EP3381587A1

EP3381587A1 - Nozzle, casting device, and casting method

Info

Publication number: EP3381587A1
Application number: EP15909368.1A
Authority: EP
Inventors: Wook Kim
Original assignee: Posco Co Ltd
Current assignee: Posco Holdings Inc
Priority date: 2015-11-27
Filing date: 2015-12-22
Publication date: 2018-10-03
Anticipated expiration: 2035-12-22
Also published as: JP6582132B2; EP3381587B1; CN108778568A; WO2017090819A1; JP2018534147A; CN108778568B; EP3381587A4

Abstract

The present disclosure relates to a nozzle, a casting apparatus and a casting method. The apparatus includes a tundish in which a molten steel is received; a submerged entry nozzle connected to a bottom of the tundish and including a nozzle body and a liner surrounding at least a portion of an inner wall of the nozzle body and containing MgO stabilized ZrO 2 (MSZ); and a power supply electrically connecting the molten steel received in the tundish and the nozzle body with each other, thereby suppressing a nozzle clogging via an electrochemical deoxidation reaction.

Description

TECHNICAL FIELD

The present disclosure relates to a nozzle, a casting apparatus and a casting method, and more particularly to a nozzle, a casting apparatus and a casting method capable of suppressing a clogging phenomenon via an electrochemical deoxidation reaction.

RELATED ART

Continuous casting process is a process in which a ladle containing a refined molten steel is placed in a continuous casting apparatus and then molten steel in a liquid state is transformed into a solid cast-piece by moving from the ladle to a mold through a tundish. In this connection, a submerged entry nozzle is located at the bottom of the tundish and moves the molten steel from the tundish to the mold, and is immersed in the molten steel and contacts with the molten steel for a long time. Therefore, an excellent durability is required. The submerged entry nozzle is made of Al₂O₃-C material, which is composed of alumina (Al₂O₃), which is excellent in a fire resistance and a corrosion resistance against a molten metal, and graphite (C), which has a small wettability in relation to an inclusion (slag component) and a small expansion amount and a good thermal conductivity.
The submerged entry nozzle is a cylindrical refractory that acts as a flow path to supply the molten steel from the tundish to the mold. During the movement of the molten steel into the submerged entry nozzle, a clogging layer grows from an inner wall of the nozzle toward a center of the nozzle due to a temperature drop, an interfacial reaction at an interface between the molten steel and the nozzle inner wall, and an inclusion adhesion to the nozzle inner wall in the molten steel. This nozzle clogging causes interruption of the continuous casting process, which causes adverse effects such as a productivity and a cast-piece quality deterioration, etc. Therefore, in order to prevent such nozzle clogging, a porous type submerged entry nozzle which supplies inert gas from an inside of the nozzle to the molten steel to prevent adhesion of the inclusion by bubbles, a melting loss type nozzle which introducing a refractory which reacts with aluminum oxide which is mainly causing the nozzle clogging to form a low melting point compound to melt the nozzle clogging layer together with a nozzle material, and a refractory material which inhibits an adhesion of the inclusion or a contact with the molten steel are introduced.

SUMMARY

The present disclosure provides a nozzle, a casting apparatus and a casting method capable of preventing a nozzle clogging phenomenon via an electrochemical deoxidation reaction during the casting.
The present disclosure provides a nozzle, a casting apparatus and a casting method for improving a casting process efficiency and a productivity.
A nozzle according to an embodiment of the present disclosure may including: a nozzle body having an inner hollow portion through which a molten steel may move and a discharging hole through which the molten steel may move outside the inner hollow portion; and a liner surrounding at least a portion of an inner wall of the nozzle body and containing MgO stabilized ZrO₂ (MSZ).
The nozzle body may contain Al₂O₃, wherein the nozzle body may contain 20% by weight to 30% by weight of carbon content.
The liner may contain 80 to 95% by weight of MgO stabilized ZrO₂ and 5 to 20% by weight of carbon.
The MgO stabilized ZrO₂ may contain 8 to 15 mol% of magnesia (MgO).
A dummy ring may be provided on at least one of a top and a bottom of the liner with respect to a longitudinal direction of the liner.
The dummy ring may contain a carbon content.
The dummy ring may have a length of 1 to 2% based on a total length of the liner.
A casting apparatus according to an embodiment of the present disclosure may including: a tundish in which molten steel is received; a submerged entry nozzle connected to a bottom of the tundish wherein the submerged entry nozzle includes a nozzle body and a liner surrounding at least a portion of an inner wall of the nozzle body and containing MgO stabilized ZrO₂ (MSZ); and a power supply electrically connecting the molten steel received in the tundish and the nozzle body with each other;
The nozzle body may contain Al₂O₃, and the nozzle body may contain 20% by weight to 30% by weight of carbon content.
The liner may contain 80 to 95% by weight of MgO stabilized ZrO₂ and 5 to 20% by weight of carbon.
The MgO stabilized ZrO₂ containing 8 to 15 mol% of magnesia (MgO).
A dummy ring may be provided on at least one of a bottom and a top of the liner with respect to a longitudinal direction of the liner.
The dummy ring may contain a carbon content.
The dummy ring may have a length of 1 to 2% based on a total length of the liner.
The apparatus may include an electrode immersed in the molten steel in the tundish, and the power supply may apply a power to the electrode and the submerged entry nozzle.
A casting method according to an embodiment of the present disclosure for casting a cast-piece by injecting a molten steel received in a tundish into a mold through a submerged entry nozzle, wherein the submerged entry nozzle may include a nozzle body connected to the tundish, and a liner defined on an inner wall of the nozzle body and containing MgO stabilized ZrO₂, wherein the molten steel and the nozzle body may be electrically connected with each other to discharge oxygens contained in the molten steel to the submerged entry nozzle side.
When the molten steel and the nozzle body are electrically connected with each other, the metal oxide produced in the molten steel may be decomposed into an oxygen ion and a cation, and, then, the oxygen ion may be transferred to the nozzle body through the liner, such that the oxygen in the molten steel may be discharged to the submerged entry nozzle side.
The molten steel and the submerged entry nozzle may be electrically connected with each other while using the molten steel as a cathode and using the submerged entry nozzle as an anode.
In electrically connecting the molten steel and the submerged entry nozzle with each other, 0.1 to 10 mA/cm² of a current density may be applied.
A dummy ring may be provided on at least one of a top and a bottom of the liner, and the dummy ring may be dissolved in casting the cast-piece to form a space.
The nozzle, the casting apparatus and the casting method according to the present disclosure may suppress or prevent the clogging of the inner hollow portion of the nozzle, for example, the submerged entry nozzle used in the casting process. That is, by forming the liner using a solid electrolyte enabling the electrochemical deoxidation at the inner hollow portion of the nozzle in contact with the molten steel at a casting temperature and electrically connecting the molten steel and the submerged entry nozzle, it is possible to suppress or prevent the nozzle clogging due to an inclusion such as the metal oxide or the like stacking on the inner wall of the submerged entry nozzle which is contacting the molten steel during casting. Through this, an interfacial oxygen concentration on the inner wall of the nozzle and a wettability of the inner wall of the nozzle and the molten steel may be reduced. Thus, the inclusion formation and the wettability of the molten steel, which are the main causes of the nozzle clogging are improved, so that the nozzle clogging may be suppressed or prevented. Therefore, it is possible to solve problems such as suspension of casting result from the nozzle clogging, thereby improving a casting efficiency and the productivity, and it is possible to improve a quality of the cast-piece manufactured using this. Further, a lifetime of the nozzle may be increased to reduce a time and cost of replacing the nozzle.
Further, since the liner is formed using the solid electrolyte having an excellent ion conductivity inside the submerged entry nozzle, a power consumption for inhibiting the inclusion formation may be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic view of a casting apparatus according to an embodiment of the present disclosure.
Figure 2 is a cross-sectional view of a nozzle applied to a casting apparatus according to an embodiment of the present disclosure.
Figure 3 is a schematic diagram of a deoxidation reaction occurring in an inner hollow portion of a nozzle during the casting.
Figure 4 is a cross-sectional view showing a change in an internal structure of the nozzle during the casting.

DETAILED DESCRIPTION

An embodiment of the present disclosure will now be described in detail with reference to the accompanying drawings. However, the present disclosure is not limited to an embodiment disclosed below, but may be embodied in various different forms. An embodiment of the present disclosure, however, is provided in order to make the present disclosure complete and to give a complete knowledge of the invention to those of ordinary skill in the art. The drawings may be exaggerated or expanded to illustrate an embodiment of the present disclosure, wherein like reference numerals refer to like elements throughout.
Figure 1 is a schematic view of a casting apparatus according to an embodiment of the present disclosure, Figure 2 is a cross-sectional view of a nozzle applied to a casting apparatus according to an embodiment of the present disclosure, Figure 3 is a schematic diagram of a deoxidation reaction occurring in an inner hollow portion of a nozzle during the casting, Figure 4 is a cross-sectional view showing a change in an internal structure of the nozzle during the casting.
Referring to Figure 1, the casting apparatus, for example a continuous casting apparatus, may be provided with a tundish 10 for storing and dispensing a molten steel 60 from a ladle, which is a container for refined molten steel, a stopper 20 and a sliding plate 30 for adjusting a flow rate of the molten steel 60, a submerged entry nozzle 40 discharging the molten steel 60 to a mold 50 and the mold 50 for solidifying the molten steel 60 into a cast-piece 61. Although Figure 1 shows that the stopper 20 and the sliding plate 30 are provided at the same time in order to adjust the flow rate of the molten steel, in actual operation, either the stopper 20 or the sliding plate 30 may be used. Further, the casting apparatus may include a power supply 70 for supplying a voltage to the molten steel in the tundish and the submerged entry nozzle 40.
Referring to Figure 2, the submerged entry nozzle 40 may include an inner hollow portion through which the molten steel may move, a nozzle body 41 having a discharging hole 42 through which the molten steel may move outside, for example to the mold, a liner 43 configured to surround at least a part of an inner wall of the nozzle body 41 and containing MgO stabilized ZrO₂ (MSZ). Further, although not shown, the submerged entry nozzle 40 may include a slag line portion 47 surrounding at least a portion of an outer wall of the nozzle body 41.
The nozzle body 41 may be formed in a cylindrical shape having at least an open top so as to have the inner hollow portion through which the molten steel may move. Further, in a lower side of the nozzle body 41, the discharging hole 42 through which the molten steel may be discharged to the outside from the inner hollow portion may be formed. The nozzle body 41 may be formed using Al₂O₃-C. In this connection, the nozzle body 41 may contain about 20 to 30 % by weight of the C content so as to have a conductivity. This is to form a conducting circuit between the submerged entry nozzle 40 and the molten steel flowing through the submerged entry nozzle 40.
The liner 43 may be defined on the inner wall of the nozzle body 41, that is, a surface contacting the molten steel. The liner 43 may be defined over the entire inner wall of the nozzle body 41, but may be defined from an upper side of the nozzle body 41 to above of the discharging hole 42. Accordingly, the liner 43 may be defined in a hollow cylindrical shape having an opening inside of the nozzle body 41 in a vertical direction along the inner wall of the nozzle body 41.
The liner 43 is defined on the inner wall of the nozzle body 41 to move oxygen ion in the molten steel toward the nozzle body 41. The liner 43 may be formed of the MgO stabilized ZrO₂ (MSZ), which is well-known as a material having an excellent ion conductivity. The MgO stabilized ZrO₂ is a solid electrolyte having a property that an ion guides electricity in a solid state, and is applied to a solid fuel cell, a probe for measuring an oxygen concentration in a molten metal, and the like.
In the present disclosure, this MgO stabilized ZrO₂ (MSZ) is used as the liner 43 to induce the oxygen ion in the molten steel toward the nozzle body 41 to suppress or prevent the formation of the inclusion, for example metal oxides such as SiO₂, Al₂O₃, TiO₂, and the like at the inner wall of the submerged entry nozzle 40.
During the casting, the oxygen contained in the molten steel forms the metal oxide at an interface between the molten steel and the inner wall of the submerged entry nozzle 40 due to its property to be activated at the interface. This produced metal oxide has a high interfacial energy with the molten steel and is spontaneously moved and adhered to the inner wall of the submerged entry nozzle 40 in the molten steel. As this process repeats and continues, a nozzle clogging occurs at the inner hollow portion of the submerged entry nozzle 40. In the present disclosure, the liner 43 is defined on the inner wall of the nozzle body 41 using the solid electrolyte having the excellent ion conductivity, and the oxygen ion is induced to the outside by electrically connecting the molten steel and the submerged entry nozzle 40, that is the nozzle body 41 so that the adhesion of the metal oxide to the inner wall of the submerged entry nozzle 40 may be suppressed or prevented.
A mechanism for preventing the metal oxide formation and adhesion will be described below.
Referring to Figure 3a, the oxygen contained in the molten steel during the casting forms the metal oxide and moves to the inner wall of the nozzle body 41. Then, as shown in Figure 3b, when the molten steel and the nozzle body 41 are electrically connected, electrons densely surrounding the metal oxide decompose the metal oxide into the oxygen ion and cations (metal ions). This decomposed oxygen ion is moved to the liner 43 having the excellent ion conductivity as shown in Figure 3c, and is discharged to the outside through pores of the nozzle body while forming oxygen gas. The cations are then absorbed into the molten steel. Through this process, that is, deoxidation, the oxygen in the molten steel is discharged to the outside the molten steel, thereby the nozzle clogging may be suppressed of prevented by inhibiting the formation and adhesion of the metal oxide in the submerged entry nozzle 40.
The liner 43 may contain 80 to 95% by weight of MgO stabilized ZrO₂ (MSZ) and 5 to 20% by weight of carbon content. In this connection, the MgO stabilized ZrO₂ (MSZ) may be composed of magnesia (MgO) of about 8 to 15 mol% and the rest of zirconia (ZrO₂) in order to inhibit a volume change due to a phase change based on a temperature change. Using the magnesia as a stabilizer in the zirconia as described above, the zirconia may maintain a relatively stable phase even at the temperature change, so that it is possible to prevent cracking or damaging of the liner 43 during the casting.
On the other hand, even if the liner 43 is manufactured using the MgO stabilized ZrO₂ stable to the temperature change, a volume expansion based on the temperature change may not be completely suppressed. Further, a coefficient of thermal expansion of the liner 43 and the nozzle body 41 are different from each other, and the coefficient of thermal expansion of the liner 43 is larger than the coefficient of thermal expansion of the nozzle body 41 so that a stress occurs between the liner 43 and the nozzle body 41 due to the volume expansion of the liner 43 during the casting, may result in cracking or damaging of the liner 43.
Therefore, a dummy ring 45 may be formed on at least one of the upper side and the lower side with respect to the longitudinal direction of the liner 43 in order to secure a space corresponding to the volume expansion of the liner 43. The dummy ring 45 may be formed to have a length of about 1 to 2% with respect to a length of the liner 43. When the length of the dummy ring 45 is shorter than the specified range, the breakage of the liner 43 is inevitable because the dummy ring 45 may not adequately cope with the volume expansion of the liner 43, and when the length of the dummy ring 45 is longer than the specified range, the nozzle body 41 may be exposed to the molten steel and the metal oxide may be produced and adhered to the nozzle body 41. The dummy ring 45 does not have to be formed if it may secure a space according to the volume expansion of the liner 43, the dummy ring 45 is inevitably formed because it is difficult to secure the space corresponding to the volume expansion of the liner 43 due to its manufacturing characteristics of the submerged entry nozzle 40. That is, the process of manufacturing the submerged entry nozzle 40 includes a press molding process and a firing process after injecting a raw material constituting the submerged entry nozzle 40 into a molding frame, this is because it is difficult to secure a specific position that is, the space corresponding to the volume expansion of the liner 43, when the raw material is injected into the molding frame. Thus, the dummy ring 45 may be formed of a material having a lower melting point than the contents constituting the liner 43. That is, the dummy ring 45 is formed on either the upper side or the lower side of the liner 43 when manufacturing the submerged entry nozzle 40, but during the casting, the dummy ring 45 may be dissolved and removed by a heat of the molten steel to secure the space for the volume expansion of the liner 43. Thus, the dummy ring 45 may be manufactured using a carbon-containing material such as graphite having a melting point higher than a firing temperature and lower than a casting temperature in manufacturing the submerged entry nozzle 40.
According to such the structure, a dummy ring 45/liner 43 or a dummy ring 45/liner 43/dummy ring 45 may be formed in the nozzle body 41 along the longitudinal direction of the nozzle body 41. Before casting, as shown in Figure 4a, there is the dummy ring 45 on the one side of the liner 43, for example, on the upper side, but during the casting, as shown in Figure 4b, the dummy ring 45 is removed by the heat of the molten steel to form the space on the upper side or the upper side and the lower side of the liner 43, by the heat of the molten steel, the liner 43 expands in a volume by 'x' to fill the space formed while the dummy ring 45 is dissolving. Thus, the stress occurring between the liner 43 and the nozzle body 41 due to the volume expansion of the liner 43 may be relaxed, thereby cracking or damaging of the liner 43 may be suppressed or prevented.
Further, the slag line portion 47 may be defined on the outer wall of the submerged entry nozzle 40. The slag line portion 47 is configured to enhance a corrosion resistance against a slag (or a flux 62), the molten steel, and the like, and may be formed above the discharging hole 42, for example, around a mold level of the molten steel in the mold. The slag line portion 47 may be formed using various materials, for example, a mixed material of a calcia·magnesia partially stabilized zirconia, the graphite, or the like.
The power supply 70 electrically connects the molten steel in the tundish 10 and the submerged entry nozzle 40. In this connection, a first electrode rod 72 for supplying a power to the molten steel in the tundish may be provided, and the submerged entry nozzle 40 may be used as a second electrode. In order to supply the power to the molten steel in the tundish, the first electrode 72 may be provided to be immersed in the molten steel in the tundish, and the first electrode rod 72 may be formed of the same material as the submerged entry nozzle 40, that is, the nozzle body 41. Further, the power supply 70 supplies the power, for example, a voltage or a current to the first electrode 72 and the second electrode (submerged entry nozzle 40) in the way that the first electrode 72 is as a cathode and the second electrode is as an anode. Thus, when the power is supplied to the first electrode 72 and the second electrode, the electrons move from the first electrode 72 to the second electrode side, and the oxygen ion decomposed at the interface between the molten steel and the submerged entry nozzle 40 moves in the moving direction of the electrons, that is from the molten steel to the nozzle body 41 side. Therefore, the oxygen ion in the molten steel may move to the nozzle body 41 side through the liner 43 and may be discharged to the outside, and through this process, the nozzle clogging by the adhesion of the metal oxide to the inner hollow portion of the submerged entry nozzle 40 may be suppressed or prevented.
Hereinafter, a method for manufacturing a nozzle according to an embodiment of the present disclosure will be described.
The nozzle according to the embodiment of the present disclosure may include a process of preparing the raw material for forming the submerged entry nozzle 40, a process of injecting the raw material into the molding frame for forming the submerged entry nozzle 40 to form the molded product, and a process of forming the submerged entry nozzle 40 via firing the molded product.
The process of preparing the raw material may include processes of preparing a raw material for forming the nozzle body 41, a raw material for forming the liner 43 and a raw material for forming the dummy ring 45.
When the raw materials are prepared, each raw material is injected into the molding frame to form the molded product of the submerged entry nozzle 40. At this time, a cylindrical core material may be inserted into the molding frame, and a spacer for forming the liner and the dummy ring may be inserted to be spaced apart from the core material. Then, between the spacer and the core material, the raw materials for forming the liner 43 and the dummy ring 45 are sequentially injected, and between the spacer and the molding frame, the raw material for forming the nozzle body 41 is injected. After the spacer is removed, the raw materials injected into the molding frame are pressed to form the molded product for forming the submerged entry nozzle 40.
Thereafter, the molded product is drawn from the molding frame, and the molded product is fired at a temperature of about 1000 °C or less in the firing furnace to produce the submerged entry nozzle 40. In the process of firing the molded product, the dummy ring 45 may maintain a shape formed during the forming of the molded product.
When the casting is performed using the thus formed submerged entry nozzle 40, the dummy ring 45 is dissolved and removed by a heat of the molten steel, thereby the space corresponding to the volume expansion of the liner 43 may be easily secured at the upper portion or the lower portion of the liner 43. Accordingly, when the volume of the liner 43 is expanded by the molten steel during the casting, the space in which the dummy ring 45 is removed may prevent cracking or damaging in the liner 43.
Hereinafter, a method for casting a cast-piece using a casting apparatus according to an embodiment of the present disclosure will be described.
The casting method according to the embodiment of the present disclosure is a method of casting the cast-piece 61 by injecting the molten steel 60 in the tundish 10 into the mold 50 through the submerged entry nozzle 40, oxygen contained in the molten steel may be discharged to the submerged entry nozzle side by electrically connecting the molten steel 60 and the submerged entry nozzle 40.
A circuit may be configured to electrically connect the molten steel 60 and the submerged entry nozzle 40 prior to casting. The circuit is configured to immerse the first electrode 72 into the molten steel in the tundish and connect the first electrode 72 and the second electrode, that is, the nozzle body 41 using a wire. Then, the first electrode 72 and the second electrode are connected to the power supply 70 provided outside by the wire.
Then, when casting starts, the molten steel 60 in the tundish 10 is injected into the mold 50, and the power is supplied to the first electrode 72 and the nozzle body 41, which is the second electrode, by the power supply 70. In this connection, the first electrode 72 is set to be the cathode and the second electrode is set to be the anode so that the current flows from the first electrode 72 to the second electrode side.
The power supplied to the first electrode 72 and the second electrode by the power supply 70 may be adjusted to have a current density of about 0.1 to 10 mA/cm². This is because the liner 43 defined on an inner portion the nozzle body 41 has the very high ion conductivity, so that oxygen ion may smoothly move even if the relatively small current flows. In this connection, when the current density is smaller than the suggested range, an ionization of the metal oxide and the movement of the oxygen ion are not smoothly carried out. Further, since the ionization of the metal oxide and the movement of the oxygen ion are smoothly carried out within the suggested range of the current density, it is not necessary to make the current density larger than the suggested range.
When the power is supplied to the first electrode 72 and the second electrode thus, the electrons move from the first electrode 72 to the nozzle body 41 which is the second electrode, and thus the current flows from the first electrode 72 to the second electrode. Describe again with reference to Figure 3, when the power is supplied to the first electrode 72 and the second electrode, the electrons are concentrated around the metal oxide produced on the inner wall side of the submerged entry nozzle 40, the metal oxide is decomposed into the oxygen ion and the cations. The oxygen ion thus decomposed moves in the moving direction of the electrons, that is, from the molten steel to the nozzle body 41. At this time, the oxygen ion is transferred to the nozzle body 41 through the liner 43 produced in the inner wall of the submerged entry nozzle 40. Since the liner 43, the solid electrolyte, is permeable only to the oxygen ion, the cations dissolve into the molten steel and are absorbed. This process is continuously performed while the power is supplied, and it is possible to suppress or prevent the metal oxide from being produced and adhered to the inner wall of the submerged entry nozzle 40. Therefore, it is possible to prevent the nozzle clogging which may be caused by the formation and adhesion of the metal oxide.
Hereinafter, test results using a casting apparatus according to an embodiment of the present disclosure will be described below.
For the test, the submerged entry nozzle was manufactured forming the liner with the solid electrolyte on the inner wall portion of the submerged entry nozzle and the other portion without the liner. Using the submerged entry nozzle thus produced, casting was performed under a test facility of a 13-ton scale of the molten steel. In this connection, the power was supplied such that 2 mA/cm² of the current density was applied. Further, in order to accelerate the nozzle clogging, a condition which may be producing a large amount of the Al₂O₃ inclusion in the molten steel was applied. Thereafter, the submerged entry nozzle used in the test was cut and an inside thereof was observed.
As a result of the experiment, it was confirmed that the inclusion layer of 0.3 mm or less was adhered to the region where the liner was defined, and in the region B where the liner was not defined, a mixture of the inclusion and an impurity had the inclusion layer of about 1.8 to 3.5 mm.
Through this test, it was confirmed that when the liner containing the solid electrolyte is formed on the submerged entry nozzle and the molten steel and the submerged entry nozzle are electrically connected, the oxygen in the molten steel is removed and the formation and adhesion of the metal oxide at the inner wall of the submerged entry nozzle is prevented.
Although the preferred embodiments of the present disclosure have been shown and described, those skilled in the art will be understood that the present disclosure is not intended to be limited to the embodiments shown herein but is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the present disclosure as defined by the appended claims. Accordingly, the technical protection scope of the present disclosure should be defined by the following claims.

Industrialabilitv

According to the present disclosure, the nozzle, the casting apparatus and the casting method may improve the productivity of the cast-piece by suppressing or preventing the nozzle clogging in the continuous casting process for casting the cast-piece.

Claims

a nozzle comprising:
a nozzle body having an inner hollow portion through which molten steel moves, and a discharging hole defined therein through which the molten steel moves outside the inner hollow portion; and

a liner surrounding at least a portion of an inner wall of the nozzle body and containing MgO stabilized ZrO₂ (MSZ).
The nozzle according to claim 1, wherein the nozzle body contains Al₂O₃, wherein the nozzle body contains 20% by weight to 30% by weight of carbon content.
The nozzle according to claim 1, wherein the liner contains 80 to 95% by weight of MgO stabilized ZrO₂ and 5 to 20% by weight of carbon.
The nozzle of claim 3, wherein the MgO stabilized ZrOz contains 8 to 15 mol% of magnesia (MgO).
The nozzle of claim 4, wherein a dummy ring is provided on at least one of a top and a bottom of the liner with respect to a longitudinal direction of the liner.
The nozzle of claim 5, wherein the dummy ring contains a carbon content.
The nozzle of claim 6, wherein the dummy ring has a length of 1 to 2% based on a total length of the liner.
A casting apparatus comprising:
a tundish receiving molten steel therein;

a submerged entry nozzle connected to a bottom of the tundish, wherein the submerged entry nozzle includes a nozzle body, and a liner surrounding at least a portion of an inner wall of the nozzle body, wherein the liner contains MgO stabilized ZrO₂ (MSZ); and

a power supply electrically connecting the molten steel received in the tundish and the nozzle body with each other.
The apparatus of claim 8, wherein the nozzle body contains Al₂O₃,
wherein the nozzle body contains 20% by weight to 30% by weight of carbon content,
wherein the liner contains 80 to 95% by weight of MgO stabilized ZrO₂, and 5 to 20% by weight of carbon, wherein the MgO stabilized ZrO₂ contains 8 to 15 mol% of magnesia (MgO).
The apparatus of claim 9, wherein a dummy ring is provided on at least one of a top and a bottom of the liner with respect to a longitudinal direction of the liner.
The apparatus of claim 8, wherein the apparatus includes an electrode immersed in the molten steel in the tundish,
wherein the power supply applies a power to the electrode and the submerged entry nozzle.
A casting method for casting a cast-piece by injecting molten steel received in a tundish into a mold through a submerged entry nozzle,
wherein the submerged entry nozzle includes a nozzle body connected to the tundish, and a liner defined on an inner wall of the nozzle body, wherein the liner contains MgO stabilized ZrO₂,

wherein the method includes electrically connecting the molten steel and the nozzle body with each other to discharge oxygens contained in the molten steel to a side of the submerged entry nozzle.
The method of claim 12, wherein when the molten steel and the nozzle body are electrically connected with each other, metal oxides produced in the molten steel are decomposed into oxygen ions and cations, and, then, the oxygen ions are transferred through the liner to the nozzle body, such that oxygens in the molten steel are discharged to a side of the submerged entry nozzle.
The method of claim 13, wherein the molten steel and the submerged entry nozzle are electrically connected with each other while using the molten steel as a cathode and using the submerged entry nozzle as an anode.
The method of claim 14, wherein in electrically connecting the molten steel and the submerged entry nozzle with each other, 0.1 to 10 mA/cm² of a current density is applied.
The method of claim 13, wherein a dummy ring is provided on at least one of a top and a bottom of the liner, wherein the dummy ring is dissolved during casting the cast-piece to form a space.