EP2690184A1 - Produit plat en acier laminé à froid et son procédé de fabrication - Google Patents

Produit plat en acier laminé à froid et son procédé de fabrication Download PDF

Info

Publication number
EP2690184A1
EP2690184A1 EP12178332.8A EP12178332A EP2690184A1 EP 2690184 A1 EP2690184 A1 EP 2690184A1 EP 12178332 A EP12178332 A EP 12178332A EP 2690184 A1 EP2690184 A1 EP 2690184A1
Authority
EP
European Patent Office
Prior art keywords
cold
temperature
content
hot
flat steel
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.)
Granted
Application number
EP12178332.8A
Other languages
German (de)
French (fr)
Other versions
EP2690184B1 (en
Inventor
Brigitte Dr. Hammer
Thomas Dr. Heller
Frank Dr. Hisker
Rudolf Prof.Dr.-Ing. Kawalla
Grzegorz Korpala
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ThyssenKrupp Steel Europe AG
Original Assignee
ThyssenKrupp Steel Europe AG
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by ThyssenKrupp Steel Europe AG filed Critical ThyssenKrupp Steel Europe AG
Priority to EP12178332.8A priority Critical patent/EP2690184B1/en
Priority to JP2015523569A priority patent/JP6202579B2/en
Priority to US14/417,659 priority patent/US20150218684A1/en
Priority to CN201380048837.7A priority patent/CN104641008B/en
Priority to PCT/EP2013/065838 priority patent/WO2014016421A1/en
Publication of EP2690184A1 publication Critical patent/EP2690184A1/en
Application granted granted Critical
Publication of EP2690184B1 publication Critical patent/EP2690184B1/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold 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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • 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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips 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
    • 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
    • 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
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
    • 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
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • 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
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • 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
    • C21D2211/008—Martensite

Definitions

  • the invention relates to a cold-rolled steel flat product having a tensile strength Rm of at least 1400 MPa and an elongation A80 of at least 5%. Products of this type are characterized by a very high strength in combination with good elongation properties and are suitable as such, in particular for the production of components for motor vehicle bodies.
  • the invention likewise relates to a method for producing a flat steel product according to the invention.
  • alloy contents are stated here only in “%”, this always means “% by weight”, unless expressly stated otherwise.
  • the cast strip is hot rolled at a conventional reduction rate. Hot rolling is terminated at a final temperature at which all copper is still in solid solution in the ferrite and / or austenite matrix. Then, the strip is subjected to a rapid cooling step to hold the copper in supersaturated solid solution in the ferrite and / or austenite solution. After coiling into a coil, a cold strip can be rolled from the hot strip thus obtained with a cold rolling amount of 40-80%. This cold strip is then subjected to a recrystallizing annealing, where it is brought as quickly as possible to a lying in the range of 840 ° C annealing temperature and held there to bring the largest possible proportion of the copper contained in the steel in solution.
  • Another method for producing an extremely strong cold strip is from US 7,591,977 B2 known.
  • a hot rolled strip (containing wt%) of 0.1-0.25% C, 1.0-2.0% Si and 1.5-3.0% Mn having a cold rolling degree of 30-70 rolled to a cold-rolled strip, which is then subjected to a continuous heat treatment.
  • the cold strip is heated in a first annealing step to a lying above its Ar3 temperature first annealing temperature to bring in the cold strip carbides in solution.
  • a cooling proceeding from the first annealing temperature takes place, with a cooling rate of at least 10 ° C./s, to a second annealing temperature.
  • This second annealing step carried out for bainite formation is carried out until the structure of the cold strip consists of at least 60% bainite and at least 5% residual austenite and the remainder polygonal ferrite.
  • the aim is that the structure is as completely as possible bainitic and other structural constituents are present in traces at best.
  • the cold-rolled strip obtained in this way achieves tensile strengths of up to 1180 MPa at an elongation of at least 9% and, if necessary, can be covered with a metallic, corrosion-protective layer.
  • the object of the invention was to provide a cold rolled flat steel product which is manufactured in a simple and reliable way can and has an optimized combination of further increased strength and good ductility.
  • a method for producing such a cold-rolled steel flat product should be mentioned.
  • the solution according to the invention of the abovementioned object consists in that at least the working steps specified in claim 12 are run through to produce a cold-rolled flat steel product according to the invention.
  • a steel strip according to the invention has a three-phase structure, the dominant constituent of which is bainite and which, moreover, consists of retained austenite and the remainder of martensite.
  • the bainite content is at least 60% by volume and the residual austenite content is in the range from 10% to 25% by volume, the remainder of the microstructure in each case also being filled with martensite.
  • the optimum martensite content is at least 10% by volume.
  • Such a composite structure gives the best combination of Rm * A80 at the required tensile strength.
  • the retained austenite is in a cold strip according to the invention predominantly film-like with small globular islands of blocky retained austenite with a particle size ⁇ 5 microns, so that the retained austenite has a high stability and, consequently, a low tendency to undesirable conversion to martensite and allows the TRIP effect.
  • Cold rolled strip produced according to the invention regularly reaches tensile strengths Rm of more than 1400 MPa, with strains A80 which likewise regularly exceed 5%. Accordingly, the quality Rm * A80 of flat steel products according to the invention is regularly above 7000 MPa *%, with grades Rm * A80 of at least 13500 MPa *% being typically achieved.
  • An inventive cold strip as such has a optimal combination of extreme strength and sufficient formability.
  • the martensite starting temperature ie the temperature at which martensite is formed in steel processed according to the invention, can be determined according to the Thermodynamic Exatrapolation and Martensite Start-Temperature of Substituted Alloyed Steels "by H. Bhadeshia, published in Metal Science 15 (1981), pages 178-180 explained procedure can be calculated.
  • the C content of the flat steel product according to the invention can be set to at least 0.25% by weight, in particular at least 0.27% by weight or at least 0.28% by weight, wherein the be used by the comparably high carbon content effects particularly safe when the C content in the range of> 0.25 to 0.5 wt .-%, in particular 0.27 to 0.4 wt .-% or 0.28 - 0.4 wt .-%, is.
  • the strength-increasing effect of copper can also be used in a cold-rolled flat steel product according to the invention.
  • a minimum content of 0.15% by weight of Cu, in particular at least 0.2% by weight of Cu may be present in the flat steel product according to the invention.
  • a particularly effective contribution to strength is made by Cu, if it contains at least 0.55 wt .-% in the flat steel product according to the invention is present, whereby negative effects of the presence of Cu can be limited by limiting the Cu content to at most 1.5% by weight.
  • the martensite start temperature can be lowered and the tendency of the bainite to convert to pearlite or cementite can be suppressed.
  • Cr at levels up to the upper limit of not more than 2% by weight given in accordance with the invention promotes the ferritic transformation, with optimum effects of the presence of Cr in the cold-rolled flat steel product of the invention when the Cr content is reduced to 1.5% by weight. % is limited.
  • the positive influence of Cr can be used particularly effectively if at least 0.3% by weight of Cr is present in the flat steel product according to the invention.
  • Ti, V or Nb which is also optional, can help to create finer-grained microstructures and promote bainitic transformation.
  • these microalloying elements carry through the Formation of precipitates to increase hardness.
  • the positive effects of Ti, V and Nb in the cold-rolled flat steel product according to the invention can be used particularly effectively if their content is in each case in the range from 0.002 to 0.15% by weight, in particular 0.1% by weight does not exceed.
  • Si is present in a flat steel product according to the invention in contents of 0.4-2.5% by weight and causes a marked solid solution hardening.
  • the Si content can be set to at least 1.0 wt .-%.
  • Al can partially replace the Si content in the steel processed according to the invention. At the same time, Al and Si are deoxidizing during steelmaking. For this purpose, a minimum content of 0.01 wt .-% Al can be provided. Higher contents of Al prove to be useful, for example, if the addition of Al should set the hardness or tensile strength of the steel to a lower value in favor of improved ductility.
  • Si and Al Another function of Si and Al is to suppress carbide formation in the bainite and thus to stabilize the retained austenite by dissolved C.
  • the formation of the structure prescribed according to the invention can be ensured, in particular, by the contents of the steel processed according to the invention and, accordingly, the contents of the flat steel product according to the invention of Mn, Cr, Ni, Cu and C having the following condition 1 ⁇ 0 . 5 % Mn + 0 . 167 % Cr + 0 . 125 % Ni + 0 . 125 % Cu + 1 .
  • 334 % C ⁇ 2 meet, where with% Mn the respective Mn content in wt .-%, with% Cr of the respective Cr content in wt .-%, with% Ni of the respective Ni content in wt .-%, with% Cu of the respective Cu content in wt .-% and with% C of the respective C content in wt .-% are designated.
  • the precursor cast from a composite steel according to the invention is first brought to a temperature or maintained at a temperature sufficient to terminate the hot rolling carried out from said temperature at a hot rolling end temperature in the range of 830-1000 ° C lie.
  • the hot strip is cooled on the roller table following the relevant stand. This is followed by the roller table Hot strip in a coiler, where it is wound into a coil.
  • the reel temperature must be at least 560 ° C, so that a relatively soft hot-band structure of ferrite and pearlite is formed.
  • An optimum temperature profile for this purpose results when the hot rolling end temperature is in the range of 850-950 ° C., in particular in the range of 880-950 ° C.
  • the precursor is heated or maintained at a temperature in the range of 1100-1300 ° C temperature before hot rolling.
  • the structure of the hot strip thus obtained consists mainly of ferrite and pearlite. The risk of grain boundary oxidation can be minimized by limiting the coiler temperature to a maximum of 750 ° C.
  • the hot strip After coiling, the hot strip is cold rolled, wherein the hot strip can of course be descaled chemically or mechanically before cold rolling in the usual way.
  • the cold rolling is carried out with a degree of cold rolling of at least 30%, in particular at least 45%, in order to accelerate the recrystallization and conversion during the subsequent annealing. In general, a better surface quality is achieved by maintaining a correspondingly high degree of cold rolling. Cold rolling degrees of at least 50% have proven to be particularly favorable for this purpose.
  • the cold strip according to the invention undergoes an annealing cycle in a continuous pass, in which it is heated in a first annealing phase to a temperature of at least 800 ° C., preferably at least 830 ° C. This first annealing phase lasts at least as long that the cold strip is completely austenitized. This typically requires 50-150 seconds.
  • the product is quenched, the cooling rate being at least 8 ° C / s, in particular 10 ° C / s.
  • the target temperature of this quenching is a holding temperature which is at most 470 ° C and higher than the martensite start temperature MS, starting from the martensite in the structure of the cold strip.
  • the range of 300-420 ° C, in particular 330-420 ° C can be used as an indication of the range in which the holding temperature should be.
  • the cold strip is kept in the holding temperature range in the second annealing phase, specifically until the structure of the cold strip has changed to at least 20% by volume in bainite.
  • the holding can be carried out as an isothermal hold on the holding temperature achieved during the cooling or as a slow decrease in temperature within the holding temperature range.
  • the flat steel product produced according to the invention can be treated in the usual way with a metallic protective layer be occupied. This can be done for example by hot dip coating. If an annealing is required before the application of the metallic coating, the heat treatment provided according to the invention can be carried out as part of this annealing.
  • the correspondingly assembled steel melts have been cast in a conventional manner into a strand from which slabs have been divided.
  • the thin slabs were then heated to a reheating temperature in a conventional manner as well.
  • the heated slabs were hot rolled in a conventional hot rolling mill to hot strip with a thickness of 2 mm.
  • the hot rolling end temperature was in the range of 830 - 900 ° C. Starting from this temperature, the hot strips were cooled to a lying above 560 ° C reel temperature and then coiled into coils.
  • the hot strips thus obtained are descaled after coiling and cold rolled after descaling at cold rolling degrees of 50% to cold strip.
  • a larger number of samples of these cold strips were then subjected to a heat treatment in which they were heated in a first annealing step at a heating rate of at least 1.9 ° C / s to a first annealing temperature in the range of 830-850 ° C was. At this temperature, the cold strips were held for a period of 120 seconds until fully warmed.
  • a quenching in which cold strips were quenched with a cooling rate of at least 8 ° C / s to a holding temperature T2, which was in the range of 350-420 ° C.
  • the holding temperatures T2 for a first batch of tests were 300 ° C, 310 ° C, 330 ° C, 340 ° C, 375 ° C, 390 ° C and 410 ° C.
  • the cold strip samples have been kept for an annealing period t2.
  • Fig. 1 the tensile strengths Rm achieved are plotted against the respective annealing temperature T2. It can be seen that the cold strip samples made of the steel S5 only achieved the required minimum tensile strength of 1400 MPa under certain annealing conditions, whereas the tensile strengths of the cold strip samples produced from the other steels always safely exceeded the minimum limit of 1400 MPa. The reason for this is the comparatively low carbon content of the steel S5, which is located at the lower limit of the content range prescribed according to the invention.
  • Fig. 2 the tensile strengths of the cold strip samples produced from the steel S4 are plotted over the annealing time t2 of the second annealing stage. It turns out that the cold strip samples held at a holding temperature of 310 ° C., 330 ° C. and 350 ° C., ie in the holding temperature range of 310 ° to 350 ° C., have reached the required tensile strength Rm of 1400 MPa irrespective of the respective annealing time t 2.
  • Fig. 3 the tensile strengths of the cold strip samples produced from the steel S5 are plotted over the annealing time t2 of the second annealing stage. It can be seen here that the cold strip samples held at a holding temperature of 350 ° C. and 390 ° C., ie in the holding temperature range of 350 ° -390 ° C., reach the required tensile strength R m of 1400 MPa if the annealing time t 2 is shorter than 145 s.
  • Fig. 4 the strain A80 of the cold strip samples produced from the steel S4 is plotted over the annealing time t2 of the second annealing stage.
  • Fig. 5 the strain A80 of the cold strip samples produced from the steel S5 is plotted over the annealing time t2 of the second annealing stage.
  • the cold strip samples have the required elongation A80 of at least 5%, regardless of their respective holding temperature T2 and independently of the respective holding temperature Reach annealing time t2. Accordingly, while maintaining a short annealing time and suitably low holding temperatures T2, a cold-rolled steel flat product according to the invention can be produced from the steel S5 despite its comparatively low C content, in which a high tensile strength Rm is combined with a sufficient elongation A80.
  • Fig. 6 is shown in a section of an enlargement of a cross section of a cold strip according to the invention.
  • residual austenite blocks RA-b are marked and a point is highlighted by an encircling, on which film-like retained austenite RA-f is present in a lamellar layering.
  • Table 1 stolen C Mn Si Cu Cr Ti Nb V al N other S1 0.52 1.48 0.40 1.51 0, 88 0, 009 - 0.093 1,400 - - S2 0.301 1.41 1.46 1.47 0.87 0,014 0.005 0.09 0,021 0.0015 Ni: 0.021 Mo: ⁇ 0.002 S3 0,505 1.50 0.40 0, 6 1.30 0.011 - 0.098 0,012 0,002 Ni: 0.63 Mo: 0.30 S4 0.384 1.97 0.41 0.57 1.37 0.0016 - ⁇ 0.0005 0,018 0.0014 Ni: 0.59 Mo: 0.30 S5 0.252 1.47 2.15 0.32 0.41 0,020 - 0.11 0.009 - Ni: 0.02 Mo: ⁇ 0.002 In% by weight, Remaining iron and unavoidable impurities

Abstract

Cold-rolled flat steel product having a tensile strength of 1400 MPa and an elongation A80 of 5%, comprises iron and inevitable impurities consisting of: 0.10-0.60 wt.% of carbon; 2.5 wt.% of silicon; upto 3 wt.% of aluminum; 0.4-3 wt.% of manganese; upto 1 wt.% of nickel; upto 2 wt.% of copper; upto 0.4 wt.% of molybdenum; upto 2 wt.% of chromium; upto 1.5 wt.% of cobalt; upto 0.2 wt.% of titanium; upto 0.2 wt.% of niobium; and upto 0.5 wt.% of vanadium. A structure of the steel flat product comprises 20 vol.% of bainite, 10-35 vol.% of retained austenite and the balance of martensite. An independent claim is included for producing the cold-rolled flat steel product, comprising: supplying a pre-product in the form of a slab, a thin slab or a cast tape; hot rolling the pre-product to form a hot-rolled strip, where the hot-rolling temperature is 830[deg]C when the hot-rolled strip leaves the final rolling; cooling the hot-rolled strip at a cold temperature, which is between the hot-rolling temperature and 560[deg]C; cold-rolling the hot-rolled strip to form a cold rolled strip with a cold-rolling reduction of 30%; and heat treating the cold-rolled strip, where the cold-rolled strip in the heat-treatment is subjected to 800[deg]C that is an annealing temperature, cooled based on the annealing temperature with a cooling speed of 8[deg]C/seconds at a retaining Temperature, which is in a retaining temperature range whose upper limit is 470[deg]C and lower limit is higher than a martensite start temperature, and maintained at the retaining temperature for a period, which is sufficient for the cold rolled strip.

Description

Die Erfindung betrifft ein kaltgewalztes Stahlflachprodukt mit einer Zugfestigkeit Rm von mindestens 1400 MPa und einer Dehnung A80 von mindestens 5 %. Produkte dieser Art zeichnen sich durch eine sehr hohe Festigkeit in Kombination mit guten Dehnungseigenschaften aus und sind als solche insbesondere für die Herstellung von Bauteilen für Kraftfahrzeugkarosserien geeignet.The invention relates to a cold-rolled steel flat product having a tensile strength Rm of at least 1400 MPa and an elongation A80 of at least 5%. Products of this type are characterized by a very high strength in combination with good elongation properties and are suitable as such, in particular for the production of components for motor vehicle bodies.

Ebenso betrifft die Erfindung ein Verfahren zur Herstellung eines erfindungsgemäßen Stahlflachprodukts.The invention likewise relates to a method for producing a flat steel product according to the invention.

Unter dem Begriff "Stahlflachprodukt" werden hier durch einen Walzprozess erzeugte Stahlbleche oder Stahlbänder sowie davon abgeteilte Platinen und desgleichen verstanden.The term "flat steel product" here by a rolling process produced steel sheets or steel strips and divided therefrom boards and the like understood.

Sofern hier Legierungsgehalte lediglich in "%" angegeben sind, ist damit immer "Gew.-%" gemeint, sofern nicht ausdrücklich etwas anderes angegeben ist.If alloy contents are stated here only in "%", this always means "% by weight", unless expressly stated otherwise.

Aus der EP 1 466 024 B1 ( DE 603 15 129 T2 ) ist ein Verfahren zur Herstellung eines Stahlflachprodukts bekannt, das Zugfestigkeiten von deutlich mehr als 1000 MPa aufweisen soll. Um dies zu erreichen, wird eine Stahlschmelze, die (in Gew.-%) 0,0005 - 1 % C, 0,5 - 10 % Cu, bis zu 2 % Mn, bis zu 5 % Si, bis zu 0,5 % Ti, bis zu 0,5 % Nb, bis zu 5 % Ni, bis zu 2 % Al und als Rest Eisen und herstellungsbedingt unvermeidbare Verunreinigungen aufweist. Die Schmelze wird zu einem Band gegossen, dessen Dicke max. 10 mm beträgt und das durch Besprengen mit Wasser oder einem Wasser-Luft-Gemisch rasch auf eine Temperatur von höchstens 1000 °C abgekühlt wird. Anschließend wird das gegossene Band mit einer üblichen Reduktionsrate warmgewalzt. Das Warmwalzen wird bei einer Endtemperatur beendet, bei der sich das gesamte Kupfer noch in fester Lösung in der Ferrit- und/oder Austenitmatrix befindet. Dann wird das Band einem Schritt einer schnellen Abkühlung unterzogen, um das Kupfer in übersättigter fester Lösung in der Ferrit- und/oder Austenitlösung zu halten. Nach einem Haspeln zu einem Coil kann aus dem so erhaltenen Warmband mit einem 40 - 80 % betragenden Kaltwalzgrad ein Kaltband gewalzt werden. Dieses Kaltband wird dann einer rekristallisierenden Glühung unterzogen, bei der es möglichst schnell auf eine im Bereich von 840 °C liegenden Glühtemperatur gebracht und dort gehalten wird, um einen möglichst großen Anteil des im Stahl enthaltenen Kupfers in Lösung zu bringen. Anschließend erfolgt eine schnelle Abkühlung auf eine 400 - 700 °C betragende Temperatur, bei der sich erneut Cu-Ausscheidungen bilden. Auf diese Weise soll durch Ausscheidungshärtung das angestrebte Festigkeitsniveau des Stahls erreicht werden. Gleichzeitig soll der Kupfergehalt die Korrosions- und Versprödungsbeständigkeit des Stahls durch Bildung einer Schutzoxidschicht erhöhen.From the EP 1 466 024 B1 ( DE 603 15 129 T2 ) a method for producing a flat steel product is known, the tensile strengths of significantly more than 1000 MPa should have. To achieve this, a molten steel containing (in% by weight) 0.0005-1% C, 0.5-10% Cu, up to 2% Mn, up to 5% Si, up to 0.5 % Ti, up to 0.5% Nb, up to 5% Ni, up to 2% Al and the remainder iron and inevitable impurities due to production. The melt is poured into a tape whose thickness is max. 10 mm and which is rapidly cooled by spraying with water or a water-air mixture to a temperature of at most 1000 ° C. Subsequently, the cast strip is hot rolled at a conventional reduction rate. Hot rolling is terminated at a final temperature at which all copper is still in solid solution in the ferrite and / or austenite matrix. Then, the strip is subjected to a rapid cooling step to hold the copper in supersaturated solid solution in the ferrite and / or austenite solution. After coiling into a coil, a cold strip can be rolled from the hot strip thus obtained with a cold rolling amount of 40-80%. This cold strip is then subjected to a recrystallizing annealing, where it is brought as quickly as possible to a lying in the range of 840 ° C annealing temperature and held there to bring the largest possible proportion of the copper contained in the steel in solution. This is followed by a rapid cooling to a 400-700 ° C amount of temperature at which again form Cu precipitates. In this way, the desired strength level of the steel is to be achieved by precipitation hardening. At the same time, the copper content should increase the corrosion and embrittlement resistance of the steel by forming a protective oxide layer.

Ein weiteres Verfahren zur Herstellung eines extrem festen Kaltbands ist aus der US 7,591,977 B2 bekannt. Gemäß diesem Verfahren wird ein (in Gew.-%) 0,1 - 0,25 % C, 1,0 - 2,0 % Si und 1,5 - 3,0 % Mn enthaltendes Warmband mit einem Kaltwalzgrad von 30 - 70 % zu einem Kaltband gewalzt, das dann einer im kontinuierlichen Durchlauf absolvierten Wärmebehandlung unterzogen wird. Dabei wird das Kaltband in einem ersten Glühschritt auf eine oberhalb seiner Ar3-Temperatur liegende erste Glühtemperatur erwärmt, um im Kaltband vorhandene Karbide in Lösung zu bringen. Anschließend erfolgt eine von der ersten Glühtemperatur ausgehende, mit einer Abkühlgeschwindigkeit von mindestens 10 °C/s erfolgende Abkühlung auf eine zweite Glühtemperatur. Diese ist so gewählt, dass sich im Kaltband Bainit bildet, und liegt typischerweise im Bereich von 300 - 450 °C. Dieser zur Bainitbildung durchgeführte zweite Glühschritt wird so lange ausgeführt, bis das Gefüge des Kaltbands zu mindestens 60 % aus Bainit und zu mindestens 5 % aus Restaustenit sowie als Rest aus polygonalem Ferrit besteht. Dabei wird angestrebt, dass das Gefüge möglichst vollständig bainitisch ist und andere Gefügebestandteile allenfalls in Spuren vorliegen. Das so beschaffene Kaltband erreicht Zugfestigkeiten von bis zu 1180 MPa bei einer Dehnung von mindestens 9 % und kann erforderlichenfalls mit einer metallischen, vor Korrosion schützenden Schicht belegt werden.Another method for producing an extremely strong cold strip is from US 7,591,977 B2 known. According to this method, a hot rolled strip (containing wt%) of 0.1-0.25% C, 1.0-2.0% Si and 1.5-3.0% Mn having a cold rolling degree of 30-70 rolled to a cold-rolled strip, which is then subjected to a continuous heat treatment. In this case, the cold strip is heated in a first annealing step to a lying above its Ar3 temperature first annealing temperature to bring in the cold strip carbides in solution. Subsequently, a cooling proceeding from the first annealing temperature takes place, with a cooling rate of at least 10 ° C./s, to a second annealing temperature. This is chosen so that bainite forms in the cold strip, and is typically in the range of 300-450 ° C. This second annealing step carried out for bainite formation is carried out until the structure of the cold strip consists of at least 60% bainite and at least 5% residual austenite and the remainder polygonal ferrite. The aim is that the structure is as completely as possible bainitic and other structural constituents are present in traces at best. The cold-rolled strip obtained in this way achieves tensile strengths of up to 1180 MPa at an elongation of at least 9% and, if necessary, can be covered with a metallic, corrosion-protective layer.

Vor dem Hintergrund des voranstehend erläuterten Standes der Technik bestand die Aufgabe der Erfindung darin, ein kaltgewalztes Stahlflachprodukt zu schaffen, dass auf einfache und betriebssichere Weise hergestellt werden kann und eine optimierte Kombination aus weiter gesteigerter Festigkeit und guter Verformbarkeit aufweist. Darüber hinaus sollte ein Verfahren zur Herstellung eines solchen kaltgewalzten Stahlflachprodukts genannt werden.Against the background of the prior art explained above, the object of the invention was to provide a cold rolled flat steel product which is manufactured in a simple and reliable way can and has an optimized combination of further increased strength and good ductility. In addition, a method for producing such a cold-rolled steel flat product should be mentioned.

In Bezug auf das kaltgewalzte Stahlflachprodukt ist diese Aufgabe erfindungsgemäß durch das in Anspruch 1 angegebene Stahlflachprodukt gelöst worden.With regard to the cold-rolled flat steel product, this object has been achieved according to the invention by the flat steel product specified in claim 1.

In Bezug auf das Verfahren besteht die erfindungsgemäße Lösung der voranstehend genannten Aufgabe darin, dass zur Herstellung eines erfindungsgemäßen kaltgewalzten Stahlflachprodukts mindestens die in Anspruch 12 angegebenen Arbeitsschritte durchlaufen werden.With regard to the method, the solution according to the invention of the abovementioned object consists in that at least the working steps specified in claim 12 are run through to produce a cold-rolled flat steel product according to the invention.

Vorteilhafte Ausgestaltungen der Erfindung sind in den abhängigen Ansprüchen angegeben und werden nachfolgend wie der allgemeine Erfindungsgedanke im Einzelnen erläutert.Advantageous embodiments of the invention are specified in the dependent claims and are explained below as the general inventive concept in detail.

Das erfindungsgemäße kaltgewalzte Stahlflachprodukt zeichnet sich dadurch aus, dass es neben Eisen und unvermeidbaren Verunreinigungen (in Gew.-%)

  • C: 0,10 - 0,60 %,
  • Si: 0,4 - 2,5 %,
  • Al: bis zu 3,0 %
  • Mn: 0,4 - 3,0 %,
  • Ni: bis zu 1,0 %,
  • Cu: bis zu 2,0 %,
  • Mo: bis zu 0,4 %,
  • Cr: bis zu 2 %,
  • Co: bis zu 1,5 %,
  • Ti: bis zu 0,2 %,
  • Nb: bis zu 0,2 %,
  • V: bis zu 0,5 %,
enthält. Dabei besteht das Gefüge des erfindungsgemäßen Stahlflachprodukts im kaltgewalzten Zustand zu mindestens 20 Vol.-% aus Bainit, zu 10 - 35 Vol.-% aus Restaustenit und als Rest aus Martensit, wobei es selbstverständlich ist, dass im Gefüge des Stahlflachprodukts technisch unvermeidbare Spuren anderer Gefügebestandteile vorhanden sein können. Ein so beschaffenes erfindungsgemäßes kaltgewalztes Stahlflachprodukt erzielt regelmäßig Zugfestigkeiten Rm von mindestens 1400 MPa und eine Dehnung A80 von mindestens 5 %. Der C-Gehalt des Restaustenits beträgt typischerweise mehr als 1,0 Gew.-%.The cold-rolled flat steel product according to the invention is characterized in that in addition to iron and unavoidable impurities (in% by weight)
  • C: 0.10-0.60%,
  • Si: 0.4-2.5%,
  • Al: up to 3.0%
  • Mn: 0.4 - 3.0%,
  • Ni: up to 1.0%,
  • Cu: up to 2.0%,
  • Mo: up to 0.4%,
  • Cr: up to 2%,
  • Co: up to 1.5%,
  • Ti: up to 0.2%,
  • Nb: up to 0.2%,
  • V: up to 0.5%,
contains. At least 20% by volume of bainite, 10% to 35% by volume of retained austenite and the remainder of martensite in the cold-rolled state, it being understood that technically unavoidable traces of others are present in the microstructure of the flat steel product Microstructure constituents can be present. Such a cold rolled flat steel product of the present invention regularly achieves tensile strengths Rm of at least 1400 MPa and an elongation A80 of at least 5%. The C content of the retained austenite is typically more than 1.0% by weight.

Das erfindungsgemäße Verfahren zum Herstellen eines erfindungsgemäß beschaffenen Stahlflachprodukts umfasst folgende Arbeitsschritte:

  • Bereitstellen eines Vorprodukts in Form einer Bramme, Dünnbramme oder eines gegossenen Bands, das neben Eisen und unvermeidbaren Verunreinigungen (in Gew.-%) C: 0,10 - 0,60 %, Si: 0,4 - 2,5 %, Al: bis zu 3,0 %, Mn: 0,4 - 3,0 %, Ni: bis zu 1,0 %, Cu: bis zu 2,0 %, Mo: bis zu 0,4 %, Cr: bis zu 2 %, Co: bis zu 1,5 %, Ti: bis zu 0,2 %, Nb: bis zu 0,2 %, V: bis zu 0,5 % enthält;
  • Warmwalzen des Vorprodukts zu einem Warmband in einem oder mehreren Walzstichen, wobei das erhaltene Warmband beim Verlassen des letzten Walzstichs eine Warmwalzendtemperatur von mindestens 830 °C aufweist;
  • Haspeln des erhaltenen Warmbands bei einer Haspeltemperatur, die zwischen der Warmwalzendtemperatur und 560 °C liegt;
  • Kaltwalzen des Warmbands zu einem Kaltband mit einem Kaltwalzgrad von mindestens 30 %;
  • Wärmebehandeln des erhaltenen Kaltbands, wobei das Kaltband im Zuge der Wärmebehandlung
    • auf eine mindestens 800 °C betragende Glühtemperatur erwärmt wird,
    • optional über eine Glühdauer von 50 - 150 s bei der Glühtemperatur gehalten wird,
    • ausgehend von der Glühtemperatur mit einer mindestens 8 °C/s betragenden Abkühlgeschwindigkeit auf eine Haltetemperatur abgekühlt wird, die in einem Haltetemperaturbereich liegt, dessen Obergrenze 470 °C beträgt und dessen Untergrenze höher ist als die Martensitstarttemperatur MS, ab der Martensit im Gefüge des Kaltbands entsteht, und
    • im Haltetemperaturbereich über einen Zeitraum gehalten wird, der ausreicht, um im Gefüge des Kaltbands mindestens 20 Vol.-% Bainit zu bilden.
The method according to the invention for producing a flat steel product according to the invention comprises the following steps:
  • Providing a precursor in the form of a slab, thin slab or cast strip which, in addition to iron and unavoidable impurities (in% by weight) C: 0.10-0.60%, Si: 0.4-2.5%, Al : up to 3.0%, Mn: 0.4 - 3.0%, Ni: up to 1.0%, Cu: up to 2.0%, Mo: up to 0.4%, Cr: up to 2%, Co: up to 1.5%, Ti: up to 0.2%, Nb: up to 0.2%, V: up to 0.5%;
  • Hot rolling the precursor into a hot strip in one or more rolling passes, the resulting hot strip having a hot rolling end temperature of at least 830 ° C when leaving the last pass;
  • Coiling the resulting hot strip at a reel temperature that is between the hot rolling end temperature and 560 ° C;
  • Cold rolling the hot strip to a cold strip having a cold rolling degree of at least 30%;
  • Heat treating the cold strip obtained, wherein the cold strip during the heat treatment
    • is heated to a minimum of 800 ° C annealing temperature,
    • is held at the annealing temperature over an annealing period of 50 - 150 s,
    • is cooled starting from the annealing temperature with a cooling rate of at least 8 ° C / s to a holding temperature, which is in a holding temperature range whose upper limit is 470 ° C and whose lower limit is higher than the martensite start temperature MS, starting from the martensite in the structure of the cold strip , and
    • held in the holding temperature range for a period sufficient to form at least 20 vol .-% bainite in the structure of the cold strip.

Ein erfindungsgemäßes Stahlband weist ein dreiphasiges Gefüge auf, dessen dominierender Bestandteil Bainit ist und das darüber hinaus aus Restaustenit sowie als Rest aus Martenisit besteht. Optimaler Weise liegt dabei der Bainitanteil bei mindestens 60 Vol.-% und der Restaustenitanteil im Bereich von 10 - 25 Vol.-%, wobei auch hier der Rest des Gefüges jeweils durch Martensit aufgefüllt ist. Der optimale Martensitanteil beträgt mindestens 10 Vol.-%. Ein derart zusammengesetztes Gefüge bewirkt die beste Kombination vonRm*A80 bei der geforderten Zugfestigkeit.A steel strip according to the invention has a three-phase structure, the dominant constituent of which is bainite and which, moreover, consists of retained austenite and the remainder of martensite. Optimally, the bainite content is at least 60% by volume and the residual austenite content is in the range from 10% to 25% by volume, the remainder of the microstructure in each case also being filled with martensite. The optimum martensite content is at least 10% by volume. Such a composite structure gives the best combination of Rm * A80 at the required tensile strength.

Neben den Hauptkomponenten "Bainit", "Restaustenit" und "Martensit" können Gehalte an anderen Gefügebestandteilen vorhanden sein, deren Anteile jedoch zu gering sind, um einen Einfluss auf die Eigenschaften des erfindungsgemäßen Kaltbands zu haben. Der Restaustenit liegt in einem erfindungsgemäßen Kaltband überwiegend filmartig mit kleinen globularen Inseln von blockigem Restaustenit mit einer Korngröße <5 µm vor, so dass der Restaustenit eine hohe Stabilität und damit einhergehend eine geringe Neigung zur unerwünschten Umwandlung in Martensit besitzt sowie den TRIP-Effekt ermöglicht.In addition to the main components "bainite", "retained austenite" and "martensite" contents of other structural constituents may be present, but their shares are too low to have an influence on the properties of the cold strip according to the invention. The retained austenite is in a cold strip according to the invention predominantly film-like with small globular islands of blocky retained austenite with a particle size <5 microns, so that the retained austenite has a high stability and, consequently, a low tendency to undesirable conversion to martensite and allows the TRIP effect.

Erfindungsgemäß erzeugtes Kaltband erreicht regelmäßig Zugfestigkeiten Rm von mehr als 1400 MPa, bei Dehnungen A80, die ebenso regelmäßig oberhalb von 5 % liegen. Dementsprechend liegt die Güte Rm*A80 von erfindungsgemäßen Stahlflachprodukten regelmäßig oberhalb von 7000 MPa*%, wobei typischerweise Güten Rm*A80 von mindestens 13500 MPa*% erreicht werden. Ein erfindungsgemäßes Kaltband verfügt als solches über eine optimale Kombination aus extremer Festigkeit und ausreichender Umformbarkeit.Cold rolled strip produced according to the invention regularly reaches tensile strengths Rm of more than 1400 MPa, with strains A80 which likewise regularly exceed 5%. Accordingly, the quality Rm * A80 of flat steel products according to the invention is regularly above 7000 MPa *%, with grades Rm * A80 of at least 13500 MPa *% being typically achieved. An inventive cold strip as such has a optimal combination of extreme strength and sufficient formability.

Die Martensitstarttemperatur, d. h. die Temperatur, ab der sich in erfindungsgemäß verarbeitetem Stahl Martensit bildet, kann gemäß der im Artikel " Thermodynamic Exatrapolation and Martensite-Start-Temperature of Substitutionally Alloyed Steels" von H. Bhadeshia, erschienen in Metal Science 15 (1981), Seiten 178 -180 erläuterten Vorgehensweise berechnet werden.The martensite starting temperature, ie the temperature at which martensite is formed in steel processed according to the invention, can be determined according to the Thermodynamic Exatrapolation and Martensite Start-Temperature of Substituted Alloyed Steels "by H. Bhadeshia, published in Metal Science 15 (1981), pages 178-180 explained procedure can be calculated.

Kohlenstoff verzögert im erfindungsgemäßen Stahl die Umwandlung in Ferrit/Perlit, senkt die Martensitstarttemperatur MS ab und trägt zur Erhöhung der Härte bei. Um diese positiven Effekte zu nutzen, kann der C-Gehalt des erfindungsgemäßen Stahlflachprodukts auf mindestens 0,25 Gew.-%, insbesondere mindestens 0,27 Gew.-% oder mindestens 0,28 Gew.-%, gesetzt werden, wobei sich die durch den vergleichbar hohen Kohlenstoffgehalt erzielten Effekte dann besonders sicher nutzen lassen, wenn der C-Gehalt im Bereich von > 0,25 - 0,5 Gew.-%, insbesondere 0,27 - 0,4 Gew.-% oder 0,28 - 0,4 Gew.-%, liegt.In the steel according to the invention, carbon retards the transformation into ferrite / perlite, lowers the martensite starting temperature MS and contributes to increasing the hardness. To take advantage of these positive effects, the C content of the flat steel product according to the invention can be set to at least 0.25% by weight, in particular at least 0.27% by weight or at least 0.28% by weight, wherein the be used by the comparably high carbon content effects particularly safe when the C content in the range of> 0.25 to 0.5 wt .-%, in particular 0.27 to 0.4 wt .-% or 0.28 - 0.4 wt .-%, is.

Auch in einem erfindungsgemäßen kaltgewalzten Stahlflachprodukt kann die festigkeitssteigernde Wirkung von Kupfer genutzt werden. Hierzu kann im erfindungsgemäßen Stahlflachprodukt ein Mindestgehalt von 0,15 Gew.-% Cu, insbesondere mindestens 0,2 Gew.-% Cu, vorhanden sein. Einen besonders wirksamen Beitrag zur Festigkeit leistet Cu, wenn es in Gehalten von mindestens 0,55 Gew.-% im erfindungsgemäßen Stahlflachprodukt vorhanden ist, wobei sich negative Auswirkungen der Anwesenheit von Cu dadurch begrenzen lassen, dass der Cu-Gehalt auf höchstens 1,5 Gew.-% beschränkt wird.The strength-increasing effect of copper can also be used in a cold-rolled flat steel product according to the invention. For this purpose, a minimum content of 0.15% by weight of Cu, in particular at least 0.2% by weight of Cu, may be present in the flat steel product according to the invention. A particularly effective contribution to strength is made by Cu, if it contains at least 0.55 wt .-% in the flat steel product according to the invention is present, whereby negative effects of the presence of Cu can be limited by limiting the Cu content to at most 1.5% by weight.

Mn in Gehalten von mindestens 0,4 Gew.-% und bis zu 3 Gew.-%, insbesondere bis zu 2,5 Gew.-%, fördert im erfindungsgemäß verarbeiteten Stahl die Bainitbildung, wobei die optional zusätzlich vorhandenen Gehalte an Cu, Cr und Ni ebenfalls zur Bildung von Bainit beitragen. Abhängig von den jeweils anderen Bestandteilen des erfindungsgemäß verarbeiteten Stahls kann es dabei zweckmäßig sein, den Mn-Gehalt auf maximal 2 Gew.-% zu beschränken oder den Mindestgehalt an Mn auf 1,5 Gew.-% zu erhöhen.Mn in contents of at least 0.4 wt .-% and up to 3 wt .-%, in particular up to 2.5 wt .-%, promotes bainite formation in the steel processed according to the invention, wherein the optional additionally present levels of Cu, Cr and Ni also contribute to the formation of bainite. Depending on the respective other constituents of the steel processed according to the invention, it may be expedient to limit the Mn content to a maximum of 2% by weight or to increase the minimum content of Mn to 1.5% by weight.

Auch durch die optionale Zugabe von Cr kann die Martensitstarttemperatur abgesenkt und die Neigung des Bainits zur Umwandlung in Perlit oder Zementit unterdrückt werden. Des Weiteren fördert Cr in Gehalten bis zu der erfindungsgemäß vorgegebenen Obergrenze von maximal 2 Gew.-% die ferritische Umwandlung, wobei sich optimale Wirkungen der Anwesenheit von Cr im erfindungsgemäßen kaltgewalzten Stahlflachprodukt dann ergeben, wenn der Cr-Gehalt auf 1,5 Gew.-% beschränkt ist. Besonders wirksam nutzen lässt sich der positive Einfluss von Cr, wenn mindestens 0,3 Gew.-% Cr im erfindungsgemäßen Stahlflachprodukt vorhanden sind.Also by the optional addition of Cr, the martensite start temperature can be lowered and the tendency of the bainite to convert to pearlite or cementite can be suppressed. Furthermore, Cr at levels up to the upper limit of not more than 2% by weight given in accordance with the invention promotes the ferritic transformation, with optimum effects of the presence of Cr in the cold-rolled flat steel product of the invention when the Cr content is reduced to 1.5% by weight. % is limited. The positive influence of Cr can be used particularly effectively if at least 0.3% by weight of Cr is present in the flat steel product according to the invention.

Durch die ebenfalls optionale Zugabe von Ti, V oder Nb kann die Entstehung von feinkörnigerem Gefüge unterstützt und die bainitische Umwandlung gefördert werden. Darüber hinaus tragen diese Mikrolegierungselemente durch die Bildung von Ausscheidungen zur Steigerung der Härte bei. Besonders effektiv lassen sich die positiven Wirkungen von Ti, V und Nb im erfindungsgemäßen kaltgewalzten Stahlflachprodukt dann nutzen, wenn ihr Gehalt jeweils im Bereich von 0,002 - 0,15 Gew.-% liegt, insbesondere 0,1 Gew.-% nicht überschreitet.The addition of Ti, V or Nb, which is also optional, can help to create finer-grained microstructures and promote bainitic transformation. In addition, these microalloying elements carry through the Formation of precipitates to increase hardness. The positive effects of Ti, V and Nb in the cold-rolled flat steel product according to the invention can be used particularly effectively if their content is in each case in the range from 0.002 to 0.15% by weight, in particular 0.1% by weight does not exceed.

Si ist in einem erfindungsgemäßen Stahlflachprodukt in Gehalten von 0,4 - 2,5 Gew.-% vorhanden und bewirkt eine deutliche Mischkristallverfestigung. Um diesen Effekt besonders sicher zu nutzen, kann der Si-Gehalt auf mindestens 1,0 Gew.-% gesetzt werden. Ebenso kann es zur Vermeidung negativer Einflüsse zweckmäßig sein, den Si-Gehalt auf maximal 2 Gew.-% zu beschränken.Si is present in a flat steel product according to the invention in contents of 0.4-2.5% by weight and causes a marked solid solution hardening. In order to use this effect particularly safely, the Si content can be set to at least 1.0 wt .-%. Likewise, to avoid negative influences, it may be expedient to limit the Si content to a maximum of 2% by weight.

Al kann im erfindungsgemäß verarbeiteten Stahl den Si-Gehalt zu einem Teil ersetzen. Gleichzeitig wirkt Al wie auch Si bei der Stahlherstellung desoxidierend. Hierzu kann ein Mindestgehalt von 0,01 Gew.-% Al vorgesehen werden. Höhere Gehalte an Al erweisen sich beispielsweise dann als zweckmäßig, wenn durch die Zugabe von Al die Härte oder Zugfestigkeit des Stahls zu Gunsten einer verbesserten Verformbarkeit auf einen niedrigeren Wert eingestellt werden soll.Al can partially replace the Si content in the steel processed according to the invention. At the same time, Al and Si are deoxidizing during steelmaking. For this purpose, a minimum content of 0.01 wt .-% Al can be provided. Higher contents of Al prove to be useful, for example, if the addition of Al should set the hardness or tensile strength of the steel to a lower value in favor of improved ductility.

Eine weitere Funktion von Si und Al besteht darin, die Karbidbildung im Bainit zu unterdrücken und damit den Restaustenit durch gelösten C zu stabilisieren.Another function of Si and Al is to suppress carbide formation in the bainite and thus to stabilize the retained austenite by dissolved C.

Die positiven Einflüsse der gleichzeitigen Anwesenheit von Al und Si können dadurch besonders effektiv genutzt werden, wenn die Gehalte an Si und Al innerhalb der erfindungsgemäß vorgegebenen Grenzen folgende Bedingung erfüllen: %Si + 0,8%Al > 1,2 Gew.-% (mit %Si: jeweiliger Si-Gehalt in Gew.-%, %Al: jeweiliger Al-Gehalt in Gew.-%).The positive effects of the simultaneous presence of Al and Si can thereby be used particularly effectively if the contents of Si and Al within the According to the invention predetermined limits meet the following condition:% Si + 0.8% Al> 1.2 wt .-% (with% Si: respective Si content in wt%,% Al: respective Al content in wt .-% ).

Die Bildung des erfindungsgemäß vorgegebenen Gefüges lässt sich insbesondere dadurch gewährleisten, dass die Gehalte des erfindungsgemäß verarbeiteten Stahls und dementsprechend die Gehalte des erfindungsgemäßen Stahlflachprodukts an Mn, Cr, Ni, Cu und C die folgende Bedingung 1 < 0 , 5 % Mn + 0 , 167 % Cr + 0 , 125 % Ni + 0 , 125 % Cu + 1 , 334 % C < 2

Figure imgb0001

erfüllen, wobei mit %Mn der jeweilige Mn-Gehalt in Gew.-%, mit %Cr der jeweilige Cr-Gehalt in Gew.-%, mit %Ni der jeweilige Ni-Gehalt in Gew.-%, mit %Cu der jeweilige Cu-Gehalt in Gew.-% und mit %C der jeweilige C-Gehalt in Gew.-% bezeichnet sind.The formation of the structure prescribed according to the invention can be ensured, in particular, by the contents of the steel processed according to the invention and, accordingly, the contents of the flat steel product according to the invention of Mn, Cr, Ni, Cu and C having the following condition 1 < 0 . 5 % Mn + 0 . 167 % Cr + 0 . 125 % Ni + 0 . 125 % Cu + 1 . 334 % C < 2
Figure imgb0001
meet, where with% Mn the respective Mn content in wt .-%, with% Cr of the respective Cr content in wt .-%, with% Ni of the respective Ni content in wt .-%, with% Cu of the respective Cu content in wt .-% and with% C of the respective C content in wt .-% are designated.

Zur Herstellung eines erfindungsgemäßen Stahlflachprodukts wird das aus einem erfindungsgemäß zusammengesetzten Stahl gegossene Vorprodukt zunächst auf eine Temperatur gebracht oder auf einer Temperatur gehalten, die ausreicht, um das ausgehend von dieser Temperatur durchgeführte Warmwalzen bei einer Warmwalzendtemperatur zu beenden, die im Bereich von 830 - 1000 °C liegen. Nach dem Verlassen des letzten für das Warmwalzen verwendeten Walzgerüsts kühlt das Warmband auf dem sich an das betreffende Walzgerüst anschließenden Rollgang ab. Im Anschluss an den Rollgang läuft das Warmband in eine Haspeleinrichtung, in der es zu einem Coil gewickelt wird.To produce a flat steel product according to the invention, the precursor cast from a composite steel according to the invention is first brought to a temperature or maintained at a temperature sufficient to terminate the hot rolling carried out from said temperature at a hot rolling end temperature in the range of 830-1000 ° C lie. After leaving the last rolling stand used for hot rolling, the hot strip is cooled on the roller table following the relevant stand. This is followed by the roller table Hot strip in a coiler, where it is wound into a coil.

Die Haspeltemperatur muss mindestens 560 °C betragen, damit ein relativ weiches Warmbandgefüge aus Ferrit und Perlit entsteht. Ein für diesen Zweck optimaler Temperaturverlauf ergibt sich, wenn die Warmwalzendtemperatur im Bereich von 850 - 950 °C, insbesondere im Bereich von 880 - 950 °C, liegt. Typischerweise wird dazu das Vorprodukt vor dem Warmwalzen auf eine im Bereich von 1100 - 1300 °C liegende Temperatur erwärmt oder bei dieser Temperatur gehalten. Das Gefüge des so erhaltenen Warmbands besteht hauptsächlich aus Ferrit und Perlit. Die Gefahr einer Entstehung von Korngrenzenoxidation kann dadurch minimiert werden, dass die Haspeltemperatur auf maximal 750 °C beschränkt wird.The reel temperature must be at least 560 ° C, so that a relatively soft hot-band structure of ferrite and pearlite is formed. An optimum temperature profile for this purpose results when the hot rolling end temperature is in the range of 850-950 ° C., in particular in the range of 880-950 ° C. Typically, the precursor is heated or maintained at a temperature in the range of 1100-1300 ° C temperature before hot rolling. The structure of the hot strip thus obtained consists mainly of ferrite and pearlite. The risk of grain boundary oxidation can be minimized by limiting the coiler temperature to a maximum of 750 ° C.

Nach dem Haspeln wird das Warmband kaltgewalzt, wobei das Warmband vor dem Kaltwalzen selbstverständlich in üblicher Weise chemisch oder mechanisch entzundert werden kann.After coiling, the hot strip is cold rolled, wherein the hot strip can of course be descaled chemically or mechanically before cold rolling in the usual way.

Das Kaltwalzen erfolgt mit einem Kaltwalzgrad von mindestens 30 %, insbesondere mindestens 45 %, um die Rekristallisation und Umwandlung beim anschließenden Glühen zu beschleunigen. Generell ergibt sich zudem durch Einhaltung eines entsprechend hohen Kaltwalzgrades eine bessere Oberflächenqualität. Kaltwalzgrade von mindestens 50 % haben sich hierfür als besonders günstig erwiesen. Nach dem Kaltwalzen absolviert das erfindungsgemäß erhaltene Kaltband in einem kontinuierlichen Durchlauf einen Glühzyklus, bei dem es in einer ersten Glühphase auf eine Temperatur von mindestens 800 °C, bevorzugt mindestens 830 °C, erwärmt wird. Diese erste Glühphase dauert mindestens so lange, dass das Kaltband vollständig austenitisiert ist. Hierzu sind typischerweise 50 - 150 s erforderlich.The cold rolling is carried out with a degree of cold rolling of at least 30%, in particular at least 45%, in order to accelerate the recrystallization and conversion during the subsequent annealing. In general, a better surface quality is achieved by maintaining a correspondingly high degree of cold rolling. Cold rolling degrees of at least 50% have proven to be particularly favorable for this purpose. After cold rolling, the cold strip according to the invention undergoes an annealing cycle in a continuous pass, in which it is heated in a first annealing phase to a temperature of at least 800 ° C., preferably at least 830 ° C. This first annealing phase lasts at least as long that the cold strip is completely austenitized. This typically requires 50-150 seconds.

Am Ende der ersten Glühphase wird das Produkt abgeschreckt, wobei die Abkühlgeschwindigkeit mindestens 8 °C/s, insbesondere 10 °C/s, beträgt. Die Zieltemperatur dieser Abschreckung ist eine Haltetemperatur, die höchstens 470 °C beträgt und höher ist als die Martensitstarttemperatur MS, ab der Martensit im Gefüge des Kaltbands entsteht. In der Praxis kann als Anhalt für den Bereich, in dem die Haltetemperatur liegen soll, der Bereich von 300 - 420 °C, insbesondere 330 - 420 °C, angewendet werden.At the end of the first annealing phase, the product is quenched, the cooling rate being at least 8 ° C / s, in particular 10 ° C / s. The target temperature of this quenching is a holding temperature which is at most 470 ° C and higher than the martensite start temperature MS, starting from the martensite in the structure of the cold strip. In practice, the range of 300-420 ° C, in particular 330-420 ° C, can be used as an indication of the range in which the holding temperature should be.

Ausgehend von der jeweiligen Haltetemperatur wird das Kaltband in der zweiten Glühphase im Haltetemperaturbereich gehalten und zwar so lange, bis sich das Gefüge des Kaltbands zu mindestens 20 Vol.-% in Bainit gewandelt hat. Das Halten kann dabei als isothermes Halten auf der bei der Abkühlung erreichten Haltetemperatur oder als langsam erfolgende Temperaturabnahme innerhalb des Haltetemperaturbereichs durchgeführt werden.Based on the respective holding temperature, the cold strip is kept in the holding temperature range in the second annealing phase, specifically until the structure of the cold strip has changed to at least 20% by volume in bainite. The holding can be carried out as an isothermal hold on the holding temperature achieved during the cooling or as a slow decrease in temperature within the holding temperature range.

Das erfindungsgemäß erzeugte Stahlflachprodukt kann in üblicher Weise mit einer metallischen Schutzschicht belegt werden. Dies kann beispielsweise durch Schmelztauchbeschichten erfolgen. Sofern vor dem Auftrag der metallischen Beschichtung ein Glühen erforderlich ist, kann die erfindungsgemäß vorgesehene Wärmebehandlung im Rahmen dieses Glühens durchgeführt werden.The flat steel product produced according to the invention can be treated in the usual way with a metallic protective layer be occupied. This can be done for example by hot dip coating. If an annealing is required before the application of the metallic coating, the heat treatment provided according to the invention can be carried out as part of this annealing.

Nachfolgend wird die Erfindung anhand von Ausführungsbeispielen näher erläutert.The invention will be explained in more detail by means of exemplary embodiments.

Es sind fünf Stähle S1 - S5 erschmolzen worden, deren Zusammensetzung in Tabelle 1 angegeben ist.Five steels S1-S5 have been melted, the composition of which is given in Table 1.

Die entsprechend zusammengesetzten Stahlschmelzen sind auf konventionelle Weise zu einem Strang vergossen worden, von dem Brammen abgeteilt worden sind. Die Dünnbrammen sind anschließend auf ebenso konventionelle Weise auf eine Wiedererwärmungstemperatur erwärmt worden.The correspondingly assembled steel melts have been cast in a conventional manner into a strand from which slabs have been divided. The thin slabs were then heated to a reheating temperature in a conventional manner as well.

Die erwärmten Brammen sind in einer ebenfalls konventionellen Warmwalzstaffel zu Warmbändern mit einer Dicke von 2 mm warmgewalzt worden.The heated slabs were hot rolled in a conventional hot rolling mill to hot strip with a thickness of 2 mm.

Die Warmwalzendtemperatur lag jeweils im Bereich von 830 - 900 °C. Ausgehend von dieser Temperatur sind die Warmbänder auf eine oberhalb von 560 °C liegende Haspeltemperatur abgekühlt worden und anschließend zu Coils gehaspelt worden.The hot rolling end temperature was in the range of 830 - 900 ° C. Starting from this temperature, the hot strips were cooled to a lying above 560 ° C reel temperature and then coiled into coils.

Die so erhaltenen Warmbänder sind nach dem Haspeln entzundert und nach dem Entzundern bei Kaltwalzgraden von 50 % zu Kaltband kaltgewalzt worden.The hot strips thus obtained are descaled after coiling and cold rolled after descaling at cold rolling degrees of 50% to cold strip.

Eine größere Zahl von Proben dieser Kaltbänder sind dann einer Wärmebehandlung unterzogen worden, bei der sie in einem ersten Glühschritt mit einer Erwärmungsgeschwindigkeit von mindestens 1,9 °C/s auf eine erste Glühtemperatur erwärmt worden sind, die im Bereich von 830 - 850 °C lag. Bei dieser Temperatur sind die Kaltbänder über eine Dauer von 120 s gehalten worden, bis sie vollständig durcherwärmt waren.A larger number of samples of these cold strips were then subjected to a heat treatment in which they were heated in a first annealing step at a heating rate of at least 1.9 ° C / s to a first annealing temperature in the range of 830-850 ° C was. At this temperature, the cold strips were held for a period of 120 seconds until fully warmed.

Anschließend erfolgte eine Abschreckung, bei der Kaltbänder mit einer mindestens 8 °C/s betragenden Abkühlgeschwindigkeit auf eine Haltetemperatur T2 abgeschreckt worden sind, die im Bereich von 350 - 420 °C lag. Konkret lagen die Haltetemperaturen T2 bei einer ersten Charge von Versuchen bei 300 °C, 310 °C, 330 °C, 340 °C, 375 °C, 390 °C und 410 °C. Bei der jeweiligen Haltetemperatur T2 sind die Kaltbandproben für eine Glühdauer t2 gehalten worden.This was followed by a quenching, in which cold strips were quenched with a cooling rate of at least 8 ° C / s to a holding temperature T2, which was in the range of 350-420 ° C. Specifically, the holding temperatures T2 for a first batch of tests were 300 ° C, 310 ° C, 330 ° C, 340 ° C, 375 ° C, 390 ° C and 410 ° C. At the respective holding temperature T2, the cold strip samples have been kept for an annealing period t2.

In Fig. 1 sind die erzielten Zugfestigkeiten Rm über die jeweilige Glühtemperatur T2 aufgetragen. Es zeigt sich, dass die aus dem Stahl S5 gefertigten Kaltbandproben jeweils nur unter bestimmten Glühbedingungen die geforderte Mindestzugfestigkeit von 1400 MPa erreichen, während die Zugfestigkeiten der aus den anderen Stählen hergestellten Kaltbandproben stets sicher über der Mindestgrenze von 1400 MPa lagen. Als Grund hierfür ist der vergleichbar geringe, an der unteren Grenze des erfindungsgemäß vorgegebenen Gehaltsbereichs liegende Kohlenstoffgehalt des Stahls S5 ermittelt worden.In Fig. 1 the tensile strengths Rm achieved are plotted against the respective annealing temperature T2. It can be seen that the cold strip samples made of the steel S5 only achieved the required minimum tensile strength of 1400 MPa under certain annealing conditions, whereas the tensile strengths of the cold strip samples produced from the other steels always safely exceeded the minimum limit of 1400 MPa. The reason for this is the comparatively low carbon content of the steel S5, which is located at the lower limit of the content range prescribed according to the invention.

In Fig. 2 sind die Zugfestigkeiten der aus dem Stahl S4 erzeugten Kaltbandproben über die Glühdauer t2 der zweiten Glühstufe aufgetragen. Es zeigt sich, dass die bei einer Haltetemperatur von 310 °C, 330 °C und 350 °C, also im Haltetemperaturbereich von 310 - 350 °C, gehaltenen Kaltbandproben die geforderte Zugfestigkeit Rm von 1400 MPa unabhängig von der jeweiligen Glühdauer t2 erreicht haben.In Fig. 2 the tensile strengths of the cold strip samples produced from the steel S4 are plotted over the annealing time t2 of the second annealing stage. It turns out that the cold strip samples held at a holding temperature of 310 ° C., 330 ° C. and 350 ° C., ie in the holding temperature range of 310 ° to 350 ° C., have reached the required tensile strength Rm of 1400 MPa irrespective of the respective annealing time t 2.

In Fig. 3 sind in gleicher Weise die Zugfestigkeiten der aus dem Stahl S5 erzeugten Kaltbandproben über die Glühdauer t2 der zweiten Glühstufe aufgetragen. Es zeigt sich hier, dass die bei einer Haltetemperatur von 350 °C und 390 °C, also im Haltetemperaturbereich von 350 - 390 °C, gehaltenen Kaltbandproben die geforderte Zugfestigkeit Rm von 1400 MPa erreichen, wenn die Glühdauer t2 kürzer als 145 s ist.In Fig. 3 In the same way, the tensile strengths of the cold strip samples produced from the steel S5 are plotted over the annealing time t2 of the second annealing stage. It can be seen here that the cold strip samples held at a holding temperature of 350 ° C. and 390 ° C., ie in the holding temperature range of 350 ° -390 ° C., reach the required tensile strength R m of 1400 MPa if the annealing time t 2 is shorter than 145 s.

In Fig. 4 ist die Dehnung A80 der aus dem Stahl S4 erzeugten Kaltbandproben über die Glühdauer t2 der zweiten Glühstufe aufgetragen. Die bei einer Haltetemperatur von 310 °C, 330 °C und 350 °C, also im Haltetemperaturbereich von 310 - 350 °C, gehaltenen Kaltbandproben haben die geforderte Mindestdehnung A80 unabhängig von der jeweiligen Glühdauer t2 erreicht.In Fig. 4 the strain A80 of the cold strip samples produced from the steel S4 is plotted over the annealing time t2 of the second annealing stage. The held at a holding temperature of 310 ° C, 330 ° C and 350 ° C, ie in the holding temperature range of 310 - 350 ° C, cold strip samples have reached the required minimum strain A80 regardless of the respective annealing time t2.

In Fig. 5 ist die Dehnung A80 der aus dem Stahl S5 erzeugten Kaltbandproben über die Glühdauer t2 der zweiten Glühstufe aufgetragen. Auch hier zeigt sich, dass die Kaltbandproben die geforderte Dehnung A80 von mindestens 5 % unabhängig von ihrer jeweiligen Haltetemperatur T2 und unabhängig von der jeweiligen Glühdauer t2 erreichen. Dementsprechend kann bei Einhaltung einer kurzen Glühdauer und geeignet niedrigen Haltetemperaturen T2 auch aus dem Stahl S5 trotz seines vergleichsweise niedrigen C-Gehalts ein erfindungsgemäßes kaltgewalztes Stahlflachprodukt erzeugt werden, bei dem eine hohe Zugfestigkeit Rm mit einer ausreichenden Dehnung A80 kombiniert ist.In Fig. 5 the strain A80 of the cold strip samples produced from the steel S5 is plotted over the annealing time t2 of the second annealing stage. Here, too, it can be seen that the cold strip samples have the required elongation A80 of at least 5%, regardless of their respective holding temperature T2 and independently of the respective holding temperature Reach annealing time t2. Accordingly, while maintaining a short annealing time and suitably low holding temperatures T2, a cold-rolled steel flat product according to the invention can be produced from the steel S5 despite its comparatively low C content, in which a high tensile strength Rm is combined with a sufficient elongation A80.

In Fig. 6 ist in einem Ausschnitt eine Vergrößerung eines Querschnitts eines erfindungsgemäßen Kaltbands dargestellt. Dabei sind beispielhaft Restaustenitblöcke RA-b markiert und eine Stelle durch eine Umkreisung hervorgehoben, an der filmartiger Restaustenit RA-f in einer lamellenartigen Schichtung vorliegt. Tabelle 1 Stahl C Mn Si Cu Cr Ti Nb V Al N Sonstige S1 0,52 1,48 0,40 1,51 0, 88 0, 009 - 0,093 1,400 - - S2 0,301 1,41 1,46 1,47 0,87 0,014 0,005 0,09 0,021 0,0015 Ni: 0,021 Mo: <0,002 S3 0,505 1,50 0,40 0, 6 1,30 0,011 - 0,098 0,012 0,002 Ni: 0,63 Mo: 0,30 S4 0,384 1,97 0,41 0,57 1,37 0,0016 - <0,0005 0,018 0,0014 Ni: 0,59 Mo: 0,30 S5 0,252 1,47 2,15 0,32 0,41 0,020 - 0,11 0,009 - Ni: 0,02 Mo: <0,002 Angaben in Gew.-%,
Rest Eisen und unvermeidbare Verunreinigungen In Fig. 6 is shown in a section of an enlargement of a cross section of a cold strip according to the invention. Here, by way of example, residual austenite blocks RA-b are marked and a point is highlighted by an encircling, on which film-like retained austenite RA-f is present in a lamellar layering. Table 1 stole C Mn Si Cu Cr Ti Nb V al N other S1 0.52 1.48 0.40 1.51 0, 88 0, 009 - 0.093 1,400 - - S2 0.301 1.41 1.46 1.47 0.87 0,014 0.005 0.09 0,021 0.0015 Ni: 0.021 Mo: <0.002 S3 0,505 1.50 0.40 0, 6 1.30 0.011 - 0.098 0,012 0,002 Ni: 0.63 Mo: 0.30 S4 0.384 1.97 0.41 0.57 1.37 0.0016 - <0.0005 0,018 0.0014 Ni: 0.59 Mo: 0.30 S5 0.252 1.47 2.15 0.32 0.41 0,020 - 0.11 0.009 - Ni: 0.02 Mo: <0.002 In% by weight,
Remaining iron and unavoidable impurities

Claims (15)

Kaltgewalztes Stahlflachprodukt, mit einer Zugfestigkeit Rm von mindestens 1400 MPa und einer Dehnung A80 von mindestens 5 %, enthaltend neben Eisen und unvermeidbaren Verunreinigungen (in Gew.-%): C: 0,10 - 0,60 %, Si: 0,4 - 2,5 %, Al: bis zu 3,0 % Mn: 0,4 - 3,0 %, Ni: bis zu 1,0 %, Cu: bis zu 2,0 %, Mo: bis zu 0,4 %, Cr: bis zu 2 %, Co: bis zu 1,5 %, Ti: bis zu 0,2 %, Nb: bis zu 0,2 %, V: bis zu 0,5 %,
wobei das Gefüge des Stahlflachprodukts zu mindestens 20 Vol.-% aus Bainit, zu 10 - 35 Vol.-% aus Restaustenit und als Rest aus Martensit besteht. Cold-rolled steel flat product, having a tensile strength Rm of at least 1400 MPa and an elongation A80 of at least 5%, containing in addition to iron and unavoidable impurities (in% by weight): C: 0.10-0.60%, Si: 0.4-2.5%, Al: up to 3.0% Mn: 0.4 - 3.0%, Ni: up to 1.0%, Cu: up to 2.0%, Mo: up to 0.4%, Cr: up to 2%, Co: up to 1.5%, Ti: up to 0.2%, Nb: up to 0.2%, V: up to 0.5%,
wherein the structure of the flat steel product consists of at least 20% by volume of bainite, 10 to 35% by volume of retained austenite and the remainder of martensite. Stahlflachprodukt nach Anspruch 1, dadurch
gekennzeichnet, dass sein C-Gehalt mindestens 0,25 Gew.-% beträgt.Flat steel product according to claim 1, characterized
characterized in that its C content is at least 0.25 wt .-%. Stahlflachprodukt nach einem der voranstehenden Ansprüche, dadurch
gekennzeichnet, dass sein C-Gehalt mindestens 0,27 Gew.-% beträgt.Flat steel product according to one of the preceding claims, characterized
characterized in that its C content is at least 0.27 wt .-%. Stahlflachprodukt nach einem der voranstehenden Ansprüche, dadurch

gekennzeichnet, dass sein Si-Gehalt mindestens 1,0 Gew.-% beträgt.Flat steel product according to one of the preceding claims, characterized

characterized in that its Si content is at least 1.0 wt .-%. Stahlflachprodukt nach einem der voranstehenden Ansprüche, dadurch
gekennzeichnet, dass sein Al-Gehalt mindestens 0,01 Gew.-% beträgt.Flat steel product according to one of the preceding claims, characterized
characterized in that its Al content is at least 0.01 wt .-%. Stahlflachprodukt nach einem der voranstehenden Ansprüche, dadurch
gekennzeichnet, dass sein Cu-Gehalt mindestens 0,2 Gew.-% beträgt.Flat steel product according to one of the preceding claims, characterized
characterized in that its Cu content is at least 0.2 wt .-%. Stahlflachprodukt nach Anspruch 5, dadurch
gekennzeichnet, dass sein Cu-Gehalt mindestens 0,55 Gew.-% beträgt.Flat steel product according to claim 5, characterized
characterized in that its Cu content is at least 0.55 wt .-%. Stahlflachprodukt nach einem der voranstehenden Ansprüche, dadurch
gekennzeichnet, dass sein Cr-Gehalt mindestens 0,3 Gew.-% beträgt.Flat steel product according to one of the preceding claims, characterized
characterized in that its Cr content is at least 0.3 wt .-%. Stahlflachprodukt nach einem der voranstehenden Ansprüche, dadurch gekennzeichnet, dass seine Gehalte an Mn, Cr, Ni, Cu und C die folgende Bedingung erfüllen: 1 < 0 , 5 % Mn + 0 , 167 % Cr + 0 , 125 % Ni + 0 , 125 % Cu + 1 , 334 % C < 2
Figure imgb0002
 mit %Mn: jeweiliger Mn-Gehalt in Gew.-%, %Cr: jeweiliger Cr-Gehalt in Gew.-%, %Ni: jeweiliger Ni-Gehalt in Gew.-%, %Cu: jeweiliger Cu-Gehalt in Gew.-%, %C: jeweiliger C-Gehalt in Gew.-%. Flat steel product according to one of the preceding claims, characterized in that its contents of Mn, Cr, Ni, Cu and C satisfy the following condition: 1 < 0 . 5 % Mn + 0 . 167 % Cr + 0 . 125 % Ni + 0 . 125 % Cu + 1 . 334 % C < 2
Figure imgb0002
 with% Mn: respective Mn content in% by weight, % Cr: respective Cr content in% by weight, % Ni: respective Ni content in wt%, % Cu: respective Cu content in% by weight, % C: respective C content in% by weight. Stahlflachprodukt nach einem der voranstehenden Ansprüche, dadurch
gekennzeichnet, dass sein Gefüge mindestens 50 Vol.-% Bainit enthält.Flat steel product according to one of the preceding claims, characterized
in that its structure contains at least 50 vol .-% bainite. Stahlflachprodukt nach einem der voranstehenden Ansprüche, dadurch
gekennzeichnet, dass sein Gefüge 10 - 25 Vol.-% Restaustenit enthält.Flat steel product according to one of the preceding claims, characterized
characterized in that its structure contains 10 to 25% by volume of retained austenite. Verfahren zum Herstellen eines gemäß einem der Ansprüche 1 bis 11 beschaffenen Stahlflachprodukts umfassend folgende Arbeitsschritte: - Bereitstellen eines Vorprodukts in Form einer Bramme, Dünnbramme oder eines gegossenen Bands, das neben Eisen und unvermeidbaren Verunreinigungen (in Gew.-%) C: 0,10 - 0,60 %, Si: 0,4 - 2,5 %, Al: bis zu 3,0 % Mn,: 0,4 - 3,0 %, Ni: bis zu 1,0 %, Cu: bis zu 2,0 %, Mo: bis zu 0,4 %, Cr: bis zu 2 %, Co: bis zu 1,5 %, Ti: bis zu 0,2 %, Nb: bis zu 0,2 %, V: bis zu 0,5 % enthält; - Warmwalzen des Vorprodukts zu einem Warmband in einem oder mehreren Walzstichen, wobei das erhaltene Warmband beim Verlassen des letzten Walzstichs eine Warmwalzendtemperatur von mindestens 830 °C aufweist; - Haspeln des erhaltenen Warmbands bei einer Haspeltemperatur, die zwischen der Warmwalzendtemperatur und 560 °C liegt; - Kaltwalzen des Warmbands zu einem Kaltband mit einem Kaltwalzgrad von mindestens 30 %; - Wärmebehandeln des erhaltenen Kaltbands, wobei das Kaltband im Zuge der Wärmebehandlung - auf eine mindestens 800 °C betragende Glühtemperatur erwärmt wird, - ausgehend von der Glühtemperatur mit einer mindestens 8 °C/s betragenden Abkühlgeschwindigkeit auf eine Haltetemperatur abgekühlt wird, die in einem Haltetemperaturbereich liegt, dessen Obergrenze 470 °C beträgt und dessen Untergrenze höher ist als die Martensitstarttemperatur MS, ab der Martensit im Gefüge des Kaltbands entsteht, und - auf der Haltetemperatur über einen Zeitraum gehalten wird, der ausreicht, um im Gefüge des Kaltbands mindestens 20 Vol.-% Bainit zu bilden. A method for producing a flat steel product obtained according to any one of claims 1 to 11, comprising the following steps: Providing a precursor in the form of a slab, thin slab or a cast strip which, in addition to iron and unavoidable impurities (in% by weight) C: 0.10-0.60%, Si: 0.4-2.5%, Al: up to 3.0% Mn ,: 0.4 - 3.0%, Ni: up to 1.0%, Cu: up to 2.0%, Mo: up to 0.4%, Cr: to 2%, Co: up to 1.5%, Ti: up to 0.2%, Nb: up to 0.2%, V: up to 0.5%; Hot rolling of the precursor into a hot strip in one or more rolling passes, the resulting hot strip having a hot rolling end temperature of at least 830 ° C when leaving the last pass; - coiling the resulting hot strip at a coiler temperature between the hot rolling end temperature and 560 ° C; - Cold rolling of the hot strip to a cold strip with a cold rolling degree of at least 30%; - Heat treating the cold strip obtained, wherein the cold strip during the heat treatment is heated to a minimum of 800 ° C annealing temperature, - Is cooled starting from the annealing temperature with a minimum of 8 ° C / s cooling rate to a holding temperature, which is in a holding temperature range whose upper limit is 470 ° C and whose lower limit is higher than the martensite start temperature MS, from the martensite in the structure of the cold strip arises, and - Is maintained at the holding temperature for a period sufficient to form at least 20 vol .-% bainite in the structure of the cold strip. Verfahren nach Anspruch 12, dadurch
gekennzeichnet, dass die Warmwalzendtemperatur 850 - 950 °C beträgt.The method of claim 12, characterized
characterized in that the hot rolling end temperature is 850 - 950 ° C. Verfahren nach einem der Ansprüche 12 oder 13,
dadurch gekennzeichnet, dass die Haltetemperatur 300 - 420 °C beträgt.Method according to one of claims 12 or 13,
characterized in that the holding temperature is 300 - 420 ° C. Verfahren nach einem der Ansprüche 12 bis 14,
dadurch gekennzeichnet, dass das Kaltband nach der Wärmebehandlung mit einer metallischen Schutzschicht belegt wird.Method according to one of claims 12 to 14,
characterized in that the cold strip is coated after the heat treatment with a metallic protective layer.
EP12178332.8A 2012-07-27 2012-07-27 Produit plat en acier laminé à froid et son procédé de fabrication Active EP2690184B1 (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
EP12178332.8A EP2690184B1 (en) 2012-07-27 2012-07-27 Produit plat en acier laminé à froid et son procédé de fabrication
JP2015523569A JP6202579B2 (en) 2012-07-27 2013-07-26 Cold rolled flat steel product and method for producing the same
US14/417,659 US20150218684A1 (en) 2012-07-27 2013-07-26 Cold-Rolled Flat Steel Product and Method for the Production Thereof
CN201380048837.7A CN104641008B (en) 2012-07-27 2013-07-26 Flat cold-rolled bar product and manufacture method thereof
PCT/EP2013/065838 WO2014016421A1 (en) 2012-07-27 2013-07-26 Cold-rolled flat steel product and method for the production thereof

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP12178332.8A EP2690184B1 (en) 2012-07-27 2012-07-27 Produit plat en acier laminé à froid et son procédé de fabrication

Publications (2)

Publication Number Publication Date
EP2690184A1 true EP2690184A1 (en) 2014-01-29
EP2690184B1 EP2690184B1 (en) 2020-09-02

Family

ID=48877247

Family Applications (1)

Application Number Title Priority Date Filing Date
EP12178332.8A Active EP2690184B1 (en) 2012-07-27 2012-07-27 Produit plat en acier laminé à froid et son procédé de fabrication

Country Status (4)

Country Link
US (1) US20150218684A1 (en)
EP (1) EP2690184B1 (en)
JP (1) JP6202579B2 (en)
WO (1) WO2014016421A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102017209982A1 (en) * 2017-06-13 2018-12-13 Thyssenkrupp Ag High strength steel sheet with improved formability
EP3418412A4 (en) * 2016-02-19 2019-08-21 Nippon Steel Corporation Steel

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102015119839A1 (en) * 2015-11-17 2017-05-18 Benteler Steel/Tube Gmbh High energy absorbing steel alloy and tubular steel product
WO2017085135A1 (en) 2015-11-16 2017-05-26 Benteler Steel/Tube Gmbh Steel alloy with high energy absorption capacity and tubular steel product
WO2017109539A1 (en) * 2015-12-21 2017-06-29 Arcelormittal Method for producing a high strength steel sheet having improved strength and formability, and obtained high strength steel sheet
KR101822292B1 (en) 2016-08-17 2018-01-26 현대자동차주식회사 High strength special steel
KR101822295B1 (en) 2016-09-09 2018-01-26 현대자동차주식회사 High strength special steel
CN108546881B (en) * 2018-05-16 2020-06-26 东北大学 Preparation method of yield-platform-free cold-rolled medium manganese steel thin strip
DE102021119047A1 (en) 2021-07-22 2023-01-26 Thyssenkrupp Steel Europe Ag Method for producing a cold-rolled flat steel product with a bainitic matrix and cold-rolled flat steel product with a bainitic matrix

Citations (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1553202A1 (en) * 2004-01-09 2005-07-13 Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) Ultra-high strength steel sheet having excellent hydrogen embrittlement resistance, and method for manufacturing the same
EP1466024B1 (en) 2002-01-14 2007-07-25 ARCELOR France Method for the production of a siderurgical product made of carbon steel with a high copper content, and siderurgical product obtained according to said method
EP1975266A1 (en) * 2005-12-28 2008-10-01 Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) Ultrahigh-strength steel sheet
US7591977B2 (en) 2004-01-28 2009-09-22 Kabuhsiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) High strength and low yield ratio cold rolled steel sheet and method of manufacturing the same
EP2105514A1 (en) * 2006-12-11 2009-09-30 Kabushiki Kaisha Kobe Seiko Sho High-strength steel sheet
EP2246456A1 (en) * 2008-01-31 2010-11-03 JFE Steel Corporation High-strength steel sheet and process for production thereof
US20100307644A1 (en) * 2007-05-11 2010-12-09 Arcelormittal France Process for manufacturing cold-rolled and annealed steel sheet with a very high strength, and sheet thus produced
EP2267176A1 (en) * 2008-02-08 2010-12-29 JFE Steel Corporation High-strength hot-dip galvanized steel sheet with excellent processability and process for producing the same
EP2325346A1 (en) * 2008-09-10 2011-05-25 JFE Steel Corporation High-strength steel plate and manufacturing method thereof
EP2327810A1 (en) * 2008-09-10 2011-06-01 JFE Steel Corporation High-strength steel sheet and method for production thereof
WO2011111333A1 (en) * 2010-03-09 2011-09-15 Ｊｆｅスチール株式会社 High-strength pressed member and method for producing same
WO2011111330A1 (en) * 2010-03-09 2011-09-15 Ｊｆｅスチール株式会社 High-strength steel sheet and method for producing same
EP2436794A1 (en) * 2009-05-29 2012-04-04 Kabushiki Kaisha Kobe Seiko Sho High strength steel sheet having excellent hydrogen embrittlement resistance

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1832667A1 (en) * 2006-03-07 2007-09-12 ARCELOR France Method of producing steel sheets having high strength, ductility and toughness and thus produced sheets.
JP2010065272A (en) * 2008-09-10 2010-03-25 Jfe Steel Corp High-strength steel sheet and method for manufacturing the same
JP5504636B2 (en) * 2009-02-04 2014-05-28 Ｊｆｅスチール株式会社 High strength hot rolled steel sheet and method for producing the same

Patent Citations (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1466024B1 (en) 2002-01-14 2007-07-25 ARCELOR France Method for the production of a siderurgical product made of carbon steel with a high copper content, and siderurgical product obtained according to said method
DE60315129T2 (en) 2002-01-14 2008-04-10 Arcelor France METHOD FOR PRODUCING AN UNWORKED STEEL HARDWARE PRODUCT HAVING A HIGH COPPER CONTENT AND THEREFORE OBTAINED IRON SHED PRODUCT
EP1553202A1 (en) * 2004-01-09 2005-07-13 Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) Ultra-high strength steel sheet having excellent hydrogen embrittlement resistance, and method for manufacturing the same
US7591977B2 (en) 2004-01-28 2009-09-22 Kabuhsiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) High strength and low yield ratio cold rolled steel sheet and method of manufacturing the same
EP1975266A1 (en) * 2005-12-28 2008-10-01 Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) Ultrahigh-strength steel sheet
EP2105514A1 (en) * 2006-12-11 2009-09-30 Kabushiki Kaisha Kobe Seiko Sho High-strength steel sheet
US20100307644A1 (en) * 2007-05-11 2010-12-09 Arcelormittal France Process for manufacturing cold-rolled and annealed steel sheet with a very high strength, and sheet thus produced
EP2246456A1 (en) * 2008-01-31 2010-11-03 JFE Steel Corporation High-strength steel sheet and process for production thereof
EP2267176A1 (en) * 2008-02-08 2010-12-29 JFE Steel Corporation High-strength hot-dip galvanized steel sheet with excellent processability and process for producing the same
EP2325346A1 (en) * 2008-09-10 2011-05-25 JFE Steel Corporation High-strength steel plate and manufacturing method thereof
EP2327810A1 (en) * 2008-09-10 2011-06-01 JFE Steel Corporation High-strength steel sheet and method for production thereof
EP2436794A1 (en) * 2009-05-29 2012-04-04 Kabushiki Kaisha Kobe Seiko Sho High strength steel sheet having excellent hydrogen embrittlement resistance
WO2011111333A1 (en) * 2010-03-09 2011-09-15 Ｊｆｅスチール株式会社 High-strength pressed member and method for producing same
WO2011111330A1 (en) * 2010-03-09 2011-09-15 Ｊｆｅスチール株式会社 High-strength steel sheet and method for producing same

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
VON H. BHADESHIA: "Thermodynamic Exatrapolation and Martensite-Start-Temperature of Substitutionally Alloyed Steels", METAL SCIENCE, vol. 15, 1981, pages 178 - 180

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3418412A4 (en) * 2016-02-19 2019-08-21 Nippon Steel Corporation Steel
DE102017209982A1 (en) * 2017-06-13 2018-12-13 Thyssenkrupp Ag High strength steel sheet with improved formability

Also Published As

Publication number Publication date
US20150218684A1 (en) 2015-08-06
JP6202579B2 (en) 2017-09-27
WO2014016421A1 (en) 2014-01-30
EP2690184B1 (en) 2020-09-02
CN104641008A (en) 2015-05-20
JP2015528065A (en) 2015-09-24

Similar Documents

Publication Publication Date Title
EP2690183B1 (en) Hot-rolled steel flat product and method for its production
EP2383353B1 (en) High tensile steel containing Mn, steel surface product made from such steel and method for producing same
EP2028282B1 (en) Dual-phase steel, flat product made of such dual-phase steel and method for manufacturing a flat product
EP2855718B1 (en) Flat steel product and process for producing a flat steel product
EP2031081B1 (en) Dual-phase steel, flat product made of such dual-phase steel and method for manufacturing a flat product
EP2809819B1 (en) Ultrahigh-strength multiphase steel having improved properties during production and processing
EP2690184B1 (en) Produit plat en acier laminé à froid et son procédé de fabrication
EP2668302B1 (en) Method for manufacturing a strip from a high strength multi-phase steel having excellent forming properties
EP2439290B1 (en) Multiphase steel, cold rolled flat product produced from this multiphase steel and method for producing same
EP2840159B1 (en) Method for producing a steel component
WO2015144529A1 (en) Method for producing a high-strength flat steel product
EP3535431B1 (en) Steel product with an intermediate manganese content for low temperature application and production method thereof
EP2905348B1 (en) High strength flat steel product with bainitic-martensitic structure and method for manufacturing such a flat steel product
EP3504349B1 (en) Method for producing a high-strength steel strip with improved properties for further processing, and a steel strip of this type
EP2439291A1 (en) Multiphase steel, cold rolled flat product produced from this multiphase steel and method for producing same
WO2008052918A1 (en) Method for manufacturing flat steel products from a steel forming a martensitic structure
DE2924167A1 (en) METHOD OF MANUFACTURING COLD-ROLLED STEEL SHEET WITH DOUBLE-PHASE STRUCTURE
EP3512968B1 (en) Method for producing a flat steel product made of a manganese-containing steel, and such a flat steel product
EP1398390B1 (en) Steel with a very fine ferritic and martensitic microstructure having a high tensile strength
EP1453984B1 (en) Method for the production of hot strip or sheet from a micro-alloyed steel
EP1396550A1 (en) Method for manufacturing hot strip
DE102016115618A1 (en) Process for producing a high-strength steel strip with improved properties during further processing and such a steel strip
EP3964591A1 (en) Hot-rolled steel sheet product and method for producing a hot-rolled steel sheet product
DE102018132816A1 (en) Process for the production of thermo-mechanically produced profiled hot-rolled products
WO2021213647A1 (en) Hot-rolled flat steel product and method for the production thereof

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

AX Request for extension of the european patent

Extension state: BA ME

17P Request for examination filed

Effective date: 20140728

RBV Designated contracting states (corrected)

Designated state(s): AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: EXAMINATION IS IN PROGRESS

17Q First examination report despatched

Effective date: 20180307

GRAP Despatch of communication of intention to grant a patent

Free format text: ORIGINAL CODE: EPIDOSNIGR1

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: GRANT OF PATENT IS INTENDED

INTG Intention to grant announced

Effective date: 20200310

GRAS Grant fee paid

Free format text: ORIGINAL CODE: EPIDOSNIGR3

GRAA (expected) grant

Free format text: ORIGINAL CODE: 0009210

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE PATENT HAS BEEN GRANTED

AK Designated contracting states

Kind code of ref document: B1

Designated state(s): AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

REG Reference to a national code

Ref country code: GB

Ref legal event code: FG4D

Free format text: NOT ENGLISH

REG Reference to a national code

Ref country code: AT

Ref legal event code: REF

Ref document number: 1308863

Country of ref document: AT

Kind code of ref document: T

Effective date: 20200915

Ref country code: CH

Ref legal event code: EP

REG Reference to a national code

Ref country code: DE

Ref legal event code: R096

Ref document number: 502012016329

Country of ref document: DE

REG Reference to a national code

Ref country code: IE

Ref legal event code: FG4D

Free format text: LANGUAGE OF EP DOCUMENT: GERMAN

REG Reference to a national code

Ref country code: LT

Ref legal event code: MG4D

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: FI

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

Ref country code: LT

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

Ref country code: BG

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20201202

Ref country code: GR

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20201203

Ref country code: NO

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20201202

Ref country code: HR

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

Ref country code: SE

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

REG Reference to a national code

Ref country code: NL

Ref legal event code: MP

Effective date: 20200902

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: PL

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

Ref country code: RS

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

Ref country code: LV

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: PT

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20210104

Ref country code: NL

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

Ref country code: RO

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

Ref country code: SM

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

Ref country code: CZ

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

Ref country code: EE

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: AL

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

Ref country code: IS

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20210102

Ref country code: ES

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

REG Reference to a national code

Ref country code: DE

Ref legal event code: R097

Ref document number: 502012016329

Country of ref document: DE

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: SK

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

PLBE No opposition filed within time limit

Free format text: ORIGINAL CODE: 0009261

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: NO OPPOSITION FILED WITHIN TIME LIMIT

26N No opposition filed

Effective date: 20210603

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: SI

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

Ref country code: DK

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: IT

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

REG Reference to a national code

Ref country code: DE

Ref legal event code: R119

Ref document number: 502012016329

Country of ref document: DE

REG Reference to a national code

Ref country code: CH

Ref legal event code: PL

GBPC Gb: european patent ceased through non-payment of renewal fee

Effective date: 20210727

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: MC

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

REG Reference to a national code

Ref country code: BE

Ref legal event code: MM

Effective date: 20210731

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: LI

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 20210731

Ref country code: GB

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 20210727

Ref country code: DE

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 20220201

Ref country code: CH

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 20210731

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: LU

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 20210727

Ref country code: FR

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 20210731

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: IE

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 20210727

Ref country code: BE

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 20210731

REG Reference to a national code

Ref country code: AT

Ref legal event code: MM01

Ref document number: 1308863

Country of ref document: AT

Kind code of ref document: T

Effective date: 20210727

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: AT

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 20210727

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: HU

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT; INVALID AB INITIO

Effective date: 20120727

Ref country code: CY

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: MK

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200902