EP0939141B1 - Steel plate with aluminum coating having stress cracking resistance - Google Patents

Steel plate with aluminum coating having stress cracking resistance Download PDF

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Publication number
EP0939141B1
EP0939141B1 EP99400414A EP99400414A EP0939141B1 EP 0939141 B1 EP0939141 B1 EP 0939141B1 EP 99400414 A EP99400414 A EP 99400414A EP 99400414 A EP99400414 A EP 99400414A EP 0939141 B1 EP0939141 B1 EP 0939141B1
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EP
European Patent Office
Prior art keywords
layer
aluminium
outer layer
thickness
sheet
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EP99400414A
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German (de)
French (fr)
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EP0939141A1 (en
Inventor
Didier Mareuse
Thérèse Six
Pierre Jean Krauth
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Sollac SA
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Sollac SA
Lorraine de Laminage Continu SA SOLLAC
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/12—Aluminium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C23C2/261—After-treatment in a gas atmosphere, e.g. inert or reducing atmosphere
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
    • C23C2/29—Cooling or quenching
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S428/00—Stock material or miscellaneous articles
    • Y10S428/922—Static electricity metal bleed-off metallic stock
    • Y10S428/923—Physical dimension
    • Y10S428/924—Composite
    • Y10S428/925—Relative dimension specified
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S428/00—Stock material or miscellaneous articles
    • Y10S428/922—Static electricity metal bleed-off metallic stock
    • Y10S428/923—Physical dimension
    • Y10S428/924—Composite
    • Y10S428/926—Thickness of individual layer specified
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12639—Adjacent, identical composition, components
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12736—Al-base component
    • Y10T428/1275—Next to Group VIII or IB metal-base component
    • Y10T428/12757—Fe
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12736—Al-base component
    • Y10T428/12764—Next to Al-base component

Definitions

  • the invention relates to aluminized sheets.
  • a metallic coating based on aluminum on a sheet is a commonly used means of protecting a steel sheet against corrosion, in particular in the case where the temperature of use of this sheet exceeds about 400 ° C.
  • the thickness of the metal coating in question is generally between 5 and 100 ⁇ m.
  • the slats are in the form of needles, it is therefore difficult to distinguish, in practice, needles and coverslips.
  • the internal layer of alloy having a fragile behavior one seeks generally to limit its thickness.
  • Silicon is the most commonly used alloying inhibitor; to be effective, its weight concentration must generally be greater than 6% in the soaking bath.
  • Certain aluminized sheets can then be subjected to heat treatments, either to modify their properties, or even normal use (example: thermal screens); so it is important not to not significantly increase the thickness of the internal alloy layer.
  • the inner layer can be subdivided into several sublayers comprising still other phases; at the interface between inner layer 1 and steel 2, we can sometimes find an underlay comprising the phases following: a phase called ⁇ (Fe2Al5), a phase called ⁇ (FeAl3), one or several phases based on aluminum nitride; the thickness of this underlay generally does not exceed 1 ⁇ m.
  • This outer layer may also include alloying phases to based on aluminum, silicon and iron, in particular of eutectic composition with low melting point.
  • 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.
  • Table I summarizes the possible composition and the temperature of fusion of the phases present in the coatings obtained after soaked in an aluminizing bath (the composition and temperature of fusion are specified in this same table).
  • phase inclusions ⁇ 6 have an elongated shape whereas the inclusions of phase ⁇ 5 generally have a globular shape.
  • composition of the coating phases Composition: % by mass HAVE Yes Fe Fusion temperature Bath ⁇ 91 > 6 3 (saturation) 675 ° C (T ° C hardened) eutectic 87 12.2 0.8 ⁇ 577 ° C Dendrites Al ⁇ 98 ⁇ 1.5 ⁇ 0,5 ⁇ 660 ° C Slats Si Majority silicon 1412 ° C ⁇ 6 needles 55 14 31 > 577 ° C Phase ⁇ 5 55 to 62 6 to 12 31 to 36 > 577 ° C
  • the object of the invention is to offer a sheet with a coating based on of aluminum is more resistant to cracking by deformation, i.e. a sheet which is more resistant to corrosion after shaping.
  • nitride at the interface or free nitrogen in the steel blocks or limits the growth of the thickness of the internal layer of alloy.
  • the duration of heat treatment, in the phase where said temperature is higher than 570 ° C, is less than or equal to 15 seconds.
  • the steel grade In a manner known per se, the steel grade, the conditions for applying the coating and the composition of the bath, in particular the content of alloying inhibitor, so that the thickness of the inner layer 1 alloy does not exceed that of the outer layer 3.
  • silicon is introduced as alloying inhibitor in the bath, with a content greater than or equal to 6% in weight; preferably, the silicon content is greater than or equal to 8%.
  • the annealing step can be performed under an atmosphere containing ammonia.
  • the outer layer 3 comprises, in addition to the dendrites based aluminum, other phases 4 in the form of needles or elongated lamellae distributed in the thickness of this layer between the dendrites.
  • This projection p is shown in FIG. 1 in the particular case any strip, the strip referenced 5.
  • the treatment time is less than 15 seconds from so as to limit and / or prevent the increase in layer thickness internal alloy.
  • the heat treatment according to the invention has has the effect of significantly reducing the proportion of needles and strips in this outer layer.
  • the aluminum coating is applied so as to the thickness of said internal alloy layer is less than or equal to 5 ⁇ m and the heat treatment according to the invention is carried out so that the thickness of said internal alloy layer remains less than or equal to 5 ⁇ m.
  • the minimum temperature of the treatment according to the invention corresponds to the melting temperature of the phase of the outer layer corresponding to the Al-Si-Fe eutectic composition.
  • the maximum temperature of the treatment according to the invention corresponds to the melting temperature of the aluminum dendrites of the outer layer.
  • This heat treatment can be carried out in air, even if the coating oxidizes slightly on the surface.
  • the aluminized sheet according to the invention therefore resists corrosion better after shaping, in the sense that the coating better protects the steel.
  • the structure of the coating of the aluminized sheet according to the invention is shown schematically in Figure 2 and shown in Figure 6; the general structure remains the same: on steel 2, an internal layer 7 of alloy and a layer external 8 mainly composed of aluminum.
  • the treatment according to the invention generates a structural rearrangement of the layer external leading to the disappearance and / or partition of the lamellae or needles of this layer.
  • the heat treatment according to the invention would therefore have the technical effect first to rearrange the structure of the outer layer so as to obtain a structure opposing the propagation of cracks.
  • the heat treatment according to the invention must also be adapted for prevent or limit the increase in thickness of the inner layer 7 of alloy, because this layer is particularly fragile.
  • the conditions of the heat treatment according to the invention can therefore be optimized in a manner known per se between these two compromises : sufficient rearrangement of the outer layer and slight increase in the thickness of the internal layer of alloy.
  • the heat treatment according to the invention is of short duration, which is an important advantage compared to long-term annealing treatments and at a lower temperature.
  • This heat treatment can therefore advantageously be carried out in line on conventional dip coating installations.
  • this heat treatment is applied so as to heat the outer layer more than the inner alloy layer.
  • the heat treatment according to the invention can also improve appreciably the surface reflectivity of the sheet, in particular in the field wavelengths between 1.5 and 5 ⁇ m; we get this advantage additional especially when performing heat treatment under non-oxidizing atmosphere.
  • the treatment according to the invention is not limited to a surface gloss treatment; indeed some effective brightening treatments cause significant increase of the thickness of the internal layer of alloy, which is contrary to the invention described here.
  • a steel grade containing a content greater than or equal to 10 -2 % by weight of nitrogen is used. free.
  • AlN aluminum nitrides
  • the aluminized steel sheet according to the invention has the following analysis (element contents expressed in thousandths of% by weight): Composition of the steel of Example 1 Element VS mn P S Yes al Or Cr Cu NOT 10 -3 % 53 300 10 15 6 22 20 20 7 11
  • the other elements are in the state of traces; the titanium content is less than 10 -3 %.
  • a significant part of the nitrogen contained in this steel is said to be "free", the other part being essentially combined with aluminum in the form of aluminum nitride (AIN); the AIN content having been evaluated at approximately 1.4 10 -3 % by weight of “nitrogen” equivalent, it is deduced therefrom that the content of free nitrogen is of the order of 10 -2 % by weight in this steel.
  • AIN aluminum nitride
  • a coating based on both sides of this sheet is applied aluminum with a total thickness of approximately 15 ⁇ m; this coating is applied as previously described by soaking in an aluminum bath containing silicon.
  • the average silicon content in the coating is 7% about.
  • this treatment consists in heating the sheet at the speed of 4 ° C / s up to a temperature of 578 ° C, and, as soon as this temperature is reached, blowing with nitrogen to obtain a speed of cooling between 10 and 15 ° C / s.
  • the schematic device is used in FIG. 4: it is a vertical oven 13 comprising two series of electrical resistors 14; the sample to be treated 15, made of aluminized sheet, is suspended from a support rod 16; to measure the temperature of heat treatment, a thermocouple 17, type K (chromel-alumel) is used, 0.2 mm in diameter and class 1 ( ⁇ T ° C x 0.004, i.e. ⁇ 2.4 ° C at 600 ° C); this thermocouple 17 is welded to the face coated with the aluminized sheet.
  • a thermocouple 17 type K (chromel-alumel) is used, 0.2 mm in diameter and class 1 ( ⁇ T ° C x 0.004, i.e. ⁇ 2.4 ° C at 600 ° C); this thermocouple 17 is welded to the face coated with the aluminized sheet.
  • the coating according to the invention is very resistant better cracking than the coating according to the prior art which has not undergone heat treatment.
  • Example 1 Aluminized sheet Folding type Average number of cracks / mm Average crack width observations Before heat treatment 0T 10 40 ⁇ m Inner layer separation and large cracks. 1T 8 62 ⁇ m 2T 5 7 ⁇ m 3T 2 7 ⁇ m After heat treatment (invention) 0T 5 41 ⁇ m Little or no internal layer detachments 1T 3 55 ⁇ m 2T 0 - 3T 0 -
  • the aluminized steel sheet according to the invention has the following analysis (element contents expressed in thousandths of% by weight): Composition of the steel of Example 2 Element VS mn P S Yes al Or Cr Cu NOT 10 -3 % 3 230 10 13 8 46 16 23 20 12
  • the other elements are in the state of traces.
  • a special feature of this steel also lies in its temperature of winding at the end of hot rolling: ⁇ 620 ° C.
  • This steel is aluminized and then heat treated according to the invention in the same conditions as in Example 1.
  • An aluminized sheet according to the invention is then obtained.
  • Example 2 Aluminized sheet Folding type Average number of cracks / mm Average crack width Before heat treatment 0T 11 31 ⁇ m 1T 8 28 ⁇ m 2T 6 7 ⁇ m 3T 2 3 ⁇ m After heat treatment (invention) 0T 10 17 ⁇ m 1T 3 10 ⁇ m 2T 1 3 ⁇ m 3T ⁇ 1 3 ⁇ m

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Abstract

The steel sheet is coated with aluminum based alloy. After solidification of the applied coating, the sheet is subjected to a heat treatment that carries at least the outer layer (8) to a temperature greater than 570oC and lower than 660oC. Fabrication of a steel sheet (2) coated with an aluminum based metallic coating, principally subdivided into two layers, an inner layer (7) made up of one or several alloys with an iron, aluminum and/or silicon base and an outer layer (8) made up essentially of an aluminum based alloy. Other phases in the form of needles or elongated platelets (9) are distributed throughout the aluminum based alloy, which is applied by soaking in a bath of an aluminum based alloys. After solidification of the applied coating, the sheet is subjected to a heat treatment that carries at least the outer layer (8) to a temperature greater than 570oC and lower than 660oC. Sheet steel coated with an aluminum based alloy in accordance with this method is also claimed.

Description

L'invention concerne les tôles aluminiées.The invention relates to aluminized sheets.

L'application d'un revêtement métallique à base d'aluminium sur une tôle est un moyen couramment utilisé pour protéger une tôle d'acier contre la corrosion, notamment dans le cas où la température d'utilisation de cette tôle dépasse 400°C environ.The application of a metallic coating based on aluminum on a sheet is a commonly used means of protecting a steel sheet against corrosion, in particular in the case where the temperature of use of this sheet exceeds about 400 ° C.

L'épaisseur du revêtement métallique en question est généralement comprise entre 5 et 100 µm.The thickness of the metal coating in question is generally between 5 and 100 µm.

On connaít plusieurs procédés pour appliquer un revêtement métallique sur une tôle, voir par exemple la demande européenne EP-A-710732.We know several methods for applying a metallic coating on a sheet, see for example European application EP-A-710732.

On peut par exemple procéder par plaquage d'un film d'aluminium sur la tôle à revêtir, mais ce procédé est coûteux.One can for example proceed by plating an aluminum film on the sheet to be coated, but this process is expensive.

On peut par exemple procéder par trempage de la tôle dans un bain liquide à base d'aluminium.We can for example proceed by soaking the sheet in a bath aluminum-based liquid.

Lorsqu'on utilise ce procédé par trempage, comme décrit dans l'article de la revue STAHL und EISEN, vol.111, n°12, 12/12/91, pp.111-116 (THYSSEN Forschung, Duisburg), notamment à la figure 4 et au milieu de la page 112, le revêtement comprend :

  • une couche interfaciale ou interne essentiellement composée d'un ou plusieurs alliages à base de fer et d'aluminium,
  • et une couche externe comprenant essentiellement une phase principale à base d'aluminium et, accessoirement, d'autres phases sous formes d'aiguilles ou de lamelles allongées dispersées dans ladite phase principale ; l'article cite la présence de phases eutectiques entre les dendrites d'aluminium solidifiées.
When this dipping process is used, as described in the article in the journal STAHL und EISEN, vol. 111, no. 12, 12/12/91, pp. 111-116 (THYSSEN Forschung, Duisburg), in particular at FIG. 4 and in the middle of page 112, the covering comprises:
  • an interfacial or internal layer essentially composed of one or more alloys based on iron and aluminum,
  • and an outer layer essentially comprising a main phase based on aluminum and, incidentally, other phases in the form of needles or elongated lamellae dispersed in said main phase; the article cites the presence of eutectic phases between the solidified aluminum dendrites.

Comme, vues en coupe, les lamelles se présentent sous forme d'aiguilles, il est donc difficile de distinguer, en pratique, des aiguilles et des lamelles.As seen in section, the slats are in the form of needles, it is therefore difficult to distinguish, in practice, needles and coverslips.

La couche interne d'alliage ayant un comportement fragile, on cherche généralement à limiter son épaisseur.The internal layer of alloy having a fragile behavior, one seeks generally to limit its thickness.

Pour limiter l'épaisseur de cette couche d'alliage, on utilise généralement des bains de trempage contenant un inhibiteur d'alliation entre l'aluminium et l'acier. To limit the thickness of this alloy layer, we generally use soaking baths containing an alloying inhibitor between aluminum and steel.

Le silicium est l'inhibiteur d'alliation le plus couramment utilisé ; pour être efficace, sa concentration pondérale doit généralement être supérieure à 6% dans le bain de trempage.Silicon is the most commonly used alloying inhibitor; to be effective, its weight concentration must generally be greater than 6% in the soaking bath.

Il existe d'autres moyens connus pour limiter l'épaisseur de cette couche d'alliage, comme de procéder, avant revêtement, à une légère nitruration de la surface à revêtir, par exemple en effectuant le recuit de recristallisation de l'acier à revêtir sous une atmosphère contenant des traces d'ammoniac.There are other known means for limiting the thickness of this layer of alloy, as to proceed, before coating, to a light nitriding of the surface to be coated, for example by performing recrystallization annealing of the steel to be coated in an atmosphere containing traces of ammonia.

Certaines tôles aluminiées peuvent être ensuite soumises à des traitements thermiques, soit pour modifier leurs propriétés, soit même en utilisation normale (exemple : écran thermiques) ; aussi importe-t-il alors de ne pas augmenter sensiblement l'épaisseur de la couche interne d'alliage.Certain aluminized sheets can then be subjected to heat treatments, either to modify their properties, or even normal use (example: thermal screens); so it is important not to not significantly increase the thickness of the internal alloy layer.

Pour limiter ce risque de croissance de la couche interne d'alliage lors de traitements thermiques ultérieurs, il est connu d'utiliser des nuances d'acier contenant des teneurs suffisantes en azote libre (par exemple ≥ 10-2% en poids) ; ces aciers peuvent être des aciers renitrurés ; on se reportera à ce sujet aux articles suivants :

  • T.Yamada et H.Kawase, présenté au 5ème « IAVD Meeting » en 1989 (IAVD : « International Association for Vehicle Design »).
  • Y.Hirose et Y.Uchida, dans le Supplément de la revue du « Japan Institute of Metals », n°3, 1983.
To limit this risk of growth of the internal layer of alloy during subsequent heat treatments, it is known to use steel grades containing sufficient contents of free nitrogen (for example ≥ 10 -2 % by weight); these steels can be renitrided steels; we will refer to this subject in the following articles:
  • T.Yamada and H.Kawase, presented at the 5th "IAVD Meeting" in 1989 (IAVD: "International Association for Vehicle Design").
  • Y. Hirose and Y. Uchida, in the Supplement to the review of the "Japan Institute of Metals", n ° 3, 1983.

Comme schématisé à la figure 1, lorsqu'on applique le revêtement au trempé, le revêtement qu'on obtient se subdivise alors en deux couches principales superposées :

  • une couche interne 1, appliquée sur l'acier 2, essentiellement composée d'un ou plusieurs alliages à base de fer et d'aluminium, voire de silicium, notamment d'une phase dite τ5 et/ou d'une phase dite τ6.
  • une couche externe 3 essentiellement composée d'aluminium sous forme de larges dendrites ; ces dendrites sont souvent (pas toujours) saturées en fer, et, le cas échéant, en silicium en solution solide.
As shown diagrammatically in FIG. 1, when the coating is applied by dipping, the coating which is obtained is then subdivided into two main superposed layers:
  • an internal layer 1, applied to the steel 2, essentially composed of one or more alloys based on iron and aluminum, or even silicon, in particular of a phase called τ5 and / or a phase called τ6.
  • an outer layer 3 essentially composed of aluminum in the form of large dendrites; these dendrites are often (not always) saturated with iron, and, where appropriate, with silicon in solid solution.

La couche interne peut se subdiviser en plusieurs sous-couches comprenant encore d'autres phases ; à l'interface entre la couche interne 1 et l'acier 2, on peut parfois trouver une sous-couche comprenant les phases suivantes : une phase dite η (Fe2Al5), une phase dite  (FeAl3), une ou plusieurs phases à base de nitrure d'aluminium ; l'épaisseur de cette sous-couche ne dépasse généralement pas 1 µm.The inner layer can be subdivided into several sublayers comprising still other phases; at the interface between inner layer 1 and steel 2, we can sometimes find an underlay comprising the phases following: a phase called η (Fe2Al5), a phase called  (FeAl3), one or several phases based on aluminum nitride; the thickness of this underlay generally does not exceed 1 µm.

Au niveau de la couche externe 3, lorsqu'on a utilisé un bain contenant du silicium, on observe généralement des phases plus riches en silicium et/ou en fer que les dendrites d'aluminium ; ces phases présentent souvent une forme allongée de lamelle ou d'aiguilles.At the outer layer 3, when a bath containing silicon, we generally observe phases richer in silicon and / or iron than aluminum dendrites; these phases often have a form elongated coverslip or needles.

Comme phases 4 de formes allongées, on a par exemple identifié :

  • des lamelles essentiellement composées de silicium,
  • des aiguilles essentiellement composées d'une phase intermétallique τ6.
As phases 4 of elongated forms, we have for example identified:
  • lamellae essentially composed of silicon,
  • needles essentially composed of an intermetallic phase τ6.

Cette couche externe peut également comporter des phases d'alliage à base d'aluminium, de silicium et de fer, notamment de composition eutectique à bas point de fusion.This outer layer may also include alloying phases to based on aluminum, silicon and iron, in particular of eutectic composition with low melting point.

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.

Le tableau I ci-après récapitule la composition possible et la température de fusion des phases en présence dans les revêtements qu'on obtient après trempé dans un bain d'aluminiage (dont la composition et la température de fusion sont précisées dans ce même tableau).Table I below summarizes the possible composition and the temperature of fusion of the phases present in the coatings obtained after soaked in an aluminizing bath (the composition and temperature of fusion are specified in this same table).

La phase τ6 est prépondérante lorsque le bain contient plus de 8% en poids de silicium ; les inclusions de phase τ6 présentent une forme allongée alors que les inclusions de phase τ5 ont généralement une forme globulaire.The τ6 phase is predominant when the bath contains more than 8% weight of silicon; phase inclusions τ6 have an elongated shape whereas the inclusions of phase τ5 generally have a globular shape.

On a constaté que les tôles d'acier revêtues d'une couche interne d'alliage à base de fer, aluminium et/ou silicium et d'une couche externe composée essentiellement d'aluminium résistaient mal à la corrosion après déformation. It has been found that the steel sheets coated with an internal layer of alloy based on iron, aluminum and / or silicon and an outer layer composed mainly of aluminum did not resist corrosion well after deformation.

En effet, une déformation comme un pliage provoque généralement des fissures qui débouchent à la surface du revêtement métallique ; ces fissures diminuent la résistance à la corrosion de l'acier. Composition des phases du revêtement Composition :
% massique AI Si Fe Température Fusion Bain <91 >6 3
(saturation) 675°C
(T°C trempé) Eutectique 87 12,2 0,8 ≈ 577°C Dendrites Al ≥98 ≤ 1,5 ≤0,5 ≈ 660°C Lamelles Si Silicium majoritaire 1412°C Aiguilles τ6 55 14 31 > 577°C Phase τ5 55 à 62 6 à 12 31 à 36 > 577°C Indeed, a deformation such as a folding generally causes cracks which open onto the surface of the metallic coating; these cracks reduce the corrosion resistance of the steel. Composition of the coating phases Composition:
% by mass HAVE Yes Fe Fusion temperature Bath <91 > 6 3
(saturation) 675 ° C
(T ° C hardened) eutectic 87 12.2 0.8 ≈ 577 ° C Dendrites Al ≥98 ≤ 1.5 ≤0,5 ≈ 660 ° C Slats Si Majority silicon 1412 ° C Τ6 needles 55 14 31 > 577 ° C Phase τ5 55 to 62 6 to 12 31 to 36 > 577 ° C

L'invention a pour but d'offrir une tôle dont le revêtement à base d'aluminium résiste mieux à la fissuration par déformation, c'est à dire une tôle qui résiste mieux à la corrosion après mise en forme.The object of the invention is to offer a sheet with a coating based on of aluminum is more resistant to cracking by deformation, i.e. a sheet which is more resistant to corrosion after shaping.

A cet effet, l'invention a pour objet un procédé de fabrication d'une tôle d'acier revêtue d'un revêtement métallique à base d'aluminium se subdivisant principalement en deux couches :

  • une couche interne composée essentiellement d'un ou plusieurs alliages à base de fer, aluminium et/ou silicium,
  • une couche externe qui est composée essentiellement d'une phase à base d'aluminium et accessoirement d'autres phases sous forme d'aiguilles ou de lamelles allongées réparties dans ladite phase à base d'aluminium, et dont l'épaisseur est supérieure ou égale à celle de la dite couche interne d'alliage,
   dans lequel on applique ledit revêtement métallique à base d'aluminium par trempé dans un bain liquide à base d'aluminium,
   caractérisé en ce que, après solidification de ladite couche appliquée, on soumet ladite tôle à un traitement thermique adapté pour porter au moins ladite couche externe à une température supérieure à 570°C et inférieure à 660°C, dans des conditions notamment de durée, vitesses de chauffage et de refroidissement, adaptées :
  • pour que l'épaisseur de ladite couche externe reste supérieure ou égale à celle de la dite couche interne d'alliage,
  • et pour que la projection de la longueur de toutes lesdites aiguilles ou lamelles sur une direction perpendiculaire au plan de ladite couche externe soit strictement inférieure à l'épaisseur de cette couche.
To this end, the subject of the invention is a process for manufacturing a steel sheet coated with a metallic coating based on aluminum, which is mainly subdivided into two layers:
  • an internal layer essentially composed of one or more alloys based on iron, aluminum and / or silicon,
  • an outer layer which is essentially composed of an aluminum-based phase and incidentally other phases in the form of needles or elongated lamellae distributed in said aluminum-based phase, and whose thickness is greater than or equal to that of said internal alloy layer,
in which said metallic aluminum-based coating is applied by dipping in a liquid aluminum-based bath,
characterized in that, after solidification of said applied layer, said sheet is subjected to a heat treatment suitable for bringing at least said outer layer to a temperature above 570 ° C and below 660 ° C, under conditions notably of duration, suitable heating and cooling speeds:
  • so that the thickness of said external layer remains greater than or equal to that of said internal alloy layer,
  • and so that the projection of the length of all said needles or strips on a direction perpendicular to the plane of said outer layer is strictly less than the thickness of this layer.

Dans cette gamme de température, supérieure à 570°C et inférieure à 660°C, on est assuré de la fusion des phases eutectiques de la couche externe (c.f. température de fusion de l'eutectique au tableau I ≈ 577°C) et du maintien à l'état solide des dendrites d'aluminium (c.f. température de fusion de ces dendrites au tableau I ≈ 660°C).In this temperature range, greater than 570 ° C and less than 660 ° C, we are assured of the fusion of the eutectic phases of the outer layer (see the eutectic melting temperature in Table I ≈ 577 ° C) and the maintenance in the solid state of aluminum dendrites (cf. melting temperature of these dendrites in table I ≈ 660 ° C).

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

  • ledit bain à base d'aluminium contient au moins 6 % en poids de silicium.
  • ledit bain à base d'aluminium contient au moins 8 % en poids de silicium, auquel cas la proportion de phase τ6 est plus importante dans le revêtement, au dépens de celle de phase τ5.
  • la durée du traitement thermique, dans la phase où ladite température est supérieure à 570°C, est inférieure ou égale à 15 secondes.
The invention may also have one or more of the following characteristics:
  • said aluminum-based bath contains at least 6% by weight of silicon.
  • said aluminum-based bath contains at least 8% by weight of silicon, in which case the proportion of phase τ6 is greater in the coating, at the expense of that of phase τ5.
  • the duration of the heat treatment, in the phase where said temperature is greater than 570 ° C., is less than or equal to 15 seconds.

L'invention a également pour objet une tôle d'acier revêtue d'un revêtement métallique à base d'aluminium se subdivisant principalement en deux couches :

  • une couche interne composée essentiellement d'un ou plusieurs alliages à base de fer, aluminium et/ou silicium,
  • une couche externe qui est composée essentiellement d'une phase à base d'aluminium et accessoirement d'autres phases sous forme d'aiguilles ou de lamelles allongées réparties dans ladite phase à base d'aluminium, et dont l'épaisseur est supérieure ou égale à celle de la dite couche interne d'alliage,
   susceptible d'être obtenue par un procédé selon l'une quelconque des revendications précédentes,
   caractérisée en ce que la projection de la longueur de toutes lesdites aiguilles ou lamelles sur une direction perpendiculaire au plan de ladite couche externe est strictement inférieure à l'épaisseur de cette couche à l'endroit desdites lamelles ou aiguilles considérées.The subject of the invention is also a steel sheet coated with a metallic coating based on aluminum which is mainly subdivided into two layers:
  • an internal layer essentially composed of one or more alloys based on iron, aluminum and / or silicon,
  • an outer layer which is essentially composed of an aluminum-based phase and incidentally other phases in the form of needles or elongated lamellae distributed in said aluminum-based phase, and whose thickness is greater than or equal to that of said internal alloy layer,
capable of being obtained by a process according to any one of the preceding claims,
characterized in that the projection of the length of all of said needles or strips on a direction perpendicular to the plane of said outer layer is strictly less than the thickness of this layer at the location of said considered strips or needles.

Selon cette caractéristique, en considérant le revêtement de la tôle et quelles que soient les variations de l'épaisseur de la couche externe de ce revêtement, aucune aiguille ou lamelle ne traverse en continu cette couche externe.According to this characteristic, considering the coating of the sheet and regardless of the variations in the thickness of the outer layer of this coating, no needle or strip continuously passes through this layer external.

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

  • l'épaisseur de ladite couche interne d'alliage est inférieure ou égale à 5 µm ; cette épaisseur plus faible permet de limiter les risques d'apparition de fissures.
  • ledit revêtement comprend des composés à base de nitrures d'aluminium intercalés entre l'acier de ladite tôle et ladite couche interne.
  • la teneur en azote libre dudit acier est supérieure ou égale à environ 10-2 % en poids.
The invention may also have one or more of the following characteristics:
  • the thickness of said internal alloy layer is less than or equal to 5 μm; this smaller thickness makes it possible to limit the risks of the appearance of cracks.
  • said coating comprises compounds based on aluminum nitrides interposed between the steel of said sheet and said inner layer.
  • the content of free nitrogen in said steel is greater than or equal to about 10 -2 % by weight.

La présence de nitrure à l'interface ou d'azote libre dans l'acier, bloque ou limite la croissance de l'épaisseur de la couche interne d'alliage.The presence of nitride at the interface or free nitrogen in the steel blocks or limits the growth of the thickness of the internal layer of alloy.

L'invention a également pour objet un procédé de mise en forme d'une tôle d'acier revêtue d'un revêtement métallique à base d'aluminium se subdivisant principalement en deux couches :

  • une couche interne composée essentiellement d'un ou plusieurs alliages à base de fer, aluminium et/ou silicium,
  • une couche externe qui est composée essentiellement d'une phase à base d'aluminium et accessoirement d'autres phases sous forme d'aiguilles ou de lamelles allongées réparties dans ladite phase à base d'aluminium, et dont l'épaisseur est supérieure ou égale à celle de la dite couche interne d'alliage,
   caractérisé en ce que, avant l'étape de mise en forme à proprement parler de ladite tôle, on soumet ladite tôle à un traitement thermique adapté pour porter au moins ladite couche externe à une température supérieure à 570°C et inférieure à 660°C, dans des conditions notamment de durée, vitesses de chauffage et de refroidissement, adaptées :
  • pour que l'épaisseur de ladite couche externe reste supérieure ou égale à celle de la dite couche interne d'alliage,
  • et pour que la projection de la longueur de toutes lesdites aiguilles ou lamelles sur une direction perpendiculaire au plan de ladite couche externe soit strictement inférieure à l'épaisseur de cette couche.
The invention also relates to a process for shaping a steel sheet coated with a metallic coating based on aluminum, which is mainly subdivided into two layers:
  • an internal layer essentially composed of one or more alloys based on iron, aluminum and / or silicon,
  • an outer layer which is essentially composed of an aluminum-based phase and incidentally other phases in the form of needles or elongated lamellae distributed in said aluminum-based phase, and whose thickness is greater than or equal to that of said internal alloy layer,
characterized in that, before the actual shaping step of said sheet, said sheet is subjected to a heat treatment suitable for bringing at least said outer layer to a temperature above 570 ° C and below 660 ° C , under conditions including duration, heating and cooling rates, suitable:
  • so that the thickness of said external layer remains greater than or equal to that of said internal alloy layer,
  • and so that the projection of the length of all said needles or strips on a direction perpendicular to the plane of said outer layer is strictly less than the thickness of this layer.

La durée du traitement thermique, dans la phase où ladite température est supérieure à 570°C, est inférieure ou égale à 15 secondes.The duration of heat treatment, in the phase where said temperature is higher than 570 ° C, is less than or equal to 15 seconds.

L'invention sera mieux comprise à la lecture de la description qui va suivre, donnée à titre d'exemple non limitatif, et en référence aux figures annexées sur lesquelles :

  • la figure 1 est une représentation schématique de la structure des couches de revêtement d'une tôle aluminiée selon l'art antérieur.
  • la figure 2 est une représentation schématique de la structure des couches de revêtement d'une tôle aluminiée selon l'invention.
  • la figure 3 est une illustration du mode de pliage des tôles dans la méthode d'évaluation de la résistance à la fissuration.
  • la figure 4 représente schématiquement le dispositif utilisé pour mettre en oeuvre l'invention telle que décrite dans l'exemple 1.
  • les figures 5, 5 bis d'une part, et 6 d'autre part, sont des microphotographies en coupe illustrant les représentations schématiques respectivement des figures 1 et 2.
The invention will be better understood on reading the description which follows, given by way of nonlimiting example, and with reference to the appended figures in which:
  • Figure 1 is a schematic representation of the structure of the coating layers of an aluminized sheet according to the prior art.
  • Figure 2 is a schematic representation of the structure of the coating layers of an aluminized sheet according to the invention.
  • Figure 3 is an illustration of the bending mode of the sheets in the method of evaluation of the resistance to cracking.
  • FIG. 4 schematically represents the device used to implement the invention as described in example 1.
  • FIGS. 5, 5 bis on the one hand, and 6 on the other hand, are microphotographs in section illustrating the schematic representations of FIGS. 1 and 2 respectively.

Pour l'application du revêtement métallique sur une tôle d'acier 2, on procède au trempé d'une manière connue en elle-même et adaptée à la nuance d'acier utilisée.For the application of the metallic coating on a steel sheet 2, we carries out the quenching in a manner known per se and adapted to the steel grade used.

Le procédé classique d'aluminiage au trempé comporte en général les étapes suivantes:

  • dégraissage et nettoyage de la surface de la tôle,
  • recuit de l'acier, généralement sous atmosphère inerte ou réductrice,
  • directement en sortie de recuit, trempé dans un bain liquide à base d'aluminium,
  • en sortie de trempé, essorage pour réguler l'épaisseur du revêtement et refroidissement pour solidifier le revêtement.
The conventional dip aluminizing process generally includes the following steps:
  • degreasing and cleaning of the sheet surface,
  • annealing of steel, generally in an inert or reducing atmosphere,
  • directly after annealing, soaked in a liquid aluminum-based bath,
  • at the end of the quench, spin to regulate the thickness of the coating and cooling to solidify the coating.

En se reportant aux figures 1 et 5 et 5 bis, on obtient alors une tôle aluminiée telle que précédemment décrite dont le revêtement se subdivise principalement en deux couches :

  • une couche interne 1 composée essentiellement d'un ou plusieurs alliages à base de fer, aluminium et/ou silicium,
  • une couche externe 3 composée essentiellement d'une phase à base d'aluminium.
Referring to FIGS. 1 and 5 and 5a, there is then obtained an aluminized sheet as previously described, the coating of which is mainly subdivided into two layers:
  • an internal layer 1 essentially composed of one or more alloys based on iron, aluminum and / or silicon,
  • an outer layer 3 essentially composed of an aluminum-based phase.

(La séparation entre le substrat d'acier 2 et la couche 1 a été marquée en pointillé sur les figures 5 et 5 bis).(The separation between steel substrate 2 and layer 1 has been marked in dotted on Figures 5 and 5a).

D'une manière connue en elle-même, on adapte la nuance d'acier, les conditions d'application du revêtement et la composition du bain, notamment la teneur en inhibiteur d'alliation, pour que l'épaisseur de la couche interne 1 d'alliage ne dépasse pas celle de la couche externe 3.In a manner known per se, the steel grade, the conditions for applying the coating and the composition of the bath, in particular the content of alloying inhibitor, so that the thickness of the inner layer 1 alloy does not exceed that of the outer layer 3.

Pour limiter l'épaisseur de cette couche 1, on introduit du silicium comme inhibiteur d'alliation dans le bain, à une teneur supérieure ou égale à 6% en poids ; de préférence, la teneur en silicium est supérieure ou égale à 8%.To limit the thickness of this layer 1, silicon is introduced as alloying inhibitor in the bath, with a content greater than or equal to 6% in weight; preferably, the silicon content is greater than or equal to 8%.

Pour limiter l'épaisseur de cette couche 1, l'étape de recuit peut être réalisée sous atmosphère contenant de l'ammoniac.To limit the thickness of this layer 1, the annealing step can be performed under an atmosphere containing ammonia.

Comme on le voit sur les figures 5 et 5 bis et comme représenté à la figure 1, la couche externe 3 comprend, outre les dendrites à base d'aluminium, d'autres phases 4 sous forme d'aiguilles ou de lamelles allongées réparties dans l'épaisseur de cette couche entre les dendrites.As seen in Figures 5 and 5a and as shown in Figure 1, the outer layer 3 comprises, in addition to the dendrites based aluminum, other phases 4 in the form of needles or elongated lamellae distributed in the thickness of this layer between the dendrites.

On constate qu'une proportion significative d'aiguilles et/ou de lamelles débouchent sur la surface interne ou externe de la couche ; la longueur de ces aiguilles ou lamelles « débouchantes » est supérieure ou égale à l'épaisseur de la couche ; plus précisément, la projection de la longueur de ces aiguilles ou lamelles sur une direction perpendiculaire au plan de la couche est au moins égale à l'épaisseur de cette couche. It is found that a significant proportion of needles and / or strips lead to the internal or external surface of the layer; the length of these “through” needles or strips is greater than or equal to the thickness layer; more precisely, the projection of the length of these needles or lamellae in a direction perpendicular to the plane of the layer is at less equal to the thickness of this layer.

On a représenté sur la figure 1 cette projection p dans le cas particulier d'une lamelle quelconque, la lamelle référencée 5.This projection p is shown in FIG. 1 in the particular case any strip, the strip referenced 5.

On constate par exemple que, pour les lamelles référencées 6, la valeur de cette projection correspond à celle de l'épaisseur de la couche 3.We note for example that, for the lamellae referenced 6, the value of this projection corresponds to that of the thickness of layer 3.

Selon l'invention, on procède ensuite à l'étape suivante :

  • on soumet la tôle aluminiée à un traitement thermique adapté pour porter au moins la couche externe 3 du revêtement à une température supérieure à 570°C et inférieure à 660°C ;
  • les conditions du traitement thermique, notamment la durée, les vitesses de chauffage et de refroidissement, sont adaptées :
    • pour que l'épaisseur de ladite couche interne 1 d'alliage reste inférieure à celle de la dite couche externe,
    • et pour que, dans ladite couche externe, la projection de la longueur toutes lesdites aiguilles ou lamelles sur une direction perpendiculaire au plan de ladite couche externe soit strictement inférieure à l'épaisseur de cette couche.
According to the invention, the following step is then carried out:
  • the aluminized sheet is subjected to a heat treatment suitable for bringing at least the outer layer 3 of the coating to a temperature above 570 ° C and below 660 ° C;
  • the conditions of the heat treatment, in particular the duration, the heating and cooling rates, are adapted:
    • so that the thickness of said internal layer 1 of alloy remains less than that of said external layer,
    • and so that, in said outer layer, the projection of the length of all said needles or strips on a direction perpendicular to the plane of said outer layer is strictly less than the thickness of this layer.

Dans la phase du traitement thermique où la température est supérieure à 570°C, la durée de traitement est inférieure à 15 secondes de manière à limiter et/ou à empêcher l'augmentation d'épaisseur de la couche interne d'alliage.In the heat treatment phase where the temperature is greater than 570 ° C, the treatment time is less than 15 seconds from so as to limit and / or prevent the increase in layer thickness internal alloy.

On constate également que le traitement thermique selon l'invention a pour effet de diminuer sensiblement la proportion d'aiguilles et de lamelles dans cette couche externe .It can also be seen that the heat treatment according to the invention has has the effect of significantly reducing the proportion of needles and strips in this outer layer.

De préférence, on applique le revêtement à base d'aluminium de façon à ce que l'épaisseur de ladite couche interne d'alliage soit inférieure ou égale à 5 µm et on effectue le traitement thermique selon l'invention pour que l'épaisseur de ladite couche interne d'alliage reste inférieure ou égale à 5 µm.Preferably, the aluminum coating is applied so as to the thickness of said internal alloy layer is less than or equal to 5 μm and the heat treatment according to the invention is carried out so that the thickness of said internal alloy layer remains less than or equal to 5 μm.

La température minimum du traitement selon l'invention correspond à la température de fusion de la phase de la couche externe correspondant à la composition eutectique Al-Si-Fe.The minimum temperature of the treatment according to the invention corresponds to the melting temperature of the phase of the outer layer corresponding to the Al-Si-Fe eutectic composition.

La température maximum du traitement selon l'invention correspond à la température de fusion des dendrites d'aluminium de la couche externe. The maximum temperature of the treatment according to the invention corresponds to the melting temperature of the aluminum dendrites of the outer layer.

Ce traitement thermique peut être effectué sous air, même si le revêtement s'oxyde légèrement en surface.This heat treatment can be carried out in air, even if the coating oxidizes slightly on the surface.

Ainsi, en se basant sur ces critères de définition de traitement thermique, on constate que l'on parvient à améliorer sensiblement la résistance à la fissuration du revêtement.Thus, based on these criteria for defining heat treatment, we see that we manage to significantly improve the resistance to coating cracking.

Ces constatations peuvent être effectuées de la manière suivante :

  • on plie des échantillons de tôle 11 en angle fermé (voir figure 3) en intercalant dans le pli de la tôle une ou plusieurs cales 12, chaque cale ayant l'épaisseur de l'échantillon de tôle ; ainsi, des plis « 0T », « 1T » et « 2T », ... correspondent respectivement au pliage sans cale, avec une seule cale et avec deux cales ; la figure 3 représente donc un pliage « 2T ».
  • sur une coupe métallographique pratiquée dans le pli, on observe alors, à l'extérieur du pli, le nombre de fissures débouchant à la surface du revêtement par millimètre de pli.
These findings can be made as follows:
  • sheet metal samples 11 are folded at a closed angle (see FIG. 3) by inserting one or more shims 12 in the fold of the sheet, each shim having the thickness of the sheet sample; thus, folds "0T", "1T" and "2T", ... correspond respectively to folding without shims, with a single shim and with two shims; FIG. 3 therefore represents a “2T” folding.
  • on a metallographic section made in the fold, we then observe, outside the fold, the number of cracks opening onto the surface of the coating per millimeter of fold.

On trouvera plus de précisions sur ce mode d'évaluation dans le texte de la norme dite « ECCA T7 » intitulée, en langue anglaise, « Resistance to cracking on bending », publiée par la « European Coil Coating Association », norme T7, dans la version du 2 avril 1996.More details on this method of evaluation can be found in the text of the standard known as "ECCA T7" entitled, in English, "Resistance to cracking on bending ", published by the" European Coil Coating Association ", standard T7, in the version of April 2, 1996.

Contrairement à la définition officielle de cette norme, on a effectué le pliage de manière à ce que la direction du pli corresponde à celle du laminage de la tôle.Contrary to the official definition of this standard, the folding so that the direction of the fold corresponds to that of the rolling sheet metal.

En comparant des observations effectuées sur des tôles aluminiées avant traitement thermique selon l'invention et sur les mêmes tôles traitées selon l'invention, on constate donc, pour des plis identiques, une diminution sensible du nombre de fissures par millimètre de pli.By comparing observations made on aluminized sheets before heat treatment according to the invention and on the same sheets treated according to the invention, there is therefore, for identical folds, a significant reduction the number of cracks per millimeter of fold.

Du fait de la diminution des fissures, on améliore sensiblement la résistance à la corrosion de l'acier de ces tôles, après déformation.Due to the reduction in cracks, the corrosion resistance of the steel of these sheets, after deformation.

La tôle aluminiée selon l'invention résiste donc mieux à la corrosion après mise en forme, au sens que le revêtement protège mieux l'acier.The aluminized sheet according to the invention therefore resists corrosion better after shaping, in the sense that the coating better protects the steel.

La structure du revêtement de la tôle aluminiée selon l'invention est schématisée à la figure 2 et représentée à la figure 6 ; la structure générale reste identique : sur l'acier 2, une couche interne 7 d'alliage et une couche externe 8 composée essentiellement d'aluminium.The structure of the coating of the aluminized sheet according to the invention is shown schematically in Figure 2 and shown in Figure 6; the general structure remains the same: on steel 2, an internal layer 7 of alloy and a layer external 8 mainly composed of aluminum.

Par comparaison avec la tôle aluminiée avant traitement (figures 1 et 5, 5 bis), on observe principalement les différences suivantes :

  • que les aiguilles et/ou lamelles restantes 9 sont beaucoup plus courtes qu'avant le traitement thermique, et qu'on est parvenu, grâce au traitement thermique selon l'invention, à obtenir que la projection de leur longueur dans une direction perpendiculaire au plan de cette couche est strictement inférieure à l'épaisseur de cette couche.
  • que la couche externe peut maintenant contenir des inclusions en forme de « pavés », qui semblent contenir essentiellement du silicium.
  • que la teneur moyenne en aluminium de la couche externe 8 est supérieure à la teneur moyenne en aluminium de la couche externe 3 des figure 1, 5 ou 5 bis.
  • que la proportion d'aiguilles et/ou de lamelles 9 a pu diminuer.
By comparison with the aluminized sheet before treatment (FIGS. 1 and 5, 5a), the following differences are mainly observed:
  • that the remaining needles and / or strips 9 are much shorter than before the heat treatment, and that we have managed, thanks to the heat treatment according to the invention, to obtain that the projection of their length in a direction perpendicular to the plane of this layer is strictly less than the thickness of this layer.
  • that the outer layer can now contain inclusions in the form of "blocks", which seem to contain essentially silicon.
  • that the average aluminum content of the outer layer 8 is greater than the average aluminum content of the outer layer 3 of Figures 1, 5 or 5a.
  • that the proportion of needles and / or strips 9 may have decreased.

A titre d'exemple, sur la figure 2, on a représenté en p' la valeur la plus élevée de cette projection correspondant à la lamelle ou aiguille référencée 10 ; on constate ainsi qu'elle est largement inférieure à l'épaisseur moyenne de la couche 8.By way of example, in FIG. 2, the most significant value has been represented at p ' high of this projection corresponding to the lamella or needle referenced 10 ; it can thus be seen that it is much less than the average thickness of the layer 8.

Sans préjuger d'une explication définitive, on pense que le traitement thermique selon l'invention engendre un réarrangement structural de la couche externe conduisant à la disparition et/ou à la partition des lamelles ou aiguilles de cette couche.Without prejudging a definitive explanation, it is believed that the treatment according to the invention generates a structural rearrangement of the layer external leading to the disappearance and / or partition of the lamellae or needles of this layer.

Ainsi, en cas de déformation de cette tôle, les fissures qui apparaissent par exemple dans la couche interne 7 fragile d'alliage ne peuvent alors plus se propager aussi facilement dans la couche externe 8.Thus, in the event of deformation of this sheet, the cracks which appear for example in the fragile inner layer of alloy 7 can no longer be spread as easily in the outer layer 8.

Le traitement thermique selon l'invention aurait donc pour effet technique premier de réarranger la structure de la couche externe de manière à obtenir une structure s'opposant à la propagation de fissures.The heat treatment according to the invention would therefore have the technical effect first to rearrange the structure of the outer layer so as to obtain a structure opposing the propagation of cracks.

Le traitement thermique selon l'invention doit être également adapté pour empêcher ou limiter l'augmentation d'épaisseur de la couche interne 7 d'alliage, car cette couche est particulièrement fragile. The heat treatment according to the invention must also be adapted for prevent or limit the increase in thickness of the inner layer 7 of alloy, because this layer is particularly fragile.

Les conditions du traitement thermique selon l'invention peuvent donc être optimisées d'une manière connue en elle-même entre ces deux compromis : réarrangement suffisant de la couche externe et faible augmentation de l'épaisseur de la couche interne d'alliage.The conditions of the heat treatment according to the invention can therefore be optimized in a manner known per se between these two compromises : sufficient rearrangement of the outer layer and slight increase in the thickness of the internal layer of alloy.

Le traitement thermique selon l'invention est de courte durée, ce qui est un avantage important par rapport à des traitements de recuit de longue durée et à plus basse température.The heat treatment according to the invention is of short duration, which is an important advantage compared to long-term annealing treatments and at a lower temperature.

Ce traitement thermique peut donc être avantageusement effectué en ligne sur les installations classiques de revêtement au trempé.This heat treatment can therefore advantageously be carried out in line on conventional dip coating installations.

De préférence, ce traitement thermique est appliqué de manière à chauffer davantage la couche externe que la couche interne d'alliage.Preferably, this heat treatment is applied so as to heat the outer layer more than the inner alloy layer.

Pour procéder ainsi au traitement thermique, on peut utiliser des moyens classiques de chauffage, comme :

  • des moyens de chauffage à la flamme,
  • des moyens de chauffage par rayonnement infrarouge,
  • des moyens de chauffage par induction, de préférence à haute fréquence pour obtenir une épaisseur de peau aussi faible que possible, voire comparable à l'épaisseur de la couche externe.
To do the heat treatment in this way, conventional heating means can be used, such as:
  • flame heating means,
  • means of heating by infrared radiation,
  • induction heating means, preferably at high frequency to obtain a skin thickness as small as possible, or even comparable to the thickness of the outer layer.

Le traitement thermique selon l'invention peut également améliorer sensiblement la réflectivité de surface de la tôle, notamment dans le domaine de longueurs d'onde compris entre 1,5 et 5 µm ; on obtient cet avantage supplémentaire notamment lorsqu'on effectue le traitement thermique sous atmosphère non oxydante.The heat treatment according to the invention can also improve appreciably the surface reflectivity of the sheet, in particular in the field wavelengths between 1.5 and 5 µm; we get this advantage additional especially when performing heat treatment under non-oxidizing atmosphere.

Mais, dans ce cas, il convient de noter que le traitement selon l'invention ne se limite pas à un traitement de brillantage de la surface ; en effet, certains traitements efficaces de brillantage provoquent une augmentation importante de l'épaisseur de la couche interne d'alliage, ce qui est contraire à l'invention décrite ici.But, in this case, it should be noted that the treatment according to the invention is not limited to a surface gloss treatment; indeed some effective brightening treatments cause significant increase of the thickness of the internal layer of alloy, which is contrary to the invention described here.

Pour limiter l'augmentation de l'épaisseur de la couche interne d'alliage lors du traitement thermique selon l'invention, on utilise de préférence une nuance d'acier contenant une teneur supérieure ou égale à 10-2 % en poids d'azote libre. To limit the increase in the thickness of the internal alloy layer during the heat treatment according to the invention, preferably a steel grade containing a content greater than or equal to 10 -2 % by weight of nitrogen is used. free.

On utilise par exemple des aciers calmés à l'aluminium et bobinés à basse température après laminage à chaud ; en bobinant à une température inférieure ou égale à 610°C, on limite la formation de nitrures d'aluminium (AlN) et on maintient alors la teneur en azote libre à un niveau suffisamment élevé.For example, steels calmed with aluminum and wound with low temperature after hot rolling; by winding at a temperature less than or equal to 610 ° C, the formation of aluminum nitrides (AlN) is limited and the content of free nitrogen is then maintained at a sufficiently high level.

Au moment de l'application du revêtement métallique au trempé, cet azote libre forme des phases à base de nitrure d'aluminium à l'interface entre l'acier et la couche interne.When applying the metallic coating to the dip, this nitrogen free form of aluminum nitride-based phases at the interface between steel and the inner layer.

Pour limiter l'augmentation de l'épaisseur de la couche interne d'alliage lors du traitement thermique selon l'invention, on peut, avant application du revêtement, nitrurer la surface de l'acier à revêtir ou simplement réaliser le recuit avant trempé sous une atmosphère contenant de l'ammoniac.To limit the increase in the thickness of the internal alloy layer during the heat treatment according to the invention, it is possible, before application of the coating, nitriding the surface of the steel to be coated or simply performing the annealing before soaking in an atmosphere containing ammonia.

Les exemples suivants illustrent l'invention.The following examples illustrate the invention.

Exemple 1 : Example 1 :

Cet exemple a pour but d'illustrer l'invention dans le cas de l'aluminiage d'une nuance d'acier dite « calmée aluminium ».The purpose of this example is to illustrate the invention in the case of aluminizing of a steel grade called "aluminum calm".

La tôle d'acier à aluminier selon l'invention présente l'analyse suivante (teneurs en élément exprimées en millième de % en poids) : Composition de l'acier de l'exemple 1 Élément C Mn P S Si Al Ni Cr Cu N 10-3 % 53 300 10 15 6 22 20 20 7 11 The aluminized steel sheet according to the invention has the following analysis (element contents expressed in thousandths of% by weight): Composition of the steel of Example 1 Element VS mn P S Yes al Or Cr Cu NOT 10 -3 % 53 300 10 15 6 22 20 20 7 11

Les autres éléments sont à l'état de traces ; la teneur en titane est inférieure à 10-3 %.The other elements are in the state of traces; the titanium content is less than 10 -3 %.

Une partie importante de l'azote contenue dans cet acier est dite « libre », l'autre partie étant essentiellement combinée à l'aluminium sous forme de nitrure d'aluminium (AIN) ; la teneur en AIN ayant été évaluée à 1,4 10-3 % environ en poids d'équivalent « azote », on en déduit que la teneur en azote libre est de l'ordre de 10-2 % en poids dans cet acier.A significant part of the nitrogen contained in this steel is said to be "free", the other part being essentially combined with aluminum in the form of aluminum nitride (AIN); the AIN content having been evaluated at approximately 1.4 10 -3 % by weight of “nitrogen” equivalent, it is deduced therefrom that the content of free nitrogen is of the order of 10 -2 % by weight in this steel.

On applique sur les deux faces de cette tôle un revêtement à base d'aluminium d'épaisseur totale de 15 µm environ ; ce revêtement est appliqué comme précédemment décrit au trempé dans un bain d'aluminium contenant du silicium.A coating based on both sides of this sheet is applied aluminum with a total thickness of approximately 15 µm; this coating is applied as previously described by soaking in an aluminum bath containing silicon.

La teneur pondérale moyenne en silicium dans le revêtement est de 7% environ.The average silicon content in the coating is 7% about.

On applique ensuite à cette tôle aluminiée le traitement thermique selon l'invention ; ce traitement consiste à chauffer la tôle à la vitesse de 4°C/s jusqu'à la température de 578°C, et, dès que cette température est atteinte, de refroidir par soufflage d'azote de manière à obtenir une vitesse de refroidissement comprise entre 10 et 15°C/s.Then applied to this aluminized sheet heat treatment according to the invention; this treatment consists in heating the sheet at the speed of 4 ° C / s up to a temperature of 578 ° C, and, as soon as this temperature is reached, blowing with nitrogen to obtain a speed of cooling between 10 and 15 ° C / s.

Pour effectuer ce traitement thermique, on utilise le dispositif schématisé à la figure 4 : il s'agit d'un four vertical 13 comportant deux séries de résistances électriques 14 ; l'échantillon à traiter 15, en tôle aluminiée, est suspendu à une canne de support 16 ; pour mesurer la température de traitement thermique, on utilise un thermocouple 17 , de type K (chromel-alumel), de diamètre 0,2 mm et de classe 1 (± T°C x 0,004, soit ±2,4°C à 600°C) ; ce thermocouple 17 est soudé sur la face revêtue de la tôle aluminiée.To carry out this heat treatment, the schematic device is used in FIG. 4: it is a vertical oven 13 comprising two series of electrical resistors 14; the sample to be treated 15, made of aluminized sheet, is suspended from a support rod 16; to measure the temperature of heat treatment, a thermocouple 17, type K (chromel-alumel) is used, 0.2 mm in diameter and class 1 (± T ° C x 0.004, i.e. ± 2.4 ° C at 600 ° C); this thermocouple 17 is welded to the face coated with the aluminized sheet.

Après traitement thermique, on obtient alors une tôle aluminiée selon l'invention.After heat treatment, an aluminized sheet is then obtained according to the invention.

Des observations métallographiques réalisées sur des échantillons montrent que l'épaisseur de la couche interne d'alliage du revêtement a peu varié suite au traitement thermique : 2,7 µm avant traitement, 4 µm après traitement ; cette épaisseur reste donc inférieure à 5 µm.Metallographic observations made on samples show that the thickness of the inner alloy layer of the coating has little varied following heat treatment: 2.7 µm before treatment, 4 µm after treatment ; this thickness therefore remains less than 5 μm.

On caractérise alors l'amélioration de la résistance à la fissuration du revêtement comme précédemment décrit, en comptant le nombre de fissures débouchantes par millimètre de pli sur une coupe métallographique.The improvement in the crack resistance of the coating as previously described, counting the number of cracks outlets per millimeter of fold on a metallographic section.

Les résultats obtenus sont reportés au tableau III ci-après.The results obtained are reported in Table III below.

On observe donc que le revêtement selon l'invention résiste beaucoup mieux à la fissuration que le revêtement selon l'art antérieur qui n'a pas subi de traitement thermique.It is therefore observed that the coating according to the invention is very resistant better cracking than the coating according to the prior art which has not undergone heat treatment.

On constate également que la couche interne d'alliage se décolle moins par déformation après le traitement thermique selon l'invention. Résultats de pliage de l'exemple 1 Tôle aluminiée Type de pliage Nombre moyen de fissures/mm Largeur moyenne des fissures Observations Avant traitement thermique 0T 10 40 µm Décollements couche interne et larges fissures. 1T 8 62 µm 2T 5 7 µm 3T 2 7 µm Après traitement thermique (invention) 0T 5 41 µm Pas ou peu de décollements de la couche interne 1T 3 55 µm 2T 0 - 3T 0 - It is also found that the internal layer of alloy is less peeled off by deformation after the heat treatment according to the invention. Folding results of Example 1 Aluminized sheet Folding type Average number of cracks / mm Average crack width observations Before heat treatment 0T 10 40 µm Inner layer separation and large cracks. 1T 8 62 µm 2T 5 7 µm 3T 2 7 µm After heat treatment (invention) 0T 5 41 µm Little or no internal layer detachments 1T 3 55 µm 2T 0 - 3T 0 -

Exemple 2 : Example 2 :

Cet exemple a pour but d'illustrer l'invention dans le cas de l'aluminiage d'une nuance d'acier dite « ultra bas carbone » ou « ULC » (« Ultra Low Carbon » en langue anglaise).The purpose of this example is to illustrate the invention in the case of aluminizing a steel grade called "ultra low carbon" or "ULC" ("Ultra Low Carbon "in English).

La tôle d'acier à aluminier selon l'invention présente l'analyse suivante (teneurs en élément exprimées en millième de % en poids) : Composition de l'acier de l'exemple 2 Élément C Mn P S Si Al Ni Cr Cu N 10-3 % 3 230 10 13 8 46 16 23 20 12 The aluminized steel sheet according to the invention has the following analysis (element contents expressed in thousandths of% by weight): Composition of the steel of Example 2 Element VS mn P S Yes al Or Cr Cu NOT 10 -3 % 3 230 10 13 8 46 16 23 20 12

Les autres éléments sont à l'état de traces.The other elements are in the state of traces.

Une particularité de cet acier réside également dans sa température de bobinage en sortie de laminage à chaud : < 620°C.A special feature of this steel also lies in its temperature of winding at the end of hot rolling: <620 ° C.

Du fait de sa très basse teneur en carbone, le principal agent durcissant de cet acier est l'azote libre qu'il contient ; cet acier présente de ce fait une formabilité très supérieure à l'acier décrit dans l'exemple 1.Due to its very low carbon content, the main hardening agent of this steel is the free nitrogen it contains; this steel therefore presents a much higher formability than the steel described in Example 1.

Cet acier est aluminié puis traité thermiquement selon l'invention dans les mêmes conditions que dans l'exemple 1. This steel is aluminized and then heat treated according to the invention in the same conditions as in Example 1.

On obtient alors une tôle aluminiée selon l'invention.An aluminized sheet according to the invention is then obtained.

Comme précédemment, les observations métallographiques montrent que l'épaisseur de la couche interne d'alliage du revêtement a peu varié suite au traitement thermique.As before, metallographic observations show that the thickness of the internal alloy layer of the coating varied little due to heat treatment.

On caractérise alors l'amélioration de la résistance à la fissuration du revêtement comme dans l'exemple 1.The improvement in the crack resistance of the coating as in Example 1.

Les résultats obtenus sont reportés au tableau V.The results obtained are reported in Table V.

Comme précédemment, on observe que le revêtement selon l'invention résiste beaucoup mieux à la fissuration que le revêtement selon l'art antérieur qui n'a pas subi de traitement thermique. Résultats de pliage de l'exemple 2 Tôle aluminiée Type de pliage Nombre moyen de fissures/mm Largeur moyenne des fissures Avant traitement thermique 0T 11 31 µm 1T 8 28 µm 2T 6 7 µm 3T 2 3 µm Après traitement thermique (invention) 0T 10 17 µm 1T 3 10 µm 2T 1 3 µm 3T <1 3 µm As previously, it is observed that the coating according to the invention is much more resistant to cracking than the coating according to the prior art which has not undergone heat treatment. Folding results of Example 2 Aluminized sheet Folding type Average number of cracks / mm Average crack width Before heat treatment 0T 11 31 µm 1T 8 28 µm 2T 6 7 µm 3T 2 3 µm After heat treatment (invention) 0T 10 17 µm 1T 3 10 µm 2T 1 3 µm 3T <1 3 µm

Claims (8)

  1. Process for manufacturing a steel sheet (2) coated with an aluminium-based metal coating subdivided mainly into two layers:
    an inner layer (7) essentially composed of one or more alloys based on iron, aluminium and/or silicon,
    an outer layer (8) which is essentially composed of an aluminium-based phase and secondarily of other phases in the form of elongate lamellae or needles (9) distributed in the said aluminium-based phase, the thickness of the outer layer being greater than or equal to that of the said inner alloy layer,
    in which the said aluminium-based metal coating is applied by dipping it into a liquid aluminium-based bath,
    characterized in that, after the said applied layer has solidified, the said sheet is subjected to a heat treatment suitable for raising at least the said outer layer (8) to a temperature above 570°C but below 660°C at which temperature the melting of the eutectic phases of the outer layer is ensured, under conditions, especially heating and cooling rate conditions, suitable:
    for the thickness of the said outer layer (8) to remain greater than or equal to that of the said inner alloy layer (7) and
    for the projection of the length of all the said needles or lamellae (9) on a direction perpendicular to the plane of the said outer layer (8) to be strictly less than the thickness of this layer (8) and, in order to substantially reduce the proportion of needles and lamellae in this outer layer, the duration of the heat treatment, in the phase in which the said temperature is above 570°C, being less than or equal to 15 seconds.
  2. Process according to Claim 1, characterized in that the said aluminium-based bath contains at least 6% silicon by weight.
  3. Process according to either of Claims 1 and 2, characterized in that the said aluminium-based bath contains at least 8% silicon by weight.
  4. Steel sheet coated with an aluminium-based metal coating subdivided mainly into two layers:
    an inner layer (7) essentially composed of one or more alloys based on iron, aluminium and/or silicon,
    an outer layer (8) which is essentially composed of an aluminium-based phase and secondarily of other phases in the form of elongate lamellae or needles (9) distributed in the said aluminium-based phase, the thickness of the outer layer being greater than or equal to that of the said inner alloy layer (7),
    capable of being obtained by a process according to any one of the preceding claims,
    characterized in that the projection of the length of all the said needles or lamellae (9) on a direction perpendicular to the plane of the said outer layer (8) is strictly less than the thickness of this layer (8).
  5. Sheet according to Claim 4, characterized in that the thickness of the said inner alloy layer (7) is less than or equal to 5 µm.
  6. Sheet according to either of Claims 4 and 5, characterized in that the said coating comprises compounds based on aluminium nitrides interpolated between the steel (2) of the said sheet and the said inner layer (7).
  7. Sheet according to any one of Claims 4 to 6, characterized in that the free nitrogen content of the said steel (2) is greater than or equal to approximately 10-2% by weight.
  8. Process for forming a steel sheet coated with an aluminium-based metal coating subdivided mainly into two layers:
    an inner layer (7) essentially composed of one or more alloys based on iron, aluminium and/or silicon,
    an outer layer (8) which is essentially composed of an aluminium-based phase and secondarily of other phases in the form of elongate lamellae or needles (9) distributed in the said aluminium-based phase, the thickness of the outer layer being greater than or equal to that of the said inner alloy layer (7),
    characterized in that, before the step of actually forming the said sheet, the said sheet is subjected to a heat treatment suitable for raising at least the said outer layer (8) to a temperature above 570°C but below 660°C at which temperature the melting of the eutectic phases of the outer layer is ensured, under conditions, especially heating and cooling rate conditions, suitable:
    for the thickness of the said outer layer (8) to remain greater than or equal to that of the said inner alloy layer (7) and
    for the projection of the length of all of the said needles or lamellae (9) on a direction perpendicular to the plane of the said outer layer (8) to be strictly less than the thickness of this layer (8) and, in order to substantially reduce the proportion of needles and lamellae in this outer layer, the duration of the heat treatment, in the phase in which the said temperature is above 570°C, being less than or equal to 15 seconds.
EP99400414A 1998-02-25 1999-02-22 Steel plate with aluminum coating having stress cracking resistance Expired - Lifetime EP0939141B1 (en)

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FR2775297B1 (en) * 1998-02-25 2000-04-28 Lorraine Laminage SHEET WITH CRACK RESISTANT ALUMINUM COATING
KR20070119096A (en) * 2001-06-15 2007-12-18 신닛뽄세이테쯔 카부시키카이샤 High-strength alloyed aluminum-system palted steel sheet
EP1485514A1 (en) * 2002-03-18 2004-12-15 Karl Merz Method and device for the alfin processing of components
WO2007118939A1 (en) * 2006-04-19 2007-10-25 Arcelor France Method of producing a welded part having very high mechanical properties from a rolled and coated sheet
WO2009090443A1 (en) * 2008-01-15 2009-07-23 Arcelormittal France Process for manufacturing stamped products, and stamped products prepared from the same
DE102008006771B3 (en) * 2008-01-30 2009-09-10 Thyssenkrupp Steel Ag A method of manufacturing a component from a steel product provided with an Al-Si coating and an intermediate of such a method
JP5218703B2 (en) * 2010-06-21 2013-06-26 新日鐵住金株式会社 Hot-dip Al-plated steel sheet excellent in heat blackening resistance and method for producing the same
KR102227111B1 (en) 2018-11-30 2021-03-12 주식회사 포스코 Hot press formed part, and manufacturing method thereof
US11549167B2 (en) 2018-11-30 2023-01-10 Posco Steel sheet plated with Al—Fe alloy for hot press forming having excellent corrosion resistance and heat resistance, hot press formed part, and manufacturing method therefor
US20230323522A1 (en) * 2022-04-11 2023-10-12 Cleveland-Cliffs Steel Properties Inc. Super cqht high temperature alloy-resistant aluminized steel with moderate formability

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US4595980A (en) * 1983-07-27 1986-06-17 International Business Machines Corp. Interactive data processing system having concurrent multi-lingual inputs
JPS61113754A (en) * 1984-11-09 1986-05-31 Nippon Steel Corp Heat resistant aluminized steel sheet retaining its luster
US5023113A (en) * 1988-08-29 1991-06-11 Armco Steel Company, L.P. Hot dip aluminum coated chromium alloy steel
DE4222211C1 (en) * 1992-07-07 1993-07-22 Mtu Muenchen Gmbh
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KR100212596B1 (en) * 1995-02-24 1999-08-02 하마다 야스유키(코가 노리스케) Hot-dip aluminized sheet, process for producing the sheet, and alloy layer control device
US5789089A (en) * 1995-05-18 1998-08-04 Nippon Steel Corporation Hot-dipped aluminum coated steel sheet having excellent corrosion resistance and heat resistance, and production method thereof
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