Process for temper-passing a steel strip coated with a zm coating

Abstract

The invention relates to a process for temper-passing a steel strip according to claim 1 which has been coated with a ZM coating.

Description

[0001] Method for tempering a steel strip coated with a ZM coating

[0002] The invention relates to a method for skin-passing a steel strip coated with a ZM coating, the method comprising the following steps:

[0003] - Providing a steel band;

[0004] - hot-dip coating the steel strip with a zinc-based coating to produce a hot-dip coated steel strip, wherein the steel strip passes through a molten bath comprising aluminum between 0.5 and 8.0 wt.% and magnesium between 0.5 and 8.0 wt.%, the remainder being zinc and unavoidable impurities;

[0005] - Cooling the hot-dip coated steel strip to solidify the coating on the steel substrate after leaving the molten bath;

[0006] - Tempering the hot-dip coated steel strip with a specific tempering force sW, whereby the steel strip has a yield strength Re and a tensile strength R m has.

[0007] To ensure effective corrosion protection for cold-forming steels in the automotive sector, steel substrates (Z strips) are traditionally coated with a Zn-based hot-dip coating. This provides active corrosion protection, meaning that the comparatively less noble Zn coating is sacrificed for the more noble steel substrate. In addition to traditional hot-dip galvanizing (Z), zinc-magnesium-aluminum hot-dip coatings, or "ZM" for short, are playing an increasingly important role. These offer advantages over traditional hot-dip zinc in terms of corrosion resistance and cold formability. However, under unfavorable conditions, a ZM surface after storage and subsequent phosphating can lead to problems during further processing.

[0008] The focus is particularly on improving the adhesive properties of cement coatings. The object of the present invention is also to ensure problem-free processing of cement surfaces. At the same time, in a world with limited resources, the efficient use of energy and materials is becoming increasingly important. Another key object of the invention is therefore to ensure further processing that is resource-efficient and safe. Safety here refers to human health and environmental compatibility. Therefore, not only in the product or the intermediate products, but also during the individual process steps, no additional hazardous substances should be used compared to the state of the art. For resource-saving production and further processing, no additional process steps should be introduced compared to the state of the art.

[0009] EP 3 416 760 B1 discloses that typical specific rolling forces during skin passing are in the range of 1.9 kN / mm.

[0010] The inventors have surprisingly found that improved adhesive properties of ZM coatings are achieved when the ZM coating applied in the melt bath is cooled to a temperature of 340 °C with an average cooling rate of between 5 and 40 K / s and the following conditions are met during skin passing:

[0011] 0.80 <= sW * R m 0 ' 3 <= 1.20 [10 4 ' 2 *No.' 7 *m 0 ' 4 ] and 0.850 <= sW * R e 0 ' 3 <= 1 .20 [10 4 ' 2 *No.' 7 *m-0.4]

[0012] After hot-dip coating, which preferably comprises stripping off the excess molten coating and thus adjusting the coating thickness, the coated steel strip is cooled, in particular to a temperature below 100°C, preferably to room temperature. Phase formation in the coating essentially occurs during the hot-dip coating and cooling process, at molten bath temperatures of approximately 460°C + / - 15°C until cooling to approximately 340°C. At 340°C, diffusion essentially stops due to the solidification of the coating. It is advantageous to stop the diffusion processes as quickly as possible after hot-dip coating by setting an average cooling rate up to 340°C of at least 3 K / s, in particular at least 5 K / s, preferably at least 10 K / s, and more preferably at least 15 K / s. Depending on the composition of the melt pool, cooling begins when the coating is stripped off, thus beginning the solidification of the coating.When a temperature of approximately 340 °C is reached, it is assumed that the coating has reached its end of solidification. The average cooling rate is preferably a maximum of 40 K / s, in particular a maximum of 35 K / s. This temperature corresponds essentially to a temperature measured at the surface of the coating, for example, using a pyrometer. The method for measuring surface temperatures is well known among experts.

[0013] Through skin-passing, a surface structure is imprinted into the hot-dip coated steel sheet, which can, for example, be a deterministic surface structure. A deterministic surface structure refers, in particular, to regularly recurring surface structures that have a defined shape and / or design or dimension. This also includes, in particular, surface structures with a (quasi-)stochastic appearance, which are composed of stochastic form elements with a recurring structure. Alternatively and preferably, the introduction of a stochastic surface structure is also conceivable.

[0014] The skin-passing of the ZM coating is accompanied by a specific skin-pass force, abbreviated as sW, which corresponds to the skin-pass force in kN per width of the steel strip to be skin-passed in mm. The optimal specific skin-pass force is not selected to be too high in order to avoid unnecessary wear on the skin-pass rolls and the resulting increased energy consumption for generating a technically unnecessary high skin-pass force. A key challenge in calibrating an optimal specific skin-pass force is that ZM coatings are used on different steel strips. The minimum necessary skin-pass force, which can produce a surface with improved adhesive properties, depends heavily on the strength of the steel strip.It has been shown that for steel strips with particularly high strength, good adhesion of the cement mortar coating can be achieved even with a lower skin-pass force, whereas for softer steel strips, a higher skin-pass force is required. To account for this, mechanical parameters such as the yield strength R must be considered. e and the tensile strength R m of the steel strip must be taken into consideration. The mechanical properties mentioned are determined, for example, by a tensile test on longitudinal specimens at room temperature according to DIN EN ISO 6892-1, Method B. Yield and tensile strength are given in MPa. The yield strength is also referred to as the proof strength.

[0015] Thus, the conditions are 0.80 <= sW * R m 03 <= 1.20 and 0.850 <= sW * R e 0 3 <= 1.20 during dressing. The unit of measurement of the expression sW * R m 03 and sW * R e 03corresponds to 10 4 ' 2 *No.' 7 *m-°' 4 .

[0016] The steel strip can be a hot-rolled steel strip or a cold-rolled steel strip or can be made from a hot-rolled steel strip or a cold-rolled steel strip.

[0017] Cold-rolled steels according to DIN EN 10346 are preferred, such as multi-phase, IF, BH, or micro-alloyed steels. Multi-phase steels are used in the automotive sector for bodywork. Examples of steels of this type are available under the standard designations HCT490X, HCT590X, or HCT780X.

[0018] 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.

[0019] BH steel is 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 exterior body applications. Steels of this type are available under the standard designations HX180BD, HX220BD, HX260BD, and HX300BD.

[0020] Micro-alloyed steel is used in the automotive sector to make body components. Micro-alloyed steel exhibits a fine-grained microstructure, giving it high fatigue strength and a high yield strength. It is primarily used for complex deep-drawn parts in automotive construction. Examples of steels of this type are available under the standard designations HC260LA, HC300LA, HC340LA, HC380LA, HC420LA, HC460LA, HC500LA, and HC550LA.

[0021] Furthermore, hot-rolled strips according to DIN EN 10149-2 or DIN EN 10025-2 can also be considered.

[0022] Lightly or unalloyed iron usually has a pronounced yield strength ReH. With a pronounced yield strength, once a certain stress is exceeded, the so-called yield point effect occurs. The material continues to expand without an increase in stress. This results in a stress drop above which plastic deformation begins. This yield point effect is due to the Cottrell effect. Because of the stress drop during the yield point effect, an upper and a lower yield point can be determined. Steel, characterized as an iron alloy with chromium, manganese, etc. admixture, displays finer crystal structures than lightly or unalloyed iron. Therefore, the yield point cannot be measured unambiguously in a tensile test. There is a continuous transition between the elastic and plastic ranges of the steel and the steel does not display a pronounced yield point ReH.The limit is therefore not clearly identifiable, and the yield strengths must be assumed. An example of an assumed limit is the yield strength of 0.2%. For technical materials such as steel, the yield strength Rp0.2% is generally determined as a substitute for the non-existent yield strength ReH, and this is also the case for the purposes of the invention. Unlike the yield strength, the 0.2% yield strength can always be clearly determined from the stress-strain diagram. In the present invention, this yield strength of 0.2% is referred to and used as the yield strength Re.

[0023] The thickness of the steel strip is, for example, 0.3 to 6.0 mm, in particular 0.5 to 5.0 mm, preferably 0.7 to 4.0 mm.

[0024] In order to further reduce unnecessary wear and energy consumption, the dressing process should preferably be carried out in such a way that the following conditions are met [10 4 ' 2 *No.' 7 *m 0 '4 ]: in particular 0.80 <= sW * R m 0 3 <= 1.150 and 0.850 <= sW * R e 0 3 <= 1.150; preferably 0.80 <= sW * R m 0 3 <= 1.10 and 0.850 <= sW * R e 0 3 <= 1.10; preferably 0.80 <= sW * R m 03 <= 1.050 and 0.850 <= sW * R e 03 <= 1.050; particularly preferred 0.80 <= sW * R m 03 <= 1.0 and 0.850 <= sW * R e 0 3 <= 1.0; more preferably 0.80 <= sW * R m 03 <= 0.950 and 0.850 <= sW * R e 0 3 <= 1.0.

[0025] 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 in individual or cumulative 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, for example up to 3 wt.%, particularly due to the formation of the Fe2Al6 boundary layer. The remainder is zinc.Steel sheets cut 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 wt.%, particularly preferably 5.0 wt.%, in particular at most 4.0 wt.% and an aluminum content of at most 8.0 wt.%, preferably at most 7 wt.%, particularly preferably 5.0 wt.%, in particular at most 4.0 wt.%.

[0026] In particular, to set a predetermined thickness of the cement 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 stripped off. After leaving the molten bath, the steel strip coated with the liquid melt is passed through a stripping device having means, for example nozzles, in particular slot nozzles, which act on both sides of the steel strip with a gaseous stripping medium to strip off the liquid melt. The thickness of the cement coating can be set, in particular, between at least 4 pm, preferably at least 5 pm, and a maximum of 58 pm, preferably a maximum of 55 pm.In a particular embodiment, the thickness of the cementitious metal coating is at least 1.0 pm, in particular at least 2 pm, preferably at least 3 pm, more preferably at least 5 pm and at most 25 pm, in particular at most 20 pm and preferably at most 15 pm, more preferably at most 10 pm. Below the minimum limits, adequate cathodic corrosion protection cannot be guaranteed, and above the maximum limit, joining problems can arise when connecting a steel sheet cut from the steel strip produced according to the invention or a component made therefrom to another component. In particular, if the specified maximum limit for the thickness of the cementitious metal coating is exceeded, a stable process cannot be ensured during thermal joining or welding.

[0027] According to one embodiment, the hot-dip coated steel strip, skin-passed under the aforementioned conditions, can be wetted with an aqueous cleaning solution. An acidic or alkaline solution can be used as the aqueous cleaning solution. The surface of the hot-dip coated steel strip can be wetted with an aqueous cleaning solution for a time of 1 to 60 s, in particular between 2 and 50 s, preferably between 3 and 40 s, more preferably between 3 and 30 s, and at a temperature of 15 to 80°C, in particular between 20 and 80°C, preferably between 30 and 80°C, more preferably between 40 and 80°C. Wetting with an aqueous cleaning solution can be terminated by rinsing with water and / or an aqueous solution.

[0028] According to one embodiment, the hot-dip coated steel strip, which has been tempered under the conditions specified above and optionally cleaned, can be conditioned with an aqueous solution of an inorganic acid. The aqueous solution of an inorganic acid has a pH of less than 7, in particular less than 6, preferably less than 5, and more preferably less than 4. The pH can be at least 0.5, in particular at least 1.0, preferably at least 1.5. An inorganic acid is selected from the group containing or consisting of: H2SO4, HCl, HNO3, H3PO4, H2SO3, HNO2, HF, or a mixture of two or more of these acids is used as an aqueous solution. The determination of the pH is known.

[0029] The surface of the hot-dip coated material can be wetted with an aqueous solution of an inorganic acid for a time of 0.1 to 5 s and at a temperature of 10°C to 90°C. The coating is wetted with an aqueous solution of an inorganic acid for a time of at least 0.1 s, in particular at least 0.2 s, preferably at least 0.3 s, 0.4 s, more preferably at least 0.5 s, and a maximum of 5 s, in particular a maximum of 4 s, preferably a maximum of 3 s, 2 s, 1.8 s, more preferably a maximum of 1.5 s, 1.2 s, or 1.0 s. The coating is wetted with an aqueous solution of an inorganic acid at a temperature of 10 °C to 90 °C, in particular 20 °C to 70 °C, preferably 20 °C to 50 °C, more preferably 20 °C to 40 °C, particularly preferably 20 °C to 30 °C.

[0030] The wetting can be terminated by rinsing with water and / or an aqueous solution. For this purpose, the wetting with an aqueous solution of an inorganic acid is interrupted by rinsing with water and / or an alcohol, for example selected from the group containing or consisting of methanol, ethanol, propanol, isopropanol, ethanol, in particular isopropanol, or an aqueous solution. In one alternative, the rinsing takes place in two sub-steps: in a first sub-step with water; in a second sub-step with an alcohol or an aqueous solution of an alcohol as specified above. In another alternative, the rinsing with water and an alcohol takes place in one step, preferably as a mixture of water with one of the alcohols specified above. Rinsing is preferably carried out continuously, wherein in particular a method selected from the group consisting of spraying, atomizing, dipping, and application (coil coating method) can be used.Preferably, after wetting by rinsing, drying is carried out, whereby the “rinsed” coating is preferably dried by increasing the temperature (up to a maximum of 100 °C) or by a fan.

[0031] Alternatively, the rinsed coating is air-dried, for example without any additional aids.

[0032] According to one embodiment, the hot-dip coated steel strip, which has been tempered under the conditions specified above, and optionally cleaned and / or conditioned, can be wetted with an aqueous activating solution. The aqueous activating solution can contain or consist of: 0.8 to 1.5 g / l of a titanium salt, which is selected in particular from the group consisting of titanium dioxide, potassium titanium fluoride, dipotassium hexafluorotitanate, titanyl sulfate, titanium tetrachloride, titanium tetrafluoride, titanium trichloride, titanium hydroxide, titanium nitrite, titanium nitrate, potassium titanium oxidoxalate, and titanium carbide; the remainder being water and unavoidable impurities.

[0033] Alternatively or additionally, an aqueous activating solution can contain or consist of: at least one compound from the group oxalic acid, nickel phosphate, manganese phosphate, calcium phosphate, iron phosphate, aluminum phosphate, cobalt (III) phosphate, copper, copper sulfate, copper nitrate, copper chloride, copper carbonate, copper oxide, silver, cobalt, nickel, Jernstedt salt, lead acetate, tin (tetra)chloride, arsenic oxide, zirconium chloride, zirconium sulfate, zirconium, iron, lithium, Zn3(PO4)2, Zn2Fe(PO4)2, Zn2Ni(PO4)2, Zn2Mn(PO4)2, Zn2Ca(PO4)2.

[0034] The surface of the hot-dip coated steel strip can be wetted with an aqueous activating solution for a time of 1 to 60 s, in particular between 2 and 50 s, preferably between 3 and 40 s, preferably between 3 and 30 s, and at a temperature of 15 to 80 °C, in particular from 20 to 80 °C, preferably from 30 to 80 °C, preferably from 40 to 80 °C.

[0035] Alternatively, activation can be omitted, thus saving a step in the overall process and thus, according to a preferred embodiment, the surface of the hot-dip coated steel strip is not wetted with an aqueous activation solution. According to a further embodiment, the hot-dip coated steel strip, which has been skin-tested under the conditions specified above, is oiled. The oil is preferably applied to provide temporary corrosion protection.

[0036] In a further alternative embodiment, a service can take place after each of the above-mentioned steps: after wetting with the aqueous cleaning solution and optionally rinsing, after conditioning with an inorganic acid and termination of the conditioning by rinsing and optionally drying, and / or activation.

[0037] In the following, specific embodiments of the invention are explained in more detail.

[0038] Four different steel strips, each 1.0 mm thick, were coated with a cemented metal (ZM) coating. They were passed through a melt containing 1.6 wt.% Al, 1.2 wt.% Mg, the remainder Zn, and unavoidable impurities. Stripping took place in an air atmosphere, and the stripping gas used was a nitrogen-air mixture with a volume ratio of 30:70. An average cooling rate of 24 K / s was selected up to 340 °C. The thickness of the cemented metal (ZM) coating for all coated steel strips was 12 μm per side in the solidified state.

[0039] Subsequently, all four steel strips were skin-passed using EDT skin-pass rolls with a stochastic surface texture. The specific skin-pass force sW was varied for each steel strip during the skin-passing process to evaluate the influence of the skin-pass force.

[0040] Several samples were cut from different sections of the steel strips, in which different specific tempering forces were applied.

[0041] Samples I consisted of a steel material with the composition in wt.%:

[0042] C: 0.0025%;

[0043] Si: 0.018%;

[0044] Mn: 0.145%;

[0045] P: 0.01%;

[0046] S: 0.01%;

[0047] Al: 0.038%; Cr: 0.037%;

[0048] Cu: 0.033%;

[0049] Mo: 0.009%;

[0050] N: 0.004%;

[0051] Ni: 0.01%;

[0052] Nb: 0.0045%;

[0053] Ti: 0.082%;

[0054] V: 0.004%;

[0055] Sn: 0.01%;

[0056] Rest Fe and unavoidable impurities, with R e = 150 MPa and R m = 300 MPa.

[0057] Samples II consisted of a steel material with the composition in wt.%:

[0058] C: 0.0022%;

[0059] Si: 0.018%;

[0060] Mn: 0.23%;

[0061] P: 0.01%;

[0062] S: 0.01%;

[0063] AI: 0.05%;

[0064] Cr: 0.04%;

[0065] Cu: 0.05%;

[0066] Mo: 0.0087%;

[0067] N: 0.001%;

[0068] Ni: 0.02%;

[0069] Nb: 0.0028%;

[0070] Ti: 0.001%;

[0071] V: 0.002%;

[0072] Sn: 0.0098%;

[0073] Ca: 0.002%;

[0074] Rest Fe and unavoidable impurities, with R e = 210 MPa and R m = 330 MPa.

[0075] Samples III consisted of a steel material with the composition in wt.%:

[0076] C: 0.062%;

[0077] Si: 0.21%; Mn: 0.77%;

[0078] P: 0.01%;

[0079] S: 0.01%;

[0080] AI: 0.03%;

[0081] Cr: 0.11%;

[0082] Cu: 0.1%;

[0083] Mo: 0.02%;

[0084] N: 0.003%;

[0085] Ni: 0.12%;

[0086] Nb: 0.021%;

[0087] Ti: 0.005%;

[0088] V: 0.005%;

[0089] B: 0.0006%;

[0090] Rest Fe and unavoidable impurities, with R e = 380 MPa and R m = 470 MPa.

[0091] Samples IV consisted of a steel material with the composition in wt%:

[0092] C: 0.07%;

[0093] Si: 0.02%;

[0094] Mn: 0.02%;

[0095] P: 0.01%;

[0096] S: 0.01%;

[0097] AI: 0.05%;

[0098] Cr: 0.01%;

[0099] Cu: 0.01%;

[0100] Mo: 0.01%;

[0101] N: 0.003%;

[0102] Ni: 0.01%;

[0103] Nb: 0.001%;

[0104] Ti: 0.002%;

[0105] V: 0.002%;

[0106] Sn: 0.01%;

[0107] Ca: 0.002%;

[0108] Rest Fe and unavoidable impurities, with R e = 270 MPa and R m = 380 MPa. Before testing, samples I to IV were treated as follows:

[0109] - Cleaning by immersion in an aqueous cleaning solution, Ridoline 124 N with a concentration of 12 ml / l, the remainder being water and unavoidable impurities, pH = 1; and a temperature of 55 °C, wetting time 5 s;

[0110] - Rinse with demineralized water by immersion at a temperature of 20 °C, wetting time 5 s.

[0111] Adhesive tests were conducted on samples I to IV, which were subjected to different skin-pass forces and subsequently cleaned, using the adhesive Sikapower 492. The fracture behavior was evaluated according to DIN EN ISO 10365. A distinction is made between three types of fracture:

[0112] - cohesive failure: the fracture occurs in the adhesive;

[0113] - adhesive failure: the fracture occurs at the interface between the surface / oxide layer and the adhesive; and

[0114] - special cohesive failure near the substrate: the failure occurs in the adhesive near the interface between the surface / oxide layer and the adhesive.

[0115] The higher the proportion of cohesive failure, the higher the proportion of adhesive bonds that meet the practical requirements. The adhesive bond should fail in the area of ​​the adhesive itself, not at the interface between the surface of the respective component and the adhesive.

[0116] The results of the tests on the adhesive behavior and the specific skin-pass forces used to skin-pass the individual sections from which the samples were cut are summarized in Table 1. The number 0 indicates the results determined for samples in their initial state. The other results, which were determined for samples that underwent a climate change test in 40, 60 and 90 cycles according to DIN EN ISO 11997-B, are marked 40, 60 and 90. Furthermore, the determined fracture fractions adhesive, cohesive and cohesive near interface (ad / ko / koG) are given in %; the total does not necessarily reach 100%, since possible further fracture fractions may occur, for example in small proportions.

[0117]

[0118] Table 1

[0119] The aim is to improve the fracture pattern so that cohesive failure increases so that suitability for bonding can be ensured.

Claims

Patent claims 1. A method for temper rolling a steel strip coated with a ZM coating, the method comprising the following steps: - Providing a steel band; - hot-dip coating the steel strip with a zinc-based coating to produce a hot-dip coated steel strip, wherein the steel strip passes through a molten bath comprising aluminum between 0.5 and 8.0 wt.% and magnesium between 0.5 and 8.0 wt.%, the remainder being zinc and unavoidable impurities, - Cooling the hot-dip coated steel strip to solidify the coating on the steel strip after leaving the molten bath, - Tempering of the hot-dip coated steel strip with a specific tempering force sW [kN / mm], whereby the steel strip has a yield strength R e [MPa] and a tensile strength R m[MPa], characterized in that the cooling of the ZM coating applied in the melt bath is carried out up to a temperature of 340 °C with a cooling rate between 3 and 40 K / s and that the following conditions are met during skin passing: 0.80 <= sW * R m -0 ' 3 <= 1.20 [10 4 ' 2 *N 0 ' 7 *m _0 ' 4 ] and 0.850 <= sW * R e -°' 3 <= 1.20 [10 4 ' 2 *No.' 7 *m-0.4] 2. Method according to claim 1, wherein the following conditions are met during the tempering: 0.80 <= sW * R m -0 ' 3 <= 0.950 [10 4 ' 2 *No.' 7 *m 0 ' 4 ] and 0.850 <= sW * R e 0 ' 3 <= 1.0 [10 4 ' 2 *N 0 ' 7 *m _0 ' 4 ].

3. A process according to any one of the preceding claims, wherein the molten bath comprises Al and Mg in an amount of at least 0.8% by weight each.

4. A process according to any one of the preceding claims, wherein the molten bath comprises Al and Mg in an amount of at least 1.0% by weight each.

5. Method according to one of the preceding claims, wherein a predetermined thickness of the ZM coating in the solid state is set between 2 and 60 pm per side.

6. Method according to one of the preceding claims, wherein the hot-dip coated steel strip is wetted with an aqueous cleaning solution.

7. A method according to any one of the preceding claims, wherein the hot-dip coated steel strip is conditioned with an aqueous solution of an inorganic acid.

8. A method according to any one of the preceding claims, wherein the hot-dip coated steel strip is wetted with an aqueous activating solution.

9. Method according to one of the preceding claims, the steel strip is a hot-rolled strip according to DIN EN 10149-2 or DIN EN 10025-2.

10. Method according to one of claims 1 to 8, wherein the steel strip is a cold-rolled strip according to DIN EN 10346.

Images