JP5768774B2 - Method for continuous casting of hollow round section slab and mold for continuous casting of hollow round section slab - Google Patents

Description

  The present invention relates to a continuous casting method for hollow round cross-section slabs, and more particularly to a continuous casting method for slabs made of ordinary steel, high alloy steel, stainless steel, Ni-base alloy and the like. The present invention also relates to a continuous casting mold for a hollow round section slab.

  Seamless pipes (seamless pipes) made of plain steel, high alloy steel, stainless steel, Ni-base alloy, etc., are usually used to make round billets by dividing ingots and bloom slabs. As a Mannesmann method, a Eugene Sejurune method, a mandrel method and the like.

  In recent years, from the viewpoint of rationalization, billets are often produced by continuous casting, and the billets are often supplied directly to the pipe making process as a pipe making material without going through a lump process. Patent Document 1 discloses a method for directly producing a hollow round cross-section slab having a shape close to a product (hereinafter also simply referred to as “hollow slab”). Since the hollow cast slab can be directly supplied to the pipe making process, it is not necessary to go through the splitting process, and it is possible to reduce the load on the pipe making because it is hollow.

  However, the centrifugal casting method described in Patent Document 1 is a batch type, and there is a limitation on the length of a slab that can be manufactured, and there is a limitation that only a slab of the same length can be manufactured. .

  On the other hand, Patent Documents 2 to 4 disclose a method of manufacturing a hollow cast piece by continuous casting. According to continuous casting, the yield can be improved and the length of the slab is less limited.

  In continuous casting of a hollow slab, unlike a continuous casting of a general solid slab, the cooling method of the hollow inner surface of the slab during casting is an important problem. Insufficient cooling of the hollow inner surface may cause bulging due to the molten steel static pressure, or breakout due to fracture of the solidified shell.

  In Patent Document 2, in order to cope with this problem, when molten steel is cooled by a water-cooled outer mold and a core mold to generate and grow a solidified shell from both inner and outer peripheral surfaces, There has been proposed a method of directly cooling the hollow inner surface of a slab by injecting cooling water from the lower end of a spray water supply pipe penetrating from the upper part to the lower part of the mold.

  However, the use of water for cooling the hollow inner surface of the slab during casting is very dangerous for the following reasons.

  Since the cooling water sprayed on the hollow inner surface flows below the slab, as described in Patent Document 2, if a water passage hole is provided in the head portion of the dummy bar, the cooling water is formed outside the slab. Discharged. However, the possibility of breakout often occurring in continuous casting of a general solid slab cannot be denied even in continuous casting of a hollow slab. Breakout is a phenomenon in which molten steel flows out when the solidified shell is remelted or the solidified shell is broken by friction between the mold surface and the solidified shell.

  When the molten steel flows out in the hollow of the hollow slab by breakout, the water flow holes in the head portion of the dummy bar may be blocked by solidification of the flowing molten steel. When the water passage hole is blocked, the cooling water stays without being discharged, and the molten steel flows into the staying water. Since this series of phenomena proceeds in a very short time, even if the breakout is detected and the cooling water is stopped immediately, it is not possible to completely prevent the molten steel from flowing into the staying water.

  In this case, the staying water is instantly vaporized and expanded, and the inside of the hollow slab is a closed space, so that a so-called steam explosion occurs. When a steam explosion occurs in the hollow slab, the blast escapes from the gap between the core mold and the solidified shell on the inner surface side of the slab to the upper part of the mold, or the molten steel is removed from the broken solidified shell side of the mold. It will be blown up to the outside. This is a very dangerous situation for workers around the mold.

  Patent Documents 3 and 4 propose a continuous casting method for hollow cast pieces to which a hot water supply method in which a tundish and an outer mold are directly connected is applied. In this direct hot water supply method, the slab is not pulled out continuously but is pulled out intermittently, so that a cold shut mark deeper than a normal oscillation mark is generated on the surface of the slab. For this reason, since the surface of the slab is indispensable, the yield is greatly reduced.

  Also, in the methods proposed in Patent Documents 3 and 4, it is very difficult to control the contact point (so-called triple point) between the tundish, the mold, and the molten steel, so breakout is likely to occur and stable operation is possible. Have difficulty. Further, in the tundish, the initial solidified shell formed of the core mold and the initial solidified shell formed of the outer mold are different in positions where they start to be formed, so that the slab is likely to be bent. In addition, the inside of the core mold and the hollow cast slab becomes a closed space, and when a breakout occurs, there is no escape space for molten steel and cooling water, which may lead to a steam explosion.

JP 2011-212688 A JP-A-60-221152 Japanese Patent Laid-Open No. 3-268843 JP-A-6-304702

  The present invention has been made in view of the above problems, and it is difficult for breakouts to occur, and even if a breakout occurs, it is possible to prevent the occurrence of a secondary disaster due to a steam explosion, and It is an object of the present invention to provide a continuous casting method of a hollow slab and a mold that can be used in this method, which can obtain a slab that is free of bending and has a good quality such as surface properties.

  The present inventor is capable of preventing a breakout from occurring, and even if a breakout occurs, it is possible to prevent a steam explosion from occurring, and to obtain a hollow cast piece having a good quality. The method was examined.

  When continuously casting a hollow slab, it is very important to prevent the occurrence of a steam explosion in the hollow of the slab. In order to prevent steam explosion, the hollow inner surface of the slab is cooled sufficiently to secure a solidified shell with sufficient thickness to make it difficult to break the solidified shell, and in case the solidified shell breaks Therefore, it is necessary not to make the hollow space a closed space.

  The inventor obtained the following knowledge as a result of the study. For the continuous casting of the hollow round section slab, a core mold arranged concentrically with the outer mold is used, and a plurality of cooling water flow paths are provided so as to penetrate from the upper end to the lower end in the vicinity of the surface of the core mold. By providing a vent hole in the center of the core mold so as to penetrate from the upper end to the lower end, the possibility of breakout and steam explosion can be extremely reduced. By sufficiently cooling the hollow inner surface of the slab with cooling water discharged from the cooling water flow path of the core mold, it is possible to suppress the temperature rise of the solidified shell due to recuperation and increase the thickness of the solidified shell. Therefore, the possibility of occurrence of breakout can be reduced. By providing a vent hole in the core mold, the inside of the slab can be opened to the outside. Further, since the hollow inner surface of the slab can be sufficiently cooled, a slab having good quality can be obtained.

This invention is made | formed based on these knowledge, The summary is shown to the continuous casting method of the hollow round-section slab shown to following (1)-(5), and (6) and (7) . It is in a mold for continuous casting of hollow round section slabs.

(1) A continuous casting method of a hollow round cross-section slab having a water cooling structure and using a cylindrical outer mold and a cylindrical core mold arranged concentrically, wherein the core mold is in the vicinity of the surface. A plurality of cooling water passages penetrating from the upper end to the lower end, and a vent hole penetrating from the upper end to the lower end in the center, the cooling water supplied from the upper end of the cooling water passage of the core mold and discharged from the lower end, The inner surface of the hollow round cross-section slab being cast is cooled from directly under the core mold, and the cross-sectional shape of the cooling water flow path of the core mold is an arc-shaped slit at the bottom of the core mold A continuous casting method of a hollow round section cast piece characterized by the above.

(2) The hollow round cross-section slab according to (1), wherein the cooling water flow path of the core mold is inclined radially outward from the upper end to the lower end of the core mold. Continuous casting method.

(3) A continuous casting method of a hollow round cross-section slab having a water-cooled structure and concentrically arranged cylindrical outer mold and columnar core mold, wherein the core mold is near the surface A plurality of cooling water passages penetrating from the upper end to the lower end, and a vent hole penetrating from the upper end to the lower end in the center, the cooling water supplied from the upper end of the cooling water passage of the core mold and discharged from the lower end, The inner surface of the hollow round cross-section slab being cast is cooled from directly under the core mold, and the cooling water flow path of the core mold is inclined radially outward from the upper end to the lower end of the core mold. A continuous casting method of a hollow round section slab characterized by the above.

(4) Any of (1) to (3) above, wherein the core mold is longer in the casting direction than the outer mold, and the lower end of the core mold protrudes from the lower end of the outer mold. A method for continuously casting the hollow round section slab according to claim 1.

(5) The continuous casting method for a hollow round cross-section slab according to any one of (1) to (4), wherein the outer mold and the core mold oscillate in synchronization.

(6) A mold for continuous casting of a hollow round section cast piece having a water cooling structure and concentrically arranged from an outer mold and a core mold, the core mold being located near the surface from the upper end to the lower end A plurality of cooling water passages penetrating through and a vent hole penetrating from the upper end to the lower end in the center, and the shape of the cross section of the cooling water passage of the core mold is an arc-shaped slit at the lower part of the core mold A mold for continuous casting of a hollow round cross-section slab characterized by comprising:
(7) A continuous casting mold of a hollow round cross-section slab having a water-cooling structure and concentrically arranged from an outer mold and a core mold, the core mold being located near the surface from the upper end to the lower end A plurality of cooling water passages penetrating through and a vent hole penetrating from the upper end to the lower end in the center, and the cooling water passage of the core mold is directed radially outward from the upper end to the lower end of the core mold. A mold for continuous casting of a hollow round section slab characterized by being inclined.

  According to the continuous casting method and mold of the hollow round cross-section slab of the present invention, breakout is unlikely to occur, and even if a breakout occurs, it is possible to prevent the occurrence of a secondary disaster due to a steam explosion. In addition, a slab having good quality can be obtained.

It is a longitudinal cross-sectional view which shows the outline of the casting_mold | template periphery of the continuous casting apparatus which can apply the continuous casting method of this invention. It is an enlarged view of the mold periphery of the continuous casting apparatus shown in FIG. 1, (a) is a longitudinal sectional view, and (b) is a plan view. It is a bottom view of a core mold. It is a figure which shows an example of the preferable shape of the cooling water flow path of a core mold, The figure (a) is a perspective view, The figure (b) is sectional drawing. It is a figure which shows the start method of casting using the continuous casting apparatus shown in FIG.

1. FIG. 1 is a longitudinal sectional view schematically showing the periphery of a mold of a continuous casting apparatus to which the continuous casting method of the present invention can be applied. The mold is composed of a cylindrical outer mold 1 and a columnar core mold 2, and the core mold 2 is disposed concentrically inside the outer mold 1. The outer mold 1 and the core mold 2 are both made of copper and have a water cooling structure. An immersion nozzle 4 for supplying molten steel 3 is inserted between the outer mold 1 and the core mold 2 from above. A cooling water header 5 is connected above the core mold 2, and a plurality of cooling water supply pipes 6 are connected to the cooling water header 5. A plurality of support rolls 8 that support the outer peripheral surface of the slab 7 are arranged below the outer mold 1.

  An oscillation table 9 is connected to the outer peripheral surface of the outer mold 1. It is preferable that the outer mold 1 and the core mold 2 oscillate in synchronization. In FIG. 1, the oscillation table 9 and the cooling water supply pipe 6 are connected by a connecting member 10, and the outer mold 1 and the core mold 2 can be oscillated with their phases synchronized. A plurality of cooling water supply pipes 6 and connecting members 10 are arranged, and it is preferable to arrange them symmetrically with respect to the core mold 2 in the horizontal direction. The number of the cooling water supply pipe 6 and the connecting member 10 is not limited as long as the immersion nozzle 4 can be disposed in the mold.

  The inner diameter of the outer mold 1 and the outer diameter of the core mold 2 are smaller toward the upper end and smaller toward the lower end so as to correspond to the solidification shrinkage of the slab, that is, in a taper shape in the mold for casting the solid slab. A corresponding shape is preferred.

  2 is an enlarged view of the periphery of the mold of the continuous casting apparatus shown in FIG. 1, wherein FIG. 2 (a) is a longitudinal sectional view and FIG. 2 (b) is a plan view. As shown in the figure, the core mold 2 is provided with a plurality of cooling water passages 2a penetrating from the upper end to the lower end near the surface, and a vent hole 2b penetrating from the upper end to the lower end is provided at the center. ing. Due to the air holes 2b, the hollow space of the slab 7 can be made an open space even during continuous casting. FIG. 2B shows a state in which two immersion nozzles 4 having a cross-sectional shape obtained by cutting out a part of a ring are arranged. In the figure, the water cooling structure of the outer mold 1 is omitted, but the outer mold 1 is provided with a slit-type cooling water channel used for continuous casting of a general slab.

  Cooling water is supplied from the cooling water header 5 to the cooling water flow path 2a. The cooling water 11 supplied from the upper end of the cooling water flow path 2 a is discharged from the lower end of the cooling water flow path 2 a and contacts the inner surface of the hollow slab 7. The slab 7 is in a state where the molten steel 3 is held inside the solidified shell 7a immediately after being discharged from the mold. Since the cooling water 11 discharged from the cooling water flow path 2a can sufficiently cool the entire inner surface of the slab 7, and the solidified shell 7a can be formed uniformly thick, a breakout due to remelting or breaking of the solidified shell 7a. The possibility of is low.

  A spray device is disposed between the support rolls 8 so that the cooling water spray 12 can be sprayed on the outer peripheral surface of the slab 7.

  FIG. 3 is a bottom view of the core mold. 4A and 4B are diagrams showing an example of a preferable shape of the cooling water flow path of the core mold. FIG. 4A is a perspective view, and FIG. 4B is a cross-sectional view. As shown in FIG. 3 and FIG. 4, the shape of the cross section of the cooling water flow path 2a of the core mold 2 is an arc-shaped slit at the lower part of the core mold 2 (the part below the middle between the upper end and the lower end). Preferably there is. Thereby, it is possible for the cooling water 11 to flow on the inner surface of the slab 7 in the form of a circular arc spray. When the arc-shaped cooling water 11 flows, the cooling water 11 discharged from the core mold 2 is cast into the slab 7 as compared with the case where the cross-sectional shape of the cooling water flow path 2a is circular or oval as a whole. Therefore, the solidified shell 7a can be formed more uniformly.

  The cooling water flow path 2a of the core mold 2 is preferably inclined radially outward from the upper end to the lower end of the core mold 2 as shown in FIG. Thereby, the cooling water 11 discharged | emitted from the core casting_mold | template 2 is easy to contact with the inner surface of the slab 7, and a cooling effect becomes higher.

  A support roll 8 that supports the outer peripheral surface of the slab 7 is disposed below the outer mold 1, but a member that supports the inner surface of the slab is not provided below the core mold 2. Therefore, the solidified shell 7 a of the slab 7 is more easily deformed by the static pressure of the molten steel 3 on the inner side than on the outer side. In addition, immediately below the mold, the solidified shell 7a has a lower thickness because the temperature on the inner side is higher than that on the outer side. Because of these factors, the slab 7 is more likely to break out on the inner side than on the outer side. Therefore, it is preferable that the solidified shell 7a is formed thicker by increasing the contact time with the core mold 2. Therefore, the core mold 2 that cools and supports the inner surface of the slab 7 is as long as possible in the casting direction, and is arranged so that the lower end of the core mold 2 protrudes from the lower end of the outer mold 1. Is preferred. However, since the friction between the core mold 2 and the slab 7 increases as the core mold 2 is longer, the length of the core mold 2 has an upper limit. For example, when the length of the outer mold 1 is 900 mm, the length of the core mold 2 is suitably 900 mm to 1500 mm.

2. FIG. 5 is a view showing a casting start method using the continuous casting apparatus shown in FIG. A dummy bar 13 is disposed below the outer mold 1 and the core mold 2, and the molten steel 3 is supplied (hot water supply) to the upper portion of the dummy bar 13 from the tundish (not shown) using the immersion nozzle 4. As a hot water supply method, a method using a funnel-shaped member without using an immersion nozzle can be applied.

  The dummy bar 13 has a cylindrical shape having the same cross-sectional shape as the cast slab. When the molten steel 3 is supplied and the immersion nozzle 4 is immersed in the molten steel and the solidified shell 7a is formed, the dummy bar 13 is pulled downward, and the continuous casting of the hollow slab 7 is started as shown in FIG. To do. Thereby, it is possible to perform continuous casting similar to a normal solid slab.

  Powder is disposed on the surface (meniscus) of the molten steel 3 supplied between the outer mold 1 and the core mold 2 and the outer mold 1 and the core mold 2 are oscillated, thereby allowing the slab 7 and the outer Lubrication is performed so that seizure does not occur between the mold 1 and the core mold 2. As described above, it is preferable to synchronize the phases of the outer mold 1 and the core mold 2 during the oscillation.

  For the continuous casting method of the present invention, steel types such as ordinary steel, high alloy steel, stainless steel, and Ni-base alloy can be applied.

  Below, the test done in order to confirm the effect of this invention is demonstrated.

1. Test Method A test for continuously casting a hollow slab was performed using the continuous casting apparatus shown in FIGS. The outer mold had an inner diameter of 250 mm and a length of 900 mm. The core mold had a copper plate thickness of 30 mm, an outer diameter of 125 mm, a length of 900 mm, the same as the outer mold, and a vent hole diameter of 65 mm. Thereby, as for the dimension of the hollow slab casted, the outer diameter was 250 mm and the inner diameter was 125 mm.

  The core mold was provided with 12 cooling water passages. In the present invention example 1, the cooling water flow path is a circular shape having a cross section of 10 mm in diameter over the entire length, that is, a cylindrical shape. Further, in Example 2 of the present invention, the core mold has a circular shape with a diameter of 10 mm at the upper end, and an arc shape with an arc length of 13 mm and a width of 5 mm at the lower end. Both cooling water channels were provided so as to incline radially outward from the upper end to the lower end of the core mold.

  The flow rate of the cooling water for the core mold was 10 m / s. This flow rate is equivalent to that applied to a slit-like cooling water flow path of a general continuous casting water-cooled copper mold.

  A lower part of the outer mold was provided with a mold spray zone having a length of 260 mm in the casting direction and a first zone having a length of 1740 mm as a secondary cooling zone. In both the mold spray zone and the first zone, the cooling water was sprayed as an air mist spray, and the cooling water amounts were 100 L / min and 150 L / min, respectively. The air flow rate was 10 m / s at the nozzle outlet. Each set value in the secondary cooling is a value commonly used in general continuous billet casting.

  The oscillation of the mold was a stroke of 4 mm and a cycle number of 175 cpm, and the phases of the outer mold and the core mold were synchronized.

  Two immersion nozzles having a cross-sectional shape obtained by cutting out a part of a ring as shown in FIG. 2B were arranged.

  The steel used for continuous casting was 13% Cr steel (liquidus temperature 1505 ° C, solidus temperature 1490 ° C). The casting speed of the slab was 1.0 m / min, and the position of 100 mm in the casting direction from the upper end of the mold was used as the molten steel meniscus. As the powder, a powder having a viscosity of 5 poise, a basicity of 0.9, and a solidification temperature of 1130 ° C. used for continuous casting of a general round billet was used.

2. Test Results The surface condition of the hollow cast pieces continuously cast in Invention Examples 1 and 2 was evaluated. In Example 1 of the present invention, the irregularities on the inner surface of the slab were reduced to a sufficient degree in normal use. This is considered to be because the inner surface of the slab was sufficiently cooled by the cooling water discharged from the core mold.

  In Invention Example 2, both the unevenness of the inner surface of the cast slab and the bending of the seamless pipe produced by rolling the slab were less than in Invention Example 1. Moreover, the internal quality of the slab was also uniform compared to Example 1 of the present invention. This is thought to be because the inner surface of the slab could be cooled more uniformly than the case of Example 1 of the present invention because the shape of the lower end of the cooling water flow path was an arc shape.

  Further, in the inventive examples 1 and 2, no breakout occurred at all. Therefore, when a breakout was generated during continuous casting as a test, no steam explosion occurred. Although some cooling water was blown up, all the leaked steel from the lower part of the mold was sucked into the lower part of the hollow slab, and in any case, continuous casting could be safely stopped.

  According to the continuous casting method and mold of the hollow round cross-section slab of the present invention, breakout is unlikely to occur, and even if a breakout occurs, it is possible to prevent the occurrence of a secondary disaster due to a steam explosion. In addition, a slab having good quality can be obtained.

1: outer mold, 2: core mold, 2a: cooling water flow path, 2b: vent hole, 3: molten steel,
4: immersion nozzle, 5: cooling water header, 6: cooling water supply pipe, 7: slab,
7a: solidified shell, 8: support roll, 9: oscillation table,
10: connecting member, 11: cooling water, 12: cooling water spray, 13: dummy bar

Claims (7)

A continuous casting method of a hollow round section slab having a water-cooled structure and using a cylindrical outer mold and a cylindrical core mold arranged concentrically,
The core mold includes a plurality of cooling water passages penetrating from the upper end to the lower end near the surface, and a vent hole penetrating from the upper end to the lower end in the center,
Cooling water supplied from the upper end of the cooling water flow path of the core mold and discharged from the lower end cools the inner surface of the hollow round cross-section slab being cast from directly under the core mold ,
A continuous casting method of a hollow round cross-section slab , wherein a shape of a transverse cross section of a cooling water flow path of the core mold is an arc-shaped slit at a lower portion of the core mold .   The continuous casting method of a hollow round cross-section slab according to claim 1, wherein the cooling water flow path of the core mold is inclined radially outward from the upper end to the lower end of the core mold. A continuous casting method of a hollow round section slab having a water-cooled structure and using a cylindrical outer mold and a cylindrical core mold arranged concentrically,
The core mold includes a plurality of cooling water passages penetrating from the upper end to the lower end near the surface, and a vent hole penetrating from the upper end to the lower end in the center,
Cooling water supplied from the upper end of the cooling water flow path of the core mold and discharged from the lower end cools the inner surface of the hollow round cross-section slab being cast from directly under the core mold,
A continuous casting method of a hollow round cross-section slab, wherein the cooling water flow path of the core mold is inclined radially outward from an upper end to a lower end of the core mold. The hollow circle according to any one of claims 1 to 3 , wherein the core mold is longer in the casting direction than the outer mold, and a lower end of the core mold protrudes from a lower end of the outer mold. Method for continuous casting of cross-section slabs. The continuous casting method for a hollow round cross-section slab according to any one of claims 1 to 4, wherein the outer mold and the core mold oscillate in synchronization. A mold for continuous casting of a hollow round cross-section slab comprising an outer mold and a core mold having a water cooling structure and concentrically arranged,
The core mold includes a plurality of cooling water passages penetrating from the upper end to the lower end near the surface, and a vent hole penetrating from the upper end to the lower end in the center ,
A mold for continuous casting of a hollow round cross-section slab , wherein a shape of a cross section of a cooling water flow path of the core mold is an arc-shaped slit at a lower portion of the core mold.   A mold for continuous casting of a hollow round cross-section slab comprising an outer mold and a core mold having a water cooling structure and concentrically arranged,
  The core mold includes a plurality of cooling water passages penetrating from the upper end to the lower end near the surface, and a vent hole penetrating from the upper end to the lower end in the center,
  A continuous casting mold for a hollow round cross-section slab, wherein the cooling water flow path of the core mold is inclined radially outward from the upper end to the lower end of the core mold.

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