JP2855392B2 - Cold rolled plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold-rolled sheet having different double-sided performances, which has sharpness after coating on the outer surface and press workability on the other surface.

[0002]

2. Description of the Related Art Conventionally, a cold-rolled steel sheet for working is dull-finished on the surface of the steel sheet in order to facilitate press working. That is, the lubricating oil for processing is stored in the unevenness formed on the surface of the steel sheet during the press working, and serves to reduce the wear of the die and the steel sheet and to prevent seizure. In addition, research on press formability has been carried out from both the steel sheet side as a material and the forming technique. However, the required characteristics of steel sheets are becoming more sophisticated and diversified as products become more accurate and more complex. For this reason, in the present condition, in the temper rolling for finally adjusting the roughness of the steel sheet, a work roll that has been dulled by shot blasting, electric discharge, laser or the like is used to transfer the roughness to the steel sheet surface.

[0003] In addition, the exterior steel plate of an automobile body or a home appliance is painted to give an aesthetic appearance, but at this time, it is excellent in so-called sharpness in that the aesthetic appearance is not impaired by irregular reflection of the painted surface. Is required. Therefore, for example, by improving the surface roughness profile of the steel sheet, reducing the unevenness of the painted surface after painting and increasing the proportion of the horizontal portion, improving the regular reflectance of light and reducing the distortion of the mapping, Japanese Patent Publication No. 3-38923 is known as a steel sheet capable of improving the sharpness after painting as compared with the conventional steel sheet. In addition, as in Japanese Patent Publication No. 3-39661,
This is a steel plate for coating that can greatly improve the sharpness, but the larger the center line surface roughness Ra, the larger the amplitude of peaks and valleys, so the unevenness of the coated surface becomes severe, and the irregular reflection of light As a result, the glossiness is impaired, and the image quality is degraded due to the necessity of mapping, thereby deteriorating the sharpness.

[0004]

As described above, by reducing the unevenness of the painted surface after painting and increasing the proportion of the horizontal portion, the improvement of the regular reflectance of light and the distortion of the mapping are reduced, and While improving the sharpness afterwards, the press workability deteriorates. On the other hand, when the center line surface roughness Ra is increased in order to enhance the press workability, the amplitude of peaks and valleys increases, so that the unevenness of the painted surface becomes severe, irregular reflection of light occurs, and gloss is impaired. This leads to both sides that distortion is caused, image clarity is reduced, and sharpness is deteriorated. Therefore, the present invention seeks to achieve both enhanced sharpness and improved press workability.
It is an object of the present invention to provide an advantageous solution with respect to improved sharpness and press workability.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems and enhances sharpness on one side and improves press workability on the other side, so that both sharpness and press workability are excellent. On cold rolled sheets. The gist of the invention is that a cold rolled sheet provided with different roughness on the front and back surfaces of a steel sheet by imparting different roughness to a pair of upper and lower work rolls for rolling and temper rolling. Has a diameter d of 50 to
Regular concaves and convexes having a depth of 200 μm, a depth h of 2 to 16 μm, and a distance P between adjacent concave centers of 0.5 to 2.5 μm are provided, and the other surface has an average roughness Ra of 0.6 to 1. A cold-rolled sheet characterized by having random irregularities of 1 μm.

[0006]

The present invention will be described below in detail with reference to the drawings. FIG. 1 is an explanatory view showing a profile for forming a rough surface of a steel sheet according to the present invention. As shown in FIG. 1, the average diameter d of the outer edge of the valley 2 on the surface of the steel plate 1 is 50 to 200 μm.
m, the depth h of the concave portion from the intermediate flat portion 3 is 2 to 16 μm, and the condition range in which the regular concave / convex shape having the distance P between the adjacent concave portions of 0.5 to 2.5 μm is described. First, when the diameter d is less than 50 μm, a metal contact portion occurs due to insufficient supply of lubricating oil to the surface of the convex portion of the steel sheet, so that press workability is poor and flaws and the like are likely to occur. On the other hand, when the thickness exceeds 200 μm, the press workability is good, but since the unevenness does not disappear on the surface after coating, the sharpness deteriorates.

Next, the depth h of the recess from the intermediate flat portion is set to 2 to 1
The reason why the thickness is set to 6 μm is that if the depth of the concave portion is less than 2 μm, the concave portion is crushed by the surface pressure during molding and the lubricant cannot be secured, and the frictional resistance increases. If the concave portion depth exceeds 16 μm, the unevenness does not disappear on the surface. Sharpness deteriorates. Further, the reason why the regular concave-convex having the distance P between the adjacent concave centers of 0.5 to 2.5 μm is provided is that when the distance is less than 0.5 μm, the convexes are formed due to the overlapping of the concaves and the protrusions are removed during the press working. This is because the generation of iron powder increases and the press workability is impaired. Conversely, if the thickness exceeds 2.5 μm, the number of flat portions increases, the number of surfaces in contact with metal during press processing increases, and the friction coefficient between the dies increases. As a result, flaws easily occur between the steel sheet and the die.

FIG. 2 is a schematic cross-sectional view showing a state where temper rolling is performed by a dulled roll. Using a work roll that has been subjected to dulling by laser or the like, in the temper rolling step, by applying a light reduction rate to a steel sheet, for example, an annealed cold-rolled steel sheet, the dull of the roll is transferred to the steel sheet surface, A rough surface is formed on the surface. When the surface of the steel sheet is microscopically observed in this process, as shown in FIG. 2, the flange 5 is pressed against the surface of the steel sheet 1 with a substantially uniform height on the surface of the roll 4 by a strong pressure. A local compositional flow of the material occurs near the surface of the thin steel sheet 1 that is softer than the material, and the metal of the steel sheet 1 flows into the inside of the crater 6 of the roll 4 to form a rough surface. At this time, the top surface 8 of the trapezoidal ridge protruding inside the crater 6 becomes a flat surface while maintaining the original steel plate surface.
The intermediate flat 9 pressed against the flat surface 7 outside the flange 5 between the adjacent craters 6 becomes a flat surface as it is,
The flat top surface 8 is slightly higher or at the same level as the intermediate flat portion 9.

On the other hand, the other surface has an average roughness Ra of 0.6.
That is, random irregularities of up to 1.1 μm are provided. The surface roughness of a steel sheet is the most important factor for press formability, and the surface roughness is also required to control the state of contact with a press die to suppress the occurrence of die galling. Therefore, when the average roughness Ra is less than 0.6 μm, seizure tends to occur during press working. Also, 1.1
When the thickness exceeds μm, the sharpness after coating is not sufficiently good.
By providing random irregularities in the range of 0.6 μm to 1.1 μm, the effect of improving the oil pool by providing random roughness is achieved, and press formability can be improved.

FIG. 3 is a view showing a microscopic morphology of a cold rolled sheet surface by a micrograph. As shown in FIG. 3, it can be seen that an arrangement is shown in which the diameters of the holes and the recesses and the distance between the recess centers are regularly constant. FIG. 4 is a diagram showing a microscopic form of a back surface of the cold-rolled plate by a micrograph. FIG. 4 shows a random uneven state. This random roughness improves the oil pool and provides a plate with good press formability.

FIG. 5 is a view showing a cylindrical deep drawing test of the cold rolled steel sheet of the present invention. As an evaluation test of the inner plate for an automobile, the presence or absence of cracks (pressing / workability) after working was investigated, and the evaluation was made based on the limit drawing ratio (L, D, R). L, D, and R are obtained by calculating the maximum raw plate diameter that can be deep drawn using a mold having a punch diameter of 32 mm, and calculating the ratio between the maximum raw plate diameter and the punch diameter. As a result, the steel sheet of the present invention shows that the L, D, and R of the conventional material are 2.35 while the L and D of the present material are 2.35 according to FIG.
The D and R values are as high as 2.45, and are excellent in deep drawability and mold galling resistance. Although the above description has been made mainly with respect to a steel plate, the present invention is not limited to a steel plate, but can be applied to a galvanized steel plate, an electroplated steel plate, a stainless steel plate, and an aluminum plate.

[0012]

As described above, it is possible to manufacture a cold-rolled sheet having both pressability and high sharpness after painting as compared with the conventional steel sheet, and to produce a steel sheet for automobiles which could not be obtained conventionally. Has good press workability and can completely solve quality problems such as cracks.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a profile for forming a rough surface of a steel sheet according to the present invention;

FIG. 2 is a schematic cross-sectional view showing a state in which temper rolling is performed by a dulled roll;

FIG. 3 is a diagram showing a microscopic morphology of a cold-rolled plate surface by a micrograph,

FIG. 4 is a diagram showing a microscopic morphology of a back surface of a cold-rolled plate by a micrograph,

FIG. 5 is a view showing a cylindrical deep drawing test of the cold-rolled steel sheet of the present invention;

FIG. 6 is a diagram showing the results of press workability evaluation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel plate 2 Surface trough 3 Intermediate flat part 4 Roll 5 Flange 6 Crater 7 Flat surface 8 Flat top surface 9 Intermediate flat part

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-2-41702 (JP, A) JP-A-3-170694 (JP, A) JP-A-4-200902 (JP, A) JP-A-3- 193202 (JP, A) JP 3-39761 (JP, B2) JP 3-38923 (JP, B2) (58) Fields studied (Int. Cl. ⁶ , DB name) B21B 1/00

Claims (1)

(57) [Claims] 1. A cold rolled sheet having different roughnesses on the front and back surfaces of a steel sheet by imparting different roughnesses to a pair of upper and lower work rolls for rolling, and performing temper rolling. Is 50 to 200 μm, and the recess depth h is 2 to 16.
μm, and the distance P between adjacent concave centers is 0.5 to 2.5 μm
A cold-rolled sheet characterized by having regular irregularities provided thereon and random irregularities having an average roughness Ra of 0.6 to 1.1 μm provided on the other surface.