DE102021110644A1 - Process and coating for anti-scale coating of a steel sheet, in particular a body component - Google Patents

Abstract

In order to provide a method for anti-scale coating of steel sheets made of high-strength steel materials, in which the risk of hydrogen embrittlement of the steel material is minimized and which ensures sufficient weldability of the coated steel sheets, a method (100) for anti-scale coating of a steel sheet, in particular a body component, is proposed. comprising the steps:- providing a steel sheet made of a steel material with a tensile strength in the hardened state of at least 1700 MPa,- providing a coating, the coating comprising a binder and metal pigments, and- coating the steel sheet with the coating.

Description

The present invention relates to a method for anti-scale coating of a steel sheet, in particular a body component, and a coating for anti-scale coating of a steel sheet, in particular a body component.

During the hot forming of sheet steel for body components, blanks are heated for a period of three to six minutes, depending on the sheet thickness, at 870°C to 950°C in an oven or conductively, inductively or via infrared radiation and then formed in a hot forming tool in the further course of the process and then deterred. In the case of uncoated sheet steel or blanks, scale forms at elevated temperatures due to air contact inside and outside the furnace. The formation of scale leads to contamination of the hot forming tool and significantly increases its wear. Components with a high degree of deformation, or with a high component complexity, cannot be reliably manufactured due to the strongly fluctuating inhomogeneous friction conditions. During production, the hot forming tool must be cleaned at short intervals by vacuuming or mechanically removing the scale. This reduces the output.

From the U.S. 2005/0065269 A1 discloses a corrosion-inhibiting mixture containing corrosion-inhibiting pigments and amorphous silicon dioxide modified with metal ions, which also contains at least one compound of the general formula M _n (X) _m , in which the variables and the index have the following meanings: M at least one central atom selected from the group of Lewis acceptors, X Lewis donor ligands having at least one bridging atom selected from the elements of main groups 5 and 6 of the Periodic Table of the Elements, n 1 to 500 and m 3 to 2,000.

From the US 2010/0098956 A1 a coating material for protecting metals from corrosion and/or scaling is known, with means for achieving weldability, in particular by means of spot welding processes, of the applied coating material being provided, with the coating material being able to be applied in a wet-chemical manner, and with the coating material changing by more in high-temperature processes than 600°C and is suitable as a primer for other coating materials. To achieve weldability, an easily oxidized organic or inorganic-organic binder with easily oxidized organic components is combined with an electrically conductive metallic or non-metallic filler.

the U.S. 2012/0009340 A1 discloses a coating for protecting metal against cathodic corrosion, containing 10 to 90% by weight of metallic magnesium particles in the form of pigments, powders, pastes or granules with individual grain sizes of 100 nm to 100 μm and 10 to 90% by weight of conductive or semiconductive components.

For sheet steel made of a steel material with a tensile strength in the hardened state of approx. 1,500 MPa, there are coating solutions for scale and corrosion protection. So it is known to coat steel sheets made of a 22MnB5 steel material by means of an AlSi hot-dip coating. These hot-dip coatings are applied in a layer thickness between 20 and 30 µm. They are brought up to temperature exclusively in gas or electric furnaces for hot forming with holding times > 2 minutes in order to guarantee diffusion of iron into the coating and thus the stability of the coating. Rapid heating methods such as conductive, inductive or infrared heating (NIR) with holding times of < 1 min result in molten metal and are therefore not usable

However, such AlSi hot-dip coatings are unsuitable for high-strength steel materials with a tensile strength in the hardened state of more than 1,700 MPa. The reason lies in the higher susceptibility of high-strength steel materials to hydrogen-induced cracking and grain boundary weakening. Due to hydrogen embrittlement, high-strength steel materials coated in AlSi hot-dip processing cannot be reliably processed.

In order to solve these problems, attempts have been made to use steel materials with lower tensile strengths and significantly increased sheet thicknesses. Attempts were also made to enable formability despite the lack of a coating by adapting the geometry of the steel sheets. However, this is only possible within narrow process limits.

There is therefore a need in the technical field for a method for anti-scale coating of steel sheets made of high-strength steel materials and for an anti-scale coating.

The present invention is based on the object of providing a method for anti-scale coating of steel sheets made of high-strength steel materials, in which the risk of hydrogen embrittlement of the steel material is mini and which ensures adequate weldability of the coated steel sheets. Another object underlying the present invention is to provide an anti-scale coating for a steel sheet.

• - Bereitstellen eines Stahlblechs aus einem Stahlwerkstoff mit einer Zugfestigkeit im gehärteten Zustand von mindestens 1.700 MPa,
• - Bereitstellen einer Beschichtung, wobei die Beschichtung ein Bindemittel und Metallpigmente umfasst, und
• - Beschichten des Stahlblechs mit der Beschichtung.

In order to achieve the object on which the invention is based, a method for anti-scale coating of a steel sheet, in particular a body component, is proposed, comprising the steps

• - Provision of a steel sheet made of a steel material with a tensile strength in the hardened state of at least 1,700 MPa,
• - providing a coating, the coating comprising a binder and metallic pigments, and
• - coating the steel sheet with the coating.

Surprisingly, it has been shown that a sheet steel coated with a coating comprising a binder and metal pigments and made from a high-strength steel material with a tensile strength in the hardened state of at least 1,700 MPa can be further processed reliably. With a steel sheet coated in this way, there is little or no hydrogen embrittlement, so that the formability of the steel sheet is guaranteed and the risk of delayed crack formation is minimized. In addition, passive corrosion protection can also be provided if necessary.

In the prior art, coatings comprising a binder and metal pigments have hitherto only been used for steel sheets made from a steel material with a tensile strength in the hardened state of approximately 1,500 MPa. Up until the present invention, there were no attempts or efforts to use such a coating for high-strength steels with a tensile strength in the hardened state of approximately 1,700 MPa or higher.

It is preferably provided that the steel material is a 34MnB5 steel.

Such steels are also known under the designation CR1900. A 34MnB5 steel material has a tensile strength in the hardened condition of more than 1,700 MPa. Before the invention, steel sheets made of 34MnB5 steel materials could not be coated with an anti-scale coating to a sufficient extent without problems occurring in formability due to hydrogen embrittlement.

With further advantage, it can be provided that the carbon content of the steel material is greater than 0.22% by weight, preferably greater than 0.27% by weight, more preferably greater than 0.30% by weight, particularly preferably greater than or equal to 0.34% by weight .%, is.

Steel materials with a carbon content of more than 0.22% have increased tensile strengths in the hardened condition, which are in the range of 1,700 MPa or more.

34MnB5 steel materials have a carbon content of 0.34% by weight.

Furthermore, the steel material can be a heat-treated steel and contain proportions of manganese.

The steel sheet can preferably be produced by cold rolling the steel material.

Provision is preferably made for the coating to be applied to the steel sheet in a wet-chemical process, in particular in a coil coating process, more particularly on a coil coating system, or in a spraying process, or in a doctor blade process.

With the coating provided according to the method, steel sheets made of a high-strength steel material with a tensile strength in the hardened state of at least 1,700 MPa can also be coated in a coil coating method compared to the prior art.

It is further preferably provided that the binder is a silane, preferably methyltriethoxysilane (MTEOS), propyltriethoxysilane (PTeos), phenyltriethoxysilane (PhTeos), tetraethoxysilane (TEOS), 3-glycidyloxypropyltriethoxysilane (GPTS), aminopropyltriethoxysilane (APTS), and/or a silicone, preferably a silicone resin and/or a metal alkoxide, preferably a butylate, a propylate, or a butyl glycolate of Ti, Zr, Al, Si.

The binder can also contain mixtures of the components mentioned above. Mixtures of metal alkoxides with silanes are particularly preferred. Titanium butylate is used as a particularly preferred metal alkoxide. In this case, different mixing ratios of the alkoxides and/or silanes and/or silicones, in particular the silicone resins, can preferably be provided.

Pre-hydrolysis of the silanes, silicones or metal alkoxides with water or acids can preferably be carried out using a sol-gel process. The resulting hydrolyzate is referred to as a binder.

It can further preferably be provided that the metal pigments comprise Al, Mg, Zn or Sn or mixtures thereof, the metal pigments preferably comprising Al flakes or Al powder or mixtures thereof.

The Al flakes preferably have an average grain size D50 of 5-50 μm, particularly preferably 10-40 μm, very particularly preferably 20-30 μm.

A larger size of the Al flakes results in a smaller relative surface area and thus less oxide formation. In the case of smaller Al flakes, there is a greater contact resistance due to the higher oxide formation and thus poorer weldability.

The contact resistance of sheets coated on both sides with approx. 2-3 μm is preferably 4 mOhm or less for a sheet thickness of 1.25 mm after a holding time of 3 minutes at 920° C. With a particle size of 20-25 µm, there is a volume resistance of 2.8 mOhm. The uncoated sheet also shows 2.8 mOhm. The volume resistance can be measured with the copper electrodes commonly used in resistance spot welding and an electrode pressure of 3000 N.

The ratio of the binder to the metal pigments, measured on the solid, is preferably between 10:90% by weight and 70:30% by weight, particularly preferably between 20:80% by weight and 40:60% by weight.

Provision is preferably made for the coating to contain a solvent to adjust the solids content of the coating solution.

The solvent can be, for example, xylene, butyl glycol or butyl acetate. In principle, the solvent can be a standard solvent for coil coating processes.

More preferably, it can be provided that the coating comprises at least one additive, preferably curing catalysts, in particular amines, phosphates, phosphate esters, inorganic acids, and/or dyes or color pigments.

Provision is preferably made for the ratio of curing catalysts to binder to be between 0% and 10%, particularly preferably between 0.5% and 5%.

By adding additives in the form of dyes or color pigments, the heat absorption properties of the steel sheet coated with the coating can be adjusted. This is particularly advantageous for the further processing of the coated steel sheet in an oven, for example in an oven of a hot-forming plant.

The steel thickness of the steel sheet is preferably between 0.8 mm and 2.5 mm.

More preferably, it can be provided that the coating contains customary anti-corrosion pigments, such as oxides, phosphates, sulfides of Ca, Ba, Zn, Zn, Mg or Fe, particularly preferably Zn phosphate or Mg phosphate pigments or mixtures thereof.

The ratio of metal pigments to anti-corrosion pigments is preferably from 1:0.1 to 1:0.5.

With a further advantage it can be provided that the coating is applied to the steel sheet with a wet layer thickness of 5 μm to 25 μm, preferably from 1 μm to 20 μm, particularly preferably from 1.5 μm to 10 μm, and or that the coating has a Dry layer thickness from 0.5 μm to 10 μm, preferably from 1.5 μm to 5 μm, particularly preferably from 2 μm to 4 μm.

The solids in the coating solution are preferably between 20% by weight and 80% by weight, particularly preferably between 20% by weight and 50% by weight.

A further advantage of the coating used according to the method lies in the fact that the coating can be phosphated after hot forming. In addition, a steel sheet coated according to the process has particularly good adhesion properties for paints after hot forming. The paints can be applied in particular in a cathodic dip coating process.

• - Trocknen und/oder Härten der Beschichtung, bevorzugt nach dem Coilcoating, weiter bevorzugt in einem Gas- oder Elektroofen, bei einer Temperatur von bis zu 300°, bevorzugt von 100° bis 300°, besonders bevorzugt von 200° bis 250°, und/oder über einen Trockenzeitraum von weniger als 10 min, bevorzugt von weniger als 5 min, besonders bevorzugt von weniger als 2 min,

umfasst. It is preferably provided that the method includes the step:

• - drying and/or curing of the coating, preferably after coil coating, more preferably in a gas or electric oven, at a temperature of up to 300°, preferably from 100° to 300°, particularly preferably from 200° to 250°, and /or over a drying period of less than 10 minutes, preferably less than 5 minutes, particularly preferably less than 2 minutes,

includes.

Inductive or conductive heating or infrared (NIR) heating is also possible for rapid hardening processes.

The curing of the coating can, in particular, also take place at room temperatures. However, it is preferably provided that the curing takes place under coil coating conditions at temperatures between 200° C. and 250° C. and more preferably with holding times of less than 2 minutes.

The method can therefore be carried out efficiently and quickly.

• - Herstellen eines Blechschnitts durch Schneiden des Stahlblechs in einer Schneideanlage, und
• - Bereitstellen des Blechschnitts an einer Warmumformanlage,

umfasst.More preferably, it can be provided that the method has the steps:

• - producing a sheet metal section by cutting the steel sheet in a cutting machine, and
• - Provision of the sheet metal cutting at a hot forming plant,

includes.

A steel sheet coated according to the method, in particular a coil coated according to the method, can preferably be provided on a blanking plant. The sheet metal section can be cut mechanically. It is also possible for a shaped blank to be cut by means of laser or water jet cutting. All hot-forming applications known from the prior art are conceivable, such as tailored welded blanks or tailored rolled blanks or patch boards.

The sheet metal section, in particular the shaped blank, can be provided at a hot-forming plant. A hot forming plant consists of a furnace inlet, a heating device, for example a gas-heated or electrically heated roller hearth furnace, and a furnace outlet with a centering table. The sheet metal section can also be heated, in particular rapid heating, by inductive or conductive methods or by means of contact heating or fast infrared (NIR).

The coated sheet metal section is heated and mechanically formed in the hot forming plant. The sheet metal section can be hardened over a specific closing time and by applying a high surface pressure.

• - Erwärmen des Blechschnitts in einer Erwärmungsanlage der Warmumformanlage, bevorzugt konduktiv oder induktiv oder in einem gasbeheizten oder elektrisch beheizten Rollenherdofen, auf eine Temperatur oberhalb der Austentisierungstemperatur des Stahlwerkstoffs, bevorzugt auf mehr als 800°C, besonders bevorzugt auf mehr als 870°C, wobei der Blechschnitt nach Erreichen der Austentisierungstemperatur weniger als 5 Minuten, bevorzugt weniger als 2 Minuten, weiter bevorzugt weniger als 1 min, insbesondere bevorzugt weniger als 30 Sekunden, in der Erwärmungsanlage verbleibt, umfasst.

With a further advantage it is provided that the method includes the step:

• - Heating the sheet metal section in a heating system of the hot forming system, preferably conductively or inductively or in a gas-heated or electrically heated roller hearth furnace, to a temperature above the austenitization temperature of the steel material, preferably to more than 800°C, particularly preferably to more than 870°C, wherein the sheet metal section remains in the heating system for less than 5 minutes, preferably less than 2 minutes, more preferably less than 1 minute, particularly preferably less than 30 seconds after the austenitizing temperature has been reached.

The austenitization temperature of the steel material, in particular the steel material made from 34MnB5 steel, is generally above 750°C. When the shaped blank or the sheet metal section has reached the austenitizing temperature, the sheet metal section preferably remains in the hot-forming system for an additional furnace dwell time of less than 2 minutes in order to ensure complete austenitization and to set a homogeneous material structure. It is particularly preferred if the additional residence time in the oven is about 20 to 30 seconds.

In comparison to the well-known AlSi melt coatings, no longer residence time in the oven is required for diffusion. It can preferably be provided that a maximum oven residence time is not exceeded, the maximum oven residence time preferably being at most 10 minutes, more preferably at most 6 minutes, in particular preferably at most 2 minutes. The maximum oven residence time is particularly preferably 2 to 6 minutes.

With the coating applied according to the method, a significantly reduced oven dwell time compared to the prior art is possible due to the better emission coefficient and the significantly reduced layer thickness. In addition, the use of a protective gas or a special furnace atmosphere can be dispensed with. Optionally, air may be added to control the dew point in the hot stamping facility, particularly in a gas heated or electrically heated roller hearth furnace of the hot stamping facility.

Provision can preferably be made for a dew point measurement and control to be carried out for critical components with the supply of dried air (e.g. TP=-5°C). In principle, partial heating of the blank or differential cooling of the blank can also be carried out during operation of the hot-forming plant.

In the hot forming plant, the anti-scale effect occurs on the sheet steel or at least significantly less scale on the surface of the sheet metal section compared to uncoated reference material, since the thin coating protects the steel material from oxygen and prevents oxygen from diffusing. Hydrogen embrittlement does not occur.

• - Einlegen des Blechschnitts in ein Presshärtewerkzeug, wobei der Blechschnitt bevorzugt in dem Presshärtewerkzeug in einem Warmumformungsschritt umgeformt und/oder durch einen Kontaktdruck über eine Zuhaltezeit gehärtet wird, und
• - Entnahme des geformten Blechschnitts aus dem Presshärtewerkzeug, bevorzugt bei einer Temperatur des Blechschnitts von unterhalb 250°C,

umfasst.With a further advantage it can be provided that the method has the steps:

• - Insertion of the sheet metal section in a press-hardening tool, wherein the sheet metal section is preferably formed in the press-hardening tool in a hot-forming step and/or hardened by contact pressure over a closed time, and
• - removal of the shaped sheet metal section from the press-hardening tool, preferably at a temperature of the sheet metal section below 250°C,

includes.

In this case, it can preferably be provided that the sheet metal section has a temperature of approx. 600° C. when it is placed in the press-hardening tool, although this can also deviate from this in some areas due to soft zones caused by the component. The press-hardening tool can be media-cooled; partial heating of individual mold segments of the press-hardening tool is also conceivable. In addition, hot trimming or hot punching can be carried out in the press-hardening tool. The shaped sheet metal section is then preferably cooled to a temperature below 250° C., thereby hardened and then removed from the press-hardening tool.

• - Beschneiden des Blechschnitts, bevorzugt in einem Warmbeschnitt während oder nach der Umformung, und/oder in einem Laserbeschnitt nach der Umformung, umfasst.

It is preferably provided that the method includes the step:

• - Trimming of the sheet metal section, preferably in a hot trimming during or after the forming, and/or in a laser trimming after the forming.

• - Zumindest teilweises Entfernen der Beschichtung, bevorzugt in einem Medienstrahlprozess,

umfasst.More preferably, it can be provided that the method includes the step:

• - At least partial removal of the coating, preferably in a media blasting process,

includes.

The coating can be removed from the sheet metal section or component surface partially and/or only on one side of the sheet metal section or component. The reason for this lies in the increased contact resistance of the layer after hot forming or in the formation of oxidic layers.

At least partial removal of the coating is not absolutely necessary, but can take place in areas of the steel sheet or the sheet metal section to which further sheet metal sections are to be joined. This enables process-reliable joining of the sheet metal sections, and in particular of body components produced from the sheet metal sections.

The sheet metal sections can also be referred to as components.

The media blasting process can be, for example, a wheel blasting process.

• - Verbauen des Blechschnitts als Bauteil in einer Karosserie, und
• - bevorzugt Durchführung eines Tauchlackierungsverfahren für die Karosserie, umfasst.

With a further advantage it can be provided that the method includes the step:

• - Installing the sheet metal section as a component in a body, and
• - preferably carrying out a dip coating process for the body, includes.

The installation of the sheet metal section as a component in a body can take place conductively or by means of spot or laser welding, in particular by means of resistance spot welding. Form-fitting connections or an adhesive method can also be provided. Optionally, however, blasting of the components can also be dispensed with.

With a further advantage, the sheet metal section, or the body including the sheet metal section, can be painted. The painting can be done in a cathodic dip painting process (KTL process).

A particular advantage of the invention is that the applied coating does not have to be removed for the painting process. A zinc phosphate layer forms on the thin coating. In contrast to known AlSi coatings, the steel sheet coated according to the method can therefore be phosphated.

A further solution to the problem on which the invention is based consists in providing a body component comprising a steel sheet which has been coated in accordance with a method described above.

A further solution to the problem on which the invention is based consists in providing an anti-scale coating for a steel sheet, in particular for a body component.

The anti-scale coating comprises a binder and a metal pigment.

The anti-scale coating can be formed in accordance with the coating described in connection with the method. What is particularly advantageous about the anti-scale coating according to the invention is that it can be used to coat a sheet steel made of a high-strength steel material with a tensile strength in the hardened state of at least 1,700 MPa.

The anti-scale coating comprises a binder and one or more metal pigments. It can contain a solvent and additional additives such as anti-corrosion pigments, leveling additives, dyes or color pigments.

The solvent can be xylene, butyl glycol, butyl acetate. In principle, the solvent can be a standard solvent for coil coating processes.

Yet another solution to the problem on which the invention is based is a method for producing a body component, the method comprising the method described above for anti-scale coating of a steel sheet.

Possible processes for producing the coating are explained below by way of example and not by way of limitation:

example 1

Batch 1: 100 g of aluminum flakes are placed and 100 g of xylene are poured over them. The batch is left to stand in a closed vessel for 24 hours and then homogenized for 2 hours using a slow-running stirrer.

Mixture 2: In a second container, 200 g of tetra-n-isopropyl orthotitanate and 50 g of tetraethoxysilane (TEOS) are mixed with 100 g of butyl glycol. With stirring, 50 g of 1% sulfuric acid are slowly added dropwise over a period of 3 hours so that no precipitation occurs. The batch is stirred slowly for a further 24 hours.

The hydrolyzate (batch 2) is then added to the pasted and homogenized aluminum (batch 1) with vigorous stirring, and stirring is continued for 24 hours.

The finished coating material can be applied to steel coils by roller application, e.g. in a coil coating system, and baked at a PMT (peak metal temperature) of approx. 250°C. It can also be applied by spraying or squeegeeing onto cut blanks or molded blanks or cut components.

The sheet metal sections obtained after the coated coils have been cut to size can be used at temperatures of up to 1,000°C for subsequent hot forming processes (press hardening) without scaling occurring.

Subsequent processing steps, such as welding processes (e.g. MAG welding, spot welding), can be carried out with a target layer thickness of 2.5 to 4 µm.

Further processing steps, such as phosphating processes or KTL coating, are also possible.

If the coating is used purely as a forming aid, the coating can also be sandblasted without any problems.

example 2

Batch 1: 100 g of aluminum flakes are placed and 100 g of xylene are poured over them. The batch is left to stand in a closed vessel for 24 hours and then homogenized for 2 hours using a slow-running stirrer.

Mixture 2: In a second container, 200 g of tetra-n-isopropyl orthotitanate and 50 g of methyltriethoxysilane (TEOS) are mixed with 100 g of butyl glycol. With stirring, 50 g of 1% phosphoric acid are slowly added dropwise over a period of 3 hours so that no precipitation occurs. The batch is stirred slowly for a further 24 hours.

Batch 3: 100 g of Pigmentan 465 M (Pigmentan) are made into a paste in 100 g of BG overnight.

The hydrolyzate (batch 2) and the anti-corrosion pigment (batch 3) are then added to the pasted and homogenized aluminum (batch 1) with vigorous stirring, and stirring is continued for 24 hours.

The finished coating material can be applied to high-strength steel coils by roller application, e.g. in a coil coating system, and baked at a PMT (peak metal temperature) of approx. 250°C. It can also be applied to cut-to-size components using the spray or squeegee method.

The sheet metal sections obtained after the coated coils have been cut to size can be used at temperatures of up to 1,000°C for subsequent hot forming processes (press hardening) without any scaling occurring.

Subsequent processing steps such as welding processes (eg MAG welding, spot welding) can be carried out with a target layer thickness of 2.5 to 4 µm.

Further processing steps such as phosphating processes or KTL coating are also possible.

In corrosion tests on the coated and formed sheet metal sections, after 24 hours of exposure in the salt spray test (DIN EN ISO 9227), a significantly improved corrosion resistance compared to uncoated sheet metal sections is shown.

Example 3

Batch 1: 100 g of aluminum flakes are placed and 100 g of xylene are poured over them. The batch is left to stand in a closed vessel for 24 hours and then homogenized for 2 hours using a slow-running stirrer.

Mixture 2: In a second container, 150 g of 3-glycidoxypropyltriethoxysilane (GPTS), 100 g of silica sol 300/30 are slowly hydrolyzed with 5 g of HCl conc with vigorous stirring, stirred for 24 hours and then mixed with 100 g of butyl glycol.

Batch 3: 100 g of Pigmentan 465 M (Pigmentan) are made into a paste in 100 g of BG overnight.

The hydrolyzate (batch 2) and the anti-corrosion pigment (batch 3) are then added to the pasted and homogenized aluminum (batch 1) with vigorous stirring, and stirring is continued for 24 hours.

The finished coating material can be applied to high-strength steel coils by roller application, e.g. in a coil coating system, and baked at a PMT (peak metal temperature) of approx. 250°C. It can also be applied to cut-to-size components using the spray or squeegee method.

The sheet metal sections obtained after the coated coils have been cut to size can be used at temperatures of up to 1,000°C for subsequent hot forming processes (press hardening) without any scaling occurring.

Subsequent processing steps such as welding processes (e.g. MAG welding, spot welding) can be carried out with a target layer thickness of 2.5 to 4 µm.

Further processing steps such as phosphating processes or KTL coating are also possible.

In corrosion tests on the coated and formed sheet metal sections, after 24 hours of exposure in the salt spray test (DIN EN ISO 9227), a significantly improved corrosion resistance compared to uncoated sheet metal sections is shown.

example 4

Mixture 1: 100 g of aluminum flakes (Eckard, Stapa 2 n.L.) are placed and 100 g of xylene are poured over them. The batch is left to stand in a closed vessel for 24 hours and then homogenized for 2 hours using a slow-running stirrer.

Mixture 2: In a second container, 100 g silicone resin flakes REN 100 flakes (Wacker) are dissolved in 100 g butyl glycol with stirring 24 and 5 g phosphoric acid ester MDHA (Clariant) are added.

Batch 3: 100 g of Pigmentan 465 M (Pigmentan) are made into a paste in 100 g of BG overnight.

The pasted and homogenized aluminum (batch 1) is then mixed with the silicone resin (batch 2) and the anti-corrosion pigment (batch 3) with vigorous stirring and stirred for a further 24 hours.

The finished coating material can be applied to high-strength steel coils by roller application, e.g. in a coil coating system, and baked at a PMT (peak metal temperature) of approx. 250°C. It can also be applied to cut-to-size components using the spray or squeegee method.

The sheet metal sections obtained after the coated coils have been cut to size can be used at temperatures of up to 1,000°C for subsequent hot forming processes (press hardening) without any scaling occurring.

Subsequent processing steps such as welding processes (e.g. MAG welding, spot welding) can be carried out with a target layer thickness of 2.5 to 4 µm.

Further processing steps such as phosphating processes or KTL coating are also possible.

In corrosion tests on the coated and formed sheets, after 24 hours of aging in the salt spray test (DIN EN ISO 9227), a significantly improved corrosion resistance compared to uncoated sheet metal sections is shown.

• 1 ein Ablaufdiagramm für ein Verfahren zur Zunderschutzbeschichtung eines Stahlbleches, und
• 2 ein Ablaufdiagramm für ein Verfahren zur Herstellung eines mit einer Zunderschutzbeschichtung versehenen Karosseriebauteils.

The invention is explained in more detail below with reference to the accompanying figures. Show it:

• 1 a flow chart for a method for anti-scaling coating of a steel sheet, and
• 2 a flow chart for a method for producing a body component provided with an anti-scale coating.

1 shows a flowchart for a method 100 for anti-scale coating of a steel sheet.

In a first step S1, a steel sheet made from a steel material with a tensile strength in the hardened state of at least 1,700 MPa is provided. In a second method step S2, which can take place at the same time as or before method step S1, a coating is provided, the coating comprising a binder and metal pigments. In a third method step S3, the steel sheet is coated with the coating.

2 shows a flowchart for a method 100 for producing a body component provided with an anti-scale coating.

In a first process step T1, a steel sheet is produced from a steel material with a tensile strength in the hardened state of at least 1,700 MPa in a cold rolling process. In a second process step T2, the rolled steel sheet is made available for a process for anti-scale coating. In a third method step T3, which can take place at the same time as the second method step or before the first or second method step, a coating is provided, the coating comprising a binder and metal pigments. In a fourth method step T4, the steel sheet is coated with the coating. In a fifth process step T5, the steel sheet provided with the coating is hardened at a temperature of 200°C to 250°C. In a sixth method step T6, the steel sheet is provided for the production of a sheet metal section on a cutting system. In a seventh method step T7, the sheet metal section is provided at a hot-forming plant. In an eighth method step T8, the sheet metal section is heated in the hot forming plant to a temperature above the austenitizing temperature of the steel material and remains in the hot forming plant for about 20 to 30 seconds after the austenitizing temperature has been reached. In a ninth method step T9, the sheet metal section removed from the hot-forming system is placed in a press-hardening tool. In a tenth method step T10, the sheet metal section removed from the press-hardening tool is at least partially freed from the coating by means of a media blasting process, and in a further method step T11 the sheet metal section is installed as a body component in a body. Then, in a twelfth method step T12, the body can be painted in a dip coating process.

Reference List

100

procedure

S1-S3

process steps

T1-T12

process steps

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US 2005/0065269 A1 [0003]
• US 2010/0098956 A1 [0004]
• US 2012/0009340 A1 [0005]

Claims (13)

Method (100) for anti-scale coating of a steel sheet, in particular a body part, comprising the steps: - Provision of a steel sheet made of a steel material with a tensile strength in the hardened state of at least 1,700 MPa, - providing a coating, the coating comprising a binder and metallic pigments, and - coating the steel sheet with the coating. Method (100) according to claim 1 , characterized in that the steel material is a 34MnB5 steel and/or that the carbon content of the steel material is greater than 0.22% by weight, preferably greater than 0.27% by weight, more preferably greater than 0.30% by weight, more preferably greater than or equal to 0.34% by weight. Method (100) according to claim 1 or 2 , characterized in that the coating is applied to the steel sheet in a wet-chemical process, preferably in a coil coating process, in particular on a coil coating system, in a spray process, in a doctor blade process. Method (100) according to one of the preceding claims, characterized in that the binder is a silane, preferably methyltriethoxysilane MTEOS, propyltriethoxysilane PTeos, phenyltriethoxysilane PhTeos, tetraethoxysilane TEOS, 3-glycidyloxypropyltriethoxysilane GPTS, aminopropyltriethoxysilane APTS, and/or a silicone, preferably a silicone resin. and/or a metal alkoxide, preferably a butylate, a propylate, or a butyl glycolate of Ti, Zr, Al, Si, and/or that the metal pigments comprise Al, Mg, Zn or Sn or mixtures thereof, the metal pigments preferably Al flakes or Al powder, the Al flakes particularly preferably having an average particle size D50 of 5-50 μm, more preferably of 10-40 μm, very particularly preferably of 20-30 μm. Method (100) according to claim 4 , characterized in that the silanes and/or the silicones and/or the metal alkoxides are prehydrolyzed with water or acids via a sol-gel process. Method (100) according to one of the preceding claims, characterized in that the coating comprises at least one additive, preferably curing catalysts, in particular amines, phosphates, phosphate esters, inorganic acids, and/or dyes, and/or that the coating particularly preferably contains anti-corrosion pigments Zn phosphate or Mg phosphate or mixtures thereof. Method (100) according to any one of the preceding claims, further comprising the step of: - Drying and/or curing of the coating, preferably in a gas or electric oven, at a temperature of up to 300°, preferably from 100° to 300°, particularly preferably from 200° to 250°, and/or over a drying period of less than 10 minutes, preferably less than 5 minutes, particularly preferably less than 2 minutes. Method (100) according to any one of the preceding claims, further comprising the steps of: - producing a sheet metal section by cutting the steel sheet in a cutting machine, and - Providing the sheet metal cut at a hot forming plant. Method (100) according to claim 8 , further comprising the step of: - heating the sheet metal section in a heating system of the hot forming system, preferably conductively or inductively or in a gas-heated or electrically heated roller hearth furnace, to a temperature above the austenitizing temperature of the steel material, preferably to more than 800° C., particularly preferably to more than 870°C, the sheet metal section remaining in the heating system for less than 5 minutes, preferably less than 2 minutes, more preferably less than 1 minute, particularly preferably less than 30 seconds after the austenitizing temperature has been reached. Method (100) according to claim 9 , further comprising the steps of: - placing the sheet metal section in a press-hardening tool, the sheet metal section preferably being formed in the press-hardening tool in a hot-forming step and/or hardened by contact pressure over a holding time, and - removing the shaped sheet metal section from the press-hardening tool, preferably with a Sheet metal cutting temperature below 250°C. Method (100) according to claim 10 , further comprising the step of: - trimming the sheet metal section, preferably in a hot trimming during or after the forming, and/or in a laser trimming after the forming. Method (100) according to claim 11 , further comprising the step of: - at least partially removing the coating, preferably in a media blasting process. Body component comprising a steel sheet coated according to a method according to one of the preceding claims.

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