KR20110034470A - Method for fine adjusting second cooling step of continuous slab casting - Google Patents

Abstract

PURPOSE: A second cooling method for continuous casting is provided to increase the amount of second cooling water and reduce the surface defects of slab due to the change of heat flux in a continuous casting process. CONSTITUTION: A second cooling method for continuous casting comprises the following steps. Heat flux is measured on the molten steel inside the mold. The measured heat flux data and normal heat flux data are compared. The increment and decrement of the cooling water is calculated based on the calculated deviation for secondary cooling. The amount of the second water is corrected based on the increment and decrement of the cooling water.

Description

Secondary cooling method of continuous casting {METHOD FOR FINE ADJUSTING SECOND COOLING STEP OF CONTINUOUS SLAB CASTING}

The present invention relates to a secondary cooling method of continuous casting, and more particularly, to a secondary cooling method of continuous casting to increase or decrease the number of secondary cooling in order to reduce the surface defects of the cast steel according to the heat flux change in the continuous casting process will be.

In general, a process of continuously solidifying molten steel treated with a desired component in a predetermined form is called continuous casting. The continuous casting machine for continuous casting is produced in a steelmaking furnace and received molten steel transferred to a ladle, and then supplied to a mold for continuous casting to produce slabs of a constant size.

Conventional continuous casting machine comprises a cooling table for cooling the molten steel of the tundish primarily in the mold to form a cast having an arbitrary shape, connected to the mold to cool while moving the cast slab formed in the mold for continuous casting, do.

That is, the molten steel tapping out of the tundish is formed of slabs (Slab) or blooms (Bloom), billets (Billet) having a predetermined width and thickness in the mold, and the molten steel is first cooled in the mold and then cooled. Secondary cooling is performed by the coolant injected while moving along the stage, and is transferred while maintaining the shape formed in the mold.

The cooling zone for secondary cooling of the cast steel is divided into cooling zones for each unit requiring cooling water adjustment, and in continuous casting, the cooling water amount is preset for each cooling zone to reduce surface defects generated during cooling solidification. .

However, when the molten steel is not leaked when the molten steel is moved from the ladle to the tundish, and the oxygen opening is performed, Al ₂ O ₃ and MnO increase in large quantities due to the reoxidation of the molten steel. When the reclaimed molten steel is injected into the mold, Al ₂ O ₃ and the like contained in the molten steel are raised to the mold melt surface in the mold to change the physical properties of the mold powder on the melt surface. Such a change in the physical properties of the mold powder causes a change in the heat flux of the cast steel, thereby causing a lot of problems such as defects such as cracks on the surface of the cast steel.

In addition, when the physical properties (for example, viscosity, etc.) of the mold powder changes, the heat transfer amount from the cast steel to the mold may change, causing break-out due to the difference between the long and short sides of the solidified cast steel.

Accordingly, the present invention has been proposed to solve the above-described problems, and an object of the present invention is to provide secondary cooling of a continuous casting to increase or decrease the secondary cooling quantity in order to reduce the surface defects of the cast steel according to the heat flux change in the continuous casting process. In providing a method.

Secondary cooling method of the continuous casting according to an embodiment of the present invention comprises a heat flux measurement step of measuring the heat flux for the molten steel in the mold variable by the oxygen opening of the ladle in the playing process; A coolant amount increase / decrease calculation step of calculating a coolant amount increase / decrease amount for secondary cooling based on a deviation calculated by comparing the measured heat flux data with the heat state data in a steady state; And a second cooling step of correcting the preset second coolant amount based on the amount of increase and decrease of the coolant and spraying the coolant on the cast steel to perform the second cooling. Characterized in that it comprises a.

The heat flux in the heat flux measurement step is preferably calculated based on the total amount of heat with respect to the area of molten steel in the mold.

In addition, it is preferable that the amount of cooling water in the step of calculating the amount of cooling water increasing or decreasing increases or decreases the amount of cooling water within a range of 0.3 to 0.5 times the deviation between the measured heat flux value at the time of oxygen opening and the heat flux value at the time of no oxygen opening.

In the second cooling step, the cooling water is preferably injected in accordance with the amount of the second cooling water corrected from the molten steel with oxygen holes to the slab first cooled in the mold.

In the second cooling step, when the deviation between the measured heat flux data and the steady state heat flux data is reduced, it is preferable to restore the corrected second coolant amount to a preset second coolant amount to perform second cooling.

On the other hand, the secondary cooling method of the continuous address according to the present invention comprises a heat flux measuring step of measuring the heat flux for the molten steel in the mold in the playing process; Calculating the amount of increase and decrease of the cooling water for calculating the amount of increase and decrease of the cooling water for the second cooling based on the deviation calculated by comparing the measured heat flux data with the heat flux data in the steady state; And a second cooling step of correcting the preset second coolant amount based on the amount of increase and decrease of the coolant and spraying the coolant on the cast steel to perform the second cooling. Characterized in that it comprises a.

According to the present invention, in order to reduce the surface defects of the cast steel according to the heat flux change in the continuous casting process, the secondary cooling water quantity is increased or decreased to reduce the defect occurrence rate on the surface of the cast steel.

Through this, it is possible to reduce the amount of breakout caused by the solidification shell abnormality of the oxygen opening site to improve the operation rate.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

1 is a block diagram showing a continuous casting installation to which the present invention is applied, Figure 2 is a diagram showing an example of the heat flux changes in the mold long side and the mold short side when opening the oxygen, Figure 3 is a change in the mold powder properties when the oxygen opening 4 is a diagram illustrating an example, a diagram schematically illustrating the inside of a mold according to the present invention, FIG. 5 is a diagram schematically illustrating a system configuration to which the present invention is applied, and FIG. 6 is an embodiment of the present invention. 2 is a diagram illustrating a procedure of a secondary cooling method of continuous casting according to the present invention.

Referring to FIG. 1, in general, a continuous casting facility initially cools a ladle 10 for storing molten steel of a tundish and a molten steel 2 that is pulled out of the tundish 1 and the tundish 1 to form an arbitrary shape. The eggplant includes a mold 3 forming the cast piece 6, and a cooling table connected to the mold 3 to cool and move the cast piece 6 formed in the mold 3 during continuous casting. That is, the molten steel 2 which is stepped out of the ladle 10 and the tundish 1 may have a slab or a slab having a predetermined width and thickness in the mold 16, such as slab, bloom, or billet. 6), the molten steel is first cooled in the mold 3 and then moved along the cooling table, and at the same time, the molten steel is secondarily cooled while the cooling water is injected from the cooling water injector 5 onto the cast steel, and thus, in the mold 3. It is conveyed while maintaining the formed shape. As such, the cooling zone for secondary cooling of the cast 3 is divided into units of cooling zones for each unit requiring cooling water amount adjustment. In continuous casting, the amount of cooling water is preset for each cooling zone to reduce surface defects generated during cooling solidification. This is called a secondary cooling pattern.

In more detail, a process of continuously solidifying molten steel treated with a desired component in a predetermined form is called continuous casting (hereinafter referred to as 'casting'). Continuous solidification of molten steel is a mold and a roll made of copper (Cu) material. It runs through the secondary cooling zone where the coolant is sprayed directly between the rolls.

In particular, in the steelmaking refining process, most of the refining process is performed in the ladle 10, and molten steel is transferred to the ladle unit in the playing process. The refined molten steel is seated on the turret of the performance equipment, and when the injection of molten steel in the ladle being cast is completed, the molten steel is moved to the casting position and the molten steel is moved to the tundish when the sliding nozzle is opened.

However, conventionally, even when the sliding nozzle (not shown) configured to pull out the molten steel 11 from the ladle 10 does not open, the molten steel 11 does not flow out. In this case, oxygen is blown into the pores forcibly. The molten steel 11 flows out into the tundish 1. This is called oxygen opening or forced opening.

Meanwhile, referring to FIGS. 2 and 3, in the process of oxygen opening, oxygen is blown into the discharge port of the ladle 10, and thus the long hole may not be used. For example, in the case of Al Killed molten steel, Al ₂ O ₃ and MnO increase in volume due to reoxidation, and when the reclaimed molten steel is injected into the mold (3), some of Al ₂ O ₃ contained in the molten steel is molded. In (3), the surface of the mold 3 is floated to change the physical properties of the mold powder P on the surface of the mold.

As such, when Al ₂ O _3, etc. in the mold powder P increases, the viscosity of the mold powder increases, and as a result, the amount of heat transfer from the slab S to the mold 3 changes. For example, the mold long side part decreases and the mold short side part increases. As a result, the solidified shell solidified in the mold has a long side portion thinner than a normal side portion, and the short side portion becomes relatively thick, resulting in break-out and casting cracks on the surface of the slab Incidence will increase.

If the molten steel level of the tundish 1 is lowered below a certain level in the past, when the time since the start of the oxygen injection is long, the circumferential speed is reduced, but most of the casting is performed in the same manner as in the normal part. The quality defects increase in the cast part. That is, even when the coagulation shell thickness and temperature are changed due to the oxygen openings, the cooling water is adjusted only after the parts of the oxygen openings move, so that the response is slow. If surface cracks have already occurred due to the heat flux change in the mold 3, the cracks propagate to generate large cracks. Even if the coolant is adjusted, it takes a long time to stop propagation of the large cracks. Will increase.

Therefore, referring to FIG. 4, in the secondary cooling method according to an exemplary embodiment of the present invention, a heat flux measurement step of measuring a heat flux of molten steel in a mold that is varied by oxygen openings of a ladle in a playing process, and measured heat flux data Calculating the amount of cooling water increase and decrease for the second cooling based on the deviation calculated by comparing the heat flux data with the steady state, and correcting the preset second amount of cooling water based on the amount of cooling water increasing and decreasing. Therefore, it comprises a secondary cooling step of performing the secondary cooling by spraying the cooling water to the cast steel.

Here, the heat flux in the heat flux measurement step is preferably calculated based on the total amount of heat with respect to the area of the molten steel in the mold 3. For example, if a slab is produced with a 1200 mm width thin slab, if the circumferential speed is 4.8 m / min, the heat flux will be measured from 2.7 MW / m ² to 2.9 MW / m ² . Since the heat flux measurement method is a known matter, a detailed description thereof will be omitted.

In addition, it is preferable that the amount of cooling water in the step of calculating the amount of cooling water increasing or decreasing increases or decreases the amount of cooling water within a range of 0.3 to 0.5 times the deviation between the measured heat flux value at the time of oxygen opening and the heat flux value at the time of no oxygen opening. That is, when the heat flux deviation is 10%, the secondary cooling water amount is corrected by increasing or decreasing by 3 to 5%.

In the secondary cooling step, the cooling water is preferably injected in accordance with the amount of the secondary cooling water that has been corrected from the molten steel with oxygen holes to the slab primary cooled in the mold 3. For example, when the molten steel does not flow even when the sliding nozzle configured to pull out the molten steel from the ladle 10 does not leak, oxygen-opened molten steel 11 is transferred to the cast state through the mold 3. In this case, coolant is sprayed on the cast according to the second cooling pattern corrected in the above-described manner to reduce the occurrence of defects.

In addition, in the secondary cooling step, when the deviation between the measured heat flux data and the steady state heat flux data is reduced, it is preferable to restore the corrected secondary coolant amount to the preset secondary coolant amount to perform secondary cooling. For example, when the oxygen-opened molten steel is transferred to the cast steel state through the mold 3, the cooling water is injected to the cast steel according to the secondary cooling pattern corrected in the above-described manner, and then all the oxygen-opened molten steel is discharged. Afterwards, the second amount of coolant is sprayed back to reduce the occurrence of additional defects.

5 and 6, the system to which the secondary cooling method according to the embodiment of the present invention is applied will be described in more detail by way of example. The system includes a normal heat flux data DB 30 for each circumferential speed, a heat flux measurement unit 40 for measuring a heat flux inside the mold, a calculation unit 50 for comparing the measured heat flux and the normal heat flux data, and calculating a correction amount of the second cooling amount; Accordingly, it can be configured to include a secondary cooling control unit 60 to control the injection of the cooling water to the cast steel to proceed with the secondary cooling.

That is, when the heat flux in the mold is changed due to Al ₂ O ₃ generated by reoxidation generated during oxygen opening, the calculation unit 50 calculates the amount of cooling increase and decrease to be corrected from the deviation from the heat flux outside the normal range. Then, the secondary cooling control unit 60 controls to spray by subtracting the amount of secondary cooling water from directly under the mold 3.

To this end, it is necessary to utilize the long side and short side heat flux measurement unit 40 in the mold, and set the normal heat flux range at the corresponding circumference on the normal heat flux data DB 30 for each circumference.

The heat flux measurement unit 40 measures in real time the heat flux of the long side of the mold, the heat flux of the short side, and the short / long side heat flux ratio value in real time, and when the value of the heat flux measured in real time in the mold during oxygen opening is out of the normal range. It can be configured to display it externally.

In addition, the calculation unit 50 calculates the amount of secondary cooling water required to form a uniform solidification shell from the deviation of the heat flux value when it is out of the proper heat flux range. And it is preferable that the secondary cooling control part 60 injects the amount of cooling water in the secondary cooling stand under a mold independently of the long side and the short side. That is, when the heat flux of the long side decreases and the heat flux of the short side increases due to oxygen opening, the operation unit 50 calculates the long side and short side secondary coolant correction amounts directly under the mold and adds or subtracts the set secondary cooling pattern.

On the other hand, the secondary cooling control unit 60 is injected by the normal secondary cooling pattern by releasing the added or subtracted correction amount after the reflowed portion is injected and the heat flux returns to the normal state range after a certain time.

Therefore, in the present invention, since the secondary cooling water amount is corrected directly under the mold, the result of the heat flux change in the mold, which appears during oxygen opening, even if surface cracks occur due to the heat flux change in the mold, the cast surface defect is adjusted by adjusting the cooling water amount before propagating to the large size. The incidence rate can be reduced.

Referring to the second cooling method of the playing step according to an embodiment of the present invention as an example. In the description, it will be described with reference to the flowchart shown in FIG.

First, oxygen lattice is carried out during the molten steel in the ladle (S10). At this time, the heat flux measuring unit 40 measures the heat flux of the molten steel in the mold and provides it to the calculating unit 50 (S20). The calculation unit 50 reads the normal heat flux data for each circumference in the normal heat flux data DB 30 for each circumferential speed and compares the measured heat flux values (S30). For example, the normal heat flux data for each circumferential speed is that when the slab is produced with a thin slab of 1200 mm width, if the circumferential speed is 4.8 m / min, the heat flux is set to 2.7 MW / m ² to 2.9 MW / m ² .

Next, if the deviation occurs between the measured heat flux data and the normal heat flux data for each peripheral speed (S40; Y), the calculation unit 50 calculates the amount of cooling water correction in proportion to the deviation (S50). For example, when the measured heat flux is 2.52 MW / m ² , the deviation from the median value of the normal heat flux data for each main speed is varied by 10%. Thus, the preset secondary cooling water amount is corrected to the calculated cooling water amount correction amount and provided to the second cooling control unit. That is, the amount of secondary cooling on the predetermined secondary cooling pattern is increased or decreased by 3 to 5%. Then, the secondary cooling control unit 60 injects the cooling water according to the amount of the secondary cooling water corrected from the molten steel with oxygen openings to the slab first cooled in the mold.

In addition, when the deviation between the measured heat flux data and the heat state data in the steady state is reduced, the secondary cooling controller 60 may restore the corrected second coolant amount to the preset second coolant amount to perform secondary cooling. Do. For example, when the molten steel is transported to the cast steel state through the molten oxygen-molded molten steel, the coolant is sprayed on the cast steel according to the second cooling pattern corrected in the above-described manner. Spray additional coolant to reduce additional defects.

According to the present invention, in order to reduce the surface defects of the cast steel according to the heat flux change in the continuous casting process, the secondary cooling water quantity is increased or decreased to reduce the defect occurrence rate on the surface of the cast steel.

Through this, it is possible to reduce the amount of breakout caused by the solidification shell abnormality of the oxygen opening site to improve the operation rate.

As mentioned above, although one preferred embodiment of the present invention has been illustrated and described, the present invention is not limited to the specific embodiments described above, and the present invention belongs to the present invention without departing from the gist of the present invention as claimed in the claims. Various modifications may be made by those skilled in the art, and these modifications should not be individually understood from the technical spirit or the prospect of the present invention.

1 is a block diagram showing a continuous casting installation to which the present invention is applied.

Figure 2 is a table showing an example of the heat flux changes in the mold long side and the mold short side at the time of oxygen opening.

Figure 3 is a table showing an example of a change in the physical properties of the mold powder when oxygen openings.

4 schematically shows the interior of a mold according to the invention;

5 is a diagram schematically showing a system configuration to which the present invention is applied.

6 is a view showing a sequence of a secondary cooling method of continuous casting according to an embodiment of the present invention.

Description of the Related Art [0002]

1: tundish 2, 11: molten steel

3: mold 5: coolant spray

6: cast 10: ladle

30: normal heat flux data DB by circumferential speed

40: heat flux measurement unit 50: calculation unit

60: secondary cooling control unit P: mold powder

S: Cast (Slab)

Claims (6)

A heat flux measurement step of measuring a heat flux of molten steel in the mold which is varied by oxygen openings of the ladle in a playing process; Calculating a cooling water amount increase / decrease amount for calculating a cooling water amount increase / decrease amount for secondary cooling based on the deviation calculated by comparing the measured heat flux data with the heat state data in a steady state; And A second cooling step of performing a second cooling by correcting a predetermined second cooling water amount based on the amount of increase and decrease of the cooling water and spraying the cooling water on the cast steel accordingly; Secondary cooling method of the continuous casting comprising a. The method according to claim 1, The heat flux of the heat flux measuring step is A secondary cooling method of continuous casting, characterized in that the calculation based on the total heat amount to the area of the molten steel in the mold. The method according to claim 1, The amount of increase and decrease of the cooling water in the step of calculating the amount of cooling water increases, The secondary cooling method of the continuous casting, characterized in that the amount of cooling water increases or decreases in the range of 0.3 to 0.5 times the difference between the measured heat flux value at the time of oxygen opening and the heat flux value at the time of oxygen opening. The method according to claim 1, The secondary cooling step, And a cooling water is sprayed from the molten steel with oxygen to the slab first cooled in the mold in accordance with the corrected amount of the second cooling water. The method according to any one of claims 1 to 4, The secondary cooling step, When the deviation between the measured heat flux data and the heat flux data in the steady state is reduced, the secondary cooling method of the continuous casting, characterized in that to perform the second cooling by restoring the corrected second coolant amount to a predetermined second coolant amount. A heat flux measurement step of measuring a heat flux of molten steel in the mold in the playing process; Calculating a cooling water amount increase / decrease amount for calculating a cooling water amount increase / decrease amount for secondary cooling based on the deviation calculated by comparing the measured heat flux data with the heat state data in a steady state; And A second cooling step of performing a second cooling by correcting a preset second cooling water amount based on the amount of increase and decrease of the cooling water and spraying the cooling water on the cast steel accordingly; Secondary cooling method of the continuous casting comprising a.

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