JPH0557310A - Steel plate being excellent in coating sharpness of image and press formability - Google Patents

Abstract

PURPOSE:To provide the steel plate for coating whose press formability is improved remarkably by controlling a steel plate surface roughness pattern. CONSTITUTION:This steel plate being excellent in coating sharpness of image and press formability is constituted so that plural minute recessed parts are provided on the surface of the steel plate, and as for a shape of the recessed part concerned, it is satisfied that the diameter (d) is 50-500mum, depth (h) of the recessed part is 16-40mum, and the total of the recessed part volume per 1mm<2> steel plate surface is >=8X10<6>mum<3>, a center distance between adjacent recessed parts in the rolling direction is (P1)=1.0d-2.0d, and an inter-line center distance of the rolling direction line is (P2)=1.0d-2.0d.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention aims to improve paint 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, 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 carried out 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. .. For this reason, as a current situation, in temper rolling to finally adjust the steel plate roughness, a work roll dull-processed by shot blasting, electric discharge, or laser etc. is used on the steel plate surface to transfer the roughness to the steel plate surface. ing. Also,
The evaluation criteria in 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. also 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 them an aesthetic appearance. At this time, the appearance is not impaired by the diffuse reflection of the coated surface, that is, the so-called sharpness is excellent. Is required.

As a conventional technique as described above, Japanese Patent Application Laid-Open No. 62-62
No. 168602 “Painting steel sheet and its manufacturing method”
There is. The content is that the center line average roughness Ra of the surface is 0.
Within the range of 3 to 2.0 μm, and the microscopic morphology that constitutes the surface roughness is such that it encloses a trapezoidal mountain portion having a flat mountain crest surface and all or part of its periphery. An intermediate flat formed between the formed groove-like valley and the peak and higher than the bottom of the valley and lower than or equal to the crest surface of the peak outside the valley. And the average center-to-center distance between adjacent peaks is Sm, the average diameter of the outer edge of the valley is D, the average diameter of the flat peak of the peak is d ₀ , and the flat peak of the peak is flat. When the ratio of the sum of the area of the flat surface of the intermediate flat portion to the total area is defined as η (%), 0.85 ≦ Sm ≦ 1.7, Sm−D <280 (μ
m), 30 ≦ d ₀ ≦ 500 (μm), 20 ≦ η ≦ 85
It is a steel plate for painting that is configured to satisfy (%).

The profile of the surface of the roll and the steel sheet in the above conventional description is 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 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 : 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 peak surface 8 of mountain portion 10 and area occupancy η ₂ of intermediate flat portion 9)

[0005]

For example, in the case of an outer panel for an automobile, the conventional technique can sufficiently obtain the image clarity and press formability. However, the inner panel for an automobile has a more severe press formability than the outer panel. 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 plate is generally good because the larger the volume of the recess on the surface of the steel plate, the more the wet oil for press working that wets the recess. As an annular recess volume semicircular cross section in which the width α of the flange 2 of the recesses one per roll surface to the diameter of the prior art (ring), u = (1/2) × (πα 2/4) × π (D + d ₀ ) / 2 (1) The width α of the flange 2 on the roll surface 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) Further, 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 portion, and concave portion volume V per 1 mm ^2. The area η of the flat portion is shown in Tables 2a and 2b of the 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.

[0006]

[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 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.

[0008]

DISCLOSURE 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 sheet, and the recesses have a diameter d of 50-50.
0 μm, recess depth h is 16 to 40 μm, steel plate surface 1 mm
The total volume of recesses per ² satisfies 8 × 10 ⁶ μm ³ or more, and the center distance between recesses adjacent in the rolling direction (P ₁ ) = 1.
0d to 2.0d, center distance between rows of rolling direction row (P ₂ ) =
It is a steel sheet excellent in coating image clarity and press formability, which is characterized by being 1.0d to 2.0d.

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 21 is irradiated with a laser to have a diameter of 50.
Form a hole of ˜500 μm. Numeral 27 is a protrusion having chromium as a main component and protruding so that the height H is in the range of 16 to 40 μm from the surface of the roll adhered onto the hole recess 26, and the center distance between the hole recesses 26 adjacent to each other in the rolling direction ( P ₁ )
= 1.0D to 2.0D, center distance between rows of rolling direction rows (P
c) = 1.0D to 2.0D. If the height H of the protrusions 27 exceeds 40 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.
It is preferably about 0 μm or less. However, when it is less than 16 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. 1B shows a sectional shape of the steel sheet according to the present invention which is 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 μm recess is formed. Hole recess 2 adjacent to the rolling direction
6 center distance (P ₁ ) = 1.0 d to 2.0 d, and center direction distance between rolling direction rows (P ₂ ) = 1.0 d to 2.0 d. For members such as automobile inner plates that are required to have both image clarity and pressability, if this pitch is made too large, the surface roughness of the steel sheet will decrease, and slippage during rolling and material variation due to elongation change will occur. This leads to problems such as deterioration of steel plate quality such as deterioration and 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 4 from the height of the protrusion 27 shown above.
0 μm, and if the steel plate recess depth becomes lower than 16 μm,
The depth of the recesses on 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. Note that the shape of the recess of the steel plate takes into consideration the oil sump effect at the time of pressing, the lubrication effect on the steel plate surface, etc.
A trapezoidal shape and a rectangular shape are also conceivable, and the shape of the steel plate recess may be 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 the same as the concave portion excluding the circular portion having the diameter d.
P₁= P₂= P, then η = 1- (πd²/ 4) × n / (1000 × 1000) = 1− (π / 4) × (d / P)² (7) Since P = 1.0d to 2.0d, η = 0.215 to 0.804 (8) The volume of each recess according to the present invention is u = (πd²/ 4) × h (9), 1 mm according to the present invention²The concave volume per hit is
P₁= P₂= P and h = 16 to 40 μm, V = u × n = (π / 4) × (d / P)²× h × 10⁶  = H * (1- [eta]) * 10⁶  = (16-40) 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 relationship with the concave volume V per hit is shown by using equation (10).
You

[0012]

[Table 2]

The numbers in parentheses in Table 2 are for the calculation of 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.

[0014]

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, as shown in FIG.
m resin 22 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. 3B, the resin-coated roll 21 is processed by high-density energy, for example, a laser beam 23. That is, the laser beam 23 is radiated from the surface of the resin 22 coated to dissolve and remove the resin in that portion. Hole recess 26 after the resin is dissolved and removed
The diameter can be adjusted by 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 set so that the hole diameter is in the range of 50 to 500 μm. Select. To perform laser processing on the roll surface described above, move the laser processing head while rotating the resin-coated roll,
Laser irradiation is performed at a processing frequency based on a preset pitch interval P and a roll rotation speed.

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. 3C shows the surface state after chrome plating, in which the electrolytically plated curved chromium projection 27 is attached to the hole recess 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
A chrome protrusion 27 is 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 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. 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 ) because the surface of the steel sheet is frequently cracked after the press working because there is not enough lubricating oil for press working. 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.
All the steel sheets according to the prior art have a recess volume V of 8.00 × 10.
^In contrast to less than ⁶ , all the steel sheets according to the present invention have a recess volume V of 8.00 × 10 ⁶ or more.

[0017]

[Table 3]

[0018]

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 the conventional laser steel sheet, and it is possible to press the inner plate for automobiles, which was not possible in the past. It has good processing characteristics and can solve quality problems such as cracks.

[Brief description of drawings]

1 shows a roll (A) for producing a steel sheet according to the present invention and 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 process drawing showing a method for manufacturing 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 view showing a steel plate surface according to the prior art;

FIG. 6 is an area ratio η of a flat portion of 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 Roller surface crawler 2 Roll surface flange 3 Roll 7 Steel plate 8 Crest surface 9 Intermediate flat part of steel plate surface 10 Crest part of steel plate surface 11 Valley part of steel plate surface 21 Roll according to the present invention -Rule 22 Resin 23 Laser beam 24 Steel sheet according to the present invention 25 Chrome plating 26 Hole recess 27 Protrusion

 ─────────────────────────────────────────────────── ─── 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 plurality of concave portions are provided on the surface of a steel plate,
The shape of the recesses is such that the diameter d is 50 to 500 μm, the recess depth h is 16 to 40 μm, and the total volume of the recesses per 1 mm ^{2 of} the steel plate surface is 8 × 10 ⁶ μm ³ or more, and between the recesses adjacent to each other in the rolling direction. Center distance (P ₁ ) = 1.0d to 2.0d, center distance between rolling direction rows (P ₂ ) = 1.0d to 2.0d
A steel sheet with excellent paint clarity and press formability.