JP5040845B2 - Steel continuous casting method - Google Patents

Description

  The present invention relates to a method for continuous casting of steel, for example, a slab having a substantially rectangular cross-sectional shape, for example, made of hypoperitectic steel having a carbon concentration of 0.10 to 0.13 mass%, which is likely to cause short pieces of fogging. Alternatively, when continuous casting is performed by twin casting, in which two blooms are continuously cast with one set of drive systems, the occurrence of burrs on the short side of the slab or the short side of the slab while maintaining productivity. The present invention relates to a method capable of continuous casting while preventing breakout.

  As is well known, in continuous casting of steel, molten steel contained in a tundish is first supplied to a continuous casting mold via an immersion nozzle, and is first cooled by cooling water in the continuous casting mold to be put into the outer skin. The slab has a solidified shell and an unsolidified portion inside. This slab is continuously manufactured by being cooled by secondary cooling in the region of a pair of guide rolls installed continuously in the slab drawing direction, and finally drawn out after being completely solidified. . A slab of various sizes from a large cross-section to a small cross-section is supplied to the rolling process downstream of the continuous casting, but a slab having a relatively small cross-sectional area inevitably has a casting amount per unit time. Since it becomes small, the productivity of continuous casting tends to be low.

  Therefore, in order to improve the productivity of continuous casting of slabs with a relatively small cross-sectional area, the drawing rolls and their drive mechanisms following the multiple molds are integrated, and multiple slabs are cast simultaneously with a single drive system. A casting method may be employed. A method of casting two slabs simultaneously with one set of drive system is called “twin casting”, and a method of casting three slabs simultaneously is called “triple casting”. In contrast to this, a conventional continuous casting method in which one slab is cast with one set of drive systems is also referred to as “single casting”.

  Patent Document 1 discloses an invention for combining a small-section twin casting and a large-section single casting with a single continuous casting machine. Patent Document 2 discloses an invention for producing a high-quality slab even in twin casting or triple casting. As disclosed in Patent Documents 1 and 2, twin casting and triple casting are divided in the width direction by arranging one or two middle partitions in the middle of the width direction of the continuous casting mold. Is done.

  As described above, various apparatuses and methods for carrying out twin casting in continuous casting of steel have been disclosed. However, continuous casting of a slab or bloom having a substantially rectangular cross section is performed with two sets of driving systems. When twin casting for casting slabs at the same time is performed, the position of the immersion nozzle for supplying molten steel is fixed by the tundish, so that it cannot be easily moved. Therefore, when casting slabs having different slab widths using the tundish at the same immersion nozzle attachment position, the immersion nozzles may deviate from the center position of the slab width.

  This restriction is that when continuous casting is performed while changing the slab width by moving the short side copper plate, the immersion nozzle is inevitably arranged offset from the center in the width direction of the slab to one side. This will increase the impact. Because of this restriction, the collision flow velocity to the short piece becomes uneven on the left and right sides, and the short piece close to the nozzle may cause fogging or breakout.

  For such a problem, Patent Document 3 describes a continuous casting method that defines the shape of the vicinity of the discharge hole of the two-hole type immersion nozzle, and a discharge flow on the short side from the immersion nozzle to the short piece. A continuous casting method is disclosed in which the applied static magnetic field is stronger than the applied static magnetic field on the long side.

Furthermore, in Patent Document 4, four electromagnetic coils for braking the molten steel discharge flow are arranged in total on the single side in the width direction of the slab, so that only the partition side of the twin mold is switched by switching the power supply side. And a continuous casting method that selects application of the full width.
JP 2003-53488 A JP 2006-95586 A JP 2006-150434 A JP 2005-230849 A

  As described above, various apparatuses and methods for carrying out twin casting, including those applied to casting of slabs and blooms, have been disclosed, and each contributes to stable operation and improvement of slab quality. In the continuous casting operation in which the width of the piece and the casting speed change from moment to moment, appropriate conditions were not obtained depending on the conditions. For this reason, it is necessary to identify the conditions that can prevent short piece burring and breakout by performing trial and error every time the slab width and casting speed change, or by performing flow analysis considering the influence of magnetic field. there were.

  In view of such a situation, the present invention is simple even when the casting conditions such as the width of the slab and the casting speed are changed without performing flow analysis considering the trial and error of the actual continuous casting and the magnetic field. An object of the present invention is to provide a method for continuously casting a slab under such a suitable condition by identifying conditions that can prevent short pieces from being fogged or broken out by a simple index.

  The inventors of the present invention performed the evaluation of the quality of the slab that was actually continuously cast and the analysis of the flow in the continuous casting mold, resulting in the flow situation in the continuous casting mold, the fogging in the short piece, and this. Due to the fact that there is a good correlation with the occurrence of breakout and the flow condition in the continuous casting mold by using an index that simply calculates the speed at which the discharge flow from the immersion nozzle collides with the short-side copper plate As a result of finding out that the quality of the slab to be predicted can be predicted and intensively studying based on these findings, the present invention has been completed.

  The present invention provides a short-side copper plate in which molten steel having a carbon concentration of 0.10% by mass or more and 0.13% by mass or less contained in a tundish is disposed so as to be movable in the mold width direction via an immersion nozzle. Continuous casting of steel, characterized in that when it is supplied to a continuous casting mold that can change the width of the slab by having it continuously cast, it satisfies the following formula (1). Is the method.

ΔT · Q ² /d·(1−0.0001·B)≦320 (1)
In the equation (1), ΔT is the molten steel superheat degree (° C.) in the tundish, B is the magnetic field strength (G) applied to the discharge flow of the molten steel supplied from the immersion nozzle, and the molten steel in the mold It is the maximum value of the magnetic field strength applied to this discharge flow at the center of the thickness, Q is the supply amount of molten steel from the immersion nozzle (ton / min / piece), and d is the immersion nozzle at the upper end of the continuous casting mold. It is the shortest distance (m) from the center to the short side copper plate surface.

Here, the magnetic field strength B refers to a value measured at the thickness center position in the mold using a gauss meter.
In the present invention, the molten steel having a carbon concentration of 0.10% by mass to 0.13% by mass contained in the tundish is fixed at an intermediate position in the mold width direction through two immersion nozzles. Are supplied to a continuous casting mold capable of changing the width of the slab by having an inner partition arranged in this manner and a short-side copper plate arranged so as to be movable in the mold width direction, and simultaneously supplying two slabs. A method of continuous casting from the center of the immersion nozzle to the center between the surface of the intermediate partition holding the molten steel pool in which the nozzle is immersed and the surface of the short side copper plate at the upper end of the continuous casting mold When the eccentricity obtained by dividing the distance by the distance from the surface of the inner partition to the surface of the short side copper plate at the upper end of the continuous casting mold is 5% or more, supply of molten steel from the immersion nozzle The amount is 1.5 (ton / min And this) or more, and a continuous casting method of steel, characterized in that the continuous casting under conditions satisfying the following relationship (2).

ΔT · Q ² /d·(1−0.0001·B)≦320 (2)
In equation (2), ΔT is the molten steel superheat degree (° C.) in the tundish, B is the magnetic field strength (G) applied to the molten steel discharge flow supplied from the immersion nozzle, and the molten steel in the mold It is the maximum value of the magnetic field strength applied to this discharge flow at the center of the thickness, Q is the supply amount of molten steel from the immersion nozzle (ton / min / piece), and d is the immersion nozzle at the upper end of the continuous casting mold. The shortest distance (m) from the center to the inner partition surface or the short side copper plate surface.

In these continuous casting methods according to the present invention, the continuously cast slab is exemplified as a slab or a bloom having a substantially rectangular cross-sectional shape.
For example, by the continuous casting method of steel according to the present invention,
(A) It has a short-side copper plate in which molten steel having a carbon concentration of 0.10% by mass or more and 0.13% by mass or less contained in a tundish is arranged so as to be movable in the mold width direction via an immersion nozzle. When changing the slab width or the casting speed during continuous casting by feeding to a continuous casting mold capable of changing the slab width by the above formula (1), The new operating conditions after this change are determined so that the relationship of the above is satisfied, and continuous casting is performed by changing the slab width or casting speed based on the determined operating conditions, or (b) tundish Molten steel with a carbon concentration of 0.10 mass% or more and 0.13 mass% or less contained in the metal is moved in the mold width direction through the two partition nozzles and in the middle of the mold width direction. By having a short-side copper plate that can be arranged If the slab width or casting speed is changed while supplying two continuous slabs to the continuous casting mold where the slab width can be changed and continuously casting continuously, prior to this change At the top of the casting mold, the distance from the center of the immersion nozzle to the center between the surface of the partition that holds the molten steel pool in which this nozzle is immersed and the surface of the short side copper plate is the top of the continuous casting mold. When the eccentricity obtained by dividing by the distance from the surface of the inner partition to the surface of the short side copper plate is 5% or more, the supply amount of molten steel from this immersion nozzle is 1.5 (ton / min / This is the above, and the operating conditions after this change are determined so that the relationship of the above formula (2) is satisfied, and the slab width or casting speed is changed based on the determined operating conditions, and continuous casting is performed. It becomes possible to do.

  According to the present invention, not only twin casting but also single casting can maintain the high productivity in the continuous casting of hypoperitectic steel, and can prevent the occurrence of short piece fogging so as to produce a slab. Become. Further, according to the present invention, for example, when the slab width or casting speed is changed during continuous casting, prior to this change, new operating conditions after the change that can prevent the occurrence of short piece burrs are easily and easily realized. By quickly determining and changing the slab width or casting speed based on the determined conditions, it becomes possible to perform continuous casting after this change while preventing the occurrence of short piece burring.

The best mode for carrying out the present invention will be described below together with the principle of the present invention with reference to the accompanying drawings.
The present inventors performed quality evaluation and flow analysis of a slab that was actually continuously cast, and found that there was a good correlation between the flow state in the mold and the short-chip burrs and breakout. Furthermore, it has been found that deterioration of the slab quality due to the flow situation in the mold can be predicted by an index that simply calculates the speed at which the discharge flow from the immersion nozzle collides with the short side. The present invention has been completed based on these findings.

  As described above, in continuous casting of steel, a casting method in which a plurality of slabs are simultaneously cast with a set of drive systems may be employed in order to improve productivity. This method is often applied especially when casting slabs with a small cross-sectional area, such as billets, and integrates a drawing roll and its drive mechanism following a plurality of molds, resulting in high production with less expensive equipment costs. Can be realized.

  However, when this technique is applied to continuous casting of slabs or blooms having a substantially rectangular cross section, twin casting is performed using castings with different slab widths using tundish at the same immersion nozzle mounting position. When a piece is cast, the submerged nozzle may deviate from the center position of the width of the slab. For this reason, the collision flow velocity to the short piece becomes uneven on the left and right sides, and the short piece on the side close to the immersion nozzle may cause fogging or breakout.

Therefore, we conducted flow analysis during twin casting under various conditions, and investigated the correspondence with the occurrence of short side burrs when continuous casting was actually performed.
FIG. 1 is an explanatory diagram showing dimensions and the like in the vicinity of the mold.

  As shown in FIG. 1, the inner partition 2 of 220 mm width was arrange | positioned in the center of the width direction of the continuous casting mold 1, and the installation width of the two immersion nozzles 3 and 4 was set to 900 mm, and the twin casting was performed. By moving the short side copper plates 5 and 6 in the width direction of the continuous casting mold 1, the distance from the surface of the inner partition to the surface of the short side copper plate at the upper end of the mold at the time of twin casting, that is, the width w of the strand is 500 mm to 1100 mm. It changed in the range of. Thus, the distance between the surface of the partition 2 and the center of the immersion nozzles 3 and 4 is constant at 340 mm, whereas the distance between the center of the immersion nozzles 3 and 4 and the surfaces of the short side copper plates 5 and 6 is the strand. Varies depending on the width w. FIG. 2 is a graph showing the relationship between the width w of the strand and the distance (distance to the short side) between the center of the immersion nozzles 3 and 4 and the surface of the partition 2 or the short-side copper plates 5 and 6. .

  When the distance between the surface of the partition 2 and the center of the immersion nozzles 3 and 4 and the distance between the center of the immersion nozzles 3 and 4 and the surfaces of the short side copper plates 5 and 6 are extremely different, 4, the collision flow velocity of the molten steel supplied from 4 becomes non-uniform, and there is a risk that a short piece located on the side close to the immersion nozzles 3, 4 will cause a burrs and breakout due to this. In order to prevent this, the electromagnetic brake 7 is arranged at a position sandwiching the immersion nozzles 3 and 4 so that the magnetic field strengths of the electromagnetic coils 7c and 7d on the inner partition 2 side and the outer electromagnetic coils 7a and 7b are equal. By applying a current to the electromagnetic coils 7a to 7d, instability of the flow of molten steel in the continuous casting mold 1 is prevented.

  As described above, when twin casting is performed, slabs having different slab widths are cast using the tundish at the same immersion nozzle mounting position, so that the immersion nozzle deviates from the center position of the slab width. An eccentric case occurs. It is easy to guess that the greater the degree of eccentricity, the greater the risk of occurrence of burrs and breakouts due to this in the short piece. In addition to being limited, if measures such as a reduction in the casting speed are taken, the casting efficiency is lowered, so that the advantages of twin casting cannot be fully exhibited.

  Therefore, in the present invention, particularly when performing twin casting, the surface of the inner partition holding the molten steel pool in which the nozzle is immersed from the center of the immersion nozzle at the upper end of the continuous casting mold and the surface of the short side copper plate It is also applicable when the eccentricity obtained by dividing the distance to the center by the distance from the surface of the inner partition at the upper end of this continuous casting mold to the surface of the short side copper plate is 5% or more. Features.

  In addition, twin casting is performed mainly for the purpose of improving productivity as described above, so that the casting speed, that is, the amount of molten steel supplied from the immersion nozzle per unit time is significantly reduced. There is no point in preventing wrinkles. Therefore, in the case of twin casting, the supply amount of molten steel from the immersion nozzle is set to 1.5 (ton / min / bar) or more as a more effective aspect in the implementation of the present invention.

  The short piece of burrs can be pulled out when the solidified shell is not strong enough in the continuous casting mold 1 to break the thin or weak part of the solidified shell and leak the molten steel. It is generated by. When short piece fogging occurs, it may remain as a coil surface flaw or end flaw even after hot rolling, so the slab must be maintained before hot rolling. Further, if a short piece of fog occurs at the bottom of the mold or after passing through the mold, it may lead to a breakout of the short piece.

  That is, a short piece of fog is likely to occur when the thermal energy of the collision flow is larger than the thermal energy required for melting the solidified shell. Furthermore, it is considered that the thermal energy of the collision flow increases in proportion to the degree of superheat of the molten steel, which is the difference between the melting point of the steel and the temperature of the molten steel, and the flow rate of the discharge flow to the solidified shell. On the other hand, it is considered that in a steel type that solidifies inhomogeneously, such as hypoperitectic steel, the thermal energy necessary for melting the shell becomes small in a thin portion of the solidified shell, and fogging is likely to occur.

  Therefore, the strength of the collision flow of molten steel is indexed based on hydrodynamic knowledge. The discharge flow from the immersion nozzles 3 and 4 is supplied by the molten steel static pressure in the tundish. At this time, the flow rate Q when the molten steel supplied by gravity is discharged through a path of a certain cross-sectional area can be expressed as in equation (3).

Q = s (2gh) ^1/2 ··· (3)
In the formula (3), s indicates the cross-sectional area of the inner holes of the immersion nozzles 3 and 4, and h indicates the required head height. In continuous casting, since the flow rate is adjusted at the bottom of the tundish, h is not the height of the molten steel head in the tundish but the virtual required head height for obtaining this flow rate. Although the flow resistance of the immersion nozzles 3 and 4 is ignored, the flow rate of the immersion nozzles 3 and 4 in slab casting is controlled by a sliding gate even if the machine and casting conditions are different. Since the molten steel is supplied to the inside of the continuous casting by a two-hole nozzle having a sufficient opening area, there is no problem because it can be said that the situation is similar.

The discharge flow rate is determined by the discharge pressure P, and the discharge pressure is proportional to h. That is, under the condition that the same immersion nozzles 3 and 4 are used, the discharge flow rate is proportional to the square of the discharge flow rate.
P∝h∝Q ²・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ （4）
The discharge flow rate attenuates the distance from the center of the immersion nozzles 3 and 4 to the inner partition 2 or the short-side copper plates 5 and 6 in inverse proportion to d (m). Therefore, the short side collision flow velocity index Ni indicating the short side collision speed is obtained as shown in Equation (5).

Ni = Q ² / d (5)
According to the equation (5), the collision speed at the short side copper plates 5 and 6 or the inner partition 2 is proportional to the square of the discharge flow rate Q and is inversely proportional to the distance d to the shorter side copper plates 5 and 6 or the inner partition 2. To do. At first glance, the short side collision flow velocity index Ni appears to be small under the condition where the slab width is wide. However, if the casting speed is the same, the discharge amount Q increases in proportion to the width w of the strand. The discharge flow that collides with the side copper plates 5 and 6 or the partition 2 increases in proportion to the width of the strand.

  FIG. 3 is a graph showing the relationship between the short side collision flow velocity index Ni obtained by the equation (5) under various conditions and the short side collision flow velocity calculated by the flow analysis. As shown in the graph of FIG. 3, the short side collision flow velocity index Ni and the short side collision flow velocity index have a substantially linear relationship regardless of various conditions, and the short side collision flow velocity index Ni is Although it is a simple index, it can be seen that the short-side collision flow velocity can be obtained without the need for flow analysis.

  FIG. 4 shows the relationship between the short side collision flow velocity index Ni and the molten steel superheat degree, and the occurrence state of fogging when the subperitectic steel having a carbon concentration of 0.10 mass% or more and 0.13 mass% or less is twin-cast. It is a graph which shows a relationship.

  From the graph shown in FIG. 4, the fogging generated in the short piece occurs when the short side collision flow velocity is large, but even when the slab width, casting speed and nozzle arrangement are the same, the molten steel has a high degree of superheat. It turns out that it gets worse. As described above, it is considered that a short piece of fog is generated when the thermal energy of the collision flow is larger than the thermal energy necessary for melting the solidified shell. That is, the thermal energy of the collision flow is increased when the temperature of the discharge flow is high in addition to the increase of the short-side collision flow velocity, leading to fogging and breakout. Thus, since both the molten steel superheat degree ΔT and the short side collision speed are positively correlated with the thermal energy of the collision flow, the occurrence of fogging shows the molten steel superheat degree ΔT and the short side collision speed. It is considered to be proportional to the product of the index Ni.

  Although the thermal energy of the discharge flow is accurately proportional to the superheat degree of the discharge flow, it is difficult to measure the superheat degree of the molten steel inside the continuous casting mold 1, so that the commonly measured tan It was decided to substitute the molten steel superheat degree ΔT in the dish.

  Further, when a magnetic field is applied to the discharge flow supplied from the immersion nozzles 3 and 4 by the electromagnetic brake 7, the discharge flow is attenuated and the flow velocity is reduced. FIG. 5 shows an example of the result of examining the influence on the collision flow velocity of the short side copper plates 5 and 6 by the application of the electromagnetic brake 7 inside the continuous casting mold 1 by the flow analysis in consideration of the influence of the application of the magnetic field. It is a graph. In the graph of FIG. 5, the collision flow velocity of the short-side copper plates 5 and 6 changes depending on the conditions. The relative value when only the maximum value B of the magnetic field strength applied to the discharge flow is changed at the central position is shown.

Here, the magnetic field strength refers to a value measured at the thickness center position in the mold using a gauss meter.
As a result of the flow analysis, linear short-side collision speed decay occurs in the range of magnetic field strength B from 0 to 5000 G. When a magnetic field of about 3000 G is applied to the discharge flow supplied from the immersion nozzles 5 and 6, the short-side collision occurs. The flow rate was found to decrease by about 30%. As a result of performing the same analysis under various conditions, this damping state indicates that the shape of the continuous casting mold 1 and the coil 7 that applies the static magnetic field are applied as long as the main stream of the discharge flow almost passes through the center of the static magnetic field. It was found that the shape was the same without being influenced by the shape of the steel and the casting conditions.

  Based on the above results, as an index for preventing the occurrence of short piece fogging, the above-described equation (5) has the effect of the application of the electromagnetic brake 7 on the term of the molten steel superheat degree ΔT (1−0.0001). -The short piece fogging index Di taking into account B) was obtained.

Di = ΔT · Q ² /d·(1−0.0001·B) (6)
Here, ΔT is the superheat degree (° C.) of the molten steel in the tundish, B is the magnetic field strength (G) applied to the discharge flow of the molten steel supplied from the immersion nozzle, and Q is the molten steel from the immersion nozzle. The supply amount (ton / min / piece), and d is the shortest distance (m) from the center of the immersion nozzle to the short side copper plate at the upper end of the continuous casting mold. Note that B has an upper limit of 5000 G, which is a practical range of electromagnetic brakes.

  For the short piece fogging index Di, subperitectic steel having a carbon concentration of 0.10 mass% or more and 0.13 mass% or less, various slab widths, casting speeds, eccentricity ratios of immersion nozzles, molten steel superheat degree and electromagnetic Continuous casting was carried out under the brake conditions, and the occurrence of short piece fogging was investigated. It is known that hypoperitectic steel is likely to solidify unevenly, and thus short-side fogging is generally likely to occur.

  FIG. 6 is a graph showing the relationship between the result of this investigation and this index. As shown in the graph in the same figure, a good correlation was observed between the short piece fogging index Di and the occurrence state of short piece fogging. In other words, when continuously casting hypoperitectic steel, the occurrence of short piece fogging can be prevented by continuous casting under the condition that the short piece fog index Di is 320 or less.

  This index does not include a variable that depends on whether it is single-casting or twin-casting. Therefore, if casting is performed so as to satisfy the expression (5), it is natural that the occurrence of short-side burrs can be prevented not only in twin casting but also in single casting.

  As described above, the main purpose of the present invention is to prevent fogging and breakout during twin casting. However, the index of the present invention is not limited to twin casting, and the discharge flow flows in the horizontal direction of the slab in the mold. Any condition that creates a flow that collides with the short-side copper plate is effective. That is, although the molten steel flow situation in the mold changes depending on the discharge amount at the time of casting, the discharge hole diameter of the immersion nozzle, the discharge angle, the blown Ar flow rate, etc., the provisions of the present invention can also be applied to ordinary single casting.

Further, the present invention will be described more specifically with reference to examples.
In order to confirm the effect of the present invention, a continuous casting test was conducted. Table 1 shows the specifications of the continuous casting machine used in this continuous casting test. As shown in Table 1, this continuous casting machine is a 7-point bending and 6-point straight vertical bending type 2-strand slab continuous casting machine with a slab thickness of 250 mm, and the vertical length is 2.5 m. The radius of curvature is 9.4 m and the captain is 32.7 m. The continuous casting mold has a maximum width of 2300 mm, and by placing the core inside the slab as a partition that divides the slab into two pieces, twin casting with a slab width of 500 mm to 1100 mm can be performed. It is a single and twin casting machine that can perform single casting if it is not arranged. The dimensions of each part near the continuous casting mold, such as the arrangement of the immersion nozzle and electromagnetic brake, are the same as those of the continuous casting mold 1 shown in FIG.

  Using this continuous casting machine, hypoperitectic steel having a carbon concentration of 0.10% by mass to 0.13% by mass was continuously cast. Table 2 summarizes the casting conditions and the occurrence state of short piece fogging.

  The occurrence of short piece fogging was investigated by allowing the cast pieces after continuous casting to cool and visually observing the appearance. And when it was less than 5 places per slab and the size of one burrs was within 50 mm, it was judged that it was minor, and when it exceeded this, it was determined that burrs were generated. When fogging occurred in twin cast slabs, all were on the inner partition side and none occurred on the outside.

Inventive Examples 1 and 2 and Comparative Examples 1 and 2 in Table 2 are obtained by casting the same steel type at the same slab size and casting speed. Even if the setting position of the immersion nozzle and the casting conditions are the same, as shown in Comparative Examples 1 and 2, when the short piece fogging index Di exceeds 320 because the molten steel superheat degree ΔT is high,
Obviously, the fogging is worse, but as shown in Invention Example 2, even when the molten steel superheat degree ΔT is high, an electromagnetic brake is applied to the side of the partition where the distance to the short piece is short, and the short piece fogging index Di is set to 320 or less. By doing so, generation of fogging can be prevented.

  Inventive Examples 3 to 6 and Comparative Examples 3 to 5 in Table 2 are results obtained by variously changing the slab width and casting speed. As shown in Comparative Examples 3 to 5, when the casting conditions are set so that the short piece fog index Di exceeds 320, the short piece generates blurring. However, as shown in Invention Examples 3 to 6, the short piece fog index Di is 320 or less. If the casting conditions are set so that the occurrence of fogging can be prevented. Inventive Example 3 and Comparative Example 3 are those in which the eccentricity is 0, that is, single casting, but even in the case of single casting as shown in Comparative Example 3, casting is performed so that the short piece fogging index Di exceeds 320. When the conditions were set, fogging occurred on the short piece although it was slight.

  Furthermore, Invention Examples 7 and 8 in Table 2 are results when the slab width is as narrow as 520 mm and 700 mm. In particular, in Example 8, the distance to the short side copper plate is very close on the inner partition side and the outer side, but the supply amount Q of the molten steel is also small, so that the short piece fogging index Di on the inner partition side and the outer side is not required even if no electromagnetic brake is applied. No. 171 and 161 were small, and no fogging occurred.

FIG. 1 is an explanatory view showing dimensions and the like in the vicinity of a continuous casting mold. FIG. 2 is a graph showing the relationship between the width w of the strand and the distance (distance to the short side) between the center of the immersion nozzles 3 and 4 and the surface of the partition 2 or the short-side copper plates 5 and 6. . It is a graph which shows the relationship between the short side collision flow velocity parameter | index Ni and the short side collision flow velocity. The graph which shows the relationship between the short side collision flow velocity parameter | index Ni and molten steel superheat degree, and the generation | occurrence | production state of a fogging when the subperitectic steel whose carbon concentration is 0.10 mass% or more and 0.13 mass% or less is twin-casting. It is. FIG. 5 is a graph showing an example of a result of examining the influence on the collision flow velocity of the short side copper plate by the application of the electromagnetic brake inside the continuous casting mold by the flow analysis in consideration of the influence of the application of the magnetic field. FIG. 6 is a graph showing sub-peritectic steel having a carbon concentration of 0.10% by mass to 0.13% by mass with various slab widths, casting speeds, submerged nozzle eccentricity, and molten steel superheat degree for the short piece fogging index Di. It is a graph which shows the result of having continuously cast on the conditions of electromagnetic brake conditions, and having investigated the generation | occurrence | production state of the short piece fogging habit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Continuous casting mold 2 Middle partition 3, 4 Immersion nozzle 5, 6 Short side copper plate 7 Electromagnetic brakes 7a-7d Electromagnetic coil

Claims (2)

The molten steel having a carbon concentration of 0.10 to 0.13% by mass contained in the tundish has a short-side copper plate arranged so as to be movable in the mold width direction through the immersion nozzle, thereby reducing the slab width. When feeding to a continuous casting mold that can be changed and continuously casting,
A continuous casting method for steel, characterized by performing continuous casting under conditions satisfying the relationship of the following formula (1).
ΔT · Q ² /d·(1−0.0001·B)≦320 (1)
In the equation (1), ΔT is the molten steel superheat degree (° C.) in the tundish, B is the magnetic field strength (G) applied to the discharge flow of the molten steel supplied from the immersion nozzle, Is the maximum value of the magnetic field strength applied to the discharge flow at the center of the molten steel thickness, Q is the amount of molten steel supplied from the immersion nozzle (ton / min / piece), and d is the upper end of the continuous casting mold. The shortest distance (m) from the center of the immersion nozzle to the surface of the short side copper plate. An intermediate partition in which molten steel having a carbon concentration of 0.10 to 0.13% by mass accommodated in the tundish is fixed and arranged at an intermediate position in the mold width direction via two immersion nozzles and the mold A method of continuously casting two slabs simultaneously by supplying a continuous casting mold capable of changing the slab width by having a short-side copper plate arranged movably in the width direction,
The distance from the center of the immersion nozzle to the center between the surface of the intermediate partition holding the molten steel pool in which the nozzle is immersed and the surface of the short-side copper plate at the upper end of the continuous casting mold, When the eccentricity obtained by dividing by the distance from the surface of the inner partition at the upper end of the casting mold to the surface of the short side copper plate is 5% or more,
The amount of molten steel supplied from the immersion nozzle is 1.5 (ton / min / bar) or more, and
A continuous casting method for steel, characterized by performing continuous casting under conditions satisfying the relationship of the following formula (1).
ΔT · Q ² /d·(1−0.0001·B)≦320 (2)
In the equation (2), ΔT is the molten steel superheat degree (° C.) in the tundish, B is the magnetic field strength (G) applied to the discharge flow of the molten steel supplied from the immersion nozzle, Is the maximum value of the magnetic field strength applied to the discharge flow at the center of the molten steel thickness, Q is the amount of molten steel supplied from the immersion nozzle (ton / min / piece), and d is the upper end of the continuous casting mold. The shortest distance (m) from the center of the immersion nozzle to the inner partition surface or the short-side copper plate surface.

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