JPH07284897A - Continuous casting method and its apparatus - Google Patents

Abstract

PURPOSE:To prevent the internal defect of segregation and center crack, and the corner crack caused by bulging even at the time of high speed casting. CONSTITUTION:In a continuous casting method for slab for drawing a cast slab from the lower part of a mold after pouring molten steel 5 into the mold 2, at least one pair or more in the rear part or all guide roll pairs among plural guide roll pairs 9 supporting the long sides of the cast slab at the position corresponding to unsolidified zone in the cast slab below the mold are supported in contact with the cast slab by length shorter than the length of the long side of the cast slab. By this method, the corner crack caused by the bulging, the inner defect of the center segregation and center crack, etc., are prevented and the sound cast slab having good quality can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting method in continuous casting, and more particularly to a continuous casting method and apparatus for controlling solidification when casting a rectangular cross-section slab.

[0002]

2. Description of the Related Art A continuous casting machine has one of the functions of a continuous casting machine to solidify molten steel into a target size and shape.
Therefore, the continuous casting machine is generally composed of a mold, a slab guide, and a secondary cooling facility for the purpose of restraining the solidified shell and controlling its shape at the same time as forming the solidified shell on the outer periphery of the molten steel.

When casting molten steel in a continuous casting machine,
Molten steel solidifies from the outer periphery, and the solidified shell retains the unsolidified molten steel inside the slab, but the solidified shell deforms under the static pressure of the molten steel (so-called bulging), and the bulging amount is It tends to increase when the width is large, the solidified shell thickness is small, and the slab temperature in the secondary cooling zone is high.

The narrow slab and the short side of the slab have a shape effect that the bulging of the solidified shell is restrained by the corner portion of the slab, and the bulging of the long side or the short side is suppressed.

Therefore, in the case of casting a slab called a bloom or billet having a cast side width of 0.7 m or less, or even in a continuous casting machine for a slab having a slab with a slab width of 0.7 m or more,
There is little bulging on the short side of the slab (usually 0.2 m to 0.35 m thickness), and in general, a few slab guides are installed directly under the mold, and thereafter no slab guide is installed between the solidification completion points. .

However, in the case of a continuous casting machine for slabs having a width of 0.7 m or more, which exceeds the range of blooms and billets, the bulging generated on the long side of the slab cannot be expected to be restrained by the corner portion of the slab, and the bulging is suppressed. In order to control the shape of the slab, a slab guide is installed in the range from just below the mold to the completion of solidification of the slab.

Further, when casting is performed in a continuous casting facility having a slab guide between just below the mold and the solidification completion point, such as a continuous casting machine for slabs, especially in terms of quality of slabs used for thick plates, steel pipes, etc. One of the problems is the internal defects such as center segregation and center cracking.

The occurrence of this internal defect has a close relationship with the bulging of the slab and a guide roll installed to support the slab from immediately below the mold to between the solidification completion points. When the solidified shell bulges at the stage where the solidified shell has grown, and then the solidified shell is corrected, the opposed solidified shells contact each other and the concentrated molten steel is confined in the center of the slab.

During the process in which the contained molten steel solidifies and contracts, it absorbs the concentrated molten steel near the solidification interface, causing segregation of the center,
This causes internal defects such as central cracking.

[0010]

As a means for preventing center segregation, a method of reducing the vicinity of the solidification completion point as represented by Japanese Utility Model Laid-Open No. 1-100661 has been conventionally adopted. Since the point moves up and down in the casting direction depending on the casting speed and the cooling method, it is very difficult to accurately reduce the solidification completion point, which is complicated in terms of equipment and operation.

In order to solve these problems in the conventional continuous casting process and to propose a simpler apparatus, the present inventors have previously shown in FIG. 1 in the invention of Japanese Patent Application No. 5-127408. A casting method has been proposed in which the slab guide 3 after having the required shell strength is opened to prevent center segregation.

However, at low casting draw rates,
The distance from the start of solidification to the completion of solidification is short, and the solidification shell in the casting direction has a large rigidity and is very effective compared to the solidification shell in the width direction.However, as the casting speed increases and the surface temperature increases, the shell rigidity increases. Since the amount of bulging increases due to the decrease, cracks 8 occur at the corners of the slab shown in Fig. 2, so it is necessary to install a slab guide near the solidification completion point. The problem of internal defects such as cracks could not be solved.

The present invention solves the above-mentioned problems in the prior art, prevents internal defects such as center segregation and center cracking even during high speed casting, and further prevents corner cracking due to bulging and its apparatus. I will provide a.

[0014]

[Means for Solving the Problems]

(1) According to the method of the present invention, in a continuous casting method of a slab in which molten steel is injected into a mold and a cast piece is pulled out from the lower side of the mold, the long side of the cast piece at a position corresponding to the non-solidified area of the cast piece under the mold is set. Out of a plurality of slab guide rolls to be supported, at least one pair behind or all slab guide rolls are continuously cast by contacting and supporting the slab with a length shorter than the long side length of the slab. Is a continuous casting method.

(2) Further, in the continuous casting method of the above item (1), it is a continuous casting method in which the slab is brought into contact with and supported by a slab guide roll shorter than the long side length of the slab.

(3) The continuous casting method according to the above (1) or (2) is a continuous casting method in which the contact support length between the slab guide and the slab is shorter than the width of the unsolidified zone.

(4) In the apparatus of the present invention, molten steel is poured into the mold, the cast piece is pulled out from the lower side of the mold, and the long side of the cast piece at the position corresponding to the non-solidified area of the cast piece under the mold is a cast guide roll. In a continuous casting device supported by, at least a pair of rear of the slab guide rolls, or all the slab guide rolls are configured by a single roll whose length is shorter than the long side length of the slab. It is a continuous casting device.

(5) Further, in the continuous casting apparatus of the above item (4), the length of each of the slab guides is shorter than the width of the non-solidified zone.

[0019]

The operation of the present invention will be described in detail below with reference to FIGS. 3 (a) and 3 (b) showing the structure of the present invention.

First, the molten steel injected into the mold 2 from the immersion nozzle 1 holds the solidified shell 6 by the mold 2 and the slab guide roll 3, and the spray 4 completes the solidification while cooling the surface of the slab.

In the present invention, the slab guide roll 3 is
Generally, the slab is held at the same interval as the lower end dimension of the mold 2 and over the entire width of the slab, but the solidified shell 6 causes the bulging by the molten steel 5 in the solidified shell to a width narrower than the width of the slab. With the same effect as restraint of the slab corners such as bloom by restraining, it grows to a solidified shell thickness capable of suppressing corner cracking due to bulging, and thereafter, between the solidification completion points, a width narrower than the slab width and also an unsolidified width. Only the narrower width is supported by the slab guide 9 (hereinafter referred to as bulging guide), and the unsolidified portion which is not supported in the width direction holds the molten steel by the solidified shell and completes solidification.

The unsolidified portion in the width direction of the slab can be calculated by the following equation (1).

[0023]

## EQU1 ## W = W ₀ -2k√t (1) where W: unsolidified width (mm) W ₀ : slab width (mm) k: solidification coefficient (generally, depending on cooling conditions Two
5-28) t: Arrival time (minutes) from the mold surface

By supporting the slab with this bulging guide 9, the amount of bulging can be greatly reduced, so that corner cracking due to bulging of the slab can be prevented, and at the same time, it is caused by the correction of the bulging solidified shell. It is possible to prevent the contained molten steel from being contained and further prevent the center segregation caused by the solidification shrinkage of the contained molten steel.

The reason why the slab guide of the full width of the slab is required in the initial stage of casting is that the bulging guide 9 is discontinuous in the casting direction, unlike the constraint by the slab corner portion of the bloom, This is because the effect of bulging between rolls is added and cracks may occur at the corners of the slab.

Further, here, since the bulging of the slab is guided only to the extent that corner cracking does not occur, complicated equipment and operation for reducing with a slab guide roll are not required.

[0027]

EXAMPLE A continuous casting method according to the present invention is shown in FIG.
Casting was performed according to the configuration shown in (b).

1, casting conditions, (1) casting size, slab width: 160 cm, slab thickness: 35 cm, (2) casting speed, 0.5 m / min, (3) slab surface temperature, 800 ° C., (4) ) Mold length: 100 cm, mold effective length (L0): 90 cm, (5) slab guide full width slab guide area (L1): 1200
cm, (6) Area of bulging guide shorter than unsolidified width of cast slab (L2): 800 cm, bulging guide length: (upper) 60 cm, (lower) 20 c
m,

2. As a result of the casting experiment, the entire region L1 + L2 (2000c) of the cast slab in the casting direction
The center segregation that occurs when m) is cast only with the slab guide rolls can be eliminated by using the bulging guide 9 during the casting, and the maximum bulging amount on one side can be suppressed to 10 mm or less. It was possible to cast a slab with no internal defects such as cracks and corner cracks.

On the other hand, as Comparative Example 1, when the guide rolls having the full width were provided in the L2 region as well, center segregation occurred. Further, as Comparative Example 2, when no guide roll was provided in the L2 region, corner cracking occurred.

[0031]

As described above, according to the apparatus and casting method of the present invention, the bulging amount can be greatly reduced by supporting the slab with the bulging guide.
It is possible to prevent internal defects such as corner cracks due to bulging, and to prevent defects such as center segregation and center cracks due to confinement of concentrated molten steel even when the casting speed is fast and the slab surface temperature is high. It is possible to manufacture pieces.

[Brief description of drawings]

FIG. 1 shows a configuration example of conventional slab continuous casting, (a)
The figure is a side sectional view and the figure (b) is a front view.

FIG. 2 is a cross-sectional view showing a state of corner cracking due to bulging of a slab cross section.

FIG. 3 shows a structural example of slab continuous casting according to the present invention, in which (a) is a side sectional view and (b) is a front view.

[Explanation of symbols]

1 Immersion Nozzle 2 Mold 3 Cast Piece Guide Roll 4 Spray 5 Molten Steel 6 Solidified Shell 7 Cast Piece Placement 8 Corner Crack 9 Bulging Guide L0 Effective Mold Length L1 Range of Restraining the Entire Width of the Cast Piece by the Mold and the Cast Guide Roll L2 Range in which only the narrower width than the unsolidified width is supported by the slab guide roll

Claims (5)

[Claims] 1. In a continuous casting method of a slab in which molten steel is poured into a mold and a cast piece is pulled out from the lower side of the mold, a plurality of pieces supporting a long side of the cast piece at a position corresponding to a non-solidified area of the cast piece under the mold are supported. Among the slab guide rolls, at least one pair of slab guide rolls or all slab guide rolls at the rear are contact-supported with the slab by a length shorter than the long side length of the slab for continuous casting. Continuous casting method. 2. The slab is brought into contact with and supported by a slab guide roll that is shorter than the long side length of the slab.
The continuous casting method described. 3. The continuous casting method according to claim 1 or 2, wherein the contact supporting length between the slab guide and the slab is shorter than the width of the non-solidified zone for continuous casting. 4. A continuous casting apparatus in which molten steel is poured into a mold, a slab is pulled out from below the mold, and a long side of the slab at a position corresponding to the slab unsolidified region below the mold is supported by a slab guide roll. A continuous casting apparatus, characterized in that at least a pair of rear of the slab guide rolls or all of the slab guide rolls are constituted by a single roll whose length is shorter than the long side length of the slab. 5. The continuous casting apparatus according to claim 4, wherein the length of each of the slab guides is made shorter than the width of the unsolidified region.