EP3686293B1 - Bande ou feuille d'acier laminée à froid en phase complexe haute résistance et présentant une ductilité élevée - Google Patents

Bande ou feuille d'acier laminée à froid en phase complexe haute résistance et présentant une ductilité élevée Download PDF

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EP3686293B1
EP3686293B1 EP19153131.8A EP19153131A EP3686293B1 EP 3686293 B1 EP3686293 B1 EP 3686293B1 EP 19153131 A EP19153131 A EP 19153131A EP 3686293 B1 EP3686293 B1 EP 3686293B1
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EP
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Prior art keywords
cold rolled
rolled steel
steel strip
sheet according
mpa
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German (de)
English (en)
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EP3686293A1 (fr
Inventor
Johannes REHRL
Martin Gruber
Florian WINKELHOFER
Thomas Hebesberger
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Voestalpine Stahl GmbH
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Voestalpine Stahl GmbH
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Priority to EP19153131.8A priority Critical patent/EP3686293B1/fr
Priority to ES19153131T priority patent/ES2889200T3/es
Priority to US17/423,762 priority patent/US20220112575A1/en
Priority to CN201980089651.3A priority patent/CN113316649A/zh
Priority to PCT/EP2019/082857 priority patent/WO2020151856A1/fr
Publication of EP3686293A1 publication Critical patent/EP3686293A1/fr
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
    • 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
    • C21D8/0273—Final recrystallisation annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0468—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment between cold rolling steps
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0473—Final recrystallisation annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D2211/001—Austenite
    • 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 present invention relates to high strength steel strips and sheets suitable for applications in automobiles.
  • the invention relates to high ductility high strength complex phase cold rolled steel having a tensile strength of at least 1380 MPa and an excellent formability.
  • Automotive body parts are often stamped out of sheet steels, forming complex structural members of thin sheet.
  • such parts cannot be produced from conventional high strength steels, because of a too low formability of the complex structural parts.
  • multi-phase Transformation Induced Plasticity aided steels TRIP steels
  • TRIP steels have gained considerable interest in the last years, in particular for use in auto body structural parts and as seat frame materials.
  • TRIP steels possess a multi-phase microstructure, which includes a meta-stable retained austenite phase, which is capable of producing the TRIP effect.
  • the austenite transforms into martensite, which results in remarkable work hardening.
  • This hardening effect acts to resist necking in the material and postpones failure in sheet forming operations.
  • the microstructure of a TRIP steel can greatly alter its mechanical properties.
  • the most important aspects of the TRIP steel microstructure are the volume percentage, size and morphology of the retained austenite phase, as these properties directly affect the austenite to martensite transformation, when the steel is deformed. There are several ways by which it is possible to chemically stabilize austenite at room temperature.
  • the austenite In low alloy TRIP steels the austenite is stabilized through its carbon content and the small size of the austenite grains.
  • the carbon content necessary to stabilize austenite is approximately 1 wt. %.
  • high carbon content in steel cannot be used in many applications because of impaired weldability.
  • TRIP-aided steel with a Bainitic Ferrite matrix (TBF)-steels have been known for long and attracted a lot of interest, mainly because the bainitic ferrite matrix allows an excellent stretch flangability. Moreover, the TRIP effect ensured by the strain-induced transformation of metastable retained austenite islands into martensite, remarkably improves their drawability.
  • TBF Bainitic Ferrite matrix
  • CP steels are characterized by very high strength levels and at the same time a high yield point and are therefore often used for crash-relevant components in cars.
  • a high strength steel sheet having elevated tensile properties and formability while containing Ti and B is disclosed in EP 2 757 171 A1 .
  • these steels disclose several attractive properties there is a demand for steel sheets having a higher tensile strength in combination with a good workability, in particular, in applications where the local elongation and is great of importance for avoiding edge tearing, such as for advanced forming operations as bending and roll forming.
  • the present invention is directed to cold rolled steels having a tensile strength of at least 1380 MPa and an excellent formability, wherein it should be possible to produce the steel sheets on an industrial scale in a Continuous Annealing Line (CAL).
  • the invention aims at providing a steel having a composition and microstructure that can be processed to complicated high strength structural members, where the local elongation is of importance.
  • the steel strip or sheet of the present invention should have a high hole expandability as expressed by the Hole Expanding Ratio (HER) or ( ⁇ ). In this application lambda ( ⁇ ) will be used for this parameter.
  • the steel should also have a good weldability, in particular with respect to Resistance Spot Welding (RSW) since RSW is the dominating welding process used in the mass fabrication of automobiles.
  • RSW Resistance Spot Welding
  • the steel sheet has a composition consisting of the following alloying elements (in wt. %): C 0.15 - 0.25 Si 0.7 - 1.4 Mn 2.3 - 3.2 Cr ⁇ 0.8 Mo ⁇ 0.2 Al 0.03 - 1.0 Nb ⁇ 0.04 V ⁇ 0.04 Ti 0.01 - 0.04 B 0.001 - 0.005 Ti/B 5 - 30 Cu ⁇ 0.15 Ni ⁇ 0.15 balance Fe apart from impurities, the balance consists of iron and impurities.
  • C stabilizes the austenite and is important for obtaining sufficient carbon within the retained austenite phase.
  • C is also important for obtaining the desired strength level.
  • an increase of the tensile strength in the order of 100 MPa per 0.1 %C can be expected.
  • C is lower than 0.15 % then it is difficult to attain a tensile strength of 1380 MPa. If C exceeds 0.25 %, then the weldability is impaired.
  • the upper limit may thus be 0.24, 0.23 or 0.22 %.
  • the lower limit may be 0.16, 0.17, 0.18, 0.19, or 0.20 %.
  • Si acts as a solid solution strengthening element and is important for securing the strength of the thin steel sheet. Si suppresses the cementite precipitation and is essential for austenite stabilization.
  • the upper limit is therefore 1.4 % and may be restricted to 1.3 or 1.2 %.
  • the lower limit may be 0.75 or 0.80 %.
  • Manganese is a solid solution strengthening element, which stabilises the austenite by lowering the M s temperature and it also prevents ferrite and pearlite to be formed during cooling.
  • Mn lowers the A c3 temperature and is important for the austenite stability. At a content of less than 2.2 % it might be difficult to obtain the desired amount of retained austenite, a tensile strength of 980 MPa and the austenitizing temperature might be too high for conventional industrial annealing lines. In addition, at lower contents it may be difficult to avoid the formation of polygonal ferrite.
  • the upper limit may therefore be 3.1, 3.0, 2.9, 2.8, 2.7, 2.6, 2.5 or 2.4 %.
  • the lower limit may be 2.4%.
  • Cr is effective in increasing the strength of the steel sheet.
  • Cr is an element that forms ferrite and retards the formation of pearlite and bainite.
  • the A c3 temperature and the M s temperature are only slightly lowered with increasing Cr content.
  • Cr results in an increased amount of stabilized retained austenite.
  • the amount of Cr is limited to 0.8 %.
  • the upper limit may be 0.75, 0.70, 0.65, 0.60, 0.55, 0.50, 0.45 or 0.40, 0.35, 0.30 or 0.25 %.
  • the lower limit may be 0.01, 0.05, 0.10, 0.15, 0.20 or 0.25 %.
  • the lower limit of Cr is 0.10 % in a preferred embodiment of the present invention.
  • Al promotes ferrite formation and is also commonly used as a deoxidizer.
  • Al like Si, is not soluble in the cementite and therefore it delays the cementite formation during bainite formation considerably. Additions of Al result in a remarkable increase in the carbon content in the retained austenite.
  • the M s temperature is also increased with increasing Al content.
  • a further drawback of Al is that it results in a drastic increase in the A c3 temperature.
  • a main disadvantage of Al is its segregation behavior during casting. During casting Mn is enriched in the middle of the slabs and the Al-content is decreased. Therefore, in the middle of the slab a significant austenite stabilized region or band may be formed.
  • the upper level may be 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2 or 0.1 %.
  • the lower limit may be set to 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1 %. If Al is used for deoxidation only, then the upper level may then be 0.09, 0.08, 0.07 or 0.06 %. For securing a certain effect the lower level may set to 0.03 or 0.04 %.
  • Nb is commonly used in low alloyed steels for improving strength and toughness, because of its influence on the grain size. Nb increases the strength elongation balance by refining the matrix microstructure and the retained austenite phase due to the precipitation of NbC.
  • the steel may contain Nb in an amount of ⁇ 0.04 %, preferably ⁇ 0.03 %. A deliberate addition of Nb is not necessary according to the present invention. The upper limit may therefore be restricted to ⁇ 0.01 %.
  • V is similar to that of Nb in that it contributes to precipitation hardening and grain refinement.
  • the steel may contain V in an amount of ⁇ 0.04 %, preferably ⁇ 0.03 %.
  • a deliberate addition of V is not necessary according to the present invention.
  • the upper limit may therefore be restricted to ⁇ 0.01 %.
  • Ti is commonly used in low alloyed steels for improving strength and toughness, because of its influence on the grain size by forming carbides, nitrides or carbonitrides.
  • Ti is a strong nitride former and can be used to bind the nitrogen in the steel.
  • the effect tends to be saturated above 0.04 %.
  • the lower amount should be 0.01 % and may be set to 0.02 %.
  • B suppresses the formation of ferrite and improves the weldability of the steel sheet. In order to have a noticeable effect at least 0.001 % should be added. However, excessive amounts of B deteriorate the workability.
  • the upper limit is therefore 0.005 %.
  • a preferred range is 0.002 - 0.004 %.
  • Ca may be used for the modification of the non-metallic inclusions.
  • the upper limit is 0.01% and may be set to 0.005 or 0.004 %.
  • Cu is an undesired impurity element that is restricted to ⁇ 0.15 % by careful selection of the scrap used.
  • the upper limit may be restricted to 0.12, 0.10, 0.08 or 0.06 %.
  • Ni is also an undesired impurity element that is restricted to ⁇ 0.15 % by careful selection of the scrap used.
  • the upper limit may be restricted to 0.12, 0.10, 0.08 or 0.06 %.
  • the ratio Ti/B is preferably adjusted to be in the range of 5 - 30 in order to secure an optimal fixation of the nitrogen in the steel, resulting in free unbounded boron in the steel.
  • such ratio can be adjusted to be in the range of 8 - 11.
  • the cold rolled steel sheets of the present invention have a microstructure mainly consisting of retained austenite embedded in a matrix of tempered martensite (TM), i.e. the amount of tempered martensite is at least ⁇ 40 %, generally ⁇ 50 %.
  • TM tempered martensite
  • the microstructure may also contain up to 40 % bainitic ferrite (BF) and up to 20 % fresh martensite (FM).
  • BF bainitic ferrite
  • FM fresh martensite
  • the amount of FM may be limited to 15, 10, 8 or 5 %.
  • Retained austenite is a prerequisite for obtaining the desired TRIP effect.
  • the amount of retained austenite should therefore be in the range of 2 - 20 %.
  • the lower limit of retained austenite may be set to 3, 4, 5, 6, 7 or 8 %.
  • a preferred range is 5 - 15 %.
  • the amount of retained austenite was measured by means of the saturation magnetization method described in detail in Proc. Int. Conf. on TRIP-aided high strength ferrous alloys (2002), Ghent, Belgium, p. 61-64 .
  • Polygonal ferrite (PF) is not a desired microstructural constituent and is therefore limited to ⁇ 10 %, preferably ⁇ 5 %, ⁇ 3 % or ⁇ 1 %. Most preferably, the steel is free from PF.
  • the mechanical properties of the claimed steel are important and at least one of the following requirements should be fulfilled: tensile strength (R m ) ⁇ 1380 MPa yield strength (R p0.2 ) ⁇ 1000 MPa total elongation (A 80 ) ⁇ 5 % hole expansion ratio ( ⁇ ) ⁇ 40 % yield ratio (R p0.2 / R m ) ⁇ 0.60
  • the lower limit for the tensile strength (R m ) may be set to 1390, 1400, 1410, 1420 or 1430 MPa.
  • the lower limit for the yield strength (R p0.2 ) may be set to 1010, 1020, 1030, 1040, 1050 or 1460 MPa.
  • the lower limit for the total elongation (A 80 ) may be set to 6 or 7 %.
  • the lower limit for the hole expansion ratio ( ⁇ ) may be set to 45, 50, 55 or 60 %.
  • the lower limit for the yield ratio (R p0.2 / R m ) should be at least 0.60 and may be set to 0.64, 0.66, 0.68, 0.70 or 0.72.
  • the R m , R p0.2 and A 80 values are derived according to the European norm EN 10002 Part 1, wherein the samples were taken in the longitudinal direction of the strip.
  • the hole expanding ratio ( ⁇ ) is determined by the hole expanding test according to ISO/WD 16630:2009 (E). In this test a conical punch having an apex of 60 ° is forced into a 10 mm diameter punched hole made in a steel sheet having the size of 100 x 100 mm 2 . The test is stopped as soon as the first crack is determined and the hole diameter is measured in two directions orthogonal to each other. The arithmetic mean value is used for the calculation.
  • the product of the tensile strength and the hole expansion ratio R m x ⁇ was calculated to evaluate the balance between the strength and the workability formability i.e. the stretch- flangeability.
  • the product of the tensile strength and the hole expansion ratio R m x ⁇ of the cold rolled steel of the present invention should preferably be at least 60000 MPa%.
  • the lower limit of this product can be set to 65000, 70000,75000, 80000 or 85000 MPa%.
  • the bendability was evaluated by the ratio of the limiting bending radius (Ri), which is defined as the minimum bending radius with no occurrence of cracks, and the sheet thickness, (t).
  • a 90° V-shaped block is used to bend the steel sheet in accordance with JIS Z2248.
  • the samples were examined both by eye and under optical microscope with 25 times magnification in order to investigate the occurrence of cracks.
  • the value obtained by dividing the limit bending radius with the thickness (Ri/t) should be less than 5.
  • the value (Ri/t) should be ⁇ 4, ⁇ 3 or ⁇ 2.
  • the yield strength of the cold rolled steel of the present invention can be increased by subjecting the steel to Bake Hardening (BH).
  • the increase in yield strength after 2 % stretching in a tensile test BH 2 may be at least 30 MPa, wherein the BH 2 -value is determined in accordance with DIN EN10325.
  • the lower limit may be set to 35, 40 or 45 MPa.
  • the mechanical properties of the steel strips and sheets of the present invention can be largely adjusted by the alloying composition and the microstructure.
  • Conventional steelmaking using continuous casting and hot rolling is used to produce a hot rolled strip.
  • the hot rolled strip is pickled and thereafter batch annealed at about 580 °C for a total time of 10 hours in order to reduce the tensile strength of the hot rolled strip and thereby reducing the cold rolling forces before cold rolling to a final thickness.
  • the cold rolled strips may thereafter be subjected to continuous annealing in a Continuous Annealing Line (CAL).
  • the microstructure may be adjusted by the heat treatment in the CAL, in particular by the isothermal treatment temperature in the overaging step.
  • such isothermal treatment temperature in the overaging step is a bit below Ms temperature (such as 50°C to 100°C below Ms) but it is possible to heat treat in the overaging step at Ms temperature or up to 100°C above Ms.
  • the material is then annealed and thereafter cooled to a temperature below the M s temperature, reheated to a partitioning temperature above the M s temperature, held at this temperature for partitioning and finally cooled to room temperature.
  • the material subjected to Q&P may also be subjcctcd to a batch annealing step at a low temperature (about 200 °C) in order to fine tune the mechanical properties, in particular the yield strength and the hole expansion ratio.
  • the material produced via isothermal route in the CAL may also be subjected to a batch annealing step at a low temperature (about 200 °C) in order to fine tune the mechanical properties, in particular the yield strength and the hole expansion ratio.
  • a steel having the following composition was produced by conventional metallurgy by converter melting and secondary metallurgy: C 0.20 Si 0.85 Mn 2.5 Cr 0.34 Al 0.049 Ti 0.026 B 0.0035 Cu 0.01 Ni 0.01 P 0.01 S 0.0005 N 0.0035 balance Fe and impurities.
  • the steel was continuously cast and cut into slabs.
  • the slabs were reheated and subjected to hot rolling to a thickness of about 2.8 mm.
  • the hot rolling finishing temperature was about 900 °C and the coiling temperature about 550 °C.
  • the hot rolled strips were pickled and batch annealed at about 580 °C for a total time of 10 hours in order to rcducc the tensile strength of the hot rolled strip and thereby reducing the cold rolling forces.
  • the strips were thereafter cold rolled in a five stand cold rolling mill to a final thickness of about 1.35 mm and finally subjected to continuous annealing in a Continuous Annealing Line (CAL).
  • CAL Continuous Annealing Line
  • the annealing cycle consisted of heating to a temperature of about 850 °C, soaking for about 120 s, cooling during 30 seconds to an overaging temperature of about 250 °C, thereafter isothermal holding at the overaging temperature for about 3 minutes and finally cooling to the ambient temperature.
  • the strip thus obtained had a matrix of TM and contained 9 % BF, 8% FM and 11% RA.
  • the strip had a tensile strength (R m ) of 1450 MPa and a yield strength (R p0.2 ) of 1080 MPa.
  • the total elongation (A 80 ) was 7% and the hole expansion ratio ( ⁇ ) was 59 %. Accordingly, the product R m x ⁇ was 85500 MPa%.
  • the R m and R p0.2 values are derived according to the European norm EN 10002 Part 1, wherein the samples were taken in the longitudinal direction of the strip.
  • the elongation (A 80 ) is derived in accordance with the same norm.
  • the hole expanding ratio ( ⁇ ) is the mean value of three samples subjected to hole expansion tests (HET) according to ISO/TS16630:2009 (E).
  • the material of the present invention can be widely applied to high strength structural parts in automobiles.
  • the high ductility high strength cold rolled steel strips and sheets of the present invention are particularly well suited for the production of parts having high demands on the local elongation.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
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  • Crystallography & Structural Chemistry (AREA)
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  • Metallurgy (AREA)
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Claims (10)

  1. Une bande ou une feuille d'acier laminée à froid ayant
    a) une composition constituée (en% en poids) de : C 0,15 à 0,25 Si 0,7 - 1,4 Mn 2,3 - 3,2 Cr ≤ 0,8 Mo ≤ 0,2 Al 0,03 - 1,0 Nb ≤ 0,04 V ≤ 0,04 Ti 0,01 - 0,04 B 0,001 - 0,005 Ti/B 5 - 30 Cu ≤ 0,15 Ni ≤ 0,15 Ca ≤ 0,01
    le reste étant du Fe hormis des impuretés,
    b) une microstructure polyphasée comprenant (en% vol.) : martensite trempée ≥ 40 ferrite bainitique ≤ 40 martensite fraîche ≤ 20 austénite retenue 2 - 20 ferrite polygonale ≤ 10
    c) les propriétés mécaniques suivantes une résistance à la traction (Rm) ≥ 1380 MPa limite d'élasticité (Rp0.2) ≥ 1000 MPa allongement total (Aso) ≥ 5 % taux d'expansion de trou (λ) ≥ 40 % pliage (Ri/t) < 5
  2. Une bande ou feuille d'acier laminée à froid selon la revendication 1, dans laquelle la composition d'acier comprend Cr 0,1 - 0,8
    et éventuellement au moins l'un parmi Cu ≤ 0,10 Ni ≤ 0,10 Nb ≤ 0,005 V ≤ 0,01 Ca ≤ 0,005
  3. Une bande ou feuille d'acier laminée à froid selon la revendication 1 ou la revendication 2, dans laquelle la quantité d'austénite retenue est d'au moins 4 % en volume et la quantité de ferrite polygonale est inférieure à 6 % en volume.
  4. Une bande ou feuille d'acier laminée à froid selon la revendication 1, 2 ou 3, dans laquelle la microstructure polyphasée satisfait aux exigences suivantes (en % en volume) : martensite trempée ≥ 50 ferrite bainitique ≤ 30 martensite fraîche ≤ 15 austénite retenue 5 - 15 ferrite polygonale ≤ 5
    et / ou au moins une des exigences suivantes taux d'expansion de trou (λ) ≥ 50 % Rmxλ ≥ 60000 Mpa% rapport d'élasticité (Rp0,2/Rm) ≥ 0,60
  5. Une bande ou feuille d'acier laminée à froid selon l'une quelconque des revendications précédentes, dans laquelle l'augmentation de la limite d'élasticité après 2% d'étirage dans un essai de traction, la valeur BH2, est d'au moins 30 MPa.
  6. Une bande ou feuille d'acier laminée à froid selon l'une quelconque des revendications précédentes, dans laquelle la microstructure polyphasée remplit au moins l'une des exigences suivantes (en % en volume): martensite trempée ≥ 60 ferrite bainitique ≤ 20 martensite fraîche ≤ 10 austénite retenue 6 - 14 ferrite polygonale ≤ 3
    et / ou au moins une des exigences suivantes taux d'expansion de trou (λ) ≥ 55 % Rmxλ ≥ 65000 Mpa%
  7. Une bande ou feuille d'acier laminée à froid, dans laquelle la composition d'acier satisfait à au moins l'une des exigences suivantes en ce qui concerne la teneur en impuretés (en % en poids) : P ≤ 0,02 S ≤ 0,005 N 0,002 - 0,006
  8. Une bande ou feuille d'acier laminée à froid selon l'une quelconque des revendications précédentes, ayant
    a) une composition satisfaisant à au moins l'une des exigences suivantes en ce qui concerne la teneur en impuretés (en % en poids): P ≤ 0,01 S ≤ 0,003 N 0,003 - 0,005 Sn ≤ 0,015 Zr ≤ 0,006 As ≤ 0,012 Ca ≤ 0,005 H ≤ 0,0003 O ≤ 0,0020
  9. Une bande ou feuille d'acier laminée à froid selon l'une quelconque des revendications précédentes répondant à toutes les exigences des revendications 1, 2 et 3 et, éventuellement, aux exigences de la revendication 4.
  10. Une bande ou feuille d'acier laminée à froid selon l'une quelconque des revendications précédentes, dans laquelle l'acier laminé à froid est pourvu d'une couche contenant du Zn.
EP19153131.8A 2019-01-22 2019-01-22 Bande ou feuille d'acier laminée à froid en phase complexe haute résistance et présentant une ductilité élevée Active EP3686293B1 (fr)

Priority Applications (5)

Application Number Priority Date Filing Date Title
EP19153131.8A EP3686293B1 (fr) 2019-01-22 2019-01-22 Bande ou feuille d'acier laminée à froid en phase complexe haute résistance et présentant une ductilité élevée
ES19153131T ES2889200T3 (es) 2019-01-22 2019-01-22 Tira o chapa de acero de fase compleja laminado en frío de alta resistencia y alta ductilidad
US17/423,762 US20220112575A1 (en) 2019-01-22 2019-11-28 A high strength high ductility complex phase cold rolled steel strip or sheet
CN201980089651.3A CN113316649A (zh) 2019-01-22 2019-11-28 高强度高延展性的复相的冷轧钢带或板
PCT/EP2019/082857 WO2020151856A1 (fr) 2019-01-22 2019-11-28 Bande ou tôle d'acier à phase complexe, laminée à froid, très résistante et hautement ductile

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SE545210C2 (en) * 2020-12-23 2023-05-23 Voestalpine Stahl Gmbh Coiling temperature influenced cold rolled strip or steel

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JP5365216B2 (ja) * 2008-01-31 2013-12-11 Ｊｆｅスチール株式会社 高強度鋼板とその製造方法
JP5136609B2 (ja) * 2010-07-29 2013-02-06 Ｊｆｅスチール株式会社 成形性および耐衝撃性に優れた高強度溶融亜鉛めっき鋼板およびその製造方法
WO2014020640A1 (fr) * 2012-07-31 2014-02-06 Ｊｆｅスチール株式会社 Tôle d'acier galvanisée par immersion à chaud à résistance élevée qui présente une excellente aptitude au moulage et une excellente aptitude à la fixation de formes, ainsi que procédé de fabrication de cette dernière
JP5609945B2 (ja) * 2012-10-18 2014-10-22 Ｊｆｅスチール株式会社 高強度冷延鋼板およびその製造方法
CN105940134B (zh) * 2014-01-29 2018-02-16 杰富意钢铁株式会社 高强度冷轧钢板及其制造方法
EP3128027B1 (fr) * 2014-03-31 2018-09-05 JFE Steel Corporation Tôle en acier laminée à froid à grande résistance mécanique, ayant un rapport élevé de limite d'élasticité, et son procédé de production
SE539519C2 (en) * 2015-12-21 2017-10-03 High strength galvannealed steel sheet and method of producing such steel sheet
WO2019063081A1 (fr) * 2017-09-28 2019-04-04 Thyssenkrupp Steel Europe Ag Produit plat en acier et son procédé de fabrication

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