ULTRAHIGH STRENGTH MULTIPHASE STEEL AND METHOD FOR PRODUCING A STEEL STRIP FROM SAID MULTIPHASE STEEL

Abstract

The invention relates to an ultrahigh strength multiphase steel having a minimum tensile strength of 980 MPa containing (in wt. %): C0.075 to 0.115; Si0.400 to 0.500; Mn1.900 to 2.350; Cr0.250 to 0.400; Al0.010 to 0.060; N0.0020 to 0.0120; P0.020; S0.0020; Ti0.005 to 0.060; Nb0.005 to 0.060; V0.005 to 0.020; B0.0005 to 0.0010; Mo0.200 to 0.300; Ca0.0010 to 0.0060; Cu0.050; Ni0.050; Sn0.040; H0.0010; and residual iron, including customary steel-accompanying smelting-related impurities, wherein the total content of Mn+Si+Cr is 1.750 to 2.250 wt. % with a view to a processing window which is as wide as possible during the annealing process, in particular during the continuous annealing process, of cold strips of said steel.

Claims

1.-41. (canceled)

42. A method, comprising: producing a pre-strip from a multi-phase steel in a state of a slab, with the multi-phase steel having a minimum tensile strength of 980 MPa in a non-quenched state containing (in wt. %) C0.075 to 0.115 Si0.400 to 0.500 Mn1.900 to 2.350 Cr0.250 to 0.400 Al0.010 to 0.060 N0.0020 to 0.0120 P0.020 S0.0020 Ti0.005 to 0.060 Nb0.005 to 0.060 V0.005 to 0.020 B0.0005 to 0.0010 Mo0.200 to 0.300 Ca0.0010 to 0.0060 Cu0.050 Ni0.050 Sn0.040 H0.0010, with the remainder being iron, including typical steel-associated, smelting-related impurities, wherein the total content of Mn-Si+Cr is 1.750 wt. % to 2.250 wt. % with regard to a processing window which is as wide as possible during annealing of cold strips of this steel; hot-rolling the pre-strip into a steel strip with a hot strip thickness to be achieved; proceeding from a previously fixed slab thickness and a previously selected pre-strip having a defined but variable thickness, hot-rolling hot strips with a same thickness with a degree of thinning by rolling of 72% to 87% with end thickness to be achieved; cold-rolling the hot strip into a cold strip with an end thickness to be achieved, heating the steel strip cold-rolled to the end thickness during the continuous annealing to an annealing temperature in a range of approximately 700 to 950 C. to produce a required multi-phase microstructure; cooling the annealed steel strip from the annealing temperature at a cooling rate between approximately 15 and 100 C./s to a first intermediate temperature of approximately 300 to 500 C. followed by a cooling rate between approximately 15 and 100 C./s to a second intermediate temperature of approximately 160 to 250 C., and cooling the steel strip in air at a cooling rate of approximately 2 to 30 C./s until room temperature is reached or at a cooling rate between approximately 15 and 100 C./s from the first intermediate temperature to room temperature, or cooling the annealed steel strip to a temperature of approximately 400 to 470 C. such that cooling is stopped prior to entry of the steel strip into a melting bath, then the steel strip undergoes a hot-dip finishing procedure, and after undergoing the hot-dip finishing procedure, continuing cooling at a cooling rate between approximately 15 and 100 C./s to an intermediate temperature of approximately 200 to 250 C., and cooling the steel strip in air at a cooling rate of approximately 2 to 30 C./s until room temperature is reached, or cooling the annealed steel strip to an intermediate temperature of approximately 200 to 250 C. such that prior to entry of the steel strip into a melting bath, maintaining the steel strip at the intermediate temperature for approximately 1 to 20 s, then the steel strip is heated to a temperature of approximately 400 to 470 C., undergoes a hot-dip finishing procedure, and after undergoing the hot-dip finishing procedure, is cooled again at a cooling rate between approximately 15 and 100 C./s to an intermediate temperature of approximately 200 to 250 C., and subsequently cooled in air at a cooling rate of approximately 2 to 30 C./s to room temperature.

43. The method of claim 42, wherein the cold strip is continuously annealed.

44. The method of claim 43, wherein, proceeding from a selected hot strip having a specific thickness or selected hot strips having different thicknesses, cold strips with degrees of thinning by cold-rolling of 10% to 70% are produced with the end thickness to be achieved.

45. The method of claim 43, further comprising, during the continuous annealing, increasing an oxidation potential during annealing with an installation configuration comprised of a direct fired furnace region (NOF) and a radiant tube furnace (RTF) by a CO content in the NOF of less than 4 vol. %; and setting in the RTF an oxygen partial pressure of a furnace atmosphere, which is reducing for iron, in accordance with a following equation,
18>Log pO.sub.2-5*Si.sup.0.3-2.2*Mn.sup.0.45-0.1*Cr.sup.0.4-12.5*(ln B).sup.0.25 wherein Si, Mn, Cr and B designate corresponding alloy proportions in steel in wt. %, pO.sub.2 designates the oxygen partial pressure in mbar, and wherein in order to avoid oxidation of the steel strip directly prior to dipping in the melting bath a dew point of a gas atmosphere is set at 30 C. or below.

46. The method of claim 43, further comprising, during the continuous annealing, increasing an oxidation potential during annealing with an installation configuration comprised of only a radiant tube furnace (RFT) by setting in the RTF an oxygen partial pressure of a furnace atmosphere, which is reducing for iron, in accordance with a following equation,
12>Log pO.sub.2-5*Si.sup.0.25-3*Mn.sup.0.5-0.1*Cr.sup.0.5-7*(ln B).sup.0.5 wherein Si, Mn, Cr and B designate corresponding alloy proportions in steel in wt. %, pO.sub.2 designates the oxygen partial pressure in mbar, and wherein in order to avoid oxidation of the steel strip directly prior to dipping in the melting bath the dew point of the gas atmosphere is set at 30 C. or below.

47. The method of claim 42, further comprising temper-rolling the steel strip after undergoing annealing or the hot-dip finishing procedure.

48. The method of claim 42, further comprising stretch-bending-straightening the steel strip after undergoing annealing or the hot-dip finishing procedure.

49. The method of claim 42, further comprising: cutting a blank from the steel strip; heating the blank to a temperature above Ac3; deforming the heated blank into a component; and hardening the component in a tool or in air.

50. A steel strip produced by a method as set forth in claim 42, said steel strip comprising a minimum hole expansion value according to ISO 16630 of at least 20%.

51. The steel strip of claim 50, wherein the minimum hole expansion value according to ISO 16630 is 25%.

52. The steel strip of claim 50, comprising a minimum bending angle according to VDA 238-100 of 70 in a longitudinal direction or transverse direction.

53. The steel strip of claim 50, comprising a minimum bending angle according to VDA 238-100 of 85 in a longitudinal direction or transverse direction.

54. The steel strip of claim 50, comprising a minimum product value Rm of 100000 MPa, wherein Rm is a tensile strength, and is a bending angle according to VDA 238-100.

55. The steel strip of claim 50, comprising a minimum product value Rm of 120000 MPa, wherein Rm is a tensile strength, and is a bending angle according to VDA 238-100.

56. The steel strip of claim 50, comprising a delayed fracture free state for at least 6 months thus meeting the requirements of SEP 1970 for hole pull and hoop test pieces.

57. A steel strip, comprising in wt. %: C0.075 to 0.115 Si0.400 to 0.500 Mn1.900 to 2.350 Cr0.250 to 0.400 Al0.010 to 0.060 N0.0020 to 0.0120 P0.020 S0.0020 Ti0.005 to 0.060 Nb0.005 to 0.060 V0.005 to 0.020 B0.0005 to 0.0010 Mo0.200 to 0.300 Ca0.0010 to 0.0060 Cu0.050 Ni0.050 Sn0.040 H0.0010, with the remainder being iron, including typical steel-associated, smelting-related impurities, wherein a total content of Mn-Si+Cr is 1.750 wt. % to 2.250 wt. %, said steel strip comprising a minimum hole expansion value according to ISO 16630 of at least 20%.

Description

[0228] Further features, advantages and details of the invention will be apparent from the following description of exemplified embodiments Illustrated in a drawing.

[0229] In the figures:

[0230] FIG. 1 shows (schematically) the process chain for the production of a strip consisting of the steel according to the invention,

[0231] FIG. 2 shows (schematically) the time-temperature curve of the process steps of hot-rolling and cold-rolling and continuous annealing (with optional hot-dip finishing), as well as component manufacturing, optional quenching (air-hardening) and optional tempering by way of example for the steel according to the invention,

[0232] FIG. 3 shows the chemical composition (examples 1 to 4) of the steel according to the invention,

[0233] FIG. 4a shows mechanical characteristic values (transversely to the rolling direction) of the steel according to the invention in the hot-rolled state (HR),

[0234] FIG. 4b shows mechanical characteristic values (transversely to the rolling direction) of the steel according to the invention in the cold-rolled state (CR),

[0235] FIG. 5a shows solidification behavior during cold-rolling of the steel according to the invention, characteristic values transversely to the rolling direction,

[0236] FIG. 5b shows solidification behavior during cold-rolling of the steel according to the invention, cold flow curve,

[0237] FIG. 6a shows mechanical characteristic values (transversely to the rolling direction) of the steel according to the invention in the fine sheet state (HDG),

[0238] FIG. 6b shows results of the hole expansion tests according to ISO 16630 and of the plate bending test according to VDA 238-100 on the steel according to the invention, in the fine sheet state (HDG),

[0239] FIG. 7a shows mechanical characteristic values (transversely to the rolling direction) of the steel according to the invention in the state HR, CR and HDG; example 1 (pre-strip thickness 40 mm),

[0240] FIG. 7b shows mechanical characteristic values (transversely to the rolling direction) of the steel according to the invention in the state HR, CR and HDG; example 2 (pre-strip thickness 45 mm),

[0241] FIG. 7c shows mechanical characteristic values (transversely to the rolling direction) of the steel according to the invention in the state HR, CR and HDG; example 3 (pre-strip thickness 50 mm),

[0242] FIG. 7d shows mechanical characteristic values (transversely to the rolling direction) of the steel according to the invention in the state HR, CR and HDG; example 4 (pre-strip thickness 55 mm),

[0243] FIG. 7e shows mechanical characteristic values (transversely to the rolling direction) of the steel according to the invention in the state HR, CR and HDG as an overview,

[0244] FIG. 8a shows method 1, temperature-time curves (annealing variants shown schematically),

[0245] FIG. 8b shows method 2, temperature-time curves (annealing variants shown schematically),

[0246] FIG. 8c shows method 3, temperature-time curves (annealing variants shown schematically).

[0247] FIG. 1 schematically illustrates the process chain for the production of a strip from the steel according to the invention. The process routes possible in the invention are shown. Up until acid-cleaning, the process route is the same for all steels according to the invention, thereafter, deviating process routes are followed depending on the desired results. For example, after acid-cleaning, the acid-cleaned hot strip can be cold-rolled and hot-dip finished with different degrees of thinning by rolling. A soft annealed hot strip or soft annealed cold strip can also be cold-rolled and hot-dip finished.

[0248] Material can also optionally be processed without a hot-dip finishing procedure, i.e. only within the scope of continuous annealing with and without subsequent electrolytic galvanizing. From the optionally coated material a complex component can now be produced. Subsequently, a quenching process can optionally take place, such as e.g. air-hardening where the heat-treated component is cooled in the air. Optionally, a tempering step can conclude the thermal treatment of the component.

[0249] FIG. 2 schematically illustrates the time-temperature curve of the process steps of hot rolling and continuous annealing of strips made from the alloy composition according to the invention. The time- and temperature-dependent conversion for the hot rolling process and also for a heat treatment after cold-rolling, component manufacture, as well as optional quenching with optional tempering are shown.

[0250] FIG. 3 shows in examples 1 to 4 which come from a melt in order to exclude the analytical influence in this case, the alloy compositions of the steel according to the invention, depending upon the produced pre-strip thickness. Cold strips having a cold strip desired thickness of 1.50 mm were produced from a hot strip desired thickness of 2.30 mm. Depending upon the pre-strip thickness, to be produced, prior to hot-rolling, example 1 shows the alloy composition for a pre-strip thickness of 40 mm, example 2 for a pre-strip thickness of 45 mm, example 3 for a pre-strip thickness of 50, example 4 for a pre-strip having a thickness of 55 mm.

[0251] FIG. 4 shows the mechanical characteristic values (transversely to the rolling direction) of the steel according to the invention in the hot-rolled state (HR, Hot Rolled) in FIG. 4a and in the cold-rolled state (CR, Cold Rolled) in FIG. 4b.

[0252] FIG. 5 shows the solidification behavior, via the mechanical characteristic values transversely to the rolling direction, during cold-rolling of the steel according to the invention, in a table in FIG. 5a and in a graph as a cold flow curve in FIG. 5b.

[0253] FIG. 6 shows the mechanical characteristic values (transversely to the rolling direction) of the steel according to the invention in the fine sheet state (HDG, Hot Dipped Galvanized) in FIG. 6a and the results of the hole expansion tests according to ISO 16630 and of the plate bending test according to VDA 238-100 in the fine sheet state (HDG) longitudinally and transversely to the rolling direction, as well as the corresponding products with the tensile strength, in FIG. 6b.

[0254] FIG. 7 shows the mechanical characteristic values (transversely to the rolling direction) of the steel according to the invention in the state HR, CR and HDG using a pre-strip thickness of 40 mm in FIG. 7a, 45 mm in FIG. 7b, 50 mm in FIG. 7c, 55 mm in FIG. 7d and in FIG. 7e as a summarizing graphical overview.

[0255] FIG. 8 schematically illustrates three variations of the temperature-time curves according to the invention in the case of annealing treatment and cooling and of austenitisation conditions which differ in each case.

[0256] By means of the different temperature controls according to the invention within said range, mutually different characteristic values and/or also different hole expansion results and bending angles are produced. Principal differences are thus the temperature-time parameters during the heat treatment and the following cooling.

[0257] Method 1 (FIG. 8a) presents the annealing and cooling of the produced steel strip cold-rolled to the end thickness in a continuous annealing installation. Firstly, the strip is heated to a temperature in the range of about 700 to 950 C. (Ac1 to Ac3). The annealed steel strip is then cooled from the annealing temperature at a cooling rate between approximately 15 and 100 C./s to an intermediate temperature (ZT) of approximately 200 to 250 C. This schematic illustration does not show a second Intermediate temperature (approximately 300 to 500 C.).

[0258] The steel strip is then cooled in air at a cooling rate between approximately 2 and 30 C./s until room temperature (RT) is reached or cooling at a cooling rate between approximately 15 and 100 C./s is maintained until room temperature is reached.

[0259] Method 2 (FIG. 8b) shows the process according to method 1 but the cooling of the steel strip is briefly interrupted during passage through the hot-dipping vessel for the purposes of a hot-dip finishing procedure, in order then to continue the cooling at a cooling rate between approximately 15 and 100 C./s to an intermediate temperature of approximately 200 to 250 C. The steel strip is then cooled in air at a cooling rate between approximately 2 and 30 C./s until reaching room temperature. Method 2 corresponds to annealing, e.g. hot-dip galvanizing with combined direct fired furnace and radiant tube furnace, as depicted in FIG. 8b.

[0260] Method 3 (FIG. 8c) likewise shows the process according to method 1 in a hot-dip finishing procedure but cooling of the steel strip is Interrupted by a short pause (approximately 1 to 20 s) at an intermediate temperature in the range of approximately 200 to 400 C. and heating is effected to the temperature (ST) required for the hot-dip finishing procedure (approximately 400 to 470 C.). The steel strip is then cooled to an intermediate temperature of approximately 200 to 250 C. The subsequent cooling in air of the steel strip takes place at a cooling rate of approximately 2 and 30 C./s until room temperature is reached.

[0261] Method 3 corresponds e.g. to a process being carried out in a continuous annealing installation, as depicted in FIG. 8c. In addition, in this case, by means of an induction furnace, reheating of the steel is optionally achieved directly prior to the zinc bath.

[0262] The decreases from the slab with respect to the pre-strip vary in the subsequent examples from 78% to 84% for subsequent hot-rolling to a hot strip thickness of 2.30 mm with corresponding decreases of 94% to 96%. In a single cold-rolling step, the cold strip desired thickness of 1.50 mm is achieved with a degree of thinning by cold-rolling of 35%. It is impressively shown that both for very low pre-strip thicknesses and also for greater pre-strip thicknesses, and the range therebetween, relatively uniform values provided with a conventional fluctuation range are achieved for the tensile strength and yield strength, transversely to the rolling direction. The steel according to the invention similarly permits the use of a master hot strip thickness with varying degrees of thinning by cold-rolling, as well as the use of master cold strip thicknesses without influencing the previous fact.

[0263] By way of example, for industrial manufacturing for the hot-dip galvanizing (HDG) according to method 3 as shown in FIG. 8c, the following examples form part of so-called feasibility tests which are Intended to prove that the variable pre-strip thicknesses can significantly influence the cold-rollability, such as the necessary rolling forces, without the higher hot strip strength (HR), and higher cold strip strength (CR), with a decreasing pre-strip thickness, leading to considerable fluctuations in the fine sheet (HDG):

EXAMPLE 1

[0264] (1.50 mm cold strip from 2.30 mm master hot strip and a pre-strip thickness of 40 mm)
Alloy composition in wt. %. A steel according to the invention comprising 0.104% C; 0.443% Si; 2.178% Mn; 0.012% P; 0.0004% S; 0.0045% N; 0.038 Al; 0.330% Cr; 0.208% Mo; 0.0372% Ti; 0.0332% Nb; 0.007% V; 0.0006% B; 0.0020% Ca; 0.027% Cu; 0.047% Ni; 0.008% Sn; 0.00038% H according to method 3 corresponding to FIG. 8c hot-dip finished, the slab material of 250 mm was rolled prior to the hot-rolling in the pre-line into a pre-strip of 40 mm in a reversing manner with a percentage decrease of 84% and subsequently hot-rolled in the hot wide strip line at a desired end rolling temperature of 910 C. with a decrease of 94% and reeled at a desired reeling temperature of 650 C. with a master hot strip thickness of 2.30 mm and cold rolled after acid-cleaning without additional heat treatment (such as e.g. batch-type annealing) to 1.50 mm in one pass (degree of thinning by cold-rolling 35%).

[0265] Fine Sheet State (HDG)

The yield strength ratio Re/Rm in the transverse direction was 66%.

TABLE-US-00001 elasticity limit (Rp0.2) 706 MPa tensile strength (Rm) 1071 MPa elongation at fracture (A80) 10.9% bake-hardening-index (BH2) 492 MPa hole expansion ratio according to ISO 16630 39% bending angle according to VDA 238-100 121/112 (longitudinal, transverse)
The material characteristic values transversely to the rolling direction would correspond e.g. to a HC660XD.

[0266] Initial State (HR)

The yield strength ratio Re/Rm in the transverse direction was 77%.

TABLE-US-00002 yield strength (Re) 826 MPa tensile strength (Rm) 1070 MPa elongation at fracture (A80) 10.0%

[0267] Intermediate State (CR) in the Transverse Direction

TABLE-US-00003 yield strength (Re) 1246 MPa tensile strength (Rm) 1305 MPa elongation at fracture (A80) 2.0%

EXAMPLE 2

[0268] (1.50 mm cold strip from 2.30 mm master hot strip and a pre-strip thickness of 45 mm)
Alloy composition in wt. %
A steel according to the invention comprising 0.104% C; 0.443% Si; 2.178% Mn; 0.012% P; 0.0004% S; 0.0045% N; 0.038 Al; 0.330% Cr; 0.208% Mo; 0.0344% Ti; 0.0372% Nb; 0.007% V; 0.0006% B; 0.0020% Ca; 0.027% Cu; 0.047% Ni; 0.008% Sn; 0.00038% H according to method 3 corresponding to FIG. 8c hot-dip finished, the slab material of 250 mm was rolled prior to the hot-rolling in the pre-line into a pre-strip of 45 mm in a reversing manner with a percentage decrease of 82% and subsequently hot-rolled in the hot wide strip line at a desired end rolling temperature of 910 C. with a decrease of 95% and reeled at a desired reeling temperature of 650 C. with a master hot strip thickness of 2.30 mm and cold rolled after acid-cleaning without additional heat treatment (such as e.g. batch-type annealing) to 1.50 mm in one pass (degree of thinning by cold-rolling 35%).

[0269] Fine Sheet State (HDG)

The yield strength ratio Re/Rm in the transverse direction was 67%.

TABLE-US-00004 elasticity limit (Rp0.2) 720 MPa tensile strength (Rm) 1077 MPa elongation at fracture (A80) 10.4% bake-hardening-index (BH2) 51 MPa hole expansion ratio according to ISO 16630 35% bending angle according to VDA 238-100 128/114 (longitudinal, transverse)
The material characteristic values transversely to the rolling direction would correspond e.g. to a HC660XD.

[0270] Initial State (HR)

The yield strength ratio Re/Rm in the transverse direction was 70%.

TABLE-US-00005 yield strength (Re) 725 MPa tensile strength (Rm) 1030 MPa elongation at fracture (A80) 10.2%

[0271] Intermediate State (CR) in the Transverse Direction

TABLE-US-00006 yield strength (Re) 1224 MPa tensile strength (Rm) 1260 MPa elongation at fracture (A80) 1.5%

EXAMPLE 3

[0272] (1.50 mm cold strip from 2.30 mm master hot strip and a pre-strip thickness of 50 mm)
Alloy composition in wt. %
A steel according to the invention comprising 0.104% C; 0.443% Si; 2.178% Mn; 0.012% P; 0.0004% S; 0.0045% N; 0.038 Al; 0.330% Cr; 0.208% Mo; 0.0344% Ti; 0.0372% Nb; 0.007% V; 0.0006% B; 0.0020% Ca; 0.027% Cu; 0.047% Ni; 0.008% Sn; 0.00038% H according to method 3 corresponding to FIG. 8c hot-dip finished, the slab material of 250 mm was rolled prior to the hot-rolling in the pre-line into a pre-strip of 50 mm in a reversing manner with a percentage decrease of 80% and subsequently hot-rolled in the hot wide strip line at a desired end rolling temperature of 910 C. with a decrease of 96% and reeled at a desired reeling temperature of 650 C. with a master hot strip thickness of 2.30 mm and cold rolled after acid-cleaning without additional heat treatment (such as e.g. batch-type annealing) to 1.50 mm in one pass (degree of thinning by cold-rolling 35%).

[0273] Fine Sheet State (HDG)

The yield strength ratio Re/Rm in the transverse direction was 65%.

TABLE-US-00007 elasticity limit (Rp0.2) 704 MPa tensile strength (Rm) 1084 MPa elongation at fracture (A80) 10.4% bake-hardening-index (BH2) 55 MPa hole expansion ratio according to ISO 16630 38% bending angle according to VDA 238-100 127/115 (longitudinal, transverse)
The material characteristic values transversely to the rolling direction would correspond e.g. to a HC660XD.

[0274] Initial State (HR)

The yield strength ratio Re/Rm in the transverse direction was 69%.

TABLE-US-00008 yield strength (Re) 695 MPa tensile strength (Rm) 1010 MPa elongation at fracture (A80) 8.8%

[0275] Intermediate State (CR) in the Transverse Direction

TABLE-US-00009 yield strength (Re) 1203 MPa tensile strength (Rm) 1255 MPa elongation at fracture (A80) 1.9%

EXAMPLE 4

[0276] (1.50 mm cold strip from 2.30 mm master hot strip and a pre-strip thickness of 55 mm)
Alloy composition in wt. %
A steel according to the invention comprising 0.104% C; 0.443% Si; 2.178% Mn; 0.012% P; 0.0004% S; 0.0045% N; 0.038 Al; 0.330% Cr; 0.208% Mo; 0.0344% TI; 0.0372% Nb; 0.007% V; 0.0006% B; 0.0020% Ca; 0.027% Cu; 0.047% Ni; 0.008% Sn; 0.00038% H according to method 3 corresponding to FIG. 8c hot-dip finished, the slab material of 250 mm was rolled prior to the hot-rolling in the pre-line into a pre-strip of 55 mm in a reversing manner with a percentage decrease of 78% and subsequently hot-rolled in the hot wide strip line at a desired end rolling temperature of 910 C. with a decrease of 96% and reeled at a desired reeling temperature of 650 C. with a master hot strip thickness of 2.30 mm and cold rolled after acid-cleaning without additional heat treatment (such as e.g. batch-type annealing) to 1.50 mm in one pass (degree of thinning by cold-rolling 35%).

[0277] Fine Sheet State (HDG)

The yield strength ratio Re/Rm in the transverse direction was 66%.

TABLE-US-00010 elasticity limit (Rp0.2) 708 MPa tensile strength (Rm) 1077 MPa elongation at fracture (A80) 10.4% bake-hardening-index (BH2) 58 MPa hole expansion ratio according to ISO 16630 40% bending angle according to VDA 238-100 123/111 (longitudinal, transverse)

[0278] Initial State (HR)

The yield strength ratio Re/Rm in the transverse direction was 70%.

TABLE-US-00011 yield strength (Re) 679 MPa tensile strength (Rm) 967 MPa elongation at fracture (A80) 9.6%

[0279] Intermediate State (CR) in the Transverse Direction

TABLE-US-00012 yield strength (Re) 1158 MPa tensile strength (Rm) 1230 MPa elongation at fracture (A80) 2.5%

CONCLUSION

[0280] It is not possible to see a significant influence of the pre-strip thickness on the mechanical characteristic values on the fine sheet (HDG).

[0281] This statement applies to the degree of thinning by cold-rolling of 35% used in the examples, but could also be applied without restriction to variable degrees of thinning by cold-rolling.

[0282] The invention has been described above with the aid of fine sheet steel sheets with an end thickness to be achieved of 1.50 mm in the thickness range of 0.50 to 3.00 mm. It is also possible, if required, to produce end thicknesses in the range of 0.10 to 4.00 mm.