JP2023178223A - Continuous casting method for steel - Google Patents

Abstract

To provide a continuous casting method for steel that can produce cast pieces with excellent surface and internal quality.SOLUTION: Provided is a continuous casting method for steel in which when molten steel is fed into a casting mold from a sliding nozzle at the bottom of a tundish through an immersion nozzle, the immersion nozzle is made to have a transverse cross-sectional shape of the outside of an immersion part into the molten steel in the casting mold as an ellipse or streamlined shape, and a length ratio D1/D2 of one axis D1 approximately parallel to a casting mold long side and the other axis D2 perpendicular to the one axis is in the range of 1.00 to 3.00, a ratio S1/S0 of a cross-sectional area S1 at a smallest cross-sectional area part of the inner hole to a cross-sectional area S0 of a nozzle hole of the sliding nozzle is in the range of 0.96 to 1.30, and a ratio N1/S1 of an area N1 of one of the discharge holes to the cross-sectional area S1 is in the range of 0.96 to 1.20.SELECTED DRAWING: Figure 1

Description

The present invention relates to a continuous steel casting method in which molten steel is supplied into a mold from a sliding nozzle provided at the bottom of a tundish through a submerged nozzle.

BACKGROUND OF THE INVENTION A continuous steel casting method is generally used in which molten steel is supplied from a ladle to a mold via a tundish, which is an intermediate container. At that time, the immersion nozzle installed at the bottom of the tundish is immersed in the molten steel in the mold for casting. For example, when pouring molten steel into a mold for casting slabs having a rectangular cross-sectional shape, a submerged nozzle having one discharge hole on each side of the mold is usually used. As a device for controlling the flow rate of molten steel passing through such an immersion nozzle, a stopper installed in the tundish or a sliding nozzle installed at the bottom of the tundish is used.

Generally, sliding nozzles may have two plates or three plates. In the case of two plates, the sliding direction is the width direction (direction parallel to the long side of the mold), so a drift occurs in the width direction. In the case of three plates, since the sliding direction is the thickness direction (direction perpendicular to the long side of the mold), drift occurs in the thickness direction. On the other hand, in the case of stopper control, it is said that drifting is less likely to occur because hot water falls uniformly from around the stopper. However, since the stopper is made of refractory material and has buoyancy in molten steel, the axis of the stopper and the axis of the upper nozzle are not necessarily coaxially disposed, making it impossible to prevent drifting.

Various techniques have been developed in the past in order to stabilize the flow of molten steel discharged from a submerged nozzle and to produce slabs having good surface quality and internal quality. Patent Document 1 discloses a continuous casting method in which the angle in the horizontal plane between the sliding nozzle and the discharge flow is 80 to 90 degrees in order to prevent the phenomenon of one-sided flow of molten steel in the mold. Patent Document 2 discloses an injection method in which a submerged nozzle has a rectangular cross section and the injection flow from the injection nozzle to the mold is maintained at a uniform low-speed downward flow for casting. Patent Document 3 discloses a continuous casting method for producing slabs free of surface and internal defects by using slit-shaped discharge holes to disperse and homogenize the flow of molten steel discharged from a submerged nozzle.

Patent Document 4 discloses a submerged nozzle equipped with twisted tape-shaped swirl vanes inside. Patent Document 5 discloses a continuous casting method that prevents uneven flow of molten steel from a discharge hole by introducing an inert gas into a submerged nozzle and controlling the internal pressure.

Patent Document 6 discloses that the cross-sectional shape of the immersion nozzle inner hole is flat such as an ellipse, the long axis thereof is parallel to the long side of the mold, and the sliding direction of the sliding nozzle is perpendicular to the long axis. The technology has been disclosed. This stabilizes the flow of molten steel within the immersion nozzle.

Japanese Patent Application Publication No. 2002-301549 Japanese Unexamined Patent Publication No. 58-74257 Japanese Patent Application Publication No. 9-285852 Japanese Patent Application Publication No. 2000-237852 Japanese Patent Application Publication No. 9-225604 JP2007-69222A

However, even with the above-mentioned prior art method, it is still not possible to stabilize the flow of molten steel discharged into the mold and sufficiently prevent drift. It has not been possible to sufficiently prevent surface defects caused by inclusions called slivers that occur on the coil surface after rolling and bubble defects called blowholes caused by argon blown into the submerged nozzle.

The present invention solves the above-mentioned conventional problems and prevents the entrainment of non-metallic inclusions such as alumina, which cause slivers, and argon bubbles, which cause blowholes, by stabilizing the discharge flow from the immersion nozzle. It is an object of the present invention to provide a continuous steel casting method that can produce slabs with excellent surface and internal quality.

In the continuous casting method of steel according to the present invention, which advantageously solves the above problems, when molten steel is supplied into the mold from a sliding nozzle provided at the bottom of a tundish through a submerged nozzle, the submerged nozzle is placed inside the mold. The cross-sectional shape of the outer shape of the part immersed in the molten steel is elliptical or streamlined, and the cross-sectional shape of the inner hole has one axis _D1 substantially parallel to the long side of the mold and another axis perpendicular to the one axis. The length ratio D ₁ /D ₂ with D ₂ is in the range of 1.00 to 3.00, and the cross-sectional area S ₁ at the minimum cross-sectional area portion of the inner hole and the cross-sectional area S ₀ of the nozzle hole of the sliding nozzle are The ratio S ₁ /S ₀ is in the range of 0.96 to 1.30, and the ratio N ₁ /S ₁ between the area N ₁ of one side of the discharge hole and the cross-sectional area S ₁ is 0.96 to 1.20. It is characterized by having a range of .

The method for continuous casting of steel according to the present invention is as follows:
a. The immersion nozzle is arranged so that the direction of the one axis is substantially parallel to the long side of the mold, and the direction of the one axis is arranged so that the direction of the one axis is substantially parallel to the long side of the mold, and the direction of the one axis is arranged so that the direction of the one axis is substantially parallel to the long side of the mold. providing at least one pair of discharge holes on both sides of the
b. The immersion nozzle is arranged so that the direction of the one axis is substantially parallel to the long side of the mold, and the discharge hole is deflected within 60° with respect to the opposing long side of the mold to discharge molten steel. providing at least one pair of discharge holes on both sides;
c. The immersion nozzle is arranged so that the distance between the other shaft-side outer surface and the long-side inner wall of the mold is 80 mm or more;
d. Performing casting while imparting swirling properties to the molten steel in the mold using an electromagnetic stirring device;
It is thought that this could be a more preferable solution.

According to the present invention, the outer shape of the part of the immersion nozzle immersed in the molten steel in the mold is made elliptical or streamlined, the length ratio of the long axis and short axis of the cross-sectional shape of the inner hole is specified, and the long axis is set in the mold. Placed parallel to the long side. Thereby, the molten steel in the mold near the immersion nozzle can be immersed without disturbing the flow, and the surface flow velocity of the meniscus portion can be ensured. Furthermore, the ratio between the cross-sectional area of the inner hole of the submerged nozzle and the cross-sectional area of the nozzle hole of the sliding nozzle was determined, and the ratio between the area of the discharge hole and the cross-sectional area of the inner hole of the submerged nozzle was determined. This makes it possible to prevent drifting without causing nozzle blockage due to air being sucked into the submerged nozzle.

Furthermore, it is preferable that the long axis of the immersed part of the immersed nozzle is arranged substantially parallel to the long side of the mold, and that at least one pair of discharge holes is provided on both sides in the long axis direction. This can prevent the molten steel discharge flow from penetrating deeply into the unsolidified portion from the meniscus.

In addition, the immersion nozzle is arranged such that the long axis of the immersion part is approximately parallel to the long side of the mold, and the discharge hole is deflected within a predetermined angle with the opposing long side of the mold to discharge molten steel. Preferably, at least one pair of discharge holes is provided on the surface. By doing so, it is possible to impart a swirling flow to the molten steel in the mold. As a result, it is possible to prevent non-metallic inclusions from being captured in the solidified shell, thereby producing a slab with excellent surface properties.

Furthermore, it is preferable to optimize the distance between the short axis side outer surface of the immersion nozzle and the long side inner wall of the mold. By doing so, the molten steel can be cast while ensuring a sufficient flow rate of the molten steel near the immersion nozzle.

In addition, it is preferable to perform casting while imparting swirling properties to the molten steel in the mold using an electromagnetic stirring device. By doing so, it is possible to prevent nonmetallic inclusions and the like from being captured in the solidified shell, and to produce a slab with excellent surface properties.

1 is a longitudinal cross-sectional view of a mold and a submerged nozzle suitable for a continuous steel casting method according to an embodiment of the present invention. It is a figure which shows the cross-sectional shape of the minimum cross-sectional area part of an immersion nozzle, Comprising: (a) shows an ellipse shape, (b) shows an axially symmetrical streamline shape. FIG. 3 is a schematic top view showing the positional relationship between the mold and the immersion nozzle inside the mold, where (a) shows the case where the discharge hole is parallel to the long side of the mold, and (b) shows the case where the discharge hole is oriented on the long side. Indicates a case of deflection.

Embodiments of the present invention will be specifically described below. Note that each drawing is schematic and may differ from the actual drawing. Furthermore, the following embodiments are intended to exemplify devices and methods for embodying the technical idea of the present invention, and the configuration is not limited to the following. That is, the technical idea of the present invention can be modified in various ways within the technical scope described in the claims.

As a result of analyzing the flow of molten steel in a submerged nozzle and a mold, the inventors obtained the following knowledge and completed the present invention.

In the case of a conventional immersion nozzle in which the cross-sectional shape of the immersion nozzle inner hole is a perfect circle, when the sliding nozzle is slid, the sliding direction of the sliding nozzle inside the immersion nozzle is distorted because the opening is biased to one side. A drifting flow toward . This drift increases the variation in the flow rate of molten steel from the submerged nozzle discharge hole, and increases the maximum discharge flow rate.

As the maximum discharge flow rate increases, the depth into which the discharge flow penetrates into the unsolidified portion increases. Therefore, inclusions such as deoxidized products such as alumina and continuous casting powder and argon bubbles blown into the immersion nozzle penetrate deep into the unsolidified portion of the molten steel and remain without being able to float. It was also found that this leads to product surface defects and internal defects such as cracks. Further, if the external cross-sectional shape of the immersed nozzle is a perfect circle, the resistance of the immersed part of the immersed nozzle to the flow of molten steel in the mold increases, and the meniscus surface flow velocity decreases. It was found that when the flow on the meniscus surface collides with the immersion nozzle, the flow velocity becomes non-uniform and vortices are formed around the continuous casting powder, leading to surface defects.

In order to prevent these, it is possible to cast the nozzle inner hole with a flat cross-sectional shape such as an ellipse or an oblong, or a streamlined shape, with the long axis direction approximately parallel to the long side direction of the mold. It was found to be effective.

FIG. 1 is a schematic longitudinal cross-sectional view showing a schematic configuration of continuous casting equipment for carrying out the continuous steel casting method according to the present embodiment, as viewed from the short side of a slab. A sliding nozzle 1 is provided at the bottom of a tundish (not shown). An immersion nozzle 2 is connected below the sliding nozzle 1. Molten steel is injected into the mold 3 from the immersion nozzle 2 . In the example of FIG. 1, an electromagnetic stirring coil 4 for stirring molten steel in the mold is installed in the mold 3. The sliding nozzle 1 has a nozzle hole 11 with a cross-sectional area _S0 . In the example shown in FIG. 1, it is a three-plate type which is sandwiched between an upper plate 5 and a lower plate 6 and whose sliding direction SD is a direction perpendicular to the long side of the mold 3. The solidified shell cooled and solidified in the mold 3 is pulled out in the casting direction CD.

In this embodiment, the sliding nozzle 1 has a nozzle hole 11 that is perfectly circular. Moreover, the shape of the upper inner hole 21 of the immersion nozzle 2 is a perfect circle. The lower inner hole 21 of the immersion nozzle 2 has an elliptical shape as shown in FIG. 2(a) or an axisymmetric streamline shape as shown in FIG. 2(b). Since the thickness of the nozzle refractory is approximately constant in the immersion nozzle, the cross-sectional shape of the inner hole governs the outer shape. Here, the ellipse includes a long ellipse and does not include a perfect circle. Moreover, instead of an ellipse, it may be an oval shape having a parallel portion in which the short side of the rectangle is replaced with a circular arc. Furthermore, the term "streamlined" refers to a shape consisting of a curved line that, when placed in a flow, does not generate vortices around it and minimizes the resistance it receives from the flow. In a uniform flow, the tip is rounded and the rear end is pointed.

As illustrated in Fig. 2(a), in an ellipse or an oblong, the length of one major axis (major axis) _D1 and the length of the minor axis (major axis) that is orthogonal to this diameter) _D2 . In the axially symmetrical streamline shown in Figure 2(b), the length of one axis parallel to the flow is _D1 , and the length of the perpendicular line drawn from the peripheral point farthest from the one axis to the one axis is the other. It is defined as half of the axis length _D2 . As will be described later, the molten steel flows between the immersion nozzle installed at the center (in the width and thickness directions) of the rectangular mold when viewed from above and the long side of the opposing mold. It is preferable to flow the molten steel in the opposite direction, and by making the outer shape of the immersed part of the immersion nozzle into an axially symmetric streamlined shape, it is possible to reduce the generation of vortices on the surface of the molten steel in the mold.

In this embodiment, the immersion nozzle 2 is immersed in the molten steel in the mold in an arrangement as shown in FIGS. 3(a) and 3(b). The minimum cross-sectional area portion 23 of the immersion nozzle 2 had an elliptical cross-sectional shape. In this embodiment, the long axis direction LA of the immersion nozzle 2 is arranged parallel or substantially parallel to the long side of the mold 3 as one axial direction, and the short axis direction SA is the other axial direction. When a horizontal swirling flow is applied to the molten steel in a rectangular mold when viewed from above, the molten steel near the immersion nozzle flows parallel to the long side, so if it is installed as shown in Figure 3 (a) or (b), the flow resistance will be reduced. can be reduced. In this case, the short axis direction SA is perpendicular or substantially perpendicular to the long sides of the mold. Here, "arranged substantially parallel to the long side" means to allow installation error precision of equipment and devices, and deviations within 5 degrees are allowed.

In the example of FIG. 3(a), the immersion nozzle 2 is provided with a pair of two discharge holes 22 on both sides of the long axis direction LA, so that molten steel can be discharged in the direction of the short side of the opposing mold. . The number of discharge holes 22 may be at least one pair, or may be two pairs. With this arrangement, it is possible to prevent the molten steel discharge flow from penetrating deeply from the meniscus in the casting direction CD.

In the example shown in FIG. 3(b), a pair of discharge holes 22 are provided so as to discharge the molten steel at an angle θ with the opposing long sides of the mold, so that a swirling flow can be formed in the molten steel in the mold. , the solidified shell near the meniscus can be cleaned to prevent inclusions from adhering. The number of discharge holes 22 may be at least one pair, or may be two pairs. The deflection angle θ is preferably within 60°. More preferably, it is within 30°. If the deflection angle θ is too large, the discharge flow from the submerged nozzle will collide with the solidified shell on the long side, and there is a risk of operational accidents such as internal cracks and breakouts due to delayed solidification of the solidified shell. Further, the deflection angle θ does not include 0°, and is more preferably 5° or more from the viewpoint of effectively generating a swirling flow of molten steel in the mold.

In this embodiment, it is preferable that the sliding direction of the sliding nozzle 1 be perpendicular to the longitudinal direction LA of the inner hole of the submerged nozzle 2. It is possible to suppress the width of the molten steel in the direction in which the molten steel drifts within the immersion nozzle 2, thereby allowing the molten steel to flow uniformly in the longitudinal direction LA. Therefore, the drift of the molten steel in the immersion nozzle 2 that occurs when the sliding nozzle 1 is slid can be reduced.

In the immersion nozzle 2 having the inner hole 21 having the above-described shape, the length ratio D ₁ /D ₂ of one axial length D ₁ and the other axial length D ₂ is determined by the minimum cross-sectional area portion 23 directly above the discharge hole 22 . must be in the range of 1.00 to 3.00. If the length ratio D ₁ /D ₂ is less than 1.00, the flatness of the inner hole 21 will be reversed, and the occurrence of drift in the sliding direction of the sliding nozzle 1 cannot be effectively prevented. Moreover, there is a possibility that the inner hole cross-sectional area S ₁ of the submerged nozzle 2 becomes too small than the nozzle hole cross-sectional area S ₀ of the sliding nozzle 1 . On the other hand, if the length ratio D ₁ /D ₂ exceeds 3.00, the immersion nozzle becomes too flat and the risk of breakage increases, and in addition, there is not enough molten steel flow rate in case of alumina blockage that occurs during casting. It is difficult to maintain the level of hot water in the mold, making it impossible to control the hot water level in the mold, and fluctuations in the hot water level may result in a situation where stable operation cannot be continued. In addition, in the immersion nozzle 2 having a plurality of discharge holes 22 above and below, the minimum cross-sectional area portion 23 is the upper end position of the uppermost discharge hole 22.

As described above, the inner hole 21 of the submerged nozzle 2 not only changes in shape from the top to the bottom, but also decreases in cross-sectional area. The ratio S ₁ /S ₀ of the cross-sectional area S ₁ of the minimum cross-sectional area portion 23 directly above the discharge hole 22 and the cross-sectional area S ₀ of the nozzle hole 11 of the sliding nozzle 1 needs to be in the range of 0.96 to 1.30. be. If this ratio S ₁ /S ₀ is less than 0.96, the supply of molten steel will be insufficient when the opening degree of the sliding nozzle increases in the unsteady part where the height of the molten steel in the tundish decreases. As a result, the level of the molten metal in the mold cannot be controlled, and fluctuations in the level of the molten metal may cause a situation in which stable operation cannot be continued. On the other hand, when the ratio S ₁ /S ₀ exceeds 1.30, the influence of the flatness of the inner hole becomes small, and the effect of suppressing drifting in the sliding direction decreases. At the same time, there is a concern that the nozzle itself will become larger and the running cost will increase. Further, negative pressure is generated in the step between the lower nozzle 6 and the immersed nozzle 2, which may cause air to be sucked in, and there is also a high possibility that a drift will occur in the molten steel in the immersed nozzle as the sliding nozzle 1 slides.

At the start of casting, molten steel is injected from a pot, fills a tundish, and before being injected into a mold via an immersion nozzle, heat is absorbed by each refractory and the temperature of the molten steel decreases. If this temperature drop is large, the temperature drops below the freezing point and solidification of the molten steel occurs within the immersion nozzle, resulting in a so-called suspended state. In such a case, as "manual intervention at the start of casting", for example, an oxygen pipe is inserted through the discharge hole of the submerged nozzle, and oxygen is sprayed onto the solidified surface to melt it. This manual intervention at the start of casting is not only dangerous for workers, but also impedes the stable operation of continuous casting due to poor quality.

Further, the ratio N ₁ /S ₁ between the area N ₁ of one side of the discharge hole 22 and the cross-sectional area S ₁ needs to be in the range of 0.96 to 1.20. When the discharge holes 22 are provided in pairs on both sides of the immersion nozzle 2, the area _N1 of one side of the discharge holes 22 is the total area of the discharge holes 22 on one side. When the discharge hole 22 is provided at the bottom of the submerged nozzle 2, the area _N1 of one side of the discharge hole 22 is calculated by adding up the area of the discharge hole 22 at the bottom. In addition, when placing importance on the surface quality of the product, it is preferable not to arrange the discharge holes 22 at the bottom of the immersion nozzle, but to arrange the discharge holes 22 only on the side surface. If the ratio N ₁ /S ₁ is less than 0.96, nozzle clogging is likely to occur, and there is a risk that fluctuations in the molten metal level will increase or that the molten steel discharge rate will be insufficient compared to the required discharge rate, making stable operation impossible. There is. On the other hand, when the ratio N ₁ /S ₁ exceeds 1.20, the balance of the discharge amount between the opposing discharge holes is lost, and the flow rate of one discharge hole increases, which is called a drift. Due to the drift, there is a risk that inclusions and the like may be sent deep into the unsolidified portion of the molten steel in the casting direction CD. Furthermore, there is a risk that nozzle clogging may occur at the flow rate reduction portion at the discharge port, increasing fluctuations in the melt level. In addition, if the drift becomes extremely large, there is a risk of operational accidents such as breakouts occurring.

As shown in FIG. 3(a), it is preferable that the distance L _S between the short axis side outer surface of the immersion nozzle 2 and the long side inner wall of the mold 3 be 80 mm or more. Here, the distance L _S is the smaller of the distances between the two opposing long sides of the mold. If the distance _LS is less than 80 mm, a sufficient flow rate of molten steel cannot be obtained when generating a swirling flow in the mold, for example, when molten steel is electromagnetically stirred, so that inclusions that cause surface defects are removed from the solidified shell. This is because there is a high possibility that it will be captured.

As shown in FIGS. 1, 3(a) and 3(b), it is preferable to install an electromagnetic stirring coil 4 for electromagnetic stirring in the mold 3. Casting can be performed while imparting swirling properties to the molten steel in the mold 3. By electromagnetically stirring molten steel, it is possible to prevent inclusions and the like from being captured in the solidified shell, and to produce slabs with excellent surface properties.

Next, examples of the present invention will be described. Note that the present invention is not limited only to the following examples.

300 tons of molten ultra-low carbon steel was melted in a converter-RH degassing process. The temperature of the molten steel in the tundish was set to 1560 to 1580°C, and the molten steel was injected into the mold using a three-layer sliding nozzle, a two-layer sliding nozzle, and an immersion nozzle to form a casting with a thickness of 250 mm and a width of 1200 to 1600 mm. Pieces were produced at a casting speed of 1.6-2.0 mm/min. During casting, the molten steel was swirled horizontally using electromagnetic stirring. The steel plate was a cold-rolled steel plate with a thickness of 0.7 to 1.2 mm. The effectiveness was evaluated based on the coil defect inclusion rate (number of defects/coil length (m)) and the presence or absence of nozzle clogging during casting. Tables 1-1 and 1-2 show the results of continuous casting tests under various conditions. The shape of the inner hole of the immersion nozzle in the table is the shape of the minimum cross-sectional area portion 23 directly above the upper discharge hole, and the shape of the inner hole of the immersion nozzle is the shape of the minimum cross-sectional area portion 23 directly above the upper discharge hole. Except for No. 19, it has an elliptical shape. 19 forms a streamlined shape. In addition, D ₁ is the length of one axis parallel to the long side of the mold (mm), D ₂ is the length of another axis perpendicular to the one axis (mm), and S ₁ is the minimum cross-sectional area of the immersion nozzle 2. 23 cross-sectional area (mm ² ), S ₀ is the cross-sectional area (mm ² ) of the nozzle hole 11 of the sliding nozzle 1, θ is the angle (°) between the direction of the immersion nozzle discharge hole and the long side of the mold, and n is the immersion The number of discharge holes 22 of the nozzle 2, _N1 / _S1 is the ratio of the area of one of the discharge holes to the cross-sectional area of the minimum cross-sectional area 23 of the submerged nozzle 2, and _LS is the outer surface of the short axis side of the submerged nozzle 2. The distance (mm) from the inner wall on the long side of the mold, ηD is the coil defect occurrence rate and represents the percentage (%/m) of the number of defects per coil length (m). The success rate at the start of casting is expressed as the manual intervention rate at the start of casting, expressed as a percentage of the number of manual interventions to the total number of starts. The smaller the manual intervention rate, the more stable the operation. The rate of occurrence of abnormalities due to fluid level fluctuations is expressed as a percentage of the number of fluid surface fluctuations relative to the number of castings. In Tables 1-1 and 1-2, SD represents the relationship between the sliding direction of sliding nozzle 1 and the long side of the mold, "orthogonal" means a three-layer sliding nozzle, and "parallel" means a two-layer sliding nozzle. show.

Processing No. Nos. 1 to 19 are the results of casting tests conducted within the scope of the present invention. The coil defect incidence rate ηD is also 1.9% or less, and the quality results are very good. Furthermore, no nozzle blockage occurred during casting. The rate of manual intervention at the start of casting was low, the rate of abnormalities due to fluctuations in the metal level was low, and operations were stable.

Processing No. 20 is a case where the flatness degree D ₁ /D ₂ of the nozzle is large. In this case, it is presumed that the refractory itself is difficult to manufacture and easily cracks, and the resistance to passage of molten steel becomes large, causing nozzle clogging. In addition, if _D1 / _D2 is too large, the shape of the inner hole becomes flat, and if alumina blockage occurs during casting, a sufficient flow rate of molten steel cannot be secured and abnormalities may occur due to fluctuations in the molten metal level. The rate was high.
Processing No. 21 is a case where the ratio S ₁ /S ₀ is small. In this case, nozzle blockage occurred during pouring into the mold. This is presumed to be because the nozzle inner diameter cross-sectional area was smaller than the nozzle hole cross-sectional area of the sliding nozzle 1. Even if S ₁ becomes small, that is, even if S ₀ is fully open, the flow resistance of molten steel is large in the S ₁ portion, the molten steel flow rate decreases, and the required amount of molten steel is not supplied. A so-called suspended shelf condition occurs in the _S1 section, which not only significantly reduces the controllability of molten metal level fluctuations, but also significantly increases the temperature drop of molten steel at the start of casting, and the rate of manual intervention at the start of casting is extremely high. As a result, stable operation could not be achieved.
Processing No. 22 is a case where the ratio S ₁ /S ₀ is large. In this case, a rectification effect could not be obtained, and the occurrence of abnormalities due to fluctuations in the molten metal level during casting was high. This resulted in deterioration in coil quality and blockage of the nozzle at the final stage of casting.
Processing No. No. 23 is a case where the nozzle flatness D ₁ /D ₂ is smaller than 1.00, and the lengths of the major axis and the minor axis are reversed. Moreover, the ratio S ₁ /S ₀ became smaller. As a result, the flow resistance caused by the submerged nozzle increased, and the quality deteriorated. Even if S ₁ becomes small, that is, even if S ₀ is fully open, the flow resistance of molten steel is large in the S ₁ portion, the molten steel flow rate decreases, and the required amount of molten steel is not supplied. A so-called suspended shelf condition occurs in the _S1 section, which not only significantly reduces the controllability of molten metal level fluctuations, but also significantly increases the temperature drop of molten steel at the start of casting, and the rate of manual intervention at the start of casting is extremely high. As a result, stable operation could not be achieved.
Processing No. 24 is a case where the area _N1 of the discharge hole is too small with respect to the minimum cross-sectional area _S1 of the nozzle. Although the coil performance improved, nozzle blockages were occasionally observed during casting. When _N1 is smaller than _S1 , the flow resistance of molten steel at the discharge hole is large, the flow rate of molten steel decreases, and the required amount of molten steel is not supplied. As a result, not only the controllability of the melt level fluctuation was significantly reduced, but also the drop in molten steel temperature at the start of casting was significantly large, and the rate of manual intervention at the start of casting was extremely high, making stable operation impossible.
Processing No. 25 is a case where the area _N1 of the discharge hole is too large with respect to the minimum cross-sectional area _S1 of the nozzle. Due to the large discharge hole, no rectification effect was observed, and the occurrence of abnormalities due to fluctuations in the melt level during casting was high. Therefore, the coil quality did not improve.

From the above results, the features of the present invention, namely, the length ratio D ₁ /D ₂ of the orthogonal axes of the cross-sectional shape of the submerged nozzle and the inner hole, and the cross-sectional area ratio of the inner hole of the submerged nozzle and the nozzle hole of the sliding nozzle. By setting S ₁ /S ₀ and the area ratio N ₁ /S ₁ between the discharge hole and the inner hole of the immersion nozzle to appropriate values, continuous casting can be operated stably from the start to the end. can. If any of the characteristics of the present invention are not met, stable operation is possible for a short period of time, but if any of the factors that affect stable operation, such as controllability during fluid level fluctuations, starting stability, or alumina blockage, The problem worsens and the stable operation of continuous casting is impaired.

The unit of mass "ton" herein represents 10 ³ kg.

The continuous steel casting method of the present invention allows stable operation without clogging of the immersion nozzle, and reduces the occurrence of product defects, which is industrially useful.

1 Sliding nozzle 2 Immersion nozzle 3 Mold 4 Electromagnetic stirring coil 5 Upper plate 6 Lower plate 11 Nozzle hole 21 Inner hole 22 Discharge hole 23 Minimum cross-sectional area SD Sliding direction CD Casting direction LA One axial direction (long axis direction)
SA Other axis direction (short axis direction)
_D1 One axis (length), major axis _D2 Other axis (length), minor axis L _S Distance between the outer surface of the immersion nozzle and the long side of the mold

Claims (6)

When feeding molten steel into the mold from the sliding nozzle installed at the bottom of the tundish through the immersion nozzle,
The immersion nozzle has an elliptical or streamlined outer cross-sectional shape of the immersion part into the molten steel in the mold,
The length ratio D ₁ /D ₂ of one axis D ₁ substantially parallel to the long side of the mold and the other axis D ₂ perpendicular to the one axis in the cross-sectional shape of the inner hole is set to 1.00 to 3. The range is 00,
The ratio S ₁ /S ₀ of the cross-sectional area S ₁ at the minimum cross-sectional area portion of the inner hole and the cross-sectional area S ₀ of the nozzle hole of the sliding nozzle is in the range of 0.96 to 1.30,
A continuous casting method for steel, wherein the ratio N ₁ /S 1 of the area _{N 1} of one side of the discharge hole and the cross-sectional area S ₁ is in the range of 0.96 to 1.20. The immersion nozzle is arranged so that the direction of the one axis is substantially parallel to the long side of the mold, and the direction of the one axis is arranged so that the direction of the one axis is substantially parallel to the long side of the mold, and the direction of the one axis is arranged so that the direction of the one axis is substantially parallel to the long side of the mold. The continuous casting method for steel according to claim 1, wherein at least one pair of discharge holes is provided on both sides of the steel. The immersion nozzle is arranged so that the direction of the one axis is substantially parallel to the long side of the mold, and the discharge hole is deflected within 60° with respect to the opposing long side of the mold to discharge molten steel. 2. The continuous steel casting method according to claim 1, wherein at least one pair of discharge holes are provided on both side surfaces. The continuous casting method for steel according to any one of claims 1 to 3, wherein the immersion nozzle is arranged such that the distance between the other shaft side outer surface and the long side inner wall of the mold is 80 mm or more. . The continuous casting method for steel according to any one of claims 1 to 3, wherein casting is performed while imparting swirling properties to the molten steel in the mold using an electromagnetic stirring device. The continuous steel casting method according to claim 4, wherein casting is performed while giving swirling properties to the molten steel in the mold using an electromagnetic stirring device.

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