] [Table 1]

[0020] In Table 1, Examples 1 to 3 are equipped with the specified antioxidant, reaction inhibitor, and fusion inhibitor as defined in the present invention. There was "no" melting of the fusion inhibitor, and it was determined that fusion with the stopper could be prevented. In contrast, Comparative Examples 1 and 2 are examples where the antioxidant components are outside the scope of the present invention. As the melting point (glass transition temperature) of the antioxidant decreases and the antioxidant itself becomes more easily melted, the anti-fusion material also becomes more easily melted, and as a result, melting of the anti-fusion material was observed. Comparative Example 3 is an example in which silica-lime fibers were used as the anti-fusion material. The anti-fusion material itself became more prone to melting, and as a result, melting of the anti-fusion material was detected. Comparative Example 4 is an example without a reaction inhibitor, in which case the antioxidant easily penetrates to the fusion-preventing material, resulting in the fusion-preventing material melting. [Explanation of Symbols]

[0021] 1. Immersion nozzle (nozzle for continuous casting) 11 Contact area with stopper 12 Refractory material for the upper end 13. Refractory material for the main body 14 Antioxidants 15 Reaction inhibitors 16 Anti-fusing material 2 Stoppers 21 Antioxidants

Claims

[Claim 1] A continuous casting nozzle that fits with a stopper to control the flow rate of molten steel in continuous casting of molten steel, The system comprises a refractory material disposed at the upper end including the contact portion with the stopper, an antioxidant coating the surface of the refractory material, a reaction inhibitor disposed on the surface side of the antioxidant so as to include the contact portion, and a fusion inhibitor disposed on the surface side of the reaction inhibitor so as to include the contact portion. The aforementioned antioxidant is SiO ２ The component is 50% by mass or more and 85% by mass or less, B ２ O ３ Contains 1% to 20% by mass of the component, Na ２ O component, K ２ O component and P ２ O ５ The total content of the components is 10% by mass or less (including 0). The reaction inhibitor is carbonaceous, The aforementioned anti-fusion material consists of at least one of alumina fibers and alumina-silica fibers, in a nozzle for continuous casting.

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