EP3360621A1 - Method for producing a thermoformed and press-hardened steel sheet component - Google Patents
Method for producing a thermoformed and press-hardened steel sheet component Download PDFInfo
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- EP3360621A1 EP3360621A1 EP18152864.7A EP18152864A EP3360621A1 EP 3360621 A1 EP3360621 A1 EP 3360621A1 EP 18152864 A EP18152864 A EP 18152864A EP 3360621 A1 EP3360621 A1 EP 3360621A1
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- temperature
- steel sheet
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- martensite
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- 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
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- 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
-
- 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
-
- 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
- C21D2211/008—Martensite
Definitions
- the invention relates to a method for producing a hot-formed and press-hardened sheet steel component according to the preamble of claim 1.
- the sheet steel component is made of a hardenable steel having a tensile strength Rm greater than 1500 MPa, in particular> 1650 MPa to 2250 MPa.
- Hot-forming steels such as 22MnB5 exhibit an almost complete martensitic structure with a nominal tensile strength of 1500 MPa after the hot-forming process.
- the ductility of this structure is often characterized by the elongation at break. This is approximately between 4 to 6% at 22MnB5.
- the bending angle is given in a so-called platelet bending test according to VDA 238-100 as a further characteristic value for characterizing the ductility. For example, for 22MnB5 bending angles between 50 ° and 65 ° are to be expected.
- strengths of these hot-forming steels are further increased by, for example, increasing the carbon content up to 2000 MPa.
- the hot-formed steel sheets are increasingly sensitive, that is, more brittle, to stresses.
- a subsequent time-consuming tempering treatment is often required to reduce the brittleness.
- additional tempering treatment increases the process time during hot working and results in additional tooling for performing the tempering treatment.
- Exemplary is from the DE 10 2013 010 946 B3 a generic method for producing a hot-formed and press-hardened sheet steel component known. This is heat treated in a heat treatment step above the material specific austenitizing temperature. This is followed by an insertion step in which the steel sheet is inserted into a hot-forming tool at an insertion temperature which corresponds approximately to the austenitizing temperature. In the following press hardening step, the steel sheet is hot formed and cooled down to a withdrawal temperature. In the DE 10 2013 010 946 B3 the cooling process is interrupted above the so-called martensite finish temperature at which a transformation from austenite to martensite is largely completed, whereby a small proportion of retained austenite in the structure preserved.
- the steel sheet component is removed in a removal step from the open forming tool, and at a take-off temperature above the martensite finish temperature, and transferred to a heating device, wherein cooling of the sheet steel component is less than 200 ° C is avoided.
- a heating device In the heating device is a tempering treatment in which the retained austenite is stabilized in the sheet steel component and even after further cooling of the sheet steel component to room temperature in which the steel sheet component structure is maintained.
- the retained austenite reduces the stress between the martensite needles and, at high strengths, causes the structure to have a significantly increased elongation at break or ductility compared to martensite.
- the object of the invention is to provide a method for producing a hot-formed and press-hardened sheet steel component in which the ductility of sheet steel components is increased at higher strengths Rm greater than 1500 MPa, compared to the above prior art at a reduced process time and in reduced use of tools.
- the steel sheet member is cooled in the press-hardening step with the forming tool closed to a take-off temperature which is in a temperature range close to the material-specific martensite finish temperature Mf, specifically in a temperature range of the martensite finish temperature Mf + / - 10%.
- a take-off temperature which is in a temperature range close to the material-specific martensite finish temperature Mf, specifically in a temperature range of the martensite finish temperature Mf + / - 10%.
- the yield strength or a 0.2% yield strength or elastic limit of the sheet steel component may be> 1100 MPa, preferably 1250 MPa to 1950 MPa.
- the removal temperature of the sheet steel component is a temperature offset below the material-specific martensite finish temperature.
- the steel sheet component is removed with the removal temperature below the martensite finish temperature.
- a purely martensitic structure in the sheet steel component leads to a high steel sheet component strength, but at the same time to an increase in brittleness, so that depending on the carbon content only a slight deformation with elongations at break, usually less than 7% is possible.
- the elongation at break of a sheet steel component can be increased if a proportion of retained austenite remains in the martensitic microstructure of the sheet steel component, as can also be seen from FIG DE 10 2013 010 946 B3 evident. This is done by an incomplete transformation of austenite into martensite, so that retained austenite is retained in the finished sheet steel component.
- the time course of the cooling can be followed by a cooling curve in which the steel sheet component temperature is reduced from a closing time, at which the forming tool is closed, to a transition time with a large first cooling rate, in particular greater than 27 ° C / s, and is further cooled in the further time after the transition time with a greatly reduced second transition cooling rate until a flat cooling line G with a slope, ie with a third cooling rate.
- the third cooling rate may be 15 ° C / s to 3 ° C / s.
- the sheet steel component temperature at the transition time or at the beginning of the cooling line G by a temperature offset above the martensite finish temperature, but below the material-specific martensite start temperature, in the a transformation from austenite to martensite begins.
- a temperature offset above the martensite finish temperature, but below the material-specific martensite start temperature in the a transformation from austenite to martensite begins.
- the austenite is almost completely converted into martensite.
- due to the greatly reduced cooling rate after the transition time a slow cooling is achieved by means of which the formation of retained austenite is promoted.
- the forming tool has a heating device with which the, the steel sheet component facing tool surface is heated or tempered.
- the forming tool can be heated in the press hardening step, in particular to a tool temperature in the range of 100 ° C to 250 ° C, which can be easily set in the Abkühlkurve Presshärte Kunststoff.
- the cooling process can be continued without interruption and continuously, and more preferably with a fourth cooling rate, which corresponds to the third cooling rate or is designed smaller than this, that is, for example, at 1 ° C / s to 5 ° C / s lies.
- This fourth cooling phase thus represents an annealing of the component in order to further reduce the brittleness.
- the steel sheet component can be transferred after the press hardening step in a storage station in which the cooling process is continued by air cooling with ambient air.
- the above method is particularly applicable to a steel sheet metal component having a sheet thickness of exemplarily 1.5 mm, which has a carbon content C of more than 0.25% by weight, in particular> 0.27% by weight to 0.40% by weight. %.
- the steel sheet may contain alloying constituents which contribute to austenite stabilization and thus lead to a component structure in which, in addition to the martensite, retained austenite is also contained.
- FIG. 1 is roughly outlined schematically a plant, based on the first basic process sequence for the production of a hot-formed and press-hardened sheet steel component is explained.
- the plant has a continuous furnace 1, a forming tool 3 for hot forming and press hardening of sheet steel components, and a storage station 5 in which the sheet steel components are stored.
- a steel sheet 6 is transferred from a hardenable steel in the continuous furnace 1 and heated there over the material-specific Austenitmaschinestemperatur Ac3 of the steel used, the may be at 930 ° C by way of example.
- the thus heated steel sheet 6 is transferred in the hot state in the forming tool 3 and there hot-formed in a press-hardening step to a sheet steel component 7 and quenched at the same time.
- the high steel sheet component temperature during hot forming ensures outstanding forming behavior.
- the forming tool 3 has an only indicated heating unit 9 whose mode of action is described later.
- the process flow during the inserting step, the press-hardening step and the taking-out step will be described below on the basis of the temperature-time diagram of FIG FIG. 3 explained in more detail, in which the solid lines, the time courses of the sheet steel component temperature and the Umformwerkmaschine temperature are shown.
- an opening state and a closing state of the forming tool 3 are indicated by a dotted line.
- the forming tool 3 in a mold clamping phase .DELTA.t is to be closed, which may for example be 2 to 5 s and the forming tool 3 during the press hardening step in a tool holding phase H .DELTA.t kept closed.
- the tool holding phase .DELTA.t H is in the FIG. 3 exemplary about 8s.
- the tool holding phase ⁇ t H may be 15s, for example.
- the tool holding phase .DELTA.t H can generally be of any period of time and in particular in a range of 2 to 30s.
- the forming tool 3 is opened in a mold opening phase .DELTA.t, which can amount to 2 to 5 s.
- the heating unit 9 is preferably heated to a tool temperature ⁇ W in the range of 100 ° C to 250 ° C during the press-hardening step.
- a tool temperature ⁇ W in the range of 100 ° C to 250 ° C during the press-hardening step.
- the sheet steel component 7 is transferred to the deposition station 5.
- the cooling process is continued without interruption and continuously, with a fourth cooling rate a 4 , which may be at 1 ° C / s to 5 ° C / s. This is preferably achieved by air cooling with ambient air.
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Abstract
Die Erfindung betrifft ein Verfahren zur Herstellung eines warmumgeformten und pressgehärteten Stahlblechbauteils (7) aus härtbarem Stahl mit einer Zugfestigkeit (Rm) größer als 1500 MPa, vorzugsweise >1650 bis 2250 MPa, in welchem Verfahren das Stahlfeinblech (6) in einem Wärmebehandlungsschritt auf über die werkstoffspezifische Austenitisierungstemperatur Ac3 wärmebehandelt wird, in einem daran anschließenden Einlegeschritt das Stahlfeinblech (6) mit einer Einlegetemperatur (ϑ1) in ein Umformwerkzeug (3) eingelegt wird, in einem Presshärteschritt das Stahlblechbauteil (7) warmumgeformt und zugleich bis auf eine Entnahmetemperatur (ϑ4 abgekühlt wird, und in einem Entnahmeschritt das Stahlblechbauteil (7) mit der Entnahmetemperatur (ϑ4) aus dem geöffneten Umformwerkzeug (3) entnommen wird. Erfindungsgemäß wird das Stahlblechbauteil (7) im Presshärteschritt bei geschlossenem Umformwerkzeug (3) bis auf eine Entnahmetemperatur (ϑ4) abgekühlt, die in einem Temperaturbereich nahe der werkstoffspezifischen Martensit-Finish-Temperatur Mf liegt, bei der eine Umwandlung von Austenit zu Martensit zum größten Teil abgeschlossen ist, insbesondere in einem Temperaturbereich der Martensit-Finish-Temperatur Mf von +/- 10%. The invention relates to a method for producing a hot - worked and press - hardened steel sheet component (7) made of hardenable steel having a tensile strength (Rm) greater than 1500 MPa, preferably> 1650 to 2250 MPa, in which method the steel sheet (6) in a heat treatment step on the In a subsequent insertion step, the steel sheet (6) is inserted into a forming tool (3) with an insertion temperature (θ 1 ), the steel sheet component (7) is hot-formed in a press-hardening step and at the same time reduced to a removal temperature (θ 4 In a removal step, the steel sheet component (7) with the removal temperature (θ 4 ) is removed from the opened forming tool 3. According to the invention, the steel sheet component (7) in the press hardening step is closed with the forming tool (3) closed except for a removal temperature (θ 4) cooled in a tempera in the vicinity of the material-specific martensite finish temperature Mf at which austenite to martensite transformation is largely completed, in particular in a martensite finish temperature Mf temperature range of +/- 10%.
Description
Die Erfindung betrifft ein Verfahren zur Herstellung eines warmumgeformten und pressgehärteten Stahlblechbauteils nach dem Oberbegriff des Patentanspruches 1. Das Stahlblechbauteil ist aus einem härtbaren Stahl mit einer Zugfestigkeit Rm größer als 1500 MPa, insbesondere >1650 MPa bis 2250 MPa hergestellt.The invention relates to a method for producing a hot-formed and press-hardened sheet steel component according to the preamble of claim 1. The sheet steel component is made of a hardenable steel having a tensile strength Rm greater than 1500 MPa, in particular> 1650 MPa to 2250 MPa.
Warmumformstähle, wie zum Beispiel 22MnB5, weisen nach dem Warmumformprozess ein nahezu vollständiges martensitisches Gefüge mit einer nominellen Zugfestigkeiten von 1500 MPa auf. Die Duktilität dieses Gefüges wird oft mit der Bruchdehnung gekennzeichnet. Diese liegt bei 22MnB5 in etwa zwischen 4 bis 6 %. Darüber hinaus wird der Biegewinkel in einem sogenannten Plättchenbiegeversuch nach VDA 238-100 als weiterer Kennwert zur Charakterisierung der Duktilität angegeben. Für zum Beispiel 22MnB5 sind Biegewinkel zwischen 50° und 65° zu erwarten. Aktuell werden Festigkeiten dieser Warmumformstähle durch zum Beispiel die Erhöhung des Kohlenstoffanteils weiter bis auf 2000 MPa gesteigert. Bei höheren Festigkeiten reagieren die Warmumformstahlbleche jedoch zunehmend empfindlicher, das heißt spröder, auf Belastungen. Bei Stahlfeinblechwerkstoffen (Blechdicke bei zum Beispiel 1,5 mm) mit Festigkeiten Rm größer als 1500 MPa ist deshalb oft eine nachträgliche zeitaufwendige Anlassbehandlung erforderlich, um die Sprödigkeit zu reduzieren. Eine solche zusätzliche Anlassbehandlung erhöht jedoch die Prozessdauer bei der Warmumformung und führt zu einem zusätzlichen Werkzeugeinsatz zur Durchführung der Anlassbehandlung.Hot-forming steels, such as 22MnB5, exhibit an almost complete martensitic structure with a nominal tensile strength of 1500 MPa after the hot-forming process. The ductility of this structure is often characterized by the elongation at break. This is approximately between 4 to 6% at 22MnB5. In addition, the bending angle is given in a so-called platelet bending test according to VDA 238-100 as a further characteristic value for characterizing the ductility. For example, for 22MnB5 bending angles between 50 ° and 65 ° are to be expected. Currently, strengths of these hot-forming steels are further increased by, for example, increasing the carbon content up to 2000 MPa. At higher strengths, however, the hot-formed steel sheets are increasingly sensitive, that is, more brittle, to stresses. In the case of steel sheet materials (sheet thickness of, for example, 1.5 mm) with strengths Rm greater than 1500 MPa, a subsequent time-consuming tempering treatment is often required to reduce the brittleness. However, such additional tempering treatment increases the process time during hot working and results in additional tooling for performing the tempering treatment.
Beispielhaft ist aus der
Die Aufgabe der Erfindung besteht darin, ein Verfahren zur Herstellung eines warmumgeformten und pressgehärteten Stahlblechbauteils bereitzustellen, bei dem die Duktilität von Stahlblechbauteilen bei höheren Festigkeiten Rm größer als 1500 MPa gesteigert wird, und zwar im Vergleich zum obigen Stand der Technik bei einer reduzierten Prozessdauer sowie bei reduziertem Werkzeugeinsatz.The object of the invention is to provide a method for producing a hot-formed and press-hardened sheet steel component in which the ductility of sheet steel components is increased at higher strengths Rm greater than 1500 MPa, compared to the above prior art at a reduced process time and in reduced use of tools.
Die Aufgabe ist durch die Merkmale des Patentanspruches 1 gelöst. Bevorzugte Weiterbildungen der Erfindung sind in den Unteransprüchen offenbart.The object is solved by the features of claim 1. Preferred embodiments of the invention are disclosed in the subclaims.
Gemäß dem kennzeichnenden Teil des Patentanspruches 1 wird das Stahlblechbauteil im Presshärteschritt bei geschlossenem Umformwerkzeug bis auf eine Entnahmetemperatur abgekühlt, die in einem Temperaturbereich nahe der werkstoffspezifischen Martensit-Finish-Temperatur Mf liegt, und zwar insbesondere in einem Temperaturbereich der Martensit-Finish-Temperatur Mf +/- 10%. Ein solcher Temperaturbereich ist im Hinblick auf einen nachteiligen Stahlblechbauteil-Verzug nach dem Presshärteschritt unkritisch.According to the characterizing part of claim 1, the steel sheet member is cooled in the press-hardening step with the forming tool closed to a take-off temperature which is in a temperature range close to the material-specific martensite finish temperature Mf, specifically in a temperature range of the martensite finish temperature Mf + / - 10%. Such a temperature range is uncritical in view of disadvantageous sheet steel component distortion after the press hardening step.
Die Streckgrenze bzw. eine 0,2-%-Dehngrenze oder Elastizitätsgrenze des Stahlblechbauteils kann bei >1100MPa liegen, vorzugsweise 1250MPa bis 1950MPa.The yield strength or a 0.2% yield strength or elastic limit of the sheet steel component may be> 1100 MPa, preferably 1250 MPa to 1950 MPa.
Besonders bevorzugt ist eine Prozessführung, bei der die Entnahmetemperatur des Stahlblechbauteils um einen Temperaturversatz unterhalb der werkstoffspezifischen Martensit-Finish-Temperatur liegt. Im Entnahmeschritt wird daher das Stahlblechbauteil mit der Entnahmetemperatur unterhalb der Martensit-Finish-Temperatur entnommen. Auf diese Weise ist gewährleistet, dass bei der Stahlblechbauteil-Entnahme die Martensitbildung abgeschlossen ist, wodurch sich das Bauteil im weiteren Prozessverlauf nicht mehr aufgrund von Eigenspannungen verzieht, die ansonsten bei einer weiteren Umwandlung von Austenit zu Martensit erfolgen könnte.
Ein rein martensitisches Gefüge in dem Stahlblechbauteil führt zu einer hohen Stahlblechbauteil-Festigkeit, jedoch gleichzeitig zu einer Erhöhung der Sprödigkeit, so dass je nach Kohlenstoffgehalt nur eine geringfügige Verformung mit Bruchdehnungen üblicherweise kleiner als 7% ermöglicht ist. Die Bruchdehnung eines Stahlblechbauteils kann dagegen gesteigert werden, wenn im martensitischen Gefüge des Stahlblechbauteils ein Anteil von Restaustenit verbleibt, wie es auch aus der
A purely martensitic structure in the sheet steel component leads to a high steel sheet component strength, but at the same time to an increase in brittleness, so that depending on the carbon content only a slight deformation with elongations at break, usually less than 7% is possible. On the other hand, the elongation at break of a sheet steel component can be increased if a proportion of retained austenite remains in the martensitic microstructure of the sheet steel component, as can also be seen from FIG
Eine solche unvollständige Umwandung von Austenit zu Martensit wird erfindungsgemäß durch einen speziellen zeitlichen Verlauf der Abkühlung im Presshärteschritt bewerkstelligt. Bevorzugt kann der zeitliche Verlauf der Abkühlung einer Abkühlkurve folgen, bei der die Stahlblechbauteil-Temperatur von einem Schließzeitpunkt, zu dem das Umformwerkzeug geschlossen wird, bis zu einem Übergangszeitpunkt mit einer großen ersten Abkühlrate reduziert wird, insbesondere größer als 27°C/s, und bei der im weiteren Zeitverlauf nach dem Übergangszeitpunkt mit einer stark reduzierten zweiten Übergangs-Abkühlrate weiter abgekühlt wird, bis sich eine flache Abkühlgerade G mit einer Steigung, d.h. mit einer dritten Abkühlrate, einstellt. Die dritte Abkühlrate kann exemplarisch bei 15°C/s bis 3°C/s liegen. Dabei ist es im Hinblick auf die Gefügezusammensetzung bevorzugt, wenn die Stahlblechbauteil-Temperatur zum Übergangszeitpunkt (bzw. zu Beginn der Abkühlgerade G) um einen Temperaturversatz oberhalb der Martensit-Finish-Temperatur, jedoch unterhalb der werkstoffspezifischen Martensit-Start-Temperatur liegt, bei der eine Umwandlung von Austenit zu Martensit beginnt. Bei einer solchen Abkühlkurve wird einerseits gewährleistet, dass der Austenit nahezu vollständig in Martensit umgewandelt wird. Andererseits wird aufgrund der nach dem Übergangszeitpunkt stark reduzierten Abkühlrate eine langsame Abkühlung erzielt, mittels der die Bildung von Restaustenit unterstützt wird.Such an incomplete transformation of austenite to martensite is accomplished according to the invention by a specific time course of the cooling in the press hardening step. Preferably, the time course of the cooling can be followed by a cooling curve in which the steel sheet component temperature is reduced from a closing time, at which the forming tool is closed, to a transition time with a large first cooling rate, in particular greater than 27 ° C / s, and is further cooled in the further time after the transition time with a greatly reduced second transition cooling rate until a flat cooling line G with a slope, ie with a third cooling rate. By way of example, the third cooling rate may be 15 ° C / s to 3 ° C / s. It is preferred in terms of structural composition, if the sheet steel component temperature at the transition time (or at the beginning of the cooling line G) by a temperature offset above the martensite finish temperature, but below the material-specific martensite start temperature, in the a transformation from austenite to martensite begins. In such a cooling curve, on the one hand ensures that the austenite is almost completely converted into martensite. On the other hand, due to the greatly reduced cooling rate after the transition time, a slow cooling is achieved by means of which the formation of retained austenite is promoted.
Im Hinblick auf eine prozesstechnisch einfache Auslegung der oben beschriebenen Abkühlkurve ist es bevorzugt, wenn das Umformwerkzeug eine Heizeinrichtung aufweist, mit der die, dem Stahlblechbauteil zugewandte Werkzeugfläche aufheizbar oder temperierbar ist. In diesem Fall kann das Umformwerkzeug beim Presshärteschritt insbesondere auf eine Werkzeugtemperatur im Bereich von 100°C bis 250°C aufgeheizt werden, wodurch sich die Abkühlkurve im Presshärteschritt einfach einstellen lässt. Im weiteren Prozessverlauf nach der Entnahme aus dem Umformwerkzeug kann der Abkühlvorgang unterbrechungsfrei und kontinuierlich fortgesetzt werden, und zwar besonders bevorzugt mit einer vierten Abkühlrate, die der dritten Abkühlrate entspricht oder kleiner als diese ausgelegt ist, das heißt zum Beispiel bei 1°C/s bis 5°C/s liegt. Diese vierte Abkühlphase stellt somit ein Anlassen des Bauteils dar, um die Sprödigkeit weiter zu reduzieren.
Zur Fortsetzung des Abkühlvorgangs kann das Stahlblechbauteil nach dem Presshärteschritt in eine Ablagestation transferiert werden, in der der Abkühlvorgang durch Luftkühlung mit Umgebungsluft fortgesetzt wird.With regard to a process-technically simple design of the cooling curve described above, it is preferred if the forming tool has a heating device with which the, the steel sheet component facing tool surface is heated or tempered. In this case, the forming tool can be heated in the press hardening step, in particular to a tool temperature in the range of 100 ° C to 250 ° C, which can be easily set in the Abkühlkurve Presshärteschritt. In the further course of the process after the Removal from the forming die, the cooling process can be continued without interruption and continuously, and more preferably with a fourth cooling rate, which corresponds to the third cooling rate or is designed smaller than this, that is, for example, at 1 ° C / s to 5 ° C / s lies. This fourth cooling phase thus represents an annealing of the component in order to further reduce the brittleness.
To continue the cooling process, the steel sheet component can be transferred after the press hardening step in a storage station in which the cooling process is continued by air cooling with ambient air.
Das obige Verfahren ist insbesondere auf ein Stahlfeinblechbauteil mit einer Blechdicke von beispielhaft 1,5 mm anwendbar, die einen Kohlenstoffgehalt C von größer als 0,25 Gew% aufweist, insbesondere >0,27Gew.% bis 0,40Gew. %. Zudem kann das Stahlfeinblech Legierungsbestandteile enthalten, die zu einer Austenitstabilisierung beitragen und dadurch zu einem Bauteilgefüge führen, in dem neben dem Martensit auch Restaustenit enthalten ist.The above method is particularly applicable to a steel sheet metal component having a sheet thickness of exemplarily 1.5 mm, which has a carbon content C of more than 0.25% by weight, in particular> 0.27% by weight to 0.40% by weight. %. In addition, the steel sheet may contain alloying constituents which contribute to austenite stabilization and thus lead to a component structure in which, in addition to the martensite, retained austenite is also contained.
Nachfolgend wird ein Ausführungsbeispiel der Erfindung anhand der Figuren beschrieben.Hereinafter, an embodiment of the invention will be described with reference to the figures.
Es zeigen:
- Figur 1
- eine Anlagenskizze, anhand der die in der
Figur 2 angedeutete Prozessabfolge zur Herstellung eines warmumgeformten und pressgehärteten Stahlblechbauteils veranschaulicht ist; - Figur 2
- in einem Blockschaltdiagramm die Prozessabfolge zur Herstellung des Stahlblechbauteils; und
Figur 3- ein Diagramm, dass den zeitlichen Verlauf der Stahlblechbauteil-Temperatur beim Einlegen in das Umformwerkzeug und beim anschließenden Presshärten zeigt.
- FIG. 1
- an investment sketch, on the basis of which in the
FIG. 2 indicated process sequence for producing a hot-formed and press-hardened sheet steel component is illustrated; - FIG. 2
- in a block diagram the process sequence for the production of the sheet steel component; and
- FIG. 3
- a diagram showing the time course of the sheet steel component temperature when placed in the forming tool and the subsequent press hardening.
In der
Nachfolgend wird der Prozessverlauf während des Einlegeschritts, des Presshärteschritts und des Entnahmeschritts anhand dem Temperatur-Zeit-Diagramm der
Mit Bezug auf die
- So ist in
der Figur 3 der Presshärteschritt so ausgelegt, dass der zeitliche Verlauf der Abkühlung einer Abkühlkurve folgt, bei der die Stahlblechbauteil-Temperatur vom Schließzeitpunkt t2 bis zu einem Übergangszeitpunkt t3 mit einer extrem großen ersten Abkühlrate a1 reduziert wird, die größer als 27°C/s ist. Im weiteren Zeitverlauf nach dem Übergangszeitpunkt t3 wird mit einer stark reduzierten zweiten Abkühlrate a2 weiter gekühlt, bis sich eine flache Abkühlgerade G mit einer dritten Abkühlrate a3 einstellt. Die dritte Abkühlrate a3 liegt exemplarisch bei insbesondere kleinerals 15°C/sbis 3°C/s. Wie aus derFig. 3 hervorgeht, liegt die Stahlblechbauteil-Temperatur zu Beginn der Abkühlgeraden G noch oberhalb der Mf-Temperatur. Zum Zeitpunkt t5 schneidet die Abkühlgerade G die Mf-Temperatur, d.h. die Stahlblechbauteil-Temperatur unterschreitet die Mf-Temperatur. Mittels der flachen Abkühlgeraden G wird also die Stahlblechbauteil-Temperatur, die beim Übergangszeitpunkt t3 noch um einen Temperaturversatz Δϑ1 oberhalb der Martensit-Finish-Temperatur Mf liegt, langsam auf eine Entnahmetemperatur ϑ4 reduziert, die um einen Temperaturversatz Δϑ2 unterhalb der Martensit-Finish-Temperatur Mf liegt, die inder Figur 3 in etwa 300°C ist.
- So is in the
FIG. 3 the press-hardening step is designed such that the time course of the cooling follows a cooling curve in which the steel sheet component temperature from the closing time t 2 to a transition time t 3 with an extremely large first Cooling rate a 1 is reduced, which is greater than 27 ° C / s. In the further course of time after the transition time t 3 is further cooled with a greatly reduced second cooling rate a 2 until a flat cooling line G with a third cooling rate a 3 sets. The third cooling rate a 3 is exemplary in particular less than 15 ° C / s to 3 ° C / s. Like from theFig. 3 As can be seen, the steel sheet component temperature at the beginning of the cooling line G is still above the Mf temperature. At time t 5 , the cooling line G cuts the Mf temperature, ie the steel sheet component temperature falls below the Mf temperature. By means of the flat Abkühlgeraden G so, the sheet steel component temperature t at the transition time of 3 is still a temperature offset Δθ 1 above the martensite finish temperature Mf, slowly θ to a removal temperature 4 is reduced, which is a temperature displacement Δθ 2 below the martensite -Finish-temperature Mf lies in theFIG. 3 is about 300 ° C.
Die in der
Im weiteren Prozessverlauf nach dem Presshärteschritt wird das Stahlblechbauteil 7 in die Ablagestation 5 transferiert. In der Ablagestation 5 wird der Abkühlungsprozess unterbrechungsfrei und kontinuierlich fortgesetzt, und zwar mit einer vierten Abkühlrate a4, die bei 1°C/s bis 5°C/s liegen kann. Dies wird bevorzugt durch Luftkühlung mit Umgebungsluft erreicht.In the further course of the process after the press hardening step, the
- 1 Durchlaufofen1 continuous furnace
- 3 Umformwerkzeug3 forming tool
- 5 Ablagestation5 storage station
- 6 Stahlfeinblech6 steel sheet
- 7 Stahlblechbauteil7 sheet steel component
- 9 Heizeinheit9 heating unit
- t1 Einlegezeitpunktt 1 insertion time
- t2 Schließzeitpunktt 2 closing time
- t3 Übergangszeitpunktt 3 transitional time
- t4 Entnahmezeitpunktt 4 removal time
- t5 Zeitpunkt, zu dem die Stahlblechbauteil-Temperatur die Mf-Temperatur unterschreitett 5 Time at which the steel sheet component temperature falls below the Mf temperature
- a1, a2, a3, a4 Abkühlratena 1 , a 2 , a 3 , a 4 cooling rates
- ϑ1 Einlegetemperaturθ 1 insertion temperature
- ϑ2 Schließtemperaturθ 2 closing temperature
- ϑ3 Übergangstemperaturθ 3 transition temperature
- ϑ4 Entnahmetemperaturθ 4 extraction temperature
- Δtzu WerkzeugschließphaseΔt to tool closing phase
- ΔtH WerkzeughaltephaseΔt H tool holding phase
- Δtauf WerkzeugöffnungsphaseΔt on tool opening phase
- Δϑ1, Δϑ2 TemperaturversätzeΔθ 1 , Δθ 2 temperature offsets
- G AbkühlgeradeG cooling straight
Claims (9)
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DE102017202294.9A DE102017202294B4 (en) | 2017-02-14 | 2017-02-14 | Process for producing a hot-formed and press-hardened sheet steel component |
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EP (1) | EP3360621A1 (en) |
CN (1) | CN108425001A (en) |
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WO2020244974A1 (en) * | 2019-06-03 | 2020-12-10 | Volkswagen Aktiengesellschaft | Process for producing a hot-formed and press-hardened sheet steel component |
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SE543021C2 (en) | 2018-09-13 | 2020-09-29 | Husqvarna Ab | Cutting blade for a robotic work tool |
DE102019201883A1 (en) * | 2019-02-13 | 2020-08-13 | Thyssenkrupp Steel Europe Ag | Method for producing a sheet steel component |
US20220119929A1 (en) * | 2019-03-20 | 2022-04-21 | Nippon Steel Corporation | Hot-stamping formed body |
DE102019217496B4 (en) * | 2019-11-13 | 2022-02-24 | Volkswagen Aktiengesellschaft | Process for the production of a hot-formed and press-hardened sheet steel component |
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DE102005032113B3 (en) * | 2005-07-07 | 2007-02-08 | Schwartz, Eva | Thermal deformation and partial hardening apparatus, e.g. for automobile components, comprises mold of at least two parts, each formed from segments adjustable to different temperatures |
DE102006019395A1 (en) * | 2006-04-24 | 2007-10-25 | Thyssenkrupp Steel Ag | Apparatus and method for forming blanks of higher and highest strength steels |
EP2014777A1 (en) * | 2007-07-11 | 2009-01-14 | Neue Materialien Bayreuth GmbH | Method and device for thermal treatment of metal sheet |
WO2009113938A1 (en) * | 2008-03-12 | 2009-09-17 | Gestamp Hardtech Ab | A method of shaping and hardening a sheet steel blank |
US20160145707A1 (en) * | 2013-06-28 | 2016-05-26 | Daimler Ag | Process and Installation for Producing a Press-Hardened Sheet Steel Component |
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KR101682868B1 (en) * | 2011-07-21 | 2016-12-05 | 가부시키가이샤 고베 세이코쇼 | Method for producing hot-pressed steel member |
DE102016113542B3 (en) | 2016-07-22 | 2017-08-24 | Benteler Defense Gmbh & Co. Kg | Method for producing a tank component |
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2017
- 2017-02-14 DE DE102017202294.9A patent/DE102017202294B4/en active Active
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2018
- 2018-01-23 EP EP18152864.7A patent/EP3360621A1/en not_active Withdrawn
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Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
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DE102005032113B3 (en) * | 2005-07-07 | 2007-02-08 | Schwartz, Eva | Thermal deformation and partial hardening apparatus, e.g. for automobile components, comprises mold of at least two parts, each formed from segments adjustable to different temperatures |
DE102006019395A1 (en) * | 2006-04-24 | 2007-10-25 | Thyssenkrupp Steel Ag | Apparatus and method for forming blanks of higher and highest strength steels |
EP2014777A1 (en) * | 2007-07-11 | 2009-01-14 | Neue Materialien Bayreuth GmbH | Method and device for thermal treatment of metal sheet |
WO2009113938A1 (en) * | 2008-03-12 | 2009-09-17 | Gestamp Hardtech Ab | A method of shaping and hardening a sheet steel blank |
US20160145707A1 (en) * | 2013-06-28 | 2016-05-26 | Daimler Ag | Process and Installation for Producing a Press-Hardened Sheet Steel Component |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
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WO2020244974A1 (en) * | 2019-06-03 | 2020-12-10 | Volkswagen Aktiengesellschaft | Process for producing a hot-formed and press-hardened sheet steel component |
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DE102017202294B4 (en) | 2019-01-24 |
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