EP2665837A1 - Method to produce a hot formed part, and part thus formed - Google Patents

Method to produce a hot formed part, and part thus formed

Info

Publication number
EP2665837A1
EP2665837A1 EP12700452.1A EP12700452A EP2665837A1 EP 2665837 A1 EP2665837 A1 EP 2665837A1 EP 12700452 A EP12700452 A EP 12700452A EP 2665837 A1 EP2665837 A1 EP 2665837A1
Authority
EP
European Patent Office
Prior art keywords
blank
hot forming
temperature
forming press
heated
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.)
Ceased
Application number
EP12700452.1A
Other languages
German (de)
French (fr)
Inventor
Willem Cornelis Verloop
Marc Jacco VAN GENDEREN
Ronald Theodoor Van Tol
Guido Cornelis Hensen
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
Priority to EP12700452.1A priority Critical patent/EP2665837A1/en
Priority to EP14163594.6A priority patent/EP2754723A3/en
Publication of EP2665837A1 publication Critical patent/EP2665837A1/en
Ceased legal-status Critical Current

Links

Classifications

    • 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
    • B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
    • B21J3/00—Lubricating during forging or pressing
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
    • 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

Abstract

The invention relates to a. method for manufacturing a coated steel part having very high mechanical properties using hot forming techniques. According to the invention, the method comprises the following steps: • providing a coated steel blank comprising a steel substrate with a coating layer • heating the blank to a temperature of 800° C or more in a furnace • transporting the heated blank from the furnace and placing the blank in a hot forming press • hot forming the blank in the press to form the coated steel part • quenching the coated steel part wherein the heated blank has a temperature of at most 780° C when placed in the hot forming press. The invention also relates to a hot formed part manufactured using the method according to the invention.

Description

METHOD TO PRODUCE A HOT FORMED PART, AND PART THUS
FORMED
The invention relates to a method for manufacturing a coated steel part having very high mechanical properties using hot forming techniques, and a part thus formed.
Hot forming of parts is well-known in the art and is used in the automotive industry to produce complex parts with a reduced weight.
It has been found that hot forming of parts for instance using Zn or Zn alloy coated steel is susceptible to the forming of micro-cracks due to the hot forming process, wherein the micro-cracks are present not only in the coating, but also in the part itself. The micro-cracks in the hot formed part are seen as undesirable.
It is an object of the invention to provide a method for manufacturing a coated steel part having very high mechanical properties using hot forming techniques that avoid or at least diminish the occurrence of micro-cracks in the hot formed part.
It is another object of the invention to provide a method for manufacturing a coated steel part having very high mechanical properties using hot forming techniques that is faster than the known methods.
According to the invention one or more of the above objects are reached using a method for manufacturing a coated steel part having very high mechanical properties using hot forming techniques, comprising the following steps:
• providing a coated steel blank comprising a steel substrate with a coating layer
• heating the blank to a temperature of 800° C or more in a furnace
• transporting the heated blank from the furnace and placing the blank in a hot forming press
· hot forming the blank in the press to form the coated steel part
• quenching the coated steel part
wherein the heated blank has a temperature of at most 780° C when placed in the hot forming press.
The inventors have found that the forming of micro-cracks is strongly influenced by the temperature of the blank when it is placed in the hot forming press and the temperature at which the hot formed part is formed in the hot forming press. At high temperatures, such as used in the art, many micro-cracks are formed in the substrate, which often have a depth of more than 10 μηι. Lowering the temperature at which the coated blank is placed in the hot forming press reduced the micro-cracks in number and depth. It has been found that cooling the heated blank to a temperature of at most 780° C when placed in the hot forming press already reduces the number and depth of the micro-cracks to a considerable extent.
Preferably, the blank is heated to a temperature of 850° C or more, more preferably a temperature of 880° C or more, and still more preferably to a temperature of 900° C or more. Usually the coated blank is heated to a temperature such that the substrate is fully and homogenously austenitised before it is placed in the hot forming press.
According to a preferred embodiment the heated blank has a temperature of at least 500° C when placed in the hot forming press, more preferably a temperature of at least 600° C, and still more preferably a temperature of at least 650° C. The temperature of the blank can be below the Arl temperature when placed into the blank, but preferably the blank is not cooled too far because the cooling rate is very critical at low temperatures.
Preferably the heated blank has a temperature of at most 740° C when placed in the hot forming press, and more preferably a temperature of at most 700° C. The temperature of the blank should be as low as possible to prevent (large) micro-cracks. Thus, it is optimal if the temperature of the blank is between 650° C and 700° C when the blank is placed in the hot forming press.
According to a preferred embodiment the heated blank is at least partially cooled between the furnace and the hot forming press by forced cooling, preferably with an average cooling velocity of at least 30° C/sec, more preferably with an average cooling velocity of at least 40° C/sec, still more preferably with an average cooling velocity of at least 60° C/sec, most preferably with an average cooling velocity of at least 80° C/sec. Forced cooling effectively reduces the blank temperature at a cooling rate that is higher than the cooling rate obtainable when the blank is cooled in open air. A high cooling velocity is preferred, so the time in which the blank is kept between the furnace and the hot forming press can be as short as possible. This is advantageous so as to realise desired high strength of the formed part and so as to reduce oxidation of the coating on the blank. Preferably the heated steel blank is transported between the furnace and the hot forming press in a time span of at most 10 seconds, more preferably in a time span of at most 8 seconds, and still more preferably in a time span of at most 6 seconds. A short transportation time is also advantageous to reduce the cycle time to produce a hot formed part.
According to a preferred embodiment the heated blank is cooled between the furnace and the hot forming press using accelerated cooling making use of gas, such as cooling with forced air flow, cooling with forced N2 flow, or cooling with forced C02 flow or cooled C02 using solid C02. Use of a gas flow to cool the blank provides a high cooling capacity which can be easily controlled.
According to another preferred embodiment the heated blank is cooled between the furnace and the hot forming press using liquid or solid material, such as liquid or solid C02 particles or metal cooling plates. Liquid or solid material will provide a fast cooling rate, but is more difficult to control. Solid C02 particles, for instance have the advantage of a fast cooling capacity and the additional advantage that oxide layers on the coating are at least partially removed at the same time, but solid C02 particles are more difficult to supply at the right time period. Metal cooling plates that are brought into contact with the heated blank provide a very fast cooling rate, but a tight control of the cooling time is required.
Preferably the coating on the blank is a metallic coating, preferably a coating layer of zinc or a zinc alloy. Zinc or zinc alloy can provide an active corrosion protection.
In this regard, it is preferred when the zinc alloy consists of 0.3 - 4.0% Mg and 0.05 - 6.0% Al, optionally at most 0.2% of one or more additional elements, unavoidable impurities, the remainder being zinc. It has been found that such a zinc alloy provides a better corrosion resistance to the hot formed part.
It is an option when the zinc or zinc alloy layer is pre-diffused in the substrate. The pre-diffused coating makes it possible to heat the blank fast to a temperature above the Ac3 temperature.
Preferably the zinc or zinc alloy coated steel blank contains an average of 10 - 75 % iron in the coating after heating the blank in the furnace, preferably an average of 25 - 55 %. This amount of iron in the coating ensures that the (initial) zinc or zinc alloy coating does not evaporate at temperatures above the Ac3 temperature. According to a preferred embodiment the hot forming press is internally cooled such that the blank is cooled with a cooling velocity of at least 50° C/sec during the first second after the press is fully closed, preferably with a cooling velocity of at least 100° C/sec during the first second. This very fast cooling rate after the hot forming press is fully closed makes that the austenitic structure of the heated blank is transformed fully or almost fully to a martensitic structure.
Preferably the hot forming press is fully closed in at most one second. This fast closing of the hot forming press is advantageous so as to fast cool also the portions of the blank that are not in immediate contact with the press.
According to another preferred embodiment of the invention there is provided a hot formed part manufactured according to the above method, wherein the substrate of the part is free of micro-cracks having a depth of more than 15 μπι, and preferably the substrate is free of micro-cracks having a depth of more than 10 μπι. Parts having less deep micro-cracks are preferred over parts having deeper micro-cracks.
According to another preferred embodiment of the invention there is provided a hot formed part manufactured according to the above method, wherein the micro-cracks in the substrate have an average depth of at most 3 μπι in five surface area's of the blank with a size of 1 cm2. Parts having on average shallow micro-cracks are preferred over parts having deep micro-cracks on average.

Claims

Method for manufacturing a coated steel part having very high mechanical properties using hot forming techniques, comprising the following steps:
• providing a coated steel blank comprising a steel substrate with a coating layer
• heating the blank to a temperature of 800° C or more in a furnace
• transporting the heated blank from the furnace and placing the blank in a hot forming press
• hot forming the blank in the press to form the coated steel part
• quenching the coated steel part
wherein the heated blank has a temperature of at most 780° C when placed in the hot forming press.
Method according to claim 1, wherein the blank is heated to a temperature of 850° C or more, preferably a temperature of 880° C or more, more preferably to a temperature of 900° C or more.
Method according to claim 1 or 2, wherein the heated blank has a temperature of at least 500° C when placed in the hot forming press, preferably a temperature of at least 600° C, and more preferably a temperature of at least 650° C.
Method according to any one of the preceding claims, wherein the heated blank has a temperature of at most 740° C when placed in the hot forming press, and preferably a temperature of at most 700° C.
Method according to any one of the preceding claims, wherein the heated blank is at least partially cooled between the furnace and the hot forming press by forced cooling, preferably with an average cooling velocity of at least 30° C/sec, more preferably with an average cooling velocity of at least 40° C/sec, still more preferably with an average cooling velocity of at least 60° C/sec, most preferably with an average cooling velocity of at least 80° C/sec.
6. Method according to any one of the preceding claims, wherein the heated steel blank is transported between the furnace and the hot forming press in a time span of at most 10 seconds, preferably in a time span of at most 8 seconds, and more preferably in a time span of at most 6 seconds.
7. Method according to claims 5 or 6, wherein the heated blank is cooled between the furnace and the hot forming press using accelerated cooling making use of gas, such as cooling with forced air flow, cooling with forced N2fiow, or cooling with forced C02 flow or cooled C02 using solid C02.
8. Method according to claims 5 or 6, wherein the heated blank is cooled between the furnace and the hot forming press using liquid or solid material, such as liquid or solid C02 particles or metal cooling plates.
Method according to any one of the preceding claims, wherein the coating on the blank is a metallic coating, preferably a coating layer of zinc or a zinc alloy, and more preferably the zinc alloy consists of 0.3 - 4.0% Mg and 0.05 - 6.0% Al, optionally at most 0.2% of one or more additional elements, unavoidable impurities, the remainder being zinc.
Method according to claim 9, wherein the zinc or zinc alloy layer is pre-diffused in the substrate.
Method according to claim 9or 10, wherein the zinc or zinc alloy coated steel blank contains an average of 10 - 75 % iron in the coating after heating the blank in the furnace, preferably an average of 25 - 55 %.
Method according to any one of the preceding claims, wherein the hot forming press is internally cooled such that the blank is cooled with a cooling velocity of at least 50° C/sec during the first second after the press is fully closed, preferably with a cooling velocity of at least 100° C/sec during the first second.
13. Method according to any one of the preceding claims, wherein the hot forming press is fully closed in at most one second.
14. Hot formed part manufactured according to the method of any one of claims 1 - i 13, wherein the substrate of the part is free of micro-cracks having a depth of more than 15 μηι, and preferably the substrate is free of micro-cracks having a depth of more than 10 μπι.
15. Hot formed part manufactured according to the method of any one of claims 1 - 13, wherein the micro-cracks in the substrate have an average depth of at most 3 μιη in five surface area's of the blank with a size of 1 cm2.
EP12700452.1A 2011-01-17 2012-01-17 Method to produce a hot formed part, and part thus formed Ceased EP2665837A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP12700452.1A EP2665837A1 (en) 2011-01-17 2012-01-17 Method to produce a hot formed part, and part thus formed
EP14163594.6A EP2754723A3 (en) 2011-01-17 2012-01-17 Method to produce a hot formed part, and part thus formed

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
EP11000315 2011-01-17
EP12700452.1A EP2665837A1 (en) 2011-01-17 2012-01-17 Method to produce a hot formed part, and part thus formed
PCT/EP2012/000186 WO2012097976A1 (en) 2011-01-17 2012-01-17 Method to produce a hot formed part, and part thus formed

Related Child Applications (1)

Application Number Title Priority Date Filing Date
EP14163594.6A Division EP2754723A3 (en) 2011-01-17 2012-01-17 Method to produce a hot formed part, and part thus formed

Publications (1)

Publication Number Publication Date
EP2665837A1 true EP2665837A1 (en) 2013-11-27

Family

ID=44003816

Family Applications (2)

Application Number Title Priority Date Filing Date
EP14163594.6A Ceased EP2754723A3 (en) 2011-01-17 2012-01-17 Method to produce a hot formed part, and part thus formed
EP12700452.1A Ceased EP2665837A1 (en) 2011-01-17 2012-01-17 Method to produce a hot formed part, and part thus formed

Family Applications Before (1)

Application Number Title Priority Date Filing Date
EP14163594.6A Ceased EP2754723A3 (en) 2011-01-17 2012-01-17 Method to produce a hot formed part, and part thus formed

Country Status (3)

Country Link
EP (2) EP2754723A3 (en)
CN (1) CN103403195B (en)
WO (1) WO2012097976A1 (en)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB201116668D0 (en) * 2011-09-27 2011-11-09 Imp Innovations Ltd A method of forming parts from sheet steel
EP3122486A1 (en) * 2014-03-28 2017-02-01 Tata Steel IJmuiden BV Method for hot forming a coated steel blank
JP6152836B2 (en) * 2014-09-25 2017-06-28 Ｊｆｅスチール株式会社 Manufacturing method of hot press-formed product
DE102014114394B3 (en) * 2014-10-02 2015-11-05 Voestalpine Stahl Gmbh Method for producing a hardened steel sheet
DE102015001408A1 (en) * 2015-02-06 2016-08-11 Eisenmann Se Plant for the form hardening of workpieces

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006015849A2 (en) 2004-08-09 2006-02-16 Voestalpine Automotive Holding Gmbh Method for press quenching components consisting of sheet steel
DE102006019395A1 (en) 2006-04-24 2007-10-25 Thyssenkrupp Steel Ag Apparatus and method for forming blanks of higher and highest strength steels
DE102008039264A1 (en) 2008-08-22 2010-03-04 Schuler Cartec Gmbh & Co. Kg Method for tempering with intermediate cooling
EP2324938A1 (en) 2009-10-23 2011-05-25 ThyssenKrupp Umformtechnik GmbH Method and thermal recasting assembly for producing a hardened, thermally recast workpiece
EP2623226A1 (en) 2010-09-30 2013-08-07 Kabushiki Kaisha Kobe Seiko Sho Press-molded article and method for producing same

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JP4506128B2 (en) * 2003-08-29 2010-07-21 住友金属工業株式会社 Hot press-formed product and method for producing the same
DE102004006093B3 (en) 2004-02-06 2005-12-01 Fes Gmbh Fahrzeug-Entwicklung Sachsen Method for producing a three-dimensionally shaped armor component for vehicle bodies
DE102005003551B4 (en) 2005-01-26 2015-01-22 Volkswagen Ag Method for hot forming and hardening a steel sheet
JP4733522B2 (en) * 2006-01-06 2011-07-27 新日本製鐵株式会社 Method for producing high-strength quenched molded body with excellent corrosion resistance and fatigue resistance
JP4825882B2 (en) * 2009-02-03 2011-11-30 トヨタ自動車株式会社 High-strength quenched molded body and method for producing the same

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WO2006015849A2 (en) 2004-08-09 2006-02-16 Voestalpine Automotive Holding Gmbh Method for press quenching components consisting of sheet steel
DE102006019395A1 (en) 2006-04-24 2007-10-25 Thyssenkrupp Steel Ag Apparatus and method for forming blanks of higher and highest strength steels
DE102008039264A1 (en) 2008-08-22 2010-03-04 Schuler Cartec Gmbh & Co. Kg Method for tempering with intermediate cooling
EP2324938A1 (en) 2009-10-23 2011-05-25 ThyssenKrupp Umformtechnik GmbH Method and thermal recasting assembly for producing a hardened, thermally recast workpiece
EP2623226A1 (en) 2010-09-30 2013-08-07 Kabushiki Kaisha Kobe Seiko Sho Press-molded article and method for producing same

Non-Patent Citations (2)

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Title
H. KARBASIAN ET AL: "A review on hot stamping", JOURNAL OF MATERIALS PROCESSING TECHNOLOGY, vol. 210, no. 15, 1 November 2010 (2010-11-01), pages 2103 - 2118, XP055141086, ISSN: 0924-0136, DOI: 10.1016/j.jmatprotec.2010.07.019 *
See also references of WO2012097976A1 *

Also Published As

Publication number Publication date
EP2754723A3 (en) 2016-08-31
WO2012097976A1 (en) 2012-07-26
CN103403195B (en) 2016-05-04
EP2754723A2 (en) 2014-07-16
CN103403195A (en) 2013-11-20

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