US20210156012A1 - Steel strip, sheet or blank for producing a hot formed part, part, and method for hot forming a blank into a part - Google Patents

Steel strip, sheet or blank for producing a hot formed part, part, and method for hot forming a blank into a part Download PDF

Info

Publication number
US20210156012A1
US20210156012A1 US16/633,198 US201816633198A US2021156012A1 US 20210156012 A1 US20210156012 A1 US 20210156012A1 US 201816633198 A US201816633198 A US 201816633198A US 2021156012 A1 US2021156012 A1 US 2021156012A1
Authority
US
United States
Prior art keywords
blank
steel
hot
sheet
temperature
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.)
Abandoned
Application number
US16/633,198
Other languages
English (en)
Inventor
Radhakanta Rana
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.)
Tata Steel Ijmuiden BV
Original Assignee
Tata Steel Ijmuiden BV
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 Tata Steel Ijmuiden BV filed Critical Tata Steel Ijmuiden BV
Assigned to TATA STEEL IJMUIDEN B.V. reassignment TATA STEEL IJMUIDEN B.V. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: RANA, Radhakanta
Publication of US20210156012A1 publication Critical patent/US20210156012A1/en
Abandoned legal-status Critical Current

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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing 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
    • C22C38/20—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
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/28—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
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • 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
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
    • B21D22/02—Stamping using rigid devices or tools
    • B21D22/022—Stamping using rigid devices or tools by heating the blank or stamping associated with 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/62—Quenching devices
    • C21D1/673—Quenching devices for die quenching
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • 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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • 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
    • 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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys

Definitions

  • the present invention relates to a steel strip, sheet or blank for producing a hot formed part; a hot formed part; and a method for producing a hot formed part.
  • a steel typically used for hot-forming is 22MnB5 steel.
  • This boron steel can be furnace-heated and is usually austenitized between 870-940° C., transferred from furnace to forming tool, and stamped into the desired part geometry, while the part is at the same time cooled.
  • the advantage of such boron steel parts produced this way is that they display a high ultimate tensile strength for anti-intrusive crashworthiness due to their fully martensitic microstructure, but at the same time they display a low ductility and bendability which in turn results in a limited toughness and thus a poor impact-energy absorptive crashworthiness.
  • Fracture toughness measurement is an useful tool to indicate the crash energy absorption of steels. When the fracture toughness parameters are high, generally a good crash behavior is obtained.
  • Yet another object of the present invention is to provide a method for hot-forming a steel blank into a part.
  • the present invention relates to a steel strip, sheet or blank for producing hot formed parts having the following composition in weight %:
  • the hot formed part produced from the steel strip, sheet or blank in accordance with the present invention displays an improved combination of tensile strength, ductility and bendability, and thereby impact toughness when compared to conventional hot-formed boron steels.
  • the two steel blanks are joined by laser welding before hot stamping and then the hybrid blank is stamped into the B-pillar.
  • the invented higher strength steel can replace the lower strength steel of the lower part with a higher energy absorption capability.
  • the steel strip, sheet or blank for producing hot formed parts as described above has the following composition in weight %:
  • Mn 1.0-2.1, preferably 1.2-1.8, and/or
  • Nb 0.02-0.08, preferably 0.03-0.07, and/or
  • N 0.001-0.008, preferably 0.002-0.005
  • Si ⁇ 0.1, preferably ⁇ 0.05
  • Al ⁇ 0.1, preferably ⁇ 0.05,
  • Cu ⁇ 0.1, preferably ⁇ 0.05
  • V ⁇ 0.15, preferably ⁇ 0.05
  • Carbon is added for securing good mechanical properties.
  • C is added in an amount of 0.03 wt % or more to achieve high strength and to increase the hardenability of the steel. When too much carbon is added there is the possibility that the toughness and weldability of the steel sheet will deteriorate.
  • the C amount used in accordance with the invention is therefore in the range of from 0.03-0.17 wt %, preferably in the range of from 0.05-0.17 wt %, and more preferably in the range of from 0.07-0.15 wt %.
  • Mn is used because it promotes hardenability and gives solid solution strengthening.
  • the Mn content is at least 0.65 wt % to provide adequate substitutional solid solution strengthening and adequate quench hardenability, while minimising segregation of Mn during casting and while maintaining sufficiently low carbon equivalent for automotive resistance spot-welding techniques.
  • Mn is an element that is useful in lowering the Ac 3 temperature. A higher Mn content is advantageous in lowering the temperature necessary for hot press forming. When the Mn content exceeds 2.5 wt %, the steel sheet may suffer from poor weldability and poor hot and cold rolling characteristics that affect the steel processability.
  • the Mn amount used in accordance with the invention is in the range of from 0.65-2.5 wt %, preferably in the range of from 1.0-2.1 wt %, and more preferably in the range of from 1.2-1.8 wt %.
  • Chromium improves the hardenability of the steel and facilitates avoiding the formation of ferrite and/or pearlite during press quenching. In this respect it is observed that the presence of ferrite and/or pearlite in the microstructure is detrimental to mechanical properties for the targeted microstructure in this invention.
  • the amount of Cr used in the invention is in the range of from 0.2-2.0 wt %, preferably in the range of from 0.5-1.7 wt %, more preferably in the range of 0.8-1.5 wt %.
  • manganese and chromium are used in such an amount that Mn+Cr ⁇ 2.7, preferably Mn+Cr is in the range of from 0.5-2.5, and more preferably Mn+Cr is in the range of from 2.0-2.5.
  • Titanium is added to form TiN precipitates to scavenge out N at high temperatures while the steel melt cools. Formation of TiN prohibits formation of B 3 N 4 at lower temperatures so that B, which is also an essential element for this invention, becomes more effective. Stoichiometrically, the ratio of Ti to N (Ti/N) addition should be >3.42.
  • the amount of titanium is in the range of from 0.01-0.1 wt %, preferably in the range of from 0.015-0.07 wt %, and more preferably in the range of from 0.025-0.05 wt %.
  • Niobium has the effect of forming strengthening precipitates and refining microstructure.
  • Nb increases the strength by means of grain refinement and precipitation hardening. Grain refinement results in a more homogeneous microstructure improving the hot-forming behavior, in particular when high localized strains are being introduced. A fine, homogeneous microstructure also improves the bending behavior.
  • the amount of Nb used in the invention is in the range of from 0.01-0.1 wt %, preferably in the range of from 0.02-0.08 wt %, and more preferably in the range of from 0.03-0.07 wt %.
  • Boron is an important element for increasing the hardenability of steel sheets and for further increasing the effect of stably guaranteeing strength after quenching.
  • B is present in an amount in the range of from 0.0005-0.005 wt %, preferably in the range of from 0.0005-0.004 wt %, more preferably in the range of from 0.001-0.003 wt %.
  • N has an effect similar to C.
  • N is suitably combined with titanium to form TiN precipitates.
  • the amount of N according to the invention is at most 0.01 wt %.
  • the amount of N is in the range of 0.001-0.008 wt %.
  • N is present in an amount in the range of from 0.002-0.005 wt %.
  • Mn, Cr and B are used in such amounts that (B ⁇ 1000)/(Mn+Cr) is in the range of from 0.185-2.5, preferably in the range of from 0.2-2.0, and more preferably in the range of from 0.5-1.5.
  • the (B ⁇ 1000)/(Mn+Cr) ratio as applied in accordance with the present invention establishes an adequate hardenability of the steel.
  • Silicon is also added to promote hardenability and adequate substitutional solid solution strengthening.
  • the Si amount used in the invention is at most 0.1 wt %, preferably at most 0.5 wt %.
  • Aluminium is added to deoxidize the steel.
  • the Al amount is at most 0.1 wt %, preferably at most 0.05 wt %.
  • Molybdenum is added to improve the hardenability of the steel and facilitate the formation of bainite.
  • the Mo amount used in accordance with the invention is at most 0.1 wt %, preferably at most 0.05 wt %.
  • Copper is added to improve hardenability and increase strength of the steel. If present, Cu is used in accordance with the invention in an amount of at most 0.1 wt %, preferably at most 0.05 wt %.
  • P is known to widen the intercritical temperature range of a steel. P is also an element useful for maintaining desired retained austenite. However, P may deteriorate the workability of the steel. In accordance with the invention P should be present in an amount of at most 0.03 wt %, preferably at most 0.015 wt %.
  • the amount of sulphur needs to be minimised to reduce harmful non-metallic inclusions.
  • S forms a sulfide based inclusions such as MnS, which initiates crack, and deteriorates processability. Therefore, it is desirable to reduce the S amount as much as possible.
  • the amount of S is at most 0.025 wt %, preferably an amount of at most 0.01 wt %.
  • the amount of 0 is at most 0.01 wt %, preferably at most 0.005 wt %.
  • Vanadium may be added to form V(C, N) precipitates to strengthen the steel product.
  • the amount of vanadium, if any, is at most 0.15 wt %, preferably at most 0.05 wt %.
  • Nickel may be added in an amount of at most 0.15 wt %. Ni can be added to increase the strength and toughness of the steel.
  • Calcium may be present in an amount of up to 0.05 wt %, preferably up to 0.01 wt %. Ca is added to spheroidize the sulphur containing inclusions and to minimize the amount of elongated inclusions. However, the presence of CaS inclusions will still lead to inhomogeneities in the matrix; it is thus best to reduce the amount of S.
  • 1000*B divided by the sum of Mn and Cr has to be between 0.185 and 2.5, preferably between 0.5 and 1.5. This limitation improves the hardenability of the steel.
  • the steel strip, sheet or blank is provided with a zinc based coating, an aluminium based coating or an organic based coating.
  • a zinc based coating reduces oxidation and/or decarburization during a hot forming process.
  • the zinc based coating is a coating containing 0.2-5.0 wt % Al, 0.2-5.0 wt % Mg, optionally at most 0.3 wt % of one or more additional elements, the balance being zinc and unavoidable impurities.
  • the additional elements can be selected from the group comprising Pb or Sb, Ti, Ca, Mn, Sn, La, Ce, Cr, Ni, Zr or Bi. Pb, Sn, Bi and Sb are usually added to form spangles.
  • the total amount of additional elements in the zinc alloy is at most 0.3 wt. %. These small amounts of an additional element do not alter the properties of the coating nor the bath to any significant extent for the usual applications.
  • each is preferably present in an amount of at most 0.03 wt %, preferably each is present in an amount of at most 0.01 wt %. Additional elements are usually only added to prevent dross forming in the bath with molten zinc alloy for the hot dip galvanizing, or to form spangles in the coating layer.
  • the hot formed part produced from a steel strip, sheet or blank in accordance with the present invention has a microstructure comprising at most 60% bainite, the remainder being martensite.
  • the microstructure comprises at most 50 vol. % of bainite, the remainder being martensite. More preferably, the microstructure comprises at most 40 vol. % of bainite, the remainder being martensite.
  • the martensite provides a high strength, whereas the softer bainite improves the ductility. The small strength difference between martensite and bainite helps in maintaining a high bendability due to lack of weak phase interfaces.
  • the hot formed part in accordance with the present invention displays excellent mechanical properties.
  • the part has a tensile strength (TS) of at least 750 MPa, preferably of at least 800 MPa, more preferably of at least 900 MPa, and further has a tensile strength of at most 1400 MPa.
  • TS tensile strength
  • the part suitably has a total elongation (TE) of at least 5%, preferably 5.5%, more preferably at least 6% and most preferably at least 7%, and/or a bending angle (BA) at 1.0 mm thickness of at least 100°, preferably at least 115°, more preferably at least 130° and most preferably at least 140°.
  • TE total elongation
  • BA bending angle
  • the present invention also relates to the use of hot formed parts as described above, as structural part in the body-in-white of a vehicle.
  • Such parts are made of the present steel strip, sheet or blank. These parts have a high strength, high ductility and a high bendability.
  • parts in the form of structural parts of vehicles are very attractive since they exhibit excellent crash energy absorption and in turn, down-gauging and lightweighting opportunities based on crashworthiness compared to the use of conventional hot-formed boron steels and cold-formed multiphase steels.
  • the present invention also relates to a method for producing a part in accordance with the present invention.
  • the present invention also relates to a method for hot-forming a steel blank or a preformed part into an part comprising the steps of:
  • the part After the cooling of the part to a temperature below the Mf temperature, the part can for instance be further cooled to room temperature in air, or can be forcibly cooled to room temperature.
  • the blank to be heated in step (a) is provided as an intermediate for the subsequent steps.
  • the steel strip or sheet from which the blank is produced can be obtained by standard casting processes.
  • the steel strip or sheet is cold-rolled.
  • the steel strip or sheet can suitably be cut to a steel blank.
  • a preformed steel part may also be used. The preformed part may be partially or entirely formed into the desired geometry, preferably at ambient temperature.
  • the steel blank is heated in step (a) to a temperature T 1 for a time period t 1 .
  • the temperature T 1 is 50-100° C. higher than the Ac 3 temperature of the steel, and/or the temperature T 2 is above the Ar 3 temperature.
  • T 1 is 50-100° C. above the Ac 3 temperature
  • the steel is fully or almost fully austenitized within the time period t 1 , and the cooling during step (b) is easily possible.
  • the microstructure is a homogenous austenitic microstructure the formability is enhanced.
  • the time period t 1 is at least 1 minute and at most 7 minutes. Too long a time period t 1 may result in coarse austenitic grains, which will deteriorate the final mechanical properties
  • the heating apparatus to be used in step (a) may for instance be an electric or gas powered furnace, electrical resistance heating device, infra-red induction heating device.
  • step (b) the heated steel blank or preformed part is transferred to a hot-forming tool during a transport time t 2 during which the temperature of the heated steel blank or preformed part decreases from temperature T 1 to a temperature T 2 , wherein the transport time t 2 is at most 20 seconds.
  • Time t 2 is the time needed to transport the heated blank from the heating apparatus to the hot-forming tool (e.g. press) and till the hot-forming apparatus is closed.
  • the transfer of the blank or preformed part may cool from temperature T 1 to temperature T 2 by the act of natural air-cooling and/or any other available cooling method.
  • the heated blank or preformed part may be transferred from the heating apparatus to the forming tool by an automated robotic system or any other transfer method.
  • Time t 2 may also be chosen in combination with T 1 , t 1 and T 2 in order to control the microstructural evolution of steel at the commencement of forming and quenching.
  • t 2 is equal or less than 12 seconds, preferably t 2 is equal or less than 10 s, more preferably t 2 is equal or less than 8 s, and most preferably equal or less than 6 s.
  • the blank or preformed part can be cooled from temperature T 1 to a temperature at a cooling rate V 2 of at least 10° C./s.
  • V 2 is preferably in the range of from 10-15° C./s.
  • the cooling rate should be higher, for instance at least 20° C./s, up to 50° C./s or more.
  • step (c) a heated blank or preformed part is formed into a part having the desired geometry.
  • the formed part is preferably a structural part of a vehicle.
  • step (d) the formed part in the hot-forming tool is cooled to a temperature below the Mf temperature of the steel with a cooling rate V 3 of at least 30° C./s.
  • the cooling rate V 3 in step (d) is in the range of from 30-150° C./s, more preferably in the range of from 30-100° C./s.
  • the present invention provides an improved method of introducing during hot-forming operation the desired bainitic phase into the steel microstructure.
  • the present method enables the production of hot formed steel parts displaying an excellent combination of high strength, high ductility and high bendability.
  • One or more steps of the method according to the present invention may be conducted in a controlled inert atmosphere of hydrogen, nitrogen, argon or any other inert gas in order to prevent oxidation and/or decarburisation of said steel.
  • FIG. 1 shows a schematic representation of an embodiment of the method according to the invention.
  • FIG. 2 shows a cross-section through a drop tower for axial crash tests.
  • the horizontal axis represents the time t
  • the vertical axis represents the temperature T.
  • the time t and temperature T are indicated diagrammatically in FIG. 1 . No values can be derived from FIG. 1 .
  • a steel blank or preformed part is (re)heated up to the austenitizing temperature above Ac 1 at a particular (re)heating rate. Once the Ac 1 has been exceeded the (re)heating rate is lowered until the blank or preformed part has reached a temperature higher than the Ac 3 . Then the strip, sheet or blank is held at this particular temperature for a period of time. Subsequently, the heated blank is transferred from the furnace to the hot forming tool, during which cooling of the blank by air occurs to some extent. The blank or preformed part is then hot-formed into a part and cooled down (or quenched) at a cooling rate of at least 30° C./s. After reaching a temperature below the Mf temperature of the steel, the hot-forming tool is opened and the formed article is cooled down to room temperature.
  • Steel blanks with dimensions of 220 mm ⁇ 110 mm ⁇ 1.5 mm were prepared from a cold-rolled steel sheet having the composition as shown in Table 1. These steel blanks were subjected to hot forming thermal cycles in a hot dip annealing simulator (HDAS) and an SMG press. The HDAS was used for slower cooling rates (30-80° C./s) whereas the SMG press was used for fastest cooling rate (200° C./s). The steel blanks were reheated to a T 1 of respectively 900° C. (36° C. above Ac 3 ) and 940° C. (76° C. above Ac 3 ), soaked for 5 min. in nitrogen atmosphere to minimize surface degradation. The blanks were then subjected to transfer cooling for a drop in temperature of 120° C.
  • HDAS hot dip annealing simulator
  • SMG press was used for fastest cooling rate (200° C./s).
  • the steel blanks were reheated to a T 1 of respectively 900° C. (36° C. above Ac 3 )
  • the samples with bending axis parallel to the rolling direction were identified as longitudinal (L) bending specimens whereas those with bending axis perpendicular to the rolling direction were denoted as perpendicular (T) bending specimens.
  • J-integral fracture toughness and drop tower axial crash tests were conducted.
  • Compact tension specimens according to NFMT76J standard were prepared from both longitudinal and transverse directions for fracture toughness tests.
  • the specimens were tested according to ASTM E1820-09 standard at room temperature.
  • the pre-cracks were introduced by fatigue loading.
  • the final tests were done with tensile loading with anti-buckle plates to keep the stress in plane for sheet material.
  • CTOD is the Crack Tip Opening Displacement and is a measure of how much the crack opens at either failure (if brittle) or maximum load.
  • J is the J-integral and is a measure of toughness that takes account of the energy, so it is calculated from the area under the curve up to failure or maximum load.
  • K q is the value of stress intensity factor measured at load P q , where P q is determined by taking the elastic slope of the loading line, then taking a line with 5% less slope and defining P q as the load where this straight line intersects the loading line.
  • Drop tower axial crash tests were done in SMG-pressed condition with a load of 200 kg and a loading speed of 50 km/hour for the load to hit the crash boxes having a closed top hat geometry ( FIG. 2 ) with 500 mm height (transverse to the rolling direction).
  • the back plates of 100 mm width were spot-welded to the profiles to prepare the crash boxes.
  • Table 3 the yield strength (YS), ultimate tensile strength (UTS), uniform elongation (UE), and total elongation (TE) are shown for steel composition A after a variety of cooling rates V 3 .
  • Table 3 shows the microstructure in terms of martensite (M) and bainite (B). It will be clear from Table 3 that an ultimate tensile strength of greater than 800 MPa was achieved at the different cooling rates V 3 .
  • the high and improved crash behavior of hot formed steel composition A in accordance with the present invention when compared to the conventional steel products of similar strength is due to the higher bending angle and higher fracture toughness properties.
  • the steel component need to fold which is determined by its bendability, whereas on the other hand the energy absorption capability before failure is determined by its fracture toughness parameters.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Coating With Molten Metal (AREA)
  • Heat Treatment Of Articles (AREA)
  • Heat Treatment Of Steel (AREA)
US16/633,198 2017-07-25 2018-07-23 Steel strip, sheet or blank for producing a hot formed part, part, and method for hot forming a blank into a part Abandoned US20210156012A1 (en)

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
EP17183092.0 2017-07-25
EP17183092 2017-07-25
EP17186911 2017-08-18
EP17186911.8 2017-08-18
PCT/EP2018/069939 WO2019020575A1 (fr) 2017-07-25 2018-07-23 Bande, tôle ou ébauche en acier pour la fabrication d'une pièce formée à chaud, et procédé de formage à chaud d'une ébauche pour former une pièce

Publications (1)

Publication Number Publication Date
US20210156012A1 true US20210156012A1 (en) 2021-05-27

Family

ID=62904499

Family Applications (1)

Application Number Title Priority Date Filing Date
US16/633,198 Abandoned US20210156012A1 (en) 2017-07-25 2018-07-23 Steel strip, sheet or blank for producing a hot formed part, part, and method for hot forming a blank into a part

Country Status (8)

Country Link
US (1) US20210156012A1 (fr)
EP (1) EP3658692B1 (fr)
JP (1) JP7326247B2 (fr)
KR (2) KR20240142610A (fr)
BR (1) BR112020000917A2 (fr)
ES (1) ES2899238T3 (fr)
MX (1) MX2020000928A (fr)
WO (1) WO2019020575A1 (fr)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20220013393A (ko) * 2019-05-28 2022-02-04 타타 스틸 이즈무이덴 베.뷔. 열간-스탬프 부품을 생산하기 위한 강철 스트립, 시트 또는 블랭크, 열간-스탬프 부품, 및 블랭크를 부품으로 열간-스탬핑하는 방법
KR20220102651A (ko) * 2020-01-16 2022-07-20 닛폰세이테츠 가부시키가이샤 핫 스탬프 성형체
KR102345608B1 (ko) * 2020-12-23 2021-12-30 현대제철 주식회사 핫 스탬핑 부품, 및 이의 제조 방법

Family Cites Families (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE435527B (sv) 1973-11-06 1984-10-01 Plannja Ab Forfarande for framstellning av en detalj av herdat stal
FR2735148B1 (fr) 1995-06-08 1997-07-11 Lorraine Laminage Tole d'acier laminee a chaud a haute resistance et haute emboutissabilite renfermant du niobium, et ses procedes de fabrication.
JP4449795B2 (ja) * 2005-03-22 2010-04-14 住友金属工業株式会社 熱間プレス用熱延鋼板およびその製造方法ならびに熱間プレス成形部材の製造方法
JP5586008B2 (ja) 2007-02-23 2014-09-10 タタ、スティール、アイモイデン、ベスローテン、フェンノートシャップ 強度が非常に高い最終製品の熱機械的成形方法およびその方法により製造された製品
DK2434027T3 (en) 2009-05-22 2015-12-07 Jfe Steel Corp Steel materials for welding with high heat input
MX2012014594A (es) 2010-06-14 2013-02-21 Nippon Steel & Sumitomo Metal Corp Articulo moldeado y estampado en caliente, proceso para produccion de placa de acero para estampado en caliente, y proceso para produccion de un articulo moldeado y estampado en caliente.
MX359051B (es) * 2010-10-22 2018-09-13 Nippon Steel & Sumitomo Metal Corp Proceso para producir un artículo moldeado por estampación en caliente, y artículo moldeado por estampación en caliente.
WO2013149734A1 (fr) 2012-04-05 2013-10-10 Tata Steel Ijmuiden B.V. Bande d'acier ayant une faible teneur en si
DE102013009232A1 (de) 2013-05-28 2014-12-04 Salzgitter Flachstahl Gmbh Verfahren zur Herstellung eines Bauteils durch Warmumformen eines Vorproduktes aus Stahl
CA2924812A1 (fr) * 2013-09-19 2015-03-26 Tata Steel Ijmuiden B.V. Acier pour le formage a chaud
EP2851440A1 (fr) * 2013-09-19 2015-03-25 Tata Steel IJmuiden BV Acier pour formage à chaud
JP6303580B2 (ja) * 2014-02-19 2018-04-04 新日鐵住金株式会社 熱処理用鋼板およびその製造方法
WO2015144318A1 (fr) 2014-03-28 2015-10-01 Tata Steel Ijmuiden B.V. Procédé de formage à chaud d'une pièce brute d'acier enduit
TWI563101B (en) * 2014-05-15 2016-12-21 Nippon Steel & Sumitomo Metal Corp Hot-formed steel sheet member
CA2979923A1 (fr) * 2015-03-16 2016-09-22 Tata Steel Ijmuiden B.V. Acier pour formage a chaud
WO2017006144A1 (fr) 2015-07-09 2017-01-12 Arcelormittal Acier pour trempe à la presse et pièce trempée à la presse fabriquée à partir d'un tel acier
JP6606897B2 (ja) * 2015-07-16 2019-11-20 日本製鉄株式会社 熱処理用鋼板およびその製造方法と、ホットスタンプ成形品
JP2018532045A (ja) 2015-09-22 2018-11-01 タタ、スティール、アイモイデン、ベスローテン、フェンノートシャップＴａｔａ Ｓｔｅｅｌ Ｉｊｍｕｉｄｅｎ Ｂｖ 優れた伸びフランジ成形性を有するロール成形可能な高強度熱間圧延鋼板、および該鋼の製造方法
KR20170075046A (ko) * 2015-12-22 2017-07-03 주식회사 포스코 내식성이 우수한 열간 프레스 성형품 및 그 제조방법

Also Published As

Publication number Publication date
JP2020528963A (ja) 2020-10-01
JP7326247B2 (ja) 2023-08-15
EP3658692A1 (fr) 2020-06-03
BR112020000917A2 (pt) 2020-07-21
KR20240142610A (ko) 2024-09-30
WO2019020575A1 (fr) 2019-01-31
EP3658692B1 (fr) 2021-11-10
KR20200035259A (ko) 2020-04-02
MX2020000928A (es) 2020-07-22
ES2899238T3 (es) 2022-03-10

Similar Documents

Publication Publication Date Title
US11572599B2 (en) Cold rolled heat treated steel sheet and a method of manufacturing thereof
US11365468B2 (en) Cold rolled and heat treated steel sheet and a method of manufacturing thereof
US10253388B2 (en) Steel sheet for hot press formed product having superior bendability and ultra-high strength, hot press formed product using same, and method for manufacturing same
CN106471147A (zh) 高强度多相钢、生产方法和用途
JP2017002384A (ja) 耐スポット溶接部破断特性に優れた鋼板及びその製造方法
CN112673122A (zh) 屈强比优异的超高强度高延展性钢板及其制造方法
WO2020239891A1 (fr) Bande, tôle ou ébauche en acier pour la fabrication d'une pièce estampée à chaud, et procédé d'estampage à chaud d'une ébauche pour former une pièce
US20170081739A1 (en) High-strength flat steel product having a bainitic-martensitic microstructure and method for producing such a flat steel product
EP3658692B1 (fr) Bande, feuille ou ébauche d'acier pour produire une pièce formée à chaud, pièce et procédé de formage à chaud d'une ébauche en une pièce
KR20190052683A (ko) 망간 함유 평탄 강으로 이루어지는 평탄 강 제품을 제조하는 방법 및 이러한 평탄 강 제품
CA3141566C (fr) Tole d'acier laminee a froid et revetue et son procede de fabrication
JPH11350064A (ja) 形状凍結性と耐衝撃特性に優れる高強度鋼板及びその製造方法
JP4265152B2 (ja) 伸びおよび伸びフランジ性に優れた高張力冷延鋼板およびその製造方法
JP4265153B2 (ja) 伸びおよび伸びフランジ性に優れた高張力冷延鋼板およびその製造方法
KR101166995B1 (ko) 이상조직을 갖는 고강도 고성형성 용융아연도금강판 제조방법
CN110945148B (zh) 用于制备热成形零件的钢带材、片材或坯料，零件，和用于将坯料热成形为零件的方法
KR102472740B1 (ko) 저합금 3세대 첨단 고강도 강 및 제조방법
US20210180150A1 (en) Ultrahigh-strength and high-ductility steel sheet having excellent cold formability, and manufacturing method therefor
CA3163376A1 (fr) Tole d'acier laminee a froid et traitee thermiquement et procede de fabrication de celle-ci
EP4308736A1 (fr) Bande, feuille ou ébauche d'acier et procédé de production d'une pièce formée à chaud ou d'une pièce préformée traitée à chaud
JPH11350063A (ja) 形状凍結性と耐衝撃特性に優れる高強度鋼板及びその製造方法
EP4118246A1 (fr) Procédé de fabrication d'un article en acier et article
JP2024138480A (ja) 熱処理された冷間圧延鋼板及びその製造方法

Legal Events

Date Code Title Description
AS Assignment

Owner name: TATA STEEL IJMUIDEN B.V., NETHERLANDS

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:RANA, RADHAKANTA;REEL/FRAME:051593/0045

Effective date: 20200109

STPP Information on status: patent application and granting procedure in general

Free format text: DOCKETED NEW CASE - READY FOR EXAMINATION

STPP Information on status: patent application and granting procedure in general

Free format text: NON FINAL ACTION MAILED

STPP Information on status: patent application and granting procedure in general

Free format text: FINAL REJECTION MAILED

STPP Information on status: patent application and granting procedure in general

Free format text: ADVISORY ACTION MAILED

STPP Information on status: patent application and granting procedure in general

Free format text: NON FINAL ACTION MAILED

STPP Information on status: patent application and granting procedure in general

Free format text: RESPONSE TO NON-FINAL OFFICE ACTION ENTERED AND FORWARDED TO EXAMINER

STPP Information on status: patent application and granting procedure in general

Free format text: NON FINAL ACTION MAILED

STPP Information on status: patent application and granting procedure in general

Free format text: FINAL REJECTION MAILED

STCB Information on status: application discontinuation

Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION