JPH07178526A - Continuous casting method anf apparatus therefor - Google Patents

Abstract

PURPOSE:To stably obtain a cast slab having uniform composition over the whole range in the width direction without center segregation by using a mold provided with many recessed parts or recessed lines in the center part of a long side surface, thereby slowly cooling the center part of the long side surface of a slab. CONSTITUTION:This method is constituted of single or combined method by which the center part of the long side surface is slowly cooled. (a) The recessed parts are provided on the inner wall surface 11 at the center part 1h of the long side surface. The recessed parts can be provided with many fine small holes by machining of drilling machining, milling machining, etc., or shot-blasting, etc. (b) Secondary cooling water flowing density at the center part 9i in the slab width is defined as <=75% of water flowing density at the part 9c except the center part. The secondary cooling spraying is executed by the method such as water spraying, mist spraying so that the piping systems for secondary cooling water are separated from each other in both zone. (c) A heat-insulating layer consisting of low thermal-conductive material is provided at the part in contact with the center part 6h of the slab width of a supporting roll, reduction roll and drawing roll for continuous casting. The formation of the heat- insulating layer is executed by thermal-spraying ceramic material or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting method and apparatus for preventing center segregation of a slab in continuous casting of a slab having a rectangular cross section.

[0002]

2. Description of the Related Art When a slab is manufactured by a continuous casting method,
Internal defects, often called central segregation, are a problem. The center segregation of the continuously cast slab is C,
This is a phenomenon in which molten steel components such as S, P, Si, and Mn are positively segregated, which is a particularly serious problem in thick plate materials, and is known to cause deterioration of toughness in the segregated portion and hydrogen-induced cracking. ing. Unlike the case of steel ingot, which is determined only by metallurgical factors, the center segregation of continuously cast slabs is often influenced by mechanical factors specific to continuous casting machines, and its generation mechanism is complicated and its morphology is diverse. is there.

The occurrence of center segregation in a continuously cast slab is greatly affected by the solidification structure in the center of the slab and the dendrite residual molten steel at the end of solidification moves macroscopically due to bulging or solidification shrinkage. It is known that this occurs due to localized accumulation of concentrated molten steel.
As one of the measures for preventing the center segregation, there has been proposed a method of suppressing the flow of the concentrated molten steel by compensating for the solidification shrinkage of the final solidification portion by reducing the vicinity of the solidification tip portion by some method.

However, the improvement of the center segregation by only the rolling reduction can be achieved by any means of rolling reduction and die reduction.
As shown in FIG. 10, with the slab-shaped slab, the width (L)
If solidification nonuniformity in the direction is unavoidable, there is a drawback that improvement of the center segregation cannot be obtained over the entire width direction. As shown in FIG. 10 (a), in the slab-shaped slab, the width end portion (1/4 L to short side surface (edge)) is larger than the width center portion (1/4 L to 3/4 L). Side A and 3 /
From 4L to the short side surface (edge) side B, the progress of coagulation is slow, and as shown in FIG. 10 (b), the final coagulation position is different in the width direction, so uniform rolling cannot be performed. As shown, the segregation 21 deteriorates in the portion where the solidification of the slab 10 is delayed.

It is highly possible that the origin of this non-uniform solidification in the width direction occurs in the mold, and as shown in FIG.
It is considered that the solidification is delayed in the portion where the discharge flow of the molten metal 3 from the immersion nozzle 2 hits. Furthermore, mold 1
In the inside, since the contact between the center of the width and the mold 1 is good due to bulging, the progress of solidification proceeds near the width center of the slab rather than at the width end. In addition, it is considered that this non-uniform solidification in the width direction is promoted by the secondary cooling after leaving the mold 1. In addition, 4 shows a solidification shell and 5 shows powder.

As a method of improving the center segregation by eliminating the uneven solidification in the width direction, the solidification thickness of the slab is 5 to 90 times the thickness of the slab.
%, The strength of the cooling in the width direction of the slab is varied so as to uniformly grow the solidified shell in the width direction of the slab, and at least two pairs or more are provided near the crater end of the slab. Place the reduction roll of
A method of applying a predetermined reduction (Japanese Patent Publication No. 54-39216) has been proposed. The method disclosed in Japanese Patent Publication No. 54-39216 focuses on secondary cooling, but since quantitative description of cooling is not given, there is no reproducibility of improvement of center segregation at the edge portion, Moreover, since the solidification delay portion changes depending on the width of the slab, it is very difficult to control the cooling so as to follow it by only the secondary cooling, and the control range tends to vary. As a result, there is a problem that the surface quality of the slab, such as surface cracking, is adversely affected.

[0007] Further, Japanese Patent Application No. Hei.
No. 24760, there is proposed a step thickness mold in which the thickness of the slab is increased as shown in FIG. 18 only in the part where the solidification progresses in the width center part on the long side of the mold (step part 1g ). However, in this method, the step portion 1 of the mold 1 is
Since it is necessary to set the thickness of g at least 3 mm or more, it is difficult to set the slab pass line, and there is a problem in that slab bulging at the step portion 1g easily induces internal cracking. . Furthermore, this method is not practical because it is difficult to change the width of the slab.

Further, the interval between the guide rolls arranged in the drawing direction immediately below the casting mold in the thickness direction of the cast piece is gradually increased to cause bulging, and the thickness of the slab cast piece is set to 2 to the short side of the mold. After triple the amount, a method of performing light reduction with a small-diameter roll near the crater end (JP-A-1-
178355, Material and Process vol. 2 (19
89), p1159) have been proposed. However, in the method disclosed in Japanese Patent Laid-Open No. 1-178355 and the like, the phenomenon of bulging is left to the slab, so the unsolidified thickness is not stable and stable. Further, since the drum-shaped slab is rolled down, the rolling down amount at the width center portion becomes large, and it is difficult to carry out uniform rolling down in the width direction.

Another method is to include a large number of recesses evenly arranged on the entire surface or a part of the inside of the mold,
A mold in which the diameter or width of the recess is 2.5 mm or less, and the ratio of the total area of the recess in the inner surface of the mold including the recess is 20% or more and 90% or less (Japanese Patent Publication No. 57-11735). Gazette), a notch having a depth of 0.5 to 1.0 mm and a width of 0.3 to 1.0 mm is provided in the vicinity of the meniscus of molten steel in the mold on the surface of the mold, and the notch is parallel to the slab drawing direction. At a distance of 5 to 10 mm and satisfying the relation between the casting speed (Vc) and the mold vibration period (f) during casting to be 10> Vc / f × 1000 (Japanese Patent Laid-Open No. 2-6037). Gazette) etc. have been proposed.

[0010]

[Problems to be Solved by the Invention] Japanese Patent Publication No. 57-11
The method disclosed in Japanese Patent Laid-Open No. 735, JP-A No. 2-6037, etc. is to provide a concave zone on the surface of the mold on the molten steel side to gently cool the initial solidification zone, and to prevent the contact between the inner surface of the mold and the molten steel. By reducing the area ratio, gentle cooling is performed as a whole, and unevenness in the amount of heat removal is reduced to prevent surface defects such as vertical cracks. However, since all of these methods are mainly intended to prevent surface flaws such as vertical cracks by the overall slow cooling of molten steel in the initial solidification region, recesses are installed over the entire long side surface. ,
There is no idea of setting a recessed zone at a specific site.
It is known that a light reduction at the final stage of solidification is effective for improving the center segregation of the slab in continuous casting.
However, there is a problem in that, if only the light reduction is performed, the effect of improving the center segregation over the entire width direction cannot be expected when uneven solidification occurs in the width direction of the slab.

An object of the present invention is to provide a continuous casting method and apparatus capable of eliminating uneven solidification in the slab width direction in order to effectively function the effect of light reduction for improving the center segregation of the slab in continuous casting. is there.

[0012]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to achieve the above object, and as a result, solidification when molten steel passes through the mold, heat removal of the mold, and center segregation. The following findings have been obtained regarding the relationship. In the vicinity of the width end portion of the slab, the unsolidified thickness is larger than that in the width center portion due to the synergistic effect of two actions described below. That is,
(1) The action that the molten steel discharge flow from the immersion nozzle hits the short side, and the progress of solidification is delayed in the vicinity of the width end, which is the vicinity thereof,
(2) Due to bulging, the solidified shell at the center of the width has good contact with the mold, while the solidified shell at the width end has poor contact with the mold. Also due to the synergistic effect of the relative delay of coagulation.

Such non-uniform solidification in the width direction of the long side surface in the mold remains until the final stage of solidification, and segregation deteriorates in the part where solidification is delayed even if compensation for the solidification shrinkage due to light pressure is performed. Therefore, by providing a gentle cooling action for correcting the unevenness of the solidification behavior in the width direction of the long side surface to the central portion of the width, the heat removal action can be maintained uniformly over the entire width direction, and a uniform reduction is possible. It was clarified that it became, and this invention was reached.

That is, the first invention of the present application is a continuous casting method for continuously casting a slab-shaped slab, characterized in that the central portion of the long side surface of the slab is gently cooled as compared with a portion other than the central portion. .

The second invention of the present application is a method for slowly cooling the central portion of the long side surface of the slab as compared with the central portion other than the central portion, wherein a large number of concave portions are formed in the central portion of the long side surface along the casting direction of the mold. Alternatively, the continuous casting method is characterized in that a recessed line is provided and the mold cooling water flow velocity in the central portion of the long side surface is set to 70% or less of the cooling water flow velocity in the portions other than the central portion.

Further, the third invention of the present application is a method for slowly cooling the central portion of the long side surface of the slab as compared with the central portion other than the central portion, wherein the secondary cooling water amount density of the central portion of the slab width is changed to the water amount density other than the central portion. Is less than 75% of the continuous casting method.

Furthermore, the fourth invention of the present application is a mold for continuous casting of a slab having a rectangular cross section in which an inner wall defining a casting space is formed by a pair of long side surfaces facing each other and a pair of short side surfaces facing each other. In the above, there is provided a continuous casting mold characterized in that a large number of concave portions or concave lines are provided in the central portion of the long side surface along the casting direction.

According to a fifth aspect of the present invention, in a continuous casting mold in which a large number of recesses or ridges are provided in the central portion of the long side surface along the casting direction, from the vicinity of the meniscus to the mold outlet side along the drawing direction. The continuous casting mold is characterized in that a large number of recesses or grooves are provided only in the spaces.

The sixth invention of the present application is a continuous casting mold in which a large number of recesses or ridges are provided in the central portion of the long side surface along the casting direction. And the distance between the molten steel surface of the mold and the molten steel surface of the mold other than the central portion are larger than the distance between the molten steel surface and the molten steel surface by 5 mm or more.

Further, a seventh invention of the present application is a support roll, a reduction roll and a drawing roll for continuous casting of a slab-shaped slab, which is made of a material having a low thermal conductivity in a portion in contact with the central portion of the slab width of the roll. A roll for continuous casting, characterized in that a heat insulating layer is provided.

Furthermore, the eighth invention of the present application is a support roll, a reduction roll and a drawing roll for continuous casting of slab-shaped slabs, wherein a large number of recesses or depressions are provided in a portion in contact with the slab width central portion of the roll. A continuous casting roll characterized by having a strip.

A ninth invention of the present application is a continuous casting method in which the central portion of the long side surface of the slab is slowly cooled as compared with the central portion other than the central portion, and a large number of concave portions are formed in the central portion of the long side surface along the casting direction of the mold. Alternatively, the continuous casting method is characterized in that a recessed line is provided and the secondary cooling water amount density in the central portion of the slab width is set to 75% or less of the water amount density other than the central portion.

Further, the tenth invention of the present application is a continuous casting apparatus for gently cooling the central portion of the long side surface of the slab as compared with the central portion other than the central portion, in which a large number are provided at the central portion of the long side surface along the casting direction of the mold. And the support roll,
The continuous casting apparatus is characterized in that a large number of concave portions are provided in portions of the pressing roll and the drawing roll which are in contact with the central portion of the slab width.

Furthermore, the eleventh invention of the present application is in contact with the central portion of the slab width of the support roll, the pressing roll and the drawing roll in the continuous casting method in which the central portion of the long side surface of the slab is slowly cooled compared to the central portion other than the central portion. The continuous casting method is characterized in that a large number of recesses are provided in the portion and the secondary cooling water amount density in the central part of the slab width is set to 75% or less of the water amount density in the parts other than the central part.

Furthermore, the twelfth invention of the present application is a continuous casting method in which the central portion of the long side surface of the slab is slowly cooled as compared with the central portion other than the central portion, in the central portion of the long side surface along the casting direction of the mold. A large number of recesses or grooves are provided, and a large number of recesses are provided in the portions of the supporting roll, the pressing roll, and the drawing roll that are in contact with the central portion of the slab width. Is less than 75% of the continuous casting method.

[0026]

As shown in FIG. 10 (a), in the conventional continuous casting of the slab, the vicinity of the width end of the slab (A and B in the figure)
The solidification is delayed at this point, which causes the center segregation near the width end to deteriorate. The mode of this uneven solidification is shown in FIG.
As shown in FIG. 5, the vertical cross section has a W-shaped crater end shape, and is therefore referred to as W-shaped non-uniform solidification. The present inventors investigated the relationship between the uneven solidification in the slab width direction and the center segregation of the width end and the width center. FIG. 19 shows the relationship between the unsolidified thickness difference D _max -D _{min in the} width direction of the slab and the center segregation degree of C at the position 150 mm from the slab edge and at the center of the width when light reduction is performed at the final stage solidification part. Here, the unsolidified thickness difference D _max -D _min is an index of the uneven solidified amount in the width direction of the slab, and as shown in FIG. 17, the maximum unsolidified thickness D _max and the minimum unsolidified thickness in the slab width direction. This is the difference in the unsolidified thickness D _min . Further, in the present invention, since the main purpose is uniform reduction in the light reduction zone, the value of the unsolidified thickness difference _{Dmax- Dmin in} the width direction of the cast piece on the entry side of the light reduction zone is adopted. The unsolidified thickness can be measured by a FeS addition method, a Pb addition method, a rivet driving method, a white band (WB method) by electromagnetic stirring of a strand, or the like. The C segregation degree (C / C ₀ ) indicating the degree of center segregation is measured by measuring the C concentration in the center segregation part at the center of the slab width by emission spectrometry at 10 points, and the peak value C and the average C of the steel. It was evaluated as the ratio of the concentration C ₀ .

[0027] As shown in FIG. 19, the range of improvement center segregation across the width together as approximately 1.0 C a segregation ratio (C / C ₀₎ of the width end and the width central portion, -2 ≦ D _max - D
It became clear that _min ≦ 2. This is shown in FIG.
Since the solidification in the width direction is uniform as shown in (a),
This is because the light reduction was performed uniformly. Further, in the range of the unsolidified thickness difference D _max −D _min > 2 in the width direction of the cast slab, D _max −
As the D _min increases, the C segregation degree (C
/ C ₀ ) only slightly increases, but C near the width end
The segregation degree (C / C ₀ ) significantly increases. C near the width edge
FIG. 12 shows that the segregation degree (C / C ₀ ) greatly increases.
This is because, as shown in (b), the solidification profile is a W-shaped non-uniform solidification in which solidification is delayed in the vicinity of the width end, so that the width end is not rolled down. Degree of C segregation in the width center (C / C ₀ )
Is slightly increased because the molten steel flows in the width direction due to the non-uniform reduction in the width direction.

Further, the unsolidified thickness difference D _{max in the} width direction of the cast piece
In the range of −D _min <-2, the C segregation degree (C / C ₀ ) in both the width center part and the width end part slightly increases as D _max −D _min decreases, but increases to a range that poses a practical problem. I didn't. In addition, the difference in unsolidified thickness in the width direction of the slab D _max −D _min <−
The C segregation degree (C / C ₀ ) in the range of 2 is substantially uniform, and the C segregation degree (C / C ₀ ) at the width end is greatly deteriorated as in the range of D _max -D _min > 2. There was no such thing.
The coagulation profile in this region is as shown in FIG. This solidification form will be referred to as U-shaped non-uniform solidification because the crater end shape is U-shaped in the vertical cross section. That is, the U-shaped non-uniform solidification has a solidification mode in which solidification is completed first in the vicinity of the width end and finally solidification is completed in the width center, so that light reduction easily occurs near the width end,
It means that it is difficult to apply light reduction at the center of the width. Also in this case, since the light reduction in the width direction is a non-uniform reduction, the C segregation degree (C / C ₀ ) slightly increases due to the molten steel flow in the width direction. However, even after the completion of solidification at the width end portion, the reduction occurs in the width center portion, so that the C segregation degree (C /
C ₀ ) does not get worse. W-type non-uniform solidification (Fig. 12 (b))
In the case of U-shaped non-uniform solidification (FIG. 12 (c)), even if the same non-uniform pressure is applied, the final solidification is performed on the portion 3a (width end in FIG. 12 (b), center width in FIG. 12 (c)). The effectiveness of is different for the following reasons. That is, in the case of W-shaped non-uniform solidification (FIG. 12 (b)), the width end after the completion of solidification of the width center part has three regions 4a with large reduction resistance, whereas the U-shaped non-uniform solidification ( This is because, in the case of FIG. 12C, the central portion of the width after the completion of the solidification of the width end portion requires only two regions 4a having a large reduction resistance.

From the above, what should be avoided in preventing the center segregation of the slab is the difference in unsolidified thickness D _max -D _{min in the} width direction of the slab.
> 2, ideally −2 ≦ D _max −D _min ≦ 2
However, if D _max −D _min ≦ 2, a slab with center segregation suppressed in the slab width direction can be obtained. In order to suppress center segregation in the entire width direction, the solidification profile as shown in the current W-type non-uniform solidification (Fig. 12 (b)) is controlled by cooling the slab in the width direction to obtain uniform solidification (Fig. 12 (a)) and U-type non-uniform solidification (FIG. 12 (c)) are important, and in particular, gentle cooling of the central portion of the width of the slab is extremely effective.

In the example of FIG. 10 (a) which conceptually shows an example of the solidification profile in the width direction of the slab in the mold, the slab width center portion for gentle cooling in the present invention has a long side surface in the mold. Is W, and the solidified shell thickness at positions 1 / 20L and 19 / 20L from the short side edge A is the minimum in the width direction (the maximum unsolidified thickness is Dmax),
The shell thickness increases between L → 1 / 4L and between 19 / 20L → 3 / 4L. And between 1 / 4L and 3 / 4L, the solidified shell thickness is maximum in the width direction (the unsolidified thickness is the minimum Dm.
in), which is almost constant. Therefore, by setting the heat removal capacity distribution of the slab according to the solidification profile in the width direction as shown in FIG. 1, the thickness of the solidified shell 4 becomes substantially constant in the width direction as shown in FIG. It becomes possible to control the unsolidified thickness in the width direction. That is, the central part of the width where the slow cooling should be performed is in the vicinity of 1 / 4L to 3 / 4L, and further, the width direction solidification profile is investigated in advance, and the portion where the solidification progresses quickly is slowly cooled. Is preferred. The gentle cooling of the slab width center is ideally for keeping the unsolidified thickness in the width direction at a constant value, but unfortunately, the gradual cooling of the width center is too much to make the U-shaped uneven. Even if solidification occurs, center segregation does not pose a practical problem as described above, and a solidification profile more preferable than W-type nonuniform solidification can be obtained.

FIG. 20 shows the slow cooling rate S.E. at the center of the width from the slab solidification start position to the slab solidification end position. C. R. And the unsolidified thickness difference _{Dmax- Dmin in} the slab width direction are shown. Here, S. C. R. Is calculated by the equation (1). S. C. R. (%) = Q _s / Q _c × 100 (1) Formula Q _s : Average of heat flow velocity in the center of width from the solidification start position of the slab to the case of performing mild reduction when the slab width center is gently cooled Value (kcal / m ² · hr) Q _c : Average value of heat flow velocity (kcal) at the center of the width from the solidification start position of the slab to the light reduction when the slab width direction cooling control is not performed (conventional method) / M ² · hr) Note that the comparison of Q _s and Q _c is based on the same size, the same steel type, the same casting speed, and the same molten steel superheat degree.

In the example shown in FIG. C. R. Was 90% or less, it was possible to achieve a range of unsolidified thickness difference D _max −D _min ≦ 2 in which the center segregation in the entire width direction was good. Further, as shown in FIG. 1, the cooling in the central portion of the width is performed by the mold 1 (FIG. 1A), the secondary cooling device 9 (FIG.
(B)), continuous casting rolls 6, 7, 8 (FIG. 1 (c)), the S. C. R. Can be 90% or less. Furthermore, as a method of gentle cooling, a method of installing a recess or a groove (hereinafter referred to as a recess) on the inner wall of the mold (molten steel surface) or the surface of the roll, a method of reducing the cooling water flow velocity of the mold only in the width center, Any method may be used, such as a method of installing a slow cooling layer made of a low thermal conductivity material such as ceramics spraying or plating on the inner wall (molten steel surface) or the surface of the roll.

The effect of gentle cooling of the long side surface of the slab becomes greater as the solidified shell thickness becomes smaller and the heat resistance becomes smaller. From this point of view, it is most effective to take measures for gentle cooling in the mold. Furthermore, the inventors
It was found that the method of intentionally providing the air gap is the most effective in the slow cooling.

In the first invention of the present application, the central portion of the long side surface of the slab is cooled more slowly than the central portion, so that the heat removal amount in the central portion of the width of the slab slab is larger than that in other portions. Since it becomes smaller, solidification in the width direction of the long side surface of the slab becomes substantially uniform, uniform reduction in the light reduction zone is possible, and center segregation in the entire width direction of the slab can be suppressed.

In the second invention of the present application, a large number of concave portions are provided in the central portion of the long side surface along the casting direction of the mold, and the mold cooling water flow rate at the central portion of the long side surface is set to the cooling water flow rate other than the central portion. by 70% or less, as shown in FIG. 23 showing the relationship between the mold cooling water flow rate u and the mold surface temperature T _surf, mold surface temperature T _surf the Nagahenmen central portion rises about 100 ° C.. When the mold surface temperature T _surf rises, the slab surface temperature also rises, so the strength of the solidified shell becomes small, the continuous casting powder easily flows between the solidified shell and the mold, and the powder thickness becomes large. Therefore, the cooling water flow velocity reducing section can be gently cooled. However, although only controlling the mold cooling water flow velocity u in the width direction has no effect on reducing the unsolidified thickness difference D _max -D _min , by using a mold in which a concave portion is provided in the width center portion of the mold inner wall, Is effective. Further, the nonuniform solidification relaxation ability is improved as compared with the case where the cooling water flow rate is not changed by using a mold having a large number of recesses in the central portion of the long side surface, so that the casting speed increases and the immersion It is also possible to deal with the case where the molten steel discharge flow from the nozzle becomes large.

FIG. 24 shows a mold in which a large number of concave portions are provided in the center of the long side surface of the second invention of the present application, and a mold center in which only the mold cooling water flow rate u in the width direction is controlled and other than the width center part. The relationship between the cooling water flow rate ratio u _c / u _e and the unsolidified thickness difference D _max -D _min is shown. In the second invention of the present application, the uncooled thickness difference D _max −D _min is significantly reduced by setting the mold cooling water flow rate u _c in the width center part to 70% or less of the cooling water flow rate u _{e in} the parts other than the center part. ing. On the other hand, when only the cooling water flow velocity u in the width direction is controlled using a conventional mold in which a large number of concave portions are not provided in the central portion of the long side surface, the cooling water flow velocity u _c in the central portion is set to 10% or less. However, the unsolidified thickness difference _{Dmax- Dmin} is hardly reduced. Nagahenmen template cooling water flow rate u _c of the central portion to 70% or less of the cooling water flow rate u _e other than the central portion, as shown in FIG. 5, the mold cooling water flow rate u _c of the central portion 1j of the mold 1 So as to be 70% or less of the cooling water flow rate u _e of 1k other than the central part, the cooling water of the width center part 1j and the cooling water of 1k other than the width center part are set as separate piping systems, and the cooling water flow speeds are individually set. Can be achieved by

In the third invention of the present application, the secondary cooling water amount density in the central portion of the slab width is 75% of the water amount density other than the central portion.
FIG. 27 showing the relationship between the water amount density in the width center part of the secondary cooling water and the water amount density ratio Q _c / Q _e × 100 other than the center part and the unsolidified thickness difference D _max -D _{min by} the following. As described above, it is possible to set the unsolidified thickness difference D _max −D _min to 2 mm or less. To make the secondary cooling water volume density in the central part of the slab width 75% or less of the water content density other than the central part,
As shown in (b), the water amount density (L
/ Min · m ² ) is 75% of the water density of 9c except for the central part
Connect the secondary cooling water piping system to the width center part 9i
And 9c other than the width center part can be achieved by a separate system. The secondary cooling water may be sprayed by any method such as water spray or mist spray. FIG. 21 (b) shows the transition of the unsolidified thickness difference D _max -D _{min in} the casting direction when the secondary cooling in the third invention of the present application is applied from the time when the mold is discharged until the end of the light reduction. Figure 21
As shown in (b), the unsolidified thickness difference D _max -D _min is 2
It is clear that the effect of the widthwise control of the secondary cooling water amount density is that it decreases after exiting the mold, and that it greatly decreases on the entry side of the light reduction zone, and that it has a nonuniform solidification relaxation capability.

In the fourth invention of the present application, since a large number of recesses are provided at the center of the long side surface along the casting direction, the heat removal capability of the recesses is small and the center portion of the long side surface is cooled slowly. As a result, the solidification of the long side surface of the slab in the width direction becomes substantially uniform, uniform reduction in the light reduction zone is possible, and center segregation in the width direction of the slab can be suppressed. The mold of the fourth invention of the present application is a mold having a rectangular cross section with a high aspect ratio like a slab, as shown in FIGS. 2 and 3, in which a concave portion 1a is provided in a specific portion of the inner wall surface of the long side surface 11. Then, Fig. 2
Shows the case of the concave stripe 1a, and FIG. 3 shows an example of the case where the shape of the concave portion 1a is a dimple. In any case, the recess 1a can be obtained by machining with a drilling machine, a milling machine, or the like. In addition, if the area ratio of the recess installation zone 1b required for gentle cooling is secured, a method of providing a large number of fine small holes by shot blasting or the like is also possible.

In addition to the shapes of the recesses shown in FIGS. 2 and 3, the same effect can be obtained even if the recesses are inclined at a certain angle. However, since a recessed shape that is too complicated is difficult to process and is not practical, a recessed stripe shape as shown in FIG. 2 is generally used. Recessed strip 1a as shown in FIG. 2 (b) or FIG.
When the concave portion 1a as shown in FIG. 2 is installed, the air gap 6 ₁ becomes large as shown in FIG. 2 (c). For example, when a recessed line having a depth of about 200 μm is installed, the heat transfer resistance is
As shown in (1), it greatly increases to more than twice as much as that of a normal mold having no recessed line, the heat removal capability becomes extremely small, and gentle cooling becomes possible. In the case of a normal mold, the air gap amount δ at the lower end of the mold is estimated to be 50 to 90 μm, so 2
It can be seen that the order of 00 μm is very large.

The installation position of the recess 1a in the mold is the first
This is similar to the method of setting the slow cooling zone of the invention. As a preferred embodiment, the mold of the present invention shown in FIGS. 2 and 3 has a position 1b where solidification proceeds rapidly near the center of the width of the inner surface on the long side (the surface in contact with molten steel) (for example, the width of the long side is W). , 1 /
The concave portion 1 is provided on the width center side from the 4L position to the 3 / 4L position).
a is installed, and the heat removal capability is reduced so that the part is slowly cooled. At the position 1c where the solidification progresses slowly at the width end (between the edges of about 1 / 4L and between the edges of 3 / 4L in the above-described example), the heat removal capability is maintained as it is without setting the recessed zone. However, as in the case of the first invention of the present application, the positions where the solidification shell thickness becomes maximum and minimum vary depending on the nozzle shape and the casting speed. Therefore, the width-direction solidification profile should be investigated in advance and the width-direction solidification profile should be adjusted accordingly. It is desirable to determine the position where the recess is installed.

According to a fifth aspect of the present invention, in a continuous casting mold in which a large number of recesses or ridges are provided in the central portion of the long side surface along the casting direction, the mold outlet side from the vicinity of the meniscus along the drawing direction. Since a large number of recesses are provided only up to, the recesses may cause operational troubles such as breakout if the recesses are simply installed near the meniscus. Therefore, as shown in FIG. Precise specifications are required for processing the recess, such as (the width of the groove or the diameter of the dimple) needs to be reduced. Therefore, when breakout is likely to occur, the use of a mold in which the concave portion is not installed in the meniscus portion has an advantage that the concave portion is not so strict in specifications.

Since the main object of the conventional slow cooling mold is to prevent surface flaws such as vertical cracks of the slab, it is absolutely necessary to install the concave portion near the meniscus, but the main object of the fifth invention of the present application is. Since the width direction uncoagulated thickness in the terminal coagulation region is controlled to be constant, it is not always necessary to install the concave portion 1a in the vicinity of the meniscus 1d, but rather the meniscus 1d.
No concave zone is intentionally installed in the vicinity.
However, if the recess installation position is far away from the meniscus 1d, the slow cooling effect cannot be expected, so it is necessary to set the upper edge level of the recess zone as close to the meniscus as possible without causing trouble. As shown in FIG. 15, the relationship between the distance H between the upper edge of the recessed zone and the meniscus 1d and the thickness of the solidified shell at the outlet of the mold is as shown in FIG. Therefore, the slow cooling effect cannot be expected so much as compared with the mold in which the concave portion is installed up to the meniscus 1d. Upper edge of concave zone and meniscus 1
If the distance H from d is set to about 100 mm, there is a sufficient cooling effect as shown in FIG. 15, and therefore, the unsolidified thickness can be controlled to a constant value in the width direction, and trouble such as breakout can be prevented. Worry is as low as conventional molds.

The following specifications are desirable for the shape of the recesses and the space between the adjacent recesses in the mold of the present invention.
FIG. 22 shows the influence of the depth d _m of the recessed portion at the center of the width and the total area ratio α _{m of the} recessed zones on the unsolidified thickness difference D _max -D _min when the molds of the fourth and fifth inventions of the present application are used. Indicates.
Here, the total area ratio α _m of the recessed zone is defined by the following equation (2). Total area ratio α _m (%) = (total area of concave portion 1a / area of long side surface of mold) × 100 (2) Formula For both the molds of the fourth and fifth inventions of the present application, the depth d _{m of the} concave portion
It is possible to set the range of the unsolidified thickness difference D _max −D _min ≦ 2 for improving the center segregation in the entire width direction by the combination of the total area ratio α _m of the concave zone and the total area ratio α _m . However, since the mold of the fifth invention of the present application has no recess in the meniscus portion, both the depth d _{m of} the recess and the total area ratio α _m of the recess zones need to be larger than those of the mold of the fourth invention of the present application. There is.

However, considering the operational stability such as prevention of metal adhesion to the recess and prevention of powder intrusion, the mold of the fourth invention of the present application has a recess depth d _m of 0.2 ≦ d _m ≦ 1.0,
The total area ratio α _m of the recessed zone is α _m ≧ 25, and in the mold of the fifth invention of the present application, the depth d _{m of the} recessed portion is 0.5 ≦ d _m ≦
2.0, the total area ratio α _m of the recessed zones is preferably in the range of α _m ≧ 25. In the mold of the fifth invention of the present application, it is necessary to reduce the value of the depth d _m of the concave portion because the concave portion is installed in the meniscus, so that the metal is easily attached to the concave portion or the powder enters This is because it is easy to do so, and the restrictions are large. As shown in FIG. 14, the heat transfer resistance when the recess depth is 0.2 mm or more is about 40 × 10.
^-4 hr · ° C / kcal, the heat transfer resistance of the normal mold is about 2
The heat transfer resistance is more than double that of 0 × 10 ⁻⁴ hr · ° C./kcal.

Furthermore, the width or diameter Wm of the recess differs in the molds of the fourth and fifth inventions of the present application. That is, in the mold of the fourth invention of the present application, since there is a recess near the meniscus, it is desirable that the width or diameter Wm of the recess be 1.0 mm or less from the viewpoint of preventing powder from flowing into the recess zone. On the other hand, in the mold of the fifth invention of the present application, the width or diameter Wm of the recess is preferably 200 mm or less from the viewpoint of preventing bulging, but it is more rigorous than the slow cooling mold of the fourth invention of the present application having a recess near the meniscus. It is not necessary to design the width or the diameter Wm, and in this respect, the mold of the fifth invention of the present application has a greater degree of freedom in recess processing. Im between adjacent recesses
Is preferably 10 mm or less from the viewpoint of preventing uneven solidification of the recess installation portion. This is because when the distance Im is larger than 10 mm, the difference in thickness between the solidified shells 4 corresponding to the concave portion 1a and the concave portion 1e becomes large as shown in FIG.

Next, the uneven solidification mitigation effect of the molds of the fourth and fifth inventions of the present application will be described by focusing on the transition of the uneven solidification amount in the casting direction. The transition of the unsolidified thickness difference D _max -D _min between when using the mold of the present invention and when using the conventional mold is shown in FIG.
It is shown as (a). In addition, when using the mold of the present invention, the recess specifications are as shown in Tables 1 and 2. Unsolidified thickness difference D _max that occurred in the mold when using the conventional mold
-D _min increases up to 2.0 m below the meniscus. This is because the temperature distribution in the widthwise slab at the outlet of the mold is non-uniform as shown in FIG. 13, so that non-uniform cooling is promoted in the secondary cooling region. After that, due to the difference in heat transfer resistance between the part where the progress of solidification is delayed and the part where the progress of solidification is early,
The unsolidified thickness difference D _max -D _min decreases, but the unsolidified thickness difference D _max -D _min is 10 even on the entry side of the light reduction zone.
There is about mm (shell thickness on one side: 5 mm). This unsolidified thickness difference D _max- D _min corresponds to about 1.0 m in terms of the final solidified position difference ΔL (FIG. 10 (b)), which leads to unevenness in the width direction under light pressure reduction and at the solidification delay portion. The degree of segregation will be increased. On the other hand, in the case of the mold of the fourth invention of the present application, the difference in the unsolidified thickness _Dmax- D in the mold is almost equal.
_Since there is no _min , this unsolidified thickness difference D _max -D _min is maintained in a none state up to the entry side of the light reduction zone.

[0047]

[Table 1]

[0048]

[Table 2]

In the sixth invention of the present application, in a continuous casting mold in which a large number of recesses or ridges are provided in the central portion of the long side surface along the casting direction, the surface of the mold cooling water in the central portion of the long side surface is By making the distance of the molten steel surface of the mold 5 mm or more larger than the distance between the surface of the mold cooling water other than the central portion and the surface of the mold cooling water, the distance d ₁ from the surface of the mold cooling water to the molten steel surface of the mold and the mold surface temperature T _surf As shown in FIG. 25 showing the relationship, when the distance d ₁ from the mold cooling water surface to the mold molten steel surface differs by 5 mm, the mold surface temperature T _surf differs by about 100 ° C. Therefore, as in the case of the mold cooling water flow rate u described above, slow cooling can be achieved by increasing the thickness of the continuous casting powder. The present inventors have no effect on the reduction of the unsolidified thickness difference D _max -D _min by controlling the distance d ₁ from the surface of the mold cooling water to the surface of the molten steel in the mold, but the control of the inner wall of the mold is not effective. It has been found that a very good effect is exhibited by combining with the molds of the fourth and fifth inventions of the present application in which the concave portion is provided in the width center portion. For each sixth surface of the mold cooling water of the mold in the width direction of the aspect of the invention the mold with controlled only the distance d ₁ of the mold the molten steel surface in FIG. 26, from the surface of the mold cooling water to the distance d ₁ of the mold molten steel surface The relationship of unsolidified thickness difference _{Dmax- Dmin} is shown. In the mold of the sixth invention of the present application, the distance d ₁ from the surface of the mold cooling water at the center of the width to the molten steel surface of the mold is made 5 mm or more larger than the distance d _{1 of the} surface of the molten mold from the surface of the cooling water of the mold other than the central portion. As a result, the unsolidified thickness difference D _max -D _min is significantly reduced. On the other hand, in the mold in which only the distance d _{1 of the} molten steel surface from the surface of the mold cooling water in the width direction is controlled, the distance d _{1 of the} molten steel surface of the mold from the surface of the cooling water in the central portion is set to the cooling temperature of the molds other than the central portion. ₁ from the distance d ₁ from the water surface to the molten steel surface of the mold
Even if the thickness was increased by 0 mm, the unsolidified thickness difference D _max -D _min was hardly reduced.

The transition of the unsolidified thickness difference D _max -D _{min in} the casting direction when the mold of the present invention is used is shown in FIG. 21 (a). FIG. 21 (a) shows the mold of the fifth invention of the present application in which the meniscus portion is not provided with a recess, and the width direction control of the distance d ₁ from the mold cooling water surface to the mold molten steel surface is performed. The mold has substantially the same behavior as the mold of the fourth invention, and the unsolidified thickness difference D _max -D _min is almost completely absent in the mold, and this state is maintained even at the light pressure zone entering side. That is, also in the mold of the sixth invention of the present application, it is apparent that the nonuniform solidification relaxation ability is improved by controlling the width direction of the distance d ₁ from the mold cooling water surface to the molten steel surface of the mold. Therefore, in the mold of the sixth invention of the present application, in order to obtain the desired nonuniform solidification relaxation ability, the recessed portion is provided on the molten steel surface side, and the width direction control of the distance d ₁ from the surface of the mold cooling water to the molten steel surface of the mold is performed. This makes it possible to set the specifications of the recesses in a stable operation direction, as in the second invention of the present application. Furthermore, the mold of the sixth invention of the present application has the advantage that the structure of the cooling water can be simplified because the cooling water piping system can be made the same in the width center and in other areas. Further, since the uneven solidification relaxation ability of the mold of the sixth invention of the present application is improved as compared with the molds of the fourth and fifth inventions of the present application, the casting speed is increased and the molten steel discharge flow from the immersion nozzle is increased. It is also possible to deal with the case.

As the name implies, the support rolls, reduction rolls, and drawing rolls for continuous casting play the role of supporting and drawing the slab, and at the same time, have the role of cooling the slab by contact heat transfer with the slab. Is playing. Since an ordinary continuous casting machine has at least 20 rolls or more, the influence of roll cooling on the solidification characteristics of the continuous cast slab is great. In the seventh invention of the present application, the width of the support roll for continuous casting of the slab-shaped slab, the reduction roll, and the drawing roll provided with the heat insulating layer made of the low thermal conductivity material in the portion in contact with the central portion of the slab width. The cooling capacity of the central part is slower than that of other parts, and the central part of the long side surface can be gently cooled, solidification in the width direction of the long side surface of the slab is almost uniform, and uniform rolling in the light reduction zone is achieved. It is possible to suppress center segregation in the entire width direction of the slab. As the heat insulating layer of the low thermal conductivity material used for the supporting roll, the pressing roll and the drawing roll of the seventh invention of the present application, Al ₂ O ₃ , Z
Examples include a method of spraying a ceramic material such as rO ₂ and a method of increasing the thickness of the Ni and Ni—Cr plated layers. Generally, continuous casting rolls are used together with secondary cooling, and therefore, when the ceramic material contains water, problems such as deterioration occur. Therefore, a method of increasing the thickness of the Ni and Ni-Cr plated layers is practical. . However, if water is not used as in dry casting, Al
A method of spraying a ceramic material such as ₂ O ₃ or ZrO ₂ may also be effective.

In the continuous casting roll of the seventh invention of the present application, the relationship between the thickness t of the heat insulating layer made of the low thermal conductivity material and the unsolidified thickness difference D _max -D _min , which is arranged in the roll width center, is shown in FIG. Show. FIG. 28 shows a roll having ZrO ₂ sprayed on the central portion. The secondary cooling is dry casting, and the number of rolls through which the slab passes until the final solidification position is 50. As shown in FIG. 28, the unsolidified thickness difference D increases as the thickness t of the heat insulating layer of the roll increases.
_max- D _min is reduced, and the thickness t of the heat insulating layer of the roll is 1 mm
By the above, it is possible to make the unsolidified thickness difference D _max −D _min ≦ 2 mm, which can improve the center segregation of the entire slab in the width direction. Unsolidified thickness difference D when the continuous casting roll of the seventh invention of the present application is applied from the time when the mold is released until the end of the light reduction.
_As shown in FIG. 21 (b), the transition of _max- D _{min in} the casting direction decreases the unsolidified thickness difference D _max -D _min after leaving the mold due to the effect of the roll cooling width direction control. It is clear that it has almost no heterogeneous solidification relaxation ability on the entrance side.

In the eighth invention of the present application, a large number of concave portions are provided at the portions in contact with the central portion of the slab width of the support roll, the pressing roll and the drawing roll for continuous casting of the slab-shaped slab, whereby the width central portion is provided. The cooling capacity of the slab is slower than that of other parts, and the central part of the long side surface can be gently cooled, solidification in the width direction of the long side surface of the slab is almost uniform, and uniform reduction in the light reduction zone is possible. Thus, center segregation in the entire width direction of the slab can be suppressed. The shapes of the recesses of the supporting roll, the pressing roll and the drawing roll of the eighth invention of the present application may be concave stripes or dimples, as in the case of the above-mentioned mold, as long as they have the required slow cooling ability. Further, the processing method may be mechanical processing using a drilling machine, a milling machine or the like, or a method using shot blasting or the like.

The specifications of the recesses of the supporting roll, the pressing roll and the drawing roll of the eighth invention of the present application are determined as follows. 29. In FIG. 29, in the continuous casting roll of the eighth invention of the present application, the depth d _r of the concave portion and the area ratio α _{r of the} concave portion zone and the unsolidified thickness difference D _max −D arranged in the width center portion of the roll
Indicates the relationship of _min . The area ratio α _r of the recessed zone is defined by the following equation (3). Area ratio α _r (%) = total area of recesses / area corresponding to roll long side surface × 100 (3) Formula The continuous casting roll according to the eighth aspect of the present invention has a depth d _{r of} recesses.
The unsolidified thickness difference D that can improve the center segregation of the entire slab in the width direction by the combination of the area ratio α _r of
It is possible to have _max- D _min ≦ 2 mm. However, from the viewpoint of preventing roll wear, it is preferable that the recesses have specifications such that the area ratio α _r ≦ 50% of the recess zone and the depth d _r ≦ 2.0 mm of the recess.

The interval or diameter Wr of the recesses of the continuous casting roll of the eighth invention of the present application may theoretically be within a range capable of preventing bulging of the slab in the recesses, but in order to prevent the inflow of secondary cooling water. 1.0 mm or less is suitable. Eighth of the present application
The distance Ir between adjacent concave portions of the continuous casting roll of the invention is preferably 1.0 mm or more from the viewpoint of preventing roll wear.
Unsolidified thickness difference D _max -D _min when the continuous casting roll of the eighth invention of the present application is applied from the time when the mold is released until the end of the light reduction.
21 (b), the transition of the casting direction is substantially the same as that of the continuous casting roll of the seventh invention of the present application.
That is, the unsolidified thickness difference D _max -D _min decreases after exiting the mold due to the effect of controlling the width direction of roll cooling, and becomes almost nonexistent on the entry side of the light reduction zone, and has a nonuniform solidification relaxation ability. It is clear.

In the second to eighth inventions of the present application, any of (1) widthwise cooling control by the mold, (2) widthwise cooling control by secondary cooling, and (3) widthwise cooling control by rolls. However, by combining at least two or more of these (1) to (3), it is possible to obtain the slow cooling capacity of the width center portion of a very large slab. The combination of (1) to (3) can be arbitrarily selected, but by combining at least two or more of these (1) to (3), the required slow cooling capacity can be obtained. By reducing the slow cooling capacity of each part in order to obtain it, it becomes possible to uniformly control the cooling in the width direction from the initial solidification region to the final solidification region. Therefore, according to the present invention, it is possible to flexibly cope with changes in operating parameters such as casting speed, degree of superheat of molten steel, secondary cooling conditions, and the like.

In the ninth invention of the present application, a large number of recesses or ridges are provided in the central portion of the long side surface along the casting direction of the mold, and the secondary cooling water amount density in the central portion of the slab width is set to the amount of water other than the central portion. By setting the density to 75% or less, the solidification in the width direction of the long side surface of the slab is almost achieved by the synergistic effect of the mild cooling effect of the mold in the width direction central portion and the slow cooling of the width direction center portion by the secondary cooling water. It becomes uniform, uniform rolling in the light rolling zone is possible, and center segregation in the entire width direction of the slab can be suppressed.

Further, in the tenth invention of the present application, a large number of recesses or ridges are provided in the central portion of the long side surface along the casting direction of the mold, and the central portion of the slab width of the supporting roll, the pressing roll and the drawing roll is provided. By providing a large number of recesses in the part in contact with the slab, the synergistic effect of mild cooling of the widthwise center part by the mold and the slow cooling of the widthwise center part by the support rolls, reduction rolls and drawing rolls The solidification in the width direction is almost uniform, uniform reduction in the light reduction zone is possible, and center segregation in the entire width direction of the slab can be suppressed.

Further, in the eleventh invention of the present application, a large number of concave portions are provided in the portions of the supporting roll, the pressing roll and the drawing roll in contact with the central portion of the slab width, and the secondary cooling water amount density in the central portion of the slab width is set to the central portion. Water density other than 7
By making it 5% or less, the effect of gentle cooling of the widthwise central portion by the supporting roll, the pressing roll and the drawing roll,
Due to the synergistic effect of the slow cooling of the widthwise central part by the secondary cooling water, the solidification in the width direction of the long side surface of the slab becomes almost uniform,
Uniform reduction in the light reduction zone is possible, and center segregation in the entire width direction of the slab can be suppressed.

Furthermore, in the twelfth invention of the present application, a large number of recesses or ridges are provided in the central portion of the long side surface along the casting direction of the mold, and the slab width central portion of the support roll, the pressing roll and the drawing roll is provided. By providing a large number of recesses in the part in contact with the slab and setting the secondary cooling water amount density in the central part of the slab width to 75% or less of the water amount density other than the central part, the effect of gentle cooling of the central part in the width direction by the mold and supporting By the synergistic effect of the gentle cooling of the widthwise central portion by the rolls, the pressing rolls and the drawing rolls, and the gentle cooling of the widthwise central portion by the secondary cooling water, the solidification in the widthwise direction of the long side surface of the slab is made uniform, Uniform reduction is possible in the light reduction zone, and center segregation in the entire width direction of the slab can be prevented.

FIG. 30 shows the case where the mold of the fourth invention of the present application is used, the mold of the fourth invention of the present application and the ninth invention of using the secondary cooling of the third invention of the present application, and the fourth invention of the present application. No. 10 using the mold of No. 6 and the continuous casting roll of the eighth invention of the present application
In the case of the invention, the mold recess depth d _{m is obtained} for each of the case of the twelfth invention using the mold of the fourth invention of the present application, the secondary cooling of the third invention of the present application, and the continuous casting roll of the eighth invention of the present application. And the unsolidified thickness difference _{Dmax- Dmin} were investigated.
The result is shown in FIG. As shown in FIG. 30, in the case of the same mold recess depth d _m , the fourth invention, the ninth invention, and the tenth invention
The unsolidified thickness difference D _max -D _min decreases in the order of the invention and the twelfth invention, and the same unsolidified thickness difference D _max -D _min can be obtained by applying the combination of the second to eighth inventions of the present application. Therefore, the flexibility of operation will be greatly increased.

The mold of the fifth invention of the present application and the third mold of the present invention
The continuous casting method in which the secondary cooling of the invention and the roll for continuous casting of the eighth invention of the present application are combined is carried out by a mold to a meniscus under 4.0 m.
21 (b) shows the transition of the unsolidified thickness difference D _max -D _{min in} the casting direction when applied up to. Figure 21
As shown in (b), in the case of K in which the mold of the fifth invention of the present application, the secondary cooling of the third invention of the present application, and the continuous casting roll of the eighth invention of the present application are combined, the unsolidified thickness difference D _max. -D _min almost disappeared in the mold, and then 4.0 below the meniscus.
It is apparent that the film has nothing at m, and has an extremely large gentle cooling capacity (uneven solidification relaxation capacity) at the center of the width. As is clear from the above results, there are many combinations of the second to eighth inventions other than the ninth to twelfth inventions of the present application, but all of them have an extremely large width like the ninth to twelfth inventions. It is obvious that the central portion has a slow cooling ability, and it goes without saying that it is included in the present invention.

[0063]

【Example】

Example 1 As a continuous casting machine, a curved continuous casting machine having a bending radius of 12.5 m shown in FIG. 9 was used, and molten metal 3 had a degree of superheat of molten steel ΔT20 ° C.
C: 0.15 to 0.20% of 40K steel for thick plates, the mold 1 having the structure shown in FIG.
Casting, casting speed 0.8m / min, mold length 700
When a slab slab having a thickness of 250 mm and a width of 2000 mm is cast through the support roll group 6, the reduction roll group 7, and the pinch roll 8, the specifications of the secondary cooling device shown in Table 4 and the continuous casting shown in Table 5 are used. According to the roll specifications, a slab slab was obtained by lightly reducing the final zone of solidification with a reduction zone length of 5 m and a reduction gradient of 1 mm / m. The distance (mm) from the slab edge and the C segregation degree (C / C ₀ ) of the obtained slab slab were measured, and the unsolidified thickness difference D _max -D _min in the slab width direction on the rolling zone entering side was measured. It was measured. The results are shown in Table 6. The unsolidified thickness was measured by the FeS addition method.

Example 2 As a continuous casting machine, a bending type continuous casting machine having a bending radius of 12.5 m shown in FIG. 9 was used, and molten metal 3 had a degree of superheat of molten steel ΔT of 20 ° C.
C: 0.15 to 0.20% of 40K steel for thick plates, the mold 1 having the structure shown in FIG.
Casting, casting speed 0.8m / min, mold length 700
When a slab slab having a thickness of 250 mm and a width of 2000 mm is cast through the support roll group 6, the reduction roll group 7, and the pinch roll 8, the specifications of the secondary cooling device shown in Table 4 and the continuous casting shown in Table 5 are used. According to the roll specifications, a slab slab was obtained by lightly reducing the final zone of solidification with a reduction zone length of 5 m and a reduction gradient of 1 mm / m. The distance (mm) from the slab edge and the C segregation degree (C / C ₀ ) of the obtained slab slab were measured, and the unsolidified thickness difference D _max -D _min in the slab width direction on the rolling zone entering side was measured. It was measured. The results are shown in Table 6. The unsolidified thickness was measured by the FeS addition method.

Example 3 As a continuous casting machine, a bending type continuous casting machine having a bending radius of 12.5 m shown in FIG. 9 was used, and the molten metal 3 had a degree of superheat of molten steel ΔT of 20 ° C.
C: 0.15 to 0.20% of 40K steel for thick plates, the mold 1 having the structure shown in FIG.
Casting, casting speed 0.8m / min, mold length 700
When a slab slab having a thickness of 250 mm and a width of 2000 mm is cast through the support roll group 6, the reduction roll group 7, and the pinch roll 8, the specifications of the secondary cooling device shown in Table 4 and the continuous casting shown in Table 5 are used. According to the roll specifications, a slab slab was obtained by lightly reducing the final zone of solidification with a reduction zone length of 5 m and a reduction gradient of 1 mm / m. The distance (mm) from the slab edge and the C segregation degree (C / C ₀ ) of the obtained slab slab were measured, and the unsolidified thickness difference D _max -D _min in the slab width direction on the rolling zone entering side was measured. It was measured. The results are shown in Table 6. The unsolidified thickness was measured by the FeS addition method.

Example 4 As a continuous casting machine, a bending type continuous casting machine having a bending radius of 12.5 m shown in FIG. 9 was used, and the molten metal 3 had a degree of superheat of molten steel ΔT of 20 ° C.
C: 0.15 to 0.20% of 40K steel for thick plates, the mold 1 having the structure shown in FIG.
Casting, casting speed 0.8m / min, mold length 700
When a slab slab having a thickness of 250 mm and a width of 2000 mm is cast through the support roll group 6, the reduction roll group 7, and the pinch roll 8, the specifications of the secondary cooling device shown in Table 4 and the continuous casting shown in Table 5 are used. According to the roll specifications, a slab slab was obtained by lightly reducing the final zone of solidification with a reduction zone length of 5 m and a reduction gradient of 1 mm / m. The distance (mm) from the slab edge and the C segregation degree (C / C ₀ ) of the obtained slab slab were measured, and the unsolidified thickness difference D _max -D _min in the slab width direction on the rolling zone entering side was measured. It was measured. The results are shown in Table 6. The unsolidified thickness was measured by the FeS addition method.

Example 5 As a continuous casting machine, a bending type continuous casting machine having a bending radius of 12.5 m shown in FIG. 9 was used, and the molten metal 3 had a molten steel superheat degree ΔT of 20 ° C.
C: 0.15 to 0.20% of 40K steel for thick plate, the mold 1 having the structure shown in FIG.
Casting, casting speed 0.8m / min, mold length 700
When a slab slab having a thickness of 250 mm and a width of 2000 mm is cast through the support roll group 6, the reduction roll group 7, and the pinch roll 8, the specifications of the secondary cooling device shown in Table 4 and the continuous casting shown in Table 5 are used. According to the roll specifications, a slab slab was obtained by lightly reducing the final zone of solidification with a reduction zone length of 5 m and a reduction gradient of 1 mm / m. The distance (mm) from the slab edge and the C segregation degree (C / C ₀ ) of the obtained slab slab were measured, and the unsolidified thickness difference D _max -D _min in the slab width direction on the rolling zone entering side was measured. It was measured. The results are shown in Table 6. The unsolidified thickness was measured by the FeS addition method.

Example 6 A bending type continuous casting machine having a bending radius of 12.5 m shown in FIG. 9 was used as the continuous casting machine, and the molten metal 3 had a degree of superheat of molten steel ΔT of 20 ° C.
C: 0.15 to 0.20% of 40K steel for thick plates is cast from the immersion nozzle 2 into the conventional mold 1, and the casting speed is 0.8 m.
/ Min, mold length 700 mm, thickness 250 mm, width 2
When casting a 000 mm slab slab through the support roll group 6, the reduction roll group 7, and the pinch roll 8, the secondary cooling device having the structure shown in FIG. According to the equipment specifications and the specifications of the continuous casting roll shown in Table 5, a slab slab was obtained by lightly reducing the final stage of solidification with a reduction zone length of 5 m and a reduction gradient of 1 mm / m. The distance (mm) from the slab edge of the obtained slab slab and the C segregation degree (C / C
₀ ) and the unsolidified thickness difference D _max -D _min in the slab width direction on the side of entering the reduction zone. The results are shown in Table 6. The unsolidified thickness was measured by the FeS addition method.

Example 7 As a continuous casting machine, a bending type continuous casting machine having a bending radius of 12.5 m shown in FIG. 9 was used, and the molten metal 3 was molten steel superheat degree ΔT 20 ° C.
C: 0.15 to 0.20% of 40K steel for thick plates is cast from the immersion nozzle 2 into the conventional mold 1, and the casting speed is 0.8 m.
/ Min, mold length 700 mm, thickness 250 mm, width 2
When casting a 000 mm slab slab through the support roll group 6, the reduction roll group 7, and the pinch roll 8, the support roll group, the reduction roll group, and the pinch roll group having the structure shown in FIG. 7 are used. With the specifications of the secondary cooling device shown and the specifications of the continuous casting rolls shown in Table 5, the reduction zone length is 5
m, a reduction gradient of 1 mm / m, and lightly reduced at the final stage of solidification to obtain a slab slab. While measuring the distance (mm) from the slab edge and the C segregation degree (C / C ₀ ) of the obtained slab slab,
Unsolidified thickness difference D in the width direction of the slab on the side entering the reduction zone
_{The max-} D _min was measured. The results are shown in Table 6. In addition,
The unsolidified thickness was measured by the FeS addition method.

Example 8 As a continuous casting machine, a bending type continuous casting machine having a bending radius of 12.5 m shown in FIG. 9 was used, and the molten metal 3 had a degree of superheat of molten steel ΔT of 20 ° C.
C: 0.15 to 0.20% of 40K steel for thick plates is cast from the immersion nozzle 2 into the conventional mold 1, and the casting speed is 0.8 m.
/ Min, mold length 700 mm, thickness 250 mm, width 2
When casting a 000 mm slab slab through the support roll group 6, the reduction roll group 7, and the pinch roll 8, the support roll group, the reduction roll group, and the pinch roll group having the structure shown in FIG. 8 are used. With the specifications of the secondary cooling device shown and the specifications of the continuous casting rolls shown in Table 5, the reduction zone length is 5
m, a reduction gradient of 1 mm / m, and lightly reduced at the final stage of solidification to obtain a slab slab. While measuring the distance (mm) from the slab edge and the C segregation degree (C / C ₀ ) of the obtained slab slab,
Unsolidified thickness difference D in the width direction of the slab on the side entering the reduction zone
_{The max-} D _min was measured. The results are shown in Table 6. In addition,
The unsolidified thickness was measured by the FeS addition method.

Example 9 As a continuous casting machine, a bending type continuous casting machine having a bending radius of 12.5 m shown in FIG. 9 was used, and the molten metal 3 had a degree of superheat of molten steel ΔT of 20 ° C.
C: 0.15 to 0.20% of 40K steel for thick plates, the mold 1 having the structure shown in FIG.
Casting, casting speed 0.8m / min, mold length 700
When a slab slab having a thickness of 250 mm, a width of 2000 mm and a width of 2000 mm is cast through the support roll group 6, the reduction roll group 7, and the pinch roll 8, the secondary cooling device having the structure shown in FIG. 1 (b) is used, With the specifications of the secondary cooling device shown in Table 4 and the specifications of the continuous casting rolls shown in Table 5, a reduction zone length of 5
m, a reduction gradient of 1 mm / m, and lightly reduced at the final stage of solidification to obtain a slab slab. While measuring the distance (mm) from the slab edge and the C segregation degree (C / C ₀ ) of the obtained slab slab,
Unsolidified thickness difference D in the width direction of the slab on the side entering the reduction zone
_{The max-} D _min was measured. The results are shown in Table 6. In addition,
The unsolidified thickness was measured by the FeS addition method.

Example 10 As a continuous casting machine, a bending type continuous casting machine having a bending radius of 12.5 m shown in FIG. 9 was used, and the molten metal 3 had a degree of superheat of molten steel ΔT of 20 ° C.
C: 0.15 to 0.20% of 40K steel for thick plates, the mold 1 having the structure shown in FIG.
Casting, casting speed 0.8m / min, mold length 700
When casting a slab slab having a thickness of 250 mm and a width of 2000 mm through the support roll group 6, the reduction roll group 7, and the pinch roll 8, the support roll having the structure shown in FIG. The specifications of the secondary cooling device shown in Table 4 and the specifications of the continuous casting roll shown in Table 5 are used.
A slab slab was obtained by lightly reducing the final stage of solidification at a reduction zone length of 5 m and a reduction gradient of 1 mm / m. The distance (mm) from the slab edge and the C segregation degree (C / C ₀ ) of the obtained slab slab were measured, and the unsolidified thickness difference D _max -D _min in the slab width direction on the rolling zone entering side was measured. It was measured. The results are shown in Table 6. The unsolidified thickness was measured by the FeS addition method.

Example 11 As a continuous casting machine, a bending type continuous casting machine having a bending radius of 12.5 m shown in FIG. 9 was used, and the molten metal 3 had a degree of superheat of molten steel ΔT of 20 ° C.
C: 0.15 to 0.20% of 40K steel for thick plates is cast from the immersion nozzle 2 into the conventional mold 1, and the casting speed is 0.8 m.
/ Min, mold length 700 mm, thickness 250 mm, width 2
When casting a 000 mm slab slab through the support roll group 6, the reduction roll group 7, and the pinch roll 8, as a part of the secondary cooling device and the support roll group having the structure shown in FIG. Use the support roll of the structure shown,
Using the specifications of the secondary cooling device shown in Table 4 and the specifications of the continuous casting roll shown in Table 5, a slab slab was obtained by lightly reducing the final stage of solidification with a reduction zone length of 5 m and a reduction gradient of 1 mm / m. The distance (mm) from the slab edge of the obtained slab slab and the C segregation degree (C /
C ₀ ) was measured, and the unsolidified thickness difference D _max −D _min in the slab width direction on the rolling zone entry side was measured. The results are shown in Table 6. The unsolidified thickness was measured by the FeS addition method.

Example 12 As the continuous casting machine, a bending type continuous casting machine having a bending radius of 12.5 m shown in FIG. 9 was used, and the molten metal 3 had a degree of superheat of molten steel ΔT of 20 ° C.
C: 0.15 to 0.20% of 40K steel for thick plates, the mold 1 having the structure shown in FIG.
Casting, casting speed 0.8m / min, mold length 700
When casting a slab slab having a thickness of 250 mm and a width of 2000 mm through the support roll group 6, the reduction roll group 7, and the pinch roll 8, the secondary cooling device and the support roll group having the structure shown in FIG. 8 is used as a part of the structure, the specifications of the secondary cooling device shown in Table 4 and the specifications of the continuous casting roll shown in Table 5 are used, and the reduction zone length is 5
m, a reduction gradient of 1 mm / m, and lightly reduced at the final stage of solidification to obtain a slab slab. While measuring the distance (mm) from the slab edge and the C segregation degree (C / C ₀ ) of the obtained slab slab,
Unsolidified thickness difference D in the width direction of the slab on the side entering the reduction zone
_{The max-} D _min was measured. The results are shown in Table 6. In addition,
The unsolidified thickness was measured by the FeS addition method.

Comparative Example 1 As a continuous casting machine, a bending type continuous casting machine having a bending radius of 12.5 m shown in FIG. 9 was used, and the molten metal 3 had a degree of superheat of molten steel ΔT of 20 ° C.
C: 0.15 to 0.20% of 40K steel for thick plates is cast from the dipping nozzle 2 into the mold 1 having the specifications shown in Table 3 in which grooves are installed over the entire width of the long side surface, and the casting speed is 0.8 m. /
min, mold length 700 mm, thickness 250 mm, width 20
When casting a 00 mm slab slab through the support roll group 6, the reduction roll group 7, and the pinch roll 8,
In the width direction cooling control of the secondary cooling device and the support roll, the reduction roll, and the width direction cooling control of the pinch roll, the specifications of the secondary cooling device shown in Table 4 and the specifications of the continuous casting roll shown in Table 5 are used. A slab slab was obtained by lightly reducing the final stage of solidification at a reduction zone length of 5 m and a reduction gradient of 1 mm / m. The distance (mm) from the slab edge of the obtained slab slab and the C segregation degree (C /
C ₀ ) was measured, and the unsolidified thickness difference D _max −D _min in the slab width direction on the rolling zone entry side was measured. The results are shown in Table 6. The unsolidified thickness was measured by the FeS addition method.

Comparative Example 2 As a continuous casting machine, a bending type continuous casting machine having a bending radius of 12.5 m shown in FIG. 9 was used, and the molten metal 3 had a molten steel superheat degree ΔT of 20 ° C.
C: 0.15 to 0.20% of 40K steel for thick plates is cast from the immersion nozzle 2 into the conventional mold 1, and the casting speed is 0.8 m.
/ Min, mold length 700 mm, thickness 250 mm, width 2
When casting a 000 mm slab slab through the support roll group 6, the reduction roll group 7, and the pinch roll 8, the width direction cooling control of the secondary cooling device and the support roll, the reduction roll, and the pinch roll width direction cooling control are performed. With the specifications of the secondary cooling device shown in Table 4 and the specifications of the continuous casting roll shown in Table 5, the reduction zone length is 5 m and the reduction gradient is 1 mm / m.
At the end of solidification, a light reduction was applied to form a slab slab. The distance (mm) from the slab edge and the C segregation degree (C / C ₀ ) of the obtained slab slab were measured, and the unsolidified thickness difference D _max -D _min in the slab width direction on the rolling zone entering side was measured. It was measured.
The results are shown in Table 6. The unsolidified thickness was measured by the FeS addition method.

[0077]

[Table 3]

[0078]

[Table 4]

[0079]

[Table 5]

[0080]

[Table 6]

As is clear from Table 6, in the conventional continuous casting methods of Comparative Examples 1 and 2, the center segregation at the position close to the slab edge was remarkable, but in the cases of Examples 1 to 12 of the present invention, The center segregation of the portion near the edge was significantly reduced, and a good cast piece having a uniform composition in the width direction and a C segregation degree of about 1.00 could be manufactured. Also, strictly speaking,
In Examples 4 and 12, moderate cooling at the center of the width was too effective and the unsolidified thickness difference D _max −D _min ≦ −2, resulting in U-shaped non-uniform solidification, and thus the degree of C segregation at the center of the width slightly increased. However, this is not a practical problem. In addition, Examples 9 to 12
Is a combination of the mold of Example 3 and the widthwise cooling control of the secondary cooling and the roll cooling, but the slow cooling capacity is obviously improved and contributes to the alleviation of the W-type non-uniform solidification.

In the first and second embodiments of the present invention, the breakout frequency can be made equal to that of the conventional mold by reducing the recess width W. In addition, Examples 3 to 5, 9 to 10 and 1 of the present invention
In No. 2, the breakout frequency was the same as that of the conventional mold.

[0083]

As described above, according to the continuous casting method and apparatus of the present invention, the uneven solidification in the width direction of the slab is eliminated, and the light reduction at the final stage of solidification is uniformly performed in the width direction. The center segregation of the portion is significantly improved, and it becomes possible to stably cast a slab having a uniform composition in the entire width direction and having no center segregation.

[Brief description of drawings]

FIG. 1 shows several examples of cooling in the continuous casting method of the present invention. FIG. 1 (a) is an example of moderate cooling in the width center part by a mold, and FIG. 1 (b) is a moderate cooling in the width center part by secondary cooling. Example of
FIG. 6C is a diagram showing an example of gentle cooling in the width center portion by a roll.

2A and 2B show an example of a mold in which the concave portions of the present invention are in the form of ridges. FIG. 2A is a plan view of the mold, and FIG. 2B is a plan view of the mold long side surface from the inner surface (surface on the molten steel side). The view, (c), is a vertical cross-sectional view showing the generation state of the solidified shell.

FIG. 3 is a view of a long side surface of a mold of the present invention in which the recess has a dimple shape, as viewed from the inner surface (surface on the molten steel side).

4A and 4B show an example of another mold in which the concave portion of the present invention has a concave shape, in which FIG. 4A is a view of the long side surface of the mold seen from the inner surface (surface on the molten steel side), and FIG. FIG. 4 is a vertical cross-sectional view showing a generation state of a solidified shell.

FIG. 5 is a plan view showing an example of the mold of the present invention.

FIG. 6 is a plan view showing an example of the mold of the present invention.

FIG. 7 is a plan view showing an example of gentle cooling in the width center portion by the heat insulating layer of the low thermal conductivity material in the roll of the present invention.

FIG. 8 is a plan view showing an example of moderate cooling of the width center portion by the concave portion in the roll of the present invention.

FIG. 9 is a diagram showing an example of a continuous casting apparatus used in Examples.

FIG. 10 is a conceptual diagram of uneven solidification in the width direction of a slab cast by a conventional mold, where (a) is a conceptual diagram showing a cross section of the slab during casting, and (b) is a longitudinal section of the slab during casting. And (c) are conceptual diagrams of the state of center segregation of the product slab.

FIG. 11 is a conceptual diagram showing a flow of molten steel discharged from an immersion nozzle which is considered to be one of causes of uneven solidification in the width direction of a slab.

FIG. 12 is a conceptual diagram comparing the solidification states of the case of using the mold of the present invention and the case of using the conventional mold. FIG. 12 (a) is a case in which the situation of forming solidified shells in the width direction is uniform according to the present invention. Is a conceptual diagram showing conventional W-type non-uniform solidification, and (c) is a conceptual diagram showing U-type non-uniform solidification when the center of the width is excessively cooled by the present invention. is there.

FIG. 13 is a conceptual diagram showing the widthwise distribution of the surface temperature of a cast piece at the mold outlet in the case of (a) to (c) of FIG.

FIG. 14 is a graph showing the relationship between the heat transfer resistance and the amount of air gap between the inner wall of the mold and the slab.

FIG. 15 is a graph showing the relationship between the distance H between the upper edge of the recessed zone and the meniscus in the inventive mold and the mold outlet shell thickness.

FIG. 16 is a space I between adjacent recesses in the mold of the present invention.
It is a conceptual diagram which shows the solidification shell production | generation situation when is large.

FIG. 17 is a definition diagram of an unsolidified thickness difference D _max −D _min of a slab.

FIG. 18 is a conceptual view of a conventional step thickness mold.

FIG. 19 is a graph showing the relationship between the unsolidified thickness difference D _max −D _min at the slab width end and the width center and the C segregation degree.

FIG. 20: Slow cooling rate S. from the solidification start position of the slab to the end of solidification of the slab. C. R. It is a graph which shows the relationship between the unsolidified thickness difference _{Dmax- Dmin} .

FIG. 21 shows changes over time in the casting direction of the unsolidified thickness difference D _max -D _min in the case of applying the present invention and in the conventional case. FIG. 21 (a) shows the case of the conventional casting apparatus and that of the present application. 2,
The graph which shows the case where 4th-6th invention is applied, (b) is a graph which shows the case of the conventional casting device and the case of K which combined 3rd, 7th-8 of this application, and this invention.

FIG. 22 shows the influence of the recess depth d _m and the recess zone area ratio α _{m in} the width center on the unsolidified thickness difference D _max -D _min when the molds of the fourth and fifth inventions of the present application are used. In the graph,
(A) is a graph when the mold of the fourth invention of the present application is used, and (b) is a graph when the mold of the fifth invention of the present application is used.

FIG. 23 is a graph showing the relationship between the mold cooling water flow rate u and the mold surface temperature T _surf .

FIG. 24 shows the mold cooling water flow rate u _c at the center of the width of the mold and the mold cooling water flow rate u other than the center when the second invention of the present application is applied and when only the mold cooling water flow rate in the width direction is controlled. is a graph showing the relationship between the specific u _c / u _e × 100 as unsolidified thickness difference D _max -D _min of _e.

FIG. 25 is a graph showing the relationship between the mold surface temperature T _surf and the distance d ₁ from the mold cooling water surface to the mold molten steel surface.

FIG. 26 is a difference Δd _{1 in} the distance d ₁ from the mold cooling water surface to the mold molten steel surface other than the center of the width of the mold in which only the mold cooling water flow velocity in the mold width direction of the sixth invention of the present application is controlled. It is a graph which shows the relationship between the unsolidified thickness difference _{Dmax- Dmin} .

FIG. 27 is a ratio Q _c / Q _e × 1 of the water amount density Q _c at the center of the width and the water amount density Q _{e at} other than the center of the secondary cooling device of the third invention of the present application
It is a graph which shows the relationship of 00 and unsolidified thickness difference _{Dmax- Dmin} .

FIG. 28 is a graph showing the relationship between the thickness t of the heat insulating layer at the center of the width of the continuous casting roll of the seventh invention of the present application and the unsolidified thickness difference D _max −D _min .

FIG. 29 is a non-solidified thickness difference D _max between the recess depth d _r and the recess zone area ratio α _{r in} the width center portion of the continuous casting roll of the eighth invention of the present application.
Is a graph showing the effect on -D _min.

FIG. 30 shows the mold of the fourth invention of the present application and the mold of the fourth invention of the present application in the case of the ninth invention of using the secondary cooling of the third invention of the present application when the mold of the fourth invention of the present application is used. Eighth of the present application
In the case of the tenth invention using the continuous casting roll of the invention,
The respective mold recess depths d _m and unsolidified thickness differences in the case of the twelfth invention using the mold of the fourth invention of the present application, the secondary cooling of the third invention of the present application, and the continuous casting roll of the eighth invention of the present application D
It is a graph which shows the relationship with _{max- Dmin} .

[Explanation of symbols]

11 mold long side surface 12 mold short side surface 1a, 6a, 7a, 8a recess 1b recess installation zone 1c recess not installed zone 1d meniscus 1e no recess 1f mold cooling water channel 1g step 1h slow cooling zone 1i slow cooling means applying part 1j Cooling water reduced zone (central width portion) 1k Cooling water non-reduced zone (other than central width portion) 1l Part with small d _{1 of} mold (central width portion) 1m Part with large d _{1 of} mold (other than central width portion) 1n Surface of cooling water of mold 1o Surface of molten steel of mold 2 Immersion nozzle 3 Molten metal 3a Solidification delay part 4 Solidification shell 4a Larger reduction resistance part 5 Powder 6 ₁ Air gap 6 Support roll group 7 Reduction roll group 8 Pinch roll 6b , 7b, 8b Heat-insulating layer 6c, 7c, 8c Slow cooling means non-installed zone 6e, 7e, 8e No concave portion 6h, 7h, 8h Slow cooling zone 9 Spray 10 sprays 9j non slow cooling zone follows the cooling device 9c non slow cooling zone 9h in slow cooling zone 9i slow cooling zone slab

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location B22D 11/128 340 B (72) Inventor Nobufumi Kasai 3rd light, Kashima-cho, Kashima-gun, Ibaraki Sumitomo Kashima Steel Works, Kinka Kogyo Co., Ltd.

Claims (12)

[Claims] 1. A continuous casting method for continuously casting a slab-shaped slab, characterized in that the central portion of the long side surface of the slab is gently cooled as compared with a portion other than the central portion. 2. A method of slowly cooling a central portion of a long side surface of a slab as compared with a portion other than the central portion, wherein a large number of concave portions or concave lines are provided in the central portion of the long side surface along the casting direction of the mold. A continuous casting method, characterized in that the mold cooling water flow velocity in the central portion of the side surface is 70% or less of the cooling water flow velocity in portions other than the central portion. 3. In the method of gently cooling the central part of the long side surface of the slab as compared with the part other than the central part, the secondary cooling water amount density in the central part of the slab width is set to 75% or less of the water amount density other than the central part. A continuous casting method characterized by: 4. A continuous casting mold of a slab having a rectangular cross section in which an inner wall defining a casting space is formed by a pair of long side faces facing each other and a pair of short side faces facing each other, and a length along a casting direction. A continuous casting mold characterized in that a large number of recesses or grooves are provided in the central portion of the side surface. 5. A continuous casting mold having a large number of recesses or grooves at the center of the long side surface along the casting direction,
A continuous casting mold characterized in that a large number of recesses or ridges are provided only between the vicinity of the meniscus and the mold outlet side along the drawing direction. 6. A continuous casting mold having a large number of recesses or ridges at the center of the long side surface along the casting direction,
The distance between the mold cooling water surface at the center of the long side and the molten steel surface of the mold is 5 more than the distance between the surface of the mold cooling water other than the center and the molten steel surface of the mold.
A mold for continuous casting, which is characterized by being larger than mm. 7. A support roll, a reduction roll, and a drawing roll for continuous casting of slab-shaped slabs, wherein a heat insulating layer made of a low thermal conductivity material is provided at a portion in contact with the central portion of the slab width of the roll. Characteristic continuous casting roll. 8. A support roll, a reduction roll, and a drawing roll for continuous casting of slab-shaped slabs, characterized in that a large number of recesses are provided in a portion in contact with the central portion of the slab width of the roll. For rolls. 9. A continuous casting method in which a central portion of a long side surface of a slab is slowly cooled as compared with a central portion other than the central portion, and a large number of recesses or ridges are provided in the central portion of the long side surface along the casting direction of the mold. The continuous casting method is characterized in that the secondary cooling water amount density in the central part of the slab width is set to 75% or less of the water amount density other than the central part. 10. A continuous casting apparatus for slowly cooling a central portion of a long side surface of a slab as compared with a portion other than the central portion, wherein a large number of recesses or ridges are provided in the central portion of the long side surface along the casting direction of the mold. At the same time, the continuous casting apparatus is characterized in that a large number of concave portions are provided in the portions of the supporting roll, the pressing roll, and the drawing roll in contact with the central portion of the slab width. 11. A continuous casting method in which a central portion of a long side surface of a slab is slowly cooled compared to a portion other than the central portion, and a large number of recesses are provided in portions of the supporting roll, the pressing roll and the pulling roll which contact the central portion of the slab width. At the same time, the secondary casting water amount density in the central portion of the slab width is set to 75% or less of the water amount density other than in the central portion. 12. A continuous casting method in which a central portion of a long side surface of a slab is gently cooled as compared with a portion other than the central portion, and a large number of recesses or ridges are provided in the central portion of the long side surface along the casting direction of the mold. , The supporting roll, the pressing roll, and the drawing roll are provided with a large number of concave portions in the portions in contact with the central portion of the slab width, and the secondary cooling water density of the central portion of the slab width is set to 75% or less of the water density other than the central portion Characteristic continuous casting method.