JPH10180306A - Hot rolling method for preventing peripheral flaw on steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate occurrence of a peripheral flaw caused by that overlapped parts having double bulge parts on the end faces of a material is rolled into the width of product, moreover to cope with it easily and rapidly in the process of rolling and to make this method applicable to the designated material of finishing temp. such as a controlled rolled stock. SOLUTION: In this rolling method, edge shape measuring devices 1 such as a laser range finder are provided on both sides of a roller table of a roughing mill, after completing broadside rolling, the shapes of the end faces parallel to the longitudinal direction L of a slab S2 which is rotated 90 deg. are measured and the measured results is calculated with an operation processor 2, and the bulge shapes at end faces and amount of overlap are recognized. When the hape is the double bulge shape, whether the width of product is obtained from the material to be rolled in the process of rolling or not is judged and, when the material is judged that the width of product is not obtained (the width of product > the width of the material to be rolled-the amounts of overlap at both ends), the broadside rolling is again executed for the deficient amount, the width of product is secured by spreading the width of the material to be rolled and the overlap parts are made so at to prevent the overlapped part from go into the width of product.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot rolling method capable of reducing four-period flaws caused by a double bulge-shaped overlapping portion at an end face of a material to be rolled into a product width in hot rolling of a thick steel plate or the like. It is about.

[0002]

2. Description of the Related Art For example, in plate rolling, a forming and rolling process in which a material to be rolled is rolled several times in a longitudinal direction, and a material to be rolled is rotated by 90 °.
A tentering rolling step of rolling and rolling to a predetermined width (= product width + ear allowance); and a finish rolling for rolling a material to be rolled by 90 ° and rolling in the longitudinal direction to obtain a predetermined thickness and length. It consists of three steps.

[0003] In such a thick plate rolling, a seam flaw (edge crack) which is continuous in the longitudinal direction is generated in a product after rolling, for example, at a position 20 mm from the end face of the material to be rolled. If there is a flaw, there is a problem that an extra ear margin is required and the yield is reduced. Such seam flaws are due to the fact that wrinkles formed on the end face of the material to be rolled out in the previous step appear on the surface of the material to be rolled during reversible rolling in tentering rolling, and this is formed by rolling in the next step. You.

[0004] On the other hand, a phenomenon occurs in which a double bulge-shaped overlap portion bites into an end face of the product after rolling, and the bite of such a double bulge-shaped overlap portion falls within the product width. If it reaches the point, not only will the product be immediately downgraded, but it will also require an extra ear allowance to avoid downgrade, and in this case, the yield will also be reduced. Such a double bulge-shaped overlap portion is formed at the time of reversible rolling in tentering rolling.

Conventionally, techniques for preventing the occurrence of seam flaws or controlling the double bulge shape include:
The following methods have been proposed.

[0006] Japanese Patent Application Laid-Open No. 56-19908 discloses a method in which after rolling under light pressure, the material to be rolled is reduced to 90%.
° The initial tentative rolling under light pressure to roll and extend only the surface layer of the material to be rolled, forming a double bulge overlap at the end of the material to be rolled, so that the edge cracking part is from the end face to the center inside This is a method for preventing the occurrence of flaws by preventing large intrusion and then performing tentative rolling under normal rolling.

[0007] Japanese Patent Application Laid-Open No. 1-210113 discloses a method in which a shape of an end face of a material to be rolled along a rolling direction is measured during rolling, and cooling devices located at upper and lower portions of the material to be rolled are measured based on the measurement result. By controlling
Apply a cooling difference to the front and back surfaces of the material to be rolled during rolling, control the elongation difference between the front and back surfaces, position the double bulge overlap position and the inflection point of the single bulge at the center of the plate thickness, and seam flaws on the front and back surfaces This is a method of reducing the depth amount toward the center inside.

[0008] Japanese Patent Application Laid-Open No. H08-112611 measures a shape of an end face of a material to be rolled along a rolling direction during rolling, and based on the measurement result, a billet heating furnace in a heating step of a material to be rolled next. By controlling the upper and lower heating amounts (upper and lower burner gas flow ratios), the difference in elongation between the front and back surfaces of the material to be rolled is controlled, and the overlap position of the double bulge and the inflection point of the single bulge are located at the center of the plate thickness. This is a method of reducing the depth of the seam flaws on the front and back sides toward the center inside.

[0009]

However, the above-described method is a method for preventing seam flaws by positively forming a double bulge overlap at the end of the material to be rolled. Therefore, there is a problem that the yield is deteriorated.

In the method of (1), after measuring the shape of the end face of the slab during hot rolling, the upper and lower cooling waters are controlled to adjust the temperature of the front and back surfaces, and after such cooling, rolling is restarted.
There is a disadvantage that the rolling pitch (slab / hour) is reduced. Further, with a specified finishing temperature material such as a controlled rolled material for improving the strength and toughness, cooling controlled rolling under predetermined conditions cannot be performed, and application to a controlled rolled material or the like is difficult.

In the method of (1), the end face shape of the material to be rolled in the middle of rolling is measured, and the upper and lower burner gas flow ratio in the heating furnace in the heating step of the material to be rolled after the next material is controlled based on the measurement result. For this reason, there is a problem that it is impossible to cope with a material in the middle of rolling.

Further, any of the methods (1) to (4) is a method for reducing the depth of the seam flaws on the front and back surfaces of the material to be rolled, and the double bulge-shaped overlap portion at the end surface of the material to be rolled is cut into the product width. Therefore, there is a problem that it is impossible to cope with the four-round flaw caused by the above.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to produce a four-round defect due to the double bulge-shaped overlapping portion at the end face of a material to be rolled being cut into the product width. Can be eliminated, and it is possible to respond easily and quickly during the rolling,
It is still another object of the present invention to provide a hot rolling method for preventing four-round flaws of a steel sheet, which can be applied to a specified finishing temperature material such as a controlled rolled material.

[0014]

As shown in FIG. 1, a hot rolling method for preventing four-round flaws in a steel sheet according to the present invention, in a tentative rolling step of hot rolling of a steel sheet, is performed in a longitudinal direction of a material to be rolled. The shape of the parallel end face is measured, the bulge shape and the amount of overlap of the end face are recognized from the measurement result, and when the overlap portion of the double bulge bites into the product width, the tentering rolling is performed again. And

The end surface shape of the material to be rolled is measured by an end surface shape measuring device such as a laser distance meter installed on both sides of a roller table of a rough rolling mill. The measurement result of this end face shape measuring device is processed by a processing unit, and when the value obtained by subtracting the overlap amount of both end faces from the rolling width of the material to be rolled is smaller than the product width, the shortage is re-examined. Out rolling is performed.

In the above configuration, after the tentering rolling is completed, the shapes of both end faces parallel to the longitudinal direction of the rolled material to be rolled by 90 ° are measured. The bulge shape and the overlap amount of the material end face are recognized. In the case of the double bulge shape, it is determined whether or not the product width can be sampled in the material to be rolled in the middle of rolling [rolling material to be rolled-overlapping amount at both ends].
When it is determined that the product width cannot be collected (product width> rolled material width−overlapping amount at both ends), tentering rolling is performed again, and the width of the material to be rolled is increased to secure the product width. . As a result, in the finished product after the finish rolling, the overlap portion of the double bulge does not bite into the product width, and it is possible to eliminate all four-periphery flaws due to the bite in the overlap product width.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to an embodiment shown in the drawings. This is an example applied to hot rolling of a continuously cast slab. The hot rolling line includes a rough rolling step of performing a forming (shape adjustment) reduction and a tentering reduction by a rough rolling machine, and a finishing rolling step of performing a finishing reduction by a finishing rolling machine. As shown in FIG. 1 (b), under the forming pressure, the slab longitudinal direction L is set as the rolling direction, under the tentering pressure, the slab is turned by 90 ° to set the slab width direction W as the rolling direction, and under the finishing pressure, the slab is set as the rolling direction. Rolling is further performed by 90 ° and the slab longitudinal direction L is set as a rolling direction.

In such a hot rolling line, FIG.
(A), the roughing mill established the end surface shape measuring device 1 such as a laser distance meter on both sides of the roller table, after tentering rolling completion, 90 ° turning has been the longitudinal direction L of the slab S ₂ Is measured by scanning a laser or the like in the thickness direction of the slab. The measurement result of each end face shape measuring instrument 1 is input to the arithmetic processing device 2 and the arithmetic processing device 2
, The end face bulge shape and the amount of overlap are recognized, and based on the result, the necessity of re-width rolling is determined.

In the above configuration, after the slab S is extracted from the heating furnace, normal hot rolling is started, the slab is turned 90 ° after the completion of the tentering pass, and the slab S ₂ on the roller table is rotated in the longitudinal direction. Are measured by the end face shape measuring instrument 1. The arithmetic processing unit 2 determines whether or not it has a double bulge shape from the measurement result, and if it has a double bulge shape, calculates the overlap amount a, and based on the overlap amount at both end faces at this time. Then, it is determined whether or not the product width can be collected from the material to be rolled in the middle of rolling, and if it is determined that the product width cannot be collected, re-width rolling is performed. The following equation is used to determine whether or not the product width collection is possible.

[0020]

(Equation 1)

[0021] Finish rolling is performed after the tentering rolling, and a cut product is obtained by cutting and removing the margin of the ear. When the formula (1) is satisfied, re-rolling rolling is performed in a pass corresponding to the overlap amount. As a result, the formula (2) is satisfied. If the formula (2) is satisfied, in the product after finish rolling, the double bulge-shaped overlap portion does not bite into the product width, and the product of the overlap portion is formed. There is no flaw around the product due to biting into the width, and the product is not downgraded. Also, the seal flaws on the front and back surfaces at the product end do not enter the product width similarly to the overlap portion. In the case of the single bulge shape, since there is no overlap portion, four-round flaws due to the overlap portion do not occur, and the finish rolling is performed as it is.

Further, according to the present invention, since the tentering rolling may be added, it is possible to easily and quickly respond during the rolling, and it is possible to prevent the occurrence of four-period flaws due to the overlapping portion on all the slabs. it can. In addition, since it is only necessary to add a simple measuring device to ordinary hot rolling equipment, it is possible to prevent the occurrence of four-round flaws due to the overlapped portion at low cost. Furthermore, since it can be handled only by rolling,
Normal water-cooling control can be performed, and the present invention can be applied to a finish temperature designation material such as a controlled rolled material.

[Specific Numerical Examples] Each slab shown in the table of FIG. 2 is heated at 1140 ° C. for 4 hours, and thereafter, when the shape forming pass and the tentering rolling pass are completed by the horizontal rolls of the rough rolling mill. FIG. 2 shows the result of measuring the end face shape of the material to be rolled with a laser distance meter.

In the case of FIG. 2 (a), although the tentering rolling has been completed to the predetermined rolling width, the end face shape of the material to be rolled has a double bulge shape on both the drive side and the work side. Since the overlap amount is 12 mm on the drive side and 10 mm on the work side, the rolling width cannot be actually secured. For this reason, when a re-width rolling pass was added for 12 mm + 10 mm = 22 mm, an expanded planned rolling width (a product-collectable width + a both-overlap amount) was obtained, and a product-width could be secured. 2 (b) and 2 (c) also have a double bulge shape, and when re-rolling rolling passes are added according to the depth of the double bulge shape, FIG.
The same effect as (a) was obtained.

From the above, according to the present invention, the four-period flaw caused by the bite of the overlapped portion at the end of the product is conventionally known as 0.1%.
8% increased to 0.2%, and the downgrade increased from 0.3% to 0.1%.

Although the continuous casting slab has been described above, the present invention is not limited to this, and it goes without saying that the present invention can be applied to hot rolling of other thick plates such as a bulk slab.

[0027]

As described above, the present invention measures the shape of the end face parallel to the longitudinal direction of the material to be rolled in the tentative rolling step of hot rolling of a steel sheet, and determines the bulge shape / overlap of the material to be rolled. Since the amount is recognized, the necessity of the re-width rolling is determined based on the amount, and the product width is secured by the re-width rolling, the following effects are obtained.

(1) The double bulge-shaped overlap portion and the seal flaw do not enter the end face of the product after cutting the product, thereby preventing the occurrence of four-round flaws and preventing the yield from lowering due to a grade drop or an extra ear margin. be able to.

(2) Since the tentering rolling may be performed again after the tentering rolling, it is possible to respond easily and quickly during the rolling, and it is possible to prevent the occurrence of four-period defects in all the materials to be rolled. Further, since it is only necessary to add a simple measuring device to the ordinary rolling equipment, it is possible to cope with the cost at a low cost.

(3) Since it can be dealt with only by rolling, normal water cooling control can be performed, and the invention can be applied to a material having a specified finishing temperature such as a controlled rolled material.

[Brief description of the drawings]

FIG. 1A is a schematic perspective view showing an apparatus for carrying out a four-roll flaw preventing hot rolling method according to the present invention, and FIG. 1B is a schematic plan view showing a state of a slab in a hot rolling step. .

FIG. 2 is an explanatory diagram showing an overlap amount for various slab / product sizes.

[Explanation of symbols]

 S: slab (slab, steel plate) a: overlap amount 1: end face shape measuring device 2: arithmetic processing unit

Claims (1)

[Claims] 1. In a tentative rolling step of hot rolling of a steel sheet, a shape of an end face parallel to a longitudinal direction of a material to be rolled is measured,
From this measurement result, the bulge shape and the amount of overlap of the end face are recognized, and when the overlap portion of the double bulge bites into the product width, the width rolling is performed again. Rolling method.