JPH06246306A - Steel plate with excellent painting distinctness of image and pressing workability - Google Patents

Abstract

(57) [Abstract] [Purpose] The present invention provides a steel sheet having excellent paint clarity even after press working. [Structure] On both front and back surfaces of a steel sheet, the sizes of scattered convex top surfaces are 10 to 1000 μm, and the convex peak distance is 50.
˜2200 μm, the roughness Ra of the recesses is 0.8 μm or less, the protrusions are dispersed and dispersed so that the average area ratio of the recesses is 70% or more, and the heights of the protrusion vertices scattered on one side of the steel plate are 2 or more.
In the range of up to 12 μm, and the height of the convex portion on the other surface side is 3 to 20.
A steel plate with excellent paint clarity and press workability, which is characterized by making it higher than one side in the range of μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to steel sheets which are used for outer panels of automobiles and home electric appliances and have excellent image clarity and press workability. Here, the steel sheet means a plate-shaped product to be used after coating, and for example, hot rolled steel sheet, cold rolled steel sheet, surface treated steel sheet (electroplated steel sheet, hot dip plated steel sheet, alloying hot dip plated steel sheet, vapor deposition plating Steel plate, molten salt electrolytic plating steel plate, etc.), for example, stainless steel plate,
It also includes aluminum plates and copper plates.

[0002]

2. Description of the Related Art Generally, steel sheets used for automobile bodies and outer panels of home electric appliances are used as products by press forming. However, as the precision and complexity of products increase, the demand for steel sheets has increased. Are becoming more sophisticated and diversified than ever before, and in particular, recently, demands for coating image clarity and press formability are increasing. For example, in order to improve the image clarity of the product itself, it can be surely improved by increasing the coating film thickness, but there is a problem that the coating cost becomes high. At present, three or four coatings are applied to ensure the clarity of the coating, but it is strongly desired to omit the number of coatings to two or three in order to save the process and reduce the coating cost. There is. In order to meet such demands, for example, Japanese Patent Laid-Open No. 63-1327.
As described in No. 01 publication, fine irregularities are provided on a rolling roll by using a laser, and steel plates are rolled using the rolling roll.
It is known to obtain a steel plate having excellent paint clarity.

[0003]

In order to improve the coating clarity, it is advantageous that the surface of the steel sheet is flat and close to a mirror surface. Therefore, various proposals have been made in the direction of making the surface finer. However, if it is simply mirror-finished, flaws are likely to become apparent in the heat treatment process and the plating process in the manufacturing process of steel sheets, and surface flaws occur during piling and press working after cutting of steel sheets, resulting in surface defects and various measures. Is proposed. By the way, when manufacturing a product, press working is a prerequisite, but in this case, a grindstone may be hung to improve the surface appearance after working, which causes a problem that the whetstone hanging pattern is raised after coating. Further, since the steel plate roughness changes due to press working, there is a problem that the sharpness deteriorates as the working degree becomes severe. Therefore, there is a strong demand for a steel sheet that can maintain good paint clarity even after processing.

Further, recently, since parts having a complicated shape are pressed, it is desired that the slidability during molding be good. Especially for surface-treated steel sheets such as galvanized steel sheets and alloyed hot-dip galvanized steel sheets, the die and the plating layer tend to adhere to each other under high surface pressure, and the friction resistance increases. Has a narrow problem. The present invention, in order to accurately meet the quality problems required for the above-described clear-cut steel sheet, is a steel sheet that improves sliding characteristics during press forming and can secure good clearness even after press working. Is to provide.

[0005]

SUMMARY OF THE INVENTION According to the present invention, the sizes of scattered convex top surfaces on both front and back surfaces of a steel sheet are 10 to 100.
0 μm, the peak-to-peak distance between the peaks is 50 to 2200 μm, the recess area ratio is 70% or more, and the roughness of the recess is Ra 0.8 μm or less. Is in the range of 2 to 12 μm, and the height of the convex portion on the other surface side is higher than that of the one surface side in the range of 3 to 20 μm. It is provided. That is, the present invention is characterized by imparting different roughness profiles on the front and back sides to improve the slidability at the time of press molding and at the same time ensure good paint clarity even after press molding. .

The morphology of the roughness profile of the present invention will now be described in detail. We investigated various conditions of roughness profile to maintain good paint clarity before and after processing and significantly improve press formability. It has been found that it is important to surely improve the roughness profile which is composed of the flat concave portions to be occupied and the minute convex portions scattered in a discrete manner, and it is possible to surely improve it. If it is not processed, there is no problem, but if it is processed, there is a problem that the conventional art deteriorates the paint clarity. In order to ensure good paint clarity even after press working, the height of the convex portion on the other side, which is the inner surface side during press forming, on the front and back sides of the steel sheet should be higher than the height of the convex portion on the one surface side that is the outer surface. I found that I can improve it.
More recently, since severe press formability is required, further improvement in formability has been desired, and the present invention has been reached by analyzing the optimum structure of the steel sheet surface that improves both of these.

Next, the main points of the present invention will be described in order. The paint clarity is related to the roughness and area ratio of the recesses in the steel sheet. Therefore, it is desirable that the roughness of the concave portion be as flat as possible and close to a mirror surface, but Ra is 0.8 μm for industrially advantageous production.
If it is m or less, the clearness of the coating can be sufficiently secured, which is satisfactory. Further, the higher the area ratio of the recesses, the more advantageous it is in improving the image clarity of the coating, but it is desirable to secure the area ratio of the recesses in the range of 70 to 96%. If the area ratio of the recesses is less than 70%, it is difficult to secure the image clarity even if the roughness of the recesses is improved. On the other hand, if it is more than 96%, the sharpness is good, but the scratch resistance and the slidability during pressing are deteriorated, which is not preferable. On the other hand, the coated image clarity after processing deteriorates if it is smaller than 70% or larger than 96%, so the above range is optimal.

On the other hand, regarding the form of the convex portion, the size of the convex top portion is 10 to 1000 μmφ, the height of the convex portion on one side of the steel plate that is the outer surface of the molded part is 2 to 12 μm, and the steel plate that is the inner surface of the molded part, etc. It is necessary that the height of the convex portion on the surface side is higher than that on the single surface side in the range of 3 to 20 μm or less. Naturally, it is desirable that the convex portions are discretely distributed in the area ratio of 30 to 4%. When the size of the top surface of the convex portion is smaller than 10 μm, the surface pressure of the die cannot be resisted during the press working and the surface is crushed, so that there is no effect of providing the convex portion, which is not preferable.
On the other hand, if it is larger than 1000 μm, the contact area ratio with the die during press working is increased, so that the slidability is deteriorated and the coating clarity is deteriorated, which is not preferable.

By the way, the height of the convex portion on one side of the steel plate is set to 2 to 12
The reason for setting the μm range is that the outer surface side of the pressed product attaches a minimum amount of protrusions to the extent that scratch resistance can be ensured because the paint clarity is important. That is, if it is less than 2 μm, the scratch resistance is deteriorated, so that the surface of the steel sheet is flawed in the manufacturing process of the steel sheet, and roll flaws and scratches are generated in the steel sheet transporting step, and these defects emerge after coating, which is preferable. Absent. On the contrary, even if it is larger than 12 μm, not only these improving effects are not observed, but also when the coating film thickness is not sufficient, the convex portions are raised after coating, which is not preferable.

On the other hand, the reason why the height of the convex portion on the other surface side of the steel plate, which is the inner surface side of the molded part, is set higher than that on the one surface side in the range of 3 to 20 μm will be described. On the other side of the steel sheet, the paint clarity is not a problem, but rather is important for securing the slidability during forming and suppressing the deterioration of the clarity due to the change in roughness after pressing. That is, during press forming, the bead portion and the wrinkle holding portion are subjected to processing accompanied by sliding under high surface pressure, so that the friction resistance between the die and the steel plate surface increases, slidability deteriorates, and In this case, there is a problem that the plating layer may peel off. In order to avoid this problem, it is important to reduce the microscopic contact surface area ratio between the die and the steel plate surface, and in order to ensure slidability under high pressure, the steel plate has a convex area ratio of 30 to 30%. It is desirable to secure the height in the range of 4% and set the height of the convex portion to 3 μm or more and 20 μm or less.

That is, if the area ratio of the convex portions exceeds 30%, the area ratio of contact with the die increases, and the effect of reducing the frictional resistance is lost. On the other hand, if it is less than 4%, the surface pressure cannot be withstood at high pressure, and the material is crushed and loses its effect.
Further, if the height of the convex portion is less than 3 μm, the effect of reducing the frictional resistance is lost, which is not preferable, and even if it is higher than 20 μm, the effect of reducing the frictional resistance is saturated and the coating clarity may be deteriorated. Not preferable.

Next, the reason why the height of the convex portion on the other surface side is made higher than that on the one surface will be described. As a result of various studies on the reason why the coating sharpness deteriorates after the press working, it was found that the undulation component of the roughness of the other surface floats on the one surface side due to the reduction of the punch during the press working. As a result of studying this preventive measure, it was found that by making the height of the convex portion on the other surface side higher than the height of the convex portion on the one surface side, good paint clarity on the one surface side can be maintained even after processing. At the same time, as a result, the frictional resistance at the time of high surface pressure sliding is maintained at a low level, which is desirable.

It is usual that the steel sheet is subjected to various rolling such as hot rolling, cold rolling and temper rolling to control the sheet thickness, the material and the shape. Therefore, since the roughness profiles of various rolls are transferred to the surface of the steel sheet, there are waviness components having various wavelengths of roughness. There are various industrial difficulties in removing this undulation component, and there is a problem that it cannot be improved by a cost-effective method.

The reason why the image clarity is deteriorated by pressing is that
This is because the roughness of the back surface is transferred to the opposite surface during molding. That is, when pressed under a high pressure from the other surface side by a punch having a smooth surface, the waviness component on the other surface side is extruded to the one surface side, and the waviness component of the roughness on the one surface side increases, The paint clarity will deteriorate. As a result of various studies on a solution to this problem, we found that it can be avoided by increasing the height of the convex portion on the other surface contacting the punch. At the same time, this convex portion has the effect of reducing the microscopic true contact area ratio with the punch or die, reducing the frictional resistance under high surface pressure, improving the slidability during press molding, and improving the moldability range. Has the advantage of expanding.

As described above, in order to suppress the transfer of the roughness waviness component from the other surface side, in addition to the height of the convex portion, the arrangement interval thereof is also important. Generally, the protrusions may be arranged at intervals such that the area ratio of the protrusions is 30 to 4%, but 50 to 2200 μm.
An interval in the range of is preferred. If it is less than 50 μm, the interval between the convex portions is too small, so that the effect of suppressing the transfer of the waviness component is reduced. On the other hand, if it is larger than 2200 μm, the molding load that one convex portion bears becomes excessive, so that the height is 3 to 20 μm.
If the height of the convex portion is in the range of m, it is easily crushed and has no effect.

In order to avoid this problem, it is conceivable to increase the area ratio of the convex portion or increase the size of the top surface of the convex portion, but in either case, the sliding resistance is increased or the transfer of waviness is prevented. It is not effective because it is ineffective or, on the contrary, deteriorates. As described above, in the present invention, it is possible to prevent the waviness component on the other surface side from being transferred to the one surface side during press molding, and to maintain good coating clarity on the one surface side.
At the same time, the purpose is to reduce the frictional sliding resistance during press forming, and as a result of the basic examination of various roughness profiles, the present invention has been achieved.

As described above, the press formability of the steel sheet is remarkably improved by arranging the convex portions having different heights on the front and back sides of the steel sheet discretely and optimally in consideration of the size, height, arrangement interval, and area ratio. It is a feature of the present invention that the effect of transferring waviness to one surface due to the processing of the other surface of the steel sheet before and after processing can be reduced and excellent coating sharpness can be secured.

In order to obtain the steel sheet of the present invention, it is advantageous to obtain a fine concavo-convex pattern on a rolling roll by using, for example, a microlithography method, and to roll the steel sheet using the rolling roll. As shown in FIG. 1, the method is as follows. The roll surface coated with a resist material that is sensitive to a specific wavelength is irradiated with light of a specific wavelength to expose it, and after development, the roll surface is etched by chemical etching or vapor phase etching. ,
By removing the cured resist portion, a fine uneven pattern is provided. FIG. 3 shows a schematic sectional view of the steel sheet thus obtained. In the figure, P is the peak-to-peak distance, D is the size of the peak of the protrusion, and t is the height of the protrusion.

[0019]

EXAMPLE As shown in FIG. 1, a temper rolling roll (finishing roughness Ra: 2.4 μm) was provided with a fine concavo-convex pattern by a microlithography method. Using the work roll, the alloyed hot-dip galvanized steel sheet (sheet thickness 0.8 mm) produced by a normal continuous hot-dip galvanizing line was temper-rolled at a rolling reduction of 1.0%. The obtained steel sheets were compared and investigated before and after processing in terms of coating clarity and sliding resistance. In addition,
The Ra of the recesses of the steel sheet thus manufactured is about 0.5 in all cases.
It was in the range of 5 to 0.70 μm. The size (D) of the top surface of the convex portion of the steel plate surface, the area ratio of the concave portions and the interval (P) of the convex portions are photographed by an optical microscope, quantitatively evaluated by an image analyzer, and the average value is calculated. I asked. Further, the height of the convex portion was obtained by averaging the peak heights corresponding to the convex portions of the steel plate from the cross-sectional profile curve measured by a stylus roughness meter. The height of the convex portion was determined by the height difference from the average height of the peak portion of the profile curve of the concave portion around the convex portion to the peak position of the convex portion.

As a method for testing the paint clarity, the steel sheet after temper rolling is coated with a film thickness of about 80 μm and then subjected to JI.
The coating clarity was evaluated by the "specular gloss measurement method" of S-Z8741. As a friction slidability evaluation test method, a square bead test apparatus for L-shaped tension shown in FIG. 2 was used, and the relationship between the pressing load and the tensile load was determined by a tensile tester. Here, the pressing load (Pc), which is the limit of plate breakage, is used for comparison and evaluation, and the larger the value of Pc, the smaller the frictional resistance and the better the slidability. As the test conditions, one test steel plate is used for each holding load, the plate width is 17 mm, the sliding length is 250 mm, the pulling speed is 500 mm / min, and the rust preventive oil for normal galvanized steel plate is used as the lubricating oil. (Viscosity 6 cst 40 ° C.) by coating amount 1 g /
After applying m ² , it was subjected to the test.

As a method of evaluating the sharpness after processing, 750 is used.
Punch shoulder radius 10 with deep drawing using mm square punch
It was extruded by 0 mm. Note that one side of the steel plate is used as the evaluation surface and the other side is pressed as the punch side, and at the shoulder part of the processed product that corresponds to the part that contacts the punch, the coating clarity on the one side that is the outer surface side of the processed product And
The paint clarity was compared and evaluated by a visual evaluation method. Visual evaluation: (good) ○-△ -x (poor) The test results are shown in Table 1. As a result, the steel sheet produced according to the present invention has a high coating sharpness before and after the comparative example of the present invention and before and after processing, and also has a good friction sliding property. Is clearly superior in terms of both coating clarity and slidability.

[0022]

[Table 1]

[0023]

INDUSTRIAL APPLICABILITY According to the present invention, by limiting the morphology and distribution of the projections on the surface of the steel sheet and the difference in height between the front and back to a certain range, the image clarity of the coating is improved and at the same time the sliding resistance is reduced to achieve press forming It is possible to obtain a steel sheet which has improved paintability and which is excellent in coating image clarity even after press forming.

[Brief description of drawings]

FIG. 1A, FIG. 1B, FIG. 1C, and FIG. 1D are explanatory views showing an example of an unevenness imparting process step of the present invention by a lithography method.

FIG. 2 is a schematic diagram showing a test device for measuring sliding resistance of a steel plate.

FIG. 3 is a schematic sectional view of a steel sheet obtained by the present invention.

[Explanation of symbols]

 1 Hopper 2 Liquid Photosensitive Resin 3 Air 4 Photosensitive Resin Supply Device 5 Photosensitive Resin Layer 6 Laser Oscillator 7 Laser 8 Slit 9 Chopper 10 Photosensitive Hardening Part 11 Sprayer 12 Dissolvent 13 Exposed Part 14 Convex Bead 15 Test Steel Plate 16 Receiving Type dice

Claims (1)

[Claims] 1. The front and back surfaces of a steel sheet have scattered convex top surfaces having a size of 10 to 1000 μm, a convex peak distance of 50 to 2200 μm, and a concave roughness Ra of 0.8 μm or less and an average area of concave portions. The projections are dispersed discretely so that the ratio is 70% or more, and the heights of the projection vertices scattered on one side of the steel plate are in the range of 2 to 12 μm, and the height of the projections on the other side is 3
A steel plate excellent in coating image clarity and press workability, which is characterized in that it is higher than one side in the range of up to 20 μm.