JP5030385B2 - Support roll unit replacement method and continuous casting method - Google Patents

Description

  The present invention relates to a support roll unit replacement method and a continuous casting method.

As a continuous casting apparatus, there is one having a support roll unit including a plurality of a pair of support rolls for supporting a cast piece pulled out from a mold (for example, Patent Document 1 and Patent Document 2).
In such a continuous casting apparatus, a plurality of support roll units are arranged in the drawing direction of the slab, one support roll provided on the support roll unit is fixed, and the other support roll is movable in the thickness direction of the slab. These two support rolls are cast while being drawn while supporting the slab.

As described above, when a slab is cast by a continuous casting apparatus, it is common that center segregation occurs in the central portion of the slab. Since the quality of a slab deteriorates when the state of center segregation of the slab is poor, various methods such as improving the state of center segregation with a support roll have been proposed (for example, Patent Document 3).
If casting of a slab is performed for a long period of time, the support roll on the fixed side and the support roll on the moving side in the support roll unit are worn out or break down, so it is necessary to replace them regularly. In such a case, the support roll unit is replaced with a new one.
JP-A-5-15956 Japanese Patent Laid-Open No. 2003-290893 Japanese Patent Laid-Open No. 5-8003

However, when the support roll unit is replaced with a new one, there is a problem that the center segregation of the slab is deteriorated in spite of improving the state of center segregation.
In view of the above problems, an object of the present invention is to provide a support roll unit replacement method and a continuous casting method that do not adversely affect the center segregation of a slab.

The technical means for solving the problems in the present invention includes a support roll unit including a plurality of support rolls that support a slab that is pulled out from a mold, and a plurality of the support roll units are provided in a direction in which the slab is pulled out. A support roll corresponding to a central segregation-affected area that affects the center segregation of the slab, in a continuous casting apparatus provided with one support roll fixed and the other support roll movable in the thickness direction of the slab in replacing the support roll unit which is adapted to replace the unit, among the plurality of support rolls units installed in the continuous casting apparatus, and eject the support roll unit to be exchanged, the new support roll unit, The new support roll unit will be set in the part after removal. When setting the slab, the level difference between the support surface of the slab supported by the fixed support roll of the new support roll unit and the support surface of the slab supported by the fixed support roll of the adjacent support roll unit A new support roll unit is set so that the vertical distance between the fixed side support roll and the movable side support roll is constant within a range of 0.1 to 1.5 mm excluding 0 to less than 0.1 mm. In the point.

The inventors verified the cause of the deterioration of the center segregation of the slab by replacing the support roll unit from various angles. That is, normally, when the support roll unit is replaced with a new one, a step is generated between the fixed support rolls adjacent to each other since the roll diameters of the replaced support roll and the non-replaced support roll are different. Therefore, paying attention to this, the relationship between the step and the center segregation was examined.
When the step was in the range of 0.1 to 1.5 mm, the center segregation of the cast slab was excellent even when the slab was cast. It was recognized that the center segregation of the cast slab deteriorated when the step was larger than 1.5 mm.

If it verifies in detail, when a level | step difference will exceed 1.5 mm, when extracting a slab, the extraction track | orbit of the center part will change with a level | step difference greatly. The pulling trajectory of the center part of the slab changes greatly, for example, which can cause a fine crack in the solid phase (shell) part in the slab, and the molten steel in the slab can enter the crack part. Conceivable, which makes central segregation worse.
Therefore, the inventors set the difference in level between the support roll units at the time of replacement in order to prevent deterioration of center segregation even if the slab is cast after replacing the support roll unit. The range of 1.5 mm was found by various experiments.

It is preferable to replace all of the support roll units corresponding to the central segregation-affected area so that the level difference between the adjacent fixed-side support rolls is in the range of 0.1 to 1.5 mm.
According to this, even if the slab is pulled out while being supported by the support roll, the drawing orbit of the slab does not change greatly, and there is no influence on the center segregation due to the step.
It is preferable to replace the support roll unit to be replaced in the central segregation-affected area so that the step between the adjacent fixed-side support rolls has a predetermined value.

Another means of the present invention includes a support roll unit including a plurality of support rolls that support a slab drawn from a mold, and a plurality of the support roll units are provided in the drawing direction of the slab. In a continuous casting method in which a roll is fixed and the other support roll is movable in the thickness direction of the slab, in the continuous casting method for casting the slab, it is installed in the continuous casting apparatus before casting the slab. among the plurality of support roll unit which is to eject the support roll unit to be exchanged, the new support roll unit, when the fact of setting a part after extraction and setting the new support roll unit The support surface of the slab supported by the fixed support roll of the new support roll unit The step with the support surface of the slab supported by the fixed support roll of the support roll unit adjacent to this is in the range of 0.1 to 1.5 mm excluding 0 to less than 0.1 mm, and the fixed support roll The new support roll unit is set so that the vertical distance between the moving support roll and the moving side support roll is constant, and the slab is cast after setting the new support roll unit.

  According to this, even if the slab was cast, the center segregation of the slab did not deteriorate and was good.

  According to this invention, even if a level | step difference arises between adjacent support rolls, it can prevent a bad influence on center segregation.

First, an example of a continuous casting apparatus will be described in explaining the support roll unit replacement method and continuous casting method of the present invention. However, this invention is not limited to what uses this installation.
As shown in FIG. 1, the continuous casting apparatus includes a ladle 2 for storing molten steel 1, a tundish 3 for temporarily storing molten steel 1 from the ladle 2, and molten steel supplied from the tundish 3. 1 and a mold 4 for molding 1. Further, the continuous casting apparatus has a support roll unit 8 including a plurality of pairs of support rolls 6 and 7 that support the cast piece 5 drawn out from the mold 4. In this embodiment, the continuous casting apparatus is a bloom-type continuous casting apparatus that casts a slab 5 having a thickness of 300 to 400 mm and a width of 500 to 700 mm.

A plurality of support roll units 8 are provided in the direction in which the slab 5 is drawn from directly under the mold 4. This support roll unit 8 makes the support roll 6 that supports one side of the slab 5 (hereinafter, the fixed side support roll 6) immovable in the thickness direction of the slab 5 and supports the other side of the slab 5. (Hereinafter, the moving side support roll 7) is movable in the thickness direction of the slab 5.
That is, a plurality of fixed-side support rolls 6 are collectively attached to a fixed frame 9 fixed to a continuous casting apparatus, and a plurality of movable-side support rolls 7 are collectively attached to a moving frame 10 connected to an elevating device. A roll unit 8 is configured.

The fixed frame 9 and the moving frame 10 are arranged in an arc shape so that the support surfaces of the fixed side support roll 6 and the movement side support roll 7 are along a track with a predetermined radius r, and then are arranged horizontally.
As described above, in the continuous casting apparatus, the molten steel 1 stored in the ladle 2 is poured into the tundish 3, the molten steel 1 temporarily stored in the tundish 3 is supplied to the mold 4, and the molten steel 1 is removed with the mold 4. By performing primary cooling, a rectangular slab 5 (slab) having a solidified surface can be formed.

When the slab 5 is pulled out, the fixed side support roll 6 and the movable side support roll 7 prevent the occurrence of bulging of the slab 5 with the slab 5 interposed therebetween, and the fixed side support roll 6 and the movable side support roll 7. The thickness of the slab 5 is maintained at a predetermined width. At this time, the fixed-side support roll 6 supports the bottom side of the slab 5, and the moving-side support roll 7 supports the upper side facing the bottom side of the slab 5.
The slab 5 pulled out while being supported by the support rolls 6 and 7 is cooled by a secondary cooling device provided between the support roll units 8, and the inside gradually solidifies as it goes downstream. At this time, since the slab 5 is gradually solidified from the outside toward the center, central segregation occurs in the central portion of the slab 5. This center segregation can be improved by making the temperature of the molten steel 1 and the distance D between the fixed support roll 6 and the movable support roll 7 appropriate when casting.

Here, the center segregation influence area A, which affects the center segregation in continuous casting, is an area where the center solid phase ratio in the slab 5 is 20% to 70%. For example, when casting a slab 5 having a carbon content (nonmetallic inclusion amount) of 0.7 to 0.9% at a casting speed of 0.57 to 0.60 m / min, the central solid fraction is 20%. The region of ˜70% is in the range of 11 to 24 mm when viewed from the uppermost meniscus in the mold 4, and this is the central segregation influence area A.
In this central segregation influence area A, the level difference between the fixed support roll 6 of the support roll unit 8 and the fixed support roll 6 of the support roll unit 8 adjacent thereto is in the range of 0.1 to 1.5 mm. In this state, the slab 5 is cast.

As shown in FIGS. 2 and 3, the step is a distance between the support surface S at the fixed side support roll 6 and the support surface S at the fixed side support roll 6 of the support roll unit 8 adjacent thereto. And when casting the slab 5, the distance is maintained over the whole area in the center segregation influence area A.
Further, when the support roll unit 8 is replaced, the step H between the fixed support roll 6 of the support roll unit 8 and the fixed support roll 6 of the support roll unit 8 adjacent thereto is 0.1 to 1.. The support roll unit 8 is exchanged so as to be in the range of 5 mm. When the support roll unit 8 is replaced with a new one, the fixed side support roll 6 and the moving side support roll 7 are renewed.

As shown in FIG. 2, in the horizontal part in the center segregation influence area A, for example, when replacing the middle support roll unit 8 among the three support roll units 8 arranged in the horizontal direction, The middle support roll unit 8 is replaced with a new support roll unit 8a so that the level difference H between the support roll unit 8a and the old support roll unit 8b adjacent thereto is in the range of 0.1 to 1.5 mm. To do.
Specifically, in the old support roll units 8b on both sides, the wear amount of the old support roll 6b is measured in advance, and when the wear amount is in the range of 0.1 to 1.5 mm, the middle support roll Replace unit 8 with new support unit 8a.

In this way, when the support roll 6 is new, its diameter is the same as the other support rolls 6 (the diameters of the support rolls 6 are the same at the time of replacement), so the friction amount of the old support roll 6b is 0. When it is in the range of 1 to 1.5 mm, even if the support roll 6 is new, the step with the old support roll 6b adjacent to the support roll 6 is inevitably a wear amount of the old support roll 6b of 0.1 to 1.5 mm. of ing and scope.

Further, the entire support roll unit 8 corresponding to the center segregation influence area A is exchanged, or only the support roll unit 8 to be exchanged is exchanged in the center segregation influence area A.
As shown in FIG. 3, in the arc part in the center segregation influence area A, for example, when replacing the lower support roll unit 8 among the support roll units 8 arranged in the vertical direction, the support of the fixed support roll 6 is supported. The lower support roll unit 8 is arranged so that the surface S follows a track having a predetermined radius r. A step H is generated between the lower new support roll unit 8a set after replacement, and the old support roll unit 8b adjacent to the lower support roll unit 8b. However, the step H becomes a predetermined value in the arc portion as well as the horizontal portion. Thus, the lower support roll unit 8 may be replaced with a new support roll unit 8a.

As described above, even when the support roll unit 8 is replaced with a new one, the slab 5 is cast in a state where the step H is in the range of 0.1 to 1.5 mm. At this time, in each support roll unit 8, the vertical distance D (distance D in the thickness direction of the slab 5) between the moving side support roll 7 and the fixed side support roll 6 is substantially constant.
As described above, it has been experimentally confirmed that if the slab 5 is cast in a state where the step H is in the range of 0.1 to 1.5 mm, the state of center segregation is good. That is, it was found that if the step H is in the range of 0.1 to 1.5 mm, the deviation of the carbon content in the center portion in the slab 5 is small and the state of center segregation is good.

In order to evaluate the state of central segregation, the inventors manufactured slabs 5 while varying the steps as shown in FIGS. 4 and 5, and from the slabs 5 at each step, a width of 600 mm and a thickness of 380 mm. , A sample having a length of 250 mm was taken, a hole was made in the center portion of the slab 5 with a 5.0 mmφ drill, and a total of 25 chips were taken at a pitch of 10 mm in the longitudinal direction (drawing direction). The variation in the carbon content contained in the central portion of 5 was examined.
As an evaluation of the variation in the carbon content, as shown in FIG. 6, the largest value of the carbon content among the 25 chips is set as Cmax, and a molten steel 1 obtained by sampling a predetermined amount from the tundish 3 at the time of casting. Cmax / C0 was calculated with C0 as the carbon content of the sample, and the degree of carbon content in the center portion of the slab 5 with respect to the carbon content contained in the molten steel 2 was summarized.

FIG. 6 summarizes the relationship between Cmax / C0 and the step H by performing casting several times while changing the step H.
As shown in FIG. 6, when the step H is 0.1 to 1.5 mm, the value of Cmax / C0 is 1.1 or less (Cmax / C0 ≦ 1.1) and the ideal value (Cmax / C = 1.0), carbon is relatively rarely biased in the center portion of the slab 5, and the state of center segregation was good. When the level difference H exceeded 1.5 mm, the value of Cmax / C0 varied over a wide range from 1.0 to 1.4, and many of the values exceeded 1.1.

Here, a steel cord material was manufactured from the cast slab 5 in order to evaluate the slab 5 having a Cmax / C0 value of 1.1 or less and good center segregation.
First, the slab 5 (width 600 mm, thickness 380 mm) was heated in a heating furnace for about 3 hours, and then turned into a billet of 155 mm × 155 mm. The billet was rolled into a 5.5 mmφ wire, and the wire was further processed to produce steel. Cord material was manufactured.
As shown in FIG. 7, in the process of processing the wire into a steel cord material, the number of breaks was examined. When the value of Cmax / C0 was 1.1 or less, no breakage occurred.

This is because, in the process of casting the slab 5, when producing a steel cord material having a high strength and a relatively small diameter because the deviation of the carbon content in the central portion of the slab 5 is small, It is considered that the wire did not break even when stress such as tension was applied to. On the other hand, when the value of Cmax / C0 exceeded 1.1, many disconnections occurred. Contrary to the above, the carbon content in the center portion of the slab 5 is greatly biased and the strength is weakened, and the wire rod (cast slab) was not able to withstand stress such as tension during the processing and was disconnected. it is conceivable that.
Therefore, it was proved that the center deviation did not deteriorate even if the cast piece 5 was cast in a state where the step H was in the range of 0.1 to 1.5 mm.

It is the schematic of a continuous casting apparatus. It is an arrangement plan of support roll units in a horizontal part. It is an arrangement plan of support roll units in an arc portion. It is a sample figure of slab. It is L sectional drawing of FIG. It is a figure which shows the relationship between a level | step difference and Cmax / C0. It is a figure which shows the relationship between Cmax / C0 and the frequency | count of a disconnection.

Explanation of symbols

Slab 6 fixed support roll 7 moving support roll 8 support roll unit 8a new support roll unit 8b old support roll unit 9 fixed frame 10 moving frame H step S support surface

Claims (5)

A support roll unit having a plurality of paired support rolls for supporting a slab pulled out from the mold; a plurality of the support roll units are provided in the direction of drawing the slab to fix one support roll; and the other Replacement method of a support roll unit that replaces a support roll unit corresponding to a central segregation-affected area that affects the center segregation of the slab in a continuous casting apparatus that enables the support roll to move in the thickness direction of the slab. In
Among the plurality of support rolls units installed in the continuous casting apparatus, and eject the support roll unit to be exchanged, the new support roll unit, and to setting the part after extraction,
When setting the new support roll unit, the support surface of the slab supported by the fixed support roll of the new support roll unit and the support of the slab supported by the fixed support roll of the support roll unit adjacent thereto New support roll so that the level difference from the surface is in the range of 0.1 to 1.5 mm excluding 0 to less than 0.1 mm, and the vertical distance between the fixed support roll and the moving support roll is constant. A method for replacing a support roll unit, characterized by setting the unit.   The replacement of the support roll unit according to claim 1, wherein all of the support roll units corresponding to the center segregation influence area are exchanged so that the adjacent fixed-side support rolls have the step. Method.   2. The support roll unit according to claim 1, wherein the support roll unit to be exchanged is exchanged in a central segregation-affected area so that the adjacent fixed-side support rolls have the steps. method of exchange.   The method for replacing a support roll unit according to any one of claims 1 to 3, wherein the center segregation-affected area is a region where a central solid phase ratio in the slab is 20% to 70%. A support roll unit having a plurality of paired support rolls for supporting a slab pulled out from the mold; a plurality of the support roll units are provided in the direction of drawing the slab to fix one support roll; and the other In the continuous casting method in which the support roll is movable in the thickness direction of the slab and the slab is cast,
Among the plurality of support rolls units installed in the continuous casting apparatus prior to casting the cast piece, and eject the support roll unit to be exchanged, the new support roll unit and setting the part after extraction When setting the new support roll unit, the support surface of the slab supported by the fixed support roll of the new support roll unit and the cast support supported by the fixed support roll of the support roll unit adjacent thereto. The step with the support surface of the piece is in the range of 0.1 to 1.5 mm excluding 0 to less than 0.1 mm, and the vertical distance between the fixed side support roll and the moving side support roll is constant. Set a new support roll unit,
A continuous casting method characterized by casting a slab after setting a new support roll unit.

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