JPH05269506A - Steel strip excellent in image clarity of coating and press formability - Google Patents

Abstract

PURPOSE:To remarkably improve image clarity of coating and press formability by controlling the pattern of surface roughness of a steel strip. CONSTITUTION:Plural microscopic recessed parts are provided on the surface of the steel strip and the shape of the end part in the breadthwise direction of that steel strip satisfies that the diameter (d) is 50 to 200mum, the depth (h) of recessed part is 16 to 40mum and the total of the volume of recessed part per mm<2> of the surface of the steel strip is >=8X10<6>mum<3> and the center distance p1 between adjacent recessed parts in the rolling direction is taken as 1.0d to 2.0d and the center distance pc between lines of the lines in the rolling direction as 1.0d to 2.0d. The shape in the middle part in the breadthwise direction of that steel strip satisfies that the diameter (d) is 50 to 200mum, the depth (h) of recessed part is 16 to 40mum and the total of the volume of the recessed part per mm<2> on the surface of the steel strip is 1 to 8X10<6>mum<3> and the area rate of the flat part except the recessed parts on the surface of the steel strip is >=0.6 and the center distance p1 between adjacent recessed parts in the rolling direction is taken as 1.5d to 4.0d and the center distance between lines of the lines in the rolling direction as 1.5d to 4.0d.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention aims to improve coating sharpness and press formability by regulating a steel plate surface roughness pattern. 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, a cold-rolled steel sheet for working has a dull finish on its surface in order to facilitate press working. That is, during press working, the lubricating oil for working is stored in the unevenness formed on the surface of the steel sheet, which has the function of reducing friction between the die 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 plates are becoming more sophisticated and diversified. .. Therefore, as a current situation, in temper rolling to finally adjust the steel plate roughness, a work roll that has been dull-processed by shot plast, electric discharge, or laser on the steel plate surface is used to transfer the roughness to the steel plate surface. ing. Also,
The evaluation standard in actual press forming is not sufficient only by the mechanical properties (r value, El value, etc.) of the steel sheet that have been conventionally used, and the steel plate surface roughness lubricating oil etc. also has a great influence on the press formability. ..

On the other hand, exterior steel sheets for automobile bodies, home appliances, etc. are coated with a finish to give them an aesthetic appearance. At this time, it is necessary not to spoil the aesthetic appearance due to irregular reflection of the coated surface. It is required to have excellent properties. As a conventional technique as described above, Japanese Patent Application 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 trapezoidal peak portion having a flat top surface and a groove formed so as to surround the whole or a part of the circumference in a range of 0 μm and which constitutes the surface roughness -Shaped valley portion and an intermediate flat portion formed between the mountain portion and outside the valley portion, the height being higher than the bottom of the valley portion and lower than or equal to the crest surface of the mountain 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 sheet is configured to satisfy ≦ d ₀ ≦ 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).
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 mountain portion 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 : Of the mountain portion 10 of the steel plate surface Height of the flat crest surface 8 from the intermediate flat portion 9 Sm: Average center-to-center distance between adjacent craters 1 on the roll surface = Average center-to-center distance between adjacent mountain portions 10 on the steel plate surface α: Of the flange 2 on the roll surface Width η: Area of flat portion (sum of area occupancy η ₁ of flat crest surface 8 of mountain portion 10 and area occupancy η ₂ of intermediate flat portion 9)

[0005]

For example, in the case of outer panels for automobiles, the conventional technique can sufficiently obtain the coating clarity and press formability. However, the inner panels for automobiles have more severe press formability than outer panels. Therefore, the conventional technique has a drawback that it cannot be applied to automobile inner plates that require 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 concave portion is represented by 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 surface of the roll is the above-mentioned publication page 6 column 4 column 17
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 μm, α = 20 to 40 μm (the above publication, page 8, column 1, column 1)
Since 9 rows), V = (0.499 to 5.389) × 10 ⁶ / (Sm / D) ² (5) Table 1 shows Sm / D, area η of flat part, and concave part volume V per 1 mm ^2. The area η of the flat portion is shown in Tables 2a and 2b of the above publication, and the volume V of the concave portion per 1 mm ² is Sm / D; 0.85 to 1.75 in the above equation (5). Is substituted.

[0007]

[Table 1]

In Table 1, the area of the flat portion is such that η 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 . For automobile inner plates that require severe press formability without deteriorating the 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 lubricating oil for press working that has a large volume of the concave portion that wets the concave portion.

[0009]

SUMMARY OF THE INVENTION The present invention advantageously solves the problems of the prior art in which minute and plural recesses are provided on the surface of a steel strip, and the shape of the end portion in the width direction of the steel strip is , The diameter d is 50 to 200 μm, the recess depth h is 16 to 40 μm,
The total concave volume per 1 mm ^{2 of} steel strip surface is 8 × 10 ⁶ μm
³ or more are satisfied, and the center distance between concave portions adjacent to each other in the rolling direction (p ₁ ) = 1.0 d to 2.0 d, the center distance between rows of rolling direction rows (pc) = 1.0 _{d to} 2.0 _d , The shape of the central portion in the width direction of the steel strip has a diameter d of 50 to 200 μm, a recess depth h of 16 to 40 μm, a total recess volume per 1 mm ^{2 of} the steel plate surface of 1 to 8 × 10 ⁶ μm ³ , and a steel strip. Satisfying the area ratio of 0.6 or more in the flat portion excluding the concave portions on the surface, the center distance between concave portions adjacent in the rolling direction (p ₁ ) = 1.5 d to 4.0 d, the center distance between rows in the rolling direction row (p _c ) = 1.5d to 4.0d
It is a steel strip with excellent paint clarity and press formability.

The present invention will be described below with reference to the drawings.
FIG. 1A shows 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-
A hole of 200 μm is formed. A portion 4 is opposed to the end of the steel strip, and 4 has a height H of 1 from the surface of the roll adhered on the hole 5.
It is a projection containing chromium as a main component and protruding so as to be in the range of 6 to 40 μm, and the center distance between holes 2 adjacent to each other in the rolling direction (p ₁ ) = 1.0 D to 2.0 D, between rows in the rolling direction row. to dispose at center distance (p _c) = 1.0D~2.0D intervals.
In a portion facing the central portion of the steel strip, 4 is a protrusion containing chromium as a main component, which is protruded so that the height H is in the range of 16 to 40 μm from the surface of the roll attached to the hole 5, and Center distance between holes 2 adjacent to (p ₁ ) = 1.5D
4.0D, center distance between rows of rolling direction rows (p _c ) = 1.5
It is 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 from the roll surface during rolling, causing breakage due to rolling load. Therefore, the lower the height of the protrusions 4, the better it is about 40 μm or less. Is preferred. But 16
If it is less than μm, the depth of the recesses transferred to the surface of the steel sheet is small and the roughness is also small, 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 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 schematically shows a plan view of the surface of the steel sheet according to the present invention.
A recess of 0 μm is formed. At the end of the steel strip, the hole height h of the recess is a protrusion in the range of 16 to 40 μm, and the center distance (P ₁ ) between the holes 2 adjacent to each other in the rolling direction is 1.0 D to
2.0D, rolling center row-to-row center distance (P ₂ ) = 1.0
It is arranged at intervals of D to 2.0D. In the central part of the steel strip, there is a projection in which the hole height h of the recess is in the range of 16 to 40 μm,
Center distance between holes 2 adjacent in the rolling direction (P ₁ ) = 1.5D
˜4.0 D, center distance between rows of rolling direction rows (P ₂ ) = 1.
It is arranged at intervals of 5D to 4.0D.

In a member such as an inner plate for automobiles, which is required to have both functions of image clarity and pressability, if the pitch is too large, the surface roughness of the steel sheet 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 at the center 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 image clarity after coating will deteriorate. Therefore, the lower limit of the pitch at the center of the steel strip is 1.
The upper limit of the pitch at the end of the steel strip is 1.5D. If the pitch is less than 1.0D, the holes of the recesses are overlapped with each other and the press formability is significantly deteriorated. Therefore, the lower limit of the pitch at the end of the steel strip is set to 1.0D. The upper limit of the depth of the recess of the steel plate is 40 μm from the height of the projection 4 described above, and when the depth of the recess is lower than 16 μm, the depth of the recess on the surface of the steel plate is low and the roughness is small, and the object of the present invention cannot be achieved. ..

The shape of the recess of the steel plate is trapezoidal when considering the oil sump effect during pressing and the effect of lubrication on the surface of the steel plate.
Also, a square-shaped object may be considered, and the recess shape of the steel plate may be any shape. If this method is applied, it is not necessary to adopt a midway rough roughness pattern as in the past, and the center of the width has a pattern with excellent sharpness and the width end has a press property, that is, a mold gallability. A good pattern can be adopted, and the possibility of steel plate can be greatly expanded. That is, the thin steel sheet of the present invention is a steel sheet in which the roughness pattern on the surface of the steel sheet differs in the width direction at the end portion and the central portion.

In determining the area η of the flat portion according to the present invention, the number n of concave portions per 1 mm ² at the end portion in the width direction of the steel strip is 1 mm = 1000 μm, so n = (1000 / P ₁ ) × (1000 / P ₂ ) (6) The area ratio η of the flat portion is P because the concave portion excludes the circular portion 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 = 1.0d Since it is ~ 2.0d, η = 0.215 to 0.804 (8).

The recess volume per one according to the invention is u = When ^{(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) × It becomes 10 < ⁶ > = (16-40) * (1- (eta)) * 10 < ⁶ > (micrometer < ³ > / mm < ² >) (10). Table 2 shows the relationship between the flat area ratio η at the widthwise end of the steel strip according to the present invention and the recess volume V per 1 mm ² using the equation (10).

[0017]

[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 volume V of the concave portion per 1 mm ² is less than 8.00 × 10 ⁶ , the concave portion is The lower limit of V is 8.00 × 10 ⁶ (μm ³ / mm ² ), since the surface of the steel sheet is frequently cracked after the press working because there is not enough lubricating oil for press working to wet it.

In determining the flat area ratio η according to the present invention, first, the number n of recesses per 1 mm ² is 1 m.
Since m = 1000 μm, 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 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. Since it is 5d to 4.0d, (the lower limit of η is 0.
Therefore, η = 0.651 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 = 16 to 40 μm, V = u × n = (π / 4) × (d / P) ² × h × 10 ⁶ = h × (1-η) × 10 ⁶ = ( ^{16 to} 40) × (1−η) × 10 ⁶ (μm ³ / mm ² ) (10) ′. Table 3 shows the relationship between the flat area ratio η at the widthwise center of the steel strip according to the present invention and the recess volume V per 1 mm ² by using the equation (10) ′. (The upper limit of the concave volume V is 8.
00 × 10 ⁶ )

[0021]

[Table 3]

In Table 3, the area ratio η of the flat portion is 0.215 to
At 0.840, the volume V of recesses per 1 mm ² is 8.00
It becomes 39.25 × 10 ⁶ (μm ^{3 to} mm ² ). In the case of automobile outer panels that require improved coating clarity without deteriorating press formability, those having a large flat area ratio η 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. The numerical value in the parentheses is the lower limit of the concave volume V per 1 mm ^{2 of} 1 × 10 ⁶ (μm
³ / mm ² ).

[0023]

EXAMPLE FIG. 3 is an explanatory view of a roll manufacturing method for manufacturing a steel sheet according to the present invention. According to the present invention, first, as shown in FIG.
m resin 6 is coated. The resin to be coated has properties such as alkali resistance, chromic acid resistance, and insulation properties, and is preferably an alkali resin or a plating sealing resin so that it can be easily removed in a later step, and the roll surface has a thickness of 16 to 50 μm. 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. 3 (B), the resin-coated roll 3 has a high density energy, for example, a laser beam 12.
Processed by. That is, the surface of the resin 6 coated with the laser beam 12 is irradiated to dissolve and remove the resin in that portion. The diameter of the hole recess 13 after the resin is dissolved and removed is
It can be adjusted by the laser irradiation conditions, particularly the laser output and the gap between the condensing lens and the roll (focus shift). In the present invention, the laser irradiation conditions are selected so that the hole diameter is in the range of 50 to 500 μm. 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. ..

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 chrome, and is plated only on the hole portion with a thickness approximately equal to or less than the thickness of the resin depending on the set plating conditions. .. FIG. 3 (C) shows the surface state after chrome plating, in which the electroplated curved chrome projections 15 are attached to the hole recesses 13 formed by the resin 6 and the surface of the roll 3. Then
As shown in FIG. 3D, the roll having the chromium projections 15 is immersed in a solvent in which the solvent is dissolved or brushed with the solvent to remove the resin on the surface. And
As shown in FIG. 3D, the chromium protrusions 15 are exposed on the surface of the roll 3 from which the resin has been removed.

First, the inventors examined in detail the pressing method of the automobile outer panel. As a result, generally, an outer plate such as a door is blanked (punched) along the steel plate 7 in the shape of a dotted line 16 and then pressed in the shape of a solid line 17 as shown in FIG. 7A. 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 FIG. 7B. The parts (A) and (C) are barely visible in the product stage. On the other hand, part (B) is a part where the appearance is important, but the deformation during pressing is very small. Therefore, it was found that the press formability was dominated by the (A) and (C) parts having a width of about 10 to 20 cm, and the sharpness was dominated by the (B) part.

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 the steel sheet shape pattern at the widthwise end of the steel strip is obtained. Is shown in Table 4. 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 for automobile inner plates, the presence or absence of cracks (pressing / workability) is investigated after processing and the limit drawing ratio (L,
It was evaluated by D, R). These L, D and R are punch diameter 32
The maximum raw plate diameter that can be deep-drawn using a mm die is obtained, and the maximum raw plate diameter is determined from the ratio of the punch diameter.
The steel sheet of the present invention is No. Nos. 1 to 9 and Comparative Example No.
It shows with 10-12. If the volume V of recesses per 1 mm ² is less than 8.00 × 10 ⁶ , a lubricating oil for press working that wets the recesses 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 ).

[0027]

[Table 4]

Steel plate shape pattern in the central portion of the steel strip of the present invention
Is shown in Table 3. Diameter d (μm), center distance between recesses P
₁(Μm), center distance P between rows in rolling direction₂(Μm), concave
Part depth h (μm), flat area ratio η, steel plate surface 1 mm
²Contact concave volume V (× 10⁶μm ³/ Mm²),
As an evaluation test, phosphorus is applied to each shape pattern of the steel sheet.
After chemical conversion treatment with acid salt, after chemical conversion treatment, undercoat, click
On-ED coating 18 to 20 μm thick, intermediate coating 30 to 35 μ
m thickness or topcoat, topcoat 30-35μ
2 or 3 coats of m thickness were applied. That
N as measured by a freshness meter as a sharpness evaluation of the painted surface after painting
The SI value was measured.

The results are shown in Table 5 together with the image clarity (NSI value) and the press workability. The steel plate of the present invention is No. Nos. 1 to 9 and Comparative Example No. It shows with 10-12. It is sufficient that the volume V of the concave portions per 1 mm ² is 8.00 × 10 ⁶ in order to satisfy the coating image clarity without deteriorating the press moldability required for the outer panel for automobiles, etc. Good, but conversely the area ratio η of flatness decreases, so
The above value was set as the upper limit. On the other hand, when the concave volume V per 1 mm ² is less than 8.00 × 10 ⁶ , the press formability required for outer panels for automobiles is deteriorated and the lubricating oil for working is insufficient, so that the surface of the steel sheet is pressed after the press working. Since cracks often occur, the lower limit of V is 1.00 × 10 ⁶ (μm ³ / mm ² ).
Becomes

[0030]

[Table 5]

FIG. 6 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 concave 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 8.0.
While it is less than 0 × 10 ⁶ , the width direction end portion of the steel sheet according to the present invention has a recess volume V of 8.00 × 10 ⁶ or more,
Excellent press formability. In the central portion of the steel sheet according to the present invention, the area ratio of the flat portion is higher than that of the prior art and the image clarity is excellent.

[0032]

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 painting, as compared with conventional laser steel sheets, and press working of automobile steel sheets that could not be done conventionally. The characteristics are good and it is possible to solve quality problems such as cracks.

[Brief description of drawings]

FIG. 1 is a view showing a sectional shape of a roll and a steel plate used in the present invention.

FIG. 2 is a diagram schematically showing a plan view of a steel plate surface according to the present invention.

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

FIG. 4 is a view showing a profile of a roll and a surface of a steel plate according to a conventional technique.

FIG. 5 is a cross-sectional view of a roll and a steel plate surface according to a conventional technique.

FIG. 6 is a diagram showing the relationship between the area ratio of a flat portion and the volume of a recess.

FIG. 7 is a diagram showing an automobile outer plate.

[Explanation of symbols]

 1 Roll surface crater 2 Roll surface flange 3 Roll 4 Projection 5 Hole 6 Resin 7 Steel plate 8 Flat crest surface 9 Intermediate flat part of steel plate surface 10 Steel plate surface mountain part 11 Steel plate surface trough 12 Laser beam 13 Hole recess 14 Chrome plating 15 Chrome protrusion 16 Dotted line 17 Solid line

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shuichi Shiozawa 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corporation Stock of Kimitsu Works

Claims (1)

[Claims] 1. A microscopic plurality of recesses are provided on the surface of a steel strip,
The shape of the end portion in the width direction of the steel strip has a diameter d of 50 to 200.
μm, recess depth h is 16 to 40 μm, steel strip surface is 1 mm ²
The total volume of the concave portions per contact satisfies 8 × 10 ⁶ μm ³ or more,
Center distance between concave portions adjacent to each other in the rolling direction (p ₁ ) = 1.0 d
～2.0D, inter-column center distance in the rolling direction columns (p _c) = 1.
0d to 2.0d, the shape of the central portion in the width direction of the steel strip has a diameter d of 50 to 200 μm and a recess depth h of 16 to 4
0 μm, the total volume of recesses per 1 mm ^{2 of} steel plate surface is 1 to
8 × 10 ⁶ μm ³ , the area ratio of the flat part excluding the recesses on the steel strip surface of 0.6 or more, and the center distance between recesses adjacent to each other in the rolling direction (p ₁ ) = 1.5d to 4.0d, rolling inter-row center distance direction columns (p _c) = coating, characterized in that it has a 1.5d~4.0d DOI and press formability superior steel strip.