JPH04333310A - Steel sheet for painting having excellent press formability - Google Patents

Abstract

PURPOSE:To provide the steel sheet for painting which is greatly improved in press workability by regulating the surface roughness patterns of the steel sheet. CONSTITUTION:This steel sheet for painting which has the excellent press formability is formed by providing many microrecessed parts having circular, elliptical and polygonal or other shapes on the surface of the steel sheet. The shapes of these recessed parts are so determined that the diameter d satisfies a range of 50 to 200mum, the depth h of the recessed parts 2 to 16mum, and the volume of the recessed parts 1X10<3> to 1X10<6>mum range. The center-to-center distance (p1) between the adjacent recessed parts in a rolling direction is specified to 1.0 to 1.5d and the center-to-center distance (p2) between the arrays of the rolling direction arrays to 0.1 to 1.5d. The cold rolled steel sheet for painting having the press formability and the high brightness after painting in combination is produced. The roll life is greatly improved by controlling the shapes of chromium projections.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated steel plate with excellent press formability, which has significantly improved press formability by controlling the surface roughness pattern of the steel plate.

0002

2. Description of the Related Art Generally, the surface of a cold-rolled steel plate for processing is dull-finished to facilitate press working. In other words, during press working, lubricating oil for processing is stored in the unevenness formed on the surface of the steel plate, reducing friction between the die and the steel plate.
This is because it also acts to prevent burn-in. Also,
Research on press formability has been conducted from both the steel plate material side and the forming technology, but as products become more precise and complex, the properties required for steel plates are becoming more sophisticated.
It is becoming more diverse. For this reason, currently, in temper rolling, which finalizes the roughness of the steel sheet, a work roll that has been dulled by shot blasting, electric discharge, laser, etc. is used to roughen the surface of the steel sheet. The roughness is transferred to the surface. In addition, as evaluation criteria for actual press forming, the conventionally used mechanical properties of steel sheets (r value, El value, etc.) alone are insufficient, and steel sheet surface roughness, lubricating oil, etc. also have a large influence on press formability. effect. For example, roll surface roughness R
a. Japanese Patent Publication No. 59-34441 discloses a method for producing cold-rolled steel sheets with excellent press formability by temper rolling using dull rolls with controlled PPi. By improving the angle profile and reducing the unevenness of the surface of the paint film after painting, and increasing the proportion of the horizontal part, we are able to improve the specular reflectance of light and reduce distortion of the mapping. Japanese Patent Application Laid-open No. 168602/1983 is known as a steel plate that can improve image sharpness compared to conventional steel sheets.

0003

[Problem to be solved by the invention] These known patents are
Although it is excellent in terms of improving press formability and sharpness after painting, however, Japanese Patent Publication No. 59-34441 states that the surface roughness of the steel plate must be regulated. There are drawbacks, and even
It has arbitrary surface roughness Ra and PPi, and does not give any suggestion regarding the manufacturing method of cold rolled steel sheet. Also,
In JP-A No. 62-168602, the microscopic form constituting the surface roughness is such that it surrounds a trapezoidal peak having a flat peak surface and all or part of its periphery. By forming the groove-like troughs formed in the grooves, the sharpness of the coating film after painting is improved. However, because the groove-like troughs are in a ring-like pattern, the amount of processing lubricating oil that accumulates in the convex parts formed on the surface of the steel sheet during press forming is small, and the press formability is sufficiently satisfied. The disadvantage is that it is not possible to obtain

0004

[Means for Solving the Problems] The present invention advantageously solves the problems of the prior art, and is characterized by having a large number of minute shapes such as circles, ellipses, polygons, etc. on the surface of a steel plate. In addition, the shape of the recess satisfies a diameter d50 to 200 μm, a recess depth h 2 to 16 μm, and a recess volume 1×10 3 to 1×10 6 μm, and the center between adjacent recesses in the rolling direction. Distance (p1) 1.0d~1
．． 5d, center distance between rows in rolling direction (p2) 0.1d~
A steel plate for painting with excellent press formability characterized by having a thickness of 1.5d.

[0005] The present invention will be explained in detail below with reference to the drawings. FIG. 1 is an explanatory diagram of the roll manufacturing method according to the present invention. In the present invention, first, as shown in FIG. 1(A), the surface of a roll 1 is coated with a resin 2 having a thickness of about 20 to 30 μm. The coating resin has properties such as alkali resistance, chromic acid resistance, and insulation properties, and is preferably an alkaline resin or a plating sealing resin, etc., so that it can be easily removed in a subsequent process. For example, acrylic resin, Examples include methacrylic resin, methacrylic acid ester, polyolefin resin, epoxy resin, alkyd resin, vinyl chloride resin, and polyamide resin. These resins are coated on the roll surface to a thickness of about 20 to 30 μm. Coating methods include roll pull-out method using non-rotating rolls, electrodeposition coating method, roll coater using rotating rolls, spraying, and coating.
It is uniformly adhered to the roll surface by means such as coating with tar, powder coating, or wrapping a film-like resin, and then dried. Next, as shown in FIG. 1(B), the resin-coated roll 1 is processed by high-density energy, for example, a laser beam 3. That is, the laser beam 3 is irradiated from the surface of the coated resin 2 to melt and remove the resin in that area. Concave diameter d10~50μm after resin is dissolved and removed
It can be adjusted by adjusting the hole diameter, laser irradiation conditions, especially laser output, and the gap (focal shift) between the condenser lens 4 and the roll, and in the present invention, the hole diameter is in the range of 50 to 200 μm. Set the laser irradiation conditions so that To perform laser processing on the roll surface described above, the laser processing head is moved while rotating the resin-coated roll, and processing is performed based on a preset pitch interval P. This is done by irradiating laser at different frequencies and roll rotation speeds. Ray
After the laser processing, the roll of the present invention is subjected to chromium plating 5 in a chromium plating solution, as shown in FIG. 1(C). The plating conditions were a current density of 20 to 50 A/dm2 in a chromic acid solution, and a concave diameter of d10 to 50 after the resin was dissolved and removed.
The diameter of the hole is 5 to 20 μm, that is, the hole diameter is 5 to 20 μm, which is formed by the laser processing described above by performing electrolytic plating under conditions such as an input current of 2000 A to 20000 A depending on the effective area ratio of the chrome plated part. It is possible to attach chrome protrusions with round or oval tips. At this time, since the resin is an insulating material, chromium does not adhere to its surface, and depending on the plating conditions, only the hole is plated to a thickness that is approximately equal to or less than the thickness of the resin. . FIG. 1(D) shows the surface condition after chromium plating, in which holes 6 formed by the resin 2 and the surface of the roll 1 have electrolytically plated curved chrome protrusions 7 attached thereto. Next, the resin on the surface of the roll having the chrome protrusions 7 is removed by immersing it in a solvent or brushing it with a solvent. Then, as shown in FIG. 1(D), the resin is removed from the roll 1.
A chrome protrusion 7 is exposed on the surface. Through the above steps, the present invention can manufacture a roll in which curved chrome protrusions are provided on the surface of the roll 1 at a predetermined pitch.

FIG. 2(A) schematically shows a cross section of a roll according to the present invention, in which the surface of the roll 1 is irradiated with a laser to form holes with a diameter of 50 to 200 μm. do. 7 is
Diameter D and height H from the roll surface attached to the hole 6
It is a protrusion mainly composed of chromium that protrudes so that the distance is in the range of 5 to 20 μm, and the center distance P between the rows in the rolling direction
They are arranged at intervals of c=0.1D to 1.5D. Also, protrusion 7
If the height H exceeds 20 μm, the protrusions 7 will be
The height of the protrusion 7 is preferably about 10 μm or less, because the height of the protrusion 7 is preferably as low as possible, since the protrusion 7 may fall off due to the surface of the protrusion or break due to the rolling load. However, if the thickness is less than 2 μm, the depth of the recesses transferred to the surface of the steel sheet will be low, and the roughness will also be low, making it impossible to achieve the object of the present invention. In addition, Figure 2 (
B) shows the cross-sectional shape of a steel plate that was temper-rolled with rolls having the above-mentioned surface shape and was transferred at a rate of 40 to 100%. Note that if the transfer rate is 40% or less, the depth of the recesses transferred to the surface of the steel plate will be low and the roughness will also be small, making it impossible to achieve the object of the present invention.

FIGS. 3(A) and 3(B) schematically show planes of a steel sheet cross section and a roll cross section according to the present invention, in which a recessed portion with a diameter d50 to 200 μm is formed on the surface of the steel sheet. Center distance between adjacent recesses in the rolling direction P1=1.0d~1
．． 5d and the center distance between rows in the rolling direction P2 = 0.1d to 1
．． Arranged at 5d intervals. If this pitch is too large, the amount of oil reservoir per unit area of the steel plate will be reduced, which will lead to press cracking problems in parts that require severe press processing such as steel plates for automobiles, such as floor board centers, door inners, etc. Furthermore, if the diameter is too small, the present invention is limited to the above range in view of the ability (variation range) of laser pulses during roll processing. Next, the upper limit of the depth of the recess in the steel sheet is set to 16 μm from the height of the protrusion shown above, and when the depth of the recess in the steel sheet becomes lower than 2 μm, the depth of the recess on the surface of the steel sheet becomes low and the roughness becomes small. cannot be achieved. In addition, considering the oil reservoir effect during pressing and the lubrication effect on the surface of the steel plate, the shape of the recess in the steel plate has circular, elliptical, rectangular, and polygonal shapes when viewed from the planar shape of the recess in the steel plate.
Similarly, when viewed from the cross-sectional shape, circular, elliptical, rectangular, polygonal, trapezoidal, and angular shapes are also considered, and at least they are not groove-like ring-shaped valleys as in the above-mentioned Japanese Patent Application Laid-Open No. 62-168602. Any shape may be used as long as it is a concave shape. This point is also the first feature.

FIG. 4 is a diagram showing the relationship between the steel plate recess volume and hole pitch of the cold rolled steel plate according to the present invention. When the center distance between adjacent recesses in the rolling direction P1 = 1.0 d to 1.5 d and the center distance between rows in the rolling direction P2 = 0.1 d to 1.5 d, the steel plate recess volume is 1 x 10 3 to 1 x 10 6 μm 3 The range is the best in pressability and image clarity. When the volume of the recessed portion of the steel plate is 1×10 3 or less, the coating clarity improves, but the oil reservoir volume during pressing decreases, leading to mold galling during pressing. In addition, when the volume of the recess in the steel plate is 1 x 106 μm3 or more, the pressability improves due to a dramatic increase in the oil reservoir volume during pressing, but the paint sharpness deteriorates due to the increase in waviness on the steel plate. Therefore, in the present invention, it is limited to the above range. That is, the steel plate has the recess shape described above, and the volume of the steel plate recess is 1×10 3 to 1×10 6 μm.
By having a volume of 3, it is possible to obtain a pressable steel plate with good image clarity. That is, this point is the second feature.

[0009]

[Example] Acrylic resin was applied to the surface of a work roll for a 5% Cr forged steel temper rolling roll with a diameter of 600 mmφ.
It was coated uniformly to a thickness of 20 μm to 30 μm and then dried. After that, 8 to 2
A YAG pulse laser with 0 W power was irradiated to form a circular recess. That is, by changing the focal length of pulsed laser light with a constant peak value and pulse width using a condensing lens,
While rotating the roll and moving the laser head, the roller - Irradiate the roll surface, penetrate the coated resin, and slightly melt the roll surface to form a circular recess. Ray
After the laser processing, the roll is subjected to alkaline electrolysis at a temperature of 45 to 50℃.
Degreasing was performed for a degreasing time of 100 to 150 seconds, and chromium plating was performed using a chromic acid solution. That is, electrolytic plating was performed in a chromic acid solution to adhere chromium approximately 8 μm thick to the holes formed on the roll surface. At this time, since the acrylic resin that coated the roll surface had insulating properties, the resin-coated surface was not plated with chrome, but the holes were plated with chrome to a thickness that was approximately the same as the thickness of the resin. After plating, the resin covering the surface was removed by brushing with a solvent. As a result, chrome projections of approximately 8 μm were squarely arranged on the roll surface. Using the rolling roll manufactured in this way, a cold rolled steel plate with a thickness of 0.75 mm was coated with an elongation rate of 1.2.
% temper rolling was performed, and the rough surface formed on the roll surface was transferred to the steel plate. Table 1 shows the steel plate shape pattern at that time. The shape patterns of each steel plate shown in Table 1 were evaluated using the limit drawing ratios (L, D, R). These L, D, and R are the maximum blank diameter D that can be deep drawn using a die with a punch diameter of 32 mm.
was determined from the ratio to the punch diameter d. That is, L,
D, R=Dmax/d, and the results are shown in Table 2 along with press workability and roll life.

0010

[Table 1]

[0011]

[Table 2] As is clear from Table 2, it can be seen that Samples 1 to 5 according to the present invention are extremely superior to conventional samples 6 to 8, especially in terms of pressability steel sheets and roll life.

0012

[Effects of the Invention] The present invention makes it possible to produce cold-rolled steel sheets for painting that have superior pressability compared to conventional laser steel sheets, and by controlling the shape of chrome protrusions, roll life can be dramatically extended. You can improve your performance.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the roll manufacturing method according to the present invention,

FIG. 2 is a partial sectional view of the roll of the present invention and a steel plate rolled using the roll of the present invention;

FIG. 3 is a partial plan view of the roll of the present invention and a steel plate rolled using the roll of the present invention;

FIG. 4 is a diagram showing the relationship between the steel plate recess volume and hole pitch of the steel plate of the present invention.

[Explanation of symbols]

1 roll, 2 Resin, 3 Laser beam, 4 Condensing lens, 5 Chrome plating, 6 holes, 7.Protrusion.

Claims (1)

[Claims] [Claim 1] A steel plate surface is provided with a large number of minute recesses having shapes such as circles, ellipses, polygons, etc., and the shape of the recesses is such that the diameter d is 50 to 200 μm and the recess depth h is 2 to 200 μm.
16 μm, the recess volume satisfies the range of 1×103 to 1×106 μm, and the center distance between adjacent recesses in the rolling direction (p1
) 1.0d to 1.5d, center distance between rows in rolling direction (p
2) A steel plate for painting with excellent press formability, characterized by having a thickness of 0.1 d to 1.5 d.