KR101597254B1 - Submerged nozzle for continuous casting - Google Patents

Abstract

According to the present invention, a submerged nozzle for continuous casting comprises: a nozzle body in a pipe shape; an internal unit enclosing an inner wall of the nozzle body; and a discharge part disposed on a lower portion of the nozzle body. The internal unit is made of a mixture comprising perovskite (CaTiO_3), calcium zirconate (CaZrO_3), calcium silicate (CaO·SiO_2), and graphite (C).

Description

[0001] Submerged nozzle for continuous casting [0002]

The present invention relates to an immersion nozzle for continuous casting, and more particularly, to an immersion nozzle for continuous casting capable of suppressing nozzle clogging by forming a low melting point material by reacting with alumina (Al ₂ O ₃ ) inclusions.

In a typical continuous casting process, the molten steel contained in the ladle is injected into the tundish, the molten steel injected from the tundish is continuously injected into the mold to cool the molten steel first, and then the cooling water is sprayed on the surface of the primary cooled steel And cools the molten steel according to cooling the steel to produce a cast steel. At this time, in the process of supplying the molten steel accommodated in the tundish into the mold, the molten steel is interrupted by the gate or the stopper provided at the outflow port of the tundish, and is supplied into the mold through the immersion nozzle.

Alumina (Al ₂ O ₃ ) inclusions exist in the molten steel, and micro-inclusions that are not removed by floating separation adhere to the inner wall of the immersion nozzle connecting the tundish and the mold, thereby causing clogging of the immersion nozzle. In order to solve this problem, a method has been proposed in which Ar gas is supplied to the inner wall of an immersion nozzle to trap inclusions on the inner wall of the immersion nozzle by tracing inclusions into bubbles, And a method of forming an alumina and a low melting point material on the inner wall to remove the inclusions.

The method of using Ar gas can reduce the adhesion of inclusions on the inner wall of the immersion nozzle to some extent, but there is a limitation in suppressing the adhesion of inclusions due to the cooling effect by the Ar gas. In addition, the method of forming a layer of a material containing CaO in the inner layer is considered to be one of the most effective methods for suppressing the adhesion of inclusions on the inner wall of the immersion nozzle. A layer of material containing CaO is there is calcium zirconate (CaZrO _3), calcium silicate (CaO and SiO _2), graphite (C) is used, as shown in Patent No. 1994-0014253 disclose Korea, in these casting temperature And CaO is reacted with alumina to inhibit inclusion adherence.

However, if the elution of CaO run out of a refractory material such as CaO. 2Al ₂ O _3, CaO and 7Al ₂ O ₃ is formed, which results can be rather occurs when the acceleration nozzle clogging.

Further, in order to form a low-melting material (12CaO and 7Al ₂ O ₃₎ effective and need to increase the CaO content in my study, it is necessary to increase the amount of calcium zirconate for this purpose. However, when the content of calcium zirconate is increased, ZrO ₂ is destabilized by CaO elution, and phase transition from cubic or monoclinic to tetragonal proceeds at the casting temperature, resulting in volume change do. As a result, problems such as cracking or dropout may occur during casting, so that the calcium zirconate content is increased and the CaO content is not increased. If molten steel at 1550 ° C is directly contacted at room temperature, cracks may be generated in the immersion nozzle due to instantaneous expansion due to thermal shock, so that the immersion nozzle is preheated at 800 to 1100 ° C. In this case, It is necessary to thoroughly control the preheating of the immersion nozzle.

The present invention provides an immersion nozzle for continuous casting capable of inhibiting inclusion adherence by allowing an alumina inclusion to easily form a low melting point compound upon adhering to the inner wall.

The present invention provides an immersion nozzle for continuous casting which can increase the CaO content without causing problems such as cracking or dropout at casting during casting.

The present invention provides an immersion nozzle for continuous casting in which hollow portions are formed by using a mixture containing rare earth titanate (CaTiO ₃ ), calcium zirconate (CaZrO ₃ ), calcium silicate (CaO · SiO ₂ ) and graphite (C) do.

The immersion nozzle for continuous casting according to the embodiments of the present invention includes a tubular nozzle body, an inner workpiece at least partially surrounding the inner wall of the nozzle body, and a discharge port provided at a lower portion of the nozzle body, Is formed of a mixture containing rare earth titanium (CaTiO ₃ ), calcium zirconate (CaZrO ₃ ), calcium silicate (CaO 揃 SiO ₂ ) and graphite (C).

The inner workings are formed to have a thickness of 3 mm to 5 mm.

The above rare earth titanate, calcium zirconate, calcium silicate and graphite are added in an amount of 95 wt% to 99 wt% with respect to 100 wt% of the mixture to be mixed with 1 wt% to 5 wt% of the binder.

The titanium titanate and calcium zirconate are contained in an amount of 40 wt% to 90 wt% with respect to 100 wt% of the mixture.

The rare earth titanate is contained at 5% to 50% of calcium zirconate.

The graphite is contained in an amount of 5 wt% to 35 wt% with respect to 100 wt% of the mixture.

The calcium silicate is contained in an amount of 1 wt% to 25 wt% with respect to 100 wt% of the mixture.

The discharge port is formed of a mixture containing rare earth titanate, calcium zirconate, calcium silicate and graphite.

The discharge port has a smaller content of CaO than the inner work.

The content of CaO in the inner workings is 15 wt% to 35 wt%, and the content of CaO in the outlet is 10 wt% to 25 wt%.

The inner and outer openings are formed with a porosity of 15% to 35%.

The embodiment of the present invention is characterized in that the inner working of the immersion nozzle for continuous casting is carried out by mixing a mixture containing rare earth titanate (CaTiO ₃ ), calcium zirconate (CaZrO ₃ ), calcium silicate (CaO 揃 SiO ₂ ) . According to the present invention, even if the preheating time of the immersion nozzle is short or the preheating temperature is low, the possibility of occurrence of problems such as cracking and dropout is reduced, and as the content of TiO ₂ is increased and CaO content is increased, It is possible to effectively suppress the inclusion of the inclusion. Therefore, the lifetime of the immersion nozzle can be increased, and productivity and cost reduction can be achieved at the same time.

1 is a schematic view of a continuous casting apparatus to which an immersion nozzle according to an embodiment of the present invention is applied.
2 is a sectional view of an immersion nozzle for continuous casting according to an embodiment of the present invention;
3 is a photograph of Al ₂ O ₃ -C, CaZrO ₃ and CaTiO ₃ after alumina adhesion test.
Figs. 4 to 7 show the results of the reactivity test of samples in which CaTiO ₃ and CaZrO ₃ were molded at different ratios on an alumina substrate.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of other various forms of implementation, and that these embodiments are provided so that this disclosure will be thorough and complete, It is provided to let you know completely.

FIG. 1 is a schematic view of a continuous casting apparatus including an immersion nozzle according to an embodiment of the present invention, and FIG. 2 is a sectional view of the immersion nozzle of the present invention.

Referring to FIG. 1, the continuous casting apparatus to which the present invention is applied includes a tundish 200 for storing molten steel subjected to a steelmaking process in a ladle 100, a molten steel disposed below the tundish 200 to solidify the molten steel, A gate 400 for controlling the tapping of molten steel disposed correspondingly below the outflow port 210 of the tundish 200 and a tundish 400 corresponding to the lower portion of the gate 400, And an immersion nozzle 500 for guiding molten steel in the mold 200 to the mold 300. The sliding gate may include upper and lower fixing plates 410 and 420 and a sliding plate 430 provided between the upper fixing plate 410 and the lower fixing plate 420. [ . This continuous casting apparatus can control the tapping of molten steel by controlling the communication between the tapping tunnel 210 of the tundish 200 and the dipping nozzle 500 by sliding the sliding plate 430. However, the present invention is not limited to this, and any means that can control the communication between the tapping tunnel 201 of the tundish 200 and the immersion nozzle 500 may be used.

The immersion nozzle 500 includes a nozzle body 510 formed in a tubular shape to guide molten steel in the tundish 200 into the mold 300 as shown in FIG. 2, and an inner wall of the inner wall of the nozzle body 510 The slag line 530 outside the nozzle body 510 and the molten steel in the immersion nozzle 500 which are formed to be symmetrical to each other on both sides of the lower portion of the nozzle body 510, (Not shown).

The nozzle body 510 can be manufactured using any one of Al ₂ O ₃ -C and Al ₂ O ₃ -SiO ₂ -C, and is formed into a tube shape so that molten steel can flow. The slag portion 530 may be formed using a ZrO ₂ -C material and may be formed on the outer surface of the nozzle body 510 on the discharge port 540.

The inner work 520 is formed on the inner wall of the nozzle body 510. That is, the inner coating 520 may be formed on the inner wall of the immersion nozzle 500 to have a predetermined thickness, for example, 3 mm to 5 mm, to be in contact with molten steel. At this time, the inner cover 520 may be formed so as not to protrude from the inner wall of the nozzle body 510. That is, the inner layer 520 may be formed at a depth of 3 mm to 5 mm on the inner wall of the immersion nozzle 500. Of course, the inner coating 520 may be inserted into the inner wall of the immersion nozzle 500 at a certain depth and the other may protrude from the inner wall of the immersion nozzle 500 or be protruded from the inner wall of the immersion nozzle 500. In addition, the inner portion 520 may be formed to have a length of 50% or more from the lower side in the longitudinal direction of the nozzle body 510. Of course, it is preferable that the inner coating 520 is formed on the entire inner wall of the nozzle body 510. The inner layer 520 of the present invention can be formed using a mixture of a rare earth titanate (CaTiO ₃ ), calcium zirconate (CaZrO ₃ ), calcium silicate (CaO SiO ₂ ), graphite (C) have. By forming the inner work 520 with a mixture containing rare earth titanate, CaO is eluted by the following reaction and CaO reacts with alumina to inhibit inclusion adherence.

CaTiO ₃ → CaO + TiO ₂

CaZrO ₃ → CaO + ZrO ₂

CaO. ZrO _{2 -} > CaO + ZrO ₂

12CaO + 7Al ₂ O ₃ ? 12CaO 7Al ₂ O ₃

That is, CaO and TiO ₂ are separated from the rare earth titanate, CaO and ZrO ₂ are separated from calcium zirconate, and CaO and alumina react with each other to form 12CaO 7Al ₂ O ₃ , whereby the inclusion adherence of the inner wall of the immersion nozzle 500 . Here, the rare-earth titanium segregates into CaO and TiO ₂ before the calcium zirconate is separated into CaO and ZrO ₂ since the activation energy is lower than that of calcium zirconate. Therefore, before CaO is separated from calcium zirconate, CaO is first separated from the rare-earth titanate, so that the total CaO content is increased. As a result, the reactivity between CaO and alumina is improved, can do. At this time, after CaO is separated, TiO ₂ and ZrO ₂ serve to maintain the shape of the inner layer 520. However, if the amount of calcium zirconate is increased to increase the content of CaO, ZrO ₂ may be destabilized and cracks may be generated during casting. That is, when CaO is separated from calcium zirconate, ZrO ₂ remains and CaO used as a stabilizer of ZrO ₂ is separated, so that ZrO ₂ is not stabilized, and when the molten steel comes into contact with the inner rim 520, Cracks and the like are generated during the preheating of the substrate 500. However, when TiO ₂ is included, TiO ₂ remaining after separation of CaO from the rare-earth titanium stones remains in a stabilized state, and cracks are not generated because CaO is not used as a stabilizer. Therefore, since there is TiO ₂ separated from the titanium thin sheet, there is a low possibility that problems such as cracking and dropout are eliminated even if the preheating time of the immersion nozzle 500 is short or the preheating temperature is low. Further, although ZrO ₂ does not react with alumina, TiO ₂ can further suppress inclusion adhesion by reacting with alumina. That is, although the main reaction of CaO and alumina is described in the above reaction formula, TiO ₂ also reacts with alumina. As a result, the content of CaO can be increased without increasing the content of calcium zirconate by containing the rare earth titanate, and the reactivity with alumina can be further improved by reacting TiO ₂ with alumina, can do. In addition, since TiO ₂ does not use CaO as a stabilizer, it is possible to prevent occurrence of cracks and the like during casting.

The inner coat 520 according to the present invention is formed by mixing a rare earth titanate, calcium zirconate, calcium silicate, graphite and a binder. The inner coat material containing the rare earth titanate is mixed at 95 wt% to 99 wt% The binder may be mixed in an amount of 1 wt% to 5 wt%. That is, with respect to 100 wt% of the mixture of the inner coating material and the binder, the inner coating material is mixed at 95 wt% to 99 wt%, and the binder is mixed at 1 wt% to 5 wt%. As the binder, a thermosetting resin such as phenol resin can be used. When the binder is less than 1 wt%, mixing of the inner coating material is difficult, and when the binder is more than 5 wt%, the inner layer 520 is difficult to be formed due to high humidity. Also, in the mixture, the titanite and calcium zirconate may be contained in an amount of 40 wt% to 90 wt%. That is, about 100 wt% of the mixture of the inner coating material and the binder, about 15 wt% to 90 wt% of zeolite and calcium zirconate may be contained. The rare earth titanate and calcium zirconate are required to be contained in an amount of 40 wt% or more to maintain the shape of the inner layer 520 since TiO ₂ and ZrO ₂ serve to maintain the shape of the inner layer 520 after the CaO is eluted , And 90 wt% or less for the addition of other ingredients. The rare earth titanate may be contained at 5% to 50% of calcium zirconate. That is, the titanium thin sheet may be contained in an amount of 5 wt% to 50 wt% with respect to 100 wt% of the mixture of the rare earth titanium oxide and calcium zirconate. When the rare earth titanate is mixed with calcium zirconia in an amount of less than 5%, the effect of the present invention is insignificant. When it is mixed in an amount exceeding 50 wt%, the reactivity is excessive and the life of the immersion nozzle 500 can be shortened. That is, when the titanium oxide particles are contained in excess of the rare earth titanate, the inner layer 520 is quickly consumed due to the excessive reaction, and the lifetime of the immersion nozzle 500 may be shortened. And graphite may be contained in an amount of 5 wt% to 35 wt% with respect to 100 wt% of the mixture. Graphite should be added in an amount of 5 wt% or more for heat transfer to the outside of the immersion nozzle 500, and oxidized when it is added in excess of 35 wt% or more. Also, calcium silicate may be contained in a 1wt% to about 25wt% to 100wt% to configuration and a mixture of CaO and SiO ₂ + 2CaO and SiO _2. In order to induce the reaction with alumina, the amount of calcium silicate should be more than 1 wt%, and when it is added in an amount of more than 25 wt%, the reaction is excessive and the lifetime of the immersion nozzle 500 Can be shortened.

On the other hand, the discharge port 540 may be made of the same material as the inner casing 520. That is, it can be formed using a mixture of rare earth titanate, calcium zirconate, calcium silicate and graphite (C) and a binder. However, the discharge port 540 may be formed to have a lower content than the content of the mixture of the inner workings 520 so that the total CaO content is less than the total CaO content of the inner portion 520. That is, the CaO content of the rare earth titanate, calcium zirconate, calcium silicate and graphite may be 15 wt% to 35 wt% and the discharge port 540 may be 10 wt% to 25 wt%. Meanwhile, it is preferable that the inner rotor 520 and the discharge port 540 are made to have a porosity of 15% to 35%. If the porosity of the inner work 520 and the discharge port 540 is dense to less than 15%, cracks may be generated during casting, and if the porosity is more than 35%, the strength may be lowered.

As described above, the immersion nozzle 500 according to an embodiment of the present invention includes the inner body 520 formed on the inner wall of the nozzle body 510 as a mixture of rare earth titanate (CaTiO ₃ ), calcium zirconate (CaZrO ₃ ) It is formed of a material including calcium silicate (CaO and SiO ₂₎ and graphite (C). It is possible to increase the content of CaO without increasing the content of calcium zirconate and to react the alumina with TiO ₂ to improve the reactivity with alumina so that the adhesion of inclusions can be further suppressed, It is possible to prevent the occurrence of cracks or the like.

Fig. 3 is a photograph of alumina adherence reaction test of Al ₂ O ₃ -C, CaZrO ₃ and CaTiO ₃ as a photograph after the alumina adhesion reaction test depending on the material of the sample. 3 (a) is a photograph of an Al ₂ O ₃ -C substrate, FIG. 3 (b) is a photograph of a CaZrO ₃ substrate, and FIG. 3 (c) is a photograph of a CaTiO ₃ substrate. As shown in the figure, the inclusion level of Al ₂ O ₃ -C is the lowest, and CaZrO ₃ and CaTiO ₃ are higher in the order. Al ₂ O ₃ --C contained 98 wt% of Al ₂ O ₃ and 2 wt% of others, CaZrO ₃ had 57 wt% of Al ₂ O ₃ , CaO-Al ₂ O ₃ compounds were 37 wt%, and other 6 wt%. In addition, CaTiO ₃ had 15 wt% of Al ₂ O ₃ , 78 wt% of CaO-Al ₂ O ₃ compound, and other 7 wt%. Therefore, the most reactive CaTiO ₃ is easier to dissolve CaO in the material than CaZrO ₃ , and CaO is easy to make alumina and low melting point material. As a result, when CaTiO ₃ is added to the inner wall 520 and the discharge port 540 of the immersion nozzle 500, the inclusion of the immersion nozzle 500 can be effectively suppressed.

FIGS. 4 to 7 show the results of forming CaTiO ₃ and CaZrO ₃ on an alumina substrate at a ratio of 0: 100, 30:70, 50:50, and 70:30, respectively, and keeping them at 1550 ° C. for 3 hours to observe the reactivity to be. Here, FIGS. 4 to 7 (a) show the reactivity of Al, and FIGS. 4 to 7 (b) show the reactivity of Ca. As shown in FIGS. 4 to 7 (b), it can be seen that Ca in the sample is diffused into the alumina substrate. When CaTiO ₃ and CaZrO ₃ are mixed at a ratio of 30:70, the sample remains intact, In the case of 50:50, it is confirmed that the sample is active but not dissolved, and remains after 3 hours. However, when CaTiO ₃ and CaZrO ₃ are mixed at a ratio of 70:30, it is confirmed that all of the samples are dissolved and dissolved in 3 hours. In this case, the reaction can not be used for immersing the immersion nozzle because of too fast reaction. Therefore, the content of CaTiO ₃ is preferably added in not more than 50% compared to CaZrO _3.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the embodiments are for the purpose of illustration only and are not to be construed as limitations. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention.

500: immersion nozzle 510: nozzle body
520: My study 530: Slagrain
540:

Claims (11)

A nozzle body having a tubular shape, an inner circumference provided at least partially surrounding the inner wall of the nozzle body, and a discharge port provided at a lower portion of the nozzle body,
Wherein the inner workings are formed from a mixture comprising rare earth titanate (CaTiO ₃ ), calcium zirconate (CaZrO ₃ ), calcium silicate (CaO SiO ₂ ) and graphite (C).
The immersion nozzle for continuous casting according to claim 1, wherein the inner workings are formed to a thickness of 3 mm to 5 mm.
The continuous casting dipping nozzle according to claim 1 or 2, wherein said rare earth titanate, calcium zirconate, calcium silicate and graphite are added in an amount of 95 wt% to 99 wt% with respect to 100 wt% of said mixture and mixed with 1 wt% to 5 wt% .
4. The immersion nozzle for continuous casting according to claim 3, wherein said titanium titanate and calcium zirconate are contained in an amount of 40 wt% to 90 wt% with respect to 100 wt% of said mixture. 5. The immersion nozzle for continuous casting according to claim 4, wherein said rare earth titanate is contained in an amount of 5% to 50% based on calcium zirconate.
The continuous immersion nozzle for continuous casting according to claim 4, wherein the graphite is contained in an amount of 5 wt% to 35 wt% with respect to 100 wt% of the mixture.
The continuous immersion nozzle for continuous casting according to claim 6, wherein the calcium silicate is contained in an amount of 1 wt% to 25 wt% with respect to 100 wt% of the mixture.
The continuous immersion nozzle according to claim 1 or 2, wherein the discharge port is formed of a mixture containing rare earth titanate, calcium zirconate, calcium silicate and graphite.
10. The immersion nozzle for continuous casting according to claim 8, wherein the discharge port has a CaO content smaller than that of the inner work.
[12] The immersion nozzle for continuous casting according to claim 9, wherein the content of CaO in the inner workings is 15 wt% to 35 wt%, and the content of CaO in the outlet is 10 wt% to 25 wt%.
11. The immersion nozzle for continuous casting according to claim 10, wherein the inner and outer openings are formed with a porosity of 15% to 35%.

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