STEEL HAVING IMPROVED PROCESSING PROPERTIES FOR WORKING AT ELEVATED TEMPERATURES

Abstract

A flat steel product for hot forming, a formed shaped sheet metal part and methods of production of the same. The flat steel product and the shaped sheet metal part have improved properties, especially in conjunction with an aluminum-based anticorrosion coating.

Claims

1.-17. (canceled)

18. A flat steel product for hot forming, comprising: a steel substrate composed of steel comprising iron and by weight comprising: C 0.06-0.5%, Si: 0.05-0.6%, Mn: 0.4-3.0%, Al: 0.06-1.0%, 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 unavoidable impurities ?0.2%, where an Al/Nb ratio of Al content to Nb content is: Al/Nb?20.0 when Mn?1.6% by weight; and Al/Nb?30.0 when Mn?1.7% by weight.

19. The flat steel product of claim 18, wherein the steel further comprises one or more elements by weight comprising: 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%, and W: 0.001-1.0%.

20. The flat steel product of claim 19, wherein 0.7%<Mn+Cr<3.5% by weight.

21. The flat steel product of claim 18, wherein Ti<3.42 N.

22. The flat steel product of claim 18, further comprising an anticorrosion coating on at least one side of the steel substrate.

23. The flat steel product of claim 22, wherein the anticorrosion coating is an aluminum-based anticorrosion coating and has an alloy layer and an Al base layer.

24. The flat steel product of claim 23, wherein the alloy layer comprises 35-60% by weight of Fe, constituents limited to a total of not more than 5.0% by weight, and balanced aluminum, and the Al base layer comprises 1.0-15% by weight of Si, 2-4% by weight of Fe, up to 5.0% by weight of alkali metals or alkaline earth metals, up to 10% Zn, constituents limited to a total of not more than 2.0% by weight, and balanced aluminum.

25. The flat steel product of claim 18, further comprising one or more properties of: a yield point with a continuous progression (Rp0.2) or a yield point with a difference (?Re) between an upper yield point limit (ReH) and a lower yield point limit (ReL) of not more than 45 MPa; a uniform expansion Ag of at least 10%; and an elongation at break A80 at least 15% or at least 20%.

26. A shaped sheet metal part formed from a flat steel product, comprising: a steel substrate composed of steel comprising iron and by weight comprising: C: 0.06-0.5%, Si: 0.05-0.6%, Mn: 0.4-3.0%, Al: 0.06-1.0%, 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 unavoidable impurities ?0.2%, where an Al/Nb ratio of Al content to Nb content is: Al/Nb?20.0 when Mn?1.6% by weight; and Al/Nb?30.0 when Mn?1.7% by weight; and an anticorrosion coating.

27. The shaped sheet metal part of claim 26, the steel further comprises one or more elements by weight comprising: 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%, and W: 0.001-1.0%.

28. The shaped sheet metal part of claim 26, wherein the steel substrate of the shaped sheet metal part has a microstructure having at least in part more than 80% or more than 90% martensite and/or lower bainite, and wherein former austenite grains of the martensite have an average grain diameter of less than 14 ?m, less than 12 ?m, or less than 10 ?m.

29. The shaped sheet metal part of claim 28, further comprising fine precipitates in the microstructure of the steel substrate in a form of niobium carbonitrides and/or titanium carbonitrides.

30. The shaped sheet metal part of claim 26, at least in part comprising one or more properties of: a yield point of at least 950 MPa, at least 1100 MPa, at least 1300 MPa, or at least 1500 MPa; a tensile strength of at least 1000 MPa, at least 1100 MPa, at least 1300 MPa, or at least 1800 MPa; an elongation at break A80 of at least 4%, at least 5%, or at least 6%; and a bending angle of at least 30?, at least 40?, or at least 50?.

31. The shaped sheet metal part of claim 26, wherein an electrochemical potential of a surface of the shaped sheet metal part in a corrosive medium is at least ?0.50 V.

32. The shaped sheet metal part of claim 26, wherein the anticorrosion coating is an aluminum-based anticorrosion coating comprising an alloy layer and an Al base layer, and in a cross section of the alloy layer, over a measurement length of 500 ?m, an area occupied by pores in the alloy layer is less than 250 ?m.sup.2, and wherein a proportion of the area occupied by pores has a diameter of not less than 0.1 ?m is less than 10%.

33. The shaped sheet metal part of claim 32, wherein a Nb content in the alloy layer is greater than 0.010% by weight, greater than 0.015% by weight, or greater than 0.018% by weight.

34. The shaped sheet metal part of claim 26, further comprising a welding range of at least 0.9 kA.

35. A process for producing a shaped sheet metal part, comprising: providing a sheet metal blank made of a flat steel product, comprising: a steel substrate composed of steel comprising iron and by weight comprising: C 0.06-0.5%, Si: 0.05-0.6%, Mn: 0.4-3.0%, Al: 0.06-1.0%, 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 unavoidable impurities ?0.5%, where an Al/Nb ratio of Al content to Nb content is: Al/Nb?20.0 when Mn?1.6% by weight; and Al/Nb?30.0 when Mn?1.7% by weight; heating the sheet metal blank such that at least in part a AC3 temperature of the sheet metal blank is exceeded and a temperature T.sub.ins of the sheet metal blank on insertion into a forming tool provided for hot press forming at least in part has a temperature above Ms+100? C., wherein Ms is a martensite start temperature; inserting the heated sheet metal blank into a forming tool, wherein a transfer time t.sub.trans required for removal from a heating device and insertion of the sheet metal blank is not more than 20 s or not more than 15 s; hot press forming the sheet metal blank to the shaped sheet metal part, wherein the sheet metal blank during the hot press forming is cooled down to a target temperature T.sub.target over a period t.sub.tool of more than 1 s at a cooling rate r.sub.tool of at least in part more than 30 K/s and kept at the target temperature T.sub.target; and removing the shaped sheet metal part cooled to the target temperature T.sub.target from the forming tool.

36. The process of claim 35, wherein the steel further comprises one or more elements by weight comprising: 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%, and W: 0.001-1.0%.

37. The process of claim 35, wherein the producing the shaped sheet metal part further comprises producing the flat steel product for hot forming having an anticorrosion coating, comprising: providing a slab or thin slab composed of the steel; through-heating the slab or thin slab at a temperature (T1) of 1100-1400? C.; hot rolling the slab or thin slab to produce a hot-rolled flat steel product, wherein a final rolling temperature (T3) is 750-1000? C.; descaling the hot-rolled flat steel product; annealing the flat steel product at an annealing temperature (T5) of 650-900? C.; cooling the flat steel product to a dipping temperature (T6) of 650-800? C. or 670-800? C.; coating the flat steel product cooled to the dipping temperature with the anticorrosion coating by hot dip coating in a melt bath at a melt temperature (T7) of 660-800? C. or 680-740? C.; and cooling the coated flat steel product to a room temperature, wherein a first cooling time t.sub.MT in a temperature range between 600? C. and 450? C. is more than 10 s or more than 14 s, and a second cooling time t.sub.LT in a temperature range between 400? C. and 300? C. is more than 8 s or more than 12 s.

38. The process of claim 37, further comprising: pre-rolling the through-heated slab or thin slab to produce an intermediate product having an intermediate product temperature (T2) of 1000-1200? C.; coiling the hot-rolled flat steel product, wherein a coiling temperature (T4) is not more than 700? C.; cold-rolling the flat steel product, wherein a degree of cold rolling is at least 30%; and skin pass-rolling the coated flat steel product.

39. The process of claim 37, wherein the melt bath used in the hot dip coating comprises a anticorrosion material to be applied to the flat steel product in liquid form, and wherein the anticorrosion material comprises up to 15% by weight of Si, 2-4% by weight of Fe, up to 5% by weight of alkali metals or alkaline earth metals, up to 10% Zn, constituents limited to a total of not more than 2.0% by weight, and balanced aluminum.

Description

[0244] The figures show:

[0245] FIG. 1a a schematic diagram of a sample of the invention having a small number of pores, obtained from a section image.

[0246] FIG. 1b a schematic diagram of a reference sample having an increased number of pores, obtained from a section image.

[0247] FIG. 2a a schematic diagram of a sample of the invention having a small number of pores after a corrosion test, obtained from a section image.

[0248] FIG. 2b in each case a schematic diagram of a reference sample having an increased number of pores after a corrosion test, obtained from a section image.

[0249] FIG. 3 a grain diagram of reconstructed austenite.

[0250] The effect of the invention was shown by conducting multiple experiments. For this purpose, slabs having the compositions specified in table 1 and having a thickness of 200-280 mm and width of 1000-1200 mm were created, heated up to a respective temperature T1 in a pusher furnace and kept at T1 for between 30 and 450 min until the temperature T1 in the core of the slabs had been attained and the slabs were thus through-heated. The production parameters are reported in table 2. The slabs with their respective through-heating temperature T1 were discharged from the pusher furnace and subjected to hot rolling. The experiments were executed in the form of a continuous hot strip rolling operation. For this purpose, the slabs were first pre-rolled to an intermediate product of thickness 40 mm, and the intermediate products, which can also be referred to as preliminary strips in the case of hot strip rolling, each had an intermediate product temperature T2 at the end of the pre-rolling phase. Immediately after the pre-rolling, the preliminary strips were sent to finish rolling, such that the intermediate product temperature T2 corresponds to the rolling start temperature for the finish-rolling phase. The preliminary strips were rolled to hot strips having a final thickness of 3-7 mm and the respective final rolling temperatures T3 specified in table 2, cooled down to the respective coiling temperature and wound up to coils at the respective coiling temperatures T4 and then cooled down in stationary air. The hot strips were descaled in a conventional manner by pickling before being subjected to a cold rolling operation with the degrees of cold rolling specified in table 2. The cold-rolled flat steel products were heated to a respective annealing temperature T5 in a tunnel annealing furnace and kept at annealing temperature for 100 s in each case, before being cooled down to their respective dipping temperature T6 at a cooling rate of 1 K/s. The cold strips were guided at their respective dipping temperature T6 through a molten coating bath at temperature T7. The composition of the coating bath is specified in table 3. After the coating, the coated strips were blown dry in a conventional manner, which produced coating layers having different layer thicknesses (see table 3). The strips were first cooled down to 600? C. at an average cooling rate of 10-15 K/s. Later on in the cooling between 600? C. and 450? C. and between 400? C. and 300? C., the strips were cooled down over the cooling periods T.sub.MT and T.sub.LT specified in table 2. Between 450? C. and 400? C. and below 220? C., the strips were cooled at a cooling rate of 5-15 K/s in each case.

[0251] Table 4 is a collation of which steel variant (see table 1) was combined with which process variant (see table 2) and which coating (see table 3).

[0252] Steel compositions D, E and F are reference examples that are not in accordance with the invention. Correspondingly, experiments 3, 10, 11, 12, 13, 17 and 18 are not in accordance with the invention.

[0253] The thickness of the steel strips produced in all experiments was between 1.4 mm and 1.7 mm.

[0254] After cooling to room temperature, samples were taken transverse to rolling direction from the cooled steel strips according to DIN EN ISO 6892-1 sample form 2 (annex B table B1). The samples were subjected to a tensile test according to DIN EN ISO 6892-1 sample form 2 (annex B table B1). Table 4 gives the results of the tensile test. In the course of the tensile test, the following material indices were ascertained: yield point type, which is referred to as Re for a pronounced yield point and as Rp for a continuous yield point, and the yield point value Rp0.2 in the case of a continuous yield point, the values for the lower stretching limit ReL, the upper stretching limit ReH and the difference of upper and lower stretching limit ?Re in the case of a pronounced yield point, tensile strength Rm, uniform elongation Ag and elongation at break A80. All samples have a continuous yield point Rp or an only slightly pronounced yield point with a difference ?Re between upper and lower yield points of not more than 45 MPa and a uniform elongation Ag of at least 11.5%. For samples 3 and 17 there is a marked yield point Re, and for all other samples a continuous yield point Rp. For samples 3 and 17, table 4 reports the lower yield point ReL and the upper yield point ReH. For all other samples, the Rp0.2 yield point is reported.

[0255] Blanks have been divided from each of the 20 steel strips thus produced, and these have been used for the further experiments. In these experiments, shaped sheet metal part samples 1 have been shaped by hot press forming from the respective blanks 1-24 in the form of sheets of size 200?300 mm.sup.2. Entries in table 7 show which of the 20 coating experiments corresponds to which forming experiment. For this purpose, the blanks have been heated in a heating device, for example in a conventional heating furnace, from room temperature at an average heating rate r.sub.furnace (between 30? C. and 700? C.) in a furnace with a furnace temperature T.sub.furnace. The total time in the furnace, comprising heating and holding, is referred to as t.sub.furnace. The dew point of the furnace atmosphere in all cases was ?5? C. Subsequently, the blanks have been taken from the heating device and inserted into a forming tool at temperature T.sub.tool. At the juncture of removal from the furnace, the blanks had assumed the furnace temperature. The transfer time t.sub.trans, composed of the removal from the heating device, transport to the tool and insertion into the tool, was between 5 and 14 s. The temperature T.sub.ins of the blanks for insertion into the forming tool was in all cases above the respective martensite start temperature+100? C. In the forming tool, the blanks have been formed to the respective shaped sheet metal part, and the shaped sheet metal parts were cooled in the tool at a cooling rate r.sub.tool. The residence time in the tool is referred to as t.sub.tool. Finally, the samples have been cooled down to room temperature under air. Table 5 gives the parameters mentioned for various variants, where RT is an abbreviation of room temperature.

[0256] Table 5 shows very different variants for the forming process. While there is virtually complete formation of martensitic microstructure, for example, in the case of variant II (see table 8, experiment 1), the comparatively slow cooling of the variants X with the high tool temperature T.sub.tool leads to altered microstructure formation with high ferrite contents, the effect of which takes the form of a higher elongation at break A80.

[0257] Table 6 lists the essential parameters for a further-developed process variant. In these experiments, the sheet metal blank is not heated in a furnace with constant furnace temperature as in the above-described experiments; instead, the sheet metal blanks were heated stepwise in regions with different temperature. The experiments were conducted in a roller hearth furnace with different heating zones. In principle, however, the process can also be implemented in multiple separate furnaces. The blanks were first introduced into an intake range of the furnace at an intake temperature T.sub.intake. The blanks were moved therefrom through a central region into an exit region of the furnace with an exit temperature T.sub.exit. Table 6 gives the intake temperature T.sub.intake, the exit temperature T.sub.exit and the maximum furnace temperature T.sub.max experienced by the blanks. In most cases, the maximum furnace temperature was assumed in the exit region. In variant A.X, however, the maximum furnace temperature was assumed in the central region. The further progression was identical to the process described above. The corresponding parameters are reported in table 6.

[0258] Table 7 is a collation of the overall results for the shaped sheet metal parts obtained. The first columns give the sample number, the steel type according to table 1, the process variant according to table 2, the coating according to table 2, and the hot forming variant according to table 5 or table 6. The further columns give the yield point, tensile strength, elongation at break A80. These values were ascertained according to DIN EN ISO 6892-1 sample form 2 (annex B table B1) on samples transverse to the rolling direction. The bending angle has been ascertained according to VDA standard 238-100 with a bending axis transverse to the rolling direction. The bending angle ascertained is calculated in each case by the formula specified in the standard from the path of the ram (the bending angle ascertained (also referred to as maximum bending angle) is the bending angle at which the force has its maximum in the bending experiment). In order to eliminate the effect of the sheet thickness on the bending angle, the correct bending angle was calculated from the ascertained bending angle by the formula

[00017]$\mathrm{Bending}{\mathrm{angle}}_{\mathrm{corrected}}=\mathrm{Bending}{\mathrm{angle}}_{\mathrm{found}}.Math.\sqrt{\mathrm{Sheet}\mathrm{thickness}}$

where the sheet thickness should be inserted into the formula in mm. This applies to sheet thicknesses greater than 1.0 mm. In the case of sheet thicknesses of less than 1.0 mm, the corrected bending angle corresponds to the bending angle ascertained. Table 7 gives the maximum bending angle measured. In order to determine the corrected bending angle, these numerical values should accordingly be multiplied by the root of the sheet thickness reported in table 4.

[0259] The mechanical indices in table 7 were ascertained after a cathodic dip coating had been applied to the formed shaped sheet metal part. During this coating process, the shaped sheet metal parts were heated to 170? C. and kept at that temperature for 20 minutes. Subsequently, the components are cooled down to room temperature under ambient air.

[0260] Table 8 reports the microstructure properties of the shaped sheet metal part. The contents in the microstructure are reported in area %. All inventive examples have a martensite content of more than 90%.

[0261] In addition, table 8 reports the properties of the fine precipitates in the microstructure. The precipitates are niobium carbonitrides and titanium carbonitrides, both of which contribute to grain refining. The precipitates are determined with the aid of electron images and x-ray images (TEM and EDX) using carbon extraction replicas. The carbon extraction replicas were produced on longitudinal sections (20?30 mm). The magnification in the measurement was between 10 000-fold and 200 000-fold. Using these images, the precipitates can be divided into coarse and fine precipitates. Fine precipitates refer to all precipitates having a diameter of less than 30 nm. The other precipitates are referred to as coarse precipitates. By simple counting, the proportion of fine precipitates in the total number of precipitates in the measurement field is ascertained. For the fine precipitates, in addition, the average diameter is calculated by computer-assisted image analysis. In the inventive samples, the proportion of fine precipitates is more than 90%. The average diameter of the fine precipitates is additionally below 11 nm.

[0262] In addition, table 8 reports the grain diameter of the former austenite grains. For this purpose, the austenite grains were reconstructed by means of the ARPGE software from EBSD measurements. The software parameters were: [0263] Nishiyama-Wassermann orientation relationship [0264] Tolerance for grain identification 7? [0265] Tolerance for parent growth nucleation 7? [0266] Tolerance for parent grain growth 15? [0267] Minimum accepted grain size 10 pixels

[0268] For grain identification, a maximum variance in the orientation of 5? and a minimum grain diameter of 5 pixels according to DIN EN ISO 643 were assumed.

[0269] By way of example, FIG. 3 shows a corresponding reconstruction of the austenite from experiment no. 1. In this case, the average diameter of the former austenite grains is 7.5 ?m. In all inventive examples, the average grain diameter of the former austenite grains is below 14 ?m. In two experiments, the grain diameter of the former austenite grains has not been determined. The entry in table 8 therefore reads n.d. (not determined).

[0270] Table 9 reports the performance properties of the shaped sheet metal part. Firstly reported is the area occupied by pores in the alloy layer over a measurement length of 500 ?m. In all inventive examples, this area is less than 250 ?m.sup.2.

[0271] It is clearly apparent that, in the coating variants and ? and ? that do not contain any Mg, more pores are formed. This relates to experiments 1, 3, 4, 5, 7, 10, 12, 16 and 18. By contrast, the other, Mg-containing layers show fewer pores. The Nb content in the alloy layer which is reported in table 9 is an average of the Nb content in that layer. Although the Nb content in the alloy layer declines slightly toward the surface and is characterized approximately by a linear decline within the layer.

[0272] In addition, table 9 gives the proportion of the area occupied by pores with a diameter of not less than 0.1 ?m. In all inventive examples, this proportion is less than 10%. The total area of the pores and the proportion of pores larger than 0.1 ?m was ascertained using sections by computer-assisted image analysis. By way of example, FIG. 1a shows a section of experiment 1 with a fine pore structure, and FIG. 1b, by way of comparison, a section of experiment 12 with a coarser pore structure in the alloy layer. The coarser pores are clearly apparent in FIG. 1b as black spots in the alloy layer. FIGS. 2a and 2b show the effects of the coarser pores after a corrosion test. FIGS. 2a and 2b shows sections of the same experiments after a corrosion test in each case. For this purpose, the samples were transferred to a corrosive medium, and a current was applied in order to simulate prolonged electrochemical corrosion. The corrosive medium used was an aqueous 5% NaCl solution having a pH of 7. The current was 1 mA/cm.sup.2 for a duration of 6 hours. It is clearly apparent that, in FIG. 2b, the layer was almost completely detached, whereas, in FIG. 2a, the layer still had good connection to the substrate. The inventive examples with finer pores thus withstand corrosion much better than the reference examples with the coarser pore structure.

[0273] Table 8 also gives the welding range according to SEP 1220-2. In all variants of the invention, the welding range is at least 0.9 and not more than 1.6 kA.

[0274] Table 8 also gives the electrochemical potential. The electrochemical potential is determined according to DIN standard DIN 50918 (2018 September) (measurement of resting potential in homogeneous mixed electrodes). The absolute value reported should be regarded as a reference to the standard hydrogen electrode. A corrosive medium used in the measurement is an aqueous 5% NaCl solution having a pH of 7, which represents typical corrosion conditions in the automotive sector. It is clearly apparent that all samples have an electrochemical potential greater than ?0.50 V. [0275] 1. A flat steel product for hot forming, comprising a steel substrate composed of steel consisting of, as well as iron and unavoidable impurities (in % by weight), [0276] C: 0.06-0.5%, [0277] Si: 0.05-0.6%, [0278] Mn: 0.4-3.0%, [0279] Al: 0.06-1.0%, [0280] Nb: 0.001-0.2%, [0281] Ti: 0.001-0.10% [0282] B: 0.0005-0.01% [0283] P: ?0.03%, [0284] S: ?0.02%, [0285] N: ?0.02%, [0286] Sn: ?0.03%, [0287] As: ?0.01% [0288] and optionally one or more of the elements Cr, Cu, Mo, Ni, V, Ca, W in the following contents: [0289] Cr: 0.01-1.0%, [0290] Cu: 0.01-0.2%, [0291] Mo: 0.002-0.3%, [0292] Ni: 0.01-0.5%, [0293] V: 0.001-0.3%, [0294] Ca: 0.0005-0.005%, [0295] W: 0.001-1.0%. [0296] 2. The flat steel product according to sentence 1, [0297] characterized in that [0298] the following conditions are applicable to the Al/Nb ratio of Al content to Nb content: [0299] Al/Nb?20.0 when Mn?1.6% by weight [0300] and [0301] Al/Nb?30.0 when Mn?1.7% by weight. [0302] 3. The flat steel product according to either of sentences 1-2, wherein at least one of the following conditions is applicable to the element contents: [0303] Ti>3.42*N [0304] 0.7% by weight<Mn+Cr<3.5% by weight [0305] 4. The flat steel product according to any of the preceding sentences, characterized in that it has an anticorrosion coating on at least one side. [0306] 5. The flat steel product according to sentence 4, [0307] characterized in that [0308] the anticorrosion coating is an aluminum-based anticorrosion coating and has an alloy layer and an Al base layer. [0309] 6. The flat steel product according to sentence 5, [0310] characterized in that [0311] the alloy layer consists of 35-60% by weight of Fe, optional further constituents, the contents of which are limited to a total of not more than 5.0% by weight, and aluminum as the balance [0312] and/or [0313] the Al base layer consists of 1.0-15% by weight of Si, optionally 2-4% by weight of Fe, optionally up to 5.0% by weight of alkali metals or alkaline earth metals, optionally up to 10% Zn and optional further constituents, the contents of which are limited to a total of not more than 2.0% by weight, and aluminum as the balance. [0314] 7. The flat steel product according to any of sentences 1-6 [0315] characterized in that [0316] the flat steel product has a yield point with a continuous progression (Rp0.2) or a yield point with a difference (?Re) between the upper yield point limit (ReH) and lower yield point limit (ReL) of not more than 45 MPa [0317] and/or [0318] the flat steel product has a uniform expansion Ag of at least 10% [0319] and/or [0320] the flat steel product has an elongation at break A80 at least 15%, preferably at least 20%. [0321] 8. A process for producing a flat steel product for hot forming having an anticorrosion coating, comprising the following steps: [0322] a) providing a slab or thin slab composed of steel consisting of, as well as iron and unavoidable impurities (in % by weight), [0323] C: 0.06-0.5%, [0324] Si: 0.05-0.6%, [0325] Mn: 0.4-3.0%, [0326] Al: 0.06-1.0%, [0327] Nb: 0.001-0.2%, [0328] Ti: 0.001-0.10% [0329] B: 0.0005-0.01% [0330] P: ?0.03%, [0331] S: ?0.02%, [0332] N: ?0.02%, [0333] Sn: ?0.03% [0334] As: ?0.01% [0335] and optionally one or more of the elements Cr, Cu, Mo, Ni, V, Ca, W in the following contents: [0336] Cr: 0.01-1.0%, [0337] Cu: 0.01-0.2%, [0338] Mo: 0.002-0.3%, [0339] Ni: 0.01-0.5% [0340] V: 0.001-0.3% [0341] Ca: 0.0005-0.005% [0342] W: 0.001-1.0%, [0343] b) through-heating the slab or thin slab at a temperature (T1) of 1100-1400? C.; [0344] c) optionally pre-rolling the through-heated slab or thin slab to give an intermediate product having an intermediate product temperature (T2) of 1000-1200? C.; [0345] d) hot rolling to give a hot-rolled flat steel product, where the final rolling temperature (T3) is 750-1000? C.; [0346] e) optionally coiling the hot-rolled flat steel product, where the coiling temperature (T4) is not more than 700? C.; [0347] f) descaling the hot-rolled flat steel product; [0348] g) optionally cold-rolling the flat steel product, where the degree of cold rolling is at least 30%; [0349] h) annealing the flat steel product at an annealing temperature (T5) of 650-900? C.; [0350] i) cooling the flat steel product to a dipping temperature (T6) of 650-800? C., preferably 670-800? C.; [0351] j) coating the flat steel product cooled to dipping temperature with an anticorrosion coating by hot dip coating in a melt bath at a melt temperature (T7) of 660-800? C., preferably 680-740? C.; [0352] k) cooling the coated flat steel product to room temperature, where the first cooling time t.sub.MT in the temperature range between 600? C. and 450? C. is more than 10 s, especially more than 14 s, and the second cooling time t.sub.LT in the temperature range between 400? C. and 300? C. is more than 8 s, especially more than 12 s; [0353] l) optionally skin pass-rolling the coated flat steel product. [0354] 9. The process according to sentence 8, [0355] wherein the following conditions are applicable to the Al/Nb ratio of Al content to Nb content of the steel of the slab or thin slab: [0356] Al/Nb?20.0 when Mn?1.6% by weight [0357] and [0358] Al/Nb?30.0 when Mn?1.7% by weight. [0359] 10. The process according to either of sentences 8-9, [0360] characterized in that a melt bath used in the hot dip coating contains the anticorrosion material to be applied to the flat steel product in liquid form, consisting of up to 15% by weight of Si, optionally 2-4% by weight of Fe, optionally up to 5% by weight of alkali metals or alkaline earth metals and optionally up to 10% Zn, and optional further constituents, the contents of which are limited to a total of not more than 2.0% by weight, and aluminum as the balance. [0361] 11. A shaped sheet metal part formed from a flat steel product comprising a steel substrate composed of steel consisting of, as well as iron and unavoidable impurities (in % by weight), [0362] C 0.06-0.5%, [0363] Si: 0.05-0.6%, [0364] Mn: 0.4-3.0%, [0365] Al: 0.06-1.0%, [0366] Nb: 0.001-0.2%, [0367] Ti: 0.001-0.10% [0368] B: 0.0005-0.01% [0369] P: ?0.03%, [0370] S: ?0.02%, [0371] N: ?0.02%, [0372] Sn: ?0.03% [0373] As: ?0.01% [0374] and optionally one or more of the elements Cr, Cu, Mo, Ni, V, Ca, W in the following contents: [0375] Cr: 0.01-1.0%, [0376] Cu: 0.01-0.2%, [0377] Mo: 0.002-0.3%, [0378] Ni: 0.01-0.5% [0379] V: 0.001-0.3% [0380] Ca: 0.0005-0.005% [0381] W: 0.001-1.0% [0382] and an anticorrosion coating. [0383] 12. The shaped sheet metal part according to sentence 11, [0384] wherein the following conditions are applicable to the Al/Nb ratio of Al content to Nb content: [0385] Al/Nb?20.0 when Mn?1.6% by weight [0386] and [0387] Al/Nb?30.0 when Mn?1.7% by weight. [0388] 13. The shaped sheet metal part according to either of sentences 11-12, [0389] characterized in that [0390] the steel substrate of the shaped sheet metal part has a microstructure having at least in part more than 80% martensite and/or lower bainite, preferably more, at least in part more than 90% martensite and/or lower bainite, [0391] and where the former austenite grains of the martensite preferably have an average grain diameter of less than 14 ?m, especially less than 12 ?m, preferably less than 10 ?m. [0392] 14. The shaped sheet metal part according to any of sentences 11-13, [0393] characterized in that [0394] the shaped sheet metal part at least in part has a yield point of at least 950 MPa, especially at least 1100 MPa, preferably at least 1300 MPa, especially at least 1500 MPa, and/or [0395] the shaped sheet metal part at least in part has a tensile strength of at least 1000 MPa, especially at least 1100 MPa, preferably at least 1300 MPa, especially at least 1800 MPa, and/or [0396] the shaped sheet metal part at least in part has an elongation at break A80 of at least 4%, preferably at least 5%, more preferably at least 6%, [0397] and/or [0398] the shaped sheet metal part at least in part has a bending angle of at least 30?, especially at least 40?, preferably at least 50?. [0399] 15. The shaped sheet metal part according to any of sentences 11-14, [0400] characterized in that [0401] the shaped sheet metal part has fine precipitates in the microstructure, especially in the form of niobium carbonitrides and/or titanium carbonitrides. [0402] 16. The shaped sheet metal part according to any of sentences 11-15, [0403] characterized in that [0404] the electrochemical potential of the surface of the shaped sheet metal part in a corrosive medium is at least ?0.50 V. [0405] 17. The shaped sheet metal part according to any of sentences 11-16, [0406] characterized in that [0407] the anticorrosion coating is an aluminum-based anticorrosion coating and comprises an alloy layer and an Al base layer, [0408] and wherein, in the cross section of the alloy layer, over a measurement length of 500 ?m, the area occupied by pores in the alloy layer is less than 250 ?m.sup.2, [0409] and wherein, in particular, the proportion of the area occupied by pores having a diameter of not less than 0.1 ?m is less than 10%. [0410] 18. The shaped sheet metal part according to any of sentences 11-17, [0411] characterized in that [0412] the welding range is at least 0.9 kA. [0413] 19. The shaped sheet metal part according to any of sentences 11-18, [0414] characterized in that the Nb content in the alloy layer is greater than 0.010% by weight, [0415] preferably greater than 0.015% by weight, especially greater than 0.018% by weight. [0416] 20. A process for producing a shaped sheet metal part, comprising the following steps: [0417] a) providing a sheet metal blank made of a flat steel product according to any of sentences 1-7; [0418] b) heating the sheet metal blank in such a way that at least in part the AC3 temperature of the blank is exceeded and the temperature T.sub.ins of the blank on insertion into a forming tool provided for hot press forming (step c)) at least in part has a temperature above Ms+100? C., where Ms denotes the martensite start temperature; [0419] c) inserting the heated sheet metal blank into a forming tool, where the transfer time t.sub.trans required for the removal from the heating device and the insertion of the blank is not more than 20 s, preferably not more than 15 s; [0420] d) hot press forming the sheet metal blank to the shaped sheet metal part, wherein the blank, in the course of hot press forming, is cooled down to the target temperature T.sub.target over a period t.sub.tool of more than 1 s at a cooling rate r.sub.tool of at least in part more than 30 K/s, and optionally kept at that temperature; [0421] e) removing the shaped sheet metal part cooled to the target temperature T.sub.target from the tool; [0422] 21. The process according to sentence 20, wherein the temperature attained at least in part in the sheet metal blank in step b) is between Ac3 and 1000? C., preferably between 850? C. and 950? C. [0423] 22. The process according to any of sentences 20-22, wherein the target temperature T.sub.target of the shaped sheet metal part is at least partly below 400? C., preferably below 300? C.

TABLE-US-00001 TABLE 1 (steel types) Steel C Si Mn Al Cr Nb Ti B P S N Sn As Cu Mo Ca Ni Al/Nb A 0.22 0.145 1.1 0.18 0.2 0.032 0.017 0.0024 0.004 0.0007 0.0034 0.03 5.6 B 0.35 0.16 1.1 0.21 0.118 0.026 0.0096 0.0025 0.005 <0.0005 0.0035 0.005 0.003 0.019 0.005 0.001 0.032 8.1 C 0.131 0.20 1.17 0.13 0.21 0.021 0.004 0.0021 0.011 0.005 0.0059 0.04 0.025 0.0012 0.06 6.2 D* 0.087 0.12 1.52 0.05 0.1 0.04 0.008 0.0010 0.015 0.003 0.009 0.02 0.1 0.05 0.034 1.3 E* 0.235 0.3 1.3 0.05 0.28 0.003 0.040 0.0035 0.02 0.003 0.007 0.03 0.01 0.03 0.03 0.005 0.025 16.7 F* 0.37 0.3 1.4 0.05 0.18 0.003 0.040 0.0035 0.015 0.003 0.007 0.03 0.01 0.05 0.035 0.003 0.03 16.7 G 0.15 0.3 1.15 0.1 0.3 0.028 0.015 0.0030 0.015 0.005 0.0060 0.03 0.01 0.12 0.05 0.003 0.027 3.6 H 0.165 0.45 2.4 0.75 0.75 0.03 0.035 0.002 0.02 0.003 0.005 0.03 0.01 0.1 0.048 25.0 I 0.46 0.2 0.8 0.2 0.12 0.03 0.010 0.0025 0.005 0.0005 0.0035 0.005 0.003 0.019 0.005 0.001 0.019 6.7 J 0.23 0.17 0.6 0.07 0.25 0.005 0.021 0.0007 0.006 0.0007 0.0034 0.015 0.006 0.041 0.01 0.001 0.03 14.0 Balance: iron and unavoidable impurities. Figures each in % by weight; *noninventive reference examples

TABLE-US-00002 TABLE 2 (production conditions for flat steel product) Pro- cess var- T1 T2 T3 T4 DCR T5 T6 T7 t.sub.MT t.sub.LT iant [? C.] [? C.] [? C.] [? C.] [%] [? C.] [? C.] [? C.] [s] [s] a 1250 1075 850 630 55 773 685 678 15 13 b 1280 1110 860 620 50 787 708 686 15 13 c 1205 1060 820 550 55 768 684 683 18 15 d 1210 1120 910 580 55 770 685 685 18 15 e 1205 1065 830 555 45 655 650 680 15 13 f 1210 1110 900 575 70 760 720 700 20 18 g 1320 1080 840 620 50 805 715 710 23 20 h 1315 1090 910 655 55 870 800 720 25 23 i 1300 1120 830 585 35 895 800 725 30 28 j 1310 1095 915 630 65 830 740 710 25 25 k 1240 1080 870 620 50 823 728 710 35 30 l 1280 1100 870 630 55 808 713 708 18 15 m 1280 1085 870 580 50 793 715 708 22 20 n 1285 1105 885 640 65 755 685 675 13 11 Some figures rounded

TABLE-US-00003 TABLE 3 (coating variant) Layer thickness Coating Melt analysis (on one side) variant Si Fe Mg Others Al [?m] ? 9.5 3 0.3 <1% balance 10 ? 8 3.5 0.5 <1% balance 40 ? 10 3 <0.01 <1% balance 25 ? 8.2 3.8 0.25 <1% balance 27 ? 10.5 3.1 0.33 <1% balance 30 ? 8.1 3.9 <0.01 <1% balance 25

TABLE-US-00004 TABLE 4 (flat steel product) Thickness of Elongation Uniform Coating the steel Rp0.2 at break elongation experiment strip Process Coating Yield point or ReL ReH Rm A80 Ag no. Steel [mm] variant variant type [MPa] [MPa] [MPa] [%] [%] 1 A 1.5 m ? continuous 536 634 20 13 2 A 1.5 l ? continuous 488 618 21 14 3* D 1.4 a ? pronounced 436 447 600 19 13 4 C 1.5 b ? continuous 443 636 22 14 5 C 1.5 j ? continuous 464 671 21 12 6 C 1.6 k ? continuous 427 588 23 13 7 B 1.5 a ? continuous 493 717 20 12 8 B 1.5 j ? continuous 436 682 21 13 9 B 1.5 b ? continuous 451 693 20 12 10* F 1.6 a ? continuous 403 591 24 13 11* F 1.6 f ? continuous 411 603 20 13 12* E 1.6 c ? continuous 452 657 18 11 13* E 1.7 c ? continuous 395 602 19 12 14 G 1.6 h ? continuous 401 553 23 12 15 H 1.6 d ? continuous 483 622 20 11 16 I 1.4 e ? continuous 511 723 16 10 17* D 1.6 g ? pronounced 408 418 527 21 13 18* F 1.5 i ? continuous 371 553 26 14 19 J 1.5 n ? continuous 444 632 19 13 20 A 1.5 m ? n.d. n.d. n.d. n.d. n.d. n.d. *noninventive reference examples

TABLE-US-00005 TABLE 5 (hot forming parameters) Average heating Furnace Cooling Hot rate r.sub.furnace Transfer dew rate forming [30-700? C.] T.sub.furnace t.sub.furnace time point T.sub.ins T.sub.tool t.sub.tool r.sub.tool T.sub.target variant [K/s] [? C.] [min.] [s] [? C.] [? C.] [? C.] [s] [K/s] [? C.] I 8 925 6 8 ?5 800 RT 15 50 50 II 5 920 6 6 ?5 815 RT 6 300 40 III 15 920 5 5 ?5 830 RT 15 50 50 IV 10 880 6 7 ?5 740 100 10 50 120 V 8 950 3 12 ?5 770 100 10 50 120 VI 10 925 4 7 ?5 810 RT 10 450 40 VII 5 920 10 7 ?5 807 RT 15 50 50 VIII 5 920 12 8 ?5 796 RT 15 100 50 IX 5 920 12 14 ?5 728 100 10 200 110 X 5 920 6 10 ?5 792 550 15 30 560 Some figures rounded

TABLE-US-00006 TABLE 6 (hot forming parameters) Average heating Cooling Hot rate r.sub.furnace Transfer Dew rate forming [30-700? C.] T.sub.intake T.sub.max T.sub.exit t.sub.furnace time point T.sub.ins T.sub.tool t.sub.tool r.sub.tool T.sub.target variant [K/s] [? C.] [? C.] [? C.] [min.] [s] [? C.] [? C.] [? C.] [s] [K/s] [? C.] A.I 4 700 930 930 6 8 ?5 795 RT 15 100 50 A.II 5 750 910 910 6 8 ?5 775 RT 15 100 50 A.III 6 800 930 930 5 6 ?5 820 RT 15 100 50 A.IV 7.5 830 930 930 5 10 ?5 770 RT 15 100 50 A.V 8 850 950 950 4.5 8 ?15 810 RT 15 100 50 A.VI 6 750 955 910 5 6 +5 792 RT 15 100 50 A.VII 7 830 950 950 4.5 12 +5 776 RT 15 100 50 A.VIII 4.5 750 880 880 6 8 +15 761 RT 15 100 50 A.IX 5 800 880 880 6 10 +15 745 RT 15 100 50 A.X 5.5 800 920 880 6 8 +20 760 RT 15 100 50 A.XI 6 800 930 930 12 7 ?20 804 RT 15 100 50 Some figures rounded

TABLE-US-00007 TABLE 7 (shaped sheet metal part) Forming Coating Hot Yield Tensile Bending experiment experiment Process Coating forming point strength A80 angle no. no. Steel variant variant variant [MPa] [MPa] [%] [?] 1 1 A m ? II 1203 1451 5.4 64 2 2 A l ? I 1152 1390 5.8 67 3* 3 D a ? I 444 683 16.6 130 4 4 C b ? I 1002 1224 6.1 87 5 5 C j ? V 971 1182 5.4 84 6 6 C k ? VII 993 1212 5.3 82 7 7 B a ? II 1422 1856 5.3 45 8 8 B j ? III 1411 1846 5.5 46 9 9 B b ? IV 1391 1823 5.0 43 10* 10 F a ? II 1400 1854 5 43 11* 11 F f ? IX 1380 1830 5.2 44 12* 12 E c ? II 1134 1486 5.6 60 13* 13 E c ? I 1136 1484 5.8 54 14 14 G h ? II 982 1197 5.5 82 15 15 H d ? X 853 1107 7.2 87 16 16 I e ? VIII 1622 1893 4.5 36 17* 17 D g ? V 420 660 17.2 135 18* 18 F i ? IX 1361 1816 5.4 45 19 20 A m ? X 449 634 18.2 134 20 20 A m ? VI 1218 1509 5.1 62 21 19 J n ? I 1189 1478 5.5 58 22 19 J n ? IV 1158 1402 5.8 63 23 1 A m ? A.III 1162 1471 5.4 61 24 1 A m ? A.VI 1195 1482 5.1 59

TABLE-US-00008 TABLE 8 (microstructure) Microstructure Forming Fine (Nb, Ti)(C, N) Grain diameter experiment Residual precipitates Proportion of the former no. Martensite Bainite Ferrite austenite [%]/average diameter austenite grains 1 99.9 0.1 94%/7 nm 7.5 ?m 2 99.5 0.5 n.d. 6.8 ?m 3* 38.5 martensite + bainite 60% 1.5 25%/12 nm 21 ?m 4 100 97%/5 nm 9.5 ?m 5 99 1 96%/5 nm 11 ?m 6 100 98%/5 nm 10 ?m 7 99.9 0.1 96%/6 nm 7.1 ?m 8 99.9 0.1 94%/8 nm 6.4 ?m 9 99.9 0.1 94%/6 nm 6.1 ?m 10* 99.9 0.1 Coarse precipitates only 9 ?m 11* 100 Coarse precipitates only 11 ?m 12* 100 Coarse precipitates only 14.8 ?m 13* 99.9 0.1 Coarse precipitates only 13.7 ?m 14 99.5 0.5 97%/7 nm 9.5 ?m 15 95.5% bainite + martensite 4.5 98%/7 nm n.d. 16 100 0 n.d. 10.8 mm 17* 42% martensite + bainite 57 1.0 23%/13 ?m 19 ?m 18* 100 Coarse precipitates only 12 ?m 19 32% martensite + bainite 67% 1.0 n.d. n.d. 20 99.5 0.5 n.d. 5.8 ?m 21 99.9 0.1 n.d. n.d. 22 97.5 2.5 . n.d. n.d. 23 100 n.d. n.d. n.d. 24 100 n.d. n.d. n.d. *noninventive reference examples

TABLE-US-00009 TABLE 9 (properties of the shaped sheet metal part) Area occupied by Proportion of the pores over a area occupied by measurement pores with a Average Nb Forming length of 500 ?m in diameter of not content in the alloy Welding experiment the alloy layer in less than 0.1 ?m layer in % by Electrochemical range in no. ?m.sup.2 in % weight potential in V kA 1 200 7 0.027 ?0.325 1.2 2 85 4 0.029 ?0.351 1.4 3* 175 35 0.030 ?0.301 0.8 4 180 7 0.018 ?0.338 1.2 5 200 8 0.019 ?0.378 1.1 6 75 4 0.020 ?0.370 1.5 7 190 5 0.021 ?0.325 1.3 8 100 2.5 0.022 ?0.338 1.4 9 60 2 0.019 ?0.384 1.4 10* 185 23 0.001 ?0.447 0.8 11* 135 42 0.002 ?0.418 0.6 12* 185 30 0.001 ?0.417 0.8 13* 100 25 0.001 ?0.435 0.8 14 110 4 0.024 ?0.338 1.6 15 125 7 0.026 ?0.383 1.4 16 190 7 0.025 ?0.412 0.9 17* 110 27 0.031 ?0.305 0.8 18* 200 45 0.001 ?0.407 0.5 19 135 6 0.025 ?0.418 1.3 20 74 4 0.029 ?0.364 1.5 *noninventive reference examples