EP4261309A1 - Cold-rolled steel sheet product and method for producing a cold-rolled steel sheet product - Google Patents
Cold-rolled steel sheet product and method for producing a cold-rolled steel sheet product Download PDFInfo
- Publication number
- EP4261309A1 EP4261309A1 EP22168199.2A EP22168199A EP4261309A1 EP 4261309 A1 EP4261309 A1 EP 4261309A1 EP 22168199 A EP22168199 A EP 22168199A EP 4261309 A1 EP4261309 A1 EP 4261309A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- cold
- flat steel
- steel product
- rolled
- rolled flat
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 9
- 239000010960 cold rolled steel Substances 0.000 title claims 5
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 103
- 239000010959 steel Substances 0.000 claims abstract description 103
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 20
- 238000001816 cooling Methods 0.000 claims abstract description 20
- 238000000137 annealing Methods 0.000 claims abstract description 14
- 238000010438 heat treatment Methods 0.000 claims abstract description 11
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 8
- 238000005097 cold rolling Methods 0.000 claims abstract description 6
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 5
- 229910000734 martensite Inorganic materials 0.000 claims description 17
- 229910001566 austenite Inorganic materials 0.000 claims description 13
- 229910052804 chromium Inorganic materials 0.000 claims description 12
- 238000005098 hot rolling Methods 0.000 claims description 11
- 238000000034 method Methods 0.000 claims description 11
- 229910052782 aluminium Inorganic materials 0.000 claims description 10
- 229910052759 nickel Inorganic materials 0.000 claims description 10
- 229910052719 titanium Inorganic materials 0.000 claims description 10
- 229910052720 vanadium Inorganic materials 0.000 claims description 10
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 9
- 229910052750 molybdenum Inorganic materials 0.000 claims description 9
- 229910052758 niobium Inorganic materials 0.000 claims description 9
- 229910052721 tungsten Inorganic materials 0.000 claims description 9
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 8
- 229910052796 boron Inorganic materials 0.000 claims description 8
- 239000012535 impurity Substances 0.000 claims description 8
- 239000000203 mixture Substances 0.000 claims description 8
- 229910052802 copper Inorganic materials 0.000 claims description 7
- 229910001563 bainite Inorganic materials 0.000 claims description 6
- 230000000717 retained effect Effects 0.000 claims description 6
- 229910052717 sulfur Inorganic materials 0.000 claims description 6
- 229910052757 nitrogen Inorganic materials 0.000 claims description 5
- 238000003303 reheating Methods 0.000 claims description 5
- 229910000859 α-Fe Inorganic materials 0.000 claims description 5
- 238000005266 casting Methods 0.000 claims description 4
- 229910052742 iron Inorganic materials 0.000 claims description 4
- 238000005554 pickling Methods 0.000 claims description 4
- 150000002910 rare earth metals Chemical class 0.000 claims description 4
- 229910052749 magnesium Inorganic materials 0.000 claims description 3
- 229910052698 phosphorus Inorganic materials 0.000 claims description 3
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 3
- 239000000047 product Substances 0.000 description 41
- 239000011651 chromium Substances 0.000 description 16
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 15
- 239000011572 manganese Substances 0.000 description 14
- 239000010936 titanium Substances 0.000 description 12
- 230000015572 biosynthetic process Effects 0.000 description 11
- 239000010949 copper Substances 0.000 description 11
- 239000010955 niobium Substances 0.000 description 10
- 238000012360 testing method Methods 0.000 description 9
- -1 carbon nitrides Chemical class 0.000 description 8
- 230000000694 effects Effects 0.000 description 8
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- 239000011777 magnesium Substances 0.000 description 6
- 238000003466 welding Methods 0.000 description 6
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 5
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 5
- 238000010276 construction Methods 0.000 description 5
- 238000005260 corrosion Methods 0.000 description 5
- 230000007797 corrosion Effects 0.000 description 5
- 238000005520 cutting process Methods 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 4
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 4
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 4
- 239000011575 calcium Substances 0.000 description 4
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 4
- 150000004767 nitrides Chemical class 0.000 description 4
- 239000010703 silicon Substances 0.000 description 4
- 239000011593 sulfur Substances 0.000 description 4
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 4
- 239000010937 tungsten Substances 0.000 description 4
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 4
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 3
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 3
- 239000010941 cobalt Substances 0.000 description 3
- 229910017052 cobalt Inorganic materials 0.000 description 3
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 3
- 238000001887 electron backscatter diffraction Methods 0.000 description 3
- 239000000155 melt Substances 0.000 description 3
- 239000011733 molybdenum Substances 0.000 description 3
- 230000003647 oxidation Effects 0.000 description 3
- 238000007254 oxidation reaction Methods 0.000 description 3
- 229910001562 pearlite Inorganic materials 0.000 description 3
- 239000002244 precipitate Substances 0.000 description 3
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 229910052791 calcium Inorganic materials 0.000 description 2
- 229910001567 cementite Inorganic materials 0.000 description 2
- 238000011109 contamination Methods 0.000 description 2
- 230000003111 delayed effect Effects 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 150000001247 metal acetylides Chemical class 0.000 description 2
- 239000004200 microcrystalline wax Substances 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 238000001953 recrystallisation Methods 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- GNFTZDOKVXKIBK-UHFFFAOYSA-N 3-(2-methoxyethoxy)benzohydrazide Chemical compound COCCOC1=CC=CC(C(=O)NN)=C1 GNFTZDOKVXKIBK-UHFFFAOYSA-N 0.000 description 1
- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- 229910052582 BN Inorganic materials 0.000 description 1
- FGUUSXIOTUKUDN-IBGZPJMESA-N C1(=CC=CC=C1)N1C2=C(NC([C@H](C1)NC=1OC(=NN=1)C1=CC=CC=C1)=O)C=CC=C2 Chemical compound C1(=CC=CC=C1)N1C2=C(NC([C@H](C1)NC=1OC(=NN=1)C1=CC=CC=C1)=O)C=CC=C2 FGUUSXIOTUKUDN-IBGZPJMESA-N 0.000 description 1
- 229910052684 Cerium Inorganic materials 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- 239000004164 Wax ester Substances 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- 230000001476 alcoholic effect Effects 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- AZDRQVAHHNSJOQ-UHFFFAOYSA-N alumane Chemical class [AlH3] AZDRQVAHHNSJOQ-UHFFFAOYSA-N 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- ZMIGMASIKSOYAM-UHFFFAOYSA-N cerium Chemical compound [Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce] ZMIGMASIKSOYAM-UHFFFAOYSA-N 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 230000001934 delay Effects 0.000 description 1
- 230000003009 desulfurizing effect Effects 0.000 description 1
- 238000003618 dip coating Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000010410 layer Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- JMANVNJQNLATNU-UHFFFAOYSA-N oxalonitrile Chemical compound N#CC#N JMANVNJQNLATNU-UHFFFAOYSA-N 0.000 description 1
- 239000011574 phosphorus Substances 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 239000004848 polyfunctional curative Substances 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 239000011241 protective layer Substances 0.000 description 1
- 238000004080 punching Methods 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 238000004088 simulation Methods 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 238000009864 tensile test Methods 0.000 description 1
- 150000003568 thioethers Chemical class 0.000 description 1
- 238000012549 training Methods 0.000 description 1
- 229910052727 yttrium Inorganic materials 0.000 description 1
- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0405—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing of ferrous alloys
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
- C21D8/0426—Hot rolling
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
- C21D8/0463—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment following hot rolling
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
- C21D8/0473—Final recrystallisation annealing
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
- C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
Definitions
- the invention relates to a cold-rolled flat steel product which has a low sensitivity to edge cracks and good formability, here characterized by a high Marciniak hole expansion (LAW), with a high tensile strength Rm, yield strength Rp and elongation at break A80.
- LAW Marciniak hole expansion
- Dual-phase steels (DP steels) with good hole expansion according to ISO 16630 are known from the prior art, for example in the application WO 2013/182622 .
- this hole expansion test does not adequately represent the real forming processes in automobile construction.
- the Marciniak hole expansion test offers the opportunity to test the DP steels in a practical manner, close to the actual later forming reality. This shows the need to change the known DP steels in order to create a special structure that is suitable for the demands in automobile construction. Such a steel with a special structure is the subject of this invention.
- the flat steel products described in the invention are typically rolled products, such as steel strips or sheets as well as blanks and blanks made from them.
- the structure is determined on cross sections that are etched with 3% Nital (alcoholic nitric acid).
- the structure is determined in a scanning electron microscope at 5000x magnification to determine the proportion of plate-like and other non-plate-like bainite and at 20,000 to 50,000x magnification to determine the plate length, width and distance between the plates.
- the proportion of retained austenite is determined using X-ray diffractometry.
- the grain boundaries of the structure are determined using electron backscatter diffraction (EBSD).
- EBSD electron backscatter diffraction
- samples are taken from the 1/3 layer of the strip thickness of the flat steel product. These samples are embedded and prepared as a longitudinal section. Immediately before the EBSD examination, the surface is treated again in a polishing step. The EBSD measurement is carried out in a 90*90 ⁇ m measuring field in 0.1 ⁇ m steps. Large-angle and small-angle grain boundaries are determined in the recorded data.
- a small angle grain boundary is a grain boundary that is a boundary between two grains with a small difference in orientation. The small angle grain boundary is defined up to a rotation angle ⁇ up to and including 15°. In the present invention, misorientations below five degrees ( ⁇ ⁇ 5) are not considered a grain boundary.
- the grain boundaries are referred to as high-angle grain boundaries.
- the grain boundary lengths are determined for all large-angle and small-angle grain boundaries by specifying the described definition of the small-angle and large-angle grain boundaries in the analysis software TSL OIM Analyzes 8.0 from Ametek and then automatically determining the grain boundary lengths for the measuring range.
- the hole diameters are measured using a camera from IDS type UI-1240ML-M-GL with a telecentric lens (TC13080 from Opto Engineering). To ensure sufficient lighting, an optional lighting ring is attached to the camera. The distance between the camera and the sample must be chosen so that sufficient image resolution is achieved in the evaluation area. The diameter of the expanded hole should fill >50% of the image axes.
- the test is carried out with a hold-down force of 400 kN and a pulling speed of 1 ⁇ 0.2 mm/s until a crack or constriction is present. During the experiment, images are recorded at a frequency of 10 Hz. In the evaluation, the last image is selected in which no constriction or crack can be seen.
- the object of the present invention is to adjust the structure in a DP steel in such a way that the steel is suitable for the stress in automobile construction, ie with a high Marciniak hole expansion (LAW) of at least 9.0% is suitable.
- LAW Marciniak hole expansion
- Carbon “C” is contained in the steel according to the invention in levels of 0.02% to 0.25%. Carbon ensures high strength in the steel according to the invention by playing a decisive role in the formation of martensite and expanding the area in which austenite is formed. An optimized setting was found at values of C ⁇ 0.140%, since from this value onwards sufficient martensite components or sufficiently hard martensite are formed to further increase the strength. However, if the carbon content is too high, excessively large carbides are formed, which are ineffective in increasing strength. In addition, the weldability is reduced. For this reason, the carbon content in the present invention is limited to 0.25%, preferably 0.17%.
- Silicon “Si” is an important solid solution hardener. In addition, it is needed to adjust the special structure in this invention, because it delays cementite precipitation and thus suppresses pearlite formation. It can also increase the residual austenite content, which can be converted to martensite later in the process. For this effect and increased corrosion resistance, a proportion of at least 0.05%, and especially a proportion of at least 0.11%, has proven to be particularly effective. On the other hand, too high a silicon content leads to grain boundary oxidation occurring and can deteriorate coatability and surface properties. In addition, if the silicon content is too high, recrystallization processes can be delayed, which affects the ratio of the large and small angle grain boundaries. Therefore, the silicon content is limited to 0.8%, preferably 0.6%, particularly preferably 0.45%.
- Manganese “Mn” is contained in the steel according to the invention. With a content of 1.0% or more, Mn enables martensite formation because pearlite formation is suppressed. A proportion of at least 1.2% and particularly advantageous a proportion of at least 1.5% have proven to be advantageous. However, too high a Mn content can lead to severe segregation, which is why the Mn content is limited to 3.0%. In addition, a high Mn content severely limits weldability and reduces corrosion resistance. Therefore, an Mn content of a maximum of 2.5% and in particular 2.3% has proven to be particularly advantageous.
- Sulfur "S” can lead to the formation of Mn sulfides, which severely impair the formable properties. Therefore, the content in the steel according to the invention is limited to 0.01%, although a limitation to 0.005% and in particular to 0.003% can be advantageous. Contamination with sulfur cannot be completely avoided during steel production.
- Nitrogen “N” can lead to the formation of coarse Ti and Al nitrides at levels above 0.010%. To avoid these nitrides, a maximum content of 0.007% has proven to be particularly advantageous. Nitrogen contamination cannot be completely avoided during steel production.
- impurities P, S, and N other elements can also be present as impurities in the steel. These other elements are grouped under the “unavoidable impurities”.
- the content of these “unavoidable impurities” is preferably a maximum of 0.2% in total, preferably a maximum of 0.1%.
- the optional alloying elements “Al, Cr, Cu, Nb, Mo, Ni, Ti, V, B, Co, W” described below, for which a lower limit is specified, can also occur in levels below the respective lower limit as unavoidable impurities in the steel substrate . In this case, they are also counted among the "unavoidable impurities", the total content of which is limited to a maximum of 0.2%, preferably a maximum of 0.1%.
- Aluminum “Al” can be added to the steel of the invention to increase corrosion resistance and increase the retained austenite content.
- a higher residual austenite content results from the addition of aluminum by delaying the formation of cementite precipitates.
- an aluminum content of greater than or equal to 0.05% in the flat steel product according to the invention has proven to be advantageous.
- too high an aluminum content can lead to the formation of coarse Al nitrides, which have an embrittling effect and thus poorer formability.
- higher Al contents can lead to poorer casting behavior, as aluminum compounds can lead to clogging.
- the present invention therefore limits the aluminum content to 1.0%, preferably 0.8%.
- chromium “Cr” By adding chromium “Cr”, the formation of bainite can be delayed, whereby a higher proportion of martensite is achieved in the flat steel product according to the invention.
- hardenability is increased by chromium.
- a chromium content of greater than or equal to 0.10% has proven to be particularly advantageous.
- chromium can lead to grain boundary oxidation through the formation of Cr oxides.
- the chromium content here is therefore limited to 1.0%, preferably 0.9%.
- the addition of copper "Cu” to the flat steel product according to the invention improves the corrosion resistance and can form very fine strength-increasing Cu precipitates. Therefore, an addition of at least equal to 0.01% may be advantageous in the present invention.
- the copper content should be limited to 0.5%, otherwise so-called red brittleness can occur in the hot rolling process, i.e. cracks can form in the slab.
- niobium “Nb” can be added to the flat steel product according to the invention.
- fine, strength-increasing carbon nitrides are formed.
- a content of at least 0.0005% has proven to be advantageous.
- the strength-increasing effect of carbon nitrides is exhausted as soon as the niobium content becomes too high.
- high levels of niobium can impair cold formability and welding properties.
- Molybdenum "Mo” also forms fine, strength-increasing carbon nitrides in small amounts. An addition of greater than or equal to 0.001% has therefore proven to be advantageous. However, the strength-increasing effect of carbon nitrides is exhausted as soon as the molybdenum content becomes too high. In addition, high levels of molybdenum can impair cold formability and welding properties. Here, a content of a maximum of 0.1%, preferably 0.050%, particularly preferably 0.007%, has proven to be advantageous.
- Nickel “Ni” increases the amount and stability of austenite and reduces red brittleness with Cu.
- nickel can improve Marciniak hole expansion (LAW). Therefore, at least 0.01%, particularly advantageously 0.015% Ni, is optionally added to the flat steel product according to the invention. For cost reasons, however, the addition should be limited as little as possible to a maximum of 0.2%, preferably 0.1% and particularly preferably to 0.06%.
- Titanium "Ti” binds nitrogen in the steel and thus prevents the formation of brittle boron nitrides.
- titanium can also form strength-increasing carbon nitrides.
- an addition of greater than or equal to 0.001%, preferably 0.004%, has proven to be advantageous. If too much titanium is added, the advantage of the strength-increasing carbon nitrides is exhausted because they become too large.
- coarse, brittle Ti nitrides can form. Limiting the titanium content to a maximum of 0.1%, preferably 0.03% and particularly preferably 0.006%, has proven to be advantageous for the flat steel product according to the invention.
- vanadium "V” can be added to the steel according to the invention, which also forms fine carbon nitrides in small amounts.
- the carbon nitrides can pin the grain boundaries. Pinning reduces grain coarsening at high temperatures, which has a positive effect on the ratio of large-angle grain boundary lengths to small-angle grain boundary lengths.
- vanadium is added to the steel according to the invention. If too much vanadium is added, the carbon nitride precipitates become larger and therefore ineffective.
- the amount of vanadium added is limited for cost reasons. In the steel according to the invention, the amount is limited to 0.1%, preferably 0.030% and particularly preferably 0.0015%.
- boron "B” leads to an increase in strength.
- at least 0.0002%, particularly preferably at least 0.001%, can be added to the steel according to the invention become. If the amount of boron added is too high, iron borides are formed. These iron borides can melt at approx. 1200° C and cause material failure. For this reason, the boron content in the steel according to the invention is limited to 0.005%, preferably 0.0015%.
- Mg can have a desulfurizing and deoxidizing effect. Therefore, 0.0003% can be added to the steel according to the invention.
- the addition of Mg is limited to a maximum of 0.5% Mg, preferably 0.1%, particularly preferably 0.003%.
- Calcium "Ca” can be added to the flat steel product according to the invention in order to bind the free sulfur. Free sulfur segregates to the grain boundaries and thereby leads to failure of the material, i.e. the Marciniak hole expansion deteriorates. Therefore, an optional amount of at least equal to 0.0001% can be added to the flat steel product according to the invention. In large quantities, calcium is no longer soluble in the flat steel product, which is why the addition is limited to a maximum of 0.1%, preferably 0.010%, particularly preferably 0.003%.
- Cobalt “Co” increases the amount and stability of austenite.
- a cobalt addition of at least 0.001% has proven to be particularly advantageous.
- a maximum of 0.1%, preferably 0.010%, particularly preferably 0.0007%, of cobalt should be added to the steel according to the invention.
- Tungsten “W” has a desulphurizing and deoxidizing effect in the steel according to the invention.
- strength-increasing carbides can be formed with the help of tungsten.
- Tungsten can therefore optionally be added at a level of at least 0.01%. For cost reasons, a maximum of 0.3% tungsten is used in the present invention.
- the steel product according to the invention can optionally contain the rare earth metals (SEM) such as: cerium “Ce”, lathane "La” and yttrium “Y” in total with a maximum content of 0.5%. Larger SEM contents can lead to problems when casting the steel. A minimum sum of all SEM elements of at least 0.003% is advantageous, as this has a desulphurizing and deoxidizing effect.
- SEM rare earth metals
- the carbon equivalent should be a maximum of 1.30%, preferably 0.70%, otherwise there will be an excessive tendency for cracks in the weld metal or the heat-affected zone during welding. In addition, the heat-affected zone can become significantly brittle.
- resistance spot welding it is also desirable to set the carbon equivalent as low as possible to ensure welding under industrial conditions.
- the cold-rolled flat steel product according to the invention in particular according to the method according to the invention, is characterized in that the steel has a structure consisting of at least two phases, which comprises more than 5% martensite and more than 20% ferrite as well as up to 65% bainite and up to 10% retained austenite .
- the martensite content is limited to 90% and particularly preferably 80% in order to ensure sufficient ductility for component shaping.
- the martensite content preferably consists of fresh and tempered martensite.
- with martensite contents greater than 50% up to 10% of the martensite can be present as tempered martensite.
- the ferrite content in particular can be limited to 80% so that the desired strength can be adjusted.
- the ferrite content is at least 30%.
- the bainite content is limited to a maximum of 20%.
- the microstructure of the flat steel product according to the invention has a special ratio of the large angle grain boundary length to the small angle grain boundary length.
- High angle grain boundaries impede the movement of dislocations from one grain to the other. Due to their significantly higher dislocation density, small-angle grain boundaries cause hardening in the grain, which leads to different deformation resistances and is equivalent to a notch effect. This notch causes localized deformations and reduces hole expansion.
- the microstructure according to the invention is characterized by the ratio of the large-angle grain boundary lengths to the small-angle grain boundary lengths of more than 4.0, preferably more than 4.5, particularly preferably 6.0. It has been shown that under such conditions the mechanical properties are positively influenced, in particular the Marciniak hole expansion.
- the cold-rolled flat steel product is characterized by an elongation at break A80 of at least 8%, preferably at least 10%, particularly preferably at least 14%.
- the tensile strength Rm is at least 570 MPa, preferably at least 590 MPa.
- This product of elongation at break A80 and tensile strength Rm can be achieved by effectively preventing dislocation movements. These dislocation movements are reduced by the special ratio of large-angle grain boundary lengths to small-angle grain boundary lengths.
- the yield strength Rp0.2 of the steel is 350 MPa to 850 MPa.
- the Marciniak hole expansion in a special embodiment of the flat steel product is at least 9.0%, preferably at least 10.0%, particularly preferably 12.0%.
- the Marciniak hole expansion test offers the opportunity to test the DP steels in a practical manner, close to the actual later forming reality.
- composition according to the invention of the slab according to the invention applies to the composition according to the invention of the slab according to the invention and the optional possible variations.
- the slab according to the invention is reheated to a temperature of 1200-1300 ° C.
- This causes austenite to form in the product.
- the lower limit of the reheating temperature T HOM should be at least 1200 ° C so that homogeneity in the structure in the slab is achieved. If an upper limit of 1300° C is exceeded at the heating temperature, melting can occur on the slab or the slab can break because the high-temperature strength is exceeded.
- the slabs have a thickness of 200-300 mm.
- the product according to the invention is hot-rolled in a conventional manner using units known from the prior art to a final thickness of 1.5 to 7 mm, preferably 1.7 to 4 mm.
- the hot rolling final temperature (T WE for short) is at least 800° C., preferably 920° C.
- the hot rolling final temperature is particularly preferably above the Ac3 temperature.
- the hot strip After hot rolling, the hot strip is coiled at a temperature of 400 °C - 700 °C, preferably at 500 °C - 600 °C.
- T HA reel temperatures
- martensite forms too quickly, which leads to high strength and makes later deformation problematic. Above 600°C the risk of grain boundary oxidation increases.
- the coil After reeling, the coil is cooled to room temperature.
- the hot strip is pickled in order to remove the scale.
- Pickling can preferably be carried out chemically using hydrochloric and/or sulfuric acid. Pickling is particularly preferably carried out in a temperature range of 80 to 95 °C.
- the flat steel product is cooled to room temperature.
- the cold-rolled flat steel product is then brought to an annealing temperature T annealing of more than 800 ° C in a continuous furnace.
- the heating intensity is preferably: 3000 kJ s ⁇ mm and particularly preferred 3150 kJ s ⁇ mm .
- the average heating intensity according to the invention leads to recrystallization processes taking place preferably before recovery processes. This will make more large-angle grain boundaries are formed, so that the inventive ratio of large-angle grain boundaries to small-angle grain boundaries can be established.
- a typical annealing time during which the flat steel product is kept at the annealing temperature is preferably at least 10 s.
- the maximum annealing time is preferably 1000 s.
- the cooling to room temperature can take place in two intermediate steps, with the cold-rolled flat steel product in the first intermediate step from annealing temperature to a first cooling temperature T 1 with an average cooling rate ⁇ 1 of less than 100 K/s, preferably less than 10 K/s, particularly preferably less than 5 K /s, and wherein cold-rolled flat steel product is cooled in the second intermediate step to a second maximum cooling temperature T 2 with a cooling rate ⁇ 2 less than 100 K/s, the following applies to the cooling temperatures T 1 , T 2 : T 1 > T 2 , 450°C ⁇ T 1 ⁇ 800 °C (preferably 650°C ⁇ T 1 ⁇ 750 °C) and 400 °C ⁇ T 2 ⁇ 600 °C
- the flat steel product according to the invention can be provided with a metallic protective layer.
- a metallic protective layer In particular, zinc-based hot-dip coatings can be used. This coating occurs between steps f) and g) in the process described above.
- the flat steel product can be tempered to level out pronounced yield points, strip waviness and to achieve ideal roughness.
- a cold deformation of 0.2-3% is particularly preferred.
- the flat steel product can optionally be oiled between or after the last processing step.
- the oiling serves as temporary corrosion protection until the next processing step or for transport.
- melts AF were produced.
- the composition of the melts is given in Table 1.
- the melts were cast into slabs in a conventional continuous casting plant and the slabs were then reheated.
- the slabs were then rolled into hot strips with a specific hot rolling final temperature T WE .
- the hot strip was then coiled and pickled at a coiling temperature T HA .
- the corresponding process temperatures can be found in Table 2.
- the hot strip thus obtained was then rolled in a conventional manner into a cold strip with a strip thickness d.
- This cold strip was then heated with a heating intensity I to an annealing temperature T and cooled to room temperature.
- the rates during cooling are given in Table 2.
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Abstract
Die Erfindung betrifft ein kaltgewalztes Stahlflachprodukt und dessen Herstellungsprozess. Das Stahlflachprodukt besteht aus einem Stahl mit 0,02 - 0,25 % C, 0,05 - 0,8 % Si, 1,0 - 3,0 % Mn und optional Ni ≥0,01 %, und weist ein Verhältnis der Großwinkelkorngrenzenlängen zu Kleinwinkelkorngrenzenlängen mit mehr als 4,0 auf. Die Marciniak-Lochaufweitung (LAW) des Stahlflachprodukts beträgt mindestens 9,0%. Während des Herstellungsprozesses wird das Stahlflachprodukt nach dem Kaltwalzen auf eine Glühtemperatur von über 800 °C mit einer mittleren Aufheizintensität zwischen 200 °C und 800 °C von mindestens 2900kJs⋅mm gebracht. Das anschließende Abkühlen auf Raumtemperatur kann optional in zwei Schritten erfolgen. Optional kann das Stahlflachprodukt beschichtet werden.The invention relates to a cold-rolled flat steel product and its manufacturing process. The flat steel product consists of a steel with 0.02 - 0.25% C, 0.05 - 0.8% Si, 1.0 - 3.0% Mn and optionally Ni ≥0.01%, and has a ratio of Large angle grain boundary lengths to small angle grain boundary lengths with more than 4.0. The Marciniak hole expansion (LAW) of the flat steel product is at least 9.0%. During the manufacturing process, after cold rolling, the flat steel product is brought to an annealing temperature of over 800 °C with an average heating intensity between 200 °C and 800 °C of at least 2900 kJs⋅mm. The subsequent cooling to room temperature can optionally be done in two steps. The flat steel product can optionally be coated.
Description
Auf Grund steigender Leichtbauanforderungen im Automobilbau kommen zunehmend hoch- und höchstfeste Stähle für die Fahrzeugkarosserie zum Einsatz. Die Entwicklung geeigneter Stahlwerkstoffe verfolgt dabei eine optimale Kombination höchster Festigkeit bei gleichzeitig guter Duktilität. Hierzu werden Stähle verwendet, bei denen ein komplexes Mehrphasengefüge eingestellt wird. Allerdings zeigen diese Stähle eine hohe Kantenrissempfindlichkeit speziell an gestanzten Bauteilen. Kritische Herstellungsprozesse sind dabei das Biegen, Tiefziehen, Schneiden und Stanzen. Die Lochaufweitung stellt ein Verfahren zur Untersuchung und Beurteilung der Kantenrissempfindlichkeit und des lokalen Dehnungsvermögens eines Materials dar und erlaubt die Simulation vergleichbarer Beanspruchungen an Realbauteilen z.B. im Bereich von Entlastungslöchern.Due to increasing lightweight construction requirements in automobile construction, high- and ultra-high-strength steels are increasingly being used for vehicle bodies. The development of suitable steel materials aims to achieve an optimal combination of maximum strength and good ductility. For this purpose, steels are used in which a complex multi-phase structure is created. However, these steels are highly sensitive to edge cracks, especially on stamped components. Critical manufacturing processes include bending, deep drawing, cutting and punching. Hole expansion is a method for examining and assessing the sensitivity to edge cracks and the local expansion capacity of a material and allows the simulation of comparable stresses on real components, e.g. in the area of relief holes.
Die Erfindung betrifft ein kaltgewalztes Stahlflachprodukt das eine niedrige Kantenrissempfindlichkeit und eine gute Umformbarkeit, hier gekennzeichnet durch eine hohe Marciniak-Lochaufweitung (LAW), bei hoher Zugfestigkeit Rm, Dehngrenze Rp und Bruchdehnung A80 aufweist.The invention relates to a cold-rolled flat steel product which has a low sensitivity to edge cracks and good formability, here characterized by a high Marciniak hole expansion (LAW), with a high tensile strength Rm, yield strength Rp and elongation at break A80.
Aus dem Stand der Technik sind Dualphasen-Stähle (DP-Stähle) mit einer guten Lochaufweitung nach ISO 16630 bekannt, wie zum Beispiel in der Anmeldung
Bei den in der Erfindung beschriebenen Stahlflachprodukten handelt es sich typischerweise um Walzprodukte, wie Stahlbänder oder Bleche sowie daraus hergestellte Zuschnitte und Platinen.The flat steel products described in the invention are typically rolled products, such as steel strips or sheets as well as blanks and blanks made from them.
In der vorliegenden Anmeldung sind alle Angaben zu Gehalten bezüglich der Stahlzusammensetzung auf das Gewicht bezogen, sofern nicht ausdrücklich anders erwähnt. Alle nicht näher bestimmten, im Zusammenhang mit einer Stahllegierung stehenden "%-Angaben" sind daher als Angaben in "Gew.-%" zu verstehen.In the present application, all information on contents relating to the steel composition is based on weight, unless expressly stated otherwise. All unspecified “% data” relating to a steel alloy are therefore to be understood as “% by weight” data.
Mit Ausnahme der auf das Volumen (Angabe in "Vol.-%") bezogenen Angaben zum RestaustenitGehalt des Gefüges eines erfindungsgemäßen Blechformteils beziehen sich Angaben zu den Gehalten der verschiedenen Gefügebestandteile jeweils auf die Fläche eines Schliffs einer Probe des jeweiligen Erzeugnisses (Angabe in Flächenprozent "Flächen-%"), soweit nicht ausdrücklich anders angegeben.With the exception of the information on the residual austenite content of the structure of a sheet metal part according to the invention based on the volume (indicated in "% by volume"), information on the contents of the various structural components refer to the area of a section of a sample of the respective product (indicated in area percent "). Area %"), unless expressly stated otherwise.
Das Gefüge wird an Querschliffen bestimmt, die einer Ätzung mit 3% Nital (alkoholische Salpetersäure) unterzogen werden. Die Gefügebestimmung erfolgt im Rasterelektronenmikroskop bei 5000-facher Vergrößerung für die Bestimmung des Anteils des plattenartigen und anderen nicht plattenartigen Bainits und bei 20.000- bis 50.000-facher Vergrößerung für die Bestimmung der Plattenlänge, -breite und des Plattenabstands. Der Anteil an Restaustenit wird röntgendiffraktometrisch bestimmt.The structure is determined on cross sections that are etched with 3% Nital (alcoholic nitric acid). The structure is determined in a scanning electron microscope at 5000x magnification to determine the proportion of plate-like and other non-plate-like bainite and at 20,000 to 50,000x magnification to determine the plate length, width and distance between the plates. The proportion of retained austenite is determined using X-ray diffractometry.
Die Korngrenzen des Gefüges wird mit einem Electron Backscatter Diffraction (EBSD) bestimmt. Dafür werden Proben aus der 1/3 -Lage der Banddicke des Stahlflachprodukts entnommen. Diese Proben werden eingebettet und als Längsschliff präpariert. Direkt vor der EBSD Untersuchung wird die Oberfläche nochmal in einem Politurschritt behandelt. Die EBSD Messung erfolgt in einem 90*90 µm großen Messfeld in 0,1 µm Schritten. In den aufgenommenen Daten werden Großwinkel- und Kleinwinkelkorngrenzen bestimmt. Als Kleinwinkelkorngrenze wird eine Korngrenze bezeichnet, die ein Grenze zwischen zwei Körnern mit einem kleinen Orientierungsunterschied ist. Die Kleinwinkelkorngrenze ist definiert bis zu einem Rotationswinkel θ bis einschließlich 15°. In der vorliegenden Erfindung werden Missorientierungen unterhalb von fünf Grad ( θ< 5) nicht als Korngrenze gewertet. Oberhalb eines Rotationswinkels θ von 15° werden die Korngrenzen als Großwinkelkorngrenzen bezeichnet. Für alle Großwinkel- und Kleinwinkelkorngrenzen werden die Korngrenzenlänge bestimmt, indem der Analysesoftware TSL OIM Analyses 8.0 der Fa. Ametek die beschriebene Definition der Kleinwinkel- und Großwinkelkorngrenzen vorgegeben und dann die Korngrenzenlängen für den Messbereich automatisch bestimmt werden.The grain boundaries of the structure are determined using electron backscatter diffraction (EBSD). For this purpose, samples are taken from the 1/3 layer of the strip thickness of the flat steel product. These samples are embedded and prepared as a longitudinal section. Immediately before the EBSD examination, the surface is treated again in a polishing step. The EBSD measurement is carried out in a 90*90 µm measuring field in 0.1 µm steps. Large-angle and small-angle grain boundaries are determined in the recorded data. A small angle grain boundary is a grain boundary that is a boundary between two grains with a small difference in orientation. The small angle grain boundary is defined up to a rotation angle θ up to and including 15°. In the present invention, misorientations below five degrees (θ < 5) are not considered a grain boundary. Above a rotation angle θ of 15°, the grain boundaries are referred to as high-angle grain boundaries. The grain boundary lengths are determined for all large-angle and small-angle grain boundaries by specifying the described definition of the small-angle and large-angle grain boundaries in the analysis software TSL OIM Analyzes 8.0 from Ametek and then automatically determining the grain boundary lengths for the measuring range.
Mechanische Eigenschaften, wie Zugfestigkeit Rm, Streckgrenze Rp0,2, Bruchdehnung A80, die hier berichtet werden, sind im Zugversuch gemäß DIN-EN ISO 6982-1 ermittelt worden, soweit nicht ausdrücklich anders angegeben.Mechanical properties such as tensile strength Rm, yield strength Rp0.2, elongation at break A80, which are reported here, were determined in tensile tests in accordance with DIN-EN ISO 6982-1, unless expressly stated otherwise.
Für den Marciniak-Lochaufweitungstest wird aus dem erfindungsgemäßen Stahlflachprodukt Platinen in der Größe von ca. 220mm*200mm, allerdings mindestens in der Größe von ca. 180mm*180mm, geschnitten. In die Platine wird ein Stanzloch im Durchmesser von 20 mm durch ein mechanisches Scherschneiden erzeugt. Es werden für alle Proben identische Schneidparameter eingestellt. Die Breite des Schneidspalts liegt im Bereich von 10 bis 12 % der Dicke des untersuchten Stahlflachprodukts. Durch die Verwendung von identisch gestanzten Stanzlöchern ist ein Einfluss durch den Schneidprozess ausgeschlossen und es werden identische Bedingungen für alle Stempelgeometrien erreicht. Es wird nun das Marciniakwerkzeug mit einem Flachbodenstempel mit einem Durchmesser von 100 mm und einem Stempelkopfradius von 13 mm verwendet. Mittels des Werkzeuges wird das Stanzloch aufgeweitet. Verglichen damit wird bei einem Lochaufweitungsversuch nach ISO 16630 ein Loch mittels eine Kegelsstempel aufgeweitet. In dem hier angewendeten Marciniak-Lochaufweitungsverfahren bilden sich durch den Flachbodenstempel niedrige Dehnungsgradienten orthogonal zur Kante, die der Umformsituation im Presswerk sehr nahekommen.For the Marciniak hole expansion test, blanks in the size of approximately 220mm*200mm, but at least in the size of approximately 180mm*180mm, are cut from the flat steel product according to the invention. A punch hole with a diameter of 20 mm is created in the board using mechanical shear cutting. Identical cutting parameters are set for all samples. The width of the cutting gap is in the range of 10 to 12% of the thickness of the flat steel product examined. By using identically punched punch holes, influence from the cutting process is excluded and identical conditions are achieved for all punch geometries. The Marciniak tool with a flat-bottom punch with a diameter of 100 mm and a punch head radius of 13 mm is now used. The punch hole is expanded using the tool. In comparison, in a hole expansion test according to ISO 16630, a hole is expanded using a cone punch. In the Marciniak hole expansion process used here, the flat-bottom punch creates low strain gradients orthogonal to the edge, which are very close to the forming situation in the press shop.
Die Vermessung der Lochdurchmesser erfolgt mit einer Kamera der Firma IDS Typ UI-1240ML-M-GL mit einem telezentrischen Objektiv (TC13080 der Firma Opto Engineering). Um eine ausreichende Beleuchtung sicherzustellen wird optional ein Beleuchtungsring an der Kamera angebracht. Der Abstand der Kamera zur Probe ist so zu wählen, dass eine ausreichende Bildauflösung in Auswerteberich erzielt wird. Der Durchmesser des ausgeweiteten Lochs sollte >50% der Bildachsen ausfüllen. Der Versuch wird mit einer Niederhaltekraft von 400 kN und einer Ziehgeschwindigkeit von 1 ± 0,2 mm/s ausgeführt, bis ein Riss oder eine Einschnürung vorlag. Während des Versuches werden Bilder in einer Frequenz von 10 Hz aufgenommen. In der Auswertung wird das letzte Bild ausgewählt, auf dem noch keine Einschnürung oder Riss zu sehen ist. Um den Lochdurchmesser D zu bestimmen werden die Innenkanten des Lochdurchmessers in quer, längs und 2-mal diagonal zur Richtung bestimmt. Diese bestimmten Lochdurchmesser werden dann gemittelt. Dies wird mindestens an 3 Löchern wiederholt und ebenfalls gemittelt. Der gemittelte Lochdurchmesser wird mit dem Referenzlochdurchmesser verglichen und daraus eine Lochaufweitung LAW=D-D0/D0*100 bestimmt.The hole diameters are measured using a camera from IDS type UI-1240ML-M-GL with a telecentric lens (TC13080 from Opto Engineering). To ensure sufficient lighting, an optional lighting ring is attached to the camera. The distance between the camera and the sample must be chosen so that sufficient image resolution is achieved in the evaluation area. The diameter of the expanded hole should fill >50% of the image axes. The test is carried out with a hold-down force of 400 kN and a pulling speed of 1 ± 0.2 mm/s until a crack or constriction is present. During the experiment, images are recorded at a frequency of 10 Hz. In the evaluation, the last image is selected in which no constriction or crack can be seen. To determine the hole diameter D, the inner edges of the hole diameter are determined in the transverse, longitudinal and twice diagonal directions. These specific hole diameters are then averaged. This is repeated on at least 3 holes and also averaged. The average hole diameter is compared with the reference hole diameter and a hole expansion LAW=DD 0 /D 0 *100 is determined.
Aufgabe der vorliegenden Erfindung ist es das Gefüge in einem DP-Stahl so einzustellen, dass der Stahl für die Beanspruchung im Automobilbau, d.h. mit einer hohen Marciniak-Lochaufweitung (LAW) von mindestens 9,0%, geeignet ist. Gelöst wird die Aufgabe durch das Einstellen eines besonderen Verhältnisses von Großwinkelkorngrenzenlängen zu Kleinwinkelkorngrenzenlängen.The object of the present invention is to adjust the structure in a DP steel in such a way that the steel is suitable for the stress in automobile construction, ie with a high Marciniak hole expansion (LAW) of at least 9.0% is suitable. The task is solved by setting a special ratio of large-angle grain boundary lengths to small-angle grain boundary lengths.
Die Erfindung beschreibt ein kaltgewalztes Stahlflachprodukt, das
- aus einem Stahl mit der nachfolgend angegebenen Zusammensetzung bestehend aus (in Gew.-%)
- C: 0,02 - 0,25 %,
- Si: 0,05 - 0,8 %,
- Mn: 1,0 - 3,0 %,
- P: maximal 0,04 %
- S: maximal 0,01 %
- N: maximal 0,01 %
- besteht.
- Optional eines oder mehrere der folgenden Elemente aus der Gruppe "Al, Cr, Cu, Nb, Mo, Ni, Ti, V, B, Co, W":
- Al: 0,05 - 1,0 %
- Cr: 0,10 - 1,0 %
- Cu: 0,01 - 0,5 %
- Nb: 0,0005- 0,1 %
- Mo: 0,001 - 0,1 %
- Ni: 0,01-0,2%
- Ti: 0,001-0,1 %
- V: 0,0001 - 0,1 %
- B: 0,0002- 0,005 %
- Mg: 0,0003 -0,5 %
- Ca: 0,0001 - 0,1 %
- Co: 0,001- 0,1 %
- W: 0,01- 0,3 %
- und optional einem oder mehrere Elemente aus der Gruppe der seltenen Erden Metalle (SEM) mit der Maßgabe:
- Summe aller SEM: maximal 0,5 %
- Rest Eisen und unvermeidbare Verunreinigungen,
- wobei das Verhältnis der Großwinkelkorngrenzenlängen zu Kleinwinkelkorngrenzenlängen mehr als 4,0 beträgt.
- made of a steel with the following composition consisting of (in wt.%)
- C: 0.02 - 0.25%,
- Si: 0.05 - 0.8%,
- Mn: 1.0 - 3.0%,
- P: maximum 0.04%
- S: maximum 0.01%
- N: maximum 0.01%
- consists.
- Optionally one or more of the following elements from the group "Al, Cr, Cu, Nb, Mo, Ni, Ti, V, B, Co, W":
- Al: 0.05 - 1.0%
- Cr: 0.10 - 1.0%
- Cu: 0.01 - 0.5%
- Nb: 0.0005-0.1%
- Mon: 0.001 - 0.1%
- Ni: 0.01-0.2%
- Ti: 0.001-0.1%
- V: 0.0001 - 0.1%
- B: 0.0002-0.005%
- Mg: 0.0003 -0.5%
- Approximately: 0.0001 - 0.1%
- Co: 0.001-0.1%
- W: 0.01-0.3%
- and optionally one or more elements from the group of rare earth metals (SEM) with the proviso:
- Total of all SEM: maximum 0.5%
- residual iron and unavoidable impurities,
- where the ratio of the large angle grain boundary lengths to the small angle grain boundary lengths is more than 4.0.
Kohlenstoff "C" ist in dem erfindungsgemäßen Stahl in Gehalten von 0,02 % bis 0,25 % enthalten. Kohlenstoff sorgt im erfindungsgemäßen Stahl für eine hohe Festigkeit, in dem es bei der Martensitbildung eine entscheidende Rolle spielt und das Gebiet in dem Austenit gebildet wird, erweitert. Hierbei wurde eine optimierte Einstellung bei Werten von C ≥0,140 % gefunden, da sich ab diesem Wert ausreichend Martensitanteile bzw. ausreichend harter Martensit bilden, um die Festigkeit weiter zu erhöhen. Ist der Kohlenstoffgehalt allerdings zu groß, bilden sich zu verstärkt große Karbide, die für die Festigkeitssteigerung unwirksam sind. Zudem wird die Schweißbarkeit verringert. Aus diesem Grund ist der Kohlenstoffgehalt in der vorliegenden Erfindung auf 0,25 %, bevorzugt auf 0,17 % begrenzt.Carbon “C” is contained in the steel according to the invention in levels of 0.02% to 0.25%. Carbon ensures high strength in the steel according to the invention by playing a decisive role in the formation of martensite and expanding the area in which austenite is formed. An optimized setting was found at values of C ≥0.140%, since from this value onwards sufficient martensite components or sufficiently hard martensite are formed to further increase the strength. However, if the carbon content is too high, excessively large carbides are formed, which are ineffective in increasing strength. In addition, the weldability is reduced. For this reason, the carbon content in the present invention is limited to 0.25%, preferably 0.17%.
Silizium "Si" ist ein wichtiger Mischkristallhärter. Zudem wird es zur Einstellung des besonderen Gefüges in dieser Erfindung benötigt wird, denn es verzögert die Zementitausscheidung und unterdrückt somit die Perlitbildung. Außerdem kann es den Restaustenitgehalt erhöhen, der später im Verfahren in Martensit umgewandelt werden kann. Für diese Wirkung und einen erhöhten Korrosionswiderstand hat sich ein Anteil von mindestens gleich 0,05 %, und besonders ein Anteil von mindestens gleich 0,11 %, als besonders wirksam herausgestellt. Ein zu hoher Siliziumgehalt führt andererseits dazu, dass Korngrenzenoxidation auftritt und die Beschichtbarkeit und Oberflächeneigenschaften verschlechtern kann. Außerdem können bei einem zu hohen Siliziumgehalt Rekristallisationsvorgänge verzögert werden, was sich auf das Verhältnis der Groß- und Kleinwinkelkorngrenzen auswirkt. Daher ist der Gehalt von Silizium auf 0,8 %, bevorzugt 0,6 %, besonders bevorzugt 0,45 %, begrenzt.Silicon "Si" is an important solid solution hardener. In addition, it is needed to adjust the special structure in this invention, because it delays cementite precipitation and thus suppresses pearlite formation. It can also increase the residual austenite content, which can be converted to martensite later in the process. For this effect and increased corrosion resistance, a proportion of at least 0.05%, and especially a proportion of at least 0.11%, has proven to be particularly effective. On the other hand, too high a silicon content leads to grain boundary oxidation occurring and can deteriorate coatability and surface properties. In addition, if the silicon content is too high, recrystallization processes can be delayed, which affects the ratio of the large and small angle grain boundaries. Therefore, the silicon content is limited to 0.8%, preferably 0.6%, particularly preferably 0.45%.
Im erfindungsgemäßen Stahl ist Mangan "Mn" enthalten. Mit einem Gehalt ab 1,0 %, ermöglicht Mn die Martensitbildung, da die Perlitbildung unterdrückt wird. Als vorteilhaft hat sich ein Anteil von mindestens gleich 1,2 % und besonders vorteilhaft ein Anteil von mindestens gleich 1,5 % herausgestellt. Allerdings kann ein zu hoher Mn Anteil zu starken Seigerungen führen, weswegen der Mn-Anteil auf 3,0 % beschränkt ist. Außerdem schränkt ein hoher Mn-Anteil die Schweißeignung stark ein und verringert den Korrosionswiderstand. Daher hat sich ein Mn-Anteil von maximal 2,5 % und insbesondere von 2,3 % als besonders vorteilhaft herausgestellt.Manganese “Mn” is contained in the steel according to the invention. With a content of 1.0% or more, Mn enables martensite formation because pearlite formation is suppressed. A proportion of at least 1.2% and particularly advantageous a proportion of at least 1.5% have proven to be advantageous. However, too high a Mn content can lead to severe segregation, which is why the Mn content is limited to 3.0%. In addition, a high Mn content severely limits weldability and reduces corrosion resistance. Therefore, an Mn content of a maximum of 2.5% and in particular 2.3% has proven to be particularly advantageous.
Die Zugabe von Phosphor "P" schränkt die Schweißeignung stark ein und sollte daher auf 0,04% beschränkt sein, wobei Gehalte von 0,025 %, insbesondere von 0,022 % besonders vorteilhaft sind. Im erfindungsgemäßen Stahl hat es sich herausgestellt, dass es vorteilhaft sein kann, wenn P mit mindestens gleich 0,002 %, insbesondere 0,006 %, enthalten ist, da dadurch die Mischkristallhärtung gefestigt wird.The addition of phosphorus "P" severely limits the suitability for welding and should therefore be limited to 0.04%, with levels of 0.025%, in particular 0.022%, being particularly advantageous. It has been found in the steel according to the invention that it can be advantageous if P is contained at least equal to 0.002%, in particular 0.006%, since this strengthens the solid solution hardening.
Schwefel "S" kann zur Bildung von Mn-Sulfiden führen, welche die Umformbareigenschaften stark verschlechtern. Daher ist im erfindungsgemäßen Stahl der Gehalt auf 0,01% beschränkt, wobei eine Beschränkung auf 0,005 % und insbesondere auf 0,003 % vorteilhaft sein kann. Eine Verunreinigung mit Schwefel lässt sich während der Stahlherstellung nicht komplett vermeiden.Sulfur "S" can lead to the formation of Mn sulfides, which severely impair the formable properties. Therefore, the content in the steel according to the invention is limited to 0.01%, although a limitation to 0.005% and in particular to 0.003% can be advantageous. Contamination with sulfur cannot be completely avoided during steel production.
Stickstoff "N" kann bei Gehalten über 0,010 % zur Bildung von groben Ti- und Al-Nitriden führen. Zur Vermeidung dieser Nitride hat sich ein maximaler Gehalt von 0,007 % als besonders vorteilhaft herausgestellt. Während der Stahlherstellung lässt sich eine Verunreinigung durch Stickstoff nicht komplett vermeiden.Nitrogen “N” can lead to the formation of coarse Ti and Al nitrides at levels above 0.010%. To avoid these nitrides, a maximum content of 0.007% has proven to be particularly advantageous. Nitrogen contamination cannot be completely avoided during steel production.
Neben den zuvor erläuterten Verunreinigungen P, S, und N können auch noch weitere Elemente als Verunreinigungen im Stahl vorhanden sein. Diese weiteren Elemente werden unter den "unvermeidbaren Verunreinigungen" zusammengefasst. Bevorzugt beträgt der Gehalt an diesen "unvermeidbaren Verunreinigungen" in Summe maximal 0,2 %, bevorzugt maximal 0,1 %. Die nachfolgend beschriebenen optionalen Legierungselemente "Al, Cr, Cu, Nb, Mo, Ni, Ti, V, B, Co, W", für die eine Untergrenze angegeben ist, können auch in Gehalten unterhalb der jeweiligen Untergrenze als unvermeidbare Verunreinigungen im Stahlsubstrat vorkommen. In dem Fall werden sie ebenfalls zu den "unvermeidbaren Verunreinigungen" gezählt, deren Gesamtgehalt auf maximal 0,2 %, bevorzugt maximal 0,1 % begrenzt ist.In addition to the previously explained impurities P, S, and N, other elements can also be present as impurities in the steel. These other elements are grouped under the “unavoidable impurities”. The content of these “unavoidable impurities” is preferably a maximum of 0.2% in total, preferably a maximum of 0.1%. The optional alloying elements “Al, Cr, Cu, Nb, Mo, Ni, Ti, V, B, Co, W” described below, for which a lower limit is specified, can also occur in levels below the respective lower limit as unavoidable impurities in the steel substrate . In this case, they are also counted among the "unavoidable impurities", the total content of which is limited to a maximum of 0.2%, preferably a maximum of 0.1%.
Aluminium "Al" kann dem erfindungsgemäßen Stahl hinzugefügt werden, um den Korrosionswiderstand zu erhöhen und den Restaustenitanteil zu erhöhen. Ein höher Restaustenitanteil ergibt sich bei Zugabe von Aluminium durch eine Verzögerung der Bildung von Zementitausscheidungen. Es hat sich hierfür im erfindungsgemäßen Stahlflachprodukt ein Aluminiumanteil von größer gleich 0,05 % als vorteilhaft herausgestellt. Anderseits kann ein zu hoher Alumniumanteil zu einer Bildung von groben Al-Nitriden führen, die zu einer versprödenden Wirkung und damit zu einer schlechteren Umformbarkeit führen. Zudem können höhere Al-Gehalte zu einem schlechteren Gießverhalten führen, da Aluminiumverbindungen zu Clogging führen können. In der vorliegenden Erfindung ist daher eine Begrenzung des Aluminiumgehaltes auf 1,0 %, bevorzugt 0,8 %, vorgesehen.Aluminum "Al" can be added to the steel of the invention to increase corrosion resistance and increase the retained austenite content. A higher residual austenite content results from the addition of aluminum by delaying the formation of cementite precipitates. For this purpose, an aluminum content of greater than or equal to 0.05% in the flat steel product according to the invention has proven to be advantageous. On the other hand, too high an aluminum content can lead to the formation of coarse Al nitrides, which have an embrittling effect and thus poorer formability. In addition, higher Al contents can lead to poorer casting behavior, as aluminum compounds can lead to clogging. The present invention therefore limits the aluminum content to 1.0%, preferably 0.8%.
Durch Zugabe von Chrom "Cr" kann die Bainitbildung verzögert werden, wodurch in dem erfindnungsgemäßen Stahlflachprodukt ein höherer Martensitanteil erreicht wird. Außerdem wird die Härtbarkeit durch Chrom erhöht. Ein Chromanteil von größer gleich 0,10 % hat sich als besonders vorteilhaft herausgestellt. Chrom kann allerdings durch die Bildung von Cr-Oxiden zu Korngrenzenoxidation führen. Daher ist der Chromgehalt hier auf 1,0 %, bevorzugt 0,9 %, begrenzt.By adding chromium “Cr”, the formation of bainite can be delayed, whereby a higher proportion of martensite is achieved in the flat steel product according to the invention. In addition, hardenability is increased by chromium. A chromium content of greater than or equal to 0.10% has proven to be particularly advantageous. However, chromium can lead to grain boundary oxidation through the formation of Cr oxides. The chromium content here is therefore limited to 1.0%, preferably 0.9%.
Die Zugabe von Kupfer "Cu" in das erfindungsgemäße Stahlflachprodukt verbessert die Korrosionsbeständigkeit und kann sehr feine festigkeitssteigernde Cu-Ausscheidungen bilden. Daher kann eine Zugabe von mindestens gleich 0,01 % vorteilhaft in der vorliegenden Erfindung sein. Allerdings sollte der Kupfergehalt auf 0,5 % begrenzt sein, da ansonsten im Warmwalzprozess zur sogenannten Rotbrüchigkeit, d.h. es bilden sich Risse in der Bramme, kommen kann.The addition of copper "Cu" to the flat steel product according to the invention improves the corrosion resistance and can form very fine strength-increasing Cu precipitates. Therefore, an addition of at least equal to 0.01% may be advantageous in the present invention. However, the copper content should be limited to 0.5%, otherwise so-called red brittleness can occur in the hot rolling process, i.e. cracks can form in the slab.
Optional kann dem erfindungsgemäßen Stahlflachprodukt Niob "Nb" hinzugefügt werden. Bei Zugabe von Niob in geringen Mengen bilden sich feine, festigkeitssteigernde Kohlenstoffnitride. Hierbei hat sich ein Gehalt von mindestens gleich 0,0005 % als vorteilhaft herausgestellt. Der festigkeitssteigernde Effekt der Kohlenstoffnitride erschöpft sich allerdings, sobald der Niobgehalt zu groß wird. Außerdem können hohe Gehalte von Niob die Kaltformbarkeit und die Schweißeigenschaften verschlechtern. Hier hat sich ein Gehalt von maximal 0,1 %, bevorzugt 0,007 %, als vorteilhaft herausgestellt.Optionally, niobium “Nb” can be added to the flat steel product according to the invention. When small amounts of niobium are added, fine, strength-increasing carbon nitrides are formed. A content of at least 0.0005% has proven to be advantageous. However, the strength-increasing effect of carbon nitrides is exhausted as soon as the niobium content becomes too high. In addition, high levels of niobium can impair cold formability and welding properties. A content of a maximum of 0.1%, preferably 0.007%, has proven to be advantageous here.
Molybdän "Mo" bildet ebenfalls bei geringen Mengen feine, festigkeitssteigernde Kohlenstoffnitride. Daher hat sich eine Zugabe von größer gleich 0,001 % als vorteilhaft herausgestellt. Der festigkeitssteigernde Effekt der Kohlenstoffnitride erschöpft sich allerdings, sobald der Molybdängehalt zu groß wird. Außerdem können hohe Gehalte von Molybdän die Kaltformbarkeit und die Schweißeigenschaften verschlechtern. Hier hat sich ein Gehalt von maximal 0,1 %, bevorzugt 0,050 %, besonders bevorzugt 0,007 %, als vorteilhaft herausgestellt.Molybdenum "Mo" also forms fine, strength-increasing carbon nitrides in small amounts. An addition of greater than or equal to 0.001% has therefore proven to be advantageous. However, the strength-increasing effect of carbon nitrides is exhausted as soon as the molybdenum content becomes too high. In addition, high levels of molybdenum can impair cold formability and welding properties. Here, a content of a maximum of 0.1%, preferably 0.050%, particularly preferably 0.007%, has proven to be advantageous.
Nickel "Ni" erhöht die Menge und Stabilität des Austenits und mindert die Rotbrüchigkeit mit Cu. Außerdem kann Nickel die Marciniak-Lochaufweitung (LAW) verbessern. Daher wird dem erfindungsgemäßen Stahlflachprodukt optional mindestens gleich 0,01 %, besonders vorteilhaft 0,015 % Ni, hinzugefügt. Aus Kostengründen soll die Zugabe allerdings möglichst gering auf maximal 0,2 %, bevorzugt 0,1 % und besonders bevorzugt auf 0,06 % begrenzt werden.Nickel "Ni" increases the amount and stability of austenite and reduces red brittleness with Cu. In addition, nickel can improve Marciniak hole expansion (LAW). Therefore, at least 0.01%, particularly advantageously 0.015% Ni, is optionally added to the flat steel product according to the invention. For cost reasons, however, the addition should be limited as little as possible to a maximum of 0.2%, preferably 0.1% and particularly preferably to 0.06%.
Titan "Ti" bindet Stickstoff im Stahl und verhindert somit die Bildung versprödender Bornitride. Außerdem kann Titan bei geringer Menge auch festigkeitssteigernde Kohlenstoffnitride bilden. Hier hat sich eine Zugabe von größer gleich 0,001 %, bevorzugt 0,004 %, als vorteilhaft herausgestellt. Bei einer zu hohen Zugabe von Titan erschöpft sich der Vorteil der festigkeitssteigernden Kohlenstoffnitride, da sie zu groß werden. Des Weiteren können sich grobe versprödende Ti-Nitride bilden. Eine Begrenzung des Titangehaltes auf maximal 0,1 %, bevorzugt 0,03 % und besonders bevorzugt 0,006 % hat sich für das erfindungsgemäße Stahlflachprodukt als vorteilhaft erwiesen.Titanium "Ti" binds nitrogen in the steel and thus prevents the formation of brittle boron nitrides. In addition, in small amounts, titanium can also form strength-increasing carbon nitrides. Here an addition of greater than or equal to 0.001%, preferably 0.004%, has proven to be advantageous. If too much titanium is added, the advantage of the strength-increasing carbon nitrides is exhausted because they become too large. Furthermore, coarse, brittle Ti nitrides can form. Limiting the titanium content to a maximum of 0.1%, preferably 0.03% and particularly preferably 0.006%, has proven to be advantageous for the flat steel product according to the invention.
Optional kann dem erfindungsgemäßen Stahl Vanadium "V" hinzugefügt werden, welches in geringen Mengen ebenfalls feine Kohlenstoffnitride bildet. Die Kohlenstoffnitride können die Korngrenzen pinnen. Durch das Pinnen wird die Kornvergröberung bei hohen Temperaturen vermindert, was positiv auf das Verhältnis Großwinkelkorngrenzenlängen zu Kleinwinkelkorngrenzenlängen wirkt. Hierzu wird dem erfindungsgemäßen Stahl mindestens gleich 0,0001 %, bevorzugt 0,002 %, Vanadium hinzugefügt. Bei einer zu hohen Zugabe von Vanadium werden die Kohlenstoffnitridausscheidungen größer und somit unwirksam. Außerdem ist die Menge der Zugabe von Vanadium aus Kostengründen begrenzt. Im erfindungsgemäßen Stahl ist die Menge auf 0,1 %, bevorzugt, 0,030 % und besonders bevorzugt aus 0,0015 % begrenzt.Optionally, vanadium "V" can be added to the steel according to the invention, which also forms fine carbon nitrides in small amounts. The carbon nitrides can pin the grain boundaries. Pinning reduces grain coarsening at high temperatures, which has a positive effect on the ratio of large-angle grain boundary lengths to small-angle grain boundary lengths. For this purpose, at least 0.0001%, preferably 0.002%, vanadium is added to the steel according to the invention. If too much vanadium is added, the carbon nitride precipitates become larger and therefore ineffective. In addition, the amount of vanadium added is limited for cost reasons. In the steel according to the invention, the amount is limited to 0.1%, preferably 0.030% and particularly preferably 0.0015%.
Die Zugabe von Bor "B" führt zu einer Festigkeitssteigerung. Dafür können dem erfindungsgemäßen Stahl mindestens gleich 0,0002 %, besonders bevorzugt mindestens 0,001 %, hinzugefügt werden. Bei einer zu hohen Zugabemenge von Bor bilden sich Eisenboride. Diese Eisenboride können bei ca. 1200° C schmelzen und ein Materialversagen hervorrufen. Aus diesem Grund ist der Boranteil im erfindungsgemäßen Stahl auf 0,005 %, bevorzugt 0,0015 %, begrenzt.The addition of boron "B" leads to an increase in strength. For this purpose, at least 0.0002%, particularly preferably at least 0.001%, can be added to the steel according to the invention become. If the amount of boron added is too high, iron borides are formed. These iron borides can melt at approx. 1200° C and cause material failure. For this reason, the boron content in the steel according to the invention is limited to 0.005%, preferably 0.0015%.
Die optionale Zugabe von Magnesium "Mg" kann entschwefelnd und desoxidierend wirken. Daher kann dem erfindungsgemäßen Stahl 0,0003 % hinzugefügt werden. Aus Kostengründen wird die Mg Zugabe begrenzt auf maximal 0,5% Mg, bevorzugt 0,1 % besonders bevorzugt 0,003 %.The optional addition of magnesium “Mg” can have a desulfurizing and deoxidizing effect. Therefore, 0.0003% can be added to the steel according to the invention. For cost reasons, the addition of Mg is limited to a maximum of 0.5% Mg, preferably 0.1%, particularly preferably 0.003%.
Kalzium "Ca" kann dem erfindungsgemäßen Stahlflachprodukt zugeführt werden, um den freien Schwefel abzubinden. Freier Schwefel segregiert zu den Korngrenzen und führt dadurch zum Versagen des Materials, d.h. die Marciniak-Lochaufweitung verschlechtert sich. Daher kann dem erfindungsgemäßen Stahlflachprodukt eine optionale Menge von mindestens gleich 0,0001 % hinzugefügt werden. In hohen Mengen ist Kalzium im Stahlflachprodukt nicht mehr löslich, weswegen die Zugabe auf maximal 0,1 %, bevorzugt 0,010 %, besonders bevorzugt 0,003 % begrenzt wird.Calcium "Ca" can be added to the flat steel product according to the invention in order to bind the free sulfur. Free sulfur segregates to the grain boundaries and thereby leads to failure of the material, i.e. the Marciniak hole expansion deteriorates. Therefore, an optional amount of at least equal to 0.0001% can be added to the flat steel product according to the invention. In large quantities, calcium is no longer soluble in the flat steel product, which is why the addition is limited to a maximum of 0.1%, preferably 0.010%, particularly preferably 0.003%.
Kobalt "Co" erhöht die Menge und die Stabilität des Austenits. Als besonders vorteilhaft hat sich eine Kobaltzugabe von mindestens gleich 0,001 % erwiesen. Aus Kostengründen sollen dem erfindungsgemäßen Stahl maximal 0,1 %, bevorzugt 0,010 %, besonders bevorzugt 0,0007 %, Kobalt hinzugefügt werden.Cobalt “Co” increases the amount and stability of austenite. A cobalt addition of at least 0.001% has proven to be particularly advantageous. For cost reasons, a maximum of 0.1%, preferably 0.010%, particularly preferably 0.0007%, of cobalt should be added to the steel according to the invention.
Wolfram "W" wirkt im erfindungsgemäßen Stahl entschwefelnd und desoxidierend. Außerdem können mit Hilfe von Wolfram festigkeitssteigernde Karbide gebildet werden. Optional kann daher Wolfram mit mindestens gleich 0,01 % hinzugefügt werden. Aus Kostengründen wird in der vorliegenden Erfindung maximal 0,3 % Wolfram eingesetzt.Tungsten “W” has a desulphurizing and deoxidizing effect in the steel according to the invention. In addition, strength-increasing carbides can be formed with the help of tungsten. Tungsten can therefore optionally be added at a level of at least 0.01%. For cost reasons, a maximum of 0.3% tungsten is used in the present invention.
Im erfindungsgemäßen Stahlfachprodukt können optional die seltenen Erden Metalle (SEM) wie z.B.: Cer "Ce", Lathan "La" und Yttrium "Y" in Summe mit einem Maximalgehalt von 0,5 % enthalten sein. Größere Gehalte der SEM können zu Problemen beim Gießen des Stahls führen. Vorteilhaft ist eine minimale Summe aller SEM Elemente von mindestens gleich 0,003 %, da dies eine entschwefelnde sowie desoxidierende Wirkung hat.The steel product according to the invention can optionally contain the rare earth metals (SEM) such as: cerium "Ce", lathane "La" and yttrium "Y" in total with a maximum content of 0.5%. Larger SEM contents can lead to problems when casting the steel. A minimum sum of all SEM elements of at least 0.003% is advantageous, as this has a desulphurizing and deoxidizing effect.
Das erfindungsgemäße Stahlflachprodukt kann eine Kohlenstoffäqivalent Cäq
Das erfindungsgemäße kaltgewalztes Stahlflachprodukt insbesondere nach dem erfindungsgemäßen Verfahren ist dadurch gekennzeichnet, dass der Stahl ein mindestens aus zwei Phasen bestehendes Gefüge aufweist, das mehr als 5 % Martensit und mehr als 20 % Ferrit sowie bis zu 65% Bainit und bis zu 10 % Restaustenit umfasst. In einer bevorzugten Ausführung ist der Martensitanteil auf 90% und besonders bevorzugt 80% begrenzt, um eine ausreichende Duktilität für die Bauteilformung zu gewährleisten. Der Martensitgehalt besteht bevorzugt aus frischem und angelassenem Martensit. In einer besonderen Ausführungsform bei Martensitgehalten größer 50 % können bis zu 10 % des Martensits als angelassener Martensit vorliegen. Außerdem kann insbesondere der Ferritanteil auf 80 % begrenzt sein, damit die gewünschte Festigkeit eingestellt werden kann. Bei einer Weiterbildung ist der Ferritgehalt mindestens gleich 30%. In einer besonderen Ausführung ist der Bainitanteil auf maximal 20 % begrenzt.The cold-rolled flat steel product according to the invention, in particular according to the method according to the invention, is characterized in that the steel has a structure consisting of at least two phases, which comprises more than 5% martensite and more than 20% ferrite as well as up to 65% bainite and up to 10% retained austenite . In a preferred embodiment, the martensite content is limited to 90% and particularly preferably 80% in order to ensure sufficient ductility for component shaping. The martensite content preferably consists of fresh and tempered martensite. In a special embodiment, with martensite contents greater than 50%, up to 10% of the martensite can be present as tempered martensite. In addition, the ferrite content in particular can be limited to 80% so that the desired strength can be adjusted. In the case of further training, the ferrite content is at least 30%. In a special version, the bainite content is limited to a maximum of 20%.
Die Mikrostruktur des erfindungsgemäßen Stahlflachprodukts weist ein besonderes Verhältnis der Großwinkelkorngrenzenlänge zur Kleinwinkelkorngrenzenlänge auf. Großwinkelkorngrenzen behindern die Bewegung von Versetzungen von einem Korn in das andere. Kleinwinkelkorngrenzen bewirken durch ihre deutlich höhere Versetzungsdichte eine Verfestigung im Korn, welches zu unterschiedlichen Verformungswiderständen führt und einer Kerbwirkung gleichkommt. Diese Kerbe verursacht lokalisierte Verformungen und vermindert die Lochaufweitungen. Die erfindungsgemäße Mikrostruktur zeichnet sich durch das Verhältnis der Großwinkelkorngrenzenlängen zu Kleinwinkelkorngrenzenlängen mit mehr als 4,0, bevorzugt mehr als 4,5, besonders bevorzugt 6,0, aus. Es hat sich gezeigt, dass bei derartigen Verhältnissen die mechanischen Eigenschaften positiv beeinflusst werden, insbesondere die Marciniak-Lochaufweitung.The microstructure of the flat steel product according to the invention has a special ratio of the large angle grain boundary length to the small angle grain boundary length. High angle grain boundaries impede the movement of dislocations from one grain to the other. Due to their significantly higher dislocation density, small-angle grain boundaries cause hardening in the grain, which leads to different deformation resistances and is equivalent to a notch effect. This notch causes localized deformations and reduces hole expansion. The microstructure according to the invention is characterized by the ratio of the large-angle grain boundary lengths to the small-angle grain boundary lengths of more than 4.0, preferably more than 4.5, particularly preferably 6.0. It has been shown that under such conditions the mechanical properties are positively influenced, in particular the Marciniak hole expansion.
Bei einer speziellen Ausgestaltung zeichnet sich das kaltgewalzte Stahlflachprodukt durch eine Bruchdehnung A80 von mindestens 8%, bevorzugt mindestens 10 %, besonders bevorzugt mindestens 14 %, aus. Die Zugfestigkeit Rm beträgt mindestens 570 MPa, bevorzugt mindestens 590 MPa. Als besonders vorteilhaft hat sich ein Produkt aus Bruchdehnung A80 und Zugfestigkeit Rm von mindestens 8000 MPa%, bevorzugt 10000 MPa% herausgestellt. Dieses Produkt aus Bruchdehnung A80 und Zugfestigkeit Rm kann sich durch ein wirksames Verhindern von Versetzungsbewegungen einstellen. Diese Versetzungsbewegungen sind vermindert durch das besondere Verhältnis von Großwinkelkorngrenzenlängen zu Kleinwinkelkorngrenzenlängen.In a special embodiment, the cold-rolled flat steel product is characterized by an elongation at break A80 of at least 8%, preferably at least 10%, particularly preferably at least 14%. The tensile strength Rm is at least 570 MPa, preferably at least 590 MPa. A product of elongation at break A80 and tensile strength Rm of at least 8000 MPa%, preferably 10000 MPa%, has proven to be particularly advantageous. This product of elongation at break A80 and tensile strength Rm can be achieved by effectively preventing dislocation movements. These dislocation movements are reduced by the special ratio of large-angle grain boundary lengths to small-angle grain boundary lengths.
Bei einer Weiterbildung beträgt die Streckgrenze Rp0,2 des Stahls 350 MPa bis 850 MPa.In a further development, the yield strength Rp0.2 of the steel is 350 MPa to 850 MPa.
Die Marciniak-Lochaufweitung in einer speziellen Ausgestaltung des Stahlflachprodukts beträgt mindestens 9,0 %, bevorzugt mindestens 10,0 %, besonders bevorzugt 12,0 %. Der Marciniak-Lochaufweitungstest bietet die Möglichkeit praxisgerecht, nah an der wirklichen späteren Umformungsrealität, die DP-Stähle zu testen.The Marciniak hole expansion in a special embodiment of the flat steel product is at least 9.0%, preferably at least 10.0%, particularly preferably 12.0%. The Marciniak hole expansion test offers the opportunity to test the DP steels in a practical manner, close to the actual later forming reality.
Das erfindungsgemäße Stahlflachprodukt wird in einem besonderen Verfahren hergestellt wobei unter anderem folgende Arbeitsschritte durchlaufen werden:
- a) Vergießen eines Stahls mit der erfindungsgemäßen Zusammensetzung zu einer Bramme;
- b) Wiedererwärmen der Bramme auf eine 1200 - 1300 ° C betragende Wiedererwärmungstemperatur THOM;
- c) Warmwalzen der wiedererwärmten Bramme zu einem Warmband, wobei die Warmwalzendtemperatur TWE des Warmbands bei Beendigung des Warmwalzens 800-1000°C beträgt (bevorzugt 920-950°C);
- d) Haspeln des Warmbands bei einer Haspeltemperatur THA von 400 - 700 °C (bevorzugt 500-600°C) ;
- e) Beizen des Warmbands;
- f) Kaltwalzen des Warmbands in einem oder mehreren Kaltwalzschritten zu einem kaltgewalzten Stahlflachprodukt mit einer Banddicke d;
- g) Aufheizen des Stahlflachproduktes auf eine Glühtemperatur T glüh von mehr als 800°C, wobei die mittlere Aufheizintensität I zwischen 200°C und 800 °C mindestens
- h) Abkühlen des kaltgewalzten Stahlflachprodukts auf Raumtemperatur
- a) casting a steel with the composition according to the invention to form a slab;
- b) reheating the slab to a reheating temperature T HOM of 1200 - 1300 ° C;
- c) hot rolling the reheated slab into a hot strip, the hot rolling end temperature T WE of the hot strip at the end of the hot rolling being 800-1000 ° C (preferably 920-950 ° C);
- d) coiling the hot strip at a coiling temperature T HA of 400 - 700 ° C (preferably 500 - 600 ° C);
- e) pickling of the hot strip;
- f) cold rolling the hot strip in one or more cold rolling steps to form a cold-rolled flat steel product with a strip thickness d;
- g) Heating the flat steel product to an annealing temperature T annealing of more than 800 ° C, with the average heating intensity I between 200 ° C and 800 ° C at least
- h) Cooling the cold-rolled flat steel product to room temperature
Im Folgenden werden die einzelnen Arbeitsschritte detailliert beschrieben:The individual work steps are described in detail below:
Für die erfindungsgemäße Zusammensetzung der erfindungsgemäßen Bramme und die optionalen Variationsmöglichkeiten gelten dieselben Hinweise, die bereits im Zusammenhang mit der Zusammensetzung des erfindungsgemäßen Stahlflachproduktes getroffen wurden.The same information that has already been made in connection with the composition of the flat steel product according to the invention applies to the composition according to the invention of the slab according to the invention and the optional possible variations.
Die erfindungsgemäße Bramme wird in diesem Arbeitsschritt auf eine Temperatur von 1200-1300° C wiedererwärmt. Dadurch bildet sich in dem Produkt Austenit. Die untere Grenze der Wiedererwärmungstemperatur THOM sollte mindestens 1200 ° C betragen, damit eine Homogenität im Gefüge in der Bramme erreicht wird. Wird eine Obergrenze von 1300° C bei der Erwärmungstemperatur überschritten, kann es auf der Bramme zu Aufschmelzungen kommen oder die Bramme zerbrechen, da die Warmfestigkeit überschritten wird. Dabei weisen die Brammen eine Dicke von 200-300 mm auf.In this step, the slab according to the invention is reheated to a temperature of 1200-1300 ° C. This causes austenite to form in the product. The lower limit of the reheating temperature T HOM should be at least 1200 ° C so that homogeneity in the structure in the slab is achieved. If an upper limit of 1300° C is exceeded at the heating temperature, melting can occur on the slab or the slab can break because the high-temperature strength is exceeded. The slabs have a thickness of 200-300 mm.
Das erfindungsgemäße Produkt wird in konventioneller Weise mit aus dem Stand der Technik bekannten Aggregaten warmgewalzt bis zu einer Enddicke von 1,5 bis 7 mm, bevorzugt 1,7 bis 4 mm. Die Warmwalzendtemperatur (kurz TWE) liegt mindestens gleich bei 800° C, bevorzugt 920 ° C. Besonders bevorzugt liegt die Warmwalzendtemperatur oberhalb der Ac3 Temperatur.The product according to the invention is hot-rolled in a conventional manner using units known from the prior art to a final thickness of 1.5 to 7 mm, preferably 1.7 to 4 mm. The hot rolling final temperature (T WE for short) is at least 800° C., preferably 920° C. The hot rolling final temperature is particularly preferably above the Ac3 temperature.
Dabei ist die zu überschreitende Mindesttemperatur Ac3 gemäß der von
Nach dem Warmwalzen wird das Warmband bei einer Temperatur von 400 °C -700 °C bevorzugt bei 500 °C- 600 °C gehaspelt. Bei Haspeltemperaturen (kurz THA) unterhalb von 500 °C bildet sich zu schnell Martensit, was zu einer hohen Festigkeit führt und eine spätere Verformung problematisch macht. Oberhalb von 600°C steigt die Gefahr einer Korngrenzenoxidation. Nach dem Haspel wird das Coil auf Raumtemperatur abgekühlt.After hot rolling, the hot strip is coiled at a temperature of 400 °C - 700 °C, preferably at 500 °C - 600 °C. At reel temperatures (T HA for short) below 500 °C, martensite forms too quickly, which leads to high strength and makes later deformation problematic. Above 600°C the risk of grain boundary oxidation increases. After reeling, the coil is cooled to room temperature.
In einem folgenden Schritt wird das Warmband gebeizt, um eine Entfernung des Zunders zu erreichen. Bevorzugt kann das Beizen chemisch mittels Salz- und/oder Schwefelsäure erfolgen. Besonders bevorzugt erfolgt das Beizen in einem Temperaturbereich 80 bis 95 °C.In a subsequent step, the hot strip is pickled in order to remove the scale. Pickling can preferably be carried out chemically using hydrochloric and/or sulfuric acid. Pickling is particularly preferably carried out in a temperature range of 80 to 95 °C.
Anschließend wird das Warmband kaltgewalzt. Dies geschieht in einem oder mehreren Kaltwalzschritten bis zu einer Endbanddicke von d= 0,5-3 mm und einem Umformgrad von bis 80 %.The hot strip is then cold rolled. This is done in one or more cold rolling steps up to a final strip thickness of d = 0.5-3 mm and a degree of deformation of up to 80%.
Das Stahlflachprodukt wird auf Raumtemperatur abgekühlt.
Anschließend wird das kaltgewalzte Stahlflachprodukt in einem Durchlaufofen auf eine Glühtemperatur T glüh von mehr als 800°C gebracht. Die mittlere Aufheizintensität
The cold-rolled flat steel product is then brought to an annealing temperature T annealing of more than 800 ° C in a continuous furnace. The average heating intensity
Eine typische Glühdauer bei der das Stahlflachprodukt bei der Glühtemperatur gehalten wird, beträgt bevorzugt mindestens gleich 10 s. Maximal beträgt die Glühdauer bevorzugt 1000 s.A typical annealing time during which the flat steel product is kept at the annealing temperature is preferably at least 10 s. The maximum annealing time is preferably 1000 s.
Nachdem das Stahlflachprodukt auf T glüh gebracht wird, wird es auf Raumtemperatur abgekühlt. Dieser Abkühlschritt erfolgt im Mittel mit höchstens 100 K/s. Insbesondere kann das Abkühlen auf Raumtemperatur in zwei Zwischenschritten erfolgen, wobei das kaltgewalzte Stahlflachprodukt in dem ersten Zwischenschritt von Glühtemperatur auf eine erste Abkühltemperatur T1 mit einer mittleren Abkühlrate θ1 kleiner 100K/s, bevorzugt kleiner 10 K/s, besonders bevorzugt kleiner 5 K/s, abgekühlt wird und wobei kaltgewalzte Stahlflachprodukt in dem zweiten Zwischenschritt auf eine zweite maximale Abkühltemperatur T2 mit einer Abkühlrate θ2 kleiner 100 K/s abgekühlt wird, wobei für die Abkühltemperaturen T1, T2 gilt:
T 1 > T 2, 450°C ≤ T 1 ≤ 800 °C (bevorzugt 650°C ≤ T 1 ≤ 750 °C) und 400 °C ≤ T 2 ≤ 600 °CAfter the flat steel product is brought to T annealing , it is cooled to room temperature. This cooling step takes place on average at a maximum of 100 K/s. In particular, the cooling to room temperature can take place in two intermediate steps, with the cold-rolled flat steel product in the first intermediate step from annealing temperature to a first cooling temperature T 1 with an average cooling rate θ 1 of less than 100 K/s, preferably less than 10 K/s, particularly preferably less than 5 K /s, and wherein cold-rolled flat steel product is cooled in the second intermediate step to a second maximum cooling temperature T 2 with a cooling rate θ 2 less than 100 K/s, the following applies to the cooling temperatures T 1 , T 2 :
T 1 > T 2 , 450°C ≤ T 1 ≤ 800 °C (preferably 650°C ≤ T 1 ≤ 750 °C) and 400 °C ≤ T 2 ≤ 600 °C
Durch das zweistufige Abkühlen kann Perlit im ersten Schritt vermieden werden, ohne energetisch aufwändige hohe Abkühlraten verwenden zu müssen. Im zweiten Schritt kann durch hohe Abkühlraten die Umwandlung von Restaustenit in Martensit bewirkt werden.Through two-stage cooling, pearlite can be avoided in the first step without having to use energetically expensive high cooling rates. In the second step, high cooling rates can be used to convert retained austenite into martensite.
Optional kann das erfindungsgemäße Stahlflachprodukt mit einer metallischen Schutzschicht versehen werden. Insbesondere Schmelztauchbeschichtungen auf Zink-Basis können verwendet werden. Diese Beschichtung folgt zwischen den Arbeitsschritten f) und g) in dem oben beschriebenen Verfahren.Optionally, the flat steel product according to the invention can be provided with a metallic protective layer. In particular, zinc-based hot-dip coatings can be used. This coating occurs between steps f) and g) in the process described above.
Optional kann das Stahlflachprodukt dressiert werden um ausgeprägte Streckgrenzen, Bandwelligkeiten einzuebnen und eine ideale Rauheit einzustellen. Besonders bevorzugt ist eine Kaltverformung von 0,2-3 %.Optionally, the flat steel product can be tempered to level out pronounced yield points, strip waviness and to achieve ideal roughness. A cold deformation of 0.2-3% is particularly preferred.
Außerdem kann das Stahlflachprodukt optional zwischen oder nach dem letzten Verarbeitungsschrittt beölt werden. Die Beölung dient als temporärer Korrosionsschutz bis zum nächsten Verarbeitungsschritt oder für den Transport.In addition, the flat steel product can optionally be oiled between or after the last processing step. The oiling serves as temporary corrosion protection until the next processing step or for transport.
Nachfolgend wird die Erfindung anhand von Ausführungsbeispielen näher erläutert. Zur Erprobung der Erfindung wurden 6 Schmelzen A-F hergestellt. Die Zusammensetzung der Schmelzen sind Tabelle 1 angegeben. Die Schmelzen wurden in einer konventionellen Stranggießanlage zu Brammen vergossen und anschließend wurden die Brammen wiederwärmt. Anschließend wurden die Brammen zu Warmbändern mit einer spezifischen Warmwalzendtemperatur TWE gewalzt. Das Warmband wurde anschließend bei einer Haspeltemperatur THA gehaspelt und gebeizt. Die entsprechenden Prozesstemperaturen können Tabelle 2 entnommen werden.The invention is explained in more detail below using exemplary embodiments. To test the invention, 6 melts AF were produced. The composition of the melts is given in Table 1. The melts were cast into slabs in a conventional continuous casting plant and the slabs were then reheated. The slabs were then rolled into hot strips with a specific hot rolling final temperature T WE . The hot strip was then coiled and pickled at a coiling temperature T HA . The corresponding process temperatures can be found in Table 2.
Das so erhaltene Warmband wurde anschließend in konventioneller Weise zu einem Kaltband mit einer Banddicke d gewalzt. Dieses Kaltband wurde anschließend mit einer Aufheizintensität I aufgeheizt auf eine Glühtemperatur T glüh und auf Raumtemperatur abgekühlt. Die Raten während der Abkühlung sind in Tabelle 2 angegeben.The hot strip thus obtained was then rolled in a conventional manner into a cold strip with a strip thickness d. This cold strip was then heated with a heating intensity I to an annealing temperature T and cooled to room temperature. The rates during cooling are given in Table 2.
An den so hergestellten Kaltbänder wurden, die bereits beschriebenen mechanischen Eigenschaften und die Mikrostruktur im Lichtmikroskop bestimmt. Neben der Mikrostruktur wurde die Korngrenzenlänge bestimmt und von Groß-und Klinwinkelkorngrenzen bestimmt. Alle diese Messwerte sind in Tabelle 3 aufgeführt.
Claims (14)
dadurch gekennzeichnet, dass Si ≥0,11%.Cold-rolled flat steel product according to claim 1,
characterized in that Si ≥0.11%.
dadurch gekennzeichnet, dass das Ni ≥0,015 % ist.Cold-rolled flat steel product according to claims 1 to 2,
characterized in that the Ni is ≥0.015%.
dadurch gekennzeichnet, dass V ≥0,0001 % ist.Cold-rolled flat steel product according to claims 1 to 5,
characterized in that V ≥0.0001%.
dadurch gekennzeichnet, dass die Bruchdehnung A80 mindestens 8%, und
die Zugfestigkeit Rm mindestens 570 MPa, beträgt.Cold-rolled flat steel product t according to one of claims 1 to 6,
characterized in that the elongation at break A80 is at least 8%, and
the tensile strength Rm is at least 570 MPa.
dadurch gekennzeichnet, dass das Produkt aus Bruchdehnung A80 und Zugfestigkeit Rm mindestens 8000 MPa%, beträgt.Cold-rolled flat steel product according to one of claims 1 to 7,
characterized in that the product of elongation at break A80 and tensile strength Rm is at least 8000 MPa%.
dadurch gekennzeichnet, dass die Marciniak-Lochaufweitung (LAW) mindestens 9,0% beträgt.Cold-rolled flat steel product according to one of claims 1 to 8,
characterized in that the Marciniak hole expansion (LAW) is at least 9.0%.
dadurch gekennzeichnet, dass der Stahl ein mindestens aus zwei Phasen bestehendes Gefüge aufweist, das (in Vol.-%) mehr als 5% Martensit und mehr als 20% Ferrit sowie bis zu 65% Bainit und bis zu 10% Restaustenit umfasst.Cold-rolled flat steel product according to one of claims 1 to 9,
characterized in that the steel has a structure consisting of at least two phases, which comprises (in vol.%) more than 5% martensite and more than 20% ferrite as well as up to 65% bainite and up to 10% retained austenite.
dadurch gekennzeichnet, dass der Stahl ein Kohlenstoffäquivalent Cäq
characterized in that the steel has a carbon equivalent of C eq
dadurch gekennzeichnet, dass der Stahl ein Kohlenstoffäquivalent Cäq aufweist mit
characterized in that the steel has a carbon equivalent C eq with
dadurch gekennzeichnet, dass das Abkühlen des kaltgewalzten Stahlflachprodukts auf Raumtemperatur zwei Zwischenschritte aufweist, wobei das kaltgewalzte Stahlflachprodukt in dem ersten Zwischenschritt von Glühtemperatur auf eine erste Abkühltemperatur T1 mit einer Abkühlrate kleiner 10K/s (bevorzugt kleiner 5 K/s) abgekühlt wird und wobei das kaltgewalzte Stahlflachprodukt in dem zweiten Zwischenschritt auf eine zweite Abkühltemperatur T2 mit einer Abkühlrate kleiner 100 K/s abgekühlt wird,
wobei für die Abkühltemperaturen T1, T2 gilt:
T 1 > T 2, 450 °C ≤ T 1 ≤ 800 °C (bevorzugt 650 °C ≤ T 1 ≤ 750 °C) und 400°C ≤ T 2 ≤ 600 °CMethod according to claim 13,
characterized in that the cooling of the cold-rolled flat steel product to room temperature has two intermediate steps, the cold-rolled flat steel product being cooled in the first intermediate step from annealing temperature to a first cooling temperature T 1 with a cooling rate of less than 10 K/s (preferably less than 5 K/s) and where the cold-rolled flat steel product is cooled in the second intermediate step to a second cooling temperature T2 with a cooling rate of less than 100 K/s,
where the following applies to the cooling temperatures T 1 , T 2 :
T 1 > T 2 , 450 °C ≤ T 1 ≤ 800 °C (preferably 650 °C ≤ T 1 ≤ 750 °C) and 400 °C ≤ T 2 ≤ 600 °C
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