JP2017124415A - Continuous casting method and continuous casting facility - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a continuous casting method adoptable even under a condition having a small capacity of recuperation, capable of suppressing crack on the cast slab L side, and to provide a continuous casting facility.SOLUTION: In a continuous casting method for recuperating after secondary cooling and reforming linearly a cast slab 11 discharged from a template 12 of a continuous casting facility 10, an L side corner part 19 of the cast slab 11 is cooled by water to a temperature below an A1 transformation point, in a cooling zone 20 provided on the furthermore downstream side than a recuperation completion position after secondary cooling of the cast slab 11, and further its temperature is raised over an A3 transformation point, and then the cast slab 11 is reformed linearly.SELECTED DRAWING: Figure 1

Description

The present invention relates to a continuous casting method and a continuous casting facility for straightening a slab that has come out of a mold of a continuous casting facility and traveled along a curved path.

In a curved type and vertical bending type continuous casting machine, it is essential to straighten a bent slab. However, the temperature of the slab drops until it reaches the correction point, and ferrite is precipitated in a film form at the (austenite) grain boundary and becomes brittle, so when the slab is straightened, When tensile strain is generated on the slab L side, that is, on the curved inner side of the slab, cracks occur and the quality of the final product is degraded. In particular, since the temperature of the slab is the lowest at the corners at the four corners of the cross section, cracks are likely to occur in the regions at both ends in the width direction even at the corners on the slab L side.
Then, the technique which suppresses that a crack arises in the slab L side when correcting a slab to linear form is proposed, and the specific example is described in patent document 1. FIG.

In the continuous casting method of Patent Document 1, the slab is rapidly cooled by secondary cooling so that the surface temperature of the slab is not higher than the A3 transformation point and the surface temperature of the slab is increased to not lower than the A3 transformation point by recuperation. Correction is performed in a state where the surface temperature is less than 850 ° C.
By cooling the slab with water, cooling the surface temperature below the A3 transformation point, and reheating it, the crystal grains can be refined and the critical stress against cracking at the corner on the slab L side can be increased.

JP 2002-86252 A

However, in the secondary cooling, the slab is cooled from the four sides, and the entire width direction is cooled on each side, so that the temperature drop of the entire slab is remarkable. At that time, in particular, the slab corner portion has a significantly lower temperature than other parts, and the slab corner cooled below the A3 transformation point when the technique of Patent Document 1 is employed under the condition that the recuperated capacity of the slab is small. It has been proved by logical verification and experimental verification that it is impossible to stably raise the temperature of the part to the A3 transformation point or higher by recuperation.
For this reason, the range which can apply the technique of patent document 1 is limited, for example, when the technique of patent document 1 is employ | adopted for the bloom and billet with a small recuperation capacity, it is effective in the crack of the slab L side corner part. In some cases, it could not be suppressed.
The present invention is made in view of such circumstances, and provides a continuous casting method and a continuous casting facility that can suppress cracks on the slab L side (particularly, cracks at the corners) that can be employed even under conditions where the recuperation capacity is small. The purpose is to do.

The continuous casting method according to the first aspect of the present invention is a continuous casting method in which a slab taken out from a mold of a continuous casting facility is subjected to secondary cooling and then reheated and straightened to correct the slab in a secondary cooling manner. After cooling the L-side corner of the slab to a temperature lower than the A1 transformation point in a cooling zone provided downstream from the subsequent recuperation completion position, and further raising the temperature above the A3 transformation point, Straighten the piece straight.

In the continuous casting method according to the first invention, the L-side corner portion of the slab is preferably cooled to 300 to 700 ° C.

In the continuous casting method according to the first aspect of the present invention, it is preferable that the temperature increase of the L-side corner portion of the slab is performed only by reheating the slab.

In the continuous casting method according to the first aspect of the present invention, it is preferable to compensate for an insufficient amount of recuperation for heating the L-side corner of the slab by heating the L-side corner of the slab.

In the continuous casting method according to the first aspect of the invention, the L-side corner is preferably heated by induction heating.

The continuous casting equipment according to the second invention in accordance with the above object is the continuous casting equipment for reheating the slab taken out from the mold after secondary cooling and straightening it, from the recuperation completion position after the secondary cooling. A nozzle that is provided on the downstream side and cools below the A1 transformation point by spraying cooling water on the L-side corner of the slab, and the slab cooled below the A1 transformation point is heated to a temperature higher than the A3 transformation point. And a straightening roll for straightening the slab on the downstream side of the position.

The continuous casting equipment according to a second aspect of the present invention includes a heating device that is provided on the downstream side of the nozzle and that heats the L-side corner portion of the slab, which is heated by recuperation, to a temperature equal to or higher than the A3 transformation point. preferable.

In the continuous casting facility according to the second aspect of the invention, the heating device is preferably an induction heating device that performs induction heating.

The continuous casting method according to the first aspect of the invention and the continuous casting equipment according to the second aspect of the invention are the cooling zone provided downstream from the recuperation completion position after the secondary cooling, and water-cools the L-side corner of the slab. After cooling to below the A1 transformation point and further raising the temperature above the A3 transformation point, the slab is straightened. Accordingly, by cooling the L side corner of the slab with water in the cooling zone and intensively reducing the temperature of the L side corner, the temperature drop of the entire slab can be suppressed, and the subsequent L side corner It is possible to increase the temperature rise width due to the recuperation. For this reason, even for billets and blooms that have a smaller recuperation capacity than slabs, the temperature of the slab can be reliably raised to the A3 transformation point or higher by the point where straightening is corrected, and the slab L side In particular, the occurrence of cracks at the corners can be suppressed.

In the continuous casting method according to the first aspect, when the L-side corner portion of the slab is cooled to 300 to 700 ° C., the occurrence of cracks in the slab L-side corner portion can be stably suppressed.
This has been confirmed by experimental verification.

In the continuous casting method according to the first aspect of the present invention, when the temperature rise of the L-side corner portion of the slab is performed only by reheating the slab, it is necessary to add a heating device to raise the temperature of the L-side corner portion. It is economical.

In the continuous casting method according to the first aspect of the present invention, the shortage of the recuperated amount for heating the L-side corner of the slab is compensated by heating the L-side corner of the slab, or the second In the continuous casting equipment according to the invention, when the heating device is provided to heat the L-side corner portion of the slab that is heated by recuperation to the A3 transformation point or higher, the L-side corner portion that is water-cooled below the A1 transformation point is provided. It is possible to reliably set the temperature above the A3 transformation point.
Further, in the continuous casting method according to the first invention and the continuous casting equipment according to the second invention, when the L-side corner portion of the slab is heated by induction heating, the L-side corner portion of the slab is highly efficient. Heating is possible.

It is explanatory drawing of the continuous casting installation with which the continuous casting method which concerns on one embodiment of this invention is applied. (A), (B) is explanatory drawing which shows the position of a nozzle. It is a graph which shows the temperature transition of slab.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
As shown in FIG. 1, a continuous casting facility 10 to which a continuous casting method according to an embodiment of the present invention is applied includes a mold 12 from which a slab 11 is taken out and a plurality of support rolls 13. A plurality of nozzles 14 for cooling the cast slab 11 with water and performing secondary cooling are provided in the vicinity of the mold 12.

The plurality of support rolls 13 are arranged along the traveling path of the slab 11, and the slab 11 is guided by the support roll 13 and proceeds. The temperature of the slab 11 is lowered by the cooling water sprayed from the nozzle 14 and natural heat dissipation, and the solidified shell 15 formed on the surface of the slab 11 increases in thickness as the slab 11 advances.
A curved portion is provided in the traveling path of the slab 11. A plurality of straightening rolls 16 are arranged on the downstream side of the plurality of support rolls 13 in the traveling path of the slab 11, and the slab 11 bent through the curved portion is bent back by the plurality of straightening rolls 16. Straightened straight.

In the present embodiment, the slab 11 is a bloom or billet. The bloom and billet have a cross-sectional area of 200 mm × 200 mm or more, and the billet has a cross-sectional area of 50 mm × 50 mm or more and less than 200 mm × 200 mm. Prepare.
In addition, the slab has a long side length of at least twice that of the short side, and usually has a short side of 50 mm or more and a long side of 800 to 3000 mm.

Further, a nozzle 17 that blows cooling water to the secondary-cooled slab 11 is disposed downstream of the region where the nozzles 14 are disposed along the traveling direction of the slab 11.
The nozzle 14 is disposed on each of the four surfaces including the slab L side 18 corresponding to the curved inner side of the slab 11, and the cooling water is sprayed on each of the four surfaces of the slab 11, whereas the nozzle 17 is disposed on the slab 11. Are disposed only in the vicinity of one end and the other end of the slab L side 18 (hereinafter, the vicinity of the one end and the other end of the slab L side 18 are respectively referred to as “L side corner portion 19”). Cooling water is sprayed on the side corner portion 19.

Moreover, the nozzle 14 installed in the arrangement | positioning area | region of the support roll 13 is in the position which opposes the width direction center of the surface of the slab 11 about each of the 4 surface sides of the slab 11, as shown to FIG. 2 (A). It arrange | positions and sprays a cooling water on the whole surface of the slab 11. FIG.

On the other hand, as shown in FIG. 2 (B), the nozzles 17 are arranged at positions facing the region of the slab L side 18 of the L side corner portion 19, respectively, and the L side corners on one side and the other side, respectively. Cooling water is sprayed on the part 19. Therefore, in the cooling zone in which the nozzle 17 is disposed (hereinafter referred to as “corner cooling zone 20”), the cooling water is not directly sprayed on the portion other than the L-side corner portion 19, and the slab L side Cooling water is not sprayed on three surfaces other than 18.
Therefore, compared with the secondary cooling zone 21 in which the plurality of nozzles 14 are arranged, the corner cooling zone 20 can suppress the temperature drop of the entire slab 11 and concentrate the L-side corner portion 19 of the slab 11. Can be cooled.

The corner cooling zone 20 is close to the recuperation completion position on the downstream side of the recuperation completion position of the slab 11 secondary-cooled in the secondary cooling zone 21 (in this embodiment, downstream from the recuperation completion position). (In the range of 2 m on the side). The recuperation completion position is a position where the temperature of the L-side corner portion 19 of the slab 11 that has undergone secondary cooling is highest due to recuperation of the slab 11.
On the upstream side from the recuperation completion position, the temperature of the L-side corner portion 19 of the slab 11 is low, and when the corner cooling zone 20 is provided upstream from the recuperation completion position, the temperature of the L-side corner portion 19 is reduced by cooling. It cannot be lowered rapidly. In this regard, it has been confirmed by experimental verification that the occurrence of cracks in the L-side corner portion 19 can be suppressed by increasing the cooling rate of the L-side corner portion 19. It is not preferable to provide it upstream. Further, since the solidified shell 15 is thinner toward the upstream side, if the corner cooling zone 20 is provided upstream from the recuperation completion position, the risk of quality troubles such as BO (breakout) increases.

On the other hand, when the corner cooling zone 20 is provided on the downstream side of the recuperation completion position and away from the recuperation completion position, the slab 11 is straightened from the corner cooling zone 20 (hereinafter referred to as “correction zone 22”). The distance until the L-side corner portion 19 recovers to the correction band 22 is shortened. Therefore, before the slab 11 passes through the correction band 22, the L-side corner portion 19 cannot be set to a temperature equal to or higher than the A3 transformation point (850 ° C. in the present embodiment).
Therefore, it can be said that the corner cooling zone 20 is preferably provided in the vicinity of the recuperation completion position on the downstream side of the recuperation completion position.

Further, as shown in FIG. 2B, the L-side corner portion 19 is a range of L1 inward from one side of the surface of the slab L side 18 and the other side corner portion, and the slab L side 18. It is a region where the range of L2 is adjusted from the corners on one side and the other side of the surface to the slab S side (curved outside of the slab), and when the slab 11 is straightened, cracks are generated in these ranges. Occur. In this embodiment, L1 = 100 mm and L2 = 0 mm, but it goes without saying that the optimum values of L1 and L2, that is, the range in which cracks occur, vary depending on the casting conditions such as the steel type and casting speed.

In the continuous casting method according to the present embodiment, the amount of water in the nozzle 14 is adjusted based on the casting speed and the profile of the slab 11, and the temperature of the L-side corner portion 19 is set at the recuperation completion position after secondary cooling. A3 transformation point or higher.
And in the corner cooling zone 20, the capacity | capacitance of the cooling water blown off from the nozzle 17 is adjusted, and the L side corner part 19 is cooled to the range of 300-700 degreeC which is less than A1 transformation point.
The slab 11 cooled in the corner cooling zone 20 is heated to a range of not less than A3 transformation point and not more than 1100 ° C. by reheating of the slab 11, and then proceeds to a straightening zone 22 for straightening the slab 11 into a straight line. The slab 11 is straightened by the plurality of straightening rolls 16 in the straightening band 22.

Accordingly, the straightening roll 16 straightens the slab 11 on the downstream side of the position where the slab 11 cooled below the A1 transformation point is heated to the A3 transformation point or higher.
Here, the reason why the upper limit after the temperature rise of the slab 11 is set to 1100 ° C. is that when the recuperation temperature becomes too high, the crystal grains become coarse and the crack reduction effect decreases.
The temperature of the L-side corner 19 when passing through the correction band 22 may be equal to or higher than the A3 transformation point or lower than the A3 transformation point.

Here, two reasons for cooling the L-side corner portion 19 in the range of 300 to 700 ° C. in the corner cooling zone 20 will be described below.
(Reason 1) When the L-side corner portion 19 is cooled to less than 300 ° C. in the corner cooling zone 20, the slab 11 passes through the corner cooling zone 20, and then the L-side corner portion 19 is only reheated by the slab 11. It is impossible to stably raise the temperature to a temperature equal to or higher than the A3 transformation point.
(Reason 2) When the temperature of the L-side corner portion 19 is not set to 700 ° C. or lower due to cooling in the corner cooling zone 20, the effect of refining the crystal grain size is small. The occurrence of cracks in the side corner portion 19 cannot be suppressed.
Reason 1 and reason 2 are confirmed by logical verification and experimental verification.

The cooling temperature of the slab (that is, the reached temperature of the L-side corner portion cooled by the corner cooling zone) and the recuperated temperature (that is, the maximum of the L-side corner portion that the slab reaches by the temperature rise due to recuperation after cooling) Table 1 below shows an example of a laboratory test result in which the effect of the (temperature) on the crack occurrence state of the L-side corner when straightening the slab is verified by experiment.

The verification result described as “Evaluation” in the table is the crack occurrence state of the L-side corner portion, where “X” indicates a case where the crack occurs remarkably, and “◯” indicates a case where the crack hardly occurs.
The casting speed was 0.5 m / min, and the slab size was 400 mm × 500 mm.

Further, even when the L-side corner portion 19 is cooled to less than 300 ° C. in the corner cooling zone 20, the L-side corner portion 19 is heated using the heating device 23 shown in FIG. If it supplements, it is possible to heat up the L side corner part 19 stably more than A3 transformation point. That is, the heating device 23 is provided on the downstream side of the nozzle 14 and heats the L-side corner portion 19 of the slab 11 whose temperature is raised by recuperation so as to be higher than the A3 transformation point.

When the heating device 23 is used, the effect of the same level as when the L-side corner portion 19 is set to the A3 transformation point or higher by the recuperation of the slab 11, that is, when the slab 11 is straightened, the L-side corner portion. It has been confirmed that the effect of stably suppressing the occurrence of cracks in 19 can be obtained.
Here, it has been confirmed by experiments that an induction heating device is adopted as a heating device, and the L side corner portion 19 can be stably adjusted by heating the L side corner portion 19 by induction heating. .

Next, examples carried out for confirming the effects of the present invention will be described.
After cooling the L-side corner by water cooling under the conditions of casting speed 0.5m / min and slab size 400mm x 500mm, investigate how many times the L-side corner rises only by reheating the slab An experimental simulation was conducted.
The experiment was conducted on two cases. Case 1 was reheated after secondary cooling, and the L-side corner was further cooled in the corner cooling zone, and the L-side corner was cooled to 600 ° C. This is a case where the cooling in the corner cooling zone is not performed and the cooling is performed until the L-side corner portion reaches 600 ° C. in the secondary cooling zone.

The experimental results are as shown in the graph of FIG. 3, and the case 1 represented by a solid line is represented by a broken line on the downstream side of the corner cooling zone and the L-side corner portion exceeding 850 ° C. which is the A3 transformation point. In case 2, the temperature rose to 750 ° C. by recuperation, but the temperature did not exceed the A3 transformation point. For this reason, as for the crack generation situation of the L side corner part of the slab straightened straightly, the case 1 has almost no crack and the case 2 has a remarkable crack.
In case 1, the recirculation completion position is a circled position where the temperature of the L-side corner is highest on the downstream side of the secondary cooling zone.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and all changes in conditions and the like that do not depart from the gist are within the scope of the present invention.
For example, the slab is not limited to bloom or billet, and slab can be used.
Further, the arrangement position of the corner cooling zone is not limited to a range of 2 m from the recuperation completion position of the slab, and may be, for example, a range of 15 m.

10: continuous casting equipment, 11: slab, 12: mold, 13: support roll, 14: nozzle, 15: solidified shell, 16: straightening roll, 17: nozzle, 18: slab L side, 19: L side corner 20: Corner cooling zone, 21: Secondary cooling zone, 22: Correction zone, 23: Heating device

Claims (8)

In the continuous casting method in which the slab taken out from the mold of the continuous casting facility is reheated after secondary cooling and straightened,
In the cooling zone provided downstream of the recuperation completion position after secondary cooling of the slab, the L-side corner of the slab is cooled with water to cool below the A1 transformation point, and further rises above the A3 transformation point. After the heating, the continuous casting method is characterized in that the slab is straightened. The continuous casting method according to claim 1, wherein the L-side corner portion of the slab is cooled to 300 to 700 ° C. 3. The continuous casting method according to claim 1, wherein the temperature rise of the L-side corner portion of the slab is performed only by recuperation of the slab. 3. The continuous casting method according to claim 1, wherein an insufficient amount of recuperation for heating the L-side corner portion of the slab is compensated by heating the L-side corner portion of the slab. Continuous casting method. 5. The continuous casting method according to claim 4, wherein the L-side corner portion is heated by induction heating. 6. In continuous casting equipment that reheats the slab from the mold after secondary cooling and straightens it,
A nozzle that is provided downstream from the recuperation completion position after the secondary cooling, sprays cooling water to the L-side corner portion of the slab and cools it below the A1 transformation point, and is cooled below the A1 transformation point. A continuous casting facility comprising: a straightening roll that straightens the slab at a position downstream of a position where the slab is heated to an A3 transformation point or higher. The continuous casting equipment according to claim 6, further comprising a heating device provided on the downstream side of the nozzle and heating the L-side corner portion of the slab, which is heated by recuperation, to a temperature equal to or higher than the A3 transformation point. Continuous casting equipment. The continuous casting equipment according to claim 7, wherein the heating device is an induction heating device that performs induction heating.

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