JP2005211924A - Method for continuously casting steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform a continuous casting using mold powder with which even in the case of requesting different characteristics in the mold powders to the center part and the peripheral part of a molten steel surface in the mold, this request is satisfied when the steel is continuously cast. <P>SOLUTION: When the steel is continuously cast, just above the molten steel surface 19 in the mold of at least the long wall 2 side of the mold, a weir 6 is set along the long walls of the mold, and at the peripheral part of the outside of the weir, the mold powder 13 having lower viscosity in comparison with that at the center part in the inside of the weir is supplied. In this case, it is desirable that the viscosity of the mold powder supplied at the peripheral part is made to be ≤2/3 times of the viscosity of the mold powder supplied at the center part, and the setting position of the weir is made to be in the range of ≥20 mm to ≤50 mm distance from the long wall of the mold. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a continuous casting method of steel, and more particularly to a method of continuous casting using mold powders having different characteristics on the center side of the molten steel surface in the mold and on the mold wall surface side.

  In general, in continuous casting of steel, molten steel is continuously poured into a mold while continuously or intermittently supplying mold powder onto a molten steel surface in the mold. This mold powder melts and covers the molten steel surface, prevents oxidation of the molten steel surface, retains heat, absorbs non-metallic inclusions that float from molten steel such as alumina as a deoxidation product, and molds It flows between the solidified shell and the solidified shell, and plays a role and function such as lubrication between the mold and the solidified shell and heat removal control of the solidified shell. Thus, mold powder is used as an indispensable thing in continuous casting of steel.

  In recent years, demands for cost reductions such as resource saving, energy saving and yield improvement have been strengthened, and with the aim of improving the productivity of continuous casting machines, even with a slab continuous casting machine with a large cross-sectional shape, a slab drawing speed of 2.0 m / High-speed casting with min or more has been performed. When the slab drawing speed is increased, the amount of mold powder consumed per unit surface area of the slab is reduced, and breakout due to seizure between the mold and the solidified shell tends to occur. As a measure for preventing this breakout, conventionally, for example, as proposed in Patent Document 1, the viscosity of the mold powder at 1300 ° C. is reduced to about 0.5 to 1.5 poise (0.05 to 0.15 Pa · s). It has been practiced to increase the viscosity, increase the amount of mold powder flowing in, and ensure lubricity.

  However, as a characteristic of the mold powder, it is required that there is little entanglement in the molten steel. Originally, the molten mold powder is mixed and mixed in the molten steel not only by the density difference from the molten steel but also by the viscosity. When the viscosity of the mold powder is lowered as described above, the frequency of the mold powder being caught in the molten steel increases. In particular, in the case of high-speed casting, the amount of molten steel supplied into the mold per unit time increases, and the molten steel flow in the mold becomes intense, so that the mold powder is more entangled. The encapsulated mold powder causes quality defects and decreases the product yield, and increases the manufacturing cost.

  In high-speed casting, a method of applying a magnetic field to the molten steel in the mold and slowing down the molten steel flow velocity by the generated electromagnetic force is employed. When used, it is virtually impossible to reliably prevent the mold powder from being caught.

  On the other hand, in Patent Document 2, in order to prevent entrainment of mold powder during high-speed casting, the surface tension at 1250 ° C. is set to 290 dyne / cm or more, the break point is set to 1000 ° C. or less, and the slab drawing speed (V: m / Min) and a viscosity (η: poise) at 1300 ° C., a method of continuous casting using a high-viscosity mold powder in which 6.0 <η × V is proposed. According to Patent Document 2, good lubrication can be ensured even with a high viscosity mold powder by adjusting the surface tension and breakpoint of the mold powder to the above ranges. In Patent Document 2, the break point is 10 ° C. from the temperature at which when the viscosity of the molten mold powder is lowered and the viscosity is measured, the crystal is crystallized in the measurement sample and the viscosity cannot be measured. It is said that the temperature is high.

  However, in the case of a high-viscosity mold powder as in Patent Document 2, in the case of high-speed casting in which the slab drawing speed exceeds 2.0 m 2 / min, the mold powder is consumed even if it can be prevented from being caught. Since the amount is insufficient and the lubricating action is reduced, breakout due to seizure between the mold and the solidified shell cannot be stably prevented.

In addition, as a technique for preventing the entrainment of mold powder, the molten steel flow rate is not controlled by the application of electromagnetic force as described above. For example, as disclosed in Patent Document 3, the molten steel surface in the mold is made of a refractory. There is also proposed a method for preventing the entrainment of mold powder by installing a chamfer plate and forcing the molten steel flow to collide with the chamfer plate to forcibly decelerate the molten steel flow velocity on the mold surface. However, in such a method, the molten steel flow that collided with the jammer plate may cause turbulence or bypass the side surface of the jammer plate in an attempt to avoid the jammer plate, thereby forming a vortex flow. On the other hand, the entrainment of the mold powder may increase, and at present, a method using an electromagnetic force is generally performed.
Japanese Patent Laid-Open No. 61-150752 Japanese Patent Laid-Open No. 2-25254 Japanese Examined Patent Publication No.59-37711

  In this way, the mold powder has various roles and functions, but there are many things that conflict with these roles and functions, particularly at the center side of the molten steel surface in the mold and the mold wall surface side. It is impossible to satisfy all roles and functions with one type of mold powder. Therefore, conventionally, as a method for dealing with such problems, it has been common to sacrifice one of the characteristics or make the characteristics intermediate between the two characteristics. As a result, it was impossible to solve all the quality and operational problems caused by mold powder such as breakout due to seizure, entrainment of mold powder, vertical cracks, etc., and any problems occurred. .

  The present invention has been made in view of the above circumstances. The purpose of the present invention is to require different characteristics for the mold powder to be used in each part of the molten steel surface in the mold when continuously casting steel. Even if it is a case, it is providing the continuous casting method of steel which can be continuously cast using the mold powder which satisfies the request | requirement.

  The inventors of the present invention diligently studied and studied to solve the above problems. The discussion and research results are explained below.

  It has been found that the characteristics required for the mold powder differ depending on the molten steel surface part in the mold and the side part of the solidified shell in the mold, and are roughly divided into two. That is, the role / function of the mold powder on the molten steel surface in the mold is mainly to keep the molten steel surface warm and prevent oxidation, and to absorb non-metallic inclusions that float, and to ensure these roles / functions. The properties of the mold powder do not depend much on the casting conditions, and can be dealt with by maintaining an optimum range. In addition, as a characteristic of the mold powder on the molten steel surface in the mold, it is required that there is little entrainment in the molten steel. On the other hand, the role and function of the mold powder in the side part of the solidified shell in the mold is mainly the lubrication between the mold and the solidified shell and the heat removal control of the solidified shell. Therefore, it is necessary to change the characteristics of the mold powder according to each casting condition.

  For example, on the molten steel surface in the mold, a relatively high-viscosity mold powder with low mold powder entrainment frequency is required, whereas on the solidified shell side wall, a relatively low-viscosity mold corresponding to the slab drawing speed is required. Powder is required. The higher the casting speed, the higher the required viscosity of the molten steel surface in the mold, and the lower the viscosity of the solidified shell side wall, the greater the difference in viscosity required between the two. In addition, it is not necessary to change the melting rate of the mold powder according to the casting conditions on the molten steel surface in the mold, but the melting rate corresponding to the consumption of the mold powder is required on the side of the solidified shell, It is necessary to change the melting rate according to the conditions.

  As described above, since the required characteristics of the mold powder are different between the molten steel surface part in the mold and the side part of the solidified shell in the mold, the above-mentioned is achieved by supplying the mold powder having appropriate characteristics to each part. The knowledge that the problem was solved was obtained. However, it is impossible to supply the mold powder separately to the molten steel surface part and the side part of the solidified shell independently, and therefore the mold powder required at the side part of the solidified shell is not Add to the mold near the mold surface of the molten steel surface in the mold that is close to the contact surface between the mold and the solidified shell, that is, to the periphery of the molten steel surface in the mold. It was decided to add to the center of the inner molten steel surface.

  The present invention has been made on the basis of the above examination results. In the continuous casting method of steel according to the first invention, when steel is continuously cast, at least directly above the molten steel surface in the mold on the long side of the mold. In addition, a weir is installed along the long side of the mold, and a mold powder having a viscosity lower than that of the central portion inside the weir is supplied to the peripheral portion outside the weir. is there.

  In the continuous casting method of steel according to the second invention, in the first invention, the viscosity of the mold powder supplied to the peripheral portion is 2/3 times or less than the viscosity of the mold powder supplied to the central portion. It is characterized by.

  The continuous casting method for steel according to a third invention is characterized in that, in the first or second invention, the installation position of the weir is in a range of 20 mm or more and 50 mm or less from the long side of the mold. It is.

  According to the present invention, a dam is installed along the long side of the mold directly above the molten steel surface in the mold on the long side of the mold, and the peripheral part outside the weir is compared with the central part inside the dam. As a result, a low-viscosity mold powder is supplied, so that the amount of mold powder flowing into the gap between the mold and the solidified shell is ensured even during high-speed casting, preventing breakout due to seizure between the mold and the solidified shell. In addition, since a highly viscous mold powder is supplied to the central portion, the entrainment of the mold powder is suppressed, and a high quality slab can be cast. That is, according to the present invention, stable casting with few quality defects and prevention of breakout is achieved, and industrially beneficial effects such as resource saving and energy saving are brought about.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 and 2 are diagrams showing an example of an embodiment of the present invention. FIG. 1 is a schematic plan view of a mold part of a slab continuous casting machine, and FIG. 2 is a part of the mold part of the slab continuous casting machine. It is a schematic longitudinal cross-sectional view which shows this.

  As shown in FIGS. 1 and 2, a mold 1 of a slab continuous casting machine includes a pair of opposed mold long sides 2 and a pair of opposed mold short sides 3 housed in the mold long side 2. The immersion nozzle 4 is arranged with the lower end portion inserted into the internal space of the mold 1 surrounded by the mold long side 2 and the mold short side 3. The immersion nozzle 4 is installed at the bottom of a tundish (not shown) disposed at a predetermined position above the mold 1. Further, a weir 6 is installed in the interior space of the mold 1 to bisect the interior space of the mold 1 into a central portion and a peripheral portion. The lower end 6a of the weir 6 is not immersed in the molten steel 10 in the mold, but is disposed in the molten layer 15 or the unmolten layer 14 of the mold powder above the molten steel surface 19 in the mold by a distance d. ing.

  The weir 6 uses a graphite-containing refractory material such as alumina-graphite, graphite-silicon carbide, magnesia-graphite, and zirconia-graphite, a carbide material such as silicon carbide, and a normal refractory material such as alumina and silica. be able to. In addition, since the weir 6 does not contact with the molten steel 10 in principle, a metal material such as steel, cast iron, or water-cooled copper can be used. The weir 6 is supported by a support device (not shown) capable of moving up and down, and is controlled by this support device so that the position of the lower end 6a of the weir 6 becomes a predetermined height position.

  The weir 6 is provided with at least one hole penetrating the metal tube-covered optical fiber 7 in the vertical direction of the weir 6. One end of the metal tube-covered optical fiber 7 wound around the drum (not shown) is connected to the weir 6. An optical fiber feeder (not shown) is inserted from the upper side to the lower side. The other end of the metal tube-coated optical fiber 7 is connected to a radiation thermometer (not shown), and the temperature is measured by the radiation thermometer based on the amount of light input to the metal tube-coated optical fiber 7 inserted to the lower end position of the weir 6. It has a structure that can be measured. That is, the temperature of the molten layer 15 at the lower end position of the weir 6 can be measured via the metal tube-coated optical fiber 7. At this time, the tip of the metal tube-coated optical fiber 7 is melted and damaged by the heat of the molten layer 15, and by continuously sending out the new metal tube optical fiber 7 by the amount of the melted, continuous temperature measurement is enabled. Yes. This configuration (optical fiber) is not essential for the implementation of the present invention, but if present, the present invention can be implemented more effectively.

  A mold powder supply device 8 and a mold powder supply device 9 are installed above the mold 1, and the mold powder supply device 8 has a mold powder supply device 8 on the center side of the mold surface 19 divided by the weir 6. The first mold powder 12 is supplied. On the other hand, the second mold powder 13 is independently supplied by the mold powder supply device 9 to the peripheral side which is the outside of the mold hot water surface 19 partitioned by the weir 6. It has come to be. Although only one mold powder supply device 8 and one mold powder supply device 9 are shown in the figure, the number of installations can be increased as appropriate. When the first mold powder 12 and the second mold powder 13 are compared, at least the viscosity is different between them, and the viscosity of the second mold powder 13 is lower than the viscosity of the first mold powder 12. ing. Further, the first mold powder 12 and the second mold powder 13 can change other characteristics such as melting temperature, surface tension, and melting rate. The mold powder supply devices 8 and 9 can be constituted by a combination of a hopper and a supply pipe with a screw feeder, for example.

  A continuous casting method of steel according to the present invention using the slab continuous casting machine having such a configuration will be described below.

  The molten steel 10 in the tundish is injected into the inner space of the mold 1 through the immersion nozzle 4. The molten steel 10 is injected toward the mold short side 3 from the discharge hole 5 immersed in the molten steel 10 in the mold. The molten steel 10 injected into the mold 1 is cooled by the mold 1, and a solidified shell 11 is formed in a portion that contacts the mold 1. When a predetermined amount of molten steel 10 is injected into the mold 1, a pinch roll (not shown) installed on the downstream side of the mold 1 is driven so that the outer shell is a solidified shell 11, and the molten steel 10 is contained inside. Drawing of a slab having an unsolidified layer is started. The slab is continuously drawn downward while being supported by a slab support roll (not shown) installed on the downstream side of the mold 1. After the start of drawing, the slab drawing speed is increased to a predetermined slab drawing speed while controlling the position of the molten steel surface 19 to a substantially constant position in the mold. Before starting the drawing of the slab, mold powder is added onto the molten steel surface 19 in the mold. In this case, it is not necessary to install the weir 6 yet, and mold powder for non-steady casting or mold powder for low-speed casting is used throughout the molten steel surface 19. The mold powder for non-stationary casting is generally a mold powder having a low viscosity and a high melting rate so that it melts and plays a desired role even when the molten steel temperature at the initial casting stage is low.

  When the slab extraction speed reaches a predetermined value, for example, about 0.8 to 1.0 m 2 / min during the increase of the slab extraction speed, the weir 6 is installed inside the mold 1. In this case, since the position of the molten steel surface 19 is detected by a molten metal level detection device (not shown) such as a vortex distance meter, the position of the weir 6 is determined based on the vertical dimension of the weir 6. The installation position can be adjusted, that is, the distance d can be set to a predetermined value. Further, the temperature of the molten layer 15 at the lower end position of the weir 6 is measured by the metal tube-covered optical fiber 7 inserted through the weir 6, and the distance d is set to a predetermined distance from the relationship between the distance d obtained by measurement in advance and the molten layer temperature. It can also be a value. During casting, the weir 6 may be damaged by the molten layer 15, and in this case, the vertical dimension of the weir 6 changes. In such a case, temperature measurement data by the metal tube-covered optical fiber 7 is used. The distance d is controlled based on the above.

  If the weir 6 is installed at a predetermined position, the first mold powder 12 is supplied to the central portion of the molten steel surface 19 in the mold by the mold powder feeder 8, while the peripheral portion of the molten steel surface 19 in the mold The second mold powder 13 is supplied by the mold powder supply machine 13. The added unmelted layer 14 of the first mold powder 12 and the unmelted layer 14 of the second mold powder 13 receive heat from the molten steel 10 and are melted independently and melted below the unmelted layer 14. Layer 15 is formed. In this case, since the lower end 6a of the weir 6 and the molten steel surface 19 are separated from each other by a distance d, the molten layer 15 of the first mold powder 12 passes through the weir 6 and flows out to the peripheral portion, and the second mold. It is mixed with the molten layer 15 of the powder 13 and flows between the mold 1 and the solidified shell 11.

  From the viewpoint of efficiently exhibiting the characteristics of each added mold powder, it is preferable to install the weir 6 so that the distance between the weir 6 and the mold long side 2 is in the range of 20 to 50 mm. If the distance between the weir 6 and the mold long side 2 is less than 20 mm, it is difficult to stably supply the second mold powder 13 to the peripheral side, while the distance between the weir 6 and the mold long side 2 is If it exceeds 50 mm, the low-viscosity second mold powder 13 will be added to the center of the molten steel surface 19, and the low-viscosity second mold powder 13 may be caught in the molten steel 10. Because there is.

  The molten layer 15 absorbs non-metallic inclusions such as alumina floating from the molten steel 10 in the mold and changes its composition. If the degree of composition change becomes severe, the properties of the mold powder change and the desired role / function may not be exhibited. Therefore, the molten layer 15 of the first mold powder 12 is also formed between the mold 1 and the solidified shell 11. Therefore, the distance d needs to be updated so that the distance d exceeds zero. By adjusting the distance d, the outflow amount of the first mold powder 12 to the second mold powder 13 can be adjusted. By controlling the amount of outflow of the first mold powder 12 to the peripheral portion, the desired purpose can be reliably obtained. However, since the second mold powder 13 is affected by the mixed first mold powder 12 and changes its characteristics, the second mold powder 13 is used from the viewpoint of ensuring lubrication between the mold 1 and the solidified shell 11. The viscosity of 13 is preferably set to 2/3 times or less of the viscosity of the first mold powder 12 in advance.

  The mold powder that has flowed in between the mold 1 and the solidified shell 11 forms a solidified layer 16 at the portion that contacts the mold 1, while the molten powder 15 remains solidified at the portion that contacts the solidified shell 11. It is pulled out together with the shell 11. When the solidified shell 11 is pulled downward and the thickness of the solidified shell increases, the amount of solidification shrinkage of the solidified shell 11 increases, and an air gap 18 is formed between the mold 1 and the solidified shell 11 along with this solidification shrinkage. The Reference numeral 17 shown in FIG. 2 is a fixed object called “slag bear” formed by fixing a molten or semi-molten mold powder to the mold 1.

  The characteristics of the first mold powder 12 and the characteristics of the second mold powder 13 other than the viscosity can be arbitrarily set according to casting conditions such as the slab drawing speed, slab cross-sectional size, and steel type.

  For example, in the case of high speed casting in which the slab drawing speed exceeds 2.0 m 2 / min, the viscosity of the first mold powder 12 is relatively increased to prevent entrainment into the molten steel 10, while the second The viscosity of the mold powder 13 is relatively lowered so that the mold 1 and the solidified shell 11 are smoothly lubricated. In this case, the viscosity at 1300 ° C. of the first mold powder 12 is about 2 to 6 poise, and the viscosity at 1300 ° C. of the second mold powder 13 is the viscosity (η: poise) and the slab drawing speed (V: m 2 / min). ) × V = 1 to 3.5 (poise · m 2 / min) in relation to Further, in the second mold powder 13, it is necessary to adjust the melting rate to match the consumption, that is, to increase the melting rate. However, since the first mold powder 12 is mixed into the second mold powder 13, it is necessary to determine characteristics such as viscosity in consideration of the mixing amount.

  In addition, when casting a steel type having a strong sensitivity to vertical cracks such as medium carbon steel, it is effective to slow down the cooling in the mold from the viewpoint of preventing vertical cracks. A mold powder having a low viscosity and a high crystallization temperature is suitable. On the other hand, the first mold powder 12 does not need to have a low viscosity and is preferably made to have a higher viscosity than the second mold powder 13 from the viewpoint of preventing entrainment.

  Further, in the case of preventing the slab surface from being carburized by carbon added as a melting rate adjusting agent to the mold powder, the second mold powder 13 is a mold having a low carbon content as a melting rate adjusting agent. On the other hand, as the first mold powder 12, a mold powder having a normal carbon content can be used. Carburization with mold powder occurs when the unmelted layer 14 and the molten steel 10 are in direct contact, and in the central portion of the molten steel surface 19, the unmelted layer 14 and the molten steel 10 are very rarely in contact, This is because there is almost no carburization by mold powder at the center of the molten steel surface 19. Also in this case, the viscosity of the second mold powder 13 needs to be lower than the viscosity of the first mold powder 12.

  In short, the first mold powder 12 has a function of absorbing non-metallic inclusions floating from the molten steel 10, a function of keeping the molten steel surface 19 warm and preventing oxidation, and prevention of mold powder entrainment. On the other hand, the second mold powder 13 secures lubrication between the mold 1 and the solidified shell 11, and further controls the heat removal of the solidified shell 11 and prevents carburization. The characteristics may be selected according to each purpose.

  Note that the installation method of the weir 6 does not need to completely surround and separate the central side and the peripheral side near the mold as shown in FIG. 1. For example, FIG. As shown, the molten steel surface 19 may be divided by a pair of opposing weirs 6 and 6 arranged along the long side 2 of the mold. The vortex flow on the molten steel surface 19 that causes the mold powder to be entrained is generated in the vicinity of the immersion nozzle 4 and at least that portion is separated in FIG. 3, so that the entrainment of the mold powder can be prevented. FIG. 3 is a diagram showing an example of another embodiment of the present invention, and is a schematic plan view of a mold part of a slab continuous casting machine.

  As described above, according to the present invention, the weir 6 is installed along the long side of the mold immediately above the molten steel surface 19 in the mold, and the peripheral portion outside the weir is inside the weir. Since mold powder having a lower viscosity than the central portion is supplied, the amount of mold powder flowing into the gap between the mold 1 and the solidified shell 11 is ensured even during high-speed casting. In addition to preventing break-out due to seizure, the mold powder having a high viscosity is supplied to the central portion, so that the entrainment of the mold powder is suppressed and a high quality slab can be cast.

  In addition, this invention is not necessarily limited to the range of the said description, A various change is possible. For example, the present invention can be carried out in accordance with the above in a bloom continuous caster or billet continuous caster having a mold cross-sectional area smaller than that of a slab continuous caster. Moreover, you may change the characteristic of 1st mold powder 12 itself, and the characteristic of 2nd mold powder 13 itself according to a casting condition every moment.

  In the vertical bending type slab continuous casting machine in which the weir having the shape shown in FIG. 1 is installed, the thickness of the slab is 250 mm, the width is 1350 mm, the molten steel components are C: 0.001 to 0.0025 mass%, and Si: 0. 0.1% by mass or less, Mn: 0.05 to 0.3% by mass, P: 0.002 to 0.035% by mass, S: 0.005 to 0.015% by mass, sol.Al: 0.02 to A very low carbon slab slab of 0.05% by mass was cast at a slab drawing speed of 2.5 m 2 / min.

  At the center of the molten steel surface in the mold, a mold powder having a viscosity at 1300 ° C. of 3.5 poise is used. On the periphery of the molten steel surface in the mold, a mold powder having a viscosity at 1300 ° C. of 0.5 poise is used. Casted. For comparison, casting was also performed without adding a weir and adding a mold powder having a viscosity at 1300 ° C. of 2.0 poise over the entire surface of the molten steel (conventional example). These cast slabs were rolled into thin steel plate products, and the thin steel plate products were subjected to an ultrasonic flaw detection test to investigate surface defects caused by mold powder.

  As a result, the surface defect occurrence index due to the mold powder was 0.5 in the conventional example, but 0.1 or less in the example of the present invention, and the entrainment of the mold powder was greatly reduced by the present invention. I understood that. Further, in both the examples of the present invention and the conventional examples, the lubrication between the mold and the solidified shell was good, and there was no breakout due to seizure between the mold and the solidified shell.

It is a figure which shows embodiment of this invention, Comprising: It is a plane schematic diagram of the casting_mold | template part of a slab continuous casting machine. It is a figure which shows embodiment of this invention, Comprising: It is a schematic longitudinal cross-sectional view which shows a part of casting_mold | template part of a slab continuous casting machine. It is a figure which shows other embodiment of this invention, Comprising: It is a plane schematic diagram of the casting_mold | template part of a slab continuous casting machine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mold 2 Mold long side 3 Mold short side 4 Immersion nozzle 5 Discharge hole 6 Weir 7 Metal pipe covering optical fiber 8 Mold powder supply device 9 Mold powder supply device 10 Molten steel 11 Solidified shell 12 First mold powder 13 2nd mold powder 14 Unmelted layer 15 Melted layer 16 Solidified layer 17 Slag bear 18 Air gap 19 Molten steel surface

Claims (3)

  When continuously casting steel, a dam is installed along the long side of the mold, at least directly above the molten steel surface in the mold on the long side of the mold, and the outer part of the dam is inside the dam. A continuous casting method of steel, characterized in that a mold powder having a lower viscosity than that of a central portion is supplied.   The method of continuous casting of steel according to claim 1, wherein the viscosity of the mold powder supplied to the peripheral portion is 2/3 times or less of the viscosity of the mold powder supplied to the central portion.   The continuous casting method of steel according to claim 1 or 2, wherein the installation position of the weir is within a range of 20 mm or more and 50 mm or less from the long side of the mold.

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