JP2000280053A - Continuous casting of thin casting piece - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a surface crack of a casting piece in a pressurized zone for prolonging a roll life by always maintaining a surface temperature of the casting piece in a pressurized zone at almost even with alternating comparative water volume in the pressurized zone according to a width ratio of a pressurized slab. SOLUTION: A pressurizing zone is provided at a curvature part of a continuous casting machine. In a case that a comparative water volume of a pressurizing zone before pressurization is set as Q0 (l/min), a comparative water volume at a pressurizing time and after the pressurization is completed as Q (l/min), a casting piece width before the pressurization as y0 (mm) and, a casting piece width at the time of pressurization as y, cooling water volume is adjusted in a range Q=a× (y/y0)×Q0, α=0.6-1.0 from the start of pressurization. Thus, cooling of the pressurized casting piece can be performed without a need of large cooling water, and also surface crack of the casting piece can be reduced to substantially 0. Since cooling water volume can be thus lessened, a casting piece temperature is secured normally at 900 deg.C or above and a deformation resistance of the casting piece is reduced, resulting in a prolongation of the roll life.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously casting thin slabs, and more particularly to a method for continuously casting thin slabs in which unsolidification rolling is performed.

[0002]

2. Description of the Related Art In a typical casting method for a thin plate, a slab obtained by continuous casting is once cooled and then rolled in a rolling step. This method requires reheating when hot-rolling the air-cooled slab after continuous casting, which is disadvantageous in terms of cost of energy used.

[0003] In recent years, a hot-rolling direct-coupling process for supplying a slab from a continuous casting machine to a rolling mill at a high temperature as it is has been developed. Efforts have been made to develop a continuous casting technique for thin slabs in which the rolling process can be omitted.

[0004] As a method of producing a thin slab by continuous casting, a slab continuously drawn from a mold is further reduced while being rolled down by a plurality of reduction roll pairs while an unsolidified phase remains in the center. There is a method of cooling into a thin slab. This is a so-called unsolidification rolling method.

[0005] Many inventions have already been proposed in the non-solidification rolling method even in the past. For example, with respect to the rolling method, JP-A-6-182515, JP-A-7-68
No. 359, JP-A-8-47758, JP-A-8-52552
And Japanese Patent Laid-Open No. 2-2
No. 07953, Japanese Unexamined Patent Application Publication No. 8-215815, etc. have proposed respective remedies.

[0006]

However, in the course of subsequent research and development, such a conventional technique tends to cause cracks on the surface of the slab in the rolling zone,
It was found that defects such as short roll life were observed.

Therefore, an object of the present invention is to prevent the surface of a slab from cracking in a rolling zone in a non-solidification rolling method,
Another object of the present invention is to develop a technology that can extend the life of the roll.

[0008]

Here, as a result of various studies and studies made by the present inventors, such disadvantages are found in the prior art in the control of the cooling water in the reduction zone. I knew it wasn't going.

Certainly, even in the prior art, for example,
-90187 and JP-A-8-90182,
Although the specific water content of the entire continuous casting machine is disclosed, there is no disclosure as to the importance of cooling during or after the completion of the reduction in the reduction zone, that is, the secondary cooling, and the cooling water conditions.

For example, Japanese Patent Application Laid-Open No. 8-90187 discloses an invention of a method and an apparatus for continuous casting of thin slabs. 70-150 mm, slab support roll and reduction roll roll pitch 100-250 mm, casting speed 2.5
~ 6m / min, secondary cooling specific water volume 1.5 ~ 4.5 l / kg ・ steel
And teach you that. However, in this case, only the specific water volume of the entire continuous casting machine is specified, but the appropriate secondary cooling water conditions during and after the reduction in the reduction zone are not described.

According to the findings of the present inventors, when the thickness of the slab is gradually reduced in the reduction zone, the thickness of the unsolidified phase becomes smaller than before the reduction, so that the cooling condition is reduced. , The solidification proceeds rapidly and the slab temperature decreases. This is more pronounced as the amount of reduction is greater and as the reduction zone is closer to the mold. Therefore, the specific water volume at the time of rolling in the rolling zone must be gradually reduced because there is a possibility that slab surface quality defects may occur or operational troubles may occur.

In the continuous casting method of a wide thin cast slab disclosed in Japanese Patent Application Laid-Open No. Hei 8-90182, unsolidification reduction is performed in a roller apron having a fixed arc arrangement, and the short side is reduced in the reduction zone. It is taught that the reduction is completed at a temperature where the slab temperature within 100 mm does not fall below 900 ° C. Further, Japanese Patent Application Laid-Open No. 6-297125 describes a method of reducing the pressure while performing cooling control so that the slab temperature becomes 500 to 650 ° C.

[0013] However, in these methods, the reason for securing a high temperature at the time of rolling is to perform rolling in a non-brittle zone,
Further, it is for promoting the coarsening of carbonitrides to prevent surface cracks, and does not describe appropriate secondary cooling water conditions during and after the reduction. In the rolling zone, when cooling at the same specific water volume during rolling or after the completion of rolling and before the start of unsolidified rolling, the solution of the problem that the slab temperature decreases and cracks easily occur on the slab surface in the rolling zone No suggestion is made.

Further, in the prior art, the slab temperature at the time of rolling is too low, the slab deformation resistance increases, the roll in the rolling zone is significantly burdened, and the roll life is shortened. No solution provided.
In addition, the same applies to a problem that when a slab is used for direct rolling, a huge energy loss occurs in a hot-rolling heating furnace.

Japanese Patent Application Laid-Open No. Hei 10-272545 discloses that, before a reduction zone, a scale is removed after removing the surface scale of a slab using a descaling device, and a reduction is performed without performing the descaling. A method is described in which the specific water volume is reduced and the temperature of the output from the machine is kept constant. In the case of this method, since the descaling device is used before the reduction, the slab temperature during the reduction is reduced by about 300 ° C. as compared with a normal case. Therefore, the deformation resistance of the slab at the time of reduction becomes too large, and a robust reduction device is required to reduce to a predetermined target thickness, and enormous equipment costs are required.

In order to prevent such a problem by changing the condition of the secondary cooling water, a method of extremely reducing the specific water amount in the reduction zone can be considered. It takes a long time to expect the above-mentioned recuperation, and it passes through the reduction zone before the recuperation is realized, so that there is almost no effect. In addition, it is difficult to keep the slab temperature in the rolling zone constant, and there is a disadvantage that surface quality defects such as lateral cracks are easily generated newly. Also, this publication, similarly to the above publication, only specifies a decrease in the specific water volume of the entire machine, but does not describe the appropriate secondary cooling water conditions in the rolling zone during and after the rolling is completed.

Accordingly, the present invention relates to an unsolidified rolling continuous casting method for producing a thin cast by rolling down a cast slab having an unsolidified phase in a rolling zone, wherein the slab thickness ratio is reduced. By changing the specific water amount of the rolling zone in accordance with the conditions, the surface temperature of the slab of the rolling zone is always kept almost constant to reduce the surface defects of the unsolidified rolling slab, This is a method for extending the life and preventing troubles in drawing slabs.

From another aspect, the present invention is directed to reducing the thickness of a slab drawn from the mold of a continuous caster by rolling the slab in a reduction zone during a period having an unsolidified phase. An unsolidified rolling continuous casting method for producing thin cast slabs, in which a rolling zone is provided in a curved portion of a continuous casting machine, the specific water volume of the rolling zone before rolling is reduced to Q ₀ (l / min), rolling is completed, and rolling is completed. Q (l / min) the ratio amount of water after the reduction before the slab thickness y ₀ (m
m), assuming that the thickness of the slab at the time of rolling is y, the cooling water amount is adjusted within the range of Q = α × (y / y ₀ ) × Q ₀ and α = 0.6 to 1.0 from the start of rolling. This is a continuous casting method for thin cast pieces.

[0019] The reduction zone is usually composed of a plurality of reduction segments, and therefore the invention further provides, in a further aspect, a slab drawn from the mold of a continuous casting machine.
An unsolidified rolling continuous casting method for producing a thin cast by reducing the thickness of the slab by rolling down in a rolling zone during a period having an unsolidified phase. A reduction zone consisting of a reduction segment is provided, and the specific water volume of the reduction segment before reduction in the i-th reduction segment is Q _0i (l / min), and the specific water volume of the i-th reduction segment at the time of reduction and after completion of the reduction is Q _i (l / min), when the thickness of the slab before rolling is y _0i (mm) and the thickness of the slab after rolling is y _i (where 1 ≦ i ≦ n), the rolling starts in the i-th rolling segment From Q _i = α × (y _i / y _0i ) × Q
_0i , α = 0.6 to 1.0 This is a continuous casting method for a thin cast piece characterized by adjusting the specific water amount in the i-th rolling segment during rolling in the range of 0.6 to 1.0.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic explanatory view showing a basic configuration of a continuous casting machine (hereinafter referred to as a machine) which is desirable for carrying out the method of the present invention.

In the figure, the machine comprises a mold 1, a roller apron zone 2, and a pinch roll zone 3. The type of the machine may be any of a normal curved type and a VB type. The roller apron belt 2 is composed of a group of rolls 4, a part of which is a group of drive rolls 4 '. Roller apron belt 2
Inside, an unsolidified rolling zone comprising a plurality of segments (seg) 6 provided with a rolling cylinder 5 on a roll 4 and / or a driving roll 4 ′ for rolling down the unsolidified slab 11 into a thin slab 12. 7 are provided.

The unsolidified rolling reduction zone 7 in the roller apron zone 2 is composed of a total of about 5 segments as shown in the drawing, and is preferably provided between the meniscus 10 of the molten steel 9 in the mold 1 and a length of about 8 m. . The pinch roll band 3 is a normal one comprising a group of pinch rolls 8 provided downstream of the roller apron band 2.

In FIG. 1, the cooling water spray is omitted for the sake of clarity. In particular, in the reduction zone 7, the cooling water spray is provided before and after each of the reduction rolls of each segment 6. The installation location, number, etc. of the cooling water spray in the present invention may be conventional ones, and are not particularly limited in the present invention, so the following description is omitted.

The mold size is about 80 to 150 mm in thickness, and
It is about 1000-1800mm. This is 50 ~
The target thickness is 100 mm. Therefore, in the above machine, it is desirable that the unsolidified rolling pattern has a rolling amount of about 2 to 10 mm per segment. The desirable range of the casting speed in the steady state is 2.0 to 5.0 m / min.
Casting of min or more can be easily performed.

Although the reduction of the specific water amount in the reduction zone of the present invention can be carried out in the middle of the reduction, it is most preferable to carry out the reduction simultaneously with the start of the uncoagulation reduction. that is,
This is because there is no cast slab having a low surface temperature.

Here, the specific water volume in the reduction zone is defined as follows. Specific water volume in reduction zone (1 / Kg-steel) = Water volume in reduction zone
(1 / min) / Amount of molten steel per unit time (Kg / min) Here, according to the present invention, the specific water amount in each of the rolling segments is adjusted according to the thickness ratio of the slab to be reduced in each of the rolling segments. Then, the slab surface temperature is made as uniform as possible. Specifically, when the specific water amount in one reduction segment is determined in this way, the flow rate of the water spray upstream or downstream of each of the plurality of reduction rolls provided therein is set as a whole in the segment. The water is divided and supplied so as to satisfy the specific water volume. Usually, since the amount of reduction of each reduction roll in one reduction segment is the same, the division of the specific water amount in the reduction segment is equally divided.

Next, according to the present invention, the specific water amount Q = α × (y / y ₀ ) × Q ₀ in the reduction zone is reduced, and the coefficient of α is set to 0.
The reason for setting the value to 6 to 1.0 will be described. After reduction completed to change the ratio amount of water even to the substantially same cast slab surface temperature, the slab thickness before and after reduction When y _0, y, a reduction ratio, i.e. (y / y ₀₎ Therefore, since the surface temperature of the slab decreases, the cooling condition must be relaxed accordingly.
That is, the specific water amount is (y / y ₀ ) with respect to the specific water amount Q _O before reduction.
Is reduced in accordance with the ratio.

At this time, the factor α is considered as the closer the rolling zone is to the mold, the more the solidification progresses due to the rolling. If the specific water content is determined only by the ratio of the slab thickness, the slab surface temperature becomes excessively low. It is because it becomes. The value of α is most preferably 0.6 to 0.8 when the rolling zone is within 5 m from the mold, and 0.8 to 1.0 when the rolling zone is 5 m or more.
If α ≦ 0.5, the surface temperature of the slab is too high, so that the scale is increased and there is a risk of slab pulling out and bulging in the machine. When α ≧ 1.1, the above-described problem due to a decrease in the slab temperature occurs. Therefore, the α value is most preferably in the range of 0.6 to 1.0.

Here, since the reduction zone is usually composed of a plurality of reduction segments, the determination of the specific water volume in the above-described reduction zone needs to be similarly performed in each of the reduction segments constituting the reduction zone. Thus, in such a case, the invention is described as follows.

That is, the present invention reduces the thickness of a slab drawn from the mold of a continuous casting machine in a rolling zone during a period having an unsolidified phase, thereby reducing the thickness of the slab to form a thin slab. An unsolidified rolling continuous casting method to be manufactured, wherein a rolling zone composed of n rolling segments is provided in a curved portion of a continuous casting machine, and a specific water volume of a _rolling segment before rolling in an i-th rolling segment is Q _0i (l / min), the specific water volume at the time of reduction and after completion of the i-th reduction segment is Q _i (l / min), the slab thickness before reduction is y _0i (mm), and the slab thickness at the time of reduction is y _{If i} (where 1 ≦ i ≦
n), Q _i from the start of reduction in the ith reduction segment
= Α × (y _i / y _0i ) × Q _0i , wherein α = 0.6 to 1.0. It is.

FIG. 2 is an explanatory diagram of an example of the arrangement of the segments S _{1 to} S ₅ constituting the reduction zone 7 and the water spray W provided thereon. When the specific water amount in the i-th segment Si is obtained as described above, the water spray is divided equally into water sprays W ₁ , W ₂ and W ₃ .

Since the water sprays between the segments overlap, one of them can be omitted as shown in the figure. In that case, the specific water amount of the water spray between the segments is preferably controlled as belonging to the downstream segment.

Thus, according to the present invention, a large amount of cooling water of 1.5 to 4.5 l / kg · steel is not required unlike the prior art, and the total amount of the reduction zone is, for example, 1.5 to 1.5 l / kg · steel.
The slab can be cooled with a specific water volume of less than l / kg · steel, usually less than 1.0 l / kg · steel, and the surface cracks can be practically zero (crack occurrence rate 0.05% or less). You can. Of course, since the specific water amount can be reduced in this manner, the slab temperature can be normally maintained at 900 ° C. or higher, and the slab deformation resistance is reduced, which leads to the extension of the roll life.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Carbon content using a curved machine shown in FIG.
0.10% medium carbon steel was cast at a steady casting speed of 5.0 m / min. The mold size was 100 mm in thickness and 1500 mm in width. Using this, unsolidification rolling operation was performed to the target thin slab size of 80 mm and 60 mm in thickness.

The rolling zone in the machine is provided between the first segment and the fifth segment of the roller apron belt, which is 3 m below the mold, and has a length of 5 m (each segment length is 1 m).
m) The amount of reduction was 4 and 8 mm uniform thickness per segment.

As examples of the present invention, when the specific water amount of each segment of the reduction zone is reduced according to the reduction thickness, and when the specific water amount of the reduction zone is not changed as Comparative Example 1, the present invention is referred to as Comparative Examples 2 and 3. The cases where the casting was performed under the conditions deviating from the above are shown.

Comparative Example 4 is a case in which the descaling is performed after descaling with high-pressure water before the rolling zone. The specific water volume of each reduction segment before the reduction was 0.2 l / kg-steel, and the specific water volume gradually decreased from the start of the reduction.

In order to confirm the effects of the present invention, a thermocouple of a slab was attached from the mold exit side, and the temperature history of the slab surface was measured. The scale thickness of the slab and the load force of pulling out the drive roll in the machine were measured. In addition, the surface quality of the slab was investigated, and the number of cracks generated per 10 m of the slab and the coil failure rate of the slab were compared. The results are shown together in Tables 1 and 2 and FIGS. 2 and 3 together with the specific water amount (calculated value in the present invention) of each segment.

In Comparative Examples 1 and 3 (when α = 1.1), the surface temperature of the slab was 300 to 50 in the reduction zone.
The temperature decreased by about 0 ° C., and the number of cracks generated and the coil defect rate deteriorated. In the case of Comparative Example 2 (α = 0.5), the slab surface temperature increased by about 150 to 200 ° C. in the reduction zone, and the drive roll pulling force increased about twice as the slab scale thickness increased.

In the case of Comparative Example 4, although the slab surface temperature dropped by 300 ° C. or more before the rolling zone and reheated in the rolling zone, the number of slab cracks increased and the coil defect rate deteriorated. .

In the example of the present invention, the slab temperature was almost constant in the rolling zone, and the best results were obtained in both the number of cracks generated and the defective coil rate. In addition, as a result, the roll life was 120 to 100% when Comparative Example 1 was 100 (%), for example.
The improvement effect is remarkable.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

As described above, according to the present invention, the surface temperature of the slab in the rolling zone can be kept almost constant, so that the surface defects of the unsolidified rolling slab can be reduced, and the roll in the rolling zone can be reduced. , And the trouble of drawing slabs can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a continuous casting machine for carrying out the present invention.

FIG. 2 is an explanatory diagram of an arrangement of a cooling spray in each segment constituting a reduction zone.

FIG. 3 is a graph showing the history of the slab surface temperature when the slab thickness is changed from 100 mm to 80 mm.

FIG. 4 is a graph showing the history of the slab surface temperature when the slab thickness is changed from 100 mm to 60 mm.

Continued on the front page (72) Inventor Masafumi Hanao 4-33, Kitahama, Chuo-ku, Osaka City Inside Sumitomo Metal Industries Co., Ltd. (72) Toshihiko Murakami 4-33, Kitahama, Chuo-ku, Osaka City Sumitomo Gold (72) Inventor Masahiko Oka 4-5-33 Kitahama, Chuo-ku, Osaka-shi Sumitomo Metal Industries Co., Ltd. (72) Inventor Masahiro Ikeda 5-2 Sokai-cho, Niihama-shi, Ehime Sumitomo Heavy Industries, Ltd. F-term (reference) in Niihama Works 4E004 KA14 MC02

Claims (2)

[Claims] 1. A method of producing a thin cast piece by reducing the thickness of a cast piece drawn from a mold of a continuous casting machine in a rolling zone during a period having an unsolidified phase to reduce the thickness of the cast piece. A rolling continuous casting method, wherein a rolling zone is provided in a curved portion of a continuous casting machine, and a specific water amount of the rolling zone before rolling is set to Q
₀ (l / min), the specific water volume at the time of rolling down is Q (l / min), the thickness of the slab before rolling is y ₀ (mm), and the thickness of the slab at the time of rolling is y. α × (y / y ₀ ) × Q ₀ , α = 0.6 to 1.0
A continuous casting method for thin cast slabs, wherein the specific water amount in the rolling zone during rolling is adjusted within the range of (1). 2. A method for producing a thin cast piece by reducing the thickness of a cast piece drawn from a mold of a continuous casting machine in a rolling zone during a period having an unsolidified phase to reduce the thickness of the cast piece. A rolling continuous casting method, wherein a rolling zone composed of n rolling segments is provided in a curved portion of a continuous casting machine, and a specific water amount of a _rolling segment before rolling in an i-th rolling segment is Q _0i (l / min), When the specific water volume after the reduction in this i-th reduction segment is Q _i (l / min), the slab thickness before the reduction is y _0i (mm), and the slab thickness after the reduction is y _i ( 1 ≦ i ≦ n), Q _i = α × (y _i / y _0i ) × from the start of the reduction in the i-th reduction segment
Q _0i , α = 0.6 to 1.0 A continuous casting method of a thin slab, wherein the specific water amount in the i-th rolling segment during rolling is adjusted.