JP4272601B2 - Continuous casting equipment and continuous casting method - Google Patents

Description

  The present invention relates to a continuous casting facility and a continuous casting method for casting a continuous cast slab having a square cross section.

  In continuous casting of molten metal, for example, continuous casting of molten steel, the molten steel is injected into the mold, the molten steel is solidified at a portion in contact with the mold to form a solidified shell, and the solidified shell is drawn together with the molten steel below the mold, Solidification is completed and a slab is formed. The cross-sectional shape of the slab is generally a rectangular shape including a rectangle and a square.

  The slab exiting the mold has a thin solidified shell due to the low thermal conductivity of steel and the short residence time in the mold. Equipment is needed.

  As described in Non-Patent Document 1, the slab support method directly under the mold includes a foot roll method shown in FIG. 6 (a), a cooling plate method shown in FIG. 6 (b), and a cooling shown in FIG. 6 (c). A grid method is adopted. In the foot roll method, while cooling the slab 1 using the foot roll 20, cooling water or air is sprayed onto the slab 1 by the spray nozzle 24 to cool it. In the cooling plate system, for example, as described in Patent Document 1, the slab 1 immediately below the mold is supported by the cooling plate 21 and at the same time from the spray nozzle 24 in the opening 23 provided on the surface of the cooling plate. Solidification of the slab is promoted by the injected cooling water. Patent Document 2 relates to a cooling grid system, and in order to prevent breakout, it is important to stably maintain the slab directly under the mold as well as primary cooling in the mold. Recently, the secondary cooling has been replaced with a conventional roll. It is described that many cooling grid devices are used. That is, the slab continuously drawn out from the mold is supported by the cooling grid 22 disposed immediately below the mold, and at this time, the slab is sprayed from the cooling water spray 24 disposed in the opening 23 between the cooling grids. Cooled by cooling water.

  In continuous casting, particularly continuous casting in which the thickness of a slab increases, such as bloom continuous casting, it is necessary to support the slab directly below the mold on four sides of the slab. In any of the foot roll method, the cooling plate method, and the cooling grid method, when the slab thickness is large, all four surfaces of the slab are supported.

Japanese Utility Model Publication No. 55-116760 Japanese Patent Laid-Open No. 60-87961 Page 646, "3rd Edition Steel Handbook II Steelmaking and Steelmaking" edited by the Japan Iron and Steel Institute

  In continuous casting in which a continuous casting slab having a square cross section is cast, when a method of supporting four surfaces of a slab with a cooling plate for supporting a slab immediately below the mold, particularly when the casting speed is increased, FIG. As shown to (a), the internal crack 14 may generate | occur | produce near the corner part inside the slab 1 which completed casting. The internal crack 14 is formed by the impurity-concentrated molten steel entering the cracked portion of the solidified shell generated near the solid-liquid interface, and this part has the quality of the slab produced because the impurities are concentrated. It causes a decrease.

  When continuous casting is performed at a high speed and the casting speed is high, the frequency of occurrence of breakout directly under the mold increases. In particular, in the foot roll method, breakout occurs frequently during high speed casting. Further, the cooling plate 21 and the cooling grid 22 both have an opening 23 for disposing the cooling water spray nozzle 24 in the slab support surface. When the molten metal leaking part of the solidified shell that occurred in the mold or directly under the mold passes under the mold, the scab-like irregularities of the molten metal part get caught in these spray nozzle openings, and breakout occurs at the slab support part directly under the mold. There is a situation that cannot be prevented.

  A first object of the present invention is to prevent internal cracks that occur when a cooling plate is used to support a slab directly under a mold. Another object of the present invention is to provide a mold direct slab support system that does not cause breakout even during high speed casting.

That is, the gist of the present invention is as follows.
(1) An injection means 7 for directly injecting cooling water or air water to the corner portion 12 of the slab 1 and its peripheral portion at the lower part of a mold for casting a continuous cast slab having a square cross section; A plate-like support means 5 for supporting the four surfaces of the slab at each of the portions excluding the corner portion 12 and its peripheral portion and having a cooling means 7 on the back surface thereof ; the distance X between the width end portion 15 and the slab corners 12 of the right and left both in the upper end of the flat support means 5, the solidified shell thickness t _U or more and solidified shell thickness t _U at the upper end position is 2 times or less, in the portion other than the upper end, the solidified shell thickness at the lower end position of the distance X _U above and planar substrate means between the width end portion and the corner portion of the slab of the plate-shaped supporting means at the top continuous casting and equal to or less than twice the t _L Equipment.
(2) At the lower part of the mold for casting a continuous casting slab having a square cross section, the plate-like support means 5 supports the four surfaces of the slab at the portions excluding the corner portion 12 and its peripheral portion, and the plate-like support. The means 5 has a cooling means 7 on its back surface, and the distance X between the width end portion 15 of the flat plate-like support means 5 and the corner portion 12 of the slab is left and right at the upper end of the flat plate-like support means 5. The solidified shell thickness t _U at the upper end position and not more than twice the solidified shell thickness t _U , and at the portion other than the upper end, between the width end portion of the flat plate-like supporting means at the upper end and the corner portion of the slab Of the solidified shell thickness t _L at the lower end position of the flat plate supporting means and not more than twice the distance X _U, and directly cooled to the corner portion 12 of the slab 1 exposed between adjacent flat plate supporting means and its peripheral portion It is characterized by jetting water or air Continue casting method.

  In the present invention, at the lower part of a mold for casting a continuous cast slab having a square cross section, the four surfaces of the slab are supported by the flat plate support means at the portions excluding the corner portion and the peripheral portion thereof, and adjacent flat plate shapes. By directly injecting cooling water or air water to the corner portion of the slab exposed between the supporting means and its peripheral portion, it is possible to prevent the occurrence of internal cracks near the corner portion inside the slab. Further, the flat plate supporting means has a cooling means on the back surface thereof, and since there is no opening for the slab cooling spray nozzle, it is possible to reduce the occurrence frequency of breakout occurring in high speed casting.

  An embodiment of the present invention will be described with reference to FIGS. 1 to 3 by taking as an example a continuous bloom bloom casting of a slab having a square cross section, that is, a rectangular or square cross section.

  In the present invention, the slab 1 guided directly under the mold is supported by the flat plate support means 5 on its four surfaces. The flat plate support means 5 is a flat plate shape having no opening on the surface in contact with the slab 1, and the slab 1 is removed while being supported by being in contact with the flat plate support means 5. The plate-like support means 5 has a cooling means 7 on the back surface thereof. Specifically, as shown in FIG. 4, the side facing the slab of the plate-like support means 5 is formed of a metal plate 8 having a high thermal conductivity such as copper, and the back surface of the metal plate 8 (on the slab) A cooling water passage 10 is formed on the opposite side of the contacting surface, and the metal plate 8 is cooled by circulating the cooling water 9 from the back surface. The metal plate 8 is supported by the back support plate 11. When copper is used as the material of the metal plate 8, the surface in contact with the slab can be coated with Ni plating or the like to improve the wear resistance of the surface. As for the copper material and the surface coating method, it is preferable to apply the technique used in the water-cooled copper mold.

  In the conventional cooling plate system, when the slab directly below the mold is supported from four surfaces, the entire width in the width direction of each surface of the slab is supported by the cooling plate. Therefore, as shown in FIG. 5B, the entire surface of the slab 1 including the corner portion 12 is supported by the cooling plate 21.

  On the other hand, in the slab cast using the cooling plate system that supports the entire surface of the slab, especially when the casting speed is increased, the vicinity of the slab corner 12 as shown in FIG. A phenomenon in which an internal crack 14 occurs immediately below the surface layer of was observed. As described above, the internal crack is formed by the impurity-concentrated molten steel entering the cracked portion of the solidified shell generated near the solid-liquid interface, and this portion is a cast slab produced because the impurity is concentrated. Cause deterioration of quality.

  As a result of investigating the cause of the occurrence of internal cracks, in the solidified portion cooled by the cooling plate directly under the mold, the cooling of the vicinity of the slab corner 12 is insufficient as shown in FIG. A phenomenon in which the corner portion 12 is delayed was observed. When such a phenomenon is observed, particularly when high-speed casting is performed, a crack is generated at the solidification interface of the slab corner portion 12, and the impurity-enriched molten steel enters the crack and solidifies as it is. Was found to form.

  The present invention does not support the slab directly under the mold in the entire width direction, but as shown in FIG. 1, the flat plate-like support means 5 has the slab 1 in the portion excluding the corner portion 12 and its peripheral portion. In other words, a method in which the corner portion 12 of the slab 1 and its peripheral portion are not supported by the plate-like support means 5 is employed. And the cooling water was directly sprayed by the injection means 6 to the corner part 12 of the slab exposed between the adjacent flat plate support means and its peripheral part, and the slab was cooled. As a result, it was found that the cooling of the slab corner portion 12 was strengthened, the slab cooling delay in the vicinity of the corner portion was eliminated, and the occurrence of internal cracks could be prevented.

That is, the continuous casting equipment of the present invention is an injection means 6 for directly injecting cooling water or air water to the corner portion 12 of the slab 1 and its peripheral portion at the lower part of the mold for casting a continuous cast slab having a square cross section. And plate-like support means 5 for supporting each of the four surfaces of the slab at portions other than the corner portion 12 and its peripheral portion of the slab 1 and having a cooling means 7 on the back surface thereof. Is a continuous casting facility with a basic structure . By performing continuous casting using such a continuous casting facility, it is possible to prevent the occurrence of internal cracks near the slab corner.

  For direct cooling to the corner portion of the slab exposed between adjacent flat plate supporting means and its peripheral portion, a method of directly injecting cooling water to the slab using a spray nozzle, or using a water spray nozzle A method can be employed in which the cooling water is atomized and the air is directly injected onto the slab. The nozzles for injecting cooling water and air are referred to collectively as the injection means 6 here.

  It is preferable to determine the amount of cooling water or the like so that the direct cooling of the slab corner portion and the peripheral portion by the jetting means 6 is approximately the same as the cooling capacity by the flat plate support means 5 at the slab center.

  When the slab is supported by the flat plate-like support means 5 of the present invention at a portion excluding the corner portion and its peripheral portion of the slab, the flat plate support means 5 does not support the corner portion of the slab and its peripheral portion. There is a preferred range for the area size.

  If the area of the area that is not supported by the plate-like support means 5 near the corner portion of the slab is too narrow, the direct cooling effect by injecting cooling water or air water cannot be sufficiently obtained. As a result, as shown in FIG. 3A, a solidification delay of the slab corner portion 12 occurs and an internal crack 14 is generated. Conversely, as shown in FIG. 3 (b), if the area of the area not supported by the flat plate supporting means 5 near the corner of the slab is too wide, the slab for preventing bulging at the corner of the slab. The support is not sufficient, and the internal crack 14 may increase by bulging the slab corners outward.

The said range of this invention is demonstrated based on Fig.2 (a). The distance X between the width end portion 15 of the flat plate-like support means 5 and the corner portion 12 of the slab is set to be equal to or greater than the solidified shell thickness t, thereby ensuring a sufficient range of direct cooling with cooling water or air. Since the effect of direct cooling can be sufficiently obtained, the cooling delay of the slab corner can be prevented. Further, by setting the distance X between the width end portion 15 of the plate-like support means 5 and the corner portion 12 of the slab to be not more than twice the solidified shell thickness t, the bulging in which the slab corner portion swells outward is prevented. It is possible to prevent and perform good casting. It is more preferable that the distance X between the width end portion 15 of the flat plate-like support means 5 and the corner portion 12 of the slab is 1.5 times or less the solidified shell thickness t.

In the casting direction, as shown in FIG. 2 (b), at the upper end 16 of the flat plate support means 5, the distance X between the width end portion 15 of the flat plate support means 5 and the corner portion 12 of the slab is the upper end. The solidified shell thickness t _U at the position is greater than or equal to twice the solidified shell thickness t _U. The distance between the width end portion 15 and the slab corners 12 of the flat plate-like support means in a flat plate-like support means the upper end 16 is denoted by X _U.

As the solidified shell grows, the solidified shell thickness t gradually increases in the casting direction even within the range of the flat plate support means 5. Therefore, with respect to the distance X between the width end portion 15 of the flat plate support means 5 and the corner portion 12 of the slab at a portion other than the upper end of the flat plate support means 5, the flat plate support means at the flat plate support means upper end 16. We adjusted to be 2 times the solidified shell thickness t _L at the lower end 17 at a distance X _U above and planar substrate means between the width end portion of the slab corners of.

  The length in the casting direction of the flat plate-like support means 5 of the present invention is determined based on the same concept as the bulging suppression in the conventional cooling plate system and the like, and no restriction is generated.

  Powder adheres to the surface of the slab drawn downward from the lower end of the mold. When the slab is introduced into the flat plate support means of the present invention, the slab fixing powder is peeled and crushed at the upper end of the flat plate support means and removed from the surface of the slab. If the powder peeled from the surface of the slab is deposited in the space between the mold and the flat plate support means, cooling of the slab is hindered, which is not preferable.

  In the present invention, the space between the lower end of the mold and the upper end of the flat plate supporting means is sufficient to discharge the powder peeled from the slab surface to the back side of the flat plate supporting means, and this space. Therefore, it is necessary to keep the slab in a range where no bulging occurs. An interval of about 10 mm is preferable because the powder peeled off from the surface of the slab can be discharged to the back side of the plate-like support means and the occurrence of bulging can be suppressed.

  In order to discharge the crushed powder or to accelerate the cooling of the slab, a spray nozzle is arranged in the space between the mold and the flat plate support means, and cooling water and air are directed from the spray nozzle toward the slab. It is good also as injecting water.

  The slab that has passed through the mold shrinks due to solidification shrinkage as it goes downward. The degree of coagulation shrinkage is about 0.5% / m. Further, in the present invention, since the slab is supported by the flat plate-like support means, expansion of the slab due to bulging can be suppressed. Therefore, in order to support the slab accurately along the solidification shrinkage of the slab and to ensure contact, a so-called casting direction taper that becomes narrower as the distance between the two flat plate supporting means facing each other decreases. It is preferable to provide it. On the other hand, when the taper in the casting direction is too large, the slab is subjected to compression below the flat plate-like support means, and a corrective crack is generated. In the present invention, when the taper in the casting direction of the plate-like support means is 1.0% / m or less, it becomes possible to perform good casting without occurrence of straightening cracks.

  At the upper end of the flat plate support means, the distance between the two flat plate support means facing each other is the same as the distance between the mold surfaces facing each other at the lower end of the mold, or within the range of the value obtained by subtracting the amount of solidification shrinkage. This is preferable. The amount of solidification shrinkage means the amount by which the slab solidifies and shrinks at the distance between the lower end of the mold and the upper end of the plate-like support means. By setting such an interval, the slab introduced into the flat plate supporting means is favorably supported by the flat plate supporting means without causing bulging. At the same time, when the slab is introduced into the flat plate-like supporting means, it is possible to perform casting without causing excessive compression and no occurrence of straightening internal cracks.

  Further, it is preferable that the two flat plate-like support means facing each other are fixed so that the distance between them is constant. This is because the fixed installation can increase the equipment strength and make the interval always constant, thereby reducing the equipment cost. Adopting elastic pressing in which the interval changes with the slab pressing force is not preferable because the interval changes with the slab pressing force.

  When high-speed casting is performed, the thickness of the shell that grows in the mold becomes thin, so that the gap between the mold and the slab becomes smaller due to bulging deformation in the mold, which tends to cause uneven powder inflow or insufficient inflow. Cracking breakout due to non-uniform shell thickness and starting point of occurrence of constraining breakout (hot water leakage portion) are likely to occur.

  When the slab support under the mold is of the foot roll type (FIG. 6A), the leaked portion exposed at the lower end of the mold is not repaired at all, and a breakout occurs immediately. In addition, since the distance between rolls is wide in the foot roll method, when the shell thickness is reduced by high-speed casting, the shell is easily broken at this portion due to the molten steel static pressure, and breakout is likely to occur. In particular, when the shell thickness is non-uniform, breakout occurs at the foot roll portion at the portion where the shell thickness is thin.

  When the conventional cooling plate method (FIG. 6 (b)) or the cooling grid method (FIG. 6 (c)) is adopted as the slab support system under the mold, the spray nozzle 24 is disposed in both cases to replace the slab. It has an opening 23 for direct cooling by spraying. When the hot water leaking portion reaches the opening 23 in the process of passing the cooling plate 21 or the cooling grid 21, the scab-like unevenness of the hot water leaking portion is caught in the opening, and the hot water leaking portion expands and breaks. It will lead to out.

  Unlike the foot roll method, the flat plate support means 5 of the present invention has a short distance between the lower end of the mold and the slab support start point, so that the occurrence of breakout can be suppressed as compared with the foot roll method. Furthermore, unlike the conventional cooling plate method and cooling grid method, the flat plate-like support means 5 of the present invention is generated in the mold because there is no opening for placing the spray nozzle on the surface in contact with the slab. The scab-like unevenness of the hot water leaking portion is not caught and the hot water leaking portion is repaired and closed while passing through the flat plate-like support means, so that the occurrence of breakout can be prevented.

  The present invention was applied to a curved bloom continuous casting apparatus having a mold size of 240 mm square. The mold size at the lower end of the mold is 240 mm square, the casting type is S45C, and the casting speed is 1.7 m / min.

  As shown in FIG. 4, as the flat plate support means 5 of the present invention, the side facing the cast piece of the flat plate support means 5 is formed of a copper metal plate 8, and the back surface of the metal plate 8 (the surface in contact with the cast piece). The cooling water passage 10 is formed on the opposite side), and the cooling water 9 is circulated from the back surface to cool the metal plate 8. The metal plate 8 is supported by the back support plate 11. Ni plating coating is performed on the surface of the metal plate 8 in contact with the slab. The length in the casting direction of the flat plate supporting means 5 is 340 mm. The facing distance at the upper end of the flat plate supporting means 5 was the same as the mold facing distance at the lower end of the mold, and the taper of the flat supporting means 5 was 0.5% / m. The distance between the lower end of the mold and the upper end of the flat plate supporting means was 10 mm.

  As the injection means 6 at the slab corner portion, a wide-angle air-water injection nozzle is arranged at the center portion of the flat plate support means 5 in the casting direction for each corner to directly cool the entire corner portion and peripheral portion. It was decided to.

As for the solidified shell thickness t, the solidified shell thickness t _{U at} the upper end of the flat plate-like support means 5 was 14 mm, and the solidified shell thickness t _{L at the} lower end was 17 mm.

In one plate-like support means 5, the distance X between the width end portion 15 of the plate-like support means 5 and the corner portion 12 of the slab is the same for any corner portion, and in any casting direction. The value of X was also the same for the site. A value obtained by dividing the value of X by the solidified shell thickness t _U at the upper end of the plate-like support means 5 is α. Six types of flat plate support means 5 were manufactured, and α was changed from 0 to 2.5 as shown in Table 1. The behavior of the rate of occurrence of internal cracks (%) when performing continuous casting using these flat plate-like support means 5 was investigated. Table 1 shows the results.

As is clear from Table 1, it can be seen that the internal crack occurrence rate is low in the range of α = 1.0 to 2.0. That is, the distance X between the width end portion 15 of the flat plate supporting means 5 and the corner portion 12 of the slab is equal to or greater than the solidified shell thickness t _U at the upper end position of the flat plate supporting means 5 and twice the solidified shell thickness t _U. It can be seen that the incidence of internal cracks is low when More preferably, α is in the range of 1.0 to 1.5.

  In the present invention example using the above plate-like support means, the breakout occurrence rate directly under the mold was 0.03%. In the conventional method adopting the foot roll method, the breakout occurrence rate directly under the mold was 0.09%, so it is clear that the breakout occurrence rate is reduced by adopting the method of the present invention.

It is a figure which shows the continuous casting installation of this invention, (a) is a perspective view, (b) is a plane sectional view, (c) is sectional drawing including a casting_mold | template. It is a figure which shows the relationship between the distance X between the width | variety edge part of a flat support means, and the corner part of a slab, and the solidification shell thickness t, (a) is a plane sectional view, (b) is an elevation view. . It is a plane sectional view showing the slab cooling situation directly under the mold, (a) when the plate-like support means is too close to the corner portion, (b) is the plate-like support means is too far away from the corner portion It is a figure which shows a case. It is a figure which shows the cooling structure of the flat support means of this invention, (a) is an elevational sectional view, (b) is a BB arrow sectional drawing. (A) is a slab cross-sectional view showing the state of occurrence of internal cracks in the cross-section of the slab, and (b) is a partial cross-sectional view for explaining the solidification delay generated at the corner of the slab by the cooling plate method. It is a figure which shows the conventional casting mold bottom support system, (a) is the front view and side sectional view about a foot roll system, (b) is the front view and partial sectional view about a cooling plate system, (c) is cooling It is a front view about a grid system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cast piece 2 Solidified shell 3 Unsolidified molten steel part 4 Mold 5 Flat plate support means 6 Injection means 7 Cooling means 8 Metal plate 9 Cooling water 10 Cooling water passage 11 Back surface support plate 12 Corner part 13 Cast piece surface 14 Internal crack 15 Flat plate Width end 16 upper end 17 lower end 20 foot roll 21 cooling plate 22 cooling grid 23 opening 24 spray nozzle X distance between width end of flat plate support means and corner of cast slab X _U flat plate support The distance between the width end of the flat plate support means and the corner of the slab at the upper end of the means t The solidified shell thickness of the slab t The solidified shell thickness of the slab at the upper end of the _U flat support means t _L Flat plate support Solidified shell thickness of the slab at the lower end of the means

Claims (2)

Injecting means for directly injecting cooling water or air to the corner portion of the slab and its peripheral portion, and the corner portion of the slab and its peripheral portion at the lower part of the mold for casting the continuous cast slab having a square cross section Plate-like support means for supporting each of the four surfaces of the slab at the removed portion and having a cooling means on the back surface thereof , a width end portion of the plate-like support means, a corner portion of the slab, The distance between the left and right sides is not less than the solidified shell thickness at the upper end position and not more than twice the solidified shell thickness at the upper end of the plate-like support means. Continuous casting equipment characterized in that it is not less than the distance between the width end portion of the plate-like support means and the corner portion of the slab and not more than twice the thickness of the solidified shell at the lower end position of the plate-like support means . At the bottom of the mold for casting a continuous casting slab having a rectangular cross section, the four surfaces of the slab are supported by flat plate support means at portions other than the corner portion and its peripheral portion, and the flat plate support means is the back surface thereof. Has a cooling means,
The distance between the width end portion of the flat plate supporting means and the corner portion of the slab is equal to or larger than the solidified shell thickness at the upper end position and 2% of the solidified shell thickness at the upper end of the flat plate supporting means. In a portion other than the upper end, the solidified shell thickness at the lower end position of the flat plate supporting means is twice the distance between the width end portion of the flat plate supporting means and the corner portion of the slab at the upper end. And
A continuous casting method characterized by injecting cooling water or air directly into a corner portion of a slab exposed between adjacent flat plate supporting means and its peripheral portion.

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