Immersion nozzle for casting and steel casting method using the same

Abstract

To provide an immersion nozzle for casting which can prevent the clogging of the immersion nozzle with alumina by preventing the sticking of metal to the inner wall of the immersion nozzle, and to provide a method for casting steel using the same.SOLUTION: An immersion nozzle for casting includes a nozzle body, a molten-steel outflow passage, a molten-steel discharge port, a slag-line material-quality portion, a lining material, a nozzle flange portion, and a nozzle bottom portion, wherein a heat-insulating layer having a thickness of 0. 1mm or more and 1 / 2 or less of a refractory thickness of the immersion nozzle for casting is provided in the nozzle body so as to surround the molten-steel outflow passage.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a submerged entry nozzle for casting that discharges molten steel from a tundish into a mold with its lower portion submerged in the molten steel in the mold, and a method for casting steel using the same. In this specification, the term "x to y" indicating a range of values ​​means x or more and y or less, including the boundary value. Furthermore, one charge means molten steel per ladle (one ladleful). Furthermore, continuous casting means continuous casting of multiple charges. [Background technology]

[0002] In casting immersion nozzles, especially those used in continuous casting, clogging of the immersion nozzle occurs due to the precipitation of alumina in the steel during the casting of aluminum-killed steel. This not only adversely affects the quality of the cast steel slabs, but also increases the frequency of replacement of the immersion nozzle, inevitably reducing the production efficiency of the slabs.

[0003] Therefore, in order to prevent such clogging of the submerged entry nozzle, the techniques described in Patent Documents 1 to 7 have been proposed. The techniques described in Patent Documents 1 to 4 involve injecting Ar gas, an inert gas, into the molten steel outflow path that passes through the center of the submerged entry nozzle, and forming a film of the inert gas to prevent the precipitation of alumina.

[0004] Furthermore, Patent Documents 5 and 6 disclose a method for suppressing clogging of the SEN by adding CaO to the material forming the inner wall of the SEN, generating an Al2O3-CaO-based low-melting-point compound through a reaction between Al2O3 adhering to the inner wall of the SEN and the CaO in the SEN material, and causing this compound to flow out and float up into a mold.

[0005] Furthermore, the technology disclosed in Patent Document 7 aims to prevent clogging of the submerged entry nozzle by providing a heat insulating layer within the refractory material of the submerged entry nozzle. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-221277 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-254145 [Patent Document 3] Japanese Patent Application Publication No. 11-285790 [Patent Document 4] Japanese Patent Application Publication No. 62-130754 [Patent Document 5] Japanese Patent Application Laid-Open No. 2007-130653 [Patent Document 6] Japanese Patent Publication No. 62-024846 [Patent Document 7] Japanese Patent Application Laid-Open No. 2013-215763 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the techniques described in Patent Documents 1 to 4 have difficulty completely suppressing alumina adhesion to the submerged entry nozzle for the following reasons. Specifically, alumina adhesion is highly dependent on the amount of Ar gas injected, and a large injection amount can be expected to suppress adhesion. However, a large amount of Ar gas bubbles flows into the molten steel, which can cause the molten steel surface to become unstable, resulting in scabbing defects and blow defects caused by the bubbles. For this reason, a large amount of Ar gas cannot be injected in actual operation. On the other hand, if the injection amount of Ar gas is small, an inert gas film is not sufficiently formed, and the alumina adhesion prevention effect cannot be expected. Thus, in actual operation, in order to ensure steel quality and suppress alumina adhesion at the same time, one of the two must be sacrificed, making it difficult to completely suppress alumina adhesion to the submerged entry nozzle.

[0008] Furthermore, in the methods described in Patent Documents 5 and 6, a high flow rate of the molten steel in the submerged entry nozzle is an essential condition for causing the low-melting-point compound to flow into the mold. If the flow rate of the molten steel in the submerged entry nozzle is low, i.e., if the casting speed is slow, the low-melting-point compound will adhere to the inner wall of the submerged entry nozzle, which can lead to the problem of being unable to prevent clogging of the submerged entry nozzle.

[0009] Furthermore, the method described in Patent Document 7 does not take into consideration the temperature drop of molten steel at the beginning and end of casting, and the heat insulating layer is located above the slag line, which has the disadvantage of insufficient heat retention effect in the immersed part of the submerged entry nozzle.

[0010] Therefore, the inventors focused on the influence of the immersion nozzle on the quality of steel slabs, which is the most important requirement in steelmaking, and conducted a detailed study of the boundary between the immersion nozzle and the alumina deposit by observing immersion nozzles that had experienced alumina clogging. As a result, it was found that alumina does not adhere directly to the refractory surface of the SEN. Specifically, it was found that a base metal layer, which is formed mainly due to a temperature drop of molten steel at the beginning of casting or when the casting speed is reduced, is always present on the refractory surface of the SEN, and that alumina adheres to the base metal layer due to irregularities or reactions in the base metal layer, and that alumina grows from this base metal layer.

[0011] The inventors discovered that when molten steel passes through the immersion nozzle, heat escapes to the outside through the thickness of the immersion nozzle, causing the temperature of the molten steel inside the immersion nozzle to drop, which in turn causes a base metal layer to adhere to the molten steel outlet channel inside the immersion nozzle, which then causes further alumina to adhere, resulting in the progression of blockage of the molten steel outlet channel.The inventors then devised a specific means for preventing heat from escaping to the outside through the thickness of the immersion nozzle, and completed the present invention.

[0012] Specifically, the present invention aims to provide a casting submerged entry nozzle that can prevent clogging of the submerged entry nozzle with alumina by preventing the adhesion of base metal to the inner wall of the submerged entry nozzle, and a steel casting method using the same. This is expected to improve the casting efficiency by improving the stability and productivity of steel casting, and also to improve the quality of the steel by reducing surface and internal defects. [Means for solving the problem]

[0013] A first aspect of the present invention that advantageously solves the above-mentioned problems is a casting submerged entry nozzle, which comprises a nozzle body, a molten steel outflow path, a molten steel discharge port, a slag line material portion, a lining material, a nozzle flange portion, and a nozzle bottom portion, and is characterized in that an insulating layer having a thickness of 0.1 mm or more and not more than half the thickness of the refractory material of the casting submerged entry nozzle is provided within the nozzle body so as to surround the molten steel outflow path.

[0014] Furthermore, in the casting immersion nozzle according to the first aspect, (a) providing the heat insulating layer in a region from the lower end of the nozzle flange portion to the lower end of the slag line material portion or in a region from the lower end of the nozzle flange portion to the upper end of the molten steel discharge port so as to surround the molten steel outflow path within the nozzle body; (b) further providing the heat insulating layer at the nozzle bottom; (c) the heat insulating layer is a layer including at least one selected from an air layer, a low thermal conductive gas layer, and a low thermal conductive material layer; and (d) The low thermal conductive gas layer is provided in the nozzle body so as to surround the molten steel outflow passage, and is formed by blowing inert gas into a communicating gap. This would be a more preferable solution.

[0015] A second aspect of the present invention, which advantageously solves the above-mentioned problems, is a method for casting steel using the casting submerged entry nozzle according to the first aspect, characterized in that the adhesion of base metal to the inner tube of the nozzle body and the adhesion of alumina are prevented by suppressing a decrease in the temperature of the molten steel. [Effects of the Invention]

[0016] According to the present invention, an insulating layer is formed at least within the refractory material of the nozzle body so as to surround the molten steel outlet passage, thereby reducing the amount of heat escaping to the outside through the thickness of the nozzle body. This increases the wall temperature of the molten steel outlet passage, suppressing the deposition of base metal on the inner tube of the nozzle body. This also suppresses the growth of alumina originating from the base metal, preventing nozzle clogging in the casting submerged entry nozzle. For these reasons, the stability and productivity of steel casting can be improved, and it is also expected that surface and internal defects in the steel will be reduced, thereby improving quality. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic vertical cross-sectional view showing a casting submerged entry nozzle according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic vertical cross-sectional view illustrating a method for calculating a heat flux in the casting submerged entry nozzle according to the embodiment. [Figure 3] 1 is a graph comparing the effects of the casting submerged entry nozzle according to the above embodiment with those of a conventional casting submerged entry nozzle. [Figure 4] FIG. 1 is a scatter diagram showing the correlation between the total thickness of the base metal and the alumina deposition thickness and the heat flux in the invention examples and the comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following describes in detail embodiments of the present invention. The following embodiments exemplify structures and methods for embodying the technical idea of ​​the present invention, and are not intended to limit the configuration to the following. In other words, the technical idea of ​​the present invention can be modified in various ways within the technical scope described in the claims.

[0019] [First embodiment] <Submerged Entry Nozzle for Casting> The first embodiment of the present invention is a submerged entry nozzle for casting. FIG. 1 is a schematic longitudinal sectional view showing a casting submerged entry nozzle according to this embodiment. The casting submerged entry nozzle 1 in FIG. 1 is for continuous casting and is connected to the bottom of a tundish (not shown). This casting submerged entry nozzle 1 comprises a nozzle body 2, a molten steel outlet 3, a molten steel discharge port 4, a slag line material portion 5, a lining material 6, a nozzle flange portion 7, and a nozzle bottom portion 8. The nozzle body 2 is the straight body portion of the casting submerged entry nozzle according to this embodiment. The nozzle body 2 is formed in a cylindrical shape, and the hollow molten steel outlet 3 is provided in its center. The molten steel outlet 4 is formed in the lower portion of the nozzle body 2. Here, the molten steel outlet 4 penetrates the nozzle body 2 together with the tubular lining material 6 stretched on the inner surface of the nozzle body 2 facing the molten steel outlet 3, and is positioned so as to face in a direction intersecting the axis of the nozzle body 2. A refractory material or the like is used as the lining material 6.

[0020] During use, the submerged entry nozzle for casting 1 is inserted into a mold (not shown) of continuous casting equipment. In Fig. 1, reference numeral 11 denotes molten steel in the mold, and reference numeral 12 denotes the lower surface of a slag layer 9, which is also the upper surface of the molten steel 11. The slag layer 9 floats above the upper surface of the molten steel 12, and the upper surface of the slag layer 10 is the upper surface of the slag layer 9. That is, during use, the lower part of the submerged entry nozzle for casting 1 is immersed in the molten steel and slag layer.

[0021] The slag line material portion 5 is located in the nozzle body 2 above the molten steel discharge port 4 and has a longitudinal dimension corresponding to the range of the slag layer 9 formed on the surface of the molten steel in the mold and moving up and down. Specifically, the slag layer upper surface 10, which is the surface of the slag layer 9, may move up to the upper end of the slag line material portion 5, and the slag layer lower surface (upper surface of the molten steel) 12, which is the interface between the slag layer 9 and the molten steel 11, may move up to the lower end of the slag line material portion 5. In other words, the portion of the slag line material portion 5 above its lower end may be exposed above the molten steel surface. The nozzle flange portion 7 is located at the upper end of the nozzle body 2 and is connected to a tundish (not shown). The nozzle bottom portion 8 is located at the lower end of the nozzle body 2 and is located below the molten steel discharge port 4.

[0022] The casting submerged entry nozzle according to this embodiment further has a heat insulating layer 13. By providing a heat insulating layer, it is possible to suppress a decrease in the temperature of the molten steel and the nozzle refractory, which can cause base metal layer adhesion and ultimately alumina adhesion.

[0023] Here, it is believed that the base metal layer adheres due to a temperature drop when molten steel begins to pass through the casting immersion nozzle. Specifically, while the presence or absence of an insulating layer is thought to have no effect on the nozzle temperature until the start of casting, it is important to consider the temperature drop that occurs between the time the nozzle temperature rise stops and the time the molten steel passes through. That is, near the start of casting, the temperature of the casting immersion nozzle goes through three stages: a temperature rise due to the heating, a temperature drop due to the heating stop, and a temperature rise due to the inflow of molten steel. The temperature drop due to the heating stop is the lowest point, and this is also the time when base metal layer adhesion is likely to occur. In this case, the presence of an insulating layer can reduce the amount of heat flowing to the refractory material, thereby suppressing base metal layer adhesion. In particular, an insulating layer provided at the nozzle bottom, as described below, is effective. Furthermore, the nozzle temperature also decreases toward the end of continuous casting, increasing the likelihood of base metal layer adhesion. In other words, the probability of base metal layer adhesion increases at the start and end of continuous casting. Although the casting speed does not change during continuous casting, the temperature of the molten steel drops when, for example, the ladle is replaced, which can cause the base metal layer to adhere.

[0024] In this embodiment, the insulating layer 13 is formed within the wall thickness of the nozzle body 2, for example, from the lower end of the nozzle flange 7 to the lower end of the slag line material portion 5, or from the lower end of the nozzle flange 7 to the upper end of the molten steel discharge port 4, so as to surround the molten steel discharge port 3. In this case, the insulating layer 13 is formed in a cylindrical shape concentric with the molten steel discharge port 3. The insulating layer 13 may be formed from the inner pipe of the nozzle outward, i.e., so as to be in contact with the lining material 6. However, from the viewpoint of ensuring the strength of the nozzle body 2, it is preferable to provide the insulating layer 13 approximately in the center of the refractory thickness of the nozzle body 2. This can prevent breakage due to spalling. Hereinafter, the region from the lower end of the nozzle flange 7 to the lower end of the slag line material portion 5 will be referred to as the first region, and the region from the lower end of the nozzle flange 7 to the upper end of the molten steel discharge port 4 will be referred to as the second region. Here, due to the structure of the submerged entry nozzle, if spalling occurs due to the thermal load from the discharge hole, cracks may propagate, making it more difficult to provide the insulating layer 13 in the second region than in the first region. However, even when providing the insulating layer 13 in the second region, it is possible to maintain strength by, for example, arranging it in a grid pattern. By providing the insulating layer 13 in the second region, as described below, an insulating effect can be obtained even in the portions of the submerged entry nozzle covered with the slag layer and molten steel. Furthermore, the insulating layer 13 may be provided on the nozzle bottom 8 in addition to the one provided on the nozzle main body 2. When the insulating layer 13 is also provided on the nozzle bottom 8, the insulating layer may have various shapes, such as a disk shape or a plate shape, provided that the strength of the nozzle bottom 8 is ensured. By providing the insulating layer 13 on the nozzle bottom 8 as well, it is expected that the effect of suppressing heat conduction to the outside of the nozzle, which will be described later, will be further improved. Furthermore, by providing the insulating layer 13 on the nozzle bottom 8, it is possible to obtain an effect of preventing base metal adhesion in the portion of the inner tube of the nozzle main body 2 located directly above the nozzle bottom 8 and in the vicinity thereof, and it is also possible to stabilize the flow rate of molten steel discharged from the molten steel discharge port 4.

[0025] In the casting submerged entry nozzle 1 having the configuration shown in Fig. 1, a heat insulating layer 13 is provided in the region (second region) extending from the lower end of the nozzle flange portion 7 to the upper end of the molten steel discharge port 4, and in the nozzle bottom portion 8. In addition to the configuration shown in Fig. 1, the casting submerged entry nozzle of the present invention may have the heat insulating layer 13 provided in, for example, the first region and the nozzle bottom portion 8, or may have the heat insulating layer 13 only in the first region.

[0026] When the insulating layer 13 is provided on the nozzle body 2, its thickness (diameter of the nozzle body) is set to 0.1 mm or more. The upper limit of the thickness can be set within a range that ensures the strength of the nozzle body 2. Specifically, an insulating layer having a thickness of 0.1 mm or more and half or less of the thickness of the refractory material of the casting submerged entry nozzle 1 is preferred. Considering the influence of contact heat conduction between powder particles in a nozzle body molded by powder sintering, the lower limit of 0.1 mm is also the minimum thickness that can be applied to the nozzle refractory. However, assuming that a low thermal conductivity material layer (described later) is used as an insulating layer, a thickness less than 0.1 mm may be adopted if the low thermal conductivity of the low thermal conductivity material is significantly low. Here, the refractory thickness of the casting submerged entry nozzle 1 refers to the thickness of the refractory excluding the slag line material portion 5 in the nozzle body 2, and the thickness of the refractory constituting the nozzle bottom 8 in the nozzle bottom. A thickness less than 0.1 mm may not achieve the desired heat conduction suppression effect, while a thickness exceeding half the refractory thickness of the casting submerged entry nozzle 1 may result in the nozzle body 2 being unable to maintain sufficient strength. Furthermore, the upper and lower limits for the insulating layer 13 provided on the nozzle bottom 8 are the same as those described above. In this case, the thickness dimension of the heat insulating layer 13 is the dimension in the vertical direction (corresponding to the axial direction of the straight body portion) at the nozzle bottom 8.

[0027] Here, examples of the heat insulating layer 13 include an air layer, a low thermal conductive gas layer, and a low thermal conductive material layer, etc. These various heat insulating layers will be described in detail below.

[0028] <Air layer> When forming an air layer as an insulating layer in the first or second region, a cylindrical member made of a material that burns away during firing of the casting submerged entry nozzle 1 and having a shape identical to or similar to the desired insulating layer is first embedded inside the refractory material (or refractory substance) that forms the nozzle body 2. Furthermore, the inside of the nozzle body 2 is lined with a refractory material that serves as a lining. When the entire casting submerged entry nozzle 1 is fired in this state, the cylindrical member burns away, forming a cylindrical air layer. When forming the insulating layer 13 in the first region, both ends of the air layer in the nozzle longitudinal direction are naturally closed by the lower end of the nozzle flange portion 7 and the lower end of the slag line material portion 5. When forming the insulating layer 13 in the second region, both ends of the air layer in the nozzle longitudinal direction are naturally closed by the lower end of the nozzle flange portion 7 and the upper end of the molten steel discharge port 4. In this manner, the insulating layer 13, or air layer, is formed.

[0029] The reason why the shape of the member made of the material to be burned away is the same as or similar to that of the heat insulating layer is that the refractory material may deform when fired for the casting submerged entry nozzle 1, and the shape of the material to be burned away may not completely match the shape of the air layer formed by the burnout. The same method as above can also be used to form an air layer as a heat insulating layer not only in the first region or the second region but also in the nozzle bottom 8. Furthermore, due to the permeability (porosity) of the nozzle refractory itself, there is no need to provide a separate passage for air escape when thermal expansion occurs, for example, at the top of the nozzle.

[0030] <Low thermal conductivity gas layer> When a low-thermal-conductivity gas layer is formed as an insulating layer in the first or second region, a gas with low thermal conductivity is used. Specifically, argon, xenon, nitrogen, or other gases may be used. To form a low-thermal-conductivity gas layer, for example, an inert gas, such as argon gas, may be injected into a cylindrical, interconnected gap surrounding the molten steel outlet 3 formed in advance within the refractory material of the nozzle body 2 during casting operation. In this case, a mechanism for introducing the inert gas may be provided within the nozzle flange 7. When the inert gas is drawn into the inner tube of the nozzle body 2 due to negative pressure, it is expected to contribute to preventing oxidation of the molten steel. Specifically, when the inert gas is delivered to the molten steel outlet 4, negative pressure may be created in a specific area near the molten steel outlet, causing the inert gas to be drawn in. This inert gas injection configuration is particularly useful when forming an insulating layer in the second region. That is, when a low-thermal-conductivity gas layer is used as an insulating layer, the low-thermal-conductivity gas layer can function as both an insulating layer and an inert gas passage. This allows for alumina deposition prevention measures to be implemented at multiple locations, in addition to the upper nozzle (not shown), which also flows inert gas, from the viewpoint of washing away deposited alumina with inert gas bubbles. Furthermore, when an insulating layer is provided in the first region, the interconnected voids must extend at least to the lower end of the slag line material portion 5. When an insulating layer is provided in the second region, the interconnected voids must extend at least to the upper end of the molten steel discharge port 4. Here, the same method as above can be used when forming a low thermal conductive gas layer as a heat insulating layer not only in the first or second region but also in the nozzle bottom 8.

[0031] <Low thermal conductivity material layer> When forming a low thermal conductive material layer as a heat insulating layer in the first region or the second region, a material having a lower thermal conductivity than the material of the nozzle body 2 is used. The low thermal conductive material layer can be disposed in the refractory of the nozzle body 2, for example, by a method of laminating layers from the inside to the outside by firing or the like when molding the nozzle body 2. Furthermore, when a solid low thermal conductive material layer is used as a heat insulating layer, the thermal conductivity of the nozzle refractory itself can be reduced.

[0032] The following heat transfer calculations were performed to simulate the material of the low thermal conductivity layer. The upper exterior of the nozzle was assumed to be at ambient temperature, and the air inside the nozzle was assumed to be at 1500°C, approximately the same temperature as the molten steel. Aiming to increase the temperature of the nozzle's inner surface by 30°C or more above normal, heat transfer calculations were performed by varying the material and thickness of the low thermal conductivity layer used as an insulating layer. For example, assuming that the refractory material of the casting submerged entry nozzle is alumina and carbon, if silica, with a thermal conductivity of 1.0 W / m·K, is used for the low thermal conductivity layer, the thickness is preferably 5 mm to 10 mm. If zirconia, with a thermal conductivity of 3.0 W / m·K, is used for the low thermal conductivity layer, the thickness is preferably 10 mm to 15 mm. By using a low thermal conductivity layer made of the above materials with a thermal conductivity lower than that of the nozzle refractory and with a thickness within the above range, effects equivalent to those of the air layer or low thermal conductivity gas layer can be achieved. Here, when forming a low thermal conductive material layer as a heat insulating layer not only in the first or second region but also in the nozzle bottom 8, the same materials and methods as those described above can be used.

[0033] Here, for example, when a heat insulating layer 13 is provided in the nozzle bottom 8 provided at the lower end of the nozzle body 2 in addition to the first or second region in the nozzle body 2, one or more of the air layer, low thermal conductive gas layer, and low thermal conductive material layer may be appropriately combined and arranged. For example, the heat insulating layer 13 arranged in either the first region or the second region and the heat insulating layer 13 arranged in the nozzle bottom 8 may be of the same type or different types.

[0034] It is also possible to place another layer on the inner surface of the lining material in a region above the upper surface 10 of the slag layer 9. This other layer preferably has the function of preventing the heat transfer of the molten steel flowing down inside and / or preventing the reaction of the adhering base metal.

[0035] In the casting submerged entry nozzle 1 according to this embodiment, molten steel supplied from an upper tundish flows into the nozzle body 2 from the upper end of the molten steel outlet channel 3, and the molten steel that flows down is discharged into the mold from the molten steel discharge port 4 provided at the bottom of the nozzle body 2. At this time, in the region above the slag layer upper surface 10, which is the upper surface of the slag layer 9, i.e., in the region of the casting submerged entry nozzle 1 that is not immersed in either the slag layer 9 or the molten steel 11, the heat of the molten steel flowing down the molten steel outlet channel 3 via the lining material 6 and the nozzle body 2 attempts to escape to the outside of the casting submerged entry nozzle 1.

[0036] The casting submerged entry nozzle 1 according to this embodiment has an insulating layer 13 at least in the first region of the nozzle body 2. This suppresses the conduction of heat from the molten steel flowing through the molten steel outlet channel 3 in this region of the casting submerged entry nozzle 1 to the outside, allowing the molten steel to move downward without excessive cooling. In other words, the provision of the insulating layer 13 at least within the nozzle body 2 in the casting submerged entry nozzle 1 according to this embodiment effectively suppresses the heat conduction of the molten steel. Meanwhile, in the region below the slag layer upper surface 10, which is the upper surface of the slag layer 9, i.e., in the region of the casting submerged entry nozzle 1 immersed in both the slag layer 9 and the molten steel 11, the slag layer 9 and the molten steel 11 cover the exterior of the casting submerged entry nozzle 1, so that the temperature of the molten steel inside the casting submerged entry nozzle 1 hardly drops. Here, as described above, by providing the insulating layer 13 in the second region of the nozzle body 2 and the nozzle bottom 8, it is possible to expect an effect of suppressing the thermal conduction of molten steel even in the region below the slag layer upper surface 10, which is the upper surface position of the slag layer 9.

[0037] In this way, in the casting submerged entry nozzle 1 according to this embodiment, by appropriately adjusting the location of the insulating layer 13, it is possible to prevent the heat of the molten steel in the nozzle body 2 from escaping to the outside in both the region above the slag layer upper surface 10, which is the upper surface of the slag layer 9, and the region below the slag layer upper surface 10, thereby preventing a decrease in the temperature of the molten steel in both of these regions. Specifically, for example, in an estimate based on an air layer of 0.1 mm, the presence or absence of an insulating layer results in a difference of approximately 300°C in the temperature of the inner surface of the nozzle.

[0038] Furthermore, for example, if the casting submerged entry nozzle is preheated to 1000°C before the start of casting and the temperature of the molten steel when it flows in is 1550°C, the temperature of the molten steel may normally drop by approximately 200 to 300°C. When considering the degree of temperature drop at the nozzle outer surface, which is the interface, the presence of the insulating layer makes the temperature of the nozzle outer surface (nozzle outer wall surface) relatively lower. Also, from the perspective of heat flux, which is the amount of heat per unit area that flows out from the nozzle refractory, providing the insulating layer reduces heat removal from inside the nozzle, lowering the temperature of the nozzle outer surface. Specifically, the heat flux was calculated using Fourier's law, a quantitative method shown below, and it was found that the heat flux was 7000 W / m 2 It has become clear that it is more preferable to use an insulating layer as described below. FIG. 2 is a schematic vertical cross-sectional view illustrating a method for calculating heat flux in this embodiment. FIG. 2(a) is an explanatory diagram illustrating a method for calculating heat flux when an air layer is provided as an insulating layer in the center of the SEN refractory. On the other hand, FIG. 2(b) is an explanatory diagram illustrating a method for calculating heat flux when the SEN refractory is not provided with an insulating layer. In FIG. 2(a), T∞ represents the atmospheric temperature. Tc represents the temperature of the outer wall surface of the SEN. Tb represents the temperature of the refractory wall surface on the outer side across the air layer. Ta represents the temperature of the refractory wall surface on the inner side across the air layer. δ1 represents the thickness of the inner and outer refractories separated by the air layer. δ2 represents the thickness of the air layer. Furthermore, in FIG. 2(b), T∞ represents the atmospheric temperature. Tc represents the temperature of the outer wall surface of the SEN. δ3 represents the overall thickness of the SEN refractory. Here, in FIGS. 2(a) and 2(b), δ1, δ2, and δ3 have the relationship δ3=2δ1+δ2.

[0039] For example, the thickness δ1 of the inner and outer refractories separated by the air layer is set to 0.01275 m (12.75 mm), the thickness δ2 of the air layer as a heat insulating layer is set to 0.001 m (1.0 mm), the thickness δ3 of the entire SEN refractory is set to 0.0265 m (26.5 mm), the atmospheric temperature T∞ is set to 25°C, the temperature of the inner wall surface of the SEN is set to 1500°C, the thermal conductivity k1 of the SEN refractory is set to 23.6 W / m K, the thermal conductivity k2 of the air layer is set to 0.024 W / m K, and the heat transfer coefficient h of the atmosphere is set to 5 W / m K. 2When the heat flux Q and the temperature Tc of the outer wall surface of the submerged entry nozzle are set to K, the heat flux Q and the temperature Tc of the outer wall surface of the submerged entry nozzle can be calculated as follows, depending on whether or not an insulating layer (air layer) is provided.

[0040] [With insulation layer] When an air layer was provided as a heat insulating layer, the heat flux Q and the temperature Tc of the outer wall surface of the submerged entry nozzle were calculated using the following formulas 1 and 2. [Number 1] 1500-T∞=Q*(δ1 / k1+δ2 / k2+δ1 / k1+1 / h) [Number 2] Tc-T∞=Q / h First, when the above corresponding values ​​are substituted into Equation 1, the heat flux is Q = 6262 W / m 2 Then, by substituting the heat flux value, the atmospheric temperature, and the heat transfer coefficient of the atmosphere into Equation 2, the temperature of the outer wall surface of the submerged nozzle was calculated to be Tc = 1282°C.

[0041] [Without insulation layer] When no heat insulating layer was provided, the heat flux Q and the temperature Tc of the outer wall surface of the submerged entry nozzle were calculated using the following Equations 3 and 4. [Number 3] 1500-Tc=Qδ3 / k1 [Number 4] Tc-T∞=Q / h First, when the above corresponding values ​​were substituted into the formula 1500-T∞=Q(δ3 / k1+1 / h) obtained by adding formula 3 and formula 4, the heat flux was Q=7557W / m 2 Then, by substituting the heat flux value, the atmospheric temperature, and the heat transfer coefficient of the atmosphere into Equation 4, the temperature of the outer wall surface of the submerged nozzle was calculated to be Tc = 1542°C.

[0042] From the above results, it was confirmed that when an air layer was provided as an insulating layer, the temperature Tc of the outer wall surface of the submerged entry nozzle was 260°C lower than when no insulating layer was provided, and that there was an insulating effect. Note that, since the casting submerged entry nozzle of this embodiment is formed in a cylindrical shape, the heat flux calculation was performed taking into account the difference between its inner and outer areas, and the position of the insulating layer in a cylindrical coordinate system. In other words, from the perspective of heat flux, the effect of the insulating layer was evaluated based on the temperature of the nozzle outer wall surface.

[0043] By suppressing the temperature drop of the molten steel inside the nozzle body 2, it becomes possible to maintain the temperature of the casting submerged entry nozzle 1. This makes it difficult for a bare metal layer to adhere to the inner surface of the casting submerged entry nozzle 1, specifically the surface of the lining material 6 arranged inside the nozzle body 2, thereby achieving the effect of preventing bare metal adhesion. By suppressing the adhesion of the bare metal layer, the growth of alumina starting from the bare metal layer is also significantly reduced, making it possible to prevent the molten steel outflow path 3 from being blocked or narrowed by alumina. Here, the process by which a metal layer is formed on the inner surface of the casting submerged entry nozzle, alumina adheres to the metal layer, and the alumina grows can be thought of as occurring, for example, through the following specific mechanism. Generally, when casting a slab in continuous casting, the temperature inside the tundish is controlled within a range of 20°C to 40°C above the solidification temperature to prevent delayed solidification in the mold. Because molten steel is poured from the tundish to the mold through a casting submerged entry nozzle, if the heat removal rate at the submerged entry nozzle is large (20 to 40°C), the molten steel at the outlet of the submerged entry nozzle may drop to its solidification temperature. In this case, the molten steel passing through the submerged entry nozzle adheres to the inner wall of the nozzle and solidifies, forming a metal layer. This effect is particularly pronounced at the start of casting, when the casting submerged entry nozzle is not yet fully heated, or when the casting speed is reduced. Once the metal adheres to the inside of the submerged entry nozzle, unevenness occurs on the inner wall surface of the nozzle, making it easier for alumina inclusions to adhere to the metal layer. Starting from this point, alumina accumulates and grows, causing problems in operation.

[0044] In this regard, a conventional method for suppressing alumina adhesion has been to inject an inert gas, such as Ar gas, into the inner wall of the submerged entry nozzle to seal the nozzle. However, because the inert gas is injected at a temperature lower than the temperature of the molten steel, this can lower the temperature of the molten steel and potentially promote the deposition of base metal on the inner wall of the submerged entry nozzle. In contrast, the casting submerged entry nozzle according to this embodiment further suppresses the temperature drop of the molten steel by providing a heat insulating layer in a predetermined location, thereby minimizing the temperature drop caused by the injection of the inert gas. That is, this embodiment prevents base metal adhesion to the inner wall of the casting submerged entry nozzle from a different perspective than conventional methods, thereby preventing clogging of the submerged entry nozzle with alumina. This can improve the stability and productivity of steel casting and is also expected to improve quality by reducing surface and internal defects in the steel. 1 illustrates the casting submerged entry nozzle according to this embodiment as a two-hole nozzle, it goes without saying that this embodiment can also be applied to various multi-hole nozzles, such as a four-hole nozzle. Naturally, the same effects as those described above can also be achieved in the case of various multi-hole nozzles, such as a four-hole nozzle.

[0045] [Second embodiment] <Steel casting method> The second embodiment of the present invention is a method for casting steel using the submerged entry nozzle for casting described in the first embodiment, and is intended to stably cast steel. When casting is performed using the submerged entry nozzle for casting, the heat insulating layer 13 provided inside the nozzle body 2 and at the nozzle bottom 8 makes it possible to suppress a drop in the temperature of the molten steel. This prevents base metal from adhering to the inner tube of the nozzle body 2, and also prevents alumina from adhering from this point. Furthermore, by appropriately selecting and combining various heat insulating layers and their positions as described above, it is expected that the heat conduction suppression effect provided by the heat insulating layer 13 can be further improved.

[0046] In this way, in this embodiment as well, clogging of the submerged entry nozzle by alumina can be prevented by preventing the base metal from adhering to the inner wall of the submerged entry nozzle for casting, which can improve the stability and productivity of steel casting and is also expected to reduce surface and internal defects in the steel, thereby improving quality. [Example]

[0047] The present invention will be specifically described below based on examples, but the present invention is not limited to the examples shown below.

[0048] <Example> To compare molten steel of the same cleanliness, a two-strand system was used. A conventional casting submerged entry nozzle and a casting submerged entry nozzle according to the present invention were attached to each strand of the same tundish. Continuous casting was performed for seven or more consecutive cups (400 minutes or more) for a comparative evaluation. Among the examples, the example using the casting submerged entry nozzle according to the present invention was designated as an inventive example, and the example using the conventional casting submerged entry nozzle was designated as a comparative example. Here, the cleanliness of molten steel refers to the oxygen concentration (oxygen amount) in the molten steel. The thickness of the base metal and the alumina deposit were measured at two locations on the inner tube of the submerged entry nozzle: a location directly above the upper surface 10 of the slag layer (the upper surface of the slag layer 9) and a location directly above the discharge hole 4. The average thicknesses were used for evaluation. The sum of the thickness of the base metal and the alumina deposit was also calculated. In comparing the examples and comparative examples at each number of rows, the Ar gas flow rate was 10 L / min in all cases, the dimensions of the molten steel discharge port were 90 mm × 90 mm in side view in all cases, and the inner pipe material used as the lining material was a carbon-free material. In the examples, either an air layer or a low thermal conductive material layer was used as the insulating layer, and the insulating layer was located in the first or second region. In the comparative examples, a casting submerged entry nozzle without an insulating layer was used. The thermal conductivity of the air layer used in Examples 1 to 6 was 0.024 W / m·K, and the thermal conductivity of the low thermal conductive material layer used in Example 7 was 1.00 W / m·K. The thermal conductivity of the submerged entry nozzle refractory in Comparative Examples 1 to 5 was 23.6 W / m·K. Table 1 shows the measurement results obtained for each example and comparative example. Heat flux calculations were performed as described above.

[0049] FIG. 3 is a graph showing an example comparing the effects of a casting submerged entry nozzle according to the present invention (invention example) with those of a conventional casting submerged entry nozzle (comparison example). This graph shows the results of measuring the thickness of the base metal and alumina adhering to the wall surface (surface of the lining material) of the molten steel outlet channel of each casting submerged entry nozzle, and the results are shown as index values. The results shown in FIG. 3 were obtained under the following conditions: several dozen consecutive cups, an Ar gas flow rate of 10 L / min, a molten steel outlet dimension of 90 mm × 90 mm, and an inner tube made of alumina graphite. In the comparison shown in FIG. 3, the casting submerged entry nozzle according to the invention example used an air layer as an insulating layer, with a thickness of 1.0 mm and positioned in the second region. On the other hand, the casting submerged entry nozzle according to the comparison example did not have an insulating layer, as described above.

[0050] (Example 1) In Example 1, an insulating layer was placed in the first region, and continuous casting was performed with seven consecutive cups. An air layer was used as the insulating layer, and the thickness of the insulating layer was set to 0.1 mm. The measured thickness of the base metal deposit was 8.0 mm, and the alumina deposit thickness was 12.6 mm. Furthermore, the calculated heat flux value was 7405 W / m 2 It was.

[0051] (Example 2) In Example 2, an insulating layer was placed in the first region, and continuous casting was performed with nine consecutive passes. An air layer was used as the insulating layer, and the thickness of the insulating layer was set to 0.5 mm. The measured thickness of the base metal deposit was 5.2 mm, and the alumina deposit thickness was 9.8 mm. Furthermore, the calculated heat flux value was 6849 W / m 2 It was.

[0052] (Example 3) In Example 3, an insulating layer was placed in the first region, and continuous casting was performed with eight consecutive cups. An air layer was used as the insulating layer, and the thickness of the insulating layer was set to 1.0 mm. The measured thickness of the base metal deposit was 2.8 mm, and the alumina deposit thickness was 5.2 mm. Furthermore, the calculated heat flux value was 6262 W / m 2 It was.

[0053] (Example 4) In Example 4, an insulating layer was placed in the second region, and continuous casting was performed with eight consecutive cups. An air layer was used as the insulating layer, and the thickness of the insulating layer was set to 0.1 mm. The measured thickness of the base metal deposit was 6.2 mm, and the alumina deposit thickness was 10.3 mm. Furthermore, the calculated heat flux value was 7405 W / m 2 It was.

[0054] (Example 5) In Example 5, an insulating layer was placed in the second region, and continuous casting was performed with nine consecutive passes. An air layer was used as the insulating layer, and the thickness of the insulating layer was set to 0.5 mm. The measured thickness of the base metal deposit was 4.4 mm, and the alumina deposit thickness was 8.5 mm. Furthermore, the calculated heat flux value was 6849 W / m 2 It was.

[0055] (Example 6) In Example 6, an insulating layer was placed in the second region, and continuous casting was performed with eight consecutive cups. An air layer was used as the insulating layer, and the thickness of the insulating layer was set to 1.0 mm. The measured thickness of the base metal deposit was 1.5 mm, and the alumina deposit thickness was 5.2 mm. Furthermore, the calculated heat flux value was 6262 W / m 2 It was.

[0056] (Example 7) In Example 7, the heat insulating layer was placed in the second region, and continuous casting was performed with seven consecutive cups. A silica layer, which is a low thermal conductive material layer, was used as the heat insulating layer, and the thickness of the heat insulating layer was set to 1.0 mm. The measured thickness of the base metal deposit was 7.2 mm, and the alumina deposit thickness was 13.8 mm. Furthermore, the calculated heat flux value was 7521 W / m 2 It was.

[0057] (Comparative Example 1) In Comparative Example 1, continuous casting was performed using a casting submerged entry nozzle without a heat insulating layer, with seven passes in succession. The measured thickness of the base metal deposit was 7.3 mm, and the alumina deposit thickness was 15.3 mm. The calculated heat flux value was 7557 W / m 2 It was.

[0058] (Comparative Example 2) In Comparative Example 2, continuous casting was performed using a casting submerged entry nozzle without a heat insulating layer, with nine passes in succession. The measured thickness of the base metal deposit was 8.0 mm, and the alumina deposit thickness was 16.8 mm. The calculated heat flux value was 7557 W / m 2 It was.

[0059] (Comparative Example 3) In Comparative Example 3, continuous casting was performed using a casting submerged entry nozzle without a heat insulating layer, with eight passes in succession. The measured thickness of the base metal deposit was 8.7 mm, and the thickness of the alumina deposit was 15.5 mm. The calculated heat flux value was 7557 W / m 2 It was.

[0060] Comparative Example 4 In Comparative Example 4, continuous casting was performed using a casting submerged entry nozzle without a heat insulating layer, with eight passes in succession. The measured thickness of the base metal deposit was 8.7 mm, and the alumina deposit thickness was 15.2 mm. The calculated heat flux value was 7557 W / m 2 It was.

[0061] (Comparative Example 5) In Comparative Example 5, continuous casting was performed using a casting submerged entry nozzle without a heat insulating layer, with nine passes in succession. The measured thickness of the base metal deposit was 8.6 mm, and the thickness of the alumina deposit was 16.6 mm. The calculated heat flux value was 7557 W / m 2 It was.

[0062] [Table 1]

[0063] As is clear from the results shown in Table 1, in Comparative Examples 1 to 5, the thickness of the base metal deposition was 10.2 mm to 12.6 mm, and the thickness of the alumina deposition on top of that was 21.3 mm to 24.5 mm, whereas in Invention Examples 1 to 7, the base metal layer and the alumina layer on top of that were reduced by 20% or more.

[0064] Furthermore, as described above, in the Examples of the present invention, continuous casting was carried out using a two-strand facility, with the casting submerged entry nozzle according to the Examples and the casting submerged entry nozzle according to the Comparative Examples attached to each strand of the same tundish. Therefore, Examples 1, 2, and 3, which used a casting submerged entry nozzle with a heat insulating layer in the first region, correspond to Comparative Examples 1, 2, and 3, respectively, and Examples 4, 5, 6, and 7, which used a casting submerged entry nozzle with a heat insulating layer in the second region, correspond to Comparative Examples 4, 5, 4, and 1, respectively. Furthermore, when the atmospheric temperature at the upper outside of the nozzle was set to 30°C, the temperature inside the nozzle was set to 1550°C, and the temperature of the nozzle outer surface (outer wall surface) was set to 700°C to 800°C, the temperature of the nozzle outer surface was reduced to 600°C to 700°C by providing an insulating layer. 4 is a scatter diagram showing the correlation between the total thickness of the base metal and the alumina deposition thickness and the heat flux in each of the invention examples and comparative examples. As is clear from FIG. 4, in the invention examples, the heat flux was 7000 W / m 2 It has become clear that when the following heat insulating layer is used, the effect of the heat insulating layer in suppressing deposition of base metal and alumina is remarkable and more preferable.

[0065] As described above, in the example of the present invention, the amount of the base metal layer attached inside the casting immersion nozzle was reduced, and as a result, the amount of the alumina layer that grew from this base metal layer was also drastically reduced. This makes it possible to improve the stability and productivity of steel casting. It also makes it possible to prevent deterioration in steel quality due to the formation of the alumina layer. Furthermore, by reducing the frequency of replacement of the casting immersion nozzle, it is expected that the production efficiency of steel will improve.

[0066] In the embodiment of the present invention, the casting submerged entry nozzle has two layers, consisting of a nozzle body and a lining material, and as described above, it is possible to form another layer on the inner surface of the lining material. In addition to the layer formed on the inner surface of the lining material, another layer may be formed on the outer surface of the nozzle body. Examples of layers formed on the outer surface of the nozzle body include a slag layer in the mold and a heat-resistant layer corresponding to the position and temperature of the molten steel. [Industrial Applicability]

[0067] The submerged entry nozzle for casting and the steel casting method using the same according to the present invention are particularly useful in preventing problems such as nozzle clogging during continuous casting by suppressing alumina deposition caused by base metal layer adhesion. This can improve the stability and productivity of steel casting, and is also expected to reduce surface and internal defects in the steel, thereby improving quality. [Explanation of symbols]

[0068] 1. Submerged Entry Nozzle for Casting 2 Nozzle body 3 Molten steel outflow channel 4 Molten steel outlet 5 Slag line material section 6 Lining material 7 Nozzle flange 8 Nozzle bottom 9 Slag layer 10 Slag layer top surface 11 Molten Steel 12 Top surface of molten steel 13 Insulation layer

Claims

1. A casting submerged entry nozzle comprising: a nozzle body, a molten steel outflow channel, a molten steel discharge port, a slag line material portion, a lining material, a nozzle flange portion, and a nozzle bottom portion, a heat insulating layer having a thickness of 0.1 mm or more and not more than half the thickness of the refractory material of the casting submerged nozzle, the heat insulating layer being provided within the nozzle body so as to surround the molten steel outflow path.

2. 2. The casting submerged entry nozzle according to claim 1, wherein the heat insulating layer is provided in a region from a lower end of the nozzle flange portion to a lower end of the slag line material portion, or in a region from the lower end of the nozzle flange portion to an upper end of the molten steel discharge port, so as to surround the molten steel outflow path within the nozzle body.

3. 2. The casting submerged entry nozzle according to claim 1, further comprising a heat insulating layer provided at the nozzle bottom.

4. 2. The casting submerged entry nozzle according to claim 1, wherein the heat insulating layer comprises at least one layer selected from the group consisting of an air layer, a low thermal conductive gas layer, and a low thermal conductive material layer.

5. 5. The casting submerged entry nozzle according to claim 4, wherein the low thermal conductive gas layer is provided within the nozzle body so as to surround the molten steel outflow path, and is formed by blowing an inert gas into a communicating gap.

6. 6. A method for casting steel using the casting submerged entry nozzle according to claim 1, wherein a decrease in the temperature of molten steel is suppressed, thereby preventing base metal from adhering to the inner tube of the nozzle body and preventing alumina from adhering to the inner tube.

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