JPS63281715A - Sheet metal prominent in deep drawability - Google Patents

Abstract

PURPOSE:To improve brilliance and press forming performance by changing a roughness pattern on the surface of a sheet belt at the central section and at the edge sections in the width direction. CONSTITUTION:The surface roughness pattern of a sheet metal 0.5-1.2mm in thickness is changed at least at one edge section and at the central section. The roughness is provided by rolling with rolls worked by laser dull finish, etc. Regarding the roughness pattern, the three dimensional average roughness (SRa) and/or the number of crests per unit area (SPc) at the edge sections are/is made to be superior to the SRa, SPc at the central section. The edge section contains 10-20% of the total width of the steel belt and receives the largest deformation in a pressing time. This sheet metal has a prominent deep drawability and a high brilliance on the coated surface and can be used for car outer panels, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a steel plate that is excellent in both image clarity and deep drawability by laser dal processing.

<Prior art and its problems> Generally, steel sheets used for automobile exterior panels are required to have excellent deep drawability and a beautiful surface. Particularly recently, the sharpness of images after painting has become an issue. Therefore, a laser dull processing method was developed with the aim of greatly improving image clarity or deep drawability after painting, and the inventors have already applied for numerous patents.

For example, there is Japanese Patent Application No. 7769/1986 which aims to improve image clarity using the laser dull processing method, and Japanese Patent Application No. 29661/80 which aims to improve press formability.
There is No. 1 etc.

All conventional steel plate roughening methods, including not only the laser dull processing method but also the shot dull processing method, are aimed at imparting uniform roughness to the cable plate surface. Indeed, it is generally very useful for all steel plate surfaces to have the same surface texture.

Conventionally, emphasis has been placed on either improving the sharpness of the steel plate uniformly over the entire surface or improving press formability. Eclectic surfaces that aim to be in between the characteristics of each have also been proposed.

However, in today's world, where there is a strong desire to develop steel sheets with even better image clarity and formability, this is insufficient.

For example, in order to obtain very good image clarity, it is necessary to increase the proportion of flat parts on the surface of a steel plate, but it is known that this increases the likelihood of mold galling.

On the other hand, in order to prevent mold galling, the roughness must be increased to some extent, which generally deteriorates image clarity.
Steel sheets with excellent image clarity or press formability have either of the above-mentioned contradictory characteristics, but it has become extremely difficult to achieve both.

For example, FIG. 4 shows typical experimental results.

Figure 4 shows cold-rolled steel plate 5PCE for deep drawing with different surface roughness.
In contrast, the relationship between the sharpness after two coats (DOI: value measured with a Dorigon Dot meter) and the limit aperture ratio when no press oil is used is shown. When the three-dimensional average roughness (5Ra) and the number of three-dimensional peaks (SPc), which will be explained in detail later in the present invention, increase, the critical drawing ratio increases and deep drawability is improved, but the sharpness may deteriorate. Recognize. Steel sheets with good sharpness in one-way feeding have poor deep drawability.

As described above, with conventional methods, it has been insufficient to completely achieve both image sharpness and deep drawability, even with the laser dull processing method.

<Object of the Invention> The object of the present invention is to control the roughness pattern in the width direction of the steel sheet, and to improve both image clarity and press formability by focusing on the characteristics of press forming of automobile outer panels and the advantages of the laser dull processing method. We strive to provide superior thin steel sheets.

<Configuration of the Invention> The present invention provides a thin steel sheet with excellent deep drawability, characterized in that the roughness pattern on the surface of the steel strip is different in the width direction from at least one end portion to the center portion.

Here, the roughness pattern is the three-dimensional average roughness of the at least one end (hereinafter referred to as SRa) and/or the peak e per unit area! A thin steel sheet with excellent deep drawability in which i<hereinafter referred to as SPc) is greater than SRa and/or SPc in the central portion is preferable.

The present invention will be explained in detail below.

First, the inventors conducted a detailed study on a method for pressing automobile outer panels. As a result, the exterior panels of doors etc. are generally
As shown in the figure, a steel plate 1 is blanked (punched) in the shape shown by dotted lines 2, and then pressed in the shape shown by solid lines 3. As shown in Figure 1b, the cross section of the pressed product has a relatively flat central part (B) and 1. It consists of end parts (A) and (C) that undergo large deformation during pressing. At the finished product stage, parts (A) and (11;) are hardly visible. On the other hand, although the appearance of part (B) is important, the deformation during pressing is very small. Therefore, the press formability is (A), (with a width of about 10 to 20 cm).
It was found that the sharpness of the image is controlled by the (8) area.

Therefore, it was found that ideally, the properties of the steel sheet would be further improved by imparting an appropriate roughness to the processed area. However, it has been impossible to change the roughness in the width direction using only the conventional shot dal processing method due to equipment or technical reasons.

As a result of intensive study, the inventors came to the conclusion that the laser dull processing method could be used. -Zardal processing method is
As shown in Japanese Patent Application No. 61-7769, a steel plate is manufactured using a roll whose surface is roughened by forming a large number of micro pits by intermittently irradiating the surface of a rotating roll with a laser beam. This is a method of processing.

According to this method, it is possible to sufficiently change or control the roughness pattern in the width direction of the roll.

In other words, it was discovered that the highest roughness pattern for automobile exterior panels could be achieved by attaching a pattern aimed at high image clarity in the center of the roll and a pattern aimed at press formability at the end of the roll. .

By applying this method, there is no need to adopt a roughness pattern that is half-way as in the past, and instead a pattern with excellent image clarity is created at the center of the width, and a pattern with excellent pressability, or mold galling, is created at the edges of the width. This makes it possible to adopt a good pattern, greatly expanding the possibilities of steel sheets.

That is, the thin steel plate of the present invention is a steel plate in which the roughness pattern on the surface of the steel plate is different between the ends and the center in the width direction.

Here, the edge of the surface of the steel plate 1 refers to approximately 10% to 10% of the steel strip gold mine.
This refers to the 20% edge part, which is mainly the part that undergoes large deformation during pressing, and is located at both ends of the central part, as shown in Figure 1b (8).
, (C). At the end, SRa, SP, which will be described later
As explained above, the effect of increasing c is effective only in the deep drawn part, so the end part is preferably about 100 to 200 mm from the end in the width direction of the steel sheet.

In addition, the central part of the steel plate surface is about 60% to 8% of the steel plate gold mine.
This refers to the 0% central portion, which is mainly the portion that undergoes small deformation during pressing, and is shown by (B) in Figure 1b.

The thickness of the steel plate 1 may be any thin steel plate, but a thickness of 0.5 to 1.2 mm is preferable.

The roughness pattern may be formed by any method as long as the profile can be controlled, but in principle it is most preferable to apply the laser dull processing method. Roughness is formed on the steel plate surface by rolling with a roll processed by laser dull processing method, shot dull processing method, etc., and the maximum height RIna
Typical examples include those evaluated by x, 10-point average height Rz, etc.

In particular, if the roughness pattern evaluated by SRa and/or SPc below is
G) and the central part (B), in particular, SRa and/or SPc of at least one end are different from the SR of the central part.
Preferably, the steel plate is higher than a and/or SPc.

Here, the three-dimensional average roughness SRa is defined as follows.

A portion of area SM is extracted from the roughness curved surface on its center plane, and orthogonal coordinate axes, X axis, Y
The roughness curve is expressed as Z=f (x.

y), the value given by the following formula is expressed in one unit.

However, Lxx L, -S.

The number of three-dimensional peaks SPc is defined as follows.

A width detection level and a valley detection level are set up and down by a specified hysteresis width in parallel above and below the center plane, and the number of peaks is counted and expressed in terms of per specified area.

As a method for evaluating sharpness, DOI (Distinctness of Reflection) is used.
d Image) was adopted. As shown in FIG. 5, the DOI value is determined by assuming that Rs is the intensity of reflected light 5 when light 4 incident at an incident angle of 30° is reflected at a reflection angle of 30'', and that the reflection angle is 30°±0. The intensity of the reflected light 6 reflected at 3゛ is R
When, 0.3 D OI = 100 (Rs-Ro, 3)/Rs.

When the DOI value is 85 or more, the image clarity after painting is excellent.

The effect of changing the roughness in the width direction in this way is most preferably to be changed continuously in the width direction by taking advantage of the characteristics of laser dull processing, but in special cases (for example, if the gloss changes there) ) may be changed rapidly.

In addition, the method for continuously changing this roughness is to keep the pitch of the micro pits of Laserdal constant and change only the depth (in other words, SPc It is preferable to keep SRa constant and only change SRa. By doing so, it becomes possible to avoid changes in rolling characteristics in the width direction of the steel sheet. Otherwise, there is a high possibility that the shape of the steel sheet will be defective during rolling.

If the laser dull processing method is used, it is easy to change the pattern in the width direction, and moreover, it is possible to form a single part as desired.

For sharpness, it is very effective to apply laser dulling to reduce SRa and remove waviness.
In particular, as shown in FIG. 2, which will be explained later in the example, SRa was processed using the laser dull processing method, and SRa was set to 1.2.
It is desirable to set it to 54 or less.

Furthermore, as shown in FIG. 3, which will be explained later in Examples, in order to make the critical drawing ratio 2.0 or more even when the steel plate is degreased, that is, without oil, SRa must be 1.5- or more. Alternatively, it can be seen that it is desirable that SPc is 30/- or more.

Therefore, it is desirable that the SRa of the central portion (B) of the steel plate be made as small as possible, while that of the end portions (A) and (C) of the steel plate be made as large as possible in SPc and/or SRa.

The effects of the present invention are particularly noticeable on cold-rolled steel sheets for deep drawing, but of course hot-rolled steel sheets may also be used.

<Example> The present invention will be specifically explained below using Examples.

(Example and Comparative Example) A cold-rolled steel plate for deep drawing (JIS standard 5PCE) with a plate thickness of 0.7 mm and a width of 1100 mm in the as-annealed state was used as the material,
Temper rolling was performed using rolls having various types of roughness patterns as shown in Table 1. The reduction ratio in all temper rolling was kept constant at 0.8%.

In addition, when changing the roughness, it was changed continuously at a point 150 to 200 mm from the end. Roughness measurement was performed by three-dimensional roughness measurement.

Press formability was evaluated using a full-size door model mold by changing the position of the wrinkle presser and measuring the range (mm) until cracks or wrinkles occur. The image clarity was evaluated by measurement using a Dorigonmeter (Do I) after three coats were applied.

The evaluation results of press formability and image clarity are shown in Table 1.

According to Table 1, types A, D, and E of the examples of the present invention had a sufficiently wide press molding range and a high DOI value. On the other hand, in the case of the comparative example in which the entire steel plate was finished with a uniform roughness as in the past, it was impossible to achieve both press forming range and image clarity.

<Effects of the Invention The steel sheet of the present invention has a roughness pattern on the surface of the steel strip in the width direction.
Since the edges and center are different, it is a thin steel plate with excellent image clarity and preformability.

It is especially used for automobile exterior panels, and has excellent deep drawability and high image clarity on the painted surface.

[Brief explanation of the drawing]

FIG. 1a is a diagram illustrating a press line for a steel plate for automobile exterior panels. FIG. 1b is a cross section of the steel plate for automobile exterior panels after pressing. FIG. 2 is a graph showing the relationship between SRa and the 001 value. FIG. 3 is a graph showing the relationship between SRa and SPc values. FIG. 4 is a graph showing the relationship between SRa, SPc, critical aperture ratio, and image sharpness. FIG. 5 is a diagram illustrating a method for measuring DOI. Explanation of symbols 1... Steel plate, 2... Dotted line, 3... Solid line, 4... Incident light, 5.6... Reflected light, (8), (C) -... Edge , (B) -...Central Patent Applicant Kawasaki Steel Co., Ltd. Agent Patent Attorney Nozomu Watanabe Nejiri Patent Attorney Yo Ishii -FIG, 1
b FIG, 2 SRa < pm) FIG, 3 SRa (Hm> FIG, 4

Claims (2)

[Claims] (1) A thin steel sheet with excellent deep drawability, characterized in that the roughness pattern on the surface of the steel strip is different in the width direction between at least one end and the center. (2) The roughness pattern is such that the three-dimensional average roughness (hereinafter referred to as SRa) of the at least one end portion and/or the number of peaks per unit area (hereinafter referred to as SPc) is the same as the SRa of the central portion and/or A thin steel sheet with excellent deep drawability according to claim 1, which has a hardness greater than SPc.