JP2012066302A - Continuous casting method and continuous casting apparatus of steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a continuous casting method and a continuous casting apparatus of steel capable of obtaining a cast slab of excellent internal quality and less center segregation and center porosity even when a crater end shape extends at both ends in the width direction.SOLUTION: When continuously casting a cast slab by arranging a light rolling-reduction zone for drawing the cast slab while executing the light rolling-reduction zone thereof by gradually narrowing the opening of rolls holding the cast slab at the terminating end of solidification of the cast slab, a convex roll having the roll diameter at the center in the width direction being larger than the roll diameter at both ends is disposed on an upstream side section of the light rolling-reduction zone. The temperature distribution in the width direction on a surface of the cast slab is measured before the cast slab reaches the light rolling-reduction zone. When the temperature at the center position in the width direction is lower than the temperature at both ends in the width direction by the prescribed value, the light rolling-reduction is executed around the center portion in the plate thickness by the convex roll.

Description

  The present invention relates to a continuous casting method and continuous casting equipment for steel in which molten steel is drawn while being solidified to continuously produce a slab.

  The continuous casting method of steel, which is drawn continuously while solidifying the molten steel, has the great advantage that the yield is good and the productivity is high, and the final slab such as slab, bloom, billet, etc. is directly applied from the molten steel. Widely implemented as a casting method that can be manufactured continuously.

  However, when steel is continuously cast, elements such as C, P, and S are segregated (concentrated) at the center of the slab thickness.

  As a technique to improve the center segregation that occurs during continuous casting of such steels, the roll interval at the end of solidification is controlled against segregation caused by molten steel flow due to solidification shrinkage at the end of solidification, A technique for improving segregation by lightly reducing is known.

  For example, in Patent Document 1, when casting a slab by continuous casting, a bulging force is positively applied to the solidified shell between the mold and the liquidus crater end of the slab (in the middle of solidification). A technology is disclosed in which the thickness of the unsolidified layer in the slab is increased, and then the central segregation is reduced by applying a reduction (at the end of solidification) to the slab between the liquidus crater end and the solidus crater end. ing.

  Further, in Patent Document 2, in a method in which a slab is pressed in a thickness direction with a reduction roll during continuous casting, at least one crown roll is provided as the reduction roll, and the central portion of the slab and the vicinity thereof are provided. A light reduction casting technique for reducing the pressure is disclosed.

  Further, Patent Document 3 discloses a first reduction step of bulging the width center of the slab and then lowering this portion, and then, before the solidification in the vicinity of both ends of the slab is completed, A casting technique is disclosed in which both ends of the slab are rolled down using a roll having a roll diameter in the vicinity of the portion larger than the roll diameter in the center of the width.

JP-A-60-6254 JP 60-162560 A JP 2001-334353 A

  In the technology for reducing center segregation described in Patent Document 1, a bulging force is applied to a slab before light reduction to increase the thickness of the unsolidified layer in the slab, that is, the central portion in the width direction of the slab. Yes. However, when the thickness is increased, there is a concern that so-called “breakout” may occur in which the solidified shell is broken and molten steel is spilled, and there is a limit to the amount by which the thickness can be increased. For this reason, under light pressure after increasing the thickness, it is often necessary to lightly reduce the portion other than the portion where the thickness has been increased, which leads to an increase in the light pressure load. As a result, the predetermined light pressure cannot be achieved, and the center segregation is often not improved so much. In addition, this light reduction technology is a technology corresponding to the case where the crater end shape is substantially flat in the width direction, and it is difficult to cope with the case where the crater end shape is changed to a shape that becomes longer at both ends in the width direction. .

  In the continuous casting method described in Patent Document 2, it is a technique of rolling down the width center portion of a slab using a roll having a convex crown, and a technique of efficiently rolling down without causing an increase in light rolling load. It is. However, since the slab is reduced by the convex roll, a thickness distribution is given to the slab after the reduction in the width direction, and the slab after casting may be warped due to the thickness distribution. . In the subsequent rolling, the rolling pass schedule is determined on the assumption that the slab has a rectangular cross section, so that there may be a problem in that the planar shape of the rolling is poor and the yield is lowered. In addition, this light reduction technology is a technology corresponding to the case where the crater end shape is substantially flat in the width direction, and it is difficult to cope with the case where the crater end shape is changed to a shape that becomes longer at both ends in the width direction. .

  The continuous casting method described in Patent Document 3 is a technique for reliably reducing the both ends of the slab width, which tends to be the final solidification position in the width direction of the slab, and improving center segregation and porosity. There is a problem that a roll having a special shape for rolling down is required, and the roll by the roll having the special shape can be used only in this case. In addition, a thickness distribution in the width direction is generated in the slab that has been reduced, and, as in Patent Document 2, there may be a problem in rolling in a subsequent process. Furthermore, since it is necessary to bulge the central portion in the width direction, if the bulging conditions are wrong, the breakout described above may occur during bulging.

  The present invention has been made in view of such circumstances, and even when the crater end shape extends at both ends in the width direction, it is possible to obtain a slab of good internal quality with little center segregation and center porosity. It is an object of the present invention to provide a continuous casting method and continuous casting equipment for steel.

  In order to solve the above-mentioned problems, the present inventors have repeatedly measured the temperature distribution in the width direction of the slab during casting, and repeatedly investigated the variation in the width direction of the slab temperature. As a result, it was confirmed that the temperature distribution in the width direction of the slab is generally approximately equal, but the temperature in the central portion in the width direction may greatly decrease due to some factor. And when the temperature of the width direction center part fell large in this way, it also confirmed that the center segregation and porosity of the width direction both ends of a slab deteriorate. As a result of further investigations to improve the center segregation and porosity at both ends in the width direction, when a temperature drop in the center portion in the width direction is detected, that portion is positively raised in the upstream portion of the light pressure belt by a convex roll. I found out that it was effective to reduce the pressure.

  The present invention has been completed by further studies based on these findings, and provides the following (1) to (6).

  (1) A roll that injects molten steel into a mold and solidifies the slab formed by solidifying the surface in the mold while guiding it to a plurality of rolls, and sandwiches the slab at the final stage of solidification of the slab. Is a continuous casting method of steel in which a slab is continuously cast using a continuous casting facility in which a slab is placed under light reduction and the slab is pulled down while being squeezed down, and upstream of the light reduction slab On the side part, a convex roll having a roll diameter at the center in the width direction larger than the roll diameters at both ends is arranged, and the temperature distribution in the width direction of the slab surface is measured before the slab reaches the lightly pressed zone, A continuous casting method of steel, characterized in that when the temperature at the center in the direction is lower than the temperature at both ends in the width direction by a predetermined temperature, the convex roll is used to lightly reduce the center of the slab in the width direction.

  (2) When the temperature at the center in the width direction of the slab surface is a predetermined temperature lower than the temperatures at both ends in the width direction in (1) above, the amount of light reduction by the convex roll is controlled according to the temperature difference. A continuous casting method for steel characterized by the above.

  (3) In the above (1) or (2), when the temperature of the center part in the width direction on the slab surface is lower than the temperature at both end parts in the width direction, the center part in the width direction is centered by the convex roll. A method of continuous casting of steel, characterized in that after light reduction, light reduction is performed with rolls having the same diameter in the width direction at both ends in the width direction.

  (4) A steel continuous casting facility in which molten steel is poured into a mold and the cast slab formed by solidifying the surface in the mold is drawn while being solidified while being guided by a plurality of rolls. A light pressure belt that is placed at the end of the solidification phase, gradually narrows the opening of the roll that holds the slab, and pulls out the slab while lightly squeezed, and before the slab reaches the light pressure zone, A thermometer for measuring the temperature distribution in the width direction, the light pressure lower belt has a convex roll having a roll diameter at the center in the width direction larger than the roll diameters at both ends at the upstream side portion. A steel continuous casting facility characterized in that when the temperature in the center in the width direction is a predetermined temperature lower than the temperature at both ends in the width direction, the convex roll performs light reduction around the center in the width direction of the slab. .

  (5) In the above (4), when the temperature at the center in the width direction is a predetermined temperature lower than the temperatures at both ends in the width direction, a control device that controls the amount of light reduction by the convex roll according to the temperature difference. Furthermore, the continuous casting equipment of the steel characterized by comprising.

  (6) In the above (4) or (5), the light pressure lower belt is disposed in the upstream portion, and a first light roll having a convex roll having a roll diameter at the center in the width direction larger than the roll diameter at both ends. A central portion in the width direction, comprising a reduction segment and one or a plurality of second light reduction segments that are arranged in a downstream portion of the first light reduction segment and perform light reduction by a roll having the same diameter in the width direction When the temperature of is lower than the temperature at both ends in the width direction by a predetermined temperature, the first light pressure-lowering segment is subjected to light reduction centered on the widthwise center of the slab by the convex roll, and then the second A steel continuous casting facility characterized in that light reduction is performed around both ends in the width direction of the slab in the light reduction segment.

  According to the present invention, when the temperature at the center position in the width direction is lower than the temperature at both ends in the width direction, the amount of light reduction is controlled by the convex roll of the first light reduction segment according to the temperature difference. Since the slab is lightly reduced, the center of the slab whose crater end position has shifted to the upstream side can be actively lightly reduced first, and then the normal slab can be reduced. Can be appropriately performed in the width direction of the slab. For this reason, it is possible to prevent deterioration of center segregation due to insufficient light pressure and increase in center porosity, and a slab having good internal quality can be obtained. Further, since the slab after light reduction has a substantially rectangular cross section, the slab is not warped, and the subsequent rolling can be performed in the same manner as in the prior art.

It is a schematic structure figure showing the continuous casting equipment of steel concerning one embodiment of the present invention. It is the schematic which shows the light reduction segment used for the continuous casting installation of FIG. It is a schematic diagram which shows the roll shape used as an upper roll of the light pressure reduction segment of the light pressure reduction zone uppermost stream side in the continuous casting installation of FIG. It is a figure which shows the example of the surface temperature distribution of slab width direction. It is a figure which shows the relationship between the surface temperature measurement deviation of the width direction, and the amount of light reduction of an upstream segment. It is a schematic diagram which shows the cross-sectional shape of the slab which lightly reduced by the light pressure reduction segment of the light pressure reduction zone uppermost stream side in the continuous casting equipment of FIG.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram showing a steel continuous casting facility according to an embodiment of the present invention. This continuous casting equipment 1 includes a tundish 3 for storing molten steel, a mold 5 into which molten metal in the tundish 3 is poured, and a slab 7 in which the molten metal is cooled and solidified in the mold 5. It has a curved band 20 that guides downward and secondary cooling of the slab 7, and a horizontal band 21 that performs final solidification of the slab 7.

  A thermometer 25 for measuring the temperature distribution in the width direction of the surface of the slab 7 is installed at a position moving from the curved band 20 to the horizontal band 21.

  The curved belt 20 has a plurality of pairs of guide rolls 9 for holding the slab 7 and guiding it downward, and the cooling water 11 is sprayed on the slab 7 while the slab 7 is guided downward by the guide roll 9. Then, secondary cooling is performed, and the solidified thickness of the slab 7 gradually increases.

  The horizontal belt 21 is provided with a light pressure lower belt 22 in which a plurality of pairs of light pressure lower rolls are arranged. In the light pressure lower belt 22, the roll opening is gradually narrowed so that the slab 7 is pulled out while being lightly reduced. It has become.

  In the continuous casting facility 1, the rolls provided in the horizontal belt 21 are supported by a plurality of pairs in one frame to constitute a device called a segment. A plurality of these segments are arranged.

  Specifically, in the horizontal belt 21, three lightly reduced segments A, B1, and B2 that are configured to allow the slab 7 to be lightly reduced are arranged in order from the upstream side along the casting direction. A light reduction belt 22 is constituted by the reduction segments A, B1, and B2. Among these, the lightly reduced segment A constitutes a first lightly reduced segment for actively lightly reducing the central portion in the width direction of the slab, and the lightly reduced segments B1 and B2 are first lightly reduced segments. Consists of 2 lightly pressed segments. Note that the number of second lightly-under-pressed segments is not limited to two, and may be one or three or more.

  As shown in FIG. 2, the lightly reduced segments B1 and B2 have eight pairs of lightly reduced rolls 13 arranged in a state of being supported by the frame 15 so as to sandwich the slab 7 from above and below (FIG. 1). (Only three pairs are shown for convenience). On the frame that supports the upper roll of these lightly-lowering rolls 13, only four hydraulic cylinders 17 (two on the upstream side and one on the downstream side are shown; actually, two on the left and right sides are provided on the upstream side and the downstream side. ), And the slab 7 can be lightly reduced at a predetermined reduction setting by adjusting the distance between the rolls by these hydraulic cylinders 17. And the reduction setting can be changed for each segment during casting. In addition, the light pressure roll 13 is a roll with the same diameter in the width direction.

  As shown in FIG. 3, the light pressure lower segment A constituting the uppermost stream side portion of the light pressure lower belt 22 has a light pressure lower roll 13 ′ which is a convex roll having a different diameter in the width direction and a large central diameter as shown in FIG. 3. It has been incorporated. This lightly rolling roll 13 'has a small diameter from both ends to a and d of 1/8 length in the width direction, and is expanded from a and d to b and c of 1/4 length in the width direction, Between b-c which is a center part is a large-diameter convex part. On the other hand, a light pressure lower roll 13 having the same diameter in the width direction is incorporated as the lower roll. The other structure is the same as that of the light reduction segments B1 and B2, and has 8 pairs of light reduction rolls.

  In addition, the number of the lightly rolling rolls of the lightly rolling segments A, B1, and B2 is not limited to eight pairs. In general, the number of rolls in the segment is 6 to 8 pairs, but may be other than that.

  The temperature data acquired by the thermometer 25 is sent to the control device 30, and the control device 30 determines the lightly-undercompressed segment A according to the difference between the temperature at the center in the width direction of the slab 7 and the temperature at both ends in the width direction. A command is sent to the hydraulic cylinder 17 to adjust the roll interval of the light reduction segment A to control the amount of light reduction of the slab 7 by the light reduction roller 13 'which is a convex roll.

  Specifically, as shown in FIG. 4, when the horizontal axis represents the width direction position of the slab and the vertical axis represents temperature (° C.), there is usually almost no difference in the width direction as indicated by the wavy line. The slab width direction temperature causes a supercooling phenomenon at the center in the width direction as indicated by the solid line for some reason, and a temperature difference of ΔT occurs at both ends in the width direction. This ΔT is a predetermined value. If it exceeds, it is determined that supercooling has occurred. Then, the reduction amount ΔR in the light reduction segment A is determined based on the relationship between the temperature change ΔT (° C.) and the reduction amount ΔR (mm) as shown in FIG. In FIG. 5, when ΔT exceeds ΔT0, it is judged that supercooling has occurred, and the reduction starts, and when ΔT is ΔT1, the reduction amount in the light reduction segment A is set to ΔR1. The control device 30 has the relationship as shown in FIG. For example, if ΔT0 = 50 ° C., ΔT1 = 150 ° C., and ΔR1 = 2 mm, when ΔT exceeds 50 ° C., the reduction amount of 2 / (150-50) mm per 1 ° C. of the supercooling temperature Thus, the slab 7 is controlled to be lightly reduced.

Next, the operation | movement at the time of actually continuous casting in the continuous casting equipment of the steel comprised as mentioned above is demonstrated.
The molten metal stored in the tundish 3 is injected into the mold 5, and the injected molten metal is cooled by the surface of the mold 5 to become a slab 7 whose surface is solidified. The slab 7 is guided downward in the curved band 20 by the guide roll 9 and is sprayed with cooling water 11 to be secondarily cooled, whereby the solidification thickness of the slab 7 gradually increases.

  Then, the slab at the end of solidification that has reached the horizontal band 21 following the curved band 20 is gradually narrowed in the light pressure lower band 22 and pulled out while being lightly reduced. As a result, a completely solidified slab 7 is obtained.

  Conventionally, the slab 7 has been lightly squeezed by providing only a lightly squeezed segment having a normal structure such as the above-described lightly squeezed segments B1 and B2 in the lightly squeezed belt. However, the temperature of the slab 7 whose temperature is substantially uniform in the width direction may be greatly reduced due to some factor in the width direction central part. It has been found that deterioration of central segregation and increase in porosity occur.

  Therefore, in this embodiment, a thermometer 25 for measuring the surface temperature distribution in the width direction of the slab 7 is provided at a position immediately before the light pressure lower belt 22 and moves from the curved belt 20 to the horizontal belt 21, and the light pressure lower belt 22 A temperature reduction measured by the thermometer 25 is shown in FIG. 4 by providing a light reduction segment A using a light reduction roll 13 ′, which is a convex roll as shown in FIG. When the amount of decrease in temperature ΔT at the center of the slab width direction shown exceeds a predetermined value, the roll is opened by the hydraulic cylinder 17 so as to positively reduce the slab 7 with a predetermined light reduction amount in the light reduction segment A. Adjust the degree. At this time, in the lightly reduced segment A, the central portion in the width direction of the slab 7 is mainly squeezed by the convex roll, so the cross-sectional shape of the slab 7 is recessed in the central portion in the width direction as shown in FIG. It becomes a shape. Therefore, in the next lightly reduced segments B1 and B2, the reduction of both ends in the width direction of the slab 7 is performed at the center, and when passing through the lightly reduced belt 22, the cross-sectional rectangular shape having a substantially uniform thickness in the width direction. It becomes the slab of.

  It is said that the supercooling phenomenon in which the surface temperature near the center in the width direction of the slab is lower than the other parts is influenced by the flowing water and stagnant water upstream of the secondary cooling. In fact, it is not yet elucidated and no measures have been established. In any case, in reality, overcooling may occur or be canceled for some reason during casting, and the position in the width direction where this overcooling occurs may be near the center of the width. Many. When such supercooling occurs, the crater end position at the position in the width direction (the center in the width direction) where supercooling has occurred becomes upstream of the normal. That is, the crater end shape extends at both ends in the width direction. Even if normal light reduction is performed in such a state, the light pressure is insufficiently reduced, leading to central segregation and deterioration of porosity at the end in the width direction. Therefore, it is appropriate to lightly reduce the central portion in the width direction where overcooling has occurred on the upstream side than usual, and for this purpose, in the present invention, the central portion in the width direction of the slab is lightly reduced with a convex roll. is there. Further, when supercooling occurs, the average temperature of the slab is lowered than usual, and the light reduction load for performing a predetermined light reduction increases, but the light reduction segment A in the upstream portion of the light reduction belt 22 With a convex roll, only the vicinity of the center of the width is squeezed, and in the lightly squeezed segments B1 and B2 in the downstream part, the slab is squeezed around the ends of the slab with the center being recessed with a normal roll. It is easy to secure a predetermined amount of light reduction.

  As described above, according to the present embodiment, according to the temperature distribution in the width direction of the slab, light reduction of the slab can be appropriately performed in the width direction of the slab. Thus, an increase in center porosity can be prevented, and a slab having good internal quality can be obtained.

  The carbon steel having a carbon content of 0.05 mass% and a manganese content of 1.3 mass% was cast using the continuous casting facility shown in FIG. The slab (slab) thickness at this time was 250 mm, and the slab width was 2000 mm. Under the casting conditions of this steel type, the crater end is usually located in the lightly-reduced segment B1 or B2 in the lightly-reduced belt, so that the standard lightening is performed so that the lightly-reduced segments B1 and B2 each perform light reduction of 2 mm each. It defines the reduction conditions. In addition, since the light reduction segment has 8 sets of rolls, the reduction amount is 0.25 mm per set of rolls.

  During actual casting, the temperature distribution in the width direction before light reduction of the slab was generally flat in the width direction as indicated by the broken line in FIG. 4, but the width as indicated by the solid line in FIG. 4 during the casting. A supercooling phenomenon occurred in which the temperature in the center was lowered. Specifically, the temperature at the left end in the slab width direction (position 1/8 (250 mm) from the left end in the width direction of the slab) is 920 ° C., and the temperature at the right end (position 7/8 (1750 mm) from the left end). The temperature was 940 ° C., and the temperature at the center position (1000 mm from the left end) was 800 ° C. at the minimum.

  Therefore, in the example of the present invention, as the upper roll of the lightly pressed segment A, a convex roll having the shape shown in FIG. 3, wherein a is 1/8 (250 mm) from the left end, b is 1/4 (500 mm) from the left end, c is 3/4 (1500 mm) from the left end, and d is 7/8 (1750 mm) from the left end. As shown in FIG. 5, ΔT0 = 50 ° C., ΔT1 = 150 ° C., ΔR1 = 2 mm. The rolling reduction of the light rolling segment A was changed so as to conform to the above, and light rolling was performed to obtain a slab having a shape with a recessed central portion in the width direction as shown in FIG. As described above, the temperature at the left end in the slab width direction is 920 ° C., the temperature at the right end is 940 ° C., the average value is 930 ° C., and the temperature at the center temperature is at least 800 ° C. During the casting, ΔT reached a maximum of 130 ° C., and the amount of reduction in segment A was 1.6 mm. In the subsequent light reduction segments B1 and B2, both end portions of the slab with the concave central portion in the width direction were reduced by 0.25 mm per roll. On the other hand, in the comparative example, the light reduction in the light reduction segment A was not performed, and the reduction of only the light reduction segments B1 and B2 was performed under the same conditions as in the above-described example of the present invention.

  The center segregation in the width direction and the distribution of porosity in the slab cast under the conditions of the present invention example and the comparative example as described above were investigated. As a result, in the example of the present invention, a slab having excellent internal quality with very little central segregation in the entire width direction and no porosity was obtained, whereas in the comparative example, light reduction was performed particularly at both ends in the width direction. There were many central segregations and porosity that seemed to be insufficient. This is presumably because in the comparative example, the segments B1 and B2 tried to lightly reduce the center position at the same time in addition to both ends in the width direction of the slab, so that the light reduction load was increased and the predetermined light reduction could not be performed. Thus, the effect of the present invention was demonstrated.

DESCRIPTION OF SYMBOLS 1; Continuous casting equipment 3; Tundish 5; Mold 7; Slab 9; Guide roll 11; Cooling water 13; Light pressure roll 13 '; Light pressure roll (convex roll)
17; Hydraulic cylinder 20; Curved band 21; Horizontal band 22; Light pressure lower band 25; Thermometer 30; Control device A, B1, B2; Light pressure lower segment

Claims (6)

The molten steel is poured into the mold, and the slab formed by solidifying the surface in the mold is solidified while being guided by a plurality of rolls, and the opening of the roll that sandwiches the slab at the end of solidification of the slab Is a steel continuous casting method in which a slab is continuously cast using a continuous casting facility in which a light reduction belt is arranged to draw out while gradually reducing the slab.
A convex roll in which the roll diameter at the center in the width direction is larger than the roll diameters at both ends is arranged on the upstream side portion of the light pressure lower belt, and the width direction temperature of the slab surface before the slab reaches the light pressure lower belt. The distribution is measured, and when the temperature at the center in the width direction is lower than the temperature at both ends in the width direction, the convex roll is used to perform light reduction around the center in the width direction of the slab. Steel continuous casting method.   2. The amount of light reduction by the convex roll is controlled according to the temperature difference when the temperature at the center in the width direction of the slab surface is lower than the temperature at both ends in the width direction. The continuous casting method of steel described in 1.   When the temperature at the center position in the width direction on the surface of the slab is lower than the temperature at both ends in the width direction, the diameter in the width direction is equal after performing light reduction with the convex roll as the center at the center portion of the plate thickness. 3. The continuous casting method for steel according to claim 1, wherein light rolling is performed with a roll centering on a sheet thickness width direction. A steel continuous casting facility in which molten steel is poured into a mold, and the slab formed by solidifying the surface in the mold is drawn while being solidified while being guided by a plurality of rolls,
A light pressure lower belt that is arranged at the final solidification portion of the slab, gradually narrows the opening of the roll that sandwiches the slab, and pulls out the slab while lightly reducing it,
A thermometer for measuring the temperature distribution in the width direction of the slab surface before the slab reaches the light pressure lower zone,
The light pressure lower belt has a convex roll in which the roll diameter in the width direction central part is larger than the roll diameters at both ends in the upstream part,
A steel continuous casting facility characterized in that when the temperature in the center in the width direction is a predetermined temperature lower than the temperature at both ends in the width direction, the convex roll performs light reduction around the center in the width direction of the slab. .   When the temperature at the center in the width direction is lower than the temperature at both ends in the width direction by a predetermined temperature, it further comprises a control device that controls the amount of light reduction by the convex roll according to the temperature difference. Item 5. The continuous casting equipment for steel according to Item 4. The light pressure lower belt is disposed in the upstream portion, and has a first light pressure lower segment having a convex roll having a roll diameter in the center in the width direction larger than the roll diameters at both ends, and downstream of the first light pressure lower segment. Having one or a plurality of second light reduction segments arranged on the side portion and performing light reduction by a roll having the same diameter in the width direction;
When the temperature of the central portion in the width direction is lower than the temperatures at both ends in the width direction by performing light reduction centering on the center portion in the width direction of the slab by the convex roll in the first light reduction segment 6. The continuous casting equipment for steel according to claim 4 or 5, wherein the second light reduction segment performs light reduction about the both ends in the width direction of the slab.

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