WO2024188967A1

WO2024188967A1 - Process for temper-passing a steel strip coated with a zm coating

Info

Publication number: WO2024188967A1
Application number: PCT/EP2024/056425
Authority: WO
Inventors: Niloofar JAFARIAN SURAKI; Stefan BIENHOLZ; Sebastian STILLE
Original assignee: Thyssenkrupp Steel Europe Ag
Priority date: 2023-03-14
Filing date: 2024-03-11
Publication date: 2024-09-19
Also published as: DE102023106292A1

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

Process for skin passing a steel strip coated with a ZM coating

The invention relates to a method for skin passing 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 aluminium 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 substrate after it leaves the molten bath;

- Skin passing of the hot-dip coated steel strip with a specific skin passing force sW, whereby the steel strip has a yield strength R _e and a tensile strength R _m .

In order to ensure effective corrosion protection for cold-forming steels in the automotive sector, steel substratesZ strips are traditionally provided with a Zn-based hot-dip coating. This offers active corrosion protection, i.e. the comparatively base Zn coating is sacrificed for the more noble steel substrate. In addition to classic hot-dip galvanizing "Z", zinc-magnesium-aluminium hot-dip coatings, known as "ZM" for short, are playing an increasingly important role. These offer advantages over classic hot-dip zinc in terms of corrosion behavior and cold formability. However, a ZM surface can lead to problems during further processing under unfavorable conditions after storage and subsequent phosphating.

The focus is in particular on providing better adhesive properties for ZM coatings. The aim of the present invention is also to ensure problem-free processing of ZM surfaces. At the same time, in a world with limited resources, efficient use of energy and material is becoming increasingly important. The other essential aim of the invention is therefore to ensure further processing in a resource-saving and safe manner. Safety here refers to human health and environmental compatibility. Therefore, no additional hazardous substances should be used compared to the state of the art, not only in the product or the intermediate products, but also during the individual process steps. For resource-saving production and In further processing, no additional process steps should be introduced compared to the state of the art.

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

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

0.80 <= sW * R _m ⁰ ' ³ <= 1.20 [10 ⁴ ' ² *N°' ⁷ *m ⁰ ' ⁴ ] and 0.850 <= sW * R _e ⁰ ' ³ <= 1 .20 [10 ⁴ ' ² *N°' ⁷ *m- 0.4]

After hot-dip coating, which preferably includes stripping off the excess hot-dip 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. The phase formation in the coating essentially takes place during hot-dip coating and cooling, at temperatures of the melt bath of around 460 °C +/- 15 °C until cooling to approx. 340 °C. At 340 °C, the 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, preferably at least 15 K/s. Depending on the composition of the melt pool, cooling begins when the coating is stripped off, and thus the coating begins to solidify. When a temperature of approx. 340 °C is reached, it is assumed that the end of the coating's solidification should have been reached. The average cooling rate is preferably a maximum of 40 K/s, in particular a maximum of 35 K/s. The temperature corresponds essentially to a temperature measured on the surface of the coating, for example using a pyrometer. The method of measuring the temperature on surfaces is familiar in specialist circles.

By means of the tempering process, a surface structure is embossed into the hot-dip coated steel sheet, which can be, for example, a deterministic surface structure. Deterministic surface structure refers in particular to regularly recurring surface structures that have a defined shape and/or design or dimension. In particular, this also includes 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.

The skin-passing of the ZM coating is accompanied by a specific skin-passing force, called sW for short, which corresponds to the skin-passing force in kN per width of the steel strip to be skin-passed in mm. The optimal specific skin-passing force is not chosen to be too high in order to avoid unnecessary technical wear on the skin-passing rollers and the resulting increased energy consumption to generate a high skin-passing force that is not technically necessary. A major challenge in calibrating an optimal specific skin-passing force is that ZM coatings are used on different steel strips. The minimum necessary skin-passing force, which can produce a surface with improved adhesive properties, depends heavily on the strength of the steel strip. It has been shown that with steel strips with particularly high strength, good adhesive properties of the ZM coating can be achieved even with a lower skin-passing force, while a higher skin-passing force is required for softer steel strips. In order to take this into account, mechanical parameters such as the yield strength R _e and the tensile strength R _m of the steel strip must be taken into account. The mechanical parameters mentioned are determined, for example, by a tensile test on longitudinal specimens at room temperature in accordance with DIN EN ISO 6892-1, method B. Yield strength and tensile strength are given in MPa. The yield strength is also referred to as the proof strength.

Thus, the conditions 0.80 <= sW * R _m ⁰³ <= 1.20 and 0.850 <= sW * R _e ^{0 3} <= 1.20 must be observed when dressing. The unit of measurement of the expression sW * R _m ⁰³ and sW * R _e ⁰³ corresponds to 10 ⁴ ' ² *N°' ⁷ *m-°' ⁴ .

The steel strip can be a hot-rolled strip (hot-rolled steel strip) or a cold-rolled strip (cold-rolled steel strip) or can be made from a hot-rolled strip or a cold-rolled strip.

Cold rolled strips according to DIN EN 10346 are preferred, such as multiphase, IF, BH or micro-alloyed steel. A multiphase steel is used in the automotive sector in the bodywork. Examples of steels of this type are available under the standard designation HCT490X, HCT590X or HCT780X.

An IF steel has no interstitially embedded alloying elements, i.e. no iron atoms are blocked by carbon or nitrogen atoms in the metal lattice. This creates a very soft steel with very good forming properties. It is used primarily for complicated deep-drawn parts in automobile construction. Steels of this type are available under the standard designations DX52D, DX53D, DX54D, DX55D, DX56D, DX57D HX160YD, HX180YD, HX220YD and HX260YD.

A BH steel is characterized by a significant increase in yield strength during paint baking (typically at 170 °C for 20 minutes) in combination with very good formability. Furthermore, these steels have very good dent resistance, which is why they are preferred for outer skin applications. Steels of this type are available under the standard designation HX180BD, HX220BD, HX260BD and HX300BD.

A micro-alloyed steel is processed into body components in the automotive sector. A micro-alloyed steel has a fine-grained microstructure and gives it high fatigue strength and a high yield strength. It is used primarily for complicated deep-drawn parts in automotive construction. Examples of steels of this type are available under the standard designation HC260LA, HC300LA, HC340LA, HC380LA, HC420LA, HC460LA, HC500LA and HC550LA.

Furthermore, hot-rolled strips according to DIN EN 10149-2 or DIN EN 10025-2 may also be considered.

Iron that is lightly alloyed or not alloyed usually has a pronounced yield strength ReH. With a pronounced yield strength, the so-called yield point effect occurs after a certain stress is exceeded. The material continues to expand without an increase in stress. This leads to a drop in stress, at which point plastic deformation begins. This yield point effect is based on the Cottrell effects. Due to the drop in stress 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, shows finer crystal structures than low-alloy or non-alloyed iron. Therefore, the yield strength cannot be clearly measured in a tensile test. There is a continuous transition between the elastic and plastic range of the steel and the steel does not show a pronounced yield strength 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 usually and also in the sense of the invention determined as a replacement for the existing yield strength ReH. In contrast to 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.

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.

In order to further reduce unnecessary wear and energy consumption, the dressing should preferably be carried out in such a way that the following conditions are satisfied [10 ⁴ ' ² *N°' 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 preferably 0.80 <= sW * R _m ⁰³ <= 1.0 and 0.850 <= sW * R _e ^{0 3} <= 1.0; further preferably 0.80 <= sW * R _m ⁰³ <= 0.950 and 0.850 <= sW * R _e ^{0 3} <= 1.0.

The ZM coating, applied in the hot-dip coating process, comprises a zinc alloy with, in addition to zinc (remainder) and unavoidable impurities, additional elements such as aluminum with a content of between 0.1 and 8.0 wt.% and magnesium with a content of 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 can be present as impurities in the melt bath in individual or cumulative 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.%. In an alternative, the concentration of Fe can be higher, for example up to 3% by weight, particularly due to the formation of the Fe ₂ Al ₆ boundary layer. The remainder is zinc. Steel sheets separated from steel strips or steel sheet components made from them with a zinc-based anti-corrosive coating have very good cathodic corrosion protection and have been used in automobile construction for years. If improved corrosion protection is required, the coating has a magnesium content of at least 0.8% by weight, in particular at least 1.0% by weight, preferably at least 1.1% by weight, and aluminum content of at least 0.8% by weight, in particular at least 1.0% by weight. The coating has magnesium with a content of maximum 8.0 wt.%, preferably maximum 7 wt.%, particularly preferably 5.0 wt.%, in particular maximum 4.0 wt.% and aluminum with a content of maximum 8.0 wt.%, preferably maximum 7 wt.%, particularly preferably 5.0 wt.%, in particular maximum 4.0 wt.%.

In particular, to set a predetermined thickness of the ZM coating, which in the solid state can be between 1 pm and 60 pm per side, the melt applied to the steel strip while it is still in the liquid state is stripped off by passing the steel strip coated with liquid melt through a stripping device after leaving the melt bath, which has 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 ZM 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 special embodiment, the thickness of the ZM coating is at least 1.0 pm, in particular at least 2 pm, preferably at least 3 pm, preferably at least 5 pm and a maximum of 25 pm, in particular a maximum of 20 pm and preferably a maximum of 15 pm, preferably a maximum of 10 pm. Below the minimum limits, sufficient cathodic corrosion protection cannot be guaranteed and above the maximum limit, joining problems can occur when connecting a steel sheet cut from the steel strip produced according to the invention or a component made from it to another component. In particular, if the specified maximum limit of the ZM coating thickness is exceeded, a stable process cannot be ensured during thermal joining or welding.

According to one embodiment, the hot-dip coated steel strip, which has been skin-finished 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 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, 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. The wetting can be terminated with an aqueous cleaning solution by rinsing with water and/or an aqueous solution.

According to one embodiment, the hot-dip coated steel strip, which has been skin-rolled 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, 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: H ₂ SO ₄ , HCl, HNO ₃ , H ₃ PO ₄ , H ₂ SO ₃ , HNO ₂ , HF, or a mixture of 2 or more of these acids is used as an aqueous solution. The determination of the pH is known.

The surface of the hot-dip coated material can be wetted with the 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, 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, preferably a maximum of 1.5 s, 1.2 s, 1.0 s. The wetting of the coating with an aqueous solution of an inorganic acid takes place 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.

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 an alternative, the rinsing takes place in 2 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 stated above. In another alternative, the rinsing with water and an alcohol takes place in one step, preferably as Mixture of water with one of the alcohols specified above. Rinsing is preferably carried out continuously, whereby in particular a method selected from the group or 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 blower.

In an alternative, the “rinsed” coating is air-dried, for example without any additional aids.

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 activation solution. The aqueous activation 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 titanium dioxide, potassium titanium fluoride, dipotassium hexafluorotitanate, titanyl sulfate, titanium tetrachloride, titanium tetrafluoride, titanium trichloride, titanium hydroxide, titanium nitrite, titanium nitrate, potassium titanium oxidoxalate, titanium carbide, the remainder being water and unavoidable impurities.

Alternatively or additionally, an aqueous activation 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, Zn ₃ (PO ₄ ) 2, Zn ₂ Fe(PO ₄ ) ₂ , Zn ₂ Ni(PO ₄ ) 2, Zn ₂ Mn(PO ₄ ) ₂ , Zn ₂ Ca(PO ₄ ) ₂ .

The surface of the hot-dip coated steel strip can be wetted with an aqueous activation 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.

Alternatively, activation can be omitted, which saves 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-rolled under the conditions specified above, is oiled. The oil is preferably applied to ensure temporary corrosion protection.

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, if necessary, rinsing, after conditioning with an inorganic acid and termination of the conditioning by rinsing and, if necessary, drying, and/or activation.

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

Four different steel strips, each with a thickness of 1.0 mm, were coated with a ZM coating by passing them through a melt containing 1.6 wt.% Al, 1.2 wt.% Mg, the remainder Zn and unavoidable impurities. Stripping was carried out in an air atmosphere and a nitrogen-air mixture with a volume ratio of 30:70 was used as the gaseous stripping gas, with an average cooling rate of 24 K/s being selected up to 340 °C. The thickness of the ZM coating on all coated steel strips was 12 pm per side in the solidified state.

Subsequently, all four steel strips were skin-passed using so-called EDT skin-pass rolls and a stochastic surface texture. The specific skin-pass force sW was varied for each steel strip during skin-passing in order to evaluate the influence of the skin-pass force.

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

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

C: 0.0025%;

Si: 0.018%;

Mn: 0.145%;

P: 0.01%;

S: 0.01%;

AIC: 0.038%; Cr: 0.037%;

Cu: 0.033%;

Mo: 0.009%;

N: 0.004%;

Ni: 0.01%;

Nb: 0.0045%;

Ti: 0.082%;

V: 0.004%;

Sn: 0.01%;

Balance Fe and unavoidable impurities, with R _e = 150 MPa and R _m = 300 MPa.

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

C: 0.0022%;

Si: 0.018%;

Mn: 0.23%;

P: 0.01%;

S: 0.01%;

A1: 0.05%;

Cr: 0.04%;

Cu: 0.05%;

Mo: 0.0087%;

N: 0.001%;

Ni: 0.02%;

NB: 0.0028%;

Ti: 0.001%;

V: 0.002%;

Sn: 0.0098%;

Ca: 0.002%;

Balance Fe and unavoidable impurities, with R _e = 210 MPa and R _m = 330 MPa.

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

C: 0.062%;

Si: 0.21%; Mn: 0.77%;

P: 0.01%;

S: 0.01%;

A1: 0.03%;

Cr: 0.11%;

Cu: 0.1%;

Mo: 0.02%;

N: 0.003%;

Ni: 0.12%;

NB: 0.021%;

Ti: 0.005%;

V: 0.005%;

B: 0.0006%;

Balance Fe and unavoidable impurities, with R _e = 380 MPa and R _m = 470 MPa.

Samples IV consisted of a steel material with the composition in wt.%:

C: 0.07%;

Si: 0.02%;

Mn: 0.02%;

P: 0.01%;

S: 0.01%;

A1: 0.05%;

Cr: 0.01%;

Cu: 0.01%;

Mo: 0.01%;

N: 0.003%;

Ni: 0.01%;

Nb: 0.001%;

Ti: 0.002%;

V: 0.002%;

Sn: 0.01%;

Ca: 0.002%;

Balance Fe and unavoidable impurities, with R _e = 270 MPa and R _m = 380 MPa. Before testing, samples I to IV were treated as follows:

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

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

Adhesive tests were carried out on samples I to IV, which were subjected to different skin-pass forces and subsequently cleaned, using the adhesive Sikapower 492. The fracture behaviour was assessed in accordance with DIN EN ISO 10365. A distinction is made between three types of fracture:

- cohesive failure: the failure occurs in the adhesive;

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

- special cohesive fracture close to the substrate: the fracture occurs in the adhesive near the interface between the surface/oxide layer and the adhesive.

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

The results of the tests of the adhesive behavior and the specific dressing forces with which the individual sections from which the samples were separated were dressed are summarized in Table 1. The value 0 indicates the results that were determined for samples in the initial state. The other results that 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 with 40, 60 and 90. Furthermore, the determined fracture fractions adhesive, cohesive and cohesive near the interface (ad/ko/koG) are given in %, which does not have to reach 100% in total, since possible further fracture fractions can occur, for example in small proportions.

Table 1

The aim is to improve the fracture pattern so that cohesive failure increases so that adhesive suitability can then be ensured.

Claims

Patent claims

1. A method for skin passing 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 aluminium 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 it has left the molten bath,

- Dressing the hot-dip coated steel strip with a specific dressing 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 dressing: 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 *N°' ⁷ *m- 0.4]

2. Method according to claim 1, wherein the following conditions are met during the skin passing: 0.80 <= sW * R _m ^-0 ' ³ <= 0.950 [10 ⁴ ' ² *N°' ⁷ *m ⁰ ' ⁴ ] and 0.850 <= sW * R _e ⁰ ' ³ <= 1.0 [10 ⁴ ' ² *N ⁰ ' ⁷ *m ^_0 ' ⁴ ].

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

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

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. Method according to 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 strip according to DIN EN 10346.