Multistage process for coating components having steel surfaces with corrosion protection

Abstract

The present invention relates to a multistage process in which a series of components which each have surfaces of steel are initially provided with a conversion layer based on the elements Zr and / or Ti and are subsequently dip-coated, wherein the conversion treatment stage is followed by a rinsing stage in which at least the surfaces of steel of each component are brought into contact with an aqueous composition containing hydrogen peroxide. In the process according to the invention, excellent corrosion protection on the surfaces of steel is achieved even under unfavourable process conditions which usually promote corrosion defects on the steel surfaces and have a negative effect overall on the corrosion protection.

Description

[0001] Multi-stage process for corrosion protection coating of components with steel surfaces

[0002] The present invention relates to a multi-stage process in which a series of components, each with steel surfaces, is first coated with a conversion layer based on the elements Zr and / or Ti and then dip-coated. The conversion treatment step is followed by a rinsing step in which at least the steel surfaces of each component are brought into contact with an aqueous composition containing hydrogen peroxide. In the process according to the invention, excellent corrosion protection is achieved on the steel surfaces, even under unfavorable process conditions that typically promote corrosion defects on the steel surfaces and have an overall detrimental effect on corrosion protection.

[0003] In the corrosion-protective pretreatment of components with surfaces made of steel, galvanized steel, and / or aluminum, thin-film passivation based on amorphous conversion coatings based on oxides and hydroxides of the elements Zr and / or Ti has become widely established as an alternative to phosphating, which forms crystalline coatings. Efforts to further develop this type of conversion coating are primarily aimed at establishing resource-saving and chromium-free passivations that provide an excellent adhesion base for subsequently applied paint systems, particularly dip coatings, with the aim of achieving corrosion protection comparable to that achieved with trication zinc phosphating.Especially for amorphous thin films, such as those resulting from conversion treatments from acidic aqueous solutions containing water-soluble compounds of the elements Zr and / or Ti, controlled layer formation and the growth of coatings that are as defect-free as possible are of great importance. For this purpose, the prior art focuses on influencing the kinetics of layer formation, as described in WO 2023 / 275270, and proposes, for example, sequential formation of the conversion layer in several wet-chemical process steps to create the layer deposits based on the hydroxides and oxides of the elements Zr and / or Ti, which bring about the most complete conversion possible of the conversion treatment based on fluorocomplexes of the elements Zr and / or Ti. This is intended to prevent fluorides from remaining in the thin film, which can cause local layer defects upon contact with corrosive media.Another process for conversion coating formation, described as an example in EP 1 455 002 A1, aims to reduce the proportion of fluorides in the conversion coating and the associated improvement in corrosion behavior and paint adhesion to a subsequently applied electrocoat. EP 1 455 002 A1 proposes adding magnesium, calcium, a Si-containing compound, zinc, or copper to the conversion solution and, alternatively or in combination, drying the conversion coating or rinsing it with an alkaline aqueous composition.On the other hand, serial anti-corrosive pre-treatment in industrial painting lines has shown that the drying of the conversion coating on components with steel surfaces, whether deliberately induced after the conversion treatment stage or simply unavoidable due to the spatial conditions of the respective painting line when transferring the components to the dip-coating stage, is problematic for corrosion protection, paint adhesion and the appearance of the paint finish, with the latter disadvantage being particularly due to the formation of flash rust during drying and / or longer transfer times or temporary plant downtime.

[0004] Based on this state of the art, the present task is to establish a process for providing conversion coatings on metal surfaces, particularly steel surfaces, that are as defect-free as possible. This process, during industrial pretreatment and dip-coating of a wide variety of components, provides high robustness against corrosive deterioration during the phase of transferring the components from the conversion treatment stage to the dip-coating stage. The process is intended to achieve conversion coatings, especially on steel, that are not prone to flash rust formation and can therefore be dip-coated even in the partially dried state without loss of corrosion protection.

[0005] Ideally, this prevents fluctuations in corrosion protection performance and the appearance of dip-coated components during exceptionally long transfer times from the conversion treatment zone to the painting zone, for example, during a temporary plant shutdown. The process must also be suitable for effectively protecting components consisting of a mix of different metals, especially steel, zinc, and aluminum, from corrosion.

[0006] This object is achieved by a multi-stage process for the corrosion-protective treatment of components in series, which comprise steel surfaces, in which each component of the series undergoes the successive treatment stages i)-iii): i) conversion treatment stage comprising bringing into contact with an acidic aqueous composition containing a. at least 0.05 mmol / kg of fluorocomplexes of the elements Zr and / or Ti calculated as the amount of the elements Zr and / or Ti, and b. an amount of free fluoride; ii) rinsing stage comprising one or more immediately successive rinsing steps, wherein at least one rinsing step is carried out by bringing into contact with an aqueous composition having a pH above 4.00 containing at least 20 mg / kg of hydrogen peroxide; iii) coating stage comprising dip painting by bringing into contact with an aqueous dispersion of an organic binder.A series corrosion-protective treatment of components occurs when a large number of components are brought into contact with the treatment solution provided in the respective treatment stages i)-iii) of the process according to the invention and typically stored in system tanks, with the individual components being brought into contact sequentially and thus separated in time. The system tank is the container in which the respective treatment solution—that is, the acidic aqueous composition of the conversion treatment stage, the aqueous composition containing hydrogen peroxide of the rinsing stage, and the aqueous dispersion containing the organic binder of the coating stage—is located for the purpose of the series corrosion-protective treatment according to the present invention.

[0007] If, within the scope of the present invention, reference is made to the treatment of a component composed of a metallic material, in particular to the surfaces of the steel material to be treated in the process according to the invention, this includes all materials that contain more than 50 at.% of the respective element, i.e. iron in the case of steel. A corrosion-protective treatment always affects the surfaces of the component that are formed from metallic materials. The material can be a uniform material or a coating. For example, galvanized steel grades according to the invention consist of both steel and zinc, whereby at the cut edges and grinding points, for example of an automobile body made of galvanized steel, surfaces of steel can be exposed and, according to the invention, the steel material is then pretreated.

[0008] Insofar as in the context of the present invention the concentration of an active component or compound is given as an amount of substance (mol, mmol, g, mg) per kilogram, this is the amount of substance based on the weight of the respective total composition.

[0009] The components treated according to the present invention can be any spatial structure of any shape and design that originates from a manufacturing process, in particular semi-finished products such as strips, sheets, rods, pipes, etc. and composite structures assembled from the aforementioned semi-finished products, in particular automobile bodies, wherein the semi-finished products are preferably connected to one another by gluing, welding and / or flanging to form the composite structure.

[0010] Preferably, the components of the series are first cleaned and / or degreased prior to conversion treatment step i), particularly preferably using an alkaline, aqueous, surfactant-containing composition. In connection with such cleaning / degreasing of the components to be treated for corrosion protection in the process according to the invention, it has been found that alkaline pretreatment steps influence the susceptibility of the steel surfaces to flash rust. Particularly when treating components that have zinc surfaces in addition to steel surfaces, the zinc surfaces are often passivated prior to conversion treatment step i) using an iron-containing alkaline degreasing or cleaning step, in which the steel surfaces are also treated accordingly.The steel surfaces that undergo such a so-called icing process in conjunction with the other surfaces of the component prove to be particularly susceptible to the formation of flash rust, which, however, can be effectively prevented by the present method according to the invention.

[0011] In a preferred embodiment of the method according to the invention for the corrosion-protective treatment of components in series, which in addition to steel surfaces also include zinc surfaces, each component of the series first undergoes an alkaline treatment stage before the aforementioned successive treatment stages i)-iii) are carried out, wherein within the alkaline treatment stage, in at least one treatment step, at least the surfaces of steel and zinc of the components of the series are brought into contact with an alkaline aqueous composition which

[0012] (a) at least 50 mg / kg, preferably at least 100 mg / kg of iron(III) ions,

[0013] (b) at least 100 mg / kg of phosphate ions,

[0014] (c) optionally at least one complexing agent, which is preferably selected from organic compounds which have at least one functional group selected from -COOX, -OPO3X and / or -PO3X, where X represents either a H atom or an alkali and / or alkaline earth metal atom, and / or from condensed phosphates calculated as PO4, wherein the alkaline aqueous composition has a free alkalinity of at least 1 point, but preferably less than 6 points, and a pH of at least 10.5, preferably at least 11.0. The free alkalinity is determined by titrating 2 ml of bath solution, preferably diluted to 50 ml, with a 0.1 N acid such as hydrochloric acid or sulfuric acid to a pH of 8.5. The consumption of acid solution in ml indicates the free alkalinity point.

[0015] Treatment stages i)-iii) of the process according to the invention each comprise at least one treatment step involving contacting the components of the series with a more precisely defined aqueous composition characteristic of the treatment stage. For the purpose of contacting, these characteristic compositions are either stored or kept in system tanks. Contacting can occur either in the system tank, for example, by immersion in a composition stored there, or outside the system tank, for example, by spraying a composition stored in the system tank in a spray chamber.

[0016] The rinsing stage ii) is of central importance for the success of the process according to the present invention. During the rinsing stage, the components of the series are freed from any wet film adhering to the conversion treatment stage – firstly, to effectively complete the conversion of the surface, and secondly, to prevent the carryover of active components into the dip-coating stage. For this purpose, the rinsing stage consists of one or more immediately consecutive rinsing steps. In the context of the present invention, rinsing steps are immediately consecutive if the components are not subjected to another wet-chemical treatment step that is not a rinsing step in the meantime, and if, after the complete removal of a component of the series, for example, from a system tank containing a rinsing composition,or after completion of contacting a surface of the component with an aqueous composition stored in the system tank of a rinsing step, no more than 120 seconds, preferably no more than 90 seconds, particularly preferably no more than 60 seconds, elapse before a surface of the component is brought into contact with an aqueous composition of coating stage iii). For the actual function of a rinsing stage, which consists in preventing the carryover of active components into downstream wet-chemical treatment stages, it is beneficial and therefore also preferred within the scope of the present invention if rinsing stage ii) comprises several immediately successive rinsing steps for contacting the components of the series with an aqueous composition stored in the system tank of the respective rinsing step,wherein preferably at least a partial volume of the aqueous composition stored in the system tank of the last rinsing step is fed back into the system tank of the first rinsing step of the rinsing stage ii) and is replaced in the system tank of the last rinsing step of the rinsing stage ii) by an at least equally large partial volume of an aqueous composition, wherein this aqueous composition for replacing the partial volume fed back into the system tank of the first rinsing step preferably has a specific conductivity of less than 20 pScrrr, 1 has.

[0017] Within the rinsing stage, the wet film from the conversion treatment stage should be removed as far as possible without incorporating additional elements into the fresh conversion layer. In particular, it is important to avoid the absorption of elements that have a detrimental effect on corrosion protection performance into the conversion layer. Therefore, it is preferred if the aqueous composition of the single or final rinsing step of rinsing stage ii), preferably every aqueous composition of all rinsing steps of rinsing stage ii),

[0018] (a) less than 10 mg / kg of compounds of the metals Bi, Ni, Co and / or Cu dissolved in water, calculated as the amount of the respective element in the aqueous composition, preferably less than 10 mg / kg of compounds of such metals dissolved in water which have a standard reduction potential greater than -0.40 V (SHE), calculated as the amount of the respective element in the aqueous composition,

[0019] (b) a total of less than 1000 mg / kg, preferably less than 100 mg / kg, particularly preferably less than 50 mg / kg of surfactants, preferably of surface-active organic compounds, particularly preferably of organic compounds, (c) a total of less than 100 mg / kg, preferably less than 10 mg / kg of organosilanes and / or siloxanes, preferably of compounds of the element silicon dissolved in water,

[0020] (d) a total of less than 100 mg / kg, preferably less than 20 mg / kg, particularly preferably less than 5 mg / kg of compounds of the elements Zr and / or Ti dissolved in water,

[0021] (e) less than 50 mg / kg in total, preferably less than 10 mg / kg each, of sodium and / or potassium ions,

[0022] (f) less than 50 mg / kg, preferably less than 10 mg / kg, of zinc ions in total, and / or

[0023] (g) contains a total of less than 100 mg / kg, preferably less than 10 mg / kg, of phosphates dissolved in water, preferably of phosphorus-containing compounds dissolved in water.

[0024] The standard reduction potential is the reduction potential of the electrochemical half-cell Me / Me determined against the standard hydrogen electrode H2 / H+ (pH=0) n+ at a metal ion activity of 1 mol / l and 20 °C.

[0025] The metallic surfaces of the components of the series freshly conversion-coated in treatment stage i) according to the method according to the invention are effectively protected in rinsing stage ii) against corrosive impairment during transfer to coating stage iii) due to the at least one rinsing step in the presence of hydrogen peroxide, such that a homogeneous appearance of the components after dip coating and, in addition, an improvement in the corrosion protection properties, in particular on the surfaces of steel, is observed.

[0026] This is still the case even if the wet film adhering to the components has already been significantly degraded during the transfer from the rinsing stage to the dip coating, and conditions exist that significantly promote corrosive deterioration, in particular the formation of flash rust on the conversion-coated components. Accordingly, the process according to the invention is preferably used when the wet film adhering to the steel surfaces upon contact with a first aqueous composition of treatment stage iii) is reduced by at least 50%, particularly preferably by at least 80%, and especially preferably by at least 90%, in each case based on the mass of the wet film, compared to the wet film adhering to the steel surfaces immediately after the rinsing stage ii).

[0027] In terms of plant technology, the aforementioned conditions, which are typically disadvantageous for corrosion-protective treatment comprising conversion layer formation and dip-coating, are favored by longer transfer times of the components to the dip-coating stage. Accordingly, the process according to the invention is preferably also used when the transfer of each component from rinsing stage ii) to treatment stage iii) requires at least the time required for each component to complete rinsing stage ii) (rinsing stage duration), particularly preferably at least twice, especially preferably at least three times this time (rinsing stage duration), and very particularly preferably when the transfer of each component from rinsing stage ii) to treatment stage iii) requires more than 120 seconds, preferably more than 150 seconds, particularly preferably more than 180 seconds.

[0028] Likewise, a temporary plant shutdown for components located in the intermediate zone between the conversion treatment stage and the dip coating, or a complete drying of the wet film initially adhering to the components, often leads to significant corrosive damage to the freshly formed conversion coating. Accordingly, the process according to the invention is preferably also used where a drying step is performed before treatment stage iii) and after rinsing stage ii). A drying step in this sense is the drying of the wet film adhering to the component using technical means, for example, by supplying thermal energy, an air stream, and / or extended transfer times between two wet-chemical treatment steps.

[0029] The positive effect of rinsing stage ii) against corrosive damage to the conversion coating and the metal substrate, in particular the formation of flash rust on steel, requires the presence of hydrogen peroxide in at least one rinsing step of rinsing stage ii), which leads to appropriate conditioning of the conversion coating. It has also proven advantageous in this context if, after rinsing stage ii), a wet film remains on the surfaces of the component which still contains a quantity of hydrogen peroxide. In a preferred embodiment of the process according to the invention, the wet film adhering to the surfaces of steel immediately after rinsing stage ii) should therefore still contain a quantity of hydrogen peroxide which is preferably at least 10 mg / kg, more preferably at least 50 mg / kg, and especially preferably at least 100 mg / kg of hydrogen peroxide, based on the mass of the adhering wet film.The concentration of hydrogen peroxide in the adhering wet film can be quantitatively determined after blowing off a portion of the wet film from the component with nitrogen using a redox titration with potassium permanganate solution as Titrans. The amount of hydrogen peroxide in the wet film after discharge from the rinsing stage can be adjusted, for example, via the maximum concentration of hydrogen peroxide in the peroxide-containing rinsing step of rinsing stage ii) and / or, in the case of multiple rinsing steps, by placing the peroxide-containing rinsing step in the specific rinsing sequence, for example, as the last rinsing step of rinsing stage ii).In this context and also overall for sufficient resistance to corrosive damage to the conversion coating and the metal substrate, in particular the formation of flash rust in steel, it is advantageous and therefore preferred in the process according to the invention if the aqueous composition of the rinsing step of rinsing stage ii) with the highest concentration of hydrogen peroxide contains at least 100 mg / kg, preferably at least 400 mg / kg, particularly preferably at least 1000 mg / kg, but preferably not more than 5000 mg / kg of hydrogen peroxide.

[0030] The pH of the aqueous composition of the rinsing step of rinsing stage ii) with the highest concentration of hydrogen peroxide is preferably above 4.50, more preferably above 5.00, most preferably above 5.50, and especially preferably above 6.00, but the pH is preferably not above 8.00, more preferably not above 7.50. It is generally advantageous if all other compositions for rinsing (bringing into contact) the components in all rinsing steps of rinsing stage ii) are aqueous and have a pH in the range above 6.00 to preferably 8.00, more preferably 7.50.

[0031] The components can be brought into contact with the aqueous composition(s) of rinsing step ii) by immersion in the system tank of the respective rinsing step containing the respective aqueous composition or by spraying the respective aqueous composition stored in the system tank. For effective and resource-saving conditioning of the conversion layer in rinsing stage ii), it is preferred if the components are brought into contact in the rinsing step of rinsing stage ii) that is carried out with the aqueous composition with the highest concentration of hydrogen peroxide by spraying, preferably by atomizing, the aqueous composition stored in the system tank of this rinsing step.

[0032] The rinsing step ii) of the process according to the invention is ideally suited for the conditioning of Zr and / or Ti-based conversion coatings deposited from acidic, aqueous, fluoride-containing compositions. The conversion layer formation in treatment step i) yields an amorphous oxide / hydroxide coating based on the elements Zr and / or Ti containing fluoride.

[0033] For the formation of homogeneous, continuous conversion coatings, it is preferred if the proportion of free fluoride is above 5 mg / kg, particularly preferably above 10 mg / kg, most preferably above 20 mg / kg, but preferably not exceeding 100 mg / kg, particularly preferably 80 mg / kg, and most preferably not exceeding 60 mg / kg. The amount of free fluoride is determined potentiometrically at 20 °C in the respective provided solution after calibration with fluoride-containing buffer solutions without pH buffering using a fluoride-sensitive measuring electrode.

[0034] For the same reason, it is preferred if the proportion of fluorocomplexes of the elements Zr and / or Ti, calculated as the amount of the elements Zr and / or Ti, is above 0.10 mmol / kg, particularly preferably above 0.20 mmol / kg, but preferably does not exceed 5.0 mmol / kg, particularly preferably 2.0 mmol / kg. Typical representatives of these compounds are hexafluorotitanic acid (H2TiFe) and its water-soluble salts and / or hexafluorozirconic acid (H2ZrFe) and its water-soluble salts.

[0035] Furthermore, for the formation of the most homogeneous and compact amorphous conversion layer possible, it is advantageous if the pH of the acidic aqueous composition in treatment stage i) is not set too acidic. Therefore, it is preferred if the pH of the acidic aqueous composition in treatment stage i) is above 3.0, particularly preferably above 3.5, especially preferably above 4.0, but preferably below 4.5, since otherwise the precipitation of sparingly soluble hydroxides of the elements Zr and / or Ti in the system tank of the conversion treatment becomes problematic and can only be controlled within a narrow process window.

[0036] The corrosion-protective coating in the process according to the invention comprises, in coating step iii), the dip coating of the series components. Such dip coating is carried out by deposition from an aqueous dispersion of an organic binder and can be carried out autophoretically or electrophoretically. Within the scope of the present invention, the electrophoretic coating variant is preferred, which in turn is preferably carried out as cathodic electrocoating.

[0037] In the process according to the invention, components can be coated with a corrosion-protective coating, i.e., conversion-treated and dip-coated, which comprise other metallic materials in addition to steel, preferably components that are assembled in a composite structure, for example, automobile bodies, and which, in addition to the aforementioned steel surfaces, also have surfaces made of aluminum and / or zinc, particularly preferably aluminum and zinc. Suitable metallic materials whose surfaces can be pretreated with a corrosion-protective coating in the process according to the invention include, in addition to steel: zinc, electrolytic (ZE), hot-dip galvanized (Z), alloy galvanized (ZA), (ZF), and (ZM), and aluminum-coated (AZ), (AS) strip steel, as well as the light metals aluminum and magnesium and their alloys. Example:

[0038] In a series of tests on the corrosion-protective treatment of steel substrates, steel sheets (CRS) were wet-chemically treated as follows and the sheets were assessed for corrosive infiltration of the paint layer structure after a salt spray test according to VW PV 1210 after 30 cycles and stone chipping according to DINI EN ISO 20567-1.

[0039] (A) Cleaning & degreasing step a. Spray degreasing at 55 °C for 60 seconds b. Immersion degreasing at 55 °C for 120 seconds, each with a cleaner from Henkel AG & Co. KGaA (pH 11.5; total alkalinity 12 points) based on Bonderite® C-AK 2011 and with deionized water (K ​​< 1 pScrrr 1 ) containing 2.50 g / L of PO4.

[0040] (B) Freezing stage by immersion at 60°C for 90 seconds based on Bonderite® C-AK 2020 (Henkel AG & Co. KGaA) and prepared with deionized water, adjusted to pH 12.1 (free alkalinity 1.6 points) containing PO4 2.00 g / L

[0041] P2O7 1.80 g / L

[0042] HEDP 7.35 g / L

[0043] Iron (III) 0.35 g / L Zinc 1.00 g / L

[0044] (C) Rinsing stage with deionized water (K ​​< 1 pScrrr 1 ) a. by spraying at 20°C for 30 seconds b. by immersion at 20°C for 30 seconds

[0045] (D) Conversion treatment step at 35°C for 120 seconds based on Bonderite® M-NT 1850 (Henkel AG & Co. KGaA) and prepared with deionized water, adjusted to pH 4.7 containing

[0046] Zr 150 mg / L

[0047] Cu 10 mg / L

[0048] Zn 0.6 g / l

[0049] F-free 50 mg / kg determined potentiometrically using a fluoride-sensitive electrode

[0050] NO3 6 g / l

[0051] (E) Rinse stage 1 a. with deionized water (K ​​< 1 pScrrr 1 ); or b. 1.00 g / L H2O2 in deionized water (K ​​< 1 pScrrr 1 )

[0052] (F) Rinse stage 2 a. with deionized water (K ​​< 1 pScm -1); or b. 1.00 g / L H2O2 in deionized water (K ​​< 1 pScrrr 1 )

[0053] (G) Air drying

[0054] (H) Cathodic dip coating with Cathoguard® 800 (BASF SE) with a dry film thickness of 20 pm

[0055] The steel sheets were tested after the conversion coating, which was a layer application measured by X-ray fluorescence analysis of zirconium in the range of 45-55 mg / m 2 provided, in the subsequent rinsing stages 1 and 2 either with deionized water (K ​​< I pScrrr 1 ) or a solution containing hydrogen peroxide.

[0056] Table 1 summarizes the corrosion results from the salt spray test. It shows that a hydrogen peroxide rinse is able to significantly improve corrosive infiltration at the scribe and paint adhesion after stone impact (CE vs. E1-E3). If the hydrogen peroxide rinse is applied immediately after the conversion treatment, paint adhesion can be further improved (E1 vs. E3).

[0057] Table 1

Claims

Patent claims:

1. A process for the corrosion-protective treatment of components in series, which comprise steel surfaces, in which each component of the series undergoes the successive treatment stages i) - iii): i) conversion treatment stage comprising bringing into contact with an acidic aqueous composition containing a. at least 0.05 mmol / kg of fluorocomplexes of the elements Zr and / or Ti calculated as the amount of the elements Zr and / or Ti, and b. an amount of free fluoride; ii) rinsing stage comprising one or more immediately successive rinsing steps, wherein at least one rinsing step is carried out by bringing into contact with an aqueous composition having a pH above 4.00 containing at least 20 mg / kg of hydrogen peroxide; iii) coating stage comprising dip painting by bringing into contact with an aqueous dispersion of an organic binder.

2. Process according to claim 1, characterized in that the wet film adhering to the surfaces of steel immediately after the rinsing stage ii) contains an amount of hydrogen peroxide which is preferably at least 10 mg / kg, particularly preferably at least 50 mg / kg and especially preferably at least 100 mg / kg of hydrogen peroxide based on the mass of the adhering wet film.

3. Method according to one or both of the preceding claims, characterized in that the rinsing stage ii) comprises several immediately successive rinsing steps for bringing the components of the series into contact with an aqueous composition stored in the system tank of the respective rinsing step, wherein preferably at least a partial volume of the aqueous composition stored in the system tank of the last rinsing step is fed back into the system tank of the first rinsing step of the rinsing stage ii) and is replaced in the system tank of the last rinsing step of the rinsing stage ii) by an at least equally large partial volume of an aqueous composition, wherein this aqueous composition for replacing the partial volume fed back into the system tank of the first rinsing step preferably has a specific conductivity of less than 20 pScm 1 has.

4. Process according to one or more of the preceding claims, characterized in that the aqueous composition of the only or last rinsing step of rinsing stage ii), preferably each aqueous composition of all rinsing steps of rinsing stage ii) (a) less than 10 mg / kg of compounds of the metals Bi, Ni, Co and / or Cu dissolved in water, calculated as the amount of the respective element in the aqueous solution Composition, preferably less than 10 mg / kg of compounds dissolved in water of such metals which have a standard reduction potential greater than -0.40 V (SHE), calculated as the amount of the respective element in the aqueous composition, (b) a total of less than 1000 mg / kg, preferably less than 100 mg / kg, particularly preferably less than 50 mg / kg of surfactants, preferably of surface-active organic compounds, particularly preferably of organic compounds, (c) a total of less than 100 mg / kg, preferably less than 10 mg / kg, of organosilanes and / or siloxanes, preferably of compounds of the element silicon dissolved in water, (d) a total of less than 100 mg / kg, preferably less than 20 mg / kg, particularly preferably less than 5 mg / kg of compounds of the elements Zr and / or Ti dissolved in water, (e) less than 50 mg / kg in total, preferably less than 10 mg / kg each, of sodium and / or potassium ions, (f) less than 50 mg / kg, preferably less than 10 mg / kg, of zinc ions in total, and / or (g) contains a total of less than 100 mg / kg, preferably less than 10 mg / kg, of phosphates dissolved in water, preferably of phosphorus-containing compounds dissolved in water.

5. Method according to one or more of the preceding claims, characterized in that the wet film adhering to the surfaces of steel when brought into contact with a first aqueous composition of the treatment stage iii) is reduced by at least 50%, preferably by at least 80%, particularly preferably by at least 90%, in each case based on the mass of the wet film, compared to the wet film adhering to the surfaces of steel immediately after the rinsing stage ii).

6. Method according to one or more of the preceding claims, characterized in that the transfer of each component from the rinsing stage ii) to the treatment stage iii) takes at least the time required by each component to pass through the rinsing stage ii) (rinsing stage duration), preferably at least twice, particularly preferably at least three times this time (rinsing stage duration), particularly preferably the transfer of each component from the rinsing stage ii) to the treatment stage iii) takes more than 120 seconds, preferably more than 150 seconds, particularly preferably more than 180 seconds.

7. Process according to one or more of the preceding claims, characterized in that a drying step is carried out before the treatment step iii) and after the rinsing step ii).

8. Process according to one or more of the preceding claims, characterized in that the aqueous composition of the rinsing step of rinsing stage ii) with the highest concentration of hydrogen peroxide contains at least 100 mg / kg, preferably at least 400 mg / kg, particularly preferably at least 1000 mg / kg, but preferably not more than 5000 mg / kg of hydrogen peroxide.

9. Process according to one or more of the preceding claims, characterized in that the aqueous composition of that rinsing step of rinsing stage ii) with the highest concentration of hydrogen peroxide has a pH above 4.50, preferably above 5.00, particularly preferably above 5.50, especially preferably above 6.00, but preferably not above 8.00, particularly preferably not above 7.

50.

10. Method according to one or more of the preceding claims, characterized in that the bringing into contact of the components with the aqueous composition(s) of the rinsing step ii) is carried out by immersion into the system tank of the respective rinsing step containing the respective aqueous composition or by spraying the respective aqueous composition stored in the system tank.

11. Method according to claim 10, characterized in that the contacting of the components in that rinsing step of rinsing stage ii) which is carried out with the aqueous composition having the highest concentration of hydrogen peroxide is carried out by spraying, preferably by atomizing, the aqueous composition stored in the system tank of this rinsing step.

12. Method according to one or more of the preceding claims, characterized in that the components of the series are first cleaned and / or degreased before the conversion treatment stage i).

13. Method according to one or more of the preceding claims, characterized in that the components of the series have surfaces of zinc in addition to surfaces of steel, and before the conversion treatment stage i) each component of the series first undergoes an alkaline treatment stage, wherein within the alkaline treatment stage in at least one treatment step, at least the surfaces of steel and zinc of the components of the series are brought into contact with an alkaline aqueous composition which (a) at least 50 mg / kg, preferably at least 100 mg / kg of iron(III) ions, (b) at least 100 mg / kg of phosphate ions, wherein the alkaline aqueous composition has a free alkalinity of at least 1 point and a pH of at least 10.

5.

14. Method according to one or more of the preceding claims, characterized in that the components of the series have, in addition to the surfaces of steel, also surfaces of aluminum and / or zinc, preferably aluminum and zinc.

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