Steel plate with a deterministic surface structure

Abstract

The present invention relates to a steel plate (1, 1') finished with a deterministic surface structure (2) and a method for manufacturing the same. The surface structure (2) is pressed into the steel plate (1, 1') starting from the surface (1.1) of the steel plate (1, 1'), the surface structure (2) has a plurality of recesses (2.1), each recess (2.1) has a surrounding side region (2.3), the side region leads into a valley region (2.2) starting from the surface (1.1), when observed in a cross-sectional view, each recess (2.1) has a depth profile (2.11), the depth profile includes two opposed side partial regions (2.31) and a valley partial region (2.21) extending between the side partial regions (2.31) and connecting the side partial regions (2.31), the depth profile (2.11) is divided into a left part and a right part of the depth profile (2.11), the depth profile (2.11) extends asymmetrically, the left part of the depth profile (2.11) extends from a highest point (P1) to a lowest point (P3), and the right part of the depth profile (2.11) extends from a highest point (P2) to the lowest point (P3), and the side partial regions (2.31) and the valley partial region (2.21) of the left part and the right part of the depth profile (2.11) are different at least in terms of height (h), width (b) and slope (α).

Description

Field of the Invention

[0001] The present invention relates to a steel sheet finished with a deterministic surface structure. Furthermore, the present invention also relates to a method for manufacturing a steel sheet finished with a deterministic surface structure. Background Art

[0002] Steel sheets finished with a deterministic surface structure of this type are known from the prior art. See, for example, the patent document EP 2 892 663 B1. Summary of the Invention

[0003] There is a need for optimization in the known prior art, especially for the targeted modeling of the surface structure of steel sheets finished with a deterministic surface structure.

[0004] Therefore, an object of the present invention is to provide a steel sheet finished with a deterministic surface structure, which provides a targeted change in the surface structure compared to the prior art.

[0005] This object is achieved by a steel sheet finished with a deterministic surface structure.

[0006] Providing a targeted surface structure on the finished steel sheet is important for other processes, especially in the further processing industry for manufacturing automotive components. During component manufacturing, especially in the forming process, it is advantageous that the process media used, such as oil and / or lubricants, must be present in the necessary coverage amounts at positions important for the forming process. These positions important for the forming process are usually the contact surfaces between the steel sheet and the forming tool, and thus are not the indentations or recesses where the process media preferably accumulate in the steel sheet, but the surfaces in the form of raised areas on the steel sheet. The inventors have determined that if the surface structure has a plurality of recesses, each recess having a surrounding side region that leads from the surface into a valley region, and where, when observed in a cross-sectional view, each recess has a deep profile that includes two opposing side partial regions and a valley partial region that extends between the side partial regions and connects the side partial regions, and where the deep profile is divided into a left part and a right part of the deep profile, and where the deep profile extends asymmetrically, and where the side partial regions and the valley partial regions of the left part and the right part of the deep profile differ at least in terms of height, width, and / or slope, then a targeted surface structure can be provided in the steel sheet finished with a deterministic surface structure compared to the prior art.

[0007] It is determined by the targeted modeling of the surface structure and the asymmetric orientation of the correspondingly formed deep profile that, during forming, although the asymmetry has an adverse effect on the forming result, where the areas of the surface of the steel sheet (which are particularly adjacent to the side part areas and valley part areas having a steeper slope and / or a larger width and are in contact with the forming tool) are subjected to higher forming forces because they offer higher resistance, it has surprisingly been found that the process medium accumulates highly specifically in the side part areas and valley part areas having a steeper slope and / or a larger width, depending on the amount and / or type of the process medium (e.g., depending on the fluidity), and is thus available for use in the areas important for the process, whereby the resistance can be reduced, so that the adverse proportion of the forming can be compensated for by a targeted influence on the local process medium distribution. The process medium accumulates particularly at the wide and steep side part areas and valley part areas due to capillary action. The height is particularly important because the height defines the area of the side part area where the capillary action starts. However, in the case of a constant amount of process medium, an excessive height may have an adverse effect on the forming process because the medium has to travel a longer distance from the valley (part) area to reach the areas important for the process.

[0008] A deterministic surface structure can be understood as a recurring surface structure having a defined shape and / or configuration, see EP 2 892 663 Bl. In addition, particularly surfaces having a (similar) random appearance belong to this, but these surfaces are applied by means of a deterministic texturing method and are thus composed of deterministic shape elements.

[0009] A steel sheet is generally understood as a flat steel product that can be provided in the form of a sheet, a slab, or a strip.

[0010] The side area surrounding the recess, together with the valley area integrally connected to the side area, defines a closed volume of the surface structure that is pressed into the steel sheet by finishing. The closed volume, the so-called void volume, can be coordinated with the process medium to be applied, particularly the oil phase, by means of a forming method for subsequent processing.

[0011] Other advantageous design options and improvements result from the following description. One or more features in the present invention can be combined with one or more other features to form other design options of the present invention.

[0012] According to a design of the steel plate according to the present invention, the deep profile is observed along and / or transverse to the finishing rolling direction. By the action of the finishing rolls, it is possible to specifically influence along and / or transverse to the finishing rolling direction, because the shaping elements of the finishing rolls preferably have a targeted asymmetry of recesses in the finishing rolling direction, but also alternatively or additionally transverse to the finishing rolling direction, which acts on the surface of the steel plate, sinks into the surface of the steel plate and produces recesses.

[0013] The geometry (size and depth) of the defined surface structure (negative shape) on the finished steel plate depends in particular on how the corresponding geometry (positive shape, shaping element) on the finishing roll is designed. The laser texturing method is preferably used to be able to set a targeted structure (positive shape) on the surface of the finishing roll by material removal. In particular, by specifically controlling the energy, pulse duration and selecting the appropriate wavelength of the laser beam acting on the surface of the finishing roll, a positive influence can be exerted on the design of the structure. Fs pulses, ps pulses and ns pulses are all suitable for material removal, but the way of energy coupling and removal on the solid surface is significantly different, and the size of the heat affected zone (HAZ) is also different. The shorter the pulse duration, the less energy can flow out of the laser focus into the surroundings (HAZ), for example. The longer the pulse, the more radiation energy is coupled into the already formed plasma or reflected by the plasma, and thus cannot be directly coupled into the surface of the finishing roll. The pulse leaves a substantially circular pit on the surface of the finishing roll, which forms the surface or raised surface (surface) on the steel plate after the finishing process in the case of multiple pits, and thus forms the contact surface between the steel plate and the forming tool. The reduction of the pulse duration has an impact on the structure of the pit. In particular, the diameter of the pit can be reduced. By reducing the pulse energy, especially when using short or ultrashort pulse lasers, the geometry (positive shape) on the surface of the finishing roll can be specifically set. This is achieved, for example, when the pulse duration of the laser (with which the surface of the finishing roll is textured) is reduced in the direction towards the removal threshold and thus geometric structures can be produced on the finishing roll with higher resolution. Similarly, this can be achieved by increasing the beam characteristic quality (M 2 ) and the aperture of the ideal aspherical focusing optics. In particular, through the high resolution or small pit area resulting from the low-energy interaction between the laser and the finishing roll, the side (partial) area can be specifically set to any height, width and / or slope (angle of the side area).

[0014] According to a design of the steel plate according to the invention, when observed in the plane of the surface, the recess has a face, and the face has a center of gravity. Through the center of gravity, a deep profile is observed along and / or transverse to the finishing rolling direction. The deep profile extending, for example, along or alternatively or additionally transverse to the finishing rolling direction through the center of gravity (which can clearly define the face of the recess when observed in the plane of the surface) can show asymmetry. In particular, the side and valley partial regions of the left and right parts of the deep profile are different in terms of height, width, and / or slope.

[0015] According to a design of the steel plate according to the invention, the left part of the deep profile extends from the highest point to the lowest point, and the right part of the deep profile extends from the highest point to the lowest point, where the deep profile has a symmetry factor A ≤ 0.9, where A corresponds to the quotient of the integrals of the left and right parts of the deep profile, and the integral of the larger value is the denominator of the quotient. In particular, the deep profile has a symmetry factor A ≤ 0.85, preferably A ≤ 0.8, preferably A ≤ 0.75, further preferably A ≤ 0.7, and particularly preferably A ≤ 0.67. The smaller the symmetry factor is set, the stronger the plate is regulated along a predefined direction, so that better friction characteristics and / or better flow resistance characteristics (laminar or turbulent flow of the fluid) can be obtained along this direction compared to other directions.

[0016] According to a design of the steel plate according to the invention, the steel plate is coated with a metallic coating, especially a zinc-based coating applied by hot dip coating. Preferably, in addition to zinc and inevitable impurities, the coating can also contain other elements in the coating, such as aluminum with a content of at most 5 wt% and / or magnesium with a content of at most 5 wt%. The steel plate with a zinc-based coating has very good cathodic corrosion protection, which has been used in automobile manufacturing for many years. If improved corrosion protection is provided, the coating additionally contains magnesium with a content of at least 0.3 wt%, especially at least 0.6 wt%, preferably at least 0.9 wt%. Aluminum can be present in place of or in addition to magnesium with a content of at least 0.3 wt% to especially improve the bonding of the coating to the steel plate and especially basically prevent iron from diffusing from the steel plate into the coating during the heat treatment of the coated steel plate, thereby further maintaining positive corrosion characteristics. Here, the thickness of the coating can be between 1 and 15 μm, especially between 2 and 12 μm, preferably between 3 and 10 μm. Insufficient cathodic corrosion protection cannot be ensured below the minimum limit, and when above the maximum limit, bonding problems may occur when connecting the steel plate according to the invention or a component made thereof to another component, especially when the stable process during thermal bonding or welding cannot be ensured when exceeding the maximum limit of the coating thickness. During hot dip coating, the steel plate is first coated with the corresponding coating and then conveyed for finishing. The finishing is carried out after hot dip coating the steel plate.

[0017] According to an alternative design of the steel sheet according to the invention, the steel sheet is coated with a metallic coating, in particular a zinc-based coating, which is applied by electrolytic coating. Here, the thickness of the coating can be between 1 and 10 μm, in particular between 1.5 and 8 μm, preferably between 2 and 5 μm. Compared with hot-dip coating, the steel sheet can first be finished and then electrolytically coated. Depending on the thickness of the coating, the roughness in the side regions can be substantially maintained even after electrolytic coating. Alternatively, it is also conceivable to first perform electrolytic coating and then finishing.

[0018] It is also possible to consider not providing a coating, for example not providing a metallic coating. It is also possible to consider coating the steel sheet, for example, with a non-metallic coating in a coating device, where the steel sheet is finished before or after being coated with the non-metallic coating.

[0019] According to a design of the steel sheet according to the invention, in particular the coated steel sheet is also provided with a process medium, in particular oil, where in particular the process medium is accommodated in the surface structure with a coverage amount of up to 2 g / m 2 Due to the dimensions of the surface structure, the demand for the process medium is small, and thus the coverage amount is limited to at most 2 g / m 2 , in particular at most 1.5 g / m 2 , preferably at most 1.0 g / m 2 , preferably at most 0.6 g / m 2 , further preferably at most 0.4 g / m 2 . In particular due to the asymmetry, the process medium accumulates substantially locally in the recesses in the side partial regions and the valley partial regions with a steeper gradient, a higher height and / or a greater width after application and provides for additional processes, such as for forming processes, preferably for deep drawing processes, closer to or adjacent to positions important for the forming process, to improve lubrication and reduce friction and thus reduce the wear of forming tools, such as forming devices, preferably (deep drawing) pressing devices. In particular, the accumulation of the process medium on tribologically unfavorable regions can be effectively suppressed, and this accumulation does not contribute to the transfer of the process medium into the actual contact zone or friction zone. Thus, the steel sheet according to the invention has very good tribological properties with a lower demand for the process medium and is environmentally friendly due to less resource use compared to steel sheets known from the prior art, in particular oiled steel sheets.

[0020] According to a second aspect, the present invention relates to a method for manufacturing a steel sheet that is finished with a deterministic surface structure, comprising the following steps: preparing a steel sheet; finishing the steel sheet with a finishing roll, wherein the surface of the finishing roll acts on the surface of the steel sheet with a deterministic surface structure such that after finishing, the surface structure is pressed into the steel sheet starting from the surface of the steel sheet, wherein the surface structure has a plurality of recesses, wherein each recess has a surrounding side region that leads into a valley region starting from the surface, wherein, when observed in a cross-sectional view, each recess has a depth profile that includes two opposing side partial regions and a valley partial region that extends between the side partial regions and connects the side partial regions, wherein the depth profile is divided into a left part and a right part of the depth profile, wherein the depth profile extends asymmetrically, and wherein the side partial regions and the valley partial regions of the left part and the right part of the depth profile differ at least in terms of height, width, and / or slope.

[0021] By the action of force, the surface (positive shape) of the finishing roll forms a surface structure on the surface of the steel sheet, which surface structure defines recesses (negative shape) each having a valley region and a side region, and which substantially corresponds to the surface (positive shape) of the finishing roll. The finishing roll for constructing a deterministic surface structure can be machined using suitable devices, for example by means of a laser, see also EP 2 892 663 B1. In addition, other removal methods can also be used to provide the surface on the finishing roll, such as cutting manufacturing methods with geometrically determined or undetermined cutting edges, chemical or electrochemical, optical or plasma-induced methods, which methods are suitable for enabling the steel sheet to be finished with a surface structure and corresponding asymmetry.

[0022] To avoid repetition, reference is accordingly made to the embodiments of the steel sheet finished with a deterministic surface structure according to the present invention.

[0023] According to a design of the method according to the present invention, the steel sheet is coated by hot-dip coating before the steel sheet is provided. Preferably, the melt for hot-dip coating can contain other elements in addition to zinc and inevitable impurities, such as aluminum with a content of at most 5% by weight and / or magnesium with a content of at most 5% by weight.

[0024] According to another design of the method according to the present invention, the finished steel sheet is coated by electrolytic coating after the steel sheet is finished.

[0025] According to a design of the method according to the present invention, after finishing, the steel sheet is additionally provided with a process medium, preferably oil, wherein the process medium is applied with a coverage amount of at most 2 g / m 2 and further preferably with a coverage amount of at most 0.4 g / m 2 . Description of the Drawings

[0026] The specific design of the present invention will be described in detail below with reference to the accompanying drawings. The accompanying drawings and the accompanying description of the features generated should not be construed as limited to the respective designs, but are used to illustrate exemplary designs. In addition, the various features can be used with each other, or in combination with the features described above, for possible further expansion and improvement of the present invention, especially in additional designs not shown. The same components are always provided with the same reference numerals.

[0027] In the accompanying drawings:

[0028] Figure 1 ) shows an AFM image of a section of a coated steel sheet finished with a deterministic surface structure according to an embodiment of the present invention,

[0029] Figure 2 ) shows Figure 1 a partial cross-sectional view of cross-section X in

[0030] Figure 3 ) shows Figure 1 a partial cross-sectional view of cross-section Y in

[0031] Figure 4 ) shows Figure 1 a partial cross-sectional view of cross-section Z in Specific embodiments

[0032] In Figure 1 ) an atomic force microscope AFM image of a section of a coated steel sheet (1, 1') finished with a deterministic surface structure (2) according to an embodiment of the present invention is shown. The steel sheet (1, 1') can be an uncoated steel sheet (1), that is, without a metal coating or a non-metal coating in particular, or a steel sheet (1') coated with a metal coating (1.2). The deterministic surface structure (2) shows always recurring I-shaped indentations as recesses (2.1). In the case of substantially rectangular recesses, the center of gravity (S) in the plane of the surface (1.1) can be determined relatively quickly and simply. Other embodiments of the recesses are also conceivable and applicable and are not limited to I-shaped indentations. The surface structure (2) is pressed in by means of a finishing roll (not shown), wherein the surface of the finishing roll is structured by means of a laser, see EP 2892 663B1. Each recess (2.1) has a surrounding side region (2.3) that leads from the surface (1.1) into a valley region (2.2).

[0033] The scanning area of the atomic force microscope (Atomic Force Microscopy, AFM) is 90×90μm 2The area of ​​the scanning area is 25×60μm 2 The three regions (white boxes) of the image are studied in more detail. The deep profiles (2.11) determined from the three regions (X, Y, Z) are summarized as the average deep profiles (2.11) X, Y, Z (shown by dashed lines) and in Figures 2 to 4 The depth profile determined in this way is shown in an enlarged partial section in FIG. (2.11). Depending on the resolution of the measuring instrument used, only one depth profile can also be used as a representative (partial) section for the evaluation, rather than forming an average value from a plurality of depth profiles as in this case. Figures 2 to 4 The views in the drawings are respectively viewed in sectional views (X, Y, Z), each recess (2.1) having a deep profile (2.11) comprising two opposite side partial regions (2.31) and a valley partial region (2.21) extending between the side partial regions (2.31) and connecting the side partial regions (2.31), wherein the deep profile (2.11) is divided into a left part and a right part of the deep profile (2.11), wherein the deep profile (2.11) extends asymmetrically, wherein the side partial regions (2.31) and the valley partial regions (2.21) of the left and right parts of the deep profile (2.11) differ at least in height (h), width (b) and / or inclination (α). The sectional view (Y) extends, for example, through the center of gravity (S) of the recess (2.1), wherein the deep profile (2.1) can extend in the rolling direction or transversely to the rolling direction.

[0034] The width (b) is understood to mean the width between the respective highest corresponding points (P1, P2) and the deepest point (P3). The height (h) is determined between each highest point (P1, P2) and the deepest point (P3). Therefore, at these points (P1, P2, P3), the deep profile (2.11) can be definedly divided into a left part and a right part of the deep profile (2.11), wherein the left part of the deep profile (2.11) extends from the highest point (P1) to the deepest point (P3), and the right part of the deep profile (2.11) extends from the highest point (P2) to the deepest point (P3). The deep profile (2.11) has an asymmetry factor A≤0.9, wherein A corresponds to the quotient of the integral (Int) of the left and right parts of the deep profile (2.11), wherein the integral (Int) with the larger value is the denominator of the quotient. The integral between the points (P1, P3), the left part and the points (P3, P2), the right part, corresponds to the left and right areas (shown in shade) of the deep contour (2.11) below the deep contour function. In the following Table 1, the three studied areas are compared with their characteristic values:

[0035] region h_P1,P3 h_P3,P2 b_P1,P3 b_P3,P2 Int_P1,P3 Int_P3,P2 A X 2.66 μm 2.29 μm 18.75 μm 26.76 μm <![CDATA[13.45μm 2 > <![CDATA[20.68μm 2 > 0.65 Y 2.52 μm 2.08 μm 20.51 μm 26.95 μm <![CDATA[16.21μm 2 > <![CDATA[24.55μm 2 > 0.66 Z 3.10 μm 2.41 μm 19.53 μm 23.63 μm <![CDATA[20.99μm 2 > <![CDATA[14.78μm 2 > 0.70

[0036] Table 1

[0037] In a further study, a process medium in the form of a forming oil was applied to a steel sheet (1, 1') according to the invention, which was coated, in particular, with a metal coating and finished with a defined surface structure (2), and it was shown that the process medium, due to a specifically adjusted asymmetry, collects in a part of the deep contour (2.11) in one (or more) recesses (2.1) along the preferred direction of the steel sheet, so that it can be deposited in a further deep drawing test at a location that is important in terms of the forming process with the necessary coverage. As a reference, a dry steel sheet according to the invention, i.e. not coated with a process medium, was subjected to the same conditions as a plurality of steel sheets coated with a process medium in the surface structure (2) with different coverages of 0.5, 1, 1.5 and 2 g / m 2 The steel sheets according to the invention coated with a process medium were subjected to deep drawing tests. The results showed that, as expected, high wear occurred in the dry steel sheets due to the high friction forces, while the steel sheets coated with the process medium showed essentially the same results and no significant wear was detected. It can thus be shown that the 0.5 g / m2 in the steel sheets according to the invention, which were especially coated and finished with a defined surface structure, 2 A covering layer of process medium is sufficient to achieve correspondingly good results.

Claims

1. A steel sheet (1, 1') finished with a deterministic surface structure (2), wherein, The surface structure (2) is pressed into the steel sheet (1, 1') starting from the surface (1.1) of the steel sheet (1, 1'), wherein the surface structure (2) has a plurality of recesses (2.1), wherein each recess (2.1) has a surrounding side region (2.3), which side region leads from the surface (1.1) into a valley region (2.2), and wherein, when observed in a sectional view, each recess (2.1) has a depth profile (2.11), which depth profile comprises two opposing side partial regions (2.31) and a valley partial region (2.21) extending between the side partial regions (2.31) and connecting the side partial regions (2.31), and wherein the depth profile (2.11) is divided into a left part and a right part of the depth profile (2.11). It is characterized in that the depth profile (2.11) extends asymmetrically, wherein the left part of the depth profile (2.11) extends from a highest point (P1) to a lowest point (P3), and the right part of the depth profile (2.11) extends from a highest point (P2) to the lowest point (P3), and wherein the side partial regions (2.31) and the valley partial regions (2.21) of the left part and the right part of the depth profile (2.11) differ at least with respect to height (h), width (b) and slope (α).

2. The steel plate according to claim 1, wherein The depth profile (2.11) is observed along and / or transversely to the finishing rolling direction.

3. The steel plate according to claim 1 or 2, wherein, The recess (2.1) has a face (2.12) when observed in the plane (E) of the surface (1.1), which face has a center of gravity (S), and the depth profile (2.11) is observed through the center of gravity along and / or transversely to the finishing rolling direction.

4. The steel plate according to claim 1, wherein, The depth profile (2.11) has a symmetry factor A ≤ 0.9, where A corresponds to the quotient of the integrals of the left part and the right part of the depth profile (2.11), and the integral with the larger value is the denominator of the quotient.

5. Steel sheet according to claim 1, wherein the steel sheet (1') has a metallic coating.

6. Steel sheet as claimed in claim 5, wherein the steel sheet (1') is coated with a zinc-based coating, which coating is applied by hot dip coating.

7. Steel sheet according to claim 5, wherein the steel sheet (1') is coated with a zinc-based coating, which coating is applied by electrolytic coating.

8. The steel plate according to claim 1, wherein, The steel plates (1, 1') are additionally provided with a process medium, where the process medium is accommodated in the surface structure (2) in a coverage amount of at most 2 g / m 2 .

9. A method for manufacturing a steel sheet (1, 1') finished with a defined surface structure (2), comprising the following steps: - providing a steel sheet - The steel plate is finished with a finishing roll, wherein the action of the finishing roll on the surface of the steel plate is set with a deterministic surface structure such that after finishing, the surface structure (2) is pressed into the steel plate (1, 1') starting from the surface (1.1) of the steel plate (1, 1'), wherein the surface structure (2) has a plurality of recesses (2.1), wherein each recess (2.1) has a surrounding side region (2.3), which side region leads from the surface (1.1) into a valley region (2.2), wherein, when observed in a cross-sectional view, each recess (2.1) has a depth profile (2.11), which depth profile includes two opposing side partial regions (2.31) and a valley partial region (2.21) extending between the side partial regions and connecting the side partial regions (2.31), wherein the depth profile (2.11) is divided into a left part and a right part of the depth profile (2.11), wherein the depth profile (2.11) extends asymmetrically, wherein the left part of the depth profile (2.11) extends from a highest point (P1) to a lowest point (P3), and the right part of the depth profile (2.11) extends from a highest point (P2) to the lowest point (P3), and wherein the side partial regions (2.31) and the valley partial regions (2.21) of the left part and the right part of the depth profile (2.11) differ at least in terms of height (h), width (b) and slope (α).

10. The method according to claim 9, wherein the steel plate is coated by hot dip coating before the steel plate is provided.

11. The method according to claim 9, wherein after the steel plate is finished, the finished steel plate is coated by electrolytic coating.

12. The method according to any one of claims 9 to 11, wherein, The steel plates (1, 1') are additionally provided with a process medium, wherein the process medium is applied in a coverage amount of up to 2 g / m 2 .

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