KR20110072493A - Apparatus for reducing brittleness in slab and method for operating the same - Google Patents

Abstract

PURPOSE: An apparatus for reducing brittleness of a slab and an operating method thereof are provided to improve the quality of a tail portion manufactured in a late state of a continuous casting process. CONSTITUTION: An apparatus for reducing brittleness of a slab includes a regulator(420), a cooling water injection nozzle(410) and a controller(400). The regulator adjusts the casting velocity of molten steel which is being drawn. The cooling water injection nozzle jets cooling water when a slab is transferred along a transferring roller. The controller reduces a normal casting velocity in stages at a predetermined interval, and then restores the reduced speed to the normal casting velocity. The cooling water injection nozzle jets different quantities of cooling waters in respective stages so as to control the regulator and the cooling water injection nozzle.

Description

Apparatus for reducing brittleness in slab and method for operating the same}

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

In general, the continuous casting process of the cast steel is made by using ladle, tundish and cutting equipment. The molten steel formed in the steelmaking process is cast through the ladle, tundish and cutting equipment to have a thick thickness. A slab about 150-300 mm is produced. Thereafter, by hot rolling, which is a subsequent process, a strip having a thickness of about 3 to 20 mm is manufactured.

The cast steel continuously cast through the tundish is continuously manufactured while moving between the up and down conveying rollers to which the coolant is injected, and is then cut into a predetermined length by a cutting facility and transferred to the collecting cabinet by the table roller.

Typically, a capping operation is performed at the end of the continuous casting process in which one continuous casting process is finished, and such capping operation is not solidified in a cast (hereinafter, referred to as a 'tail part') at the end of the continuous casting process. This is to stabilize the molten steel.

However, after the capping operation is performed, the brittleness of the tail is high (hardness is high and ductility is low so that it is easily broken). In particular, it appears seriously in a grain-oriented electrical steel sheet having a high silicon content.

Due to such increased brittleness, there is a problem in that the tail portion of the cast steel is broken even in a weak impact as shown in FIG. 1. When the cast piece is pulled out of the mold while being supercooled, cracking of the tail part occurs due to friction between the tail part and the roller.

If a part of the tail part broken and fallen off is stuck between the roller and the roller as shown in Fig. 2, it causes a serious installation accident such as stagnation of the cast and damage of the roller during casting.

In addition, there is a problem in that the casting process is delayed and productivity is lowered because it requires a non-casting time to remove the broken tail part by checking the equipment every time the casting process is finished.

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

Embodiment of the present invention, the casting speed adjusting unit for adjusting the casting speed of the molten steel is drawn, the cooling water spray nozzle for spraying the cooling water when the cast steel is conveyed along the feed roller, and the remaining capacity of the tundish may reach a certain reference value At this time, the control unit for controlling the casting speed adjusting unit and the cooling water injection nozzle to reduce the normal casting speed by a step at a time interval, and then increase the speed to restore to the normal casting speed, and to vary the amount of the cooling water in each step. Include.

Deceleration and acceleration are made in stages by varying the holding time for each stage, and are characterized by maintaining the value within 2 minutes ± 20% at the lowest stage of deceleration.

An embodiment of the present invention is a process for detecting whether the remaining capacity of the tundish reaches a specific reference value, and if the specific reference value is reached, the casting speed is reduced and stepped up step by step at regular intervals to restore the normal casting speed Speed control process, and the amount of cooling water to spray by varying the amount of cooling water in 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 product manufactured at the end of the continuous casting process. In addition, it is possible to prevent the breakage of the tail portion to reduce the loss of the process equipment. In addition, cracking of the tail part does not occur, thereby improving productivity. In addition, it is possible to prevent safety accidents due to reduced inspection of the facility of the worker, and also to reduce the worker workload.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention in more detail. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the embodiments are intended to complete the disclosure of the present invention and to those skilled in the art to fully understand the scope of the invention. It is provided to inform you. Like numbers refer to like elements in the figures.

Figure 3 is a perspective view showing a casting cast manufacturing process for producing a cast in accordance with an embodiment of the present invention.

Filling the molten steel with impurities removed and chemical composition in the ladle 120 installed in the ladle turret, and making the tundish 110 through the ladle nozzle 122 provided in the ladle 120; tundish).

The molten steel stored in the tundish 110 is supplied to the mold 140 through an immersion nozzle 130 made of a cylindrical refractory brick, and then passes through an internal space of the mold 140 having long and short sides. Cast slabs 150 having the same cross section as the cross section of the mold are continuously cast.

In the mold 140, a dummy bar 160 that guides the cast 150 to be drawn out enters an open lower portion of the mold 140, and the first molten steel introduced into the mold 140 is a dummy bar head. The uneven portion of 170 is solidified at the boundary. The solidified molten steel is continuously manufactured as the cast steel 150 while moving between the feed rollers which are pulled up and down by the dummy bar 160 and the coolant is sprayed as the plurality of feed rollers 180 installed in the moving track are driven.

The conveying roller is positioned above and below to convey the cast pieces 150 in between. The body portion of the feed roller is made of the same length and diameter, the shaft of the plurality of feed rollers 180 is connected to the bearing block is set and driven.

The cast steel 150 conveyed along the conveying roller 180 placed up and down is cut into a predetermined length by the cutting device 190 disposed on the outlet side, and is transferred to the hot rolling process by the table roller 182. .

Cooling water is injected at the time of conveying along the feed roller 180, which is forcibly cooled by using the cooling water to solidify quickly and uniformly from the outside into a predetermined cross-sectional size. Therefore, when the cast steel from the mold 140 is transported along the feed roller 180, the cooling water is sprayed on the surface of the cast steel to quickly solidify the cast steel 150 around the feed roller.

Meanwhile, at the end of the continuous casting process in which one continuous casting process is finished, a capping operation is performed to stabilize unmelted steel in the cast steel. The capping operation may be performed by stagnant cooling after completion of molten steel injection into the mold, or by adding a coolant to the cast steel.

In the case of the grain-oriented electrical steel sheet, the capping operation of stabilizing the cast steel by decelerating and increasing the casting speed step by step at a predetermined time interval when the remaining tundish capacity reaches a specific reference value is performed. ) Brittleness (high hardness, low ductility, low breakage characteristics) is a problem.

In other words, in the case of directional electrical steel casting, when the casting speed is decelerated and accelerated step by step at a time interval based on the remaining capacity of tundish, due to the component characteristics (high Si steel) of the oriented electrical steel sheet, There is a problem that the brittleness of the tail (high hardness, low ductility, low breakage characteristics) is increased. This brittleness is caused by the weakening of the solidification by the generation of large pipes cavitation inside the tail.

Therefore, a brittle phenomenon occurs due to the brittleness of the tail part, and in order to prevent such a brittle phenomenon, brittleness must be reduced. The embodiment of the present invention achieves brittle reduction by controlling the deceleration speed and the amount of cooling water while reducing the speed and increasing the casting speed step by step at a predetermined time interval after the tundish residual capacity reaches a specific reference value.

In particular, due to the component characteristics (high Si steel) of the grain-oriented electrical steel sheet, the brittleness (high hardness and low ductility) at the end of the continuous address process varies depending on the numerical value specific to the deceleration speed and the amount of cooling water.

Embodiment of the present invention is controlled as the optimum deceleration speed and the amount of cooling water to reduce the brittleness of the tail when decelerating and increasing the casting speed step by step at a 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 to tail portions of slabs in a continuous casting process according to an embodiment of the present invention.

The coolant spray nozzle unit 410 is a nozzle which is located in the feed roller to inject the coolant for cooling the cast steel, it may be implemented in the form of various coolant spray nozzle unit. For example, as shown in FIG. 5, the spray spray nozzle 520 for cooling the cast steel 150 and the cross spray nozzle 530 for cooling the roll surface may be implemented.

The fret spray nozzle 520 is used in the slab width direction to cover the slab width of about 1 to 2 meters, and the roll 510 cooling to cool the inside of the roll using a water cooling method or Alternatively, a method of cooling the surface of the roll 510 using the cross spray nozzle 530 is used. The cross spray nozzle 530 sprays cooling water to flow between the roll 510 and the roll 510.

The casting speed controller 420 controls the casting speed of the 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, and the casting speed can be controlled by adjusting the drawing speed.

The control unit 400 decelerates and increases the casting speed step by step at a predetermined time interval when the remaining tundish capacity reaches a specific reference value (end of the continuous casting process), and optimal casting speed and cooling to reduce brittleness of the tail portion. The cooling water injection nozzle imposed casting speed control unit is controlled by the value of the quantity.

In detail, in the capping operation performed at the end of the continuous casting process, when the remaining molten steel in the tundish reaches a specific reference value, the controller 400 decelerates step by step at a predetermined time interval from the starting point and increases the speed. That is, when molten steel flows out of the tundish into the mold and the molten steel in the tundish decreases to a certain reference value, it is judged at the end of the continuous casting process and then decelerated step by step at a certain time interval from then, and then restored to the normal casting speed. Proceed with the process.

It is preferable that the specific reference value is a reference value when it becomes about 21.4% in the total 100% capacity of the tundish. The value may have an error and may be set to a value between 20% and 22%. For example, assuming that the total capacity of the tundish is 70 tons, the molten steel in the tundish is decelerated and accelerated step by step at regular time intervals.

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

If the residual molten steel in the tundish is reduced to a certain reference value (e.g. 15 tonnes of residual molten steel for a total 70 tonne capacity), then, as shown in Figure 6, the normal casting speed-> 1.3 m / min-> 1.0 m / min -> 0.5m / min-> 0.8m / min-> 1.0m / min-> 1.3m / min-> After deceleration and increase in the order of normal casting speed, restore to normal casting speed.

However, in the case of oriented electrical steel sheet, due to its characteristics (high Si steel), brittleness (high hardness, low ductility and low brittleness) is shown to be strong. Such brittleness is maintained at 0.5 m / min speed, which is the lowest deceleration step. It depends greatly on the amount of cooling water.

As shown in the following [Table 1], when it is necessary to maintain 2 minutes at the lowest speed step of 0.5 m / min, only a good capping without debris of the slab tail portion at the end of the continuous casting process ) Can work.

TABLE 1

Casting speed Retention time Presence of debris Capping state

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

According to the experimental results described in [Table 1], the capping state may be good if the capping state is maintained at the minimum deceleration speed of 0.5 m / min at 3 minutes, but fragments are generated. Becomes bad.

Therefore, in order to perform good capping without generating fragments of the slab tail portion at the end of the continuous casting process, the minimum deceleration speed of 0.5 m / min is maintained for 2 minutes. Furthermore, it is desirable to keep it as a time within ± 20% tolerance of 2 minutes because deviation may occur depending on the casting width.

On the other hand, as described above, when the casting speed is decelerated and increased step by step at a time interval at the end of the continuous casting process on the basis of the remaining tundish capacity, it is sprayed by varying the amount of cooling in each step.

Table 2 below describes examples of the holding time and the amount of cooling in the order of speed change when the casting speed is reduced 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 quantity First stage 1.3 m / min A First quantity 2nd step 1.0 m / min B First quantity × (1.0 ÷ 1.3) 3rd step 0.8 m / min C First quantity × (0.8 ÷ 1.3) 4th step 0.5m / min D (particularly 2 minutes is preferred) First quantity × (0.5 ÷ 1.3) 5th step 1.0 m / min E First quantity × (1.0 ÷ 1.3) 6th step 1.3 m / min F First quantity × (1.3 ÷ 1.3)

The cooling water quantity in each stage is injected in proportion to the reduction ratio of the casting speed of the current stage as compared with the casting speed in the initial deceleration stage (first stage). That is, the cooling water quantity which has the numerical value which multiplied the cooling water quantity (1st quantity) sprayed in the initial deceleration stage by the reduction ratio of the present stage based on the casting speed in an initial deceleration stage is injected.

Current stage cooling quantity = Cooling quantity injected in the first deceleration stage × (casting stage 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 the above [Table 2], the cooling quantity of the fourth stage is equal to the first quantity, which is the cooling quantity injected in the initial deceleration stage (first stage) (the current stage). It can be seen that the value is determined by multiplying the speed 0.5 m / min ÷ 1.3 m / min (the initial deceleration speed).

As a result, the control unit 400 decelerates and increases the casting speed step by step at a predetermined time interval at the end of the continuous casting process in which the tundish residual capacity reaches a specific reference value in the above manner, thereby reducing the brittleness of the tail portion of the cast steel, As a result, the generation of debris in the tail portion can be prevented.

7 is a flowchart showing a brittleness reduction process of the 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 it becomes 21.4% in the total 100% capacity of the tundish. For example, assuming that the total capacity of the tundish is 70 tons, it is determined that a specific reference value is reached when the molten steel in the tundish is 15 tons.

When the specific reference value is reached, the normal casting speed is decelerated step by step at a predetermined time interval and then increased to restore the normal casting speed (S720). As shown in Figure 6 by varying the holding time step by step to reduce and increase the casting speed to restore the normal casting speed.

If the residual molten steel in the tundish is reduced to a certain reference value (e.g. 15 tonnes of residual molten steel for a total 70 tonne capacity), then, as shown in Figure 6, the normal casting speed-> 1.3 m / min-> 1.0 m / min -> 0.5m / min-> 0.8m / min-> 1.0m / min-> 1.3m / min-> After deceleration and increase in the order of normal casting speed, restore to normal casting speed.

As a result of many experiments, as shown in [Table 1], it is necessary to maintain 2 minutes at the lowest speed step of 0.5 m / min to achieve a good capping operation without debris of the slab tail part at the end of the continuous casting process. Can be.

On the other hand, when the deceleration and acceleration proceeds step by step, it is injected by varying the amount of cooling water (S730). The amount of cooling water determined by "Current quantity of cooling of the present stage = the quantity of cooling injected at the initial deceleration stage x (the casting rate of the current stage ÷ the casting rate of the initial deceleration stage)" is sprayed in different stages.

Although the invention has been described with reference to the accompanying drawings and the preferred embodiments described above, the invention is not limited thereto, but is defined by the claims that follow. Accordingly, one of ordinary skill in the art may variously modify and modify the present invention without departing from the spirit of the following claims.

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

2 is a photograph showing a state in which tail portion debris is caught between a roll and a roll.

Figure 3 is a perspective view showing 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 to tail portions of slabs in a continuous casting process according to an embodiment of the present invention.

5 is a view showing a state in which the cooling water is sprayed on the continuously cast slab according to an embodiment of the present invention.

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

7 is a flowchart showing a brittleness reduction process of the cast steel according to an embodiment of the present invention.

Claims (9)

Casting speed adjusting unit for adjusting the casting speed of the molten steel drawn; A coolant spray nozzle for spraying coolant when the cast steel is conveyed along a feed roller; And When the remaining capacity of the tundish reaches a specific reference value, the normal casting speed is decelerated step by step at a predetermined time interval and then increased to restore the normal casting speed, and the casting speed is sprayed by varying the amount of the cooling water in each step. Control unit controlling the control unit and the coolant spray nozzle Brittle reduction device of the cast steel comprising a. The apparatus of claim 1, wherein the specific reference value is when residual molten steel having a specific ratio value set to a value between 20% and 22% in the total 100% capacity of the tundish remains. The apparatus for reducing brittleness of cast steels according to claim 1, wherein the deceleration and the speed increase are performed step by step by varying the holding time in each step. The apparatus for reducing brittleness according to claim 3, wherein the slab is held at a value within 2 minutes ± 20% at the lowest deceleration step. Detecting whether the remaining capacity of the tundish reaches a certain reference value; A casting speed adjusting process of decelerating the normal casting speed step by step at a predetermined time interval when the specific reference value is reached and then increasing the speed to restore the normal casting speed; And Cooling water control process to spray by varying the amount of cooling water in each stage of casting speed Brittleness reduction method of the cast steel comprising a. The method for reducing brittleness of cast steels according to claim 5, wherein the deceleration and the speed increase are performed in stages by varying the holding time in each stage. The method of claim 5, wherein the casting speed adjustment process, the normal casting speed-> 1.3m / min-> 1.0m / min-> 0.5m / min-> 0.8m / min-> 1.0m / min-> 1.3m / min-> method for reducing the brittleness of the cast, characterized in that the deceleration and increase in the order of the normal casting speed. The method of claim 7, wherein the casting speed of 0.5 m / min is maintained at a value within 2 minutes ± 20%. The method according to claim 5, wherein the cooling water amount adjustment step, the cooling water amount obtained by "current cooling amount = cooling quantity injected in the initial deceleration stage x (current casting speed ÷ casting speed of the first deceleration stage)" for each step. Brittle reduction method characterized in that the injection by different.

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