JP2022065814A - Mold for continuous casting and continuous casting method for steel - Google Patents

Abstract

To secure solidification uniformity in molten steel and suppress corner cracking in a cast slab.SOLUTION: A mold for continuous casting to be used in a continuous casting facility where steel is continuously casted includes: a pair of long side copper plates; and a pair of short side copper plates that is held between the pair of long side copper plates, and that is movable along a long side direction of the long side copper plates. The short side copper plate has: two or more gradients differing in a casting direction so that a plurality of tapered parts is formed on an internal surface side of the mold to be supplied with molten steel; and protrusions extending in the casting direction, at both ends in a short side direction on the internal surface side. A tapering rate of the tapered parts at the uppermost stream side in the casting direction is 1.1%/m-3.5%/m. In a plan view of the mold, the protrusion is formed such that a length of a contact part contacting the molten steel is shorter than a sum of a short side direction length and a long side direction length of the mold, and a difference thereof is 3 mm or more.SELECTED DRAWING: Figure 5

Description

The present invention relates to a mold for continuous casting used in a continuous casting facility for continuously casting steel, and a method for continuously casting steel using the mold.

In continuous casting of molten steel, when molten steel is injected into the mold, the molten steel portion in contact with the mold solidifies to form a solidified shell and is pulled out below the mold. The solidification of the molten steel further progresses in the secondary cooling zone below the mold, and finally a continuously cast slab is formed. The mold is formed of a water-cooled copper plate on the side in contact with the molten steel. The continuous casting mold of the continuous casting apparatus for casting slabs is formed by using two long-sided copper plates and two short-sided copper plates, and the two short-sided copper plates are sandwiched between the two long-sided mold plates. Assembled like a mold. The width of the short-sided copper plate is approximately equal to the thickness of the slab to be cast.

In the process of moving the solidified shell, which is undergoing solidification in the mold, downward, the solidified shell undergoes solidification and contraction as the solidification progresses. Therefore, the solidified shell that started solidification at the meniscus position of the molten metal in the mold shrinks when it reaches the lower end of the mold, and the width and thickness of the slab during solidification become smaller than the meniscus position. ing. In continuous casting of slabs, since the slab is wider than the thickness, the amount of solidification shrinkage in the slab width direction is large, and voids are likely to occur between the mold and the solidification shell. If a gap is created between the mold and the solidified shell below the mold due to the solidification shrinkage of the solidified shell, heat removal from the solidified shell to the mold is hindered, sufficient mold cooling cannot be performed, and support by the mold is lost. The solidified shell will cause bulging that swells outward.

Therefore, at least the short side of the mold is provided with a taper. Providing a taper means that the distance between the opposite short sides is narrowed with respect to the distance at the meniscus position above the mold at the lower end of the mold.

If the short side taper amount is too small, the contact between the solidified shell and the short side mold plate becomes non-uniform, resulting in an imbalance in cooling. As a result, internal cracks due to non-uniform growth of the solidified shell and vertical cracks are likely to occur on the surface of the slab corresponding to the portion where the solidified thickness is particularly thin in the vicinity of the solidified shell corner on the long side. Further, when the short side taper amount is too large, the contact between the solidified shell and the short side copper plate becomes strong, and excessive stress is applied to the solidified shell. As a result, the solidified shell breaks, and breakout occurs due to the break of the shell. In addition, the mold life may be shortened due to an increase in the frictional force between the solidified shell and the mold.

The surface of the conventional short-sided copper plate in contact with the solidified shell is processed into a flat surface from the upper part to the lower part. It is a so-called single taper. However, the solidification shrinkage rate of the solidification shell is not constant at each position in the casting direction in the mold, is fast near the meniscus, and becomes slower as it approaches the lower end of the mold. Therefore, it is considered that the surface of the solidified shell in contact with the short-sided copper plate is not a flat surface, but a curved surface is formed so that the taper amount of the solidified shell decreases toward the lower side of the mold. For example, Patent Documents 1 and 2 disclose a method of casting a short-sided copper plate using a mold having a multi-step taper of two steps or three or more steps in the casting direction.

Japanese Unexamined Patent Publication No. 2008-49385 Japanese Unexamined Patent Publication No. 2009-160645 Japanese Patent No. 5999294

Here, in difficult-to-cast steel grades such as peritectic steel accompanied by δ-γ transformation during solidification, the solidification shrinkage of the solidified shell is large due to the phase transformation during solidification. Therefore, it is required to strongly taper the uppermost tapered portion of the multi-stage tapered portions of the mold so as to follow the solidification shrinkage. However, it has been found that the corner shape of the slab becomes sharper when the uppermost tapered portion of the mold in which the short-sided copper plate is formed with a multi-step taper is further tapered and cast. FIG. 6 shows an example of the cross-sectional shape of a slab cast by using two types of molds.

First, in general continuous casting using a mold in which the corners of the mold are perpendicular and the taper ratio of the short-sided copper plate is 1.0% / m or less, in the vicinity of the corners between the long-sided copper plate and the short-sided copper plate, The molten steel is exhausted from each of the long side and the short side. Therefore, in the vicinity of the corner portion, solidification proceeds faster than in the width center portion of the long side copper plate and the short side copper plate, and the corner portion solidifies and shrinks. On the other hand, in the central part of the width, bulging occurs due to the static pressure of the molten steel, and the material is deformed so as to bulge outward. Therefore, the slab bulges outward in the center of the width as shown in the slab shape A in FIG. 6, and the corner portion having a large solidification shrinkage has a slightly sharp shape.

Further, in a mold having a right angle mold corner and a multi-step taper, in order to reduce the air gap between the slab and the mold, the uppermost taper portion has a taper rate of 1.1% on the short side copper plate. It is assumed that a strong taper of / m or more is used. Then, the heat removal of the mold and the slab near the corner portion is promoted, and the corner portion of the slab becomes sharper than the slab shape A as shown in the slab shape B in FIG.

As described above, when the shape of the corner portion of the slab is sharpened, the scale tends to accumulate in the recess of the off-corner portion, and the possibility of scratches during rolling increases. Therefore, there is a need for a technique for improving the shape of the slab while making the uppermost tapered portion strongly tapered.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is continuous casting capable of improving the slab shape while making the uppermost tapered portion strongly tapered. To provide a mold and a method for continuous casting of steel.

In order to solve the above problems, according to a certain viewpoint of the present invention, it is a mold for continuous casting used in a continuous casting facility for continuous casting of steel, and is sandwiched between a pair of long-sided copper plates and a pair of long-sided copper plates. The short-sided copper plate comprises a pair of short-sided copper plates that can be moved along the long-side direction of the long-sided copper plate, so that the short-sided copper plate has a plurality of tapered portions formed on the inner surface side of the mold to which the molten steel is supplied. It has two or more different gradients in the casting direction, and has protrusions extending in the casting direction at both ends in the short side direction on the inner surface side, and the taper ratio of the taper portion on the most upstream side in the casting direction is , 1.1% / m or more and 3.5% / m or less, and the length of the contact portion in contact with the molten steel is the length in the short side direction and the long side of the mold when the mold is viewed in a plan view. A mold for continuous casting is provided, which is shorter than the sum of the directional lengths and is formed so that the difference is 3 mm or more.

The distance in the casting direction from the average position of the meniscus position to the first taper change point of the short-sided copper plate may be 50 mm or more and 300 mm or less.

Further, the taper ratio of the tapered portion on the most downstream side in the casting direction may be 0.5% / m or more and less than 1.9% / m, and may be equal to or less than the taper ratio of the tapered portion on the upstream side.

The mold may be formed to have two tapered portions.

Further, in order to solve the above-mentioned problems, according to another viewpoint of the present invention, it is a continuous casting method of steel, in which a pair of long-sided copper plates and a pair of long-sided copper plates are sandwiched between the long-sided copper plates. It comprises a pair of short-sided copper plates that can be moved along the direction, and the short-sided copper plates have two or more different in the casting direction such that a plurality of tapered portions are formed on the inner surface side of the mold to which the molten steel is supplied. It has a gradient and has protrusions extending in the casting direction at both ends in the short side direction on the inner surface side, and the taper ratio of the tapered portion on the most upstream side in the casting direction is 1.1% / m. It is 3.5% / m or less, and the length of the contact portion in contact with the molten steel of the protruding portion in a plan view of the mold is larger than the sum of the length in the short side direction and the length in the long side direction of the mold. A method for continuously casting steel is provided, in which steel is cast using a mold for continuous casting, which is short and is formed so that the difference is 3 mm or more.

As described above, according to the present invention, it is possible to improve the shape of the slab while making the uppermost tapered portion strongly tapered.

It is explanatory drawing which shows the schematic structure of the continuous casting equipment which concerns on one Embodiment of this invention. It is a schematic sectional drawing which shows the shape of the mold which concerns on the same embodiment. It is a schematic diagram which shows the shape when the corner part of a mold is a right angle corner. It is a schematic diagram which shows one shape example of the corner part of a mold. It is a schematic diagram which shows the other shape example of the corner part of a mold. It is a schematic diagram which shows the other shape example of the corner part of a mold. It is a schematic diagram which shows the other shape example of the corner part of a mold. It is a schematic diagram which shows the example of the cross-sectional shape of the slab cast by each mold about the mold (without protrusion) of a right-angled corner, and the mold with a protrusion formed. FIG. 2 is a cross-sectional view taken along the line II of FIG. It is a schematic diagram which shows the example of the cross-sectional shape of the slab cast by using the mold of two kinds of shapes.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals, so that duplicate description will be omitted.

[1. Configuration of continuous casting equipment]
First, with reference to FIGS. 1 and 2, a schematic configuration of a continuous casting facility including a mold according to an embodiment of the present invention will be described. FIG. 1 is an explanatory diagram showing a schematic configuration of a continuous casting facility 1 according to the present embodiment. FIG. 2 is a schematic cross-sectional view showing the shape of the mold 10 according to the present embodiment. Note that FIG. 2 shows a state in which the mold 10 is cut at an arbitrary position in the casting direction (vertical direction).

The continuous casting facility 1 according to the present embodiment is an apparatus for continuously casting molten steel 2 using a mold 10 for continuous casting to manufacture slabs 3. The continuous casting facility 1 shown in FIG. 1 is a vertical bending type continuous casting facility 1, but the present invention is not limited to this example, and can be applied to various other continuous casting facilities such as a curved type or a vertical type. be. The continuous casting facility 1 includes a mold 10, a ladle 4, a tundish 5, a dipping nozzle 6, and a secondary cooling device 7.

The ladle 4 is a movable container for transporting the molten steel 2 from the outside to the tundish 5. The ladle 4 is arranged above the tundish 5, and the molten steel 2 in the ladle 4 is supplied to the tundish 5. The tundish 5 is arranged above the mold 10 to store the molten steel 2 and remove inclusions in the molten steel 2. The dipping nozzle 6 extends downward from the lower end of the tundish 5 toward the mold 10, and its tip is immersed in the molten steel 2 in the mold 10. The immersion nozzle 6 continuously supplies the molten steel 2 from which inclusions have been removed by the tundish 5 into the mold 10.

The mold 10 is a square cylindrical mold formed according to the width and thickness of the slab 3. As shown in FIG. 2, the mold 10 according to the present embodiment uses a pair of short-sided copper plates 11 and a pair of long-sided copper plates 13 to form a pair of short-sided copper plates 11 on the inner surface of the pair of long-sided copper plates 13. It is assembled so as to be sandwiched from both sides in the short side direction (X direction) by 13a. The pair of short-sided copper plates 11 are configured to be movable along the long-sided direction (Y direction) of the long-sided copper plate 13. That is, the mold 10 according to the present embodiment is a mold having a variable width. A detailed description of the shape of the mold 10 will be described later.

The copper plates 11 and 13 constituting the mold 10 are, for example, water-cooled copper plates. The molten steel 2 in contact with the inner surfaces 11a and 13a of the copper plates 11 and 13 is cooled to produce a slab 3 including an unsolidified portion 3b inside the solidified shell 3a of the outer shell. As the solidified shell 3a moves toward the lower side of the mold 10, solidification of the internal unsolidified portion 3b progresses, and the thickness of the solidified shell 3a of the outer shell gradually increases. The slab 3 including the solidified shell 3a and the unsolidified portion 3b is pulled out from the lower end of the mold 10.

The secondary cooling device 7 is provided in the secondary cooling zone 9 below the mold 10, and cools the slab 3 drawn from the lower end of the mold 10 while supporting and transporting the slab 3. The secondary cooling device 7 includes a plurality of pairs of support rolls 8 arranged on both sides of the slab 3 in the thickness direction, and a plurality of spray nozzles (not shown) for injecting cooling water onto the slab 3. Have. The support rolls 8 provided in the secondary cooling device 7 are arranged in pairs on both sides of the slab 3 in the thickness direction, and function as a support and transport means for transporting the slab 3 while supporting it. By supporting the slab 3 from both sides in the thickness direction by the support roll 8, it is possible to prevent breakout and bulging of the slab 3 during solidification in the secondary cooling zone 9.

The support roll 8 forms a transport path (pass line) for the slab 3 in the secondary cooling zone 9. As shown in FIG. 1, this path line is vertical just below the mold 10 (vertical band 9A), then curves in a curved line (curved band 9B), and finally becomes horizontal (horizontal band 9C). ). The support roll 8 is provided on the vertical band 9A, and is a support roll that supports the slab 3 immediately after being pulled out from the mold 10, a pinch roll that is a drive type roll that pulls out the slab 3 from the mold 10, a curved band 9B, and a horizontal band. It is provided on the band 9C and consists of a segment roll that supports and guides the slab 3 along the pass line.

The slab 3 that has passed through the secondary cooling zone 9 is then cut to a predetermined length by a slab cutting machine (not shown) installed in the subsequent stage of the horizontal zone 9C. The cut slab 3 moves on the table roll and is transported to the equipment in the next process. The overall configuration of the continuous casting facility 1 has been described above.

[2. Mold shape]
[2-1. overview]
Regarding the mold 10 of the continuous casting equipment 1, in the present embodiment, in order to improve the shape of the slab while making the uppermost tapered portion strongly tapered, the inner surface 11a of the short side copper plate 11 at the mold corner is formed in the space inside the mold. Form a protrusion that projects toward it. The protruding portion is a portion where the short-sided copper plate 11 is deformed to fill the right-angled corner of the mold 10.

Here, FIG. 3A shows the shape when the corner portion of the mold 10 is a right-angled corner. Further, FIGS. 3B to 3E show an example of the shape of the corner portion of the mold 10 according to the present embodiment. 3A to 3E show one corner of the four corners of the mold 10. The shape of the protrusion 12 may be the same for all four corners, or different shapes may be included in the four corners according to the requirements of the post-process.

For example, as shown in FIG. 3B, the protruding portion 12 may be formed so as to fill the right-angled corner with a straight line 12a connecting the short-sided copper plate 11 and the long-sided copper plate 13 in a plan view of the mold 10. The triangular chamfered shape as shown in FIG. 3B is also called a chamfer shape. Alternatively, as shown in FIG. 3C, the protruding portion 12 may be formed so as to fill the right-angled corner with an arc 12b connecting the short-sided copper plate 11 and the long-sided copper plate 13 in a plan view of the mold 10. That is, the protruding portion 12 may have an R shape.

Further, as shown in FIG. 3D, the protruding portion 12 may be formed so as to fill the right-angled corner with the two arcs 12c and 12d in a plan view of the mold 10. At this time, the arc 12c in contact with the long-sided copper plate 13 may be formed so as to be convex toward the inside of the mold 10 so as to be in contact with the long-sided copper plate 13 at an angle as close to vertical as possible. Further, the arc 12d in contact with the short side copper plate 11 may be convex toward the corner side of the mold 10 so as to be in contact with the short side copper plate 11 at an angle as small as possible.

Further, as shown in FIG. 3E, the protrusion 12 fills the right-angled corner with two arcs 12e and 12g and one straight line 12f connecting the two arcs 12e and 12g in a plan view of the mold 10. It may be formed. At this time, as in FIG. 3D, the arc 12e in contact with the long-sided copper plate 13 may be formed so as to be convex toward the inside of the mold 10 so as to be in contact with the long-sided copper plate 13 at an angle as close to vertical as possible. Further, the arc 12g in contact with the short side copper plate 11 may be convex toward the corner side of the mold 10 so as to be in contact with the short side copper plate 11 at an angle as small as possible.

The shape of the corner portion of the mold 10 as shown in FIGS. 3D and 3E is easy to process, and deformation at the corner portion can be suppressed.

By using the mold 10 having the protrusion as shown in FIGS. 3B to 3E, the chamfered slab can be continuously cast. 4 shows a cross section of a slab cast using each of the right-angled corner molds (without protrusions) shown in FIG. 3A and the molds having arcuate protrusions shown in FIG. 3C. An example of the shape is shown. As shown in FIG. 4, the corners of the slab cast using the right-angled corner mold were sharpened. On the other hand, in the corner portion of the slab cast by using the mold having the protruding portion formed, the corner shape of the mold was transferred to the slab and the shape was chamfered. From this, it was confirmed that by forming the protruding portion 12 on the inner surface 11a of the short-sided copper plate 11 at the corner of the mold, the sharpening of the corner portion of the slab is eliminated.

On the other hand, when casting a slab with chamfered corners, by providing a protrusion at the corner of the mold, the contact length between the molten steel and the copper plate is reduced as compared with the case of a right-angled corner, and the corner of the mold is formed. The amount of heat removed decreases. Therefore, the surface temperature of the corner portion of the slab rises. If the protrusion is provided at the corner of the mold, the shell thickness is reduced as compared with the case where the mold has a right-angled corner due to a decrease in the amount of heat removed.

Further, in the initial stage of solidification, when the mold has a right-angled corner, a gap mainly generated near the short side of the corner portion is formed, and when the protruding portion is provided at the corner portion, the protruding portion itself and the protruding portion and the short portion are provided. It occurs near the short side of the corner portion consisting of the side copper plate surface. That is, when the protruding portion is provided at the corner portion of the mold, the region where the gap is generated is enlarged as compared with the case of the right-angled corner portion.

For this reason, heat removal from the solidified shell to the mold is hindered, and the solidified shell cannot be sufficiently cooled. This is not limited to the case where the triangular protruding portion is provided at the corner portion, and for example, the contact length between the molten steel and the copper plate is reduced as compared with the case where the mold has a right-angled corner, as shown in FIGS. 3C to 3E. The same applies when the protruding portion is provided at the corner portion of the mold. Regarding this, as described above, by making the tapered portion of the short-sided copper plate strongly tapered, it is possible to promote the heat removal of the mold and the slab near the corner portion. Therefore, for a multi-stage taper mold, the function of each shape can be exhibited by both making the uppermost taper portion strongly tapered and providing a protruding portion inside the mold.

Further, by using a mold having a protruding portion inside the mold, the corner portion of the slab cast using such a mold has a surface temperature of the slab as compared with the case of casting using a mold having right-angled corners. Can be prevented from cracking the corners of the surface of the slab. This is due to the following mechanism.

The molten steel injected into the mold is heat-extracted from the long side and the short side at the corners of the mold. Therefore, due to the effect of the two-sided cooling, the amount of heat removed from the corner portion of the mold is larger than that of the central portion of the width of the long-sided copper plate, and the surface temperature is lowered. In the secondary cooling zone after leaving the mold, the temperature at the center of the long side width of the slab is about 900 ° C., but the temperature at the corner of the slab may be 800 ° C. or lower. When the temperature of the corner portion of the slab is 800 ° C. or lower, cracks occur in the corner portion. This is because the slab is bent in the continuous casting machine in the temperature region where ductility is lost, which is called the embrittlement region, and therefore tensile stress acts. Therefore, the effect of two-sided cooling is suppressed by providing a protruding portion instead of making the corner portion of the mold a right angle (for example, Patent Document 3). Thereby, the temperature of the corner portion of the slab in the secondary cooling zone can be set to the same temperature as the central portion of the long side width (that is, 800 ° C. or higher). As a result, the corner portion does not become supercooled as compared with the central portion having the long side width, and the corner cracking of the slab can be reduced.

In continuous casting using a mold in which the uppermost tapered part is strongly tapered and a protrusion is provided inside the mold, difficult-to-cast steel grades such as peritectic steel in which the solidification shell has a large solidification shrinkage due to phase transformation during solidification. It is also effective against. By using a mold having such a shape, it is possible to prevent vertical cracks, corner cracks, and internal cracks on the surface of the slab, and to improve the cross-sectional shape of the slab to prevent scratches during rolling. It is possible to improve the quality of slabs during continuous casting of difficult-to-cast steel grades.

[2-2. Basic configuration]
The shape of the mold 10 according to the present embodiment will be described with reference to FIGS. 2 and 5. FIG. 5 is a cross-sectional view taken along the line I-I of FIG. In addition, in FIGS. 2 and 5, the shape is exaggerated in order to explain the structure of the mold 10 in an easy-to-understand manner.

As described above, the mold 10 according to the present embodiment is composed of a pair of short-sided copper plates 11 and a pair of long-sided copper plates 13. When the mold 10 is viewed in a plan view from the height direction, as shown in FIG. 2, the mold 10 has a substantially rectangular space (the "rectangular shape" of the present invention) due to a pair of short-sided copper plates 11 and a pair of long-sided copper plates 13. It corresponds to "space".) V is formed. The inner surface 11a of the short-side copper plate 11 of the mold 10 according to the present embodiment is provided with protruding portions 12 protruding toward the inside of the space V at both ends in the short-side direction. The protrusion 12 extends along the height direction (also referred to as Z direction and casting direction) of the mold 10.

Here, the short-sided copper plate 11 has two or more different gradients in the casting direction so that the mold 10 has a plurality of tapered portions and has a multi-step taper. The multi-step taper is formed so that its gradient (that is, the taper ratio) becomes smaller toward the downstream side in the casting direction. In the initial stage of solidification of the upper stage of the mold 10 (that is, on the upstream side in the casting direction), the solidification shell is thin and the heat is removed from the molten steel, so that the solidification shell shrinks greatly. Therefore, it is necessary to make the taper gradient relatively large. On the other hand, at the lower end of the mold 10 (that is, the most downstream in the casting direction), the solidified shell is thick because it is grown, and the heat removed from the molten steel is less than that in the upper stage of the mold. Therefore, the solidification shrinkage of the solidification shell is small, and it is necessary to make the taper gradient relatively small. From such a mechanism, the gradient of the upper tapered portion in the mold 10 is increased, and the gradient of the tapered portion is gradually set to be smaller toward the downstream side in the casting direction in which solidification proceeds.

If the slope of the upper taper portion of the mold 10, which is called reverse taper, is set to be small and the slope of the tapered portion is gradually increased toward the downstream side in the casting direction, the following problems will occur. it is conceivable that. First, in the upper stage of the mold 10, although the solidification shrinkage of the solidification shell is large, the gradient of the tapered portion is small, so that the air gap at the corner cannot be sufficiently reduced. Therefore, internal cracks occur and the internal quality of the slab deteriorates. On the other hand, at the lower end of the mold 10, although the solidification shrinkage of the solidification shell is small, the gradient of the tapered portion is large, so that the slab and the mold come into strong contact with each other, and a large frictional force is generated. Due to the restraint by the mold, the wear of the mold copper plate progresses and the life of the mold is shortened, so that the productivity is lowered and there is a concern that breakout may occur in which the slab breaks. Therefore, the multi-step taper is formed so that its gradient becomes smaller toward the downstream side in the casting direction.

For example, the mold 10 shown in FIGS. 2 and 5 has a two-step taper because the short-side copper plate 11 has two different gradients θ ₁ and θ ₂ . In FIGS. 2 and 5, the inner surface 11a of the short-sided copper plate 11 forming the taper on the most upstream side (that is, upward) in the casting direction is set as the first inclined surface 11a1, and the taper on the most downstream side (that is, downward) in the casting direction is set. The inner surface 11a of the short-sided copper plate 11 to be formed is referred to as a second inclined surface 11a2. Further, in the mold 10, the taper formed by the first inclined surface 11a1 is referred to as the _first tapered portion T1, and the taper formed by the second inclined surface 11a2 is referred to as the _second tapered portion T2.

At this time, the taper ratio R of the tapered portion (that is, the first tapered portion T ₁ ) on the most upstream side in the casting direction is set to 1.1% / m or more and 3.5% / m or less. The taper rate R [% / m] is expressed by the following formula (1).

R = {( _WT - _WB ) / _WV / ΔL} x 100 ... (1)

In the above equation (1), _WT [m] is the distance between the opposite short-side copper plates 11 at the upper position, _WB [m] is the distance between the opposite short-side copper plates 11 at the lower position, _WV [m]. Is the distance between the opposite short-sided copper plates 11 at any position in the casting direction (hereinafter, also referred to as “reference distance”), and ΔL [m] is the length in the casting direction between the upper position and the lower position. The spacing _WT at the upper position and the spacing _WB at the lower position may be any distance between the upper position and the lower position in the casting direction in the tapered portion having the same gradient, and the casting direction position can be arbitrarily selected. You may.

For example, in the first taper portion _{T 1} , the interval WT at the upper position is the interval W ₀ at the upper end of the mold 10, and the interval _WB at the lower position is the interval W ₁ at the lower end of the first taper portion T ₁ . May be. _At this time, ΔL is the length X1 of the _first tapered portion T1 in the casting direction. Similarly, in the second tapered portion T ₂ , the spacing WT at the upper position is the spacing W ₁ at the upper end of the second tapered portion _{T 2} , and the spacing _WB at the lower position is the spacing W at the lower end of the mold 10. It may be ₂ . _At this time, ΔL is the length X2 of the _second tapered portion T2 in the casting direction. Here, the reference interval _WV is the interval _WM of the short-sided copper plates 11 at the average position of the meniscus position.

When the taper rate of the first taper portion T ₁ is smaller than 1.1% / m, a gap is generated between the mold 10 and the slab at the corner portion of the mold 10, and the growth of the solidified shell is hindered. .. Then, the thickness of the solidified shell becomes thin in the vicinity of the corner portion of the slab, and after leaving the mold 10, bulging occurs in the slab due to the static pressure of the molten steel, and tensile stress is generated. At this time, since the portion where the solidified shell is thin has low strength, internal cracking may occur, which may affect the product quality. Therefore, the taper rate of the _first taper portion T1 is set to 1.1% / m or more.

On the other hand, when the taper of the uppermost stage is larger than 3.5% / m, the mold 10 and the slab come into strong contact with each other. Then, a large frictional binding force acts on the solidified shell, and the solidified shell may be broken. When the solidified shell is broken, a breakout occurs in which unsolidified molten steel flows out. Therefore, the taper rate of the _first taper portion T1 is set to 3.5% / m or less.

Here, Table 1 shows the results of investigating the taper ratio of the tapered portion on the most upstream side in the casting direction and the presence or absence of internal cracks and breakouts in the slab. In Table 1, when casting a slab having a slab width of 1250 to 2300 mm and a slab thickness of 200 to 400 mm using the continuous casting equipment shown in FIGS. 1, 2 and 5, the tapered portion on the most upstream side in the casting direction (tapered portion). That is, the results of changing the taper ratio of the _first taper portion T1) and examining the presence or absence of internal cracking and breakout of the slab at that time are shown. The shape of the protruding portion 12 of the mold 10 is such that the length C of the contact portion in contact with the molten steel is 36 mm, the length C _X in the short side direction of the mold 10 is 30 mm, and the long side direction of the mold 10 when the mold 10 is viewed in a plan view. A 20 mm triangular shape with a length of _CY was formed.

From the results in Table 1, in order to prevent internal cracking and breakout of the slab, the taper rate of the tapered portion on the most upstream side in the casting direction should be 1.1% / m or more and 3.5% / m or less. It turns out that it should be done. The taper ratio in Table 1 was calculated using the above equation (1). At this time, the reference interval _WV was set to the interval _WM of the short side copper plates 11 at the average position of the meniscus position.

Further, the mold 10 according to the present embodiment is provided with a protruding portion 12. By providing the protruding portion 12, it is possible to prevent the phenomenon that the corner portion of the slab becomes supercooled as compared with the central portion having the long side width. The shape of the protrusion 12 may be triangular in a plan view of the mold 10, as shown in FIGS. 2 and 3B, for example. However, the present invention is not limited to such an example, and the protrusion 12 may have another shape, for example, as shown in FIGS. 3C to 3E. In each of the projecting portions 12, the length C of the contact portion in contact with the molten steel is shorter than the sum of the length C _X in the short side direction and the length _CY in the long side direction of the mold 10 when the mold 10 is viewed in a plan view. Moreover, it may be formed so that the difference is 3 mm or more. That is, the length C of the contact portion of one protruding portion 12 satisfies the following formula (2).

3 [mm] ≤ {(C _X + _CY ) -C} ... (2)

For example, the length C ₁ of the straight line 12a of the protrusion 12 shown in FIG. 3B and the length C ₁ of the arc 12b of the protrusion 12 shown in FIG. 3C are the length C of the contact portion in contact with the molten steel itself. (C = C ₁ ). Further, in the protruding portion 12 shown in FIG. 3D, the length C of the contact portion in contact with the molten steel is represented by the sum of the length C ₁ of the arc 12c and the length C ₂ of the arc 12d (C = C). ₁ + C ₂ ). Further, in the protruding portion 12 shown in FIG. 3E, the length C of the contact portion in contact with the molten steel is represented by the sum of the length C ₁ of the arc 12e, the length C ₂ of the arc 12g, and the length C ₃ of the straight line 12f. (C = C ₁ + C ₂ + C ₃ ). When the length C of the contact portion of one protrusion 12 is represented in this way, the four protrusions 12 at the corners of the mold 10 are each formed so as to satisfy the above formula (2).

The relationship of the above equation (2) uses numerical simulation by changing the sum of the length C of the contact portion in contact with the molten steel and the length C _X in the short side direction and the length _CY in the long side direction of the mold 10. Based on the results of performing the solidification analysis. The length C of the contact portion is shorter than the sum of the length C _X in the short side direction and the length _CY in the long side direction of the mold 10, and the difference ΔC (= (C _X + _CY ) −C) is less than 3 mm. In that case, the surface temperature of the corner portion did not increase, and the effect of the protruding portion 12 did not appear. From this, the length C of the contact portion in contact with the molten steel is made shorter than the sum of the length C _X in the short side direction and the length _CY in the long side direction of the mold 10, and the difference ΔC is 3 mm or more. ..

When the difference ΔC was 3 mm or more, the corner surface temperature gradually increased, but when the difference ΔC was more than 20 mm, the increase margin of the corner surface temperature was saturated even if the difference ΔC was further increased. On the other hand, when the cast cross section is narrowed, the yield is lowered (that is, the productivity is deteriorated). Therefore, the difference ΔC (= (C _X + _CY ) −C) may be 20 mm or less.

Here, in Table 2, the difference ΔC (= (C _X + _CY ) between the length C of the contact portion in contact with the molten steel and the sum of the length C _X in the short side direction and the length _CY in the long side direction of the mold 10. )-C) is shown as a result of investigating the quality of the slab when changed. In Table 2, the shape of the protrusion 12 of the mold used when casting a slab having a slab width of 1250 to 2300 mm and a slab thickness of 200 to 400 mm is changed by using the continuous casting equipment shown in FIGS. 1, 2 and 5. The results of examining the presence or absence of surface cracks in the slab are shown. The taper rate of the tapered portion on the most upstream side in the casting direction was set to 2.0% / m. The taper rate was calculated using the above equation (1). At this time, the reference interval _WV was set to the interval _WM of the short side copper plates 11 at the average position of the meniscus position.

The surface cracks of the slab were evaluated as follows.
A: No surface cracks B: Almost no surface cracks C: Fine surface cracks occur, but can be removed and there is no problem with product quality D: Surface cracks occur significantly and there is a problem with product quality

From the results in Table 2, in order to prevent surface cracking of the slab, the length C of the contact portion in contact with the molten steel is set to the short side length C _X and the long side length _CY of the mold 10. It can be seen that it should be shorter than the sum of and the difference ΔC should be 3 mm or more. Further, when the difference ΔC exceeds 20 mm, the increase allowance of the corner surface temperature is saturated even if the difference ΔC is further increased. From this, from the viewpoint of suppressing the decrease in yield, the difference ΔC may be 20 mm or less.

As long as the above formula (2) is satisfied, the contact portion of the protrusion 12 may have a shape having, for example, one or a plurality of corners in a plan view of the mold 10, as shown in FIG. 3C or FIG. 3D. As shown, the shape may be defined by one or a plurality of arcs (curves), or may be a shape defined by a combination of straight lines and arcs (curves) as shown in FIG. 3E. ..

Here, if the protruding portion 12 is provided at the corner portion of the mold 10, the contact length between the molten steel and the copper plate is reduced as compared with the case where the corners are at right angles, and the amount of heat removed from the mold corner portion is reduced. Therefore, the surface temperature of the slab corner portion rises. On the other hand, due to the decrease in the amount of heat removed, the thickness of the solidified shell is reduced as compared with the case where the corners are at right angles. Further, the voids generated between the mold and the slab at the initial stage of solidification are generated in a wider region when the protrusions are provided at the corners of the mold as compared with the case of the right-angled corners. For this reason, heat removal from the solidified shell to the mold is hindered, sufficient mold cooling cannot be performed, and the solidified shell remains thin. As a result, bulging may occur, and the solidified shell of the slab may crack near the corner of the long side copper plate, which is thinner than the central part of the long side width, and internal defects called internal cracks may occur. There is sex.

In order to prevent the occurrence of internal defects, the short side copper plate of the mold 10 is provided with a taper. However, if the mold 10 is provided with a strong taper having a large gradient over the entire casting direction, the frictional binding force between the mold 10 and the slab increases, and breakout may occur. In particular, when the mold 10 is provided with the protrusion 12, the length C of the contact portion in contact with the molten steel is the length C in the short side direction of the mold 10 when the short side copper plate 11 provided with the protrusion 12 is considered alone. It is larger than _X (that is, C> C _X ). Therefore, the contact range between the mold 10 and the slab increases, and the frictional binding force tends to increase more easily.

However, in the mold 10 according to the present embodiment, as described above, the short side copper plate 11 is provided with two or more gradients different in the casting direction so that a plurality of tapered portions are formed on the inner surface side of the mold 10. There is. As a result, even if the protruding portion 12 is provided, the non-uniformity of solidification at the corners of the slab can be suppressed in the upper part of the mold 10 having a large solidification shrinkage, and the slab and the mold can be suppressed in the lower part of the mold 10 having a small solidification shrinkage. The strong contact with 10 can be alleviated.

Further, in the mold 10 according to the present embodiment, the taper ratio R of the taper portion (that is, the first taper portion T ₁ ) on the most upstream side in the casting direction is 1.1% / m or more 3.5 on the short side copper plate 11. A gradient is provided so as to be% / m or less. As a result, it is possible to avoid that the gradient of the short side copper plate 11 is too small, a gap is generated near the corner portion of the long side copper plate 13, and the growth of the solidified shell is hindered. Further, the gradient of the short side copper plate 11 is too large, the frictional force between the mold 10 and the slab increases, and it is possible to prevent the occurrence of breakout due to the breakage of the solidified shell.

In the mold 10 according to the present embodiment, the short side copper plate 11 is provided with two or more gradients different in the casting direction so that a plurality of tapered portions are formed on the inner surface side of the mold 10. The plurality of tapered portions are formed so that the gradient (that is, the taper ratio) becomes smaller toward the downstream side in the casting direction.

As a method of providing a plurality of gradients in the casting direction on the inner surface of the short-sided copper plate 11 of the mold 10, for example, there is a method of using a parabolic taper having a curved inner surface. However, since the taper rate of the tapered portion on the most upstream side in the casting direction becomes a large value exceeding 3.5% / m, a large frictional binding force acts on the solidified shell, and the solidified shell may be broken. If the solidified shell is torn, unsolidified molten steel may flow out to the outside, causing operational troubles such as breakout. Further, in the parabolic taper mold, the taper rate fluctuates greatly due to the fluctuation of the meniscus position. For this reason, when the meniscus position changes due to clogging of the immersion nozzle or the like, a portion having a small taper rate is generated, and vertical cracks occur in the slab.

Furthermore, when continuous casting is performed to prevent melting of the dipping nozzle due to slag, casting is performed by changing the position of the meniscus. The number of times that continuous casting can be performed continuously is small, and the casting efficiency is lowered. For this reason as well, in the mold 10 according to the present embodiment, the short side copper plate 11 is provided with two or more gradients different in the casting direction so that a plurality of tapered portions are formed on the inner surface side of the mold 10. ..

In addition, a mold using a parabolic taper having a curved inner surface has a complicated shape and is difficult to process, which increases the manufacturing cost. On the other hand, for example, as shown in FIG. 5, by forming the two tapered portions T ₁ and T ₂ on the inner surface side of the mold 10, the shape of the mold 10 is not complicated, and the mold 10 can be easily processed at low cost and short. An appropriate gradient can be set for the side copper plate 11.

By continuously casting steel using such a mold 10, it is possible to ensure the uniformity of solidification of the molten steel and suppress corner cracking of the slab.

[2-3. Additional configuration]
By adding the following configuration to the above-mentioned basic configuration of the mold 10, it is possible to further secure the uniformity of solidification of the molten steel and suppress corner cracking of the slab.

(A) Position of the first taper change point For example, in the casting direction from the average position M of the meniscus position to the first taper change point of the short side copper plate 11 (hereinafter, also referred to as “ _first taper change point”) P1. The distance X _M (hereinafter, also simply referred to as “distance X _M ”) may be 50 mm or more and 300 mm or less. Since the meniscus position changes during casting, the average position M of the meniscus position is used as a reference here. By setting the distance X _M to 50 mm or more, it is possible to take a long range with a large taper ratio. As a result, the formation of a gap between the mold and the slab can be suppressed by increasing the taper at the uppermost stage of the multi-stage taper, and the effect of promoting the growth of the solidified shell can be sufficiently obtained. That is, it is possible to suppress the thickness of the slab shell from becoming thin and suppress the occurrence of internal cracks. As a result, even if minute internal cracks occur when the taper rate of the _first taper portion T1 is 1.1% / m or more, the influence thereof can be suppressed to the extent that the product quality does not matter.

Further, by setting the distance XM in the casting direction from the average position _M of the meniscus position to the _first taper change point P1 to 300 mm or less, the range where the taper ratio is large becomes too long and the mold 10 and the slab become strong. It is possible to avoid contact. As a result, a large frictional binding force acts on the solidified shell, the solidified shell is broken, and it is possible to suppress the occurrence of breakout in which unsolidified molten steel flows out.

Here, Table 3 shows the results of investigating the distance XM in the casting direction from the average position _M of the meniscus position to the _first taper change point P1 and the presence or absence of internal cracking and breakout of the slab. In Table 3, when casting a slab having a slab width of 1250 to 2300 mm and a slab thickness of 200 to 400 mm using the continuous casting equipment shown in FIGS. 1, 2 and 5, the distance _XM is changed at that time. The results of investigating the presence or absence of internal cracks and breakouts in the slab of the slab are shown. The taper rate of the tapered portion on the most upstream side in the casting direction was set to 2.0% / m. The taper rate was calculated using the above equation (1). At this time, the reference interval _WV was set to the interval _WM of the short side copper plates 11 at the average position of the meniscus position. Further, the shape of the protruding portion 12 of the mold 10 is such that the length C of the contact portion in contact with the molten steel is 36 mm, the length C _X in the short side direction of the mold 10 is 30 mm, and the length of the mold 10 when the mold 10 is viewed in a plan view. It has a triangular shape with a side length _CY of 20 mm.

From the results in Table 3, in order to prevent internal cracking and breakout of the slab, the distance X _M in the casting direction from the average position M of the meniscus position to the first taper change point P ₁ of the short side copper plate 11 It can be seen that the value may be 50 mm or more and 300 mm or less.

When the distance X _M was 100 mm, no internal cracks occurred in the slab even when the taper ratio of the first taper portion T ₁ was 2.3% / m or more. Further, when the distance X _M was set to 200 mm, no internal crack occurred in the slab even when the taper ratio of the first taper portion T ₁ was 1.9% / m or more. In addition, by setting the distance _XM to 300 mm, internal cracking did not occur even if the taper ratio of the _first taper portion T1 was 1.1% / m or more.

(B) Taper ratio of the tapered portion on the most downstream side in the casting direction Further, the taper ratio of the tapered portion on the most downstream side in the casting direction is 0.5% / m or more and less than 1.9% / m, and is on the upstream side. It may be less than or equal to the taper rate of the taper portion of. For example, in the mold 10 shown in FIG. 5, the second tapered portion T ₂ is the tapered portion on the most downstream side in the casting direction. Here, the taper rate is calculated using the above equation (1). The reference interval _WV was set to the interval _WM of the short-sided copper plates 11 at the average position of the meniscus position.

If the taper ratio of the tapered portion on the most downstream side in the casting direction is 0.5% / m or more, a gap is less likely to occur between the solidified shell that has solidified and shrunk and the mold 10. As a result, the droplets of the cooling water that spray-cools the slab after leaving the mold 10 and the water vapor do not enter the gap, and the corrosion of the copper plate of the mold 10 can be suppressed.

On the other hand, if the taper rate of the tapered portion on the most downstream side in the casting direction is less than 1.9% / m, the taper rate does not become too high with respect to the solidification shrinkage of the slab, and the mold 10 and the slab are in strong contact with each other. Can be suppressed. Since the solidified shell is sufficiently grown in the lower part of the mold 10, the solidified shell is hardly broken and breakout occurs. However, by preventing the taper ratio from becoming too high, the grown solidified shell and the copper plate of the mold 10 do not come into strong contact with each other, and wear of the surface of the copper plate of the mold 10 can be suppressed.

In this way, the taper ratio of the taper portion on the most downstream side in the casting direction is 0.5% / m or more and less than 1.9% / m, and is equal to or less than the taper ratio of the taper portion on the upstream side. The life of the copper plate of the mold 10 can be extended, and the frequency of replacing the copper plate can be reduced.

Here, Table 4 shows the results of examining the taper ratio of the tapered portion on the most downstream side in the casting direction and the presence or absence of corrosion and wear of the copper plate of the mold 10 after 2000 charging. In Table 4, when casting a slab having a slab width of 1250 to 2300 mm and a slab thickness of 200 to 400 mm using the continuous casting equipment shown in FIGS. 1, 2 and 5, the tapered portion on the most downstream side in the casting direction (tapered portion). That is, the results of checking the presence or absence of corrosion and wear of the copper plate of the mold 10 after 2000 charging by changing the taper ratio of the _second tapered portion T2) are shown. The taper rate of the tapered portion on the most upstream side in the casting direction was set to 2.0% / m. Further, the shape of the protruding portion 12 of the mold 10 is such that the length C of the contact portion in contact with the molten steel is 36 mm, the length C _X in the short side direction of the mold 10 is 30 mm, and the length of the mold 10 when the mold 10 is viewed in a plan view. It has a triangular shape with a side length _CY of 20 mm.

From the results in Table 4, the taper ratio of the taper portion on the most downstream side in the casting direction shall be 0.5% / m or more and less than 1.9% / m, and shall be less than or equal to the taper ratio of the taper portion on the upstream side. As a result, it can be seen that the occurrence of corrosion and wear of the copper plate of the mold 10 can be suppressed, and the life of the copper plate of the mold 10 can be extended.

(C) Relationship between the taper ratio of the taper portion on the most upstream side in the casting direction and the taper portion on the most downstream side. It may be 1.1 times or more and 2.0 times or less of. For example, in the mold 10 shown in FIG. 5, the first tapered portion T ₁ is the tapered portion on the most upstream side in the casting direction, and the second tapered portion T ₂ is the tapered portion on the most downstream side in the casting direction.

Here, in Table 5, the taper ratio of the taper portion on the most upstream side in the casting direction (hereinafter, also referred to as “taper ratio”) with respect to the taper ratio of the taper portion on the most downstream side in the casting direction, and internal cracks and breaks in the slab. The result of checking whether or not the out occurred is shown. In Table 5, when casting a slab having a slab width of 1250 to 2300 mm and a slab thickness of 200 to 400 mm using the continuous casting equipment shown in FIGS. 1, 2 and 5, the taper ratio is changed at that time. The results of investigating the presence or absence of internal cracks and breakouts in the slab are shown. The taper rate of the tapered portion on the most upstream side in the casting direction was set to 2.0% / m. The taper rate was calculated using the above equation (1). At this time, the reference interval _WV was set to the interval _WM of the short side copper plates 11 at the average position of the meniscus position. Further, the shape of the protruding portion 12 of the mold 10 is such that the length C of the contact portion in contact with the molten steel is 36 mm, the length C _X in the short side direction of the mold 10 is 30 mm, and the length of the mold 10 when the mold 10 is viewed in a plan view. It has a triangular shape with a side length _CY of 20 mm.

As shown in Table 5, the occurrence of internal cracks in the slab can be suppressed by setting the taper ratio to 1.1 or more. Further, if the taper ratio is 2.0 or less, the occurrence of breakout can be suppressed. From this, the taper ratio is set to 1.1 or more and 2.0 or less (that is, the taper ratio of the taper portion on the most upstream side in the casting direction is 1.1 times or more and the taper ratio of the taper portion on the most downstream side in the casting direction 2). It can be seen that it is desirable to make it 0 times or less).

Using the continuous casting equipment shown in FIGS. 1, 2 and 5, slabs having a slab width of 1250 to 2300 mm and a slab thickness of 200 to 400 mm were cast. At this time, the taper ratio of the taper portion on the most upstream side in the casting direction (first taper portion T ₁ ), the taper ratio of the taper portion on the most downstream side in the casting direction (second taper portion T ₂ ), and the first taper change point. The position of the slab was changed, and the quality of the manufactured slab, the stability of operation, and the life of the copper plate of the mold were verified. The verification results are shown in Table 6 below. The quality of the slab, the stability of operation, and the life of the copper plate of the mold were evaluated based on the following evaluation criteria. The taper rate was calculated using the above equation (1). At this time, the reference interval _WV was set to the interval _WM of the short side copper plates 11 at the average position of the meniscus position. Further, the shape of the protruding portion 12 of the mold 10 is such that the length C of the contact portion in contact with the molten steel is 36 mm, the length C _X in the short side direction of the mold 10 is 30 mm, and the length of the mold 10 when the mold 10 is viewed in a plan view. It has a triangular shape with a side length _CY of 20 mm.

The quality of the slab was evaluated by the presence or absence of internal cracks in the manufactured slab.
A: No internal cracks B: Almost no internal cracks C: Small internal cracks occur but there is no problem with product quality D: Internal cracks occur and there is a problem with product quality

Operational stability was evaluated based on the presence or absence of breakouts.
A: No breakout, no small trace of solidified shell torn on slab surface B: Almost no breakout, no small trace of solidified shell torn on slab surface C: Almost no breakout, solidified shell on slab surface There was a small mark that was torn, but it can be removed in the post-process, and there is no problem with the quality of the product. D: Breakout occurred

The life of the copper plate of the mold was evaluated according to the following criteria for those caused by corrosion of the copper plate and those caused by wear.
A: No need to replace up to 2000 charges (excellent in productivity)
B: No need to replace up to 1500 charge C: No need to replace up to 1000 charge (productivity is a little low)
D: Replacement is required when the charge is 1000 or less (remarkably low productivity)

As shown in Table 6, in Examples 1 to 14, the taper ratio of the _first tapered portion T1, which is the tapered portion on the most upstream side in the casting direction, is 1.1% / m or more and 3.5% / m or less. Therefore, the quality of the slab was not a problem and the operation was stable. On the other hand, in Comparative Example 1, since the taper rate of the _first taper portion T1 was smaller than 1.1% / m, no breakout occurred, but internal cracks occurred in the slab. Further, in Comparative Example 2, since the taper rate of the _first tapered portion T1 was larger than 3.5% / m, the occurrence of internal cracking of the slab was reduced as compared with Comparative Example 1, but breakout occurred. ..

Further, in Examples 4 to 6 and 8 to 14, the distance in the casting direction from the average position of the meniscus position to the first taper change point (“first taper change point position” in Table 6) is 50 mm or more and 300 mm or less. As a result, the occurrence of internal cracks and breakouts in the slab was further reduced. Further, in Examples 8 to 13, the taper rate of the _second tapered portion T2, which is the tapered portion on the most downstream side in the casting direction, is 0.5% / m or more and less than 1.9% / m, and is on the upstream side. Since the taper ratio was less than that of the tapered portion of the above, the life of the copper plate was extended and the productivity could be improved.

In addition, as Comparative Examples 3 and 4, the same verification was carried out in the case where there is only one tapered portion formed inside the mold (that is, in the case of a single taper). As a result, when a strong taper having a relatively large gradient was provided as in Comparative Example 3, internal cracks hardly occurred in the slab, but the frictional binding force between the mold and the slab increased, resulting in a break. Out occurred. As described above, in the case of a single taper, it is difficult to set a large gradient of the tapered portion because breakout occurs, but from the results of Examples 3 and 4 and Table 1 above, a plurality of tapered portions inside the mold. By providing the above, it is possible to provide a tapered portion having a larger gradient. As a result, even if a protrusion is provided, non-uniform solidification of the corners of the slab can be suppressed in the upper part of the mold having a large solidification shrinkage, and the slab and the mold 10 can be held in the lower part of the mold having a small solidification shrinkage. Strong contact can be alleviated. When the gradient was made smaller than that of Comparative Example 3 as in Comparative Example 4, breakout did not occur, but internal cracks occurred in the slab.

Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that any person having ordinary knowledge in the field of the art to which the present invention belongs can come up with various modifications or modifications within the scope of the technical ideas described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.

10 Mold 11 Short-sided copper plate 11a Inner surface of short-sided copper plate 12 Protruding part 12a, 12f Straight line 12b, 12c, 12d, 12e, 12g Arc 13 Long-sided copper plate 13a Inner surface of long-sided copper plate T ₁ First taper part T ₂ Second taper Department

Claims (5)

A mold for continuous casting used in continuous casting equipment for continuous casting of steel.
A pair of long-sided copper plates and
A pair of short-sided copper plates sandwiched between the pair of long-sided copper plates and movable along the long-side direction of the long-sided copper plates, and a pair of short-sided copper plates.
Equipped with
The short-sided copper plate is
It has two or more gradients different in the casting direction so that multiple tapered portions are formed on the inner surface side of the mold to which the molten steel is supplied.
It has protrusions extending in the casting direction at both ends in the short side direction on the inner surface side.
The taper rate of the taper portion on the most upstream side in the casting direction is 1.1% / m or more and 3.5% / m or less.
In the protruding portion, the length of the contact portion in contact with the molten steel is shorter than the sum of the length in the short side direction and the length in the long side direction of the mold when the mold is viewed in a plan view, and the difference is 3 mm. A mold for continuous casting formed as described above. The mold for continuous casting according to claim 1, wherein the distance in the casting direction from the average position of the meniscus position to the first taper change point of the short-sided copper plate is 50 mm or more and 300 mm or less. Claim 1 or 2 that the taper rate of the tapered portion on the most downstream side in the casting direction is 0.5% / m or more and less than 1.9% / m, and is equal to or less than the taper rate of the tapered portion on the upstream side. The mold for continuous casting described in. The mold for continuous casting according to any one of claims 1 to 3, wherein the mold has two tapered portions. It is a continuous casting method of steel.
A pair of long-sided copper plates and
A pair of short-sided copper plates sandwiched between the pair of long-sided copper plates and movable along the long-side direction of the long-sided copper plates, and a pair of short-sided copper plates.
Equipped with
The short-sided copper plate is
It has two or more gradients different in the casting direction so that multiple tapered portions are formed on the inner surface side of the mold to which the molten steel is supplied.
It has protrusions extending in the casting direction at both ends in the short side direction on the inner surface side.
The taper rate of the taper portion on the most upstream side in the casting direction is 1.1% / m or more and 3.5% / m or less.
The length of the contact portion of the protruding portion in contact with the molten steel when the mold is viewed in plan is shorter than the sum of the length in the short side direction and the length in the long side direction of the mold, and the difference is 3 mm. A method for continuously casting steel, in which steel is cast using a mold for continuous casting, which is formed as described above.

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