Steel plate with temporary double corrosion protection layers

Abstract

The invention relates to a hot-dip and temper-rolled steel sheet, comprising a steel substrate and a temper-rolled metal coating, which is arranged on the steel substrate and contains not only zinc and unavoidable impurities, but also aluminum in an amount of 0.5 to 8.0 wt.% and magnesium in an amount of 0.5 to 8.0 wt.%, characterised in that the metal coating contains, in addition to zinc and unavoidable impurities, 0.5 to 8.0 wt.% of aluminum and 0.5 to 8.0 wt.% of magnesium. And the metal coating is provided with double temporary corrosion protection layers. The invention also relates to a method for producing such a steel sheet and to the use thereof for producing a spot-free phosphatized steel sheet.

Description

[0001] The present invention relates to a hot-dip and flat-rolled steel sheet comprising a steel substrate and a flat-rolled metal coating arranged on the steel substrate and containing not only zinc and unavoidable impurities, but also aluminum in an amount of 0.5 to 8.0 wt.% and magnesium in an amount of 0.5 to 8.0 wt.%, characterized in that the metal coating comprises a double-layered temporary corrosion protection layer. The invention also relates to a method for manufacturing such a steel sheet and its use for manufacturing a spot-free phosphatized steel sheet.

[0002] Hot-dip metal sheets comprising a metal coating which not only contains zinc and unavoidable impurities, but also aluminum and magnesium in the coating, are also referred to as ZM metal sheets (coating: ZM) and have been used for many years as metal sheets with higher corrosion protection (compared to metal sheets without such a coating).

[0003] Such metal sheets are used, inter alia, for the manufacture of automobiles or white goods (e.g. electric cookers, refrigerators, freezers, washing machines, dryers and dishwashers). This requires no optical defects, such as spots, shade differences, orange peel, etc., when painted.

[0004] Hot-dipping with a zinc melt containing Al and Mg leads to the formation of not only Zn oxides, but also Al and Mg oxides on the coating surface during cooling after the hot-dip bath, wherein a mainly magnesium-rich oxide layer is observed on the surface. This oxide layer has different chemical properties compared to established pure zinc or zinc-aluminum coatings due to the relatively high dipole moment corresponding to the difference in electronegativity (ΔEN = 2.27) of the Mg oxide. In addition to the oxides, corresponding hydroxides are also present, especially when in contact with water.

[0005] Since the additional steps after hot dip coating and skin pass rolling are usually carried out at different times and / or places, these metal sheets are provided with a temporary corrosion protection layer and, optionally, with a functional coating beforehand, i.e. below the temporary corrosion protection layer. For phosphating and / or painting, the layers on the metal coating have to be removed again. The removal is usually achieved via one or more cleaning steps. It can be the case that the cleaning is not completely achieved, i.e. residues of the coating and / or of the temporary corrosion protection layer remain at least on sub-areas of the skin-passed steel sheet. Such residues, dirt residues such as chips, dust or other particles, and, for example, oil originating from the equipment used, accumulate preferentially in the skin-pass grooves before and after cleaning. Due to the high dipole moment of Mg oxide, the polar end of polarizable or dipolar compounds or amphiphilic molecules also binds more strongly on the surface. The cleaning performance of the surface is thus deteriorated. This has a negative effect on the pre- and post-treatment processes which require an oil- and dirt-free surface, such as phosphating and painting. The described situation leads, inter alia, to inhomogeneous phosphating. This means that the phosphating thickness is inhomogeneous and optical flaws can also occur. As a result, the areas of the phosphating layer consist of zinc phosphate crystals of different sizes which, macroscopically, appear inhomogeneous, i.e. exhibit a light-dark difference. The dark spots usually consist of relatively large phosphate crystals, while the lighter spots consist of relatively small phosphate crystals. Both the inhomogeneous phosphating thickness and the optical flaws lead to inhomogeneous painting, i.e. inhomogeneous KTL deposition, and the resulting reduced corrosion resistance.

[0006] It is an object of the present application to provide a skin-passed ZM metal sheet which has a temporary corrosion protection layer which, on the one hand, ensures good corrosion protection before further processing of the metal sheet and, on the other hand, makes the metal sheet easy to process further. This means that the corrosion protection layer must not exhibit the above-mentioned defects in the further process steps up to painting and the final finished product and must not cause any other obstacles either. In particular, the ideal uniformity and homogeneous deposition of the relatively thin phosphating layer should be achieved and the occurrence of spots in the phosphating layer should be avoided. This first requires a complete, uniform and homogeneous temporary corrosion protection layer to be applied, in particular the pearl string / worm-like structure in the CuSO4 test known to the person skilled in the art should no longer be visible after application. Furthermore, the ZM metal sheet provided with the temporary corrosion protection layer should not require any new process steps or equipment. The individual components of the temporary corrosion protection layer must therefore be precisely matched to one another. In addition, other aspects, such as environmental protection, sustainability, in particular health, should also be taken into account.

[0007] This object is achieved by the features of claim 1.

[0008] The invention provides a hot-dip coated and calendered steel sheet comprising a steel substrate and a calendered metallic coating arranged on one or both sides of the steel substrate and containing not only zinc and unavoidable impurities, but also aluminum in an amount of 0.5 to 8.0 wt.% and magnesium in an amount of 0.5 to 8.0 wt.%, characterized in that the metallic coating comprises a double-layered temporary corrosion protection layer.

[0009] In the present context, the term "metallischen dressierten Überzugs" is only used to clarify that the substrate provided with the coating is subjected to calendering. That is, the calendering rolls come into contact with the metallic coating. The coating is arranged on one or both sides of the steel substrate, preferably on both sides. If the coating is arranged on only one side of the steel substrate, the calendering rolls come into direct contact with the steel substrate on this side.

[0010] The ZM coating applied in the hot-dip coating process contains a zinc alloy which contains not only zinc (balance) and unavoidable impurities, but also further elements, such as aluminum in an amount of 0.1 to 8 wt.% and magnesium in an amount of 0.1 to 8 wt.%. Impurities which can be present in the melt bath include elements selected from the group of Si, Sb, Bi, Zr, Ni, Cr, Pb, Ti, Ca, Mn, Sn, La, Ce, Fe and Cr, in an individual or cumulative amount of at most 0.5 wt.%, in particular at most 0.4 wt.%, preferably at most 0.3 wt.%. Impurities which can be present in the coating include elements selected from the group of Si, Sb, Bi, Zr, Ni, Cr, Pb, Ti, Ca, Mn, Sn, La, Ce, Fe and Cr, in an individual or cumulative amount of at most 0.5 wt.%, in particular at most 0.4 wt.%, preferably at most 0.3 wt.%, wherein in one alternative the concentration of Fe can be higher due to the above-mentioned diffusion. The balance is zinc. Steel sheets cut from steel strips or steel sheet components made therefrom having a zinc-based corrosion protection coating exhibit very good cathodic corrosion protection and have been used in automotive manufacturing for many years. If an increase in corrosion protection is intended, the coating contains magnesium in an amount of at least 0.8 wt.%, in particular at least 1.0 wt.%, preferably at least 1.1 wt.%, and aluminum in an amount of at least 0.8 wt.%, in particular at least 1.0 wt.%. The coating contains magnesium in an amount 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 aluminum in an amount 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.%. In one alternative, the determination of these concentrations is carried out according to or based on DIN EN ISO 10111:2019 and / or DIN EN ISO 11885:2009 as wet-chemical coating determination.

[0011] In order to establish a ZM coating of a predetermined thickness, which can be 1 to 60 pm on each side in the solid state, the melt, which is still in the liquid state, applied to the steel strip is wiped off by passing the steel strip coated with the liquid melt through a wiping device, which comprises, for example, a jet, in particular a slit jet, or the like, which, after leaving the melt bath, acts on both sides of the steel strip with a gaseous wiping medium in order to wipe off the liquid melt. This makes it possible to achieve an asymmetric coating, i.e. different on both sides. The thickness of the ZM coating can be adjusted to be at least 4 pm, preferably at least 5 pm, and at most 58 pm, preferably 5 pm and at most 55 pm, on each side independently of one another in each case. In a particular embodiment, the thickness of the coating is at least 1 pm, preferably at least 2 pm, particularly preferably at least 3 pm, in particular at least 5 pm and at most 25 pm, preferably at most 20 pm, particularly preferably at most 15 pm, and in particular at most 10 pm, on each side independently of one another in each case. In one alternative, the coating thickness is gravimetrically determined by dissolution and converted into a thickness on the basis of the mass, or determined by metallography of microsections, in accordance with DIN EN ISO 101 1 1.

[0012] Below the minimum limit, sufficient cathodic corrosion protection cannot be ensured, and above the maximum limit, problems can arise when connecting the steel sheet according to the application or a component made therefrom to other components.

[0013] In one alternative, the coating weight of the ZM coating is 1 g / m 2 to 650 g / m 2 , i.e. 0.5 g / m 2 to 320 g / m 2 , particularly preferably 10 g / m 2 to 500 g / m 2 , i.e. 5 g / m 2 to 250 g / m 2 , on each side independently of one another in each case. In another alternative, asymmetric coating can also be carried out.

[0014] One embodiment provides a steel sheet having a double-layered temporary corrosion protection layer free of Cr. Free of Cr is to be understood to mean that Cr is present in a concentration of at most 1000 ppm, preferably 500 ppm, in particular 100 ppm [according to VdL Richtlinie 01 "VdL-Richtlinie Deklaration Beschichtungsstoffe" Richtlinie zur Erklarung von Lacken, Lackiers, Beschichtungen, Putzen, Füllmitteln, Grundierungen und verwandten Produkten, Mai 2019 (7. Auflage), Verband der deutschen Lack- und Druckfarbenindustrie e. V.].

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

[0016] The intermediate layer is bound to the metallic coating by chemical adsorption, i.e. by chemical bonds. In the broadest sense, chemical bonds are ionic bonds, covalent bonds, coordinate bonds or weak bonds via electrostatic attraction or van der Waals forces.

[0017] In one alternative, the intermediate layer is produced by a chemical reaction of the aqueous treatment dispersion with the metallic substrate, as a result of which the adsorbate (i.e. the aqueous treatment dispersion) and / or the adsorbent (i.e. the metallic ZM coating) undergoes a chemical change. In another alternative, the components of the aqueous dispersion covalently bind to the components of the ZM coating.

[0018] In one embodiment, the intermediate layer contains or consists of a polymer, for example an organic polymer based on acrylic acid or a derivative thereof. In one 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 copolymers, modified polyacrylic acid or polyacrylic acid,

[0020] - 1 part by weight of a phosphate component, and

[0021] - optionally 1 / 10 to 5 / 10 parts by weight of a metal-containing component selected from the group consisting of Zn, Ca, Mg and / or Al.

[0022] In another alternative, the intermediate layer contains or consists of organosilicon compounds, preferably selected from one or more compounds of 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, which have functional groups, such as -OR, wherein R is H or an alkyl group, preferably Ci to C7, vinyl, phenyl, benzyl; -NR2, wherein R is H or an alkyl group, preferably Ci to C7, vinyl, phenyl, benzyl; condensation products obtained from the dehydration of hydrolyzed alkoxysilanes, i.e. silanols or alkoxysilanes with hydroxyl groups; at least one silane, silanol and / or siloxane with at least one alkoxy group, with at least one amide group, with at least one amino group, with at least one urea group, and condensation products, copolymers and polymers of at least two of the above-mentioned compounds.

[0023] Alternatively or in addition, the silanes, silanols, siloxanes, alkoxysilanes and derivatives thereof mentioned above are selected from the group comprising or consisting of bis-tri(methoxy / ethoxy)silylalkanes, such as bis-triethoxysilyl ethane, methyltrimethoxysilane, tetraethoxysilane, aminopropyltriethoxysilane, 4- aminodialkylalkyldialkoxysilane, 2-aminoethyl-3-aminopropyltrimethoxysilane, 2- aminoethyl-3-aminopropyltriethoxysilane, gamma-aminalkyltrialkoxysilane, 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, ureidopropyltrimethoxysilane, gamma-ureidoalkyltrialkoxysilane, 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) dialkylenetriamine, 3-glycidyloxypropyltrimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl- butylene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N,N-bis[3-(trimethoxysilyl)propyl]ethylenediamine and / or N-2-aminoalkyl-3-aminopropyltrialkoxysilane, wherein alkyl is 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 consisting of at least two of the above-mentioned compounds and / or polymers thereof.

[0024] In the context of the present application, siloxanes are understood to mean compounds of the following formula: wherein R is H or alkyl, preferably Ci to C7 and n = 0 to 20. Polymers wherein R = alkyl are referred to as silicones. Alkoxysilanes have the general formula (RO)4-Si, wherein R is alkyl, preferably Ci to C7.

[0025] In one alternative, the aqueous dispersion can additionally contain an inorganic salt, for example a salt having a cation selected from the group comprising or consisting of Zr 4+ , Zn 2+ , Ca 2+ , Mg 2+ and Al 3+ and an anion selected from the group comprising or consisting of Cl - , NO3 - , SO4 2- and PO4 3- . In one alternative, Cu is present as an oxide.

[0026] The intermediate layer is preferably applied as an aqueous dispersion. In this dispersion, at least a portion of the organosilicon compounds is in hydrolyzed or alkoxylated form. At least a portion of the organosilicon compounds reacts to form a polymer, for example a polysiloxane. In the form of the hydrolyzed or alkoxylated organosilicon compounds and / or the polysiloxane, they react with the hydroxyl groups of the metal to eliminate water or alcohol and form a strong bond with the substrate. In the meantime and subsequently to drying, the organosilicon compounds, which are now covalently bound to the surface, condense with one another to form a network-like structure, which in turn forms a homogeneous intermediate layer that is uniformly distributed over the surface of the coating.

[0027] In the context of the present application, the term "aqueous dispersion" refers to compositions in which particles and / or droplets are dispersed in water as well as colloidal and / or molecularly dispersed compositions. In one alternative, the aqueous dispersion contains an organic solvent, in particular an alcohol, preferably methanol or ethanol, a lower ketone or ether having at most 7, preferably 5 carbon atoms.

[0028] In one embodiment, the Si content of the intermediate layer is at least 0.5 mg / m 2 , preferably at least 1.0 mg / m 2 , particularly preferably at least 1.5 mg / m 2 , in particular at least 2.0 mg / m 2 and at most 20.0 mg / m 2 or 15.0 mg / m 2 , preferably at most 10.0 mg / m 2 or 8.0 mg / m 2 , particularly preferably at most 7.0 or 8.0 mg / m 2 , in particular at most 3.0 or 2.5 mg / m 2The quantitative determination of the coating layer weight is achieved, for example, by X-ray fluorescence analysis (XRF) or GDOES (glow discharge optical emission spectroscopy). The coating layer weight of a specific element of the intermediate layer is the specified mass per unit area, which expression is to be understood to mean that the intermediate layer contains the reported mass of the respective element per unit area, regardless of the form, i.e. in elemental state, atomic state, ionic state or oxidic state. In the case of a Si concentration of the steel sheet, i.e. of the steel substrate, which interferes with the Si determination in the intermediate layer, i.e. which can lead to false results, the person skilled in the art refers to or makes a difference measurement on the steel sheet without the intermediate layer or in an area where the layer has been removed for measurement purposes. The reported values relate to the abundance of the element Si (silicon) regardless of its form of occurrence, i.e. regardless of whether the element is present in the form of neutral atoms, in the form of ions or in the form of compounds, such as organic compounds (e.g. alcohols, esters, polymers or complexes), oxides, salts or hydroxides, etc.

[0029] The second layer of the two-layer temporary corrosion protection layer contains or consists of a corrosion protection oil, preferably a mineral oil, particularly preferably a naphthenic base oil containing 15 to 60% by weight, preferably 20 to 50% by weight, of benzenesulfonic acid Na and / or Ca salts having mono-C10-16-alkyl derivatives and / or mono-C16-24-alkyl derivatives as organic radicals.

[0030] Compared to a layer structure without an intermediate layer employed according to the application, the intermediate layer not only ensures temporary corrosion protection, but also reduces or prevents the adsorption of polarizable or polar molecules on the corrosion-protective metal coating.

[0031] One embodiment also relates to a steel sheet according to the application, characterized in that the intermediate layer contains a rheological additive. Since the intermediate layer is applied in the form of an aqueous solution or aqueous dispersion, the rheology, in particular the viscosity, of the solution or dispersion is of great importance. An aqueous dispersion containing the compounds of the subsequent intermediate layer and the rheological additive is a system in which the components precisely match one another on the one hand and also the substrate on the other hand. In the matching, in particular the polarity of the composition and the substrate is taken into account.

[0032] In one alternative, the additive employed is a substance from the class of additives, such as, for example, a layered silicate, an associative thickener, a synthetic layered silicate, a liquid rheological additive or an activity enhancer for fumed silica. The rheological additive is preferably selected from the group containing or consisting of acrylate thickeners, carboxymethyl cellulose, methyl cellulose, polyurea thickeners, polyurethane thickeners, layered silicates, fumed silica, gelatin, alginates, monosaccharides and / or polysaccharides, in particular Xanthan, Guarether and Xanthangummi.

[0033] It is particularly preferred to combine the above-mentioned organosilicon compounds with rheological additives containing or based on polyurethanes or polysaccharides or heteropolysaccharides, preferably modified polysaccharides or heteropolysaccharides, such as guar gum and / or xanthan gum, in particular swell-delayed guar gum ethers or xanthan gum molecules or modified xanthan gum molecules.

[0034] The combination of the composition of the subsequent intermediate layer with the rheological additive ensures complete wetting of the surface of the substrate. This results in a uniform, homogenous dried intermediate layer. Homogenous means the property of a layer to have the same macroscopic properties over all areas. Furthermore, the rheological additive can allow a reduction in the thickness of the intermediate layer compared to without the rheological additive.

[0035] In one embodiment, the intermediate layer contains activated particles as an alternative or in addition to the rheological additive. The activated particles are preferably activated particles for the subsequent phosphating of the steel sheet.

[0036] In one alternative, the activated particles used are compounds selected from the group containing or consisting of colloidal titanium phosphate, surface conditioners based on phosphate particles, in particular based on zinc phosphate, and metal oxides or salts as sources of phosphate and titanium.

[0037] It is preferred to use compounds dispersible in water, such as oxalates of silver or copper compounds, combinations of disodium phosphate with titanium compounds, in particular with water-soluble titanium compounds, such as titanium phosphate or sodium titanium phosphate oxide, zinc phosphate, and mixtures of zinc phosphate with metal oxides, such as zinc oxide or iron oxide and mixtures thereof. The activated particles are preferably selected from the group containing or consisting of titanium dioxide, titanium dioxide hydrate, dipotassium hexafluorotitanate, hexafluorotitanic acid, titanium sulfate, titanium disulfate, titanium oxysulfate, titanium oxide sulfates, titanium oxide chlorides, potassium titanium fluoride, titanium tetrachloride, titanium tetrafluoride, titanium trichloride, titanium hydroxide, titanium nitrite, titanium nitrate, potassium titanium oxalate, and titanium carbide. Titanium salts are particularly good crystallization nucleating agents for the crystallization of metal phosphates, such as zinc phosphate. Alternatively or additionally, the aqueous dispersion can contain activated particles which are 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.

[0038] It is particularly preferred that at least one compound selected from the group comprising or, as the case can be, consisting of spherical zinc oxide nanoparticles and tri-zinc di-orthophosphoric acid is used in combination with the intermediate layer and, optionally, the rheological additive.

[0039] The aqueous dispersion containing the subsequent intermediate layer, i.e. including the rheological additive and, optionally, the activated particles and, optionally, further additives or components, is a composition in which all components match each other precisely and also with the substrate. The stability of the aqueous dispersion must be taken into account, for example the particle density, the separation rate distribution and the particle size distribution. These and other stability criteria and methods for determining the stability can be determined in accordance with ISO 13318, ISO / TR 13097:2013 and / or ISO / TR 18811:2018. The aqueous dispersion shows no particle sedimentation (at the temperature of use) without mechanical mixing or stirring, in particular for at least 60 minutes, preferably 120 minutes, particularly preferably 180 minutes, in particular 240 minutes or more. The matching with the substrate can be verified, for example, via the CuSO4 test.

[0040] The present application also provides the use of the above-mentioned organosilicon compounds as corrosion protection, in particular as a corrosion protection layer. The present application also provides the use of the above-mentioned organosilicon compounds in combination with the above-mentioned rheological additive and, alternatively or additionally, in combination with the above-mentioned activated particles as corrosion protection, in particular as a corrosion protection layer. The rheological additive and / or the activated particles are embedded in the corrosion protection layer of the organosilicon compound. Thus, a first corrosion protection layer of the organosilicon compound containing the rheological additive and / or the activated particles is of interest.

[0041] The above-mentioned intermediate layer forms a complete, uniform and homogeneous layer. This can be demonstrated by the so-called CuSO4 test. For this purpose, the steel sheet after application of the aqueous dispersion is dried and, optionally, rinsed before drying. The oil- and fat-free surface is immersed in a solution of a 5% by weight CuSO4 solution for about 10 seconds. Then, rinsing is carried out in deionized water with gentle swirling.

[0042] During immersion in the CuSO4solution, the metal bare areas react with the free copper ions and copper metal is deposited in the form of black or metallic precipitates. In areas that have been post-treated with inertization (passivation or sealing, etc.), there is less (if any) copper deposition and the deposition is less deep. This is clearly seen from the contrast between light and dark in the case of unevenly coated layers. A string of pearls / worm-like structure is formed, known to the person skilled in the art, i.e. a series of light or dark points, which can be 0.2 to 1.0 mm or more in width and several centimeters in length, or in some cases, the length can extend over the entire width of the sheet. The metal sheet provided with an intermediate layer according to the present application shows no string of pearls or worm-like structure in this CuSO4test. Thus, in the context of the present application, a complete, uniform and homogeneous intermediate layer is a layer that shows no string of pearls or worm-like structure in the CuSO4test as described above after deoiling / degreasing.

[0043] The steel sheet according to the present application can further have at least one other functional coating, such as an adhesion promoting layer, a forming aid, a passivation layer or a combination thereof.

[0044] In one alternative, the intermediate layer / the aqueous dispersion with which it is coated contains or does not contain an epoxy-based binder system.

[0045] According to the present application, the steel substrate employed according to the present application is a hot-rolled strip or a cold-rolled strip. These can be obtained by processes known to the person skilled in the art. The steel substrate can be used in the form of a steel strip, so-called coil stock, or so-called blanks, which are preferably obtained by cutting segments from the hot- or cold-rolled strip by appropriate processes.

[0046] Another embodiment employs a steel sheet, characterized in that the steel substrate comprises an alloy containing or consisting of the following elements in % by weight:

[0047] C: 0.0003% to 0.250%,

[0048] Si: 0.0005% to 0.70%,

[0049] Mn: 0.0005% to 2.0%,

[0050] P: up to 0.15%,

[0051] S: up to 0.050%,

[0052] N: up to 0.10%,

[0053] Al: 0.0050% to 1.50%,

[0054] optionally one or more of the following elements:

[0055] -Nb: max. 0.20%,

[0056] -Ti: 0.20%,

[0057] -V: 0.0050% to 0.10%,

[0058] -B: max. 0.030% and / or

[0059] -Cu: max. 0.80% and / or

[0060] -Cr: max. 0.80% and / or

[0061] -Ni: max. 0.20% and / or

[0062] -Mo: max. 0.150% and / or

[0063] -Sn: max. 0.10%,

[0064] -the remainder being iron and unavoidable impurities.

[0065] In one alternative, the substrate is a steel sheet made of an interstitially free alloy according to DIN EN 10346. The IF alloy of the steel substrate contains or consists of the following elements in wt%:

[0066] -C: 0.0003% to 0.015%, in particular 0.0005% to 0.010%, preferably 0.001% to 0.005%,

[0067] -Si: 0.0005% to 0.50%, in particular 0.0010% to 0.40%, preferably 0.0010% to 0.30%,

[0068] -Mn: 0.0005% to 1.60%, in particular 0.010% to 1.55%, preferably 0.010% to 1.50%,

[0069] -P: max. 0.10%, in particular max. 0.080%, preferably 0.0002% to 0.060%,

[0070] -S: max. 0.050%, in particular max. 0.040%, preferably 0.0003% to 0.030%,

[0071] -N: max. 0.10%, in particular max. 0.080%, preferably 0.0001% to 0.070%,

[0072] - Al: 0.0010% to 1.0%, in particular 0.0010% to 0.90%, preferably 0.0010% to 0.80%,

[0073] - one or two of the following elements:

[0074] - Nb: 0.0001% to 0.20%, in particular 0.0002% to 0.10%, preferably 0.0003% to 0.050%,

[0075] - Ti: 0.0005% to 0.20%, in particular 0.010% to 0.150%, preferably 0.010% to 0.120%,

[0076] - optionally one or more of the following elements:

[0077] - B: max. 0.0050% and / or Cu max. 0.20% and / or Cr max. 0.20% and / or Ni max. 0.20% and / or Mo max. 0.150% and / or Sn max. 0.10%,

[0078] - the remainder being iron and unavoidable impurities.

[0079] IF steels do not contain interstitially ingalagerte alloying elements, i.e. no iron atoms in the metal lattice are blocked by carbon or nitrogen atoms. This results in a very soft, very good formable steel. It is used, inter alia, in automotive manufacturing for complex deep-drawn parts. This type of steel is available under the standard designations DX52D, DX53D, DX54D, DX55D, DX56D, DX57D HX160YD, HX180YD, HX220YD and HX260YD. These are cold-rolled steels.

[0080] In one alternative, the substrate is a steel sheet made of a Bake-Hardening alloy according to DIN EN 10346. The steel substrate of the Bake-Hardening alloy contains or consists of the following elements in % by weight:

[0081] - C: 0.0004% to 0.080%, in particular 0.0010% to 0.060%, preferably 0.0010% to 0.040%,

[0082] - Si: 0.0005% to 0.50%, in particular 0.0010% to 0.40%, preferably 0.010% to 0.20%,

[0083] - Mn: 0.0005% to 1.50%, in particular 0.0010% to 1.40%, preferably 0.0020% to 1.20%,

[0084] - P: max. 0.150%, in particular max. 0.10%, preferably 0.0010% to 0.050%,

[0085] - S: max. 0.050%, in particular max. 0.040%, preferably 0.0005% to 0.030%,

[0086] - N: max. 0.050%, in particular max. 0.030%, preferably 0.0002% to 0.010%,

[0087] - Al: 0.0050% to 1.0%, in particular 0.010% to 0.50%, preferably 0.010% to 0.150%,

[0088] - optionally one or more of the following elements:

[0089] - Nb: max. 0.040% and / or Ti max. 0.030% and / or B max. 0.0030% and / or Cu max. 0.20% and / or Cr max. 0.20% and / or Ni max. 0.20% and / or Mo max. 0.150% and / or Sn max. 0.10%,

[0090] - the remainder being iron and unavoidable impurities.

[0091] BH steels are characterized by a significant increase in yield strength during the paint baking process (typically 20 minutes at 170°C) while having very good formability. These steels also generally exhibit very good dent resistance, which is why these steels are preferentially used for outer shell applications. This type of steel can be obtained under the standard names HX180BD, HX220BD, HX260BD and HX300BD. These are cold-rolled steels.

[0092] In one alternative, 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%:

[0093] - C: 0.050% to 0.250%, in particular 0.060% to 0.250%, preferably 0.070% to 0.250%,

[0094] - Si: 0.020% to 0.50%, in particular 0.020% to 0.40%, preferably 0.020% to 0.30%,

[0095] - Mn: 1.30% to 2.0%, in particular 1.40% to 1.90%, preferably 1.50% to 1.80%,

[0096] - P: max. 0.10%, in particular max. 0.080%, preferably max. 0.060%,

[0097] - S: max. 0.050%, in particular max. 0.040%, preferably max. 0.030%,

[0098] - N: max. 0.10%, in particular max. 0.050%, preferably max. 0.030%,

[0099] - Al: 0.010% to 0.150%, in particular 0.010% to 0.10%, preferably 0.010% to 0.090%,

[0100] - optionally one or more of the following elements:

[0101] - Cu: max. 0.80% and / or Cr max. 0.70% and / or Nb max. 0.10% and / or Ti max. 0.20%,

[0102] - the remainder being iron and unavoidable impurities.

[0103] Exemplary steels of this type can be obtained under the standard designation HCT490X, HCT590X or HCT780X. These are cold-rolled steels.

[0104] In one alternative, 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%:

[0105] - C: 0.020% to 0.20%, in particular 0.020% to 0.150%, preferably 0.020% to 0.140%,

[0106] - Si: 0.010% to 0.70%, in particular 0.010% to 0.60%, preferably 0.010% to 0.50%,

[0107] - Mn: 0.020% to 2.0%, in particular 0.020% to 1.90%, preferably 0.020% to 1.80%,

[0108] - P: max. 0.070%, in particular max. 0.060%, preferably max. 0.050%,

[0109] - S: max. 0.050%, in particular max. 0.040%, preferably max. 0.030%,

[0110] - N: max. 0.080%, in particular max. 0.060%, preferably max. 0.040%,

[0111] - Al: 0.010% to 1.0%, in particular 0.010% to 0.50%, preferably 0.010% to 0.10%,

[0112] - at least one of the following elements:

[0113] - Nb: 0.010% to 0.150%, in particular 0.010% to 0.120%, preferably 0.010% to 0.10% and / or

[0114] - Ti: 0.010% to 0.20%, in particular 0.010% to 0.180%, preferably 0.010% to 0.150% and / or

[0115] - V: 0.0050% to 0.10%, in particular 0.0060% to 0.10%, preferably 0.0090% to 0.10% and / or

[0116] - optionally one or more of the following elements:

[0117] - B: max. 0.0050% and / or Cu max. 0.40% and / or Cr max. 0.50%,

[0118] - the remainder being iron and unavoidable impurities.

[0119] The micro-alloyed steel has a microstructure with fine grains, which gives it a high fatigue strength, optimum weldability and a high yield load limit. It is used in particular for complex deep-drawn parts in automobile construction. Exemplary steels of this type are available under the standard designations HC260LA, HC300LA, HC340LA, HC380LA, HC420LA, HC460LA, HC500LA and HC550LA. These are cold-rolled steels.

[0120] The application also relates to a method for producing a hot-dip coated and calendered steel sheet as described above, comprising the following steps:

[0121] a) providing a steel sheet as a steel substrate,

[0122] b) hot-dip coating a metal coating on one or both sides of the steel substrate, which metal coating contains not only zinc and unavoidable impurities, but also further elements, for example aluminum in an amount of 0.5% to 8.0% by weight and magnesium in an amount of 0.5% to 8.0% by weight,

[0123] c) calendering the hot-dip coated steel sheet from step b),

[0124] d) applying a first layer as an intermediate layer to the steel sheet from step c),

[0125] e) applying a second layer containing or consisting of a corrosion protection oil to the intermediate layer.

[0126] Step a employs a steel sheet as described above as steel substrate.

[0127] The hot dip coating process according to step b is known per se to the skilled person. The hot dip coating can additionally comprise one or more of the following steps: cleaning the substrate prior to the hot dip coating bath, heating the substrate prior to the hot dip coating bath; wiping the melt after the hot dip coating bath using a squeegee to establish the desired coating, cooling the coated substrate to harden the melt, optionally applying a coating smoothing agent; optionally applying further functional coating layers, such as adhesion promoting layers, forming aids, passivation layers or combinations thereof.

[0128] The smoothing in step c is known per se to the skilled person and is described, for example, in the handbook "Umformen", Gunter Spur, ISBN: 978-3-446-43004-4, page 155. The surface of the steel sheet after smoothing can exhibit a random surface structure. This is produced with smoothing rolls whose surface is textured by a so-called EDT process. The surface of the steel sheet after smoothing can alternatively exhibit a deterministic surface structure. This is produced with smoothing rolls whose surface is textured by laser. It is even conceivable for the surface to have a pseudo-random surface structure after smoothing. These surface structures have a (quasi-)random appearance consisting of random elements with a repeating structure. Prior to applying the first corrosion protection layer, an optional cleaning step, preferably an alkaline cleaning step, can be carried out, optionally using a cleaning agent, followed by a rinsing and optionally drying step.

[0129] In step d, the first intermediate layer is applied to the smoothed steel sheet in the form of an aqueous dispersion. The application is carried out by spraying, dipping or coating processes, preferably using a roll coater or a chemical applicator at an ambient temperature of 10 to 50°C, preferably 20 to 40°C.

[0130] The aqueous dispersion contains the polymer or the organosilicon compound as described above in a concentration of at least 0.001 wt.%, preferably at least 0.01 wt.%, particularly preferably at least 0.04 wt.% or 0.06 wt.%, especially at least 0.08 wt.% and at most 5.0 wt.% or 1.0 wt.%, preferably at most 0.5 wt.% or 0.25 wt.%, particularly preferably at most 0.15 wt.% and especially at most 0.12 wt.% based on the element Si.

[0131] Alternatively, based on at least one organosilicon 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.-%, especially 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.-%, especially at most 0.06 wt.-% of at least one of the above-mentioned organosilicon compounds.

[0132] In one embodiment, the aqueous dispersion contains one or more of the above-mentioned rheological additives, and in another embodiment, alternatively or additionally, contains activated particles, as described above.

[0133] The rheological additive is present in an active substance concentration of at least 0.01 wt.-%, preferably at least 0.025 wt.-%, particularly preferably at least 0.05 wt.-%, especially 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.-%, especially at most 0.25 wt.-% or 0.15 wt.-%.

[0134] The activated 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.-%, especially 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 wt.-% or 0.5 wt.-%, especially at most 0.25 wt.-% or 0.15 wt.-%.

[0135] Alternatively, the aqueous dispersion is a basic aqueous dispersion having a pH of at least 8.0, preferably at least 9.0, particularly preferably at least 9.5, especially at least 10.0 and at most 13.0, preferably at most 12.5, particularly preferably at most 12.0 or 11.0, especially at most 10.5.

[0136] In another alternative, the aqueous dispersion has a density at 20 °C of at least 0.90 g / cm 3 , preferably at least 0.95 g / cm 3 , particularly preferably at least 1.00 g / cm 3 , and at most 1.30 g / cm 3 , preferably at most 1.20 g / cm 3 , particularly preferably at most 1.10 g / cm 3 , especially at most 1.0 g / cm 3 .

[0137] In another 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, and especially at least 1.0, and at most 2.0, preferably at most 5.0, particularly preferably at most 10.0, and especially at most 15.0.

[0138] In one embodiment, the aqueous dispersion is Cr-free. With regard to the term Cr-free (chromium-free), see above.

[0139] Another embodiment relates to the above method, wherein after applying the aqueous dispersion, the steel sheet is rinsed, followed by drying, preferably without prior rinsing in a so-called rinse-free process.

[0140] Optionally, further functional coating layers, such as adhesion promoting layers, forming aids, passivation layers or combinations thereof, are applied.

[0141] The present application also provides the use of the steel sheet according to the present application provided with the above temporary corrosion protection layer for the manufacture of a spot-free phosphatized steel sheet.

[0142] The present application also provides a method for the manufacture of a spot-free phosphatized steel sheet, comprising the following steps:

[0143] f) providing a steel sheet according to the above of the present application or manufactured by the above method,

[0144] g) cleaning the steel sheet, and

[0145] h) phosphatizing the cleaned steel sheet.

[0146] In the context of the present application, a spot is defined as a region that appears darker (on the surface). The dark region is preferably delimited by dark points, which are characterized in that they are darker than other (and thus brighter) points arranged within the immediately adjacent region. In the present context, a point (Punkt) is not to be understood as a mathematically point without extension, but as a pixel or group of pixels, for example. Such a dark point only has a common border with brighter points in a subregion of its periphery. In the remaining subregion of its periphery, it has a common border with dark points of essentially the same brightness as the delimiting dark point. Thus, the above dark region is mainly composed of the latter dark points and the delimiting dark points of the former.

[0147] In the context of the present application, a spot-free phosphatization and / or a homogenously uniform phosphatization and / or a phosphatization layer is a layer that, when visually inspected using a reflected light microscope, fulfills at least one, preferably two, particularly preferably all of the following criteria:

[0148] - the crystal orientation of the phosphate crystals determined optically at a magnification of 1000x: at least 20% of the phosphate crystals are perpendicular to the substrate surface, preferably at least 40%, particularly preferably at least 60%, in particular at least 80%;

[0149] - the crystal diameter of the phosphate crystals determined optically at a magnification of 1000x is from 0.5 pm to 10 pm, preferably from 1.0 pm to 5 pm;

[0150] - the pore size of the pores in the phosphate crystal layer determined at a magnification of 200x in an area of approximately 300 pm x 300 pm is equal to the average crystal diameter (see above), preferably smaller than the average crystal diameter, particularly preferably free of pores;

[0151] - the number of pores determined at a magnification of 200x in an area of approximately 300 pm x 300 pm is from 3 to 5, preferably from 1 to 2, particularly preferably free of pores.

[0152] After the provision of the above-described steel sheet according to the application in step f or the manufacture of the steel sheet by the above-described method, the steel sheet is cleaned, preferably using an alkaline cleaning agent, immediately or optionally after a further step, for example uncoiling, straightening or bending and / or stretch-straightening. The cleaning optionally further comprises one or more rinsing steps. This step g removes the above-described temporary double-layer corrosion protection layer before phosphating. The alkaline cleaning agent achieves reliable removal of the oil layer. Even if the intermediate layer is not completely removed, the intermediate layer according to the application in some cases remains locally even after cleaning and ensures a spot-free phosphating. The intermediate layer prevents insoluble deposits, especially in the flat-rolled grooves, while the activating particles present in one alternative act as crystallization nucleators for the phosphating.

[0153] In bodywork manufacture, for example, the steel sheet is usually supplied to the bodywork manufacturer in the unphosphated state, whereupon the manufacturer optionally cuts the steel sheet from the coil, shapes it into components, optionally connects individual components to one another and provides the individual or connected components obtained with a phosphating layer by means of a dip or spray process. These steps can also be carried out individually or in combination in the context of the present application.

[0154] It is preferred when step g of the method according to the application is carried out by treating the steel sheet from step f with at least one cleaning agent. According to the application, the cleaning agent can be acidic, neutral or alkaline.

[0155] In a preferred embodiment, an alkaline cleaner is employed. In an alternative, the alkaline cleaner is an alkaline aqueous dispersion having a pH of at least 8.0, preferably at least 9.0, particularly preferably at least 10.0, especially 11.0 and at most 14.0, preferably at most 13.0, particularly preferably at most 12.0, especially at most 11.5. Substances having cleaning activity, such as surfactants, are preferably present in amounts deemed suitable by the person skilled in the art. According to the application, it is preferred when any other components of the cleaner, such as are selected from the group consisting of sodium hydroxide or potassium hydroxide and mixtures thereof. Step g can also be carried out by applying mechanical energy, for example by scrubbing the surface to be cleaned or by applying water and / or cleaner to the surface under high pressure. Step g of the method according to the application is preferably carried out at a temperature of from 20°C to 80°C.

[0156] In an alternative, the cleaning step is followed by the application of a further activation dispersion containing the above-mentioned activated particles.

[0157] In a further alternative, only a small amount of further activation dispersion, if any, is applied to the steel sheet according to the application, since the steel sheet already contains activated particles which have not been removed by the cleaning solution.

[0158] A further advantage of the steel sheet according to the application is that activated particles are already present on the coating surface, so that a defect-free phosphatization can be achieved even in the case of incomplete cleaning.

[0159] The final phosphatization step (step h) of the method according to the application can be carried out in any known manner. Phosphatization solutions known to the person skilled in the art are suitable for the phosphatization step. In particular advantageous in terms of forming a microcrystalline zinc phosphate coating which ensures high paint adhesion or corrosion resistance is, for example, a tricationic phosphatization solution, which is likewise known in the prior art for this purpose. Contact with an acidic phosphatization solution containing or consisting of phosphoric acid, zinc ions and, for example, nitrite ions as accelerators, leads to the conversion of the cleaned and optionally activated steel sheet surface.

[0160] The phosphatization of the flat steel product provided and pretreated according to the application can preferably be achieved by using an aqueous phosphatization solution containing:

[0161] - 5 - 20 g / l of phosphoric acid,

[0162] - 1 - 20 g / l of orthophosphate and / or dihydrogen phosphate,

[0163] - 0.5 - 6 g / l of zinc salt,

[0164] - 0.5 - 2 g / l of manganese salt,

[0165] - 0.5 - 2 g / l of nickel salt,

[0166] - the balance is water and unavoidable impurities.

[0167] When the content of free acid in the phosphating solution is in the range of 4 to 8 points and the ratio of total acid to free acid is in the range of 2.5 to 5 points, this is preferred. When the content of free acid is in the range of 5 to 7 points, fine-crystalline phosphate crystals are formed particularly reliably. When the ratio of total acid to free acid is kept in the range of 2.8 to 4.5 points, this achieves the same purpose. When the phosphating solution is free of Cr, this is particularly preferred. With regard to the term free of Cr (free of chromium), see above.

[0168] Activation (step c) and phosphating (step d) can be carried out independently of one another in conventional wet-on-wet or dry-on-wet coating steps. The wet-on-wet process can further increase process efficiency, since an intermediate drying step can be dispensed with. In contrast, the dry-on-wet process can be used particularly flexibly.

[0169] In principle, there are several methods which are generally suitable for the coating of treatment solutions or dispersions as described above. For flat strip products and smaller production quantities, the solution or dispersion can be applied by hand brushing, spraying and rolling processes. In the automotive sector, the immersion and spraying processes or a combination of the two processes are most commonly used, since they have no restrictions on the quantity, shape and size of the surface to be phosphated and allow high throughputs. The coating of the oil can also be carried out in an electrostatic manner.

[0170] Any activation and phosphating (step h) can preferably be carried out independently of one another in conventional wet-on-wet or dry-on-wet coating steps. One or more rinsing steps can be carried out after phosphating and, optionally, a final drying step before painting (preferably coating with a KTL coating).

[0171] In the context of the present application, all the above-mentioned different embodiments or alternatives can be combined. Example

[0172] 1. Sample preparation:

[0173] To verify the effect of the present application, blanks were cut from conventionally produced IF steel strips as samples RF (reference), ZW1, ZW2 and ZW3. In each case, the steel substrate was made of a commercially available steel of the grade M3A33, the composition of which is reported in Table 1.

[0174] Table 1

[0175]

[0176] balance is iron and unavoidable impurities,

[0177] The reported amounts are in weight %.

[0178] The steel strip sampled had a Zn-Al-Mg coating ("ZM coating") which was applied to its surface by hot dipping in a conventional manner and consisted of 1.6 wt% Al, 1.2 wt% Mg, the balance Zn and unavoidable impurities.

[0179] For further experiments, blanks were cut from this ZM-coated steel strip and further processed on a pilot-plant scale.

[0180] After hot dipping, the blanks were surface-coated with the respective dispersions using a chemical coater, as follows:

[0181] RF: ZM, without interlayer, without further treatment;

[0182] ZW1 : ZM + interlayer, applied as aqueous dispersion containing an organosilicon compound with a Si element content of 0.1 wt%;

[0183] ZW2: ZM + interlayer, applied as aqueous dispersion containing an organosilicon compound with a Si element content of 0.1 wt% + 0.1 wt% of activated particles (containing spherical zinc oxide nanoparticles and tri-zinc di-n-ortho-phosphate) + 0.5 wt% of polyurethane thickener Agocel AC 6240;

[0184] ZW3: ZM + interlayer, applied as aqueous dispersion containing an organosilicon compound with a Si element content of 0.1 wt% + 0.1 wt% of activated particles (containing spherical zinc oxide nanoparticles and tri-zinc di-n-ortho-phosphate) + 5 wt% of polyurethane thickener Agocel AC 6240;

[0185] The blanks were oiled using a roll coater with ANTICORIT PL 3802 39 S.

[0186] 2. CuSO4 test:

[0187] The blanks were deoiled or degreased with gasoline or n-heptane and immersed in a solution of 5 wt% CuS04solution for about 6 seconds. They were then rinsed in DM (deionized) water with gentle swirling and visually inspected.

[0188] None of the samples provided with an interlayer (ZW1, ZW2, ZW3) showed the dark, darkly colored precipitates typical of untreated surfaces, while on the reference RF the bright-dark contrast in the form of a string of pearls or worm-like structures was clearly visible.

[0189] 3. Phosphatization:

[0190] The blanks (RF, ZW1, ZW2 and ZW3) with the respective coating described above were stored for four weeks (65°C and 70% atmospheric humidity). Phosphating was carried out on pilot scale according to a process to obtain an approach to the OEM result:

[0191] - degreasing using Gardoclean S 5176;

[0192] - rinsing using deionized water;

[0193] - activation using Gardolene ZL 6 (Chemetall);

[0194] - wet-on-wet phosphating using Gardobond 24 T (Chemetall).

[0195] 4. Analysis of the phosphatized layer:

[0196] Visual analysis was carried out using a reflected light microscope. The results are summarized in Table 2.

[0197] Table 2

[0198]

[0199] The evaluation was based on the following criteria:

[0200] Table 3

[0201]

[0202] The crystal arrangement (A) and the crystal diameter (B) were determined optically under a reflected light microscope at a magnification of 1000x. In order to determine the closure of the phosphating layer, i.e. the pore size (C) and the number of pores (D), an area of about 300 pm x 300 pm was examined at a magnification of 200x. The weighted evaluation was carried out according to the following formula:

[0203] Total = 0.5 x A + 1 x B + 1.5 x (C+D)

[0204] The results show that the metal sheet according to the application achieves the stated object, in particular provides excellent temporary corrosion protection, thus enabling homogeneous, spot-free phosphating.

Claims

1. A hot-dip galvanized and flat-rolled steel sheet, comprising a steel substrate and a flat-rolled metal coating, said metal coating being disposed on one or both sides of said steel substrate, and containing not only zinc and unavoidable impurities, but also aluminum in a content of 0.5 wt% to 8.0 wt% and magnesium in a content of 0.5 wt% to 8.0 wt%, characterized in that, The metal coating includes a double-layer temporary corrosion protection layer.

2. The steel plate according to claim 1, characterized in that, It has a Cr-free double-layer temporary corrosion protection layer.

3. The steel plate according to any one of the preceding claims, characterized in that, The double-layer temporary corrosion protection layer includes an intermediate layer as the first layer and a second layer containing or composed of corrosion protection oil disposed above the first layer.

4. The steel plate according to claim 3, characterized in that, The intermediate layer contains an organosilicon compound.

5. The steel plate according to claim 3 or 4, characterized in that, The Si coating weight of the intermediate layer is at least 0.5 mg / m³. 2 And at most 20 mg / m 2 .

6. The steel plate according to any one of claims 3 to 5, characterized in that, The intermediate layer contains rheology additives.

7. The steel plate according to any one of claims 3 to 6, characterized in that, The intermediate layer contains an organosilicon compound, one or more compounds selected from the group consisting of: silanes, silanols, siloxanes, alkoxysilanes, derivatives of silanes, silanols, siloxanes and / or alkoxysilanes, and polymers and derivatives thereof.

8. The steel plate according to any one of claims 3 to 7, characterized in that, The intermediate layer contains activated particles.

9. The steel plate according to any one of claims 3 to 8, characterized in that, The second layer disposed on the intermediate layer contains or is composed of mineral oil.

10. The steel plate according to any one of the preceding claims, characterized in that, The steel substrate comprises an alloy containing or composed of the following elements, in weight percent: C: 0.0003% to 0.250%; Si: 0.0005% to 0.70%; Mn: 0.0005% to 2.0%; P: Maximum 0.15%; S: Maximum 0.050%; N: Maximum 0.10%; Al: 0.0050% to 1.50%; Optionally, one or more of the following elements: Nb: Maximum 0.20%, Ti: 0.20%; V: 0.0050 to 0.10%; B: Maximum 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: Maximum 0.10%, The balance consists of iron and unavoidable impurities.

11. A method for manufacturing a hot-dip galvanized and flat-rolled steel sheet according to any one of claims 1 to 10, comprising the following steps: a) Provide steel plates as steel substrates. b) A hot-dip galvanized metal coating is applied to one or both sides of the steel substrate. The metal coating contains not only zinc and unavoidable impurities, but also other elements, such as aluminum at a content of 0.5% to 8.0% by weight and magnesium at a content of 0.5% to 8.0% by weight. c) The hot-dip galvanized steel sheet from step b is leveled and rolled. d) Apply the first intermediate layer to the steel plate from step c. e) Apply a second corrosion protection layer.

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

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

14. Use of the steel plate according to any one of claims 1 to 10 or the steel plate manufactured according to any one of claims 11 or 12 for the manufacture of spot-free phosphated steel plates.

15. A method for manufacturing spot-free phosphated steel sheet, comprising the following steps: - To manufacture the steel plate according to any one of claims 1 to 10 or the steel plate manufactured according to any one of claims 11 to 13. - Clean the steel plate, and - Phosphate the cleaned steel sheet.

16. The method according to claim 14, characterized in that, After cleaning, apply an activation layer.

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