JP3408962B2 - Continuous hot rolling method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot rolling method in which a sheet bar after rough rolling is partially joined to a preceding sheet bar during finish rolling in the plate thickness direction and continuously rolled.

[0002]

2. Description of the Related Art A hot-rolled steel sheet is manufactured by rolling a sheet bar rolled to a predetermined thickness by a rough rolling mill group, finish rolling it by a finishing mill group, and winding the sheet bar by a coiler. .

In recent years, for the purpose of improving productivity and quality, a leading sheet bar (hereinafter referred to as a leading material) and a succeeding sheet bar (hereinafter referred to as a rear sheet) are provided between a rough rolling mill group and a finishing rolling mill group. Continuous hot rolling is performed in which the material is used as a line material and is continuously finished and rolled. In such continuous hot rolling, several methods have been proposed for joining the sheet bars.

For example, Japanese Patent Application Laid-Open No. 60-244401 discloses a method of pressing sheet bars that are rapidly heated by a solenoid type coil to join them together. In this method, if the seat bar is stopped and heated, the productivity is reduced, and if the seat bar is heated while traveling, equipment for running the joining device including a large heating device is required. There is a problem of high cost.

Further, Japanese Patent Application Laid-Open No. 7-256304 discloses a method of joining sheet bars together using a laser beam. In this method, since the laser oscillator can be installed off-line, the joining device can be made compact. However, since the sheet bar is melt-bonded from the upper surface side by the laser beam,
Due to the problem of burn-through, the entire thickness of the sheet bar cannot be welded, and there is an unbonded region that is not bonded in the plate thickness direction. Further, from the viewpoint of improving productivity, it is desirable to complete the joining in a short time even with a wide material, but if the joining time is shortened, the welding depth becomes smaller and the unbonded region in the plate thickness direction further increases. In this case, there is a problem that the joint portion is broken by the tension between the stands during the subsequent finish rolling.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to shorten the joining time in a method of partially joining a leading sheet bar and a trailing sheet bar in the plate thickness direction and continuously finishing rolling. Therefore, it is an object of the present invention to provide a method for finish rolling without breaking the joined portion of the sheet bar even if the initial joining ratio in the plate thickness direction is lowered.

[0007]

SUMMARY OF THE INVENTION According to the present invention, the rear end of a sheet bar after the preceding rough rolling is joined to the rear end of the sheet bar after the subsequent rough rolling by partially joining the sheet bar in the plate thickness direction. In the hot rolling method of rolling into a roll, the plate crown ratio in the vicinity of the joint on the first stand entry side of the finish rolling mill is C ₀ , and that on the first stand exit side is C ₁ , where C ₁ < The continuous hot rolling method is characterized in that the first stand of the finish rolling mill is used for rolling so as to obtain C ₀ .

That is, as shown in FIG. 1 (a), the work roll crown of the rolling mill is convexly rolled, and as shown in FIG. 1 (b), the work roll of the rough rolling mill is concavely crowned. To make the entry-side material crown of the first stand of the finish rolling mill convex and roll it, or, as shown in FIG. 1 (c), give a concave crown to the work roll of the rough rolling mill to finish rolling mill. This is to make the entry side material crown of the first stand convex and the work roll of the finish rolling machine first stand a convex crown for rolling.

When finishing rolling is performed by giving a convex crown to the work roll of the first stand of the finishing rolling mill, the amount of roll crown is 200 μm / radius or more per cylinder length, which is higher than the primary curve and lower than the secondary curve. Grant with. The work roll of the rough rolling mill is provided with a concave crown, that is, the finishing rolling mill No. 1
When a convex crown is applied to the material on the entry side of the stand, use a concave crown of the work roll of the rough rolling mill at
It is preferable to give a curve of m / radius or more and higher than first-order and second-order or less.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION As shown in FIG. 2, the present inventors have joined the sheet bar partially from the upper surface side in the plate thickness direction, that is, from the upper surface side to a certain thickness, and then bonded the sheet thickness to the bonded portion. The finish rolling was performed in a state where there was a portion that was not joined in the direction (hereinafter, referred to as an unjoined portion). After that, the joint portion after finish rolling was cut out at each width position, and the joint strength was examined. As a result, it was found that the joint strength at the width center portion was lower than that at the plate edge and ¼ width. Further, in the wide material, the strength at the center of the width was remarkably reduced, and a through hole was also observed at the center of the width. Also, by observing the joint after rolling, the thickness of the portion that was joined by welding before rolling (hereinafter referred to as the initial joint) was constant over the entire width except for the plate edge. It was found that the difference in the bonding strength between the width center part and the 1/4 width is due to the difference in the strength improvement due to the roll bonding of the unbonded part in the width direction.

FIG. 3 shows an initial plate thickness of 40 mm by FEM analysis.
A joining material of sheet bars having widths of 1300 mm and 1600 mm and a joining rate of 40% in the sheet thickness direction was subjected to one pass of finish rolling with a reduction rate of 0.5. Although the planar shape of the joined portion is shown, the unjoined portion does not depend on the plate width and closes most quickly at a position of 200 to 300 mm from the plate end, whereas the closing of the width center part lags behind most. Therefore, the unbonded portion at a position of 200 to 300 mm from the plate edge is rolled and bonded most quickly, and naturally the bonding strength after rolling is also improved. On the other hand, in the center of the width where the unjoined part is slow to close, first, the position 200 to 300 mm from the plate edge is closed, and compressive stress acts on this closed part. Stress acts. This tensile stress reduces the compressive stress that acts on the unbonded part in the width center during rolling, and the unbonded part in the width center closes by the end of rolling, but only weak rolling bonding is obtained, improving the strength. The margin is smaller than other width positions.

This phenomenon occurs due to the non-coincidence of the planar shapes of the unbonded portions of the trailing edge of the preceding material and the leading edge of the following material. The joining of wide materials in which the planar shape of the trailing edge of the preceding material is fishtail-shaped. It has been found that the central part of the width is more difficult to roll-bond than the plate end side, and the bonding strength of the central part of the width is significantly reduced.

Therefore, the rolling conditions were examined so that the timings of the rolling and joining were made to coincide in the width direction, that is, the planar shapes of the trailing edge of the preceding material and the leading edge of the following material were matched. As a result, as shown in FIG. 4 (a), a convex crown is applied to the work roll of the first stand of the finishing mill (FIG. 1 (a)), so that the planar shape of the trailing edge of the preceding material is changed from the fish tail shape. It was found that the tongue shape can be changed to match the planar shape of the tip of the following material. This effect is obtained by changing the width direction distribution of the rolling direction tension by applying the reduction ratio distribution in the width direction, and thus when a convex crown is applied to the entry side material of the finishing rolling mill ( Figure 1
Also in (b)), as shown in FIG. 4 (b), the same effect can be obtained. As a matter of course, the same effect can be obtained even when a convex crown is applied to both the work roll of the finish rolling mill and the entry side material.

The present invention pays attention to this phenomenon and applies a convex crown to the work roll of the first stand of the finish rolling mill, the material on the inlet side of the finish rolling mill, or both of them to change the reduction ratio in the width direction. By doing so, the timing of rolling and joining can be matched in the width direction, and eventually the joining strength can be made uniform in the width direction.

As the crown amount applied to the work roll of the first stand of the finish rolling mill is larger, it is easier to change the planar shape of the trailing end of the preceding material from the fishtail shape to the tongue shape in the wide width material. However, as shown in FIG. 5, a sufficient effect can be obtained even with 200 μm / radius per barrel length.

Since the roll curve changes the widthwise distribution of the tension in the rolling direction even in a wide material, the reduction in the width center portion becomes sharply larger than other width positions, that is, it is desirable that it is closer to a straight line. As shown in 6, the plate width is 1300
A quadratic curve is sufficient if it is less than or equal to mm.

When a convex crown is applied to the material on the inlet side,
A work roll provided with a concave crown may be used for the rough rolling mill. At that time, the amount of concave crowns to be applied to the work rolls of the rough rolling mill is the same as that when the convex rolls are applied to the work rolls of the first stand of the finishing rolling mill (200 μm / radius), and the crown ratio change is the same. As a result of searching after considering the elastic deformation of the roll, it was found that it was 200 μm / radius per cylinder length.

[0018]

Example: The total width of the preceding material and the following material having a plate width of 1300 mm is
A sheet bar (thickness 40 mm, length 9000 mm) 30% laser-bonded in the plate thickness direction from the upper surface side is heated to 1200 ° C., and a convex crown is formed under the conditions as shown in Table 1 in the work roll of the first stand of the rolling mill. (Diameter 850 mm (center of width)) or 1.2-degree curve was applied to the material on the inlet side, and finish rolling to a plate thickness of 3 mm was performed by a finishing rolling mill group. Table 2 shows the condition of the joint after rolling in each example. As is clear from Table 2, according to the present invention, no fracture or reduction in strength at the width center portion is observed at the joint after finish rolling.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

According to the present invention, in continuous hot rolling in which sheet bars are partially joined in the plate thickness direction and finish rolling, finish rolling is performed so that the plate crown ratio is reduced at the first stand of the finishing rolling mill. By performing the rolling, it is possible to match the rolling joining timing of the unjoined portion and make the strength of the joined portion uniform in the width direction, and as a result, even when the initial joining ratio in the plate thickness direction is low, during finish rolling. It is possible to prevent breakage at the joint portion. Moreover, since the initial joining ratio can be reduced, it is possible to shorten the joining time.

[Brief description of drawings]

FIG. 1 shows a schematic diagram of the method of the present invention. (A) is a case where a work roll of the first stand of the finish rolling mill is rolled with a convex crown, (b) is a case where a roll is provided with a convex crown, and (c) is a work roll and This is a case where a convex crown is applied to any of the side materials and rolling is performed.

FIG. 2 shows a cross section in the rolling direction in which the preceding material and the following material are butted and then partially joined in the plate thickness direction.

FIG. 3 is a plan view of an unbonded portion during finish 1-pass rolling,
(A) is 1300 mm wide, (b) is 1600 mm wide
This is the case for mm.

FIG. 4A is a plan view of an unjoined portion during rolling when a work roll of the first stand of the finish rolling mill is provided with a convex crown, and FIG. 4 shows a planar shape of an unbonded portion during rolling when a convex crown having a crown ratio change equivalent to that of the work roll crown of the first stand of the finish rolling mill (FIG. 4A) is applied to the entry side material.

FIG. 5 shows the difference in the planar shape of the unbonded part due to the difference in the convex crown amount of the first stand of the finish rolling mill.
μm / radius, (b) is a case where a convex crown of 400 μm / radius is given by a quadratic curve.

6A and 6B show a difference in planar shape of an unbonded portion due to a difference in roll curve, wherein FIG. 6A is a 1.2-dimensional curve and FIG. 6B is a quadratic curve.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-288906 (JP, A) JP-A-6-39404 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B21B 1/00-1/46 B21B 27/00-27/02

Claims (3)

(57) [Claims] 1. A hot rolling method in which a leading end of a subsequent rough-rolled sheet bar is partially joined to a trailing end of a preceding rough-rolled sheet bar in the plate thickness direction and continuously rolled. , 200μ per cylinder length on the first stand of the finishing mill
A convex crown with a radius of m / radius or higher is higher than the primary and secondary or higher.
Using the work roll given by the curve below, when the plate crown ratio in the vicinity of the joint on the first stand entry side of the finish rolling mill is C ₀ , and that on the first stand exit side is C ₁ , C
A continuous hot rolling method comprising rolling at a first stand of a finish rolling mill such that ₁ <C ₀ . 2. A rear end of a sheet bar after the preceding rough rolling.
The end of the sheet bar after rough rolling in the
Odor in hot rolling method in which parts are joined and rolled continuously
Then, in the final pass of the rough rolling, a work roll in which a concave crown of 200 μm / radius or more per cylinder length is given with a curve higher than the primary and secondary or less is used .
The plate crown ratio in the vicinity of the joint on the bond entry side is C ₀ ,
It on the stand delivery side when the C _1, and C ₁ <C ₀
Continuous hot rolling method you characterized that you rolling in the first stand of the finishing mill so. 3. The rear end of the sheet bar after the preceding rough rolling.
The end of the sheet bar after rough rolling in the
Odor in hot rolling method in which parts are joined and rolled continuously
Then, in the final pass of rough rolling, a work roll having a concave crown with a curve higher than the first order and not more than the second order is used .
Higher than primary and secondary on the first stand of the finishing mill
Use a work roll with a convex crown with the following curve
The plate near the joint on the first stand entry side of the finish rolling mill.
The crown ratio is C ₀ , and that on the exit side of the first stand is C ₁ .
The first rolling mill of the finishing mill so that C ₁ <C ₀
Features and to that continuous hot rolling method to rolling in stand.