WO2021052809A1

WO2021052809A1 - Sheet steel having a deterministic surface structure

Info

Publication number: WO2021052809A1
Application number: PCT/EP2020/075021
Authority: WO
Inventors: Oliver Vogt; Fabian JUNGE; Christine Bischoff; Burak William Cetinkaya
Original assignee: Thyssenkrupp Steel Europe Ag
Priority date: 2019-09-17
Filing date: 2020-09-08
Publication date: 2021-03-25
Also published as: DE102019214133A1

Abstract

The invention relates to particularly coated sheet steel (1) which is skin pass rolled to have a deterministic surface structure (2), and to a method for the production thereof.

Description

Sheet steel with a deterministic surface structure

The invention relates, in particular, to a coated steel sheet with a deterministic surface structure. Furthermore, the invention relates to a method for producing a particularly coated steel sheet dresed with a deterministic surface structure.

From the prior art, generic, in particular coated, steel sheets skinned with a deterministic surface structure are known, see for example patent specification EP 2 892 663 B1 negative skew Rsk is set in order to keep the coefficient of friction for forming processes low and thus the shaping of such structured, coated steel sheets positive, see laid-open document EP 3 354 360 A1.

With regard to the known prior art, there is a need for optimization, in particular with a view to reducing the oil layer.

The task is therefore to provide a sheet steel skinned with a deterministic surface structure which, compared to the prior art, provides properties that are equivalent or better, while at the same time reducing the amount of oil used.

The object is achieved with the features of claim 1.

The inventors have found that, in the case of a steel sheet which is coated in particular and which has a deterministic surface structure, equivalent or better properties can be provided compared to the prior art, in particular with a reduced use of oil at the same time, if the surface structure, starting from a surface of the coated steel sheet in particular, can be provided up to is embossed to a texture depth of a maximum of 2 pm in the coated steel sheet, in particular, the texture depth corresponding to the distance between the highest peak and the deepest valley of the surface structure profile. The texture depth of the surface structure is in particular up to a maximum of 1.8 μm, preferably up to a maximum of 1.6 μm, preferably up to a maximum of 1.4 μm, particularly preferably up to a maximum of 1.2 μm, in order to minimize the oil requirement. The texture depth is at least 0.3 pm, in particular at least 0.5 pm to ensure that a corresponding expression of a deterministic surface structure with the corresponding advantages on a particularly coated steel sheet can be provided in the first place. In particular, the texture depth corresponds to the value Rt according to DIN EN ISO 4287, where Rt is the maximum distance between the highest peak and the deepest valley of the surface structure along a defined measuring section, see DIN EN ISO 4287.

A deterministic surface structure is understood to mean recurring surface structures which have a defined shape and / or configuration, cf. EP 2 892 663 Bl. In particular, this also includes surfaces with a (guasi-) stochastic appearance, which, however, are created by means of a deterministic texturing process are brought and are thus composed of deterministic form elements.

A surface structure profile is to be understood as a course or a profile of the surface structure in a section along a defined measuring section.

Sheet steel is generally to be understood as a flat steel product which can be provided in sheet form or in the form of a plate or in the form of a strip.

The steel sheet formed according to the invention can be uncoated or preferably be coated. If the steel sheet is coated, the coating of the coated steel sheet comprises a metallic coating.

Further advantageous refinements and developments can be found in the description below. One or more features from the claims, the description and also the drawing can be linked with one or more other features from them to form further embodiments of the invention. One or more features from the independent claims can also be linked by one or more other features.

According to one embodiment of the steel sheet according to the invention, the surface structure has a flank area which, starting from the surface of the particularly coated steel sheet, extends to a valley area and is formed at an angle between 1 ° and 89 ° to the perpendicular of the particularly coated steel sheet. The angle can in particular be formed between 50 ° and 87 °, preferably between 60 ° and 85 °, particularly preferably between 65 ° and 82 °. The valley and flank area (negative form) of the upper The surface structure essentially corresponds to the surface (positive shape) on a skin-pass roller, which forms or impresses the surface structure by corresponding action on the, in particular, coated steel sheet. The flank area surrounding and forming the surface structure, together with the valley area connected in one piece to the flank area, defines a closed volume of the surface structure embossed in the in particular coated steel sheet by means of skin-passaging. According to the invention, the closed volume, the so-called empty volume, is in particular between 0.25 and 1.5 cm ³ / m ² and can be adapted to the forming agent to be applied, in particular oil, for later processing by means of forming processes.

According to one embodiment of the steel sheet according to the invention, the surface of the steel sheet, in particular coated, has a positive skew Rsk in accordance with DIN EN ISO 4287. The skewness Rsk is by definition a measure of the asymmetry of the amplitude density curve, see DIN EN ISO 4287.Surprisingly, the inventors found that, compared to the negative skewness Rsk, which in the prior art is advantageous and therefore a surface with good load-bearing behavior is given, despite positive skew Rsk, accordingly Rsk> 0, where 0 should be included in (Rsk> = 0), a result comparable or improved to the prior art can be achieved, with the distribution of the amplitude density in the direction of the valley area or in the valley area of the surface structure, process media such as oils, lubricants, forming aids, etc. can be better (retained) for further processes within the surface structure and thus also in small quantities.

According to one embodiment of the steel sheet according to the invention, the steel sheet is coated with a zinc-based coating, which is applied by hot-dip coating, in addition to zinc and unavoidable impurities, additional elements such as aluminum with a content of up to 5% by weight and / or magnesium with a Content of up to 5% by weight can be contained in the coating. Steel sheets with a zinc-based coating have very good cathodic corrosion protection, which has been used in automobile construction for years. If improved corrosion protection is provided, the coating also has magnesium with a content of at least 0.3% by weight, in particular at least 0.6% by weight, preferably at least 0.9% by weight. Aluminum can alternatively be present or in addition to magnesium with a content of at least 0.3% by weight, in particular to improve the bonding of the coating to the steel sheet and in particular a diffusion of iron from the steel sheet into the coating when exposed to heat treatment of the coated steel sheet essentially to avoid, for example good adhesion can be guaranteed. The thickness of the coating can be between 1.5 and 15 gm, in particular between 2 and 12 gm, preferably between 3 and 10 gm. Below the minimum limit, no adequate cathodic corrosion protection can be guaranteed and above the maximum limit, joining problems can occur when joining the steel sheet according to the invention or a component made from it to another component; in particular, if the maximum limit specified is exceeded, no stable process during thermal joining or joining can occur Welding can be ensured.

According to one embodiment of the steel sheet according to the invention, the coating of the coated steel sheet has a thickness which is equal to or greater than the texture depth of the surface structure. This is advantageous because the deformation resistance of the coating is lower than the deformation resistance of the steel sheet, so that lower forces are required to impress the surface structure compared to the surface structure known from the prior art, which not only depends on the thickness of the coating but also on the Part is also embossed into the surface of the substrate or steel sheet.

According to one embodiment of the steel sheet according to the invention, the particularly coated steel sheet is additionally oiled with an oil, the oil in particular being absorbed in the surface structure ^{with a layer of up to 1.4 g / m 2.} Due to the dimensioning of the surface structure, there is little need for oil, so that the coating is up to 1.4 g / m ² , in particular up to 1.1 g / m ² , preferably up to 0.8 g / m ² , preferably up to may be limited to 0.5 g / m ^2. In particular, due to the capillary effect, the oil is deposited after oiling on the flank and / or valley area of the surface structure and is available for further processes, such as for shaping processes, preferably for deep-drawing processes, in order to improve lubrication and reduce friction and thus reducing the wear and tear on the shaping means, such as shaping devices, preferably (deep-drawing) presses. In particular, an accumulation of the oil in tribologically unfavorable areas that do not contribute to the oil supply into the actual contact or friction zone can be effectively suppressed. For example, an edition of at least 0.2 g / m ² , in particular at least 0.3 g / m ^2, should be taken into account. Thus, the steel sheet according to the invention with a reduced oil layer has very good tribological properties and, compared to the oiled steel sheets known from the prior art, is more environmentally friendly, in particular due to the lower use of resources. According to a second aspect, the invention relates to a method for producing a special coated steel sheet with a deterministic surface structure, comprising the following steps:

- Provision of an in particular coated steel sheet,

Skin-passing of the steel sheet, which is coated in particular, with a skin-pass roller, the surface of the skin-pass roller, which acts on the surface of the steel sheet in particular being coated, is set up with a deterministic surface structure in such a way that, after skin-passing, the surface structure starting from a surface of the steel sheet which is coated in particular up to is embossed to a texture depth of a maximum of 2 pm in the coated steel sheet, the texture depth corresponding to the distance between the highest peak and the deepest valley of the surface structure profile.

The surface (positive shape) of the skin pass roller forms a surface structure through the action of force on the surface of the coated steel sheet in particular, which defines a valley and flank area (negative shape) and essentially corresponds to the surface (positive shape) of the skin pass roller. The skin pass roller for the formation of a deterministic surface structure can be processed with suitable means, for example by means of lasers, see EP 2 892 663 Bl.

In order to avoid repetition, reference is made in each case to the statements relating to the steel sheet according to the invention, in particular coated with a deterministic surface structure.

According to one embodiment of the method according to the invention, the surface of the dressing roller is set up in such a way that after skin-passing the surface of the steel sheet, in particular coated, has a positive skew Rsk according to DIN EN ISO 4287.

According to one embodiment of the method according to the invention, before the steel sheet is provided, the steel sheet is coated by hot-dip coating. In addition to zinc and unavoidable impurities, the melt for hot-dip coating can preferably contain additional elements such as aluminum with a content of up to 5% by weight and / or magnesium with a content of up to 5% by weight. According to one embodiment of the method according to the invention, the steel sheet, which is particularly coated, is additionally oiled with oil after the skin pass, the oil with a layer of up to 1.4 g / m ² , preferably with a layer of up to 0.5 g / m ² is applied.

In the following, specific embodiments of the invention are explained in more detail with reference to the drawing. The drawing and accompanying description of the resulting features are not to be read in a limiting manner to the respective configurations, but serve to illustrate exemplary configurations. Furthermore, the respective features can be used with one another as well as with features of the above description for possible further developments and improvements of the invention, especially in the case of additional configurations which are not shown. The same parts are always provided with the same reference numerals.

The drawing shows in

FIG. 1 shows a partial view of a coated steel sheet, dressed with a deterministic surface structure, in an atomic force microscope image,

Figure 2 is a schematic cross-sectional view along the section A-A in Figures 1 and

FIG. 3 shows a partial view of a coated, oiled steel sheet, dressed with a deterministic surface structure, in a Raman spectroscopy.

FIG. 1 shows a partial view of a coated steel sheet (1) dressed with a deterministic surface structure (2) in an atomic force microscope image according to an embodiment of the invention. The deterministic surface structure (2) is examined below using the example of a recurring I-shaped impression. Other embodiments are also conceivable and applicable and are not restricted to an I-shaped impression. Figure 1 shows two adjacent I-shaped impressions. The surface structure (2) is embossed starting from a surface (1.1) of the coated steel sheet (1) up to a texture depth (T) of a maximum of 2 pm in the coated steel sheet (1), the texture depth (T) being the distance between the highest peak (2.11) and the deepest valley (2.12) of the surface structure profile (3), see also FIG. 2.

FIG. 2 shows a cross-sectional view along the line AA in FIG. 1, it being easy to see that the surface structure (2) has a flank area (2.3) which extends from the surface (1.1) to a valley area (2.2) runs and to the vertical (0) of the coated steel sheet (1) is formed at an angle (a) between 1 ° and 89 °. In this exemplary embodiment, the angle (a) is approx. 80 °, whereby the different scalings in the figure must be taken into account. The texture depth (T) in this exemplary embodiment be approximately 1.3 μm, the texture depth (T) corresponding to the distance between the highest peak (2.11) and the deepest valley (2.12) of the surface structure profile (3). In this exemplary embodiment, the surface structure profile (3) is shown in section along a defined measuring section of approx. 35 μm (x-axis). The flank area (2.3) surrounding and forming the surface structure (2) defines, together with the one-piece valley area (2.2) connected or connected to the flank area (2.3), a closed volume of the surface structure (2) embossed in the coated steel sheet (1) by means of skin-passaging ), see also Figures 1 and 3. The coating (1.2) of the coated steel sheet (1) has a thickness (D) which is equal to or greater than the texture depth (T) of the surface structure (2). The transition between the coating (1.2) and the steel substrate is only shown symbolically in dashed lines in FIG. The thickness (D) of the coating was about 2 μm. The design of the surface structure according to the invention can also be implemented on an uncoated steel sheet.

The coated steel sheets (1) with a deterministic surface structure (2) are oiled with oil, which is advantageous in further processes, especially in shaping processes, such as deep-drawing processes. In the closed volume of the surface structure (2), oil collects during or after the oiling of the coated steel sheet (1) along the circumferential flank area (2.3), which is the bright spot in the Raman spectroscopic image shown in FIG corresponds, whereby the volume (I-shaped impression) is not completely filled, so that the valley area (2.2) of the surface structure (2) is not or only partially wetted with oil, whereby the need for oil can be reduced and thereby the Oil coverage is limited to a maximum of 1.4 g / m ² who can.

The examined in Figures 1 to 3 according to the invention coated, with a deterministic surface structure (2) skinned sheet steel (1) with an exemplary recurring I-shaped embossing, was produced as follows. A coated steel sheet was provided. Before the coated steel sheet was provided, the steel sheet was coated with a zinc-based coating by hot-dip coating. In addition to zinc and unavoidable impurities, the melt for hot-dip coating can preferably also contain aluminum with a content of up to 5% by weight and / or magnesium with a content of up to 5% by weight. The hot-dip coating has been Functionally carried out, especially in a continuous and conventional hot-dip coating system. After coating, the coated steel sheet was skin-pass with a skin-pass roller, the surface of the skin-pass roller, which acted on the surface (1.1) of the coated steel sheet (1), being set up with a deterministic surface structure in such a way that, after skin pass, a surface structure ( 2) starting from a surface (1.1) of the coated steel sheet (1) up to a texture depth (T) of a maximum of 2 μm was embossed into the coated steel sheet (1). The individual process steps are not shown.

Four coated, tempered steel sheets (VI to V4) were produced for further investigations. The type of coating was chosen the same for all steel sheets, a zinc-based coating (zinc and unavoidable impurities), which was applied in the standard fire-coating process and was approx. 7 μm thick. VI and V2 correspond to steel sheets according to the invention (1) and V3 and V4 form reference sheets with the difference to VI and V2 that the skin pass roller had a stochastic surface structure, the surface of the skin pass roller being structured, for example, by means of EDT, and thus also a stochastic surface structure was embossed into the reference sheets, where the texture depth was also limited to a maximum of 2 pm starting from the surface. Texture depths (T) of the surface structure (2) were each 1.5 μm and 1.8 μm. The structure depths (T) relate to the value Rt according to DIN EN ISO 4287. Table 1 shows a comparison of the steel sheets (1) according to the invention and reference sheets.

Table 1

The surface parameters RPc (number of peaks determined along a defined length / measuring section, in the above case per mm) and Rsk can be determined from DIN EN ISO 4287. It can be seen, inter alia, that the steel sheets VI and V2 according to the invention have a positive skew Rsk compared to the reference sheets V3 and V4 with a negative skew Rsk. Theoretically, this should result in a poorer load-bearing behavior of the surface. The information in Table 1 in relation to a strip drawing test and a cup drawing test according to DIN EN 1669, which was carried out on all four steel sheets VI to V4 under the same conditions, surprisingly show that better results in comparison between V1 / V2 and V3 / V4 could be achieved. The evaluation was based on the following criteria:

++ means that both the coefficient of friction determined in the strip drawing test and the thinning at the outlet of the punch edge on the formed sheet steel is lower than with reference V4 (coefficient of friction 15% lower, slight thinning less than 5% of the original sheet steel thickness),

+ means that the minimum thinning on the formed sheet steel is more than 5% but less than 10% of the original sheet steel thickness, whereby the coefficient of friction is approx. 10% lower than for reference V4, and

0 indicates a clearly recognizable thinning without cracks, which is no longer in the tolerable range (15% to 25% of the original sheet steel thickness).

In addition, it was possible at the same time to reduce the oil layer on sheet steel VI and V2 coated according to the invention and treated with a deterministic surface structure to below 1.4 g / m ² , the amount being sufficient to achieve a correspondingly good result.

Claims

1. With a deterministic surface structure (2) dressed steel sheet (1), characterized in that the surface structure (2) starting from an upper surface (1.1) of the steel sheet (1) up to a texture depth (T) of a maximum of 2 miti in the Sheet steel (1) is embossed, the texture depth (T) corresponding to the distance between the highest peak (2.11) and the deepest valley (2.12) of the surface structure profile (3).

2. Steel sheet according to claim 1, wherein the surface structure (2) has a flank area (2.3) which, starting from the surface (1.1), extends to a valley area (2.2) and at an angle to the perpendicular (0) of the steel sheet (1) (a) is formed between 1 ° and 89 °.

3. Steel sheet according to one of the preceding claims, wherein the surface (1.1) of the steel sheet (1) has a positive skew Rsk according to DIN EN ISO 4287.

4. Steel sheet according to one of the preceding claims, wherein the steel sheet is coated with egg nem zinc-based coating (1.2) which is applied by hot-dip coating, wherein in the coating (1.2) in addition to zinc and unavoidable impurities, additional elements such as aluminum with a content of up to 5 wt .-% and / or magnesium with a content of up to 5 wt .-% in the coating (1.2) can be kept ent.

5. Steel sheet according to claim 4, wherein the coating (1.2) of the coated steel sheet (1) has a thickness (D) which is equal to or greater than the texture depth (T) of the surface structure (2).

6. Steel sheet according to one of the preceding claims, wherein the steel sheet (1) is additionally oiled with an oil, wherein in particular the oil is received in the surface structure (2) ^{with an amount of up to 1.4 g / m 2.}

7. A method for producing a steel sheet (1) dressed with a deterministic surface structure (2) comprising the following steps:

- Provision of a steel sheet, - Skin pass the steel sheet with a skin pass roller, the surface of the Dres sierwalze, which acts on the surface of the steel sheet, is set up with a deterministic surface structure rule that after the skin pass the surface structure (2) starting from a surface (1.1) of the steel sheet (1) is embossed into the steel sheet (1) up to a texture depth (T) of a maximum of 2 gm, the texture depth (T) being the distance between the highest peak (2.11) and the deepest valley (2.12) of the surface structure profile (3) corresponds to.

8. The method according to claim 7, wherein the surface of the skin-pass roller is set up in such a way that, after skin-passing, the surface (1.1) of the steel sheet (1) has a positive skew Rsk according to DIN EN ISO 4287.

9. The method according to claim 7 or 8, wherein prior to providing the steel sheet, the steel sheet is coated by hot-dip coating.

10. The method according to claim 9, wherein the melt for hot dip coating can contain zinc and unavoidable impurities, additional elements such as aluminum with a content of up to 5% by weight and / or magnesium with a content of up to 5% by weight .

11. The method according to any one of claims 7 to 10, wherein the steel sheet (1) after the Dres Sieren is additionally oiled with oil, wherein the oil is applied with an amount of up to 1.4 g / m ² .

12. The method according to claim 11, wherein the oil is applied up to 0.5 g / m ² with an application.