EP3541966B1 - Method for producing chassis parts from micro-alloyed steel with improved cold workability - Google Patents

Method for producing chassis parts from micro-alloyed steel with improved cold workability Download PDF

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Publication number
EP3541966B1
EP3541966B1 EP17818037.8A EP17818037A EP3541966B1 EP 3541966 B1 EP3541966 B1 EP 3541966B1 EP 17818037 A EP17818037 A EP 17818037A EP 3541966 B1 EP3541966 B1 EP 3541966B1
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EP
European Patent Office
Prior art keywords
max
cold
temperature
plate
sheet
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EP17818037.8A
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German (de)
French (fr)
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EP3541966A1 (en
Inventor
Ingwer Denks
Stefan MÜTZE
Christian PELZ
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Salzgitter Flachstahl GmbH
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Salzgitter Flachstahl GmbH
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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
    • B21D22/02—Stamping using rigid devices or tools
    • B21D22/04—Stamping using rigid devices or tools for dimpling
    • 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
    • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D53/00—Making other particular articles
    • B21D53/88—Making other particular articles other parts for vehicles, e.g. cowlings, mudguards
    • 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
    • C21D1/26—Methods of annealing
    • 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
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • 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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • 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
    • 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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • 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
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2221/00—Treating localised areas of an article

Definitions

  • Chassis components can be, for example, axle beams, wishbones, multi-link rear axles, twist beam axles, front axles, links, as well as longitudinal and cross members.
  • chassis components by cold forming is, for example, from the laid-open specification DE 10 2008 060 161 A1 known.
  • a method for producing a chassis component with increased fatigue strength is disclosed.
  • a material is used for cold forming, consisting of (in percent by weight): carbon (C): 0.22% to 0.25%, silicon (Si): 0.20% to 0.30%, manganese (Mn): 1.20% to 1.40%, phosphorus (P): maximum 0.020%, sulfur (S): maximum 0.010%, aluminum (AI): 0.020% to 0.060%, boron (B): 0.0020% to 0 , 0035%, chromium (Cr): 0.10% to 0.20%, titanium (Ti): 0.020% to 0.050%, molybdenum (Mo): maximum 0.35%, copper (Cu): maximum 0.10 %, Nickel (Ni): maximum 0.30%, remainder iron and impurities from the melting process.
  • the semi-Cr 0.10%
  • a sheet metal blank primarily from hot strip, is cut to size at room temperature.
  • Mechanical cutting processes such as shearing or punching, but more rarely also thermal cutting processes, such as laser cutting, for application.
  • Thermal separation processes are significantly more cost-intensive compared to mechanical separation processes, so that they are only used in exceptional cases.
  • the cut blank is placed in a forming tool and formed into a finished chassis component in single or multi-stage forming steps.
  • the cut edges especially when they are raised or raised, e.g. with collar operations in perforated plates, particularly stressed.
  • Various previous damage can be present at the cut edges.
  • a notch effect can occur which is caused by the topography of the cut surface.
  • the previously mentioned damage to the sheet metal edges can lead to premature failure in subsequent forming operations or while driving.
  • the testing of the deformation behavior of cut sheet metal edges with regard to their sensitivity to edge cracks is carried out with a hole expansion test according to ISO 16630.
  • a hole expansion test according to ISO 16630.
  • the measured variable is the change in the hole diameter related to the initial diameter at which the first crack through the sheet occurs at the edge of the hole.
  • the object of the present invention is to provide a method for producing chassis components from microalloyed steel, produced from cold-formed blanks, which have an improved formability of work-hardened, mechanically separated sheet metal edges.
  • hot strip is preferred over cold strip in many applications.
  • micro-alloyed hot strip according to the invention with the stated composition range is that, in combination with the heat treatment according to the invention, a particularly favorable structure is formed in the transition area to the base material.
  • This transition area is also known as the heat affected zone.
  • This area is particularly at risk with regard to the formation of cracks when pulling the collar. The reason is that there are high tensions when the collar is formed, but at the same time, in contrast to the edge and the base material, the structure tends to be inhomogeneous and therefore has a comparatively low resistance to crack propagation.
  • the inhomogeneity is especially the formation of high hardness differences between the phase components is unfavorable with regard to crack resistance.
  • the differences in hardness between the phase components are reduced, in particular by the addition of micro-alloying elements mentioned, and the overall edge crack resistance is thus increased.
  • the reduction in the hardness differences between the structural components is due in particular to the specified contents of micro-alloying elements (V, Nb, Ti).
  • the effect of the mentioned micro-elements is in particular that the hardness of the naturally comparatively soft ferrite increases significantly due to the formation of precipitates.
  • the effect is known as precipitation strengthening. Since the carbon-rich, hard structural components (bainite, martensite) also to be expected in the transition area do not increase in hardness in the same way due to the formation of precipitates, the hardness differences are homogeneous.
  • At least up to Ac1, preferably up to above Ac3, is heated.
  • it is advantageous to heat for example, 100 ° C. above AC3.
  • a partial, preferably complete, conversion into austenite takes place, which converts to martensite and / or bainite as a result of the subsequent rapid cooling.
  • the final structure in the edge area of the shear-cut edges therefore usually consists of martensite and / or bainite as well as small proportions of tempered basic structure.
  • the proportion of the tempered basic structure decreases with increasing edge distance, while the proportion of the original basic structure increases with increasing edge distance.
  • the edge area treated according to the invention differs from the shear-cut state, apart from the structural change, in that the work hardening is eliminated.
  • the newly formed structure without strain hardening is clearly preferable to the structure in the shear-cut state with strain hardening in terms of crack tolerance, although the newly formed structure can tend to have a somewhat lower toughness.
  • Chassis components represent an application example in which high demands are placed on the formability of the flat component areas and the sheared edges be asked. An optimum in the formability of both areas can already mean a decisive advantage in the design of new component geometries.
  • the critical formability can be shown with the help of the deformation limit diagram.
  • An optimum is achieved when the deformation limit curve reaches the highest possible level.
  • the susceptibility of the sheared edges to cracking is not reflected by the position of the deformation limit curve. It is empirically proven that a high level of the deformation limit curve is often associated with a high susceptibility to cracking of the sheared edge.
  • Chassis components produced according to the invention have the advantage that the present alloy composition of the material has a high tensile strength of up to 1100 MPa.
  • the steel advantageously has a particularly high strain hardening, which has a positive effect on the mechanical properties of the fully formed chassis component.
  • cut and / or punched edges as well as sheet metal edges are produced which have a particularly high deformability during the hole expansion test without cracking the sheet metal edges.
  • Tests have shown that to improve the hole expansion capacity it is not necessary to carry out the cutting process even at an increased temperature of the cut edge areas, but that it is sufficient to only cut the work-hardened, shard-influenced cut edge areas in an unexpectedly short time interval in the range of less than 10 seconds but usually between 0.1 and 2.0 seconds to heat up to a temperature of at least 700 ° C. According to the invention, this can be detached from the cutting or punching process and the subsequent ones Manufacturing steps happen at any point in time before forming into a component.
  • the effect of heat occurs over the entire sheet metal thickness and in the plane direction of the board in an area that corresponds at most to the sheet metal thickness.
  • the duration of the heat exposure depends on the type of heat treatment process.
  • the heating itself can take place in any way, for example conductively, inductively via radiation heating or by means of laser processing.
  • Conductive heating as it is often used for example in the automotive industry using spot welds as an example, is ideal for heat treatment.
  • a spot welding machine with rather short exposure times is advantageously suitable for the treatment of punched holes in the plate, whereas the inductive process, radiation heating or laser processing with longer exposure times can be used for longer edge sections to be treated.
  • an advantageous further development of the invention provides for these areas to be flushed with inert gases, for example argon.
  • inert gases for example argon.
  • the inert gas purging takes place during the duration of the heat treatment. but can also, if it appears necessary, also take place shortly before the start and / or in a limited period of time after the heat treatment has been carried out.
  • the heat input is therefore only very concentrated in the shard-influenced cut edge areas and is therefore associated with comparatively little energy expenditure, in particular with regard to processes in which the entire plate is heated or a stress-relieving annealing that is orders of magnitude more time-consuming is used.
  • the process window for the temperature to be achieved in the cut edge area is also very large and covers a temperature range from 700 ° C to a solidus temperature of approx. 1500 ° C.
  • the inventive heating of the cut edges prior to cold forming of the blank has the advantage over the known measures to reduce the sensitivity to edge cracks that the heat treatment only changes the microstructure of the edge areas influenced by the shard and the strength is generally not reduced but increased.
  • the insensitivity to edge cracks in the sense of a greater hole expansion capacity can thus be improved by a factor of 2 to 5.
  • the scrap can be significantly reduced due to the significantly increased formability of the critical shard-influenced sheet metal edge areas and, on the other hand, previously necessary joining operations can be carried out, for example, by collar operations that can now be carried out during training, e.g. can be saved by storage locations.
  • the heat treatment of the cut edge areas to be cold formed can be carried out completely at any point in time after the cutting or stamping processes and before the forming of the blank or as an intermediate step in multi-stage forming operations of the blank for the production of chassis components, so that the process steps cutting or punching the blank, Heat treatment of the cut edges and reshaping of the blank are completely decoupled from each other. This makes production much more flexible than is possible according to the state of the art with the integration of an edge modification through heat treatment.
  • the process can be integrated as an intermediate production step in series production, which specifies a cycle in the range of 0.1 to 10 seconds.
  • the production of sheet metal components in the automotive sector in several successive steps is therefore a predestined area of application.
  • the forming of the blank prepared in this way can also advantageously be carried out with the forming tools already available in production, since no additional heating devices, such as e.g. Ovens are necessary to heat the circuit board itself. This enables cost-effective production and, due to the decoupling of the production steps, a high degree of flexibility in the production process.
  • the heating of the cut edges can also take place immediately after the mechanical cutting or punching processes or immediately before forming into a component, in a work step combined with the respective production process, if this appears advantageous.
  • the cutting and punching devices can be provided with a downstream heat treatment device or this can be connected directly upstream of the forming device for cold forming of the blank.
  • the board itself can advantageously e.g. be flexibly rolled with different thicknesses or be assembled from cold or hot strip of the same or different thickness.
  • the invention can advantageously be used for hot-rolled or cold-rolled steel strips with tensile strengths of 600 MPa to 1100 MPa, which can be provided with a corrosion-inhibiting layer as a metallic and / or organic coating.
  • the metallic coating can for example consist of zinc or an alloy of zinc or of magnesium or of aluminum and / or silicon.

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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)
  • Heat Treatment Of Sheet Steel (AREA)

Description

Die Erfindung betrifft ein Verfahren zur Herstellung von Fahrwerksbauteilen aus mikrolegiertem Stahl mit verbesserter Kaltumformbarkeit, hergestellt aus kaltumgeformten Platinen gemäß Patentanspruch 1, wobei die Platinen eine verbesserte Kaltumformbarkeit kaltverfestigter, mechanisch getrennter Kantenbesitzen. Fahrwerksbauteile können zum Beispiel Achsträger, Querlenker, Mehrlenkerhinterachsen, Verbundlenkerachsen, Vorderachse, Lenker sowie Längs- und Quertraversen sein.The invention relates to a method for the production of chassis components from microalloyed steel with improved cold formability, made from cold-formed blanks according to claim 1, the blanks having an improved cold formability of work-hardened, mechanically separated edges. Chassis components can be, for example, axle beams, wishbones, multi-link rear axles, twist beam axles, front axles, links, as well as longitudinal and cross members.

Die Herstellung von Fahrwerksbauteilen durch Kaltumformen ist zum Beispiel aus der Offenlegungsschrift DE 10 2008 060 161 A1 bekannt. Offenbart wird ein Verfahren zur Herstellung einer Fahrwerkskomponente mit erhöhter Dauerfestigkeit. Für die Kaltumformung wird ein Werkstoff eingesetzt, bestehend aus (in Gewichtsprozent): Kohlenstoff (C): 0,22% bis 0,25%, Silizium (Si): 0,20% bis 0,30%, Mangan (Mn): 1,20% bis 1,40%, Phosphor (P): maximal 0,020%, Schwefel (S): maximal 0,010%, Aluminium (AI): 0,020% bis 0,060%, Bor (B): 0,0020% bis 0,0035%, Chrom (Cr): 0,10% bis 0,20%, Titan (Ti): 0,020% bis 0,050%, Molybdän (Mo): maximal 0,35%, Kupfer (Cu): maximal 0,10%, Nickel (Ni): maximal 0,30%, Rest Eisen und erschmelzungsbedingte Verunreinigungen. Zur Erhöhung der Dauerfestigkeit des Bauteils wird das Halbzeug einer Nitrierbehandlung unterzogen. Die Kaltumformbarkeit kaltverfestigter, mechanisch getrennter Blechkanten wird nicht thematisiert.The production of chassis components by cold forming is, for example, from the laid-open specification DE 10 2008 060 161 A1 known. A method for producing a chassis component with increased fatigue strength is disclosed. A material is used for cold forming, consisting of (in percent by weight): carbon (C): 0.22% to 0.25%, silicon (Si): 0.20% to 0.30%, manganese (Mn): 1.20% to 1.40%, phosphorus (P): maximum 0.020%, sulfur (S): maximum 0.010%, aluminum (AI): 0.020% to 0.060%, boron (B): 0.0020% to 0 , 0035%, chromium (Cr): 0.10% to 0.20%, titanium (Ti): 0.020% to 0.050%, molybdenum (Mo): maximum 0.35%, copper (Cu): maximum 0.10 %, Nickel (Ni): maximum 0.30%, remainder iron and impurities from the melting process. To increase the fatigue strength of the component, the semi-finished product is subjected to a nitriding treatment. The cold formability of work-hardened, mechanically separated sheet metal edges is not discussed.

Üblicherweise wird zur Herstellung eines Fahrwerksbauteils zunächst eine Blechplatine, vornehmlich aus Warmband bei Raumtemperatur auf Maß geschnitten. Als Schneidverfahren kommen zumeist mechanische Trennverfahren, wie z.B. das Abscheren oder Stanzen, seltener aber auch thermische Trennverfahren, wie z.B. das Laserschneiden, zur Anwendung. Thermische Trennverfahren sind deutlich kostenintensiver im Vergleich zu mechanischen Trennverfahren, so dass diese nur in Ausnahmefällen eingesetzt werden.Usually, to manufacture a chassis component, a sheet metal blank, primarily from hot strip, is cut to size at room temperature. Mechanical cutting processes such as shearing or punching, but more rarely also thermal cutting processes, such as laser cutting, for application. Thermal separation processes are significantly more cost-intensive compared to mechanical separation processes, so that they are only used in exceptional cases.

Nach dem Zuschneiden wird die zugeschnittene Platine in ein Umformwerkzeug gelegt und in ein- oder mehrstufigen Umformschritten zu einem fertigen Fahrwerksbauteil umgeformt.After cutting, the cut blank is placed in a forming tool and formed into a finished chassis component in single or multi-stage forming steps.

Vor der Kaltumformung werden diverse weitere Fertigungsschritte, wie z.B. Stanz- und Schneidoperationen an der Platine und das Anbringen von Lochungen zur Gewichtsreduzierung oder Durchführungen von Leitungen etc. durchgeführt, und es werden fallweise während der Umformung kombinierte Umstell- oder Aufweitoperationen an den gelochten Abschnitten vorgenommen.Various other manufacturing steps, such as punching and cutting operations on the board and the making of perforations, are carried out before cold forming Weight reduction or lead-throughs of lines etc. are carried out, and, on a case-by-case basis, combined resetting or expanding operations are carried out on the perforated sections during the forming process.

Bei der Kaltumformung werden die Schnittkanten, insbesondere wenn sie auf- bzw. hochgestellt werden, z.B. bei Kragenoperationen in gelochten Platinen, besonders belastet. An den Schnittkanten können diverse Vorschädigungen vorliegen. Zum einen bedingt durch eine Kaltverfestigung des Werkstoffs, hervorgerufen durch das mechanische Trennen, das eine totale Umformung bis zur Materialtrennung darstellt. Zum anderen kann eine Kerbwirkung auftreten, welche durch die Topographie der Schnittfläche entsteht.During cold forming, the cut edges, especially when they are raised or raised, e.g. with collar operations in perforated plates, particularly stressed. Various previous damage can be present at the cut edges. On the one hand, due to the strain hardening of the material, caused by the mechanical separation, which represents a total deformation up to the material separation. On the other hand, a notch effect can occur which is caused by the topography of the cut surface.

Gerade bei hoch- und höchstfesten Blechwerkstoffen tritt daher abhängig von der konkreten Legierungszusammensetzung und dem Gefüge bei der anschließenden Umformung eine erhöhte Risswahrscheinlichkeit in den Randbereichen dieser Schnittkanten auf.Particularly in the case of high-strength and ultra-high-strength sheet materials, depending on the specific alloy composition and the structure, there is an increased probability of cracks in the edge areas of these cut edges during the subsequent forming.

Die genannten Vorschädigungen an den Blechkanten können zum vorzeitigen Versagen bei nachfolgenden Umformoperationen bzw. im Fahrbetrieb führen. Die Prüfung des Umformverhaltens geschnittener Blechkanten im Hinblick auf deren Kantenrissempfindlichkeit wird mit einem Lochaufweitversuch nach ISO 16630 durchgeführt. Beim Lochaufweitversuch wird in das Blech durch Scherschneiden ein kreisrundes Loch eingebracht, das dann durch einen konischen Stempel aufgeweitet wird. Die Messgröße ist die auf den Ausgangsdurchmesser bezogene Änderung des Lochdurchmessers, bei der am Rand des Lochs der erste Riss durch das Blech auftritt.The previously mentioned damage to the sheet metal edges can lead to premature failure in subsequent forming operations or while driving. The testing of the deformation behavior of cut sheet metal edges with regard to their sensitivity to edge cracks is carried out with a hole expansion test according to ISO 16630. In the hole widening test, a circular hole is made in the sheet metal by shear cutting, which is then widened by a conical punch. The measured variable is the change in the hole diameter related to the initial diameter at which the first crack through the sheet occurs at the edge of the hole.

Um die vorab beschriebene Kantenrissempfindlichkeit bei der Kaltumformung von schergeschnittenen oder gestanzten Blechkanten zu minimieren, sind z.B. Ansätze zur Veränderung der Legierungszusammensetzung und Werkstoffprozessierung (z.B. gezieltes Einstellen von bainitischen Gefügen)oder der Verfahrenstechnik beim Kaltbeschnitt der Platine (z.B. über Modifikationen von Schneidspalt, Geschwindigkeit, Mehrfachbeschnitt etc.) bekannt.In order to minimize the previously described sensitivity to edge cracks during cold forming of sheared or punched sheet metal edges, e.g. Approaches to changing the alloy composition and material processing (e.g. targeted setting of bainitic structures) or the process engineering for cold cutting of the blank (e.g. via modifications of the cutting gap, speed, multiple trimming, etc.) are known.

Diese Maßnahmen sind entweder teuer und aufwändig (z.B. mehrstufige Schneidoperationen, Instandhaltung von 3-D Schnitten etc.), oder sie liefern noch keine optimalen Ergebnisse.These measures are either expensive and complex (e.g. multi-stage cutting operations, maintenance of 3-D cuts, etc.), or they do not yet provide optimal results.

Aus der Offenlegungsschrift DE 10 2012 002 079 A1 ist ein höchstfester mikrolegierter Mehrphasenstahl für ein kalt- oder warmgewalztes Stahlband mit hoher Kantenrissbeständigkeit bekannt.From the publication DE 10 2012 002 079 A1 is a high-strength micro-alloyed multiphase steel for a cold or hot-rolled steel strip with high edge crack resistance.

Des Weiteren ist es aus der Offenlegungsschrift DE 10 2009 049 155 A1 bekannt, zumindest den Bereich der Schnittkante auf eine definierte Temperatur zu erwärmen und das Schneiden bei dieser Temperatur durchzuführen, um die Umformbarkeit der geschnittenen Kanten zu verbessern und so die Kaltverfestigung im Bereich der Schnittkante zu reduzieren oder zu vermeiden. Nachteilig sind hierbei der zur Erwärmung des Bleches notwendige hohe technische und wirtschaftliche Aufwand einerseits und andererseits die für die Zwangskopplung von Erwärmung der Platine und unmittelbar nachfolgendem Schneiden, die die Produktion unflexibler machen.It is also from the patent application DE 10 2009 049 155 A1 known to heat at least the area of the cut edge to a defined temperature and to perform the cutting at this temperature in order to improve the deformability of the cut edges and thus reduce or avoid strain hardening in the area of the cut edge. Disadvantages here are the high technical and economic outlay required to heat the sheet metal, on the one hand, and, on the other hand, the forced coupling of the heating of the blank and the immediately subsequent cutting, which make production less flexible.

Aus der Offenlegungsschrift DE 10 2011 121 904 A1 ist es zudem bekannt, ein schergeschnittenes Blech kalt umzuformen und vor weiteren Umformvorgängen die kaltverfestigten Bereiche lokal mittels eines Lasers zu erwärmen mit dem Ziel einer partiellen Entfestigung. Nachteilig ist hierbei insbesondere die lokale Entfestigung, die hinsichtlich des eingesetzten oft hoch- und höchstfesten Materials insbesondere bei Belastungssituationen und unter schwingender Beanspruchung eine Ungänze darstellt. Darüber hinaus ist unklar, wo genau die Erwärmung stattfinden und wie die lokale Erwärmung mit Temperatur und Zeitverlauf konkret erfolgen soll. Des Weiteren ist unklar, wie und in welchem Maße durch die partielle Entfestigung das Umformvermögen des bereits kaltumgeformten Bleches verbessert werden kann.From the publication DE 10 2011 121 904 A1 It is also known to cold-form a shear-cut sheet metal and, before further forming processes, to heat the work-hardened areas locally by means of a laser with the aim of partial softening. A particular disadvantage here is the local softening, which in terms of the often high-strength and extremely high-strength material used, especially in stressful situations and under vibrating loads, represents a lack of strength. In addition, it is unclear where exactly the warming takes place and how the local warming should actually take place with the temperature and the course of time. Furthermore, it is unclear how and to what extent the deformability of the already cold-formed sheet can be improved by the partial softening.

Aus der Offenlegungsschrift DE 10 2014 016 614 A1 ist ein Verfahren zur Herstellung eines kaltumgeformten Bauteils aus einer bei Raumtemperatur schergeschnittenen Blechplatine mit fallweise diversen weiteren bei Raumtemperatur durchgeführten Fertigungsschritten, wie z.B. Lochstanz- oder Schneidoperationenbekannt, bei dem die bei den Schneid- oder Stanzoperationen kalt verfestigten Blechkantenbereiche, welche eine anschließende Kaltumformung bei der Herstellung des Bauteils erfahren, auf eine Temperatur von mindestens 600°C erwärmt werden und die Zeit der Temperaturbeaufschlagung weniger als 10 Sekunden beträgt. Hierdurch soll die Kaltumformbarkeit dieser kaltverfestigten Blechkanten deutlich verbessert werden. Anwendung findet dieses Verfahren u.A. bei mikrolegierten Stählen. Es finden sich jedoch keinerlei Hinweise auf eine konkrete Legierungszusammensetzung der dort offenbarten Stähle und die Auswirkung der Wärmebehandlung auf das entstehende Gefüge.From the publication DE 10 2014 016 614 A1 a method for producing a cold-formed component from a sheet metal blank sheared at room temperature with, in some cases, various other production steps carried out at room temperature, such as hole punching or cutting operations, is known in which the sheet metal edge areas cold-hardened during the cutting or punching operations, which are then subjected to cold forming during production experience of the component, heated to a temperature of at least 600 ° C and the time the temperature is applied is less than 10 seconds. This is intended to significantly improve the cold formability of these work-hardened sheet metal edges. This process is used, among other things, for micro-alloyed steels. However, there is no indication of a specific alloy composition of the steels disclosed there and the effect of the heat treatment on the resulting structure.

Derzeitiger Stand der Technik ist daher eine aufwändige Nacharbeit der hochgestellten Kanten. Ein sehr hoher Ausschuss in der Produktion bei unterschiedlichen Verarbeiternist üblich. Die Darstellung komplexer Bauteilgeometrien ist zudem mit dem aus der Offenlegungsschrift DE 10 2008 060 161 A1 bekannten Werkstoff nicht möglich, und damit ist die konstruktive Gestaltungsfreiheit eingeschränkt.The current state of the art is therefore a complex reworking of the raised edges. A very high level of rejects in production with different processors is common. The representation of complex component geometries is also compatible with the Disclosure document DE 10 2008 060 161 A1 known material is not possible, and this restricts the freedom of design.

Aufgabe der vorliegenden Erfindung ist es, ein Verfahren zur Herstellung von Fahrwerksbauteilen aus mikrolegiertem Stahl, hergestellt aus kalt umgeformten Platinen, anzugeben, welche eine verbesserte Umformbarkeit kaltverfestigter, mechanisch getrennter Blechkanten besitzen.The object of the present invention is to provide a method for producing chassis components from microalloyed steel, produced from cold-formed blanks, which have an improved formability of work-hardened, mechanically separated sheet metal edges.

Nach der Lehre der Erfindung wird diese Aufgabe durch ein Verfahren mit folgenden Schritten gelöst:

  • Bereitstellen eines Warmbandes oder eines Warmbandblechs, aufweisend folgende Legierungszusammensetzung in Gewichts.-%: C: 0,04 bis 0,12, Si: max. 0,7, Mn: 1,0 bis 2,2, P: max.0,02, S: max. 0,002, N: max. 0,03, V: 0,005 bis 0,5, Nb: 0,005 bis 0,1, Ti: 0,005 bis 0,2, (V+Nb+Ti: min. 0,05max. 0,4) sowie eines oder mehrere der Elemente aus der Summe von Cu+Cr+ Ni: max. 1 (mind. 0,0) mit Cr: max. 0,9, Ni: max. 0,5, Cu: max. 0,5, sowie optional Mo: max. 0,5, Rest Eisen und erschmelzungsbedingte Verunreinigungen,
  • Zuschneiden einer Platine bei Raumtemperatur sowie optionaler Durchführung weiterer Stanz- oder Schneidoperationen, zur Erzielung von Aussparungen, Löchern oder Durchbrüchen an der Platine bei Raumtemperatur
  • Erwärmen ausschließlich der durch die Schneid- oder Stanzoperationen kalt verfestigten Blechkantenbereiche der Platine auf eine Temperatur von mindestens 700°Cmit einer Haltezeit von höchstens 10 Sekunden und anschließender Abkühlung an Luft
  • Kaltumformen der Platine in einem oder mehreren Schritten zu einem Fahrwerksbauteil bei Raumtemperatur.
According to the teaching of the invention, this object is achieved by a method with the following steps:
  • Providing a hot strip or a hot strip sheet, having the following alloy composition in% by weight: C: 0.04 to 0.12, Si: max. 0.7, Mn: 1.0 to 2.2, P: 0.02 max, S: max. 0.002, N: max. 0.03, V: 0.005 to 0.5, Nb: 0.005 to 0.1, Ti: 0.005 to 0.2, (V + Nb + Ti: min. 0.05 max. 0.4) and one or more of the Elements from the sum of Cu + Cr + Ni: max. 1 (at least 0.0) with Cr: max. 0.9, Ni: max. 0.5, Cu: max. 0.5, as well as optional Mo: max. 0.5, remainder iron and impurities from the melting process
  • Cutting a board to size at room temperature and optionally carrying out further punching or cutting operations to achieve recesses, holes or openings on the board at room temperature
  • Heating exclusively of the sheet metal edge areas of the blank that have been cold-hardened by the cutting or punching operations to a temperature of at least 700 ° C with a holding time of no more than 10 seconds and subsequent cooling in air
  • Cold forming of the blank in one or more steps into a chassis component at room temperature.

Auf Grund der geringeren Herstellungskosten wird Warmband gegenüber Kaltband in vielen Anwendungsfällen bevorzugt.Because of the lower production costs, hot strip is preferred over cold strip in many applications.

Der Vorteil von erfindungsgemäß mikrolegiertem Warmband mit dem genannten Zusammensetzungsbereich besteht darin, dass in Kombination mit der erfindungsgemäßen Wärmebehandlung im Übergangsbereich zum Grundwerkstoff ein besonders günstiges Gefüge ausgebildet wird. Dieser Übergangsbereich ist auch als Wärmeeinflusszone bekannt. Insbesondere zu nennen ist der geringe Härteunterschiede in den zu erwartenden Gefügebestandteilen und ein vergleichsweise geringer Härteabfall im Übergangsberereich gegenüber dem Grundwerkstoff. Dieser Bereich ist hinsichtlich der Rissausbildung beim Kragenziehen besonders gefährdet. Der Grund ist, dass hohe Spannungen bei der Formung des Kragens vorliegen, gleichzeitig aber im Gegensatz zur Kante und zum Grundwerkstoff, das Gefüge zur Inhomogenität neigt und daher gegenüber Rissausbreitung einen vergleichsweise geringen Widerstand aufweist. Bezüglich der Inhomogenität ist insbesondere die Ausbildung von hohen Härteunterschieden zwischen den Phasenbestandteilen hinsichtlich des Risswiderstandes ungünstig. Bei mikrolegierten Stählen mit oben genannter Zusammensetzung werden die Härteunterschiede zwischen den Phasenbestandteilen insbesondere durch die genannte Zugabe von Mikrolegierungselementen verringert und so insgesamt der Kantenrisswiderstand erhöht. Die Verringerung der Härteunterschiede zwischen den Gefügebestandteilen ist insbesondere auf die angegebenen Gehalten an Mikrolegierungselemente (V, Nb, Ti) zurückzuführen. Dabei besteht die Wirkung der genannten Mikroelemente insbesondere darin, dass durch Ausscheidungsbildung die Härte des natürlicherweise vergleichsweise weichen Ferrits bedeutend zunimmt. Die Wirkung ist als Ausscheidungsverfestigung bekannt. Da die ebenfalls in dem Übergangsbereich zu erwartenden kohlenstoffreichen, harten Gefügebestandteile (Bainit, Martensit) nicht in gleicher Weise durch Ausscheidungsbildung in der Härte zunehmen, wird eine Homogenität der Härteunterschiede erreicht.The advantage of micro-alloyed hot strip according to the invention with the stated composition range is that, in combination with the heat treatment according to the invention, a particularly favorable structure is formed in the transition area to the base material. This transition area is also known as the heat affected zone. Particular mention should be made of the small differences in hardness in the expected structural components and a comparatively small drop in hardness in the transition area compared to the base material. This area is particularly at risk with regard to the formation of cracks when pulling the collar. The reason is that there are high tensions when the collar is formed, but at the same time, in contrast to the edge and the base material, the structure tends to be inhomogeneous and therefore has a comparatively low resistance to crack propagation. Regarding the inhomogeneity is especially the formation of high hardness differences between the phase components is unfavorable with regard to crack resistance. In the case of micro-alloyed steels with the above-mentioned composition, the differences in hardness between the phase components are reduced, in particular by the addition of micro-alloying elements mentioned, and the overall edge crack resistance is thus increased. The reduction in the hardness differences between the structural components is due in particular to the specified contents of micro-alloying elements (V, Nb, Ti). The effect of the mentioned micro-elements is in particular that the hardness of the naturally comparatively soft ferrite increases significantly due to the formation of precipitates. The effect is known as precipitation strengthening. Since the carbon-rich, hard structural components (bainite, martensite) also to be expected in the transition area do not increase in hardness in the same way due to the formation of precipitates, the hardness differences are homogeneous.

Eine effektive Wirkung ist erst bei einem Summengehalt von V+Nb+Ti: min. 0,05 zu erwarten. Aufgrund eines gewissen Sättigungsverhaltens und aus Kostengründen sind Gehalte über V+Nb+Ti = 0,4 nicht sinnvoll.An effective effect is only with a total content of V + Nb + Ti: min. 0.05 expected. Due to a certain saturation behavior and for cost reasons, contents above V + Nb + Ti = 0.4 are not sensible.

Bei dem erfindungsgemäßen Verfahren wird mindestens bis Ac1, vorzugsweise bis über Ac3 erwärmt. Vorteilhaft kann zur Verringerung der Behandlungsdauer üblicherweise zum Beispiel 100°C über AC3 erwärmt werden.In the process according to the invention, at least up to Ac1, preferably up to above Ac3, is heated. In order to reduce the duration of the treatment, it is advantageous to heat, for example, 100 ° C. above AC3.

Hierbei erfolgt eine teilweise, vorzugsweise vollständige Umwandlung in Austenit, der durch die anschließende rasche Abkühlung in Martensit und/oder Bainit umwandelt. Das finale Gefüge im Randbereich der schergeschnittenen Kanten besteht also üblicherweise aus Martensit und/oder Bainit sowie geringe Anteile von angelassenem Grundgefüge. Der Anteil des angelassenen Grundgefüges nimmt mit zunehmendem Randabstand ab, während der Anteil des ursprünglichen Grundgefüges mit zunehmenden Randabstand zunimmt.A partial, preferably complete, conversion into austenite takes place, which converts to martensite and / or bainite as a result of the subsequent rapid cooling. The final structure in the edge area of the shear-cut edges therefore usually consists of martensite and / or bainite as well as small proportions of tempered basic structure. The proportion of the tempered basic structure decreases with increasing edge distance, while the proportion of the original basic structure increases with increasing edge distance.

Der erfindungsgemäß behandelte Randbreich unterscheidet sich vom schergeschnittenen Zustand abgesehen von der Gefügeänderung darin, dass die Kaltverfestigung eliminiert ist. In der Summe ist das neugebildete Gefüge ohne Kaltverfestigung dem Gefüge im schergeschnittenen Zustand mit Kaltverfestigung hinsichtlich der Anrisstoleranz deutlich zu bevorzugen, obwohl tendenziell das neugebildete Gefüge eine etwas geringere Zähigkeit aufweisen kann.The edge area treated according to the invention differs from the shear-cut state, apart from the structural change, in that the work hardening is eliminated. Overall, the newly formed structure without strain hardening is clearly preferable to the structure in the shear-cut state with strain hardening in terms of crack tolerance, although the newly formed structure can tend to have a somewhat lower toughness.

Fahrwerksbauteile stellen ein Anwendungsbeispiel dar, bei dem hohe Anforderungen an die Umformbarkeit der flächigen Bauteilbereiche als auch der schergeschnittenen Kanten gestellt werden. Ein Optimum in der Umformbarkeit beider Bereiche kann bereits einen entscheidenden Vorteil in der Konstruktion neuer Bauteilgeometrien bedeuten.Chassis components represent an application example in which high demands are placed on the formability of the flat component areas and the sheared edges be asked. An optimum in the formability of both areas can already mean a decisive advantage in the design of new component geometries.

Bei der Umformung flächiger Bauteilbereiche lässt sich die kritische Umformbarkeit mit Hilfe des Grenzformänderungsdiagramms darstellen. Ein Optimum wird erreicht, wenn die Grenzformänderungskurve ein möglichst hohes Niveau erreicht. Die Rissanfälligkeit der schergeschnittenen Kanten wird hingegen nicht durch die Lage der Grenzformänderungskurve wiedergegeben. Empirisch belegt ist, dass häufig ein hohes Niveau der Grenzformänderungskurve mit einer hohen Rissanfälligkeit der schergeschnittenen Kante einhergeht.When forming flat component areas, the critical formability can be shown with the help of the deformation limit diagram. An optimum is achieved when the deformation limit curve reaches the highest possible level. The susceptibility of the sheared edges to cracking, however, is not reflected by the position of the deformation limit curve. It is empirically proven that a high level of the deformation limit curve is often associated with a high susceptibility to cracking of the sheared edge.

Ein Optimum in der Umformbarkeit beider Bereiche lässt sich daher nur durch Kombination des erfindungsgemäßen Verfahrens mit dem erfindungsgemäßen Werkstoff erreichen, der ein hohes Niveau der Grenzformänderungskurve aufweist.An optimum in the formability of both areas can therefore only be achieved by combining the method according to the invention with the material according to the invention, which has a high level of the deformation limit curve.

Erfindungsgemäß hergestellte Fahrwerksbauteile weisen den Vorteil auf, dass die vorliegende Legierungszusammensetzung des Werkstoffs eine hohe Zugfestigkeit von bis zu 1100 MPa aufweist.Chassis components produced according to the invention have the advantage that the present alloy composition of the material has a high tensile strength of up to 1100 MPa.

Zudem weist der Stahl vorteilhaft eine besonders hohe Kaltverfestigung auf, was sich positiv auf die mechanischen Eigenschaften des fertig geformten Fahrwerksbauteils niederschlägt.In addition, the steel advantageously has a particularly high strain hardening, which has a positive effect on the mechanical properties of the fully formed chassis component.

In Kombination mit der Legierungszusammensetzung und mit dem erfindungsgemäßen wärmebehandelten Gefüge werden Schnitt- und/oder Stanzkanten sowie Blechkanten erzeugt, die ein besonders hohes Umformvermögen beim Lochaufweitversuch ohne Rissbildung an den Blechkanten aufweisen.In combination with the alloy composition and with the heat-treated structure according to the invention, cut and / or punched edges as well as sheet metal edges are produced which have a particularly high deformability during the hole expansion test without cracking the sheet metal edges.

Die vorgeschlagene Behandlung von schergeschnittenen Kanten von Platinenbereichen, die während der Formung zu einem Fahrwerksbauteil eine erhebliche Kaltverformung erfahren, führt zu einer ausgeprägten Reduzierung der Rissbildung im Fertigungsprozess.The proposed treatment of sheared edges of blank areas, which undergo considerable cold deformation during the forming into a chassis component, leads to a marked reduction in the formation of cracks in the manufacturing process.

Versuche haben gezeigt, dass es zur Verbesserung des Lochaufweitvermögens nicht notwendig ist, den Schneidprozess selbst bei erhöhter Temperatur der Schnittkantenbereiche durchzuführen, sondern dass es ausreichend ist, nur die kaltverfestigten, scherbeeinflussten Schnittkantenbereiche in einem unerwartet kurzen Zeitintervall im Bereich von weniger als 10 Sekunden, in der Regel aber zwischen 0,1 und 2,0 Sekunden, auf eine Temperatur von mindestens 7 00°Caufzuheizen. Erfindungsgemäß kann dies losgelöst vom Schneid- oder Stanzprozess und den nachfolgenden Fertigungsschritten zu einem beliebigen Zeitpunkt vor der Umformung zu einem Bauteil geschehen.Tests have shown that to improve the hole expansion capacity it is not necessary to carry out the cutting process even at an increased temperature of the cut edge areas, but that it is sufficient to only cut the work-hardened, shard-influenced cut edge areas in an unexpectedly short time interval in the range of less than 10 seconds but usually between 0.1 and 2.0 seconds to heat up to a temperature of at least 700 ° C. According to the invention, this can be detached from the cutting or punching process and the subsequent ones Manufacturing steps happen at any point in time before forming into a component.

Die Wärmeeinwirkung erfolgt dabei über die gesamte Blechdicke und in Ebenenrichtung der Platine in einem Bereich, der höchstens der Blechdicke entspricht. Die Dauer der Wärmeeinwirkung richtet sich dabei nach der Art des Wärmebehandlungsverfahrens.The effect of heat occurs over the entire sheet metal thickness and in the plane direction of the board in an area that corresponds at most to the sheet metal thickness. The duration of the heat exposure depends on the type of heat treatment process.

Die Erwärmung selbst kann auf beliebige Weise zum Beispiel konduktiv, induktiv über Strahlungserwärmung oder mittels Laserbearbeitung erfolgen. Hervorragend geeignet für die Wärmebehandlung ist die konduktive Erwärmung, wie sie zum Beispiel in der Automobilfertigung vielfach am Beispiel von Punktschweißungen angewendet wird. Vorteilhaft eignet sich zum Beispiel eine Punktschweißmaschine mit eher kurzen Einwirkzeiten zur Behandlung von gestanzten Löchern in der Platine, wohingegen bei zu behandelnden längeren Kantenabschnitten das induktive Verfahren, Strahlungserwärmung oder Laserbearbeitung mit längeren Einwirkzeiten in Frage kommt.The heating itself can take place in any way, for example conductively, inductively via radiation heating or by means of laser processing. Conductive heating, as it is often used for example in the automotive industry using spot welds as an example, is ideal for heat treatment. For example, a spot welding machine with rather short exposure times is advantageously suitable for the treatment of punched holes in the plate, whereas the inductive process, radiation heating or laser processing with longer exposure times can be used for longer edge sections to be treated.

Zum Schutz der erwärmten Schnittkantenbereiche vor Oxidation sieht eine vorteilhafte Weiterbildung der Erfindung vor, diese Bereiche mit Inertgasen, zum Beispiel Argon, zu spülen. Die Inertgasspülung erfolgt dabei während der Dauer der Wärmebehandlung. kann aber auch, falls es notwendig erscheint, zusätzlich schon kurz vor Beginn und/oder in einem begrenzten Zeitraum noch nach Durchführung der Wärmebehandlung erfolgen.To protect the heated cut edge areas from oxidation, an advantageous further development of the invention provides for these areas to be flushed with inert gases, for example argon. The inert gas purging takes place during the duration of the heat treatment. but can also, if it appears necessary, also take place shortly before the start and / or in a limited period of time after the heat treatment has been carried out.

Somit erfolgt die Wärmeeinbringung nur sehr konzentriert in den scherbeeinflussten Schnittkantenbereichen und ist daher mit einem vergleichsweise geringem Energieaufwand verbunden, insbesondere hinsichtlich Verfahren, bei denen die gesamte Platine einer Erwärmung zugeführt wird oder eine um Größenordnungen zeitlich aufwendigere Spannungsarmglühung Anwendung findet.The heat input is therefore only very concentrated in the shard-influenced cut edge areas and is therefore associated with comparatively little energy expenditure, in particular with regard to processes in which the entire plate is heated or a stress-relieving annealing that is orders of magnitude more time-consuming is used.

Das Prozessfenster für die zu erreichende Temperatur im Schnittkantenbereich ist zudem sehr groß und umfasst einen Temperaturbereich von 700°C bis hin zur Solidustemperatur von ca. 1500°C.The process window for the temperature to be achieved in the cut edge area is also very large and covers a temperature range from 700 ° C to a solidus temperature of approx. 1500 ° C.

Die Versuche haben außerdem gezeigt, dass allein die Eliminierung der Kaltverfestigung entscheidend für eine deutliche Verbesserung des Lochaufweitvermögens ist und die nicht ausheilbaren Ungänzen, wie z.B. Poren, einer untergeordneten Bedeutung zukommen. Dies ist unabhängig davon, ob die Wärmebehandlung unterhalb oder oberhalb der Umwandlungstemperatur Ac1stattfindet.The tests have also shown that the elimination of work hardening alone is decisive for a significant improvement in the hole expansion capacity and that the non-healable imperfections, such as pores, are of secondary importance. This is independent of whether the heat treatment takes place below or above the transition temperature Ac1.

Wird die Wärmebehandlung oberhalb von Ac1 durchgeführt, kommt es nach Behandlung im Zuge einer raschen Abkühlung aufgrund des umgebenden kalten Materials bei umwandlungsfähigen Stählen zu einer Umwandlung in sogenannte metastabile Phasen. Das daraufhin einstellende Gefüge wird sich vom Ausgangszustand hinsichtlich einer erhöhten Festigkeit unterscheiden.If the heat treatment is carried out above Ac1, transformation into so-called metastable phases occurs after treatment in the course of rapid cooling due to the surrounding cold material. The resulting structure will differ from the initial state in terms of increased strength.

Eine Gefügeumwandlung mit einer damit in aller Regel einhergehenden Härte- und Festigkeitssteigerung hat überraschenderweise keinen negativen Einfluss auf das Lochaufweitvermögen, unabhängig davon, ob ein im Vergleich zum Ausgangsgefüge härteres und weniger zähes Gefüge eingestellt wird, so dass auch Behandlungstemperaturen der Schnittkanten bis hin zur Solidusgrenze möglich sind. Entscheidend bleibt in jedem Falle, dass die durch das Schneiden eingebrachte Kaltverfestigung weitestgehend eliminiert wird.Surprisingly, a structural transformation with an increase in hardness and strength associated with it has no negative influence on the hole expansion capacity, regardless of whether a structure that is harder and less tough than the original structure is set, so that treatment temperatures of the cut edges up to the solidus limit are also possible are. In any case, it remains decisive that the work hardening introduced by the cutting is largely eliminated.

Um die erfindungsgemäßen Ziele zu erreichen, reicht es nach den vorliegenden Untersuchungen nicht aus, eine Erwärmung unterhalb 700°C für die Dauer einiger Sekunden durchzuführen, da eine deutliche Reduzierung der durch den mechanischen Trennvorgang eingebrachten Versetzungen erfolgen muss.In order to achieve the goals according to the invention, according to the present investigations it is not sufficient to carry out heating below 700 ° C. for a period of a few seconds, since the dislocations introduced by the mechanical separation process must be significantly reduced.

Die erfindungsgemäße Erwärmung der Schnittkanten vor der Kaltumformung der Platine hat gegenüber den bekannten Maßnahmen zur Verminderung der Kantenrissempfindlichkeit den Vorteil, dass durch die Wärmebehandlung nur der scherbeeinflussten Kantenbereiche mikrostrukturell verändert und die Festigkeit dabei in der Regel nicht verringert, sondern erhöht wird. Die Unempfindlichkeit gegenüber Kantenrissen im Sinne eines größeren Lochaufweitvermögens kann damit um den Faktor 2 bis Faktor 5verbessert werden.The inventive heating of the cut edges prior to cold forming of the blank has the advantage over the known measures to reduce the sensitivity to edge cracks that the heat treatment only changes the microstructure of the edge areas influenced by the shard and the strength is generally not reduced but increased. The insensitivity to edge cracks in the sense of a greater hole expansion capacity can thus be improved by a factor of 2 to 5.

Bei der industriellen Anwendung der Schnittkantenerwärmung an erfindungsgemäßen mikrolegierten Stählen für Fahrwerksbauteile kann aufgrund der deutlich erhöhten Umformbarkeit der kritischen scherbeeinflussten Blechkantenbereiche einerseits der Ausschuss deutlich gesenkt werden und andererseits können bislang notwendige Fügeoperationen zum Beispiel durch jetzt durchführbare Kragenoperationen bei der Ausbildung z.B. von Lagerstellen eingespart werden.In the industrial application of cutting edge heating on microalloyed steels according to the invention for chassis components, on the one hand, the scrap can be significantly reduced due to the significantly increased formability of the critical shard-influenced sheet metal edge areas and, on the other hand, previously necessary joining operations can be carried out, for example, by collar operations that can now be carried out during training, e.g. can be saved by storage locations.

Die erfindungsgemäßen Verfahrensschritte zur Herstellung von Fahrwerksbauteilen in Kombination mit der Legierungszusammensetzung und dem Gefüge des mikrolegierten Stahls erlaubt durch das verbesserte Umformvermögen der Schnittkantenbereiche komplexere Bauteilgeometrien und somit eine größere konstruktive Freiheit bei Verwendung derselben Werkstoffe. Zudem wird die Dauerfestigkeit des kalt umgeformten Bauteils erwartungsgemäß aufgrund des sich einstellenden, zwar möglicherweise im Vergleich zum Ausgangszustand härteren aber homogenen Gefüges nicht verringert, sondern vorteilhaft erhöht.The method steps according to the invention for the production of chassis components in combination with the alloy composition and the structure of the micro-alloyed Due to the improved formability of the cut edge areas, steel allows more complex component geometries and thus greater design freedom when using the same materials. In addition, as expected, the fatigue strength of the cold-formed component is not reduced, but advantageously increased, due to the resultant, possibly harder but homogeneous structure compared to the initial state.

Die Wärmebehandlung der kalt umzuformenden Schnittkantenbereiche kann vollständig zu einem beliebigen Zeitpunkt nach den Schneid- oder Stanzprozessen und vor der Umformung der Platine oder als Zwischenschritt bei mehrstufigen Umformoperationen der Platine zur Herstellung von Fahrwerksbauteilen durchgeführt werden, so dass die Prozessschritte Schneiden bzw. Stanzen der Platine, Wärmebehandlung der Schnittkanten und Umformung der Platine voneinander vollständig entkoppelt sind. Somit wird die Fertigung deutlich flexibler, als es nach dem Stand der Technik bei Integration einer Kantenmodifikation durch Wärmebehandlung möglich ist.The heat treatment of the cut edge areas to be cold formed can be carried out completely at any point in time after the cutting or stamping processes and before the forming of the blank or as an intermediate step in multi-stage forming operations of the blank for the production of chassis components, so that the process steps cutting or punching the blank, Heat treatment of the cut edges and reshaping of the blank are completely decoupled from each other. This makes production much more flexible than is possible according to the state of the art with the integration of an edge modification through heat treatment.

Aufgrund der im Vergleich zu bekannten Maßnahmen kurzen Behandlungsdauer kann das Verfahren in einer Serienfertigung, die eine Taktung im Bereich von 0,1 bis 10 Sekunden vorgibt, als Zwischenfertigungsschritt integriert werden. Insbesondere die Fertigung von Blechkomponenten im Automobilbereich in mehreren aufeinander folgenden Schritten stellt somit einen prädestinierten Anwendungsbereich dar.Due to the short treatment time compared to known measures, the process can be integrated as an intermediate production step in series production, which specifies a cycle in the range of 0.1 to 10 seconds. In particular, the production of sheet metal components in the automotive sector in several successive steps is therefore a predestined area of application.

Die Umformung der so vorbereiteten Platine kann zudem vorteilhaft mit den bereits in der Produktion vorhandenen Umformwerkzeugen durchgeführt werden, da keine zusätzlichen Erwärmungseinrichtungen, wie z.B. Öfen, zum Aufheizen der Platine selbst notwendig sind. Dies ermöglicht eine weiterhin kostengünstige Fertigung und durch die Entkopplung der Fertigungsschritte eine hohe Flexibilität im Produktionsablauf.The forming of the blank prepared in this way can also advantageously be carried out with the forming tools already available in production, since no additional heating devices, such as e.g. Ovens are necessary to heat the circuit board itself. This enables cost-effective production and, due to the decoupling of the production steps, a high degree of flexibility in the production process.

Nach einer vorteilhaften Weiterbildung der Erfindung kann die Erwärmung der Schnittkanten jedoch abhängig vom vorgesehenen Produktionsablauf, wenn dies vorteilhaft erscheint, auch unmittelbar nach den mechanischen Schneid- oder Stanzprozessen oder unmittelbar vor der Umformung zu einem Bauteil, in einem mit dem jeweiligen Fertigungsprozess kombinierten Arbeitsschritt erfolgen. Zum Beispiel können die Schneid- und Stanzeinrichtungen mit einer nachgeschalteten Wärmebehandlungsvorrichtung versehen sein oder diese kann der Umformeinrichtung zum Kaltumformen der Platine direkt vorgeschaltet sein.According to an advantageous development of the invention, however, depending on the intended production process, the heating of the cut edges can also take place immediately after the mechanical cutting or punching processes or immediately before forming into a component, in a work step combined with the respective production process, if this appears advantageous. For example, the cutting and punching devices can be provided with a downstream heat treatment device or this can be connected directly upstream of the forming device for cold forming of the blank.

Die Platine selbst kann vorteilhaft z.B. flexibel mit unterschiedlichen Dicken gewalzt sein oder aus Kalt- oder Warmband gleicher oder unterschiedlicher Dicke gefügt sein.The board itself can advantageously e.g. be flexibly rolled with different thicknesses or be assembled from cold or hot strip of the same or different thickness.

Die Erfindung ist vorteilhaft anwendbar für warm- oder kaltgewalzte Stahlbänder mit Zugfestigkeiten von 600 MPa bis 1100 MPa, die mit einer korrosionshemmenden Schicht als metallischem und/oder organischem Überzug versehen sein können. Der metallische Überzug kann zum Beispiel aus Zink oder einer Legierung aus Zink oder aus Magnesium oder aus Aluminium und/oder Silizium bestehen.The invention can advantageously be used for hot-rolled or cold-rolled steel strips with tensile strengths of 600 MPa to 1100 MPa, which can be provided with a corrosion-inhibiting layer as a metallic and / or organic coating. The metallic coating can for example consist of zinc or an alloy of zinc or of magnesium or of aluminum and / or silicon.

Die Eignung von beschichteten Stahlbändern erklärt sich aus der Möglichkeit, die Behandlung des Kantenbereichs auf einen Abstand zur Kante zu beschränken,der vom Betrag geringer als die Blechdicke ist, da in diesem Bereich der überwiegende Anteil der schädlichen Kaltverfestigung beim Scherschneiden vorliegt. So kann bei Blechdicken von einigen Millimetern Dicke der Bereich bis zu einem Abstand zur Kante von einigen hundert Mikrometern bereits ausreichend sein, so dass beispielsweise der wirksame Korrosionsschutz einer metallischen korrosionshemmenden Schicht nicht oder nur unerheblich beeinflusst wird.The suitability of coated steel strips is explained by the possibility of restricting the treatment of the edge area to a distance from the edge that is less than the thickness of the sheet metal, since this area is where the majority of the harmful strain hardening occurs during shear cutting. With sheet metal thicknesses of a few millimeters, the area up to a distance of a few hundred micrometers from the edge can be sufficient, so that, for example, the effective corrosion protection of a metallic corrosion-inhibiting layer is not or only negligibly affected.

Claims (16)

  1. Method for the production of a running gear component from microalloyed steel, having improved cold formability of cold-hardened, mechanically separated sheet edges, having the following method steps:
    - providing a hot strip or a hot strip sheet, having the following alloy composition in % by weight: C: 0.04 to 0.12, Si: max. 0.7, Mn: 1.4 to 2.2, P: max. 0.2, S: max. 0.002, N: max. 0.03, V: 0.005 to 0.5, Nb: 0.005 to 0.1, Ti: 0.005 to 0.2, with 0.05 ≤ V+Nb+Ti ≤ 0.4 and also one or more of the elements from the sum of Cu+Cr+Ni: max. 1, with Cr: max. 0.9, Ni: max. 0.5, Cu: max. 0.5, and also optionally Mo: max. 0.5, remainder iron and melting-caused impurities,
    - cutting a plate to size at room temperature and also optional implementation of further stamping or cutting operations, in order to obtain recesses, holes or openings on the plate at room temperature
    - heating exclusively the sheet edge regions of the plate, cold-hardened by the cutting or stamping operations, to a temperature of at least 700°C with a retaining time of at most 10 seconds and subsequent cooling in air
    - cold forming of the plate in one or more steps to form a running gear component at room temperature.
  2. Method according to claim 1,
    characterised in that
    the time of the temperature application is 0.02 to 10 seconds.
  3. Method according to claim 2,
    characterised in that
    the time of the temperature application is 0.1 to 2 seconds.
  4. Method according to claims 1 to 3,
    characterised in that
    the heating of the cold-hardened sheet edge regions is effected to a temperature of 700°C to solidus temperature.
  5. Method according to claim 4,
    characterised in that
    the heating of the cold-hardened sheet edge regions is effected to a temperature of Ac1 to solidus temperature.
  6. Method according to claims 1 to 5,
    characterised in that
    the heating to forming temperature is effected inductively, conductively, by means of radiation heating or by means of laser radiation.
  7. Method according to claim 6,
    characterised in that
    the heating is effected by means of a resistance welding device or by means of a laser.
  8. Method according to at least one of the claims 1 to 7,
    characterised in that
    the plate is formed in one or in several steps.
  9. Method according to at least one of the claims 1 to 8,
    characterised in that
    the sheet plate has an organic and/or metallic coating.
  10. Method according to claim 9,
    characterised in that
    the metallic covering comprises Zn and/or Mg and/or A1 and/or Si.
  11. Method according to at least one of the claims 1 to 10,
    characterised in that
    the heat treatment is effected in the plane direction of the plate, starting from the sheet edge, in a region which corresponds at most to the sheet thickness.
  12. Method according to one of the claims 1 to 11,
    characterised in that
    the region about the position of the heat treatment is protected from oxidation.
  13. Method according to one of the claims 1 to 12,
    characterised in that
    for protection from oxidation, the region about the position of the heat treatment is scoured by means of an inert gas at least during the heat effect.
  14. Method according to claim 13,
    characterised in that
    the region about the position of the heat treatment is scoured by means of an inert gas in addition before and/or after the heat effect.
  15. Use of a steel consisting of the following alloy composition in % by weight:
    C: 0.04 to 0.12, Si: max. 0.7, Mn: 1.4 to 2.2, P: max. 0.2, S: max. 0.002, N: max. 0.03, V: 0.005 to 0.5, Nb: 0.005 to 0.1, Ti: 0.005 to 0.2, and 0.05 ≤ V+Nb+Ti ≤ 0.4 and also one or more of the elements from the sum of Cu+Cr+Ni: max. 1, with Cr: max. 0.9, Ni: max. 0.5, Cu: max. 0.5, and also optionally Mo: max. 0.5,
    remainder iron and melting-caused impurities, for the production of a running gear component by cold forming a plate, in which the plate is mechanically cut to size, before the forming, from a strip or sheet at room temperature, and occasionally further stamping or cutting operations are implemented in order to obtain recesses or openings at room temperature, in which, before forming into a running gear component, a heat treatment of at least 700°C over a time period of at most 10 seconds is implemented on the cut or stamped sheet edges which have undergone a cold hardening.
  16. Use of a steel according to claim 15 for the production of axial supports, suspension arms, multi-link rear axles, twist beam axles, front axles, connecting rods, longitudinal and transverse tie-bars.
EP17818037.8A 2016-11-15 2017-11-15 Method for producing chassis parts from micro-alloyed steel with improved cold workability Active EP3541966B1 (en)

Applications Claiming Priority (2)

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DE102016121902.9A DE102016121902A1 (en) 2016-11-15 2016-11-15 Process for the production of chassis parts made of micro-alloyed steel with improved cold workability
PCT/DE2017/100969 WO2018091038A1 (en) 2016-11-15 2017-11-15 Method for producing chassis parts from micro-alloyed steel with improved cold workability

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EP3541966B1 true EP3541966B1 (en) 2020-12-30

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JP2022108601A (en) 2021-01-13 2022-07-26 トヨタ自動車株式会社 Forming and processing method

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