WO2002053301A1

WO2002053301A1 - Hot rolling method and hot rolling line

Info

Publication number: WO2002053301A1
Application number: PCT/JP2001/011401
Authority: WO
Inventors: Yukihiro Matsubara; Toshiki Hiruta; Masanori Kitahama; Kazuya Miyagawa; Futoshi Goto; Kazuo Onda; Eiji Tohyama; Takeshi Hirabayashi
Original assignee: Kawasaki Steel Corporation
Priority date: 2000-12-28
Filing date: 2001-12-26
Publication date: 2002-07-11
Also published as: CN1426330A; US20030084972A1; KR20020079921A; EP1346780A4; EP1346780A1

Abstract

A hot rolling method capable of making crystal grains finer; and a hot rolling line. Specifically, a hot rolling line for metal plates comprises a finish rolling mill, a leveler, and a cooling system which are disposed in the order mentioned toward the downstream side in the direction of conveyance of the metal plate. The hot rolling method comprises, in the hot rolling line, the steps of subjecting the metal plate, which results from completion of finish rolling applied to the metal piece, to repeated bending by the leveler, and then cooling the same.

Description

Specification

Hot rolling method and hot rolling line

Technical field

The present invention relates to a hot rolling method and a hot rolling line for producing a high-strength metal plate. Background art

A hot rolling line for a steel sheet will be described as a typical example of a metal sheet. Steel sheets are generally manufactured, for example, in a hot rolling line schematically shown in FIG.

The metal piece of the material is called a slab or sheet par. The slab may be extracted by being heated in a heating furnace (not shown), or may be directly sent in a hot state from an upper process without passing through the heating furnace. In some cases, the sheet-par is directly supplied to the finishing mill 3 to omit the rolling by the rough mill 2 to produce a steel sheet. Reference numerals 5c and 5d in FIG. 13 are mandrels. The rotation speed is controlled by a control device (not shown) attached to the coilers 5a and 5b, respectively. The coiler winds the metal plate 1 cooled by the cooling device 4 around a mandrel to produce a coil-shaped metal plate product. The slap paper to be rolled between these facilities is transported by a number of staple rollers (not shown).

In order to increase the strength of the metal sheet product, various methods of hot rolling steel for miniaturizing crystal grains have been studied. A typical example is a so-called controlled rolling method disclosed in Japanese Patent Application Laid-Open No. 63-223124. The principle of the controlled rolling method is that when transforming from austenite (hereinafter referred to as) to ferrite (hereinafter referred to as), α: increase the γ grain boundaries where nuclei are formed and reduce lattice defects such as dislocations. By introducing it in a larger amount, a number of a grains are generated at the time of transformation from “7 to α” to achieve the refinement of crystal grains. Grain refinement or dislocation In order to introduce lattice defects, it is effective to apply as large a strain as possible to the steel sheet. However, since the thickness of the slap or sheet par and the thickness of the product are fixed, there is a limit to the amount of strain that can be introduced in the normal rolling process. Generally, it is said that the average crystal grain size of 5 μm is the limit in controlled rolling.

Japanese Patent Application Laid-Open No. 60-44106 discloses that in a hot rolling line in which a high-temperature material is connected and a finishing mill for hot rolling is arranged, a tension applying device is arranged near the exit of the final stand of the finishing mill. By doing so, it is disclosed that an ultrathin product having a uniform shape can be obtained.

Further, although the tension applying device disclosed in Japanese Patent Application Laid-Open No. 60-44106 has a large number of bending rolls, a metal plate after finish rolling is used so that an ultrathin product having a uniform shape can be obtained. The bending strain that can be imparted to the metal plate after finish rolling was insufficient only by applying tension to the metal sheet.

The present invention realizes the refinement of the crystal grains in the structure of the metal plate by applying a strain to the metal plate without changing the thickness of the slab or sheet bar and the product plate thickness, and thereby achieves hot working for increasing the strength more than before. A rolling method and a hot rolling line are proposed. Another object of the present invention is to provide a hot rolling method and a hot rolling line that can further refine crystal grains under practical leveler conditions. In addition, the metal plate referred to in the present invention includes a metal band. Disclosure of the invention

The present inventors have conducted intensive studies on increasing the strength of a metal plate, and as a result, have found a method of giving a strain to a metal plate without changing the thickness of a slab or sheet par and a product plate thickness. A roller leveler (hereinafter simply referred to as “leveler”), in which upper and lower work rolls (hereinafter simply referred to as “rolls”) are arranged in a staggered manner, is installed after the finish rolling mill exit side. It has been found that it is effective to repeatedly bend the metal plate after finish rolling with the leveler. Bending deformation can apply strain without reducing the thickness of the metal plate, so repeating this process can apply strain to the metal plate. In some cases, the work roll of the leveler may not be evenly distorted in the width direction of the metal plate due to the pressure applied from the metal plate. To prevent this, the upper and lower work rolls may be backed up by backup rolls. By installing the leveler between the finishing mill and the coiler, the present invention can be realized by adding to a conventional hot rolling line, and equipment costs can be reduced and productivity may be reduced. Absent.

In the present invention, a leveler capable of repeatedly applying bending strain to a metal plate is installed on the finish rolling mill exit side. By additionally applying strain, for example, in the case of steel, further refinement of γ grains (addition of grain boundaries) is aimed at. At the same time, lattice defects such as dislocations in γ grains are introduced, and α grains can be further refined. The product metal plate will be made stronger by further miniaturizing the metal crystal grains. The metal plate strained by the leveler is further cooled, brought to a desired temperature, and wound up. Further, the present inventors provide a cooling device on the exit side of the finishing mill and on the entrance side of the leveler, cool the metal plate to a predetermined temperature, and further repeatedly perform bending. At the same time.

The present invention is as described below.

1. In a hot rolling line for metal sheets, a finishing mill, a leveler for imparting bending strain to the metal sheets, and a cooling device are arranged in this order from upstream to downstream in the metal sheet transport direction. Features Hot rolling line for metal sheets.

2. In a hot rolling line for metal sheets, a finishing mill, a leveler in which work rolls are each packed up by a pack-up roll, and a cooling system, A hot rolling line for metal sheets, wherein the metal sheet is arranged from upstream to downstream in the metal sheet transport direction.

3. In the hot rolling line for metal sheets, a finishing mill, a cooling device, a leveler, and a cooling device are arranged in this order from upstream to downstream in the metal sheet transport direction. Hot rolling line for metal sheet.

4. In the hot rolling line for metal sheets, the finishing mill, the cooling equipment, the leveler whose work rolls are backed up by back-up rolls, and the cooling equipment are further connected upstream of the metal sheet transport direction. A hot rolling line for metal sheets, which is arranged in this order from downstream to downstream.

5. In the hot rolling line for the metal sheet, the joining equipment, the finishing mill, the leveler for imparting bending strain to the metal sheet, the cooling equipment, the cutting device, and the coiler are transferred upstream in the metal sheet transport direction. A hot rolling line for metal sheets, which is arranged in that order from downstream to downstream.

6. In the hot rolling line for metal sheets, the joining equipment, the finishing mill, the leveler whose work ports are each packed up by the pack-up ports, the cooling equipment, the cutting equipment, and the coiler Are arranged from upstream to downstream in the metal sheet conveying direction and in that order.

7. In the hot rolling line for metal sheets, the joining equipment, the finishing mill, the cooling equipment, the leveler, and the cooling equipment, the cutting equipment, and the coiler are arranged from upstream to downstream in the metal sheet conveying direction. A hot rolling line for metal sheets, which is arranged in that order.

8. In the hot rolling line for metal sheets, joining equipment, finishing mill, cooling equipment, leveler whose work port is packed up by backup port, cooling equipment, and cutting. The equipment and the coiler are transported by the metal plate A hot rolling line for metal sheets, which is arranged in the order from the upstream to the downstream.

9. The hot rolling line according to any one of 1 to 8, wherein the leveler has a work roll having a diameter of 300 mm or less.

10. The hot rolling line according to any one of 1 to 8, wherein the leveler is a leveler having three to thirty work rolls.

11. The hot rolling line according to any one of 1 to 8, wherein the work rolls of the leveler are driven.

12. The hot rolling line according to any one of 1. to 8., wherein a guide is provided in a gap between the work rolls of the upper and lower work rolls / workers of the leveler.

13. The hot rolling line according to any one of 1. to 8., wherein the surface roughness Ra of the work roll of the leveler is set to 0.5 <Ra <2.0 μm.

14. The leveler according to 1. to 8., wherein the leveler has at least one small-diameter work roll whose diameter is less than 40 times the thickness of the metal plate after finish rolling. The hot rolling line according to any one of the above.

15. In the hot rolling line described in 1.-8, the leveler has at least one non-driven small-diameter work piece having a diameter of less than 40 times the thickness of the metal plate after finish rolling. A hot rolling line characterized in that the diameter of the remaining work rolls is at least 40 times the thickness of the metal sheet after finish rolling, and the work rolls can be driven.

16. The hot rolling line according to item 8., wherein the leveler has at least one non-driven small-diameter work roll whose diameter is less than 40 times the thickness of the metal plate after finish rolling. The small-diameter work roll and the small-diameter work roll A drive torque can be transmitted from the pack-up roll to the small-diameter work rolls via gears provided at respective necks of the rolls, and the diameter of the remaining work rolls is a metal plate after finish rolling. A hot rolling line characterized in that it is at least 40 times as thick as the steel and is configured to be driven.

17. In a hot rolling method in which rolling including finish rolling is hotly performed on a metal piece, the metal plate after the finish rolling applied to the metal piece is repeatedly bent by a leveler, and then cooled. Hot rolling method.

18. The hot rolling method according to 17, wherein the metal plate is cooled after the finish rolling and before the repeated bending.

19. The hot rolling method as described in 17. or 18., wherein the temperature of the metal plate after the repeated bending is in a range of ₃ points of Ar + 50 to 81 " ₃ points / 100 ° C. .

20. The hot rolling method as described in 17. or 18., wherein the work roll of the leveler has a roll pushing amount of +1 to 1030 mm.

21. The hot rolling method according to 17. or 18., wherein the temperature of the metal plate after the finish rolling is at least _three points of Ar.

22. Carry out tracking of the tip and tail end of the metal plate, tighten the upper and lower work rolls after the tip of the metal plate has passed the corresponding work roll of the leveler, and before the tail end comes off. The hot rolling method as described in 17. or 18., characterized in that control is performed to open the upper and lower work rolls corresponding to.

23. The hot rolling method according to 17. or 18., wherein the finish rolling is performed after joining a preceding sheet bar and a succeeding sheet par. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a layout diagram of an example of a hot rolling line according to the present invention. FIG. 1B is a layout diagram of a preferred hot rolling line.

FIG. 2 is a schematic diagram illustrating details of a leveler applied to the present invention and cooling equipment. FIG. 3A is a partial longitudinal sectional view showing a roll arrangement of an example of a leveler used in the present invention. FIG. 3B is a schematic view showing a driving mechanism of a large-diameter work roll adjacent to the upper-small-diameter work roll shown in FIG. 3A.

FIG. 3C is a diagram showing the effect of the ratio of the work roll diameter of the leveler to the thickness of the metal plate on the average crystal grain size of the metal plate.

FIG. 4 is a configuration diagram of a drive mechanism for driving a small-diameter work roll of a leveler used in the present invention.

FIG. 5A is a schematic diagram illustrating deformation between rolls of a metal plate in a leveler.

FIG. 5B is a schematic diagram when the pushing amount of the leveler is negative.

FIG. 5C is a diagram showing the relationship between the work roll diameter and the bending strain of the leveler.

FIG. 6 is a schematic diagram showing the state of a passing trap at the tip of a metal plate in a leveler. FIG. 7 is a schematic diagram showing a leveler passing plate trap due to a metal plate slip. Figure

Fig. 8 is a graph showing the relationship between the surface roughness of the leveler work roll and the rate of slip occurrence. .

FIG. 9 is a schematic diagram showing how the measuring roll is installed on the hot rolling line. FIG. 10 is a diagram showing the configuration of the measuring roll.

FIG. 11 is a layout diagram of another preferred hot rolling line according to the present invention.

FIG. 12 is a graph comparing the tensile strength and the average crystal grain size of the present invention example and the conventional example. FIG. 13 is an arrangement diagram of a hot rolling line for producing a conventional steel sheet. BEST MODE FOR CARRYING OUT THE INVENTION The hot rolling line according to the present invention will be described with reference to FIGS. 1A and IB. In FIG. 1A and FIG. IB, the rough rolling mill 2, the first cooling equipment 4, the mandrels 5c and 5d, and the coilers 5a and 5b are assumed to be installed in the conventional hot rolling line shown in FIG. Since they are the same, the same reference numerals are given and the description is omitted.

FIG. 1A shows the first embodiment. In this hot rolling line, a finishing mill 3, a leveler 6, and a cooling facility 4 are arranged in this order from upstream to downstream of the rolling line. Hereinafter, the cooling equipment 4 is also referred to as a first cooling equipment 4.

FIG. 1B shows a second embodiment. In this hot rolling line, in addition to the facilities of the hot rolling line shown in FIG. 1A, a second cooling facility 7 is arranged between the finishing mill 3 and the leveler 6. In the finishing mill 3, reference numeral 3a denotes a work roll, and 3b denotes a pack-up roll, which are incorporated in a housing (not shown).

The leveler 6 includes three or more work rolls 6a arranged in a zigzag pattern or a backup roll 6b for backing up the work roll 6a. The diameter of the crawl 6a is desirably 300 mm or less from the viewpoint of imparting a leveler additional strain described later. If the diameter of the work roll 6a is less than 180 mm, the pack-up roll 6b is provided. It is desirable.

In this hot rolling line, the metal piece S is rolled by the finish rolling mill 3 to form the metal plate 1, and then the metal plate 1 after finish rolling is repeatedly bent and then cooled. Due to the strain applied by the leveler 6 in the longitudinal direction of the metal sheet, the crystal grains of the metal sheet product can be refined. '

Here, in the case of steel, before the metal plate completes the transformation from γ to α, the metal plate is repeatedly bent by the leveler 6 to refine the α grains. At that time, it is more effective to repeatedly bend the metal plate in the two-phase temperature range where the α phase is slightly present, rather than repeatedly bending the metal plate in the γ single-phase temperature range. This is preferable because α grains can be refined.

The mechanism of grain refinement in this steel is as follows: (1) increase of γ grain boundaries due to refinement of γ grains; (2) introduction of lattice defects such as dislocations in one grain; It is considered that it is generated.

As shown in FIG. 1B, in addition to the first cooling facility 4, a second cooling facility 7 is arranged between the final stand of the finishing mill and the leveler. In the hot rolling line provided with the second cooling equipment 7, the metal plate 1 can be cooled to a desired temperature after the finish rolling and before the metal plate 1 is repeatedly bent. This is preferable because the crystal grains of the metal sheet product can be further refined.

The second cooling facility 7 can have the same configuration as the conventional first cooling facility 4. For example, it comprises a cooling nozzle that outputs cooling water to the front and back surfaces of the metal plate 1, a control device that controls the flow of the cooling water, a radiation thermometer that measures the surface temperature of the metal plate 1, and the like. It is desirable that the temperature of the metal plate 1 immediately before repeated bending is 900 to 750 ° C in the case of steel.

As shown in FIG. 5A, the bending strain ε per one time in the leveler 6 is δ / L on the surface of the metal plate 1 when the center distance between the lower rolls 6a is 2 L and the roll pushing amount is δ. Proportional to ² . Here, δ = 0 indicates a state in which a metal plate is sandwiched between upper and lower work rolls. The distance that the work roll is pushed in from this state is represented by ten. It is known that the bending strain ε per one time applied to the surface of the metal plate by the leveler 6 is approximately given by equation (1).

( 1 set

ε = a X δ / L ² here,

a: 2 X h

h: The thickness of the metal plate 1.

Figure 5C shows the relationship between the diameter d of the work roll 6a and the bending strain ε per stroke on the metal plate surface. However, the results are obtained when the plate thickness is 4 mm, the center distance 2 L between the work rolls 6 a is d + 10 mm, and the roll pushing amount δ is the maximum pushing amount. The bending strain ε at one time on the metal plate surface is inversely proportional to the diameter d of the work roll 6a. When the diameter d of the work roll 6a exceeds 300rain, the bending strain ε per one time on the surface of the metal plate becomes very small. Therefore, the diameter d of the work roll 6a is desirably 300 mm or less. As the diameter of the work roll 6a increases, the center distance 2L between the work rolls also increases, and the length of the leveler in the rolling line direction increases. The cooling length of the cooling device must also be ensured. As a result, the length of the hot rolling line becomes longer. The larger the diameter of the work roll 6a, the larger the device. From the above viewpoint, the diameter d of the work roll 6a is desirably 300 mm or less. The strain applied to the metal plate 1 by the leveler 6 can be obtained by multiplying the equation (1) by the number of times of bending (n_2). Here, n is the number of work rolls. As shown in FIGS. 3A and 3B, when the work roll 6a 'having a smaller diameter than the other work rolls is provided in the leveler 6, the radius of curvature of the bending by the small work roll 6a' becomes smaller. However, the strain applied to the metal plate 1 increases. The present inventors have found that when the value of a in equation (1) is mXh, the value approaches an actual strain value. Here, the value of m is more than 2 and up to about 3. m varies depending on conditions such as the amount of indentation δ of the leveler 6 and the tension applied to the metal plate 1 and can be determined experimentally. From the following equation (2), the strain applied to the surface of the metal plate 1 when the small-diameter work roll 6a 'is provided can be obtained. Equation (2)

_£ = h X 6 X {2 Xn l / (L l) ² + (mXn 2) / (L 2) ² } where

n 1: Number of bends by large diameter work roll

n 2: Number of bending by small diameter work roll

L 1: Half of the center distance between large diameter work rolls

L 2: Half of the center distance between two rolls 6 a facing each other with a small-diameter work roll and a metal plate in between

n = n 1 + n 2 + 2

The large-diameter work roll means a work roll 6a other than the small-diameter work roll 6a '.

By the way, if the roll pushing amount δ becomes too large to increase the longitudinal bending strain ε on the surface of the metal plate 1, as shown in Fig. 6, the tip of the metal plate 1 cannot pass normally through the leveler. Cases arise. To prevent this, it is desirable to limit δ to +30 mm or less. On the other hand, from the viewpoint of imparting the minimum necessary strain to the metal plate and miniaturizing the crystal grains, it is desirable that δ be + lmm or more. If the radius r of the peak opening 6a is reduced, the Lorenole interval 2L is narrowed, and the Lonore pushing amount δ is maintained, the longitudinal bending strain ε on the surface of the metal plate 1 can be increased. However, the work roll 6a may become thin and bend due to the reaction force from the metal plate 1 caused by the roll pressing. If the diameter of the work roll 6a is less than 180 mm, it is desirable to have a backup roll that reinforces the work roll 6a. The backup roll is an integrated backup port composed of an integral roll member in the roll axis direction. Rolls, or a divided pack-up roll composed of a plurality of roll members in the roll axis direction. The present invention is not limited to this.

It is also conceivable that the leveler 6 keeps the bending strain ε in the longitudinal direction on the surface of the metal plate 1 at one time constant, increases the number of bendings, and imparts a desired bending strain ε. However, when the number of work rolls exceeds 30, the temperature of the metal plate 1 decreases, and the problem that the reaction force from the metal plate 1 becomes too large occurs. For this reason, it is preferable that the number of the work rolls of the leveler arranged in the hot rolling line of the present invention is 30 or less.

Further, it is preferable that each of the work rolls of the leveler is driven.駆動 By making one crawl driven, it is possible to repeatedly perform bending while feeding the metal plate. In principle, the driving speed is the same as the traveling speed of the metal plate. However, when the leading end or tail end of the metal plate is located between the final stand of the finishing mill and the coiler, exceptional speed is taken. That is, the speed at the tip is higher than the traveling speed of the metal plate. The speed at the tail end is lower than the running speed of the metal plate. It is preferable to prevent the doubling of the metal plate and the accompanying running obstacle of the metal plate. For the tip, it is preferably 103 to 140% of the running speed of the metal plate. In addition, although it depends on the thickness and traveling speed of the metal plate, the traveling speed of the tail end is preferably 60 to 95% of the traveling speed of the metal plate.

The surface roughness Ra of the leveler work roll applied to the present invention is preferably 0.5 <Ra <2.0 μπι. This is to prevent the metal plate from passing through the inside of the leveler as shown in Fig. 7. Here, the surface roughness Ra refers to Ra (arithmetic average roughness) defined in JIS B 0601-1994, and was measured in the roll axis direction of the work roll with a cutoff value of 0.8 mm and an evaluation length of 4 mm. Value.

The reason for setting the surface roughness Ra of the leveler work roll to 0.5 μm and Ra is as follows. It is on the street. If Ra is less than 0.5 im, a slip may occur between the metal plate and the work roll of the leveler, and the metal plate may not pass through the leveler (see FIG. 7). Subsequent metal sheets are folded at the leveler entrance to form a threading trap, and rolling must be stopped. Therefore, in order to suppress such threading trapping due to slippage in the leveler, the surface roughness Ra of the work roll of the leveler is set to 0.5 μχ and Ra to prevent slippage in the leveler. The stable leveling plate inside the leveler is designed. Figure 8 shows the relationship between the surface roughness Ra (μπι) of the leveler work roll and the slip occurrence rate (%). It can be seen that when the surface roughness Ra of the work roll of the leveler exceeds 0.5 ηι, the slip generation rate (%) in the leveler decreases.

This investigation was performed using the hot rolling line shown in FIG. 1 under the same conditions as Example 12 (Example 1 of the present invention) described later. Bending was repeatedly performed while changing the surface roughness Ra (^ m) of the work roll of the leveler. For each surface roughness Ra (Aim) of the work roll, the ratio of the number of coils of the metal plate that led to the passing-through trap by the slip in the leveler to the total number of treated coils was defined as the slip occurrence rate. The surface roughness Ra (^ m) was measured at five points in the roll axis direction of the first crawl of the leveler, and the average value was obtained.

The slip inside the leveler often occurred when the work roll of the leveler was pushed in before the tip of the metal plate after reaching the leveler reached the coiler pinch roll or the coiler.

The cause can be estimated as follows. The force in the direction to advance the metal plate that can be transmitted from the work roll of the leveler to the metal plate without slipping is F w, the pushing force given by the work roll of the final stand of the finishing mill is F _c , and the force applied through the metal plate in the leveler is F _c . Let F r be the force required to plate. The sum of If the surface roughness R a of the work rolls of the leveler is small, when the repetition bending the leveler in a state of tension to the metal plate tip of leveler exit side is not granted, the F _w and F c Is smaller than Fr, and inside the leveler Causes the metal plate to slip. On the other hand, if you roughen the surface roughness R a of the work rolls of the leveler, F _w is increased, the metal plate is estimated not to slip in the sum F r greater than Do connexion leveler of F _w and F c You.

The reason for setting the surface roughness Ra of the work roll of the leveler to Ra 2.0 m is that when the surface roughness Ra of the work roll of the leveler is 2.0 μΐΆ or more, the work roll surface roughness Is transferred to the surface of the metal plate to increase the surface roughness of the metal plate. In the case of steel plate, partial peeling of the scale is caused, and surface quality is impaired.

In the present invention, in a hot rolling line for metal sheets, a finishing mill, a leveler, and a cooling facility are arranged in this order from upstream to downstream in the metal sheet transport direction. The metal plate after finishing rolling applied to the metal piece is repeatedly bent by a leveler, and then cooled. By doing so, the crystal grains are refined and a high-strength metal sheet product is obtained. If the surface roughness Ra of the work roll of the above-mentioned leveler is set to 0.5 <a <2.0 μm, the trouble of passing through the inside of the leveler is reduced. This is preferable because the operation rate of the rolling line can be increased and the surface properties of the metal sheet can be maintained well.

Incidentally, a problem may occur when the tail end of the metal plate passes through the leveler. While the tail end is passing through the leveler, the metal plate may suddenly meander in the width direction, bend in a wrinkle shape and pass through the leveler. This phenomenon is called narrowing. The leveler work roll may be scratched, and the scratch may be transferred to the subsequent metal plate, resulting in poor surface quality. In order to solve this problem, it is preferable to install a threading guide 6c or a side guide 6d between the work rolls 6a, as in the case of the tip problem. The side guides 6d have guide plates arranged on both sides facing each other so as to sandwich the metal plate 1 in the width direction. Another method is to track the position of the tail end of the metal plate and widen the gap between the upper and lower work rolls of the leveler just before the tail end enters the leveler. Here, tracking will be described. Tracking is to detect where the leading edge and the trailing edge of the metal plate are on the hot rolling line sequentially in real time. For example, the measuring ring 8 shown in FIG. 10 is installed on the entrance side of the finishing mill as shown in FIG. Index from the stored data in the computer that does not indicate the thickness ratio of the entrance and exit of the finishing mill. This sheet thickness ratio is multiplied by the number of pulse force parts generated by the measuring roll 8. Thus, the position of the metal plate on the hot rolling line can be determined. The starting point of the pulse count shall be when the tip of the metal plate enters the roll of the final stand of the finishing mill.

The measuring roll 8 is pressed against the metal plate 1 and rotates. A pulse is generated each time it rotates a predetermined angle (for example, 0.025 mm in circumference). The speed of the metal plate on the entry side of the finishing mill is measured by force-counting the pulse generated by the measuring ring roll 8 by a control device (not shown). After that, by multiplying the thickness ratio between the entrance and exit of the finishing mill, the speed and tip position of the metal sheet on the exit of the finishing mill can be known in real time. The tracking of the tail end of the metal plate requires some contrivance. The starting point is the time when the tail end of the metal plate comes off the roll of the final stand of the finishing mill. Tracking is obtained by, for example, integrating the product of the winding diameter and the number of rotations of the mandrel from the time when the metal plate is wound around the coiler 5a or 5b. The winding diameter is calculated by adding the product of the number of turns and the thickness to the diameter of the mandrel 5c or 5d. As another example, while the starting point is the same, the roll diameter and the number of revolutions of the final stand of the finishing mill can be obtained by a control device (not shown), and the advance rate can be indexed from data stored in a computer (not shown). Alternatively, there is a method in which calculation is performed using a model formula and multiplication is performed. Alternatively, a laser speedometer can be used instead of the measuring roll. Any method can be applied as long as the method can track the positions of the tip and the tail in real time, which are useful in practicing the present invention. The position of the tail end of the metal plate 1 with respect to the levelers, etc. If the determination can be made in the above, control may be performed to open and close the roller of the leveler in accordance with the determination. FIG. 11 shows a hot rolling line according to the third embodiment. The case where the cooling device 7 is not installed before the leveler 6 corresponds to the present invention example (3), and the case where the cooling device 7 is installed corresponds to the present invention example (4). The preceding sheet par (preceding metal plate la) and the succeeding sheet bar (subsequent metal plate lb) are joined by the joining equipment 10. Next, after the metal plate 1 is rolled by the finishing mill 3, the metal plate 1 is repeatedly bent and deformed by the leveler 6. Next, the metal plate 1 is cut by the cutting equipment 16 and wound into two coilers 5a and 5b.

The joining equipment 10 joins a plurality of sheet pars. At the joint, it is possible to prevent the passage of the plate in the leveler 6 as shown in FIG. 6 and the narrowing in the leveler 6 described above. The yield of high-strength metal plates can be greatly improved as compared with a case where sheet pars are rolled one by one and a metal plate having a front end and a tail end is repeatedly bent and deformed with a leveler 6 for each one.

The joining equipment 10 is mainly composed of a group of devices including a coil box 11, a cropper 9a, and a joining device 12, and further includes a paring device 13, a joining cooling device 14, and a sheet paring device indicated by dotted lines in FIG. A heating device 15 or the like may be added to this. The welding principle is not only the combination of induction heating and pressure welding, but also filler wire welding with a laser. Any of these methods may be used, or any other method may be used.

For tracking, the pulse may be counted in the same manner, with the tip of the first joint being the above-mentioned tip, and the tail end of the last joint being regarded as the above-mentioned tail end. Further, as described above, a method using a laser type speedometer instead of the measuring roll may be employed. In short, any method can be used as long as the position of the tip and tail can be tracked in real time.

The sheet bars are joined, continuously finish-rolled, and repeatedly bent and bent according to the present invention. Apply to the metal plate. This makes it possible to increase the strength of the entire length of the metal plate, including the joints in the middle, excluding the end of the first joint and the tail end of the last joint, which is advantageous in yield. As shown in FIG. 1B, a cooling system 7 is provided between the exit side of the finishing mill and the leveler. One preferable example is to cool the metal plate 1 after finish rolling to a predetermined temperature and then repeatedly perform bending with the leveler.

In the case of steel, in order to obtain a high-strength steel sheet, the exit temperature of the final stand of the finishing mill is usually 8 points or more. If a cooling system 7 is provided on the leveler entry side, cooling can be performed before the leveler after finish rolling. Maximize the effect of crystal grain refinement by setting the temperature at the leveler exit side to a temperature range from Ar ₃ points or less, which is the temperature at which transformation from y to α starts, to Ar ₃ points-50 ° C or more. be able to.

Refining effect of the crystal grains, than if you make multiple bending strain in a temperature range of more than ₃ points Ar, mostly multiple times in transformation during the metal structure is present slightly α grains V grain Larger when bending strain is applied. This has a greater effect that dislocations introduced into the γ grains become nucleation sites for OL grains. Even if bending bending is applied multiple times after the transformation from γ to α is completed, the effect of refining the crystal grains is considered to be small.

For example, as shown by a dotted line in FIG. 2, the cooling equipment 7 includes a cooling nozzle 7c for emitting cooling water to the front and back surfaces of the metal plate 1, a control device 7b for controlling the ejection of the cooling water from the cooling nozzle 7c, It comprises a δ radiation thermometer 7a for measuring the temperature of the surface of the metal plate 1. It is possible to perform cooling to a predetermined temperature according to the surface temperature of the metal plate 1. The cooling equipment 4 can have a similar configuration. The metal plate 1 can be cooled in a predetermined cooling pattern and at a predetermined winding temperature. The control device 4b and the control device 7b can be integrated into one unit, and information can be shared to perform temperature control. Reference numeral 4a denotes a radiation thermometer provided near the outlet side of the cooling equipment 4, and 4c denotes a cooling nozzle provided in the cooling equipment 4. In Figure 2, Leveler 6 is exaggerated for clarity. The levelers arranged in the hot rolling lines according to the first and second embodiments increase the strain applied to the metal plate 1 by using at least one work roll as a small-diameter work roll. can do. Preferably, the small-diameter work roll is not driven and the remaining large-diameter work roll is drivable (see FIGS. 3A and 3B). It is preferable that the diameter d of the small-diameter work rolls 6a and 6a is less than 40 times the thickness h of the metal plate after finish rolling. The large-diameter work roll 6a preferably has a diameter d that is at least 40 times the thickness h of the metal plate after finish rolling. A spindle yoke 61a of a known universal joint (universal joint) 61 shown in FIG. 3B is fitted in the oval neck portion of the large-diameter work row / roller 6a. The large-diameter work roll is rotationally driven by a motor (not shown) via a universal joint 61. A gear box having a plurality of gears may be interposed between the motor and the universal joint 61.

FIG. 3A is a partial schematic longitudinal sectional view of an example of a leveler arranged in the hot rolling line according to the first and second embodiments. FIG. 3B is a schematic diagram showing a driving mechanism of one upper and smaller diameter work roll 6a arranged on the leveler and two large diameter work rolls 6a adjacent thereto. Other large-diameter work rolls 6a and back-up rolls 6b are omitted. Reference numeral 63 in FIG. 3B denotes a bearing, and the work rolls 6a and 6a 'and the backup roll 6b are rotatably supported by a frame of a leveler (not shown) via bearings.

The leveler used in the present invention preferably has at least one small-diameter work roll 6a, whose diameter d is less than 40 times the thickness h of the metal plate after finish rolling. The reason for this is that at least one small-diameter work roll with a diameter of less than 40 times the thickness of the metal plate after finish rolling is arranged on at least one leveler, and the bending strain per one stroke of the small-diameter work roll is ε. And the crystal grains of the product can be further refined. You. Figure 3C shows the effect of the ratio dZh of the work roll diameter d of the leveler to the thickness h of the metal plate on the average crystal grain size of the metal plate. The thickness of the steel sheet on the exit side of the finishing mill is 4 mm and 5 mm. The hot rolling conditions are as follows: the finishing temperature is 900 ° C, the steel sheet speed at the finishing mill is 720m / min, and the winding temperature is 600 ° C. From Fig. 3C, it can be seen that by setting the diameter d of the work roll to less than 40 times the thickness h of the metal plate after finish rolling, the crystal grains of the product can be reduced. The reason that the work roll diameter d is expressed as d Z h with respect to the thickness h of the metal plate is that if the work roll diameter d is reduced, the roll interval 2 L can be reduced, and it is proportional to the reciprocal of d / h. This is because distortion is added. In the leveler used in the present invention, it is preferable that the large-diameter work roll 6a can be driven and the small-diameter work roll 6a is not driven. As described below, it is difficult to drive the small-diameter work roll 6a '. The upper work roll on the leveler must be able to move up and down. _C diameter work rolls 6a is this to be driven by a motor that uses a universal joint for instance ', because smaller diameter, and also be used for small-diameter shaft corresponding spindle yoke universal joint. This does not allow sufficient torque transmission. If the motor is designed to have a large drive torque facility to transmit a large torque, the universal joint may not be able to withstand mechanical strength and may be damaged. As described above, it is difficult to directly drive the small-diameter work roll 6a, using the universal joint. On the other hand, with a large-diameter work roll 6a whose diameter is 40 times or more the thickness of the metal plate after finish rolling, even if the work roll is driven directly using an up-persal joint, there is no problem in strength. Absent. Therefore, only the large-diameter work roll 6a should be driven so as to transmit the torque including both the large-diameter work roll 6a required for bending the metal plate and the non-driven small-diameter work roll. Is preferred.

The leveler arranged in the hot rolling line according to the present invention has a work roll of at least 1 It is preferable that the number of the work rolls is 30 or less, and that about 1/3 of the number of the work rolls is a small-diameter work roll having the above diameter.

The reason for this is that if the number of the non-driven small-diameter work rolls _6a , among the one work roll arranged on the leveler, is up to four, the metal plate on the non-driven small-diameter work roll 6a ' The torque required for bending can be transmitted to the remaining seven large-diameter crawls 6a from the unity-passal joint connected to it without any problem in strength. On the other hand, if the number of non-driven small-diameter single crawls 6a 'is 5 or more out of the 11 work rolls arranged on the leveler, there is a problem with the strength of the unity basal joint connected to the large-diameter work roll. Occurs.

If the non-driven small-diameter work rolls 6a, out of the 30 work rolls installed on the leveler 6, are up to 10, the bending of the metal plate on the non-driven small-diameter work rolls 6a 'is performed. The necessary torque can be transmitted from the unity basal joint 61 connected to the remaining 20 large-diameter work rolls 6a without any problem in strength. On the other hand, if the number of non-driven work rolls is increased to 11 or more out of the 30 work rolls arranged on the leveler 6, the dual joint 61 connected to the large-diameter work roll 6a has strength. The above problems arise. As described above, if the number of small-diameter work rolls is about 1/3 of the total number of work rolls / rolls, even if the small-diameter work rolls 6a 'are not driven, the unity bass joint that drives the large-diameter work rolls 6a can be used. The large-diameter work roll 6a can be driven without generating the torque transmission problem of 61.

As a large-diameter work roll for a leveler, the larger the diameter, the more advantageous it is in transmitting the required torque. However, the diameter of the large-diameter work roll 6a is desirably 300 mm or less from the viewpoint of imparting sufficient strain to the metal plate and reducing the size of the apparatus.

In the hot rolling lines according to the first and second embodiments described above, metal pieces are processed. Do not join before top rolling. As shown in FIG. 11, the hot rolling line according to the third embodiment is connected to the hot rolling line according to the first and second embodiments by a known joining equipment 10 and continuous. A cutting facility 16 for cutting the metal plate 1 is provided. After the metal pieces S are joined, finish rolling is performed, so that the continuous metal plate 1 can be cut between runs.

The joining equipment 10 in FIG. 11 is equipment for joining the tail end of the preceding metal piece and the tip of the following metal piece. It mainly consists of a coil box 11, a cropper 9a, and a joining device 12. The welding device 12 is composed of a welding machine using induction heating or a laser. Further, a deburring device 13, a joint cooling device 14, a sheet bar heating device 15 and the like shown by dotted lines may be added thereto. Further, it is preferable that the second cooling facility 7 is arranged.

According to the hot rolling line according to the third embodiment, the second and subsequent metal plates 1 can be repeatedly bent by the leveler 6 over the entire length from the front end thereof. For this reason, the production yield of high-strength metal sheets is greatly improved. It is preferable to the hot rolling lines according to the first and second embodiments that are configured to roll the metal pieces S one by one.

By the way, the levelers arranged in the hot rolling lines according to the first, second, and third embodiments are such that when the small-diameter work rolls 6a are not driven as shown in FIGS. 3A and 3B, When the thickness of the metal plate is increased, slip may occur between the rolls during repeated bending. Sri Tsu _c between the rolls slips rubbed flaw defect caused by the flops may occur in the metal plate, a leveler illustrated example FIG 3 A, Figure 3 B, a small diameter is positioned on the metal plate 1 Work This occurs between the roll 6a, and the backup roll 6b, which is disposed adjacent to the small-diameter work roll 6a, so as to reinforce the work roll 6a. Therefore, in order to prevent slip between rolls in the leveler, Fig. 4A and Fig. 4B The mechanism shown is conceivable. Gears 64 and 64 'are provided on the neck of the small-diameter work roll 6a' and the neck of the pack-up roll 6b, respectively. The driving torque is transmitted from the backup roll 6b to the small-diameter work rolls 6a, via the gears 64, 64 '. In the figure, reference numeral 64 denotes a gear fixed to the neck of the pack-up opening 6b by a key or the like, and reference numeral 64 'denotes a gear fixed to the neck of the small-diameter work roll 6a' by a key or the like. In FIG. 4A, the load torque of the small-diameter work roll 6a 'is transmitted in the following order. Gear 64 fixed diameter Wa one crawling 6 _a, 'and the gear 64 which is fixed to the pack-up roll 6b, the neck portion of the pack-up roll 6b, the spindle yoke 61a, Interview two per monkey joint 61, a plurality of with it Gearbox 65 with gears, motor (not shown). The driving torque from the motor is supplied in the reverse order.

FIG. 4A is a configuration diagram of a drive mechanism for driving the small-diameter work roll 6a ′ using the unity vasal joint 61. This is suitable when the passing speed of the metal plate 1 is relatively low, about 300 m / min. FIG. 4A shows one small-diameter work roll 6a 'arranged on the upper side and one backup roll 6b reinforcing the small-diameter work roll 6a'. Illustration of other rolls is omitted. In the figure, reference numeral 62 denotes a bearing box provided with a bearing 63 for supporting the roll in rotation, and 66 denotes a spindle support.

According to the driving mechanism of the small-diameter work roll 6a 'of the leveler, the small-diameter work roll is driven from the pack-up roll 6b via gears provided on the neck of the small-diameter work roll 6a' and the neck of the backup roll 6b. The driving torque can be transmitted to the roll 6a '. The remaining work rolls have a large diameter and can be driven. According to such a mechanism, slip between rolls can be prevented. The equipment cost is slightly higher than when the small diameter work rolls 6a, 6a are not driven.

On the other hand, when the metal plate 1 is passed through the leveler at a speed as high as about 100 mZ, the possibility of breakage increases due to the drive limit of the up-persal joint. There Thus, a drive mechanism for the small-diameter work roll 6a 'as shown in FIG. 4B is preferable. Fig. 4B shows the configuration of several small-diameter work rolls 6a (four shown) arranged on the leveler and a back-up roll 6b that reinforces the work roll 6a '. Knockers and rolls are directly connected to the shaft of the motor 67, and can withstand high-speed rotation because a universal joint is not used.

The small diameter work roll is driven from the backup roll through gears. Not only the large-diameter work roll 6a but also the small-diameter work roll 6a 'can be driven. It is the same as the drive mechanism of the small-diameter work roll 6a 'shown in FIG. 4A except that the backup roll 6b is directly connected to the motor 67 axis. The description of the driving torque transmission path to the small-diameter work roll 6a 'is omitted.

However, in the leveler shown in FIG. 4B, a drive motor 67, a spindle support 66, and the like are installed on an elevating plate 68 for integrally moving the related components of the upper work roll 6a. Items related to the upper work roll 6a 'are raised and lowered by a lifting mechanism (not shown). If the related parts of the upper work roll 6a are integrated as an elevating mechanism, there is no problem in strength even at a high rotation speed of 50 mm and a peripheral speed of 1000 m / min, that is, 12700 rotations. The drive torque can be transmitted to the work roll 6a '.

In order to further reduce the diameter of the work roll 6a, as shown in FIG. 4C, the related product of the upper work roll 6a is an integral lifting mechanism, and the drive motor 67 and the axis of the upper work roll 6a 'are coaxial. And a drive mechanism directly connected to the drive mechanism. Incidentally, the pack app roll is not shown. At this time, since the work rolls 6a, which are adjacent to each other are too small in diameter, as can be seen from FIG. 4C, the drive motors 67 are arranged on both sides in the width direction of the metal plate 1 across the hot rolling line. Still, the drive motors 67 on the same side mechanically interfere with each other due to the installation space. To prevent this, δ Change the length of the drive motor spindle 69 that fits. According to such a small diameter work roll drive mechanism, the diameter of the upper small diameter work roll can be reduced to 25 mm. In the hot rolling line described above, the present inventors conducted various experiments on steel. As a result, we have obtained a new finding that the temperature at which repetitive bending at a leveler is applied has a significant effect on the effect of reducing the size of α grains.

The test material was 0.2 C—0.7Si-2.OMn—0.15Ti steel. It was rolled to a thickness of 4 mm by a finishing mill. The number of work rolls in the leveler was 23, the work roll diameter was 190 mm, the center axis distance of the work roll was 200 mm, and the roll pushing amount was 20 mm. After repeatedly bending with a leveler, it was wound up with a coiler. The Ar ₃ point temperature of the above steel is 750 ° C. The experiment was performed by changing the finish rolling speed in various ways and adjusting the cooling time so that the steel sheet temperature at the leveler exit side was 550 to 800, and the crystal grain size and tensile strength of the experimental material were measured. Was measured.

Incidentally, the temperature of the steel sheet was measured by installing a thermometer (not shown) at a position 1 m downstream from the lowest roll of the leveler. Regarding the crystal grain size, the average cross-sectional area of the crystal grains was determined based on JIS G 0552, and the average grain size was calculated assuming that the average cross-sectional area was circular. The tensile strength was determined by cutting a No. 5 test piece in accordance with JIS Z 2201 and performing a tensile test. The test piece was finish-rolled, the steel sheet wound up by a coiler was rewound at another place, and a No. 5 test piece was cut out in accordance with JIS Z 2201. The measurement of the crystal grain size and the tensile strength was performed by cutting out a measurement sample from the central portion in the longitudinal direction of the coil, that is, a portion subjected to repeated bending by a leveler.

Table 1 shows the results of these tests and measurements. In Table 1, Experimental Material No. 1 is a conventional example, and no leveler was used on the exit side of the finishing mill. Experimental materials Nos. 2 to 7 show the results of repeated bending using a leveler with a steel plate temperature at the exit side of the leveler of 800 to 550 ° C and a roll indentation of 20 mm. I have.

As is clear from Table 1, in contrast to No. 1 of the conventional example that does not use a leveler, in Nos. 2 to 5 where a leveler is used and the steel sheet temperature at the leveler exit side is 650 ° C or more, the crystal grains are It has been miniaturized. From this fact, it can be seen that it is preferable that the metal plate temperature at the leveler exit side be in the range of Ar ₃ points + 50 ° C. to Ar ₃ points / 100 ° C. In particular, Repera delivery temperature is Ar ₃ point ~ Ar ₃ point by 50 ° C to become No. 3, in No. 4, the crystal grains are extremely fine.

On the other hand, in Nos. 6 and 7 where the leveler exit side temperature is 600 ° C or less, the deformation temperature at the leveler is low, which corresponds to the repeated bending after transformation from γ to α. It can be seen that only the strain was applied to the α grains and the crystal grains were not refined.

The reason that these suitable temperature ranges exist can be estimated as follows. In these temperature ranges, the metallic structure under deformation is mostly y grains, and is in the process of transformation with a few α grains. If this is deformed, it can be estimated that the dislocations introduced into the γ grains have a large effect of directly forming the nucleation sites of the α grains.

As described above, it is possible to refine crystal grains by repeatedly bending a finish-rolled metal plate with a leveler. After the finish rolling, cooling is performed in front of the leveler, and the temperature on the exit side of the leveler is set to 50 ° C. from the Ar ₃ point to the Ar ₃ point—50 ° C., so that the miniaturization effect in the present invention can be maximized.

In order to accurately control the temperature of the metal plate at the leveler output side, the above-mentioned tracking is performed, and appropriate cooling is performed based on the metal plate temperature measured at the finish rolling mill output side. It is preferable that the metal plate is repeatedly bent by a leveler after the temperature is set to a predetermined temperature. Based on the temperature, rolling speed, etc. of the metal sheet on the exit side of the finishing mill, it is possible to repeatedly perform bending using the leveler while optimally maintaining the metal sheet temperature on the exit side of the leveler. Example 1

As an example to verify the effect of the present invention, experimental materials of two types of steels A and B shown in Table 2 were hot-rolled, and a comparative study of a conventional example and examples 1 and 2 of the present invention was performed. .

In hot rolling, the temperature at the exit of the finishing mill is 900 ° C, and the thickness of the steel sheet at the exit of the finishing mill is ϊΖΟιη 側 πΰη. In the conventional example, in the hot rolling line, after the above-described finish rolling, cooling which is normally performed is performed, and the coil is wound up by a coiler.

In Example 1 of the present invention, the conditions were basically the same as those of the conventional example. Repeated bending was performed using a leveler with a spacing of 200 mm and a roll indentation of 20 mm, then cooled and wound up with a coiler.

The center of the uppermost roll of the leveler was set 30 m downstream from the center of the final stand roll of the finishing mill. The longitudinal surface strain applied to the hot-rolled steel sheet by this leveler is approximately 0.34.

In Example 2 of the present invention, the conditions are basically the same as those of the conventional example. However, the finish further during the entry side of the outlet side and the leveler of the mill performs the cooling by the cooling device is disposed, the steel sheet temperature is Ar ₃ point ~ Ar ₃ point in leveler exit side - 50 ° C and so as Temperature control. After repeated bending with a leveler, it was cooled again and wound up with a coiler. The cooling device was installed in multiple punctures between the final stand of the finishing mill and the leveler. The maximum cooling water flow per unit surface area of the steel sheet is 3200 1 / m ² per minute (equivalent to the front and back of the steel sheet). For the steel plate after finish rolling, the number of punctures for injecting cooling water on both the upper and lower sides is adjusted to follow the running of the steel plate to eliminate local temperature unevenness in the longitudinal direction while reducing the steel plate on the leveler exit side. The temperature was controlled so as to be 50 ° C. at _three points of Ar to _three points of Ar.

Table 3 shows the measurement results of crystal grain size and tensile strength for the conventional example and the present invention examples 1 and 2. Shown in comparison. The cut-out position of the measurement sample, the definition of the crystal grain size and the tensile strength, and the measurement method are the same as those described above.

Compared to the conventional examples (No. Π, No. 14) without using a leveler, the present invention examples 1 (No. 12, No. 15) and (No. 13, No. 16) have higher strength. Furthermore, the strength of the inventive example 2 (No. 13, No. 16) using the cooling device is higher than that of the inventive example 1 (No. 12, No. 15) using no cooling device. You can see that. Fig. 12 shows a comparison between the tensile strength and the average grain size of experimental materials Nos. 11 to 13.

Example 2

The hot rolling line shown in FIG. 1A was used in which the finishing mill, the leveler, and the first cooling equipment were arranged in this order from upstream to downstream of the rolling line. The slab was hot-rolled, finished to a thickness of 4 mm, and then cooled. The average grain size and tensile strength of ferrite of the resulting hot-rolled steel sheet product were examined.

The average grain size is determined by cutting a sample for measurement from the center in the longitudinal direction and the center in the width direction of the steel sheet product, obtaining the average cross-sectional area of the crystal grains in accordance with JIS G 0552, and assuming that it is circular. Was calculated. The tensile strength was determined by cutting out a measurement sample from the center in the longitudinal direction of the steel sheet product, producing a No. 5 test piece in accordance with JIS Z 2201, and performing a tensile test at room temperature.

The steel sheet was made of Ti-added steel with the components shown in Table 4.The exit temperature of the final stand of the finishing mill was 900 ° C, the steel sheet speed at the exit of the final stand of the finishing mill was 720 m / min, and the coiler winding temperature was 600. ° C.

In Invention Examples 1 to 6, as shown in Table 5, the finish rolling was performed using a leveler having at least two small-diameter work rolls whose diameter was less than 40 times the thickness of the metal plate after finish rolling. The steel plate that has been subjected to bending is repeatedly bent, and the shape of the leveler after use I checked the condition. In Invention Examples 1 to 6, the driving method of the small-diameter work roll 6a of the leveler was the gearing method shown in FIG. 4B.

In the repeated bending, the distance between the center axes of the work rolls in the upper and lower directions is 2 L (the distance between the upper side and the lower side) is 155 mm in Invention Examples 1 and 5 (the diameter of the small-diameter work roll is 10 Omm) and 180 mm in Invention Examples 2 to 4 ( The small-diameter work roll diameter was 150 mm) and the roll pushing amount δ was 20 mm, and the leveler applied strain was set to the value in Table 5. The leveler added strain was calculated with m in Equation (2) set to 3. The operation was suddenly stopped during the operation of the leveler, and the curvature of the steel sheet by the small-diameter work roll was measured. It has been separately confirmed that the leveler applied strain obtained from this experiment accurately matches the leveler applied strain calculated at m = 3. As the work roll diameter becomes smaller (for example, comparison of Invention Examples 1 and 2) and as the number of small-diameter work rolls introduced is increased (for example, comparison of Invention Examples 3 and 4), the leveler additional strain becomes larger. Table 4 shows the _three- point Ar temperature of the steel sheet. Rolling was performed so that the steel sheet temperature on the leveler entry side was as shown in Table 5. The leveler was installed 30m downstream from the center of the final stand of the finishing mill so that the center of the uppermost roll of the leveler coincided.

In Invention Example 6, in addition to the first cooling facility, a second cooling facility was arranged, and the second cooling facility was used to cool the steel sheet after finish rolling and before repeated bending, and to enter the leveler entrance side. Table 5 shows the steel sheet temperature at the time of the test, and the other conditions were the same as those of the above-mentioned invention example 2.

Here, the second cooling equipment was installed in multiple banks between the final stand of the finishing mill and the leveler. Maximum cooling water flow rate per unit surface area of steel sheet (upper and lower sides) 32 per minute

00 1, which is a Zm ^2. For the steel sheet after finish rolling, the number of punctures for injecting cooling water on both the upper and lower sides was adjusted to follow the running of the steel sheet to eliminate local temperature unevenness in the longitudinal direction. In the comparative example, a leveler having only a large-diameter work roll was used, and the other conditions were the same as those of the inventive examples 1 to 6, and the steel plate subjected to finish rolling was repeatedly bent.

On the other hand, as a conventional example, in the hot rolling line shown in FIG. 1A, before installing the leveler, a steel slab having the same composition as the above invention examples 1 to 6 was used, and the other conditions were the same as those of invention examples 1 to 6. Finish rolling was performed in the same manner as above, followed by cooling.

Table 5 shows the average crystal grain size and tensile strength of ferrite of the obtained examples, comparative examples, and conventional examples of the hot-rolled steel sheet products. Table 5 also shows the state of the leveler after use in the invention examples and comparative examples.

From the results in Table 5, it can be seen from the results in Tables 1 to 6 that repeated bending was performed using a leveler having a small-diameter work roll and that the grain size of the steel sheet product was refined compared to the conventional example in which the bending was not repeatedly performed by the leveler. We can see that we can do it.

In addition, in Invention Example 6 in which the metal sheet after finish rolling was cooled by the second cooling device, the steel sheet was cooled by the second cooling device before repeated bending without the second cooling device. The crystal grains could be made finer as compared with Invention Example 2 under the same conditions except that it was not performed.

Also, in the invention example, by increasing the number of small-diameter work rolls, it is possible to make the average crystal grain of the product fine, and the tensile strength of the steel sheet product corresponds to the crystal grain ^. _c Note seen that has a fine things as high strength, in the case of invention examples 1 to 6 and Comparative examples, by repeated bending by the leveler, with ① gamma grains to increase the gamma grain boundaries finer, ② Since lattice defects such as dislocations were introduced into the γ grains, it is estimated that the α grains in the steel sheet product were refined from the conventional example. Industrial applicability According to the present invention, it has become possible to further increase the strength of a metal plate as compared with the related art. In addition, since the mechanical properties can be easily controlled without changing the components of the metal plate, it is useful from the viewpoint of reducing the steelmaking load, and has an energy saving effect. Further, in a small-diameter work roll leveler, crystal grains can be further refined, and a product with higher strength can be obtained as compared with a leveler having only a large-diameter work roll.

table 1

Table 2

Steel grade composition

A F e-0.2C- 0.7S one 2.OM n -0.15T i

B F e -0.07C- 1.8S one 1.5 n — 0.03T i

Table 3

No. Steel grade Rera Cooling unit Crystal grain size Tensile strength Remarks

11 A 4.7 / m 670 MPa Conventional example

12 A o 2.6jU m 750 Pa Invention Example 1

13 Ao o 1.6j «m 830MPa Invention Example 2

14 B 10.9ju m 410MPa Conventional example

15 B o 8.4jU m 510MPa Inventive example 1

16 B oo 7.1 // m 550 Pa Invention Example 2 Table 4

Table 5

O: Applicable device, 1: Not applicable device-h: Strip thickness after finish rolling (h = 4 mm)

Leveler with small-diameter work rolls * ": Work rolls with 23 work rolls and a diameter of 190 mm (d / h = 7.5) except for the small-diameter work rolls in the table, and small and small diameters for work rolls Both can be driven

Leveler with only work rolls other than small diameter * ² ): 23 work rolls, all of which can be driven by a work roll with a diameter d of 19 Omm (d / h = 47.5)

State after use of leveler o: No abnormality

Claims

The scope of the claims

1. In the metal sheet hot rolling line, a finishing mill, a leveler for imparting bending strain to the metal sheet, and a cooling device are arranged in this order from upstream to the metal sheet conveying direction. A hot rolling line for metal sheets.

2. In the hot rolling line for metal sheets, the finishing mill, the leveler whose work rolls are each backed up by backup rolls, and the cooling equipment are arranged in this order from upstream to downstream in the metal sheet transport direction. A hot rolling line for metal sheets, which is provided.

4. In the hot rolling line for metal sheets, the finishing mill, the cooling equipment, the leveler in which the work rolls are each packed up by the pack-up rolls, and the cooling equipment are further placed upstream of the metal sheet transport direction. A hot rolling line for metal sheets, which is arranged in this order from downstream to downstream.

5. In the hot rolling line for the metal sheet, the joining equipment, the finishing mill, the leveler for imparting bending strain to the metal sheet, the cooling equipment, the cutting device, and the coiler are arranged from the upstream side in the metal sheet conveying direction. A hot rolling line for metal sheets, which is arranged downstream in that order.

6. In the hot rolling line for metal sheets, the joining equipment, the finishing mill, the leveler whose work rolls are each packed up by the pack-up roll, the cooling equipment, the cutting equipment, and the coiler Are arranged from upstream to downstream in the metal sheet conveying direction and in that order.

8. In the hot rolling line for metal sheets, joining equipment, finishing mill, cooling equipment, leveler in which work rolls are each packed by backup rolls, and cooling equipment, cutting equipment, A hot rolling line for metal sheets, wherein a coiler and a metal sheet are arranged in this order from the upstream of the metal sheet conveying direction to the upstream.

9. The hot rolling line according to any one of claims 1 to 8, wherein the leveler has a work roll having a diameter of 300rani or less.

10. The hot-rolling line according to any one of claims 1 to 8, wherein the leveler is a leveler having three to thirty work rolls.

11. The hot rolling line according to any one of claims 1 to 8, wherein each of the work rolls of the leveler is driven.

12. The hot rolling line according to any one of claims 1 to 8, wherein a guide is provided in a gap between each of the upper and lower work rows / workers of the leveler.

13. The hot rolling line according to any one of claims 1 to 8, wherein the surface roughness Ra of the work roll of the leveler is 0.5 <Ra <2.0 μαι.

14. The leveler according to any one of claims 1 to 8, wherein the leveler has at least one small-diameter work roll whose diameter is less than 40 times the thickness of the metal plate after finish rolling. Hot rolling line according to Crab.

15. The hot rolling line according to any one of claims 1 to 8, wherein the leveler has at least one non-driven small-diameter work roll whose diameter is less than 40 times the thickness of the metal plate after finish rolling, The remaining work roll is a hot rolling line characterized in that the diameter is at least 40 times the thickness of the metal plate after finish rolling, and the work roll is drivable.

16. The hot rolling line according to any one of claims 1 to 8, wherein the leveler has at least-non-driven small-diameter work rolls having a diameter of less than 40 times the thickness of the metal plate after finish rolling, The small-diameter work roll is configured such that a drive torque can be transmitted from the backup roller to the small-diameter work roll via gears provided at respective necks of the small-diameter single crawl and its pack-up roll. For the remaining work rolls, the diameter is at least 40 times the thickness of the metal plate after finish rolling, and A hot rolling line characterized by being drivable.

17. In a hot rolling method in which rolling including finish rolling is hotly performed on a metal piece, the metal sheet after the finish rolling applied to the metal piece is repeatedly bent by a leveler, and thereafter A hot rolling method characterized by cooling.

18. The hot rolling method according to claim 17, wherein the metal plate is cooled after the finish rolling and before the repeated bending.

19. the repeated bending temperature of the metal sheet after working, Ar ₃ point + 50 ° C~Ar ₃ points - hot rolling direction according to claim 17 or 18, characterized in that in the range of 100

20. The hot rolling method according to claim 17, wherein the work roll of the leveler has a roll pushing amount of +1 to 1030 mm.

21. The hot rolling method according to claim 17, wherein the temperature of the metal plate after the finish rolling is at least _three points of Ar.

22. Carry out tracking of the tip and tail end of the metal plate, tighten the upper and lower work rolls after the tip of the metal plate has passed the corresponding work roll of the leveler, and before the tail end comes off. 19. The hot rolling method according to claim 17, wherein control is performed to open upper and lower work rolls corresponding to the following.

23. The hot rolling method according to claim 17, wherein the finish rolling is performed after a preceding sheet par and a subsequent sheet par are joined.