JPH05200491A - Manufacture of continuously cast slab - Google Patents

Abstract

PURPOSE:To reduce rolling reduction force at the time of executing a method for reducing center segregation by executing the rolling reduction from a side surface at the step containing unsolidified layer. CONSTITUTION:Short side faces in the cross section of a mold are made to be the shape projecting to the outside as a triangle state and an angle alpha in the internal angle of a bottom side in the triangle state is secured to >=30 deg. and molten metal is poured into this mold to execute a continuous casting. In this way, the rolling reduction with rolls executed before the solidification completes is facilitated and further, the center segregation is easily prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous cast slab manufacturing method, and more particularly to a continuous cast slab manufacturing method for reducing center segregation.

[0002]

2. Description of the Related Art Conventionally, as a technique for reducing the center segregation of continuously cast slabs, there is "a method for producing continuously cast slabs without semi-macro segregation (Japanese Patent Laid-Open No. 59-70444)". This is because the roll pitch is 450 over at least 2 m from the solidus crater end of the slab toward the upstream side.
Reduction rate of 0.5 mm / m by the reduction roll set to less than mm
The method is characterized by lightly reducing the pressure. It is well known that reduction of unsolidified cast is an effective method for reducing center segregation like this method.

However, even when rolling the unsolidified slab, it is difficult to secure an effective amount of rolling down to the side of the slab due to the rigidity of the shell developed from the side of the continuously cast slab, that is, the side shell. There was a problem that was. Various attempts have been made to improve this problem, but they are all represented by "a method for producing a continuous cast piece subjected to reduction (Japanese Patent Laid-Open No. 184455)". It was limited to the concept of changing the roll diameter in the axial direction and applying reduction without receiving the resistance of the side shell.

[0004]

According to such a conventional method, although the center segregation is surely eliminated, the amount of reduction on the short side of the slab cross section is reduced because only the center of the side shell is reduced. There is a problem in that it cannot be sufficiently removed, and segregation of the components in that part is unavoidable. The purpose of the present invention is to
Instead of the method of rolling down while avoiding the resistance of the side shell as in the prior art, a method of reducing the resistance of the side shell, ensuring an effective amount of rolling down on both sides, and reducing the center segregation at that location. Is to provide.

[0005]

Therefore, the present inventors have
After various studies, the side surface of the horizontal section of the mold was changed from the conventional smooth shape to a triangular shape so that the short side could easily buckle, thereby reducing the resistance of the side shell, and in such a state. Then, the inventors have found that the problem of the present invention can be solved by applying a reduction to the unsolidified slab and completed the present invention.

[0006] Therefore, the gist of the present invention is that the short side surface of the horizontal cross section of the mold is formed in the shape of a triangle protruding outward, and the angle α of the inside angle of the base of the triangle is 30 ° or more,
While injecting molten metal there and continuously casting,
It is a method for producing a continuously cast slab in which rolling is performed before solidification is completed. Of course, in carrying out the present invention, it is needless to say that a more excellent effect can be obtained by combining it with various methods for preventing center segregation that have been proposed so far.

[0007]

The operation of the present invention will be described more specifically with reference to the accompanying drawings. Figure 1 (a) shows a conventional mold
10 shows a horizontal cross section, and FIG. 10 (b) shows a horizontal cross section of the mold 12 used in the present invention. Conventionally, the short side of the mold section 14
Also, although it was linear like the long side 16, the short side 14 of the mold cross section according to the present invention has a triangular shape protruding outward. The long side 16 may be the same as the conventional one.

The reason why the triangular portion 20 is provided on the short side 14 is to facilitate buckling when the roll is pressed. Therefore, the triangular shape is empirically α = 30 degrees or more, preferably 30 degrees. It should be ~ 70 degrees. Others are not specifically limited, but it is preferable that the slab is the object in the vertical direction toward the drawing, since it is convenient for handling in a later step, and therefore the triangular portion 20 is preferably an isosceles triangle. .

FIG. 2 shows a method 1 for carrying out the method according to the invention.
FIG. 3 is a schematic explanatory view of the embodiment, and FIG. 3 shows the mold cross section and the solidified state of the cast metal at that time. FIG. 3 (a) shows a cross section of the cast metal at the roll pressure lower surface in the conventional example, and FIG. 3 (b) shows a cross section of the cast metal at the roll pressure lower surface by the method according to the present invention. That is, according to the present invention, the molten steel 1 from the tundish is poured into the mold 3, and the solidified shell 2 generated from the outside is pulled out from the mold 3 while holding the unsolidified layer 5 inside. The rolling is performed by the rolling rolls 4 provided at a plurality of predetermined pitches in a state in which the unsolidified layer 5 is partially provided.

At this time, as described in JP-A-59-70444, the roll pitch is 450 mm or less over the range of at least 2 m from the solidus crater end of the cast toward the upstream side. It is also possible to carry out a light reduction at a reduction rate of 0.5 mm / m or more by the reduction roll set to. In the case of the present invention, the rolling reduction may be 0.3 mm / m or more.

Further, in producing a continuously cast slab,
The segregation of inclusions may be minimized by stirring the molten steel with electromagnetic force. As described above, according to the method for producing a continuously cast slab of the present invention, the molten steel 1 is injected into the casting mold 3 having a triangular horizontal cross section in FIG. It is a method of rolling down with the rolling roll 4 before completion. As shown in FIG. 3 (a), in the conventional method, the side shell 2A became a pillar, and the effective reduction amount could not be obtained due to the resistance to the rigidity, but as shown in FIG. 3 (b), in the present invention, the side shell 2A was used. 2B can be easily buckled by the reduction from the reduction roll 4A, and an effective reduction amount can be secured with a low reduction force.

[0012]

EXAMPLES Next, the present invention will be described more specifically by way of examples. Using the apparatus shown in FIG. 2, continuous cast slabs were produced under the casting conditions shown in Table 1. Roll reduction of unsolidified slab is 3 from the crater end toward the upstream side.
It was carried out at a point 0.5 m downstream from m. The center segregation of this slab was measured as shown in FIG. 4 (a) and compared with that of the conventional method. The mold cross section of the conventional method is shown in FIG. 1 (a), and is represented by α = 0 degree in Table 1.

The results are shown graphically in FIG. 4 (b). C / on the vertical axis
Co represents the degree of center segregation of the carbon component of the slab. FIG. 5 is a graph for evaluating the internal defect index of a thick plate, and shows the rate of occurrence of internal defects when the rate of occurrence of internal defective plates at the standard time is 1. As can be seen from these results, according to the present invention, an effective amount of reduction can be secured and the center segregation can be greatly reduced, and as a result, the production of sound cast pieces is facilitated.

Comparative Example In this example, the example was repeated under the conditions shown in Table 1 except that α = 20 degrees. The results are shown graphically in Figure 4 (b).

[0015]

[Table 1]

[0016]

As a result of the present invention, the center segregation of continuously cast slabs is greatly reduced, and in particular, as shown in FIG. 5, the internal defect index in a thick plate is halved compared to the conventional method.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a mold cross section, FIG. 1 (a) shows a mold cross section used in a conventional method, and FIG. 1 (b) shows a mold cross section used in the present invention.

FIG. 2 is a schematic diagram of a continuous casting method for explaining the implementation of the method according to the present invention.

FIG. 3 is a schematic view of a cross section of a continuously cast slab including an unsolidified layer, and FIG. 3 (a) is a slab cross section of a conventional method.
(b) is a slab cross section in the present invention.

FIG. 4 is a graph showing the formation of center segregation in Examples and Comparative Examples, FIG. 4 (a) is an explanatory diagram of analysis points, and FIG. 4 (b) is a graph showing the results.

FIG. 5 is a graph showing the result of the example in comparison with that of the conventional example.

[Explanation of symbols]

 1: Molten steel 2: Solidified shell 3: Mold 4: Rolling roll 5: Unsolidified layer 2A, 2B: Solidified shell 4A: Rolled down roll 5A, 5B: Unsolidified layer

Claims (1)

[Claims] 1. The mold has a shape in which the short side surface of the horizontal section of the mold is bulged outward in a triangular shape, and the angle α of the inner angle of the base of the triangle.
Is 30 ° or more, and a molten metal is poured therein to continuously perform casting, and a roll casting is performed before solidification is completed.