JP7087749B2 - Continuous metal casting method - Google Patents

Description

The present invention relates to a method for continuously casting a metal by continuously casting a slab using a mold having a water-cooled structure.

In the continuous casting method for producing slabs and other slabs, molten metal is supplied into a mold having a water-cooled structure using a dipping nozzle, and the molten metal is cooled in the mold to grow a solidified shell to grow the slabs. It is configured to be continuously cast.
Here, in the above-mentioned continuous casting method, for example, as shown in Patent Documents 1 and 2, the amount of cooling water is controlled in a secondary cooling zone in which cooling water is directly sprayed on the slabs produced from the mold. Is being done.

On the other hand, when slabs are continuously cast using a mold having a water-cooled structure, it is necessary to control the amount of cooling water supplied into the mold in order to improve the surface quality of the slabs.
Therefore, for example, Patent Document 3-5 discloses a method of controlling the amount of cooling water according to the casting speed.

Japanese Unexamined Patent Publication No. 61-049760 Japanese Unexamined Patent Publication No. 2007-253202 Japanese Unexamined Patent Publication No. 49-107928 Japanese Unexamined Patent Publication No. 52-046331 Japanese Unexamined Patent Publication No. 07-227659

By the way, at the end of casting, a shrinkage cavity is formed in the top portion of the slab, so the top portion is cut and removed. Here, when the depth of the shrinkage nest becomes long, the area to be cut and removed becomes long, and the yield decreases. Therefore, it is required to reduce the depth of the shrinkage cavities generated at the end of casting.

Further, when continuous casting is performed, the dipping nozzle may be blocked with the passage of casting time. In this case, the casting is temporarily stopped and the immersion nozzle is replaced. That is, when the immersion nozzle is blocked, the immersion nozzle is removed from the mold, a new immersion nozzle is prepared, or the inside of the immersion nozzle is cleaned, and the new immersion nozzle or the immersion nozzle after cleaning is used. By mounting it in the mold again, casting can be restarted.
However, when the dipping nozzle is replaced, the solidified shell grows in the mold and collapses in the state where casting is stopped, so that a new dipping nozzle or a washed dipping nozzle cannot be reattached to the mold. was there.

As described above, the casting speed is low at the end of casting or when the immersion nozzle is replaced. Therefore, as shown in Patent Document 3-5, when the amount of cooling water is controlled according to the casting speed, the cooling water amount is controlled. There was a risk that the amount of cooling water would be insufficient and the mold material or the like would be thermally deteriorated.
Further, as shown in Patent Document 3-5, when the cooling water amount is controlled according to the casting speed, the control becomes complicated, the control of the cooling water amount becomes unstable due to the disturbance during the actual operation, and the casting becomes stable. There was a risk that it could not be implemented.

The present invention has been made in view of the above-mentioned situation, and suppresses the growth of the solidified shell in the mold even at the end of casting or at the time of exchanging the dipping nozzle, and the depth of the shrinkage cavity after the completion of casting. It is an object of the present invention to provide a method for continuously casting a metal, which can be made shallow, can efficiently replace a dipping nozzle, and can suppress thermal deterioration of a molding material.

In order to solve the above problems, the metal continuous casting method according to the present invention is a metal continuous casting method in which slabs are continuously cast using a mold having a water-cooled structure, and the amount of cooling water supplied to the mold is increased. The control mode has a steady flow control mode in which the amount of cooling water is controlled during steady casting and a low flow control mode in which the amount of cooling water is controlled to be smaller than that during steady casting. In the process of reducing the casting speed, casting is performed. When the speed becomes lower than the threshold value, the steady flow control mode is switched to the low flow control mode, and the solidification shell is suppressed from growing in the mold when the casting speed is low . The switching from the steady flow control mode to the low flow control mode is performed when the casting speed is lower than the threshold value for a certain period of time in the process of lowering the casting speed .

According to the continuous casting method of metal having this configuration, when the casting speed becomes lower than the threshold value in the process of decelerating the casting speed, the steady flow control mode is switched to the low flow control mode. Therefore, even if the casting speed is sufficiently reduced at the end of casting and at the time of exchanging the immersion nozzle, the growth of the solidified shell in the mold is suppressed, and the depth of the shrinkage cavity is reached at the end of casting. Can be made shallower, and when the immersion nozzle is replaced, the replaced immersion nozzle can be easily inserted into the mold.
Further, by securing the amount of cooling water as the low flow rate control mode, it is possible to suppress the thermal deterioration of the mold material.
Further, since the control mode is switched according to the threshold value of the casting speed, the control of the cooling water amount is suppressed from becoming unstable due to disturbance or the like, and the casting can be performed stably. ..

Here, in the continuous metal casting method of the present invention, in the process of switching from the steady flow rate control mode to the low flow rate control mode and lowering the casting speed, the casting speed is lower than the threshold value for a certain period of time. Since it is configured to be carried out at the time of continuation, even if the casting speed temporarily becomes lower than the threshold value due to the variation in the casting speed, the control mode is not immediately switched, so that the cooling water amount can be further controlled. It will be stable.

Further, in the continuous metal casting method of the present invention, the mode may be switched to the steady flow rate control mode when the low flow rate control mode is maintained for a predetermined time or longer.
In this case, when the low flow rate control mode is maintained for a predetermined time or longer, the steady flow rate control mode is forcibly switched to, so that the state where the amount of cooling water is small is not maintained for a long time, and the heat deterioration of the mold material is caused. It is possible to surely suppress it.

Further, in the continuous metal casting method of the present invention, the threshold value for switching from the steady flow rate control mode to the low flow rate control mode is changed according to the speed change amount θ per hour when the casting speed is decelerated. It may be configured to be used.
In this case, since the threshold value is changed according to the rate change amount θ per hour when the casting speed is decelerated, the growth of the solidified shell in the mold is suppressed even when the casting is suddenly stopped, for example. Is possible.

As described above, according to the present invention, it is possible to suppress the growth of the solidified shell in the mold even at the end of casting or at the time of exchanging the immersion nozzle, and to make the depth of the shrinkage cavity shallow after the end of casting. Moreover, it is possible to provide a continuous metal casting method capable of efficiently performing the replacement work of the dipping nozzle and suppressing thermal deterioration of the mold material.

It is explanatory drawing which shows an example of the continuous casting apparatus which carries out the continuous casting method of metal which is an embodiment of this invention. It is a schematic explanatory drawing around the mold of the continuous casting apparatus shown in FIG. FIG. 2 is a cross-sectional view taken along the line XX in FIG. FIG. 2 is a cross-sectional view taken along the line YY in FIG. It is explanatory drawing which shows the change of the casting speed and the amount of cooling water in the continuous metal casting method which is an embodiment of this invention.

Hereinafter, the method for continuous metal casting according to the embodiment of the present invention will be described with reference to the attached drawings. The present invention is not limited to the following embodiments.
First, an example of a continuous casting apparatus for carrying out the continuous metal casting method according to the embodiment of the present invention will be described with reference to FIGS. 1 to 4.

In the continuous casting apparatus 1 shown in FIG. 1, molten steel is transferred from a converter by a ladle 2, molten steel is transferred to a tundish 4 via a long nozzle 3, large inclusions are levitated and separated in the tundish 4, and then a dipping nozzle is used. The molten steel is supplied into the mold 30 via the 20 and the slab is continuously cast.
The slab produced from the mold 30 is pulled downward by a support roll group 40 composed of a plurality of support rolls 41 and curved by a bending roll 42.

Further, in the steel continuous casting apparatus 1 of the present embodiment, as shown in FIGS. 2 to 4, a mold 30, a dipping nozzle 20 for discharging molten steel into the mold 30, and an upper portion in the mold 30 are provided. The electromagnetic stirring device 50 for stirring the molten steel and the non-oxidizing gas introducing means 10 for introducing the non-oxidizing gas into the molten steel in the immersion nozzle 20 are provided.
Here, as shown in FIGS. 2 and 3, the tundish 4 and the immersion nozzle 20 are connected to each other via the upper nozzle 6 and the sliding nozzle 7.

As shown in FIG. 4, the mold 30 in the present embodiment has a cylindrical shape having a casting space having a rectangular cross section, and a slab having a cross section matching the shape of the casting space is cast.
As shown in FIG. 4, the mold 30 includes a pair of long side mold plates 31 (31A, 31B) constituting a pair of long side walls and a pair of short side mold plates 32 (31A, 31B) constituting a pair of short side walls. 32A, 32B), a back plate 33 that supports the long side mold plate 31 from the back side, and a back plate 34 that supports the short side mold plate 32 from the back side.

Here, in the horizontal cross section of the mold 30, the direction along the long side mold plate 31 is the mold width direction, and the direction along the short side mold plate 32 is the mold thickness direction.
In the present embodiment, the short side mold plates 32 (32A, 32B) are sandwiched by a pair of long side mold plates 31 (31A, 31B) so that they can be moved along the mold width direction, and the widths are different. The structure is such that the slab can be cast in the same mold 30.
The above-mentioned immersion nozzle 20 is located at the center in the mold width direction and the center in the mold thickness direction, and the opening of the discharge hole 22 (22A, 22B) is the short side mold plate 32 (32A, 32B) of the mold 30. They are arranged so as to face each other.

Here, on the back side of the back plate 33 that supports the long side mold plate 31, an electromagnetic agitator 50 is provided along the long side direction (mold width direction) of the long side mold plate 31 as shown in FIG. It is arranged.
The electromagnetic agitator 50 generates a moving magnetic field in the molten steel in the mold 30 to force the molten steel to flow. Here, by reversing the direction of the moving magnetic field by the electromagnetic agitator 50 on the long side mold plate 31A side and the direction of the moving magnetic field by the electromagnetic agitator 50 on the other long side mold plate 31B side. , A swirling flow is generated in the molten steel in the mold 30.

Argon gas, which is a kind of non-oxidizing gas, is blown into the molten steel supplied through the immersion nozzle 20 by the non-oxidizing gas introducing means 10.
Then, as shown in FIGS. 2 and 3, the solidified shell S grows on the surfaces of the long-side mold plate 31 and the short-side mold plate 32 of the mold 30.
Further, on the molten steel stored in the mold space, the continuously cast powder 9 is used to keep the molten steel warm and to ensure the lubricity between the solidified shell S and the long side mold plate 31 and the short side mold plate 32. Is supplied.

In the continuous metal casting method of the present embodiment, as shown in FIG. 5, as a control mode of the amount of cooling water supplied to the mold 30, a steady flow rate control mode controlled by the amount of cooling water at the time of steady casting is used. It has a low flow rate control mode that controls with a smaller amount of cooling water than during steady casting.
In the present embodiment, the amount of cooling water in the low flow rate control mode is within the range of 45% or more and 90% or less of the amount of cooling water in the steady flow rate control mode.

Regarding the lower limit of the amount of cooling water in the low flow rate control mode, the drainage temperature is such that the cooling water does not boil in the mold 30 when the cooling water (drainage) discharged from the mold 30 is circulated and used. It is preferable to set it to.
Further, it is preferable to set the upper limit of the amount of cooling water in the low flow rate control mode in consideration of the growth of the solidified shell S in the mold 30.

Here, as shown in FIG. 5, when the casting speed becomes lower than the threshold _VCD in the process of reducing the casting speed in order to stop the casting or replace the immersion nozzle, the steady flow rate Switch from control mode to low flow control mode.
In the present embodiment, the switching holding timer is provided, and the mode is configured to switch from the steady flow rate control mode to the low flow rate control mode when the casting speed is lower than the threshold value _VCD for the _TD time. ing.

Here, the casting speed threshold _VCD for switching from the steady flow rate control mode to the low flow rate control mode is configured to be changed according to the speed change amount θ per hour when the casting speed is decelerated.
Specifically, when the speed change amount θ per hour when decelerating the casting speed becomes a certain value or more and the casting speed is rapidly decelerated, the casting speed is switched from the steady flow rate control mode to the low flow rate control mode. The threshold _VCD will be set high and the mode will be switched to the low flow control mode at an early stage of the deceleration process.

Further, in the present embodiment, a fixed-time forced switching timer is provided. By this fixed time type forced switching timer, when the low flow rate control mode is maintained for a predetermined time or longer, it is forcibly switched to the steady flow rate control mode.

Further, in the present embodiment, when the casting is restarted at the start of casting or after the immersion nozzle is replaced, as shown in FIG. 5, the casting speed is higher than the threshold _VIN in the process of increasing the casting speed. When it becomes high, it switches from the low flow rate control mode to the steady flow rate control mode.
In the present embodiment, the switching holding timer is provided, and is configured to switch from the low flow rate control mode to the steady flow rate control mode when the casting speed is higher than the threshold value _VIN for _TI time. ing.

As described above, the amount of cooling water supplied to the mold 30 is controlled in the steady flow rate control mode or the low flow rate control mode when the casting is stopped from the start of casting and the casting is restarted by replacing the immersion nozzle. Will be done.

According to the continuous metal casting method of the present embodiment having the above configuration, the casting speed is increased in the process of reducing the casting speed in order to stop the casting or to replace the immersion nozzle 20. Since the configuration is such that the steady flow control mode is switched to the low flow control mode when the value becomes lower than the threshold _VCD , the casting speed is sufficiently lowered at the end of casting or when the immersion nozzle 20 is replaced. Even so, the growth of the solidified shell S in the mold 30 is suppressed.
As a result, at the end of casting, the depth of the shrinkage cavities can be made shallow, and the yield can be improved. Further, when the immersion nozzle 20 is replaced, the replaced immersion nozzle 20 can be easily inserted into the mold 30.

Further, by securing a constant amount of cooling water as the low flow rate control mode, it is possible to suppress thermal deterioration of the long side mold plate 31 and the short side mold plate 32.
Furthermore, since the control configuration is relatively simple, such as switching the control mode according to the casting speed threshold _VCD , unstable control due to disturbance or the like is suppressed, and stable casting can be performed. ..

Further, in the present embodiment, the switching holding timer is provided so that the steady flow rate control mode is switched to the low flow rate control mode when the casting speed is lower than the threshold value _VCD for the _TD time. Since it is configured, even if the casting speed temporarily becomes lower than the threshold _VCD due to the variation in the casting speed (so-called chattering), the control mode is not switched immediately, so that the control becomes more stable.

Further, in the present embodiment, a fixed-time forced switching timer is provided, and when the low flow rate control mode is maintained for a predetermined time or longer, it is configured to be forcibly switched to the steady flow rate control mode. Therefore, the low flow rate control mode in which the amount of cooling water is small is not maintained more than necessary, and it is possible to reliably suppress the thermal deterioration of the long side mold plate 31 and the short side mold plate 32.

Further, in the present embodiment, the threshold _VCD for switching from the steady flow rate control mode to the low flow rate control mode is changed according to the speed change amount θ per hour when the casting speed is decelerated. The speed change amount θ per hour when decelerating the casting speed becomes a certain value or more, and when the casting speed is rapidly decelerated, the casting speed threshold V for switching from the steady flow rate control mode to the low flow rate control mode. Since the _CD is set high and the mode is switched to the low flow rate control mode at an early stage of the deceleration process, it is possible to suppress the growth of the solidified shell S in the mold 30 even when the casting is suddenly stopped. ..

Further, in the present embodiment, when the casting is restarted at the start of casting or after the immersion nozzle 20 is replaced, as shown in FIG. 5, the casting speed is the threshold _VIN in the process of increasing the casting speed. Since it is configured to switch from the low flow rate control mode to the steady flow rate control mode when the value becomes higher than that, the casting speed is sufficiently high at the start of casting or when the casting is restarted after the immersion nozzle 20 is replaced. Before the speed is increased, the growth of the solidified shell S can be sufficiently suppressed, and casting can be stably carried out.

Although the method for continuous metal casting according to the embodiment of the present invention has been described above, the present invention is not limited to this, and can be appropriately changed without departing from the technical idea of the present invention.
For example, in the present embodiment, the continuous casting apparatus and the mold shown in FIGS. 1 to 4 have been described as an example, but the present invention is not limited to this, and the continuous casting apparatus and the mold having other configurations may be used. Can be applied.

Further, in the present embodiment, the switching holding timer and the fixed-time forced switching timer have been described as provided, but these may not be provided.
Further, in the present embodiment, the threshold value _VCD for switching from the steady flow rate control mode to the low flow rate control mode is changed according to the speed change amount θ per hour when the casting speed is decelerated. Not limited.

Further, in the present embodiment, the casting speed becomes higher than the threshold _VIN in the process of increasing the casting speed at the start of casting, at the start of casting, or when the casting is restarted after the immersion nozzle 20 is replaced. In the above description, the configuration is described as switching from the low flow rate control mode to the steady flow rate control mode, but the present invention is not limited to this.

The results of the confirmation experiment carried out to confirm the effect of the present invention are shown below.
The continuous casting of carbon steel having the composition shown in Table 1 was carried out using the continuous casting apparatus and the mold described in the above-mentioned [Mode for Carrying Out the Invention]. The cross-sectional size of the slab was 2200 mm × 3000 mm. Further, the casting speed in the steady state was set to 1.10 mpm.

As an example of the present invention, as described in the above [Mode for Carrying Out the Invention], when the casting speed becomes lower than the threshold value _VCD , the steady flow rate control mode is used to control the amount of cooling water supplied to the mold. Control was carried out to switch from to the low flow rate control mode.
As a comparative example, the amount of cooling water supplied to the mold was controlled without providing the low flow rate control mode.

After 3 minutes had passed since the casting was stopped, the amount of collapse of the solidified shell formed on the surface of the opposite long-side mold plate (distance from the surface of the long-side mold plate) was measured.
Further, after the casting was completed, the top portion of the slab was cut stepwise every 100 mm, and the depth of the shrinkage cavity was evaluated.
The evaluation results are shown in Table 2.

As shown in Table 2, the amount of collapse of the solidified shell 3 minutes after the casting was stopped was 50 to 100 mm in the comparative example, whereas it was suppressed to 20 to 30 mm in the example of the present invention.
The depth of the shrinkage cavities was 800 mm in the comparative example, whereas it was 700 mm in the example of the present invention.

From the above, according to the example of the present invention, it is possible to suppress the growth of the solidified shell in the mold even at the end of casting or at the time of exchanging the immersion nozzle, and to make the depth of the shrinkage cavity shallow after the end of casting. Moreover, it was confirmed that the replacement work of the immersion nozzle can be efficiently performed.

20 Immersion nozzle 30 Mold S solidification shell

Claims (3)

It is a continuous metal casting method in which slabs are continuously cast using a water-cooled mold.
As a control mode for the amount of cooling water supplied to the mold, there is a steady flow rate control mode in which the amount of cooling water is controlled during steady casting, and a low flow rate control mode in which the amount of cooling water is controlled to be smaller than that during steady casting.
In the process of decelerating the casting speed, when the casting speed becomes lower than the threshold value, the steady flow rate control mode is switched to the low flow rate control mode.
It is configured to suppress the growth of the solidified shell in the mold when the casting speed is low.
The metal is characterized in that switching from the steady flow rate control mode to the low flow rate control mode is performed when the casting speed is kept lower than the threshold value for a certain period of time in the process of lowering the casting speed . Continuous casting method. The continuous metal casting method according to claim 1 , wherein when the low flow rate control mode is maintained for a predetermined time or longer, the mode is switched to the steady flow rate control mode. Claim 1 or claim 2 is characterized in that the threshold value for switching from the steady flow rate control mode to the low flow rate control mode is changed according to the speed change amount θ per hour when the casting speed is decelerated. The method for continuous casting of metal according to.

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