Method for producing a coating on profile components made of sheet steel

Abstract

Method for producing a coating on profile components (2) made of sheet steel, characterized by the following steps: - Providing profile components that are at least partially hardened, in particular press-hardened (2), - Application of metal powder to the surface of the profile components (2), - Heat treatment of the profile components (2) in a heat treatment room (1), wherein the profile components (2) are moved into a heat treatment area (6) of the heat treatment room (1) which has an inert gas atmosphere, wherein - the profile components (2) are moved upwards into the inert gas atmosphere when the gas density of the inert gas atmosphere is less than the gas density of air or - the profile components (2) are moved downwards into the inert gas atmosphere when the gas density of the inert gas atmosphere is greater than the gas density of air and - the heat treatment takes place in an inert gas atmosphere at a temperature between 300°C and 500°C and over a period of 5 min to 120 min. and - during heat treatment, the coating is formed by a diffusion process between the profile components (2) and the metal powder, after which - the profile components (2) are removed from the heat treatment room (1).

Description

[0001] The invention relates to a method for producing a coating on profile components made of sheet steel, in particular on structural or body components of motor vehicles.

[0002] The coating of profile components made of sheet steel is intended to improve their properties. This can increase, in particular, corrosion resistance and wear resistance.

[0003] Processes for applying firmly adhering coatings made of amorphous materials to metallic surfaces are well known in the art. These include hot-dip galvanizing, spray galvanizing, electrogalvanizing, and sherardizing (diffusion galvanizing).

[0004] Sherardizing is internationally specified in DIN EN ISO 17668:2016 "Zinc diffusion coatings on iron - Sherardizing - Requirements." The process is diffusion-controlled and is carried out via a heat treatment, whereby a coating is created via the vapor phase of the zinc. The coating deposition occurs through a phase reaction with the surface of the metallic profile components, forming a zinc-iron alloy layer. The layer grows from the surface of the profile components and is therefore close to the contour.

[0005] DE 10 2005 002 706 A1 describes a method for applying a solid metallic coating, particularly made of zinc or a zinc alloy, to a profile component made of sheet steel as state-of-the-art. In this process, the profile component is sprayed with a metal powder in a treatment chamber. The metal powder is electrostatically deposited over the entire surface of the profile component. In a subsequent heat treatment process, a diffusion process occurs between the steel sheet and the metal powder, forming the coating. The coating of the profile components takes place in a continuous process. However, this inherently innovative and efficient process has not yet produced coatings of satisfactory quality.

[0006] EP 2 271 784 B1 discloses a method for coating the surface of a metallic profile component with zinc, which is carried out as a sherardizing process. The profile components to be coated are heat-treated together with zinc as the coating agent at a temperature between 200°C and 500°C in a reaction chamber. The reaction chamber is, in particular, a slowly rotating, closed container, for example, a drum or a rotary kiln. Before the heat treatment begins, the oxygen content of the atmosphere in the reaction chamber is adjusted to less than or equal to 5 vol. Furthermore, a flux is supplied to the reaction chamber before the heat treatment. However, this process is relatively complex and cost-intensive.

[0007] In general, it should be noted that the sherardizing process, which involves heat treatment in slowly rotating, closed containers or retorts, is very complex and time-consuming. In addition to the retort, a filler may also be heated, so large thermal masses must be heated. The temperature of the coating material is controlled indirectly via the drum wall. This process is very slow and difficult to control. Furthermore, the components are heated indirectly via the retort.

[0008] This means that the material properties of the profile components to be coated can be adversely affected.

[0009] A comparable technology is disclosed in DE 10 2004 035 049 A1. There, a saturation mixture with a proportion of approximately 99% to 100% finely dispersed zinc powder is used. A heat-conducting filler in the form of granules or beads is simultaneously introduced into a container containing the steel profile products for the coating process.

[0010] The production of a coating on profile components made of steel or sheet steel is also described in WO 2014 / 089 624 A1.

[0011] DE 10 2008 020 576 A1 describes a process for diffusion galvanizing in a reaction chamber. The components to be coated are mounted on a rotating rack outside the reaction chamber before the rack is introduced into the reaction chamber. After the rack with the components is introduced into the reaction chamber and positioned on rollers for rotation, the reaction chamber is sealed gas-tight and then evacuated and filled with oxygen-free nitrogen. This process is repeated several times. The reaction chamber is then heated to the heat treatment temperature. During the heating period, coating agent in the form of zinc powder is introduced into the reaction chamber via an injector.

[0012] US 2003 / 0 000 611 A1 relates to a process for the continuous heat treatment of metals under an inert gas atmosphere in a tunnel furnace in a continuous flow under an argon-containing atmosphere. The pressure selectively generated in the argon-containing atmosphere in the tunnel furnace is adjustable by controlling the height of the inlet and / or outlet and is said to be higher than atmospheric pressure.

[0013] Furthermore, DE 10 2009 051 183 A1 discloses a heat treatment furnace, in particular for soldering at least one component.

[0014] Based on the prior art, the invention is based on the object of demonstrating a rational and efficient process for producing high-quality coatings on profile components made of sheet steel.

[0015] The solution to this problem consists in a method according to claim 1.

[0016] Advantageous embodiments and further developments of the method according to the invention are the subject of the dependent claims.

[0017] A method according to the invention for producing a coating on profile components made of sheet steel provides the following steps: - Providing profile components that are at least partially hardened, in particular press-hardened, - Application of metal powder to the surface of the profile components, - heat treatment of the profile components in a heat treatment chamber, wherein the profile components are moved into a heat treatment area of ​​the heat treatment chamber which has an inert gas atmosphere, wherein - the profile components are moved upwards into the inert gas atmosphere if the gas density of the inert gas atmosphere is lower than the gas density of air or - the profile components are moved downwards into the inert gas atmosphere if the gas density of the inert gas atmosphere is greater than the gas density of air and - the heat treatment is carried out in an inert gas atmosphere at a temperature between 300°C and 500°C and for a period of 5 minutes to 120 minutes and - during heat treatment, the coating is formed by a diffusion process between the profile components and the metal powder, after which - the profile components are led out of the heat treatment room.

[0018] The steps listed above for producing a coating on profile components and sheet steel are carried out sequentially.

[0019] Profile components that are hardened at least in certain areas, in particular press-hardened, are provided. In particular, the profile components are hot-formed and press-hardened profile components. In this case, a steel sheet made of a boron-alloyed steel, in particular a boron-manganese steel alloy, is heated to a temperature above AC3 and then quickly formed, i.e. generally in less than 5 seconds, and clamped in the press tool, subjected to rapid cooling so that a martensitic and / or bainitic microstructure is achieved. These measures result in a product with high dimensional accuracy, good dimensional stability and high strength values, which is very suitable for structural, body and safety components in vehicles. The profile components can also be hardened only in certain areas, i.e. have locally different microstructures and / or material properties.

[0020] Forming can be performed directly or indirectly. In direct hot forming, the component is austenitized at a temperature dependent on the steel, transferred to the cooled die or press tool, and then formed. This allows for complex geometries to be formed because the material exhibits excellent formability at high temperatures.

[0021] In indirect hot forming, the component is first preformed or deep-drawn cold or unheated. The component is then heated to the austenitizing temperature and finally formed. This additional step expands the forming limits for very complex geometries.

[0022] After the forming process, the profile components are subjected to a cleaning process before being fed into the coating process.

[0023] A metal powder is applied to the surface of the profile components. This can be pure zinc powder or a zinc alloy powder. A metal powder formulated with additives can also be used.

[0024] To apply the metal powder to the surface of the profile components, the profile components are brought into contact with the metal powder. This can be done by dusting or powdering the profile components with metal powder. The profile components can also be passed through a fluidized bed of metal powder. The metal powder adheres to the surface of the profile components through cohesion. A thin, non-adherent layer of metal powder forms on the surface of the profile components.

[0025] Before applying the metal powder to the surface of the profile components to be coated, a liquid adhesion promoter can be applied to the profile components. A liquid, particularly an aqueous solution, is used as the adhesion promoter. The adhesion promoter is particularly preferably applied as a liquid film.

[0026] The metal powder can also be applied to the surface of the profile components electrostatically. In this case, a fine metal powder, particularly a zinc powder with a thin oxide layer, is atomized in a nozzle and guided along an electrode so that the individual metal powder particles become statically charged. An electric field is created between the electrode in the nozzle and the profile components to be coated, which form the counter electrodes. The metal powder particles are guided along the electric field lines to the profile component and, due to the shape of the field lines relative to the nozzle, also reach the rear surfaces of the profile components. This causes the coating material to wrap around the edges. When the metal powder particles touch the component surface, they discharge and then adhere to the surface of the profile components due to van der Waals forces and similar phenomena.

[0027] The metal powder is preferably applied via electroneutral deposition of the metal powder onto the surface of the profile components. For this purpose, a liquid adhesion promoter is applied to the surface of the profile components. The surface of the profile components is moistened, preferably by applying a liquid film based on an aqueous solution, a flux, or pure water. The moist profile components are then brought into contact with the coating powder. The moisture causes the powder to adhere to the surface of the profile components. If necessary, a drying step is carried out after powder application. The adhesion of the powder to the surface of the profile components is sufficient so that even vibrations resulting from further transport of the profile components to be coated do not lead to the powder layer being removed.

[0028] After the metal powder is applied to the surface of the profile components, they are transported to a heat treatment chamber. The heat treatment of the profile components takes place in the heat treatment chamber, with the profile components being moved into a heat treatment area of ​​the heat treatment chamber, which has an inert gas atmosphere.

[0029] The inert gas atmosphere is formulated in its composition and gas density so that it is either lighter than air, i.e., the ambient air, or heavier than air. The relative density is the quotient of the density of the inert gas and the density of the ambient air in the heat treatment chamber. It represents the weight ratio between the inert gas and the ambient air. An inert gas with a relative density less than 1.0 is lighter than air and therefore rises. An inert gas with a relative density greater than 1.0 is heavier than air and therefore falls.

[0030] The profile components are moved upwards into the inert gas atmosphere if the gas density of the inert gas atmosphere is lower than the gas density of air. Alternatively, the profile components are moved downwards into the inert gas atmosphere if the gas density of the inert gas atmosphere is higher than the gas density of air. The decisive factor is the relative density, i.e., the ratio between the density of the inert gas and the density of air.

[0031] The heat treatment area can be located in the upper part of the heat treatment chamber. In this case, an inert gas is used whose density is less than that of air. The inert gas atmosphere is located in the upper part of the heat treatment chamber. This measure displaces the atmospheric oxygen from the upper part of the heat treatment chamber, creating an oxygen-poor or even oxygen-free atmosphere. If the density of the inert gas is greater than the gas density of air, the inert gas sinks downwards relative to the air. The heat treatment area is then located in the lower part of the heat treatment chamber. In this case, the atmospheric oxygen is displaced from the lower part of the heat treatment chamber, creating an oxygen-poor or even oxygen-free atmosphere.

[0032] The inert gas atmosphere can consist of nitrogen N2 or contain nitrogen N2 as its main component. Main component means that the relevant inert gas is present in a proportion of more than 50% in the inert gas atmosphere. An inert gas atmosphere made of nitrogen or based on nitrogen is lighter than air. The gas density is lower than the gas density of air. This inert gas atmosphere therefore accumulates in the upper heat treatment area of ​​the heat treatment chamber. The gas density is generally measured in kg / m 3 At a temperature of 20°C and a pressure of 1013 mbar, the density of air is approximately 1.204 kg / m 3 The density of nitrogen under these conditions is 1.251 kg / m 3 .

[0033] The inert gas atmosphere can also be heavier than air. The inert gas atmosphere can then consist of carbon dioxide (CO2) or contain carbon dioxide (CO2) as its main component. At 20°C and an ambient pressure of 1013 mbar, carbon dioxide (CO2) has a density of 1.977 kg / m³. 3 .

[0034] Pure nitrogen has a molar mass of 14 g / mol. Dry air has a molar mass of 28.9 g / mol. Carbon dioxide has a molar mass of 44 g / mol.

[0035] For a heat treatment chamber whose heat treatment area is located above the profile component inlet, an inert gas atmosphere is formulated so that its molar mass is less than 20 g / mol. For a heat treatment chamber whose heat treatment area is located below the profile component inlet, i.e., the feed level, an inert gas atmosphere with a molar mass greater than 35 g / mol is set.

[0036] During heat treatment, the coating is formed through a diffusion process between the profile components and the metal powder. The heat treatment is carried out with precise temperature control. The heat treatment temperature is between 300°C and 500°C, particularly between 360°C and 420°C.

[0037] The heat treatment room is equipped with suitable heating means to generate the heat treatment temperature in the heat treatment area.

[0038] The heat treatment takes place in a low-oxygen atmosphere. The oxygen content in the heat treatment area should be less than 0.2%. The oxygen content in the inert gas atmosphere present in the heat treatment area is preferably less than 0.01%. The heat treatment thus takes place in an oxygen-reduced inert gas atmosphere.

[0039] The heat treatment is carried out over a period of 5 minutes to 120 minutes, in particular over a period of 5 minutes to 50 minutes. Advantageously, the heat treatment extends over a period of 5 minutes to 30 minutes, preferably over a period of 10 minutes to 30 minutes.

[0040] During the heat treatment, a firmly adhering coating forms on the profile components to be coated by diffusion. Specifically, the coating is a zinc-iron alloy layer. This corresponds to a sherardizing layer. However, compared to the known sherardizing process, the heating and cooling phases of the process according to the invention are significantly shortened because only the profile components themselves are directly heated by convection and then cooled. In a known sherardizing process, a retort and, if necessary, a filler are always heated as well, so that considerably larger thermal masses must be heated. Furthermore, in the known procedure, the components are heated indirectly by heating the retort.

[0041] With the process according to the invention, the tensile strength of the components is reduced to a lesser extent. The yield strength and ductility change favorably compared to the initial values.

[0042] During heat treatment, the profile components are guided through the heat treatment chamber on a conveyor. This can occur in a single pass or in a recirculation through the heat treatment chamber. In a single pass, the entrance and exit for the profile components into the heat treatment chamber are located on different sides of the heat treatment chamber. In a recirculation process, the entrance and exit for the profile components are preferably on the same side of the heat treatment chamber. An opening in the heat treatment chamber can form the entrance and exit. However, the openings for the entrance and exit can also be provided horizontally or vertically offset from one another in one side or side wall of the heat treatment chamber.

[0043] The heat treatment area and the inert gas atmosphere in the heat treatment room are enclosed laterally by side walls and above or below by the ceiling or floor in a particularly gas-tight manner, with the inert gas atmosphere directly bordering the area with ambient air on a side that is not or only incompletely closed.

[0044] Following heat treatment, the components are cooled and unloaded from the transport vehicle. The profile components are cleaned before and / or after unloading from the transport vehicle. This is particularly advantageous for profile components still on the transport vehicle. Cleaning can involve a simple washing process, e.g., using a high-pressure cleaner. Cleaning agents can be added to the washing liquid. A warm or hot detergent or washing liquid can also be used. Pure dry cleaning using compressed air or suction is also possible.

[0045] Optionally, the coated profile components can be subjected to further surface treatment, such as phosphating or passivation. This can also be done in a separate treatment system for the profile components already on the transport vehicle. This can be done, for example, by applying a reagent in a bath or spray.

[0046] The invention creates a process in which a significant cost reduction is expected. Furthermore, a significant increase in throughput and performance is achievable. The method according to the invention is advantageous in terms of controllability. The method according to the invention is rational and efficient. It enables the production of high-quality coatings on profile components made of sheet steel.

[0047] The method according to the invention is particularly suitable for the production of crash-relevant automotive structural components that require very good corrosion protection and very high strength combined with relatively high ductility. These include all vehicle body components located in the floor area, i.e., those exposed to high corrosion stress and / or that must provide a high section modulus in the event of a crash without failing. These are components exposed to buckling or bending loads and / or axial loads. These include A-, B-, and C-pillars, cross members, as well as bumpers, seat cross members, firewalls, sills, and longitudinal members, as well as protective components of drive battery housings.

[0048] One aspect of the invention provides that profile components made of a tempering steel are used, which, in addition to iron Fe and unavoidable impurities due to production, contains in wt.% Carbon C 0,20 - 0,25 Silicon Si 0,20 - 0,30 Manganese Mn 1,10 - 1,40 Phosphorus P maximum 0.020 Sulfur S maximum 0.005 Nitrogen N maximum 0.01 Aluminum Al 0,020 - 0,060 Boron B 0,0020 - 0,0035 Chromium Cr 0,10 - 0,30 Titanium Ti 0,020 - 0,050 Molybdenum Mo maximum 0.35 Copper Cu maximum 0.10 Nickel Ni maximum 0.3 consists.

[0049] Another aspect provides for the use of profile components made of a tempering steel which, in addition to iron Fe and unavoidable impurities due to the manufacturing process, contains in weight percent Carbon C 0,21 - 0,26 Silicon Si 0,15 - 0,30 Manganese Mn 1,10 - 1,35 Phosphorus P maximum 0.020 Sulfur S maximum 0.010 Nitrogen N maximum 0.01 Aluminum Al 0,010 - 0,060 Boron B 0,0010 - 0,0025 Chromium Cr maximum 0.08 Titanium Ti 0,020 - 0,070 Molybdenum Mo maximum 0.04 Copper Cu maximum 0.08 Nickel Ni maximum 0.05 consists.

[0050] The tempering steels defined above can be used to produce profile components for motor vehicles that exhibit a purely or predominantly martensitic structure after hardening. The tensile strengths after the coating process range between 1,300 MPa and 1,500 MPa.

[0051] Another aspect of the invention provides that profile components made of a tempering steel are used, which, in addition to iron Fe and unavoidable impurities due to production, contains in wt.% Carbon C 0,3 - 0,4 Silicon Si 0,15 - 1,0 Manganese Mn 0,5 - 2,0 Phosphorus P maximum 0.05 Sulfur S maximum 0.01 Nitrogen N maximum 0.01 Chromium Cr 0,05 - 1,0 Nickel Ni maximum 0.3 Copper Cu maximum 0.1 Molybdenum Mo maximum 0.5 Aluminum Al maximum 0.1 Niobium Nb 0,02 - 0,1 Vanadium V maximum 0.06 Titanium Ti maximum 0.1 Boron B 0,001 - 0,01 consists.

[0052] Another advantageous tempering steel consists of iron and unavoidable impurities in wt.% of Carbon C 0,32 - 0,38 Silicon Si 0,2 - 0,50 Manganese Mn 0,8 - 1,5 Phosphorus P maximum 0.02 Sulfur S maximum 0.005 Nitrogen N maximum 0.005 Chromium Cr 0,1 -0,5 Nickel Ni maximum 0.1 Copper Cu maximum 0.05 Molybdenum Mo maximum 0.3 Aluminum Al maximum 0.06 Niobium Nb 0,02 - 0,06 Vanadium V maximum 0.05 Titanium Ti maximum 0.01 Boron B 0,001 - 0,005 consists.

[0053] The tensile strengths of the coated profile components made of a tempered steel as described above are between 1,800 MPa and 2,200 MPa.

[0054] The invention is further described below with reference to the drawings. They show: Fig. 1 technically schematic view of a heat treatment room with the passage of profile components during heat treatment; Fig. 2 an alternative design of a heat treatment room; Fig. 3 shows a technical diagram of a further design of a heat treatment room and the process of carrying out heat treatment of profile components; Fig. 4 again an alternative of a heat treatment room and the implementation process for the heat treatment of profile components and Fig.5 another alternative of a heat treatment room and an implementation process for the heat treatment of profile components.

[0055] Corresponding components or component parts are shown in the Fig. 1 to 5 are provided with the same reference numerals.

[0056] Fig. 1 shows a heat treatment room 1 in which profile components 2 made of sheet steel are subjected to a heat treatment in order to form a coating by a diffusion process between the profile components 2 and a metal powder applied to the surface of the profile components 2.

[0057] To produce the coating, profile components 2 that are at least partially hardened, in particular press-hardened, are provided. A metal powder is applied to the surface of the profile components 2. The metal powder is preferably made of zinc or a zinc alloy. Before the metal powder is applied to the surface of the profile components 2, they can be subjected to a cleaning process. Cleaning is carried out, for example, mechanically by compressed air blasting or wheel blasting with solid blasting media.

[0058] The metal powder can be applied to the surface of the profile components 2 electrostatically. Electroneutral deposition of the metal powder on the surface of the profile components 2 is advantageous. In particular, the surface of the profile components 2 is moistened for this purpose, preferably by applying a liquid film based on an aqueous solution, a flux, or pure water. Consequently, a liquid adhesion promoter is applied to the surface of the profile components 2. The moist profile components 2 are then brought into contact with the metal powder. The moisture causes the powder to adhere to the surface of the profile components 2. If necessary, a drying step is carried out after the powder application.

[0059] After the metal powder has been applied to the surface of the profile components 2, they are transported to the heat treatment room 1 and introduced into it. Fig.1 shows a profile component 2 coated with metal powder in the image plane on the left, before it is introduced into the heat treatment chamber 1 via an entrance 3 in the floor 4 of the latter.

[0060] For heat treatment, the profile components 2 are guided into the heat treatment chamber 1 by means of a transport means 5, shown here only in outline. The arrows in the indicated transport means 5 indicate the directions of movement of the profile components 2.

[0061] The heat treatment chamber 1 has a heat treatment area 6 in which an inert gas atmosphere is present. The heat treatment area 6 with the inert gas atmosphere is located in the image plane of the Fig.1 above the insertion level for the profile components 2. The inert gas atmosphere consists of nitrogen (N2) or contains nitrogen as its main component. Nitrogen, or the nitrogen-based inert gas atmosphere, has a gas density that is lower than that of air. The heat treatment area 6 with the inert gas atmosphere is located in the upper area of ​​the heat treatment chamber 1 above the insertion level of the profile components 2. Below the heat treatment area 6 with the inert gas atmosphere is an area 7 with air. This is atmospheric ambient air. The inert gas atmosphere borders directly on the ambient air.

[0062] The profile components 2 are guided into the heat treatment chamber 1 via the inlet 3. In the heat treatment chamber 1, the profile components 2 are moved into the heat treatment area 6, which has an inert gas atmosphere. For this purpose, the profile components 2 are moved upward into the inert gas atmosphere. Consequently, an upward movement of the profile components 2 takes place from the insertion level into the heat treatment area 6 with the inert gas atmosphere.

[0063] For the duration of the heat treatment, the profile components 2 remain in the heat treatment area 6 of the heat treatment room 1.

[0064] The heat treatment chamber 1 is provided with heating means not shown here, by means of which the heat treatment temperature is generated.

[0065] The heat treatment of the profile components 2 in the inert gas atmosphere takes place at a temperature between 300°C and 500°C for a period of 5 minutes to 120 minutes. A diffusion process between the profile components 2 and the metal powder forms a coating on the surface. The coating is, in particular, a zinc diffusion coating consisting of a zinc-iron coating.

[0066] The profile components 2 are then lowered from the upper level in the heat treatment area 6 and led out of the heat treatment room 1. This is done via an exit 8. In the heat treatment room 1, as shown in the Fig.As shown in Figure 1, the inlet 3 and the outlet 8 are located offset from one another in the floor 4 of the heat treatment chamber 1. The profile components 2 are guided through the heat treatment chamber 1 in a continuous motion. This means that the profile components 2 are brought into the heat treatment chamber 1 via the inlet 3 and moved upwards into the heat treatment area 6 with the inert gas atmosphere. The profile components 2 remain there for the duration of the heat treatment and the coating formation. The movement is then continued, and the profile components 2 are guided downwards from the heat treatment area 6 and out of the heat treatment chamber 1 via the outlet 8.

[0067] The components are unloaded from the transport means 5. Before or after unloading, the coated components can be subjected to any subsequent treatment processes, such as phosphating or passivation.

[0068] In the heat treatment room 1, as in the Fig.2, the inlet 3 and the outlet 8 are located on opposite side walls 9, 10 of the heat treatment chamber 1. Otherwise, the process sequence for producing a coating on the profile components 2 corresponds to the procedure described above. The profile components 2 provided with the metal powder are moved into the heat treatment area 6 of the heat treatment chamber 1, which has an inert gas atmosphere. The gas density of the inert gas atmosphere is lower than the gas density of the air below or of the area 7, which is filled with air in the heat treatment chamber 1. The profile components 2 are moved upwards into the inert gas atmosphere, where they are subjected to heat treatment, whereby the coating is formed as a zinc diffusion coating through a diffusion process between the profile components 2 and the metal powder, in particular the zinc powder.The profile components 2 are then led out of the heat treatment room 1 via the exit 8.

[0069] In the heat treatment room 1, as in the Fig. As shown in Figure 3, the profile components 2 are guided in a circuit during heat treatment, i.e., the profile components 2 are introduced into the heat treatment chamber 1 via a side wall 9 of the heat treatment chamber 1 and removed again via the same side wall 9. This can occur via a common inlet and outlet, or via adjacent or stacked inlets and outlets. The heat treatment and the formation of the coating on the profile components 2 are carried out as previously described using the temperature and time regimes outlined.

[0070] Another heat treatment room 1 is in the Fig.4. Here, too, the profile components 2 are moved in a circuit through the heat treatment chamber 1. For this purpose, the profile components 2 are moved upwards into the heat treatment area 6 and into the inert gas atmosphere. The removal of the profile components 2 from the heat treatment area 6 or heat treatment chamber 1 occurs in the opposite direction by a downward movement of the profile components 2, which is opposite to the upward movement. The introduction and removal of the profile components 2 takes place on the same side wall 9 of the heat treatment chamber 1 via an entrance and an exit, respectively.

[0071] In heat treatment room 1, as in the Fig.5, there is a heat treatment area 6 with an inert gas atmosphere, wherein the gas density of the inert gas atmosphere is greater than the gas density of air. Accordingly, the heat treatment area 6 is below the floor level above which the supply and removal of the profile components 2 takes place. The heat treatment area 6 is located above the floor 11 of the heat treatment room 1. The inlet 3 and the outlet 8 into the heat treatment room 1 are located in the ceiling 12 of the heat treatment room 1. The inert gas atmosphere consists of carbon dioxide (CO2) or contains carbon dioxide (CO2) as its main component. The gas density of carbon dioxide is greater than the gas density of air. The inert gas or inert gas atmosphere therefore has a relative density greater than 1.0 and is heavier than air. The inert gas thus falls downwards. Above the heat treatment area 6 and the inert gas atmosphere is the area 7 with air.

[0072] The profile components 2 are brought into the heat treatment chamber 1 via the entrance 3. In the heat treatment chamber 1, the profile components 2 are moved downward into the heat treatment area 6 and the inert gas atmosphere. Consequently, the profile components 2 are lowered or lowered. In the heat treatment area 6, the profile components 2 remain at the heat treatment temperature for the duration of the heat treatment. The coating on the profile components 2 is formed. This is a metal diffusion coating, in particular a zinc diffusion coating.

[0073] The profile components 2 are then moved upwards out of the heat treatment area 6 and brought out of the heat treatment room 1 via the exit 8.

[0074] In all heat treatment processes described above, the heat treatment takes place in an inert gas atmosphere at a temperature between 300°C and 500°C, in particular at a temperature between 360°C and 420°C.

[0075] The heat treatment takes place over a period of 5 minutes to 120 minutes. In particular, the heat treatment takes place over a period of 5 minutes to 50 minutes, preferably up to 30 minutes.

[0076] The heat treatment area 6 and the inert gas atmosphere in the heat treatment room 1 are enclosed in a gas-tight manner laterally and upwards or downwards by side walls 9, 10, floor 4 or ceiling 12, wherein the inert gas atmosphere directly borders the area 7 with ambient air on a side that is not or only incompletely closed. Reference symbol: 1 heat treatment room 2 profile component 3 Entrance 4 Floor 5 means of transport 6 Heat treatment area 7 Area 8 Exit 9 Side wall 10 Side wall 11 Floor 12 Ceiling

Claims

[1] Method for producing a coating on profile components (2) made of sheet steel, characterized by following steps: - Providing profile components (2) which are at least partially hardened, in particular press-hardened, - applying metal powder to the surface of the profile components (2), - heat treatment of the profile components (2) in a heat treatment chamber (1), wherein the profile components (2) are moved into a heat treatment area (6) of the heat treatment chamber (1) which has an inert gas atmosphere, wherein - the profile components (2) are moved upwards into the inert gas atmosphere if the gas density of the inert gas atmosphere is lower than the gas density of air or - the profile components (2) are moved downwards into the inert gas atmosphere if the gas density of the inert gas atmosphere is greater than the gas density of air and - the heat treatment is carried out in an inert gas atmosphere at a temperature between 300°C and 500°C and for a period of 5 minutes to 120 minutes and - during the heat treatment, the coating is formed by a diffusion process between the profile components (2) and the metal powder, after which - the profile components (2) are led out of the heat treatment chamber (1). [2] Method according to claim 1, characterized by that the oxygen content in the inert gas atmosphere is less than or equal to 0.2%. [3] Method according to claim 1 or 2, characterized by that the inert gas atmosphere consists of nitrogen N2 or contains nitrogen N2 as its main component. [4] Method according to claim 1 or 2, characterized by that the inert gas atmosphere consists of carbon dioxide CO2 or contains carbon dioxide CO2 as its main component. [5] Method according to one of claims 1 to 4, characterized bythat a liquid adhesion promoter is applied to the profile components (2) before the metal powder is applied. [6] Method according to claim 5, characterized by that the profile components (2) are dried after the application of the metal powder and before the heat treatment. [7] Method according to one of claims 1 to 6, characterized by that the heat treatment takes place at a temperature between 360° C and 420° C. [8] Method according to one of claims 1 to 7, characterized by that the heat treatment takes place over a period of 5 min to 50 min, preferably up to 30 min. [9] Method according to one of claims 1 to 8, characterized by that profile components (2) are guided through the heat treatment chamber (1) in a continuous or circulating manner. [10] Method according to one of claims 1 to 9, characterized by that a metal powder made of zinc or a zinc alloy is used. [11] Method according to one of claims 1 to 10, characterized by that the heat treatment area (6) with the inert gas atmosphere is enclosed laterally by side walls (9, 10) and upwards or downwards by a ceiling (12) or floor (4, 11), in particular in a gas-tight manner, wherein the inert gas atmosphere directly borders on ambient air on a side which is not or only incompletely closed. [12] Method according to one of claims 1 to 11, characterized by that profile components (2) are used made of a heat-treatable steel which, in addition to iron Fe and impurities unavoidable during production, consists in weight percent of Carbon C 0,20 - 0,25 Silicon Si 0,20 - 0,30 Manganese Mn 1,10 - 1,40 Phosphorus P maximum 0.020 Sulfur S maximum 0.005 Nitrogen N maximum 0.01 Aluminum Al 0,020 - 0,060 Boron B 0,0020 - 0,0035 Chromium Cr 0,10 - 0,30 Titanium Ti 0,020 - 0,050 Molybdenum Mo maximum 0.35 Copper Cu maximum 0.10 Nickel Ni maximum 0.3 consists. [13] Method according to one of claims 1 to 11, characterized by that profile components (2) are used made of a heat-treatable steel which, in addition to iron Fe and impurities unavoidable during production, consists in weight percent of Carbon C 0,21 - 0,26 Silicon Si 0,15 - 0,30 Manganese Mn 1,10 - 1,35 Phosphorus P maximum 0.020 Sulfur S maximum 0.010 Nitrogen N maximum 0.01 Aluminum Al 0,010 - 0,060 Boron B 0,0010 - 0,0025 Chromium Cr maximum 0.08 Titanium Ti 0,020 - 0,070 Molybdenum Mo maximum 0.04 Copper Cu maximum 0.08 Nickel Ni maximum 0.05 consists. [14] Method according to one of claims 1 to 11, characterized by that profile components (2) are used made of a heat-treatable steel which, in addition to iron Fe and impurities unavoidable during production, consists in weight percent of Carbon C 0,3 - 0,4 Silicon Si 0,15 - 1,0 Manganese Mn 0,5 - 2,0 Phosphorus P maximum 0.05 Sulfur S maximum 0.01 Nitrogen N maximum 0.01 Chromium Cr 0,05 - 1,0 Nickel Ni maximum 0.3 Copper Cu maximum 0.1 Molybdenum Mo maximum 0.5 Aluminum Al maximum 0.1 Niobium Nb 0,02 - 0,1 Vanadium V maximum 0.06 Titanium Ti maximum 0.1 Boron B 0,001 - 0,01 consists. [15] Method according to claim 14, characterized by that the tempering steel, in addition to iron Fe and unavoidable impurities due to manufacturing, contains in weight percent Carbon C 0,32 - 0,38 Silicon Si 0,2 - 0,50 Manganese Mn 0,8 - 1,5 Phosphorus P maximum 0.02 Sulfur S maximum 0.005 Nitrogen N maximum 0.005 Chromium Cr 0,1 -0,5 Nickel Ni maximum 0.1 Copper Cu maximum 0.05 Molybdenum Mo maximum 0.3 Aluminum Al maximum 0.06 Niobium Nb 0,02 - 0,06 Vanadium V maximum 0.05 Titanium Ti maximum 0.01 Boron B 0,001 - 0,005 consists.

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