US20160107222A1 - Method for Warm Forming of Super High Tensile Strength Steel Sheet - Google Patents

Method for Warm Forming of Super High Tensile Strength Steel Sheet Download PDF

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Publication number
US20160107222A1
US20160107222A1 US14/692,334 US201514692334A US2016107222A1 US 20160107222 A1 US20160107222 A1 US 20160107222A1 US 201514692334 A US201514692334 A US 201514692334A US 2016107222 A1 US2016107222 A1 US 2016107222A1
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United States
Prior art keywords
steel sheet
tensile strength
high tensile
super high
strength
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Abandoned
Application number
US14/692,334
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English (en)
Inventor
Young Tae Kim
Moon Ki Bae
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Hyundai Motor Co
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Hyundai Motor Co
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Publication date
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Assigned to HYUNDAI MOTOR COMPANY reassignment HYUNDAI MOTOR COMPANY ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: BAE, MOON KI, KIM, YOUNG TAE
Publication of US20160107222A1 publication Critical patent/US20160107222A1/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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
    • B21J1/00—Preparing metal stock or similar ancillary operations prior, during or post forging, e.g. heating or cooling
    • B21J1/06—Heating or cooling methods or arrangements specially adapted for performing forging or pressing operations
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
    • B21C37/00—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape
    • B21C37/02—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape of sheets
    • 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 method for warm forming of a super high tensile strength steel sheet by simultaneously improving strength and formability.
  • the super high tensile strength steel sheet refers to a steel material that may have greater tensile strength than a high tensile strength steel sheet having a tensile strength of about 50 kg/mm 2 and may have further improved strain hardening, quenching, annealing, tempering, normalizing, precipitation hardening, grain refinement, solid solution strengthening, and the like using various strengthening mechanisms.
  • the super high tensile strength steel sheet may have reduced formability that is in inverse proportion to the improvement of the strength.
  • the super high tensile strength steel sheet may not be applied to parts having a complicated shape, parts having a deep forming depth, or the like due to reduced formability of the super high tensile strength steel sheet, and thus, many attempts to improve the formability of the super high tensile strength steel sheet by heating have been conducted.
  • the super high tensile strength steel sheet may not be used as the vehicle parts due to the reduction in strength , a twist of a member, and a dimensional change thereof.
  • the super high tensile strength steel sheet for vehicle parts has been manufactured by a hot stamping method which may improve formability by heating a steel sheet at a temperature of about 900° C. or greater. Accordingly, the steel sheet may be formed and obtain high strength by rapidly cooling a steel sheet simultaneously with performing press forming using a special mold in which cooling water is circulated.
  • the hot stamping method may provide the steel sheet with an improved strength of about 150 K or greater by transforming an austenite phase of a steel sheet into a martensite phase.
  • the hot stamping method may not cause a spring back even after extracting the steel sheet and may further prevent a dimension of parts from changing, since the parts within the mold are completely cooled in a fixed state.
  • the hot stamping method may have low productivity to a level of 2 SPM, because a specific mold in which the cooling water is circulated should be used, laser trimming of a draw panel should be performed, and the steel sheet is completely cooled within the mold.
  • a heating temperature of the steel sheet may increase to an A 3 transformation temperature or greater of austenite, when the super high tensile strength steel sheet is processed by the precipitation hardening, strengthening effect of the steel sheet due to precipitates may be reduced.
  • re-crystallization may occur by high-temperature heat applied to the steel sheet, and thus most of the strengthening effects may be reduced and a lattice structure and a lattice constant may be deformed depending on a change in a crystalline phase, and as a result, a dimension of the steel sheet may also be changed.
  • the hot stamping method which has been currently rapidly applied may not be considered as an optimal method for manufacturing a super high tensile strength steel sheet for vehicle parts. Therefore, the present invention may provide a method to solve the above-mentioned problems.
  • a CERTAIN method of manufacturing a steel strip for vehicle reinforcement parts has been reported in “Steel Strip For The Automotive Reinforcement Parts And Method Of Manufacturing Thereof(KR 10-0530068)”.
  • the vehicle reinforcement parts manufactured by the method including performing homogenization treatment on aluminum killed steel at 1050 to 1300° C., hot rolling thereon at a finishing rolling temperature condition of 850 to 950 ° C. which is just above an Ar3 transformation point, winding it at a temperature range of 650 to 800 ° C., and performing cold rolling thereon at a cold reduction ratio of 30 to 80% may have improved heat treatment properties.
  • a quenched steel sheet, parts from the steel sheet and the method of manufacturing thereof have been developed as reported in “Quenched Steel Sheet Having Ultra High Strength, Parts Made Of It And The Method For Manufacturing Thereof(KR 10-0878614)”.
  • the quenched steel sheet may have improved tensile strength by heat treatment hardening and then improved yield strength after suffering from painting heat treatment.
  • the present invention provides a method for warm forming of a super high tensile strength steel sheet.
  • the method may increase productivity and accurate strength, by securing thermal structure stability and dimensional stability when the super high tensile strength steel sheet is heated and formed.
  • a method for warm forming of a super high tensile strength steel sheet may include: heating a steel sheet having a single-phase structure at A l transformation temperature or less; pressing, in a mold, the heated steel sheet to be formed in a predetermined shape; and extracting and cooling the pressed steel sheet.
  • the steel sheet may be a steel sheet having a single-phase martensite structure or a steel sheet having a single-phase ferrite structure.
  • the steel sheet having the single-phase ferrite structure may have improved strength by precipitation hardening.
  • a temperature of the mold used in the pressing may be controlled by heat transferred from the heated steel sheet without additional heating and cooling.
  • FIG. 1 is an exemplary graph illustrating elongation and strength of a steel sheet having a multi-phase structure strengthened by a strengthening mechanism for each temperature in the related art
  • FIG. 2 is an exemplary graph illustrating that a strength of the steel sheet is changed when the steel sheet having the multi-phase structure and an exemplary steel sheet having a single-phase structure according to an exemplary embodiment of the present invention are heated at about 400° C. to 700° C. and then cooled; and
  • FIG. 3 is an exemplary graph illustrating a change in temperature, a change in strength, and a change in elongation of an exemplary super high tensile strength steel sheet at the time of warm forming according to the exemplary embodiment of the present invention.
  • vehicle or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum).
  • a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles.
  • the terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting of the invention.
  • the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.”
  • a method for warm forming of a super high tensile strength steel sheet described below is an exemplary embodiment of the present invention, and is not limited to the exemplary embodiment but may be implemented in various forms.
  • the strengthening mechanism When the strengthening mechanism is applied to a steel sheet, a phase change and a structure change of the steel sheet may internally occur and thus the strength of the steel sheet may be sharply increased, but the formability may be reduced in inverse proportion to the strength and have inappropriate characteristics to manufacture parts having a complicated shape. Accordingly, to apply the steel sheet manufactured by the strengthening mechanism to the parts having a complicated shape, the formability may be improved by a separate heating process. That is, parts having a predetermined shape may be manufactured by heating the steel sheet at high temperature to increase the elongation of the steel sheet and then performing the press forming thereon.
  • the present invention provides a method for warm forming of a super high tensile strength steel sheet.
  • the strengthening mechanism and the lattice structure may not react sensitively to temperature and additional cooling process such as quenching or water cooling may not be used.
  • the method for warm forming of a super high tensile strength steel may include a heating process, a press process, and a cooling process.
  • the heating process may be a process of heating the steel sheet to improve the formability of the steel sheet and setting the heating temperature of the steel sheet to be A 1 transformation temperature or less.
  • Mechanical physical properties of the steel sheet may be sharply changed depending on the heating temperature. For example, when the temperature of the steel sheet increases, vibration energy of the lattice may be increased and thus an elasto-plastic behavior may be changed to a viscoelastic behavior and thus the elongation may be increased as illustrated in FIG. 1 .
  • FIG. 1 is an exemplary graph illustrating the elongation and the strength of the steel sheet which has a multi-phase structure strengthened by the strengthening mechanism at each temperature of room temperature, about 300° C., about 400° C., about 500° C., and about 600° C., respectively.
  • the steel sheet when the temperature of the steel sheet is room temperature, the steel sheet may have a strength of about 1200 MPa. As the temperature increases, the strength may be reduced and the elongation may be increased in inverse proportion to the strength.
  • the increase in elongation of the steel sheet may mean improvement of formability, and thus, when the formality is improved, the parts having a complicated shape may be easily manufactured by the press forming.
  • the steel sheet having the multi-phase structure in which phases such as ferrite, austenite, and martensite are mixed may deteriorate from a phase change, a structure change, and a change in a lattice structure, and the like as temperature increases. As the temperature of the steel sheet increases, the strength may be reduced, thereby failing to solve technical problems in the related art. Therefore, in the heating process according to the exemplary embodiment of the present invention, the steel sheet having a single-phase structure, not the multi-phase structure, may be applied. For example, the steel sheet having the single-phase structure may be heated to a A 1 transformation temperature or less.
  • FIG. 2 is an exemplary graph illustrating that the strength of the steel sheet is changed when the steel sheet having the multi-phase structure and the steel sheet having the single-phase structure are heated at about 400° C. to 700° C. and then cooled.
  • the final strength of the cooled steel sheet may not be changed substantially compared to initial strength before the steel sheet is heated.
  • a final strength of the steel sheet having the multi-phase structure may be sharply reduced after being cooled.
  • both the strength and the formability may be improved.
  • heat may be applied until the A 1 transformation temperature or less of the steel sheet to prevent the dimensional stability from reducing due to the phenomenon of the phase change, the structure change, the change in the lattice structure, the change in the lattice constant, and the like which may be caused when the high heat of the A 1 transformation temperature or greater applied to the steel sheet having the single-phase structure. Further, reduction of the strength due to reduced strengthening mechanism may be prevented.
  • the steel sheet having the single-phase structure may have a single-phase structure of martensite or ferrite to provide improved strength required for the super high tensile strength steel sheet.
  • the martensite may have a needle-shaped structure and substantially improved strength and thus may be suitably used for the super high tensile strength steel sheet.
  • the ferrite may have relatively less strength than the martensite but may have improved strength by various strengthening mechanisms, and thus, may be applied to the method for warm forming of the super high tensile strength steel sheet according to the exemplary embodiment of the present invention.
  • a steel sheet of which the strength is improved by the precipitation hardening may be applied among the steel sheets having the ferrite structure, and thus, the improved strength required for the super high tensile strength steel sheet may be obtained. Since the heating temperature is also equal to or less than the A l transformation temperature, the precipitation hardening effect may remain without deterioration.
  • the press process may form the steel sheet heated by the heating process in a predetermined shape. In particular, when the method for warm forming according to the exemplary embodiment of the present invention is applied, since the strength, the phase, the structure, the lattice structure, the lattice constant, and the like of the steel sheet are not changed, the quenching in the related art may not be performed.
  • the press process may use various methods for forming a steel sheet.
  • cooling may not be performed at the time of the press forming, and thus cooling time may not be required.
  • the temperature of the mold may be controlled by heat transferred from the steel sheet heated without additional heating and cooling, and thus the generally used mold may be used, unlike a specific mold including cooling water as used in the related art.
  • the air cooling process may extract and then cool the steel sheet from the press process.
  • the steel sheet may be extracted from inside of the mold after the steel sheet is cooled to prevent the shape of the pressed steel sheet from changing and the steel sheet from reducing.
  • extracting and cooling the steel sheet may be completed without performing additional cooling after the press process.
  • the strength, the phase, the structure, the lattice structure, the lattice constant, and the like of the steel sheet may not be changed, there is no need of using the cooling method such as cooling water and quenching that requires substantial period of time .
  • the air cooling may be applied effectively.
  • the steel sheet may be cooled by air as being immediately extracted without waiting, and as a result, a production efficiency may be substantially improved.
  • FIG. 3 is an exemplary graph illustrating the change in temperature, the change in strength, and the change in elongation of an exemplary super high tensile strength steel sheet according to the exemplary embodiment of the present invention during an exemplary warm forming process at a temperature range of 200° C. to 600° C. according to the exemplary embodiment of the present invention.
  • the temperature may be maintained less than the A 1 transformation temperature of the applied steel sheet.
  • the strength may be gradually reduced to a predetermined level and the elongation may be improved in inverse proportion thereto.
  • the temperature of the steel sheet may be substantially reduced. Since the additional heating apparatus is not mounted in the mold and thus the temperature of the mold is in a less state than that of the heated mold, when the heated steel sheet contacts the mold, the temperature may be sharply reduced. Further, to the contrary, the reduced strength may be increased again and thus the predetermined level may be maintained, and the elongation may be substantially reduced and then the predetermined level may be maintained.
  • the elongation may be substantially reduced and then maintained at the predetermined level at the time of the press process due to the temperature of the steel sheet that may be sharply reduced and then maintained at the predetermined level. As such, the elongation may be reduced and thus the pressed steel sheet may not be easily deformed and the shape of the steel sheet may be maintained.
  • the temperature of the steel sheet may be reduced to the room temperature over time, and to the contrary, the strength may be further increased and the elongation may be reduced, and thus the further forming may not be performed.
  • improved strength of the steel sheet may be obtained simultaneously with improved formability when forming the parts having a complicated shape thereby improving the productivity.
  • the present invention may provide various advantages as follows.
  • the present invention may improve the productivity since phase change may not occur and additional cooling process may not be required.
  • the present invention may perform the heating at the A 1 transformation temperature or less to minimize the waste of heating time and energy.
  • the present invention may improve strength while manufacturing the parts having a complicated shape.
  • the present invention may manufacture the super high tensile strength steel sheet having substantially improved dimensional stability and thermal structural stability.
  • the present invention may maintain the processing hardening effect applied to the steel sheet.

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  • 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)
  • Shaping Metal By Deep-Drawing, Or The Like (AREA)
  • Mounting, Exchange, And Manufacturing Of Dies (AREA)
US14/692,334 2014-10-16 2015-04-21 Method for Warm Forming of Super High Tensile Strength Steel Sheet Abandoned US20160107222A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
KR10-2014-0139781 2014-10-16
KR1020140139781A KR20160045177A (ko) 2014-10-16 2014-10-16 초고장력 강판의 온간 성형 방법

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US20160107222A1 true US20160107222A1 (en) 2016-04-21

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US14/692,334 Abandoned US20160107222A1 (en) 2014-10-16 2015-04-21 Method for Warm Forming of Super High Tensile Strength Steel Sheet

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US (1) US20160107222A1 (de)
JP (1) JP2016078119A (de)
KR (1) KR20160045177A (de)
CN (1) CN106191406A (de)
DE (1) DE102015208752A1 (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20180171423A1 (en) * 2016-12-15 2018-06-21 Hyundai Motor Company Three-Dimensional Cooling Type Hot-Stamping Method and System and Vehicle Structural Member Manufactured by the Same

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB201713741D0 (en) * 2017-08-25 2017-10-11 Imp Innovations Ltd Fast warm stamping method for metal sheets
KR101880115B1 (ko) 2018-03-20 2018-07-19 대우공업 (주) 스프링백 현상을 억제시킨 냉간 프레스 성형 시스템 및 방법
KR102370994B1 (ko) 2021-04-28 2022-03-07 대우공업 (주) 바우싱거 효과 및 아이어닝 기법을 활용한 딥 드로잉 프레스 성형장치 및 딥 드로잉 프레스 성형방법

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013132821A1 (ja) * 2012-03-06 2013-09-12 Ｊｆｅスチール株式会社 温間プレス成形方法および自動車骨格部品

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100530068B1 (ko) 2001-12-17 2005-11-22 주식회사 포스코 열처리특성이 우수한 자동차 보강재용 냉연강판과 그제조방법
KR100878614B1 (ko) 2005-12-01 2009-01-15 주식회사 포스코 열처리 경화형 초고강도 강판, 이를 이용한 열처리 경화형부재와 그 제조방법

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013132821A1 (ja) * 2012-03-06 2013-09-12 Ｊｆｅスチール株式会社 温間プレス成形方法および自動車骨格部品
US20150064052A1 (en) * 2012-03-06 2015-03-05 Jfe Steel Corporation Warm press forming method and automobile frame component

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20180171423A1 (en) * 2016-12-15 2018-06-21 Hyundai Motor Company Three-Dimensional Cooling Type Hot-Stamping Method and System and Vehicle Structural Member Manufactured by the Same
US11078551B2 (en) * 2016-12-15 2021-08-03 Hyundai Motor Company Three-dimensional cooling type hot-stamping method and system and vehicle structural member manufactured by the same

Also Published As

Publication number Publication date
CN106191406A (zh) 2016-12-07
KR20160045177A (ko) 2016-04-27
DE102015208752A1 (de) 2016-04-21
JP2016078119A (ja) 2016-05-16

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