EP3473735B1 - Procédé de traitement permettant d'obtenir des performances progressives et élément associé - Google Patents

Procédé de traitement permettant d'obtenir des performances progressives et élément associé Download PDF

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Publication number
EP3473735B1
EP3473735B1 EP16905967.2A EP16905967A EP3473735B1 EP 3473735 B1 EP3473735 B1 EP 3473735B1 EP 16905967 A EP16905967 A EP 16905967A EP 3473735 B1 EP3473735 B1 EP 3473735B1
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EP
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Prior art keywords
zone
blank
hard
austenite
soft
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EP16905967.2A
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German (de)
English (en)
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EP3473735A1 (fr
EP3473735C0 (fr
EP3473735A4 (fr
Inventor
Hongliang Yi
Pengju DU
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Easyforming Steel Technology Co Ltd
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Easyforming Steel Technology Co Ltd
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Priority claimed from CN201610440901.1A external-priority patent/CN106011418B/zh
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    • 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
    • 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
    • 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
    • B21D37/00—Tools as parts of machines covered by this subclass
    • B21D37/16—Heating or cooling
    • 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
    • B21D53/00—Making other particular articles
    • B21D53/88—Making other particular articles other parts for vehicles, e.g. cowlings, mudguards
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/62—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
    • 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
    • C22C38/02—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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • 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
    • C21D2211/008—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
    • C21D2221/00—Treating localised areas of an article
    • 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
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • 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
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing 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
    • 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

Definitions

  • the present invention relates to a treatment process for obtaining gradient properties. Specifically, the invention relates to a process for realizing gradient properties on the same component, wherein the stamping process, the heat treatment method and the mechanical properties of the hard zone are different from the stamping process and the heat treatment method of the soft zone thereof.
  • the invention also relates to components made via the treatment process, which has both a hard zone and a soft zone with different mechanical properties.
  • Automotive lightweighting is one of the effective means and ways to achieve energy saving and emission reduction.
  • Automotive lightweighting can be realized by reasonable designs and advanced forming methods.
  • the use of high-strength steel can ensure the safety of automobile while achieving lightweighting.
  • high-strength steel has low stretch flangeability and a low hole expansion ratio, so there are problems such as easy cracking during stamping and increased springback of the parts after the stamping.
  • a forming method called hot stamping or hot forming for manufacturing a vehicle component having a strength of 1000 MPa or more has been commercialized.
  • the hot formed component has high strength, its elongation is very low.
  • the safety component has high strength to effectively resist the intrusion of an collision object, but ductility and toughness of the whole or a part of the component are required to ensure high collision energy absorption.
  • the traditional hot forming steel 22MnB5 can hardly achieve both high strength and high ductility in a single hot forming process.
  • the industry has developed tailored properties technologies so that a single part is made up of two different regions with high strength and high elongation respectively, such as a B-pillar, with high strength and good intrusion resistance at the upper end and lower strength and better elongation at the lower end for energy absorption.
  • the tailored properties are usually achieved through two approaches: the tailor welded blank technology and the segmented/gradient strengthening technology.
  • tailor welded blank technology is to use laser welding in some locations to weld two steel sheets of different compositions and different thicknesses together and obtain different properties after treatment. Dissimilar materials and different thicknesses make the welding difficult and increase production procedures and the potential for weak welds or damage.
  • the segmented/gradient strengthening technology generally controls the cooling rate of a part during the hot stamping process, thus obtaining different structures to achieve different properties. It mainly comprises controlling the thermal conductivity of the die, including active cooling ( CN102212742 A ), and passive cooling ( CN104831020A , CN103521581A , CN103409613A ). In CN102212742A , by designing a flexibility controllable hot stamping die with cooling water channels, different regions of the part are designed with different water flow speeds to achieve different cooling rates.
  • CN104831020A through the water channel design in the die, the temperature is different with the distance that the cooling water flows in the die, and a non-uniform temperature field is formed in the die to realize gradient control in the stamping process.
  • Both CN103521581A and CN103409613A achieve property gradients by changing the cooling rate of the part by a thermal barrier coating on the die.
  • WO2006/038868A1 describes a method for achieving gradient properties which controls the cooling rate by controlling the air gaps formed by the grooves between the die and the part to be stamped.
  • US2013/0048160A1 pre-cools a region of the part to be softened between austenitizing and hot stamping of the steel sheet to obtain a soft phase structure, and then conducts hot stamping to realize gradient properties of the part.
  • CN101861265A describes a B-pillar for a vehicle and a method of manufacturing the same. The purpose thereof is to design a B-pillar with gradient properties, with a soft zone of at least 30 mm long near the lower end (the fixation part) of the B-pillar, which is manufactured by controlling the cooling rate of the soft zone.
  • CN103878237A discloses a method for processing a hot formed part from high-strength steel, which performs localized annealing on a uniform component after the hot forming to realize gradient properties of the part.
  • the method requires designing a special induction heating coil which has a high annealing temperature of 600 to 1000 °C, preferably 800 °C, and is air cooled to 100 to 500 °C after the annealing.
  • US 2002/0104591 A1 discloses a B-column as body component for a motor vehicle.
  • the B-column constitutes a longitudinal steel profile.
  • the longitudinal steel profile has a first lognitudinal portion comprised of a martensitic material structure and a strength of more than 1400 N/mm 2 and has a second longitudinal portion of higher ductility with a predominantly ferritic-perlitic material structure and a strength of below 850 N/mm 2 .
  • the present invention relates to a process for realizing gradient properties on the same part, wherein the stamping process, the heat treatment method and the mechanical properties of the hard zone are different from the stamping process and the heat treatment method of the soft zone thereof.
  • the invention also relates to components having both a hard zone and a soft zone, wherein the hard zone can ensure small collision deformation due to high strength, and the soft zone can guarantee collision energy absorption due to high elongation.
  • a treatment process for obtaining gradient properties comprising the steps of: A. preparing a blank, dividing the blank into a region to be formed as a hard zone, and a region to be formed as a soft zone; B. heating the region to be formed as the hard zone to 720 °C to 850 °C, such that its microstructure is transformed into austenite, and meanwhile maintaining the temperature of the region to be formed as the soft zone below 720 °C; C. stamping the entire blank and cooling it by any cooling method after the stamping; D. conducting carbon partitioning treatment on the hard zone of components obtained after the stamping to diffuse carbon from martensite to austenite.
  • a component having gradient properties characterized in that the component is made by the treatment processes of the preferred embodiments described above.
  • the heating processes of the hard zone and the soft zone are different (the soft zone is not fully austenitic-heated), and the stamping process is the same for the soft zone and the hard zone, so that no die modification is required and the process is reliable.
  • Another solution of the present invention is to first form a formed component by a stamping process, and then separately heat treat the soft zone, which has no influence on the stamping die or the process. It is worth emphasizing that it can be ensured that the soft zone elongation obtained by the two solutions of the present invention is greater than 15%, preferably 25 to 35%, which is far superior to the state of the art.
  • the components with gradient properties include, but are not limited to, a B-pillar, an A-pillar, a front longitudinal beam, and the like of an automobile.
  • Hard zone refers to the quench hardened region with high strength on the part
  • soft zone refers to the region with low strength and high elongation.
  • the hard zone is a region of the upper end that needs to prevent collision intrusion
  • the soft zone is a region of the lower end that needs to absorb collision energy.
  • the microstructure of the soft zone includes: by area, from 30% to 60% of retained austenite, from 40% to 70% of martensite or ferrite with a body-centered cubic crystal structure, and less than 3% of carbide.
  • the mechanical properties of the soft zone are: a tensile strength of 900-1500 MPa, and an elongation greater than 15%.
  • the microstructure of the hard zone includes, by area, from 3% to 23% of retained austenite, less than 2% of carbide, and the remainder being martensite.
  • the mechanical properties of the hard zone are: a yield strength greater than 1200 MPa, a tensile strength greater than 1600 MPa, and an elongation greater than 10%.
  • the treatment process for obtaining gradient properties according to the invention is defined in claim 1.
  • the component with gradient properties according to the invention is defined in claim 7.
  • the preferred embodiments are defined in the dependent claims.
  • a steel material for stamping which includes in weight percent 0.22 to 0.48% of C, 5 to 9.5% of Mn, 0.2 to 3.0% of Si+Al, and the remainder being Fe and unavoidable impurities, wherein the steel material is one of hot-rolled coil (sheet), hot-rolled pickled coil (sheet), cold-rolled annealed coil (sheet), and cold-rolled coated coil (sheet).
  • the soft zone portion is obtained by the heat treatment wherein it is heated before the stamping (solution 1, wherein the soft zone temperature is controlled during the austenitizing heating of the hard zone) or after the hot stamping (solution 2, wherein the soft zone is heated separately) to 600 to 720 °C and then soaked for 0.5 to 60 minutes (wherein the time can be selected from 1, 3, 5, 10, 20, 30, 40 and 50, etc.).
  • solution 1, wherein the soft zone temperature is controlled during the austenitizing heating of the hard zone
  • solution 2 wherein the soft zone is heated separately
  • the soft zone obtains retained austenite with a volume fraction of 30% to 60%, a martensite (ferrite) structure with a volume fraction of 40% to 70%, and carbide of less than 3%.
  • the carbon content and manganese content as originally designed in the alloy are 0.22% and 5% or more respectively, and in the heating process of the soft zone, carbon and manganese are diffused and enriched into the austenite,.
  • the carbon content in the retained austenite finally measured under the above heating process is 0.5% or more, the manganese content is more than 7%, and the austenite grain size is less than 2 ⁇ m or the austenite lath thickness is less than 1 ⁇ m, compared with the prior art manganese steel, it is not necessary to achieve or be close to the carbon and manganese content in austenite in thermodynamic equilibrium to form stable retained austenite.
  • the retained austenite itself has high deformability and toughness, and the martensite transformation and/or deformation twinning in the retained austenite are/is beneficial to improving the energy absorption and the elongation of the steel sheet.
  • the steel material of the present invention is based on a high carbon and medium manganese composition, the carbon content being between 0.22 and 0.48%, preferably between 0.25 and 0.45%, and the manganese content being between 5 and 9.5%, preferably between 6 and 8%.
  • Both carbon and manganese are austenite stabilizing elements, which can strongly reduce the austenitizing temperature of steel and the martensite transformation start temperature. During the annealing heat treatment, a structure of alternative austenite/ferrite laths is formed, and the carbon and manganese are partitioned into the austenite to stabilize the austenite to below room temperature.
  • the retained austenite itself has high deformability and toughness, and can also undergo a TRIP effect during the deformation to gradually transform into martensite, which improves the strength and ductility of the steel material.
  • the steel material of the invention has an optimized composition design and annealing process, wherein the retained austenite has high carbon and manganese, part of the austenite has high stacking fault energy, and deformation twinning is produced during the deformation, which can further improve the work hardening rate and meanwhile improve the material strength and ductility.
  • the preferable annealing temperature needs to be increased, resulting in a decrease in the contents of carbon and manganese in the austenite and coarse grains, thus leading to poor austenite stability and a decrease in the toughness of the steel during the deformation.
  • the carbon content is high, a hyper-eutectoid structure may be formed.
  • a large number of coarse carbides are easily formed to deteriorate the mechanical properties of the steel, and a further increase of the carbon content deteriorates the toughness of the hard zone.
  • the steel material further comprises at least one of the following elements: Cr: 0.001% to 5%; Mo: 0.001% to 2.0%; W: 0.001% to 2.0%; Ti: 0.0001% ⁇ 0.4%; Nb: 0.0001% to 0.4%; Zr: 0.0001% to 0.4%; V: 0.0001% to 0.4%; Cu: 0.0005% to 2%; Ni: 0.0005% to 3.0%; B: 0.0001% to 0.005 %.
  • the combination of ultra-high strength and toughness of the stamped component can be further ensured, so that the mechanical properties thereof can be reached: a yield strength of 0.5 to 1.2 GPa, a tensile strength of 1.0 to 1.5 GPa, and a product of strength and elongation (tensile strength ⁇ elongation) of 25 GPa % or more.
  • the steel material comprises a hot-rolled steel sheet, a cold-rolled steel sheet, or a steel sheet with a coating.
  • the steel sheet with a coating may be a zinc-coated steel sheet which is a hot-rolled steel sheet or a cold-rolled steel sheet on which a metal zinc layer is formed.
  • the zinc-coated steel sheet includes one selected from the group consisting of hot-dip galvanizing (GI), galvannealing (GA), and zinc plating or zinc-iron plating (GE).
  • the steel sheet with a coating may be a hot-rolled steel sheet or a cold-rolled steel sheet on which an aluminum-silicon layer is formed, or a steel sheet with an organic coating or a steel sheet with other alloyed coatings.
  • a blank such as a steel sheet, a steel coil, or a blanked sheet or a preformed component is prepared.
  • the blank may be, for example, a blank having the composition and properties of the above steel material.
  • the entire blank is annealed, wherein the steel sheet and the steel coil can be heat treated in a continuous annealing production line or a continuous annealing coating production line of a steel plant.
  • the entire blank can be heated to 600-720 °C, soaked for 0.5-60 minutes, and then cooled by any means (such as gas cooling, air cooling in a continuous annealing production line, or cooling in a hot stamping die or air cooling) to a temperature of -100 °C or more, preferably to room temperature.
  • the microstructure of the blank includes, by area: from 30% to 60% of retained austenite, from 40% to 70% of martensite or ferrite with a body-centered cubic crystal structure, and less than 3% of carbide, wherein the retained austenite includes, by weight percent, 7% or more of Mn and 0.5% or more of carbon.
  • the blank has a tensile strength of 900 to 1500 MPa and an elongation of 15% or more, so that the blank has good formability at room temperature.
  • the region to be formed as the hard zone is heated to 720 to 850 °C to transform its microstructure into austenite, while ensuring that the region to be formed as the soft zone is at a temperature lower than 720 °C in the process (for example, the region to be formed as the soft zone is not heated but maintained at room temperature or is heated to 650 °C).
  • the hard zone may first be inductively heated to, for example, 650 °C, while the soft zone is not heated (maintained at room temperature or rising to a lower temperature due to heat conduction during heating of the hard zone), and then the entire blank is placed in a furnace at a temperature of, for example, 780 °C to be heated.
  • the heating time required for heating from 650 °C to 780 °C is short, such as 40 seconds, and then the temperature is maintained for 20 seconds, for instance, to achieve homogenization of the austenite structure, so the entire blank is in the furnace at 780 °C for one minute, for example.
  • the soft zone cannot be heated to 780 °C in the furnace at 780 °C due to the its low temperature upon entry into the furnace.
  • a conventional hot formed steel material for example, 22MnB5 cannot achieve homogenization of the austenite structure within a heating time of one minute because its austenitizing temperature is much higher than that of the material involved in the present invention.
  • the entire blank is subjected to stamping.
  • the hard zone can be cooled to 150 to 260 °C below its martensite transformation start temperature point (Ms) by any cooling method (for example, in-die cooling or air cooling).
  • the soft zone can be cooled by a cooling method that is the same as that of the hard zone, such as in-die cooling or air cooling.
  • the microstructure of the soft zone includes, by area: from 30% to 60% of austenite, from 40% to 70% of martensite or ferrite with a body-centered cubic crystal structure, and less than 3% of carbide.
  • the hard zone of the component obtained after the stamping i. e., the formed component
  • carbon partitioning treatment for example, heating the hard zone to 160 to 450 °C and maintaining the temperature for 1 to 10000 seconds to cause carbon to diffuse from supersaturated martensite to austenite, so that the austenite is enriched in carbon, thereby greatly improving the stability of the austenite and increasing its residual amount at room temperature.
  • a phase transformation from martensite to austenite occurs, thereby increasing the residual austenite content and improving the mechanical properties.
  • the same carbon partitioning treatment can be performed with the hard zone, or the carbon partitioning treatment is not performed (that is, the hard zone is separately subjected to carbon partitioning treatment).
  • the mechanical properties of the soft zone of the formed component can reach a tensile strength of 900 to 1500 MPa and an elongation of 15% or more.
  • a blank such as a steel sheet, a steel coil, or a blanked sheet or a preformed component is prepared.
  • the blank may be, for example, a blank having the composition and properties of the above steel material.
  • the regions of the blank to be formed as the soft zone and the hard zone are simultaneously heated and soaked for 0.5 to 60 minutes, wherein the region to be formed as the soft zone is heated to and kept at a temperature of 600 to 720 °C, and the region to be formed as the hard zone is heated to and kept at a temperature of 720 to 850 °C to transform its microstructure into austenite.
  • the microstructure of the soft zone includes, by area: from 30% to 60% of retained austenite, from 40% to 70% of martensite or ferrite with a body-centered cubic crystal structure, and less than 3% of carbide, wherein the retained austenite includes, by weight percent, 7% or more of Mn and 0.5% or more of carbon, while the hard zone contains a full austenitic structure and less than 3% of the carbide.
  • the hard zone can first be inductively heated to, for instance, 650 °C, while the soft zone is heated by induction to, for instance, 500 °C, and then the entire blank is placed in a furnace at a temperature of, for example, 780 °C to be heated.
  • the heating time required for heating from 650 °C to 780 °C is short, such as 40 seconds, and then the temperature is maintained for 20 seconds, for instance, to achieve homogenization of the austenite structure, so the entire blank is in the furnace at 780 °C for one minute, for example.
  • the soft zone cannot be heated to 780 °C in the furnace at 780 °C due to the its low temperature upon entry into the furnace.
  • the entire blank is subjected to stamping, and after the stamping, is cooled by any cooling method (in-die cooling or air cooling).
  • the hard zone is cooled to 150 to 260 °C below its martensite transformation start temperature point, and the soft zone is cooled to any temperature of -50 °C or more.
  • the formed component as a whole is cooled by the cooling method of the hard zone, and the microstructure and properties of the soft zone are also satisfactory.
  • the hard zone of the formed component is subjected to carbon partitioning treatment; for example, heating the hard zone to 160 to 450 °C and maintaining the temperature for 1 to 10000 seconds to cause carbon to diffuse from supersaturated martensite to austenite, so that the austenite is enriched in carbon, thereby greatly improving the stability of the austenite and increasing its residual amount at room temperature.
  • carbon partitioning treatment for example, heating the hard zone to 160 to 450 °C and maintaining the temperature for 1 to 10000 seconds to cause carbon to diffuse from supersaturated martensite to austenite, so that the austenite is enriched in carbon, thereby greatly improving the stability of the austenite and increasing its residual amount at room temperature.
  • a phase transformation from martensite to austenite occurs, thereby increasing the residual austenite content and improving the mechanical properties.
  • the same carbon partitioning treatment can be performed with the hard zone, or the carbon partitioning treatment is not performed (that is, the hard zone is separately subjected to carbon partitioning treatment).
  • the mechanical properties of the soft zone of the formed component can reach a tensile strength of 900 to 1500 MPa and an elongation of 15% or more.
  • a blank such as a steel sheet, a steel coil, or a blanked sheet or a preformed component is prepared.
  • the blank may be, for example, a blank having the composition and properties of the above steel material.
  • the entire blank is heated to 720 to 850 °C and soaked for 0.5 to 60 min so that it has a full austenite structure and less than 3% of carbide.
  • the entire blank is subjected to stamping, and after the stamping, is cooled by any cooling method (in-die cooling or air cooling).
  • any cooling method in-die cooling or air cooling.
  • the region to be formed as the hard zone is cooled to 150 to 260 °C below its martensite transformation start temperature point, and the soft zone is cooled to any temperature from -100 °C to 600 °C.
  • the formed component as a whole is cooled by the cooling method of the hard zone, and the microstructure and properties of the soft zone are also satisfactory.
  • the region to be formed as a hard zone of the formed component obtained after the stamping is subjected to carbon partitioning treatment; for example, heating the hard zone to 160 to 450 °C and maintaining the temperature for 1 to 10000 seconds to cause carbon to diffuse from supersaturated martensite to austenite, so that the austenite is enriched in carbon, thereby greatly improving the stability of the austenite and increasing its residual amount at room temperature.
  • a phase transformation from martensite to austenite occurs, thereby increasing the residual austenite content and improving the mechanical properties.
  • the same carbon partitioning treatment can be performed with the hard zone, or the carbon partitioning treatment is not performed (that is, the hard zone is separately subjected to carbon partitioning treatment).
  • the mechanical properties of the soft zone of the formed component can reach a tensile strength of 900 to 1500 MPa and an elongation of 15% or more.
  • the soft zone is separately heat treated again, heated to 600 to 720 °C, soaked for 0.5 to 60 minutes, and then cooled to room temperature in any manner (for example, air cooling).
  • the microstructure of the steel material includes, by area: from 30% to 60% of retained austenite, from 40% to 70% of martensite or ferrite with a body-centered cubic crystal structure, and less than 3% of carbide, wherein the retained austenite includes, by weight percent, 7% or more of Mn and 0.5% or more of carbon, and its mechanical properties reach a tensile strength of 900 to 1500 MPa and an elongation of 15% or more.
  • a blank such as a steel sheet, a steel coil, or a blanked sheet or a preformed component is prepared.
  • the blank may be, for example, a blank having the composition and properties of the above steel material.
  • the entire blank is heated to 720 to 800 °C and soaked for 0.5 to 60 min so that it has a full austenite structure and less than 3% of carbide.
  • the entire blank is subjected to stamping, and after the stamping, is cooled by any cooling method (in-die cooling or air cooling).
  • any cooling method in-die cooling or air cooling.
  • the region to be formed as the hard zone is cooled to 150 to 260 °C below its martensite transformation start temperature point, and the soft zone is cooled to any temperature of -100 °C or more.
  • the formed component as a whole is cooled by the cooling method of the hard zone, and the microstructure and properties of the soft zone are also satisfactory.
  • the soft zone is separately heat treated again; for instance, it is heated to 600 to 720 °C, soaked for 0.5 to 60 minutes, and then cooled to room temperature in any manner (for example, air cooling).
  • the microstructure of the steel material includes, by area: from 30% to 60% of retained austenite, from 40% to 70% of martensite or ferrite with a body-centered cubic crystal structure, and less than 3% of carbide, wherein the retained austenite includes, by weight percent, 7% or more of Mn and 0.5% or more of carbon, and its mechanical properties reach a tensile strength of 900 to 1500 MPa and an elongation of 15% or more.
  • the region to be formed as the hard zone of the formed component obtained after the stamping is subjected to carbon partitioning treatment; for example, heating the hard zone to 160 to 450 °C and maintaining the temperature for 1 to 10000 seconds to cause carbon to diffuse from supersaturated martensite to austenite, so that the austenite is enriched in carbon, thereby greatly improving the stability of the austenite and increasing its residual amount at room temperature.
  • a phase transformation from martensite to austenite occurs, thereby increasing the residual austenite content and improving the mechanical properties.
  • the same carbon partitioning treatment can be performed with the hard zone, or the carbon partitioning treatment is not performed (that is, the hard zone is separately subjected to carbon partitioning treatment).
  • the mechanical properties of the soft zone of the formed component can reach a tensile strength of 900 to 1500 MPa and an elongation of 15% or more.
  • the soft zone may be heated by means of flame heating, induction heating, laser heating, or the like, or the whole compnent enters the heating furnace to be treated by different heating temperatures in the soft and hard zones.
  • thermal radiation resistant baffles are placed above and below the hard zone, a heat-insulating material wraps the hard zone, or a heat-insulating coating is applied on the hard zone.
  • the heating processes of the hard zone and the soft zone are different (the soft zone is not fully austenitic-heated), but the stamping process is the same for the soft zone and the hard zone, so that no die modification is required and the process is reliable.
  • FIG. 5 is a schematic view of an automobile B-pillar comprising a hard zone and a soft zone made by the above-described process of the present invention, wherein the hard zone is a region of the upper end that needs to prevent collision intrusion, and the soft zone is a region of the lower end that needs to absorb collision energy.
  • the microstructure of the soft zone of the formed component includes, by area: from 30% to 60% of retained austenite, from 40% to 70% of martensite or ferrite with a body-centered cubic crystal structure, and less than 3% of carbide.
  • the mechanical properties of the soft zone are: a tensile strength of 900-1500 MPa, and an elongation greater than 15%.
  • the microstructure of the hard zone includes, by area, from 3% to 23% of retained austenite, from 0 to 2% of carbide, and the remainder being martensite.
  • the mechanical properties of the hard zone are: a yield strength greater than 1200 MPa, a tensile strength greater than 1600 MPa, and an elongation greater than 10%.

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  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
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Claims (8)

  1. Procédé de traitement pour l'obtention de propriétés de gradient, caractérisé par le fait qu'il comprend les étapes suivantes de :
    A. préparation d'une ébauche, division de l'ébauche en une région devant être formée comme une zone dure et une zone devant être formée comme une zone tendre, une teneur en carbone de l'ébauche étant comprise entre 0,22 et 0,48 % pour cent en poids, une teneur en manganèse de l'ébauche étant comprise entre 5 et 9,5 % pour cent en pourcentage en poids, 0,2 à 3,0 % pour cent en poids de Si+A1, et éventuellement au moins l'un parmi, en pourcentage en poids, Cr 0,001 % à 5 %, Mo 0,001 % à 2,0 %, W 0,001 % à 2 %, Ti 0,0001 % à 0,4 %, Nb 0,0001 % à 0,4 %, Zr 0,0001 % à 0,4 %, V 0,0001 % à 0,4 %, Cu 0,0005 % à 2 %, Ni 0,0005 % à 3 %, B 0,0001 % à 0,005 %, le reste étant Fe et des impuretés inévitables ;
    B. chauffage de la région devant être formée comme la phase dure jusqu'à 720 à 850 °C, de sorte que sa microstructure soit transformée en austénite, et en maintenant pendant ce temps une température de la région devant être formée comme la zone souple en dessous de 720 °C;
    C. estampage de l'ébauche entière et refroidissement de celle-ci par un quelconque procédé de refroidissement après l'estampage ;
    D. conduite d'un traitement de partitionnement de carbone sur la zone dure d'un composant obtenu après l'estampage pour diffuser du carbone de la martensite à l'austénite.
  2. Procédé de traitement pour l'obtention de propriétés de gradient selon la revendication 1, caractérisé en ce que, après l'étape A et avant l'étape B, le procédé comprend en outre les étapes de conduite d'un traitement de recuit de l'ébauche entière, c'est-à-dire, un chauffage de l'ébauche entière jusqu'à 600 à 720 °C, un trempage pendant 0,5 à 60 minutes, et ensuite un refroidissement de celle-ci jusqu'à la température ambiante par un quelconque procédé de refroidissement.
  3. Procédé de traitement pour l'obtention de propriétés de gradient selon la revendication 1, caractérisé en ce que, dans l'étape B, les régions de l'ébauche devant être formée en tant que zone souple et zone dure sont simultanément chauffées et trempées pendant 0,5 à 60 minutes, la région devant être formée en tant que zone souple étant chauffée jusqu'à, et maintenue à, une température de 600 °C et inférieure à 720 °C.
  4. Procédé de traitement pour l'obtention de propriétés de gradient selon l'une quelconque des revendications 1 à 3, caractérisé en ce que, dans l'étape C, la zone dure est refroidie jusqu'à 150 à 260 °C en dessous de son point de température de début de transformation de martensite, et la zone souple est refroidie jusqu'à une quelconque température de -100 °C ou plus.
  5. Procédé de traitement pour l'obtention de propriétés de gradient selon l'une quelconque des revendications 1 à 3, caractérisé en ce que, dans l'étape D, la zone dure est chauffée jusqu'à 160 à 450 °C et trempée pendant 1 à 10 000 secondes.
  6. Procédé de traitement pour l'obtention de propriétés de gradient selon l'une quelconque des revendications 1 à 3, caractérisé en ce que, dans l'étape D, la zone souple est traitée par le même traitement de partitionnement de carbone conduit dans la zone dure, ou n'est pas traitée.
  7. Composant doté de propriétés de gradient, caractérisé en ce que le composant est fabriqué par le procédé de traitement selon l'une quelconque des revendications 1 à 6, la microstructure de la zone souple du composant comprenant, par surface : 30 % à 60 % d'austénite conservée, 40 % à 70 % de martensite ou de ferrite dotée d'une structure cristalline cubique centrée et moins de 3 % de carbures, et les propriétés mécaniques de la zone souple étant : une résistance en traction de 900 à 1 500 MPa et une élongation supérieure à 15 % ; la microstructure de la zone dure comprenant, par surface : 3 % à 23 % d'austénite conservée, 0 à 2 % de carbures et le reste étant de la martensite, les propriétés mécaniques de la zone dure étant : une limite d'élasticité supérieure à 1 200 MPa, une résistance en traction supérieure à 1 600 MPa et une élongation supérieure à 10 %.
  8. Composant selon la revendication 7, caractérisé en ce que le composant comprend un pilier B, un pilier A et une poutre longitudinale avant d'une automobile.
EP16905967.2A 2016-06-20 2016-07-20 Procédé de traitement permettant d'obtenir des performances progressives et élément associé Active EP3473735B1 (fr)

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CN201610440901.1A CN106011418B (zh) 2015-12-04 2016-06-20 用于获得梯度化性能的处理工艺及其构件
PCT/CN2016/090629 WO2017219427A1 (fr) 2015-12-04 2016-07-20 Procédé de traitement permettant d'obtenir des performances progressives et élément associé

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US10619223B2 (en) 2016-04-28 2020-04-14 GM Global Technology Operations LLC Zinc-coated hot formed steel component with tailored property
WO2019222950A1 (fr) 2018-05-24 2019-11-28 GM Global Technology Operations LLC Procédé pour améliorer à la fois la résistance et la ductilité d'un acier trempé sur presse
US11612926B2 (en) 2018-06-19 2023-03-28 GM Global Technology Operations LLC Low density press-hardening steel having enhanced mechanical properties
US11530469B2 (en) 2019-07-02 2022-12-20 GM Global Technology Operations LLC Press hardened steel with surface layered homogenous oxide after hot forming
CN114589236A (zh) * 2020-12-07 2022-06-07 上海赛科利汽车模具技术应用有限公司 铝热成型变强度零件的制造工艺及制造装置

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US5972134A (en) * 1997-10-02 1999-10-26 Benteler Ag Manufacture of a metallic molded structural part
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CZ307654B6 (cs) * 2011-04-04 2019-01-30 Západočeská Univerzita V Plzni Způsob výroby plechového ocelového výlisku s lokálně modifikovanými vlastnostmi
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CN103409613B (zh) * 2013-08-30 2014-09-10 上海交通大学 实现热冲压制件梯度性能分布的方法
CN106687607A (zh) * 2014-09-22 2017-05-17 麦格纳国际公司 包括产生局部软区的热磁回火工艺的用于制造结构部件的方法
CN104668326B (zh) * 2015-03-05 2016-08-24 山东大王金泰集团有限公司 一种高强度钢材零部件性能梯度化分布的热冲压方法
CN104729278B (zh) * 2015-03-30 2016-09-28 盐城科奥机械有限公司 运动托辊式厢式加热炉及热成形分段强化工艺
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