JP2000176607A - Production method of round cast billet with continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a producing method of a round cast billet with a continu ous casting, with which center segregation in the round cast billet can be re duced and center porosity can be eliminated and the desired roundness can be secured even in the case of varying the powering speed. SOLUTION: When the round cast billet is produced by applying rolling reduction to the continuously cast billet 4 having unsolidified part in the inner part and almost round shape in the cross section with one pair of unsolidified rolling reduction horizontal rolls 7, 7 and after forming the cross section to almost elliptic shape, the rolling reduction is applied with one pair of caliber vertical rolls 8, 8 for forming, the rolling reduction rate with one pair of the unsolidified rolling reduction horizontal rolls 7, 7, is decided based on the difference between the minor axis (d1) of the continuously cast billet 4 and the diameter (d2) of the round cast billet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing round billet slabs by continuous casting, and more particularly to a method for producing round billet slabs for pipe making by continuous casting using a so-called unsolidified rolling and post-solidification molding method. About.

[0002]

2. Description of the Related Art When a round billet slab is manufactured by continuous casting, if the material of the round billet slab is low carbon steel, bearing steel or high Cr steel, segregation occurs at the center of the slab which solidifies last.
(Center segregation), casting defects such as cracks in the shaft core and porosity.

If a round billet slab having such a casting defect is used as it is in the production of a seamless pipe, an inner surface defect frequently occurs in the product due to the casting defect, and the product does not become a product.

Therefore, in order to suppress the casting defects of the round billet slab and improve the inner surface quality, there are a number of techniques for preventing the occurrence of casting defects by rolling down the cast continuous cast slab. Proposed. These techniques are referred to as unsolidification rolling and post-solidification molding methods.

For example, JP-A-10-249490 and JP-A-10-249490
In the publication No. -146651, the central portion of the continuous cast slab is subjected to a large reduction with a pair of reduction rolls at a position of an unsolidified portion,
Thereafter, a method of forming a perfect circle is disclosed. According to these methods, a large reduction is performed when the central portion is not solidified, thereby giving a flow to the concentrated molten steel in the central portion and discharging the steel to the upstream of the casting. Therefore, it is said that the center segregation of the round billet slab can be reduced and the center porosity can be eliminated.

[0006]

However, when these methods are applied to an actual continuous casting line,
It was found that when the casting speed was changed, the roundness of the obtained round billet castability was deteriorated, and the round billet slab was sometimes formed into a shape that could not be manufactured.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a continuous casting method capable of reducing the center segregation of a round billet slab, eliminating the center porosity, and ensuring a desired roundness even when the casting speed is varied. To provide a method for producing a round billet slab.

[0008]

Means for Solving the Problems The present inventors have studied to solve the above-mentioned problems, and have obtained the following knowledge and findings.

When the casting speed is increased, when the forming process is performed using a vertical roll, the thickness return amount of the slab in the vertical direction increases. Therefore, by determining the amount of reduction of the horizontal roll with respect to the slab having an unsolidified portion therein according to the thickness return amount determined by the casting speed, the roundness is maintained constant, and the desired roundness is maintained. Degree can be secured.

Here, the gist of the present invention is that a continuous cast slab having an unsolidified portion therein and having a substantially circular cross section is rolled down by one or more pairs of horizontal rolls. After making the cross section approximately elliptical, by rolling down with one or more pairs of vertical rolls of a hole, when producing a round billet slab, the short diameter of the continuous casting slab having a substantially elliptical shape , Based on the deviation from the diameter of the round billet slab,
A method for producing a round billet slab by continuous casting, characterized in that the amount of reduction by a pair of horizontal rolls is determined.

From another aspect, the present invention provides a method of rolling a continuous cast slab having an unsolidified portion therein and having a substantially circular cross section with one or more pairs of vertical rolls. After making the cross section substantially elliptical, by rolling down with one or more pairs of hole-shaped horizontal rolls, when producing round billet slabs, the short diameter of the continuous cast slab having a substantially elliptical shape and A method of manufacturing a round billet slab by continuous casting, wherein a rolling reduction by a pair of vertical rolls is determined based on a deviation from a diameter of the round billet slab. In the present invention, the “transverse section” means a section substantially perpendicular to the length direction of the continuous cast slab.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a method for producing a round billet slab by continuous casting according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is an explanatory view schematically showing a manufacturing process 10 of a round billet slab by continuous casting in the present embodiment. FIG. 2 is an explanatory view showing the cross-sectional shape of the slab 4 in FIG. 1, and FIG.
FIG. 2B is a sectional view taken along line BB in FIG.
(c) is a CC sectional view in FIG. 1.

In FIG. 1, molten steel 3 poured from a tundish 1 into a continuous casting mold 2 having a circular horizontal cross-sectional shape is cooled in the mold 2 and a solidified shell is formed outside. An unsolidified portion remains inside the formed solidified shell.

The slab 4 drawn from the mold 2 enters the pinch roll zone 6 via the spray cooling zone 5. At this time, the cross-sectional shape of the slab 4 remains substantially circular as shown in FIG.

The slab 4 having passed through the pinch roll band 6 is greatly reduced by a pair of unsolidified rolling horizontal rolls 7 and 7 while the central portion remains unsolidified. The slab 4 greatly reduced by the pair of unsolidified reduction horizontal rolls 7 is
As shown in FIG. 2B, it has a substantially elliptical cross-sectional shape.

Thereafter, the slab 4 having the shape shown in FIGS. 1 and 2 (b) is rounded by a pair of forming vertical rolls 8 provided in a region where the inside of the slab is completely solidified. Molded. In the illustrated example, only one pair of the pair of forming vertical rolls 8 and 8 is provided, but if necessary, the vertical rolls and the horizontal rolls are alternated, such as a forming vertical roll, a forming horizontal roll, and so on. May be provided in a plurality of stages. Further, after providing a plurality of vertical forming rolls, a plurality of horizontal forming rolls may be provided.

Further, in the present embodiment, the slab 4 is flatly and largely reduced by the unsolidified reduction horizontal rolls 7 and 7 and the molding is performed by the forming vertical rolls 8 and 8. For example, a slab 4 is formed by a non-solidified vertical roll.
May be flattened to a large pressure and formed by a horizontal roll for forming. And the slab 4 is pulled out by a pinch roll 9.
To form a round billet slab 4 ′ for manufacturing a seamless pipe.

Here, a pair of unsolidified rolling down horizontal rolls 7,
7, the large flat cast piece 4 as shown in FIG. 2 (b) is formed into a predetermined shape by a pair of forming vertical rolls 8 and 8 as shown in FIG. 2 (c). During the forming and rolling, a phenomenon occurs in which the thickness of the slab 4 returns to the direction (vertical direction in FIG. 2 (c)) orthogonal to the pressing direction of the pair of forming vertical rolls 8, 8.

That is, assuming that the short diameter of the cast piece 4 having a substantially elliptical shape in FIG. 2B is d ₁ and the diameter of the round billet cast piece 4 in FIG. 2C is d ₂ , the thickness of the slab 4 only (d ₂ -d _1), so that the increased.
Here, the short diameter d ₁ of the slab 4 and the diameter d of the round billet slab 4
₁ deviation between _{d 3 = (d 2 -d 1} ), is defined as "thickness return amount".

During continuous casting in the round billet slab manufacturing process 10 shown in FIG. 1, when the casting speed is increased, the slab temperature in each step increases, and the deformation resistance of the slab 4 decreases. I do. Therefore, the thickness return amount d ₃ increases.

When the thickness return d ₃ is too large, the slab 4
FIG. 3 schematically shows an example of a situation in which the target diameter is exceeded.
As illustrated in FIG. 3, when the thickness return amount d ₃ is too large, the slab 4 is out chewing from the gap of the pair of the forming vertical rolls 8,8, the bulging portion 4 '' is formed. For this reason, the slab 4 has a shape in which pipe production is impossible.

FIG. 4 shows a slab 4 having a diameter of 178 mm from a slab 4 having a diameter of 225 mm.
The casting speed x (m / min) during molding and the thickness return y (m
m) is a graph showing the relationship with m. In FIG. 4, y
= 68x -82.8, a correlation coefficient R ² = 0.9863. As shown in FIG. 4, when the pouring speed is increased, the slab thickness return amount increases.

Therefore, in this embodiment, in order to prevent the casting slab 4 from biting out from the gap between the pair of forming vertical rolls 8 as shown in FIG. In anticipation of an increase in the slab thickness return amount due to an increase in the casting speed, the amount of large reduction performed by the unsolidified reduction horizontal rolls 7 is increased.

More specifically, assuming that the increase in the slab thickness return amount due to the increase in the casting speed is Δr, and the rolling reduction already set before the increase in the casting speed is r ₀ , The reduction amount r ₁ of the unsolidified reduction horizontal rolls 7 after the increase is r ₁ = r ₀ + Δ
r.

As a result, the bite of the slab 4 from the gap between the pair of forming vertical rolls 8 as shown in FIG.
As a result, the desired roundness can be ensured even when the casting speed is varied while reducing the central segregation of the round billet slab and eliminating the central porosity.

[0027]

EXAMPLES Further, a method for producing a round billet slab by continuous casting according to the present invention will be described more specifically with reference to examples.

Using substantially the same equipment as that used in the round billet slab manufacturing process 10 shown in FIG. 1 and using a continuous casting mold having a circular horizontal cross-sectional shape having a diameter of 225 mm under the conditions shown in Table 1,
A round billet slab 4 'was cast.

The rolling position of the unsolidified rolling horizontal rolls 7, 7 was 23 m from the melt meniscus, and the rolling position of the forming vertical roll 8 was 32 m from the melt meniscus. The hole type R of the horizontal roll 7 under unsolidified pressure was 178 mm. The casting speed was 1.55 to 1.65 m / min, and the spray cooling water volume was 0.10 l / kg · steel. Cast steel grade [C] = 1.0
% Steel.

[0030]

[Table 1]

In Table 1, in Examples 1 to 5, all the unsolidified rolling reductions according to the casting speed were performed in accordance with the present invention. mm, and the amount of biting of the cast slab 4 from the gap between the pair of forming vertical rolls 8 was as good as 0 mm.

On the other hand, in Comparative Examples 1 to 5, the unsolidified rolling reduction was constant irrespective of the change in casting speed. The piece 4 is bitten out of the gap between the pair of forming vertical rolls 8, 8, and the billet 4 ′ has a shape that cannot be formed.
It became.

[0033]

As described above, according to the present invention,
The center segregation of the round billet slab could be reduced, the center porosity could be eliminated, and the desired roundness could be secured even when the casting speed was varied. The significance of the present invention having such an effect is extremely remarkable.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a manufacturing process of a round billet slab by continuous casting in an embodiment.

FIG. 2 is an explanatory view showing a cross-sectional shape of a slab in FIG. 1; FIG. 2 (a) is a cross-sectional view taken along line AA in FIG. 1;
2 is a sectional view taken along the line BB in FIG. 1, and FIG. 2 (c) is a sectional view taken along the line CC in FIG.

FIG. 3 is an explanatory diagram schematically showing an example of a situation where the thickness return amount is too large and exceeds a target diameter of a slab.

[Fig. 4] Casting speed during molding in the production of a 178 mm diameter round billet slab by continuous casting from a 225 mm diameter slab.
4 is a graph showing the relationship between (m / min) and the slab thickness return (mm).

[Explanation of symbols]

4 continuous casting slab 4 'round billet slab 7 unsolidified rolling horizontal roll 8 forming vertical roll d ₁ minor d ₂ the diameter

Claims (2)

[Claims] 1. A continuous cast slab having an unsolidified portion therein and having a substantially circular cross section is reduced by one or more pairs of horizontal rolls to make the cross section substantially elliptical. When producing a round billet slab by rolling down with one or more pairs of vertical rolls of a hole type, the short diameter of the continuous cast slab having the substantially elliptical shape and the diameter of the round billet slab And determining the amount of reduction by the pair of horizontal rolls based on the deviation from the above. 2. A continuous cast slab having an unsolidified portion therein and having a substantially circular cross section is reduced by one or more pairs of vertical rolls to make the cross section substantially elliptical. When producing a round billet slab by rolling down with one or more pairs of hole-shaped horizontal rolls, the short diameter of the continuous cast slab having the substantially elliptical shape and the diameter of the round billet slab And determining the amount of reduction by the pair of vertical rolls based on the deviation from the above.