JP6922668B2 - Hot rolling method and hot rolling machine line - Google Patents

Description

The present invention relates to a hot rolling method and a hot rolling mill row, and more particularly to a hot rolling method and a hot rolling mill row that can suppress the occurrence of edge cracks during rolling while rolling at a high rolling ratio. ..

In hot rolling, there are rolled materials that require a high rolling load, and these are classified as high-load materials and difficult-to-process materials. When rolling such a material at a higher rolling ratio, there is a problem that the load applied to the rolling mill increases to a level exceeding the equipment limit. On the other hand, as a general measure, it is known that a steel sheet is rolled (high-strength rolling) by applying a high tension to the steel sheet in order to reduce the rolling load.

However, in high-strength rolling, there is a problem that cracks (edge cracks) occur at both ends of the steel sheet in the plate width direction during rolling. In particular, high-load materials and difficult-to-process materials have low ductility during machining deformation and are often materials that are prone to edge cracking, and edge cracking may occur more frequently when high-strength rolling is performed. If a large amount of edge cracking occurs, manufacturing troubles such as breakage of the steel sheet and damage to the roll occur, and the manufacturing yield is greatly reduced.

In response to such edge cracks, steel materials with high ductility are welded to both ends of the steel sheet in the plate width direction and then rolled to prevent the occurrence of edge cracks, and after rolling to the product thickness, the welded portion is formed. There is a measure to trim and cut off the edge in the width direction including the plate.

Further, as an apparatus for deforming the end portion of a steel plate in the plate width direction, an apparatus called an edger such as Patent Document 1 and Patent Document 2 is well known.

Jikkai Sho 62-142401 Japanese Patent No. 2689612

However, in the method of welding a steel material having high ductility to both ends in the plate width direction of the steel plate and then rolling and trimming the steel material, it is necessary to weld and cut the steel material, which is very laborious and costly. Further, the edger as described in Patent Document 1 and Patent Document 2 does not solve the edge crack, and the countermeasure against the edge crack has not been studied.

Therefore, in view of the above problems, it is an object of the present invention to provide a hot rolling method capable of suppressing the occurrence of edge cracks while rolling at a high rolling ratio. Also provided is a hot rolling mill train for this method.

The inventors have focused on the fact that edge cracking occurs when a steel sheet in a tension state in which stress is locally strong at the end in the plate width direction is rolled by applying a high tension. Then, it was considered to suppress the occurrence of edge cracks by rolling the end portion in the plate width direction after making it into a low tensile stress state or a compressive stress state. Therefore, by rolling down the steel plate in the plate width direction between the stands in front of the stands that apply high tension, the end portion in the plate width direction can be brought into a low tensile stress state or a compressive stress state. The present invention was completed with the finding that edge cracking does not occur even after high-tensile rolling.
More specifically, a device for rolling in the plate width direction is installed between the stands, and the steel plate is rolled in the plate width direction using the device, so that the cross-sectional shape of the steel plate is the thickness at the end in the plate width direction. After deforming into a form thicker than the plate thickness at the central portion in the plate width direction, horizontal rolling is performed under the pressure in the plate thickness direction. As a result, the stress state at the end in the plate width direction, which tends to be in a high tensile stress state due to the occurrence of edge drop in normal horizontal rolling, is changed to a low tensile stress state or a compressive stress state. be able to. Here, the low tensile stress state means a tensile stress state to the extent that cracks due to brittle fracture do not occur at the widthwise end portion of the plate during and after rolling.
Hereinafter, the present invention will be described.

One aspect of the present invention, in the hot rolling mill train having a plurality of stands, to pressure the steel plate is passing plate in front of every other stand plate width direction, immediately after rolling in a plate width direction This is a hot rolling method in which tension is applied to a steel sheet between a stand and the next downstream stand.

Here, by reducing in the plate width direction, the plate thickness at the end portion in the plate width direction of the steel plate may be reduced so as to be thicker than the plate thickness in the center in the plate width direction.

The reduction in the plate width direction may be performed by a roller, and further, a simple device such as a roller incorporated in a side guide may be used.

Another aspect of the present invention is a hot rolling mill row in which a plurality of stands having rolling mills are arranged so that the steel plate to be passed can be rolled down in the plate width direction, and the plate width at a position where the steel plate is passed. It is equipped with a plurality of plate width direction rolling devices in which rollers are arranged on both sides in the direction, the plate width direction rolling device is arranged in front of every other stand, and the stand immediately after the plate width direction rolling device is arranged and its It is a hot rolling mill train that makes it possible to apply tension to the steel sheet between the next downstream stands.

According to the present invention, the occurrence of edge cracking can be suppressed even in the case of high-strength rolling.

It is a figure explaining the hot rolling method concerning one form. 2 (a) and 2 (b) are views for explaining the cross-sectional shape of the steel plate. It is a figure explaining the deformation of a steel plate by reduction in a plate width direction. It is a figure explaining the stress state at the end portion in the plate width direction of a steel plate by reduction in a plate width direction. It is a figure which showed a part of the manufacturing equipment of a hot-rolled steel sheet schematically. It is a figure which paid attention to the stand between the stands provided with the plate width direction reduction device 30, and the stand adjacent to the downstream side thereof.

The present invention will be described based on the embodiments shown in the drawings. However, the present invention is not limited to these forms.

FIG. 1 shows a diagram illustrating a hot rolling method according to one form. In FIG. 1, three stands 1, 2, and 3 are shown from the upstream side, and each of the stands 1, 2, and 3 has rolling mills 1a, 2a, and 3a. A plate width direction reduction device 5 is arranged between the stand 1 and the stand 2.

In the hot rolling method according to one form, rolling in the plate width direction is performed between the stands (between the stands 1 and 2) immediately before between the stands (between the stands 2 and 3) to which high tension is applied. conduct. More specifically, it is as follows.

A plate width direction reduction device 5 is arranged between the stands immediately before the stands that apply high tension, and the steel plate is reduced in the plate width direction.
As a result, specifically, as shown in FIG. 2, the cross-sectional shape of the steel plate S is deformed. FIG. 2A shows the cross-sectional shape of the steel plate S immediately before the steel plate S is reduced in the plate width direction, and FIG. 2B shows the cross-sectional shape of the steel plate S after the reduction in the plate width direction. .. As can be seen by comparing FIGS. 2 (a) and 2 (b), the thickness of the end portion in the plate width direction of the steel plate becomes thicker than the plate thickness in the center in the plate width direction due to the reduction in the plate width direction of the steel plate. It becomes a shape.

FIG. 3 shows a graph of one example of deformation of the steel sheet due to reduction in the plate width direction. The horizontal axis of this graph is the dimensionless width reduction amount defined by "plate width direction reduction amount / plate thickness", and the vertical axis is the edge swelling amount shown by a in FIG. 2 (b) as the "edge swelling amount". / The amount of dimensionless edge swelling defined by "plate thickness".
As can be seen from FIG. 3, the dimensionless edge swelling amount can be increased by increasing the dimensionless width reduction amount.

Then, by forming the plate thickness at the end portion of the steel plate in the plate width direction to be thicker than the plate thickness at the center in the plate width direction in this way, the stress state at the end portion in the plate width direction of the steel plate can be changed. Specifically, the tensile stress state can be relaxed or the compressive stress state can be set. This makes it possible to prevent edge cracking from occurring even when high-strength rolling is performed between the next stands.

FIG. 4 shows a graph of one example of the stress state at the end portion in the plate width direction due to the deformation of the steel plate due to the reduction in the plate width direction. The horizontal axis of FIG. 4 is the dimensionless width reduction amount as in FIG. On the other hand, the vertical axis of FIG. 4 is the dimensionless width end stress defined by “plate width direction end stress / deformation resistance”. The dimensionless width end stress means that the negative side is in the tensile stress state and the positive side is in the compressive stress state.
As can be seen from FIG. 4, the dimensionless width end stress can be increased by increasing the dimensionless width reduction amount. That is, the tensile stress state can be relaxed or the state can be shifted to the compressive stress state.

High tension is applied and rolled at the next stand where the reduction in the plate width direction is performed in this way. Here, high tension means that a stress of about 10% or more and 40% or less is applied in terms of the deformation resistance ratio of the steel sheet. This is based on the viewpoint that tension is applied for a sufficient load reduction effect such as 5% or more as the load reduction of the rolling mill. That is, if the tension is less than 10% of the deformation resistance ratio of the steel sheet, the effect of reducing the rolling load may be insufficient. On the other hand, the higher the tension, the greater the effect of reducing the rolling load, but troubles such as width necking and fracture are more likely to occur. Therefore, in hot rolling, a tension greater than about 40% is substantially applied to the deformation resistance ratio of the steel sheet. It's difficult.

In the rolling mills (rolling machine 2a and rolling mill 3a) constituting between the stands to which high tension is applied, rolling is performed in a state where high tension is applied, and the rolling load is reduced. Therefore, rolling can be performed with a higher rolling reduction ratio. Then, the steel plate is compressed in the plate width direction between the stands immediately before it, and the rolling direction stress at the end in the plate width direction is improved on the compression side, so that a high tension is applied on average between the stands immediately after that. However, the occurrence of edge cracking can be suppressed.

FIG. 5 is a conceptual diagram showing a hot finish rolling mill row 10 among the hot-rolled steel sheet manufacturing equipment (hereinafter, may be referred to as “manufacturing equipment”) according to one form. In FIG. 5, the steel plate S is conveyed from the left side (upstream side, upper process side) to the right side (downstream side, lower process side) of the paper surface, and the top and bottom of the paper surface are in the vertical direction. Here, the pass line is shown by a broken line. The direction from the upstream side (upper process side) to the downstream side (lower process side) may be described as the plate width direction, and the direction of the plate width of the steel plate S to be passed is the plate width direction in the direction orthogonal to this. May be described. In addition, in the figure, the description of the repeated reference numerals may be omitted for the sake of readability.

As shown in FIG. 5, the manufacturing facility includes a hot finish rolling mill row 10. Although illustration and description are omitted, a heating furnace, a rough rolling mill row, and the like are arranged on the upstream side of the hot finish rolling mill row 10. A cooling device, a winder, and the like are arranged on the downstream side of the hot finish rolling mill row 10. Further, in order to convey the steel plate S, a conveying roll is provided as needed.

The hot finish rolling mill row 10 of this embodiment has first stands 11 to seventh stands 17 from the upstream side, and these are arranged along the plate passing direction. In this embodiment, each stand is provided with rolling mills 21 to 27, and is provided between the stands between the first stand 11 and the second stand 12, between the stands between the third stand 13 and the fourth stand 14, and between the stands. A plate width direction reduction device 30 is arranged between the stands of the fifth stand 15 and the sixth stand 16. Further, in this embodiment, a looper 40 is arranged between each stand.
In this embodiment, in the rolling mills 21 to 27 of the first stand 11 to the seventh stand 17, two backup rolls 21a to 27a are provided vertically in a housing (not shown), and the two backup rolls 21a to backup are provided. Two work rolls 21b to 27b are arranged above and below between the rolls 27a. Then, rolling is performed by passing the steel plate S, which is a rolled material, between the two work rolls 21b and 27b.
Such a stand is known, and each component provided on the stand is also known.

Here, the three plate width direction reduction devices 30 are arranged as described above, but the present invention is not limited to this, and as will be described later, between the stands immediately before the stands that apply high tension and / or the most. The plate width direction reduction device 30 is arranged on the upstream side of the first stand 11, which is a stand arranged on the upstream side.

FIG. 6 is a view of the finishing rolling mill row 10 from above, focusing on the third stand 13 to the fifth stand 15, and the lower work rolls 23b, 24b, 25b, and the work rolls 23b, 24b, 25b. It is a figure which conceptually represented the steel plate S passing over the above, and the sheet width direction rolling reduction device 30. Therefore, in FIG. 6, the vertical direction of the paper surface is the plate width direction of the steel plate. Further, the direction indicated by the straight arrow in FIG. 6 is the plate passing direction.

As can be seen from FIG. 6, in the present embodiment, the plate width direction reduction device 30 includes a side guide 31, a roller 32, and a hydraulic device 33.

The side guide 31 is a set of guide members arranged so as to sandwich the steel plate S from both sides in the plate width direction. Therefore, the side guide 31 is configured to have a certain length in the through plate direction. However, the guide 31 guides the steel plate S, and does not reduce the steel plate S in the plate width direction. On the other hand, the side guide 31 guides the steel plate S, and from the viewpoint of preventing the steel plate S from approaching the plate, its function cannot be exhibited even if the side guide 31 is too far from the steel plate S. Therefore, the side guides 31 are arranged with a predetermined interval with respect to the end portion of the steel plate S in the plate width direction.

The roller 32 is a roller arranged on the side guide 31 so as to project from the side guide 31 toward the end portion of the steel plate S in the plate width direction. The roller 32 is composed of a columnar roller that rotates in a horizontal plane with an axis extending in the vertical direction as a rotation axis. Therefore, the roller 32 is arranged in contact with the steel plate S so as to reduce the end portion of the steel plate S in the plate width direction on its outer peripheral surface.

Here, the rollers may be driven or non-driven. Further, the roller may be cylindrical as described above, or may have a concave outer peripheral surface so that the center is thinner than both ends in the direction of the rotation axis. According to this, the end surface of the steel plate S in contact with the outer peripheral surface of the roller acts so as to be naturally arranged in the deepest concave portion, and the steel plate S can be stably passed through.

The hydraulic device 33 moves the side guide 31 and the roller 32 arranged on the side guide 31 in the plate width direction of the steel plate S, and receives a reaction force from the steel plate S when the roller 32 presses down the steel plate S. This is a device that supports the side guide 31 and the roller 32. This includes known hydraulic equipment.

By reducing the steel plate S in the plate width direction by such a plate width direction reduction device 30, the cross-sectional shape of the steel plate S is deformed, and the plate thickness at the end portion in the plate width direction is thicker than the plate thickness at the center portion. Can be. As a result, it is possible to change the stress state of the end portion in the plate width direction, which normally tends to be in a tensile stress state due to the occurrence of edge drop, to a lower degree of tensile stress state or compressive stress state. Become.

Then, according to the finishing rolling mill row 10 as described above and the manufacturing equipment provided with the same, even if high-strength rolling is performed between the stands adjacent to the downstream side between the stands on which the plate width direction rolling reduction device 30 is arranged. It is possible to suppress the occurrence of edge cracking.
Since high-strength rolling can be performed, the rolling load can be reduced and high-pressure rolling can be performed.

Next, a method of hot finish rolling by the hot finish rolling mill row 10 will be described.

The steel plate S that has reached the hot finish rolling mill row 10 is rolled by the rolling mill 21 of the first stand 11 and reaches between the stands between the first stand 11 and the second stand 12. A plate width direction reduction device 30 is arranged between the stands, and the steel plate S is reduced in the plate width direction. The reduction in the plate width direction is as described above.

As described above, the end portion of the steel plate S in the plate width direction is deformed between the stands of the first stand 11 and the second stand 12, and the steel plate S in the state where the deformation is applied is the rolling mill 22 of the second stand 12. Rolled by. The looper 40 may or may not be used between the stands. When the looper 40 is used, it is necessary to minimize the operating amount and operating speed of the looper 40 when deforming in the plate width direction so that buckling of the steel plate does not occur.

The steel plate S is rolled by the rolling mill 22 of the second stand 12 and the rolling mill 23 of the third stand 13 so that high tension is applied between the second stand 12 and the third stand 13. The looper 40 may or may not be used between the stands. The high tension is as described above.

In the rolling mill 22 of the second stand 12 and the rolling mill 23 of the third stand 13, rolling is performed in a state where high tension is applied, and the rolling load is reduced. Therefore, rolling can be performed with a higher rolling reduction ratio. Then, the steel plate S is pressed between the first stand 11 and the second stand 12 in the plate width direction, and the rolling direction stress at the end in the plate width direction after rolling at the second stand 12 is improved to the compression side. Therefore, even if a high tension is applied between the second stand and the third stand on average, the occurrence of edge cracking can be suppressed.

After that, rolling is performed in the same manner by applying rolling in the plate width direction between the stands of the third stand 13 and the fourth stand 14 and applying high tension between the stands of the fourth stand 14 and the fifth stand 15. Further, a reduction in the plate width direction is applied between the stands of the fifth stand 15 and the sixth stand 16, and a high tension is applied between the stands of the sixth stand 16 and the seventh stand 17.
That is, rolling has the above-mentioned effect by performing rolling in the plate width direction on the upstream side and applying high tension on the downstream side between adjacent stands. The plate width direction reduction is performed between the stands immediately before the stands that apply high tension. Therefore, even if the plate width direction reduction device is arranged between continuous stands, one of them cannot be used. Therefore, it is a capital investment to arrange the reduction device at a distance between one stand or more. It is efficient from the viewpoint of.

As an example of the present invention and a comparative example, rolling was performed under different conditions using a hot rolling mill train having four stands of a first stand to a fourth stand. The diameter of the work roll in each stand of the hot rolling mill row is 800 mm, and the distance between the stands is 5.5 m. The rolled material used is a steel material containing 0.15% by mass of C and 2.0% by mass of Mn.

<Comparative example 1>
As Comparative Example 1, rolling was performed without applying tension between the stands. The rolling load of each stand in Comparative Example 1 serves as a reference for the following examples (Comparative Example 2, Comparative Example 3, Invention Example 1, and Invention Example 2).
Table 1 shows the conditions and results. The items shown in Table 1 are as follows.
The "average deformation resistance" is the average deformation resistance of the steel sheet during rolling of each stand.
"Inside plate thickness" and "outside plate thickness" are the plate thicknesses of the steel plates before and after rolling of each stand.
"Backward tension" and "forward tension" are the magnitudes of the backward tension and the front tension at each stand.
The "rolling load" is the rolling load at each stand.
For "edge cracks", the edge portion of the steel sheet in the plate width direction is observed at a position 2 m downstream of the work roll during rolling, and it is determined that edge cracks have "generated" when a crack of 3 mm or more occurs. Other than that, it is regarded as "not generated". In addition, when it becomes "occurrence" on the upstream side, it becomes "occurrence" on the downstream side.

<Comparative example 2>
In Comparative Example 2, tension was applied between the stands with respect to Comparative Example 1, but reduction in the plate width direction between the stands was not performed. Table 2 shows the conditions and results. In Table 2, the "load reduction rate" represents the reduction rate of the rolling load with respect to the rolling load of Comparative Example 1 as a percentage.

As can be seen from Table 2, the load reduction effect due to the application of tension was observed, but edge cracking occurred in the portion where high tension was applied.

<Comparative example 3>
In Comparative Example 3, the tension was changed as compared with Comparative Example 2. Table 3 shows the conditions and results.

As can be seen from Table 3, as a result of increasing the tension applied to the stands 1 and 2, the rolling load could be further reduced at the stands 1 and 2, but edge cracking also occurred here.

<Example 1 of the present invention>
In Example 1 of the present invention, in addition to the conditions of Comparative Example 2, a plate width direction reduction device similar to the plate width direction reduction device 30 was installed between the stands between the second stand and the third stand. Then, the plate width direction reduction was performed with a non-dimensional width reduction amount of 0.2, that is, a plate width direction reduction amount of 1 mm at a position 1 m upstream from the work roll rolling position of the third stand. The rollers of the plate width direction reduction device are columnar and have a diameter of 100 mm.
When the plate before rolling on the third stand was sampled after rolling in the plate width direction and the dimensions were measured, the non-dimensional edge swelling amount was 0.055, that is, the edge swelling amount was 0.275 mm. Table 4 shows the conditions and results.

The same rolling load reduction effect as in Comparative Example 2 was obtained, and the occurrence of edge cracks could be prevented.

<Example 2 of the present invention>
In Example 2 of the present invention, in addition to the conditions of Comparative Example 3, the reduction in the plate width direction by the same plate width direction reduction device as in Example 1 of the present invention is performed on the upstream side of the first stand, and the second stand and the third stand. I went to two places between the stands. At each location, the dimensionless width reduction amount was 0.2, and the dimensionless edge swelling amount was 0.055. Table 5 shows the conditions and results.

The same rolling load reduction effect as in Comparative Example 3 was obtained, and the occurrence of edge cracks could be prevented.

1, 2, 3 Stands 1a, 2a, 3a Rolling Machine 5 Plate Width Direction Rolling Device 10 Hot Finish Rolling Machine Row 11 1st Stand 12 2nd Stand 13 3rd Stand 14 4th Stand 15 5th Stand 16 6th Stand 17 7th Stand 21-27 Rolling Machine 30 Plate Width Direction Rolling Device 40 Outside Cooling Device

Claims (4)

In a hot rolling mill row with multiple stands
And rolling the steel plate to be strip passing in front of the stand of every other plate width direction to impart tension to the steel sheet between the stand and the next downstream stand immediately after rolling in the plate width direction heat Inter-rolling method. The hot rolling method according to claim 1, wherein the plate thickness at the end portion in the plate width direction of the steel plate is made thicker than the plate thickness at the center in the plate width direction by rolling down in the plate width direction. The hot rolling method according to claim 1 or 2, wherein the rolling reduction in the plate width direction is performed by a roller installed on a side guide provided on the entrance side of the rolling mill. A row of hot rolling mills in which a plurality of stands having rolling mills are arranged.
A plurality of plate width direction reduction devices are provided so that the steel plate to be passed can be reduced in the plate width direction and rollers are arranged on both sides in the plate width direction at the position where the steel plate is passed.
The plate width direction rolling device is arranged in front of every other stand, and tension is applied to the steel plate between the stand immediately after the plate width direction rolling device is arranged and the next downstream stand. A row of hot rolling mills made possible.

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