EP0848076B1 - Method for hot-dip coating of a steel plate; galvanized or aluminized steel plate obtained therefrom - Google Patents

Method for hot-dip coating of a steel plate; galvanized or aluminized steel plate obtained therefrom Download PDF

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Publication number
EP0848076B1
EP0848076B1 EP97402985A EP97402985A EP0848076B1 EP 0848076 B1 EP0848076 B1 EP 0848076B1 EP 97402985 A EP97402985 A EP 97402985A EP 97402985 A EP97402985 A EP 97402985A EP 0848076 B1 EP0848076 B1 EP 0848076B1
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EP
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Prior art keywords
coating
iron
layer
sheet
metal
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EP97402985A
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German (de)
French (fr)
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EP0848076A1 (en
Inventor
Philippe Guesdon
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Sollac SA
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Sollac SA
Lorraine de Laminage Continu SA SOLLAC
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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
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/024—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by cleaning or etching
    • 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
    • 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
    • C23C2/026—Deposition of sublayers, e.g. adhesion layers or pre-applied alloying elements or corrosion protection

Definitions

  • the coating conditions in particular the recrystallization heat treatment atmosphere and the nature of the bath, are therefore best suited to the formation and wetting of a surface of pure iron.
  • the disadvantage of dipping steel sheet coating processes is that the coating conditions must be adapted to the type of steel grade to to coat, in particular according to the nature and the proportion of the elements addition it contains, to obtain a wettable surface and a coating adherent.
  • the addition, in the bath, of an alloying inhibitor such as aluminum, makes it possible to limit the interfacial layer (here: Fe 2 Al 5 ) to a very small thickness, generally less than 0.01 ⁇ m.
  • the object of the invention is, on a dip coating line, to avoid to have to significantly modify the coating conditions according to the nuances steel to be coated.
  • the object of the invention is also, in particular in the case of aluminizing, to make more resistant and / or higher-grade coatings by dipping in aluminium.
  • the function of the first sublayer is essentially a function "Barrier” or “anti-ally” between the elements of the substrate, in particular the iron, and those of the metallic coating, such as generally zinc and / or aluminum; as such, the first underlay plays a role comparable to that of silicon in an aluminum bath, or that of aluminum in a zinc bath, that is to say a role of inhibition of the alliance with the substrate.
  • this first underlay must therefore be sufficient high to form a barrier to the diffusion of the elements of the sheet metal substrate towards its surface, but must remain sufficiently small (less than or equal to 0.1 ⁇ m) to avoid risks of flaking of the coated sheet (for example flaking after folding).
  • the function of the second sublayer is essentially a function "wetting" in the coating bath; the nature of this second underlay must therefore be adapted to that of the bath; if necessary, a second function of this second sublayer is to provide a “Resource” or controlled quantity of elements of addition and of alloying coating applied by dipping.
  • this first undercoat is applied before the annealing heat treatment step, its function is also to limit diffusion towards the surface of the elements of addition of steel, where some of them may oxidize in the annealing atmosphere.
  • the continuous coating installation includes, from upstream to downstream, cleaning means, means for depositing a first undercoat thin oxide, means for depositing a second thin sublayer metal, heat treatment means, quenching means, means for wringing and regulating thickness and means for solidification.
  • the coating installation also includes means for making continuously scroll the sheet metal strip to be coated in the installation.
  • the means for depositing a first sub-layer and the means for deposition of a second sub-layer can be for example means of vacuum deposition, electrodeposition deposition means, or means chemical vapor deposition.
  • the first embodiment of the invention relates to galvanization without alloy: we will therefore use a zinc bath with aluminum additive at more than 0.15% to inhibit the iron-zinc alloy in a conventional manner.
  • Zinc-based coating called non-alloy galvanizing, the average iron content remains below about 1%, while being higher than that of iron in the bath (which is generally 0.03% in weight).
  • the sheet to be coated therefore runs through the coating installation using the scrolling means.
  • the sheet metal surface to be coated is cleaned, for example by passing through an open flame.
  • a oxide underlay of average thickness between 0.01 and 0.1 ⁇ m.
  • this underlay must be high enough to form a barrier to the diffusion of the elements of addition of the steel from the sheet to its surface, but sufficiently small (less than or equal to 0.1 ⁇ m) to avoid risks of flaking of the coated sheet (for example when bending).
  • this first sub-layer is adapted to provide one or more oxides as stable as possible under the conditions of the stages following of the process.
  • the nature of the first sub-layer is oxide of chromium (trivalent) or zirconium oxide.
  • this second sub-layer is, in the present case of non-alloy coating, adapted to provide the iron resources which will be necessary, at the time of quenching, to form a conventional inhibition layer of the Fe 2 Al 5 type. ; as this inhibition layer which forms on soaking is always very thin, a thickness of less than 0.5 ⁇ m of iron for this second sub-layer will always in practice provide a sufficient resource.
  • this second sub-layer must, conversely, remain low enough to prevent the formation of iron-zinc alloy in quantity significant, which would risk dispersing in the thickness of the coating layer and deteriorate its properties.
  • the surface obtained has good wettability thanks to the second underlay, external, of metallic iron.
  • this preliminary surface preparation is that it can be fixed thus a “universal” surface identical for all steel grades to coating in the same installation, and that we can then use the same dip coating conditions (annealing atmosphere, temperature soaking bath etc.) for all these steel grades (for one type of coating given).
  • the procedure is a conventional, known in itself: heat annealing treatment of recrystallization, quenching, spinning to regulate the thickness deposited and finally solidification of the coating.
  • the first and second sublayers have been applied before the annealing heat treatment, the first undercoat prevents the diffusion towards the surface of the elements of addition of steel and their oxidation at vicinity of this surface.
  • the first and second sub-layers after the annealing heat treatment step are advantageous because a deterioration of the "bi-layer is avoided "By heat treatment, the risk is all the greater as this" bi-layer Is thick, as is generally the case with alloy coatings described below.
  • the "barrier" function of the first undercoat makes it possible to avoid, during tempering, the formation of "outburst” (in English) or alloy growths in the substrate-coating interface.
  • the second embodiment of the invention relates to galvanization with ally; for this purpose, a zinc bath will be conventionally used aluminum additive less than 0.15% (or without aluminum); installation then comprises, downstream, conventional heat treatment means of alliance.
  • the thickness of the first sub-layer (oxide) must also be high enough to form a barrier to diffusion iron from the substrate in the coating, at processing temperatures thermal alloy (conventionally around 500 ° C in the case of zinc coatings) which are generally lower than temperatures annealing (conventionally around 800 ° C).
  • the structure of an alloyed galvanized coating is laminated in several superimposed sublayers of different iron-zinc alloy phases, richer in zinc from the surface, richer in iron from the substrate-coating interface.
  • Alloyed galvanized coating taken as a whole generally an average iron content of between 8 and 14% by weight.
  • the invention in particular to the first oxide sublayer, can now adapt in a manner known per se the conditions of the alloy heat treatment to obtain an alloyed galvanized coating whose structure is no longer stratified into several different phases of alloys iron-zinc; a coating is then obtained which no longer contains, essentially, only one alloy phase in its thickness.
  • the thickness of this layer is generally greater than 6 ⁇ m.
  • the structure of the coating layer is therefore homogeneous in its thickness ; the phase which mainly constitutes it may obviously contain impurities or inclusions.
  • alloyed galvanized sheets according to the invention have properties different depending on the nature of this phase; depending on the case, we thus obtain a very good resistance to dusting, or very good resistance to flaking, or very good hardness, or even other known properties attached to the phase considered.
  • the nature of the coating can easily be adapted galvanized alloy depending on the use of the sheet.
  • the third embodiment of the invention relates to galvanization without alloying using a zinc bath with aluminum additive at less than 0.15%, that is to say a zinc bath normally used in the prior art for the coating of zinc alloy coating.
  • the thickness of this second sublayer is less than 0.5 ⁇ m.
  • An advantage of the invention is therefore to be able to use the same types baths for non-alloy coatings and for alloy coatings.
  • the invention therefore makes it possible to facilitate the management of the metal baths of coating.
  • the fourth embodiment of the invention relates to aluminization "Without alliances": a bath will therefore be used in a conventional manner of aluminum containing more than 6% of silicon to limit the alloy at the interface steel-coating.
  • a non-alloyed aluminization is a coating based on aluminum with an average iron content of around 10%, while being higher than that of iron in the bath (which is generally around 3% in weight).
  • the sheet metal surface to be coated is cleaned and then the treatment is carried out thermal annealing, as for a conventional aluminizing operation.
  • an oxide undercoat of medium thickness is deposited between 0.01 and 0.1 ⁇ m and previously adapted to the barrier function described.
  • the nature of the first sub-layer is oxide of chromium (trivalent) or zirconium oxide.
  • the deposition means of the second sub-layer it is deposited then a sub-layer of a phase of an alloy of iron and aluminum which, at solid state, is likely to be in equilibrium with the coating bath to liquid state.
  • the parameters that define this balance and, therefore, said phase and its composition include the bath temperature during the soaking step and the composition of the bath, which in practice is saturated with iron.
  • the silicon content of the bath being greater than 6%, preferably said alloy of iron and aluminum corresponds to the so-called ⁇ 5 phase or to the so-called phase ⁇ 6 which are alloys of aluminum, iron and silicon.
  • the ⁇ 5 phase has a hexagonal structure; it is sometimes called ⁇ H or H; the iron content of this phase is generally between 29 and 36% by weight; the silicon content of this phase is generally between 6 and 12% by weight; the balance consists mainly of aluminum.
  • the ⁇ 6 phase has a monoclinic structure; it is sometimes called ⁇ or M; the iron content of this phase is generally between 26 and 29% in weight ; the silicon content of this phase is generally between 13 and 16% by weight; the balance consists mainly of aluminum.
  • this second sub-layer is, in the present case of non-alloy coating, suitable for providing good adhesion to the layer of aluminum to be applied by dipping.
  • the procedure is a classic, known in itself: soaked in the coating bath, spin to regulate the thickness deposited and finally solidification of the coating.
  • a steel sheet coated with an aluminum-silicon alloy is then obtained. comparable to those of the prior art with, at the process level, the advantages identical to those previously described, in particular those of the first embodiment.
  • the interfacial layer is considered fragile; this drawback results in the appearance of cracks in the coating when the sheet is bent; the addition of more than 6% of silicon in the bath is generally intended to limit the thickness of this interfacial layer to a value of the order of 3 ⁇ m.
  • This surface layer contains for example of the order of 3% by weight of iron, of the order of 9% by weight of silicon, the rest being essentially made of aluminum; this layer therefore generally comprises phase inclusions based on silicon or aluminum alloy, iron and silicon; it seems that the presence of these phases leads to a weakening of this surface layer and a decrease in corrosion protection.
  • the thickness of the second sub-layer according to the invention is weak, in particular less than 0.5 ⁇ m
  • a coating is obtained whose interfacial layer of iron-aluminum-silicon alloy has a thickness less than that encountered in aluminized sheets at quenched from the prior art, in particular less than 1 ⁇ m.
  • the total thickness of the metal layer is more than 6 ⁇ m.
  • the aluminum content of the surface layer depends on the content of aluminum in the coating bath; it is generally greater than 80%; it is commonly of the order of 87% by weight.
  • the average iron content of the coating (which takes into account the iron contained in the interfacial layer) is then much less than 10% in weight; it is then less than or equal to 6% by weight.
  • aluminized sheets according to the invention having the structure previously described using a bath aluminum with a silicon content of less than 6%, i.e. a bath - pondered to lead to alloyed aluminum coatings.
  • the coating bath contains little or no of an alloying inhibitor, such as silicon, a sheet coated with a aluminum-based layer with an interfacial alloy layer yet a small thickness.
  • an alloying inhibitor such as silicon
  • the two sublayers according to the invention therefore serve as an inhibitor to replace the silicon in the bath.
  • the surface layer of the coating then contains much less of inclusions of the phases mentioned above, which improves the resistance to coating cracking and corrosion protection.
  • the following example illustrates the first embodiment of the invention:
  • the first is deposited and the second vacuum sublayers by magnetron sputtering.
  • First sublayer Cr2O3 - thicknesses: a test at 30 nm and a test at 50 nm.
  • Second undercoat pure iron - thicknesses: a test at 30 nm and a test at 50 nm.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
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  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
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Abstract

Prior to top coating steel sheet by dipping in a bath of molten zinc or aluminium alloy, the sheet is cleaned, annealed and given a first coating of at least one oxide 0.01-0.1 microns thick and a second coating of an alloy containing at least 20% iron. Also claimed are steel sheets respectively dip-coated with Fe-Zn alloy or Al based alloy on top of the first and second coatings.

Description

L'invention concerne un procédé de revêtement métallique d'une tôle d'acier dans lequel :

  • on nettoie la surface de ladite tôle à revêtir,
  • on effectue un traitement thermique de recuit, notamment de recristallisation, de ladite tôle nettoyée,
  • on trempe ladite tôle traitée dans un bain liquide de métal de revêtement,
  • on extrait ensuite la tôle du bain,
  • et on solidifie la couche métallique de revêtement entraínée sur la tôle à la sortie dudit bain.
The invention relates to a method of metallic coating of a steel sheet in which:
  • the surface of said sheet to be coated is cleaned,
  • an annealing heat treatment, in particular recrystallization, of said cleaned sheet is carried out,
  • said treated sheet is dipped in a liquid coating metal bath,
  • we then extract the sheet from the bath,
  • and solidifies the metal coating layer driven on the sheet at the outlet of said bath.

Pour obtenir une forte adhérence du revêtement métallique sur la tôle d'acier, sans pour autant créer une couche importante d'alliage entre le substrat d'acier et le revêtement, il importe de préparer, avant trempé, une surface bien propre et bien mouillable, l'idéal étant réputé être une surface exempte d'oxydes, c'est à dire de fer pur dans le cas présent de tôle d'acier.To obtain a strong adhesion of the metallic coating on the sheet steel, without creating a significant layer of alloy between the steel substrate and coating, it is important to prepare, before hardening, a very clean and well wettable surface, the ideal being deemed to be a surface free of oxides, ie of pure iron in the present case of sheet steel.

D'une manière générale, les conditions de revêtement, notamment l'atmosphère de traitement thermique de recristallisation et la nature du bain, sont donc adaptées au mieux à la formation et au mouillage d'une surface de fer pur.In general, the coating conditions, in particular the recrystallization heat treatment atmosphere and the nature of the bath, are therefore best suited to the formation and wetting of a surface of pure iron.

Comme la présence d'oxydes à la surface risque de dégrader sa mouillabilité, on empêche l'apparition d'oxydes ou on les élimine généralement en effectuant le traitement thermique de recuit de recristallisation sous atmosphère non oxydante ou même réductrice.As the presence of oxides on the surface risks degrading its wettability, preventing the appearance of oxides or generally eliminating them by carrying out the heat treatment of recrystallization annealing under non-oxidizing or even reducing atmosphere.

Pour certaines nuances d'acier (acier au silicium, par exemple), cette précaution concernant l'atmosphère de recuit ne suffit malheureusement pas pour éliminer la présence d'oxydes en surface ; il faut alors modifier d'autres étapes du procédé (par exemple : créer une couche d'oxyde en profondeur au moment du nettoyage afin de bloquer la diffusion des éléments d'addition oxydables de l'acier, puis recuire sous atmosphère très réductrice pour retrouver, en extrême surface seulement, une couche de fer pur).For some steel grades (silicon steel, for example), this caution regarding the annealing atmosphere is unfortunately not enough to eliminate the presence of oxides on the surface; it is then necessary to modify others process steps (for example: creating a deep oxide layer at the cleaning time in order to block the diffusion of the addition elements oxidizable from steel, then anneal under a very reducing atmosphere to find, on the extreme surface only, a layer of pure iron).

L'inconvénient des procédés de revêtement de tôles d'acier au trempé est qu'il faut adapter les conditions de revêtement au type de nuance d'acier à revêtir, notamment en fonction de la nature et de la proportion des éléments d'addition qu'il contient, pour obtenir une surface mouillable et un revêtement adhérent. The disadvantage of dipping steel sheet coating processes is that the coating conditions must be adapted to the type of steel grade to to coat, in particular according to the nature and the proportion of the elements addition it contains, to obtain a wettable surface and a coating adherent.

Dans le bain de revêtement et à la sortie du bain, il est également très important de pouvoir bien contrôler l'alliation éventuelle, à l'interface acier-revêtement, entre le métal de revêtement et l'acier.In the coating bath and at the outlet of the bath, it is also very important to be able to properly control the possible alloying, at the steel-coating interface, between the coating metal and the steel.

Dans le cas de la galvanisation, l'addition, dans le bain, d'un inhibiteur d'alliation comme l'aluminium, permet de limiter la couche interfaciale (ici : Fe2Al5) à une épaisseur très faible, généralement inférieure à 0,01 µm.In the case of galvanization, the addition, in the bath, of an alloying inhibitor such as aluminum, makes it possible to limit the interfacial layer (here: Fe 2 Al 5 ) to a very small thickness, generally less than 0.01 µm.

Dans le cas de l'aluminiage, il faut rajouter dans le bain des quantités importantes de silicium pour limiter l'épaisseur de la couche interfaciale d'alliage Fe, Al, Si dont l'épaisseur reste cependant de l'ordre de 3 à 6 µm.In the case of aluminizing, it is necessary to add in the bath quantities important silicon to limit the thickness of the interfacial layer of Fe, Al, Si alloy, the thickness of which however remains of the order of 3 to 6 μm.

On obtient dans ce cas, non pas un revêtement d'aluminium, mais un revêtement d'alliage aluminium-silicium.In this case, we obtain not an aluminum coating, but a aluminum-silicon alloy coating.

Une telle couche interfaciale, entre le substrat d'acier et le revêtement d'alliage aluminium-silicium, fragilise fortement le revêtement obtenu.Such an interfacial layer, between the steel substrate and the coating of aluminum-silicon alloy, greatly weakens the coating obtained.

L'invention a pour but, sur une ligne de revêtement au trempé, d'éviter d'avoir à modifier sensiblement les conditions de revêtement selon les nuances d'acier à revêtir.The object of the invention is, on a dip coating line, to avoid to have to significantly modify the coating conditions according to the nuances steel to be coated.

L'invention a également pour but, notamment dans le cas de l'aluminiage, de réaliser au trempé des revêtements plus résistants et/ou à plus forte teneur en aluminium.The object of the invention is also, in particular in the case of aluminizing, to make more resistant and / or higher-grade coatings by dipping in aluminium.

L'invention a pour objet un procédé du type précité caractérisé en ce que, après l'étape de nettoyage et avant l'étape de trempé :

  • on applique sur ladite surface une première sous-couche à base d'au moins un oxyde d'épaisseur moyenne comprise entre 0,01 et 0,1 µm,
  • et on applique ensuite, sur ladite première sous-couche, une deuxième sous-couche métallique contenant au moins 20% en poids de fer.
The subject of the invention is a method of the aforementioned type characterized in that, after the cleaning step and before the quenching step:
  • a first undercoat based on at least one oxide with an average thickness of between 0.01 and 0.1 μm is applied to said surface,
  • and then a second metal sublayer containing at least 20% by weight of iron is applied to said first sub-layer.

Grâce à cette préparation dans laquelle on applique les deux sous-couches, on obtient ainsi une surface « universelle » prête au trempé.Thanks to this preparation in which the two sub-layers are applied, this gives a "universal" surface ready for soaking.

La fonction de la première sous-couche est essentiellement une fonction « barrière » ou « anti-alliation» entre les éléments du substrat, notamment le fer, et ceux du revêtement métallique, comme généralement le zinc et/ou l'aluminium ; à ce titre, la première sous-couche joue un rôle comparable à celui de silicium dans un bain d'aluminium, ou à celui de l'aluminium dans un bain de zinc, c'est à dire un rôle d'inhibition de l'alliation avec le substrat.The function of the first sublayer is essentially a function "Barrier" or "anti-ally" between the elements of the substrate, in particular the iron, and those of the metallic coating, such as generally zinc and / or aluminum; as such, the first underlay plays a role comparable to that of silicon in an aluminum bath, or that of aluminum in a zinc bath, that is to say a role of inhibition of the alliance with the substrate.

L'épaisseur de cette première sous-couche doit donc être suffisamment élevée pour former barrière à la diffusion des éléments du substrat de la tôle vers sa surface, mais doit rester suffisamment faible (inférieure ou égale à 0,1 µm) pour éviter des risques d'écaillage de la tôle revêtue (par exemple écaillage après pliage). The thickness of this first underlay must therefore be sufficient high to form a barrier to the diffusion of the elements of the sheet metal substrate towards its surface, but must remain sufficiently small (less than or equal to 0.1 µm) to avoid risks of flaking of the coated sheet (for example flaking after folding).

La fonction de la deuxième sous-couche est essentiellement une fonction de « mouillage » dans le bain de revêtement ; la nature de cette deuxième sous-couche doit donc être adaptée à celle du bain ; le cas échéant, une deuxième fonction de cette deuxième sous-couche est de fournir une « ressource » ou quantité contrôlée en éléments d'addition et d'alliation au revêtement appliqué au trempé.The function of the second sublayer is essentially a function "wetting" in the coating bath; the nature of this second underlay must therefore be adapted to that of the bath; if necessary, a second function of this second sublayer is to provide a “Resource” or controlled quantity of elements of addition and of alloying coating applied by dipping.

Dans le cas particulier où cette première sous-couche est appliquée avant l'étape de traitement thermique de recuit, sa fonction est également de limiter la diffusion vers la surface des éléments d'addition de l'acier, où certains d'entre eux risquent de s'oxyder dans l'atmosphère de recuit.In the particular case where this first undercoat is applied before the annealing heat treatment step, its function is also to limit diffusion towards the surface of the elements of addition of steel, where some of them may oxidize in the annealing atmosphere.

L'invention peut également présenter une ou plusieurs des caractéristiques suivantes :

  • ladite première sous-couche et ladite deuxième sous-couche sont appliquées après l'étape de recuit.
The invention may also have one or more of the following characteristics:
  • said first sublayer and said second sublayer are applied after the annealing step.

Cette disposition permet de limiter les risques de détérioration des deux sous-couches appliquées : par oxydation au recuit dans le cas d'une deuxième sous-couche contenant de l'aluminium, ou par suite des contraintes thermiques qui se développent lors du recuit, notamment lorsque ces sous-couches sont plus épaisses (cas des revêtements alliés par exemple).

  • ledit acier est un acier allié ou microallié contenant des éléments d'addition oxydables dans les conditions dudit traitement thermique de recuit, notamment du silicium.
This arrangement makes it possible to limit the risks of deterioration of the two sublayers applied: by oxidation during annealing in the case of a second sublayer containing aluminum, or as a result of thermal stresses which develop during annealing, in particular when these sub-layers are thicker (case of alloy coatings for example).
  • said steel is an alloyed or microalloyed steel containing oxidizable addition elements under the conditions of said annealing heat treatment, in particular silicon.

Comme exemple d'éléments d'addition qui peuvent être oxydables dans ces conditions, on trouve : Si, Mn, Cr, Al, Ti, Nb, B, Mo, Mg, V, Sb, Cu ; dans les aciers alliés ou microalliés, la teneur totale de ces éléments dépasse 0,1% en poids.As an example of addition elements which can be oxidizable in these conditions, we find: Si, Mn, Cr, Al, Ti, Nb, B, Mo, Mg, V, Sb, Cu; in alloyed or microalloyed steels, the total content of these elements exceeds 0.1% in weight.

Lors d'un traitement thermique de recuit, il est connu que ces éléments, lorsqu'ils ne sont pas combinés et stabilisés, diffusent vers la surface où ils peuvent être susceptibles de s'oxyder ; cette surface oxydée nuit ensuite à la mouillabilité dans le bain de revêtement ; l'application des première et deuxième sous-couche selon l'invention empêche ces inconvénients.During an annealing heat treatment, it is known that these elements, when not combined and stabilized, diffuse to the surface where they may be liable to oxidize; this oxidized surface then harms the wettability in the coating bath; the application of the first and second sub-layer according to the invention prevents these drawbacks.

Des caractéristiques additionnelles du procédé selon l'invention font l'objet des revendications 4 à 12.Additional features of the process according to the invention make the subject of claims 4 to 12.

L'invention a également pour objet des tôles d'acier susceptibles d'être obtenues par le procédé selon l'invention :

  • tôle revêtue d'une couche métallique à base d'alliage de fer et de zinc appliquée au trempé caractérisée en ce que ladite couche est homogène en épaisseur et est principalement constituée d'une seule phase d'alliage fer-zinc.
  • tôle revêtue d'une couche métallique à base d'aluminium appliquée au trempé, ladite couche étant stratifiée et comprenant une couche interfaciale composée essentiellement d'un ou plusieurs alliages à base de fer et aluminium, caractérisée en ce que l'épaisseur de ladite couche interfaciale est inférieure à 1 µm ; de préférence, la couche stratifiée comprend également une couche superficielle dont la teneur en aluminium est supérieure ou égale à 90%.
The subject of the invention is also steel sheets capable of being obtained by the process according to the invention:
  • sheet coated with a metallic layer based on an iron and zinc alloy applied by quenching, characterized in that said layer is homogeneous in thickness and mainly consists of a single phase of iron-zinc alloy.
  • sheet coated with a metallic layer based on aluminum applied by dipping, said layer being laminated and comprising an interfacial layer composed essentially of one or more alloys based on iron and aluminum, characterized in that the thickness of said layer interfacial is less than 1 µm; preferably, the laminated layer also comprises a surface layer whose aluminum content is greater than or equal to 90%.

Des caractéristiques additionnelles des tôles selon l'invention font l'objet des revendications 16 à 17.Additional characteristics of the sheets according to the invention are the subject from claims 16 to 17.

L'invention sera mieux comprise à la lecture de la description qui va suivre, donnée à titre d'exemple non limitatif dans le cas du revêtement en continu d'une bande de tôle d'acier.The invention will be better understood on reading the description which will follow, given by way of nonlimiting example in the case of the coating in continuous strip of steel sheet.

L'installation de revêtement en continu comprend, de l'amont vers l'aval, des moyens de nettoyage, des moyens de dépôt d'une première sous-couche mince d'oxyde, des moyens de dépôt d'une deuxième sous-couche mince métallique, des moyens de traitement thermique, des moyens de trempage, des moyens d'essorage et de régulation d'épaisseur et des moyens de solidification.The continuous coating installation includes, from upstream to downstream, cleaning means, means for depositing a first undercoat thin oxide, means for depositing a second thin sublayer metal, heat treatment means, quenching means, means for wringing and regulating thickness and means for solidification.

Dès le début du traitement thermique de recuit de recristallisation jusqu'à la solidification de la couche de revêtement, on prévoit également des moyens de contrôle de l'atmosphère dans laquelle défile la tôle à revêtir.From the start of the recrystallization annealing heat treatment until solidification of the coating layer, means are also provided control of the atmosphere in which the sheet to be coated runs.

L'installation de revêtement comprend également des moyens pour faire défiler en continu la bande de tôle à revêtir dans l'installation.The coating installation also includes means for making continuously scroll the sheet metal strip to be coated in the installation.

Tous les moyens de l'installation sont connus en eux-mêmes et ne seront donc pas décrits ici en détail.All means of installation are known in themselves and will not be therefore not described here in detail.

Les moyens de dépôt d'une première sous-couche et les moyens de dépôt d'une deuxième sous-couche peuvent être par exemple des moyens de dépôt sous vide, des moyens de dépôt par électrodéposition, ou des moyens de dépôt chimique en phase vapeur.The means for depositing a first sub-layer and the means for deposition of a second sub-layer can be for example means of vacuum deposition, electrodeposition deposition means, or means chemical vapor deposition.

On va maintenant décrire la mise en oeuvre du procédé selon l'invention dans cette installation pour revêtir une bande de tôle en acier, par exemple un acier IF-Ti (Interstitial Free, c'est à dire sans interstitiel au titane) ou un acier au silicium.We will now describe the implementation of the method according to the invention in this installation for coating a strip of steel sheet, for example a IF-Ti steel (Interstitial Free, i.e. without interstitial to titanium) or steel silicon.

Le premier mode de réalisation de l'invention concerne la galvanisation sans alliation : on utilisera donc un bain de zinc additivé d'aluminium à plus de 0,15 % pour inhiber l'alliation fer-zinc d'une manière classique.The first embodiment of the invention relates to galvanization without alloy: we will therefore use a zinc bath with aluminum additive at more than 0.15% to inhibit the iron-zinc alloy in a conventional manner.

On appelle galvanisation sans alliation un revêtement à base de zinc dont la teneur moyenne en fer reste inférieure à environ 1%, tout en étant supérieure à celle du fer dans le bain (qui est généralement de 0,03% en poids).Zinc-based coating, called non-alloy galvanizing, the average iron content remains below about 1%, while being higher than that of iron in the bath (which is generally 0.03% in weight).

La tôle à revêtir défile donc dans l'installation de revêtement à l'aide des moyens de défilement.The sheet to be coated therefore runs through the coating installation using the scrolling means.

A l'aide des moyens de nettoyage, on nettoie la surface de tôle à revêtir, par exemple par passage à la flamme nue.Using the cleaning means, the sheet metal surface to be coated is cleaned, for example by passing through an open flame.

A l'aide des moyens de dépôt de la première sous-couche, on dépose une sous-couche d'oxyde d'épaisseur moyenne comprise entre 0,01 et 0,1 µm.Using the means for depositing the first sub-layer, a oxide underlay of average thickness between 0.01 and 0.1 µm.

L'épaisseur de cette sous-couche doit être suffisamment élevée pour former barrière à la diffusion des éléments d'addition de l'acier de la tôle vers sa surface, mais suffisamment faible (inférieure ou égale à 0,1 µm) pour éviter des risques d'écaillage de la tôle revêtue (par exemple au pliage).The thickness of this underlay must be high enough to form a barrier to the diffusion of the elements of addition of the steel from the sheet to its surface, but sufficiently small (less than or equal to 0.1 µm) to avoid risks of flaking of the coated sheet (for example when bending).

Après ce premier dépôt, on peut effectuer un traitement thermique destiné à stabiliser ladite première sous-couche, à savoir, notamment, obtenir un oxyde qui ne risque plus de se transformer dans les étapes suivantes du procédé.After this first deposit, a heat treatment intended for stabilizing said first sub-layer, namely, in particular, obtaining an oxide which no longer risks being transformed in the following stages of the process.

La nature de cette première sous-couche est adaptée pour fournir un ou des oxydes aussi stables que possible dans les conditions des étapes suivantes du procédé.The nature of this first sub-layer is adapted to provide one or more oxides as stable as possible under the conditions of the stages following of the process.

De préférence, la nature de la première sous-couche est de l'oxyde de chrome (trivalent) ou de l'oxyde de zirconium.Preferably, the nature of the first sub-layer is oxide of chromium (trivalent) or zirconium oxide.

A l'aide des moyens de dépôt de la seconde sous-couche, on dépose ensuite une sous-couche de fer métallique.Using the deposition means of the second sub-layer, it is deposited then a metallic iron underlay.

L'épaisseur de cette deuxième sous-couche est, dans le cas présent de revêtement non allié, adaptée pour offrir les ressources en fer qui seront nécessaires, au moment du trempé, pour former une couche classique d'inhibition de type Fe2Al5 ; comme cette couche d'inhibition qui se forme au trempé est toujours très mince, une épaisseur de moins de 0,5 µm de fer pour cette deuxième sous-couche offrira toujours en pratique une ressource suffisante.The thickness of this second sub-layer is, in the present case of non-alloy coating, adapted to provide the iron resources which will be necessary, at the time of quenching, to form a conventional inhibition layer of the Fe 2 Al 5 type. ; as this inhibition layer which forms on soaking is always very thin, a thickness of less than 0.5 μm of iron for this second sub-layer will always in practice provide a sufficient resource.

L'épaisseur de cette deuxième sous-couche doit, à l'inverse, rester suffisamment faible pour éviter la formation d'alliage fer-zinc en quantité significative, qui risquerait d'ailleurs de se disperser dans l'épaisseur de la couche de revêtement et d'en détériorer les propriétés.The thickness of this second sub-layer must, conversely, remain low enough to prevent the formation of iron-zinc alloy in quantity significant, which would risk dispersing in the thickness of the coating layer and deteriorate its properties.

On obtient alors une surface prête au revêtement au trempé à proprement parler, la tôle étant à ce stade revêtue de deux sous-couches superposées, une sous-couche d'oxyde recouverte d'une sous-couche de fer métallique.We then obtain a surface ready for coating by properly soaking speak, the sheet being at this stage coated with two superimposed sub-layers, an oxide sublayer covered with a metallic iron sublayer.

La surface obtenue présente une bonne mouillabilité grâce à la deuxième sous-couche, externe, de fer métallique. The surface obtained has good wettability thanks to the second underlay, external, of metallic iron.

L'avantage de cette préparation de surface préalable est qu'on peut fixer ainsi une surface « universelle » identique pour toutes les nuances d'acier à revêtir dans la même installation, et qu'on peut alors utiliser les mêmes conditions de revêtement au trempé (atmosphère du recuit, température du bain de trempage etc.) pour toutes ces nuances d'acier (pour un type de revêtement donné).The advantage of this preliminary surface preparation is that it can be fixed thus a “universal” surface identical for all steel grades to coating in the same installation, and that we can then use the same dip coating conditions (annealing atmosphere, temperature soaking bath etc.) for all these steel grades (for one type of coating given).

Pour la suite du procédé selon l'invention, on procède d'une manière classique, connue en elle-même : traitement thermique de recuit de recristallisation, trempé, essorage pour réguler l'épaisseur déposée et enfin solidification du revêtement.For the remainder of the method according to the invention, the procedure is a conventional, known in itself: heat annealing treatment of recrystallization, quenching, spinning to regulate the thickness deposited and finally solidification of the coating.

Ainsi, grâce à la préparation de surface qui consiste à déposer deux sous-couches au préalable sur la tôle nettoyée on parvient, sur une même installation, à revêtir des tôles d'acier de nuances différentes dans les mêmes conditions, ce qui simplifie considérablement l'exploitation des installations de revêtement et permet d'améliorer sensiblement leur productivité.Thus, thanks to the surface preparation which consists in depositing two undercoats beforehand on the cleaned sheet we arrive, on the same installation, to coat steel sheets of different grades in the same conditions, which considerably simplifies the operation of coating and significantly improves their productivity.

Comme ici, les première et deuxième sous-couches ont été appliquées avant le traitement thermique de recuit, la première sous-couche empêche la diffusion vers la surface des éléments d'addition de l'acier et leur oxydation au voisinage de cette surface.As here, the first and second sublayers have been applied before the annealing heat treatment, the first undercoat prevents the diffusion towards the surface of the elements of addition of steel and their oxidation at vicinity of this surface.

Selon une variante de l'invention, on peut appliquer les première et deuxième sous-couches après l'étape de traitement thermique de recuit ; cette disposition est avantageuse parce qu'on évite une détérioration du « bi-couche » par le traitement thermique, risque d'autant plus grand que ce « bi-couche » est épais comme, généralement, dans le cas des revêtement alliés décrits ci-après.According to a variant of the invention, the first and second sub-layers after the annealing heat treatment step; this arrangement is advantageous because a deterioration of the "bi-layer is avoided "By heat treatment, the risk is all the greater as this" bi-layer Is thick, as is generally the case with alloy coatings described below.

Dans le cas des revêtements alliés, la fonction « barrière » de la première sous-couche permet d'éviter, au moment du trempé, la formation « d'outburst » (en langue anglaise) ou d'excroissances d'alliage dans l'interface substrat-revêtement.In the case of alloy coatings, the "barrier" function of the first undercoat makes it possible to avoid, during tempering, the formation of "outburst" (in English) or alloy growths in the substrate-coating interface.

Le deuxième mode de réalisation de l'invention concerne la galvanisation avec alliation ; à cet effet, on utilisera d'une manière classique un bain de zinc additivé d'aluminium à moins de 0,15 % (ou sans aluminium) ; l'installation comporte alors, en aval, des moyens classiques de traitement thermique d'alliation.The second embodiment of the invention relates to galvanization with ally; for this purpose, a zinc bath will be conventionally used aluminum additive less than 0.15% (or without aluminum); installation then comprises, downstream, conventional heat treatment means of alliance.

On met alors en oeuvre le procédé selon l'invention comme dans le premier mode de réalisation précédemment décrit à la différence près que :

  • on applique la première sous-couche et la deuxième sous-couche après le traitement thermique de recuit ;
  • l'épaisseur de la deuxième sous-couche (de fer métallique) est, dans le cas présent de revêtement allié, adaptée pour offrir la ressource ou quantité de fer nécessaire pour l'alliation de la couche de revêtement ; l'épaisseur de cette sous-couche est alors fonction de l'épaisseur de revêtement et du taux d'alliation visés ;
  • directement après essorage de la tôle, on la traite thermiquement dans des conditions adaptées de manière à obtenir l'alliation du fer contenu dans la deuxième sous-couche avec le métal du revêtement entraíné après trempé.
The method according to the invention is then implemented as in the first embodiment described above, with the difference that:
  • the first undercoat and the second undercoat are applied after the annealing heat treatment;
  • the thickness of the second sub-layer (of metallic iron) is, in the present case of alloy coating, adapted to provide the resource or quantity of iron necessary for the alloying of the coating layer; the thickness of this sub-layer is then a function of the coating thickness and the targeted alloying rate;
  • directly after wringing of the sheet, it is heat treated under suitable conditions so as to obtain the alloy of the iron contained in the second sub-layer with the metal of the coating driven after quenching.

Selon ce mode de réalisation, l'épaisseur de la première sous-couche (d'oxyde) doit être aussi suffisamment élevée pour former barrière à la diffusion du fer du substrat dans le revêtement, aux températures du traitement thermique d'alliation (classiquement de l'ordre de 500°C dans le cas des revêtements à base de zinc) qui sont en général inférieures aux températures de recuit (classiquement de l'ordre de 800°C).According to this embodiment, the thickness of the first sub-layer (oxide) must also be high enough to form a barrier to diffusion iron from the substrate in the coating, at processing temperatures thermal alloy (conventionally around 500 ° C in the case of zinc coatings) which are generally lower than temperatures annealing (conventionally around 800 ° C).

Grâce à la sous-couche de fer, on peut contrôler avec une grande précision la quantité totale de fer dans le revêtement allié, toujours indépendamment de la nuance d'acier de la tôle à revêtir.Thanks to the iron underlay, we can control with great precision the total amount of iron in the alloy coating, always regardless of the steel grade of the sheet to be coated.

On voit donc que la facilité d'exploitation déjà mentionnée pour l'installation de revêtement non allié vaut également pour une installation de revêtement allié.We therefore see that the ease of operation already mentioned for the installation of non-alloy coating also applies to an installation of alloy coating.

Classiquement, la structure d'un revêtement galvanisé allié est stratifiée en plusieurs sous-couches superposées de phases différentes d'alliage fer-zinc, plus riches en zinc auprès de la surface, plus riches en fer auprès de l'interface substrat-revêtement.Conventionally, the structure of an alloyed galvanized coating is laminated in several superimposed sublayers of different iron-zinc alloy phases, richer in zinc from the surface, richer in iron from the substrate-coating interface.

Un revêtement galvanisé allié pris dans son ensemble présente généralement une teneur moyenne en fer comprise entre 8 et 14% en poids.Alloyed galvanized coating taken as a whole generally an average iron content of between 8 and 14% by weight.

Du substrat vers la surface, on peut ainsi trouver les sous-couches suivantes : une phase gamma (Γ), plusieurs phases delta (δ dite « compacte » et δ), une phase dzéta (ζ).From the substrate to the surface, we can thus find the sub-layers following: a gamma phase (Γ), several delta phases (δ called “compact”) and δ), a dzeta phase (ζ).

Si l'alliation est incomplète, on trouve encore, en surface, de la phase éta (η) correspondant à du revêtement initial de galvanisation non allié au fer.If the alloy is incomplete, we still find, on the surface, the eta phase (η) corresponding to the initial coating of galvanization not alloyed with iron.

Grâce à l'invention, notamment à la première sous-couche d'oxyde, on peut maintenant adapter d'une manière connue en elle-même les conditions du traitement thermique d'alliation de façon à obtenir un revêtement galvanisé allié dont la structure n'est plus stratifiée en plusieurs phases différentes d'alliages fer-zinc ; on obtient alors un revêtement ne contenant plus, essentiellement, qu'une seule phase d'alliage dans son épaisseur. Thanks to the invention, in particular to the first oxide sublayer, can now adapt in a manner known per se the conditions of the alloy heat treatment to obtain an alloyed galvanized coating whose structure is no longer stratified into several different phases of alloys iron-zinc; a coating is then obtained which no longer contains, essentially, only one alloy phase in its thickness.

La tôle obtenue présente alors la structure suivante, en partant du substrat d'acier :

  • une sous-couche à base d'au moins un oxyde qui est intercalée entre le substrat d'acier et ladite couche de revêtement et dont l'épaisseur moyenne est comprise entre 0,01 et 0,1 µm ;
  • une couche de revêtement d'une phase d'alliage fer-zinc, telle qu'une phase Γ, δ ou ζ.
The sheet obtained then has the following structure, starting from the steel substrate:
  • an undercoat based on at least one oxide which is interposed between the steel substrate and said coating layer and whose average thickness is between 0.01 and 0.1 μm;
  • a coating layer of an iron-zinc alloy phase, such as a Γ, δ or ζ phase.

L'épaisseur de cette couche est en général supérieure à 6 µm.The thickness of this layer is generally greater than 6 µm.

La structure de la couche de revêtement est donc homogène dans son épaisseur ; la phase qui la constitue principalement peut évidement contenir des impuretés ou inclusions.The structure of the coating layer is therefore homogeneous in its thickness ; the phase which mainly constitutes it may obviously contain impurities or inclusions.

Ces tôles galvanisées alliées selon l'invention présentent des propriétés différentes selon la nature de cette phase ; selon les cas, on obtient ainsi une très bonne résistance au poudrage, ou une très bonne résistance à l'écaillage, ou une très bonne dureté, voire d'autres propriétés connues attachées à la phase considérée.These alloyed galvanized sheets according to the invention have properties different depending on the nature of this phase; depending on the case, we thus obtain a very good resistance to dusting, or very good resistance to flaking, or very good hardness, or even other known properties attached to the phase considered.

Grâce à l'invention, on peut facilement adapter la nature du revêtement galvanisé allié en fonction de l'utilisation de la tôle.Thanks to the invention, the nature of the coating can easily be adapted galvanized alloy depending on the use of the sheet.

Le troisième mode de réalisation de l'invention concerne la galvanisation sans alliation à l'aide d'un bain de zinc additivé d'aluminium à moins de 0,15 %, c'est à dire d'un bain de zinc normalement utilisé dans l'art antérieur pour la préparation de revêtement de zinc allié.The third embodiment of the invention relates to galvanization without alloying using a zinc bath with aluminum additive at less than 0.15%, that is to say a zinc bath normally used in the prior art for the coating of zinc alloy coating.

En procédant (à cette différence près) comme dans le premier mode de réalisation, on parvient, avec le même bain que pour réaliser des revêtement alliés, à un revêtement non allié comme dans le premier mode de réalisation de l'invention.By proceeding (except for this difference) as in the first mode of realization, we arrive, with the same bath as to realize coatings alloyed, to a non-alloyed coating as in the first embodiment of the invention.

De préférence, pour limiter les risques d'alliation avec du fer de la deuxième sous-couche, l'épaisseur de cette deuxième sous-couche est inférieure à 0,5 µm.Preferably, to limit the risk of alloying with iron of the second sublayer, the thickness of this second sublayer is less than 0.5 µm.

Un avantage de l'invention est donc de pouvoir utiliser les mêmes types de bains pour des revêtement non alliés et pour des revêtements alliés.An advantage of the invention is therefore to be able to use the same types baths for non-alloy coatings and for alloy coatings.

L'invention permet donc de faciliter la gestion des bains métalliques de revêtement.The invention therefore makes it possible to facilitate the management of the metal baths of coating.

Le quatrième mode de réalisation de l'invention concerne l'aluminisation « sans alliation » : on utilisera donc d'une manière classique un bain d'aluminium contenant plus de 6% de silicium pour limiter l'alliation à l'interface acier-revêtement. The fourth embodiment of the invention relates to aluminization "Without alliances": a bath will therefore be used in a conventional manner of aluminum containing more than 6% of silicon to limit the alloy at the interface steel-coating.

On appelle aluminisation « sans alliation » un revêtement à base d'aluminium dont la teneur moyenne en fer est de l'ordre de 10%, tout en étant supérieure à celle du fer dans le bain (qui est généralement de l'ordre de 3% en poids).A non-alloyed aluminization is a coating based on aluminum with an average iron content of around 10%, while being higher than that of iron in the bath (which is generally around 3% in weight).

Il s'agit donc ici d'un revêtement considéré comme « non allié » au fer.This is therefore a coating considered to be “not alloyed” with iron.

On nettoie la surface de tôle à revêtir puis on effectue le traitement thermique de recuit, comme pour une opération classique d'aluminiage.The sheet metal surface to be coated is cleaned and then the treatment is carried out thermal annealing, as for a conventional aluminizing operation.

Comme précédemment, à l'aide des moyens de dépôt de la première sous-couche, on dépose une sous-couche d'oxyde d'épaisseur moyenne comprise entre 0,01 et 0,1 µm et adaptée à la fonction barrière précédemment décrite.As before, using the means of filing the first undercoat, an oxide undercoat of medium thickness is deposited between 0.01 and 0.1 µm and previously adapted to the barrier function described.

De préférence, la nature de la première sous-couche est de l'oxyde de chrome (trivalent) ou de l'oxyde de zirconium.Preferably, the nature of the first sub-layer is oxide of chromium (trivalent) or zirconium oxide.

A l'aide des moyens de dépôt de la seconde sous-couche, on dépose ensuite une sous-couche d'une phase d'un alliage de fer et d'aluminium qui, à l'état solide, est susceptible d'être en équilibre avec le bain de revêtement à l'état liquide.Using the deposition means of the second sub-layer, it is deposited then a sub-layer of a phase of an alloy of iron and aluminum which, at solid state, is likely to be in equilibrium with the coating bath to liquid state.

Les paramètres qui définissent cet équilibre et, donc, ladite phase et sa composition, comprennent la température du bain pendant l'étape de trempé et la composition du bain, qui, en pratique, est saturé en fer.The parameters that define this balance and, therefore, said phase and its composition, include the bath temperature during the soaking step and the composition of the bath, which in practice is saturated with iron.

Comme cette phase est en équilibre avec le bain, elle ne se dissout pas significativement dans le bain au moment du trempé.As this phase is in equilibrium with the bath, it does not dissolve significantly in the bath at the time of soaking.

La teneur en silicium du bain étant supérieure à 6%, de préférence ledit alliage de fer et d'aluminium correspond à la phase dite τ5 ou à la phase dite τ6 qui sont des alliages d'aluminium, de fer et de silicium.The silicon content of the bath being greater than 6%, preferably said alloy of iron and aluminum corresponds to the so-called τ5 phase or to the so-called phase τ6 which are alloys of aluminum, iron and silicon.

La phase τ5 a une structure hexagonale ; elle est parfois appelée αH ou H ; la teneur en fer de cette phase est généralement comprise entre 29 et 36% en poids ; la teneur en silicium de cette phase est généralement comprise entre 6 et 12% en poids ; le solde se compose essentiellement d'aluminium.The τ5 phase has a hexagonal structure; it is sometimes called α H or H; the iron content of this phase is generally between 29 and 36% by weight; the silicon content of this phase is generally between 6 and 12% by weight; the balance consists mainly of aluminum.

La phase τ6 a une structure monoclinique ; elle est parfois appelée β ou M ; la teneur en fer de cette phase est généralement comprise entre 26 et 29% en poids ; la teneur en silicium de cette phase est généralement comprise entre 13 et 16% en poids ; le solde se compose essentiellement d'aluminium.The τ6 phase has a monoclinic structure; it is sometimes called β or M; the iron content of this phase is generally between 26 and 29% in weight ; the silicon content of this phase is generally between 13 and 16% by weight; the balance consists mainly of aluminum.

L'épaisseur de cette deuxième sous-couche est, dans le cas présent de revêtement non allié, adaptée pour offrir une bonne adhérence à la couche d'aluminium à appliquer au trempé.The thickness of this second sub-layer is, in the present case of non-alloy coating, suitable for providing good adhesion to the layer of aluminum to be applied by dipping.

On obtient alors une surface prête au revêtement au trempé à proprement parler, la tôle étant à ce stade revêtue de deux sous-couches superposées, une sous-couche d'oxyde recouverte d'une sous-couche métallique contenant du fer.We then obtain a surface ready for coating by properly soaking speak, the sheet being at this stage coated with two superimposed sub-layers, an oxide undercoat covered with a metal undercoat containing iron.

Pour la suite du procédé selon l'invention, on procède d'une manière classique, connue en elle-même : trempé dans le bain de revêtement, essorage pour réguler l'épaisseur déposée et enfin solidification du revêtement.For the remainder of the method according to the invention, the procedure is a classic, known in itself: soaked in the coating bath, spin to regulate the thickness deposited and finally solidification of the coating.

On obtient alors une tôle d'acier revêtue d'un alliage aluminium-silicium comparable à ceux de l'art antérieur avec, au niveau du procédé, les avantages identiques à ceux précédemment décrits, notamment à ceux du premier mode de réalisation.A steel sheet coated with an aluminum-silicon alloy is then obtained. comparable to those of the prior art with, at the process level, the advantages identical to those previously described, in particular those of the first embodiment.

La tôle aluminiée obtenue peut être identique aux tôles aluminiées, c'est à dire que la couche de revêtement comporte aux moins deux strates :

  • une couche interfaciale d'alliage d'aluminium, de fer et de silicium, se présentant par exemple sous forme de phases τ5 et/ou τ6.
  • une couche superficielle présentant une composition proche de celle du bain, dont l'épaisseur est généralement sensiblement supérieure à celle de la couche interfaciale.
The aluminized sheet obtained can be identical to the aluminized sheet, that is to say that the coating layer comprises at least two layers:
  • an interfacial layer of aluminum, iron and silicon alloy, for example in the form of τ5 and / or τ6 phases.
  • a surface layer having a composition close to that of the bath, the thickness of which is generally substantially greater than that of the interfacial layer.

La couche interfaciale est réputée fragile ; cet inconvénient se traduit par l'apparition de fissures dans le revêtement lorsqu'on plie la tôle ; l'addition de plus de 6% de silicium dans le bain a généralement pour but de limiter l'épaisseur de cette couche interfaciale à une valeur de l'ordre de 3 µm.The interfacial layer is considered fragile; this drawback results in the appearance of cracks in the coating when the sheet is bent; the addition of more than 6% of silicon in the bath is generally intended to limit the thickness of this interfacial layer to a value of the order of 3 μm.

Cette couche superficielle contient par exemple de l'ordre de 3% en poids de fer, de l'ordre de 9% en poids de silicium, le reste étant essentiellement constitué d'aluminium ; cette couche comprend donc généralement des inclusions de phases à base de silicium ou d'alliage d'aluminium, de fer et de silicium ; il semble que la présence de ces phases entraíne un fragilisation de cette couche superficielle et une diminution de la protection contre la corrosion.This surface layer contains for example of the order of 3% by weight of iron, of the order of 9% by weight of silicon, the rest being essentially made of aluminum; this layer therefore generally comprises phase inclusions based on silicon or aluminum alloy, iron and silicon; it seems that the presence of these phases leads to a weakening of this surface layer and a decrease in corrosion protection.

Avantageusement, lorsque l'épaisseur de la deuxième sous-couche selon l'invention est faible, notamment inférieure à 0,5 µm, on obtient un revêtement dont la couche interfaciale d'alliage fer-aluminium-silicium présente une épaisseur inférieure à celle que l'on rencontre dans les tôles aluminiées au trempé de l'art antérieur, notamment inférieure à 1 µm.Advantageously, when the thickness of the second sub-layer according to the invention is weak, in particular less than 0.5 μm, a coating is obtained whose interfacial layer of iron-aluminum-silicon alloy has a thickness less than that encountered in aluminized sheets at quenched from the prior art, in particular less than 1 μm.

La tôle obtenue présente alors la structure suivante, en partant du substrat d'acier :

  • une sous-couche à base d'au moins un oxyde qui est intercalée entre le substrat d'acier et ladite couche de revêtement et dont l'épaisseur moyenne est comprise entre 0,01 et 0,1 µm ;
  • une couche interfaciale composée essentiellement d'un ou plusieurs alliages à base de fer et aluminium, notamment sous forme de phase dite τ5 ou τ6, dont l'épaisseur est inférieure à 1 µm.
  • une couche superficielle à base d'aluminium, dont l'épaisseur est en général supérieure à 5 µm.
The sheet obtained then has the following structure, starting from the steel substrate:
  • an undercoat based on at least one oxide which is interposed between the steel substrate and said coating layer and whose average thickness is between 0.01 and 0.1 μm;
  • an interfacial layer composed essentially of one or more alloys based on iron and aluminum, in particular in the form of a phase called τ5 or τ6, the thickness of which is less than 1 μm.
  • an aluminum-based surface layer, the thickness of which is generally greater than 5 μm.

L'épaisseur totale de la couche métallique est supérieure à 6 µm.The total thickness of the metal layer is more than 6 µm.

La teneur en aluminium de la couche superficielle dépend de la teneur en aluminum dans le bain de revêtement ; elle est en général supérieure à 80% ; elle est couramment de l'ordre de 87% en poids.The aluminum content of the surface layer depends on the content of aluminum in the coating bath; it is generally greater than 80%; it is commonly of the order of 87% by weight.

La teneur moyenne en fer du revêtement (qui prend en compte le fer contenu dans la couche interfaciale) est alors nettement inférieure à 10% en poids ; elle est alors inférieure ou égale à 6% en poids.The average iron content of the coating (which takes into account the iron contained in the interfacial layer) is then much less than 10% in weight; it is then less than or equal to 6% by weight.

Grâce à la faible épaisseur de la couche interfaciale, on obtient une tôle aluminiée résistant mieux à la fissuration.Thanks to the small thickness of the interfacial layer, a sheet is obtained aluminized more resistant to cracking.

Sur le plan du procédé, on peut même réaliser des tôles aluminiées selon l'invention présentant la structure précédemment décrite en utilisant un bain d'aluminium dont la teneur en silicium est inférieure à 6%, c'est à dire un bain -réputé conduire à des revêtements aluminiés alliés.In terms of process, it is even possible to produce aluminized sheets according to the invention having the structure previously described using a bath aluminum with a silicon content of less than 6%, i.e. a bath - reputed to lead to alloyed aluminum coatings.

Selon cette variante du procédé, il conviendra alors d'appliquer une deuxième sous-couche répondant à la formule FeAl3, qui est une phase en équilibre avec ce type de bain saturé en fer.According to this variant of the method, it will then be necessary to apply a second sub-layer corresponding to the formula FeAl 3 , which is a phase in equilibrium with this type of bath saturated with iron.

Ainsi, alors que le bain de revêtement ne contient pas ou contient peu d'inhibiteur d'alliation, comme du silicium, on obtient une tôle revêtue d'une couche à base d'aluminium dont la couche interfaciale d'alliage présente pourtant une faible épaisseur.So while the coating bath contains little or no of an alloying inhibitor, such as silicon, a sheet coated with a aluminum-based layer with an interfacial alloy layer yet a small thickness.

Les deux sous-couches selon l'invention servent donc d'inhibiteur d'alliation en remplacement du silicium dans le bain.The two sublayers according to the invention therefore serve as an inhibitor to replace the silicon in the bath.

Puisqu'il n'est plus nécessaire d'introduire un inhibiteur d'alliation dans le bain de revêtement, il devient possible d'obtenir des revêtements ne contenant pas d'inhibiteur d'alliation.Since it is no longer necessary to introduce an alloying inhibitor into the coating bath, it becomes possible to obtain coatings not containing no alloying inhibitor.

On peut ainsi obtenir des revêtements plus riches en aluminium que dans l'art antérieur ; comme le bain est, en pratique, saturé en fer (3% en poids) et pour des teneurs en silicium inférieures à 6%, on obtient des revêtements contenant plus de 90% en poids d'aluminium, voire plus de 96% en poids d'aluminium.It is thus possible to obtain coatings richer in aluminum than in prior art; as the bath is, in practice, saturated with iron (3% by weight) and for silicon contents lower than 6%, one obtains coatings containing more than 90% by weight of aluminum, or even more than 96% by weight aluminum.

La couche superficielle du revêtement contient alors beaucoup moins d'inclusions des phases précédemment citées, ce qui améliore la résistance à la fissuration du revêtement et la protection contre la corrosion. L'exemple suivant illustre le premier mode de réalisation de l'invention :The surface layer of the coating then contains much less of inclusions of the phases mentioned above, which improves the resistance to coating cracking and corrosion protection. The following example illustrates the first embodiment of the invention:

On cherche à revêtir deux tôles d'acier : l'une de nuance IF-Ti et l'autre de marque SOLDUR de la Société SOLLAC qui présente la composition suivante : C : 0,099 %- Mn : 1,260 %- P : 0,011 % - S : 0,01 % - Si : 0,259 % - Al : 0,028 % - Ni : 0,017 % - Cr : 0,016 % - Cu : 0,006 % - Mo : 0,001 % - Sn : 0,001 % - Nb : 0,057 % - V : 0,002 % - Ti : 0,003 %- N : 0,004 %.We are looking to coat two steel sheets: one of IF-Ti grade and the other of SOLDUR brand of SOLLAC which has the following composition: C: 0.099% - Mn: 1.260% - P: 0.011% - S: 0.01% - Si: 0.259% - Al: 0.028 % - Ni: 0.017% - Cr: 0.016% - Cu: 0.006% - Mo: 0.001% - Sn: 0.001% - Nb: 0.057% - V: 0.002% - Ti: 0.003% - N: 0.004%.

Selon l'invention, après nettoyage de la surface, on dépose la première et la deuxième sous-couches sous vide par pulvérisation magnétron.According to the invention, after cleaning the surface, the first is deposited and the second vacuum sublayers by magnetron sputtering.

Première sous-couche : Cr2O3 - épaisseurs : un essai à 30 nm et un essai à 50 nm.First sublayer: Cr2O3 - thicknesses: a test at 30 nm and a test at 50 nm.

Deuxième sous-couche : fer pur - épaisseurs : un essai à 30 nm et un essai à 50 nm.Second undercoat: pure iron - thicknesses: a test at 30 nm and a test at 50 nm.

Galvanisation :

  • recuit : maintien de la tôle à revêtir à la température de environ 800°C pendant environ 1 minute sous une atmosphère d'azote contenant 5 à 10% d'hydrogène.
  • bain de zinc contenant 0,16% d'aluminium, 0,03% de fer, à 455°C.
  • conditions de trempé : avant trempé, la tôle d'acier est refroidie à 470°C; le temps d'immersion étant fixé à environ 3 secondes.
  • épaisseur couche déposée (après essorage) : 10 µm.
Galvanization:
  • annealing: maintaining the sheet to be coated at the temperature of approximately 800 ° C. for approximately 1 minute under a nitrogen atmosphere containing 5 to 10% of hydrogen.
  • zinc bath containing 0.16% aluminum, 0.03% iron, at 455 ° C.
  • quenching conditions: before quenching, the steel sheet is cooled to 470 ° C; the immersion time being fixed at approximately 3 seconds.
  • thickness of the deposited layer (after spinning): 10 µm.

Par le même procédé, on réalise la même qualité de revêtement sur les deux nuances d'acier, pourtant fort différentes ; on constate notamment que les deux types de tôles présentent une excellente mouillabilité dans le bain de galvanisation.By the same process, the same quality of coating is produced on the two steel shades, yet very different; we note in particular that two types of sheets have excellent wettability in the galvanizing.

Claims (17)

  1. Process for the metal coating of a steel sheet, in which:
    the surface of the said sheet to be coated is cleaned;
    an annealing heat treatment is carried out on the said cleaned sheet;
    the said heated sheet is dipped into a liquid bath of the coating metal;
    the sheet is then removed from the said bath; and
    the metal coating layer entrained on the sheet as it leaves the said bath is solidified,
       characterized in that, after the cleaning step and before the dipping step:
    a first underlayer based on at least one oxide, with a mean thickness of between 0.01 and 0.1 µm, is applied to the said surface, and then
    a second metal underlayer, containing at least 20% iron by weight, is applied to the said first underlayer.
  2. Process according to Claim 1, characterized in that the said first underlayer and the said second underlayer are applied after the annealing step.
  3. Process according to either of Claims 1 and 2, characterized in that the steel is an alloy steel or microalloy steel containing additional elements that are oxidizable under the conditions of the said annealing heat treatment, especially silicon.
  4. Process according to any one of Claims 1 to 3, characterized in that the said first underlayer is based on trivalent chromium oxide or on zirconium oxide.
  5. Process according to any one of Claims 1 to 4, characterized in that:
    the said coating metal is based on zinc and
    the said second metal underlayer is based on iron.
  6. Process according to any one of Claims 1 to 4, characterized in that:
    the said coating metal is based on aluminium and
    the said second metal underlayer is based on an iron-aluminium alloy in equilibrium with the said iron-saturated bath.
  7. Process according to Claim 6, characterized in that:
    the silicon content of the said bath is less than 6% and
    the said iron-aluminium alloy corresponds to the compound FeAl3.
  8. Process according to Claim 6, characterized in that:
    the silicon content of the said bath is greater than 6% and
    the said iron-aluminium alloy also contains silicon and has a composition corresponding to a phase called the τ5 phase or a phase called the τ6 phase.
  9. Process according to any one of the preceding claims for the preparation of a coating called a "non-iron-alloyed" coating, characterized in that the mean thickness of the said second underlayer applied is less than 0.5 µm.
  10. Process according to Claim 9, characterized in that, when the said coating metal is based on zinc, the aluminium content of the said metal bath is less than 0.15%.
  11. Process according to Claim 9, characterized in that, when the said coating metal is based on aluminium, the silicon content of the said metal bath is less than 6%.
  12. Process according to any one of Claims 1 to 8, for the preparation of a coating called an "iron-alloyed" coating, containing a predetermined amount of iron, characterized in that:
    the thickness of the said second underlayer is suitable for providing the coating with the said amount of iron, and
    after the sheet has been removed from the bath, an alloying heat treatment is carried out under conditions suitable for alloying the iron contained in the said second underlayer with the said metal coating layer entrained on the sheet.
  13. Steel sheet hot-dipped coated with a metal layer based on an iron-zinc alloy, capable of being obtained by a process according to Claim 12, characterized in that the said layer is homogeneous in terms of thickness and mainly consists of a single phase of an iron-zinc alloy.
  14. Steel sheet hot-dipped coated with an aluminium-based metal layer, that can be obtained by a process according to any one of Claims 6 to 8 and Claims 9 and 11 which depend on any one of Claims 6 to 8, the said layer being laminated and comprising an interfacial layer essentially composed of one or more iron-aluminium-based alloys, characterized in that the thickness of the said interfacial layer is less than 1 µm.
  15. Sheet according to Claim 14, the said laminated metal layer of which also comprises a surface layer, characterized in that the aluminium content of the said surface layer is greater than or equal to 90%.
  16. Sheet according to any one of Claims 13 to 15, characterized in that it includes an underlayer based on at least one oxide, which is sandwiched between the steel substrate and the said coating layer and the mean thickness of which is between 0.01 and 0.1 µm.
  17. Sheet according to any one of Claims 13 to 16, characterized in that the thickness of the said metal layer is greater than 6 µm.
EP97402985A 1996-12-11 1997-12-10 Method for hot-dip coating of a steel plate; galvanized or aluminized steel plate obtained therefrom Expired - Lifetime EP0848076B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9615195 1996-12-11
FR9615195A FR2756846B1 (en) 1996-12-11 1996-12-11 PROCESS FOR THE TEMPER COATING OF A STEEL SHEET

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EP0848076A1 EP0848076A1 (en) 1998-06-17
EP0848076B1 true EP0848076B1 (en) 2001-08-22

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EP (1) EP0848076B1 (en)
AT (1) ATE204614T1 (en)
DE (1) DE69706269T2 (en)
DK (1) DK0848076T3 (en)
ES (1) ES2162220T3 (en)
FR (1) FR2756846B1 (en)
PT (1) PT848076E (en)

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EP2312011A1 (en) 2009-10-15 2011-04-20 Georg Fischer Automotive AG Method for metallic coating of a casting mould part and aluminized casting mould part produced according to the method

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LU60512A1 (en) * 1970-03-11 1971-11-08
DE3150998C2 (en) * 1981-12-23 1984-06-20 Peri-Werk Artur Schwörer GmbH & Co KG, 7912 Weißenhorn Process for hot-dip galvanizing and specific part for hot-dip galvanizing
JPS61194186A (en) * 1985-02-25 1986-08-28 Nippon Steel Corp Production of composite steel pipe
JPS61243162A (en) * 1985-04-19 1986-10-29 Nippon Steel Corp Production of al series hot dipped steel plate excellent in heat resistance
JP2769350B2 (en) * 1989-03-28 1998-06-25 新日本製鐵株式会社 Manufacturing method of hot-dip coated steel sheet
JPH05132747A (en) * 1991-11-12 1993-05-28 Kawasaki Steel Corp Manufacture of galvanized chromium-containing steel sheet

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PT848076E (en) 2002-01-30
ATE204614T1 (en) 2001-09-15
FR2756846B1 (en) 1999-01-08
DE69706269T2 (en) 2002-05-08
DK0848076T3 (en) 2001-11-12
EP0848076A1 (en) 1998-06-17
ES2162220T3 (en) 2001-12-16
DE69706269D1 (en) 2001-09-27
FR2756846A1 (en) 1998-06-12

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