JP4673719B2 - Dipping nozzle for continuous casting and method for continuous casting of steel - Google Patents

Description

  The present invention relates to an immersion nozzle for continuous casting and a continuous casting method for steel.

  In continuous casting of molten metal such as molten steel, an immersion nozzle attached to the bottom of the continuous casting tundish is placed in the mold, and the molten metal is injected into the mold from the lower end of the immersion nozzle. The portion in contact with the solidified to form a solidified shell, which is successively drawn out into a roll band below the mold, and solidification proceeds. Finally, solidification is completed and a slab is obtained.

  The immersion nozzle has a bottomed cylindrical shape, and a discharge hole for discharging the molten metal into the mold is disposed at the bottom of the side wall. In continuous casting of slabs and blooms, two discharge holes are arranged in an axially symmetrical position in the cylinder of the nozzle so as to discharge the molten metal in the width direction of the slab. Hereinafter, the two discharge holes are also referred to as left and right discharge holes.

  The molten metal supplied from the tundish through the immersion nozzle into the mold flows out from the left and right discharge holes into the mold. The flow rate of the molten metal flowing out from the left and right discharge holes is large, and the molten metal flow collides with the solidified shell located on the side wall of the mold and is divided into an upward flow and a downward flow. If the flow velocity of the downward flow is too high, the downward flow penetrates deeply into the molten metal, and inclusions and argon bubbles associated with the downward flow cannot be lifted and caught by the solidified shell, resulting in slab inclusion defects and bubble defects. become. On the other hand, when the flow rate of the upward flow is too large, the upward flow becomes a meniscus reversal flow at the meniscus in the mold. When a stirring flow is caused in the molten metal in the mold by electromagnetic stirring in the mold, a sufficient stirring flow cannot be obtained at the collision portion between the stirring flow and the meniscus reversal flow.

  A nozzle having a slit 3 that opens to the outside downward is known at the bottom of the immersion nozzle (FIG. 10). The slit 3 is opened by connecting the cylindrical bottom portion 4 and the bottom portions 6 of the left and right discharge holes. Since the molten metal flowing out into the mold through the immersion nozzle also flows out from the slit 3 in addition to the left and right discharge holes 2, the flow velocity of the molten metal flowing out from the discharge holes 2 can be relatively reduced, and the downflow and rise The flow velocity is also reduced. As a result of the reduction of the flow velocity of the downward flow, inclusions and argon bubbles that penetrate deeply into the molten metal along with the downward flow can be reduced. As a result of the reduction in the flow velocity of the upward flow, it is possible to reduce the quality defect caused by the fluctuation of the molten metal in the molten metal meniscus in the mold, and to reduce the adverse effect on the stirring flow due to the electromagnetic stirring in the mold. In this way, the immersion nozzle having two discharge holes and slits is hereinafter also referred to as “dispersion nozzle”.

  In Patent Documents 1 and 2, by using an immersion nozzle having a discharge hole and a slit as described above, the downward flow in the mold is reduced, and interference between the stirring flow and the meniscus reversal flow by electromagnetic stirring in the mold is further reduced. The point which can be made small is described.

  During the molten metal injection, nonmetallic inclusions are likely to deposit and adhere to the surface in contact with the molten metal inside the immersion nozzle. The same applies to an immersion nozzle having a slit. If non-metallic inclusions adhere to the vicinity of the slit, the slit becomes thin or clogged. In Patent Document 3, the shape of the inner surface of the bottom of the immersion nozzle is a surface inclined toward the side wall at an inclination angle of 30 ° or more with respect to the horizontal starting from the slit, so that the slit is formed during casting. It is said that it is possible to sufficiently prevent thinning or blockage.

JP 2001-205396 A Japanese Patent Laid-Open No. 2003-25048 Japanese Patent Laid-Open No. 2000-126849

  In the immersion nozzle having two discharge holes and slits, the molten metal flowing out from the immersion nozzle has a uniform melt flow in any direction from the lower side of the immersion nozzle to the discharge hole opening direction. It is desirable to do. This is because if the molten metal flow is directed only in a specific direction, the flow velocity in that direction is increased, and the flow toward the deep part of the molten metal and the discharge flow from the discharge holes are increased. However, when a water model experiment was performed on the molten metal flow in the mold, as shown in FIG. 11B, when the conventional dispersion nozzle was used, the downward flow 37 and the opening of the discharge hole directed downward of the immersion nozzle were used. A phenomenon was observed in which the discharge flow 34 directed in the direction was large, the flow in the oblique direction between the downward flow 37 and the discharge flow 34 was reduced, and the downward flow 37 and the discharge flow 34 were discontinuous. In this case, the effect using the dispersion nozzle cannot be sufficiently exhibited.

  A tundish stopper or a sliding nozzle is used for the purpose of adjusting the flow rate of the molten metal from the tundish through the immersion nozzle. When the sliding nozzle is used, if the sliding nozzle opening area is reduced in order to reduce the molten metal flow rate, the opening part is displaced from the central axis of the immersion nozzle. When a water model experiment was performed on the molten metal flow in the mold, as shown in FIGS. 12D and 12F, when the conventional dispersion nozzle was used, the opening portion of the sliding nozzle was displaced from the central axis of the immersion nozzle. In some cases, it was found that the direction of the discharge flow 34 from the discharge hole is shifted 39 from the discharge hole opening direction. This causes a problem that the flow velocity of the discharge flow does not decrease and collides with the long side to cause non-uniform growth of the solidified shell, or the upward flow strongly swings the meniscus.

  The surface of the molten metal in the mold is coated with continuous casting powder. The powder becomes molten powder depending on the temperature of the molten metal, fills the space between the mold and the solidified shell, promotes lubrication of both, and floats in the molten metal in the mold. It has a function of adsorbing metal inclusions and removing them from the system. When the flow near the molten metal surface is disturbed, molten powder covering the molten metal surface is entrained in the molten metal and is taken into the solidified shell as it is, causing a slab defect. Accordingly, it is necessary to keep the vicinity of the molten metal surface in the mold as small as possible. When a water model experiment was performed on the molten metal flow in the mold, it was found that the powder on the molten metal surface might be sucked into the discharge hole of the immersion nozzle. The powder sucked into the discharge hole is discharged immediately after being discharged into the discharge flow, and when it reaches the deep part of the molten metal, it is trapped by the solidified shell and causes a slab defect.

  In the present invention, in continuous casting using an immersion nozzle having two discharge holes and a slit, the downward flow in the mold and the discharge flow are not discontinuous, and even when a sliding nozzle is used, the discharge hole It is an object of the present invention to provide an immersion nozzle that does not cause a deviation in the direction of the molten metal flow.

  Another object of the present invention is to provide an immersion nozzle in which molten powder covering the molten metal surface is not sucked into the discharge hole in continuous casting using an immersion nozzle having two discharge holes and a slit.

That is, the gist of the present invention is as follows.
(1) It has a bottomed cylindrical shape, and two discharge holes 2 are arranged in a cylindrically symmetrical position at the lower part of the cylindrical side wall, and the cylindrical bottom part 4 and the bottom parts 6 of both discharge holes are connected to the outside. An opening slit 3 is provided, and a portion of the cylindrical bottom 4 in contact with the slit 3 is inclined upward toward the cylindrical side wall 5, and a portion of the discharge hole bottom 6 in contact with the slit 3 is upward toward the discharge hole side wall 7. An immersion nozzle for continuous casting characterized in that there is substantially no step between the surface formed by the cylindrical bottom portion 4 and the surface formed by the discharge hole bottom portion 6.
(2) The inclination angle θ ₁ toward the cylindrical side wall 5 at the portion in contact with the slit 3 in the cylindrical bottom 4 and the inclination angle θ ₂ toward the discharge hole side wall 7 in the portion in contact with the slit 3 at the discharge hole bottom 6 are 30 ° upward. It is the above, The immersion nozzle for continuous casting as described in said (1) characterized by the above-mentioned.
(3) The continuous contact casting according to (1) or (2) above, wherein the portion in contact with the cylindrical side wall 5 at the discharge hole top 8 forms a curved surface that smoothly contacts the cylindrical side wall 5. Immersion nozzle.
(4) Any one of the above (1) to (3), characterized in that an orifice portion 21 having an opening cross-sectional area smaller than the opening cross-sectional area of the cylinder is provided between the nozzle upper end and the discharge hole 2. An immersion nozzle for continuous casting according to claim 1.
(5) The immersion nozzle for continuous casting according to any one of the above (1) to (4), wherein ribs 22 are provided to connect between both side surfaces of the slit 3.
(6) The opening width of the slit 3 is in the range of 0.15 to 0.40 times the square root of the discharge hole opening cross-sectional area, as described in any one of (1) to (5) above Immersion nozzle for continuous casting.
(7) A part or the whole of the cylindrical side surface 7 and the bottom 4, the discharge hole 2 and the slit 3 in contact with the molten metal is made of carbonless spinel, magnesia graphite, zirconia graphite, or silicaless alumina graphite. An immersion nozzle for continuous casting as described in any one of (1) to (6) above.
(8) Using the immersion nozzle for continuous casting according to any one of (1) to (7) above, C: 0.01% or less, Si: 1% or less, Mn: 3% or less, P: 0.15% or less, S: 0.05% or less, Al: 0.015% or less, Ti: 0.005% or more and 0.3% or less, REM: 0.001% or more, Ca: 0.0004 % Or less, N: 0.004% or less, and casting a slab composed of the remaining Fe and inevitable impurities.

  The present invention relates to an immersion nozzle having two discharge holes and a slit, wherein a portion in contact with the slit in the bottom of the cylinder and a portion in contact with the slit in the bottom of the discharge hole are inclined upward, and the surface formed by the bottom of the cylinder and the discharge Since there is substantially no step between the surface formed by the bottom of the hole, the downward flow in the mold and the discharge flow can be continued, and even when a sliding nozzle is used, the discharge flow from the discharge hole Does not cause a gap.

  According to the present invention, in the immersion nozzle having two discharge holes and a slit, the portion of the top of the discharge hole that is in contact with the side wall of the cylinder forms a curved surface that smoothly contacts the side wall of the cylinder. Peeling that occurs at the top of the resin is reduced, so that suction of molten powder into the discharge holes is eliminated.

  The behavior of the molten metal injected into the mold through the immersion nozzle was confirmed by a water model experiment. As an actual continuous casting apparatus, a 1/2 water model experimental apparatus was used assuming a slab width of 1500 mm and a thickness of 250 mm. The liquid phase part from the meniscus to 5.8 m was reproduced in actual size. Hereinafter, the “actual size” means a size at 1/1 scale.

  Various types of immersion nozzles having two discharge holes 2 and slits 3 were used as the immersion nozzle 1. In addition, the molten metal behavior was also investigated when the sliding nozzle plate 29 was half open and the sliding nozzle opening was displaced from the axial center of the immersion nozzle. In the inner cylinder of the immersion nozzle, the entire length is not filled with the molten metal. Therefore, an air blowing port is provided on the upper part of the immersion nozzle so that the molten metal filling length in the immersion nozzle is the same as that in casting of the actual molten steel. In addition, since the molten metal flow due to electromagnetic stirring in the mold is reproduced, a swirling flow can be generated in the mold by the stirring blade.

  First, it was evaluated to what depth the liquid flow flowing out of the immersion nozzle 1 penetrates into the mold. Bubbles are mixed in the liquid flowing out from the discharge hole 2 and the slit 3 of the immersion nozzle 1 into the mold. If the depth at which this bubble penetrates is measured and compared for each immersion nozzle type, the penetration depth of the liquid can be relatively compared.

As the immersion nozzle 1 of the example of the present invention, the type shown in FIG. 2 and the type shown in FIG. 6 were used. Each of the types shown in FIGS. 2 and 6 is provided with a slit 3 that opens to the outside by connecting the cylindrical bottom portion 4 and the bottom portions 6 of both discharge holes, and the portion of the cylindrical bottom portion 4 that contacts the slit 3 faces the cylindrical side wall 5. The portion that is inclined upward and is in contact with the slit 3 in the discharge hole bottom 6 is inclined upward toward the discharge hole sidewall 7, and the surface formed by the cylindrical bottom 4 and the surface formed by the discharge hole bottom 6 There is no step between them. 2 and 6, the outer diameter of the immersion nozzle is 153 mm, the inner diameter of the cylindrical portion is 85 mm, the sectional area of the discharge hole 2 is 2820 mm ² , and the height of the slit 3 is as shown in FIGS. It is 30 mm, the width is 15 mm, and the inclination angle θ is 45 °. In the case shown in FIG. 6, the portion of the discharge hole top 8 that is in contact with the cylindrical side wall 5 is in smooth contact with the cylindrical side wall 5 with a curved surface 11 having a curvature radius of 60 mm.

  Moreover, the type shown in FIG. 10 was used as the immersion nozzle of the comparative example. The type shown in FIG. 10 is the same as the type shown in FIGS. 2 and 6 in that the slit 3 that opens to the outside by connecting the cylindrical bottom part 4 and the bottom parts 6 of both discharge holes is provided. The portion of the discharge hole bottom 6 that contacts the slit 3 is not inclined upward toward the discharge hole sidewall 7, and a step 13 is formed between the surface formed by the cylindrical bottom 4 and the surface formed by the discharge hole bottom 6. Have. The dimensions of the immersion nozzle shown in FIG. 10 are actual, the outer diameter of the immersion nozzle, the inner diameter of the cylindrical portion, the cross-sectional area of the discharge hole, the slit width is 30 mm, the step 13 is 28 mm, and the slit height is 30 mm. .

  The liquid flow in the liquid filling the mold was evaluated based on the behavior of bubbles mixed in the liquid flowing out from the immersion nozzle. The result is shown in FIG. In the comparative example of FIG. 10 type, as shown in FIG. 11B, the downward flow 36 is large, and the flow toward the angle between the discharge flow 34 and the downward flow 37 is less than that. On the other hand, in the present invention examples of FIGS. 2 and 6, as shown in FIG. 11A, the flow toward the angle between the discharge flow 34 and the downward flow 37 increases, whereby the discharge flow 34 and the downward flow are increased. 37 formed a continuous flow, and as a result, the arrival position of bubbles carried downward by the downward flow 36 and the downward flow 37 became shallow. Although the slit width in the comparative example of FIG. 10 type was double that of the example of the present invention, the arrival position of the bubbles carried downward by the downward flow 37 was almost the same. The bubble arrival position reached only 2/3 of the depth of the present invention example shown in FIGS. 2 and 6 compared to the comparative example shown in FIG. The type shown in FIG. 2 and the type shown in FIG.

  Next, the effect of the opening position of the sliding nozzle plate 29 located immediately above the immersion nozzle on the molten metal flow was evaluated by a water model test. As shown in FIGS. 12A, 12C, and 12E, a plate simulating the sliding nozzle plate 29 is inserted above the immersion nozzle, and the sliding nozzle opening position is arranged so as to deviate from the axial center of the immersion nozzle 1. . In (a) and (c), the opening position is shifted to the left side of the figure, and in (e), the opening position is shifted to the right side of the figure. About the used immersion nozzle, (a) uses the example of the present invention shown in FIG. 6, and (c) and (e) use the comparative example shown in FIG.

  It was evaluated whether or not the discharge flow 34 flowing out from the discharge hole 2 of the immersion nozzle 1 has a deviation 39 with respect to the long side 30 of the mold when the mold is viewed from above. In addition, it was also confirmed whether or not the vortex 38 was present in the immersion nozzle.

  In the comparative example shown in FIG. 12C (the sliding nozzle opening position shifts to the left in the figure), a clockwise vortex 38 is generated in the immersion nozzle, and the discharge is performed as shown in FIG. 12D. A shift 39 occurred in the flow 34. Further, in the comparative example shown in (e) (the sliding nozzle opening position shifts to the right in the figure), a counterclockwise vortex 38 is generated in the immersion nozzle, as shown in FIG. 12 (f). A deviation 39 occurred in the discharge flow 34. On the other hand, in the example of the present invention shown in FIG. 12 (a), although the opening position of the sliding nozzle is shifted to the left side of the drawing, the generation of the vortex 38 is not observed in the immersion nozzle, Further, as shown in FIG. 12B, the occurrence of the shift 39 in the discharge flow 34 was not observed.

  As described above, as a result of the water model experiment, in the immersion nozzle provided with the slit 3 that opens to the outside by connecting the cylindrical bottom portion 4 and the bottom portions 6 of both discharge holes, the slit 3 in the cylindrical bottom portion 4 and the discharge hole bottom portion 6 When the contact portions are inclined, and there is no step between the surface formed by the cylindrical bottom portion 4 and the surface formed by the discharge hole bottom portion 6, the cylindrical bottom portion 4 and the discharge hole bottom portion 6 are not inclined. Furthermore, compared with the case where the step 13 exists, there is an effect of preventing the molten metal flowing out from the immersion nozzle from entering deep into the mold, and the opening of the sliding nozzle plate is shifted from the axis of the immersion nozzle. It was also revealed that the discharge flow was kept normal.

  Furthermore, the presence or absence of a phenomenon in which the molten powder on the surface of the molten metal in the mold was sucked into the discharge hole was evaluated by a water model experiment. The water model experiment apparatus used is the same as that described above. The immersion nozzle type shown in FIGS. 2 and 6 is used, and the dimensions are the same as those used in the water model experiment.

  First, a water model test was performed using an immersion nozzle of the type shown in FIG.

  Bubbles are mixed in the discharge flow 34 flowing into the mold from the immersion nozzle 1. These bubbles are floating as the molten metal flows in the mold. It has been found that a phenomenon occurs in which bubbles included in the molten metal near the upper portion of the discharge hole 2 are sucked into the discharge hole 2. The backflow of bubbles into the discharge hole 2 suggests that a negative pressure portion exists inside the discharge hole 2. If a non-smooth corner exists in the liquid flow path in the submerged nozzle, separation may occur in the liquid flow at the corner, resulting in a negative pressure. As a non-smooth corner of the liquid flow path in the immersion nozzle, there is a portion in contact with the cylindrical side wall 5 at the top 8 of the discharge hole.

  Therefore, as shown in FIG. 6, an immersion nozzle in which a portion in contact with the cylindrical side wall 5 at the discharge hole top portion 8 forms a curved surface 11 smoothly in contact with the cylindrical side wall was prototyped. By making the liquid flow path into the smooth curved surface 11 in this way, it is difficult for the liquid flow to be peeled off and negative pressure to be hardly generated.

  When a water model experiment was performed using an immersion nozzle of the type shown in FIG. 3, the phenomenon that bubbles included in the molten metal near the upper portion of the discharge hole 2 was sucked into the discharge hole 2 was not observed.

  Next, a layer of silicon oil (specific gravity 0.97) as a molten powder was formed on the surface of the molten metal in the mold of the water model experimental apparatus. The layer thickness is 10 mm in actual size. The surface of the molten metal in the mold was intentionally disturbed to create a situation where the molten powder sinks to the vicinity of the discharge hole 2. As shown in FIG. 13, when the experiment was performed using the immersion nozzle shown in FIGS. 2 and 6, in the type shown in FIG. 2, the powder sucked into the discharge hole 2 by the molten powder that has entered the vicinity of the discharge hole 2. 40 occurrences were seen. The molten powder sucked into the discharge hole 2 is trapped in a deep portion of the slab along with the discharge flow 34 and is likely to become a slab internal defect. On the other hand, in the type shown in FIG. 6, the molten powder that has entered the vicinity of the discharge hole 2 was not sucked into the discharge hole 2.

  As is apparent from the above water model experiment, as shown in FIG. 6, by using an immersion nozzle in which the portion in contact with the cylindrical side wall 5 in the discharge hole top 8 forms a curved surface 11 that smoothly contacts the cylindrical side wall, It is possible to prevent the powder sucking phenomenon into the hole 2 and to prevent the occurrence of defects inside the slab.

Next, the relationship between the bubble penetration depth into the molten metal and the width of the slit 3 was confirmed by a water model experiment. The type shown in FIG. 6 was used as the immersion nozzle type. In the actual size conversion, the discharge hole opening cross-sectional area was 2820 mm ² , and the width of the slit 3 was changed in the range of 10 to 30 mm, and the bubble penetration depth into the molten metal was evaluated. A type having no slit was also evaluated. The liquid discharge speed (actual size conversion) from the immersion nozzle was set to two types, 714 L / min and 571 L / min.

FIG. 14 shows the evaluation results. The horizontal axis is expressed as slit width / (discharge hole opening cross-sectional area) ^1/2 . The plot with 0 on the horizontal axis is an evaluation result of a type having no slit. As apparent from FIG. 14, the shape of the immersion nozzle of the present invention, that is, the portions in contact with the slit 3 in the cylindrical bottom portion 4 and the discharge hole bottom portion 6 are inclined, and the surface formed by the cylindrical bottom portion 4 and the discharge hole bottom portion 6. In the shape having no step with respect to the surface formed, the opening range of the slit has a preferable range in which the bubble penetration depth is minimized within the range of 0.40 times or less the square root of the discharge hole opening cross-sectional area. Exists.

  When actually determining the slit width, it is necessary to consider the adhesion of non-metallic inclusions. The narrower the slit width, the more likely the clogging of the slit due to the adhesion of non-metallic inclusions occurs. Therefore, it is preferable to select the widest possible width within the range where the bubble penetration depth is minimized. If the opening width of the slit is 0.15 times or more the square root of the discharge hole opening cross-sectional area, it is preferable because inclusions hardly adhere to the slit portion in actual casting.

  Here, a preferred embodiment of the immersion nozzle of the present invention will be described.

In the immersion nozzle 1 of the present invention provided with a slit 3 that opens to the outside by connecting the cylindrical bottom 4 and the bottom 6 of both discharge holes, the portion of the cylindrical bottom 4 that contacts the slit 3 is inclined upward toward the cylindrical side wall 5. The tilt angle θ is the tilt angle θ, and the portion of the discharge hole bottom 6 that is in contact with the slit 3 is set to the same tilt angle θ. In order to distinguish the two, the inclination angle of the cylindrical bottom portion 4 is the inclination angle θ ₁ , and the inclination angle of the discharge hole bottom portion 6 is the inclination angle θ ₂ (see FIG. 2).

  A preferable range of the inclination angle θ is 30 to 60 °. When the inclination angle θ is less than 30 °, a vortex in the nozzle such as the vortex 38 may be generated. On the other hand, when the inclination angle θ exceeds 60 °, the top of the discharge hole approaches the meniscus, which is disadvantageous for powder entrainment. The inclination angle θ is more preferably 40 ° or more.

Although it is preferable to match the inclination angle of the cylindrical bottom 4 theta ₁ and the inclination angle theta ₂ of the discharge hole bottom 6 may not necessarily coincide. When θ ₁ and θ ₂ are different, the difference between the two is preferably 10 ° or less.

  If the surface of the cylindrical bottom part 4 and the surface of the discharge hole bottom part 6 are formed as the same plane as shown in FIG. 2, the shape of the immersion nozzle becomes simple, which is preferable. On the other hand, as shown in FIG. 3, the surface of the cylindrical bottom portion 4 and the surface of the discharge hole bottom portion 6 may be in contact with each other at an angle as long as no step is provided on the joint surface. As shown in FIG. 3, if the direction of the discharge hole bottom 6 is inclined in a direction that decreases toward the outer periphery of the immersion nozzle, the direction of the molten metal discharge flow from the discharge hole is combined with the inclination of the discharge hole top 8. It becomes possible to adjust suitably.

  The step between the surface formed by the cylindrical bottom portion 4 and the surface formed by the discharge hole bottom portion 6 is not required to have a substantial step, and the step does not necessarily have to be completely zero. As shown in FIG. 4, the effects of the present invention can be exhibited even when a slight level difference 12 exists. The phrase “substantially not having a step” is sufficient as long as the step does not impair the continuity of the discharge flow 34 and the downward flow 37. More specifically, if the step is about 5 mm or less, the effect of the present invention can be exhibited.

The cross-sectional shape of the discharge hole 2 is preferably a home base shape as shown in FIGS. On the other hand, as shown in FIG. 5, the cross-sectional shape of the discharge hole 2 may be a shape based on a cylinder or a curved surface. The surface of the cylindrical bottom 4 can also be a curved surface. In this case, the inclination angle theta ₁ of the cylindrical bottom part 4, the inclination angle theta ₂ of the discharge hole bottom 6, a cylindrical bottom portion 4 or the discharge hole bottom 6 each may be decided to use the average inclination angle in the vicinity of contact with the slit 4 .

  As described above using the results of the water model experiment, it is preferable that the portion in contact with the cylindrical side wall 5 in the discharge hole top 8 forms the curved surface 11 that smoothly contacts the cylindrical side wall 5. Thereby, the molten metal flow can be made difficult to peel off from the discharge hole top portion 8 in the vicinity of the top portion of the discharge hole 2, the powder entrainment into the discharge hole 2 can be prevented, and the entrained powder rides on the discharge flow and becomes a slab. It can be prevented from being wrapped inside.

  As the shape of the curved surface 11, the curvature radius R that smoothly connects the discharge hole top 8 and the side wall 5 is determined by the wall thickness t and the discharge angle φ as shown in FIG. If φ is small, there is a problem in the strength of the material, but since R can be increased, it is advantageous for preventing flow separation. For example, in the case of φ = 45 °, it is preferable that the radius of curvature R is 50 to 100 mm.

  In the immersion nozzle of the present invention, as shown in FIG. 7, it is preferable to form an orifice portion 21 having an opening cross-sectional area smaller than the opening cross-sectional area of the cylinder between the upper end of the nozzle and the discharge hole. By forming the orifice portion 21, the generation of the vortex 38 in the immersion nozzle is further reduced with respect to the molten metal flow in the immersion nozzle and the mold when the opening of the sliding nozzle plate is shifted from the axis of the immersion nozzle. In addition, the occurrence of the deviation 39 of the discharge flow 34 in the mold can be further reduced.

  The shape of the orifice may be a shape that is concentric with the axis of the immersion nozzle and has a narrowed inner diameter. The inner diameter of the orifice part may be about 0.7 to 0.9 times the inner diameter of the part other than the orifice part. If it is less than 0.7 times, the diameter is too thin and the molten metal flow is hindered. If it exceeds 0.9 times, the effect of forming the orifice portion cannot be exhibited.

  The position in the vertical direction in the immersion nozzle that forms the orifice portion 21 is preferably arranged at a site corresponding to the meniscus of the immersion nozzle length.

  In the immersion nozzle having a slit, when the flow rate of the molten metal is increased, the force to push and widen the slit increases. In particular, when the inclination angle θ is provided as in the present invention, the force for expanding the slit is further increased.

  In the immersion nozzle of the present invention, as shown in FIG. 8, it is preferable to form ribs 22 that connect between both side surfaces of the slit 3. As a result of having the ribs 22, even when the force for expanding the slit is increased, the immersion nozzle 1 can be prevented from being deformed or broken.

  The most commonly used immersion nozzle material for continuous casting is alumina graphite. This is because alumina graphite has a feature that combines the high fire resistance of alumina with the low molten steel wettability of graphite, and has good corrosion resistance to molten steel. For the part (powder line) that is on the outer periphery of the immersion nozzle and that is in contact with the molten powder, a material having excellent melt resistance even when in contact with the molten powder, for example, zirconia graphite may be used.

  In normal molten steel continuous casting, particularly in Al-killed steel continuous casting, non-metallic inclusions are deposited inside the alumina graphite immersion nozzle, and problems such as blocking of discharge holes and slits are likely to occur. On the contrary, depending on the component of the molten metal, the nozzle made of alumina graphite may be eroded and the inside of the nozzle may be melted during casting. In the immersion nozzle for continuous casting according to the present invention, a part or all of the cylindrical side surface and the bottom, the discharge hole and the surface of the slit in contact with the molten metal are carbonless spinel, low carbon spinel, magnesia graphite, zirconia graphite, silicaless. It is preferable to use any material of alumina graphite. Any material of carbonless spinel, low carbon spinel, magnesia graphite, zirconia graphite, and silicaless alumina graphite is collectively referred to herein as “high melting resistance refractory 23”.

  FIG. 9 shows an example in which the side surface 5 and the bottom of the cylinder of the immersion nozzle, the entire surface of the discharge hole 2 and the slit 3 in contact with the molten metal are used as the material of the high fusing resistance refractory 23. For other portions of the immersion nozzle, alumina graphite is usually used as the refractory 24. In FIG. 9, the part where irregular hatching is applied is the part where the high melting resistance refractory 23 is exposed, and the part where the irregular hatching and oblique hatching overlap is a cross section of the part where the high melting resistance refractory 23 is used. It is. On the other hand, the part where hatching is not performed is a part where the refractory 24 is normally exposed, and the part where only oblique hatching is performed is a cross section of the part where the refractory 24 is used.

Among the high melting resistance refractories 23, carbonless spinel is a material that is made of a spinel (MgO · Al ₂ O ₃ ) material excellent in chemical wear and excluding carbon that causes physical wear. Carbon spinel is obtained by adding a small amount (about 10% or less) of graphite for the purpose of supplementing the spall property of the carbonless spinel material. Magnesia graphite is a material made of magnesia, which has a high melting point and excellent corrosion resistance, and is made up of graphite, which is a defect of magnesia, and is made of graphite. The silica-less alumina graphite is a material that excludes silica added to supplement the spall resistance in the alumina graphite brick to improve the corrosion resistance.

  The immersion nozzle for continuous casting of the present invention described above can be used in continuous casting of all metals including steel. The effect of steel can be exerted in any component system that is normally continuously cast.

  The immersion nozzle of the present invention is, in mass%, C: 0.01% or less, Si: 1% or less, Mn: 3% or less, P: 0.15% or less, S: 0.05% or less, Al: 0.00%. 015% or less, Ti: 0.005% or more and 0.3% or less, REM: 0.001% or more, Ca: 0.0004% or less, N: 0.004% or less, and the balance is Fe and inevitable impurities. It can also be used for continuous casting of slabs. Continuous casting of steel with such components is effective against nozzle clogging because there is little adhesion of non-metallic inclusions to the nozzle during continuous casting, and surface defects due to clustered inclusions are unlikely to occur. Since product defects such as press cracks caused by objects are not easily generated, a slab for producing a thin steel sheet having good surface properties and internal quality can be provided.

  Here, the reason for limiting the steel components will be described.

  C is set to 0.01% by mass or less in order to be applied to a highly workable thin steel sheet that requires strict characteristics in both surface properties and internal quality. More preferably, it is 0.005 mass% or less.

  Si has the effect of strengthening the steel and may be contained in an appropriate amount depending on the required strength, but if it exceeds 1% by mass, the deep drawability deteriorates, so it is 1% by mass or less. Si may not be contained.

  About Mn, there exists an effect | action which strengthens steel and it may contain a suitable quantity according to required intensity | strength, but since deep drawability will fall when it exceeds 3 mass%, it shall be 3 mass% or less.

  P has an effect of strengthening the steel and may contain an appropriate amount depending on the required strength, but if it exceeds 0.15% by mass, the deep drawability deteriorates, so it is made 0.15% by mass or less.

  Regarding S, if it exceeds 0.05% by mass, the S concentration in the non-metallic inclusion becomes 5% by mass or more and causes nozzle clogging.

If the Al concentration exceeds 0.015% by mass, the Al ₂ O ₃ concentration in the nonmetallic inclusions becomes too high, causing nozzle clogging and deterioration of the surface properties of the steel sheet. .

  As for Ti, if it is less than 0.005% by mass, the Ti concentration is too small and the deoxidation is insufficient, and the surface properties of the steel sheet deteriorate. If the Ti concentration exceeds 0.3% by mass, the amount of Ti oxide produced is too large, and the thin steel plate is hardened to deteriorate the workability. Therefore, the content is set to 0.005% or more and 0.3% or less.

  Further, REM is contained to control the composition of nonmetallic inclusions in the molten steel. At this time, the REM concentration should be 0.001% by mass or more. If it is less than 0.001% by mass, the REM concentration in the non-metallic inclusions is insufficient and the predetermined performance cannot be obtained.

  If Ca exceeds 0.0004 mass%, the CaO concentration in the nonmetallic inclusions becomes too high and causes press cracking, so the content is made 0.0004 mass% or less.

  N lowers the workability, so is 0.004% by mass or less. More preferably, it is 0.002 mass% or less.

  Moreover, you may add Nb: 0.1 mass% or less, B: 0.05 mass% or less, and Mo: 1 mass% or less as needed.

  Nb is an element effective for refining crystal grains of a steel sheet, and is effective in improving the deep drawability of a thin steel sheet. However, if added over 0.1% by mass, there is a possibility of causing a problem that the deformation resistance of the steel is remarkably increased.

  By adding B, secondary work embrittlement when deep drawing or the like is performed can be prevented. However, if added over 0.05% by mass, there is a possibility of causing a problem that the deformation resistance of the steel is remarkably increased.

  By adding Mo, the tensile strength of the steel can be increased. However, even if added over 1% by mass, the effect is saturated, and Mo is an expensive element, and even when added from the viewpoint of cost reduction, the content is made 1% by mass or less.

  Moreover, you may add Ni, Cu, and Cr in the range of 1 mass% or less as needed. When these elements are added, the corrosion resistance of the steel sheet can be improved. However, even if added in excess of 1% by mass, the effect is saturated, and in some cases, it may cause surface flaws in the manufactured slab.

  When continuous casting of molten steel having the components described above is performed, adhesion of non-metallic inclusions to the immersion nozzle is prevented, while the inner surface of the immersion nozzle made of alumina graphite is eroded during casting and continuous with a sufficient life. Casting may not be possible. Therefore, in applying the immersion nozzle of the present invention in continuous casting of molten steel having the above components, as shown in FIG. 9, the side surface 5 of the cylinder and the surface of the bottom portion 4, the discharge hole 2 and the slit 3 are in contact with the molten metal. It is preferable to use an immersion nozzle using the high melting damage resistant refractory 23 in part or all. As a result, adhesion of non-metallic inclusions to the immersion nozzle can be prevented, and at the same time, melting damage of the immersion nozzle can be prevented, and a steel plate with good quality can be provided while using the immersion nozzle for a long time. It becomes possible to manufacture a slab.

  Steel was continuously cast using a vertical bending slab continuous casting machine (vertical length 2.5 m) using the immersion nozzle of the present invention. The slab thickness is 240 mm, the slab width is 1000 to 2000 mm, and the ladle capacity is 300 tons.

  As the varieties to be cast, varieties 1 (mass% C: 0.01% or less, Si: 0.05% or less, Mn: 0.5% or less, P: 0.15% or less, S: 0.05% Hereinafter, Al: 0.015% or less, Ti: 0.02-0.07%, REM: 0.001-0.010%, Ca: 5 ppm or less, N: 40 ppm or less) and variety 2 (ordinary low charcoal) Al killed steel) is mixed. As for the mixing ratio of the varieties 1 and 2, the occupancy ratio of the varieties 2 is about 0 to 40%.

Example 1
Continuous casting is performed using the immersion nozzle shown in FIG. 2 as Example 1 of the present invention, the immersion nozzle shown in FIG. 6 as Example 2 of the present invention, and the nozzle shown in FIG. The number of bubbles was compared with the number of inclusions. All the immersion nozzles are made of alumina graphite refractory, the discharge hole opening cross-sectional area is 2820 mm ² , the discharge angle φ is 45 °, and the slit width is 15 mm. In Inventive Examples 1 and 2, the angle θ is 45 °, and in Inventive Example 2, the radius of curvature of the curved surface 11 is 60 mm.

  FIG. 15A shows the result of cutting out a 75 mm portion from the upper surface of a 240 mm thick type 1 slab and counting the number of bubbles having a diameter of 0.1 mm or more. The number of bubbles in Comparative Example 1 is displayed as 1 relative. It can be seen that both the inventive examples 1 and 2 have a significantly reduced number of bubbles as compared with the comparative example 1.

  FIG. 15B shows the result of cutting out a 120 mm portion from the upper surface of a 240 mm thick type 1 slab and counting the number of inclusions having a size of 106 μm or more in the slab. The number of inclusions in Comparative Example 1 is set as 1, and relative display is performed. As compared with Comparative Example 1, it is clear that Example 1 of the present invention has a reduced number of inclusions, and Example 2 of the present invention has a further reduced number of inclusions.

(Example 2)
A continuous casting was carried out using the immersion nozzle (shown in FIG. 6) of the present invention example 2 used in Example 1 above and the immersion nozzle shown in FIG. Went. The shape of the immersion nozzle of Invention Example 3 is the same as that of Invention Example 2. As the material of the immersion nozzle of Example 3 of the present invention, alumina graphite refractory was usually used for the refractory 24 portion, and carbonless spinel was used for the high refractory refractory 23 portion.

  Casting is performed for 400 minutes using an immersion nozzle, and the reduced thickness is shown in FIG. The refractory erosion amount of Example 2 of the present invention is indicated as 1, and relative display is made. The immersion nozzle of Example 3 of the present invention has a reduced amount of erosion compared to Example 2 of the present invention that does not use a high refractory refractory as a result of using a high refractory refractory on the inner peripheral surface of the nozzle. It is clear that

It is a figure which shows the immersion nozzle of this invention, (a) is AA arrow sectional drawing, (b) is BB arrow sectional drawing, (c) is CC arrow sectional drawing. It is a figure which shows a part of immersion nozzle of this invention, (a) is AA arrow sectional drawing, (b) is BB arrow sectional drawing, (c) is CC arrow sectional drawing, (D) is a DD arrow sectional drawing. It is a figure which shows a part of immersion nozzle of this invention, (a) is AA arrow sectional drawing, (b) is BB arrow sectional drawing, (c) is CC arrow sectional drawing, (D) is a DD arrow line view. It is a figure which shows a part of immersion nozzle of this invention, (a) is AA arrow sectional drawing, (b) is BB arrow sectional drawing, (c) is CC arrow sectional drawing. is there. It is a figure which shows a part of immersion nozzle of this invention, (a) is AA arrow sectional drawing, (b) is BB arrow sectional drawing, (c) is CC arrow sectional drawing. is there. It is a figure which shows a part of immersion nozzle of this invention, (a) is AA arrow sectional drawing, (b) is BB arrow sectional drawing, (c) is CC arrow sectional drawing, (D) is an AA arrow cross-sectional perspective view. It is a figure which shows the immersion nozzle of this invention, (a) is AA arrow sectional drawing, (b) is BB arrow sectional drawing, (c) is CC arrow sectional drawing. It is a figure which shows a part of immersion nozzle of this invention, (a) is AA arrow sectional drawing, (b) is BB arrow sectional drawing, (c) is CC arrow sectional drawing, (D) is an AA arrow cross-sectional perspective view. It is a figure which shows a part of immersion nozzle of this invention, (a) is AA arrow sectional drawing, (b) is BB arrow sectional drawing, (c) is CC arrow sectional drawing, (D) is a DD arrow line view. It is a figure which shows the conventional immersion nozzle, (a) is AA arrow sectional drawing, (b) is BB arrow sectional drawing, (c) is CC arrow sectional drawing. It is the figure which looked at the condition of water model experiment from the side, (a) is an example of the present invention, and (b) is a comparative example. It is a figure which shows the condition of a water model experiment, (a) (c) (e) is a longitudinal cross-sectional view of an immersion nozzle, (b) (d) (f) corresponds to (a) (c) (e). FIG. 6 is a view of the situation of the water model experiment from above, (a) and (b) are examples of the present invention, and (c) to (f) are comparative examples. It is the figure which looked at the situation of water model experiment from the side. In a water model experiment, it is a figure which shows the relationship between a slit width and bubble penetration depth. It is a figure shown about the influence which immersion nozzle shape has on slab quality, (a) relates to the number of bubbles, and (b) relates to the number of inclusions. It is a figure shown about the influence which the dipping nozzle material has on the amount of nozzle fusing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Submerged nozzle 2 Discharge hole 3 Slit 4 Cylindrical bottom part 5 Cylindrical side wall 6 Discharge hole bottom part 7 Discharge hole side wall 8 Discharge hole top part 11 Curved surface 12 Slight level difference 13 Level difference 14 Recessed part 21 Orifice part 22 Rib 23 High melting resistance refractory 24 Refractory material 29 Sliding nozzle plate 30 Long side 31 Short side 32 Molten metal 33 Molten powder layer 34 Discharge flow 35 Upflow flow 36 Downflow flow 37 Meniscus reversal flow 37 Downward flow 38 Vortex 39 Deviation 40 Powder suction

Claims (8)

  It has a bottomed cylindrical shape, and two discharge holes are arranged at a position symmetrical to the cylinder at the bottom of the cylindrical side wall, and a slit that opens to the outside by connecting the bottom of the cylinder and the bottom of both discharge holes is provided. The portion in contact with the slit at the bottom of the cylinder is inclined upward toward the cylindrical side wall, the portion in contact with the slit at the bottom of the discharge hole is inclined upward toward the side wall of the discharge hole, and the surface formed by the cylindrical bottom An immersion nozzle for continuous casting characterized by having substantially no step between the surface formed by the bottom of the discharge hole.   The inclination angle toward the cylindrical side wall of the portion in contact with the slit at the bottom of the cylindrical portion and the inclination angle toward the discharge hole side wall of the portion in contact with the slit at the bottom of the discharge hole is 30 ° or more upward. Immersion nozzle for continuous casting.   3. The immersion nozzle for continuous casting according to claim 1, wherein a portion of the top of the discharge hole that is in contact with the side wall of the cylinder forms a curved surface that smoothly contacts the side wall of the cylinder.   The continuous casting casting according to any one of claims 1 to 3, wherein an orifice portion having an opening cross-sectional area smaller than a cylindrical opening cross-sectional area is provided between the nozzle upper end and the discharge hole. Immersion nozzle.   The immersion nozzle for continuous casting according to any one of claims 1 to 4, further comprising a rib for connecting between both side surfaces of the slit.   6. An immersion nozzle for continuous casting according to claim 1, wherein the opening width of the slit is in the range of 0.15 to 0.40 times the square root of the discharge hole opening cross-sectional area. .   A part or all of the side surface and bottom of the cylinder, the surface in contact with the molten metal of the discharge hole and the slit is made of any material of carbonless spinel, low carbon spinel, magnesia graphite, zirconia graphite, silicaless alumina graphite. An immersion nozzle for continuous casting according to any one of claims 1 to 6.   The immersion nozzle for continuous casting according to any one of claims 1 to 7, wherein C: 0.01% or less, Si: 1% or less, Mn: 3% or less, P: 0.15% in mass%. Hereinafter, S: 0.05% or less, Al: 0.015% or less, Ti: 0.005% or more and 0.3% or less, REM: 0.001% or more, Ca: 0.0004% or less, N: 0 A continuous casting method of steel, characterized by casting a slab of 0.004% or less and comprising the balance Fe and inevitable impurities.

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