JP2009291814A - Method for casting slab - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for casting a slab by which the occurrence of trouble such as drawing failure of a slab can surely be prevented, molten metal can be prevented from being leaked from the end edge part of the slab, and the quality of the slab at the end-edge part can be enhanced. <P>SOLUTION: In the method for casting the slab 5 by pouring molten steel from a tundish 3 into a mold 4, in order to promote the solidification of the end-edge part 25 of the slab 5, a casting rate is decelated by ≥0.5m/min until the pouring of the molten steel in the tundish 3 into the mold 4 is completed, and after decelation, the casting rate is accelerated into the range of 90-110% of the normal rate. Until the end-edge part 25 of the slab 5 passes through a straigtening part 13, the cooling water quantity density for cooling the end-edge part 25 of the slab 5 is defined as ≥0.5m<SP>3</SP>/m<SP>2</SP>/hr, and when the end-edge part 25 of this slab 5 passes through a horizontal part 14, supporting rolls 6 for supporting the slab 5, are retracted by ≥10 mm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a casting method for casting a slab using, for example, a continuous casting machine.

Conventionally, many casting methods have been developed in which molten steel in a tundish is poured into a mold to cast a slab. Among them, for example, Patent Documents 1 to 3 are focused on the casting method when pulling out the terminal portion (the topmost portion) of the slab.
In the slab strand drawing control method in the continuous casting disclosed in Patent Document 1, the inlet side and outlet side pinch rolls for drawing and moving the slab strand are arranged before and after the forging machine, and the slab strand is drawn from the mold. In performing the forging process, in the final drawing process of the slab strand, the top part of the strand is detected, and when the top part reaches the entrance pinch roll, the roll opening of the pinch roll is expanded, The pulling force of the slab strand and the roll rotation speed in the delivery side pinch roll are controlled corresponding to the forging process operation.

In Patent Document 1, in the final drawing process, when the topmost part reaches the entry side pinch roll, the roll opening degree of the pinch roll is increased, and the drawing force and roll rotation speed of the slab strand in the exit side pinch roll are increased. By controlling in accordance with the forging process, an appropriate forging process can be applied to the region up to the top even when the strand is warped.
In the continuous casting method of Patent Document 2, at least a part of the cooling zone upstream of the slab top portion generated in the process of ending molten steel is a non-water cooling zone in which cooling water is not directly applied to the slab top portion. The zone is moved in the support guide passage in correspondence with the slab top.

In the steel-curved continuous casting method of Patent Document 3, the casting is finished without significantly reducing the casting speed at the end of continuous casting, and then the casting speed is returned to the steady speed at the time of redrawing.
Japanese Patent Publication No. 07-108442 Japanese Patent No. 3377340 JP 58-184049 A

Although the technique of Patent Document 1 can smoothly pull out a slab even if warpage occurs at the end portion of the slab, the object to be cast is bloom. That is, since the bloom casting technique is different from the technique for casting the slab (for example, cooling control), the actual situation is that the terminal portion of the slab cannot be pulled out smoothly using the technique of Patent Document 1.
Patent Documents 2 and 3 are continuous casting techniques at the end of casting, but even if these techniques are used for casting a slab, it is impossible to reliably pull out the end portion of the slab. Is the actual situation.

  Therefore, in the present invention, in the casting of the slab, it is possible to reliably prevent the occurrence of trouble caused by the end portion of the slab, to surely prevent the leakage of hot water from the end portion of the slab, and the end portion of the slab It aims at providing the casting method of the slab which can improve the quality of slab.

In order to achieve the above object, the present invention has taken the following measures.
That is, in a casting method in which molten steel in the tundish is poured into a mold to cast a slab, until the pouring of pouring the molten steel in the tundish into the mold is promoted in order to promote solidification of the end portion of the slab. In addition, the casting speed is reduced by 0.5 m / min or more, and after the casting speed is increased in the range of 90 to 110% of the steady speed, until the end of the slab passes through the correction part, The density of water for cooling the end portion is set to 0.5 m ³ / m ² / hr or more, and when the end portion of the slab passes through the horizontal portion, the support roll supporting the slab is retracted by 10 mm or more.

The inventor examined the conditions for smooth casting from various points in casting the slab. In casting slabs, there are many troubles that occur due to the end of the slab. In particular, we will further investigate the cause of the trouble caused by the end of the slab, and eliminate the problems described above. These conditions were found through experiments and the like.
Thereby, it is possible to reliably prevent the occurrence of troubles caused by the end portion of the slab, reliably prevent the leakage of hot water from the end portion of the slab, and improve the quality of the end portion of the slab. .

  According to the present invention, in the casting of a slab, it is possible to reliably prevent troubles such as a slab pull-out failure, prevent hot water leakage from the terminal portion of the slab, and improve the quality of the terminal portion of the slab. Can do.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a continuous casting machine (slab continuous casting machine) for casting a slab, and is an apparatus for performing the slab casting method of the present invention. In addition, a slab continuous casting machine is not limited to the apparatus shown next.
As shown in FIG. 1, a continuous casting machine 1 is cast by a tundish 3 that temporarily stores molten steel 2, a mold 4 that supplies (pouring) molten steel 2 from the tundish 3, and a mold 4. A plurality of support rolls 6 for supporting the slab 5, a plurality of pinch rolls 7 for applying a pulling force for pulling out the slab 5, and a cooling means (cooling nozzle) 8 for cooling the slab 5.

The tundish 3 has a bottomed box shape as a whole, and an immersion nozzle 9 is provided at the bottom of the tundish 3. The immersion nozzle 9 can be opened and closed by a slide valve, and the injection of the molten steel 2 into the mold 4 is stopped or restarted by opening and closing the slide valve.
The support roll 6 is disposed downstream from the bottom of the mold 4 in order. Here, paying attention to the support roll 6 and looking at the profile (roll profile) of the continuous casting machine 1, the continuous casting machine 1 is configured by arranging the support roll 6 in the vertical direction from the mold 4 toward the downstream side. The bent portion 11 formed by arranging the support roll 6 while being bent gradually inward from the end portion on the downstream side of the vertical portion 10, and the support roll 6 on the downstream side of the bent portion 11. Arrange the arc portion 12 formed by arranging the arcs inward (trajectory is arcuate) from the end, and the support rolls 6 so as to be gradually horizontal from the downstream end of the arc portion 12. And a horizontal portion 14 formed by arranging the support roll 6 in a horizontal state from the downstream end portion of the correction portion 13 in a vertical direction. Mold is a continuous casting machine. At least the horizontal portion 14 is provided with a pinch roll 7 as appropriate. The pinch roll 7 may be provided in the vertical portion 10, the bending portion 11, the arc portion 12, and the correction portion 13 in addition to the horizontal portion 14.

Specifically, as shown in FIG. 1, the support roll 6 arranged on the outside and the pinch roll 7 arranged on the outside are mounted on the fixed frame 20 a that is immovable and the support roll 6 arranged on the inside. And the pinch roll 7 arrange | positioned inside is mounted | worn with the movable frame 20b which can move freely.
Accordingly, the plurality of support rolls 6 and the pinch rolls 7 attached to the fixed frame 20a cannot move, and the plurality of support rolls 6 and the pinch rolls 7 attached to the movement frame 20b move in the thickness direction of the slab 5. Can be done.

In the continuous casting machine 1, the molten steel 2 produced from the converter, secondary refining equipment, etc. is transported to the tundish 3 with a ladle, and the molten steel 2 in the ladle is poured into the tundish 3 and then immersed. The slab 5 is cast by opening the nozzle 9 and supplying the molten steel 2 to the mold 4 (pouring). The slab 5 cast by the mold 4 is pulled out downstream by the driving force of the pinch roll 7 while being supported by the support roll 6, and the surface and the inside are gradually cooled by the cooling nozzle 8.
The slab casting method of the present invention will be described below.

As shown in FIG. 1 to FIG. 4, this slab casting method is particularly advantageous in that the terminal portion 25 of the slab 5 (for example, a range within about 1.0 m in the longitudinal direction from the endmost portion of the slab 5) 25 is removed from the mold 4. The process from drawing out, correcting at the correcting section 13 and extracting at the horizontal section 14 is focused on.
As shown in FIGS. 2 and 3, before the pouring of molten steel 2 from the tundish 3 to the mold 4 is completed, and at the end of casting, the casting speed (drawing speed) of the slab 5 drawn in a steady state is set. Decelerate by 0.5 m / min or more (S1).
Thus, when the drawing speed is reduced by 0.5 m / min or more at the end of casting, the slab 5 is promoted to solidify in the mold 4, and the end of the slab 5 is pulled out from the mold 4. In addition, the molten steel 2 is prevented from overflowing from the mold 4.

  Then, after pouring the molten steel 2 from the tundish 3 to the mold 4 (after reducing the drawing speed), the reduced drawing speed is increased in the range of 90 to 110% of the steady speed (S2). Specifically, after the slide valve is closed and the supply of molten steel from the immersion nozzle 9 to the mold 4 is stopped, the decelerated pulling speed once decelerated is changed to a steady speed of 90 to 110 which is the speed before decelerating. The speed is increased to the range of%. Here, in other words, the range of 90 to 110% of the steady speed can be said to be a range of ± 10% based on the steady speed. Therefore, the range of 90 to 110% of the steady speed is hereinafter referred to as ± 10% of the steady speed. Sometimes.

When the drawing speed is increased (when the speed is increased), if the drawing speed is less than −10% of the steady speed and is small, the slab 5 may be overcooled and the slab 5 may not be straightened by the straightening unit 13 or the like. There is.
On the other hand, when the drawing speed is increased, if the drawing speed is larger than + 10% of the steady speed, the slab 5 is not sufficiently cooled, so that the end portion side of the slab 5 is not sufficiently solidified and the water leaks. May occur.
Therefore, when increasing the drawing speed that has been decelerated, the speed must be within a range of ± 10% of the steady speed (90 to 110% of the steady speed) and not too slow and not too fast. There is.

After the end portion 25 of the slab 5 is pulled out from the mold 4, while the end portion 25 passes through the correction portion 13, the water density for cooling the end portion 25 is 0.5 m ³ / m ² / hr or more. The cooling water of the cooling nozzle is controlled so as to become (S3). That is, the water amount of the cooling nozzle is adjusted so that the water amount density of the cooling nozzle with respect to the end portion 25 of the slab 5 is 0.5 m ³ / m ² / hr or more.
It is known from past operations that the quality (surface) of the slab 5 is deteriorated when the water density of the cooling nozzle with respect to the terminal portion 25 of the slab 5 is less than 0.5 m ³ / m ² / hr. Is 0.5 m ³ / m ² / hr or more. From the viewpoint of preventing overcooling, the water density is preferably less than 4.7 m ³ / m ² / hr.

As shown in FIG. 5, when the end portion 25 of the slab 5 passes through the horizontal portion 14, the end portion 25 of the slab 5 is bent in the thickness direction (moving frame 20b side). In other words, the end 25 side of the slab 5 is slightly bent upward.
Considering the influence of the bent end portion 25 of the slab 5, as shown in FIG. 5A, when the end portion 25 of the slab 5 passes through the horizontal portion 14, the bent portion at the end portion 25 of the slab 5 ( When the support roll 6 pushes the support roll 6 upward (which may be referred to as a deformed portion), the surface of the support roll 6 may be wrinkled and possibly damaged.

Further, as shown in FIG. 5B, when the end portion 25 of the slab 5 passes through the horizontal portion 14, the deformed portion 25a of the end portion 25 of the slab 5 is caught by the support roll 6, and the slab 5 cannot be removed. There is a fear.
Therefore, as shown in FIG. 4, in the present invention, when the end portion 25 of the slab 5 passes through the horizontal portion 14, the support roll 6 that supports the slab 5 is retracted by 10 mm or more (S4).
Hereinafter, the retracting of the support roll 6 by 10 mm or more will be described in detail including the structure.

As shown in FIG. 4, in the horizontal portion 14, four support rolls 6 are rotatably attached to one fixed frame 20 a, and are located at the center of one fixed frame 20 a and between the support rolls 6. A pinch roll 7 is rotatably mounted. The support roll 6 is attached to the fixed frame 20a so as not to move, and the pinch roll 7 is attached to the fixed frame 20a so as to be movable in the thickness direction of the slab 5 by a hydraulic cylinder or the like.
In the horizontal portion 14, four support rolls 6 are rotatably mounted on one moving frame 20 b, and the pinch roll 7 rotates between the support rolls 6 on the center side of one moving frame 20 b. It is installed freely. The support roll 6 is attached so as not to move with respect to the moving frame 20b, and the pinch roll 7 is attached to the moving frame 20b so as to be movable in the thickness direction of the slab 5 by a hydraulic cylinder 22 or the like.

When the end portion 25 of the slab 5 passes through the horizontal portion 14, the moving frame 20b through which the end portion 25 passes is moved from the steady position to the thickness of the slab 5 so that the end portion 25 of the slab 5 and the support roll 6 do not interfere with each other. The support roll 6 is retracted by 10 mm or more from the casting position set by the thickness of the slab 5.
The retraction of the moving frame 20b from the steady position is preferably performed immediately before the end portion 25 passes, that is, immediately before the end portion 25 enters the moving frame 20b, and is best retracted in order from the upstream. Thus, by retracting the moving frame 20b, interference between the support roll 6 and the slab 5 is prevented, and damage to the support roll 6 is prevented.

When the moving frame 20b is retracted, not only the support roll 6 but also the pinch roll 7 moves away from the slab 5. In the present invention, the pinch roll 7 is movable with respect to the moving frame 20b. The pinch roll 7 is in contact with the surface of the slab 5 even when the moving frame 20b is retracted, so that the hydraulic cylinder 22 or the like moves the slab 5 so as to contact the surface of the slab 5. The pulling force is given to the.
In addition, even if the terminal part 25 of the bent slab 5 reaches the pinch roll 7 with the moving frame 20b retracted, the pinch roll 7 does not push the terminal part 25 in the thickness direction with a predetermined force, but in the thickness direction. It has become something that can move and escape. That is, it has a structure that escapes in the thickness direction (upward) by the damper action of the hydraulic cylinder 22 that moves the pinch roll 7.

Then, when the end portion 25 of the slab 5 passes through the horizontal portion 14 and comes out from the exit side of the continuous casting machine, the casting is finished (S5).
Table 1 shows the implementation conditions when casting the slab with a continuous slab caster. Tables 2 to 3 summarize the results of casting by the slab casting method of the present invention and the results of not casting by the slab casting method of the present invention based on the implementation conditions of Table 1. is there.

  As shown in Table 1, the continuous casting machine was a vertical bending type continuous casting machine, and the length of the vertical portion was 2.9 m. A casting machine having an arc portion radius of 10.7 to 53.5 m was used. The cast slab 5 was made into three types with different widths and thicknesses. The distance at which the support roll 6 (moving frame 22b) was retreated at the horizontal portion 14, that is, the retraction amount (expansion amount) was 0 to 65 mm.

In the experimental results shown in Tables 2 to 3, when no trouble occurred, “Good” is indicated, when there is no leakage, Good “Good”, and when there is no quality problem, Good “Good”. A case where any problem occurred was defined as a failure “x”.
In Experiment No. 1 to Experiment No. 6, Experiment No. 10 to Experiment No. 18, Experiment No. 25 to Experiment No. 30, and Experiment No. 34 to Experiment No. 51, the difference between the casting speed at the steady state and the casting speed at the end of casting (speed down) The amount of casting is 0.5 m / min or more, and the subsequent casting speed is increased within a range of ± 10% with reference to the casting speed in a steady state (the speed increase is within ± 10%), and the end portion of the slab 5 When the water volume density for cooling 25 (water volume density applied to the end portion) is 0.5 m ³ / m ² / hr or more and the retracting amount (expansion amount) of the support roll 6 is 10 mm or more, the experimental results for all items Was good.

In these experiments, the pulling failure that the slab 5 cannot be pulled out when the terminal portion 25 of the slab 5 is caught on the support roll 6, or the support roll 6 is damaged when the terminal portion 25 of the slab 5 is caught on the support roll 6. It was possible to reliably prevent the destruction of the equipment (trouble, good “○”).
Further, when the support roll 6 rotates while the slab 5 is caught on the support roll 6, oysters may enter the surface of the support roll 6, but such troubles can also be prevented ( Trouble, good “○”).

When the cooling of the end portion 25 of the slab 5 is not sufficient, when the slab 5 reaches the horizontal portion 14 and the slab 5 is turned from the vertical direction to the horizontal direction, the unsolidified molten steel in the slab 5 flows toward the end portion 25 side. The portion 25 is melted and unsolidified molten steel leaks to the outside and adheres to equipment such as the support roll 6. However, in the method of the present invention described above, such hot water leakage does not occur. (Hot water leak, good “○”).
Furthermore, in the terminal part 25 of the slab 5, the quality equivalent to the stationary part other than the terminal part 25 could be maintained (quality, good “◯”).

In Experiment No. 7 to Experiment No. 9, since the difference between the casting speed at the steady state and the casting speed at the end of casting (speed down amount) was less than 0.5 m / min, the terminal portion 25 of the slab 5 is not sufficiently cooled. As a result, unsolidified molten steel leaked to the outside (hot water leakage, defective “×”).
In Experiment No. 19 to Experiment No. 21, when the casting speed is increased based on the casting speed at the steady state, it is −20% of the casting speed at the steady state, which is very slow. It became cooled and deformed and caught on the support roll 6 (trouble, defective “×”).
In Experiment No. 22 to Experiment No. 24, when the casting speed is increased based on the casting speed at the time of steady state, it is + 20% of the casting speed at the time of steady state, which is very fast. Not cooled and a water leak occurred (hot water leak, defective “×”).

In Experiment No. 31 to Experiment No. 33, the water density for cooling the end portion 25 of the slab 5 was less than 0.5 m ³ / m ² / hr, so that the end portion 25 of the slab 5 was lowered to a predetermined temperature. When the slab 5 was corrected from the bent state, the surface was cracked, and the quality equivalent to that of the steady portion could not be maintained (quality, defective “x”).
In Experiment No. 52 to Experiment No. 66, since the retracted amount (expansion amount) of the support roll 6 was less than 10 mm, troubles such as defective pulling out and equipment destruction occurred (trouble, defective “x”).

   The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a conceptual diagram of a continuous casting machine. It is the flowchart which showed the procedure of the casting method of a slab. It is the figure which showed the change of drawing speed (casting speed). It is the figure which retracted the support roll 10 mm or more. (A) shows an example in which the deformed portion at the end of the slab 5 comes into contact with the support roll and breaks the support roll, and (b) shows that the deformed portion at the end of the slab is caught by the support roll and the slab comes off. It is the figure which showed the example which disappears.

Explanation of symbols

1 Continuous casting machine 3 Tundish 4 Mold 5 Slab 6 Support roll 13 Straightening part 14 Horizontal part 25 End part of slab

Claims (1)

In a casting method in which molten steel in a tundish is poured into a mold to cast a slab,
In order to promote the solidification of the end portion of the slab, the casting speed is reduced by 0.5 m / min or more by the time of pouring the molten steel in the tundish into the mold, and the casting speed is reduced to the steady speed after the deceleration. Increase the speed in the range of 90-110%,
Until the end portion of the slab passes through the correction portion, the water density for cooling the end portion of the slab is set to 0.5 m ³ / m ² / hr or more,
A slab casting method, wherein when the end portion of the slab passes through a horizontal portion, a support roll supporting the slab is retracted by 10 mm or more.

Images