JPH11179498A - Continuous casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure the flowing speed of molten steel around an immersion nozzle, to prevent the lowering of temp. and the development of defect in a cast slab by arranging one pair of electromagnetic stirring devices having specific device width and with a specific positional relation to an immersion nozzle along the long sides in a mold using the immersion nozzle. SOLUTION: The molten steel 2 supplied through the immersion nozzle 5 is rapidly cooled in the mold 6, and the formed solidified shell is drawn and further, fully solidified with secondary cooling water. In the above continuous casting method, one pair of electromagnetic stirring devices 13 are arranged along the long sides 6A in the mold 6 to control the fluid of the molten steel in the mold. In the electromagnetic stirring device 13, the device length S is set equal to the outer diameter D or more of the immersion nozzle 5 and <=0.3 times of the length W of the long side 6a in the mold. Further, the distance between the centers of the electromagnetic stirring devices 13 and the immersion nozzle 5 in the width direction of the mold is set at within 0.5 times of the device width S. At this time, one pair of the electromagnetic stirring devices 13, 13 are desirable to be set in point symmetry with respect to the center of the immersion nozzle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a continuous casting method.

[0002]

2. Description of the Related Art Continuous casting of steel is usually performed using a continuous casting facility as shown in FIG. That is, the molten steel 2 injected from the ladle 1 into the tundish 4 via the long nozzle 3 is continuously injected into the mold 6 via the immersion nozzle 5. The injected molten steel 2 is cast 6
The solidified shell 10 is formed on the inner surface of the
Is formed. The solidified shell 10 is cooled by the secondary cooling water while being supported by the guide rolls 8, and is turned into a slab 7 which has been solidified in all cross sections, and is continuously pulled out by the pinch rolls 9. In FIG. 6, reference numeral 11 denotes mold powder for coating the free surface of the molten steel in the mold, 12 denotes an electromagnetic stirring device for controlling the flow of the molten steel in the mold, and a and b denote bending portions and straightening portions in the drawing path.

[0003]

When an electromagnetic stirring device is not provided, as shown in FIG.
The molten steel 2 discharged from the discharge hole 5A collides with the inner surface on the side of the mold short side 6B and divides up and down. The rising flow reaches the center of the mold width from the left and right along the molten steel free surface, and collides there and descends. Flows toward. When the slab width is large, stagnation occurs in the molten steel flow near the center of the mold width, particularly near the meniscus around the immersion nozzle where the heat removal is large and the heat supply is insufficient. , A temperature drop occurs such that the distribution X decreases from the position B to the position A. FIG. 5A is a plan view showing the molten steel temperature measuring position in the mold, FIG. 5B is a graph showing the molten steel temperature distribution measured at the temperature measuring position in FIG. 5A, and the distribution in FIG. Y will be described later.

[0004] When such a temperature drop occurs, unmelted mold powder is entrained in molten steel, a vertical crack in a slab, and the like, resulting in a large quality problem. For example, according to the results of investigation on a slab for a thick plate, mold powder, blowhole defects and surface defects due to vertical cracks are as shown in Table 1,
All of them are concentrated at a position corresponding to the periphery of the immersion nozzle where the molten steel temperature has dropped (near position A in FIG. 5).

Conventionally, measures such as raising the discharge angle of the immersion nozzle have been taken, but it has not been possible to sufficiently prevent the molten steel temperature around the immersion nozzle from decreasing.

[0006]

[Table 1]

On the other hand, there is known a technique in which an electromagnetic stirrer is provided over the entire width of a mold to control the flow of molten steel in the mold by applying an electromagnetic force to the molten steel in the mold (for example, Japanese Patent Laid-Open No.
According to this, the temperature drop of the molten steel around the immersion nozzle can be reduced, but on the other hand, the swelling of the molten steel tends to occur on the short side of the mold, and the end of the slab width due to the entrainment of the mold powder there. In particular, there has been a problem that the defect occurrence rate particularly at corners increases.

The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object the present invention.

[0009]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that if the molten steel flow rate around the immersion nozzle is in the range of 20 to 40 cm / sec, the defect occurrence rate at the center of the slab is low. It has been found that if the “height height index of the short side”, which is obtained by classifying and indexing the height of the molten metal surface on the short side of the mold at a pitch of 2 mm, is 1 or less, the defect occurrence rate on the side surface of the slab is low. Therefore, the present invention has been made by further studying a method capable of controlling the molten steel flow velocity around the immersion nozzle and the short-side swelling height index within the above-described preferable range.

According to the present invention, there is provided a continuous casting method using an immersion nozzle.
A pair of electromagnetic stirrers with a device width of 0.3 times or less are installed one by one on the long side of the mold, with the center-to-center distance between the electromagnetic stirrer and the immersion nozzle in the mold width direction within 0.5 times the device width. A continuous casting method characterized by casting molten steel in one horizontal direction with electromagnetic stirring.

[0011] In the present invention, it is preferable that the pair of electromagnetic stirrers is arranged point-symmetrically with respect to the center of the immersion nozzle.

[0012]

1 and 2 are plan views showing one embodiment of the present invention. As shown in FIGS. 1 and 2, according to the present invention, a pair of electromagnetic stirrers 13, 13 having a predetermined device width are connected to mold long sides 6A, 6A.
Then, the molten steel is arranged one by one with a predetermined positional relationship with the center of the immersion nozzle 5, and the molten steel is cast while being electromagnetically stirred in one horizontal direction.

The reason why the width S of the electromagnetic stirring device 13 is limited to D ≦ S ≦ 0.3 W with respect to the outer diameter D of the immersion nozzle and the length W of the long side of the mold is based on the following investigation results. Electromagnetic stirrer 13,
As shown in FIG. 1, 13 are arranged so that their centers are located at the same position as the center of the immersion nozzle 5 in the direction of the long side of the mold. When S was changed and the molten steel surface flow velocity around the immersion nozzle 5 and the short-side swelling height index were investigated, as shown in FIG. 3, when S became smaller than D, the molten steel surface flow velocity rapidly dropped to less than 20 cm / sec. On the other hand, it has been found that when S exceeds 0.3 W, the short-side swell index exceeds 1 and sharply increases. For this reason, the range of the apparatus width S was limited to D ≦ S ≦ 0.3W.

On the other hand, the reason why the center-to-center distance between the electromagnetic stirring device and the immersion nozzle in the width direction of the mold was set to within 0.5 times the device width was based on the following investigation results. As shown in FIG. 2, the electromagnetic stirrers 13 and 13 of S = D to 0.3 W are obliquely opposed to each other at a distance L from the center of the immersion nozzle 5 in the mold width direction (≡long side of the mold). In order to perform casting while electromagnetically stirring the molten steel in one horizontal direction, the distance L (≡distance between the center of the electromagnetic stirring device and the immersion nozzle in the width direction of the mold) is changed. When the molten steel surface flow velocity around the nozzle 5 and the short side swell height index were investigated, as shown in FIG. 4, when L exceeded 0.5 S, the molten steel surface flow velocity was less than 20 cm / sec. 0 to
In the range of 0.5S, the surface velocity of the molten steel falls within the range of 20-40cm / sec, and the value of L when the short-side swelling height index is a minimum value of 1 or less is also included in this range 0-0.5S. I found out. From this, the range of the distance L is
Limited to 0 ≦ L ≦ 0.5S.

It is preferable that the pair of electromagnetic stirring devices be arranged point-symmetrically with respect to the center of the immersion nozzle so that the molten steel on both long sides of the mold of the immersion nozzle flows in opposite directions at the same flow rate. . Thus, instead of disposing the electromagnetic stirring device over the entire width of the mold as in the past,
By locally disposing only around the immersion nozzle, which is a section of the mold width, the molten steel that is about to stagnate in a narrow flow path between the immersion nozzle and the long side of the mold is electromagnetically stirred in one horizontal direction, The heat supply to the submerged nozzle is made uniform, for example, as shown by the distribution Y in FIG. 5, the temperature drop of the molten steel around the submerged nozzle is eliminated, and the defects caused by the lack of heat in the meniscus portion around the submerged nozzle as shown in Table 1 Can be completely eliminated. In addition, the part on the short side of the mold on the long side of the mold (at least
(The range of up to 0.2 W) is not affected by the electromagnetic stirring force, so that the molten steel in this portion is not excessively stirred, and therefore, the swelling of the molten metal due to the collision with the short side of the mold is suppressed, which is caused by this. Defects at the end of the slab width (particularly at the corners) do not occur.

The strength of the magnetic force of the electromagnetic stirrer is set so that the surface velocity of the molten steel between the immersion nozzle and the long side of the mold is 20 to 40 cm / sec. For example, the width is 1500 to 2500 mm and the thickness is 200 to 200 cm / sec.
The preferred range for continuously casting a 350 mm slab at a casting speed of 0.4 to 1.0 m / min is 0.04 to 0.30 T.

[0017]

[Embodiment] A continuous casting facility shown in FIG.
In a continuous casting of slabs at a casting speed of 0.6 m / min, molten steel is supplied from a horizontal two-hole immersion nozzle (outer diameter D = 130 mm) to a slab mold with a thickness of 260 mm and a width of 2400 mm from a horizontal two-hole immersion nozzle (outer diameter D = 130 mm). An electromagnetic stirrer having a device width S of 500 mm and a capacity of 300 kVA is disposed at a position near the meniscus on the long side of the mold with a distance L = 0 mm between the center of the mold and the immersion nozzle in the width direction of the mold. For the example in which the present invention was applied as T, the defect occurrence rate on the slab surface (the number of defect occurrence slabs / the total number of slabs × 100;%) was investigated, and the conventional example 1 was cast without electromagnetic stirring. Table 2 shows the results of comparison with Conventional Example 2 in which stirring was performed. According to Table 2, the defect occurrence rate in the slab width central portion in Conventional Example 1 and the slab corner portion in Conventional Example 2 was high, whereas the defect occurrence rate was 0% in any slab width portion in Examples. The effect is clear.

[0018]

[Table 2]

[0019]

As described above, according to the present invention, it is possible to completely prevent the occurrence of defects at the portion corresponding to the periphery of the immersion nozzle and the width end of the continuous cast slab, and to completely eliminate the defect care. The straightening of the rolling process is further promoted, and a remarkable improvement in productivity and energy saving can be achieved. Further, since the electromagnetic stirrer is provided only in a part of the mold width, there is an effect that the manufacturing cost and the operating cost are reduced to about 1/2 as compared with the conventional type in which the electromagnetic stirring device is provided over the entire mold width.

[Brief description of the drawings]

FIG. 1 is a plan view showing one embodiment of the present invention.

FIG. 2 is a plan view showing one embodiment of the present invention.

FIG. 3 is a graph showing a relationship between an apparatus width S of an electromagnetic stirring apparatus, a molten steel surface flow velocity, and a short-side swelling height index.

FIG. 4 is a graph showing a relationship between a component L in a longitudinal direction of a mold of a distance between centers of an immersion nozzle and an electromagnetic stirrer, a molten steel surface flow velocity, and a short-side rising height index.

FIG. 5A is a plan view showing a molten steel temperature measuring position in a mold;
(B) is a graph which shows the molten steel temperature distribution measured at the temperature measuring position of (a).

FIG. 6 is a schematic diagram showing a continuous casting facility.

FIG. 7 is a schematic view showing an example of molten steel flow in a mold.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ladle 2 Molten steel 3 Long nozzle 4 Tundish 5 Immersion nozzle 6 Mold 6A Mold long side 6B Mold short side 7 Cast piece 8 Guide roll 9 Pinch roll 10 Solidification shell 11 Mold powder 12 Electromagnetic stirring device (conventionally, the whole mold width) Arrangement) 13 Electromagnetic stirrer (in the present invention, arranged in a part of the mold width) a Bending part b Straightening part

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigenobu Takada 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref. (Without address) Inside Mizushima Works, Kawasaki Steel Corporation (72) Inventor Nobutaka Goto 1, Mizushima-Kawasaki-dori 1 Chome (without address) Mizushima Works, Kawasaki Steel Corporation (72) Inventor Koichi Tozawa 1-chome, Mizushima Kawasaki-dori, Kurashiki, Okayama Prefecture (without address) Mizushima Works, Kawasaki Steel Corporation (72) Inventor, Satoshi Nakajima Okayama Prefecture 1-chome, Kawasaki-dori, Mizushima, Kurashiki-shi (without address) Inside Mizushima Steel Works, Kawasaki Steel Co., Ltd. (72) Inventor Yuji Wakatsuki 1-chome, through-drink, Kawasaki-dori, Mizushima, Kurashiki-shi, Okayama Prefecture (without address) Inside Mizushima Works, Kawasaki Steel Corporation

Claims (2)

[Claims] In a continuous casting method using an immersion nozzle, a pair of electromagnetic stirrers having an apparatus width not less than the outer diameter of the immersion nozzle and not more than 0.3 times the length of the long side of the mold are provided, one for each of the long sides of the mold. A continuous casting method, wherein a distance between centers of an electromagnetic stirrer and an immersion nozzle in a mold width direction is set within 0.5 times the apparatus width, and molten steel is cast in one horizontal direction by electromagnetic stirring. 2. The method according to claim 1, wherein the pair of electromagnetic stirring devices are arranged point-symmetrically with respect to the center of the immersion nozzle.