JP2854428B2 - Continuous hot rolling of billets - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous hot rolling method suitable for continuously hot rolling several to several tens of steel pieces such as sheet bars, slabs, billets or blooms. .

[0002]

2. Description of the Related Art Conventionally, in a hot rolling line, a slab to be rolled is heated one by one, roughly rolled, and then finish rolled to finish a hot rolled sheet having a desired thickness. In the final rolling method, it is easy to cause line stoppage due to poor rolling material biting in the finish rolling, and the yield is greatly reduced due to poor shape at the leading and trailing ends of the rolling material. In order to do so, prior to the finish rolling, a rolling method has been adopted in which the rear end and the front end of the steel slabs are joined together and continuously supplied to a hot rolling line. Japanese Patent Application Laid-Open No. 61-144203 is referred to as a reference concerning such continuous rolling of billets.

[0003]

SUMMARY OF THE INVENTION The above-mentioned JP-A-61-144203 is disclosed.
In the technology disclosed in the above publication, the rear end of a slab conveyed in advance (hereinafter referred to as a precedence slab) and a slab conveyed subsequently (hereinafter referred to as , The subsequent billet)
Are butted over the entire surface thereof, and both ends in the width direction thereof are pre-joined, and rolling is to be performed in this state. However, in such a technique, it is necessary to lengthen the joining time in order to provide a sufficient joining strength to the pre-joined portion, and it is necessary to take measures to extend the line.
In this regard, the inventors have previously described in Japanese Patent Application No. 2-203991 or Japanese Patent Application No. 2-203992 a method of simply and quickly joining steel slabs at the entry side of hot rolling. Proposed. However, the gap provided between the billets may not completely disappear during the rolling process, and in such a case, particularly when rolling such as applying tension for adjusting the width dimension, the joint is broken. It was hard to say that separation would not occur, leaving room for some improvement.

[0004] A new rolling method capable of joining the billets simply and quickly on the entry side of the rolling equipment and further strengthening the joining between the billets as the finish rolling progresses. Is an object of the present invention.

[0005]

SUMMARY OF THE INVENTION According to the present invention, hot rolling is performed by continuously feeding a preceding steel slab which has undergone a rough rolling step and a subsequent steel slab which is subsequently conveyed to the steel slab to a finishing rolling facility. In doing so, at the entry side of the finish rolling facility, the contact area in a state where each end is brought into contact with the rear end of the preceding steel slab and / or the front end of the subsequent steel slab is at least a region near both edges in the width direction. After cutting, each slab is subjected to heating and pressing treatments and butt-joined, and then subjected to rolling to reduce the crown ratio of the slab at the initial stage of finish rolling, characterized by continuous hot working of the slab. It is a rolling method, and as the rolling for reducing the crown ratio, a method in which a convex crown is added to a billet in a rough rolling stage or a method in which a concave crown is added in an initial stage of finish rolling is advantageously applicable. I do.

FIG. 1 shows the structure of a facility suitable for carrying out the present invention. In FIG. 1, reference numeral 1 denotes a preceding steel slab which passed through a rough rolling mill a, and reference numeral 2 denotes a continuation of the preceding steel slab 1 to be conveyed. 3 is a hot finishing rolling equipment in which rolling mills F ₁ , F ₂ ... Having a work roll bending function are arranged in tandem, and 4 is a profile of the billet on the output side of the rough rolling mill a. A profile measuring device for measuring, 5 is arranged on the entry side of the rolling equipment 3, a cutting device for cutting the front end and the rear end of the slab into a predetermined shape, 6 is a heating device for heating the slab,
Reference numeral 7 denotes a scale breaker for removing scale generated on the surfaces of the billets 1 and 2 prior to finish rolling.

In hot rolling of a slab according to the present invention, first, as shown in FIG. 2, a rear end of a preceding slab 1 and a succeeding slab 2 are cut by a cutting device 5 having a curved blade or the like.
Is cut so that the contact area in the abutting state of the front ends of the pieces becomes at least both edge areas in the width direction, and then a combination of heating by the heating device 6 and pressing operation by adjusting the conveying speed of the steel slabs 1 and 2 is performed. As shown in FIG. 3, the preceding and subsequent slabs 2 are brought into close contact with each other by generating compressive stress in the vicinity of both edges, and are fed to the finish rolling equipment 3 in this state. As shown in FIG. 4, in a rough rolling stage, in which a convex crown is previously applied to the billets 1 and 2, if a sufficient metal flow can be obtained by ordinary rolling, a work in a finishing rolling mill is used. bending control of the roll is not required (however, the steel strip middle plate thickness H ₀ before rolling, the thickness h ₀ of the steel strip width end of the front rolling, the steel strip middle plate thickness H ₁ after rolling, rolling when the thickness h ₁ of the steel strip width end portion of the post _{(H 0 -h 0) / H} 0> (H
₁ -h ₁₎ / H ₁ comprising performing rolling. (See FIGS. 10 and 11).
Furthermore, even in the case where the above-described convex crown is provided in the rough rolling stage or the rolling is performed so that the thickness in the plate width direction becomes uniform, the work piece is controlled by bending work rolls in the initial stage of the finish rolling. On the other hand, a concave crown is provided, and rolling is performed so as to eliminate the gap formed at the joint of the billets by promoting the metal flow in the central portion in the width direction.

[0008]

[Action] The leading billet 1 on the entrance side of the hot finishing rolling equipment 3
In the butt joining of the steel slab and the subsequent slab 2, as shown in FIG. 3 above, local joining is performed only in the vicinity of both edges in the width direction of each slab. Joined in a short time. In this state, when the rolling as shown in FIG.
At the front end and the rear end of the billets 1 and 2, the gap is eliminated by the promotion of the metal flow in the central region in the width direction, and as shown in FIG.
It will be firmly joined over the entire width direction,
Therefore, even in the case where tension is applied to the rolled material for the purpose of adjusting the width dimension in the finish rolling, the two are not easily broken and separated.

In changing the crown ratio of the billet,
Assuming that the amount of change in the crown ratio is as follows: ΔCr / H = (H ₀ −h ₀ ) / H ₀ − (H ₁ −h ₁ ) / H ₁ × 100 (%), ΔCr / H is 1.0 to 3.0%. It is preferable to set the range. The reason is that if it is less than 1.0%, sufficient bonding strength cannot be obtained, and if it exceeds 3.0%, the change in crown ratio is too large and the shape is disturbed.

The cutting shapes of the ends of the slabs are shown in FIG. 2 in which the ends of the preceding slab 1 and the succeeding slab 2 are cut concavely at the same curvature. The rear end portion is concave, but their curvatures are different as shown in FIG. 7, or one of the flat shapes is flat and the other is concave as shown in FIG. 8, one is convex. A shape having various shapes such as that shown in FIG. 9 in which the concave curvature is slightly larger than the convex curvature by making the other concave is applicable. The gap between the billets is preferably about 10 mm or less in any case in the joined state after heating and pressing in order to completely eliminate the gap in the finish rolling stage. As a cutting method for obtaining the above-mentioned shape, shearing, gas cutting or laser fusing can be applied, but in particular, when cutting into a concave shape with a specific curvature, two curved blades that do not require time for shape processing. Are advantageously adapted.

[0011] The billet 1 on the entry side of the finishing mill 3
As the heating means for performing the local butt-joining of item 2, in addition to heating by a burner or high-frequency heating by a solenoid type coil, an alternating magnetic field generating coil is used to alternately penetrate the steel piece in the thickness direction. Applying a magnetic field,
Heating by the so-called transverse method (Japanese Patent Application No. 2-2039
No. 91) can be applied.

[0012] When joining steel slabs,
Heating and raising the temperature in the vicinity of both edges of the billet, which is the part to be welded, to the target welding temperature, and pressing the billets together after stopping the heating, or a heating / heating method A joining form in which the slabs are pressed each other when they are continued (however, they do not exceed the temperature at which the joints are to be joined melt) and the slabs are pressed in advance when the target joining temperature is reached
Various bonding modes such as a bonding mode in which heating is performed (including pressing until a predetermined bonding margin is obtained) can be adopted, and the bonding margin (contact length after bonding) in this case is shown in FIG. Thus, in order to avoid breakage in the initial stage of the finish rolling, it is preferable that at least 0.1 W (W: full width of the billet) on one side and at least 0.2 W on both sides.

According to the present invention, in the rough rolling step, a convex crown is given to the steel slab as shown in FIG.
Fig. 11 in hot finish rolling after local joining of
When rolling Toka, or rough rolling phase convex crown or at the plate width direction of the mill finishing When the thickness is rolled to be uniformly F ₁ or several stages of rolling mill including this concave as Various modes such as the case of giving a crown are conceivable. However, in order to effectively promote the metal flow at the center in the width direction of the slab and eliminate the gap, the leading slab 1
It is preferable to reduce at least the unjoined portion of the steel slab 2 and the subsequent slab 2 at a reduction ratio of 20% or more.

As means for changing the crown ratio, besides a work roll bender, a pair cross type in which a pair of rolls are crossed to reduce the pressure, a type in which a taper piston slides, or a crown of the roll itself is used. Various types such as a variable crown type mechanically changed can be applied.

[0015]

[Embodiment] A rolling equipment as shown in FIG. 1 having a tandem rolling mill of 7 stands is applied, and has a width of 1000 mm and a thickness of 1000 mm.
In the continuous hot rolling of a sheet bar (steel type: low-carbon steel) having a thickness of 30 mm, first, the rear end and the front end of the sheet bar are cut at the entry side of the hot rolling equipment 3 and FIG. And then subjected to heating, pressing and finish rolling under the following conditions to finish a hot-rolled sheet having a thickness of 3 mm. a) Heating method: Heating by the transverse method by applying an alternating magnetic field b) Heating temperature: 1400 ° C c) Heating time: 2.4 seconds d) Pressing force: 3 kg / mm ² e) Input power: 2000 kw f) Joining form : pre-pressing while heating the gap g: 10 mm g) bonding margins: on one side 100 mm × 2 h) rolling by the rolling mill F _1: entry-side crown ratio 30 mm-2
The crown ratio is reduced so that 9.2 mm / 30 mm = + 0.027 (convex crown) and the outgoing crown ratio is 18 mm-18.0 mm / 18 mm = 0. As a result, it was confirmed that the joint portion of the sheet bar did not break and separate during rolling, and stable rolling was performed.

On the other hand, the front end and the rear end of the sheet bar remain flat without being cut so that both edges in the width direction become a joining area, and rolling is performed to change the crown ratio. However, when the other conditions were the same, the joining at the initial stage of the finish rolling was sometimes insufficient, and the joint was sometimes broken during the rolling.

Next, the rolling equipment provided with a tandem rolling mill of 7 stands is applied to perform continuous hot rolling of a sheet bar (steel type: low carbon steel) having a width of 1000 mm and a thickness of 30 mm. On the entry side of the rolling equipment 3, the rear end and the front end of the sheet bar are cut to form a plane shape as shown in FIG. 2 and then heated according to the following conditions.
Pressing and finish rolling were performed to complete a hot-rolled sheet having a thickness of 3 mm. a) Heating method: Heating by the transverse method by applying an alternating magnetic field b) Heating temperature: 1400 ° C c) Heating time: 3 seconds d) Pressing force: 3 kg / mm ² e) Pressing time: 3 seconds f) Joining form: while pressing heated gap g: 10 mm g) bonding margins: on one side 100 mm × 2 h) rolling by the rolling mill F _1: entry-side crown ratio 30 mm-30
mm / 30mm = 0, exit crown ratio 17.8mm-18.0mm / 17.8
Reduce the crown ratio so that mm = -0.011.
As a result, even in the case of performing such rolling, it was confirmed that the joint portion of the sheet bar did not break and separate during rolling, and that rolling was performed stably.

[0018]

Thus, according to the present invention, the preceding and succeeding slabs are first pre-joined on the entry side of the finish rolling facility, and the ends of the slabs are brought into contact over the entire width direction at the finish rolling stage to be joined. Since the part is further strengthened, there is no joy that the joint part breaks and separates during rolling, and continuous hot rolling with high productivity can be realized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a configuration of equipment suitable for carrying out the present invention.

FIG. 2 is a diagram showing a planar shape of a joint portion of a steel slab.

FIG. 3 is a diagram showing a planar shape after joining of a steel slab.

FIG. 4 is an explanatory view of a joining procedure of a billet.

FIG. 5 is a diagram showing a rolling state of a billet.

FIG. 6 is a diagram showing a joining state of a preceding slab and a succeeding slab.

FIG. 7 is a view showing a planar shape of a joint portion of a steel slab.

FIG. 8 is a diagram showing a planar shape of a joint portion of a steel slab.

FIG. 9 is a diagram showing a planar shape of a joint portion of a steel slab.

FIG. 10 is a view showing a cross section of a steel slab.

FIG. 11 is a diagram showing a cross section of a billet after rolling.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Leading slab 2 Subsequent slab 3 Hot finishing rolling equipment 4 Profile measuring device 5 Cutting device 6 Heating device 7 Scale breaker

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Fujio Aoki 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Corp. Inside Chiba Works (72) Inventor Masanori Kitahama 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Corp. (58) Investigated field (Int.Cl. ⁶ , DB name) B21B 1 / 26,15 / 00 B23K 20/00

Claims (3)

(57) [Claims] 1. A hot-rolling machine which continuously feeds a preceding slab which has undergone a rough rolling process and a subsequent slab which is conveyed following the slab to a finish rolling facility and performs hot rolling. On the entry side, a cutting process is performed on the rear end portion of the preceding slab and / or the front end portion of the subsequent slab so that the contact area in the abutted state of each end is at least the area near both edges in the width direction. A continuous hot rolling method for steel slabs, wherein each slab is subjected to a heating and pressing treatment to perform butt joining, and then subjected to rolling at an initial stage of finish rolling to reduce the crown ratio of the slab. 2. The continuous hot rolling method according to claim 1, wherein the rolling for reducing the crown ratio of the slab gives a convex crown in a rough rolling step. 3. The continuous hot rolling method according to claim 1, wherein the rolling for reducing the crown ratio of the slab gives a concave crown at an initial stage of finish rolling.