Steel sheet with temporary double-layered corrosion protection

Abstract

The invention relates to a hot-dip coated and skin-passed steel sheet which has a steel substrate and a metal skin-passed coating which is arranged on the steel substrate and which contains an aluminum content of 0.5 to 8.0 wt.% and a magnesium content of 0.5 to 8.0 wt.% in addition to zinc and unavoidable impurities. The invention is characterized in that the metal coating has a temporary double-layered corrosion protection. The invention additionally relates to a method for producing such a steel sheet and to the use thereof in order to produce a stainless phosphatized steel sheet.

Description

[0001] Steel sheet with double-layer temporary corrosion protection

[0002] The invention relates to a hot-dip coated and temper-passed steel sheet comprising a steel substrate and a metallic, temper-passed coating applied to the steel substrate, containing, in addition to zinc and unavoidable impurities, aluminum with a content of 0.5 to 8.0 wt.% and magnesium with a content of 0.5 to 8.0 wt.%. The metallic coating provides a double-layer temporary corrosion protection. Furthermore, the invention relates to a method for producing such a steel sheet and its use for producing a spot-free phosphated steel sheet.

[0003] Hot-dip coated sheets, which have a metallic coating which, in addition to zinc and unavoidable impurities, also contains aluminum and magnesium in the coating, are also referred to as ZM sheets (the coating is referred to as ZM for short) and have been used for years as sheets with increased corrosion protection (compared to sheets without such a coating).

[0004] Such sheets are used in particular for the manufacture of automobiles or white goods (such as electric stoves, refrigerators, freezers, washing machines, dryers, and dishwashers). This requires a coating that is free of optical defects such as spots, light-dark coloring, orange peel, etc.

[0005] During hot-dip plating with zinc melts containing Al and Mg, in addition to Zn oxides, Al and Mg oxides form on the surface of the coating during the cooling process after the hot-dip bath. A predominantly magnesium-rich oxide layer is observed on the surface. Due to the higher dipole moment corresponding to the electronegativity difference of Mg oxide (AEN=2.27), the oxide layer has different chemical properties than established pure zinc or zinc-aluminum coatings. In addition to oxides, the corresponding hydroxides are also present, especially upon contact with water.

[0006] Since the further steps after hot-dip coating and skin passing are usually carried out at different times and / or locations, these sheets are provided with temporary corrosion protection and, if necessary, a functional coating beforehand (i.e. underneath the temporary corrosion protection). For phosphating and / or painting, the layers arranged on the metallic coating have to be removed again. Removal is usually carried out in one or more cleaning steps. It can happen that the cleaning is not complete, i.e. that residues of the coating and / or temporary corrosion protection remain on at least parts of the skin passing steel sheet. Such residues, but also dirt residues such as chips, dust or other particles as well as oil, which originate, for example, from the equipment used both before and after cleaning, tend to accumulate in the skin passing valleys.Due to the high dipole moment of magnesium oxide, polarizable or dipolar compounds or polar ends of amphiphilic molecules applied to it are also more strongly bound to the surface. This impairs the surface's cleaning properties. This has a negative impact on pre- and post-treatment processes (such as phosphating and painting), which require a surface free of oil and dirt. In particular, the conditions described lead to uneven phosphating. This means that, on the one hand, the phosphating is unevenly thick and, on the other hand, can also exhibit optical defects. The result is a phosphate layer that consists in certain areas of zinc phosphate crystals of varying sizes, which appear uneven when viewed macroscopically, i.e., exhibit a light-dark color.Dark spots typically consist of larger phosphate crystals, while lighter spots consist of smaller phosphate crystals. Both uneven phosphate coating thickness and optical defects lead to uneven coating, i.e., uneven e-coating, and thus reduced corrosion resistance.

[0007] The object of the present invention is to provide a temper-passed ZM sheet which has temporary corrosion protection which, on the one hand, ensures good corrosion protection until further processing of the sheet and, on the other hand, enables further processing without any problems. This means that the corrosion protection must no longer exhibit the disadvantages described above during the subsequent process steps up to painting and ultimately completion of the products, nor must it cause any further obstacles. In particular, the aim is to achieve the most uniform and homogeneous deposition of a thinner phosphate layer and to avoid spots in the phosphate layer. This first requires the application of complete, uniform and homogeneous temporary corrosion protection; in particular, the strings of pearls / worm-shaped structure known to those skilled in the art in the CuSO4 test must no longer be recognizable after coating.Furthermore, the cement-based metal sheet coated with temporary corrosion protection must not require any new process steps or equipment. The individual components of the temporary corrosion protection must therefore be precisely coordinated with one another. Furthermore, other aspects such as environmental protection, sustainability, and especially health must be taken into account.

[0008] The problem is solved with the features of claim 1.

[0009] The present invention relates to a hot-dip coated and tempered steel sheet comprising a steel substrate and a metallic, tempered coating arranged on one or both sides of the steel substrate, containing, in addition to zinc and unavoidable impurities, aluminum with a content of 0.5 to 8.0 wt.% and magnesium with a content of 0.5 to 8.0 wt.%, characterized in that the metallic coating has a double-layer temporary corrosion protection.

[0010] In this context, the term "metallic skin-pass coating" is intended to clarify that the coated substrate is skin-passed. This means that the skin-pass rolls are brought into contact with the metallic coating. The coating is applied to one or both sides of the steel substrate, preferably both sides. If the coating is applied to only one side of the steel substrate, the skin-pass roll makes direct contact with the steel substrate on that side.

[0011] The zinc coating, applied using the hot-dip coating process, comprises a zinc alloy containing, in addition to zinc (balance) and unavoidable impurities, additional elements such as aluminum with a content between 0.1 and 8.0 wt.% and magnesium with a content between 0.1 and 8.0 wt.%. Elements from the group Si, Sb, Bi, Zr, Ni, Cr, Pb, Ti, Ca, Mn, Sn, La, Ce, Fe, and Cr may be present as impurities in the molten bath, either individually or cumulatively, in amounts of up to 0.5 wt.%, in particular up to 0.4 wt.%, preferably up to 0.3 wt.%. Elements from the group Si, Sb, Bi, Zr, Ni, Cr, Pb, Ti, Ca, Mn, Sn, La, Ce, Fe, and Cr may be present as impurities in the coating, either individually or cumulatively, in amounts of up to 0.5 wt.%, in particular up to 0.4 wt.%, preferably up to 0.3 wt.%. Alternatively, the concentration of Fe may be higher due to the diffusion described above. The remainder is zinc.Steel sheets, separated from steel strips or steel sheet components produced therefrom with a zinc-based corrosion protection coating, have very good cathodic corrosion protection and have been used in automotive engineering for years. If improved corrosion protection is required, the coating has a magnesium content of at least 0.8 wt.%, in particular at least 1.0 wt.%, preferably at least 1.1 wt.% and an aluminum content of at least 0.8 wt.%, in particular at least 1.0 wt.%. The coating has a magnesium content of at most 8.0 wt.%, preferably at most 7.0 wt.%, particularly preferably at most 5.0 wt.%, in particular at most 4.0 wt.% and an aluminum content of at most 8.0 wt.%, preferably at most 7.0 wt.%, particularly preferably at most 5.0 wt.%, in particular at most 4.0 wt.%.Alternatively, these concentrations are determined using wet-chemical methods in accordance with or based on DIN EN ISO 10111:2019 and / or DIN EN ISO 11885:2009.

[0012] In particular, to set a predetermined thickness of the cement mortar coating, which in the solid state can be between 1 pm and 60 pm per side, the melt applied to the steel strip while still in the liquid state is scraped off. After leaving the molten bath, the steel strip coated with the liquid melt is passed through a scraping device which has means, for example nozzles, in particular slot nozzles, which act on both sides of the steel strip with a gaseous scraping medium to scrape off the liquid melt. This makes it possible to achieve an asymmetric coating, i.e. different layers on both sides. The thickness of the cement mortar coating can be set, in particular, independently of one another, for each side, between at least 4 pm, preferably at least 5 pm and a maximum of 58 pm, preferably between 5 and a maximum of 55 pm.In a particular embodiment, the thickness of the coating is at least 1 μm, preferably at least 2 μm, particularly preferably at least 3 μm, in particular at least 5 μm and a maximum of 25 μm, preferably a maximum of 20 μm, and particularly preferably a maximum of 15 μm, in particular a maximum of 10 μm, independently of one another, per side. Alternatively, the coating thickness is determined gravimetrically by detachment according to DIN EN ISO 10111 and conversion from mass to thickness based on density, or metallographically in a micrograph.

[0013] Below the minimum limits, adequate cathodic corrosion protection cannot be guaranteed, and above the maximum limit, joining problems may arise when connecting the steel sheet according to the invention or a component made from it to another component. Alternatively, the cement mortar coating is applied with a coating weight of 1 to 650 g / m2, i.e., 0.5 to 320 g / m2 per side, particularly preferably 10 to 500 g / m2, i.e., 5 to 250 g / m2 per side. In a further alternative, an asymmetric coating is also possible.

[0014] One version features a steel sheet with a Cr-free, double-layer temporary corrosion protection. Cr-free means that Cr is present in a maximum concentration of 1000 ppm, preferably 500 ppm, and especially 100 ppm [according to VdL Guideline 01 "VdL Guideline for Declaration of Coating Materials" (Guideline for the Declaration of Lacquers, Paints, Glazes, Renders, Leveling Compounds, Primers, and Related Products, as of May 2019 (7th revision) of the German Association of the Paint and Printing Ink Industry).

[0015] In a further embodiment, the steel sheet is characterized in that the double-layer temporary corrosion protection has an intermediate layer as the first layer and, arranged thereon, a second layer containing or consisting of a corrosion protection oil.

[0016] The intermediate layer is bonded to the metallic coating by chemisorption, i.e., by chemical bonding. In the broadest sense, chemical bonding can be an ionic bond, a covalent bond, a coordinate bond, or a weak bond via electrostatic attraction or van der Waals forces.

[0017] In one alternative, this intermediate layer is created by the chemical reaction of an aqueous treatment dispersion with the metallic substrate, which chemically alters the adsorbate, i.e., the aqueous treatment dispersion, and / or the adsorbent, i.e., the metallic cement coating. In another alternative, components of the aqueous dispersion are covalently bonded to components of the cement coating.

[0018] In one embodiment, the intermediate layer contains or consists of polymers, such as organic polymers based on acrylic acid or derivatives thereof. In an alternative, the intermediate layer contains or consists of:

[0019] 1 / 4 to 3 parts by weight of a polymer selected from the group consisting of maleic acid / polyacrylic acid copolymer, modified polyacrylic acid or polyacrylic acid,

[0020] 1 part by weight of a phosphate component and optionally 1 / 10 to 5 / 10 parts by weight of a metal-containing component selected from the group Zn, Ca, Mg and / or Al.

[0021] In a further alternative, this intermediate layer contains or consists of organic silicon compounds, preferably one or more compounds selected from the group comprising or consisting of: silanes, silanols, siloxanes, alkoxysilanes, derivatives of silanes, siloxanes and / or alkoxysilanes, and polymers and derivatives thereof. Preferred derivatives are one or more compounds selected from the group comprising or consisting of: silanes, siloxanes, alkoxysilanes with functional groups such as -OR with R as H or alkyl, preferably C1 to C7, vinyl, phenyl, benzyl; -NR2 with R as H or alkyl, preferably C1 to C7, vinyl, phenyl, benzyl; condensation products with elimination of water of hydrolyzed alkoxysilanes, i.e. silanols orAlkoxysilanes with hydroxyl groups; at least one silane, silanol and / or siloxane with at least one alkoxy group, with at least one amido group, with at least one amino group, with at least one urea group, as well as condensation products, copolymers and polymers of at least two of the above-mentioned compounds.

[0022] Alternatively or additionally, the above-mentioned silanes, silanols, siloxanes, alkoxysilanes and derivatives thereof are selected from the group comprising or consisting of: bis-tri(m)ethoxysilylalkane, for example bis-triethoxysilylethanes, methyltrimethoxysilane, tetraethoxysilane, aminopropyltriethoxysilane, 4-amino-dialkylalkyldialkoxysilane, 2-aminoethyl-3-amino-propyltrimethoxysilane, 2-aminoethyl-3-amino-propyltriethoxysilane, gamma-aminoalkyltrialkoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-alkylaminoisoalkyltrialkoxysilane, poly(aminoalkyl)alkyldialkoxysilane, aminoalkylaminoalkyltrialkoxysilane, N-(gamma-trialkoxysilylalkyl)dialkylenetriamine;Aminoalkylaminoalkyldialkoxysilane, aminoalkyltrialkoxysilane, bis-aminosilane, bis-diaminosilane, bis-(trialkoxysilylalkyl)amine such as bis(trimethoxysilylpropyl)amine and / or bis(triethoxysilylpropyl)amine, bis-(trialkoxysilyl)ethane, N-(aminoalkyl)aminoalkyldialkoxysilane, vinyltriacetoxysilane, vinyltrimethoxysilane, ureidopropyl-itrimethoxysilane, gamma-uridoalkyltrialkoxysilane, bis-trimethoxysilylpropylurea;3-[2-(2-Aminoalkylamino)alkylamino]alkyltrialkoxysilane, 3-(2-Aminoethylamino)propyldimethoxymethylsilane, N-(3-(Trialkoxysilyl)alkyl)alkylenediamine, N-beta-(aminoalkyl)-gamma-aminoalkyltrialkoxysilane, 4-Amino-dialkylalkyltrialkoxysilane, 3-(trimethoxysilyl)propyl methacrylate, gamma-(trialkoxysilylalkyl)dialkylentriamine, 3-glycidoxypropyltrimethoxysilane, 3-triethoxysilyl-N-(l,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N,N-Bis[3-(trimethoxysilyl)propyl]ethylenediamine and / or N-2-aminoalkyl-3-aminoproplyltrialkoxysilane with alkyl are preferably selected from the group comprising or consisting of: methyl, ethyl and / or propyl, such as N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2(aminoethyl)-3-aminopropyltriethoxysilane, combinations of at least two of the above-mentioned compounds and / or polymers thereof;

[0023] For the purposes of the invention, siloxane compounds of the formula: R3Si—[O—SiR2]n—O—SiR3, where R is H or alkyl, preferably C1 to C7, and n=0 to 20, are described. Polymers thereof with R=alkyl are referred to as silicones. Alkoxysilanes have the general formula (RO)4-Si, where R is alkyl, preferably C1 to C7.

[0024] Alternatively, the aqueous dispersion may additionally contain inorganic salts, such as salts with cations selected from the group containing or consisting of Zr 4+ , Zn 2+ , Ca 2+ , Mg 2+ , and Al 3+ and anions selected from the group containing or consisting of CF, NO3-, SO4 2 ' and PO4 3 '.

[0025] The intermediate layer is preferably applied as an aqueous dispersion. In this dispersion, at least some of the organic silicon compounds are hydrolyzed or alkoxylated. At least some of the organic silicon compounds react to form polymers, such as polysiloxanes. In the form of the hydrolyzed or alkoxylated organic silicon compounds and / or polysiloxanes, they react with the hydroxyl groups of the metal, releasing water or alcohol, and forming a strong bond with the substrate. Condensation occurs simultaneously and subsequently during drying between the organic silicon compounds, now covalently bonded to the surface, resulting in the formation of a network-like structure that creates a homogeneous intermediate layer evenly distributed over the surface of the coating.

[0026] For the purposes of the invention, the term "aqueous dispersion" encompasses a composition in which particles and / or droplets are dispersed in water, as well as colloidally dispersed and / or molecularly dispersed compositions. Alternatively, the aqueous dispersion contains organic solvents, in particular alcohols, preferably methanol or ethanol, lower ketones, or ethers with up to 7, preferably 5, carbon atoms.

[0027] In one embodiment, the intermediate layer has a Si content of at least 0.5 mg / m2, preferably at least 1.0 mg / m2, particularly preferably at least 1.5 mg / m2, in particular at least 2.0 mg / m2 and a maximum of 20.0 mg / m2 or 15.0 mg / m2, preferably a maximum of 10.0 mg / m2 or 8.0 mg / m2, particularly preferably a maximum of 7.0 or 8.0 mg / m2, in particular a maximum of 3.0 or 2.5 mg / m2. A quantitative determination of the applied layer weight is carried out, for example, by X-ray fluorescence analysis (XRF) or GDOES (Glow Discharge Optical Emission Spectroscopy). The expression that the intermediate layer has a layer weight with a deposit of a certain element in a specified mass per unit area means that the intermediate layer contains the corresponding element (regardless of the form, i.e. elemental, atomic, ionic or oxidic) in the specified mass per unit area.In the event that the Si concentration of the steel sheet, i.e., the steel substrate, interferes with the Si determination in the intermediate layer, thus potentially leading to erroneous results, the expert performs reference or differential measurements at locations on the steel sheet where no intermediate layer is present or where the intermediate layer has been removed for measurement purposes. This information relates to the occurrence of the element Si (silicon), regardless of its form. It therefore does not matter whether this element is present as neutral atoms, as ions, or in compounds such as organic compounds, such as alcohols, esters, polymers or complexes, oxides, salts, hydroxides, or similar.

[0028] The second layer of the double-layer temporary corrosion protection contains or consists of a corrosion protection oil, preferably a mineral oil, particularly preferably containing 15 - 60 wt.%, preferably 20 - 50 wt.% of a naphthenic base oil with 1.0 - 10 wt.%, preferably 1.2 - 8 wt.% Na and / or Ca sulfonates from benzenesulfonic acid with mono-C10-16 alkyl derivatives and / or mono-C16-24 alkyl derivatives as organic radicals.

[0029] The intermediate layer not only ensures temporary corrosion protection, but also reduces or prevents, in comparison to a layer structure without the intermediate layer used according to the invention, the adsorption of polarizable or polar molecules to the metallic coating of the corrosion protection.

[0030] An embodiment further relates to the steel sheet according to the invention, characterized in that the intermediate layer contains rheological additives. Since the intermediate layer is applied as an aqueous solution or aqueous dispersion, the rheology, in particular the viscosity of the solution or dispersion, is crucial. The aqueous dispersion, in which the compounds of the subsequent intermediate layer and the rheological additives are located, is a system in which the components are precisely matched to one another and, on the other hand, additionally matched to the substrate. During the matching process, particular consideration is given to the polarity of the composition and the substrate.

[0031] Alternatively, substances from additive classes such as phyllosilicates, associative thickeners, synthetic layered silicates, liquid rheology additives, or enhancers for fumed silica are used. Rheological additives are preferably selected from the group containing or consisting of: acrylate thickeners, carboxymethylcellulose, methylcellulose, polyurea thickeners, polyurethane thickeners, layered silicates, fumed silica, gelatin, alginates, mono- and / or polysaccharides, including xanthan gum, guar ether, and xanthan gum.

[0032] Particularly preferred is the combination of the above-mentioned organic silicon compounds with rheological additives containing or based on polyurethane or polysaccharides or heteropolysaccharides, preferably modified polysaccharides or heteropolysaccharides, such as guar and / or xanthan gum, in particular slow-swelling guar ether or xanthan gum molecules or modified xanthan gum molecules.

[0033] The combination of the composition for the subsequent intermediate layer with the rheology additives ensures complete wetting of the substrate surface. This results in a uniform, homogeneous dry intermediate layer. Homogeneity refers to the property of the layer exhibiting the same macroscopic properties at all points. Furthermore, the rheology additives can reduce the thickness of the intermediate layer compared to the absence of rheology additives.

[0034] In one embodiment, the intermediate layer contains activation particles as an alternative or in addition to the rheological additives. The activation particles are preferably activation particles for subsequent phosphating of the steel sheets.

[0035] Alternatively, compounds selected from the group containing or consisting of: colloidal titanium phosphate, surface conditioning agents based on phosphate particles, in particular based on zinc phosphates and metal oxides or salts as phosphate and titanium sources, are used as activation particles. Preference is given to water-dispersible compounds, for example, oxalates of silver or copper compounds, disodium phosphate in combination with titanium compounds, in particular with water-soluble titanium compounds, for example, titanium phosphate or sodium titanyl phosphates, zinc phosphates, and mixtures of zinc phosphates and metal oxides, e.g., zinc or iron oxides, and mixtures thereof.The activation particles are preferably selected from the group containing or consisting of: titanium dioxide, titanium dioxide hydrate, dipotassium hexafluorotitanate, hexafluorotitanic acid, titanium sulfate, titanium disulfate, titanyl sulfate, titanium oxide sulfate, titanyl chloride, titanium potassium fluoride, titanium tetrachloride, titanium tetrafluoride, titanium trichloride, titanium hydroxide, titanium nitrite, titanium nitrate, potassium titanium oxide oxalate, and titanium carbide. Titanium salts are particularly good crystal nuclei for the crystallization of metal phosphates such as zinc phosphate.Alternatively or additionally, the aqueous dispersion may contain activation particles, at least one compound selected from the group containing or consisting of: oxalic acid, Zn3(PO4)2, Zn2Fe(PO4)2, Zn2Ni(PO4)2, Zn2Mn(PO4)2, Zn2Ca(PO4)2, Mn2Fe(PO4)2, nickel phosphate, manganese phosphate, calcium phosphate, iron phosphate, aluminum phosphate, cobalt(I) phosphate, cobalt(III) phosphate, copper, copper sulfate, copper nitrate, copper chloride, copper carbonate, copper oxide, silver, cobalt, nickel, Jernstedt salt, lead acetate, tin chloride, tin tetrachloride, arsenic oxide, zirconium chloride, zirconium sulfate, zirconium, iron, lithium, zinc phosphate, iron phosphate, zinc oxide and iron oxide.

[0036] Particularly preferably, in combination with the intermediate layer and optionally the rheology additives, at least one compound selected from the group containing or consisting of spherical zinc oxide nanoparticles and trizinc bis(orthophosphate) is used.

[0037] The aqueous dispersion containing the compounds of the subsequent intermediate layer, including the rheological additives and, if applicable, activation particles and optionally other additives or components, is a composition in which all components are precisely matched to one another and also to the substrate. Attention must be paid to the stability of the aqueous dispersion, for example, the particle density, the separation velocity distribution, and the particle size distribution. These and other criteria and methods for determining stability can be determined according to ISO 13318, ISO / TR 13097:2013; and / or ISO / TR 18811:2018. In particular, the aqueous dispersion exhibits no particle sedimentation (at application temperature) for at least 60 minutes, preferably 120 minutes, more preferably 180 minutes, and in particular 240 minutes or more without mechanical mixing or stirring.The adaptation to the substrate can be verified, for example, using a CuSO4 test. The present invention further relates to the use of the above-mentioned organic silicon compounds as corrosion protection, in particular as a corrosion protection layer. A further subject matter is the use of the above-mentioned organic silicon compounds in combination with the above-mentioned rheology additives and, alternatively or additively, in combination with the above-mentioned activation particles as corrosion protection, in particular as a corrosion protection layer. The rheology additives and / or the activation particles are embedded in the corrosion protection layer made of organic silicon compounds. This is therefore a first corrosion protection layer made of organic silicon compounds with embedded rheology additives and / or activation particles.

[0038] The intermediate layer described above forms a complete, uniform, and homogeneous layer. This can be verified by the so-called CuSO4 test. For this purpose, the steel sheet is dried after application of the aqueous dispersion, and rinsed if necessary before drying. The oil- or grease-free surface is immersed in a 5 wt% CuSO4 solution for approximately 10 seconds. The surface is then rinsed in demineralized water by gently swirling.

[0039] When immersed in the CuSO4 solution, bare metal areas react with the free copper ions, and metallic copper is deposited in the form of a black or metallic precipitate. In areas with an inerting post-treatment (passivation, sealing, or similar), less or no copper is deposited, and the precipitate is less dark. In the case of inhomogeneously applied layers, this is clearly visible due to the light-dark contrast. The pearl strings / worm-shaped structure known to those skilled in the art forms, i.e. a series of light or dark dots that can have a width of 0.2 to 1.0 mm or more and a length of several centimeters, possibly even a length across the entire sheet width. The sheets coated with the intermediate layer according to the invention do not exhibit any pearl strings or worm-shaped structures in this CuSO4 test.A complete, uniform and homogeneous intermediate layer is defined in the sense of the invention, i.e. a layer which, after deoiling or degreasing in a CuSO4 test as described above, does not exhibit any strings of pearls or worm-shaped structures.

[0040] The steel sheet according to the invention may further comprise at least one additional functional coating, such as an adhesion-promoting layer, a forming aid, a passivation layer, or a combination thereof. Alternatively, the intermediate layer or the aqueous dispersion applied thereto does not comprise or contain any epoxy-based adhesive systems.

[0041] According to the invention, the steel substrate to be used is a hot-rolled or cold-rolled strip. These can be obtained by processes known to those skilled in the art. The steel substrate can be used in the form of steel strips, so-called coils, or as so-called blanks, which are preferably obtained by cutting pieces from a hot-rolled or cold-rolled strip using suitable processes.

[0042] In a further embodiment, a steel sheet is used, characterized in that the steel substrate comprises an alloy containing or consisting of the following elements in wt.%:

[0043] - C: 0.0003 to 0.250%,

[0044] - Si: 0.0005 to 0.70%,

[0045] - Mn: 0.0005 to 2.0%,

[0046] - P: up to 0.15%,

[0047] - S: up to 0.050%,

[0048] - N: up to 0.10%,

[0049] - AI: 0.0050 to 1.50%,

[0050] - optionally one or more of the following elements:

[0051] - Nb: up to 0.20%,

[0052] - Ti: 0.20%,

[0053] - V: 0.0050 to 0.10%,

[0054] - B: up to 0.030% and / or

[0055] - Cu: up to 0.80% and / or

[0056] - Cr: up to 0.80% and / or

[0057] - Ni: up to 0.20% and / or

[0058] - Mon: up to 0, 150% and / or

[0059] - Sn: up to 0.10%,

[0060] - The remainder is iron and unavoidable impurities. Alternatively, the substrate is a steel sheet made of an interstitial-free alloy according to DIN EN 10346. The IF alloy of the steel substrate contains or consists of the following elements in wt.%:

[0061] - C: 0.0003 to 0.015%, in particular 0.0005 to 0.010%, preferably 0.001 to 0.005%,

[0062] - Si: 0.0005 to 0.50%, in particular 0.0010 to 0.40%, preferably 0.0010 to 0.30%,

[0063] - Mn: 0.0005 to 1.60%, in particular 0.010 to 1.55%, preferably 0.010 to 1.50%,

[0064] - P: up to 0.10%, in particular up to 0.080%, preferably 0.0002 to 0.060%,

[0065] - S: up to 0.050%, in particular up to 0.040%, preferably 0.0003 to 0.030%,

[0066] - N: up to 0.10%, in particular up to 0.080%, preferably 0.0001 to 0.070%,

[0067] - AI: 0.0010 to 1.0%, in particular 0.0010 to 0.90%, preferably 0.0010 to 0.80%,

[0068] - one or both of the following elements:

[0069] - Nb: 0.0001 to 0.20%, in particular 0.0002 to 0.10%, preferably 0.0003 to 0.050%,

[0070] - Ti: 0.0005 to 0.20%, in particular 0.010 to 0.150%, preferably 0.010 to 0.120%,

[0071] - optionally one or more of the following elements:

[0072] - B: up to 0.0050% and / or Cu up to 0.20% and / or Cr up to 0.20% and / or Ni up to 0.20% and / or Mo up to 0.150% and / or Sn up to 0.10%,

[0073] - Residual iron and unavoidable impurities.

[0074] An IF steel has no interstitial alloying elements, meaning that no iron atoms in the metal lattice are blocked by carbon or nitrogen atoms. This results in a very soft steel with excellent formability. It is primarily used for complex deep-drawn parts in automotive engineering. Steels of this type are available under the standard designations DX52D, DX53D, DX54D, DX55D, DX56D, DX57D, HX160YD, HX180YD, HX220YD, and HX260YD. These are cold-rolled steels.

[0075] Alternatively, the substrate is a steel sheet made of a bake-hardening alloy according to DIN EN 10346. The bake-hardening alloy of the steel substrate contains or consists of the following elements in wt.%:

[0076] - C: 0.0004 to 0.080%, in particular 0.0010 to 0.060%, preferably 0.0010 to 0.040%, - Si: 0.0005 to 0.50%, in particular 0.0010 to 0.40%, preferably 0.010 to 0.20%,

[0077] - Mn: 0.0005 to 1.50%, in particular 0.0010 to 1.40%, preferably 0.0020 to 1.20%,

[0078] - P: up to 0.150%, in particular up to 0.10%, preferably 0.0010 to 0.050%,

[0079] - S: up to 0.050%, in particular up to 0.040%, preferably 0.0005 to 0.030%,

[0080] - N: up to 0.050%, in particular up to 0.030%, preferably 0.0002 to 0.010%,

[0081] - AI: 0.0050 to 1.0%, in particular 0.010 to 0.50%, preferably 0.010 to 0.150%,

[0082] - optionally one or more of the following elements:

[0083] - Nb: up to 0.040% and / or Ti up to 0.030% and / or B up to 0.0030% and / or Cu up to 0.20% and / or Cr up to 0.20% and / or Ni up to 0.20% and / or Mo up to 0.150% and / or Sn up to 0.10%,

[0084] - Residual iron and unavoidable impurities.

[0085] BH steels are characterized by a significant increase in yield strength during paint baking (typically at 170 °C for 20 minutes) combined with excellent formability. Furthermore, these steels possess very good dent resistance, which is why they are preferred for outer skin applications. Steels of this type are available under the standard designations HX180BD, HX220BD, HX260BD, and HX300BD. These are cold-rolled steels.

[0086] Alternatively, the substrate is a steel sheet made of a multiphase alloy according to DIN EN 10346. The multiphase alloy of the steel substrate contains or consists of the following elements in wt.%:

[0087] - C: 0.050 to 0.250%, in particular 0.060 to 0.250%, preferably 0.070 to 0.250%,

[0088] - Si: 0.020 to 0.50%, in particular 0.020 to 0.40%, preferably 0.020 to 0.30%,

[0089] - Mn: 1.30 to 2.0%, in particular 1.40 to 1.90%, preferably 1.50 to 1.80%,

[0090] - P: up to 0.10%, in particular up to 0.080%, preferably up to 0.060%,

[0091] - S: up to 0.050%, in particular up to 0.040%, preferably up to 0.030%,

[0092] - N: up to 0.10%, in particular up to 0.050%, preferably up to 0.030%,

[0093] - AI: 0.010 to 0.150%, in particular 0.010 to 0.10%, preferably 0.010 to 0.090%,

[0094] - optionally one or more of the following elements:

[0095] - Cu: up to 0.80% and / or Cr up to 0.70% and / or Nb up to 0.10% and / or Ti up to 0.20%;

[0096] - The remainder consists of iron and unavoidable impurities. Examples of steels of this type are available under the standard designation HCT490X, HCT590X, or HCT780X. These are cold-rolled steels.

[0097] Alternatively, the substrate is a steel sheet made of a micro-alloyed alloy according to DIN EN 10268. The alloy of the steel substrate contains or consists of the following elements in wt.%:

[0098] - C: 0.020 to 0.20%, in particular 0.020 to 0.150%, preferably 0.020 to 0.140%,

[0099] - Si: 0.010 to 0.70%, in particular 0.010 to 0.60%, preferably 0.010 to 0.50%,

[0100] - Mn: 0.020 to 2.0%, in particular 0.020 to 1.90%, preferably 0.020 to 1.80%,

[0101] - P: up to 0.070%, in particular up to 0.060%, preferably up to 0.050%,

[0102] - S: up to 0.050%, in particular up to 0.040%, preferably up to 0.030%,

[0103] - N: up to 0.080%, in particular up to 0.060%, preferably up to 0.040%,

[0104] - AI: 0.010 to 1.0%, in particular 0.010 to 0.50%, preferably 0.010 to 0.10%,

[0105] - at least one of the following elements:

[0106] - Nb: 0.010 to 0.150%, in particular 0.010 to 0.120%, preferably 0.010 to 0.10% and / or

[0107] - Ti: 0.010 to 0.20%, in particular 0.010 to 0.180%, preferably 0.010 to 0.150% and / or

[0108] - V: 0.0050 to 0.10%, in particular 0.0060 to 0.10%, preferably 0.0090 to 0.10% and / or

[0109] - optionally one or more of the following elements:

[0110] - B: up to 0.0050% and / or Cu up to 0.40% and / or Cr up to 0.50%,

[0111] - Residual iron and unavoidable impurities.

[0112] A microalloyed steel exhibits a fine-grained microstructure, which gives it high fatigue strength, optimal weldability, and high yield strengths. It is primarily used for complex deep-drawn parts in automotive engineering. Examples of steels of this type are available under the standard designations HC260LA, HC300LA, HC340LA, HC380LA, HC420LA, HC460LA, HC500LA, and HC550LA. These are cold-rolled steels.

[0113] The present invention also relates to a method for producing a hot-dip coated and skin-passed steel sheet as described above, comprising the following steps: a) providing a steel sheet as a steel substrate, b) hot-dip coating the steel substrate on one or both sides with a metallic coating which, in addition to zinc and unavoidable impurities, contains additional elements such as aluminum with a content of 0.5 to 8.0 wt.% and magnesium with a content of 0.5 to 8.0 wt.% in the coating, c) skin-passing the hot-dip coated steel sheet from step b, d) applying a first layer as an intermediate layer to the steel sheet from step c, e) applying a second layer to the intermediate layer containing or consisting of corrosion protection oil.

[0114] In step a, a steel sheet as described above is used as the steel substrate.

[0115] Methods for hot-dip coating according to step b are known per se to those skilled in the art. Hot-dip coating may additionally comprise one or more of the following steps: cleaning the substrate before the hot-dip bath, heating the substrate, wiping the melt using nozzles after the hot-dip bath to achieve the desired coating thickness, cooling the coated substrate to cure the melt, optionally applying a temper passivating agent; optionally applying further functional coatings, such as an adhesion-promoting layer, a forming aid, a passivation layer, or a combination thereof.

[0116] The skin-passing process in step c is known per se to those skilled in the art and is described, for example, in the handbook "Umformen" (Forming), Günter Spur, ISBN: 978-3-446-43004-4, page 155. The surface of the steel sheet after skin-passing can have a stochastic surface structure. This is created using skin-passing rolls whose surfaces are textured using a so-called EDT process. Alternatively, the surface of the steel sheet after skin-passing can have a deterministic surface structure. This is created using skin-passing rolls whose surfaces are textured using a laser. A surface with a pseudo-stochastic surface structure after skin-passing would also be conceivable. These surface structures have a (quasi-)stochastic appearance, composed of stochastic elements with a recurring structure.If necessary, a cleaning step, preferably an alkaline cleaning step, optionally with detergents, is carried out before the application of the first corrosion protection layer. This step may be followed by a rinsing and, if necessary, a drying step. In step d, the first intermediate layer is applied to the skin-passed steel sheet in the form of an aqueous dispersion. Application is carried out by spraying, dipping, or coating, preferably using a roll coater or chem-coater, at an ambient temperature of 10–50 °C, preferably 20–40 °C.

[0117] The aqueous dispersion contains polymers or organic silicon compounds as described above, in a concentration based on Si as an element of at least 0.001 wt%, preferably of at least 0.01 wt%, particularly preferably of at least 0.04 wt% or 0.06 wt%, in particular of at least 0.08 wt% and of at most 5.0 wt% or 1.0 wt%, preferably of at most 0.5 wt% or 0.25 wt%, particularly preferably of at most 0.15 wt%, in particular of at most 0.12 wt%.

[0118] Alternatively, based on at least one organic silicon compound, the aqueous dispersion contains at least 0.0001 wt.%, preferably at least 0.001 wt.%, particularly preferably at least 0.01 wt.% or 0.025 wt.%, in particular at least 0.04 wt.% and at most 5.0 wt.% or 1.0 wt.%, preferably at most 0.5 wt.% or 0.1 wt.%, particularly preferably at most 0.075 wt.%, in particular at most 0.06 wt.% of at least one of the above-mentioned organic silicon compounds.

[0119] In one embodiment, the aqueous dispersion contains one or more of the rheology additives described above and, in another embodiment, alternatively or additively, activation particles as described above.

[0120] The rheology additives are present in a concentration of active ingredient of at least 0.01 wt%, preferably of at least 0.025 wt%, particularly preferably of at least 0.05 wt%, in particular of at least 0.075 wt% and of at most 5.0 wt% or 2.5 wt%, preferably of at most 1.0 wt%, particularly preferably of at most 0.75 or 0.5 wt%, in particular of at most 0.25 or 0.15 wt%.

[0121] The activation particles are present in the aqueous dispersion in a concentration of at least 0.01 wt.%, preferably at least 0.025 wt.%, particularly preferably at least 0.05 wt.%, in particular at least 0.075 wt.% and at most 5.0 wt.% or 2.5 wt.%, preferably at most 1.0 wt.%, particularly preferably at most 0.75 or 0.5 wt.%, in particular at most 0.25 or 0.15 wt.%. In one alternative, the aqueous dispersion is an alkaline aqueous dispersion with a pH of at least 8.0, preferably at least 9.0, particularly preferably at least 9.5, in particular at least 10.0 and at most 13.0, preferably at most 12.5, particularly preferably at most 12.0 or 11.0, in particular at most 10.5.

[0122] In a further alternative, the aqueous dispersion has a density at 20 °C of at least 0.90 g / cm3, preferably at least 0.95 g / cm3, particularly preferably at least 1.00 g / cm3 and at most 1.30 g / cm3, preferably at most 1.20 g / cm3, particularly preferably at most 1.10 g / cm3 and in particular at most 1.0 g / cm3.

[0123] In a further alternative, the aqueous dispersion has a dynamic viscosity at 20 °C in mPa*s of at least 0.6, preferably at least 0.75, particularly preferably at least 0.9, in particular at least 1.0 and at most 2.0, preferably at most 5.0, particularly preferably at most 10.0, in particular at most 15.0.

[0124] In one version, the aqueous dispersion is Cr-free. For the term Cr-free (chromium-free), see above.

[0125] A further embodiment relates to the process described above, wherein the steel sheet is rinsed after application of the aqueous dispersion and then dried, preferably without prior rinsing, in the so-called no rinse process.

[0126] If necessary, further functional coatings are applied, such as an adhesion-promoting layer, a forming aid, a passivation or a combination thereof.

[0127] Furthermore, the present invention relates to the use of a steel sheet according to the invention provided with the temporary corrosion protection described above for producing a spot-free phosphated steel sheet.

[0128] The present invention also further provides a process for producing a spot-free phosphated steel sheet comprising the following steps: f) providing a steel sheet according to the invention as described above or a steel sheet produced by the process described above, g) cleaning the steel sheet and h) phosphating the cleaned steel sheet.

[0129] For the purposes of the invention, spots are defined as apparently dark areas (on the surface). Preferably, a dark area is delimited by dark points which are characterized by the fact that they are darker than other, hence brighter points arranged in the immediate vicinity. In this sense, a point is not to be understood as a mathematical point, which has no extent, but rather, for example, as a pixel or group of pixels. Such a dark point only has a common border with brighter points in a partial area of ​​its circumference. In the remaining partial area of ​​its circumference, it has a common border with dark points which have essentially the same brightness as this delimiting dark point. An above-mentioned dark area thus essentially consists of the latter-mentioned dark points and the former-mentioned delimiting dark points.

[0130] For the purposes of the invention, a spot-free phosphating and / or a homogeneous and uniform phosphating and / or phosphate layer is a layer which, when visually inspected using a reflected light microscope, has at least one, preferably two, particularly preferably all of the following criteria:

[0131] - Crystal orientation optically determined with a magnification of 1000x: at least 20% of the phosphate crystals perpendicular to the substrate surface, preferably at least 40%, particularly preferably at least 60%, in particular at least 80%;

[0132] - crystal diameter of the phosphate crystals with a magnification of 1000x optically determined from 0.5 pm to 10 pm, preferably 1.0 pm to 5 pm;

[0133] - Hole size of the holes in the layer of phosphate crystals at 200x magnification on an area of ​​approximately 300 pm x 300 pm determined equal to the mean crystal diameter (see above), preferably smaller than the mean crystal diameter, particularly preferably no holes;

[0134] - Number of holes at 200x magnification on an area of ​​approximately 300 pm x 300 pm determined from 3 - 5 holes, preferably from 1 - 2 holes, most preferably no holes.

[0135] The provision of a steel sheet according to the invention described above or a steel sheet produced by the method described above in step f is followed immediately or optionally after further steps, such as decoiling, straightening, or bending and / or stretch-leveling, by cleaning the steel sheet, preferably with alkaline cleaners. Optionally, the cleaning also includes one or more rinsing steps. This step g removes the temporary double-layer corrosion protection coating described above prior to phosphating. The alkaline cleaners reliably remove the oil layer. Should the intermediate layer not be completely removed, the intermediate layer applied according to the invention, which may remain in part even after cleaning, nevertheless ensures spotless phosphating.On the one hand, the intermediate layer prevents non-removable deposits, especially in the skin pass valleys, and on the other hand, the activation particles present in an alternative act as crystallization nuclei for the phosphating.

[0136] In the manufacture of automobile bodies, for example, it is common for the steel sheets to be delivered unphosphated to the manufacturer of the automobile bodies, who then cuts the steel sheets from a coil, forms them into components, joins individual components together, and applies the resulting individual or joined components with the phosphate coating in a dipping or spraying process. These steps can be carried out individually or in combination within the meaning of the invention.

[0137] Preferably, step g of the process according to the invention is carried out by treating the steel sheet from step f with at least one cleaning agent. According to the invention, the cleaning agent can be acidic, neutral, or alkaline.

[0138] In a preferred embodiment, an alkaline cleaning agent is used. In one alternative, the alkaline cleaning agent is an alkaline aqueous dispersion with a pH of at least 8.0, preferably at least 9.0, more preferably at least 10.0, in particular 11.0 and at most 14.0, preferably at most 13.0, more preferably at most 12.0, in particular at most 11.5. The cleaning-active substances, for example surfactants, are preferably present in an amount that appears suitable to a person skilled in the art. According to the invention, further components of the cleaning agent are preferred, for example selected from the group consisting of sodium hydroxide or potassium hydroxide and mixtures thereof. Step g can furthermore be carried out using mechanical energy, for example by brushing the surfaces to be cleaned or by applying water and / or cleaning agent to the surface under high pressure.Step g of the process according to the invention is preferably carried out at a temperature of 20 to 80 °C. Alternatively, the cleaning step is followed by the application of a further activation dispersion containing the activation particles described above.

[0139] In another alternative, no further activation dispersion is applied or only a smaller amount is applied to the steel sheets according to the invention, since these already contain activation particles that were not removed by the cleaning solution.

[0140] A further advantage of the steel sheets according to the invention is the fact that even in the case of incomplete cleaning, activation particles are already present on the surface of the coating and enable defect-free phosphating.

[0141] The final phosphating step (step h) of the process according to the invention can be carried out in any known manner. Phosphating solutions known to those skilled in the art are suitable for the phosphating step. A trication ion phosphating solution, such as is already known for this purpose from the prior art, has proven particularly advantageous with regard to the formation of a microcrystalline zinc phosphate coating that ensures high paint adhesion or corrosion resistance. Upon contact with the acidic phosphating solution containing or consisting of phosphoric acid, zinc ions, and, for example, nitrite ions as accelerators, a conversion of the cleaned and optionally activated surface of the steel sheet takes place.

[0142] Preferably, the phosphating of a flat steel product provided and pretreated according to the invention can be accomplished by using an aqueous phosphating solution which

[0143] - 5 - 20 g / l phosphoric acid,

[0144] 1 - 20 g / l orthophosphate and / or dihydrogen phosphate,

[0145] - 0.5 - 6 g / l of a zinc salt,

[0146] - 0.5 - 2 g / l of a manganese salt,

[0147] - 0.5 - 2 g / l of a nickel salt,

[0148] - The remainder contains water and unavoidable impurities. The phosphating solution preferably contains a free acid content in the range of 4 to 8 points, and the ratio of total acid to free acid in the range of 2.5 to 5 points. Fine-crystalline phosphate crystals are formed particularly reliably with a free acid content in the range of 5 to 7 points. The same purpose is served if the ratio of total acid to free acid is kept in the range of 2.8 to 4.5 points. The phosphating solution is particularly preferably Cr-free. For the term Cr-free (chromium-free), see above.

[0149] Activation (step c)) and phosphating (step d)) can be performed independently of each other in a regular wet-on-wet or dry-on-wet application step. A wet-on-wet process can further increase process efficiency, as an intermediate drying step is eliminated. The dry-on-wet process, on the other hand, offers particularly flexible application.

[0150] In general, several methods are possible for the application of treatment solutions or dispersions as described above. For flat strip products and smaller quantities, the solutions or dispersions can be applied by hand, spray coating, or roller application. In the automotive industry, dipping and spraying processes, or a combination of the two, are most commonly used, as they have no limitations on the quantity, shape, and size of the surfaces to be phosphated and enable high throughput. Oil can also be applied electrostatically.

[0151] Preferably, any activation and phosphating (step h) are carried out independently of each other in a regular wet-on-wet or dry-on-wet application step. Phosphating can be followed by one or more rinsing steps and, if necessary, a final drying step before painting, preferably the application of a KT coating.

[0152] Within the scope of the invention, all of the aforementioned different embodiments or alternatives can be combined. Examples:

[0153] 1. Preparation of samples:

[0154] To test the effectiveness of the invention, blanks were cut from conventionally produced IF steel strip as samples RF (reference), ZW1, ZW2, and ZW3. The steel substrate in each case consisted of a commercially available steel sold under the designation M3A33, the composition of which is given in Table 1.

[0155] Table 1

[0156] Rest iron and unavoidable impurities, contents in wt.%

[0157] The steel strip from which the samples were taken had a Zn-Al-Mg coating (“ZM coating”) applied to its surfaces by conventional hot-dip coating and consisting of 1.6 wt% Al, 1.2 wt% Mg, and the remainder Zn and unavoidable impurities.

[0158] For further tests, blanks were cut from this ZM coated steel strip and further processed at a pilot plant scale.

[0159] The boards were coated with a dispersion using a chem-coater after hot-dip coating, as follows:

[0160] RF: ZM without intermediate layer, without further treatment;

[0161] ZW1: ZM + intermediate layer, applied as an aqueous dispersion with organic silicon compounds with Si element content 0.1 wt.%;

[0162] ZW2: ZM + intermediate layer; applied as an aqueous dispersion with organic silicon compounds with a Si element content of 0.1 wt.% + 0.1 wt.% activation particles (containing spherical zinc oxide nanoparticles and tricinc bis(orthophosphate)) + 0.5 wt.% polyurethane thickener Agocel AC 6240; ZW3: ZM + intermediate layer; applied as an aqueous dispersion with organic silicon compounds with a Si element content of 0.1 wt.% + 0.1 wt.% activation particles (containing spherical zinc oxide nanoparticles and tricinc bis(orthophosphate)) + 5 wt.% polyurethane thickener Agocel AC 6240.

[0163] The boards were oiled with ANTICORIT PL 3802 39 S using a roll coater.

[0164] 2. CuSO4 test:

[0165] The circuit boards were deoiled or degreased with benzine or n-heptane and immersed in a 5 wt% CuSO4 solution for approximately 6 s. They were then rinsed in demineralized water by gentle swirling and visually inspected.

[0166] In all samples treated with the intermediate layer (ZW1, ZW2, ZW3), no deep dark precipitate was visible, as is typical for non-treated surfaces, whereas on the reference RF, light-dark contrasts in the form of strings of pearls or worm-shaped structures were clearly visible.

[0167] 3. Phosphating:

[0168] Circuit boards with the respective coatings, as described above (RF, ZW1, ZW2, and ZW3), were exposed to aging for four weeks (65°C and 70% room humidity). Phosphating was performed in a pilot-scale process to produce near-OEM results:

[0169] - Degrease with Gardoclean S 5176,

[0170] - Rinse with deionized water,

[0171] - Activation with Gardolene ZL 6 (Chemetall),

[0172] - Wet-on-wet phosphating with Gardobond 24 T (Chemetall).

[0173] 4. Examination of the phosphate layer:

[0174] The examination was performed visually using a reflected-light microscope. The results are summarized in Table 2. Table 2

[0175] The evaluation is based on the following criteria: Table 3

[0176] Crystal orientation (A) and crystal diameter (B) were determined optically using a reflected-light microscope at a magnification of 1000x. For the integrity of the phosphate layer, i.e., hole size (C) and hole quantity (D), an area of ​​approximately 300 pm x 300 pm was examined at a magnification of 200x. The weighted evaluation was performed according to the formula:

[0177] Total = 0.5 x A + 1 x B + 1.5 x (C+D)

[0178] The results demonstrate that the sheets according to the invention fulfill the stated objectives and, in particular, provide excellent temporary corrosion protection, enabling homogeneous, spot-free phosphating.

Claims

Patent claims 1. Hot-dip coated and tempered steel sheet comprising a steel substrate and a metallic tempered coating arranged on one or both sides of the steel substrate, containing, in addition to zinc and unavoidable impurities, aluminum with a content of 0.5 to 8.0 wt.% and magnesium with a content of 0.5 to 8.0 wt.%, characterized in that the metallic coating has a double-layer temporary corrosion protection.

2. Steel sheet according to claim 1, characterized in that a Cr-free double-layer temporary corrosion protection is present.

3. Steel sheet according to one of the preceding claims, characterized in that the double-layer temporary corrosion protection has an intermediate layer as a first layer and, arranged thereover, a second layer containing or consisting of a corrosion protection oil.

4. Steel sheet according to claim 3, characterized in that the intermediate layer contains organic silicon compounds.

5. Steel sheet according to claim 3 or 4, characterized in that the intermediate layer has a layer weight with a coating of at least 0.5 mg / m2 and a maximum of 20 mg / m2 Si.

6. Steel sheet according to one of claims 3 to 5, characterized in that the intermediate layer contains rheological additives.

7. Steel sheet according to one of claims 3 to 6, characterized in that the intermediate layer contains organic silicon compounds, one or more compounds selected from the group comprising or consisting of: silanes, silanols, siloxanes, alkoxysilanes, derivatives of silanes, silanols, siloxanes and / or alkoxysilanes and polymers and derivatives thereof.

8. Steel sheet according to one of claims 3 to 7, characterized in that the intermediate layer contains activation particles.

9. Steel sheet according to one of claims 3 to 8, characterized in that the second layer arranged on the intermediate layer contains or consists of a mineral oil.

10. Steel sheet according to one of the preceding claims, characterized in that the steel substrate comprises an alloy containing or consisting of the following elements in wt.%: C: 0.0003 to 0.250%; Si: 0.0005 to 0.70%; Mn: 0.0005 to 2.0%; P: up to 0.15%; S: up to 0.050%; N: up to 0.10%; AI: 0.0050 to 1.50%; optionally one or more of the following elements: Nb: up to 0.20%; Ti: 0.20%; V: 0.0050 to 0.10% B: up to 0.030% and / or Cu: up to 0.80% and / or Cr: up to 0.80% and / or Ni: up to 0.20% and / or Mo: up to 0, 150% and / or Sn: up to 0.10%; Rest iron and unavoidable impurities.

11. A method for producing a hot-dip coated and tempered steel sheet according to one of claims 1 to 10, comprising the following steps: a) providing a steel sheet as a steel substrate, b) one- or two-sided hot-dip coating of the steel substrate with a metallic coating which, in addition to zinc and unavoidable impurities, contains additional elements such as aluminum with a content of 0.5 to 8.0 wt.% and magnesium with a content of 0.5 to 8.0 wt.% in the coating, c) temper rolling of the hot-dip coated steel sheet from step b, d) applying a first intermediate layer to the steel sheet from step c, e) applying a second corrosion protection layer.

12. The method according to claim 11, characterized in that the first intermediate layer is applied as an aqueous, alkaline dispersion.

13. The method according to claim 11 or 12, characterized in that the first intermediate layer is dried, optionally without prior rinsing.

14. Use of a steel sheet according to one of claims 1 to 10 or a steel sheet produced according to one of claims 11 or 12 for producing a spot-free phosphated steel sheet.

15. A process for producing a spot-free phosphated steel sheet comprising the following steps: - Providing a steel sheet according to any one of claims 1 to 10 or a steel sheet produced according to any one of claims 11 to 13; - Cleaning the steel sheet and - Phosphating the cleaned steel sheet.

16. The method according to claim 14, characterized in that an activation layer is applied after cleaning.

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