EP2414562A1

EP2414562A1 - Method for producing a steel component provided with a metal coating protecting against corrosion and steel component

Info

Publication number: EP2414562A1
Application number: EP10706201A
Authority: EP
Inventors: Patrik Kuhn; Manfred Meurer; Jens Kondratiuk; Wilhelm Warnecke; Werner SCHÜLER
Original assignee: ThyssenKrupp Steel Europe AG
Current assignee: ThyssenKrupp Steel Europe AG
Priority date: 2009-08-25
Filing date: 2010-02-24
Publication date: 2012-02-08
Anticipated expiration: 2030-02-24
Also published as: CN102625863B; CA2758629A1; EP2290133A1; KR20120054563A; ZA201107674B; PL2290133T3; EP2290133B1; JP5650222B2; JP2013503254A; BRPI1015352A2; AU2010288814B2; US10053752B2; CA2758629C; AU2010288814A1; PL2414562T3; ATE554190T1; ES2384135T3; KR101674625B1; US20120164472A1; US9284655B2

Abstract

The method for the production of a steel component provided with a metallic coating protected against corrosion, comprises providing a flat steel product that is produced from steel material containing 0.3-3 wt.% of manganese, where the steel material has an yield strength of 150-1100 MPa and a tensile strength of 300-1200 MPa, and coating the flat steel product with a corrosion protection coating that consists of zinc-nickel (ZnNi) alloy coating consisting of gamma -ZnNi-phase electrolytically deposited on the flat steel product. The method for the production of a steel component provided with a metallic coating protected against corrosion, comprises providing a flat steel product that is produced from steel material containing 0.3-3 wt.% of manganese, where the steel material has an yield strength of 150-1100 MPa and a tensile strength of 300-1200 MPa, coating the flat steel product with a corrosion protection coating that consists of zinc-nickel (ZnNi) alloy coating consisting of gamma -ZnNi-phase electrolytically deposited on the flat steel product, where the coating consists of nickel (7-15 wt.%) and also zinc and unavoidable impurities, heating a board formed from the flat steel product at 800[deg] C amounting to platinum temperature, forming the steel component from the platinum in a form tool and hardening the steel component through cooling at a temperature, in which the steel component exists itself in a condition suitable for forming compensation or hardening structure, with a cooling rate that suffices for forming the compensation structure or hardening structure. The formation of the steel component is carried out as pre-forming and the steel component is formed after heating. The zinc-nickel alloy coating consists of finished steel component of gamma -ZnNi and I ->zinc iron. A manganese-containing layer is present in the finished steel component on the corrosion protection coating, in which manganese is available in metallic or oxidic form. The manganese-containing layer has a thickness of 0.1-5 mu m and the manganese content of the manganese-containing layer is 0.1-18 wt.%. The corrosion protection coating comprises an additional zinc-layer before forming the steel component, where the zinc-layer is applied before forming the steel component on the zinc-nickel alloy coating. The thickness of the zinc-layer is 2.5-12.5 mu m. The corrosion protection coating of the finished steel component comprises a zinc-rich layer lying on the nickel-containing alloy coating. The formation of the steel component is carried out as hot forming and the forming and cooling of the steel component are carried out by a hot forming tool. The formation of the steel component and hardening are carried out in two separated processes. An independent claim is included for a steel component.

Description

METHOD FOR PRODUCING A STEEL BOTTOM PART PROVIDED WITH A METALLIC COATING PREVENTED COATING SHELF

AND STEEL COMPONENT

The invention relates to a method for producing a steel component provided with a metallic, corrosion-protective coating by forming a flat steel product made of a Mn steel which is provided with a ZnNi alloy coating prior to forming the steel component.

When it comes to "steel products", it refers to steel strips, sheet steel or derived boards and the like.

To the required in modern body construction combination of low weight, maximum strength and

To provide protective effect, are nowadays used in such areas of the body, which may be particularly high loads in the event of a crash, made of high-strength steels hot-pressed components.

In hot press hardening, steel blanks separated from cold or hot rolled steel strip are heated to a forming temperature generally above the austenitizing temperature of the respective steel and heated to a tool in a heated state Forming press laid. In the course of the subsequent transformation, the sheet metal blank or the component formed from it undergoes rapid cooling due to the contact with the cool tool. The cooling rates are set so that in the component

Hartegefuge results.

A typical example of a steel suitable for hot press hardening is known by the name "22MnB5" and in the steel wrench 2004 under the name "22MnB5"

To find material number 1.5528.

In practice, the advantages of the known MnB steels which are particularly suitable for hot press hardening are counteracted by the disadvantage that manganese-containing steels in the

Generally impervious to wet corrosion and difficult to passivate. These compared to

lower alloyed steels when exposed to elevated

Chloπdionen concentrations high tendency to local although limited, but intense corrosion makes the

Use of belonging to the material group of high-alloy steel sheets steel just difficult in the body shop. In addition, manganese-containing steels tend to

Flat corrosion, reducing the spectrum of their

Availability is also limited.

Therefore, it is being sought ways to provide even manganese-containing steels with a metallic coating that protects the steel from corrosive attack.

According to the method described in EP 1 143 029 Bl for producing components by hot press hardening _ "5 -

For this purpose, a steel sheet is first provided with a Zxnk coating and then heated before the hot deformation so that when heated on the

Flat steel product through a transformation of

Coating on the steel sheet sets an intermetallic compound. Oi ese is to protect the steel sheet against corrosion and decarburization and during the

Hot forming in the pressing tool take over a lubricating function.

In the experiment, the in EP 1 143 029 Bl in

To realize the general form of proposed practice in practice, there were many problems. Thus, it proved difficult to apply the Zmkuberzug on the steel substrate, that after the formation of the intermetallic compound sufficient adhesion of the coating on the steel substrate, a sufficient coatability of the coating for a subsequently applied paint and a sufficient

Resistance of both the coating itself and the steel substrate is ensured against the formation of cracks in the hot forming.

A suggestion, how Zmkuberzuge can be produced on steel bands, on which particularly well one

organic coating, is described in EP 1 630 244 A1. Accordingly, on the zu

processing steel sheet, for example, electrolytically or using another known

Coating process up to 20 wt .-% Fe

applied Zn layer. Subsequently, the thus coated steel sheet from room temperature 850 - 950 ⁰ C heated and at 700 - 950 ⁰ C.

thermoformed. As particularly suitable for the

Generation of the Zn layer is mentioned in the electrolytic deposition. The Zn layer may also be used as an alloy layer according to the known method

be educated. As possible alloy constituents of this layer, EP 1 630 244 A1 mentions Mn, Ni, Cr, Co, Mg, Sn and Pb and also Be, B, Si, P, S, Ti, V, W, Mo, Sb, Cd , Nb, Cu and Sr as additional

Alloy components mentioned.

It is essential for the process described in EP 1 630 244 A1 that the 1-50 μm thick Zn coating present on it comprises an iron Zmk solid solution phase and has a zinc oxide layer whose average thickness is limited to not more than 2 μm. For this purpose, according to the known method, either the cooling conditions when heating to that for the hot press molding

Required temperature selected so that it comes at best to a controlled oxide formation, or it is after hot forming the existing on the steel component obtained oxide layer by means of a span- or

Particle removal process at least partially removed so far that according to EP 1 630 244 Al maximum thickness of the oxide layer is met. These too

known procedure thus requires extensive

Measures, on the one hand, the desired

Anticorrosive effect of the Zn coating and on the other hand to ensure the required good coatability and paint adhesion in a resulting after thermoforming paint. From DE 32 09 559 Al a further method is known with which a zinc-nickel alloy coating can be deposited electrolytically on a steel strip. In the course of this process, the strip to be coated becomes intense before the ZnNi coating is deposited

subjected to electroless pre-treatment to produce on it a thin zinc-nickel-containing primary layer.

Subsequently, the actual zinc-nickel coating is then applied electrolytically. So that the electrolytic deposition of the alloy coating is constant with a predetermined composition, separate, each containing only one alloying element anodes are used. These are connected to separate circuits in order to adjust the current flowing through them and thus the delivery of the respective metal in the electrolyte targeted.

The results of a systematic investigation of the properties of Zmklegierungsuberzugen on a

Steel sheet, which consisted of a hard steel, are contained in WO 2005/021822 A1. The coating consisted essentially of zinc and additionally contained one or more oxygen-affine elements in a total amount of 0.1-15 wt .-% based on the total coating. The oxygen-affine elements are specifically named Mg, Al, Ti, Si, Ca, B and Mn. The steel sheet coated in this way was then brought to a temperature that was necessary for hardening under the action of atmospheric oxygen. In this heat treatment, a superficial oxide layer of the oxygen-affine element (s) formed. According to one of the experiments described in WO 2005/021822 A1, a ZnNi coating has been produced on a sheet of unspecified composition by electrochemical deposition of zinc and nickel. The weight ratio of zinc to nickel in the

Corrosion protection layer was at a layer thickness of 5 microns about 90/10. The thus coated sheet has been annealed for 270 s at 900 ⁰ C in the presence of atmospheric oxygen. The diffusion of the steel with the zinc layer resulted in a thin diffusion layer of zinc, nickel and iron. At the same time, most of the zinc oxidized to zinc oxide.

According to those documented in WO 2005/021822 Al

Observations made the ZnNi coating thus obtained a pure barrier protection without cathodic

Its surface showed a scaled, green appearance with small locality

Chipping on which the oxide layer does not adhere to the steel. These faults are justified according to WO 2005/021822 in that the coating itself is not sufficient

Oxygenated element contained.

Against this background, the invention was to

The underlying task is to provide a simple to implement in practice method that allows, with relatively little effort a steel component

which is provided with a well-adhering and safe from corrosion protective metallic coating. In addition, a corresponding procured steel component should be specified. With regard to the method, this object has been achieved according to a first variant of the invention in that in the production of a steel component, the process steps specified in claim 1 are passed through.

An alternative, the above task in

corresponding manner loose variant of

erfmdungsgemaßen method is specified in claim 2.

The first variant of the erfmdungsgemaßen method comprises forming the steel component in the so-called "direct" method, while the second

Process variant includes the forming of the steel component in the so-called "indirect" method.

Advantageous embodiments of erfmdungsgemaßen

Variants of the method are specified in the claims relating to claims 1 or 2 and explained below.

With regard to the steel component, the

erfmdungsgemaße solution of the above object is that such a component m claim 14 specified

Features. Advantageous variants of

erfmdungsgemaßen steel component m are on the claim

Specify 14 jerk-related claims and explained below.

In a erfmdungsgemaßen method for producing a provided with a metallic, corrosion-resistant coating steel component is, first

Flat steel product, ie a steel strip or steel sheet, provided, from a 0.3 to 3 wt .-% manganese-containing, higher-strength and curable

Steel material is produced. This one has one

Yield strength of 150-1100 MPa and a tensile strength of 300-1200 MPa.

Typically, this steel material may be a high strength MnB steel in per se known

Act composition. Accordingly, in addition to iron and unavoidable impurities (in% by weight), the steel processed according to the invention may contain 0.2-0.5% C, 0.5-3.0% Mn, 0.002-0.004% B, and optionally one or more elements of Group "Si, Cr, Al, Ti" contained in the following contents: 0.1-0.3% Si, 0.1-0.5% Cr, 0.02-0.05% Al, 0.025-0.04 % Ti.

The inventive method is suitable for the production of steel components both from conventionally only hot rolled hot strip or sheet as well as from conventionally cold rolled steel strip or

-sheet.

The correspondingly created and provided

Flat steel product is coated with a corrosion protection coating, this coating according to the invention comprises a zinc-nickel alloy coating applied electrolytically to the steel substrate, consisting of γ-ZnNi single-phase phase. This ZnNi alloy coating alone can form the corrosion coating or be supplemented by further protective layers applied to it. The decisive factor is that the γ-zinc-nickel phase of the ZnNi alloy coating resting on the steel substrate is already realized by the electrolytic coating. That is, unlike in coating processes, in which only m result of heating to the temperature required for the subsequent hot forming and curing and the thereby incipient

Diffusion processes forms an alloy layer, is in erfmdungsgemaßer approach even before heating on the flat steel product a

Alloy layer of certain composition and structure composed of zinc and nickel. The proportions of Zn and Ni and the

Deposition conditions during the production of the ZnNi alloy layer is selected so that the ZnNi alloy layer is formed as a single-phase, consisting of Ni5Zn21 phase coating with a cubic lattice structure. It should be noted that this γ-ZnNi phase layer is not stoichiometric when deposited over an electrolyte

Composition, but at nickel contents ranging from 7 to 15%, wherein at

Ni contents of up to 13 wt .-%, in particular from 9 to 11 wt .-%, particularly good properties of the coating result.

Among the above-mentioned "deposition conditions" of the electrolytic coating are, for example, the type of flow on the substrate to be coated, the flow rate of the electrolyte, the Ni / Zn ratio of the electrolyte, the orientation of the electrolyte

Electrolytic current in relation to each too steel coating substrate, the current density, the

Temperature and the pH of the electrolyte

summarized . Erfmdungsgemaß these are

In order to harmonize influence variables, the desired single-phase ZnNi coating should be compatible with the

erfmdungsgemaß predetermined Ni contents sets. For this purpose, the parameters mentioned can be varied in each case as follows, depending on the respective system technology available:

The type of flow on the substrate to be coated:

Laminar or turbulent; in both laminar and turbulent flow of the electrolyte on

Coating flat steel product set up good coating results. However, in many practical coating equipment, turbulent flow will be preferred in practice due to the more intensive exchange between electrolyte and steel substrate.

- flow rate of the electrolyte: 0.1 - 6 m / s;

Ni / Zn ratio of the electrolyte: 0.4 - 4;

- Orientation of the electrolyte flow m with respect to the steel substrate to be coated: The

Coating of the steel substrate can be done in both vertically and horizontally aligned cells;

- current density: 10 - 140 A / dm2;

- temperature of the electrolyte: 30 - 70 ⁰ C;

- pH of the electrolyte: 1 - 3.5. A particular advantage of the electrolytic coating according to the invention

Flat steel product with a ZnNi alloy layer of exactly predetermined composition and structure also consists in the fact that the coating produced from it has a matt, rough surface, the lower one

Reflectivity than the Zn coatings typically produced in the course of known hot stamping processes. As a result, according to the invention coated steel flat products have an increased

Wärmeabsorbtionsvermögen, so that the subsequent heating to the respective board or

Component temperature faster and with less

Energy expenditure can be made. The so enabled

shorter oven times and energy savings make the process according to the invention particularly economical.

From the coated in accordance with the invention

Flat steel product is then formed a steel plate. This can be divided in a conventional manner of the respective steel strip or steel sheet. It is also conceivable that the flat steel product in the

Coating already has the shape required for the subsequent shaping of the component, ie the board corresponds.

The thus provided in accordance with the invention with a single-phase ZnNi alloy coating steel plate is then heated according to the first variant of the method according to the invention to a not less than 800 ⁰ C amounting platinum temperature and then from the

heated board shaped the steel component. According to the In the second variant of the method, on the other hand, the steel component is at least preformed from the blank, and only then the heating to a component temperature of at least 800 ^° C. is carried out.

In the course of warming up to the at least 800 ⁰ C

Amount end Blank or component temperature begins gradually at temperatures below 700 ⁰ C m of the applied on the steel substrate ZnNi alloy layer a partial substitution of atoms, in which the lntermetallischeγ zinc lSJickel phase (Ni5Zn21) m is an r-ZmK Iron phase (Fe3ZnlO) rearranges. From about 750 ⁰ C is then formed with further progressing heating an α-Ferπt mixed crystal, the Zn and Ni are present dissolved. This process continues until the

Steel substrate on the three-piece board or

Component temperature of at least 800 ⁰ C is heated and is present on the steel substrate, a biphasic coating consisting of an α-Fe mixed crystal in which Zn and Ni are dissolved, and a mixed gamma phase Zn _x Ni (Fe) ₇ , m the Ni atoms are substituted by Fe atoms and vice versa. At m erfmdungsgemaßer manner generated

Accordingly, there is no longer a pure alloy layer component, but there is a two-phase coating, which consists for the most part of OC-Fe (Zn, Ni) - mixed crystal and the intermetallic

Compounds of Zn, Ni and Fe are possibly present to a minimized extent. In contrast to the prior art, in which initially applied a zinc coating on the steel substrate and in which then in the course of the carried out before the hot deformation by a transformation of the coating on the steel sheet sets an intermetallic compound, one starts in the inventive procedure from the outset with a on the steel substrate electrolytically

separated, from a purposefully generated

intermetallic compound existing

Alloy coating, which converts by far the largest part into mixed crystal in the annealing process for the shaping or hardening.

The finished product thus has a coating which consists of at least 70% by weight, in particular at least 75%, and typically up to 95% by weight, in particular 75-90%, of mixed crystal and residues of intermetallic phase. Depending on the annealing conditions and the thickness of the respective coating, these are distributed as dispersed small-volume accumulations between the mixed crystals or are on the mixed crystal.

Specifically, the original alloy coating in the state diagram changes from the Zn-rich corner to the Fe-rich corner. Accordingly, an iron zinc alloy is present on the finished steel component. That is, in the procedure according to the invention, a coating is obtained which is no longer zinc-based but consists of an iron-based alloy.

According to the first variant of the invention

Method is the inventively heated to a temperature of at least 800 ⁰ C board to the

Shaped steel component. This can be done, for example, that the board immediately after the heating to the mold used in each case is required. On the way to the mold, it is inevitable inevitable to a cooling of the board, so that in the case of such following the heating hot forming the temperature of the board when entering the mold is usually lower than the plate temperature at the outlet of the furnace. By doing

Forming the steel plate m is formed in a conventional manner to the steel component.

If the shaping at sufficiently high temperatures for the formation of Harte- or Vergutungsgefuge

carried out, let the steel component obtained, starting from the 3eweiligen temperature with a

Cool down cooling speed, which is sufficient for the emergence of Vergutungs- or Hartegefuge in his steel substrate. This process is very special

carry out economically in the thermoforming tool itself.

Accordingly, the erfmdungsgemaße is suitable

Method due to the insensitivity of the m

according to the invention coated steel flat product against cracks in the steel substrate and abrasion, especially for single-stage hot press molding, in which a

Hot forming and the cooling of the steel component taking advantage of the heat of the previously carried out heating to the board temperature in one go in one

Tool be performed.

In the second variant of the method, first the board is formed and then without interposed

Heat treatment from this board formed the steel component. The shaping of the steel component takes place typically a cold forming operation wherein one or more cold forming operations are performed. The degree of cold forming can be so high that the steel component obtained is substantially completely finished. However, it is also conceivable to perform the first shaping as preforms and to finish the steel component after heating in a mold. This can be done with the

Hartevorgang be combxmert by the hard is performed as a molding in a suitable mold. In this case, the steel component is placed in a finished final shape imaging tool and for the

Training the desired Harte- or Vergutungsgefuges sufficiently quickly cooled. The form hardening thus enables a particularly good dimensional stability of the steel component. The change in shape during the molding process is usually low.

Regardless of which of the two variants of the

erfmdungsgemaßen method are applied, neither the shape nor the need to form the hard or Vergutungsgefuges cooling must be performed in a special deviating from the prior art manner. Rather, known methods and existing devices can be used for this purpose.

Due to the fact that in accordance with the invention an alloy coating is already produced on the board to be deformed, in the case of thermoforming or molding at elevated temperatures there is no risk that it will soften the coating and, consequently, adhesions of coating material to the m with it Contact coming planes of the tool is coming. The Mn content of the invention processed

Steel substrate of 0.3 to 3 wt .-%, in particular 0.5 to 3 wt .-%, comes in combination with the present invention on the steel flat product produced from α-Fe (Zn, Ni) - mixed crystal and a minor proportion of intermetallic compounds existing coating of particular importance. Thus, the Mn present in the steel substrate in the steel component produced according to the invention contributes to the good adhesion of the coating.

Before heating to the board or

Component temperature contains the invention

applied corrosion protection coating each less than 0.1 wt .-% manganese. During the subsequent heating to the board or component temperature, diffusion of the manganese present in the steel substrate then begins in the direction of the free surface of the anticorrosive coating applied according to the invention.

On the one hand, the Mn atoms diffusing into the ZnNi alloy layer upon heating cause an intensive coupling of the coating to the steel substrate.

On the other hand, Mn reaches a substantial part of the surface of the invention produced

Corrosion protection coating and stores there in

metallic and or oxidic form. The thickness of the Mn-containing layer present in this way on the coating produced according to the invention - hereinafter the

For simplicity, only "Mn oxide layer" called - is typically 0.1 - 5 microns. The positive effects of the Mn oxide layer are particularly safe when their thickness is at least 0.2 .mu.m, in particular at least 0.5 microns. The Mn content of the anticorrosive coating is in this near-surface, adjacent to the surface Mn-containing layer at 1-18 wt .-%, in particular 4-7 wt .-%.

In addition to the coupling to the steel substrate described above, the deposited on the coating produced in accordance with the invention ensures a pronounced Mn oxide layer of a particularly good adhesion of the

Corrosion protection coating applied organic

Beschij tungen. The inventive approach is therefore particularly suitable for the production of parts for vehicle bodies, which are provided after their shaping with a paint job.

Knders as at In the text ^" S ^" taτid of the art is a removal of the invention obtained

pronounced oxide layer according to the invention is not absolutely necessary. Rather, a practice-oriented embodiment of the process variants according to the invention provides that the oxide layer obtained by the procedure according to the invention remains selectively on the corrosion protection coating, since this oxide layer not only has a particularly good coatability, but due to its

In addition, a comparatively high conductivity according to the invention also a total good weldability

produced and procured steel components.

The use of steels with an Mn content of less than 0.3% by weight results in a coating with a yellowish appearance, indicating that on the coating there is an oxide layer mainly composed of ZnO. The coating thus obtained shows, after thermoforming, similar to the experiment reported in WO 2005/012822, local flaking and scaling. A erfmdungsgemaß on a

On the other hand, a coating produced at least 0.3% by weight of Mn-containing steel has a brownish surface which is free from tipping and flaking.

The erfmdungsgemaß on the flat steel product

deposited ZnNi coating is applied in practice with a thickness of 0.5 - 20 microns. A particularly good protective effect of erfmdungsgemaß generated

ZnNi coating sets itself then when it is deposited more than 2 microns thick on the flat steel product. Typical thicknesses of a coating produced according to the invention are in the range from 2 to 20 μm, in particular from 5 to 10 μm.

A further optimized protection of erfmdungsgemaß

produced steel component against corrosion can be achieved by the corrosion protection coating

in addition to the ZnNi alloy coating applied to the flat steel product comprises a Zn layer which is also applied to the ZnNi layer prior to the heating step. It then lies on the for the

Further processing to the erfmdungsgemaßen component prepared flat steel product before heating to the respective board or component temperature before an at least two-layer anti-corrosion coating, whose first layer of the erfmdungsgemaßer manner ZnNi alloy layer and its second layer of the formed thereon, consisting only of zinc Zn layer is formed.

The additionally applied, typically 2.5-12.5 μm thick Zn layer is present in the finished steel component according to the invention as a Zn-rich layer, into the Mn and Fe of the steel substrate and Ni from the ZnNi layer

can be emerald. Zn partially reacts to Zn oxide and forms with the Mn from the base material produced on the erfmdungsgemaß

Corrosion protection coating lying Mn-containing layer. The order of an additional Zn-layer of the

Corrosion protection coating before heating for the

Hot forming thus leads to a further improvement of the cathodic corrosion protection.

It turned out that in the finished

thermoformed and cured state even at

Presence of the additional Zn layer on the

Surface of the anti-corrosion coating, the Mn oxide layer described in detail above is present. This is just as in a combination of a ZnNi and Zn-layer corrosion protection coating the good weldability and the good suitability of a

erfmdungsgemaß generated and procured steel component for a paint safely.

The additional Zn layer of the corrosion protection coating can be deposited electrolytically, just like the previously applied ZnNi layer. This can be done, for example, in a continuous pass through, multi-stage device for electrolytic - -

Layering the first stages of ZnNi alloy coating on the respective steel substrate and in the steps passed through the Zn layer deposited on the ZnNi layer.

As explained above, a steel component according to the invention is produced by hot press molding and has a steel substrate consisting of 0.3-3 wt% manganese steel and a corrosion protection coating applied thereto comprising a coating layer comprising at least 70 mass% α-Fe (Zn, Ni) mixed crystal and the remainder of an intermetallic compound of Zn, Ni and Fe, and has on its free surface a Mn-containing layer in which Mn is present in metallic or oxidic form. Depending on the annealing time, the annealing temperature and the thickness of the coating layer are the

intermetallic compounds in α-Fe (Zn, Ni) - Mischkπstall dispersed as klemvolumige speckles.

In addition, the anticorrosive coating m in the manner already described above may comprise a Zn layer resting on the ZnNi layer, wherein also in this case the Mn-containing layer on the

Corrosion protection coating is present.

To get an optimal result of the electrolytic

To ensure coating, the flat steel product before the electrolytic coating in a conventional manner may be subjected to a pretreatment in which the surface of the steel substrate is treated so that it has a for the subsequently performed coating with the corrosion layer optimally prepared

Has surface condition. For this purpose, one or more of the pre-treatment steps enumerated below can be run through:

- Alkaline degreasing of the flat steel product in a degreasing bath. Typically this contains

Degreasing bath 5 - 150 g / l, in particular 10 - 20 g / l, of a surfactant cleaner. The temperature of the

Degreasing bath is 20 - 85 ⁰ C, with a particularly good activity at a bath temperature of 65 - 75 ⁰ C sets. This is especially true if the degreasing is carried out electrolytically, in which case particularly good cleaning results are achieved when at least one cycle of anodic and cathodic sample polarity is passed through. It may prove advantageous if at the

alkaline cleaning not only electrolytic

Damp degreasing, but before the electrolytic cleaning already a spray / brush cleaning with the alkaline medium is performed.

- Rinsing the flat steel product, this rinse using clear water or demineralized water

is carried out.

- picking the flat steel product. When pickling the flat products are passed through an acid bath, which rinses the oxide layer of them, without the

Attack surface of the flat steel product itself. Through the deliberately carried out step of pickling the Oxidabtrag is controlled so that one for the electrolytic banding favorably set surface obtains. After picking, rewinding of the flat steel product may be expedient to remove remnants of the acid used in pickling from the flat steel product.

- If a coil of the flat steel product is carried out, the flat steel product can meanwhile

be mechanically brushed to eliminate even stuck particles from its surface.

- On the pretreated flat steel product still

Existing liquids are usually removed by means of squeezing rollers prior to entry into the electrolyte bath.

As practical examples for leading to a particularly good result of the electrolytic coating pretreatments are the following variants:

Example 1:

A hood-annealed cold-rolled strip becomes alkaline

degreased and in addition electrolytically degreased. The degreasing bath at a concentration of 15 g / l contains a commercial cleaner available under the name "Ridolme C72" containing more than 25%

Sodium hydroxide, 1-5% of a fatty alcohol ether and 5-10% of an ethoxylated, propoxylated and

methylated C12-18 alcohol. The bath temperature amounts to 65 ⁰ C. The dwell time in the spray degreasing is 5 s. This is followed by a burst cleaning. In the course of the tape is electrolytic

degreased at a residence time of 3 s with anodic and cathodic polarity and a current density of

15 A / dm ² . This is followed by a multi-stage coil with demineralized water at room temperature

Bursten insert on. The residence time in the coil is 3 s. In the following, a hydrochloric acid (20 g / l, temperature 35-38 ⁰ C) is passed through with a residence time of 11 s. After an 8 s coil with

demineralized water, the plate is überfuhrt after passing through a squeezing in the electrolysis cell. In this the erfmdungsgemaße

Coating of the steel strip or sheet, as explained in detail below with reference to the exemplary embodiments. That from the electrolytic coating

emerging flat steel product can be multi-stage rinsed with water and demineralized water at room temperature. The total residence time in the coil is 17 s. Afterwards, the flat steel product then passes through a drying section.

Example 2:

Hot Strip (pickled) becomes the Good 22MnB5 (1.5528)

alkaline degreased and degreased electrolytically. In addition, the band learns in the alkaline

Spray degreasing a Burstreimgung. The degreasing bath contains a concentration of 20 g / l

commercially available, under the name "Ridolme 1893"

available cleaner containing 5 - 10% sodium hydroxide and 10 - 20% potassium hydroxide. The bath temperature amounts to 75 ⁰ C. The dwell time in the spray degreasing is 2 s. In the further course, the tape

degreased electrolytically at a residence time of 4 s with anodic and cathodic polarity at one

Current density of 15 A / dm ² . This is followed by a multi-stage sink with demineralized water

Room temperature with upstream brush insert on. The residence time is 3 s. The following is a

Hydrochloric acid (90 g / l, temperature max 40 ^° C.) at a residence time of 7 s. After a

five-stage cascade rinse with demineralized water, the sheet is after passing through a

Abguetschvorrichtung transferred to the electrolytic cell and there, as in the following with reference to the

Embodiments described, provided in accordance with the invention with a corrosion protection coating. After leaving the plant to the electrolytic

Coating the now coated according to the invention flat steel product is rinsed in three stages with demineralized water at 50 ⁰ C. Following the sample passes through a drying section with circulating air dryer, wherein the

Air temperature is more than 100 ⁰ C.

Example 3:

Bonnet annealed cold strip of grade 22MnB5 (1.5528) is alkaline degreased and degreased electrolytically. The degreasing bath at a concentration of 20 g / l contains a cleaner containing 1-5% C12-18 fatty alcohol polyethylene glycol butyl ether and 0.5-2% potassium hydroxide. The bath temperature is 75 ⁰ C. The

Dwell time in the horizontal spray rinse is 12 s. This is followed by a double brush cleaning at. In the further course, the strip is electrolytically degreased at a residence time of 9 s with anodic and cathodic polarity and a current density of

10 A / dm ² . This is followed by a multi-stage coil with demineralized water at room temperature

Brush set. The length of stay is 3 s. in the

Next, a hydrochloric acid decap (100 g / l;

Room temperature) at a residence time of 27 s

run through. After a combined burst and

Spπtzfπschwaserspule is the sheet after the

Passing through a squeezing in the

Electrolysis cell überfuhrt. This is where the

inventive electrolytic deposition of the

Corrosion protection coating, as explained below with reference to the exemplary embodiments. Subsequent to the electrolytic coating is then in

erfmdungsgemaßer manner coated flat steel product two-stage with water and deionized water at 40 ⁰ C spooled. Total residence time 18 s. In connection

the sample goes through a drying section

Umluftgeblase with a circulating air temperature of 75 ⁰ C.

Optimal work results arise when the

Board or component temperature m known per se maximum 920 ⁰ C, in particular 830 - 905 ⁰ C, amounts. This is especially true when shaping the

Steel component is carried out as hot forming following the heating to the board or component temperature so that the heated board ("direct" method) or the heated steel component ("indirect" method) at the expense of a certain

Temperature loss in each of the subsequently used Mold is placed. Especially reliable is the final hot forming then

If the board or component temperature 850-880 ⁰ C amounts.

The heating to the board or component temperature can be done in a conventional manner in a continuous flow in a continuous furnace. Typical quenching times are in the range of 3 to 15 mm, whereby a coating layer which on the one hand is optimally designed and on the other hand particularly economical production conditions result when the quenching times are in the range of 180 to 300 s or the quenching is terminated as soon as the quenching time is reached

respective steel substrate is warmed by the coating applied to it. Alternatively, however, it is also possible to carry out the heating by means of an inductively or conductively operating heating device. This allows a particularly rapid and accurate heating to the respective predetermined temperature.

The invention of exemplary embodiments is explained in more detail below. Show it:

Fig. 1 shows the result of a GDOS measurement of a

erfmdungsgemaßen coating after the

Hot forming for the elements 0, Mn, Zn, Ni and Fe;

FIG. 2 shows the measurement result illustrated in FIG. 1 in isolation for the element Mn; FIG. Fig. 3 is a schematic representation of the structure of a coating at different times of production;

Fig. 4.5 Schilffbilder one on a in

erfmdungsgemaßer manufactured component existing coating.

They are cold-rolled and recrystallizing annealed as well as temper rolled strip material samples A - Z

- hereinafter for the sake of simplicity only as "Samples A - V2" called - have been provided - the m emer in the continuous pass passed

electrolytic galvanizing line have been provided with a ZmkNickel alloy layer. In addition, a sample "Z" has been hot-dip coated for comparison.

For the respective samples A - Z consisting of a hardenable steel, the essential Mn contents in the column "Mn content" of Table 2 are given here. Accordingly, Samples A-Q and Z each contained Mn contents of more than 0.3 wt%, while the Mn contents of Samples Vl, V2 were below the threshold of 0.3 wt%.

Each of the band-shaped samples A-V2 has first undergone a cleaning treatment, in the following

Steps were completed in succession:

First, the respective sample A - V2 m in a 60 ⁰ C warm alkaline detergent bath at a residence time of 6 s of a spray cleaning with Bursteneinsatz been subjected.

This was followed by an electrolytic over 3 s

Degreasing at a current density of 15 A / dm ² .

This was followed by a double clear water spool with brush insert. The duration of this winding treatment was 3 s in each case.

The following is a pickling with for 8 s

Hydrochloric acid at a concentration of 150 g / l at room temperature.

Finally, a three-stage cascade flushing took place.

The thus pretreated samples A - V2 have been subjected to an electrolytic coating m an electrolysis cell. In Table 1, for each of the samples A-V2, the respectively set operating parameters "Zn" = Zn content of the electrolyte in g / l, "Ni" = Ni content of the electrolyte in g / l, "Na2SO4" = Na2SO4- Salary of

Electrolytes in g / l, "pH" = pH value of the electrolyte, "T" = temperature of the electrolyte m ⁰ C, "cell type" = orientation of the band electrification by the electrolyte, "flow rate" = flow rate of the electrolyte mm / s and " Strorαdichte "= current density in A / dm ² indicated.

For comparison, the sample Z has been conventionally hot-dip galvanized. In Table 2, in addition to the Mn contents of the respective samples A-V2, the characteristics of the ZnNi coatings are

recorded under these conditions electrolytically deposited. It turns out that in the variants A - H and N - P a erfflndungsgemaße

single-phase γ-ZnNi coating, whereas in variants I - K η-Zn, i. elemental zinc, and γ-ZnNi coexistent.

In the L and M variants, a thin layer of pure nickel has been applied to the steel substrate prior to application of the ZnNi layer (so-called "nickel flash"). These are pure

Nickel deposits that are under the single-phase γ-ZnNi coating. Because such a multi-layered

Structure has no positive effect on the properties to be achieved, these variants have also been referred to as not erfmdungsgemaß, as according to the

Variants I - K samples obtained.

The Ni content of the sample Q was too high, so that this was also not considered erfmdungsgemaß.

The samples Vl and V2 have been produced on a steel with a too low Mn content. Therefore, these samples are not referred to erfmdungsgemaß, although they had a erfmdungsgemaßen γ-ZnNi coating.

From the electrolytically coated samples A-H and N-P to be regarded as erfmdungsgemaß with respect to the single-phase structure of their ZnNi alloy coating boards 1 to 23 have been divided. In addition, of the two-layer ZnNi nickel-flash coated ZnNi coatings, L and M are

Blanks 31-35, from the due to the high Ni content of their coating also not considered to be inventions sample Q a board 36, from the

Comparison produced samples Vl and V2 boards 31 - 40 and from the comparison sample Z a board 41 has been divided.

The boards 1 to 41 are then on the in

Table 3 indicated "T-furnace" over a Gluhzeit "t-Gluh" heated and m one

conventional hot-pressing tool was hot-formed in one stage to each one steel component and cooled so quickly that Hartegefuge set in the steel substrate.

For each of the generated from the boards 1 to 41

Steel components has been assessed and examined in the course of the hot-pressing deformation hot forming behavior, whether it is in the hot press forming a

Cracking has occurred in the respective steel substrate. The results of this assessment and test are also entered in Table 3.

The molded from the boards 1 to 36 and 41

Steel components were then subjected to a salt spray test in accordance with DIN EN ISO 9227. If corrosion of the base metal has been detected after 72h or 144h, the m is noted in the columns "base metal corrosion 72h" and "base metal corrosion 144h" in table 3. It turned out that the steel components made from the

Boards 9 to 23, which had Ni contents of 9 - 13 wt .-% in their originally applied ZnNi alloy coating, in addition to an optimal forming behavior

had superior corrosion resistance.

In the steel component that from the conventional

coated, obtained from the sample Z board 41 has been formed, although a good

Warmumformverhalten. However, she fulfilled the to the

Prevention of cracking of their steel substrate

not set requirements.

The steel components made from blanks 37-40 divided from comparative samples V1 and V2 showed flaking and insufficient corrosion resistance of the coating. As this is a

Exclusion criterion is at this

Steel components no further testing has been carried out.

The GDOS measuring method ("GDOS" = Glow Discharge Optical Emission Spectrometry) is a standard method for the rapid detection of a

Concentration profile of coatings. It is

For example, in the VDI Lexikon Werkstofftechmk, ed. by Hubert Graf, VDI-Verlag GmbH, Dusseldorf 1993,

described.

In Fig. 1 is the typical result of the GDOS measurement of corrosion protection coating of a m erfmdungsgemaßer manner generated and procured steel component shown. The contents of Mn (short

dashed line), O (dotted line), Zn (long dashed line), Fe (dash-dotted line) and Ni (solid line) are plotted over the coating layer thickness. It can be seen that there is a high concentration of Mn on the surface of the coating, which diffuses from the steel substrate through the coating on its surface and is oxidized there with the ambient oxygen. In the ZnNi-containing layer of the coating, however, the Mn content is significantly lower and only increases again in the steel substrate. This becomes particularly clear with reference to FIG. 2. On the other hand, the Ni content of the coating is substantially constant over its entire thickness

constant .

In a further experiment, a recrystallized cold strip is first electrolytically with a, as in the inventive samples described above

single phase consisting of γ-ZnNi phase

ZnNi alloy coating has been plated. The layer thickness of the γ-ZnNi alloy coating was 7 μm at a Ni content of 10%. Subsequently, on these

ZnNi alloy coating also electrolytically a 5 micron thick, pure zinc Zn layer has been applied.

From the thus obtained, with a two-ply

Anticorrosive coating provided cold strip boards have been divided, which have been heated to a platinum temperature of 880 ⁰ C within 5 minutes. After hot working and hardening, a corrosion protection layer was present on the resulting steel component. At the The surface also had a pronounced Mn oxide layer under which a Zn-rich layer existed, under which was again a ZnNi layer resting on the steel substrate.

To check which development is on the

each board applied coating during the

Warming takes place on the platinum temperature and how the coating is obtained on the resulting finished component is provided in erfmdungsgemaßer manner with a ZnNi alloy coating first samples the structure of the coating after the electrolytic coating, after heating to 750 ⁰ C followed by cooling and finally on after a heating to 880 ⁰ C finished molded and cured component has been examined. The states of the coating at the respective three points in time can be described as follows: a) After the coating (FIG. 3, FIG. 1):

The coating is single phase, intermetallic, of gamma-Zmk nickel (Ni5Zn21). At most there is a very thin native oxide skin that is negligible in its effect, which is free of Mn. b) heating up to about 750 ^° C. (FIG. 3, FIG. 2)

On the coating, a Zn / Mn oxide layer has formed. The coating is metallographically biphasic. Both gamma phases are formed, each partially replacing Fe with Ni and vice versa. The phases are isomorphic with respect to their crystal structure. It is characteristic that the Ni content in the coating m

Direction of the base material decreases and analogously decreases the Fe content in the direction of the free surface. This form of Uberzugsausbildung is up to about 750 ⁰ C before, but can be very short, below the for a

Heatsinking the respective board lying times still to be proven. Typical examples of the

Composition of the γ-ZnNi (Fe) and the F-FeZn (Ni) phase of the coating are given in the following table:

c) Result of the annealing process (FIG. 3, pictures 3, 4):

With continued heating, the coating is still largely intermetallic, partly both gamma phases γ-ZnNi and F-ZnFe are adjacent to each other. However, in the course of the glowing process (from approx.

750 ⁰ C) formed in the coating an α-Fe Mischknstall in which Zn and Ni are dissolved.

With continued heating, the Zn / Mn oxide layer is still present. The coating turns out to be metallographic and radiographic two-phase. It forms a mixed gamma phase (γ / F-ZnNi (Fe)) from. It is characteristic that this phase is rather rich in Ni. At the phase boundary steel coating a new phase is formed. There is an α-Fe Solid solution in which Zn and Ni are dissolved. The obsession occurs due to the high

Cooling speed. Typical examples of the

Composition of the layers of the coating are given in the following table:

The finished component is always a two-phase coating, consisting of an α-Fe Mischkπstall in which Zn and Ni zwangsgelost present and a mixed gamma phase Zn _x Ni (Fe) _y , substituted in the Ni atoms by Fe atoms and vice versa.

Depending on the time when the Gluhbehandlung

is completed, and from the annealing temperature, the mixed gamma phase is "γ / r-ZnNi (Fe)" in the α-Fe

Mixed-crystal area "α-Fe (Zn, Ni) -MK" dispersed, which now extends below the oxide layer "ZnMn oxide". This type of phase education is fostered by:

• no temperatures

® long oven lay times

• low layer thicknesses

Typical examples of the composition of the layers of the coating are given in the following table:

By way of example, two states of the coating obtained after completion of the annealing treatment are shown in FIG. 3, FIGS. 3 and 4.

Fig. 3, Figure 3, indicates the state of the coating, which occurs when comparably low annealing temperatures, short furnace lay times or large

Layer thicknesses of the coating can be maintained. FIG. 4 shows a photomicrograph of a cut of a coating produced in accordance with the invention and in this state.

Fig. 3, Figure 4, however, shows a structure of the coating, which sets at high annealing temperatures, comparably long annealing time or lower coating thickness of the coating. In this case, the state shown in Fig. 3, Fig. 3, and Fig. 4 represents an intermediate stage, which is passed on the way to the state shown in Fig. 3, Figure 4, state. In Fig. 5 is a

A photomicrograph of a section of a prepared in accordance with the invention, in this state located coating shown.

It can be stated that in the above-explained phase c) (FIG. 3, FIGS. 3 and 4) the α- Fe (Zn, Ni) mixed crystal <30 mass% Zn and the

Mixed gamma phase γ / F-ZnNi (Fe)> 65 mass% Zn.

Due to the high Zn content of the mixed gamma phase γ / T-ZnNi (Fe), an increased corrosion protection effect is achieved

achieved compared to pure Zn / Fe systems.

The invention thus provides a method with which a component provided with a metallic coating which adheres well and is particularly effective against corrosion can be produced in a simple manner. For this purpose, a steel material containing from 0.3 to 3 wt .-% manganese and a yield strength of 150 - 1100 MPa and a tensile strength of 300 - 1200 MPa having produced

Flat steel product with a corrosion protection coating

coated, one on the steel flat product electrolytically deposited, single-phase of γ-ZnNi phase

existing ZnNi alloy coating containing in addition to zinc and unavoidable impurities 7 - 15 wt .-% nickel. From the flat steel product, a board is then obtained, which is either heated directly to at least 800 ⁰ C and then formed into the steel component or first formed to the steel component, which is then heated to at least 800 ⁰ C. The steel component obtained in each case is finally hardened by being cooled with a sufficient for the formation of hardness structure cooling rate from a temperature at which the steel component in a for the formation of temper or hardened structure

suitable condition is located. 00

Table 1

Table 2

4

Values in () = thickness of Ni flash

2 ⁾ salt spray test DINENISO 9227 Table 3

Claims

PATENT AT SPRU

1. A method of making one with a

metallic, anticorrosive coating steel component comprising the following

Steps: a) To provide a flat steel product produced from a steel material containing 0.3 to 3% by weight of manganese, which has a yield strength of 150 to 1100 MPa and a tensile strength of 300 to 1200 MPa. b) coating the flat steel product with a

Anticorrosive coating, which consists of a one-phase, γ-ZnNi phase electrodeposited on the steel flat product

ZnNi alloy coating comprising, in addition to zinc and unavoidable impurities, 7 to 15% by weight of nickel; c) heating one from the flat steel product

formed board to a minimum of 800 ⁰ C amounting platinum temperature; d) forming the steel component from the board in a mold, and e) hardening of the steel component by cooling from a temperature at which the steel component is in a suitable condition for the formation of Vergutungs- or Hartegefuge state, with a cooling rate sufficient to form the Vergutungs- or Hartegefuge.

2. A method for producing a with a

metallic, anticorrosive coating steel component comprising the following

Steps: a) To provide a flat steel product produced from a steel material containing 0.3 to 3% by weight of manganese, which has a yield strength of 150 to 1100 MPa and a tensile strength of

300-1200 MPa; b) coating the flat steel product with a

Anti-corrosive coating comprising a ZnNi alloy coating, electrolytically deposited on the steel flat product and comprising γ-ZnNi single-phase phase, containing, in addition to zinc and unavoidable impurities, 7-15% nickel by weight; c) forming the steel component from one of the

Flat steel product formed board in a mold; d) heating the steel component to a minimum of 800 ⁰ C component temperature component; e) hardening of the steel component by cooling from a temperature at which the steel component is in a suitable condition for the formation of Vergutungs- or Hartegefuge state, with a cooling rate sufficient to form the Vergutungs- or Hartegefuges.

3. The method of claim 2, d a d u r c h

e g e n e s e s, the forming of the steel component (step c)) is carried out as preforming and the steel component is finished shaped after heating (step d)).

4. Method according to one of the preceding claims, characterized in that the coating protecting against corrosion on the

finished steel component comprises a coating layer which consists of at least 70% by mass of oc-Fe (Zn, Ni) mixed crystal and the balance of intermetallic compounds of Zn, Ni and Fe.

5. The method of claim 4, d a d u r c h

e n c ia n, the s

intermetallic compounds are dispersed in α ~ Fe (Zn, Ni) mixed crystal.

6. Method according to one of the preceding claims, characterized in the finished steel component on the

Corrosion protection coating is a Mn-containing layer is present in the Mn in metallic or oxidic form.

7. The method of claim 6, d a d u r c h

e n c ia n, the s

Mn-containing layer is 0.1 - 5 microns thick.

8. The method of claim 4 to 7, d a d u r c h

g e n c i n e s, the s

Mn content of the Mn-containing layer is 0.1 to 18 wt%.

9. A method according to any one of the preceding claims, wherein the anticorrosive coating prior to forming the steel component comprises an additional Zn layer which is also coated on the ZnNi alloy coating prior to forming the steel component.

10. The method of claim 9, d a d u r c h

e n c ia n, the s

Zn layer 2.5 - 12.5 microns thick.

11. Method according to one of claims 9 or 10, characterized in that the anticorrosion coating of the finished product is present

Steel component one on the nickel containing

Alloy coating lying Zn-rich layer

includes.

12. Method according to one of the preceding claims, characterized in that the forming of the steel component as thermoforming

is carried out and the forming and cooling of the steel component in one go in one

Hot forming tool can be performed.

13. The method according to any one of claims 1 to 12,

d a d u r c h e c e s, e e s the steel component forming and hardening

be performed sequentially in two separate steps.

14. Steel component with a 0.3 -3 wt .-%

Manganese-containing steel existing steel substrate and one applied to the steel substrate

Corrosion protection coating, one to at least

70 wt% of α-Fe (Zn, Ni) mixed crystal and the remainder of Zn, Ni and Fe intermetallic compounds, and a Mn-containing layer on the free surface thereof in which Mn is present in metallic or oxidic form.

15. Steel component according to claim 14, d a d u r c h

e n c ia n, the s

intermetallic compounds are dispersed in the Ot-Fe (Zn, Ni) mixed crystal.

16. Stahlbautei] according to claim 14 or 15, d a d u r c h e c e n e c e s e s, d a s s

ZnNi alloy coating is more than 2 μm thick.

17. Steel component according to one of claims 14 to 16,

and the ZnNi alloy coating contains 1-15 wt% Ni.

18. Steel component according to one of claims 14 to 17,

In other words, the Mn content of the Mn-containing layer is 1 to 18% by weight.

19. Steel component according to one of claims 14 to 18,

For example, the thickness of the Mn-containing layer is 0.1-5 .mu.m

amounts.

20. Steel component according to one of claims 14 to 19,

characterized in that the anti-corrosion coating comprises a high-concentration coating on the ZnNi alloy coating.

21. steel component according to one of claims 14 to 20, d a d u r c h e c e n e c e n e, s t s s on the Mn-containing layer is an organic

Coating is applied.