Continuous casting method of steel and mold for continuous casting

Abstract

To suppress deformation of corner parts of a mold.SOLUTION: In a steel continuous casting method, a mold to be poured with a molten steel comprises: a pair of long side copper plates; and a pair of short side copper plates sandwiched by the pair of long side copper plates and movable in the long side direction of the long side copper plates. The long side copper plates and the short side copper plates are provided with plural slits through which cooling water circulates in a casting direction at the inside, and the feed of the cooling water circulating through the slits is controlled by a control device so that the cooling speed of the end part region in the long side copper plates corresponding to the corner parts of the mold is made higher than that of the central regions in the long side copper plates.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method for continuous casting of steel and a mold for continuous casting used therefor.

Background Art

[0002] In the continuous casting of molten steel, when the molten steel is poured into the mold, the molten steel portion in contact with the mold solidifies to form a solidified shell, which is drawn out below the mold. The solidification of the molten steel further proceeds in the secondary cooling zone below the mold, and finally a continuous casting slab is formed. The mold is formed with a water-cooled copper plate on the side in contact with the molten steel. The continuous casting mold of a continuous casting apparatus for casting a slab is formed using two long-side copper plates and two short-side copper plates, and is assembled so that the two short-side copper plates are sandwiched between the two long-side mold plates. The width of the short-side copper plate is approximately equal to the thickness of the slab to be cast.

[0003] The molten steel poured into the mold is heat-extracted from the long-side and short-side respectively at the corner portion of the mold. For this reason, due to the effect of two-sided cooling, the heat extraction amount at the corner portion of the mold becomes larger and the surface temperature decreases compared with the central portion of the width of the long-side copper plate. In the secondary cooling zone after 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 portion of the slab may be 800 °C or lower. When the temperature at the corner portion of the slab becomes 800 °C or lower, cracks occur in the corner portion. This is because the slab is bent in the continuous casting machine within the temperature range where ductility is lost, which is called the embrittlement range, and tensile stress acts. Therefore, it is necessary to set the temperature at the corner portion of the slab to the same temperature as the central portion of the long-side width (that is, 800 °C or higher) to prevent the phenomenon that the corner portion is supercooled compared with the central portion of the long-side width.

[0004] For example, Patent Documents 1 to 4 disclose that by providing a chamfer having a chamfered shape instead of making the corner portion of the mold a right angle, the effect of two-sided cooling is suppressed. Thereby, the temperature at the corner portion of the slab in the secondary cooling zone can be made 800 °C or higher, and the corner cracking of the slab can be reduced.

Prior Art Documents

Patent Document

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] When a chamfer is provided in a continuous casting mold for casting slabs of various widths by adjusting the interval between short-side copper plates, the chamfer is provided on the short-side copper plates. When using such a mold, the chamfer may plastically deform due to the heat from the molten steel during casting, and a gap may occur between the long-side copper plate and the short-side copper plate when the copper plate cools after casting. When such a gap occurs, ingots may enter the gap at the start of the next casting, which may cause operational troubles such as breakout. Such a phenomenon also occurs similarly at the corner part of a continuous casting mold without a chamfer. Therefore, it is important to appropriately cool the corner part of the mold including the chamfer.

[0007] Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a continuous casting method for steel and a continuous casting mold capable of suppressing deformation of the corner part of the mold.

Means for Solving the Problems

[0008] In order to solve the above problems, according to an aspect of the present invention, there is provided a method for continuous casting of steel, wherein the mold into which molten steel is poured includes a pair of long-side copper plates and a pair of short-side copper plates sandwiched between the pair of long-side copper plates and movable along the long-side direction of the long-side copper plates. A plurality of slits through which cooling water flows along the casting direction are provided inside the long-side copper plates and the short-side copper plates. The supply of the cooling water flowing through the slits is controlled by a control device such that the cooling rate of the end region of the long-side copper plate corresponding to the corner portion of the mold is higher than that of the central region of the long-side copper plate.

[0009] The control device may increase the flow rate of the cooling water flowing through the slits in the end region of the long-side copper plate compared to the slits in the central region of the long-side copper plate.

[0010] Alternatively, the control device may increase the flow velocity of the cooling water flowing through the slits in the end region of the long-side copper plate compared to the slits in the central region of the long-side copper plate.

[0011] Or, when a plurality of slits are provided in the thickness direction of the long-side copper plate at least in the end region of the long-side copper plate, the control device may increase the number of slits through which the cooling water is supplied in the end region of the long-side copper plate compared to the central region of the long-side copper plate.

[0012] Further, the short-side copper plates may have dams extending in the casting direction at both end portions in the short-side direction on the inner surface side of the mold. At this time, the end region of the long-side copper plate may be a region corresponding to the dams.

[0013] Also, in order to solve the above problems, according to another aspect of the present invention, there is provided a continuous casting mold used in a continuous casting facility for continuously casting steel, comprising: a pair of long-side copper plates; and a pair of short-side copper plates sandwiched between the pair of long-side copper plates and movable along the long-side direction of the long-side copper plates. A plurality of slits through which cooling water flows along the casting direction are provided inside the long-side copper plates and the short-side copper plates. The slits in the long-side copper plates are configured such that the cooling rate of the end region of the long-side copper plate corresponding to the corner portion of the mold is higher than that of the central region of the long-side copper plate.

[0014] A plurality of slits may be provided in at least the end region of the long-side copper plate in the thickness direction of the long-side copper plate.

[0015] Further, the short-side copper plates have chutes extending in the casting direction at both end portions in the short-side direction on the inner surface side of the mold, and the end region of the long-side copper plate may be a region corresponding to the chutes.

Advantages of the Invention

[0016] As described above, according to the present invention, deformation of the corner portion of the mold can be suppressed.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0018] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

[0019] [1. Configuration of Continuous Casting Equipment] First, with reference to FIGS. 1 and 2, a schematic configuration of a continuous casting equipment including a mold according to an embodiment of the present invention will be described. FIG. 1 is an explanatory view showing a schematic configuration of the continuous casting equipment 1 according to this embodiment. FIG. 2 is a schematic plan view showing the shape of the mold 10 according to this embodiment.

[0020] The continuous casting equipment 1 according to this embodiment is an apparatus for continuously casting molten steel 2 using a mold 10 for continuous casting to produce a slab 3. The continuous casting equipment 1 shown in FIG. 1 is a vertical bending type continuous casting equipment 1, but the present invention is not limited to such an example and is applicable to various other continuous casting equipment such as a curved type or a vertical type. The continuous casting equipment 1 includes a mold 10, a ladle 4, a tundish 5, a submerged nozzle 6, and a secondary cooling device 7.

[0021] The ladle 4 is a movable container for transporting molten steel 2 from the outside to the tundish 5. The ladle 4 is disposed above the tundish 5, and the molten steel 2 in the ladle 4 is supplied to the tundish 5. The tundish 5 is disposed above the mold 10, stores the molten steel 2, and removes inclusions in the molten steel 2. The submerged 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 submerged nozzle 6 continuously supplies the molten steel 2 from which inclusions have been removed in the tundish 5 into the mold 10.

[0022] The mold 10 is a rectangular tube-shaped 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 is assembled using a pair of short-side copper plates 11 and a pair of long-side copper plates 13 such that the pair of short-side copper plates 11 are sandwiched from both sides in the short-side direction (X direction) by the inner surfaces 13a of the pair of long-side copper plates 13. The pair of short-side copper plates 11 are configured to be movable along the long-side direction (Y direction) of the long-side copper plates 13. That is, the mold 10 according to the present embodiment is a mold with variable width. A detailed description of the shape of the mold 10 will be given later.

[0023] 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 such copper plates 11 and 13 is cooled, and a slab 3 including an unfrozen portion 3b inside the solidified shell 3a of the outer shell is manufactured. As the solidified shell 3a moves downward along the mold 10, the solidification of the internal unfrozen portion 3b progresses, and the thickness of the solidified shell 3a of the outer shell gradually increases. The slab 3 including such a solidified shell 3a and an unfrozen portion 3b is pulled out from the lower end of the mold 10.

[0024] The secondary cooling device 7 is provided in the secondary cooling zone 9 below the mold 10, and cools the slab 3 pulled out from the lower end of the mold 10 while supporting and transporting it. The secondary cooling device 7 has a plurality of pairs of support rolls 8 arranged on both sides in the thickness direction of the slab 3 and a plurality of spray nozzles (not shown) for spraying cooling water onto the slab 3. The support rolls 8 provided in the secondary cooling device 7 are arranged in pairs on both sides in the thickness direction of the slab 3 and function as support and transport means for supporting and transporting the slab 3. By supporting the slab 3 from both sides in the thickness direction by the support rolls 8, breakout and bulging of the slab 3 during solidification in the secondary cooling zone 9 can be prevented.

[0025] The support roll 8 forms the conveyance path (pass line) of the slab 3 in the secondary cooling zone 9. As shown in Fig. 1, this pass line is vertical directly below the mold 10 (vertical zone 9A), then curves in a curved shape (curved zone 9B), and finally becomes horizontal (horizontal zone 9C). The support roll 8 consists of a support roll provided in the vertical zone 9A to support the slab 3 immediately after being drawn out from the mold 10, a pinch roll which is a driving roll for pulling out the slab 3 from the mold 10, and segment rolls provided in the curved zone 9B and the horizontal zone 9C to support and guide the slab 3 along the pass line.

[0026] 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 at the subsequent stage of the horizontal zone 9C. The cut slab 3 moves on the table roll and is conveyed to the equipment of the next process. The overall configuration of the continuous casting equipment 1 has been described above.

[0027] [2. Cooling of the Mold] [2-1. Cooling of the Mold with a Changer] Next, based on FIGS. 2 and 3 to 5, the cooling of the mold 10 according to the present embodiment provided with the changer 12 will be described. Fig. 3 is a partially enlarged view of the corner portion of the mold provided with the right-angled triangular changer 12, showing the state before use and the state after repeated use in casting. Fig. 4 is an explanatory view showing an example of the cooling of the mold 10 according to the present embodiment. Fig. 5 is an explanatory view showing another example of the cooling of the mold 10 according to the present embodiment. In the cooling slits 31 and 33 shown in the upper part of Fig. 4 and Fig. 5, the slits through which cooling water is supplied at the reference flow rate are shown in gray. Also, the slits through which cooling water is supplied at a flow rate larger than the slits through which cooling water is supplied at the reference flow rate are shown in black, and the slits where the supply of cooling water is stopped are shown in white.

[0028] As described above, the mold 10 according to this embodiment is composed of a pair of short-side copper plates 11 and a pair of long-side copper plates 13. When the mold 10 is viewed in plan from the height direction, as shown in FIG. 2, a substantially rectangular space is formed in the mold 10 by the pair of short-side copper plates 11 and the pair of long-side copper plates 13. On the inner surface 11a of the short-side copper plate 11 of the mold 10 according to this embodiment, chamfers 12 protruding toward the inside of the space V are provided at both end portions in the short-side direction. The chamfers 12 extend along the height direction (i.e., the casting direction) of the mold 10. The chamfers 12 only need to be provided on the short-side copper plates 11 so as to protrude from the corner portions of the mold 10 toward the space V side, and their shapes are not particularly limited. For example, as shown in FIG. 2, the chamfers 12 may be right-angled triangular in plan view.

[0029] In this embodiment, regarding the long-side copper plate 13 of the mold 10, in the long-side direction (Y direction), the portion corresponding to the corner portion of the mold 10 is defined as the end region A, and the portion other than the end region A is defined as the central region B of the long-side copper plate 13. In the mold 10 in which the chamfers 12 are provided at the corner portions of the mold 10, as shown in FIG. 2, the end region A is the portion corresponding to the chamfers 12.

[0030] Here, when the chamfers 12 are not provided in the mold 10, at the inner corner portions of the mold 10, the molten steel is cooled by the two surfaces of the long-side copper plate 13 and the short-side copper plate 11, so it is more likely to be cooled than other portions. For this reason, an air layer called an air gap is likely to be formed between the slab and the inner surface of the mold 10 at the inner corner portions of the mold 10. Since the air gap is a factor that causes internal cracks in the solidified shell, it is preferably not generated as much as possible. Therefore, by providing the chamfers 12 at the inner corner portions of the mold 10 as shown in FIG. 2, for example, it is possible to suppress the significant cooling of the molten steel at the corner portions and suppress the generation of the air gap.

[0031] On the one hand, when the chamfer 12 is provided on the mold 10, due to the thermal load during casting, the chamfer 12 may yield and deform, resulting in a gap between the long-side copper plate 13 and the short-side copper plate 11. For example, as shown in FIG. 3, when a right-angled triangular chamfer 12 is provided on the mold 10, before the mold 10 is used, the chamfer 12 extends straight along the height direction (Z direction, casting direction) of the mold 10 at both ends in the short-side direction of the short-side copper plate 11. However, when casting is repeated using such a mold 10 with the short-side copper plate 11, in a region with a severe thermal load, the chamfer 12 deforms so as to fall inward.

[0032] That is, as shown in FIG. 3, when the mold 10 is viewed in plan, before use (the upper side of FIG. 3), the side surface of the short-side copper plate 11 is in contact with the inner surface 13a of the long-side copper plate 13, and the tip of the chamfer 12 is in contact with the inner surface 13a of the long-side copper plate 13. When a slab is cast using such a mold 10, due to the heat from the molten steel, each copper plate 11, 13 constituting the mold 10 tends to thermally expand. At this time, since the long-side copper plate 13 is not constrained in its width direction (i.e., the long-side direction (Y direction)), it can expand freely. However, the short-side copper plate 11 is sandwiched by the long-side copper plates 13 and is constrained in its width direction (i.e., the short-side direction (X direction)), so it cannot expand freely. Therefore, in a region with a severe thermal load, the copper plate 11 yields and deforms due to thermal stress. Such deformation of the copper plate 11 appears significantly in the region with a severe thermal load from the meniscus position to about 20 mm below in the height direction of the mold 10.

[0033] Furthermore, after casting, when the mold temperature decreases, each copper plate 11, 13 constituting the mold 10 thermally contracts. The copper plates 11, 13 that have deformed and yielded at high temperature contract from their shapes. Therefore, as shown in the lower side of FIG. 3, the tip 14 of the chamfer 12 separates from the inner surface 13a of the long-side copper plate 13, and a gap of size d is generated. The size d of the gap is the distance from the inner surface 13a of the long-side copper plate 13 to the tip 14 of the chamfer 12. As casting is repeated, the deformation amount of the tip 14 of the chamfer 12 accumulates and increases, and the size d of the gap gradually increases.

[0034] Therefore, in the continuous casting method according to the present embodiment, the cooling rate of the end region A of the long-side copper plate 13 corresponding to the corner portion of the mold 10 is made larger than the cooling rate of the central region B of the long-side copper plate 13, and the heat extraction amount at the corner portion is increased.

[0035] A plurality of slits through which cooling water flows along the casting direction are provided inside the long-side copper plate 13 and the short-side copper plate 11 of the mold 10. For example, as shown in FIG. 4, inside the short-side copper plate 11 of the mold 10, a cooling slit 31 composed of a plurality of slits (such as slits 31a to 31c) provided along the short-side direction is provided. Similarly, inside the long-side copper plate 13 of the mold 10, a cooling slit 33 composed of a plurality of slits (such as slits 331a to 331f) provided along the long-side direction is provided. By controlling the supply of the cooling water flowing through the cooling slits 31 and 33, the cooling rate of the mold 10 can be changed.

[0036] Here, in order to examine the change in the temperature distribution of the mold 10 due to the difference in the cooling rate of the mold 10, the change in the temperature distribution of the mold 10 when the flow rate of the cooling water supplied to the cooling slits 31 and 33 is changed was examined. First, as shown on the left side of FIG. 4, when the cooling water was supplied to each slit of the cooling slits 31 and 33 at the same flow rate, the chamfer 12 located at a position away from the slit was difficult to be cooled, and the temperature became higher than other locations. For this reason, the deformation of the tip 14 of the chamfer 12 as shown in FIG. 3 is likely to occur, and there is a possibility of generating a gap between the long-side copper plate 13.

[0037] On the other hand, as shown on the right side of FIG. 4, when the flow rate of the cooling water in the slits 331c and 331d in the end region A of the long-side copper plate 13 is made larger than that of the other slits, the temperature of the chamfer 12, which was at a higher temperature than other locations when the flow rate of the cooling water was the same, decreased, and the temperature of the mold 10 could be made substantially uniform.

[0038] In this way, by making the cooling rate of the end region A of the long-side copper plate 13 higher than that of the central region B, the heat transfer coefficient of the end region A is increased, and the heat extraction amount at the corner of the mold 10 is increased. As a result, the heat load at the corner of the mold 10 where the chamfer 12 is provided is reduced, and thermal deformation of the chamfer 12 is prevented. Consequently, no gap occurs between the chamfer 12 and the long-side copper plate 13, and the occurrence of operation troubles such as breakout can also be suppressed.

[0039] As a method of making the cooling rate of the end region A of the long-side copper plate 13 higher than that of the central region B, for example, as described above, the flow rate of the cooling water flowing through the slits in the end region A of the long-side copper plate 13 may be made higher than that of the slits in the central region B. That is, among the cooling slits 33 of the long-side copper plate 13, the flow rate of the cooling water flowing through the slits 331a to 331d in the end region B is made higher than that of the other slits. At this time, the flow rate of the cooling water in the slits 331c and 331d corresponding to the chamfer 12 among the slits 331a to 331d in the end region B may be increased. By increasing the flow rate of the cooling water in the end region A of the long-side copper plate 13, as shown in the lower right of FIG. 4, the temperature of the mold 10 can be made substantially uniform.

[0040] Also, as another method of making the cooling rate of the end region A of the long-side copper plate 13 higher than that of the central region B, for example, the flow rate of the cooling water flowing through the slits in the end region A of the long-side copper plate 13 may be made higher than that of the slits in the central region B. By changing the flow rate of the cooling water, the same effect as when the flow rate of the cooling water is changed can be obtained.

[0041] Alternatively, a plurality of slits may be provided in at least the end region A of the long-side copper plate 13 in the thickness direction (X direction) of the long-side copper plate 13, and cooling water may be supplied to more slits in the end region A than in the central region B of the long-side copper plate 13. For example, as shown in FIG. 5, the cooling slits 33 of the long-side copper plate 13 are formed by two rows of slits 331a to 331f and slits 332a to 332d. Then, for example, as shown in FIG. 5, in the end region A, cooling water is circulated through two rows of slits 331a to 331d, 332a, and 332b, and in the central region B, cooling water is circulated only through one row of slits, for example, slits 331e and 331f. Thereby, the cooling rate of the end region A of the long-side copper plate 13 can be made larger than the cooling rate of the central region B. That is, the cooling slits 33 of the long-side copper plate 13 are configured such that the cooling rate of the end region A is larger than that of the central region B.

[0042] Note that the slits provided in the long-side copper plate 13 may be three or more rows in the thickness direction of the long-side copper plate 13. Also, as shown in FIG. 5, a plurality of rows of slits may be provided in the central region B of the long-side copper plate 13, but it is not always necessary to provide a plurality of rows of slits in the central region B. If a plurality of rows of slits are provided in the central region B, for example, even when the casting width is changed, the cooling rate of the portion corresponding to the corner portion can be increased.

[0043] Note that the supply of cooling water to the slits provided inside the mold 10 is controlled by a control device (not shown). The control device controls the supply of the cooling water flowing through the slits, such as the flow rate and flow volume of the cooling water and the selection of the slits to which the cooling water is supplied. Thereby, the cooling rate of the end region A of the long-side copper plate 13 corresponding to the corner portion of the mold 10 can be made larger than the cooling rate of the central region B.

[0044] [2-2. Cooling of the mold without a chamfer] Next, based on FIGS. 6 and 7, the cooling of the mold 10 without a chiller will be described. FIG. 6 is a schematic plan view showing the shape of the mold 10 without a chiller. FIG. 7 is a partial enlarged view showing the corner portion of the mold 10 shown in FIG. 6.

[0045] Even when no chiller is provided, the mold 10 is composed of a pair of short-side copper plates 11 and a pair of long-side copper plates 13 as shown in FIG. 6. When the mold 10 is viewed in plan from the height direction, as shown in FIG. 6, a substantially rectangular space V is formed in the mold 10 by the pair of short-side copper plates 11 and the pair of long-side copper plates 13. The four corners of the space V formed by the short-side copper plates 11 and the long-side copper plates 13 are defined as corner portions 15. The corner portions 15 are so-called right-angled corners.

[0046] Here, even in the mold 10 without a chiller 12 as shown in FIG. 6, for the long-side copper plate 13, in the long-side direction (Y direction), the portion corresponding to the corner portion 15 of the mold 10 is defined as an end region A, and the portion other than the end region A is defined as the central region B of the long-side copper plate 13. Note that the end region A corresponding to the corner portion of the mold 10 may be a region extending a predetermined length toward the center side in the long-side direction (Y direction) from the corner of the mold 10 as shown in FIG. 6. The predetermined length may be set, for example, to include a portion that is difficult to be cooled by the cooling water supplied to the cooling slits 31 and 33.

[0047] Even when the chamfer 12 is not provided on the mold 10, due to the thermal load during casting, the corners of the mold 10 may yield and deform, resulting in a gap between the long-side copper plate 13 and the short-side copper plate 11. That is, before using the mold 10, the end face of the short-side copper plate 11 is in contact with the inner surface of the long-side copper plate 13. However, when casting is repeated using the mold 10, in the region with severe thermal load, the short-side copper plate 11 at the corner portion 15 deforms. Then, after casting, when the mold temperature decreases, each copper plate 11, 13 constituting the mold 10 thermally contracts. The copper plates 11, 13 that have deformed and yielded at high temperature contract from their shapes. For this reason, the tip of the short-side copper plate 11 at the corner portion 15 separates from the inner surface 13a of the long-side copper plate 13, and a gap is generated between the long-side copper plate 13 and the short-side copper plate 11. As casting is repeated, the amount of deformation of the short-side copper plate 11 accumulates and increases, and the size of the gap gradually becomes larger.

[0048] Therefore, the cooling rate of the end region A of the long-side copper plate 13 corresponding to the corner portion 15 of the mold 10 is made larger than the cooling rate of the central region B of the long-side copper plate 13, and the heat extraction amount in the corner portion 15 is increased.

[0049] For example, as shown in FIG. 7, inside the short-side copper plate 11 of the mold 10, a cooling slit 31 composed of a plurality of slits (such as slits 31a to 31c, etc.) provided along the short-side direction is provided, and inside the long-side copper plate 13, a cooling slit 33 composed of a plurality of slits (such as slits 331a to 331f, etc.) provided along the long-side direction is provided. In this embodiment, by controlling the supply of cooling water flowing through the cooling slits 31, 33 by the control device so that the cooling rate of the end region A of the long-side copper plate 13 is larger than the cooling rate of the central region B, deformation of the corner portion 15 of the mold 10 is suppressed.

[0050] As a method of making the cooling rate of the end region A of the long-side copper plate 13 higher than that of the central region B, as described above, there is a case of increasing the flow rate of the cooling water flowing through the slit in the end region A of the long-side copper plate 13 compared to the slit in the central region B. That is, among the cooling slits 33 of the long-side copper plate 13, the flow rate of the cooling water flowing through the slits 331a to 331d in the end region B is made higher than the flow rate of the other slits. At this time, among the slits 331a to 331d in the end region B, the flow rate of the cooling water in the slits 331c and 331d corresponding to the corner portion 15 may be increased. By increasing the flow rate of the cooling water in the end region A of the long-side copper plate 13, the temperature of the mold 10 can be made substantially uniform.

[0051] Also, as another method of making the cooling rate of the end region A of the long-side copper plate 13 higher than that of the central region B, for example, the flow rate of the cooling water flowing through the slit in the end region A of the long-side copper plate 13 may be increased compared to the slit in the central region B. By changing the flow rate of the cooling water, the same effect as when the flow rate of the cooling water is changed can be obtained.

[0052] Alternatively, as described with reference to FIG. 5, a plurality of slits may be provided in at least the end region A of the long-side copper plate 13 in the thickness direction (X direction) of the long-side copper plate 13, and more cooling water may be supplied to more slits in the end region A than in the central region B of the long-side copper plate 13. Thereby, the cooling rate of the end region A of the long-side copper plate 13 can be made higher than the cooling rate of the central region B.

[0053] As described above, the continuous casting method of steel according to one embodiment of the present invention has been described. According to this embodiment, the supply of the cooling water flowing through the slit is controlled by the control device so that the cooling rate of the end region of the long-side copper plate corresponding to the corner portion of the mold is higher than that of the central region of the long-side copper plate. As a result, the corner portion of the mold is appropriately cooled, so that the temperature distribution of the mold becomes substantially uniform, and deformation of the corner portion can be suppressed. As a result, the occurrence of operation troubles such as breakout can be suppressed.

[0054] In this embodiment, a cooling slit for increasing the cooling rate is provided in the end region of the long-side copper plate corresponding to the corner portion of the mold. Here, as a method for cooling the corner portion of the mold, for example, as described in Patent Document 3 above, a method of providing a cooling slit or a water passage hole in the end region of the short-side copper plate corresponding to the chamfer forming portion of the mold is also conceivable. However, in order to lower the temperature at the tip of the chamfer, it is necessary to provide a cooling slit or the like sufficiently close to the chamfer. However, depending on the shapes of the chamfer, the cooling slit, and the water passage hole, it may be difficult to configure them in this way. In particular, if a cooling slit or the like is placed too close to the side surface of the short-side copper plate (side surface 11b in FIG. 2) that serves as the sliding surface with the long-side copper plate, the thickness of the short-side copper plate at the position where the cooling slit or the like is formed becomes thin. As a result, due to the stress caused by sliding friction, the heat stress caused by the heat input from the molten steel and the cooling by the cooling water, cracks may occur on the sliding surface of the short-side copper plate. If cracks occur on the sliding surface of the short-side copper plate, the risk of a steam explosion occurring due to the contact between the cooling water leaking into the mold from the cracks and the molten steel increases.

[0055] For these reasons, it is desirable to avoid providing a cooling slit or a water passage hole in the end region of the short-side copper plate corresponding to the chamfer forming portion of the mold. On the other hand, since the long-side copper plate is not restricted in the long-side direction and can deform freely, it is less likely to deform due to stress and less likely to crack compared to the short-side copper plate. Therefore, as in this embodiment, it is desirable to provide a cooling slit for increasing the cooling rate in the end region of the long-side copper plate.

Example

[0056] (Example A: Cooling of a mold provided with a chamfer) Regarding the mold provided with a chamfer as shown in FIG. 2, for each shape of the chamfer, the cooling conditions necessary for suppressing the deformation occurring at the tip of the chamfer were verified by simulation. The casting conditions in the simulation were set to cast a slab with a casting speed of 1.0 m / min, a carbon content of 0.1%, a slab width of 2000 mm, and a slab thickness of 250 mm.

[0057] In this verification, for a chamfer in the shape of a right triangle in plan view, assuming six types of chamfers with the lengths of the line segments in the direction parallel to the short-side copper plate (X direction in Fig. 2) being x and the lengths of the line segments in the direction parallel to the long-side copper plate (Y direction in Fig. 2) being y, as shown in Table 1 below. Table 1 also shows the temperature increase amount ΔT at the tip of each chamfer when taking the temperature of the corner part (right angle corner) of the mold where the chamfer shown in Fig. 6 is not provided as a reference. The temperature increase amount ΔT is a value calculated by heat transfer analysis.

[0058] [Table 1]

[0059] As shown in Table 1, when (length x, length y) is (10 mm, 10 mm), (20 mm, 20 mm), (30 mm, 30 mm) and expands in similar shapes, the temperature increase amount ΔT increases monotonically as 64 °C, 84 °C, 90 °C. On the other hand, when the length y is fixed at 10 mm and the length x is increased to 10 mm, 20 mm, 30 mm, the temperature increase amount ΔT decreases monotonically as 64 °C, 50 °C, 38 °C. This is because as the length x increases, the angle at the tip of the chamfer gradually approaches 90°, and the slab temperature decreases due to the effect of two-sided cooling.

[0060] Next, the thermal deformation amount (the size d of the gap in Fig. 3) at the tip of the chamfer assumed from the temperature increase amount ΔT at the tip of the chamfer was obtained by stress analysis. The results are shown in Table 2 below.

[0061] [Table 2]

[0062] Regarding the thermal deformation amount at the tip of the chamfer, there is an operating index that stable casting can start if it is 0.50 mm or less. However, from Table 2, it was found that when a chamfer is provided at the corner of the mold, the thermal deformation amount at the tip of the chamfer exceeds 0.50 mm. In addition, when stress analysis was similarly performed for the corner part (right-angled corner) of the mold without a chamfer, the thermal deformation amount was 0.47 mm.

[0063] Therefore, aiming to suppress the thermal deformation amount at the tip of the chamfer to be equivalent to the thermal deformation amount when the corner part of the mold is a right-angled corner, the cooling capacity of the end region of the long-side copper plate required to make the temperature increase amount ΔT at the tip of the chamfer zero was examined. In this verification, a mold having slits as shown in Fig. 4 was assumed, and for the slits (slits 331c, 331d) in the end region of the long-side copper plate, the flow velocity and flow rate of the cooling water required to make the temperature increase amount ΔT at the tip of the chamfer zero were obtained by heat transfer analysis.

[0064] Table 3 below shows the flow velocity of the cooling water required in the slits in the end region of the long-side copper plate, and Table 4 below shows the flow rate of the cooling water per slit required in the slits in the end region of the long-side copper plate. The flow velocity of the cooling water in the slits other than the slits in the end region of the long-side copper plate was 7.0 m / s, and the flow rate of the cooling water was 28.2 L / min. The flow velocity and flow rate of the cooling water in these slits are the same as those of the cooling water in the slits of the mold without a chamfer.

[0065]

Table 3

[0066]

Table 4

[0067] From Tables 3 and 4, by making the flow velocity and flow rate of the cooling water in the slit in the end region of the long-side copper plate larger than those of the cooling water in the other slits, the temperature increase amount ΔT at the tip of the chamfer can be made zero, and the thermal deformation amount at the tip of the chamfer can be made equivalent to the thermal deformation amount when the corner portion of the mold is a right angle corner. That is, by making the cooling rate in the end region of the long-side copper plate larger than that in the central region, the deformation of the corner portion of the mold can be suppressed.

[0068] In addition, in the above verification, the required flow velocity and flow rate of the cooling water in the slit in the end region of the long-side copper plate were obtained based on the temperature increase amount ΔT at the tip of the chamfer calculated in advance by heat transfer analysis, but the present invention is not limited to such an example. For example, based on the measured temperature of the thermocouple inserted between the slits of the cooling water of the mold copper plate, the required flow velocity and flow rate of the cooling water in the slit in the end region of the long-side copper plate may be obtained. By providing a chamfer at the corner portion of the mold, the temperature of the copper plate rises, and the measured temperature of the thermocouple also rises. Therefore, when the measured temperature of the thermocouple is higher than the temperature of the corner portion when the corner portion of the mold is a right angle corner, by making the flow velocity and flow rate of the cooling water in the slit in the end region of the long-side copper plate larger than those of the cooling water in the other slits, the deformation of the corner portion of the mold can be suppressed.

[0069] (Example B: Cooling of a mold with a right angle corner) The thermal deformation amount (the gap between the long-side copper plate and the short-side copper plate) at the corner portion and the life of the short-side copper plate of a mold without a chamfer as shown in FIG. 6 were verified by simulation. The casting conditions in this simulation were the same as those in Example A described above. In this verification, a mold having slits as shown in FIG. 7 was assumed, and verification was performed for the case where the flow velocity of the cooling water was the same for all slits (comparative example) and the case where the flow velocity of the cooling water in the slits (slits 331c, 331d) in the end region of the long-side copper plate was set larger than that of the other slits (example). The simulation results are shown in Table 5 below.

[0070]

Table 5

[0071] As shown in Table 5, in the examples to which the present invention was applied, the amount of thermal deformation of the corner portion was reduced compared to the comparative examples. By reducing the amount of thermal deformation of the corner portion, the life of the short-side copper plate could be extended.

[0072] As described above, the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that those having ordinary knowledge in the technical field to which the present invention pertains can conceive of various modification examples or correction examples within the scope of the technical idea described in the claims, and these are also naturally understood to belong to the technical scope of the present invention.

Explanation of Reference Numerals

[0073] 10 Mold 11 Short-side copper plate 11a Inner surface of the short-side copper plate 11b Side surface of the short-side copper plate 12 Chamfer 13 Long-side copper plate 13a Inner surface of the long-side copper plate 14 Tip of the chamfer 15 Corner portion 31, 33 Cooling slit A End region of the long-side copper plate B Central region of the long-side copper plate

Claims

1. A method for continuous casting of steel, wherein the mold into which molten steel is poured comprises a pair of long-side copper plates and a pair of short-side copper plates sandwiched by the pair of long-side copper plates and movable along the long-side direction of the long-side copper plates, and a plurality of slits through which cooling water flows along the casting direction are provided inside the long-side copper plates and the short-side copper plates, the short-side copper plates have chutes extending in the casting direction at both end portions in the short-side direction on the inner surface side of the mold, the end regions of the long-side copper plates are regions corresponding to the chutes, and the supply of cooling water flowing through the slits is controlled by a control device so that the cooling rate of the end regions of the long-side copper plates corresponding to the corner portions of the mold is higher than that of the central region of the long-side copper plates. A method for continuous casting of steel.

2. The method for continuous casting of steel according to claim 1, wherein the control device increases the flow rate of cooling water flowing through the slits in the end regions of the long-side copper plates compared to the slits in the central region of the long-side copper plates.

3. The method for continuous casting of steel according to claim 1, wherein the control device increases the flow velocity of cooling water flowing through the slits in the end regions of the long-side copper plates compared to the slits in the central region of the long-side copper plates.

4. At least in the end regions of the long-side copper plates, a plurality of slits are provided in the thickness direction of the long-side copper plates, and the control device increases the number of slits through which cooling water is supplied in the end regions of the long-side copper plates compared to the central region of the long-side copper plates. The method for continuous casting of steel according to claim 1.

5. A continuous casting mold used in a continuous casting facility for continuous casting of steel, comprising a pair of long-side copper plates, and a pair of short-side copper plates sandwiched by the pair of long-side copper plates and movable along the long-side direction of the long-side copper plates, and In the long-side copper plate and the short-side copper plate, a plurality of slits through which cooling water flows along the casting direction are provided inside. The short-side copper plate has chills extending in the casting direction at both end portions in the short-side direction on the inner surface side of the mold. The end region of the long-side copper plate is a region corresponding to the chill. The slits in the long-side copper plate are configured such that the cooling rate of the end region of the long-side copper plate corresponding to the corner portion of the mold is higher than that of the central region of the long-side copper plate. A mold for continuous casting.

6. The continuous casting mold according to claim 5, wherein a plurality of slits are provided in at least the end region of the long-side copper plate in the thickness direction of the long-side copper plate.

Images