JP2000176616A - Method for continuously casting thin cast slab - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a continuous casting method of a thin cast slab, with which the warping deformation thereof after executing rolling reduction is prevented and the drawing-out working thereof is facilitated and the temp. thereof kept high. SOLUTION: In the continuous casting method of a steel reducing the thickness by using at least one pair of rolling reduction rolls to execute the rolling reduction on the way of the ordinary casting, the rolling reduction is executed at the position of the cast slab containing unsolidified part, and a water ratio Q (l/kg of steel) of secondary cooling water for cooling the cast slab after completing the rolling reduction, is regulated to the quantity satisfying Q <=0.6 × (y/y1) × Q1. Wherein, Q1 is the water ratio (l/kg of steel) of the secondary cooling water in the case of executing no rolling reduction under containing of the unsolidified state at the downstream side of the casting direction from the rolling reduction roll pair, (y) is the target thickness (mm) of the cast slab after executing the rolling reduction and (y1) is the thickness (mm) of the cast slab before starting the rolling reduction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for obtaining a thin slab by reducing a position including an unsolidified portion of a slab during casting without reducing the slab. The present invention relates to a method for secondary cooling of a thin slab after rolling.

[0002]

2. Description of the Related Art In recent years, in continuous casting of steel, attempts have been made to obtain slabs having a thickness and a shape close to a product from the viewpoints of construction costs of related equipment and reduction of personnel in a manufacturing process. . Particularly in the production of hot-rolled steel strips, a method has been proposed that combines the production of a thin slab having a thickness of about 50 mm by a continuous casting method and the subsequent rolling by a simple hot-rolling equipment arranged on a production line. Has been put to practical use.

[0003] In a continuous casting method for obtaining a thin slab, the thickness of a mold is set to about 100 to 150 mm.
There is an unsolidified rolling method in which the slab is reduced to a slab thickness of about m.

In JP-A-8-90182 and JP-A-8-90187, the thickness of the slab at the exit of the mold is set to 70 to 150 mm, and the slab is reduced at the position of the slab including the unsolidified portion. The thickness of the slab is about 50 to 70 mm, the casting speed is 3 to 6 m / min, and the secondary cooling specific water amount is 1.
A continuous casting method of a thin slab cast at a condition of 5 to 4.5 liters / kg-steel has been proposed.

[0005] In these methods, there is a problem that the specific water amount of the secondary cooling of the thin slab after rolling is too large, and the thin slab is supercooled. In particular, the upper surface side of the thin slab is often supercooled, and in that case, the thin slab warps as the upper surface side shrinks. When such deformation occurs in the thin slab, in extreme cases, it becomes difficult to pull out the thin slab. In addition, although the thin slab can be drawn, there is a problem that the energy required for heating the thin slab increases during subsequent rolling due to the low temperature.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a position including an unsolidified portion of a slab is reduced while casting is being performed without reducing the slab to reduce the thickness of the slab. When manufacturing slabs, prevent warping deformation of thin slabs, facilitate the work of drawing thin slabs, keep the temperature of the thin slabs high, and energy required for heating when rolling continuously It is an object of the present invention to provide a continuous casting method of a thin cast piece that can reduce the temperature.

[0007]

SUMMARY OF THE INVENTION The gist of the present invention is a continuous casting method for steel in which a slab is reduced by using at least one pair of reduction rolls to reduce the thickness of the slab during normal casting. The reduction is performed at the position of the slab including the unsolidified portion, and the specific water amount Q (liter / kg-steel) of the secondary cooling for cooling the slab after the completion of the reduction satisfies the following formula (A). The method is for continuous casting of thin slabs.

Q ≦ 0.6 × (y / y1) × Q1 (A) Here, Q1: ratio of secondary cooling when unsolidification reduction is not performed downstream of the reduction roll pair in the casting direction. Water volume (liter / k
g: steel) y: target thickness of slab after reduction (mm) y1: thickness of slab before start of reduction (mm) The thickness of thin slab after reduction targeted by the present invention is 30 to 70.
mm, the thickness of the slab before starting the reduction is 90-150m
m.

When reducing the position including the unsolidified portion of the cast slab, it is reduced by at least one pair of reduction rolls. When the reduction amount is increased, the reduction is carried out by sharing a plurality of pairs of reduction rolls so that cracks do not occur in the slab.

During normal casting, that is, during casting without reducing the slab, when reducing the position including the unsolidified portion of the slab to obtain a thin slab, It is preferable to start the reduction of the slab after the final solidified portion of the slab is located downstream of the final reduction roll pair in the casting direction. If the final solidification part starts rolling down in the state upstream of the final reduction roll pair in the casting direction, the reduction roll pair downstream from the final solidification part will reduce the slab after complete solidification. In some cases, it may not be possible to reduce the thickness of the target thin slab to the target thickness due to the limitations of the rolling equipment.

After the reduction of the slab is started, after the thickness of the slab after the reduction reaches the target thickness, the specific water amount of the secondary cooling of the thin slab after the reduction by the final pair of reduction rolls is determined. By reducing the thickness to the range that satisfies the condition represented by the above formula (A), it is possible to prevent the thin slab pressed down to the target thickness from being overcooled.

[0012]

FIG. 1 is a diagram schematically showing an example of the configuration of a continuous casting apparatus for carrying out the method of the present invention. FIG. 1A is a diagram schematically illustrating a state in which casting is performed without reducing the slab. FIG. 1 (b)
It is a figure which shows typically the state which starts reduction of a slab, and the thickness of the slab after reduction has reached the target thickness.

The molten steel 8 injected into the mold 1 solidifies,
A solidified shell 9 is formed. The slab 10 including the unsolidified portion is reduced to a target thickness of the slab by a pair of reduction rolls 4 having a reduction cylinder 5.
Is drawn downstream in the casting direction. FIG. 1 shows an example in which three reduction roll segments 6 are arranged, and two reduction rolls 4 are arranged in each reduction roll segment.

A secondary cooling device (not shown) for cooling the slab is provided between the mold outlet and the final roll pair.
In addition, a secondary cooling device 11 for cooling the slab is disposed downstream of the final draft roll pair in the casting direction.

The preferred size of the slab to be used in the present invention is 90 to 150 mm in thickness and 1000 to 1 in width at the exit of the mold.
It is 800 mm, and the thickness after reduction is 30 to 70 mm. The casting speed is not particularly limited, but when the thickness of the slab at the exit of the mold is such a size, casting can be performed at a speed of 3 to 8 m / min.

In the method of the present invention, the specific water amount Q of the secondary cooling of the thin slab after the reduction by the final reduction roll pair after the time when the thickness of the slab after the reduction reaches the target thickness is defined as: The specific water amount satisfies the condition represented by the above-described equation (A).

First, Q1 on the right side of equation (A), that is,
Specific cooling water volume (liter / kg-) for secondary cooling of the slab downstream of the final reduction roll pair in the casting direction when the reduction is not performed
The method for obtaining (steel) will be described below.

First, without reducing the thickness, a thickness 9
When casting a slab of 0 to 150 mm at a speed of 3 to 8 m / min, the specific water volume of the secondary cooling of the slab from the mold outlet to the final pair of reduction rolls is Q2 (liter / kg-steel). . As will be described later, if the thickness of the slab at the exit of the mold and the thickness of the target thin slab after rolling down are determined, the value of the specific water amount Q2 is determined in accordance with the casting speed.

Under the condition of cooling the slab between the exit of the mold and the final pair of reduction rolls at a constant value of specific water volume Q2, Q
1 is determined as follows. That is, under the condition that a slab having a thickness of 90 to 150 mm at the mold outlet is cast without reduction, the final solidified portion of the slab is located upstream of the final pinch roll in the casting direction in accordance with the casting speed. What is necessary is just to determine the minimum value of Q1 such that The value of the minimum Q1 is that, in the case of a large Q1, the slab is only supercooled, and as described above, only the heating energy required for the subsequent rolling is increased. In this way, the specific water amount Q1 for the secondary cooling of the slab that is downstream of the final pair of reduction rolls in the casting direction when the reduction is not performed is determined in accordance with the casting speed.

Here, the specific water amount Q2 of the secondary cooling of the slab from the exit of the mold to the final pair of reduction rolls when the reduction is not performed is obtained as follows. This specific water amount Q2 is also applied when reducing. That is, of the cooling water amount for secondary cooling the slab from the mold outlet to the final reduction roll pair, the amount of cooling water for secondary cooling the slab between the first reduction roll pair and the final reduction roll pair accounts for. Since the ratio is small, the specific water amount Q2 may be applied even when the reduction is performed.

Incidentally, the thickness of the slab at the exit of the mold is 90 to 90 mm.
When a 150 mm slab is reduced into a thin slab having a thickness of 30 to 70 mm by rolling, the position of the final solidified portion of the thin slab from the meniscus is located upstream of the position of the final rolling roll pair in the casting direction. It is desirable to do. This is because bulging may occur if an unsolidified portion of a thin slab exists at the position of the pinch roll downstream of the final reduction roll pair in the casting direction.

As described above, the specific water amount Q2 is determined by
After the reduction to 0 to 70 mm, the central part of the slab may be completely solidified by the final reduction roll pair in accordance with the casting speed.

Next, the reason why Q ≦ 0.6 × (y / y1) × Q1 will be described. That is, the thickness of the slab at the exit of the mold was 90 to 150 mm,
In the case of rolling down to a thin slab of about 0 mm, it is necessary to reduce the specific water volume of the secondary cooling more than in proportion to the reduction of the thickness of the slab. By lowering the slab by the reduction roll, the cooling of the slab is accelerated. Therefore, in the secondary cooling of the thin slab after the reduction, it is necessary to reduce the specific water amount of the secondary cooling more than in proportion to the decrease in the thickness of the slab.

The thin cast slab after the rolling was reduced to a specific water volume of 0.6 × (y /
When the cooling exceeds y1) × Q1, the thin slab is supercooled, and as described above, the temperature of the thin slab is significantly reduced or the thin slab is warped. In an extreme case, it is difficult to pull out the thin slab. Further, even if drawing is possible, energy loss due to a remarkable decrease in the temperature of the thin slab becomes large.

The lower limit of the specific water volume of the secondary cooling of the thin slab after rolling at a position downstream of the final rolling roll pair in the casting direction is not particularly limited. It is desirable that the specific water volume be as low as necessary for protection. Since the lower limit of the specific water amount varies depending on the continuous casting machine, a value suitable for the continuous casting machine may be obtained. However, the size of the slab is 90 to 150 mm in thickness and 10 in width at the mold exit.
00-1800mm, thickness 30-70mm after rolling down,
When the casting speed is about 3 to 8 m / min, the lower limit specific water volume is usually about 0.03 liter / kg-steel.

The continuous casting machine includes a curved type, a vertical bending type and the like.

[0027]

EXAMPLE A low-carbon aluminum-killed steel having a C content of 0.05% by weight was cast at a speed of 5.0 m / min using a vertical bending type continuous casting machine having an apparatus configuration shown in FIG. The length of the vertical portion was 1.5 m, and the reduction of the position of the slab including the unsolidified portion was performed in the range from the vertical portion to the meniscus 1.5 to 6 m, and the space between the portions was uniformly reduced by five roll segments. . Each roll segment is provided with two pairs of reduction rolls. The slab width is 1500 mm, the thickness of the slab at the exit of the mold is 100 mm, and the target thin slab thickness after rolling is 70, 6
There were three types, 0 and 50 mm.

Since the continuous caster used in the test has two strands, the specific water amount of one strand in the secondary cooling of the slab downstream of the final pair of the reduction rolls is determined under the conditions specified in the present invention. In the other strand, the specific water amount of the secondary cooling of the slab in the same region was tested at a large value outside the range specified in the present invention.

Incidentally, the specific water amount Q1 for secondary cooling of the slab downstream of the final reduction roll pair in the casting direction when the reduction is not performed was set to 0.34 (liter / kg-steel).

The obtained thin slab is lengthened 10 m in the casting direction.
Cut on a horizontal table, tie one end and the other end of the thin slab with a thread, measure the distance between the thread and the thin slab at the center position of the thin slab length, Its value, that is, length 10m
The amount of warpage was defined as the degree of deformation (mm) of the thin slab.

Further, the surface temperature of the thin slab at the entrance and exit of the first pinch roll during casting was measured. An optical thermometer was used for temperature measurement.

Tables 1 to 3 show test conditions and test results.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3]

Table 1 shows Example 1, in which the thickness of the slab at the outlet of the mold was reduced from 100 mm to a thin slab having a thickness of 50 mm by reducing the position of the slab including the unsolidified portion. Table 2 shows Example 2.
The thickness of the slab at the exit of the mold was reduced to 100 mm to reduce the position of the slab including the unsolidified portion to a thin slab having a thickness of 60 mm. Table 3 shows Example 3, in which the thickness of the slab at the outlet of the mold was reduced from 100 mm to a thin slab having a thickness of 70 mm by reducing the position of the slab including the unsolidified portion.

Test Nos. Of Examples of the present invention in Examples 1 to 3 Nos. 1 to 5; 11 to 14 and No. 19 ~
In No. 22, the thickness of the thin slab after reduction is 50, 60, 70 m
In each case m, the surface temperature of the thin slab at the first pinch roll exit side was as high as 880 ° C. to 960 ° C., which was good. The deformation degree of the thin slab was as small as 0 to 2 mm, which was favorable.

Test Nos. Of Comparative Examples in Examples 1 to 3 Nos. 6 to 10; Nos. 15 to 18 and Nos. 23 ~
In Test No. 26, Test No. With the exception of 10, the secondary cooling specific water volume of the thin slab downstream of the final pair of reduction rolls in the casting direction in the casting direction was tested at a value larger than the range specified in the present invention. The temperature of the thin slab at the pinch roll exit side was as low as 670 ° C. to 750 ° C., and the degree of deformation of the thin slab was as large as 15 to 30 mm. In particular, in the test in which the degree of deformation of the thin slab was 25 mm or more, it was difficult to pull out the thin slab.

Test No. In 10, the specific water amount of the secondary cooling of the thin slab downstream of the final pair of reduction rolls in the casting direction is reduced to a value below the value for protecting the pinch roll from the heat of the thin slab. Tested. Although bulging did not occur in the thin slab, the temperature of the thin slab was too high,
Many scales were generated on the surface of the thin slab, and the pinch roll slipped, making it difficult to pull out the slab.

[0040]

According to the method of the present invention, the secondary cooling of the thin cast slab after the reduction by the final pair of upper and lower reduction rolls after the thickness of the slab after the reduction reaches the target thickness. By making the conditions appropriate, it is possible to prevent the warp deformation of the thin slab due to supercooling, facilitate the work of drawing out the thin slab, keep the temperature of the thin slab high, and heat it during subsequent rolling. It is possible to prevent an increase in energy required for the above.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing an example of a configuration of a continuous casting apparatus for carrying out a method of the present invention.

[Explanation of symbols]

1: mold 2: guide roll 3: pinch roll 4: reduction roll 5: reduction cylinder 6: reduction roll segment 7: unsolidified portion 8: molten steel 9: solidified shell 10: cast piece 11: from the final pair of reduction rolls Secondary cooling device for thin slabs downstream in the casting direction

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Yoshinori Tanizawa 4-5-33 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Inside Sumitomo Metal Industries, Ltd. (72) Inventor Masafumi Hanao 4 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture No. 5-33, Sumitomo Metal Industries Co., Ltd. (72) Inventor Masahiko Oka 4-5-33, Kitahama, Chuo-ku, Osaka City, Osaka Prefecture F-term (reference) 4E004 KA14 MC02 MC07

Claims (1)

[Claims] 1. A continuous casting method of steel in which a thickness of a slab is reduced by using at least one pair of reduction rolls during normal casting to reduce the thickness of the slab, wherein the reduction includes an unsolidified portion. The method is performed at the position of the slab, and the specific water amount Q (liter / kg-steel) of the secondary cooling for cooling the slab after the completion of the reduction is set to an amount satisfying the following formula (A). A continuous casting method for slabs. Q ≦ 0.6 × (y / y1) × Q1 (A) Here, Q1: the specific water amount (liter) of the secondary cooling when the unsolidification reduction on the downstream side in the casting direction from the reduction roll pair is not performed. / K
g: steel) y: target thickness of slab after reduction (mm) y1: thickness of slab before start of reduction (mm)