EP0703298B1 - Procédé de fabrication d'un acier présentant une bonne aptitude à la mise en forme et une bonne résistance à l'indentation - Google Patents

Procédé de fabrication d'un acier présentant une bonne aptitude à la mise en forme et une bonne résistance à l'indentation Download PDF

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Publication number
EP0703298B1
EP0703298B1 EP95401923A EP95401923A EP0703298B1 EP 0703298 B1 EP0703298 B1 EP 0703298B1 EP 95401923 A EP95401923 A EP 95401923A EP 95401923 A EP95401923 A EP 95401923A EP 0703298 B1 EP0703298 B1 EP 0703298B1
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EP
European Patent Office
Prior art keywords
carbon
annealing
temperature
steel
sheet
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.)
Expired - Lifetime
Application number
EP95401923A
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German (de)
English (en)
French (fr)
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EP0703298A1 (fr
Inventor
José Manuel Rubianes
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.)
Sollac SA
Original Assignee
Sollac SA
Lorraine de Laminage Continu SA SOLLAC
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Publication of EP0703298A1 publication Critical patent/EP0703298A1/fr
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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
    • 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
    • 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
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing

Definitions

  • the present invention relates to a method of manufacturing a mild low carbon steel with good formability and good resistance to indentation, as well as a sheet obtained by this process.
  • this type of sheet When using this type of sheet, for example to make bodywork elements of automobile bodywork or appliance bodywork appliances, it is shaped by stamping or folding.
  • the non-deformed parts maintain their initial elastic limit Re and the deformed parts have a elastic limit increased due to the hardening they have undergone.
  • the elastic limit of the element can increase, which results in significant hardening said element.
  • the steel sheet used from the rolled coil must be cold and annealed has the lowest possible elastic limit Re for facilitate the shaping and it is also necessary that on the finished part, ie after the paint has cured, the elastic limit Re is raised so that the part exhibits good resistance to indentation, of the gravel type or marking of surfaces by contact with small objects (typical case of contact of the key around the lock on a car door), and in order to reduce it the thickness and thus reduce the weight, which is a very important factor in the automotive field.
  • This type of increase in yield strength is dictated by the shape of the part and is therefore undergone, it is difficult to control it without passing by a modification of the form.
  • a first solution to obtain a steel having a good BH property consists in developing a steel calmed with aluminum, without addition of titanium, or niobium, either in continuous annealing or in base annealing, with optionally addition of phosphorus and / or manganese and / or silicon.
  • This type of steel allows an increase in the elastic limit due to BH of around 40 MPa.
  • a second solution consists in producing an IF steel under stoichiometric in continuous annealing.
  • These steels are produced by adding titanium and / or niobium, which will precipitate with nitrogen and carbon from steel, in the form, between other, titanium nitride, titanium carbide and / or niobium.
  • Control of the titanium and / or niobium content as well as carbon and nitrogen makes it possible to control, during the production of steel, the carbon content remaining in solution in the steel.
  • a third solution consists in developing steel by so-called IF CHRX.
  • These steels are produced by adding titanium and / or niobium, in quantities such that they trap all the nitrogen and carbon in solution. This steel is then continuously annealed at a temperature higher than 850 ° C and cools very quickly at a speed higher than 80 ° C per second.
  • EP 0 075 803 discloses a process intended to limit the aging of the sheets which consists in carrying out an annealing comprising a bearing between 680 ° C and 850 ° C followed by a second level between 350 ° C and 450 ° C and a third level between 200 ° C and 300 ° C, but this process does not resolve the problem of secondary hardening during firing after painting.
  • the invention relates to a method for manufacturing a sheet of mild low carbon steel by hot rolling a slab, then rolling to cold from hot rolled sheet, and annealing from cold rolled sheet.
  • the invention consists in performing after cold rolling a first continuous annealing which allows solution the carbon contained in the steel followed by a possible level of overaging which reprecipitates carbon in solution while limiting the reduction of the carbon content in solution in the steel to 6 ppm, and to be carried out then a second annealing at low temperature which precipitates the carbon in solution in the form of iron carbide, and an operation is carried out work hardening by light rolling called "skin-pass".
  • Low carbon mild steel is a steel having the following composition in thousandths of a weight percent: carbon 1 to 100 phosphorus 0 to 100 aluminum 10 to 100 manganese 0 to 1000 nitrogen 1 to 10 silicon 0 to 1000 sulfur 0 to 25, the rest being iron and residuals from the production process.
  • the cycle of the first annealing consists to raise the temperature of the sheet to a temperature t1 between 750 and 900 ° C and maintain this temperature for a period of 30 seconds at 10 minutes, then cool the sheet to a temperature t2 and maintain this temperature t2 for a determined time to achieve a plateau of overaging.
  • the overage stage is not necessarily isothermal, but, as shown in FIG. 1, we can admit a temperature change during this plateau.
  • the conditions of temperature t2 and of duration of the overage plateau are, as seen in FIG. 2, included in the unshaded domain represented on a duration / temperature graph by the rectangle defined by the abscissae 0 and 15 min and the ordinates 0 and 850 ° C, except for the hatched portion A delimited by points A1, A2, A3, A4, A1, whose duration / temperature coordinates are as follows: A1 15 mins. 440 ° C A2 40 sec. 440 ° C A3 40 sec. 350 ° C A4 15 mins. 250 ° C
  • the cooling speed of the sheet to go from the annealing temperature t1 to that of the cooling level t2 and after cooling bearing is not of great importance in the process according to the invention and can for example be between 1 and 1000 ° C.
  • the conditions of temperature and duration of the second annealing at low temperature are included in the field represented on a duration / temperature curve by the portion B not hatched delimited by the points B1, B2, B3, B4, B5, B6, B1 whose duration / temperature coordinates are as follows: B1 1 hr 50 ° C B2 3 mins 170 ° C B3 8 p.m. 170 ° C B4 48 h 120 ° C B5 100 h 120 ° C B6 100 h 40 ° C
  • the second annealing takes place at a temperature of the order of 75 ° C for a long period of the order of 25 hours.
  • This second annealing at low temperature makes it possible to precipitate a part of the carbon in solution in the form of iron carbide and therefore of decrease the carbon content in solution which allows the steel to have good aging properties and therefore not to degrade too much during of storage.
  • part of the iron carbide will dissolve to reform carbon in solution which results in a good BH property.
  • the invention therefore consists in limiting the decrease in the carbon content in solution in order to maintain a content of around 10 to 15 ppm, then transform this carbon into a solution into carbide of iron during second annealing, to reform a sufficient quantity of carbon in solution after baking the paint to give the piece after baking paint with good BH properties.
  • Iron carbides that are not dissolved will exert a beneficial influence on the BH property.
  • This steel after cold rolling underwent a first annealing at 800 ° C with an overcurrent plateau at 400 ° C for 30 seconds.
  • Each sample was stored for 30 days at temperature room to control their aging.
  • the work hardening coefficient was measured after 6 days, 9 days, 15 days, 22 days and 30 days.
  • the work hardening coefficient does not change significantly over time and remains high, which means that the natural aging of the mechanical characteristics remains limit.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Heat Treatment Of Steel (AREA)
  • Processing And Handling Of Plastics And Other Materials For Molding In General (AREA)
  • Encapsulation Of And Coatings For Semiconductor Or Solid State Devices (AREA)
  • Moulds For Moulding Plastics Or The Like (AREA)
EP95401923A 1994-09-23 1995-08-22 Procédé de fabrication d'un acier présentant une bonne aptitude à la mise en forme et une bonne résistance à l'indentation Expired - Lifetime EP0703298B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9411481A FR2724946B1 (fr) 1994-09-23 1994-09-23 Procede de fabrication d'un acier presentant une bonne aptitude a la mise en forme et une bonne resistance a l'indentation
FR9411481 1994-09-23

Publications (2)

Publication Number Publication Date
EP0703298A1 EP0703298A1 (fr) 1996-03-27
EP0703298B1 true EP0703298B1 (fr) 2002-11-20

Family

ID=9467287

Family Applications (1)

Application Number Title Priority Date Filing Date
EP95401923A Expired - Lifetime EP0703298B1 (fr) 1994-09-23 1995-08-22 Procédé de fabrication d'un acier présentant une bonne aptitude à la mise en forme et une bonne résistance à l'indentation

Country Status (8)

Country Link
US (1) US5645656A (es)
EP (1) EP0703298B1 (es)
AT (1) ATE228174T1 (es)
DE (1) DE69528874T2 (es)
DK (1) DK0703298T3 (es)
ES (1) ES2187544T3 (es)
FR (1) FR2724946B1 (es)
PT (1) PT703298E (es)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19740148C1 (de) 1997-09-12 1999-07-15 Thyssenkrupp Stahl Ag Verfahren zur Herstellung von beulfesten einbrennlackierten Bauteilen aus alterungsempfindlichem Stahl
FR2790009B1 (fr) * 1999-02-22 2001-04-20 Lorraine Laminage Acier dual-phase a haute limite d'elasticite
US7419496B2 (en) * 2004-08-03 2008-09-02 Staudner Rupert A Trocar with retractable cutting surface

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5157623A (en) * 1974-11-18 1976-05-20 Nippon Kokan Kk Takaitosoyakitsukekokaseitosugureta hijikoseiomotsukochoryokureienkohanno seizohoho
US3936324A (en) * 1975-03-14 1976-02-03 Nippon Kokan Kabushiki Kaisha Method of making high strength cold reduced steel by a full continuous annealing process
JPS5857492B2 (ja) * 1980-09-25 1983-12-20 新日本製鐵株式会社 自動車用高強度冷延鋼板の製造方法
JPS5852436A (ja) * 1981-09-19 1983-03-28 Nippon Steel Corp プレス加工性および時効性の優れた冷延鋼板の製造方法
FR2678641B1 (fr) * 1991-07-04 1998-11-20 Lorraine Laminage Acier a emboutissabilite amelioree et procede de fabrication de toles destinees a l'emboutissage.
FR2694024B1 (fr) * 1992-07-23 1994-10-14 Lorraine Laminage Tôle améliorée pour emboutissage en rétreint et procédé de fabrication d'une telle tôle.

Also Published As

Publication number Publication date
DE69528874D1 (de) 2003-01-02
DK0703298T3 (da) 2003-03-17
FR2724946B1 (fr) 1996-12-13
FR2724946A1 (fr) 1996-03-29
PT703298E (pt) 2003-03-31
EP0703298A1 (fr) 1996-03-27
DE69528874T2 (de) 2003-07-17
ES2187544T3 (es) 2003-06-16
US5645656A (en) 1997-07-08
ATE228174T1 (de) 2002-12-15

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