EP2513346A2 - Method for producing an easily deformable flat steel product, flat steel product, and method for producing a component from such a flat steel product - Google Patents

Method for producing an easily deformable flat steel product, flat steel product, and method for producing a component from such a flat steel product

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Publication number
EP2513346A2
EP2513346A2 EP10787425A EP10787425A EP2513346A2 EP 2513346 A2 EP2513346 A2 EP 2513346A2 EP 10787425 A EP10787425 A EP 10787425A EP 10787425 A EP10787425 A EP 10787425A EP 2513346 A2 EP2513346 A2 EP 2513346A2
Authority
EP
European Patent Office
Prior art keywords
steel product
flat steel
flat
annealing
product
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP10787425A
Other languages
German (de)
French (fr)
Other versions
EP2513346B1 (en
Inventor
Wilhelm Warnecke
Manfred Meurer
Jens Kondratiuk
Marc Blumenau
Martin Norden
Thiemo Wuttke
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ThyssenKrupp Steel Europe AG
Original Assignee
ThyssenKrupp Steel Europe AG
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Publication date
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Publication of EP2513346A2 publication Critical patent/EP2513346A2/en
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • 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
    • B21D31/00—Other methods for working sheet metal, metal tubes, metal profiles
    • 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
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C21D1/76—Adjusting the composition of the atmosphere
    • 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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0257—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment with diffusion of elements, e.g. decarburising, nitriding
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese

Definitions

  • the invention relates to a process for producing a readily deformable, a C content of 0.1 to 0.4 wt .-% having flat steel product, wherein the
  • the invention relates to a correspondingly produced flat steel product and method for
  • Corrosion protection coating provided steel sheet for the hot forming and a possibly subsequently or in combination with the hot working performed hardening are heated to a temperature which is above the melting temperature of the metal of the protective coating, there is the danger of so-called
  • JP 60-159120 A It is generally known from JP 60-159120 A that the bending properties of a steel sheet can be improved by a decarburization treatment which produces a near-surface, 20-100 ⁇ m thick surface layer with a reduced C content in relation to the core region of the steel sheet.
  • this measure is not associated with this prior art Nor does it concern higher or high strength steels having C-contents of at least 0.1% by weight.
  • decarburization is carried out according to the Boudouard equilibrium reactions according to the following
  • decarburization can improve certain properties of a steel product.
  • GB 1 189 464 proposes the "open-coil" method.
  • a hard-rolled, cold-rolled strip is wound loosely into a coil such that a free space exists between the individual winding layers of the coil. That at the subsequent
  • Annealing treatment in a hood furnace flowing through the free spaces annealing gas then sweeps over the entire
  • the steel strip can be provided with a hot dip coating to improve its corrosion resistance.
  • the steel sheet obtained in this way has a particularly good deformability. However, its strength values do not match those
  • Automotive bodies should be shaped.
  • the steel strip treated accordingly has an increased deformability compared to the base material, which reduces the risk of brittle fracture under high external load.
  • DE 102007061489 A1 has proposed a process in which a ductile boundary layer which is advantageous for the forming is produced on a steel sheet by carrying out a selective oxidation of the solidifying alloying elements. In the process, every decarburization is deliberately counteracted.
  • the object of the invention was to provide a method which makes it possible in an economical manner to produce a readily deformable, high-strength or very high-strength steel flat product.
  • Components are given from such a flat steel product.
  • the above-stated object has been achieved according to the invention in that, in the production of a flat steel product, the steps specified in claim 1 are completed.
  • the process according to the invention for producing a readily deformable flat steel product which has a C content of 0.1-0.4% by weight, in particular less than 0.4% by weight, is based on the idea of the relevant flat steel product in a continuous furnace one
  • the annealing treatment according to the invention is carried out under an annealing atmosphere, the 0.1 - 25 vol .-% H 2 , H 2 0 and the balance N 2 and
  • the dew point of the annealing atmosphere is in the range of -20 ° C and +60 ° C. At the same time is in the
  • the flat steel product is further inventively in the course of annealing to a 600 - 1100 ° C.
  • Wt .-% in particular up to 0.38 wt .-%, contains carbon, adjust by an annealing treatment, which leads to a Randentkohlung of the steel material. This edge decarburization causes a ductilization of the
  • the invention is thus based on the idea of a
  • Hot-forming steel flat products i.
  • Steel surface can run off for a subsequent application of a corrosion protection layer, but has a decoupled reaction mechanism.
  • the inventive method is characterized in particular by the fact that it can be carried out in a particularly economical manner using a continuous furnace. This makes it possible to use the method according to the invention in
  • Anticorrosive coating are hot-dip coated.
  • the invention makes use of the knowledge that the risk of liquid metal embrittlement can be minimized by the fact that it can be controlled by a specific method
  • Flat steel product of the susceptible to liquid metal embrittlement temperature range can be shifted so that it does not coincide with the typical for the hot forming temperature interval.
  • the annealing treatment in this case may include edge decarburization, surface conditioning and recrystallization of the base material and then the
  • Procedure can be performed in-line following the annealing treatment.
  • produced flat steel product can on the steel substrate known coating systems which are based on Zn, Al, Zn-Al, Zn-Mg, Zn-Ni, Al-Mg, Al-Si or Zn-Al-Mg.
  • Hot dip finishing can be a steel strip which has been provided in accordance with the invention in a continuous annealing with a ductile decarburized boundary layer,
  • a metallic, a metallic ⁇ inorganic or a metallic-organic coating by electrolytically, for example, with a Zn, a ZnNi or a ZnFe coating, PVD or CVD deposition or by means of another metal-organic or metal inorganic coating method is coated.
  • the invention thus provides that the flat steel product is hot-dip coated in a work step carried out continuously following the annealing treatment. It can the
  • oxidation of the surface of the flat steel product can be carried out before the fire coating.
  • the annealing treatment according to the invention can be carried out in a conventional manner
  • a method according to the invention is produced
  • Core layer of the flat steel product has increased ductility.
  • the thickness of the ductile layer can be determined in a customary manner in accordance with DIN EN ISO 3887
  • Total carbonation depth The distance from the surface to the point where the content of carbon corresponds to that of the unaffected core region. In this way, in the near-surface region, a hardness in the decarburized surface layer region which is not higher than 75% of the hardness of the core region, i.
  • Flat steel product is characterized at least near its free surface typically by a ferritic microstructure. This is true for a multiphase
  • decarburized edge layer sets a ferritic near-surface microstructure, just as for a single-phase, typically ferritic steel, in which the decarburization invention results in a ductilization of the near-surface ferrite.
  • a flat steel product produced according to the invention is suitable in the same way for cold and hot forming, wherein its particular advantages in particular in the hot forming of provided with a metallic protective layer, in particular a galvanized steel sheets or bands show.
  • Cold forming steels typically have a tensile strength of 500-1500 MPa.
  • Hot working can be inventively steels
  • the flat steel product according to the invention may first be heated to a heating temperature above its Acl temperature and then hot formed into the component.
  • the steel flat product according to the invention can also be heated without problems to a heating temperature which is at least equal to the Ac3 temperature of the flat steel product. Even with such a high
  • Heating temperature is minimized in a steel flat product according to the invention, the risk of embrittlement even if the flat steel product is provided with a metallic coating whose
  • Melting temperature is less than or equal to
  • Heating temperature is.
  • the ductility of the surface layer achieved by the surface layer decarburization according to the invention prevents cracking and thus ensures that no molten metal of the coating in the
  • Flat steel products are particularly advantageous for hot forming. This is achieved in that, according to the invention, a decarburization is induced by a targeted annealing gas-metal reaction in a continuous furnace, through which a ductile,
  • the invention is based on
  • Figure 1 is a vertical section of a surface according to the invention decarburized steel sample.
  • FIG. 2 shows a vertical section of a conventionally annealed comparative sample
  • hard-cold-rolled strip samples are in each case a multi-phase steel "MP” and a steel used commonly for hot forming “WU” has been produced.
  • the compositions of steels MP and WU are given in Table 1.
  • Hot-dip galvanizing is performed.
  • FIG. 1 shows the micrograph of the sample produced from the steel MP and annealed according to the invention. It can be clearly seen that, as a consequence of the procedure according to the invention, a decarburised, near-surface microstructure region (boundary layer "R")
  • Discharge Optical Emission Spectrometre is a standard method for the rapid detection of a concentration profile of coatings. It is
  • Carbon distribution of the conventionally treated sample and the solid line represents the carbon distribution of the invention treated sample.
  • Fig. 3 clearly shows that the sample treated according to the invention has a pronounced decarburized edge layer R whose thickness is about 40 ⁇ .
  • a surface layer is not present in the conventionally treated sample.
  • Edge region R has a microhardness of 163 HV and the non-decarburized core region K has a hardness of 255 HV.
  • The% ratio Hv R / Hv K of hardness Hv R of the decarburized edge region R to hardness Hv K of the core region K was thus 64%, which was well below that according to the invention for this ratio predetermined value of 75%.
  • the sample is symbolized by the black and the bending angle Bw of the conventionally generated sample by the white bar.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
  • Coating With Molten Metal (AREA)

Abstract

The invention relates to a method by means of which an easily deformable flat steel product having a carbon content of 0.1-0.4 wt % can be produced in a cost-effective manner. To this end, according to the invention, an annealing treatment is carried out under an annealing atmosphere comprising 0.1-25 vol % of H2, H2O, with the remainder being N2 and technically unavoidable impurities, and having a dew point of between -20°C and +60°C, wherein the ratio of H2O/H2 of the annealing atmosphere is no greater than 0.957. The flat steel product is thereby heated to a holding temperature of 600-1100°C in the course of the annealing treatment, at which it is held for a holding time of 10-360 s, so that the flat steel product obtained after the annealing treatment comprises a 10-200 µm thick ductile edge layer (R) adjacent to the free surface thereof, having a ductility that is greater than the interior core layer (K) of the flat steel product covered by the edge layer. The invention further relates to a correspondingly produced flat steel product particularly suitable for hot or cold forming, and to a method for producing components made of such a flat steel product.

Description

VERFAHREN ZUM HERSTELLEN EINES GUT UMFORMBAREN STAHLFLACHPRODUKTS, STAHLFLACHPRODUKT UND VERFAHREN  METHOD FOR PRODUCING A WELL FORMABLE STEEL FLAT PRODUCT, STEEL FLAT PRODUCT AND METHOD
HERSTELLUNG EINES BAUTEILS AUS EINEM SOLCHEN STAHLFLACHPRODUKT  PRODUCTION OF A COMPONENT FROM SUCH A STEEL FLAT PRODUCT
Die Erfindung betrifft ein Verfahren zum Herstellen eines gut umformbaren, einen C-Gehalt von 0,1 - 0,4 Gew.-% aufweisenden Stahlflachprodukts, bei dem das The invention relates to a process for producing a readily deformable, a C content of 0.1 to 0.4 wt .-% having flat steel product, wherein the
Stahlflachprodukt in einem Durchlaufofen einer Flat steel product in a continuous furnace
Glühbehandlung unterzogen wird. Annealing is subjected.
Darüber hinaus betrifft die Erfindung ein entsprechend hergestelltes Stahlflachprodukt sowie Verfahren zum Moreover, the invention relates to a correspondingly produced flat steel product and method for
Herstellen von Bauteilen aus einem solchen Manufacture of components from such
Stahlflachprodukt . Flat steel product.
Stahlflachprodukte der hier in Rede stehenden Art werden insbesondere zur Herstellung von Karosserie- und Flat steel products of the type in question are used in particular for the production of bodywork and
Fahrwerksteilen für Automobile benötigt. Dabei werden an die Stahlflachprodukte hinsichtlich ihrer Chassis parts needed for automobiles. Here are the flat steel products in terms of their
Umformeigenschaften höchste Anforderungen gestellt. Dies betrifft sowohl die Kalt- als auch die Warmumformbarkeit . Forming properties highest requirements. This applies to both cold and hot workability.
Eine besondere Schwierigkeit stellt die Warmumformung von verzinkten Stahlflachprodukten zu hoch- bzw. höchstfesten Stahlbauteilen dar. Bei solchen Stahlbauteilen A special difficulty is the hot forming of galvanized flat steel products to high- or high-strength steel components. In such steel components
gewährleistet die in der Regel auf Zink oder einer Zinklegierung basierende Schutzbeschichtung einen usually ensures zinc or one Zinc alloy based protective coating one
ausreichenden kathodischen Korrosionsschutz. adequate cathodic corrosion protection.
Muss jedoch ein mit einer metallischen However, one must have a metallic one
Korrosionsschutzbeschichtung versehenes Stahlblech für die Warmumformung und ein gegebenenfalls anschließend oder in Kombination mit der Warmumformung durchgeführtes Härten auf eine Temperatur erwärmt werden, die oberhalb der Schmelztemperatur des Metalls der Schutzbeschichtung liegt, so besteht die Gefahr der so genannten  Corrosion protection coating provided steel sheet for the hot forming and a possibly subsequently or in combination with the hot working performed hardening are heated to a temperature which is above the melting temperature of the metal of the protective coating, there is the danger of so-called
"Flüssigmetallversprödung" . Zu dieser Versprödung des Stahls kommt es, wenn schmelzflüssiges Metall des "Liquid metal embrittlement". This embrittlement of the steel occurs when molten metal of the
Überzugs in die sich bei der Verformung an der Oberfläche des jeweiligen Stahlflachproduktes bildenden Kerben eindringt. Das in das Stahlsubstrat gelangende flüssige Metall lagert sich dort an den Korngrenzen ab und reduziert so die maximal aufnehmbaren Zug- und Coating in which penetrates during the deformation of the surface of the respective flat steel product notches. The liquid metal entering the steel substrate deposits there at the grain boundaries and thus reduces the maximum absorbable tensile and
Druckspannungen . Compressive stresses.
Besonders kritisch erweist sich die Gefahr der Particularly critical is the danger of
Flüssigmetallversprödung bei höher- und hochfesten Liquid metal embrittlement at higher and higher strength
Stählen, die nur eine begrenzte Duktilität aufweisen und die infolgedessen bei ihrer Umformung zur Bildung von oberflächennahen Rissen neigen. Steels which have only limited ductility and which consequently tend to form near-surface cracks during their forming.
Aus der JP 60-159120 A ist es allgemein bekannt, dass sich die Biegeeigenschaften eines Stahlblechs durch eine Ent kohlungsbehandlung verbessern lassen, durch die eine oberflächennahe, 20 - 100 pm dicke Randschicht mit einem gegenüber dem Kernbereich des Stahlblechs vermindertem C-Gehalt erzeugt wird. Jedoch steht diese Maßnahme bei diesem Stand der Technik weder im Zusammenhang mit Stahlblechen, die mit einer metallischen Schutzschicht überzogen sind, noch betrifft sie höher- oder hochfeste Stähle mit C-Gehalten von mindestens 0,1 Gew.-%. It is generally known from JP 60-159120 A that the bending properties of a steel sheet can be improved by a decarburization treatment which produces a near-surface, 20-100 μm thick surface layer with a reduced C content in relation to the core region of the steel sheet. However, this measure is not associated with this prior art Nor does it concern higher or high strength steels having C-contents of at least 0.1% by weight.
Die Entkohlungsneigung einer kohlenstoffhaltigen The decarburization tendency of a carbonaceous
Stahllegierung ergibt sich aus dem Oxidationsverhalten des gelösten Kohlenstoffs. Auf Grund seiner großen Steel alloy results from the oxidation behavior of the dissolved carbon. Because of his big
Beweglichkeit neigt der im Gitter gelöste Kohlenstoff bei einer Wärmebehandlung zur Effusion. Die je nach Agility, the carbon dissolved in the lattice tends to effusion during a heat treatment. The depending on
C-Potenzial der Gasphase, unter der die Wärmebehandlung stattfindet, mit oder ohne gleichzeitige Verzunderung auftretende Entkohlung stellt deshalb eines der ältesten Probleme bei der Herstellung und Verarbeitung von Stahl dar . C potential of the gas phase, under which the heat treatment takes place, with or without simultaneous scaling occurring decarburization is therefore one of the oldest problems in the production and processing of steel.
Prinzipiell erfolgt eine Entkohlung gemäß den Boudouard- Gleichgewichtsreaktionen gemäß den folgenden In principle, decarburization is carried out according to the Boudouard equilibrium reactions according to the following
Reaktionsprozessen: Reaction processes:
[C] + 1/2 02 <-> CO [C] + 1/2 0 2 <-> CO
[C] + 02 <-> C02 [C] + 0 2 <-> C0 2
[C] + co2 <-> co2 [C] + co 2 <-> co 2
[C] + H2 <-> CH mit [C] = gelöster Kohlenstoff [C] + H 2 <-> CH with [C] = dissolved carbon
In großtechnischen Glühanlagen mit einer typischen In large-scale annealing plants with a typical
Schutzgasatmosphäre, welche sowohl Wasserstoff, Inert gas atmosphere, which is both hydrogen,
Stickstoff als auch Wasserdampf enthält, bildet sich folgende Gleichgewichtsreaktion aus: Contains nitrogen as well as water vapor, the following equilibrium reaction forms:
H2 + 1/2 02 <-> H20 Wasserhaltige Gasatmosphären erweisen sich dabei H2 + 1/2 0 2 <-> H 2 0 Hydrous gas atmospheres turn out to be
besonders reaktiv gegenüber Kohlenstoff. Deshalb tritt zu den erwähnten Ent kohlungsreaktionen noch eine weitere und für die Praxis besonders bedeutsame heterogene especially reactive to carbon. Therefore, there is another heterogeneous to the abovementioned Ent coalation reactions and another particularly significant for practice
Gleichgewichtsreaktion hinzu: Equilibrium reaction added:
[C] + H20 <-> CO + H2 [C] + H 2 0 <-> CO + H 2
Gezielt angewandt, können durch eine Entkohlung bestimmte Eigenschaften eines Stahlproduktes verbessert werden. When used in a targeted way, decarburization can improve certain properties of a steel product.
Um diese Erkenntnis in der Praxis effektiv nutzen zu können, ist in der GB 1 189 464 das "Open-Coil"-Verfahren vorgeschlagen. Bei diesem Verfahren wird ein walzhartes, kaltgewalztes Band so lose zu einem Coil gewickelt, dass zwischen den einzelnen Wickellagen des Coils jeweils ein Freiraum vorhanden ist. Das bei der anschließenden In order to be able to use this knowledge effectively in practice, GB 1 189 464 proposes the "open-coil" method. In this process, a hard-rolled, cold-rolled strip is wound loosely into a coil such that a free space exists between the individual winding layers of the coil. That at the subsequent
Glühbehandlung in einem Haubenofen durch die Freiräume strömende Glühgas überstreicht dann die gesamte Annealing treatment in a hood furnace flowing through the free spaces annealing gas then sweeps over the entire
Stahloberfläche gleichmäßig, so dass ein gleichmäßiges Entkohlungsergebnis über die gesamte Länge des Steel surface evenly, so that a uniform decarburization over the entire length of the
behandelten Stahlbands erzielt wird. Die so durchgeführte Glühbehandlung benötigt jedoch mehrere Stunden. treated steel strip is achieved. However, the annealing treatment thus carried out takes several hours.
Ein wirtschaftlicher durchführbares Verfahren zum An economical feasible method for
Entkohlungsglühen von Stahlband in einem Durchlaufofen unter einer reduzierenden Glühatmosphäre ist in der DE-OS 2 105 218 beschrieben. Gemäß diesem bekannten Verfahren wird das jeweilige Stahlband bei einer Decarburization annealing of steel strip in a continuous furnace under a reducing annealing atmosphere is described in DE-OS 2,105,218. According to this known method, the respective steel strip at a
Glühtemperatur von weniger als 780°C über eine Annealing temperature of less than 780 ° C over a
ausreichend lange Glühdauer so lange geglüht, bis der Kohlenstoffgehalt im Stahlband beim Austritt aus dem Durchlaufofen weniger als 0,01% beträgt. Anschließend kann das Stahlband mit einer Schmelztauchbeschichtung versehen werden, um seine Korrosionsbeständigkeit zu verbessern. Das auf diese Weise erhaltene Stahlblech weist eine besonders gute Verformbarkeit auf. Jedoch entsprechen seine Festigkeitswerte nicht den sufficiently long annealing time so long annealed until the carbon content in the steel strip at the exit from the Continuous furnace is less than 0.01%. Subsequently, the steel strip can be provided with a hot dip coating to improve its corrosion resistance. The steel sheet obtained in this way has a particularly good deformability. However, its strength values do not match those
Anforderungen, die heute regelmäßig an Stahlflachprodukte gestellt werden, aus denen Bauteile für Requirements that are regularly made today on flat steel products that make up components for
Automobilkarosserien geformt werden sollen. Automotive bodies should be shaped.
Ebenfalls auf das "Open Coil" -Verfahren ist bei einem aus der WO 2009/024472 AI bekannten Vorschlag zurückgegriffen worden, gemäß dem für ein aus einem Werkzeugstahl Also on the "open coil" method has been used in a known from WO 2009/024472 AI proposal, according to the one for a tool steel
bestehendes Stahlband, das insbesondere für die existing steel strip, especially for the
Herstellung von Schneidwerkzeugen und desgleichen Production of cutting tools and the like
bestimmt ist und einen C-Gehalt von mindestens 0,4 Gew.-% aufweist, eine Randschichtentkohlung vorgeschlagen worden ist, um eine hohe Härte mit einer guten Verformbarkeit zu kombinieren. Im Bereich der entkohlten Randschicht weist das entsprechend behandelte Stahlband eine gegenüber dem Grundwerkstoff erhöhte Verformbarkeit auf, wodurch die Gefahr eines Sprödbruchs unter hoher äußerer Last verringert ist. is determined and has a C content of at least 0.4 wt .-%, a Randschichtentkohlung has been proposed to combine a high hardness with a good ductility. In the area of the decarburized boundary layer, the steel strip treated accordingly has an increased deformability compared to the base material, which reduces the risk of brittle fracture under high external load.
Im Gegensatz zu den in der WO 2009/024472 AI betrachteten Anwendungen ist der Fachmann im Allgemeinen bemüht, bei hoch- und höchstfesten Stählen, die für die Herstellung von hochfesten Bauteilen bestimmt sind, die glühbedingte Entkohlung bzw. Randent kohlung möglichst zu vermeiden. Nach allgemeiner Auffassung beeinflusst die Entkohlung die für diese Anwendungen wichtigen mechanischen In contrast to the applications considered in WO 2009/024472 AI, the skilled person generally endeavors to avoid as far as possible incandescent decarburization or carbonization in the case of high-strength and ultra-high-strength steels intended for the production of high-strength components. Decarburization is believed to affect the mechanical properties of these applications
Werkstoffeigenschaften negativ. Dieser Vorstellung folgend, ist in der DE 102007061489 AI ein Verfahren vorgeschlagen worden, bei dem an einem Stahlblech eine für die Umformung vorteilhafte duktile Randschicht erzeugt wird, indem eine selektive Oxidation der verfestigenden Legierungselemente durchgeführt wird. Dabei wird gezielt jeder Entkohlung entgegengewirkt. Material properties negative. Following this idea, DE 102007061489 A1 has proposed a process in which a ductile boundary layer which is advantageous for the forming is produced on a steel sheet by carrying out a selective oxidation of the solidifying alloying elements. In the process, every decarburization is deliberately counteracted.
Vor dem Hintergrund des voranstehend erläuterten Standes der Technik bestand die Aufgabe der Erfindung darin, ein Verfahren anzugeben, das es auf wirtschaftliche Weise erlaubt, ein gut umformbares, hoch- bzw. höchstfestes Stahlflachprodukt zu erzeugen. Darüber hinaus sollte ein für die Warm- oder Kaltumformung besonders geeignetes Stahlflachprodukt und Verfahren zur Herstellung von Against the background of the prior art explained above, the object of the invention was to provide a method which makes it possible in an economical manner to produce a readily deformable, high-strength or very high-strength steel flat product. In addition, a particularly suitable for hot or cold forming steel flat product and method for the production of
Bauteilen aus einem solchen Stahlflachprodukt angegeben werde . Components are given from such a flat steel product.
In Bezug auf das Herstellverfahren ist die voranstehend angegebene Aufgabe erfindungsgemäß dadurch gelöst worden, dass bei der Herstellung eines Stahlflachproduktes die in Anspruch 1 angegebenen Arbeitsschritte absolviert werden. With regard to the manufacturing method, the above-stated object has been achieved according to the invention in that, in the production of a flat steel product, the steps specified in claim 1 are completed.
In Bezug auf das Produkt ist die oben angegebene Aufgabe erfindungsgemäß durch das in Anspruch 9 angegebene With regard to the product, the above-mentioned object according to the invention by the specified in claim 9
Stahlflachprodukt gelöst worden. Flat steel product has been solved.
In Bezug auf die Verfahren zur Herstellung eines Bauteils ist die oben genannte Aufgabe schließlich erfindungsgemäß durch die in den Ansprüchen 13 und 15 angegebenen With regard to the method for producing a component, the above-mentioned object is finally achieved according to the invention by those specified in claims 13 and 15
Verfahren gelöst worden. Vorteilhafte Ausgestaltungen der Erfindung sind in den von den jeweiligen unabhängigen Ansprüchen abhängigen Ansprüchen angegeben und werden nachfolgend erläutert. Procedure has been solved. Advantageous embodiments of the invention are specified in the claims dependent on the respective independent claims and are explained below.
Das erfindungsgemäße Verfahren zum Herstellen eines gut umformbaren Stahlflachprodukts, das einen C-Gehalt von 0,1 - 0,4 Gew.-%, insbesondere weniger als 0,4 Gew.-%, aufweist, geht aus von dem Gedanken, das betreffende Stahlflachprodukt in einem Durchlaufofen einer The process according to the invention for producing a readily deformable flat steel product which has a C content of 0.1-0.4% by weight, in particular less than 0.4% by weight, is based on the idea of the relevant flat steel product in a continuous furnace one
Glühbehandlung zu unterziehen, bei der es zu einer To undergo annealing treatment, which leads to a
Randschichtent kohlung kommt. Dazu wird die Glühbehandlung erfindungsgemäß unter einer Glühatmosphäre durchgeführt, die 0,1 - 25 Vol.-% H2, H20 und als Rest N2 sowie Randschichtent kohlung comes. For this purpose, the annealing treatment according to the invention is carried out under an annealing atmosphere, the 0.1 - 25 vol .-% H 2 , H 2 0 and the balance N 2 and
technisch bedingt unvermeidbare Verunreinigungen enthält. Der Taupunkt der Glühatmosphäre liegt dabei im Bereich von -20 °C und +60 °C. Gleichzeitig ist in der contains technically unavoidable impurities. The dew point of the annealing atmosphere is in the range of -20 ° C and +60 ° C. At the same time is in the
Glühatmosphäre das Verhältnis H2O/H2 höchstens gleich 0,957 einzustellen, um eine optimal entkohlende Wirkung zu erreichen. Annealing atmosphere to set the ratio H 2 O / H 2 at most equal to 0.957 to achieve an optimal decarburizing effect.
Das Stahlflachprodukt wird des Weiteren erfindungsgemäß im Zuge der Glühbehandlung auf eine 600 - 1100 °C The flat steel product is further inventively in the course of annealing to a 600 - 1100 ° C.
betragende Haltetemperatur erwärmt, bei der es für eine 10 - 360 s dauernde Haltezeit unter der erfindungsgemäß zusammengesetzten Atmosphäre gehalten wird. heated holding temperature at which it is held for a 10 - 360 s lasting time under the inventively assembled atmosphere.
Im Ergebnis weist das nach der erfindungsgemäßen As a result, according to the invention
Glühbehandlung erhaltene Stahlflachprodukt eine Annealing treatment obtained flat steel product one
10 - 200 μιη dicke, an seine freie Oberfläche angrenzende duktile Randschicht mit einer Duktilität auf, die größer ist als die Duktilität der innenliegenden, von der 10 - 200 μι η thick, adjacent to its free surface ductile surface layer with a ductility which is greater than the ductility of the inner, of the
Randschicht bedeckten Kernschicht des Stahlflachprodukts. Entgegen der im Stand der Technik bestehenden Überzeugung gelingt es mit der Erfindung, die gewünschte Surface layer covered core layer of the flat steel product. Contrary to the conviction existing in the prior art, it is possible with the invention, the desired
Eigenschaftskombination aus hoher Festigkeit und guter Verformbarkeit bei einem Stahlblech, das 0,1 - 0,4 Property combination of high strength and good ductility in a steel sheet, the 0.1 - 0.4
Gew.-%, insbesondere bis zu 0,38 Gew.-%, Kohlenstoff enthält, durch eine Glühbehandlung einzustellen, welche zu einer Randentkohlung des Stahlwerkstoffs führt. Diese Randentkohlung bewirkt eine Duktilisierung des Wt .-%, in particular up to 0.38 wt .-%, contains carbon, adjust by an annealing treatment, which leads to a Randentkohlung of the steel material. This edge decarburization causes a ductilization of the
oberflächennahen Gefügebereichs, welche dem andernfalls umformbedingten Rissversagen des Werkstoffs near-surface microstructure, which otherwise the deformation-induced cracking failure of the material
entgegenwirkt . counteracts.
Die Erfindung basiert somit auf dem Gedanken, eine The invention is thus based on the idea of a
Randentkohlung von walzharten, für die Kalt- oder Border decarburization of hardwrought, for the cold or
Warmumformung vorgesehenen Stahlflachprodukten, d.h. Hot-forming steel flat products, i.
Stahlbändern oder -blechen, so durchzuführen, dass das nach der Glühbehandlung erhaltene Flachprodukt einen duktilen, typischerweise ferritischen, oberflächennahen Randbereich bestimmter Dicke auf den ersten Kornlagen aufweist, welcher die Umformeigenschaften des Steel strip or sheet to be carried out so that the product obtained after the annealing treatment has a ductile, typically ferritic, near-surface edge region of certain thickness on the first grain layers, which the forming properties of
Stahlprodukts sowohl für die Kalt- als auch für die Steel product for both the cold and the
Warmumformung verbessert. Insbesondere ist die Gefahr einer Riss- oder Kerbbildung an der Oberfläche des Hot forming improved. In particular, the risk of cracking or serration on the surface of the
Stahlprodukts bei dessen Umformung minimiert. Minimized steel product during its transformation.
Für das erfindungsgemäße Verfahren wesentlich ist dabei, dass die Randentkohlung des oberflächennahen Gefüges zwar zeitgleich zu einer Glühkonditionierung der For the process according to the invention, it is essential that the surface decarburization of the near-surface microstructure at the same time as the annealing conditioning of the
Stahloberfläche für einen nachfolgenden Auftrag einer Korrosionsschutzschicht ablaufen kann, jedoch einen entkoppelten Reaktionsmechanismus besitzt. 201 Steel surface can run off for a subsequent application of a corrosion protection layer, but has a decoupled reaction mechanism. 201
So erfolgt die Randentkohlung des oberflächennahen Thus, the edge decarburization of the near-surface occurs
Gefügebereichs nach folgendem Zusammenhang: Microstructure according to the following context:
[C] + H20 <-> CO + H2 mit fC] = gelöster Kohlenstoff, wogegen die Oxidations-/Reduktionsreaktion der Oberfläche wie folgt abläuft: x[Me] + yH20 <-> [MexOy] +yH2 mit [Me] = jeweiliges Metall [C] + H 2 0 <-> CO + H 2 with fC] = dissolved carbon, whereas the oxidation / reduction reaction of the surface proceeds as follows: x [Me] + yH 2 0 <-> [Me x O y ] + yH 2 with [Me] = respective metal
x,y = stöchiometrische Koeffizienten.  x, y = stoichiometric coefficients.
Überraschenderweise gelingt es bei Anwendung der Surprisingly, when using the
erfindungsgemäß vorgegebenen Glühbedingungen, die According to the invention predetermined annealing conditions, the
gewünschte Entkohlungstiefe auch bei sehr kurzen desired decarburization depth even with very short
Konditionierungszeiten zu erzielen. So zeichnet sich das erfindungsgemäße Verfahren insbesondere dadurch aus, dass es auf besonders wirtschaftliche Weise unter Verwendung eines Durchlaufofens durchgeführt werden kann. Dies ermöglicht es, das erfindungsgemäße Verfahren in To achieve conditioning times. Thus, the inventive method is characterized in particular by the fact that it can be carried out in a particularly economical manner using a continuous furnace. This makes it possible to use the method according to the invention in
kontinuierlich ablaufende Herstellungsprozesse continuous production processes
einzubinden, die hohe Bandgeschwindigkeiten voraussetzen, wie es beispielsweise in Feuerbeschichtungsanlagen der Fall ist, in denen im kontinuierlichen Durchlauf Incorporate, which require high belt speeds, as is the case for example in fire-coating plants, in which in continuous flow
Stahlbänder wärmebehandelt und mit einem Steel strips heat treated and with a
Korrosionsschutzüberzug schmelztauchbeschichtet werden. Anticorrosive coating are hot-dip coated.
Dementsprechend sieht eine besonders vorteilhafte Accordingly, a particularly advantageous looks
Ausgestaltung der Erfindung vor, dass das Embodiment of the invention that the
Stahlflachprodukt nach der Glühbehandlung mit einer metallischen Schutzschicht beschichtet wird. Die Flat steel product after annealing with a metallic protective layer is coated. The
Erfindung macht sich insbesondere bei dieser Variante des erfindungsgemäßen Verfahrens die Erkenntnis zu Nutze, dass sich die Gefahr einer Flüssigmetallversprödung dadurch minimieren lässt, dass durch eine gezielte In particular, in this variant of the method according to the invention, the invention makes use of the knowledge that the risk of liquid metal embrittlement can be minimized by the fact that it can be controlled by a specific method
Modifikation des oberflächennahen Bereiches des Modification of the near - surface area of the
Stahlflachproduktes der für die Flüssigmetallversprödung anfällige Temperaturbereich so verschoben werden kann, dass dieser sich nicht mit dem für die Warmumformung typischen Temperaturintervall deckt. Flat steel product of the susceptible to liquid metal embrittlement temperature range can be shifted so that it does not coincide with the typical for the hot forming temperature interval.
Im Fall, dass das erfindungsgemäße Herstellverfahren einer nachfolgenden Schmelztauchbeschichtung vorgelagert ist, erfolgt die erfindungsgemäß durchgeführte In the event that the production process according to the invention is preceded by a subsequent hot-dip coating, the process according to the invention is carried out
Glühbehandlung zeitgleich zur Oberflächenkonditionierung für die nachgeschaltete Oberflächenveredelung durch Kontrolle der oberflächennahen Kohlenstoffeffusion über eine heterogene Glühgas-Metall-Reaktion. Annealing at the same time as surface conditioning for downstream surface finishing by controlling the near-surface carbon effusion via a heterogeneous annealing gas-metal reaction.
Dabei ist es besonders vorteilhaft, das erfindungsgemäße Verfahren in einer Feuerbeschichtungsanlage anzuwenden, da die Glühbehandlung in diesem Fall die Randentkohlung, Oberflächenkonditionierung und Rekristallisation des Grundwerkstoffs umfassen kann und anschließend die It is particularly advantageous to apply the method according to the invention in a fire-coating plant, since the annealing treatment in this case may include edge decarburization, surface conditioning and recrystallization of the base material and then the
Schmelztauchbeschichtung in einem kontinuierlichen Hot dip coating in a continuous
Verfahrensablauf in-line auf die Glühbehandlung folgend durchgeführt werden kann. Procedure can be performed in-line following the annealing treatment.
Im Zuge der bevorzugt durch Schmelztauchbeschichten durchgeführten Oberflächenveredelung eines In the course of the surface refinement, preferably carried out by hot-dip coating, of a
erfindungsgemäß erzeugten Stahlflachproduktes können auf dem Stahlsubstrat an sich bekannte Überzugssysteme aufgebracht werden, die auf Zn, AI, Zn-Al, Zn-Mg, Zn-Ni, AI-Mg, Al-Si oder Zn-Al-Mg basieren. According to the invention produced flat steel product can on the steel substrate known coating systems which are based on Zn, Al, Zn-Al, Zn-Mg, Zn-Ni, Al-Mg, Al-Si or Zn-Al-Mg.
Alternativ oder ergänzend zur in-line erfolgenden Alternatively or in addition to in-line
Schmelztauchveredelung kann ein Stahlband, welches in erfindungsgemäßer Weise in einer Durchlaufglühe mit einer duktilen entkohlten Randschicht versehen wurde, Hot dip finishing can be a steel strip which has been provided in accordance with the invention in a continuous annealing with a ductile decarburized boundary layer,
nachträglich einen metallischen, einen metallisch¬ anorganischen oder einen metallisch-organischen Überzug erhalten, indem es elektrolytisch z.B. mit einem Zn-, einem ZnNi- oder einem ZnFe-Überzug, per PVD- oder CVD- Abscheidung oder mittels eines anderen metall-organischen oder metall-anorganischen Überzugsverfahrens beschichtet wird . subsequently obtained a metallic, a metallic ¬ inorganic or a metallic-organic coating by electrolytically, for example, with a Zn, a ZnNi or a ZnFe coating, PVD or CVD deposition or by means of another metal-organic or metal inorganic coating method is coated.
Gemäß einer für die Praxis besonders wichtigen According to a particularly important for the practice
Verfahrensvariante sieht die Erfindung somit vor, dass das Stahlflachprodukt in einem kontinuierlich auf die Glühbehandlung folgend durchgeführten Arbeitsschritt schmelztauchbeschichtet wird. Dabei kann die Process variant, the invention thus provides that the flat steel product is hot-dip coated in a work step carried out continuously following the annealing treatment. It can the
Schmelztauchbeschichtung in an sich bekannter Weise als Feuerbeschichtung, insbesondere Feuerverzinkung, Hot dip coating in a conventional manner as a fire coating, in particular hot dip galvanizing,
durchgeführt werden. Um dabei eine optimale Haftung der Beschichtung auf dem Stahlsubstrat zu sichern, kann vor der Feuerbeschichtung eine Oxidation der Oberfläche des Stahlflachprodukts durchgeführt werden. be performed. In order to ensure optimal adhesion of the coating on the steel substrate, oxidation of the surface of the flat steel product can be carried out before the fire coating.
Um die mechanischen Eigenschaften weiter zu optimieren, kann sich an die erfindungsgemäße Glühbehandlung eine in konventioneller Weise durchgeführte In order to further optimize the mechanical properties, the annealing treatment according to the invention can be carried out in a conventional manner
Überalterungsbehandlung anschließen . Dem voranstehend Erläutertem entsprechend weist ein Connect overaging treatment. The above explained accordingly
Stahlflachprodukt, das durch Anwendung eines Flat steel product produced by using a
erfindungsgemäßen Verfahrens hergestellt ist, einen A method according to the invention is produced
C-Gehalt von 0,1 - 0,4 Gew.-% und eine 10 - 200 μιτι dicke duktile Randschicht auf, die eine gegenüber der C content of 0.1-0.4 wt .-% and a 10 - 200 μιτι thick ductile edge layer, which is one compared to
Kernschicht des Stahlflachprodukts erhöhte Duktilität besitzt . Core layer of the flat steel product has increased ductility.
Die Dicke der duktilen Schicht lässt sich in üblicher Weise gemäß der in der DIN EN ISO 3887 festgelegten The thickness of the ductile layer can be determined in a customary manner in accordance with DIN EN ISO 3887
Vorgehensweise bestimmen. Demnach ist die Determine the procedure. Accordingly, the
Gesamtent kohlungstiefe der Abstand von der Oberfläche bis zu dem Punkt, an dem der Gehalt an Kohlenstoff dem des unbeeinflussten Kernbereichs entspricht. Auf diese Weise stellt sich im oberflächennahen Bereich eine Härte im entkohlten Randschichtbereich ein, die nicht höher ist als 75 % der Härte des Kernbereichs, d.h.  Total carbonation depth The distance from the surface to the point where the content of carbon corresponds to that of the unaffected core region. In this way, in the near-surface region, a hardness in the decarburized surface layer region which is not higher than 75% of the hardness of the core region, i.
H (entkohlt ) /H (Kernbereich) = 3/4. H (decarburized) / H (core area) = 3/4.
Die duktile Randschicht eines erfindungsgemäßen The ductile surface layer of an inventive
Stahlflachproduktes zeichnet sich mindestens nahe seiner freien Oberfläche typischerweise durch ein ferritisches Gefüge aus. Dies gilt für einen mehrphasigen Flat steel product is characterized at least near its free surface typically by a ferritic microstructure. This is true for a multiphase
Grundwerkstoff, bei dem sich im Bereich der Base material, which is used in the field of
erfindungsgemäß entkohlten Randschicht ein ferritisches oberflächennahes Gefüge einstellt, genauso wie für einen einphasigen, typischerweise ferritischen Stahl, bei dem die erfindungsgemäße Entkohlung in einer Duktilisierung des oberflächennahen Ferrits resultiert. decarburized edge layer according to the invention sets a ferritic near-surface microstructure, just as for a single-phase, typically ferritic steel, in which the decarburization invention results in a ductilization of the near-surface ferrite.
Ein erfindungsgemäß erzeugtes Stahlflachprodukt eignet sich in gleicher Weise zur Kalt- und Warmformgebung, wobei sich seine besonderen Vorzüge insbesondere bei der Warmumformung von mit einer metallischen Schutzschicht, insbesondere einer Verzinkung, versehenen Stahlblechen oder -bändern zeigen. Die erfindungsgemäß für die A flat steel product produced according to the invention is suitable in the same way for cold and hot forming, wherein its particular advantages in particular in the hot forming of provided with a metallic protective layer, in particular a galvanized steel sheets or bands show. The invention for the
Kaltumformung vorgesehenen Stähle weisen typischerweise eine Zugfestigkeit von 500 - 1500 MPa auf. Für die Cold forming steels typically have a tensile strength of 500-1500 MPa. For the
Warmumformung lassen sich erfindungsgemäß Stähle Hot working can be inventively steels
einsetzen, die nach der Warmumformung eine Zugfestigkeit von 900 - 200 MPa besitzen. which have a tensile strength of 900-200 MPa after hot working.
Im Fall, dass ein erfindungsgemäßes Stahlflachprodukt durch Warmumformung zu einem Bauteil geformt werden soll, kann das erfindungsgemäße Stahlflachprodukt gemäß der Erfindung zunächst auf eine oberhalb seiner Acl- Temperatur liegende Erwärmungstemperatur erwärmt und dann zu dem Bauteil warmumgeformt werden. In the event that a steel flat product according to the invention is to be formed into a component by hot forming, the flat steel product according to the invention may first be heated to a heating temperature above its Acl temperature and then hot formed into the component.
Soll sich der Warmumformung beispielsweise eine Härtung anschließen, kann das erfindungsgemäße Stahlflachprodukt problemlos auch auf eine Erwärmungstemperatur erwärmt werden, die mindestens gleich der Ac3-Temperatur des Stahlflachprodukts ist. Selbst bei einer so hohen If, for example, hardening is to follow the hot working, the steel flat product according to the invention can also be heated without problems to a heating temperature which is at least equal to the Ac3 temperature of the flat steel product. Even with such a high
Erwärmungstemperatur ist bei einem erfindungsgemäß erzeugten Stahlflachprodukt auch dann die Gefahr einer Versprödung minimiert, wenn das Stahlflachprodukt mit einer metallischen Beschichtung versehen ist, deren Heating temperature is minimized in a steel flat product according to the invention, the risk of embrittlement even if the flat steel product is provided with a metallic coating whose
Schmelztemperatur kleiner oder gleich der Melting temperature is less than or equal to
Erwärmungstemperatur ist. Die durch die erfindungsgemäße Randschichtentkohlung erzielte Duktilität der Randschicht verhindert eine Rissbildung und stellt so sicher, dass kein geschmolzenes Metall der Beschichtung in den Heating temperature is. The ductility of the surface layer achieved by the surface layer decarburization according to the invention prevents cracking and thus ensures that no molten metal of the coating in the
Kernbereich des Stahlsubstrats eindringen kann. Das erfindungsgemäße Verfahren verbessert somit Core area of the steel substrate can penetrate. The method according to the invention thus improves
insbesondere die Umformeigenschaften von in particular the forming properties of
oberflächenveredelten hoch-/ höchstfesten surface-refined high / ultra-high strength
Stahlflachprodukten sowohl für die Kalt- als auch für die Warmumformung, wobei erfindungsgemäße, mit einem  Flat steel products for both cold and hot forming, according to the invention, with a
metallischen Schutzüberzug beschichtete coated metallic protective coating
Stahlflachprodukte sich besonders vorteilhaft für die Warmumformung eignen. Dies wird dadurch erreicht, dass erfindungsgemäß durch eine gezielte Glühgas-Metall- Reaktion in einem Durchlaufofen eine Randentkohlung induziert wird, durch die sich eine duktile, Flat steel products are particularly advantageous for hot forming. This is achieved in that, according to the invention, a decarburization is induced by a targeted annealing gas-metal reaction in a continuous furnace, through which a ductile,
typischerweise ferritische Randschicht bildet. Diese schirmt den festen, spröden Stahl-Grundwerkstoff gegen einen von der Oberfläche ausgehenden Rissfortschritt während der Umformung ab. typically forms ferrite boundary layer. This shields the solid, brittle steel base material against surface crack propagation during forming.
Nachfolgend wird die Erfindung anhand von The invention is based on
Ausführungsbeispielen näher erläutert. Es zeigen: Embodiments explained in more detail. Show it:
Fig. 1 einen senkrechten Anschliff einer erfindungsgemäß randschichtentkohlten Stahlprobe; Figure 1 is a vertical section of a surface according to the invention decarburized steel sample.
Fig. 2 einen senkrechten Anschliff einer konventionell geglühten Vergleichsprobe; FIG. 2 shows a vertical section of a conventionally annealed comparative sample; FIG.
Fig. 3 GDOES-Tiefenprofile des Kohlenstoffgehaltes der in den Figuren 1 und 2 dargestellten Proben; Fig. 3 GDOES depth profiles of the carbon content of the samples shown in Figs. 1 and 2;
Fig. 4 die Ergebnisse von Drei-Punkt-Biegeversuchen mit den in Fig. 1 und 2 dargestellten Proben. 4 shows the results of three-point bending tests with the samples shown in FIGS. 1 and 2.
Zur Überprüfung der durch das erfindungsgemäße Verfahren erzielten Effekte sind jeweils walzharte Kaltbandproben eines Mehrphasenstahls "MP" sowie eines üblicherweise für die Warmumformung eingesetzten Stahls "WU" erzeugt worden. Die Zusammensetzungen der Stähle MP und WU sind in Tabelle 1 angegeben. To test the effects achieved by the method according to the invention, hard-cold-rolled strip samples are in each case a multi-phase steel "MP" and a steel used commonly for hot forming "WU" has been produced. The compositions of steels MP and WU are given in Table 1.
Rest Eisen und unvermeidbare Verunreinigungen  Remaining iron and unavoidable impurities
Tabelle 1 Table 1
Zwei aus den Stählen MP und WU gefertigte Proben sind in einem Durchlaufofen für eine Randschichtentkohlung einer erfindungsgemäßen Glühbehandlung unterzogen worden. Die dabei angewendeten Glühparameter sind in der Spalte Two samples made of the steels MP and WU have been subjected to an annealing treatment according to the invention in a continuous furnace for surface-layer decarburization. The used annealing parameters are in the column
"Erfindungsgemäß" der nachfolgenden Tabelle 2 angegeben. "According to the invention" the following Table 2 indicated.
Zum Vergleich sind zwei weitere aus den Stählen MP und WU gefertigte Proben in dem Durchlaufofen einer For comparison, two more samples made of steels MP and WU in the continuous furnace are one
konventionellen Glühung unterzogen worden, wie sie üblicherweise zur Vorbereitung einer been subjected to conventional annealing, as they are usually used to prepare a
Schmelztauchverzinkung durchgeführt wird. Hot-dip galvanizing is performed.
Um die mechanischen Eigenschaften der Proben zu To the mechanical properties of the samples too
optimieren, ist zusätzlich eine Überalterungsbehandlung durchgeführt worden. Diese hat keinen Einfluss auf die Ausbildung der entkohlten Randschicht, sondern erfolgte lediglich optional zur Verbesserung der Eigenschaften des Bandes . Die bei der Überalterungsbehandlung angewendeten, In addition, an overaging treatment has been performed. This has no influence on the formation of the decarburized surface layer, but was merely optional to improve the properties of the tape. The applied in the overaging treatment,
beide Versuche gleichen Parameter sind ebenfalls  both attempts same parameters are also
Tabelle 2 angegeben.  Table 2 given.
Tabelle 2  Table 2
In Fig. 1 ist das Schliffbild der aus dem Stahl MP erzeugten und erfindungsgemäß glühbehandelten Probe dargestellt. Es ist deutlich zu erkennen, dass sich in Folge der erfindungsgemäßen Vorgehensweise ein entkohlter oberflächennaher Gefügebereich (Randschicht "R") FIG. 1 shows the micrograph of the sample produced from the steel MP and annealed according to the invention. It can be clearly seen that, as a consequence of the procedure according to the invention, a decarburised, near-surface microstructure region (boundary layer "R")
eingestellt hat.  has set.
Das Schliffbild der ebenfalls aus dem Stahl MP erzeugten, jedoch einer konventionellen Glühbehandlung unterzogenen Probe zeigt dagegen keinen entkohlten Bereich (Fig. 2). An den erfindungsgemäß und konventionell glühbehandelten, aus dem Stahl MP erzeugten Proben sind zusätzlich On the other hand, the micrograph of the sample likewise produced from the steel MP but subjected to a conventional annealing treatment shows no decarburized area (FIG. 2). In addition to the inventively and conventionally annealed, produced from the steel MP samples
GDOES-Messungen des Kohlenstoffgehaltes durchgeführt worden. Bei dem GDOES- essverfahren ( "GDOES" = Glow GDOES measurements of carbon content have been carried out. In the GDOES essay procedure ("GDOES" = Glow
Discharge Optical Emission Spectrometre ) handelt es sich um ein Standartverfahren zum schnellen Erfassen eines Konzentrationsprofils von Beschichtungen . Es ist Discharge Optical Emission Spectrometre) is a standard method for the rapid detection of a concentration profile of coatings. It is
beispielsweise im VDI-Lexikon Werkstofftechnik, hrsg. von Hubert Grafen, VDI-Verlag GmbH, Düsseldorf 1993 For example, in the VDI Lexicon Materials, ed. by Hubert Grafen, VDI-Verlag GmbH, Dusseldorf 1993
beschrieben . described.
Das Ergebnis der GDOES-Messungen ist in Fig. 3 The result of the GDOES measurements is shown in FIG. 3
zusammengefasst , wobei die gestrichelte Linie die summarized, wherein the dashed line the
Kohlenstoffverteilung der konventionell behandelten Probe und die durchgezogene Linie die Kohlenstoffverteilung der erfindungsgemäß behandelten Probe wiedergibt. Carbon distribution of the conventionally treated sample and the solid line represents the carbon distribution of the invention treated sample.
Auch Fig. 3 zeigt deutlich, dass die erfindungsgemäß behandelte Probe eine ausgeprägte entkohlte Randschicht R aufweist, deren Dicke ca. 40 μτα beträgt. Dagegen liegt eine solche Randschicht bei der konventionell behandelten Probe nicht vor. Also, Fig. 3 clearly shows that the sample treated according to the invention has a pronounced decarburized edge layer R whose thickness is about 40 μτα. By contrast, such a surface layer is not present in the conventionally treated sample.
Anhand von Mikrohärte-Messungen konnte nachgewiesen werden, dass der bei der aus dem Stahl MP erzeugten, erfindungsgemäß wärmebehandelten Probe entkohlte On the basis of microhardness measurements, it was possible to prove that the sample heat-treated according to the invention produced from steel MP decarburized
Randbereich R eine Mikrohärte von 163 HV und der nicht entkohlte Kernbereich K eine Härte von 255 HV aufweist. Das %-Verhältnis HvR/HvK aus Härte HvR des entkohlten Randbereichs R zu Härte HvK des Kernbereichs K betrug somit 64 % und lag damit deutlich unter dem erfindungsgemäß für dieses Verhältnis vorgegebenen Wert von 75 %. Edge region R has a microhardness of 163 HV and the non-decarburized core region K has a hardness of 255 HV. The% ratio Hv R / Hv K of hardness Hv R of the decarburized edge region R to hardness Hv K of the core region K was thus 64%, which was well below that according to the invention for this ratio predetermined value of 75%.
Im Anschluss an die Giühung erfolgte eine Following the Giühung was a
Oberflächenveredelung der Proben, bei der Zink Surface refinement of the samples by zinc
elektrolytisch auf die Proben aufgebracht worden ist. has been applied electrolytically to the samples.
Anschließend ist ein Drei-Punkt-Biegeversuch an den beschichteten Proben sowohl vor als auch nach einer Subsequently, a three-point bending test is performed on the coated samples both before and after one
Presshärtung durchgeführt worden. Die Ergebnisse der Versuche sind für die aus dem Stahl MP gefertigten Proben in Fig. 4 zusammengefasst . Der Biegewinkel Bw der Press hardening has been carried out. The results of the tests are summarized in FIG. 4 for the samples made of the steel MP. The bending angle Bw of
erfindungsgemäß erzeugten Probe ist darin durch den schwarzen und der Biegewinkel Bw der konventionell erzeugten Probe durch den weißen Balken symbolisiert. Auch hier wird deutlich, dass die erfindungsgemäß According to the invention, the sample is symbolized by the black and the bending angle Bw of the conventionally generated sample by the white bar. Again, it is clear that the invention
erzeugten und behandelten Proben deutlich bessere Umform- und Biegeeigenschaften aufweisen als die konventionell verarbeiteten Proben. produced and treated samples have significantly better forming and bending properties than the conventionally processed samples.
Für die aus dem Stahl WU erzeugten, glühbehandelten, verzinkten und verformten Proben konnten für die For the GW steel produced, annealed, galvanized and deformed samples could be used for the
erfindungsgemäß und die konventionell glühbehandelten Proben vergleichbare Ergebnisse nachgewiesen werden. According to the invention and the conventionally annealed samples comparable results can be detected.

Claims

P A T E N T A N S P R Ü C H E PATENT APPLICATIONS
1. Verfahren zum Herstellen eines gut umformbaren 1. A method for producing a good formable
Stahlflachprodukts, das einen C-Gehalt von  Flat steel product containing a C content of
0,1 - 0,4 Gew.-% aufweist, bei dem das  0.1 - 0.4 wt .-%, wherein the
Stahlflachprodukt in einem Durchlaufofen einer  Flat steel product in a continuous furnace
Glühbehandlung unterzogen wird, d a d u r c h g e k e n n z e i c h n e t, d a s s die Glühbehandlung unter einer Glühatmosphäre durchgeführt wird, die 0,1 - 25 Vol.-% H2, H20 und als Rest N2 sowie technisch bedingt unvermeidbare Annealing is performed, characterized in that the annealing is carried out under an annealing atmosphere, the 0.1 - 25 vol .-% H 2 , H 2 0 and the balance N 2 and technically unavoidable
Verunreinigungen enthält und die einen zwischen  Contains impurities and one between
-20 °C und +60 °C liegenden Taupunkt aufweist, wobei das Verhältnis H20/H2 der Glühatmosphäre höchstens gleich 0,957 ist, und d a s s das Stahlflachprodukt im Zuge der -20 ° C and + 60 ° C lying dew point, wherein the ratio H 2 0 / H 2 of the annealing atmosphere is at most equal to 0.957, and that the flat steel product in the course of
Glühbehandlung auf eine 600 - 1100 °C betragende Haltetemperatur erwärmt wird, bei der es für eine 10 - 360 s dauernde Haltezeit gehalten wird, so dass das nach der Glühbehandlung erhaltene  Annealing treatment is heated to a 600 - 1100 ° C holding temperature, where it is held for a 10 - 360 s lasting time, so that received after the annealing treatment
Stahlflachprodukt eine 10 - 200 μιτι dicke, an seine freie Oberfläche angrenzende duktile Randschicht mit einer Duktilität aufweist, die größer ist als die innenliegende, von der Randschicht bedeckte Flat steel product has a ductile boundary layer with a ductility which is 10 to 200 μm thick and is adjacent to its free surface and which has a ductility which is greater than that inside, covered by the edge layer
Kernschicht des Stahlflachprodukts.  Core layer of the flat steel product.
2. Verfahren nach Anspruch 1, d a d u r c h 2. The method of claim 1, d a d u r c h
g e k e n n z e i c h n e t, d a s s das  g e n c i n e s, the s
Stahlflachprodukt nach der Glühbehandlung mit einer metallischen Schutzschicht beschichtet wird.  Flat steel product is coated after the annealing with a metallic protective layer.
3. Verfahren nach Anspruch 2, d a d u r c h 3. The method of claim 2, d a d u r c h
g e k e n n z e i c h n e t, d a s s das  g e n c i n e s, the s
Stahlflachprodukt in einem kontinuierlich auf die Glühbehandlung folgend durchgeführten Arbeitsablauf schmelztauchbeschichtet wird.  Flat-rolled steel is hot-dip coated in a sequence continuously following the annealing treatment.
4. Verfahren nach Anspruch 2, d a d u r c h 4. The method of claim 2, d a d u r c h
g e k e n n z e i c h n e t, d a s s das  g e n c i n e s, the s
Stahlflachprodukt nach der Glühbehandlung  Flat steel product after annealing
feuerbeschichtet wird.  is fire-coated.
5. Verfahren nach Anspruch 4, d a d u r c h 5. The method of claim 4, d a d u r c h
g e k e n n z e i c h n e t, d a s s vor der Feuerbeschichtung eine Oxidation der Oberfläche des Stahlflachprodukts durchgeführt wird.  However, prior to the fire coating, oxidation of the surface of the flat steel product is performed.
6. Verfahren nach einem der Ansprüche 2 oder 3, 6. The method according to any one of claims 2 or 3,
d a d u r c h g e k e n n z e i c h n e t, d a s s das Stahlflachprodukt mit einem metallischorganischen Überzug beschichtet wird. characterized in that the flat steel product is coated with an organometallic coating.
7. Verfahren nach einem der Ansprüche 2 oder 3, 7. The method according to any one of claims 2 or 3,
d a d u r c h g e k e n n z e i c h n e t, d a s s das Stahlflachprodukt mit einem metallischanorganischen Überzug beschichtet wird.  The steel flat product is coated with a metallic inorganic coating.
8. Verfahren nach einem der voranstehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t, d a s s der C-Gehalt des Stahlflachproduktes weniger als 0,38 Gew.-% beträgt. 8. The method according to claim 1, wherein the C content of the flat steel product is less than 0.38% by weight.
9. Stahlflachprodukt, hergestellt durch Anwendung eines gemäß einem der voranstehenden Ansprüche 9. Flat steel product made by applying one of the preceding claims
ausgebildeten Verfahrens, mit einem C-Gehalt von 0,1 - 0,4 Gew.-% und einer 10 - 200 μιη dicken  trained method, with a C content of 0.1-0.4 wt .-% and a 10 - 200 μιη thick
duktilen Randschicht, die eine gegenüber der  ductile boundary layer, which is one opposite the
Kernschicht des Stahlblechs erhöhte Duktilität besitzt .  Core layer of the steel sheet has increased ductility.
10. Stahlflachprodukt nach Anspruch 9, d a d u r c h g e k e n n z e i c h n e t, d a s s die duktile Randschicht mindestens nahe der freien Oberfläche des Stahlflachprodukts ein ferritisches Gefüge aufweist. 10. Flat steel product according to claim 9, characterized in that the ductile surface layer has a ferritic structure at least near the free surface of the flat steel product.
11. Stahlflachprodukt nach einem der Ansprüche 9 oder 10, d a d u r c h g e k e n n z e i c h n e t, d a s s der C-Gehalt des Stahlflachproduktes höchstens 11. Flat steel product according to one of claims 9 or 10, characterized in that the C content of the flat steel product is at most equal
0,38 Gew.-% beträgt. 0.38 wt .-% is.
12. Stahlflachprodukt nach einem der Ansprüche 9 oder 10, d a d u r c h g e k e n n z e i c h n e t, d a s s die Härte der entkohlten Randschicht (R) höchstens12. Flat steel product according to one of claims 9 or 10, characterized in that the hardness of the decarburized surface layer (R) is at most equal
75 % der Härte des Kernbereichs (K) des 75% of the hardness of the core area (K) of the
Stahlflachproduktes beträgt.  Flat steel product is.
13. Verfahren zum Herstellen eines Bauteils aus einem 13. A method for producing a component from a
gemäß einem der Ansprüche 9 bis 12 ausgebildeten Stahlflachprodukt, d a d u r c h  according to one of claims 9 to 12 formed flat steel product, d a d u r c h
g e k e n n z e i c h n e t, d a s s das  g e n c i n e s, the s
Stahlflachprodukt einer Warmumformung unterzogen wird, bei der es zunächst auf eine oberhalb seiner Acl-Temperatur liegende Erwärmungstemperatur erwärmt und dann zu dem Bauteil warmumgeformt wird.  Steel flat product is subjected to hot working, in which it is first heated to a heating temperature above its Acl temperature and then hot-formed into the component.
14. Verfahren nach Anspruch 13, d a d u r c h 14. The method of claim 13, d a d u r c h
g e k e n n z e i c h n e t, d a s s die  e n c ia n, the s
Erwärmungstemperatur mindestens gleich der  Heating temperature at least equal to
Ac3-Temperatur des Stahlflachprodukts ist.  Ac3 temperature of the flat steel product is.
15. Verfahren zum Herstellen eines Bauteils aus einem gemäß einem der Ansprüche 9 bis 12 ausgebildeten Stahlflachprodukt, d a d u r c h 15. A method for producing a component from a formed according to one of claims 9 to 12 steel flat product, d a d u r c h
g e k e n n z e i c h n e t, d a s s das  g e n c i n e s, the s
Stahlflachprodukt zu dem Bauteil kaltumgeformt wird.  Flat steel product is cold formed into the component.
EP10787425.7A 2009-12-10 2010-12-03 Method for producing an easily deformable flat steel product Active EP2513346B1 (en)

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