Metal plate component and method for producing the same

Abstract

The present invention relates to a metal sheet component made of a hot-formed flat steel product, which flat steel product comprises a steel substrate and an Al-based corrosion protection layer applied to the steel substrate. The composition of the steel substrate in mass % is: C: 0.1 - 0.4%, Mn: 0.5 - 3.0%, Si: 0.05 - 0.5%, Cr: 0.005 - 1.0%, B: 0.0005 - 0.01%, and one or more alloying elements in the groups of "V, Ti, Nb, Al, Ni, Cu, Mo, W" respectively. Provided that the contents of the alloying elements selectively present respectively are determined as follows: V: 0.001 - 0.2%, Ti: 0.001 - 0.1%, Nb: 0.001 - 0.1%, Al: 0.01 - 0.2%, Ni: 0.01 - 0.4%, Cu: 0.01 - 0.8%, Mo: 0.002 - 1.0%, W: 0.001 - 1.0%, the balance being iron and unavoidable impurities, where the unavoidable impurities include P with a content less than 0.1%, S with a content less than 0.05%, and N with a content less than 0.01%, and where the component is selectively hardened. In order to provide optimal prerequisites for good adhesion of such a component to a cladding, the present invention provides that an adhesive section is provided on the free outer side of the corrosion protection coating, said adhesive section being for applying an adhesive to bond the metal sheet component to another component, where at least in the region of the adhesive section there is an SDR value of 3 - 30% determined according to ISO 25178.

Description

Field of the Invention

[0001] The present invention relates to a metal plate component made from a hot-formed flat steel product. The flat steel product is formed from a steel substrate, the composition of which in mass % is: C: 0.1 - 0.4%, Mn: 0.5 - 3.0%, Si: 0.05 - 0.5%, Cr: 0.005 - 1.0%, B: 0.0005 - 0.01%, and one or more optional alloying elements from the groups "V, Ti, Nb, Al, Ni, Cu, Mo, W", provided that the contents of the alloying elements present selectively are determined as follows: V: 0.001 - 0.2%, Ti: 0.001 - 0.1%, Nb: 0.001 - 0.1%, Al: 0.01 - 0.2%, Ni: 0.01 - 0.4%, Cu: 0.01 - 0.8%, Mo: 0.002 - 1.0%, W: 0.001 - 1.0%, the balance being iron and unavoidable impurities, where the unavoidable impurities include P with a content of less than 0.1%, S with a content of less than 0.05%, and N with a content of less than 0.01%. An aluminum-based corrosion protection layer is applied to the steel substrate.

[0002] The present invention also relates to a method for producing such a component. Background Art

[0003] Components of the above type and their production methods are known, for example, from WO 2008 / 053273 A1.

[0004] "Flat steel product" is understood here as a rolled product whose length and width are both significantly greater than its thickness. These products particularly include steel strips, steel plates, and cut pieces obtained therefrom.

[0005] In the present context, unless otherwise expressly stated, information regarding the contents of alloying components always relates to mass (the data unit is mass %).

[0006] In components produced by hot-forming flat steel products coated with an aluminum-based corrosion protection layer, special challenges arise if, for example, in the field of modern automotive body production, these components are to be bonded to another component. This applies regardless of the material composition of the second component to which adhesion takes place.

[0007] Adhesives that have hitherto been commonly used for hot-forming surfaces are designed for uncoated materials or for zinc surfaces. Aluminum surfaces and surfaces made from aluminum alloys have a disadvantage compared to zinc-based corrosion protection layer surfaces in that the aluminum oxide layer formed on the free surface of the aluminum corrosion protection layer hinders good adhesion, since the chemical bonding of adhesives under zinc conditions to aluminum oxide is significantly worse than to zinc surfaces. Summary of the Invention

[0008] Against this background, the aim is to provide a component which is provided with an aluminum or aluminum alloy coating on at least one surface and which provides optimal prerequisites for good adhesion on its coating.

[0009] Likewise, a method for producing such a component is to be given.

[0010] This object is achieved by a component having at least the features given in claim 1.

[0011] Regarding the method, the solution to the object put forward above lies in carrying out the working steps specified in claim 6 in the production of the component according to the invention. It is of course understood here that, when applying the method according to the invention, the person skilled in the art autonomously supplements the working steps which are known to him and which are customarily carried out in methods of this type in the prior art.

[0012] Advantageous embodiments of the invention are given in the dependent claims and are explained in detail below together with the general inventive concept.

[0013] In line with the prior art explained at the beginning, the component according to the invention is formed from a hot-formed flat steel product which comprises

[0014] - a steel substrate, the composition of which in mass % is:

[0015] C: 0.1 - 0.4%,

[0016] Mn: 0.5 - 3.0%,

[0017] Si: 0.05 - 0.5%,

[0018] Cr: 0.005 - 1.0%,

[0019] B: 0.0005 - 0.01%,

[0020] and one or more alloying elements optionally selected from the groups "V, Ti, Nb, Al, Ni, Cu, Mo, W", provided that the contents of the alloying elements selectively present are determined as follows:

[0021] V: 0.001 - 0.2%,

[0022] Ti: 0.001 - 0.1%,

[0023] Nb: 0.001 - 0.1%,

[0024] Al: 0.01 - 0.2%,

[0025] Ni: 0.01 - 0.4%,

[0026] Cu: 0.01 - 0.8%,

[0027] Mo: 0.002 - 1.0%,

[0028] W: 0.001 - 1.0%,

[0029] The balance consists of iron and unavoidable impurities, where the unavoidable impurities include P with a content of less than 0.1%, S with a content of less than 0.05%, and N with a content of less than 0.01%.

[0030] and

[0031] - An Al corrosion protection layer applied to the steel substrate.

[0032] As a supplement to its hot forming, the component according to the invention can exist in a hardened state. For this purpose, the component can be hardened in a manner known per se during hot forming (so-called "press hardening"), or heat-treated downstream of the hot forming process (see the aforementioned WO 2008 / 053273 A1).

[0033] According to the invention, an adhesive section is provided on the free outer side of the corrosion protection coating of the component, which is used to apply an adhesive to bond the metal sheet component to another component, where the surface of the corrosion protection coating has an SDR value of 3 - 30% determined according to ISO 25178 at least in the area of the adhesive section.

[0034] The present invention is based on the recognition that in an aluminum-based cladding, it is necessary to ensure a particularly strong mechanical anchoring of the adhesive on the surface to achieve optimal adhesive adhesion.

[0035] For this purpose, the present invention provides that there is a surface texture at least in the adhesive section, but preferably on the entire surface of the component according to the invention, through which the actual surface area of the adhesive section that can be effectively used for the adhesion of the adhesive to the component is increased compared to a completely flat surface. This increase is due to the formation of peaks and valleys on the surface of the adhesive section according to the invention at least. Due to, for example, the inclined surfaces extending from the peak tips to the corresponding valley bottoms or delimiting the valleys, the effective surface area where the reaction occurs between the adhesive and the coated steel sheet of the component during adhesion is significantly larger than the area occupied by the surface of the adhesive section if it were completely flat. Here, the "SDR value" determined according to ISO 25178 corresponds to the percentage by which the actual surface area of the adhesive section is larger than the surface area that would exist in the adhesive section if it were completely flat due to the texture formed by the peaks and valleys on its surface. ISO 25178 also stipulates that the roughness value should be measured using a white light interferometer.

[0036] Regarding the durability of the adhesive connection produced on a sheet metal part according to the invention, it has now been found that it is advantageous if the SDR value is between 3% and 30%.

[0037] For SDR values below 3%, the surface participating in the reaction within the adhesive section would be too small, and there would not be sufficient mechanical interlocking between the relevant surface and the adhesive to ensure the required adhesive connection.

[0038] If the sheet metal part is to be painted, a high SDR value above 30% is desirable. With a high SDR value, optimal adhesion of the paint to the substrate can be ensured, and a paint finish that also meets the particularly strict requirements present, for example, in automotive bodies, is achieved. However, practical studies have shown that during adhesion, an SDR value above 30% leads to unfavorable fracture behavior. Therefore, when the SDR value exceeds 30%, the "fracture surface SFC" is 5 - 25%. In contrast, if the SDR value is below 3%, the "fracture surface SFC" is 28 - 51%. The optimal standardized "fracture surface SFC" value of 90 - 100% only occurs within the range of the SDR of 3 - 30% specified according to the invention.

[0039] "SFC" here refers to the standardized "surface fracture within cohesion" ("SURFACE FRACTURE"). At an SFC value of 90 - 100%, the adhesion between the adhesive and the finishing layer fails, i.e., between the adhesive and the aluminum corrosion protection layer, rather than within the adhesive or the finishing layer itself.

[0040] When the fracture surface is damaged, it is desirable for it to occur at that location. To determine the SFC value, an adhesive is applied to the samples, they are bonded together, cured according to the method applicable to the respective adhesive, and then separated from each other using a tensile testing machine. Subsequently, the fracture surface is optically evaluated. The total fracture surface is considered to be 100%.

[0041] The surface enlarged according to the invention is obtained in such a way that peaks and valleys are formed on the surface of the flat steel product deformed into a sheet metal part by thermoforming. According to the understanding of the invention, an SRD value exceeding 30% here means that the ratio of the valley depth to the valley width can be so unfavorable that due to its viscosity, the adhesive can no longer completely fill the valleys between the tips ( = peaks), and thus can no longer fully utilize the surface available for interlocking in the adhesive section.

[0042] Particularly problematic here is that, during the thermoforming process, surface properties cannot be set during the application of the corrosion protection layer or by subsequent skin pass rolling as in the case of cold-formed strips. This is because the coating is molten during the heating of the sheet metal material required for the thermoforming process. This results in the roughness of the uncoated cold strip having a greater influence on the surface roughness of the thermoformed part than the surface topography present on its surface after the strip has been coated with an aluminum coating.

[0043] Due to the lack of a unified standard for testing adhesive bonds, the properties of the adhesives applied to and reported and defined here on both inventive and non-inventive sheet metal parts were determined in accordance with Stahl-Eisen-Prüfblatt SEP (Steel Testing Sheet)_1220_6 (Draft).

[0044] The present invention also limits the SDR value present on the surface of a sheet metal part provided with an Al coating according to the invention, which is formed from this sheet metal material, taking into account the best thermoforming ability of the sheet metal material. An excessively high SDR value results in a high average surface roughness Rz. The average surface roughness Rz is also determined in accordance with DIN EN ISO 4287 / 1 and corresponds to the average of the individual surface roughness depths of five successive individual measuring lengths in the roughness profile. In each measuring section, the extreme values are added to form a range and divided by the number of measuring sections. An excessively high Rz value has an adverse effect in the thermoforming tool because, there, the tips present on the surface of the sheet metal material cause scratch formation or an increased degree of contamination due to the interrupted tips and thus the formation of dust. The average surface roughness Rz is preferably limited to a maximum of 2 μm to avoid excessive dust formation during the thermoforming process.

[0045] This risk can also be effectively eliminated by ensuring that the tip value RPc of the surface of the aluminized flat steel product from which each respective inventive sheet metal part is to be formed is not greater than 200 per cm. The standardized tip value RPc is determined in accordance with DIN EN10049 / DIN EN ISO 4287 and corresponds to the number of local tips successively exceeding the upper intersection line c1 and the lower intersection line c2. The number of tips is based on a length of 1 cm and is independent of the selected measuring length.

[0046] The true surface can only be determined using special measuring methods and can only be compared with an ideally smooth surface. The more easily determinable value is the above-mentioned RPc value. In aluminum and aluminum alloys, after thermoforming, this value has a direct relationship with the true surface, which is described by the characteristic value SDR.

[0047] Then, the size F of the true surface of the adhesive section real can be estimated as follows:

[0048] Freal = e 0.2 RpC

[0049] In contrast, the size F of the completely flat surface of the bonding section eben can be determined purely computationally from its geometric limit. Then the result of the SDR value is

[0050] SDR = (F real - F eben ) / F eben × 100%

[0051] The steel substrate of the metal sheet component according to the invention consists of a conventional steel suitable for these purposes, and its composition is selected as follows:

[0052] In the steel of the flat steel product for forming the component according to the invention, the role of carbon ("C") is to delay the formation of ferrite and bainite. At the same time, due to the presence of C, retained austenite is stabilized and the Ac3 temperature is reduced. The C content in the steel of the flat steel product according to the invention is limited to a value of 0.10% to 0.4% by mass. To ensure the hardenability of the flat steel product and a tensile strength of at least 1000 MPa for the press-hardened product formed therefrom according to the invention, a C content of at least 0.10% by mass is necessary. If a higher strength level is to be achieved, the C content can be adjusted to > 0.15% by mass for this purpose. If the C content is increased to a value > 0.19% by mass, the hardenability can be further improved. Components composed of flat steel products alloyed according to the invention containing more than 0.19% by mass have a very good combination of hardenability and strength. However, a C content exceeding 0.4% by mass has an adverse effect on the mechanical properties of the flat steel product, because a C content greater than 0.4% by mass promotes the formation of brittle martensite during the press-hardening process. In addition, the weldability is also adversely affected by the high C content. If optimized weldability is to be ensured, the C content can be adjusted to at most 0.3% by mass, especially less than 0.3% by mass, for this purpose. By reducing the C content to < 0.25% by mass, the weldability can be significantly improved again, and in the press-hardened state, a good ratio of force absorption and maximum bending angle can be additionally achieved in the bending test according to VDA 238-100.

[0053] Silicon (“Si”) is used to further increase the hardenability of the flat steel products formed according to the invention and alloyed according to the invention by mixed crystal strengthening and the strength of the press-hardened products thus formed. In addition, silicon also enables the use of Ferro-Silizio-Mangan as an alloying agent, which has a favorable effect on production costs. When the silicon content is 0.05% by mass, the hardening effect already appears. When the Si content is greater than 0.15% by mass, there is a significant increase in strength. However, an Si content exceeding 0.5% by mass has an adverse effect on the coating behavior, especially on aluminum-based coatings. Therefore, in order to improve the surface quality of the flat steel products with coatings, the Si content is preferably set to be less than 0.4% by mass.

[0054] In the alloy of the steel of the flat steel products for forming the components according to the invention, manganese (“Mn”) acts as a hardening element because it greatly delays the formation of ferrite and bainite. At a manganese content below 0.5% by mass, during the press-hardening process, ferrite and bainite are formed even at a very fast cooling rate, which should be avoided. Therefore, if a martensitic microstructure is to be ensured, especially in regions with large deformations, a manganese content greater than 0.9% by mass is preferred. However, an Mn content greater than 3.0% by mass has an adverse effect on the processing properties. In particular, weldability is severely limited, which is why the Mn content of the flat steel products according to the invention is limited to at most 3.0% by mass, especially at most 1.6% by mass.

[0055] The content of chromium (“Cr”) in the steel of the flat steel products for forming the components according to the invention is 0.005 - 1.0% by mass. Chromium affects the hardenability of the flat steel products because it slows down the rate of diffusion transformation during the press-hardening process. Starting from a content of 0.005% by mass, Cr has a favorable effect on the hardenability in the flat steel products according to the invention, where a Cr content > 0.1% by mass is preferred for reliable process implementation, especially to prevent the formation of bainite. However, if the chromium content of the steel exceeds 1.0% by mass, the coating behavior deteriorates. To obtain the best surface quality, the Cr content can be limited to at most 0.4% by mass.

[0056] Boron (“B”) can be selectively alloyed into the steel of the flat steel product forming a component according to the present invention to improve the hardenability of the flat steel product. Boron atoms or boron precipitates deposited on the austenite grain boundaries reduce the grain boundary energy, whereby the nucleation of ferrite is inhibited during the press hardening process. Starting from a B content of at least 0.0005% by mass, a significant effect on the hardenability is produced. Conversely, when the B content exceeds 0.01% by mass, more and more boron carbides, boron nitrides or boron carbonitrides are formed, which in turn become preferred nucleation sites for ferrite nucleation and reduce the hardening effect. For this reason, according to the present invention, the content of B is limited to at most 0.01% by mass.

[0057] In order to adjust specific properties of the steel or the flat steel product produced therefrom, alloying elements including one, two or more of the group consisting of V, Ti, Nb, Al, Ni, Cu, Mo, W can be selectively added to the steel respectively, wherein the content of the alloying elements selectively present respectively should be determined in the following manner:

[0058] Even a minimum amount of vanadium (“V”) of at least 0.001% by mass can prevent the accumulation of free carbon present in the steel of the flat steel product processed according to the present invention at dislocations. Therefore, the aging resistance of the steel is improved. Starting from a V content of 0.2% by mass, this effect no longer increases. The aging inhibition effect of vanadium is particularly evident at a V content of up to 0.009% by mass, wherein the maximum effect occurs starting from a V content of 0.002% by mass.

[0059] If desired, titanium (“Ti”) can be added to the steel of the flat steel product forming a component according to the present invention in a content of 0.001 - 0.1% by mass to combine the nitrogen present in the steel. To reliably achieve this, a Ti content %Ti of at least 3.42 times the nitrogen content %N (%Ti = 3.42 × %N) can be set.

[0060] Aluminum (“Al”) can selectively be present in the steel of the flat steel product forming a component according to the present invention in a content of 0.01 - 0.2% by mass. Therefore, an Al content of up to 0.1% by mass has proven to be particularly effective. Aluminum is used as a deoxidizer for binding oxygen. In addition, aluminum can also inhibit the formation of cementite. To reliably bind oxygen, at least 0.01% by mass of Al is required in the steel. However, since the Ac3 temperature is also significantly pushed up as the Al alloy content increases, the Al content is limited to 0.2% by mass. At a content exceeding 0.2% by mass, Al severely hinders the transformation to austenite before hot forming, so that austenitization can no longer be carried out effectively in terms of time and energy.

[0061] If desired, niobium (“Nb”) can be added to the steel of the flat steel product forming the component according to the invention in an amount of 0.001 - 0.1% by mass in order to bind free carbon by forming iron carbides, which has a favorable effect on the aging behavior.

[0062] Nickel (“Ni”) stabilizes the austenite phase of the steel of the flat steel product forming the component according to the invention, and thus can be selectively added to the alloy to lower the Ac3 temperature and inhibit the formation of ferrite and bainite. In addition, nickel also has a positive effect on hot rolling properties. However, a content exceeding 0.4% by mass no longer contributes to the positive effect of the presence of nickel. Therefore, the Ni content is preferably limited to less than 0.4% by mass.

[0063] Hardenability can be improved by selectively adding at least 0.1% by mass of Cu. In addition, copper can improve the resistance of uncoated metal sheets or cut edges to atmospheric corrosion. However, the hot rolling property deteriorates due to the presence of copper.

[0064] This effect can be counteracted by adding at least 0.01% by mass of Ni. Starting from a copper content of 0.8% by mass, the hot rolling ability significantly decreases due to the low melting point copper phase on the surface, so a content exceeding 0.8% by mass should be avoided.

[0065] To improve process stability, molybdenum (“Mo”) can be selectively added to the steel of the flat steel product forming the component according to the invention. Mo can significantly slow down the formation of ferrite. Starting from a Mo content of 0.002% by mass, molybdenum carbon clusters and even ultra-fine molybdenum carbides are dynamically formed at the grain boundaries, which significantly slows down the mobility of the grain boundaries, thus significantly slowing down the diffusion phase transformation. In addition, the grain boundary energy is reduced by Mo, thereby reducing the nucleation rate of ferrite. Therefore, the effective utilization of the positive effect of Mo is ensured by limiting the Mo content to a maximum of 1.0% by mass.

[0066] Tungsten (“W”) can be selectively added to the alloy in an amount of 0.001 - 1.0% by mass to slow down the formation of ferrite. When the content of tungsten is at least 0.001% by mass, a positive effect on hardenability has already been produced. Due to cost reasons, at most 1.0% by mass of tungsten is added to the alloy. The remaining components of the steel forming the steel substrate of the flat steel product hot-formed according to the invention and the metal sheet component obtained therefrom by hot forming are iron and inevitable impurities, where the inevitable impurities include P with a content less than 0.1% by mass, S with a content less than 0.05%, and N with a content less than 0.01%. Therefore, the content of these impurities is very small respectively so that they do not have any influence on the properties of the steel and the metal sheet produced therefrom.

[0067] For this purpose, the sum of the contents of the impurities is preferably limited to less than 2% by mass.

[0068] The corrosion protection coating present on the hot-formed flat steel product according to the invention and thus on the metal sheet component according to the invention can consist of pure aluminum or an aluminum alloy. Accordingly, the anti-corrosion coating can consist of aluminum, wherein, in the aluminum alloy layer provided for anti-corrosion protection, in addition to technically unavoidable impurities, 3-15% by mass of Si, 2-3.5% by mass of Fe and / or at least one alkaline earth metal or transition metal can be selectively contained respectively, and the total content of the alkaline earth metal or transition metal is 0.1-0.5%. Therefore, the content of impurities is generally limited to at most 1%.

[0069] The Si content of the corrosion protection layer contributes to the sufficient but not maximum formation of the iron-aluminum alloy layer, thus ensuring good enough adhesion under the same given cold forming. This effect can be achieved particularly reliably at a Si content of at least 7% by mass, especially at least 9% by mass. Here, in the corrosion protection coating provided according to the invention, the effect of Si can be utilized particularly effectively at a Si content of at most 12% by mass, especially at most 10% by mass.

[0070] Iron ("Fe") can be present in the anti-corrosion coating provided according to the invention of the metal sheet component according to the invention at a content of 2-3.5% by mass. The Fe present in the coating at these contents contributes to the formation of an alloy layer between the steel substrate and the coating and supports the adhesion of the coating in this way.

[0071] The corrosion protection layer can contain at least one alkaline earth metal or transition metal at a content of 0.05-2% by mass in order to form a thin, covering oxide layer on the free upper side of the corrosion protection layer. If the sum of the contents of at least one alkaline earth metal and / or at least one transition metal present in the coating of the metal sheet component according to the invention is 0.1-0.5% by mass, especially 0.15-0.4% by mass, the presence of these metals has proven to be particularly advantageous. Among the alkaline earth metals and transition metals that can be considered, it has been found that magnesium and calcium can particularly achieve the purpose, but strontium, barium, zirconium and titanium can also be used.

[0072] In principle, any method that is capable of depositing a sufficiently thin layer on the steel substrate can be used to apply the protective coating provided according to the invention on the respective steel substrates. For this purpose, traditional hot-dip coating ("hot-dip aluminizing") is particularly suitable, which can particularly economically produce corrosion protection on steel sheets.

[0073] According to the foregoing explanation, the method of the invention for producing the metal sheet component according to the invention includes the following working steps:

[0074] a) Provide a hot-rolled flat steel product, which includes a steel substrate. The composition of the steel substrate is as follows by mass%: C: 0.1 - 0.4%, Mn: 0.5 - 3.0%, Si: 0.05 - 0.5%, Cr: 0.005 - 1.0%, B: 0.0005 - 0.01%, and one or more alloying elements in the groups of "V, Ti, Nb, Al, Ni, Cu, Mo, W" respectively. The condition is that the content of the alloying elements selectively present is determined as follows: V: 0.001 - 0.2%, Ti: 0.001 - 0.1%, Nb: 0.001 - 0.1%, Al: 0.01 - 0.2%, Ni: 0.01 - 0.4%, Cu: 0.01 - 0.8%, Mo: 0.002 - 1.0%, W: 0.001 - 1.0%, and the balance is iron and unavoidable impurities. The unavoidable impurities include P with a content less than 0.1%, S with a content less than 0.05%, and N with a content less than 0.01%.

[0075] b) Selectively pickle the hot-rolled strip.

[0076] c) Cold-roll the hot-rolled strip into a cold-rolled strip, where the cold rolling is selectively carried out in more than one rolling pass, and where annealing treatment is also selectively carried out on the cold-rolled strip obtained after each previous cold rolling step between the cold rolling steps.

[0077] d) Coat the cold-rolled strip with an aluminum-based corrosion protection coating.

[0078] e) Skin-pass roll the cold-rolled strip with a corrosion protection layer.

[0079] f) Cut out cut pieces from the skin-pass rolled cold-rolled strip.

[0080] g) Heat the cut piece to a hot forming temperature of 850 - 950 °C.

[0081] h) Hot form the heated cut piece into a component.

[0082] Optionally, the component obtained in step h) can be hardened in addition to hot forming. This hardening can be carried out in a manner known per se simultaneously with the hot forming carried out in step h), or in a heat treatment process downstream of the hot forming. If the hot forming and hardening are completed in one operation, it is also called "press hardening" or "single-stage" hot forming and hardening process. In contrast, the process in which the flat steel product is first hot formed and then hardened in a second step by appropriate heat treatment is called a "two-stage process". Whether it is a combined, single-stage or two-stage hot forming and hardening, the measures required therefor and the process parameters to be adjusted are known to those skilled in the art (for example, see the aforementioned WO2008 / 053273 A1).

[0083] Here, according to the present invention, by cold rolling (working step c)) and / or skin pass rolling (working step e)), the cold-rolled strip has a surface texture at least in a surface section of the free outer side of the corrosion protection layer, which has a maximum wavelength in the range of 0.1 mm to 1.0 mm, wherein this surface section forms an adhesive section in the thermoformed part, and this adhesive section is provided for applying an adhesive to bond the sheet metal part to another part.

[0084] When generally manufacturing sheet metal parts from flat steel products provided with a corrosion protection coating, the following working steps are carried out in sequence: "producing steel and its pre-products cast therefrom, such as slabs, thin slabs or cast strips, in a steel mill", "hot rolling the pre-product into a hot-rolled strip ("hot-rolled strip")", "pickling the hot-rolled strip to remove scale and dirt residues adhering to the strip", "cold rolling the hot-rolled strip into a cold-rolled strip ("cold-rolled strip")", "coating the cold-rolled strip with an aluminum-based corrosion protection coating", "skin pass rolling and / or final treatment of the surface of the cold-rolled strip provided with the corrosion protection coating", "fully heating the cold-rolled strip provided with the corrosion protection coating to the thermoforming temperature" and "thermoforming the cold-rolled strip heated to the thermoforming temperature into a sheet metal part", wherein, of course, further working steps can be carried out between the working steps specifically mentioned here, and these further working steps are carried out in the conventional production and processing of forming the cold-rolled strip into a sheet metal part to ensure a normal working process and an optimized working result.

[0085] Exemplarily, the following can be used as a basis for the parameters set in each of the working steps carried out in detail when producing the cold-rolled strip for forming a sheet metal part according to the present invention.

[0086] a) Providing a hot-rolled flat steel product:

[0087] - Melting a steel melt in a conventional manner, which is composed according to the present invention as explained above for this purpose, and casting the steel melt into a slab in the same conventional manner;

[0088] - Heating the slab in a furnace to a slab pulling-out temperature Bzt of 1200 - 1270 °C at which the slab is pulled out of the furnace;

[0089] - Hot rolling the slab into a hot-rolled strip ("hot-rolled strip") with a thickness of 3 - 5 mm, wherein the hot rolling includes a preliminary rolling with a thickness reduction of 80 - 90% and a final rolling with a thickness reduction of 85 - 95%, wherein the overall formability achieved by hot rolling is 95 - 99.5%, wherein the thickness reduction ΔdF achieved in the last rolling pass is 1 - 25%, and wherein the hot rolling end temperature is 850 - 950 °C;

[0090] - Cool the obtained hot-rolled strip to a coiling temperature of 620 - 780 °C, with a cooling rate of 4 - 30 K / s;

[0091] - Coil the hot-rolled flat steel product into a coil;

[0092] b) Pickle the hot-rolled steel strip to remove the scale;

[0093] c) Perform single-stage or multi-stage cold rolling on the hot-rolled steel strip to form a cold-rolled steel strip ("cold-rolled steel strip"), where the total formability achieved by cold rolling is 70 - 90%.

[0094] Therefore, in the conventional production of cold-rolled and hot-dip coated steel strips, a final surface treatment is carried out after coating, during which the surface structure is optimized for subsequent working steps. However, it has been found that such a final surface treatment has no effect on the surface topography of the sheet metal parts produced by hot forming from cold-rolled strips or cut pieces obtained therefrom.

[0095] On the contrary, the roughness of the cold-rolled strip is at least important for the surface topography of the hot-formed products produced according to the invention in the area of the bonding section of the sheet metal parts. This is especially true when applying a corrosion protection coating to the steel base of the cold-rolled strip by hot dip coating ("hot dip aluminizing"). By applying the aluminum melt, the strip is first leveled by placing the melt on top of the peaks and valleys of the surface structure and covering them. During the reheating process required for hot forming, the cold-rolled and hot-dip coated flat steel product is heated to a temperature above 600 °C, and the coating softens again, thus reproducing the roughness of the cold-rolled strip.

[0096] In order to generate a surface texture according to the invention in the section of the surface of the corrosion protection layer that forms the bonding section in the subsequent part during cold rolling, each corresponding cold-rolled strip can be cold-rolled in the last rolling pass of cold rolling, where the cold rolling degree is 10 - 75%, the strip speed at the inlet of the rolling mill is 10 - 600 m / min, the strip speed at the outlet of the rolling mill is 20 - 1000 m / min, the rolling force is 150 - 1300 kN, and the tensile force is 5 - 110 kN. The rolling roughness Ra is 1.0 - 5.0 μm, and the tip number Rpc is 15 - 50 1 / μm.

[0097] Similarly, in order to contribute to shaping the surface state with an SDR value of 3 - 30% according to the invention in the area of the bonding section of the sheet metal part according to the invention, the cut piece can be held at the hot forming temperature for 2 - 15 minutes in working step g) so as to be subsequently formed into a sheet metal part. Detailed Description

[0098] The present invention will be explained in more detail below with reference to the embodiments.

[0099] In the first experiment, a steel strip as a steel substrate having the composition shown in Table 1 was coated by conventional hot-dip coating with a corrosion protection coating composed of 10% by mass of Si, 3.5% by mass of Fe, up to 1% by mass of inevitable impurities, and the balance of aluminum. The application weight on each side of the steel strip was set to 70 g / m 2 .

[0100] Slabs were punched out from the steel strip and then continuously annealed at an annealing temperature of 925 °C for 5 minutes, and then hot-formed into metal plate components respectively. The SDR value determined according to ISO 25178 in the bonding section on the free surface of the obtained metal plate components was 18%.

[0101] These components were bonded to each other by applying an epoxy adhesive Betamate 1620MB in the area of the bonding section, which was provided by Dow Automotive (see the data sheet "BETAMATE TM 1620MB", published by Dow Europe GmbH, Edition 02, June 29, 2010). When the fracture surface was subsequently inspected, a standard of 95% of the ideal fracture surface SFC could be achieved.

[0102] In an additional test series, four steel melts A-D were produced, and their compositions are listed in Table 2. The compositions of the steel melts A-D corresponded to those of conventional steels, which were provided for the production of flat steel products. From these flat steel products, metal plate components with high strength were produced in the same known manner by hot forming and sufficiently rapid cooling associated therewith, or by subsequent heat treatment including cooling at a sufficient cooling rate.

[0103] Hot-rolled strips were manufactured from steels A-D in a conventional manner, which were pickled in the same conventional manner and then cold-rolled in multiple stages to form cold-rolled strips with a thickness of 1.5 mm respectively.

[0104] Except for the last stage, the cold rolling was also carried out in a conventional manner.

[0105] In contrast, in the last stage of cold rolling, the average values of parameters such as "the speed at the entrance of the cold rolling mill", "the speed at the exit of the cold rolling mill", "the rolling force", and "the tension acting on the cold-rolled strip" were adjusted as shown in Table 3 in order to obtain a defined surface roughness on the obtained cold-rolled strip.

[0106] For the cold-rolled strips K1-K6 obtained in this way, the SDR value of the surface was determined according to ISO 25178.

[0107] Subsequently, Al corrosion protection coatings Z1 - Z3 with different compositions were applied to the cold-rolled strips K1 - K6 in a conventional manner, and their compositions are given in Table 4. The SDR values were also determined on the surfaces of the cold-rolled strips K1 - K6 coated with the respective corrosion protection coatings Z1 - Z3 in accordance with ISO 25178.

[0108] Cutting pieces were separated from the hot-dip galvanized cold-rolled strips K1 - K6, heated to the annealing temperature TG for an annealing duration tG in a continuous furnace, and held there. Table 5 records the correspondence of the corrosion protection coatings Z1 - Z3 with the cold-rolled strips K1 - K6 produced from steels A - D, the application weights AG achieved on each side, the respective annealing times tG, and the respective annealing temperatures TG.

[0109] The cutting pieces heated to the annealing temperature TG were hot-formed into sheet metal components in a hot press tool in a conventional manner. After cooling to room temperature, the SDR values of the finished sheet metal components were determined at least in the bonding sections on the surface that were subsequently to be bonded.

[0110] Then, according to the production regulations, the sheet metal components were bonded to similar components with each other using the adhesive Betamate 1620MB, and the SFC values of the bonding were determined in the manner explained above.

[0111] Table 6 shows the SDR values determined on the cold-rolled strips K1 - K6 after cold rolling (“SDR cold-rolled strips”), after hot-dip galvanizing (“SDR hot-dip”), and on the sheet metal components hot-formed from the respective cold-rolled strips K1 - K6 (“SDR sheet metal components”), as well as the “standardized fracture surface SFC” determined for the bonding.

[0112] These tests confirmed that the SDR values present in the cold-rolled strips equivalently exist in the finished sheet metal components in a technical sense, and the SDR values generated on the sheet metal components in accordance with the method of the present invention result in a fracture surface SFC that represents the best bonding suitability.

[0113] C Si Mn P S Al Cr + Mo Ti B 0.22 0.35 1.35 0.022 0.008 0.010 0.4 0.03 0.004

[0114] Table 1, data are given in mass %, the rest is iron and unavoidable impurities

[0115] Steel C Si Mn P S Al Nb Ti B A 0.08 0.33 0.95 0.025 0.020 0.013 0.09 0.010 0.005 B 0.23 0.38 1.3 0.020 0.007 0.013 - 0.03 0.004 C 0.38 0.37 1.38 0.020 0.008 0.013 - 0.10 0.005 D 0.20 0.35 1.35 0.020 0.008 0.012 - 0.02 0.004

[0116] Table 2, data are given in mass %, the rest is iron and unavoidable impurities

[0117] Steel Inlet velocity Outlet velocity Rolling force Tension A 280 m / min 620 m / min 795 kN 60 kN B 133 m / min 300 m / min 844 kN 67 kN C 304 m / min 670 m / min 755 kN 65 kN D 219 m / min 390 m / min 918 kN 68 kN

[0118] Table 3

[0119] Al coating Mg Si Fe Z1 0.3 9.5 3 Z2 -- 9.5 3.5 Z3 -- 10 3

[0120] Table 4. The data are given in mass %, the balance being iron and inevitable impurities

[0121] Cold-rolled strip Steel Coating <![CDATA[AG[g / m 2 *]]> tG [min] TG [℃] K1 A Z2 69 5 925 K2 B Z1 70 5 925 K3 C Z2 75 5 920 K4 D Z3 65 6 925 K5 B Z1 70 6 900 K6 D Z3 71 6 920

[0122] Table 5

[0123]

[0124] Table 6

Claims

1. A metal sheet component, - which is made of a hot - formed flat steel product, The flat steel product includes a steel substrate, and an Al - based corrosion - protection coating applied on the steel substrate, The composition of the steel substrate in mass % is: C:0.1-0.4％, Mn: 0.5 - 3.0%, Si: 0.05 - 0.5%, Cr:0.005-1.0％， B：0.0005-0.01％， and one or more alloying elements optionally selected from the groups of "V, Ti, Nb, Al, Ni, Cu, Mo, W", provided that the contents of the alloying elements selectively present are determined as follows: V:0.001-0.2％, Ti: 0.001 - 0.1%, Nb: 0.001 - 0.1%, Al:0.01-0.2％, Ni: 0.01 - 0.4%, Cu: 0.01 - 0.8% Mo: 0.002 - 1.0%, W：0.001-1.0％， the balance being iron and unavoidable impurities, where the unavoidable impurities include P with a content less than 0.1%, S with a content less than 0.05%, and N with a content less than 0.01%, wherein the component is selectively hardened, It is characterized in that, There is an adhesive section on the outer side of the corrosion - protection coating, and the adhesive section is used to apply an adhesive to bond the metal sheet component to another component, and the surface of the corrosion - protection coating has an SDR value of 3 - 30% determined according to ISO 25178 at least in the area of the adhesive section.

2. The metal plate component according to claim 1, characterized in that, In the adhesive section, the standard tip value RPc is not greater than 200 / cm.

3. The metal plate component according to claim 1, wherein The average surface roughness Rz in the adhesive section is not greater than 2 μm.

4. The metal plate component according to claim 1, characterized in that, The corrosion - protection coating contains 3 - 15% of Si, 2 - 3.5% of Fe, and / or at least one alkaline earth metal or transition metal in mass %, where the total content of the alkaline earth metal or transition metal is 0.1 - 0.5%.

5. The metal plate component according to claim 4, characterized in that, The corrosion - protection coating contains an alkaline earth metal or transition metal from the group of "Mg, Ca, Sr, Ba, Zr, Ti".

6. A method for producing the metal sheet component according to any one of claims 1 to 5, the method comprising the following working steps: a) Providing a hot - rolled flat steel product, the flat steel product including a steel substrate, the composition of the steel substrate in mass % being: C: 0.1 - 0.4%, Mn: 0.5 - 3.0%, Si: 0.05 - 0.5%, Cr: 0.005 - 1.0%, B: 0.0005 - 0.01%, and one or more alloying elements optionally selected from the groups of "V, Ti, Nb, Al, Ni, Cu, Mo, W", provided that the contents of the alloying elements selectively present are determined as follows: V: 0.001 - 0.2%, Ti: 0.001 - 0.1%, Nb: 0.001 - 0.1%, Al: 0.01 - 0.2%, Ni: 0.01 - 0.4%, Cu: 0.01 - 0.8%, Mo: 0.002 - 1.0%, W: 0.001 - 1.0%, the balance being iron and unavoidable impurities, where the unavoidable impurities include P with a content less than 0.1%, S with a content less than 0.05%, and N with a content less than 0.01%, b) Selectively pickling the hot - rolled strip, c) Cold - rolling the hot - rolled strip into a cold - rolled strip, d) Coating the cold - rolled strip with an Al - based corrosion - protection coating, e) Temper rolling cold-rolled strip with a corrosion protection coating, f) Cutting out cut pieces from the temper-rolled cold-rolled strip, g) Heating the cut piece to a hot forming temperature of 850 - 950 °C, h) Hot forming the heated cut piece into a component, It is characterized in that By cold rolling and / or temper rolling, on the outer side of the corrosion protection coating of the cold-rolled strip, at least one surface section has a surface texture with a maximum wavelength in the range of 0.1 mm to 1.0 mm, wherein the surface section forms an adhesion section in the finished hot-formed component, and the adhesion section is provided for applying an adhesive to bond the metal sheet component to another component.

7. The method according to claim 6, wherein Cold rolling of the cold-rolled strip is carried out in the last rolling pass of cold rolling, wherein the cold rolling degree is 10 - 75%, the strip speed at the inlet of the rolling mill is 10 - 600 m / min, the strip speed at the outlet of the rolling mill is 20 - 1000 m / min, the rolling force is 150 - 1300 kN, and the tensile force is 5 - 110 kN.

8. The method according to claim 6 or 7, characterized in that, The rolling roughness Ra in cold rolling is 1.0 - 5.0 μm, and the peak value Rpc is 15 - 50 / μm.

9. The method according to claim 6, wherein In working step g), the cut piece is held at the hot forming temperature for 2 - 15 min.

10. The method according to claim 9, characterized in that In working step g), the cut piece is held at the hot forming temperature for 3 - 10 min.

11. The method according to claim 6, wherein The component is hardened after or during working step h).

12. The method according to claim 11, wherein The hardening is carried out in a pressure forming hardening manner along with the hot forming.

13. The method according to claim 6, wherein the cold rolling is carried out in more than one rolling pass.

14. The method according to claim 13, wherein annealing treatment is carried out on the cold-rolled strip obtained respectively after the previous cold rolling step between the cold rolling steps.

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