JP2017060983A - Continuously casting nozzle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the on-preheating solubility of bio-soluble fibers constituting a heat insulation cap containing bio-soluble fibers in a continuously casting nozzle to which the heat insulation cap is fitted on preheating.SOLUTION: In a continuously casting nozzle 10 comprising layers 15, 16 of an antioxidant material applied to cover the outer periphery of a nozzle body 11 consisting of a carbon-containing refractory and having an inner hole 12 through which molten steel passes, the outermost periphery layer 14a of the antioxidant material applied over a region A to which a heat insulation cap containing bio-soluble fibers is fitted on preheating the continuously casting nozzle has a vitrification start temperature of 700°C or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a continuous casting nozzle used for continuous casting of steel.

  In continuous casting of steel, for example, molten steel of 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). At this time, since a severe heat load is applied to the continuous casting nozzle and, for example, a crack or breakage may occur, the continuous casting nozzle is preheated in advance to prevent breakage. In addition, as the refractory constituting the continuous casting nozzle, for example, a material containing carbon such as zirconia-graphite material (hereinafter referred to as ZG material) or alumina-graphite material (hereinafter referred to as AG material) is used. Has been. For this reason, a method for suppressing and further preventing the oxidation of carbon during preheating has been proposed.

  For example, Patent Document 1 discloses that an antioxidant is applied to the surface of a continuous casting nozzle made of an AG material in order from the highest effective temperature of the antioxidant effect to the lowest, thereby providing a multilayered antioxidant. Techniques for forming layers are disclosed. Patent Document 2 discloses a low-melting glass, a transition metal oxide, a metal that acts as a glass network former, and a silica-based liquid binder as a first layer. An antioxidant for graphite-containing refractories, in which a mixture of a raw material and a silica-based liquid binder is formed as a second layer, is disclosed.

  Furthermore, in Patent Document 3, the outer periphery of the antioxidant layer formed on the outer periphery of the nozzle for continuous casting is covered with a heat insulating material, which is surrounded by a chamber, and a non-oxidizing gas is blown into the chamber, so that the oxygen concentration is 10 vol%. A technique for preheating the continuous casting nozzle in the following atmosphere is disclosed. Further, when preheating the nozzle for continuous casting, a heat retaining cap made of a heat insulating material is used instead of using a chamber as in Patent Document 3, and this heat retaining cap is fitted and preheated. In this case, the heat retaining cap is fitted so as to cover the outer periphery of the antioxidant layer formed on the outer periphery of the continuous casting nozzle.

Here, as described in paragraph 0029 of Patent Document 3, a refractory ceramic fiber has been conventionally used as a material for a heat insulating material and a heat retaining cap that covers the outer periphery of the antioxidant layer. However, since refractory ceramic fibers may be harmful to the human body, in recent years there has been a demand for changes to biosoluble fibers that are less harmful to the human body. Development is also progressing. For example, Patent Document 4 discloses that 75 to 80% by weight of SiO ₂ , 10 to 14% by weight of CaO, 4 to 9% by weight of MgO, 0.1 to ₂ for the purpose of achieving both biosolubility and heat insulation. wt% of _ZrO 2, 0.5 to 1.5 wt% _Al 2 _{O 3,} and 0.1 to 1.5 comprising a weight% _B 2 _{O 3,} biosoluble for high temperature insulation material Ceramic fibers are disclosed.

  Under such circumstances, the present inventors conducted a preheating experiment of the nozzle for continuous casting using the biosoluble fiber as the material for the above-described heat retention cap. There arises a problem that the soluble fiber melts and the fiber structure and the layer structure cannot be maintained, and the heat insulating effect is greatly impaired. In addition, the heat retaining cap is removed after preheating, but when the biosoluble fiber constituting the heat retaining cap is melted during preheating, it becomes difficult to remove the preheated fiber and cannot be reused.

JP 51-81811 A JP-A-5-43354 JP 2008-105042 A Special table 2013-520580 gazette

  The problem to be solved by the present invention is that, in a continuous casting nozzle in which a heat retaining cap containing a biosoluble fiber is fitted during preheating, the biosoluble fiber constituting the heat retaining cap is melted during preheating. It is to suppress.

  When the present inventors observed the behavior of the heat retention cap (biosoluble fiber layer) during preheating, a phenomenon was observed in which the heat retention cap reacted with the inner antioxidant layer during melting and melted. Accordingly, the present inventors have devised means for suppressing the melting reaction between the heat retaining cap and the antioxidant material layer in consideration of the actual condition of preheating of the continuous casting nozzle, and have arrived at the present invention.

  That is, the continuous casting nozzle of the present invention is a continuous casting nozzle comprising a layer of an antioxidant material coated so as to cover the outer periphery of a nozzle body made of a refractory containing carbon and having an inner hole through which molten steel passes. In addition, the outermost peripheral layer of the antioxidant applied to the region into which the heat retaining cap containing the biosoluble fiber is fitted during the preheating of the continuous casting nozzle has a vitrification start temperature of 700 ° C. or higher. It is characterized by this.

  The features of the present invention will be described in detail below.

  In general, the preheating of the continuous casting nozzle using the heat retaining cap is performed by burner heating from the lower portion of the inner hole, and at that time, the heat retaining cap is fitted into the lower region of the inner hole. Therefore, in the continuous casting nozzle at the time of preheating, the lower region where the heat retention cap is fitted becomes high temperature of about 700 ° C. or higher and 1450 ° C. or lower, while the upper region where the heat retention cap is not fitted is 500 ° C. or higher. It becomes a relatively low temperature of less than about 700 ° C. In order to cope with such a wide temperature range, conventionally, as disclosed in Patent Documents 1 and 2, the antioxidant layer is an antioxidant that is effective in a high temperature range (700 ° C. or higher and about 1450 ° C. or lower). In general, an anti-oxidant effective in a low temperature range (500 ° C. or more and less than 700 ° C.) is laminated on the substrate.

However, antioxidants effective in the low temperature range contain a large amount of alkali metal oxides and alkaline earth metal oxides that form a main component SiO ₂ and a low melting point compound, and biosoluble fibers are also the same. In addition, in order to enhance the biosolubility, the above-mentioned alkali metal oxides and alkaline earth metal oxides are included in a large amount. Therefore, when a heat retention cap comprising biosoluble fibers is fitted on a conventional antioxidant layer, the antioxidant is effective in a low temperature range that contains a large amount of alkali metal oxides and alkaline earth metal oxides. And the biosoluble fiber are in contact with each other, the mutual reaction between them tends to lower the melting point of the reaction product. As a result, the biosoluble fiber melts early and the fiber structure and layer structure cannot be maintained. The heat insulation effect is greatly impaired, and the heat retaining cap is fused with the antioxidant layer and is difficult to remove.

  In contrast, the outermost peripheral layer of the antioxidant layer applied to the region where the heat retention cap is fitted during preheating in the continuous casting nozzle of the present invention has a high vitrification start temperature of 700 ° C. or higher. As a result, melting of the heat retaining cap (biosoluble fiber) due to the reaction between the biosoluble fiber constituting the heat retaining cap and the antioxidant layer is suppressed, the heat insulating effect is maintained, and the aforementioned fusion is also suppressed. Is done.

  In the present invention, the vitrification start temperature at which the antioxidant layer vitrifies is an AG material refractory for an immersion nozzle in an electric furnace maintained at a temperature of 100 ° C. between 400 ° C. and 1400 ° C. A sample coated with an antioxidant of 0.5 mm in thickness is taken out after holding for 1 hour, cooled to room temperature, then visually observed on the surface of the sample, and the lowest holding temperature at which gloss is seen on the surface. .

  As described above, according to the present invention, in the continuous casting nozzle in which the heat retaining cap containing the biosoluble fiber is fitted during preheating, the biosoluble fiber constituting the heat retaining cap is melted during preheating. Can be suppressed. Therefore, it can suppress that the heat insulation effect of the heat retention cap is greatly impaired by preheating. Further, since the heat retention cap can be prevented from being fused with the antioxidant layer, the heat retention cap can be easily removed after preheating, and the removed heat retention cap can be reused.

It is sectional drawing which shows the nozzle for continuous casting which concerns on one Embodiment of this invention. It is sectional drawing which shows the preheating state of the nozzle for continuous casting of FIG.

  FIG. 1 is a sectional view showing a continuous casting nozzle according to an embodiment of the present invention, and FIG. 2 is a sectional view showing a preheated state thereof.

  The continuous casting nozzle shown in FIG. 1 is an immersion nozzle 10, and the nozzle body 11 is made of a refractory containing carbon such as ZG material or AG material as in the prior art. It has a hole 12. The lower part of the inner hole 12 branches in two directions toward the side, forming a pair of discharge holes 13 and 13. In addition, in the immersion nozzle, the discharge holes may be four holes or a single hole in addition to the two holes as shown in FIG.

  When preheating the immersion nozzle 10, as shown in FIG. 2, the heat retaining cap 20 is fitted from below so as to cover the region A including the lower portion of the immersion nozzle 10 to be immersed in molten steel. Heating is performed by a burner 30 inserted into the discharge hole 13. If it does so, the high temperature combustion gas from the burner 30 will flow from the lower part of the inner hole 12 to the upper part, and the area | region A in which the heat retention cap 20 was inserted is preheated to about 1200 degreeC, for example. On the other hand, the region B in which the heat retaining cap 20 is not fitted is, for example, about 500 ° C. After preheating, the heat retaining cap 20 in the region A is removed, and the region A is separately wrapped with biosoluble fibers.

  Referring to FIG. 1 again, in the region A where the heat retaining cap 20 is fitted in the immersion nozzle 10, the high-temperature antioxidant material composed of a single layer of the first antioxidant material layer 14 a so as to cover the outer periphery of the nozzle body 11. Layer 15 is applied. On the other hand, in the region B where the heat retaining cap 20 is not fitted, the low-temperature antioxidant comprising two layers of the first antioxidant material layer 14a and the second antioxidant material layer 14b so as to cover the outer periphery of the nozzle body 11. A material layer 16 is applied, and a biosoluble fiber layer 17 is disposed so as to cover the outer periphery of the low-temperature antioxidant material layer 16. The high-temperature antioxidant material layer 15 and the low-temperature antioxidant material layer 16 preferably have a thickness of about 0.2 to 0.8 mm, and the biosoluble fiber layer 17 has a thickness of about 1 to 25 mm. Preferably there is. In this embodiment, when the immersion nozzle 10 is preheated, the region B is further wound with a biosoluble fiber 18 as shown in FIG.

  Here, when the thickness of the antioxidant material layers 15 and 16 is less than 0.2 mm, when the antioxidant material is vitrified, it partially penetrates into the AG material and the ZG material, thereby preventing the antioxidant function. Is insufficient, or when the thickness is greater than 0.8 mm, the antioxidant may be peeled off due to the difference in expansion between the antioxidant, the AG material, and the ZG material. Therefore, the most preferable thickness of the antioxidant layer is 0.4 to 0.6 mm. However, depending on the size (inner and outer diameter, total length) of the immersion nozzle used, the thickness of the antioxidant layer is set. You only have to set it.

  The first antioxidant layer 14a has a vitrification start temperature of 700 ° C. or higher, and the second antioxidant layer 14b has a vitrification start temperature of 500 ° C. or 600 ° C. That is, in the present embodiment, the high-temperature antioxidant layer 15 is composed of a single layer of the first antioxidant layer 14a having a vitrification start temperature of 700 ° C. or higher, and the low-temperature antioxidant layer 16 is the start of vitrification. The second antioxidant layer 14b having a temperature of 500 ° C. or 600 ° C. is included as the outermost peripheral layer.

The first antioxidant layer 14a having a vitrification start temperature of 700 ° C. or higher is a component after heat treatment in an oxidizing atmosphere of 1000 ° C., and SiO ₂ is 40 mass% or more and 80 mass% or less, and Al ₂ O ₃ is 3 Containing 20% by mass or more and 3% by mass or more and 20% by mass or less of B ₂ O ₃ with the balance being Na ₂ O, Li ₂ O, K ₂ O, CaO, Fe ₂ O ₃ , TiO ₂ , MgO and It can be comprised by the antioxidant which consists of one or several components selected from the group of CoO. The second antioxidant material layer 14b of vitrification start temperature of 500 ° C. or 600 ° C. is a component after the heat treatment in the 1000 ° C. oxidizing atmosphere, the SiO ₂ more than 20 wt% 50 wt% or less, Al ₂ O ₃ 30 wt% to 10 wt% or _less, B 2 _{O 3} of 10 wt% or more than 2 _mass%, Na 2 O, one or more components selected from the group of _{K 2} O and _P 2 _{O 5} 10 The antioxidant can be composed of one or more components selected from the group consisting of Li ₂ O, CaO, Fe ₂ O ₃ , TiO ₂ , MgO, and CoO. . Thus, the vitrification temperature can be adjusted by adjusting the components of the antioxidant.

On the other hand, the heat retaining cap 20 fitted into the region A is formed by forming a biosoluble fiber into a bottomed cylindrical shape, and has an opening 21 into which the tip of the burner 30 can be inserted. The biosoluble fiber constituting the heat retaining cap 20 is composed of 25% by mass or more and 80% by mass or less of SiO ₂ and 15% by mass or more of one or more components selected from the group of MgO, CaO, and K ₂ O. It can contain below mass%. Further, the biosoluble fiber constituting the heat retaining cap 20 further contains 40% by mass or less of Al ₂ O ₃ and 20% by mass or less of ZrO ₂ with the balance being Fe ₂ O ₃ , Na ₂ O, P _2. It can also consist of one or more components selected from the group of O ₅ , Cr ₂ O ₃ , Li ₂ O and TiO ₂ . The thickness of the heat retaining cap 20 is preferably about 5 to 20 mm. The biosoluble fiber layer 17 in the region B can also be composed of biosoluble fibers composed of the aforementioned component ranges.

In this embodiment, the high-temperature antioxidant layer 15 in the region A is composed of a single layer of the first antioxidant layer 14a. However, it is configured by laminating a plurality of layers of antioxidant materials having different components. May be. In this case, the vitrification start temperature of the outermost peripheral layer among the plurality of antioxidant layers constituting the high-temperature antioxidant layer 15 may be 700 ° C. or higher, but all layers, that is, the high-temperature antioxidant material The vitrification start temperature of the entire layer 15 is preferably 700 ° C. or higher. The vitrification start temperature of the high-temperature antioxidant layer 15 is more preferably 900 ° C. or higher. Vitrification start temperature of the high-temperature oxidation prevention material layer 15 is adjustable by adjusting the components of one or more antioxidant materials constituting the high-temperature oxidation prevention material layer 15, the SiO ₂ One example By increasing the amount, the vitrification start temperature can be increased.

  In the present embodiment, the low-temperature antioxidant material layer 16 in the region B is composed of the two layers of the first antioxidant material layer 14a and the second antioxidant material layer 14b. A single layer of the layer 14b can also be used.

  In the immersion nozzle 10 shown in FIG. 1, a preheating test was performed with the structure of the antioxidant layer as shown in Table 1. The preheating time was 120 minutes, and the temperature in the vicinity of the discharge hole 13 when the preheating was completed was 1200 ° C. The refractory constituting the nozzle body 11 is an AG material containing 25% by mass of graphite, which is generally used for immersion nozzles.

In addition, the “antioxidant layer in region B” in Examples 1 to 7 is for low temperature with a vitrification start temperature of 500 ° C. on the antioxidant layer for high temperature used in “antioxidant layer in region A”. An antioxidant layer is laminated to form two layers. The “antioxidant layer in region B” of Comparative Example 2 has the same configuration as the “antioxidant layer in region B” of Example 4, and in Comparative Example 2, “antioxidant layer in region A”. The same structure as that of the “antioxidant layer in region B” was used. Example 6 is a case where the thickness of the antioxidant layer is 0.2 mm, and Example 7 is a case where the thickness of the antioxidant layer is 0.8 mm. Further, as the biosoluble fiber constituting the heat retaining cap fitted into the region A, except for Example ₂ , 77% by mass of SiO ₂ which is a commercial product X, 20% by mass of MgO, and Al ₂ O ₃ The biosoluble fiber containing 2% by mass is used, and for Example 2, a commercially available fiber containing 74% by mass of SiO ₂ , 24% by mass of CaO and 1% by mass of MgO is used. did. Example 5 is a case where the thickness of the heat retaining cap is 3 mm.

  After the preheating test, for the immersion nozzles of each example, the fusion state of the heat retention cap and the oxidation occurrence state of the AG material were confirmed by cross-sectional observation, etc., and for the immersion nozzles of Examples 1 to 7, The insulation cap was easy to remove, and the AG material was good without oxidation. In particular, Example 4 was good.

  On the other hand, in the comparative example 1, in the region A, the biosoluble fiber constituting the heat retaining cap is melted and integrated with the antioxidant material layer, and aggregation of the antioxidant material with a vitrification start temperature of 500 ° C. occurs. The local oxidation of the AG material and the fusion of the heat retaining cap were confirmed. In Comparative Example 2, oxidation of the AG material was not observed, but fusion of the heat retaining cap was confirmed. In Comparative Examples 1 and 2 in which fusion of these heat retention caps was confirmed, it was difficult to remove the heat retention cap.

10 Immersion nozzle (nozzle for continuous casting)
DESCRIPTION OF SYMBOLS 11 Nozzle body 12 Inner hole 13 Discharge hole 14a 1st antioxidant material layer 14b 2nd antioxidant material layer 15 Antioxidant material layer for high temperature 16 Antioxidant material layer for low temperature 17 Biosoluble fiber layer 18 Biosoluble fiber 20 Thermal insulation cap 21 Open hole 30 Burner

Claims (5)

A nozzle for continuous casting comprising a layer of an antioxidant material coated to cover the outer periphery of a nozzle body made of a refractory containing carbon and having an inner hole through which molten steel passes,
Continuous casting, in which the outermost peripheral layer of the antioxidant applied to the region into which the heat retaining cap containing the biosoluble fiber is fitted during preheating of the continuous casting nozzle has a vitrification start temperature of 700 ° C. or higher. Nozzle.   The continuous casting nozzle according to claim 1, wherein the outermost peripheral layer of the antioxidant applied to the region where the heat retention cap is fitted has a vitrification start temperature of 900 ° C. or higher.   3. The continuous casting nozzle according to claim 1, wherein the layer of the antioxidant applied to the region where the heat retention cap is not fitted includes a layer having a vitrification start temperature of 500 ° C. or 600 ° C. 4. The outermost peripheral layer of the antioxidant applied to the region where the heat retention cap is fitted is a component after heat treatment in an oxidizing atmosphere at 1000 ° C., and SiO ₂ is 40 mass% to 80 mass%, Al ₂ O ₃ 3 mass% or more and 20 mass% or less, B ₂ O ₃ is contained 3 mass% or more and 20 mass% or less, and the balance is Na ₂ O, Li ₂ O, K ₂ O, CaO, Fe ₂ O ₃ , TiO ₂ , An antioxidant comprising at least one component selected from the group consisting of MgO and CoO at least in part,
The layer of the antioxidant applied to the region where the cap for heat insulation is not fitted is a component after heat treatment in an oxidizing atmosphere at 1000 ° C., and SiO ₂ is 20 mass% or more and 50 mass% or less, and Al ₂ O ₃ 10% by weight to 30% by _weight, B 2 _{O 3} of 10 wt% or more than 2 _mass%, Na _{2 O, K} 2 O and _P 2 _O one selected from the group of ₅ or more components than 10 wt% containing 40% by mass or less, the balance comprises at least a portion of _{Li 2 O, CaO, Fe 2} O 3, TiO 2, antioxidant material consisting of MgO and CoO one or more components selected from the group of claim The nozzle for continuous casting according to any one of 1 to 3. The biosoluble fiber contains SiO ₂ in an amount of 25% by mass to 80% by mass and one or more components selected from the group of MgO, CaO, and K ₂ O, in an amount of 15% by mass to 35% by mass. Item 5. The continuous casting nozzle according to any one of Items 1 to 4.

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