JP2017042797A - Continuous casting nozzle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent thermal insulation effect by a biosoluble fiber layer from being greatly impaired by preheating, in a continuous casting nozzle in which the biosoluble fiber layer is disposed so as to cover the outer periphery of an antioxidant layer.SOLUTION: A continuous casting nozzle 10 comprises: antioxidant layers 15, 16 coated so as to cover the outer periphery of a nozzle body 11, which is made of a refractory containing carbon and has an inner hole to allow for the passage of molten steel; and a biosoluble fiber layer 17 coated so as to cover the outer periphery of the antioxidant layer. The outermost peripheral layer 14a of the antioxidant layer is coated on an area surrounded by a device 30 having a thermal insulation function during preheating of the continuous casting nozzle, and has a vitrification starting temperature of 700°C or higher.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.

Here, as described in paragraph 0029 of Patent Document 3, a refractory ceramic fiber has been conventionally used as a heat insulating material covering 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 a continuous casting nozzle using a biosoluble fiber as a heat insulating material covering the outer periphery of the antioxidant layer. Melted and the fiber structure and layer structure could not be maintained, and the heat insulation effect was greatly impaired.

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 to suppress the disappearance of the heat insulating effect due to the biosoluble fiber layer by preheating in the continuous casting nozzle in which the biosoluble fiber layer is disposed so as to cover the outer periphery of the antioxidant layer. There is to do.

  When the present inventors observed the behavior of the biosoluble fiber layer during preheating, a phenomenon was observed in which the biosoluble fiber layer reacted and melted with the antioxidant layer on the inside during preheating. Accordingly, the present inventors have devised means for suppressing the melting reaction between the biosoluble fiber layer and the antioxidant material layer in consideration of the preheating conditions of the continuous casting nozzle, and have arrived at the present invention. did.

  That is, the continuous casting nozzle of the present invention comprises a layer of an antioxidant material, which is made of a refractory containing carbon and has an inner hole through which molten steel passes, and is coated so as to cover the outer periphery of the nozzle body. A continuous casting nozzle comprising a layer of biosoluble fiber disposed so as to cover the outer periphery of the layer, and the oxidation applied to a region surrounded by a device having a heat retaining function when the continuous casting nozzle is preheated The outermost peripheral layer of the preventing material has a vitrification start temperature of 700 ° C. or higher.

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

  In general, the preheating of the continuous casting nozzle is performed by burner heating from the upper part or the lower part of the inner hole. In the continuous casting nozzle, particularly in the area requiring preheating, the temperature is kept to increase the effect of the preheating. The area is surrounded by a device having a function. Therefore, in the continuous casting nozzle at the time of preheating, the region surrounded by the device having a heat retaining function is a high temperature of about 700 ° C. or higher and 1450 ° C. or lower, while the region not surrounded is a comparison of about 500 ° C. or higher and lower than 700 ° C. Low. 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 biosoluble fiber is laminated on a conventional antioxidant material layer, the antioxidant and biosoluble fiber that are effective in a low temperature range containing a large amount of alkali metal oxides and alkaline earth metal oxides are in contact with each other. As a result, the reaction product tends to lower the melting point further due to the mutual reaction. As a result, the biosoluble fiber melts at an early stage and the fiber structure and the layer structure cannot be maintained, and the heat insulating effect is greatly impaired.

  In contrast, in the continuous casting nozzle of the present invention, the outermost peripheral layer of the antioxidant layer applied to the region surrounded by the device having a heat retaining function during preheating has a vitrification start temperature as high as 700 ° C. or higher. It is. Thereby, melting of the biosoluble fiber layer due to the reaction between the biosoluble fiber layer and the antioxidant material layer is suppressed, and the heat insulating effect is maintained.

  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 biosoluble fiber layer is disposed so as to cover the outer periphery of the antioxidant layer, the heat insulating effect of the biosoluble fiber layer is prevented from being greatly impaired by preheating. can do.

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

  FIG. 1 is a cross-sectional view showing a preheating state of a continuous casting nozzle according to an embodiment of the present invention. The continuous casting nozzle shown in the figure is an immersion nozzle 10, and its 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. 1, an area including a lower portion of the immersion nozzle 10 to be immersed in molten steel is surrounded by a pot 30 (an apparatus having a heat retaining function), and then the inner hole 12 is heated by the burner 20 from the top. Then, the high-temperature combustion gas from the burner 20 flows from the upper part of the inner hole 12 to the lower part, and further flows out of the pair of discharge holes 13 and 13 into the pot 30, and the region surrounded by the pot 30 is, for example, 1200. Preheated to about ℃. Since the combustion gas in the pot 30 is discharged upward, the region not surrounded by the pot 30 is also preheated, for example, at about 500 ° C.

  In the region surrounded by the pot 30 in the immersion nozzle 10, a high temperature antioxidant layer 15 made of a single layer of the first antioxidant layer 14 a is applied so as to cover the outer periphery of the nozzle body 11, and this high temperature oxidation is performed. A biosoluble fiber layer 17 is disposed so as to cover the outer periphery of the prevention material layer 15. On the other hand, in the region not surrounded by the pot 30 in the immersion nozzle 10, the low-temperature antioxidant material composed of the two layers of the first antioxidant material layer 14 a and the second antioxidant material layer 14 b so as to cover the outer periphery of the nozzle body 11. The layer 16 is applied, and the biosoluble fiber layer 17 is disposed so as to cover the outer periphery of the low-temperature antioxidant 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.

  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.

  Next, when the thickness of the biosoluble fiber layer 17 is less than 1 mm, the heat insulating effect is insufficient, or the biosoluble fiber layer may easily disappear when reacted with the antioxidant. is there. When it is larger than 25 mm, there is a decrease in workability (being difficult to wind) due to an increase in the thickness of the biosoluble fiber layer. Therefore, the most preferable thickness of the biosoluble fiber is 4 to 12.5 mm. However, the thickness of the biosoluble fiber layer may be set according to the preheating conditions used. In consideration of the severe heat load of the continuous casting nozzle, a method of increasing the thickness of the biosoluble fiber layer in the vicinity of the discharge hole or in the ZG material portion from the upper portion of the immersion nozzle may be used.

  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 biosoluble fiber layer 16 contains 15% by mass or more and 35% by mass or less of one or more components selected from the group consisting of 25% by mass and 80% by mass and SiO ₂ and MgO, CaO, and K ₂ O. It can be composed of biosoluble fibers. The biosoluble fiber 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 O ₅ , Cr ₂ O ₃ , It can also consist of one or more components selected from the group of Li ₂ O and TiO ₂ .

In the present embodiment, the high-temperature antioxidant layer 15 is composed of a single layer of the high-temperature antioxidant layer 14a. However, the high-temperature antioxidant layer 15a may be formed by laminating a plurality of layers of antioxidant materials having different components. 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 is composed of two layers of the first antioxidant material layer 14a and the second antioxidant material layer 14b. A single layer may be used.

  In the immersion nozzle 10 shown in FIG. 1, a preheating test was performed with the structure of the antioxidant layer and the biosoluble fiber 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.

The “antioxidant layer in the region not surrounded by the pot” in Examples 1 to 7 was vitrified on the high-temperature antioxidant layer used for the “antioxidant layer in the region surrounded by the pot”. A low-temperature antioxidant material layer having a starting temperature of 500 ° C. is laminated to form two layers. The “antioxidant layer in the region not surrounded by the pot” in Comparative Example 2 has the same configuration as the “antioxidant layer in the region not surrounded by the pot” in Example 4, and in Comparative Example 2, the “antioxidant layer in the region not surrounded by the pot” The “antioxidant layer in the enclosed area” has the same configuration as the “antioxidant layer in the area not enclosed by the pot”. 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. Furthermore, the biosoluble fiber layer 17 covering the outer periphery of these antioxidant layers is composed of 74% by mass of SiO ₂ which is a commercial product A, 24% by mass of CaO and 1% by mass of MgO except for Example 2. using the biosoluble fiber containing, for example 2, the SiO ₂ 77 wt% is a commercially available product B, and MgO 20 wt%, using the biosoluble fibers containing _Al 2 _{O 3} 2 wt% did. Example 5 is a case where the thickness of the biosoluble fiber layer is 1 mm.

  After the preheating test, the remaining state of the biosoluble fiber layer and the oxidation occurrence state of the AG material were confirmed by cross-sectional observation and the like for each of the submerged nozzles. The conductive fiber layer remained and the AG material was excellent without oxidation. In particular, Example 4 was good.

  On the other hand, in Comparative Example 1, in the region surrounded by the pot, the biosoluble fiber layer 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 disappearance of the healthy biosoluble fiber layer were confirmed. In Comparative Example 2, no oxidation of the AG material was observed, but the disappearance of a sound biosoluble fiber layer was confirmed.

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 20 Burner 30 Pot ( (Device with thermal insulation function)

Claims (5)

A layer of an antioxidant material applied 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, and a living body arranged to cover the outer periphery of the layer of the antioxidant material A continuous casting nozzle comprising a layer of soluble fiber,
The nozzle for continuous casting, wherein the outermost peripheral layer of the antioxidant applied to the region surrounded by the device having a heat retaining function during preheating of the continuous casting nozzle has a vitrification start temperature of 700 ° C or higher.   2. The continuous casting nozzle according to claim 1, wherein the outermost peripheral layer of the antioxidant applied to a region surrounded by the device having a heat retaining function has a vitrification start temperature of 900 ° C. or higher.   The nozzle for continuous casting according to claim 1 or 2, wherein the layer of the antioxidant applied to the region not surrounded by the device having the heat retaining function includes a layer having a vitrification start temperature of 500 ° C or 600 ° C. The outermost peripheral layer of the antioxidant applied to the region surrounded by the device having the heat retaining function 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 , An antioxidant comprising at least one component selected from the group consisting of TiO ₂ , MgO and CoO, at least in part,
The layer of the antioxidant applied to the region not surrounded by the device having the heat retaining function 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 mass or more and 30% by mass or less, B ₂ O ₃ by 2% by mass or more and 10% by mass or less, and 10% by mass of one or more components selected from the group of Na ₂ O, K ₂ O and P ₂ O ₅ 40% by mass or less, and the balance contains at least a part of an antioxidant made of one or more components selected from the group consisting of Li ₂ O, CaO, Fe ₂ O ₃ , TiO ₂ , MgO and CoO. Item 4. The continuous casting nozzle according to any one of Items 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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