JPH08150402A - Manufacture of thick steel plate without seam flaw - Google Patents

Abstract

PURPOSE: To suppress the occurrence of seam flows in the end parts in the width direction and to drastically improve yield by repeating rolling reduced in the rolling reduction at the time of biting-out of a slab as compared to that at the time of biting-in at plural times in a lateral spreading rolling pass. CONSTITUTION: The rolling reduction at the rear end of the slab 2 is reduced as compared to that at the top end of the slab 2 at a 1st rolling pass 1. At the next reverse rolling pass, the top end of the slab 2 is the side of thick thickness and the rolling reduction at the time of biting-in is increased, but a turn-around at the top end is not increased because the middle in thickness is concaved as compared to the surface and back faces in the cross-sectional shape of the slab at the time of biting-in. In this way, the turn-around to the surface and back faces of linear flaws occurred on the side faces of the slab is suppressed. Rolling reduction may be reduced only in the vicinity of the rear end part of the slab 2 at the 1st rolling pass 1, rolling may be executed so that thickness at the rear end of the slab is thickened as compared to that at the top end and, besides, rolling such as thickness from the top end to the rear end is fixed is permitted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention produces seam flaws extending in the rolling direction on the front and back surfaces at the widthwise end portions of a thick steel sheet when manufacturing the thick steel sheet by tentering rolling and finish rolling the billet. The present invention relates to a method for manufacturing a thick steel plate without performing the above.

[0002]

2. Description of the Related Art When manufacturing thick steel plates, falling defects called seam flaws extending in the rolling direction are apt to occur on the front and back surfaces of the widthwise ends of the thick steel plates. In order to prevent the occurrence of this seam flaw, several methods have been proposed so far.
For example, Japanese Examined Patent Publication No. 41-16928 proposes a method of performing corner cutting on the longitudinal end of the ingot. Further, in Japanese Patent Publication No. 59-39202,
There has been proposed a method of rolling a corner portion of a slab for thick plates into a rounded shape with a radius of curvature of 20 to 80 mm.
These edge processing methods are reliable for preventing seam flaws, but have problems in workability, mass productivity, and yield loss.

A method of forming the slab side surface by edging rolling with a hole-shaped roll is disclosed in Japanese Examined Patent Publication No. 50-146.
No. 32, JP-A-62-199202, JP-A-62-224406 and the like. These methods require a hard roll having a hole shape suitable for the slab thickness, and a hard roll having various hole shapes according to the slab thickness.

Further, in Japanese Patent Laid-Open No. 58-192607, taper rolling in which the amount of reduction during biting in tenter rolling is reduced and the amount of reduction during rolling is sequentially increased and the thin side of the slab is the biting side. A rolling method has been proposed in which rolling is repeated. This method is to suppress the rise of the slab tip at the time of tenter rolling, and to prevent the occurrence of seam flaws.

[0005]

DISCLOSURE OF THE INVENTION The present invention suppresses the unevenness of the side surface, which becomes a seam flaw at the end of rolling, from wrapping around to the front and back surfaces due to the balling at the time of tenter rolling, and by extension, the width direction of the product after finish rolling. It is an object of the present invention to provide a method for manufacturing a thick steel plate which further improves the quality yield by preventing seam flaws generated at the ends.

[0006]

Means for Solving the Problems The gist of the present invention is to manufacture a thick steel plate by reverse rolling a steel strip to a predetermined width, rolling it 90 °, and finish rolling. In the tenter rolling pass, a method for producing a thick steel plate without seam flaws, characterized by repeating rolling twice or more with a reduction in biting of the billet of the tenter rolling pass being smaller than that during biting. It is in.

[0007]

FIG. 4 shows a general process for manufacturing a thick steel plate by rolling a billet. In general, a steel slab is shape-adjusted and rolled, then tentering and finish-rolled to form a thick steel plate. The inventors of the present invention have obtained the following findings through a thorough investigation of the occurrence of seam flaws.

The front and back surface temperatures of the steel slabs are lower than the internal temperature due to heat radiation to the atmosphere and heat removal to the rolls during tenter rolling. Above all, since the front and back surfaces and the side surfaces serve as heat dissipation surfaces at the ends in the longitudinal direction and the width direction, the temperature drop is remarkable.
Such non-uniformity in temperature causes irregularity in the shape of the end portion, that is, unevenness, because a difference in deformation resistance occurs in the longitudinal direction and the width direction. Among them, when biting the billet into the rolling mill and rolling when biting out from the rolling mill, non-uniform deformation usually occurs, so the irregular shape of the front and rear ends of the billet during tenter rolling is This becomes remarkable in combination with the shape irregularity caused by the temperature nonuniformity described above. The unevenness on the side surface at the front and rear ends of the billet that occurs during tenter rolling should be such that the convex part wraps as the ballering (a phenomenon in which the center part of the side plate thickness overhangs in the longitudinal direction) grows during tenter rolling. It becomes a linear flaw.

The linear flaws wrapped on the front and rear end side surfaces of the steel piece are
As the plate thickness decreases during tentering and rolling, it wraps around the edges of the front and back surfaces of the steel plate. After that, since the steel slab is turned by 90 ° and finish-rolled, flaws on the front and back surfaces of the front and rear ends of the steel slab generated during tentering are linear flaws extending in the longitudinal direction, that is, seam flaws. Further, the present inventors have obtained the following findings by observing the metal flow of the front and rear ends of the steel piece during tenter rolling.

At the time of biting the steel piece as shown in FIG. 2 (a), the tip corner portion is crushed by the contact with the roll,
Roll down to the exit side of the roll bite. When biting, the length of contact between the roll and the steel slab (contact length) is short, and only the metal near the front and back surfaces of the steel slab tip is drawn into the roll bite. Indentation occurs at the part. As shown in Fig. 2 (b), when the tip of the billet is rolled to near the exit of the roll bite, the contact length becomes long,
The center part of the thickness of the tip projects more than the vicinity of the front and back surfaces, but near the exit of the roll bite, the contact angle θ with the roll is small, so the deformation of the entire tip part is small, and it is formed near the entrance of the roll bite. Combined with the cross-sectional shape (the central portion of the plate thickness is depressed), the wraparound of the front end side surface after rolling to the front and back surfaces is small.

On the other hand, when the rear end of the steel piece when biting out enters near the entrance of the roll bite, the contact length is long and the contact angle θ with the roll is as shown in FIG. 2 (c). Is large, the rear end portion is deformed in the entire area in the plate thickness direction, and overhang occurs particularly in the center part of the plate thickness where the temperature is high. In the process of rolling the billet rear end to the vicinity of the roll bite exit as shown in FIG. 2D, the vicinity of the front and back surfaces of the billet rear end is pulled in the roll bite exit direction by frictional force.
In the central portion of the plate thickness, the rear end has a free surface, so that metal flows in the direction of the roll bite entrance. Due to this effect, the wraparound of the side surface of the rear end of the billet to the front and back surfaces is much larger than that at the tip of the billet.

From the above, seam flaws are not directly caused by the swelling of the rolled material during biting in tenter rolling, but the unevenness generated on the front and rear end side faces during tenter rolling wraps and bites. It has been found that this is caused by wraparound to the front and back surfaces during bite rolling, especially during bite rolling. Further, the wraparound amount of the leading end at that time is not only small as compared with the rear end as shown in FIG. 3, but also does not become so large even if the amount of reduction is large.

Therefore, according to the present invention, in order to prevent the linear flaws generated on the side surface of the steel piece from wrapping around the front and back surfaces, FIG.
As shown in (a), the amount of reduction at the rear end (bite side) of the billet is made smaller than that at the tip of the billet (bite side) to prevent the trailing side of the billet from wrapping around the front and back surfaces. To do. As shown in FIG. 1 (c), the tip of the billet is thicker in the next reverse rolling pass (the billet rear end in the previous rolling pass).
Therefore, the amount of reduction at the time of biting becomes large, but as described above, the cross-sectional shape of the tip of the steel piece at the time of biting does not become large because the center portion of the plate thickness is depressed compared to the front and back surfaces.

Regarding the first rolling pass for carrying out the present invention, FIG. 1 (a) shows the case of taper rolling in which the amount of reduction is successively reduced from the front end to the rear end of the steel slab. By reducing the rolling amount at the rear end in the rolling pass,
Since it is essential to suppress the wraparound of the side surface of the rear end of the billet to the front and back surfaces, rolling may be performed to reduce the reduction amount only near the rear end of the billet as shown in FIG. 1 (b). . This also applies to the reverse rolling passes after the second rolling pass for carrying out the present invention.

As for the reverse rolling passes after the second rolling pass for carrying out the present invention, as shown in FIG. 1 (c), the roll gap is increased during the reverse rolling, that is, after the billet after performing the reverse rolling pass. In addition to rolling such that the plate thickness at the edge becomes larger than that at the tip, for example, the roll gap as shown in FIG. 1D becomes constant during reverse rolling, that is, the plate thickness of the steel slab after the reverse rolling pass is performed. The rolling may be constant from the front end to the rear end. This is because the bite side (thick side) of the steel strip in the previous rolling pass becomes the bite side in the next reverse rolling, so even if the roll gap is constant, the rolling reduction during biting in the reverse rolling pass is performed. This is because the amount is smaller than the amount of reduction when biting.

The amount of reduction from the time of biting to the time of biting can be changed by changing the roll gap during rolling. It is desirable that the difference in the amount of reduction between biting and biting is larger, but the thick side of the steel piece (the biting side in the previous rolling pass) will be the biting side in the next reverse rolling pass.
The plate thickness after biting out must be less than or equal to the plate thickness that becomes the biting limit of the next reverse rolling pass. The plate thickness that becomes the biting limit can be easily estimated from the plate thickness after rolling in the previous rolling pass, the reduction amount in the next reverse rolling pass, and the roll diameter.

Regarding the tenter rolling pass for carrying out the present invention, the full tenter rolling pass is the best, but a part of a plurality of tenter rolling passes, for example, a tenter rolling with a reduction amount per one pass. It may be limited to rolling passes that are larger than the passes.

[0018]

[Example] Thickness 280, width 1800, length 3800 mm
The continuous casting slab (steel slab) 2 of No. 1 was heated to 1100 ° C., and was tentered and rolled to a width of 4200 mm by the reverse rolling machine 1 having a work roll diameter of 1200 mm as shown in FIG.
Rotated and finished rolled to a plate thickness of 20 mm. The reduction of the rolling reduction at the time of biting was performed by gradually increasing the roll gap during rolling. Table 1 shows rolling conditions when the present invention was carried out, and Table 2 shows rolling results. As is clear from Table 2, according to the present invention, there is no seam flaw generated at the width end of the thick steel plate after finish rolling, or even when it occurs, the occurrence position is compared to the conventional method. Moved to the width end.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

According to the present invention, it is possible to suppress the occurrence of seam flaws at the widthwise end portion after finish rolling or move the occurrence position to the widthwise end portion without impairing the rolling efficiency. . As a result, it is possible to significantly improve the yield by reducing the maintenance ratio and the width edge trimming amount in the production of thick plates.

[Brief description of drawings]

FIG. 1 is a schematic view of a rolling method according to the present invention,
(A) is the first rolling pass of the present invention (in the case of taper rolling), (b) is the first rolling pass (in the case of taper rolling only at the trailing end), and (c) is the second rolling pass (roll gap). (When increasing during rolling), (d) shows subsequent tentering rolling passes (when the roll gap is constant during rolling).

FIG. 2 is a diagram showing a longitudinal cross-sectional shape of a steel piece during biting in tenter rolling and biting rolling, (a) when the tip of the steel piece is biting, (b) is a roll of the steel tip. (C) shows when the rear end of the billet passes near the entrance of the roll bite, and (d) shows when the rear end of the billet bites out.

FIG. 3 is a diagram showing the relationship between the amount of wraparound of the front and rear end side surfaces to the front and back surfaces and the rolling reduction rate.

FIG. 4 is a schematic view of a general plate rolling process.

[Explanation of symbols]

 1 rolling mill 2 billet

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yukihiro Chiba 1 Nishinosu, Oita City, Oita Prefecture New Nippon Steel Co., Ltd. Oita Works

Claims (1)

[Claims] 1. When manufacturing a thick steel sheet by reverse-rolling a billet to a predetermined width by reverse rolling, turning 90 °, and finish rolling, in the tenter-rolling pass, in the tenter-rolling pass, A method for producing a thick steel plate having no seam flaw, which comprises repeating rolling twice or more with a reduction in the rolling reduction of the billet when biting out compared to when biting.