JP3058091B2 - Method and apparatus for manufacturing continuous billet of round billet - 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 reducing center segregation and center porosity generated at the center of a slab in continuous casting of round billets of carbon steel, stainless steel, high alloy steel, and the like. is there.

[0002]

2. Description of the Related Art In a method of manufacturing a seamless pipe by a Eugene Sejournel method or a Mannesmann method from a continuous casting process to a rolling or forging process, recently,
As a method of increasing the efficiency of the process by partially omitting the steps such as continuous rolling below the continuous casting step, a method called near net shape casting, which casts a round billet having a size closer to the final product shape, is being pursued. ing.

However, in the round billet slab, center segregation and center porosity occur during casting, which remains inside the slab. If the degree is large, the problem is that the inner surface flaw of the pipe is generated after piping. There is a point.

Therefore, as a countermeasure against the above-described center segregation and center porosity, there has been proposed a method of manufacturing a continuously cast slab for improving the internal quality (see Japanese Patent Application Laid-Open No. 3-124352). This technology uses a roll having a diameter of 2 to 5 times the thickness of the slab to reduce the unsolidified portion inside the slab, so that the rolling force is lower than when the solidified slab is reduced. It is intended to reduce the occurrence of center segregation and center porosity without necessity, and a certain reduction effect can be expected.

However, since the above-described method for producing a continuous cast slab is intended for a slab or a bloom having a rectangular cross-sectional shape such as a slab or a bloom, this method can be applied to an ordinary round billet slab having a circular cross-sectional shape. The following problems occur when the method is applied.

[0006]

FIG. 1 is a schematic cross-sectional view of a conventional unsolidified rolling method directly applied to a round billet cast piece, in which a pair of upper and lower rolls 10 and 12 are round billet cast. The piece 14 is pressed down in the outline arrow direction, and the unsolidified portion 16 at the center is pressed.

However, as described above, the round billet slab
When 14 is inline-rolled using the conventional unsolidification rolling method, if the rolling volume is increased, the roundness is impaired by the rolling deformation indicated by arrows in the left and right direction, and the roundness accuracy deteriorates, and such a whole If an elliptical billet is used, it will not be possible to make a pipe as it is. Further, when the billet extends and deforms in the direction perpendicular to the rolling direction in this way, a tensile stress is generated at the solidification interface 18 in the upper and lower portions of the round billet slab 14, and there is a risk of generating a so-called internal crack 20. .
The internal cracks 20 seen at the solidification interface 18 have attracted segregated molten steel to the cracks, and when observed on the cross section of the cast slab after solidification, as segregation lines in which components such as C, P, S, and Mn are concentrated. It remains. These segregation lines are generally called internal cracks and contribute to the generation of scratches on the inner surface of the pipe during pipe production.

In addition, when the rolling reduction is large, in addition to the impairment of roundness and the occurrence of internal cracks, the drawing resistance of the slab increases and sometimes the drawing becomes impossible, and the continuous casting operation itself becomes impossible.

However, on the other hand, when the reduction amount is reduced due to the above-mentioned problems, the center porosity,
If the pipe is manufactured without sufficiently improving the center segregation, the inner surface of the pipe is frequently damaged.

Accordingly, an object of the present invention is to produce a round billet slab for pipe making having a good roundness, no internal cracks, a low center porosity, and a low center segregation in continuous casting. A method and apparatus are provided.

[0011]

Means for Solving the Problems The present inventors have repeated various experiments and investigations on the means for solving the above-mentioned problems, thereby simultaneously performing uncoagulation reduction from vertical and horizontal directions, Knowing that the above-mentioned problems can be achieved by performing perfect circular molding by reduction after solidification,
The present invention has been completed.

Here, the present invention is as follows.

(1) In continuous round billet casting, at least one unsolidified rolling stand provided with a pair of horizontal rolls and a pair of vertical rolls in the same vertical section, and a solidification comprising a pair of vertical rolls provided downstream thereof Using an in-line rolling equipment equipped with a vertical rolling stand and a solidified horizontal rolling stand consisting of a pair of horizontal rolls, the slab is reduced in the unsolidified rolling stand at a position before complete solidification of the slab in an unsolidified state. And then, after complete solidification of the slab, reducing the cross-sectional area while reducing the cross-sectional shape of the slab by applying pressure to the slab in the solidified vertical reduction stand and the solidified horizontal reduction stand to adjust the cross-sectional shape of the slab. Manufacturing method of a continuous billet of a round billet.

(2) At the one unsolidified rolling stand located at a position before complete solidification, the rolling amount of one roll pair is made larger than the rolling amount of the other roll pair, and once formed into an oval slab. The method according to the above (1), wherein a perfect circle is formed by at least one roll pair in the solidification vertical reduction stand and the solidification horizontal reduction stand after complete solidification.

(3) The method according to the above (2), wherein the roll diameter of the roll pair for which the reduction amount is increased in the unsolidified rolling stand is made larger than the roll diameter of the other roll pairs.

(4) The method according to the above (2) or (3), wherein at least one of the roll pairs in the unsolidified drafting stand that takes a large amount of rolling is a driving roll.

According to another aspect of the present invention, in a round billet continuous casting facility, at least one roll having a pair of horizontal rolls and a pair of vertical rolls in the same vertical section is provided.
A round having a non-solidification rolling stand, a solidification vertical rolling stand comprising a pair of vertical rolls provided downstream thereof, and a solidification horizontal rolling stand comprising a pair of horizontal rolls. This is an apparatus for producing billet continuous cast slabs.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the center segregation and the center porosity are caused by solidification shrinkage at the final stage of solidification of a slab.
By applying a reduction more than or equal to the internal shrinkage, the cross-sectional area of the slab can be reduced or prevented by reducing the cross-sectional area.

In the case of a billet having a rectangular cross section, unsolidification rolling is performed by a pair of rolls from above and below, but in a billet cast piece having a round cross section, two horizontal rolls as in the related art are used for in-line reduction. When the non-solidification rolling is performed in step (1), as shown in FIG. 1, there is a high possibility that internal cracks are generated due to extension deformation in a direction perpendicular to the rolling direction. In addition, it becomes an elliptical shape due to elongation and deformation in a direction perpendicular to the rolling-down direction.

Therefore, in the present invention, as shown in the schematic diagram in FIG. 2, the round billet cast piece 14 whose center is not solidified in the same cross section is formed by upper and lower roll pairs 22, 24, left and right roll pairs 26, 28, the unsolidification pressure is reduced simultaneously from four directions, whereby the elongation deformation as shown in FIG. 1 can be suppressed, the cause of the occurrence of internal cracks can be reduced, and the inhibition of roundness can be reduced. can do. In the illustrated example, the rolls constituting each roll pair are shown as a caliber, but the roll surface at this time may be completely flat.

However, in any case, the roundness cannot be completely guaranteed by the simultaneous reduction of four rolls in at least one unsolidified reduction stand. After complete solidification, this time, the roundness is increased by forming a perfect circle by a solidification vertical reduction stand consisting of a pair of vertical rolls and a solidification horizontal reduction stand consisting of a pair of horizontal rolls as a post-solidification reduction stand. be able to.

The reason for installing such a post-solidification rolling stand after complete coagulation is that a four-roll unsolidified rolling stand is installed at the end of coagulation, which is effective in reducing center segregation and center porosity. In order to avoid the occurrence of such internal cracks at the time of unconsolidated unsolidification, since there is a place restriction to provide in the area and there is a possibility that internal cracks may occur by molding under unsolidified pressure. It is.

The order of installation of the vertical rolls and the horizontal rolls as the post-solidification rolling stand is not particularly limited, but depends on the degree of reduction of the horizontal rolls and the vertical rolls in the four-roll unsolidified rolling stand. Should be determined.

FIG. 3 shows an example of the arrangement in the continuous casting machine. FIG. 3 is a schematic explanatory view of a continuous cast slab manufacturing apparatus according to the present invention. In the figure, a round billet slab 34 drawn from a mold 32 is cooled by water cooling in a cooling roll group 36, and cooling is promoted. Next, after passing through a guide roll group 38, it is sent to an unsolidified rolling roll group 40 composed of upper and lower roll pairs, and is sequentially reduced. Perform coagulation reduction and complete uncoagulation reduction. In the illustrated example, only one unsolidified rolling stand 42 according to the present invention for performing simultaneous rolling from four directions is provided, but it may be provided in multiple stages toward the upstream. In some cases, the unsolidified rolling roll group 40 composed of the upper and lower roll pairs may be entirely constituted by the unsolidified rolling stand according to the present invention.

By providing the unsolidified rolling stands in multiple stages as described above, the effect of maintaining roundness can be enhanced by adjusting the rolling amounts, but the equipment becomes complicated, so that it is usually used. It is preferable to provide only one stage. Prior to this, the unsolidification reduction may be performed in a multi-stage manner by a flat roll slightly in a horizontal or vertical direction as in the conventional case.

The solidified round billet 43 which has thus been subjected to the unsolidification reduction is then converted into a solidification vertical reduction stand 44 composed of, for example, a pair of vertical rolls, and a solidification horizontal roll composed of a pair of horizontal rolls. After passing through the press-down stand 46, it is formed into a perfect circle to obtain a round billet slab for manufacturing a seamless pipe. The solidification vertical reduction stand 44 at this time,
The number of the coagulation horizontal reduction stands 46 may be further provided if necessary, and there is no particular limitation on which one is first.
Reference numeral 48 indicates a pinch roll.

In the present invention, the reason why the perfect circular forming is performed by dividing into a horizontal roll and a vertical roll is because there is no problem of internal cracking due to elongation deformation as under unsolidified pressure.
This is because the horizontal roll and the vertical roll are divided and arranged, because there is no place restriction and the cost is low. Also in this case, the roll used may be either a caliber type or a flat type.

In a preferred embodiment of the present invention, the one unsolidified rolling stand located at a position before complete solidification sets the rolling reduction of a pair of rolls larger than the remaining pair of rolling reductions, thereby forming an elliptical casting. Once molded into a piece, it is formed into a perfect circle with at least one roll in the solidification vertical reduction stand and solidification horizontal reduction stand after complete solidification, for the following reason.

In other words, various analyzes have shown that it is more effective to allow a certain degree of elliptical deformation rather than uniformly reducing the pressure in four directions in order to reduce the cross-sectional area of the unsolidified portion. It has been found by examination. This is because when the rolling is uniformly reduced in four directions, the slab extends in the axial direction and the reduction in the cross section is reduced accordingly. However, considering the occurrence of internal cracks and ensuring roundness, some reduction is required mainly in the direction perpendicular to the reduction direction, and the desired ratio [(smaller reduction amount) / (mainly in the reduction direction) Reduction amount)] is 20 to 80%. Within this range, there is no problem of internal cracking, and it is possible to form a perfect circle with two pairs of rolls after complete solidification.

According to another preferred embodiment of the present invention, the roll diameter of the roll pair for which the rolling reduction is increased in the unsolidified rolling stand is made larger than the roll diameter of the other roll pairs.
The reason is as follows.

As described above, the role of the roll pair for increasing the reduction amount is mainly to reduce the internal cross-sectional area, and it is necessary that the reduction from the surface effectively penetrates the inside. When the roll diameter is small, the reduction from the surface is mainly absorbed as a metal flow in the axial direction near the surface layer of the slab, and the permeability into the inside is deteriorated. By making this roll diameter large, the permeability under rolling can be increased. The desirable roll diameter is 1 to 5 times the slab diameter. The larger the size, the better, but if it is more than five times, the equipment cost will increase significantly.

According to still another aspect of the present invention, at least one roll of a roll pair that takes a large amount of reduction in the unsolidified drafting stand is used as a driving roll for the following reason.

That is, when the four rolls simultaneously reduce the cross section so as to narrow the cross section, the reduction of the slab due to the reduction is accompanied by a remarkable increase. In a normal continuous casting machine, the drawing force of the slab is generated by a so-called pinch roll.However, in the case of a round slab, the contact area between the slab and the roll is small, and there is a possibility that a sufficient drawing force may not be secured. is there. The pull-out resistance of a slab usually occurs due to the frictional force between the mold and the slab, pressure such as bending correction, etc., which are extremely small as compared with the pull-out resistance at the time of in-line reduction.

In the four-roll unsolidification rolling device, at least one of the roll pairs to be lowered (both may be used but one of them is lower in cost) is mainly used as a driving roll.
Applying a pinch force to the slab together with the rolling reduces not only the problem of the contact area described above, but also does not require a new increase in the pulling force of the pinch roll 48, and is economically advantageous. Next, the operation and effect of the present invention will be described more specifically with reference to examples.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A 0.2% C steel having a diameter of 250 mm is formed by rolling an unsolidified rolling stand 42 consisting of four rolls having a configuration substantially equivalent to the structure shown in FIG. 3, followed by a solidifying vertical rolling stand 44 and a solidifying horizontal rolling stand 46. Was cast into a round billet slab 43 using a continuous casting apparatus equipped with 4 roll unsolidified press stand 42
Is located 30 m from the melt meniscus, and the solidification vertical reduction stand 44 and the solidification horizontal reduction stand 46 are located 33 m and 35 m from the melt meniscus, respectively. A pinch roll 48 is provided downstream of the solidification horizontal pressing stand 46.

The casting speed was 1.8 m / min, and the cooling power by the secondary cooling spray was 0.2 m specific water volume between 6 m below the mold.
l / kg · steel. The complete solidification position at this time is a point 31 m downstream from the molten metal meniscus, and the unsolidification reduction is performed by a 4-roll unsolidification reduction stand.
(Hereinafter, referred to as “V stand”) and a solidified horizontal rolling stand (hereinafter, referred to as “H stand”) can perform the down-forming of the slab after complete solidification. Each of the horizontal roll and the vertical roll has a diameter of 400 mm and a flat shape, but may have a caliber shape in some cases.

Table 1 shows the manufacturing conditions in Examples 1 to 4 and Comparative Examples 1 to 4, respectively. For setting the amount of reduction of the cast slab, a spacer was set according to the amount of reduction, and the casting was pushed off. In some cases, a displacement control mechanism for the hydraulic cylinder may be provided to control the amount of reduction. The rolling capacity is up to 200 Ton for each roll,
Depending on the amount of reduction at that time, the reduction reaction force was within this value.

In Example 1, the roll diameter of each roll of the four-roll unsolidified rolling stand was 400 mm, and the rolling amount was the same.
20 mm. The reduction amount of the V stand and the H stand was 5 mm. In Example 2, the reduction amount of the horizontal roll of the four-roll unsolidified reduction stand was increased to 40 mm, and accordingly, the reduction amount of the V-stand for perfect circular molding was set to 20 mm.

In the third embodiment, the diameter of the horizontal roll having a large reduction amount of the four-roll unsolidified reduction stand of the second embodiment is set to 600 mm.
And the others were the same as in Example 2. Example 4
The drive roll was the upper roll of the horizontal roll of the 4-roll unsolidified pressing stand, and the other components were the same as in Example 2.

In Comparative Example 1, only the horizontal roll of the 4-roll unsolidified rolling stand was reduced by 20 mm by simulating the existing method, and the V-shaped stand and the H-stand, which are round forming stands, were not used.

Comparative Example 2 is the same as Example 1 except that the four-roll unsolidified rolling stand is the same as Example 1, but does not use the V and H stand. Comparative Examples 3 and 4
Is a case in which either one of the V and H stands of Example 1 was not formed into a perfect circle.

In each of the above examples, after casting the slab,
From the cold slab, a 2 m-long sample of the steady casting portion was cut out, and 21 cross-sectional plates were sampled from the sample at a pitch of 100 mm.

The presence or absence of internal cracks was confirmed from the sulfur print of the cross section of the cross section plate. Furthermore, a 5 mm diameter chip was taken out from the center (when the deformation was large, the center of gravity), and the carbon concentration C was analyzed.
o was used as an index for evaluating central segregation.

Further, the total area of porosity observed in the cross section is determined, and the porosity area ratio is calculated from the ratio to the slab cross-sectional area.
(%) And porosity was evaluated. Also, determine the center of gravity of the cross section, measure the distance from the center of gravity in the circumferential direction at a 30 ° pitch, and divide the difference (vertical cross section) from the radius of the perfect circle to be obtained by the radius of the perfect circle. The roundness deviation rate (%) was defined, and the roundness was evaluated. The roundness deviation rate of billet slab to be provided to the pipe making process is within 3%.

Further, in Examples 2 and 4, the torque of the pinch rolls during the pull-down with the uncoagulated pressing stand and the pinch rolls following the coagulating pressing stand was measured, and the ratio of the torque generated in Examples 4 and 2 was measured. (%). Table 2 summarizes the test results for each example. The value of each parameter indicates the average value of 21 cross-sectional plate samples.

In Example 1, as compared with Comparative Example 1, the effects of simultaneous reduction of four rolls in terms of preventing internal cracking, reducing center segregation, reducing center porosity, and improving roundness are evident. Also, by comparing with Comparative Examples 2, 3, and 4, the effect of providing both the solidification vertical and horizontal pressure reduction stands in terms of improving roundness is apparent.

In Example 2, the amount of reduction of the horizontal rolls of the four-roll unsolidified reduction stand was set to be large, and the porosity and the roundness were almost the same (clear the pipe making standard).
The effect of reducing center segregation is apparent.

In Example 3, the roll diameter of the horizontal roll of the 4-roll unsolidified rolling stand was increased, and as a result, the internal permeability under rolling was improved, and the porosity,
The reduction of center segregation is further advanced than in Example 2. Roundness is almost the same. From these results, it was confirmed that the effect of increasing the diameter of the roll pair for increasing the reduction was confirmed.

The effect of the fourth embodiment is the same as that of the second embodiment in terms of porosity, center segregation and roundness, but the pulling torque of the pinch roll 48 is reduced to 5% of that of the second embodiment. Substantially, it is at a level where only the four-roll unsolidified pressing stand can be pulled out.

[0050]

[Table 1]

[0051]

[Table 2]

[0052]

According to the present invention, it is possible to supply a round billet slab having a good internal quality and a high roundness to a pipe making process following a continuous casting.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing the state of occurrence of internal cracks due to unsolidification rolling of a round billet slab.

FIG. 2 is a schematic explanatory view showing unsolidification reduction in four directions in the same cross section.

FIG. 3 is a schematic explanatory view of an inline rolling-down facility for round billet slabs according to the present invention.

[Explanation of symbols]

32: Mold 34: Round billet slab 36: Cooling roll group 38: Guide roll group 40: Non-solidification reduction roll group 42: Non-solidification reduction stand 43: Round billet slab 44: Solidification vertical reduction stand 46: Solidification horizontal reduction stand 48: Pinch roll

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor: Sumitomo Shiode 4-5-33 Kitahama, Chuo-ku, Osaka-shi Sumitomo Metal Industries, Ltd. (56) References JP-A-8-206804 (JP, A) JP-A-1-289552 (JP, A) JP-A-7-108358 (JP, A) JP-A-6-134550 (JP, A) JP-A-50-85523 (JP, A) JP-A-4-197566 (JP) JP-A-10-34304 (JP, A) JP-A-10-34201 (JP, A) JP-A-3-124352 (JP, A) JP-A-9-201602 (JP, A) JP-A-9-201601 (JP, A) JP-A-9-300053 (JP, A) JP-A-6-269903 (JP, A) JP-A-7-124704 (JP, A) JP-A-63-33152 (JP, A A) Japanese Utility Model Showa 61-143740 (JP, U) Japanese Utility Model Showa 60-113148 (JP, U) Japanese Patent Publication No. 44-17366 (JP, U) B1) (58) investigated the field (Int.Cl. ^7, DB name) B22D 11/128 350 B22D 11/00 B22D 11/20

Claims (5)

(57) [Claims] In a continuous round billet casting, a solidified vertical comprising at least one unsolidified rolling stand provided with a pair of horizontal rolls and a pair of vertical rolls in the same vertical section, and a pair of vertical rolls provided downstream thereof. Using an in-line rolling equipment equipped with a rolling stand and a solidified horizontal rolling stand consisting of a pair of horizontal rolls, the slab is unrolled in the unsolidified rolling stand at a position before complete solidification of the slab. And then, after complete solidification of the slab, reducing the cross-sectional area while applying a reduction to the slab in the solidification vertical reduction stand and the solidification horizontal reduction stand to adjust the circularity of the cross-sectional shape of the slab. For producing round billet continuous cast slabs. 2. The method according to claim 1, wherein the unsolidified rolling stand at a position before complete solidification takes a rolling amount of one roll pair larger than a rolling amount of another roll pair, and once forms an oval slab. The method according to claim 1, wherein after the solidification is completed, at least one pair of rolls in the solidification vertical reduction stand and the solidification horizontal reduction stand forms a perfect circle. 3. The method according to claim 2, wherein the roll diameter of the roll pair for which the amount of reduction is increased in the unsolidified rolling stand is made larger than the roll diameters of the other roll pairs. 4. The method according to claim 2, wherein at least one roll of a pair of rolls that increases the amount of reduction in the unsolidified reduction stand is a drive roll. 5. A solidification machine comprising at least one unsolidified rolling stand provided with a pair of horizontal rolls and a pair of vertical rolls in the same vertical section in a continuous round billet casting facility, and a pair of vertical rolls provided downstream thereof. An apparatus for producing a continuous billet of round billets, comprising an inline rolling-down facility comprising a vertical rolling-down stand and a solidified horizontal rolling-down stand comprising a pair of horizontal rolls.