Method for producing a press-hardened steel sheet component having an aluminum-based coating, as well as a raw sheet blank and a press-hardened steel sheet component produced therefrom

Abstract

The invention relates to a method for producing a press-hardened component, comprising the following steps: - providing a steel strip with an aluminum-based coating; - applying an inorganic iron-containing conversion layer on the aluminum-based coating, the layer weight being 3-30 mg / m 2 Cold rolling the steel strip into flexible rolled strip with strip sections of varying sheet thickness; cutting a raw slab from the flexible rolled strip, wherein the raw slab has varying sheet thicknesses with thinnest and thickest sheet sections; and press-forming and hardening the raw slab into a component. Alternatively, cold rolling can be performed before cutting, and the conversion coating applied before or after cutting, or, instead of cold rolling, at least two aluminum-coated steel strip sections with varying sheet thicknesses can be welded together, with the conversion coating applied before or after welding.

Description

Technical Field

[0001] The present invention relates to a method for producing a press-hardened sheet steel component having very good paintability and weldability in all areas of the component, the component being produced from a raw sheet metal blank having different sheet metal thicknesses, wherein the raw sheet metal blank has an aluminum-based hot-dip coating. Furthermore, the present invention relates to a raw sheet metal blank having different sheet metal thicknesses and an aluminum-based coating, and a press-hardened component produced from such a raw sheet metal blank. In the following, the term "different sheet metal thicknesses of the raw sheet metal blank" is understood to mean a sheet metal thickness difference, wherein the sheet metal thickness of the thinner portion of the raw sheet metal blank is only 80% or less of the sheet metal thickness of the sheet metal portion with the greatest sheet metal thickness. Background Art

[0002] Aluminum-based coatings are understood below to mean metallic coatings in which aluminum is the main component by mass percentage. Examples of possible aluminum-based coatings are aluminum, aluminum-silicon (AS), aluminum-zinc-silicon (AZ), and the same coatings with mixtures of additional elements such as magnesium, manganese, titanium, and rare earth elements. For such coatings, a typical layer coating on both sides is approximately 60 g / m 2 About 200g / m 2 .

[0003] It's well known that hot-formed steel sheets are increasingly used, particularly in automotive manufacturing. This process, also known as press hardening, allows the production of high-strength components, primarily for use in the vehicle body area. In principle, press hardening can be performed using two different process variants: a direct method or an indirect method. In the indirect method, the forming and hardening process steps are performed separately, whereas in the direct method, they are performed together in a single tool. However, in the following, only the direct method will be considered.

[0004] In the direct process, a steel sheet slab is heated above the so-called austenitizing temperature (Ac3), the thus heated slab is then transferred to a mold and formed into the finished component in a single forming step, where it is passed through a cooled mold while being cooled at a rate exceeding the critical cooling rate of the steel, thus producing a hardened component.

[0005] Known hot-formable steels for this field of application are, for example, the manganese-boron steel "22MnB5" and, more recently, also the air-temperable steels according to European Patent EP 2 449 138 B1.

[0006] In addition to uncoated steel sheets, steel sheets with press-hardened anti-scaling protection are also used in the automotive industry. Besides increasing the corrosion resistance of the finished component, this also has the advantage that the blanks or components do not scale in the furnace. This reduces wear on the stamping tools due to flaking, and the components do not have to be extensively sandblasted before further processing.

[0007] German patent DE 69933 751 T2 discloses the production of components by hot forming in a forming tool and quenching a preform made of press-hardenable steel coated with an aluminum alloy. Here, the sheet coated with the aluminum alloy is heated to above 700°C before forming, forming intermetallic alloy compounds based on iron, aluminum, and silicon on the surface. The sheet is then formed and cooled at a rate above the critical cooling rate.

[0008] For example, published document DE 10 2015 122 410 A1 discloses methods for producing crash-related body parts. These methods use raw sheet metal blanks with an aluminum-based coating that are individually tailored to the component requirements. For example, formed sheet metal blanks of varying material thickness and / or quality are used. So-called flexible rolled sheets have varying material thicknesses at the same material quality to meet the requirements. For welded sheet metal blanks (TWB = Tailored Welded Blanks), the material quality can also be varied in addition to the material thickness. Components considered for this method include, for example, A-pillars, B-pillars, longitudinal beams, crossbeams, bumpers, side impact beams, wheel arches, and the like within the entire body-in-white of a vehicle in the automotive industry.

[0009] When using aluminum-based coatings, such as aluminum silicon (AS), it has been found problematic that components formed in typical automotive cathodic dip coating (CDC) processes have poor paint suitability if the heating time used during press hardening is too short. If the heating time is too short, the CD-coated substrate may have insufficient paint adhesion.

[0010] Therefore, the aluminum-based coating must be fully alloyed with the iron in the steel substrate during the heating process before press hardening in order to ensure good paint adhesion, for example in the cathodic dip coating process. During the heating process, a diffusion zone consisting of Fe(Al,Si) is formed on the steel substrate, followed by regions with different intermetallic phases. In addition, due to oxidation in the furnace and during transfer to the press, only a very thin aluminum oxide layer forms on the surface. The corresponding layer structure is Figure 1 Shown in.

[0011] However, aluminum-based coatings must not be excessively alloyed, as this can cause problems during joining, particularly during spot welding. The thickness of the so-called diffusion layer between the steel and the coating is often considered a limit to suitability for spot welding. In the Volkswagen Group standard TL4225, this limit is, for example, a maximum of 16 μm.

[0012] For starting slabs with different sheet thicknesses, the aluminum-based coating must be sufficiently alloyed in the areas of greater sheet thickness for good paint adhesion, while the alloying must not be too strong in the thinner areas of the slab to prevent a negative impact on weldability. Typical sheet thicknesses of steel strips used as starting material are between 0.50 and 3.00 mm, preferably between 0.75 and 2.50 mm.

[0013] However, it has been shown that raw slabs with different sheet thicknesses heat to varying degrees during the heating process prior to press hardening. Regions of the raw slab with smaller sheet thicknesses heat significantly faster than regions with larger sheet thicknesses. Consequently, metallographic examinations often reveal only a very thin diffusion layer in component regions with larger sheet thicknesses, while regions with smaller sheet thicknesses exhibit diffusion layer thicknesses approaching the permitted upper limit of 16 μm. This results in press-hardened components with non-uniform properties.

[0014] Aluminum-coated raw slabs with varying sheet thicknesses therefore have a limited process window for heating in a roller hearth furnace, for example, during press hardening. The thicker slab sections determine the minimum heating time in the furnace to ensure adequate paint adhesion, while the thinner slab sections limit the maximum residence time in the furnace to ensure good weldability. The resulting process window is particularly small with large thickness differences, such as a slab with a sheet thickness of 2.0 mm in the thickest area and 1.0 mm in the thinnest area. Summary of the Invention

[0015] The object of the present invention is therefore to provide a method for producing press-hardened sheet steel components from starting blanks with varying sheet thicknesses and an aluminum-based coating, wherein a larger process window is achieved during heating compared to starting blanks with a constant sheet thickness and wherein the press-hardened components exhibit uniform properties with respect to paintability and weldability. Furthermore, the invention is directed to providing a starting blank and a press-hardened component produced therefrom.

[0016] The teaching of the present invention comprises a method for producing a press-hardened component from raw sheet metal blanks having different sheet metal thicknesses, wherein the raw sheet metal blanks have an aluminum-based coating, the method comprising the following steps:

[0017] -Provide steel strips with aluminum-based coatings;

[0018] - an inorganic iron-containing conversion layer is applied to the aluminum-based coating with a layer weight of 3-30 mg / m 2 ;

[0019] - cold rolling the steel strip into flexible rolled strip with strip sections of different sheet thicknesses;

[0020] Cutting a raw slab from the flexible rolled strip, wherein the raw slab has different sheet thicknesses with thinnest and thickest sheet sections;

[0021] -The raw slab is pressed and hardened into a component.

[0022] The teaching also includes a method for producing a press-hardened component from raw sheet metal blanks having different sheet metal thicknesses, wherein the raw sheet metal blanks have an aluminum-based coating, the method comprising the following steps:

[0023] -Provide steel strips with aluminum-based coatings;

[0024] - cold rolling the steel strip into flexible rolled strip with strip sections of different sheet thicknesses;

[0025] Cutting a raw slab from the flexible rolled strip, wherein the raw slab has different sheet thicknesses with thinnest and thickest sheet sections;

[0026] Before or after cutting the raw slab, at least in the region of the thickest sheet section, an inorganic iron-containing conversion layer is applied locally or over the entire surface to the aluminum-based coating, with a layer weight of 3-30 mg / m² in terms of iron. 2 ;

[0027] -The raw slab is pressed and hardened into a component.

[0028] Another alternative teaching of the present invention comprises a method for producing a press-hardened component from raw sheet metal blanks having different sheet metal thicknesses, wherein the raw sheet metal blanks have an aluminum-based coating, the method comprising the following steps:

[0029] - providing at least two steel strip sections with an aluminum-based coating, the steel strip sections having different sheet thicknesses;

[0030] - welding the steel strip segments together to form a raw slab, wherein the raw slab has different sheet thicknesses with thinnest and thickest sheet segments;

[0031] Before or after welding together, at least in the region of the thickest sheet metal sections, an inorganic iron-containing conversion layer is applied locally or over the entire surface to the aluminum-based coating, with a layer weight of 3-30 mg / m² in terms of iron.2 ;

[0032] -The raw slab is pressed and hardened into a component.

[0033] In the method according to the invention, during the heating during the press hardening process, a relatively large process window is very advantageously achieved compared to the uniform thickness of the original sheet metal blank, and similarly relatively uniform properties with regard to paintability and weldability are achieved on the press-hardened component.

[0034] In principle, it is also possible to apply the aluminum-based coating after flexible rolling, instead of starting the method according to the invention with a steel strip already provided with an aluminum-based coating.

[0035] For economic reasons and to sufficiently reduce the weight of the press-hardened component, the sheet thickness of the thinnest sheet section of the original slab should be at most 80% of the thickness of the thickest sheet section of the original slab, preferably 70% or less.

[0036] The core of the invention thus consists in applying an inorganic, iron-containing conversion layer which is applied as a precoat to the aluminum-based coating of the raw slab or the steel strip therefor and which increases the heating rate when heating the raw slab.

[0037] In order to achieve the largest possible process window during heating, the heating rate in the thickest sheet section of the starting slab should be significantly increased compared to the thinnest sheet section. This can be achieved using various method variants, which are briefly described below.

[0038] In principle, however, even increasing the heating rate by the same percentage in the thickest and thinnest slab sections results in an adjustment in the resulting necessary heating time. For example, if the average heating rate in both regions is increased by 50% (from 4 to 6 K / s in the thinnest region and from 2 to 3 K / s in the thickest region), the difference in heating time between the thickest and thinnest slab sections, for example, from 20°C to 800°C, is reduced from 195 seconds to 130 seconds. Thus, slabs with different sheet thicknesses already experience an adjustment in the heating rate if the precoat layer is applied over the entire surface with a constant coating weight.

[0039] Therefore, according to the invention, the teaching of the present invention also includes a raw sheet for producing a press-formed hardened steel component with an aluminum-based coating, wherein the raw sheet has different sheet thicknesses, characterized in that the inorganic iron-containing conversion layer has an average thickness of 3-30 mg / m 2 , advantageously 5-25 mg / m 2 , particularly advantageously 7-20 mg / m 2 The iron-based layer is reconstructed on the aluminum-based coating.

[0040] According to the present invention, the starting slab can be produced from flexible rolled steel strip or from welded sheet metal sections (TWB, Tailor Welded Blanks). When the sheet metal sections are welded together, it is advantageous to provide for these sections to have different strengths as needed to account for the different stresses in operation. For economic reasons, the difference in material strength should be greater than 50 MPa. Suitable steel grades for the starting slab include all hardenable steel grades, in particular manganese-boron steels, such as 22MnB5.

[0041] For slabs formed by joining together two or more original slabs (TWB) with different slab thicknesses, only the slab section with the largest slab thickness can be provided partially or completely with an inorganic iron-containing conversion layer as a pre-coating so that the heating rates in the different slab sections are close to each other.

[0042] In an advantageous embodiment of the present invention, it is also conceivable to apply an inorganic, iron-containing conversion layer to slabs having more than two sheet thicknesses by adapting the iron layer to the respective sheet thickness by uniformly heating the resulting slab. In the case of joined slabs formed from various sheet thicknesses, the inorganic, iron-containing conversion layer can be applied as a precoat to the aluminum-based coating of the steel strip at the steelmaker. Ultimately, however, precoating individual slabs or slab regions with an inorganic, iron-containing conversion layer is also an embodiment of the present invention.

[0043] For slabs with varying sheet thicknesses due to the cold rolling step, the inorganic iron-containing conversion layer can be applied as a precoat over the entire surface before or after the cold rolling step, but it can also be applied partially after the cold rolling process, only in the areas with the greatest sheet thickness. Partial application after the rolling step, applied only to the thicker slab areas, is most effective, allowing for full adjustment of the heating rate. Application before the rolling step also allows for significant adjustment of the heating rate, as the flexible rolling step significantly reduces the effectiveness of the precoat in the thinner rolled slab sections.

[0044] The pre-coating according to the invention comprises applying an iron compound preferably in a wet chemical process. This comprises at least applying a solution of an iron compound which reacts with the aluminum-based metal coating advantageously in a reaction without external current.

[0045] The treatment is preferably carried out in the presence of compounds of other metals, for example from the group of cobalt, molybdenum and tungsten. For example, molybdates, tungstates or cobalt nitrates significantly accelerate the deposition of iron, but they themselves only deposit very small amounts, thus making the method according to the invention even more effective.

[0046] Advantageously, the removal of the naturally occurring oxide layer on the aluminum-based hot-dip coating and the deposition of the iron compound can be carried out simultaneously in a single wet-chemical step using an alkaline medium. This deposition process can be carried out in a continuously operating system at strip speeds of up to 120 m / min or more. The amount of active ingredient required can be less than 100 mg / min. 2 .

[0047] During the study period, it was found that from about 3mg / m 2 , advantageously about 5mg / m 2 , particularly advantageously with respect to 7 mg / m 2 The maximum layer weight of iron should not exceed 30 mg / m 2 Furthermore, the increase in heating rate is only marginal and the spot welding properties begin to deteriorate after press hardening, so that for economic and technical reasons a higher layer weight does not make sense. Advantageously, a maximum of 25 mg / m² for iron applies. 2 , particularly advantageously with respect to iron up to 20 mg / m 2 , to keep the cost of active ingredients as low as possible.

[0048] The layer weight is determined using ICP-OES (Optical Emission Spectroscopy with Inductively Coupled Plasma). To this end, the conversion layer formed on the surface is chemically stripped off and then analyzed and referenced to commercially available elemental standards.

[0049] The treatment of the coated steel strip surface according to the invention can advantageously be carried out in a treatment section downstream of a continuously operating hot-dip coating system or in a separate process section of a separate system, for example, using a spray boom with nozzles or in an immersion process. The separate system can be, for example, a strip coating system. The alkaline cleaning and subsequent rinsing prior to the treatment according to the invention advantageously remove the (native) oxide layer formed by atmospheric oxidation on the aluminum-based coating, thereby creating the desired starting conditions for the deposition of iron and / or its compounds according to the invention.

[0050] The amount of iron deposited on the surface can be influenced by the starting solution concentration and its temperature, the treatment time, the spray pressure, the shear forces of the sprayed solution relative to the surface of the metal strip to be treated and the volume in contact with the surface.

[0051] The teaching of the present invention also includes a press-hardened component made of a raw sheet metal blank with an aluminum-based coating, which has different sheet thicknesses, with thinnest and thickest sheet metal sections, characterized in that a diffusion zone is formed between the steel substrate and the aluminum-based coating, which zone consists of metal of the coating and the steel substrate, wherein the diffusion zone in the areas of different sheet thicknesses, based on the raw sheet metal blank, has a maximum thickness difference that satisfies the following relationship:

[0052] Dl max ≤8*((D1-D2) / D1),

[0053] in,

[0054] D1: the thickest plate section of the original slab;

[0055] D2: the thinnest plate section of the original slab;

[0056] Dl max : Maximum thickness difference of the diffusion layer thickness on the hardened component.

[0057] In an advantageous embodiment of the invention, the maximum thickness difference D1 max The following relationship is satisfied:

[0058] Dl max ≤6*((D1-D2) / D1).

[0059] In a particularly advantageous embodiment of the present invention, the maximum thickness difference D1 max The following relationship is satisfied:

[0060] Dl max ≤4*((D1-D2) / D1).

[0061] These relationships are Figure 2 The three straight lines represent the above relationship D1. max ≤8*((D1-D2) / D1), D1 max ≤6*((D1-D2) / D1) and D1 max ≤4*((D1-D2) / D1). The area above the solid line represents D1 max The region of ≤8*((D1-D2) / D1) illustrates the region that has been achievable so far with the prior art. The region below the solid straight line constitutes the region according to the present invention.

[0062] According to the invention, the thickness of the diffusion zone between the steel and the aluminum-based coating should advantageously be between 2 and 14 μm, particularly advantageously between 4 and 12 μm, in a range of different sheet thicknesses in order to ensure a sufficiently high, but not excessive, degree of alloying.

[0063] To explain these relationships, the results of laboratory tests are described below.

[0064] Made of hardenable steel 22MnB5 with a sheet thickness of 1.5 mm and a nominal layer weight of 150 g / m2 on both sides 2 The sheet strips made of aluminum-silicon coating were rolled in half 50% in a laboratory cold rolling mill and cut into 200×600 mm 2 Sample size where the thickness transition is in the middle ( Figure 3 ).

[0065] Thermocouples were placed at the edge of the sample and the heating rate was recorded in two sample areas in a furnace preheated to 920° C. The thickness of the diffusion layer was then determined metallographically in several areas of the sample.

[0066] This procedure was also carried out on samples treated with an iron-containing coating before or after the cold rolling step. The tested variants V1 to V4 were as follows: V1 - rolled (reference); V2 - pre-coated, followed by rolling; V3 - rolled, followed by pre-coated; V4 - rolled, followed by partial pre-coating. These different variants V1 to V4 were Figure 4 are schematically outlined (not to scale).

[0067] exist Figures 5a to 5d The resulting heating curves for variants V2 to V4 are shown, each compared to a reference measurement for variant V1. The temperature difference between the thick and thin sections of the sample is also plotted as a function of the heating time. It is clear how the iron-containing precoat modifies the heating rate, particularly by significantly increasing the heating rate in the thick section of the sample. This significantly increases the process window for heating during press hardening.

[0068] Table 1 summarizes the resulting diffusion layer thicknesses, which were determined metallographically on several polished sections of the corresponding sample areas (thick / thin) and averaged. The breakdown in Table 1 is for the sake of clarity. The diffusion layer thicknesses were determined according to the current version of the Volkswagen factory standard TL 4225.

[0069]

[0070]

[0071] Table 1

[0072] These results were combined with additional studies that examined the influence of the iron-containing coating on the heating rate and diffusion layer thickness for various sheet thicknesses, heating times, and heating temperatures. Here, too, an almost linear increase in the diffusion layer thickness with heating time was observed. As a result of these studies, the previously proposed formula-based relationship between the maximum thickness difference of the diffusion layer and the sheet thickness difference of the original slab was empirically determined.

[0073] As mentioned above, the approximation of the heating rate results in small differences in the diffusion layer thickness and thus in uniform properties of the component with respect to paintability and spot weldability. Particularly advantageous is a diffusion layer thickness of between 2 and 14 μm, particularly advantageously between 4 and 12 μm, with respect to the alloying degree of the entire component.

[0074] When components are produced by press hardening, the iron-containing precoating on the slab does not remain. Rather, during the heating process, for example in a roller hearth furnace, by precoating the raw slab with an inorganic, iron-containing conversion layer according to the invention, an aluminum-rich oxide layer doped with iron cations is formed. The iron cations inhibit the otherwise common self-limitation of aluminum oxide layer growth and lead to the formation of significantly thicker aluminum oxide layers during the heat treatment, achieving aluminum oxide layer thicknesses of more than 50 nm.

[0075] On the contrary, if Figure 1 As mentioned above, the thickness of the conventional aluminum oxide layer on press-hardened components with an aluminum-based coating without an iron-containing precoating is significantly reduced. Therefore, the component according to the invention has an aluminum oxide layer thickened by more than 50 nm, at least in the areas with high sheet thickness of the original slab, which is produced by the iron-containing precoating in combination with heating before press hardening.

[0076] An exemplary advantageous method sequence is described below:

[0077] - hot rolling, pickling and optionally cold rolling of suitable steel strip;

[0078] - Annealing the steel strip in a hot-dip coating plant at a temperature between 500 and 950° C. in a reducing atmosphere, followed by hot-dip coating in an aluminum-based melt and providing the steel strip with an aluminum-based coating having a density between 60 and 200 g / m² on both sides. 2 The layers between are heavy;

[0079] - The aluminum-based coating is then covered with an inorganic iron-containing conversion layer having an iron content of 3-30 mg / m 2 The layer weight;

[0080] - flexibly rolling the steel strip with the aluminum-based coating so that the thin regions of the resulting steel strip have a thickness of 70% or less of the thickness of the thick regions of the steel strip;

[0081] - manufacturing slabs from flexible rolled strip, whereby thick and thin sheet sections are located within each cut slab;

[0082] - The component is produced by heating a slab to a temperature between 750 and 1000° C. in a roller hearth furnace to form an austenitic structure in at least part of the slab and subsequently forming it into a component in a tool while rapidly cooling it, thereby producing a martensitic hard structure in at least part of the component.

Claims

1. A method for producing a press-hardened component, the method comprising the following steps: -Provide steel strips with aluminum-based coatings; - an inorganic iron-containing conversion layer is applied to the aluminum-based coating with a layer weight of 3-30 mg / m 2 ; - cold rolling the steel strip into flexible rolled strip with strip sections of different sheet thicknesses; - cutting a raw slab from the flexible rolled strip, wherein the raw slab has different sheet thicknesses with thinnest and thickest sheet sections; - The raw slab is pressed and hardened into a component.

2. A method for producing a press-hardened component, wherein: The method has the following steps: -Provide steel strips with aluminum-based coatings; - cold rolling the steel strip into flexible rolled strip with strip sections of different sheet thicknesses; Cutting a raw slab from the flexible rolled strip, wherein the raw slab has different sheet thicknesses with thinnest and thickest sheet sections; Before or after cutting the raw slab, at least in the region of the thickest sheet section, an inorganic iron-containing conversion layer is applied locally or over the entire surface to the aluminum-based coating, wherein the layer weight with respect to iron is 3-30 mg / m 2 ; - The raw slab is pressed and hardened into a component.

3. A method for producing a press-hardened component, wherein: The method has the following steps: - providing at least two steel strip sections with an aluminum-based coating, the steel strip sections having different sheet thicknesses; - welding the steel strip segments together to form a raw slab, wherein the raw slab has different sheet thicknesses with thinnest and thickest sheet segments; Before or after welding together, at least in the region of the thickest sheet metal sections, an inorganic iron-containing conversion layer is applied locally or over the entire surface to the aluminum-based coating, with the layer weight being 3-30 mg / m² in terms of iron. 2 ; -The raw slab is pressed and hardened into a component.

4. The method according to any one of claims 1 to 3, characterized in that The inorganic iron-containing conversion layer has an iron content of 5-25 mg / m2 on the aluminum-based coating. 2 The layer weight.

5. The method according to any one of claims 1 to 3, characterized in that The inorganic iron-containing conversion layer has an iron content of 7-20 mg / m2 on the aluminum-based coating. 2 The layer weight.

6. The method according to any one of claims 1 to 5, characterized in that The inorganic iron-containing conversion layer is formed on the aluminum-based metal coating by applying a solution of an iron compound in a reaction with the aluminum-based metal coating without the flow of external current.

7. The method according to any one of claims 1 to 5, characterized in that The thickness of the thinnest sheet section of the original slab is at most 80% of the thickness of the thickest sheet section of the original slab.

8. The method according to any one of claims 1 to 5, characterized in that The thickness of the thinnest plate section of the original slab is 70% or less of the thickness of the thickest plate section of the original slab.

9. A raw sheet blank for producing a press-formed hardened steel component having an aluminum-based coating, wherein: The original slab has different plate thicknesses, characterized in that the inorganic iron-containing conversion layer is 3-30 mg / m 2 The iron-based layer is constructed on an aluminum-based coating.

10. The original slab according to claim 9, characterized in that The inorganic iron-containing conversion layer contains 5-25 mg / m 2 The iron-based layer is constructed on the aluminum-based coating.

11. The original slab according to claim 9, characterized in that The inorganic iron-containing conversion layer contains 7-20 mg / m 2 The iron-based layer is constructed on the aluminum-based coating.

12. The raw slab according to claim 9, which is made of flexible rolled steel strip.

13. The raw slab of claim 9, which is made from steel strip segments welded together.

14. The original slab according to claim 13, characterized in that The belt sections welded together have different strengths, with the difference in their tensile strength being greater than 50 MPa.

15. The raw slab according to at least one of claims 9 to 14, characterized in that Use hardenable manganese-boron steel.

16. The raw slab according to any one of claims 9 to 14, characterized in that On the original slab, at least in the region of the thickest plate section, the inorganic iron-containing conversion layer has a concentration of 3-30 mg / m2 with respect to iron. 2 The layer weight is coated on the aluminum base coating.

17. A press-hardened component made from a raw sheet metal blank with an aluminum-based coating, having different sheet thicknesses, including thinnest and thickest sheet sections, characterized in that A diffusion zone is formed between the steel substrate and the aluminum-based coating, which zone consists of the metal of the steel substrate and the coating, wherein the diffusion zone in the regions of different sheet thicknesses has a maximum thickness difference with respect to the original sheet that satisfies the following relationship: <h2 style=";text-align:left;direction:ltr">Dl<h2 style=";text-align:left;direction:ltr"> max <h2 style=";text-align:left;direction:ltr"> ≤8*((D1-D2) / D1), in, D1: the thickest plate section of the original slab; D2: the thinnest plate section of the original slab; Dl max : Maximum thickness difference of the diffusion layer thickness on the hardened component.

18. The press-hardened component according to claim 17, wherein The maximum thickness difference of the diffusion layer on the hardened component is D1 max ≤6*((D1-D2) / D1).

19. The press-hardened component according to claim 18, wherein The maximum thickness difference of the diffusion layer on the hardened component is D1 max ≤4*((D1-D2) / D1).

20. The press-hardened component according to at least one of claims 17 to 19, characterized in that The thickness of the diffusion zone between the steel and the aluminum-based coating is advantageously between 2 and 14 μm within a range of different sheet thicknesses.

21. The press-hardened component according to claim 20, wherein The thickness of the diffusion zone between the steel and the aluminum-based coating is advantageously between 4 and 12 μm within a range of different sheet thicknesses.

22. Press-hardened component according to at least one of claims 17 to 19, characterized in that In the region of the thickest sheet metal section of the starting sheet metal blank, the component has an aluminum oxide layer with a thickness of at least 50 nm on the component surface.

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