EP4093896A1

EP4093896A1 - Steel component comprising an anti-corrosion layer containing manganese

Info

Publication number: EP4093896A1
Application number: EP21701244.2A
Authority: EP
Inventors: Sebastian STILLE; Stefan BIENHOLZ; Stefan Krebs; Oliver Bendick
Original assignee: ThyssenKrupp Steel Europe AG
Current assignee: ThyssenKrupp Steel Europe AG
Priority date: 2020-01-24
Filing date: 2021-01-15
Publication date: 2022-11-30
Also published as: CN115003848A; CN115003848B; US20230047998A1; US12043902B2; WO2021148312A1

Abstract

The invention relates to a steel component (13) comprising a steel substrate (15) having an anti-corrosion coating (17) provided on at least one face of the steel substrate (15). The anti-corrosion coating (17) comprises an alloy layer (19) containing manganese. In the anti-corrosion coating, the alloy layer (19) containing manganese forms the alloy layer lying nearest to the surface. The alloy layer (19) containing manganese also comprises iron and another metal.

Description

Steel component with a manganese-containing corrosion protection layer

The invention relates to a steel component with a manganese-containing corrosion protection layer, a flat steel product for producing such a steel component, and a method for producing the steel component or the flat steel product.

When "flat steel products" are mentioned here, they mean steel strips, steel sheets or blanks and the like obtained from them.

In order to offer the combination of low weight, maximum strength and protective effect required in modern body construction, hot-pressed components made of high-strength steels are used today in those areas of the body that could be exposed to particularly high loads in the event of a crash.

In hot press hardening, also known as hot forming, steel blanks, which are separated from cold or hot rolled steel strip, are heated to a deformation temperature generally above the austenitizing temperature of the respective steel and placed in the heated state in the tool of a forming press. In the course of the subsequent reshaping, the sheet metal blank or the component formed from it undergoes rapid cooling through contact with the cool tool. The cooling rates are set so that a hardness structure results in the component. The structure is converted into a martensitic structure.

Typical steels that are suitable for hot press hardening are steels A-E, the chemical composition of which is listed in Table 5.

The advantages of the known manganese-boron steels, which are particularly suitable for hot press hardening, are offset in practice by the disadvantage that steels containing manganese are generally not resistant to wet corrosion. This strong tendency to locally limited, but intensive corrosion when exposed to increased chloride ion concentrations in comparison to lower alloyed steels makes the use of steels belonging to the material group of high-alloy steel sheets difficult, especially in bodywork. In addition, steels containing manganese tend to corrode surfaces, which also limits their range of uses. It is also known from studies that with Mn-B quenched and tempered steels for complex crash-relevant structural components in vehicle bodies under unfavorable conditions, for example with increased hydrogen input and with the presence of increased tensile stresses, there is a potential risk of a There is hydrogen embrittlement or the risk of hydrogen-induced delayed crack formation. The hydrogen entry is favored by the higher absorption capacity of the steel substrate in the austenitic structure state during the annealing treatment.

In the prior art, there are various proposals which aim to reduce the hydrogen uptake of steels containing manganese during the tempered state or to provide such steels with a metallic coating that protects the steel from corrosive attack. A distinction is made between active and passive corrosion protection systems.

Active corrosion protection systems are usually produced by continuously applying a zinc-containing corrosion protection coating. Passive corrosion protection systems, on the other hand, are typically produced by applying an aluminum-containing coating, in particular an aluminum-silicon coating (AlSi), which offers a good barrier effect with regard to corrosive attacks.

However, the use of zinc-containing anti-corrosion coatings has the disadvantage that zinc has a relatively low melting point of approx. 419 ° C. During the hot forming process, the liquid, zinc-containing coating penetrates the base material and leads to severe cracking there (so-called liquid metal embrittlement).

There are also several negative aspects with previous aluminum-containing anti-corrosion coatings. The energy consumption of a hot-dip coating system for the production of AISi coatings is relatively high due to the high melting temperature of the coating material. In addition, these coatings on manganese-boron steels can only be cold formed to a certain extent. Due to a hard intermetallic Fe-Al-Si phase, the coating flakes off during the cold forming process. This limits the degree of deformation. The AISi coatings therefore regularly require direct hot forming. In combination with a cathodic dip coating, which enables the lacquer layer to adhere well to the surface of the AISi coating, a good barrier effect can be achieved with regard to achieve corrosive attacks. Furthermore, with this coating variant, the entry of hydrogen into the steel material must be taken into account, which can make it necessary to use a dew point control on the continuous furnace for the press hardening process under unfavorable process conditions. The energy consumption associated with dew point control causes additional costs in component manufacture.

Various coatings for hot forming are known from US 2017/0029955, including manganese-containing alloy layers.

Proceeding from this, the invention was based on the object of providing an alternative coating which is suitable for hot forming and which adequately protects the hot-formed steel component from corrosion.

This object is achieved by a steel component comprising a steel substrate with a corrosion protection coating present on at least one side of the steel substrate. The anti-corrosion coating comprises a manganese-containing alloy layer, the manganese-containing alloy layer forming the alloy layer of the anti-corrosion coating that is closest to the surface, and the manganese-containing alloy layer comprising iron and a further metal.

For the purposes of this application, a layer is referred to as comprising or containing an element if the mass fraction of this element is greater than 0.5% by weight. The manganese-containing alloy layer thus contains a mass fraction of manganese that is greater than 0.5% by weight, a mass fraction of iron that is greater than 0.5% by weight, and a mass fraction of another metal that is also greater than 0.5 Wt%.

In the following, mass fractions are usually abbreviated with the element symbol, i.e. the following applies: Mn> 0.5% by weight and Fe> 0.5% by weight. The mass fraction of the additional metal is abbreviated with X, unless the metal is specified. It is therefore true that X> 0.5% by weight.

In particular, the object is achieved by a steel component comprising a steel substrate with an anti-corrosion coating present on at least one side of the steel substrate. Included the anti-corrosion coating comprises a manganese-containing alloy layer, the manganese-containing alloy layer forming the alloy layer of the anti-corrosion coating that is closest to the surface, and the manganese-containing alloy layer comprising:

Manganese another metal from the group aluminum, chromium, copper, tin, optionally one or more alloy elements from the group magnesium, calcium, strontium, zirconium, zinc, silicon, aluminum, chromium, copper, tin with the proviso that the total proportion of all Alloy elements from this group in total is less than 2% by weight

Remainder iron and unavoidable impurities.

Alternatively, the task is also achieved by a special design of the steel component (hereinafter referred to as Cu-Zn variant). In this case, the steel component comprises a steel substrate with an anti-corrosion coating present on at least one side of the steel substrate. The anti-corrosion coating comprises a manganese-containing alloy layer, the manganese-containing alloy layer comprising:

Manganese another metal from the group copper, tin, optionally one or more alloy elements from the group magnesium, calcium, strontium, zircon, zinc, silicon, aluminum, chromium, copper, tin with the proviso that the total proportion of all alloy elements from this group in total is less than 2% by weight

Remainder iron and unavoidable impurities.

In a preferred further development of the Cu-Zn variant, the manganese-containing alloy layer forms the alloy layer of the corrosion protection coating that is closest to the surface.

In a special development of the Cu-Zn variant, the corrosion protection coating has at least one further functional layer which is arranged closer to the surface than the manganese-containing alloy layer.

The steel substrate of a steel component described above is typically a steel with a martensitic structure, preferably a manganese-boron steel with a martensitic structure. The steel substrate is particularly preferably a steel from the group of AE steels, the chemical analysis of which is given in Table 5. Table 5 is to be understood in such a way that the element proportions are given in percent by weight for each steel from the group of steels AE. A minimum and a maximum weight fraction is specified here. For example, steel A thus has a carbon content C: 0.05% by weight - 0.10% by weight. If the lower limit is 0, the element is to be understood as optional. No entry in the table means that there is no limit for the element. For the elements chromium and molybdenum in steels C-E, there is only an upper limit for the sum of the element contents of chromium and molybdenum. In addition to the elements listed in the table, the steels AE can contain other optional elements, eg Cu, N, Ni, V, Sn, Ca. The remainder consists of iron.

It has surprisingly been found that such a ternary alloy system with iron and manganese shows a particularly good barrier effect against corrosion. The anti-corrosion coating also acts as a sacrificial or protective anode. In contrast to the zinc-containing anti-corrosion coatings mentioned at the beginning, the anti-corrosion coating according to the invention has a higher melting point, so that it is well suited for hot forming and the liquid metal embrittlement is significantly reduced.

In a preferred embodiment variant, the manganese-containing alloy layer contains more than 10% by weight of manganese, in particular more than 20% by weight of manganese, preferably more than 30% by weight, particularly preferably more than 40% by weight of manganese. This ensures that, on the one hand, the melting point of the alloy layer is sufficiently high and, on the other hand, that active corrosion protection occurs. In addition, a high proportion of manganese leads to a darkening of the surface due to the formation of manganese oxide on the surface. This improves the energy consumption in the furnace, which in turn leads to energy savings.

In a special configuration of the steel component, the manganese-containing alloy layer makes contact with the steel substrate. This means that the manganese-containing alloy layer is also the only alloy layer in the anti-corrosion coating, as it is both the alloy layer closest to the surface and makes direct contact with the steel substrate (with the Cu-Zn variant, this is the case with at least one of the special developments). In any case, the direct contact with the steel substrate supports the effect as a sacrificial anode for corrosion protection. A further developed variant of the steel component comprises a corrosion protection coating with an oxide layer on the surface of the corrosion protection coating. The oxide layer is formed spontaneously through reaction with atmospheric oxygen. If the manganese-containing alloy layer is also the alloy layer closest to the surface, and the oxide layer essentially contains manganese oxide, oxides of the further metal and / or oxides of the optional alloy elements. If a further functional layer is arranged closer to the surface than the manganese-containing alloy layer, the oxide layer essentially contains oxides of the materials of the further functional layer. The thickness of the oxide layer is typically 20 nm to 300 nm, preferably 50 nm to 200 nm, and additionally protects the steel component from corrosion.

In the case of special designs of the steel component, the electrochemical potential of the manganese-containing alloy layer is more negative than the electrochemical potential of the steel substrate. This achieves the effect of the alloy layer as a sacrificial anode and thus the active corrosion protection of the steel substrate. In particular, the difference between the electrochemical potentials of the steel substrate and the manganese-containing alloy layer is greater than 50 mV, in particular greater than 100 mV, preferably 150 mV, particularly preferably greater than 200 mV. It has been shown that a large difference in the electrochemical potentials leads to particularly good active corrosion protection.

The electrochemical potential was determined in accordance with DIN standard "DIN 50918 (Section 3.1) (1978.06)" ("Rest potential measurement on homogeneous mixed electrodes"). In so far as absolute values instead of difference values are given for the electrochemical potential in the following, this refers to the reference to the standard hydrogen electrode.

The other metal of the manganese-containing alloy layer is selected from the group consisting of aluminum, chromium, copper and tin. Tests have shown that ternary alloy systems made from iron, manganese and an element from the group of aluminum, chromium, copper and tin are particularly suitable as corrosion protection. In addition, these elements are comparatively non-toxic and reasonably inexpensive. In addition, the melting point is high enough to sufficiently reduce the liquid metal embrittlement during hot forming. Furthermore, all of these combinations show good active protection against corrosion.

Optionally, the manganese-containing alloy layer comprises one or more alloy elements from the group of magnesium, calcium, strontium, zirconium, zinc, silicon, aluminum, chromium, copper, Tin with the proviso that the total proportion of all alloy elements from this group is less than 2% by weight. In contrast to the other metal from the group of aluminum, chromium, copper, tin, the optional alloy elements can also be present in proportions of less than 0.5% by weight.

Alloying these elements has the advantage that they form oxides and relatively little hydrogen is released when they form oxides with water vapor. Therefore, relatively little hydrogen penetrates into the manganese-containing alloy layer and the substrate during hot forming. The additional alloy therefore protects against hydrogen embrittlement.

At the same time, with such a small additional alloy (in total less than 2% by weight), the elements have no or only a very little influence on the electrochemical properties, that is to say the cathodic protection. It is therefore also justified to carry out the electrochemical investigations in exemplary embodiments without this addition alloy.

In a preferred variant, the manganese-containing alloy layer contains no other elements besides iron and the further metal mentioned. The mass fractions of all other elements are therefore less than 0.5% by weight.

In special configurations, the iron content of the manganese-containing alloy layer is more than 2.0% by weight, in particular more than 3.0% by weight, preferably 5.0% by weight, particularly preferably 10.0% by weight. A certain amount of iron automatically diffuses into the alloy layer during hot forming.

In a special embodiment, the manganese-containing alloy layer contains iron and aluminum, the iron content being less than 24% by weight, in particular less than 20% by weight, preferably less than 15% by weight, particularly preferably less than 12% by weight, and the manganese content is greater than 40% by weight. In particular for the variant with an iron content of less than 12% by weight and a manganese content of greater than 40% by weight, it has been shown that the result is an electrochemical potential that is less than -400 mV. For a steel substrate made of a manganese-boron steel with an electrochemical potential of -250mV, the manganese-containing alloy layer ensures very good active corrosion protection.

The manganese-boron steels mentioned with a martensitic structure, in particular the steels AE according to Table 5, have an electrochemical potential in the range of -250mV ± 100mV depending on exact chemical composition. The advantages of the manganese-containing alloy layer in conjunction with a steel substrate, the steel of which has an electrochemical potential of -250mV, are explained here and below by way of example. The same applies to other steel substrates with a different chemical potential within the range of -250mV ± 100mV.

In a further special embodiment, the manganese-containing alloy layer contains iron and tin, the iron content being less than 20% by weight and the tin content being less than 30% by weight; in this variant the tin content is preferably greater than 6% by weight. It has been shown that for manganese-containing alloy layers with this relative composition there is an electrochemical potential that is consistently less than -250mV, so that active corrosion protection results for the manganese-boron steel mentioned.

In a further special embodiment, the manganese-containing alloy layer contains iron and copper, the ratio of iron content to copper content being greater than 0.05. It has been shown that for manganese-containing alloy layers with this mass ratio there is an electro-chemical potential that is consistently less than -250mV, so that active corrosion protection results for the manganese-boron steel mentioned.

In particular, it has been shown that it is advantageous if the iron content Fe and copper content Cu meet the following relation:

Fe <45 wt% - 1.18 Cu

In this case, the electrochemical potential is consistently less than -500mV, which leads to better active corrosion protection in connection with the manganese-boron steel mentioned.

In a preferred variant, the iron content Fe and copper content Cu also fulfills the following relationship:

Fe <20 wt% - 0.66 Cu

In this case, the electrochemical potential is consistently less than -650mV, which leads to an even better active corrosion protection in connection with the manganese-boron steel mentioned. In a further special embodiment, the manganese-containing alloy layer contains iron and chromium, the iron content Fe and the chromium content Cr fulfilling the following relationship:

20 wt% <Fe + Cr <50 wt%

In this range the electrochemical potential is consistently less than -350mV, which leads to very good active corrosion protection in connection with the manganese-boron steel mentioned.

The steel component is developed in such a way that the manganese-containing alloy layer is at least 70% by volume, preferably at least 80% by volume, in the solid state at a temperature of 880 ° C. This means that hot forming is possible in an uncomplicated manner without the liquefied layer sticking to tools or liquid metal embrittlement.

The steel component mentioned above is in particular a press-hardened steel component, preferably a steel component of a motor vehicle, preferably selected from the group consisting of bumper beam, side impact beam, pillars and body reinforcements.

The object according to the invention is also achieved by a flat steel product for producing a steel component as described above. The flat steel product comprises a steel substrate with an anti-corrosion coating on at least one side of the steel substrate, the anti-corrosion coating including a manganese-containing alloy layer and the manganese-containing alloy layer forming the alloy layer of the anti-corrosion coating that is closest to the surface. The manganese-containing alloy layer includes:

Manganese another metal from the group aluminum, chromium, copper, tin optionally one or more alloy elements from the group magnesium, calcium,

Strontium, zirconium, zinc, silicon, aluminum, chromium, copper, tin, with the proviso that the total proportion of all alloying elements from this group is less than 2

Wt%

Remainder iron and unavoidable impurities.

Alternatively, the object is also achieved by a special design of the flat steel product (hereinafter referred to as Cu-Zn variant). The flat steel product includes a ok

Steel substrate with an anti-corrosion coating present on at least one side of the steel substrate, the anti-corrosion coating comprising a manganese-containing alloy layer. The manganese-containing alloy layer includes:

Manganese another metal from the group copper, tin, optionally one or more alloy elements from the group magnesium, calcium, strontium, zircon, zinc, silicon, aluminum, chromium, copper, tin, with the proviso that the total proportion of all alloy elements from this group in Sum is less than 2% by weight

Remainder iron and unavoidable impurities.

In a preferred further development of the Cu-Zn variant, the manganese-containing alloy layer forms the alloy layer of the corrosion protection coating that is closest to the surface. The direct contact with the steel substrate supports the effect as a sacrificial anode for corrosion protection.

The flat steel product can in particular be used to produce a steel component as described above. The flat steel product therefore has the corresponding advantages that are explained above in connection with the steel component.

The manganese-containing alloy layer of the flat steel product can already contain an iron content. However, this is then typically a few percentage points lower than in the hot-formed steel component. Alternatively, the manganese-containing alloy layer of the flat steel product can also be ironless. In both cases, the iron content increases during hot forming, since iron diffuses from the steel substrate into the manganese-containing alloy layer. The exact proportion of iron that diffuses into the manganese-containing alloy layer can be controlled by the process parameters during hot forming. The higher the temperature during hot forming and the longer the flat steel product is kept at this temperature, the more iron diffuses into the manganese-containing alloy layer. In a preferred embodiment, the manganese-containing alloy layer of the flat steel product contains more than 10% by weight of manganese, in particular more than 20% by weight of manganese, preferably more than 30% by weight, particularly preferably more than 40% by weight. % Manganese, in particular more than 50% by weight manganese. This ensures that, on the one hand, the melting point of the alloy layer is sufficiently high. On the other hand, it is ensured that the manganese content is sufficiently high even after hot forming to guarantee active corrosion protection.

In a special configuration of the flat steel product, the manganese-containing alloy layer makes contact with the steel substrate. This means that the manganese-containing alloy layer is also the only alloy layer in the anti-corrosion coating, as it is both the alloy layer closest to the surface and directly contacts the steel substrate (with the Cu-Zn variant, this is at least the case with one of the special developments). In any case, the direct contact with the steel substrate supports the effect as a sacrificial anode for corrosion protection.

In a further development of the flat steel product, the steel substrate is a steel with a ferritic-pearlitic structure, preferably a manganese-boron steel with a ferritic-pearlitic structure, particularly preferably a manganese-boron steel with a ferritic-pearlitic structure, which is produced by heat treatment can be converted into a martensitic structure in the form of a thermal hardening treatment. As a result, the steel substrate is particularly suitable for producing a steel component explained above by hot forming.

The object according to the invention is also achieved by a method for producing an aforementioned flat steel product. The process comprises at least the following steps:

- Production or provision of a steel substrate, the structure of the steel substrate being convertible into a martensitic structure by hot forming,

Application of a manganese-containing alloy layer to form a corrosion protection coating, the manganese-containing alloy layer comprising: i. Manganese ii. another metal from the group aluminum, chromium, copper, tin iii. optionally one or more alloy elements from the group magnesium, calcium, strontium, zircon, zinc, silicon, aluminum, chromium, copper, tin, Iron with the proviso that the total proportion of all alloy elements from this group is less than 2% by weight iv. The remainder is iron and unavoidable impurities and the manganese-containing alloy layer (19) forms the alloy layer of the corrosion protection coating that is closest to the surface.

Alternatively, the object according to the invention is achieved by a special embodiment of the method for producing an aforementioned flat steel product (Cu-Zn variant). The process comprises at least the following steps:

Application of a manganese-containing alloy layer to form a corrosion protection coating, the manganese-containing alloy layer comprising: i. Manganese ii. another metal from the group copper, tin iii. optionally one or more alloy elements from the group magnesium, calcium, strontium, zirconium, zinc, silicon, aluminum, chromium, copper, tin, iron with the proviso that the total proportion of all alloy elements from this group is less than 2% by weight. iv. Remainder iron and unavoidable impurities.

The methods have the same advantages that are explained above with reference to the flat steel products or the steel components.

In particular, the manufacturing process is developed in such a way that the manganese-containing alloy layer is applied using a process selected from the group consisting of electrolytic deposition, physical vapor deposition (PVD), immersion process, chemical vapor deposition, slurry process, thermal Spraying, roll cladding and combinations thereof. In the case of the above-mentioned manganese-containing alloy layer, physical vapor deposition is particularly advantageous, since no hydrogen is introduced into the substrate in this process. In addition, the PVD process enables coating with high-melting alloys, which is not so easy, for example, in the hot-dip process.

The object according to the invention is also achieved by a method for producing an aforementioned steel component. The method for manufacturing a steel component comprises at least the following steps:

- Provision of a previously explained flat steel product or production of a previously explained flat steel product, in particular according to the method described above,

- Hot forming of the provided or manufactured flat steel product, so that the steel component results.

The hot forming of the provided or manufactured flat steel product is preferably designed in such a way that it comprises the following steps:

- Heating the flat steel product in a furnace with a furnace temperature of 830 ° C to 980 ° C, preferably 830 ° C to 910 ° C, the residence time of the flat steel product in the furnace being at least 1 and at most 18 minutes

- Discharge of the flat steel product from the furnace and insertion in a forming tool

- Forming the flat steel product into a steel component in the forming tool

To avoid major heat losses, the transfer time between the furnace and the forming tool is typically a maximum of 10 seconds.

Optionally, the flat steel product in the forming tool can be cooled during the forming process at cooling rates of 20-1000 K / s, preferably 25-500 K / s, in order to harden the steel substrate.

Alternatively, the flat steel product can first be formed into a steel component in the forming tool and then the steel component can be cooled at cooling rates of 20-1000 K / s, preferably 25-500 K / s, in order to harden the steel substrate.

The flat steel product is typically placed in the furnace at room temperature, so that the dwell time t can include both a heating phase and a holding phase at the furnace temperature. The method for producing a steel component is developed in particular in such a way that the steel flat product provided or produced comprises as steel substrate a steel with a structure which can be converted into a martensitic structure by heat treatment, preferably a steel with a ferrite-pearlitic structure, particularly preferably a manganese Boron steel with a ferritic-pearlitic structure, and hot forming includes:

- a thermal hardening treatment in which the structure is converted into a martensitic structure, and preferably

a mechanical treatment, preferably a mechanical reshaping, before, during and / or after the thermal hardening treatment.

In particular, the aforementioned manufacturing method of a steel component is further developed in such a way that iron diffuses from the steel substrate into the manganese-containing alloy layer during hot forming, so that a manganese-containing alloy layer results, including another metal from the group aluminum, chromium, copper, tin, and optionally one or more alloy elements from the group magnesium, calcium, strontium, zirconium, zinc, silicon, aluminum, chromium, copper, tin with the proviso that the total proportion of all alloy elements from this group is less than 2% by weight. and the remainder being iron and unavoidable impurities. In particular, the electrochemical potential of the manganese-containing alloy layer is more negative than the electrochemical potential of the steel substrate, in particular the difference between the electrochemical potentials of the steel substrate and the manganese-containing alloy layer is greater than 50mV, in particular greater than 100mV, preferably 150mV, particularly preferably greater than 200mV.

In particular, the aforementioned manufacturing method of a steel component is developed in such a way that the hot forming comprises at least the following steps:

- a thermal treatment in which the structure of the provided or manufactured component is kept at a temperature above Ac3 until the structure is completely or partially converted into an austenitic structure,

- mechanical forming of the component, before, during and / or after the thermal treatment, - Cooling of the component from the temperature above Ac3, during and / or after the mechanical forming, preferably to a temperature of less than 100 ° C, so that a martensitic structure is created, preferably with a cooling rate> 20 K / s.

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

FIG. 1 shows a schematic representation of a steel component with a corrosion protection coating;

FIG. 2 shows the electrochemical potential of a manganese-containing alloy layer which contains aluminum;

FIG. 3 shows the electrochemical potential of a manganese-containing alloy layer which contains tin;

FIG. 4 shows the electrochemical potential of a manganese-containing alloy layer which contains copper;

FIG. 5 shows the electrochemical potential of a manganese-containing alloy layer which contains chromium;

FIG. 1 shows a schematic representation of a steel component 13. The steel component 13 comprises a steel substrate 15 and a corrosion protection coating 17. The corrosion protection coating 17 comprises a manganese-containing alloy layer 19. The manganese-containing alloy layer 19 is the alloy layer of the corrosion protection coating 17 that is closest to the surface 19 the steel substrate 15. The manganese-containing alloy layer is therefore the only alloy layer of the corrosion protection coating 17.

Furthermore, the anti-corrosion coating 17 comprises an oxide layer 20 on the surface of the anti-corrosion coating 17. The oxide layer 20 is formed spontaneously by reaction with atmospheric oxygen and essentially contains manganese oxide and oxides of the other metal.

In the contact area with the anti-corrosion coating 17, the steel substrate 15 has a ferrite border 21. The ferrite border 21 is a high iron content diffusion layer with a thickness between 1 pm and 6 pm, which can form during hot forming. For the purposes of this application, the ferrite border 21 is considered to be part of the steel substrate 15. Depending on the configuration of the process parameters during hot forming, the thickness of the ferrite seam 21 can vary or there can also be no ferrite seam 21. FIG. 2 shows the electrochemical potential of a manganese-containing alloy layer which contains aluminum. The electrochemical potential as a function of the aluminum content and the iron content is shown in a grayscale representation. The remaining mass fraction is made up of manganese in each case. The underlying measured values are shown in Table 1.

FIG. 3 shows the electrochemical potential of a manganese-containing alloy layer which contains tin. The electrochemical potential as a function of the tin content and the iron content is shown in a grayscale representation. The remainder of the mass fraction is formed by manganese. The underlying measured values are shown in Table 2.

FIG. 4 shows the electrochemical potential of a manganese-containing alloy layer which contains copper. The electrochemical potential as a function of the copper content and the iron content is shown in a grayscale representation. The remainder of the mass fraction is formed by manganese. The underlying measured values are shown in Table 3. The reference numeral 23 denotes a line which defines the boundary of the area

Fe <45 wt% - 1.18 Cu indicates. The points to the left below the line 23 therefore fulfill this relation. Correspondingly, the reference numeral 25 denotes a line which defines the boundary of the area

Fe <20 wt .-% - 0.66 Cu indicates.

FIG. 5 shows the electrochemical potential of a manganese-containing alloy layer which contains chromium. The electrochemical potential as a function of the chromium content and the iron content is shown in a grayscale representation. The remaining mass fraction is made up of manganese in each case. The underlying measured values are shown in Table 4. Table 1

Table 2

Table 3

Table 4

Claims

1. Steel component (13) comprising a steel substrate (15) with an anti-corrosion coating (17) present on at least one side of the steel substrate (15), the anti-corrosion coating (17) comprising a manganese-containing alloy layer (19), characterized in that the manganese-containing alloy layer (19) the alloy layer of the closest to the surface

Forms corrosion protection coating (17) and wherein the manganese-containing alloy layer (19) comprises:

- manganese

- Another metal from the group aluminum, chromium, copper, tin

- optionally one or more alloy elements from the group magnesium, calcium, strontium, zirconium, zinc, silicon, aluminum, chromium, copper, tin with the proviso that the total proportion of all alloy elements from this group is less than 2% by weight.

- remainder iron and unavoidable impurities.

2. Steel component (13) according to claim 1, wherein the manganese-containing alloy layer (19) contains more than 10 wt .-% manganese.

3. Steel component (13) according to one of claims 1 to 2, wherein the manganese-containing alloy layer (19) contacts the steel substrate (15).

4. Steel component (13) according to one of claims 1 to 3, wherein the further metal is selected from the group consisting of aluminum, chromium, copper, tin.

5. Steel component (13) according to one of claims 1 to 4, wherein the manganese-containing alloy layer (19) contains iron and aluminum, the iron content being less than 24% by weight and the manganese content being greater than 40% by weight

6. Steel component (13) according to one of claims 1 to 4, wherein the manganese-containing alloy layer (19) contains iron and tin, the iron content being less than 20% by weight and the tin content being less than 30% by weight .

7. Steel component (13) according to one of claims 1 to 4, wherein the manganese-containing alloy layer (19) contains iron and copper, the ratio of iron content to copper content being greater than 0.05.

8. Steel component (13) according to claim 7, wherein the iron content Fe and copper content Cu satisfy the following relation:

Fe <45 wt% - 1.18 Cu

9. Steel component (13) according to one of claims 1 to 4, wherein the manganese-containing alloy layer (19) contains iron and chromium, the iron content Fe and the chromium content Cr meeting the following relation:

20 wt% <Fe + Cr <50 wt%

10. Steel component (13) according to one of the preceding claims, wherein the electrochemical potential of the manganese-containing alloy layer (19) is more negative than the electrochemical potential of the steel substrate (15).

11. Steel component (13) according to claim 10, wherein the difference between the electrochemical potentials of steel substrate (15) and mangan-containing alloy layer (19) is greater than 50mV, in particular greater than 100mV, preferably 150mV, particularly preferably greater than 200mV.

12. Flat steel product for producing a steel component (13) by means of hot forming according to one of the preceding claims, comprising a steel substrate (15) with an anti-corrosion coating (17) present on at least one side of the steel substrate (15), the anti-corrosion coating (17 ) comprises a manganese-containing alloy layer (19), characterized in that the manganese-containing alloy layer (19) is the alloy layer of the closest to the surface

- manganese - Another metal from the group aluminum, chromium, copper, tin

- remainder iron and unavoidable impurities.

13. A method for producing a flat steel product according to claim 12, comprising the following steps:

- Production or provision of a steel substrate (15), the structure of the steel substrate (15) being convertible into a martensitic structure by hot forming,

- Applying a manganese-containing alloy layer (19) to form a corrosion protection coating (17), the manganese-containing alloy layer (19) comprising: i. Manganese ii. another metal from the group aluminum, chromium, copper, tin iii. optionally one or more alloy elements from the group of magnesium, calcium, strontium, zirconium, zinc, silicon, aluminum, chromium, copper, tin, iron with the proviso that the total proportion of all alloy elements from this group is less than 2 Wt% iv. Remainder iron and unavoidable impurities

- and wherein the manganese-containing alloy layer (19) forms the alloy layer of the corrosion protection coating that is closest to the surface.

14. The method according to claim 13, wherein the application of the manganese-containing alloy layer (19) takes place by means of a method selected from the group consisting of electrolytic deposition, physical vapor deposition (PVD), immersion method, chemical vapor deposition ,, Slurry process, thermal spraying, roll cladding and combinations thereof.

15. A method for producing a steel component (13) according to one of claims 1 to 11, with the following steps:

- providing a flat steel product according to one of claims 12 to 13 or manufacturing a flat steel product according to a method according to one of claims 14 or 15,

- Hot forming of the provided or manufactured flat steel product, so that the steel component (13) results.

16. The method according to claim 15, wherein during the hot forming, iron diffuses from the steel substrate (15) into the manganese-containing alloy layer (19), so that a manganese-containing alloy layer (19) results,

- wherein the manganese-containing alloy layer (19) comprises: i. Manganese ii. another metal from the group aluminum, chromium, copper, tin iii. optionally one or more alloy elements from the group of magnesium, calcium, strontium, zirconium, zinc, silicon, aluminum, chromium, copper, tin with the proviso that the total proportion of all alloy elements from this group is less than 2% by weight. iv. Remainder iron and unavoidable impurities,

- and / or wherein the electrochemical potential of the manganese-containing alloy layer (19) is more negative than the electrochemical potential of the steel substrate (15), in particular the difference between the electrochemical potentials of the steel substrate and the manganese-containing alloy layer is greater than 50mV, in particular greater 100mV, preferably 150mV, particularly preferably greater than 200mV.