JP3161109B2 - Continuous casting equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for continuously casting metal,
In particular, the present invention relates to a continuous casting apparatus for preventing center segregation of a slab-shaped cast piece.

[0002]

2. Description of the Related Art Conventionally, when a slab is manufactured by a continuous casting method, an internal defect called center segregation has often been a problem. This “center segregation” is a phenomenon in which molten steel components such as C, S, P, Si, and Mn are positively segregated at the center of the thickness of the slab, that is, at the final solidified portion. The center segregation is a particularly serious problem in a material for a thick plate, and is known to cause a decrease in toughness in a segregated portion and hydrogen-induced cracking.

It has been found that the center segregation occurs because the molten steel remaining between the dendrite trees at the end of solidification moves macroscopically due to bulging or solidification shrinkage, and the concentrated molten steel is locally accumulated. ing.

Therefore, as a countermeasure for preventing center segregation,
By rolling down the vicinity of the solidification tip in some way,
There is a method of compensating for the coagulation contraction of the terminal coagulation part, and methods based on various technical ideas have been proposed so far.

For example, Japanese Patent Application Laid-Open No. 63-252655 discloses a light reduction method using a group of light reduction rolls, and Japanese Patent Application Laid-Open No. 61-42460 discloses a large reduction method using at least one pair of reduction rolls. However, such a roll reduction method has a problem that the reduction amount cannot be so large because it can be reduced only in a point-like manner.

Japanese Unexamined Patent Publication No. 1-170566 discloses a large rolling method using a forging die, but the equipment cost is very high, and the large amount of rolling causes negative segregation at the center. There was a disadvantage that it was easy.

Further, the above-described method of improving the center segregation by the reduction is based on the case where there is uneven solidification in the width direction as shown in FIGS. 5 (a) and 5 (b) in both the roll reduction and the mold reduction. In other words, when the solidification progresses slowly at the width end (3/10 to 1 / 10W) compared to the width center (2/5 to 4 / 5W), and when segregation is observed, it is uniform in the width direction. There was a drawback that segregation deteriorated in the portion where the solidification was delayed due to the inability to perform a significant reduction. It is highly probable that the origin of the widthwise solidification non-uniformity occurs in the mold 2, and as shown in FIGS. 6A and 6B, the discharge flow of the molten metal 5 from the immersion nozzle 4 in the mold 2 , That is, 2/5 to 4 / 5W (W:
It is considered that solidification was delayed in portions other than the slab width). It is considered that the solidification unevenness is promoted by the unevenness in the width direction of the secondary cooling. Reference numeral 6 denotes powder, 7 denotes a solidified shell, 8 denotes a molten powder bath, and 9 denotes a solidified powder.

As other methods for improving center segregation, a method of applying electromagnetic stirring within a specific range as described in JP-A-63-157749, and a method described in JP-A-1-113157 are described. As described above, there is a method in which ultrasonic vibration is applied to a slab, but none of these methods has resulted in a fundamental solution when uneven solidification in the width direction is observed.

[0009]

It is known that reduction casting at the end of solidification is effective for improving center segregation in continuous cast slabs. However, reduction casting has a problem that, when uneven solidification in the width direction of the slab occurs, the effect of improving center segregation over the entire area in the width direction cannot be expected.

[0010] Here, an object of the present invention is to provide a continuous casting apparatus capable of eliminating uneven solidification in the width direction of a slab in order to effectively perform reduction casting for improving center segregation.

[0011]

SUMMARY OF THE INVENTION The present inventors have previously disclosed in Japanese Patent Application No. 4-24760 a method for eliminating solidification non-uniformity, in which only the solidified portion of the center of the width of the long side of the mold where solidification progresses rapidly is removed. A variant mold with a large mold thickness was proposed. However, even with this method, it is not easy to completely eliminate uneven solidification.

[0012] The present inventors, as a result of subsequent research and development,
The present invention has been completed with the idea of providing a kind of heating device around the mold as a means for eliminating uneven solidification in the width direction of the slab.

Therefore, the present invention relates to a continuous casting apparatus for casting a slab-shaped cast piece, wherein a portion within a central portion 2 / 5W to 4 / 5W (W: cast strip width) of a long side of a mold having a rectangular cross section is provided. A continuous casting apparatus characterized by having a structure provided with a coil for passing an alternating current circulating around a mold having a water cooling structure having a slit.

From another aspect, the present invention is a continuous casting apparatus for slab-shaped slabs, comprising a coil for supplying an alternating current around the water-cooled mold around the mold,
In addition, the center of the long side of the mold having a rectangular cross section is 2 / 5W to 4 / 5W (W:
The continuous casting apparatus is characterized in that the distance between the coil and the mold in a portion within (slab width) is smaller than the distance between the coil and the mold in other places.

According to still another aspect, the present invention is a slab-shaped continuous casting apparatus, comprising: a coil having a water-cooled structure surrounding a mold for supplying an alternating current surrounding the mold;
A continuous casting apparatus characterized in that a shielding plate made of a ferromagnetic material is arranged at a portion other than a central portion 2 / 5W to 4 / 5W (W: slab width) of a long side of a rectangular cross section.

[0016]

Next, the operation of the present invention will be described more specifically with reference to the accompanying drawings. The present invention, in order to effectively function the reduction casting for the center segregation improvement,
In order to eliminate uneven solidification in the width direction of the slab, it is a continuous casting apparatus provided with a solidification shell heating function described below at the center of the slab width, and its main parts are shown in FIGS. 1 (a) and 1 (b). As shown in Fig. 5, a rectangular mold 2 for a slab, such as a slab, and a plurality of energizing coils 3 are wound around the mold.
The long side of the mold is denoted by reference numeral 2 and the short side is denoted by reference numeral 2 '.
The molten metal 5 from the immersion nozzle 4 is shielded from the outside by an upper powder 6, and a solidified shell 7 is formed around the periphery thereof by heat removal from the mold wall. A molten powder bath 8 is formed at the boundary between the powder 6 and the molten metal 5, and the wall surface of the mold is covered with a solidified powder 9.

According to the first embodiment of the present invention, in order to eliminate uneven solidification, as shown in FIG. A slit 1 is provided in a portion within width (hereinafter the same))). In this device, when an alternating current is applied, the mold temperature rises due to the generation of Joule heat, slow cooling is realized, and the progress of solidification in the portion of the mold where the coil is provided is delayed. In the portion where the slit is provided in the mold 2, the influence of the current extends to the inner surface of the mold (the molten steel side), and further slow cooling is realized as compared with the portion without the slit.

Therefore, the central part of the width where solidification progresses quickly is 2/5.
If a slit 1 is provided only within ~ 4 / 5W and an electromagnetic force is applied to a current-carrying coil as a heating means, the temperature of the mold rises, so that it cools more slowly than the width end where no slit 1 is provided. , The solidification of the center of the width was delayed,
As shown in (b), the solidification progresses at the center of the width and at the end of the width are almost equal.

It should be noted that the present invention can eliminate uneven solidification on both sides of the top and bottom without worrying about the pass line of the continuous casting machine.
It has advantages over conventional continuous casting equipment with profiled molds that can only be applied to the top side.

Next, according to a second embodiment of the present invention, FIG.
As shown in the figure, the structure is basically composed of a rectangular mold 2 and a plurality of energizing coils 3 wound around the mold 2. In the case of this embodiment, the width central portion 2/5 to 4 / 5W coil 3 and the distance of the mold 2 l ₂ of coil 3 and the distance l ₁ is the other part of the mold 2 within
Has a smaller structure.

The reason for this is as in the case of the above-described embodiment.
Since the electromagnetic force is inversely proportional to the square of the distance between the coil and the mold,
This is because slow cooling in the center of the width is realized, and solidification progresses in the center of the width is slowed down as shown in FIG. 7 (a) → FIG. 7 (b), and uniform solidification in the width direction is realized.

Further, according to the third aspect of the present invention, as shown in FIG. 3, the rectangular mold 2 and a plurality of energizing coils 3 around the mold 2 have the structure described above. In the case of this embodiment, the width is 2/5 to
A magnetic field shield plate 10 made of a ferromagnetic material is arranged in a portion other than 4 / 5W, and since magnetic force is absorbed by the ferromagnetic material at the width end, gentle cooling by Joule heat is realized only in the center of the width. . That is, as shown in FIG. 7 (a) → FIG. 7 (b), the solidification progresses at the center of the width is slowed, and uniform solidification in the width direction is realized.

In the case of the second and third aspects of the present invention, as in the case of the first aspect, by providing a slit in the mold, the width center portion can be more effectively reduced. Uniform solidification in the width direction is achieved by slow cooling.

Thus, the slab obtained by the continuous casting apparatus according to the present invention is a slab that has been uniformly solidified in the width direction. Central segregation of the slab is more effectively prevented.

That is, according to the present invention, since the reduction is uniformly applied in the width direction, the flow of the concentrated molten steel is effectively suppressed, and the center segregation is improved in the entire width direction. Next, the operation and effect of the present invention will be specifically described with reference to examples.

[0026]

EXAMPLE In this example, slab-shaped slabs were continuously cast using the molds shown in FIGS. 1 to 3 and a continuous casting apparatus shown in FIG. In FIG. 4, the molten metal 5 cast from the immersion nozzle 4 into the mold 2 provided with the energizing coil 3 is solidified and drawn out by a conventional means via the support roll group 11, the pressing roll group 12, and the pinch roll 13. You.

The specifications and casting conditions of the apparatus used in this example are summarized below. (1) Continuous casting equipment: Bending type continuous casting machine (Bending radius: 12.5m) (2) Slab size: 250mm thickness x 2000mm width (slab shape) (3) Electricity coil: Outer diameter 30mm, wall thickness 2mm, winding number
3. Current effective value 20000A Frequency 20KHZ (4) Steel type: C 0.15 ~ 0.20% 40K steel for thick plate (5) Superheat degree of molten steel ΔT: 20 ° C, (6) Casting speed: 0.8m / min (7) Solidification End-stage rolling: Rolling zone length 5m, rolling gradient 1mm /
m Example 1 is based on the specifications (1) to (7) and the casting conditions described above.
The mold was constructed as shown in FIG. 1 (a) and continuously cast. The mold has 40 slits at the center of the width 800 mm, slit width 0.2 mm, length 150 mm
Met.

In Example 2, continuous casting was performed under the specifications and casting conditions (1) to (7) described above, with the mold portion having the structure shown in FIG. The distance between the mold and the slit was 5 mm at the center of the width and 10 mm at the other portions. In Example 3, continuous casting was performed under the specifications and casting conditions described in (1) to (7) above, with the mold portion having a structure as shown in FIG. A magnetic field shielding plate made of steel was attached to a portion other than the center of the mold width 800 mm.

Further, in all the examples of the present invention, as shown in FIG. 4, light reduction was performed by the reduction roll group 12 at the end of solidification. For comparison, an example in which similar casting was performed without applying an electromagnetic force is shown as a comparative example. Even in the case of the comparative example, the same light rolling at the end of coagulation was performed.
These results are summarized in Table 1.

[0030]

[Table 1]

As is clear from the results shown in Table 1, Example 1
In all of Examples 3 to 3, the center segregation at the end in the width direction was greatly improved as compared with the comparative example, and a slab having a uniform composition in the width direction could be produced. In addition, the average C segregation degree of the examples of the present invention was significantly improved as compared with the comparative example.

[0032]

According to the present invention, uneven solidification in the width direction of the slab is eliminated, light reduction at the end of solidification is performed uniformly in the width direction, center segregation at the width end is greatly improved, and It has become possible to produce a slab having a uniform composition.

[Brief description of the drawings]

FIG. 1 (a) shows a continuous casting apparatus 1 according to the present invention.
FIG. 1B is a schematic perspective view showing an example, and FIG.

FIG. 2 is an upper sectional view showing another example of the continuous casting apparatus according to the present invention.

FIG. 3 is an upper sectional view showing still another example of the continuous casting apparatus according to the present invention.

FIG. 4 is a schematic explanatory view showing a continuous casting operation using the continuous casting apparatus according to the present invention.

FIG. 5 shows a conceptual diagram of uneven solidification of a slab, and FIG.
Is a conceptual diagram during casting, and FIG. 5 (b) is a conceptual diagram of the center segregation state of the product slab.

6 is a conceptual diagram showing the cause of uneven solidification of the slab, FIG. 6 (a) is a schematic sectional view, and FIG. 6 (b) is a sectional view of the obtained slab.

7A and 7B are conceptual diagrams showing an improved state of uneven solidification when the present invention is applied. FIG. 7A shows a case where the present invention is not applied, and FIG. It is a conceptual diagram when coagulation was achieved.

[Explanation of symbols]

 Reference Signs List 1 slit 2 water-cooled copper mold (long side) 2 'water-cooled copper mold (short side) 3 energizing coil 4 immersion nozzle 5 molten metal 6 powder 7 solidified shell 8 molten powder bath 9 solidified powder 10 magnetic field shielding plate (ferromagnetic material) ) 11 Support roll group 12 Roll-down roll group 13 Pinch roll

Continuation of the front page (56) References JP-A-5-228583 (JP, A) JP-A-4-333351 (JP, A) JP-A-63-252644 (JP, A) JP-A-60-6254 (JP) JP-A-5-15949 (JP, A) JP-A-4-138843 (JP, A) JP-A-63-192543 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB (Name) B22D 11/04 311 B22D 11/055

Claims (3)

(57) [Claims] 1. A continuous casting apparatus for casting a slab-shaped cast piece, comprising a central part 2 / 5W to 4 / 5W (W:
A continuous casting apparatus characterized by having a structure provided with a coil for passing an alternating current surrounding the mold around a water-cooled structure having a slit in a portion within (slab width). 2. A continuous casting apparatus for casting a slab-shaped cast piece, comprising a coil for passing an alternating current around the water-cooled mold, and a long side of the rectangular cross-section mold. A continuous casting apparatus characterized in that a distance between a coil and a mold in a portion within a central portion of 2 / 5W to 4 / 5W (W: slab width) is smaller than a distance between a coil and a mold in other portions. 3. A continuous casting apparatus having a slab shape, comprising a coil for passing an alternating current around the mold having a water-cooled structure, and a central portion 2 / 5W on a long side of a rectangular cross section. A continuous casting apparatus characterized in that a ferromagnetic shielding plate is arranged in a portion other than ~ 4 / 5W (W: slab width).