JP5822638B2 - Method for preventing generation of surface defects on the pressed surface of continuous cast pieces - Google Patents

Description

  The present invention relates to the production of cast slabs with few surface defects, and in particular, when a cast slab produced by reduction by continuous casting (hereinafter referred to as “continuous cast slab”) is subjected to block rolling to form a steel slab. The present invention relates to a method for preventing a surface defect consisting of surface flaws occurring at the position of the steel piece corresponding to the recessed portion of the surface of the continuous cast piece that has been reduced.

  In the continuous casting of molten steel, the stirring in the mold, which has been conventionally performed as a technique for improving the center segregation of the continuous cast slab, is performed, the dendrite in the front of the solidified part is allowed to settle, and fine equiaxed crystals are generated. Down flow of molten steel due to solidification shrinkage by applying electromagnetic rolling technology to prevent bridging in the zone, or repeatedly rolling down the solid-liquid two-phase zone of the continuous cast slab to the solidification completion point with a rolling roll or flat press A reduction technique for preventing this is known. In particular, with regard to the reduction technique, the unsolidified area is center-renewed by preventing the downward flow of the molten steel due to shrinkage by multi-stage compression using a reduction roll of a continuous casting apparatus having convex portions of different widths. There is known a method for improving the above (see, for example, Patent Document 1).

  However, in continuous cast slabs produced by rolling down with a continuous casting device, the continuous cast slabs that have been squeezed by a rolling roll having a convex portion having a smaller width than the continuous cast slabs, Since a dent is formed, if the continuous cast piece forming the dent is split-rolled into a steel slab, a surface defect in which the dent remains in the steel slab after the batch rolling is generated. It was.

JP-A-8-132205

  The problem to be solved by the present invention is that the depressed portion of the surface of the continuously cast slab produced by squeezing with a continuous casting apparatus remains in the steel slab after partial rolling, and this dent is a surface defect. Therefore, it is an object of the present invention to provide a continuous cast piece manufacturing method using a reduction roll of a continuous casting apparatus that makes it possible to detoxify the recessed portion of the pressed surface.

When the inventors diligently researched, in a cross section perpendicular to the casting direction at the position where the rolling roll and the continuous cast piece contacted with the rolling roll having a narrower width than the continuous cast piece being drawn from the continuous casting apparatus, The rising angle θ ₁ formed by the inclined surface of the convex portion that protrudes inclined from the rolling roll and the surface of the continuous cast piece that abuts the horizontal surface of the convex portion is 5 ° ≦ θ ₁ ≦ 15 °, and has a convex portion. the supplementary angle theta ₂ of the rising angle theta ₁ of the inclined surface of the projection of the pressure roll and obtuse 165 ° ≦ θ ₂ ≦ 175 ° is supplementary angle of the rising angle theta ₁ of the above, supplementary to the rising angle theta ₁ The continuous cast piece being drawn is drawn down from the continuous casting machine by the convex part of the reduction roll with an obtuse angle of θ ₂ to form a concave part in the continuous cast piece, and the continuous cast piece having this concave part is further subjected to split rolling. And detoxifying the surface defects generated at the position of the steel slab after the partial rolling corresponding to the dent of the continuous cast slab It found that it is Rukoto, in which to obtain a manufacturing method of continuous casting pieces by reduction rolls of a continuous casting apparatus of the present invention.

That is, the means for solving the problem of the present invention is that the rolling roll having a narrower convex portion than the continuous cast piece being drawn from the continuous casting apparatus is perpendicular to the casting direction at a position where the continuous cast piece is in contact with the continuous cast piece. In such a cross-section, the rising angle θ ₁ formed by the inclined surface of the convex portion protruding obliquely from the rolling roll and the surface of the continuous cast piece in contact with the horizontal surface of the convex portion is 5 ° ≦ θ ₁ ≦ 15 °, Thus the supplementary angle theta ₂ of the rising angle theta ₁ of the inclined surface of the projection of the pressure roll having a convex portion with an obtuse angle consisting of 165 ° ≦ θ ₂ ≦ 175 ° is supplementary angle of the rising angle theta ₁ above, this rise The continuous cast piece being drawn is drawn down from the continuous casting device by the convex part of the reduction roll with the complementary angle θ ₂ of the angle θ _{1 being} an obtuse angle, thereby forming a concave part in the continuous cast piece, and the continuous casting having this concave part. The piece is further rolled in pieces and the steel pieces after the piece rolling corresponding to the dents in the continuous cast pieces are rolled. It is a manufacturing method of continuous casting pieces by reduction rolls of a continuous casting apparatus which comprises harmless surface defects that are generated in the location.

  According to the present invention, the dent formed on the reduced surface of the continuous cast piece produced by the reduction by the reduction roll at the time of drawing from the continuous casting apparatus does not remain in the steel piece after the block rolling, and therefore The present invention improves the surface properties of continuous cast slabs, such as surface flaws generated on steel slabs by the method of the present invention in the conventional method. There is an effect to prevent.

It is a schematic diagram which shows the positional relationship of the continuous cast piece before reduction of a cross section perpendicular | vertical to a drawing direction from the continuous casting equipment of this invention, and a reduction roll. It is a schematic diagram which shows the positional relationship of the continuous cast piece after reduction of the cross section perpendicular | vertical to a drawing direction from the continuous casting installation of this invention, and a reduction roll. It is a schematic diagram which shows the positional relationship of the continuous cast piece after reduction of the cross section perpendicular | vertical to the drawing direction from the conventional continuous casting equipment, and a reduction roll.

  Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the continuous cast piece 1 drawn from the mold of the continuous casting apparatus has a width of 530 mm and a thickness of 380 mm, and has a convex portion 4 having a width smaller than the continuous cast piece 1 width of 530 mm. The surface 1a is rolled down by the rolling roll 3 it has. As a result of this reduction, a recessed portion 2 formed by the convex portion 4 of the reduction roll 3 is formed on the surface 1b that has been reduced as shown in FIG. The formed dent 2 remains in the steel slab during the subsequent ingot rolling and becomes a surface defect.

Remaining surface defects during the slabbing is obtuse supplementary angle theta ₂ of the rising angle theta ₁ recessed portion of the second pressure has been surface 1b of the continuous casting strip 1 which is rolling at a reduction roll 3 of a continuous casting apparatus By making it, it can prevent remaining as a surface flaw after partial rolling. Therefore, in the vertical continuous casting apparatus, as shown in FIG. 1, the continuous cast piece 1 and the reduction roll in a cross section perpendicular to the casting direction at the position where the reduction roll 3 and the continuous cast piece 1 are in contact with each other. It is preferable that the rising angle θ ₁ formed by the inclined surface 5 of the reduction roll 3 and the surface 1a of the continuous cast piece 1 when the roll 3 is in contact is 5 ° ≦ θ ₁ ≦ 15 °. If the rising angle θ ₁ between the continuous cast piece 1 and the surface 1a to be reduced is 5 ° ≦ θ ₁ ≦ 15 °, the rising angle θ of the recessed portion 2 of the reduced surface 1b as shown in FIG. _Since the complementary angle θ _{2 of 1} becomes obtuse with 165 ° ≦ θ ₂ ≦ 175 °, it is possible to prevent the recessed portion 2 from remaining as a surface defect, which is a surface defect, after the block rolling.

When the rising angle θ ₁ formed with the surface 1a to be rolled down of the continuous cast piece 1 is larger than 15 °, the recess 2 of the surface 1b of the continuous cast piece 1 that has been rolled down is not smoothed during the batch rolling, In the steel slab after ingot rolling, surface flaws are generated due to the remaining depression 2 on the surface of the continuous cast slab 1 that has been reduced.

In addition, when the rising angle θ ₁ formed with the surface 1a to be rolled down of the continuous cast piece 1 is smaller than 5 °, the recessed portion 2 of the continuous cast piece 1 does not remain as a defect, but it is reduced during the drawing down at the time of drawing. Since the load of the roll 3 becomes large and the continuous cast piece 1 cannot be sufficiently reduced, a central defect occurs in the continuous cast piece 1. In order to perform sufficient reduction so that the center defect does not occur, further capital investment such as modification of the drive motor of the reduction roll 3 is required.

As seen in Table 1, in Examples 1 to 5 of the present invention, the rising angle θ ₁ formed by the inclined surface 5 of the reduction roll 3 and the surface 1a of the continuous cast piece 1 to be reduced is 5 ° ≦ θ ₁ ≦ 15 °. since it is, the supplementary angle theta ₂ of the rising angle theta ₁ of the recessed portion 2 of the surface of the continuous casting strip 1 is obtuse. As a result, the surface flaw after the partial rolling, which occurs when the dent 2 of the continuous cast piece 1 remains in the steel slab, was not seen, and a very good result was obtained. Further, since the rising angle θ ₁ formed with the surface 1a to be rolled down of the continuous cast piece 1 is 5 ° ≦ θ ₁ ≦ 15 °, the continuous cast piece 1 has no center defect. there were.

On the other hand, in Comparative Examples 1-6 in Table 1, the recessed portion rising angle theta ₁ of the supplementary theta ₂ of 2 can not be obtuse, surface defects due to residual of the recess 2 in the steel piece after slabbing is generated .

  Further, in Comparative Examples 7 to 11 in Table 1, the surface flaws of the steel pieces after the ingot rolling did not occur in the same manner as in Inventive Examples 1 to 5, and good results were obtained for the front and rear properties. However, since the load on the rolling roll 3 becomes large and the continuous cast piece 1 cannot be sufficiently reduced, a central defect occurs in the continuous cast piece 1. When sufficient reduction is performed with the reduction roll 3 so as not to cause a central defect, it is difficult to apply because further capital investment such as remodeling to make a motor that can handle the load of the reduction roll 3 is required. It was.

As an embodiment of the present invention, in a continuous casting apparatus, a rolling roll 3 in which the rising angle θ ₁ formed by the inclined surface 5 of the rolling roll 3 and the surface 1a to which the continuous cast piece 1 is rolled is θ ₁ = 10 ° is provided. A pair of chrome molybdenum steel of SCM420 specified by JIS G4053 in contact with the rolling roll 3 under the condition that the casting speed is 0.5 m / min. A continuous cast piece 1 having a cross section shown in FIG. 1 was manufactured in which the length of 1a was 530 mm, and the length of the surface 1c that was not pressed without contacting the reduction roll 3 was 380mm.

Continuous casting piece 1 obtained are supplementary theta ₂ rising angle theta ₁ of the recessed portion 2 of the pressure by the surface 1b at a reduction roll 3 during withdrawal are made obtuse, in a steel specimen after slabbing There was no generation of surface flaws due to the remaining indented portion 2 of the continuous cast piece 1, and an extremely good result was obtained.

1 Continuous cast slab 1a Surface to be rolled down 1b Surface to be rolled down
1c Surface not to be rolled down
2 Indented part 3 Rolling roll 4 Convex part 5 Inclined surface θ ₁ Rising angle formed by the horizontal surface of the continuous cast piece and the inclined surface of the reducing roll θ ₂ Complement angle of the rising angle θ ₁ of the convex part of the reducing roll

Claims (1)

Convex projecting obliquely from the rolling roll in a cross section perpendicular to the casting direction at the position where the rolling roll having a narrower convex part than the continuous casting piece being drawn from the continuous casting apparatus is in contact with the continuous casting piece. The rising angle θ ₁ formed between the inclined surface of the convex portion and the surface of the continuous cast piece in contact with the horizontal surface of the convex portion is set to 5 ° ≦ θ ₁ ≦ 15 °, and the inclined surface of the convex portion of the rolling roll having the convex portion the supplementary angle theta ₂ of the rising angle theta ₁ is obtuse consisting 165 ° ≦ θ ₂ ≦ 175 ° is supplementary angle of the rising angle theta ₁ above, reduction rolls the supplementary theta ₂ of the rising angle theta ₁ and an obtuse angle The continuous cast piece being drawn from the continuous casting apparatus is pressed down by the convex portion to form a concave portion in the continuous cast piece, and the continuous cast piece having this concave portion is further batch-rolled to form a concave portion of the continuous cast piece. Continuously characterized by detoxifying the surface flaws generated at the position of the steel slab after ingot rolling corresponding to Method for producing a continuously cast piece by pressure roll forming apparatus.

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