MANUFACTURE OF SEMI-FINISHED PRODUCTS AND STRUCTURAL COMPONENTS WITH LOCALLY DIFFERENT MATERIAL THICKNESSES

Abstract

A method for producing a semifinished product with locally different material thicknesses may involve preparing a multilayer, metal material composite, which has a plurality of layers with different ductilities, and rolling the material composite in a method for flexible rolling through a rolling gap formed between two rollers. The rolling gap may be configured such that regions with different material thicknesses are formed. In some cases, the multilayer, metal material composite is rolled at room temperature. Further, the plurality of layers of the multilayer, metal material composite may include a first outer layer disposed on a first side of a middle layer and a second outer layer disposed on a second side of the middle layer, with the second side of the middle layer being opposite the first side.

Claims

1.-15. (canceled)

16. A method for producing a semifinished product with locally different material thicknesses, the method comprising: preparing a multilayer, metal material composite, wherein the multilayer, metal material composite has a plurality of layers with different ductilities; and rolling the multilayer, metal material composite by way of a method for flexible rolling through a rolling gap formed between two rollers, wherein the rolling gap is configured such that regions with different material thicknesses are formed in the multilayer, metal material composite.

17. The method of claim 16 wherein the multilayer, metal material composite is rolled at room temperature.

18. The method of claim 16 wherein the multilayer, metal material composite is rolled at a temperature above an austenitizing temperature of the plurality of layers.

19. The method of claim 16 wherein the multilayer, metal material composite is rolled at a temperature in a range from 700 C. to 1300 C.

20. The method of claim 16 wherein the plurality of layers of the multilayer, metal material composite comprises a first outer layer disposed on a first side of a middle layer and a second outer layer disposed on a second side of the middle layer, the second side of the middle layer being opposite the first side.

21. The method of claim 20 wherein a coating is disposed on a side of the first outer layer that is opposite the middle layer.

22. The method of claim 20 wherein the multilayer, metal material composite has a symmetrical layer structure with respect to the middle layer.

23. The method of claim 20 wherein the first and second outer layers have a higher ductility than the middle layer.

24. The method of claim 20 wherein the middle layer, the first outer layer, and the second outer layer are comprised of a carbon-containing steel, wherein a carbon content in the first and second outer layers is lower than in the middle layer.

25. The method of claim 20 wherein the middle layer, the first outer layer, and the second outer layer are comprised of a manganese-containing steel, wherein a manganese content in the first and second outer layers is lower than in the middle layer.

26. The method of claim 20 wherein the middle layer, the first outer layer, and the second outer layer are comprised of a silicon-containing steel, wherein a silicon content in the first and second outer layers is lower than or equal to a silicon content in the middle layer.

27. The method of claim 20 wherein the middle layer, the first outer layer, and the second outer layer are comprised of a chromium-containing steel, wherein a chromium content in the first and second outer layers is lower than or equal to a chromium content in the middle layer.

28. The method of claim 20 wherein the middle layer, the first outer layer, and the second outer layer are comprised of at least one of a carbon-containing steel, a manganese-containing steel, a silicon-containing steel, or a chromium-containing steel, wherein a sum of a carbon content, a manganese content, a silicon content, and a chromium content in the first and second outer layers is less than a sum of a carbon content, a manganese content, a silicon content, and a chromium content in the middle layer.

29. The method of claim 20 wherein a thickness of the first and second outer layers is in a range of 5% to 40% of a total thickness of the multilayer, metal material composite.

30. A method for producing a structural component with locally different material thicknesses, the method comprising: preparing a semifinished product, wherein the semifinished product has a plurality of layers with different ductilities; and rolling the semifinished product by way of a method for flexible rolling through a rolling gap formed between two rollers, wherein the rolling gap is configured such that regions with different material thicknesses are formed in the semifinished product, wherein the semifinished product is formed in a hot state to obtain the structural component.

31. A semifinished product with locally different material thicknesses, the semifinished product comprising a plurality of layers with different ductilities, wherein the plurality of layers comprises a first outer layer disposed on a first side of a middle layer and a second outer layer disposed on a second side of the middle layer, the second side of the middle layer being opposite the first side, wherein the plurality of layers has a symmetrical layer structure with respect to the middle layer, wherein the first and second outer layers have a higher ductility than the middle layer.

32. The semifinished product of claim 31 comprising a coating disposed on a side of the first outer layer that is opposite the middle layer.

33. The method of claim 31 wherein a thickness of the first and second outer layers is in a range of 5% to 40% of a total thickness of the semifinished product.

34. The method of claim 31 wherein the middle layer, the first outer layer, and the second outer layer are comprised of at least one of a carbon-containing steel, a manganese-containing steel, a silicon-containing steel, or a chromium-containing steel, wherein a sum of a carbon content, a manganese content, a silicon content, and a chromium content in the first and second outer layers is less than a sum of a carbon content, a manganese content, a silicon content, and a chromium content in the middle layer.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0031] FIG. 1 shows a schematic sectional illustration of an apparatus for flexible rolling.

[0032] FIG. 2 shows a schematic sectional illustration of a multilayer, metal material composite.

[0033] FIG. 3 shows a sectional illustration of a first material composite.

[0034] FIG. 4 shows a sectional illustration of a second material composite.

[0035] FIG. 5 shows the profile of the carbon content over the cross section of a material composite.

[0036] FIG. 6 shows flow curves of different layers of a material composite and of a material composite.

[0037] FIG. 7 shows a sectional illustration of a multilayer, metal material composite after cold rolling.

[0038] FIG. 8 shows a sectional illustration of the material composite from FIG. 7 after hot forming.

[0039] FIG. 9 shows the tensile strength and the yield strength of the material composite after hot forming for different material thicknesses.

[0040] FIG. 10 shows the bending force, the bending angle and the energy of the material composite after hot forming for different material thicknesses.

EMBODIMENTS OF THE INVENTION

[0041] FIG. 1 illustrates by way of example an apparatus 1 for flexible rolling in which the method according to the invention can be realized. The apparatus comprises two rollers 2, 3 between which a rolling gap 4 is formed. A first roller 3 is formed in a stationary manner, while a second roller 4 is movable linearly on a straight line G connecting the axes of rotation of the two rollers 3, 4. Via the movement of the second roller 4, the rolling gap 4 can be set. Thus, by means of the apparatus 1, the degree of rolling can be set, in particular continuously.

[0042] A multilayer, metal material composite 5, which comprises a plurality of layers with different ductilities, is fed to the rolling gap 4. If the rolling gap 4 is increased in size, regions 6 with a greater material thickness are created in the rolled material composite. By contrast, if the rolling gap 4 is reduced in size, regions 7 with a smaller material thickness are created in the rolled material composite.

[0043] The apparatus 1 allows both flexible rolling at room temperature (cold rolling) and flexible rolling at increased temperature (hot rolling). To this end, the material composite can be heated to a temperature above the austenitizing temperature of the layers of the material composite, for example to a temperature in the range from 700 C. to 1300 C., preferably in the range from 880 C. to 920 C., particularly preferably to 900 C., and then rolled.

[0044] FIG. 2 shows a schematic sectional illustration of a strand-form, in particular strip-form, material composite 5. The material composite 5 comprises a middle layer 12. On a first side of the middle layer 12, a first outer layer 11 is arranged, and on a second side of the middle layer 12 on the opposite side from the first side, a second outer layer 13 is arranged. Coatings 10, 14 are provided on the outer sides of the outer layers which are on the opposite side from the middle layer 12. Thus, the material composite 5 has a symmetrical structure with regard to the middle layer 12. The materials of the outer layers 11, 13 are selected such that they consist of an identical steel material. The middle layer 12 is made of a steel material different than the outer layers 11, 13. The steel materials of the middle layer 12 and of the outer layers 11, 13 are selected such that the outer layers 11, 13 have a higher ductility and lower degree of hardening than the middle layer 12. In addition, the outer layers 11, 13 have a lower hardening capacity than the middle layer 12.

[0045] FIG. 3 shows a section through a first exemplary embodiment of a material composite 5.1. The material composite 5.1 comprises a middle layer 12 made of a steel material with the following composition, which will be denoted material A1 in the following text: [0046] Carbon: 0.20 to 0.27% by weight; [0047] Silicon: 0.15 to 0.35% by weight; [0048] Manganese: 1.10 to 1.40% by weight; [0049] Aluminum: 0.015 to 0.060% by weight; [0050] Chromium: 0.05 to 0.25% by weight; [0051] Titanium: 0.015 to 0.040% by weight; [0052] Boron: 0.0015 to 0.0040% by weight; [0053] Phosphorus: 0.025% by weight; [0054] Sulfur: 0.004% by weight; [0055] Copper: 0.15% by weight; [0056] Molybdenum: 0.10% by weight; [0057] Nitrogen: 0.01% by weight [0058] Nickel: 0.15% by weight; [0059] Niobium: 0.006% by weight; [0060] Vanadium: 0.01% by weight; [0061] Tin: 0.03% by weight; [0062] Calcium: 0.0050% by weight; [0063] Arsenic: 0.01% by weight; [0064] Cobalt: 0.01% by weight. [0065] Measurement data from a chemical analysis of the material A1 in % by weight can be found in Table 1.

[0066] Alternatively, the middle layer 12 can be made from a steel material with the following composition, which is denoted material A2 in the following text: [0067] Carbon: 0.30 to 0.50% by weight; [0068] Silicon: 0.10 to 0.35% by weight; [0069] Manganese: 1.10 to 1.50% by weight; [0070] Aluminum: 0.015 to 0.060% by weight; [0071] Chromium: 0.05 to 0.45% by weight; [0072] Titanium: 0.015 to 0.045% by weight; [0073] Boron: 0.0015 to 0.0045% by weight; [0074] Phosphorus: 0.025% by weight; [0075] Sulfur: 0.004% by weight; [0076] Copper: 0.15% by weight; [0077] Molybdenum: 0.1% by weight; [0078] Nitrogen: 0.01% by weight [0079] Nickel: 0.1% by weight; [0080] Niobium: 0.006% by weight; [0081] Vanadium: 0.01% by weight; [0082] Tin: 0.03% by weight; [0083] Calcium: 0.0010 to 0.0050% by weight; [0084] Arsenic: 0.01% by weight; [0085] Cobalt: 0.01% by weight.

[0086] Measurement data from a chemical analysis of the material A2 in % by weight can be found in Table 1.

[0087] The outer layers 11, 13 of the material composite 5.1 shown in FIG. 3 are made from a steel material with the composition described below. This is denoted material B1. [0088] Carbon: 0.055 to 0.085% by weight; [0089] Silicon: 0.12 to 0.29% by weight; [0090] Manganese: 0.70 to 0.90% by weight; [0091] Aluminum: 0.020 to 0.060% by weight; [0092] Chromium: 0.20% by weight; [0093] Titanium: 0.01% by weight; [0094] Phosphorus: 0.010 to 0.030% by weight; [0095] Sulfur: 0.012% by weight; [0096] Copper: 0.20% by weight; [0097] Molybdenum: 0.045% by weight; [0098] Nitrogen: 0.01% by weight [0099] Nickel: 0.20% by weight; [0100] Niobium: 0.010 to 0.030% by weight;

[0101] Measurement data from a chemical analysis of the material B1 in % by weight can be found in Table 1.

[0102] Alternatively, the outer layers 11, 13 can be made from a steel material with the following composition, which is denoted material B2 in the following text: [0103] Carbon: 0.01 to 0.06% by weight; [0104] Silicon: 0.10% by weight; [0105] Manganese: 0.02 to 0.35% by weight; [0106] Aluminum: 0.015 to 0.065% by weight; [0107] Chromium: 0.10% by weight; [0108] Titanium: 0.003 to 0.25% by weight; [0109] Boron: 0.0004% by weight; [0110] Phosphorus: 0.020% by weight; [0111] Sulfur: 0.020% by weight; [0112] Copper: 0.10% by weight; [0113] Molybdenum: 0.025% by weight; [0114] Nitrogen: 0.01% by weight [0115] Nickel: 0.15% by weight; [0116] Niobium: 0.006% by weight; [0117] Tin: 0.015% by weight;

[0118] Measurement data from a chemical analysis of the material B2 in % by weight can be found in Table 1.

[0119] In the material composite 5.1 shown in FIG. 3, the outer layers 11, 13 made of the material B1 have a thickness which exhibits in each case about 10% of the total thickness of the material composite 5.1. The thickness of the middle layer 12 made of the material A1 is about 80% of the total thickness of the material composite 5.1. Provided on each surface of the outer layers 11, 13 is a coating 10, 14, which has a thickness which is less than 1% of the total thickness of the material composite 5.1. The coatings 10, 14 are aluminum-silicon coatings.

[0120] FIG. 4 shows a second exemplary embodiment of a material composite 5.2. In this material composite 5.2, the middle layer 12 is likewise formed from the material A1 and the outer layers 11, 13 are formed from the material B1. The outer layers 11, 13 each have a thickness of about 20% of the total thickness of the material composite 5.2, and the middle layer 12 has a thickness of about 60% of the total thickness of the material composite 5.2. Provided on each surface of the outer layers 11, 13 is a coating 10, 14, which has a thickness which is less than 1% of the total thickness of the material composite 5.2. The coatings 10, 14 are aluminum-silicon coatings.

[0121] FIG. 5 illustrates the carbon content of a material composite 5.3 which comprises a middle layer 12 made of the material A2 and outer layers 11, 13 made of the material B1. The outer layers 11, 13 each have a thickness of about 10% of the total thickness of the material composite 5.3. Furthermore, the carbon content of a material composite 5.4 which comprises a middle layer 12 made of the material A2 and outer layers 11, 13 made of the material B1 is shown. The outer layers 11, 13 of the material composite 5.4 each have a thickness of about 20% of the total thickness of the material composite 5.4. The carbon content is plotted over the material thickness, wherein the axis of symmetry, extending through the middle layer 12, of the material composite 5.3, 5.4 is at the sheet thickness of 0 m. It can be seen that the carbon content in the middle layer 12 has a maximum and decreases continuously in the transition regions from the middle layer 12 to the outer layers 11, 13. In the outer layers 11, 13, the carbon content reaches a minimum. In this respect, the carbon content in the outer layers 11, 13 is less than in the middle layer. In each particular material composite 5.3, 5.4, diffusion processes during the production and processing thereof have the result that the individual elements of each particular steel material diffuse from those regions which have a higher concentration of each particular element into those regions which have a lower concentration. For this reason, the material composites 5.3, 5.4 in the outer layers 11, 13 have a concentration of carbon which is increased compared with the material B1 used to form each particular outer layer 11, 13.

[0122] FIG. 6 shows flow curves for the harder material A1 used for the middle layer 11 and for the softer materials B1 and B2 used for the outer layers 11, 13. Furthermore, flow curves of the material composite 5.1 according to FIG. 3 and of the material composite 5.2 according to FIG. 4 are given. The flow curves were taken at a strain rate of 0.004 1/s to SEP 1220. It can be seen that the flow stress kf of the material A1 of the middle layer 12 is greater than the flow stress kf of the material B1, B2 of the outer layers 11, 13, in particular in a range of the degree of forming phi of 0 to 0.1. The flow stress kf of the material B1, B2 of the outer layers 11, 13 is in a range of less than 550 MPa at a degree of forming phi in the range from 0 to 0.15. The flow stress kf of the material A1 of the middle layer has, at a degree of forming phi of 0.05 to 0.15, a flow stress kf of greater than 500 MPa.

[0123] FIG. 7 shows the layer structure of a material composite 5 processed by flexible rolling at room temperature by means of an apparatus 1 according to FIG. 1. The degree of rolling was 50% in the portion shown. It can clearly be seen that the layer structure of the material composite 5 has been retained. In particular, the individual layers of the material composite 5 were not separated from one another.

[0124] Furthermore, the relative ratio of the thicknesses of the individual layers 10, 11, 12, 13, 14 of the material composite 5 is retained during flexible rolling. Therefore, thicker regions and thinner regions of the material composite 5, which have an identical relative layer thickness distribution, can be produced.

[0125] FIG. 8 shows a corresponding region of the material composite 5 from FIG. 7 after a subsequent heating step for hot forming, in particular during press hardening. As a result of the heating above the austenitizing temperature, diffusion processes for example of the carbon are accelerated, with the result that mixing of the individual layers occurs. In addition, the constituents of the coating 10 are mixed with the outer layers 11, 13 adjoining the coating. On account of the mixing, homogenization of the material properties in the cross-sectional direction of the material composite 5 occurs.

[0126] FIG. 9 shows the tensile strength and the yield strength for regions with different material thicknesses. In FIG. 10, the bending force, the bending angle and the energy, likewise for different material thicknesses, are plotted. The measurement of the strength and of the bending angle for regions of the produced structural component with different material thicknesses yielded virtually constant values for material thicknesses in the range from 0.8 mm to 1.8 mm. It was thus found that both regions of the material composite 5 with a smaller material thickness and regions with a greater material thickness have a virtually identical hardening behavior, this being attributable to the identical relative layer thickness distribution in these regions. In this respect, it is not possible to establish any dependence of the material properties, in particular of the strength and of the bending angle, in the material composite 5, in contrast to monolithic materials. On account of this hardening behavior which is independent of the material thickness, the maximum producible residual ductility of the material composite 5 is not limited by the minimum material thickness, and so greater thickness differences can be set during flexible rolling. Therefore, the weight of the structural components produced can be reduced further.

LIST OF REFERENCE SIGNS

[0127] 1 Apparatus for flexible rolling

[0128] 2 Roller

[0129] 3 Roller

[0130] 4 Rolling gap

[0131] 5 Material composite

[0132] 5.1 Material composite

[0133] 5.2 Material composite

[0134] 5.3 Material composite

[0135] 5.4 Material composite

[0136] 6 Thick region

[0137] 7 Thin region

[0138] 10 Coating

[0139] 11 Outer layer

[0140] 12 Middle layer

[0141] 13 Outer layer

[0142] 14 Coating

[0143] A1, A2 Material of the middle layer

[0144] B1, B2 Material of the outer layers

[0145] G Straight line