Steel plate with a deterministic surface structure

Abstract

The invention relates to a steel sheet (1) which is particularly coated and finished with a defined surface structure (2) and to a method for producing the same.

Description

Field of the Invention

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

[0002] Steel sheets of this type, in particular coated and finished with a defined surface structure, are known from the prior art, for example from patent document EP 2 892 663 B1.

[0003] Regarding the known prior art, there is a need for optimization, especially in terms of reducing the oil coating. Summary of the Invention

[0004] Accordingly, the object is to provide a steel sheet, in particular coated and finished with a defined surface structure, which provides the same or better properties compared to the prior art while reducing the use of oil.

[0005] This object is solved by the features of claim 1.

[0006] The inventors have found that in a steel sheet, in particular coated and finished with a defined surface structure, if the surface structure is stamped into the steel sheet, in particular coated, starting from the surface of the steel sheet, in particular coated, the same or better properties can be provided compared to the prior art, in particular with a reduced use of oil at the same time, wherein the surface structure has a side region which extends from the surface up to a valley region, and wherein, according to the invention, at least the valley region has a roughness Ra of less than 300 nm, preferably to minimize the oil requirement. By limiting the roughness Ra (wherein the measuring method for determining the Ra value is given in DIN ISO EN 4287), at least in the valley region of the surface structure, the roughness Ra is less than 300 nm, in particular less than 250 nm, preferably less than 200 nm, more preferably less than 150 nm, further preferably less than 100 nm, and in particular it is possible to influence the local oil distribution such that in the range of the capillary forces acting in the direction towards the side region within the structure, the valley region is not wetted by oil or is only slightly wetted by oil and accumulates along the side region. The smaller the roughness Ra is set in the valley region, the stronger the influence of the capillary acting force in the direction towards the side region, so that a steel sheet, in particular coated, with a reduced oil requirement can be provided by the construction of the defined surface structure according to the invention.

[0007] A deterministic surface structure can be understood as a recurring surface structure having a defined shape and / or configuration, see EP 2 892 663 B1. In addition, particularly belonging thereto are surfaces having a (similar) random appearance, which surfaces are, however, applied by means of a deterministic texturing method and thus consist of deterministic shape elements.

[0008] A steel sheet is generally understood as a flat steel product which can be provided in the form of a sheet, a slab or a strip.

[0009] The steel sheet constructed according to the invention can be uncoated or preferably coated. If the steel sheet is coated, the coating of the coated steel sheet comprises a metallic covering.

[0010] Other advantageous designs and improvements result from the following description. One or more features from the claims, the description and the drawings can be combined with one or more other features to form other designs of the invention. One or more features from the independent claims can also be combined with one or more other features.

[0011] In one design of the steel sheet according to the invention, the surface structure has a lateral region which extends from the surface to a valley region and is configured at an angle between 1° and 89° relative to the perpendicular of the steel sheet, in particular of the coated steel sheet. This angle can in particular be configured between 50° and 87°, preferably between 60° and 85°, particularly preferably between 65° and 82°. The valley region and the lateral region (negative shape) of the surface structure essentially correspond to the surface (positive shape) on a finishing roll, which finishing roll structures or stamps out the surface structure by acting accordingly on the steel sheet, in particular the coated steel sheet. The lateral region surrounding and configuring the surface structure together with the valley region integrally connected to the lateral region defines the closed volume of the surface structure stamped into the steel sheet, in particular the coated steel sheet, by finishing. The closed volume, the so-called void volume, can be coordinated with the forming medium to be applied, in particular an oil phase, by means of a forming method for subsequent processing.

[0012] According to a design of the steel sheet of the present invention, the steel sheet is coated with a zinc-based coating applied by hot dip coating, wherein in the coating, in addition to zinc and inevitable impurities, additional elements such as aluminum with a content of at most 5% by weight and / or magnesium with a content of at most 5% by weight may be included in the coating. The steel sheet with a zinc-based coating has very good cathodic corrosion protection, which has been applied in the automotive manufacturing for many years. If improved corrosion protection is provided, the coating additionally has a magnesium content of at least 0.3% by weight, especially at least 0.6% by weight, preferably at least 0.9% by weight. Aluminum may be present in a content of at least 0.3% by weight instead of or in addition to magnesium to especially improve the connection of the coating on the steel sheet and especially basically avoid the diffusion of iron from the steel sheet into the coating during the heat treatment of the coated steel sheet, whereby good adhesion ability can be ensured, for example. 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, while joining problems may occur when joining the steel sheet according to the present invention or a member made thereof with another member above the maximum limit, especially when the thickness of the coating exceeds the given maximum limit, the stable process during thermal joining or welding cannot be ensured.

[0013] According to a design of the steel sheet of the present invention, the especially coated steel sheet is additionally oiled with oil, wherein, especially, the oil is at most 2 g / m 2 The coating of is accommodated in the surface structure. Due to the dimension design of the surface structure, only little oil is required, so that the coating is limited to at most 2 g / m 2 , especially at most 1.5 g / m 2 , preferably at most 1.2 g / m 2 , preferably at most 1 g / m 2 . Especially due to the strong capillary force in the direction of the side regions and the small roughness in the valley regions, the oil accumulates basically along the side regions and / or at the transition between the side regions and the valley regions of the surface structure after oiling and is used for further processes, such as for forming processes, preferably for deep drawing processes, to improve lubrication and reduce friction and thus reduce the wear of forming devices, such as forming apparatuses, preferably (deep drawing) presses. Especially, the accumulation of oil in tribologically unfavorable regions can be effectively suppressed, which is not conducive to the delivery of oil to the actual contact zone or friction zone. Therefore, the steel sheet with a reduced oil coating according to the present invention has very good tribological properties and is more environmentally friendly especially due to less resource use compared to the oiled steel sheets known in the prior art.

[0014] According to a second aspect, the present invention relates to a method for manufacturing a steel sheet especially coated and finished with a deterministic surface structure, comprising the following steps:

[0015] - Providing especially coated steel sheets,

[0016] - Finishing especially coated steel sheets with a finishing roll, wherein the surface of the finishing roll acting on the surface of the especially coated steel sheet is provided with a defined surface structure such that after finishing the surface structure is pressed into the especially coated steel sheet starting from the surface of the especially coated steel sheet, wherein the surface structure has a flank region which extends from the surface up to a valley region, and wherein at least the valley region has a roughness Ra of less than 300 nm.

[0017] The surface (positive shape) of the finishing roll constructs such a surface structure by the force acting on the surface of the especially coated steel sheet, which surface structure defines a valley region and a flank region (negative shape) and substantially corresponds to the surface (positive shape) of the finishing roll. The finishing roll for constructing such a defined surface structure can be machined by suitable means, for example by means of laser machining, see EP 2 892 663 B1. Furthermore, other removal methods can also be used to provide the surface on the finishing roll, for example cutting manufacturing methods with geometrically defined or undefined cutting edges, chemical or electrochemical, optical or plasma-induced methods, which are suitable for achieving a roughness Ra of less than 300 nm in the valley region of the surface structure of the steel sheet to be finished, at least in the coated region. Alternatively or additionally, the finishing roll can also be subjected to a post-processing process, preferably a grinding process, whereby in particular the part of the finishing roll which forms the valley region in the especially coated steel sheet, in this case the corresponding peak region or plateau on the surface of the finishing roll, is levelled, whereby the roughness can optionally be further reduced.

[0018] For the sake of avoiding repetition, reference is made respectively to the embodiments of the especially coated steel sheets finished with a defined surface structure according to the invention.

[0019] According to one embodiment of the method according to the 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 additional elements in addition to zinc and inevitable impurities, such as aluminium in a content of at most 5 wt% and / or magnesium in a content of at most 5 wt%.

[0020] According to one embodiment of the method according to the invention, the steel sheet is additionally oiled after finishing, wherein the oil is applied with a coating of at most 2 g / m 2 preferably at most 1 g / m 2 of coating. Description of the Drawings

[0021] 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 obtained should not be construed as being limited to the corresponding design, but are used to illustrate exemplary designs. In addition, the corresponding features can be used among each other and together with the features described above for possible further extensions and improvements of the present invention, especially in additional designs not shown. The same components are always provided with the same reference numerals.

[0022] In the accompanying drawings

[0023] Figure 1 a) and Figure 1 b) respectively show schematic partial cross-sectional views of a coated steel sheet finished with a deterministic surface structure according to the first and second embodiments of the present invention,

[0024] Figure 2 a), 2b) and Figure 2 c) show partial views of a coated steel sheet finished with a random surface structure according to the prior art, and

[0025] Figure 3 a), 3b) and 3c) show partial views of a coated steel sheet finished with a deterministic surface structure according to the third embodiment of the present invention. Detailed implementation

[0026] In Figure 1 a) and Figure 1 b), schematic partial cross-sectional views of a coated steel sheet (1) finished with a deterministic surface structure (2) according to the first and second embodiments of the present invention are respectively shown. The surface structure (2) is stamped into the coated steel sheet (1) starting from the surface (1.1) of the steel sheet (1), wherein the surface structure (2) has a side region (2.3) that extends from the surface (1.1) until the valley region (2.2). At least the valley region (2.2) has a roughness Ra of less than 300 nm. According to the cutting method, the valley region (2.2) can be set by a corresponding corresponding region (hill region / high platform) on a finishing roll (not shown), and the corresponding finishing roll (not shown) for finishing the coated steel sheet (1) is processed by the cutting method. Additionally, the finishing roll can be reprocessed by means of a grinding process, wherein the hill region / high platform is leveled accordingly, so that a further reduction in the roughness Ra in the valley region (2.2) can be achieved. Furthermore, in the appendix Figure 1It can be clearly seen in a) and 1b) that the surface structure (2) has side regions (2.3) which extend from the surface (1.1) to the valley regions (2.2) and are formed at an angle (a) of 1° to 89° relative to a perpendicular (0) to the coated steel sheet (1). The side regions (2.3) surrounding and forming the surface structure (2) together with the valley regions (2.2) which are integrally connected or joined to the side regions (2.3) define a closed volume of the surface structure (2) which is stamped into the coated steel sheet (1) by means of a finishing process. FIG. 1b) shows in the valley regions (2.2) a flatter and thus lower roughness Ra than FIG. 1a), which is processed by means of a ground finishing roller (not shown), so that a defined surface structure (2) can be produced on the coated steel sheet (1), which surface structure can be provided at least in the valley regions (2.2) of the surface structure (2) with a roughness Ra of in particular less than 250 nm, preferably less than 200 nm, preferably less than 150 nm, further preferably less than 100 nm. The design of the surface structure according to the invention can also be realized on uncoated steel sheets.

[0027] exist Figure 2 2a), 2b) and 2c) show partial views of coated steel sheets finished with a random surface structure according to the prior art. The surface structure was finished with the aid of a finishing roller (not shown) that was structured by EDT and subsequently ground. Figure 2 a) shows a cross-sectional view of the morphology of a sheet provided with a zinc coating, measured using an atomic force microscope (AFM). The 60×12.5 μm 2 The roughness Ra of the surface (U) of the sheet metal is shown by way of example, wherein a value of Ra=323 nm was determined. The oil distribution on a sheet metal surface provided with a zinc coating, which was finished by means of an EDT-structured and subsequently ground finishing roller (not shown), is shown, wherein the oil distribution on the sheet metal surface provided with a zinc coating is shown by way of example ... Figure 2 In b), a segment is drawn using optical microscopy, whereas Figure 2 In c), the same section is plotted using Raman spectroscopy, where the oil coating appears brighter. The valley regions of the surface structure are partially filled with oil, the oil coating is greater than 2 g / m 2 .

[0028] Another result appears in the observation Figure 3 3a), 3b) and 3c) of a partial view of a steel sheet (1) coated and finished with a defined surface structure according to a third exemplary embodiment of the invention. The surface structure is finished with the aid of a finishing roller (not shown) which is structured by laser and subsequently ground. The defined surface structure (2) is investigated using the example of a recurring I-shaped punching. Other embodiments are also conceivable and applicable and are not limited to I-shaped punching. Figure 3a), 3b) and 3c) show two I-shaped stamping parts arranged side by side. Figure 3 a) shows a cross-sectional view of the sheet metal topography (1, 2) provided with a zinc coating (1.2) measured by an atomic force microscope (AFM). In the valley region (2.2), the roughness Ra with respect to the surface (U) of 60×12.5 μm 2 is determined, where the value Ra = 77 nm is determined. Exemplarily shown is the oil distribution on the sheet metal topography (1, 2) provided with a zinc coating (1.2) finished by means of a laser-structured and subsequently ground finishing roll (not shown), where Figure 2 b) shows the section drawn by optical microscopy and Figure 2 c) shows the same section, however drawn by Raman spectroscopy, where the oil coating is shown brighter. The valley region (2.2) of the surface structure (2) is substantially not wetted by oil, and the oil accumulates along the side region (2.3) or at the transition between the side region (2.3) and the valley region (2.2) due to capillary action and the reduced roughness with Ra < 300 nm in the valley region (2.2). The oil coating can be reduced to 1.5 g / m 2 , in particular reduced to 1 g / m 2 .

[0029] For further research, four coated and finished steel sheets (V1 to V4) are manufactured. The type of coating is selected to be the same for all steel sheets, a zinc-based coating (zinc and inevitable impurities), which is applied in a hot-dip coating process and has a thickness of approximately 7 μm. V1 and V2 correspond to the steel sheets (1) according to the invention, while V3 and V4 form reference plates different from V1 and V2, i.e., the finishing roll has a random surface structure, where the surface of the finishing roll is structured, for example, by EDT, and thus also stamps a random surface structure into the reference plates. Table 1 gives a comparison of the steel sheets (1) according to the invention and the reference plates.

[0030] Table 1

[0031]

[0032] The determination of the surface parameters Ra (arithmetic mean roughness value), Rz (average roughness), and RPc (number of peaks measured along a defined length, in the above case per mm) can be derived from DIN EN ISO 4287 and the characteristic value for the long-wave waviness Wsa (arithmetic mean waviness) according to SEP1941. However, surprisingly, the data in Table 1 for the strip tensile test (Streifenziehversuch), the cup tensile test carried out under the same conditions in all four steel sheets V1 to V4 according to DIN EN 1669, show that better results can be obtained in the comparison between V1 / V2 and V3 / V4. The evaluation is based on the following criteria:

[0033] ++ indicates that the friction coefficient determined in the strip tensile test and the thinning at the exit of the punch edge of the formed steel sheet are both smaller (small thinning below 5% of the initial steel sheet thickness),

[0034] + indicates that the minimum thinning at the formed steel sheet exceeds 5% but is below 10% of the initial steel sheet thickness,

[0035] 0 indicates that the thinning clearly visible without tearing is no longer within the tolerable range (15% to 25% of the initial steel sheet thickness), and

[0036] - indicates that fracture occurs.

[0037] In addition, at the same time, the oil coating at the steel sheets V1 and V2 coated according to the invention and finished with a defined surface structure can be reduced to less than 1.5 g / m 2 , where this amount is sufficient to obtain correspondingly good results.

Claims

1. A steel sheet (1) finished with a deterministic surface structure (2), wherein, The surface structure (2) is stamped into the steel sheet (1) starting from the surface (1.1) of the steel sheet (1), wherein the surface structure (2) has a side region (2.3) that extends from the surface (1.1) up to the valley region (2.2), characterized in that the valley region (2.2) has a roughness Ra of less than 300 nm, the steel sheet is coated with a zinc-based coating (1.2), and the coated steel sheet is additionally oiled with oil.

2. The steel plate according to claim 1, wherein, The side region (2.3) is configured at an angle (a) between 1° and 89° with respect to the perpendicular (0) of the steel sheet (1).

3. The steel plate according to claim 1, wherein, The zinc-based coating (1.2) is applied by hot-dip coating, and in addition to zinc and inevitable impurities, the coating (1.2) contains other elements, including up to 5 wt% aluminum and / or up to 5 wt% magnesium.

4. The steel plate according to any one of the preceding claims, wherein, Oil with a maximum of 2 g / m 2 The coating is received in the surface structure (2).

5. A method for manufacturing a steel sheet (1) finished with a deterministic surface structure (2), comprising the following steps: - providing a steel sheet coated with a zinc-based coating (1.2), - finishing the steel sheet with a finishing roll, wherein the surface of the finishing roll acting on the steel sheet surface is provided with a deterministic surface structure such that after finishing, the surface structure (2) is stamped into the steel sheet (1) starting from the surface (1.1) of the steel sheet (1), wherein the surface structure (2) has a side region (2.3) that extends from the surface (1.1) to the valley region (2.2), and wherein the valley region (2.2) has a roughness Ra of less than 300 nm, - the steel sheet (1) is additionally oiled with oil after finishing.

6. The method according to claim 5, wherein the steel sheet is coated by hot-dip coating before the steel sheet is provided.

7. The method according to claim 6, wherein the melt for hot-dip coating contains additional elements in addition to zinc and inevitable impurities, including up to 5 wt% aluminum and / or up to 5 wt% magnesium.

8. The method according to any one of claims 5 to 7, wherein with a coating of up to 2 g / m 2 to apply the oil.

9. The method according to claim 8, wherein the oil is applied with a coating of up to 1 g / m 2 .

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