JPH08206806A - Vertical type continuous casting method of large cross sectional cast bloom - Google Patents

Abstract

PURPOSE: To produce a large cross sectional cast bloom without causing bulging and cracking by specifying the relation between casting velocity and the length of long wall side and specifying the spraying rate of cooling water. CONSTITUTION: The rectangular large area cast bloom is produced by using a vertical type continuous casting apparatus and drawing out while cooling with cooling water from the lower part of a mold. In this case, when Vmm/min is denoted for the casting velocity and Lmm for the length of the long wall side in the cross section of the cast bloom, the relation of VL<=15×10<4> mm<2> /min is satisfied. Further, the spraying rate of cooling water in the range from just below the mold to [16V-the length in the vertical direction of the cast bloom (mm)] is made to be 1-100cm<3> /cm<2> .min and after this position, the spraying rate of cooling water is made to be below the above spraying rate and <=5 cm<3> /cm<2> .min to execute the operation. In this way, the large area cast bloom without causing bulging and cracking can be produced with simplified equipment construction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a thickness of 600 to 1, for example.
The present invention relates to a method for continuously manufacturing a large-section cast slab having a sectional size of 000 mm and a width of 700 to 3000 mm as continuously as possible.

[0002]

2. Description of the Related Art The widespread use of continuous casting operations in the steel manufacturing industry has greatly contributed to cost rationalization in terms of yield improvement, energy saving and labor saving. For these reasons, in recent years, it has been attempted to apply the continuous casting method even when casting a large-section cast slab, which has been conventionally considered difficult.

However, for example, a thickness of 1000 mm,
For large-section slabs each having a width exceeding 3000 mm, continuous casting is difficult due to dimensional constraints, and the actual situation is that the ordinary agglomeration method is still applied. On the other hand, for example, thickness 600 to 1000 mm, width 700 to 30
Attempts have also been made to apply the continuous casting method to large-section slabs having a size of 00 mm, but the addition of bending deformation such as in a curved continuous casting machine causes cracks to occur, and it is also necessary to improve the facility. Since it will be a large scale, a vertical casting machine (hereinafter referred to as "vertical semi-continuous casting machine" according to the popular name) is used to manufacture such large-section slabs as continuously as possible. Casting is the mainstream.

By the way, when casting a large cross-section slab,
Immediately after leaving the lower part of the mold, the slab, even after a certain amount of solidified shell is formed by the mold, the thickness of the solidified shell becomes extremely thin relative to the cross-sectional area of the slab,
The unsolidified region inside is extremely large. For this reason, there is a problem that bulging is likely to occur when manufacturing a large-section cast slab. Further, in the case of a large-section slab, there is a problem that the temperature difference between the surface of the slab and the inside becomes large, and thermal stress cracking easily occurs.

Various techniques have been proposed so far for solving the above-mentioned inconveniences that occur when casting a large-section slab. For example, in JP-A-58-187237, a vertical type semi-continuous casting apparatus is provided with a cooling mold and a slab supporting grid below the mold, and the side surface of the steel ingot is supported by the grid to the bottom of the steel ingot. It has been proposed to prevent bulging and reduce center porosity by progressively solidifying from the lower part of the steel ingot to the point of strong cooling. Further, Japanese Patent Laid-Open No. 63-33163 proposes a technique for reducing cracks by compressing and deforming a slab with a reduction device after completion of solidification. Furthermore, JP-A-6
No. 3-180351 proposes a technique in which a support frame and a mist nozzle that are operated by a cylinder are provided directly below a water-cooled mold, the side surface of the slab is cooled by the mist nozzle, and pressure is applied to the slab by the support frame. .

[0006]

However, each of the techniques proposed so far has a drawback that the device configuration becomes complicated and large, and the equipment cost increases. In particular, it is not possible to expect a sufficient investment effect for equipment that performs small-scale production on the scale of several thousand tons per month, such as large-section slabs, and it is expected that the equipment cost will be reduced with a simpler equipment structure. Has been done.

The present invention has been made in order to solve the technical problems in the prior art, and its purpose is to provide a large cross section without causing bulging or cracking even with a simpler equipment structure. It is an object of the present invention to provide a vertical continuous casting method capable of producing a slab.

[0008]

According to the method of the present invention which has achieved the above object, a vertical semi-continuous casting apparatus equipped with a mold for casting a large cross-section cast piece is used and cooled from below the mold with cooling water. When pulling out and casting a rectangular large-section cast slab, when the casting speed is V (mm / min) and the long side length of the cast slab is L (mm), VL ≦ 15 × 10 ⁴
While satisfying the relationship of (mm ² / min), the length (m in the vertical direction of the 16V-internal mold slab in the vertical direction (m
m)] to a water amount density of 1 to 10
0 cm ³ / cm ² · min, the water density after that is 5 cm ³ / cm ² · mi or less than the water density
It is a vertical continuous casting method for a large-section cast slab, which has the gist of operating as n.

As described above, the large-section cast slab of the present invention has a thickness of 600 to 1000 mm and a width of 700.
It is assumed that the diameter is up to 3000 mm, and according to the present invention, such a large-section cast piece can be efficiently manufactured. Furthermore, in the present invention, it is also effective to carry out the conventionally used hot top after the completion of casting.

[0010]

In order to achieve the above object, the present inventors examined the optimum conditions in the vertical continuous casting method from various angles. As a result, the casting speed V (mm / min) and the long side length L (mm) of the slab cross section were VL ≦ 15 × 10.
^If the relationship of ⁴ (mm ² / min) is satisfied and the water quantity density of the cooling water from directly below the mold is appropriately adjusted according to the cooling region, a large-section cast piece can be produced without bulging. The inventors have found what is possible and have completed the present invention.

FIG. 1 is a graph showing the influence of the casting speed V (mm / min) and the long side length L (mm) of the slab cross section on the occurrence of bulging. As you can see from this figure,
To prevent bulging, VL ≦ 15 × 10
^It can be seen that it is necessary to satisfy the relationship of ⁴ (mm ² / min).

Further, in the present invention, as described above, the length (m in the vertical direction of 16V-internal mold slab in the vertical direction (m
m)] to a water amount density of 1 to 10
It is necessary to set it to 0 cm ³ / cm ² · min. That is,
In the cooling region where the solidified shell becomes relatively thin, as in the range up to [16V-internal casting mold vertical direction length (mm)], the water density of the cooling water is 1 to 100 cm ³ / cm ² · m.
As in, it is necessary to perform strong cooling as much as possible so that cracking does not occur. This water density is 1 cm ³ / cm ²
If it is less than min, the relatively thin solidified shell cannot withstand the molten steel static pressure of the slab and bulging occurs. Further, when supercooled such that the water amount density exceeds 100 cm ³ / cm ² · min, the surface temperature of the slab becomes too low and cracks occur.

After the above range, the solidified shell is sufficiently grown, and bulging or cracking does not occur at a water amount density of 5 cm ³ / cm ² · min or less. However, if the water amount density at this time exceeds 5 cm ³ / cm ² · min, the thermal stress of the solidified shell becomes excessive and cracks are likely to occur. In addition, as described above, the water amount density should be 5 cm during the previous cooling.
^Although it may be ³ / cm ² · min or less, in such a case, the water density may be maintained as it is or may be decreased, and it is not necessary to intentionally increase the water density. Further, the means for cooling with cooling water is not particularly limited, and it goes without saying that mist spray cooling may be used in addition to normal spray cooling.

According to the method of the present invention, for example, the slab cross-sectional size is 700 mm × 1400 mm, and the length in the vertical direction of the mold is 4 mm.
In the case of 00 mm, the slab support mechanism is 500 m from directly below the mold.
About m is sufficient, and a large-scale slab supporting mechanism unlike the prior art is not required, and a high-quality slab can be obtained. Further, when a large cross-section slab is manufactured according to the conditions specified in the present invention, friction between the slab and the mold is significantly reduced, and the mold vibration mechanism that has been conventionally required is not necessary, thereby further increasing the equipment cost. There is also an advantage that it can be reduced.

When producing a large-section cast slab, the solidification time of the slab is long, and therefore, after the casting is completed, it is preferable that the slab head is kept warm (hot top) until the slab is completely solidified. As a result, shrinkage cavities in the head of the slab can be prevented, and a slab with good yield can be obtained. As a concrete procedure of such a hot top, for example, the following (1),
The method of (2) is mentioned.

(1) After the casting is completed, the water cooling is stopped and the slab is air-cooled, and the slab is quickly pushed up onto the mold by a predetermined length,
Enclose the top side of the slab with an adiabatic heat insulation frame, add immediate-acting heat-retaining agent and slow-acting heat-retaining agent in this order, or add self-fluxing flux to heat by energization Until the hot top.

(2) Immediately after the completion of casting, the slab is pushed up onto the mold by a predetermined length, and the heat insulating heat insulating frame surrounds the top surface of the slab to provide a fast-acting heat-retaining agent and a slow-acting heat-retaining agent. In this order, or by adding a self-fluxing flux, the mixture is heated by energization, and the slab is hot-topped until the solidification of the slab is completed while adjusting the surface temperature of the slab (for example, 400 ° C. or higher) by the amount of cooling water.

In carrying out the method of the present invention, a conventional vertical semi-continuous casting apparatus can be used, but the present inventors have previously proposed a useful construction of the vertical semi-continuous casting apparatus ( Japanese Patent Application No. 5-292262), this vertical type semi-continuous casting apparatus is more effective. The configuration of this vertical semi-continuous casting apparatus will be described with reference to the drawings.

FIG. 2 is a schematic explanatory view showing a constitutional example of a vertical type semi-continuous casting apparatus previously proposed by the present inventors, in which 1 is a mold, 2 is a foot roll (slab support roll), 5 is a wire, 7 is a carriage, 8 is a dummy head, 10 is a slab, 11 is a ladle, 13 is a dipping nozzle, and 14 is a pulley. Although not shown in FIG. 2, in this vertical type semi-continuous casting apparatus, a spray nozzle for ejecting cooling water for cooling the surface of the slab 10, a carriage guide for guiding the carriage 7 up and down, and a wire 5 are used. A drum shaft and the like for fixing both edges of the are provided.

In the vertical semi-continuous casting apparatus shown in FIG. 2, in short, the wire winch mechanism pulls up the carriage holding the dummy head to insert the dummy head and pull out the slab.
The wire winch mechanism is equipped with one system because the wire weight is loosened according to the casting speed by lowering the carriage's own weight to exceed the withdrawal resistance of the slab and is lowered along with the carriage guide guide by its own weight. It is sufficient to simplify the structure of the cast strip drawing apparatus.

The casting speed for producing a large-section slab is generally set slower than the casting speed for producing a normal slab from the viewpoint of preventing bulging. The invention may be followed. From such a viewpoint, the casting speed at the time of carrying out the present invention depends on the cross-sectional size (FIG. 1), but is 0.05 to 0.10 m /
About min (50 to 100 mm / min) is suitable.

The present invention will be described in more detail with reference to the following examples, but the following examples are not intended to limit the present invention, and any design changes made to the gist of the preceding and the following will be applied to the present invention. It is included in the technical scope.

[0023]

Example Using the vertical semi-continuous casting apparatus shown in FIG. 2, a slab having a cross-sectional size of 700 mm × 1400 mm was manufactured. At this time, 1 to 1300mm from directly under the mold
The water amount density was set to 0 cm ³ / cm ² · min, and thereafter, the water amount density was set to 1 cm ³ / cm ² · min.
Further, the vertical length of the mold is 400 mm (the vertical length of the slab is 300 mm in the mold), the foot roll is in the range from directly below the mold to 500 mm, and the casting speed is 0.07 m / min.
(100 mm / min). As a result, a good slab without bulging or cracking was obtained.

[0024]

The present invention is configured as described above, and it is possible to manufacture a large-section cast slab without causing bulging or cracking, and it can be realized by a more simplified equipment structure.

[Brief description of drawings]

FIG. 1 is a graph showing influences of a casting speed V (mm / min) and a long side length L (mm) of a slab cross section on occurrence of bulging.

FIG. 2 is a schematic explanatory view showing a configuration example of a vertical type semi-continuous casting apparatus previously proposed by the present inventors.

[Explanation of symbols]

 1 Mold 2 Foot Roll 5 Wire 7 Carriage 8 Dummy Head 10 Cast Piece 11 Ladle 13 Immersion Nozzle 14 Pulley

Claims (3)

[Claims] 1. When casting a rectangular large-section slab by using a vertical continuous casting apparatus equipped with a mold for casting a large-section slab and pulling it out from the lower part of the mold while cooling it with cooling water, When the speed is V (mm / min) and the long side length of the slab cross section is L (mm), VL ≦ 15 × 10 ⁴
While satisfying the relationship of (mm ² / min), the length (m in the vertical direction of the slab in the mold [16V−mold) was measured from directly below the mold.
m)] to a water amount density of 1 to 10
0 cm ³ / cm ² · min, the water density after that is 5 cm ³ / cm ² · mi or less than the water density
A vertical-type continuous casting method for a large-section cast slab, characterized in that the operation is performed at n or less. 2. The large-section slab has a thickness of 600 to 100.
The one having a width of 0 mm and the width of 700 to 3000 mm.
The vertical continuous casting method described in. 3. The vertical type continuous casting method according to claim 1, wherein a hot top is carried out after the casting is completed.