JP2827927B2 - Sharpness steel plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sharp steel sheet, that is, a steel sheet having a painted steel sheet surface with high sharpness.

[0002]

2. Description of the Related Art Outer panels of automobiles and home electric appliances are finally coated and used in order to improve the corrosion resistance and appearance, and these coated steel sheets are used by users of such products. As the needs are becoming more and more upscaled year by year, further improvement in aesthetics is required. Particularly, regarding the appearance of automobiles, the vividness of gloss, that is, the so-called sharpness after painting, has been rapidly spotlighted as an important factor that determines the image of the product.

[0003] Here, the "clarity" is a measure of how sharp and undistorted the image is when an object is reflected on the painted surface. Determined by the sharpness measurement device being developed.

Conventionally, the sharpness has been improved by improving the coating and the coating conditions. However, the surface properties of the steel sheet itself before coating is also an important factor for improving the sharpness. Normal,
The evaluation of sharpness is performed based on the PGD value. For example, when the PGD value of a coated steel sheet is 0.8 or more, it is determined that the sharpness of the coated steel sheet is excellent. This corresponds to a PGD value of 0.7 or more in the case of unpainted steel sheets. In other words, if the PGD value measured on a bare steel plate is 0.7 or more, the PGD
This is because the value is 0.8 or more.

[0005] The PGD value is measured by a PGD meter (Portable Disti).
nctness of Gloss meter). The measurement principle evaluates how far a figure similar to the character of the eye test can be identified. Therefore, in this specification,
When the bare steel plate has a PGD value of 0.7 or more, it is considered that the sharpness is good.

[0006] Conventionally, as a method for improving the sharpness of such a steel sheet, for example, it has been proposed to reduce the filtering center line waviness Wca of the steel sheet surface (Japanese Patent Laid-Open No. Sho 62).
-230402, JP-A-63-132728, JP-B-6-132
No. 23409). FIG. 1 shows a filtered undulation curve. As can be seen by comparing the upper graph with the lower graph, the smaller the value of Wca, the better the sharpness.

Here, "Wca" is defined in JIS B 0610, and the image obtained by the roughness curve is further processed by setting the cutoff value of the low-pass filter to 0.8 mm, and the center line average roughness at that time is obtained. Shown here. The conventional normal dull finish steel sheet has a Wca value of about 0.7 to 1.2 μm. In addition, the combination of the limitation of the surface roughness is combined. However, the sharpness is not necessarily improved only by a decrease in the Wca value. It is necessary to additionally define the surface roughness such as Ra. There is also a problem in terms of moldability.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a steel sheet having excellent sharpness, in which the surface of the steel sheet after painting shows high sharpness.

[0009]

Means for Solving the Problems In order to enhance the sharpness, various methods have been tried to improve the sharpness after painting by lowering Wca as a steel sheet surface property, and to lower Wca. I have. However, in many cases, the sharpness was not always improved only by the decrease in Wca. for that reason,
Actually, even in the past, it was necessary to further limit the surface roughness such as Ra.

FIG. 2 is a graph showing the relationship between Wca and the PGD value. Even with the same Wca, the value of sharpness varies greatly, and the sharpness cannot be uniquely determined with Wca. You can see that. Therefore, it is understood that a new management standard other than Wca is necessary.

[0011] Even in the past, there is a method of frequency analysis of the steel sheet surface properties as a new management standard for that purpose. However, frequency analysis generally requires a very long time because a three-dimensional roughness meter is used, and is not an index that can be easily managed on site (Japanese Patent Application Laid-Open No. 3-54412).

Here, the present inventor has proposed a new index:
The present inventors have found that a steel sheet having high sharpness can be stably manufactured by introducing the number of peaks (hereinafter, referred to as PC) of a filter undulation curve, and completed the present invention.

Therefore, the gist of the present invention is that the filtering center line waviness Wca (cutoff value of the low-pass filter of 0.8 mm) on the surface of the steel sheet is 0.65 μm or less, and Wca is expressed by the following formula (1).
This is a brilliant steel sheet characterized by having a surface property satisfying the following.

Wca × PC ≦ 6 (1) where PC is the number of peaks per inch having a height of 1.0 μm or more in the surface undulation curve (cutoff value of the low-pass filter of 0.8 mm). .

[0015]

Next, the reason why the above-mentioned limitation is applied in the present invention will be described in detail together with its operation. The present invention focuses on the surface properties of a steel sheet, particularly an index that can be measured by a two-dimensional roughness meter, and defines the conditions.

That is, according to the present invention, the surface properties of a steel sheet having high sharpness reduce Wca,
Is realized by lowering. As described above with reference to FIG. 1, conventionally, the sharpness of a sharpened steel sheet is improved as the surface undulation curve Wca is smaller. But,
As shown in FIG. 3, when Wca is the same, the sharpness becomes better as the number of peaks of the filter undulation curve is smaller. If the number of peaks is large even if Wca is reduced, the sharpness becomes good.

Accordingly, the present invention is, from another aspect, a method for producing a steel sheet having good sharpness by reducing Wca and the number of peaks (PC) on the steel sheet surface.

FIG. 4 is a graph showing the relationship between Wca × PC and the PGD value.
The PGD value can be regulated, and if this is used, Wca
It can be seen that the PGD value can be set to 0.7 or more by setting xPC ≦ 6, and stable sharpness can always be ensured. Here, PC and, as shown in FIG. 5, the number of peaks per inch height above 1.0 [mu] m in filtered waviness curve _{(Pc 1, Pc 2 ···)} .

By the way, PC is the convex number of the filter waviness curve for the frequency where the sectional curve exceeds 800 μ, and Ra is the center line average roughness (JIS curve) for the frequency (roughness curve) where the sectional curve is 800 μ or less. B 0601), and Wca has a sectional curve of 80
This is the center line average roughness for frequencies exceeding 0 μ (undulation curve), and there is no relationship between PC and Ra. When the number of peaks is small, the unevenness existing on the surface after painting is reduced, the surface is smoothed, and the sharpness is improved.

Therefore, in order to improve sharpness according to the present invention, according to a preferred embodiment, both Wca and PC are reduced. In that case, preferably Wca
, PC change, the roll surface for temper rolling is 0.5 ≤ Wc
It is changed by using a roll with a ≦ 1.0 and Pcv ≦ 15 and changing the rolling reduction. For example, Wca and PC increase as the rolling reduction increases, and Wca and PC decrease as the rolling reduction decreases. The Pc
v is based on the undulation curve of the roll surface,
The number of concaves (per inch) with a depth of 1μ or more in the filter undulation curve.

In the following, the effects of the various conditions defined in the present invention and the reasons for limiting the conditions will be described. Wca is 0.65
In the region exceeding μm, there is a strong correlation between the decrease in Wca and the improvement in sharpness. However, when the thickness is 0.65 μm or less, there are many variations, and the sharpness may not be improved.

Therefore, in the present invention, PC is introduced as a new index when Wca is 0.65 or less. PC
When the peak height is less than 1.0 μm, the peak height is set to 1.0 μm or more because the peak does not remain as unevenness on the surface after coating due to the leveling of the paint.

When the value of the equation (1) exceeds 6, the sharpness deteriorates. Therefore, the equation (1) is set to 6 or less. The physical meaning of Wca × PC is the unevenness of the undulation curve. Thus, according to the present invention, it is possible to obtain a steel plate having high sharpness only by using an index obtained by a relatively simple two-dimensional roughness meter as the surface roughness measurement.

Next, the operation of the present invention will be described more specifically with reference to an embodiment of the present invention.

[0025]

EXAMPLES Although the rolling roll for obtaining the steel sheet according to the present invention is not particularly specified, in this example, a roll subjected to ordinary dulling was used. First, using the above-mentioned rolling rolls, a previously prepared 0.8 mm-thick steel sheet for automobile (normal steel sheet, electroplated steel sheet, hot-dip galvanized steel sheet) was subjected to temper rolling at a rolling reduction of 1.0% or more. Wca and PC were changed by variously changing the rolling reduction of the temper rolling.

After the temper rolling, the obtained steel sheet was examined for its surface properties using a two-dimensional roughness tester, and the sharpness was examined. The test procedure for sharpness was as follows.

That is, a 25 μm polyester tape was stuck on the surface of the steel sheet, and in this state, the PGD value of the surface of the steel sheet was measured with a mapping vividness meter. This is a simple evaluation method of sharpness, and has a correlation with sharpness after painting.

If the measured PGD value is 0.7 or more, the
The PGD value was 0.8 or more, which was regarded as good sharpness. These results are summarized in Table 1.

Next, the various PGDs obtained as a result of these
The steel sheet with the values was subjected to a chemical conversion treatment, electrodeposited, intermediately and overcoated (total thickness: 90μ), and the PGD value was measured after coating. The results are also shown in Table 1. PG after painting
It can be seen that the D value was 0.8 or more and the sharpness was good.

[0030]

[Table 1]

[0031]

The steel sheet according to the present invention has high sharpness, is easy to manage, and can be manufactured stably.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a filtering undulation curve.

FIG. 2 is a graph showing a relationship between Wca and a PGD value.

FIG. 3 is an explanatory diagram of a relationship between a filtering undulation curve and sharpness.

FIG. 4 is a graph showing the relationship between Wca × PC and PGD value.

FIG. 5 is an explanatory diagram of a definition of a PC.

Claims (1)

(57) [Claims] (1) The filtering center line waviness Wca (cutoff value of a low-pass filter of 0.8 mm) on the surface of a steel sheet is 0.65 μm or less;
A clarity steel sheet characterized in that Wca has a surface property satisfying the following expression (1). Wca × PC ≦ 6 (1) where PC is the number of peaks per inch having a height of 1.0 μm or more on the surface of the filter waviness curve (cutoff value of the low-pass filter of 0.8 mm).