JPH0740005A - Method for continuously casting wide and thin cast slab - Google Patents

Abstract

PURPOSE:To enable continuous casting of a wide and thin cast slab having little surface crack and internal crack by using a mold whose casting short sides are formed as continuous recessed shape in the casting direction for an inner peripheral surface. CONSTITUTION:An unsolidified cast slab 13, in which only periphery part is solidified and the inner part is unsolidified condition, is formed in the mold for continuous casting. The cross sectional shape of this unsolidified cast slab 13 is the projecting shape in the short sides. In order to form this shaped slab, the mold whose short sides are formed as the continuous recessed shape in the casting direction for the inner peripheral surface of the mold, is used. A rolling reduction zone is arranged just below the mold and the rolling reduction is executed to the cast slab 13 by using rolling reduction rolls. Further, the short sides of the cast slab 1 are heated before executing the rolling reduction. By this method, extending quantity in the casting direction is reduced by bulging the solidified shells at the short sides to the outside at the time of executing the rolling reduction to the unsolidified cast slab. Therefore, shearing tension strain at the boundary part between the solidified shell at the long side and the solidified shell at the short side, is relaxed and the deforming resistance at the short side can be made to be small.

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 wide and thin slabs, and more particularly to a method for continuously producing wide and thin slabs with few surface cracks and internal cracks.

[0002]

2. Description of the Related Art In recent years, significant progress in refining technology and casting technology has facilitated the production of slabs with good quality properties, and the idea of labor-saving and energy-saving has increased. In addition to non-ferrous metals with relatively low melting points as well as iron-based metals, attempts to manufacture thin plate materials directly and continuously from molten metal without performing omissions or hot rolling have been made. Various proposals have been made such as a continuous casting method using a caster or a modified cross-section mold [Schlehmann-Jimmark method] (JP-A-60-158955, JP-A-62-220249, etc.). One of them is an unsolidification reduction technique in which a continuously cast slab is subjected to reduction in an unsolidified state (for example, Japanese Patent Laid-Open Nos. 61-9954 and 63-171).
No. 254, etc.).

[0003] This unsolidifying reduction technique is to roll-roll down before the solidification of a continuously cast slab is completed. Particularly, if unrolling is performed so that the unsolidified portion remains after the rolling, The rolled portion is only the solidified shell on the short side, and most of the solidified shell on the long side is only subjected to bending deformation.Therefore, compared with conventional hot rolling, the rolling load during unsolidified rolling is reduced. Also, the torque is extremely small, and there is an advantage that the rolling equipment can be downsized.

[0004]

However, under the non-coagulation pressure as described above, as shown in FIG.
Since the unsolidified layer 1a exists inside the unsolidified slab 1,
As shown in FIG. 10 (a), when the unrolled slab 1 having the solidified shell 1b of the same thickness in which the short side is right angled over the entire length is pressed by the rolling roll, the solidified shell 1b on the short side is
However, as shown in FIG. 10 (b), the solidification interface is cracked by the bending strain acting on the solidification interface and the so-called internal crack 1d, in which the concentrated molten steel enters, is generated in terms of quality. It becomes a problem.

Further, due to the reduction by the reduction roll, only the solidified shell 1b on the short side is compressed and deformed to extend in the casting direction. On the other hand, most of the solidified shells 1c on the long side are bent without being compressed and deformed by the pressing rolls, so that the elongation in the casting direction is caused by the elongation of the solidified shells 1b on the short side. Only those caused by tensile stress.

Therefore, in the case of unsolidified pressure, there is a great risk that shear tensile strain will occur at the boundary portion between the long side solidified shell 1c and the short side solidified shell 1b and surface crack 1e will occur. There is also [see FIG. 10 (c)].

The present invention solves the above-mentioned problems in the unsolidification reduction technique, a method for continuously casting wide and thin slabs with less surface cracks and internal cracks in the slab, and the rolling reduction used in this method. It is an object to provide a method that enables simplification of a device.

[0008]

In order to achieve the above-mentioned object, the continuous casting method for wide and thin cast pieces according to the present invention is a wide and thin piece for rolling down a cast piece while an unsolidified layer is present inside the cast piece. In the continuous casting method of the slab, the inner peripheral surface is to use a mold having a mold short side that is a concave shape continuous in the casting direction, further, before the reduction of the slab, the slab short side. It heats.

[0009]

In the present invention, the shape of the slab to be uncoagulated and pressed is that the short side of the mold has a convex shape. The amount of elongation in the casting direction decreases. Therefore, the shear tensile strain at the boundary between the long side solidified shell and the short side solidified shell is relaxed. Further, since the short side of the slab is heated before roll reduction, the deformation resistance of the short side portion becomes small, and the roll reduction apparatus can be a simple apparatus in terms of equipment.

FIG. 3 demonstrates the above. 3, the pipe thickness H and the wall thickness h shown in Table 1 are obtained by the hydraulic cylinder 3 through the load cell 2 as shown in FIG.
When the square tube lead test piece 4 having the short side is pulled out from between the non-driving rolls 5, pushed in, or pressed by the roll, the long side cross-sectional area SL and the short side cut of the square tube lead test piece 4 are cut. Ratio with area SS (cross-sectional area ratio) [SL / S
FIG. 3 is a diagram showing the relationship between S] and elongation strain εl in the casting direction. 3A to 3J in FIG. 3 are the cases where the shape of the short side of the square tube lead test piece 4 is the shape shown in FIGS. 5A to 5D. ■ H shows Fig. 5 (b), ■ I shows Fig. 5
(C) and (J) are the results of FIG. 5 (d)]. Note that FIG.
The strain measurement was performed by scribing a grid pattern on the outer peripheral surface of the square tube lead test piece 4 and determining the elongation of the grid pattern.

[0011]

[Table 1]

From FIG. 3, the shape of the slab to be unsolidified is
When the short side is formed into a convex shape ((G) in FIG.
It can be seen that in H), the elongation strain in the casting direction is smaller than that in the case of the rectangular slab. In addition, since a mold having a concave mold short side is used, as shown in FIG.
As shown in (a), there is no solidified shell 1b having a shape close to a right angle inside the mold, and local stress concentration points are eliminated. Therefore, even if the amount of protrusion is large, the frequency of occurrence of internal cracks is low. That is, the operation of the present invention can be proved.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A continuous casting method for wide and thin cast pieces according to the present invention will be described below with reference to an embodiment shown in FIGS. FIG. 1 is a cross-sectional view showing an example of the essential part of an unsolidified cast piece applied to the method of the present invention, and FIG. 2 is a schematic view of the process of the method of the present invention.

In FIG. 2, reference numeral 11 denotes a mold used for carrying out the method of the present invention. In the present invention, the inner peripheral surface of the short side of the mold constituting the mold 11 is a concave mold continuous in the casting direction. Use one. Reference numeral 12 denotes a rolling down zone disposed directly below the mold 11. A rolling down roll 12a in the rolling down zone 12 pulls out from the casting mold 11 and a short side thereof is heated by, for example, a heating burner 12b. The strip 13 is rolled down to the required thickness. 14
Is a static control zone for performing further auxiliary reduction when the reduction zone 12 cannot be reduced to a predetermined thickness,
Reference numeral 15 is a pinch roll for pulling out the slab. In addition, among the rolls in the rolling-down zone 12 and the static control zone 14, the black-painted rolls indicate drive rolls.

The present invention is a method for continuously casting wide and thin slabs using the continuous casting apparatus as described above.
As shown in FIG. 1, the cross-sectional shape of the unsolidified slab 13 in which only its periphery is solidified and the inside is unsolidified is convex on the short side. Then, the unsolidified slab 13 having such a shape is heated on its short side to reduce the deformation resistance of the short side before the reduction by the reduction roll 12a, or is reduced in the reduction zone 12 without heating. The roll 12a is rolled down to a required thickness. Incidentally, the heating method is not particularly limited, but the heat insulating cover 16 as shown in FIG.
A method of arranging between a and a method of heating the heating burner 12b as shown in (b) from between the pressing rolls 12a, or an induction heating method (not shown) may be adopted. Further, it is also effective to cut the width of the secondary cooling water or mask the "dripping water" flowing along the slab.

In the present invention, since the unsolidified slab 13 having the short side formed in a convex shape is pressed down, the elongation in the casting direction is larger than that of the conventional rectangular unsolidified slab. , And the shear tensile strain at the boundary between the long side solidified shell and the short side solidified shell is relaxed. Also,
There is also no part of the solidified shell where the stress is concentrated. Furthermore, when the short side of the slab is heated before the roll is rolled down, the deformation resistance of the part is reduced, so that the rolling down device may be simple. Therefore, the surface cracks and internal cracks that have occurred in the case of the conventional unsolidification reduction method can be reduced by applying the method of the present invention.

Next, the results of experiments conducted to confirm the effects of the present invention will be described. [Experiment 1] A slab having a width of 1500 mm and a thickness of 100 mm was prepared from molten steel of medium carbon aluminum killed steel having the chemical composition shown in Table 2 by using a multi-point straightening type continuous casting device having a bending radius of 5.0 m and a casting speed of 5. Continuous casting was performed at 0 m / min. The first strand is an unsolidified slab having the shape shown in FIG. 1, and the second strand is a conventional rectangular unsolidified slab for comparison.
The slab supplied from the final pinch roll was reduced to a thickness of 60 mm after being pressed to a thickness of 0 mm to 60 mm.

[0018]

[Table 2]

The occurrence of internal cracks and surface cracks thus obtained is shown in FIGS. 7 (a) and 7 (b). However, in the present invention in which the short side to which unsolidified pressure is reduced has a convex shape, no surface cracks occur, Further, it can be seen that the internal cracking is also reduced to 1/10 or less as compared with the conventional method. The surface cracking strength rate in FIG. 7 is a value obtained by dividing the total length of surface cracking measured by visual observation of the surface by the total length of the slab, and the internal cracking strength rate is the sulfa of the slab longitudinal section. It is a value obtained by dividing the internal crack length measured by printing by the total length of the sulfur-printed slab.

[Experiment 2] Using a multi-point straightening type continuous casting apparatus similar to that of Experiment 1, from the molten steel of medium carbon aluminum killed steel having the chemical composition shown in Table 3, the short side shape has a width of the shape shown in FIG.
A slab with a thickness of 00 mm and a thickness of 100 mm is cast at a casting speed of 5.0.
Continuous casting was performed at m / min. In this experiment 2, a burner type slab edge heater was installed in front of the reduction zone, the short side of the slab was heated from 800 ° C to 1100 ° C or higher, and then 1
The reduction situation was compared between the case where the thickness was reduced to 00 mm to 60 mm and the case where the thickness was reduced to 100 mm to 60 mm without heating. Coke oven gas was used as the fuel for the burner, and its air ratio was adjusted so as to create a reducing atmosphere.

[0021]

[Table 3]

FIG. 8 shows a comparison of the hydraulic pressure reduction force of the pressure reducing device depending on whether or not the short side of the cast slab is heated. By heating the short side, the deformation strength of the short side is reduced and the reduction is easily promoted. I understand. Further, FIG. 9 shows a comparison of pull-out resistance of the pinch roll depending on whether or not the short side of the slab is heated.
It can be seen that by heating the short side, the pullout resistance of the pinch roll is reduced, and the reduction is easily performed. Furthermore, depending on the casting speed, if heating of the short side is not performed, 6
In some cases, it may not be possible to roll down to a thickness of 0 mm.
In some cases, stable casting of a slab having a thickness of mm was hindered.
From the above results, the effectiveness of heating the short side can be seen.

[0023]

As described above, according to the method of the present invention, it becomes possible to continuously cast wide and thin slabs with few surface cracks and internal cracks, and the hot rolling step can be largely omitted. Further, by heating the short side of the slab before the roll is rolled, the rolling is facilitated, and the equipment of the rolling-down device can be simplified.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a main part of an unsolidified cast piece applied to the method of the present invention.

FIG. 2 is a schematic diagram of the process of the method of the present invention.

FIG. 3 is an experimental result chart showing elongation in the casting direction of the solidified shell portion on the short side when the shape on the short side is changed.

FIG. 4 is an explanatory diagram of the experimental apparatus of FIG.

5 (a) to 5 (d) are diagrams showing short side shapes used in the experiment of FIG.

FIG. 6 is a view showing an example of a heating means for a short side of a slab, (a)
Shows the one using the heat insulating cover, and (b) shows the one using the heating burner.

7 (a) and 7 (b) are drawings for explaining the effect of the first method of the present invention.

FIG. 8 is a drawing for explaining the effect of the second method of the present invention.

FIG. 9 is a drawing for explaining the effect of the second method of the present invention.

10 (a) to 10 (c) are drawings for explaining the problems of the conventional method.

[Explanation of symbols]

 11 mold 12a rolling roll 12b heating burner 13 unsolidified slab

Claims (2)

[Claims] 1. In a continuous casting method for wide and thin cast pieces, wherein a non-solidified layer is present inside a cast piece, in a continuous casting method of a wide thin cast piece, a short side of a mold having a concave shape whose inner peripheral surface is continuous in the casting direction. A continuous casting method for wide and thin slabs, characterized by using a mold having the same. 2. The continuous casting method for wide and thin slabs according to claim 1, wherein the short sides of the slabs are heated before pressing the slabs.