Dipping nozzles for continuous casting and continuous casting methods for steel

Abstract

This invention provides an immersion nozzle for continuous casting capable of suppressing the entrainment of protective slag into molten steel. It is an immersion nozzle for injecting molten steel from a tundish into a mold of a continuous casting machine, characterized by comprising: a molten steel rectifying section immersed in molten steel and disposed above the molten steel surface formed inside the mold; and a tubular section extending through the molten steel rectifying section in the vertical direction and discharging molten steel into the interior of the mold. The cross-sectional shape of the molten steel rectifying section, at least within a predetermined range in the casting direction from the molten steel surface to the molten steel, is an elliptical or streamlined shape having a major axis in the width direction of the mold. The molten steel rectifying section has a continuous shape in which the ratio of the minor axis b to the major axis a in the cross-sectional shape of the outer periphery of the molten steel rectifying section is 0.95 or less. The cross-sectional shape of the outer periphery of the tubular section is circular or elliptical in the width direction of the mold, and the ratio of the length β of another axis orthogonal to one axis substantially parallel to the long side of the mold to the length α of that axis is 0.90 or more and 1.1 or less.

Description

Technical Field

[0001] This invention relates to a continuous casting immersion nozzle and a continuous casting method for steel. More specifically, it relates to a continuous casting immersion nozzle for injecting molten steel into a mold during continuous casting, and a continuous casting method for steel using the continuous casting immersion nozzle. More specifically, it relates to a continuous casting immersion nozzle capable of suppressing the entrainment of protective slag used for lubrication or similar purposes into the molten steel during continuous casting, and a continuous casting method for steel. Background Technology

[0002] When using a continuous casting machine to continuously cast molten steel, molten steel is first poured from the tundish into the mold. As the molten steel is poured into the mold, it is cooled, forming an initial solidified shell on the surface. Then, through a secondary cooling zone following the formation of the initial solidified shell, the molten steel is cooled, thereby allowing solidification to proceed into the interior of the molten steel.

[0003] In steel casting, a complex oxide known as a protective slag is continuously supplied into the mold to improve the lubrication between the initial solidified shell and the mold. After being supplied into the mold, the protective slag, which becomes molten, penetrates between the mold and the initial solidified shell.

[0004] On the other hand, molten protective slag also floats on the surface of the molten steel in the mold (the meniscus). This protective slag floating on the surface of the molten steel in the mold (the meniscus) is drawn into the molten steel flow generated inside the mold. If the protective slag drawn into the molten steel flow is captured by the initial solidification shell, it will become a surface defect when the cast steel becomes a steel product, significantly impairing the quality of the steel product.

[0005] However, various studies have been conducted to date regarding the phenomenon of mold flux being drawn into the molten steel flow generated within the mold. The main causes of this phenomenon are known to be infiltration caused by the molten steel flow at the surface (meniscus) of the mold and entrapment caused by eddies in the molten steel flow. From this perspective, methods to prevent mold flux from being drawn into the molten steel flow have been proposed, including methods based on electromagnetic brakes and methods based on the appropriate shape of the discharge orifice and inner surface of the immersion nozzle.

[0006] For example, Patent Document 1 (Japanese Patent No. 3491099) proposes a method that prevents the slag from being drawn in by applying a static magnetic field to the meniscus to apply a braking force to the molten steel and reducing the flow velocity of the meniscus.

[0007] Furthermore, Patent Document 2 proposes an impregnation nozzle that suppresses the adhesion of inclusions to the discharge hole by appropriately adjusting the aspect ratio and area of ​​the discharge hole, thereby suppressing the deflection caused by the blockage of the discharge hole and preventing the entrapment of protective slag.

[0008] In addition, a dipping nozzle is proposed in Patent Document 3 (Japanese Patent No. 6963192), which suppresses the occurrence of suction phenomenon in the discharge hole by appropriately shaping the inner tube of the dipping nozzle, and prevents the mixing of protective slag with molten steel.

[0009] Patent document 4 (Japanese Patent No. 7175513) discloses an immersion nozzle that makes the inner circumferential surface of the discharge hole spherical to make the distribution of the molten steel flow velocity from the discharge hole uniform, thereby preventing the entrapment of protective slag into the molten steel.

[0010] Patent Document 1: Japanese Patent Application Publication No. 07-314100

[0011] Patent Document 2: Japanese Patent Application Publication No. 2001-129645

[0012] Patent Document 3: Japanese Patent Application Publication No. 2021-094585

[0013] Patent Document 4: Japanese Patent Application Publication No. 2021-126663

[0014] However, the above-mentioned prior art still has the following unresolved problems. That is, the continuous casting method of steel using a static magnetic field described in Patent Document 1 requires equipment to apply a static magnetic field. Therefore, in addition to the huge cost, the average flow velocity at the meniscus is suppressed. However, in the event of a sudden high flow velocity at the meniscus caused by nozzle blockage or other reasons, the flow velocity cannot be sufficiently suppressed, and the effect of suppressing the entrapment of protective slag is insufficient.

[0015] Furthermore, the methods described in Patent Documents 2-4 for optimizing the discharge orifice and inner surface shape of the immersion nozzle can be expected to suppress the entrapment of mold flux in the early stages of casting. However, the immersion nozzles described in Patent Documents 2-4 for preventing mold flux entrapment experience considerable nozzle blockage and melting due to the discharge flow, causing deviations from the appropriate nozzle shape in the later stages of the casting process, resulting in a sudden flow of high-velocity molten steel at the meniscus. Thus, the immersion nozzles described in Patent Documents 1-4 have the problem of failing to adequately suppress the entrapment of mold flux into the molten steel. Summary of the Invention

[0016] The present invention was made in view of the above circumstances, and its object is to provide a continuous casting immersion nozzle for injecting molten steel into a continuous casting mold in continuous casting of steel, which can suppress the entrainment of protective slag into the molten steel, and a continuous casting method for steel.

[0017] To solve the aforementioned problems, the inventors conducted various experiments and discovered that by using a continuous casting immersion nozzle with a specific shape, the entrapment of protective slag into the molten steel could be suppressed, resulting in steel products with less protective slag remaining on the casting sheet. This invention is based on the above insights, and its main points are as follows.

[0018] The present invention, which advantageously solves the above-mentioned problems, relates to an immersion nozzle for continuous casting, which is an immersion nozzle for injecting molten steel from a tundish into a mold of a continuous casting machine, characterized in that...

[0019] The above-mentioned impregnation nozzle has the following features:

[0020] A molten steel straightening section, immersed in the molten steel, and disposed above the molten steel surface, protruding upwards from the molten steel surface formed inside the mold; and

[0021] The tubular section extends vertically through the molten steel rectifying section and discharges the molten steel into the interior of the mold.

[0022] The cross-sectional shape of the aforementioned molten steel straightening section, at least within a specified range from the molten steel surface in the casting direction of the molten steel, is an elliptical or streamlined shape having a major axis in the width direction of the mold.

[0023] The aforementioned molten steel rectifying section has a continuous shape in which the ratio of the minor axis b to the major axis a, i.e., (b / a), in the cross-sectional shape of the outer periphery of the aforementioned molten steel rectifying section is 0.95 or less.

[0024] The cross-sectional shape of the outer periphery of the tubular part is circular or elliptical in the width direction of the mold, and the ratio of the length β of another axis orthogonal to the length α of the first axis, which is approximately parallel to the long side of the mold, to the length α of the first axis, i.e., (β / α), is 0.90 or more and 1.1 or less.

[0025] Furthermore, it is believed that the continuous casting immersion nozzle involved in the present invention, having the aforementioned continuous shape within a range of 50 mm or more from the molten steel surface in the casting direction of the molten steel in (a) the aforementioned molten steel rectifier section, can be considered a more preferred solution.

[0026] Furthermore, the steel manufacturing method of the present invention, which advantageously solves the above-mentioned problems, is characterized in that molten steel in the tundish is injected into the mold of the continuous casting machine using the aforementioned continuous casting immersion nozzle.

[0027] According to the immersion nozzle for continuous casting of the present invention, even when a fast flow of molten steel is generated at the meniscus due to flow deviation or the like, eddy currents can be suppressed near the immersion nozzle. Therefore, not only in the early stage of the casting process, but also in the later stage of the casting process, large-scale equipment is not required to suppress the entrainment of protective slag into the molten steel. Attached Figure Description

[0028] Figure 1A This is a schematic diagram showing an example of an impregnation nozzle for continuous casting according to the present invention, and is a perspective view of the impregnation nozzle for continuous casting.

[0029] Figure 1B This is a top view of the immersion nozzle used in continuous casting.

[0030] Figure 1C This is a longitudinal sectional view taken by cutting along the centerline of the discharge hole in the tubular part of the continuous casting impregnation nozzle.

[0031] Figure 2 It is a schematic diagram illustrating the flow of molten steel within a mold using a conventional dipping nozzle.

[0032] Figure 3 This is a diagram schematically illustrating the flow state of molten steel within a mold using the immersion nozzle for continuous casting according to the present invention. Detailed Implementation

[0033] [First Implementation]

[0034] The immersion nozzle for continuous casting according to the first embodiment will be described. The immersion nozzle for continuous casting according to this embodiment is used for injecting molten steel from a tundish into a mold of a continuous casting machine. Its characteristic feature is that the immersion nozzle comprises: a molten steel rectifying section immersed in the molten steel and disposed above the molten steel surface, protruding upwards from the molten steel surface formed inside the mold; and a tubular section penetrating the molten steel rectifying section in the vertical direction and discharging the molten steel into the interior of the mold.

[0035] The cross-sectional shape of the aforementioned molten steel rectifying section, at least within a specified range from the molten steel surface to the casting direction of the molten steel, is an elliptical or streamlined shape having a major axis in the width direction of the mold. The molten steel rectifying section has a continuous shape in which the ratio of the minor axis b to the major axis a, i.e., (b / a), in the cross-sectional shape of the outer periphery of the molten steel rectifying section is 0.95 or less.

[0036] The cross-sectional shape of the outer periphery of the tubular part is circular or elliptical in the width direction of the mold, and the ratio of the length β of another axis orthogonal to the length α of the first axis, which is approximately parallel to the long side of the mold, to the length α of the first axis, i.e., (β / α), is 0.90 or more and 1.1 or less.

[0037] Generally, the semi-finished product called a steel billet, produced by continuous casting by pouring molten steel into a mold of a continuous casting machine, has a width that is more than twice its thickness; therefore, the width of the billet is exceptionally large relative to its thickness. The mold into which the molten steel is poured has a pair of long sides facing each other in the front-to-back direction and a pair of short sides facing each other in the left-to-right direction. The mold is configured such that the short sides can move inside the long sides.

[0038] The continuous casting immersion nozzle for injecting molten steel into a mold has multiple discharge holes for injecting molten steel into the mold. Multiple discharge holes can also be formed by a pair of discharge holes. A pair of discharge holes can also be formed facing the short sides of the mold, which are opposite each other in the left-right direction. The continuous casting immersion nozzle injects molten steel into the mold from the discharge holes formed facing the short sides of the mold.

[0039] Furthermore, the inventors analyzed the flow state of molten steel inside the mold. Specifically, they conducted experiments using a water model of molten steel to analyze the flow state inside the mold, numerical simulations, measurements based on sensors installed inside the mold, and analysis of castings (billets) made from the molten steel. The results demonstrated the following mechanism related to the flow of molten steel inside the mold.

[0040] First, most of the slag entrapment is caused by eddies in the molten steel generated near the immersion nozzle. Second, if the velocity of the molten steel at the meniscus near the immersion nozzle is too high, eddies in the molten steel are generated near the nozzle, and the protective slag is entrapped into the molten steel. Third, due to inclusions in the molten steel, if the nozzle becomes clogged and the flow of molten steel from one of the discharge holes formed on one side of the nozzle becomes too high, the velocity of the molten steel at the meniscus becomes even higher. Fourth, even if the discharge holes formed on the nozzle are not clogged, the velocity and direction of the molten steel discharged from the nozzle change over time. Therefore, when the velocity of the molten steel is too high and its direction is towards the meniscus, the velocity of the molten steel at the meniscus becomes even higher.

[0041] Based on this mechanism, the inventors further advanced their research and development. In order to suppress the generation of eddies near the immersion nozzle, they discovered that the cross-sectional shape of the immersion nozzle and the shape of the immersion nozzle in the casting direction are very important. That is, the reason for the generation of eddies near the immersion nozzle is that the flow velocity of molten steel around the immersion nozzle is too high, and the flow of molten steel is separated from the immersion nozzle, generating eddies next to the immersion nozzle on the downstream side of the mold.

[0042] From this technical perspective, the inventors discovered that by making the cross-sectional shape of the outer periphery of the immersion nozzle a streamlined or elliptical shape that is wide in the mold width direction, the molten steel flow near the immersion nozzle becomes smooth, thereby suppressing the generation of eddies. Hereinafter, the structure of the continuous casting immersion nozzle of this embodiment, which smooths the molten steel flow near the immersion nozzle and suppresses the generation of eddies, will be described.

[0043] <Schematic diagram of an impregnation nozzle for continuous casting>

[0044] This is a schematic diagram illustrating an example of an impregnation nozzle for continuous casting according to the present invention. Figure 1A This is a three-dimensional view of an impregnation nozzle used in continuous casting. Figure 1B This is a top view of an immersion nozzle used in continuous casting. Figure 1C This is a longitudinal sectional view taken by cutting through the centerline of the discharge hole of the continuous casting impregnation nozzle.

[0045] In addition, Figures 1A-1C In the attached diagram, reference numeral 100 is an immersion nozzle for continuous casting, 123 is a discharge hole (short side of the left mold), 124 is a discharge hole (short side of the right mold), 101 is a molten steel rectification section, 103 is a molten steel flow path, 122 is the bottom of the tubular section 102 (the bottom surface of the part below the molten steel rectification section), a is the major diameter of the molten steel rectification section 101, b is the minor diameter of the molten steel rectification section 101, α is the major diameter of the tubular section 102 below the molten steel rectification section, β is the minor diameter of the tubular section 102 below the molten steel rectification section, and h is the length of the molten steel rectification section 101 continuously along the casting direction from the position of the molten steel surface (squirting surface) 201, that is, the immersion depth of the molten steel rectification section 101 immersed in the molten steel 200.

[0046] like Figures 1A-1C As shown, the continuous casting immersion nozzle 100 of this embodiment is an immersion nozzle for injecting molten steel 200 from a tundish (not shown) into the mold 300 of a continuous casting machine. The continuous casting immersion nozzle 100 of this embodiment has a generally straight tube shape, with an inner hole 121 and a tubular portion 102 having multiple discharge holes near its bottom surface as its basic structure. Moreover, the technical feature of the continuous casting immersion nozzle 100 is that a molten steel rectifying portion 101 is added to the tubular portion 102, which is used to reduce the generation of eddies formed by the molten steel flow generated by the molten steel flow at the molten steel surface (striated surface) 201 formed inside the mold 300.

[0047] Figures 1A-1CThe continuous casting immersion nozzle 100 shown is an example of an immersion nozzle whose cross-sectional shape is elliptical on the outer periphery of the molten steel rectifying section 101 at the molten steel surface (straight surface) 201. That is, the continuous casting immersion nozzle 100 is an immersion nozzle having a molten steel rectifying section 101 and a tubular section 102, and having a pair of discharge holes symmetrically arranged around the core of the nozzle relative to the vertical direction of the tubular section 102. Furthermore, the mold 300 is composed of a short side 301, a long side 302, and a bottom side 303.

[0048] The following describes the molten steel straightening section 101 and the tubular section 102 of the immersion nozzle 100 for continuous casting.

[0049] <Steel rectifier section of immersion nozzle for continuous casting>

[0050] The continuous casting immersion nozzle 100 includes a molten steel rectifying section 101. This molten steel rectifying section 101 is immersed in molten steel 200 and is disposed above the molten steel surface 201 formed inside the mold 300. That is, a portion of the molten steel rectifying section 101 is immersed in the molten steel 200 inside the mold 300, and another portion of the molten steel rectifying section 101 is exposed from the molten steel surface (curved surface) 201 formed inside the mold 300 toward the tundish.

[0051] The molten steel rectifying section 101 only needs to have a portion immersed in the molten steel 200 and another portion exposed from the molten steel surface (curved surface) 201 formed inside the mold 300 toward the tundish. Considering the flow rate of the molten steel 200 and the changes in the molten steel surface (curved surface) 201, for example, it can be configured to expose the other portion of the molten steel rectifying section 101 within a range of 0.1 to 50 mm above the molten steel surface (curved surface) 201. In particular, considering the changes in the molten steel surface (curved surface) 201, it is preferable that the molten steel rectifying section 101 is provided at least 1.0 mm above the molten steel surface (curved surface) 201 in the tundish direction.

[0052] The molten steel straightening section 101 of the continuous casting immersion nozzle 100, at least within a predetermined range from the molten steel surface 201 to the casting direction of the molten steel 200, has a cross-sectional shape of an ellipse or streamlined shape having a major axis in the width direction of the mold 300. Here, the ellipse includes an elongated ellipse. Alternatively, it can be an elongated circle with a parallel portion having a short side of a rectangle replaced by a circular arc instead of an ellipse. Furthermore, a streamlined shape refers to a shape formed by a curve that minimizes resistance to the flow of molten steel 200 when the molten steel straightening section 101 is placed in the flow of molten steel 201 and does not generate eddies around it.

[0053] For example, in the uniform flow of molten steel 200, the streamlined front end of the molten steel rectifying section 101 can be formed into a pointed shape. Alternatively, the cross-sectional shape of the outer periphery of the molten steel rectifying section 101 can be formed into a point-symmetric and line-symmetric streamlined shape. By forming the cross-sectional shape of the outer periphery of the molten steel rectifying section 101 into a point-symmetric and line-symmetric streamlined shape, the generation of eddies formed by the molten steel flow at the molten steel surface (striate surface) 201 inside the mold 300 can be reduced, which is therefore preferable.

[0054] The molten steel rectifying section 101 has a continuous shape in which the ratio of the minor diameter b to the major diameter a in the cross-sectional shape of the outer periphery of the molten steel rectifying section 101, i.e., (b / a), is 0.95 or less. Because the ratio of the minor diameter b to the major diameter a in the cross-sectional shape of the outer periphery of the molten steel rectifying section 101 is 0.95 or less, the molten steel rectifying section 101 becomes a shape that makes fluid separation difficult even if the molten steel flow rate of the molten steel 200 is too high. The flow of the molten steel 200 will not separate from the molten steel rectifying section 101, and eddies will not be generated next to the nozzle on the downstream side in the casting direction, which is therefore preferable.

[0055] From this technical point of view, the ratio of the minor diameter b to the major diameter a in the cross-sectional shape of the outer periphery of the molten steel rectifying section 101, i.e., (b / a), can also be 0.85 or less, preferably 0.65 or less, and more preferably 0.50 or less.

[0056] The cross-sectional shape of the outer periphery of the molten steel rectifying section 101 has a continuous shape in which the ratio of the minor diameter b to the major diameter a, i.e., (b / a), is 0.95 or less, and is formed within a predetermined range below the molten steel surface (mensural surface) 201 in the casting direction of the molten steel 200. The predetermined range in which this continuous shape is formed can be appropriately set taking into account the height of the molten steel surface (mensural surface) 201 formed inside the mold 300, the flow state of the molten steel 200, etc., and is set so that the flow of the molten steel 200 will not be separated from the molten steel rectifying section 101 and eddies will not be generated on the molten steel surface next to the nozzle.

[0057] Furthermore, the cross-sectional shape of the outer periphery of the molten steel rectifying section 101 is sometimes affected by the mold flux. Therefore, it is preferable to set the outer diameter shape according to the aforementioned conditions based on the amount of loss of the molten steel rectifying section 101 in advance. Moreover, the following method is often adopted: by varying the depth of the molten steel rectifying section 101 immersed in the molten steel 200 along with the casting time, the same position of the molten steel rectifying section 101 is prevented from contacting the mold flux. Even when such a method is adopted, it is preferable to set the aforementioned conditions according to the envisioned immersion depth of the molten steel rectifying section 101 in the molten steel at the beginning and end of the casting process.

[0058] <Tubular section of immersion nozzle for continuous casting>

[0059] The continuous casting immersion nozzle 100 has a tubular portion 102 inside, through which a molten steel rectifying section 101 extends vertically. The tubular portion 102 is equivalent to an immersion nozzle composed of a generally straight tube shape. The molten steel rectifying section 101 and the tubular portion 102 can be integrally formed, or they can be formed separately and then assembled. The tubular portion 102 discharges molten steel 200 from the tundish into the interior of the mold 300. The tubular portion 102 has an upper end extending toward the tundish and a lower end extending toward the bottom edge 303 of the mold.

[0060] Here, the tubular portion 102 has a generally straight shape, and the shape of its upper end and its lower end can be approximately the same. However, the shape of the tubular portion 102 can also be slightly different, as long as the molten steel 200 supplied from the tundish flows from the upper end of the tubular portion 102 towards the multiple discharge holes formed near the bottom surface. An inner hole 121 is formed inside the tubular portion 102. A tubular portion bottom surface 122 is formed at the bottom of the tubular portion 102. The inner hole 121 formed inside the tubular portion 102 becomes a molten steel flow path 103 for the molten steel 200 injected from the upper end of the tubular portion 102 to flow to the vicinity of the tubular portion bottom surface 122 of the tubular portion 102.

[0061] Furthermore, the tubular portion 102 has a discharge hole 123 and a discharge hole 124 at its lower end as a pair of discharge holes for discharging molten steel 200 into the mold 300. The discharge hole 123 is opposite to the short mold side 301 located on the left side in the width direction of the mold 300. The discharge hole 124 is opposite to the short mold side 301 located on the right side in the width direction of the mold 300.

[0062] Molten steel 200 is injected through an inner hole 121 formed at the upper end of a tubular portion 102 that protrudes from the center of the upper surface 112 of the molten steel rectifying section 101 and is disposed in the direction of the tundish.

[0063] The inner hole 121 of the tubular portion 102 penetrates the interior 111 of the molten steel rectifying section 101 and connects from the upper end of the tubular portion 102 to the lower end of the tubular portion 102. Therefore, molten steel 200 injected from the inner hole 121 formed at the upper end of the tubular portion 102 is transported toward the bottom surface 122 of the tubular portion 102 in the casting direction via the inner hole 121 formed at the lower end of the tubular portion 102 formed inside the molten steel rectifying section 101.

[0064] Molten steel 200, transported in the casting direction from the inner hole 121 of the tubular portion 102, reaches the bottom surface 122 of the tubular portion. The molten steel 200 reaching the bottom surface 122 of the tubular portion is discharged into the interior of the mold 300 as a discharge flow 202 from the discharge holes 123 and 124 of the tubular portion 102. The molten steel 200 discharged into the interior of the mold 300 is then accumulated, thereby forming a molten steel surface (meniscus) 201 inside the mold 300.

[0065] Next, the shape of the tubular portion 102 and the discharge holes 123 and 124 formed below the tubular portion 102 will be described. If the cross-sectional shape of the outer periphery of the tubular portion 102 is formed into an elliptical or streamlined shape that is approximately the same as the cross-sectional shape of the outer periphery of the molten steel rectifying portion 101 up to the vicinity of the discharge holes 123 and 124, then the discharge direction length of the discharge holes 123 and 124 will necessarily be longer than that of a typical immersion nozzle.

[0066] Therefore, the risk of clogging of the immersion nozzles increases significantly, which not only contributes to defects caused by protective slag, but also to other steelmaking-related defects, hindering productivity.

[0067] Furthermore, when continuously casting molten steel 200 with the same casting width, compared to continuous casting of molten steel 200 using a conventional dipping nozzle, the discharge position of molten steel 200 is closer to the short side 301 of the mold 300. As a result, the discharge flow of molten steel 200 from the discharge holes 123 and 124 formed in the tubular portion 102 collides with the short side 301 of the mold at an excessively high speed. The initial solidified shell formed on the surface of the molten steel 200 dissolves again, and the thickness of the initial solidified shell is insufficient when it leaves the mold 300, resulting in a so-called "steel leakage" of molten steel 200.

[0068] Based on the above, for the continuous casting immersion nozzle 100 according to this embodiment, the cross-sectional shape of the outer periphery of the tubular portion 102 is circular or elliptical in the width direction of the mold 300, and the ratio of the length β of the other axis orthogonal to the length α of the other axis that is approximately parallel to the long side of the mold 300, i.e., (β / α), is 0.90 or more and 1.1 or less.

[0069] That is, near the discharge holes 123 and 124 of the tubular portion 102, the cross-sectional shape of the outer periphery of the tubular portion 102 is circular or elliptical in the width direction of the mold 300, and the ratio of the length β of another axis orthogonal to the length α of the first axis that is approximately parallel to the long side of the mold 300, i.e., (β / α), needs to be set to 0.90 or higher.

[0070] If the ratio of the length β of another axis orthogonal to the length α of the first axis, which is approximately parallel to the long side of the mold 300, to that first axis, i.e. (β / α), is 0.90 or higher, the risk of clogging of the impregnation nozzle will not increase. It will not only not contribute to defects caused by protective slag, but also not contribute to other steelmaking defects, and is therefore preferred.

[0071] On the other hand, if the value of (β / α) is greater than 1.1, the wall thickness of the discharge orifice flow path is too small, making it impossible to adjust the discharge flow in the vertical direction. Therefore, the upper limit of the value of (β / α) is set to below 1.1.

[0072] In addition, Figures 1A-1C In the described continuous casting immersion nozzle 100, the angles of the discharge holes 123 and 124 are approximately 90 degrees relative to the axial direction of the immersion nozzle. However, the angles, shapes, pool depths, and shapes of these discharge holes can be changed to appropriate values ​​according to the casting conditions and the required quality of the casting.

[0073] In this way, the continuous casting immersion nozzle 100 according to this embodiment has a molten steel rectifying section 101 and a tubular section 102 with a predetermined shape, so that the flow of molten steel 200 will not be separated from the molten steel rectifying section 101, and no eddy current of molten steel 200 will be generated next to the nozzle on the downstream side in the casting direction, thereby suppressing the risk of immersion nozzle blockage and inclusion adhesion.

[0074] As explained above, according to the invention of this embodiment, in the immersion nozzle used to inject molten steel into the mold for continuous casting in continuous casting of steel, the entrainment of protective slag into the molten steel can be suppressed.

[0075] [Second Implementation]

[0076] The second embodiment of the continuous casting immersion nozzle will be described. Based on the first embodiment, the continuous casting immersion nozzle of this embodiment is characterized in that the molten steel straightening section has the aforementioned continuous shape within a range of 50 mm or more from the molten steel surface in the casting direction of the molten steel. That is, the continuous shape of the continuous casting immersion nozzle of this embodiment is formed such that it is continuous for at least 50 mm from the molten steel surface (meniscus) 201 relative to the casting direction of the molten steel 200.

[0077] If the continuous shape is 50 mm or more, there is no possibility that the eddy current generated by the stripping of the molten steel 200 produced in the casting direction below which does not have the continuous shape will reach the molten steel surface (curved surface) 201 and the molten steel 200 will be entrained in the protective slag, so it is preferred.

[0078] Furthermore, the continuous shape of the molten steel rectifying section 101 is continuously formed in a manner that satisfies the condition of not covering the discharge hole 123 and the discharge hole 124.

[0079] In this way, for the continuous casting immersion nozzle 100 according to this embodiment, the eddies generated by the stripping of the molten steel 200 will not reach the molten steel surface (meniscus) 201. As a result, the continuous casting immersion nozzle 100 according to this embodiment can further suppress the entrainment of protective slag into the molten steel 200.

[0080] As explained above, according to the invention of this embodiment, it is possible to suppress the eddy currents generated by the stripping of molten steel flow in the lower part of the casting direction which does not have a continuous shape from reaching the molten steel surface (curved surface), and to prevent the entrapment of protective slag into the molten steel.

[0081] [Third Implementation]

[0082] The steel manufacturing method according to the third embodiment will be described. The steel manufacturing method according to this embodiment is characterized by using the continuous casting immersion nozzle according to the above embodiments to manufacture steel. First, in the steel manufacturing method according to this embodiment, the continuous casting immersion nozzle 100 according to this embodiment is provided at the bottom of the tundish.

[0083] Next, the tundish is positioned above the mold 300 such that the immersion nozzle 100 for continuous casting is located approximately at the center of the space formed by the mold 300. Thus, in the steel manufacturing method according to this embodiment, the components required for continuous casting of molten steel, namely the tundish, the immersion nozzle 100 for continuous casting, and the mold 300 for continuous casting, are prepared and configured.

[0084] Furthermore, in the steel manufacturing method according to this embodiment, molten steel 200 is poured from a ladle containing molten steel 200 smelted in a refining furnace such as a converter into an intermediate ladle, while molten steel 200 is poured from the intermediate ladle into a mold 300 via a continuous casting dipping nozzle 100. The molten steel 200 is injected into the mold 300 via the continuous casting dipping nozzle 100, thereby accumulating inside the mold 300. Through the accumulation of the molten steel 200 inside the mold 300, a molten steel surface (meniscus) 201 is formed inside the mold 300.

[0085] In the continuous casting of molten steel 200, a protective slag is supplied to the molten steel 200 that has been poured into the mold 300. The protective slag, supplied to the mold 300 and in a molten state, penetrates into the initial solidified shell formed inside the mold 300 due to the cooling of the molten steel 200. On the other hand, a portion of the protective slag supplied to the mold 300 and in a molten state floats on the surface (meniscus) 201 of the molten steel in the mold 300.

[0086] Furthermore, when the protective slag is injected into the mold 300, inert gases such as argon and nitrogen can also be blown into the molten steel 200 supplied to the molten steel 200 and flowing down the molten steel flow path 103 of the continuous casting immersion nozzle 100 via the sliding nozzle, the upper nozzle, etc.

[0087] Figure 2 This diagram schematically illustrates the flow state of molten steel within a mold when casting molten steel using a conventional dipping nozzle. Here, in Figure 2 In the figure, reference numeral 301 is the short side of the continuous casting mold, reference numeral 201 is the molten steel surface (equivalent to a meniscus), reference numeral 202 is the discharge flow from the discharge hole 123, reference numeral 203 is the branched upward flow formed by the branch of the discharge flow 202 from the discharge hole, reference numeral 204 is the meniscus flow, reference numeral 205 is the stripping flow generated from the stripping point along the immersion nozzle, and reference numeral 206 is the vortex of molten steel 200 formed in the stripping flow.

[0088] like Figure 2 As shown, it can be understood that the discharge flow of molten steel 200 from the immersion nozzle 400 varies over time, and the discharge flow 202 of molten steel 200 from the discharge hole 124 on the right side becomes stronger. The discharge flow 202 of molten steel 200 is in a state of obliquely deep immersion in the casting direction.

[0089] On the other hand, the discharge flow 202 from the left discharge hole 123, compared to the discharge flow 202 from the right discharge hole 124, is directed upwards (towards the tundish side) and, after colliding with the short side 301 of the continuous casting mold, becomes a flow toward the molten steel surface (mensural surface) 201. Furthermore, after reaching the molten steel surface (mensural surface) 201, the discharge flow 202 from the left discharge hole 123 becomes a mensural flow 204 toward the immersion nozzle 400. At this time, no mensural flow 204 is generated on the right side of the discharge hole 124; instead, a mensural flow 204 is generated from the left side of the immersion nozzle 400 toward the right side.

[0090] In this way, when using Figure 2In the case of casting molten steel 200 using a conventional immersion nozzle 400, a stripping flow 205 is generated at the stripping point of the meniscus flow 204 due to the stripping of the discharge flow 202 from the discharge orifice 123 of the immersion nozzle 400. As a result, the discharge flow 202 is disrupted on the right side of the immersion nozzle 400 due to the stripping flow 205, leading to the formation of a vortex 206 by the molten steel 200. The protective slag floating on the surface (meniscus) 201 of the molten steel is entrained by this vortex 206, deteriorating the quality of the steel product.

[0091] Figure 3 This diagram schematically illustrates the flow state of molten steel within a mold when casting molten steel using a continuous casting immersion nozzle. Furthermore, Figure 3 The reference numerals shown in the figures are consistent with... Figure 2 The reference numerals shown are identical, with reference numeral 207 indicating the flow of molten steel 200 behind the nozzle that has not been stripped away.

[0092] like Figure 3 As shown, when casting molten steel 200 using the continuous casting immersion nozzle 100 according to this embodiment, no peeling from the immersion nozzle occurs in the discharge flow 202 flowing left and right of the immersion nozzle 100.

[0093] Furthermore, depending on the conditions during continuous casting of molten steel 200, even if peeling occurs from the molten steel flow of the continuous casting dipping nozzle 100 in the left and right flow of molten steel 200, it is minimal, and the frequency of vortex generation 206 is drastically reduced. Moreover, when casting molten steel 200 using the continuous casting dipping nozzle 100, the elliptical portion in the casting direction is also formed into a continuous shape ensuring a specified length, thus suppressing the generation of peeling flow 205 and vortex 206 caused by the molten steel flow of molten steel 200 below the molten steel surface (mensural surface) 201 and facing the same direction as the molten steel surface (mensural surface) 201.

[0094] Furthermore, in the continuous casting of molten steel 200, it is known that the discharge holes 123 and 124 of the continuous casting immersion nozzle 100 become clogged with inclusions and other contaminants as the pouring time progresses. If a blockage occurs near one of the discharge holes 123 and 124 of the continuous casting immersion nozzle 100, a large amount of molten steel 200 is discharged from only one side of the discharge hole. Since a large amount of molten steel 200 is discharged from only one side of the discharge hole, the flow velocity of the molten steel towards the molten steel surface (meniscus) 201 increases, thus becoming an important factor in the entrainment of protective slag.

[0095] However, when casting molten steel 200 using the continuous casting dipping nozzle 100, even if the discharge holes 123 and 124 of the continuous casting dipping nozzle 100 become blocked by inclusions or the like, the entrapment of protective slag into the molten steel 200 can be suppressed. That is, by using the continuous casting dipping nozzle 100 according to the above embodiment to continuously cast molten steel 200, steel products such as casting sheets with excellent surface quality and suppressed entrapment of protective slag can be obtained.

[0096] Furthermore, in recent years, during continuous casting operations of molten steel, magnetic fields are applied to the molten steel within the continuous casting mold to control its flow and suppress the trapping of inclusions in the casting. Even when casting molten steel 200 using the continuous casting immersion nozzle 100 described in this embodiment, a static magnetic field can be applied to the discharge stream to suppress the intrusion of inclusions. Even when a rotating magnetic field is applied to impart a cleaning effect for flushing inclusions, the effect of the present invention will not be affected, and therefore, there is no problem in using both methods.

[0097] In this way, according to the steel manufacturing method of this embodiment, the molten steel 200 is continuously cast by using the immersion nozzle 100 for continuous casting according to the above embodiment, so that the protective slag entrained by the molten steel flow is not captured by the initial solidification shell, and will not become a surface defect when the cast molten steel 200 becomes a steel product, and will not damage the quality of the steel product.

[0098] As explained above, according to the invention of this embodiment, most of the eddies generated on the lateral side of the immersion nozzle for continuous casting that determine the entrapment of mold flux can be suppressed. Therefore, according to the steel manufacturing method of this embodiment, the entrapment of mold flux can be stably prevented, and castings with excellent surface quality can be obtained.

[0099] [Other Implementation Methods]

[0100] The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above embodiments. Various modifications that can be understood by those skilled in the art can be made regarding the structure and details of the present invention within the technical scope of the present invention. Furthermore, systems or apparatuses that arbitrarily combine the various features included in the various embodiments are also included within the technical scope of the present invention.

[0101] Example

[0102] The effects of the present invention will be specifically described below based on embodiments, but the present invention is not limited to these embodiments.

[0103] <Example 1 of the Invention>

[0104] In a live continuous casting machine for steel billets, continuous casting operation was carried out using the immersion nozzle for continuous casting described in this invention. The cross-sectional dimensions of the continuously cast billets were 220-260 mm thick and 1000-2000 mm wide. Furthermore, argon was used as the inert gas blown into the immersion nozzle for continuous casting, and the optimal protective slag was selected and added to the meniscus based on the billet drawing speed and steel grade.

[0105] (Design specifications for impregnation nozzles for continuous casting)

[0106] The continuous casting immersion nozzle according to the present invention was manufactured, and steel was manufactured using the manufactured continuous casting immersion nozzle. In Example 1 of the invention, the cross-sectional shape of the outer tube, i.e., the molten steel immersion section, of the continuous casting immersion nozzle was set to an elliptical shape. Furthermore, in Example 1 of the invention, when the major diameter of the outer circumference of the elliptical outer tube was set to a and its minor diameter to b, the ratio of them, i.e., (b / a), was set to 0.91, the distance h of the continuous elliptical shape from the meniscus position along the casting direction of the molten steel was set to 50 mm, and when the major diameter of the outer tube of the tubular section below the molten steel rectifier was set to α and its minor diameter to β, the ratio of them, i.e., (β / α), was set to 1.0 to manufacture the continuous casting immersion nozzle.

[0107] (Evaluation of steel products and manufacturing processes)

[0108] Using the immersion nozzle for continuous casting manufactured in Invention Example 1, the molten steel flow rate was set to 3.4 ton / min, thereby casting the molten steel to produce steel products. In Invention Example 1, the continuous casting mold used was a mold without a magnetic field generating device. The steel billet casting produced by the billet continuous casting machine was hot-rolled to produce hot-rolled steel sheets. Surface defects caused by mold flux on the hot-rolled steel sheets were investigated, and the mold flux remaining on the casting sheets was evaluated based on these surface defects. That is, the lower the defect index of the steel product, the less mold flux remaining on the casting sheets.

[0109] Furthermore, the following structure is employed: In the casting of molten steel, the thickness of the solidified shell inside the mold is inferred based on the temperature behavior of the thermocouple on the short side of the mold. If the thickness is below a threshold, the risk of steel leakage increases, and an alarm is triggered. Therefore, in Invention Example 1, the presence or absence of a steel leakage alarm is also evaluated as part of the assessment of the operability of continuous casting.

[0110] In this way, the evaluation of steel products is based on the defect indicators of the steel products. Furthermore, the manufacturing method of the steel using the immersion nozzle for continuous casting manufactured in Invention Example 1 was evaluated based on the presence or absence of a steel leakage alarm. Table 1 shows the evaluation results of the design of the immersion nozzle for continuous casting, the steel products, and the manufacturing process of Invention Example 1.

[0111] <Examples 2-4 of the invention>

[0112] Except for changing the cross-sectional shape of the outer tube (i.e., the molten steel immersion part) of the continuous casting immersion nozzle, the ratio (b / a) when the major diameter of the outer tube is set to a and the minor diameter is set to b, the distance (h) of the continuous elliptical shape from the meniscus position along the casting direction of the molten steel, and the ratio (β / α) when the major diameter of the outer circumference of the tubular part is set to α and the minor diameter is set to β, the continuous casting immersion nozzle was manufactured in the same manner as in Invention Example 1.

[0113] Furthermore, using the continuous casting immersion nozzles manufactured in Examples 2-4, steel products were manufactured by casting molten steel in the same manner as in Example 1, except for changing the molten steel flow rate. In addition, the steel products manufactured in Examples 2-4 and the method for manufacturing steel using the manufactured continuous casting immersion nozzles were evaluated in the same manner as in Example 1. Table 1 shows the evaluation results of the design of the continuous casting immersion nozzles, the steel products, and the manufacturing process of Examples 2-4.

[0114] <Comparative Examples 1-4>

[0115] To compare with Invention Examples 1-4, the design of the continuous casting dipping nozzle was modified, and the continuous casting dipping nozzles of Comparative Examples 1-4 were manufactured. Casting was performed using the continuous casting dipping nozzles manufactured in Comparative Examples 1-4. That is, except that casting was performed using the continuous casting dipping nozzles manufactured in Comparative Examples 1-4, the molten steel was cast under the same conditions as in the Invention Examples. In addition, the steel products manufactured in Comparative Examples 1-4 and the manufacturing method of the steel using the manufactured continuous casting dipping nozzles were evaluated in the same manner as in Invention Example 1. Table 1 shows the evaluation results of the design of the continuous casting dipping nozzles of Comparative Examples 1-4, the steel products, and the manufacturing process.

[0116] As shown in Table 1, the design specifications of the immersion nozzles for continuous casting manufactured in Comparative Examples 1 to 4 are as follows.

[0117] Comparative Example 1: A continuous casting impregnation nozzle that satisfies the relationship (b / a) > 0.95

[0118] Comparative Example 2: A continuous casting immersion nozzle that satisfies the relationship (b / a) ≤ 0.95 and h < 50 mm

[0119] Comparative Example 3: A continuous casting immersion nozzle satisfying the relationships (b / a) ≤ 0.95, h ≥ 50 mm, and (β / α) < 0.9.

[0120] Comparative Example 4: A continuous casting immersion nozzle satisfying the relationships (b / a) ≤ 0.95, h ≥ 50 mm, and (β / α) > 1.1.

[0121]

[0122] Table 1 shows the operating conditions and results. Comparing Invention Examples 1-4 with Comparative Examples 1-1-1-3, the defect index of the steel products of Invention Examples 1-4 was significantly improved. Furthermore, in Comparative Examples 2-1 and 2-2, although improvements were observed compared to Comparative Examples 1-1-1-3, they were not sufficient. In Comparative Examples 3-1 and 3-2, the quality of the steel products was good, but a steel leakage alarm was triggered in the latter half of the casting process, thus halting the casting.

[0123] Furthermore, in Comparative Example 3-2, a leakage alarm was triggered at the initial stage of casting, causing the casting to be stopped. Consequently, a suitable casting for use as a steel product could not be obtained, making it impossible to evaluate the quality of the steel product. In Comparative Examples 4-1 and 4-2, although good steel product quality, comparable to Invention Examples 1-4, was obtained, the inner tube of the dipping nozzle became clogged with inclusions during casting, causing the casting to stop. Therefore, it is evident that by applying the continuous casting dipping nozzle according to this invention, the defect index of steel products can be significantly reduced, and stable manufacturing operations can be achieved.

[0124] Industrial availability

[0125] The immersion nozzle for continuous casting according to the present invention can suppress the generation of eddies near the immersion nozzle and suppress the entrapment of protective slag, thus enabling the production of steel products such as castings with excellent surface quality, and enabling stable operation of continuous casting of molten steel. Therefore, it is helpful to the development of related industries such as ironmaking and is useful in industry.

[0126] Explanation of reference numerals in the attached figures

[0127] 100…Immersion nozzle for continuous casting; 101…Steel rectifier section; 102…Tube section (below the steel rectifier section); 103…Steel flow path; 111…Lower surface of rectifier section; 112…Upper surface of rectifier section; 121…Inner hole; 122…Bottom surface of tubular section (below the steel rectifier section); 123…Discharge hole (left short side of the mold); 124…Discharge hole (right short side of the mold); 200…Steel; 201…Steel surface (curved surface); 202…Discharge flow; 20 3… Branching upward flow; 204… Curved surface flow; 205… Stripping flow; 206… Vortex (molten steel); 207… Backflow; 300… Mold; 301… Short side of mold; 302… Long side of mold; 303… Bottom side of mold; 400… Immersion nozzle (existing); a… Long diameter of molten steel rectifying section; b… Short diameter of molten steel rectifying section; α… Diameter of tubular section (one axis); β… Diameter of tubular section (the other axis); h… Length of the continuous rectifying section from the molten steel surface (curved surface) towards the casting direction.

Claims

1. A continuous casting immersion nozzle, used for injecting molten steel from a tundish into a mold of a continuous casting machine, characterized in that, The impregnation nozzle has the following features: A molten steel straightening section is immersed in the molten steel and is disposed above the molten steel surface, which is exposed above the molten steel surface formed inside the mold. and The tubular section extends vertically through the molten steel rectifying section and discharges the molten steel into the interior of the mold. The cross-sectional shape of the molten steel rectifying section is, at least within a specified range from the molten steel surface in the casting direction of the molten steel, an elliptical or streamlined shape having a major axis in the width direction of the mold. The molten steel rectifying section has a continuous shape in which the ratio of the minor axis b to the major axis a, i.e., (b / a), in the cross-sectional shape of the outer periphery of the molten steel rectifying section is 0.95 or less. The cross-sectional shape of the outer periphery of the tubular portion is circular or elliptical in the width direction of the mold, and the ratio of the length β of another axis orthogonal to the length α of the first axis, which is approximately parallel to the long side of the mold, to the length α of the first axis, i.e., (β / α), is 0.90 or more and 1.1 or less.

2. The immersion nozzle for continuous casting according to claim 1, characterized in that, The molten steel rectifying section has the continuous shape within a range of 50 mm or more from the molten steel surface in the casting direction of the molten steel.

3. A continuous casting method for steel, characterized in that, Molten steel in the tundish is injected into the mold for continuous casting using the immersion nozzle for continuous casting as described in claim 1 or 2.

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