JPH01107904A - Steel sheet for surface friction anisotropic drawing - Google Patents

Abstract

PURPOSE:To improve workability by providing rugged shapes which are different with respect to the other direction in a specific direction and/or the arrangement thereof. CONSTITUTION:The surface roughness patterns (a), (b) of the fine rugged shapes are anisotropically regular patterns having the rugged shape arrangement different with respect to the other in the vertical direction of the plane of the figure. The isotropic regular patterns having the rugged shape arrangements which are the same both in the vertical and lateral directions are likewise shown in the pattern C. The surface characteristics of the patterns (a), (b) are such that the sliding resistance in the lateral direction is large than in the vertical direction. The surface characteristics are nearly the same in both directions in the pattern C. The anisotropies of such surface friction are effectively utilized and the practical anisotropies are decreased by offsetting with the anisotropies in the internal quality of the steel sheet; in addition, the workability of bending, etc., in the specific directions is improved by the combination of both the anisotropies.

Description

[Detailed Description of the Invention] (Industrial Application Field) By controlling the direction of the surface roughness pattern of the steel sheet, anisotropy is imparted to the surface texture of the steel sheet, thereby improving workability such as drawing and bending. This paper attempts to propose a steel plate for drawing with surface friction anisotropy.

In general, most thin steel sheets, especially cold-rolled steel sheets, are formed into the desired shape by mechanical processing such as drawing or bending.
It is then subjected to painting and other treatments before being put into use. This kind of mf
It has been said that it is best for the four-plate material to be uniform and equidirectional.

However, in reality, the tensile properties of steel sheets usually have strong in-plane anisotropy, and therefore, in order to improve the properties of steel sheets, the first step is to reduce that anisotropy. has been considered essential.

In other words, the r value is important for improving drawability, but it is known that it is extremely difficult to control the in-plane direction because it strongly depends on the crystal orientation. Even now, many efforts are being made to control it, but it is still difficult to say that it has been sufficiently controlled.

(Prior Art) For conventional steel plates, it has been strongly required that the surface be homogeneous and uniform in both micro and macro aspects. Therefore, the roll surface roughening method of skin pass rolling, which is performed for the purpose of imparting roughness to the surface of a steel sheet, also includes shot blasting, electric discharge dulling, and the recently developed laser dulling method (
(Japanese Unexamined Patent Publication No. 62-11922, etc.) However, the first objective is to obtain a homogeneous surface.

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 case where very strict deep drawability is required. That is, when very deep and uniform drawing workability is required, even if the anisotropy of the internal substance is controlled to near the limits of the current technology, the properties obtained may still be insufficient.

(Problem to be solved by the invention) Regarding drawing steel sheets, despite many years of efforts, it is not due to the improvement of internal anisotropy, which is considered unavoidable, but rather to the effects caused by it. It is an object of the present invention to achieve effective improvement in processability by appropriately controlling the anisotropy of the surface texture to a level that is comparable to or superior to that of other materials.

(Means for Solving the Problems) The present invention provides a steel plate having a surface roughness pattern of fine irregularities, which has a different irregularity shape and/or arrangement thereof in a specific direction than in other directions. This is a steel sheet for drawing with surface friction anisotropy.

Figure 1 (a), (b), and (c) schematically show a steel plate with a finely uneven surface roughness pattern, and (a) and (b) are shown in the vertical direction of the paper. , an anisotropic regular pattern with a different arrangement of unevenness compared to the others, and (c) an isotropic regular pattern with the same arrangement of unevenness on both the top and bottom, left and right sides, and their surface texture is ( In a) and (b), the sliding resistance in the left-right direction is greater than in the vertical direction, while in c) it is almost the same in both directions.

Needless to say, in addition to the cases shown in FIGS. 1(a) and (b), the types include cases such as those shown in FIGS. 2(a) to (d).

The inventors have discovered that the workability of a thin steel sheet is greatly influenced by its surface texture as well as its internal quality, and that control thereof may be effective in some cases. That is, in the case of deep drawing as shown in FIG. 3, where the main part of the die is shown broken, in addition to the deformation resistance of the material itself against drawing deformation, the frictional resistance between the steel plate 2 and the die 1 is important.

Needless to say, a steel sheet with good deep drawability is easily deformed in the sheet width direction (high Lankford value 2r value), and in addition to high tensile strength, it is important that the coefficient of friction is low.

Furthermore, in actual drawing of a cylindrical shape, there is non-uniformity in the cup height after drawing, as shown in Fig. 4(a).
, The occurrence of ears as distinguished in (b) becomes a problem. Conventionally,
It has been thought that the only way to improve the anisotropy caused by deep drawing is to improve the internal quality of the material. However, there are limits to controlling the in-plane anisotropy of the internal properties of steel sheets, and it has been almost impossible to control it completely.

Furthermore, recently, requirements for the appearance after painting have become stricter, and it has also become necessary to control the gloss after painting.

This invention has been developed to satisfy the various demands for such steel plate surfaces.

The inventors studied various requirements for recent products and problems in the conventional technology, and as a result, they discovered that it is possible to impart anisotropy to the surface texture by controlling the surface roughness profile or arrangement of irregularities. We found that the roughness profile and uneven arrangement can maintain macroscopic uniformity.

In other words, the shape or shape of the minimum unit that constitutes the roughness is used to impart anisotropy to the surface texture without impairing the required press formability or handling properties during steel plate processing. It was discovered that it is effective to control the arrangement of the aggregate.

While conventional steel plate surface roughness, especially the surface roughness of press steel plates, has been based on the assumption that it is isotropic, this invention focuses on the usefulness of using isotropy and anisotropy differently. It is something. For example, the appearance may be uniform, and the anisotropy of the surface friction coefficient may be controlled.

Therefore, even if anisotropy is provided, it is not the purpose of this invention to produce an extremely extreme change in shape, ie, anisotropy in surface texture that would impair the appearance after painting. For example, conventional machining groove patterns or grinding patterns, even if they affect the surface properties, do not provide a good appearance after painting and cannot be put to practical use in rows.
Therefore, the feature of the present invention is that it has succeeded in controlling the anisotropy of the coefficient of friction of a steel sheet for pressing without any deterioration of the appearance properties under normal use conditions, that is, in the normal roughness range.

Now, the experimental results that formed the basis of this invention will be explained. The experiment was conducted using 5 pcc of general cold-rolled steel plate as the material. Laser dull processing was applied to small temper rolling rolls to obtain various roughness and patterns, and steel plates with many surface patterns were obtained by adjusting the rolling reduction of temper rolling. The frictional resistance of these steel plates under lubricated conditions was measured. We tried organizing the results using many parameters, but among them, we found the effect of the average bite angle θ, as shown in Figure 5, as a parameter that can help organize the results better. still,
Such angular parameters could not even be specified when conventional steel plates with random roughness were used.

Furthermore, as a result of various experiments, it was found that the size and density (spacing) of the convex portions have a subtle effect on the coefficient of friction. Therefore, we found that it is possible to control the friction coefficient by combining them. The typical roughness pattern and the anisotropy of the friction coefficient will be explained in the first section.
As mentioned above with reference to the figure.

For such roughness control, the best method is laser dull processing on temper rolls, which can control each unevenness, but the purpose of the present invention can also be achieved by electron beam processing or photoetching. It is.

In other words, in normal laser dull processing, Fig. 6 (a)
), the laser darts are concentric, and the direction of the blown oxygen gas is as uniform as possible given the equipment. The pits formed under each of these conditions have a round shape as shown in FIG. 3(b). On the other hand, when giving directionality, Fig. 7 (a), (b) or Fig. 8 (a), (b)
) or the methods shown in FIGS. 7 and 8 may be combined. That is, by making the blown gas eccentric as shown in FIG. 7(a) or by making the cross section of the laser beam elliptical or rectangular as shown in FIG. 8(a), the formed pit becomes elongated. Such processing becomes possible by improving the control system of conventional laser dull processing equipment.

[Example] Figures 9(a) and 9(b) show the anisotropy of the r value (Lankford value) and friction coefficient of a conventional steel plate (JIS, 5PCC) with a surface roughness of No. 50 Schottdal. The change in the ear height of a cylindrical cup aperture with an aperture ratio of 2.2 and a diameter of 36 mm+ is shown.

Here, the change in r value is based on JIS data cut out from various directions.
This is a value measured using a No. 5 tensile test piece.

Also, the friction coefficient is 100% under load with press oil applied.
The coefficient of kinetic friction is measured when the weight is 1 kg.

In this case, the change in r value is typical of a steel plate for deep drawing, whereas the surface friction coefficient of a conventional steel plate is almost isodirectional as shown in the figure.

As a result, when a cylindrical cup drawing test was performed, the height of the cup edge changed in response to the anisotropy of the r value. In such conventional steel sheets, the only way to reduce the occurrence of ears is to reduce the anisotropy of the r value of the material.

According to this invention, a pattern as shown in FIG. 10 was transferred to a test steel plate cut from the same coil as in FIG. 9 using a skin pass roll. This pattern is characterized by a small coefficient of friction in the rolling direction and a large coefficient of friction in a direction perpendicular to the rolling direction. Therefore, as shown in FIG. 11, it was confirmed that the anisotropy in the forming characteristics of the steel plate as a whole becomes extremely small, as it compensates for the anisotropy in the ease of deformation of the steel plate.

On the other hand, it goes without saying that by selecting the pattern conversely, it is possible to control the anisotropy of the gloss while maintaining the uniformity and isotropy of the friction coefficient.

This is because it can be easily achieved, for example, by changing only the arrangement of isodirectionally shaped pits.

Furthermore, by regularly arranging pits having a square or triangular shape, it is also possible to cause light scattering to occur only in one direction. In this case, the shape of the pits can be changed as shown in Figure 12. , the anisotropy of the friction coefficient became almost negligible.

In order to make the present invention more effective, it is also effective to change the anisotropy at each position in the width direction of the plate (for example, at the center and at the ends).

Furthermore, it is also possible to intentionally impart strong surface anisotropy, including materials whose mechanical properties can be considered to be essentially isotropic.

(Effects of the Invention) According to the present invention, the internal quality of the steel sheet can be improved by utilizing the surface characteristics, especially the anisotropy of surface friction, without substantially inhibiting the general purpose of dull finishing applied to steel sheets for drawing. The de facto anisotropy can be significantly reduced by canceling it out with the anisotropy, and the workability such as bending in a specific direction can be significantly improved by adding the regeneration anisotropy. Furthermore, intentional control of surface gloss becomes possible.

[Brief explanation of the drawing]

Figure 1 shows the relationship between roughness patterns and friction coefficients. Figure 2 is an explanatory diagram showing other examples of roughness patterns. Figure 3 is a schematic diagram showing the state of deformation of a steel plate during cylindrical deep drawing. Yes, Figure 4 is a comparison diagram showing the state of ear formation during cup squeezing, Figure 5 is a diagram showing the influence of the bite angle, Figures 6 and 7
Figure 8 is a comparison diagram of anisotropy imparting methods during laser dull processing, Figure 9 is a diagram showing the deep drawing characteristics of a steel plate with a conventional No. 50 dull surface, and Figure 10 is anisotropic. Fig. 11 is a diagram showing the deep drawing characteristics of a steel plate consisting of the pits shown in Fig. 10, and Fig. 12 shows an example of a surface with anisotropy of gloss. FIG. Figure 1 (a) (b) <
C Noro 0 Ro O
○ ○ ○ ○ 0
Wlr→÷7 AγY Reikai meeting o O. Q Oo 00 ρρaaa including ρ ) ρ (ρ'%'l)'b
'b'> ρﾆﾆﾆﾆﾆﾎﾎﾎﾊﾀﾀﾀﾀﾀﾀ? fToan Figure 11 (a) (b)

Claims (1)

[Claims] 1. A steel plate with a surface roughness pattern of fine irregularities, for use in surface friction anisotropic drawing, characterized by having a different irregularity shape and/or arrangement thereof in a specific direction than in other directions. steel plate.