JP2004283849A - Method for producing continuously cast slab - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To cast a slab while controlling the conditions so that a crater end shape in the width direction of the cast slab becomes a target state by grasping the crater end varying in the width direction of the cast slab. <P>SOLUTION: When the slab is continuously cast by using a continuous caster 1 provided with a low rolling-reduction zone 11 for applying low rolling-reduction to the cast slab 14, the position of the crater end 17 is detected by allowing transverse wave of magnetic ultrasonic wave sent from a sensor 12 to pass through the cast slab. The extent of light rolling-reduction in the light rolling-reduction zone is changed according to the difference between the detected shortest crater end position and the detected longest crater end position, and thus this difference between the shortest crater end position and the longest crater end position is reduced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００５０】
先ず、最初に軽圧下帯における軽圧下量を０．４ｍｍ／ｍとして鋳造した。このときの最長クレータエンド位置はメニスカスから３０．８ｍの位置、最短クレータエンド位置はメニスカスから２８．２ｍの位置であり、クレータエンド山谷差は２．６ｍであった。この場合の偏析度（Ｃ_ｍａｘ ／Ｃ_０ ）は１．３３であり、高い値となった。
【００５１】
そこで、軽圧下量を０．９ｍｍ／ｍに変更し、その他の鋳造条件は同一のまま鋳造を続けた。その結果、最長クレータエンド位置はメニスカスから２９．４ｍ位置、最短クレータエンド位置はメニスカスから２８．３ｍ位置となり、クレータエンド山谷差が１．１ｍとなって、軽圧下量の変更によりクレータエンド山谷差を大幅に短縮することができた。又、この場合の偏析度（Ｃ_ｍａｘ ／Ｃ_０ ）は１．０５であり、軽圧下量が０．４ｍｍ／ｍの場合に比べ、中心偏析が大幅に低減された。
【００５２】
次に、軽圧下量を１．１ｍｍ／ｍに変更し、その他の鋳造条件は同一のまま鋳造を続けた。その結果、最長クレータエンド位置はメニスカスから２９．５ｍ位置、最短クレータエンド位置はメニスカスから２８．３ｍ位置となり、クレータエンド山谷差は１．２ｍで、軽圧下量が０．９ｍｍ／ｍの場合と比べてほとんど変化はしなかった。しかし、この場合の偏析度（Ｃ_ｍａｘ ／Ｃ_０ ）は０．９８であり、若干の負偏析になっていた。これは、軽圧下量がやや大きすぎたために生じたと推測される。尚、負偏析とは（Ｃ_ｍａｘ ／Ｃ_０ ）が１未満の場合である。
【００５３】
このように、軽圧下量を変更することにより、鋳片幅方向のクレータエンド山谷差を短縮することができ、更に、クレータエンド山谷差を２ｍ以下にすることにより中心偏析を低減することができた。
【００５４】
【発明の効果】
本発明によれば、連続鋳造鋳片を製造する際に、鋳片幅方向におけるクレータエンド山谷差を小さく制御しながら鋳造することができ、その結果、鋳片の中心偏析の低減、並びに、鋳造速度上限値までの増速による生産性の向上などが可能となり、工業上有益な効果がもたらされる。
【図面の簡単な説明】
【図１】クレータエンド山谷差に及ぼす軽圧下量の影響の１例を示す図である。
【図２】本発明を実施したスラブ連続鋳造機の概略図である。
【図３】クレータエンド形状の例を示す図である。
【図４】中心偏析度に及ぼす軽圧下量の影響の１例を示す図である。
【符号の説明】
１ 連続鋳造機
２ 鋳型
３ 鋳片支持ロール
４ 搬送ロール
５ ガス切断機
６ 二次冷却帯
１１ 軽圧下帯
１２ 送信用横波電磁超音波センサー
１３ 受信用横波電磁超音波センサー
１４ 鋳片
１５ 凝固殻
１６ 未凝固層
１７ クレータエンド[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a continuously cast slab of steel, and more particularly to a method for producing a continuously cast slab while controlling a completely solidified position in a slab width direction.
[0002]
[Prior art]
In continuous casting of steel, it is extremely important to determine the position of the completely solidified position (hereinafter, referred to as “crater end position”) of the continuously cast slab during casting. This is because detecting the crater end position greatly contributes to the improvement of the productivity and quality of the slab.
[0003]
For example, when the casting speed is increased to improve productivity, the crater end position moves downstream in the casting direction of the slab. When the crater end position exceeded the range of the slab support roll, the slab swelled due to the static iron pressure (hereinafter, referred to as "bulging"). Problems arise. Further, in the light rolling operation for reducing the center segregation of the slab and improving the quality, it is necessary to control the casting speed and the secondary cooling water amount so that the crater end position is located in the light rolling zone.
[0004]
Further, it is known that the slab slab has a flat cross section, so that the crater end position is not uniform in the width direction and the shape varies with time. The different crater end shapes in the width direction are also major factors that determine the quality and productivity of the slab.
[0005]
For example, in order to reduce the center segregation of the slab, it is necessary to make the crater end position uniform in the slab width direction even in the light reduction operation using the light reduction band. When the crater end position is different in the slab width direction, the light reduction amount in the light reduction zone differs at each position in the slab width direction, and a sufficient center segregation improvement effect cannot be obtained at a position where the light reduction amount is small. Also, if the casting speed is maximized to improve productivity, the crater end position may extend beyond the range of the slab support roll, in which case bulging may occur. Problems such as deterioration of the internal quality occur.
[0006]
In order to solve such a problem, many means have been proposed for determining the solidification state inside the slab. For example, Patent Literature 1 discloses an apparatus that scans a transmitter and a receiver of a shear wave ultrasonic wave in a slab width direction and detects a crater end shape in the slab width direction. Further, in Patent Document 2, the solidification thickness of a slab is measured at a plurality of locations in the slab width direction, and the position and shape of a crater end are estimated from the solidification thickness. A casting method is disclosed in which the amount of secondary cooling water is changed to control the position and shape of the crater end to a target state.
[0007]
[Patent Document 1]
JP-A-62-148851
[Patent Document 2]
JP-A-57-139457
[Problems to be solved by the invention]
However, Patent Literature 1 does not disclose a specific method for setting the crater end shape to a target state, and Patent Literature 2 changes a casting speed or a secondary cooling water amount. When the casting speed is reduced, the productivity is reduced, and when the secondary cooling strength is changed, the surface temperature of the slab changes, so that the surface flaws of the slab may occur frequently. Furthermore, in Patent Literature 2, since the crater end shape is estimated from the solidified thickness, the accuracy is inferior to the case where the crater end position is directly detected.
[0010]
As described above, conventionally, the crater end position in the slab width direction is detected, and the crater end shape is determined based on the detected crater end position, that is, the crater end shape, without lowering the productivity of the continuous casting machine, and An effective means for controlling the target state without deteriorating the surface quality has not been proposed.
[0011]
The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce the productivity of a continuous casting machine by capturing the shape of a crater end that varies spatially and temporally in the width direction of a slab. By providing a continuous cast slab production method capable of performing casting while controlling the crater end shape in the slab width direction to a target state without lowering the slab surface quality without reducing the slab surface quality. is there.
[0012]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above-mentioned problems. The examination and research results are described below.
[0013]
In a continuous casting machine equipped with a light reduction zone, the casting speed, the secondary cooling water amount and the light reduction amount in the light reduction zone were variously changed. Crater end closest to the molten steel surface (hereinafter referred to as "meniscus") (hereinafter referred to as "shortest crater end". However, since the range from the short side of the slab to 100 mm is supercooled, this range is excluded. The position of) greatly depends on the casting speed and the amount of secondary cooling water, while the crater end position farthest from the meniscus (hereinafter referred to as the “longest crater end”) determines not only the amount of secondary cooling water and the casting speed but also It was found that the pressure largely depends on the light reduction amount in the light reduction zone.
[0014]
In addition, light reduction is to reduce the volume of the slab centrally by gradually reducing the slab at a speed corresponding to the solidification shrinkage speed of the slab, and to reduce the volume of solute elements such as carbon, phosphorus and sulfur. The solidification phase is a technique to reduce the center segregation of the slab by suppressing the solidification shrinkage from moving to the slab center position on the downstream side in the casting direction due to solidification shrinkage. This is an apparatus for performing the reduction, the interval between the rolls and the opposing slab support roll is set so as to gradually narrow toward the downstream in the casting direction of the slab, the rolling force on the slab Is a group of roles that can be provided with a. In the present invention, the light reduction amount is indicated by the slab reduction amount per meter in the casting direction.
[0015]
Among the crater end shapes, those that particularly define quality conditions are the longest crater end position, and when the casting speed is controlled based on the longest crater end position, the casting speed becomes slow, which is preferable because productivity is impaired. Absent. Further, the change of the casting speed changes the flow pattern of the molten steel in the mold and causes entrainment of the mold powder, so that it is not preferable as the control means of the longest crater end position.
[0016]
On the other hand, even if the amount of light reduction in the light reduction zone is changed, there is no effect on productivity and slab surface quality. Therefore, if the longest crater end position can be shortened by changing only the light reduction amount, casting can be performed at a high casting speed, and high productivity can be secured.
[0017]
Therefore, the present inventors conducted a casting test in which the light reduction amount was changed in the range of 0.4 mm / m to 1.1 mm / m, and investigated the effect of the light reduction amount on the longest crater end position. The test was performed using a vacuum high-frequency melting furnace, and the composition was C: 0.1 mass% (hereinafter, referred to as “%”), Si: 0.3%, Mn: 1.3%, P: 0.005%, S: 0.005%, Ti: 0.01%, sol. Al: 0.04% of medium carbon steel is melted, and a small test continuous casting machine (slab slab cross-sectional shape: width 800 mm, thickness 100 mm) is used to add mold powder into a mold and a casting speed of 1.1 m. / Min. At the crater end position, a solidification state determination sensor that determines the solidification state of the slab by forming a pair of a sensor that transmits a transverse wave of the electromagnetic ultrasonic wave and a sensor that receives the transverse wave of the electromagnetic ultrasonic wave, Several were installed in the direction. These sensors are movable in the slab width direction, and the crater end positions in the entire slab width direction can be detected by a pair of sensors. Further, the light reduction zone is provided in a range of 1.8 to 6.0 m from the meniscus, and is composed of a group of rolls having a diameter of 220 mm capable of applying a reduction force to the slab.
[0018]
As a result, when the light reduction amount in the light reduction zone was 0.4 mm / m (level 1), the shortest crater end position was 2.4 m from the meniscus, and the longest crater end position was 4.5 m. . The distance from the shortest crater end position to the longest crater end position (hereinafter referred to as "crater end valley difference") was 2.1 m.
[0019]
When the light reduction amount of the light reduction zone is 0.7 mm / m (level 2), the shortest crater end position is 2.3 m from the meniscus and the longest crater end position is 3.4 m. The difference was 1.1 m. It was confirmed that the difference between the crater end peak and valley was reduced by 1.0 m as compared with the level 1.
[0020]
When the light reduction amount of the light reduction zone is 1.1 mm / m (level 3), the shortest crater end position is 2.4 m from the meniscus, and the longest crater end position is 2.9 m. The difference was 0.5 m. It was confirmed that the difference between the crater end and the valley was reduced by 0.6 m compared to the level 2.
[0021]
From these tests, it is possible to shorten the longest crater end position without changing the shortest crater end position only by changing the light reduction amount in the light reduction zone, that is, to shorten the crater end peak-valley difference. It turned out to be possible. Of course, it is also an effective means to change the casting speed and the amount of secondary cooling water within the range where the quality of the slab is not impaired in accordance with the change in the light reduction amount.
[0022]
FIG. 1 shows the relationship between the crater end valley difference and the light reduction amount obtained by test casting in a small test continuous casting machine in which only the light reduction amount was changed without changing the casting speed and the secondary cooling water amount. .
[0023]
The present invention has been made based on the above-described study results, and the method for producing a continuous cast slab according to the first invention uses a continuous caster provided with a light reduction zone for lightly reducing the slab. When casting a continuous cast slab, the crater end position is detected by transmitting transverse waves of electromagnetic ultrasonic waves to the slab, and the difference between the detected shortest crater end position and the detected longest crater end position is calculated. Accordingly, the amount of light reduction in the light reduction zone is changed to reduce the difference between the shortest crater end position and the longest crater end position.
[0024]
The method of manufacturing a continuous cast slab according to a second aspect of the present invention is the method of the first aspect, wherein the shortest crater end position and the longest crater end position are controlled within a range of a low-pressure lower zone to reduce center segregation of the slab. It is characterized by the following.
[0025]
In the method for producing a continuous cast slab according to a third invention, in the second invention, the light reduction amount in the light reduction band is changed within a range of 0.5 mm / m to 1.3 mm / m. It is a feature.
[0026]
A method of manufacturing a continuous cast slab according to a fourth invention is characterized in that, in the second or third invention, a difference between the shortest crater end position and the longest crater end position is adjusted to 2 m or less. is there.
[0027]
A method of manufacturing a continuous cast slab according to a fifth invention is characterized in that, in the first invention, the longest crater end position is controlled near a machine end of a continuous casting machine.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 2 is a schematic view of a continuous slab casting machine embodying the present invention.
[0029]
As shown in FIG. 2, a continuous casting machine 1 is provided with a mold 2 for injecting and solidifying molten steel. Below the mold 2, a plurality of sets including a pair of opposed rolls are provided. The slab support roll 3 is provided. A plurality of transport rolls 4 and a gas cutting machine 5 that is located above the transport rolls 4 and is synchronized with the casting speed of the slab 14 are installed downstream of the slab support rolls 3. In addition, the slab support roll 3 has a first cooling zone 7a, 7b, a second cooling zone 8a, 8b, a third cooling zone 9a, 9b, and a fourth cooling zone from directly below the mold 2 to the downstream side. A secondary cooling zone 6 composed of a total of eight cooling zones divided into zones 10a and 10b is provided.
[0030]
In each cooling zone of the secondary cooling zone 6, a plurality of spray nozzles (not shown) for air mist spray or water spray are installed, and the secondary cooling water is sprayed from the spray nozzle to the surface of the slab 14. Is sprayed. In each cooling zone, the cooling zone on the side opposite to the reference surface (upper surface side) of the continuous casting machine 1 is indicated by a, and the cooling zone on the reference surface side (lower surface side) is indicated by b. Although the total number of cooling zones is eight in FIG. 2, it may be divided into any number according to the length of the continuous casting machine 1.
[0031]
Further, the continuous casting machine 1 is provided with a light reduction zone 11 for lightly reducing the slab 14 as a part of the slab support roll 3. The light pressure lower zone 11 is composed of a plurality of sets of slab support rolls 3 and is set so that the gap between the opposing slab support rolls 3 gradually decreases toward the downstream side of the slab 14 in the casting direction. The structure is such that a rolling force can be applied to the slab 14. FIG. 2 shows a state in which solidification of the slab 14 is completed in the light reduction zone 11, but FIG. 2 shows a state in which solidification is completed in the light reduction zone 11 to prevent center segregation. The operation of extending the position of the crater end 17 of the slab 14 to the end of the continuous casting machine 1, that is, the position of the slab support roll 3 on the gas cutting machine 5 side is also performed.
[0032]
In the gap between the slab support rolls 3 on the downstream side of the secondary cooling zone 6, a transmitting transverse electromagnetic ultrasonic sensor constituting a part of a solidification state determining device for detecting the position of the crater end 17 of the slab 14 12 (12a, 12b) and the receiving transverse wave electromagnetic ultrasonic sensor 13 (13a, 13b) are installed at three places in the casting direction. In FIG. 2, the transmitting shear wave electromagnetic ultrasonic sensor 12 and the receiving shear wave electromagnetic ultrasonic sensor 13 are installed at three locations in the casting direction, but the number of installations is not limited to three and may be any number. The greater the number, the more accurately the position of the crater end 17 can be detected. However, as will be described later, even one can detect the shortest crater end position and the longest crater end position. You only have to decide the number of installations.
[0033]
The solidification state determination device includes a sensor unit including a transverse electromagnetic wave sensor 12 for transmission and a transverse electromagnetic wave sensor 13 for reception, which are arranged to face each other with a slab 14 therebetween, and a transmission signal to the transverse electromagnetic wave sensor 12 for transmission. And a reception processing system (not shown) for processing a reception signal received by the reception transverse electromagnetic wave ultrasonic sensor 13. The transversal electromagnetic wave ultrasonic sensor 12 for transmission and the transversal electromagnetic wave ultrasonic sensor 13 for reception are mounted on a mount (not shown) movable in the width direction of the slab 14, and the sensor 12 and the sensor 13 are synchronized. The crater end 17 can be detected over the entire width of the slab 14 by moving. That is, since the crater end 17 is movable in the slab width direction, the situation of the crater end 17 in the slab width direction can be grasped.
[0034]
The transmission transverse electromagnetic ultrasonic sensor 12 transmits a transmission signal as a transverse electromagnetic ultrasonic wave, and the reception transverse electromagnetic ultrasonic sensor 13 receives a transmission signal of the electromagnetic ultrasonic wave transmitted through the cast piece 14. The position of the crater end 17 is detected by processing the received signal. When the molten steel remains, the transverse electromagnetic ultrasonic wave does not pass through the cast piece 14, and the transmission signal is propagated to the receiving transverse electromagnetic ultrasonic sensor 13 after the solidification is completed.
[0035]
The installation position of the sensor unit of the coagulation state determination device is slightly upstream of the position where the crater end 17 is not desired to extend further downstream, for example, 0 to 3 m upstream from the exit of the light pressure lowering zone 11. Is desirable. If the sensor unit is set at this position using a transverse wave as the ultrasonic wave to be transmitted, when the sensors 12 and 13 are scanned in the slab width direction, the position where the transmitted signal reaches the bare end is the longest crater end position. Since the shortest crater end position can be obtained from the average temperature of the slab obtained from the propagation time at the position where the signal propagation time is the shortest, the sensor portion may be one in the casting direction.
[0036]
In the case of shear waves, the lower the slab temperature, the higher the transmission speed. In the slab width direction, the temperature of the slab at the portion corresponding to the shortest crater end position is the lowest, and therefore the propagation time is shortest at this portion. That is, the position where the propagation time is shortest in the slab width direction is an extension of the shortest crater end position. Since the average temperature of the slab can be determined from the propagation time, the relation between the average temperature of the slab and the crater end position is determined in advance by heat transfer calculation or the like. The position can be estimated. In this way, the shortest crater end position can be obtained.
[0037]
Also, the relational expression between the ratio between the longest propagation time and the shortest propagation time when the sensor section is scanned in the width direction and the ratio between the distance from the meniscus to the longest crater end position and the distance from the shortest crater end position are given by: It may be prepared in advance, and the amount of light reduction may be controlled so that the difference between the longest crater end position and the shortest crater end position is reduced based on it. This relational expression can be obtained by obtaining the longest crater end position and the shortest crater end position by a method different from that of the solidification state determination device, for example, a tacking method or a lead addition method. According to this method, the ratio between the distance from the meniscus to the longest crater end position and the distance from the meniscus to the shortest crater end position can be obtained with high accuracy only by the ratio of the propagation times.
[0038]
Also, when the sensor is scanned in the width direction, the sensors are fixed at two positions, the longest propagation time and the shortest propagation time, and the casting speed is increased, and the transverse wave transmission signal of each sensor disappears. From the casting speed, the longest crater end position and the shortest crater end position can be determined.
[0039]
In the continuous casting machine 1 having such a configuration, the method for producing a continuous cast slab according to the present invention is performed as follows.
[0040]
Molten steel is cast into the mold 2 through an immersion nozzle (not shown). The molten steel cast in the mold 2 is cooled in the mold 2 to form a solidified shell 15, and is continuously cast downward as a slab 14 having an unsolidified layer 16 therein while being supported by the slab support roll 3. Pulled out. The slab 14 is cooled in the secondary cooling zone 6 while an appropriate amount of light reduction is applied by the light reduction zone 11, the thickness of the solidified shell 15 is increased, and solidification is eventually completed to the center. At that time, the position of the crater end 17 is detected by a coagulation state determining device including the transmission transverse electromagnetic ultrasonic sensor 12 and the reception transverse electromagnetic ultrasonic sensor 13.
[0041]
From the detected position of the crater end 17 in the slab width direction, the shortest crater end position and the longest crater end position are obtained, and the difference between the longest crater end position and the shortest crater end position, that is, the crater end peak-valley difference, The light reduction amount of the light reduction band 11 is changed so that the difference between the crater end peaks and valleys in the one width direction is reduced.
[0042]
Usually, the positions of the shortest crater end position and the longest crater end position in the slab width direction also change during casting. However, when the slab 14 is cooled in a state where the spray nozzle is not clogged, the shortest crater end position is located at the center of the slab width, and the longest crater end position is 200 mm from the short side surface of the slab. It is located at a distance from the front and back. For this reason, the crater end shape is often a W shape as shown in FIG. However, in this case, the crater end shape is not symmetrical at the left and right with respect to the center of the slab 14, and a difference occurs at the left and right in the width direction as shown in FIG. In such a case, the crater end peak-valley difference is strictly the difference L1 in the figure, but the light reduction amount may be changed based on either the difference L1 or the difference L2.
[0043]
When casting for the purpose of reducing the center segregation, it is necessary to control both the shortest crater end position and the longest crater end position within the range of the light pressure lower zone 11, so that, for example, the shortest crater end position is set to the light pressure lower zone. The casting speed and the amount of secondary cooling water are adjusted so as to be at the position of the central portion of No. 11, and the light reduction amount is changed to reduce the crater end peak-valley difference. In this case, since the center segregation is reduced as the crater end valley difference is smaller, it is preferable to control the crater end valley difference to 2 m or less.
[0044]
Further, in the case of casting for the purpose of reducing the center segregation of the slab 14, it is preferable to perform the light reduction in the range of 0.5 mm / m to 1.3 mm / m. When the amount of light reduction is less than 0.5 mm / m, the effect of reducing the center segregation is small. On the other hand, when the amount exceeds 1.3 mm / m, the amount of light reduction becomes excessive and negative segregation becomes severe, which is not preferable. FIG. 4 shows the relationship between the degree of segregation of carbon at the center of the slab and the amount of light reduction obtained by test casting in which the amount of light reduction was changed.
[0045]
When performing casting at the maximum casting speed in order to increase the productivity of the continuous casting machine 1, it is necessary to position the crater end 17 on the exit side of the continuous casting machine 1, so that, for example, the shortest crater end position is The casting speed and the amount of secondary cooling water are adjusted so as to be between the transmitting transverse electromagnetic ultrasonic sensor 12a and the sensor 12b shown in FIG. 2, and further, the light is adjusted so that the longest crater end position does not exceed the position of the sensor 12b. Change the amount of reduction.
[0046]
The cast piece 14 thus cast is cut by the gas cutter 5 to obtain a cast piece 14a.
[0047]
As described above, according to the present invention, it is possible to manufacture the slab 14 while reducing the difference between the crater end peaks and valleys in the slab width direction, to improve center segregation, to improve productivity of a continuous casting machine, and the like. Can be obtained.
[0048]
【Example】
Low carbon steel and medium carbon steel having the compositions shown in Table 1 were cast using a continuous casting machine (machine length 49.2 m) shown in FIG. In this continuous casting machine, the low pressure lowering zone is arranged in a range of 14.8 to 31.8 m from the meniscus. The slab had a cross-sectional size of 250 mm in thickness and 2100 mm in width, and was cast at a casting speed of 1.4 m / min and a secondary cooling water amount of 1.2 l / min as a specific water amount. The method for investigating the degree of segregation of the slab in the present embodiment is as follows. A sample of 250 mm in the thickness direction of the slab, 20 mm in the width direction, and 300 mm in the casting direction is sampled from the slab, and a slab thickness of 5 mm is used. Chips were collected from 20 places at the center and 4 places at the 1/4 thickness part, and analyzed by a carbon-sulfur combustion analyzer. The degree of segregation (C _max / C ₀ ) is the ratio of the maximum concentration of carbon (C _max ) at the center of the slab in the thickness direction to the average standard concentration (C ₀ ) at a quarter thickness, and the carbon segregates. If not, the degree of segregation is 1.0.
[0049]
[Table 1]

[0050]
First, casting was performed at a light reduction amount of 0.4 mm / m in the light reduction zone. At this time, the longest crater end position was 30.8 m from the meniscus, the shortest crater end position was 28.2 m from the meniscus, and the crater end valley difference was 2.6 m. In this case, the degree of segregation (C _max / C ₀ ) was 1.33, which was a high value.
[0051]
Therefore, the light reduction was changed to 0.9 mm / m, and the casting was continued while the other casting conditions were the same. As a result, the longest crater end position is 29.4 m from the meniscus, the shortest crater end position is 28.3 m from the meniscus, and the crater end valley difference is 1.1 m. Could be greatly reduced. In this case, the degree of segregation (C _max / C ₀ ) was 1.05, and the center segregation was significantly reduced as compared with the case where the light reduction amount was 0.4 mm / m.
[0052]
Next, the light reduction amount was changed to 1.1 mm / m, and the casting was continued while the other casting conditions were the same. As a result, the longest crater end position is 29.5 m from the meniscus, the shortest crater end position is 28.3 m from the meniscus, the crater end valley difference is 1.2 m, and the light reduction amount is 0.9 mm / m. There was little change in comparison. However, in this case, the degree of segregation (C _max / C ₀ ) was 0.98, indicating a slight negative segregation. This is presumed to have occurred because the light reduction amount was slightly too large. Note that negative segregation is a case where (C _max / C ₀ ) is less than 1.
[0053]
As described above, by changing the light reduction amount, the crater end peak-valley difference in the slab width direction can be reduced, and the center segregation can be reduced by setting the crater end peak-valley difference to 2 m or less. Was.
[0054]
【The invention's effect】
According to the present invention, when manufacturing a continuous cast slab, casting can be performed while controlling the crater end peak-valley difference in the slab width direction to be small, and as a result, reduction of center segregation of the slab, and casting It is possible to improve the productivity by increasing the speed to the upper limit value of the speed, and to bring about an industrially beneficial effect.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of the effect of a light reduction amount on a crater end peak-valley difference.
FIG. 2 is a schematic view of a continuous slab casting machine embodying the present invention.
FIG. 3 is a diagram illustrating an example of a crater end shape.
FIG. 4 is a diagram showing an example of the effect of a light reduction amount on the degree of center segregation.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Continuous casting machine 2 Mold 3 Slab support roll 4 Carrier roll 5 Gas cutting machine 6 Secondary cooling zone 11 Light pressure lower zone 12 Transverse electromagnetic ultrasonic sensor for transmission 13 Transverse electromagnetic ultrasonic sensor for reception 14 Slab 15 Solidified shell 16 Unsolidified layer 17 Crater end

Claims (5)

When casting a continuous cast slab using a continuous casting machine equipped with a light reduction zone for lightly reducing the slab, the crater end position is detected by transmitting transverse waves of electromagnetic ultrasonic waves to the slab. In accordance with the difference between the detected shortest crater end position and the detected longest crater end position, the amount of light reduction in the light underpressure band is changed to reduce the difference between the shortest crater end position and the longest crater end position. A method for producing a continuous cast slab. The method for producing a continuous cast slab according to claim 1, wherein the shortest crater end position and the longest crater end position are controlled within a range of a light pressure lowering band to reduce center segregation of the slab. The method for producing a continuous cast slab according to claim 2, wherein the light reduction amount in the light reduction zone is changed within a range of 0.5 mm / m to 1.3 mm / m. The method for producing a continuous cast slab according to claim 2 or 3, wherein a difference between the shortest crater end position and the longest crater end position is adjusted to 2 m or less. The method for producing a continuous cast slab according to claim 1, wherein the longest crater end position is controlled near an end of the continuous caster.

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