EP2240622B1 - Method for producing a component from a steel product provided with an al-si coating and intermediate product of such a method - Google Patents

Method for producing a component from a steel product provided with an al-si coating and intermediate product of such a method Download PDF

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Publication number
EP2240622B1
EP2240622B1 EP09705444A EP09705444A EP2240622B1 EP 2240622 B1 EP2240622 B1 EP 2240622B1 EP 09705444 A EP09705444 A EP 09705444A EP 09705444 A EP09705444 A EP 09705444A EP 2240622 B1 EP2240622 B1 EP 2240622B1
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Prior art keywords
steel product
temperature
coating
steel
heating
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EP09705444A
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German (de)
French (fr)
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EP2240622A1 (en
Inventor
Friedhelm Macherey
Franz-Josef Lenze
Michael Peters
Manuela Ruthenberg
Sascha Sikora
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ThyssenKrupp Steel Europe AG
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ThyssenKrupp Steel Europe AG
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C10/00—Solid state diffusion of only metal elements or silicon into metallic material surfaces
    • C23C10/28—Solid state diffusion of only metal elements or silicon into metallic material surfaces using solids, e.g. powders, pastes
    • C23C10/34—Embedding in a powder mixture, i.e. pack cementation
    • C23C10/36—Embedding in a powder mixture, i.e. pack cementation only one element being diffused
    • C23C10/48—Aluminising
    • C23C10/50—Aluminising of ferrous surfaces
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C26/00—Coating not provided for in groups C23C2/00 - C23C24/00
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/12—Aluminium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C23C2/261—After-treatment in a gas atmosphere, e.g. inert or reducing atmosphere
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12736—Al-base component
    • Y10T428/1275—Next to Group VIII or IB metal-base component
    • Y10T428/12757—Fe

Definitions

  • the invention relates to a method for producing a component from a coated with an Al-Si protective coating steel product. Moreover, the invention also relates to an intermediate product which arises in the course of such a process and can be used for the production of components of the type in question.
  • Steel products of the type in question are typically steel strips or sheets which are provided in a manner known per se, for example by means of fire aluminizing, with an Al-Si coating. However, it can also be preformed semifinished products, which are preformed, for example, from sheet metal and then molded to the respective component.
  • the component formed from the respective steel product is protected against corrosion during its practical use.
  • the Al-Si protective coating also already offers the anticorrosive effect, in particular the protection against scaling, immediately after the coating of the steel substrate and keeps it in the course of the forming process at. This is especially true when the shaping is carried out as so-called "press hardening".
  • the starting material to be formed is brought to a temperature at which a at least partly austenitic structure is present, and is deformed in a warm state prior to shaping. Either already during the thermoforming process or immediately thereafter, the resulting component is then accelerated cooled to form hardness structure.
  • a starting material for press hardening flat products such as sheet metal blanks, or already pre-or final molded semi-finished products can be used.
  • the Al-Si coating prevents tinder from forming on the steel product, which would severely hinder the molding process. In this way, it is possible to form components of high-strength, heat-treatable steels, which are exposed to particularly high loads in practice.
  • a steel grade typically used for this purpose is known in practice as "22MnB5". From steel grades of this type, for example, body parts of motor vehicles are manufactured, which must have a high strength with low flat product thickness and, consequently, comparably low weight. Likewise, however, other steel grades, such as deep-drawing steels known under the trade designation “DX55D”, according to DIN EN 10327 composite type, as well as microalloyed steels alloyed according to DIN EN 10292, under the Description "HX300 / 340 LAD" commercially available type, press-form hardened. It is also possible to use the starting products, which are composed in the manner of tailored blanks / patchwork blanks of several sheets.
  • Al-Si coating In order for the Al-Si coating to adhere to the steel substrate so strongly that it does not crack or chip during forming, it is necessary to subject the Al-Si-coated steel product to heat treatment prior to forming, in which iron is precipitated the steel substrate is alloyed into the Al-Si coating.
  • the aim is to pass through the coating over its entire thickness to ensure that there are no breaks or chips in the upper layers of the coating, which are adjacent to the free outer surface of the coated flat product.
  • the type or degree of alloying of Al-Si coatings also has an influence on the weldability and paintability of the components produced by press-hardening.
  • a method of the type described above is in the EP 1 380 666 A1 described.
  • a steel sheet coated with an Al-Si coating is first heated to 900 ° C to 950 ° C over a period of 2 to 8 minutes. Thereafter, the coated steel sheet is cooled to a temperature of 700-800 ° C and thermoformed at that temperature. Subsequently, the formed steel part is rapidly cooled to a temperature below 300 ° C to produce a martensitic structure in the obtained steel part.
  • the heat treatment of the coating provided steel substrate is carried out so that by diffusion of the iron from the steel substrate after the heat treatment, the iron content in the coating in a range between 80% and 95%. In this way, a thermoformed component is to be obtained in which a good weldability and good formability combined with a high corrosion protection.
  • a problem in the implementation of the heat treatment required for the alloying out is that in addition to the setting of a sufficient heating temperature, a certain amount of furnace time must be maintained. The duration over which the respective steel product must be kept in the oven results from the heating rate of the substrate and the required alloying of the substrate with the Al-Si layer.
  • the prior art is a bake time of five to 14 minutes.
  • heating ovens carried out prior to hot working, of the Al-Si coated steel products use radiant heaters.
  • Basic research on the heating behavior of steel products provided with Al-Si coatings has shown in this context that in such furnaces the reflection of the heat radiation at the surface of the respective coating leads to a reduced heating rate in comparison to uncoated or organically or inorganically coated materials. As a result, a relatively long period of time for the warming must be accepted.
  • This long period of time leads to the processor of the provided with an Al-Si coating flat products to long process times, which not only extends the cycle times in component manufacturing, but also increases the cost of the equipment required for the heating furnace.
  • the object of the invention was based on the background of the prior art explained above to provide a method that allows shorter processing times in the processing of Al-Si coated steel products without the risk of corrosive attacks or disadvantages in a subsequent cutting of the coated flat products must be accepted.
  • the steel product processed according to the invention can be a flat steel product, such as a steel sheet or steel strip, or a semi-finished product preformed, for example, from a steel sheet, that is finally deformed in the hot press hardening carried out according to the invention. Also can be processed according to the invention of several composite in the manner of tailored blanks / patchwork blanks sheets.
  • this first alloying step is carried out by setting an appropriate temperature and treatment time so that the Al-Si coating is only partially alloyed with iron of the steel product after the first heating step.
  • the steel product provided with the incompletely ironed-through coating according to the invention can be cooled to room temperature and stored until it is fed to the respective component for further processing. Since the Al-Si coating is only partially alloyed in the first heating step, the Al-Si coating has a low susceptibility to corrosion even after the first heating step, so that its storage, transport and other operations carried out in advance of the second heat treatment are easy can be carried out without the need for additional measures.
  • the coating which has only partially ironed out in the course of the first heating step retains a toughness which, even after the first heating step, still allows the flat products obtained to be cut or cut with simple cutting operations, without resulting in lasting damage to the coating layer ,
  • the flat product obtained after the first heating step and provided with a pre-alloyed coating according to the invention undergoes a second heating step.
  • This second heating step is usually performed at the final processor, while the first heat treatment step to be completed is usually at the producer of the steel products.
  • the second heating step is usually completed immediately before the hot forming.
  • the steel product provided in accordance with the invention with only a pre-alloyed Al-Si coating is heated to the heating temperature required for the subsequent hardening, which is above the Ac1 temperature at which the steel product has an at least partially porous structure.
  • the temperature and duration of the second heating step are to be adjusted according to the invention such that the Al-Si coating is completely alloyed with Fe of the steel product in the course of the second heating step.
  • the coating which according to the invention is only partially alloyed with the steel substrate, has a degree of reflection which, compared with the heating of flat products provided with completely alloyed Al-Si-Fe coatings, has a significantly higher heating rate when heated in radiant furnaces to the heating temperature allowed without causing the coating to drain off.
  • An obtained in accordance with the invention intermediate product is thus characterized in that it with a only with the iron of the steel substrate incompletely pre-alloyed Al-Si coating is provided.
  • the starting material which is now provided with a fully alloyed Si-Al-Fe coating, is then shaped in a manner known per se in a suitable thermoforming tool to form the desired component.
  • the resulting component may be a finished-molded component or a semi-finished product which is subsequently subjected to further deformation steps.
  • thermoforming is finally cooled controlled to produce hardness in the steel substrate.
  • the working steps “thermoforming” and “cooling” can be carried out in particular in the manner known from “compression molding”.
  • the procedure according to the invention thus makes it possible, in a cost-effective and at the same time particularly efficient manner, to provide an aluminized component produced by press-forming hardening within shorter processing times.
  • the expense for the heating step usually carried out at the producer of the steel product is not shortened due to the fact that the process time and the treatment temperature for the partial Al alloying of the Al-Si layer with the iron of the steel substrate are shortened compared with the prior art , but also the usually at the processor of the invention with only incompletely alloyed Al-Si coating carried out second heating step in a shorter process time can run at a correspondingly reduced energy consumption and minimized equipment costs.
  • the temperature of the first heating step is at least 500 ° C, but at the same time at most equal to the A C1 temperature of the steel product.
  • temperatures which are in the range from 550 to 723 ° C., in particular from 550 to 700 ° C. are therefore suitable in particular for the first heating step.
  • the mechanical technological characteristics of the steel product are not deteriorates and the basic structure remains intact in its components.
  • the time to be scheduled for the first heating step at these heating temperatures is 4 to 24 hours when heated in the hood furnace for Al-Si coating thicknesses in the starting state of 10 to 30 ⁇ m (corresponding to 80 to 150 g / m 2 ). It is also conceivable to heat in a continuous furnace or chamber furnace, the heating times in each case be less than one hour.
  • the temperature and duration of the first treatment step are in each case adjusted so that the Al-Si coating, measured starting from the steel substrate, is alloyed with Fe over at least 50%, in particular 70-99%, preferably 90-99%, of its thickness ,
  • the first heating step may be carried out in a bell annealing furnace, chamber furnace or in a continuous annealing furnace.
  • a master alloy in a continuous furnace, which is arranged directly inline at the outlet of a coating plant, similar to a system for galvannealing the case and the heating in a temperature range between 600 and 723 ° C takes place.
  • the steel product obtained according to the invention and provided with a partially alloyed Al-Si coating can be heated to the required heating temperature in a continuous furnace in the second heating step to be heated.
  • the second heating can be effected inductively, conductively or by means of thermal radiation.
  • the samples have been subjected to a heat treatment corresponding to the first heating step of the process according to the invention in a test oven simulated in a crucible annealing furnace for eight hours each time.
  • a first part of samples was annealed at 500 ° C, a second part at 550 ° C and a third part at 600 ° C.
  • further samples have passed through the continuous furnace at 950 ° C in six minutes. This is a typical heat treatment for press-hardening in which the Al-Si coating layer is alloyed. After the respective anneals, the samples were cooled to room temperature.
  • the obtained samples each had a non-fully alloyed Al-Si coating layer except for the sample heat-treated at 950 ° C.
  • the previously annealed and cooled samples are in a second heating step corresponding annealing treatment in a radiant oven to a heating temperature of 950 ° C was heated, in which the steel substrate had austenite microstructure.
  • the heating rates were recorded, ie it was monitored how quickly the samples were heated to the target temperature of 950 ° C.
  • the temperature T of the respective samples is plotted over the annealing time t.
  • the sample annealed for a not annealed in a first heating step upstream (curve "- ° C / - s").
  • the times required for the alloying in the austenitizing furnace before the hot working can be significantly reduced. It was thus shown that a time saving of at least 90 s is expected compared to the conventional procedure can be. With this time saving, the furnaces needed for heating before hot forming can be made smaller. In the maintenance of conventional size ovens cooling to room temperature in about 10 days, whereas in the possible reduction of the furnace size by the invention with a time saving of at least 2 to 3 days can be expected for the cooling.

Abstract

A process for producing a component from a steel product coated with a protective Al—Si coating, and an intermediate product that arises during the course of such a process and that can be used to produce components of the type concerned here. The steel product coated with the Al—Si coating, undergoes a first heating stage in which the temperature and the duration of the heat treatment are set such that the Al—Si coating is only partially pre-alloyed with Fe from the steel product. Then, the steel product, in a second heating stage, is heated to a heating temperature, above the Ac1 temperature, at which the steel product has an at least partially austenitic structure, wherein the temperature and the duration of the second heating stage are set such that the Al—Si coating is fully alloyed with Fe from the steel product. After the steel product is heated to the heating temperature, it is shaped to form the component and the component obtained is cooled in a controlled manner, in order to obtain a martensitic structure.

Description

Die Erfindung betrifft ein Verfahren zum Herstellen eines Bauteils aus einem mit einem Al-Si-Schutzüberzug überzogenen Stahlprodukt. Darüber hinaus betrifft die Erfindung auch ein Zwischenprodukt, das im Zuge eines solchen Verfahrens entsteht und für die Herstellung von Bauteilen der in Rede stehenden Art genutzt werden kann.The invention relates to a method for producing a component from a coated with an Al-Si protective coating steel product. Moreover, the invention also relates to an intermediate product which arises in the course of such a process and can be used for the production of components of the type in question.

Bei Stahlprodukten der hier in Rede stehenden Art handelt es sich typischer Weise um Stahlbänder oder -bleche, die in an sich bekannter Weise beispielsweise durch Feueraluminieren mit einem Al-Si-Überzug versehen sind. Es kann sich dabei jedoch auch um vorgeformte Halbzeuge handeln, die beispielsweise aus Blechen vorgeformt und dann zu dem jeweiligen Bauteil fertig geformt werden.Steel products of the type in question are typically steel strips or sheets which are provided in a manner known per se, for example by means of fire aluminizing, with an Al-Si coating. However, it can also be preformed semifinished products, which are preformed, for example, from sheet metal and then molded to the respective component.

Durch den Al-Si-Überzug ist das aus dem jeweiligen Stahlprodukt geformte Bauteil während seines praktischen Einsatzes gegen Korrosion geschützt. Die Korrosionsschutzwirkung, insbesondere den Schutz vor Verzunderung, bietet der Al-Si-Schutzüberzug jedoch auch schon bereits unmittelbar nach der Beschichtung des Stahlsubstrats und behält sie im Zuge des Umformvorgangs bei. Dies gilt insbesondere dann, wenn die Formgebung als so genanntes "Presshärten" durchgeführt wird.Due to the Al-Si coating, the component formed from the respective steel product is protected against corrosion during its practical use. However, the Al-Si protective coating also already offers the anticorrosive effect, in particular the protection against scaling, immediately after the coating of the steel substrate and keeps it in the course of the forming process at. This is especially true when the shaping is carried out as so-called "press hardening".

Beim Presshärten wird das zu verformende Ausgangsprodukt vor der Formgebung auf eine Temperatur gebracht, bei der ein zumindest teilaustenitisches Gefüge vorliegt, und im warmen Zustand verformt. Entweder schon während des Warmformvorgangs oder unmittelbar daran anschließend wird das erhaltene Bauteil dann beschleunigt abgekühlt, um Härtegefüge zu bilden. Als Ausgangsprodukt für das Presshärten können Flachprodukte, wie Blechzuschnitte, oder bereits vor- bzw. endgeformte Halbzeuge verwendet werden.In press-hardening, the starting material to be formed is brought to a temperature at which a at least partly austenitic structure is present, and is deformed in a warm state prior to shaping. Either already during the thermoforming process or immediately thereafter, the resulting component is then accelerated cooled to form hardness structure. As a starting material for press hardening flat products, such as sheet metal blanks, or already pre-or final molded semi-finished products can be used.

Während des Presshärtens verhindert der Al-Si-Überzug, dass sich auf dem Stahlprodukt Zunder bildet, der den Formgebungsvorgang massiv behindern würde. Auf diese Weise ist es möglich, auch aus hochfesten, vergütbaren Stählen Bauteile zu formen, die in der Praxis besonders hohen Belastungen ausgesetzt sind.During press hardening, the Al-Si coating prevents tinder from forming on the steel product, which would severely hinder the molding process. In this way, it is possible to form components of high-strength, heat-treatable steels, which are exposed to particularly high loads in practice.

Eine typischerweise für diesen Zweck verwendete Stahlgüte ist in der Praxis unter der Bezeichnung "22MnB5" bekannt. Aus Stahlgüten dieser Art werden beispielsweise Karosserieteile von Kraftfahrzeugen gefertigt, die bei geringer Flachproduktdicke und damit einhergehend vergleichbar geringem Gewicht eine hohe Festigkeit besitzen müssen. Ebenso können jedoch auch andere Stahlgüten, wie beispielsweise Tiefziehstähle der unter der Handelsbezeichnung "DX55D" bekannten, gemäß DIN EN 10327 zusammengesetzten Art, sowie mikrolegierte Stähle der gemäß DIN EN 10292 legierten, unter der Bezeichnung "HX300/340 LAD" im Handel erhältlichen Art, pressformgehärtet werden. Auch ist es möglich, die Ausgangsprodukte zu verwenden, die nach Art von Tailored Blanks/Patchwork Blanks aus mehreren Blechen zusammengesetzt sind.A steel grade typically used for this purpose is known in practice as "22MnB5". From steel grades of this type, for example, body parts of motor vehicles are manufactured, which must have a high strength with low flat product thickness and, consequently, comparably low weight. Likewise, however, other steel grades, such as deep-drawing steels known under the trade designation "DX55D", according to DIN EN 10327 composite type, as well as microalloyed steels alloyed according to DIN EN 10292, under the Description "HX300 / 340 LAD" commercially available type, press-form hardened. It is also possible to use the starting products, which are composed in the manner of tailored blanks / patchwork blanks of several sheets.

Damit der Al-Si-Überzug auf dem Stahlsubstrat so fest haftet, dass er bei der Umformung nicht bricht oder abplatzt, ist es erforderlich, das mit dem Al-Si-Überzug versehene Stahlprodukt vor der Umformung einer Wärmebehandlung zu unterziehen, bei dem Eisen aus dem Stahlsubstrat in den Al-Si-Überzug einlegiert wird. Ziel ist dabei, den Überzug über seine gesamte Dicke durchzulegieren, um sicherzustellen, dass es auch in den oberen, an die freie Außenseite des überzogenen Flachprodukts angrenzenden Schichten des Überzugs zu keinen Brüchen oder Abplatzungen kommt. Die Art bzw. der Grad der Durchlegierung von Al-Si-Überzügen hat darüber hinaus auch Einfluss auf die Schweiß- und Lackierbarkeit der durch Presshärten hergestellten Bauteile.In order for the Al-Si coating to adhere to the steel substrate so strongly that it does not crack or chip during forming, it is necessary to subject the Al-Si-coated steel product to heat treatment prior to forming, in which iron is precipitated the steel substrate is alloyed into the Al-Si coating. The aim is to pass through the coating over its entire thickness to ensure that there are no breaks or chips in the upper layers of the coating, which are adjacent to the free outer surface of the coated flat product. The type or degree of alloying of Al-Si coatings also has an influence on the weldability and paintability of the components produced by press-hardening.

Ein Verfahren der voranstehend beschriebenen Art ist in der EP 1 380 666 A1 beschrieben. Bei diesem Verfahren wird ein mit einem Al-Si-Überzug beschichtetes Stahlblech zunächst über eine Dauer von 2 bis 8 Minuten auf 900 °C bis 950 °C erwärmt. Daraufhin wird das beschichtete Stahlblech auf eine 700 - 800 °C betragende Temperatur abgekühlt und bei dieser Temperatur warmverformt. Anschließend wird das geformte Stahlteil schnell auf eine Temperatur unterhalb von 300 °C abgekühlt, um ein martensitisches Gefüge in dem erhaltenen Stahlteil zu erzeugen. Die Wärmebehandlung des mit dem Überzug versehenen Stahlsubstrats wird dabei so durchgeführt, dass durch Diffusion des Eisens aus dem Stahlsubstrat nach der Wärmebehandlung der Eisenanteil im Überzug in einem Bereich zwischen 80 % und 95 % liegt. Auf diese Weise soll ein warmgeformtes Bauteil erhalten werden, bei dem eine gute Schweißeignung und eine gute Formbarkeit mit einem hohen Korrosionsschutz kombiniert sind.A method of the type described above is in the EP 1 380 666 A1 described. In this method, a steel sheet coated with an Al-Si coating is first heated to 900 ° C to 950 ° C over a period of 2 to 8 minutes. Thereafter, the coated steel sheet is cooled to a temperature of 700-800 ° C and thermoformed at that temperature. Subsequently, the formed steel part is rapidly cooled to a temperature below 300 ° C to produce a martensitic structure in the obtained steel part. The heat treatment of the coating provided steel substrate is carried out so that by diffusion of the iron from the steel substrate after the heat treatment, the iron content in the coating in a range between 80% and 95%. In this way, a thermoformed component is to be obtained in which a good weldability and good formability combined with a high corrosion protection.

Ein Problem bei der Durchführung der für das Durchlegieren erforderlichen Wärmebehandlung besteht darin, dass dabei neben der Einstellung einer ausreichenden Erwärmungstemperatur eine gewisse Ofenliegezeit eingehalten werden muss. Die Dauer, über die das jeweilige Stahlprodukt im Ofen gehalten werden muss, resultiert aus der Aufheizgeschwindigkeit des Substrates und der benötigten Durchlegierung des Substrates mit der Al-Si-Schicht. Stand der Technik ist eine Ofenliegezeit von fünf bis 14 Minuten.A problem in the implementation of the heat treatment required for the alloying out is that in addition to the setting of a sufficient heating temperature, a certain amount of furnace time must be maintained. The duration over which the respective steel product must be kept in the oven results from the heating rate of the substrate and the required alloying of the substrate with the Al-Si layer. The prior art is a bake time of five to 14 minutes.

In der Praxis werden zum vor der Warmumformung durchgeführten Erwärmen der mit Al-Si-Überzügen versehenen Stahlprodukte Strahlungsöfen eingesetzt. Grundlagenuntersuchung zum Aufheizverhalten von mit Al-Si-Überzügen versehenen Stahlprodukten haben in diesem Zusammenhang ergeben, dass in solchen Öfen die Reflexion der Wärmestrahlung an der Oberfläche des jeweiligen Überzugs zu einer reduzierten Aufheizgeschwindigkeit im Vergleich zu unbeschichteten bzw. organisch oder anorganisch beschichteten Werkstoffen führt. Damit einhergehend muss eine verhältnismäßig lange Zeitdauer für die Erwärmung in Kauf genommen werden.In practice, heating ovens, carried out prior to hot working, of the Al-Si coated steel products use radiant heaters. Basic research on the heating behavior of steel products provided with Al-Si coatings has shown in this context that in such furnaces the reflection of the heat radiation at the surface of the respective coating leads to a reduced heating rate in comparison to uncoated or organically or inorganically coated materials. As a result, a relatively long period of time for the warming must be accepted.

Diese lange Zeitdauer führt beim Verarbeiter der mit einem Al-Si-Überzug versehenen Flachprodukte zu langen Prozesszeiten, durch die nicht nur die Taktzeiten bei der Bauteilherstellung verlängert, sondern auch der apparative Aufwand für den für die Erwärmung benötigten Ofen erhöht wird.This long period of time leads to the processor of the provided with an Al-Si coating flat products to long process times, which not only extends the cycle times in component manufacturing, but also increases the cost of the equipment required for the heating furnace.

Technisch wäre es auch möglich, den Stahl-Grundwerkstoff der Flachprodukte mit seiner Beschichtung durch induktive oder konduktive Erwärmung schneller aufzuheizen. Auch könnte die Aufheizung durch erzwungene Konvektion der Wärmestrahlung beschleunigt werden. Im Fall einer beschleunigten Erwärmung besteht allerdings die Gefahr, dass der Legierungsprozess in der Al-Si-Überzugsschicht langsamer abläuft als die Aufheizgeschwindigkeit mit dem Ergebnis, dass die Al-Si-Schicht nicht vollständig oder fehlerhaft durchlegiert wird. Im Extremfall kann es sogar dazu kommen, dass die Al-Si-Schicht vom Stahlprodukt abfließt.Technically, it would also be possible to heat the steel base material of the flat products faster with its coating by inductive or conductive heating. Also, the heating could be accelerated by forced convection of heat radiation. In the case of accelerated heating, however, there is a risk that the alloying process in the Al-Si coating layer proceeds more slowly than the heating rate, with the result that the Al-Si layer is not completely or incorrectly alloyed. In extreme cases, it may even happen that the Al-Si layer flows away from the steel product.

Aus der DE 10 2004 007 071 B4 ist ein Versuch bekannt, die Prozesszeit beim Verarbeiter der mit einem Al-Si-Überzug versehenen Flachprodukte dadurch zu verkürzen, dass das Durchlegieren des Überzugs und die Erwärmung des Stahlflachprodukts auf Erwärmungstemperatur in zwei getrennten Arbeitsschritten durchgeführt wird. Dieses Vorgehen erlaubt es, den Prozess der Durchlegierung beim Hersteller des mit dem Al-Si-Überzug versehenen Stahlflachprodukts durchzuführen. Beim Verarbeiter kann die Erwärmung des mit dem dann bereits durchlegierten Überzug versehenen Stahlflachprodukts beispielsweise mittels Induktion oder Konduktion in optimal kurzer Zeit erfolgen, ohne dass dabei auf die Ausbildung des Überzugs Rücksicht genommen werden muss. Dementsprechend ist es bei Anwendung des bekannten Verfahrens grundsätzlich möglich, Stahlflachprodukte, die beim Hersteller bereits mit einem vollständig durchlegierten Überzug versehen sind, in einem Zwischenlager zu speichern, aus dem sie dann im Bedarfsfall für die Weiterverarbeitung beim Verarbeiter kurzfristig abgerufen werden können.From the DE 10 2004 007 071 B4 For example, it is known to shorten the process time in the processor of the flat-plate products provided with an Al-Si coating by performing the alloying of the coating and heating the steel flat product to heating temperature in two separate operations. This procedure makes it possible to perform the alloying process at the manufacturer of the Al-Si coated flat steel product. In the processor, the heating of the steel flat product provided with the then already alloyed coating can be heated, for example by means of induction or conduction be done optimally short time, without having to take into account the formation of the coating. Accordingly, when using the known method, it is basically possible to store flat steel products, which are already provided with a completely alloyed coating by the manufacturer, in an intermediate store, from which they can then be retrieved in case of need for further processing by the processor at short notice.

Als problematisch erweist sich bei dem voranstehend erläuterten Vorschlag allerdings, dass der vollständig durchlegierte Überzug selbst sowohl während der Lagerung der vorproduzierten Stahlflachprodukte im Zwischenlager als auch im Zuge der beim Verarbeiter durchlaufenen Arbeitsschritte einem korrosiven Angriff ausgesetzt ist. Dieses Problem ergibt sich aus dem Eisenanteil, der an der freien Oberfläche des durchlegierten Überzugs vorhanden ist. Um eine solche Oberflächenkorrosion zu unterdrücken, sind aufwändige Schutzmaßnahmen erforderlich, die die mit der Entkopplung von Durchlegierung und Presshärten erreichten Vorteile zum großen Teil wieder aufzehren. Hinzukommt, dass ein unter Umständen vor dem Warmumformen erforderlich werdender Zuschnitt der mit dem durchlegierten Überzug überzogenen Flachproduktplatinen schwierig ist, da durchlegierte Al-Si-Schichten hart und spröde sind.Vor dem Hintergrund des voranstehend erläuterten Standes der Technik lag der Erfindung die Aufgabe zu Grunde, ein Verfahren zu schaffen, das verkürzte Verarbeitungszeiten beim Verarbeiter von mit einem Al-Si-Überzug versehenen Stahlprodukten ermöglicht, ohne dass dazu die Gefahr von korrosiven Angriffen oder Nachteile bei einem nachträglichen Zuschnitt der beschichteten Flachprodukte in Kauf genommen müssen.However, the above-described proposal proves to be problematic in that the completely alloyed coating itself is exposed to a corrosive attack both during the storage of the pre-produced flat steel products in the interim storage facility and in the course of the operations carried out by the processor. This problem arises from the amount of iron present on the exposed surface of the galled coating. In order to suppress such a surface corrosion, elaborate protective measures are required, which consume the advantages achieved with the decoupling of alloy and press hardening to a large extent again. In addition, it may be difficult to cut the flat product boards coated with the overcoated coating, possibly before hot stamping, because Al-Si layers which have been alloyed are hard and brittle. The object of the invention was based on the background of the prior art explained above to provide a method that allows shorter processing times in the processing of Al-Si coated steel products without the risk of corrosive attacks or disadvantages in a subsequent cutting of the coated flat products must be accepted.

Erfindungsgemäß ist diese Aufgabe durch das in Anspruch 1 angegebene Verfahren gelöst worden. Vorteilhafte Ausgestaltungen dieses Verfahrens sind in den auf Anspruch 1 rückbezogenen Ansprüchen angegeben.According to the invention, this object has been achieved by the method specified in claim 1. Advantageous embodiments of this method are specified in the dependent claims on claim 1.

Bei dem erfindungsgemäß verarbeiteten Stahlprodukt kann es sich um ein Stahlflachprodukt, wie ein Stahlblech oder Stahlband, oder ein beispielsweise aus einem Stahlblech vorgeformtes Halbzeug handeln, dass beim erfindungsgemäß durchgeführten Warmpresshärten fertig verformt wird. Auch lassen sich in erfindungsgemäßer Weise aus mehreren nach Art von Tailored Blanks/Patchwork Blanks zusammengesetzte Bleche verarbeiten.The steel product processed according to the invention can be a flat steel product, such as a steel sheet or steel strip, or a semi-finished product preformed, for example, from a steel sheet, that is finally deformed in the hot press hardening carried out according to the invention. Also can be processed according to the invention of several composite in the manner of tailored blanks / patchwork blanks sheets.

Auch beim erfindungsgemäßen Verfahren findet eine zweistufige Wärmebehandlung statt, wobei es ebenfalls in Übereinstimmung mit dem Stand der Technik im ersten Erwärmungsschritt zum Einlegieren von Eisen aus dem Stahlsubstrat in den Al-Si-Überzug kommt.In the method according to the invention, a two-stage heat treatment takes place, and it also comes in accordance with the prior art in the first heating step for alloying iron from the steel substrate in the Al-Si coating.

Im Unterschied zum Stand der Technik wird dieser erste Legierungsschritt jedoch durch Einstellung einer geeigneten Temperatur und Behandlungsdauer so ausgeführt, dass der Al-Si-Überzug nach dem ersten Erwärmungsschritt nur unvollständig mit Eisen des Stahlprodukts durchlegiert ist.However, unlike the prior art, this first alloying step is carried out by setting an appropriate temperature and treatment time so that the Al-Si coating is only partially alloyed with iron of the steel product after the first heating step.

Anschließend kann das mit dem erfindungsgemäß unvollständig durchlegierten Überzug versehene Stahlprodukt auf Raumtemperatur abgekühlt und gelagert werden, bis es der Weiterverarbeitung zum jeweiligen Bauteil zugeführt wird. Da der Al-Si-Überzug im ersten Erwärmungsschritt nur unvollständig legiert wird, weist der Al-Si-Überzug auch nach dem ersten Erwärmungsschritt eine geringe Korrosionsanfälligkeit auf, so dass seine Lagerung, sein Transport und die weiteren im Vorfeld der zweiten Wärmebehandlung durchgeführten Arbeitsschritte problemlos durchgeführt werden können, ohne dass dazu zusätzliche Maßnahmen erforderlich sind.Subsequently, the steel product provided with the incompletely ironed-through coating according to the invention can be cooled to room temperature and stored until it is fed to the respective component for further processing. Since the Al-Si coating is only partially alloyed in the first heating step, the Al-Si coating has a low susceptibility to corrosion even after the first heating step, so that its storage, transport and other operations carried out in advance of the second heat treatment are easy can be carried out without the need for additional measures.

Gleichzeitig behält der erfindungsgemäß im Zuge des ersten Erwärmungsschritts nur teilweise durchlegierte Überzug eine Zähigkeit, die es auch nach dem ersten Erwärmungsschritt noch erlaubt, die dabei erhaltenen Flachprodukte mit einfachen Schneidoperationen zu zerteilen oder zu beschneiden, ohne dass es dabei zu einer nachhaltigen Beschädigung der Überzugsschicht kommt.At the same time, according to the invention, the coating which has only partially ironed out in the course of the first heating step retains a toughness which, even after the first heating step, still allows the flat products obtained to be cut or cut with simple cutting operations, without resulting in lasting damage to the coating layer ,

Vor seiner Umformung zu dem Bauteil durchläuft das nach dem ersten Erwärmungsschritt erhaltene, erfindungsgemäß mit einem nur vorlegierten Überzug versehene Flachprodukt einen zweiten Erwärmungsschritt. Dieser zweite Erwärmungsschritt wird in der Regel beim Endverarbeiter durchgeführt, während der erste zu absolvierende Wärmebehandlungsschritt in der Regel beim Erzeuger der Stahlprodukte ablaufen wird.Before being converted to the component, the flat product obtained after the first heating step and provided with a pre-alloyed coating according to the invention undergoes a second heating step. This second heating step is usually performed at the final processor, while the first heat treatment step to be completed is usually at the producer of the steel products.

Der zweite Erwärmungsschritt wird dabei üblicher Weise unmittelbar vor der Warmformgebung absolviert werden. Im Zuge des zweiten Erwärmungsschritts wird das in erfindungsgemäßer Weise nur mit einem vorlegierten Al-Si-Überzug versehene Stahlprodukt auf die für die nachfolgende Härtung erforderliche Erwärmungstemperatur erwärmt, die oberhalb der Ac1-Temperatur liegt, bei der das Stahlprodukt ein zumindest teilaustentisches Gefüge aufweist. Erforderlichenfalls lässt sich auch eine mindestens der Ac3-Temperatur entsprechende oder darüber liegende Erwärmungstemperatur einstellen, um im zu verformenden Ausgangsprodukt ein weitestgehend vollständiges Austenitgefüge einzustellen.The second heating step is usually completed immediately before the hot forming. In the course of the second heating step, the steel product provided in accordance with the invention with only a pre-alloyed Al-Si coating is heated to the heating temperature required for the subsequent hardening, which is above the Ac1 temperature at which the steel product has an at least partially porous structure. If necessary, it is also possible to set a heating temperature which corresponds to or lies above at least the Ac3 temperature in order to set a largely complete austenite structure in the starting product to be deformed.

Dabei sind die Temperatur und Dauer des zweiten Erwärmungsschritts erfindungsgemäß so einzustellen, dass der Al-Si-Überzug im Zuge des zweiten Erwärmungsschritts vollständig mit Fe des Stahlprodukts durchlegiert wird.In this case, the temperature and duration of the second heating step are to be adjusted according to the invention such that the Al-Si coating is completely alloyed with Fe of the steel product in the course of the second heating step.

Überraschend hat sich in diesem Zusammenhang ergeben, dass der erfindungsgemäß mit dem Stahlsubstrat nur unvollständig legierte Überzug einen Reflektionsgrad aufweist, der gegenüber der Erwärmung von mit vollständig durchlegierten Al-Si-Fe-Überzügen versehenen Flachprodukten deutlich höhere Aufheizgeschwindigkeit bei der Erwärmung in Strahlungsöfen auf die Erwärmungstemperatur erlaubt, ohne dass ein Abfließen des Überzugs erfolgt.Surprisingly, it has been found in this connection that the coating, which according to the invention is only partially alloyed with the steel substrate, has a degree of reflection which, compared with the heating of flat products provided with completely alloyed Al-Si-Fe coatings, has a significantly higher heating rate when heated in radiant furnaces to the heating temperature allowed without causing the coating to drain off.

Ein in erfindungsgemäßer Weise erhaltenes Zwischenprodukt ist somit dadurch gekennzeichnet, dass es mit einem nur mit dem Eisen des Stahlsubstrats unvollständig vorlegierten Al-Si-Überzug versehen ist.An obtained in accordance with the invention intermediate product is thus characterized in that it with a only with the iron of the steel substrate incompletely pre-alloyed Al-Si coating is provided.

Nach dem zweiten Erwärmungsschritt wird das nun mit einem durchlegierten Si-Al-Fe-Überzug versehene Ausgangsprodukt dann in an sich bekannter Weise in einem geeigneten Warmformwerkzeug zu dem gewünschten Bauteil umgeformt. Bei dem erhaltenen Bauteil kann es sich um ein fertig endgeformtes Bauteil handeln oder um ein Halbzeug, das anschließend weiteren Verformungsschritten unterzogen wird.After the second heating step, the starting material, which is now provided with a fully alloyed Si-Al-Fe coating, is then shaped in a manner known per se in a suitable thermoforming tool to form the desired component. The resulting component may be a finished-molded component or a semi-finished product which is subsequently subjected to further deformation steps.

Bereits während der Warmformgebung oder unmittelbar anschließend wird das warmgeformte Bauteil schließlich kontrolliert abgekühlt, um im Stahlsubstrat Härtegefüge zu erzeugen. Die Arbeitsschritte "Warmformen" und "Abkühlen" lassen sich dabei insbesondere in der vom "Pressformhärten" bekannten Weise durchführen.Already during the hot forming or immediately thereafter, the thermoformed component is finally cooled controlled to produce hardness in the steel substrate. The working steps "thermoforming" and "cooling" can be carried out in particular in the manner known from "compression molding".

Die erfindungsgemäße Vorgehensweise erlaubt es somit, auf kostengünstige und gleichzeitig besonders effiziente Weise, ein aluminiertes, durch Pressformhärten erzeugtes Bauteil innerhalb verkürzter Verarbeitungszeiten zur Verfügung zu stellen. Dabei ist nicht der Aufwand für den in der Regel beim Produzenten des Stahlprodukts durchgeführten Erwärmungsschritt aufgrund dessen verkürzt, dass die Prozesszeit und die Behandlungstemperatur für die nur teilweise erfolgende Legierung der Al-Si-Schicht mit dem Eisen des Stahlsubstrats gegenüber dem Stand der Technik verkürzt ist, sondern auch der in der Regel beim Verarbeiter des mit dem erfindungsgemäß nur unvollständig legierten Al-Si-Überzug durchgeführte zweite Erwärmungsschritt in verkürzter Prozessdauer bei entsprechend vermindertem Energiebedarf und minimiertem apparativen Aufwand ablaufen kann.The procedure according to the invention thus makes it possible, in a cost-effective and at the same time particularly efficient manner, to provide an aluminized component produced by press-forming hardening within shorter processing times. In this case, the expense for the heating step usually carried out at the producer of the steel product is not shortened due to the fact that the process time and the treatment temperature for the partial Al alloying of the Al-Si layer with the iron of the steel substrate are shortened compared with the prior art , but also the usually at the processor of the invention with only incompletely alloyed Al-Si coating carried out second heating step in a shorter process time can run at a correspondingly reduced energy consumption and minimized equipment costs.

Die Tatsache, dass nach dem erfindungsgemäß durchgeführten ersten Erwärmungsschritt in der Al-Si-Schicht ein geringerer Fe-Anteil vorhanden ist als im nach dem Warmpresshärten erhaltenen Bauteil, bei der nur ein minimales Korrosionsrisiko besteht, erlaubt es insbesondere, das Stahlprodukt zwischen dem ersten und dem zweiten Erwärmungsschritt auf Raumtemperatur abzukühlen und zu lagern, bevor es dann der Weiterverarbeitung zugeführt wird. Die Korrosionsschutzwirkung der nach dem ersten Erwärmungsschritt vorhandenen, nur unvollständig legierten Al-Si-Schicht ist dabei so groß, dass sich das Stahlprodukt zwischen dem ersten und dem zweiten Erwärmungsschritt problemlos an Luft beispielsweise zwischen dem Werk des Erzeugers des Stahlprodukts und dem Werk des Endverarbeiters transportieren lässt.The fact that a lower Fe content is present in the Al-Si layer after the first heating step carried out according to the invention than in the component obtained after hot press hardening, in which there is only a minimal risk of corrosion, allows the steel product to be interposed between the first and the second the second heating step to cool to room temperature and store before it is then sent for further processing. The anticorrosion effect of the incompletely alloyed Al-Si layer present after the first heating step is so great that the steel product can easily be transported between the first and the second heating step in air, for example, between the plant of the producer of the steel product and the factory of the final processor leaves.

Praktische Versuche haben ergeben, dass die Temperatur des ersten Erwärmungsschritts mindestens 500 °C beträgt, gleichzeitig jedoch höchstens gleich der AC1-Temperatur des Stahlprodukts ist. In der Praxis eignen sich daher für den ersten Erwärmungsschritt insbesondere Temperaturen, die im Bereich von 550 - 723 °C, insbesondere 550 - 700 °C, liegen. Durch eine Erwärmung in diesem Temperaturbereich werden die mechanisch technologischen Kennwerte des Stahlproduktes nicht verschlechtert und das Grundgefüge bleibt in seinen Bestandteilen erhalten.Practical tests have shown that the temperature of the first heating step is at least 500 ° C, but at the same time at most equal to the A C1 temperature of the steel product. In practice, temperatures which are in the range from 550 to 723 ° C., in particular from 550 to 700 ° C., are therefore suitable in particular for the first heating step. By heating in this temperature range, the mechanical technological characteristics of the steel product are not deteriorates and the basic structure remains intact in its components.

Die für den ersten Erwärmungsschritt bei diesen Erwärmungstemperaturen einzuplanende Zeitdauer beträgt bei Al-Si-Überzugsdicken im Ausgangszustand von 10 - 30 µm (entsprechend 80 - 150 g/m2) 4 - 24 h bei einer Erwärmung im Haubenofen. Es ist auch eine Erwärmung im Durchlaufofen oder Kammerofen denkbar, wobei die Erwärmungszeiten dabei jeweils weniger als eine Stunde betragen.The time to be scheduled for the first heating step at these heating temperatures is 4 to 24 hours when heated in the hood furnace for Al-Si coating thicknesses in the starting state of 10 to 30 μm (corresponding to 80 to 150 g / m 2 ). It is also conceivable to heat in a continuous furnace or chamber furnace, the heating times in each case be less than one hour.

Bevorzugt werden Temperatur und Dauer des ersten Behandlungsschritts dabei jeweils so eingestellt, dass der Al-Si-Überzug, gemessen ausgehend von dem Stahlsubstrat, über mindestens 50 %, insbesondere 70 - 99 %, bevorzugt 90 - 99 %, seiner Dicke mit Fe legiert ist.In each case, the temperature and duration of the first treatment step are in each case adjusted so that the Al-Si coating, measured starting from the steel substrate, is alloyed with Fe over at least 50%, in particular 70-99%, preferably 90-99%, of its thickness ,

Abhängig von der beim Hersteller des Stahlprodukts vorhandenen Ofentechnik kann der erste Erwärmungsschritt in einem Haubenglühofen, Kammerofen oder in einem Durchlaufglühofen durchgeführt werden. Im Fall der Verarbeitung eines Stahlflachproduktes ist es dabei möglich, eine Vorlegierung in einem Durchlaufofen zu erhalten, der direkt inline am Austritt einer Beschichtungsanlage angeordnet ist, ähnlich wie dies bei einer Anlage für das Galvannealing der Fall ist und die Erwärmung in einem Temperaturbereich zwischen 600 und 723 °C erfolgt. Genauso kann das erfindungsgemäß erhaltene, mit einem nur teilweise legierten Al-Si-Überzug versehene Stahlprodukt im zweiten Erwärmungsschritt in einem Durchlaufofen auf die erforderliche Erwärmungstemperatur erwärmt werden. Dabei kann die zweite Erwärmung induktiv, konduktiv oder mittels Wärmestrahlung erfolgen.Depending on the furnace technology available from the manufacturer of the steel product, the first heating step may be carried out in a bell annealing furnace, chamber furnace or in a continuous annealing furnace. In the case of processing a flat steel product, it is possible to obtain a master alloy in a continuous furnace, which is arranged directly inline at the outlet of a coating plant, similar to a system for galvannealing the case and the heating in a temperature range between 600 and 723 ° C takes place. In the same way, the steel product obtained according to the invention and provided with a partially alloyed Al-Si coating can be heated to the required heating temperature in a continuous furnace in the second heating step to be heated. In this case, the second heating can be effected inductively, conductively or by means of thermal radiation.

Nachfolgend wird die Erfindung anhand eines Ausführungsbeispiels näher erläutert.The invention will be explained in more detail with reference to an embodiment.

Es wurden Proben eines 1,5 mm dicken Stahlblechs untersucht, das neben Eisen und unvermeidbaren Verunreinigungen (in Gew.-%) C: 0,226 %, Si: 0,25 %, Mn: 1,2 %, Cr: 0,137 %, Mo: 0,002 %, Ti: 0,034 %, B: 0,003 % enthielt und durch konventionelles Feueraluminieren mit einem 20 µm (entsprechend 120g /m2) dicken Al-Si-Überzug versehen worden war.Samples of a 1.5 mm thick steel sheet were examined, which besides iron and unavoidable impurities (in wt%) C: 0.226%, Si: 0.25%, Mn: 1.2%, Cr: 0.137%, Mo : 0.002%, Ti: 0.034%, B: 0.003%, and had been provided with a 20 μm (corresponding to 120 g / m 2 ) thick Al-Si coating by conventional fire aluminizing.

Die Proben sind in einem einem Haubenglühofen nachgebildeten Versuchsofen für jeweils acht Stunden einer dem ersten Erwärmungsschritt des erfindungsgemäßen Verfahrens entsprechenden Wärmebehandlung unterzogen worden. Ein erster Teil von Proben ist dabei bei 500 °C, ein zweiter Teil bei 550 °C und ein dritter Teil bei 600 °C geglüht worden. Zusätzlich haben weitere Proben in sechs Minuten bei 950 °C den Durchlaufofen durchlaufen. Dies stellt eine typische Wärmebehandlung zum Presshärten dar, bei der die Al-Si-Überzugsschicht durchlegiert wird. Nach den jeweiligen Glühungen sind die Proben auf Raumtemperatur abgekühlt worden. Die erhaltenen Proben wiesen bis auf die bei 950 °C wärmebehandelte Probe jeweils eine nicht vollständig durchlegierte Al-Si-Überzugsschicht auf.The samples have been subjected to a heat treatment corresponding to the first heating step of the process according to the invention in a test oven simulated in a crucible annealing furnace for eight hours each time. A first part of samples was annealed at 500 ° C, a second part at 550 ° C and a third part at 600 ° C. In addition, further samples have passed through the continuous furnace at 950 ° C in six minutes. This is a typical heat treatment for press-hardening in which the Al-Si coating layer is alloyed. After the respective anneals, the samples were cooled to room temperature. The obtained samples each had a non-fully alloyed Al-Si coating layer except for the sample heat-treated at 950 ° C.

Anschließend sind die zuvor geglüht und abgekühlten Proben in einer dem zweiten Erwärmungsschritt entsprechenden Glühbehandlung in einem Strahlungsofen auf eine Erwärmungstemperatur von 950 °C erwärmt worden, bei der das Stahlsubstrat Austenitgefüge besaß. Dabei wurden die Aufheizraten erfasst, d. h. es wurde überwacht, wie schnell die Proben auf die Zieltemperatur von 950 °C aufgeheizt worden sind.Subsequently, the previously annealed and cooled samples are in a second heating step corresponding annealing treatment in a radiant oven to a heating temperature of 950 ° C was heated, in which the steel substrate had austenite microstructure. The heating rates were recorded, ie it was monitored how quickly the samples were heated to the target temperature of 950 ° C.

In Diag. 1 ist die Temperatur T der jeweiligen Proben über die Glühzeit t eingetragen. Zusätzlich ist in Diag. 1 die für eine nicht in einem vorgeschalteten ersten Erwärmungsschritt geglühte Probe eingetragen (Kurve "- °C / - s").In Diag. 1, the temperature T of the respective samples is plotted over the annealing time t. In addition, in Diag. 1 the sample annealed for a not annealed in a first heating step upstream (curve "- ° C / - s").

Es zeigt sich, dass sich bei den untersuchten Proben optimale Aufheizraten ergeben, wenn die Proben im ersten Erwärmungsschritt im Haubenofen für 8 h bei 550 °C oder 600 °C geglüht worden sind. Ein genauso gutes Aufheizverhalten wurde für die im Durchlaufofen bei 950 °C für sechs Minuten geglühten Proben festgestellt.It can be seen that in the samples tested optimum heating rates result when the samples are annealed in the first heating step in the hood furnace for 8 h at 550 ° C or 600 ° C. An equally good heating behavior was observed for the samples annealed in the continuous furnace at 950 ° C for six minutes.

Das schlechtere Aufheizverhalten der zuvor bei 500 °C für 8 h geglühten Proben ist darin begründet, dass sich bei diesen Proben in der oberen, nicht legierten Schicht des Al-Si-Überzugs die Reflektion der Strahlung genauso verhält, wie bei herkömmlichen Al-Si-Überzügen im Anlieferungszustand ohne vorherige Wärmebehandlung.The worse heating behavior of the samples previously annealed at 500 ° C. for 8 h is due to the fact that with these samples in the upper, unalloyed layer of the Al-Si coating, the reflection of the radiation behaves in exactly the same way as with conventional Al-Si coatings. Covers as delivered without prior heat treatment.

Mit dem erfindungsgemäßen Prozess lassen sich die Zeiten, die für die Durchlegierung im Austenitisierungsofen vor der Warmumformung benötigt werden, deutlich verkürzen. So konnte gezeigt werden, dass gegenüber der konventionellen Vorgehensweise ein Zeitgewinn von mindestens 90 s erwartet werden kann. Mit diesem Zeitgewinn können die für die Erwärmung vor der Warmformgebung benötigten Öfen kleiner konzipiert werden. Bei der Wartung der Öfen mit konventioneller Größe erfolgt ein Abkühlen auf Raumtemperatur in etwa 10 Tagen, wohingegen bei der durch die Erfindung möglichen Reduzierung der Ofengröße mit einem Zeitgewinn von mindestens 2 bis 3 Tagen für die Abkühlung gerechnet werden kann.With the process according to the invention, the times required for the alloying in the austenitizing furnace before the hot working can be significantly reduced. It was thus shown that a time saving of at least 90 s is expected compared to the conventional procedure can be. With this time saving, the furnaces needed for heating before hot forming can be made smaller. In the maintenance of conventional size ovens cooling to room temperature in about 10 days, whereas in the possible reduction of the furnace size by the invention with a time saving of at least 2 to 3 days can be expected for the cooling.

Claims (13)

  1. Process for producing a component from a steel product coated with a protective Al-Si coating wherein, during the course of the process:
    - the steel product coated with the Al-Si coating undergoes a first heating stage in which the temperature and the duration of the heat treatment are set such that the Al-Si coating is only incompletely pre-alloyed with Fe from the steel product,
    - the steel product, in a second heating stage, is heated to a heating temperature, above the Ac1 temperature, at which the steel product has an at least partially austenitic structure, wherein the temperature and duration of the second heating stage are set such that the Al-Si coating is fully alloyed with Fe from the steel product during the course of the second heating stage,
    - the steel product heated to the heating temperature is shaped to form the component, and
    - the component obtained is cooled in a controlled manner, in order to obtain a martensitic structure.
  2. Process according to claim 1, characterised in that the steel product is cooled to room temperature, between the first and the second heating stage.
  3. Process according to claim 2, characterised in that the steel product is transported into air between the first and the second heating stage.
  4. Process according to one of the preceding claims, characterised in that the temperature of the first heating stage is at least 500°C and, at the same time, is at most the same as the AC1 temperature of the steel product.
  5. Process according to one of the preceding claims, characterised in that the temperature of the first heating stage is 550 - 723°C, in particular 550-700°C.
  6. Process according to one of the preceding claims, characterised in that the first heating stage is carried out in a bell-type annealing furnace.
  7. Process according to one of claims 1 to 5, characterised in that the first heating stage is carried out in a continuous furnace.
  8. Process according to one of the preceding claims, characterised in that the heating temperature to which the steel product is heated in the second heating stage corresponds to at least the Ac3 temperature.
  9. Process according to one of the preceding claims, characterised in that the second heating stage is carried out in a continuous furnace.
  10. Process according to claims 1 to 8, characterised in that the second heating stage is carried out in a chamber furnace.
  11. Process according to one of the preceding claims, characterised in that the steel product consists of quenched and tempered steel.
  12. Process according to one of the preceding claims, characterised in that the steel product is a flat steel product such as a steel sheet or a steel strip.
  13. Process according to one of claims 1 to 11, characterised in that the steel product is a preformed, semi-finished product.
EP09705444A 2008-01-30 2009-01-29 Method for producing a component from a steel product provided with an al-si coating and intermediate product of such a method Active EP2240622B1 (en)

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DE102008006771A DE102008006771B3 (en) 2008-01-30 2008-01-30 A method of manufacturing a component from a steel product provided with an Al-Si coating and an intermediate of such a method
PCT/EP2009/050980 WO2009095427A1 (en) 2008-01-30 2009-01-29 Method for producing a component from a steel product provided with an al-si coating and intermediate product of such a method

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CA2713381A1 (en) 2009-08-06
ATE520798T1 (en) 2011-09-15
DE102008006771B3 (en) 2009-09-10
ES2368820T3 (en) 2011-11-22
CA2713381C (en) 2016-03-29
US8349098B2 (en) 2013-01-08
KR20100108608A (en) 2010-10-07
WO2009095427A1 (en) 2009-08-06
CN101932747B (en) 2013-02-13
EP2240622A1 (en) 2010-10-20
PT2240622E (en) 2011-09-30
MX2010008390A (en) 2010-10-04
CN101932747A (en) 2010-12-29
PL2240622T3 (en) 2012-01-31
JP5666313B2 (en) 2015-02-12
US20110056594A1 (en) 2011-03-10
JP2011514440A (en) 2011-05-06

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