Classifications

• • 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
• • 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
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12771—Transition metal-base component
  • Y10T428/12785—Group IIB metal-base component
  • Y10T428/12792—Zn-base component
  • Y10T428/12799—Next to Fe-base component [e.g., galvanized]
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12771—Transition metal-base component
  • Y10T428/12861—Group VIII or IB metal-base component
  • Y10T428/12951—Fe-base component
  • Y10T428/12972—Containing 0.01-1.7% carbon [i.e., steel]

Definitions

• the invention relates to a dual-phase steel, the structure of which consists essentially of martensite and ferrite or bainite, shares of retained austenite may be present and the dual-phase steel has a tensile strength of at least 950 MPa.
• the invention likewise relates to a flat product produced from such a dual-phase steel and to methods for producing such a flat product.
• flat product typically includes steel strips and sheets of the type according to the invention.
• the EP 1 431 107 A1 a steel that is not only good deep-draw, but also has high tensile strength, a flat product produced from it and a method for its production known.
• the well-known steel contains besides iron and the unavoidable impurities (in% by weight) 0.08 - 0.25% C, 0, 001 - 1.5% Si, 0, 01 - 2.0% Mn, 0, 001 - 0.06% P, to to 0.05% S, 0.001-0.007% N and 0.008-0.2% Al.
• the upper limit of the content of Mn of 1.5% has been set in view of the decrease in the r values associated with exceeding this limit, with Mn contents in the range of 0.04 for optimizing the r values of the known steel sheet - 0.8 wt .-%, in particular 0.04 - 0.12 wt .-%, have been considered advantageous.
• the known steel to further increase its strength in addition to other optionally added alloying elements also contents of B from 0.0001 to 0.01 wt .-% B, of Ti, Nb and / or V in a total amount of 0.001 to 0.2 wt .-% and Sn, Cr, Cu, Ni, Co, W and / or Mo in a total amount of 0.001 - have 2.5 wt .-%.
• B contents of B from 0.0001 to 0.01 wt .-% B, of Ti, Nb and / or V in a total amount of 0.001 to 0.2 wt .-% and Sn, Cr, Cu, Ni, Co, W and / or Mo in a total amount of 0.001 - have 2.5 wt .-%.
• the total content of these elements is limited to the respective upper limit.
• the steels described have strengths of more than 850 MPa, they do not have a dual-phase structure, but theirs Structure consists either only of martensite or only of ferrite or bainite. Also found in the EP 1 431 407 A1 this is not an example, for example, by which the effects of Cr, Mo, Ti or B could be reconstructed with simultaneously small amounts of Si or higher contents of Mn. Rather, those in the EP 1 431 407 A1 Examples given that according to this prior art, the strength has been adjusted substantially by a suitable vote of the Mn and Si contents to the respective steel alloy.
• the Martenistanteil of the steel in question is about 5% to 20% of the predominantly martensitic-ferritic microstructure.
• a flat product produced in this way has strengths of at least 500 N / mm 2 and at the same time good formability, without requiring particularly high contents of certain alloying elements.
• the object of the invention was to develop a steel and a flat product produced therefrom which has a strength of at least 950 MPa and good deformability.
• the steel should have a surface finish which, using a simple manufacturing process, allows a flat product produced from this steel, in the uncoated or corrosion-protective coating state, to deform into a complex shaped component, such as a part of an automobile body.
• a method should also be given that allows in a simple manner to produce in the above-mentioned manner manufactured flat products.
• a the above-mentioned object solving flat product according to claim 20 according to the invention characterized in that it consists of a composite according to the invention and procured steel.
• a steel according to the invention is characterized by high strengths of at least 950 MPa, in particular more than 980 MPa, with regularities of 1000 MPa and more being achieved on a regular basis. At the same time it has a yield strength of at least 580 MPa, in particular at least 600 MPa, and has an elongation A 80 of at least 10%.
• steel according to the invention is particularly suitable for the production of complex shaped, highly loaded in practical use components, such as those required in the field of bodywork for automobiles.
• the alloy of a steel according to the invention is composed so that it has a martensite content of at least 20%, preferably more than 30%, up to a maximum of 70%.
• the remainder of the microstructure of a dual-phase steel according to the invention consists respectively of ferrite and / or bainite (bainitic ferrite + carbides).
• the high strengths and good elongation properties have been achieved by the adjustment of the dual-phase structure according to the invention. This has been made possible by a narrow selection of the contents of the individual alloying elements present in a steel according to the invention besides iron and unavoidable impurities.
• the invention provides a C content of 0.10-0.20 wt%.
• the minimum content of carbon of 0.10 wt .-% has been chosen to achieve the formation of martensitic structure with sufficient hardness and to set the desired combination of properties of the steel according to the invention.
• carbon hinders the formation of the desired ferritic / bainitic portion of the structure.
• higher C contents have a negative effect on the weldability, which is of particular importance for the application of the material according to the invention, for example in the field of automotive engineering.
• the advantageous effect of carbon in a steel according to the invention can be used particularly reliably if the C content of a steel according to the invention is 0.12-0.18% by weight, in particular 0.15-0.16% by weight ,
• Si also serves to increase the strength by hardening the ferrite or bainite.
• the effect of Si is particularly safe when the Si content of a steel according to the invention is at least 0.2 wt .-%, in particular at least 0.25 wt .-% .
• the upper limit of the Si content has at the same time been set at 0.6% by weight. Also, adherence to this upper limit minimizes the risk of grain boundary oxidation. In this case, an unfavorable influence of Si on the properties of the steel according to the invention can be avoided with even greater certainty that the Si content of the steel according to the invention is limited to 0.4% by weight, in particular 0.35% by weight.
• the Mn content of a steel according to the invention is in the range of 1.5-2.5% by weight, in particular 1.5-2.35% by weight, in order to utilize the strength-increasing effect of this element.
• the presence of Mn supports the formation of martensite.
• the contents of Mn provided according to the invention prevent the formation of perlite during cooling after annealing, in particular in the case where a cold strip is produced from steel according to the invention and this cold strip is finally annealed.
• the upper limit of the contents of Mn is on 2.5 wt .-% set in inventive steel.
• the possibly negative influences of Mn on a steel according to the invention can be excluded with increased certainty that the Mn content is limited to 2.20% by weight, in particular 2.00% by weight.
• Cr also strengthens in a dual-phase steel according to the invention in contents of 0.2-0.8% by weight. This effect occurs in particular when the Cr content is at least 0.3% by weight, in particular at least 0.5% by weight. At the same time, however, the Cr content of a steel according to the invention is limited to 0.8% by weight in order to reduce the risk of grain boundary oxidation and to ensure good elongation properties of the steel according to the invention. Also, adherence to this upper limit achieves a surface that can be well provided with a metallic coating. Negative effects of the contents of Cr are avoided, in particular, if the upper limit of the chromium content of a steel according to the invention is set to not more than 0.7% by weight, in particular 0.6% by weight.
• the presence of titanium at levels of at least 0.02% by weight also contributes to increasing the strength of a steel according to the invention by forming fine precipitates of TiC or Ti (C, N) and contributing to grain refining.
• Another positive effect of Ti is the setting of possibly present nitrogen, so that the formation of boron nitrides in the steel according to the invention is prevented. These would have a strong negative impact on the elongation properties and, consequently, on the formability of a flat product according to the invention.
• Ti thus ensures, in the case of an addition of boron to increase the strength, that the boron can fully develop its effect.
• too high Ti contents lead to unfavorably high recrystallization temperatures, which has a negative effect, in particular, when cold-rolled flat products are produced from steel according to the invention, which are finally annealed. Therefore, the upper limit of the Ti content has been limited to 0.08 wt%, especially 0.06 wt%.
• the positive influence of Ti on the properties of a steel according to the invention can be used particularly reliably if its Ti content is 0.03-0.055% by weight, in particular 0.040-0.050% by weight.
• the strength of the steel according to the invention is also increased by the amounts of B, which are optionally provided according to the invention, of up to 0.002% by weight and, as in the case of the addition of Mn, Cr and Mo in the case of the production of cold strip of steel according to the invention, the critical cooling rate lowered after annealing. Therefore, according to a particularly practical embodiment of the invention, the B content is at least 0.0005 wt .-%. At the same time, however, excessively high contents of B can reduce the deformability of the steel according to the invention and adversely affect the expression of the dual-phase structure desired according to the invention. Optimized effects of boron therefore result in a steel according to the invention Contents of 0.0007 - 0.0016 wt .-%, in particular 0.0008 - 0.0013 wt .-%.
• the inventively optional levels of molybdenum contribute to increasing the strength of a steel according to the invention.
• the presence of Mo does not adversely affect the coatability of the flat product with a metallic coating and its ductility.
• Practical experiments have shown that the positive effects of Mo up to contents of 0.25% by weight, in particular 0.22% by weight, can be used particularly effectively, even from a cost point of view.
• contents of 0.05% by weight Mo have a positive effect on the properties of the steel according to the invention.
• the desired effect of molybdenum in a steel according to the invention occurs in particular if its Mo content is 0.065-0.18% by weight, in particular 0.08-0.13% by weight, is.
• Mo contents of less than 1.7% by weight and / or Cr contents of less than 0.4% by weight are present in the steel according to the invention, it is advantageous to secure the required strength of the invention Steel 0.05 - 0.22 wt .-% Mo added.
• Aluminum is used in the melting of a steel according to the invention for deoxidizing and for setting nitrogen which may be present in the steel.
• Al may be added in amounts of less than 0.1% by weight to the steel of the present invention, with the desired effect of Al being particularly safe occurs when its contents in the range of 0.01 to 0.06 wt .-%, in particular 0.020 to 0.050 wt .-%, are.
• Nitrogen is allowed in inventive steel only in amounts of up to 0.012 wt .-%, in order to avoid the formation of boron nitrides especially in the simultaneous presence of B.
• the N content is preferably limited to 0.007% by weight.
• the P content according to the invention is preferably limited to ⁇ 0.1 wt .-%, in particular ⁇ 0.02 wt .-%, with particularly good results at P contents of ⁇ 0.010 wt .-% can be achieved.
• existing flat products can be supplied as immediately after hot rolling hot strip, ie without subsequently performed cold rolling process, further processing.
• obtained hot strip in uncoated state form highly resilient components. If these components are to be particularly protected against corrosion, then the hot strips can be provided before or after their transformation to the respective component with a metallic protective coating.
• the hot strips produced from steel according to the invention can first be subjected to cold rolling and subsequent annealing, in which case they can be further processed as cold strip, if appropriate after application of a metallic coating which protects against corrosion.
• the flat product according to the invention is provided with a metallic protective coating, this can be done, for example, by hot-dip galvanizing, galvannealing or electrolytic coating. If necessary, a pre-oxidation can be carried out before the coating in order to ensure a secure connection of the metallic coating to the respective substrate to be coated.
• a present as a hot strip flat product having a tensile strength of at least 950 MPa and a dual-phase structure consisting of 20-70% martensite, up to 8% of retained austenite and the remainder of ferrite and / or bainite is first composed according to the invention Dual phase steel melted, the melt cast into a precursor, such as slab or thin slab, reheated or held the precursor at a hot rolling start temperature of 1100-1300 ° C, the precursor at a hot rolling end temperature of 800-950 ° C to the Hot rolled hot strip and the hot strip obtained at a reel temperature of up to 570 ° C reeled.
• the dual-phase structure of the as such subsequently no longer rolled hot strip can be adjusted to obtain the desired combination of properties.
• the hot strip obtained in the manner according to the invention should remain uncoated or be electrolytically coated with a metallic coating as a hot strip, no annealing of the flat product is required. If, on the other hand, the hot-rolled strip is to be coated with a metallic coating by hot-dip galvanizing, then it is first annealed at a maximum annealing temperature of 600 ° C. and then cooled to the temperature of the
• Coating bath which may be, for example, a zinc bath, cooled. After passing through the zinc bath, the coated hot strip can be conventionally cooled to room temperature.
• a dual phase steel composed according to the invention is melted, the corresponding molten steel is cast into a precursor, such as a slab or thin slab, and the primary product is reheated or held at a hot rolling start temperature of 1100 to 1300 ° C. , the precursor hot rolled at a hot rolling end temperature of 800 - 950 ° C to a hot strip, the hot strip coiled at a reel temperature of 500 - 650 ° C, the hot strip after coiling cold rolled, the resulting cold strip at annealed at a 700-900 ° C annealing temperature and the cold strip cooled after annealing controlled.
• Coiling temperatures in the range of up to 580 ° C have proven to be particularly advantageous in connection with the production of cold strip, because when exceeding the coiler temperature of 580 ° C, the risk of grain boundary oxidation increases. With low reel temperatures, the strength and yield strength of the hot strip increases, so that the hot strip can be cold rolled more and more difficult. Accordingly, the cold strip to be cold rolled to cold strip is preferably at least 530 ° C, in particular at least 550 ° C, reeled.
• the cold strip produced according to the invention remains uncoated or is to be electrolytically coated, an annealing treatment in a continuous annealing anneal takes place as a separate working step.
• the maximum annealing temperatures achieved are in the range of 700-900 ° C at heating rates of 1-50 K / s.
• the annealed cold strip for the targeted setting of the desired property combination according to the invention is preferably cooled in such a way that in the temperature range of 550-650 ° C cooling rates of at least 10 K / s are achieved in order to suppress the formation of perlite.
• the strip can be held for a period of 10 to 300 s or cooled directly to room temperature at a cooling rate of 0.5 to 30 K / s.
• the cold strip is to be coated by hot dip galvanizing, then the steps of annealing and coating can be combined.
• the steps of annealing and coating can be combined.
• the strip is then held at this temperature for 10-200 seconds.
• the strip is then cooled to the temperature of the respective coating bath, which is typically below 500 ° C., which is typically a zinc bath, the cooling rate also being more than 10 K in the temperature range 550-650 ° C. in this case / s should be.
• the cold strip can be held at the respective temperature for 10 - 300 s.
• the annealed cold strip passes through the respective coating bath, which is preferably a zinc bath. This is followed by either cooling to room temperature to obtain a conventionally hot-dip galvanized cold-rolled strip or rapid heating followed by cooling to room temperature to produce a galvannealed cold-rolled strip.
• Such cold-rolled cold rolled strip according to the invention typically has thicknesses of 0.8-2.5 mm.
• the cold-rolled strip may be in the coated or uncoated state of a temper rolling mill be subjected to be applied in which lying in the range of up to 2% lying Dressiergrade.
• the hot rolled strips thus obtained were rewound at a coiler temperature of 550 ° C., adjusted to an accuracy of +/- 30 ° C., before being cold rolled to a thickness of 50%, 65% and 70%, respectively from 0.8 mm to 2 mm cold rolled.
• the cold strips obtained have been subjected to annealing and controlled cooling in the manner already described above in general form for a cold-rolled strip to be delivered uncoated.
• Table 2 shows the microstructural state, the mechanical properties as well as the respectively set cold rolling degrees and strip thicknesses for the cold strips produced in the first test series from melts 1 to 16.
• Table 1 melt C Si Mn al Not a word Ti Cr B P S N 1 0,149 0.30 1.97 0,007 - - 0.45 0.0004 0,003 0,004 0.0013 2 0,150 0.30 1.97 ⁇ 0.005 - 0.023 0.45 0.0021 0.005 0,004 0,015 3 0,152 0.30 1.99 0.005 - - 0.46 0.0004 0,004 0,004 0.0014 4 0,157 0.30 1.97 0, 005 - - 0.81 0.0005 0,004 0,004 0.0017 5 0.153 0.30 1.50 0.005 - - 0.81 0.0004 0,004 0,004 0.0015 6 0,150 0.02 1.98 ⁇ 0.005 - 0.023 0.80 0.0022 0,004 0.005 0.0015 7 0,152 0.60 1.97 ⁇ 0.005 - 0,021 0.45 0.0022 0,004 0,004 0.0024 8th 0.154 0.19 2.07 0,004 - 0,022 0.60 0.0011 0,004 0,007 0.0052 9 0.16

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• Chemical & Material Sciences (AREA)
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• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Sheet Steel (AREA)

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• 2007
  • 2007-08-15 ES ES07114398T patent/ES2387040T3/es active Active
  • 2007-08-15 PL PL07114398T patent/PL2028282T3/pl unknown
  • 2007-08-15 EP EP07114398A patent/EP2028282B1/fr active Active
• 2008
  • 2008-08-07 WO PCT/EP2008/060381 patent/WO2009021897A1/fr active Application Filing
  • 2008-08-07 US US12/673,388 patent/US20100273024A1/en not_active Abandoned
  • 2008-08-07 CN CN2008801034262A patent/CN101802233B/zh active Active
  • 2008-08-07 JP JP2010520536A patent/JP5486496B2/ja not_active Expired - Fee Related

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