(19)
(11)EP 3 327 153 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
11.11.2020 Bulletin 2020/46

(21)Application number: 16200246.3

(22)Date of filing:  23.11.2016
(51)International Patent Classification (IPC): 
C21D 7/02(2006.01)
C22C 38/38(2006.01)
C22C 38/04(2006.01)

(54)

METHOD FOR MANUFACTURING A COMPLEX-FORMED COMPONENT

VERFAHREN ZUR HERSTELLUNG EINER KOMPLEX GEFORMTEN KOMPONENTE

PROCÉDÉ DE PRODUCTION D'UN COMPOSANT DE FORME COMPLEXE


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(43)Date of publication of application:
30.05.2018 Bulletin 2018/22

(73)Proprietor: Outokumpu Oyj
00180 Helsinki (FI)

(72)Inventors:
  • Fröhlich, Thomas
    D-40878 Ratingen (DE)
  • Lindner, Stefan
    D-47877 Willich (DE)


(56)References cited: : 
EP-A1- 2 090 668
US-A- 4 217 136
US-A1- 2015 376 749
DE-A1- 19 607 828
US-A1- 2010 258 218
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description


    [0001] The present invention relates to a method for manufacturing a multi-stage forming operation by very complex parts with austenitic materials by a combination of cold forming and annealing treatments. During the forming operation, the formation of twins have been achieved in austenitic materials ductility diminishes.

    [0002] In car body engineering components with a complex forming geometry are manufactured with soft deep drawing steels. There are requirements to fulfil a higher strength lightweight, package or safety targets, available high strength steels like dual-phase steels, multi-phase steels or complex phase steels reach their limit of formability very often. The defined-adjusted mechanical values and microstructure parts (during steel-manufacturing) react sensitive to following forming or heat treatment steps during component manufacturing. Therefore they change undesirably their properties.

    [0003] One solution are hot-forming operations like the so-called press-hardening, where heat-treatable manganese-boron steels are heated up to austenitization temperature (over 900°C), through hardening for a specific holding time and then formed at those high temperatures in a hot-forming tool to the resulting component. At the same time of the forming operation, the heat is discharged from the sheet to the contact areas of the tool und therefore cooled-down. The process is described for example in the US20040231762A1. With the process of hot-forming, complex parts can be realized by using a high-strength material. But the residual elongation is on a lowest level (most of the time <5%).

    [0004] Therefore following cold forming steps are not possible as well as high energy absorption during a crash situation of a car body component. Furthermore not at any time, a tensile strength of 1,500MPa is requested, for example when the system becomes too stiff. Additionally the investment, repair and energy costs as well as the necessary room for the roller head furnaces are very high with marginal cycle times in comparison to cold forming operations. Moreover the corrosion protection is on a lower level in comparison to coated cold-forming steels.

    [0005] For a lot of decades austenitic stainless steels are used in the application field of domestic goods for complex cold forming parts like sinks. The established materials are alloyed with chromium and nickel by using the hardening effect of TRIP (TRansformation Induced Plasticity) where the metastable austenitic microstructure is changed into martensite during a forming load. At room temperature the austenitic microstructure is stable because of the lower martensitic starting temperature. In the literature this effect is well-known as "deformation induced martensite formation". A drawback of using these materials for complex cold-forming operations is that the formally austenitic material changes the properties to a martensitic microstructure with lower ductility, increasing of hardness and therefore a decrease of the resulting energy absorption potential. Furthermore the process is not reversible. The advantages of an austenitic material like the nonmagnetic properties get loss and cannot be used in the component situation of the material. The irreversible microstructure change is a big drawback for complex multi-staged forming operations where the residual elongation is insufficient. Furthermore the effect of TRIP is sensitive to temperature which results in a further investment need for tool cooling. Moreover those materials show the danger of stress induced delayed cracking when changing their microstructure during a forming process to martensite. The stacking fault energy of those materials with TRIP-effect is lower than SFE <20mJ/m2. Additionally the danger of hydrogen embrittlement is given by the martensite transformation.

    [0006] The described austenitic stainless steels with TRIP effect are in initial state nonmagnetic. The publication DE102012222670A1 describes a method for the local heating of components manufactured by stainless steels using the TRIP effect and the out of this effect rising forming martensite. Furthermore equipment for inductive heating of austenitic stainless steels with martensite transformation is created by a recrystallization locally in the martensite areas of the component.

    [0007] The publication WO2015028406A1 describes a method to harden a metal sheet, whereat by shot peening or grit blasting the surface is hardened. As a result the surface is more scratch-resistant for sink applications. Especially the usage of metastable chromium-nickel alloyed 1.4301 is pointed out.

    [0008] European patent application publication EP 2 090 688 A1 describes a process for producing a high strength steel product from a hot-rolled and /or cold-rolled and annealed TWIP steel. At least part of the TWIP steel is subsequently subjected to a cold reduction to obtain the desired ratio of yield strength and tensile strength in that part.

    [0009] The object of the present invention is to eliminate some drawbacks of the prior art and to establish a method for manufacturing of a complex-formed component of austenitic steel having non-magnetic properties at the end and during all process steps. The multistage process with a combination of forming and heating results in reversible material properties, which is achieved by TWIP hardening effect and the stable austenitic microstructure. The essential features of the present invention are enlisted in the appended claims.

    [0010] The steel used in the invention contains interstitial disengaged nitrogen and carbon atoms so that the sum of the carbon content and the nitrogen content (C+N) is at least 0,4 weight %, but less than 1,2 weight %, and the steel advantageously can also contain more than 10,5 weight % chromium, being thus an austenitic stainless steel. Another ferrite former like chromium is silicium, which works as a deoxidizer during steel manufacturing. Futher silicium increase the strength and hardness of the material. In the present invention the silicium content of the steel is less than 3.0 weight-% to restrict hot-crack-affinity during welding, more preferably less than 0.6 weight-% to avoid the saturation as a deoxidizer, further more preferably less than 0.3 weight-% to avoid low-melting phases on Fe-SI basis and to restrict an undesirable decrease of the stacking fault energy. In case the steel contains essential contents of at least one ferrite phase former, such as chromium or silicium, a compensation with the contents of the austenite phase formers like carbon or nitrogen, but also such as manganese weight-% is between 10% and less than or equal to 26%, preferably between 12-16%, carbon and nitrogen both weight % values are more than 0.2% and less than 0.8%, nickel weight % is equal or less than 2.5%, preferably less than 1.0%, or copper weight % is less or equal than 0.8%, preferably between 0.25 - 0.55 % will be done in order to have a balanced and sole content of austenite in the microstructure of the steel.

    [0011] The present invention exists in that complex forming parts can be realized with a multi-staged cold forming and heating operation under retention or optimization of the austenitic material properties after finishing the forming operation.

    [0012] The forming steps of the multi-staged process are carried out by hydro-mechanical deep-drawing processes like sheet-hydroforming or internal high-pressure forming.

    [0013] Furthermore the forming steps of the multi-staged process are carried out by deep-drawing, pressing, plunging, bulging, bending, spinning or stretch forming.

    [0014] According to the present invention an austenitic steel with an elongation A80 is equal or more than 50% is used in a multi-staged forming process, whereby the material is characterized by a TWIP (Twinning induced Plasticity) hardening effect, a specific adjusted stacking fault energy between 20 more than or equal SFE less than or equal 30 mJ/m2, preferably 22-24 mJ/m2 and therefore stable austenitic microstructure as well as stable nonmagnetic properties during the complete forming process.

    [0015] The invention relates to a method for a multi-stage forming operation, where forming and heating are consisting by two different steps of operation, where multi-stage metal-forming process includes at least two different (or independent from each other) steps where at least one step is a forming step. The other can be a further forming step or for example a heat treatment. Furthermore in the invention is described a subsequent process which includes forming and heating for creating complex formed parts and which uses to reach this target an austenitic (stainless) steel with TWIP hardening effect with its specific properties and possibilities for complex forming parts manufactured out of austenitic steel with utilization of the TWIP (Twinning Induced Plasticity) hardening effect. During heating the twins in the microstructure of the used TWIP material are dissolved and during forming the twins in the microstructure of the used TWIP material are rebuilt.

    [0016] Complex formed parts in state of the art for the sheet fabricating industry are white goods, consumer goods or car body engineering. Furthermore the extensive-designed and complex forming geometries have the benefit of saving number of parts, or integrating additional functions. A multi-staged complex-formed component as a white good can be found like a kitchen sink or bathes in domestic appliances like a drum of a dish washer or washing machine. Furthermore functional or constructive requirements like package limitations e.g. longitudinal member of a car or volume specifications such as tanks, reservoirs are also suitable for a complex constructive configuration. Additionally design aspects e.g. sink or load path of crash structures such as crash box with bumper systems for cars can be further solutions to the method of invention. Furthermore the invention is suitable for hang-on parts of transportation systems, like complex-formed doors or door-side impact beams, as well as for interior parts like seat structures especially seat back walls. The component deformed according to the present invention can be applied for transport systems, such as cars, trucks, busses, railway or agricultural vehicles, as well as for automotive industry like an airbag sleeve or an fuel filler pipe. The multistage forming operation is an alternating process of cold forming e.g. lower than 100°C and not under -20°C, but preferably at room temperature and following short-time heating. The number of process steps depends on the forming complexity.

    [0017] The present invention is illustrated in more details referring to the attached drawings where

    Fig. 1 shows hardness-comparison of different process,

    Fig. 2 shows the formation of twins as a metallographic inspection,

    Fig. 3 shows forming degree diagram of a an austenitic TWIP steel,

    Fig. 4 shows effect of hardening from a stamped edge,

    Fig. 5 shows effect of surface hardening by shot peening,

    Fig. 6 shows effect of surface nitriding heat treatment on the mechanical properties of an austenitic TWIP steel, and

    Fig. 7 shows a multi-stage metal-forming process.



    [0018] Fig. 1 shows the result of a hardness measured component after such a forming and heating operation. Hardness-comparison of different process steps of the multi-staged forming operation: Initial, base material (left), after first forming step with a forming degree of 20% (middle) and after heating process (right); for every state 10 hardness point per measured.

    [0019] In Fig. 2 the formation of twins is shown as a metallographic inspection in figure 2, related to the hardness measurement in figure 1.

    [0020] Fig. 3 shows the forming degree diagram of austenitic TWIP steel with 12-17% of chromium and manganese.

    [0021] In Fig. 4 is shown the effect of hardening from a stamped edge for a 12-17% chromium and manganese alloyed TWIP steel.

    [0022] Fig. 5 shows the effect of surface hardening by shot peening on full-austenitic TWIP steel.

    [0023] In Fig. 6 is shown the effect of surface nitriding heat treatment on the mechanical properties of an austenitic TWIP steel in annealed condition Rp0,2 = yield strength, A80 = elongation after fracture, Ag = uniform elongation, sample definition: A = sampled in initial annealed condition, N = sample after nitriding treatment.

    [0024] In Fig. 7 a multi-stage metal-forming process consists of different heating and forming steps with utilization of the TWIP hardening effect.

    [0025] The material used in the method will be hardened during the forming operation because of the TWIP effect, but the material will maintain the austenitic microstructure. For an austenitic TWIP material the forming degree shall be less than or equal to 60%, preferably less than or equal to 40%. If the forming potential, defined by the forming degree of the material is at the end of the method or if high tooling forces for forming are required, the second step, a heating step can be started. During the following heating step, the twins are dissolved and the material will be softened again. Because of the before defined material characteristics, the method is a reversible process. The heating process can be integrated into one forming tool with induction or conduction. The heating temperature must be between 750 and 1150°C, preferably between 900 and 1050°C. The process can be repeated as many times as required to establish the desired complex geometry.

    [0026] The initial thickness of the sheet used for the multi-staged process shall be less than 3.0 mm, preferably between 0.25 and 1.5 mm. It is also possible to use flexible rolled sheets with the present invention, too.

    [0027] The component is in the form of a sheet, a tube, a profile, a wire or a joining rivet.

    [0028] The formations of twins are shown as a metallographic inspection in figure 2, related to the hardness measurement in figure 1. The formation of twins by forming and dissolving by heating can be pointed out very well. With a further forming step after heating, the formation of twins is restarted again and the component will be hardened again. This process can be used alternated and repeated as many times as required to reach the geometry as well as target mechanical values for strength and elongation. Therefore the last step of the multi-staged forming operation can be a forming step with a defined forming degree as well as a locally heating step. For the use of a TWIP-steel which is alloyed with 12-17% of chromium as well as manganese, the forming diagram is used to adjust the sufficient values of the finished component, figure 3. As seen in figure 3, the invention is especially suitable for high or ultra-high strength steels having a minimum yield strength level more or equal than 500 MPa. The heating steps can be designed with induction, conduction or also infrared technology. Heating-up rates of 20K/s are possible and do not influence the behavior of the twins.

    [0029] Additionally forming operations can be integrated to the forming tool. As a result the hardening effect for state of the art operations can be reached over 160% of the base material. This drawback of edge hardening can be solved also by a following heating step. As a result the edge crack sensitive can be reduced significantly.

    [0030] A further positive aspect of the invention is the possibility to create a compressive stress value on the surface by an upset forming operation such as shot peening, grit blasting or high frequency pounding to reduce edge crack or surface crack sensitivity as well as a better fatigue behavior when the multi-stage formed component is under fatigue stressed conditions e.g. automotive component. Such surface treatment is in general well-known but the combination with the pointed out material characteristic shows new properties because the microstructure and therefore the material properties (e.g. non-magnetic) will be constant. The combination of process and material results in the values are shown in table 1, where the effect of surface hardening (shot peening) and subsequent heat treatment are on the residual stress level of full-austenitic TWIP steels.
    Table 1
    materialYield strengthResidual stresses on the surface [MPa]
    [MPa]Initial stateAfter shot peeningAfter an subsequent heat treament
    TWIP steel 515 28 -811 -560
    annealed condition
    TWIP steel 811 102 -889 -589
    strain hardened


    [0031] In table 1, a plus sign means tensile stresses on the surface; a minus sign means a compressive stress level.

    [0032] The general deviation of the measuring method can be +/- 30MPa. It can be shown with table 1. that the material stresses in initial state, especially for the strain hardened cold-rolled variants, can be transferred by an upset forming operation into uncritical compressive values. Such an operation can be also integrated into the multi-stage forming process because a high compressive load level can be also maintained after a subsequent heat treatment.

    [0033] A multi-staged complex-formed component can be used as an automotive component, like a wheel-house, bumper system, channel or as a chassis component e.g. suspension arm. Furthermore a multi-staged complex-formed component as a mounting part can be used in transportation systems like a door, a flap, a flender beam or a load-bearing flank, a interior part of a transport system like a seat structure component e.g. seat backrest.

    [0034] There are also possibilities to create a multi-staged complex-formed component as a part of a fuel injection system like a filler neck or as a tank or storage for cars, trucks, transport systems, railway, agricultural vehicles as well as for automotive industry, and further in building and a pressure vessel or boiler or to be used of a multi-staged complex-formed component as battery electric vehicles or hybrid cars like a battery case.

    [0035] An additional surface effect like an upset forming operation can be reached with a nitriding or carburizing heat treatment. Both elements, nitrogen and carbon, operate as austenite formers and therefore this elements stabilize the local stacking fault energy and the resulting hardening effect, TWIP mechanism. The effect of nitriding or carburizing is in a hardening of the near surface structure of the component as shown in figure 5. Furthermore, the near surface structure influence for the mechanical values of the TWIP steel, represent as shown the mechanical values in figure 6.

    [0036] A nitriding or carburizing surface treatment with a heating temperature between 500 and 650°C, preferably between 525 and 575°C, is integrated into the multi-staged process to create a scratch-resistance and at the same time non-magnetic surface of the component.

    [0037] A multi-stage metal-forming process can be seen in figure 7, which includes a sheet, plate, tube 1 at least two different (or independent from each other) steps where at least one step is a forming step 2. The next step 3 is heat treatment. The number of multi-stage process 4 steps depends on the forming complexity 5. As a final result of the method is a complex-formed component 6.


    Claims

    1. A method for manufacturing a complex-formed component (6) in a multi-stage process (4) where cold forming (2) at a temperature in the range of - 20°C to 100°C and heating (3) are alternated for at least two multi-stage process (4) steps, the material being an austenitic stainless steel with TWIP hardening effect, whereby the steel has an initial elongation of A80 greater than or equal to 30%, the steel has a specific adjusted stacking fault energy SFE in the range 20 to 30 mJ/m2, and the forming degree is less than or equal to 60 % characterized in the temperature during the heating steps being in the range of 750°C to 1150°C so, that the material during every process step and a component produced has an austenitic microstructure with non-magnetic reversible properties.
     
    2. The method according to the claim 1, characterized the initial thickness of the sheet (1) used for the multi-staged process (4) should be less than 3.0mm, preferably between 0.25 and 1.5mm.
     
    3. The method according to claim 1 or 2, characterized in that the sum of the carbon content and the nitrogen content (C+N) in the austenitic steel to be deformed in more than 0,4% weight %, but less than 1,2 weight %.
     
    4. The method according to any of the preceding claims, characterized in that the component is in the form (1) of a sheet, a tube, a profile, a wire or a joining rivet.
     
    5. The method according to any of the preceding claims, characterized in that the used material is a stable full-austenitic steel (1) using the TWIP hardening mechanism with a defined stacking fault energy (SFE) in the range 22-24 mJ/m2.
     
    6. The method according to any of the preceding claims, characterized in that the used material has an initial elongation A80 greater than or equal to 50%.
     
    7. The method according to any of the preceding claims, characterized in that the used austenitic TWIP steel has a manganese weight-content between 10% and less than or equal to 26%, preferably between 12 and 16% manganese.
     
    8. The method according to any of the preceding claims, characterized in that the used austenitic TWIP steel is a stainless steel with more than 10.5% chromium, preferably between 12 and 17% chromium.
     
    9. The method according to any of the preceding claims, characterized in that the forming steps of the multi-staged process (4) are carried out by deep-drawing, pressing, plunging, bulging, bending, spinning or stretch forming.
     
    10. The method according to any of the preceding claims, characterized in that the forming steps of the multi-staged process (4) are carried out by hydro-mechanical deep-drawing processes like sheet-hydroforming or internal high-pressure forming.
     
    11. The method according to any of the preceding claims, characterized in that heating temperature of the heating steps (3) is at a temperature range of 900 to 1050°C.
     
    12. The method according to any of the preceding claims, characterized in that the heating steps (3) of the multi-staged process (4) are carried out by induction heating, conduction heating or infrared heating.
     
    13. The method according to any of the preceding claims, characterized in that a forming process (2) is integrated into the multi-staged process (4) as a non-final step before a subsequent heating step (3).
     
    14. The method according to any of the preceding claims, characterized in that an upset forming treatment on the surface like shot peening, grit blasting or high frequency pounding is integrated into the multi-staged process to create a scratch-resistant and compressive-loaded surface of the component, which is at the same time non-magnetic.
     
    15. The method according to any of the preceding claims, characterized in that a nitriding or carburizing surface heat treatment with a heating temperature between 500 and 650°C, preferably between 525 and 575°C, is integrated into the multi-staged process (4) to create a scratch-resistance and at the same time non-magnetic surface of the component.
     
    16. The use of a multi-staged complex-formed component manufactured by a method according to any of claims 1 to 15 as a white good like a kitchen sink or bathes in domestic appliances like a drum of a dish washer or washing machine.
     
    17. The use of a multi-staged complex-formed component manufactured by a method according to any of claims 1 to 15 as an automotive component like a wheel-house, bumper system, channel or as a chassis component (e.g. suspension arm).
     
    18. The use of a multi-staged complex-formed component manufactured by a method according to any of claims 1 to 15 as a mounting part for transportation systems like a door, a flap, a fender beam or a load-bearing flank, a interior part of a transport system like a seat structure component.
     
    19. The use of a multi-staged complex-formed component manufactured by a method according to any of claims 1 to 15 as a part of a fuel injection system, like a filler neck or as a tank or storage for cars, trucks or as a pressure vessel or boiler.
     
    20. The use of a multi-staged complex-formed component manufactured by a method according to any of claims 1 to 15 in battery electric vehicles or hybrid cars like a battery case.
     


    Ansprüche

    1. Verfahren zum Herstellen eines komplex geformten Bauteils (6) in einem Mehrstufenprozess (4), wobei Kaltumformen (2) bei einer Temperatur in dem Bereich von -20 °C bis 100 °C und Erhitzen (3) für mindestens zwei Schritte im Mehrstufenprozess (4) abwechselnd ausgeführt werden, wobei das Material ein austenitischer rostfreier Stahl mit TWIP-Härtungseffekt ist, wobei der Stahl eine anfängliche Elongation Aso von größer als oder gleich 30 % aufweist, der Stahl eine spezifische eingestellte Stapelfehlerenergie SFE in dem Bereich von 20 bis 30 mJ/m2 aufweist und der Umformungsgrad weniger als oder gleich 60 % beträgt, dadurch gekennzeichnet, dass die Temperatur während der Erhitzungsschritte in dem Bereich von 750 °C bis 1.150 °C ist, sodass das Material während jedes Prozessschrittes und ein hergestelltes Bauteil ein austenitisches Gefüge mit unmagnetischen, reversiblen Eigenschaften aufweisen.
     
    2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die anfängliche Dicke des Blechs (1), das für den mehrstufigen Prozess (4) benutzt wird, weniger als 3,0 mm, bevorzugt zwischen 0,25 und 1,5 mm, betragen sollte.
     
    3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass die Summe aus dem Kohlenstoffgehalt und dem Stickstoffgehalt (C + N) in dem austenitischen Stahl, der verformt werden soll, mehr als 0,4 Gewichts-%, jedoch weniger als 1,2 Gewichts-% beträgt.
     
    4. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass das Bauteil in der Form (1) eines Blechs, eines Rohrs, eines Profils, eines Drahtes oder einer Verbindungsniete ist.
     
    5. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass das benutzte Material ein stabiler vollaustenitischer Stahl (1) ist, bei dem der TWIP-Härtungsmechanismus mit einer definierten Stapelfehlerenergie (SFE) in dem Bereich von 22 bis 24 mJ/m2 ist benutzt wird.
     
    6. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass das benutzte Material eine anfängliche Elongation Aso von größer als oder gleich 50 % aufweist.
     
    7. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass der benutzte austenitische TWIP-Stahl einen Mangan-Gewichtsanteil zwischen 10 % und weniger als oder gleich 26 %, bevorzugt zwischen 12 und 16 %, Mangan aufweist.
     
    8. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass der benutzte austenitische TWIP-Stahl ein rostfreier Stahl mit mehr als 10,5 % Chrom, bevorzugt zwischen 12 und 17 % Chrom, ist.
     
    9. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Umformschritte des mehrstufigen Prozesses (4) mittels Tiefziehen, Pressen, Kragenziehen, Stauchen, Biegen, Drücken oder Recken durchgeführt werden.
     
    10. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Umformschritte des mehrstufigen Prozesses (4) durch hydromechanische Tiefziehprozesse wie Außenhochdruckumformen oder Innenhochdruckumformen durchgeführt werden.
     
    11. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Erhitzungstemperatur der Erhitzungsschritte (3) in einem Temperaturbereich von 900 bis 1.050 °C ist.
     
    12. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Erhitzungsschritte (3) des mehrstufigen Prozesses (4) durch induktives Erhitzen, konduktives Erhitzen oder Infraroterhitzen durchgeführt werden.
     
    13. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass ein Umformprozess (2) in den mehrstufigen Prozess (4) als ein nichtfinaler Schritt vor einem nachfolgenden Erhitzungsschritt (3) einbezogen wird.
     
    14. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass eine Stauchumformbehandlung an der Oberfläche wie Kugelstrahlen, Kiesstrahlen oder Hochfrequenzhämmern in den mehrstufigen Prozess einbezogen wird, um eine kratzfeste und druckbelastete Oberfläche des Bauteils zu erzeugen, die zugleich unmagnetisch ist.
     
    15. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass eine Aufstickungs- oder Aufkohlungs-Oberflächenbehandlung mit einer Erhitzungstemperatur zwischen 500 und 650 °C, bevorzugt zwischen 525 und 575 °C, in den mehrstufigen Prozess (4) einbezogen wird, um eine kratzfeste und zugleich unmagnetische Oberfläche des Bauteils zu erzeugen.
     
    16. Benutzung eines mehrstufig gefertigten, komplex geformten Bauteils, das mittels eines Verfahrens nach einem der Ansprüche 1 bis 15 hergestellt ist, als Weißware wie eine Küchenspüle oder Bäder in Haushaltsanwendungen wie einer Trommel einer Geschirrspülmaschine oder einer Waschmaschine.
     
    17. Benutzung eines mehrstufig gefertigten, komplex geformten Bauteils, das mittels eines Verfahrens nach einem der Ansprüche 1 bis 15 hergestellt ist, als ein Kraftfahrzeug-Bauteil wie ein Radkasten, Stoßfängersystem, Kanal oder als ein Fahrgestell-Bauteil (z.B. Querlenker).
     
    18. Benutzung eines mehrstufig gefertigten, komplex geformten Bauteils, das mittels eines Verfahrens nach einem der Ansprüche 1 bis 15 hergestellt ist, als ein Einbauteil für Transportsysteme wie eine Tür, eine Klappe, ein Prellblock oder eine lasttragende Flanke, ein Innenraumteil eines Transportsystems wie ein Sitzstruktur-Bauteil.
     
    19. Benutzung eines mehrstufig gefertigten, komplex geformten Bauteils, das mittels eines Verfahrens nach einem der Ansprüche 1 bis 15 hergestellt ist, als ein Teil eines Kraftstoffeinspritzsystems wie ein Einfüllstutzen oder als ein Tank oder Speicher für Personenkraftwagen, Lastkraftwagen oder als ein Druckgefäß oder Siedegefäß.
     
    20. Benutzung eines mehrstufig gefertigten, komplex geformten Bauteils, das mittels eines Verfahrens nach einem der Ansprüche 1 bis 15 hergestellt ist, in batterieelektrischen Fahrzeugen oder Hybrid-Personenkraftfahrzeugen wie ein Batteriefach.
     


    Revendications

    1. Procédé de fabrication d'un composant de forme complexe (6) dans un procédé en plusieurs étapes (4) dans lequel le formage à froid (2) à une température comprise dans la plage de -20 °C à 100 °C et le chauffage (3) sont alternés pendant au moins deux étapes du procédé en plusieurs étapes (4), le matériau étant un acier inoxydable austénitique présentant un effet de trempe TWIP, selon lequel l'acier présente un allongement initial de Aso supérieur ou égal à 30 %, l'acier présente une énergie de défaut d'empilement EDE ajustée spécifique comprise dans la plage de 20 à 30 mJ/m2, et le degré de formage est inférieur ou égal à 60 % caractérisé en ce que la température pendant les étapes de chauffage est comprise dans la plage de 750 °C à 1150 °C, de sorte que le matériau pendant chaque étape du procédé et un composant produit ont une microstructure austénitique ayant des propriétés réversibles non magnétiques.
     
    2. Procédé selon la revendication 1, caractérisé en ce que l'épaisseur initiale de la feuille (1) utilisée pour le procédé en plusieurs étapes (4) devrait être inférieure à 3,0 mm, de préférence entre 0,25 et 1,5 mm.
     
    3. Procédé selon la revendication 1 or 2, caractérisé en ce que la somme de la teneur en carbone et de la teneur en azote (C + N) de l'acier austénitique à déformer est de plus de 0,4 % en poids, mais de moins de 1,2 % en poids.
     
    4. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que le composant se présente sous la forme (1) d'une feuille, d'un tube, d'un profilé, d'un fil ou d'un rivet de jonction.
     
    5. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que le matériau utilisé est un acier entièrement austénitique (1) stable utilisant le mécanisme de trempe TWIP avec une énergie de défaut d'empilement (EDE) définie comprise dans la plage de 22 à 24 mJ/m2.
     
    6. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que le matériau utilisé présente un allongement initial Aso supérieur ou égal à 50 %.
     
    7. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que l'acier TWIP austénitique utilisé a une teneur pondérale en manganèse comprise entre 10% et inférieure ou égale à 26 %, de préférence entre 12 et 16 % de manganèse.
     
    8. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que l'acier TWIP austénitique utilisé est un acier inoxydable ayant plus de 10,5 % de chrome, de préférence entre 12 et 17 % de chrome.
     
    9. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que les étapes de formage du procédé en plusieurs étapes (4) sont réalisées par emboutissage profond, pressage, plongée, gonflement, pliage, filage ou formage par étirage.
     
    10. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que les étapes de formage du procédé en plusieurs étapes (4) sont réalisées par des procédés d'emboutissage profond hydromécanique tels que l'hydroformage de feuille ou le formage interne à haute pression.
     
    11. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que la température de chauffage des étapes de chauffage (3) se situe dans une plage de température de 900 à 1050 °C.
     
    12. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que les étapes de chauffage (3) du procédé en plusieurs étapes (4) sont réalisées par chauffage par induction, chauffage par conduction ou chauffage infrarouge.
     
    13. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce qu'un procédé de formage (2) est intégré au procédé en plusieurs étapes (4) en tant qu'étape non finale avant une étape de chauffage (3) ultérieure.
     
    14. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce qu'un traitement de formage contrarié sur la surface comme le grenaillage, le sablage ou le martelage à haute fréquence est intégré dans le procédé en plusieurs étapes pour créer une surface résistante aux rayures et chargée par compression du composant, qui est en même temps non magnétique.
     
    15. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce qu'un traitement thermique de surface de nitruration ou de carburation avec une température de chauffage comprise entre 500 et 650 °C, de préférence entre 525 et 575 °C, est intégré dans le procédé en plusieurs étapes (4) pour créer une surface résistant aux rayures et en même temps non magnétique du composant.
     
    16. Utilisation d'un composant de forme complexe multi-étagé fabriqué par un procédé selon l'une quelconque des revendications 1 à 15 en tant qu'article blanc comme un évier de cuisine ou des bains dans des appareils ménagers comme un tambour d'un lave-vaisselle ou d'une machine à laver.
     
    17. Utilisation d'un composant de forme complexe multi-étagé fabriqué par un procédé selon l'une quelconque des revendications 1 à 15 en tant que composant automobile comme un logement de roue, un système de pare-chocs, un canal ou en tant que composant de châssis (par exemple un bras de suspension).
     
    18. Utilisation d'un composant de forme complexe multi-étagé fabriqué par un procédé selon l'une quelconque des revendications 1 à 15 en tant que pièce de montage pour des systèmes de transport tels qu'une porte, un volet, une poutre d'aile ou un flanc de porte-charge, une partie intérieure d'un système de transport comme un composant de structure de siège.
     
    19. Utilisation d'un composant de forme complexe multi-étagé fabriqué par un procédé selon l'une quelconque des revendications 1 à 15 en tant que pièce d'un système d'injection de carburant, comme un goulot de remplissage ou en tant que réservoir ou stockage pour voitures, camions ou en tant qu'équipement sous pression ou chaudière.
     
    20. Utilisation d'un composant de forme complexe multi-étagé fabriqué par un procédé selon l'une quelconque des revendications 1 à 15 dans les véhicules électriques à batterie ou les voitures hybrides comme un boîtier de batterie.
     




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    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description