Method for applying a layer onto a flat steel product

Abstract

The invention relates to a method for applying a layer (10) onto a flat steel product (100) in that the flat steel product (100) coming from a furnace (14) is moved through a snout (12) and a subsequent zinc-aluminium alloy melt bath (11), wherein the snout (12) comprises an outer wall (120) which separates an interior of the snout (12) from its surroundings, wherein the flat steel product (100) is moved through said interior, and wherein an end region (121) of the outer wall (120) is submerged under a surface of the zinc alloy melt bath (11), wherein a protective gas is introduced into the snout (12) in such a manner that in the interior of the snout (12) directly above the surface of the zinc alloy melt bath (11), a gas mixture is set which has a dew point in a range between -80°C and -40°C, preferably between -75°C and -50°C.

Description

METHOD FOR APPLYING A COATING TO A FLAT STEEL PRODUCT TECHNICAL FIELD

[0001] The present invention relates to a method by which flat steel products can be coated with a layer based on zinc-aluminium (ZnAl) or zinc-aluminium-magnesium (ZnAlMg), e.g. as a protective coating. STATE OF THE ART

[0002] It is well known that flat steel products 100, such as steel strips or steel sheets, are provided with a ZnAl, ZnAlMg, or ZnAlFe coating to improve their corrosion resistance. In practice, this is usually done by introducing the flat steel product 100 from a furnace 14 into a molten zinc alloy bath 11 (hereinafter referred to as the bath), as indicated in Fig. 1 using an exemplary device 150. To produce ZnAlFe coatings, the steel strip coated with a ZnAlFe coating is additionally subjected to a thermal post-treatment, whereby the reaction of the coating with the steel base material leads to the formation of a ZnAlFe coating. To protect the flat steel product 100 from oxidation, it is typically introduced into the bath 11 on the inlet side E through a nozzle 12 with a protective gas atmosphere.In bath 11, the flat steel product 100 is deflected by at least one (zinc bath) roller 13 and moved upwards out of bath 11 on the exit side A. This. Continuously operating process is generally called hot-dip coating.

[0003] Hot-dip coating processes are known from the prior art, in which a protective gas is introduced into the nozzle. Typically, humidified N2 or HNX gas with a dew point of -30°C to -10°C is used. The relevant documents are listed below, and their contents are briefly described where relevant.

[0004] For example, US 2018 / 0105916 Al, filed in 2016, describes the hot-dip coating of sheets of two different steel types, each with a sheet thickness ranging from 0.6 mm to 1.2 mm and a sheet width ranging from 900 mm to 1250 mm. The sheet feed rate is 60 m / min to 100 m / min. Type A steel has the following chemical composition: C: 0.001 wt%, Si: 0.01 wt%, Mn: 0.1 wt%, P: 0.003 wt%, S: 0.005 wt%, and Al: 0.03 wt%, with the balance being Fe and incidental impurities, and has a tensile strength of 270 MPa. Type B steel has the following chemical composition: C: 0.12 wt%, Si: 1.0 wt%, Mn: 1.7 wt%, P: 0.006 wt%, S: 0.006 wt% and Al: 0.03 wt%, and a balance of Fe and incidental impurities and has a tensile strength of 780 MPa.A nitrogen-hydrogen mixture containing or free of water vapor is fed into the nozzle, with the dew point of the shielding gas being adjustable by the water vapor content. For both steel grades, it has been shown, in a dew point range of -40°C to -20°C, that oxide film-induced defects decrease with decreasing dew point, while ash-induced or zinc dust-induced defects increase. A dew point range of -33°C to -27°C provides favorable conditions for preventing both defects.

[0005] There are other examples where steel sheets with different compositions are coated with different alloys under different conditions. The choice of steel sheet material in combination with the coating has a significant influence on the parameters that must be set in the manufacturing process to avoid defects.

[0006] Patent EP 0 172 682 B1 filed by Armco Inc. in 1985 concerns the control of zinc vapor during the hot-dip coating of an iron-based metal strip. On the inlet side of the dip bath, an oxygen-reduced atmosphere containing a small amount of water vapor is provided in an enclosed area (comparable to nozzle 12 in Fig. 1). This small amount of water is intended to prevent the formation of zinc vapor on the surface of the dip bath. The dew point of the gas used at the inlet side is adjusted so that no zinc vapor should form.

[0007] In addition to pure corrosion protection, there are increasingly stringent requirements regarding the surface quality of zinc-coated flat steel products. The automotive industry, in particular, expects products that meet the highest surface requirements. However, providing homogeneous surfaces is no trivial task.

[0008] The main problems here are often surface defects in the coating, which result in visually different areas. These surface defects are recognizable as spots and can be caused by poor wetting of the flat steel product by the bath or by the ingress of slag between the flat steel product and the bath. Such surface defects are usually referred to as wetting defects (see Fig. 5), "fir tree" defects (see Fig. 7), marbling (see Fig. 6), or slag defects.

[0009] The challenge, therefore, is to develop a process for coating flat steel products that offers particularly durable and robust corrosion protection, while ensuring a surface of the protective coating that is particularly homogeneous and free of surface defects. The goal is a surface quality that meets the highest customer requirements.

[0010] In addition, this process should be as energy-efficient, cost-effective, simple and reproducible as possible. DESCRIPTION OF THE INVENTION

[0011] According to the invention, a continuous (hot-dip) process and a corresponding device are provided which allow a flat steel product to be provided with a metallic layer which can serve, for example, as a (protective) coating, said layer protecting the steel substrate of the flat steel product from external influences.

[0012] In a method according to the invention for applying a layer to a flat steel product, the flat steel product coming from a furnace is moved through a nozzle and a subsequent zinc alloy molten bath.

[0013] The flat steel product comprises a steel as described in the 2015 standard DIN EN 10346. However, steels that deviate slightly from this standard may also be used. For example, steels that meet the requirements of Table 1 below may be used: Residual iron and unavoidable impurities

[0014] The zinc alloy melt bath comprises a zinc alloy which essentially comprises: an aluminum content in a range between 0.05 wt% and 7.0 wt% and preferably between 0.1 wt% and 4.0 wt%, an optional magnesium content, in a range between 0.05 wt% and 4.0 wt% and preferably between 1.0 wt% and 3.0 wt%, and a remainder comprising zinc and optionally one or more elements selected from the group comprising Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce or Bi, wherein the content of each optional element is less than 0.1 wt%, and unavoidable impurities.

[0015] The zinc alloy melt bath has a bath temperature (TB) in a range between 420°C and 480°C, preferably between 440°C and 470°C, for ZnAl alloys, and a bath temperature in a range between 400°C and 480°C, preferably between 410°C and 460°C, for ZnAlMg alloys.

[0016] The nozzle comprises an outer wall that separates the interior of the nozzle from its surroundings. The steel flat product is moved through this interior. A lower end region of the outer wall is immersed below a surface of the zinc alloy molten bath. A dry protective gas, for example nitrogen N2, argon Ar, or an HNX gas, is introduced into the interior of the nozzle in such a way that a gas mixture is established directly above the surface of the zinc alloy molten bath. The gas mixture has a dew point in a range between -80°C and -40°C, preferably between -75°C and -50°C, or between -75°C and -55°C. The protective gas reduces or prevents the formation of oxides on the surface of the steel flat product and reduces the formation of an oxide film on the surface of the zinc alloy molten bath. The low dew point significantly reduces the formation of the oxide film on the bath surface, thereby significantly reducing surface defects.

[0017] The dew point describes the temperature at which water vapor begins to condense in a gas (here, a protective gas). Once the dew point temperature is reached, the gas can no longer absorb any additional water vapor, meaning it is saturated with water vapor.

[0018] The dew point can be determined using a thermal or capacitive dew point sensor.

[0019] Instead of directly determining the dew point, the moisture content of the shielding gas can be determined by measuring the volume fraction in ppm (also known as ppm V), from which the dew point can then be calculated. For this purpose, a measuring cell with a humidity sensor (e.g., a sensor that adsorbs the moisture in the gas and then electrolytically decomposes it) can be used.

[0020] Suitable humidity sensors include sensors based on the principle of absorption of electromagnetic waves (microwave absorption sensors) or sensors that detect a change in the dielectric constant (capacitive sensors). One example is a polymer sensor designed for measuring humidity in gases in the temperature range of interest here.

[0021] Humidity sensors of the following design or functionality can be used in all embodiments: mechanically operating measuring sensors based on the humidity-induced expansion or contraction of (usually organic) measuring elements; psychrometrically operating measuring sensors, which use two identical, highly accurate thermometers, along which the gas flow to be measured is guided at a defined speed; capacitive measuring sensors, which, for example, comprise a humidity-sensitive capacitor with two flat electrodes; Resistive measurement methods, in which, for example, the impedance of the alternating current resistance of a hygroscopic element is determined; spectrometric measurement methods, which, for example, measure the gaseous water content non-contact in the near or mid-infrared range (NIR or MIR).

[0022] The at least one sensor for determining the dew point or humidity can be arranged inside the nozzle or in a gas extraction system connected to it. Sensors in an area close to the surface of the bath produce measured values ​​that reflect the conditions prevailing at the surface as accurately as possible.

[0023] Sensors for monitoring the protective gas to be introduced can be arranged in the furnace, in an upper end of the nozzle directed towards the furnace or in a corresponding gas feed.

[0024] In addition to the gas sensors, temperature sensors can also be arranged directly next to them.

[0025] The gas used is a dry protective gas. The term "dry gas" refers to a protective gas with a dew point of approximately -70°C and below. This corresponds to a water vapor content of approximately 5 ppm and below. Thus, the dry gas has a very low residual moisture content (also called trace moisture) in a range that is typical for industrial gases. The dry gas used here can, for example, comply with the requirements of the "Specification for Industrial Nitrogen," British Standard BS 4366: 1993, for all versions. According to this standard, the water content of the gaseous dry nitrogen gas (cf. paragraph 8) is limited to a maximum of 10 / 10 6which corresponds to 1 ppm. Thus, in all embodiments, the drying gas should have a residual moisture content of less than 1 ppm and preferably less than 5 ppm.

[0026] The shielding gas can be introduced into the nozzle through an upper end area of ​​the outer wall, i.e., from the furnace. Alternatively or additionally, the introduction can occur through at least one gas inlet on the nozzle. To avoid condensation, the shielding gas can be preheated. Alternatively or additionally, the nozzle can be heated.

[0027] In one embodiment, the nozzle comprises at least one inner wall inside, which separates an inner region from an outer region of the nozzle, wherein the flat steel product is moved through the inner region of the nozzle, and wherein the protective gas is introduced into the inner region of the nozzle. This has the advantage of reducing the volume into which the protective gas is introduced. In addition, the dew point can be determined in a closer The area around the flat steel product can be adjusted more precisely and gas extraction from the nozzle can take place in a more distant area around the flat steel product, whereby the unwanted zinc vapor generated on the bath surface can be removed from the nozzle more efficiently than in the embodiment without an inner wall

[0028] In one embodiment, the shielding gas is introduced on both sides of the flat steel product. This allows for a uniform shielding gas composition on both sides of the flat steel product.

[0029] In one embodiment, the at least one inner wall is not immersed below the surface of the zinc alloy melt bath. This allows the shielding gas to flow from the inner region of the nozzle to the outer region of the nozzle in a region close to the bath. Alternatively, the inner wall can be at least partially immersed below the surface of the zinc alloy melt bath, in which case the inner wall has openings in a region above the surface of the zinc alloy melt bath through which the shielding gas can flow from the inner region of the nozzle to the outer region of the nozzle.

[0030] In one embodiment, a vertical distance between the surface of the zinc alloy melt bath and an end face of the at least one inner wall directed towards the zinc alloy melt bath is between 30 mm and 300 mm, preferably between 50 mm and 100 mm.

[0031] In one embodiment, an inner wall is provided on both sides of the flat steel product.

[0032] In one embodiment, a gas extraction system operates inside the nozzle in a suction area above the surface of the zinc alloy melt bath, whereby introduced protective gas and vapors rising from the zinc alloy melt bath are extracted.

[0033] In one embodiment, the gas extraction acts between the outer wall and the inner wall.

[0034] In one embodiment, the gas extraction works on both sides of the flat steel product.

[0035] In one embodiment, the belt speed (v) at which the steel flat product is moved through the zinc alloy melt bath, or at which the steel flat product is moved through the nozzle, is between 30 m / min and 220 m / min, preferably 30 m / min and 180 m / min.

[0036] In one embodiment, the layer to be applied meets at least one of the following conditions: A target surface area of ​​the layer per belt side, which is in the range of 20g / m 2 up to 300g / m 2 is preferably in the range 30g / m 2 up to 160g / m 2 ; A target thickness of the layer per strip side, which is in the range 3pm to 45pm, preferably in the range 4.5pm to 20pm.

[0037] In one embodiment, the protective gas is injected at a rate of 100Nm 3 / h up to 500Nm 3 / h, preferably 200Nm 3 / h up to 400Nm 3 / h introduced.

[0038] In one embodiment, the gas extraction has an extraction rate of 100Nm 3 / h up to 500Nm 3 / h, preferably 200Nm 3 / h up to 400Nm 3 / h on.

[0039] An apparatus for carrying out the method according to the invention for applying a layer to a flat steel product comprises a zinc alloy melt bath with an inlet side, an outlet side and a deflection in order to guide the flat steel product from the inlet side at a strip speed through the zinc alloy melt bath to the outlet side. The zinc alloy of the zinc alloy melt pool essentially comprises: an aluminum content in a range between 0.05 wt.% and 7.0 wt.% and preferably between 0.1 wt.% and 4.0 wt.%, an optional magnesium content in a range between 0.05 wt.% and 4.0 wt.% and preferably between 1.0 wt.% and 3.0 wt.%, and a remainder comprising zinc and optionally one or more elements selected from the group comprising Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce or Bi, wherein the content of each optional element is less than 0.1 wt.%, and unavoidable impurities.

[0040] This device is designed or configured to perform at least one of the following adjustments manually or automatically: - Increasing or lowering the temperature of the alloy melt bath, - Increasing or decreasing the blowing rate of the protective gas, - Increase or decrease the gas extraction rate - Increasing or reducing the vertical distance between the surface of the zinc alloy melt bath and the end face of the at least one inner wall directed towards the zinc alloy melt bath, - Increase or decrease the tape speed.

[0041] In all embodiments, the coated flat steel product can, as usual, be subjected to a skin-pass or temper rolling process and / or a bending-stretching process after coating. The total degree of deformation for the coated flat steel product is preferably between 0.5% and 2.5%, more preferably between 0.7% and 1.7%.

[0042] Furthermore, the coated flat steel product in all versions can be treated with the usual transport protection measures such as oiling or other chemical treatment agents, as described in point 7 of the leaflet "Characteristic Features 095 - Hot-Dip Coated Strip and Sheet", edition 2010, published by the Steel Information Centre 40039 Düsseldorf.

[0043] Further advantageous embodiments of the invention form the subject matter of the dependent claims. SHORT DESCRIPTION OF THE CHARACTERS

[0044] Embodiments of the present invention are explained in more detail below with reference to the figures. These are for illustrative purposes only and are not to be interpreted in a restrictive manner. FIG. 1 is a highly schematic representation of an exemplary first device in which the method of the invention is used; FIG. 2 is a highly schematic representation of an exemplary first device in which the method of the invention is used; FIG. 3 is a highly schematic representation of an exemplary first device in which the method of the invention is used; FIG. 4 shows the influence of protective gas supply, gas extraction, and dew point on the surface defects of the coated flat steel product; FIG. 5 shows a ZnAl coated steel flat product with wetting defect; FIG. 6 shows a ZnAlFe coated steel flat product with marbling defects; FIG. 7 a ZnAlMg coated flat steel product with a “Christmas tree” defect. DETAILED DESCRIPTION

[0045] Figures 1 to 3 show an apparatus 150 for carrying out a method for applying a layer 10 to a strip-shaped flat steel product 100. This layer 10 is produced by guiding the flat steel product 100 from an input side E to an output side A through a zinc alloy molten bath 11.

[0046] In all embodiments, the target thickness of the layer 10, which can also be specified as the target (surface) coating mass of the layer 10, is specified. Typically, there is a narrowly defined Tolerance range. As long as the layer 10 to be created is within the tolerance range(s), layer 10 essentially meets the requirements.

[0047] In at least some embodiments, the process is carried out and controlled such that the layer 10 on each strip side of the flat steel product 100 has a target thickness that lies within the tolerance window. Preferably, the target thickness of the layer 10 on each strip side in all embodiments is in the range of 3 μm to 45 μm, and particularly preferably in the range of 4.5 μm to 20 μm.

[0048] Preferably, the target surface coverage in at least some of the embodiments is in the range of 20g / m 2 up to 300g / m 2 and particularly preferably in the range of 30g / m 2 up to 160g / m 2 .

[0049] In order to be able to reliably apply such a layer 10, which essentially corresponds to the desired thickness, the zinc alloy of the zinc alloy melt bath 11 in all or at least some of the embodiments essentially comprises: - an aluminium content in the range between 0.05% and 7.0% by weight and preferably between 0.1% and 4.0% by weight, - an optional magnesium content ranging between 0.05 wt% and 4.0 wt% and preferably between 1.0 wt% and 3.0 wt%, and - a residue comprising zinc and optionally one or more elements selected from the group comprising Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce or Bi, wherein the content of each optional element is less than 0.1% by weight, and unavoidable impurities.

[0050] In addition, in all embodiments, the strip speed v at which the flat steel product 100 is moved out of the zinc alloy melt bath 11 can also be changed, whereby here too care is taken to ensure that the desired thickness of the layer 10 to be applied remains substantially constant.

[0051] Preferably, in all embodiments, several of these adjustable parameters (process and system parameters) are changed in a coordinated manner to ensure that the layer 10 that is applied corresponds to the desired thickness.

[0052] A so-called target specification of the layer 10 to be applied can specify for all embodiments that the following specification(s) must be met: - Coating layer 10 on each side of the belt should be in the range of 20g / m 2 up to 300g / m 2 , preferably range 30g / m 2 up to 160g / m 2 , lie, and / or - Target thickness of the layer (10) per strip side, which is in the range 3pm to 45pm, preferably range 4.5pm to 20pm.

[0053] The bath temperature TB of the alloy melt bath 11 can be in a range between 420°C and 480°C, preferably between 440°C and 470°C, for ZnAl alloys, and in a range between 400°C and 480°C, preferably between 410°C and 460°C, for ZnAlMg alloys. Within these range limits, the bath temperature TB can be adjusted to reduce the evaporation rate of zinc.

[0054] In all embodiments, the bath temperature TB can be adjusted, for example, by means of an inductive heating device 15 (see Figs. 1 to 3) or a resistance heater.

[0055] The strip width w of the strip-shaped flat steel product 100 is preferably in the range from 500 mm to 2500 mm in all embodiments. Particularly preferably, the strip width w of the strip-shaped flat steel product is in the range from 800 mm to 1800 mm in all embodiments.

[0056] One or more of the sensors 125 of the following design or function may be used: Temperature sensor Gas sensor - Dew point sensor - Humidity sensor.

[0057] Figure 1 shows a sensor 125 arranged in the gas extraction system 124. This sensor can be one or more of the sensors mentioned above. Several different sensors of this type can also be arranged in the gas extraction system 124. The sensor 125 can be arranged directly in the gas extraction system 124, or the sensor 125 can be connected to the gas extraction system 124 via a line.

[0058] Figures 2 and 3 each show a sensor 125 arranged within the nozzle 12 in its outer region 1202. In the illustrated embodiments, the sensor 125 is arranged at substantially the same distance from the surface of the bath 16 as the lower end of the inner wall 122. The sensor 125 can be arranged directly in the outer region 1202, or the sensor 125 can be connected to the outer region 1202 via a line.

[0059] Alternatively or additionally, further sensors of this type may be arranged in the furnace 14, in the inner region 1201 of the nozzle 12 or in the gas feed 123.

[0060] All embodiments of the device 150 may include a controller. In all embodiments, this controller may be configured as a computer-aided automation and control unit and may include a human-machine interface, a computer, and a database.

[0061] In all embodiments, the controller may be part of the overall system control of the device 150, or it may be connected to the overall system control in all embodiments.

[0062] In all embodiments, a protective gas is preferably used as gas G. Dry nitrogen (N2) or a dry nitrogen-containing gas mixture, for example a dry nitrogen-hydrogen mixture (HNX), has proven particularly effective.

[0063] Figure 4 shows the influence of shielding gas supply, gas extraction, and dew point on the surface defects on the coated flat steel product. Eight strip sections B1-B8 are arranged next to each other, with surface defects represented by black dots. The more dots a strip section has, the more surface defects it has. The strip sections B1-B8 are assigned the dew point curves at which they were coated. The strip sections have a strip width w and are shown greatly compressed in their longitudinal direction for clarity. When coating a first strip section Bl, humidified shielding gas was introduced into the nozzle, gas extraction was switched off, and a first dew point TP1 of the gas mixture lay directly above the surface of the zinc alloy molten bath at approximately -15°C.Many surface disturbances are visible in an initial area, an end area and both side areas of this band section.

[0064] During the coating of a second strip section B2 and a large portion of a third strip section B3, no humidified shielding gas was introduced into the nozzle. However, the gas extraction system was activated, which caused shielding gas in the furnace to be drawn into the nozzle. A second dew point TP2 of the gas mixture directly above the surface of the zinc alloy melt bath was approximately -38°C. Compared to the first strip section B1, fewer surface defects are visible in the beginning, end, and side areas of the second and third strip sections B2-B3.

[0065] Shortly before the end of the third belt section, B3, dry shielding gas was introduced into the nozzle. However, since the introduction of the dry shielding gas does not have a direct effect on the dew point, the effects are only noticeable in the three subsequent belt sections, B4-B6.

[0066] In the fourth to sixth strip sections B4-B6, dry shielding gas was introduced into the nozzle, the gas extraction was activated, and a third dew point (TP3) of the gas mixture directly above the surface of the zinc alloy melt bath was approximately -55°C. It is clearly evident that these strip sections exhibit fewer surface defects.

[0067] Shortly after the beginning of the seventh strip section, B7, humidified shielding gas was again introduced into the nozzle and the gas extraction system was switched off. The eighth strip section, B8, was also coated under these conditions. Since the introduction of the humidified shielding gas directly affects the dew point, the effects are immediately noticeable. With the gas extraction system switched off, a dew point quickly established directly above the surface of the zinc alloy melt bath, which was approximately -15°C. It is clearly visible that the strip sections coated under these conditions again exhibit significantly more surface defects.

[0068] It is clear that strip sections B4-B6 exhibit the fewest surface defects. The gas mixture directly above the surface of the zinc alloy melt bath in which these strip sections were coated exhibits the lowest dew point compared to the gas mixtures in which the other strip sections were coated. The significant reduction in surface defects occurs at a dew point of -50°C and -55°C, respectively.

[0069] Figure 5 shows a ZnAl coated flat steel product with wetting defects, Figure 6 shows a ZnAlFe coated flat steel product with marbling defects and Figure 7 shows a ZnAlMg coated flat steel product with "Fir Tree" defects. REFERENCE SYMBOL

Claims

CLAIMS 1. A method for applying a layer (10) to a flat steel product (100), in which the flat steel product (100) coming from a furnace (14) is moved through a nozzle (12) and a subsequent zinc alloy melt bath (11), wherein a zinc alloy of the zinc alloy melt bath (11) essentially comprises: an aluminum portion, in a range between 0.05 wt.% and 7.0 wt.% and preferably between 0.1 wt.% and 4.0 wt.%, an optional magnesium portion, in a range between 0.05 wt.% and 4.0 wt.% and preferably between 1.0 wt.% and 3.0 wt.%, and a remainder comprising zinc and optionally one or more elements selected from the group comprising Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce or Bi, wherein the content of each optional element is less than 0.1wt.-%, and unavoidable impurities, wherein the nozzle (12) comprises an outer wall (120) which separates an interior (1200) of the nozzle (12) from its surroundings, wherein the flat steel product (100) is moved through this interior (1200), and wherein an end region (121) of the outer wall (120) is immersed below a surface (16) of the zinc alloy molten bath (11), wherein a protective gas (G) is introduced into the interior (1200) of the nozzle (12) in such a way that a gas mixture is established directly above the surface of the zinc alloy molten bath (11), which gas mixture has a dew point (TP) in a range between -80°C and -40°C, preferably between -75°C and -50°C, preferably between -75°C and -55°C.

2. The method according to claim 1, wherein nitrogen or argon or an HNX gas is used as the protective gas (G).

3. The method according to claim 1, wherein the flat steel product (100) comprises a steel having a composition according to the standard DIN EN 10346.

4. The method according to claim 1, wherein the flat steel product (100) comprises a steel having a composition according to the following table: Rest iron and unavoidable impurities.

5. The method according to any one of claims 1 to 4, wherein the trunk (12) comprises at least one inner wall (122) in the interior (1200) which separates an inner region (1201) from an outer region (1202) of the trunk (12), wherein the flat steel product (100) is moved through the inner region (1201) of the trunk (12), and wherein the protective gas is introduced into the inner region (1201) of the trunk (12).

6. Method according to one of claims 1 to 5, wherein the protective gas (G) is introduced on both sides of the flat steel product (100).

7. The method according to claim 5 or 6, wherein the at least one inner wall (122) is not immersed below the surface (16) of the zinc alloy molten bath (11).

8. The method according to claim 7, wherein a vertical distance (a) between the surface (16) of the zinc alloy melt bath (11) and an end face of the at least one inner wall (122) directed towards the zinc alloy melt bath (11) is between 30mm and 300mm, preferably between 50mm and 100mm.

9. Method according to one of claims 5 to 8, wherein an inner wall (122) is provided on both sides of the flat steel product (100).

10. Method according to one of claims 1 to 9, wherein a gas extraction system acts in the interior (1200) of the nozzle (12) in a suction area above the surface of the zinc alloy melt bath (11), whereby introduced protective gas (G) and vapors rising from the zinc alloy melt bath (11) are extracted.

11. The method according to claim 10, wherein the gas extraction acts between the outer wall (120) and the inner wall (122).

12. The method according to claim 10 or 11, wherein the gas extraction acts on both sides of the flat steel product (100).

13. Method according to one of claims 1 to 12, wherein the flat steel product (100) is moved through the nozzle (12) at a belt speed (v) between 30 m / min and 220 m / min, preferably 30 m / min and 180 m / min.

14. Method according to one of claims 1 to 13, wherein the layer (10) to be applied satisfies at least one of the following conditions: A target surface coating of the layer (10) on each side of the belt, which is in the range of 20g / m 2 up to 300g / m 2 is preferably in the range 30g / m 2 up to 160g / m 2 ; A target thickness of the layer (10) per strip side, which is in the range 3pm to 45pm, preferably in the range 4.5pm to 20pm.

15. Method according to one of claims 1 to 14, wherein the protective gas (G) is injected at a rate of 100 Nm 3 / h up to 500Nm 3 / h, preferably 200Nm 3 / h up to 400Nm 3 / h is introduced.

16. The method according to any one of claims 10 to 13, wherein the gas extraction has an extraction rate of 100 Nm 3 / h up to 500Nm 3 / h, preferably 200Nm 3 / h up to 400Nm 3 / h.

17. The process according to any one of claims 1 to 16, wherein the zinc The alloy melt bath (11) comprises a ZnAl alloy and has a bath temperature (TB) in a range between 420°C and 480°C, preferably between 440°C and 470°C, or wherein the zinc alloy melt bath (11) comprises a ZnAlMg alloy and has a bath temperature (TB) in a range between 400°C and 480°C, preferably between 410°C and 460°C.

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