Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
  • C23C2/12—Aluminium or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
  • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
  • C23C2/0222—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating in a reactive atmosphere, e.g. oxidising or reducing atmosphere
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
  • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
  • C23C2/0224—Two or more thermal pretreatments
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
  • C23C28/32—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer
  • C23C28/321—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer with at least one metal alloy layer
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
  • C23C28/32—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer
  • C23C28/322—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer only coatings of metal elements only
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
  • C23C28/34—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates
  • C23C28/345—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates with at least one oxide layer
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
  • C23C28/34—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates
  • C23C28/345—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates with at least one oxide layer
  • C23C28/3455—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates with at least one oxide layer with a refractory ceramic layer, e.g. refractory metal oxide, ZrO2, rare earth oxides or a thermal barrier system comprising at least one refractory oxide layer

Definitions

• the present invention is related to a steel sheet coated with an aluminium-based coating by hot dip coating.
• Aluminium-based coated steel sheets present excellent corrosion resistance, and can be used for manufacturing ' parts for power-driven ground vehicles or cladding for buildings depending on the composition of the aluminium-based coating.
• the aluminium-based coating is substantially composed of pure aluminium, as in the coated steel product Alupur ® , a thick intermediate layer of iron and aluminium is formed at the steel/aluminium interface during the coating operation. The thickness of this intermediate layer is typically 20 ⁇ m. Due to the low ductility of this thick intermediate layer of iron and aluminium, the aluminium coated steel sheet is characterized by a low formability.
• the aluminium-based coating is composed of by weight, 90 % aluminium and 10 % silicon, such as in the Alusi ® -product , a thin intermediate layer of iron, aluminium and silicon is formed at the steel/aluminium- silicon interface, which is thinner (typically up to 5 ⁇ m) compared to the intermediate layer of iron-aluminium in the case of a pure aluminium coating. Silicon is added for reasons of reaction control between iron and aluminium, thereby allowing to control (and limit) the thickness of the intermediate layer.
• the Alusi ® coating itself is on the other hand brittle and not ductile due to the presence of silicon.
• the aluminium-based coating is composed of, by weight, 55 % aluminium, 43.4 % zinc and 1.6 % silicon (Aluzinc ® )
• Aluzinc ® a thin intermediate layer of iron, aluminium, zinc and silicon is formed at the steel/aluminium-zinc-silicon coating interface, which is thinner (typically a few ⁇ m) compared to the intermediate layer of iron-aluminium interface in the case of a pure aluminium coating.
• the silicon keeps the intermediate layer under control, but the Aluzinc ® coating itself is brittle and not ductile due to the presence of silicon.
• Japanese patent 2002-226959 discloses a process for manufacturing a steel with an aluminium-based coating, produced by hot dip coating the steel sheet in an aluminium-based bath, wherein before hot dip coating, an oxide of a metal (e.g. Cr, V, Mn, Nb, W) is formed on a steel sheet, wherein said oxide can be reduced by molten aluminium.
• a metal e.g. Cr, V, Mn, Nb, W
• a layer of alumina (A1203) is thus formed on the surface of the steel sheet, and the growth of the interfacial layer composed of Fe-Al or Fe-Al-Si is controlled to a thickness of 2 ⁇ m or less. This effect is obtained because the alumina layer slows down the diffusion of iron atoms into the bath.
• This document therefore provides a method of controlling and limiting the thickness of the intermetallic Fe-Al layer without requiring the presence of silicon in the molten aluminium bath.
• dross inter-metallic compound particles
• This dross has a density lower than that of the liquid aluminium or aluminium alloy. It rises to the surface of the bath and is entrained by the steel sheet, creating surface aspect defects of the coated steel sheet.
• a part of the metal can also be incorporated in the aluminium-based coating, and modifies its characteristics . Consequently, the surface of the bath must be cleaned to remove this dross, and the bath must be often replaced in order to avoid the presence of the metal in the aluminium-based coating.
• JP2002- 226959 Another drawback of the technique of JP2002- 226959 lies in the fact that the immersion time of the sheet in the Al-based bath is determined by the time required for the reduction of the metal oxide by the molten aluminium, in order to form the layer of alumina. Long immersion times may be necessary because of this, and the process may be slowed down.
• Document JP-09053187 is related to steel sheets coated by hot dip aluminizing. According to this document, an oxide film is formed on the sheet in a heating stage.
• an oxide film of Fe and Al, or Fe, Al and one or ⁇ two kinds among Si, Mn and Mg is formed on the surface of the steel to be plated, after which an alloy plating layer of Al or Al and one or ⁇ two kinds among Si, Mn and Mg is formed on the surface.
• the present invention aims to provide a steel sheet coated with an aluminium-based coating, which overcomes the drawbacks of the prior art.
• said sheet has an excellent formability, and is free from surface aspect defects .
• the invention equally aims to provide a process for producing such a coated steel sheet by hot dip coating the steel sheet in a molten bath of aluminium or aluminium alloy having a long life service.
• the present invention is related to products and processes such as described in the appended claims .
• a metal oxide layer is applied to at least one face of a steel sheet, and an iron oxide layer is applied on top of and in contact with that metal oxide layer.
• the invention is firstly related to the steel sheet comprising the bi-layer consisting of metal oxide and iron oxide.
• the iron oxide is reduced into metallic iron during annealing prior to dipping and dissolves gradually when being immersed in the molten Al bath, while the metal oxide is stable with respect to molten aluminium. This means that the metal oxide does not or not substantially react with molten aluminium, when the steel sheet, comprising the metal oxide layer and metallic iron layer, is immersed into a bath of molten aluminium or aluminium- alloy.
• the metal oxide can be thermodynamically inert with respect to aluminium at the temperature of the molten metal bath, normally between 500 and 800 0 C.
• metal oxides which are thermodynamically inert in said temperature range are : CaO, MgO, LiO 2 , La 2 O 3 , BeO, ThO 2 , SrO, ZrO 2 .
• the metal oxide can be non- inert with respect to aluminium, but can exhibit slow kinetics in its reaction with molten aluminium, so that no substantial reaction occurs between the metal oxide and the aluminium during the time of immersion in the bath, typically a few seconds.
• the invention is equally related to a steel sheet coated with an aluminium-based coating, said coating comprising a metal oxide layer on at least one of the faces of said steel sheet, said metal oxide layer being stable (in the sense described above) with respect to molten aluminium, and in contact with said metal oxide layer an intermediate layer comprising an iron-aluminium alloy, and in contact with said intermediate layer an aluminium or aluminium-alloy layer.
• a metal oxide which is ⁇ stable with respect to molten aluminium' is defined as : x thermodynamically inert with respect to molten aluminium OR exhibiting slow kinetics in its reaction with molten aluminium, so that no substantial reaction occurs between the metal oxide and the aluminium during a brief immersion time of a few seconds, typically between 3s and 9s, in a bath comprising molten Al' , typically at a bath temperature between 500 0 C and 800 0 C. It is specifically pointed out that the scope of the invention includes metal oxides (e.g.
• N slow' is defined by the explicit reference to the time of immersion. For a given immersion time (for example 3s) , any metal oxide which does not substantially react with molten aluminium, even though it is not thermodynamically inert with respect to molten aluminium, falls within the scope of the present invention.
• the aluminium-based coating coated on a steel sheet according to the invention is essentially silicon- free (content of silicon less than 0.5% by weight), while at the same time, the thickness of the intermediate layer is preferably not more than 5 ⁇ m.
• the stable oxide layer makes it possible to control the intermediate layer to maximum 5 ⁇ m, even though no substantial Si is present in the molten Al-bath.
• a preferred embodiment of the invention therefore involves a steel sheet, with the stable metal oxide layer described above, and in contact therewith an intermediate layer of iron-aluminium alloy and in contact with said intermediate layer, a layer of substantially pure aluminium and inevitable impurities (corresponds to the Alupur ® -coating) , wherein the intermediate layer has a thickness of preferably not more than 5 ⁇ m.
• this aluminium-based coated steel sheet therefore has the advantage of having a high formability, due to a controlled thickness of the intermediate layer and due to the non- brittle behaviour of the coating itself, as a consequence of the absence of Si.
• the aluminium-alloy layer according to the invention comprises:
• the present invention in the first place provides a solution to the problem of intermediate Fe-Al layers of excessive thickness.
• this problem was solved by adding silicon to the hot dip bath, as described above.
• the present invention offers a solution to this problem, which allows to control the thickness of the intermediate layer without requiring silicon in the bath.
• This is a beneficial result of the present invention, but it must be emphasized that the absence of silicon as such is not an essential feature of the invention : the invention can be applied even with a bath comprising silicon. In the latter case, the thickness of the intermediate layer will still be controlled and limited as a consequence of the stable oxide layer and iron oxide layer, while this control/limitation may be further strenghtened by the presence of silicon in the bath.
• the invention is equally related to the preferred process of producing a coated steel sheet according to the invention, said process comprising the following steps :
• Annealing said steel sheet comprising said metal oxide and said iron oxide layers, in a reducing atmosphere so that the iron oxide is reduced into a metallic iron layer, and immersing said annealed steel sheet into a bath of molten aluminium or aluminium alloy wherein said metallic iron gradually dissolves into said bath to form said intermediate layer of iron-aluminium alloy and wherein said metal oxide layer is stable during immersion of the annealed steel sheet into said bath.
• the preferred immersion time is between 3s and 9s.
• the process of the invention is preferably a continuous process, wherein the line speed during the immersing step is situated between 80 and 120m/min.
• the metal oxide layer and the iron oxide layer can be formed by gas phase deposition.
• the gas phase deposition steps are preferably applied in a pre-he,ating zone before the annealing furnace in a hot dip processing line.
• the annealing step is performed in said annealing furnace.
• the process can thus be performed in a standard hot dip processing line, supplemented by suitable gas phase deposition, e.g. Chemical Vapour Deposition facilities before the annealing section.
• the iron oxide is reduced and forms a metallic iron layer.
• the reduction of the iron oxide is depending on the annealing temperature and the oxidation potential of the atmosphere, making a lower dew point necessary at lower temperature to completely reduce the iron oxide.
• the typical dew point range in an annealing furnace is between -40 0 C and -30 0 C.
• the typical annealing temperature is between 750 0 C and 850 0 C and the typical overageing temperature is between 400 0 C and 500 0 C.
• Iron oxide will thus always be reduced, already during the last part of the heating up to annealing temperature .
• the iron reacts with aluminium to form an intermediate layer made of iron-aluminium alloy, which is essential for a good wetting of the surface.
• the thickness of this intermediate layer is controlled by the presence of the metal oxide layer which is stable with respect to molten aluminium, and which prohibits diffusion of iron from the steel sheet into the bath.
• the thickness of the iron-oxide layer defines the thickness of the final intermediate layer of iron-aluminium. Due to the fact that the metal oxide does not substantially react with aluminium, no metal will enter the bath and form a dross after a given operation time.
• the gas phase deposition of the metal oxide layer preferably takes place at a temperature between 35O 0 C and 550 0 C.
• the thickness of the metal oxide layer in the oxide coated steel sheet (intermediate product) and in the aluminium-based coated steel sheet (final product) is preferably 5 to 1000 nm.
• the iron oxide layer in the intermediate product is preferably between 5 and lOOOnm thick.
• the molten aluminium bath comprises no or no substantial amount of silicon (preferably max. 0.5% in weight) .
• the thickness of the intermediate layer is nevertheless controlled to a low value, preferably max. 5 ⁇ m, by the above-described influence of the stable oxide layer. Therefore, when the method of the invention is applied with a molten aluminium bath consisting of pure aluminium and inevitable impurities, the result is a steel sheet with an aluminium-based coating, comprising said metal oxide layer, an intermediate layer comprising essentially aluminium and iron (e.g. a FeAl 3 layer + a Fe 2 Al 5 layer), and having a thin thickness, preferably less than 5 ⁇ m.
• the resulting aluminized steel sheet has excellent formability, due to the thin intermediate layer, while the coating has a high resistance to cracking, due to the absence of silicon.
• composition of the bath may be other than pure aluminium, e.g. comprising aluminium and zinc, but it is preferably without a deliberate addition of silicon. Silicon is therefore preferably present at impurity level, which is preferably not more than 0.5 % by weight.
• the bath comprises by weight, 42 to 46 % zinc, the complement being aluminium and inevitable impurities.
• This could be defined as the composition for obtaining an Aluzinc ® -coating, but without the 1-2% Si.
• the intermediate layer of iron-aluminium alloy comprises aluminium, zinc and iron, and its thickness is preferably less than 5 ⁇ m.
• the composition of the molten aluminium-alloy bath can still comprise silicon, e.g., the composition may be (by weight) :
• the intermediate layer of iron-aluminium alloy comprises : aluminium, iron, silicon (FeAl 3 layer + Fe 2 Al 5 layer + Al-Fe-Si ⁇ 5) , .
• the intermediate layer of iron-aluminium alloy comprises : aluminium, zinc, iron, silicon.
• the advantage of a controlled thickness of the intermediate layer is still present and may even be more pronounced due to the presence of Si, which makes it possible to obtain an intermediate layer with a thickness of max. l ⁇ m.
• the presence of Si may make the aluminium-based coating more brittle .
• the invention is equally related to the use of steel sheet according to the invention for the production of a power-driven ground vehicle and to a cladding for buildings made of a steel sheet coated with an aluminium- based coating, according to the invention.
• Both the steel sheets and the process according to the invention provide an advantage over the classic Al-based coated sheets (Alupur, Aluzinc, Alusi) and their production methods, in that sheets according to the invention allow to control the intermediate Fe-Al layer to lower thicknesses, without requiring the presence of silicon in the Al-based bath.
• the method of the present invention involves the application of a 'stable' (see definition above) metal oxide layer and of an Fe-oxide layer on said stable oxide layer.
• the intermediate product and the final product of JP2002-226959 differ from the corresponding products of the present invention.
• the intermediate product of JP-2002- 226959 comprises a metal-oxide layer, e.g.
• JP2002-226959 does not comprise a metal oxide layer anymore (this layer has been reduced to form alumina) , underneath the intermediate layer and the Al-based coating. Furthermore, the metal oxide layer produced according to JP2002-226959 is said to be reduced by molten aluminium, whereas according to the present invention, the metal oxide layer is either thermodynamically inert or exhibiting sufficiently slow kinetics in its reaction with molten aluminium, so that the metal oxide layer stays intact. It is clear that the mechanism by which JP2002-226959 controls the intermediate layer thickness is fundamentally different from the present invention.
• an alumina layer is formed, to slow down diffusion of Fe-atoms into the Al- bath.
• the present invention prohibits said diffusion by providing a metal oxide layer which does not substantially react with the Al-bath.
• the Fe-Al intermediate layer is obtained by providing an additional Fe-oxide layer on top of the stable oxide layer.
• the final product according to that document comprises an oxide film formed by heating a steel sheet (so presumably and Fe-oxide film) , an oxide film of Fe and Al or Fe, Al and another element, and an Al alloy plating layer.
• the Fe-oxide film formed by heating is not a ⁇ stable' oxide layer in the sense of the present invention, nor is an oxide film of Fe and Al equal to an intermediate Fe-Al layer.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
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• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Physics & Mathematics (AREA)
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• Ceramic Engineering (AREA)
• Coating With Molten Metal (AREA)

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• 2006
  • 2006-02-28 EP EP06447030A patent/EP1826289A1/de not_active Withdrawn
• 2007
  • 2007-02-27 EP EP07712332A patent/EP1989339A2/de not_active Withdrawn
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