KR101149369B1 - Apparatus for reducing brittleness in slab and method for operating the same - Google Patents

Abstract

The present invention relates to an apparatus and a method for reducing brittleness of a casting produced at the end of a casting process. The embodiment of the present invention is characterized by comprising a casting speed regulating portion for regulating a casting speed of molten steel to be withdrawn, a cooling water spraying nozzle for spraying cooling water when the main portion is conveyed along the conveying roller, A control unit for controlling the casting speed adjusting unit and the cooling water spraying nozzle so as to inject the cooling water having different amounts of cooling water for each step by decelerating the normal casting speed by a predetermined time interval, .

Steel, continuous casting, cast, slab, brittle, cracked, roller

Description

TECHNICAL FIELD The present invention relates to a brittle reduction apparatus and a method of operating the brittle reduction apparatus,

The present invention relates to an apparatus and a method for reducing brittleness of a casting produced at the end of a casting process.

A typical continuous casting process is performed using a ladle, a tundish, and a cutting facility. The molten steel formed in the steelmaking process is cast through a ladle, a tundish, and a cutting equipment, A slab having a size of about 150 to 300 mm is produced. Thereafter, it is made into a strip in the form of a steel plate having a thickness of about 3 to 20 mm by a subsequent process, such as hot rolling.

The cast steel continuously cast through the tundish is continuously manufactured while moving between the upper and lower conveying rollers through which the cooling water is injected, and is then cut to a predetermined length by the cutting equipment and conveyed to the collecting hall by the table rollers.

A capping operation is usually carried out at the end of a continuous casting process in which one continuous casting process is completed. This capping operation is carried out in such a manner that the capping operation is carried out in the casting casting (hereinafter referred to as " In order to stabilize the molten steel.

However, after the capping operation is carried out, the brittleness (brittleness) of the tail increases (the hardness is high and the softness is low, and thus the brittle property is easily broken). Particularly, it is serious among oriented electrical steel sheets having a high silicon content.

As shown in Fig. 1, the brittleness increase causes a problem that the tail portion of the cast steel is broken even under a weak impact. During the withdrawal of the slab, the slabs are subcooled out of the mold, and the slab is broken due to the friction between the tail and the rollers.

As shown in FIG. 2, when a part of the tail portion that is broken and falls off is caught between the roller and the roller, it causes a serious equipment accident such as stagnation of the casting rollers and roller breakage in the casting operation.

Further, since the casting process is delayed and the productivity is lowered, it is necessary to perform the non-casting time to remove the broken tail portion at the end of the casting process.

The technical problem of the present invention is to stabilize the cast steel at the end of the continuous casting process. Further, the technical problem of the present invention is to reduce the embrittlement of the cast steel cast at the end of the continuous casting process. Further, the technical problem of the present invention is to shorten the non-casting time in the continuous casting process.

The embodiment of the present invention is characterized by comprising a casting speed regulating portion for regulating a casting speed of molten steel to be withdrawn, a cooling water spraying nozzle for spraying cooling water when the main portion is conveyed along the conveying roller, A control unit for controlling the casting speed adjusting unit and the cooling water spraying nozzle so as to inject the cooling water having different amounts of cooling water for each step by decelerating the normal casting speed by a predetermined time interval, .

It is characterized in that the deceleration and acceleration are performed step by step with different holding times at each step, and the value is maintained within 2 minutes ± 20% at the lowest deceleration stage.

The method of the present invention comprises the steps of: detecting whether a remaining capacity of a tundish reaches a specified reference value; recovering a normal casting speed at a predetermined time interval, A speed control process, and a cooling water quantity control process for spraying the cooling water with different amounts of cooling water for each step of the casting speed.

According to the embodiments of the present invention, it is possible to improve the quality of the tail portion, which is a cast produced at the end of the continuous casting process. In addition, it is possible to prevent cracking of the tail portion, thereby reducing the loss of process equipment. In addition, cracking of the tail portion does not occur and productivity can be improved. In addition, it is possible to prevent a safety accident due to a decrease in operator's facility inspection, and also to reduce workload of the worker.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It will be apparent to those skilled in the art that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, It is provided to let you know. Wherein like reference numerals refer to like elements throughout.

3 is a perspective view illustrating a cast steel slab manufacturing process for producing a cast slab according to an embodiment of the present invention.

A ladle 120 provided in a ladle turret is filled with molten steel whose impurity removal and chemical composition has been adjusted and the ladle 120 is provided with a ladle nozzle 122 through which the tundish 110 tundish.

The molten steel stored in the tundish 110 is supplied to the mold 140 through the immersion nozzle 130 made of a cylindrical refractory brick and then passes through the inner space of the mold 140 having the long and short sides A slab 150 having the same cross section as the cross section of the mold is successively cast.

A dummy bar 160 leading to the casting 150 enters the open lower portion of the mold 140 and the first molten steel introduced into the mold 140 flows through the dummy bar head (170). The solidified molten steel is continuously produced as the casting 150 while moving between the upper and lower conveying rollers where the cooling water is injected by the dummy bar 160 as a plurality of conveying rollers 180 installed in the moving track are driven.

The conveying rollers are positioned at the upper and lower sides to feed the cast strips 150 placed therebetween. The body portion of the conveying roller has the same length and diameter, and the axes of the plurality of conveying rollers 180 are connected to the bearing block to be set and driven.

The billet 150 conveyed along the conveying rollers 180 positioned above and below is cut to a predetermined length by the cutting device 190 disposed at the exit side and is conveyed by the table roller 182 to the hot rolling process .

At this time, the cooling water is injected at the time of conveyance along the conveying roller 180, which is forcibly cooled using the cooling water to quickly and uniformly coagulate from the outside at a predetermined cross-sectional size. Thus, the casting from the mold 140 ejects cooling water onto the surface of the cast steel so as to accelerate the solidification of the casting 150 around the conveying rollers as they are conveyed along the conveying rollers 180.

On the other hand, at the end of a continuous casting process in which one continuous casting process is completed, a capping operation is performed to stabilize the non-solidified molten steel in the main comfort. The capping operation may be a method of stagnating and cooling the molten steel after completion of injection of the molten steel into the mold, or a method of adding coolant to the cast steel.

In the case of the grain-oriented electrical steel sheet according to the embodiment, when the tundish remaining capacity reaches a specific reference value, the casting speed is decelerated and increased in steps at predetermined time intervals to thereby perform a capping operation for stabilizing the cast steel. ) (The hardness is high and the ductility is low and easily cracked).

That is, when the directional electric steel sheet is cast, the casting speed is gradually decreased or increased step by step at a predetermined time interval based on the residual capacity of the tundish, the component characteristic (high Si steel) There is a problem that the brittleness of the tail (high hardness and low ductility and easily cracked property) is increased. Such brittleness is caused by the coagulation weakening due to the generation of a large-sized hollow pipe inside the frame portion.

Therefore, the brittleness of the tail portion is increased by the increase of the brittleness. In order to prevent such brittleness, the brittleness should be reduced. The embodiment of the present invention reduces the brittleness through control of the deceleration speed and the cooling water amount while gradually reducing and increasing the casting speed by a predetermined time interval as the tundish remaining capacity reaches a specific reference value.

Particularly, the brittleness (high hardness and low ductility) in the tail portion of the continuous addressing process changes depending on the specific numerical value of the deceleration speed and the cooling water due to the component characteristics (high Si steel) of the oriented electrical steel sheet.

The embodiment of the present invention controls the reduction rate and the cooling rate of the tail portion so as to reduce the brittleness of the tail portion when the casting speed is decelerated and increased step by step at a predetermined time interval at the end of the continuous casting process on the basis of the remaining tundish capacity.

4 is a block diagram of an apparatus for reducing brittleness of a slab in a continuous casting process according to an embodiment of the present invention.

The cooling water spray nozzle unit 410 is a nozzle for spraying cooling water for cooling the billet, and may be realized in the form of various cooling water spray nozzles. For example, as shown in FIG. 5, a cast spray nozzle 520 for cooling the casting 150 and a cross spray nozzle 530 for cooling the roll surface can be implemented.

The fret spray nozzles 520 are three in the width direction of the strip in order to cover a width of about 1 to 2 meters. The roll 510 is cooled by using a water cooling method, Or by using a cross spray nozzle 530 to cool the surface of the roll 510. The cross spray nozzle 530 injects cooling water to flow between the roll 510 and the roll 510.

The casting speed regulator 420 controls the casting speed of molten steel supplied to the mold in the tundish. The molten steel stored in the tundish is supplied to the mold through an immersion nozzle made of a cylindrical refractory brick. The casting speed can be controlled by adjusting the supplied drawing speed.

The control unit 400 decelerates and accelerates the casting speed stepwise at intervals of a predetermined time when the tundish remaining capacity reaches a specified reference value (at the end of the continuous casting process), and the optimum casting speed and cooling And controls the cooling water jetting nozzle unit and the casting speed adjusting unit with the value of the quantity.

When the residual molten steel in the tundish reaches a predetermined reference value, the control unit 400 decelerates the molten steel in stages at a predetermined time interval thereafter, and then increases the molten steel in the capping operation at the end of the continuous casting process. That is, when the molten steel flows from the tundish into the mold and the molten steel in the tundish decreases to reach a specific reference value, it is determined to be the end of the continuous casting process, and then decelerated at a predetermined time interval from that time, .

It is preferable that the specific reference value is a reference value when the tundish becomes about 21.4% of the entire 100% capacity. The value may be set to a value between 20% and 22%, which may have an error. For example, assuming that the total capacity of the tundish is 70 tons, the deceleration and speed-up are performed step by step at a constant time interval from when the tundish becomes 15 tons in the tundish.

FIG. 6 shows an example graph in which the deceleration and the acceleration are performed step by step at regular time intervals.

When the remaining molten steel in the tundish decreases to a certain reference value (for example, 15 tonnes of remaining molten steel in the case of a total capacity of 70 tons), as shown in FIG. 6, the normal casting speed -> 1.3m / min -> 1.0m / min -> 0.5m / min -> 0.8m / min -> 1.0m / min -> 1.3m / min -> Decelerate and accelerate in the order of normal casting speed and restore to normal casting speed.

However, in the case of grain-oriented electrical steel sheets, brittleness (high hardness and low ductility) is strongly caused by its characteristics (high Si steel). Such brittleness is caused by the retention time at the rate of 0.5 m / min, It is largely influenced by the amount of cooling water.

Results of Numerous Experiments As shown in Table 1, in the case where it is necessary to maintain the minimum speed of 0.5 m / min for 2 minutes, only the capping ) Work can be accomplished.

[Table 1]

Casting speed Retention time Presence or absence of fragment Capping state

0.5 m / min 5 min Occur Good 4 min Occur Good 3 min Occur Good 2 min Not occurring Good 1 min Not occurring Bad

The results of the experiment described in [Table 1] show that when the rate of deceleration is kept at a rate of 0.5 m / min for 3 minutes, the capping state may be satisfactory, but fragments are generated. When 1 minute is maintained, Becomes defective.

Therefore, in order to perform good capping without fragmentation of the cast tail portion at the end of the continuous casting process, the lowest deceleration rate of 0.5 m / min is maintained for 2 minutes. Further, since a deviation may occur depending on the casting width, it is preferable to maintain the time within the allowable range of 2 minutes by 20%.

On the other hand, when the casting speed is decelerated and increased in stages at a predetermined time interval at the end of the continuous casting process on the basis of the remaining tundish capacity as described above, the cooling water is injected at different stages in different stages.

Table 2 below shows examples of the holding time and the cooling water amount in the order of speed change when the casting speed is decelerated and increased in six steps at regular time intervals at the end of the continuous casting process.

[Table 2]

step Casting speed Retention time Cooling water Step 1 1.3 m / min A First quantity Step 2 1.0 m / min B First quantity × (1.0 ÷ 1.3) Step 3 0.8 m / min C First quantity × (0.8 ÷ 1.3) Step 4 0.5 m / min D (particularly preferably 2 minutes) First quantity × (0.5 ÷ 1.3) Step 5 1.0 m / min E First quantity × (1.0 ÷ 1.3) Step 6 1.3 m / min F First quantity × (1.3 ÷ 1.3)

The cooling water in each step injects the cooling water in proportion to the reduction rate of the casting speed of the current stage when compared with the casting speed in the initial deceleration stage (the first stage). That is, the cooling water having the numerical value multiplied by the cooling water quantity (first water quantity) injected in the initial deceleration stage is injected to the deceleration rate of the current stage based on the casting speed in the initial deceleration stage.

Current cooling rate = cooling water jetted at the initial deceleration stage × (casting speed of current stage ÷ casting speed of initial deceleration stage)

For example, assuming that the deceleration and the speed increase are performed in the steps of Table 2, the cooling water in the fourth step is added to the first water amount which is the cooling water to be sprayed in the initial deceleration step (the first step) Min, the speed is 0.5 m / min, and the initial deceleration step speed is 1.3 m / min).

As a result, the control unit 400 reduces the brittleness of the tail portion of the cast steel by decreasing and increasing the casting speed by a predetermined time interval at the end of the continuous casting process in which the tundish remaining capacity reaches a specific reference value in the above- As a result, the generation of debris in the tail portion can be prevented.

7 is a flow chart showing a brittle reduction process of a cast steel according to an embodiment of the present invention.

First, it is determined whether the remaining capacity of the tundish reaches a specific reference value (S710). It is preferable that the specific reference value is a reference value when the tundish becomes 100% capacity and 21.4% of the entire tundish. For example, if the total capacity of the tundish is assumed to be 70 tons, it is determined that the specific reference value has been reached when the tundish becomes 15 tons in the tundish.

When the predetermined reference value is reached, a step of decelerating the normal casting speed by a predetermined time interval and then increasing the normal casting speed to a normal casting speed is performed (S720). As shown in FIG. 6, the casting speed is decelerated and increased by changing the holding time at each step to restore the casting speed to the normal casting speed.

When the remaining molten steel in the tundish decreases to a certain reference value (for example, 15 tonnes of remaining molten steel in the case of a total capacity of 70 tons), as shown in FIG. 6, the normal casting speed -> 1.3m / min -> 1.0m / min -> 0.5m / min -> 0.8m / min -> 1.0m / min -> 1.3m / min -> Decelerate and accelerate in the order of normal casting speed and restore to normal casting speed.

As a result of a number of experiments, it is necessary to maintain a minimum speed of 0.5 m / min for 2 minutes, as shown in Table 1, to achieve a good capping operation without generating fragments of the cast tail portion at the end of the continuous casting process .

On the other hand, when the deceleration and acceleration are carried out step by step, the amount of cooling water is varied so as to be sprayed (S730). The cooling water obtained by "the cooling rate of the present stage cooling water = the cooling water sprayed in the initial deceleration stage × (the casting speed of the current stage ÷ the casting speed of the initial deceleration stage)" is sprayed in different stages.

Although the present invention has been described with reference to the accompanying drawings and the preferred embodiments described above, the present invention is not limited thereto but is limited by the following claims. Accordingly, those skilled in the art will appreciate that various modifications and changes may be made thereto without departing from the spirit of the following claims.

1 is a photograph showing the phenomenon that the tail portion of the cast steel is broken.

2 is a photograph showing a state in which a piece of debris is stuck between a roll and a roll.

3 is a perspective view illustrating a cast steel production process for producing a cast steel according to an embodiment of the present invention.

4 is a block diagram of an apparatus for reducing brittleness of a slab in a continuous casting process according to an embodiment of the present invention.

FIG. 5 is a view illustrating a state in which cooling water is sprayed onto a continuous cast slab according to an embodiment of the present invention.

FIG. 6 is an exemplary graph in which the deceleration and the speed increase are performed step by step at predetermined time intervals according to the embodiment of the present invention.

7 is a flow chart showing a brittle reduction process of a cast steel according to an embodiment of the present invention.

Claims (9)

A casting speed adjusting unit for adjusting a casting speed of molten steel to be drawn; A cooling water spray nozzle for spraying cooling water when the main body is conveyed along the conveyance roller; When the remaining capacity of the tundish remaining in the entire 100% capacity of the tundish reaches a preset reference value, four steps with different time intervals at the normal casting speed, which is the casting speed when the remaining capacity reaches a preset reference value , The casting speed is sequentially increased to three stages having different time intervals at the casting speed in the lowest deceleration stage which is the last stage in which the casting speed is sequentially lowered, A control unit for controlling the casting speed adjusting unit and the cooling water spraying nozzle so as to inject the cooling water in different amounts at different stages; Wherein the brittle abatement device is a brittle abatement device. The brittle abatement device of claim 1, wherein the reference value is a value set between 20% and 22% at a total 100% capacity of the tundish. delete The brittle reducing apparatus of claim 1, wherein a time within 2 minutes ± 20% is maintained in the lowest deceleration step. Detecting whether the remaining capacity of the remaining tundish at the entire 100% capacity of the tundish reaches a preset reference value; The casting speed is sequentially lowered as four steps having different time intervals at a normal casting speed, which is a casting speed when the remaining capacity reaches a predetermined reference value, and then the lowest deceleration step, which is the last step in which the casting speed is sequentially lowered A casting speed adjusting step of sequentially increasing the casting speed to restore the casting speed to the normal casting speed; A cooling water regulating process for spraying the cooling water at different stages of the casting speed; Wherein the brittleness reduction method comprises the steps of: The brittle abatement reducing method of claim 5, wherein the reference value is a value set between 20% and 22% at the entire 100% capacity of the tundish. The method according to claim 5, wherein the casting speed adjustment process further includes a step of controlling the casting speed to be in a range of from 0.5 m / min to 0.8 m / min to 0.5 m / min when the remaining capacity reaches a predetermined reference value. characterized in that deceleration and acceleration are performed in the order of m / min -> 1.0 m / min -> 1.3 m / min -> normal casting speed, which is the casting speed when the remaining capacity reaches a preset reference value. Way. The brittle reduction method of claim 7, wherein the casting speed of 0.5 m / min is maintained within 2 minutes ± 20%. 6. The method according to claim 5, wherein the cooling water amount adjustment step includes the steps of: calculating a cooling water amount obtained by "the present step cooling amount = the cooling water amount injected in the initial deceleration step × (the casting speed of the current step ÷ the casting speed of the initial deceleration step) And the mixture is sprayed in a different manner.

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