SHEET STEEL HAVING A DETERMINISTIC SURFACE STRUCTURE

Abstract

The invention relates to a sheet steel skin-pass rolled with a deterministic surface structure, and to a method for producing it.

Claims

1. A sheet steel skin-pass rolled with a deterministic surface structure, wherein the surface structure is impressed into the sheet steel starting from a surface of the sheet steel, wherein the surface structure has a multiplicity of indentations, wherein each indentation has an encircling flank region which leads, starting from the surface, down to a valley region, wherein, as viewed in a sectional illustration, each indentation has a depth profile which comprises two opposite flank subregions and a valley subregion which runs between the flank subregions and which connects the flank subregions, wherein the depth profile is divided into a left-hand part and a right-hand part of the depth profile, wherein the depth profile runs in an asymmetrical manner, wherein the flank subregions and valley subregions of the left-hand part and of the right-hand part of the depth profile differ in at least one of height (h), width (b) and gradient ().

2. The sheet steel as claimed in claim 1, wherein the depth profile is viewed at least one of in and/or transversely to the skin-pass rolling direction.

3. The sheet steel as claimed in claim 1, wherein, as viewed in the plane (E) of the surface, the indentation has an area which has a centroid (S) through which the depth profile is viewed at least one of in and transversely to the skin-pass rolling direction.

4. The sheet steel as claimed in claim 3, wherein the left-hand part of the depth profile runs from the highest point (P1) to the lowest point (P3), and the right-hand part of the depth profile runs from the highest point (P2) to the lowest point (P3), the depth profile has a symmetry factor A0.9, where A corresponds to the ratio of the integrals of the left-hand and right-hand part of the depth profile, the integral with the larger value being the denominator of the ratio.

5. The sheet steel as claimed in claim 4, wherein the sheet steel comprises a metallic coat.

6. The sheet steel as claimed in claim 5, wherein the sheet steel is coated with a zinc-based coat which is applied by hot-dip coating.

7. The sheet steel as claimed in claim 5, wherein the sheet steel is coated with a coat zinc-based coat which is applied by electrolytic coating.

8. The sheet steel as claimed in claim 7, wherein the sheet steel is additionally provided with a process medium, wherein in particular the process medium is taken up with a surface weight of up to 2 g/m.sup.2 in the surface structure.

9. A method for producing a sheet steel skin-pass rolled with a deterministic surface structure, comprising the following steps: providing a sheet steel, skin-pass rolling the sheet steel with a skin-pass roll, wherein the surface of the skin-pass roll which acts on the surface of the sheet steel is furnished with a deterministic surface structure such that, after the skin-pass rolling, the surface structure is impressed into the sheet steel starting from a surface of the sheet steel, wherein the surface structure has a multiplicity of indentations, wherein each indentation has an encircling flank region which leads, starting from the surface, down to a valley region, wherein, as viewed in a sectional illustration, each indentation has a depth profile which comprises two opposite flank subregions and a valley subregion which runs between the flank subregions and which connects the flank subregions, wherein the depth profile is divided into a left-hand part and a right-hand part of the depth profile, wherein the depth profile runs in an asymmetrical manner, wherein the flank subregions and valley subregions of the left-hand part and of the right-hand part of the depth profile differ in at least one of height (h), width (b) and/or gradient ().

10. The method as claimed in claim 9, wherein, prior to the provision of the sheet steel, the sheet steel is coated by hot-dip coating.

11. The method as claimed in claim 9, wherein, after the sheet steel has been skin-pass rolled, the skin-pass rolled sheet steel is coated by electrolytic coating.

12. The method as claimed in claim 10, wherein the sheet steel is additionally provided with a process medium, wherein the process medium is applied with a surface weight of up to 2 g/m.sup.2.

13. The method as claimed in claim 11, wherein the sheet steel is additionally provided with a process medium, wherein the process medium is applied with a surface weight of up to 2 g/m.sup.2

14. The sheet steel as claimed in claim 6, wherein the sheet steel is additionally provided with a process medium, wherein in particular the process medium is taken up with a surface weight of up to 2 g/m.sup.2 in the surface structure.

Description

[0028] In the drawing:

[0029] FIG. 1) shows an AFM micrograph of a detail of a coated sheet steel, skin-pass rolled with a deterministic surface structure, in accordance with an exemplary embodiment according to the invention,

[0030] FIG. 2) shows a partial sectional illustration along section X in FIG. 1,

[0031] FIG. 3) shows a partial sectional illustration along section Y in FIG. 1, and

[0032] FIG. 4) shows a partial sectional illustration along section Z in FIG. 1.

[0033] FIG. 1) illustrates an atomic force microscopy (AFM) micrograph of a detail of a coated sheet steel (1, 1), skin-pass rolled with a deterministic surface structure (2), in accordance with an exemplary embodiment according to the invention. It is possible for the sheet steel (1, 1) to be an uncoated sheet steel (1), that is to say to not have an in particular metallic coat or non-metallic coat, or to be a sheet steel (1) coated with a metallic coat (1.2). The deterministic surface structure (2) exhibits a constantly repeating I-shaped impression in the form of an indentation (2.1). The centroid (S) in the plane of the surface (1.1) can be ascertained in a relatively rapid and simple manner in the case of a substantially rectangular indentation. Other embodiments of the indentation(s) are likewise conceivable and applicable, and are not restricted to an I-shaped impression. The surface structure (2) was impressed by means of a skin-pass roll (not illustrated), the surface of the skin-pass roll having been structured by means of a laser; cf. EP 2 892 663 B1. Each indentation (2.1) has an encircling flank region (2.3) which leads, starting from the surface (1.1), down to a valley region (2.2).

[0034] The scanning region of the atomic force microscopy (AFM) had an area of 9090 m.sup.2, three regions (framed in white) within the scanning region, each having an area of 2560 m.sup.2, being examined in more detail. The depth profiles (2.11) ascertained from the three regions (X, Y, Z) were combined to give a respective averaged depth profile (2.11) X, Y, Z (illustrated by dashed lines), and the depth profiles (2.11) determined therefrom have been illustrated in an enlarged view in partial section in FIGS. 2 to 4. Depending on the resolution of the measurement apparatus used, it is also possible for only one depth profile, in (partial) section, to be used in a representative manner for the evaluation, instead of forming an average from a plurality of depth profiles as in the present case. The illustrations in FIGS. 2 to 4 show, in each case viewed in a sectional illustration (X, Y, Z), that each indentation (2.1) has a depth profile (2.11) which comprises two opposite flank subregions (2.31) and a valley subregion (2.21) which runs between the flank subregions (2.31) and which connects the flank subregions (2.31), wherein the depth profile (2.11) is divided into a left-hand part and a right-hand part of the depth profile (2.11), wherein the depth profile (2.11) runs in an asymmetrical manner, wherein the flank subregions (2.31) and valley subregions (2.21) of the left-hand part and of the right-hand part of the depth profile (2.11) differ at least in height (h), width (b) and/or gradient (a). The sectional illustration (Y) runs, for example, through the centroid (S) of the indentation (2.1), the depth profile (2.1) being able to run in the rolling direction or transversely to the rolling direction.

[0035] The width (b) is understood to be the width between the respective highest assigned point (P1, P2) and the lowest point (P3). The height (h) is determined between the respective highest point (P1, P2) and the lowest point (P3). At these points (P1, P2, P3), it is thus possible for the depth profile (2.11) to be divided into a left-hand part and a right-hand part of the depth profile (2.11) in a defined manner, wherein the left-hand part of the depth profile (2.11) runs from the highest point (P1) to the lowest point (P3), and the right-hand part of the depth profile (2.11) runs from the highest point (P2) to the lowest point (P3). The depth profile (2.11) has an asymmetry factor A0.9, where A corresponds to the ratio of the integrals (Int) of the left-hand and the right-hand part of the depth profile (2.11), the integral (Int) with the larger value being the denominator of the ratio. The integrals between the points (P1, P3), left-hand part, and between points (P3, P2), right-hand part, correspond to the left-hand and right-hand area (illustrated with hatching) of the depth profile (2.11) below the depth profile function. In table 1 below, the three examined regions are compared by way of their parameters:

TABLE-US-00001 TABLE 1 Region h_P1, P3 h_P3, P2 b_P1, P3 b_P3, P2 Int_P1, P3 Int_P3, P2 A X 2.66 m 2.29 m 18.75 m 26.76 m 13.45 m.sup.2 20.68 m.sup.2 0.65 Y 2.52 m 2.08 m 20.51 m 26.95 m 16.21 m.sup.2 24.55 m.sup.2 0.66 Z 3.10 m 2.41 m 19.53 m 23.63 m 20.99 m.sup.2 14.78 m.sup.2 0.70

[0036] In a further examination, a process medium in the form of a forming oil was applied to the sheet steel (1, 1) according to the invention, which has in particular been coated with a metallic coat and skin-pass rolled with a deterministic surface structure (2), and it was shown that, owing to the asymmetry produced in a targeted manner along a preferred direction of the sheet steel, the process medium had accumulated in a part of the depth profile (2.11) within the indentation(s) (2.1), with the result that, in a further deep-drawing experiment, said process medium can be stocked in the necessary surface weight at the locations that are relevant to the forming process. As a reference, a dry sheet steel, that is to say a sheet steel according to the invention that was not coated with process medium, as well as several sheet steel according to the invention that were coated with a process medium with different surface weights of 0.5, 1, 1.5 and 2 g/m.sup.2 in the surface structure (2), was subjected to a deep-drawing experiment under identical conditions. The result was that, as expected, the high friction force caused a high degree of abrasion in the case of the dry sheet steel, and the sheet steels coated with the process medium exhibited substantially identical results and no appreciable abrasion could be identified. It has therefore been shown that a surface weight of the process medium of 0.5 g/m.sup.2 on the sheet steel which has in particular been coated and skin-pass rolled with a deterministic surface structure in accordance with the invention was sufficient to obtain a correspondingly good result.