JPS62224405A - Production of cold rolled steel sheet - Google Patents

Abstract

PURPOSE:To improve the sharpness of a coated film by using laser dull rolls, etc., for work rolls for final cold rolling and forming specifically shaped very small recesses and build-up parts to the work rolls for temper rolling, then executing rolling. CONSTITUTION:The laser dull rolls, etc., and the rolls which do not form waving components of a roughness section curve on the surface of a steel sheet are used for the work rolls of the final stand of a tandem cold rolling mill. The work rolls 3 formed with the crater-shaped recesses 1, the build-up flange parts 2 and flat parts 6 by laser beam processing in such a manner that Sm/D attains 0.85-1.7 and Sm-D attains 0.85-1.7 are used as the work rolls for temper rolling. The formation of the waving of the roughness curve is obviated and the flat surfaces 8, 9 are formed on the surface of the steel sheet 7 if the steel sheet 7 is subjected to cold rolling. The ratio of slopes is thus decreased. The sharpness of the coated film on the steel sheet 7 is, therefore, remarkably improved.

Description

[Detailed Description of the Invention] Industrial Field of Application This invention relates to a method for producing cold-rolled thin steel sheets that are used for forming, such as pressing, and painting, such as the outer panels of automobile bodies and the outer panels of household electrical appliances. It is related to.

Conventional technology In recent years, the quality of the paint finish on the body of not only passenger cars but also light cars, wagons, and even trucks after painting has become a direct indicator of the high overall quality of the car to customers. This is an extremely important quality control item because it can be visually appealing. 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 in mapping, that is, that it has excellent image clarity. The combination of gloss and image clarity is generally referred to as image clarity.

Various methods have been developed to evaluate sharpness, but the most commonly used method is the one developed by Hunter Associates in the United States.
Laboratory (++unter ASSOCiate
Driven ([) manufactured by OratOry)
ORICON )Measurement value by meter, i.e. DoI
(Distinctness of Image)
value is used. As shown in FIG. 28, this DOIf direct is calculated by inputting light into the sample S at an incident angle of 30'', and calculating the specularly reflected light intensity R5 and the scattered light intensity R6 at ±0.3° with respect to the specularly reflected angle. , 3 is expressed by the following equation.

DOI value = 100X (RS R□, 3 > /
RSIt can be said that the higher the OR value, the better the sharpness of the painted surface.Generally speaking, for paint films on the outer panels of automobiles, in order to provide a sufficiently high handling feeling, DOI is required.
It is said that it is desirable that the value is 94% or more.

By the way, cold-rolled thin steel sheets that are generally used for forming purposes such as automobile body outer panels and home appliance outer panels are degreased after cold-rolling hot-rolled steel sheets to the required thickness using a tandem cold rolling mill. It is usually manufactured by washing, rough annealing, and then temper rolling. One of the purposes of temper rolling in such processes is to give the steel plate an appropriate surface roughness by performing light rolling using a work roll with a dull surface finish, which makes it easier to use during press forming. May improve the seizure resistance of rice.

Conventionally, shot blasting and electrical discharge machining have been used as methods for dulling the surface of work rolls used in temper rolling. A work roll has an irregular roughness profile formed on its surface. Therefore, when a steel plate is temper rolled using the work roll, the surface of the steel plate also has a roughness profile consisting of irregular peaks and valleys. There are very few horizontal surfaces. When painting a steel plate that has irregular peaks and valleys in this way, the coating film is formed along the slopes between the peaks and valleys, so the proportion of the horizontal coating surface becomes extremely small. Deteriorates the clarity of the painted surface. Such problems are unavoidable in temper rolling using work rolls that have been dulled using conventional shot blasting or electric discharge machining methods, making it difficult to obtain sufficiently excellent image clarity of the coating surface. Met.

Problems to be Solved by the Invention From the above-mentioned circumstances, the inventors have already filed a patent application in 1983-776.
In No. 9, J: Improved the surface roughness profile of the steel plate to reduce the unevenness of the surface of the coating after painting and increase the proportion of the horizontal portion. We proposed a steel plate that reduces distortion and thereby significantly improves the sharpness of the painted surface after painting, and a method for efficiently manufacturing a steel plate with such an excellent surface roughness profile. There is.

That is, Japanese Patent Application No. 1983-7769 discloses a surface roughness profile formed by skin pass rolling of cold rolling erosion (first invention) and a skin pass rolling method for quenching the surface roughness profile (first invention). 2 invention). The steel plate of the first invention of the proposal has a center line average roughness R of the surface.
a is within the range of 0.3 to 2.0 pm, and the microscopic morphology constituting the surface roughness is a trapezoidal peak with a flat peak surface and all or part of its surroundings. A groove-shaped valley formed to surround the valley and a peak formed outside the valley at a height higher than the bottom of the valley and lower than or at the same height as the top surface of the peak. The average distance between the centers of adjacent peaks is 3.
m, the average diameter of the outer edge of the valley D1 the average diameter of the flat top surface of the mountain d O% The ratio of the sum of the areas of the flat top surface of the mountain and the flat surface of the intermediate flat part to the total area η (%)
When defined as 0.85≦Sm/D≦1.7 Sm D<280 (3ym) 30≦do≦500 (μm) 20≦η≦85 (%) This is a characteristic feature.

The proposed second invention relates to a method of manufacturing a steel plate for painting, in which a fine crater-shaped recess and a ring-like shape are formed on the front side at the outer edge of the recess on the surface of a work roll for temper rolling. The average center-to-center path between adjacent concave portions consisting of a set of raised ridges 1! tsm
and the diameter of the outer edge of the ring-shaped raised part Sm/D
is within the range of 0.85 to 1.7, the difference between Sm and D sm-o
The patterning process that forms a surface pattern with a value of less than 28 (lJff1) is performed using a high-density energy source such as a laser, and the work roll with the surface pattern is used as a steel plate to be temper-rolled. Use on one or both sides of
It is characterized in that the pattern on the surface of the work roll is transferred to the surface of the steel sheet by performing temper rolling with a temper rolling elongation rate λ of 0.3% or more.

As shown in Japanese Patent Application No. 1987-7769, a steel plate that has been temper-rolled using a work roll on which a predetermined surface pattern has been formed using a laser or the like and has been given a predetermined roughness profile has a roughness profile. The tops of the mountains that make up the roughness are flat, and the valleys between the mountains also have many flat parts. This large number of flat areas means that it is advantageous for flattening the outermost layer of the coating film during painting. In other words, in this case, there is less diffuse reflection of light and the sharpness of the coating surface is improved compared to the irregular rough surface that occurs when temper rolling is performed using conventional shot blast rolls or electrical discharge machining rolls. .

By the way, the invention of the above-mentioned patent application No. 7769/1987 focuses on the microscopic surface roughness profile of a steel plate formed by temper rolling, and it is true that the invention was made only from the point of view of the microscopic surface roughness profile. is advantageous in improving the sharpness of the coating surface. However, as the inventors conducted further experiments and research, they found that even when the surface @ degree profile is formed as described above using a laser-processed work roll in temper rolling, the conditions of the previous cold rolling process It has been found that if the coating is inappropriate, a defect called yuzu-ho occurs on the coating surface, resulting in poor image clarity.

In other words, in the past, it was rare to use a work roll whose surface was roughened by shot blasting as the work roll for the final stand of a tandem cold rolling mill, but in this way, a work roll with a roughened surface by shot blasting was used in the final stand. Even if a cold-rolled steel plate has a predetermined roughness profile using a work roll processed by the laser processing described above during temper rolling after annealing, a waviness component will occur in the roughness cross-sectional curve. . The pitch (wavelength) of this undulation is approximately 300 to 11,000p, but components of this wavelength appear on the painted surface even after painting, resulting in a defect called citrus skin on the painted surface, which deteriorates image clarity. That's what I do.

The reason for this is that, for reasons that will be explained in detail later, 'waviness' is generated on the surface of the dull roll due to shot blasting in the final stand of a tandem cold rolling mill, and the waviness is transferred to the steel plate, causing waviness on the steel plate. This is because the waviness does not disappear even if the steel plate is skin-pass rolled with a laser dull roll.In other words, the rolling reduction at the final stand of a tandem cold rolling mill is generally about 5 to 10%, and the rolling reduction by skin-pass rolling is approximately 5% to 10%. Since the ratio is larger than that of 0.3 to 2.0%, the waviness imparted to the steel sheet by the shot blast dull roll of the final stand of the cold rolling mill remains even after temper rolling by the laser dull roll. The situation is shown in Fig. 29. In Fig. 29, there are waviness due to the final stand work roll (short blast dull roll) on the plate surface of the steel plate 7 after cold rolling.
If the cold-rolled steel plate 7 is subjected to temper rolling using the temper rolling work roll 3 which has been given a predetermined roughness profile by laser processing, the waviness on the surface of the steel plate before tJJ rolling can be adjusted. The roughness profile of the surface of the work roll 3 for rough rolling is synthesized, and the surface condition of the steel plate 7 becomes a condition as shown in the bottom row of FIG. 29, that is, a condition in which waviness components remain. And if you paint a steel plate like this,
Waviness components remain on the coating surface, reducing image clarity.

As mentioned above, as a result of repeated experiments and studies by the present inventors regarding the cause of waviness on the surface of work rolls that have been dulled by shot blasting in the final stand of a tandem cold rolling mill, the following findings were obtained. Ta.

That is, first, using grid particles with a nominal particle size of 500 pm, which are most widely used in shot blasting, that is, particles having a grid particle size distribution as shown in Table 1, the number of particles per unit length was varied. Figure 30 (A>, (B), (C) shows the results of a computer simulation of the roughness profile of the roll surface when shot blasting is applied to the roll.
Shown below.

Table 1 Nigerid particle size distribution Figure 30 (A) shows when the number of particles is 10,000 and 150#,
Figure (B) shows the case where the number of particles is 100,000 pieces and 150 meters, and Figure (C) shows the case where the number of particles is 1 million pieces and 150 meters.The roughness profile at the top of each figure is the roughness profile. The simulation results are shown as they are, and the profile at the bottom is an average of 20 points. 30th
As can be understood from the figure (number of particles of A> 10,000 150#
In the case of (B) and (C), the number of particles is 100,111i! 150I
In the case of ryi, 1,000,000 pieces and 150 m, it can be seen that considerable undulation appears in the 20-point average. In normal shot blasting, the number of particles is 100,000 150am~10
00,000 pieces and about 150 m, so it is clear that if a roll is actually subjected to shot blasting, considerable waviness will occur.

In this way, dull processing by shot blasting essentially creates undulations.

It was also found that the material of the work roll itself had an effect on the occurrence of waviness. In other words, work rolls for cold rolling are generally made by rough forging after casting, but in such work rolls, a dendrite structure develops during the solidification process after casting, and after forging, as shown in Fig. 31. It produces a pattern. According to the results of measuring the hardness of the roll surface across this dendrite pattern, as shown in Figure 32, the hardness changes at a pitch of several hundred meters, and this change in hardness is caused by the shot blasting process. It was confirmed that the undulation of the roll surface was promoted by the roll surface.

This invention was made based on the knowledge about the occurrence of waviness as described above, and it is possible to prevent waviness from occurring on the surface of a steel plate after tandem cold rolling, and thereby to prevent the occurrence of waviness on the steel plate after skin pass rolling. It is necessary to prevent the occurrence of waviness and to prevent a decrease in the sharpness of the coated film surface after painting.

Means for Solving the Problems In order to achieve the above-mentioned objects, in the method for producing cold rolled steel sheets of the present invention, first, as the work roll of the final stand of the tandem cold rolling mill, bright rolls and laser processing are used. A roll with a dull date (laser dull roll), a roll with a redundant density by electrical discharge machining (discharge dull roll), and a center line average roughness Ra of 1, OJ
, 1 m or less shot-blasted rolls (shot-blasted dull rolls) are used to prevent waviness from occurring on the surface of the steel sheet after cold rolling. As for the temper rolling, it was decided to apply the same method as that proposed in the above-mentioned Japanese Patent Application No. 7769/1983.

Specifically, the method for producing a cold rolled steel sheet of the present invention basically involves cold rolling a hot rolled steel sheet to a desired thickness using a tandem cold rolling mill, annealing it, and then temper rolling. In the method for producing a cold rolled steel sheet, the work roll of the final stand of the tandem cold rolling is a bright roll,
The laser dull roll, discharge dull roll, and center line average roughness Ra are 1. Cold rolling is carried out using any one type of OJ, shot blast dull roll of 1 m or less, and the work roll for skin pass rolling has its surface pre-coated with minute crater-shaped recesses and The average center distance Sm between adjacent recesses, which is composed of a ring-shaped raised part on the front side at the outer edge of the recess
and the diameter of the outer edge of the ring-shaped raised part Sm/D
is within the range of 0.85 to 1.7 and the Sm-D value is less than 280 tones using a work roll formed using a high-density energy source. .3
% or more, the pattern on the surface of the work roll is transferred to the surface of the steel sheet by temper rolling.

Further, in the cold rolled steel sheet manufacturing method of the present invention, the temper-rolled steel sheet has a surface centerline average roughness Ra within the range of 0.3 to 2.0 JJIfl, and The microscopic morphology that constitutes the surface roughness consists of a trapezoidal peak with a flat top surface, a groove-like valley formed to surround all or part of the periphery, and It is formed by an intermediate flat part formed on the outside of a valley part, which is higher than the bottom of the valley part and lower than or at the same height as the top surface of the mountain part, and is the average of the adjacent peak parts. The distance between the centers is 3 m, the average diameter of the outer edge of the valley is calculated, and the average diameter of the flat top surface of the crest is 1. The sum of the areas of the flat top surface of the crest and the flat surface of the intermediate flat portion is the total area. η
(%), 0.85≦Sm/D≦1.7 Sm-D < 280 (JJII+) 30≦do≦5
00 (Ja) 20 ≦η≦ 85 (%).

Here, said! It is most desirable to use a laser as a high-density energy source used for processing work rolls for I11 quality rolling, but it is also possible to use plasma, electron beams, etc.

The most important point in the method of the present invention is that in the cold rolling process for turning hot-rolled steel sheets into cold-rolled steel sheets of the required thickness, the workpieces in the final stand of the tandem cold rolling mill are As the rolls, rolls such as those shown in the following (1) to (2) are used instead of the usual shot blast rolls that have been used in the past.

■Bright roll with a smooth surface after grinding.

■ Laser dull roll processed by laser.

■ Electric discharge dull roll subjected to dull processing by electric discharge machining.

■ Even if the roll is dulled by shot blasting, the surface roughness is much smaller than conventional ones, and the center line average roughness (Ra) is less than 1.0 μm.

The use of such rolls in the final stand is necessary to prevent waviness from occurring on the surface of the steel sheet after tandem cold rolling.

Here, since the bright roll (■) has a roll skin that has been ground as is, no waviness is generated on the roll surface due to shot blasting, and therefore there is no waviness on the surface of the steel plate rolled by the bright roll. Does not occur.

In addition, the laser dull roll (■) and the discharge dull roll (■) are both dulled by local melting of the roll surface, so they are similar to those obtained by mechanically hitting grid particles onto the roll surface by shot blasting. No waviness occurs on the roll surface. In other words, in the case of dullness by shot blasting,
When the grid particles are struck against the roll surface, that part becomes a recess and is dulled, and therefore, as already shown in the computer simulation results (Figure 30), waviness is inherently likely to occur due to the particle size distribution of the grid particles. , and previous) Although the occurrence of waviness is promoted by the variation in hardness of the roll surface caused by the dendrite structure, laser machining and electrical discharge machining are not processing methods that mechanically hit the roll surface. Therefore, there is essentially no factor that causes waviness, and it is not affected by the hardness or softness of the roll surface caused by the dendrite structure. Therefore, no waviness occurs on the surface of the rolls of (1) and (2). And no waviness occurs in the steel plate rolled by such method (1) or (2).

Generally speaking, even if it is a shot blast dull roll, if its surface roughness is small, that is, as shown in ■, the Ra
In the case of a shot-blasted dull roll having a diameter of less than i, oum, the occurrence of waviness on the roll surface is small, so that when the steel plate is rolled, the waviness of the steel plate is also small. That is, the case shown in FIG. 30(A) is an example in which the number of particles is reduced to 10,000 particles and 150 #, but in this case Ra is small, and therefore it can be seen that the waviness in the 20-point average is also small.

In addition, in order to make Ra a small value of 1.0 μm or less,
As shown in FIG. 30(A), there are methods such as reducing the number of particles per unit area during shot blasting, or using grid particles with a small particle size.

As described above, by using any of the rolls (1) to (4) as the work roll of the final stand of a tandem cold rolling mill, waviness on the surface of the steel sheet after cold rolling can be prevented. Therefore, waviness components do not occur on the surface of the steel sheet after temper rolling, which will be described below, and it is possible to prevent deterioration of the sharpness of the coating film surface due to waviness.

4. Rolling 1 plate The cold-rolled steel plate that has been cold-rolled to the required thickness as described above is annealed by continuous annealing or box annealing in accordance with the conventional method, and then temper-rolled. . In this temper rolling process, a predetermined roughness profile is formed on the surface of the steel sheet using a work roll dulled with a predetermined roughness profile by a high-density energy source, such as a laser.

The effects and conditions in the temper rolling will be explained below, divided into sections [1] to [11].

[1] Dull coating of a work roll for temper rolling using a laser: First, the effect of dulling a work roll for temper rolling using a high-density energy source, such as a laser, will be described.

While rotating the roll, laser pulses are sequentially projected onto the roll surface, and the laser energy regularly melts the roll surface to form regular crater-shaped recesses. The state is shown in FIG. In Fig. 1, 1 is 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 roll base metal forms a ring above the roll surface 3A. A flange-like raised portion (hereinafter simply referred to as 7 flange) 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 dulling by laser as described above will be briefly explained in detail.

The depth and diameter of the crater 1 on the roll surface formed by the laser pulse are determined by the magnitude of the incident laser energy and the projection time; Give the quantity that defines the value.

The metal forming the roll heated by the laser instantaneously turns into metal vapor due to the large irradiation energy density, and the vapor pressure generated at this time blows away the molten metal on the roll surface to form a crater 1, and the blown away The molten metal re-solidifies around the crater 1 to form a flange 2 surrounding the crater 1. These series of reactions can be carried out more efficiently by spraying an auxiliary gas such as oxygen gas toward the reaction points.

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 collection of these craters formed one after another creates a rough surface on the roll surface. can give.

The roughness of the surface of the roll thus formed is shown in FIGS. 2 and 3. As is clear from these figures, the outer portion of the seven lunges 2 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 rotational direction of the roll, and by controlling the frequency of the laser pulse in relation to the rotational speed of the roll in the axial direction of the roll. This can be adjusted by controlling the pitch at which the laser irradiation position is moved in the roll axis direction.

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 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, an annealed cold rolled steel plate is rolled at a light reduction rate in the skin pass rolling process. By applying this, the dull edges of the roll 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 having a substantially uniform height around the crater 1 on the surface of the roll 3 is pressed against the surface of the steel plate 7 with strong pressure, and as a result, the steel plate 7, which is softer than the material of the roll 3, is pressed against the surface of the steel plate 7. Local plastic flow of the material occurs near the surface of the steel plate 7, and the metal of the steel plate 7 flows into the crater 1 of the roll 3, forming a rough surface. At this time, the top surface 8 of the steel sheet metal raised inside the crater 1 becomes a flat surface as the original surface of the steel sheet, and is also pressed against the flat surface 6 on the outside of the flange 2 between adjacent craters 1 on the roll 3. The portion 9 of the steel plate surface remains flat as it is,
The former flat surface 8 is higher than or the same height as the latter flat surface 9. Therefore, the microscopic form of the rough surface of the steel plate 7 after temper rolling is, as shown in FIGS. A crest surface 8 of the ridge portion 10 that is located between the continuous groove-shaped trough portion 11 formed so as to surround the trough portion 11 and the adjacent ridge portion 10 and that is higher than the bottom of the trough portion 11 and located outside of the trough portion 11. and an intermediate flat part 9 formed at a lower or the same height.

As is clear from the above, on the surface of the steel plate of temper-rolled steel, the flat portion consisting of the peak surface 8 of the peak portion 10 and the intermediate flat portion 9 occupies a large proportion, and the proportion of the flat portion consisting of the peak surface 8 of the peak portion 10 and the intermediate flat portion 9 increases. In principle, the ratio of the inclined surfaces 13 in between 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). It has various peak heights close to the distribution, and when temper rolling is performed using such rolls, the peaks on the surface of the roll 3 dig into the plate surface of the steel plate 7, as shown in FIG. The rough surface profile of the rolling 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 theoretically has a large proportion of sloped surfaces formed by peaks and valleys. It is.

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 dull-dated by a laser.

Figure 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 dulled by the conventional shot blasting method. (
B) shows the definition of the inclination angle. As mentioned above, the DOI value that represents image sharpness is expressed as the ratio of scattered light of ±0.3° to the specular reflection angle, so flatness is determined when there is a large proportion of valleys with an inclination angle of 0.3° or less. However, in the case of Fig. 9 (A>, the occupancy rate of the inclination angle within ±0.3° is only 13
%, and in two dimensions (0,13) 2X 100=
It is only 1.7%. On the other hand, in the case of skin pass rolling using a laser-dulled roll, an order of magnitude higher flatness can be obtained.

[3] Roughness profile of the work roll for skin pass rolling and the surface of the steel plate after skin rolling Definition of the dimensions of each part: Here, the roughness of the work roll surface for skin skin rolling that has been dulled by laser as in Qianliao. The dimensions of each part in the profile and the dimensions of each part in the roughness profile of the steel plate temper-rolled by the rolls are defined as follows with reference to FIG.

D Average outer diameter of the flange 2 on the surface of two rolls - Average diameter of the outer edge of the trough 11 on the surface of the steel plate d: Average diameter of the crater 1 on the roll surface do: Average diameter of the flat peak surface 8 of the crest 10 on the surface of the steel plate H: Depth of the crater 1 on the roll surface hl: Height of the flange 2 on the roll surface = Depth from the intermediate flat part 9 to the bottom of the valley part 11 on the steel plate surface h2: The flat depth of the peak part 10 on the WA plate surface Height Sm of the peak surface 8 from the intermediate flat part 9: Average distance between the centers of adjacent craters 1 on the roll surface = Average distance between the centers of adjacent peaks 10 on the steel plate surface α: Width of the flange 2 on the roll surface [ 4] Influence on the area ratio η of the flat part on the surface of the steel plate after temper rolling: Using the values defined above, the pattern constituting the roughness profile of the work roll surface for temper rolling and the temper rolling We investigated how the conditions affect the area ratio η of the flat portion of the surface after temper rolling.

Here, the area ratio η of the flat portion is expressed as the sum of the area occupancy η1 of the flat peak surface 8 of the mountain portion 10 and the area occupancy η2 of the intermediate flat portion 9, as shown in FIG.

That is, 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 therefore the mountain part 1
This is because the diameter do of the peak surface 8 of 0 changes. On the other hand, η
The value of 2 is a constant value depending on the value of the ratio of Sm/D.

This ratio of 3m/D is within the range of the following equation (2), as will be described later.

0.85≦3m/D≦1.7 ・(2) and η1
is determined by the following equation (3), and as shown in equation (4), do 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)
do=kd...(4)7
72 = 1-π(D/Sm> 2/4+a((D/S
m)2cos-1(Sm/D)-m-1)...
(5) However, in formula 5), when 311110≧1, a=0 ・ (6)
When Sm/D<1, a=1 (7) From (2), (5), (6), and (7) above, η2 changes within the following range.

0.06<η2<0.81...(
8) Here, if we take the X-axis and y-axis for the roughness profile cross-sectional shape of the roll surface and steel plate surface as shown in Fig. 12, and assume that the cross-sectional shape of crater 1 is y = cos x, then d = π and C05d/2 = 0
−(9>Also C05do /2 =
From h2, do −2COS−” h2 m (10
)Here, the ratio h2 of the height h2 of the peak 10 transferred to the steel plate surface by the crater 1 and the depth H of the crater 1 is h2
/H can be called the roughness transfer rate, but in the above example, since the depth H of the crater 1 is 1, the roughness transfer rate can be expressed as h2/1, that is, h2.

The roughness transfer rate h2/1, 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) (11) This relationship was determined by the following experiment.

The original plate was 5PCC with a thickness of 0.32s and an Ra roughness of 0.38νm, which was cold-rolled using a Brimill roll as the final stand work roll of a tandem cold rolling mill.
Cold-rolled steel plates were used, and temper rolling was performed at various rolling elongation rates λ using a roll for temper rolling of 200 #φ with a Ra roughness of 3.54 μm and a Hs hardness of 94 using a laser. . The results are shown in FIG.

From Fig. 13, the roughness transfer rate h2/1 increases linearly until the rolling elongation rate λ is around 1.5%, but when λ is 1.8%, the roughness transfer rate h2/1 increases linearly.
%, the roughness transfer rate becomes saturated.

Roughly using the results in FIG. 13, the above dOlk, 1(
When the value of 2 was determined, the results shown in Table 2 were obtained.

Table 2: By the way, Ra1 is the average roughness of a cold-rolled WJtl14 plate for normal press forming. O~3. When dull processing is performed using a laser so as to obtain opm, the width α of the flange around the crater is approximately 0.09XD. Therefore d
can be expressed by the following formula.

d=0.82D...(12)
Also, if equation (12) is used for equation (4), do = 0.
82 kD (13) Therefore, equation (3) can be expressed as follows.

771 =7r (0,82kD/Sm) 2/4=
0.5281 to 2 (D/Sm) 2...Equation (14) (
5), (6), (7), (8), (14) and the results in Table 2, the area ratio η of the flat portion has the values shown in Tables 3a and 3b. If this η is illustrated according to the value of 3m/D, it can be expressed as shown in FIG. 14. Further, this relationship can be generalized by the following equation (15).

η=η1+η2 = 0.5281 to 2(D/Sm)” + 1−π/4
([)/Sm) 2+a((D/Sm)2COS-'
(Sm/D)-m-1)...(15) From FIG. 14, it is clear that the area ratio of the flat portion changes greatly depending on the ratio of Sm/D.

In addition, η changes depending on the elongation rate λ of temper rolling, especially S
When m/D is small, it is greatly affected by changes in λ.

Table 3a Table 3b [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 becomes unstable, making it difficult to dull the surface of the steel sheet. According to the experiments conducted by the present inventors, if the elongation rate of temper rolling is 0.3% or more, dull area weight is possible, so the elongation rate of temper rolling λ
was set at 0.3% or more.

6] Lower limit of flat area ratio η: The dull area of the work roll for skin-pass rolling can be varied by changing 3m, D, and d, and by changing the elongation rate λ of skin-pass rolling during laser processing. Flat area ratio η
A steel plate (both Ra is approximately 1.5 μm) was prepared, and after being painted black with 3 coats, the surface was glued.

When the I value was measured, the results shown in FIG. 15 were obtained.

It is clear from FIG. 15 that as η increases, the DOI value increases, that is, the image clarity becomes better. In general, in a car body coating film for a passenger car, it is desirable that the DOI value be 94% or more in order to provide a sufficient sense of luxury, and for that purpose, it is desirable that η be 35% or more. However, if a sufficiently high-class feel is not required, η may be 20% or more, and therefore the lower limit of η is set to 20%.

[7] Upper limit of Sm/D, Sm-D and upper limit of η: As already defined in section [3], the dimensions of each part of the roughness profile of work rolls for temper rolling such as Sm and H are as follows. As is clear from the explanation, the roughness imparted to a skin pass rolling roll by laser depends on the number of roll rotations, laser pulse frequency, laser output, feed rate at the laser irradiation point, laser irradiation time, or 02 gas, etc. The spraying of the auxiliary gas can be changed by adjusting conditions and the like. Here, 0.5 to 5 is suitable for general cold-rolled steel sheets for processing.
When achieving Ra roughness of pm by laser and dull area by temper rolling using processed rolls, the flange width α on the roll surface is about 20 to 403.1 m, and the flange height hl is 5 to 30 um. It will be about.

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 (A), (B), and (C) can be obtained. In other words, when Sm/D is 1, the adjacent continuous groove-shaped troughs 11 are in contact with each other at the top, as shown in FIG. 16 (A>), and when Sm/D>1, as shown in FIG. As shown in FIG. 16(B), adjacent troughs 11 are separated from each other, and conversely, when Sm/D<1, adjacent troughs 11 overlap each other as shown in FIG. 16(C).

Various roughness profile patterns can be obtained by changing the value of Sm/D in this way, but the present inventor manufactured rolls for skin pass rolling with various values of Sm/D by laser processing, 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. Pressing tests and painting tests were conducted on each steel plate, and the following findings were obtained.

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 existing between the steel plate 10 and the 18th
If press working is performed as shown in the figure, the metal flaking powder 13 generated during the press forming operation in the wide intermediate flat part 9 will be difficult to be captured by the valley part 11, and the metal flaking powder 13 will remain between the press tool 14 and the intermediate flat part 9. It remains between the flat part 9 and the flat part 9. Further, a significantly large Sm/D means that the space of the valley portion 11, which serves to store press lubricating oil, becomes relatively small, making it easy for poor lubrication 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 portion 9, that is, (Sm-D>
It is also necessary to regulate the absolute 9 value for the following reasons.

D When is large, both α and hl become large. In other words, when D is large, the ability to store lubricating oil during press working and the ability to trap exfoliated metal powder is large, which is important for preventing seizure, but its effectiveness is determined in the following cases. Limited. In other words, after metal exfoliation powder is generated, it gradually accumulates as press working progresses, and the range of relative sliding length between the press die and the workpiece material until seizure occurs. This may occur if there is a groove-like recess on the surface of the workpiece that can trap metal powder. In order to satisfy such conditions, the width of the intermediate flat part (S
It is necessary to make the absolute value of m-D> smaller than a certain value.

According to the above experiments conducted by the present inventors, the value of Sm/D was 1.7.
It has been found that if the temperature is exceeded, seizure occurs frequently during press forming as described above.

In addition, in order to prevent frequent seizures, the width of the intermediate flat part (Sm
It has been found that the absolute value of -D> needs to be smaller than 280J, 1m. Some results of the experiment are shown in Table 4. Note that (Sm-D>1, (sm
-D)2 values are as shown in FIG. 19, respectively.

Table 4 Also, the value of Sm/D is correlated with the area ratio η of the flat portion of the steel sheet surface, as shown in FIG. 14 described above. According to the above-mentioned experiments by the present inventors, as can be seen from Table 4, if the area ratio η of the flat portion exceeds 85%, 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 3m/D ratio is set to 1.7, the upper limit of the flat area ratio η is set to 85%, (Sm-D
> is less than 280 μm.

[8] Lower limit of Sm/D: If the Sm/D ratio is less than 0.85, roughening work rolls for temper rolling using a high-density energy source such as a laser becomes unstable, and the Ra roughness Control becomes difficult. Further, during the temper rolling operation, the roughness of the roll surface changes significantly, and defects are likely to occur due to peeling of a part of the roll that constitutes the rough surface.

This is due to the following reasons.

Normally, the width α of the flange is set within the range of α = 0.1 to 0.3D relative to the outer diameter of the flange, so that it is possible to store lubricating oil and trap exfoliated metal powder generated during press processing. be done. Here, if Sm/D exceeds 1, the second
As shown in Figure 0 (A>), the adjacent flanges 2 are far apart from each other, but if 3m/D is less than 1, the adjacent flanges 2 will overlap. In this case, when Sm=0.85D, as shown in Fig. 20 (B), molten metal generated from the molten metal generated from the next crater that is formed next rides on top of the adjacent flange 2, causing the flanges to overlap. Therefore, the height hl of the 7 lunge 2 is about twice that of the case where there is no overlap at all.

If Sm/D becomes smaller and becomes Sm<0.85D (however, α = 0.3D), as shown in Figure 20 (C), the next step will be inside the already formed crater. Molten metal from the adjacent crater formed in the crater 1 flows into the crater 1.
The depth H1, the flange height hl, and the width α will be changed. Furthermore, if molten metal flows into a crater in which molten metal has already been cooled and solidified in this way when an adjacent crater is formed, a clear boundary surface 15 will be formed between the layer that solidified earlier and the layer that solidified later. It becomes easy to peel off at the boundary surface due to external force, and it becomes easy to generate flaws during temper rolling.

For these reasons, the lower limit of Sm/D needs to be 0.85.

[9] Diameter dO of the flat peak surface of the peak on the surface of the steel plate: The flat peak surface 8 of the peak 10 that constitutes the microscopic profile of the rough surface of the steel plate surface is the surface that bears the press load during press forming. This corresponds to the so-called bearing area.

If the diameter d of this mountain top surface 8 is large, the flat area of the mountain top surface will be large, and the 3 m mentioned in the above item [7]
Similarly to the case where /D and η are large, seizure tends to occur more easily during press working. According to the inventor's experiments, it has been found that when d is 500 um, seizure is likely to occur. In addition, in order to form a wide mountain top surface 8 where dO exceeds soupm, it is necessary to create a roll crater 1.
It is also necessary to make the inner diameter of the crater larger, in which case the energy level required for laser pulse irradiation to generate the crater will be excessive, and a laser oscillator with a higher output than necessary may be used.
Alternatively, it is necessary to slow down the rotational speed of the rolls and lengthen the irradiation time, which is not only economically disadvantageous but also causes a decrease in overall processing efficiency and reliability.

Therefore, do is required to be 500 μm or less.

On the other hand, if the diameter do of the peak surface 8 of the peak part 10 is too small, the peak part 10 will be easily destroyed by compressive stress and shear stress during press working, and therefore more metal powder will be generated at the peak part. Also, burn-in is more likely to occur. According to experiments conducted by the present inventors, it has been found that seizure is likely to occur particularly when dO is less than 30 μm. Furthermore, if do is made smaller, the value of D will inevitably be made smaller, so it is possible to make dO smaller, and furthermore, as mentioned above [7
As mentioned in section J, in order to satisfy 3m/D≦1.7, the value of sm itself must be made small. In other words, it is necessary to reduce the interval between roll craters. For this purpose, it is necessary to extremely reduce the roll rotation speed when performing laser processing on the rolling work roll, or to raise the laser pulse frequency to the #A end, which is economically disadvantageous in either case. For these reasons, Yamabe 10
The diameter d of the top surface 8 of .

must be at least 303,1m.

In addition, here, the diameter do of the mountain top surface 8 is 30 to 5o in average diameter.
opm, but if the crater 1 is actually formed on a roll using a high-density energy source such as a laser and the peak part 10 is formed by temper rolling, the flat peak surface of the peak part 10 The planar shape of 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 major axis of each mountain top surface is 500 pm or less, and the average value of the short axis of each mountain top surface is 30 μm or more. Of course, it is most appropriate that the largest major axis of all the mountain top surfaces be 500 pm or less, and the smallest shortest axis of all the mountain top surfaces be 30 pm or more.

[10] Centerline surface roughness Ra of steel plate: As mentioned above, in this invention, it is important to control the microscopic profile that forms the rough surface of the steel plate. It is also necessary to control the roughness of the surface.

That is, even if the microscopic profile of the rough surface is regulated as described above, the center line average roughness Ra is 2. (If it exceeds 1,1111, the sharpness of the coating film will not be sufficiently good; on the other hand, if Ra is 0.
．． If it is less than 3J and 1m, seizure will easily occur during press working. Therefore, Ra is 0.3 to 2,03. II
It was within the range of I.

[11] Summary: From the above, it can be seen that cold-rolled steel sheets without waviness are temper-rolled using rolls that have been dulled using a high-density energy source such as a laser, and have good press formability (especially seizure resistance). ), and in order to have the excellent paint film clarity required for passenger cars after painting, preferably a DOI value of 94 or higher, the microscopic roughness of the steel plate surface must be The profile conditions are as follows: (i) The ratio η of the sum of the areas of the flat parts (the top surface of the mountain and the intermediate flat part) to the whole area (flat part area occupancy rate) is 20% or more (preferably 35% or more) ), 85% or less, (ii
) The ratio Sm/D of the average center-to-center distance Sm of the peaks and the average diameter of the outer edges of the valleys is in the range of 0.85 or more and 1.7 or less, and sm-o is less than 280 tones. (iii) The average diameter dO of the top surface of the mountain is 30JJIl.
1 or more, 5oo3. + m or less, and in addition to the roughness, the center line average roughness Ra must be 0.3
It is necessary that it be within the range of ~2.0 νm. Also,
As conditions 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 particularly important Sm/D ratio and dO
The relationship between the appropriate ranges is shown in FIG. 21 along with a summary of the reasons for limiting the ranges. In addition, Fig. 22 shows the optimum range of η (20 to 85%) when various temper rolling elongation ratios λ are taken.
The applicable range of Sm/D is shown below.

Example C0.04%, 1vln0.23%, Po, 02%, S
A hot-rolled steel plate with a thickness of 2.6InI11 containing O,014%, NO,003%, and QO,004%, with the remainder consisting of Fe and unavoidable impurities, was heated at a total rolling reduction of 6.
It was cold-rolled using a 4-stand tandem cold rolling mill to obtain a cold-rolled steel sheet having a thickness of 9% and a thickness of 0.8 m. In this cold rolling, the work roll conditions used were set to two types as shown in Examples and Comparative Examples in Table 5.

Table 5: Work roll conditions used in cold rolling The steel plates after cold rolling were subjected to continuous annealing and then temper rolling. In this temper rolling, a work roll (laser dull roll) whose surface roughness has been roughened by a laser and whose surface roughness Ra is varied within the range of 1.85 to 5.0 μm is used.
was used to temper-roll the material so that the elongation rate λ was 0.7%. The surface roughness profile of the work roll for temper rolling at this time is 0.85≦Sm/D≦1.7 Sm-D<280JJIT+ 50pm≦d≦500μm 35μm≦H≦i2o, um hx # 1/3H did.

Next, each steel plate after temper rolling was subjected to chemical conversion treatment under the following conditions.

Processing agent: fine-grained phosphate-based drug for dipping treatment Dip conditions: 43°C x 120 seconds Film weight fi: 2.3 ± 0.2 g/cni Pre-treatment and 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.

Painting position: Horizontal Painting Undercoat: Cationic ED paint 18-20μm thick Intermediate coat:
Sealer 30-35μm thick top coat 3
Sanding was not performed in each step of thickness 0 to 35 μm.

The DOI value of the coated film surface after painting was measured using a DORIGON meter. The results are shown in FIG. 23 in correspondence to the surface roughness Ra after temper rolling. Furthermore, the 23rd
In the figure, O marks indicate the cold rolling mill work roll conditions (final stand: bright roll).
The mark X shows the case where the cold rolling mill work roll conditions were the conditions of the comparative example (final stand: shot blast dull roll with Ra 3.2 νm). Also the second
In Figure 3, [Sk Ra] indicates the surface roughness (Ra) of the temper roll.

As is clear from Fig. 23, a bright roll is used as the work roll of the final stand of the tandem cold rolling mill, a bright roll is used as the work roll of the temper rolling mill, and a laser dull roll is used as the work roll of the temper rolling mill. In the case (Example 20 mark), a comparative example (marked with 20) was used, in which a shot blast dull roll of Ra 3.2 μm was used as the work roll of the final stand of the tandem cold rolling mill, and a laser dull roll was used as the work roll of the temper rolling mill. It can be seen that the image sharpness is improved by about 1 to 5 in terms of DOI value compared to the case (marked with x).

However, in Fig. 23, even if a bright roll is used as the final stand work roll of the cold rolling mill (marked O), if the Ra of the temper rolling work roll is as large as 5.0 νm, the steel plate surface Ra exceeds 2.0 μm, and in this case, the DOI value does not reach 94, indicating that the image clarity is somewhat insufficient.

Furthermore, FIG. 24 shows the three-dimensional waviness curve of the steel plate surface when cold rolled using the work roll flexibility of the cold rolling mill of the example and temper-rolled using the laser dull roll in the same manner as described above, and the cold rolling curve of the comparative example. FIG. 25 shows a three-dimensional waviness curve on the surface of a steel sheet obtained by cold rolling under the work roll conditions of an inter-roll mill and temper rolling using a laser dull roll in the same manner as described above. Note that these curves include 0, 8. Waves of the following wavelengths are cut off and displayed as three-dimensional undulations, and representative curves are shown with thick lines.

As is clear from FIGS. 24 and 25, under the conditions of the example, that is, when a bright roll is used for the final stand of the tandem cold rolling mill (FIG. 24), the final stand of the tandem cold rolling mill It can be seen that the undulations are significantly reduced compared to the case where a shot blast dull roll with Ra 3.2 voice is used (FIG. 25).

In addition to the above examples, a work roll (Ra
The three-dimensional waviness curve of a steel plate that was cold-rolled in the same manner as described above and roughly temper-rolled in the same manner as described above is
It is shown in Figure 6. In addition, the final stand of a tandem cold rolling mill has a work roll (Ra 3.
The three-dimensional waviness curve of a steel plate cold-rolled in the same manner as described above using 1 pm> and further subjected to temper rolling in the same manner as described above is shown in the 27th
As shown in the figure. It can be seen that the waviness on the steel plate surface is reduced in these cases as well.

Effects of the Invention As is clear from the above examples, according to the method of the present invention, the surface waviness of the steel plate after cold rolling can be reduced,
Finally, the waviness on the surface of the steel sheet after skin pass rolling can be made small, and this, together with the use of work rolls with a predetermined roughness profile during skin pass rolling, results in significantly superior image clarity. It becomes possible to form a coating film.

[Brief Description of the Drawings] Fig. 1 is a schematic cross-sectional view showing the state of the roll cross section when the surface of the work roll for temper rolling is dulled using laser pulses as high-density energy in the method of the present invention. , FIG. 2 is a schematic cross-sectional view showing the rough surface profile of the surface of the temper rolling work roll that has been dulled by the laser pulse, 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, and FIG. Fig. 7 (A) is a diagram showing the peak height distribution of the rough surface of the work roll surface for skin pass rolling that has been subjected to ridal processing by conventional shot blasting, and Fig. 7 (B) is a plan view of the conventional The height difference of the rough surface of the work roll surface for temper rolling that has been dulled by electrical discharge machining is not shown. A schematic diagram showing the situation when applying the basis weight, Figure 9 (A> is a diagram showing the slope angle division of the roughness of the steel plate surface when skin pass rolling is performed using a roll that has been dulled by the conventional shot blasting method. , Figure 9 (B) is Figure 9 (
Figure 10 is an explanatory diagram showing the definition of the dimensions of each part of the profile that forms the rough surface of the temper rolling roll and the steel plate, and Figure 11 is the flat part. A schematic diagram to explain the definition of the area ratio η (= η1 + η2), Figure 12 is an explanatory diagram for approximate calculation of the roughness profile of the roll surface and the steel plate surface, and Figure 13 is the temper rolling elongation rate λ. Figure 14 shows the relationship between the area ratio η of the flat portion of the steel plate surface and the temper rolling elongation rate λ, depending on various values of Sm/D. Figure 15 is a correlation diagram showing the relationship between the flat area ratio η of the steel plate and the DOI value of the coating film when three coats are applied, and Figures 16 (A), (B), ( C) is a schematic diagram showing the change in planar roughness profile of the steel plate surface when changing 3m/D, and Figure 17 is a microscopic view of the roll surface and steel plate surface when the Sm/D ratio is too large. FIG. 18 is an explanatory diagram showing the effect of press working on the steel plate in FIG. 17, and FIG. 19 is an illustration of the width of the intermediate flat part (Sm-D> Schematic diagram for
>, (B), and (C) are explanatory diagrams for showing the situation during laser processing of a work roll for temper rolling when the value of Sm/D is avoided by a center change of 0.85, No. 21 The figure is an explanatory diagram showing the relationship between the value of Sm/D and the appropriate range of the diameter dO of the peak surface of the steel plate surface.
Figure 23 is a correlation diagram showing the appropriate range of m/D, and Figure 23 is a correlation diagram showing the relationship between the centerline average roughness Ra of the steel plate surface after temper rolling and the DOI value of the 3-coat coating in Examples and Comparative Examples. , FIG. 24 is a diagram showing the three-dimensional waviness curve of the surface of the steel plate after skin pass rolling according to an example in which a bright roll is used as the work roll of the final stand of a tandem cold rolling mill.
Figure 5 is a line diagram showing the three-dimensional waviness curve of the surface of a steel plate after skin pass rolling in a comparative example using a shot blast dull roll with an Ra of 3.2 μm as the work roll of the final stand of a tandem cold rolling mill. A diagram showing a three-dimensional waviness curve on the surface of a steel plate after temper rolling according to an example in which a laser dull roll was used as a work roll in the final stand of a cold rolling mill, and FIG. 27 is a work roll in the final stand of a tandem cold rolling mill. FIG. 3 is a diagram showing a three-dimensional curvature curve on the surface of a steel sheet after skin pass rolling according to an example using a discharge dull roll. Figure 28 is a diagram showing the method for measuring the DOI value, which represents image clarity, and Figure 29 is a diagram showing the situation in which a conventional cold-rolled steel plate with undulations is temper-rolled using a laser dull roll. Explanatory diagram, Fig. 30 (A>, (B)
, (C) is a diagram showing the results of a computer simulation of the roughness profile of the roll surface when the roll surface is processed to shot plus 1, and Figure 31 shows the dendrite structure of the surface of the roll forged after casting. FIG. 32 is a diagram showing changes in the hardness of the roll surface. 1... Crater (crater-shaped recess on the surface of the work roll for i!! quality rolling), 2... Flange (ring-shaped raised part on the surface of the work roll for temper rolling), 3... For temper rolling Work roll, 7... Steel plate, 8... Middle flat part on the surface of the steel plate, 10... Mountain part on the surface of the steel plate, 1
1...Trough on the surface of the steel plate, 13...Slanted surface.

Claims (1)

[Scope of Claims] (1) A method for producing a cold-rolled steel plate in which a hot-rolled steel plate is cold-rolled to a required thickness using a tandem cold rolling mill, annealed, and then skin-pass rolled. As the work roll of the final stand of the cold rolling mill, any one of the bright rolls, laser dull rolls, discharge dull rolls, and shot blast dull rolls with a center line average roughness Ra of 1.0 μm or less is used. A work roll used for cold rolling and temper rolling has a surface that is made up 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 has an adjacent surface. The ratio Sm/D of the average center distance Sm between the matching recesses and the diameter D of the outer edge of the ring-shaped raised part is 0.8.
Using a work roll that uses a high-density energy source to form a surface pattern with an Sm-D value of less than 280 μm within the range of 5 to 1.7, the temper rolling elongation λ is 0.3% or more. A method for producing a cold-rolled steel sheet, characterized in that a pattern on the surface of a work roll is transferred to the surface of the steel sheet by temper rolling. (2) By the temper rolling, the steel plate after temper rolling has a center line average roughness Ra of the surface within the range of 0.3 to 2.0 μm, and microscopic particles constituting the surface roughness. A trapezoidal peak having a flat top surface, and a groove-shaped valley formed to surround all or part of the periphery;
An intermediate flat part formed between the peaks and outside the valley, which is higher than the bottom of the valley and lower than or at the same height as the top surface of the peak, and which is located between adjacent peaks. Sm is the average center-to-center distance of the troughs, D is the average diameter of the outer edge of the troughs, d_o is the average diameter of the flat top surfaces of the ridges, and is the area of the flat top surface of the crests and the flat surface of the intermediate flat portion. When the ratio of the sum to the total area is defined as η (%), 0.85≦Sm/D≦1.7 Sm-D<280 (μm) 30≦d_o≦500 (μm) 20≦η≦85 ( %) The method for manufacturing a cold-rolled steel sheet according to claim 1, characterized in that the patterning is performed so as to satisfy %). (3) The method for manufacturing a cold-rolled steel sheet according to claim 1 or 2, in which a laser is used as the high-density energy source.