(19)
(11)EP 2 536 857 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
21.08.2019 Bulletin 2019/34

(21)Application number: 11707337.9

(22)Date of filing:  18.02.2011
(51)International Patent Classification (IPC): 
C21D 1/673(2006.01)
C21D 8/02(2006.01)
C21D 9/48(2006.01)
C23C 28/04(2006.01)
C21D 1/68(2006.01)
C21D 8/04(2006.01)
C23C 2/02(2006.01)
C23C 18/12(2006.01)
(86)International application number:
PCT/EP2011/000785
(87)International publication number:
WO 2011/101158 (25.08.2011 Gazette  2011/34)

(54)

STRIP, SHEET OR BLANK SUITABLE FOR HOT FORMING AND PROCESS FOR THE PRODUCTION THEREOF

BANDE, FEUILLE OU ÉBAUCHE ADAPTÉE AU FORMAGE À CHAUD ET SON PROCÉDÉ DE PRODUCTION

STREIFEN, PLATTE ODER ROHLING, DER BZW. DIE ZUR WARMFORMEBUNG GEEIGNET IST, UND VERFAHREN ZU DESSEN BZW. DEREN HERSTELLUNG


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 19.02.2010 EP 10001707

(43)Date of publication of application:
26.12.2012 Bulletin 2012/52

(73)Proprietors:
  • Tata Steel Nederland Technology B.V.
    1970 CA IJmuiden (NL)
  • Tata Steel Limited
    Jamshedpur 831 001 (IN)

(72)Inventors:
  • ROUT, Tapan, Kumar
    NL-1970 CA Ijmuiden (NL)
  • GO, Johnson
    NL-1970 CA Ijmuiden (NL)
  • GAIKWAD, Anil, Vilas
    NL-1970 CA Ijmuiden (NL)

(74)Representative: Group Intellectual Property Services 
c/o Tata Steel Nederland Technology B.V. P.O. Box 10000 - 3G.37
1970 CA IJmuiden
1970 CA IJmuiden (NL)


(56)References cited: : 
EP-A1- 1 826 289
WO-A1-2005/021822
DE-A1-102007 061 489
JP-A- 8 325 689
JP-A- 10 204 580
WO-A1-2005/021820
BE-A3- 1 014 997
DE-B3-102007 022 174
JP-A- 9 053 187
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description


    [0001] The invention relates to a strip, sheet or blank suitable for hot forming at a temperature of 700° C or above, comprising a substrate of hot formable steel, optionally coated with an active corrosion protective coating. The invention also relates to a process for producing such a strip, sheet or blank.

    [0002] Such an uncoated strip, sheet or blank is known, for instance from GB 1490535, and a coated strip, sheet or blank is known from EP 0971044, relating to an Al-Si coated boron steel; the process of hot forming a zinc coated boron steel is known from for instance EP 1143029. EP 1 826 289 discloses a boron steel having a protective oxide coating of one or more of Al2O3, MgO, CaO, SiO2, B2O3 and MnO upon heating.

    [0003] Uncoated boron steels are known to form Fe oxides during the heat treatment preceding the hot forming step in a die, as a consequence whereof loose and thick oxide layers are formed on the surface, which can pollute and damage the surface of the die. Moreover, such oxide layers interfere with the welding process of the formed product during the subsequent use of the formed product, and also contaminate subsequent painting processes. Therefore, the oxide layers have to be removed after the hot forming process of the uncoated steel products, which is inefficient and costly.

    [0004] To overcome the above problems, coated boron steels have been developed, and the boron steel substrate has been covered with a metallic coating such as an Al-Si coating and a Zn based coating. So far, it has been found that it is difficult to keep the boron steel substrate covered by the metallic coating during heating and hot press forming. It is expected that this is due to removal of the metallic oxide during the heat treatment, for instance by evaporation.

    [0005] It is an object of the invention to provide a strip, sheet or blank suitable for hot forming with which the Fe oxide formation of uncoated steel sheets for hot forming is considerably reduced.

    [0006] It is a further object of the invention to provide a steel sheet coated with an active corrosion protective coating suitable for hot forming that has an improved retainment of the coating during hot forming.

    [0007] It is another object of the invention to provide a strip, sheet or blank suitable for hot forming having improved properties, such as reduced oxide formation or improved retainment of the coating for active corrosion protection, at low cost.

    [0008] It is also an object of the invention to provide a process for the production of a strip, sheet or blank that meets one or more of the objects hereinabove.

    [0009] According to the invention which is given in claims 1 to 8, one or more of the above objects are reached with a strip, sheet or blank suitable for hot forming at a temperature of 700° C or above, comprising a substrate of hot formable steel, optionally coated with an active corrosion protective coating, characterised in that the optionally coated steel substrate is provided with a ceramic based coating having a thickness of at most 25 micron.

    [0010] The inventors have found that such a ceramic coating is very suitable to greatly reduce the extent of oxidation of an uncoated steel strip, sheet and blank during the hot forming. No loose oxides were observed on the surface of the heated ceramic coated steel. The ceramic coating also retains the coating for active corrosion protection if present on the steel. The inventors have found that the thickness of the ceramic coating should be at most 25 micron since with higher thickness the coating may delaminate from the steel. The strip, sheet and blank can be used at temperatures between 700° C and 1200° C, preferably between 800° C and 1000° C.

    [0011] Preferably, the ceramic based coating comprises at least one of the group of ceramic oxides consisting of SiO2, Al2O3, MnO2, CaO, MgO2, Fe2O3, CeO2, CeNO3, AgO, ZnO, SnO2, V2O5 and HfO2. Each of these ceramic oxides or a combination thereof forms a ceramic coating that reduces the oxidation of an uncoated strip, sheet or blank during hot forming, or retains the corrosion protective coating on the steel substrate.

    [0012] According to a preferred embodiment the ceramic based coating comprises SiO2, Al2O3 and MgO2 and optionally CaO, Fe2O3 and MnO2. This combination of ceramic oxides provides a good ceramic based coating for the purpose.

    [0013] Preferably the ceramic based coating comprised 5 - 80% SiO2, 1 - 30% Al2O3 and 1 - 30% MgO2, and optionally max 5% CaO, max 10% Fe2O3 and max 10% MnO2. These percentages (in volume%) of ceramic oxides provide a good ceramic based coating which can be produced at low cost.

    [0014] According to a preferred embodiment the ceramic based coating also comprises at least one of the group consisting of polyimide polymer, acrylic polymer, poly vinyl, poly vinyl alcohol, polyurethane and silicone oil. These materials provide flexibility to the ceramic based coating.

    [0015] Preferably the ceramic based coating has a thickness of between 1 and 15 micron, preferably between 1 and 10 micron, more preferably between 2 and 5 micron. Of course a thinner coating has a lower cost; moreover, the ceramic based coating has to provide its function during the hot forming process only, which generally last only a few minutes to heat the blank and uses a very short time for the hot pressing and quenching. The coating can be applied by a spray coater, by dip coating, by a roll coater or a chemical coater, or by electrodeposition techniques.

    [0016] According to a preferred embodiment, the ceramic based coating comprises carbon black, carbon fibres, carbon nanotubes and/or nano-clays. These filler-type materials provide an additional corrosion protection to the ceramic based coating.The naotubes can be single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs) and/or multi-walled carbon nanotubes (MWCNTs).

    [0017] According to a further preferred embodiment the ceramic based coating comprised metallic pigments, such as zinc, aluminium, titania, chromate, red-oxide or magnesium pigments, preferably the metallic pigments being coated or encapsulated or derived from their alkoxide precursors. The metallic based pigments, such as zinc, aluminium, titania, chromate, red-oxid or magnesium pigments, in themselves give an active corrosion protection, especially when no active corrosion protection layer is present.

    [0018] According to a still further preferred embodiment the ceramic based coating comprises metallic fillers as expansion agents, such as Al, Fe, Sn and/or Zr. Such fillers give an additional corrosion protection and provide the ceramic based layer at lower cost.

    [0019] Preferably the hot formable steel substrate is a boron steel substrate, more preferably having the composition in weight percent:

    C between 0.04 and 0.5%

    Mn between 0.5 and 3.5%

    Si less than 1.0%

    Cr 0.01 and 1.0%

    Ti less than 0.2%

    Al less than 2.0%

    P less than 0.1%

    N less than 0.015%

    S less than 0.05%

    B less than 0.015%

    the remainder being Fe and unavoidable impurities.

    Such steel types are generally known and used for hot forming purposes.

    [0020] According to a preferred embodiment an active corrosion protective coating is present on the hot formable steel substrate, the active corrosion protective coating being a coating of one of the group of zinc based coating, aluminium based coating, cerium based coating, ZrO2 based coating, Fe-Zn based coating, magnesium pigment based coating. These are known active corrosion protective coatings, which profit from the ceramic based coating according to the invention which helps retaining the active corrosion protective coating on the steel during hot forming.

    [0021] According to a second aspect of the invention which is given in claims 9 to 12, there is provided a process for producing a strip, sheet or blank suitable for hot forming at a temperature of 700° C or above according to the first aspect of the invention above, wherein solid particles comprising at least one of the group of ceramic oxides and/or their metal alkoxides consisting of SiO2, Al2O3, MnO2, CaO, MgO2, Fe2O3, CeO2, CeNO3, AgO, ZnO, SnO2, V2O5 and HfO2 are mixed in a solvent based system or water based system and applied on the strip, sheet or blank in a layer of at most 50 micron, after which the strip, sheet or blank is cured at a temperature of at most 400° C to remove the solvent or water and to sinter the ceramic oxides.

    [0022] Using such solid particles and mixing them in a solvent or water based system makes it possible to apply the solvent or water based ceramic system on the strip, sheet or blank at a layer of at most 50 micron, such that after removing the solvent or water and sintering of the ceramic oxides a ceramic based layer is formed having a thickness of at most 25 micron.

    [0023] According to a preferred embodiment, solid particles comprising ceramic oxides consisting of SiO2, Al2O3 and MgO2 and optionally CaO, MnO2 and Fe2O3 are mixed in the solvent based system or water based system, preferably 5 - 80% SiO2, 1 - 30% Al2O3 and 1 - 30% MgO2 and optionally max 5% CaO, max 10% MnO2 and max 10% Fe2O3, and wherein optionally carbon black, carbon fibres, carbon nanotubes and/or nano-clays are mixed in the solvent based system or water based system and wherein optionally metallic pigments, such as zinc, alumina or magnesium pigments, preferably the metallic pigments being coated or encapsulated, are mixed in the solvent based system or water based system, and wherein preferably an active corrosion protective coating is present on the hot formable steel substrate, the active corrosion protective coating being a coating of one of the group of zinc based coating, aluminium based coating, cerium based coating, ZrO2 based coating, Fe-Zn based coating, magnesium pigmented coating. In this way a strip, sheet or blank is produced according to the first aspect of the invention.

    [0024] Preferably an oxide layer on the metal substrate is removed prior to the application of the ceramic based layer on the metal substrate. Removing the oxide layer provides a better adhesion between the metal substrate and the ceramic based coating.

    [0025] According to a preferred embodiment the temperature to cure and sinter the coating is performed at a temperature between 50 and 150° C. Using this temperature range provides an economic process and well-sintered ceramic oxides.

    [0026] The invention will be elucidated referring to the examples given below.

    [0027] In a first experiment, a sample of an uncoated cold rolled boron steel has been compared with cold rolled boron steel coated with a ceramic based coating.

    [0028] The boron steel used has a composition of 0.21 C, 0.192 Si, 1.189 Mn, 0.022 Ni, 0.25 Cr, 0.044 Al tot, 0.013 P, 0.035 Ti, 62 ppm N, 0.006 S and 31 ppm B (all in weight% but N and B).

    [0029] The coating used is the commercially available Berkatekt 12® manufactured by Henkel. This coating has a composition of 32 - 36% SiO2, 8 - 9% Al2O3, < 1% CaO, 7.5 - 10% MgO2 and < 2% Fe2O3, mixed in an organic compound. The coating can be applied by spraying or dipping. In this first experiment, the coating was applied by spraying after the surface of the boron steel had been thoroughly cleaned. A first coating has been applied having a thickness of 0.293 mg/cm2 (after curing and sintering), a second coating has been applied having a thickness of 0.389 mg/cm2 (after curing and sintering).

    [0030] For the uncoated cold rolled sample, thick and loose Fe oxides were found on the sample surface after heating up to 900° C during 5 minutes. Examined in SEM micrographs, large cracks were observed in the oxide layers on the surface of the sample.

    [0031] Both the samples using a Berkatekt 12® coating showed that the extent of Fe oxidation during the high temperature heat treatment is reduced significantly. Both hematite and magnetite formation were considerably suppressed during heating up to 900° C during 5 minutes.

    [0032] In a second experiment, a sample of a cold rolled boron steel coated with an active corrosion protective layer has been compared with such a sample coated with a ceramic based coating.

    [0033] The boron steel substrate used has a composition of 0.21 C, 0.192 Si, 1.189 Mn, 0.022 Ni, 0.25 Cr, 0.044 Al tot, 0.013 P, 0.035 Ti, 62 ppm N, 0.006 S and 31 ppm B (all in weight% but N and B).

    [0034] The active corrosion protective layer in this experiment is a zinc alloy layer using 1.6 weight% Mg and 1.6 weight% Al, the remainder being zinc (called MagiZinc®). The thickness of the zinc alloy layer is 70 g/m2.

    [0035] The coating used again is Berkatekt 12® applied in the same way as in the first experiment. A first coating has been applied having a thickness of 0.173 mg/cm2 (after curing and sintering), a second coating has been applied having a thickness of 0.335 mg/cm2 (after curing and sintering).

    [0036] The sample without the ceramic coating shows quite severe oxidation of the zinc alloy layer after heating up to 900° C during 5 minutes. A thick zinc oxide layer was observed in SEM micrographs.

    [0037] Both the samples using a Berkatekt 12® coating on the zinc alloy layer showed that the extent of zinc oxidation during the high temperature heat treatment of 900° C during 5 minutes is reduced significantly, as shown in SEM micrographs. In addition, it is likely that the ceramic coating prevented excessive evaporation of the zinc, and therefore higher amounts of zinc were retained in the FeZn layer (which is formed during the heating). Higher amounts of zinc will lead to improved active corrosion protection.

    [0038] When no loose oxide layers are produced during hot forming (as in the case of the above ceramic coated samples) additional surface conditioning is not necessary after hot forming.

    [0039] The ceramic coating can be applied for both direct and indirect hot forming processes, although it is expected to perform better in the former.

    [0040] The examples show that the coating weight can be varied from approximately 0.2 mg/cm2 up to approximately 0.4 mg/cm2 without influencing significantly the performance of the coating.

    [0041] In a third experiment uncoated and ceramic coated sampled that had first been provided with an active corrosion protective layer were subjected to a salt spray test and to electrical resistance tests.

    [0042] The boron steel substrate used has a composition of 0.21 C, 0.192 Si, 1.189 Mn, 0.022 Ni, 0.25 Cr, 0.044 Al tot, 0.013 P, 0.035 Ti, 62 ppm N, 0.006 S and 31 ppm B (all in weight% but N and B).

    [0043] The active corrosion protective layers in this experiment is a zinc alloy layer using 1.6 weight% Mg and 1.6 weight% Al, the remainder being zinc(called MagiZinc®), and GI. The thickness of the zinc alloy layer and GI layer is 140 g/m2.

    [0044] Prior to the measurements, the samples were treated in a preheated furnace under air at 900° C during 5 minutes.

    [0045] An electrical resistance test was performed so as to indirectly evaluate the weldability of coatings. From the literature it is known that for conventional weldable coatings the electrical resistance should be on average below 5 milli-ohms.

    [0046] The experimental setup for measuring the electrical resistance consists of two copper electrodes (diameter = 12.5mm), a low ohm meter (Rhopoint Instrumnet M210), a pressure gauge and a pneumatic press (capable of 15 ton pressure). The low ohm meter has a resolution of 1 milli-ohm and its copper wires were soldered directly into the copper electrodes to avoid any potential resistance contribution from the setup. The copper electrode surfaces in contact with the testing samples were ground on 4000 grit silicone carbide paper before use, while the reverse sides were covered with insulating tape.

    [0047] The ceramic coating used was a Berkatekt 12® coating as in the first experiment. The coating has a thickness of 0.2 mg/cm2 (after curing and sintering).

    [0048] The ceramic coating applied on the MagiZinc® coating gives an electrical resistance of 3 milli-ohms for the sample. The ceramic coating applied on the GI coating gives an electrical resistance of 2 milli-ohms for the sample. This is a significant improvement over a MagiZinc® coating and GI coating without the ceramic layer, and thus very good for industrial welding.

    [0049] The salt spray test was performed on samples of both ceramic coated MagiZinc® coated and GI coated boron steel, and on MagiZinc® coated and GI coated boron steel not coated with a ceramic layer.

    [0050] The salt spray test was performed according to ASTM B117, using a 5% NaCl solution at 35° C, with an overpressure of 2 - 3.5 mbar (200 to 350 Pascal) to create fog inside the spray chamber.

    [0051] Using the ceramic coating on the above specified active corrosion protective layers gives a slight improvement in corrosion resistance over the samples without ceramic layer. This is acceptable for industrial use.

    [0052] It will be clear to the skilled person that the invention is not limited to the above described experiments, but that the scope of the invention is determined by the accompanying claims.


    Claims

    1. Strip, sheet or blank suitable for hot forming at a temperature of 700° C or above, comprising a substrate of hot formable steel, optionally coated with an active corrosion protective coating, characterised in that the optionally coated steel substrate is provided with a ceramic based coating having a thickness of at most 25 micron on the external layer, wherein the ceramic based coating comprises 5 - 80% SiO2, 1 - 30% Al2O3 and 1 - 30% MgO2, and optionally max 5% CaO, max 10% Fe2O3 and max 10% MnO2.
     
    2. Strip, sheet or blank according to claim 1, wherein the ceramic based coating also comprises at least one of the group consisting of polyimide polymer, acrylic polymer, poly vinyl, poly vinyl alcohol, polyurethane and silicone oil.
     
    3. Strip, sheet or blank according to any one of the preceding claims, wherein the ceramic based coating has a thickness of between 1 and 15 micron, preferably between 1 and 10 micron, more preferably between 2 and 5 micron.
     
    4. Strip, sheet or blank according to any one of the preceding claims, wherein the ceramic based coating comprised carbon black, carbon fibres, carbon nanotubes and/or nano-clays.
     
    5. Strip, sheet or blank according to any one of the preceding claims, wherein the ceramic based coating comprised metallic pigments, such as zinc, aluminium, titania, chromate, red-oxide or magnesium pigments, preferably the metallic pigments being coated or encapsulated or derived from their alkoxide precursors.
     
    6. Strip, sheet or blank according to any one of the preceding claims, wherein the ceramic based coating comprises metallic fillers as expansion agents, such as Al, Fe, Sn, Cr, Ti and/or Zr.
     
    7. Strip, sheet or blank according to any one of the preceding claims, wherein the hot formable steel substrate is a boron steel substrate, preferably having the composition in weight percent:

    C between 0.04 and 0.5%

    Mn between 0.5 and 3.5%

    Si less than 1.0%

    Cr 0.01 and 1.0%

    Ti less than 0.2%

    Al less than 2.0%

    P less than 0.1%

    N less than 0.015%

    S less than 0.05%

    B less than 0.015%

    the remainder being Fe and unavoidable impurities.


     
    8. Strip, sheet or blank according to any one of the preceding claims, wherein an active corrosion protective coating is present on the hot formable steel substrate, the active corrosion protective coating being a coating of one of the group of zinc based coating, aluminium based coating, cerium based coating, ZrO2 based coating, Fe-Zn based coating, magnesium based coating.
     
    9. Process for producing a strip, sheet or blank suitable for hot forming at a temperature of 700° C or above according to any one of the preceding claims, wherein solid particles comprising ceramic oxides and/or their metal alkoxides consisting of SiO2, Al2O3 and MgO2, and optionally MnO2, CaO and Fe2O3, are mixed in a solvent based system or water based system and applied on the strip, sheet or blank in a layer of at most 50 micron, after which the strip, sheet or blank is cured at a temperature of at most 400° C to remove the solvent or water and to sinter the ceramic oxides, wherein the ceramic based coating comprises 5 - 80% SiO2, 1 - 30% Al2O3 and 1 - 30% MgO2, and optionally max 5% CaO, max 10% Fe2O3 and max 10% MnO2.
     
    10. Process according to claim 9, wherein solid particles comprising ceramic oxides consisting of 5 - 80% SiO2, 1 - 30% Al2O3 and 1 - 30% MgO2 and optionally max 5% CaO, max 10% MnO2 and max 10% Fe2O3 are mixed in the solvent based system or water based system, and wherein optionally carbon black, carbon fibres, carbon nanotubes and/or nano-clays are mixed in the solvent based system or water based system and wherein optionally metallic pigments, such as zinc, alumina or magnesium pigments, preferably the metallic pigments being coated or encapsulated, are mixed in the solvent based system or water based system, and wherein preferably an active corrosion protective coating is present on the hot formable steel substrate, the active corrosion protective coating being a coating of one of the group of zinc based coating, aluminium based coating, cerium based coating, ZrO2 based coating, Fe-Zn based coating, magnesium based coating.
     
    11. Process according to claim 9 or 10, wherein an oxide layer on the metal substrate is removed prior to the application of the ceramic based layer on the metal substrate.
     
    12. Process according to claim 9, 10 or 11, wherein the temperature to cure and sinter the coating is performed at a temperature between 50 and 150° C.
     


    Ansprüche

    1. Streifen, Platte oder Rohling, der bzw. die für die Warmformung bei einer Temperatur von 700° C oder darüber geeignet ist, umfassend ein Substrat aus warmformbarem Stahl, optional beschichtet mit einer aktiven Korrosionsschutzbeschichtung, dadurch gekennzeichnet, dass das optional beschichtete Stahlstubstrat mit einer keramikbasierten Beschichtung mit einer Dicke von höchstens 25 Mikron auf der äußeren Schicht versehen ist, wobei die keramikbasierte Beschichtung 5 - 80 % SiO2, 1 - 30 % Al2O3 und 1 - 30 % MgO2 und optional max. 5 % CaO, max. 10 % Fe2O3 und max. 10% MnO2 umfasst.
     
    2. Streifen, Platte oder Rohling nach Anspruch 1, wobei die keramikbasierte Beschichtung auch mindestens eines aus der Gruppe, bestehend aus Polyimidpolymer, Acrylpolymer, Polyvinyl, Polyvinylalkohol, Polyurethan und Silikonöl umfasst.
     
    3. Streifen, Platte oder Rohling nach einem der vorstehenden Ansprüche, wobei die keramikbasierte Beschichtung eine Dicke von zwischen 1 und 15 Mikron, vorzugsweise zwischen 1 und 10 Mikron, weiter bevorzugt zwischen 2 und 5 Mikron aufweist.
     
    4. Streifen, Platte oder Rohling nach einem der vorstehenden Ansprüche, wobei die keramikbasierte Beschichtung Ruß, Carbonfasern, Carbonnanoröhrchen und/oder Nanotonerden umfasst.
     
    5. Streifen, Platte oder Rohling nach einem der vorstehenden Ansprüche, wobei die keramikbasierte Beschichtung metallische Pigmente, wie Zink-, Aluminium-, Titandioxid-, Chromat-, rote Oxid- oder Magnesiumpigmente umfasst, wobei die metallischen Pigmente vorzugsweise beschichtet oder eingekapselt oder von ihren Alkoxidvorläufern abgeleitet sind.
     
    6. Streifen, Platte oder Rohling nach einem der vorstehenden Ansprüche, wobei die keramikbasierte Beschichtung metallische Fasern als Expansionsmittel, wie Al, Fe, Sn, Cr, Ti und/oder Zr, umfasst.
     
    7. Streifen, Platte oder Rohling nach einem der vorstehenden Ansprüche, wobei das warmformbare Stahlsubstrat ein Borstahlsubstrat ist, das vorzugsweise die folgende Zusammensetzung in Gewichtsprozent aufweist:

    C zwischen 0,04 und 0,5%

    Mn zwischen 0,5 und 3,5 %

    Si weniger als 1,0 %

    Cr 0,01 und 1,0 %

    Ti weniger als 0,2 %

    Al weniger als 2,0 %

    P weniger als 0,1 %

    N weniger als 0,015 %

    S weniger als 0,05 %

    B weniger als 0,015 %

    wobei der Rest Fe und unvermeidliche Verunreinigungen sind.


     
    8. Streifen, Platte oder Rohling nach einem der vorstehenden Ansprüche, wobei auf dem warmformbaren Stahlsubstrat eine aktive Korrosionsschutzbeschichtung vorhanden ist, wobei die aktive Korrosionsschutzbeschichtung eine Beschichtung aus der Gruppe, bestehend aus zinkbasierter Beschichtung, aluminiumbasierter Beschichtung, ceriumbasierter Beschichtung, ZrO2-basierter Beschichtung, Fe-Zn-basierter Beschichtung, magnesiumbasierter Beschichtung ist.
     
    9. Prozess zum Herstellen eines Streifens, Plattes oder Rohlings, der bzw. die sich für das Warmformen bei einer Temperatur von 700°C oder darüber geeignet ist, nach einem der vorstehenden Ansprüche, wobei Festpartikel umfassende Keramikoxide und/oder ihre Metallalkoxide, bestehend aus SiO2, Al2O3 und MgO2 und optional MnO2, CaO und Fe2O3, in einem lösemittelbasierten oder einem wasserbasierten System gemischt und auf den Streifen, Platte oder Rohling in einer Schicht von höchstens 50 Mikron aufgetragen werden, wonach der Streifen, Platte oder Rohling nach diesem Schritt bei einer Temperatur von höchstens 400° C ausgehärtet wird, um das Lösemittel oder Wasser zu entfernen und die Keramikoxide zu sintern, wobei die keramikbasierte Beschichtung 5 - 80 % SiO2, 1 - 30 % Al2O3 und 1 - 30 % MgO2 und optional max. 5 % CaO, max. 10 % Fe2O3 und max. 10 % MnO2 umfasst.
     
    10. Prozess nach Anspruch 9, wobei Feststoffpartikel umfassende Keramikoxide, bestehend aus 5 - 80 % SiO2, 1 - 30 % Al2O3 und 1 - 30 % MgO2 und optional max. 5 % CaO, max. 10 % MnO2 und max. 10 % Fe2O3 im lösemittelbasierten oder wasserbasierten System gemischt werden und wobei optional Ruß, Carbonfasern, Carbonnanoröhrchen und/oder Nanotonerden im lösemittelbasierten System oder wasserbasierten System gemischt werden und wobei optional metallische Pigmente, wie Zink-, Aluminiumoxid- oder Magnesiumpigmente, wobei die metallischen Pigmente vorzugsweise beschichtet oder eingekapselt sind, im lösemittelbasierten System oder wasserbasierten System gemischt werden, und wobei vorzugsweise eine aktive Korrosionsschutzbeschichtung auf dem warmformbaren Stahlsubstrat vorhanden ist, wobei die aktive Korrosionsschutzbeschichtung eine Beschichtung einer aus der Gruppe, bestehend aus zinkbasierter Beschichtung, aluminiumbasierter Beschichtung, ceriumbasierter Beschichtung, ZrO2-basierter Beschichtung, Fe-Zn-basierter Beschichtung, magnesiumbasierter Beschichtung ist.
     
    11. Prozess nach Anspruch 9 oder 10, wobei eine Oxidschicht auf dem Metallsubstrat vor dem Auftragen der keramikbasierten Schicht auf dem Metallsubstrat entfernt wird.
     
    12. Prozess nach Anspruch 9, 10 oder 11, wobei die Temperatur zum Aushärten und Sintern der Beschichtung bei einer Temperatur zwischen 50 und 150°C ausgeführt wird.
     


    Revendications

    1. Bande, feuille ou ébauche adaptée au thermoformage à une température supérieure ou égale à 700°C, comprenant un substrat en acier thermoformable, éventuellement revêtu d'un revêtement de protection active contre la corrosion, caractérisée en ce que le substrat en acier éventuellement revêtu est doté d'un revêtement à base de céramique possédant une épaisseur inférieure ou égale à 25 microns sur la couche externe, ledit revêtement à base de céramique comprenant de 5 à 80 % de SiO2, de 1 à 30 % de Al2O3 et de 1 à 30 % de MgO2 et éventuellement 5 % maximum de CaO, 10 % maximum de Fe2O3 et 10 % maximum de MnO2.
     
    2. Bande, feuille ou ébauche selon la revendication 1, ledit revêtement à base de céramique comprenant également au moins l'un du groupe constitué par un polymère polyimide, un polymère acrylique, un polyvinyle, un poly(alcool de vinyle), le polyuréthane et l'huile de silicone.
     
    3. Bande, feuille ou ébauche selon l'une quelconque des revendications précédentes, ledit revêtement à base de céramique possédant une épaisseur comprise entre 1 et 15 microns, de préférence entre 1 et 10 microns, idéalement entre 2 et 5 microns.
     
    4. Bande, feuille ou ébauche selon l'une quelconque des revendications précédentes, ledit revêtement à base de céramique comprenant du noir de carbone, des fibres de carbone, des nanotubes de carbone et/ou des nano-argiles.
     
    5. Bande, feuille ou ébauche selon l'une quelconque des revendications précédentes, ledit revêtement à base de céramique comprenant des pigments métalliques, tels que des pigments de zinc, d'aluminium, de titane, de chromate, d'oxyde ferrique ou de magnésium, de préférence lesdits pigments métalliques étant enrobés ou encapsulés ou dérivés de leurs précurseurs alcoolates.
     
    6. Bande, feuille ou ébauche selon l'une quelconque des revendications précédentes, ledit revêtement à base de céramique comprenant des charges métalliques en tant qu'agents de dilatation, tels que Al, Fe, Sn, Cr, Ti et/ou Zr.
     
    7. Bande, feuille ou ébauche selon l'une quelconque des revendications précédentes, ledit substrat en acier thermoformable étant un substrat en acier au bore, possédant de préférence la composition en pourcentage en poids :

    C entre 0,04 et 0,5 %

    Mn entre 0,5 et 3,5 %

    Si moins de 1,0 %

    Cr 0,01 et 1,0 %

    Ti moins de 0,2 %

    Al moins de 2,0 %

    P moins de 0,1 %

    N inférieur à 0,015 %

    S moins de 0,05 %

    B moins de 0,015 %

    le reste étant du Fe et des impuretés inévitables.


     
    8. Bande, feuille ou ébauche selon l'une quelconque des revendications précédentes, un revêtement de protection active contre la corrosion étant présent sur le substrat en acier thermoformable, ledit revêtement de protection active contre la corrosion étant un revêtement de l'un du groupe constitué par un revêtement à base de zinc, un revêtement à base d'aluminium, un revêtement à base de cérium, un revêtement à base de ZrO2, un revêtement à base de Fe-Zn, un revêtement à base de magnésium.
     
    9. Procédé de production d'une bande, d'une feuille ou d'une ébauche adaptée au thermoformage à une température supérieure ou égale à 700°C selon l'une quelconque des revendications précédentes, des particules solides comprenant des oxydes céramiques et/ou leurs alcoolates métalliques constitués de SiO2, Al2O3 et MgO2, et éventuellement MnO2, CaO et Fe2O3, étant mélangés dans un système à base de solvant ou un système à base d'eau et appliqués sur la bande, la feuille ou l'ébauche en une couche d'au plus 50 microns, après quoi la bande, la feuille ou l'ébauche étant durcie à température inférieure ou égale à 400°C pour éliminer le solvant ou l'eau et pour fritter les oxydes de céramique, ledit revêtement à base de céramique comprenant de 5 à 80 % de SiO2, de 1 à 30 % de Al2O3 et de 1 à 30 % de MgO2 et éventuellement 5 % maximum de CaO, 10 % maximum de Fe2O3 et 10 % maximum de MnO2.
     
    10. Procédé selon la revendication 9, lesdites particules solides comprenant des oxydes céramiques constitués de 5 à 80 % de SiO2, de 1 à 30 % de Al2O3 et de 1 à 30 % de MgO2 et éventuellement 5 % maximum de CaO, 10 % maximum de MnO2 et 10 % maximum de Fe2O3 étant mélangés dans le système à base de solvant ou le système à base d'eau, et éventuellement du noir de carbone, des fibres de carbone, des nanotubes de carbone et/ou des nano-argiles étant mélangés dans le système à base de solvant ou le système à base d'eau et éventuellement des pigments métalliques, tels que des pigments de zinc, d'alumine ou de magnésium, de préférence les pigments métalliques étant revêtus ou encapsulés, étant mélangés dans le système à base de solvant ou le système à base d'eau et de préférence un revêtement de protection active contre la corrosion étant présent sur le substrat en acier thermoformable, ledit revêtement de protection active contre la corrosion étant de l'un du groupe constitué par un revêtement à base de zinc, un revêtement à base d'aluminium, un revêtement à base de cérium, un revêtement à base de ZrO2, un revêtement à base de Fe-Zn, un revêtement à base de magnésium.
     
    11. Procédé selon la revendication 9 ou 10, une couche d'oxyde sur le substrat métallique étant enlevée avant l'application de la couche à base de céramique sur le substrat métallique.
     
    12. Procédé selon la revendication 9, 10 ou 11, ladite température pour durcir et fritter le revêtement étant établie à une température comprise entre 50 et 150°C.
     






    Cited references

    REFERENCES CITED IN THE DESCRIPTION



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    Patent documents cited in the description