JPH02280902A - Steel sheet for press having anisotropy in slidability - Google Patents

Abstract

PURPOSE:To reduce the defective points in forming that the steel sheet itself possesses and to improve the formability by forming the steel sheet into a specific surface roughness structure in which the nearest spacings of recessed part are constant and the direction thereof is made to coincide with a specific direction. CONSTITUTION:The steel sheet has the surface roughness structure in which the flat parts of <=0.2mum average roughness Ra occupy >=30% of the steel sheet surface and the recessed part of >=1mum depth are distributed in the flat parts thereof. The recessed part are so arranged that the nearest spacings of the recessed part are >=40mum and <=400mum and the nearest contact direction thereof coincides with the specific direction to impart the anisotropy to the slidability. The defective points in the press forming occurring in the characteristics, such as r value and El value possessed by the steel sheet itself are decreased in this way by imparting the surface characteristics to the steel sheet. The press formability is thus improved.

Description

[Detailed Description of the Invention] <Industrial Application Field> By controlling the direction of the surface roughness pattern of the steel sheet, anisotropy can be imparted to the surface texture of the steel sheet to improve workability such as drawing and bending. This paper attempts to propose a drawing-like steel plate with surface friction anisotropy.

In general, thin steel sheets, especially cold-rolled steel sheets, are often subjected to mechanical processing such as drawing or bending to obtain a desired shape, and then subjected to a coating treatment or the like before use. It has been thought that the best properties of such thin steel sheet materials are uniform and isotropic.

However, in reality, the tensile properties of steel sheets usually have in-plane anisotropy, so in order to improve the properties of steel sheets, it is first of all to reduce the anisotropy. has been considered essential.

For example, the r value is important for improving drawability, but it is known that it is extremely difficult to improve it uniformly because it strongly depends on the crystal orientation. Even today, many efforts are being made to control it, but it is still difficult to say that it has been sufficiently controlled.

I can give you if requested. That is, when very deep and uniform drawing workability is required, the formability obtained may be insufficient even if the material properties of the steel plate, such as the r value, are controlled to near the limits of current technology.

<Prior Art> Conventional steel sheets were strongly required to be uniform and isodirectional in both micro and macro dimensions. Therefore, methods for roughening the roll surface used in temper rolling, which aim to impart roughness to the surface of a steel sheet, include shot blasting, electric discharge dulling, and the recently put into practical use laser dulling (a special Publication No. 62-11922, etc.) and
In any case, the first objective is to obtain a surface with uniform roughness. However, such conventional techniques are no longer able to satisfy the various demands on the surface of steel sheets these days.

One example of this is the extremely severe deep drawability (a problem that the invention seeks to solve).Despite many years of effort, steel sheets for drawing or overhanging have poor internal quality, which is considered to be unavoidable. The purpose of the present invention is to effectively improve processability not by improving anisotropy, but by appropriately controlling the anisotropy of surface texture to rival or surpass the effects caused by the anisotropy. .

Means for Solving the Problem> That is, the present invention provides a steel plate in which a flat portion with an average roughness Ra of 0.2 μm or less occupies 30% or more of the surface of a steel plate, and the flat portion has a depth of 1 μm from the flat portion. It has a surface roughness structure in which the above recesses are distributed, and the nearest distance between the recesses is 40 μm or more,
The object of the present invention is to provide a thin steel plate for pressing having an anisotropic sliding property, which is 400 μm or less and is arranged so that its nearest direction coincides with a specific direction.

In the above-mentioned surface roughness structure, it is preferable that the direction in which the angle between the recessed portion and the flat portion has a minimum value coincides with the direction of the closest distance between the recessed portions.

The present invention will be explained in more detail below.

It was originally thought that the best properties of thin steel sheets were isotropic. However, it is known that the tensile properties of steel sheets actually exhibit different values depending on the angle with respect to the rolling direction. This effect manifests itself as the appearance of ears when narrowed down to a cylinder, for example. When forming the steel plate 2 with the mold 1 as shown in Fig. 4, if the steel plate is isotropic, no flange will occur as shown in Fig. 5a, but if it is anisotropic, the flange will not occur as shown in Fig. 5b. The ears occur as shown in . For example, in a direction where the r value (Lankford value) is small, deformation is difficult, so ears are likely to occur in that direction.

Furthermore, in the actual blanking shape, the flange dimensions are not always in the same direction with respect to the target press part, but rather the flange at a part of the corner is often large. FIG. 2 shows a blanking method, and when considering the case of cylindrical drawing, if the flange lengths are to be made in the same direction, it is necessary to form a round blank as shown by X. However, this method wastes a lot of material and is disadvantageous in terms of yield. When forming a rectangular blank as shown by Y, as shown in Fig. 3, the flange lengths of parts 3a and 3b are significantly different with respect to the cylindrical drawing punch, so the flange length after drawing is The lengths are different, and the yield decreases due to tremming. Furthermore, when anisotropy in material properties is added, it is difficult to mold a cylindrical body from a rectangular blank with a good yield, which not only makes it difficult to use the material effectively, but also causes problems such as cracks and wrinkles during molding. . Therefore, if the surface characteristics of the material are compensated for by reducing the sliding resistance in the part 3b so that the material flows easily into the cylindrical shape, it is possible to obtain a material without the formation of ears as explained in connection with Fig. 5a. Not only can materials be used effectively, but molding defects can also be prevented. Even in this blanking shape,
If the flow of material could be controlled according to the shape of the pressed product, the yield of steel sheets would be dramatically improved. Conventionally, the methods to improve the anisotropy caused by deep drawing are as follows:
It has been believed that the only option is to improve the internal quality of the material, such as the r value and E1 value. However, there are limits to controlling the in-plane anisotropy of the internal substance of a steel sheet, and it has been almost impossible to control it completely.

While conventional steel plate surface roughness, especially the surface roughness of press steel plates, has been based on the assumption that it is isotropic, the present invention focuses on the usefulness of using isotropy and anisotropy. It is something.

In the present invention, the surface roughness is such that a flat part with an average roughness Ra of 0.2 μm or less occupies 30% or more of the steel plate surface, and recesses with a depth of 1 μm or more from the flat part are distributed within the flat part. structure, the closest distance between the recesses is 40 μm or more, 40
They are arranged so that the distance is 0 μm or less and their nearest direction coincides with a specific direction.

In order to explain this, Fig. 1a is a plan view of one structural example of the steel plate of the present invention, and Fig. 1b is a diagram of a two-dimensional roughness profile showing the surface shape of the cross section taken along line I-I in Fig. 1a. shows. In FIG. 1b, nl, 412. A3. ll-
4 is a flat portion 10 included within the predetermined length 1, V,
, V2 is the closest spacing of the recesses 11 distributed within the flat portion 10.

The flat part means a part where Ra is 0.2 μm or less, and when this is 30% or more, (IL+ +, Q2+Il, +IL
4)/It≧0.3. These can be obtained from a two-dimensional roughness profile or by image processing analysis of the steel plate surface using three-dimensional roughness data. If the area ratio of the flat portion is less than 30%, the effect of oil pooling in the recesses will be reduced, and the effect of the anisotropic roughness itself will be lost, which is not preferable.

Then, the recesses are arranged on the surface of the steel plate so that the closest distance between the recesses that is 1 μm or more lower than the flat portion is 40 to 400 μm. That is, 40μm≦V, V2≦400
Set it to μm.

Outside this range, the balance between the mold galling resistance during sliding and the effect of anisotropic roughness, that is, the anisotropic effect of sliding resistance becomes unfavorable.

In this way, the direction of the closest distance between the recesses is made to coincide with a specific direction.

The direction of closest spacing between the recesses is, for example, the direction shown in FIG. 1a. In direction A, the sliding resistance between the mold and the steel plate becomes smaller during forming processes such as drawing, as shown in Figure 4.
In other words, it is a direction in which the coefficient of friction becomes smaller, and a direction in which material flows more easily during molding.

Also, the specific direction refers to the characteristics of the steel plate material (r value).

From the relationship between the shape to be further press-formed and the blanking shape, the direction in which the flange length is larger or smaller (e.g., E1 value) means the direction in which the flange length is larger. For example, the first
If direction A in figure a is aligned with the direction of the steel sheet material with a smaller r value or with less elongation, the material will flow more easily during forming processing (drawing, stretching, etc.).
The molding range will be expanded. Also, considering the blanking shape, if the direction 3b shown in FIG. 3 coincides with the direction A in FIG. become.

The above-mentioned specific direction is derived from internal characteristics formed during manufacturing of the steel sheet. For example, r values are given in the C direction that is perpendicular to the rolling direction L1 of a steel plate, and the D direction that is at 45° to L and C.

EfL values etc. are different. Any of these directions can also be selected as the specific direction.

Further, in the surface roughness structure, it is preferable that the direction in which the angle between the recessed portion and the flat portion has a minimum value also coincides with the direction of the closest distance between the recessed portions.

This will be explained using FIGS. 1C and 1d. 1st
FIG. C is a diagram showing the surface shape of the cross section taken in FIG.

On the other hand, FIG. 1d is a diagram showing the surface shape of a cross section taken along the line III--III in FIG. 1a, that is, in a direction other than the direction of nearest distance. Then, θ1. Both θ and θ are the angles formed by the flat part and the concave part, and in the present invention, θ1 is preferably set to be smaller than 82, and most preferably set to the minimum value. This is to make it easier for oil to be supplied from the inside of the recess to the sliding surface with the mold, that is, the flat part (including the convex part).

The steel plate to which the present invention is applied may be a cold-rolled steel plate, a hot-rolled steel plate, or a surface-treated steel plate thereof. It is desirable to control by rolling. In that case, it is effective to use a roll that has been subjected to laser dulling. However, the present invention does not particularly limit the manufacturing means, but discloses a roughness management index, and the same effect can be obtained as long as the roughness is within the range of the present invention. In the case of laser dulling, the bride roll is dulled using a laser to form the uneven pattern that is intended to be applied to the steel plate. This dull processing roll is pressed against the steel plate at a reduction rate that provides a desired transfer rate. As a result, when the transfer rate is within the desired range, it is possible to control the roughness within the range of the present invention, and furthermore, it is possible to control sliding properties anisotropically, which means that a steel plate with excellent formability can be obtained. can get.

<Example> The present invention will be specifically described below based on Examples.

(Example 1) A steel plate having a surface roughness structure as shown in Table 1 was produced,
A product with the longest sliding distance in the L direction and a product with the longest flange length in the D direction were press-molded. The results are also shown in Table 1.

Comparative steel 1 cracked in the L direction because it was isotropic, but inventive steel 1, the cracking limit BHF was improved by 20%.

Comparative Steel 2 had a long flange length in the D direction because it was isotropic, but in Invention Steel 2, the flange length in the D direction was reduced by 18% and the yield was improved by about 10%.

Comparative Steel 3 has a small area ratio of Ra≦0.2 μm, that is, a small flat area, so that an anisotropic effect on sliding properties cannot be obtained.

In invention steel 3, the direction of the closest distance between the recesses is in the D direction, and the angle between the flat part and the recess is also smaller in the D direction, so the flange length in the D direction is reduced by 25%, resulting in a lower yield. Improved by 20%.

Note that the measurements and tests for each characteristic were performed as follows.

(1) Ra and flatness area ratio The flatness area ratio was measured by measuring a three-dimensional curve and analyzing this raw data using an image processing device Luzex 5ooo. Ra is measured by replacing the conventional two-dimensional definition with a three-dimensional definition. That is, Ra (3-dimensional), where 5=LXL (2) Closest interval of concavity After image analysis of the three-dimensional original data using Luzex 5000 and separating it into a flat part and a concave convex part, the concave convex part The nearest neighbor interval was measured.

<Effects of the Invention> According to the present invention, the disadvantages in forming process associated with the characteristics of the steel sheet itself such as r value and Ej2 value can be alleviated by adding surface properties, and the forming processability is improved. It offers many benefits, including improved material yield, which can be used to improve

[Brief explanation of drawings]

FIG. 1a is a plan view showing an example of the construction of the preparation of the present invention. FIG. 1b is a diagram showing the surface shape of a cross section taken along line I-1 in FIG. 1a. Figures 1C and 1d are II-- of Figure 1a, respectively.
FIG. 3 is a diagram showing the surface shape of a cross section taken along line II and line III-III. FIG. 2 is a diagram showing an example of removing a blank from a steel plate. FIG. 3 is a diagram for explaining the process of forming a rectangular blank. FIG. 4 is a schematic diagram showing the state of deformation of a steel plate during cylindrical drawing. Figure 5a shows the fifth case when no ears occur when squeezing the cup.
Figure b is a schematic diagram showing the state when ears occur. Explanation of symbols 1... Mold, 2... Steel plate, 10... Flat part, 11... Concave part

Claims (2)

[Claims] (1) Flat areas with an average roughness Ra of 0.2 μm or less occupy 30% or more of the steel plate surface, and the flat area has a surface roughness structure in which recesses with a depth of 1 μm or more from the flat areas are distributed. A thin steel sheet for pressing having anisotropic sliding properties, characterized in that the distance between the closest concave portions is 40 μm or more and no more than 400 μm, and the concave portions are arranged so that the closest direction coincides with a specific direction. (2) The press having anisotropy in slidability according to claim 1, wherein in the surface roughness structure, the direction in which the angle between the recess and the flat part has a minimum value coincides with the direction of the closest distance between the recesses. Thin steel plate for use.