JPH07303951A - Secondary cooling method for continuous casting and the device thereof - Google Patents

Abstract

PURPOSE:To execute the secondary cooling having a little variation of molten metal surface caused by bulging phenomenon. CONSTITUTION:A cast slab 5 is cooled by water with gas for secondary cooling as the mixed cooling medium of the water and the compressed air while being guided through foot rolls 8a, 8b, support rolls 9a, 9b and guide rolls 10a, 10b having plural pairs in a roll guide device 6a, 6b. In a drawing-out straightening device 7a, 7b at the downstream side, the cast slab 5 almost perfectly solidified is drawn out with pinch rolls 11a, 11b. In the roll guide device 6a, 6b, the secondary cooling is executed under the condition non suitable to the continuous casting of molten alloy steel, such as stainless steel and the bulging strain is made to be <=0.3%, and the variation of the molten steel surface 4 can be restrained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and equipment for secondarily cooling the surface of a continuously cast slab using a cooling medium in which water and compressed air are mixed, and more particularly to continuous casting of molten steel of ferroalloy. It relates to the secondary cooling when doing.

[0002]

2. Description of the Related Art Prior art relating to secondary cooling in continuous casting of stainless steel is disclosed in, for example, Japanese Patent Publication No. 3-46218. The purpose of this prior art is to directly spray water on the surface of a slab under specific preferable conditions to obtain a continuous casting slag having a good rectangular cross-sectional shape. However, if this secondary cooling becomes insufficient, a bulging phenomenon in which the thickness of the slab varies will be likely to occur due to the static pressure of the unsolidified molten steel inside the slab. When this bulging phenomenon occurs, the molten metal level in the mold may fluctuate, and internal defects may occur in the slab. In addition,
According to the investigation by the present inventors, the allowable amount of bulging distortion for preventing the problem in the bulging phenomenon is
It is empirically known that it is 0.3% or less. However, when only water is used as the cooling medium in this way, water evaporates on the surface of the slab whose interior is not solidified to form a water vapor film, which hinders heat transfer and has a low cooling capacity. I knew. For this reason, JP-A-57-1871
Japanese Patent No. 50, Japanese Patent Publication No. 5-10184, Japanese Patent Publication No. 5-
In Japanese Patent No. 55222, etc., a cooling medium in which water and compressed air are mixed is used to destroy the steam film on the heat transfer surface, which hinders heat transfer, to increase the contact efficiency between the surface of the slab and the cooling medium. , Prior art for improving the capacity of secondary cooling is disclosed. If the cooling capacity in the secondary cooling is improved, the solidification of the slab is promoted, and the solidified shell thickness that does not cause the bulging phenomenon can be stably obtained at an early stage.

[0003]

In ferroalloys such as stainless steel and high nickel iron, the viscosity of molten steel is high, the thermal conductivity is relatively low in the process of solidification, and segregation phenomenon is likely to occur. Therefore, the casting speed is lower than that of ordinary steel and the continuous castability is difficult. Moreover, even in the prior art that uses a cooling medium in which water and compressed air are mixed for secondary cooling, it is clear how and how to perform continuous casting of alloy iron such as stainless steel. Even if it is implemented, the following issues must be fulfilled.

This general casting speed range [0.5-
1.2 (m / min)], stable casting operation is possible even with extremely high speed casting, and high quality slabs can be obtained.

Secondary cooling should be strengthened to prevent internal cracking of the slab, and the cross-sectional shape of the slab after continuous casting should be kept rectangular.

Secondary cooling is performed so that the allowable amount of bulging strain generated during casting can be suppressed to 0.3% or less as much as possible.

[0007] To prevent fluctuations in the molten steel level in the mold as much as possible,
To allow stable primary cooling so that a normal solidified shell is stably formed.

The above problems are related to each other and can be solved by suppressing the bulging phenomenon and reducing the fluctuation of the molten steel level in the mold as much as possible. Therefore, an object of the present invention is to generate a bulging amount exceeding an allowable amount, that is, not to generate the distortion,
Continuous casting that suppresses fluctuations in molten steel level, enables stable operation even at the highest casting speed, ensures high quality both inside and outside the cast piece after continuous casting, and obtains a cast piece with a good cross-sectional shape To provide a secondary cooling method and equipment.

[0009]

According to the present invention, molten steel of ferroalloy is continuously poured into a cylindrical mold having a rectangular cross-section with a wide inner wall and a narrow inner wall, and primary cooling is performed through the mold. When performing the secondary cooling of the surface of the slab that is continuously undrawn from the mold is continuously extracted from the mold, the surface of the slab, a mixed cooling medium of water and compressed air, compressed air / water The air-water ratio defined by the weight ratio is in the range of 0.05 to 0.15, and the surface area per unit area / unit time is 36 to 120.
[1 / m ² · min] A secondary cooling method for continuous casting characterized by spraying and cooling.

In the present invention, the air-water ratio of the cooling medium is selected in the range of 0.05 to 0.15, and the water amount density is D.
[L / m ² · min], the withdrawal speed Vc of the slab is 0.
When the range is 5 to 1.2 [m / min], the secondary cooling is performed under the condition of 20 Vc + 26 ≦ D ≦ 50 Vc + 60.

The present invention also relates to the surface of the slab,
Both wide surfaces are cooled with the cooling medium in which water and compressed air are mixed, and both narrow surfaces are cooled with water.

Further, the present invention is characterized in that the molten steel of the alloy iron is a molten steel of stainless steel.

Further, according to the present invention, molten steel of ferroalloy is continuously poured into a cylindrical mold having a rectangular cross-sectional shape having a wide inner wall and a narrow inner wall, primary cooling is performed through the mold, and 0 Secondary cooling is performed while pulling out a slab whose inside is not solidified at a casting speed in the range of 0.5 to 1.2 [m / min] to obtain a thickness of 150 to 200 [mm] and a width of 700 to 1380.
A continuous cast slab of [mm] ferroalloy is continuously cast.

Further, the slab of the present invention is characterized in that it is guided by a group of rolls which are arranged aperiodically along the drawing direction of the slab.

Further, the second cooling of the slab using the cooling medium of the present invention, which has not been solidified in the inside, is carried out to a range from immediately after the slab is pulled out of the mold to the point where it is almost completely solidified. .

Further, according to the present invention, molten steel of ferroalloy is continuously poured into a cylindrical mold having a rectangular cross-sectional shape with a wide inner wall and a narrow inner wall, primary cooling is performed through the mold, and In a facility for secondary cooling of the surface of a continuously cast slab that has not solidified, a pair roll for guiding the slab in a predetermined direction without driving is arranged on the upstream side of the slab to be withdrawn. A group of guide rolls having a plurality of pairs,
A mixed cooling medium of water and compressed air was applied to both wide surfaces of the slab in a steam-water ratio (compressed air / water weight ratio) of 0.05 to 0.15, and its surface unit area / unit time was 36. ~ 12
A roll guide device provided with a plurality of steam nozzles for cooling by injecting 0 [l / m ² · min], and arranged downstream of the cast slab to be drawn out, and driven to rotate to pull out the slab A secondary cooling equipment for continuous casting, comprising: a drawing device having a plurality of pinch rolls.

[0017]

According to the present invention, a mixed cooling medium of water and compressed air is added to the surface of the cast slab in the air-water ratio (compressed air / water weight ratio) of 0.
In the range of 05 to 0.15, by injecting 36 to 120 [l / m ² · min] per unit surface area / unit time and cooling, the slab can be quickly and sufficiently cooled, and the solidification of the shell can be significantly increased. It can be favorably promoted. By doing so, the thickness of the solidified shell is quickly increased and the mechanical strength of the solidified shell is improved, so that the bulging phenomenon is less likely to occur, and fluctuations in the molten steel level in the mold are suppressed.

Further, according to the present invention, the casting speed Vc of the slab is
Corresponding to [m / min], water density D [l / m ² · mi
n] is determined, and compressed air is mixed with the determined water amount density D so that the air / water ratio is in the range of 0.05 to 1.15 to generate a cooling medium. Thereby, appropriate secondary cooling can be easily performed corresponding to the casting speed Vc from the low speed to the high speed range.

Further, according to the invention, the cooling medium in which water and compressed air are mixed is used for cooling both wide surfaces with respect to the surface of the cast slab, and both narrow surfaces are cooled with water. In order to suppress the bulging phenomenon and to secure the rectangular cross-sectional shape after continuous casting, it is important to cool both wide surfaces that are in contact with various rolls and have a large area.
It is preferable to rapidly cool with a cooling medium having a high cooling capacity, which is a mixture of water and compressed air. The cooling of both narrow surfaces is relatively small compared to the cooling of both wide surfaces, since there is usually no roll other than the pair of side rolls directly below the mold, the surface area is relatively small, and cooling with only water as is done conventionally. Is enough. For this reason, the cost such as the power cost that is required as compared with the case where the compressed air is mixed in the whole is reduced.

Further, according to the present invention, good secondary cooling is carried out even in continuous casting of stainless steel in which the viscosity of molten steel is higher than that of ordinary steel and the thermal conductivity in the solidified state is relatively small. Therefore, stable continuous casting can be performed even when the casting speed reaches a relatively high speed of 1.2 [m / min].

Further, according to the present invention, 0.5 to 1.2 [m
/ Min] while pulling out the slab at a casting speed of 1
It is possible to continuously cast a slab having a width of 50 to 200 [mm] and a width of 700 to 1380 [mm] while suppressing the bulging strain as much as possible and reducing the fluctuation of the molten steel level in the mold.

According to the invention, in a roll group having a plurality of pair rolls for guiding the slab,
The distance between the pair rolls or the distance between the pair roll cores is irregularly configured, or the roll group as a whole is irregularly configured. That is, since the roll group that guides the slab is arranged aperiodically, resonance of bulging that occurs between the rolls is unlikely to occur, and fluctuations in the molten metal level can be suppressed to a low level.

Further, according to the present invention, in the secondary cooling of the slab which is not solidified inside, the slab is almost completely solidified immediately after the slab is pulled out from the mold by the cooling medium in which water and compressed air are mixed. Since it is performed up to the range up to, it is possible to perform high speed casting, and it is possible to perform continuous casting in a state in which bulging distortion is suppressed even when high speed casting is performed, and fluctuations in the molten metal level in the mold are reduced.

Further, according to the present invention, the surface of the slab continuously cast and continuously withdrawn is efficiently cooled by the cooling medium in which water and compressed air are mixed in the upstream side roll guide device. At the upper part of the roll guide device, the solidified shell thickness of the slab is small and the solidified shell strength is weak, so that the bulging phenomenon easily occurs. Therefore, by using a cooling medium having a high cooling capacity in which water and compressed air are mixed, it is possible to strongly improve the cooling capacity, perform strong and quick cooling, and quickly increase the solidified shell thickness.

[0025]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1 shows an outline of the structure of a continuous casting apparatus for one embodiment of the present invention, FIG. 2 schematically shows an arrangement state of a steam nozzle arranged in a roll guide apparatus along a slab width direction, and FIG. Is a schematic view of the arrangement of the steam nozzle as viewed from the narrow side of the slab, FIG. 4 is a schematic structure example of a steam nozzle for injecting a cooling medium in which water and compressed air are mixed, and FIG. 5 is a bulging phenomenon. FIG. 6 shows an example in which the distance between a plurality of pair rolls corresponding to the distance from immediately below the mold in the continuous casting apparatus, that is, the roll pitch, is compared between the conventional and the present invention, and FIG. 8 shows the relationship between the water amount density and the heat transfer coefficient between the slab / secondary cooling steam in each steam / water ratio, and FIG.
Shows the relationship between the casting speed Vc and the water amount density D, and FIG. 9 shows the effect of the bulging strain at each casting speed Vc on the molten steel level variation of the molten steel in the mold.

The outer periphery of the inner wall surface of the mold 1 shown in FIG. 1 is water-cooled. Molten steel of ferroalloy such as stainless steel or high nickel alloy is supplied into the mold 1 from a ladle through a tundish. The molten steel 2 in the mold 1 is supplied so that the height of the molten metal surface 4 is as constant as possible and does not fluctuate, is cooled by the inner wall surface of the mold 1, and the solidified shell 3 is gradually formed on the outer peripheral portion thereof. The slabs 5 that are not solidified inside are drawn out from the mold 1, and the foot rolls 8 are pair rolls.
a, 8b, support rolls 9a, 9b and guide rolls 10a, 10b are sequentially guided. The foot rolls 8a, 8b, the support rolls 9a, 9b, and the guide rolls 10a, 10b, each of which has a plurality of pairs as a pair of rolls as described above, rotate without driving in accordance with the withdrawal of the slab 5. Then, the roll guide devices 6a and 6b are configured as a whole. On the downstream side of the roll guide devices 6a and 6b, a plurality of pinch rolls 11a,
Pullout straightening devices 7a, 7b having 11b are arranged. The shape of the slab 5 is gradually corrected while being pulled out by the pull-out straightening devices 7a and 7b, and the slab 5 that has been solidified is cut into predetermined lengths at the exit side of the continuous casting equipment, and in the next step, heat treatment is performed. Hot rolling is performed.

2 and 3 show the arrangement of the steam nozzles 12a, 12b for the secondary cooling of the slab 5, the steam nozzles 12a, 12b are the rolls of the roll guide devices 6a, 6b. A plurality of secondary cooling steams 13a, 1 which are arranged and ejected in the gaps 8a, 8b, 9a, 9b, 10a, 10b
The slab 5 is strongly and quickly cooled by 3b.

FIG. 4 shows an example of the structure of the water / water nozzle 12. Inside the water / water nozzle 12, the water 14 and the compressed air 15 are mixed, and the air for secondary cooling is supplied from the opening of the nozzle tip 16. Water 13a, 13b is jetted vigorously in a wide-angle (wide) shape.

FIG. 5 shows the outline of the bulging phenomenon.
The bulging phenomenon is caused by the unsolidified molten steel 2 inside the slab 5.
By the static pressure of, the solidification shell 3 uses the pair roll and the next pair roll as a fulcrum (in FIG. 5, the foot rolls 8a and 8b as the pair rolls and the support rolls 9a and 9b as the next pair rolls are exemplified. Yes) is a phenomenon that bulges outward between the fulcrums. As a result, the cross-sectional area of the cast slab 5 changes and the cross-sectional area of the region where the molten steel 2 exists inside the slab 5 also changes.
The height of the molten metal 4 inside the molten steel 2 changes up and down, and the molten metal 4 changes.

By supplying the molten steel 2 into the mold 1 through the tundish or the like as described above, the molten steel surface 4 of the molten steel 2 in the mold 1 does not fluctuate as much as possible and does not exceed its allowable width. , Molten steel 2 in mold 1 with cooling water
Stable primary cooling, that is, formation of a normal and stable solidified shell 3 from the supplied molten steel 2, prevention of seizure, damage or damage to the inner wall surface of the mold 1 of the solidified shell 3 thus formed,
Smooth withdrawal of the slab 5 whose inside is in a non-solidified state due to vibration of the mold 1 or supply of artificial slag (mold powder) into the mold 1, and inside the slab 5 withdrawn from the inside of the mold 1. It is intended to prevent the inclusion (mixture) of impurities (inclusions) into the casting, but the occurrence of a bulging phenomenon occurring in the cast piece 5 directly under the casting mold 1 has a great influence on the fluctuation of the molten metal surface 4. To exert. In particular, in the roll guide devices 6a and 6b immediately below the mold 1, the slab 5 in the process of increasing the solidification shell 3 bulges in a lump or conversely contracts between the fulcrums of a plurality of pair rolls. ,
If the total amount of bulging or the amount of strain fluctuates, the molten metal surface 4 fluctuates greatly in response to this,
Not only can the stable secondary cooling of the slab 5 not be performed, but
As described above, the slab 5 which has a great adverse effect on the primary cooling and does not satisfactorily achieve the above-mentioned various points and is finally solidified is obtained.
There are problems in terms of quality in Japan and overseas, operational aspects such as breakout (BO) and other operational accidents and inability to operate, efficiency and productivity, and yield and cost.

Therefore, it is necessary to reduce the bulging which occurs and fluctuates in this way. For this purpose, generally, the distance between the fulcrums of a plurality of pair rolls,
The distance between the plurality of pair rolls (the distance between the cores of the plurality of pair rolls), in other words, it is necessary to shorten the roll pitch as much as possible, but it cannot be said to be sufficient.

This is because if the roll pitch is constant, it is easy to bulge or contract all at once, as described above, and it is not always possible to avoid large fluctuations in the bulging amount and its distortion.

In the above description, the terms bulging amount and bulging distortion in the bulging phenomenon have been used, but these terms will be explained below.

Here, the bulging amount (cm) is δ _B ,
The pressing force or static iron pressure (Kg / cm ² ) of the roll is P, the roll pitch (cm) is L, the elastic modulus (Kg / cm ² ) of the solidified shell is E, and the solidified shell thickness (c
When m) is S and the casting speed (m / min) is Vc, the following first equation is established.

[0035]

[Equation 1]

C1 in the first equation is a constant and can be rewritten as the second equation.

[0037]

[Equation 2]

Ηα is a shape factor and its correction factor, which is 1 in the case of a cast piece. Therefore, the bulging strain ε _B is
It is expressed as the following third equation, where C2 is a constant.

[0039]

[Equation 3]

When TS is the solidus temperature and TM is the template return temperature, E is expressed by the following equation (4).

[0041]

[Table 4]

In any case, in order to suppress the fluctuation of the molten steel surface 4 of the molten steel 2 in the mold 1, the roll guide devices 6a and 6b are specially arranged.
It is necessary to suppress a large variation in the bulging amount of the cast slab 5 and its strain with time, that is, a variation which can be called a bulging resonance phenomenon.

In FIG. 6, the roll pitch of the present invention is shown by a solid line in comparison with the conventional roll pitch shown by a dotted line. In the case of the present invention, the roll pitch is simply shortened as compared with the conventional roll pitch. Not only that, the roll pitch is finely changed, that is, the distance between the pair rolls is changed, or the roll group having a plurality of pair rolls is changed as a whole, that is, the roll pitch is arranged aperiodically. As a result, it is possible to suppress a variation that can be called a bulging resonance phenomenon and to reliably suppress such a variation in the molten metal surface 4.

FIG. 7 shows the water quantity density D and the heat transfer coefficient (W / m ² · ° C.) between the slab / secondary cooling steam at each steam / water ratio (compressed air / water weight ratio). Showed a relationship. The ratio of compressed air increases by increasing the air / water ratio, and the heat transfer coefficient improves by improving the removal effect of the water vapor film on the transfer surface. However, when the air / water ratio exceeds 0.05, the heat transfer coefficient improves. The present inventors have found that the heat transfer coefficient becomes saturated and the heat transfer coefficient becomes saturated at the air-water ratio of 0.15. Therefore, for efficient cooling, the steam-water ratio is 0.05-
A range of 0.15 is suitable.

FIG. 8 shows cooling conditions obtained from the results of experiments conducted under the conditions shown in Table 1 below.

[0046]

[Table 1]

In the region (A) shown in FIG. 8, the secondary cooling is rapid and surface cracks are likely to occur. In the region (B), the secondary cooling is slow, large bulging distortion is generated, and the fluctuation easily occurs, and the fluctuation of the molten metal surface becomes large. Such a shaded area in FIG. 8 is not preferable as the secondary cooling condition, and a white-colored (C) area without a shaded area is appropriate.

FIG. 9 shows the influence of the bulging strain on the molten metal level variation (mm) at each casting speed Vc.
Even if the aperiodic arrangement according to the present invention is applied as the roll pitch, the water amount density D according to the condition of pattern 3 in Table 1 is shown in FIG.
In the region (B), the bulging strain exceeds 0.3%, and the fluctuation amount (mm) in the molten metal surface increases as the casting speed Vc increases. In particular, when the fluctuation amount of the molten metal surface exceeds 6 mm, the surface of the slab becomes defective due to damage to the solidified shell or breakout (B.
O. There is a risk of. The water amount density D is shown in FIG. 8 (C).
It was confirmed that, in the region (2), the fluctuation amount of the molten metal surface was suppressed to 4 mm or less, and the surface of the cast piece and the cross-sectional shape of the cast piece were good. This condition includes a range between the water amount density D and the casting speed Vc in which the following fifth equation is satisfied.

20Vc + 26 ≦ D ≦ 50Vc + 60 (5) The constituent conditions of the present invention described in detail above are carried out individually or in combination as necessary, and a mixed cooling medium (water and water) of water and compressed air is used. In order to secondarily cool the slab whose interior is in a non-solidified state by using, it is necessary to perform up to the range from immediately after the slab is pulled out from directly below the mold to almost completely solidified, and it is preferable. .

Although the curved type continuous casting equipment has been described in the above embodiments, the secondary cooling can be similarly performed in other types of continuous casting equipment such as a vertical type. Further, not only molten steel such as stainless steel but also other alloyed iron such as high nickel iron can similarly exert the secondary cooling effect.

From the above experimental results, the continuous casting conditions of the stainless steel casting slag including the primary cooling conditions as shown in the following Table 2 are obtained.

[0052]

[Table 2]

[0053]

Although the present invention has been described in detail above, the present invention not only achieves the above-mentioned objects and objects of the present invention but also exerts the effects listed below, which greatly contributes to the industry. is there.

1) In secondary cooling when continuously casting ferroalloys in a continuous casting facility, it is possible to cool with a higher secondary cooling capacity by using steam having a high cooling capacity instead of conventional cooling water, By implementing the preferred secondary cooling configuration conditions according to the present invention, it is possible to uniformly cool the slab, reduce the bulging amount and its distortion at high casting speed, and suppress the molten steel level fluctuation in the mold by this reduction. Becomes

2) By improving the secondary cooling capacity, the slab that is not solidified inside can greatly reduce the length from immediately below the mold to the crater end position where it completely solidifies, and the following effects are obtained. While playing, it is possible to increase the casting speed, and it is possible to improve the capacity and productivity of the entire stable continuous casting.

3) As described in the above item 1), by performing appropriate secondary cooling constitutional conditions, fluctuations in the molten metal surface are suppressed and reduced, so that the solidified shell is not damaged or damaged in the mold and is kept normal. In addition to being formed, the inclusion of impurities (inclusions) in the cast piece is prevented. The surface defects of the slab due to molten metal leakage due to damage to the solidified shell in the mold are also prevented, and internal cracking of the slab during secondary cooling is also prevented. There is no problem with the depth of the dent that tends to occur on the wide surface at a position 100 mm to 150 mm from the end, and a rectangular cross-sectional shape can be secured.

Therefore, the solidified and produced cast slab can be of high quality both inside and on the surface.

4) Stable operation is possible without breakout (BO) during casting.

[Brief description of drawings]

FIG. 1 is a simplified cross-sectional view showing a configuration of a continuous casting facility using an embodiment of the present invention.

FIG. 2 is a diagram schematically showing the arrangement of steam nozzles in the continuous casting equipment of FIG. 1 along the width direction of a cast piece.

FIG. 3 is a diagram schematically showing the arrangement of the steam nozzle in the continuous casting facility of FIG. 1 as viewed from the narrow surface side of the slab.

4 is a diagram schematically showing a cross section of an example of a steam nozzle in the continuous casting facility of FIG. 1. FIG.

FIG. 5 is a cross-sectional view showing an outline of the bulging phenomenon as seen from the narrow surface side of the slab.

FIG. 6 is a view showing an example in which the conventional and the present invention are compared with respect to the distance between a plurality of pair rolls corresponding to the distance from directly under the mold, that is, the roll pitch, in the continuous casting equipment of FIG. 1.

FIG. 7 is a diagram showing the relationship between the water amount density D and the heat transfer coefficient between the slab / steam for secondary cooling at each steam / water ratio.

FIG. 8 shows the relationship between the casting speed Vc and the water amount density D.
It is a figure which shows an appropriate range with a white blank.

FIG. 9 is a diagram showing the influence of bulging strain at each casting speed Vc on the molten metal level variation (mm) in the mold.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold 2 Molten steel (molten metal) 3 Solidified shell 4 Molten surface 5 Cast slab 6a, 6b Roll guide device 7a, 7b Pull-out correction device 8a, 8b Foot roll 9a, 9b Support roll 10a, 10b Guide roll 11a, 11b Pinch roll 12, 12a, 12b Steam nozzle 13a, 13b Steam for secondary cooling 14 Water 15 Air 16 Nozzle tip

Claims (8)

[Claims] 1. A molten steel of ferroalloy is continuously poured into a cylindrical mold having a rectangular cross-sectional shape with a wide inner wall and a narrow inner wall, primary cooling is performed through the mold, and continuous casting is performed from the mold. When secondary cooling the surface of the cast piece that is not solidified is pulled out, on the surface of the cast piece, a mixed cooling medium of water and compressed air,
The air / water ratio defined by the compressed air / water weight ratio is 0.05 to
A secondary cooling method for continuous casting, characterized in that the surface unit area / unit time is 36 to 120 [l / m ² · min] for cooling in the range of 0.15. 2. The air-water ratio of the cooling medium is 0.05 to 0.
It is selected in the range of 15 and the water density is D [l / m ² · m
in], the withdrawing speed Vc of the slab is 0.5 to 1.2 [m
/ Min], the secondary cooling is performed under the condition that 20 Vc + 26 ≦ D ≦ 50 Vc + 60 is satisfied, the secondary cooling method for continuous casting according to claim 1. 3. With respect to the surface of the cast slab, both wide surfaces are cooled by the cooling medium in which water and compressed air are mixed, and both narrow surfaces are cooled by water. 2. The continuous casting secondary cooling method according to 2. 4. The secondary cooling method for continuous casting according to claim 1, wherein the molten steel of the ferroalloy is a molten steel of stainless steel. 5. Molten steel of ferroalloy is continuously poured into a cylindrical mold having a rectangular cross-sectional shape with a wide inner wall and a narrow inner wall, primary cooling is performed through the mold, and 0.5 to
Secondary cooling is performed while pulling out a slab whose interior is not solidified at a casting speed in the range of 1.2 [m / min] to obtain a thickness of 1
The continuous cooling secondary cooling method according to any one of claims 1 to 4, wherein a continuous cast slab of alloy iron having a width of 50 to 200 [mm] and a width of 700 to 1380 [mm] is continuously cast. 6. The continuous casting according to claim 1, wherein the slab is guided by a group of rolls arranged aperiodically along the slab withdrawal direction. Secondary cooling method. 7. The secondary cooling of a slab using the cooling medium, the interior of which is not solidified, is secondarily cooled to a range from immediately after the slab is pulled out from the mold to almost completely solidifying. The secondary cooling method of continuous casting according to any one of 1 to 6. 8. Molten steel of ferroalloy is continuously poured into a cylindrical mold having a rectangular cross-sectional shape with a wide inner wall and a narrow inner wall, primary cooling is performed through the mold, and continuous casting is performed from the mold. In a facility that secondarily cools the surface of a cast piece whose inside is not solidified, it has multiple pairs of pair rolls that are placed upstream of the drawn piece and that guide the cast piece in a predetermined direction without driving. A mixed cooling medium of water and compressed air is provided in the guide roll group and both wide surfaces of the slab with a vapor-water ratio (compressed air / water weight ratio).
A roll guide device including a plurality of steam nozzles for cooling by spraying 36 to 120 [l / m ² · min] per unit surface area / unit time in the range of 0.05 to 0.15; A secondary cooling facility for continuous casting, comprising: a drawing device having a plurality of pinch rolls, which are arranged on the downstream side of the drawn slab and are driven to rotate to draw out the slab.