KR20020054132A - Gas channel typed stopper and continuous casting method using it - Google Patents

Abstract

PURPOSE: A gas channel type stopper for continuous casting is provided which simultaneously gas bubbles molten steel and floats nonmetal inclusions in molten steel using argon gas in the state that tundish nozzle is closed by installing a plurality of channels on the lower part of the stopper, and a continuous casting method using the stopper is provided. CONSTITUTION: In a stopper installed at the upper part of a tundish nozzle to control flow rate of molten steel supplied from a tundish to a mold, the gas channel type stopper for continuous casting comprises a gas inlet pipe(15) installed inside the stopper(7a); a divider(13) which is installed on the outer circumference of the gas inlet pipe(15) to distribute gas introduced; a plurality of gas channels which are connected to the divider(13) at the lower part of the stopper(7a) and lowered to the outer circumferential surface of the stopper(7a); and a porous plug installed at the lower part of the stopper(7a). The continuous casting method by gas bubbling comprises the processes of bubbling argon gas in an argon gas flow rate of 60 to 120 L/min through a gas channel having a diameter of 40 mm or less formed on the stopper(7a) before a hole is opened; stopping argon gas bubbling through the gas channel the moment the hole is opened; and performing gas bubbling through the porous plug after the hole is opened.

Description

Gas channel type stopper for continuous casting and continuous casting method using the same

The present invention is to float and separate the non-metallic inclusions in the molten steel charged into the tundish, more specifically, to continuously solidify and delay the solidification of the molten steel by bubbling argon gas at the bottom of the stopper and to clean the molten steel by floating the nonmetallic inclusions. It relates to a gas channel type stopper for casting and a continuous casting method using the same.

In general, in the continuous casting process, as shown in the schematic diagram of the continuous casting process of FIG. 1, the molten steel 2 of the ladle 1 is supplied to the mold 4 through the tundish 3 and solidified firstly. It is a process of solidifying the molten steel 2 completely and making it into a cast steel by sprinkling cooling (5) by car.

When the molten steel is injected from the ladle 1 to the tundish 3 at the beginning of continuous casting, the nozzle filler of the ladle 1 is discharged to the tundish 3 immediately before the opening of the molten steel 2 of the ladle 1, and the turn Non-metallic inclusions such as thermal insulation and tungsten (3) refractory fragments that are put into the dish 3 are mixed into the molten steel and supplied to the mold 4 to cause defects in the cast.

Therefore, the amount of molten steel contaminants flowing into the mold 4 through the tundish 3 nozzle should be minimized or the contaminants should be floated and removed.

To this end, when the molten steel 2 is injected into the tundish 3 from the initial casting ladle 1, as the rising surface 8 in the tundish 3 rises or the residence time increases, the floating removal rate of the inclusions increases. A delayed opening technique has been developed in which a clean steel is produced by extending the residence time possible before opening (9) and inducing an upward flow to the tundish (3) hot water surface (8).

Conventionally, there have been two methods using a sliding gate and a stopper as the flow rate control method of the tundish for delayed opening.

First, the state diagram showing the flow control method of the tundish using the conventional sliding gate of FIG. 2A shows the state of gas bubbling at the time of delayed opening.

This flow rate control method increases the porosity by suppressing the solidification of the molten steel 2 in the sliding gate 6 portion in which the argon gas 10 is turned through the sliding gate 6 while the sliding gate 6 is closed. In addition, there was a method to remove the non-metallic inclusions in the molten steel (2) (Japanese JP92-78738, Korean Patent Application 1998-21266, tundish continuous casting method of sliding gate control method).

However, in the case of the flow control method using the sliding gate as described above there was a problem of ???.

Next, as shown in a state diagram of gas bubbling at the time of delayed opening according to the flow rate control method of the tundish using the conventional stopper of FIG. 2B, the molten steel bath surface 8 is raised without opening the casting initial stopper 7. There was a method of inducing the injury of the inclusions and opening and stopping the stopper when reaching the constant hot water surface 8 (Japan JP98-100541).

However, according to the tundish flow control method using the stopper as described above, if the stopper 13 is closed and the opening is delayed for a long time, the non-metallic inclusions in the molten steel 2 tend to rise, and thus the cleanliness of the molten steel 2 is improved. Since molten steel solidifies at the contact portion between the stopper 7 and the tundish nozzle 9, making it impossible to open, there is a problem that the opening delay time is very short, which is less than 1 minute.

On the other hand, Figure 2c is a side cross-sectional view of the conventional stopper is a porous plug is installed, the interior of the stopper (7) gas is empty, the lower end of the stopper 7 is provided with a porous plug 12 connected to the flow path of the gas Generate gas bubbling.

3 is a graph showing the change in the porosity rate according to the change of the delay time before the opening of the conventional stopper, the pore rate decreases as the pore time increases, and the delay time decreases sharply after 2 minutes, and thus the work is actually lost. In the normal case, the stopper is opened when the hot water surface of the tundish reaches the normal height, so that it is opened in less than one minute.

In this case, the porosity reaches almost 100%. However, in order to improve the cleanliness of the molten steel, the opening delay time of the stopper should be increased as much as possible.

However, even in the case of the stopper provided with the conventional porous plug, there is still a problem that the opening delay time must be shortened because the solidification of molten steel cannot be effectively prevented at the contact portion between the stopper 7 and the tundish nozzle 9.

The present invention has been invented to solve the problems in the prior art as described above, by installing a plurality of gas channels in the bottom of the stopper gas bubbling molten steel with argon gas in a state where the tundish nozzle is closed by the stopper and At the same time, the object of the present invention is to provide a continuous casting gas channel type stopper for floating and separating nonmetallic inclusions in molten steel and a continuous casting method using the same.

1 is a schematic diagram of a continuous casting process,

2A is a state diagram showing a flow control method of a tundish using a conventional sliding gate;

2B is a state diagram showing a flow control method of a tundish using a conventional stopper;

Figure 2c is a side cross-sectional view of a stopper installed with a conventional porous plug,

3 is a graph showing a change in the porosity according to the change in the delay time before opening the conventional stopper,

4A is a cross-sectional plan view of a lower portion of a gas channel type stopper according to the present invention;

4B and 4C are side cross-sectional views of A-A and B-B of the gas channel type stopper according to the present invention;

4D and 4E are side cross-sectional views of a comparative example of a gas channel type stopper according to the present invention;

5 is a graph showing a change in the flow rate of the tundish wall fluid according to the gas flow rate change,

6 is a graph showing the porosity of the stopper according to the gas flow rate,

7 is a graph showing the oxygen content of the cast steel according to the order of the cast steel drawn out during the casting of the initial ladle (1),

8 is a graph showing the difference in the total oxygen content between the slabs according to the gas flow rate,

9 is a graph showing the current penetration depth according to the pore diameter.

<Description of Symbols for Major Parts of Drawings>

1: ladle 2: molten steel

3: tundish 4: mold

7: stopper 8: hot noodles

9: tundish nozzle 10: argon gas

11 gas channel 12 porous plug

13: divider 15: gas introduction pipe

The continuous casting gas channel type stopper of the present invention for achieving the above object, in the stopper is provided on the top of the tundish nozzle to adjust the flow rate of the molten steel supplied from the tundish to the mold, the interior of the stopper (7a) The gas introduction pipe 15 is installed in the outer periphery of the gas introduction pipe 15, the divider 13 for distributing the introduced gas is provided, and the lower portion of the stopper 7a is connected to the divider 13 A plurality of gas channels 11 downwardly formed on the outer circumferential surface of the stopper 7a is formed, and the porous plug 12 is installed at the lower end of the stopper 7a.

In addition, the continuous casting method using the gas channel type stopper of the present invention is bubbling the argon gas flow rate of 60-120 L / min before opening through the gas channel 11 having a diameter of 40 mm or less formed in the stopper (7a) and , And stopping argon gas bubbling through the gas channel 11 at the same time as the opening, and performing only gas bubbling through the porous plug 12 after the opening.

Hereinafter, with reference to the accompanying drawings will be described in detail with respect to the present invention.

4A is a plan sectional view of the lower portion of the gas channel type stopper according to the present invention, and side cross-sectional views of AA and BB of the gas channel type stopper according to the present invention shown in FIGS. 4B and 4C. A divider 13 connected to the pipe 15 is provided, and a plurality of gas channels 11 are formed in the divider 13 in a direction downward from the inner circumferential surface of the stopper 7 to the outer circumferential surface of the stopper 7. The gas is supplied to the porous plug 12 installed at the lower end, and the gas introduction pipe 15 is formed at the center of the divider 13 so as not to overlap the gas channel 11 in the divider 13.

In addition, a flow path is formed to the gas pool processed along the outer circumferential surface of the divider 13, and a plurality of gas channels 11 are formed from the gas pool formed on the inner circumferential surface of the stopper 7 to the outer circumferential surface of the stopper 7. Gas is bubbled out of the stopper 7.

4D and 4E are side cross-sectional views of the comparative example of the gas channel stopper according to the present invention, in which the direction of the gas channel 11 is installed in the horizontal and upward directions of 30 °.

Continuous casting method by gas bubbling according to the present invention comprises the following process.

First, argon gas is bubbled by discharging a constant flow rate before opening through the gas channel 11 formed horizontally downward on the stopper 7a, and then the tundish 3 is opened by raising the stopper 7a. At the same time, argon gas bubbling through the gas channel 11 is stopped.

Next, the molten steel is charged into the mold while opening the tundish 3 and performing gas bubbling through the porous plug 12.

Hereinafter will be described in detail through the working examples and comparative examples of the present invention configured as described above.

5 is a graph showing a change in the flow rate of the tundish wall fluid according to the gas flow rate, as shown in Figure 2b is a simple rectangular tundish (transparent acrylic material having a horizontal, vertical and height of 1m, respectively, the same as the actual size) 3) is fabricated, and the results of the experiment by producing a stopper (7) of the form as shown in Figs.

And instead of molten steel in the tundish (3) produced as described above to maintain the water height of 900mm, using a stopper (7) to introduce the air of argon simulated gas to bubble the water of the molten steel mimic.

Next, the dye was injected into the water in the water adjacent to the wall of the tundish (3), and the stirring speed was examined by visually measuring the rate at which the dye circulated by gas bubbling, and the flow rate of the gas was changed to 80 ℓ / min. Experiment while doing.

5, it can be seen that as the gas flow rate increases, the stirring power is increased to increase the inclusion flotation and the molten steel stirring power. Therefore, it can be seen that the flow rate should be increased as much as possible to remove the inclusions in the tundish 3 as much as possible and to promote the circulation of the molten steel in the nozzle to improve the porosity.

FIG. 6 is a graph showing the porosity of the stopper according to the gas flow rate when the stopper 7a according to the embodiment of the present invention and the stoppers 7b and 7c according to the comparative example are used, respectively. The opening rate is slightly over 10%.

As shown in FIG. 6, it can be seen that the porosity increases as the gas flow rate of blown argon increases and the angle of the gas channel is shifted from upward to downward.

As the gas flow rate increases and the angle of the gas channel 11 decreases, the stirring of the molten steel 2 in the portion where the stoppers 7a, 7b, 7c and the tundish nozzle 9 come into contact with each other is promoted. This is because coagulation is suppressed.

According to an embodiment of the present invention, the angle of the gas channel 11 is preferably installed in a downward 30 ° direction.

Under the above conditions, when the gas flow rate of argon was 60 l / min, the porosity of the downward gas channel type stopper 7a became 100%. The most preferable embodiment of the present invention uses the downward gas channel type stopper 7a and has a gas flow rate of 60 l / min or more.

7 is a graph showing the total oxygen content of the cast steel according to the order of the cast steel drawn out during the casting of the initial ladle (1), the oxygen content represents the cleanliness of the cast steel.

In the early stage of casting, the cleanliness of molten steel is low due to contamination of molten steel. That is, the oxygen content of the cast iron is high.

The difference in the oxygen content between the first slab (# 1) and the third slab (# 3) corresponding to the normal casting time for each flow rate of the argon bubbled is a measure of the molten steel pollution degree of the first slab.

8 is a graph showing the difference in the total oxygen content between the slabs according to the gas flow rate, when the gas flow rate of argon increases, the difference in the total oxygen content between the first and third slabs decreases, but rather increases above 120ℓ / min, the molten steel cleanliness Is reduced. This is because the stirring power of the molten steel is so large that the injured inclusions are remixed into the molten steel.

On the other hand, if the diameter of the gas channel 11 is increased, the molten steel 2 may not penetrate the gas channel 11 and become gas-bubble. Therefore, the stopper 7a has a diameter of 0.1 to 0.8 mm, An argon gas channel was installed and the cross section after the casting was cut to investigate the current penetration depth of the gas channel.

FIG. 9 is a graph showing the current penetration depth according to the pore diameter. As the pore diameter increases, the current penetration depth increases, and when the pore diameter is 0.4 mm or less, there is no current penetration phenomenon.

As described above in detail, using the gas channel type stopper and the continuous casting method using the continuous casting of the present invention has the following effects.

First, since argon gas is bubbled from the gas channel downward from the bottom of the stopper to prevent solidification of the molten steel between the stopper and the tundish nozzle, the opening time can be delayed, thereby promoting the rise of non-metallic inclusions in the molten steel. You will get the effect.

Second, by adjusting the argon gas flow rate in the molten steel of the gas channel before the opening, the opening rate can be maintained at 100%, and after the opening, the gas bubbling by the porous plug can be introduced into the mold. have.

Claims (2)

In the stopper provided above the tundish nozzle to adjust the flow rate of the molten steel supplied from the tundish to the mold, a gas introduction pipe 15 is provided inside the stopper 7a, the gas introduction pipe 15 A divider 13 for distributing the introduced gas is installed at the outer circumference, and a plurality of gas channels 11 connected to the divider 13 and downward to the outer circumferential surface of the stopper 7a are formed below the stopper 7a. , Gas channel type stopper for continuous casting, characterized in that the porous plug 12 is installed at the lower end of the stopper (7a). A process of bubbling argon gas flow rate at 60-120 l / min before opening through a gas channel 11 having a diameter of 40 mm or less formed in the stopper 7a according to claim 1, and at the same time through the gas channel 11 The method of continuous casting by gas bubbling, comprising the step of stopping argon gas bubbling, and only gas bubbling through the porous plug 12 after the opening.