JP2006150434A - Continuous casting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the surface defect, such as brake-out, cracking, without lowering casting speed, even in the case of deviating an immersion nozzle to one side of a short sides. <P>SOLUTION: A continuous casting method is performed in a such way that the immersion nozzle 1 setting one pair of spouting holes 2 facingly disposed on the sidewalls near the bottom part toward the short side direction of a mold 6 is set so as to be deviated to one side of the short sides. Molten steel 7 is supplied into the mold 4 by using the immersion nozzle 1, in which the recession 3 having 10-45mm depth d is formed on the inner surface of the bottom part and the respective spouting holes 3 having the rectangular shape at longer width length with 0.5-0.8 H/W ratio of the height and the width, dividing the outlet height H with the outlet width W on the outer peripheral surface of the immersion nozzle 1 are arranged, and in the case of observing the position containing the spouting holes 2 in the immersion nozzle 1 with the vertical cross-sectional plane, an average downward angle α1 of the upper wall 2a in the spouting hole is larger than an average downward angle α2 of the lower wall 2b in the spouting hole. This immersion nozzle can soundly improve the growth of the short side solidified shell at the narrow width side, even in the case of deviating the immersion nozzle to one side of the short sides. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a continuous casting method suitable for continuous casting of a steel slab using an immersion nozzle, when the immersion nozzle is installed on one short side from the mold width center for convenience of equipment. It is.

  In continuous casting of a slab, it is preferable for the growth of a solidified shell in a mold that a dip nozzle is installed at the center in the mold width direction and the flow in the mold is formed symmetrically in the mold width direction. The reason for this is that when the immersion nozzle is installed close to one mold short side, the mold short side solidified shell is formed on the narrow side between the immersion nozzle and the short side (hereinafter referred to as “narrow side”). This is because the collision speed of the discharge flow increases and the solid formation of the solidified shell is hindered, and as a result, breakout due to remelting of the solidified shell and cracking surface defects are likely to occur.

  However, due to equipment limitations, the immersion nozzle may not be installed in the center of the mold in the width direction. In such a case, there was a problem that the casting speed had to be reduced in order to solve the above problem.

The case where the immersion nozzle cannot be installed in the center of the width of the mold due to the restrictions on the equipment is, for example, the following case.
1) In the so-called twin casting in which the short side of the partition is inserted in the center of the width of the wide mold and the two molds are adjacent to each other, in the initial casting, an immersion nozzle can be arranged in the center of the width of each mold. For example, if you change the mold width by moving the short side on one or both sides. In this case, since the distance between the immersion nozzle and the short side of the partition is fixed, the immersion nozzle cannot be installed at the center of the width of the mold in which the outer short side is moved.
Japanese Examined Patent Publication No. 1-54148

2) When the sliding gate provided at the bottom of the tundish is a two-plate type consisting of an upper fixed platen and a lower slider, and the sliding direction of the lower slider is the mold width direction. In this case, the immersion nozzle attached to the slider moves in the mold width direction in accordance with the opening / closing operation of the lower slider, so that the immersion nozzle cannot be installed at the center of the mold width.

  The problem to be solved by the present invention is that, conventionally, when the immersion nozzle cannot be installed at the center of the mold width due to equipment limitations, in order to prevent breakout and cracking surface defects, casting The point was that we had to reduce the speed.

The continuous casting method of the present invention comprises:
In order to prevent breakout and cracking surface defects without lowering the casting speed even when the immersion nozzle cannot be installed in the center of the mold width due to equipment restrictions,
In the continuous casting method when the immersion nozzle in which the pair of discharge holes arranged facing the side wall in the vicinity of the bottom portion is installed toward the short side of the mold is disposed at a position closer to one short side than the center of the mold width. There,
Forming a recess having a depth of 10 mm to 45 mm on the inner surface of the bottom,
The discharge hole is
A laterally long rectangular shape with an aspect ratio of 0.5 to 0.8 obtained by dividing the outlet height on the outer peripheral surface of the immersion nozzle by the outlet width,
When the vertical position of the position including the discharge hole of the immersion nozzle is viewed, the average downward angle of the discharge hole upper wall is larger than the average downward angle of the discharge hole lower wall.
The main feature is to supply molten steel into the mold using an immersion nozzle.

  According to the present invention, by appropriately forming the discharge hole shape, the discharge flow rate from the discharge hole on the narrow side is discharged on the wide side (hereinafter referred to as “wide side”) between the immersion nozzle and the short side. Can solve the problem of increasing compared to the discharge flow rate from the hole, and even when the immersion nozzle cannot be installed in the center of the mold width direction due to equipment restrictions, the solid growth of the short-side solidified shell on the narrow side can be achieved, Even if the casting speed is not reduced, breakout and the occurrence of cracking surface defects can be prevented.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings along with the processes leading to the establishment of the invention.
The present inventors examined the flow in the mold in the case where the immersion nozzle is installed so as to be biased to one short side with respect to the mold width center by a full-scale water model experiment and a simulation using a computer. As a result, it has been found that there are two problems caused by the immersion nozzle being biased toward one short side.

  As can be easily imagined, the first problem is that on the narrow side, the horizontal flow velocity of the discharge flow from the immersion nozzle formed in the vicinity of the mold short side to the mold short side is large, and the short side solidified shell is remelted. Is likely to occur.

  The second problem is that when the shape of the discharge hole of the submerged nozzle is inappropriate, the discharge flow rate from the discharge port on the narrow side increases compared to the discharge flow rate from the discharge port on the wide side. It is to help the problem. The cause of the occurrence of the second problem has not been clarified, but it is considered that a short-side reversal circulation flow having a high flow velocity occurs on the narrow width side, and this high-speed circulation flow causes a phenomenon of sucking out the discharge flow.

  The inventors of the present invention focused on the second problem among these two problems and worked to solve this problem. As a result, the phenomenon that the discharge flow rate from the discharge port on the narrow side increases compared to the discharge flow rate from the discharge port on the wide side can be effectively suppressed if the shape of the discharge hole of the immersion nozzle is made appropriate. I found. Furthermore, the present inventors have found that the first problem can be solved by combining asymmetrical static magnetic field application, and have achieved the present invention.

  In other words, the present inventors have conducted experiments and simulations as a result of examining the conditions that cause the phenomenon that the discharge flow rate from the discharge port on the narrow side increases compared to the discharge flow rate from the discharge port on the wide side, It has been found that the above phenomenon remarkably occurs when effective discharge is not performed from the entire surface of the discharge hole and the discharge flow velocity is low or the region where the suction flow is present in the upper part of the discharge hole.

  From such knowledge, in order to prevent the phenomenon that the discharge flow rate from the discharge port on the narrow side increases compared to the discharge flow rate from the discharge port on the wide side, effective discharge is performed from the entire discharge hole. It turned out that it should just design to a shape.

  In general, the flow in the submerged nozzle is a flow in which the main body portion descends through the cylindrical submerged nozzle and collides with the nozzle bottom to give a horizontal velocity vector. As a characteristic of such a flow, the discharge flow velocity increases as it approaches the nozzle bottom, and decreases as it moves away from the nozzle bottom. Further, the discharge angle becomes smaller as the nozzle bottom is closer (the horizontal velocity vector is larger), and becomes larger as the distance from the nozzle bottom is higher (the horizontal velocity vector is smaller).

  Because of these characteristics, if the discharge holes are square or vertically long, the flow velocity at the top of the discharge holes tends to decrease, and in some cases, a suction region tends to occur, and effective discharge is performed from the entire surface of the discharge holes. It's hard to fall.

In consideration of the fact that the flow in the immersion nozzle has the above-mentioned characteristics, the present inventors have found that the following three conditions must be satisfied at the same time in order to prevent a reduction in the flow velocity at the upper portion of the discharge hole.
First, as shown in FIG. 1 to FIG. 3A, the aspect ratio H / W of the discharge hole 2 on the outer peripheral surface of the immersion nozzle 1 divided by the outlet height H is divided by the outlet width W. This is to form a horizontally long rectangular shape of 0.5 to 0.8. This is a method of opening the discharge hole 2 near the nozzle bottom where the discharge flow is concentrated.

  The second is to provide, for example, a waterfall-shaped depression 3 having a depth d of 10 to 45 mm on the inner surface of the bottom of the immersion nozzle 1. This is a method of forming a flow that jumps up from the recess 3 and enhancing the distribution of the flow to the upper part of the discharge hole 2.

  When the depth d is less than 10 mm, the effect of the recess 3 is reduced. On the other hand, when the depth d exceeds 45 mm, the jumping flow is weakened and the immersion nozzle 1 becomes unnecessarily long and the operability is deteriorated.

  Third, as shown in FIGS. 1 to 3B, when the position including the discharge hole 2 is viewed in a longitudinal section, the average downward angle α1 of the upper wall 2a of the discharge hole 2 is set to the discharge hole. 2 is formed to be larger than the average downward angle α2 of the lower wall 2b, and the area of the discharge hole 2 is reduced toward the outlet of the discharge hole 2.

  This is a method for preventing the discharge flow from being separated from the upper and lower walls 2a and 2b of the discharge hole 2 by forming the upper and lower walls 2a and 2b of the discharge hole 2 in a shape following the characteristics of the flow in the nozzle. is there.

  That is, since the downward angle of the discharge flow is small in the vicinity of the bottom of the immersion nozzle 1, the lower wall 2b of the discharge hole 2 decreases the downward angle accordingly, while the downward angle of the discharge flow decreases as it moves away from the bottom of the immersion nozzle 1. Accordingly, the upper wall 2a of the discharge hole 2 increases the downward angle accordingly.

  At the same time, the average downward angle α1, α2 between the upper wall 2a and the lower wall 2b of the discharge hole 2 is formed as described above, and the area of the discharge hole 2 is reduced toward the outlet of the discharge hole 2, thereby It is also a technique for equalizing the flow velocity distribution at the outlet. In addition, when the upper wall 2a or the lower wall 2b of the discharge hole 2 is not linear, such as a curved shape, the average value of the inclination is obtained as the wall angle.

  That is, as a result of repeated studies as described above, the present inventors have an aspect ratio H / W of 0.5 to 0 obtained by dividing the outlet height H of the discharge hole 2 on the outer peripheral surface of the immersion nozzle 2 by the outlet width W. .8 in the shape of a horizontally long rectangle, and a recess 3 having a depth d of 10 mm to 45 mm is provided on the inner surface of the bottom of the immersion nozzle 2 and the position including the discharge hole 2 is viewed in a longitudinal section. It has been found that if the average downward angle α1 of the upper wall 2a is made larger than the average downward angle α2 of the lower wall 2b of the discharge hole 2, a suction area is hardly generated in the discharge hole 2 and the uniformity of the discharge flow rate is improved. It is.

The continuous casting method of the present invention is based on the aforementioned knowledge,
As shown in FIG. 5, the immersion nozzle 1 in which a pair of discharge holes 2 arranged opposite to the side wall near the bottom portion is installed in the short side direction of the mold 6 is closer to one short side than the center of the width of the mold 6. A continuous casting method in the case of being biased to a position,
Forming a recess 3 having a depth d of 10 mm to 45 mm on the inner surface of the bottom;
The discharge hole 2 is
A horizontal rectangular shape with an aspect ratio H / W of 0.5 to 0.8 obtained by dividing the outlet height H on the outer peripheral surface of the immersion nozzle 1 by the outlet width W,
When the position including the discharge hole 2 of the immersion nozzle 1 is viewed in a longitudinal section, the average downward angle α1 of the upper wall 2a of the discharge hole 2 is larger than the average downward angle α2 of the lower wall 2b of the discharge hole 2. Big,
The molten steel 7 is supplied into the mold 6 by using one immersion nozzle as shown in FIG.

  In the continuous casting method of the present invention, the upper and lower walls 2a of the discharge hole 2 are such that the average downward angle α1 of the upper wall 2a of the discharge hole 2 is larger than the average downward angle α2 of the lower wall 2b of the discharge hole 2. In order to more ideally realize the technique for preventing the separation of the discharge flow from the nozzle 2b, when the position including the discharge hole 2 of the immersion nozzle 1 is viewed in a longitudinal section, as shown in FIGS. The inner peripheral surface side of the immersion nozzle 1 in the upper wall 2a of the discharge hole 2 is desirably formed into an arc shape having a radius R of 30 mm to 180 mm. By doing in this way, peeling of the discharge flow from the upper wall 2a of the discharge hole 2 is suppressed more effectively, and the discharge flow velocity approaches uniformly.

  When the radius R is less than 30 mm, the change in the inclination of the upper wall 2a of the discharge hole 2 is abrupt and the discharge flow is easily separated. On the other hand, if the radius R is larger than 180 mm, the thickness of the upper wall 2a of the discharge hole 2 is reduced, and the risk of melting and cracking increases. According to the experiments and simulations of the inventors, a more preferable range of the radius R is between 40 mm and 120 mm.

  Further, when the downward angle α2 of the lower wall 2b of the discharge hole 2 is upward from the horizontal (0 °), the flow bounced up to the lower wall 2b interferes with the flow flowing obliquely downward along the upper wall 2a. However, the discharge flow is disturbed, which is not preferable. On the other hand, when the downward angle α2 is larger than 35 °, it is not preferable because the discharge flow is easily separated from the lower wall 2b.

That is, in the continuous casting method of the present invention,
When the position including the discharge hole 2 of the immersion nozzle 1 is viewed in a longitudinal section,
The inner peripheral surface side of the immersion nozzle 1 in the upper wall 2a of the discharge hole 2 has an arc shape with a radius R of 30 mm to 180 mm,
The downward angle α2 of the lower wall 2b of the discharge hole 2 is in the range of 0 ° (horizontal) to 35 °.
It is desirable to supply the molten steel 7 into the mold 6 using the immersion nozzle 1.

  In the continuous casting method of the present invention, as shown in FIGS. 2 and 3, when the bottom inner surface direction is viewed from the cross-sectional position of the immersion nozzle 1, one protrusion 4 extending parallel to the discharge direction. Is formed on the inner surface of the bottom portion, a vortex as indicated by an arrow in FIG. 4 is always formed at the bottom portion of the immersion nozzle 1, so that a flow that jumps up from the recess 3 can be stably formed. The effect of increasing the distribution of the flow to the upper part will be enhanced.

  The height h of the protrusion 4 is not particularly limited, but it is preferable to keep it within a range not exceeding the depth d of the recess 3. This is because if the height h of the protrusion 4 becomes too high, the flow intrusion into the recess 3 is prevented, and the effect of forming the splash flow by the recess 3 is reduced.

  Further, the height h of the protrusion 4 needs to be at least 5 mm, preferably 10 mm or more. This is because the effect is lost if the height h of the protrusion 4 is lower than that. The protrusion 4 may have a constant height h as shown in FIG. 3. However, the protrusion 4 has a shape in which the central portion is high as shown in FIG. Since the adverse effect of the protrusion 4 being too high is less likely to occur, it is more preferable.

  Further, the thickness t of the protrusion 4 may be constant as shown in FIG. 2 or may be made thinner toward the top as shown in FIG.

  In addition, the continuous casting method of the present invention can prevent the phenomenon that the discharge flow rate from the discharge port 2 on the narrow side increases compared to the discharge flow rate from the discharge port 2 on the wide side, but the narrow side The flow velocity that collides with the short side of the mold is still larger than that on the wide side.

  Therefore, by using an electromagnetic brake device, the static magnetic field applied to the discharge flow on the narrow side is made stronger than the static magnetic field applied to the discharge flow on the wide side, and the mold caused by the bias of the immersion nozzle 1 is used. Better results can be obtained by eliminating the unevenness of internal flow. At this time, a static magnetic field may be applied only to the narrow side.

Hereinafter, the implementation results performed to confirm the effect of the present invention will be described.
Table 1 below shows examples of the present invention, and Table 2 below shows comparative examples. The various indexes shown in Table 1 and Table 2 are values obtained by full-scale water model experiments and simulations using a computer.

Example A is an example that satisfies claim 1 of the present invention (see FIG. 1).
In this embodiment A, as an effect of satisfying claim 1 of the present invention, the discharge flow rate difference is as small as 5%. Further, the narrow side short side collision flow velocity is also suppressed to a relatively low level of 0.45 m / s.

Example B is an example that satisfies claims 1 and 2 of the present invention.
In this example B, the upper wall of the discharge hole is formed in an arc shape with respect to the example A. As an effect thereof, the discharge flow is hardly separated from the upper wall of the discharge hole, and a stable discharge flow is formed. In actual casting, an effect of reducing the adhesion of nonmetallic inclusions to the upper wall of the discharge hole can be expected.

  In Example B, the discharge flow rate difference is as small as 3%. Whether there is a significant difference between the value of 3% and the value of 5% in Example A is subtle in consideration of differences in casting conditions and experimental or measurement errors, but is qualitative. Is considered to have the effect of forming the upper wall in an arc shape. The collision flow velocity to the narrow side short side is relatively low at 0.41 m / s.

Examples C and D are examples that satisfy claims 1 to 3 of the present invention.
In these Examples C and D, a protrusion is provided on the bottom of the nozzle as compared with Example B. As a result, the discharge flow rate at the upper portion of the discharge hole is increased, and the distribution of the discharge flow rate is closer to that of Example A or Example B.

  In Example C, as shown in FIG. 2 (b), the shape of the protrusion is an isosceles triangle as viewed from the side, the length of the base is equal to the inner diameter of the nozzle bottom, and the height of the apex (the height of the protrusion). The thickness h) is constant at 15 mm and the thickness t is 10 mm. The protrusion of Example D has a length equal to the inner diameter of the nozzle bottom, a constant height h of 15 mm, a thickness t of 5 mm at the top, and 15 mm at the bottom.

  In Example C and Example D, the discharge flow rate difference was suppressed to 1% and 2%. Whether these values have a significant difference with respect to 3% of Example B is delicate considering the difference in casting conditions and experimental or measurement errors, but is significantly different from 5% of Example A. Judge that there is. This difference is considered to be a synergistic effect of claims 2 and 3.

Example E is an example that satisfies all the claims of the present invention.
In Example E, the same nozzle as in Example C is applied, and an electromagnetic brake is applied only to the narrow side. The arrangement of the electromagnetic brake coil 5 is shown in FIG. As a result of applying the electromagnetic brake, the discharge flow rate difference was 2%, and the phenomenon that the flow rate on the narrow side increased with respect to the flow rate on the wide side was completely prevented. Moreover, the collision flow velocity to the narrow side short side was sufficiently lowered to 0.29 m / s.

  The application of the electromagnetic brake to the narrow side was effective not only in reducing the collision flow velocity on the short side on the narrow side but also in eliminating the discharge flow rate difference. This is thought to be because the braking action was exerted on the discharge holes and the discharge flow velocity was reduced.

F to H shown in Table 2 are comparative examples that do not satisfy the claims of the present invention.
In these comparative examples, the shape of the opening of the discharge hole is square (Comparative Example F: see FIG. 7) or vertically long (Comparative Examples G and H), and an immersion nozzle having the same angle of the upper and lower walls of the discharge hole is used. is there.

  As a result, a phenomenon occurs in which the discharge flow rate on the narrow side increases compared to the discharge flow rate on the wide side, and the difference in discharge flow rate exceeds 20% in Comparative Example F and Comparative Example G where the electromagnetic brake is not applied. Even in Comparative Example H applied evenly on the narrow side and the wide side, it exceeded 10%.

  Moreover, the collision flow velocity to the narrow side short side exceeded 0.6 m / s in Comparative Example F and Comparative Example G where the electromagnetic brake was not applied. The collision flow velocity to the short side of the narrow side of Comparative Example H in which the electromagnetic brake was applied equally on the narrow side and the wide side was as low as 0.34 m / s, but the discharge flow rate on the narrow side is large. Since the problem has not been solved, the amount of heat supplied to the narrow side is large, and the risk of delaying the growth of the solidified shell has not been solved. The electromagnetic brake coil arrangement of Comparative Example H is as shown in FIG.

  The present invention is not limited to the above example, and it goes without saying that the embodiment may be appropriately changed within the scope of the technical idea described in each claim.

  The present invention can also be applied to triple casting or the like if the immersion nozzle cannot be installed at the center in the width direction of the mold due to restrictions on equipment.

It is the figure which showed the principal part of Example A which is an immersion nozzle used for the continuous casting method which concerns on this invention of Claim 1, (a) is the figure seen from the discharge outlet side, (b) is (a) ) Is a cross-sectional view along the line B-B in the figure. It is the same figure as FIG. 1 which showed the principal part of Example C which is an immersion nozzle used for the continuous casting method which concerns on this invention of Claim 3. It is the same figure as FIG. 1 which showed the principal part of Example D which is an immersion nozzle used for the continuous casting method which concerns on this invention of Claim 3. It is a figure similar to FIG. 1 explaining the vortex formed when the immersion nozzle used for the continuous casting method which concerns on this invention of Claim 3 is used. It is explanatory drawing in case the immersion nozzle is biased and installed in the one short side rather than the mold width center. It is the figure which showed the example of arrangement | positioning of the electromagnetic brake coil used for the continuous casting method which concerns on this invention of Claim 4. It is the same figure as FIG. 1 which showed the principal part of the immersion nozzle of the comparative example F used for the conventional continuous casting method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Immersion nozzle 2 Discharge hole 2a Upper wall 2b Lower wall 3 Depression 4 Protrusion 5 Coil 6 Mold 7 Molten steel

Claims (4)

In the continuous casting method when the immersion nozzle in which the pair of discharge holes arranged facing the side wall in the vicinity of the bottom portion is installed toward the short side of the mold is disposed at a position closer to one short side than the center of the mold width. There,
Forming a recess having a depth of 10 mm to 45 mm on the inner surface of the bottom,
The discharge hole is
A laterally long rectangular shape with an aspect ratio of 0.5 to 0.8 obtained by dividing the outlet height on the outer peripheral surface of the immersion nozzle by the outlet width,
When the vertical position of the position including the discharge hole of the immersion nozzle is viewed, the average downward angle of the discharge hole upper wall is larger than the average downward angle of the discharge hole lower wall.
A continuous casting method characterized by supplying molten steel into a mold using an immersion nozzle. When looking at the position including the discharge hole of the immersion nozzle in a longitudinal section,
The inner peripheral surface side of the immersion nozzle in the upper wall of the discharge hole has an arc shape with a radius of 30 mm to 180 mm,
An average downward angle of the discharge hole lower wall is in a range of 0 ° to 35 °;
The continuous casting method according to claim 1, wherein molten steel is supplied into the mold using the immersion nozzle. When looking at the bottom inner surface direction from the cross-sectional position of the immersion nozzle,
It has one protrusion on the bottom inner surface that extends parallel to the discharge direction.
The continuous casting method according to claim 1, wherein molten steel is supplied into the mold using the immersion nozzle. A continuous casting method in which an electromagnetic force of a static magnetic field acts on a discharge flow from an immersion nozzle,
Whether the static magnetic field applied to the discharge flow discharged to the short side from the immersion nozzle to the short side is stronger than the static magnetic field applied to the discharge flow discharged to the long side,
The continuous casting method according to any one of claims 1 to 3, wherein a static magnetic field is applied only to a discharge flow discharged to the short side.

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