JPH08132205A - Method and device for improving center segregation of cast slab in continuous casting - Google Patents

Abstract

PURPOSE: To improve the center segregation developed at the center part of a cast slab in a vertical type continuos casting and to produce the cast slab satisfied even for a high class steel of bearing steel, etc. CONSTITUTION: In the drawing-out range of the cast slab in the continuous casting apparatus, multi-stage roll pairs composed of a reference side roll and opposite side reference side roll for executing the rolling reduction of the cast slab to the solidified shrinkage part in the range of 0.0<fS<1.0 core part solid phase factor fS of the cast slab in 0.40-0.60m/min casting speed VC are arranged. The width of the projecting part in the roll for rolling reduction of the cast slab of the opposite reference side roll is set to the width adding 10-100mm to the non-solidified width in the cast slab at the roll setting position, and the height of the projecting part of the roll is made to be 5-60mm, and further, the draft of each roll in the multi-stage rolls is distributed almost uniform so that the rolling reduction speed of the roll satisfies 0.40-2.5mm/min in 0.15-0.420 the rolling reduction ratio and the interval between the reference roll and the opposite reference roll is set and each roll pair is arranged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of center segregation of a slab in a slab drawing section of a continuous casting apparatus.

[0002]

2. Description of the Related Art In continuous casting of molten steel, molten steel flows at the center of the slab in the final stage of solidification of the slab, while non-uniform solidification occurs near the boundary with the molten steel and bridging occurs at the end of solidification, resulting in bridging. As a result of the molten wood between and around it being sucked toward the center by solidification shrinkage downstream from the bridge, it was accumulated as center segregation in the center of the slab. There is an electromagnetic stirring technique as a technique for preventing the occurrence of such center segregation. This is a method in which bridging is prevented by stirring in a mold by an electromagnetic stirring technique to precipitate dendrites on the entire surface of solidification to generate fine equiaxed crystals. However, even with the electromagnetic stirring technique, the elimination of the center segregation of the slab in continuous casting was not always sufficient for high-grade steel materials.

[0003]

DISCLOSURE OF THE INVENTION The present invention provides a method and apparatus for further improving the center segregation occurring in the center of a slab in vertical type continuous casting, as compared with the prior art, and provides a high-grade steel such as bearing steel. Also produces a slab that can be satisfied.

[0004]

According to the invention of claim 1, in the method for producing a steel slab by continuous casting, the casting speed V _C is 0.4.
0 to 0.60 m / min, and the slab has an axial solid phase fraction f _S of 0.
To solidification shrinkage of less than 1.0 area greater than 0, the non-solidified regions in each position inside the shaft center solid fraction f _S is 1.0 isotherm of the slab, the reduction ratio {= total reduction Amount (mm) / unsolidified thickness (mm)} of 0.015 to 0.420 and a rolling speed of 0.40 to 2.5 mm / min, and multi-stage compression in the thickness direction from one side of the wide surface of the slab. Is a method for rolling down a slab in continuous casting, which prevents the downward flow of molten steel due to shrinkage and improves center segregation.

According to the second aspect of the invention, the axial solid fraction f of the cast slab is f.
_The method of rolling down a slab in continuous casting according to the means of the invention of claim 1, characterized in that multi-stage compression is applied to the solidification shrinkage portion of which _S is preferably between 0.2 and 0.8.

According to the third aspect of the present invention, the casting speed V _C is 0.40 to 0.6 in the cast strip drawing region of the continuous casting apparatus.
Reference side roll and multistage consisting counter reference side roll for the axis solid fraction f _S of the slab as 0 m / min to pressure the slab to solidification shrinkage of less than 1.0 area exceed 0.0 Of the rolls, and the width of the roll convex portion for rolling down the slab of the anti-reference side roll is set to 1 as the unsolidified width of the slab at the roll installation position.
With a width of 0 to 100 mm added, the height of the roll convex portion is 5 to
60 mm, and at a rolling reduction ratio of 0.015 to 0.420, the rolling reduction amount of each roll of the multi-stage roll is approximately evenly distributed so that the rolling reduction speed of the rolls satisfies 0.40 to 2.5 mm / min. A rolling apparatus for a continuous casting apparatus, characterized in that a distance between a reference roll and an anti-reference roll of a roll pair is set and arranged.

According to the fourth aspect of the present invention, the axial solid fraction f of the slab is f.
4. The invention according to claim 3, wherein a multi-stage roll pair including a reference side roll and an anti-reference side roll for rolling down the slab is provided in the region where _S is preferably 0.2 to 0.8. It is a rolling down device of the continuous casting device in the means.

According to a fifth aspect of the present invention, the number of stages of the multi-stage roll pair is from 2 to 10, and the rolling apparatus of the continuous casting apparatus according to the means of the third or fourth aspect of the present invention is characterized.

[0009]

The method of the present invention is applied to the casting speed in continuous casting of steel.
Degree V_C The allowable range of 0.40 to 0.60 m / min
To improve productivity. In this case, the axial solid fraction f of the cast slab
_S Solidification shrinkage part in the range where is greater than 0.0 and less than 1.0
On the other hand, the axial solid fraction f of the cast slab_S Inside the isotherm with 1.0
The unsolidified region at each position of
0.420 and rolling speed 0.40 to 2.5 mm / min
The amount of pressure,
The lower speed is secured and the appropriate pressure is applied to the solidification shrinkage area.
It acts on the area and prevents downward flow of concentrated molten steel,
A slightly upward flow with good segregation, which suppresses the occurrence of core segregation.
Be the one In this case, the carbon concentration of the normal part of the slab
Degree C₀ Ratio of carbon concentration C in the shaft core to C / C₀ In
Displaying the segregation of the heart, C / C₀ Is 0.95 to 1.10
The segregation is within a good range. Reduction ratio is total reduction amount (mm) / max.
The unsolidified thickness (mm) at the upper roll position. The rolling speed is
Total rolling amount (mm) / passage time (minutes) of multi-stage roll of slab
is there.

A multi-stage roll pair consisting of a reference side roll and an anti-reference side roll for carrying out the method of the present invention has a width of a roll convex portion for reducing a cast piece of the anti-reference side roll, which is cast at the roll installation position. The width is 10 to 30 mm added to the unsolidified width of the piece. That is, the width x of the unsolidified layer at each stage of the multi-stage roll is determined from the solidification profile of the cast piece, and the roll x is obtained by adding 10 to 100 mm to the width x of the unsolidified layer (width on the wide surface side of the cast piece). Width. In this case, the solidification profile is indicated by an isotherm at the solid core fraction f _S = 1.0 of the shaft, the origin of the meniscus of the slab, the ordinate of the core of the slab, and the meniscus on the ordinate. Take the square root of the arrival time tmin from
When the unsolidified thickness xmm of the wide surface side of the slab with an empty shaft is taken on the abscissa, the solidification profile is represented by Formula 1.

[0011]

## EQU1 ## ax ² + bx + c = √t = √L / V _C, where: x: unsolidified thickness of wide surface side of slab (mm) a, b, c: coefficient t: arrival time from meniscus (minutes) ) L: Reaching distance from the meniscus (m) V _C : Casting speed (m / min)

The height of the roll convex portion is 40 to 60 mm, and the average reduction amount of each step is 0.5 to 4.0 mm. Then, the number of stages of the multi-stage roll is set to 2 to 10. Therefore, the shape of the slab bloom pressed by the rolls in each stage is as shown in FIG. 4, and the slab does not crack because the slab blooms gradually. That is, the reduction resistance is reduced and the shape of the reduced bloom is made into a gentle concave shape as shown in FIG. 4 to prevent the occurrence of flaws such as folds during rolling.

The maximum roll width (uppermost roll width R ₁ : one side) is determined as follows. The effective rolling-down position is set between f _S = 0.2 and 0.8. The value is set to be slightly larger than the unsolidified width x from the axial center of the slab, which is required corresponding to the casting speed V _C. The maximum roll width (uppermost roll width R ₁ ) is determined from the maximum casting speed V _C in actual operation and the unsolidified thickness x ₁ corresponding to √t obtained from the roll position.
And _{1 = x 1 + (10~60)} mm.

The width R _n of the roll on the second stage and below is determined as follows. First, the unsolidified width x at each roll position
_{Find n} . Then, (a) the roll width immediately above (R _n-1 ).
10 to 30 mm smaller than. Therefore, the roll width becomes narrower toward the lower stage. (B) 1 for the unsolidified width x _n
Add 0 to 60 mm. R _n is determined from the conditions (a) and (b). When f _S > 0.8 at the roll position of each stage, that is, in the non-fluid region at the end of solidification, the condition (b) is ignored.

[0015]

EXAMPLE In the present invention, in the vertical continuous casting apparatus shown in FIG. 6, in addition to the rolls of 1SEC to 5SEC in the slab draw-out section, a group of 6 rolling down rolls of the new rolling down device 4 of 6SEC is newly installed. Then, 2 rolls of 5SEC and 6 rolls of 6SEC constitute 8 multi-stage rolling rolls. 7SEC is a pinch roll. In FIG. 6, 1 is a ladle, 2 is a tundish, and 3 is a mold. In this continuous casting apparatus, a bloom of bearing steel SUJ2 having a cross section of 380 mm × 490 mm is continuously cast. Fig. 1 shows the shape of 8 multi-stage rolling rolls consisting of 2 rolls of 5SEC and 6 rolls of 6SEC. FIG. 2 shows the profile of the roll on the non-reference side. FIG. 5 shows the state of the pressing force 6 exerted on the unsolidified region 7 of the solidification shrinkage portion of the slab bloom. FIG. 3 is a diagram showing an isotherm of the axial solid phase fraction f _S in the solidification contraction portion of the cast slab, and is also a diagram showing the roll width on one side of each stage of the multi-stage roll.

Table 1 shows the values of the specifications of the multi-stage rolling rolls in this example, in which the casting speed V _C was 0.55 m / min.

[0017]

[Table 1]

As a result of using the above-mentioned multi-stage reduction roll, the value of C / C ₀ showing the center segregation in the slab is 0.95 to
It was extremely good at 1.05.

[0019]

As described above, according to the present invention, in the vertical type continuous casting apparatus, the axial solid fraction f of the cast slab is f by using the multi-stage reduction roll whose width decreases as the roll width becomes lower. _In the solidification shrinkage part where _S is more than 0.0 and less than 1.0,
Appropriate reduction can be applied to the slab, the downward flow of molten steel due to contraction accompanying solidification can be prevented, and center segregation can be efficiently improved, and as a result, the allowable range of casting speed can be expanded. Therefore, the production efficiency can be improved, and high-grade steel without center segregation can be produced.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a multi-stage rolling roll of the present invention.

FIG. 2 is a view showing a roll profile of each stage in an example of the multi-stage rolling roll of the present invention.

FIG. 3 is a diagram showing an isotherm of a solid core fraction f _S of a shaft and a roll width on one side of each stage in a solidification shrinkage portion of a cast piece.

FIG. 4 is a view showing the shape of a cast slab bloom pressed by rolls of each stage.

FIG. 5 is a diagram showing a pressing force exerted on a non-solidified region of a solidification shrinkage portion of a slab bloom.

FIG. 6 is a diagram schematically showing a vertical continuous casting apparatus equipped with the new reduction device of the present invention.

[Explanation of symbols]

 1 Ladle 2 Tundish 3 Mold 4 New reduction device 5 Pinch roll 6 Reduction force 7 Unsolidified area 8 Anti-reference side roll 9 Reference side roll 10 Cast piece

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hayashi Takemoto, 3007 Nakajima, Himeji, Himeji, Nakajima, Sanryo Special Steel Co., Ltd. Special Steel Co., Ltd.

Claims (5)

[Claims] 1. A method for producing a steel material cast slab by continuous casting, casting to the velocity V _C 0.40~0.60m / min, 1 beyond the axis solid fraction f _S 0.0 of the slab With respect to the solidification shrinkage portion in the region of less than 0.0, the solid core fraction f _S of the cast slab is 1.
The unsolidified region at each position inside the isotherm of 0 has a reduction ratio of 0.015 to 0.420 and a reduction rate of 0.40.
2.5 mm / min. Multi-stage compression from one side of the wide surface of the slab in the thickness direction to prevent downward flow of molten steel due to contraction and improve center segregation. Reduction method. Wherein the axis solid fraction of the cast piece f _S is preferably 0.
2. The method for reducing a cast piece in continuous casting according to claim 1, wherein the solidification shrinkage portion between 2 and 0.8 is subjected to multi-stage compression. In the slab withdrawal region of 3. A continuous casting apparatus, the axis solid fraction f _S of the slab casting speed V _C as 0.40～0.60M / min is less than 1.0 greater than 0.0 Arrange a multi-stage roll pair consisting of a reference side roll and an anti-reference side roll for rolling down the slab with respect to the solidification shrinkage part of the area, and set the width of the roll convex part for slab reduction of the anti-reference side roll. A width obtained by adding 10 to 100 mm to the unsolidified width of the cast piece at the roll installation position, a height of the roll convex portion of 5 to 60 mm, and a reduction rate of the roll at a reduction ratio of 0.015 to 0.420. So as to satisfy 0.40 to 2.5 mm / min, the reduction amount of each roll of the multi-stage roll is distributed substantially evenly, and the interval between the reference roll and the anti-reference roll of each roll pair is set and arranged. Characterizing continuous casting machine reduction device. Wherein the axis solid fraction of the cast piece f _S is preferably 0.
4. The rolling-down device for a continuous casting apparatus according to claim 3, wherein a multi-stage roll pair consisting of a reference side roll and an anti-reference side roll is provided for rolling down the slab in the region of 2 to 0.8. . 5. The reduction device for a continuous casting device according to claim 3, wherein the number of stages of the multi-stage roll pair is 2 to 10.