JPS63132702A - Steel sheet for painting and its production - Google Patents

Abstract

PURPOSE:To improve the sharpness of a product by forming microscopically flat trapezoidal peak parts, valley parts enclosing said parts and intermediate flat parts to the surface of a steel sheet having specific roughness. CONSTITUTION:While work rolls 3 for temper rolling are rotated, laser pulses are projected one after another to the roll surface to form crater-shaped recesses 1 and flange-shaped build-up parts 2 on the roll 3 surface. The ratio Sm/d of the average distance Sm between the recesses 2 and the outside diameter D of the build-up parts 2 is specified in a 1.7-3.0 range and the value of Sm-D is specified to <=450mum. The steel sheet 7 having 0.3-2.0 m center line average height Ra of the surface is subjected to the temper rolling at <=0.3% elongation lambdaby using such rolls 3, by which the steel sheet for painting having the surface shape expressed by the equation I is obtd. Since the steel sheet has the surface shape to decrease irregular reflection of light, the sharpness of the product is improved.

Description

[Detailed description of the invention]

(Industrial Application Field) This invention relates to thin steel sheets, such as cold-rolled steel sheets, which are subjected to forming processing such as press working before or after the painting process, such as automobile body outer panels and household electrical appliance outer panels. , relates to steel sheets for painting, such as hot-dip galvanized or various electroplated steel sheets, and methods of manufacturing the same. Cold-rolled thin steel sheets, which are a typical example of this type of steel sheet for painting, are usually produced by degreasing and cleaning after cold rolling (G), followed by temper rolling after annealing. One of the purposes of rough rolling is to give the steel plate an appropriate surface roughness by performing light rolling using work rolls with a dull surface finish, thereby improving seizure resistance during press forming. . By the way, as a method for dull finishing the surface of a work roll used in such skin pass rolling, conventionally a method using shot blasting and a method using electric discharge machining have been put into practical use. In the case of dull finishing of work rolls for skin pass rolling by these methods, an irregular roughness profile is formed on the roll surface, so the surface of the steel plate after skin rolling is composed of irregular peaks and valleys. It exhibits a rough surface. When a steel plate with a rough surface is pressed, lubricating oil is stored in the valleys, reducing the frictional force between the press die and the steel plate, making the press work easier, and at the same time making it easier to press the die. Depending on the frictional force of , it is possible to trap the metal powder with a particle size of <1 in the troughs and prevent seizure. In recent years, the quality of the paint finish on the bodies of not only passenger cars but also light cars, wagons, and even trucks after painting has become a direct visual appeal to customers of the overall high quality of the car. This makes it an extremely important quality control item. By the way, there are various evaluation items for painted surfaces, but among them, it is especially important that the painted surface has low diffused reflection and has excellent gloss, and that there is little distortion of the image, that is, excellent image clarity. The combination of gloss and image clarity is generally referred to as image clarity. The sharpness of the painted surface is affected by the type of paint and the painting method, but it is also strongly influenced by the roughness of the steel plate surface that serves as the base for painting. In other words, if the flat portion of the steel plate surface has a small proportion and the rough surface is highly uneven, the painted surface will also have large unevenness, which will cause diffuse reflection of light, impairing gloss, and distorting the mapping. This results in a decrease in image clarity, which worsens the above-mentioned image clarity. In general, the roughness of a steel plate surface is often expressed by the centerline average roughness Ra, but the larger the centerline surface roughness Ra, the larger the amplitude of the peaks and valleys, and the more uneven the painted surface becomes. As a result, image clarity deteriorates. Various methods have been developed to evaluate sharpness, but the most common method is the method used by Hunter Associates in the United States.
Laboratory (Hunter As5ociatesL)
DORIGO manufactured by ABORATTORY:/ (DORIC)
ON) The measured value by the meter, that is, 001 (Dis
tinctness of Image) value is used. This Dot value is calculated at an angle of incidence of 30° with respect to the sample surface.
It is expressed by the following equation using the specularly reflected light intensity Rs and the scattered light intensity R6,3 at ±0.3° with respect to the specular reflection angle. 001 j direct = 100 X (R3-Ro, 3)
/Rs By the way, as mentioned above, when a steel plate is subjected to skin pass rolling using a work roll that has been dull finished by the conventional shot blasting method or electric discharge machining method, the surface of the steel plate will have irregular peaks and valleys. It exhibits a rough surface consisting of , and there are very few surfaces parallel to the plate surface. If four coatings are applied to the surface of a steel plate that has irregular peaks and valleys in this way, a coating film will be formed along the slope between the peaks and valleys, so for example, as will be explained later, This decreases the proportion of the painted surface and deteriorates image clarity. Conventional shot blasting and electric discharge machining methods avoid such problems, and therefore it is difficult to obtain sufficiently excellent image clarity of the coating surface. (Prior art) In order to improve the sharpness of the coating surface, attempts have been made to use laser-dulled temper-rolled work rolls (no literature found). The area ratio η of the flat part transferred to the plate surface is 8
Since it was less than 0%, it was difficult to achieve Dot of 98, making it impossible to achieve the highest quality of sharpness for automobiles. (Problems to be solved by the invention) This invention was made against the background of the above-mentioned circumstances, and by improving the roughness profile of the surface of a steel plate, the unevenness of the surface of the coating film after painting can be reduced and the surface can be flattened. By increasing the proportion of the area, we can improve the specular reflectance of light and reduce distortion of the image, providing a steel plate with excellent image clarity after painting, and at the same time, with such excellent surface roughness. It is an object of the present invention to provide a method for efficiently manufacturing a steel plate having a hardness profile. In other words, the present invention provides a steel plate for painting and a method for manufacturing the same, which can significantly improve image clarity compared to the past without making any changes to the paints and painting methods used in the past. be. (Means for solving the problem) The above purpose is advantageously achieved by the following matters. The centerline average roughness Ra of the plate surface is within the range of 0.3 to 2.0 μm, and the microscopic morphology constituting the surface roughness is
A trapezoidal ridge with a flat top surface and a groove-shaped trough formed to surround all or part of the periphery of the trapezoid and the ridge between the ridge and outside the trough. and an intermediate flat part that is higher than the bottom of the mountain and lower than or at the same height as the top surface of the mountain, and the average distance between the centers of adjacent mountain parts is Sm, and the average of the outer edges of the valley is The average diameter of the flat top surface of the ridge portion is 66, and the ratio of the sum of the areas of the flat top surface of the ridge portion and the flat surface of the intermediate flat portion to the total area of the plate surface is η. (%), 1.7 <Sm/D<3.0 Sm-D≦450 (μm) 30 (, um)≦do<500 (μm) 80%≦η≦9
A steel plate for painting (first invention), characterized in that it is configured so as to satisfy 5%. In advance, the surface of the work roll for temper rolling is made up of a set of minute or rake-shaped recesses and a ring-shaped raised part on the front side at the outer edge of the recess, and the average center distance Sm between adjacent recesses is The ratio Sm/D to the diameter of the outer edge of the ring-shaped raised part is within the range of 1.7 to 3.0, and the patterning that forms a surface pattern with Sm-D of 450 μm or less is processed. The work roll with the surface pattern applied using an energy source is used on one or both sides of the steel plate to be subjected to temper rolling, and the temper rolling elongation rate λ is 0.3% or more. A method for manufacturing a steel plate for painting (second invention), characterized in that a pattern on the surface of a work roll is transferred to the surface of the steel plate by doing so. The inventors investigated a non-traditional laser processing method for dull finishing work rolls for temper rolling, and after conducting various experiments and research, found that dull finishing using a high-density energy source such as a laser was used. Steel plates temper-rolled with finished rolls have flat peaks that make up the surface roughness, and the fact that there are many flat valleys between the peaks indicates that the coating film during baying is This means that it is advantageous for flattening the outermost layer. That is, in this case, compared to irregular rough surfaces such as those of shot-blasted materials and electric discharge machined materials, there is less diffuse reflection of light, and image clarity is considered to be improved. As a result of further experiments, we have published Japanese Patent Application No. 7769/1989 regarding a roughness profile on the surface of a steel sheet that can improve the sharpness of the paint film after painting, and a method for manufacturing a steel sheet having that roughness profile. It was disclosed in the book. However, with this, it was still difficult to achieve a sharpness of 001 of 98 or higher. Therefore, we focused on the fact that the processing rate in press processing of automobile exterior panels is small, less than 10% at most, and conducted further experiments. This led to the invention of an improved method that is more advantageous in improving image clarity. As the high-density energy source, a laser is most suitable, but plasma, electron beam, etc. are also applicable. Cold-rolled steel sheets are usually used as thin steel sheets to which the dull finish described above is applied by temper rolling, but as already mentioned, surface-treated steel sheets that have been previously subjected to hot-dip galvanizing or various types of electroplating can also be used. Depending on the situation, a hot-rolled thin plate may also be used. (Function) [1] One-dimension dulling of work roll for temper rolling using laser: First, while rotating the work roll for temper rolling using a high-density energy source, such as a laser, laser pulses are applied one after another to the surface of the roll. The roll surface is regularly melted by laser energy to form regular crater-shaped recesses. The state is shown in FIG. In Fig. 1, reference numeral 1 indicates a crater-shaped recess (hereinafter simply referred to as a crater) formed on the surface of the roll 3, and around the crater 1, the molten metal on the roll surface 3 is shaped like a ring. A flange-like raised portion (hereinafter simply referred to as 7 langes) 2 is formed. Note that the inner wall layer of the crater 1 including this flange 2 forms a heat affected zone 5 with respect to the roll base material structure 4. The depth and diameter of the crater 1 on the roll surface formed by laser pulses are determined by the magnitude of the incident laser energy and the projection time, and this is different from ordinary shot blasting. Give the amount that defines the roughness equivalent to the Ra roughness of the roll. The metal that forms the roll 3 by heating with a laser is
Due to the high irradiation energy density, it instantly turns into metal vapor, and the molten metal on the roll surface is blown away by the generated vapor pressure to form crater 1, and the blown molten metal spreads around crater 1. Refastening forms a flange 2 surrounding the crater 1. These series of behaviors can be executed more efficiently by spraying an auxiliary gas such as an acid accumulation gas toward the irradiation point. Then, by rotating or moving the roll in the axial direction and irradiating it with regular laser pulses, the above-mentioned craters 1 are regularly formed, and the roll surface becomes rough due to the collection of these craters that are formed one after another. It will be presented. The roughness of the surface of the roll thus formed is shown in Figs. 2 and 3, and as is clear from these figures,
The portion between adjacent craters 1 remains the original roll surface and becomes a flat surface 6. Here, the distance between adjacent craters is determined by controlling the frequency of the laser pulse in relation to the rotational speed of the roll in the direction in which the roll is rotationally driven, and by controlling the frequency of the laser pulse in relation to the rotational speed of the roll, and in the direction of the roll's axis by controlling the frequency of the laser pulse in relation to the rotational speed of the roll. Adjustment is possible by controlling the pitch at which the laser irradiation position is moved in the roll axis direction each time the roll is rotated. Although the above description has been made regarding the case where a laser is used as the high-density energy source, the same applies to the case where other high-density energy sources such as plasma or electron beams are used. [2] Dull rotation transfer to the surface of a steel plate by skin pass rolling: Using a work roll that has been subjected to dull processing using a laser or the like as described above, light rolling is applied to a steel plate, for example, an annealed cold rolled steel plate, in the skin pass rolling process. By performing rolling at a certain rate, the dull edges of the rolls are transferred to the surface of the steel sheet, and a rough surface is formed on the surface of the steel sheet. If we microscopically observe the surface of the steel plate during this process, we can see that the fourth
As shown in the figure, the flange 2, which has a substantially uniform height on the surface of the roll 3, is pressed against the surface of the steel plate 7 with strong pressure. Local plastic flow of the material occurs, and the metal of the steel plate 7 flows into the crater I of the roll 3, forming a rough surface. At this time, the top surface 8 of the raised trapezoidal peak on the inside of the crater 1 becomes a flat surface as the original surface of the steel plate, and the outside of the flange 2 between adjacent craters 1 on the roll 3 becomes flat. Intermediate flat 9 pressed against surface 6
remains a flat surface, and the flat top surface 8 of the former
is slightly higher than or at the same level as that of the latter intermediate flat portion 9. Therefore, as shown in FIGS. 5 and 6, the microscopic morphology of the rough surface of the steel plate 7 after temper rolling consists of a trapezoidal peak 10 having a flat peak surface 8 and the surrounding area A groove-like trough 11 formed to surround the trough 11 and a trough 11 located between the adjacent ridges IO and outside the trough 11.
and an intermediate flat part 9 which is higher than the bottom of the mountain part 10 and lower than or at the same level as the mountain top surface 8 of the mountain part 10. As is clear from the above, the surface of the steel plate after temper rolling has a large proportion of the flat part consisting of the peak surface 8 of the peak IO and the intermediate flat part 9, and the proportion of the flat part consisting of the peak 10 and the valley In principle, the ratio of the sloped surfaces 13 between the slopes 11 and 11 is reduced. On the other hand, in the case of rolls that have been roughened by shot blasting or electrical discharge machining, the ridges on the roll surface that form the roughness are normal as shown in Figures 7 (A) and (B). In this case, during the temper rolling process, the ridges on the surface of the roll 3 dig into the surface of the steel plate 7, resulting in a rough surface profile on the roll surface. and the rough surface profile of the original surface of the steel sheet 7 are combined, and the steel sheet 7 after temper rolling will theoretically have a large proportion of sloped surfaces formed by peaks and valleys. Therefore, it can be seen that in this case, the surface structure and the formation process are completely different from a steel plate that has been temper-rolled by a roll that has been dulled by a laser. FIG. 9(A) shows the slope angle distribution of the roughness of the steel plate surface after skin pass rolling when skin pass rolling is performed using rolls that have been subjected to redull processing by the conventional shot blasting method. figure(
B) shows the definition of the angle of inclination. By the way, as mentioned above, the circle I value, which expresses image sharpness, is expressed as the ratio of scattered light of ±0.3° to the specular reflection angle, so the percentage of valleys whose flatness slope angle is within 0.3° It can be judged as good if there are many, but in the case of Figure 9 (A), ±0.3°
The occupancy of the inclination angle within the range is only 13%, and in two dimensions it is only 1.7% (0,13)" [3] Definition of the dimensions of each part of the roughness profile of the steel plate surface after roll and temper rolling: Here, as mentioned above, the roll dulled by laser The dimensions of each part in the surface roughness profile and the dimensions of each part in the roughness profile of the steel plate temper-rolled by the roll are defined as follows with reference to Fig. 10: D = crawl surface Average outer diameter of the flange 2 = Average diameter of the outer edge of the valley 11 on the steel plate surface d: Average diameter of the crater ■ on the roll surface do: Average diameter of the flat peak surface 8 of the peak IO on the steel plate surface H: Roll Depth of crater 1 on the surface hl: Height of flange 2 on the roll surface = Depth from the intermediate flat part 9 on the steel plate surface to the bottom of the valley part 11 h2: w4 Flat peak of the mountain part 10 on the plate surface Height of surface 8 from intermediate flat part 9 Smm Average distance between the centers of adjacent craters 1 on the crawl surface = Average distance between the centers of adjacent peaks IO on the steel plate surface α: Width of flange 2 on the roll surface [4] Effect on the area ratio η of the flat portion on the steel plate surface after skin pass rolling: Using the values defined above, the pattern constituting the roll surface roughness profile and the skin pass rolling conditions are We investigated whether this would affect the area ratio η of the flat part on the surface after rolling.Here, the area ratio η of the flat part is, as shown in Fig. 11,
It is expressed as the sum of the area occupancy rate η1 of the flat top surface 8 of the mountain portion IO and the area occupancy rate η2 of the intermediate flat portion 9. η=η1 +η2 (1). Here, the value of η1 changes depending on the rolling reduction rate in temper rolling. This is because if the rolling reduction rate changes, the degree to which the steel sheet metal flows into the inside of the crater 1 changes, and as a result, the peak part 10
The diameter d of the peak 8 of . This is because it changes. On the other hand, η2
The value of is a constant value depending on the value of the ratio of Sm/D. This Sm/D ratio is within the range of the following equation (2), as will be described later. 1.7 <Sm/D≦3.0 −(2) and η
1 is determined by the following equation (3), and as shown in equation (4), d. has a constant relationship with d, and η2 is determined by equation (5) according to the value of Sm/D. η1−π(do/Sm) 2/4”・(3)d
, =Kd...(4)η2
= 1-π(D/Sm)2/-4+ a ((D/S
m)2CO3-'(Sm/D)-J plane/Sm)T])
...(5) However, in equation 5, when Sm/D≧1, a=0 - (6) Sm/D<1
When a=1 −C7) (2), (5), (
6) and (7), η2 changes within the following range. 0,78 <η2 <0.95...
・(8) Here, regarding the roughness profile dark surface shape of the roll surface and steel plate surface, as shown in FIG.
If we take the y-axis and assume that the cross-sectional shape of crater 1 is y = cOx, then we set d = π and C03d/2 = O... (9) Also, from C03do / 2 = h2, d, = 2C
O3-'h,, -(L□Here, the height h2 of the peak 10 transferred to the steel plate surface by the crater 1
The ratio Ih/H to the depth H of the crater 1 can be called the roughness transfer rate, but in the above example, the depth H of the crater l
Since it is set to 1, the roughness transfer rate can be expressed as h2/1, that is, h2. The roughness transfer rate is h2/l, that is, the height h2 of the peak portion 10 has a relationship determined by the rolling elongation rate λ of temper rolling. That is, h2=f(λ)...0υThis relationship was determined through the following experiment. The original plate has a thickness of 0.32μ with an Ra roughness of 0.38μm.
A 5 pcc steel plate with a diameter of 200 mm was used, and the Ra roughness was set to 3.45 μm using a laser as a roll for temper rolling.
Using a material having a diameter of mmφ and an Hs hardness of 94, skin pass rolling was performed at various rolling elongation rates λ. The results are shown in FIG. From FIG. 13, the roughness transfer rate h2/1 increases linearly until the temper rolling elongation rate λ is about 1.5%, but when λ is 1.8%, the roughness transfer rate h2/1 increases linearly.
%, the roughness transfer rate becomes saturated. Furthermore, using the results shown in FIG. 13, the above d. 2 to Sk+
When the values were determined, the results shown in Table 1 were obtained. By the way, the average roughness of a cold-rolled thin steel sheet for ordinary press forming is Ra1. When dull processing is performed using a laser so that the thickness is O~3.0 μm, the width α of the flange around the crater is approximately 0.09×D. Therefore, d can be expressed by the following formula. d=0.82D . . . Q2+ Also, if the formula is used in equation (4), do = 0.82 kD-C3). Therefore, equation (3) can be expressed as follows. 7'/+ = 7r ('0.82 k D/Sm)2
/ 4=0.5281 and 2(D/Sm)2-C4) formula (
From the results of 5), (6), (7), (8), 04) and Table 1, the area ratio η of the flat portion has the values shown in Table 2a, Table 2b, and Table 2C. . Table 2C - If this η is illustrated according to the value of Sm/D, it can be expressed as shown in FIG. 14. Further, this relationship can be generalized by the following equation 09. η=ηri+η2 = 0.5281 to 2(D/Sm)2+ 1- π/4
(D/Sm) 2+ a ((D/Sm) ” CD
S-'(Sm/D)-F;shoulder=Tgo...
・0 It is clear from FIG. 14 that the area ratio of the flat portion varies greatly depending on the ratio of Sm/D. Also! η also changes depending on the elongation rate λ during rough rolling, and in particular, when Sm/D is small, it is greatly affected by the change in λ. [5] Lower limit of temper rolling elongation λ: As mentioned above, temper rolling elongation λ affects η,
If λ is too small, the temper rolling operation itself will become unstable, making it difficult to transfer the roughness onto the surface of the steel sheet. According to experiments conducted by the inventors, if the elongation rate in temper rolling is 0.3% or more, dull transfer is possible, so the elongation rate λ in temper rolling is 0.
．． It was set at 3% or more. J6. ! Lower limit of flat area ratio η and Sm/D: When processing the dull area of a skin-pass rolling work roll with a laser, change Sm and DXa and change the elongation rate λ of skin-pass rolling. Steel plates with various flat area ratios η (all have Ra of approximately 1.5 μm) were prepared, and after being painted black with 3 coats, the surface
01: The results shown in FIG. 15 were obtained. It is clear from FIG. 15 that as η increases, the dot sensitivity increases, that is, the image sharpness improves. In the body film of recent passenger cars, it is desirable that the Dot value be 98 or more in order to exhibit the best image clarity, and for this purpose it is desirable that η be 80% or more. Therefore, from Figure 15, the lower limit of η is 80%
shall be. Therefore, the normal temper rolling reduction rate is 0.8 to 1.2%.
In order to secure η-80% in Sm/D from Fig. 14,
The lower limit of 1.7 sips. (7) Upper limit of Sm/D, Sm-D and upper limit of η: As already defined in [3], the dimensions of each part of the roll roughness profile such as Sm, H, etc. As is clear from the above, the number of roll rotations, laser pulse frequency, laser output, feed speed of the laser irradiation point, laser irradiation time, or assistance such as 02 gas when processing rolls for skin pass rolling with a laser The blowing of the gas can be changed by adjusting the conditions, etc. Here, the roughness of the roughness of 0.5 to 5 μm, which is suitable for general cold-rolled steel sheets for processing, is determined by the laser processed roll. When realized by 8-store rolling, the flange width α on the roll surface is 20
~40μm, and the flange height hl is 5~3
It is approximately 0 μm. On the other hand, the roughness profile formed on the steel plate surface is Sm/
Depending on the value of D, three types of patterns shown in FIG. 16 (8), (B), and (C) are produced. That is, when Sm/D is 1, the adjacent continuous groove-shaped valleys 11 are in contact with each other at their apexes, as shown in Fig. 15 (8), and when Sm/D is 1, as shown in Fig. 16 (B). As shown in FIG. 16C, adjacent valleys 11 are separated from each other, and conversely, when Sm/D<1, adjacent valleys 11 overlap each other as shown in FIG. 16(C)9. In this way, by changing one shift of Sm/D, it is possible to obtain many different roughness profile patterns, but the inventor manufactured skin pass rolling rolls with various Sm/D values by laser machining. A cold-rolled steel sheet that had been annealed to an appropriate skin-pass rolling reduction ratio was subjected to skin-pass rolling and dulled. Then, when we conducted a fuss processing test and a painting test on each steel plate, we obtained the following findings. That is, if the value of Sm/D of the roll becomes significantly large, when the steel plate 7 is subjected to skin pass rolling with the roll 3 to give a dull weight, as shown in FIG. The area of the intermediate flat part 9 that exists between the IO becomes too large, so if such a steel plate is press-formed as shown in FIG. The metal foil powder 13 generated during this process becomes difficult to be captured by the valley portion 11, and the metal foil powder 13 remains between the press tool 14 and the intermediate flat 9 forever. Further, a significantly large Sm/D means that the space of the valley portion 11, which serves to store press lubricating oil, becomes smaller, and therefore poor lubrication is more likely to occur. As a result, if Sm/D is too large, seizure is likely to occur during press working. Also, here, the width of the intermediate flat 9, that is, (Sm-D)
(It is necessary to regulate the absolute value of This is related to the process in which a part of the metal in part 1 rises around it and re-fixes, so if D is large, both α and hl will be large.In other words, if D is large, the lubricating oil storage capacity during press working and the metal <1 The trapping ability of the powder 13 is large, and this has an important meaning in preventing the occurrence of seizure, but its effectiveness is limited to the following cases: In other words, when metal flake powder 13 is generated After that, as the press processing progresses, it gradually accumulates, and eventually the metal is deposited within the sliding length of the press die and the workpiece material until seizing occurs. This is the case when there are four groove-like parts on the surface of the workpiece that can trap powder.In order to satisfy such conditions, the absolute value of the width of the intermediate flat part (Sm-D) must be According to the above-mentioned experiments conducted by the present inventors, in the case of preparation that does not require a very high processing rate and is used for the outside of the body of a passenger car, it is necessary to make it smaller than a certain value. The distortion rate is within 10%, and the value of Sm/D is 3.
It has been found that as long as the value does not exceed 0, seizures during press forming as described above do not occur frequently. (Fig. 23) Also, in order to prevent frequent seizures, the width of the intermediate flat part 9 (
It has been found that the absolute value of Sm-D) needs to be smaller than 450 μm. (FIG. 24) Some results of the experiment are shown in Table 3. Note that the values of (Sm −D) + and (Sm D) a in Table 3 are as shown in FIG. 19, respectively. Further, the value of Sm/D is correlated with the area ratio η of the flat portion on the surface of the steel sheet, as shown in FIG. 14 described above. According to the above-mentioned experiments by the inventors, as can be understood from Table 3 p), when the area ratio η of the flat portion exceeds 95%, seizure occurs frequently. Therefore, in this invention, in order to obtain a steel sheet with good press formability without seizure, the upper limit of the Sm/D ratio is 3.0, the upper limit of the flat area ratio η is 95%, (Sm-
D) with an upper limit of 4.0. less than um.

[9] Diameter d of the flat peak surface of the peak on the surface of the steel plate. Upper limit: The peak lO that constitutes the microscopic profile of the rough surface of the steel sheet
The flat top surface 8 is a surface that bears the press load during press forming, and corresponds to a so-called bearing area. If the diameter do of this mountain top surface 8 is large, the flat area of the mountain top surface will be large, and the S
Similar to the case where m/D and η are large, seizure tends to occur more easily during press working. According to the inventor's experiments, d. It has been found that when the thickness is 500 μm, seizure is likely to occur. In addition, in order to form a wide mountain top surface 8 with do exceeding 500 μm, it is necessary to increase the diameter of the crater l of the roll itself, and in this case, the amount of energy required for laser pulse irradiation to generate the crater is excessive. Therefore, it is necessary to use a laser oscillator with a higher output than necessary, or to slow down the rotation speed of the roll to lengthen the irradiation time, which is not only economically disadvantageous but also reduces the overall This results in a decrease in processing efficiency and reliability. Therefore d. must be 500 μm or less. On the other hand, the diameter d of the mountain top surface 8 of the mountain portion 10. If it is too small, the crest lO is likely to be destroyed by compressive stress and shear stress during press working (and therefore, more metal powder will be generated at the crest, making it easy to cause seizure in this case as well. According to the inventor's experiments, it has been found that seizure is particularly likely to occur when do is less than 30 μm.
If o is made smaller, the value of D will inevitably be made smaller, so in order to make do smaller and to satisfy Sm/D≦3.0 as stated in the above section [7], ,
The value of Sm itself must also be made small. In other words, the spacing between the roll flakes must be reduced. In order to do this, it is necessary to extremely reduce the roll rotation speed when laser processing the roll or to extremely increase the laser pulse frequency. In either case, it will be economically disadvantageous. For these reasons, the diameter d of the mountain top surface 8 of the mountain portion 10. must be 30 μm or more. In addition, here, the diameter d of the mountain top surface 8 is. The average diameter is 30-50
It is fine if it is within the range of 0 μm, but if the crater 1 is actually formed on a roll using a high-density energy source such as a laser and the peak 10 is formed by temper rolling, the peak 10 will be flat. The planar shape of the mountain top surface 8 is not necessarily a perfect circle, but is often oval or irregular. Therefore, in that case, it is desirable to adjust so that the average value of the long axis of each mountain peak is 500 μm or less, and the average value of the short axis of each mountain top surface is 30 μm or more. Of course, the largest axis of all the mountain top surfaces is 5
It is appropriate that the shortest diameter of all the peak surfaces be 30 μm or more. [10] Centerline surface roughness Ra of steel plate: As mentioned above, in this invention, it is most important to control the microscopic profile that forms the rough surface of the steel plate. Surface roughness also needs to be regulated. That is, even if the microscopic profile of the rough surface is regulated as described above, if the center line average roughness lla exceeds 2.0 μm, the sharpness of the coating film will not be sufficiently good;
．． If the thickness is less than 3 μm, seizure is likely to occur during press working. Therefore, fla was set within the range of 0.3 to 2.0 μm. [11] Summary: From the above, it is clear that steel sheets temper-rolled using rolls that have been dulled using a high-density energy source such as a laser have good press formability (especially seizure resistance), and that they meet the requirements for passenger cars after painting. eroded paint film clarity, preferably 001
In order to have a sharpness of 98% or more, the conditions for the microscopic roughness profile of the steel sheet surface are as follows:
The ratio of the sum of the areas to the entire board surface area (flat surface occupancy rate) η is 80% or more and 95% or less, (11) The average center-to-center distance Sm of the peaks and the outer edge of the valleys The ratio Sm/D to the average diameter is within the range of 1.7 or more and 3.0 or less, and Sm-D is less than 450 μm; (i+i) the average diameter d of the top surface of the mountain portion; is within the range of 3 aμm or more and 500 μm or less, and in addition, the center line average roughness Ra must be 0
, 3 to 2.0 μm. Further, as a condition for skin pass rolling, it is necessary that the elongation rate λ of the skin pass rolling is 0.3% or more. Among the above conditions, the ratio of Sm/I) and d
. FIG. 20 shows the relationship between the appropriate ranges and a summary of the reasons for limiting the ranges. (Example) As a material steel plate, C0.04%, Mn0.2%, Po,
02%, 30.015%, NO, 003%, 00.00
A 0.8 mm cold rolled steel plate was used which was cold rolled and further annealed in a box-type annealing furnace. As work rolls for temper rolling, we prepared a dull roll material that was dulled by laser pulse processing, a dull roll material that was dulled by conventional shot blasting, and a blind roll material that was not dulled. The temper rolling elongation λ of each roll is 0.5 to 2.
．． Temper rolling was performed within a range of 5%. Here, the surface roughness Ra of the bride roll is 0.15 μm, and the surface roughness Ra of the dull roll is Ra 1.1 to 5.6.
Various changes were made within the range of μm. In particular, the surface roughness profile of the roll that has been dulled by laser processing is as follows: 0.85≦Sm/D≦1.7 Sm -D <280 pm 50 /um ≦d≦500 μm 35 pm≦H ≦120/-1mh, #l/3
H and B as an example: 1.7 ≦Sm/D≦3. O 3m-D<450 50≦d≦500 35≦H≦120 hl! =i1/:3H Later was prepared. The roughness of the steel plate surface after temper rolling as described above is:
Steel plate using bride roll (prite finishing material) Te1
La was 0.08 μm, and Rag was 6 to 2.25 μm for the steel plate (dull finished material) using a dull roll. In particular, for steel sheets temper-rolled using rolls that have been subjected to dull processing rather than laser processing, the surface roughness profile is as follows: For sample A: 0.85≦Sm/D≦1.7 Sm-D<280 μm 30 pm ≦d≦500 μm For the second sample, 1.7≦Sm/D≦3.0 Sm−D<450 30×d≦500. Next, each steel plate after temper rolling was subjected to chemical conversion treatment under the following conditions. Treatment material: fine-grained phosphate-based drug for dipping treatment Dipping conditions: 43°C x 120 seconds Film weight: 2.3±0.2g/clTl Pretreatment: degreasing,
Post-washing and surface conditioning treatment: After washing with water, washing with pure water, drying and chemical conversion treatment, three coats were applied under the following conditions. Coating position: horizontal painting Undercoat: cationic BD paint 18-20 μm thick Intermediate coat: sealer 30-35 μm thick top coat 30-35 μm thick Dimensions: Sanding was not performed in each step. The surface of the paint film after painting was directly measured using a DORIGON meter. The results are shown in Figure 21 for the case of 3 coats, corresponding to the surface roughness Ra of each steel plate. In Fig. 21 and the text below, LT and t4 are steel plates temper-rolled using rolls that have been dulled by laser, EDT materials are steel plates that are temper-rolled using rolls that have been dulled by electrical discharge machining, and SB materials are dull-rolled steel sheets that have been dulled by shot blasting. Represents a steel plate temper-rolled by rolls. ￥S21 As is clear from the figure, L in the case of 3-coat painting.
The T material instep is [l[lI] compared to the E[]T material and the SB material.
The image sharpness is about 10 to 11 in terms of value, but the LT material Otsu is even worse than that, with a 001 value of 1 point (I'm worried, it has achieved a 001 value of 98. As mentioned above, the sharpness of the coating film is 9 in terms of DOI value.
It is said that 8% or more is desirable, but in the above example, in the case of the 3-coat LT material, as shown in Figure 21, the dot
It is clear that a value of 98 or higher can be obtained. Furthermore,
According to a separately conducted press working test for outer panel parts for passenger cars, it was confirmed that the LT material O sample shown in Fig. 21 did not suffer from seizure during press working. (Effects of the Invention) According to the steel plate for painting of the present invention, a remarkable effect of improving the sharpness of the coating film than before without impairing press formability can be obtained, and the steel plate for painting of the present invention According to the steel sheet manufacturing method, a steel sheet with excellent coating film clarity can be practically manufactured as described above.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional view showing the state of the cross section of the work roll when the surface of the work roll is dulled using laser pulses as high secret energy in the method of the present invention, and Fig. 2 shows the dulling by the laser pulses. is a schematic cross-sectional view showing the rough surface profile of the surface of the processed roll, FIG. 3 is a plan view of FIG. 2, and FIG. FIG. 5 is a schematic cross-sectional view showing the rough surface profile of the steel plate surface temper-rolled by the rolls described in No. 2, and FIG.
Fig. 7 (A) is a diagram showing the height distribution of the rough surface of the roll surface whose dull area was processed by conventional Nyoyo blasting. The dull area weight is a diagram showing the height distribution of the rough surface of the processed roll surface. Figure 8 is an explanatory diagram showing the situation when a steel plate is temper-rolled and dull-finished using a roll that has been dulled by the conventional method. , Figure 9 (8) is a diagram showing the inclination angle distribution of the roughness °C of the steel plate surface when skin pass rolling is performed using rolls that have been dulled by the conventional Nyoyot plast method. A diagram showing the definition of the inclination angle in Figure 9 (8), Figure 10 is an explanatory diagram showing the definition of the dimensions of each 8'19 of the profile forming the rough surface of the skin pass rolling roll and the steel plate, Fig. 11 is a schematic diagram for explaining the running speed of the area ratio η (-η1 + η2) of the flat part, Fig. 12 is an explanatory diagram for approximate calculation of the roughness profile of the steel plate surface on the roll surface, and Fig. 13 The figure is a diagram showing the relationship between temper rolling elongation rate λ and service transfer rate h2/1.
The relationship between the rolling elongation rate λ and the rolling elongation rate λ is shown according to the value of Sm/D at various degrees. Figure 16 (8), (B), (C) showing the relationship with the 001H dimension of the coating film are Sm/D
Figure 17 is an explanatory diagram showing changes in the planar roughness profile of the steel plate surface when the ratio of S+n/D is excessive. 18 is an explanatory diagram showing the effect of press working on the steel plate in FIG. 17, and FIG. 19 is (Sm/D) 11(Sm/D)2
(Schematic diagram for explaining the D relationship. Figure 20 is an explanatory diagram showing the relationship between the value of Sm/D and the appropriate range of the diameter d of the peak surface of the steel plate surface. Figure 21 is a schematic diagram for explaining the 3 in Example. Center line average roughness R of steel plate in case of coat painting
A correlation diagram showing the relationship between a and the 001 value of the coating film. Figure 22 is an explanatory diagram showing the method for measuring the 001 value, which represents image clarity. Figures 23 and 24 show the occurrence of burning and Sm/D. , (Sm-D
) This is a relationship diagram of 2. 1... Crater-shaped recess on the roll surface 2... Rigged flange 3 on the roll surface
...Roll 7...Steel plate 8...Flat peak surface of the peak on the surface of the steel plate 9...Intermediate flat area on the surface of the steel plate 10...Mountain part 11 on the surface of the steel plate... Valley 13...Inclination Fig. 1 Fig. 2 Fig. 3 Fig. 5 Fig. 7 (A) Fig. 8 Fig. 9 tan θ (θ, angle of inclination)・”Ko λ. Figure 15? 1 (%) Fig. 17 Fig. 18 Fig. 19 (Stn-D) f Fig. 20 1.7 srn/1)

Claims (1)

[Claims] 1. The centerline average roughness Ra of the plate surface is within the range of 0.3 to 2.0 μm, and the microscopic morphology constituting the surface roughness is a flat peak surface. A trapezoidal peak having It is composed of a high and intermediate flat part formed at a height lower than or at the same height as the top surface of the mountain part, and the average distance between the centers of adjacent mountain parts is Sm, and the average diameter of the outer edge of the valley part is D, The average diameter of the flat top surface of the mountain is d_0
, the ratio of the sum of the areas of the flat top surface of the mountain portion and the flat surface of the intermediate flat portion to the total area of the plate surface is defined as η (%), and 1.7<Sm/D< 3.0 Sm-D≦450 (μm) 30 (μm)≦d_0≦500 (μm) 80 (%)≦η≦95% A steel plate for painting, characterized in that it is configured to satisfy the following. 2. The surface of the work roll for temper rolling consists of a set of minute crater-shaped recesses and a ring-shaped raised part on the front side at the outer edge of the recess, and the average center distance between adjacent recesses. Ratio Sm of Sm and diameter D of the outer edge of the ring-shaped raised part
/D is within the range of 1.7 to 3.0, Sm-D is 450 μm
A patterning process that forms the following surface pattern is applied using a high-density energy source, and the work roll with the surface pattern is used on one or both sides of the steel plate to be temper-rolled. A method for manufacturing a steel plate for painting, characterized in that a pattern on the surface of a work roll is transferred to the surface of the steel plate by temper rolling with a pass rolling elongation rate λ of 0.3% or more. 3. The method for manufacturing a steel plate for painting according to claim 2, wherein a laser is used as the high-density energy source.