JP2005246442A - Immersion nozzle for continuous casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an immersion nozzle capable of suppressing the deposition of alumina even when reducing the blowing quantity of nitrogen gas and Ar gas to be blown into a molten metal pouring hole or without blowing the gas such as the nitrogen gas or the Ar gas in a continuous casting. <P>SOLUTION: In the immersion nozzle nozzle for continuous casting provided with one pair of spouting holes 4, 4 symmetrical to the axis of the immersion nozzle 1 on a side wall part 2, the bottom surface level at the position, where the surface passing through the center positions of two spouting holes and parallel to the axis in the longitudinal direction of the immersion nozzle is crossed to the inner surface at the bottom part 3 of the immersion nozzle, is made highest, and the bottom surface level at the position, where the surface crossed orthogonally to the straight line connecting the center position of the two spouting hole and passing through the axis of the immersion nozzle is crossed to the inner surface on the side wall part of the immersion nozzle, is made lowest, thereby inclining the inner surface at the bottom part of the immersion nozzle. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a continuous casting immersion nozzle used for injecting molten steel into a mold in continuous casting of steel.

In continuous casting of steel, aluminum killed steel is mainly cast. Aluminum killed steel is manufactured by deoxidizing molten steel that has been oxidatively decarburized and refined in a converter or the like, and removing oxygen in the molten steel that has been increased by oxidative decarburization and refining. The alumina particles (Al ₂ O ₃ particles) generated in this deoxidation process are removed from the molten steel based on the density difference between the molten steel and alumina, but the ascending speed of the fine alumina particles of several tens of μm or less is extremely slow. Since separation takes a long time, it is difficult to completely float and separate such fine alumina particles in an actual process, and fine alumina particles remain suspended in the aluminum killed molten steel. .

  By the way, in continuous casting of steel, when pouring molten steel from a tundish to a mold, pouring is performed using a refractory nozzle such as an immersion nozzle, a sliding nozzle and an upper nozzle. The characteristics required for these nozzles are excellent thermal shock resistance and resistance to erosion to mold powder and molten steel. Therefore, refractories made of alumina or alumina-graphite that are excellent in these characteristics are widely used. Yes. However, when aluminum killed steel is cast using an alumina or graphite-nozzle nozzle, there is a problem in that the alumina particles suspended in the molten steel adhere to and accumulate on the inner wall surface of the nozzle, causing nozzle clogging. . In particular, it is known that nozzle clogging is likely to occur with an alumina-graphite immersion nozzle.

  When the immersion nozzle is blocked, various problems occur in the casting operation and the slab quality. For example, the slab drawing speed has to be reduced, and not only the productivity is lowered, but in a severe case, the casting operation itself must be stopped. In addition, when the alumina particles deposited and coarsened on the inner wall surface of the nozzle, such as an immersion nozzle, suddenly peel off and are discharged into the mold, and become trapped by the solidified shell in the mold, a product defect occurs, resulting in a decrease in product yield. Leads to.

  Therefore, in order to prevent these problems, normally, when continuously casting aluminum killed steel, nitrogen gas or the like is formed inside the molten steel outflow hole from the tundish to the mold, which is constituted by an immersion nozzle or a sliding nozzle. Non-oxidizing gas or rare gas such as Ar gas is blown in, and the inner wall surface of the molten steel outflow hole is forcibly washed with these gases to prevent adhesion and deposition of alumina on the inner wall surface of the molten steel outflow hole such as an immersion nozzle. There are many ways to do this. However, all of the injected gas does not float in the mold, and a part of the gas is trapped in the solidified shell as gas bubbles. Since most gas bubbles coexist with inclusions, the trapped gas bubbles may become surface defects after rolling. Therefore, the structure or material of the immersion nozzle is changed to prevent the alumina from adhering in order to prevent the alumina from adhering even if the gas injection amount is small or no gas injection is performed. Many have been proposed.

For example, Patent Document 1 proposes an immersion nozzle in which a spiral groove or protrusion is provided on the inner wall surface of the immersion nozzle, thereby preventing alumina adhesion by a swirling flow formed in the internal hole of the immersion nozzle. Japanese Patent Application Laid-Open No. H10-228688 discloses an immersion nozzle in which an inverted trapezoidal protrusion that extends downward from the center of the upper end of the discharge hole is provided in the discharge hole in order to previously close the region of the discharge hole that is expected to slow down the flow. main component but have been proposed, also, Patent Document 3, the surface portion of the inner bore of the immersion nozzle in contact with molten steel, reacts with alumina in molten steel CaO · ZrO ₂ quality to produce low-melting compounds An immersion nozzle composed of a refractory material is proposed.
JP-A-57-130745 JP-A-2-169160 Japanese Patent Laid-Open No. 4-94851

  However, in the above Patent Documents 1 and 2, the effect of preventing the adhesion of alumina is not sufficient, and there are still many points to be improved. On the other hand, the method of Patent Document 3 prevents the adhesion of alumina, but the inner wall of the immersion nozzle Since it melts and reacts with alumina to produce a low melting point compound, the oxide inclusions in the molten steel itself increase, and the cleanliness of the slab deteriorates. Therefore, although the problem of quality deterioration due to gas bubbles trapped in the solidified shell has not been solved yet, blowing of gas such as nitrogen gas or Ar gas into the molten steel outflow hole such as an immersion nozzle is the main measure for preventing alumina adhesion It is the actual situation that is done as.

  The present invention has been made in view of the above circumstances, and the object of the present invention is to reduce the amount of nitrogen gas or Ar gas blown into the molten steel outflow hole such as the inner hole of the immersion nozzle, or nitrogen gas. It is an object of the present invention to provide an immersion nozzle capable of suppressing the adhesion of alumina to the immersion nozzle without blowing a gas such as Ar gas.

  The present inventors have intensively studied and studied in order to solve the above problems. The results of the examination and research are explained below.

  In order to solve the above-mentioned problem, first, in which part of the immersion nozzle the amount of alumina adhered was investigated in the immersion nozzle used for casting of the slab continuous casting machine. The used immersion nozzle is a normal immersion nozzle having a bottom part and having a pair of discharge holes in the side wall part. As a result, the position perpendicular to the straight line connecting both discharge holes, that is, 90 ° farthest in the circumferential direction of each immersion nozzle from the center position of both discharge holes when viewed in the cross section of the immersion nozzle. It was found that the alumina adhesion was intense on the inner wall surface at the position (hereinafter also referred to as “anti-discharge hole position”).

  In order to investigate this cause, a water model experiment was conducted using an immersion nozzle having the same shape as the immersion nozzle used in the actual machine, and the flow in the internal hole of the immersion nozzle was investigated. As a result, it was confirmed that stagnation of the flow occurred on the side of the side wall surface of the immersion nozzle at the position opposite to the ejection holes. Due to this stagnation of the flow, it was judged that the adhesion of alumina became intense.

  It is assumed that the molten steel that has flowed down the internal hole of the immersion nozzle flows toward the discharge hole at the bottom of the immersion nozzle, and the flow velocity at the position opposite to the discharge hole decreases. In order to eliminate the stagnation of the flow at the position of the anti-discharge hole, it was considered to use the flow generated by colliding with the bottom of the immersion nozzle.

  First, a conventional immersion nozzle was investigated by a water model experiment. Conventionally, the inner surface shape of the bottom of an immersion nozzle having a bottom is the same as a pool shape having a flat, flat bottom surface as shown in FIG. 5, or the same as the gradient of the discharge holes as shown in FIG. A mountain shape that is inclined toward the discharge hole with a gradient of is adopted. 5 and 6, 1 is an immersion nozzle, 2 is a side wall portion, 3 is a bottom portion, 4 is a discharge hole, 5 is an internal hole, and 6 is a slag line portion.

  In the case of the chevron shape shown in FIG. 6, the molten steel that has collided with the bottom 3 of the immersion nozzle 1 flows in the direction of the discharge hole 4 along the gradient of the bottom 3 without disturbing the flow. It was found that the flow stagnation at the location was particularly significant. In the case of the pool shape shown in FIG. 5, the molten steel that has collided with the bottom portion 3 is reversed to form an upward flow (hereinafter referred to as “reversed flow”). It was found that the direction of the flow was random and the turbulent flow was formed in the vicinity of the discharge hole 5 by the reverse flow, and the reverse flow was not formed so as to eliminate the stagnation of the flow at the counter discharge hole position.

  Therefore, in order to positively form a reverse flow at the position of the anti-discharge hole, as shown in FIG. 1 (detailed description of FIG. 1 will be described later), the position of the anti-discharge hole on the bottom inner surface is low and two discharge holes The inner surface of the bottom portion was inclined and inclined so that the position connecting the center positions of the two was higher. As a result, since the reverse flow is formed along the inclination of the inner surface of the bottom, it was confirmed that the reverse flow becomes a flow toward the counter discharge hole position and the flow velocity of the reverse flow increases. Thereby, it was confirmed that the stagnation of the flow at the counter discharge hole position was eliminated.

  The present invention has been made on the basis of the above examination and research results, and the continuous casting immersion nozzle according to the present invention includes a pair of discharge holes which are symmetrical with respect to the axis of the immersion nozzle in the side wall portion. In the continuous casting immersion nozzle, the bottom surface at the position where the surface passing through the central position of the two discharge holes and parallel to the longitudinal axis of the immersion nozzle intersects with the inner surface of the bottom of the immersion nozzle is the highest, The bottom of the immersion nozzle so that the bottom surface at the position where the plane intersecting the straight line connecting the center positions of the two discharge holes and passing through the axis of the immersion nozzle intersects with the inner surface of the sidewall of the immersion nozzle is the lowest. It is characterized in that the inner surface is inclined.

  According to the present invention, since the bottom surface of the immersion nozzle is inclined so that the position of the anti-discharge hole is low, the molten steel that has flowed down the internal hole of the immersion nozzle and collided with the inner surface of the bottom is inclined on the inner surface. A reversal flow directed to the anti-discharge hole position is formed along this line, the molten steel flow velocity at the anti-discharge hole position is increased by this reverse flow, and the stagnation of the flow at the anti-discharge hole position is eliminated. Adhesion of alumina on the side wall surface at the discharge hole position is suppressed. As a result, continuous casting over multiple heats can be carried out with the same immersion nozzle, and the slab quality is reduced by reducing the basic unit of tundish refractories and reducing the amount of gas blown into the internal holes of the immersion nozzle. And the like, and an industrially beneficial effect is achieved.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. 1-3 is a figure which shows embodiment of this invention, Comprising: FIG. 1 is a side schematic diagram which shows an example of the immersion nozzle for continuous casting which concerns on this invention, FIG. 2 is X- of FIG. FIG. 3 is a schematic side view as viewed from the arrow X ′, and FIG. 3 is a schematic plan view as viewed from the arrow YY ′ in FIG. 1.

As shown in FIGS. 1 to 3, the immersion nozzle 1 for continuous casting according to the present invention includes a cylindrical side wall portion 2 and a bottom portion 3 positioned below the side wall portion 2. The inner surface side becomes an internal hole 5 having an open upper end for flowing the molten steel, and the lower part of the side wall 2 communicates with the internal hole 5 so that the molten steel flowing down the internal hole 5 flows out into the mold. A pair of discharge holes 4 is provided. The two discharge holes 4 are symmetric with respect to the longitudinal axis of the immersion nozzle 1 as an axis. On the outer periphery of the side wall portion 2, a slag line portion 6 made of a refractory material having excellent corrosion resistance against slag is provided at a position corresponding to a range in contact with the mold powder. As a refractory material having excellent corrosion resistance against slag, for example, ZrO ₂ -graphite refractory can be used.

  On the inner surface of the bottom 3, the position of the center line facing the direction of both discharge holes 4, 4 is the highest, a position 90 ° away from each discharge hole 4, 4 in the circumferential direction of the immersion nozzle 1, That is, the inclined surface 7 is provided so that the anti-discharge hole position is the lowest. That is, the bottom surface at the position where the surface passing through the center position of the two discharge holes 4 and 4 and parallel to the longitudinal axis of the immersion nozzle 1 intersects with the inner surface of the bottom portion 3 is the highest. The immersion nozzle 1 is arranged such that the bottom surface at the position where the plane perpendicular to the straight line connecting the center positions of the holes 4 and 4 and passing through the axis of the immersion nozzle 1 intersects the inner surface of the side wall 2 is the lowest. The inner surface of the bottom 3 is inclined. In the figure, the highest position of the inclined surface 7 is indicated by a vertex 7a.

  In this case, in FIGS. 1 to 3, the inclined surface 7 and the side wall portion 2 intersect at an acute angle, but a curvature is applied to this portion so that a smooth flow from the inclined surface 7 to the side wall portion 2 is formed. Also good. 1 to 3, the gradient of the inclined surface 7 is constant. However, the gradient on the apex 7 a side may be increased and gradually decreased toward the side wall 2. The gradient of the inclined surface 7 may be any degree, but it may be at most about 45 ° with respect to the horizontal direction. However, if the height difference between the vertex 7a and the lowest position is small, the effect of the present invention is reduced. Therefore, it is preferable to set the gradient so as to ensure a height difference of 3 mm or more. Further, in FIGS. 1 to 3, the position of the vertex 7 a is vertically lower than the position of the discharge hole 4 on the inner surface side of the side wall portion 2, but at the same level as the position of the discharge hole 4 or from the position of the discharge hole 4. May also be set vertically upward. Furthermore, although the vertex 7a is inclined on both sides, a horizontal surface portion may be installed at the portion of the vertex 7a.

  When the immersion nozzle 1 is molded, the inner hole 5 is molded by inserting the core, that is, the shape of the inner surface of the bottom portion 3 is formed by the shape of the tip of the core. By processing the shape along the above, a bottom surface having a desired shape can be obtained. The material of the immersion nozzle 1 may be any refractory material, and for example, conventional alumina-graphite, alumina-spinel, and alumina may be used.

  In the immersion nozzle 1 according to the present invention having such a configuration, the molten steel flowing down the inner hole 5 collides with the inclined surface 7 of the bottom portion 3, and a reverse flow along the inclined surface 7 is formed. , 4 from 90 ° in the circumferential direction of the immersion nozzle 1, that is, the reverse flow flowing toward the counter discharge hole position increases, and the counter discharge hole position is forcibly agitated by the reverse flow. The stagnation of the molten steel at the position opposite to the discharge hole is eliminated. For this reason, alumina adhesion at the anti-discharge hole position where alumina adhesion was particularly severe is suppressed, and the casting possible time of the immersion nozzle 1 can be dramatically extended. Moreover, since the coarsening due to the adhesion and deposition of alumina particles in the internal hole 5 of the immersion nozzle 1 can be prevented, the large inclusions in the slab caused by the exfoliation of the coarsened alumina can be greatly reduced. it can.

  4, in a two-strand slab continuous casting machine, the immersion nozzle according to the present invention shown in FIG. 1 is installed on one strand, and the pool-shaped conventional immersion nozzle shown in FIG. 5 is installed on the other strand. Then, the investigation result of the amount of alumina adhered at the position of the anti-discharge hole when the low carbon aluminum killed steel is continuously cast for 5 heats is shown. In the immersion nozzle according to the present invention, the height difference between the apex 7a and the lowest position was 15 mm. As is clear from FIG. 4, it was confirmed that the amount of alumina deposited was significantly reduced in the immersion nozzle according to the present invention.

  During casting, it is preferable to blow a non-oxidizing gas such as nitrogen gas or a rare gas such as Ar gas into the molten steel flowing down in the internal hole 5. By blowing these gases, the adhesion of alumina is further suppressed. The present invention is not limited to the above description, and various modifications can be made. For example, in the immersion nozzle 1 described above, the discharge hole 4 is downward with respect to the horizontal direction, but the direction of the discharge hole 4 may be horizontal or upward, and the shape of the discharge hole 4 is rectangular. The shape of the discharge hole 4 may be elliptical or circular.

It is a figure which shows embodiment of this invention, Comprising: It is a side schematic diagram which shows an example of the immersion nozzle for continuous casting which concerns on this invention. FIG. 2 is a schematic side view taken along line X-X ′ in FIG. 1. FIG. 2 is a schematic plan view taken along the arrow Y-Y ′ in FIG. 1. It is a figure which compares and shows the alumina adhesion amount with the immersion nozzle which concerns on this invention, and the conventional immersion nozzle. It is a side schematic diagram of the conventional immersion nozzle whose bottom is a pool shape. It is the side surface schematic diagram of the conventional immersion nozzle whose bottom part is a mountain shape.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Submerged nozzle 2 Side wall part 3 Bottom part 4 Discharge hole 5 Internal hole 6 Slag line part 7 Inclined surface 7a Vertex

Claims (1)

  In a continuous casting immersion nozzle having a pair of discharge holes that are symmetrical to the axis of the immersion nozzle in the side wall portion, it passes through the center position of the two discharge holes and is parallel to the longitudinal axis of the immersion nozzle. The bottom surface at the position where the surface and the inner surface of the bottom of the immersion nozzle intersect is the highest, the surface orthogonal to the straight line connecting the center positions of the two discharge holes and passing through the axis of the immersion nozzle, An immersion nozzle for continuous casting, wherein the inner surface of the bottom portion of the immersion nozzle is inclined so that the bottom surface at the position where the inner surface intersects is lowest.

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