JPH05154505A - Manufacture of cold rolled steel sheet with high glossness and excellent image clarity - Google Patents

Abstract

PURPOSE:To manufacture a steel sheet with high glossness and excellent image clarity. CONSTITUTION:A rolling mill which consists of two or more roll stands is used in temper rolling, roll cross rolling is executed in at least one stand of the preceding stage and rolling is executed using laser dull rolls as work rolls in at least one stand of the poststage. Or, roll cross rolling is executed in at least one stand of a cold rolling mill, a rolling mill which consists of two or more roll stands is used in temper rolling and rolling is executed using the laser dull rolls as work rolls in at least one stand of them. Since roll cross rolling is executed, the steel sheet with high glossness can be obtained even using roll with large surface roughness. Excellent image clarity is imparted to this steel sheet by applying rolling with the laser dull roll.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention has a high gloss and
In addition, the present invention relates to a rolling method for producing a cold-rolled steel sheet which is excellent in sharpness after painting.

[0002]

2. Description of the Related Art There are various properties required for cold-rolled steel sheets, one of which is surface gloss. In order to increase the glossiness of the surface, it is necessary to perform so-called bright finish to make the surface as smooth as possible. On the other hand, in recent years, attention has been paid to the image clarity after painting. The sharpness is a property in which an image has no cloudiness or distortion, and an object can be clearly viewed. Especially, this property is often required for a cold-rolled steel plate for an outer panel of an automobile. Further, cold-rolled steel sheets are often subjected to press working, and it is essential that they have excellent workability.

The cold rolled steel sheet is finally finished by temper rolling. Conventionally, in temper rolling, in which glossiness is important such as bright steel plate, rolling is performed by a roll having a higher glossiness on the roll surface by raising the count of a grindstone for polishing a work roll. In order to manufacture steel sheets having different glossiness, it is the current situation to use work rolls polished with a grindstone having a different count each time. However, such a conventional method has the following problems.

(1) Recently, cold-rolled steel sheets are in the trend of small lots and many kinds, and there are several kinds (glossiness) of dull-finished steel sheets and bright-finished steel sheets. In order to manufacture these, it is necessary to change the roll each time, and the work efficiency is significantly reduced.

(2) In order to obtain a steel plate having high gloss, a work roll polished with a high count grindstone must be used, but it takes more time to polish with a high count grindstone. It also requires work such as exchanging grindstones, which makes roll polishing work inefficient.

(3) In temper rolling, wet rolling using a lubricating oil is carried out for those requiring a certain elongation or more. However, in wet rolling, an oil film is formed between the roll and the rolled material, and the static pressure of the oil film causes oil pits (microscopic depressions) to prevent the glossiness from increasing. On the other hand, dry rolling cannot provide the required elongation. That is, it is difficult for a single-stand temper rolling mill to obtain a product with high gloss while ensuring a predetermined elongation.

(4) The workability of the highly bright finished steel sheet is poor. This is because there are few fine irregularities that form an oil reservoir of lubricating oil on the surface of the steel sheet. Therefore, when the workability is important, the dull finish must be used, but it is difficult to secure a high glossiness and sharpness in the dull finish.

[0008]

The present invention is based on the above (1)-
The object of the present invention is to solve the problem of (4), and an object thereof is to provide a method for efficiently manufacturing a cold rolled steel sheet which has a dull finish, high glossiness and excellent image clarity. ..

[0009]

The gist of the present invention resides in the following cold rolled steel sheet manufacturing method.

(1) In temper tempering, a rolling mill comprising two or more roll stands is used, roll cross rolling is performed in at least one stand in the front stage, and a laser dull roll is used as a work roll in at least one stand in the rear stage. A method for producing a cold rolled steel sheet having high gloss and excellent image clarity, which comprises rolling.

(2) Roll cross rolling is performed on at least one stand of a cold rolling mill, and a rolling mill having two or more roll stands is used for temper rolling. A laser dull roll is used as a work roll on at least one of the stands. A method for producing a cold-rolled steel sheet having high gloss and excellent image clarity, which is characterized in that it is used for rolling.

In the present invention, "roll cross rolling" means, as shown in FIG. 2, upper and lower rolls with respect to a direction perpendicular to the rolling direction (longitudinal direction) of the rolled material (cold rolled steel sheet) 3. This means rolling with the axes inclined in opposite directions and inclined in a plane parallel to the rolling surface. In a multi-high rolling mill (4Hi mill, 6Hi mill, etc.), this inclination may be provided only on the work rolls or may be inclined together with the back up rolls. On the other hand, in the present specification, normal rolling in which both the upper and lower work rolls are rolled with their axes at right angles to the rolling direction is referred to as "parallel roll rolling".

The "laser dull roll" is a roll in which a laser beam is applied to the roll surface so that fine irregularities are regularly formed. On the metal plate rolled by such a roll, regular irregularities on the roll surface are transferred, and the image clarity after coating becomes remarkably excellent.

FIGS. 1A and 1B conceptually show a typical embodiment of the method of the present invention. In the figure, the shaded lines are the laser dull rolls.

FIG. 1A corresponds to the above method (1),
This is a temper rolling method for a steel sheet that has been manufactured by an ordinary cold rolling method and annealed, and is a case where the temper rolling mill has two stands. At this time, roll cross rolling is performed by the stand on the first stage (first stand) and the stand on the second stage (second stand).
Rolling (parallel roll rolling) using a laser dull roll as a work roll is performed with a stand. Even when the temper rolling mill has three or more stands, roll cross rolling is performed in at least one stand in the preceding stage, and laser dull roll rolling is performed in at least one stand in the subsequent stage (preferably the final stand).

FIG. 1B corresponds to the above method (2). In this case, the cold-rolled steel sheet that has been finished by roll-cross rolling in at least one pass (preferably the latter pass) in the cold rolling process is annealed, and in temper rolling, either stand (preferably the last stand) is used. Rolling is performed using a laser dull roll as a work roll.

In the method of FIG. 1 (a), since roll cross rolling is performed in the temper rolling step, there are few oil pits, as will be described later, so wet rolling can be performed.
In the method of FIG. 1 (b) as well, since the flat area ratio of the steel sheet has already become high in the cold rolling step, temper rolling may be performed by a wet method, but if a temper rolling mill having two or more stands is used. Therefore, dry rolling is desirable because sufficient elongation can be obtained even with dry rolling.

[0018]

In order to improve the glossiness of the steel sheet in cold rolling, it is important to bring the roll and the steel sheet into metal contact with each other as much as possible and to increase the surface roughness of the steel sheet surface and the flat area ratio of the steel sheet surface. In the case of bright rolling, it is common to use a smoother roll, such as by increasing the count of the roll grinding wheel. That is, in the conventional temper rolling method, the ideal method of increasing the glossiness is dry rolling and rolling using a smooth roll.

However, increasing the smoothness of the roll is
As mentioned above, it is not desirable in terms of production efficiency. Also,
There is a problem that a large elongation cannot be obtained by dry rolling.

Roll cross rolling has hitherto attracted attention as an effective means for controlling the shape of rolled material. However, it has been found that this rolling method has an effect of improving the surface glossiness of the rolled material, and the applicants of the present invention previously filed Japanese Patent Application No. 2-182835.
And Japanese Patent Application No. 3-93882.

FIG. 3 is a sectional view schematically showing a contact portion between a work roll and a steel plate during rolling. (A) shows a case of ordinary parallel roll rolling, and (b) shows a case of roll cross rolling. is there. In the case of parallel roll rolling, rolling oil is confined in the recesses of the rolls to form so-called oil pits, so that the surface of the steel sheet hitting the recesses of the roll is not smoothed. On the other hand, in the case of roll cross rolling, since the traveling directions of the roll and the steel sheet are inclined by the cross angle (θ) as shown in FIG. 2, the steel sheet is rolled as shown in FIG. 3 (b) during rolling. A smooth portion can be formed by moving the roll convex portion in the width direction. Compared with FIG. 3A, the latter clearly has many smooth portions and has a high flat area ratio.

According to the above-mentioned principle, even if the work rolls having the same surface roughness are used, the glossiness of the product steel sheet is much improved by performing the roll cross rolling. Further, since the effect of the oil pit is reduced, a steel sheet having a high gloss can be manufactured even by wet rolling using a lubricating oil.

FIG. 4 shows the test results regarding the relationship between the roll cross angle (θ) and the glossiness. The test was carried out as follows.

Using a four-stage temper rolling mill with one stand capable of changing the roll cross angle, thickness 0.8 mm, width 1200 mm
Using SPCC (JIS G 3141) cold rolled steel sheet, elongation rate 0.8%,
Temper rolling was performed at a rolling speed of 500 m / min. The diameter of the work roll was 600 mm, its surface roughness (Ra) was changed to 0.2 μm and 0.08 μm, the former was rolled with different cross angle θ, and the latter was only parallel roll rolling. .. Both are wet rolling using a lubricating oil.

As is apparent from FIG. 4, even with a roll of Ra = 0.2 μm, when the roll cross angle θ is 0.3 ° or more, the glossiness is remarkably improved. If θ is 0.3 ° or more, rolls with surface roughness Ra = 0.08 μm are used for parallel rolling (θ = 0.
A gloss level equal to or higher than that of (°) is obtained. That is, in order to obtain the same high glossiness, the method of the present invention can use a roll having a larger surface roughness than that of the conventional method, and the time for roll polishing can be greatly shortened. Also, by using rolls with the same surface roughness, it is possible to manufacture steel plates with different glossiness by changing the cross angle, so the frequency of roll replacement can be reduced even if the product specifications are diverse, and the surface roughness The need to have multiple different rolls is also reduced.

The mark Δ in FIG. 4 is an example of dry rolling of parallel rolls using rolls having Ra of 0.2 μm. In the case of dry rolling, high glossiness can be obtained even in parallel roll rolling, but in wet rolling, if θ is 0.3 ° or more, glossiness equivalent to or higher than that of dry rolling can be obtained.

From FIG. 4, it can be said that it is desirable to set the cross angle (θ) of the roll in the case of roll cross rolling to 0.3 ° or more. When θ is around 0.3 °, the improvement of glossiness becomes remarkable, and the effect is saturated at around 1.5 °. The upper limit of the cross angle is about 2 ° due to the structure of the rolling mill.

In the method of the present invention, at least one of cold rolling is used.
Roll cross rolling is performed in a stand or one or more stands before the temper rolling to increase the flat area ratio of the steel sheet, and the laser dull roll is used as a work roll in one or more stands after the temper rolling. I do. That is, by transferring regular fine irregularities of the laser dull roll onto a steel plate having a high flat area ratio, a steel plate having a high glossiness and a high image clarity can be manufactured. Hereinafter, the latter-stage rolling with the laser dull roll will be described.

Regarding rolling with a laser dull roll, a basic invention is disclosed in Japanese Patent Publication No. 62-11922, and the applicant of the present invention has also applied for a number of patents including Japanese Patent Laid-Open No. 63-303011. .. This rolling method is essentially a technique for producing a dull steel plate, not a high-gloss steel plate, so-called bright steel plate. However, the steel sheet rolled by the laser dull roll is
It is superior to the steel plate rolled by normal dull roll.

The point of interest of the present invention is that if a steel plate having a flatness and a gloss increased in advance by roll cloth rolling is rolled by a laser dull roll, a steel plate obtained by ordinary parallel roll rolling is laser dull roll rolled. Compared with the case of applying the steel sheet, it is possible to obtain a steel sheet having high gloss and excellent image clarity.

There is no particular restriction on the laser dull roll used in the method of the present invention. That is, it is important to use a roll in which fine irregularities are regularly arranged, rather than a roll having irregular irregularities on the surface such as a shot-dal roll. For example, if rolling is performed so as to give the pattern disclosed in the above-mentioned Japanese Patent Laid-Open No. 63-303011 to the surface of the steel sheet, a steel sheet excellent in sharpness and workability can be obtained. This rolling is preferably carried out at the final stand of temper rolling.

[0032]

Example 1 The following rolling was carried out using a two-stand temper rolling mill as shown in FIG. Rolled material is 0.8
mm, width 1200 mm SPCC (JIS G 3141) cold rolled steel sheet, which has been subjected to normal cold rolling and annealing.

[Invention Example 1] In the first stand, a normal dull roll having Ra of 1.8 μm was used, and roll cross rolling crossed at a cross angle (θ) of 0.3 ° was performed using a lubricating oil and a rolling load of 500. Conducted in tons.

On the second stand, a laser dull roll (Ra = 3.0 μm) with circular craters with a pitch of 250 μm was used.
m) parallel roll rolling with lubricating oil and rolling load 500
Conducted in tons.

COMPARATIVE EXAMPLE 1 In the first stand, the invention example 1 is used.
No. 1 roll cross rolling, and in the second stand, parallel roll rolling was performed with a normal dull roll.

[Comparative Example 2] Parallel roll rolling was performed in the first stand using the same dull roll, and laser dull roll rolling was performed in the second stand under the conditions.

FIG. 5 shows the image clarity (evaluated by DOI) and the glossiness (Gs) of the steel sheet obtained by the above temper rolling. The ◯ mark is the present invention example 1, the ● mark is the comparative example 1, and the Δ mark is the comparative example 2.

The image clarity was evaluated by DOI (Distinctness of Reflected Image Gloss) after a phosphate film treatment was applied as a base treatment and a cation type electrodeposition coating was applied thereon. The glossiness is 20 for the unpainted steel sheet.
The values are measured with a reflection type gloss meter at a measurement angle of 20 °.

It can be seen from FIG. 5 that the cold-rolled steel sheet temper-rolled by the method of the present invention is excellent in both glossiness and sharpness. This is a synergistic effect of increasing the flat area ratio by the roll cross rolling of the first stand and then applying the regular dull pattern by the laser dull roll rolling.

[0040]

Example 2 In the embodiment as shown in FIG. 1 (b), the following rolling was carried out using a 5-stand cold rolling mill and a 2-stand temper rolling mill. The target material is SPCC (JIS G 3
141), the finish of cold rolling was 0.8 mm in thickness and 1200 mm in width.

[Invention Example 2] In cold rolling, a normal dull roll having Ra of 3.0 μm was used in the final stand, and roll cross rolling crossed at a cross angle (θ) of 0.3 ° was used with a lubricating oil. Rolling load 700
Conducted in tons.

For temper rolling, the same two-stand rolling mill as in Example 1 was used, and a pitch of 250 was used in the second stand.
Laser dull roll with circular crater of μm (Ra ＝
Parallel roll rolling (3.0 μm) was carried out using lubricating oil at a rolling load of 500 tons.

[Comparative Example 3] Cold rolling was carried out under the same conditions as described above, and in temper rolling, parallel rolling was carried out on both the first stand and the second stand with normal dull rolls using lubricating oil.

[Comparative Example 4] In cold rolling, parallel roll rolling using the same dull roll was performed in all stands, and in the second stand for temper rolling, laser dull roll rolling was performed under the conditions.

FIG. 6 shows the sharpness and glossiness (Gs) of the steel sheet obtained by each of the above rolling methods. The ◯ mark is the present invention example 2, the ● mark is the comparative example 3, and the Δ mark is the comparative example 4.

Similar to the results shown in FIG. 5, in the method of the present invention, which is a combination of roll cross rolling in the cold rolling process and laser dull roll rolling in the temper rolling process, both glossiness and sharpness are improved. It is clear that an excellent steel plate is obtained. In comparison between FIG. 5 and FIG. 6, it can be said that the method of Example 1, that is, the method of performing roll cross rolling in the temper rolling step is more desirable for producing a steel sheet with high gloss. ..

[0047]

As is apparent from the examples, the method of the present invention performs roll cloth rolling, so that a steel sheet with high glossiness can be obtained without extremely reducing the roughness of work rolls.

Further, for example, even if the thick material is wet-rolled, there is no fear of deterioration in gloss. Furthermore, since the rolling using the laser dull roll is performed after the roll cross rolling, it is possible to impart excellent image clarity to a steel sheet having high gloss. The laser dull steel sheet is superior in workability to general bright steel sheets.

According to the method of the present invention, it is possible to manufacture steel sheets having different glossiness by changing the cross angle of roll cross rolling. Therefore, it is necessary to prepare various kinds of rolls having different polishing conditions. There is no. In addition, there is a great practical benefit that the work efficiency is improved as the roll polishing time is reduced.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the concept of the method of the present invention, (a) is a schematic view of a rolling line for carrying out the invention of claim 1 and (b) is the invention of claim 2.

FIG. 2 is a plan view (a) and a side view (b) illustrating a roll cloth rolling method.

FIG. 3 is an enlarged cross-sectional view showing a contact state between a roll and a rolled material in normal rolling (a) and roll cross rolling (b).

FIG. 4 is a graph showing the relationship between the cross angle (θ) in roll cross rolling and the glossiness of the rolled steel sheet.

5 is a graph showing the glossiness and sharpness of the steel sheet obtained in Example 1. FIG.

FIG. 6 is a graph showing the glossiness and sharpness of the steel sheet obtained in Example 2.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kiyotaka Hori 4-533 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Sumitomo Metal Industries, Ltd. (72) Inventor Ryuji Hamada 4 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture 5-53 Sumitomo Metal Industries, Ltd. (72) Tsuneo Nakano 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima-shi Mitsubishi Heavy Industries, Ltd. Hiroshima Works (72) Inventor Yu Matsuda Kannon Shin-machi, Nishi-ku, Hiroshima 4-6-22 Mitsubishi Heavy Industries, Ltd. Hiroshima Works (72) Inventor Kazuo Morimoto Kannon Shinmachi, Nishi-ku, Hiroshima City 4-6-22 Mitsubishi Heavy Industries Ltd., Hiroshima Laboratory (72) Inventor Tetsuo Kajiwara Nishi-ku, Hiroshima Kannon Shinmachi 4-6-22 Mitsubishi Heavy Industries Hiroshima Research Institute

Claims (2)

[Claims] 1. In temper rolling, a rolling mill comprising two or more roll stands is used, roll cross rolling is performed in at least one stand in the preceding stage, and laser dull rolls are used as work rolls in at least one stand in the subsequent stage. A method for producing a cold-rolled steel sheet having high gloss and excellent image clarity, which is characterized by performing 2. Roll cross rolling is performed in at least one stand of a cold rolling mill, and a rolling mill comprising two or more roll stands is used in temper rolling, and a laser dull roll is used as a work roll in at least one of the stands. A method for producing a cold-rolled steel sheet having high gloss and excellent image clarity, which is characterized by rolling by rolling.