EP3976839A1 - Procédé de fabrication d'une pièce en tôle d'acier façonnée à chaud et trempée à la presse - Google Patents

Procédé de fabrication d'une pièce en tôle d'acier façonnée à chaud et trempée à la presse

Info

Publication number
EP3976839A1
EP3976839A1 EP20729040.4A EP20729040A EP3976839A1 EP 3976839 A1 EP3976839 A1 EP 3976839A1 EP 20729040 A EP20729040 A EP 20729040A EP 3976839 A1 EP3976839 A1 EP 3976839A1
Authority
EP
European Patent Office
Prior art keywords
temperature
steel
steel sheet
press
bainitization
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP20729040.4A
Other languages
German (de)
English (en)
Inventor
Ansgar Hatscher
Uwe Diekmann
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Volkswagen AG
Original Assignee
Volkswagen AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Volkswagen AG filed Critical Volkswagen AG
Publication of EP3976839A1 publication Critical patent/EP3976839A1/fr
Pending legal-status Critical Current

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Classifications

    • 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
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
    • 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
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C21D1/20—Isothermal quenching, e.g. bainitic hardening
    • 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
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/62—Quenching devices
    • C21D1/673—Quenching devices for die quenching
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
    • 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
    • C21D8/0447—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 characterised by the heat treatment
    • C21D8/0463—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 characterised by the heat treatment following 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C22C38/18—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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • 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
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • 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
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • 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
    • B21D22/022—Stamping using rigid devices or tools by heating the blank or stamping associated with heat treatment
    • 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
    • B21D35/00—Combined processes according to or processes combined with methods covered by groups B21D1/00 - B21D31/00
    • B21D35/002—Processes combined with methods covered by groups B21D1/00 - B21D31/00
    • B21D35/005—Processes combined with methods covered by groups B21D1/00 - B21D31/00 characterized by the material of the blank or the workpiece
    • B21D35/006—Blanks having varying thickness, e.g. tailored blanks
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite

Definitions

  • the invention relates to a method for producing a hot-formed and
  • the sheet steel component is used according to the invention in vehicle construction.
  • Such a steel material can be used, for example, for a sheet steel component.
  • the strength of the steel material is a key factor.
  • Hot-formed steels, such as 22MnB5 have an almost 100% martensitic structure according to the
  • Vehicle body component is unfavorable in the event of an accident of the vehicle.
  • Steel thin sheet is inserted into a forming tool in one insertion step at an insertion temperature.
  • the thin steel sheet is placed in the forming tool hot-formed and press-hardened to form the sheet steel part.
  • Sheet steel part is removed from the opened forming tool in a removal step with a removal temperature.
  • the object of the invention is to provide a method for producing a
  • a steel is aterial with a steel alloy which is designed for processing in a hot forming process for the production of a sheet steel part in
  • Vehicle construction which has at least the following components in percent by weight:
  • the steel alloy can, for example, have iron and impurities as further constituents, the structure essentially consisting of bainite, stabilized retained austenite and martensite.
  • the relatively high carbon content of 0.30 to 0.42% can improve the stabilization of retained austenite in the steel material.
  • the carbon content should not exceed 0.42%.
  • the silicon content of 0.8 to 2.2% can stabilize the intermediate structure and retained austenite in the steel material, whereby the ductility of the steel material can be improved.
  • the manganese content is also limited, so that the steel alloy contains a maximum of 2.5% manganese, preferably only up to 1.0%, in order to achieve a homogeneous structure and disadvantageous carbide formation in the steel material prevent.
  • niobium of up to 0.06%, grain refinement can be achieved, which can also contribute to improving ductility.
  • Martensitic transformation in the press hardening step is delayed and the bainite transformation is supported in the bainitizing step.
  • Boron is used to bind nitrogen, which also improves ductility.
  • Steel material are made available, which is characterized by high strength and at the same time very high ductility.
  • the steel material can be used or used, for example, as a sheet steel component.
  • the steel alloy can preferably have at least the following components in percent by weight:
  • iron and impurities for example, can be provided as further components, the structure essentially consisting of bainite, stabilized retained austenite and martensite.
  • the steel alloy preferably has contents of chromium, nickel and / or molybdenum, the sum total of chromium, nickel and / or molybdenum preferably being less than 0.5%, preferably less than 0.35%.
  • the steel alloy thus preferably has only a very small proportion of chromium, nickel and molybdenum, which means that the amount of more expensive
  • Alloy elements in the steel alloy can be reduced.
  • the steel material After the hot forming, the steel material preferably has a yield strength Re> 600 MPa.
  • the yield point characterizes the stress up to which in
  • the material shows almost no permanent plastic deformation. This means that the material will deform, but will return to its original shape after the load has been released. The deformation remains reversible or elastic.
  • the bending angle of the steel material after hot forming is preferably equal to or greater than 80 °.
  • the elongation at break A50 of the steel material is preferably equal to or greater than 16%. This can be achieved through this high bending angle and / or the high elongation at break
  • the steel material is characterized by high strength, the steel material preferably having a tensile strength Rm> 1100 MPa.
  • the tensile strength determines the maximum mechanical tensile stress that the steel material can withstand.
  • the steel material thus has a higher ductility and tensile strength than the commonly used cold forming grades, such as DP780 or DP980.
  • a quenching process step and a subsequent bainitizing step take place between the austenitizing step and the press hardening step.
  • the steel sheet is cooled in a quenching time to a bainitizing temperature which is lower than a bainite start temperature and higher than a bainite finish temperature.
  • the steel sheet is bainitized over a bainitization time on the
  • the first exemplary embodiment is thus characterized by a method for producing a steel material which has been developed and further developed as described above, in which in a first step (that is to say austenitizing step) a primary material is converted into a first step (that is to say austenitizing step)
  • Heat treatment process goes through, in a second step the primary material a
  • Quenching process step is subjected and in a third step (bainitization step) the pre-material goes through a second heat treatment process and in a fourth step (press hardening step) the material is press hardened and in a fifth treatment step the body component is subjected to a third heat treatment step (i.e. partitioning heat treatment step).
  • the sheet steel part can then be used in a further process step after the hot forming process described above
  • Forming process in particular cold forming process, are subjected.
  • more complex components, hollow profile parts can be manufactured and / or additional hardened areas can be set in the component through work hardening.
  • the starting material (that is to say the steel sheet) is preferably formed from a steel alloy, as has been described above.
  • the treatment according to the invention of the primary material and thus the steel alloy enables a steel material to be formed which has a structure essentially of bainite, stabilized retained austenite and martensite.
  • the successive process steps first heat treatment process
  • the heat treatment process (partitioning heat treatment step) together with the special steel alloy contribute to the fact that a corresponding structure can be formed, whereby the steel material can have a high strength with significantly increased ductility.
  • the primary material is preferably austenitized.
  • the primary material is preferably austenitized.
  • the quenching process can take place, for example, by form hardening or press hardening of the primary material.
  • the quenching process is preferably carried out at a cooling rate of more than 27 ° C./s, so that the starting material can be rapidly cooled before the second heat treatment process starts.
  • the second heat treatment process (bainitization step) preferably starts when the pre-material has a temperature lower than the bainite start temperature and higher than the bainite finish temperature.
  • the bainite start temperature is the temperature at which bainite begins to form in the structure.
  • the bainite finish temperature is the temperature at which the formation of bainite in the structure stops.
  • the bainite finish temperature is usually lower than the bainite start temperature.
  • the second heat treatment process preferably starts immediately after the quenching process. By starting the second heat treatment process at a temperature of the primary material which is lower than a bainite start temperature and higher than a bainite finish temperature, the formation of bainite in the structure can be achieved. An abrupt delay in the
  • a high proportion of bainite and stabilized retained austenite can be set in the structure of the primary material.
  • the holding phase during the second heat treatment step is designed in such a way that the structure of the thin steel sheet is essentially transformed into bainite and retained austenite.
  • the holding phase in the second heat treatment step can be in a range between 30 seconds and 30 minutes, preferably between 1 minute and 6 minutes.
  • a heat treatment can also be implemented with any suitable time-temperature profile.
  • any suitable time-temperature profile For example, an isothermal profile of a steel sheet temperature can be set.
  • a heat treatment can also be implemented with any suitable time-temperature profile.
  • an isothermal profile of a steel sheet temperature can be set.
  • a heat treatment can also be implemented with any suitable time-temperature profile.
  • a ramp-shaped or step-shaped falling or rising course of a steel sheet temperature can be set. However, it is relevant that upon completion of the
  • the temperature of the steel sheet is a sufficiently large temperature offset above the martensite start temperature Ms to im
  • the temperature offset is to be dimensioned so that even with a transfer-related
  • the insertion temperature at the start of the press hardening step is greater than the martensite start temperature Ms.
  • quench hardening can take place immediately afterwards during the press hardening step, in which the structure formed from bainite and possibly retained austenite is “frozen” in the steel sheet. If the conversion is incomplete, that means the chosen second is shorter In the heat treatment step, an increased proportion of martensite can also form during the press hardening process, which can increase the hardness of the steel material.
  • a third heat treatment step partitioning heat treatment step
  • the frozen structure consisting essentially of bainite, stabilized retained austenite and optionally martensite is partitioned, that is to say stabilized by uniform
  • This heat treatment step can take place in the temperature range> 100-225 ° C for 30 seconds to 60 minutes, preferably at> 150-200 ° C for 5-30 minutes.
  • Austenitizing step in particular without the interposition of a quenching process step or a bainitizing step, immediately followed by the press hardening step.
  • Press hardening step is implemented in two parts with a first press hardening sub-step and a second press hardening step.
  • the steel sheet is raised from the insertion temperature, which is above the austenitizing temperature, to a
  • Bainitization temperature cooled which is less than a bainite start temperature and greater than a bainite finish temperature.
  • a bainitization step in which the thin steel sheet is kept at the bainitization temperature for a bainitization time. This results in a structural transformation into bainite with stabilized retained austenite.
  • the second partial press hardening step in which the thin steel sheet is rapidly cooled down to less than or equal to the martensite finish temperature.
  • the steel sheet material can therefore first be heated above the austenitizing temperature AC3 and completely austenitized.
  • the sheet steel material is relatively rapidly hot-formed in a hot-forming tool into one
  • a heat treatment with a holding phase for example in a furnace in the temperature range between bainite start and bainite finish with an essentially complete conversion of the structure to bainite and stabilized retained austenite.
  • a fourth process step i.e. second press hardening sub-step
  • the sheet steel component is rapidly cooled in a hot forming tool, preferably the same as in the first press hardening sub-step, until the martensite finish temperature is reached, followed by cooling in air.
  • the bainite partitioning takes place analogously to the first exemplary embodiment. Due to the two very short press hardening operations, possibly in the same tool, in one
  • Multi-part strategy for each press stroke realize very advantageous cycle times of a few seconds.
  • Mold hardening steps used mechanical presses instead of costly servo-hydraulic presses. It has been shown that these process steps are very short
  • the quenching process step as intermediate cooling in the transfer phase to the second furnace can take place so quickly that neither the ferrite nor the pearlite area can be reached and / or that intermediate cooling occurs in a cooling phase of less than 30 seconds, in particular by means of air cooling or using cooling plates or using rolling rollers.
  • the cooling plates or rollers can be made of steel and can be tempered so that the desired steel sheet temperature can be set more precisely.
  • Thermomechanical rolling by means of rolling rollers can improve the structural properties with regard to ductility and fine-grainedness or any existing ones
  • the scale layer can be broken up so that it can be removed more easily using compressed air, for example.
  • compressed air for example.
  • existing surface coatings can be cooled more gently and the risk of sticking to the cooling plates can be reduced.
  • intermediate cooling takes place in the transfer phase to the second furnace in such a way that a profiled semi-finished product is produced in a first shaping step by thermomechanical rolling by means of rolling rollers or at least one thickness difference (tailored rolled blank) is rolled into the thin steel sheet.
  • hot trimming can be carried out in the second hot forming step (that is to say, second press hardness substep).
  • the second hot forming step can also be designed as a profile rolling and / or bending operation in order to be able to produce profiled components.
  • the two-stage quenching or hot-forming process sequence allows various manufacturing routes (design variants) to be combined with one another.
  • the invention relates to a use of a steel material according to the previously described, developed and further developed method for producing a
  • Vehicle body component or chassis component A vehicle body component formed from a steel material of this type has, on the one hand, a low weight, so that it has a high potential for lightweight construction. Furthermore, such a vehicle body component has a high level of strength and, at the same time, very high ductility, so that the behavior of the
  • Vehicle body component can be improved in the event of an accident of the vehicle.
  • FIG. 1 shows a system sketch by means of which the process sequence indicated in FIG. 2 for the production of a hot-formed and press-hardened sheet steel component is illustrated;
  • FIG. 2 in a block diagram of the process sequence for producing the
  • FIG. 3 shows a diagram that shows the time profile of the sheet steel component temperature when it is inserted into the forming tool and during the subsequent press hardening
  • Figures 4 and 5 are views corresponding to Figures 2 and 3 of a second
  • the surface of the primary material was then sandblasted in order to remove the layer of scale that had formed on the surface during the heat treatment.
  • this starting material was then cold-rolled to a thickness of approximately 3.5 mm.
  • a heat treatment process took place for 1.5 hours at 690 ° C. in an oven under vacuum. The cooling then took place under a nitrogen atmosphere.
  • the steel material was then cold-rolled to the dimensions required for the application example with a thickness of 1.5 mm.
  • FIG. 1 a system is roughly schematically sketched, based on which initially the
  • the basic process sequence for producing a hot-formed and press-hardened sheet steel component 7 is explained.
  • the system has, for example, a continuous furnace 1, a heat treatment furnace 2 implemented as a batch furnace, a forming tool 3 for hot forming and press hardening of sheet steel components 7, and a storage station 5 in which the sheet steel components 7 produced are stored.
  • a steel sheet 6 made of a hardenable steel is transferred into the continuous furnace 1 and there in a
  • Austenitizing step AU (FIG. 3) is heated to a process temperature T A (FIG. 3) above the tool-specific austenitizing temperature Ac3 of the steel used, which is 930 ° C., for example.
  • the thin steel sheet 6 heated in this way is transferred in a transfer phase to the heat treatment furnace 2 and there subjected to a bainitization step At ⁇ (FIG. 3) at a bainitization temperature T B (FIG. 3). Subsequently, the thin steel sheet 6 heat-treated in this way is transferred to the forming tool 3 and there, in a press hardening step D ⁇ H (FIG. 3), it is hot-formed into the steel sheet component 7 and at the same time quenched to a removal temperature T from (FIG. 3).
  • the shaping tool 3 also has a temperature control / cooling device 9, which is only indicated, in order to actively cool the shaping tool 3 during the press hardening step Atx or to keep it at a predefined tool temperature.
  • a quenching process step Ats (FIG. 3) is interposed between the austenitizing step D ⁇ A and the bainitizing step At ß , in which the thin steel sheet 6 is cooled to the bainitizing temperature T B (FIG. 3) in a quenching time. This is less than a bainite start temperature Bs and greater than a bainite finish temperature Bf.
  • the bainitization step At ß the steel sheet 6 is over the
  • the cooling rate is preferably greater than 27 ° C./s. This ensures that neither the ferrite nor the pearlite area reaches P, F during cooling becomes.
  • the quenching process step Ats is preferably implemented by the transfer phase between the continuous furnace 1 and the batch furnace 2.
  • the heat-treated steel sheet 6 is inserted in an insertion step, as well as with an insert temperature T ( Figure 3) in the forming tool 3, after which occurs in a tool holding phase, the press hardening step D ⁇ H.
  • the bainitization temperature T B is greater by a temperature offset DT than a martensite start temperature Ms.
  • the bainitization step At ß an isothermal heat treatment takes place, for example, at a constant bainitization temperature TB, which here can be in a range between 450 and 500 ° C.
  • a constant bainitization temperature TB which here can be in a range between 450 and 500 ° C.
  • the invention is not limited to such an isothermal temperature control. Rather, other suitable temperature-time profiles can also be used.
  • the bainitization step At ß results in a structural transformation in the thin steel sheet 6 essentially into a bainitic intermediate structure, namely without the formation of ferrite and / or pearlite structure.
  • retained austenite and optionally martensite can also be formed, preferably as a secondary phase, by terminating the bainitization prematurely.
  • the press hardening step Atn takes place immediately in FIGS. 2 and 3 with sudden cooling down to the removal temperature T out , in particular with a cooling rate that is greater than 27 ° C./s.
  • the removal temperature T from is just below the martensite finish temperature Mf.
  • An air cooling step AW takes place after the removal step . in the storage station 5, in which the sheet steel part 7 is cooled in air to room temperature.
  • a partitioning heat treatment step Atp is carried out in FIG. 3, in which sheet steel part 7 is tempered in order to reduce the component brittleness and increase the component ductility.
  • the partitioning heat treatment step Atp takes place as an integral component during the subsequent vehicle painting process.
  • FIG. 4 or 5 - in contrast to the first exemplary embodiment in FIGS. 1 to 3 - there is neither a atm between the austenitizing step A and the press hardening step
  • Quenching process step a bainitization step interposed. Rather, that will Steel sheet after austenitization 6 inserted directly in the forming tool 3, wherein the insert temperature T is greater than the austenitizing temperature Ac3.
  • the press hardening step is implemented in two parts, namely with a first press hardening substep Atm and a second press hardening substep A.
  • the steel sheet 6 inserted in the forming tool 3 is cooled from the insertion temperature T a to a bainitizing temperature T B , which is less than a bainite start temperature Bs and greater than a bainite finish temperature Bf.
  • the cooling rate is preferably greater than 27 ° C./s.
  • a bainitization step At ß in which the thin steel sheet 6 is held at the bainitization temperature T B for a bainitization time. In this way, the structure is transformed into bainite with stabilized retained austenite.
  • the bainitization step At ß can be exemplified in one of
  • Forming tool take place separate heating device.
  • the second press hardness substep A takes place, in which the thin steel sheet 6 is cooled down to a martensite finish temperature Mf.
  • the cooling rate is preferably greater than 27 ° C./s.
  • the sheet steel part 7 thus finished is removed at a removal temperature T from in a range below the martensite finish temperature Mf and transferred to the depositing station 5.
  • An air cooling step Ati_ K takes place in the depositing station 5, in which the sheet steel part 7 formed is cooled in air to room temperature.
  • a partitioning heat treatment step Atp is carried out, in which sheet steel part 7 is tempered in order to reduce the component brittleness and increase the component ductility.

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Abstract

L'invention concerne un matériau acier comportant un alliage d'acier qui présente au moins les constituants suivants exprimés en pourcentage en poids : 0,30 à 0,42% de carbone, 0,3 à 2,5% de manganèse, 0,8 et 2,2% de silicium, jusqu'à 0,06% d'aluminium, jusqu'à 0,5% de chrome, de nickel et de molybdène, au total jusqu'à 0,06% de niobium, jusqu'à 0,1% de vanadium, jusqu'à 0,01% de titane, entre 0,001 et 0,01% de bore, jusqu'à 0,01% d'azote, jusqu'à 0,01% de soufre, jusqu'à 0,02% de phosphore, le reste étant du fer et des impuretés, une structure se composant essentiellement de bainite, d'austénite résiduelle et de martensite.
EP20729040.4A 2019-06-03 2020-05-26 Procédé de fabrication d'une pièce en tôle d'acier façonnée à chaud et trempée à la presse Pending EP3976839A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102019208040.5A DE102019208040A1 (de) 2019-06-03 2019-06-03 Verfahren zur Herstellung eines warmumgeformten und pressgehärteten Stahlblechbauteils
PCT/EP2020/064610 WO2020244974A1 (fr) 2019-06-03 2020-05-26 Procédé de fabrication d'une pièce en tôle d'acier façonnée à chaud et trempée à la presse

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EP3976839A1 true EP3976839A1 (fr) 2022-04-06

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SE435527B (sv) * 1973-11-06 1984-10-01 Plannja Ab Forfarande for framstellning av en detalj av herdat stal
MX2015014436A (es) * 2013-04-15 2016-02-03 Jfe Steel Corp Lamina de acero laminada en caliente de alta resistencia y metodo para la produccion de la misma.
JP6875916B2 (ja) * 2016-05-30 2021-05-26 株式会社神戸製鋼所 高強度鋼板およびその製造方法
DE102017202294B4 (de) * 2017-02-14 2019-01-24 Volkswagen Aktiengesellschaft Verfahren zur Herstellung eines warmumgeformten und pressgehärteten Stahlblechbauteils
DE102017215699B4 (de) * 2017-09-06 2019-09-26 Volkswagen Aktiengesellschaft Verfahren zur Herstellung eines warmumgeformten und pressgehärteten Stahlblechbauteils

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