JP3228212B2 - Method and apparatus for producing round billet slabs by continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing round billet slabs by continuous casting, and more particularly to a method for producing round billet slabs for pipe making using continuous casting followed by unsolidification rolling and post-solidification molding methods. It relates to a manufacturing method and an apparatus.

[0002]

2. Description of the Related Art When producing round billet slabs by continuous casting, the materials are low carbon steel, low alloy steel such as bearing steel, and high Cr.
In the case of steel, segregation (center segregation), axial cracks, and porosity are generated in the center that finally solidifies. If such a slab is used as it is in the production of a seamless pipe, internal flaws occur frequently and do not become a product.

[0003] In order to improve the inner surface quality of round billet slabs, there have been proposed many methods of reducing the slab after solidification is completed. For example, JP-A-9-201601 and JP-A-9-201601
After applying the reduction after solidification is completed,
Again, a method of making a round slab is disclosed.

[0004]

In contrast to such prior art, the present applicant has also proposed a method of reducing the slab during unsolidification, for example, in Japanese Patent Application Nos. 9-56478 and 9-56477. No. 9-144200. These methods disclose a method in which a central portion is subjected to a large pressure reduction at a position of an unsolidified portion and then formed into a perfect circle.

However, if the method of performing the solidification completion reduction following the above-described unsolidification reduction method is to be used for actual production, the casting upstream of the roll reduction under the roll reduction when forming into a perfect circle is performed. It has been found that a phenomenon in which the vertical direction of the piece is twisted occurs. When such a phenomenon occurs, the cast slab is not inserted into the forming roll in a predetermined desired direction, and it becomes impossible to form a perfect circular shape.

Here, an object of the present invention is to provide a technique for correctly inserting a slab into a perfect circular forming roll at the time of final perfect circular forming in either the unsolidified rolling method or the solidification completed rolling method. It is to develop.

[0007]

Means for Solving the Problems The present inventors have repeatedly studied the above-mentioned problems and obtained the following knowledge. For example, the slab before entering the perfect circular forming roll composed of a vertical roll has an elliptical shape that is crushed in the vertical direction, and the greater the ellipticity, the more easily twisting occurs.

[0008] Since the twist is generated by the escape of the slab to the direction where less force is applied during the formation of the elliptical cast slab, when the slab is inserted into a perfect circular forming roll composed of a vertical roll, the twist always occurs. It is necessary to insert while holding.

Therefore, it has been found that twisting can be prevented even with a cast piece having a large ellipticity, and as a means for that purpose, for example, when the cast piece is inserted into a perfect circular forming roll composed of a vertical roll, it is always held horizontally. The present invention has been completed by noting that it is important to place them in the opposite direction or vice versa.

Here, the present invention is as follows. (1) Following the continuous casting of a round billet, in a method for producing a round billet slab in which unsolidification is performed under a unsolidified pressure, and after solidification is completed, the round shape is performed while holding the slab by a roll provided on the upstream side. A method for producing a round billet slab by continuous casting, wherein the forming is performed by a perfect circular forming roll.

(2) In a forming area after solidification is completed in a round billet continuous casting apparatus, a perfect round forming roll and a slab holding roll are provided upstream of the perfect round forming roll. To manufacture round billet slabs by continuous casting.

(3) In continuous casting of a round billet, a non-solidifying pressure is applied by one horizontal roll, and then the vertical roll 1
A round billet slab by continuous casting, in which a horizontal roll for holding a slab is provided upstream of a vertical roll for forming a perfect circle in a process of adding a perfect circle by a step and then pulling out by a final pinch roll. Manufacturing method.

(4) In the continuous casting of a round billet, after drawing by a final pinch roll, applying a non-solidification reduction by one horizontal roll, and then applying a perfect circular molding by one vertical roll, A method for producing a round billet slab by continuous casting, wherein a horizontal roll for slab holding is installed upstream of a vertical roll.

(5) In the above (3) or (4), after forming a perfect circle by one vertical roll roll, one horizontal roll,
A method for producing round billet slabs by continuous casting, in which a plurality of round forming rolls, such as a vertical roll, are provided.

(6) The horizontal roll for holding a slab is provided within 3 m upstream of the vertical roll for forming a perfect circle.
(3) The method for producing a round billet slab by continuous casting according to any one of (5) to (5).

[0016]

Next, embodiments of the present invention will be described more specifically with reference to the accompanying drawings.

FIGS. 1 (a) and 1 (b) are schematic explanatory views showing an example of a production process of a round billet slab by continuous casting according to the present invention. As shown in FIG. 1 (a), molten steel 3 poured from a tundish 1 into a continuous casting mold 2 having a circular plane cross section is cooled in the mold 2 and a solidified shell is formed outside. The slab 4 drawn from the mold 2 is
After entering the pinch roll zone 6 through the spray cooling zone 5, the central roll is greatly reduced in a non-solidified state by a pair of horizontal rolls 7 for non-solidification reduction. Unsolidification reduction may be performed by a vertical roll pair if necessary.

At this time, the slab having an elliptical cross section passes through a pair of horizontal rolls 8 for holding slabs provided in a region after complete solidification in the illustrated example, and then to a pair of vertical rolls 9 for forming a perfect circle. It is formed into a perfect circle and becomes a round billet slab for manufacturing a seamless pipe. Then, it is pulled out by the final pinch roll 10. When the pair of round forming rolls is a horizontal roll pair, the slab holding roll is a vertical roll pair.

In the illustrated example, only one pair of rolls for forming a perfect circle is provided, but if necessary, a plurality of vertical rolls and horizontal rolls are alternately provided, such as a vertical roll, a horizontal roll, and a vertical roll. You may. When the round forming rolls are provided in multiple stages as described above, a part of the rolls may be a hole type roll.

The horizontal roll for holding the slab may be a flat roll or a caliber roll. FIG. 1 (b) is a modification of FIG. 1 (a) and shows a case where no pinch roll is provided on the downstream side of the perfect circular forming roll 9, but in the illustrated example, a vertical roll for perfect circular forming is used. It is provided in two stages.

Here, according to the findings of the present inventors, in the case of the illustrated example, the phenomenon of slab twisting due to the perfect circular forming roll is as follows.
Due to the unsolidification reduction in the vertical direction, the slab deformed into an elliptical cross section is going to be formed into a perfect circle with a vertical roll, so the contact to the roll in the horizontal direction of the slab is close to point contact,
Due to lack of stability, as shown in FIG. 2 (b), this occurs when the slab escapes in a direction in which a force is less likely to be applied to the slab.

That is, as shown in FIG. 2 (a), the cast slab having an elliptical cross section inserted into the roll for forming a perfect circle has a point contact at the tip of the ellipse with the roll for forming a perfect circle, so that it is stable. Instead, as shown in FIG. 2 (b), it is inserted into the round forming roll while rotating in the direction of the arrow. Therefore, a twist in the vertical direction is inevitable. In the illustrated example, the case where the perfect circular forming roll is a vertical roll pair is shown, but the situation is the same for a horizontal roll pair. As shown in FIG. 3, the degree of twist at this time, that is, the degree of twist, is described as a twist angle (θ) per m of the casting length.

According to the present invention, in order to maintain the state shown in FIG. 2A at the time of biting and at the time of forming a perfect circle, a slab holding roll (merely a holding In the illustrated example, horizontal rolls are arranged. Therefore, the arrangement of the horizontal rolls is not limited as long as it is in general, but the rolls are generally installed as close as possible with matching pass lines.

By the way, the degree of twist of the slab (the twist angle per 1 m of the casting length) depends on the unsolidified draft rate (the draft rate, ie, the rate of thickness change due to the draft). This relationship was experimentally determined, and what is shown in the graph is shown in FIG.

In FIG. 4, if the degree of twist exceeds 1 ° / m, the roundness at the time of molding exceeds 1.5%, and the material cannot be used as a material for a seamless pipe. In addition, the effect of improving the internal quality is obtained when the rolling reduction is 15% or more from the conventional technology. Therefore, in order to obtain the effect of improving the internal quality, the twist of the slab always becomes a problem.

According to the present invention, by providing the holding roll on the upstream side of the casting of the perfect circular forming roll, it is possible to always insert the perfect circular forming roll with the major axis of the ellipse horizontal. Twist can be prevented.

It is meaningless to provide the cast slab after casting into a round shape again by providing it on the downstream side of the casting.
The slab holding roll is preferably driven,
It may not be driven. Further, it is desirable that the pressing force be 5 to 50 tons so that the load does not further reduce the thickness of the unsolidified and reduced slab and that the slab can be sufficiently held.

As already described, if the slab holding roll can be prevented from being twisted, it can be installed at any position.
Although not limited to a particular form, it is generally desirable to install it within 3 m upstream of the forming roll on the casting side. This is because if the distance is longer than this, it is practically difficult to insert the ellipse into the vertical forming roll, for example, by always keeping the major axis of the ellipse horizontal.

FIG. 5 is a graph showing the result of experimentally determining such a relationship. If the distance between the holding horizontal roll and the round forming roll exceeds 3 m, the degree of twist exceeds 1 ° / m, so that the roundness during forming exceeds 1.5% and cannot be used as a material for a seamless pipe. next,
The operation and effect of the present invention will be described more specifically with reference to examples.

[0030]

EXAMPLE A round billet slab was cast in a continuous casting mold having a circular section of 225 mm in diameter with equipment substantially equivalent to the structure shown in FIG. Horizontal roll pair 7 for unsolidification reduction
The unsolidification rolling position was 23 m from the molten metal meniscus, and the horizontal roll 8 for slab holding and the perfect circular forming roll 9 were arranged at positions 31 m and 32 m from the molten meniscus, respectively.

The casting speed was 1.2 to 2.2 m / min, and the spray cooling specific water amount was 0.05 to 0.8 l / kg · steel. Table 1 shows the effects of applying the slab holding roll according to the present invention.

The degree of twist is the twist angle (θ) shown in FIG. 3 per casting length of 1 m. The roundness is a value obtained by dividing a value obtained by subtracting a minor diameter from a diameter by a true circular diameter and multiplying by 100. A good level of this roundness is 1.5% or less.

Example 1 is an example in which the holding speed according to the present invention is applied at a casting speed of 1.2 m / min.
Since the degree of twist is 0 ° / m and the roundness is 1.0%, stable continuous rolling operation is possible.

Example 2 is an example in which the presser roll according to the present invention is applied at a casting speed of 1.8 m / min.
Since the degree of twist is 0 ° / m and the roundness is 0.8%, stable continuous rolling operation is possible.

Example 3 is an example in which the holding speed according to the present invention is applied at a casting speed of 2.2 m / min.
Since the degree of twist is 0 ° / m and the roundness is 1.2%, stable continuous rolling operation is possible.

However, no satisfactory results were obtained in any of the comparative examples in which the pressing roll was not applied as in the present invention. Comparative Example 1 is an example in which the casting speed was set to 1.2 m / min, but the holding roll was not applied, and the twist degree was 2 m / min.
Continuous rolling operation is impossible at ° / m, and roundness is 5.0
% And 1.5%, there is a quality problem.

Comparative Example 2 is an example in which the casting speed was 1.8 m / min, but the press roll was not used, and the twist degree was 4
Continuous rolling operation is impossible at ° / m, and roundness is 7.0
% And 1.5%, there is a quality problem.

Comparative Example 3 is an example in which the casting speed was 2.2 m / min, but the pressing roll was not applied, and the twist degree was 6 m / min.
Continuous rolling operation is not possible at ° / m, and roundness is 10.0
% And 1.5%, there is a quality problem.

Next, the present invention was carried out using a continuous casting apparatus having the same structure as that shown in FIG. However, the perfect circular molding was performed in one stage. As a result, the same result as in the above example was obtained.

[0040]

[Table 1]

[0041]

As described above, according to the present invention,
When manufacturing round billet slabs using the unsolidification rolling method and the post-solidification molding method by continuous casting, continuous molding is possible with stable operation and good roundness, which is important for quality. Therefore, its practical significance is great.

[Brief description of the drawings]

FIG. 1 (a) is a schematic explanatory view showing an outline of equipment for implementing a drafting method according to the present invention, and FIG. 1 (b) is a partial explanatory view of a modified example thereof.

FIGS. 2 (a) and 2 (b) are schematic explanatory views showing a state in which a slab is twisted at the time of forming a perfect circle.

FIG. 3 is a schematic explanatory view showing the degree of twist of a slab at the time of forming a perfect circle.

FIG. 4 is a graph showing the relationship between unsolidified draft and slab twist.

FIG. 5 is a graph showing a relationship between a distance between a holding roll and a perfect circular forming roll and a degree of twist.

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Seiichiro Hayashida 1850 Minato, Wakayama Sumitomo Metal Industries Co., Ltd.Sumitomo Metal Works Ltd. (72) Inventor Katsuyoshi Iwata 1850 Minato, Wakayama City Sumitomo Metal Industries Co., Ltd. References JP-A-8-117941 (JP, A) JP-A-9-201602 (JP, A) JP-A-9-201601 (JP, A) JP-A-7-204812 (JP, A) JP-A-1 JP-A-289552 (JP, A) JP-A-51-37031 (JP, A) JP-A-10-249490 (JP, A) JP-A-10-144661 (JP, A) JP-A-10-328800 (JP, A) JP-A-9-295113 (JP, A) JP-A-3-275259 (JP, A) JP-A-10-175049 (JP, A) JP-A-10-166124 (JP, A) 34410 (JP, U) JP44-17366 (JP, B1 (58) Fields surveyed (Int. Cl. ⁷ , DB name) B22D 11/128 350 B21B 1/46 B22D 11/00

Claims (6)

(57) [Claims] 1. A method for producing a round billet slab in which continuous casting of a round billet is performed, followed by unsolidification under pressure, and after the solidification is completed, wherein the slab is held down by a roll provided on an upstream side. A method for producing round billet slabs by continuous casting, characterized in that perfect circular forming is performed by a perfect circular forming roll. 2. In a molding area after solidification in a continuous casting device for a round billet, a roll for forming a perfect circle and a roll for holding a slab are provided upstream of the roll for forming a perfect circle. , Continuous billet production equipment for round billet. 3. In the continuous casting of a round billet, a non-solidifying pressure is applied by one horizontal roll, a true circular forming is applied by one vertical roll, and then a drawing is performed by a pinch roll. Characterized by installing a horizontal roll for slab holding on the upstream side of the roll,
A method for producing round billet slabs by continuous casting. 4. A continuous roll for forming a perfect circle in a process of applying a non-solidification pressure by a single horizontal roll after drawing by a pinch roll and then applying a perfect circular forming by a vertical roll during continuous casting of a round billet. A method for producing a round billet slab by continuous casting, wherein a horizontal roll for slab holding is installed upstream of the slab. 5. The continuous casting according to claim 3, wherein after a round forming by one vertical roll, a plurality of round forming rolls such as a horizontal roll and a vertical roll are provided. Manufacturing method of round billet slab. 6. The method for producing a round billet slab by continuous casting according to claim 3, wherein the horizontal roll for holding the slab is provided within 3 m upstream of the vertical roll for forming a perfect circle. .