JPH0871607A - Continuous hot rolling method of slab - Google Patents

Abstract

PURPOSE: To join slabs in a short time, to make the joined part more rigid by bringing the end parts of the slabs into contact over the whole in the width direction and to attain continuous hot rolling of high productivity entirely without fear such as the joined part is separated by breaking in finish rolling stage. CONSTITUTION: In a method for continuously executing hot finish rolling by joining a preceding slab 1 and the succeeding slab 2, before this joining, the cutting work of the rear end part of the preceding slab 1 and tip part of the succeeding slab 2 is executed in a shape such as the butt contact regions in the rear end part of the preceding slab 1 and tip part of the succeeding slab 2 is on the middle side in the width direction except the end parts in the width direction. Before this cutting work, thining processing is applied to regions corresponding to the butt contact regions in the rear end part of the preceding slab 1 and tip part of the succeeding slab 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to continuous hot rolling of a steel slab such as a sheet bar, slab, billet or bloom which is continuously hot rolled by several to several tens of steel slabs, and is particularly stable. It is intended to propose a method that enables continuous hot rolling.

[0002]

2. Description of the Related Art Conventionally, in a hot rolling line, steel pieces to be rolled are heated one by one, subjected to rough rolling and then finish rolling to finish a hot rolled sheet having a predetermined sheet thickness. In such a rolling method, the line is likely to be stopped due to defective biting of the rolled material during finish rolling. In addition, the yield is largely reduced due to the defective shape of the leading end and the trailing end of the rolled material. Therefore, recently, in order to avoid such a problem, prior to finish rolling, the trailing end of the preceding steel slab that has undergone the rough rolling process (hereinafter referred to as the preceding steel slab) and the subsequent end of the subsequent slab that is subsequently conveyed to this slab A rolling method is adopted in which the front end of a steel slab (hereinafter referred to as a trailing steel slab) is joined, and these preceding and subsequent steel slabs are continuously fed to a finish rolling facility for hot rolling. It has started to be done. Japanese Patent Application Laid-Open No. 61-144203 discloses a document relating to continuous rolling of such billets.
There is a gazette. The technology disclosed in this publication, on the entrance side of the rolling mill, butts the rear end portion of the preceding steel piece and the leading end portion of the trailing steel piece over the entire surface thereof, and pre-joins both widthwise end portions thereof, It is intended to roll while maintaining this state.

However, the above-mentioned Japanese Patent Laid-Open No. 61-1442.
In the technique disclosed in Japanese Patent Laid-Open No. 03-03, it takes a certain amount of time to give the pre-bonded portion sufficient strength. Therefore, measures such as extension of the line must be taken. There was a problem.

In this regard, the inventors of the present invention have previously disclosed Japanese Patent Laid-Open No. 4-89.
In Japanese Patent Laid-Open No. 109 and Japanese Patent Laid-Open No. 4-89110, a method of simply and quickly joining steel pieces on the entry side of hot finish rolling was proposed. This joining method uses a shape in which at least both widthwise end regions of each steel piece come into contact with each other in the butt contact state between the steel pieces by cutting the rear and tip portions of the steel pieces prior to joining, while creating a gap in the widthwise central portion. First, both ends in the width direction are joined by heating and pressing,
Then, the joining region is expanded to the central region to join the width of the billet.

However, this Japanese Patent Laid-Open No. 4-89109
In the methods disclosed in Japanese Patent Laid-Open No. 4-89110 and Japanese Patent Laid-Open No. 4-89110, the gap generated in the central region of the billet may not be completely closed by heating, pressing, or rolling in the subsequent process. In that case, it can be said that there is no possibility of fracture separation during finish rolling, and there is a slight tendency for fracture separation when rolling is performed while applying tension for adjusting the width dimension. There was room for improvement.

[0006]

SUMMARY OF THE INVENTION The present invention advantageously solves the above-mentioned problems. Steel pieces are simply and quickly joined together, and the steel pieces are joined together as the finish rolling progresses. It is an object of the present invention to propose a novel hot rolling method for a steel slab that can be made even stronger.

[0007]

SUMMARY OF THE INVENTION The present invention joins the trailing end of a preceding steel slab that has undergone a rough rolling process and the leading end of a subsequent steel slab that is subsequently conveyed to this steel slab, In continuously feeding the steel slab and the subsequent steel slab to the finish rolling facility and performing hot rolling, prior to joining, the rear end of the preceding steel slab and the leading end of the subsequent steel slab are In a shape in which the butt contact area is closer to the center in the width direction excluding the width direction end, cutting the rear end of the preceding steel piece and the tip of the subsequent steel piece and prior to this cutting, A continuous hot rolling method for a steel slab, which comprises subjecting a region corresponding to a butt contact region in a rear end of a preceding steel slab and a front end of a subsequent steel slab to a thinning treatment.

[0008]

The present invention will be described in more detail with reference to the drawings. FIG. 1 schematically shows an example of the configuration of equipment suitable for carrying out the continuous hot rolling method of the present invention. FIG.
In the figure, reference numeral 1 is a preceding billet that has passed through the rough rolling mill 3, 2 is a trailing billet that is subsequently conveyed to the preceding billet, and 4 is a rolling mill F1, F
A hot finishing rolling facility having a tandem arrangement of 2, ..., 5 is a reduction device, and is thinned to a region corresponding to a butt contact region at the rear end portion of the preceding steel piece 1 and the leading end portion of the following steel piece 2. Apply processing. Reference numeral 6 denotes a cutting device for cutting the rear end portion of the preceding steel piece 1 and the front end portion of the trailing steel piece 2 after the thinning processing by the rolling down device 5 into a predetermined shape, and 7 indicates heating for heating the steel piece. An apparatus, and 8 are scale breakers for removing scale generated on the surfaces of the steel pieces 1 and 2 prior to finish rolling.

In performing hot rolling of a steel slab according to the present invention, first of all, with respect to the steel slab subjected to rough rolling, the trailing end of the preceding steel slab 1 and the leading end of the following steel slab 2 are processed by the rolling down device 5. A local reduction is applied to either or both of them for thinning. In FIG. 1, a device using a reduction roll as the reduction device 5 is shown. FIG. 2 schematically shows the trailing end of the preceding steel piece and the leading end of the trailing steel piece 2 that have been subjected to the thinning treatment.
As shown in FIG. 2, although this thinning process is related to the cutting process of the subsequent process, in the subsequent butt contact state of the steel slab, the steel plate except for the widthwise both ends is contacted. Apply to the area.

Next, as shown schematically in FIG. 3, one of the trailing end portion of the preceding steel piece 1 and the leading end portion of the following steel piece 2 is cut by a cutting device 6 such as a drum shear having a curved blade. For both, cutting processing is performed in a shape such that the above-described thinned regions contact each other in the butted state.

After that, the combination of the heating of the steel slab by the heating device 7 and the pressing operation of the steel slabs by adjusting the conveying speed of the steel slabs 1 and 2 is carried out between the preceding steel slab 1 and the following steel slab 2. Compressive stress is generated to join the steel pieces to each other near the center in the width direction as shown in FIG. The butt joining of the preceding steel piece 1 and the following steel piece 2 on the entry side of the hot finish rolling equipment 5 is joining in the vicinity of the central portion in the width direction of each steel piece as shown in FIG. The steel pieces are joined in an extremely short time with a gap g at the widthwise ends.

While maintaining this joined state, the steel slab is fed to the finishing rolling equipment 4, and at each stand of the finishing rolling equipment 4,
As shown in FIG. 5, when hot finish rolling is performed, the metal flow (longitudinal direction and width direction of the steel piece) in the widthwise end region of the rear end portion of the steel piece 1 and the front end portion of the steel piece 2 is increased. , Is further promoted as compared with the case where the thinning treatment is not performed. As a result, the end faces of the respective steel pieces are firmly joined to each other across the entire width direction as shown in FIG.
Even when tension is applied to the rolled material for adjusting the width dimension, the two do not easily break and separate.

In the present invention, when the thinning treatment is applied to the area in the vicinity of the central portion in the width direction of the steel slab, the relation between the sheet thickness T before the thinning treatment and the sheet thickness t after the treatment is that t / T is 0.4. ~ 0.
A range of 95 is preferred. This is because the thin-walled portion is not rolled in the first pass of the finishing rolling mill when the large reduction of t / T is less than 0.4 and the sufficient bonding strength cannot be obtained when the small reduction of more than 0.95. As for the area of the thinning treatment, the width is about the pre-joining margin (0.5 × steel piece width W or more),
The length is equivalent to the contact arc length of the roll bite (≒ (roll radius ×
The amount of reduction) ^1/2 ≈ 50-80 mm) is preferable.

Further, as a concrete means for carrying out the thinning treatment, in addition to the pressing roll shown in FIG. 1, an anvil for forging processing can be applied.

Regarding the shape of the steel slab end portion after the cutting process by the cutting device, in addition to the shape shown in FIG. 3 above, the end portions of the preceding steel slab 1 and the trailing steel slab 2 are convexly cut with the same curvature. , The front and rear ends of each of the steel pieces 1 and 2 are convex, but the curvatures are different, as shown in Fig. 7 (a), or a plan view of one of them is flat and only the other is convex. 7 (b), one of which has a concave shape and the other of which has a convex shape so that the convex curvature is somewhat larger than the concave curvature (FIG. 7 (c)).
Shown in Fig. 7, in which a plurality of convex shapes are provided in the width direction of the billet.
Various shapes such as those shown in (d) can be applied, but in any case, the gap at the widthwise end of the steel piece should be about 10 mm in the joined state after heating and pressing. It is preferable to surely fill the gap during the rolling stage. A shearing device, a gas cutting device, a laser fusing device, or the like can be applied as a cutting device for forming the flat shape of the steel piece end as described above, but when cutting into a convex or concave shape with a specific curvature, two curved lines are used. A drum shear with blades (shown in FIG. 1) is advantageously suitable in that it is not complicated to shape.

Steel slab 1, on the entry side of the finishing rolling facility 4.
As the heating means for the local butt-joining of No. 2,
In addition to heating by a burner and high-frequency heating by a coil wound around a steel slab, heating by the so-called transverse method in which an alternating magnetic field that penetrates the thickness of the slab is applied using a pair of alternating magnetic field generating coils that sandwich the steel slab ( JP-A-4-8910
No. 9), etc. can be applied.

As a joining mode for joining steel pieces, regardless of whether the steel pieces are in a contact state or in a non-contact state, a target joining temperature is a region near the central portion in the width direction of the steel pieces, which is a joining planned portion. Heating / heating up to, and pressing the steel pieces against each other after stopping the heating, regardless of whether the steel pieces are in contact with each other or in the non-contact state Joining mode that presses the steel pieces to each other when the target joining temperature is reached by not exceeding the temperature at which the planned part melts, and pressing the steel pieces in advance (pressing until a predetermined joining margin is obtained) Various joining forms such as joining by heating at the initial stage of finish rolling as shown in Fig. 8 (a) and Fig. 8 (b) can be adopted. At least 0.5 relative to the total width W of the billet to avoid fracture at W is preferable.

In the hot finish rolling after the local joining of the steel slabs 1 and 2 is completed, under the above-mentioned suitable gap conditions in order to promote the metal flow at the widthwise end portions of the steel slabs. It is preferable to roll the joint between the preceding steel piece 1 and the following steel piece 2 at a reduction rate of 20% or more. The temperature of the steel slab in this finish rolling step is about 1000 to 1100 ° C, and the cutting process to the finish rolling is performed in the widthwise central portion of the steel slab.
If it takes more than 20 seconds, the thickness of the scale generated on the cut surface of the steel slab will increase, and it may not be possible to reliably join the end positions in the width direction of the steel slab during finish rolling. The working time from cutting to joining is preferably within 20 seconds.

[0019]

【Example】

Example 1 A continuous hot rolling of a sheet bar (steel type: low carbon steel) having a width of 1000 mm and a thickness of 30 mm was first carried out by using a rolling facility having a 7-stand tandem rolling mill as shown in FIG. 1 above. At the entrance side of the cutting device 5, after subjecting the trailing end portion of the preceding sheet bar and the leading end portion of the following sheet bar to the thinning treatment under the condition of t / T = 0.6 near the center in the width direction, Each of the end portions of these sheet bars was cut to have a plane shape as shown in FIG. 9, and then heated, pressed and finish-rolled according to the following conditions to finish a hot rolled sheet having a thickness of 3 mm.

Heating method: Transverse method by applying alternating magnetic field Input power: 2000kW Heating temperature: 1400 ° C Heating time: 6.0 seconds Joining form: Press after heating Pressing force: Face pressure 3kgf / mm ² Joining cost: 500 mm gap: 10 mm

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 possible.

Example 2 Continuous hot rolling of a sheet bar (steel type: low carbon steel) having a width of 1000 mm and a thickness of 30 mm was carried out by using a rolling facility having a seven-stand tandem rolling mill as shown in FIG. 1 above. First, on the entrance side of the cutting device 5, the rear end portion of the preceding sheet bar and the leading end portion of the following sheet bar are subjected to a thinning process in which t / T = 0.95 is satisfied near the center in the width direction. After being applied, each of the end portions of these sheet bars is cut into a flat shape as shown in FIG. 9, and then subjected to heating, pressing and finish rolling according to the following conditions to obtain a hot rolled sheet having a thickness of 3 mm. Finished

Heating method: Transverse method by applying alternating magnetic field Input power: 2000kW Heating temperature: 1400 ° C Heating time: 6.0 seconds Joining form: Press after heating Pressing force: Face pressure 3kgf / mm ² Joining allowance: 500 mm gap: 10 mm

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 possible.

On the other hand, when the front end and the rear end of the seat bar are not thinned (other conditions are the same).
However, in some cases, complete joining could not be performed, an unjoined portion might remain at the end in the width direction of the steel slab, and it might break during rolling. In addition, if the thinning is not applied to the widthwise center of the front and rear ends of the sheet bar and the cutting process is not performed so that the region becomes the joining region (other conditions are the same), the finish Since the joining before rolling is insufficient and the joining time takes 20 seconds or more to securely join the sheet bars to each other in that area, increase the capacity of the heating device, extend the line in that area, etc. However, it was extremely disadvantageous to carry out continuous hot rolling of billets.

[0026]

As described above, according to the present invention, when pre-joining the leading steel piece and the trailing steel piece on the entry side of the finishing rolling facility, the joining end face shape is specified and the local thickness reducing treatment is combined. Welding can be done in a short time, and the edges of the steel pieces are contacted over the entire width direction to make the joints even stronger. And continuous hot rolling with high productivity can be realized.

[Brief description of drawings]

FIG. 1 is a schematic view of an example of equipment configuration suitable for carrying out the continuous hot rolling method of the present invention.

FIG. 2 is a schematic view of a rear end portion of a preceding steel piece and a tip end portion of a following steel piece that have been subjected to the thinning treatment according to the present invention.

FIG. 3 is a schematic view of a rear end portion of a preceding steel piece and a front end portion of a trailing steel piece that have been cut according to the present invention.

FIG. 4 is a plan view of a preceding steel piece and a following steel piece after joining.

FIG. 5 is an explanatory diagram showing a rolling condition of a steel slab.

FIG. 6 is a diagram showing a joining state of steel pieces after rolling.

FIG. 7 is a diagram showing an example of a planar shape of end portions of a preceding steel piece and a following steel piece in joining.

FIG. 8 is a diagram showing the planar shapes of the ends of the preceding steel piece and the following steel piece after joining.

FIG. 9 is a diagram showing a planar shape of a seat bar in an example.

[Explanation of symbols]

 1,1a, 1b, 1c, 1d Leading steel strip 2, 2a, 2b, 2c, 2d Trailing steel strip 3 Rough rolling mill 4 Hot finishing rolling equipment 5 Rolling down equipment 6 Cutting equipment 7 Heating equipment 8 Scale breaker

Front page continuation (72) Inventor Katsuhiro Takebayashi 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture No. 1 Kawasaki Iron & Steel Co., Ltd.

Claims (1)

[Claims] 1. A front end portion of a preceding steel piece that has undergone the rough rolling step and a rear end portion of a subsequent steel piece that is subsequently conveyed to the steel piece are joined together, and the preceding steel piece and the subsequent steel piece are joined. Prior to joining, the butt contact area between the trailing end of the preceding steel piece and the leading end of the following steel piece is adjusted to the widthwise end prior to joining when continuously feeding the steel to the finishing rolling equipment. Cutting the rear end of the preceding steel piece and the tip of the following steel piece in a shape that is closer to the center in the width direction excluding the parts, and prior to this cutting, the rear end of the preceding steel piece And a continuous hot rolling method for a steel slab, which comprises subjecting a region corresponding to a butt contact region at a leading end of the subsequent steel slab to a thinning treatment.