EP3215656B1 - Method for producing an anti-corrosion coating for hardenable steel sheets and anti-corrosion layer for hardenable steel sheets - Google Patents

Description

The invention relates to a method for producing a corrosion protection coating for hardenable steel sheets and a corrosion protection layer for hardenable steel sheets.

For the hardening of steel sheets or the production of sheet steel components made of sheet steel, which are hardened, and in particular Karossieriebauteile, there are currently two common methods.

Common to both methods is that a steel strip is produced from a steel material by hot rolling and usually also subsequent cold rolling and the steel strip is subsequently continuously galvanized. The usual galvanizing in this case is the hot dip galvanizing, in which the steel strip is passed through a trough with liquid zinc, wherein the liquid zinc adheres to the steel, the galvanized steel strip is usually conveyed vertically from the trough and then superfluous zinc is stripped with Abstreiferdüsen and the tape then optionally subjected to a heat treatment. The galvanized steel strip thus produced is then usually placed in coils, i. wound up.

In order to produce hardened steel sheet components from this steel strip, blanks of a desired size are punched out of the steel strip and these blanks are then further processed in two different ways.

In a first method, the boards are formed in a conventional manner in a multi-stage process, and in particular deep-drawn until the component is molded in its final appearance. In this case, however, usually the component is formed smaller in all three spatial directions about 2% smaller, to take into account a subsequent thermal expansion. Subsequently, this sheet metal component is heated to an austenitizing temperature, ie a temperature above Ac ₃ and optionally held until the steel material is present in the austenitic phase. Subsequently, the heated sheet steel component is transferred to a mold hardening tool and held in the mold hardening tool, in which the heated sheet steel component is usually used form-fitting, pressed by a die and a male part, but not substantially reshaped. Due to the abutment of the die and the male part, which may also be cooled, the steel component is cooled at a speed above the critical hardening rate, resulting in a transformation of the austenite substantially to martensite and results in a high hardness of the component.

In a second known method, the board is heated directly to a temperature required for curing above Ac ₃ and optionally held and then formed in a tool consisting of female and male in a single-stage stroke and cooled simultaneously by the concern of the tool on the workpiece so quickly that the curing outlined above occurs. This process is called press hardening.

Form hardening is superior to press hardening in terms of the possible geometries of a component, since more complicated or more complex spatial forms can be realized in a multi-stage forming process, wherein only comparatively simple geometries can be produced during single-stage forming press hardening.

However, the end result of both processes is a hardened sheet steel component.

Common materials for these sheet steel components are so-called boron-manganese steels, in particular the 22MnB5 most widely used for this purpose.

It is known that, in particular in the press hardening process, problems can arise in that liquid zinc interacts with the austenite present in the steel material at high temperatures which are not yet completely explainable, but cause cracks to form in the strongly deformed areas. This phenomenon is referred to as so-called "liquid metal embrittlement".

It has already been attempted to counteract this phenomenon by using conversion-delayed steel grades which are austenitized at high temperature, then intercooled and, as a result of this intermediate cooling, reach temperatures below the melting temperature of the zinc phases in the coating, and only then carry out the transformation. Due to the conversion delay, even at these relatively low temperatures, the iron is still present as austenite, so that reliable quench hardening can be achieved.

From the EP 1 439 240 A1 is a method for press or form hardening of coated steels known. Example 5 discloses a steel plate having a first layer of zinc or a zinc alloy and a second layer of nickel or cobalt. The first layer is over a melt immersion method, wherein the second layer is electrodeposited.

The EP 2 602 359 A1 relates to press hardening of coated steels, wherein the steels are coated from nickel and a zinc-nickel layer, wherein both layers are applied electrolytically.

From the WO 2005/021820 A1 is a press hardening of boards of a hardenable steel alloy and in particular a 22MnB5 known, wherein the board may be formed with an electrodeposited zinc layer and a second layer of an oxygen-affine element.

From the DE 10 2010 030 465 A1 is a method for producing a provided with a corrosion protection coating and formed of a high-strength sheet steel material formed sheet metal part known. This method comprises the steps of forming a provided starting sheet material to a sheet metal part, forming the anti-corrosion coating by electrolytic application of a zinc-nickel coating on the sheet metal part, wherein at the beginning of the coating process First, a thin nickel layer is deposited, which further prevents hydrogen embrittlement of the steel sheet material. Furthermore, a hot-formed and in particular press-hardened sheet metal part made of a high-strength sheet steel material with an electrolytically applied zinc-nickel coating is known from this. The purpose of this is to provide the nickel layer as a barrier to hydrogen typically introduced into the steel sheet material during electrolytic plating.

From the EP 2 290 133 B1 For example, there is known a method for producing a steel component provided with a metallic, corrosion-protective coating and the steel component itself. This is to provide a simple to implement in practice method is created, which allows to produce a steel component with comparatively little effort, which is provided with a well-adherent and safe from corrosion protective metallic coating, since it is stated that zinc coatings on the steel sheet for hot press hardening not adhere well. Furthermore, known coatings by oxidation of the surface should have a poor paint adhesion. According to this document, the applied anticorrosion layer should be an electrolytically applied γ-ZnNi phase, which should then well tolerate heating operations carried out for the purpose of austenitizing.

The EP 0 364 596 B1 relates to a process for the production of zinc-nickel alloy-coated thin sheets with good Pressverformeigenschaften, wherein the formability of such sheets is to be improved by a zinc-nickel alloy coating. The layer is to be deposited with about 30 g / m ² and a nickel content of 12.5%.

The object of the invention is to provide a method for producing hardened sheet steel components.

The object is achieved by a method having the features of claim 1.

Advantageous developments are characterized in the subclaims.

It is a further object of the invention to provide a corrosion protection material for hardenable steel sheets, which reduces or even prevents the liquid metal embrittlement with good cathodic protection against corrosion.

The object is achieved with a corrosion protection material having the features of claim 10.

Advantageous developments are characterized in dependent claims.

According to the invention, a multilayer anticorrosion layer is produced on a steel sheet, wherein either a very thin nickel layer of 1 .mu.m is deposited electrolytically on the steel and then a zinc layer is likewise deposited electrolytically on the nickel layer, or the thin nickel layer is formed on the steel sheet via an electrolytic deposition and then a zinc layer is applied via hot dip galvanizing. Another possibility is to apply a nickel-containing layer to a normal hot-dip galvanized sheet steel strip via a corresponding after-treatment (coater).

According to the invention, the nickel layer has a thickness of approximately 1 μm when applied as the first layer by means of electrolytic deposition.

When a galvanized zinc layer is post-treated, the outer nickel-containing layer is about 250 nm to 700 nm thick.

According to the invention, it has surprisingly been found that in the coating according to the invention or the layer structure according to the invention the nickel in no form forms a barrier against the ingress of liquid zinc to the steel, but rather the nickel reacts very quickly with the zinc and also with iron. that the melting point of the entire corrosion protection layer increases sharply, since instead of zinc-iron-Γ-phases zinc-nickel-iron phases are increasingly formed, which have a much higher melting point. This achieves that at the temperatures that are hot worked and quench hardened, there are no liquid phases that could interact with the austenite. This is also the reason why, according to the invention, an externally applied nickel layer acts in a comparable manner, with the nickel which is deposited on the outermost surface diffusing into the corrosion protection layer so rapidly that the increase in the melting point is ensured.

According to the invention, instead of nickel, or layers based on nickel, other elements which form intermetallic-less noble phases with Zn or Fe and have a higher oxidation potential than Zn, such as Cu, Co, Mn or Mo, may be used, since manganese, Molybdenum, cobalt and copper the same effects can be achieved. "Based on" here means that these elements predominantly (> 50 wt .-%) are included, but other elements are present as alloying elements. Both nickel and cobalt as well as manganese or copper do not act as a physical barrier against the diffusion of zinc and iron, but are dissolved and incorporated into the molten zinc and zinc-iron phases. In the case of a previously applied nickel layer and subsequent hot-dip galvanizing, the nickel is at least already dissolved by the zinc melt during galvanizing.

In a standard annealing for the purpose of austenitizing and subsequent forming could be found that forms a similar phase structure of the layer as in pure hot-dip galvanized layers (phs-Ultraform), but this phase structure is zinc-rich or has a greater proportion of Γ phases. That these phases are more zinc-rich, is advantageous for the cathodic corrosion protection performance of the layer.

This is further supported by the fact that a very zinc-rich near-surface layer is formed, which is not observed in standard hot-dip galvanizing in the standard annealing without nickel interlayer.

The positive effect of the nickel in the layer or as a separately applied electrolytic layer results in the consideration of bending samples. The formation of cracks by the liquid metal embrittlement is impressively reduced.

Figur 1:

eine lichtmikroskopische geätzte Schliffaufnahme eines Stahlblechs mit einer Beschichtung, wobei auf einer 1 µm dicken Nickel-Zwischenschicht eine feuerverzinkte Schicht aufgebracht wurde;

Figur 2:

die Schicht nach Fig. 1 in einer vergrößerten Darstellung;

Figur 3:

eine Schicht nach Fig. 1, wobei durch EDX element mapping die Elemente Eisen, Zink, Nickel und Aluminium in ihrer Verteilung bei einer 1 µm dicken aufgebrachten Nickelzwischenschicht dargestellt sind;

Figur 4:

ein Schliffbild der Beschichtung mit einer 0,5 µm dicken Nickelschicht und einer 10 µm dicken Zinkschicht geglüht bei 800 °C;

Figur 5:

die Schicht nach Fig. 4 mit einer 1 µm dicken Nickelschicht;

Figur 6:

eine Beschichtung nach dem Glühen, einer Haltezeit, einer Tranferzeit und einer anschließenden Kühlung zum Presshärten;

Figur 7:

eine röntgenelektronenmikroskopische Schliffaufnahme einer Korrosionsschutzschicht nach einem Austenitisierungsglühen bei 870 °C;

Figur 8:

die Schicht nach Fig. 7 mit der Verteilung des Eisens;

Figur 9:

die Schicht nach Fig. 7 mit der Verteilung des Zinks;

Figur 10:

die Schicht nach Fig. 7 mit der Verteilung des Nickels, wobei als Präparationshilfe eine Nickelstützschicht auf der Oberfläche aufgebracht ist;

Figur 11:

die Schicht nach Fig. 7 mit der Verteilung des Aluminiums;

Figur 12:

die Schicht nach Fig. 7 mit der Verteilung des Mangan;

Figur 13:

eine Beschichtung nach dem Austenitisieren und Abschrecken mit einer eingezeichneten EDX-Scanlinie;

Figur 14:

die Beschichtung nach Fig. 13 mit dem Scanprofil für die Elemente Eisen, Nickel und Zink;

Figur 15:

vier V-Proben mit Biegeradius 1,5 mm.

The invention will be explained by way of example with reference to a drawing. It shows:

FIG. 1:

a light-microscopic etched micrograph of a steel sheet with a coating, wherein on a 1 micron thick nickel intermediate layer a hot dip galvanized layer has been applied;

FIG. 2:

the layer after Fig. 1 in an enlarged view;

FIG. 3:

one layer after Fig. 1 , wherein by EDX element mapping the elements iron, zinc, nickel and aluminum are shown in their distribution in a 1 micron thick applied nickel intermediate layer;

FIG. 4:

a micrograph of the coating with a 0.5 micron thick nickel layer and a 10 micron thick zinc layer annealed at 800 ° C;

FIG. 5:

the layer after Fig. 4 with a 1 micron thick nickel layer;

FIG. 6:

a coating after annealing, a holding time, a transfer time and a subsequent cooling for press hardening;

FIG. 7:

an X-ray micrograph of a corrosion protection layer after austenitizing annealing at 870 ° C;

FIG. 8:

the layer after Fig. 7 with the distribution of iron;

FIG. 9:

the layer after Fig. 7 with the distribution of zinc;

FIG. 10:

the layer after Fig. 7 with the distribution of the nickel, wherein a nickel support layer is applied to the surface as a preparation aid;

FIG. 11:

the layer after Fig. 7 with the distribution of aluminum;

FIG. 12:

the layer after Fig. 7 with the distribution of manganese;

FIG. 13:

a coating after austenitizing and quenching with an indicated EDX scan line;

FIG. 14:

the coating after Fig. 13 with the scan profile for the elements iron, nickel and zinc;

FIG. 15:

four V samples with bending radius 1.5 mm.

The method according to the invention for producing sheet steel components may be either a press hardening method or a shape hardening method, that is, a method in which a sheet steel member is heated and then quench hardened in a tool (mold hardening), or a method in which a board is single stage formed and quench hardened (press hardening).

According to the invention, a boron-manganese steel is used as the steel material for press-hardening or mold-hardening, in which, with regard to the transformation of the austenite into other phases, the transformation can shift into deeper regions and martensite is formed.

In particular, as a retarder in such steels, ie as an element which shifts the phase transformation of austenite to martensite to lower temperatures the alloying elements boron, manganese, carbon and optionally chromium and molybdenum are present.

Steels of the general alloy composition are used for the invention (all figures in percent by weight): Carbon (C) 0.08 to 0.6 Manganese (Mn) 0.8-3.0 Aluminum (Al) 0.01-0.07 Silicon (Si) 0.01-0.5 Chrome (Cr) 0.02-0.6 Titanium (Ti) 0.01-0.08 Nitrogen (N) <0.02 Boron (B) 0.002-0.02 Phosphorus (P) <0.01 Sulfur (S) <0.01 Molybdenum (Mo) <1

Remaining iron and impurities caused by melting.

In particular, steel assemblies have proved to be suitable as follows (all figures in weight percent): Carbon (C) from 0.08 to 0.34 Manganese (Mn) 1.00-3.00 Aluminum (Al) 0.03-0.06 Silicon (Si) 0.01-0.20 Chrome (Cr) 0.02-0.3 Titanium (Ti) 0.03-0.04 Nitrogen (N) <0.007 Boron (B) 0.002-0.006 Phosphorus (P) <0.01 Sulfur (S) <0.01 Molybdenum (Mo) <1

Remaining iron and impurities caused by melting.

Thus, in particular, the conventional steels 22MnB5 or 20MnB8 are suitable.

By adjusting the alloying elements acting as conversion retarders, quench hardening, i. H. rapid cooling with a cooling rate above the critical hardening speed, even at temperatures below 780 ° C. This means that in this case, below the peritectic system of the zinc-iron system is used, i. H. only below the peritectic mechanical stresses are applied. This also means that the moment in which mechanical stresses are applied, there are no longer any liquid zinc phases which can come into contact with austenite.

A corrosion protection layer according to the invention is a multilayer corrosion protection layer, wherein a plurality of nickel layers and a plurality of zinc layers are applied to a substrate of a hardenable steel material. Instead of a nickel layer, a manganese or copper layer can also be applied.

In this case, the nickel, copper or manganese layer is preferably applied electrolytically. The zinc layer can be applied electrolytically or by a hot dip process.

In principle, it is possible first to apply the nickel layer and then a zinc layer, wherein the subsequently applied zinc layer is applied electrolytically or by hot dip.

Another possibility is to apply the zinc layer as a first layer electrolytically or by hot dip method and then apply a nickel layer thereon to the outermost surface and in particular to deposit it electrolytically.

As used herein, nickel refers to other elements that form intermetallic-less noble phases with Zn or Fe and have a higher oxidation potential than Zn, such as Cu, Co, Mn, or Mo.

The element nickel is hereby also used for copper and manganese.

Surprisingly, it has been found that correspondingly applied metallic layers obviously intervene in the phase structure of a corrosion protection layer, but themselves do not constitute a diffusion barrier. Therefore, the invention is effective even when the thin nickel, copper or manganese layer is applied to a hot dip galvanizing layer.

In Fig. 1 One recognizes a light-microscopic etched cut representation of a layer on a steel substrate. In Fig. 2 this is shown enlarged again.

In this layer, a 1 micron thick nickel intermediate layer is first applied to the steel substrate and then hot-dip galvanized, wherein the hot dip galvanizing the nickel intermediate layer was dissolved in the zinc bath.

When such a layer is measured with an EDX element distribution, it can be seen in FIG Fig. 3 that an iron equal distribution is present in the region of the steel, with the iron content decreasing at the boundary layer to the layers attached thereto. The distribution of zinc shows that the zinc content increases at the boundary to higher layers.

With regard to the nickel one recognizes that there must be an equal distribution within the layer, since there is no clear color statement regarding the nickel. The same applies to aluminum, which is included in the zinc coating for hot dip galvanizing.

In 4 and 5 In each case layers are compared, in which once the nickel intermediate layer has a thickness of 0.5 microns ( Fig. 4 ) and once a layer thickness of 1 micron ( Fig. 5 ) would have. On each of these a hot dip galvanized layer of 10 microns is deposited. Both layer samples were then heated to 800 ° C. The uppermost light coat does not belong to the anticorrosive layers, it is a preparation auxiliary layer of nickel, which was applied before the sample preparation, ie after heating and cooling.

In the case of these coatings, a two-phase structure with a light phase, which is interspersed with dark areas, is formed on the surface of the steel substrate ( Fig. 6 ). This was annealed at 870 ° C in a 1 micron thick intermediate nickel layer, then was waited for 45 s, added a transfer time of 5 s and then a cooling in a press.

One shift after Fig. 6 was measured with an EDX element distribution, whereby here too a nickel support layer is present as a preparation aid on the sample. The slice cut that was measured is in Fig. 7 shown.

In the distribution of iron ( Fig. 8 ) it can be seen that relatively little iron is present in the light phase, while the dark phase shows significant iron contents.

Zinc shows that it is highly enriched in the light phase, while it is present in much lower concentrations in the dark areas, so that apparently there is an iron-rich phase as nodules or roundish accumulation in a zinc matrix.

The nickel ( Fig. 10 ) is still very weakly recognizable in the bright zinc matrix, but is obviously not present in the iron-rich nodules, whereas aluminum ( Fig. 11 ) is distributed relatively evenly throughout the layer, albeit with enrichments in the iron-rich phases.

Manganese, which is present in the base steel material, is scarcely present in the entire layer and can only be detected in the substrate.

In a comparable layer, the element distribution was measured in depth with a so-called EDX line scan ( Fig. 13 ). In this case, the scan already starts in the nickel backing layer and goes deep into the steel base material.

For a coating that was annealed at 800 ° C, had 5 s transfer time, and then was press-cooled, the result is as in Fig. 14 you can see a corresponding distribution of the elements. The nickel peak is initially close to 100%, which is because the scan already starts in the nickel preparation layer. Subsequently, the nickel content drops, and it can be seen that the nickel content is significantly lower in the dark iron-rich zones than in the bright zinc-rich phases. Accordingly, starting from the outer one Surface iron content is very low and is about 10% and increases significantly in the dark iron-rich phase, to then reach its maximum in the steel matrix. The content of iron is inversely related to the zinc content, which was to be expected according to the two-phase formation.

From an originally existing nickel layer is no longer visible in the phase structure.

The positive effect of nickel in the layer can be seen in bending samples with a radius of 1.5 mm ( Fig. 15 ).

While with a nickel interlayer of only 0.5 .mu.m (with the complete dissolution of the nickel in the anticorrosion coating, the thickness of the nickel layer has an effect only on the amount of nickel in the layer). At 0.5 μm nickel and 10 μm hot-dip galvanized layer, this results in a crack pattern at 870 ° C., 45 s holding time, 6 s transfer time and corresponding cooling in the press, as shown in FIG Fig. 15 can be seen in the two left representations.

In contrast, with a 1 micron thick nickel layer and otherwise the same conditions a considerably finer crack pattern ( Fig. 15 , the two right representations) achieved.

The invention thus makes it possible to influence the corrosion protection layer based on zinc via an additional nickel layer, such that this layer evidently forms faster solid phases during cooling, which then do not react with the austenite of the steel substrate during forming.

In particular, in the zinc-rich bright phases of the coating, more nickel dissolves than in the dark iron-rich phases, which by themselves have a higher melting point.

Compared with a zinc-nickel layer deposited uniformly via electrolysis, the invention has the advantage that it allows a mixed application in electrolytic and hot-dip coating processes. Furthermore, the nickel layer can be easily applied to conventional, already hot-dip galvanized sheets, for which purpose both electrolytic coatings can be used as well as other coating methods, for. B. roll application, i. a roll coating method, such as a coil coating method, in which a nickel-containing layer having a thickness of 250 nm to 700 nm is applied.

Claims (16)

1. A method for producing hardened steel sheet components, wherein at least two metal layers are deposited successively on a strip of a quench-hardenable steel alloy as anti-corrosion coating on the steel substrate, the one metal layer being a layer made of zinc or based on zinc and the other layer being a layer made of a metal which forms intermetallically less noble phases with Zn or Fe and has a higher oxidation potential than Zn, namely Ni, Cu, Co, Mn or Mo, or is a layer based on these metals, and wherein steels of the general alloy composition, each in weight percent: Carbon (C) 0.08-0.6 Manganese (Mn) 0.8-3.0 Aluminum (Al) 0.01-0.07 Silicon (Si) 0.01-0.5 Chromium (Cr) 0.02-0.6 Titanium (Ti) 0.01-0.08 Nitrogen (N) < 0.02 Boron (B) 0.002-0.02 Phosphorus (P) < 0.01 Sulphur (S) < 0.01 Molybdenum (Mo) < 1 the balance being iron and smelting impurities
   are used, wherein blanks are punched out of the strip provided with the anti-corrosion coating and the blanks are either

   - heated to a temperature > Ac₃ and optionally maintained there and then formed in a press hardening tool and quench-hardened to produce the steel sheet component, or

   - the blanks are formed into a steel sheet component in the cold state and the steel sheet component is subsequently heated to a temperature > Ac₃ and quench-hardened in a die hardening tool, with the layer sequence between nickel, copper and manganese on the one hand and zinc or based on zinc on the other hand being applied repeatedly.
2. The method according to claim 1, characterized in that a material with the following alloy composition, the indication in each case in weight percent, is used as the steel material: Carbon (C) 0.08-0.34 Manganese (Mn) 1.00-3.00 Aluminum (Al) 0.03-0.06 Silicon (Si) 0.01-0.20 Chromium (Cr) 0.02-0.3 Titanium (Ti) 0.03-0.04 Nitrogen (N) < 0.007 Boron (B) 0.002-0.006 Phosphorus (P) < 0.01 Sulphur (S) < 0.01 Molybdenum (Mo) < 1 the balance being iron and smelting impurities.
3. The method according to claim 1 or 2, characterized in that the layer made of zinc or based on zinc is applied electrolytically or by a hot-dip process.
4. The method according to claims 1 to 3, characterized in that the nickel, copper or manganese layer is applied electrolytically or via a roller application process, for example a coil coating process.
5. The method according to any of the preceding claims, characterized in that the nickel, copper or manganese layer is applied in a thickness of 0.5 µm to 2 µm with electrolytic deposition or in a thickness of 250 nm to 700 nm with roller application, in particular the coil coating process.
6. The method according to any of the preceding claims, characterized in that the zinc layer or the layer based on zinc is deposited with a thickness of 6 µm to 30 µm.
7. The method according to any of the preceding claims, characterized in that the layer of nickel, copper or manganese is first deposited on the steel substrate and then the zinc layer or the coating based on zinc is deposited.
8. The method according to any of the preceding claims, characterized in that the coating made of zinc or based on zinc is applied to the layer of nickel, copper or manganese electrolytically or by hot-dip galvanizing.
9. The method according to any of the preceding claims, characterized in that the layer made of zinc or based on zinc is first applied electrolytically or by the hot-dip coating process to the steel substrate and then the nickel layer is applied electrolytically to the zinc layer or is applied to the zinc layer by a roller application process, e.g. coil coating process.
10. An anti-corrosion material for use in a method according to any of claims 1 to 10, the anti-corrosion layer having at least two layers, wherein a layer of nickel, copper or manganese is present and a layer made of zinc or based on zinc is present thereon or thereunder, a multiple sequence of the layers of nickel, copper and manganese on the one hand and zinc or layers based on zinc on the other hand being present on the steel substrate.
11. The anti-corrosion material according to claim 10, characterized in that the layer made of zinc or based on zinc is deposited electrolytically or by a hot-dip process.
12. The anti-corrosion material according to claim 10 or 11, characterized in that the nickel, copper or manganese layer is applied electrolytically or by a roller application process, for example the coil coating process.
13. The anti-corrosion material according to any of claims 10 to 12, characterized in that the nickel, copper or manganese layer has a thickness of 0.5 µm to 2 µm in the case of electrolytic deposition or a thickness of 250 nm to 700 nm in the case of a roller application process, in particular with the coil coating process.
14. The anti-corrosion material according to any of claims 10 to 13, characterized in that the zinc layer or the layer based on zinc has a thickness of 6 µm to 30 µm.
15. The anti-corrosion material according to any of claims 10 to 14, characterized in that the layer of nickel, copper or manganese is arranged on the steel substrate and thereon the zinc layer or the coating based on zinc.
16. The anti-corrosion material according to any of claims 10 to 15, characterized in that a zinc layer or a coating based on zinc, which has been deposited electrolytically or by hot-dip coating, is arranged as being applied to the steel substrate, and the nickel layer is arranged on the zinc layer, the nickel layer being applied electrolytically or by a roller application process, in particular the coil coating process.

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