JPH07284811A - Production of thick steel plate without seam flaw - Google Patents

Abstract

PURPOSE:To easily and surely suppress the generation of seam flaws in the end parts in the width direction after finish rolling by heating and rolling the surface and back faces and side end faces of corresponding parts to the end parts in the width direction of a thick steel plate or the only surface and back faces of these parts before rolling for every rolling pass. CONSTITUTION:The surface and back faces in the tip and rear end parts of a slab 4 are heated with an induction heating device 2 for surface and back faces which is provided on this side of a rolling mill 1 and cross rolling is executed. In the first one pass of the cross rolling, when the induction heating device 2 for surface and back faces and a induction heating device 3 for side faces are provided in the end parts in the width direction of the slab 4, after heating the surface and back faces and side faces in the end parts in the width direction before turning the slab 4, the slab 4 is turned by 90 deg., rolling is executed and finish rolling is executed to a prescribed thickness. In this way, yield is drastically improved by reducing repairing rate and trimming amount in the end parts of width on the manufacture of thick plate.

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 of the widthwise edges of a thick steel plate when manufacturing the thick steel plate by tentering and finishing rolling the steel slab. 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. Several methods have been disclosed so far in order to prevent the occurrence of seam flaws.

For example, Japanese Examined Patent Publication No. 41-16928 discloses a method of performing corner cutting on an end portion in the longitudinal direction of an ingot. Japanese Examined Patent Publication No. 59-39202 discloses 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 side surface of a slab by performing edging rolling with a hole-shaped roll is disclosed in Japanese Patent Publication No. 50-146.
No. 32, JP-A-62-199202, JP-A-62-224406 and the like. According to this method, the suitable hole shape differs depending on the slab thickness, and vertical rolls having various hole shapes according to the slab thickness are required.

As a seam flaw prevention technique for hot-rolled steel sheets, Japanese Unexamined Patent Publication No. 4-123802 discloses that a widthwise end portion of a rough sheet bar is heated by an end heating device before finish rolling.
A method of finishing rolling after heating to a high temperature region of 300 ° C. or higher is disclosed. However, in plate rolling,
The tenter rolling is performed to obtain the specified width dimension, and the seam flaws generated during tenter rolling grow during the subsequent finish rolling.Therefore, only the edge heating before the finish rolling ensures the seam flaw. Cannot be prevented.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to prevent the occurrence of seam flaws extending in the rolling direction on the front and back surfaces of the widthwise edges of thick steel plates, and to further improve quality and yield. It is to provide a method for manufacturing a thick steel plate.

[0007]

According to the present invention, when a thick steel sheet is manufactured by tentering rolling and finish rolling a billet, all of the rolling passes or a plurality of times including at least one time of tentering rolling are performed. In the rolling pass, a seam characterized by heating and rolling only the front and back surfaces and side end surfaces of a portion corresponding to the widthwise end portion of the thick steel plate, or only the front and back surfaces of the portion, before each rolling in each rolling pass. This is a manufacturing method for thick steel plates without flaws. The portions corresponding to the widthwise end portions of the thick steel sheet refer to the front and rear end portions of the steel piece during tenter rolling and the widthwise end portions of the steel piece during finish rolling.

[0008]

The temperature of the front and back surfaces of the steel slab becomes lower than the internal temperature of the steel slab due to heat radiation to the atmosphere and heat removal to the roll during tentering rolling and finish rolling. Above all, since the front and back surfaces and the side surfaces are the heat dissipation surfaces at the ends in the longitudinal direction and the width direction,
The temperature drops significantly. 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. In addition, when rolling the billet into the rolling mill and when rolling out from the rolling mill, uneven deformation is usually generated.Therefore, the irregular shape of the front and rear ends of the billet during tenter rolling should be performed first. It becomes remarkable in combination with the above-mentioned shape irregularity caused by the temperature nonuniformity. The front and rear ends during tenter rolling are rotated by 90 ° before finish rolling to become the width direction end during finish rolling. Therefore, the unevenness on the lateral surface in the width direction during finish rolling formed by tenter rolling wraps the convex portion along with the growth of ballering (a phenomenon in which the center part of the plate thickness of the side surface overhangs in the width direction) during finish rolling. As a result, a linear flaw is formed, and as the thickness of the steel sheet is reduced thereafter, it wraps around the edges of the front and back surfaces of the steel sheet and becomes a linear flaw extending in the longitudinal direction, that is, a seam flaw. Even when the tenter rolling is not performed, the shape irregularity of the side surface in the width direction is caused by the temperature decrease, and the depth of the flaw and the amount of wraparound to the front and back surfaces are less than those when the tenter rolling is performed. , Seam defects are observed.

By the method of the present invention, by heating the front and rear surfaces and the side end surfaces of the front and rear ends in the tenter rolling corresponding to the widthwise ends of the thick steel plate before rolling, it is possible to compensate for the temperature drop at the ends. As a result, it is possible to suppress the shape irregularity of the front and rear end portions during tentering rolling, and to prevent the occurrence of seam flaws due to the shape irregularity of the widthwise end portion after finish rolling.

Not only the same effect can be obtained by heating the widthwise end portion during finish rolling, but also when the end portion heating during tenter rolling is insufficient and a minute flaw occurs, the sheet thickness is reduced. Accordingly, it is possible to reduce the amount of the width direction side surface that wraps around the front and back surfaces, and it is possible to suppress the linear flaw generated on the width direction side surface from wrapping around the front and back surfaces.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic view showing an example of an apparatus for carrying out the present invention, and FIG. 2 is a view showing a process of rolling a steel slab to produce a thick steel plate. In general, a steel slab is shape-adjusted and rolled, then tentering and finish-rolled to form a thick steel plate. In the method of the present invention, the shape-adjusted and rolled steel slab for adjusting the thickness and cross-sectional shape of the steel slab is rotated by 90 ° and then placed on the front side of the rolling mill 1 as shown in FIG. 1 (a). The front and back surfaces of the front and rear end portions are heated by the back surface induction heating device 2, and are tentered and rolled. In the first one pass of tenter rolling, as shown in FIG. 1B, when the front and back induction heating device 2 and the side end face induction heating device 3 are installed at the widthwise end portions of the steel slab 4. Before the steel slab 4 is rotated, the front and back surfaces and the side surfaces of the widthwise end portion are heated, and then the steel slab 4 is heated to 90 degrees.
It is also possible to rotate by rolling. Next, after rotating the billet 4 that has been tentered and rolled to a predetermined width dimension by 90 °,
As shown in FIG. 1B, the front and back induction heating devices 2 and the side end face induction heating devices 3 installed in front of the rolling mill 1 heat the front and back surfaces and side faces of the widthwise end of the steel slab 4. Meanwhile, finish rolling is performed to a predetermined thickness.

As a method of heating the end portion, induction heating, gas burner, radiant heating, etc. can be considered, but induction heating is preferable.

It suffices that the heating temperature be able to compensate for the temperature decrease amount at the end, and it is sufficient to use a heating device having a capacity capable of increasing the temperature up to about 300 ° C.

It is desirable to heat both the front and back surfaces and the side end surfaces at the ends, but if there is a problem in the arrangement of the heating device on the equipment, heating from both the front and back surfaces may be sufficient.

Regarding the front and back surfaces, in the case of tenter rolling, the heating range is sufficient to obtain a steel slab having a uniform temperature distribution in the longitudinal direction, for example, a range of about 20% of the entire length from the front and rear ends. . In the case of finish rolling, a range where a steel piece having a uniform temperature distribution in the width direction can be obtained, for example, 2 from the side end face to the full width.
A range of only about 50% is sufficient. As for the side end face, the entire side end face of the steel slab is the best, but the side end face may be in the range from the vicinity of the front and back surfaces to about 20% of the thickness of the steel slab.

As for the rolling pass for applying the end heating, all the rolling passes of tenter rolling and finish rolling are preferable, but in addition to the temperature decrease, the irregular shape of the end is noticeable due to the uneven deformation of the front and rear ends. It is also sufficient to carry out at least one rolling pass at the time of tenter rolling and a plurality of rolling passes at the time of finish rolling in which the wraparound to the front and back surfaces of the side end faces becomes remarkable. In this case, for the reasons described above, it is more effective to carry out the end heating in the tenter rolling than to carry out in the finish rolling.Therefore, the more passes the end heating is carried out in the tenter rolling, the more desirable. . When there is a cost constraint such as a heating unit, the method may be performed only in the first pass of tenter rolling, which makes it easy to heat the front and rear end portions. When performing edge heating during finish rolling, to prevent temperature drop as much as possible, a method of performing it every rolling pass with a certain interval or a method of performing it several times near the final pass where the amount of balling at the edge is large is adopted. it can.

[0018]

EXAMPLES Table 1 shows rolling conditions when the present invention was applied to a steel piece having a thickness of 220 mm and a width of 1700 mm, and Table 2 shows rolling results. The amount of temperature rise by the induction heating device is about 100 ° C between the width center part and the edge part of the steel slab.
The temperature was constant. Heating is 1 for the front and back surfaces of the front and rear ends of the steel slab (340 mm from the front and rear ends) in the case of tenter rolling, and for the front and back surfaces and side surfaces of the end in the width direction of the steel slab (340 mm from the width end) in finish rolling. I went every other pass. As is clear from Table 2, according to the present invention, no seam flaw was found in the thick steel plate after finish rolling.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

According to the present invention, it is possible to easily and surely suppress the occurrence of seam flaws at the end portions in the width direction after finish rolling 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 shows an example of a device for implementing the invention.

FIG. 2 is a diagram showing a general thick plate rolling process.

[Explanation of symbols]

 1 rolling mill 2 induction heating device for front and back surfaces 3 induction heating device for side end surface 4 steel slab 5 heating part

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yukihiro Chiba 1 Nishinosu, Oita-shi, Oita New Nippon Steel Co., Ltd. Oita Works

Claims (1)

[Claims] 1. When manufacturing a thick steel sheet by tentering and finishing rolling a steel slab, all rolling passes or a plurality of rolling passes including at least one tentering rolling are performed for each rolling pass. In, before rolling, a method for producing a thick steel sheet without seam flaws, characterized by heating and rolling only the front and back surfaces and side end surfaces of a portion corresponding to the widthwise end portion of the thick steel sheet, or the front and back surfaces of the portion. .