Sheet metal molded part with improved processing properties

Abstract

The invention relates to a method for producing a molded sheet metal part having at least one first region and one second region having different material properties, and to such a molded sheet metal part.

Description

Technical Field

[0001] The invention relates to a sheet metal shaped part having improved processing properties and to a method for producing the sheet metal shaped part from a flat steel product. Background Art

[0002] When "flat steel products" or "sheet metal products" are mentioned below, these are meant to be rolled products, such as steel strips or steel sheets, which are cut into "sheet metal blanks" (also called blanks) for the production of, for example, vehicle body parts. "Sheet metal shapes" or "sheet metal components" of the type according to the invention are produced from these sheet metal blanks, the terms "sheet metal shapes", "sheet metal components" and "components" being used synonymously.

[0003] Unless expressly stated otherwise, the contents of the steel components stated in the present application are based on weight. All % data relating to steel alloys which are not further specified are therefore to be regarded as "% by weight". With the exception of the data on the content of retained austenite in the microstructure of the sheet metal forming parts according to the invention which are based on volume (expressed in "% by volume"), the data relating to the contents of the components of the different microstructures are based on the area of ​​the corresponding product sample grinding slice (expressed as area percentage "area %"), unless expressly stated otherwise. The data on the content of the atmosphere components given in the text are based on volume (expressed in "% by volume").

[0004] Unless explicitly stated otherwise, the mechanical properties reported here, such as tensile strength, yield point, elongation, were determined by tensile tests in accordance with DIN EN ISO 6892-1 (sample form 2, Appendix B Table B1, June 2020 edition). The bending angle at maximum force was determined in accordance with VDA standard 238-100. The HV5 Vickers hardness was determined in accordance with DIN EN ISO 6507 (July 2018). In this application, in the case of a clear yield point, the yield point means the yield point Re. In the case of a continuous yield point, the yield point means the value of the yield point Rp0.2.

[0005] The microstructure was determined on longitudinal sections etched with 3% Nital (alcoholic nitric acid). The proportion of retained austenite was determined by X-ray diffraction.

[0006] WO2019 / 223854A1 discloses a sheet metal part and a method for producing such a sheet metal part, wherein the tensile strength of the sheet metal part is at least 1000 MPa. The sheet metal part is made of a steel, and its composition, in addition to iron and unavoidable impurities, is (in weight %) 0.10-0.30% C, 0.5-2.0% Si, 0.5-2.4% Mn, 0.01-0.2% Al, 0.005-1.5% Cr, 0.01-0.1% P and possible other selective elements, in particular 0.005-0.1% Nb. In addition, the sheet metal part includes an anti-corrosion coating containing aluminum.

[0007] WO 2006 / 128821 and WO 2007 / 122230 A1 disclose methods for producing sheet metal profiles with improved processing properties. These methods involve the use of a profile tool with different temperature zones. Summary of the invention

[0008] Against the background of this prior art, the object of the present invention is to further improve sheet metal shaped parts so that in combination with an aluminum-based anti-corrosion coating improved processing properties are achieved. In addition, a method is to be specified with which such sheet metal shaped parts can be produced in a practical manner.

[0009] The invention achieves this object by a method for producing a sheet metal formed part having at least one first region and a second region with different material properties, the method comprising the following steps:

[0010] a. A sheet metal cut piece made of a flat steel product is provided, which comprises a steel substrate made of steel, the composition of the steel except iron and unavoidable impurities is as follows (in weight %):

[0011] C: 0.27-0.5%

[0012] Si: 0.05-0.6%

[0013] Mn: 0.4-3.0%

[0014] Al: 0.10-1.0%

[0015] Nb: 0.001-0.2%

[0016] Ti: 0.001-0.10%

[0017] B: 0.0005-0.01%

[0018] P: ≤0.03%

[0019] S: ≤0.02%

[0020] N: ≤0.02%

[0021] Sn: ≤0.03%

[0022] As: ≤0.01%

[0023] and optionally one or more elements from the group consisting of “Cr, Cu, Mo, Ni, V, Ca, W” in the following contents

[0024] Cr: 0.01-1.0%,

[0025] Cu: 0.01-0.2%,

[0026] Mo: 0.002-0.3%.

[0027] Ni: 0.01-0.5%.

[0028] V: 0.001-0.3%,

[0029] Ca: 0.0005-0.005%,

[0030] W: 0.001-1.0%;

[0031] b. Heating the sheet metal blank so that at least part of the sheet metal blank exceeds the AC3 temperature and when inserting the forming tool set for hot press forming (process step c)), the temperature T of the sheet metal blank 插入 At least part of it is above Ms+100°C, where Ms is the martensite start temperature;

[0032] c. inserting the heated sheet metal blank into a forming tool, wherein the forming tool has a temperature control device for regulating the temperature of at least one section thereof which is in contact with the sheet metal blank during hot forming, and wherein the transfer time t required for removing the blank from the heating device and inserting the blank is 转移 Maximum 20s, preferably maximum 15s;

[0033] d. hot press forming the sheet metal cut piece into a sheet metal formed piece, wherein during the hot press forming process the cut piece is cooled to a first target temperature in a first zone and to a second target temperature in a second zone and selectively maintained therein;

[0034] e. Remove the cooled sheet metal form from the tool.

[0035] Compared to known flat steel products, the steel substrate of the flat steel product used according to the invention has an aluminum content of at least 0.10% by weight, particularly preferably at least 0.11% by weight, in particular at least 0.12% by weight, and more preferably at least 0.16% by weight. The aluminum content is a maximum of 1.0% by weight, in particular a maximum of 0.8% by weight.

[0036] In a first improved variant, the aluminum content is at least 0.10% by weight, particularly preferably at least 0.11% by weight, in particular at least 0.12% by weight, more preferably at least 0.16% by weight. The maximum aluminum content in this variant is a maximum of 0.50% by weight, in particular a maximum of 0.35% by weight, more preferably a maximum of 0.25% by weight, in particular a maximum of 0.24% by weight.

[0037] In a second improved variant, the aluminum content is at least 0.50% by weight, preferably at least 0.60% by weight, more preferably at least 0.70% by weight. The maximum aluminum content in this variant is a maximum of 1.0% by weight, in particular a maximum of 0.9% by weight, more preferably a maximum of 0.80% by weight.

[0038] It is well known that aluminum ("Al") is added as a deoxidizer during steel production. In order to reliably bind oxygen in the steel melt, at least 0.01% by weight of aluminum is required. In addition, aluminum can also be used to bind undesirable nitrogen contents that are unavoidable due to production. So far, higher aluminum contents have been avoided because the Ac3 temperature also rises with increasing aluminum content. This has a negative impact on austenitization, which is very important for hot forming. However, it has been found that an increase in the aluminum content unexpectedly brings about positive effects in combination with an aluminum-based anti-corrosion coating.

[0039] During the coating of the flat steel product with an aluminum-based anticorrosion coating and the subsequent hot forming of the sheet metal cut pieces cut therefrom into sheet metal formed parts, iron diffuses from the steel substrate into the liquid anticorrosion coating. In the interdiffusion zone, an iron-aluminum compound with a relatively high density is formed by a multi-step phase transformation (Fe2Al5→Fe2Al→FeAl→Fe3Al). The formation of this higher density phase consumes more aluminum than the low density phase. The local high aluminum consumption leads to the formation of pores (vacancies) in the generated phase. These pores preferably appear in the transition zone between the steel substrate and the anticorrosion coating, where the proportion of available aluminum is mainly affected by the aluminum content of the steel substrate. In particular, a pore band may be gathered in the transition zone.

[0040] Such porosity, especially porosity zones, can lead to a number of problems:

[0041] - The pores reduce the mechanical integrity of the area. This can lead to faster layer detachment under corrosion stress.

[0042] Furthermore, after bonding or welding two components, the forces transmitted at the joint are reduced.

[0043] - Porosity changes the flow paths in the material during resistance spot welding, negatively affecting weld suitability and thereby reducing weld extent.

[0044] -Even the pores themselves promote crack formation and propagation during static and dynamic bending.

[0045] Surprisingly, it has been found that by increasing the aluminum content ("Al") in the steel substrate to the above lower limit, the formation of pores during the application of the aluminum-based anti-corrosion coating and the subsequent hot forming process can be significantly reduced. In particular, in the transition area between the steel substrate and the anti-corrosion coating, the local high aluminum consumption caused by the formation of high-density iron-aluminum compounds can be at least partially compensated by the aluminum content in the steel substrate, thereby suppressing the formation of pores, especially pore zones.

[0046] If the aluminum content is too high, in particular above 1.0 wt. % aluminum, there is a risk of aluminum oxides forming on the surface of the steel material of the alloy composition according to the invention in the resulting product, which can reduce the wetting properties during the hot-dip coating operation. In addition, higher aluminum contents promote the formation of non-metallic aluminum-based inclusions, which can have a negative impact on the impact properties. Therefore, the aluminum content is preferably selected below the above upper limit.

[0047] The bending properties of the sheet steel component are particularly supported by a niobium content ("Nb") of at least 0.001 wt. %. The niobium content is preferably at least 0.005 wt. %, in particular at least 0.010 wt. %, more preferably at least 0.015 wt. %, particularly preferably at least 0.020 wt. %, in particular at least 0.024 wt. %, more preferably at least 0.025 wt. %.

[0048] In the following method for producing a flat steel product with an anticorrosive coating for hot forming, the specified niobium content contributes particularly to the distribution of niobium carbonitrides, which form a particularly fine hardened microstructure in the subsequent hot forming operation. During the cooling process after the hot-dip coating, the coated flat steel product is kept for a certain time in a temperature range of 400° C. to 300° C. In this temperature range, the carbon in the steel substrate still has a certain diffusion rate, while the thermodynamic solubility is very low. Carbon therefore diffuses into and accumulates at lattice defects. Lattice defects are caused in particular by dissolved niobium atoms, which, due to their significantly larger atomic volume, have a crystal lattice, thereby increasing the size of the tetrahedral and octahedral interstices in the atomic lattice and increasing the local carbon solubility. As a result, agglomerates of carbon and niobium are formed in the steel substrate, which are transformed into very fine precipitates in the subsequent hot forming austenitizing step and serve as additional austenite nuclei. This results in a refined austenite microstructure with relatively small austenite grains and, therefore, also a refined hardened microstructure.

[0049] This particularly concerns the ferrite intermediate diffusion layer formed during the hot forming process. This refined ferrite microstructure in the intermediate diffusion layer helps to reduce the crack tendency under bending loads.

[0050] However, too high a Nb content leads to poor recrystallization ability. Therefore, the Nb content is at most 0.2 wt %. It is further preferred that the Nb content is at most 0.20 wt %, especially at most 0.15 wt %, particularly preferably at most 0.10 wt %, especially at most 0.05 wt %.

[0051] Both aluminum and niobium have an effect on the grain refinement of austenitization during hot forming. It has been found that Al and Nb in particular are able to refine the grain growth in austenite at relatively high temperatures (e.g. above 1200°C) by forming AlN relatively early, i.e. at higher temperatures. The formation of AlN is thermodynamically superior to the formation of NbN or NbC. The precipitation of AlN has a grain refining effect in austenite, thereby improving toughness. Increasing the Al / Nb ratio can enhance this effect. Therefore, the ratio of Al content to Nb content Al / Nb can be selected as follows:

[0052] 1≤Al / Nb,

[0053] The Al / Nb ratio is preferably ≥2, in particular ≥3. At the same time, a too high Al / Nb ratio leads to the formation of AlN which is no longer fine, but rather to the formation of increasingly coarse AlN particles, which in turn weakens the grain refinement effect. It has been found that this effect occurs earlier at low manganese contents than at high manganese contents, since the Ac3 temperature decreases with increasing manganese content. Therefore, at a low manganese content of up to 1.6 wt. %, it is advantageous to selectively set the Al / Nb ratio to:

[0054] A1 / Nb≤20.0,

[0055] This corresponds approximately to an atomic ratio of the two elements of ≤ 6. Preferably, when Mn is ≤ 1.6 wt. %, the Al / Nb ratio is ≤ 18.0, in particular ≤ 16.0, preferably ≤ 14.0, particularly preferably ≤ 12.0, in particular ≤ 10.0, preferably ≤ 9.0, in particular ≤ 8.0, more preferably ≤ 7.0.

[0056] Conversely, in the case of a higher manganese content of Mn ≥ 1.7 wt. %, a higher ratio may also be used. Thus, when the higher manganese content is 1.7 wt. % or more, the Al / Nb ratio may be selectively set as follows:

[0057] Al / Nb≤30.0,

[0058] Preferably, when Mn ≥ 1.7 wt. %, the Al / Nb ratio is ≤ 28.0, in particular ≤ 26.0, preferably ≤ 24.0, particularly preferably ≤ 22.0, preferably ≤ 20.0, in particular ≤ 18.0, in particular ≤ 16.0, preferably ≤ 14.0, more preferably ≤ 12.0, in particular ≤ 10.0, preferably ≤ 9.0, in particular ≤ 8.0, more preferably ≤ 7.0.

[0059] Regardless of the manganese content, the Al / Nb ratio is preferably set selectively to:

[0060] Al / Nb≤20.0,

[0061] The Al / Nb ratio is preferably ≤18.0, in particular ≤16.0, preferably ≤14.0, particularly preferably ≤12.0, in particular ≤10.0, preferably ≤9.0, in particular ≤8.0, more preferably ≤7.0.

[0062] Carbon ("C") is present in the steel substrate of the flat steel product in an amount of 0.27 to 0.5% by weight. Setting this level of carbon content helps to improve the hardenability of the steel because it delays the formation of ferrite and bainite and stabilizes retained austenite in the microstructure.

[0063] However, high carbon contents may have a negative effect on weldability. To improve weldability, the carbon content can be adjusted to 0.50 wt. %, preferably a maximum of 0.45 wt. %, particularly preferably 0.40 wt. %, preferably a maximum of 0.38 wt. %, in particular a maximum of 0.35 wt. %.

[0064] In order to particularly reliably utilize the positive influence of the presence of carbon, a carbon content of at least 0.30% by weight, preferably at least 0.32% by weight, in particular at least 0.33% by weight, in particular at least 0.34% by weight, preferably at least 0.35% by weight can be set. Taking into account the further provisions of the invention, these contents reliably achieve a tensile strength of at least 1700 MPa, in particular at least 1800 MPa, of the sheet metal formed part after hot pressing.

[0065] Silicon ("Si") serves to further increase the hardenability of flat steel products and the strength of press-hardened products by solid solution strengthening. Silicon also makes it possible to use iron, silicon and manganese as alloying agents, which has a favorable effect on production costs. From a Si content of 0.05% by weight, a hardening effect already occurs. With a Si content of at least 0.15% by weight, in particular at least 0.20% by weight, the strength is significantly increased. Si contents exceeding 0.6% by weight have an adverse effect on the coating properties, in particular in the case of aluminum-based coatings. To improve the surface quality of the coated flat steel products, the Si content is a maximum of 0.50% by weight, in particular a maximum of 0.30% by weight.

[0066] Manganese ("Mn") acts as a hardening element because it significantly delays the formation of ferrite and bainite. When the manganese content is less than 0.4% by weight, even at a rapid cooling rate, a significant proportion of ferrite and bainite will be formed during the die hardening process, which should be avoided as much as possible. When it is necessary to ensure a martensitic structure, especially in the higher forming area, the Mn content is at least 0.5% by weight, in particular at least 0.8% by weight, preferably at least 0.9% by weight, and particularly preferably at least 1.10% by weight. A manganese content exceeding 3.0% by weight has an adverse effect on the processing properties, so the manganese content of the flat steel product of the present invention is limited to a maximum of 3.0% by weight, preferably a maximum of 2.5% by weight. In particular, a higher manganese content can severely limit weldability, so it is preferred to limit the Mn content to a maximum of 1.6% by weight, in particular a maximum of 1.30% by weight, and in particular a maximum of 1.20% by weight. For economic reasons, it is also preferred that the manganese content is less than or equal to 1.6% by weight.

[0067] Titanium ("Ti") is a microalloying element which is added to the alloy to promote grain refinement, wherein at least 0.001% by weight of Ti, in particular at least 0.004% by weight, preferably at least 0.010% by weight of Ti should be added to ensure sufficient availability. Starting from a titanium content of more than 0.10% by weight, the cold rolling properties and recrystallization properties deteriorate significantly, so higher titanium contents should be avoided. To improve the cold rolling properties, the titanium content is preferably limited to a maximum of 0.08% by weight, in particular a maximum of 0.038% by weight, particularly preferably a maximum of 0.020% by weight, and in particular a maximum of 0.015% by weight. In addition, titanium has the effect of binding with nitrogen, thereby allowing boron to exert its strong effect of inhibiting the formation of ferrite. Therefore, in a preferred extension, the titanium content should exceed 3.42 times the nitrogen content to achieve sufficient nitrogen bonding.

[0068] Boron ("B") is added to the alloy to increase the hardenability of the flat steel product by reducing the grain boundary energy through boron atoms or boron precipitates that accumulate at the austenite grain boundaries, thereby inhibiting the nucleation of ferrite during press hardening. Boron has a significant effect on hardenability up to a content of at least 0.0005% by weight, preferably at least 0.0007% by weight, in particular at least 0.0010% by weight, and in particular at least 0.0020% by weight. However, when the content exceeds 0.01% by weight, the formation of boron carbides, boron nitrides or boron nitride carbides increases, which can become preferential nucleation sites for ferrite nucleation and again reduce the hardening effect. Therefore, the boron content should be limited to a maximum of 0.01% by weight, preferably a maximum of 0.0100% by weight, more preferably a maximum of 0.0050% by weight, in particular a maximum of 0.0035% by weight, in particular a maximum of 0.0030% by weight, and in particular a maximum of 0.0025% by weight.

[0069] Phosphorus ("P") and sulfur ("S") are impurity elements introduced into steel by iron ore and cannot be completely removed in the steelmaking process on an industrial scale. Since an increase in the P content and the S content has a negative effect on mechanical properties, such as notch impact energy, the P content and the S content should be kept as low as possible. In addition, when the P content exceeds 0.03% by weight, martensite begins to become embrittled, so the P content of the flat steel product of the present invention is limited to a maximum of 0.03% by weight, in particular a maximum of 0.02% by weight. The S content of the flat steel product of the present invention is limited to a maximum of 0.02% by weight, preferably a maximum of 0.0010% by weight, and in particular a maximum of 0.005% by weight.

[0070] Nitrogen ("N") is also present in small amounts in steel as an impurity due to the steel manufacturing process. The nitrogen content should be kept as low as possible, at a maximum of 0.02% by weight. In particular, in boron-containing alloys, nitrogen has a detrimental effect, since the formation of boron nitrides hinders the conversion inhibition of boron, so in this case, the nitrogen content is preferably at a maximum of 0.010% by weight, in particular at a maximum of 0.007% by weight.

[0071] Further typical impurities include tin ("Sn") and arsenic ("As"). The tin content is a maximum of 0.03% by weight, preferably a maximum of 0.02% by weight. The arsenic content is a maximum of 0.01% by weight, in particular a maximum of 0.005% by weight.

[0072] In addition to the impurities mentioned above (phosphorus, sulfur, nitrogen, tin and arsenic), other elements may also be present in the steel as impurities. These other elements are classified as "inevitable impurities". The total content of these "inevitable impurities" is preferably a maximum of 0.2% by weight, preferably a maximum of 0.1% by weight. The selective alloying elements Cr, Cu, Mo, Ni, V, Ca and W, for which lower limits are given below, may also be present in the steel substrate as inevitable impurities in a content below the respective lower limit. In this case, they are also counted as "inevitable impurities" and their total content is limited to a maximum of 0.2% by weight, preferably a maximum of 0.1% by weight.

[0073] Chromium, copper, molybdenum, nickel, vanadium, calcium and tungsten can be added selectively as alloying components to the steel of the flat steel product according to the invention, either individually or in combination.

[0074] Chromium ("Cr") inhibits the formation of ferrite and pearlite during the accelerated cooling of the flat steel product of the present invention and enables complete martensite formation even at relatively low cooling rates, thereby increasing hardenability.

[0075] These effects are manifested starting from a content of 0.01 wt. %, wherein a chromium content of at least 0.10 wt. %, preferably at least 0.15 wt. %, has been found to be useful for practical processing reliability. However, chromium contents that are too high can impair the coatability of the steel. Therefore, the chromium content in the steel of the steel substrate is limited to a maximum of 1.0 wt. %, preferably a maximum of 0.80 wt. %, in particular a maximum of 0.75 wt. %, preferably a maximum of 0.50 wt. %.

[0076] Vanadium ("V") can be optionally added to the alloy in an amount of 0.001-1.0 wt. %. The vanadium content is preferably a maximum of 0.3 wt. %. For cost considerations, the alloying amount of vanadium in the alloy should be a maximum of 0.2 wt. %.

[0077] Copper ("Cu") can be added to the alloy optionally, at least 0.01% by weight, preferably at least 0.010% by weight, and in particular at least 0.015% by weight, in order to increase the hardenability. In addition, copper can also improve the atmospheric corrosion resistance of the uncoated steel sheet or the cut edge. If the copper content is too high, the hot rolling properties will be significantly reduced due to the formation of low-melting copper phases on the surface, so the copper content is limited to a maximum of 0.2% by weight, preferably a maximum of 0.1% by weight, and in particular a maximum of 0.10% by weight.

[0078] Molybdenum ("Mo") can be added to the alloy selectively to increase process stability, since it significantly slows down the formation of ferrite. Starting from a molybdenum content of 0.002% by weight, molybdenum-carbon clusters are dynamically formed at the grain boundaries, up to the formation of ultrafine molybdenum carbides, which significantly slow down the migration of the grain boundaries and thus the diffusion phase transformation process. In addition, molybdenum also reduces the grain boundary energy and thus the nucleation rate of ferrite. The molybdenum content is preferably at least 0.004% by weight, in particular at least 0.01% by weight. Due to the high alloying costs of molybdenum, its content should be a maximum of 0.3% by weight, in particular a maximum of 0.10% by weight, preferably a maximum of 0.08% by weight.

[0079] Nickel ("Ni") stabilizes the austenite phase and can be added selectively to the alloy to reduce the Ac3 temperature and inhibit the formation of ferrite and bainite. Nickel also has a positive effect on the hot rolling properties, especially if copper is present in the steel. Copper deteriorates the hot rolling properties. In order to counteract the negative effect of copper on the hot rolling properties, at least 0.01% by weight of nickel can be added to the steel; the nickel content is preferably at least 0.020% by weight. For economic reasons, the nickel content should be limited to a maximum of 0.5% by weight, in particular a maximum of 0.20% by weight. The nickel content is preferably a maximum of 0.10% by weight.

[0080] Calcium ("Ca") is used in steel to improve the shape of non-metallic inclusions, in particular manganese sulfides. Rounded inclusions significantly reduce the negative influence of inclusions on hot formability, long-term strength and toughness. In order to also utilize this effect in the flat steel product according to the invention, the flat steel product according to the invention can optionally contain at least 0.0005% by weight of calcium, in particular at least 0.0010% by weight, preferably at least 0.0020% by weight. The maximum Ca content is 0.01% by weight, in particular at most 0.007% by weight, preferably at most 0.005% by weight. If the calcium content is too high, the probability of the formation of non-metallic inclusions involving calcium in the inclusions increases, which can reduce the purity of the steel and affect the toughness of the steel. Therefore, the upper limit of the calcium content should be a maximum of 0.005% by weight, preferably a maximum of 0.003% by weight, in particular a maximum of 0.002% by weight, preferably a maximum of 0.001% by weight.

[0081] Tungsten ("W") can be added to the alloy optionally in an amount of 0.001-1.0 wt. % to slow down the formation of ferrite. A tungsten content of at least 0.001 wt. % already has a positive effect on hardenability. For cost reasons, a maximum of 1.0 wt. % tungsten is added to the alloy.

[0082] In a preferred embodiment, the sum of the manganese content and the chromium content ("Mn+Cr") is greater than 0.7% by weight, in particular greater than 0.8% by weight, preferably greater than 1.1% by weight. If the sum of these two elements falls below the minimum requirement, their necessary transformation-inhibiting effect is lost. In any case, the sum of the manganese content and the chromium content should be less than 3.5% by weight, preferably less than 2.5% by weight, in particular less than 2.0% by weight, particularly preferably less than 1.5% by weight. The upper limits for these two elements are set in order to ensure coating properties and adequate welding properties.

[0083] The above statements regarding the element contents and their preferred limit values ​​also apply to the method for producing the sheet metal formed parts described below and to the sheet metal formed parts themselves.

[0084] The next stage in the method according to the invention is to heat the provided sheet metal blank (step a)) in a known manner so that the entire blank exceeds the Ac1 temperature of the blank and preferably at least partially exceeds the Ac3 temperature of the blank, and when the blank is inserted into a forming tool provided for the hot press forming operation (step c)), the insertion temperature T 插入At least partially exceeds Ms+100°C, in particular exceeds Ms+300°C. The term "partially exceeds a certain temperature (such as Ac3 or Ms+100°C)" here refers to at least 30%, in particular at least 60% of the volume of the cut piece, preferably at least 90% of the volume exceeding the corresponding temperature in the sense of this application. In all cases where a certain temperature is mentioned as being partially exceeded, it is preferred that the entire cut piece exceeds the corresponding temperature. When inserted into the forming tool, at least 30% of the cut piece has an austenitic microstructure, which means that the transformation from ferrite to austenite does not have to be completely completed when inserted into the forming tool. On the contrary, when inserted into the forming tool, up to 70% of the volume of the cut piece can be composed of other microstructure components, such as annealed bainite, annealed martensite and / or unrecrystallized or partially recrystallized ferrite. For this purpose, certain areas of the cut piece can be purposefully kept at a lower temperature than other areas during the heating process. To achieve this, heat can be supplied only to certain sections of the blank in a targeted manner, or sections requiring less heating can be isolated from heat supply. In the section of the blank material which is maintained at a lower temperature, no or only little martensite is formed during the forming process in the tool, so that the microstructure in this area is significantly softer than in other areas where a martensitic microstructure would form. In this way, in the formed sheet metal part, a softer area can be purposefully created which has the toughness best suited to the specific application purpose, while other areas of the sheet metal part have maximized strength.

[0085] By at least partially bringing the sheet metal blank to a temperature between Ac3 and 1000° C., preferably between 850° C. and 950° C., the formed sheet metal part can achieve maximum strength properties.

[0086] The minimum temperature Ac3 to be exceeded is determined by the formula given by HOUGARDY, HP in "WerkstoffkundeStahl Band 1: Grundlagen" (Material Science Steel Volume 1: Basics) (Stahleisen GmbH Publishing House, Düsseldorf, 1984, page 229), which is as follows:

[0087] Ac3=(902-225*%C+19*%Si-11*%Mn-5*%Cr+13*%Mo-20*%Ni+55*%V)℃

[0088] Among them, %C=carbon content of the steel, %Si=silicon content of the steel, %Mn=manganese content of the steel, %Cr=chromium content of the steel, %Mo=molybdenum content of the steel, %Ni=nickel content of the steel, %V=vanadium content of the steel, and the cut piece is made of this steel.

[0089] An optimally uniform distribution of the properties can be achieved by completely heating the blank in step b).

[0090] In a preferred embodiment, the average heating rate r of the sheet metal blank during heating in step b) is 炉 The average heating rate r is at least 3 K / s, preferably at least 5 K / s, in particular at least 6 K / s, preferably at least 8 K / s, in particular at least 10 K / s. 炉 It refers to the average heating rate from 30°C to 700°C.

[0091] In a preferred embodiment, the normalized average heating rate θ 标准 At least 5 Kmm / s, in particular at least 8 Kmm / s, preferably at least 10 Kmm / s. The normalized average heating rate is a maximum of 15 Kmm / s, in particular a maximum of 14 Kmm / s, preferably a maximum of 13 Kmm / s.

[0092] The average heating rate here refers to the product of the temperature rise rate from 30°C to 700°C (in K / s) and the plate thickness (in mm).

[0093] For normalized average heating, the product θ is calculated according to the furnace temperature T using the following formula: 炉 With the reference furnace temperature T of 900℃=1173.15K 炉，参考 To correct the relationship:

[0094] Θ 标准 =(T 4 炉，参考 / T 4 炉 )*Θ

[0095] The furnace temperatures are in Kelvin.

[0096] In a preferred embodiment, heating is carried out at a furnace temperature T 炉 The reaction is carried out in a furnace at a temperature of at least Ac3+10K, preferably at least 850°C, preferably at least 880°C, particularly preferably at least 900°C, especially at least 920°C, and at a maximum of 1000°C, preferably at a maximum of 950°C, particularly preferably at a maximum of 930°C.

[0097] The dew point temperature of the furnace atmosphere in the furnace is preferably at least -25°C, in particular at least -20°C, preferably at least -15°C, especially at least -5°C, particularly preferably at least 0°C, maximum +25°C, preferably maximum +20°C, in particular maximum +15°C.

[0098] In a specific embodiment variant, the heating in step b) is carried out in stages, using different temperature zones. In particular, the heating is carried out in a roller hearth furnace with different heating zones. In this case, the heating is first carried out in the first heating zone, the temperature of the first heating zone (referred to as the furnace inlet temperature) is at least 650° C., preferably at least 680° C., in particular at least 720° C. The maximum temperature of the first heating zone is preferably 900° C., in particular a maximum of 850° C. Further preferably, the maximum temperature of all heating zones in the furnace is a maximum of 1200° C., in particular a maximum of 1000° C., preferably a maximum of 950° C., particularly preferably a maximum of 930° C.

[0099] In both variants (constant furnace temperature, staged heating), the total time in the furnace t 炉 , consisting of a heating time and a holding time, preferably at least 2 minutes, especially at least 3 minutes, preferably at least 4 minutes. In addition, the total time in the furnace in both variants is preferably a maximum of 20 minutes, especially a maximum of 15 minutes, preferably a maximum of 12 minutes, and especially a maximum of 8 minutes. The longer total time in the furnace has the advantage of ensuring uniform austenitization of the sheet metal cut pieces. On the other hand, keeping too long above Ac3 will lead to grain coarsening, which is not conducive to mechanical properties. In the implementation variant of the sheet metal forming part with an aluminum-based anti-corrosion coating, keeping the part above Ac3 for too long will lead to excessive growth in the thickness of the alloy layer (also often referred to as the interdiffusion zone). This will have an adverse effect on the welding performance of the anti-corrosion coating.

[0100] The heated cut pieces are taken out of the corresponding heating device, which can be, for example, a conventional heating furnace, a known induction heating device, or a conventional device for heat preservation of steel parts, and are conveyed to the forming tool at a sufficient speed so that the temperature when it reaches the forming tool at least partially exceeds Ms+100°C, especially exceeds Ms+300°C, preferably exceeds 600°C, especially exceeds 650°C, and particularly preferably exceeds 700°C. Here, Ms represents the martensite starting temperature. In a particularly preferred variant, the temperature at least partially exceeds the Ac1 temperature. In all these variants, the temperature is in particular a maximum of 900°C. These temperature ranges ensure good material formability as a whole.

[0101] In step c), the austenitized blank is transferred from the heating device used to the forming tool preferably within a maximum of 20 seconds, in particular within a maximum of 15 seconds. Such a rapid transfer is intended to avoid excessive cooling before forming.

[0102] The forming tool has a temperature control device for controlling the temperature of at least the part thereof in contact with the sheet metal blank during hot press forming. Different areas of the forming tool can be adjusted to different temperatures in this way.

[0103] In the subsequent step d), the sheet metal cutout is hot-pressed into a sheet metal molded part, during which the cutout is cooled to and optionally maintained at a first target temperature in the first zone and a second target temperature in the second zone. Cooling to different target temperatures enables the formation of different tissue structures in different zones. In this way, different material properties of the first and second zones are ensured. For example, the two zones may differ in tensile strength, hardness and / or ductility.

[0104] The first zone can be, for example, a higher strength component area for a weld point or a flange. Such a second zone usually has a width of at least 100 cm 2 area, especially 100 to 5000 cm 2 .

[0105] The second zone can be, for example, a component region with relatively high ductility. Such a first zone usually has a maximum of 5000 cm 2 An area of ​​1 to 5000 cm 2 .

[0106] In this tool, not only is the blank formed into a sheet metal part, but different regions are also hardened simultaneously to correspondingly different target temperatures. The cooling rate r in the first zone to the first target temperature is 工具，1 In particular, it is at least 20 K / s, preferably at least 30 K / s, in particular at least 50 K / s, and in some embodiments at least 100 K / s. The cooling rate r in the second zone to the second target temperature is 工具，2 In particular, it is at least 10 K / s, preferably at least 15 K / s. The average cooling rate in the first zone is Preferably higher than the average cooling rate in the second zone The average cooling rate is related to the temperature T from the insertion 插入 to a temperature range corresponding to the first or second target temperature.

[0107] After the sheet metal shaped part has been removed in step e), the sheet metal part is cooled for a cooling time t of 0.5 to 600 seconds. 冷却 Internal cooling to a cooling temperature T below 100°C 冷却 . This is usually achieved by air cooling.

[0108] In a preferred embodiment of the method, the section that comes into contact with the sheet metal blank during the hot press forming process comprises at least a first section and a second section. The first section comes into contact with the first zone during the hot press forming process, and the second section comes into contact with the second zone during the hot press forming process. In addition, the first section is temperature-controlled to a first tool temperature and the second section is temperature-controlled to a second tool temperature, wherein the first tool temperature is preferably lower than the second tool temperature. The different sections with different tool temperatures ensure that the individual zones of the sheet metal blank that come into contact with different sections cool to different target temperatures during the hot press forming process.

[0109] The tool temperature in the section of the tool in contact with the sheet metal blank refers to the surface temperature of the section before the sheet metal blank is inserted. The temperature should be averaged over the section. The temperature can be measured, for example, by a thermal imaging camera. The temperature is then averaged over the section using image analysis.

[0110] In a preferred variant, the first tool temperature is at most 200° C. The first tool temperature is preferably between room temperature (RT) and 200° C., in particular between 20° C. and 180° C., in particular between 50° C. and 150° C. These lower first tool temperatures ensure that a correspondingly lower first target temperature can be reliably achieved.

[0111] The second tool temperature is preferably at least 200° C., in particular at least 300° C., in particular at least 400° C., preferably at least 450° C., in particular at least 500° C. Furthermore, the second tool temperature is preferably at most 600° C., in particular at most 550° C. The second tool temperature can be set in a process-reliable manner to the desired second target temperature.

[0112] The first target temperature is in particular below 400° C., preferably below 300° C., in particular below 250° C., preferably below 200° C., more preferably below 180° C., in particular below 150° C. Alternatively, the first target temperature is particularly preferably below Ms-50° C., where Ms denotes the martensite start temperature. Furthermore, the target temperature of the sheet metal formed part is preferably at least 20° C., particularly preferably at least 50° C. This lower first target temperature ensures the formation of an adequate hardened microstructure.

[0113] The second target temperature is preferably at least 200° C., preferably at least 300° C., in particular at least 400° C., preferably at least 450° C., in particular at least 500° C. In addition, the second target temperature is preferably at most 650° C., in particular at most 600° C., in particular at most 550° C. This ensures that a corresponding softened structure is formed. In particular, the second target temperature is greater than the first target temperature in order to establish different structures of the two zones.

[0114] During the hot forming process, the sheet metal blank can only cool to the temperature of the tool against which it rests. The first target temperature therefore corresponds at least to the first tool temperature. The second target temperature also corresponds at least to the second tool temperature. By removing the sheet metal blank from the tool at the right time (i.e. adjusting the dwell time t in the tool), the temperature of the blank can be controlled. 工具 ), in principle, the target temperature can be adjusted by how much higher than the corresponding tool temperature. For example, at a tool temperature of 50°C, the sheet metal form can be taken out after cooling to 350°C. To this end, the sheet metal form only needs to be taken out at the right time. However, since the current cooling rate decreases as the temperature of the sheet metal form approaches the tool temperature, the target temperature can be achieved more stably when the difference between the target temperature and the tool temperature is not large. In the case of a large difference, the current cooling rate is relatively high, so that the process is more sensitive to changes in the residence time in the tool. Therefore, the first target temperature is preferably higher than the first tool temperature by a maximum of 250K, preferably a maximum of 200K, in particular a maximum of 150K, preferably a maximum of 100K, in particular a maximum of 80K. Similarly, the second target temperature is preferably higher than the second tool temperature by a maximum of 100K, in particular a maximum of 70K, preferably a maximum of 50K, in particular a maximum of 30K. It is particularly preferred that both criteria are met at the same time.

[0115] Dwell time in the tool t 工具 Preferably at least 2s, especially at least 3s, particularly preferably at least 5s. The dwell time in the tool is preferably a maximum of 25s, especially a maximum of 20s, especially a maximum of 15s, preferably a maximum of 10s. In this way, efficient production on an industrial scale can be achieved.

[0116] In the context of this application, the calculation formula for the transition temperature is as follows:

[0117] The martensite start temperature of steel within the framework of the present specification is calculated as follows:

[0118] Ms[℃]=(490.85wt%-302.6%C-30.6%Mn-16.6%Ni-8.9%Cr+2.4%Mo--11.3%Cu+8.58%Co+7.4%W--14.5%Si)[℃ / wt%]

[0119] Wherein C% represents the C content of the corresponding steel, %Mn represents the Mn content of the corresponding steel, %Mo represents the Mo content of the corresponding steel, %Cr represents the Cr content of the corresponding steel, %Ni represents the Ni content of the corresponding steel, %Cu represents the Cu content of the corresponding steel, %Co represents the Co content of the corresponding steel, %W represents the W content of the corresponding steel, and %Si represents the Si content of the corresponding steel, all of which are measured in weight %.

[0120] The calculation formulas for Ac1 temperature and Ac3 temperature within the specified range of the steel of the present invention are as follows:

[0121] Ac1[℃]=(739wt%--22*%C-7*%Mn+2*%Si+14*%Cr+13*%Mo-13*%Ni+20*%V)[℃ / wt%]

[0122] Ac3[℃]=(902wt%-225*%C+19*%Si-11*%Mn-5*%Cr+13*%Mo-20*%Ni+55*%V)[℃ / wt%]

[0123] Wherein %C represents the C content of the corresponding steel, %Si represents the Si content of the corresponding steel, %Mn represents the Mn content of the corresponding steel, %Cr represents the Cr content of the corresponding steel, %Mo represents the Mo content of the corresponding steel, %Ni represents the Ni content of the corresponding steel, and %V represents the V content of the corresponding steel (Brandis H 1975TEW-Techn. Ber. 18-10).

[0124] In a preferred variant of the method, the cooling behavior of the sheet metal blank is set in step d) at least partially by the surface pressure of the forming tool. In particular, in the low-temperature region of the forming tool, i.e., in the first section with the first tool temperature, a change in the surface pressure can lead to significantly different cooling rates, so that the microstructure of the sheet metal blank, in particular in the first zone, can be adjusted by the surface pressure. In this case, the forming tool preferably has a device for varying the surface pressure.

[0125] In another preferred variant of the method, the forming rate in the hot press forming operation in step d) is controlled taking into account the duration of contact of the temperature-adjusted section of the forming tool with the sheet metal blank during the hot press forming. For example, the forming rate can be controlled so that the first zone comes into contact with the first section of the forming tool as quickly as possible. This allows the first zone to cool as quickly as possible, since the first section has been temperature-adjusted to a lower first tool temperature. This in turn leads to a higher strength in the first zone, since a higher martensite content is formed in this first zone. On the contrary, the forming rate will be slowed down, for example, when it is necessary to cool a specific area of ​​the sheet metal part particularly slowly in order to form a softer microstructure there. Therefore, the forming rate is preferably controlled so that the first section comes into contact with the first zone before the first zone cools to a temperature below Ms+300°C. Subsequently, the forming rate is slowed down. This preferably allows the second section to come into contact with the second zone only after the second zone has cooled to a temperature below Ms+300°C. This further contributes to the slow cooling of the second zone, which is further ensured by the higher second tool temperature.

[0126] In a specific variant, the method is further developed so that the sheet metal blank has regions of different thicknesses. The sheet metal blank described below is also further developed so that it has regions of different thicknesses.

[0127] Sheet metal cutouts with varying thicknesses (called tailored blanks) can be created in a number of ways:

[0128] - Through special cold rolling passes, in which certain areas are rolled more intensively or frequently, so that the material thickness in these areas is reduced, thus forming a thinner thickness (called "tailored rolled blanks").

[0129] - Joining together sheet metal blanks of different thicknesses by welding them together (usually with the aid of laser welding) to form a coherent sheet metal blank with areas of different thicknesses (so-called "custom welded blank").

[0130] - Welding patches (so-called "patches") to existing sheet metal cutouts by resistance spot welding or laser welding to increase the thickness in certain areas. Patches can also be applied by means of structural adhesives.

[0131] The advantage of areas of different thickness is that specific areas of the final sheet metal part (see below) can be reinforced in a targeted manner. In this way, particularly stressed areas (e.g. in a crash) can be given a correspondingly stable structure, while other areas can be made thinner to reduce the weight of the component. The end result is a weight-optimized component with targeted reinforcement in highly stressed areas.

[0132] The forming tool can be any tool of a configuration suitable for the sheet metal part to be produced, which is capable of applying the required forming and pressing forces to the correspondingly deformed sheet metal blank. For this purpose, forming tools having a die and a punch that can be inserted into the die for forming are particularly suitable.

[0133] The temperature control device can be implemented in particular in the form of a cooling device. In this case, the temperature control device is preferably arranged at or in the forming tool adjacent to the first section.

[0134] In addition, the temperature control device can be implemented in the form of a heating device in particular. In this case, the temperature control device is preferably arranged at or in the molding tool adjacent to the second section. In particular, the heating device can be one or more heating elements inserted into the molding tool hole.

[0135] In a particularly preferred embodiment variant, the temperature control device includes channels introduced into the molding tool, through which the medium flows. The advantage of this variant is that heat can be introduced into the tool by the flow of a heating medium in the channels, or heat can be taken away by the flow of a cooling medium. Depending on the required temperature, the medium can be, for example, water, ice water, oil, a low-temperature salt solution, liquid nitrogen or other fluids. Therefore, both the temperature control device as a cooling device and the temperature control device as a heating device can adopt the design of a channel introduced into the molding tool and through which the medium flows. The temperature control device as a heating device can also be alternatively or additionally configured with electric heating elements, which can be arranged on the surface or inside the molding tool. The advantage of electric heating elements is that faster temperature changes can be achieved.

[0136] In a particularly preferred embodiment variant, the section that contacts the sheet metal blank during the hot press forming process comprises at least one first section and one second section. The first section contacts the first zone during the hot press forming process, and the second section contacts the second zone during the hot press forming process. In addition, the first section is set to a first tool temperature by a temperature control device configured as a cooling device, and the second section is set to a second tool temperature by a temperature control device configured as a heating device. Thus, the forming tool comprises a cooling device for cooling the first section to the first tool temperature and a heating device for heating the second section to the second tool temperature.

[0137] The flat steel product preferably comprises an anti-corrosion coating to protect the steel substrate from oxidation and corrosion during the hot forming process and during use of the final steel component.

[0138] In a specific embodiment, the flat steel product preferably includes an aluminum-based anti-corrosion coating. The anti-corrosion coating can be applied on one or both sides of the flat steel product. The two sides of the flat steel product refer to the two opposite large sides of the flat steel product. The narrow side is called the edge.

[0139] Such an anti-corrosion coating is preferably applied to the flat steel product by a hot-dip coating method. This involves passing the flat steel product through a liquid bath containing up to 15% by weight of Si, preferably more than 1.0%, optionally 2-4% by weight of Fe, optionally up to 5% by weight of alkali metals or alkaline earth metals, preferably up to 1.0% by weight of alkali metals or alkaline earth metals, optionally up to 15% by weight of Zn, preferably up to 10% by weight of Zn, and optionally other components in a total amount of up to 2.0% by weight, the remainder being aluminum.

[0140] In a preferred variant, the Si content in the molten bath is 1.0-3.5% by weight or 7-12% by weight, in particular 8-10% by weight.

[0141] In a preferred variant, the selective content of alkali metals or alkaline earth metals in the molten bath comprises 0.1-1.0 wt.-% Mg, in particular 0.1-0.7 wt.-% Mg, preferably 0.1-0.5 wt.-% Mg. Furthermore, the selective content of alkali metals or alkaline earth metals in the molten bath may in particular comprise at least 0.0015 wt.-% Ca, in particular at least 0.01 wt.-% Ca.

[0142] During the hot-dip coating process, iron diffuses from the steel substrate into the liquid coating, resulting in the corrosion protection coating of the flat steel product forming, during solidification, in particular an alloy layer and an Al-based layer.

[0143] The alloy layer is located on the steel substrate and directly adjacent to the steel substrate. The alloy layer is mainly composed of aluminum and iron. Other elements in the steel substrate or the molten pool composition will not be significantly enriched in the alloy layer. The alloy layer is preferably composed of 35-60% by weight of Fe, especially α-iron, and the total content of other optional components is limited to a maximum of 5.0% by weight, preferably 2.0%, and the rest is aluminum, and the Al content preferably increases toward the surface. Optional other components include in particular other components in the molten pool (i.e. silicon, and possible alkali metals or alkaline earth metals, especially Mg or Ca) and other components in the steel substrate except iron.

[0144] The Al-based layer is located above the alloy layer and directly adjoins the alloy layer. The composition of the Al-based layer preferably corresponds to the composition of the melt in the molten pool. This means that it consists of 0.1-15 wt. % Si, optionally 2-4 wt. % Fe, optionally up to 5 wt. % alkali metal or alkaline earth metal, preferably up to 1.0 wt. % alkali metal or alkaline earth metal, optionally up to 15 wt. % Zn, preferably up to 10 wt. % Zn, and other optional components, the total content of which is limited to a maximum of 2.0 wt. %, and the remainder is aluminum.

[0145] In a preferred variant of the Al-based layer, the selective content of alkali metals or alkaline earth metals includes 0.1-1.0 wt.-% Mg, in particular 0.1-0.7 wt.-% Mg, preferably 0.1-0.5 wt.-% Mg. In addition, the selective content of alkali metals or alkaline earth metals in the Al-based layer includes in particular at least 0.0015 wt.-% Ca, in particular at least 0.1 wt.-% Ca.

[0146] In a further preferred variant of the corrosion protection coating, the Si content in the alloy layer is lower than the Si content in the Al-based layer.

[0147] The anti-corrosion coating preferably has a thickness of 5-60 μm, in particular 10-40 μm. In the case of a double-sided anti-corrosion coating, the coating weight of the anti-corrosion coating is in particular 30-360 g / m 2 , 15-180g / m2 for single-sided coating 2The coating weight of the anti-corrosion coating is preferably 100-200 g / m2 for double-sided coating. 2 Or single-sided coating 50-100g / m 2 The coating weight of the anti-corrosion coating is more preferably 120-180 g / m2 for double-sided coating. 2 Or single-sided coating 60-90g / m 2 .

[0148] The thickness of the alloy layer is preferably less than 20 μm, particularly preferably less than 16 μm, especially less than 12 μm, more preferably less than 10 μm, preferably less than 8 μm, especially less than 5 μm. The thickness of the Al-based layer is derived from the difference in thickness between the anticorrosion coating and the alloy layer. Even in the case of a thin anticorrosion coating, the thickness of the Al-based layer is preferably at least 1 μm.

[0149] In a preferred variant, the flat steel product comprises an oxide layer located on the corrosion protection coating. The oxide layer is located in particular on an Al-based layer and preferably forms the outermost layer of the corrosion protection coating.

[0150] The oxide layer consists in particular of more than 80% by weight of oxides, wherein the majority of the oxides (i.e. more than 50% by weight of oxides) are aluminum oxides. In addition to aluminum oxide, the oxide layer optionally comprises hydroxides and / or magnesium oxides, either alone or as a mixture. The part of the oxide layer that does not contain oxides and selective hydroxides preferably consists of metal forms of silicon, aluminum, iron and / or magnesium. For an optional embodiment of an Al-based layer containing zinc as a component, the oxide layer also contains a zinc oxide component.

[0151] The oxide layer of the flat steel product preferably has a thickness of more than 50 nm. In particular, the oxide layer has a thickness of at most 500 nm.

[0152] In another alternative embodiment, the flat steel product comprises a zinc-based anti-corrosion coating. The anti-corrosion coating can be applied to one or both sides of the flat steel product. The two sides of the flat steel product are the two oppositely disposed large sides of the flat steel product. The narrow sides are referred to as edges.

[0153] Such a zinc-based anticorrosion coating preferably contains 0.2-6.0 wt. % Al, 0.1-10.0 wt. % Mg, optionally 0.1-40 wt. % manganese or copper, optionally 0.1-10.0 wt. % cerium, optionally up to 0.2 wt. % other elements, unavoidable impurities, and the remainder zinc. In particular, the Al content is up to 2.0 wt. %, preferably up to 1.5 wt. %. The Mg content is in particular up to 3.0 wt. %, preferably up to 1.0 wt. %. The anticorrosion coating can be applied by hot-dip coating, physical vapor deposition or electrolytic methods.

[0154] The invention further relates to a sheet metal shaped part produced from the flat steel product described above in conjunction with the method. The flat steel product comprises a steel substrate which, apart from iron and unavoidable impurities, has the following composition (in wt. %):

[0155] C: 0.06-0.5%,

[0156] Si: 0.05-0.6%,

[0157] Mn: 0.4-3.0%,

[0158] Al: 0.10-1.0%,

[0159] Nb: 0.001-0.2%,

[0160] Ti: 0.001-0.10%

[0161] B: 0.0005-0.01%

[0162] P: ≤0.03%,

[0163] S: ≤0.02%,

[0164] N: ≤0.02%,

[0165] Sn: ≤0.03%

[0166] As: ≤0.01%

[0167] And selectively contain one or more of the following elements "Cr, Cu, Mo, Ni, V, Ca, W", the content is:

[0168] Cr: 0.01-1.0%,

[0169] Cu: 0.01-0.2%,

[0170] Mo: 0.002-0.3%,

[0171] Ni: 0.01-0.5%,

[0172] V: 0.001-0.3%,

[0173] Ca: 0.0005-0.005%,

[0174] W: 0.001-1.0%.

[0175] The preferred embodiments of the steel substrate of the flat steel product explained in conjunction with the above method are likewise preferred embodiments of the steel substrate of the sheet metal formed part.

[0176] The sheet metal profile according to the invention comprises at least one first region and a second region having different material properties.

[0177] In the first zone, the sheet metal formed part has:

[0178] - a yield strength of at least 1200 MPa, in particular at least 1300 MPa;

[0179] - and / or a tensile strength of at least 1400 MPa, in particular at least 1600 MPa;

[0180] - and / or an elongation at break A80 of at least 3.5%, in particular at least 4%, in particular at least 4.5%, preferably at least 5%;

[0181] - and / or a bending angle of at least 30°, in particular at least 40°, preferably at least 45°;

[0182] - and / or a yield strength ratio of at least 60% and at most 85%;

[0183] - and / or a Vickers hardness of at least 500 HV5, in particular at least 540 HV5.

[0184] In an improved variant, the yield strength of the first zone of the sheet metal profile is at least 1200 MPa, preferably at least 1300 MPa, particularly preferably at least 1400 MPa, in particular at least 1500 MPa.

[0185] In an extended variant, the first zone tensile strength of the sheet metal profile is at least 1300 MPa, preferably at least 1400 MPa, in particular at least 1600 MPa, preferably 1700 MPa, more preferably 1800 MPa.

[0186] In particular, the sheet metal profiled part has an elongation at break A80 in the first region of at least 3.5%, in particular at least 4%, in particular at least 4.5%, preferably at least 5%.

[0187] Furthermore, in a preferred variant, the bending angle of the sheet metal profile in the first region is at least 30°, in particular at least 40°, and more preferably at least 45°. The bending angle here refers to the bending angle corrected for the sheet thickness. The corrected bending angle is calculated from the measured bending angle of maximum force (according to VDA standard 238-100) (also called maximum bending angle) by the following formula:

[0188] Bending Angle 修正 =Bending angle 测量 *√Plate thickness

[0189] The plate thickness in the formula should be in mm. This formula is applicable for plate thickness greater than 1.0 mm. For plate thickness less than 1.0 mm, the corrected bending angle is the same as the measured bending angle.

[0190] In a particularly preferred variant, the first region of the sheet metal profile has a yield strength ratio (ratio of yield strength to tensile strength) of at least 60% and at most 85%. The yield strength ratio is preferably at least 65%, in particular at least 70%.

[0191] In a preferred embodiment variant, the sheet metal molded part has a Vickers hardness of at least 500 HV5 in the first region, preferably at least 550 HV5, in particular at least 570 HV5, preferably at least 580 HV5.

[0192] Vickers hardness refers qualitatively to the resistance to indentation of the test body and therefore also to plastic deformation. The advantage of using the characterization of Vickers hardness is that Vickers hardness tests can be performed even for smaller component sections. In this way, individual areas of the component can be examined in a targeted manner, where tensile tests cannot be performed due to the geometry (e.g. curved workpieces or areas with varying sheet thickness). The Vickers hardness measurement method is carried out in accordance with DIN EN ISO 6507 (2018.07). The number "5" indicates the test force in kilograms of force (kp). In the HV5 test, the test force is 5 kilograms of force (kp). In standardized tests, the measurement differences between the HV1 to HV30 tests are not significant. Therefore, the measured values ​​with different test forces will also be within the range given for HV5.

[0193] The above mentioned mechanical properties have been found to be particularly beneficial for ensuring good crash performance in automobiles.

[0194] In the second zone, the sheet metal formed part has:

[0195] - a yield strength of at most 800 MPa, in particular at most 600 MPa, in particular at most 580 MPa;

[0196] - and / or a tensile strength of at most 1000 MPa, in particular at most 800 MPa;

[0197] - and / or an elongation at break A80 of at least 8%, in particular at least 10%, in particular at least 12%;

[0198] - and / or a bending angle of at least 80°, in particular at least 90°, preferably at least 100°;

[0199] - and / or a yield strength ratio of at least 60% and at most 85%;

[0200] - and / or a Vickers hardness of maximum 320 HV5, in particular maximum 300 HV5, in particular maximum 270 HV5.

[0201] In an improved variant, the yield strength of the second zone of the sheet metal profile is at most 800 MPa, in particular at most 600 MPa, preferably at most 580 MPa, particularly preferably 560 MPa, very preferably 540 MPa.

[0202] In a further development, the second region of the sheet metal profile has a tensile strength of at most 1000 MPa, in particular at most 800 MPa, preferably 780 MPa, particularly preferably 760 MPa, very preferably 740 MPa.

[0203] In particular, the sheet metal profiled part has an elongation at break A80 in the second region of at least 8%, in particular at least 10%, in particular at least 12%, very preferably at least 14%.

[0204] Furthermore, in a preferred variant, the bending angle of the sheet metal profile in the second region is at least 80°, in particular at least 90°, particularly preferably at least 100°. The bending angle here is the bending angle corrected for the sheet thickness. The corrected bending angle is calculated from the bending angle at the maximum force measured at a specific thickness by the following formula:

[0205] Bending Angle 修正 =Bending angle 测量 *√Plate thickness

[0206] The plate thickness in the formula should be in mm. This formula is applicable for plate thickness greater than 1.0 mm. For plate thickness less than 1.0 mm, the corrected bending angle is the same as the measured bending angle.

[0207] In a particularly preferred variant, the second region of the sheet metal profile has a yield strength ratio (ratio of yield strength to tensile strength) of at least 60% and at most 85%. The yield strength ratio is preferably at least 65%, in particular at least 70%.

[0208] In a preferred embodiment, the sheet metal profile has a Vickers hardness of maximum 320 HV5, in particular maximum 300 HV5, in particular maximum 270 HV5, preferably maximum 260 HV5, in particular maximum 250 HV5, preferably maximum 240 HV5, preferably maximum 230 HV5 in the second region.

[0209] A sheet metal part with such a first and second zone design has significant advantages. Firstly, the first zone has a high-strength region that is particularly resistant to deformation. Secondly, the second zone has a relatively soft region that is particularly suitable for absorbing energy by deformation. As a result, the sheet metal part has particularly good crash properties, since firstly energy absorption, such as impact energy, can be ensured and, in addition, a high stability region is present in order to protect particularly sensitive components (e.g. the passenger compartment) from deformation. The sheet metal part is in particular a B-pillar with a soft base or a front and rear longitudinal member with a soft region.

[0210] The actual mechanical characteristic values ​​of the sheet metal parts are determined by first subjecting them to a cathodic varnishing treatment or a similar heat treatment. Cathodic varnishing operations are usually used for corresponding parts in the automotive industry. In the cathodic varnishing process, the parts are first coated in an aqueous solution. The coating is then baked by heat treatment. In this process, the sheet metal parts are heated to 170°C and kept at this temperature for 20 minutes. Subsequently, the parts are cooled to room temperature in ambient air. Since such a heat treatment may affect the mechanical characteristic parameters, the mechanical characteristic parameters (yield limit, tensile strength, yield limit ratio, elongation at break A80, bending angle, Vickers hardness) are to be understood in the sense of the present invention as the characteristic parameters of the parts that have been subjected to a cathodic varnishing treatment or the characteristic parameters of the parts that have been subjected to a heat treatment similar to cathodic varnishing after forming. In practice, the heat treatment of cathodic varnishing varies slightly. The temperature is usually 165°-180° and the holding time is 12-30 minutes. However, the influence of these changes on the mechanical characteristic parameters is negligible.

[0211] In a preferred variant, the sheet metal profile comprises a cathodic varnishing layer.

[0212] In a preferred embodiment variant, the microstructure of the first region of the sheet metal formed part comprises more than 95% martensite, in particular more than 98%.

[0213] Due to the high martensite content in the first zone, very high tensile strengths and yield limits can be achieved.

[0214] In a preferred embodiment, the average grain diameter of the pre-austenite grains of the martensite in the first zone is less than 14 μm, in particular less than 12 μm, preferably less than 10 μm, in particular less than 8 μm. Due to the fine microstructure, the microstructure is more uniform, thereby improving the mechanical properties, in particular reducing the crack sensitivity, thereby improving the bending properties and higher elongation at break.

[0215] It is further preferred that the microstructure of the sheet metal formed part in the second zone comprises less than 95% annealed martensite and bainite and optionally contains at most 60% pearlite. The residual austenite content here is particularly less than 3%, preferably less than 1%. Since annealed martensite and bainite are difficult to distinguish, the sum of annealed martensite and bainite is considered here. This sum is less than 95%, preferably less than 90%, particularly less than 80%, preferably less than 70%. In this case, bainite includes lower bainite and upper bainite. The proportion of pearlite is preferably a maximum of 50%, in particular a maximum of 40%. In particular, the proportion of pearlite is at least 35%, preferably at least 30%. The sum of annealed martensite and bainite is preferably at least 40%, in particular at least 50%, preferably at least 60%.

[0216] In a preferred embodiment, the average grain diameter of the pre-austenite grains of the annealed martensite in the second zone is less than 14 μm, in particular less than 12 μm, preferably less than 10 μm, in particular less than 8 μm. Due to the fine microstructure, the microstructure is more uniform. In turn, the mechanical properties are improved, in particular the crack sensitivity is reduced, thereby improving the bending properties and the higher elongation at break.

[0217] In a particular embodiment, the sheet metal shaped part has fine precipitates in the microstructure, in particular in the form of niobium carbonitrides and / or titanium carbonitrides. This applies to both the first region and the second region.

[0218] In the context of the present application, fine precipitates are understood to be all precipitates with a diameter of less than 30 nm. Other precipitates are referred to as coarse precipitates.

[0219] In a preferred configuration, the average diameter of the fine precipitates is at most 11 nm, preferably at most 10 nm.

[0220] In another preferred embodiment, the sheet metal molded part has mainly fine precipitates in the microstructure. This applies to the first zone and the second zone. "Mainly fine precipitates" means that more than 80%, preferably more than 90% of all precipitates are fine precipitates. This means that more than 80%, preferably more than 90% of all precipitates have a diameter of less than 30 nm.

[0221] The fine precipitates result in a particularly fine microstructure with a small grain size. Due to the fine microstructure, the microstructure is more uniform. This in turn improves the mechanical properties, especially reduces the crack sensitivity, resulting in improved bending properties and higher elongation at break. This also results in improved toughness and a more pronounced fracture necking behavior.

[0222] In an extended variant of the sheet metal profile, the sheet metal profile comprises an anti-corrosion coating. The advantage of the anti-corrosion coating is that it prevents the formation of oxide scale during austenitization during hot forming. In addition, the anti-corrosion coating protects the formed sheet metal profile from corrosion.

[0223] In a specific embodiment, the sheet metal form preferably comprises an anti-corrosion coating based on aluminum. The anti-corrosion coating of the sheet metal form preferably comprises an alloy layer and an Al-based layer. In sheet metal forms, the alloy layer is often also referred to as an interdiffusion layer.

[0224] The thickness of the corrosion protection coating is preferably at least 10 μm, particularly preferably at least 20 μm, in particular at least 30 μm.

[0225] The thickness of the alloy layer is preferably less than 30 μm, particularly preferably less than 20 μm, in particular less than 16 μm, and more preferably less than 12 μm. The thickness of the Al-based layer is determined by the difference in thickness between the corrosion protection coating and the alloy layer.

[0226] The alloy layer is located above the steel substrate and is in direct contact with it. The alloy layer composition of the sheet metal formed part preferably consists of 35-90% by weight of Fe, 0.1-10% by weight of Si, optionally up to 0.5% by weight of Mg and optionally up to 2.0% by weight of other components in total, the remainder being aluminum. Due to the further diffusion of iron into the alloy layer, the proportions of Si and Mg are lower than the corresponding proportions in the melt of the molten bath.

[0227] The alloy layer preferably has a ferrite microstructure.

[0228] The Al-based layer of the sheet metal forming part is located above the alloy layer of the steel component and is in direct contact with it. The Al-based layer of the steel component preferably has a composition of 35-55 wt. % Fe, 0.4-10 wt. % Si, optionally up to 0.5 wt. % Mg and optionally up to 2.0 wt. % other components in total, the remainder being aluminum.

[0229] The Al-based layer can have a uniform element distribution, wherein the local element content varies by a maximum of 10%. In contrast, a preferred variant of the Al-based layer has a low silicon phase and a silicon-rich phase. The low silicon phase refers to an area where the average silicon content is at least 20% lower than the average silicon content of the Al-based layer. The silicon-rich phase refers to an area where the average silicon content is at least 20% higher than the average silicon content of the Al-based layer.

[0230] In a preferred variant, the silicon-rich phase is located within the low-silicon phase. In particular, the silicon-rich phase forms at least 40% of a continuous layer, the boundaries of which are surrounded by low-silicon regions. In another alternative embodiment, the silicon-rich phase is distributed in the low-silicon phase in the form of islands.

[0231] In the context of this application, "islanded" refers to a distribution pattern in which discrete, incoherent regions are surrounded by another material - ie, "islands" of one material exist within another material.

[0232] In a preferred variant, the steel component comprises an oxide layer located on the anti-corrosion coating. The oxide layer is located in particular on the Al-based layer and preferably forms the outermost layer of the anti-corrosion coating.

[0233] The oxide layer of the steel component preferably consists of more than 80% by weight of oxides, wherein the majority of the oxides (i.e. more than 50% by weight of the oxides) are aluminum oxide. Optionally, the oxide layer comprises, in addition to aluminum oxide, hydroxides and / or magnesium oxides, either alone or as a mixture. The remainder of the oxide layer which is not oxide and optionally present hydroxides preferably consists of silicon, aluminum, iron and / or magnesium in metallic form.

[0234] The oxide layer preferably has a thickness of at least 50 nm, in particular at least 100 nm, a maximum thickness of 4 μm, in particular a maximum thickness of 2 μm.

[0235] In a particular configuration, the sheet metal form comprises a zinc-based anti-corrosion coating.

[0236] This zinc-based anticorrosion coating preferably contains up to 80% by weight of Fe, 0.2-6.0% by weight of Al, 0.1-10.0% by weight of Mg, optionally 0.1-40% by weight of manganese or copper, optionally 0.1-10.0% by weight of cerium, optionally up to 0.2% by weight of other elements, unavoidable impurities and the balance is zinc. In particular, the Al content is up to 2.0% by weight, preferably up to 1.5% by weight. The iron content due to iron diffusion is preferably more than 20% by weight, especially more than 30% by weight. In addition, the Fe content is especially up to 70% by weight, especially up to 60% by weight. The Mg content is especially up to 3.0% by weight, preferably up to 1.0% by weight. The anticorrosion coating can be applied by hot dip coating, physical vapor deposition or electrolysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0237] The present invention is described in detail by the following examples.

[0238] The diagram is as follows:

[0239] Figure 1 A schematic diagram of a sheet metal blank in a forming tool is shown when inserted into the forming tool;

[0240] Figure 2 A schematic diagram showing a sheet metal cutout in a forming tool after forming;

[0241] Figure 3 A reconstructed austenite grain map is shown. DETAILED DESCRIPTION

[0242] The following examples are provided to further illustrate the present invention.

[0243] Several experiments were conducted to demonstrate the effect of the present invention. For this purpose, steel strips (i.e. flat steel products) having the chemical compositions listed in Table 1 were produced according to conventional methods. The blank positions in Table 1 indicate that the corresponding elements were not intentionally added to the alloy. However, these elements may still be present as unavoidable impurities. Steel composition F is a reference example and does not conform to the present invention.

[0244] The steel strip produced in this way was hot-dip galvanized in a conventional manner, with the hot-dip galvanizing being carried out using the molten baths specified in Table 2. Table 2 gives the layer thickness of the corrosion protection coating per side, with both the top side and the bottom side being coated.

[0245] The thickness of the steel strip produced in all experiments was between 1.4 mm and 1.6 mm.

[0246] After cooling to room temperature, specimens were taken for each steel type transversely to the rolling direction according to DIN EN ISO 6892-1 specimen shape 2 (Appendix B Table B1). The specimens were subjected to tensile tests according to DIN EN ISO 6892-1 specimen shape 2 (Appendix B Table B1). Table 3 lists the results of the tensile tests on the flat steel products. The following material characteristic values ​​were obtained by the tensile test: yield limit type and, in the case of continuous yield limit, the yield strength value Rp0.2 (herein referred to as yield limit), tensile strength Rm, uniform elongation Ag and elongation at break A80. All specimens had a continuous yield limit and a uniform elongation Ag of at least 10%.

[0247] Cutouts are cut from the produced steel strips for further testing. The corresponding steel components are produced from these cutouts (formed blanks) by hot pressing. For further mechanical testing, test specimens are taken from these components in flat positions. During further processing, these cutouts are heated by a heating device, for example by a conventional heating furnace, from room temperature at an average heating rate r in the furnace. 炉 Heat to furnace temperature T (between 30°C and 700°C) 炉 The total duration in the furnace, including heating and holding time, is defined as t 炉 The dew point temperature of the furnace atmosphere is defined as T 露点 The blank is then removed from the heating system and placed into the forming tool within the transfer time. The blank has reached the furnace temperature when removed from the furnace. Transfer time t 传 The transport time includes the time for removal from the heating device, transfer to the tool and insertion into the tool, which is usually between 5 and 15 seconds. When inserted into the forming tool, the cut piece has reached the insertion temperature T 插入In the forming tool, the blank is formed into the corresponding sheet metal part. The residence time of the formed blank in the closed tool is defined as t 工具 Finally, the specimens were cooled in air to room temperature. Table 4a gives the general parameters of the thermoforming operation.

[0248] Figure 1 A schematic diagram of a sheet metal blank 1 when inserted into a forming tool 3 is shown. The forming tool comprises a die 5 having a notch 7 and a punch 9. The punch 9 has a basic shape of a trapezoidal cross section, having an end face and a side face 16 that tapers obliquely to the end face. The punch 9 is supported by a carrier 10 integrally connected thereto, and the side edge regions 12 and 14 of the carrier are flange-shaped and extend laterally beyond the side face 16 of the punch 9 at the upper edge. The lower edge faces 18 of the edge regions 12 and 14 are connected to the side faces 16 of the punch 9 in a horizontal direction. A first section 11 of the forming tool 3 is provided at the end face of the punch 9, and a second section 13 of the forming tool 3 is provided at the transition between the side face 16 of the punch 9 and the lower edge face 18 of the edge region 14. The first section 11 is temperature-controlled to a first tool temperature by a temperature control device 15 formed as a cooling device. The temperature control device 15 is arranged at a first temperature. Figure 1 The second section 13 is temperature-controlled to the second tool temperature by a temperature control device 17 formed as a heating device. The temperature control device 17 is Figure 1 The negative mold 5 has a further section 19 which is temperature-controlled to a third tool temperature by a temperature control device 21 designed as a cooling device.

[0249] Unlike what is shown in the figure, the sections of the die 5 and the punch 9 that are opposite to each other and thus contact the same area of ​​the sheet metal blank 1 are usually equipped with temperature control devices with the same effect. For example, usually, a temperature control device configured as a heating device is also provided in the die 5 opposite to the temperature control device 17 configured as a heating device. For better display, such a schematic is not included in the figure.

[0250] In the subsequent hot pressing of the sheet metal blank 1, the punch 9 acts on the sheet metal blank 1 at a high speed, so that the strongly cooled first section 11 is quickly separated from the first zone 31 of the sheet metal blank corresponding to it (see Figure 2 ) deep contact. In this way, the first zone 31 of the sheet metal blank 1 is quenched quickly, so that different material properties are set there than in the second zone 33 of the sheet metal blank 1. Subsequently, the advance speed of the punch 9 is slowed down in order to avoid excessive cooling in the second zone 33 in particular and to prevent the formation of hard microstructures. In particular, in the second section 13, which is temperature-controlled to the higher second tool temperature, the speed of heat removal by the punch 9 is low, so that the soft and tough microstructure of the sheet metal blank 1 in the second zone 33 in contact with the second section 13 is maintained.

[0251] Figure 2The sheet metal blank 1 is shown in the forming tool 3 at the end of forming. The sheet metal blank 1 has been formed into a sheet metal profile. It can be clearly seen that the sheet metal blank 1 (or sheet metal profile) has a first region 31 that is in contact with the first section 11 of the forming tool 3 during hot press forming. In addition, the sheet metal blank 1 (or sheet metal profile) has a second region 33 that is in contact with the second section 13 of the forming tool 3 during hot press forming. The sheet metal profile obtained by forming the sheet metal blank 1 thus has a first region 31 and a second region 33. The material properties in the first region 31 are different from the material properties in the second region 33.

[0252] Table 4b lists the thermoforming parameters, which vary in different sections or zones. They include the first tool temperature T 工具，1 and the second tool temperature T 工具，2 , the first section is temperature adjusted to the first tool temperature T 工具，1 , the second section is temperature adjusted to the second tool temperature T 工具，2 Due to the different tool temperatures, different cooling rates r must exist in the first and second zones of the sheet metal blank. 工具，1 and r 工具，2 When the sheet metal part is removed from the forming tool, the target temperatures of the first and second zones are still different and are denoted by T 目标，1 and T 目标，2 .

[0253] Tables 5a and 5b show the mechanical properties of the first and second zones of the sheet metal forming part, which are derived from the previous process results. It can be clearly seen that the first zone has a higher strength, while the second zone has a better ductility.

[0254] In addition to the determination of the mechanical properties, the microstructure of the first and second zones was determined. The results are shown in Tables 6a and 6b. In the first zone, the microstructure consists of more than 99% martensite and only a small amount of retained austenite, while in the second zone, the microstructure consists of less than 95% annealed martensite and bainite and contains a maximum of 60% pearlite. In this case, the retained austenite could not be detected and therefore its content was less than 1%.

[0255] In addition, Tables 6a and 6b list the properties of fine precipitates in the microstructure. The precipitates are niobium carbonitride and titanium carbonitride, both of which contribute to grain refinement. The precipitates were measured by electron optical and X-ray imaging (TEM and EDX) using carbon extraction replicas (referred to as "carbon extraction replicas" in the professional literature). Carbon extraction replicas are produced on longitudinal grinding slices (20x30mm). The measurement resolution is 10,000 to 200,000 times. Through these images, the precipitates can be classified into coarse precipitates and fine precipitates. Fine precipitates refer to all precipitates with a diameter of less than 30nm. Other precipitates are called coarse precipitates. The proportion of fine precipitates relative to the total number of precipitates in the measurement area is determined by counting. For fine precipitates, their average diameter is also calculated by computer-assisted image analysis. In the sample of the present invention, the proportion of fine precipitates in the first zone and the second zone exceeds 90%. The average diameter of fine precipitates is also less than 11nm. In one experiment, the precipitate could not be identified. Therefore, it is marked as "nd" (not determined) in the table.

[0256] In addition, the grain diameters of the pre-austenite grains are given in Tables 6a and 6b. For this purpose, the austenite grains were reconstructed using the ARPGE software from the EBSD measurements. The software parameters are as follows:

[0257] Nishiyama-Wassermann orientation relationship

[0258] The tolerance of grain identification is 7°

[0259] The tolerance of the parent grain growth nucleation is 7°

[0260] ·Tolerance of parent grain growth is 15°

[0261] The minimum acceptable grain size is 10 pixels

[0262] For grain identification, a maximum orientation difference of 5° and a minimum grain diameter of 5 pixels are assumed according to DIN EN ISO 643.

[0263] For example, Figure 3 The corresponding austenite reconstruction diagram is shown. In this example, the average diameter of the pre-austenite grains is 7.5 μm. In all the examples of the invention, the average diameter of the pre-austenite grains is below 14 μm.

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[0271]

Claims

1. A method for producing a sheet metal formed part having at least one first region (31) and one second region (33) with different material properties, the method comprising the following steps: a. A sheet metal cut piece (1) made of a flat steel product is provided, which comprises a steel substrate made of steel, the composition of which, except for iron and unavoidable impurities, is as follows (in weight %): C:0.27-0.5％ Si: 0.05-0.6% Mn: 0.4-3.0% Al:0.10-1.0％ Nb: 0.001-0.2% Ti: 0.001-0.10% B:0.0005-0.01％ P:≤0.03％ S:≤0.02％ N:≤0.02％ Sn:≤0.03% As:≤0.01% and optionally one or more elements from the group consisting of "Cr, Cu, Mo, Ni, V, Ca, W" in the following contents Cr:0.01-1.0％, Cu: 0.01-0.2%, Mo: 0.002–0.3%, Ni: 0.01–0.5%, V:0.001–0.3％, Ca: 0.0005–0.005%, W:0.001–1.0％； b. Heating the sheet metal blank (1) so that the AC3 temperature of the sheet metal blank (1) is at least partially exceeded and the temperature T of the sheet metal blank is reduced to 0.04°C when inserted into the forming tool (3) for the hot press forming operation (working step (c)). 插入 At least part of it is above Ms+100°C, where Ms is the martensite start temperature; c. inserting the heated sheet metal blank (1) into a forming tool (3), wherein the forming tool (3) has a temperature control device (15, 17) for regulating the temperature of at least one of its sections (11, 13) in contact with the sheet metal blank (1) during hot press forming, and wherein the transfer time t required for removing the sheet metal blank (1) from the heating device and inserting the sheet metal blank (1) is 转移 Maximum 20s, preferably maximum 15s; d. hot press forming the sheet metal cut piece (1) into a sheet metal formed part, wherein during the hot press forming process, the sheet metal cut piece (1) is cooled to a first target temperature in a first zone (31) and cooled to a second target temperature in a second zone (33) and selectively maintained there, wherein the second target temperature is greater than the first target temperature, so as to set different organizational structures in the first and second zones; e. Remove the cooled sheet metal form from the tool.

2. The method according to claim 1, characterized in that The sections (11, 13) in contact with the sheet metal blank (1) during the hot press forming process include at least one first section (11) and one second section (13), wherein the first section (11) is in contact with the first zone (31) during the hot press forming process, and the second section (13) is in contact with the second zone (33) during the hot press forming process, and the first section (11) is temperature-controlled to a first tool temperature, and the second section (13) is temperature-controlled to a second tool temperature, wherein the first tool temperature is lower than the second tool temperature.

3. The method according to claim 1 or 2, characterized in that The first tool temperature is a maximum of 200°C and / or the second tool temperature is at least 200°C.

4. The method according to claim 2 or 3, characterized in that The first target temperature is at most 250 K higher than the first tool temperature and / or the second target temperature is at most 100 K higher than the second tool temperature.

5. The method according to any one of claims 1 to 4, characterized in that The cooling behavior of the sheet metal blank (1) in step d. is determined at least in part by the surface pressure exerted in the forming tool (3).

6. The method according to any one of claims 1 to 5, characterized in that The forming rate of the hot press forming operation in step d is controlled taking into account the duration of time that the temperature-regulated sections (11, 13) of the forming tool (3) are in contact with the sheet metal blank (1) during the hot press forming.

7. The method according to any one of claims 1 to 6, characterized in that The sheet metal blank (1) has regions of different thicknesses.

8. The method according to any one of claims 1 to 7, characterized in that The forming tool (3) has a die (5) and a punch (9) which can be adjusted in a recess of the die (5) for forming.

9. The method according to any one of claims 1 to 8, characterized in that The temperature control device (15, 17) is designed as a cooling device (15) and / or a heating device (17).

10. The method according to any one of claims 1 to 9, characterized in that The sections (11, 13) that come into contact with the sheet metal blank (1) during the hot press forming process include at least one first section (11) and one second section (13), wherein the first section (11) comes into contact with the first zone (31) during the hot press forming process, and the second section (13) comes into contact with the second zone (33) during the hot press forming process, wherein the first section (11) is temperature-controlled to a first tool temperature by a temperature control device (15) designed as a cooling device, and the second section (13) is temperature-controlled to a second tool temperature by a temperature control device (17) designed as a heating device.

11. The method according to any one of claims 1 to 10, characterized in that The flat steel product comprises an aluminum-based corrosion protection coating, wherein the corrosion protection coating comprises in particular an alloy layer and an Al-based layer.

12. A sheet metal shaped part made of a flat steel product, the flat steel product comprising a steel substrate made of steel, the steel substrate having, apart from iron and unavoidable impurities, the following composition (in % by weight): C:0.27-0.5％， Si: 0.05-0.6%, Mn: 0.4-3.0%, Al:0.10-1.0％， Nb: 0.001-0.2%, Ti: 0.001–0.10% B:0.0005–0.01％ P:≤0.03％， S:≤0.02％， N:≤0.02％， Sn:≤0.03% As:≤0.01% And selectively contain one or more of the following elements "Cr, Cu, Mo, Ni, V, Ca, W", the content is: Cr:0.01-1.0％， Cu: 0.01-0.2%, Mo: 0.002–0.3%, Ni: 0.01–0.5%, V:0.001–0.3％， Ca: 0.0005–0.005%, W:0.001-1.0％， wherein the sheet metal profile comprises at least a first region and a second region, wherein the sheet metal profile has a different microstructure in a first region and in a second region, In the first zone, the sheet metal profile has: - a yield strength of at least 1200 MPa, in particular at least 1300 MPa; - and / or a tensile strength of at least 1400 MPa, in particular at least 1600 MPa; - and / or an elongation at break A80 of at least 3.5%, in particular at least 4%, in particular at least 4.5%, preferably at least 5%; - and / or a bending angle of at least 30°, in particular at least 40°, preferably at least 45°; - and / or a yield strength ratio of at least 60% and at most 85%; - and / or a Vickers hardness of at least 500 HV5, in particular at least 540 HV5, And wherein in the second zone, the sheet metal profile has: - a yield strength of maximum 800 MPa, preferably maximum 600 MPa, in particular maximum 580 MPa; - and / or a tensile strength of at most 1000 MPa, in particular at most 800 MPa; - and / or an elongation at break A80 of at least 8%, in particular at least 10%; - and / or a bending angle of at least 80°, in particular at least 90°, preferably at least 100°; - and / or a yield strength ratio of at least 60% and at most 85%; - and / or a Vickers hardness of maximum 320 HV5, in particular maximum 300 HV5, in particular maximum 270 HV5.

13. The sheet metal formed part according to claim 12, characterized in that The sheet metal formed part has a microstructure in the first zone with a martensite content of more than 95%, in particular more than 98%, and / or the sheet metal formed part has a microstructure in the second zone with a content of annealed martensite and bainite of less than 95% and optionally contains a maximum of 60% pearlite, wherein the retained austenite content is in particular less than 3%, preferably less than 1%.

14. The sheet metal formed part according to any one of claims 12 or 13, wherein The ratio of Al content to Nb content, Al / Nb, is limited by the following conditions: When Mn≤1.6 wt%, Al / Nb≤20.0 and When Mn≥1.7 wt%, Al / Nb≤30.

0.

15. The sheet metal formed part according to any one of claims 12 to 14, characterized in that The sheet metal formed part has substantially fine precipitates in the microstructure of the first region, in particular precipitates in the form of niobium carbonitrides and / or titanium carbonitrides. 16 . The sheet metal profile as claimed in claim 12 , comprising an aluminum-based anti-corrosion coating, wherein the anti-corrosion coating comprises in particular an alloy layer and an Al-based layer.

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