JPH11320063A - 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 an unsolidified rolling reduction method, in which the rolling reduction causing the trouble on the operation is avoided and the length in the unsteady part is shortened as little as possible. SOLUTION: The unsolidified rolling reduction continuous casting method for producing the thin cast slab, is executed by drawing out the cast slab 2 which is formed in a mold 1 in a vertical and bending type continuous caster and of which the inside is in the unsolidified state, and applying the rolling reduction while supporting with guide rolls. The cast slab 2 is vertically supported just below the mold 1 with two to five sets of support rolls 4 so as to become parallel with the inner surface of the mold 1 without applying the rolling reduction and the unsolidified rolling reduction is applied with rolls 4 following the support rolls. In the way, the cast slab can smoothly be drawn out and the strain caused by the bending of the cast slab can be made small. Therefore, it can be eliminated that in such a case of applying the rolling reduction just below the mold, the contact between the cast slab and the mold is worsened and the operational troubles such as longitudinal crack, breakout, are caused.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously casting thin slabs.

[0002]

2. Description of the Related Art In a continuous casting method, molten steel poured into a mold is indirectly cooled by a cooling medium flowing inside the mold, and then cooled.
This is a method in which the solidified shell is cooled by spray cooling while being moved while being supported by a guide device mainly constituted by rolls, gradually pulled out by a pinch roll, and carried out of the machine after completion of solidification.

In the recent continuous casting method, attempts have been made to obtain a semi-finished product closer to the final product from the viewpoint of labor saving (near net shaping). Particularly in the field of flat products, equipment for producing thin cast pieces in a continuous casting stage, mainly a mini-mill, has been put into practical use in order to greatly omit the rolling process.

[0004] As a method for producing a thin slab, there are:
The method can be broadly divided into an SMS (Schule-Manzi-Mag) method and an MDH (Mannesman-Demag) method. Of the former, the former is squeezed in a funnel-shaped mold to reduce the thickness, while the latter is drawn down from the mold and rolls down the unsolidified slab after rolling (hereinafter, referred to as
"Unsolidified pressure").

In the former method, the contact state of the slab is not uniform because the squeezing is performed in the mold, causing surface flaws and unstable operation due to breakout and the like. On the other hand, the latter uncoagulation reduction is compared with the complete coagulation reduction,
Since the rolling force is small, it is advantageous in that the equipment can be easily made compact.

[0006]

On the other hand, since unsolidification reduction is not equipment intended to reduce the completely solidified portion, it is necessary that an unsolidified portion thickness equal to or greater than the target reduction amount exists immediately below the roll. It is. For that purpose, it is necessary to quickly set the steady casting speed after the start of casting by, for example, rapidly raising the casting speed. However, no matter how fast the casting speed is raised, no matter how fast the casting speed is raised, if a conventional continuous casting machine is used, the unsolidified thickness cannot be reduced while the unsolidified thickness inside the slab is equal to or less than the target reduction amount. There is a problem that a thin cast slab of a target thickness cannot be obtained, and an unsteady thickness portion remains.

In order to shorten the length of the slab of the unsteady portion, it is naturally effective to bring the unsolidified rolling device closer to the mold, and several examples have been reported. For example, the unsolidification reduction of the MDH method described above is based on the Iron and Steel Make
r, April (1995), pp. 25-31, characterized in that rolling is performed in a roll device immediately below a mold in a curved continuous casting machine.

Further, CAMP-ISIJ Vol. 8 (1995) p. 950 describes the test results of rolling down from just below the mold of a vertical bending type continuous casting machine, and Japanese Patent Application Laid-Open No. 9-225612 discloses Discloses a technique for performing uncoagulation reduction.

[0009] However, the above-mentioned unsolidified reductions are all reductions from immediately below the mold, but in such reductions, when the slab is reduced, the slab at the reduction position only moves in the thickness direction. In addition, as shown in FIG. 4, the continuous slab 2 in the mold 1 also moves in the thickness direction at the same time, so that the contact state between the mold 1 and the slab 2 deteriorates, It has been found by experiments of the present inventors that it causes operational troubles such as generation of flaws and breakouts. In addition, 5 in FIG. 4 shows a reduction roll.

FIG. 5 shows a cross section taken along the line AA in FIG. 4. The contact is maintained to some extent by the bulging of the molten steel 2a by static pressure, but especially the vicinity of the corner is completely separated from the mold 1. I understand. This can be confirmed by the fact that the solidification of the slab corner is delayed or by measuring the mold temperature at the lower end of the mold with the thermocouple 3. This solidification delay is caused by adding sulfur to the mold and solidifying shell 2b at the lower end of the mold.
It can be confirmed by measuring the thickness of the sheet. Further, the fact that the slab 2 is separated from the mold 1 near the corner can be confirmed by the fact that the temperature of the mold near the corner decreases after the start of rolling.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has been made in consideration of the above-described conventional problems. It is an object of the present invention to provide a continuous casting method of a thin slab by a casting method.

[0012]

In order to achieve the above-mentioned object, a continuous casting method for a thin cast piece according to the present invention comprises the steps of: It is vertically supported without rolling down by five or less support rolls, and unsolidified rolling is performed by the rolls that follow. By doing so, the slab can be pulled out smoothly and the distortion due to the slab bending can be reduced.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A continuous casting method of a thin cast piece according to the present invention is a method for continuously drawing a cast piece having an unsolidified state formed inside a mold of a vertical bending type continuous casting machine. In an unsolidified rolling continuous casting method for producing thin cast slabs by rolling down while supporting with rolls, two or more and five or less support rolls are used so that the slabs are parallel to the inner surface of the mold immediately below the mold. It is vertically supported without performing, and unsolidified rolling is performed by a roll following this. However, the meaning of vertical support here includes a reduction of such a degree as to compensate for the heat shrinkage of the slab thickness (because it does not substantially reduce the slab). This is less than 1 mm in rolling reduction.

That is, in the continuous casting method for thin cast pieces according to the present invention, when the mold is curved from immediately below the mold as in the MDH method, the change in the pass line due to the reduction increases the drawing resistance of the cast pieces, and this is the Because it affects the inner slab, the roll group directly below the mold has a vertical part so that the slab is kept vertical as it is pulled out from the mold, and the contact state between the inner slab and the mold is affected. The greatest feature is that no reduction is performed immediately below the mold that exerts

In the continuous casting method for thin cast slabs according to the present invention, the vertical portion immediately below the mold is supported by two or more rolls because the roll is two rolls before the roll to start rolling. To reach. The reason why the vertical portion immediately below the mold is supported by five or less rolls is to minimize the length of the non-stationary portion. This corresponds to a length directly below the mold of 300 to 700 mm.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for continuously casting thin cast pieces according to the present invention will be described below with reference to an embodiment shown in FIGS. FIG.
FIG. 2 is a schematic view of a continuous casting machine for carrying out a continuous casting method of a thin slab according to the present invention. FIG. 2 is a view showing a pass line when a reduction is performed at a bending portion in the continuous casting method of a thin slab according to the present invention. FIG.

In FIGS. 1 and 2, reference numeral 1 denotes a mold of a vertical bending type continuous casting machine.
a is indirectly cooled by the cooling water at a contact portion with the inner surface of the mold 1 and gradually solidifies from the outer peripheral side thereof. The slab 2 whose outer peripheral side has solidified is supported by a group of support rolls 4 at the vertical portion immediately below the mold, and is secondary cooled in a process of being continuously pulled out by a pinch roll (not shown) to complete solidification.

In the method for continuously casting thin cast pieces according to the present invention, for example, three support rolls 4 just below the mold 1 are provided.
In the group, only the slab 2 is supported so as to be parallel to the inner surface of the mold 1, but no reduction is performed. The unsolidified reduction is performed by the roll 5 of the bending portion following the support roll 4 group.

The roll 5 may be moved independently by, for example, a hydraulic cylinder when the roll 5 is lowered. However, as shown in FIG. 2, a segment in which a plurality of rolls 5 are arranged in a single frame 6 is used. If the structure is used and the segment itself is tilted so that the rolling start roll 5a located on the most upstream side in the frame 6 is the tilting center, the rolling control can be easily performed.

By doing so, the fluctuation of the pass line acts to reduce the bending radius,
The slab can be pulled out smoothly, the distortion due to the slab bending can be reduced, and internal cracks can be reduced.

Next, the results of experiments conducted to confirm the effects of the above-described method of continuously casting thin cast pieces according to the present invention will be described. In the vertical bending type continuous casting machine having the specifications shown in Table 1 below, there are five support rolls # 1 to # 5 as vertical support portions immediately below the mold, followed by # 6 to # 10.
Bending is performed with rolls up to the number. The length of the mold of this continuous casting machine is 800 mm, and the length of the vertical portion immediately below the mold where the support roll is arranged is 700 mm.

[0022]

[Table 1]

[0023] High carbon steel (0.45 wt%
C-0.60wt% Mn-0.20wt% Si-0.01wt
% S) was cast into the continuous caster shown in Table 1 operating at a speed of 3.0 m / min and the slab thickness was 100 m.
An uncoagulated rolling test of 40 mm was performed from m to 60 mm. The rolling was performed in the following three cases. In each of the three cases, the unsolidification reduction of 40 mm was performed by five rolls, and the reduction amount of each roll was set equal to 8 mm. The contact between the slab and the mold was checked with thermocouples embedded at six points in the width direction at a position of 10 mm from the slab side below the mold.

The roll is not lowered to the # 2 roll immediately below the mold, but is reduced by the subsequent five rolls (Invention 1). Rolling is performed with the subsequent five rolls without rolling down to the # 5 roll immediately below the mold (Invention 2). The rolling is performed with five rolls from the # 1 roll immediately below the mold (Comparative Example).

FIG. 3 shows the results. In the comparative example, the temperature in the vicinity of the corner portion was lowered, and it is presumed that the contact between the slab and the mold became poor. On the other hand, in the present invention, each of them has a substantially uniform distribution in the slab width direction.

As evidenced by this fact, in the slab cast under the conditions of the comparative example, vertical cracks due to the solidification delay were sporadic near corners. Furthermore, when the internal crack generation state inside the slab was confirmed, internal cracks were generated in the comparative example, but in the present invention 1, some internal cracks were generated, but they were slighter than the comparative example. Further, in the present invention 2, no internal crack was generated.

[0027]

As described above, according to the continuous casting method of the thin slab according to the present invention, the slab can be pulled out smoothly and the distortion due to the bending of the slab can be reduced. Therefore, unlike the case where the rolling is performed directly below the mold, the contact between the cast slab and the mold is deteriorated, and there is no possibility of causing operational instability such as vertical cracking and breakout. Although the length of the unsteady portion is about 500 mm longer than when the pressure is reduced from directly below the mold, there is no problem because the length can be sufficiently accommodated in the truncated portion.

[Brief description of the drawings]

FIG. 1 is a schematic view of a continuous casting machine for performing a thin casting continuous casting method according to the present invention.

FIG. 2 shows a method for continuously casting thin cast pieces according to the present invention.
It is a figure which shows the change of the pass line when rolling down in a bending part.

FIG. 3 is an experimental result diagram showing a temperature distribution in a width direction of a lower portion of a mold.

FIG. 4 is a view showing the behavior of a slab of a conventional method of rolling down from just below a mold.

FIG. 5 is a sectional view taken along line AA of FIG. 4;

[Explanation of symbols]

 Reference Signs List 1 mold 2 slab 4 support roll 5 roll

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masahiro Ikeda 5-2, Sokai-cho, Niihama-shi, Ehime Prefecture Sumitomo Heavy Industries, Ltd. Niihama Works (72) Inventor Moriki Hashio 5-9-1 Kita Shinagawa, Shinagawa-ku, Tokyo No. 11 Sumitomo Heavy Industries, Ltd.

Claims (1)

[Claims] 1. A thin cast slab is produced by continuously pulling out a cast slab formed in a mold of a vertical bending type continuous casting machine and having an unsolidified inside and supporting it with a guide roll while rolling it down. In the unsolidified rolling continuous casting method, two or more and five or less support rolls are used to vertically support the slab just below the mold so that it is parallel to the inner surface of the mold without rolling down. A continuous casting method of a thin slab, wherein reduction is performed.