JP2530973B2 - Steel strip with excellent paint clarity and press formability - 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. . For this reason, at present, in the temper rolling to finally adjust the roughness of the steel sheet, a work roll that has been subjected to shot blasting, electric discharge, or dulling with a laser, etc. is used to transfer the roughness to the steel sheet surface. ing. Also,
The evaluation criteria in the actual press forming are not sufficient only by the mechanical properties (r value, El value, etc.) of the steel sheet that have been used conventionally, and the steel sheet surface roughness lubricating oil etc. has a great influence on the press formability. .

On the other hand, exterior steel sheets for automobile bodies, home appliances, etc. are painted to give a beautiful appearance. At this time, it is necessary to prevent the diffuse reflection of the coated surface from impairing the beautiful appearance. It is required to have excellent properties. As a conventional technique as described above, Japanese Patent Laid-Open No. 62-168
There is Japanese Patent No. 602, "Steel for coating and its manufacturing method".
The content is such that the center line average roughness Ra of the surface is 0.3 to 2.
A groove having a trapezoidal peak portion having a flat top surface and having a microscopic shape in the range of 0 μm and constituting the surface roughness thereof and surrounding the whole or a part thereof. -Shaped valley portion and an intermediate flat portion that is formed between the peak portions and outside the valley portion and higher than the bottom of the valley portion and lower than or at the same height as the crest surface of the valley portion. Moreover, the average center-to-center distance between adjacent peaks is Sm, the average diameter of the outer edges of the valleys is D, the average diameter of the flat peaks of the peaks is d ₀ , the flat peak of the peaks and the intermediate flat portion. When the ratio of the total area of the flat surfaces of No. 1 to the total area is defined as η (%), 0.
85 ≦ Sm ≦ 1.7, Sm−D <280 (μm), 30
The coating steel plate is configured to satisfy ≦ d ₀ ≦ 500 (μm) and 20 ≦ η ≦ 85 (%).

The profile of the surface of the roll and the steel sheet in the above-mentioned prior art is shown in FIGS. 6 and 7 (Japanese Patent Laid-Open No. 62-168602).
As shown in FIGS. 10 and 11 of the publication, it is as follows. D: Average outer diameter of the flange 2 on the roll surface = Average diameter of the outer edge of the valley 11 on the steel plate surface d: Average diameter of the crater 1 on the roll surface d ₀ : Average of the flat crest surface 8 of the ridge 10 on the steel plate surface Diameter H: Depth of the crater 1 on the roll surface h ₁ : Height of the flange 2 on the roll surface = Depth from the intermediate flat portion 9 of the steel plate surface to the bottom of the valley 11 h ₂ : The peak 10 of the steel plate surface Height of the flat crest surface 8 from the intermediate flat portion 9 Sm: Average center distance between adjacent craters 1 on roll surface = Average center distance between adjacent peak portions 10 on steel plate surface α: Width of flange 2 on roll surface η: Area of flat portion (sum of area occupancy η ₁ of flat crest surface 8 of mountain portion 10 and area ratio η ₂ of intermediate flat portion 9)

[0005]

For example, in the case of outer panels for automobiles, sufficient coating sharpness and press formability can be obtained by conventional techniques, but in inner panels for automobiles, press formability that is more severe than that of outer panels. Therefore, the conventional technique has a drawback that it cannot be applied to an automobile inner plate that requires severe press formability without deteriorating coating clarity. . 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.

In the prior art, the volume of the recess is as follows: u = (1/2) × (πα ² / with an annular (ring-shaped) cross section having a diameter of the flange 2 on the roll surface as the diameter per recess. 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 ⁸ × (D + d ₀ ) / (Sm / D) ² (4) Furthermore, D = d ₀ + 2α (from FIGS. 4 and 5), d ₀ = 3
0 to 500 μm, α = 20 to 40 μm (the above-mentioned publication page 1
Since column 19 line), V = (0.499 to 5.389) × 10 ⁶ / (Sm / D) ² (5) Table 1 shows Sm / D, flat part area η, and concave part volume per 1 mm ^2. V is a relationship with V, and the area η of the flat portion is shown in Tables 2a and 2b of the publication, and the volume V of the recessed portion per 1 mm ² is Sm / D; 0.85 to 1.5 in the equation (5). 75 is substituted.

[0007]

[Table 1]

In Table 1, the area η of the flat portion is 0.29 to 0.
87, the concave volume V per 1 mm ² was 0.163 to 7.
It becomes 459 × 10 ⁶ . For automobile inner plates that require severe press formability without deteriorating coating clarity, the volume V of recesses per 1 mm ² exceeds 7.5 × 10 ⁶ as compared with the prior art. However, it is required to include a large amount of press working lubricating oil that has a large volume of the concave portion that wets the concave portion.

[0009]

The present invention advantageously solves the problems of the prior art by: (1) Forming a plurality of minute recesses on the surface of a steel strip, and shaping the steel strip in the width direction. I has a diameter d of 50 to 200 μm, a recess depth h of 16 to 40 μm, and the total volume of recesses per 1 mm ^{2 of} the steel strip surface satisfies 8 × 10 ⁶ μm ³ or more, and the center distance between recesses adjacent to each other in the rolling direction. (p ₁₎ = 1.0d~2.0
d, inter-column center distance (p _c) in the rolling direction rows = 1.0D～
The shape II in the width direction of the steel strip has a diameter d of 50 to 200 μm, a recess depth h of 2 to 16 μm, and a total recess volume per 1 mm ^{2 of} the steel strip surface of 0.10 to ² ×. 10 ⁶
μm ³ , the area ratio of the flat part excluding the recesses on the surface of the steel sheet is 0.8 or more, and the center distance between recesses adjacent to each other in the rolling direction (p ₁ ) = 2.5d to 4.0d, between rows in the rolling direction row the center distance (p _c) = 2.5d~4.0d, distribution in the width direction of the steel band, paint image clarity and the press, characterized in that it is disposed between form I and form II alternately A steel strip with excellent formability.

(2) A plurality of concave portions are formed on the surface of the steel strip, and the shape I in the width direction of the steel strip has a diameter d of 50 to 20.
0 μm, recess depth h is 16 to 40 μm, steel strip surface is 1 mm
The total volume of recesses per ² satisfies 8 × 10 ⁶ μm ³ or more, and the center distance between recesses adjacent to each other in the rolling direction (p ₁ ) = 1.
0D～2.0D, inter-column center distance in the rolling direction columns (p _c) =
1.0d to 2.0d, and the shape II in the width direction of the steel strip
Has a diameter d of 50 to 200 μm and a recess depth h of 2 to 16
μm, the total volume of recesses per 1 mm ^{2 of} steel strip surface is 0.1
0 to 2 × 10 ⁶ μm ³ , the area ratio of the flat portion excluding the recesses of the steel strip surface of 0.8 or more, and the center distance between recesses adjacent to each other in the rolling direction (p ₁ ) = 2.5d to 4.0d , inter-column center distance of rolling direction columns (p _c) = a 2.5D～4.0D, characterized in the vertical direction relative to the width of the steel strip, it has provided the shape I and form II alternately A steel strip with excellent paint clarity and press formability.

Hereinafter, the present invention will be described 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 3 is irradiated with a laser to have a diameter of 50 to
A hole of 200 μm is formed. In a portion facing the shape I of the steel strip, 4 is a protrusion mainly composed of chromium protruding so that the height H is in the range of 16 to 40 μm from the roll surface attached on the hole 5, and center distance between the holes 5 adjacent to the (p ₁₎ = 1.0D~2.0D, to dispose the center distance (p _c) = 1.0D~2.0D spacing between the rows of rolling direction columns. In a portion facing the shape II of the steel strip, 4 is a protrusion mainly composed of chromium protruding so that the height H is in the range of 2 to 16 μm from the roll surface attached on the hole 5, Center distance between holes 5 adjacent to (p ₁ ) = 2.5D
4.0D, center distance between rows of rolling direction rows (p _c ) = 2.5
They are arranged at intervals of D to 4.0D.

If the height H of the protrusions 4 exceeds 40 μm, the protrusions 4 may fall off the roll surface during rolling or may be broken by the rolling load. Therefore, the lower the height of the protrusions 4, the better it is 40 μm or less. A degree 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 was 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. Figure 2
(A) and FIG. 2 (B) are sectional shapes of the rolls showing the second invention. Further, FIG. 2C shows a roll which is also used in the present invention. A pattern of shape I and shape II is attached in the circumferential direction of the roll. Similarly, FIG. 2D shows a roll used in the present invention, in which a plurality of patterns of shape I and shape II are provided in the circumferential direction of the roll.

FIG. 3 schematically shows a plan view of the surface of the steel sheet according to the present invention.
A recess of 0 μm is formed. In the shape I of the steel strip, the hole height h of the recess is a projection having a range of 16 to 40 μm, and the center distance (p ₁ ) between the holes 5 adjacent to each other in the rolling direction is 1.0 D to
2.0D, center distance between rolling rows (p ₂ ) = 1.0
It is arranged at intervals of D to 2.0D. In the shape II of the steel strip, the hole height h of the recess is a protrusion in the range of 2 to 16 μm, and the center distance between the holes 5 adjacent to each other in the rolling direction (p ₁ ) = 2.5D
4.0D, center distance between rows of rolling direction rows (p ₂ ) = 2.5
They are arranged at intervals of D to 4.0D. FIG. 4 is a view similar to FIG. 3 and schematically showing a plan view of the surface of a steel plate showing the second invention.

In a member such as an automobile inner 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, and slippage and elongation at rolling occur. This causes problems such as deterioration of material due to fluctuations, deterioration of steel plate quality and deterioration of pressability. The upper limit of the pitch in the shape II of the steel strip is 4.0D. On the other hand, if it is made too small, the waviness on the surface of the steel sheet will increase and the sharpness of the steel sheet after coating will deteriorate.
D, and the upper limit of the pitch in the shape I of the steel strip is 1.5D. If the pitch is less than 1.0D, the holes of the recesses overlap each other and the press formability is significantly deteriorated. Therefore, the lower limit of the pitch in the shape I of the steel strip is set to 1.0D. The upper limit of the steel plate recess depth is 40 μm from the height of the protrusion 4 described above,
If the depth of the recesses is less than 2 μm, the depth of the recesses on 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.

The shape of the recess of the steel plate is trapezoidal, in consideration of the oil sump effect at the time of pressing and the effect of lubricating the surface of the steel plate.
Also, a square-shaped object is conceivable, and the recess shape of the steel plate may be any shape. If this method is applied, it is not necessary to adopt a halfway roughness pattern as in the past, and a pattern with excellent sharpness is made at the center of the width, and pressability, that is, mold scuffing at the width end. A good pattern can be adopted, and the possibility of steel plate can be greatly expanded.

In determining the area ratio η of the flat portion according to the present invention, the shape I in the width direction of the steel strip is initially n = (1000 / p ₁ ) × (since the number of concave portions n per 1 mm ² is 1 mm = 1000 μm. 1000 / p ₂ ) (6) The area ratio η of the flat part is p because the concave part excludes the circular part with the diameter d.
When _{1 = p 2 = p, η} = 1- (πd 2/4) × n / (1000 × 1000) = 1- (π / 4) × (d / P) 2 (7) p = 1.0d Since it is ~ 2.0d, η = 0.215-0.804 (8).

The recess volume per one according to the invention When ^{u = (πd 2/4)} × h (9), the recess volume per 1 mm ² according to the present invention,
Since p ₁ = p ₂ = p and h = 16 to 40 μm, V = u × n = (π / 4) × (d / P) ² × h × 10 ⁶ = h × (1-η) × 10 ⁶ = (16-40) × (1−η) × 10 ⁶ (μm ³ / mm ² ) (10). Table 2 shows the relationship between the flat area ratio η and the recess volume V per 1 mm ^{2 in} the shape I in the width direction of the steel strip according to the present invention, using the equation (10).

[0018]

[Table 2]

The numbers in parentheses in Table 2 are for calculating the equation (10), and in the present invention, the lower limit of the concave volume V per 1 mm ² is 8.00 × 10 ⁶ (μm ³ / mm ² ). . In Table 2, the area ratio η of the flat portion is 0.215 to 0.840 and 1 mm.
The concave volume V per ² is 8.00 to 39.25 × 10 ⁶ . In the case of an automobile inner plate that requires severe press formability without deteriorating the coating clarity, if the recess volume V per 1 mm ² is less than 8.00 × 10 ⁶ , The lower limit of V is 8.00 × 10 ⁶ (μm ³ / mm ² ) because the surface of the steel sheet is frequently cracked after pressing because there is not enough lubricating oil for press working.

In determining the area ratio η of the flat portion according to the present invention, the shape II of the steel sheet is such that the number n of recesses per 1 mm ² is 1 mm = 1000 μm, so n = (1000 / p ₁ ) × (1000 / p ² (6) 'The area ratio η of the flat part is p because the concave part excludes the circular part having the diameter d.
When _{1 = p 2 = p, η} = 1- (πd 2/4) × n / (1000 × 1000) = 1- (π / 4) × (d / P) 2 (7) 'p = 2. Since it is 5d to 4.0d, (the lower limit of η is 0.
Therefore, η = 0.874 to 0.951 (8) ′.

The recess volume per one according to the invention When ^{u = (πd 2/4)} × h (9) ', the recess volume per 1 mm ² according to the present invention,
Since p ₁ = p ₂ = p and h = 2 to 16 μm, V = u × n = (π / 4) × (d / P) ² × h × 10 ⁶ = h × (1-η) × 10 ⁶ = (2/16) × (1−η) × 10 ⁶ (μm ³ / mm ² ) (10) ′. Table 3 shows the relationship between the flat area ratio η and the concave volume V per 1 mm ^{2 in} the shape II of the steel strip according to the present invention (1
0) 'is used to show.

[0022]

[Table 3]

In Table 3, 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 image clarity is required without deteriorating the press formability such as the outer panel for automobiles, the area ratio η of the flat portion is large with respect to the same concave portion volume V per 1 mm ^2. good. FIG. 8 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 3.

[0024]

EXAMPLE FIG. 5 is an illustration of a roll manufacturing method for manufacturing a steel sheet according to the present invention. According to the present invention, as shown in FIG.
m of resin 6 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 coating method, roll drawing method by non-rotating roll, electrodeposition coating method, roll coater by roll rotation, spraying by spraying, curtain coater, powder coating method, winding of film-like resin, etc. To evenly adhere to the roll surface and dry.

Next, as shown in FIG. 5B, the resin-coated roll 3 is processed by high-density energy, for example, a laser beam 12. That is, laser beam 1
Irradiation is performed from the surface of the resin 6 coated with 2 to dissolve and remove the resin in that portion. Hole recess 1 after resin is dissolved and removed
The three diameters can be adjusted by laser irradiation conditions, in particular, laser output and the gap between the condensing lens and the roll (focus shift). In the present invention, the hole diameter is 50 to 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, 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. .

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. 5 (C) shows the surface condition after chrome plating, in which the electrolytically plated curved chromium projection 15 is attached to the hole recess 13 formed by the resin 6 and the surface of the roll 3. Then
As shown in FIG. 5D, the roll having the chrome protrusions 15 removes the resin on the surface by immersing in a solvent in which the solvent is dissolved or by brushing with the solvent. And
As shown in FIG. 5D, the chromium protrusions 15 are exposed on the surface of the roll 3 from which the resin has been removed.

As a result, in general, an outer panel of an automobile or the like is subjected to a pressing method in the form of a solid line along the rolling method of the steel sheet 7 and the width direction as shown in FIGS. 9 and 10. The cross section of the pressed product is composed of a relatively flat central part (B) and end parts (A) and (C) which undergo large deformation during pressing, as shown in the lower part of FIG. 9 and FIG. At the product stage (A),
Part (C) is barely visible. On the other hand, part (B) is a part where the appearance is important, but the deformation during pressing is very small. Therefore, the press formability is 10 ~ width.
It was found that the portions (A) and (C) having a size of about 20 cm were dominated, and the image clarity was dominated by the portion (B).

Using the roll of the present invention, 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 a steel sheet shape pattern of steel strip shape I is displayed. 4 shows. Diameter d (μm), center distance between recesses p ₁ (μ
m), center distance between rows of rolling direction rows p ₂ (μm), depth h of concave portion (μm), area ratio η of flat portion, concave portion volume V per 1 mm ^{2 of} steel plate surface (× 10 ⁶ μm ³ / mm ² ). On the other hand, as an evaluation test of inner plates for automobiles, the presence or absence of cracks (pressing / workability) after working is investigated and the limit drawing ratio (L,
It was evaluated by D, R). These L, D and R are punch diameter 32
This is obtained by finding the maximum diameter of the blank that can be deep-drawn using a mm die, and by using the ratio between the maximum diameter of the blank and the punch diameter.
The steel sheet of the present invention is No. 1 to 9, the comparative example No.
It shows with 10-12. If the dent structure V per 1 mm ² is less than 8.00 × 10 ⁶ , the lubricating oil for press work that wets the dents may be used for those requiring severe press formability without deteriorating the coating clarity. Since it is not sufficient, cracks often occur on the surface of the steel sheet after pressing, so the lower limit of V is 8.0.
It becomes 0 × 10 ⁶ (μm ³ / mm ² ).

[0029]

[Table 4]

Table 5 shows a steel plate shape pattern in the shape II of the present invention. Diameter d (μm), center distance between recesses p ₁ (μ
m), center distance between rows of rolling direction rows p ₂ (μm), recess depth h (μm), flat area ratio η, recess volume V per 1 mm ^{2 of} steel plate surface (× 10 ⁶ μm ³ / mm ² ). On the other hand, as an evaluation test, a chemical conversion treatment with a phosphate is performed on each shape pattern of the steel sheet, and after the chemical conversion treatment, an undercoat, a cationic ED paint 18 to 20 μm thick, and an intermediate coating 30 to 35 μm.
Thickness, or topcoat, topcoat 30-35 μm
Two or three coats of thickness were applied. As an evaluation of the sharpness of the painted surface after painting, NS with a freshness meter
The I value was measured.

The results are shown in Table 5 together with the sharpness (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. In order to satisfy the coating image clarity without deteriorating the press moldability required for the outer panel for automobiles, the volume V of the concave portions per 1 mm ² of 8.00 × 10 ⁶ is sufficient, but may be more than this. Since the area ratio η of the anti-flat portion decreases, the above value is set as the upper limit. On the other hand, if the volume V of the concave portions per 1 mm ² is less than 8.00 × 10 ⁶ , the required press formability is deteriorated, and the lubricating oil for processing is insufficient, so cracks frequently occur on the surface of the steel sheet after pressing. The lower limit of V is 1.00 × 10 ⁶ (μm ³ / mm ² ).

[0032]

[Table 5]

FIG. 8 is a graph showing the relationship between the flat area ratio η 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. is there. All the steel sheets according to the prior art have a recess volume V of 8.
While it is less than 00 × 10 ⁶ , the shape I of the steel sheet according to the present invention has a recess volume V of 8.00 × 10 ⁶ or more, and the press formability is excellent. Shape of Steel Sheet According to the Invention II
Has a higher area ratio of the flat portion and superior image clarity as compared with the prior art.

[0034]

EFFECTS OF THE INVENTION According to the present invention, it becomes possible to manufacture a cold rolled steel sheet having both pressability and high image clarity after coating, as compared with the conventional laser steel sheet, and the press working characteristics of automobile steel sheet which could not be obtained conventionally. It is also good, and it is possible to solve quality problems such as cracks.

[Brief description of drawings]

FIG. 1 is a diagram showing a cross-sectional shape of a roll and a steel plate used in the present invention,

FIG. 2 is a diagram showing a cross-sectional shape of another roll and a steel plate used in the present invention,

FIG. 3 is a diagram schematically showing a plan view of a steel plate surface according to the present invention,

FIG. 4 is a diagram schematically showing a plan view of another steel plate surface according to the present invention,

FIG. 5 is a view showing a roll manufacturing process for manufacturing a steel sheet according to the present invention;

FIG. 6 is a view showing a profile of a roll and a steel plate surface according to the prior art;

FIG. 7 is a cross-sectional view of a roll and a surface of a steel plate according to the related art.

FIG. 8 is a diagram showing the relationship between the area ratio of a flat portion and the volume of a concave portion,

FIG. 9 is a diagram showing a state in which a steel sheet is subjected to pressing in a rolling direction and a width direction,

FIG. 10 is a diagram showing another state in which a steel sheet is pressed in the width direction and the rolling direction.

[Explanation of symbols]

 1 Roll surface crater 2 Roll surface flange 3 Roll 4 Protrusion 5 Hole 6 Resin 7 Steel plate 8 Flat crest surface 9 Intermediate flat part of steel plate surface 10 Crest part of steel plate surface 11 Valley part of steel plate surface 12 Laser beam 13 Hole recess 14 Chrome plating 15 Chrome protrusion

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shuichi Shiozawa 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Co., Ltd. Kimitsu Works (56) Reference JP-A-5-69006 (JP, A)

Claims (2)

(57) [Claims] 1. A microscopic plurality of recesses are provided on the surface of a steel strip,
The shape I in the width direction of the steel strip has a diameter d of 50 to 200 μm.
m, the recess depth h is 16 to 40 μm, the total recess volume per 1 mm ^{2 of} the steel strip surface satisfies 8 × 10 ⁶ μm ³ or more, and the center distance between adjacent recesses in the rolling direction (p ₁ ) is 1.0 d. ~
2.0d, inter-column center distance in the rolling direction columns (p _c) = 1.0
The shape II in the width direction of the steel strip has a diameter d of 50 to 200 μm, a recess depth h of 2 to 16 μm, and a total recess volume of 0.10 to 1 mm ^{2 of} the steel strip surface. 2x
10 ⁶ μm ³ , the area ratio of the flat portion excluding the concave portion on the surface of the steel sheet 0.
It satisfied 8 or more, inter-recess center distance adjacent to the rolling direction (p ₁₎ = 2.5d~4.0d, inter-column center distance (p _c) in the rolling direction column = the 2.5D～4.0D, A distribution of the steel strip in the width direction is a steel strip having excellent coating clarity and press formability, characterized in that the shape I and the shape II are alternately arranged. 2. The steel strip surface is provided with a plurality of minute recesses,
The shape I in the width direction of the steel strip has a diameter d of 50 to 200 μm.
m, the recess depth h is 16 to 40 μm, the total recess volume per 1 mm ^{2 of} the steel strip surface satisfies 8 × 10 ⁶ μm ³ or more, and the center distance between adjacent recesses in the rolling direction (p ₁ ) is 1.0 d. ~
2.0d, inter-column center distance in the rolling direction columns (p _c) = 1.0
The shape II in the width direction of the steel strip has a diameter d of 50 to 200 μm, a recess depth h of 2 to 16 μm, and a total recess volume of 0.10 to 1 mm ^{2 of} the steel strip surface. 2x
10 ⁶ μm ³ , the area ratio of the flat portion excluding the concave portion of the steel strip surface is 0.
It satisfied 8 or more, inter-recess center distance adjacent to the rolling direction (p ₁₎ = 2.5d~4.0d, inter-column center distance (p _c) in the rolling direction column = the 2.5D～4.0D, A steel strip excellent in coating clarity and press formability, characterized in that a shape I and a shape II are alternately arranged in a direction perpendicular to the width of the steel strip.