US20210040574A1 - Method of production of steel sheet semi-finished products by press hardening with locally-modified structure in spots for welding - Google Patents

Method of production of steel sheet semi-finished products by press hardening with locally-modified structure in spots for welding Download PDF

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Publication number
US20210040574A1
US20210040574A1 US16/584,264 US201916584264A US2021040574A1 US 20210040574 A1 US20210040574 A1 US 20210040574A1 US 201916584264 A US201916584264 A US 201916584264A US 2021040574 A1 US2021040574 A1 US 2021040574A1
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US
United States
Prior art keywords
semi
finished product
spots
temperature
welding
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Abandoned
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US16/584,264
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English (en)
Inventor
Bohuslav Masek
Ctibor Stadler
Vjaceslav Georgiev
Jiri Hammerbauer
Radek Holota
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University of West Bohemia
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University of West Bohemia
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Assigned to ZAPADOCESKA UNIVERZITA V PLZNI reassignment ZAPADOCESKA UNIVERZITA V PLZNI ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: GEORGIEV, VJACESLAV, Hammerbauer, Jiri, Holota, Radek, MASEK, BOHUSLAV, STADLER, CTIBOR
Publication of US20210040574A1 publication Critical patent/US20210040574A1/en
Abandoned legal-status Critical Current

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    • 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
    • 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
    • C21D1/62—Quenching devices
    • C21D1/667—Quenching devices for spray 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
    • 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
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
    • 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

Definitions

  • This invention relates to a method of producing steel sheet semi-finished products by press hardening with locally-modified structure in spots for welding.
  • Materials for manufacturing steel sheet semi-finished products may include high-strength MnB steels, which possess a martensitic microstructure after processing. Such materials may be useful in car body construction. These materials may be produced by press hardening, which is a method of hardening in a tool. Therefore, these materials may show good strength, but may also exhibit a relatively poor ability to undergo plastic deformation, which has highly adverse consequences in welded structures, namely spot-welded joints. The risk of the structure failing under external loading, arising for instance from a car collision, increases with strength. Fractures driven by low energy may occur in welds or in adjacent regions. This risk can be reduced by local annealing of the material in and/or adjacent to locations of welds.
  • Patent Application Publication No. US20190226045A1 describes a composition and method of production of a sheet of ferritic steel by annealing.
  • One or more embodiments of the present invention generally concern a method for producing steel sheet semi-finished products by press hardening with locally-modified structure in spots for welding.
  • the method involves heating a steel semi-finished product to a temperature at which complete transformation of ferritic-pearlitic structure to austenite occurs.
  • the semi-finished product is cooled locally in spots for welding to a temperature close to the martensite finish (M f ), after which heat conducted from the surroundings causes the temperature in these spots to rise to a temperature, at which a hardening structure becomes tempered, while the semi-finished product is transferred to a tool, in which the sheet blank is formed into a drawn part which, at the same time, is hardened in the tool.
  • the sheet semi-finished product is retrieved from the tool once the required temperature is reached.
  • the method may involve heating a steel semi-finished product to a temperature within the range of 800° C. to 980° C., where the energy supplied for heating and austenitizing is used in part for tempering the hardened spots in locations of future welds.
  • the method involves locally and intensively cooling a steel semi-finished product with a cooling medium in spots for welding for 1 to 10 seconds.
  • This invention generally relates to a method for producing steel sheet semi-finished products with a locally modified structure. More particularly, a method for producing steel sheet semi-finished products is provided that involves press hardening with locally-modified structure in spots for welding, wherein a steel blank is heated to a temperature at which ferritic-pearlitic structure completely transforms to austenite.
  • the steel semi-finished product is initially heated to a temperature within the range of 800° C. to 980° C. or 930° C. to 960° C.
  • the semi-finished product is cooled locally, in spots to be welded, to a temperature close to the martensite finish temperature (M f ), i.e., only in the locations where welds are to be made.
  • M f martensite finish temperature
  • local cooling of the steel semi-finished product in spots to be welded takes between 1 and 10 seconds. Cooling may be performed during transfer to a tool.
  • This method of cooling produces hardened spots in the semi-finished product, whereas the temperature of the remaining material is above the temperature of transformation to hardening structures, martensite and possibly bainite. Cooling is preferably affected by means of nozzles through which pressurized cooling medium is supplied to the spots to be cooled. A shroud guides the medium away from the cooled spot. The shroud also secures that a defined spot is cooled. The intensity of the process can be enhanced by providing cooling on both faces of the sheet blank.
  • a contact-based cooling method may be used, which involves pressing cooled blocks against the semi-finished product surface. Cooling is ended after the spot reaches a temperature at which a hardening structure forms. Intensive cooling dissipates heat energy only from the area to which it is applied, i.e., the spot where a weld is to be made. Cooling also removes the transformation energy released during transformation of austenite to hardening structure.
  • Heat conducted from the surroundings of the cooled spot reheats the material in the spot, which initiates annealing of its hardening structure. Since the temperature of the blank has decreased, the cooled spots cannot reaustenitize because the temperature in their surroundings is now below the Ara temperature (i.e., the temperature when the austenite begins to cool down to reverse to become ferrite again), and, therefore, the spots cannot be hardened again in the process.
  • Ara temperature i.e., the temperature when the austenite begins to cool down to reverse to become ferrite again
  • the heated blank is then placed into a tool and deep drawing is performed, at the end of which the semi-finished product rests against a mould which removes heat from the semi-finished product, thereby causing austenite to transform to martensite.
  • the resulting temperature gradient causes some of this energy to enter the undercooled spot, where this energy contributes to tempering of fresh martensite, which gradually changes to tempered martensite or bainite, i.e., ferrite and carbides.
  • the hardened press-formed part is removed from the mould and left to cool to room temperature in air.
  • the press-formed part can be removed at a different temperature, such as room temperature or at higher temperatures, when worked in a heated tool.
  • FIG. 1 shows a sheet semi-finished product being cooled in spots where welds are to be made
  • FIG. 2 shows cooling provided on both faces of the sheet semi-finished product.
  • Steel blank P made of a sheet stock of 22MnB steel of 1.5 mm thickness is placed into a continuous heating furnace. It passes through the furnace for five minutes and heats up to 950° C., at which the initial ferritic-pearlitic structure transforms to austenite. Once this heating austenitizing process ends, the semi-finished product P is pushed out from the furnace and is set, with the aid of guides and stops and after two seconds, in an exactly-defined position in the cavity of a cooling fixture. At the same time, it is approached by a cooling head fitted with cooling nozzles 1 . Over 2.5 seconds, the spots to be welded are cooled with water M pressurized at 6 bar.
  • the cooling medium M is screened from the surroundings by a concentric shroud 2 whose diameter is 12 mm.
  • the shroud 2 also guides the cooling medium M away from the spot being cooled.
  • the semi-finished product P is transferred to a tool by means of a handling device. 5 to 7 seconds after the end of cooling, the tool shuts and shapes the sheet semi-finished product P by plastic deformation into a drawn part, which is hardened in the tool at the same time.
  • the semi-finished product P is then removed from the tool and cooled to room temperature.
  • the sheet semi-finished product P is removed from the furnace, placed directly in the guides of the tool, while a cooling head 1 is positioned between the top of the mould and the blank holder, and immediately after the sheet P is set inside the mould, the cooling head performs the above-described cooling by pressing annular cooling blocks against the surface of the semi-finished product.
  • the cooling head is then withdrawn from the mould, and there is a 5 to 10 second pause followed by deep drawing and hardening in the tool.
  • the semi-finished product P is retrieved from the tool.
  • the semi-finished product P can be pushed out from the furnace and transferred by handling grippers into a tool.
  • the grippers are fitted with the above-described nozzles, which cool the spots by supplying a cooling medium for 3 seconds in the course of the transfer.
  • the spots are then reheated by heat entering from the surroundings by conduction.
  • the semi-finished product is positioned inside the tool with the use of guides and stops, after which the sheet semi-finished product P is shaped by plastic deformation into a drawn part and is hardened in the tool.
  • the semi-finished product P is then removed from the tool and cooled to room temperature.
  • the grippers do not include nozzles but cooled copper blocks which, when the semi-finished product is gripped by the grippers, are pressed by the grippers against the spots in the semi-finished product and achieve the desired cooling by heat dissipation over 4 seconds. The process then proceeds in the same fashion as the previous case.
  • the invention can find broad use in the production of high-strength steel semi-finished products by means of press hardening, where improvement of mechanical properties in regions adjacent to weld joints is required.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Articles (AREA)
US16/584,264 2019-08-07 2019-09-26 Method of production of steel sheet semi-finished products by press hardening with locally-modified structure in spots for welding Abandoned US20210040574A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CZPV2019-513 2019-08-07
CZ2019-513A CZ308209B6 (cs) 2019-08-07 2019-08-07 Způsob výroby plechových ocelových polotovarů metodou press-hardening s lokálně modifikovanou strukturou v místech určených pro svary

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CZ (1) CZ308209B6 (cs)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11904373B2 (en) 2020-10-30 2024-02-20 Zapadoceska Univerzita V Plzni Modification of a deep-drawing sheet blank for electric resistance heating

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4795486B2 (ja) * 2009-06-22 2011-10-19 新日本製鐵株式会社 鋼板の熱間プレス成形方法、鋼板の熱間プレス成形装置、及び鋼成形部材

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CZ307654B6 (cs) * 2011-04-04 2019-01-30 Západočeská Univerzita V Plzni Způsob výroby plechového ocelového výlisku s lokálně modifikovanými vlastnostmi
DE102013002625B4 (de) * 2013-02-15 2015-03-05 Audi Ag Greifervorrichtung für den Transport erwärmter Blechplatinen, sowie Verfahren zum Herstellen von warmumgeformten und/oder pressgehärteten Blechformteilen
CZ305697B6 (cs) * 2014-06-30 2016-02-10 Západočeská Univerzita V Plzni Způsob výroby ocelových dílů z plechu tažených zatepla

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4795486B2 (ja) * 2009-06-22 2011-10-19 新日本製鐵株式会社 鋼板の熱間プレス成形方法、鋼板の熱間プレス成形装置、及び鋼成形部材

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
JP 4795486 machine translation (Year: 2011) *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11904373B2 (en) 2020-10-30 2024-02-20 Zapadoceska Univerzita V Plzni Modification of a deep-drawing sheet blank for electric resistance heating

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CZ308209B6 (cs) 2020-02-26

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