JPH09141308A - Saw edge preventing method for cold rolled steel strip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a saw edge which is easily formed by cold rolling by machining and hardening a hot rolled steel belt through plastic working and then carrying outside trimming prior to cold rolling. SOLUTION: The hot rolled steel strip 1 is passed through bridle rolls 3 and high draft rolled by a cold rolling machine 4, etc. Hot-rolling scale is cracked and crushed by the high draft rolling and peeled off the steel strip 1. After scale crushed pieces remaining on the steel strip surface are removed with a brush 5, the steel strip is introduced to a spray device 6 and high-pressure water is injected from a spray nozzle 7 to clean up the steel strip surface. Then the steel strip is sent into pickling tank 8 to remove scale slightly remaining on the surface by pickling. The steel plate 1 exiting from the pickling tank 8 is trimmed by a side trimmer 10. Consequently, trouble such as edge roughening and edge cracking is eliminated and the cold rolled steel strip of high quality is obtained at high yield.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing a saw edge which tends to occur due to cold rolling.

[0002]

2. Description of the Related Art A hot-rolled steel strip is covered with a scale mainly composed of an oxide. This hot rolled steel strip
If it is sent to a lower step such as cold rolling as it is, it causes defects such as surface flaws and cracks due to the hot rolling scale.
Therefore, the hot-rolled steel strip is usually removed by pickling, and the hot-rolled steel strip is transported to a lower step. This method has problems in pickling equipment, waste acid treatment, adjustment of descaling ability, and the like, and there is also a possibility that the properties of the steel material may be deteriorated due to intrusion of hydrogen generated during pickling. In order to solve various problems caused by the pickling, various methods for removing the scale of the hot-rolled steel strip sent to the pickling step have been studied. For example, cold rolling of a hot-rolled steel strip to which scale is attached at a high pressure ratio (hereinafter referred to as black scale rolling) is disclosed in Japanese Patent Publication No. 54-133460.
JP, JP-A-57-41821, JP-A-57-41821
No. 10917, and the like. Cold rolling at a high pressure reduction causes cracks in the scale and reduces the adhesion to the steel strip, so shot blasting, high-pressure water jetting, brushing, abrasive grain grinding, etc. can easily be performed on the steel strip after cold rolling. Is separated into As a result, the scale attached to the hot-rolled steel strip carried into the pickling tank is reduced, and the load of the pickling step is reduced.

[0003]

When black-rolling a hot-rolled steel strip at a high-pressure reduction rate, the load of the pickling step is certainly reduced, but the scale fragments peeled from the surface of the steel strip are removed by the rolling rolls. It is pressed against the surface of steel strip. Since the steel strip is softer than the scale, the scale debris may be pressed against the surface of the steel strip or pressed by the pressing force of the roll. The debris pushed into the surface of the steel strip becomes difficult to remove in the pickling step, and causes defects such as surface flaws in the subsequent cold rolling step. Therefore, scale debris is removed by, for example, abrasive grinding,
Some still remain on the surface of the steel strip. For these reasons, black leather rolling has been considered unsuitable for the production of cold-rolled steel strip that requires a high-quality surface texture. And, although there are various problems described above, descaling by pickling is the mainstream.

The inventors of the present invention have conducted various studies to eliminate the reduction of the surface texture due to black skin rolling. As a result, when the surface of the rolling roll is always kept clean during descaling in high pressure rolling, It was found that a steel strip in a surface state free of residual scale is obtained even by mild pickling without pressing or pushing scale fragments on the surface of the steel strip, and filed separately. The present invention was devised to further improve the previously proposed method, by increasing the fracture surface ratio by side trimming a plastically worked hot rolled steel strip,
The purpose is to prevent the generation of saw edges in the subsequent cold rolling process.

[0005]

In order to achieve the object, the saw edge prevention method of the present invention, after work hardening a hot rolled steel strip by plastic working, side trims it prior to the cold rolling of the next step. It is characterized by Plastic working is
For example, cold rolling mills, tension levelers, etc. are used. Further, in a tandem rolling mill or a reverse rolling mill, a method of trimming a steel strip in an intermediate pass can be adopted. The line according to the invention is constructed as shown in FIG. The hot-rolled steel strip 1 with the hot-rolled scale adhered is unwound from the payoff reel 2, passed through bridle rolls 3, and rolled under high pressure by a cold rolling mill 4. The hot-rolled scale is cracked and pulverized by high-pressure rolling, and is separated from the steel strip 1. After removing the scale pulverized material remaining on the surface of the steel strip with the brush 5, it is further introduced into the spray device 6,
By spraying high pressure water from the spray nozzle 7, the surface of the steel strip is cleaned. The steel strip treated in this way is then sent to a pickling tank 8, where scales slightly remaining on the surface are pickled and removed. Then, it is taken up by the take-up reel 9.

The cold rolling mill 4 is adjusted so that the rolling reduction is 30% or more. Hot rolled steel strip 1 at such a high pressure reduction rate
When rolling, the scale layer cracks, and the scale layer separates from the base steel due to the difference in ductility between the scale layer and the base steel. The scale is, for example, the rolling force (about 2%) of the conventional tension leveler, which is incorporated as a pre-process of pickling, and mechanical repetitive bending.
It cracks and peels off. Therefore, the amount of scale brought into the pickling tank 8 is reduced, the pickling load is reduced,
Good acidity can be achieved by pickling for a short time. The cold rolled hot rolled steel strip is work hardened by plastic working. Trimming the hot-rolled steel strip in this state prevents the occurrence of uneven cut surfaces. The cause of making the cut surface uniform by cold rolling is presumed as follows.
That is, when a normal hot-rolled steel strip is cut, since the material is relatively soft, a cut surface having a sheared surface and a fractured surface is formed as shown in FIG. Irregular and discontinuous projections are formed between the sheared surface and the fractured surface, causing burrs and sags. If the shear plane becomes too large,
Roughening and cracking of the ears are likely to occur during cold rolling, and wear of the trimming blade is accelerated.

On the other hand, in the present invention, since the steel plate rolled under high pressure is work-hardened by plastic working, the ratio of the fracture surface to the trimmed cut surface is large. This is because the hardness of the steel sheet increased due to work hardening, and conversely, the fracture toughness decreased. Therefore, when the steel plate 1 after leaving the pickling tank 8 is trimmed by the side trimmer 10, troubles such as roughening of the ears and cracking of the ears are eliminated in the subsequent cold rolling step. The tendency of the fracture surface to increase due to work hardening is not limited to the black skin rolling described with reference to FIG. 1 and is the same when a cold rolled steel strip is obtained by normal cold rolling. Therefore, when trimming is performed between the stands of the tandem rolling mill, for example, between the second stand and the third stand of the rolling mill consisting of five stands, or by installing a trimmer in the mill of the reverse rolling mill and trimming in the middle pass. and when,
A steel strip with sound widthwise ends is obtained.

[0008]

EXAMPLE A hot-rolled steel strip having a thickness of 2.7 mm was cold-rolled at a reduction of 50% prior to pickling. The hot-rolled steel strip has the components and compositions shown in Table 1 and has an average thickness of 10 to 15 on the surface.
A hot-rolled steel strip with the μm hot-rolled scale still attached was used.

[0009]

The scale adhering to the steel strip 1 was peeled from the base steel by rolling under high pressure, and was almost removed from the surface of the steel strip after the brushing and spraying steps. The residual scale was also removed by pickling, and the steel strip 1 carried out from the pickling tank 8 had a sound surface with no scale. The steel strip 1 was hardened by hot rolling. That is, while the hardness of the hot rolled steel strip was HV100, the hardness of the steel strip 1 that passed through the pickling tank 8 was HV100.
It was rising to V130. When the steel strip 1 thus hardened was trimmed, the ratio of the fracture surface to the cut surface was 60% or more in area ratio, and the occurrence of burrs and sags was significantly suppressed.

The steel strip 1 after trimming was wound up on a winding reel 9 and conveyed to a cold rolling step, and cold rolled to a plate thickness of 0.3 mm. Observation of the obtained cold-rolled steel strip revealed that defects such as roughening of the ears and cracks in the ears were not detected at the ends in the width direction, and the length in the width direction was stable. Therefore, products could be obtained from the cold-rolled steel sheet with high yield. On the other hand, in the case where hot-rolled steel strip was rolled under high pressure or pickled under the same conditions except that trimming was omitted, defects such as rough edges and edge cracks occurred frequently at the widthwise end. It was necessary to remove a few millimeters from the end.

[0012]

As described above, in the present invention, the steel strip work-hardened by cold rolling is side-trimmed prior to the subsequent cold working step. The cut surface formed by the side trimming has a large fracture surface ratio because the hardened steel strip is trimmed, and is a sound cut surface with less burrs and sags. Therefore, when this steel strip is cold-rolled in the subsequent process, a high-quality cold-rolled steel strip free from rough edges and cracks can be obtained with a high yield.

[Brief description of the drawings]

FIG. 1 shows a descaling line of a hot-rolled steel strip according to the present invention.

[Figure 2] Side-trimmed cut surface

[Explanation of symbols]

1, 17: Hot rolled steel strip with scale attached 2: Payoff reel 3: Bridle roll 4: Cold rolling mill 5: Brush 6: Spray device 7: Spray nozzle 8: Pickling tank 9: Take-up reel 10 : Side trimmer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junya Hayakawa 5 Ishizu Nishimachi, Sakai City, Osaka Prefecture Nisshin Steel Co., Ltd. Sakai Works

Claims (3)

[Claims] 1. A method for preventing saw edge of a cold rolled steel strip, which comprises performing work hardening of a hot rolled steel strip by plastic working and then performing side trimming prior to cold rolling in the next step. 2. A method for preventing saw edge of a cold-rolled steel strip, which comprises plastic working according to claim 1 with a cold rolling mill or a tension leveler. 3. The saw edge preventing method according to claim 1, wherein the steel strip is trimmed in an intermediate pass of the cold rolling process.