JP2509490B2 - Steel plate with excellent paint clarity - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention aims to improve coating clarity and press formability by regulating the surface roughness pattern of a steel sheet. It is applied to rolled steel plate, aluminum steel plate, aluminum alloy steel plate and clad steel plate.

[0002]

2. Description of the Related Art Generally, the surface of a cold-rolled steel sheet for processing is dull-finished in order to facilitate press working. That is, during press working, working lubricating oil is stored in the irregularities formed on the surface of the steel sheet, thereby reducing the friction between the mold and the steel sheet and preventing seizure. Research on press formability has been conducted from both the side of the steel plate, which is the raw material, and the forming technology, but with the increasing precision and complexity of products, the required properties for steel sheets are becoming more sophisticated and diversified. . On the other hand, exterior steel sheets for automobile bodies, home appliances, etc. are painted to give them a beautiful appearance, but at this time, they should not be spoiled by diffuse reflection on the coated surface, that is, they are excellent in so-called sharpness. Is required. As a conventional technique as described above, Japanese Patent Application Laid-Open No. 62-168602
There is a gazette "Painted steel plate and its manufacturing method". The content is that the center line average roughness Ra of the surface is 0.3 to 2.0 μm.
Of the trapezoidal peak portion having a flat peak surface and the groove shape formed so as to surround all or a part of the periphery of the trapezoidal peak portion having a flat peak surface. And a middle flat portion formed between the peaks and outside the valleys, higher than the bottom of the valleys and lower than or equal to the peak surface of the peaks. Moreover, the average center-to-center distance between adjacent peaks is Sm, the average diameter of the outer edges of the valleys is D, and the average diameter of the flat peaks of the peaks is d ₀ . When the ratio of the total area of flat surfaces to the total area is defined as η (%), 0.85 ≦
Sm ≦ 1.7, Sm−D <280 (μm), 30 ≦ d ₀
The coating steel sheet is configured to satisfy ≦ 500 (μm) and 20 ≦ η ≦ 85 (%).

The profiles of the surface of the roll and the steel sheet in the above-mentioned prior art are shown in FIGS. 4 and 5 (Japanese Patent Laid-Open No. 62-168602).
10 and 11) of the publication, D: average outer diameter of flange 2 on roll surface = average diameter of outer edge of valley 11 on steel plate surface d: average diameter of crater 1 on roll surface d ₀ : Average diameter of the flat crest surface 8 of the peak portion 10 of the steel plate surface H: Depth of the crater 1 on the roll surface h ₁ : Height of the flange 2 of the roll surface = From the intermediate flat portion 9 to the valley portion 11 of the steel plate surface to the bottom depth h _2: height from the intermediate flat portion 9 of the flat summit surface 8 of the mountain portion 10 of the steel sheet surface Sm: mountain adjacent average center distance = steel sheet crater 1 adjacent the roll surface Average center-to-center distance of part 10 α: Width of flange 2 on roll surface η: Area of flat part (area occupancy η ₁ of flat crest surface 8 of peak 10 and area occupancy η ₂ of intermediate flat part 9) Sum of).

[0004]

DISCLOSURE OF THE INVENTION For example, the good finish quality of a body after being coated with an outer panel for an automobile can directly visually appeal to the customer the overall high quality of the automobile. Therefore, it is an extremely important quality control item. On the other hand, it is also important that the outer panel for automobile has good moldability and does not cause quality defects such as cracks during press working. The sharpness of the coating on the surface of the steel sheet generally improves as the number of flat portions on the surface of the steel sheet increases. On the other hand, the press formability on the surface of the steel sheet is generally good because the larger the volume of the recess on the surface of the steel sheet, the more the lubricating oil for press working that wets the recess. As a problem of the conventional technology, a ring-shaped recess on the surface of a steel sheet cannot provide a sufficient flat area on the surface of the steel sheet under the condition that the press formability does not cause a quality defect, and the car image is not clearly visible to users who purchase the vehicle. It can be said that they have been evaluated for quality as being insufficient. Therefore, it is desired to have a sufficient flat area on the surface of the steel sheet while maintaining the volume of the recesses on the surface of the steel sheet (while maintaining press formability). Further, as a problem of the conventional technique, since there is a height h ₁ from the intermediate flat portion 9 of the flat crest surface 8 of the flat portion 10 of the steel sheet surface, the flat portion of the steel sheet surface has a step, and coating There is also a point that the glossiness is impaired due to the fact that the step of the surface is also essential, and the distortion of the image is caused to deteriorate the clearness of the paint.

In the prior art, the volume of the concave portion is u = (1/2) × (πα ² / with an annular (ring-like) shape having a semicircular cross-sectional area with the diameter α of the flange 2 on the roll surface per concave portion. 4) × π (D + d ₀ ) / 2 (1) The width α of the flange 2 on the roll surface is 4 page 17 of the above publication.
From the line, α = 0.09 × D (2) Since the number of recesses per 1 mm ² is 1 mm = 1000 μm, n = (1000 / Sm) × (1000 / Sm) (3) Therefore, the recess volume per 1 mm ² is V = u × n = 4.99 × 10 ³ × (D + d ₀ ) / (Sm / D) ² (4) Furthermore, D = d ₀ + 2α (from FIGS. 4 and 5), d ₀ = 30-
500 [mu] m, [alpha] = 20-40 [mu] m (page 1 column 1 of the above publication)
Since 9 rows), V = (0.499 to 5.389) × 10 ⁶ / (Sm / D) ² (5) Table 1 shows Sm / D, flat area η, and concave volume V per 1 mm ^2. From the tables 2a and 2b of the publication, the area V of the flat portion is defined as the volume V of the concave portion per 1 mm ² in the above formula (5) by Sm / D: 0.85 to 1.75. Is substituted.

[0006]

[Table 1]

In Table 1, the area ratio η of the flat portion is 0.29 to
At 0.87, the concave volume V per 1 mm ² is 0.163 to
It becomes 7.459 × 10 ⁶ μm ³ . FIG. 6 shows a relationship diagram between the area ratio η of the flat portion and the concave portion volume V per 1 mm ² in Table 1. In order to improve the coating sharpness of the prior art, it is required to improve the area ratio η of the flat portion with respect to the same concave volume V per 1 mm ² .

[0008]

SUMMARY OF THE INVENTION The present invention advantageously solves the problems of the prior art by providing minute and plural recesses on the surface of a steel sheet, the recesses having a diameter d of 50-50.
0 μm, recess depth h is ^{2 to} 16 μm, steel plate surface 1 mm ²
The total volume of concave portions per hit is 0.10 to 2 × 10 ⁶ μm ³ , the area ratio of flat portions excluding the concave portions on the steel sheet surface is 0.8 or more, and the center distance between adjacent concave portions in the rolling direction (P ₁ ) = 2.
5d to 4.0d, center distance between rows of rolling direction rows (P ₂ ) =
It is a steel plate with excellent paint clarity, which is characterized by having 2.5d to 4.0d.

The present invention will be described below with reference to the drawings.
FIG. 1A is a cross-sectional shape of a roll used in the present invention. The surface of the roll 21 has a diameter of 50 to 500 μm.
The height H from the surface is 2 to 16 μm
The protrusions 27 whose main component is a bar is a center distance between adjacent rows in the rolling direction (P ₁ ) = 2.5D to 4.0D, and a center distance between rows in the rolling direction (P ₂ ) = 2. It is arranged at intervals of 0.5D to 4.0D. If the height H of the protrusions 27 exceeds 16 μm, the protrusions 27 may fall off the roll surface during rolling or may be broken by the rolling load. Therefore, the lower the height of the protrusions 27, the better 16 μm or less is preferable. . But 2
If it is less than μm, the depth of the recesses transferred to the surface of the steel sheet is low and the roughness is also low, so that the object of the present invention cannot be achieved.
Further, FIG. 1 (B) shows a cross-sectional shape of the steel sheet according to the present invention which is temper-rolled by a roll having the above-mentioned surface shape and transferred at a rate of 40 to 100%. If the transfer rate is 40% or less, the depth of the recesses transferred to the surface of the steel sheet will be low, and the roughness will be low, so that the object of the present invention cannot be achieved.

FIG. 2 is a schematic plan view of the surface of a steel sheet according to the present invention, in which the diameter of the steel sheet 24 is 50 to 5 mm.
A recess of 00 μm is formed. Steel plate adjacent to rolling direction
Center distance between hole concave portions 28 (P ₁ ) = 2.5D to 4.0
D, inter-column center distance in the rolling direction rows _(P 2) = 2.5D~
It is arranged at intervals of 4.0D. In a member such as an automobile outer plate which is required to have functions of both image clarity and pressability, if the pitch is too large, the surface roughness of the steel plate is lowered,
This causes problems such as occurrence of slippage during rolling, deterioration of material quality due to change in elongation, deterioration of steel plate quality, and deterioration of pressability. On the other hand, if it is too small, the waviness on the surface of the steel sheet increases, and the image clarity after coating deteriorates. Therefore, the present invention is limited to the above range. The upper limit of the depth of the recess of the steel plate is the protrusion 2 shown above.
If the height of the steel plate is 16 μm and the depth of the recess of the steel plate is lower than 2 μm, the depth of the recess on the surface of the steel plate is low and the roughness is small, so that the object of the present invention cannot be achieved. The shape of the steel plate recess is
Considering the oil sump effect at the time of pressing, the lubrication effect on the steel plate surface, and the like, trapezoidal and angular products are also conceivable, and the recess of the steel plate may have any shape.

Obtain the area ratio η of the flat portion according to the present invention
First, 1mm²The number of recesses per hit is 1
Since mm = 1000 μm, n = (1000 / P₁) × (1000 / P₂(6) The area ratio η of the flat portion is P because the concave portion excludes the circular portion having the diameter d.
₁= P₂= P, then η = 1- (πd²/ 4) × n / (1000 × 1000) = 1− (π / 4) × (d / P)² (7) Since P = 2.5d to 4.0d, η = 0.874 to 0.951 (8) Recesses per piece according to the inventionThe diameter d, depth
Assuming a cylindrical shape of h, its concave volume is u = (πd²/ 4) × h (9)It is represented by. 1 mm according to the invention²Concave volume per hit
Is P₁= P₂= P and h = 2 to 16 μm
And V = u × n = (π / 4) × (d / P)²× h × 10⁶  = H * (1- [eta]) * 10⁶  = (2 to 16) x (1- [eta]) x 10⁶(Μm³/ Mm²) (10) Table 2 shows the area ratio η and 1 mm in the flat portion according to the present invention.
²The relation with the concave volume V per hit is shown using the equation (10).
You.

[0012]

[Table 2]

In Table 2, the area ratio η of the flat portion is 0.874 to
At 0.951, the concave volume V per 1 mm ² is 0.10 to
It becomes 2.0 × 10 ⁶ (μm ³ / mm ² ). In the case where the improvement of the coating clarity is required without deteriorating the press formability such as the outer panel for automobiles, the area ratio η of the flat part is large with respect to the same concave volume V per 1 mm ^2. good. FIG. 6 shows a relationship diagram between the area ratio η of the flat portion and the concave portion volume V per 1 mm ² in Table 2.

[0014]

EXAMPLE FIG. 3 is an explanatory view of a method of manufacturing a roll for manufacturing a steel sheet according to the present invention. According to the present invention, first, as shown in FIG.
The resin 22 of μm is coated. The resin to be coated has properties such as alkali resistance, chrome acid resistance, and insulation properties, and is preferably an alkali resin or a resin for plating and sealing so that it can be easily removed in a later step. Coat to a thickness. As a method of coating, a roll drawing method by non-rotating roll, an electrodeposition coating method, a roll coater by rotating the roll, spraying by a spray,
A curtain coater, a powder coating method, a film-shaped resin, etc. are wound onto the roll surface to uniformly dry it. Next, as shown in FIG. 3B, the resin-coated roll 21 is processed by high-density energy, for example, a laser beam 23. That is, the laser beam 23
Irradiation is performed from the surface of the resin 22 coated with to dissolve and remove the resin in that portion. Hole recess 2 after the resin is dissolved and removed
The 6-diameter can be adjusted by the laser irradiation conditions, particularly the laser output and the gap between the condenser lens and the roll (defocus), and in the present invention, the hole diameter is 50-500 μm.
The laser irradiation conditions are selected so that the range is within the range. In order to perform the laser processing on the roll surface described above, the laser processing head is moved while rotating the resin-coated roll, and the laser is irradiated at the processing frequency based on the preset pitch interval P and the roll rotation number. To do.

After laser processing, as shown in FIG.
The roll of the present invention is plated with chrome in a chrome plating solution.
I do. The plating conditions are 20 to 5 in a chromic acid solution.
Laser processing is performed by performing electroplating under conditions such as a current density of 0 A / dm ² and a recess diameter after the resin is dissolved and removed, that is, a charging current of 2000 A to 20000 A according to an effective area ratio of a chromium plating portion. The chromium protrusions can be attached with a hole diameter of 5 to 20 μm formed by the above method. At this time, since the resin is an insulating substance, it does not adhere to the surface of the chromium, and is plated only on the hole portion with a thickness almost equal to or less than the thickness of the resin depending on the set plating conditions. . FIG. 3C shows the surface state after chrome plating, in which the electrolytically plated curved chrome protrusions 27 are attached to the hole recesses 26 formed by the resin 22 and the surface of the roll 21. Next, as shown in FIG. 3 (D), the roll having the chromium protrusions 27 is immersed in a solvent in which the solvent is dissolved or brushed with the solvent to remove the resin on the surface. Then, as shown in FIG. 3D, the roll 2 from which the resin has been removed
The chrome protrusions 27 are exposed on the surface of 1.

Using the roll thus manufactured,
A cold rolled steel sheet having a thickness of 0.75 mm is temper-rolled, the rough surface formed on the roll surface is transferred to the steel sheet, and the steel sheet shape pattern at that time is shown in Table 3. Diameter d (μm), center distance between recesses P
₁ (μm), center distance between rows of rolling direction P ₂ (μm), recess depth h (μm), flat area ratio η, steel plate surface 1 mm
^With respect to the concave volume V per ² (× 10 ⁶ μm ³ / mm ² ),
As an evaluation test of an outer plate for automobiles, a chemical conversion treatment with a phosphate is performed on each shape pattern of a steel plate, and after the chemical conversion treatment, an undercoat, a cationic ED paint 18 to 20 μm thick, an intermediate coat 30 to 35 μm thick, or a top coat. The top coat was coated with 2 or 3 coats having a thickness of 30 to 35 μm. The NSI value was measured by a freshness meter to evaluate the freshness of the coating film surface after the coating.

The results are shown in Table 3 together with the image clarity (NSI value) and the press workability. The steel sheet of the present invention is No. 1 to 9, the comparative example No. It shows with 10-12. A recess volume V of 2.00 × 10 ⁶ μm ³ per 1 mm ² is sufficient to satisfy the coating image clarity without deteriorating the press moldability required for an automobile outer panel or the like.
Although it may be more than this, conversely the area ratio η of the flatness decreases, so the above value was made the upper limit. On the other hand, when the volume V of the recesses per 1 mm ² is less than 0.1 × 10 ⁶ μm ³ , the press formability required for automobile outer plates and the like deteriorates, and the lubricating oil for processing is insufficient, so that the steel plate after pressing is processed. Since cracks often occur on the surface, the lower limit of V is 0.1 × 10 ⁶ (μm ³ /
mm ² ). FIG. 6 is a diagram showing the relationship between the area ratio η of the flat portion of the steel sheet according to the present invention and the steel sheet according to the prior art and the recess volume V (× 10 ⁶ μm ³ / mm ² ) per 1 mm ^{2 of the} steel sheet surface.

Table 4 shows a steel plate shape pattern according to the prior art. Average diameter D of the outer edge of the valley 11 on the surface of the steel plate,
Average diameter d ₀ of the flat peak surface 8 of the mountain portion 10 on the steel plate surface, width α of the flange 2 on the roll surface, average center-to-center distance Sm between adjacent mountain portions 10 on the steel plate surface (above, all units are μ
m), the area ratio η of the flat portion, and the recess volume ratio V (× 10 ⁶ μm ³
/ Mm ² ), as an evaluation test of the inner plate for automobiles, the presence or absence of cracks (pressing / workability) was investigated after processing and evaluated by the limiting drawing ratio (L, D, R). The conventional steel sheet of FIG. 6 has a height (h ₂ ) from the intermediate flat portion 9 of the flat crest surface 8 of the mountain portion 10 of the steel sheet surface, and thus the flat portion of the steel sheet surface has a step. , Because the step on the painted surface is also essential, the gloss is impaired, and
In order to cause the distortion of the image and deteriorate the clarity of the paint, NS
It is considered that the IC value is worse than that of the present invention.

[0019]

[Table 3]

[0020]

[Table 4]

[0021]

EFFECTS OF THE INVENTION According to the present invention, it is possible to manufacture a cold-rolled steel sheet having both pressability and high image clarity after coating, as compared with conventional laser steel sheets, and coating of automobile outer panels, which was not possible conventionally. We made it possible to improve sharpness.

[Brief description of drawings]

FIG. 1 is a diagram showing a roll (A) for producing a steel sheet according to the present invention and a surface of a steel sheet (B) according to the present invention,

FIG. 2 is a plan view of a steel plate according to the present invention,

FIG. 3 is a manufacturing process diagram of a roll for manufacturing a steel sheet according to the present invention,

FIG. 4 is a diagram showing a roll and a steel plate surface for manufacturing a steel plate according to the prior art;

FIG. 5 is a plan view of a steel plate according to the prior art,

FIG. 6 is an area ratio η of a flat portion between a steel sheet according to the present invention and a steel sheet according to a conventional technique and a recess volume V per 1 mm ^{2 of the} steel sheet surface.
It is a figure which shows the relationship with (* 10 < ⁶ > micrometer < ³ > / mm < ² >).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Crater on roll surface 2 Flange on roll surface 3 Roll 7 Steel plate 8 Crest surface 9 Intermediate flat portion on steel plate surface 10 Crest portion on steel plate surface 11 Valley on steel plate surface 21 Roll 22 resin 23 laser beam 24 according to the present invention Related steel plate 25 Chrome plating 26 Hole recess 27 Protrusion 28 Steel plate hole recess

Claims (1)

(57) [Claims] 1. A steel sheet surface is provided with a plurality of minute recesses,
The shape of the recesses is such that the diameter d is 50 to 500 μm, the recess depth h is ^{2 to 16} μm, the total volume of the recesses per 1 mm ^{2 of} the steel plate surface is 0.10 to ² × 10 ⁶ μm ³ , and the recesses on the steel plate surface are flat. The area ratio of the parts is 0.8 or more, the center distance between the recesses adjacent to each other in the rolling direction (P ₁ ) = 2.5d to 4.0d, the center distance between the rolling direction rows (P ₂ ) = 2.5d. ~ 4.0d
A steel plate with excellent paint clarity that is characterized by