JP2002001507A - Mould and continuous casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mold which may effect high speed casting and prevent a longitudinal crack, and a method of continuous casting using the mold. SOLUTION: A mold which consists of at least either of multiple apertures 16 for cooling gas ventilation or an opening 17 for cooling gas ventilation provided under the bottom end of a cooling plate and a continuous casting method, wherein an opening is provided between the surface of a molten steel side of a cooling plate 12 and flowing passage of cooling water and at the top end of the cooling plate, multiple pores 13 arranged in parallel in the casting direction are provided, the bottom end being disposed between 50-200 mm lower the corresponding position of meniscus, an opening is provided between the surface of the opposite molten steel side of the cooling plate and multiple pores and on the surface of a opposite molten steel side of the cooling plate, multiple number of apertures 7, 8 are provided for insertion of a thermal sensor to measure the temperature of the cooling plate being disposed in the width direction of mold at two different points of distance from the surface of the molten steel side of the cooling plate, and an opening is provided within an area of 250-500 mm lower the corresponding position of meniscus on the surface of the molten steel side of the cooling plate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for preventing surface defects such as vertical cracks generated on the surface of a slab when casting medium carbon steel or the like, and a continuous casting method using the mold.

[0002]

2. Description of the Related Art In order to obtain a slab of good surface quality without defects such as vertical cracks, it is important to make the thickness of a solidified shell in the vicinity of a meniscus in a mold uniform in the width direction of the mold. . This is because, if a difference occurs in the thickness of the solidified shell in the width direction of the mold, when a stress acts on the surface of the solidified shell, vertical cracks are likely to occur. In particular, medium-carbon steel is more likely to cause longitudinal cracks due to its solidification characteristics.

The cause of the difference in the thickness of the solidified shell in the width direction of the mold is that the heat flux flowing in the cooling plate on the long side of the mold toward the anti-molten steel side is not uniform in the width direction of the mold and the difference occurs. Because. In addition, the uniformity of the heat flux in the width direction of the mold
The flow of molten steel in the mold has a great effect.

FIG. 1 is a schematic diagram showing the flow of molten steel in a mold. Reduce non-metallic inclusions remaining in the slab,
In order to prevent an operation accident such as breakout, the discharge flow 4 from the discharge hole faces the short side 1a on both sides of the mold 1.
An immersion nozzle 2 having two discharge holes is usually used. The discharge flow 4 colliding with the short side of the mold is divided into an upward flow 4a toward the meniscus 5 and a downward flow 4b toward the lower part of the mold. The rising flow raises the meniscus near the short side and forms a flow 4c of the molten steel toward the vicinity of the immersion nozzle.

As described above, the flow of the molten steel 3 in the mold has the function of raising the meniscus 5, but the thickness of the molten powder 6a at the position where the meniscus is raised becomes thinner, and conversely, the molten powder 6a at the position where the meniscus is lowered. The thickness of the powder 6a increases. Reference numeral 6 in the figure indicates mold powder that has been added to the mold. When the thickness of the molten powder 6a becomes uneven in the width direction of the mold as described above, the thickness of the molten powder flowing into the gap between the cooling plate on the long side of the mold and the solidified shell 10 becomes uneven in the width direction of the mold. Easy to be. On the other hand, the heat of the molten steel or solidified shell is transmitted to the inside of the cooling plate on the long side of the mold through the molten powder and the solidified molten powder, etc. It changes depending on the thickness and the like. Therefore, when the thickness of the molten powder becomes uneven in the width direction of the mold, the heat flux flowing in the cooling plate toward the anti-molten steel side becomes uneven in the width direction of the mold.

[0006] If the heat flux in the cooling plate on the long side of the mold toward the anti-molten steel side becomes uneven in the width direction of the mold, the thickness of the solidified shell in the mold becomes uneven in the width direction of the mold. At that time, the higher the casting speed, the larger the rise of the molten steel meniscus in the mold and the more uneven the thickness of the molten powder layer in the width direction of the mold. Further unevenness in the width direction of the mold.

Therefore, as a method of preventing the occurrence of vertical cracks on the surface of a slab of medium carbon steel, the structure of the mold is improved so that the heat flux in the cooling plate on the long side of the mold toward the anti-melted steel side is reduced. Attempts have been made to make them uniform in the width direction.

Japanese Patent Application Laid-Open No. 1-278944 discloses that the structure of a mold is divided into an upper portion having a heating device and a lower portion for cooling a solidified shell, and an upper cooling plate is provided by an induction heating device provided on the upper portion of the mold. Has been proposed to make the thickness of the solidified shell in the mold uniform in the width direction of the mold.
Japanese Patent Application Laid-Open No. 10-296399 discloses that a cooling plate on the long side of a mold is provided with a vertical groove in a region near the meniscus of a cooling plate on the long side of the mold to slowly cool a solidified shell in the mold. A method has been proposed in which the heat flux flowing in the plate toward the anti-molten steel side is made uniform in the width direction of the mold.

However, in these methods, since the growth of the solidified shell in the mold is suppressed, it is necessary to make the casting speed slower than in the case of using a normal mold. If the casting speed is not reduced, an accident such as breakout is likely to occur. Reducing the casting speed means that the productivity during continuous casting is reduced.

[0010]

SUMMARY OF THE INVENTION The present invention relates to a method for casting a steel such as a medium carbon steel, which is likely to have vertical cracks on the surface thereof, without lowering the casting speed. An object of the present invention is to provide a mold for preventing the occurrence of surface defects such as vertical cracks generated on the surface, and a continuous casting method using the mold.

[0011]

Means for Solving the Problems (1) The mold of the present invention comprises:
As shown in FIG. 2, which will be described later, the following features are provided. A plurality of holes 13 provided in the cooling plate 12 on the long side of the mold 1 in parallel with the casting direction. The holes 13 are provided in the cooling plate 12
Surface of molten steel and cooling water passage (indicated by reference numeral 14 in FIG. 3)
And an opening at the upper end of the cooling plate 12. In addition, the lower end is located 50 to 20 below the meniscus equivalent position.
Between 0 mm. That is, d shown in FIG.
200 mm.

A plurality of temperature sensor insertion holes 7 provided in the cooling plate 12 in the width direction of the mold 1. The hole 7 for inserting a temperature sensor is located between the surface of the cooling plate 12 on the side opposite to the molten steel and the plurality of holes 13, and opens to the surface of the cooling plate 12 on the side of the molten steel. Further, as will be described later, the temperature sensor insertion hole 7 is a hole for inserting a temperature sensor therein, and is provided at two points at different distances from the molten steel side surface of the cooling plate 12. It is for measuring temperature.

A plurality of cooling gas blowing holes 16 provided in the cooling plate 12. The cooling gas blowing holes 16 are located below the position corresponding to the meniscus on the surface of the cooling plate 12 on the molten steel side.
It is open in the region of ~ 500 mm. That is, FIG.
D shown therein is 250 to 500 mm.

A cooling gas blowing port 17 provided below the lower end of the cooling plate. (2) A continuous casting method using the mold according to the above (1), characterized by the following. That is, the cooling gas is determined by the value of the heat flux flowing in the cooling plate toward the anti-fused steel side determined from the temperature of the cooling plate measured by the plurality of temperature sensors provided in the plurality of temperature sensor insertion holes arranged in the width direction of the mold. Adjusting the amount of cooling gas blown to the surface of the solidified shell from at least one of the blowing hole or the cooling gas blowing port. (3) The peritectic reaction equivalent Cp represented by the following formula (A) is 0.1.
The continuous casting method according to the above (2), wherein the steel having a content of 09 to 0.16% by mass is cast.

[0015] Here, C, Mn, N, Si, P, S and Al: content in steel (% by mass) The present inventor cast a steel such as a medium carbon steel, which is likely to have vertical cracks on the surface of a slab. The problem at the time of doing was solved as follows. In the method of the present invention, the opening is disposed at the upper end of the cooling plate on the long side, and the lower end is disposed at a position between 50 and 200 mm below the position corresponding to the meniscus in the cooling plate. Is used. As a result, the solidified shell located near the meniscus in the mold is uniformly and slowly cooled over substantially the entire width.

Further, the inside of the cooling plate, which is determined from the temperature of the cooling plate measured by a plurality of temperature sensors provided in a plurality of temperature sensor insertion holes provided in a width direction of the mold in the cooling plate of the mold, is placed on the side opposite to the molten steel. Depending on the value of the heat flux in the width direction of the casting mold, at least the amount of cooling gas blown from the cooling gas blow hole to the solidified shell surface or the amount of cooling gas blown from the cooling gas blow hole to the solidified shell surface To adjust. Specifically, for example, based on the value of the heat flux at the center of the width of the mold, if the heat flux of a plurality of portions on both sides thereof is smaller than that of the base, at least the position corresponding to that portion is used for cooling. The amount of cooling gas blown from the gas blowing hole or the cooling gas blowing port onto the solidified shell surface is increased. As a result, the cooling of the solidified shell in this portion can be increased, so that the cooling of the solidified shell over the entire width can be made uniform.

On the other hand, when the heat flux of the plurality of portions on both sides of the central portion of the width is larger than the heat flux of the central portion of the width of the base, at least a cooling gas blowing hole at a position corresponding to the portion. Alternatively, by reducing the amount of the cooling gas blown from the cooling gas blowing port to the surface of the solidified shell, the solidified shell in this portion can be slowly cooled, and the cooling of the solidified shell over the entire width can be made uniform.

The solidified shell in the vicinity of the meniscus is slowly cooled by using the above-described mold having a plurality of holes, and at least one of the cooling gas blow hole and the cooling gas blow hole at a position corresponding to the center of the width is provided. The cooling gas amount blown to the solidified shell surface from any of them is set to an appropriate amount. Further, the cooling gas amount in the slab width direction described above is adjusted. As a result, the heat flux in the central portion of the slab width serving as the base becomes an appropriate value, and the heat flux in the slab width direction becomes uniform, so that the solidification shell in the mold width direction is cooled without lowering the casting speed. Can be made uniform.

By making the heat flux uniform in the width direction of the mold, the thickness of the solidified shell in the mold becomes uniform in the width direction of the mold. Therefore, it is possible to prevent the occurrence of vertical cracks in the cast slab such as medium carbon steel.

When the method of the present invention is carried out using the mold of the present invention, conventional techniques such as controlling the flow of molten steel in the mold and selecting the chemical composition of the powder that precipitates a large amount of crystals can be used. Further, it is possible to more effectively prevent the occurrence of vertical cracks in the slab of medium carbon steel.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The mold and the continuous casting method of the present invention will be described below. FIGS. 2, 3 and 4 are schematic diagrams for explaining an example of the structure of the cooling plate on the long side of the mold and an example of the continuous casting method of the present invention. 2 is a longitudinal sectional view of a cooling plate on one long side of the mold (showing a cross section of the cooling plate on the long side viewed from the short side), and FIG. 3 is a sectional view taken along line A1-A2 in FIG. FIG. 4 is a sectional view taken along line B1-B2 in FIG. In the drawing, reference numeral 2 denotes an immersion nozzle, reference numeral 3 denotes molten steel, reference numeral 6 denotes mold powder, and reference numeral 6a denotes molten powder. This will be described below with reference to FIGS. 2, 3, and 4.

First, the mold of the present invention will be described. In the casting mold 1 of the present invention, an opening is formed at an upper end of the cooling plate between the molten steel side surface of the cooling plate 12 on the long side of the casting mold and the cooling water passage 14 in the cooling plate. Part, the lower end of which is 50 to 200 mm below the meniscus equivalent position in the cooling plate
And a plurality of holes 13 at positions between them. The cooling plate is provided with a normal cooling water passage 14 on the side opposite to the molten steel, and the cooling plate 12 is mounted on a back frame 15 of a mold.

The horizontal cross-sectional shape of the hole 13 is not particularly limited, but is preferably circular because it is easy to handle. The diameter of each hole is desirably 3 to 15 mm. In the case of less than 3 mm, the effect of slowly cooling the solidified shell 10 becomes small,
If it is larger than 15 mm, the life of the cooling plate 12 is shortened, which is not economical. This is because the surface of the cooling plate on the molten steel side is usually reused after being cut after casting a specified amount of molten steel.

The distance from the surface of the cooling plate 12 on the molten steel side to the center axis of the hole 13 in the casting direction is preferably 5 to 20 mm. If the distance is less than 5 mm, the life of the cooling plate is shortened as described above, and if the distance is more than 20 mm, the holes are too close to the cooling water passage 14 and structurally easily interfere with each other.

Further, the interval between the center axes of the holes 13 in the casting direction in the width direction of the mold is 3 to 20.
mm is desirable. By setting the interval in this range, the ratio of the total length of the diameter of each hole to the length of the cooling plate in the mold width direction becomes 75% or more, and the solidified shell having almost the entire width in the mold width direction is uniformly cooled slowly. can do.

The upper end of the hole 13 coincides with the upper end of the cooling plate 12 to open the hole into the atmosphere. The lower end of the hole is located at a position 50 to 200 mm below the position corresponding to the meniscus 5. And In a region of less than 50 mm below the meniscus equivalent position, the cooling plate of the mold has a small effect of cooling the solidified shell. Also, 200mm below the meniscus equivalent position
In the region below the temperature, the distance between the cooling plate of the mold and the solidified shell increases, so that the heat flux of the mold decreases. Therefore, the function of the cooling plate of the mold to cool the solidified shell is small.

The cooling plate 12 has an opening between the surface of the cooling plate 12 on the side of the molten steel and the plurality of holes 13 on the long side of the mold, and the surface of the cooling plate 12 on the side of the molten steel. A plurality of holes 7 and 8 for inserting temperature sensors for measuring the temperature of the cooling plate 12 at two points at different distances from the mold are provided in the width direction of the mold. These insertion holes 7 and 8 are desirably provided substantially horizontally.

FIGS. 2 and 3 show an example in which two sets of two temperature sensor insertion holes 7 and 8 are provided in the cooling plate in the width direction of the mold. Although one set of two temperature sensor insertion holes is provided in the same vertical section, it may be provided in the same horizontal section. Also, one temperature sensor insertion hole may be used instead of two temperature sensor insertion holes. In the case of one temperature sensor insertion hole, a thermocouple, which will be described later, may be electrically insulated from each other, and the distance between the tips of the thermocouples may be constant.

The height of the temperature sensor insertion holes 7 and 8 in the cooling plate 12 to be attached is preferably near the height corresponding to the meniscus 5 and close to the meniscus 5. Further, the positions of the tips of the temperature sensor insertion holes 7 and 8 are set to positions closer to the molten steel than the holes 13, and are preferably arranged such that the positions of the tips are mutually different by a distance of about 5 to 10 mm. . The number of sets of temperature sensors arranged in the cooling plate may be determined by the width of the mold or the like, but is preferably 2 to 10 sets.

The two temperature sensors 9 are used to determine the heat flux from the temperatures measured by the two temperature sensors whose tip positions are known. It is preferable to arrange a plurality of the above sets in the width direction of the mold. A temperature sensor is inserted into the tip of each of the temperature sensor insertion holes 7 and 8, and the temperature sensor may be a normal thermocouple.

When one set of two temperature sensor insertion holes is provided in the same vertical section and a plurality of sets are provided in the width direction of the mold, the height of the temperature sensor insertion holes 7 and 8 of each set in the cooling plate is set. Should be approximately the same.

The mold is at least 250 to 500 m below the position corresponding to the meniscus 5 of the cooling plate 12 on the long side of the mold.
A plurality of cooling gas blowing holes 16 opened on the molten steel side surface in the area of m, or a cooling gas blowing port 17 below the lower end of the cooling plate on the long side of the mold.

The cross-sectional shape of the cooling gas blowing hole 16 is not particularly limited, but is preferably circular because it is easy to handle.
The diameter of this hole is desirably 2 to 5 mm. If it is less than 2 mm, the molten powder or the like is likely to be clogged. If it is larger than 5 mm, it will be difficult to assemble the mold with the cooling water passages 14 in the cooling plate.

A through-hole 11 having an opening at the surface of the cooling plate 12 on the side of the molten steel is formed so as to communicate with the hole 16 for blowing gas for cooling. By arranging such as to the outside of the mold, a cooling gas sprayed on the slab surface can be introduced.

The position where the plurality of cooling gas blowing holes 16 are arranged is a region between 250 and 500 mm below the position corresponding to the meniscus 5 of the cooling plate 12 on the long side of the mold. The holes are preferably located at the same height. The number of the temperature sensors 9 may be determined according to the size of the mold or the like.

As the cooling gas blow port 17 provided below the lower end of the cooling plate on the long side of the mold, a steel pipe or the like can be used. At this time, the inner diameter of the pipe and the number of the pipes may be the same as those of the cooling gas blowing holes 16 described above. The lower part of the lower end of the cooling plate is preferably a distance of about 30 mm or less from the lower end of the cooling plate. If it exceeds 30 mm, it may interfere with a roll or the like in the facility structure. In addition, a slit-shaped device can be used as the cooling gas blowing port. At this time, the gap between the slits is preferably 2 to 5 mm. Further, it is preferable to divide the inside of the slit in the width direction of the mold to the same extent as the number of sets of the temperature sensors described above. This is because the amount of the cooling gas blown from each of the divided slit portions can be adjusted.

The cooling gas blown from the cooling gas blowing hole and the cooling gas blowing port may be N ₂ gas, Ar gas, or an oxygen mixed gas. When an oxygen mixed gas is used, for example, by spraying Ar gas containing about 10% oxygen on the surface of the solidified shell, not only the solidified shell is cooled but also the surface layer of the solidified shell is oxidized and removed. Pinholes, powder defects, and the like can be removed. Further, by providing a flow rate adjusting device (not shown) at a stage subsequent to the cooling gas blowing hole and the cooling gas blowing port, the cooling gas amount can be adjusted.

Next, the continuous casting method of the present invention will be described.
From the measurement information of a plurality of temperature sensors arranged in the width direction of the mold, a heat flux from the surface of the cooling plate in the mold on the molten steel side to the inside of the cooling plate is calculated using a control device. At that time, the heat flux can be obtained as follows. The heat of the molten steel and the solidified shell flows through the cooling plate toward the anti-molten steel side, and is then removed by the cooling water flowing through the cooling water passage provided in the cooling plate. Therefore, when two thermocouples arranged at positions about 5 to 10 mm apart from each other in the vicinity of the molten steel meniscus in the cooling plate measure the temperature of the cooling plate at two locations, the temperature of the two measured locations is reduced. Makes a difference. The temperature near the molten steel side is high. The heat flux (W / m ² ) is calculated by dividing the temperature difference (K) at the two locations by the distance (m) between the two measured locations, and calculating the heat conductivity (W / (m · m) specific to the metal. K)).

More specifically, the magnitude of heat transfer of the cooling plate that takes away the heat of the molten steel and the solidified shell is determined by the heat conductivity and volume specific to the material of the cooling plate, the heat conductivity and amount of the cooling water, the molten powder. Is proportional to the state of contact between the cooling plate of the mold and the solidified shell. Assuming that the heat conductivity and volume of the cooling plate and the heat conductivity and water volume of the cooling water are constant, the magnitude of heat transfer of the cooling plate is mainly proportional to the state of contact between the cooling plate of the mold and the solidified shell. become.

The value of the heat flux flowing in the cooling plate toward the anti-molten steel side obtained from the temperatures measured by the plurality of temperature sensors is given by
At least the amount of the cooling gas blown from the cooling gas blowing hole to the surface of the solidified shell is adjusted, or the amount of the cooling gas blown from the cooling gas blowing port to the surface of the solidified shell is adjusted. Specifically, for example, based on the value of the heat flux at the center of the width of the mold, if the heat flux of a plurality of portions on both sides thereof is smaller than that of the base, at least the position corresponding to that portion is used for cooling. The amount of cooling gas blown from the gas blowing hole or the cooling gas blowing port onto the solidified shell surface is increased. Thereby, the cooling of the solidified shell in this portion is strengthened, and the cooling of the solidified shell can be made uniform over the entire width in the width direction of the mold.

In the case of blowing the cooling gas only from the cooling gas blowing hole or the cooling gas blowing port, if the heat flux in the width direction of the mold is not sufficiently uniform, the cooling gas is blown from both. Good. At this time, it is desirable to adjust the blowing amount of the cooling gas so that the difference in heat flux in the width direction of the mold is within ± 10%.

The amount of the cooling gas to be blown is 1 to 30 from one cooling gas blowing hole or cooling gas blowing port.
It is good to be liter / min. At less than 1 liter / minute, the effect of cooling the solidified shell is small. If it exceeds 30 liters / minute, the cooling gas may blow up to above the mold.

The peritectic reaction equivalent C represented by the above formula (A)
It is preferable to apply the mold of the present invention and the continuous casting method of the present invention using the mold when casting steel having a p of 0.09 to 0.16% by mass.

The formula (A) was determined by simple regression analysis of the content of each element corresponding to the start and end points of the peritectic reaction using general thermodynamic equilibrium calculation software. That is, when the peritectic reaction equivalent Cp is in the range of 0.09 to 0.16% by mass, the peritectic reaction occurs in the solidification process. When a peritectic reaction occurs, vertical cracks are likely to occur on the slab surface due to its solidification characteristics. Therefore, when the mold of the present invention and the continuous casting method of the present invention are applied to the above-described steel, it is effective in preventing the occurrence of vertical cracks.

[0045]

EXAMPLE A conventional mold or a mold of the present invention having an apparatus configuration shown in FIG. 2 was mounted on a vertical bending type continuous casting machine, and a medium-carbon steel having a chemical composition shown in Table 1 was deposited to a thickness of 100 mm and a width of 800 mm.
Was cast at a speed of 1 to 2 m / min. The peritectic reaction equivalent Cp of these cast steels is 0.16% by mass, which is within the range specified by the method of the present invention.

[0046]

[Table 1] The immersion nozzle was immersed in the molten steel such that the tip of the immersion nozzle had two holes with a downward angle of 20 degrees and was 200 mm below the molten steel meniscus. The mold was operated at a height of 900 mm, and the position of the meniscus was set at a position 100 mm below the upper end of the mold. Normal mold powder was used as the mold powder added to the surface of the molten steel in the mold. The degree of superheating of the molten steel in the tundish was 5 to 40 ° C.

The mold of the present invention has a hole having an inner diameter of 5 mm,
At a distance of 10 mm in the width direction of the mold, 300 mm below the upper end of the mold in the casting direction, that is, 20 mm from the meniscus.
In a region down to 0 mm, 79 cooling plates were arranged on one long side surface per cooling plate. These holes were arranged on the long sides of both sides.

As shown in FIG. 2, one set of two temperature sensor insertion holes were arranged on the same vertical cross section of the cooling plate on one long side of each of the mold of the present invention and the conventional mold. The position of the upper temperature sensor insertion hole in the height direction of the mold was set to a height corresponding to the meniscus. Also, the distance in the horizontal direction between the tips of the two temperature sensor insertion holes is 10 mm.
It was arranged so that it might become. The tip of each thermocouple was inserted and arranged to the tip of each temperature sensor insertion hole. The distance between the tip of the temperature sensor insertion hole closer to the molten steel side and the surface of the cooling plate on the molten steel side was 20 mm.
In the width direction of the mold, a total of five sets were arranged at positions dividing the width into six equal parts including the central part of the width.

In the mold of the present invention, a cooling gas blowing hole and a cooling gas blowing port were arranged. The cooling gas blow hole had an inner diameter of 3 mm, and was arranged at a position 400 mm below the meniscus equivalent position in the cooling plate on the long side of both sides. Five cooling plates per one long side were arranged in the width direction of the mold at positions corresponding to the above-mentioned holes for inserting the temperature sensors. Through-holes having openings were arranged on the surface of the cooling plate on the side opposite to the molten steel and passed through these holes for blowing gas for cooling, and steel tubes were attached to the openings, and the tubes were taken out of the mold. A cooling gas sprayed on the surface of the solidified shell was introduced via the tubes.

The cooling gas blowing port was a steel pipe having an inner diameter of 3 mm, and was disposed below the lower end of the cooling plate on the long side of the mold. The number to be arranged and the position in the width direction of the mold were the same as the above-mentioned cooling gas blowing holes. These steel tubes were taken out of the mold, and a cooling gas sprayed on the surface of the solidified shell was introduced.

Ar gas mixed with 10% oxygen was blown onto the surface of the solidified shell from the cooling gas blowing holes and the cooling gas blowing holes. At that time, the amount of cooling gas from one cooling gas blowing hole or cooling gas blowing port is:
On the basis of the heat flux at the center of the mold width, the heat flux difference in the width direction of the mold is within ± 10%,
The volume was adjusted within a range of 30 liters / minute.

The surface of the obtained slab slab was visually observed, and the presence or absence of longitudinal cracks that easily occur in the medium carbon steel was examined. Evaluation ○ shown in Table 2 described below indicates that no vertical cracks were generated, and evaluation Δ indicates that vertical cracks were generated. In some cases, subsequent hot rolling is difficult even if it is maintained.

The cast slab was allowed to cool on a steel cooling floor, and after 24 hours, the scale peeled off the slab surface was sampled and the thickness of the scale was measured with a micrometer.
The thickness of about 10 scales was measured from one cast piece obtained in each test, and the average value was obtained. The average thickness of the scale in each test when Ar gas mixed with 10% oxygen was blown onto the slab surface using the mold of the present invention was calculated as the average of the scale in three tests using the conventional mold. The ratio divided by the thickness was determined as “scale-off ratio”. Table 2
Shows test conditions and test results.

[0054]

[Table 2] Test No. of the present invention example. 1 to No. In 3, the casting speed 1 ~
Casting at 2 m / min. From the magnitude of the value of the heat flux obtained from the temperature measured by each temperature sensor, at least 10% oxygen was supplied to the solidified shell surface from at least the cooling gas blowing hole or the cooling gas blowing port. The mixed Ar gas was blown. At this time, the amount of cooling gas blown from each cooling gas blowing hole or cooling gas blowing port to the solidified shell surface is based on the heat flux at the center of the mold width and the difference in heat flux in the width direction of the mold. The amount of gas was adjusted so that the maximum value was within ± 10%. The total amount of cooling gas is 5
It ranged from 0 to 200 liters / minute. In addition,-of the difference of the heat flux with respect to the heat flux in the center part of the width of the mold means that the heat flux is small, and + means the reverse. The surface condition of the slab slab corresponding to the casting time after the time when the heat flux was stabilized was observed.

Test No. In No. 1, the casting speed is 1 m / min, and the maximum value of the difference in heat flux in the width direction of the mold is obtained by blowing the total amount of cooling gas at 50 L / min only from the cooling gas blowing hole. Within -3%. The evaluation of the slab slab surface was evaluated as ○, and a slab having good surface quality without vertical cracks was obtained. Further, the scale-off ratio was as high as 1.3, and no powder defect was recognized in the surface layer portion of the slab.

Test No. In No. 2, the casting speed was 1.7 m /
Although it is a little faster than the minute, only from the cooling gas blow hole,
A total cooling gas amount of 100 liter / min was sprayed.
Therefore, the maximum value of the difference in heat flux in the width direction of the mold is +2.
It could only be adjusted to within 2%. However, the evaluation of the slab slab surface was evaluated as ○, and a slab having good surface quality without vertical cracks was obtained. Further, the scale-off ratio was as high as 1.8, and no powder defect was recognized in the surface layer portion of the slab.

Test No. In No. 3, the casting speed was increased to 2 m / min. Therefore, the maximum value of the difference in heat flux in the width direction of the mold is within + 3% by spraying the total amount of cooling gas at 200 L / min from both the cooling gas blowing hole and the cooling gas blowing port. Became. The evaluation of the slab slab surface was evaluated as ○, and a slab having good surface quality without vertical cracks was obtained. Further, the scale-off ratio was as high as 2.2, and no powder defect was recognized in the surface layer portion of the slab.

Test No. of the comparative example using the conventional mold. 4
In the test, the casting speed was set to 1 m / min.
o. In No. 5, the casting speed was 2 m / min. The maximum value of the difference in the heat flux in the width direction of the mold based on the heat flux at the center of the mold width because the cooling gas was not blown from the cooling gas blow hole or the cooling gas blow hole onto the solidified shell surface Increased up to -28% or + 36%. Test No. On the surface of the slab slab obtained in No. 4, some vertical cracks of evaluation (1) were generated. Test No. 2 was cast at a high speed of 2 m / min. In No. 5, a marked vertical crack of evaluation X was observed on the obtained slab surface. Further, it was recognized that powdery defects were slightly generated in the surface layer portion of the slab obtained in these tests.

[0059]

By applying the mold and the continuous casting method of the present invention, it is possible to prevent the occurrence of surface defects such as vertical cracks, particularly in high-speed casting of medium carbon steel in which vertical cracks are liable to occur on the slab surface. Is possible. Further, by oxidizing the surface layer of the solidified shell in the mold, a slab having good surface quality without pinholes and powdery defects on the surface layer can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing the flow of molten steel in a mold.

FIG. 2 is a schematic diagram for explaining an example of a structure of a cooling plate on a long side of a mold and an example of a continuous casting method according to the present invention.

FIG. 3 is a schematic diagram for explaining an example of a structure of a cooling plate on a long side of a mold and an example of a continuous casting method according to the present invention.

FIG. 4 is a schematic diagram for explaining an example of a structure of a cooling plate on a long side of a mold and an example of a continuous casting method according to the present invention.

[Explanation of symbols]

1: Mold 1a: Short side 2: Immersion nozzle 3: Molten steel 4: Discharge flow 4a: Upflow 4b: Downflow 4c: Flow of molten steel 5: Meniscus 6: Mold powder 6a: Molten powder 7: Hole for temperature sensor insertion 8 : Hole for inserting a temperature sensor 9: Temperature sensor 10: Solidified shell 11: Through hole 12: Cooling plate 13: Void hole 14: Cooling water passage 15: Back frame 16: Cooling gas blowing hole 17: Cooling gas Air outlet

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B22D 11/16 104 B22D 11/16 104B

Claims (3)

[Claims] An opening is provided at an upper end of a cooling plate between a surface of a cooling plate on a long side of a mold on a molten steel side and a cooling water passage in the cooling plate. 50-200m
m comprises a plurality of holes parallel to the casting direction in which the lower end is disposed at a position between m, between the anti-fluted steel side surface of the cooling plate on the long side of the mold and the plurality of holes, The cooling plate has an opening in the surface opposite to the molten steel, and a temperature sensor insertion hole for measuring the temperature of the cooling plate at two points at different distances from the molten steel side surface of the cooling plate is formed in the width direction of the mold. Have multiple,
A plurality of cooling gas blowing holes having openings in a region of 250 to 500 mm below a position corresponding to the meniscus on the molten steel side surface of the cooling plate on the long side of the mold and a lower end of the cooling plate on the long side of the mold. A mold for use in a continuous casting method, comprising at least one of a cooling gas blowing port provided below. 2. A continuous casting method using a mold according to claim 1, wherein a temperature of the cooling plate measured by a plurality of temperature sensors provided in a plurality of temperature sensor insertion holes arranged in a width direction of the mold is provided. By the value of the heat flux flowing toward the anti-molten steel side in the cooling plate, the amount of the cooling gas blown to the solidified shell surface is adjusted from at least one of the cooling gas blowing hole or the cooling gas blowing port. Characteristic continuous casting method. 3. A peritectic reaction equivalent Cp represented by the following formula (A):
3. The continuous casting method according to claim 2, wherein steel having a ratio of 0.09 to 0.16% by mass is cast. Here, C, Mn, N, Si, P, S and Al: content in steel (% by mass)